Quenching and Partitioning: Science and Technology
Speer, John
Matlock, David
Moor, Emmanuel De
Edmonds, David
A lecture given by John Speer, at the Adventures in the Physical Metallurgy of Steels (APMS) conference held in Cambridge University. The quench and partitioning process involves partial transformation to martensite, followed by an increase in temperature to permit the excess carbon to partition into the residual austenite. The quenching and partitioning (Q&P) concept was first introduced about a decade ago, to utilise carbon in as-quenched martensite to stabilise retained austenite and thereby enhance the mechanical properties. This presentation will provide an update of advancements made in understanding important aspects of physical metallurgy and microstructure development, within the authors laboratories and elsewhere, which have led to interest in Q&P as a potential route for producing commercial steels in volume. A variety of applications have been explored in Q&P laboratory investigations. Initial industrialisation has focused on automotive sheet steels, and substantial activity is now underway to meet aggressive near-term targets for vehicle lightweighting using Q&P steels or other novel approaches to generate microstructures with enhanced austenite fractions. The current status of some of these efforts will be reported.
 The next talk is by John Speer, who comes from the Colorado School of Mines, which is the main center for Steves research in the USA. And John Speer is one of the leaders there. He's going to talk about the quenching partitioning process, which started, you know, fairly recently and has taken off all over the world. The number of papers you see and the quenching partitioning process being tried out in many different ways is really impressive. Thank you, Harry, for your kind introduction. Can everyone hear me okay? Okay. Well, it's really a great pleasure to be here today with all of you. And I'm going to try to talk a little, in the short time we have a little bit of science and a little technology. I want to acknowledge my collaborators and co-authors, David Edmonds, who's in the room here. Our acknowledgments were supposed to be on the first slide. But I thought, as I thought back on the development of this concept and all the process, one of the great pleasures, I think, was we often don't have the time or take the time to read as much as we should. But I did have an opportunity to read a lot of the literature from the giants, and that was quite an enjoyable process. I really want to acknowledge those people who have influenced probably all of us in the room here. And I also want to thank the many collaborators and students that have worked on this over the years. A little bit of background going back to the beginning. So this quenching partitioning process was really designed as a new concept to control retained austenite. And the original process concept was that we interrupt a quench. So normally you would quench austenite, perhaps to room temperature and form martensite. But we interrupt the quench here at a temperature where the martensitic transformation is incomplete. And the idea then is some subsequent thermal treatment either at the same temperature as the quenching temperature that we called one step or at some different temperature or two step, that carbon would go from the martensite into the untransformed austenite and would therefore stabilize it so that when we then completed the quench to back down to room temperature we would have more retained austenite. So that's the basic concept. We've extended that concept more recently to the case where we may have industrial processing concepts where the partitioning process would be non-isothermal. And if we have time at the end I might make a comment or two about that. This is a little bit more complicated. But for example, in hot roll sheet production you would use the run out table cooling process to complete the partial martensitic transformation. And then the coiling temperature where you wind the coil up would serve to control the basically the time and temperature, the cooling profile that would define the extent of partitioning. So these are the sort of process concepts that we're thinking about. In the beginning we started by trying to understand what the thermodynamics would tell us about what kind of carbon partitioning could happen and how it could affect the microstructure and properties of the material. And so this is some of the simple analysis from our early papers. And again if you think about a metastable equilibrium between martensite and austenite carbon would partition to this point in equilibrium. In the case where we have varying non-equilibrium fractions of austenite and martensite though if we analyze this and if the interface is immobile what would happen is the carbon would partition until its chemical potential is uniform in the two phases. That's why we have not a common tangent construction but a point where the tangent intercepts on the carbon axis are the same. And the interesting thing about this then is depending on the phase fractions we could have multiple different conditions where the carbon potential is their equal in the phases. And so we could have very carbon enriched austenite much more than an equilibrium or less carbon enriched austenite. So depending on the phase fractions we could have some interesting carbon enrichments. And that went into the early development. And then the next step of the process was to try to understand how we would control microstructure and in that regard this is an important diagram from our early literature and so I want to just walk you through it for a moment. So if we think about quenching austenite so once the quench temperature goes below the martensite start temperature the amount of austenite that remains is diminishing, the amount of martensite that forms during the quenching is increasing with under cooling. And then so we stop at that quench temperature and then we partition the carbon and most of the carbon would like to partition back into the austenite. And so depending on how much austenite and martensite are present that defines the amount of carbon that can partition into the austenite. And so this line right here tells you the carbon concentration of the austenite if the martensite gives up all its carbon to that austenite. And so if we have a lot of martensite and just a little bit of austenite the carbon enrichment of that austenite is very great and diminishes with reduced martensite content and increased austenite. And so this tells you about the stability of the austenite at the quench temperature after partitioning before we go through the final quench to room temperature. And then depending on that stability this line tells you how much of that austenite that existed after partitioning will remain after final quenching. So this is the amount of that austenite that transforms to new martensite and so if we subtract that from the austenite that was present at the quench temperature we get this red line and that's the end result of this that tells us how much austenite we could retain at room temperature. And so this functional behavior was very important helping to guide our processing histories as we tried to verify that this concept would work. So we have this peak in the behavior associated with particular quenching temperatures. And in this fairly simple model were some assumptions that are pretty important from a physical metallurgy standpoint. First of all that we had ideal partitioning and all the carbon would like to go into the austenite that we've completely suppressed the precipitation of carbides or conventional tempering reactions that the once you form the martensite during quenching that you don't change the phase fractions anymore that is that the interface is immobile and that the austenite doesn't decompose in other ways like bayonet formation. So there have been these assumptions are not always correct and so they're the source of a lot of interesting follow-up that we can do as a metallurgical community. But still the model is very helpful to guide us. Now this particular model that I described here was actually applied more recently in a completely different class of steels the so-called medium manganese steels that are very fine grained intercritically annealed materials. So fine ferrite austenite mixtures where the austenite is really stabilized by high manganese concentrations. I'll just show you how this diagram was applied in that case it's basically the same kind of behavior except in this case the ferrite austenite fraction is controlled by the annealing temperature so the greater is the annealing temperature the more austenite we have. And then if manganese can partition into that austenite the austenite is enriched with manganese but it really depends on the phase fraction so the more austenite that you have the less manganese enrichment that you have and so the less stable is that austenite in terms of remaining at room temperature and so depending on its stability it can transform to martensite during the final quenching. If we again subtract this from the austenite curve we end up with this black and blue function that tells us how much austenite would remain at room temperature. So a very similar application of the same fundamentals to a completely different class of steels and this is actually how it worked out so this is a 7 manganese I think 0.1 carbon steel. This is the predicted austenite fraction as a function of annealing temperature again assuming full manganese partitioning between the phases this was a long annealing time and these are the experimental data showing that this model was helpful to understand the behavior of this other class of materials. So it's a very exciting time in steel development now I think I'll go on the record and say this might be one of the most exciting times for steel development ever. In the automotive community the need for increased fuel economy is dramatic and at least in the United States there's a tremendous need for steel development to reduce weight and enhance vehicle performance or maintain vehicle performance. So in terms of application of quenching and partitioning the automotive industry right now is driving that interest in application but there are other interests in ball bearings and high toughness plate steels so there's much opportunity that hasn't been explored yet in quenching and partitioning. But in the automotive industry so we saw this so-called banana diagram before where we have this range of tensile ductilities and tensile strength for a whole variety of different kinds of steel materials and I heard this described interestingly very recently by Neil Suchdev of General Motors as the miracle of steel. So we look at this somewhat mundane as experts in steel but the fact is by small variations in composition and processing we can create this tremendous window of different steel products with very different properties so the miracle of steel. But we're trying to push the properties up into higher strengths and higher ductilities so that's very challenging and yet very exciting for the community. How are we going to get there? So this is a simple model developed by my colleague David Matlock really looking at composite models for predicting uniform ductility based on phase properties and you can see if we look at combinations of ferrite and martensite we get property combinations that you would expect that are fairly parallel to the different grades on the banana diagram so ferrite by steels. If instead we look at combinations of a particular stable austenite mixed with martensite we get much better strength ductility combinations in this future need area of steels and actually if instead of using stable austenite we can control the austenite stability I don't think we really know how to tune the austenite stability in practice as well as we would like to but we can we can move this curve around as well so it's a very interesting opportunity. But in terms of how we get to the future our philosophy in automotive steel development is pretty much we need to have retained austenite in the microstructure and so that's driving interest in Q and P steels, in carbide free bainite steels, in medium manganese steels as I mentioned so very exciting time. There are a number of things on this slide that I want to mention. First of all this is all this data is all experimental data from quenching partition steels and some of the people who generated it are in the room here and this green, this shaded region over here. This represents the original target that we set out to achieve in 2003 and so we were pretty happy that our development was fairly successful in getting us some high strength materials with quite good ductility. The dashed line and the solid line here are the same predicted curves that I showed on the last slide. So we were quite happy but what's happened in the meantime is that the property targets keep getting more challenging. So one of the large automotive companies in 2010 defined a target up here which is way up in the future band of desired properties and then the next year put some targets up here. The United States Department of Energy has funded an integrated computational materials engineering program with the industry and they've set some even greater targets than the industry has set. So when we think about how successful we are in meeting property targets we also have to recognize that the challenge is increasing. So the targets are moving. I promise this is my last banana diagram for this presentation. Our original models looked at transformation behavior and subsequent models looked incorporated some partitioning kinetics and so these are some different models. We can see that the ferrite gives up its carbon rather quickly. It takes longer to equilibrate the austenite. So what's interesting about that is under certain partitioning scenarios the austenite might contain most of the carbon but with a non-uniform chemical composition gradient. We get some interesting effects then when we try to understand the stability of that austenite so we calculate it using the Køsten and Marburg equation locally but in fact we don't know how good that assumption is. So one of the questions for the community then is what is the stability of austenite in the case where we have a local concentration gradient that's on the same scale as the martensite microstructure. These are some examples so quenching partitioning has been applied now in commercial steels. First by Baosteel in China. These are commercial applications. There are other companies around the world though who I believe have a real interest in considering this technology. So in the few minutes that remain for my presentation I thought I'd present some curiosities, challenges and opportunities. We've learned a lot over the last ten years but there's still a lot of things that we don't understand and hopefully this community will come back at some future time and help. So here are Q&P property data. So this is the product of tensile strength and elongation versus the amount of retained austenite. And so our desire was to produce high amounts of retained austenite but you can see from this diagram that in fact the properties are not highly correlated with the fraction of retained austenite. So I think that we still don't completely understand what controls the work hardening behavior and the property combinations in these steels. We've learned a lot of partitioning mechanisms and some of the physical modelergy and the group that leads has led us in this regard. One of the questions is about carbide precipitation which generally speaking we don't want because it takes carbon from the microstructure that we would otherwise use for austenite stabilization. I'm showing a particular steel that's partitioned at two different temperatures. In one case we get a lot of epsilon transition carbides in the microstructure and the other case at higher temperature we get austenite stabilization. So for the community I think one of the challenges then is how do we control the stability of transition carbides other than perhaps temperature according to the models that we think we understand. But if we could turn on and turn off transition carbide formation using other means then we understand now it would be a powerful alloy design tool. The last comment I want to make we've had a lot of discussion about whether the Martensite austenite interface is stationary or mobile. There's been some interesting modeling work that's been done at Delft in particular. One of my former students Grant Thomas looked at some higher alloyed steels not intended for commercial applications but intended to study the partitioning mechanisms. One of the things that we looked at is the change in the austenite fraction during partitioning in these steels where austenite you could quench to room temperature and then partition subsequently. In a high nickel containing steel we found that the austenite fraction was stable it did enrich in carbon. So the assumption of a stationary interface was pretty good. In the case of a high manganese steel though we actually increased the austenite fraction during partitioning so clearly we think the interface was not immobile. EBSD results so the green is the austenite phase the change from left to right is with partitioning and you could see again nickel steel increase in austenite fraction nickel steel approximately constant austenite fraction. And so I mean there's pole figure diagrams really looking at what happens to the microstructure during partitioning. This is in the manganese steel these colors represent austenite orientations and so these we think are probably the original austenite grain orientations confirming that we think the austenite is growing during partitioning rather than nucleating. But we don't completely understand why that happens in one steel and not another. I think I'll bypass this slide and go to the conclusion. Quenching and partitioning science and technology continues to advance. The process has been commercialized and hopefully there will be other applications besides automotive sheet steels and growth in those applications. But challenges and opportunities remain both in terms of science as well as in technology. And I end in closing here showing some Q and P microstructures. This is one that we obtained in the laboratory intercritically annealed so we have ferrite here. This is actually a commercially produced Q and P steel. And then we have a mixture of martensite and thick austenite films. So with that I conclude my presentation and again thank you for being here. Thank you very much John for creating one of the modern concepts of automotive steels. Very interesting talk. We are open for questions. Very short question. In fact you mentioned that bay night is something that we don't want in pistils. But could you comment a little bit more about that? I understand that we don't want bay night because it takes part of the carbon. Well the viewpoint of mechanical properties I expect that maybe people should go in this direction to sort of combining some bay night with. Could you. I don't remember saying that you don't want bay night. But I think that when bay night forms from the austenite at the partitioning temperature then you really have a mixed microstructure. So you have a Q and P mechanism but you also have a you know austempering bay night formation mechanism. So you get a mixed microstructure. And I think there are some interesting properties that people are getting in cases where they do have those kinds of mixed microstructures. So hybrid mechanisms. So I think they might actually be fairly important industrially. So yes. Sanke is a very nice talk. You mentioned these medium magnetic steels. That's probably a very hot topic at the moment. And apart from manganese what's your opinion on the range of other elements such like aluminum or silicon? Well I think there are some aluminum and silicon wouldn't be strong austenite stabilizers. So you'd be looking at different concepts with those elements. So manganese is interesting because it allows us to really increase the retained austenite fractions to quite high levels. There are some other interesting concepts particularly with high aluminum where aluminum is being used to reduce the density of the steel. So those are different concepts that are a little bit outside the scope of the design concepts that I discussed today but are also of considerable interest right now. Okay. Thank you for your talk. I have a question regarding the resource from Thomas on the high nickel and high manganese steels in which he observes an increase in the fraction of austenite with the partitioning step. And I wonder if I know that at those temperatures the diffusion manganese is extremely small but I also saw some articles from another researchers in which they think that the diffusion of manganese is underestimated at low temperatures. So do you think this increase in the austenite fraction can be due to some manganese partitioning actually? So I don't know the answer to that exactly. This is a very low temperature to be thinking about manganese partitioning but I do agree not necessarily in this temperature regime but actually in the temperature regime of annealing of the medium manganese steels, so in the intercritical regime, we're getting much more manganese partitioning than you would expect from the sort of published diffusivity data. So I agree that manganese diffusion seems to be much faster than we thought it was. I don't know that that's a contributor to the temperatures that Grant Thomas was looking at here though. Because it's interesting when you have lower manganese levels, you don't see those or at least we don't observe such an increase in the fraction of austenite but at those levels it's observed so that's maybe related. So what's happening in the nickel steel then? Okay, well thank you. Okay, thank you. We have a question from the rest of the world. Not from the Netherlands, they have a question. The question is if the intercritical annealing temperature has been done in say 800 to 900, is it possible for the manganese to partition in say 100 seconds? That's the question. So are we talking about a medium manganese steel? I guess so. So I guess it doesn't really matter. But I think there's some data in the recent literature that shows that you can get significant manganese partitioning at intercritical temperatures in relatively short times. Another question from AK Steel. Is it possible for manganese carbon interaction is different compared to carbon interaction to nickel effect these? So this author is actually at AK Steel. So I'm not asking the answer to this. So is it possible that there's a carbon-nickel interaction that's different than a carbon-manganese interaction? I haven't thought about that. This might not be a good venue to be thinking out loud. John, I wonder if those unexplained experimental evidence that you saw may be related to carbon trap in some places that you have no mention and should be considered such as dislocations, twins, or other interfaces because quenching the steel before that isothermal edging, you create a high dislocation density. And I wonder if the carbon will be really comfortable on those spaces before partitioning to the austenite. Then maybe you are losing carbon in the process of carbon partitioning that cannot rule out the carbon balance that you are considering for the way of retaining the austenite at the end. And also what we have observed in carbide-free, by nitric steels is that for subsequent low temperature tempering that around the temperature that we get the epsilon carbides that you mentioned before, those dislocations segregated in carbon can be a key issue because with time and temperature, cultural atmospheres will evolve what we have seen in clusters and after that that will be the perfect nucleation site for an epsilon carbide. Then I wonder if that you investigate your dislocation densities and the carbon trap at this location, you can explain the appearance or not of epsilon carbide or more or less retaining austenite at the end in your microchurch. So that was a complicated question. But I think part of the core of that question was what's the role of carbon trapping in Q&P? And I think carbon trapping should be important and we've seen a lot of, when we have done carbon balances, we have seen instances where we're obviously not getting all the carbon out into the austenite. And if we could reach the kinds of carbon enrichments that we predict from our thermodynamics, that is if we could turn off the competing mechanisms, we could really get some interesting carbon enrichment. So carbon trapping is part of that. Although in order to study that, we've done some atom probate, to study it you also have to understand the tempering reaction and carbide precipitation. So that's all challenging and we haven't completed that kind of work yet. Yeah, according to your dictural calculation, the diffusion of carbon is still slow and the diffusion distance is limited. Is there any desirable size of retained austenite and how can we control the size of retained austenite? So, how do we control the size of the retained austenite? Maybe the size should be limited to stabilize the retained austenite. So we haven't studied experimentally ourselves yet the influence of the starting austenite grain size and morphology extensively, but I have heard that there are some people who are working on some micro-alloyed versions of quenching and partitioning where they've maybe refined the austenite and gotten some better mechanical properties. Right, the size of retained austenite between the mountain side. Right, but we really, once you make the austenite and then quench it, so then the austenite size and morphology is controlled at that point and you're moving the carbon around. Carbon moves rather fast, so you can decarbarize the martensite pretty quickly. But if you want to change the austenite size and morphology, you need to change the starting microstructure then. And at that part we haven't gotten to yet. In the medium manganese, you mentioned that the partitioning of manganese is quite critical to stabilize the retained austenite, but I think that there is also contribution from the refined grain. So what do you think about that? So what's the importance of grain refinement in those deals? So grain refinement is going to help stabilize the austenite and help increase the strength as well. So that's a critical aspect of the microstructure in those medium manganese steels that you have very fine ferrite and austenite. I agree. Thank you. Thank you. Thanks, Hank. Thank you. Thank you.
 The  next talk is by John Speer, who comes from the Colorado School of Mines, which is the  main center for Steves research in the USA.  And John Speer is one of the leaders there.  He's going to talk about the quenching partitioning process, which started, you know, fairly recently  and has taken off all over the world.  The number of papers you see and the quenching partitioning process being tried out in many  different ways is really impressive.  Thank you, Harry, for your kind introduction.  Can everyone hear me okay?  Okay.  Well, it's really a great pleasure to be here today with all of you.  And I'm going to try to talk a little, in the short time we have a little bit of science  and a little technology.  I want to acknowledge my collaborators and co-authors, David Edmonds, who's in the room  here.  Our acknowledgments were supposed to be on the first slide.  But I thought, as I thought back on the development of this concept and all the process, one  of the great pleasures, I think, was we often don't have the time or take the time to read  as much as we should.  But I did have an opportunity to read a lot of the literature from the giants, and that  was quite an enjoyable process.  I really want to acknowledge those people who have influenced probably all of us in  the room here.  And I also want to thank the many collaborators and students that have worked on this over  the years.  A little bit of background going back to the beginning.  So this quenching partitioning process was really designed as a new concept to control  retained austenite.  And the original process concept was that we interrupt a quench.  So normally you would quench austenite, perhaps to room temperature and form martensite.  But we interrupt the quench here at a temperature where the martensitic transformation is incomplete.  And the idea then is some subsequent thermal treatment either at the same temperature as  the quenching temperature that we called one step or at some different temperature or two  step, that carbon would go from the martensite into the untransformed austenite and would  therefore stabilize it so that when we then completed the quench to back down to room  temperature we would have more retained austenite.  So that's the basic concept.  We've extended that concept more recently to the case where we may have industrial processing  concepts where the partitioning process would be non-isothermal.  And if we have time at the end I might make a comment or two about that.  This is a little bit more complicated.  But for example, in hot roll sheet production you would use the run out table cooling process  to complete the partial martensitic transformation.  And then the coiling temperature where you wind the coil up would serve to control the  basically the time and temperature, the cooling profile that would define the extent of partitioning.  So these are the sort of process concepts that we're thinking about.  In the beginning we started by trying to understand what the thermodynamics would tell us about  what kind of carbon partitioning could happen and how it could affect the microstructure  and properties of the material.  And so this is some of the simple analysis from our early papers.  And again if you think about a metastable equilibrium between martensite and austenite  carbon would partition to this point in equilibrium.  In the case where we have varying non-equilibrium fractions of austenite and martensite though  if we analyze this and if the interface is immobile what would happen is the carbon would  partition until its chemical potential is uniform in the two phases.  That's why we have not a common tangent construction but a point where the tangent intercepts on  the carbon axis are the same.  And the interesting thing about this then is depending on the phase fractions we could  have multiple different conditions where the carbon potential is their equal in the phases.  And so we could have very carbon enriched austenite much more than an equilibrium or  less carbon enriched austenite.  So depending on the phase fractions we could have some interesting carbon enrichments.  And that went into the early development.  And then the next step of the process was to try to understand how we would control microstructure  and in that regard this is an important diagram from our early literature and so I want to  just walk you through it for a moment.  So if we think about quenching austenite so once the quench temperature goes below the  martensite start temperature the amount of austenite that remains is diminishing, the  amount of martensite that forms during the quenching is increasing with under cooling.  And then so we stop at that quench temperature and then we partition the carbon and most  of the carbon would like to partition back into the austenite.  And so depending on how much austenite and martensite are present that defines the amount  of carbon that can partition into the austenite.  And so this line right here tells you the carbon concentration of the austenite if the  martensite gives up all its carbon to that austenite.  And so if we have a lot of martensite and just a little bit of austenite the carbon  enrichment of that austenite is very great and diminishes with reduced martensite content  and increased austenite.  And so this tells you about the stability of the austenite at the quench temperature  after partitioning before we go through the final quench to room temperature.  And then depending on that stability this line tells you how much of that austenite  that existed after partitioning will remain after final quenching.  So this is the amount of that austenite that transforms to new martensite and so if we  subtract that from the austenite that was present at the quench temperature we get  this red line and that's the end result of this that tells us how much austenite we  could retain at room temperature.  And so this functional behavior was very important helping to guide our processing histories  as we tried to verify that this concept would work.  So we have this peak in the behavior associated with particular quenching temperatures.  And in this fairly simple model were some assumptions that are pretty important from  a physical metallurgy standpoint.  First of all that we had ideal partitioning and all the carbon would like to go into the  austenite that we've completely suppressed the precipitation of carbides or conventional  tempering reactions that the once you form the martensite during quenching that you don't  change the phase fractions anymore that is that the interface is immobile and that the  austenite doesn't decompose in other ways like bayonet formation.  So there have been these assumptions are not always correct and so they're the source  of a lot of interesting follow-up that we can do as a metallurgical community.  But still the model is very helpful to guide us.  Now this particular model that I described here was actually applied more recently in  a completely different class of steels the so-called medium manganese steels that are  very fine grained intercritically annealed materials.  So fine ferrite austenite mixtures where the austenite is really stabilized by high manganese  concentrations.  I'll just show you how this diagram was applied in that case it's basically the same kind  of behavior except in this case the ferrite austenite fraction is controlled by the annealing  temperature so the greater is the annealing temperature the more austenite we have.  And then if manganese can partition into that austenite the austenite is enriched with manganese  but it really depends on the phase fraction so the more austenite that you have the less  manganese enrichment that you have and so the less stable is that austenite in terms  of remaining at room temperature and so depending on its stability it can transform to martensite  during the final quenching.  If we again subtract this from the austenite curve we end up with this black and blue function  that tells us how much austenite would remain at room temperature.  So a very similar application of the same fundamentals to a completely different class  of steels and this is actually how it worked out so this is a 7 manganese I think 0.1 carbon  steel.  This is the predicted austenite fraction as a function of annealing temperature again  assuming full manganese partitioning between the phases this was a long annealing time  and these are the experimental data showing that this model was helpful to understand  the behavior of this other class of materials.  So it's a very exciting time in steel development now I think I'll go on the record and say  this might be one of the most exciting times for steel development ever.  In the automotive community the need for increased fuel economy is dramatic and at least in  the United States there's a tremendous need for steel development to reduce weight and  enhance vehicle performance or maintain vehicle performance.  So in terms of application of quenching and partitioning the automotive industry right  now is driving that interest in application but there are other interests in ball bearings  and high toughness plate steels so there's much opportunity that hasn't been explored  yet in quenching and partitioning.  But in the automotive industry so we saw this so-called banana diagram before where we have  this range of tensile ductilities and tensile strength for a whole variety of different  kinds of steel materials and I heard this described interestingly very recently by  Neil Suchdev of General Motors as the miracle of steel.  So we look at this somewhat mundane as experts in steel but the fact is by small variations  in composition and processing we can create this tremendous window of different steel  products with very different properties so the miracle of steel.  But we're trying to push the properties up into higher strengths and higher ductilities  so that's very challenging and yet very exciting for the community.  How are we going to get there?  So this is a simple model developed by my colleague David Matlock really looking at composite  models for predicting uniform ductility based on phase properties and you can see if we  look at combinations of ferrite and martensite we get property combinations that you would  expect that are fairly parallel to the different grades on the banana diagram so ferrite by  steels.  If instead we look at combinations of a particular stable austenite mixed with martensite we  get much better strength ductility combinations in this future need area of steels and actually  if instead of using stable austenite we can control the austenite stability I don't think  we really know how to tune the austenite stability in practice as well as we would like to but  we can we can move this curve around as well so it's a very interesting opportunity.  But in terms of how we get to the future our philosophy in automotive steel development  is pretty much we need to have retained austenite in the microstructure and so that's driving  interest in Q and P steels, in carbide free bainite steels, in medium manganese steels  as I mentioned so very exciting time.  There are a number of things on this slide that I want to mention.  First of all this is all this data is all experimental data from quenching partition  steels and some of the people who generated it are in the room here and this green, this  shaded region over here.  This represents the original target that we set out to achieve in 2003 and so we were  pretty happy that our development was fairly successful in getting us some high strength  materials with quite good ductility.  The dashed line and the solid line here are the same predicted curves that I showed on  the last slide.  So we were quite happy but what's happened in the meantime is that the property targets  keep getting more challenging.  So one of the large automotive companies in 2010 defined a target up here which is way  up in the future band of desired properties and then the next year put some targets up  here.  The United States Department of Energy has funded an integrated computational materials  engineering program with the industry and they've set some even greater targets than  the industry has set.  So when we think about how successful we are in meeting property targets we also have to  recognize that the challenge is increasing.  So the targets are moving.  I promise this is my last banana diagram for this presentation.  Our original models looked at transformation behavior and subsequent models looked incorporated  some partitioning kinetics and so these are some different models.  We can see that the ferrite gives up its carbon rather quickly.  It takes longer to equilibrate the austenite.  So what's interesting about that is under certain partitioning scenarios the austenite  might contain most of the carbon but with a non-uniform chemical composition gradient.  We get some interesting effects then when we try to understand the stability of that  austenite so we calculate it using the Køsten and Marburg equation locally but in fact we  don't know how good that assumption is.  So one of the questions for the community then is what is the stability of austenite  in the case where we have a local concentration gradient that's on the same scale as the martensite  microstructure.  These are some examples so quenching partitioning has been applied now in commercial steels.  First by Baosteel in China.  These are commercial applications.  There are other companies around the world though who I believe have a real interest  in considering this technology.  So in the few minutes that remain for my presentation I thought I'd present some curiosities, challenges  and opportunities.  We've learned a lot over the last ten years but there's still a lot of things that we  don't understand and hopefully this community will come back at some future time and help.  So here are Q&P property data.  So this is the product of tensile strength and elongation versus the amount of retained  austenite.  And so our desire was to produce high amounts of retained austenite but you can see from  this diagram that in fact the properties are not highly correlated with the fraction  of retained austenite.  So I think that we still don't completely understand what controls the work hardening  behavior and the property combinations in these steels.  We've learned a lot of partitioning mechanisms and some of the physical modelergy and the  group that leads has led us in this regard.  One of the questions is about carbide precipitation which generally speaking we don't want because  it takes carbon from the microstructure that we would otherwise use for austenite stabilization.  I'm showing a particular steel that's partitioned at two different temperatures.  In one case we get a lot of epsilon transition carbides in the microstructure and the other  case at higher temperature we get austenite stabilization.  So for the community I think one of the challenges then is how do we control the stability of  transition carbides other than perhaps temperature according to the models that we think we understand.  But if we could turn on and turn off transition carbide formation using other means then we  understand now it would be a powerful alloy design tool.  The last comment I want to make we've had a lot of discussion about whether the Martensite  austenite interface is stationary or mobile.  There's been some interesting modeling work that's been done at Delft in particular.  One of my former students Grant Thomas looked at some higher alloyed steels not intended  for commercial applications but intended to study the partitioning mechanisms.  One of the things that we looked at is the change in the austenite fraction during partitioning  in these steels where austenite you could quench to room temperature and then partition subsequently.  In a high nickel containing steel we found that the austenite fraction was stable it  did enrich in carbon.  So the assumption of a stationary interface was pretty good.  In the case of a high manganese steel though we actually increased the austenite fraction  during partitioning so clearly we think the interface was not immobile.  EBSD results so the green is the austenite phase the change from left to right is with  partitioning and you could see again nickel steel increase in austenite fraction nickel  steel approximately constant austenite fraction.  And so I mean there's pole figure diagrams really looking at what happens to the microstructure  during partitioning.  This is in the manganese steel these colors represent austenite orientations and so these  we think are probably the original austenite grain orientations confirming that we think  the austenite is growing during partitioning rather than nucleating.  But we don't completely understand why that happens in one steel and not another.  I think I'll bypass this slide and go to the conclusion.  Quenching and partitioning science and technology continues to advance.  The process has been commercialized and hopefully there will be other applications besides automotive  sheet steels and growth in those applications.  But challenges and opportunities remain both in terms of science as well as in technology.  And I end in closing here showing some Q and P microstructures.  This is one that we obtained in the laboratory intercritically annealed so we have ferrite  here.  This is actually a commercially produced Q and P steel.  And then we have a mixture of martensite and thick austenite films.  So with that I conclude my presentation and again thank you for being here.  Thank you very much John for creating one of the modern concepts of automotive steels.  Very interesting talk.  We are open for questions.  Very short question.  In fact you mentioned that bay night is something that we don't want in pistils.  But could you comment a little bit more about that?  I understand that we don't want bay night because it takes part of the carbon.  Well the viewpoint of mechanical properties I expect that maybe people should go in this  direction to sort of combining some bay night with.  Could you.  I don't remember saying that you don't want bay night.  But I think that when bay night forms from the austenite at the partitioning temperature  then you really have a mixed microstructure.  So you have a Q and P mechanism but you also have a you know austempering bay night formation  mechanism.  So you get a mixed microstructure.  And I think there are some interesting properties that people are getting in cases where they  do have those kinds of mixed microstructures.  So hybrid mechanisms.  So I think they might actually be fairly important industrially.  So yes.  Sanke is a very nice talk.  You mentioned these medium magnetic steels.  That's probably a very hot topic at the moment.  And apart from manganese what's your opinion on the range of other elements such like aluminum  or silicon?  Well I think there are some aluminum and silicon wouldn't be strong austenite stabilizers.  So you'd be looking at different concepts with those elements.  So manganese is interesting because it allows us to really increase the retained austenite  fractions to quite high levels.  There are some other interesting concepts particularly with high aluminum where aluminum  is being used to reduce the density of the steel.  So those are different concepts that are a little bit outside the scope of the design  concepts that I discussed today but are also of considerable interest right now.  Okay.  Thank you for your talk.  I have a question regarding the resource from Thomas on the high nickel and high manganese  steels in which he observes an increase in the fraction of austenite with the partitioning  step.  And I wonder if I know that at those temperatures the diffusion manganese is extremely small  but I also saw some articles from another researchers in which they think that the diffusion  of manganese is underestimated at low temperatures.  So do you think this increase in the austenite fraction can be due to some manganese partitioning  actually?  So I don't know the answer to that exactly.  This is a very low temperature to be thinking about manganese partitioning but I do agree  not necessarily in this temperature regime but actually in the temperature regime of  annealing of the medium manganese steels, so in the intercritical regime, we're getting  much more manganese partitioning than you would expect from the sort of published diffusivity  data.  So I agree that manganese diffusion seems to be much faster than we thought it was.  I don't know that that's a contributor to the temperatures that Grant Thomas was looking  at here though.  Because it's interesting when you have lower manganese levels, you don't see those or  at least we don't observe such an increase in the fraction of austenite but at those  levels it's observed so that's maybe related.  So what's happening in the nickel steel then?  Okay, well thank you.  Okay, thank you.  We have a question from the rest of the world.  Not from the Netherlands, they have a question.  The question is if the intercritical annealing temperature has been done in say 800 to 900,  is it possible for the manganese to partition in say 100 seconds?  That's the question.  So are we talking about a medium manganese steel?  I guess so.  So I guess it doesn't really matter.  But I think there's some data in the recent literature that shows that you can get significant  manganese partitioning at intercritical temperatures in relatively short times.  Another question from AK Steel.  Is it possible for manganese carbon interaction is different compared to carbon interaction  to nickel effect these?  So this author is actually at AK Steel.  So I'm not asking the answer to this.  So is it possible that there's a carbon-nickel interaction that's different than a carbon-manganese  interaction?  I haven't thought about that.  This might not be a good venue to be thinking out loud.  John, I wonder if those unexplained experimental evidence that you saw may be related to carbon  trap in some places that you have no mention and should be considered such as dislocations,  twins, or other interfaces because quenching the steel before that isothermal edging, you  create a high dislocation density.  And I wonder if the carbon will be really comfortable on those spaces before partitioning  to the austenite.  Then maybe you are losing carbon in the process of carbon partitioning that cannot rule out  the carbon balance that you are considering for the way of retaining the austenite at  the end.  And also what we have observed in carbide-free, by nitric steels is that for subsequent low  temperature tempering that around the temperature that we get the epsilon carbides that you  mentioned before, those dislocations segregated in carbon can be a key issue because with  time and temperature, cultural atmospheres will evolve what we have seen in clusters  and after that that will be the perfect nucleation site for an epsilon carbide.  Then I wonder if that you investigate your dislocation densities and the carbon trap  at this location, you can explain the appearance or not of epsilon carbide or more or less  retaining austenite at the end in your microchurch.  So that was a complicated question.  But I think part of the core of that question was what's the role of carbon trapping in  Q&P?  And I think carbon trapping should be important and we've seen a lot of, when we have done  carbon balances, we have seen instances where we're obviously not getting all the carbon  out into the austenite.  And if we could reach the kinds of carbon enrichments that we predict from our thermodynamics,  that is if we could turn off the competing mechanisms, we could really get some interesting  carbon enrichment.  So carbon trapping is part of that.  Although in order to study that, we've done some atom probate, to study it you also have  to understand the tempering reaction and carbide precipitation.  So that's all challenging and we haven't completed that kind of work yet.  Yeah, according to your dictural calculation, the diffusion of carbon is still slow and  the diffusion distance is limited.  Is there any desirable size of retained austenite and how can we control the size of retained  austenite?  So, how do we control the size of the retained austenite?  Maybe the size should be limited to stabilize the retained austenite.  So we haven't studied experimentally ourselves yet the influence of the starting austenite  grain size and morphology extensively, but I have heard that there are some people who  are working on some micro-alloyed versions of quenching and partitioning where they've  maybe refined the austenite and gotten some better mechanical properties.  Right, the size of retained austenite between the mountain side.  Right, but we really, once you make the austenite and then quench it, so then the austenite  size and morphology is controlled at that point and you're moving the carbon around.  Carbon moves rather fast, so you can decarbarize the martensite pretty quickly.  But if you want to change the austenite size and morphology, you need to change the starting  microstructure then.  And at that part we haven't gotten to yet.  In the medium manganese, you mentioned that the partitioning of manganese is quite critical  to stabilize the retained austenite, but I think that there is also contribution from  the refined grain.  So what do you think about that?  So what's the importance of grain refinement in those deals?  So grain refinement is going to help stabilize the austenite and help increase the strength  as well.  So that's a critical aspect of the microstructure in those medium manganese steels that you  have very fine ferrite and austenite.  I agree.  Thank you.  Thank you.  Thanks, Hank.  Thank you.  Thank you.
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The next talk is by John Speer, who comes from the Colorado School of Mines, which is the main center for Steves research in the USA. And John Speer is one of the leaders there. He's going to talk about the quenching partitioning process, which started, you know, fairly recently and has taken off all over the world. The number of papers you see and the quenching partitioning process being tried out in many different ways is really impressive. Thank you, Harry, for your kind introduction. Can everyone hear me okay? Okay. Well, it's really a great pleasure to be here today with all of you. And I'm going to try to talk a little, in the short time we have a little bit of science and a little technology. I want to acknowledge my collaborators and co-authors, David Edmonds, who's in the room here. Our acknowledgments were supposed to be on the first slide. But I thought, as I thought back on the development of this concept and all the process, one of the great pleasures, I think, was we often don't have the time or take the time to read as much as we should. But I did have an opportunity to read a lot of the literature from the giants, and that was quite an enjoyable process. I really want to acknowledge those people who have influenced probably all of us in the room here. And I also want to thank the many collaborators and students that have worked on this over the years. A little bit of background going back to the beginning. So this quenching partitioning process was really designed as a new concept to control retained austenite. And the original process concept was that we interrupt a quench. So normally you would quench austenite, perhaps to room temperature and form martensite. But we interrupt the quench here at a temperature where the martensitic transformation is incomplete. And the idea then is some subsequent thermal treatment either at the same temperature as the quenching temperature that we called one step or at some different temperature or two step, that carbon would go from the martensite into the untransformed austenite and would therefore stabilize it so that when we then completed the quench to back down to room temperature we would have more retained austenite. So that's the basic concept. We've extended that concept more recently to the case where we may have industrial processing concepts where the partitioning process would be non-isothermal. And if we have time at the end I might make a comment or two about that. This is a little bit more complicated. But for example, in hot roll sheet production you would use the run out table cooling process to complete the partial martensitic transformation. And then the coiling temperature where you wind the coil up would serve to control the basically the time and temperature, the cooling profile that would define the extent of partitioning. So these are the sort of process concepts that we're thinking about. In the beginning we started by trying to understand what the thermodynamics would tell us about what kind of carbon partitioning could happen and how it could affect the microstructure and properties of the material. And so this is some of the simple analysis from our early papers. And again if you think about a metastable equilibrium between martensite and austenite carbon would partition to this point in equilibrium. In the case where we have varying non-equilibrium fractions of austenite and martensite though if we analyze this and if the interface is immobile what would happen is the carbon would partition until its chemical potential is uniform in the two phases. That's why we have not a common tangent construction but a point where the tangent intercepts on the carbon axis are the same. And the interesting thing about this then is depending on the phase fractions we could have multiple different conditions where the carbon potential is their equal in the phases. And so we could have very carbon enriched austenite much more than an equilibrium or less carbon enriched austenite. So depending on the phase fractions we could have some interesting carbon enrichments. And that went into the early development. And then the next step of the process was to try to understand how we would control microstructure and in that regard this is an important diagram from our early literature and so I want to just walk you through it for a moment. So if we think about quenching austenite so once the quench temperature goes below the martensite start temperature the amount of austenite that remains is diminishing, the amount of martensite that forms during the quenching is increasing with under cooling. And then so we stop at that quench temperature and then we partition the carbon and most of the carbon would like to partition back into the austenite. And so depending on how much austenite and martensite are present that defines the amount of carbon that can partition into the austenite. And so this line right here tells you the carbon concentration of the austenite if the martensite gives up all its carbon to that austenite. And so if we have a lot of martensite and just a little bit of austenite the carbon enrichment of that austenite is very great and diminishes with reduced martensite content and increased austenite. And so this tells you about the stability of the austenite at the quench temperature after partitioning before we go through the final quench to room temperature. And then depending on that stability this line tells you how much of that austenite that existed after partitioning will remain after final quenching. So this is the amount of that austenite that transforms to new martensite and so if we subtract that from the austenite that was present at the quench temperature we get this red line and that's the end result of this that tells us how much austenite we could retain at room temperature. And so this functional behavior was very important helping to guide our processing histories as we tried to verify that this concept would work. So we have this peak in the behavior associated with particular quenching temperatures. And in this fairly simple model were some assumptions that are pretty important from a physical metallurgy standpoint. First of all that we had ideal partitioning and all the carbon would like to go into the austenite that we've completely suppressed the precipitation of carbides or conventional tempering reactions that the once you form the martensite during quenching that you don't change the phase fractions anymore that is that the interface is immobile and that the austenite doesn't decompose in other ways like bayonet formation. So there have been these assumptions are not always correct and so they're the source of a lot of interesting follow-up that we can do as a metallurgical community. But still the model is very helpful to guide us. Now this particular model that I described here was actually applied more recently in a completely different class of steels the so-called medium manganese steels that are very fine grained intercritically annealed materials. So fine ferrite austenite mixtures where the austenite is really stabilized by high manganese concentrations. I'll just show you how this diagram was applied in that case it's basically the same kind of behavior except in this case the ferrite austenite fraction is controlled by the annealing temperature so the greater is the annealing temperature the more austenite we have. And then if manganese can partition into that austenite the austenite is enriched with manganese but it really depends on the phase fraction so the more austenite that you have the less manganese enrichment that you have and so the less stable is that austenite in terms of remaining at room temperature and so depending on its stability it can transform to martensite during the final quenching. If we again subtract this from the austenite curve we end up with this black and blue function that tells us how much austenite would remain at room temperature. So a very similar application of the same fundamentals to a completely different class of steels and this is actually how it worked out so this is a 7 manganese I think 0.1 carbon steel. This is the predicted austenite fraction as a function of annealing temperature again assuming full manganese partitioning between the phases this was a long annealing time and these are the experimental data showing that this model was helpful to understand the behavior of this other class of materials. So it's a very exciting time in steel development now I think I'll go on the record and say this might be one of the most exciting times for steel development ever. In the automotive community the need for increased fuel economy is dramatic and at least in the United States there's a tremendous need for steel development to reduce weight and enhance vehicle performance or maintain vehicle performance. So in terms of application of quenching and partitioning the automotive industry right now is driving that interest in application but there are other interests in ball bearings and high toughness plate steels so there's much opportunity that hasn't been explored yet in quenching and partitioning. But in the automotive industry so we saw this so-called banana diagram before where we have this range of tensile ductilities and tensile strength for a whole variety of different kinds of steel materials and I heard this described interestingly very recently by Neil Suchdev of General Motors as the miracle of steel. So we look at this somewhat mundane as experts in steel but the fact is by small variations in composition and processing we can create this tremendous window of different steel products with very different properties so the miracle of steel. But we're trying to push the properties up into higher strengths and higher ductilities so that's very challenging and yet very exciting for the community. How are we going to get there? So this is a simple model developed by my colleague David Matlock really looking at composite models for predicting uniform ductility based on phase properties and you can see if we look at combinations of ferrite and martensite we get property combinations that you would expect that are fairly parallel to the different grades on the banana diagram so ferrite by steels. If instead we look at combinations of a particular stable austenite mixed with martensite we get much better strength ductility combinations in this future need area of steels and actually if instead of using stable austenite we can control the austenite stability I don't think we really know how to tune the austenite stability in practice as well as we would like to but we can we can move this curve around as well so it's a very interesting opportunity. But in terms of how we get to the future our philosophy in automotive steel development is pretty much we need to have retained austenite in the microstructure and so that's driving interest in Q and P steels, in carbide free bainite steels, in medium manganese steels as I mentioned so very exciting time. There are a number of things on this slide that I want to mention. First of all this is all this data is all experimental data from quenching partition steels and some of the people who generated it are in the room here and this green, this shaded region over here. This represents the original target that we set out to achieve in 2003 and so we were pretty happy that our development was fairly successful in getting us some high strength materials with quite good ductility. The dashed line and the solid line here are the same predicted curves that I showed on the last slide. So we were quite happy but what's happened in the meantime is that the property targets keep getting more challenging. So one of the large automotive companies in 2010 defined a target up here which is way up in the future band of desired properties and then the next year put some targets up here. The United States Department of Energy has funded an integrated computational materials engineering program with the industry and they've set some even greater targets than the industry has set. So when we think about how successful we are in meeting property targets we also have to recognize that the challenge is increasing. So the targets are moving. I promise this is my last banana diagram for this presentation. Our original models looked at transformation behavior and subsequent models looked incorporated some partitioning kinetics and so these are some different models. We can see that the ferrite gives up its carbon rather quickly. It takes longer to equilibrate the austenite. So what's interesting about that is under certain partitioning scenarios the austenite might contain most of the carbon but with a non-uniform chemical composition gradient. We get some interesting effects then when we try to understand the stability of that austenite so we calculate it using the Køsten and Marburg equation locally but in fact we don't know how good that assumption is. So one of the questions for the community then is what is the stability of austenite in the case where we have a local concentration gradient that's on the same scale as the martensite microstructure. These are some examples so quenching partitioning has been applied now in commercial steels. First by Baosteel in China. These are commercial applications. There are other companies around the world though who I believe have a real interest in considering this technology. So in the few minutes that remain for my presentation I thought I'd present some curiosities, challenges and opportunities. We've learned a lot over the last ten years but there's still a lot of things that we don't understand and hopefully this community will come back at some future time and help. So here are Q&P property data. So this is the product of tensile strength and elongation versus the amount of retained austenite. And so our desire was to produce high amounts of retained austenite but you can see from this diagram that in fact the properties are not highly correlated with the fraction of retained austenite. So I think that we still don't completely understand what controls the work hardening behavior and the property combinations in these steels. We've learned a lot of partitioning mechanisms and some of the physical modelergy and the group that leads has led us in this regard. One of the questions is about carbide precipitation which generally speaking we don't want because it takes carbon from the microstructure that we would otherwise use for austenite stabilization. I'm showing a particular steel that's partitioned at two different temperatures. In one case we get a lot of epsilon transition carbides in the microstructure and the other case at higher temperature we get austenite stabilization. So for the community I think one of the challenges then is how do we control the stability of transition carbides other than perhaps temperature according to the models that we think we understand. But if we could turn on and turn off transition carbide formation using other means then we understand now it would be a powerful alloy design tool. The last comment I want to make we've had a lot of discussion about whether the Martensite austenite interface is stationary or mobile. There's been some interesting modeling work that's been done at Delft in particular. One of my former students Grant Thomas looked at some higher alloyed steels not intended for commercial applications but intended to study the partitioning mechanisms. One of the things that we looked at is the change in the austenite fraction during partitioning in these steels where austenite you could quench to room temperature and then partition subsequently. In a high nickel containing steel we found that the austenite fraction was stable it did enrich in carbon. So the assumption of a stationary interface was pretty good. In the case of a high manganese steel though we actually increased the austenite fraction during partitioning so clearly we think the interface was not immobile. EBSD results so the green is the austenite phase the change from left to right is with partitioning and you could see again nickel steel increase in austenite fraction nickel steel approximately constant austenite fraction. And so I mean there's pole figure diagrams really looking at what happens to the microstructure during partitioning. This is in the manganese steel these colors represent austenite orientations and so these we think are probably the original austenite grain orientations confirming that we think the austenite is growing during partitioning rather than nucleating. But we don't completely understand why that happens in one steel and not another. I think I'll bypass this slide and go to the conclusion. Quenching and partitioning science and technology continues to advance. The process has been commercialized and hopefully there will be other applications besides automotive sheet steels and growth in those applications. But challenges and opportunities remain both in terms of science as well as in technology. And I end in closing here showing some Q and P microstructures. This is one that we obtained in the laboratory intercritically annealed so we have ferrite here. This is actually a commercially produced Q and P steel. And then we have a mixture of martensite and thick austenite films. So with that I conclude my presentation and again thank you for being here. Thank you very much John for creating one of the modern concepts of automotive steels. Very interesting talk. We are open for questions. Very short question. In fact you mentioned that bay night is something that we don't want in pistils. But could you comment a little bit more about that? I understand that we don't want bay night because it takes part of the carbon. Well the viewpoint of mechanical properties I expect that maybe people should go in this direction to sort of combining some bay night with. Could you. I don't remember saying that you don't want bay night. But I think that when bay night forms from the austenite at the partitioning temperature then you really have a mixed microstructure. So you have a Q and P mechanism but you also have a you know austempering bay night formation mechanism. So you get a mixed microstructure. And I think there are some interesting properties that people are getting in cases where they do have those kinds of mixed microstructures. So hybrid mechanisms. So I think they might actually be fairly important industrially. So yes. Sanke is a very nice talk. You mentioned these medium magnetic steels. That's probably a very hot topic at the moment. And apart from manganese what's your opinion on the range of other elements such like aluminum or silicon? Well I think there are some aluminum and silicon wouldn't be strong austenite stabilizers. So you'd be looking at different concepts with those elements. So manganese is interesting because it allows us to really increase the retained austenite fractions to quite high levels. There are some other interesting concepts particularly with high aluminum where aluminum is being used to reduce the density of the steel. So those are different concepts that are a little bit outside the scope of the design concepts that I discussed today but are also of considerable interest right now. Okay. Thank you for your talk. I have a question regarding the resource from Thomas on the high nickel and high manganese steels in which he observes an increase in the fraction of austenite with the partitioning step. And I wonder if I know that at those temperatures the diffusion manganese is extremely small but I also saw some articles from another researchers in which they think that the diffusion of manganese is underestimated at low temperatures. So do you think this increase in the austenite fraction can be due to some manganese partitioning actually? So I don't know the answer to that exactly. This is a very low temperature to be thinking about manganese partitioning but I do agree not necessarily in this temperature regime but actually in the temperature regime of annealing of the medium manganese steels, so in the intercritical regime, we're getting much more manganese partitioning than you would expect from the sort of published diffusivity data. So I agree that manganese diffusion seems to be much faster than we thought it was. I don't know that that's a contributor to the temperatures that Grant Thomas was looking at here though. Because it's interesting when you have lower manganese levels, you don't see those or at least we don't observe such an increase in the fraction of austenite but at those levels it's observed so that's maybe related. So what's happening in the nickel steel then? Okay, well thank you. Okay, thank you. We have a question from the rest of the world. Not from the Netherlands, they have a question. The question is if the intercritical annealing temperature has been done in say 800 to 900, is it possible for the manganese to partition in say 100 seconds? That's the question. So are we talking about a medium manganese steel? I guess so. So I guess it doesn't really matter. But I think there's some data in the recent literature that shows that you can get significant manganese partitioning at intercritical temperatures in relatively short times. Another question from AK Steel. Is it possible for manganese carbon interaction is different compared to carbon interaction to nickel effect these? So this author is actually at AK Steel. So I'm not asking the answer to this. So is it possible that there's a carbon-nickel interaction that's different than a carbon-manganese interaction? I haven't thought about that. This might not be a good venue to be thinking out loud. John, I wonder if those unexplained experimental evidence that you saw may be related to carbon trap in some places that you have no mention and should be considered such as dislocations, twins, or other interfaces because quenching the steel before that isothermal edging, you create a high dislocation density. And I wonder if the carbon will be really comfortable on those spaces before partitioning to the austenite. Then maybe you are losing carbon in the process of carbon partitioning that cannot rule out the carbon balance that you are considering for the way of retaining the austenite at the end. And also what we have observed in carbide-free, by nitric steels is that for subsequent low temperature tempering that around the temperature that we get the epsilon carbides that you mentioned before, those dislocations segregated in carbon can be a key issue because with time and temperature, cultural atmospheres will evolve what we have seen in clusters and after that that will be the perfect nucleation site for an epsilon carbide. Then I wonder if that you investigate your dislocation densities and the carbon trap at this location, you can explain the appearance or not of epsilon carbide or more or less retaining austenite at the end in your microchurch. So that was a complicated question. But I think part of the core of that question was what's the role of carbon trapping in Q&P? And I think carbon trapping should be important and we've seen a lot of, when we have done carbon balances, we have seen instances where we're obviously not getting all the carbon out into the austenite. And if we could reach the kinds of carbon enrichments that we predict from our thermodynamics, that is if we could turn off the competing mechanisms, we could really get some interesting carbon enrichment. So carbon trapping is part of that. Although in order to study that, we've done some atom probate, to study it you also have to understand the tempering reaction and carbide precipitation. So that's all challenging and we haven't completed that kind of work yet. Yeah, according to your dictural calculation, the diffusion of carbon is still slow and the diffusion distance is limited. Is there any desirable size of retained austenite and how can we control the size of retained austenite? So, how do we control the size of the retained austenite? Maybe the size should be limited to stabilize the retained austenite. So we haven't studied experimentally ourselves yet the influence of the starting austenite grain size and morphology extensively, but I have heard that there are some people who are working on some micro-alloyed versions of quenching and partitioning where they've maybe refined the austenite and gotten some better mechanical properties. Right, the size of retained austenite between the mountain side. Right, but we really, once you make the austenite and then quench it, so then the austenite size and morphology is controlled at that point and you're moving the carbon around. Carbon moves rather fast, so you can decarbarize the martensite pretty quickly. But if you want to change the austenite size and morphology, you need to change the starting microstructure then. And at that part we haven't gotten to yet. In the medium manganese, you mentioned that the partitioning of manganese is quite critical to stabilize the retained austenite, but I think that there is also contribution from the refined grain. So what do you think about that? So what's the importance of grain refinement in those deals? So grain refinement is going to help stabilize the austenite and help increase the strength as well. So that's a critical aspect of the microstructure in those medium manganese steels that you have very fine ferrite and austenite. I agree. Thank you. Thank you. Thanks, Hank. Thank you. Thank you.
The next talk is by John Speer, who comes from talk about the quenching partitioning process, on the development of this concept and all the partitioning process was really designed as a new non-equilibrium fractions of austenite and the amount of carbon that can partition into the diminishes with reduced martensite content and the stability of the austenite at the quench from a physical metallurgy standpoint. First of like bayonet formation. So there have been these development to reduce weight and enhance vehicle opportunity that hasn't been explored yet in quenching and partitioning. But in the automotive variety of different kinds of steel materials and microstructure and so that's driving interest in from quenching partition steels and some of the banana diagram for this presentation. Our examples so quenching partitioning has been applied now in commercial steels. First by hopefully there will be other applications besides automotive sheet steels and growth in the austenite at the partitioning temperature really increase the retained austenite fractions observes an increase in the fraction of austenite as dislocations, twins, or other interfaces losing carbon in the process of carbon mechanical properties. Right, the size of