Interview: Heat Treating - Industrial Metallurgists

July 16, 2021

Interview: Heat Treating

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This interview was with Craig Zimmerman and Rich Shapiro from Bluewater Thermal Solutions. Craig is Technical Director for all of Bluewater and Rich is General Manager of Plant 1. Both are metallurgists.

During the interview we discussed:

  • Component drawing specifications for heat treated components.
  • Component specifications that adversely affect ease of heat treating: alloy selection, heat treating process and outcome, unrealistic properties.
  • Realistic timing expectations when prototyping a heat treatment for a new component.
  • Definition of successful heat treatment: meeting specifications for material properties and dimensions.
  • Transferring a captive heat treating process to a commercial heat treater.
  • Including a heat treater in engineering discussions for alloy selection, prototyping, and improving component reliability.
  • Steps to improve the likelihood of successfully heat treating components.

Interview transcript

Michael: Good afternoon. Today I am with Rich Shapiro and Craig Zimmerman, from Bluewater Thermal. Bluewater Thermal provides heat-treating services for a variety of industries.

Rich Shapiro is the General Manager of Plant 1, in the Chicago area, and Craig Zimmerman is the Technical Director for all of the Bluewater Thermal plants, and both of them are very seasoned metallurgists. Welcome!

Both: Thank you.

Michael: Tell me briefly, what are the capabilities of Bluewater Thermal?

Craig: I would say that we’re a full service heat-treat provider. 90% of our business is probably ferrous steels or irons, although we do have one plant where we do exclusive heat-treatment of aluminum alloys there.

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(0:48) Michael: Do you ever run into situations where someone, they send you a component and they send you a drawing, and the specifications on the drawing are either incomplete or confusing?

Both: Yes.

(1:05) Michael: What happens in a situation like that?

Craig: Really, the main thing is to call whoever sent that drawing in. Let’s say it’s a buyer, and they don’t have the answers. It’s really a matter of getting to the technical people, and again, clarifying what their requirements are.

We get a lot of drawings that have the wrong name for processes on them, where it will say like “soft nitride” or things like that. There’s a lot of clarifying questions that happen when you get a drawing in, especially older drawings that may refer to some old terminology that’s not currently used anymore. There’s usually a lot of questions that go on, if that doesn’t make sense.

When you’re carburizing, there’s always a total case and effective case depth. A lot of times, the drawing will just say “carburize to the case depth.” We’ll have to ask the question “Do you want a total case depth or an effective case depth?”, which is how it’s measured and inspected. It gives you two different values. That’s another thing that happens, that’s confusing at times.

Rich: It may be, in a case where it’s total or effective case depth, sometimes the customer may not know the difference. So, you have to explain the difference in how you measure it, and what that difference is, between a total and effective case depth.

(2:24) Michael: In a case where they’re specifying the case depth, or even specifying the hardness, do you ever see situations where someone would specify something that you realize this may not work in what they’re trying to do, or it might not be the best thing in what they’re trying to do?

Craig: There’s that, where you wonder if the case is too thick on a thin part, is the entire part going to be brittle and want to crack, because there’s not enough core present in the part?

The other difference we see is distortion. A lot of times we’ll get parts, you’ll see a drawing of a thin, long part, and it will have a certain heat-treat listed on it where you know that you’re going to have to heat this part up to a very high temperature and maybe quench it rapidly, and you know that the part is going to warp or curl up or change size, to where it won’t be usable when it goes back to the customer again, because all the dimensional tolerances could be ruined by that particular heat treat.

You want to kind of alert your customer that “Hey, we can meet these requirements, but it’s really going to cause havoc to your dimensions,” and maybe discuss other options or other things you can do that might make your manufacturing a lot easier on it.

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(3:31) Michael: That makes sense. When you realize that there might be a problem, or you need more clarification, how does that affect the timing for how the project will go?

Craig: You usually try and catch all of that at the quoting stage, before they’re even making the parts or before the parts are even close to arriving in our facility. It’s when we’re coming up with the pricing estimates and those types of things, that’s when we kind of do our contractor deal. Hopefully, you can catch those things up front, the first time you see the drawing and the first time you’re maybe giving them a price for the heat treat, you can raise a lot of those questions.

Rich: It can delay a process, if you’re talking strictly on how long does that take. It really depends on how much back and forth between us and the customer. If they’re very knowledgeable, it may take a very short period of time. If they’re very knowledgeable, but we have to run some trials or something like that, it may extend the time.

You could resolve an issue like that in a week. It could take six months. It depends on the technical knowledge of who we’re dealing with. We feel pretty good at Bluewater, with the amount of metallurgists that we have, and the experience we have, that we are pretty good about knowing the outcomes. Sometimes, it’s a matter of convincing the customer of what those outcomes may be, good or bad.

Craig: A lot of times, our customer has to go back to their customer, or to the OEM, even. Sometimes you have to work your way backward up that chain with our questions, because our customer, they may be a stamper or a machine shop or a fine blanker. They may not have any idea, so they’ll have to work their way back up the chain to the OEM and ask those questions to the OEM. Sometimes that can take days, to get responses.

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(5:17) Michael: In thinking about the information on drawings, for a steel part that’s going to be through-hardened, what do you want to see on a print?

Craig: Pretty much the only thing you need for through-hardening is what hardness do you want, because it should be the same hardness pretty much through the entire cross-section of the part.

You may also get like an industrial specification where they see “heat treat for a General Motors spec,” or a John Deere spec or a Caterpillar spec, and they’ll have requirements on what they want to see out of us for furnace uniformity and how we’re calibrating our equipment, and things like that that aren’t really directly related to the heat treat, but that kind of create rules for us to work under.

So, quench and tempered, harden-tempered type of things, it’s usually “heat treat per this specification,” to a certain hardness level or a certain tensile strength, which we can convert back to hardness for ourselves.

Rich: One of things that I’ve always never really been a great fan of is you tell us the process and the outcome. Tell us the process, and if you’re telling us the process, okay, you’re going to get that outcome. If you tell us the outcome, we’ll figure out the process. But if you tell us the outcome and the process, then it can be a real challenge sometimes.

Typically, what I would like to see is one or the other. “Here is the process that you need to follow.” Okay, we’ll follow that process. Or tell us the outcome. We, as the metallurgists, will figure out the process.

(6:57) Michael: I agree with you.  If it’s a trusted supplier, a competent supplier, let them figure out how to do it. In the end, as a designer, all they should care about is the outcome. The mechanical properties of the part and the dimensions of the part.

When someone dictates things like the process, or other things that they have to monitor, what does that do to the complexity of the project, and what does that do to the cost of the project?

Craig: I would say one of the things where our hands are tied the most is a lot of times, we’re not allowed to choose the material or the grade of steel that’s being used. A lot of customers will pick certain grades because it’s easy to weld or it’s easy to stamp, or it’s easy to form, but a lot of those steels don’t have great hardenability.

So, when we go to heat treat them, especially thicker or larger parts, we may not be able to reach the hardness levels they’re looking for, with whatever quench we’re using, because they’ve kind of tied our hands by using a plain carbon steel instead of a low alloy steel, or a low hardenability steel, instead of something with a little higher hardenability.

So that, we always run into that kind of tug-of-war between us and maybe a stamping company, where the stamping company wants a low carbon steel that forms easy and stamps easy. But then it comes to the heat treat, and it’s much more difficult for us to heat treat, because it’s such a low hardenability grade. Maybe we’re not able to quench the core of that part up to the hardness levels that they’re looking for, if the part has got some thickness to it, where it can’t cool very rapidly in the quench.

We get things all the time where someone might say “I read that 1045 steel can be hardened to 55 Rockwell C.” But what they don’t always understand is that maybe a ½” thick piece of 1045 can be oil quenched up to 55 Rockwell C, but if you send us in a 4” diameter bar, we might only be able to get a 30 Rockwell C out of that same piece of 1045, just because the larger size can’t cool as fast in the quench. It doesn’t have great hardenability, so you don’t get the full hardness out of it, that your steel data sheet might tell you that you’re able to get.

Then you have to suggest “Maybe you should make this out of 4140 or 4340,” that has higher hardenability, and you’re able to through-harden it more easily, with a slower cooling rate. It might be necessary, because the part’s a massive part.

(9:06) Michael: You make some great points. Considering all the requirements for alloy selection is important if design teams want to have fewer component fabrication problems and decrease development time. In many cases, design engineers are selecting the same alloy used in previous designs, not realizing that, compared to previous designs, the differences in component shape or dimensions are enough to require using a different alloy. Or the design engineer selects an alloy used in another application and isn’t aware of all the metallurgical considerations for using the alloy.

(9:45) Michael: Why do the OEMs have specifications that call out the process? Heat treaters have a lot of experience. Why does the OEM do that?

Craig: I can tell you one story. We have a part that we heat treat where I know that the part used to be heat-treated inside that company’s captive heat treat department. They have their own recipes, they ran these parts in their own furnaces, and they knew exactly how to run them.

So, when they went to outsource that work and sent it to a commercial heat treater like us, they pretty much wrote a specification that said run it exactly the same way that we do it. Although furnaces can differ, so maybe we don’t always get the same results as them. But a lot of times, when it’s specified that highly, sometimes it is things that were heat treated captively, and now they’re outsourcing it, and they want us to follow their recipe right to the letter of exactly how they ran it in their shop.

Rich: We had a great example of that, as well, in this plant. It was a normalize job. Our forging customer shut down a furnace. They sent the parts here for normalizing. They said “Here’s the process that we want you to follow.” We tried for quite a long time to follow that process, tweak it here, tweak it there, tweak temperatures here, tweak some time there, to follow their process, but we just couldn’t quite do it.

Finally, we met with them and said “Okay, let’s review this. Let’s review what kind of furnace you had, what kind of furnace we have.” We ultimately reached a process that worked, that met theirs. It didn’t exactly follow their process, but it got to the end result, because we had to adapt their process to our furnace.

(11:35) Michael: It seems to me that the simpler process for them would have been to start off with just saying “We want a certain microstructure. We want certain properties, and you figure out what you need to do, to do that.”

Rich: Let me follow up on that same example, then. As Craig said earlier, we were dealing with a forging shop. The forging shop, this was an automotive part, so they had to go back then and deal with the OEM.

It becomes more difficult for them to then have to have to re-PPAP a part, or resubmit documentation. If they were to just say “They followed our exact process,” then it makes that whole qualification effort, on their behalf, easier. There’s a lot of that that drives it. Once a process is approved, and then you go from captive to commercial, that customer really wants to make their life simple, and not change the process.

(12:32) Michael: It sounds like it added a whole lot of time to the development cycle.

Rich: In this plant, what you think is a simple, normalized process, it’s quite a lot.

(12:44) Michael: Do you ever get design engineers calling you up to talk to you about a part they’re working on, and getting input, asking you for input for the heat treatment that was possible?

Craig: Yes, we’ll get that all time, where they’ll say “Hey, we’re making a part this way. We’re having failures, or the part is wearing out too quickly,” or things like that are happening, and they’re looking for suggestions of a different process they could do or a different type of heat treat they could do, to maybe get higher wear resistance or higher strength, or maybe a different material, looking for ideas on what kind of different materials we think might be possible for them to use. They’re just looking for a better way to make their part last longer.

Michael: It sounds like that’s a situation where they’re looking to make improvements, whether it’s in quality or reliability.

(13:30) Michael: If it’s going to be a case-hardened part, let’s say a case-hardened steel, what information should be included on a drawing?

Craig: For those, we’ll typically have – now you’ll have a case on the outside of the part and a core on the inside of the part, that are going to have different properties. The first thing is they’ll want to specify case depth, so that we know how deep into the steel we’re supposed to treat it. Then, they’ll have a case surface hardness, where they specify how hard is that case supposed to be.

Then, they’ll also have a lower value for what is the core hardness or the core yield strength supposed to be, or core tensile strength.

There are also – sometimes there will be some microstructure requirements, as well, on case hardening, where they’ll say the case needs to be 100% hardened. They’ll have requirements for maximum percentage of retained austenite that may be present, how much inner granular oxidation may be present from the surface, and any carbides or nitride networks forming on the grain boundaries.

So yeah, there’s often a lot of microstructural requirements, as well. Even for the core, as well, you can have a customer say “We want the core to be fully martensitic, or we want the core to show some ferrite.” So yeah, it gets a little more complex with the case-hardening jobs.

Rich: Yeah, and I was going to go back to my gear days of exactly that. A gear in an aerospace application may have a certain amount of retained austenite requirement, because you don’t want that retained austenite to convert to untempered martensite. In a lawnmower application, it may not be as critical. A lot of that all depends on the criticality of what the component is being used for.

In a case like that, then the heat treater does need to know if you need X amount of percent retained austenite, or intergranular oxidation, because obviously in aerospace gearing, you don’t want things like that. You don’t want a bad failure, due to some intergranular oxidation.

(15:36) Michael: What you’re saying is that the detail that’s required in certain parts may be more than in other parts, depending upon the criticalness of the part, and the reliability required for the part.

Rich: That also goes then into the type of thing with the furnace control or the furnace capability, as well. Typically, the aerospace parts are going to require a higher level of uniformity, or certain things on your furnaces, or temperature uniformity surveys. So, the criticality of the part, not only of the heat treat process, but then that also helps drive what the requirements of the furnace are, itself.

Craig: A lot of what goes with that is the frequency, how often you’re doing those tests. You might be doing temperature uniformity surveys weekly, instead of quarterly, or instead of annually, for different industries. System accuracy tests might be done more frequently for aerospace, versus general industrial type parts.

That actually affects the cost of the part. That is, if we have to do more and more of this periodic testing and qualification and calibration of all of our instruments, our furnaces, there’s a cost to that. Doing heat treatment for those critical industries that require us to do increased frequency of inspections and calibrations, it definitely drives the cost up for those parts, compared to customers that use furnaces where we don’t have to do those inspections quite so frequently.

(17:05) Michael: Have there been cases where you’ve talked to someone about their drawing, and you said “No, do it this way,” and you do it for them the way they tell you, after you’ve questioned their specifications, and you give them the part, and it meets their specifications, but it ends up not working. Has that happened?

Craig: Yeah. Probably one of the biggest issues I run into is people want to try a certain process of ours when they’re prototyping, when they’re saying “Let’s try this process on this part, because I think it would work well.” But a lot of times, I’ll run into situations where we’ll heat treat that part, but we don’t know if we can keep it straight enough or keep it round enough, or keep it flat enough.

I run into issues with that quite a bit. We’ll try a process for a company, and say “Hey, we’re going to hope for the best on your prototypes, and see if it works.” Sometimes you get done running those prototypes, and they’ll come back to you and say “Yeah, but the threads on this part changed size too much,” or the diameter grew too much, or the part shrank too much.

Sometimes you can still go back and say “Okay, what if you compensate for that in your incoming sizes? Maybe if you machine the threads a little oversized, or if you make the part a little undersized coming in to us, then we’ll know that it’s going to grow into those dimensions.”

So, sometimes on a second go-around on prototypes, you can fix things that didn’t work in the first go-around, because you saw after the first run, how things changed. Then, they’re able to compensate in the second round.

But there are some things that I’ve run, that I’ve done sample parts for people, and it just doesn’t work. They just can’t, because we heat parts up to such a high temperature, and things want to move around. You’ve got phase transformations going on, that causes the material to shift. Sometimes, you just can’t hold peoples’ dimensions perfectly, that they’re looking for, and for whatever reason, they can’t machine it afterwards.

(18:59) Michael: It sounds like sometimes, especially for a new part, a new design, that people might have to build in some time and expense for doing some experimentation.

Craig: Yeah, and sometimes you into customers that just have parts that we feasibly just can’t run through our furnaces, for whatever reason, or you run into strange geometry parts.

(19:20) Michael: It sounds like the best thing is for them to just call you up and talk to you about it and discuss it, and discuss what options are available.

Rich: To me, it’s communication, communication between the customer and us, or a heat treater. The more communication, the better. That resolves a lot of problems right up front. A lot of times, you work things out before you even touch a piece.

(19:43) Michael: It’s good advice. I think it applies to all aspects of component fabrication.

Thanks for meeting with me to do this interview. It’s been very informative.

Both: Thank you.

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