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’sOctober 2025 Ferrous & Nonferrous Heat Treatments/Mill Processingprint edition.
In today’s Technical Tuesday, Dan Herring continues his exploration of what hydrogen embrittlement is by contrasting it with other forms of embrittlement. Learn how to identify these various forms of brittle intergranular failure below!
We continue our discussion from last month concerning hydrogen-assisted cracking (aka hydrogen embrittlement) by looking at closely related phenomena, often mistaken for hydrogen embrittlement. Let’s learn more.
As a brief recap of what we discussed last month, the severity and mode of the hydrogen damage depends on:
Source of hydrogen — external (gaseous) or internal (dissolved)
Exposure time
Temperature and pressure
Level of residual and applied stresses
Type of alloy and its production method
Method of heat treatment
Treatment of exposed surfaces (barrier layers, e.g., oxide layers as hydrogen permeation barriers on metals)
Final treatment of the metal surface (e.g., galvanic nickel plating)
Presence of chemicals that may react with metals (e.g. acidic solutions)
Number of discontinuities in the metal
There are, however, several other embrittlement mechanisms that are often mistaken for hydrogen embrittlement and we will explore these here.
Quench Embrittlement
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Many high hardenability steels (e.g., 4140, 4340, 52100) are susceptible to a form of brittle intergranular failure from a phenomenon known as quench embrittlement. Under tensile or bending stress, higher carbon steels are susceptible to intergranular fracture in both the as-quenched condition and/or after low temperature tempering — generally considered “safe” from traditional embrittlement. A transition from ductile to intergranular fracture in martensitic steels having greater than 0.5% C can be embrittled even when tempered at low temperatures.
This phenomenon is different from tempered martensite embrittlement (TME) or temper embrittlement (TE), as explained below, as embrittlement occurs before tempering. The issue is exacerbated by the presence of certain embrittling elements (e.g., P, S, As, Sb, Sn, Pb) solely or when their combination reaches a high enough percentage (typically, 0.10%).
Temper Embrittlement
In broad based terms, TE involves a reduction in the normal ductility of a metal due to a physical or chemical change. TE is characterized by reduced impact toughness and occurs in certain quenched and tempered steels and even in ductile irons with susceptible compositions. This form of embrittlement does not typically affect room temperature tensile properties but causes significant reductions in impact toughness and fatigue performance. Although normally associated with tempered martensite, it can also occur if the matrix is tempered to the fully ferritic condition.
Types of Temper Embrittlement
When tempering steel, several types of embrittlement must be avoided. The first type, TME, is an irreversible phenomenon that can occur within 200−400°C (390−750°F). Years ago, it was called “blue brittleness” for the steel’s surface oxidation appearance, but this term is misleading since it can occur at temperatures below the onset of a blue coloration on steel.
Figure 1. Fracture modes in hardened steels
The second type is TE, a reversible phenomenon that occurs when steels are heated in and/or slow cooled through the temperature range of 375−575°C (705−1070°F).
Why Does it Happen?
TME and TE are examples of intergranular embrittlement. A common factor in such failures is the presence of elements that segregate to the grain boundaries. The chemical reaction rate or kinetics of segregation are such that they exhibit “C” curve behavior in the 350−550°C (660−1020°F) range; in other words, segregation does not occur uniformly. Both types of embrittlement are in part related to grain-boundary segregation of impurity elements (e.g., As, P, Sb, Sn), and both develop during thermal processing after austenitizing and quenching to martensite, usually indicated by an upward shift in ductile-to-brittle transition temperature.
TME is thought to result from the combined effects of cementite precipitation on prior-austenite grain boundaries or interlath boundaries and the segregation of impurities at prior-austenite grain boundaries. By contrast, TE is thought to be caused by the formation of carbides on decomposition of martensite, in particular, precipitation of carbides in the form of films at grain boundaries. At higher temperatures of tempering, this film disappears and cannot be restored on repeated heating at 250−400°C (480−750°F).
Which Steels Are Affected?
All steels are susceptible, so the real question becomes how susceptible and what factors affect that susceptibility. For example, while plain carbon steels may contain some of the same impurity elements that will cause the embrittlement phenomenon to occur in other steels, the segregation of these elements is often enhanced by or caused by the presence of other alloying elements in substantial quantities. As a result, alloy steels, in general, have more susceptibility than carbon steels.
It is important to understand that the degree of embrittlement is affected by the prior austenite grain size and hardness. So, if we are dealing with a fine-grained plain carbon steel of low hardness, it may not experience embrittlement symptoms despite its phosphorous content, whereas a more highly alloyed Cr-Ni steel used at higher hardness is more susceptible to its impurity content.
Widely used alloying elements, such as chromium, nickel, and manganese, tend to promote TE with the highest embrittlement effect observed in Cr-Ni and Cr-Mn steels. Small additions of molybdenum (0.2-0.3%) can diminish TE, while greater additions enhance the effect. TE can be prevented by keeping silicon and phosphorus levels as low as possible, adding up to 0.15% molybdenum and avoiding the embrittlement heat treating conditions.
Susceptibility also depends on impurity control and here is where the steelmaking process is critical. For example, in plain carbon and Cr-Mo steels (those with no Ni) where phosphorous is the most impactful embrittlement element, the percentage can be controlled by the steelmaking process. In steels that contain significant amounts of nickel, antimony and tin are more potent embrittlement elements. Phosphorous has an effect but not as large as it has in plain carbon and Cr-Mo steels. It should be noted, however, that antimony and tin in plain carbon steels can cause other hot working issues.
How Can We Correct It?
TME is irreversible, and its effects are permanent. By contrast, the effects of TE can be reversed. This is done by re-tempering above the critical temperature of 575°C (1070°F) then cooling rapidly. Impact toughness can be restored. If necessary, this process can be repeated.
A Simple Example
Alloy steel, which is susceptible to TE, will exhibit a relationship such as shown on Figure 2. Note that the impact toughness of quenched steel after tempering at 200−400°C (390−750°F) is lower than that obtained on tempering at temperatures below 200°C (390ºF). If brittle steel tempered in this range is heated above 400°C (750ºF) and transformed into a tough state, a second tempering at 250−400°C cannot return it to the brittle state. The rate of cooling from the tempering temperature range of 250−400°C has no effect on impact toughness.
Figure 2. Effect of temperature on impact toughness
The susceptibility of a given steel to TE depends on a number of factors, including grain size, hardness, steel grade, and the impurity control in the steelmaking process itself. Remember, not all steels and not all steelmaking processes are equivalent.
A heat treaters we must avoid the temptation to temper to a given hardness value without understanding the consequences of our actions. Since we do not have a simple embrittlement test that can be used on the shop floor, we must understand the phenomenon and question specifications that put us into TE ranges.
In Summary
The insidious nature of hydrogen embrittlement continues to cause concern and product failures during processing and during service, but as explained above, there are other heat treatment operations that can result in embrittlement. All of these and others (e.g., aluminum nitride embrittlement, overheating during forging, hot shortness) are responsible for many serious and in some instances catastrophic failures leading to injury or damage. All must be avoided.
References
ASTM International. 2022. ASTM B850-98 (Reapproved 2022): Standard Guide for Treatments of Steel for Reducing the Risk of Hydrogen Embrittlement. West Conshohocken, PA: ASTM International. https://www.astm.org.
Herring, D. H. 2014–2015. Atmosphere Heat Treatment, vols. 1–2. Troy, MI: BNP Media.
Herring, D. H. 2006. “The Embrittlement Phenomena in Hardened & Tempered Steels.” Industrial Heating, October.
Herring, D. H. 2004. “A Heat Treater’s Guide to Hydrogen Embrittlement.” Industrial Heating, October.
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 installment of Combustion Corner, Jim Roberts, president of U.S. Ignition, examines various burner nozzle shapes, sizes, and effects.Use this helpful resource to evaluate whether your own in-house heat treat burners are the right choice for your applications.
This informative piece was first released inHeat Treat Today’sSeptember 2025 Annual People of Heat Treat print edition.
A furnace guy walks into a bar and shouts “Straighten UP!” The other furnace guys turn to furnace guy #1: “It won’t work!” Just like last month. Let’s continue this topic.
What would you say if I asked you, “What does fire look like?” How would you describe fire to me — color, size, smell, temperature? It’s kind of a weird thing to try and do.
Figure 1. Fives Group’s North American Tempest
Last month, we ended by talking about how “air staged” burner design can make the flame exit the nozzle at a whopping 270 mph. There’s a reason that trade names for some of these burners are “Therm-Jet” and “Tempest” and “Hot Shot.” In these instances, velocity and turbulence are the game. The flame appearance is almost always a pinpoint tip, not dissimilar to what we have all seen spitting out of the tail of a fighter jet aircraft.
And, as an interesting aside, these high-velocity industrial burners can be victims of the same phenomena as a jet engine: flameouts. A tremendous amount of design time and testing has been dedicated to keeping the flame “retained” on the nozzle. If the flame lifts off the nozzle, cup, etc., it risks being blown out by the high-velocity stream of gases being produced in the guts of the burner. At these speeds, you cannot count on the burner backlighting, so a flame failure is imminent.
More Burner Types
The other types of nozzle-mixing burners are flat flame burners. These are sometimes called wall huggers or radiant wall burners. In these designs the idea is to have as little forward momentum to the flame as possible and to run the burners in a fuel-rich or highly luminous state. The design features are such that the whole wall of the furnace will be glowing radiantly and using radiation from the glowing walls to heat the product.
There are also infrared burners, where the burners are like a porous foam or screen grid and flame just glows on these surfaces. Again, the intent is radiant heat as opposed to velocity gases. These are very prevalent continuous production processes where radiant, consistent heat is required.
There are also radiant tube burners, where the flames are fired through an alloy or ceramic tube, and the flame is isolated from the process completely. The idea here is that the tube does not allow the products of combustion to make contact with the parts. Also, in most radiant tube furnaces, some sort of process atmospheres — comprised of a variety of gases to protect the products in the furnace from oxidation or to impart a metallurgic property to those parts — have been introduced to the chamber and the process.
As such, burner design engineers have to figure out how to give a very uniform heat delivery to the tube they are firing into. Many times, a burner will need to mix the air and gas very slowly (compared to direct fired furnace burners) to ensure the flame releases its radiation at a very uniform rate, so as to not distort the radiant tube itself. And the users of these variety of burners range from flame hardening to direct fired to indirect fired atmosphere processes and many more.
Figure 2. Fighter jet aircraft
We will continue this discussion point in subsequent columns because understanding these burners is critical to using them correctly. As for the original idea that flame shapes can affect all sorts of process performance, we will revisit this topic and others, because it’s all important. Different flame shapes can significantly impact combustion performance by influencing factors like flame speed, stability, heat release, and certainly one of the big design goals now, emissions reductions. We’ll tackle these topics in future columns.
Until then, I would suggest that you take a walk into the plant and check out the variety of burners that you may have. Let’s endeavor to find more about them and consider, “What would make this burner the right choice for this application?” Then, discover what you can learn about them and their history. We will tie that all together when we discuss the next installment.
Jim Roberts President US Ignition Contact Jim Roberts at jim@usignition.com
Hydrogen is essential for many heat treating processes, but what happens when your supply runs out?
In today’s episode of Heat TreatRadio,Devon Landry of Nel Hydrogen joins Heat TreatRadioHost Doug Glenn to discuss the potential risks of delivered gas and how on-site generation can secure reliable, high-purity hydrogen. This episode highlights the advantages of on-site generation and what questions to ask before making the switch.
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.
Hydrogen Usage in Thermal Processing (4:05)
Doug Glenn: All right, let’s talk hydrogen. I think the first thing I’d like to do is talk about the basics, how hydrogen is used and what it’s used for in thermal processing.
Can you give us a 30,000-foot view on hydrogen and why are we using it in thermal processes?
Devon Landry: Hydrogen is widely used in heat treat and processing. It’s a powerful reducing agent for surface cleaning and sintering success.
Hydrogen scavenges oxygen, counteracting minor furnace leaks. Photo Credit: Nel Hydrogen
It has the highest heat conductivity of any gas, so we can enter and exit parts quicker. It has lower density relative to air and nitrogen, which makes it really straightforward to manage. It burns off easily, readily, cleanly. The only true byproduct of that would be water.
Doug Glenn: We are talking about the security of hydrogen supply.
How important is it for people who need hydrogen to have it, and what happens if they don’t have it — what are the risks here?
Devon Landry: My predecessor, Dave Wolff, used to say it’s like yeast for a pizzeria. It’s a very small part of the cost, but if you don’t have yeast, you don’t have pizza. If you don’t have pizza, you don’t have business. So if you don’t have hydrogen, you can’t really run your processes.
The same with running out of hydrogen. If you’re halfway through a batch and you run out of hydrogen, that whole batch is done. If that batch isn’t finished and you don’t have any hydrogen left, you don’t have business. You have to send employees home and stop your production. You can run into a lot of problems.
Doug Glenn: If you’re processing high-value parts, it’s not just a matter of simply running out of parts and not being able to finish the load. That load could be worth a quarter of a million dollars.
Devon Landry: That’s correct, the parts are completely done; you won’t be able to use those parts — it’s a completely wasted batch. So, you would lose money, not just from excess production, but that batch as well.
On-Site Hydrogen Generation vs. Supplied (06:25)
Doug Glenn: There’s different ways of getting your hydrogen, it can be supplied or Nel, the company you’re with, supplies the equipment to manufacture hydrogen on-site. What type of risks are companies exposing themselves to if they are not generating their own hydrogen?
Devon Landry: Delivered hydrogen is really the only other way to get your hydrogen, and that’s through industrial gas suppliers. I see a shortfall in the future, especially with liquid hydrogen production. There are many hydrogen plants that are getting canceled or delayed.
Supply chain and hydrogen requirements for Artemis rocket
You see, it costs a lot of money to make these plants, and if the financial advisors deem that the plant is not going to make money, they’re not going to do it.
For the Artemis rocket, that takes a full day’s production of liquid hydrogen in the U.S. to fill up. And there are many projects out there that are requiring liquid hydrogen, which is why I see a shortfall coming.
If you can’t get the hydrogen from your industrial gas supplier, where are you going to get it?
That’s where Nel Hydrogen comes in. With generating on-site, you take control of your hydrogen supply.
Doug Glenn: You mentioned that you foresee a lack of supply and that some of these hydrogen plants aren’t being approved.
Why aren’t these plants being approved to be built?
Devon Landry: They cost a lot of money to build and industrial gas companies have a long-term strategic focus, with capital discipline kind of upfront. If you’re going to build a plant and shareholders are not going to see any returns on it, then they’re not going to do it.
So we’ve seen a lot of cancellations. They haven’t really have a good commitment to shareholder value, and they emphasize on strong fundamentals there.
Doug Glenn: At one point in time, there was a lot of talk about hydrogen fuel cells. And everybody wanted to do hydrogen. I haven’t heard much about that recently. Do you think that might have something to do with the cooling off of the hydrogen market?
Devon Landry: Yes, I think so. There was a hydrogen world out there, and people really wanted to build new plants, have fueling stations. There’s so much you can do with hydrogen. But policies around hydrogen are affected by different administrations. With the current administration, they’re taking some of those incentives away. So there’s not as much money being provided as an incentive.
Doug Glenn: This is all the more reason to be very careful about your hydrogen supply. Not only your current hydrogen supply, but in the future. With politics and different administrations, sometimes hydrogen fuel cells is on, then it’s off. As a result, supplies may be a bit dicey. Therefore, it’s probably well worth people paying close attention to where they’re getting their hydrogen now and what the future looks like.
Your input is really important here.
Proton Exchange Membrane (10:23)
Hydrogen cleans part surfaces to enhance processing results. Photo Credit: Nel Hydrogen
Doug Glenn: Tell me about PEM; what does that stand for?
Devon Landry: PEM stands for proton exchange membrane. It’s a differential pressure system, where hydrogen is allowed to pass through the membrane but oxygen cannot.
We’re taking ultra pure water with a resistivity of greater than one mega ohm. That’s going through into the cell stack and the electrolysis takes place there. The hydrogen is allowed to pass through that membrane; the oxygen is not. So, the hydrogen goes towards the process.
Doug Glenn: Oxygen and/or water is the only byproduct.
Devon Landry: Yes, and it returns to the main reservoir, and that oxygen gets vented, either out of vent stack or into the room.
Doug Glenn: The primary markets that Nel Hydrogen serves are mostly industrial, and Nel can also do much larger units. Can you tell me about that?
Devon Landry: With alkaline and PEM both, we can do megawatt style units. I handle primarily the industrial units, and we can go all the way up to 100, 200, 300 megawatt systems — a very vast range.
Doug Glenn: Most businesses in our industry would not need that much, but it’s good for our people to know that you guys have expertise, not just in the sizes that are good for them, but larger sizes as well.
Nel Series hydrogen generators Source: Nel Hydrogen
PEM Process vs. Alkaline (12:05)
Doug Glenn: We have discussed the PEM process. Can you explain the difference between how the hydrogen is extracted from the PEM process vs. alkaline?
Devon Landry: The alkaline system uses KOH, which is highly corrosive and dangerous to handle. You have to fill it up, so there’s a safety aspect with that. In addition, the purity that you’re getting out of the alkaline process is not quite as high as PEM. I think it’s 90%, but it can be 97 to 98%.
With the PEM process, the only output you’re getting is hydrogen and some water, and we mitigate that water with a dryer inside the system. We get five nines purity plus: 99.999% purity plus.
You really need that purity in a lot of the heat treating processes to give you the coloration of the pieces that you’re putting through. With the industrial gas suppliers, you often have to pay a premium to have higher purity. Many times, when you send those cylinders or a tube trailer back to get it refilled, they do not test it to find out exactly what the purity is unless you specifically request that. So your purity might differ every now and then, which means you’re not going to get the exact effect on your process that you would like.
The way the industrial suppliers are making that hydrogen is through steam methane reforming. It’s very energy-intensive, and carbon is a major by-product of that process.
Our machines are as carbon free as your electricity supply line: if you’re feeding it with solar and wind energy sources, utilizing renewable energy, then you are at a zero carbon footprint.
Doug Glenn: You would have true green hydrogen. If your electricity supplier was green, then you would be really producing green hydrogen, which would be very good.
Delivered Gas vs. Hydrogen Generation (14:55)
Doug Glenn: What questions should companies be asking if they are considering moving away from bulk or delivered gas to on-site hydrogen generation?
Devon Landry: To have a hydrogen generator on-site, you need to know your flow and your pressure. There are going to be operational and capital costs.
The capital costs are a little larger with the hydrogen generator. So you’ll need to know how much gas you’re using and what pressure you’re using at. We have calculators to determine which unit would be best for you based on those questions.
If the capital costs are a little too high, which they are for some companies, then we do have leasing options that will help with that capital cost. We can break it down monthly, even for a 10-year period of what you would be spending for your delivered gas versus a hydrogen generator on-site.
Doug Glenn: So, you can do that analysis for businesses if they can provide their current expenditures for delivered hydrogen and usage, and then you can do a comparison to advise them on what it would cost if they were to transition to on-site generation?
Devon Landry: Yes, exactly. Industrial gas suppliers can come with a lot of bills, so you have to pay attention. There could be a trailer rental fees, cylinder rental fees, delivery fees — a lot of bills combining into one. They also generally require signing a contract with them that could be seven plus years, and you have to provide quite a long notice to be relieved of those contract obligations as well.
Doug Glenn: The capital cost could potentially be different, meaning probably more for an on-site generator for hydrogen. When you think of bulk gases, the operating costs are quite low for delivered gas.
How about operational costs for hydrogen?
Devon Landry: The cost of hydrogen generation is going to be the cost of your electricity. The price per kilowatt is going to tell you how much cost per standard cubic foot that you’re going to be paying for it.
Doug Glenn: Electricity is really the only major cost operationally. How about maintenance costs?
Devon Landry: The maintenance cost depends on which machine you select. We build maintenance costs right into the calculator that tells you how much the costs will be per year. There’s a quarterly maintenance cost, which is just basically a calibration, and then a yearly maintenance kit that you can put in yourself.
Doug Glenn:Do you need to have any special personnel to run it or is it self-maintaining?
Devon Landry: It pretty much takes care of itself. If there’s a problem with it, a pop up will let you know the problem, and you can go to the manual to learn exactly what the problem is. If you have a regular maintenance crew on site, many power plants have these, then you usually have somebody that can do it.
It’s generally filter changes and updates like that.
Community Perception on Hydrogen Generation (18:25)
Doug Glenn: Pertaining to public perception, how has the community responded to hydrogen generation?
Devon Landry: Most people like it better. We like to refer to it as the good neighbor benefit. Would you rather look outside and see a gigantic tank full of combustible gas or a quarter inch, stainless steel line?
Fire marshals love it because we store less than seven standard cubic feet on our biggest machine, internally.
And then when we hit the stop button, or if the generator shuts down, the hydrogen is all vented out into the atmosphere. There’s no stored hydrogen — only a minimal amount inside the machine.
Doug Glenn: No rocket ships in your backyard.
Devon Landry: Looking out the window, I’d rather see the sky and some bushes rather than a big tank.
Is Hydrogen Generation Right for Your Company? (19:30)
Doug Glenn: Are there instances where generating hydrogen on-site doesn’t make sense for a company or when bulk delivery is a better deal?
Devon Landry: This is why we have those calculators. I don’t need a company buying a generator if it’s not going to save them money or if it’s not going to be easier for you. It’s really only practical when you’re under 10,000 standard cubic feet per hour.
Doug Glenn: Is that amount for a very large industrial manufacturing plant?
Devon Landry: Yes, that’s quite a bit.
Doug Glenn: Is there any amount that’s too small in which it wouldn’t make sense to have a generator?
Devon Landry: No, our smaller generators put out about 10 standard cubic feet per hour, about 4.9 liters per minute, and it’s on-demand. If you need the smallest amount possible, they’ll put that out for you. If you don’t need any further for the interim, it will basically sit there in idle. These generators are fully on-demand and give you exactly what you need.
Doug Glenn: Which companies currently are out there that it really makes sense for them to look at on-site hydrogen generation?
Devon Landry: Really, anybody that needs hydrogen. If you’re not excited about your delivered hydrogen, if you’re having issues with it, if the cost is too high, we have a lot of different industries that we run with. Many are heat treating and metal processing business. There’s also chromatography, gas chromatography, MOCVD, many different industries. If you have delivered hydrogen, generating hydrogen on-site would be worth looking into.
Final Thoughts (22:45)
Doug Glenn: Where is the corporate headquarters or the world headquarters for Nel Hydrogen?
Devon Landry: Nel Hydrogen is headquartered in Oslo, Norway.
Doug Glenn: How long has company existed?
Devon Landry: It started in 1927.
Doug Glenn: Where’s the main headquarters in the U.S. or North America?
Devon Landry: We’re in, Wallingford, Connecticut, and all of our PEM machines are built there.
Doug Glenn: Very good. I’d like to thank all the everyone for listening.
Hopefully you found this episode enjoyable and informative. Thanks again, Devon. Appreciate you being here.
About the Guest
Devon Landry Senior Field Engineer and Technical Lead Nel Hydrogen
Devon Landry has been an integral part of Nel for 16 years, establishing himself as a leading expert in industrial on-site hydrogen generators. With over 15 years as a Senior Field Engineer and Technical Lead in Technical Service and Customer Support, he has played a key role in delivering top-tier service and expertise to Nel’s global customer base. His extensive experience includes traveling more than 3 million miles worldwide, working across diverse industries and customer sites.
Beyond his technical proficiency, Devon brings strong leadership and business acumen. As an entrepreneur, he successfully founded and managed a craft brewery and taproom in Connecticut for six years, leading a team of seven employees. This experience further enhanced his ability to blend technical expertise with strategic management and operations.
What are the ways to improve the cleaning process of component parts and reduce smoke from residue and environmental impact? Mercury Marine faced this challenge head on with a new system. Learn more about their solution in today’s Technical Tuesday case study written by Chris Tivnan the sales manager for North America at SAFECHEM North America Inc.
This informative piece was first released inHeat Treat Today’sAugust’s 2025 Annual Automotive Heat Treating print edition.
Mercury Marine’s Need for Clean
Mercury Marine is a world leading manufacturer of marine propulsion systems headquartered in Fond du Lac, Wisconsin. A subsidiary of Brunswick Corporation, Mercury Marine designs, manufactures, and distributes engines, services, and parts for recreational, commercial, and government marine applications.
Mercury Marine has an in-house heat treatment facility for the components they manufacture. These components include gear case parts, such as propeller shafts, pinions, forward and reserve gears, and clutches. The parts undergo typical manufacturing steps like turning, milling, or gear tooth generation. Some machines allow for dry cutting, while others involve hydraulic oil. In total, more than 170 distinct metal parts require cleaning before undergoing vacuum carburizing, hardening, tempering, and/or cryogenic treatments.
Carburizing with Closed-Vacuum Solvent Cleaning
But vacuum carburizing has not always been the technology of choice for Mercury Maine. Prior to 2023, parts and components underwent initial cleaning in an aqueous washer before proceeding to atmospheric carburizing. Then, they were quenched in oil and then underwent another round of cleaning with a water-based cleaner.
Figure 1. NANO vacuum carburizing system from ECM
Mercury Marine made the strategic decision to transition from atmospheric carburizing to vacuum carburizing in 2023. The shift was motivated by concerns related to smoke and environmental impact, particularly the evaporation of oil residuals during tempering. The desire for an overall environmentally friendlier process further fueled this change.
Vacuum carburizing benefits from more stringent cleanliness requirements on parts whereby all residue oils, greases, and debris must be removed entirely to prevent contamination of the furnace and the vacuum pump system. As a result of these considerations, Mercury Marine replaced their existing aqueous cleaning process with solvent-based cleaning, convinced that this solution provided superior and consistently reliable cleaning results.
Figure 4. With lipophilic and hydrophilic properties, DOWCLENE™* 1601 removes oils and greases just as effectively as certain polar contaminants like cooling emulsions or solids (e.g., particles and abrasives). Source: ECM USA
Their furnace equipment manufacturer ECM recommended a closed-vacuum solvent-based cleaning machine (Model: SOLVACS 3S) from the manufacturer HEMO. This design could be seamlessly integrated into their NANO vacuum carburizing system.
The vacuum cleaning machine runs on the modified alcohol solvent DOWCLENE™* 1601. Because of its lipophilic and hydrophilic properties, DOWCLENE 1601 can remove oils and greases just as effectively as certain polar contaminants like cooling emulsions or solids (e.g., particles and abrasives). The solvent also has low toxicity and good biodegradability.
Enabling High Environmental and Safety Standards
The switch from aqueous to solvent cleaning initially raised some safety concerns within Mercury Marine’s environmental safety committee. However, these concerns were swiftly addressed once the committee understood the operation of a closed vacuum cleaning machine and how it contributes to the highest safety and sustainability standards.
First, the airtight design of the machine virtually eliminates air emissions. The hermetically sealed construction means there is minimal risk of contaminating groundwater. Additionally, full machine automation removes operator handling and minimizes chemical contact.
Figure 2. While closed vacuum cleaning machines enable high-quality cleaning results with strong safety and sustainability standards, HEMO designs integrate seamlessly into furnace lines
Second, the machine’s built-in distillation unit enables continuous solvent recovery — as high as 95% in Mercury Marine’s case — thereby significantly reducing chemical consumption and waste while lowering overall cleaning costs. Distillation ensures that parts are consistently cleaned in fresh solvent. The effective cleaning result is further warranted by the high solvent quality in the rinsing step, followed by vapor degreasing as the last cleaning step, which is highly effective due to high temperature difference between parts and vapor. With the drying process below 0.1 psi, a perfect drying of the parts is guaranteed.
Additionally, unlike aqueous cleaning, solvent cleaning does not consume significant water, nor does it require wastewater treatment, providing a considerable cost and environmental advantage.
Using a simple test kit, solvent conditions can be easily monitored on a regular basis. Solvent lifespan can also be extended by adding stabilizers, reducing the need for frequent bath exchanges. Due to the high stability of the cleaner, only minimal stabilizer additions have been required since the machine was first put into operation.
Leveraging CFC for Solvent Cleaning
Another crucial factor supporting solvent cleaning is the use of carbon fiber composite (CFC) workload trays and fixturing of the heat treat batch in the cleaning machine. After cleaning the parts, the CFC fixtures are directly transferred into the vacuum furnace. This streamlined workflow eliminates the need to transfer parts between different fixtures, minimizing part damage or contamination while saving time. The durability and thermal stability of CFC fixtures make them ideal for such demanding applications.
Figure 3. Industrial robots streamline the loading and unloading of components in ECM’s vacuum furnaces and facilitate part transfers between systems, ensuring a fully automated heat treatment line
Since CFC is a highly absorbent material, it can soak up liquids during the cleaning process. Any remaining residue in CFC fixtures can be released during a vacuum heat treatment process, contaminating the oven, which will impact the process and cause improper heat treatment outcomes. Unlike aqueous cleaning, which leaves some liquids behind, solvent cleaning under vacuum conditions effectively removes these absorbed residues.
Additionally, CFC fixtures must be properly dried and moisture-free before entering the vacuum furnace. Moisture can lead to contamination, inefficient carburizing, oxidation, or vacuum system problems. Solvents dry much faster than water, mitigating the risk of water vapor migration into the vacuum carburizing system.
Superior Controllability and Quality Results
Since transitioning from atmospheric to vacuum carburizing, Mercury Marine has experienced many benefits due to a significantly more consistent and repeatable heat treatment process.
It is known that residual oxygen within the furnace atmosphere can react with alloying elements on the component’s surface. This interaction can lead to the formation of an oxidation layer, potentially affecting the compressive stress profile. Such layers need to be ground off. However, with vacuum carburization, these intergranular oxidations (IGO) no longer occur.
The vacuum carburizing process follows a precise “boost and diffuse” cycle, where the presence of carbon is transferred via acetylene. This approach provides superior controllability compared to atmospheric carburizing, where natural gas is used. Additionally, the absence of open flames and the energy-efficient design contribute to reduced greenhouse gas emissions.
In the past, Mercury Marine faced cleaning challenges following oil quenching. While maintaining clean quench oil is essential, frequent oil changes can be costly. When the quench oil was not cleaned frequently enough, deposits adhered to parts, especially drive shafts with spiral oil grooves for passage. Despite attempts at aqueous cleaning, such debris could persist, and additional blasting was needed to remove them.
Vacuum carburizing has eliminated this problem as the parts now undergo gas quenching instead of oil quenching, removing the aqueous cleaning step altogether.
The investment in a new furnace system, along with the integrated closed vacuum solvent cleaning machine, has proven highly beneficial. The fully automated system ensures that technicians are not manually handling baskets, while parts are cleaned to the highest standard, enabling a seamless vacuum carburizing process. Mercury Marine has expressed great satisfaction with the results, recognizing the system as a valuable addition to their manufacturing operations.
About The Author:
Chris Tivnan Sales Manager North America SAFECHEM North America Inc.
With two decades of experience in the chemical industry, Chris assists manufacturers in determining the right choice of cleaning agent and their parts cleaning operation. He also manages relationships with regional distributors as well as local OEMs/OEAs.
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’sSeptember 2025 People of Heat Treat print edition.
If you’ve ever experience internal cracking, surface blistering, loss of ductility, or high pressure hydrogen attack, today’s Technical Tuesday might contain just the information you need to avoid it. Read below to learn from Dan Herring as he addresses what hydrogen embrittlement is, how to avoid it, and what solutions should not be pursued in order to fix it.
The other night, The Doctor decided to relax and watch a rather whimsical movie, The Great Race (1965), directed by Blake Edwards, who is perhaps better known for directing Breakfast at Tiffany’s and The Pink Panther. It is most memorable not for the actors, nor the plot, but for the infamous pie fight involving over 4,000 pies in a scene that took more than five days to film but lasted only four minutes on the big screen. Not one actor was spared the embarrassment of being hit by (multiple) pies in the face!
So, what does THIS have to do with heat treatment, you ask? Well, try as he may to believe the subject has been explained well in the past, The Doctor has been inundated recently with questions about hydrogen embrittlement (aka hydrogen-assisted cracking). Let’s learn more.
What Is It?
Hydrogen-assisted cracking (HAC) is an embrittlement phenomenon responsible for a surprising number of part cracking issues in heat treatment and is found to be the cause of many delayed field failures, especially if the components undergo secondary operations such as plating (Figure 1).
It is generally agreed that hydrogen in atomic form will enter and diffuse through a metal surface at elevated or ambient temperatures. The simple rule to remember about hydrogen is fast in, slow out. Once absorbed, atomic hydrogen often combines to form molecular hydrogen or other hydrogen molecules (e.g., methane). As these are too large to diffuse through the metal, pressure builds at crystallographic defects (e.g., dislocations and vacancies) and/or discontinuities (e.g., voids, laps/seams, inclusion/matrix interfaces) causing minute cracks to form. Whether this absorbed hydrogen causes immediate cracking or not is a complex interaction of material strength, external stresses, and temperature.
Figure 2. Intergranular fracture of a plated component (SEM image)
Most heat treaters associate hydrogen embrittlement with the plating process and the lack of a proper bake-out cycle. However, there are many other sources of hydrogen, including heat treating atmospheres; breakdown of organic lubricants left on parts; the steelmaking process (e.g., electric arc melting of damp scrap); dissociation of high-pressure hydrogen gas; arc welding (with damp electrodes); grinding (in a wet environment); and the end-use environment.
Parts undergoing electrochemical surface treatments, such as etching, pickling, phosphate coating, corrosion removal, paint stripping, and electroplating, are especially susceptible (Figure 2).
What Is The Nature and Effect of Hydrogen Attack?
Although the precise mechanism(s) is the subject of active investigation (Figure 3), the reality is that components fail due to HAC. It is generally believed that all steels above 30 HRC are vulnerable, as are materials such as copper, titanium and titanium alloys, nickel and nickel alloys, and the like. See Table A below for examples of hydrogen damage and ways to avoid it.
Figure 3a and 3b. Hydrogen embrittlement mechanism models
Since a metallurgical interaction occurs between atomic hydrogen and the atomic structure, the ability of the material to elastically deform or stretch under load is inhibited. Therefore, it becomes “brittle” under applied stress or load. As a result, the metal will break or fracture at a much lower load or stress levels than anticipated by designers. Since failures can be of a delayed nature, hydrogen embrittlement is insidious.
Table A. Problems with hydrogen damage and ways to avoid them
In general, as the strength of the steel goes up, so does its susceptibility to hydrogen embrittlement. High strength steel, such as quenched and tempered steels (e.g., 4140, 4340), or precipitation hardened steels are particularly vulnerable. It is often called the Achilles heel of high strength ferrous steels and alloys.
Nonferrous Materials and Hydrogen Embrittlement
Nonferrous materials are also not immune to attack. Tough-pitch coppers and even oxygen-free coppers are subject to a loss of (tensile) ductility when exposed to reducing atmospheres. Bright annealing in hydrogen bearing furnace atmospheres or torch/furnace brazing are typical processes that can induce embrittlement of these materials.
In copper, the process involves diffusion and subsequent reduction of cuprous oxide (Cu₂O) to produce water vapor and pure copper. An embrittled copper often can be identified by a characteristic surface blistering resulting from expansion of water vapor in voids near the surface. Purchasing oxygen-free copper is no guarantee against the occurrence of hydrogen embrittlement, but the degree of embrittlement will depend on the amount of oxygen present. For example, CDA 101 (oxygen free electronic) allows up to 5 ppm oxygen while CDA 102 (OFHC) permits up to 10 ppm. A simple bend test is often used to detect the presence of hydrogen embrittlement. Metallographic techniques can also be used to look at the near surface and for the presence of voids at grain boundaries.
Are Low Hydrogen Concentrations Also Problematic?
Of concern today is embrittlement from very small quantities of hydrogen where traditional loss-of-ductility bend tests cannot detect the condition. This atomic level embrittlement manifests itself at levels as low as 10 ppm of hydrogen — in certain plating applications it has been reported that 1 ppm of hydrogen is problematic! Although difficult to comprehend, numerous documented cases of embrittlement failures with hydrogen levels this low are known.
This type of embrittlement occurs when hydrogen is concentrated or absorbed in certain areas of metallurgical instability. This concentrating action occurs via either residual or applied stress, which tends to “sweep” through the atomic structure, moving the infiltrated hydrogen atoms along with it. These concentrated areas of atomic hydrogen can coalesce into molecular type hydrogen, resulting in the formation of high localized partial pressures of the actual gas.
How Does Hydrogen Get Out?
Hydrogen absorption need not be a permanent condition. If cracking does not occur and the environmental conditions are changed so that no hydrogen is generated on the surface of the metal, the hydrogen can re-diffuse out of the steel, and ductility is restored. Performing an embrittlement relief cycle, or hydrogen bake-out cycle (the term “bake-out” is misleading as the process involves both inward diffusion and outgassing), is a powerful method in eliminating hydrogen before damage can occur. Key variables are temperature, time at temperature, and concentration gradient (atom movement).
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Electroplating, for example, provides a source of hydrogen during the cleaning and pickling cycles, but by far the most significant source is cathodic inefficiency. To eliminate concerns, bake-out cycles and recommended temperatures/times are shown in ASTM B850-98 (latest revision) as a function of steel tensile strength (see Table 1 of the specification). However, in this writer’s eyes, a “bake-out” cycle of at least 24 hours at temperature is required for the effective elimination of hydrogen as a concern regardless of the tensile strength of the material. Also, caution should be exhibited to prevent over-tempering or softening of the steel, especially on a carburized, or induction hardened part.
Next time we will talk about quench and temper embrittlement, as well as embrittlement due to overheating during forging, all of which are often mistaken for hydrogen embrittlement.
References
ASTM International. 2022. ASTM B850-98 (Reapproved 2022), Standard Guide for Treatments of Steel for Reducing the Risk of Hydrogen Embrittlement. West Conshohocken, PA: ASTM International. https://www.astm.org.
Herring, D. H. 2004. “A Heat Treater’s Guide to Hydrogen Embrittlement.” Industrial Heating, October.
Herring, D. H. 2006. “The Embrittlement Phenomena in Hardened & Tempered Steels.” Industrial Heating, October.
Herring, D. H. 2014–2015. Atmosphere Heat Treatment, Volumes I & II. Troy, MI: BNP Media.
Krause, George. 2005. Steels: Processing, Structure, and Performance. Materials Park, OH: ASM International.
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’sAugust 2025 Automotive Heat Treating print edition.
Quench cracking during heat treatment can turn expensive components into scrap metal in seconds. In today’s Technical Tuesday article, Dan Herring (The Heat Treat Doctor®) explores more about the underlying mechanisms and proper preventative measures to save you time, money, and ensure reliable part performance.
As a young heat treater, I learned first-hand about quench cracking while running various dies for our tool and die shop — and succeeded in cracking all of them! I have never forgotten the foreman’s (rather animated) critique of my heat treating abilities. Quench cracking can be a significant problem for heat treaters, its potential consequences ranging from costly rework to premature failure in the field. Let’s learn more.
We must not only understand the mechanisms involved but also take proactive steps to avoid it. This includes careful consideration of such items as:
Material (e.g., chemistry, hardenability, form, mill processing)
Component part design (e.g., sharp radii, thin and thick sections next to one another)
Manufacturing processing steps (e.g., the effect of stress relief after rough machining)
Part loading (e.g., part orientation in relation to the quench, fixturing, total load weight)
Equipment choice (i.e., limitations and capabilities)
Quench medium (e.g., type, agitation, flow characteristics, temperature, temperature rise)
Process parameters (e.g., ramp rates, atmospheres, vacuum levels)
The Heat Treatment Challenge
Quench cracking primarily occurs during the hardening process, typically when materials are rapidly cooled via quenching. Since the cooling process introduces internal stresses within the material, it can result in crack formation. These stresses are a result of the rapid transformation of the material’s microstructure, most notably when transforming to martensite, a very hard, brittle structure.
Figure 1. Quench crack in a 4140 axle shaft
Mechanisms Involved
Failure mechanisms related to quench cracking include the following seven factors.
Material Imperfections
As material is heated, thermally induced stresses can cause existing surface or subsurface defects, such as inclusions, laps, and seams. These defects act as stress risers to open and propagate into cracks. Once a defect reaches “critical flaw size” — the smallest flaw that can lead to failure under expected operational stress levels — crack propagation will begin and lead to part failure.
Rapid or uneven heating only exacerbates this issue, especially when a material undergoes phase transformations that introduce volumetric changes.
Stress Risers
Sharp corners, steep edges around holes, and even grooves in parts create stress concentration points where quench cracking is most likely to occur. These features also result in localized heating and cooling, causing differential stresses that can initiate cracks.
The sharp edges of a part, for instance, cool much faster than the rest of the material, leading to a high risk of cracking.
Proper design modifications, such as adding radii to sharp corners, can reduce the likelihood of stress concentrations.
Rapid Cooling and Phase Transformation
The transformation from austenite to martensite during quenching is a key contributor to internal stresses. The rate at which the material cools can greatly influence these stresses. If cooling is too rapid or if tempering is delayed, the material can become overly brittle, leading to quench cracking.
Improper Heating and Overheating
Overheating during the austenitizing process can lead to coarse-grained structures that are more prone to quench cracking. Coarse grains increase the depth of hardening but reduce the material’s resistance to cracking. It is critical to avoid temperature overshoot, high ramp rates, and excessively long dwell times when heating.
Inadequate Quenching Methods
The choice of quench medium (brine, water, oil, polymer, high pressure gas, etc.) can also contribute to quench cracking. Overly aggressive quenchants may create excessive thermal stresses.
Improper Fixturing
The way parts are positioned during quenching can create problems. If parts are bunched together in a basket, uneven cooling rates will occur, with parts on the edges cooling faster than those in the center. This can lead to differential stresses and increase the risk of cracking.
Delays Between Quenching and Tempering
Quenching produces high residual stresses in the material, and if parts are not tempered soon after quenching, these stresses can lead to cracking. For materials with high hardenability, such as 4340 steel, immediate tempering (usually within 15 minutes of quenching) is critical to prevent in-service failure.
Understanding Fracture Mechanics
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Understanding these mechanisms is critically important. A material’s fracture toughness, which is the ability to resist crack growth, is defined by the stress intensity factor (KIC). This value varies based on the material’s properties and the size and geometry of the crack. The important point to remember is that when the applied stress reaches a critical threshold, cracks begin to propagate (literally at the speed of sound), leading to catastrophic failure.
Digging a bit deeper, there are three primary modes of fracture:
Tensile (Mode I): Fracture caused by tensile stress at the crack tip.
Sliding (Mode II): Fracture caused by shear stress that causes the two sides of the crack to slide.
Tearing (Mode III): Fracture caused by shear forces in a direction perpendicular to the crack plane.
Preventive Measures
Several strategies can be employed to minimize the risk of quench cracking during heat treatment. They broadly fall into the following categories.
Material Selection
Choosing the right material for the job is essential. Many designers select materials with high hardenability, forgetting that they can be prone to cracking. Additionally, one should take special care with materials that have high carbon content or are heavily alloyed.
Design Considerations
Ensure that part designs minimize stress risers. Avoid sharp corners and incorporate radii where necessary. Proper design can reduce the likelihood of cracks forming at critical locations.
Improved Manufacturing Practices
Proper stock removal during machining and addressing surface imperfections before heat treatment can prevent the initiation of cracks. Machining should aim to eliminate any seams or inclusions that might act as nucleation sites for cracks. Stress relief after rough machining is almost always a good idea.
Control of Heat Treatment Parameters
Maintain tight control over the heating and quenching processes to ensure uniformity. Avoid overheating and try to ensure that the part enters the quench medium in the best possible orientation to reduce the likelihood of creating differential cooling rates.
Figure 2. Quench crack due to a combination of rapid heating, overheating and improper
polymer quench medium concentration in a motor shaft (50x, as polished)
Quenching Media
Select the appropriate quenching medium based on the material, part geometry, and load. Less aggressive quenchants or minimizing time in the quench should be considered for materials with moderate to high hardenability.
Post-Quench Tempering
Temper parts as soon as practical after quenching to avoid concerns with internal stresses. High-hardness materials should be tempered immediately to prevent quench cracking.
Quench Cracking in Other Materials
Quench cracking is not exclusive to steel. Other materials, such as nickel and cobalt superalloys, can also experience cracking due to similar mechanisms. In these materials, the phenomena are often referred to as “fire cracking,” “strain-age cracking,” or “stress cracking.” As with steel, cracks in these materials are often linked to high residual tensile stresses on the surface and the presence of stress raisers. Strategies, such as shot peening, redesigning part geometries, and improving surface finishes, can help mitigate cracking in superalloys.
Summing Up
Quench cracking represents a significant challenge in heat treatment, but by understanding its underlying mechanisms, heat treaters and engineers can take steps to mitigate the risk. Material selection, part design, proper heat treatment procedures, and timely tempering are all critical factors in preventing quench cracking and ensuring the integrity of components. A proactive approach to addressing flaws and stress concentrators combined with careful attention to detail in every stage of the manufacturing and heat treatment process can greatly reduce the likelihood of failure and contribute to the long-term success of heat treated products.
References
Herring, Daniel H. 2012. “Quench Cracking.” Industrial Heating, April.
Herring, Daniel H. 2015. Atmosphere Heat Treatment, Volume 2. BNP Media.
Johnson, D. D. 2005. “Thermal and Mechanical Behavior of Materials.” University of Illinois.
Klarstrom, Dwaine L. 1996. “Heat Treat Cracking of Superalloys.” Advanced Materials and Processes, April.
Krauss, George. 2005. Steels: Processing, Structure and Performance. ASM International.
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.
If you are one of many heat treat professionals watching AM take over the industrial world with bated breath, it may be time to stop watching and start doing. This article highlights the rapid rise of AM and how changes in your heat treat operations may be needed.
This informative piece was first released inHeat Treat Today’sAugust 2025 Automotive Heat Treating print edition.
For manufacturers who produce customized or complex parts and components for the medical, aerospace, automotive, and other industries, additive manufacturing (AM) with metals has the potential to bring innovation and agility to the process.
However, because AM is a somewhat nascent technology, there are still challenges to address before it is widely accepted throughout the manufacturing industry. Fortunately, as research and development continue, the aerospace and automotive industries are beginning to acknowledge that parts made via AM are robust enough for use in safety-critical applications. Manufacturers who want to use AM to gain a competitive edge are advised to zero-in on the most suitable method for metals and determine in which applications AM presents an economically viable solution.
The Additive Manufacturing Market
AM, also known as 3D printing, is the process of creating an object based on a digital file, such as a computer-aided design (CAD) or one created with a laser scanner. Unlike traditional manufacturing methods that often involve cutting or subtracting material from a solid block (like machining), AM involves building up thin layers of material — usually metal, ceramic, or plastic — one by one using a 3D printer.
AI-generated image of 3D-printed turbine engine components
AM is increasingly transforming the manufacturing industry, enabling faster prototyping, customized production, lightweight parts, and complex shapes and geometries that would be impossible to manufacture using conventional casting, machining, or subtractive techniques, such as milling, grinding, carving or shaping.
For product design, prototyping, and reverse engineering applications, AM allows designers to rapidly print parts as a single piece, reducing material waste, saving time, and reducing costs, all while getting new products to market faster. Although the same advantages apply to traditional manufacturing applications, manufacturers have not been as quick to adopt the technology.
Still, the AM industry is seeing growth. A recent report from Grand View Research states that the global AM market size was valued at over $20 billion in 2023 and is expected to grow at a CAGR of 23.3% from 2023 to 2030, with unit shipments of 3D printers expected to reach 21.5 million units by 2030 thanks to a growing demand for prototyping applications in the healthcare, automotive, aerospace, and defense industries. The report also acknowledges that rigorous R&D in 3D printing will further contribute to growth.
Additive Manufacturing Techniques for Metals
Currently, three primary techniques are used for AM with metals: laser powder bed fusion (LPBF), directed energy deposition (DED), and binder jetting.
LPBF
LPBF technologies, including direct metal laser sintering, selective laser sintering, and direct metal printing, use a laser to sinter or fuse powdered metal particles until a complete part if formed. LPBF processes typically include heating the bed of powdered metal to a consistent temperature. The printer begins applying the first layer over a build plate, fuses the powder particles together with a high-powered laser, and then continues the process layer-by-layer until the part is finished.
After the part is printed using LPBF, it is removed from the powder bed, cut away from the build plate, heat treated to prevent internal stresses, and finally machined or polished to achieve the desired surface finish.
LPBF is limited by the size of the print bed, so it is not suitable for manufacturing large components or parts.
DED
DED using powdered metals also relies on a laser to produce metal parts. However, rather than spreading powder on a bed, the DED machine blows powdered metal out of the print head and uses a laser to fuse the part during construction.
DED-manufactured parts require post-processing heat treatment and machining steps. And while DED is a faster process than LPBF, there are a limited number of materials that can be used in the DED process, and the technique still needs more research and development before it sees widespread commercial use.
Binder Jetting
Binder jetting deposits a layer of loose metal followed by a layer of binder material layer by layer to create the product. During the process, a binder jetting machine distributes metal powder over the print bed to form an unbound layer. A jetting head then spreads a binder to adhere the powder. The machine continues to spread alternate layers of building material and binder to form a complete product. Sintering is generally required after printing to remove the binder, resulting in a part that is composed entirely of metal.
While binder jetting is a fast process and offers the opportunity to create and sinter parts in batches, it is currently a more expensive option. However, research and development into this technology, the availability of binder jets from companies (e.g., Markforged and HP), and the potential to use binder jetting for high-volume batch production may eventually make binder jetting the technology of choice for metal AM.
Post-Processing Heat Treatment for AM Parts
No matter the print technique, some AM-printed metal parts will require post-process heat treatment in which the printed part is subjected to specific temperatures and durations and then cooled to enhance or customize the properties of the metal material and optimize performance and reliability of the part.
Applying controlled heating and cooling cycles during post-printing heat treatment eliminates internal stresses created during the AM process to prevent distortion, cracking, and warping that would negatively impact part performance and reliability. Heat treating can also be used to increase hardness, density, strength, and fatigue resistance to optimize performance of the part. Furthermore, heat treating can be applied to customize the mechanical properties of the final part and provide specific characteristics so that it performs reliably in the intended application.
The type of heat treatment used following AM will depend upon the printing technique, metal material, and desired characteristics and properties. Annealing, sintering, normalizing, quenching, and tempering are commonly used. Hot isostatic pressing (HIP) — another post-process option that is used to reduce porosity and improve the density, performance, and reliability of AM-printed parts — will be specifically addressed in a subsequent article release.
Greater Acceptance in Industry Sectors
Metal alloy 3-D printed components
While AM has been widely used for prototyping and reverse engineering, adoption of the technology has been slower for the manufacture of finished parts and components. Stephen Feldbauer, director of Research and Development, with Abbott Furnace Co., suggests that the right approach to AM with metals depends upon the ability of manufacturers to refine their application. “Manufacturers should not take the ‘shotgun’ approach of ‘I can print anything,’” comments Feldbauer. “Instead, they should focus on what makes the most sense for them and specialize in those parts rather than just printing something because it’s possible.
However, because it provides significant benefits, AM does have application in the several manufacturing sectors. Advantages in using AM to produce parts include minimization of waste, time and cost efficiency, and the ability to customize parts for single-use applications or low-volume production runs.
Thanks to these benefits, AM is currently being used in the following industries:
Aerospace: functional parts, such as engine turbine blades and fuel systems
Automotive: various components, such as suspension systems, engine parts, and door panels
Defense: obsolete parts, as well as vehicle and weapon components
Medical: implants, prosthetics, and other apparatuses
And, as AM technology continues to expand, it is becoming more widely accepted and is most notably being employed to create safety-critical aerospace and automobile parts. For example, General Motors (GM) announced that it is using AM-printed seatbelt pillar adjustable guide loops in its all-electric Cadillac Celestiq, making them GM’s first safety-related AM-printed metal part.
The component is made by Azoth using Markforged metal binder jetting technology with a liquid binding agent. Following the process, the metal parts are then sintered, polished, and plated. Automotive sector acceptance of additive manufactured safety-critical parts is a tremendous boon for the AM industry.
Experts like Feldbauer see the need for manufacturers to make a few key decisions for this technology to become a reality. “For additive manufacturing to be a commercially viable solution,” he argues, “manufacturers must determine which parts they can 3D print with high levels of success and where printing is cost effective and profitable. Commercial viability is really the determining factor as to whether a part should be 3D printed or made using conventional manufacturing techniques.”
Currently, though, AM seems to be benefiting smaller jobs. According to Feldbauer, AM usually makes the most sense for small runs where there is a need for customized tooling; in these cases, manufacturers run into too complex of shapes or simply to time or cost intensive.
The Future of AM
While AM is increasingly accepted as a beneficial process across many industries, it still faces challenges affecting its usage more broadly, such as material restrictions, bed or plate sizes for techniques that rely on bed printing, and the need to purchase high-end printers from a market that is constantly consolidating. Research and development into the process, more diversity in technologies, increased availability of AM outsourcing companies, and the benefits associated with cost, time, and material reductions are expected to be a driving force in widespread commercial adoption.
Stephen Feldbauer, director of Research and Development with Abbott Furnace Co., updated Heat Treat Today on the state of AM in 2025
As the technology continues to mature, AM will continue to expand into industries where the availability of high-volume AM production, such as is possible with binder jetting, would reduce the cost of part manufacturing. Additionally, optimizing post-process heat treatment methods will help further enhance the cost effectiveness of AM with metals and enable more customized characteristics. These advances could make AM an attractive and economical option for manufacturers, so those who want a competitive edge should begin to focus and refine application of AM to the parts for which it will be most worthwhile.
References
Grand View Research. 2022. Additive Manufacturing Market Size, Share & Trends Analysis Report by Component, by Printer Type, by Technology, by Software, by Application, by Vertical, by Material, by Region, and Segment Forecasts, 2024 – 2030. April 2022. Grandview Research. Report ID: GVR-4-68039-922-9. https://www.grandviewresearch.com/industry-analysis/additive-manufacturing-market#
Check out our AM/3D Trivia to test your knowledge of the AM/3D industry, the processes, and the technology.
This editorial was written by the Heat Treat TodayEditorial Team.
Helium leak detection is critical to ensure system integrity, product quality, and operational efficiency in vacuum processing. With 36 years of hands-on experience, Dave Deiwert of Tracer Gas Technologies joins host Doug Glenn on the most recent episode of Heat Treat Radioto share a wealth of knowledge on the evolution of leak detection technology, practical maintenance, and best practices for leak testing.
Listeners will gain practical insights into the best leak detection practices and how to troubleshoot challenges.
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: Helium leak detection has come a long way, but not everyone has a brand new piece of equipment. So let’s talk about some of the shortcomings of older equipment and some of the improvements that you’re seeing.
Dave Deiwert: When I started in 1989, leak detectors pretty much had what were called oil diffusion pumps as the high vacuum pump. That’s the pump that creates the vacuum for the analyzer cell or mass spectrometer so they can separate helium from other gases. These diffusion leak detectors did not like to be shut down improperly or have power outages quite frequently.
You would hear stories of somebody that turned the power off of a leak detector without a proper shutdown or a power outage, and that could cause an oily mess from the diffusion pump, and maybe even crack the oil. So, you would end up having quite a maintenance event required on the leak detector before you could use it again.
In fact, these kinds of problems happened so frequently that in my young sales days when turbopump leak detectors first were introduced, as I would go in to show it to a potential client, one of the first questions was, “What happens if you have a power outage?”
I would have a little fun with that.
I’d say, “Well, let’s find out.” And I would pull the plug out of the wall, and they would say, “Oh, you can do that?” And of course you could. A turbo pump would just coast down towards a stop. Then we turn the power back on, and it’s back up.
Part of what compounded this problem with the diffusion pump is that it works by heating oil to jet mist oil vapor that goes to the top, and it’s condensed and directed back down. When power is lost, whether you turn the power off with an improper shutdown or a power outage, that pump is still hot for quite a while. It’s still trying to pump, and the backing pump, whether it’s a diffusion pump or a turbopump, is typically a rotary vane pump. With a power outage or power stop, those pumps will come to a stop very quickly. But those diffusion pumps and turbo pumps are not designed to exhaust atmosphere, so the backing pump or rotary pump comes to a stop pretty quickly, and now you have atmosphere potential on the exhaust of the diffusion pump.
The turbopump survives that much more nicely than a diffusion pump does. So the first major upgrade in the technology across the board with all the manufacturers was moving away from diffusion pumps to turbo pumps. If you buy a new leak detector from the ‘90s to today, it will very likely have a turbo pump no matter whom you buy it from and even if you buy a used one.
Size and Portability of Leak Detectors (00:06:09)
Doug Glenn: How large were these original pieces of equipment? Did you have to wheel them around?
Dave Deiwert: The very first ones I worked with predominantly would be the size of a washer/dryer. They would typically have casters on so you can roll them around.
They took up more space and certainly took up a lot more energy. You could sometimes find what they would call portable leak detectors, but they would still have diffusion pumps in them, and they’d have less features because of how small they were versus the console leak detectors.
Doug Glenn: So now nowadays they use helium leak detectors.
Dave Deiwert: Most everybody’s gotten away from console leak detectors. You can find a couple companies that have a fairly large rolls-on-caster leak detector that still has turbo pumps, and higher performing backing/ruffing pumps. But the majority of leak detectors you’re going to find are more portable and smaller in size.
Doug Glenn: Are they close in size to a briefcase?
Dave Deiwert: They average 12 to 18 inches wide by 10 to 12 inches deep and 12 to 14 inches tall, approximately. So, much smaller than a washer/dryer.
Quite frequently, these leak detectors may be sold with a cart so that you don’t have to carry them from point A to point B. It can be a little laborious to still carry them. They weigh 40 lbs or more. So quite often, the first accessory purchased with the leak detector is a cart to roll it around.
Doug Glenn: So it’s a heavy piece of carry-on luggage essentially.
Dave Deiwert: Absolutely.
Maintenance: Old vs. New Leak Detectors (00:06:37)
Evaluating a vacuum furnace for leaks
Doug Glenn: How would you compare the maintenance of those older units, assuming that you don’t lose power, versus maintenance of the newer units.
Dave Deiwert: A stereotypical experience from my field service days would be if you’re running a diffusion pump leak detector in a production environment, using it every day, then most likely you’re going to do what I call an overhaul of the leak detector. During this overhaul, you’re going to change your oils, change the filaments in the mass spectrometer, put on new valve seats, and clean the manifold.
Not everybody will do this. There are those that might go a year or two, especially if the leak detector is purely for troubleshooting, like if you have only a few furnaces. The leak detector may sit against the wall, and then you go get out to leak test a furnace. They may well get a couple of years of use out of a leak detector before needing to do any preventative maintenance or even a major overhaul.
With the new turbopump leak detectors, I think all the manufacturers now have models that most likely you’ll go multiple years without really doing anything other than changing oil in the backing pump, which you might do a couple times a year or so, keep an eye on the oil level, much more maintenance friendly and easier to do the troubleshooting and the service to it.
Filament Technology Improvements (00:08:10)
Dave Deiwert: The next major upgrade in the leak detectors across the industry was the filament design.
The old diffusion pump leak detectors predominantly had tungsten filaments, which, if you’ve ever cracked or seen a cracked light bulb that had a tungsten element in it, you know that immediately you lose the function of the light bulb. And the same thing with the filaments that are tungsten in a mass spectrometer. If it gets a pressure burst, which is what I call the event when somebody disconnects the test port from the vacuum furnace while the leak detector is still in test, that allows a pressure burst into the leak detector and tungsten filament, and most likely you will burn out the filament. As a result, you will have a maintenance event for that.
As a rule of thumb, you will get 1,000 to 2,000 hours out of an old leak detector with tungsten filaments, but you’re going to get many thousands of hours out of a Yttria coated-iridium, which I think is used across the board in the industry today. In the case of
several years even, it greatly reduces your cost of ownership with the newer leak detectors.
Performance and Cost Comparison (00:09:12)
Doug Glenn: Are there any other major differences between the old units and the new units?
Dave Deiwert: There are some extra benefits from the upgrades that we’ve talked about. The turbopumps will allow, at least modern leak detectors, us to test at a higher pressure (or less vacuum). You press “Start Leak Detector.” The test port pressure pumps down to some vacuum level. For diffusion pump leak detectors, they had to get down to typically less than 50 mTorr. Depending on the model, definitely significantly lower vacuum than the turbopump leak detectors. So, the turbopump ones with the gross leak testing capabilities, you’re probably looking at 18 to 20 torr. I think a couple of manufacturers claim they can get in the test pretty much right below atmosphere and start looking for very massive leaks.
The capabilities going to turbopump and Yttria-coated filaments has allowed manufacturers to greatly improve the performance and the robustness and reliability of the leak detectors.
Doug Glenn: In terms of cost comparison, are newer units more or less expensive than older units?
Weighing the costs and comparisons of different units
Dave Deiwert: When buying a leak detector in 1889 to early ‘90s, you’re probably looking at the low to mid-20s in price. You’re going to find they are a little higher than that now. With the market and inflation, you’re probably looking at upper 20s to low 30s for the most typical leak detectors that are purchased for the vacuum furnace industry. You can find some that are maybe two or three times that amount, but those are not needed for the industries that we’re talking about today.
Troubleshooting and Service Efficiency (00:11:00)
Dave Deiwert: If the client, their suppliers, or people who work on the leak detectors from time to time service a diffusion pump leak detector, they may want to explore an idea to troubleshoot a problem. They may not be sure what the problem is yet.
First, you’re going to do a proper shutdown of the diffusion pump leak detector to protect the oil in the diffusion pump and the cleanliness of the leak detector. You may wait a good part of an hour for that diffusion pump to cool off before you can try the troubleshooting solution you’re going to investigate. Then you’re going to wait for another good hour for it to heat back up and be ready to confirm if what you have tried to do was successful.
With a turbopump leak detector, you turn a switch off to turn the power off, and within minutes you can test out the solution on the leak detector. So you greatly expedite your troubleshooting time.
What might have been almost always a full day event of troubleshooting and servicing a diffusion leak detector turns into less than a half day, possibly even an hour or two.
In every category, the newer leak detectors are very attractive. If clients or our viewers reach out to their suppliers or potential suppliers, there will most likely be some trade-in value for your old leak detector, which will also help offset the pain and suffering of spending money on a new leak detector.
Doug Glenn: Hopefully they’ll come pick it up, too.
Where to Connect Leak Detectors on Furnaces (00:14:11)
Doug Glenn: In your column, you talk about how there’s some debate amongst users on where to hook up the leak detector on the furnace. Can you walk us through that a bit?
Dave Deiwert: I run into people who are very adamant that you hook up the leak detector in one of three places. And I’ve told salespeople that while we have our preferred location of where to hook to the leak detector, we should never visit a client and tell them they are doing it all wrong. As a field service engineer, I’ve confirmed that you can connect the leak detector at three most prominent locations, but the question is where is the most optimum place to connect it?
Leak testing a vacuum furnace
The first place is hooking the leak detector directly up to the furnace chamber, because that’s where they imagine the leaks might be. The next two locations might look like close cousins because they’re both in the series flow away from the chamber, through the pumps and out to the exhaust.
My preferred location is to connect it between the blower and the chamber. Or, if there’s
a diffusion pump, I would connect it between the blower and the diffusion pump.
The last place that you might see somebody connect it is between the blower and the backing pump or a roughing pump. They might do this to use the blower almost like a turbocharger to improve the signal to the leak detector. The disadvantage of doing that is most likely these vacuum pumps are very dirty single-stage roughing pumps. There are two concerns I have with this. One is the back stream of oil or hydrocarbons from that pump to the leak detector. And the second is the potential for back streaming, even of helium from the ballast port of the pump or the exhaust, depending on where the exhaust is terminated. If somebody exhausts the pump directly out of the building, then that’s not so much a concern. But if you connect it between the blower and the diffusion pump or the blower and the chamber, then you’re allowing the roots blower to be like an optically dense filter between the leak detector and that backing pump.
And for the two concerns that I mentioned earlier about either back streaming of helium from the leak testing or back streaming hydrocarbons from the vacuum/roughing pump, the optimal location would be to hook it up between the blower and the chamber, or if it’s a diffusion pump, between the blower and the diffusion pump. If you’re hooking it up between the diffusion pump and the roughing pump, you need to make sure that you pump down to your base pressure before you open up the valve from the leak detector to that point. You don’t want to potentially suck any diffusion pump oil into the into the leak detector.
Furnace Connection Points and Hardware (00:15:50)
Doug Glenn: Is there a feed through meant for leak detection built into the furnace, between the blower and the diffusion pump or roughing pump or on the chamber?
Dave Deiwert: There is almost always a connection point where I describe my preferred location, especially with furnaces manufactured in the last twenty years. On new furnaces sold today, it’ll be an NW25 flange, which will match up directly to the leak detector.
With the leak detectors in this industry, we’ll have an NW25 flange, which is a standard vacuum connection. You run a bellows hose from that leak detector to that point on the furnace.
I like to see a manual ball valve that’s always on the furnace at that point. You can put a blank cap on the exposed port on that valve, which can act like a dust cap. It’s always there. This facilitates doing a PM leak check, which we might talk a little bit more about later.
Now, sometimes you may go to hook it up between the blower and the furnace or the blower and the diffusion pump and there’s no connection there.
I’ve seen that, so you have to work with what you’re given. You might well see there’s a port between the blower and the backing roughing pump,
and you can use that. It’s just not the optimal place to put it.
If you put the leak detector directly on the chamber, typically there’s a small port that you can hook up to, now you’re going to be competing in what we call molecular flow with a much larger opening going to the blower. The lion’s share of helium is going to go out that large target to the blower, and you’re not going to get as much helium signal to the leak detector. So, putting the leak detector port basically right into the end of the flow, going to the blower lets you sample the flow going in that direction.
Doug Glenn: Right, which is going to be the bulk of it.
Dave Deiwert: Yes, and you’ll find a faster response time and faster cleanup and recovery of the leak rate signal when you stop spraying the helium by putting it in that location.
PM Leak Checks During Furnace Operation (00:18:05)
Doug Glenn: You briefly discussed conducting PM in the column. Can you walk us through conducting a PM leak check during a live operation of the furnace.
Dave Deiwert: First off, when you’re going to do a preventative maintenance (PM) leak check on the furnace, there are two scenarios. In the first scenario, you’re not running the furnace today. So, you roll the leak detector up and you look for leaks that you may not know are there when they’re smaller and less noticeable, so you can either mark them or repair them at your convenience before they get to be larger and more noticeable, maybe affecting quality of your process.
The second scenario is that you have a very long process. You might have enough time to do a leak check while the furnace is in process. Helium is an inert gas. If you pull a vacuum on your furnace to do some heat treating, and it’s going to be in that vacuum level for an hour or more, this may be plenty of time to do some leak testing. We definitely don’t want to compromise quality. But again, helium is an inert gas, and if you have an experienced person doing this PM leak check in an orderly fashion, it can be done safely.
Basically, you roll the leak detector up to that closed ball valve, and you would have to have the ball valve in place there if you’re doing this during a live process. So you connect the hose from the test part to this closed ball valve. You start the leak detector and put it in test. I suggest that after you put it in test, you ensure you have a good vacuum test level vacuum from the leak detector to the closed valve.
Because we don’t know initially if the vacuum level is different on the other side of the valve,
Heat Treat Radio #123 Host Doug Glenn and Dave Deiwert
I recommend momentarily stopping the test of the leak detector. I think all modern leak detectors have a standby mode so you’re not venting the test for a leak detector. You put it in standby, then you open the ball valve, and the leak detector computer can now see if the vacuum level changed to maybe potentially a level a little higher than what it wants to be at. That allows it to tell itself to pull some more vacuum along with the furnace before we actually open the test valve to the analyzer cell or the mass spectrometer.
If you’re in test, you open the ball valve, and somebody forgets that step, there can be a little vacuum differential and you may shock the leak detector and throw it out of test. This doesn’t hurt the leak detector. You just have to go and press test again. But by putting it into standby and then opening the ball valve, then putting it back into test, this saves you a step.
Once you put it into test, the next thing you’re going to make a note of is the background level of helium before you start spraying helium. I’m a big fan of people who leak test their furnace, or really anything no matter what market is, and take care of their furnaces purposefully.
If you don’t suspect any leaks or it’s a brand new furnace, you can hook your leak detector up and you put it in test, and before you spray any helium, make note of what I call the background helium signal. This is a result of any natural helium that’s in the furnace. There is five parts per million helium in the air we breathe. There’s going to be helium in the furnace, and take note of what that is.
Let’s say you notice you have two times ten minus nine background of helium on the display of the leak detector, and you haven’t sprayed any helium, you can make note of that.
So now you know you’re going to be looking for leaks for some delta change increase of that value. From there, it’s playing the hot and cold game as you pinpoint where the leak isas you spray helium.
You can do this potentially while a furnace is in process. You certainly want everybody to know what you’re doing and have an opportunity to discuss this because it could make people nervous, especially the quality manager or even the production manager. It’s something that should be talked about with the whole team to ensure everybody sees the value in it.
So we spray helium and make a note of anything we see. Next time we have an opportunity, when no production is going on, we can fix that leak at our convenience rather than wait until it might get worse.
Doug Glenn: Certainly we would want to consider whether that should be done with high-value items in the furnace.
Dave Deiwert: Yes, unless everybody is on board and understands, and you’re doing things purposely.
If you are doing a PM leak check on a sensitive process and quality of a product and you’re done testing, that manual ball valve needs to be closed before you do anything else to the leak detector. If you forget, and you press vent on the leak detector, it’s going to try to vent that whole furnace through the little vent valve of the leak detector, and that’s not going to be good.
This whole discussion point is that everybody on the team would need to buy into this idea and be very clear about what we’re going to do, how we’re going to do it.
I’m just suggesting it’s something that can be done, and if you confirm it works for you, it has value. It’s just another option for somebody to optimize the way they take care of their furnace.
Confirming Leak Location Before Repair (00:23:38)
Doug Glenn: When you’re isolating a leak, how important is it to assume or not assume that you found the leak once you get a reading on the on the meter?
Dave Deiwert: I spend a lot of time on this topic in every class that I teach because nothing is more frustrating than thinking you have found the leak when you haven’t.
Let’s say you think have found the leak on some big 10-inch gate valve. Maybe it’s too heavy for one person you have to have someone to help you take this gate valve off the system. Once you take the gate valve off the system, you put a repair kit in there, clean everything, you put it back on the furnace, and everything’s assembled. You start to furnace back up and you do a leak check and realize you still have the same leak you thought you fixed. There may be other flanges you need to check, which might require more help.
You absolutely, beyond the shadow of doubt, can know that you have found the leak because every time helium is sprayed at that place where you think the leak is, you should get the same response, same response time, same peak leak rate.
If I spray the helium at point A, where I think the leak is at, and I stop spraying, I wait for the leak rate to go back to baseline, then I go back to spray it again. The more work that is involved, the more I’m going to want to duplicate that response and make sure that is where the leak is at.
Last thing you can do, just to be sure, is what I call the “x, y, z axis.” Try to spray helium left, right, up, down, back and forth, just to make sure you’re not getting a better response to something else nearby.
Doug Glenn: By better response, do you mean a higher measurement of helium that comes through or comes through more quickly?
Dave Deiwert: That’s correct. Now, you might have the problem where there are 2, 3, or 4 connections right in the same general area, and it’s difficult to pinpoint where I’m getting I think the same response, no matter where I’m spraying the helium. To remedy this, you can put a barrier between two fittings. This barrier could be plastic, tape, putty, your hand. Try to put some barrier between the two connections so when you spray on one side now, you’re not really getting the same response you were before and can pinpoint the location of the leak more accurately.
This is an important step before you repair or remove something. If you remove a NW25 flange and you’re wrong, there’s not a lot of pain and suffering. But I guarantee you 100%, you can prove to yourself with some patience and some diligence where the leak is before you do the work of disassembly and service.
Doug Glenn: It is better to invest a little time in detection than to repair something that doesn’t need to be repaired or find out later that you fixed the wrong piece.
Dave Deiwert: Absolutely.
Repair vs. Replace: Leak Source Components (00:26:44)
Doug Glenn: Once you do find the leak and it’s through some sort of a device, whether it’s a feed through or a control or a valve, how do you decide whether to repair that item or replace it?
Discerning when to repair or replace
Dave Deiwert: If the device is something that you can disassemble, and if the manufacturer has a repair kit (a valve is a good example of that), I would recommend that you go ahead with a repair. You have already taken it apart, I would put the part in a repair kit, if you have one, to try to lengthen the time between now and the next time you look at it.
If it’s a piece that has no repair kit, then obviously you will need to repair it or replace it, depending on your skill level and what it is you’re looking at.
If you’re looking at thermocouple and the feed screws on it are leaking, you may be a little limited in what your options are. Can you apply a vacuum-friendly sealant to brush around the feed throughs to see if that would solve the problem? That may be an option. What is the cost of that thermocouple? If it’s a $20 item, I’m probably going to put another thermocouple on there. If it’s a $1,000 item, I might try brushing some vacuum-friendly sealant on and see if that takes care of the problem.
One time, I found a leaking rotary vane pump, back in my field service days.
These all have repair kits where you can replace all the gaskets, the vanes, everything. But I didn’t have one. This was early in my young career. I talked to the factory about getting one and they were going to send one. But I told the client that we had nothing to lose. Let’s open it up, see what we can find. So, we open that pump up, and it looked pretty bad inside, but we cleaned everything up, even the gaskets, put a little vacuum sealant on, and put it all back together. We made it leak tight, and we got it running again. If I had a repair kit, I’m already there, then let’s go ahead and put the repair kit in. But if you don’t have one, there’s nothing wrong with taking it apart and seeing if cleaning and
reassembly gets it going for you.
Rotary Vane Pump Field Advice (00:30:30)
Dave Deiwert: I’m going to give a little free advice, no extra charge, to people talking about rotary vane pumps. In my career, I’ve come across quite a number of rotary pumps that were having an issue. I can count on one hand, however, how many times I wasn’t able to just clean it, put it back together, and get it going again with fresh oil. And both those times involved a shaft seal leak. So, if you don’t have a shaft seal leak, in my mind, you’ve got nothing to lose by taking a rotary vane pump apart, cleaning it, and putting some fresh oil back in it.
If you’re using solvents, when you take it apart, make sure those are solvents cleared back out of there
because solvents and oil don’t play very nice. You want to make sure that solvents have been removed and degassed from your pump. This may require that you put oil in it, run it for a little while, then flush it, and put some oil in to make sure you don’t have anything remaining behind.
A little willingness to get your hands dirty, open up the rotary vane pump, and a very good chance that you can get it going by just doing that.
Doug Glenn:All right, Dave. Appreciate the good advice and your expertise.
About the Guest
Dave Deiwert
Dave Deiwert has over 35 years of technical experience in industrial leak detection gained from his time at Vacuum Instruments Corp., Agilent Vacuum Technologies (Varian Vacuum), Edwards Vacuum, and Pfeiffer Vacuum. He leverages this experience by providing leak detection and vacuum technology training and consulting services as the owner and president of Tracer Gas Technologies.
Learn more about Dave from Heat Treat Today’s July Digital Edition’s Meet the Consultant page.
Have you faced complications from inadequate quenching, tempering, or documentation? You’re not alone. Small oversights can compromise part quality and performance. In this Technical Tuesday installment Ryan Van Dyke, metallurgical engineering manager at Paulo, addresses the top five pitfalls that in-house heat treating operations encounter and when to find another solution.
This informative piece was first released inHeat Treat Today’sJuly 2025, Heat Treat Super Brands print edition.
When dealing with high-volume production, running an in-house heat treating operation may seem like it makes financial and logistical sense. The ability to immediately process large batches of the same parts, minimize handling time, and tightly integrate heat treatment into the manufacturing workflow can provide critical advantages over outsourcing.
Industries involving high-volume machining of parts (e.g., automotive fasteners and bearings) rely on heat treating in-house to maintain efficiency and cost control. When parts are produced in the millions, outsourcing heat treating risks working with an inadequate supplier, introducing unacceptable lead time delays, transportation risks, and logistical complexities that do not align with high-throughput manufacturing.
Gas nitriding furnace at Paulo
Conversely, in-house heat treat operations often lack the flexibility, specialized equipment, and process control systems that commercial heat treaters develop over years of refining best practices. I have worked with countless manufacturers with in-house heat treat who have faced challenges they were unable to solve internally — from unpredictable distortion to process inconsistency, failed audits, and more. When they turn to a commercial heat treater for help, we often find the same core issues at play.
While commercial heat treating is not always the best fit for high-volume operations, there are real risks if you choose to run heat treating in-house. Here are the five most common pitfalls I’ve seen.
Pitfall #1: Inconsistent Mechanical Properties
Understanding the Problem
Gas flow gauges for heat treating furnace
Heat treating sets the foundation for a part’s hardness, toughness, and overall performance. This is done by the controlled heating and cooling of materials in a special atmosphere and then locking in the desired microstructure.
One major challenge that impacts consistency in parts is furnace temperature uniformity. Older or improperly calibrated furnaces can create hot and cold spots, leading to localized variations in hardness and mechanical properties within the same batch. This is a common challenge in-house heat treaters face. To avoid hot spots, heat treaters must go beyond just considering equipment age — they should implement robust preventative maintenance programs and routinely calibrate furnaces to ensure consistent thermal performance across all zones.
Real-World Consequences
Distortion issues from non-uniform heating: Variations in temperature cause inconsistent thermal profiles, leading to unpredictable warping and dimensional instability. For example, a die used for stamping operations requires excessive rework after heat treatment because some areas of the part distorted unevenly due to poor furnace temperature uniformity.
Inconsistent hardness in a load: Hot and cold spots in austenitizing and tempering furnaces can cause parts in some areas to have a different final hardness than others. For example, a load of larger diameter structural bolts was tempered in a furnace with poor uniformity. Bolts located in a hot spot in one corner of the furnace showed below specification mid-radius hardness due to over-tempering.
Pitfall #2: Surface Contamination from Incorrect Gas Atmosphere Control
Understanding the Problem
Many manufacturers with in-house heat treating operations use gas atmospheres to control oxidation and facilitate processes like carburizing and nitriding. However, if the gas atmosphere is not properly monitored, it can lead to oxidation, decarburization, or uncontrolled case hardening.
Heat treaters often rely on Endothermic gas generators that produce a carbon-rich atmosphere. Without precise control of carbon potential, parts may develop non-uniform case depths, excessive soot buildup, or — the opposite extreme — decarburization, in which the surface loses carbon and thus its strength and hardness. Therefore, it’s imperative to monitor and adjust atmosphere parameters in real time using carbon probes to maintain precise control of carbon potential.
Real-World Consequences
Decarburization leading to soft surfaces: If the furnace atmosphere lacks sufficient carbon potential, the steel loses carbon at the surface, reducing hardness and durability. For example, aerospace landing gear components could be rejected if surface hardness tests show excessive decarburization, making them unsuitable for service.
Scaling and oxidation issues: Excess oxygen in the furnace leads to surface oxidation, requiring costly post-processing like machining or pickling. For example, stainless steel medical implants can develop scale during heat treatment, requiring extensive rework to restore a clean finish.
Uneven carburizing creating case depth variations: Fluctuations in furnace gas composition lead to inconsistent carbon diffusion, making case depth unpredictable. For example, a batch of industrial gears can fail inspection because some parts have insu cient case depth while others are over-cased, leading to production delays.
Quenching is one of the most stress-inducing steps in heat treatment. Rapid cooling causes phase transformations and volume changes within the steel, leading to internal stresses and distortion.
Manufacturers with in-house heat treaters often struggle with choosing the right quench medium, optimizing agitation rates, and positioning parts correctly during quenching. Additionally, many only have access to one quench medium, such as oil, and will attempt to apply it to all materials and geometries — even when a slower or faster quench rate is required. This mismatch can cause excessive distortion, high residual stresses, and even quench cracking.
Another issue is poor part orientation during quenching. If a part is improperly positioned, different areas will cool at different rates, creating non-uniform hardness and residual stress buildup, which can later cause warping or failure in service.
Real-World Consequences
Incorrect quenchant selection: If the wrong quench medium is used, such as oil when polymer or water would be more suitable, the parts could end up having inconsistent hardness in various sections due to insufficient cooling. Conversely, selecting a fast oil as a quenchant when hot oil would be more suitable could cause excessive distortion due to the faster cooling rate. For example, lifting shackles quenched in oil will not have sufficient hardening response throughout the cross-section, causing them to be rejected for service due to low strength values in the center of the part.
Insufficient quenchant agitation: If the quenchant in the quench tank is not sufficiently agitated when the parts are submerged, then cooling rates throughout the load of parts could vary, causing different amounts of hardening. For example, parts near the edges of a batch load show hardness testing within specification, while parts in the center of the load show hardness below specification.
Incorrect positioning of parts: How a part is oriented during quenching can have a large impact on the amount of distortion after heat treatment. If a part is laid horizontally rather than vertically, the amount of distortion can dramatically increase. For example, if a hollow cylinder was laid horizontally for processing, rather than vertically, the cylinder would likely be at risk of material creep during austenization, as well as deformation from the bottom of the part quenching before the top. The result would be distortion in the inner diameter and along the length in excess of the amount of additional material le for machining, causing the part to become scrap.
Pitfall #4: Brittle Failures from Inadequate Tempering
Understanding the Problem
Tempering is a critical post-quench process that reduces residual stresses and brittleness while fine-tuning hardness and toughness. After quenching, steel is in a highly stressed martensitic state, which, if left untreated, can lead to catastrophic failures in service.
If heat treaters are working under tight production schedules or have an incomplete understanding of tempering curves for different steels, then they may fall into the trap of rushing or even omitting tempering cycles. For some in-house heat treat operations, a single tempering cycle may be employed when a double temper is required, particularly for high-alloy steels like D2, H13, or certain aerospace-grade alloys.
Real-World Consequences
Brittle fracture under load: If a part is left untempered or under-tempered, the high internal stresses from quenching remain, making it prone to sudden brittle fracture when subjected to impact or fatigue loading. For example, an induction-hardened gear used in heavy machinery can snap under torque loading due to excessive quench-induced stresses. It is very common to skip tempering on induction-hardened parts, especially in in-house heat treat operations where cycle times are minimized as much as possible.
Reduced wear resistance due to over-tempering: If a steel is over-tempered (held at too high a temperature or for too long), excessive softening can occur, reducing wear resistance and surface hardness. For example, a die used in stamping operations can wear prematurely because it was tempered above its recommended range, leading to a loss of edge retention.
Excessive retained austenite leading to dimensional instability: Some steels, particularly high-carbon and high-alloy grades, require a secondary tempering cycle to stabilize the microstructure. Skipping this can leave excessive retained austenite, which converts to untempered martensite over time, causing unexpected distortion or possibly cracks forming in the material in service. For example, a precision-ground shaft can warp and develop cracks weeks after heat treatment because retained austenite transforms to untempered martensite in service, altering the part’s geometry and encouraging fractures to form.
Pitfall #5: Lack of Process Documentation & Repeatability Issues
Understanding the Problem
Heat treating is a process-sensitive operation where small variations can lead to major differences in final part properties. If a heat treat operation does not have detailed documentation and tracking systems, this will lead to inconsistencies in cycle parameters, atmosphere control, and quenching conditions.
One of the most common issues is manual adjustments without proper record-keeping, which can lead to process drift. Operators may tweak furnace temperatures, quench delays, or gas flow rates without logging the changes, creating batch-to-batch variability.
Automotive Gear
Additionally, compliance and traceability may present a challenge for manufacturers facing ISO, Nadcap, or AS9100 audits. When an auditor asks for process records, lacking verifiable data is a red flag for non-compliance.
Real-World Consequences
Batch-to-batch variability: When process parameters are not documented or followed precisely, parts in one batch may have different hardness, case depth, or dimensional stability than parts in the next batch — leading to field failures or quality escapes. For example, a manufacturer of automotive control arms may and that some components fail impact testing while others pass, leading to a full production hold to investigate process inconsistencies.
Failed audits and compliance issues: Without traceable process documentation, heat treat operations can fail compliance audits, especially for industries with strict quality requirements. For example, an aerospace supplier could lose Nadcap certification because they cannot provide accurate records of furnace temperature control, atmosphere composition, and quench parameters for critical landing gear components.
Difficulty troubleshooting heat treat issues: When a batch of parts fails post-heat treatment inspection, the root cause can be nearly impossible to determine if there are no detailed process records. For example, a fastener manufacturer might experience high rejection rates due to inconsistent case depths, but if the atmosphere carbon potential wasn’t recorded, they will not be able to pinpoint whether it was a gas mix issue, furnace drift, or soak time variance.
Expensive scrap and rework costs: A lack of process repeatability leads to high scrap rates and expensive rework to bring parts back into spec. For example, a tooling manufacturer might have to scrap an entire run of die components after discovering that an unrecorded furnace temperature deviation softened the steel below acceptable hardness levels.
Lack of lot traceability: When a heat treatment problem does occur, being able to trace it back to exactly which piece of equipment it ran in and when is critical for determining root cause. For example, many automotive seating brackets exhibit low hardness after heat treatment. However, if lot traceability to the furnace cycle was not maintained, root cause of factors like incorrect furnace temperature, inadequate carbon control, or insufficient quench agitation are much more difficult to identify.
When To Call a Commercial Heat Treater
If limited resources and/or lack of specialized expertise are in question, these five pitfalls can easily occur. Even the most well-run in-house heat treat operations must balance production efficiency, heat treat quality, and high-volume demands; additionally, it can be challenging to regularly invest in the most advanced equipment, process monitoring, or specialized personnel.
There are commercial heat treaters that have built their entire business around controlling these variables with precision. These heat treaters have invested decades into refining their heat treating processes, equipment, and metallurgical expertise to eliminate these issues before they ever become problems.
If these five pitfalls are ones your operations cannot easily avoid, consider a partnership with the right commercial heat treater to maintain parts with extreme precision, low distortion, and strict compliance specifications.
About The Author:
Ryan Van Dyke Manager of Metallurgical Engineering Paulo
Ryan Van Dyke is the manager of metallurgical engineering at Paulo, where he works closely with customers to solve challenging thermal processing issues. He’s dedicated to pushing the limits of heat treating performance, continuously innovating more efficient, reliable ways to process critical parts. Ryan was an honoree in Heat TreatToday’s 40 Under 40 Class of 2023.
For more information: Contact Ryan Van Dyke at RVanDyke@paulo.com.
Alloy R&D has resulted in a material that combines the affordability of 310 stainless steel with the high temperature properties of more expensive higher nickel alloys, like alloy 600. Be it for your muffle belt conveyor or heat treating trays, this Technical Tuesday installment by Hugh Thompson, applications engineer of Rolled Alloys, will explore the strengths of this alloy variety to determine its best application.
This informative piece was first released inHeat Treat Today’sJuly 2025 Super Brands print edition.
Increasing nickel prices initiated the development of RA 253 MA®, a versatile alloy used in various thermal applications for equipment construction. With low chromium (Cr) and nickel (Ni) levels, this alloy provides a cost-effective alternative to other pricier nickel-based materials. With microalloying control, it is priced alongside 310 stainless steel while offering high strength properties similar to the more costly 600-series alloys.
Chemically similar to 309 stainless steel, the alloy offers significantly higher creep resistance and rupture strength than 310. Its benefits include:
Oxidation resistance up to 2000°F (1090°C)
Significant hot tensile strength comparable to that of the 600-series alloys
Noteworthy creep and rupture properties
This lean austenitic stainless steel uses cerium and silicon to create a very adhesive oxide, resulting in excellent oxidation resistance. The combination of nitrogen and carbon provides creep-rupture strength double that of 310 and 309 stainless steel at 1600°F (870°C).
Chemistry
RA 253 MA has a specified chemistry, as indicated in Table A.
Table A. RA 253 MA chemistry
High Temperature Properties
Figure 1 shows the hot tensile strengths of different materials. RA 253 MA can be seen to have higher hot tensile properties than alloy 600, 310 stainless, and RA330® but lower than RA 602 CA®. It’s worth noting that while its hot tensile strength is reported up to 2200°F (1200°C), practical use is limited to 2000°F (1090°C) in oxidizing environments due to a loss of oxidation resistance at this temperature.
Figure 1. Hot tensile strengths
Figure 2 displays the allowable design stresses for pressure vessel plates according to Section II-D of the ASME 2023 (2024 revision) code. One can see that the allowable stresses for RA 253 MA are higher than those for 310 stainless and RA330 but not as high as alloy 601. ASME allows design stresses for this alloy up to 1650°F (900°C). However, RA 253 MA is utilized at higher temperatures for various applications because this temperature limit is only for pressure vessels.
Figure 2. Allowable design stresses
Figure 3 displays the actual 10,000-hour rupture strengths of different high temperature alloys. The data reveal that RA 253 MA exhibits high creep and rupture stress values comparable to alloy 601 and RA 602 CA, and it surpasses RA330; this would also surpass alloy 600.
Figure 3. 10,000-hour rupture strengths
In Figure 4, data are presented for the minimum creep rate of 0.0001% per hour. Creep refers to the rate at which metal stretches, and it is usually measured in percentage per hour. There is a phase where the creep rate remains relatively constant, known as the secondary creep rate. This rate is a key factor in designing for high temperatures. It’s important to consider that metal will creep even under light loads, as the effects of creep can be observed in material with no load other than its own weight. Therefore, in practical applications, a creep criterion is utilized for design purposes.
Figure 4. Minimum creep rate of 0.0001% per hour
The furnace industry has traditionally used a design criterion based on the stress required for a minimum creep rate of 1% in 10,000 hours or 0.0001% per hour. The design stress is typically set at a fraction of this value. For one of its criteria, ASME uses 100% of the extrapolated stress for 1% in 100,000 hours (or 0.00001% per hour). It is not recommended to extrapolate stress rupture and creep data to 100,000 hours above 1800°F (980°C). Th is comparison is provided for general guidance only.
Rupture strength is reported as a stress and number of hours. It is the stress required at a specific temperature to break a specimen within a given time. In the furnace industry, a standard criterion for setting design stresses is to use a fraction of the stress that would result in rupture at 10,000 hours. ASME uses the lower of 67% of the extrapolated 100,000 rupture stress or 100% of the extrapolated 1% in 100,000 hours minimum creep rate.
Strengths and Limitations
When compared to alloys like 309 and 310, RA 253 MA has demonstrated equal or superior oxidation resistance. At 2000°F (1090°C), it displays outstanding oxidation resistance, on par with the limit for 310 stainless steel and surpassing 309. It is important to note that although short furnace excursions up to 2100°F (1150°C) can be tolerated, consistent oxidizing temperatures above 2000°F (1090°C) can quickly degrade the material. Therefore, it is best to avoid excursions above the suggested temperature limits for any alloy.
This material has also proven to perform well in mildly carburizing environments, despite its lower alloy content. Even small amounts of oxygen in the gas, like carbon dioxide or steam, can create a thin and tough oxide layer on RA 253 MA, offering excellent protection against carbon and nitrogen pickup. However, it’s not recommended to use it in carburizing environments. Due to its lower nickel content, it is less resistant to carburization compared to higher nickel alloys such as RA330.
Table B. Ductility based on room-temperature tensile tests
In a simulation where coupons were exposed to fifteen weeks of simulated bake cycles between 1700°F–1950°F (930°C–1065°C) in “green mix” used for producing carbon electrodes, room-temperature tensile tests revealed the ductility as shown in Table B.
For RA 253 MA, the sigma phase formation process is much slower compared to 310S and 310, as shown in the TTT diagram in Figure 5 and the micrographs in Figure 6. At temperature, it is very unlikely material containing sigma phase will behave adversely. When the material is cooled to room temperature, it becomes very brittle, making it less resistant to thermal cycling. The material may crack if highly constrained and unable to expand freely during subsequent ramp-up.
Figure 5. TTT curve for sigma phase formationFigure 6. RA 253 MA grain structures with and without sigma phase
Corrosion Resistance in Salt Bath Applications
As shown in Table C, RA 253 MA may be comparable to alloy 600 when exposed to sodium and potassium salts for heat treating high speed steel.
Table C. Intergranular attack based on exposure to sodium and potassium salts
In this trial, plate samples were exposed to 210–252 cycles in preheat salts at 1300°F–1500°F (700°C–820°C), high heat salt at 2200°F (1200°C), and then quenched in 1100°F (590°C) salt. Table C shows that RA 253 MA has the potential to perform well in a salt bath environment due to its high silicon and chromium levels. While alloy selection is essential, regular maintenance and cleaning of the salt bath and surrounding areas are the most crucial factors.
In salt bath heat treating, the service life of the pot is primarily determined by maintenance not the alloy. Pots must be desludged regularly, and all old, spilled salt must be removed from the furnace refractory when changing pots
Corrosion Resistance
Table D. Sulfidation attack after exposure to an atmosphere
containing 13.6% SO2 at 1850°F (1010°C) for 1,860 hours
This alloy performs well, even in hot environments with sulfur in the presence of oxygen. However, it is not resistant to environments with reducing sulfur. Even in the presence of oxygen, the partial pressure of oxygen can be very low while stainless steel is in use. This low pressure can lead to a local sulfidation attack, even in what is considered an oxidizing atmosphere.
Table D displays the depth of intergranular oxidation and sulfidation in test samples exposed to an atmosphere containing 13.6% SO2 at 1850°F (1010°C) for 1,860 hours.
Microstructure
Table E. Charpy v-notch impact results as annealed and after
exposure (ft-lb)
The microstructure of RA 253 MA in the annealed and long-term exposure states is shown in Figure 6. In addition, Table E provides the Charpy impact values for the annealed state and at temperatures of 1292°F, 1472°F, and 1652°F (700°C, 800°C, and 900°C) over a long period of exposure.
Based on the microstructure and Charpy impact data, it is clear that sigma phase precipitation is almost non-existent at 1650°F. Moreover, the TTT diagram in Figure 5 indicates that RA 253 MA requires significantly more time to initiate sigma precipitation compared to 310 and 310S stainless steel.
Applications for Use
Given the above capabilities, RA 253 MA can be and has been successfully utilized in a variety of applications. From bell annealing furnace covers, muffle belt conveyors, car exhaust manifolds and exhaust gas flexible tubes to hot air ducts, cooling tower tubes in sulfite process pulp mills, and heat treatment trays for neutral hardening, its abilities can cover a widescope of applications throughout in-house heat treat operations.
References
Andersson, T. and T. Odelstam. “Sandvik 253MA (UNS S30815) — The Problem Solver for High Temperature Applications.” A Sandvik Publication, October 1984.
Kelly, J. Rolled Alloys. Rolled Alloys Bulletin 100. Revised September 2001.
Manwell, C. Rolled Alloys. Rolled Alloys Internal Report, Summary of Cyclic Oxidation Testing at 2000°F, August 2005.
Proprietary Report on the MA Heat Resistant Material Series.
Saum, W. Rolled Alloys. Rolled Alloys Internal Report, Summary of Oxidation Testing at 2000°F, August 2002.
About The Author:
Hugh Thompson Applications Engineer Rolled Alloys
Hugh Thompson is a metallurgical engineer at Rolled Alloys, leveraging his expertise from The University of Toledo College of Engineering to drive innovation in specialty alloy solutions. Based in Toledo, he combines deep technical knowledge with industry leadership.
