MANUFACTURING HEAT TREAT

Heat Treat Radio host Doug Glenn sits down to talk with Johan Hjärne about high pressure heat treating and an e-book recently published by Heat Treat Today in cooperation with Quintus Technologies. Learn more about high pressure heat treating in this informative interview.

Below, you can either listen to the podcast by clicking on the audio play button, or you can read an edited transcript.

The following transcript has been edited for your reading enjoyment.

Doug  Glenn (DG): For this edition of Heat Treat Radio, I have the great pleasure of sitting down with Johan Hjärne (JH) from Quintus Technologies.  Let's give the listeners a sense of who you are, how long you've been in the industry and your experience with HIPing.  If you don't mind, please introduce yourself.

JH:  Absolutely, thank you so much, Doug, for that introduction.  My name is Johan Hjärne and I work for Quintus Technologies.  I've been with the company for around 10 years now. I started up where we have our head office, which is in Västerås, Sweden, 10 years ago as an R&D manager there. Later, I had other roles like product manager for our hot isostatic presses.  I also worked as a global business development manager, responsible for the strategies for a couple of years, and since four years ago, I'm now the business unit director for Quintus Technologies here in the American region.   I am responsible for our hot and cold isostatic presses and also our other business unit which is called Sheet Metal Forming Presses.  Before I joined Quintus, I worked within the aerospace industry for 10 years.

DG:  I've been to your office, but I want everyone else to know:  You guys are located just north of Columbus, Ohio.

JH:  That's absolutely correct.  It is a little suburb of Columbus called Lewis Center just north of Columbus.

DG:  The reason we decided to get together on this podcast was because you and I and our respective teams have just successfully completed the publication of an eBook, which basically we've entitled “High Pressure Heat Treatment.”  It deals with HIPing and some other things.  So, that's the occasion for this meeting.  I want to ask you to discuss, briefly, with us about high pressure heat treating.  What is it and why did we decide to do this eBook on it?

JH:  A very good question.  As I indicated before, I have a background in the aerospace industry and when I worked there we were responsible for some components in a jet engine.  We had big castings and we typically 'HIPed and shipped' these castings.  HIPing, to at least us in the aerospace where I worked at the time, was like a black box.  We really didn't know.  We knew that the results were better if we HIPed, we could use less material, the material got stronger, etc, etc.  So, when I started at Quintus, at the same time we had made some progress with increasing the cooling rate in our HIP system.

A HIP system basically works in a way where you apply a high temperature and high pressure and then you cool down, and during this process you take away the pores.  We had realized that the cooling part of this cycle could be shortened drastically with some updates of the equipment.  At the same time, additive manufacturing started to grow.  They started, after awhile, to understand and realize that even though the process of additive manufacturing is a brilliant process, (you can do fantastic things in a short period of time), many times they ended up with porosity in the parts.

The aerospace industry, the medical implant industry, and others required that these pores be taken away.  So, they reached out to us and wondered what we could do about this.  When we said that the HIP cycle is perfect, you can remove the porosity from your part, they started to ask questions like, “Why do I need to heat treat it afterwards?  Why do I need to do something else afterwards?  Isn't this enough without gas to remove the porosity?”   That is where we started to add one and one together to see, well, the cooling rates we can apply in our modern HIP system might actually be good enough to do this heat treat section.  So, for materials that were suitable for this, we started to elaborate, and that is how we started to work with this and development it more and more.

DG:  Let's talk about the difference, then, between traditionally HIPing and what this high pressure heat treatment is.  Process-wise, what is the difference?

JH:  Process-wise, as I explained a little bit briefly before, the HIP process is basically increasing the temperature in the furnace, or in the pressure vessel, and then we apply a high pressure.  After the material has been under these conditions, we need to cool the pressure vessel to be able to take out these parts.  The next step, in many cases, is a similar heat treat process, but without any pressure.  So, basically, after the HIP step, you take out the parts from the HIP and you redo almost the same cycle, without pressure, just to be able to cool it faster and get the correct material properties.  When we realized that this cooling step was high enough and that we can do it already in the HIP system, then we could basically remove that subsequent solutionizing step.  Basically, it is applying the same cooling rate, as they had in the solutionized step, directly in the HIP unit.  Combining these two is what we call high pressure heat treatment.

The systems we have are also capable of running pressure and temperature independently.  If we take an additive part which is being printed on a build plate, you can, in principle, take that build plate, put it in one of our HIP systems, you can run a stress relief cycle to begin with where you only use an elevated temperature without any pressure whatsoever, you can increase the pressure and the temperature when you want to go into the HIP cycle, you can quench it down to do the solutionizing step and you can even, if you find it reasonable, do an aging step.  This whole process could, in principle, remove four different steps.  It is always a question of do you want to take the whole build plate and do that, or do you want to remove the parts from the build plate before you HIP and heat treat it, and so on and so forth.  That is always up to the customers.  The machines we provide are capable of taking care of the whole process, of doing it all.

DG:  Doing it all- stress relief, HIP, age, or whatever. Just for clarity sake, you've got a typical HIP process, you're going to heat it up, put it under very high pressure, then, normally, if you didn't have the high pressure heat treatment capabilities, you would have to cool that part down which is typically cooled quite slowly in a conventional HIP unit, taking more time and whatnot.  It then comes down to ambient, or close to ambient, where it can be held, you take it out, you put it back in another furnace (a normal furnace, not a HIP furnace), take the temperature back up, get it to the point where you want it, quick cool it, quench it, to a certain extent, to get the characteristics that you're looking for, and you're done.  What we're talking about here is the combination of those two processes plus potential other things like stress relief, and all that, in a single unit, correct?

JH:  Yes.  This has very beneficial effects on time.  Many of the HIP vendors do not have HIP and heat treatment in the same facility.  Now we have sold a couple of units to some new HIP vendors that have this capacity, but, historically, the HIP vendors didn't have both HIP and heat treatment.  First, the customer had to send it to a service provider for HIPing, they got the part back, they had to send it to somebody that could do the heat treat step, and then got the part back, and so on.  The time, and specifically for additive manufacturing, is important.  Keep in mind they can do a part pretty fast, anywhere between a day to two days, worst case a week, but then having to wait week after week after week to get the part back for the HIPing or for the heat treating.

DG:  So there's a substantial, potential time savings, for sure; not just process savings in between furnaces, but the fact that you can buy one furnace and do both of those things.

Let's talk for just a second about what types of products are most effectively HIPed and/or, if we can, high pressure heat treated.

JH:  As I said before, we really started to realize the potential with this technology with the additive manufacturing world.  That is were we started to realized that we can actually make a difference here.  Not only does it have a beneficial effect for the total time, but having the components under elevated temperature for a shorter period of time is actually beneficial for the microstructure; the grain doesn't grow as much.  You can take the example, again, with the first HIP cycle with having that at a certain temperature, you cool it down slowly then you heat it up again to the same high temperature for a period of time before you quench it down.  Well, then you exaggerate the component for high temperature under a much longer period.  If you can do that in just one step, the component doesn't have to be in as high a temperature for such a long period of time which means that the grains don't grow as much which gives you a better microstructure and better material properties.  That is one effect.

Another effect that we have realized is very beneficial is that when you're dealing with additive manufacturing, you end up, specifically if it's laser powder bed fusion, you end up with Argon in the pores and  Argon cannot be dissolved into the material.  With a HIPing process, the Argon pores are basically eliminated, in a way.  However, if you heat it up again, these pores start to grow and they can grow back again and be bigger.  So, if you remove that heat treat step afterwards, you don't have to be afraid of this pore growth again.  That's another beneficial effect, from a metallurgical standpoint, that we have realized.

Additive manufacturing is very well suited for this.  With that said, now we see a more increasing interest from the casting side, as well.  With these new modern HIP units we have, we can cool with velocities of several thousand  degrees per minute, a little dependent on what size, etc., but this has a very good effect on the microstructures on suitable materials like nickel-base super alloys and titanium aluminides, etc.  The casting side is now starting to get very, very interested in this technology, as well, because basically it didn't exist before.  We see a huge potential and we have seen an immense growth of requests for this technology the last couple of years.

DG:  How about just straight powder metal?  I know you're talking 3-D, but how about just straight powder metal manufacturing, because those parts tend to be a bit more porous than your normal wrought products, and things of that sort?

JH:  If you talk about powder metallurgy and HIP, you typically need to have everything canned, in a way.  Powder metallurgy, we call it near-net shape, for example, where you weld structures to a certain shape or form, you fill that with powder and then you HIP it and out comes a part which basically has a perfect microstructure.  We haven't come so far yet to start to evaluate how that will be with this high pressure heat treat, but what we have seen with the interest of this is that a lot of the HIP cycles were developed many, many years ago.  At the time, they didn't have the cooling capacity we have today and they ended up with cycles which were good, they took away the porosity.  However, with the capability to modify both the temperature and the pressure, you can come to the same fully dense part.  I'm over exaggerating  a little bit, but if you have a high temperature, you can have a lower pressure.  If you have a lower temperature, you can increase the pressure.  So, we have also focused on having a very high pressure on all of our equipment because then you have this flexibility to get to the fully dense part in the best way.  This is something I'm absolutely convinced that the powder metallurgy industry would be interested in and evaluating more, as well.

DG:  For the people who might be interested in testing a part, or something like that, are there size restraints?  Typically, what type of workzone are we talking about in a standard Quintus HIP unit?

JH:  If we talk about today, what we have on the market for relatively high cooling rates, if we're talking cooling rates in the 200-300 C/minute or 400-500, almost 600 F/minute, the production units are at 2 feet diameter, give or take (660 mm), and around 6 feet high.  But this is something that the next generation we are developing right now, we are approaching a meter and more than that, as well.   So, it's just a matter of time to grow this.  We've seen that there is the highest interest on the additive manufacturing market, which is why we have focused on that to begin with, now we're doing higher and I do not see any limitations in going up in diametrical size for this.

DG:  But it is exponentially more difficult as you get wider, yes?

JH:  Yes.  It's a good comment you make.  You have a much higher volume that you need to cool down.    But, for the cooling rates, we see, at least today, most applicable where we talk about these, as I said, 200-300 C/minute, we definitely see possibilities to go over a meter in diameter and then we have large production sized HIP units.  We do HIP units that are much bigger than that but if you start to get over 1 ½ meter and even bigger, then you're absolutely correct, then the cooling rates are drastically lower.

DG:  Could you describe, for those who may not have ever seen or understand a HIP unit, and most specifically, a high pressure heat treatment HIP unit, what does it look like?

JH:  I can start with a pressure vessel, basically.  It's basically a cylinder where you put a furnace in and in this cylinder you can increase the pressure and in the furnace you can increase the temperature so you create a pressure vessel with high pressure and high temperature.

DG:  And Johan, we're talking, typically, a vertical cylinder?

JH:  Correct.

DG:  And this high pressure vessel has a wall thickness of ….. ?

JH:  That is a good question, Doug.  Depending on size, of course, the wall thickness can be anywhere from a couple of inches to maybe the biggest wall thickness we have now is up to 200 millimeters, or something like that.  Don't hold me to these numbers.  But, the important thing is that you can do a pressure vessel design in two ways:  Either you can use a very thick-walled cylinder to contain the high pressure, or you can do a thin-walled pressure vessel, and that is where the big difference is.  At Quintus Technologies, we use a thin-walled pressure vessel and we apply a wire winding technology.  So we pre stress this cylinder with a wire, but we can also apply cooling next to or in direct contact with this pressure vessel.  What we do is create a heat exchanger with our whole system.  We also apply cooling in the lower closures and in the upper closures so what you have is a water controlled pressure vessel with a furnace in and then we can actively control how fast we would like to cool the unit with controlling the cooling of the pressure vessel.

DG:  I'm imaging, right away, thermal shock written all over this thing.  You've got a high pressure, a vessel that's at high temperature and all of a sudden you guys slam in there because you want to drop temperatures 300-400 C, 400-500 F/minute, I'm seeing a lot of thermal shock going on.  How do you deal with that?

JH:  The gas that we are working with is Argon.  Argon has an extremely good thermal conductivity.  At high temperature it, sort of, takes care of the densification process in a very good way because it takes the heat from the gas into the material.  What we then use is the colder gas in the lower region and we basically force that cold gas up into the furnace.  But we don't do that with any specific high velocity.  The velocities in  pressure vessels are pretty moderate and continuous.  And, of course, we have requirements on the pressure vessel wall.  The pressure vessel walls are strictly monitored and controlled so they can never exceed certain temperatures.  That's where we have our, sort of, safety function and control function.

We don't see any challenges with thermal shock.  The alternative of having a thick-walled cylinder might have bigger challenges when you cool from one side.  Then, you can end up with other challenges like thermal cracks, etc.  But using a thin-walled solution as we do, we don't see any issues with this.

DG:  The other major issue I would think you'd have with thick walls is you probably wouldn't be able to reach the cooling rates that you're talking about because you've got a huge heat sink sucking up all of that cold air.

A company that might be thinking about bringing this HIPing thing in-house and do high pressure heat treatment in-house, are they going to have to have any operational expertise?  In other words, do you need to hire a PhD from Harvard, or someone like that, to operate this unit?

JH:  No.  Operating a HIP unit like this is not, according to Quintus, more difficult than operating other heat treat furnaces in any way.  Of course you need a touch and feel for the unit, how it works, etc.  This is taken care of during training when we deliver the systems.  You don't have to have any PhD from Harvard to run and operate these units.

Doug, you've been in our Lewis Center office, and we have an application lab there.  If someone is interested, we are more than wiling to take on customers or somebody that just wants to know more about the technology and take a look at it.  They're more than welcome to contact me or Quintus and come and visit us.

The market is starting to get these machines out for operation.  If you are a customer that would like to try these out and have a part that is bigger than our small lab furnaces can do, there are service providers out there on the market that can do this.  We have companies like Accurate Grazing in Greenville, SC that have a couple of these units.  We have Paulo up in Cleveland, OH and on the west coast we have Stack Metallurgical in Portland, OR.  Even Canada has their first really fast unit now with Burloak and also Mexico has a company called HT-MX. For the bigger companies that decide to outsource, or any company that decides to outsource, this is a technology that is out there on the market.

DG:  Your lab there in Lewis Center will help process or 'part validate', I assume, if somebody is interested in that?  They can bring an idea, a problem or a part in development to you and you'll say, “Yes, here's what we can do and we can prove it by running it.”

JH:  Absolutely.  We have the thought that if somebody wants to evaluate this and are willing to work a little bit with us and maybe we can get some information back, we have this as a service for free.  We are not a service provider in the sense that we compete with our customers, but if someone wants to evaluate the technology and are willing to talk with us and listen to us, this is a service we do for free.

DG:  I'm going to ask you about giving out additional information where people can go to get more information, but I would like to let the listeners know that if you go to www.heattreattoday.com and in the search box just type in 'HIP' or 'HIPing' or 'hot isostatic pressing', you'll see a pretty healthy list of articles that appear there that aren't necessarily specific to high pressure heat treatment, just HIPing generally, but certainly there are articles there about high pressure heat treating, as well, from Quintus.  You can also type Quintus into the search box and you would come up with quite a few things because you guys have provided us with some good content.

That's one place you can go if you want to find out more information.  Johan, where can they go, what are you comfortable giving out as far as contact information for you and/or Quintus?

JH:  Regarding information, they can go to our homepage, of course, Quintustechnologies.com.   And don't forget the eBook, Doug.  That's a very good description of HIPing.  If you want to know more, download the eBook.  That has a good description of not only high pressure heat treatment, but also HIPing and a little bit of history of HIPing.

Otherwise, you can contact me by going to the Quintus homepage and find contact information for me.  We also have the application lab in Lewis Center.  If it has to do with HIPing, it will end up in my in-box, sooner or later.

DG:  You've got a good team there, by the way.  We know some of your other folks who you work with that are very good people.  If you're a listener and you're interested, you want to go to the Quintustechnologies.com homepage.  You can search for Johan Hjärne  on the Quintus homepage and you'll get Johan's contact information.

And yes, you make a very good point, don't forget the eBook on Heat Treat Today's site.  You can get there simply by typing into your browser- www.heattreattoday.com/ebook and you'll go to our eBook homepage which has two eBooks on there right now, the most recent being the one from Quintus.

JH:  I would also like to add something.  We talked an awful lot about the U.S., but if there are any listeners from the rest of the world, we have an application lab where we have our head office in  Västerås, Sweden, as well.  That lab is even a little bit better equipped that our lab is, so that's a fantastic opportunity if you're not situated here in North America.  We also have connections in China and Japan, but you can find more information about that on our homepage.

DG: Johan, thank you so much. Great to talk with you, thanks for your time.