We put these lectures on YouTube also, so if there's no sound, people are going to be very unhappy. So why is it that in the case of trypsil, you keep it at 400 degrees C, and you

don't get any carbides? So remember, first of all, you start with the intercritical annealing. So 0.2%, and you do intercritical annealing. And the way you do it with drip steels is you anneal at higher temperatures

than dual phase steels in order to get more austenite. So you get this austenite content, OK?

And you cool down to, so you go like this, 0.2%, this. And then the gamma phase you have at high temperature has 0.3. I think I have to look at the phase. Let's have the phase diagrams on the screen.

That will be helpful.

I don't know why it doesn't do this. There we go.

All right, so we go to drip steels.

There we go. So there we go. So it's about 0.3 to 0.4 carbon.

And of course, if I would cool this down at this time, I would go to the MS temperature and go to the MF temperature also, and I would basically get a dual phase microstructure

with 50% of martensite. But that's not what we do. We keep the temperature at this point. So that's about 400 degrees C typically. And so this austenite will undergo

a bainitic transformation. And it's a bainitic transformation that does not include carbide formation. And the reason why is the presence of silicon. And remember, when we did the introductory lectures, I said silicon suppresses carbide formation,

and there are reasons for that. You can do a number of reasons, but you can pretty much explain it by saying that, well, there are two reasons. First, the silicon is not soluble in the cementite. And the second reason is the silicon

increases the activity of carbon in ferrite. So anyway, let's just say we know that silicon suppresses carbide formation. So what happens then is instead of staying here, the carbon content during the transformation

will increase to a specific point. And I said that point is the T0 point,

giving you a carbon content that's more than 1%. And so the austenite that you have at that time, which is very enriched in carbon, will have an MS temperature below room temperature.

So when you cool down, nothing happens. It doesn't transform. All right, so why does this happen? Well, you have to remember that the phase diagram, behind the phase diagram, there is something else.

There is a thermodynamic functions. And these thermodynamic functions are basically related to the stability of the phases that

can occur in that system. So in this case, in this particular case, during the bainite transformation, I have two phases. I have ferrite, and I have austenite.

And the stability of a phase is determined by its free energy. And that's one thing. And then the other thing you need to know is that if a free energy is low, it means that the phase is more stable.

And the lower it is, it's even more stable. And if you have two phases, and the system has to decide what to do, it will choose the lower phase, the lower free energy state. So for any phase, the free energy

is function of two parameters. The temperature and the composition. So you have many elements.

So at a particular temperature at 400 degrees C, that means it will have a free energy for the ferrite phase and for the austenite phase that will depend on the composition. Yes? And you can calculate this, but it basically looks like this.

And it's a function. So this would be free energies functions. And this is the carbon content. So you have to imagine this lies behind this.

And so this point here, which we call where the G of gamma and the G of alpha are the same, composition at which they are the same, at 400 degrees C, that's this T0.

At another temperature, G being function of T, this T0 point will be somewhere else. Yes? But it lies.

So you can actually draw this T0 line of phase diagram. It lies here, somewhere like this. And what you have to imagine during the bainite,

carbide-free bainite transformation is that there is, you're thinking of a phase diagram where there's no carbon. Yes? So there's no carbon.

And I'm basically using this material, this steel, this gamma phase, bring it at this temperature. And there's no carbide formation. Then the system will want to have this carbon content in the ferrite and this carbon

content in the austenite. Yes? But it doesn't. And the reason is the following. So we have a carbon content here. That's the original carbon content.

That would be 0.3 to 0.4 carbon. That's this point. So we're here. OK. So at this stage, we can see that the free energy of gamma is larger than the free energy of ferrite.

So if I have this gamma phase, yes, I will start to make ferrite. Yes? And it's at low temperatures. Yes?

So the way that the transformation happens in this particular case is bainitic transformation. So it works in little steps. You form small units, yes? Small units, yes? And because they're ferrite, ferrite

looks a little bit like martensite, but finer, if I may say, smaller units. And I come to, when I make this unit, there is strain energy. Yes? And it kind of stops.

What happens then is the carbon content, when the carbon will leave this ferrite. Yes? It will not form carbide. Again, it's essential that there is enough silicon so that carbides are not formed because otherwise you

will get standard bainite. So the carbon is expelled, yes? And you go into austenite and goes into the surrounding austenite. So OK. So now, instead of having this 0.3, 0.4 carbon here, yes?

I have slightly higher carbon, yes? So I have this austenite, yes? And again, the free energy of this austenite

is larger than a ferrite, yes? And so I can continue to form ferrite. And ferrite will expel carbon. So this will go on. This will go on. And progressively, the austenite will increase in carbon.

Eventually, you'll reach this T0 point in composition. So can you go beyond this point? Can you go beyond this point? Can you increase the carbon content further?

No. No, why? Because if you would do this, yes? The austenite is more stable than the ferrite. So it stops here, yes? So the austenite doesn't transform fully

to ferrite or to bainitic ferrite, rather, because it just keeps on getting the carbon from the transforming ferrite.

Then you get this huge amount of carbon in the austenite. And it's retained. How much austenite? Of course, because during the bainite transformation, of course, I start with this gamma,

inter-critically annealed gamma. And I go to a retained gamma plus bainitic ferrite. So this will go into a structure where I will have, as I showed you, you have bainitic ferrite.

And then in between, you have retained austenite. How much is left? How much volume percent of retained austenite can you expect? Well, anywhere, depending on the carbon content and the composition, of course, 10% to 15%.

So we now have a microstructure, which looks schematically like this. So I have ferrite. I have ferrite, alpha.

I have bainitic ferrite, alpha B. And I have austenite. And why is this helpful to have this austenite in the microstructure? OK. Well, what you want to happen is that in the austenite,

when I apply stress and the material deforms, yes, I want to have this austenite transform

to martensite. And I want it to happen by what is called strain-induced transformation, deformation-induced transformation. What is deformation-induced transformation? It means that first, the austenite creates dislocations.

Yes? Yes? And these dislocations, these dislocation interactions, create nuclei for martensite. Yes?

And the more I strain, the more I create new nuclei for martensite. And what happens? Every time austenite is transformed to martensite, it's replaced by a much stronger phase.

That's point number one. And second, a phase that takes in a larger volume than the phase it replaces. So suppression of necking. When you suppress necking, it means you have higher uniform elongation.

Or in other words, you have more strain hardening. Yes? And that's perfect thing for any material. Yes? Because you extend plasticity. And at the same time, you increase the strength. OK.

Now, it's a very tricky thing to achieve, this strain-induced plasticity. And I just want to say a few words about this. So when you know from your undergraduate classes in ferrous metallurgy or material science

that if this is a temperature scale, yes? And if I have some kind of austenite, yes? There is this temperature, which we call MS. Yes? Take austenite.

I quench it to below MS. What do I get? I get martensite. But there are many other ways you can make martensite with the same material, with the same phase. This martensite is called a thermal martensite.

A thermal martensite. It's formed because the driving force, thermodynamic driving force for transformation to ferrite has become very high. And you can show that in many steels,

this transformation is not time-dependent. And that's why we call it a thermal. And don't ask me to explain it, because I think it's a very silly name. Because it should not be a thermal. It should be time-independent or whatever.

But anyway, it's called a thermal martensite. Good. However, in the case of austenite at room temperature, there is also an MS sigma temperature, yes?

And there's also an MD temperature, yes? That define martensite transformation, yes? First of all, let's do MD temperature, yes? MD temperature is a temperature above which

whatever you do to the austenite, in terms of deformation or adding stresses, it will never transform. So above MD, yes, austenite is stable, yes?

So I ask you a question. For stainless steels, for instance, austenitic stainless steels, what is really important? The MS temperature or the MD temperature? MD temperature is much more important, because you have austenite at room temperature, yes?

You have a very low MS temperature. But what happens when you deform the austenite and you don't want martensite to occur? Then MD is very important. You have to make sure that MD is lower than room temperature, so you don't get martensite.

In this case, we want martensite, yes? And we want martensite during deformation, yes? We don't want martensite when we apply just stress, yeah? And this is the MS temperature. The MS temperature is the temperature that defines the range where you have stress-induced

martensite, yes, and the range where you have strain-induced martensite, yeah? And for trip steels, you want to have room temperature has to be in this range of, yeah?

What is stress-induced martensite, yeah? Well, it's very simple. When you have a phase, I just told you that the free energy

of a phase is a function of temperature and composition. Well, it's also influenced by stress, right? Because when I apply a stress, elastic stress, on the material, I add energy, yeah? So if this is G as a function of T for composition constant,

yeah, single composition, then I have something like this, yeah? And say this would be the free energy of gamma. If I add stress plus stress, elastic stress, then free energy goes up.

And remember, higher free energy means less stability, OK? So I make it easier for the material to transform. And there's no deformation involved, no plastic deformation, only elastic deformation.

So that means if I'm deforming material here, I stress it elastically, kaboom, I get martensite, OK? I don't want this. I want this strengthening of the material and the expansion of the material to happen when I'm doing the deformation.

For instance, when I do pressing or typically when I do deformations, yes, I want to have the strength increase there. So I want to have room temperature in this range where you have strain-assisted transformation,

OK? Right, so what are the important elements? Again, the composition of these steels very, very what we say lean. They're not many elements, yes? And so the main element is carbon.

It's slightly higher than in the case of DP steel, so between 0.1 and 0.2. It will have an impact on the phase distribution, on the retained austenite stability. It will also be the main hardening element for martensite when I make the martensite.

And then it may have some impacts. If I have plate-type martensite, it may reduce the toughness. And of course, because I have a relatively high carbon content, it may also impact the carbon equivalent and an impact

on the weldability of these materials. But that's not a very big issue if you take care of selecting the right welding condition. The manganese is an austenite stabilizer here, yes? It strengthens the ferrite.

It suppresses perlite formation. Those are the main things. And here, very important for TRIP is the addition of silicon, aluminum, and phosphorus. And in particular, silicon, in contrast to the DP steels,

here you add silicon to suppress cementite formation. Aluminum and phosphorus have also this effect. You can also use aluminum and phosphorus to suppress cementite formation. They're all ferrite stabilizer. They accelerate ferrite formation,

increase the activity of carbon. They're also very good at strengthening ferrite. And there may be some additions of chrome and moly sometimes, but to suppress perlite formation, but not commonly added to cold rolled TRIP steels.

Now, can we make TRIP steels via hot rolling? Yes, no problem.

So this here, this diagram here, holds for cold rolled. Cold rolled, where the starting material here is cold rolled TRIP steel. And when you start to process the material, and the microstructure, the initial microstructure,

is ferrite plus perlite. No reason to start with a TRIP steel microstructure. So you do inter-critical annealing, and then the bainite transformation in your continuous annealing line.

When you make a TRIP steel in a hot strip mill, so again, you start from your austenite, which comes out of the tandem finishing mill at around 800

to 900 degrees C. And then you keep the temperatures constant. And you do this to make ferrite, and enrich the austenite in carbon during the pro-eutectoid ferrite transformation.

And then you cool down to the coiling temperature. In this case, the coiling temperature is above the MS temperature. So you do the transformation of this austenite

here transforms to retained austenite plus bainite at 400 degrees C. What happens when I'm making the retained austenite at this stage is the MS temperature decreases,

of course, because the carbon content in the austenite goes from 0.4 to 1.2. So gradually, there is a decrease in the MS temperature. And you do this, the bainite transformation, in the coil, the coiled material.

And then when you go to room temperature, of course, to room temperature, you're above the MS temperature and you don't have a martensite formation. You're left with retained austenite.

So this is the same for which I just explained. When you do continuous annealing, this is the intercritical austenite. So you have to cool it fast enough to 400 degrees C.

So you avoid ferrite formation. When you do the bainite transformation, it will start here. The MS temperature starts to drop because I add carbon to the austenite during the bainite transformation. And the bainite transformation stops

when the transformation is incomplete, when you've reached the T0 line. And then you can cool down because the MS temperature is very much lower than the room temperature. So again, if we look at the structure originally,

we'll consist of ferrite, ferritic bainite, and retained austenite. And that's the residual austenite. And you can see residual austenite strength

is less than 600 megapascal yield strength. And these are the strength values for contribution to strength of bainite and the contributions to the strength of ferrite. And you can see, for instance, well, bainite is a little bit stronger than ferrite

because it's got lots more dislocations in it, transformation dislocation. And it's got a smaller lat size than the grain size, et cetera. But it's not hugely very much stronger than regular ferrite.

So what happens is then, when this residual austenite is this changed into martensite during the transformation. And it's a high carbon martensite, 1.2% of carbon. So you're looking at 2,500 megapascal increase

in local strength. So when we have a trip effect, the material which without the trip effect would be, for this particular example here, 680 megapascal. The deformation, which gives me the transformation

to martensite, gives me a material with the strength increase close to 900 megapascal. Of course, you don't get this huge amount of strengthening. Why? Because the retained austenite is only 10% of the microstructure. So you will have an increase of about 250 megapascal

at best. So that's about what we calculate here. So very important here is the fact that the strain hardening,

when we strain harden, for instance, a high strength IF steel, what we see is that, so you have the strain hardening, as after 5% of deformation,

the n value reaches a maximum of about 0.22. And then you've got a continuous decreasing of the n value. If you do the same thing for the trip steel,

you see that you have a sustained strain hardening and can reach up to value 0.3 before you get a reduction. And so the line where the strain

is equal to this derivative here, this is called the instantaneous strain hardening. You can see where they intersect.

That gives me the uniform elongation. So I see an increase in uniform elongation as a result of this trip effect. The trip effect, you have to be aware of this, is whether or not it works, how well it works,

depends very much on the steel you have. So the choice of the chemistry of the steel, of a trip steel, depends on what you want.

So first, we already discussed it. We said, well, we want to have strain-induced martensite, and we want the transformation has to be spread over the deformation path. So we don't want to have a lot of transformation

very early on in the deformation or very late in the deformation. So for instance, you can see here, the kinetics, the amount of martensite transformation as a function of strain. And you see different types of trip steels. And you see, for instance, trip steels,

which only have silicon, they transform relatively early in the strain. Trip steels, where you have replaced part of the silicon with aluminum and phosphorus, have a much more spread

out deformation, sorry, transformation kinetics. So we won't get to this diagram, and it's a little bit too much detailed. So let's have a look at some trip grades here.

So you're looking at materials which can easily achieve close to 700 or 800 megapascal intense cell strength and have reasonable elongations, minimum of 23%.

And also, they turn out to be pretty good in terms of bake hardening. Yes? OK. So is there anything we can do to build

on this kind of alloy system? Well, yes. Why not, if the bainite transformation gives me

so much strength, why not forget about the ferrite phase altogether and make a bainitic steel, entirely bainitic, with some retained austenite? Well, these steels exist, and we call them bainitic steels. That's not. And so, for instance, if you look at the hot rolled fully

bainitic steel, so in the hot rolling line, in the hot strip mill, you hot roll the material. And then you cool down quickly. You don't need to make ferrite. You cool down quickly to the bainite transformation temperature in the coil.

And during this transformation, the MS temperature will decrease because I'm enriching austenite with carbon. And then when I cool down, I get carbon free bainite. And it's stronger than the ferrite.

I can also make a ferrite bainite steel, where I control the amount of ferrite. So for instance, here, and it's

very similar to what you would make in a trip steel, except it's got more bainite in it.

So after the hot rolling, I do a ferrite transformation, and then a bainite transformation. This is an example here of one of these ferrite bainite steels. You see very, very fine, this is 10 microns.

Remember that in HSLA steels, our grain size is less than 10 microns, but more than 5 microns. And you can see that much of this microstructure, the ferrite is even smaller.

So I have very, in these ferrite bainite structure, I have a very fine ferrite. One of the reasons why we are interested in this very fine microstructure is formability. It turns out that in trip steels and in DP steels,

because we form, because in comparison to ferrite bainite steels, the microstructure is a little bit coarser, the performance of these materials in a test called hole expansion, where you basically

have a press part which has a hole, and when you press it again, the hole expands. We see that trip steels and dual phase steels will crack at an earlier stage than the ferrite bainite

steels. That's one of the reasons why ferrite bainite steels are being used in certain applications. This is an example here of a ferrite bainite steel.

One of the things you'll see here is the steel looks a little bit like a trip steel in terms of the processing. But very important, it's a low carbon, low carbon steel.

And the other thing is the refinement that you get from the ferrite is actually due to micro alloying. Here are some properties for the 600 megapascal, very

large total elongations. Yes. This is an example of a complex phase steel grade. These are actually very similar to ferrite bainite steels,

but the micros are a bit more complex in the sense that in addition to a small ferrite grain size and bainite, it also contains martensite

and retained austenite. This is an example here of a 900. And because there is martensite and retained austenite, certainly the martensite, you get larger strengths, close to 900 megapascal.

Complex phase or CP grades, also called. And they are already standardized, these up to 980 megapascal.

Nowadays, this trend to go beyond the 980 megapascals, go beyond the gigapascals, has resulted in the development of grades which are ultra high strength, so which are

more than 1,000 megapascal. 1,500. And there's a lot of active research in the development of 2,000 megapascal grades that can in some way be formed.

One of the ways, very creative ways, in which you can increase the strength is by quench hardening and using press hardening steels. So the idea here is to say if we

have an ultra high strength steel, more than a gigapascal of strength, it becomes increasingly hard to press these materials. Obviously, you have a one gigapascal material, press this, you need more power in your press.

You'll damage your presses much more. The forces will be higher. And what's more, there is this phenomenon called elastic springback. So you press the part that's very high strength.

When you do this, you generate very high internal stresses. And the part, when you remove the dies, the part literally springs back. And this can lead to curvature of the part. It can lead to all kinds of problems related

to the dimensions of the parts. And dimension control, for instance, automotive industry is extremely important. You cannot have, when you make a part, it's got to have exact dimensions.

So if there is some elastic distortion due to springback, you will have to do, it's a big headache, basically. So one of the ways you can solve this is press hardening steel or quench hardening steels. You take the material, you make blanks,

you form a blank, it's a trimming press, and then you heat the material. And how does this material look like originally? Well, it looks very simple, ferrite bite, microstructure. So and the property of the starting microstructure

are here, less than 600 megapascal, elongation about 20. We heat it up, however, to 900 degrees C. We austenitize it, in other words. So this microstructure turns into homogeneous austenite.

And then, so that's in the heating furnace. And then we do, we press form it. We press form this austenite. But we press form it in water-cooled dyes. So what happens? You bring the material in, you press form austenite,

as you continue holding it in the press, the material will start cooling down. Yes? And the cooling rate is pretty high, yes? And you're going to make martensite. So this structure is turned into this structure.

And you know, of course, that this is the last martensite. Depending on the carbon content, I can get anywhere from 1,200 megapascal to 1,500 megapascal, and even beyond there.

OK, so to make this, so here, the properties at 900 are very soft. The material has tensile strength is less than 300. And the elongation is fabulous, right? 50, 40 to 50.

So no problems to turn this into austenite at high temperature, and then turn that into martensite, lat martensite, at room temperature in your duct.

What is this material here? We use, so for press hardening steel, we use a material that contains carbon, manganese,

and boron steel, yes? Why do we add boron? Well, to make the steel hardenable, yes? To suppress ferrite formation.

Another important point about this steel is that because you want to have boron effectively working as a hardenability agent, you add titanium.

Titanium, because titanium forms titanium nitride, yes? And there is no boron nitride formation. Because that's one of the problems, and we've discussed this in the past,

is that when you have boron, you add boron to a steel, it will usually scavenge, that is bind with nitrogen, yes? Instead of staying in solution. And this can be avoided by addition

of titanium, which then protects, as it were, the boron additions you've made. There are more interesting developments in the direction of making formable high and ultra high

carbon steels. One of the interesting concepts that is being developed, that's been developed

in the past couple of years, is what's called quenching partitioning steel, QNP steels. QNP processing of steel involves the following idea. And again, you can carry this out in a continuous annealing line if it's equipped for it.

So what you do, the idea is a clever idea, and it's also based on the idea of trying to introduce retained austenite in a microstructure, and in particular, in the martensitic microstructure.

Because when I quench from high temperature to low temperature, I just make lab martensite. Carbon is in supersaturated solution. And I don't have the trip effect,

or I don't have a trip effect plasticity enhancing mechanism. So let's look at what this quenching partitioning involves. So you austenitize your material. And so first step is quenching. And now the clever thing is, in this processing,

is that you stop in the MSMF range. So you stop here. Because the transformation is a thermal, the temperature at which you choose to do the transformation will also

define the amount of austenite you have. So if I stop here, I quench here, I will have some martensite and some retained austenite. So now the next step is you reheat this microstructure.

And what happens is this here, the martensite, which is supersaturated in carbon, will now transfer the carbon into the adjacent austenite.

And when this happens, of course, the MS temperature will drop. It will drop. So that when I cool down, some of this retained austenite, so this austenite here, some of this austenite here

will be retained. So it will not fully transform to martensite. And I'm left with a microstructure that's martensitic with pockets of retained austenite.

Now you may ask yourself, well, doesn't it take long times and everything? Well, no, the transfer of the carbon from the martensite

to the adjacent austenite happens very quickly. We're talking about matter of seconds. And the reason why is because in this partially martensitic microstructure, you have very small diffusion distances.

So for instance, here, if you look here, you have a small lathe of martensite. And this is austenite here. And you look at how long does it take to have almost a lot of carbon transferred from the lathe to the austenite.

And you see here, after five seconds, 10 seconds, 100 seconds here, a lot of the carbon is already in the austenite, over distances of the order of a tenth to two tenths of a micron.

And that's enough. You see here, for instance, after 500 seconds, it's less than 10 minutes. This is the profile of the carbon in the austenite.

And the original profile starts, of course, with this. So you can see most of the carbon is just quickly. And at 100 seconds, you're already here.

And that's about two minutes. So very quickly, you get the transfer of the carbon into the adjacent austenite. Now, you can calculate.

Again, when you make complex microstructures like this, the physical metallurgy is more complex. And it turns out that there is an optimum temperature at which you should quench. And typically, for carbon steels,

it's around 200 to 300 degrees C. And what is the maximum amount of retained austenite you can achieve? Well, around 20% of the volume, yes? And the chemistry of these steels, not very complex.

Again, low carbon here. This is typical composition. Low carbon, some silicon very often, because you want to, again, suppress carbide formation. And the properties are good here.

You see here, QNP processed materials have the same strength range as martensitic steels, except you have larger total elongations. And again, I remind you of the fact that these are the ultra-high strength grades.

So quench and partitioning offers you a lot of strength and elongations, formability that's better than the equivalent purely martensitic, lat-martensitic steels.

Nowadays, steel industry has discovered that working on microstructures can be very rewarding in terms of properties,

instead of just focusing on chemistry and chemical compositions, like the carbon content or manganese content. And the new steels are coming into consideration. One of them is TWIP steels, and these TWIP steels

are austenitic steels. They're not more ferritic steels, they're austenitic steels. And you can see here what happens in a TWIP steel is as you strain the material, you're looking here at a grain in the material. It's got some annealing twins, which

are normal in austenitic steels. But when I strain it and I look at the grain, I can see these very sharp lines, slip lines, appearing. The more I strain, the more the grain is divided and subdivided in tinier and tinier patches

surrounded by twins. OK? And so you can see this in TM very much, as what we see is that no strain.

We see a lot of stacking faults in the material. When we start straining, we see dislocations being formed in addition to more of these stacking faults. And eventually at around, say, 10%,

when you look at the microstructure, the entire microstructure is full of these very thin twins. So what happens in a normal microstructure, say you have dislocation source here. Dislocation loops are generated during plastic deformation, and they

run into grain boundaries and things like this, and you get strengthening. In the case of the mean free path, the mean free path that dislocations can travel will typically be of the order of the grain size.

And we know that making grain sizes smaller gives me strength. So when you have what's called deformation twinning, this phenomenon that I just explained, that as you strain the material, I form twins, deformation twin, the microstructure

will gradually be divided in smaller and smaller dimensions. So the dislocations will have smaller and smaller mean free paths. It's as if I had a dynamic hole patch effect.

I would strain the material, and the grain size would get smaller and smaller. So the tensile strength gets higher and higher. So that is the mechanism of strain hardening in these twist steels. And again, as I said, I'm going

to stop here with these new types of developments. And what is interesting, of course, is that thanks to the modern processing technology, we can make these things. In the past, it was much more harder, because you, for instance, had only

Batch annealing nowadays, you can do continuous annealing and you can actually do quite complex thermal treatments which allow you to make these microstructures in a relatively simple way and a reproducible way and using steels that are not highly alloyed or in terms of compositions are relatively simple.

Okay. Right, let me introduce the subject we will be discussing, starting to discuss

next week, well, excuse me, not next week, Thursday. So if I'm correct, there is a voting day on Wednesday, tomorrow, and on Friday is Memorial Day, right? So, and then there

are no classes on these days from what I understand. However, it's not holiday for us because we're meeting on Thursday, okay? So we will have, and I'm sorry to say, a quiz on Thursday, okay? But let me introduce the, so the way we'll work is we'll do bar and wire products

after the strip products and then we'll go into long products and then plate if we have enough time. So, well, this is one of these very famous products from this category is

Rebar, yes? That's used for construction, reinforcing cement construction, yes? We will

talk about a lot, oops, about wire and rod, let me go back here, and in particular we'll get lots of attention to wire and rod and five products groups, namely Rebar,

tire cord, gold heading quality steels, spring steels and bearing steels in addition to free cutting or free machining steels. And we'll discuss the concepts behind the

steels and the compositions and the processing and explain to you why certain choices are made because of the application, okay? So how does this compare to the product we discussed,

we just finished discussing, the hot rolled and cold rolled products? Well, for instance, for a company like POSCO, yes, in 2007 you see that cold rolled and hot rolled products are very, very strongly represented, yes? POSCO is also a big plate producer, but

you can see here that wire rod products are also very important, yes, industrially.

And so that's why we will be talking about them. The start of wire rod and bar starts in a wire rod, before the wire rod and bar mill in a continuous casting facility, yes,

usually combined with electrical furnace to make steels, but not necessarily. Certainly if you have an integrated mill, some of the steels can come from BOF. But anyway,

in these technologies for wire and rods and bar, you use continuous casting, yes? Of course, you don't use slabs, but you use multi-strand casters. Here, you're looking at square billets and one, two, three, six here, six strands of casting material. Very important

in this type of steels is the internal cleanliness of the steels. So you can see

this here. This is the fatigue life, as it were, for wire, yes, as a function of the oxygen content in the steel. And the oxygen content you have to see as a mirror for the

content of non-metallic inclusions, oxides, typically. So you can see that as we reduce the oxygen content, yes, we have a tremendous increase, because it's a log scale, in the

number of cycles these wires will survive, yes? And the trend is towards the use of, you know, vacuum treatments, use of the control of these non-metallic inclusions. Very often

when these wires break, what people actually find is a non-metallic inclusion that causes the fracture, yeah? And because you have wires, yes, the impact of one small inclusion

is very important. And the sheet, an inclusion, you know, the effect is diluted. But in the wire, it's not. Even if there is only one, that's where it will break, yes? So very important here. And it does have influence on the metallurgy. You know, for instance,

in certain applications like spring steels, where you do fatigue the material during its life, yes? You will avoid using aluminum-killed steels. You will specify silicon-killed steels

to make sure this type of non-metallic inclusions, alumina-type non-metallic inclusions, interfere with the, or reduce the fatigue. Okay, but we'll talk about this on Thursday after you've voted tomorrow for the party of your choice. Thank you very much.