Ask The Heat Treat Doctor® has returned to bring sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues.
This informative piece was first released in Heat Treat Today’sNovember 2025 Annual Vacuum Heat Treating print edition.
Case depth, case uniformity, and final mechanical (as well as other) properties rely not only on controlling both equipment and process variability during heat treatment, but on having clean, properly prepared part surfaces prior to and during heat treating. Expert Dan Herring encourages to learn more below.
Case hardening is a thermochemical surface treatment process designed to add a particular element or combination of elements to a material such as steel. Familiar examples include carbon (carburizing); carbon and nitrogen (carbonitriding); boron (boriding); nitrogen (nitriding); and nitrogen and carbon (nitrocarburizing — ferritic or austenitic). These processes are typically designed to increase the near surface hardness of steel after quenching.
However, various problems can arise due to either the materials or the manufacturing methods employed prior to or during heat treating that will retard or prevent absorption and/or diffusion of the desired element(s) during heat treating. Some of the metallurgical consequences can include:
Shallow or uneven case depths
Surface oxidation
Intergranular oxidation or decarburization
High levels of retained austenite
Soft spots due to incomplete hardening
Machine-Induced Surface Conditions
Improper machining prior to case hardening can compromise surface integrity. Tooling choices, improperly maintained equipment, inadequate operator training, and even environmental factors can contribute to a variety of issues.
While machining problems occur frequently, they are mostly preventable. Attention to part surface condition, cleanliness, and mechanical integrity is essential before heat treating. Training, standardizing machining protocols, planned preventative maintenance programs, and part inspection prior to heat treating will help avoid these issues. Consult Table A for further details on how the causes and effects of undesirable machine-induced surface conditions can be solved.
Splatter of Stop-off Paints on Unintended Areas
A material that masks the surface of steel and delays or prevents case hardening is called a stop-off or maskant. These materials are applied to specific areas of a steel part to prevent the diffusion of hardening elements (like carbon or nitrogen) into the surface during case hardening processes, such as carburizing, nitriding, or carbonitriding. (See Table B.)
Enriching Gas Additions (Sooting)
During the carburizing or carbonitriding process, it is not uncommon to develop a layer of soot on the surface of the parts, especially if the enriching gas additions begin before the entire load is uniformly up to temperature. In some instances, the amount of soot formation is such that the case depth or uniformity is affected. This is often difficult to diagnose, as the soot layer “washes off” during quenching in a liquid, and the part surfaces come out of the furnace looking reasonably clean.
Material-Related Issues
The use of scrap in steelmaking, especially for low alloy case hardening steels can lead to a relatively high level of impurities and tramp elements. At high temperatures these impurities tend to segregate at grain boundaries and migrate toward the surface. This type of segregation can retard case hardening by impeding element (e.g., carbon) transfer. For example, the effects of tin (Sn) and antimony (Sb) on the kinetics of carburization are particularly problematic (Figure 1).
The effect of tramp elements on retardation of carburization can be expressed in the following order (Andreas, et al. 1996), namely Sb > Sn > P > Cu > Pb. To see the effect of one such element, the carbon transfer coefficient (ß) for typical commercial steels is shown as a function of antimony (Sb) content (Figure 2).
In Summary
These are a few of the many causes delaying or preventing case hardening from being effective. There are many others, including alkaline cleaning compounds (in too high a concentration) and even phosphate and other drawing lubricants used in the manufacture of fasteners. Inspection and cleaning of the part surface prior to case hardening will avoid many of these issues. Reviewing material certification sheets for elements known to interfere with case hardening is also an effective way to anticipate problems with case hardening.
References
Herring, Daniel H. 2014. Atmosphere Heat Treatment, Volume 1. Troy, MI: BNP Media.
Herring, Daniel H. 2015. Atmosphere Heat Treatment, Volume 2. Troy, MI: BNP Media.
Ruck, Andreas, Monceau, Daniel, and Grabke, Hans Jürgen. 1996. “Effects of Tramp Elements Cu, P, Pb, Sb, and Sn on the Kinetics of Carburization of Case Hardened Steels.” Steel Research 67 (6): 242–48.
About the Author
Dan Herring “The Heat Treat Doctor” The HERRING GROUP, Inc.
Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.
In this episode of Heat TreatRadio, host Doug Glenn invites Dennis Beauchesne of ECM USA to explore the technology, benefits, scalability, and sustainability of modular heat treating systems. Together, they discuss how shared utilities, automated transfers, and adaptable heating cells can replace multiple standalone furnaces without compromising quality or precision. Learn how these systems streamline and simplify operations for future expansion — one cell at a time.
Below, you can watch the video, listen to the podcast by clicking on the audio play button, or read an edited transcript.
The following transcript has been edited for your reading enjoyment.
Introduction
Doug Glenn: I am very privileged to have with me today, Dennis Beauchesne from ECM USA. We’re going to be talking about modular heat treating systems, which is a growing category of equipment.
ECM Synergy Center (00:50)
Doug Glenn: Tell me about ECM’s Synergy Center, which is where you are at right now, on the shop floor.
The ECM Flex 600TG vacuum furnace located in the ECM Synergy Center Source: ECM USA
Dennis Beauchesne: I’m standing here in the middle of our Synergy Center. It’s about a 5,000-square-foot facility that is dedicated to proving out client parts for testing various processes, mostly LPC, but we also do a number of other processes here. We have a full metallurgical lab, 3D microscope, a number of tools, including a CMM that we can do before and after heat treat distortion testing for clients that want to know how much their parts move.
It’s a dedicated center just for clients to use. We also use the center for pre-completion of installations, final testing, and training, such as training on maintenance, understanding the software, and how everything works together.
Doug Glenn: It’s proof of process plus much more — helping clients’ proof of process.
Dennis Beauchesne: Absolutely. That’s a big part of convincing people that this process is for them and that it works on their part. We can send them ten different reports of an exact same material and part, but they want to know what their part will do.
What is Modular Heat Treating? (02:50)
Doug Glenn: On a very basic, rudimentary level, what is modular heat treating and how does it differ from what might be considered standard or normal heat treating?
Dennis Beauchesne: A modular heat treat system is one that works together to have more than one furnace working in the same platform. You may have a shop that has five or six vacuum furnaces separated — they each have their own door, vacuum system, electrical supply, quench motors…those types of components. Or you may have a series of batch IQ furnaces for carburizing; those systems are one off, which means they are individual, independent systems.
In a modular system, you try to utilize those facilities for the use of multiple heating chambers. Instead of having one vacuum furnace with one set of pumps and one gas quench motor, what we would do is have three to eight heating cells that would be utilizing one quench, depending on the process timing; that’s all done with an internal transfer car and we try to utilize one vacuum system. It’s much smaller than what you would have for three, four, or even eight cells.
If you had oil or high pressure gas quenching, which is what’s dominating right now in the modular heat treat business, you could supply basically six batch IQ hot zones to one oil quench.
The savings then are huge simply by removing five or six other quench tanks in front of this system, as well as leveraging the floor space (and the number of pits you have to dig). Other advantages including utility savings and utilizing equipment across a number of heating chambers.
Doug Glenn: This modular approach is basically separate chambers that are dedicated to doing whatever that chamber is doing, and they are all in some way interconnected. For standard units, you would heat up, pre-process, do the actual process itself, cool down, all in the same chamber. In a modular unit, you move from chamber to chamber to do each of those separate steps.
Dennis Beauchesne: Yes, I refer to it as a continuous batch.
Doug Glenn: Continuous batch. We were talking before we actually hit the record button with your colleague there, Allison DeAngelo, who just got done visiting the Heat Treat Boot Camp. We were talking about different types of furnaces, and we started talking about continuous vacuum, which of course, is almost a misnomer — a vacuum can’t be continuous because you have to open it up and break the vacuum to get stuff out. Anyhow, we talked about it basically being a batch, right? A batch furnace that’s continuous, a continuous batch furnace.
Benefits of Modular Heat Treating (06:35)
Now that we have a basic understanding of what these modular systems are, why would companies want to move from the standard type of heat treating system to a modular system?
Dennis Beauchesne: Manpower. If you are running five or six vacuum furnaces, you are going to need a number of people to open the doors, put new loads in, those kinds of tasks. With a modular system, you only have one entry or one exit area. Therefore, you are only going to load once every 15-20 minutes, and the system is going to take over and control that load going through the system.
In addition, especially in a carburizing atmosphere situation, you can have every load be a different case depth — a different process in each cell — and then the next load that goes in that same cell can be totally different from the one before. For instance, if you had a batch IQ, you typically use the same carbon potential, and you are typically going to run the next load almost identical to the one before. In contrast, with the modular system, each cell can run a different process every load.
It’s also easier to integrate automation if you are doing capacity increases.
Throughput Comparison (08:00)
Doug Glenn: What is the comparison of throughput between a standard unit and a modular unit?
Dennis Beauchesne: The throughput comparison is interesting because you typically can use a little higher temperature for a carburizing and a little higher carbon potential, and of course that’s what we specialize in here with the modular systems. You can achieve about a 30-40% gain in your cycle time. That furnace is operating very close to 100% occupancy, because when that load is done, you are moving it out right into the gas quench. Then, the next load comes and goes right into it.
Doug Glenn: You are able to increase your throughput because you have basically 100% utilization of the equipment or very close to that. Comparatively, you don’t necessarily have that in the standard equipment.
Product Quality Comparison (09:15)
Doug Glenn: Do modular systems produce higher quality products?
Dennis Beauchesne: The quality of the parts coming out of the system is improved. A vacuum environment is a very clean environment, especially if we are considering atmosphere and low pressure carburizing — it’s in a vacuum. We typically do everything in high pressure gas quenching. However, even in oil quenching under vacuum, you are going to have a much cleaner part.
Also in low pressure carburizing, the carburizing is much more uniform throughout the part because we heat it to temperature under nitrogen before the part gets to austenitizing temperature to start attracting carbon. We make sure that the full part, that’s the tooth, the root, every piece of the part, is at temperature before we start adding carbon to the load, which makes a more uniform case depth, and therefore makes a stronger part.
Doug Glenn: Since each module, each chamber, is dedicated to doing what it is supposed to do, it seems like the consistency and the reliability of the parts being processed in a modular system have a much better chance of being higher quality.
Dennis Beauchesne: You do not have six different variable chambers or six different variable systems. You just have to look at monitoring the connection between those and understanding that the vacuum levels are all the same across the levels and across the cells. Each cell can meet a different temperature and run a different process, but those are consistent across the board.
Typical Dedicated Cells/Chambers (11:10)
Doug Glenn: What would be the typical dedicated cells/chambers of a modular system?
Dennis Beauchesne: It is dependent on the processes. They are most widely used for vacuum carburizing. For pre-oxidation and preheating, we usually use an air oven outside of the system, and we connect that with an external loader. Before the load goes into the modular system, the load will go through a regular air oven, be heated to around 700°F (400°C), and then the load will be moved in.
For sintering and those kinds of applications, there is a debind step or a preheat step that would be done in one cell. Some of the processes that can be done in a modular system include:
Low pressure carburizing
Low pressure carbon nitriding (LPC)
FNC (ferritic nitrocarburizing)
Nitriding
Debinding
Sintering
Neutral hardening
The most prominent process right now is LPC, and that is being used all over the world in these systems.
Advantages of a Modular Unit for Captive Heat Treaters (12:53)
Doug Glenn: Why would a modular unit be beneficial for a captive heat treater, someone who does their own in-house heat treating, which probably means they’ve got potentially high volume, low variability as far as their workloads?
Dennis Beauchesne: The modular unit has many different advantages. First of all, floor space. You are going to save a lot of floor space by not having multiple furnaces set up separately. You will also save utilities because you would not have as many vacuum pumps or electrical systems running these furnaces on their own. You will have some shared service and utilities in that fashion.
Doug Glenn: That would also likely lead to maintenance cost savings as well, correct?
Dennis Beauchesne: Yes, it all goes down the line. Anything that you have multiples of, you are going to have much less costs than on a joint system. The modular system might be a little larger than one singular unit, but there will be fewer of them.
For vacuum carburizing applications in a captive shop, the quality and cleanliness of the part is very, very important. Gas quenching lends itself to no oil in your plant, no washers necessary for a post-quench. Typically, there’s a washer before the process starts, but you do not have to have any wash to get the oil off of the parts with a modular unit — you do not have to reclaim the oil or the water from the washer. You would not have waste oil in your plant either or any oil on your plant floor. These are some of the reasons some of the larger captive shops have gone to the modular systems.
Also, safety: There are no open flames with a modular unit, no risks of fire on the systems. They are also easier to maintain. For a fully operational, let’s say, eight-cell system for high production, captive operation, it would only take about five hours to cool that whole system down if you had to go in and work on the whole system. In comparison, it’s going to take you three to four days sometimes to cool down a typical atmosphere, high-temperature furnace.
It also takes time to heat the system up again. In a modular system, it takes about an hour and a half to heat the system up again and then you are ready to start running. That means now you can schedule your downtime on weekends or holidays. You do not have to have staff present to run anything.
You also do not have to have a secondary equipment, like Endo generators running to feed the carburizing gas. The carburizing gas is using acetylene out of cylinders, it’s not a regenerative system. You do not need a separate piece of equipment to feed to the furnace.
Another benefit is CapEx expansion. Typically, captive heat treaters do not want to buy everything upfront because their volumes are going to increase over time. In the beginning, they typically only need one or two cells ready to do a small amount of production so they can prove out the production and prove out the system. Then they can start building the system with more cells and more capacity later on. Generally, it’s two to three days of downtime to add a cell to a system. It’s very convenient to do that with a modular system. All of the utilities are typically alongside the modular system so that you can easily add those or add a cell to it over a short period of time, and those cells can be ordered a year or two down the road whenever you might need that.
You also can order peripheral equipment, like extra temper ovens or additional automation. You can add a robotics system to the layout as well. That’s why captive shops are very interested.
Finally, workforce: It’s a little bit easier to get someone to work on a modular system. These systems are completely clean and white. The one located in our Synergy Center has been there for eight years. We use it every single day, and it’s a very clean aesthetic environment for someone to work in. These systems are also water cooled, which means not a lot of extra heat in the building around you to work in.
Advantages of a Modular Unit for Commercial Heat Treaters (17:59)
Doug Glenn: What are some advantages of modular units for commercial heat treating?
Dennis Beauchesne: On the commercial heat treat side, modular units are typically useful because you can get multiple processes out of similar cells and you can have a system that has oil and a gas quench.
You can have a lot of flexibility in that one system that you have in the plant. I’ve visited hundreds of captive and commercial heat treaters. They generally have a number of furnaces in one area of the plant, and a number of furnaces in another area of the plant. A modular system gives you all the capability in one machine and one tool: oil quenching, gas quenching, FNC, nitriding low pressure, carburizing, carbonitriding, and neutral hardening all in one piece of equipment.
Automation and Robotics with Modular Heat Treating (18:57)
Doug Glenn: What automation and robotics advantages are there with modular systems?
Dennis Beauchesne: This is the new trend. People that have modular systems are now considering, “How do I automate the system to get more production out of it?” And what we’ve been doing the last five years especially is implementing systems that use CFC fixtures.
CFC fixtures are very robust in the furnace but sensitive to being controlled outside. Therefore, what we try to do is have the CFC fixtures be utilized in an automation that no humans have to interact with it. We usually use robots for external loaders and internal loaders to move the fixtures through the process.
This causes you to have a lighter load, which means less heating time, less energy being consumed. Also, the fixtures last three to four times longer if they’re not damaged. But of course, all of these systems can be using regular alloy steel as well, and we can fixture different parts. You can use baskets, we are now doing bulk loading where we have parts that are filled into baskets and then processed. We are doing that with vacuum carbonizing as well, not just neutral hardening.
So it’s really interesting to see how the limits are being pushed, as well as the different materials that we are gas quenching now. I know 20-25 years ago, we were quenching some simple materials that were very high hardenability, and today we’re quenching a lot of less hardenability steels.
Doug Glenn: Is that primarily due to increase of pressure in the quench?
Dennis Beauchesne: It’s pressure, it’s flow, it’s the intensity of the gas going through the parts. It’s also heat removal as well — heat exchangers, removing the heat out of the load faster. We also have reversing gas quench motors to reverse the flow inside from top to bottom, bottom to top, in the middle of the cycle.
Sustainability of Modular Heat Treating (22:24)
Doug Glenn: Do these systems promote sustainability and greenness?
Dennis Beauchesne: Absolutely, especially when it comes to carburizing. These systems have been compared against typical atmosphere carburizing cycles, and only about 4% of the carburizing time has gas injection, when we are actually injecting acetylene and having hydrocarbons being used in the process.
If you took the same cycle times, seven or eight hours of a carburizing cycle, you are flowing Endo gas or nitrogen methanol in the system for that full time. In contrast in a vacuum carburizing system, it’s 4-5% of the time of the cycle that you’re injecting into the furnace. Ultimately, you only have about 10% of the CO2 output that you would have in a typical atmosphere furnace.
As mentioned previously, there’s also no oil in your plant. You’re not reclaiming oil out of the water and the wash or off the floor or in your car when you leave your heat treat shop.
How Does the Modular Heat Treating System Work? (23:40)
Doug Glenn: Let’s talk through the process a little bit. You provided us with figures to aid in describing the process. We have included these. Describe how the system works.
Dennis Beauchesne: This animation is a plan view of one of our Flex systems. In the center, going left to right, is a tunnel section. This tunnel section is about an 8-foot diameter. It has an automated loader that moves down left to right or horizontally, and it transfers loads from each cell to another, in and out.
On the bottom left is a loading/unloading chamber. In that loading/unloading chamber, we remove the air once the load is put in there, and then we balance the vacuum on that cell to the tunnel’s vacuum. Then we’re capable of moving that load to an available heating cell, and that would be on the right of the system — on the top right or the bottom right of the tunnel, those are heating cells. Then recipe for that particular load will be loaded into that cell. While that load is processing, another load will be moving into the tunnel and into the other heating cell as well.
On the top left is the gas quench cell, which could be in this orientation or instead have an exit on the back as well. In this system, you could do neutral hardening, carbon nitriding, LPC, a number of the processes. This is a very valuable tool, especially in a commercial heat treat heat treat shop.
Doug Glenn: Is this whole unit, including all four chambers under vacuum? I noted there are separation doors on the purge and the entry chamber. Can this area be vacuum sealed?
Dennis Beauchesne: Yes. There are vacuum seals on the loading/unloading chamber on the bottom left and then the top left. The gas quench also has a seal from a pressure standpoint. The two heating chambers have a graphite door — we call it the flap door, and it just flaps and it doesn’t really seal actually against another face of graphite. It’s graphite-to-graphite. We pull vacuum out of there through the tunnel to create the central vacuum pressure in the system. We also pull vacuum from the cell itself, and we could also have a separate door on the front of the unit if the process necessitates that or if we feel that a door is needed there by a client.
In a normal state or a standard unit, there are no hot seals on the door, only vacuum seals on the loading/unloading chamber and the gas quench.
Doug Glenn: In the animation, your vacuum pumps are down in the bottom right, correct?
Dennis Beauchesne: Exactly, that’s a process pump.
Doug Glenn: What is located in the top left?
Dennis Beauchesne: On the top left, we have a gas quench tank. We want to ensure we have enough gas pressure and volume there to quench the load quickly. It’s very important to get the gas through the gas quench quickly.
ECM Flex 600TG vacuum furnace with two added heating cells / Source: ECM USA
Now, we have added two more additional heating cells and a central tunnel section. In essence, you just doubled the space, doubled the capacity of the unit, where you only added 50% of the space of what you had for capacity before.
We are still utilizing the same gas quench and the same loading/unloading cell. We only added utilities for the two heating cells, not for a whole gas quench or oil quench capability there; this can be added in a very short time.
Doug Glenn: Now I’m gonna go let this video roll here for a minute. There we go.
ECM Flex 600TG vacuum furnace with four added heating cells for six heating cells total
Dennis Beauchesne: So now we added another 50% capacity with two more heating cells (six heating cells total) and a tunnel section. Typically, what you want to do is to have the tunnel sized for about five years out for your capacity and then buy the cells as you need them and have it grow so then the tunnel is ready to implement.
We have just tripled the capacity of this installation, and we are only still using the same gas quench and the same loading/unloading cell. Generally, this system could go to eight cells and have just one gas quench, that’s our typical orientation.
Doug Glenn: It looks like we also added a discharge side here. Whereas before we were going in and out.
Dennis Beauchesne: Yes, this adds to the efficiency of the system because the load is already in the gas quench when it’s finishing, so it just exits out the back, out the door.
Doug Glenn: Now what do we have here?
ECM Flex 600TG vacuum furnace processing different treatments in each cell. See animation above to watch the animation in motion.
Dennis Beauchesne: We have the loads entering, and the loads will go to the first cell that is available (empty). Then that recipe would be downloaded for that cell, and then the next load will go to the next available heating cell and download that recipe into that cell. These could be two different loads.
One load could be for neutral hardening; one could be for carburizing. One could be for carburizing in a low case depth. The other one could be carburizing at a deeper case. In this case, we just see the gas quench on here, but this tunnel could also be outfitted with an oil quench as well, and you could have one load go into gas, quench one load, go into oil quench or both going to either.
Doug Glenn: This gives people a sense of what the process looks like.
Processes and Materials for the Modular System (30:29)
Doug Glenn: Are there any processes or materials that do not make sense to process them through one of these systems?
Dennis Beauchesne: If you are doing a lot of annealing and normalizing, those are longer cycles. There is some regulated cooling that occurs. This is not really the type of equipment investment that you would want to make for those processes. If you were going to use it for a few loads in your plant where you received parts that weren’t annealed or you wanted to try to anneal a part for a particular process before you went to full production, you could certainly use a modular system for that, but it’s not a cost effective methodology. Neither would we recommend preheating in the cell. However, it is very flexible for a number of other processes that we have mentioned.
The size of the part is also important to note. These systems are typically 24 inches wide and about 39 inches long and about 28 inches high. However, we will soon have a new system, the Flex Max, a 12-9-9 system. It’s a 36×48 unit that comes with an oil quench and is modular, like this. We can either do an oil quench or a slow cool cell on that system. So, we will have that capability of 36×48 in that modular system.
Other than that, restrictions on material? Very few there. Like I said, you would not want to do annealing and normalizing on a lot of parts, but you could do it in these units.
Doug Glenn: It sounds like the sweet spot is surface modification type applications, and some sintering is possible with dedicated chambers.
Dennis Beauchesne: Yes, sintering and brazing is also possible.
Doug Glenn: Does that include aluminum brazing?
Dennis Beauchesne: Not aluminum brazing, but some brazing applications.
Expenses with Modular Heat Treating Systems (33:03)
Doug Glenn: What would be considered capital expenses for this modular system?
Dennis Beauchesne: As far as capital expenses, it’s not a furnace-to-furnace comparison. Clients always ask how much our furnace is. But companies need to first take two steps back and take a look at their incoming material, how they would like to be able to modify that incoming material in their heat treat process to make sure that their outgoing quality is higher than it is today. That’s the kind of benefit that this type of modular system gives you — a better quality part, safety in your plant, and a better quality work environment with being able to turn the system off and not need additional personnel around.
These are all factors that have to be considered when thinking about the CapEx expenditure and investment. When we consider these factors, a modular system investment is a much better situation than looking at a furnace-to-furnace replacement, and that’s really the thought process that clients need to go through to understand the actual investment and value of the system.
Doug Glenn: What about the operational expenses?
Dennis Beauchesne: For instances, if you had a batch IQ sitting there, you would typically keep it running whether it has a load in it or not. With a modular system, you just shut off that cell that you’re not using. It does not take any more energy. If you are not working five days a week, you do not use it on the weekends — you shut it off. You do not use it during Christmas shutdown or any holiday shutdown, vacation shutdown. You’re able to shut it off and that means saving a lot of energy and labor by having it off.
Also, in the opposite way, you could run it lights out if you wanted, as well. You could stock up a number of loads on the automation before you leave, have the system operate it, run it, and have the load come back out before the morning. You could have it time start as well, if you wanted to start it on Monday at 5 AM, but you will not be there till 8 AM. You would come in and the furnace would be hot and ready to run a process.
There are a number of operational advances over the typical operational heat treat that’s out there today.
Doug Glenn: How does maintenance work with these systems? Say your heating element goes bad in cell number three, do I have to shut the whole system down to fix or can I fix number three and leave the rest of the system up and running?
Dennis Beauchesne: In this situation if you had a tunnel like we showed, you would typically shut off that cell; that is, if you knew that heating element was out or it wasn’t heating properly, you could shut off that cell, de-validate is what we call it, and then keep running the rest of the system until you had a window in your production that you could shut the whole system to get into that heating element.
If you had a system with doors on the front, it could be possible to go in the back while the system is operating. Then, it would be all based on your safety requirements for your plant and those kinds of things.
To do that, we have another system called the Jumbo, and it is much more flexible in the maintenance world. It has a vacuum car that moves down on rails and docks and mates with every heating cell on the system. In that line, the heating cell can actually be isolated from the rest of the line. You would just slide it back (It’s on wheels, it slides back about three feet away from the line), you put in a new piece of safety fence, and you continue to run your line. You can completely lock out/tag out that cell and work on it completely.
Doug Glenn: How would you approach a vacuum leak since the whole system is connected, right? I believe you mentioned these are graphite-on-graphite doors.
Dennis Beauchesne: You would want to fix the leak before you move on. Especially if it’s a bad leak. If it’s something that’s causing you to not maintain your process pressure, you certainly don’t want to do that, and that’s true with every vacuum piece of equipment.
ECM Modular Systems (38:55)
Doug Glenn: How many of these modular type systems does ECM have out in the marketplace?
Dennis Beauchesne: The Flex is the most popular modular system, which we discussed with the animation. We also have a number of Jumbos systems, and the unit in our Synergy Center is called a Nano, which has become more and more popular these days. The Nano has three different size chambers, but they’re typically smaller, 20x24x10 inch high size chamber. I explained a little bit about the Flex and the Jumbo is the same.
Out of those three systems, we have more than 350 modular systems, not just the heating cells, but more than 350 systems that are out in the marketplace today operating, running parts every day, running millions and millions of parts every week. Those systems are comprised of about 2,000 heating cells. As much as people hear about this being a new technology, it has actually been around about 30 years, and many companies have been using these systems and have replaced a number of pusher furnaces and those style furnaces for high-capacity installations especially.
Doug Glenn: Okay, that sounds good. I really appreciate your time.
About the Guest
Dennis Beauchesne General Manager ECM USA
Dennis Beauchesne joined ECM over 25 years ago and has since amassed extensive vacuum furnace technology experience with over 200 vacuum carburizing cells installed on high pressure gas quenching and oil quenching installations. Within the last 10 years, his expertise has expanded to include robotics and advanced automation with the heat treat industry high-demand for complete furnace system solutions. As General Manager of ECM USA, Dennis oversees customer supply, operations and metallurgical support for Canada, U.S., and Mexico for ECM Technologies. He has worked in the thermal transfer equipment supply industry for over 30 years.
Heat treatment impacts almost every facet of our lives, yet few people are aware of how important this practice is to a modern way of living. Heat treatment is a process which changes the microstructure of a metal, such as hardening, carburizing, tempering, and many others.
When a metal is formed, it undergoes heat treatment in order to make it longer lasting, change its structure so that it becomes harder or softer, or reduce the tendancy toward cracking which can form during manufacturing. To help us appreciate the impact of heat treatment on our daily lives, Tiffany Ward, daily editor for Heat Treat Today, has prepared this illustrative post.
Breakfast of Champions
You wake up in the morning and roll yourself out of bed, greeting a foggy sunrise through the window. You stumble to the kitchen to fire up your cast iron skillet.
Cast iron contains a minimum of 2% carbon
At one time, that same cast iron skillet lived a provincial life, known as simply: iron. Cast iron is made from iron with greater than 2% carbon, which is in the form of graphite. When that iron was “cast,” it was melted at a high temperature, and once cooled, it transformed into a very stable material that heats and cools uniformly. Perfect for your sunny-side-up eggs.
At the foundry, someone poured the molten metal into a mold to form the exact shape your pan is in today, and then it underwent numerous heat treat processes: annealing, normalizing, tempering, and even graphitizing (a process of converting carbon into graphite). The particular processes the skillet underwent depend upon the chemistry of the cast iron.
Almost all cast iron has carbon and nitrogen added to its surface in a process called ferritic nitrocarburizing plus post-oxidation. This heat treatment gives a shallow surface layer to the pan for better wear resistance. The skillet is heated up between around 1550°F and 1650°F inside a protective atmosphere of Endothermic gas. Endothermic gas is a generated heat treat atmosphere. It is made up of approximately 40% hydrogen, 40% nitrogen, and 20% carbon monoxide. The Endothermic gas is enriched with both a hydrocarbon gas (i.e., natural gas or propane) and ammonia so that carbon and nitrogen can be added to the iron.
There are a variety of different furnaces that can be used for ferritic nitrocarburizing. Box, pit, and tip-up furnaces are used due to their large capacity. For cast iron skillets, one common choice is the pit furnace — a cylindrical furnace typically located in the floor of a factory. Pit furnaces can hold a lot of heavyweight items, making them a good fit for the cookware now resting on your stove.
Figure Source: Herring, Daniel H., Atmosphere Heat Treatment Volume 1, BNP Media II, LLC, 2014.
You pull a knife out of your drawer and begin slicing an apple. The blade reflects a beam of sun from the window, but it isn’t your best knife. You’ve noticed that some of your knives are sharper and can resharpen more easily than others; this is because of the quality of the original material used and the heat treatment process employed in manufacturing the knife.
Perhaps the knife you chose to use today was made from high carbon steel such as 1095. The blade was heat treated using a process of hardening, quenching, and tempering. After the blade was formed, it entered a continuous mesh-belt furnace and was quenched in either oil (in the case of a 1095 steel), or in the case of stainless steel or tool steel, cooled in still air.
Source: Dan Herring, The HERRING GROUP, Inc.Figure: Batch integral-quench furnace system installation (courtesy of AFC-Holcroft). Dan Herring, The HERRING GROUP, Inc.
At the same time of hardening and quenching, the handle was joined to the blade in a process called brazing. The entire knife was heated up to an austenitizing temperature and rapidly cooled in the quenching process, giving it a particular hardness level.
The hardening process can be performed in a vacuum furnace or an atmosphere furnace. The atmosphere is typically nitrogen or, more commonly, a nitrogen/hydrogen mixture. Another option is nitrogen plus dissociated ammonia (dissociated ammonia is 75% hydrogen, 25% nitrogen).
A typical temperature for the heat treatment of high carbon 1095 steel knives is 1475ºF. Stainless steels are run at higher temperatures, typically in the range of 1800º/1950ºF and tool steels even higher, to around 2200ºF.
After breakfast you head to the bathroom. You are anxious to rid yourself of unshaven scruff, carefully running a razor over your face. The razor blades were hardened and tempered for sharpness, so that you get a smooth, clean shave.
Like knives, razor blades are hardened and are made of a medium to high carbon steel. Unlike knives, they are hardened in a continuous strip form. Envision all of your razor blades as a single, thin strip, run continuously through a furnace to heat and cool them. The blade is heated in a protective atmosphere as it runs through the furnace. On one end of the furnace is a reel that coils the strip and at the other end is an un-coiler.
Continuous style furnaces have alloy tubes inside of them that are very small in diameter, typically one inch, which run the entire length of the furnace. As the razor strip is run through the tube it is exposed to an atmosphere of nitrogen and hydrogen, typically with 3% hydrogen, to protect the razor blade surface from oxidation. Once heated, the blade enters cooling either by surrounding the tube with water or by blowing forced air on the tubes.
A process called tempering follows hardening and quenching. When you harden a material you make it stronger, but less ductile, so there is a concern that the razor blade might break. The tempering process improves ductility, removing some of the hardness but improving flexibility.
Dan Herring, The Heat Treat Doctor®, describes the balancing act this way: “On one end of the teeter totter, metallurgically, are strength properties and on the other side of the teeter-totter are ductility properties. It’s always a challenge to properly balance the teeter-totter. If you get the hardness too high, what happens to the ductility? It’s very low. As a result, the material is super hard but may crack easier. On the other hand, if ductility is too high, the material is super flexible so that it can bend like a branch of a tree in the wind, but it has little strength. You need a balance of strength and ductility in all heat treated products, which is accomplished in part by proper tempering.”
Our lives are touched by heat treatment at every turn. Highly technical processes play their role in the formation of even the most common household items. While heat treatment may seem to some a niche industry, its impact on everyday life is ubiquitous.
A special note of thanks to Dan Herring, The Heat Treat Doctor®, for his insights and contributions which informed this post.
The Heat Treat Doctor® has returned to offer sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues.
Today’s Technical Tuesday is a pre-release foretaste of the great content you can find in Heat Treat Today’sJuly 2025 Super Brands print edition.
Heat treaters and metallurgists speak a language unique to our industry and it can be confusing at times; terms like intergranular oxidation (IGO) and intergranular attack (IGA) are good examples, as these terms are often (incorrectly) used interchangeably. While these two phenomena sound similar, they have distinct mechanisms, causes, and impacts on material properties. Expert Dan Herring explores them more below.
What is IGO?
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IGO is a process by which oxygen preferentially reacts with the metal surface at the grain boundaries, creating oxides (Figure 1). It is not uncommon, for example, to see IGO present after a hardening process run in an Endothermic or nitrogen/methanol atmosphere. As parts are heated to austenitizing temperature, oxygen present due to minute air leaks or produced during the various chemical reactions with the atmosphere results in IGO. The grain boundaries are highly susceptible to oxidation because these are areas where different crystallographic grains meet and are areas of high energy due to the atomic mismatch and disruption of the regular crystal lattice structure.
Figure 1. Intergranular oxidation (IGO) along the surface of a heat treated chromium steel component. 1000X – As Polished Source: The HERRING GROUP, Inc.
What is IGA?
Figure 2. Intergranular attack (IGA) along the surface of a martensitic steel component caused by excessive submersion time in a citric acid solution. 1000X – As Polished Source: The HERRING GROUP, Inc.
IGA, on the other hand, is a broader term that refers to a corrosion phenomenon (aka chemical attack) that specifically targets the grain boundaries of a material. Unlike IGO, intergranular attack (Figure 2) is not limited to oxidation reactions but encompasses a variety of forms of attack involving such things as the formation of precipitates, the dissolution of material at grain boundaries, or the creation of corrosion cracks. Common forms of IGA include stress corrosion cracking (SCC) or sensitization in stainless steel.
In stainless steels, IGA is often triggered by high-temperature environments, usually in the range of 840º – 1560ºF (450 – 850°C) where carbon reacts with chromium to form chromium carbides at the grain boundaries, thus reducing the material’s resistance to corrosion in localized regions. In other alloys, factors like pH, chloride concentration, and temperature can lead to IGA.
Both IGO and IGA weaken the material’s structural integrity or lead to embrittlement compromising the material’s integrity.
Effect on Material Properties
The main effect of intergranular oxidation is the degradation of the mechanical properties, particularly a reduction in both ductility and toughness. As oxidation progresses along the grain boundaries, the material tends to become brittle, which can lead to premature failure under certain types of stress or thermal cycling. IGO often appears visually as a uniform discoloration or thin oxide layer on the surface. Surface pitting is not typically observed.
By contrast, IGA often appears as visible cracks, pits, or localized regions where the metal has been attacked (along the grain boundaries). This leads to a reduction in mechanical strength and can lead to SCC under certain circumstances. IGA can severely compromise the integrity of the material, particularly in critical applications like pipelines, pressure vessels, and nuclear reactors.
Materials Involved
IGO is most commonly observed in steel, aluminum, titanium, and nickel-based alloys, not only during heat treatment but when exposed to oxidizing environments in high-temperature applications, which also result in degradation and loss of material strength and other properties.
IGA tends to be more prevalent in stainless steels, corrosion-resistant alloys, and aluminum alloys. It is especially noticeable in alloys that are susceptible to sensitization (where chromium carbides precipitate at grain boundaries), leading to localized corrosion and cracks. Alloys that form a passivating oxide layer can be more susceptible to IGA if that layer is disrupted.
Principal Concerns
The main concern with intergranular oxidation is material embrittlement, leading to reduced ductility and potential failure under mechanical stress, especially in high-temperature applications. It can also affect the integrity of critical components, such as those used in aerospace or power generation industries.
By contrast, the primary impact of intergranular attack is loss of material strength, leading to structural failure, often without any clear outward signs (e.g., under chloride-induced SCC). It is more likely to cause immediate failure or a dramatic loss in performance, especially in structures exposed to corrosive environments.
How to Detect IGO and IGA
IGO is typically detected by examining the material’s surface using optical or scanning electron microscopy (SEM). Non-destructive techniques, such as X-ray diffraction (XRD), can also be used.
IGA is usually detected through methods like microstructural examination, electrochemical testing, or failure analysis. Techniques, such as SEM or energy-dispersive X-ray spectroscopy (EDS), can be used to examine the grain boundary regions for signs of corrosion.
How to Avoid IGO and IGA
IGO can be avoided by one or more of the following:
Environmental control: Making sure the heat treat furnace has no leaks, reducing oxygen partial pressure or controlling the furnace atmosphere in high-temperature heat treat operations.
Alloy design: The use of materials with stable oxide-forming elements (e.g., chromium, titanium and aluminum) or alloys with high resistance to oxidation (e.g., nickel-based superalloys).
Temperature control: Maintaining lower process temperatures and shorter times where possible to prevent oxidation at the grain boundaries.
Coatings and surface treatments: Application of protective coatings, such as copper plating, post-heat treatment aluminizing, or chrome plating, to reduce oxygen interaction with the grain boundaries during service.
IGA can be avoided by one or more of the following:
Environmental control: Reducing exposure to aggressive chemicals (e.g., chloride ions) by maintaining proper pH levels or using inhibitors in post-cleaning processes.
Proper alloy selection: Selecting materials resistant to intergranular corrosion (e.g., low carbon “L” grades of stainless steel or alloys with improved grain boundary stability).
Heat treatment: Avoiding sensitization of stainless steel by proper heat treatment methods that prevent the formation of chromium carbides at grain boundaries.
Stress relief: Reducing the likelihood of stress corrosion cracking by managing internal stresses during manufacturing and in-service conditions.
Key Differences
The differences between these phenomena are summarized in Table 1.
Table 1. Key differences between IGO and IGA Source: The HERRING GROUP, Inc.
Summing Up
While both IGO and IGA involve attack at the grain boundaries, they differ in their mechanisms, causes, and effects. From a heat treater’s perspective, IGO most often results at high temperature in oxygen-bearing furnace atmospheres, while IGA often results from pre- or post-heat treatment processing (cleaning, passivation, plating, etc.). Proper material selection, furnace and environmental control, awareness of what can happen, and inspection for these effects are key to preventing them from occurring.
References
Roberge, Pierre R., Corrosion Engineering: Principles and Practice, Mc-Graw Hill LLC, 2008.
Stene, Einar S., Fundamentals of Corrosion: Mechanisms, Causes, and Monitoring.
Schweitzer, Philip A., Fundamentals of Corrosion: Mechanisms, Causes and Preventative Methods, CRC Press, 2009.
About the Author
Dan Herring “The Heat Treat Doctor” The HERRING GROUP, Inc.
Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.
The Heat Treat Doctor® has returned to offer sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues.
This informative piece was first released in Heat Treat Today’sApril 2025 Induction Heating & Melting print edition.
Of all the case hardening processes, boronizing (a.k.a. boriding) is perhaps the least understood and least appreciated. Let’s learn more.
In this era of using coating technologies (e.g., PVD, CVD, DLC) to produce hard, wear-resistant surface layers on component parts, one often forgets that there is a thermo-chemical treatment that often can outperform many of them.
Boronizing (a.k.a. Boriding)
Table 1. Examples of hardness levels achieved by boronizing*
*The hardness of the boride layer depends on the compound formed. For example, FeB is 1900–2100 HV, Fe2B is 1800–2000 HV, while Ti2B is 3000 HV.
Boronizing is a case hardening process that produces a very high surface hardness in steels and is used for severe wear applications (see Table 1). The layer of borides (FeB and Fe2B) formed also significantly increases corrosion resistance of the steel.
Boron is added to steels for its unique ability to increase hardenability and lower the coefficient of (sliding) friction. In addition, boron is used to control phase transformation and microstructure since the time-temperature-transformation curve for the material when boron is diffused into the surface is shifted to the right.
The Process
The boronizing process is typically run in a solid (pack), liquid, or gaseous medium. Each of these methods involves the diffusion of boron into the steel’s surface, but they differ in how boron is introduced and the conditions under which they operate.
In the pack boronizing, a powder mixture of boron compounds (typically boron carbide or sodium tetrafluoroborate) is packed around the steel workpieces. This pack is placed in a retort-style furnace where it is heated, typically with an argon cover gas, to temperatures ranging from 1300°F to 1832°F (700°C to 1000°C). The heat causes the boron to diffuse into the steel surface, forming a boride layer (Figure 1).
A key advantage of this method of boronizing is that it is highly effective for producing uniform boride coatings. It is particularly suitable for large parts or components that may not be suitable for immersion in a liquid or exposure to gaseous boron compounds.
In liquid boronizing, the steel is immersed in a molten bath containing boron-bearing compounds, typically a mixture of sodium tetraborate and other chemicals. The steel absorbs boron from the bath, forming a boride layer. The liquid process tends to be faster than the solid method and can be more economical for certain applications.
One of the challenges with liquid boronizing is that the process can be difficult to control in terms of coating thickness and uniformity. Therefore, this method is often used for smaller, simpler parts rather than large or complex geometries.
Gaseous boronizing involves exposing the steel to a boron-containing gas, typically diborane (B2H6) or boron trifluoride (BF3), at elevated temperatures. The boron diffuses from the gas onto the surface of the steel, forming the boride layer. Gaseous boronizing allows for better control over the process compared to the other two methods, but it requires specialized equipment to handle the toxic and reactive nature of the boron gases.
The advantage of gaseous boronizing lies in its ability to produce a uniform and controlled boride layer, especially for complex parts or those with intricate geometries.
When working with any boron-containing compounds, adequate ventilation and other safety precautions (e.g., masks, gloves) are required. If boron tetrafloride is present, extra precautions are necessary since it is a poisonous gas.
Typical processing temperature is in the range of 1300°F–1832°F (700°C–1000°C) with time at temperature from 1 to 12 hours. Typical case depths achieved range from 0.003″–0.015″ (0.076 mm to 0.38 mm) or deeper (Figure 2). Case depths between 0.024″ and 0.030″ require longer cycles up to 48 hours in duration.
Figure 1. Typical microstructure of a boronized component
The mechanical properties of the borided alloys depend strongly on the composition and structure of the boride layers. The most desirable microstructure a er boronizing is a single-phase boride layer consisting of Fe2B2. Plain carbon and low alloy steels are good candidates for boronizing, while more highly alloyed steels may produce a dualphase layer (i.e., boron-rich FeB compounds) because the alloying elements interfere with boron diffusion. The boron-rich diffusion zone can be up to seven times deeper than the boride layer thickness into the substrate.
The hardness of the borided layer depends on the composition of the base steel (Table 1). Comparative data on steels that have been borided versus carburized or carbonitrided, nitrided or nitrocarburized are available in the literature (see Campos-Silva and Rodriguez-Castro, “Boriding,” 651–702). The surface hardness achieved through boronizing is among the highest for case hardening processes. The boride layers typically exhibit hardness values in the range of 1000 to 1800 HV. This level of hardness helps prevent surface deformation under load, which is particularly beneficial in applications involving high contact pressures, such as gears, bearings, and automotive components.
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Boronizing can also lower the coefficient of friction on the surface of the steel. This is particularly useful in applications where reduced friction is necessary, such as in sliding or rotating parts that operate under high pressures. The reduced friction helps to minimize wear and energy consumption, improving the overall efficiency and longevity of the components.
Unlike other surface-hardening methods that can compromise the core properties of the material, boronizing tends to retain the toughness and ductility of the base steel. This means the steel remains strong and resistant to cracking or breaking while also benefiting from a hard, wear-resistant surface.
By contrast, when boron is used as an alloying element in plain carbon and low alloy steels, it is added to increase the core hardenability and not the case hardenability. In fact, boron can actually decrease the case hardenability in carburized steels. Boron “works” by suppressing the nucleation (but not the growth) of proeutectoid ferrite on austenitic grain boundaries. Boron’s effectiveness increases linearly up to around 0.002% then levels off.
Figure 2. Hardness-depth profiles on different borided steel* * Notes: 1. The boriding temperature was 1740°F (950°C) with six (6) hours of exposure 2. Hardness conversion: 1 GPa = 102 HV (Vickers hardness) 3. Depth conversion: 10 micrometers = 0.00039 inches
Boronizing Applications
Given the range of benefits that boronizing offers, it has found widespread use across many industries. Some of the most common applications include:
Automotive industry: Gears, camshafts, and valve components are often boronized to enhance wear resistance and extend their service life.
Aerospace: Parts exposed to high temperatures and wear, such as turbine blades, landing gears, and other critical engine components, benefit from the hard, wear-resistant coatings created by boronizing.
Cutting tools and dies: The high surface hardness and resistance to abrasion make boronized tools highly effective for machining and forming hard materials.
Mining and earthmoving equipment: Equipment like drill bits, shovels, and conveyor parts subjected to abrasive conditions can be boronized to improve their performance and reduce downtime.
Oil and gas: Valves, pumps, and other equipment exposed to corrosive fluids in the oil and gas industry benefit from the enhanced corrosion resistance of boronizing.
In Summary
Boronizing is not for everyone, but it is safe to say that it is the “forgotten” case hardening process, one that will find increasing use in the future as demand for better tribological properties increases. It is a highly effective surface treatment process that imparts significant benefits to steel, including enhanced wear and corrosion resistance, increased surface hardness, and improved frictional properties. By carefully selecting the boronizing method and optimizing process parameters, manufacturers can produce components with superior performance in demanding applications. As industries continue to push the boundaries of material performance, boronizing can be an essential technique for producing long-lasting, high-performance steel components.
References
Campos-Silva. I. E., and G. A. Rodriguez-Castro, “Boriding to Improve the mechanical properties and corrosion resistance of steels.” In Thermochemical Surface Engineering of Steels, edited E. J. Mittemeijer and M. A. J. Somers. Woodhead Publishing, 2014.
Herring, Daniel H. Atmosphere Heat Treatment, vol. I. BNP Media, 2014.
Kulka, Michal. “Current Trends in Boriding: Techniques.” Springer Nature, 2019.
Senatorski, Jan, Jan Tacikowski, and Paweł Mączyński. “Tribological Properties and Metallurgical Characteristics of Different Diffusion Layers Formed on Steel.” Inżynieria Powierzchni 24, no. 4 (2019).
About the Author
Dan Herring “The Heat Treat Doctor” The HERRING GROUP, Inc.
Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.
In this Technical Tuesday by Paulo Duarte, project manager, Metalsolvus, explores how digital tools lead the way in vacuum hardening operations to ensure energy efficiency and processing repeatability.
This piece was originally published inHeat Treat Today’sMarch 2025 Aerospace print edition.
Vacuum hardening has been the chosen process for hardening tools used in plastic injection, die casting, and metal sheet stamping over the past few decades. Although widely used and accepted, there is still room for improvement in tool performance through quality-driven procedures. By employing easy methods of measurement, study, and testing, it is possible to enhance part integrity and mechanical properties, while simultaneously reducing heat treatment time and energy consumption. Advanced metallurgical analyses of heat treatment cycles and equipment can introduce better tools on the market, as well as provide time and cost saving heat treatments.
Basics of Vacuum Hardening
In vacuum hardening furnaces, temperature and time are carefully controlled at specific load locations to ensure optimal hardening. Optimal practices focus on heating and soaking the metal parts during heat treatment. The controlled introduction of vacuum and inert gases during the process ensures the right protective atmosphere for treatment, resulting in steel that is mainly free from oxidation and decarburization. This preserves the surface integrity of the tools.
Cooling is achieved through the injection of an inert gas into the heating chamber, with controlled pressure and adequate recirculation between the heat exchanger and the hot zone (Figure 1). Different gas injection directions are utilized depending on the load being treated, ensuring optimal cooling.
Figure 1. Cooling parts in vacuum hardening furnaces — inert gas injection on the hot chamber during cooling
Hardening of Large Tools
Heating and quenching large tools is one of the most challenging situations for vacuum hardening, as temperature control and part microstructure integrity are more difficult to obtain, which affects part quality. Large tools, typically made of hot work tool steels, are hardened in large furnaces. To minimize deformation, parts are preferably positioned vertically inside the furnace (Figure 2).
Figure 2. Large molds positioned inside the vacuum hardening furnace, two parallel cavities
Surface soaking times for big tools can significantly exceed standard austenitization and tempering times due to thermal gradients existing within the parts. Mold cores usually achieve the right soaking and tempering recommendation through accurate temperature control, monitored by well-positioned core thermocouples. A tool’s microstructure and performance will depend heavily on geometry, size, and temperature uniformity achieved during treatment. See Figure 3 for the core and surface typical hardening cycles for large tools.
Figure 3. Heating and soaking cycle for the hardening of large tools (“Heat Treatment of a AISI H11 Premium Hot-Work Tool Steel”)
The cooling phase is crucial in determining the final properties of both the surface and core of the tool. Higher gas injection pressures result in faster cooling and increased toughness, but this also introduces greater deformation risks, when directly cooled from austenitization temperature, so martempering done at low pressures is usually required.
Balancing cooling pressure is one of the most secret topics in vacuum hardening. With a variety of parameters and procedures used among heat treaters, measuring and testing is essential for achieving consistent quality for better controlling the hardening process and attaining the best part quality.
Figure 4. Microstructure and toughness obtained after the use of different hardening cooling rates (image from Transactions of the 15th NADCA Congress, 1989)
The use of higher or lower inert gas pressures directly affects the cooling rate, making it faster or slower, respectively. Regulating the gas injection pressure during the cooling phase significantly impacts the material’s toughness, even when cooling occurs within the bainitic-martensitic domain commonly observed in vacuum hardening practices. Faster cooling leads to finer microstructures, which in turn results in tougher materials. However, fully martensitic microstructures are rarely achieved in industrial vacuum hardening furnaces and are typically limited to smaller loads composed of small parts. In larger parts, the risk of pearlite formation increases, especially when cooling rates fall around 3°C/min (5°F/min) at the core, as illustrated in Figures 4 and 5.
Figure 5. Microstructure of Uddeholm Orvar Supreme steel after quenching using different cooling rates
In industrial heat treatments of large tools, accurately monitoring core temperature is challenging, as it is difficult to position a thermocouple hole exactly at the innermost location or a nearby region. This makes it harder to control the hardening process and prevent pearlite formation. Therefore, studying the process to establish effective control measures is essential for achieving the highest possible quality.
Heat treatment simulation simplifies this task by allowing the hardening process to be predicted, with thermal gradients estimated and compensated through furnace control parameter adjustments. Figure 6 presents a real case study, where the temperature distribution inside a large mold was fully characterized during the entire heat treatment cycle using FEM (Finite element method) simulation and validated through actual thermocouple measurements. FEM simulation, as a proven and highly effective technique for predicting heat treatment cycles, enables heat treaters to implement optimized, computer-supported heat treatment practices.
Figure 6. Mold temperature gradients during vacuum hardening: a) FEM mesh, b) gradients during heating at lower temperatures, c) gradients at the last pre-heating steps, and d) gradients during austenitization from Maia et al. “Study of Heating Stage of Big Dimension Steel Parts Hardening”; e) gradients during mold cooling from Pinho et al. “Modelling and Simulation of Vacuum Hardening of Tool Steels”
Vacuum Hardening Standard Block Size and Cycle Forecast
When working with loads composed of small to medium-sized parts, the core temperature of the load can be monitored using dummy standard blocks. These blocks have a central hole to accommodate the thermocouple used to control the heat treatment cycle. The dummy block should be selected to closely match the size of the largest part in the load. However, in commercial heat treatment settings, part sizes can vary widely, making it di cult to maintain a comprehensive set of dummy blocks that represents all possible heat treatment scenarios.
Once again, simulation proves valuable in helping heat treaters gather useful data to anticipate the heat treatment cycle and determine the appropriate range of dummy blocks to have available on the shop floor. The procedure for selecting the dummy block range and forecasting the corresponding heat treatment times is outlined in the following equations. Ideally, the standard block should be made from the same material as the largest part in the load. If the materials differ, the characteristic length of the block can be calculated using the first of the following equations.
Table 1. Proposed dimensional distribution range for cubic and cylindrical
standard blocks and expected cycle times in a typical 600 x 600 x 900 mm
hardening furnace (data from Figueiredo et al., “Study of a Methodology for
Selecting Standard Blocks for Hardening Heat Treatments”)
Table 1 lists a range of proposed dummy block sizes to be used for monitoring the load temperature during heat treatment. The time to end of soaking at higher temperature is also given by Table 1 for a typical 600 x 600 x 900 mm hardening furnace. Times were obtained by FEM simulation and can be used to forecast the end of austenitization in a hardening process of each dummy block.
The simulated times were validated by using real parts temperature measurement by thermocouples. These were the calculated errors based on simulation and heat treat validation trial:
Plate Example: 20 x 300 x 200 mm
Ideal standard block: diameter or edge: 51 mm
Maximum Error — same material block:
Cylindrical: -0.2% (-0.7 min)
Cubic: -0.1% (-0.4 min)
Maximum Error — block — Stainless steel 304:
Cylindrical: +2.2% (+9.2 min)
Cubic: +1.65% (+6.9 min)
EDM Block Example: 200 x 200 x200 mm
Ideal standard block: diameter or edge: 200 mm
Maximum Error — same material block:
Cylindrical: -3.9% (-22.6 min)
Cubic: 0% (0 min)
Maximum Error — block — stainless steel 304:
Cylindrical: +17.3% (+100.3 min)
Cubic: +12.2% (+70.8 min)
Optimizing the Vacuum Hardening of Tools
Figure 7. Effect of selecting different temperature ( T)
range for starting to control the isothermal stage time. a)
T criteria and respective cycle time reduction; b) surface
mechanical properties obtained by using different T;
and c) core properties after tempering at different T
range (Miranda et al., “Heat Treatment of a AISI H11
Premium Hot-Work Tool Steel,” MSC)
FEM simulation can also be used to optimize the heat treatment process, but metallurgical testing remains crucial for providing reliable insights into safely reducing cycle time and energy consumption. Typically, for setting the isothermal stage time, a tolerance of -5°C relative to the temperature setpoint is used, leading to savings in both heat treatment duration and power consumption, as shown in Figure 7a. However, Figure 7b demonstrates that higher tolerance values (ΔT) can be considered. Tolerances of up to -10°C or even -20°C can be applied for controlling the soaking time without significantly affecting the hardness and toughness of the parts. Naturally, these results depend on the desired setpoints for the isothermal stages, but Figure 7c reflects the worst-case scenario for ΔT, referring to the use of lower austenitizing and tempering temperatures commonly applied in the hardening of hot-work tool steels.
Future Trends of Vacuum Hardening
Innovations like digitalization, automation, and resource reduction, as part of Industry 5.0 initiatives, are expected to drive advancements in heat treatment processes. Long martempering, a heat treatment under development for hardening hot-work tool steels, shows promise as an alternative to traditional quenching and tempering. This process offers a balance of high hardness and toughness in significantly less time, providing energy savings and faster turnaround.
Figure 8. New long martempering heat treatment cycle: AISI H13 premium toughness for two different long martempering temperatures (“Study of The Bainitic Transformation of H13 Premium Steel”)
New Vacuum Hardening Process — Long Martempering
Long martempering is a heat treatment under development that can be used to harden hot-work tool steels. Long martempering is a process somewhat similar to austempering but is applied to steels rather than cast irons. Performed at temperatures within the martempering range, long martempering corresponds to an interrupted bainitic heat treatment with a specific process window (Figure 8) where high toughness is achieved at hardness levels exceeding those obtained through traditional quenching and tempering. Table 2 lists the mechanical properties attained for 5Cr hot-work premium tool steels.
The transformation during long martempering is not yet fully characterized in terms of microstructure, however, curved needles of bainitic ferrite are observed without carbide precipitation. This phenomenon is generally not associated with steel but rather with ausferrite in cast irons. Nonetheless, it is evident in at least H11 and H13 premium steel grades. This one day martempering treatment could potentially replace the traditional two- to three-day heat treatment cycle for large tools, offering significantly faster lead times and reduced energy consumption. Moreover, the mechanical properties achieved through long martempering are notable, as high levels of both hardness and toughness are obtained simultaneously, as demonstrated in Table 2.
Table 2. Mechanical properties of the new hardening process — long martempering
Industry 5.0
The integration of heat treatment equipment with management software enhances furnace utilization, quality control systems, and maintenance practices. Industry 5.0 can be implemented in heat treatment plants through the connection of databases that collect inputs from furnaces (e.g., temperature, time, pressure, heating elements, and auxiliary equipment performance) and production data (e.g., batch numbers, order details, operator information, cycle setup, and load weight). This data is analyzed by software to generate valuable insights for plant management, process optimization, predictive maintenance, and quality control.
A supervision interface for a 5.0 solution can monitor furnaces and control them remotely in real time (Figure 9). Operators receive updates on tasks, alerts, and production schedules. Additionally, plant productivity, efficiency, and maintenance can be tracked through the same supervision software, whether on site or remote. Automatic reporting is also possible, enabling the approval or rejection of cycles based on criteria that are not typically used in heat treatment plants. This not only improves quality but also facilitates process optimization and cost reduction.
Conclusion
Figure 10. Heat treatment quality automatic report including automatic approval
Acquiring a full understanding of furnaces in operation through data measurement and analysis allows full control over the heat treatment process. This facilitates process development, enabling cycle optimization and improvement in part quality. Additionally, testing and simulation practices can lead to cost reduction and shorter lead times.
The introduction of long martempering and Industry 5.0 will significantly enhance heat treatment processes, leading to improved delivery times and reduced operational risks. Automation and digitalization bring more data to the shop floor, improving plant management and resulting in greater efficiency, higher quality parts, and simplified task execution.
Finally, current personnel are busy with routine operations that are based on longestablished practices and may be limiting opportunities for innovation. Therefore, new teams or external consultants can be leveraged to focus on designing, studying, testing, and implementing each new heat treatment solution.
References
Fernandes, José, Laura Ribeiro, and Paulo Duarte. “Study of the Bainitic Transformation of H13 Premium Steel.” MSC thesis, Faculty of Engineering of Oporto University, 2021.
Figueiredo, Ana, Paulo Coelho, José Marafona, and Paulo Duarte. “Study of a Methodology for Selecting Standard Blocks for Hardening Heat Treatments.” MSC thesis, Faculty of Engineering of Oporto University, 2022.
Kind & Co. “Vacuum Hardening with Highest Levels of Precision.” Accessed January 30, 2025. https://www.kind-co.de/en/company/technologies/vacuum-hardening.html.
Maia, Pedro, Paulo Coelho, José Marafona, and Paulo Duarte. “Study of Heating Stage of Big Dimensions Steel Parts Hardening.” MSC thesis, Faculty of Engineering of Oporto University, 2013.
Metaltec Solutions. “Brochure Presentation.” Accessed January 30, 2025. https://www.metalsolvus.pt/en/wp-content/uploads/2019/01/plant-supervisionbrochure-V3.pdf.
Miranda, Isabel, Laura Ribeiro, and Paulo Duarte. “Heat Treatment of AISI H11 Premium Hot-Work Tool Steel.” MSC thesis, Faculty of Engineering of Oporto University, 2024.
Pinho, José Eduardo, Gil Andrade Campos, and Paulo Duarte. “Modelling and Simulation of Vacuum Hardening of Tool Steels.” MSC thesis, Aveiro University, 2017.
Ramada. “New Hardening Furnace up to 4 Tons.” Accessed January 30, 2025. https://www.ramada.pt/pt/media/noticias/novoforno-de-tempera-vacuo—ate-4-tons-.html.
Schmetz. “Schmetz Heat Treatment Furnaces.” Accessed January 30, 2025. https://edelmetal.com.tr/en/heat-treatmentfurnaces.
Schmetz. Sketch of the Cooling Process in the Vacuum Hardening Furnace: Schmetz Commercial Proposals Drawing – Metalsolvus Training Courses Documentation.
Seco/Warwick. Vector 3D Hardening Furnace Commercial Brochure.
Solar Manufacturing. “Solar Vacuum Hardening Furnace.” Accessed January 30, 2025. https://solarmfg.com/vacuum-furnaces/horizontal-iq-vacuumfurnaces.
Wallace, J.F., W. Roberts, and E. Hakulinen. “Influence of Cooling Rate on the Microstructure and Toughness of Premium Grade H13 Die Steels.” Transactions of the 15th NADCA Congress (1989).
About the Author:
Paulo Duarte is a researcher and consultant on heat treat technologies. His education and expertise in metallurgy has culminated in several articles and patents. He was a former technical manager within bohleruddeholm group for the Portuguese market and heat treatment manager with the same group. Currently, Paulo efforts focus on helping heat treaters by providing innovative, more efficient, and profitable heat treatment services to companies.
For more information: Contact Paulo Duarte at paulo.duarte@metalsolvus.pt.
Digital tools lead the way in vacuum hardening operations to ensure energy efficiency and processing repeatability. In this Technical Tuesday installment, Paulo Duarte, project manager at Metalsolvus, examines various advantages of wrought versus cast alloys in heat treat operations.
This informative piece was first released in Heat Treat Today'sMarch 2025 Aerospace print edition.
Vacuum hardening has been the chosen process for hardening tools used in plastic injection, die casting, and metal sheet stamping over the past few decades. Although widely used and accepted, there is still room for improvement in tool performance through quality driven procedures. By employing easy methods of measurement, study, and testing, it is possible to enhance part integrity and mechanical properties, while simultaneously reducing heat treatment time and energy consumption. Advanced metallurgical analyses of heat treatment cycles and equipment can introduce better tools on the market, as well as provide time and cost saving heat treatments.
Basics of Vacuum Hardening
Figure 1. Cooling parts in vacuum hardening furnaces — inert gas injection on the hot chamber during cooling
In vacuum hardening furnaces, temperature and time are carefully controlled at specific load locations to ensure optimal hardening. Optimal practices focus on heating and soaking the metal parts during heat treatment. The controlled introduction of vacuum and inert gases during the process ensures the right protective atmosphere for treatment, resulting in steel that is mainly free from oxidation and decarburization. This preserves the surface integrity of the tools.
Cooling is achieved through the injection of an inert gas into the heating chamber, with controlled pressure and adequate recirculation between the heat exchanger and the hot zone (Figure 1). Different gas injection directions are utilized depending on the load being treated, ensuring optimal cooling.
Hardening of Large Tools
Figure 2. Large molds positioned inside the vacuum hardening furnace, two parallel cavities
Heating and quenching large tools is one of the most challenging situations for vacuum hardening, as temperature control and part microstructure integrity are more difficult to obtain, which affects part quality. Large tools, typically made of hot work tool steels, are hardened in large furnaces. To minimize deformation, parts are preferably positioned vertically inside the furnace (Figure 2).
Surface soaking times for big tools can significantly exceed
standard austenitization and tempering times due to thermal gradients existing within the parts. Mold cores usually achieve the right soaking and tempering recommendation through accurate temperature control, monitored by well-positioned core thermocouples. A tool’s microstructure and performance will depend heavily on geometry, size, and temperature uniformity achieved during treatment. See Figure 3 for the core and surface typical hardening cycles for large tools.
Figure 3. Heating and soaking cycle for the hardening of large tools (“Heat Treatment of a AISI H11 Premium Hot-Work Tool Steel”)
The cooling phase is crucial in determining the final properties of both the surface and core of the tool. Higher gas injection pressures result in faster cooling and increased toughness, but this also introduces greater deformation risks, when directly cooled from austenitization temperature, so martempering done at low pressures is usually required.
Balancing cooling pressure is one of the most secret topics in vacuum hardening. With a variety of parameters and procedures used among heat treaters, measuring and testing is essential for achieving consistent quality for better controlling the hardening process and attaining the best part quality.
Figure 4. Microstructure and toughness obtained after the use of different hardening cooling rates (image from Transactions of the 15th NADCA Congress, 1989)Figure 5. Microstructure of Uddeholm Orvar Supreme steel after quenching using different cooling rates
The use of higher or lower inert gas pressures directly affects the cooling rate, making it faster or slower, respectively. Regulating the gas injection pressure during the cooling phase significantly impacts the material’s toughness, even when cooling occurs within the bainitic-martensitic domain commonly observed in vacuum hardening practices. Faster cooling leads to finer microstructures, which in turn results in tougher materials. However, fully martensitic microstructures are rarely achieved in industrial vacuum hardening furnaces and are typically limited to smaller loads composed of small parts. In larger parts, the risk of pearlite formation increases, especially when cooling rates fall around 3°C/min (5°F/min) at the core, as illustrated in Figures 4 and 5.
In industrial heat treatments of large tools, accurately monitoring core temperature is challenging, as it is difficult to position a thermocouple hole exactly at the innermost location or a nearby region. This makes it harder to control the hardening process and prevent pearlite formation. Therefore, studying the process to establish effective control measures is essential for achieving the highest possible
quality.
Figure 6. Mold temperature gradients during vacuum hardening: a) FEM mesh, b) gradients during heating at lower temperatures, c) gradients at the last pre-heating steps, and d) gradients during austenitization from Maia et al. “Study of Heating Stage of Big Dimension Steel Parts Hardening”; e) gradients during mold cooling from Pinho et al. “Modelling and Simulation of Vacuum Hardening of Tool Steels”
Heat treatment simulation simplifies this task by allowing the hardening process to be predicted, with thermal gradients estimated and compensated through furnace control parameter adjustments. Figure 6 presents a real case study, where the temperature distribution inside a large mold was fully characterized during the entire heat treatment cycle using FEM (finite element method) simulation and validated through actual thermocouple measurements. FEM simulation, as a proven and highly effective technique for predicting heat treatment cycles, enables heat treaters to implement optimized, computer-supported heat treatment practices.
Vacuum Hardening Standard Block Size and Cycle Forecast
When working with loads composed of small to medium-sized parts, the core temperature of the load can be monitored using dummy standard blocks. These blocks have a central hole to accommodate the thermocouple used to control the heat treatment cycle. The dummy block should be selected to closely match the size of the largest part in the load. However, in commercial heat treatment settings, part sizes can vary widely, making it difficult to maintain a comprehensive set of dummy blocks that represents all possible heat treatment scenarios.
Once again, simulation proves valuable in helping heat treaters gather useful data to anticipate the heat treatment cycle and determine the appropriate range of dummy blocks to have available on the shop floor. The procedure for selecting the dummy block range and forecasting the corresponding heat treatment times is outlined in the following equations. Ideally, the standard block should be made from the same material as the largest part in the load. If the materials differ, the characteristic length of the block can be calculated using the first of the equations to the right.
Table 1 lists a range of proposed dummy block sizes to be used for monitoring the load temperature during heat treatment. The time to end of soaking at higher temperature is also given by Table 1 for a typical 600 x 600 x 900 mm hardening furnace. Times were obtained by FEM simulation and can be used to forecast the end of austenitization in a hardening process of each dummy block.
Table 1. Proposed dimensional distribution range for cubic and cylindrical standard blocks and expected cycle times in a typical 600 x 600 x 900 mm hardening furnace (data from Figueiredo et al., “Study of a Methodology for Selecting Standard Blocks for Hardening Heat Treatments”)
The simulated times were validated by using real parts temperature measurement by thermocouples. These were the calculated errors based on simulation and heat treat validation trial:
Optimizing the Vacuum Hardening of Tools
Figure 7. Effect of selecting different temperature (ΔT) range for starting to control the isothermal stage time. a) ΔT criteria and respective cycle time reduction; b) surface mechanical properties obtained by using different ΔT; and c) core properties after tempering at different ΔT range (Miranda et al., “Heat Treatment of a AISI H11 Premium Hot-Work Tool Steel,” MSC)
FEM simulation can also be used to optimize the heat treatment process, but metallurgical testing remains crucial for providing reliable insights into safely reducing cycle time and energy consumption. Typically, for setting the isothermal stage time, a tolerance of -5°C relative to the temperature setpoint is used, leading to savings in both heat treatment duration and power consumption, as shown in Figure 7a. However, Figure 7b demonstrates that higher tolerance values (ΔT) can be considered. Tolerances of up to -10°C or even -20°C can be applied for controlling the soaking time without significantly affecting the hardness and toughness of the parts. Naturally, these results depend on the desired setpoints for the isothermal stages, but Figure 7c reflects the worst-case scenario for ΔT, referring to the use of lower austenitizing and tempering temperatures commonly applied in the hardening of hot-work tool steels.
Future Trends of Vacuum Hardening
Innovations like digitalization, automation, and resource reduction, as part of Industry 5.0 initiatives, are expected to drive advancements in heat treatment processes. Long martempering, a heat treatment under development for hardening hot-work tool steels, shows promise as an alternative to traditional quenching and tempering. This process offers a balance of high hardness and toughness in significantly less time, providing energy savings and faster turnaround.
New Vacuum Hardening Process — Long Martempering
Figure 8. New long martempering heat treatment cycle: AISI H13 premium toughness for two different long martempering temperatures (“Study of The Bainitic Transformation of H13 Premium Steel”)
Long martempering is a heat treatment under development that can be used to harden hot-work tool steels. Long martempering is a process somewhat similar to austempering but is applied to steels rather than cast irons. Performed at temperatures within the martempering range, long martempering corresponds to an interrupted bainitic heat treatment with a specific process window (Figure 8) where high toughness is achieved at hardness levels exceeding those obtained through traditional quenching and tempering. Table 2 lists the mechanical properties attained for 5Cr hot-work premium tool steels.
Table 2. Mechanical properties of the new hardening process — long martempering
The transformation during long martempering is not yet fully characterized in terms of microstructure, however, curved needles of bainitic ferrite are observed without carbide precipitation. This phenomenon is generally not associated with steel but rather with ausferrite in cast irons. Nonetheless, it is evident in at least H11 and H13 premium steel grades. This one day martempering treatment could potentially replace the traditional two- to three-day heat treatment cycle for large tools, offering significantly faster lead times and reduced energy consumption. Moreover, the mechanical properties achieved through long martempering are notable, as high levels of both hardness and toughness are obtained simultaneously, as demonstrated in Table 2.
The integration of heat treatment equipment with management software enhances furnace utilization, quality control systems, and maintenance practices. Industry 5.0 can be implemented in heat treatment plants through the connection of databases that collect inputs from furnaces (e.g., temperature, time, pressure, heating elements, and auxiliary equipment performance) and production data (e.g., batch numbers, order details, operator information, cycle setup, and load weight). This data is analyzed by software to generate valuable insights for plant management, process optimization, predictive maintenance, and quality control.
A supervision interface for a 5.0 solution can monitor furnaces and control them remotely in real time (Figure 9). Operators receive updates on tasks, alerts, and production schedules. Additionally, plant productivity, efficiency, and maintenance can be tracked through the same supervision software, whether on site or remote. Automatic reporting is also possible, enabling the approval or rejection of cycles based on criteria that are not typically used in heat treatment plants. This not only improves quality but also facilitates process optimization and cost reduction.
Conclusion
Acquiring a full understanding of furnaces in operation through data measurement and analysis allows full control over the heat treatment process. This facilitates process development, enabling cycle optimization and improvement in part quality. Additionally, testing and simulation practices can lead to cost reduction and shorter lead times.
The introduction of long martempering and Industry 5.0 will significantly enhance heat treatment processes, leading to improved delivery times and reduced operational risks. Automation and digitalization bring more data to the shop floor, improving plant management and resulting in greater efficiency, higher quality parts, and simplified task execution.
Finally, current personnel are busy with routine operations that are based on long established practices and may be limiting opportunities for innovation. Therefore, new teams or external consultants can be leveraged to focus on designing, studying, testing, and implementing each new heat treatment solution.
References
Fernandes, José, Laura Ribeiro, and Paulo Duarte. “Study of the Bainitic Transformation of H13 Premium Steel.” MSC thesis, Faculty of Engineering of Oporto University, 2021.
Figueiredo, Ana, Paulo Coelho, José Marafona, and Paulo Duarte. “Study of a Methodology for Selecting Standard Blocks for Hardening Heat Treatments.” MSC thesis, Faculty of Engineering of Oporto University, 2022.
Kind & Co. “Vacuum Hardening with Highest Levels of Precision.” Accessed January 30, 2025. https://www.kind-co.de/en/company/technologies/vacuum-hardening.html.
Maia, Pedro, Paulo Coelho, José Marafona, and Paulo Duarte. “Study of Heating Stage of Big Dimensions Steel Parts Hardening.” MSC thesis, Faculty of Engineering of Oporto University, 2013.
Metaltec Solutions. “Brochure Presentation.” Accessed January 30, 2025. https://www.metalsolvus.pt/en/wp-content/uploads/2019/01/plant-supervision-brochure-V3.pdf.
Miranda, Isabel, Laura Ribeiro, and Paulo Duarte. “Heat Treatment of AISI H11 Premium Hot-Work Tool Steel.” MSC thesis, Faculty of Engineering of Oporto University, 2024.
Pinho, José Eduardo, Gil Andrade Campos, and Paulo Duarte. “Modelling and Simulation of Vacuum Hardening of Tool Steels.” MSC thesis, Aveiro University, 2017.
Ramada. “New Hardening Furnace up to 4 Tons.” Accessed January 30, 2025. https://www.ramada.pt/pt/media/noticias/novo-forno-de-tempera-vacuo---ate-4-tons-.html.
Schmetz. “Schmetz Heat Treatment Furnaces.” Accessed January 30, 2025. https://edelmetal.com.tr/en/heat-treatment-furnaces.
Schmetz. Sketch of the Cooling Process in the Vacuum Hardening Furnace: Schmetz Commercial Proposals Drawing – Metalsolvus Training Courses Documentation.
Seco/Warwick. Vector 3D Hardening Furnace Commercial Brochure.
Solar Manufacturing. “Solar Vacuum Hardening Furnace.” Accessed January 30, https://solarmfg.com/vacuum-furnaces-horizontal-iq-vacuum-furnaces.
Wallace, J.F., W. Roberts, and E. Hakulinen. “Influence of Cooling Rate on the Microstructure and Toughness of Premium Grade H13 Die Steels.” Transactions of the 15th NADCA Congress (1989).
About The Author:
Paulo Duarte, project manager at Metalsolvus, is a researcher and consultant on heat treat technologies. His education and expertise in metallurgy has culminated in several articles and patents. He was a former technical manager within bohler-uddeholm group for the Portuguese market and heat treatment manager with the same group. Currently, Paulo focus on helping heat treaters by providing innovative, more efficient, and profitable heat treatment services to companies.
For more information: Contact Paulo Duarte at paulo.duarte@metalsolvus.pt.
The Heat Treat Doctor® has returned to offer sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues.
This informative piece was first released in Heat Treat Today’sMarch 2025 Aerospace Heat Treating print edition.
Last time (Air & Atmosphere Heat Treating, February 2025) we addressed the question of why normalizing is necessary. Here we look at the importance of a “still air” cool on the final result. Let’s learn more.
What Is a “Still Air” Cool?
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As we learned last month, the term “cooling in air” is associated with normalizing but poorly defined in the literature or in practice, either in terms of cooling rate or microstructural outcome. This lack of specificity has resulted not only in many different interpretations of what is needed, but in a great deal of variability in the final part microstructure.
By way of example, this writer has on multiple occasions asked what changes are made to car bottom furnace cycles where cars are pulled outside of the plant for “air cooling” (Figure 1). Questions such as, is the furnace opened and the car pulled out in inclement weather? And, is this practice done on a particularly windy day, or in a rain or snowstorm or when the temperature is below zero? An all-too-common response is, “Only if it isn’t raining ‘too hard’ or snowing ‘too much’; then, we wait a while.” No wonder part microstructures are often found to vary from part to part and load to load!
Most heat treaters agree, however, that normalizing is optimized by a cooling in “still air.” This term also hasn’t been clearly defined, but it will be here based on both an extensive survey of the literature and the most common heat treat practices. In Vacuum Heat Treatment, Volume II, I define a still air cool as: “Cooling at a rate of 40°F (22°C) per minute … to 1100°F (593°C) and then at a rate of 15°F–25°F (8°C–14°C) per minute from 1100°F (593°C) to 300°F (150°C). Any cooling rate can be used below 300°F (150°C).”
Typical car bottom normalizing furnace opening to the outside environment
In addition, many consider nitrogen gas quenching in a vacuum furnace at 1–2 bar pressure to be equivalent to a still air cool. But again, so many factors are involved that only properly positioned workload thermocouples can confirm the above cooling rates are being achieved.
Also, many use the term “air cooling” to differentiate the process from “air quenching,” “controlled cooling,” and “fan cooling.”
Recall from the previous installment of this column that any ambiguity with respect to cooling rate ought to be defined in engineering specifications and/or heat treat instructions so that the desired outcome of the process can be firmly established.
From the literature, several important observations will serve as cautionary reminders. In STEELS, George Krauss points out that: “Air cooling associated with normalizing produces a range of cooling rates depending on section size [and to some extent, load mass]. Heavier sections air cool at much lower cooling rates than do light sections because of the added time required for thermal conductivity to lower temperatures of central portions of the workpiece.”
George Totten’s work in Steel Heat Treatment indicates: “Cooling … usually occurs in air, and the actual cooling rate depends on the mass which is cooled.” He goes on to state:
After metalworking, forgings and rolled products are often given an annealing or normalizing heat treatment to reduce hardness so that the steel may be in the best condition for machining. These processes also reduce residual stress in the steel. Annealing and normalizing are terms used interchangeably, but they do have specific meaning. Both terms imply heating the steel above the transformation range. The difference lies in the cooling method. Annealing requires a slow [furnace] cooling rate, whereas normalized parts are cooled faster in still, room-temperature air. Annealing can be a lengthy process but produces relatively consistent results, where normalizing is much faster (and therefore favored from a cost point of view) but can lead to variable results depending on the position of the part in the batch and the variation of the section thickness in the part that is stress-relieved.
In “The Importance of Normalizing,” this writer offers the following caution: “It is important to remember that the mass of the part or the workload can have a significant influence on the cooling rate and thus on the resulting microstructure.”
Finally, Krauss again observes: “The British Steel Corporation atlas for cooling transformation (Ref. 13.7) establishes directly for many steels the effect of section size on microstructures produced by air cooling.” (Note: Interpretation of continuous cooling transformation (CCT) curves will be the subject of a future “Ask The Heat Treat Doctor” column.)
Since hardness is one of the most commonly used criteria to determine if a heat treat process has been successful, it should also be noted that one can usually predict the hardness of a properly normalized part by looking at the J40 value when Jominy data is available.
The Metallus (formerly TimkenSteel) “Practical Data for Metallurgists” provides an example of the type of data available to metallurgists and engineers to help define a required cooling rate for normalizing (Figure 2).
All literature references to normalizing agree (or infer) that the resultant microstructure produced plays a significant role in both the properties developed and their impact on subsequent operations.
Figure 2. Combined hardenability chart for normalized and austenitized SAE 4140 steel showing approximate still air cooling rates and resultant hardness (data based on a thermocouple located in the center of the bar diameter indicated)
Final Thoughts — The State of the Industry
It is all too common within the industry for some companies who wish to have normalizing performed on their products to specify only a hardness range on the engineering drawing or purchase order callout that is given to the heat treater.
Industry normalizing practice here in North America varies considerably from company to company. Normalizing instructions are sometimes, but not often enough, provided on either purchase orders, engineering drawings, or in specifications (industry standards or company-specific documents). These instructions range from, in the case of certain weldments, absolutely nothing (i.e., no hardness, microstructure, or mechanical properties) to referencing industry specifications (e.g., AMS2759/1) or specifying complete metallurgical and mechanical testing including hardness and microstructure.
Most commercial heat treaters often perform normalizing to client or industry specifications provided to them. Others prefer so-called “flow down” instructions in which the process recipe is provided to them. It is a common (and mistaken) belief that this removes the obligation of achieving a given set of mechanical or metallurgical properties even if they are called out by specification, drawing, or purchase order.
Also, the final mechanical properties that result from normalizing are seldom verified by the heat treater. Rather, a hardness value (or range) is reported, but hardness is not a fundamental material property, rather a composite value, one which is influenced by, for example, the yield strength, work hardening, true tensile strength, and modulus of elasticity of the material.
Krauss, George. STEELS: Processing, Structures, and Performance, ASM International, 2005.
Practical Data for Metallurgists, 17th ed. TimkenSteel, 2011
Totten, George E., ed. Steel Heat Treatment Handbook, vol. 2, 2nd ed., CRC Press, 2007.
About the Author
Dan Herring “The Heat Treat Doctor” The HERRING GROUP, Inc.
Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.
The Heat Treat Doctor® has returned to offer sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues.
This informative piece was first released in Heat Treat Today’sFebruary 2025 Air/Atmosphere Furnace Systems print edition.
People often ask two fundamental questions related to normalizing. First, is it necessary? Second, just what and how important is a “still air” cool to the end result? Let’s learn more.
Why Normalize?
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Normalizing is typically performed for one or more of the following reasons:
To improve machinability
To improve dimensional stability
To produce a homogeneous microstructure
To reduce banding
To improve ductility
To modify and/or refine the grain structure
To provide a more consistent response when hardening or case hardening
For example, many gear blanks are normalized prior to machining so that during subsequent hardening or case hardening dimensional changes such as growth, shrinkage, or warpage will be better controlled.
Normalizing imparts hardness and strength to both cast iron and steel components. In addition, normalizing helps reduce internal stresses induced by such operations as forging, casting, machining, forming or welding. Normalizing also improves chemical non-homogeneity, improves response to heat treatment (e.g., hardening), and enhances dimensional stability by imparting into the component part a “thermal memory” for subsequent lower temperature processes. Parts that require maximum toughness and those subjected to impact are often normalized. When large cross sections are normalized, they are also tempered to further reduce stress and more closely control mechanical properties.
Large paper roll normalized in a car bottom furnace and cooled (due to its mass) using the assistance of a floor fan.
Soak periods for normalizing are typically one hour per inch of cross-sectional area but not less than two hours at temperature. It is important to remember that the mass of the part or the workload can have a significant influence on the cooling rate and thus on the final microstructure. Thin pieces cool faster and are harder after normalizing than thicker ones. By contrast, after furnace cooling in an annealing process, the hardness of the thin and thicker sections is usually about the same.
Micrograph of medium-carbon AISI/SAE 1040 steel showing ferrite grains (white etching constituent) and pearlite (dark etching constituent). Etched in 4% picral followed by 2% nital. (Bramfitt and Benscoter, 2002, p. 4. Reprinted with permission of ASM International. All rights reserved.)
When people think of normalizing, they often relate it to a microstructure consisting primarily of pearlite and ferrite. However, normalized microstructures can vary and combinations of ferrite, pearlite, bainite, and even martensite for a given alloy grade are not uncommon. The resultant microstructure depends on a multitude of factors including, but not limited to, material composition, part geometry, part section size, part mass, and cooling rate (affected by multiple factors). It is important to remember that the microstructure achieved by any given process sequence may or may not be desirable depending on the design and function of the component part.
The microstructures produced by normalizing can be predicted using appropriate continuous cooling transformation diagrams and this will be the subject of a subsequent “Ask The Heat Treat Doctor” column.
In this writer’s eyes, industry best practice would be to specify the desired microstructure, hardness, and mechanical properties resulting from the normalizing operation. Process parameters can then be established, and testing performed (initially and over time) to confirm/verify results.
In many cases, the failure of the normalizing process to achieve the desired outcome centers around the lack of specificity (e.g., engineering drawing requirements, metallurgical and mechanical property call outs, testing/verification practices, and quality assurance measures). Failure to specify the required microstructure and mechanical properties/characteristics can lead to assumptions on the part of the heat treater, which may or may not influence the end result.
“Normalizing is the heat treatment that is produced by austenitizing and air cooling, to produce uniform, fine ferrite/pearlite microstructures in steel … In light sections, especially in alloy hardenable steels, air cooling may be rapid enough to form bainite or martensite instead of ferrite and pearlite.”
What Is Normalizing?
The normalizing process is often characterized in the following way: “Properly normalized parts follow several simple guidelines, which include heating uniformly to temperature and to a temperature high enough to ensure complete transformation to austenite; soaking at austenitizing temperature long enough to achieve uniform temperature throughout the part mass; and cooling in a uniform manner, typically in still air” (Herring, 2014).
It is also important to remember that normalizing is a long-established heat treatment practice. As far back as 1935, Grossmann and Bain wrote:
Normalizing is the name applied to a heat treatment in which the steel is heated above its critical range (that is, heated to make it wholly austenitic) and is then allowed to cool in air.
Since this is one specific form of heat treatment, it will be realized that the structure and mechanical properties resulting from the normalizing treatment will depend not only on the precise composition of the steel but also on the precise way in which the cooling is carried out.
The term ‘normalizing’ is generally applied to any cooling ‘in air.’ But in reality, this may cover a wide range of cooling conditions, from a single small bar cooled in air (which is fairly rapid cooling) to that of a large number of forgings piled together on a forge shop floor … which is a rather slow cool, approaching an anneal. The resulting properties in the two cases are quite different.
In plain carbon steels and in steel having a small alloy content, the air-cooled (normalized) structure is usually pearlite and ferrite or pearlite alone … More rapid cooling gives fine pearlite, which is harder; slow cooling gives coarse pearlite, which is soft. In some few alloy steels, the normalized structure in part may be bainite.
The hardness of normalized steels will usually range from about 150 to 350 Brinell (10 to 35 Rockwell C), depending on the size of the piece, its composition and hardening characteristics.
Importance of Defining Cooling Rate
In 2005, Krauss underscored the importance of defining cooling rate when he wrote: “Air cooling associated with normalizing produces a range of cooling rates depending on section size [and to some extent, load mass]. Heavier sections [and large loads] air cool at much lower cooling rates than do light sections because of the added time required for thermal conductivity to lower temperatures of central portions of the workpiece.”
Microstructures Created by Normalizing
The microstructural constituents produced by normalizing for a particular steel grade can be ferrite, pearlite, bainite, or martensite. The desired microstructure from normalizing adds an important cautionary note, as addressed by Krauss in STEELS (1990 and 2005), namely: “Normalizing is the heat treatment that is produced by austenitizing and air cooling, to produce uniform, fine ferrite/pearlite microstructures in steel … In light sections, especially in alloy hardenable steels, air cooling may be rapid enough to form bainite or martensite instead of ferrite and pearlite.”
Next time: We define a “still air” cool and look at the state of normalizing in North America.
Practical Data for Metallurgists, 17th ed. TimkenSteel.
Totten, George E., ed. Steel Heat Treatment Handbook, vol. 2, 2nd ed., CRC Press, 2007. 612-613.
About the Author
Dan Herring “The Heat Treat Doctor” The HERRING GROUP, Inc.
Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.
In this episode of Heat TreatRadio,Doug Glenn and guest Michael Mouilleseaux, general manager at Erie Steel LTD, continue their discussion of case hardness, delving into the hardening ability of materials, focusing on case hardening and effective case depth. Michael explains the differences between total and effective case depth, the impact of core hardness, and the role of material chemistry. They also discuss practical applications for heat treaters, emphasizing the importance of understanding material properties.
Below, you can watch the video, listen to the podcast by clicking on the audio play button, or read an edited transcript.
The following transcript has been edited for your reading enjoyment.
The Influence of Core Hardness on Effective Case Depth Measurement (01:03)
Doug Glenn: Today we are going to talk about a pretty interesting topic, and some interesting terminology, that has to do with hardness and hardenability of metals. For people who are not metallurgists, this may seem like a strange topic because isn’t all metal hard?
But we are going to talk more in depth about hardness of metal, hardenability of metal, and effective case depth. What we want to do is get a run down on the influence of core hardness on effective case depth measurements.
Michael Mouilleseaux: We are going to get a little bit into the weeds today on some things specific to metallurgy.
Those who are involved in high volume production carburizing know that consistency of results is extremely important. It is not just important in that we have the process centered in that the results are that way, but ultimately it has something to do with the dimensional control.
Specifically with gears, if the output from the process is not consistent, then one of the things that is going to suffer is going to be the dimensions. So, we’re going to be talking about effective case depths today.
Effective Case Depth vs. Total Case Depth (02:23)
Effective case depth is a little bit different from total case depth. Total case depth is the total depth that carbon is diffused into a part. That is very much a function of time and temperature. And there are some nuances with grain size and alloy content, but it is essentially a time and temperature phenomena.
Effective case depth vs total case depth (02:59)
Effective case depth is a little bit different. If we look at this graph, the x axis is the distance to the surface, and the y axis is hardness in Rockwell C.
If you look at the green line, this is a micro hardness traverse of a carburized part. It tells us many things. If you look at the left-hand side of the line at .005 in depth, the hardness there is 60 Rockwell C. Then it diminishes as we go further into the part: 0.010, 0.020, 0.040, 0.050.
We get to the end of that line, and we see that is the core strength. The core is a function of the material hardenability.
So, what is the effective case depth? If we look at the second vertical blue line on the right, it says “Total Visual Case.” So that’s exactly what that is. If we were to look at this part and etch it — I am presupposing that everybody understands that we would section the part — we would mount it, we would polish it, and then we would look at it in the microscope at 100x. Then, we would see a darkened area, which would be the total depth of carbon diffusion into the part. That is not a function of the material grade; there are some nuances there.
But the effective case depth is a measurement. And in North America’s SAE Standard J423, we say that we measure the case effective depth to Rockwell C 50. The surface hardness is 60, we measure the hardness in increments, and when we reach this hardness the depth that hardness achieves is 50 Rockwell. That is the effective case depth. If we look at the core hardness on that part, we can see that on this particular sample it is somewhere between 45 and 50.
Finding Material Hardenability (05:17)
Hardenability band graph (14:26)
What causes this core hardness? It has to do with the hardenability of the material.
Here we are looking at an SAE chart J1268. It is for H band material for 4320, a common gear material. This tells us a lot. It has the chemistry on it, below that it has some information for approximate diameters, and then it has, on the far right side of the diameters, we see specs for cooling in water or cooling in oil.
And between them there is the surface, the three-quarter radius, and the center. If we look at the surface of an oil quench at two inches, it has a distance from the surface of something like 4 or 5. So, if you go over the chart on the left-hand side, go to 4/16” or 5/16”, which has an HRC of 29 to 41. Even though this is a hardenability guaranteed material, for a two-inch round you would expect to have something between 29 and 41 for the surface hardness.
Now let’s look at what you would get at three-quarter radius in an oil quench. If you look at two inches, the Jominy position is [eight]. You can see that at three-quarter radius on a two-inch bar, that is an inch and three quarters, I believe, the hardness is going to be something between 23 and 34. In the center of that bar for a two-inch round, it is going to be J12, which has a hardness of 20 to 29.
That is the definition of hardenability. It is the depth that a material can be hardened. And it’s totally a function of chemistry. Davenport and Bain did the algorithms for this in the 1920s leading up to World War II.
Effect of Core Hardness (07:20)
If we are going to evaluate the effect of core hardness, we are going to look at parts that are heat treated in the same furnace to the same cycle in the same basket under all of the same conditions — the only thing different is going to be the hardenability of the material.
Methodology Slide (07:37)
Go all the way down to number three on this “Methodology” slide. The anticipated total case is going to be about 0.040 for all of these samples.
Hardenability samples measured (08:43)
This data graph has four samples on there. The red line is the measurement of Rockwell C 50. If we look at the highest hardenability sample, the blue sample has the highest core hardness and also the deepest effective case depth. And as the core hardness is reduced, you can see that where the line crosses the plane of Rockwell C 50, that is reduced as well.
Doug Glenn: Am I correct in thinking the yellow line here at the bottom has the lowest core hardness or hardenability?
MichaelMouilleseaux: Both. You’re correct.
Doug Glenn: That’s why it is crossing the red line much earlier than the others.
Michael Mouilleseaux: Yellow also has the lowest effective case depth.
Tabular data (10:22)
If we look at this in a tabular form, this is the data, and what you looked at were the microhardness traverses, per the standard using an MT-90: the hardness was (the effective case depth was) measured to Rockwell C, the total case depth was determined visually on these things, and, you’re going to say, that Michael, you’ve got four different materials there. That is correct. We also have four different hardenabilities.
In answer to the question, if these were all the same heat, would we have these same results? We would with the exception of the bottom one at 1018. There is no way that we could take an alloy steel and reduce the hardenability of that amount.
Here is what we are talking about: We know that they were all run at the same process when we look at the total enrichment on this; it’s within the margin of error 0.038 to 0.042.
We look at the effective case depth, interestingly, we have quite a variation there. The first one has the highest core hardness at 46, and the effective case depth is 0.039. Second, we have a sample where the core hardness is 44, and the effective case depth is 0.036. Third, we have a sample where the core hardness is Rockwell C 39, and we have 0.029 effective case depth. And finally, there’s the 1018 sample that was put in there just as a reference. The core hardness on that was 24 with 0.015 effective case depth.
There is a direct proportion between the core hardness and the effective case depth that you are going to be able to achieve.
Referencing back to that hardenability chart that we looked at (the very bottom, half inch section quench in moderately agitated oil), it has a Jominy position of 3. If we look at J3 on the chart, we can see that at the lower end of the chemistry composition, we could have a core hardness as low as 35, and at the upper end of the chemistry composition we could have a core hardness as high as 45.
Tabular data (10:22)
Let’s go back to the tabular data. That column for J3 is the data that was provided to us by our client from the steel mill.
When they melt a sheet of steel, it is a high value part. So, they use what is called SBQ (special bar quality). Special bar quality is subject to a lot of scrutiny and a lot of controls. One of the things provided, in addition to things like the chemistry and the internal cleanliness in the steel certification, is the hardenability of that specific heat.
You can see that the 8620, the first line, had a J3 of 44. We actually had a 46. The way to understand that is that when you’re going to melt 200 tons of steel, 100 tons of steel, or whatever amount it’s going to be, it’s not all done at one time in a single pour. It’s multiple pours out of a tundish.
The chemistry and the hardenability numbers that you got in a steel certification is going to be very close to an arithmetic average of what you would get when they test the first pours and the middle pours and the end pours. They’re going to average out.
Applying the Data (12:44)
When we’re using this data internally, we say we want to be plus or minus two points Rockwell C within the steel certified hardenability data. I can say that experientially over the years, Gerdau, SDI, Nucor (the domestic sources of SBQ bar )are very consistent in the way they make this stuff, and this is something that we can depend upon.
You could use this as a check for what you’re doing. If the steel that you have has a hardenability of 44 and if you’re not plus or minus two, you have to ask yourself why. There are only a couple of reasons that it would be outside those limits. If it’s above you, it probably is not the heat that it’s purported to be. If it is lower, it could either not be the heat that it’s purported to be, or there could be an issue with the heat treating.
As I said at the outset, we’re going to assume in this discussion that the reason that we have these numbers — the differential and core hardness — is not attributable to heat treating; it’s solely attributable to the chemical composition of the material or the hardenability.
We can use this information if we are an in-house or captive operation and are purchasing the material. We have an opportunity to define in our purchasing practice what the hardenability of the material is going to be.
As I mentioned before, the domestic sources are very consistent in the material that they produce. To produce a heat of 4320°F that has a J3 of 40 or 42 or 44, there is no cost penalty to that (in my experience involved in a major automotive supplier). It is a definition of what you want.
They are not making heats by randomly selecting chemistries for these heats and selling them. They make a recipe for a specific client. And my experience has been that they hold very true to that recipe.
If you are introducing a lot of variation into your process, not only is the output from that variable, but the cost of handling that is variable as well. A material such as this, to specify a J3 of 42 to 44, is something that is eminently doable. My experience is that the steel companies have been able to do that over time with a great amount of consistency.
Now, for those who are not involved in high volume production and do not have control of the source of the material, this chart remains usable. If someone is running a job shop or shorter term things who does not have furnace load sizes of parts, the key is to be able to mix and match things into specific processes. At least in carburizing, if we understand what the hardenability of the material is, then we have a much better opportunity of taking multiple parts and putting them into a load and determining ahead of time whether or not we are going to have consistent results.
Just one more thing that we would like to look at here is this next graph — the Caterpillar hardenability calculator. This is available from Caterpillar, and they readily share it with most all of their suppliers. I have been involved in numerous businesses and have never been refused this. You have to ask them for a copy of it.
SAE Chart J1268, which measures hardenability band for 4320 (05:47)
Michael Mouilleseaux: Using this calculator you import the chemistry of a heat, and then it automatically calculates the hardenability of that heat.
If you recall the J3 on the 4320 material that we looked at, the hardenability guaranteed it had a ten-point range. If you look at this particular heat, and this is what we call the open chemistry, this would not be a hardenability guaranteed material. The upper limit is higher than what you would see on a hardenability guaranteed material, and the lower limit is lower than what you would see. So the variation in a “Standard SAE J 48620” is going to be much wider – it will be much different.
If we look at that same J3 position, we are looking at 25 to 45, a 20-point swing in core hardness. If we go back and revisit the results we had, 39 to 46 with a seven-point swing, we had a 0.010 difference in effective case stuff. If we had a 20-point swing, you could imagine it is going to be significantly greater than that.
Two things, if you have the lower hardenability grade of material, it allows you to modify your process ahead of time to compensate for the fact that the core hardness is going to be lower in this part. Vice versa, if you have an extremely hot heat or it is high hardenability, similarly, you may be able to reduce some time and not put as much total case on the part in order to achieve what specified as effective case.
The hardenability charts are great guides in helping to establish a process and then to evaluate the consistency of that process.
One other comment about the chart is this is not a full-blown Lamont chart, which has various quench severities for different sizes. And that can be utilized to help pinpoint this. As you can see on the SAE chart, you essentially have two different quench rates. You have mild oil and water.
There are a lot of different types of quenchants that are available. The moderate quench rate that is on this chart very closely mimics what we at Erie have been able to achieve modified marquenching. Therefore, I’m able to use this chart without any offset.
Now, if you had a fast oil — petroleum-based oil is very fast — and a heat that had a J3 of 40 in which you are consistently seeing 44 out of it, then in your specific instance, your quenchant is more aggressive than what this chart was built to simulate. However, you can continue to use the chart. It’s just that you must use your experience in doing it.
So again: The strategy to control it is getting the hardenability data so that you can utilize that ahead of time — understanding what your specific heat treating operation is and, more specifically, what your quenching operation allows you to achieve.
Then, knowing that a typical section size of X in this furnace is going to give a Jominy position of Y, you can take that information and say over time, “If I have a variation here, it’s going to be an effective case depth. Is that variation attributable to the core hardness?” If it is, there is a strategy which will possibly change and tighten up the purchasing practice. If it is attributable to something else, then that gives good information to say, “There’s something in my heat treating process that I should be looking at that is attributable for this variation in case depth.”
Conclusion (22:14)
So, we waded into the weeds, and hopefully we have found our way out.
Doug Glenn: I think that explanation is going to be especially good for those who already know a little bit of metallurgy and know those charts.
Bethany Leone: Michael, for in-house heat treaters, how often do they need to be aware of the materials coming into their operations, testing it, or asking about changes that could be happening?
Michael Mouilleseaux: Hopefully this would give heat treaters worth their salt a reason to pause if they previously assumed the material does not come into play.
The next thing would be in high valued components — gears, shaft, power transmission, those kinds of things — heat lot control is typically mandated by the end user. If you have heat lot control and the unique data that goes with that, utilizing the strategy we just talked about is going to give you the ability of evaluating variation. If the primary source of variation is the material, that needs to be addressed. If the material is very consistent and yet you continue to have variation, there is obviously something in the heat treating process that needs to be addressed to reduce that variation.
Doug Glenn: Thanks for listening and thanks to Michael for presenting today. Appreciate your work, Michael.
About The Guest
Michael Mouilleseaux General Manager at Erie Steel, Ltd. Sourced from the author
Michael Mouilleseaux is general manager at Erie Steel LTD. Michael has been at Erie Steel in Toledo, OH, since 2006 with previous metallurgical experience at New Process Gear in Syracuse, NY, and as the Director of Technology in Marketing at FPM Heat Treating LLC in Elk Grove, IL. Having graduated from the University of Michigan with a degree in Metallurgical Engineering, Michael has proved his expertise in the field of heat treat, co-presenting at the 2019 Heat Treat show and currently serving on the Board of Trustees at the Metal Treating Institute.
