Secondary-hardened bainite
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Yang, Jer-Ren
A lecture given by Jer Ren Yang, at the Adventures in the Physical Metallurgy of Steels (APMS) conference held in Cambridge University. The metallurgy of a new, microalloyed bainitic steel that is capable of secondary hardening, accompanied by a simultaneous increase in strength and ductility is introduced. Ideally, a low carbon bainitic microstructure offers an excellent combination of good toughness, strength and weldability. The typical microstructure of low-carbon bainitic steels is composed of a fine substructured bainitic ferrite matrix with certain amounts of uniformly distributed carbon-rich second phases. These second phases, located among the sheaves of bainitc ferrite, consist basically of martensite/austenite (M/A) constituents. As a result of the low-angle character of boundaries of bainitic ferrite sub-unit within the sheaf structure, little or no evidence of ferrite boundaries could be detected by an optical microscope. It is worth further improving appreciation of the transformation and to evaluate the effect of substructure characteristics on the properties. The main purpose of this work was to investigate the effect of Mo addition on the development of microstructure in the hot-rolled low-carbon Nb-containing bainitic steels. The steel strips were fabricated by the combined processes of controlled-rolling and accelerated-cooling. Microstructural characterisation and mechanical testing for the corresponding strips have been investigated. The results show that the Mo addition has the advantage of producing a high volume fraction of bainite, which possesses a significant secondary hardening after tempering treatment. It is suggested that the secondary hardening effect provides an additional way to increase the strength of Nb-Mo-containing bainitic steels.
 The next talk is by Professor JR Yang. He's a leader of steel research in Taiwan as a whole and really does an enormous amount of work on steel both through the CBMM Center that he has created over there and in the whole of the Department of Materials which he led for many many years. So yeah. Ladies and gentlemen, first of all I would like to send Harry the team of APS for such wonderful organization so that I can meet you here. And Harry gave me this topic and I feel very satisfied because it's good to understand very very special phenomena. In fact secondary hardening commonly happen in many sites of steel containing high strong carbon element like chlorine, vanadium, nubbin and moly. And here I would like to report to you emphasize that secondary hardening also happen in low carbon benefit steel. So let's look at how to produce low carbon benefit steel through careful chemical alloying addition and also we need control the rolling and also a saturated cooling. We can get high quantities of benign easily in low carbon steel and ideally the low carbon benefit steel provide high toughness and high strength and of course good weldability. So we expected this steel is quite useful for automobile application and that's my subject because we have a cooperation with the CBMM company and CBMM company always push us to do the research related with steel application for automobile. And here I would like to show you the typical micro structure of low carbon benefit steel from our research result. In fact people always said always said it's a granular band line and then when we check Harry's book we know Harry has has written a beautiful review for granular band line and from that I knew that there's a paper published in 1950 by Harprican. Is that right? Yes sir. And he said the coast favorite place look like granular. But I would like to raise question here. Can this terminology granular band line signify the exact structure? Can anybody answer me? Can anybody answer me? Of course we need TEM to clarify the detail micro structure so I will give you the answer now. So we should consider the terminology of granular band line. It's long but in this talk I will keep this terminology because it's quite convenient to communicate with the people. So here we can see the subunit Benedict Ferrara here and the thickness about 200 nanometer so it's so thin and also the subunit with the same orientation so the coast Ferrara prey in fact is composed the favorite subunit and because the subunit with the same orientation and we couldn't distinguish the detail. And in my research we would like to develop the low carbon Benet steel and the China steel has prepared three steel for us and for the for these three steel we have the same composed base composed. I would like to show it here. The best composition is 0.05 carbon and magnet 1.7 magnet and niobin 0.08. Best chemical composition. For the steel one the niobin we label niobin steel because it's without morning and for the steel two with 0.1 morning and we label this year niobin morning steel. For the third steel we have 0.1 percent morning and we label this year niobin three morning. China steel prepared this three steel for us and cast into an ingot and after homogenization at 1200 degrees C for two hours the steel the ingot were hot loaded and by control low the rolling rate about 20 percent per pass and the finish loading temperature around 900 degrees C and here we can have a 5 millimeter thick strip so the reduction rate is quite high so we can imagine the grand refine also happen here. And after finish loading the strip were treated by a serrated cooling to 650 degrees C or 550 degrees C or 450 degrees C for 10 minutes for fan line transformation. So here we can have seven strip at room temperature. I would like to emphasize here because we will look at the micro charger level. Niobin 650 and that's get from the isosomal transformation at 650 degrees C and niobin morning 650 and also we have niobin 550 niobin morning 550 and niobin 455 niobin morning 455 and niobin 3455 we have seven strips. These strips were receded at 600 degrees C for different time interval from 0.5 to 8 hour to investigate whether the second didn't happen. I think the metrology data is very important. We need that because we would like to correlate it to the property. Here I would like to show you the typical structure of the so-called grand unit band line and we can see this is MA, it's martensite austenite, and it's quite easy to distinguish from MA and degenerated peri from the morphology. And here is a look at the grand unit structure, it's a grand unit band line and here is a ferrite. In fact it's very difficult to distinguish between the grand unit band line and allotmophic ferrite. So we try our every effort to distinguish. First we can see the use weaker hardness to distinguish and second we try to eat EBSD can be to distinguish. And this is our result here. This SEM for Nalbin 450 strip we have 25, 40% of the tome ferrite and 63, granular band line and 9% martensite austenite phases and 3% degenerate peri. And indeed it's very very important to have this quantitative data in order to understand the mechanical behavior. Here I would like to show you the EBS technique to understand this technique how to use it to distinguish ferrite and band line. Here is an example to show you the misorientation measurement between the subunit in granular band line. This is sub-ran A and we can get kikuchi pattern here and this is sub-ran B we can get kikuchi pattern here and in fact through the soil oil we can easily get the misorientation angle. But precisely we try to describe the misorientation by a 6 angle pair. So from the sub-ran A we can have Euler angle here and from the sub-ran B we can have Euler angle here but in fact we have reference crystal so we can get the sub-ran A relative to the reference crystal orientation matrix. And also we can get sub-ran B relative to the reference crystal so we can have these two basic orientation relationship. And then we can get the sub-ran A and sub-ran B notation matrix. So here I would like to show you the commercial data always show us this angle. Why? Because we have 24 axis angle pair and the commercial data always choose the lowest angle so when we use this software we must consider how the software engineering has done for us because we should understand the crystal-crystallic-of-meaning and in fact by using the the minima angle is quite easy to interpret but we should understand the physical meaning. Here I would like to show you two examples. For the BAN line we can have the distributive misorientation angle something like this and we have two pick here this is low angle and this is angle for 60 degrees C maybe somebody understand why it located at 60 degrees C 60 degree and for the fair right we can see the misorientation angle always a high angle so from the intensity here is very easily to distinguish BAN line and fair right region. So based on this concept and technique we quantitatively estimate the data for the strip. Nioven 450 strip and Nioven morey 450 strip. Here we consider 18 0.1 morey we can have a higher high the bitty of BAN line so the gradient of BAN line from 60 3 percent, volume percent increase to 66 percent and the fair right decrease from 25 volume percent to 14 percent so the multi addition effect is quite significant. On the other hand we can check this Nioven 550 strip and Nioven morey 550 by 18 0.1 morey we can see 0 gradient of BAN line increase to 62 gradient of BAN line. Here now the 5D strip contain 87 volume percent fair right and here is 16 volume percent fair right so basically the structure a completely different so it's very important thing we study the mechanical property we always to wish get the metacor the quantitative data in order to understand what's the mechanical behavior so that we can control the microstructure and the mechanical behavior we have both. Here I would like to show you the strength curve for the Nioven morey 550 strip and for the Nioven morey 450 strip because the structure are very similar you can see granular BAN line 62 66 or Tommi favorite 16 14 and MA 21 19 and 1 percent degenerate and 1 percent degenerate so you can see the curve look very similar and for this to strip Nioven 550 and Nioven 455 we can see this Nioven 550 contain 0 BAN line and this curve show there's a sharp ear point here because 87 percent morey in this in this steel and as to Nioven 455 we can see there is a Plato slightly Plato here because this steel contains 25 or Tommi favorite and let's compare Nioven 550 and Nioven morey 50 after template for different type interval this strip contain 0 granular BAN line so they there is no secondary hardening can be detected however for Nioven morey 550 we can see after one hour the hardening raises up quickly and there's a very strong peak occur on the after 10 after two hour temporary here also we show Nioven morey 455 Nioven 450 contain granular BAN line 66 percent and here 63 percent and we have we can detect it the second hardening after one hour temporary at 600 degree C and let's look at these two strength sake curve here okay and this curve show Nioven 65 without granular BAN line and this curve contain Nioven 63 granular BAN line and after 10 minutes one hour we expected this curve will raise up I can show you quickly here so it's quite significant the second it's hardening occurred in bay native favorite and the the micro search development seems very important so I would like to show you the the data quickly sorry okay since something wrong these two they are we couldn't couldn't show so I don't know the reason but here I would like to show you from the EBSD we can show the peak is quite significant for the now be in three morning morning because they are not a very new Bella and also we study the dislocation density for my bin 450 my bin morning 450 and my bin stream 450 and after 10 be one hour and and eight hour we can see that is okay basic doesn't change so it means the structure the structure property the disorganic structure property is quite stable for this alloy and also we use high resource 10 tm to observe the carbide and we can see the carbide always precipitate on the dislocation and it's very very tiny and the carbide always with the MC structure and this is Baker and knocking orientation relationship and also for now be more is still we can see the MC car back and Baker and new team orientation relationship and here we show the dark field image because of the car by its very tiny and we would like to observe the car by density and we try to use a traditional darkwood to observe the density and in fact the car is very very tiny and from the high ocean tm we measure the size of car by and the number of car by we we measured about 300 particle and we can see the car by size keeps very very small for now being and I'll be more steel and from the from EBSD at EBSD network we also would like to observe the chemistry for the car by and here is the data and for Cambrian at 600 degrees C for eight hour the now be my more atomic ratio is about 1.8 for example and for now be three more for 55 and the atomic ratio about one over one and finally I would like to show you the data quickly and here is quite safe naked we can have the signal hardly after a short time temporary and in fact for in that application we should consider the eos chance and tensile chance and also elongation so after one hour temporary you can see the eos chance and tensile chance increase and also the elongation also increase so it's very good to use this material for in that application because if we if we can choose the proper proper the processing and after benign forming and we hit it just for a short time and the strength and elongation both increase finally I would like to give a brief conclusion in my in our low carbon now be kind and steel and we find the Molly addition as a addition has a advantage of produce high ball interaction or granny or benign and it's good for second-term in housing during tempering and I think it's very important for industrial application and especially consider the low carbon and lower steel thank you for your attention excellent lecture thank you what is remarkable is the stability yes the structure yes and even with tempering at 600 you maintain the strength the dislocation density yes and increase ductility yes yes so the idea would be that the 600 degrees C happens during coiling yes exactly you have a lot of MAEC also so is it carbides are forming in granular brayland or in those MAEC how would you differentiate this okay it's way easy because we can we can see in the band-line region we can see the subunit as I show you and it's a sub-grand and it's completely different from the MAEF as a stereo so even after tempering also even after tempering also because tempered modern side would look the similar also okay tempering modern side always give you coarse carbide always gives you coarse carbide we can discuss later why did you use for example niobium and molybdemon and what about vanadium which is known is very effective as for hardening for example in high-speed steels okay and the second question is why did you use for example only tempering at the temperature of 600 degrees okay thank you very much yes for this alarming design in fact we we should keep we should have high mode inflation of bed so how to get high mode inflation of bed and I think the now be in a moly pay an important low what a hardening of bed so in this work we we add now being the label is 0.08 percent that's the reason we use my working instead of because we would like to increase the 150 of them and your second question is okay in fact because because of the time limited I couldn't show my result for 500 degrees C and 550 and 650 but I choose the best one 600 we have question from David Haudhig he asked in experiment procedure okay you refer the AC egg ruling the set egg ruling from a five mil thick strip or commercial simulation after I saw so much transformation at they say 450 degree C and the core the strip cool natural cool to room temperature we suppose the 10 I already there already there so we don't need to use fast cooling at the final stage is that okay and another question from Suje you say something about niobium increase the other bleedy yes and you form a granular pay night yes and how do you separate the ferrite and granular pay night that's that's the question okay because it's a low carbon steel so it's very difficult to get completely complete very nice structure so we always have us we also have some favorite so there's a reason we need a separate to the cool and also we need micro-aluminum addition so that parameter is very important for us so we just trying to prepare this material but in the question is saying how do you distinguish the ferrite from the bay night I think you answered it in your presentation this way is very easy just by because how we can distinguish because happens it's very easy and also through EBSC we can distinguish EBSC someone should comment on the fact that niobium and molybdenum dissolve in the same carbide whereas we know that doesn't happen with titanium and molybdenum do we know whether molybdenum should be soluble in niobium carbide yes I know it because we used for example niobium in high speed steels and complex carbides are performed which contains for example both the elements when you when we did the first for this calculation on the name of carbide with molybdenum and the energetically this not favorable for the name of carbide to contain the molybdenum in the molybdenum titanium molybdenum we found that the some addition of the moly molybdenum in the titanium carbide will relax to the strain energy interface strainage between the ferrite and titanium carbide but it is not clear that the same mechanism control the molybdenum accommodation in the niobium carbide. So I think you know the chemical analysis here is quite interesting of the carbide and very clear your microscopy and time for analysis. In fact this results no good because we need 3D data to understand if we just use it that's a problem we couldn't detect the exact composition for this carbide right because some carbide we always we can see some co-share structure. But there's no doubt that you get both peaks. My question is because we just temper for one hour and we can increase the stress and also increase the elongation right so we suppose the niobium the natal carbide precipitation occurs in the short term. How much niobium you have already precipitated before tempering and how effective is niobium that participate in secondary hardening. Okay I think that's a very very good question. We need very good data to perform this research in the near future. Not now because I get the specimen from industry and we need theoretical work so we need very good data to perform this experiment. We couldn't get you answer at this moment. Short question first thanks for excellent talk and it's a very difficult story that you show here how to characterize the microstructure. In fact I have questions about EBSD data. You separate between ferrite and bainite here and you use misorientation profiles. Well have you ever tried to to use not misorientation profiles but kernel average misorientation of some other type of maps in EBSD as far as both structural constituents they have different dislocation density probably better revealed there. Different criteria because yeah or there's a recent version of some software you could use even kernel map on the image quality so do you have some some experience with that. Okay I think the chemicality is a good way and also we should consider the digital space safety effect. However I think there are several measures we can we can consider which one is the best one and in fact we have used image quality to distinguish the MA faces it's quite easy because it becomes dark. And basically we know the bainite with the high digital band density so some people we can see the image quality but in fact we still can see in our results so we basically I suppose the step size is very important. In fact or this granular bainite the auto-minefair is huge much bigger than the bainite stability so so so we can distinguish it easy. I'd like to confirm that we've also we've also measured that I'm in a number of niobium carbides. Your your presentation showed very clearly that you have secondary hardening at 600 degrees and I guess that's probably the peak of the hardening. My question is what about carbide formation strengthening carbide formation in the bainitic microstructure itself. So it's obviously incomplete because you can you can increase the strength by a secondary heat treatment but can you tell us anything about the extent of precipitation during or after the bainitic transformation itself in the primary cooling stage. Okay that's that's really a very good question because we have compared both microstructure and we suppose there's a little bit difference. Also we can use a weaker hardening to test first so compare with weaker hardening. We can see the clear difference. Okay okay I think that Rocky answers your question because we have to go for lunch. Yeah the college. Yeah here is the answer. So just compare the bigger sign for the original one and the temporal one. Yeah thank you very very much. Really glad to hear that.
 The  next talk is by Professor JR Yang. He's a leader of steel research in Taiwan as a  whole and really does an enormous amount of work on steel both through the CBMM  Center that he has created over there and in the whole of the Department of  Materials which he led for many many years. So yeah. Ladies and gentlemen, first of all I  would like to send Harry the team of APS for such wonderful organization so  that I can meet you here. And Harry gave me this topic and I feel very  satisfied because it's good to understand very very special phenomena. In fact  secondary hardening commonly happen in many sites of steel containing high  strong carbon element like chlorine, vanadium, nubbin and moly. And here I would  like to report to you emphasize that secondary hardening also happen in low  carbon benefit steel. So let's look at how to produce low carbon benefit steel  through careful chemical alloying addition and also we need control the  rolling and also a saturated cooling. We can get high quantities of benign  easily in low carbon steel and ideally the low carbon benefit steel provide high  toughness and high strength and of course good weldability. So we expected this  steel is quite useful for automobile application and that's my subject  because we have a cooperation with the CBMM company and CBMM company always  push us to do the research related with steel application for automobile. And  here I would like to show you the typical micro structure of low carbon  benefit steel from our research result. In fact people always said always said  it's a granular band line and then when we check Harry's book we know Harry has  has written a beautiful review for granular band line and from that I knew  that there's a paper published in 1950 by Harprican. Is that right? Yes sir. And he said  the coast favorite place look like granular. But I would like to raise  question here. Can this terminology granular band line  signify the exact structure? Can anybody answer me? Can anybody answer me? Of course  we need TEM to clarify the detail micro structure so I will give you the answer  now. So we should consider the terminology of granular band line. It's long but in  this talk I will keep this terminology because it's quite convenient to  communicate with the people. So here we can see the subunit Benedict  Ferrara here and the thickness about 200 nanometer so it's so thin and also the  subunit with the same orientation so the coast Ferrara prey in fact is  composed the favorite subunit and because the subunit with the same  orientation and we couldn't distinguish the detail. And in my research we would  like to develop the low carbon Benet steel and the China steel has prepared  three steel for us and for the for these three steel we have the same composed base  composed. I would like to show it here. The best composition is 0.05 carbon and  magnet 1.7 magnet and niobin 0.08. Best chemical composition. For the steel one  the niobin we label niobin steel because it's without morning and for the steel  two with 0.1 morning and we label this year niobin morning steel. For the third  steel we have 0.1 percent morning and we label this year niobin three morning.  China steel prepared this three steel for us and cast into an ingot and after  homogenization at 1200 degrees C for two hours the steel the ingot were hot  loaded and by control low the rolling rate about 20 percent per pass and the  finish loading temperature around 900 degrees C and here we can have a 5  millimeter thick strip so the reduction rate is quite high so we can imagine the  grand refine also happen here. And after finish loading the strip were treated by  a serrated cooling to 650 degrees C or 550 degrees C or 450 degrees C for 10  minutes for fan line transformation. So here we can have seven strip at room  temperature. I would like to emphasize here because we will look at the  micro charger level. Niobin 650 and that's get from the isosomal transformation at  650 degrees C and niobin morning 650 and also we have niobin 550 niobin morning  550 and niobin 455 niobin morning 455 and niobin 3455 we have seven  strips. These strips were receded at 600 degrees C for different time interval  from 0.5 to 8 hour to investigate whether the second  didn't happen. I think the metrology data is very important. We need that  because we would like to correlate it to the property. Here I would like to show  you the typical structure of the so-called grand unit band line and we can  see this is MA, it's martensite austenite, and it's quite easy to distinguish from  MA and degenerated peri from the morphology. And here is a look at the grand  unit structure, it's a grand unit band line and here is a ferrite. In fact it's very difficult to  distinguish between the grand unit band line and allotmophic ferrite. So we  try our every effort to distinguish. First we can see the use weaker  hardness to distinguish and second we try to eat EBSD can be to distinguish.  And this is our result here. This SEM for Nalbin 450 strip we have 25, 40%  of the tome ferrite and 63, granular band line and 9% martensite austenite  phases and 3% degenerate peri. And indeed it's very very important to have this  quantitative data in order to understand the mechanical behavior. Here I would like  to show you the EBS technique to understand this technique how to use it  to distinguish ferrite and band line. Here is an example to show you the  misorientation measurement between the subunit in granular band line. This is  sub-ran A and we can get kikuchi pattern here and this is sub-ran B we can get  kikuchi pattern here and in fact through the soil oil we can easily get the  misorientation angle. But precisely we try to describe the misorientation by  a 6 angle pair. So from the sub-ran A we can have Euler angle here and from the  sub-ran B we can have Euler angle here but in fact we have reference crystal so  we can get the sub-ran A relative to the reference crystal orientation matrix.  And also we can get sub-ran B relative to the reference crystal so we can have  these two basic orientation relationship. And then we can get the sub-ran A and  sub-ran B notation matrix. So here I would like to show you the commercial  data always show us this angle. Why? Because we have 24 axis angle pair and the  commercial data always choose the lowest angle so when we use this software we  must consider how the software engineering has done for us because we  should understand the crystal-crystallic-of-meaning and in fact by using the  the minima angle is quite easy to interpret but we should understand the  physical meaning. Here I would like to show you two examples. For the BAN line we can  have the distributive misorientation angle something like this and we have  two pick here this is low angle and this is angle for 60 degrees C maybe somebody  understand why it located at 60 degrees C 60 degree and for the fair right we can  see the misorientation angle always a high angle so from the intensity here is  very easily to distinguish BAN line and fair right region. So based on this  concept and technique we quantitatively estimate the data for the strip.  Nioven 450 strip and Nioven morey 450 strip. Here we consider 18 0.1 morey we can  have a higher high the bitty of BAN line so the gradient of BAN line from 60  3 percent, volume percent increase to 66 percent and the fair right decrease from  25 volume percent to 14 percent so the multi addition effect is quite significant.  On the other hand we can check this Nioven 550 strip and Nioven morey 550 by 18  0.1 morey we can see 0 gradient of BAN line increase to 62 gradient of BAN line.  Here now the 5D strip contain 87 volume percent fair right and here is 16 volume  percent fair right so basically the structure a completely different so it's  very important thing we study the mechanical property we always to wish  get the metacor the quantitative data in order to understand what's the  mechanical behavior so that we can control the microstructure and the  mechanical behavior we have both. Here I would like to show you the strength  curve for the Nioven morey 550 strip and for the Nioven morey 450 strip because  the structure are very similar you can see granular BAN line 62 66 or  Tommi favorite 16 14 and MA 21 19 and 1 percent degenerate and 1 percent degenerate  so you can see the curve look very similar and for this to strip Nioven 550  and Nioven 455 we can see this Nioven 550 contain 0 BAN line and this curve  show there's a sharp ear point here because 87 percent morey  in this in this steel and as to Nioven 455 we can see there is a  Plato slightly Plato here because this steel contains 25 or Tommi  favorite and let's compare Nioven 550 and Nioven morey 50 after template for  different type interval this strip contain 0 granular BAN line so they  there is no secondary hardening can be detected however for Nioven morey 550 we  can see after one hour the hardening raises up quickly and there's a very  strong peak occur on the after 10 after two hour temporary here also we show  Nioven morey 455 Nioven 450 contain granular BAN line 66 percent and here  63 percent and we have we can detect it the second hardening after one hour  temporary at 600 degree C and let's look at these two strength sake curve here  okay and this curve show Nioven 65 without granular BAN line and this curve  contain Nioven 63 granular BAN line and after 10 minutes one hour we  expected this curve will raise up I can show you quickly here so it's quite  significant the second it's hardening occurred in bay native favorite and the  the micro search development seems very important so I would like to show you the  the data quickly sorry  okay since something wrong these two they are we couldn't couldn't show so I  don't know the reason but here I would like to show you from the EBSD we can  show the peak is quite significant for the now be in three morning morning  because they are not a very new Bella and also we study the dislocation density  for my bin 450 my bin morning 450 and my bin stream 450 and after 10 be one hour  and and eight hour we can see that is okay basic doesn't change so it means the  structure the structure property the disorganic structure property is quite  stable for this alloy and also we use high resource 10 tm to observe the  carbide and we can see the carbide always precipitate on the dislocation and  it's very very tiny and the carbide always with the MC structure and this is  Baker and knocking orientation relationship and also for now be more  is still we can see the MC car back and Baker and new team orientation relationship  and here we show the dark field image because of the car by its very tiny and  we would like to observe the car by density and we try to use a traditional  darkwood to observe the density and in fact the car is very very tiny and from  the high ocean tm we measure the size of car by and the number of car by we we  measured about 300 particle and we can see the car by size keeps very very small  for now being and I'll be more steel and from the from EBSD at EBSD network  we also would like to observe the chemistry for the car by and here is the  data and for Cambrian at 600 degrees C for eight hour the now be my more atomic  ratio is about 1.8 for example and for now be three more for 55 and the  atomic ratio about one over one and finally I would like to show you the  data quickly and here is quite safe naked we can have the signal  hardly after a short time temporary and in fact for in that application we should  consider the eos chance and tensile chance and also elongation so after one  hour temporary you can see the eos chance and tensile chance increase and  also the elongation also increase so it's very good to use this material for  in that application because if we if we can choose the proper proper the  processing and after benign forming and we hit it just for a short time and the  strength and elongation both increase  finally I would like to give a brief conclusion in my in our low carbon now  be kind and steel and we find the Molly addition as a addition has a  advantage of produce high ball interaction or granny or benign and  it's good for second-term in housing during tempering and I think it's very  important for industrial application and especially consider the low carbon and  lower steel thank you for your attention  excellent lecture thank you what is remarkable is the stability yes the  structure yes and even with tempering at 600 you maintain the strength the  dislocation density yes and increase ductility yes yes so the idea would be  that the 600 degrees C happens during coiling yes exactly you have a lot of  MAEC also so is it carbides are forming in granular brayland or in those MAEC  how would you differentiate this okay it's way easy because we can we can see  in the band-line region we can see the subunit as I show you and it's a  sub-grand and it's completely different from the MAEF as a stereo so even after  tempering also even after tempering also because tempered modern side would look  the similar also okay tempering modern side always give you coarse carbide  always gives you coarse carbide we can discuss later  why did you use for example niobium and molybdemon and what about vanadium which  is known is very effective as for hardening for example in high-speed  steels okay and the second question is why did you use for example only tempering  at the temperature of 600 degrees okay thank you very much yes for this  alarming design in fact we we should keep we should have high mode inflation  of bed so how to get high mode inflation of bed and I think the now be in a  moly pay an important low what a hardening of bed so in this work we we add  now being the label is 0.08 percent that's the reason we use my working  instead of because we would like to increase the 150 of them and your  second question is okay in fact because because of the time limited I couldn't  show my result for 500 degrees C and 550 and 650 but I choose the best one 600  we have question from David Haudhig he asked in experiment procedure okay you  refer the AC egg ruling the set egg ruling from a five mil thick strip or  commercial simulation after I saw so much transformation at they say 450 degree  C and the core the strip cool natural cool to room temperature we suppose the  10 I already there already there so we don't need to use fast cooling at the  final stage is that okay and another question from Suje you say something  about niobium increase the other bleedy yes and you form a granular pay night  yes and how do you separate the ferrite and granular pay night that's that's the  question okay because it's a low carbon steel so it's very difficult to get  completely complete very nice structure so we always have us we also have some  favorite so there's a reason we need a separate to the cool and also we need  micro-aluminum addition so that parameter is very important for us so we just  trying to prepare this material but in the question is saying how do you  distinguish the ferrite from the bay night I think you answered it in your  presentation this way is very easy just by because how we can distinguish because  happens it's very easy and also through EBSC we can distinguish EBSC someone  should comment on the fact that niobium and molybdenum dissolve in the same  carbide whereas we know that doesn't happen with titanium and molybdenum do  we know whether molybdenum should be soluble in niobium carbide yes I know  it because we used for example niobium in high speed steels and complex  carbides are performed which contains for example both the elements when you  when we did the first for this calculation on the name of carbide with  molybdenum and the energetically this not favorable for the name of carbide to  contain the molybdenum in the molybdenum titanium molybdenum we found that the  some addition of the moly molybdenum in the titanium carbide will relax to the  strain energy interface strainage between the ferrite and titanium carbide  but it is not clear that the same mechanism control the molybdenum  accommodation in the niobium carbide. So I think you know the chemical analysis here is quite interesting of the carbide and very clear your microscopy and time for analysis.  In fact this results no good because we need 3D data to understand if we just use it that's a problem we couldn't detect the exact  composition for this carbide right because some carbide we always we can see  some co-share structure. But there's no doubt that you get both peaks.  My question is because we just temper for one hour and we can increase the stress  and also increase the elongation right so we suppose the niobium the natal carbide  precipitation occurs in the short term.  How much niobium you have already precipitated before tempering and how effective is  niobium that participate in secondary hardening. Okay I think that's a very very  good question. We need very good data to perform this research in the near future.  Not now because I get the specimen from industry and we need theoretical work so  we need very good data to perform this experiment.  We couldn't get you answer at this moment.  Short question first thanks for excellent talk and it's a very difficult story that you show here how to characterize the microstructure.  In fact I have questions about EBSD data. You separate between ferrite and bainite here and you use  misorientation profiles. Well have you ever tried to to use not misorientation  profiles but kernel average misorientation of some other type of maps in EBSD as far as  both structural constituents they have different dislocation density probably  better revealed there. Different criteria because yeah or there's a  recent version of some software you could use even kernel map on the image  quality so do you have some some experience with that. Okay I think the  chemicality is a good way and also we should consider the digital space safety effect.  However I think there are several measures we can we can consider which one is  the best one and in fact we have used image quality to distinguish the MA  faces it's quite easy because it becomes dark. And basically we know the  bainite with the high digital band density so some people we can see the image quality  but in fact we still can see in our results so we basically I suppose the step  size is very important. In fact or this granular bainite the  auto-minefair is huge much bigger than the bainite stability so so so we can  distinguish it easy. I'd like to confirm that we've also we've also measured  that I'm in a number of niobium carbides. Your your presentation showed very  clearly that you have secondary hardening at 600 degrees and I guess that's  probably the peak of the hardening. My question is what about carbide formation  strengthening carbide formation in the bainitic microstructure itself. So it's  obviously incomplete because you can you can increase the strength by a  secondary heat treatment but can you tell us anything about the extent of  precipitation during or after the bainitic transformation itself in the  primary cooling stage. Okay that's that's really a very good question because we  have compared both microstructure and we suppose there's a little bit difference.  Also we can use a weaker hardening to test first so compare with weaker  hardening. We can see the clear difference.  Okay okay I think that Rocky answers your question because we have to go for lunch.  Yeah the college.  Yeah here is the answer.  So just compare the bigger sign for the original one and  the temporal one. Yeah thank you very very much.  Really glad to hear that.
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