Modern Steel Products (2014) - Grain size control: lecture 5


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Modern Steel Products (2014) - Grain size control: lecture 5
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5 (2014)
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Cooman, Bruno C. de
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A lecture about the iron-carbon equilibrium phase diagram. This is a part of a course of lectures by Professor Bruno de Cooman, of the Graduate Institute of Ferrous Technology, POSTECH, Republic of Korea. This particular lecture deals with the principles of grain size control, and thermomechanical processing. This comprehensive course leads the audience through a large variety of metallurgical aspects that influence steel products.
The Graduate Institute of Ferrous Technology (GIFT)
Sizing Computer animation Rolling (metalworking) Mechanic Tram Rolling (metalworking) Finishing (textiles) Clothing sizes Screen printing Mail (armour)
Steel Hot working Reamer Stationery Tin can Clothing sizes Sizing Computer animation Mechanical watch Typesetting Musical ensemble Musical ensemble Material Moped Tanning
Airbus A300 Steel Hot working Surfing Totholz <Schiffbau> Suitcase Messerschmitt Me 163 Aerial work platform Cougar Compound engine Roll forming Mechanical watch Alcohol proof Typesetting Material Vertical stabilizer Tin can Sizing Computer animation Cartridge (firearms) Remotely operated underwater vehicle Rolling (metalworking) Steering Ship of the line Sheet metal International Space Station Last Compound engine
Weapon Airbus A300 Steel Rolling-element bearing Roots-type supercharger Mechanical watch Surface mining Rail transport operations Mail (armour) Material Striking clock Metallurgy Blast furnace Fiat 500 (2007) Semi-finished casting products Coal Steering Mechanic Finishing (textiles) Tin can Clothing sizes Aufnäher Scrap Playground slide Sizing Computer animation Cartridge (firearms) Rolling (metalworking) Ship of the line International Space Station
Stitching awl Mechanical fan Finishing (textiles) Welding Roll forming Turning Mechanical watch Musical ensemble Surface mining Material International Space Station Blast furnace Semi-finished casting products Steel Gear Finishing (textiles) Kopfstütze Zementation <Metallurgie> Ship Space suit Sizing Outsourcing Computer animation Remotely operated underwater vehicle International Space Station Last
Typesetting Airbus A300 File (tool) Casting defect Forging Screw Roll forming Computer animation Screw Mechanical watch Alcohol proof Sewing needle Typesetting Totholz <Schiffbau> Wärmebehandlung Material Flatcar International Space Station
Typesetting Steel Hot working Stagecoach Plough Hot working Machining Cord (unit) Machine Blast furnace Fulling Cougar Turning Sizing Computer animation Alcohol proof Cartridge (firearms) Sewing needle Spare part Totholz <Schiffbau> Steering Engineering tolerance Material
Metallurgy Playground slide Computer animation Hüttenindustrie Material
I so we have been
talking about grain sizes and Wheat which was seen grain sizes influence due transformation of great size of Austinite we had also seen to that the grain size control is anyway to control strength In this sense that when you get lower grain size you have increasing the yield strength and very often also tensile strength you ultimate tensile strength and we will see later as we we talk about the products plate products in particular that a smaller grain sizes are varied but the official for toughness so and I already told you that In November In practice very often we will let control a rate size in steel products by trying to do thermal mechanical processing of of steel and had told you that so in With moral steals you did go you can reduce debt due to grain size but not very much so we cannot had shown to you when you take conventional steel you will have due to the In defamation let's say that this is desire a rolling passes for instance due to defamation and subsequent between the rolling past his 3 crystallization you get some grain refinement but at high temperature the we crystallization very fast and grain growth is also very fast in the also so the amount of refinement you can get is relatively limited but I would but this is meanwhile you can't not go much lower than 10 to 15 micron grain sizes but at al-Sadr told you that it respects you move very close to the transformation temperature recalled you you get into a temperature range where we that we call the Nomura crystallization temperature region it's very narrowly you can't really exploit this area because the it's much too close to the transformation to what happens if you if you have these costs screens Austinite Rick crystallizes and then you get transformation you get there and it will be a new product are coming from Rick crystallized Austin and they growth at the grain boundaries of the Austin the so and so what's the picture during this the mechanical and structural transformation that that you get in the differences strolling passes to Chris here you have a grain the this great s when you you pass through a role in a mail you get a pancake at which the gringos flattop has an elongated I to that's the mechanical deformation and then because you're at high temperature you get Re crystallization and this week crystallization can be even dynamic crystallizes means during the defamation the grain already a transforms to 8 new grain would very low dislocation density of the strain is high enough you can get dynamic which places and then you get between the passes as strippers at high temperature yes and you get static read crystallization of high temperature and hindering growth as this is very fast In the next the rolling steps you get a get the same process you had here in this rolling step you get pancake and flattening of the grains and if the strains large enough we can get dynamic slice Nation also did and these processes of various fact very efficient goes very quickly and so on and the time here dated between rolling past can be as as the surname the difference in rolling mill hot rolls of outstripped Mel toward the end of the finisher this this the time between 2 defamation Bassett is of the order of 1 2nd or less and but even then that distillery crystallized and then recent grain growth became so that is what happens if I year from make a plot here when you have this is the plot of the static recruits lawyers Asian kinetics so that's a very fast and then once to the explosiveness finished you get grain growth can be Internet
Halverson into past reach what happens when we both knew that when we do control viii 0 the grain size what we need to do 1st is we need to add elements that will prevented a recruit's lies station so when when you when you have work not prevented that slowdown reflected so when you have the recruits isolation units would basically happens is you have a recruit's stylization front going From a region would very low dislocation region it was very low dislocation to region would very high dislocation yes so you need to have this interface slowed down hasn't even if this is done bye by adding 90 albeit an aerial view the solutes niobium causes and effect called this look that's all you to drag him stances interface vis-a-vis interface slows down knows that boundary slows down rather you can slow down the rate crystallization kinetics and so male given us that in practice what it means that this this region of nunnery crystallization this when you at that temperature increases in so that you have here a wide All-Pro nunnery crystallization region and they're very often we add some additional manganese so that the art truly temperature drops down years and you have a larger region Of that we called Nomura crystallization is and you can then deformed the material yes in this nunnery crystallization region so the grains will get pancake they will not free crystallize pancake again no recapitalization pancake again so you get a lot of strange accumulated in the Austinite and so you have these deformed gamma grains With the formation bands in the gamma grains and then when you get To the transformation the far-right transformers not from recruits lifestyles also the from deformed and you get a considerable grain refinement so but authority
show you this picture nope no strain fair a nuclear it's at great memories when you have strained you've got a lot more very high depletion right so this is a picture we had in we doubt saying now you'll be and without this the solitude drag effect very fast regressed isolation and then them in grain growth if we have a high temperature of nonrecourse lies Asian you really don't stop the Greek crystallization which you would you do is you slow it down another kind that takes over a crystallization of static result recapitalization now looks like this S-curve here yes and that means that Ukraine's a pancake There is little little bit of Re crystallization of the 4 the structure Israeli crystallized you the former together that's it that's the way you accumulate this
straining and do that and reduction of the grains so if you look in 8 the processing of a conventional carbon manganese steel that doesn't contain any NI albeit so this it would be the temperature of rolling so you go from somewhere 1150 to close to 900 right above the 3 temperature and you look at the grain diameter so in the conventional situation every time you have a rolling past as you have a reduction in the grain size at the beginning you have very very coarse grain sizes so a you don't really the notice history re crystallization of too much but below 100 micron you can see you reduce the grain size and and in between the passes you have green growth reduced a grain size gringo yes eventually you end up with something that's pretty courts because 15 Michael in the Micro alloyed Case Nos every time you reduce you do you reduce the thickness of the sheet them he also reduce the grain size but there is no we can slice Asian and certainly no grain growth so you can accumulate to strange and you end up with grain a grain sizes which are less than 20 micron when you transform this as no far-right grain size is but considerably and small so the explanation for the slowing down of the Rick crystallization the fact you get you because you have to remember this is a process that happens at 900 thousand degrees isotopes high-temperature after the transformation has occurred in this original Mike restricted at high temperature is not visible anymore and also denial be the solubility in verite is much much lower than the Niobe him solubility in Austin I so the structure you look you you can see at room temperature where you would make your observation is very different than what it is that you have at high temperature so as a consequence it's difficult to check the theories different theories for for this grain size we find there is an alternative theory for this I it now you'll be the effect of denial and that is but the defamation enhanced precipitation has it it says basically that when you I have a lot of strain the nite you'll Carbide kid precipitate has informed very tiny precipitates at it said these Britain precipitated to rather than the solitude niobium that has but the effect on the motion of this anyone whatever the uh the explanation it appears that it's very important to have beyond there yes in solution when you doing to the role at 1 of the things that I but the people that have noticed is that this process of nite you'll give carbide precipitation is definitely the enhanced height much higher kind that takes that if there is no defamation and this is an example here but Ratso so it it it shows you the Richter slice Asian kinetics for steel and he had the precipitation kind that takes for carbide In Re crystallized Austinite don't when you do former material yes the steel at high temperature you have read crystallization kinetics and how do I represent as well I make measurements at a certain temperature at certain temperatures Of the request of the amount of work crystallization as a function of time just like I would do for transformations so and obviously at high temperature my request Asian time will be short and as I dropped the temperature the reader slice Asian time will be longer than that said these points are observations of where do we crystallization starts but this would be a recapitalization of start temperature or times just and this would be for injury crystallization and yeah look at this as a region we're crystallization so this this gives me this explains why we crystallization kinetics of the data looks like this you have basically wine 4 start of the recapitalization and the line for the end of directors like so you can see his friends at 900 deg C the end of the week crystallization is between 1 to 10 seconds yes the very short but produce less have a look at the precipitation out of niobium carbide a Re crystallize Austinite abysmal defamation and it's 8 what we call a nuclear nation and growth phenomena so you get precipitation curves that are usually little bitch see shapes and and here you have a line where did that did the precipitation starts has an eerie have aligned with the precipitation is finished now let's look at the expects the time this is this was seconds Mississippi powers it takes about but now or To get this niobium carbide to precipitate inns in Austin I normally however if we have deformed Austin right yes this is what we see 1st of all the rechristened ization yes every crystallization instead of going straight down has a update so there is around 100 degrees C the re crystallization is severely suppressed very strongly suppressed and the other thing we see is that the precipitation of my Obion carbide is tremendously enhanced but now instead of having a fight at the at having to wait for minutes or hours to get any appreciable might nailed him ,comma now it only takes you seconds or less yes so this model that's what causes the suppression of the we crystallization kinetics Of the former Austinite bye microscopic national size that niobium carbide particles is very a plausible also 10 so did you hear you actually have some so some data here you see here the static precipitation of niobium carbide and this is the the formation induced precipitate and you can see for instance this for the started takes about 100 seconds and and if you do this in the form to material it takes about 1 2nd to start and end the year at the peak that the the peak precipitation is around 900 sir when you are a rolling also the there you rolling this Austinite so you deformities and you can keep on deforming at a dozen were crystallized it also means that when you do the transformation the transformation is now from where crystallized Austinite asserted that he was not nunnery crystallized Austinite so you remember From I guess said Tuesday that when you transformed from Nomura crystallize you have 2 effects you have many more nuclear nations nuclear nations those sites and the other in fact is you have more driving force so as a consequence V transformation kind that takes years it's a transformation
kinetics so instead of being like this for an aerial view free steel you now have enhanced the kinetics of the day yes the curves for the verite nuclear nations is the most to the left To do so when you call you get lots of nuclear nation years and then will see that you get a change in the cooling rate when In when you have stripped products when you coiled OK but the important thing here is that you have enhancement of 2 transformation took the little it's me very clear as the request lice and we crystallization is suppressed but the transformation is enhanced right look at this there's no contradiction here candidates but usually found you and maybe or will be told that you have as the Micro ILO Yang additions you have nice you can have the Itanium you can have a major have and that is correct To a certain extent but these additions have are very different in their behavior and so you cannot replace niobium with tightening or the major and no 1 well why is that 1 of 1 of the reasons is the there they have different solubility and and have different stabilities in Sadr and Furcal here about the the stability so if you look at the we entity of formation was dealt T you see that and you have dieting you might try very strong then comes Niobe nitrite and you've got the series of nitrites and Carbide's adopt equivalent was and then you have much last stable vanadium carbide that means that you will have a very different behavior so in general which we see Is that there is dealt achieved the delicacy of the compound is very negative so you have of of a very stable compound but it also has a very low solubility in steel the hand compounds on this side are of course less stable and they have higher solubility calls yeah so if we use now information we have about solubility we can actually you have to look at how efficient certain micro alloy additions will be to obtain Grain refinement 10 so again if we think about this model the grain refinement is due To do suppression of free crystallization as a consequence of precipitate formation and small precipitation patient strain induced precipitate formation you would want to have precipitation during rolling during deformation can so letter that what this diagram shows that it uses is that temperature where you do do the processing and the precipitation fracture if if if France would lose look at the blue line here it means that nothing sits it was looking at niobium carbide with up to this point as this temperature nothing has precipitated and if we use the temperature of of the niobium carbide becomes starts to pursue OK and so let's look at nite this blue niobium carbide curve 1st it's calculated you you know of course that the precipitation will depend on the composition of the steel that means to the carbon content and you'll be content and the temperature this is what you should do what which we we show here for 400 ppm albeit . 1 per cent of carbon a typical composition you will have in these micro deals did you see that the precipitation starts here increases and is about complete around 900 degrees yes and there's overlap exactly yes with the rolling temperature range that we applied industrially right so this process will be very efficiently OK let's
look at vanadium carbon this but in at United circuit vanadium carbide so here you have a steel we calculate the precipitation of vanadium carbide 4 points 12 % vanadium . 1 percent of carbon is what do we see doesn't precipitated those operatives precipitates here it precipitates the roller so this not going to be interaction between the rolling and a precipitation of vanadium carbide so vanadium carbide itself has no impact all right the this and really call civil mechanical refinement grain refinement for for that you need to have a nite tried of vanadium so here you have a point at 12 major that's the same amount of native and and 100 ppm of Niger 100 ppm of Nagin for me is the high nitrogen content that's usually we don't have that much nitrogen in our steals and we don't like to have that much nitrogen in our because it gives us a lot of very sensitive mixes this very sensitive to Beijing at the age very quickly so but that we do users we will use this in and when we have certain metallurgists steelmaking metallurgist will which give us which always give us high nitrogen for instance when you produce arms deals in electric arc furnace using scrap the nitrogen content tends to be high and so that would be an ideal way To do a trial lawyer so many e-mails will tend to use vanadium microbiology conditions burial Of this stating in nitrite we would talk about nitrites so stating you might tried a good addition yes will there Is history 1st here we have a saying let's look at the lower line . 0 2 per cent I Tania 100 % but 100 ppm of nitrogen you see that the precipitation of taking United is finished before you you reach the rolling range so the same thing the fighting in nitrite will not have a large effect or any effect on the L we will not cause thermal mechanical grain refinement the at the end as efficiently as the niobium carbide until good the as I said this had to do so Carbide's I need to be In the right range in terms of size and in terms of density so did there are theories of precipitation hardening and the the steering is give you the increase in the strength in as as a function of precipitate volume fraction for different particle sizes and do it is steals Audi microbiologist deals high-strength low alloy steels microbiologist deals we see that the Best strengthening is achieved at about the 5 nanometers yes 5 memories .period all all 5 Microsoft's so they've got to be really fine 2 to give me precipitation pardon so the addition I love my inviting on vanadium has had has 2 effects effect number 1 we find the grain the fact number 2 Due to the presence of the precipitates so you have precipitation hardening you have to effect OK when you do the Micro alloys and so that's 1 of the reasons why when you add Naomi To a steel you can still use the the amount of grain refinement may be limited but you can still get strengthening as a consequence of the precipitation the presence of the vanadium carbide precipitates In many cases however please Quebec just slide which is had in many cases
however you can see here on this graph we typically have about 10 to the minus 3 In volume fraction yeah and there and we have particle sizes that we can achieve are usually between 10 5 and 10 nanometers so somewhere here yes so use only the strengthening that we can achieve will not be higher than 100 Mike 100 madam Puskas very often it's less yes but that's not too much of a problem because you get the extra strengthening also from the grain refinement and so very often and certainly when we we use now you'll be out most of the strengthening there's not come from precipitation heartening that comes from grain refinement this is shown here but is basically what what you see here is 80 Hall the patch a plot so you have the yield strength as a function of 1 over the square root both the grain size and you upward the what the straight lines which you know in the grain sizes smaller this direction here you can see the scale with Micron so few you go to lower grain sizes you have an increasing the yield strength what you see is that the nite you'll be and steals can you 2 things 1st of all they're slightly shifted upwards Baxter the impact of the precipitation strengthened and then they're shifted to the right now you could you know there's no reason why you the carbon manganese steel could achieve the same amount of strike the trouble is you cannot refine the grain in those deals the this incident with the is only deal you can get grain sizes which are of the order of 5 typically a run-of-the-mill microbiologist deals will have between 7 to 5 microns In grain size and and you can see that the the the just the strength increases appreciable you get you know with carbon manganese steals yield strength 350 maybe it is a steal 500 and more OK and the amount of the following elements you added very small it is just you know the order of 400 ppm and you don't have to add huge amounts of debt the other advantage is that you achieve the strengths by reducing the grain size His rather than increasing the amount of carbon and this brings us to the next .period Top 1st set me let me show you how some intricacies so where does this actually happened you know where where do you where is this processing of thermal mechanical controlled processing of features of the steals Don rights said so far you will see and in some distant future lectures on how they are hot strip mill looks like in detail but you basically have a slab reheating furnace a roughing man and a finishing and and it's in this finishing mail that you do this basically the thermal mechanical processing so did you choose the temperature of the furnace high enough so that all your Carbide's of niobium are solution and you keep them in solution and tell you reach the finishing mail yes there you do rolling between thousand and 900 deg C and that's where you achieve the pancake it the strain accumulation of the indeed Austin and strain induced precipitation of denial Carbide that's what you get in this In the finishing you you'd you go on the run out table this is where you you carry out of the Austinite verite phase transformation Nunez and in the coal oil yes when you coiled a material whatever and they'll be in Carbide was not precipitated will now precipitate at lower temperatures In the far-right effects 10 In the
sources now let's let's look at the temperature and position against it's a In a conventional situation yes the slab comes out of the reheating furnace goes into the roughing the finisher yes usually the TNI are indicated for a conventional situations conventional steel the TNI are as isn't this is very close to the transformation temperature so you can only achieve that temperature this end-of-year get and then you have the transformation From right but last nite to fair ideas and as I said this is the transformation will be from where crystallized Austinite so you'll have very few nuclear nations there is little nuclear nation here Of the fair at the Austin I grain boundaries and then when you call the material get pretty costs Mike rastructure if you now look at the processing the processing for there mechanically the processing is entitled him and added steals now your T and ah yes you at a temperature of Nomura crystallization is increased by these like opium editions since said To temperature that's slightly above the temperature you had at the start of the Finnish so when you deforming the finisher you can accumulate strain so at the exit of your Phoenicia no new good the cooling here where you get to transformation the transformation from Alpha from Goma to offer rather you get a nuclear nation at the grain boundaries but also In the interior so you see here to defamation as you get lots of far-right nuclear has so very fast matches of faster new band and the kind that takes of the transformation much finer grain sizes that's that's a different that's where it happens basically in the in the French hot strip mill so what which we talked
about just now is is how the people are controlling the grain size yes 1 of the then again in controlling the grain size to change the strength basically but if you can't do this you know how how do we change the strength in steals In easy way while that for the easy way to do it Standard easy way to do it in and it's still used vary widely constructional steals is basically to work with far-right perlite Mike rastructure uses of typical far-right pro-life my perspective but catalog refuse variety and this is her life and so that they the mechanical properties that we get depends almost entirely on the carbon content the rest of the all of this deal because the mechanical properties depend on the mechanical properties of the salmon typeface I have the far-right Phase I have and the volume fraction of perlite so it's 1st of all have a look at what would I mean by this can because In your far-right yes you in your Kunst In variety perlite Steele who knew you have this far-right and Pearline at the far it is being a face that's relatively soft so if you look at the stress-strain curve this is what you have for the fair it you look at the perlite here yes the perlite contains 2 phases yes variety and cement I can so basically 1 of the faces in this constituent will have this stress-strain curve and the other 1 is a Carbide's very very hot very hard nosed has stress-strain actually nobody really knows how distressed drinker salmon tied is because usually breaks before it ever you can make the bulk cement I'd always breaks before you can give it any plastic deformation but it probably has it yield string around the 3 thousand units sold this seem and that to me that these 2 phases the 7 tied and the far-right together act as 4 a composite an hour and then the stress-strain curve that I have will be for the perlite note stressing it will be somewhere in between the if I love at the tensile strength of the far-right perlite Mike rastructure it depends on the carbon content but what it actually did which actually change when you change the carbon content as if you basically increase the amount of perlite and so when you have 100 cent of perlite that's at around 0 . 8 % against you the typical strength is about a thousand years if you have around so that would be the point 4 Percent of carbon you have about 50 per cent of perlite 50 cent of far-right this and so that gives me 700 major Pascal of yields right N that is certainly for when it comes to commercial constructional steals that's basically the way strength this control by changing the amount of carbon which changes the amount of her life in the Microsoft and that's the it's very simple yes not too difficult you can see of that you can now basically designed U.S. Steel is basically by changing the carbon content yet but there is 1 problem is that the more you add carbon the more hardened all your steel becomes the easier it forms a very hard and brittle Martin site when you welder yes and that is the big problem because we like to weld steel we like to weld steel to make thanks In 2 2 to join thanks and that's it that's a problem so you can make have stronger steals but there they don't have good weld welding Properties Inc so but let's have a look now at at these the properties just let's just forget about the well-being for a moment and that's just how these properties change In the current content so the as as you increase the carbon content yes you have 2 steals which are Hi you take to it and then you have to use a high protector you see that as we increase the amount of carbon the yield strength increases yes and the tensile strength increases and if you can't measure these things you can measure the hardness and the hardness also increases but indeed with would you also sees that the material as you increase the carbon the amount of elongate ship dropped and the material doesn't have what we call impact toughness that's it it's less tough so it may be strong but you can't really do anything with it in terms of form ability it becomes very hard to weld yes and and then it's it loses toughness so the approach of adding carbon is to control the strength is interesting but obviously limited the potential for many many products well let's play
around a little bit with their the this microscopic or 1st of all you may remember that we could change polite Mike restricted but forming it by when you form perlite at lower temperatures you get a refinement of the perlite so when you have find perlite in the Microsoft dropped your nose you get in a high-strength if the perlite is chorus the strength decreases if you spherical .period the perlite so you replace the perlite with big inclusions bigger inclusions of semen type you get an even lower the strength and you can see the effect the fact on the the form ability what is improved as you you change things from Seaman tied from perlite the other 1 OK it was another thing we could do which steals exactly the same steals theirs instead of calling them slowly there's or holding them by Sept thermally To get the formation of 50 years for life transformation you can quench the material and if you quench their material so instead of having which we just saw they increasing linearly with the percentage of carbon that you get a huge increase Of the strength because we have super saturation in Martin's get very high earners material has because Martin site is of course much harder than the burglary and we use this is used that there are many things that the learned that we make all of which are basically based on Starting from far-right perlite Mike rastructure as you and then rapidly quenching the so you get Martin site and you can see depending on the application if you want to make screws or structural steels of forging dies Brill's files yeah but you will have you will increase the cobbled because you do want very hard the very very hard material in now in many situations we don't use the Martin site as such but we apply a heat treatment which is called tampering temporary when you see there now the material itself quite hard but there is a considerable reduction in then the hardness and that's the reason why this happens it is because yes is because if you look at the MicroStrategy indeed microscope you see that these are the Martin site lapse yes but inside the flats you have these little tiny little needles we have appeared and these are Carbide's remember remember that the carbon isn't super saturation when you do this aging so you hold the Martin side said 2 100 degrees for said our yes the carbon will go out of the solution and 4 Seaman tight yes Byron Carbide's that's never it's extremely small and as a consequence of high you get a considerable reduction in distress and you can you can make the material really soft if you go if you kneeling to for instance 600 deg C it's very high tempering temperature by away 10 and that tempering is usually applied because you you you know you want to avoid this very strong brittleness of of of more the brittleness of Mark site is what you want to avoid In addition the very often you also remove internal stresses that the caused by the quenching it is an important you get a loss of strength that an increase in what what's called here read that RA which says reduction of area maybe I should go back to
sliders so because I didn't know this year so when when you have a but it you carry out a tensile test on a bar shaped material the Butmir shape tensile specimens of sued breaks here you get 1st you get your Nick region diffuse neck region and that eventually you get the fracture the you measure the area here a new measure the area you had all originally and the reduction of area so a 0 minus 80 but structure divided by a 0 sometimes 100 that's a reduction of the area this up so it the reduction of areas very large so if the F is very small then but you have a very the doctor much more ductile material 2 temporary
Martin side so In a nutshell when you have Austinite you do slow cooling so you get perlite verite and to basically far-right Simone tied and the health is the a very often pro you take face Nos To when we have prototype Tory carbon contents in our steals to moderate cooling you will tend to have the composition to very nights the mike rastructure will also B. more played like an needle-like do rapid quenching you get more part is diffusion less transformation and very often because the phase this this constituent rather is a very brittle we will do reheating tampering which will give us tempered might decide yes and basing its far-right with very fine mon type particles and also the Microsoft drudgery is played like a needle like laugh Martin site as well but we discussed I had very important with the tempering is at the tampering usually doesn't change them the Microsoft dropped her crystal graphic 1 Mike rastructure of Martin the only thing I really happens is you precipitated this assignment small see this entire particle In fact you Martin site Microsoft dropped a is is very resistant to recapitalization August this is it again in a nutshell little bit more visual Martin side tempered march Saturday nights find perlite cost per lightens spheroid died this in this sequence you go from hard unless ductile materials to constituents of more Dr. Alan softer materials in before we end there is and a few things from the 1 thing we need to this cost and that is related to this recapitalization I am very often in them and when we do thermal treatments and we will do a thermal treatments which we call annealing treatments the and that not all the same decent healing treatment so 1st of all let's look at 1 time the treatment annealing treatment which we which is important but have it discussed it yet and is related to bring crystallization the treatment why why is that important in in instills in particular for for Riddick steals and even for stainless steels hot when they're hot so when you do hot working of steel would you usually have is the material will request a lot and I the future of wikis license allows us to deform the material very heavily yes the foreigner material like friends you have these big forging deformed they don't strain harder you get 3 crystallization material becomes soft again the next time you had material hasn't gotten stronger and it's still the same you know soft material at high temperature yeah so you get lowest ranked lower energy to deformed there's of course at the surface around you we'll get oxidation not so important at this stage OK so but we also called the 4 materials and in this case there is no we crystallization we will need energy to the deform and the more we did for them more we hardened material in them more energy we will only so increased strength and of course there are good reasons for for doing call deformations is because for instance you know oxidation you get better surface finish you get also better dimensional control because of the low temperature as you can imagine that at you when you do rolling a thousand degrees C the equipment Everything is thermally expanded yes and so it's more difficult to get it dude do dimensional tolerances are much more difficult to meet however the Michael structures you get after cold working years the deformed MicroStrategy the grains you can see here this agreement my crystal clear is it consists of a deformed strange a great so and in the goal before Microsoft is usually you cannot use so
you need to Re crystallize you have to obtain the properties inference is this an example here of a stainless steel so hot trolling can it when the seals are heavily alloyed like stainless steels but even even after hot rolling there will not be rechristened lies in so anyway so this is an example of this you can see the grains are all very flattened very long much strain have high dislocation density and the crystallization allows you to get coarser grains and of course very low the dislocation density so you get a material that's ready for used in a certain applications OK this if there are different types of and healing processes of course 1 of them is the 1 we just discussed sisters we crystallization to obtain the final properties and healing itself can be very complex and but usually we we say all you want is heated up certain heating rate to hold it at that temperature for some time and then you cool so not necessarily Will annealing b this simple and not only this is just the maximum temperature and the time at which you keep it there are important heating rates may be important and cooling rates may also be very important and so 10 and as we go will will see some examples of the but in general no let's let's keep things simple we have stress relief and healing so basically that's stress you you have internal stresses in your material 1 of 2 ways you you can know and removed them is by immediately when you don't need to go to very high temperatures there relieving stress only requires it rearrangement of the defects of the dislocations in you migratory so it only needs recovery this recovery processes to be active 0 ization is very much used it's an annealing process which you and you make very soft steel instance easy machining or easy why drawing is it's a very long process whereby your summoned is Ferro diced summoned tight in the starting politeness is surrounded full annealing but here you get again good forming by heating and cooling and which basically trying to get it is you want to costs of your perlite normalization that's often His use very often knows that is the way to reduced the grain size behind you reduce the grain size will remember that when you do the transformation as the nuclear nations Of the new the new face is at grain boundaries so if you go to the you heat over the A R 3 temperature you get 1 transformation you cool down you get another transformation that will refine the grain just by going To true transformation and there is also process any of them process is use is mainly used for we crystallization annually so if we look at 8 a the diagram here face diagram here so normalizing you you do full L a full transformation Rick crystallization in dealing you the only thing you want to do sorry normalizing you do full transformation process annealing you just do there we crystallization point so you you he ducked you don't go through transformation and you cool down why would you want to go through transformation while maybe you don't want to destroy certain features of the microscopic such Crystal graphic picture this In many cases that's 1 of the reasons why you know the jittery crystallization and healing only if you do stress relief yes you don't want to read crystallize the migratory you don't want to soften it you just want to remove internal stresses that you just go for it recovery process it's a much lower preacher and then this furrowed isolation units we don't want to dissolve the seven-time we just wanted to costs and rightly so we stay below this high temperature as possible but we stayed below the 81 temperature for an extended time look and I think yes so
because you couldn't read this on your your slides up which come to the end of this this introduction so these concepts we've discussed are kind of understood that you know about these 1 wind will account the products the 1st thing will do on Monday is to to going to steal standards you need to know a little bit about steel standards because that's Of course you know when you sit in school you always learn about physical metallurgist distances physical commented that you never learn about real products less so will start off well Tom loaded but the a real products and how they are not organized in the industry to cut see you USA mixed with


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