VACUUM FURNACES TECHNICAL CONTENT

HTT · Heat Treat Radio: Metal Hardening 101, Part 2 of 3

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Mark Hemsath (MH):  Thanks, Doug, it's nice to be here.

DG:  For the record, we're recording this thing right before Thanksgiving, the day before Thanksgiving, so we've got turkey on the mind here.  I've known Mark for many, many years, in fact, I would say a couple of decades now, when he was with other companies and doing other things.  He's a very well-rounded person in the industry.  He's able to speak intelligently about a lot of different things, including surface hardness, through hardness and that type of stuff.

Last time, we talked about what hardness was and why it's important.  Afterwards, you and I had some conversations and there were a couple of things I think we wanted to supplement onto that first episode.  One of those things had to do with hardness testing.  Throw out what you were thinking about that.

MH:  I think on testing, the point here is that there are many scales for testing because we have many different types of material with different hardness.  When we start getting into some of the other materials, it changes a little bit.  In the steel realm of things, the most typical is to use a diamond tip weight to try to indent the material.  Based on the pressure it takes, we get a reading.  For instance, a very thin layer may require a different type of test because one style of test may not be set up to measure such a thin hardness.  This is typical in something like nitriding where you have a white layer.  Different types of testing methodologies – there is the Brinell, Vickers, Rockwell and Newage hardness testers, and there are a lot of other things out there, as well.  In general, we are trying to test the surface hardness and then also the hardness as it traverses through the material.

DG:  The other thing that you and I were talking about was other materials besides steels that were hardenable.

MH:  I'm not an expert on aluminum, but one of the materials that we talked about is aluminum, and quite frankly, SECO/Warwick has a separate division just dedicated to aluminum because it is different.    Let's take a look at aluminum first.  Aluminum is actually rather soft and has many other benefits.  It is very commonly used in aerospace and companies like Tesla are using it today, almost predominantly, for their cars.  Just like in steels, it can get harder by using alloying elements.  Most common alloying elements are copper, manganese, silicon, magnesium, zinc and lithium.  Hardening is typically by a precipitation or age hardening.  Tempering is also very common.  So, not all aluminum alloys can be heat treated, per se, but as I was mentioning, it is a whole different world and it requires a whole different set of expertise because it is kind of a unique metal.

DG:  How about titanium?

MH:  Titanium is an increasingly popular alloy.  It is expensive and it has very high strength to weight ratio.  It is almost as light as aluminum but much stronger and also has great resistance to corrosion.  Titanium can be alloyed to add properties to the metal and it can be nitrided at higher temperature making a very thin, hard layer that is gold in color, something that I've done a little bit of in the past.

On of the other materials that you asked about are stainless steels, and this is also a whole different breed.  Recently, in the last 5 – 10 or so years, surface hardening is being applied with great success and it is actually done at low temperatures to make a very hard surface and still retain the corrosion resistance.  When you harden stainless steels via nitriding at the higher temperatures, you do get high hardness but you lose corrosion resistance.  They've made quite a bit of inroads at the low temperature end of things, so called S-phase hardening.  Certain stainless steels, martensitic stainless steels, are actually hardenable by heating and quenching.  Those have, commonly, 11 – 17% chromium and no nickel and they have a higher carbon.  Austenitic stainless steels, typically at 300 series with nickel, do not harden by heating and quenching.  These steels, as I mentioned, can be surface hardened.  Ferritic stainless steels, which is another breed, are commonly a lot of the 400 series stainlesses have 10 – 30% chromium and they do not harden by normal means.  Then, we have some special so-called alloy 17-4 PH and some of the other ones are hardenable by aging.  So, I wanted to go through some of that.  There is a lot there.  But just to discuss all of the variety of different steels out there.

DG:  Let's dive into these five different hardening processes, which we want to talk about, to give our listeners a little better sense of exactly what the process is and how they might differ from one another.  The five we're going to cover are carburizing, nitriding, carbonitriding, FNC, or ferritic nitrocarburizing, and LPC, meaning low pressure carburizing.  Let's go back and just start with, probably, what I think, is the most popular or common one, which is carburizing.  Do you agree?

MH:  Yes, I would tend to agree, especially by pounds.

DG:  First off, what is it?  We covered this last time, but just briefly, let's talk about what carburizing is.

MH:  Very briefly, carburizing is the addition of carbon which adds hardness to the surface and, as I probably mentioned before, it needs to be done at elevated temperatures.  The higher the temperature, the faster the process.

DG:  Basically, break it down.  How's it done? What's the temperature?  What's the atmosphere? What are the times?  General things like that.

MH:  Typically, it's done above 1600 degrees F, which is the austenitic temperature range, and more commonly done at 1650 – 1750 F, which is 900 – 950 C.  In the old days, they put charcoal powder, which is a carbon, near the steel or maybe in a box, and they heated it and that's how they got carbon.  They actually got carbon monoxide gas to form at high temperature and got it to go into the steel.  This will actually crack the charcoal and give you the gas.  Some people still use this, especially if they've got some very big odd shapes; it's the only way to do it.  Somewhat, it is done in other countries, but not as much here.

There is also obviously the gaseous form which is called gas carburizing.  That is typically done with carbon monoxide gas, which is typically created from cracking natural gas or using a nitrogen methanol.  For endothermic gas, it's basically about 40% nitrogen, 40% hydrogen and 20% CO.  In order to increase the carbon content of that gas, people will inject a carbon containing gas like propane or natural gas, etc.

One other method that is still in use is salt bath.  It is also somewhat common and here they use a sodium cyanide (NaCN).  Basically, most of it being done today is with gas carburizing.

DG:  As far as the actual materials?  I assume most of it's going to be your steels being carburized?

MH:  Yes.  Virtually any steel or alloy can be carburized to some extent if it has iron in it.  Iron carbides will form.  Mostly less expensive steels are done.  The so-called low carbon, low alloy steels are typically the ones that are most frequently carburized to get high surface hardness and because they kind of like the core properties that come with it.

DG:  Equipment.  You already hit on this some, but obviously for salt bath, which you mentioned, you're going to have a salt bath piece of equipment to do it.  Gas carburizing is obviously done just inside of an atmosphere furnace, in some capacity, I assume.  Can it be done continuous and/or batch?

MH:  Yes.  The most popular is batch.  The integral quench furnace, which is usually an in-and-out furnace where you have endothermic gas both in the vestibule where you put it where the quench oil is.  Then you go into the furnace, you do your hot temperature carburizing in the same gas, and then you come out hot and you're protected and then you go into the oil quench, and everything is within that atmosphere.  That's the most common.  But, as you mentioned, continuous is very viable.  The only issue with continuous is it's pretty high production and it's usually the same process over and over.  That way you can maximize the use of your quench.  Because quenching might only be 20 – 30 minutes tops, whereas the carburizing cycle might be 8, 10 or 12 hours, you're not using that quench very often.  Continuous will allow you to use a quench much more frequently and that quench might be fairly expensive, so that makes sense for doing the same parts over and over.

DG:  Right.  If you've got super high production, that would be the way to go.  And, it is probably notable to point out here, that quenching is an important part of the carburizing process.  This is not true with some of the other surface modification stuff we're going to talk about down the road, correct?

MH:  Yes.  Quenching is usually done right afterwards, to save money and to make it economical.  That's not to say that there aren't many people, like in press quenching, that will actually carburize it, slow cool it and then heat it up again and then individually quench each part.  There are also some benefits to grain growth.  If you've got a very deep case, that carburizing might cause some growth in your grains.  If you slow cool it and then heat it up quickly again and quench it, you'll transform all that back to the properties that you want.  But, yes, typically all done together.

DG:  Can we carburize using induction technology?

MH:  I'm not familiar with carburizing. . . Induction is typically heating the outer surface and cooling it very quickly and keeping that very hard and then the core will still maintain its property.  That's a thermal surface engineering process induction.  I had an old engineering friend of mine, metallurgist expert, PhD, who calls it surface engineering or thermal chemical surface engineering, because we're using both a chemical process and a temperature process.

DG:  Anything else notable on carburizing before we move on to nitriding?

MH:  The only thing is the alloying elements are common in steels.  I mentioned before low alloy steels and high alloy steels.  Alloying elements common in steels are nickel, silicon, chromium, manganese and molydenum.  Silicon and nickel are less prone to absorb carbon, whereas the carbon potentially atmosphere is increased with elements like chromium, manganese and molydenum which form more stable carbides than iron.  Alloying elements can adjust the ability to carburize.

DG:  That's the basics on carburizing.  Let's move on to nitriding.  If you can, Mark, as we plow through this, maybe draw a bit of a comparison on, for example, temperature ranges and maybe cycle times and materials, and things of that sort.  So, what about nitriding?

MH:  Nitriding is a process where nitrogen atoms are diffused into the steel surface.  I believe that nitriding is more complex than carburizing because hardness, and the types of nitrides created, are dependent on a number of different factors.  So, depending on the process, either ammonia is used or an excited nitrogen atmosphere via a plasma generator can diffuse the nitrogen into the steel surface.  What's common with nitriding is it's done at a lower temperature.  The diffusion of nitrogen is a time and temperature dependent process, so the higher you take the temperature, the faster the process will go.  But, it's still performed at much lower temperatures than carburizing.  It's actually done in the ferritic range and not in the austenitic range, typically, 915 degrees Fahrenheit up to just under 1100 degrees Fahrenheit which is 490 C to 590 C.

Nitriding is a process where nitrogen atoms are diffused into the steel surface. I believe that nitriding is more complex than carburizing because hardness, and the types of nitrides created, are dependent on a number of different factors.

DG:  You're talking 500 – 600 degrees F, roughly, lower temperature than carburizing?

MH:  Yes.

DG:  That's the temperature range.  Obviously, the atmosphere is different because we've got nitrogen as opposed to carbon, but how about process time?

MH:  We talked about the temperature.  Obviously, if you're at the higher end of that temperature, you can go a little faster, but nitriding has been known to be slower than carburizing, and it is.  The diffusion process is slower.  Gas nitriding and plasma nitriding are the two main processes.  There is also ferritic nitrocarburizing, which is a form of nitriding with salts.  But gas nitriding uses ammonia as a nitrogen donor and plasma nitriding uses nitrogen at a partial pressure with a plasma excited atmosphere.  Nitrogen creates iron nitrides in various forms in the white layer as either, what we call, an epsilon layer or a gamma prime layer.  In some instances, people don't even want that layer, they only want the nitrogen to go into the steel and create nitrides with some of the alloying elements.  This is what we call the diffusion into the alloy into the steel into the alpha.

DG:  What about case steps between carburizing and nitriding?  If you want a deeper case step do you tend to go carburizing or is there a difference in the case depth actually?

MH:  It is much more possible to do a deep case step than carburizing.  You can basically keep sending it in there and, if you can go a little bit higher temperature, you can get some pretty deep case steps with carburizing.  The difference between the nitriding, is that it's a different process.  It's a lower temperature process so it's a little bit slower, but you get a pretty hard case with the right alloy with the nitrided case.  In many instances, you can get a pretty similar performance of the part, or something that performs very well, with maybe only one-third of the case.

DG:  When we talked about carburizing, we talked about materials that were 'carburizable'.  How about in nitriding?  What materials are easiest to be nitrided and are there some that we really can't nitride?

MH:  Nitriding is kind of opposite from carburizing.  Most people will carburize the more low alloy or plain steels, whereas in nitriding, we really want to deal with alloy steels that have alloys in it that will be friendly to absorbing nitrogen.  Now, on plain hardened steels, you can get the white layer on there, but you're basically limited to just the white layer for your surface engineering, and you don't get much depth, depending upon what type of alloying elements you have.

DG:  Mark, talk for just a second about this white layer in non-technical terms, if you don't mind.  Is it, simply, the accumulation of nitrogen above the 'surface' of the metal?  What is that white layer?

MH:  No, it actually reacts with the metals in the surface layer.  Because the surface is being hit with a lot of nitrogen, the reactions there will create what we call a white layer where there is a lot of nitrogen activity and those are iron nitrides.  They also will get some carbon that will react in there.  That's a very hard layer, somewhat brittle; it is resistant to corrosion and it also has very low friction property.  A lot of people want that often but when you're going with the higher alloyed steels, there are some applications where you don't want that, let's say, bearing types et cetera where you don't want any small parts that could come off.  The white layer is prone to chipping or coming off, so you wouldn't want that in a bearing, because it's very hard and if it comes off, it can cause problems with your bearing.

DG:  I assume, with all the modern day technology and whatnot, we're able to control that white layer and/or depth of nitriding layer through your process controls and things of that sort.

MH:  Yes.  Nitriding has been around a long time, but one of the problems that they had was controlling the white layer.  Because they basically would just subject it to ammonia and you kind of got what you got.  Then they learned that if you diluted it, you could control it.   That's with gas nitriding.  Then plasma nitriding came around and plasma nitriding is a low nitriding potential process.  What that means is it does not tend to want to create white layer as much.  It's much easier to control when the process itself is not prone to creating a lot of white layer, unlike gas.  Now, in the last 10 – 15 years, people have gotten really good at controlling ammonia concentrations.  They've really learned to understand that. One of the people who was instrumental in understanding that is the inventor of our zero flow control technology, Leszek Maldzinski. Understanding how you change the ammonia nitriding potential to get the type of steel layers that you want is rather complex, but once you understand it and have the tools, you can craft the layer exactly the way you want it with ammonia gas.

DG:  You did talk about the types of equipment that can do nitriding, but just hit on those again.

MH:  Gas nitriding is typically done in a retort to safely hold the ammonia and once the gases start dissociating, we also have hydrogen in there.  Also, ammonia gas is very noxious and can be deadly, so you need something tight to hold it, and that's why they'll do it in a very tight retort.  Plasma nitriding is done under vacuum, partial pressure.  You can do that either in a hot retort or a cold wall vacuum type furnace.  Those are the two main processes.

DG:  If you had a similarly sized carburizing furnace and a nitriding furnace, would you expect that the nitriding furnace would cost more than the carburizing furnace, or vice versa?

MH:  Carburizing furnaces are a little more expensive because you have the addition of the quench and you're also at fairly high temperature.  Those are two cost drivers in carburizing.

DG:  This next one has always been a little confusing for me. Let's see if you can straighten me out:  We talked about carburizing, which is carbon.  We talked about nitriding, which is nitrogen.  And now we go to something called carbonitriding, which sounds to me like the two are holding hands and performing the process.  So, what is it?

"It can be confusing because here in the US we call it carbonitriding and we call the form of nitriding that is FNC (ferritic nitrocarburizing), nitrocarburizing.  In Europe, I've heard them exchange those names.  But, typically, in the US, we call the high temperature process, which is similar to carburizing, we call carbonitriding.  The ferritic, which usually means the low temperature, not austentitic, ferritic nitrocarburizing is a low temp form of nitriding and adding carbon.

MH:  It can be confusing because here in the US we call it carbonitriding and we call the form of nitriding that is FNC (ferritic nitrocarburizing), nitrocarburizing.  In Europe, I've heard them exchange those names.  But, typically, in the US, we call the high temperature process, which is similar to carburizing, we call carbonitriding.  The ferritic, which usually means the low temperature, not austentitic, ferritic nitrocarburizing is a low temp form of nitriding and adding carbon.  Let's go to carbonitriding which is the high temperature version.  It's typically done in low or unalloyed steels that have rather low hardenability.  Increasing the quench rate is rarely possible, so what we do is we add nitrogen and carbon to the surface to increase the surface hardness substantially.  It actually makes a very hard surface.  I usually say this is done for the cheaper steels.

DG:  Meaning the less hardenable steels?

MH:  Yes, and it's done in less alloyed steels, too, because we're just trying to get a thin hard surface on the outside, for whatever application it is.

DG:  And temperature range?  Does it tend to be similar to carburizing, up in the 1600 range?

MH:  It is, but because ammonia breaks down very rapidly at higher temperatures, we like to do this at the lower end of the austenitizing temperature, so in the 1600 – 1650 range, as opposed to the 1700 – 1800 range of carburizing.  Now, that means that the carbon transport to carbon diffusion into your steel surface will be slower, but what we're trying to do is we're trying to get both in there, the carbon and the nitrogen to make that very hard, thin surface.  And, we're trying to do it quickly, because we want to do it cheaply.

DG:  Is carbonitriding kind of an inexpensive way, if you can do it, of carburizing?

MH:  That's what I typically look at it as, yes.  And, it's possible to do a lot of these parts.  Let's say they're stampings or low expense steels.  You can sometimes do that also with ferritic nitrocarburizing if you change the steel grade a little bit.  There are a lot of different ways of hardening some of these small parts or clips or what have you.  Also very common in screws, roofing screws, etc, to get that hard point on there.  It doesn't need to be very thick, it only needs to be drilled into the roof one time.

DG:  So that's carbonitriding.  We talked about temperature ranges.  We talked a bit about the steels that we would use for that.  Equipment that is being used for carbonitriding?  I assume it's more along the lines of the carburizing?

MH:  It's virtually identical.  It's either gas atmosphere, integral quench batch furnace or can be done in continuous fashion.  A lot of people use mesh belts for it, too.

DG:  I neglected to ask you this, back on nitriding.  No quench is involved there, correct?

MH: Correct.  Nitriding has no quench.

DG:  But carbonitriding, you're quenching, because it's kind of a cheap man's carburizing.

Anything else we should know about carbonitriding?

MH:  Just that steels like 1018, 1022, the low end, there are other ones that obviously can be done, but that's typically what's being used.

DG:  Let's go on to the second to last.  We've got two more left.  Nitrocarburizing, or as it's commonly or often referred to, FNC    (ferritic nitrocarburizing), let's talk about it.

MH:  Unlike carbonitriding, which is often confused with ferritic nitrocarburizing, FNC is performed at lower temperatures just like nitriding, but it's typically done a little bit higher temperature than nitriding and it's done just below the initial austenitizing temperature which is around 570 C/1060 F, just below 1100 F you can go to if you're equipment is fairly uniform.  The reason they do that is because in ferritic nitrocarburizing, you're trying to create white layer, and white layer will be much more aggressively created at higher temperatures and also with higher levels of ammonia.

DG:  So, the temperature is the same.  Cycles times.  Obviously, the atmosphere is predominantly nitrogen with a little bit of carbon mixed in, I assume.

MH:  Right.  The nitrogen comes from the ammonia, unless it's a plasma type process, but let's talk gaseous ferritic nitrocarburizing first.  You can put a carbon gas in.  This can be an endogas to get CO, it could be CO2 injected where the CO2 actually will convert to a CO gas, and people have used other gases, but those are the two most popular forms of carbon gas.  What that does, again, because we have typically cheaper steels, they don't have a lot of carbon in the surface, so we want to have a little extra carbon there to get that really hard and aggressive epsilon layer.

DG:  Equipment to be used.  In nitriding, we were potentially using a vacuum furnace, at times.  Do we use vacuum for FNC?

MH:  Well, FNC, just like nitriding, you don't need vacuum for our nitriding furnace, we use vacuum purge.  Because we want the vessel retort to be very tight, making it a vacuum capable vessel, means it's, by definition, tight because you don't want ammonia to leak out.  But, for FNC, people have done this in any number of ways.  For example, bell furnace or tip up furnace.  I've seen people use their integral quench furnaces, the heating chamber.  All you have to do is get to that temperature just below 1100 F, get your ammonia in there and get some sort of carbon gas, and you're going to get a white layer.

DG:  I know when we were talking about nitriding earlier, you mentioned that it was done mostly in a retort, one reason was to contain the ammonia, but you don't necessarily need that in FNC?  Or, is it pretty common that you would use a retort furnace?

MH:  It's commonly done in a retort and commonly done in a pit furnace, but there are people who do it in tip up furnaces.  Like I said, there are people who do it integral quench furnaces, people do it continuously.  Obviously, when you have ammonia involved, the retort makes the environment that you're standing there much nicer, because you can put the ammonia in the furnace as opposed to around you.  Small amounts of ammonia can become choking.  I don't like other furnace designs because they're hard to seal.

DG:  Anything else you think we should know regarding nitrocarburizing?

MH:  It can be done in plasma.  It's less common.  They typically use a carbon gas like methane, or something, to put in there to try to promote some more white layer.  Like I mentioned before, plasma process is typically not very white layer friendly.  But if you put that carbon gas in there and increase the temperature, you can get some pretty decent white layer with it in a plasma setting.

DG:  Let's move on to the last one: low pressure carburizing.  Let's talk about that.

MH:  Again, carburizing is the addition of carbon, right?  So, the difference here is that when we talk low pressure, it's just like a mentioned before with plasma nitriding, it's done at a negative pressure, less than atmosphere.  We call this either low pressure carburizing or vacuum carburizing; it's the same process.  This takes place at pressures typically in the 1 to 15 torr range, which is about 1 to 20 millibar range of pressure.  If you know one atmosphere is 760 torr, so when we're going down to 1 – 15 torr, we're at pretty good vacuum.  Just like with gas carburizing, the higher the temperature, the faster the process.  What's unique with vacuum equipment, is that vacuum equipment is typically capable of going to higher temperatures which adds to the speed of carburizing.  Now, we didn't discuss the design of gas carburizing furnaces that much, but typically they're gas fired and they have radiant tubes.  In the interior of the furnace, the higher temperature you go with the really nasty carburizing atmosphere, it reduces the life of those furnaces substantially, so the people that own the furnaces don't want to go to high temperature.  If you can go 100 degrees higher in temperature, like you can with the vacuum carburizing furnace, the process gets much faster.  That means higher productivity.

One more feature, as well: the initial carburizing of steel at low pressures is actually faster than gaseous  carburizing.  The carbon flux of the surface is very high in LPC.  The diffusion is the same, once you get into the steel itself, but the flux to the surface is very high.  So, shorter, shallower cases are quick, and then, like I said, if you can increase the temperature to increase the diffusion into the steel, on deep cases you can get the cycle less than half.

DG:  How long has LPC been around?

MH:  Technically, it's been around since probably the late 60s.  It had a very slow introduction, in my mind.  That's only because they had trouble really getting it to work reliably.

DG:  Anything else we should be asking?  I assume the steels that can be carburized with LPC are essentially the same?

MH:  Yes.  Steels are the same.  Typically, you want to go a little higher temperature than you would with gas carburizing, so typically above 1700 F and more likely 1750 F – 1850 F.  The big difference is with gas carburizing, as I mentioned, we use endothermic gas which comes from natural gas and then with some enrichment, here the carbon carrier is typically acetylene and that's put in at low pressure.

The other thing is, in gas carburizing, they use oxygen probes and they try to figure out exactly what the carbon potential of the atmosphere is.  It's totally different with low pressure carburizing.  With low pressure carburizing, because you can't really measure it reliably and accurately, we use process simulation software to create the recipes.  By being able to model the surface area of the parts and the total weight of the parts and the material, the temperature and the case thickness that you want, the LPC process becomes very reliable and can perform very well.

DG:  We've had conversations with folks over at Dante Solutions and they say that this LPC is one of the most read items on their website; people are trying to figure out how to do it and how to avoid the carbides and things of that sort.  It sounds like an interesting process.

Anything else we need to talk about on LPC?

MH:  I would like to point out that most LPC has been done in vacuum furnaces in the past with high pressure gas quenching.  You mentioned it's been around a long time.  What they found with high pressure gas quenching is, number one, you can't have a lot of parts in the furnace, which means you have smaller load sizes.  In order for the gases to quench, you have to have very high pressure and also, the parts can't be that thick.

Over time, it really hasn't taken off the way I think it should have.  And some of the equipment was kind of problematic.  There was always done vacuum and oil quenching, but when they combined, and a few manufacturers do this, vacuum and oil quenching with LPC, then the oil quenching allows you basically to use the same steels to get the quench rates and to start to get some heavier loads in your furnace so that you can get the productivity.

This has now driven, what I consider to be, a viable option to gas carburizing.  For instance, with our Super IQ furnace, we use a conventional oil quench.  It's no different than the standard oil quench that most people use in their integral quench furnace.  However, the heating is done in LPC.  The difference is, instead of transferring the load in vacuum, which is what a conventional vacuum furnace will do, or transferring it in a hydrogen and nitrogen atmosphere, we transfer it only in nitrogen.

We have found out that there is no added IGO or any other problems with doing that.  What ends up happening is you can make a less expensive furnace and you don't have to use vacuum quench oils, which are a different breed- they're not as fast, they're more difficult to wash off and clean off.  We think that combination of LPC and standard oil quench makes a very high performing furnace with LPC.  So, it puts LPC into a new interest level, in my mind.  But, again, you still have to have very reliable simulation software.  We have over 10 years of experience putting that software together, so it's very reliable.

DG:  Just so the listeners know, we're doing a 3-part series and we're in #2 right now.  Next time we are going to talk about some of the more conceptual things regarding nitriding LPC and we're going to even talk a little bit about single piece flow because there's been a demand for single piece flow.  We're going to talk about some of the recent advances in some of these systems which we've hit on here just briefly.

Mark, I appreciate it.  This time, I think we've done a good job at covering carburizing, nitriding, carbonitriding, nitrocarburizing and a little bit on LPC.  Next time, we'll look forward to talking with you more about some of these other things.

Doug Glenn, Heat Treat Today publisher and Heat Treat Radio host.

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