Modern Steel Products (2014) - Strengthening mechanisms: lecture 18


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Modern Steel Products (2014) - Strengthening mechanisms: lecture 18
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18 (2014)
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Cooman, Bruno C. de
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Professor de Cooman talks about strengthening mechanisms of particular phases or phase-mixtures. This is a part of a course of lectures given at the Graduate Institute of Ferrous Technology, POSTECH, Republic of Korea.
The Graduate Institute of Ferrous Technology (GIFT)
Sizing Steel
Typesetting Ammunition Roots-type supercharger Truck Computer animation Mechanismus <Maschinendynamik> Twill Tau Empennage Steel Steel
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Roots-type supercharger Nut (hardware) Hot working Computer animation Automobile Mechanismus <Maschinendynamik> Captain's gig Steel Wire Mode of transport Steel Merinowolle
Roots-type supercharger European Train Control System Turning Computer animation Cartridge (firearms) Mechanismus <Maschinendynamik> Zugmaschine Steel Bill of materials
Camshaft Gear Sizing Computer animation Wood Mechanismus <Maschinendynamik> Engine Clothing sizes Steel Transmission (mechanics) Kurbelwelle Last
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Fiat 500 (2007) Truck Mechanismus <Maschinendynamik> Saw Keramik <Technik> Roll forming Computer animation Work hardening Spring (device) Typesetting Spare part Remotely operated underwater vehicle Gas turbine Steel Stool (seat) Steel Ship of the line Material Flatcar
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Stagecoach Mechanismus <Maschinendynamik> Train Plain bearing Casting defect Weapon Kopfstütze Sheet metal Computer animation Sharpening Automobile Sampan Typesetting Spare part Empennage Remotely operated underwater vehicle Steel Steel Material
Computer animation Mechanismus <Maschinendynamik> Stem (ship) Empennage Steel Casting defect Material Casting defect
Matrix (printing) Roll forming Turning Computer animation Cartridge (firearms) Mechanismus <Maschinendynamik> Train Steel Steel Casting defect Material Matrix (printing)
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Separation process Computer animation Mechanismus <Maschinendynamik> Steering wheel Spring (device) Steel
the use of all of them strengthening mechanisms In but the current frantic deals which were discussed in some more details what and you'll see you'll see however in many steals is a very often they have there multi complement multi-phase Microsoft ruptures and done and so the additional aspects to the strength of these Mike rastructure so 1 of the young important Mike rastructure is it's traditionally I have to say is the constituent called perlite which which you probably know from your undergraduate years already which consists of this this Lamela Mike rastructure of alternating far-right and polite and they're 2 in the strength aspects of this Microsoft at its 2 important things that is the Inter Lamela spacing and then which we call the the size of the pro-life colonies you can see here that you've got a peril lapses Lamela uh and and that there are boundaries between different regions while these regions but we call perlite colonies and
the end of the most important aspect of the this the strength of this perlite appears to be related to the Inter Lamela the spacing that's the into
Lamela space and you can see that if you plot the the yield strength of the prolific steals various paralytic steals you find a whole batch type of relationship between the strength and the inverse of the square root yes and it's very clear here and it's it's for a different politics steal some that are fully politics for instance here this is a real politics steel which which would look like
like this basically and then we have these Hi Perry there you take toyed with the list carbon steals with High levels of much higher levels of carbon so you get an increase in the strength Due to the fact that you have a lot more Seaman typed in the Microsoft Vista reason human tide in the Microsoft truck which is a very hard carbon if you if you did end until a year but this still UC approximately the same slope of about 250 mega Pascal's the Times Square Root of microloans that increase in the strength as you reduce the Disuq it the rights of its is important
now many of us have perhaps do we
actually have steals that look like That's right What will yes of the many many steals and In or used today which have this which use this MicroStrategy the political Microsoft ruptures in a lot of wire rod cables are have this microscope tour tire rolled has the structure and and makes use of this refinements to
effect to get these very high stress she conceded the strengths here very high and so on
where does the strength come from me wealth you have you have 2 phases here and so you basically have the composite and it's a composite where you have to be very high if you look at the 7 tight you have at the compound Carbide which is extremely high strengths and up to now the people have tried to measure would is the strength of human inferences if you pull on compress said and what you usually find if you if you take 7 tied you make bulk cement type and tried to deformities usually breaks you cannot perform so we don't really know exactly what the yield strength is of as a bulk material intends to break fracture before a plastic pleaded for so we kind of think it's probably around 3 thousand made Pascal 3 Duke of Pascal or perhaps more and the other face this is so is so far I and we know very well what would you do the stress-strain curve looks like it's here and it's it's at low strength of relatively long strings of phase just have a future Lee a strong material and a much softer material and if you combine them both in this yes on while you can you can you can get stress-strain curves and there's no fracture of the this human tide in this perlite and even if you give very large deformations very large strains France's associated with making very thin wires did get plastic deformation of the semen typed in this case and distress tankers for a typical Lamela assured him the picture is show here and you have a you'll string around 500 men and tensile strength are typically around a thousand made a pass so if self let me say
a few more words here so what we often do I'm in for instance constructional steals yes we will not use but like we do for wire strands building construction still will use more or less same tight it to meet moralist perlite and Mike rastructure to change the strength of our steel and and will will will talk about this in a moment but that's basically what you do you add carbon and the car but that doesn't work in solution or anything it works to make more similar to more perilous than more perlite you have the stronger it and that's a traditional way of strengthening structural steel is In fact adding carbon To make more perlite and my construction and and you can see of course if you have 100 per cent of perlite and while you kind of stuck around the gig Pascal strength so nowadays we worked very differently the reason as when you add carbon to make more perlite to make you still stronger yes you basically are there other properties and not so good toughness becomes less because the the seem entirely In the end the perlite is not very tough and it will break the easily fracture the toughness is not so good the other thing which is very important technically is joining when you when you have to weld the presence of high amounts of carbon is not a good thing and so does a consequence some people have to use other solutions a non-carbon solutions to strength steels and so will talk about those as as we see examples of steel look at so we have of course
talked about Martin side we know that in side we have lots of we can can have lots of carbon in the market side because it's a this supersaturated solution of carbon and and there are equations available that will allow you to to calculate the of this deal yield strength of Martin side if you know the carbon content and a different formulas and there may be different but dependence is on the carbon content again as I've told you it's not surprising In fact if you what some of these
equations once is an equation where they carbon the strength is proportional to the carbon content here is proportional to the square root of the carbon content that's worked as a forum for the yield strength as a function of the GOP and carbon content and you can see there's not really much difference so you can't really tell whether you have the square root of carbon or be proportional To carbon content relations between yield strength and carbon ,comma exhibited but since it is the sorrow these equations and note please that when the concentration of carbon becomes very long In March inside you can make Martin side and it will be harder than fair but it will be relatively soft yeah so what makes Martin site Strong and heart is not the fact that it's marked and cyclically transform what makes it the hard and strong and brittle etc. is the fact that you have carbon in solid solution the bill is very often you hear people say Wal-Mart inside brittle Martin site is not yes there's no reason why Martin sites should be ready the Martin side is the result of a mock acidic transformation yet and of course in certain cases such as in the case of steels and uh you will have a final microscope turn and you will have a dislocation density which is relatively high because you are you need transformation dislocations but it's not very hard as you can see here and it's certainly not necessarily brittle that's what makes a brittle and and and hard and this is the fact that you have carbon unit In solid solution and you know that this this this carbon and solid solution is very it is very unhappy because it's not the solubility of carbon in far-rightist 0 at room temperature so very quickly there will be a tendency for the carbon to move out of the the lattice us and that is the reason why I low carbon levels yes we have so little strength the reason as but because the Microsoft tractor of Martin site contains what we call last yes like a structural units tasked with boundaries and these labs contain large densities of dislocations the carbon will readily go 2 these strange field Of the dislocations and as a consequence it'll stop distorting remember this the tribunal distortion I talked about this eternal distortion disappears and so that the hardening effect of the carbon is is Ltd this yes sir now what
happens to the air Martin side also it is that in particular in engineering steels where we have relatively large carbon contents for instance 0 . 4 per cent of carbon we will temper this might rastructure so we will the carbon content said useful . 4 per cent and we will temper democracy structure and we will obtain of Carbide's particles in the Microsoft find carbide particles you can do so again if you carbon content is Long less than 0 . 2 or even lower and the carbon will go to your dislocations and it gives you a soft spot inside if it's higher for instance when you making engineering steels the woods and engineering steels his friends that you you are used to make camshafts crankshafts for for motorists for instance are used to make transmissions gears etc you use it just kind of carbon levels peace deals have . but that so you can hear you can you find out that in these deals on there is also an impact from the distance between the no the carbide particles in intemperate Martins and of course where does this come from this uh uh relational that basically comes from the the precipitation strengthening so and again you can see here and it's both for tempered Martin site and for you show that you wish you can see that the relations it 1 over the distance relations and that of course what you want to have is a high density of very small particles we already know this From all the discussion of precipitation strengthening we gave Carbide's are impenetrable particles they cannot be cut by dislocations so you need to have a high density and very small radio you know you have a strong increase in distress dissidents than another parameter
the what size also plays a role in what size being this here the size of these Microsoft structural units and this is some year showing that the lot size here they didn't do it increment of strength increment duty last size is proportional to 1 over distance the laughter with Excuse me this kind of thing some of the width of the slats here I do have to say however that
there is an alternative I deal with questions questions this idea is the following so the idea that the last all are somehow In determining the structurally determining the strength of of the market size is based on the idea that on this day did the latter boundaries act as very efficient the obstacles to dislocation and I am so if you if you look at the mike Chris Cope picture both the market side that's indeed what but you would think because you see all these small bounded all these narrow laughs and clear you can clearly see the slapped boundary the the problem is that don't miss orientation Mister orientation between the slats is actually very very very small if you've due for instance a diffraction analysis of land boundary last many laps it looks like a single crystals so these slats land boundaries are not good boundaries they're not really as efficient as real grain boundaries too stop this locations from moving because there is not much very very little Miss orientation between so the In the alternative theory is that amidst it's the packet size packet size which determines the strength of the day the marketing side which is structural and so it's a packet size when you have all original the Austinite grain has the also grain will have different In can transform far and it can be like as I told you 24 different variants well groups of variance yes Will appear together I went to the shit would win they shared the same what we call the same 1 1 1 place yes and and so you can readily visualized and and they all share the different variants but they all shared the same 1 1 1 planes so it should be in the form these these blocks Nos and and that you can see which would call packets and and that's clearly the the battery unit structural unit to I specified what the what the influences of the microscope drew on the strength of the packets right and we I'm
going to skip things about the
stress-strain curves which you are familiar with I just
want to stop here because this is a very important graph here against and I just want to make sure we we understand each other yes the with when it comes to strength hence there is of course when you from your undergraduate education you know that when things get stronger yes there tend to be last the plastic lady formal they will have something that's hard will be or strong will be brought or with you you won't be able to deform that that's not really true general if you compare ceramics and metals yes it's true but it's not right you're not comparing the same things so if you work in 1 specific area of materials like steals the stronger doesn't mean less classically formidable what would end the parameter that plays the important important role here is the the strain hardening it this spring hard am so and this is illustrated here but if you plant these stress-strain curve for what's called a highest-ranked of steel and you find his black line and so on and if you what also they strain hardening yes and that's a very simple eh just slopes Of this line In true stressed restrained I grant you know at 1 point it will intersect and back .period is the but the point of instability Beyond that point you don't have uniform defamation anymore and that's a very good measure plasticity of history and so it is you make this material stronger yes without changing the slope of this material and if I make if I have a stress-strain curve and derivative and I make exactly the same site a material which just has a higher yield strength and with exactly the same slope you are right now the intersection is here so I will have a stronger material with it which with less form ability with flats ability to deform classically in a uniform matter but you can tweak you can tweak but the strain hardening you don't have to teams b the strain hardening the same yes you can change by working on the microscopic 9 and then we already told you that on the way you do this is by storing dislocations in finding ways to store dislocations in the microscope as an example here is for instance is is a trip still has it's much stronger you can see here this 1 is about 500 made part this 1 is double the strength noble destroyed and so on it is less formidable notes that not less formal it's more it's more formidable so I by working on the MicroStrategy European independently changed Frank and former ability and and highest-ranked does not mean less form balletic I don't know whether it means less format it can mean less formally because also means more for ability as long if I don't know what to strain hardening as you know that you can't have that but at but in steals it so you have to be careful about this and yes and yes you can get you larger uniform elongation and highest-ranked no problems if you tweak the Microsoft truck tour of U.S. Steel and then you understand that the mechanical properties now in
in your notes on you you you will see that it is actually a lot you can already do that with available knowledge for instance I know this is Dave stressed train an empirical stress-strain equation let's have a look at slides back
here which 1 in areas it's
just 1 it this the swift equation it's very similar to what you're used to the hall among all the Ludwick equation but it's the swift equation it's very careful when you give
data strain hardening more yields strangle
whatever you to do To say what to what empirical equation that you fit your data which is which is almost never got and so so you always on kind of have to guess then so I to say you have this swift equation empirical equations so you have parameters this should be capital and capital B and if you could correct this and yet there are equations here empirical equations based on a large amount of data 4 variety perlite and Martin side which which will allow you to actually plot stress-strain curves for far-right perlite United market size because they're the parameter any parameter B and the parameter I have been determined and as a function of the most important and a the following elements silicon manganese phosphorus and the grain size yes there's nothing theoretical about this approach which is very engineering approach works well enough if you out if you need to win do some research certainly exploring the effect of compositions of such rights it's a good way to to work because it gives you space stress-strain curve yes rather than just the yield stress and if you haven't yet stressed brokers France's if if you say the plasticity it is like this plastic strain is 0 that means you can determine the yield strength Clinton rights is very young very nice thing to use and and and and again the use the things you see art which you expect for instance for Martin side the main effect of the the District of the main effect is is due to carbon that whatever the composition is of of Martin site the the impact of the carbon overwhelms Everything else so you can work with this
and if you do this you we will be able to plot stress-strain curves for various typical compositions for instance this is this will be for interstitial free stale the steel which which basically contains a few tenths of a per cent of power manganese and silica and no free carbon this this would be discussed before Bay nights this and there's smart inside and you can see the kind that the variety Of of strengths you you have available yes when you were work which steals and also the kind of he'll nations that are available for this this might restrict and this kind of gives you a range war range of warfare I'm pro-life and the Martin side and as a function of the carbon content and what is interesting had to seeing Is that and this is In fact that the this this overlap this overlap of properties for instance you can you it you can see here that there is a lot of overlap between market side and they know in terms of strength and and and also with nite and perlite on the lower end of this strength skill has and so I it also means just that look at the Bay nite for instance the the the property range was from 100 ppm 2 .period and the 1 for perlite goes from . 4 2 .period so the fact that you can make the same mechanical properties with a much lower carbon copy using day-night Benedict makers structure is actually actively used To make steals with the high strength but also well the with lower carbon conferences and in 1 field next that's very important lately of Line Pipe Steel development the steels used to make pipes to transport gasses for petroleum products are the result of a tendency to use by nite instead of perlite In the MicroStrategy that's 1 thing or another example it is not the the evolution of rail steals rail seals are traditionally just like wires deals are traditionally per letter yes I hope you can make Benedict rails against and it's also an evolution that's happening in certain areas what will we see people using low-carbon day-night instead of prolific Mike restrictions and that's because you can get the same type of properties actually wider range than there than perlite the reason why we don't
CDs my prescriptions as much as as we could in current technology is because making the day-night requires the different processing units more a little bit more difficult processing if you need to alloy much less but you need to compensate for the call for the loss the reduction of carbon so that means a lot and we don't know much about the behavior of the nite In applications so I that makes it difficult to introduce some of Benedict grades in many applications where they would in principle be more useful but anyway it's an evolution that's common right so that when we have multi phases more phases in in steals we can have 2 extremes of equals to the strain defamation or equals stress behavior yes and in practice we have situation somewhere in between that and this means that at the heart of the 2 phases will take on the largest stresses this softer will take on the Hi here strain 10 and this is an example here would of what happens for instance in 8 In a political MicroStrategy where you have the right actually know this is missus this is a steal this means that contains the right and semen tied but not perlite lets them so Midnapore like this form if you cool down quickly if you cool down a steel With a low carbon content slowly you will form Fahri grains and semen tight particles because this is the kind of all of this is the stress-strain curve for such a steel knows where you don't have a polite but you have simmered anyway this human tide is has is is extremely hard phase the microscopic the far-right yes this 1 here as this 1 the behavior of this deal is somewhere the actual steel industry is actually somewhere in between and if you look at every Point in the stress-strain curve off the this the steel the actual stress and strain in the far-right is here and the actual stress and strain in the of semen Titus here so you have a huge what we say partitioning of stress and strain the Microsoft and you can see this type this takes a very much larger load yes but the deformation is that the strain on the similar is very small so and and so that means that even the tight is a brittle compound interest because most of the deformation is known by the far-right matrix it takes a long time thinks it is quite some deformation quite of straining before the semen type particles actually break although although the if you take this semen tight separately and would try to to to deformity and would almost break instantly couldn't plastic pleaded for in the composite it's different so that's why you know if you wonder why in perlite you got you know I you you pulling perlite why doesn't it instantly break because the Semin tied to that's because of this phenomena you get partition plan and another element nice example of steel the wit the where was measurements of partitioning has been unfrozen duplex stainless steel contains 50 % Austinite infected Percent varieties highly alloyed steel again you can see that the the actual stress training 4 4 4 8 at certain point on the stress-strain curve of of the steel the macroscopic stress-strain curve there is the partitioning between the stresses and strains between the hard harder verite and a softer Boston right the you see the far-right will I have a higher stress and less strained and he also will have higher strain and less stressed some more on Earth
indeed multi-phase steel behavior so well so this is Martin sites stress-strain curve yes and this is I stress drinker so then you can make seals which he called the peace deals where you have Microsoft answers would contain fluoride and then some Martin site particles also in the Microsoft rupture and it's possible as as we've discussed I think already too introduced market site in the and change the amount of Martin's side so if I start with the MicroStrategy fully Ferrer take the stress-strain curve will be this what and if it's fully Martin will be here but by changing the volume fraction of Martin side I can basically very I have different stress-strain curves yes so and if I measure for instance the tensile strength the tensile strength I and this is the tensile strength here and I will see that the more I have ads Martin site the higher it becomes and in practice this relation is but almost linear so the amount of Martin side of you put him out of Martin's side volume fraction of Martin side in the x axis for DP steel and you measure the tensile strength you'll see that there is a linear relation between the tensile strength N the volume fraction of it Martin such and and so you can make basically it's the DP steel I would say but tensile strength of 500 and you can go up to thousands so that's that's quite a variety quite a range of strengths that you have there to play with this is so I'm
not going to discuss the
the former ability issues you can you can just read it
and some of the aspects
we've already discussed but
there is this graph here that I think is important which I want you to definitely have looked at Is that all we were talking I remember about reduced grain sizes In reduction of grain sizes In In skills and how when reduced the the grain size you would also decreased form ability so and this is an example of the way you can look at to this so you know that if you plot to stress-strain curve of the steel and you plot to derivatives yes where the derivative is equal to distress and that is the point of uniform elongation and that's a measure for plastic former mobility if you increase it should read a few of the crease the grain size you basically moved yes this stress-strain curve upward enter yes and so you end up where is the smaller uniformly litigation and of course if you continue doing this yes you can see that as a yes you will be able to achieve a lot of strength which you will not be able to achieve a lot of former ability so when it should be remembered that if you if you plot the strength or the tensile strength as a function of 1 over the route yes it goes like this and actually when you plotted the tensile strength of the the slope was slightly lower yes sir services whatever with a show here this is actually correct you cannot increase Sociedad reduction of the grain size doesn't allow you doesn't give you of possibilities to increase the the strain hardening To the strain hardening it is it's actually as you increase the strength through give it to reduction of the greater is actually did actually gets lower so it's actually worse than here yeah that's an important point well In general steals which tend to be single phase for or mostly single phase for erratic steals we will indeed see that when you increase the tensile strength you will see a reduction In this strain hardening stance and you can measure this the engineering approach to measuring strain hardening is looking at the end of value yes the end value from the whole among equation that's what happens this week with that's because an interstitial free steel and low-carbon steel the solution strengthen Steelers structural steel on a holistic they're basically mainly for attic states so I so if you want to increase the this strain hardening you have to work on the MicroStrategy so we
won't discuss hardness
here and fracture yes but
perhaps some the word about fracture fear just just
so we understand each other if there is any the when
when you you have just a sample that steel sample that you test so so what happens beyond the the UTS is not only important I in in certain applications it is totally unimportant To a certain extent for instance the many application where you you never strained material beyond 10 20 per cent or something like that so so you never close to navigate yes for instance when you make car bodies you never deformed material so that you get non-uniform lacking I because obviously you don't want to part to look like this and this of you in many applications the only forming that you do is within the uniforms training range that so anyway but New Testament cereal the and but having said that as the many steals that you know you strain even beyond the the UTS walked for instance I have steals you can still strained 15 per cent or more Beyond the uniform acting as you get a lot of the the the the connecting the region is very high took up so you get the diffuse neck was a that this diffuse necking is related to the creation of internal defects that so what White you get suddenly admitted that the diffuse necking has but said diffuse snack that that's this this shape change here if that's not that that's not the same as this localize neck which occurs because of mechanical reasons yes as the few snacking is related to to fact that you've you've created internal voids in a sample of him and it and that's done well at certain places you get an increase in the strain rate and and all the the formation is localized here so as soon as this occurs by the way yes it means that all this the rest of the sample here stops the foreign yes it stops no more defamation so but that means said when you doing research and you have a broken sample this area here yes and this area in that yes it is actually very different answers so if if you look at the stress-strain curve elastic part and as yes and this is the UTS this sample here has the MicroStrategy at the UTS has and this might rastructure here is the sample here it's a very different Mike rastructure so and I often see this and that and then also if you're doing as samples carefully here the MicroStrategy is here so a single specimen can tell you all wanna thinks I'm very often I see is that the students not making use of this the fact that you have a lot of information on 1 subject In terms of Mike rastructure in particular because it is a broken sample actually has information is a lot of information difference of the sample at different stages the animals and so if you
were to look at your material here went we just beyond BUT yes this is what you would see yet grain
boundaries where you have the whole or here inclusion In and around the inclusion is a voice or here this is a perlite In for a ride to see here voids at the relied variety Interfax voids but and the ability to create voids yes in the MicroStrategy actually determine what my uniform elongation To a large extent from like rastructure low point of view and actually if you
plot these the day we so if you if you if if you make bars the tensile bars and you look at the area reduction In the tensile test and you do this as a function of the percentage of semen tight you might prefer use you very strong relations yes the more you have particles that will give you that will allow you to nuclear voids in the Microsoft rupture the lower your form ability will be in quicker you will start having diffuse snacking in your material so can't went with the so-called cavity nuclear nations 2nd phases have been very strong impact on the utility of and in the Stickler the neck so so I you can improve things you can do to improve that's why you it's important to them when you design steals or in practice too it and make sure that internal cleanliness of you steal is very hot so that you don't have unnecessary sulfide ore nonmetallic inclusions in U.S. Steel because they will also impact your properties because all these these these nonmetallic inclusions these Carbide's etc. that that are not necessarily whale very often act as a cavity nuclear heating the effects of the new inclusions on the during this training
camp and this is the same holds with the you know very hard faces such as Martin side this is instance Martin side In a minute in Austin I this is an Austinite matrix and here we have some Martin site in it you can see that it's a very high carbon markets I'd buy it was it's very brittle as you can see that in this case but you don't have a cavity nuclear nation but when the market side fractures it creates a lot of cracking that goes into the the Austinite also this and you
familiar with the matter the
Sharpie test again I want to stress you because will come back to that when we discussed some of structural steels is therefore erratic steals for instance is afraid 61 per cent of manganese and binary status to you've got this incredibly sharp drop in the In the absorbed energy and it's news we associate with brittle Trans granular fracture this against the type of behavior that is due to the dislocation yes the dislocations which have the screw dislocations which have such low mobility because you don't have this effect in the Austinite unison Austinite you have much lower there pearls stresses so does the screw dislocations are not subject to these very hot strong Paris valleys so you don't get but there is a decrease yes but it's it's never that strong the so we have said
that in relation to this ductile too brittle transformation that's grain size reduction it is very positive if we not the yield strength as a function of the inverse square root of the grain size we see that on top there we see an increase In our yield stress the material becomes stronger we know this I if I I the too brittle transition temperature so where there is a sharp decline in the the absorb energy in the sharp protest I see that at the time when I reduced the grain size I have a drop in the In this transition temperature and what is very important here is that if you you a conventional way conventional steel but perlite variety with a pro-lifer like variety Mike rastructure you can only go up to here in terms of properties but you can you can you can reduce the grain size but you cannot reduce it as of March as in age a lasting human disasters where you add my albeit and it allows you to reduce the grain size considerable and so this is what the myopia additions and the the processing of these along the Nile you'll be in steals allows you to to use a reduction of the grain size from 10 to about 5 or 6 and you get an additional increase in strength and reduction in Ducktown too brittle transformation temperature you you you of course do Lewis along geisha however in the applications that where we use the DNC be nailed him alloy steels we don't need very high along the nation's when you make it line pipe you don't have huge mutilations and when you make the steel plates for offshore same thing if you basically do not deform the very much but if you can use these plates to make for shipbuilding same-sex rights abuse I'm not out so so you can live with the loss of and it's not a very huge loss that you can live with the loss of the slight lost in uniform inauguration when you reduce the great sex because you have to have 3 big advantages you knew in more strength against more toughness yes and better well ability as and wild ability is something that's very essential but in 4 offshore shipbuilding and laying pipes so I began with
the these transition temperatures so we know we can improve things with them with additions With with production story of the grain size there are certain additions which will work the other way and in particular phosphorus phosphorus will increase the I do the transition ductile brittle transition temperature for what so this is pure irony that tell brittle transition temperatures around 50 40 50 and up if you add phosphorus it increases . 2 . 6 Europe so people will not use force uncle and and that's what in a big city or in in steelmaking Byron and steelmaking phosphorus removal is so important that was still sulfur removal is important but phosphorus this is this is very important because it's difficult it's difficult to go lower than 100 TPS sold but it's very important to get as low as possible have right so phosphorus found in many applications you will not use it because the goes up since then and you know when you remember that was our best solid solution hardened their in protect steals on it's very sad but you can't use it but for silicon that was the second-best 1 so but the trouble is but this is you get the same effect as you increase the amount of silicon you increase the ducked all too brittle transition temperature and that's of course a big problem however you will notice that at lower amounts of silicon there is actually decreased if so people will add up to to half a per cent of silica also in constructional steals knowing that it has no negative impact has an end that you can use of course but even half a per cent of silicon will give you 50 60 Pascal of strength has sold out and it's something that you know it is nice to have opened but but addition there are maybe to some of the people in the here that are interested in developing steals which contain larger amount of silicon because as you know the silicon is a very interesting element in connection to Benedict steals to suppress Carbide formation and so there you know it's you want to have Silicon contents which are in the range of around 1 . 5 to have this Silicon were affected effectively suppresses so that's a little bit of a delicate a choice to make and but and very little is known about this this level of of silica incomplete in steals for structural applications but it's so it's sermons the following it's it's silicon level that is acceptable in certain cases such as and in automotive applications you know that the Nunavut reasons following it win when you test for for ducked out too brittle transitions with a the Sharpie test and you're thinking of Dick gage materials you thinking about a mm thick played for instance and so when you test them with the Sharpie test use test at very high strain rates In planes strain conditions as we say canceled sold and and and so that was a very hard mechanical conditions and high street and low temperatures yes In chief material yes because it's much thinner yes it's more difficult to obtain plane strain conditions testing conditions so even if the material is more brittle yes it will not actually behave so badly as you if it was the materials so this is also something you have to realize that anyway for for many applications of structural applications and gas and petroleum industry silicon and no I'm not tired of that half a per cent and what happens if you have 3 cent of or even more are there are situations where we have this much yes electrical steels electrical steels all have these very high silicon level and it turns out that this material these materials are indeed very brittle yes and there are cases where at this level of silicon the slabs you know the material as counsel just broke we'll just fracture in the brittle fashion just under the influence of its own weight so this Susan silicon is very sensitive in enough 2 people in it Byron and still make it because they have to offer cleanup afterward
manganese and I said so manganese here 0 Manganese have risen Maine what you get a decrease In the ductile too brittle transition temperature and an increase in the absorbed energy so to manganese is always good that's always good to use what about carbon what common it's a mix message here what you see In general with carbon is as you go from very low carbon so tend to the minus 3 means gold warrant all breeding and so that is 30 ppm of carbon 30 ppm of carbon 30 ppm of carbon I see that if I increase the common a little bit isn't afraid increase the carbon I see a decrease in the ductile too brittle transformation transition temperature and this continues up to around 10 to the minus To so that's cool .period what yes after that I see an increase by the way these are different curves because they're different phosphorus contents and so you can see here again that the more phosphorus you add that the worse it gets but this is important why does it increase here and why does it decrease here yes was very simple as long as carbon is in solid solution solid solution In the Farai yes foreign solution in the form and it will have a positive in fact on the ductile too brittle transition temperature as soon as you for the men tight particles In the mike rastructure so that's at around this maximum solubility of carbon in far-right so that's about 200 ppm still around .period only 1 .period too mass you form Simone tied like stroke and you get a worsening both the Of the increase of the adept to brittle transition temperature so why does the carbon that havoc in solution have a positive impact will do that In that is very low contents of carbon In Farai the carbon tends to go to the few dislocations that are available and the grain boundaries and in the grain boundaries so dark well-documented fact of carbon increases the grain boundary cohesion yes and that that's how we explain the reason why the carbon improves the decked out too brittle transition temperature so took so Carbone and manganese my always improve things yes and carbon also In processing so as long as carbon dissidents in solution and you can learn a
lot from looking at the the Due the fracture surfaces In in ductile too brittle transformation whether it's it's some cleavage type a fracture or whether you have inter granular fracture or whether you have what would you we describe as dimples yes and the dimples and nothing else than these voids that you for In the INS in forwards that you for that the fracture and usually these dimples will contain the nuclear case site little particle uh that's inside the Matrix and which has caused the void formation and and then finally to the breakage of this this this voice rate
so look and then we won't be talking about fatigue there's separate course on this and I will also stop now anyway and
then we will learn


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