Welcome to another episode of Heat Treat Radio, a periodic podcast where Heat Treat Radio host, Doug Glenn, discusses cutting-edge topics with industry-leading personalities. Below, you can either listen to the podcast by clicking on the audio play button, or you can read an edited version of the transcript. To see a complete list of other Heat Treat Radio episodes, click here.
Audio: Mark Hemsath on Nitriding & FNC
In this conversation, Heat Treat Radio host, Doug Glenn, an interview that Doug Glenn, publisher of Heat Treat Today and host of Heat Treat Radio, conducted with Mark Hemsath, director of nitriding and special vacuum furnaces with SECO/Vacuum Technologies, which is a SECO/WARWICK group company, located in Meadville, Pennsylvania, where he oversees nitriding, including ferritic nitrocarburizing (FNC), and also other surface engineering such as carburizing. Doug talks with Mark about nitriding and FNC.
Mark recently completed his paper for the ASM Heat Treat Show 2019, titled “Nitriding, Its Growth and the Technologies That Have Cemented Its Broad Use in Surface Engineering”, to be presented at the ASM Heat Treat Show in October 2019. In this podcast, Doug and Mark discuss why nitriding has become popular, what is nitriding and what processes does it entail, the new technologies affecting the industry, and major players in processing and supply.
Click the play button below to listen.
Transcript: Mark Hemsath on Nitriding & FNC
The following transcript has been edited for your reading enjoyment.
Are you a hard case or a case hardener? If you’re a case hardener, you might be interested in today’s episode. If you’re a hard case, well, there are other self-help podcasts you might want to consider. On today’s episode, we’re going to talk about nitride, and we’re going to talk with one of the most qualified individuals in the North American heat treat marketplace. This guy has nitriding and heat treating running in his blood.
Mark Hemsath (MH): My father was involved with a furnace manufacturer in Toledo, Ohio, and he actually brought ionitriding to the United States from Kluckner in Germany. I think, at last count, we think he had 65 patents under his name.
Doug Glenn (DG): Hi, and thank you for joining us. I’m your Heat Treat Radio host and Heat Treat Today publisher, Doug Glenn. Today on Heat Treat Radio, we’re talking nitriding with Mark Hemsath.
MH: Hi, I am Mark Hemsath with SECO/Vacuum Technologies, which is a SECO/WARWICK group company, and I am the director of nitriding and special vacuum furnaces. I am involved with everything to do with nitriding, including ferritic nitrocarburizing, and also other surface engineering such as carburized.
DG: If you have an interest in surface hardening, such as nitriding, ferritic nitrocarburizing or carburizing, you might want to take a quick cybertrip to www.heattreattoday.com where we have a substantial and growing list of resources that might be helpful to you. Heat Treat Today is one of the industry’s leading information sources for all things heat treat-related. Every Tuesday, we post a new technical article. We call it Technical Tuesday. And Heat Treat Today is the only North American-based heat treating publication offering a comprehensive list of heat treat consultants. So, if you’re a manufacturer with in-house heat treating, especially in aerospace, automotive, medical, or energy, or even general manufacturing, and you’ve lost a good bit of your organizational heat treating brains, take a look under resources on Heat Treat Today’s website, or simply Google “heat treating consultants”, and you’ll find a comprehensive list of heat treat industry consultants that can help you solve your pressing heat treating problems. Look us up on the web at www.heattreattoday.com.
Let’s get back to Mark Hemsath and our discussion on nitriding.
DG: Mark, we’ve been trying to connect for quite a while. I’m really glad we were finally able to connect.
MH: This is a perfectly opportune time to do this because I just finished my paper for the ASM Heat Treat Show, so it is all fresh in my mind.
DG: Interesting! What is the paper?
MH: My paper is “Nitriding, Its Growth and the Technologies That Have Cemented Its Broad Use in Surface Engineering”. It will be presented at the ASM Heat Treat Show in October.
DG: Hey, heat treat readers, the show Mark is referring to is being held on October 15 – 17 in Detroit. You can find out more about that show by Googling “2019 Heat Treat Show Detroit”, or by going to www.asminternational.org and searching for it there. Now, back to Mark.
Why Nitriding?
Let’s jump into the nitriding market. What are you seeing? I’ve been hearing more and more about nitriding. How about you?
MH: I think the main thing is that nitriding is growing, and it is still growing rapidly. It has grown in the past number of years, and that is one of the reasons I just wrote a paper, which is very opportune to discussing why it’s growing and why it has gone up in use in the market.
There are a number of points that I probably should point out as to why nitriding is growing: I think more and more people are discovering the positive effects of nitriding. This would include the very high surface hardness that you can get. The higher temperature hardness—in other words, it resists tempering—a carburized-type surface or an induction-hardened surface if it’s used at temperatures above the tempering temperature, it would start to reduce its hardness, whereas nitriding is done at a higher temperature (it’s done above 900° or 1000° or so F), so you would resist the decrease in hardness up to those temperatures, which is pretty nice. Also, it gives you the ability to have a high fatigue strength. The nitrided layer actually will change the fatigue properties of the metal part. Another thing that everybody usually talks about is the improved corrosion resistance. This is something unique to nitriding. It is used a lot, especially ferritic nitrocarburizing, for corrosion resistance. And the final thing I wanted to talk about is the minimal process distortion. If you compare this to carburizing where you are quenching the part, because you’re coming from the austenitic region going into the quench bath and it’s cooling very rapidly, there is a chance for your part to distort, which means you may have to follow on process it to get it back into dimension. Nitriding has a lot of benefits to it.
DG: Interesting, Mark. These seem like some pretty compelling reasons to nitride, but one of the objections I hear is that nitriding is a more expensive process. Your thoughts?
MH: It is not really as expensive as you think, because you have to take into account certain things. Let’s take carburizing, for example, or just thru hardening, for instance. You’ve got to quench it, you’ve got to wash it, and you’ve got to temper it. If anything goes wrong in that process, you’ve got to do some sort of follow on processing. You probably won’t need to do any of that after nitriding. Now, you will need to change probably some of the material and the alloying properties, but we can get into that later.
DG: Yes, fine, but perhaps a little clarification is in order. We’re talking about nitriding, but we often hear the phrase “ferritic nitrocarburizing.” Can you help us understand the difference?
MH: Yes. It is a nitriding process, but it is typically done with lower carbon materials and that is why they put carbon in there, too, so that is where they get the nitrocarburizing into the process. It is typically done at a little bit higher temperature because you’re not as much worried about the thru hardness property or the tempering properties. What you’re trying to do is to take a less expensive material, whether it’s a cast iron or inexpensive steel, and you’re trying to get a nice white layer around there, or a combination of white layer, commonly known as a compound zone. It’s a combination of epsilon and gamma prime. You can create different layers, and the carbon is going to help you with that by creating it faster and creating it a little bit harder. What that’s going to do for you on that part is give you lubricity; because of the nature of the white layer, the compound zone has a lubricious nature to it. It will give you corrosion resistance and give you that wear resistance that everybody wants in those parts.
Where Is Nitriding Being Done?
DG: So where are nitriding and FNC being used today?
MH: Today nitriding thankfully is being used everywhere. It is actually being used where chrome used to be used, such as rods for hydraulic systems. This is a post-oxidized FNC that comes out black, and it is a very nice replacement for chrome. In the automotive industry, FNC is very popular because they use cheaper materials, and it prevents not only wear and denting, but it also offers corrosion resistance for a lot of the parts, which is nice on cars. This is actually how FNC got involved with the brake rotors. On brake rotors for cars, they used to paint them. The problem was, as soon as the car got moved from the truck onto the lot and the brakes were stepped on, it would wear the paint off and start rusting. People would complain there was rust on the brakes and they hadn’t even bought the car yet. What they discovered was that if they ferritic nitrocarburized the cars, they would not get that kind of rust on their brake rotors. So that was helpful. It also provides incredible wear resistance against your brake pads.
Nitriding is also used in gears. I mention that because you have minimal or no post grinding. In aerospace, it’s used all over. They like the wear properties and corrosion. A lot of parts stay in planes for years and years and years, so they don’t want the corrosion.
Something I learned recently in the last few years in regards to the oil and gas industry, is that oil and gas are pumping a lot of stuff. They are fracking, they are pumping water and brine, and they have a lot of slurries that cause a lot of wear in pumps and pipes. It is very caustic. Nitriding works very well to extend the life of those parts.
In a lot of large parts, they plasma nitride a lot of stamping dyes—again, because it gives you dent resistance, and it’s going to give you more life on that dye because you’re stamping metals or your hot stamping forgings, etc. There are a lot of reasons to use nitriding.
DG: Are you hearing of companies converting some of their carburizing processes to nitriding or FNC?
MH: There is a lot of effort in that area. A lot of engineers don’t know about it, but they’re starting to become more aware of it. Of course, a lot of materials and components out there are already pre-engineered, and they’re already done, and now we’ve got to thru harden it, and we’ve got to carburize it. It takes a good engineering group to understand the differences and that is part of the education process. That’s why I’m happy to do this with you today. It’s an effort to try to get more people up to speed and for the engineers and component people to say, “Yes, I can do this with nitriding,” and can understand what can be done.
You can do this with gears, for instance. We’ve done it many times, and people are starting to specify it. You can do FNC of gears, and you can do nitriding of gears, too.
DG: So, it can be done. Understood. But are you hearing of any examples of where it is actually being done?
MH: It is being done more and more in motor transmissions; [that’s] where I got word of the fact that one automaker with a ten-speed transmission was going to have three or four of the gear sets be ferritic nitrocarburized versus carburized. An offshoot of carburizing is carbonitriding. Carbonitriding is basically the same thing as carburizing except that it is usually a shallower case and they use a little ammonia in there to get a little bit harder surface. However, you’re going to get distortion on that. There are a number of parts that you can change the chemistry of the steel. Although you’re paying more for the steel, you can ferritic nitrocarburize it and get the similar properties that you’re looking for for that wear component.
DG: So you’re paying more for the base steel, but you’re paying less for the post-processing of it?
MH: Yes, potentially, because you don’t need to rework it because of distortion. A lot of parts are hard to quench and not get them to move, especially small parts or flat parts. At SECO/WARWICK, we also make rotary retort furnaces. You can do washers in there, but when that washer goes into the quench, it’s going to enter at different angles. But nobody wants to take washers and individually line them up so that the edge goes into a quench. It’s just too expensive to do that. So you’re going to put up with a certain amount of distortion on that material that you’re quenching, and then have to figure out how to deal with it afterward. With ferritic nitrocarburizing, you wouldn’t have to worry about that, because there is no quench and there is no distortion.
DG: Carburizing and carbonitriding both have quenches, whereas nitriding and FNC do not require quench.
MH: Correct. Nitriding and FNC are all done typically below 1100°F, and there is no quenching. It is always a slow cool.
DG: And, therefore, we are avoiding distortion.
MH: You’re not putting it into a liquid, whether it’s a hot oil or what have you, you’re not putting it into a liquid to cause that rapid cooling, correct.
DG: And it’s a slow cool for nitriding and FNC.
MH: Yes. Nitriding will give you some growth. We typically predict, let’s say a white layer which can be all the way up to 25 microns, usually running in 10 – 25 micron range. About 60% of that will result in growth, but it is very predictable. If the engineer is worried about the size, they can put that into their stack up in how they machine it initially. You’ll get a very small growth of the material from nitriding. I think it’s in the 10,000th range, absent the white layer.
Nitriding: Gas or Plasma
DG: When I think of nitriding, I think of several approaches such as gas or plasma nitriding. Would you explain the differences?
MH: There are four major different types of nitriding. There is gas nitriding, which is an area that I play in very heavily. There is plasma nitriding, also know as ion nitriding. There is liquid or salt bath nitriding, and there is even nitriding done with fluidized beds.
Let’s go through them quickly. I’m not going to talk much about liquid that is done in salts. It is a very old process, but not a bad process. The problem that I have always found is that people don’t want to own this equipment because of all the hazards with salts, the disposal, and everything else. It is not a bad process if you’re willing to own it and run it; you can do some great things with it.
Fluidized bed is an older technology. It’s a little different. You’ve basically got particles that are being fluidized which allow heat transfer. There is an art to running and using it, but it is certainly a process that can have very good results. A long time ago, I was involved with a company where we helped them create a new fluidized bed technology. It is still being used; it just never really has taken hold that well in this country. There are some old systems out there, however.
I actually started out my career in ion and plasma. When I was in college a long time ago, in the early 1980s, I translated German to English from the German technology which was created by Kluckner. This came to the US, and I was helping the engineers to translate what they were talking about. My paper, that I was just in the process of writing, talks about some of this, and I plan on doing a webinar in the near future and talking more about this. There are some really nice benefits to plasma. This is well-documented in the literature, but there are ones that I point out that are different than some of the other processes. You have what they call sputtering. The effect of the plasma can help clean up the surface of the material. If you have some oxides, this is very beneficial if you’re doing some type of stainless which can have some problems.
Another thing that plasma is very good at is masking. A lot of times, there are parts that have a lot of threaded holes or areas where they don’t want nitriding. They might weld on it. It is very easy to mask with plasma nitriding because you can mechanically mask it. What that means is that if you have threads, you can just put a little bolt in there and they won’t get nitrided. If you have a surface, let’s say a piece of pipe, you can take some shim stalk of metal, wrap it around there, and you won’t get any nitriding where that metal is. It will nitride the metal piece that you put on there, but it won’t nitride what’s below there. So it is excellent for masking.
The other thing with ion nitriding [is] why it was popular. It’s still popular, but gas nitriding has overcome some of the negatives that it had in the past. But ion nitriding is what’s known as a low potential process, so by nature, it has a low nitriding potential. What that means is, it is difficult to get thick compound zones or white layers because the potential is fairly low. So people that wanted to nitride parts would use ion nitriding if they didn’t want the white layer to come with it. At the same time, FNC is harder in the plasma and post oxidation is a little more difficult. The equipment is not really designed to do those processes. The other thing is that the parts need to be individually placed and very nicely placed within the furnace proper, so there is more set-up work involved. But, in general, it does a wonderful job. One thing I say in my paper is once you own the equipment and you have some loads that you’re doing, you can get very repeatable results if you do the same thing every time.
The last one is gas nitriding. We actually have a process called zero flow, but it is just ammonia. Like any other process, it is a control method. What is happening with the gas nitriding today is that the advance of controls has allowed you to do a lot more with nitriding to get you similar properties than what you can get in ion. Plasma has come a long way, too, because the controls took forever to catch up with the technology. There were a lot of issues, which I discussed in my paper. Gas nitriding has seen the same type of issues. When I was in college, the computer chip was called an 8080/8086. They weren’t very advanced and they were just getting microprocessor technology and it took decades before all of this stuff got into the industrial equipment where it needs to be.
Fast-forward to this decade, 2010 to 2019, there have been tremendous advancements in the microprocessor and in electronics. For gas nitriding, we need to measure hydrogen because it’s a way for us to estimate nitriding potential. Today, that is very reliable and you can do it in situ, which means you can do it right in the furnace and get very accurate readings and you know where your nitriding potential is. The trick to gas nitriding and to doing precision gas nitriding [is] being able to craft a layer that you want. The layers are a combination of epsilon, gamma prime, and alpha. In order to get the layer that you want, first of all, you have to look at the literature and know what you’re doing. But you have to have equipment that can get you there. Today’s control systems can get you there and craft the layer that you want.
Quite frankly, the nice thing about gas nitriding is the loading can be ugly. In other words, it doesn’t have to be prim and proper like it is with ion nitriding. You can put a bunch of things into a basket, then put another basket on top of that and another one on top of that, put a lot of weight in it, and you don’t have to worry about the parts necessarily touching each other or the wire mesh that they’re sitting on or the basket. It’s going to get very well nitrided. That is not the case with ion. It’s much easier to own the equipment once you have it. Obviously the negative is that you’re using a gas (ammonia), it costs money and you have to store it and use it.
New Tech in Nitriding
DG: I want to cover two other major areas. The first one is new technologies in this field, and the second is a brief conversation of the major players. What can you tell us about the new and/or interesting technologies in this field?
MH: With plasma nitriding, they’ve been able to do a few things there. Mainly, they’ve been able to get better power supplies, pulse plasma, and they also obviously have gone to hot wall heating. That means they don’t have to heat with the plasma anymore. On the power supplies, they always had problems with arcing and a chance to burn some holes in it or pit some surfaces if you didn’t have the right power. And again, the microprocessor control that I talked about before had gotten so good, that they now have DC pulse plasma that is very fast-acting and can sense any problems within the process, and you can control it very closely. I think most people in the plasma arena have found that technology and are using it.
Gas is a little bit different. There are a lot of things going on in gas. Many, many years ago there was a process of controlling nitriding potential only by diluting with nitrogen and that was done by one of our competitors. We have a process called “zero flow” where we don’t use nitrogen. Other people will dilute with disassociated ammonia. The problem with that is that you have to buy an ammonia disassociator in order to introduce the disassociated ammonia. The reason you introduce disassociated ammonia instead of nitrogen is you’re able to much better calculate and measure nitriding potential. With a nitrogen dilution, the calculations are different, they are much more complex, and you need a lot of experience to get similar or same results that you would get with either zero flow process or with disassociated ammonia dilution.
There is some other neat stuff going on out there that I’ve gotten involved in and that we’re trying to get moving at our company, and there is a lot of stuff out there in the literature; it’s called oxi-nitriding. I’ve heard it used both for post-oxidation and for a part of the nitriding process. Oxi-nitriding to me is not post-oxidation. Oxi-nitriding is the injection of some sort of oxygen source early in the nitriding process with ammonia so that you can do some things to the surface of the steels. Let’s say with a 300 series stainless, what you’re trying to do is break apart oxygen bonds. That is pretty well proven in the literature that you can do that. It’s probably a little cleaner way of doing it than what other people do for those stainlesses and which we also do is put some sort of a chloride in there to break the bond so that you can nitride some of those more difficult stainless steels.
The other thing that people are doing and they’re doing it differently is-post oxidation. This is giving that black color. You can do that with water or you can do it with nitrous oxide which is laughing gas. And there are different temperatures you can do it at and different depths of it. We talked before about having the effect of a white layer compound zone and that helps with corrosion resistance, but we’ve also found out that putting a post oxide on it not only gives it a nice color, being a darker, near-black color, but it also helps with the corrosion resistance. On top of that, you can develop a layer that has a certain amount of porosity, and you can impregnate that with oils and that will give it even more corrosion resistance. In industries where this is very common is hydrolic cylinders, a typical front-end loader, agriculture equipment, snow plows, etc. These are usually chromed. But a lot of manufacturers are finding that a black ferritic nitrocarburized surface with post oxidation—and then they’re using oils in the cylinders anyway—will give you better wear property from the chrome and will give you very nice corrosion resistant properties. And I think it is probably a little less expensive. A lot of people are moving to that. If you see cylinders with black instead of chrome, that’s what’s happening.
Players: Processors and Suppliers
DG: Let’s move on to major players in the industry. First, who are the major players that are actually doing the nitriding?
MH: I probably can’t list them all, but as you mentioned I used to work for Advanced Heat Treat Corp. They are a very large commercial nitridor in the Midwest, and they get work from all over the country. Obviously, another big heat treater out there is Bodycote. By definition, they do quite a bit of nitriding. Nitrex Inc. makes competing furnaces against us, but they’re actually a very big nitriding house out there, and they’re probably much bigger in the nitriding than they are in the equipment business, so they’re very well versed in doing the nitriding. There is another company in Indiana that’s been growing greatly, and it’s called Advanced Nitriding Solutions. There is Ionic Technologies Inc. in South Carolina that do quite a bit of nitriding that would also be ion and gas. What we’re seeing a lot more of is that people that really are in nitriding are doing gas nitriding and they’re doing ion nitriding. They understand that nitriding is a great process and they’re trying to offer that to everybody.
The other thing is a lot of heat treat shops do just ferritic nitrocarburizing, which I call the “poor man’s nitriding.” It’s hard to screw up ferritic nitrocarburizing. If you get enough ammonia in there and you put some carbon in there, you’re going to get some sort of a layer.
DG: And how about the nitriding equipment suppliers?
MH: There are a number. There is Ion Heat. I know those guys pretty well and they are a nice little company and have some new technology. There is RUBIG, which is a big company. I’m sure there are other ones out there, but those are the main ones right now playing in the US market for plasma nitriding. RUBIG has gotten into gas nitriding, so they do offer some designs there. I think what they do is mostly pit nitriders. I break the gas nitriders into guys doing front-loading (which looks more like a regular batch furnace) versus pit. There is nothing wrong with doing pit furnaces. Both furnaces, front-loading or pit, work very much the same. They have a fan, they’ve got a retort typically, and they try to keep the parts uniform that they put the gases in. The thing with the pit is, you’ve got to have a pit. What’s nice with the pit is you can usually load it heavier. So for people who really want to have high production, like when I was at the commercial heat treater where I was, they liked the pit design because you could load them up a lot heavier. Guys doing more precision nitriding typically want the front load. It’s more like a vacuum furnace or a batch furnace within the building, etc. Companies out there for this, as I mentioned before, are Nitrex—long ago we actually used to build their equipment, so our equipment looks very similar to theirs because we designed it; SECO/WARWICK, as I mentioned makes zero flow; Lindberg/MPH makes a pit design. I think they have not gone too much into the advanced controls. They do a lot of single-stage nitriding. Other companies out there like ALD Thermal Treatment Inc. have come out with a front load. There is KGO which has a front load. And there are a lot of new entrants in the market. It’s getting kind of crowded out there. A lot of people with not a lot of experience, but I guess they have a hammer, a welding wire, and some duct tape and they’re making furnaces.
DG: Hey readers, you can hardly blame Mark for that answer. It really wasn’t a very fair question to ask him to list all of his competitors, but he did a pretty good job. But since a good solid list of suppliers might really be helpful to you, we’re going to do two things. First, I’m going to briefly round out the list here and now. I’m sure I won’t get everyone, but we do know for sure that companies like Surface Combustion, Gasbarre, and Tenova are also making nitriding furnaces.
And since I’m sure there are others, we’ll provide a more complete list of nitriding furnace manufacturers in the transcript of this episode. You can find that transcript by Googling “heat treat radio mark hemsath”, and we’ll keep an updated list of manufacturers listed there.
DG: Final question, Mark. If someone wants to learn more about nitriding, what resources would you recommend?
MH: There are a lot of good resources online. There are a few people in the industry that are extremely well versed. A good friend and associate, Daniel Herring, is called “The Heat Treat Doctor®,” and he knows all about heat treating. There is also my friend, Edward Rolinski, who is still at Advanced Heat Treat who’s very well published and you can look for his papers. A general flow developer and also fairly well published is Leszek Maldzinski.
There are a couple of guys that have been working in nitriding their whole lives and they are prolific writers, and that would be Marcel Somers and E.J. Mittenmeijer. There is actually a 
book that they put out in 2014 called Thermochemical Surface Engineering of Steels. That book contains articles by Maldzinski, Rolinski, and other people that I mentioned, but it talks about carburizing, ferritic nitrocarburizing, plasma, and gas. It’s a really great resource. It cost a few dollars, but you can also get it electronically. It is highly technical.
You can go to some of the magazines out there—Heat Treat Today, Industrial Heating continually does some small articles, and the gear guys out there publish some articles. There is a lot of stuff out there and you can find most of it on the internet.
To find other Heat Treat Radio episodes, go to www.heattreattoday.com/radio and look in the list of Heat Treat Radio episodes listed.
