Modern Steel Products (2014) - Wire & Rod Mills: lecture 23
Cooman, Bruno C. de
Professor de Cooman takes the topic of rod and bar manufacture, including non-destructive testing. Both the production and metallurgy of the alloys is described. This is a part of a course of lectures given at the Graduate Institute of Ferrous Technology, POSTECH, Republic of Korea.
 Railroad cars. Very heavy springs. Okay. So let's just have a quick view of the wire mill part. In an integrated steel plant, you will, of course, use steel from high purity steel coming from blast furnace and basic oxygen, B.O.F. furnace. And then you go to continuous casting. There it depends what your continuous castor can do. If it makes blooms, you usually need to turn these into billets, square or round billets via a blooming mill and billet mill. Or you make, if you have a castor that can make multi-strand circular or square billets, you of course don't need to do the blooming. And you go straight to the reheating furnace. Now, depending on the product, there will be more or less care taken of the surface of these billets. So if the application requires it, you will, for instance, do ultrasound testing of your billet. You'll be looking for defects in the structure that are not visible, slightly below the surface. And you can also do billet conditioning. That means you basically remove oxides and surface defects and decarburization layers on top of your billet so you have a perfectly conditioned billet. Now, these billets then go into the reheating furnace. And similarly to what we've seen for strip mills, although it looks different, of course, you do a roughing mill and then an intermediate mill and a finishing mill. And in the case of wire, we have this special cooling table, which we'll be discussing in a moment, where you do the transformation. That would be the equivalent of, say, the run-out table and the cooling in the run-out table for hot strip mill. So let's have a look at what production levels we have here. Yes. Typical, the reheating furnace will have capacities of around 100 tons, 8,200 tons per hour, the amount of steel that is being processed. The yearly production of a normal wire and bar production is usually from 350 to 500 tons, 1,000 tons per year, so typically about a little less than half a million tons a year. The billets that we use to start are 12 to 18 centimeter in section. Rolling speeds depends, of course, on the type of product you make. If you make very small wire, yes, the rolling speed at the exit will be very high, 100 meters per second. If you make bar, yes, or bar in coil, this bar that's the section of which is small enough, so you can still coil it, yes, 20 meters per second. Well, typical products that are made are wire rod, bar in coil, and bar. Bar being, it's too thick and the application doesn't allow you to bend it. And typical section diameters, so wire, typically wire rod would be 5 millimeters to 20 millimeters. Yes, the bar in coil 14 to 60 millimeters, about 6 centimeters, yes, and the round bars is that you don't bend, depends on the application again. If the section can be smaller than the bar in coil, of course, it's just what the application demands, whether you can coil it or not. Typical volume of a wire and bar production unit is that you don't make one single type of product in general. So it's kind of spread out over, about 50 percent goes into wire rod, yes, and then bars are either in coil or not in coil, and there it's about half and half, half will be, coil half will be just straight bars, yes. What's also important here is that these production units do not necessarily make only carbon steels, yes, they can also be involved in producing other types of steels. So typically the majority of the products will be carbon steels, but you may find wire and bar steel production units which produce also the same products, the same type of products, but stainless, using stainless steels, yes. So there is more variation in the type of compositions that you use, okay. So the basic layout is, as I said, the reheating furnace, here's a picture of the reheating furnace, yes. The billets come in at one side, come out through this much smaller, of course, exit port, yes. The reheated billets come out and then they go through a roughing mill, a roughing mill. And we'll see in a moment that the roughing, the process of rolling wire and bar products goes through special mills, yes, with alternating vertical and horizontal stands, yes. The roughing mill, intermediate mill, and then the finishing. And then you have lines that will do the transformation, excuse me, the cooling of a straight bar on a cooling bed. If you have bars in coils or wires, you will have the wire rods are usually, heat treated as they come out of the finisher, and the bars in coil can be heat treated or transformed after that. So this is here the finisher, yes. And so you can see the section of the product decreasing as you go through the unit. This is an intermediate part of a wire and bar mill. And you can see here that you see the rolls are, in this case, a vertical, horizontal, excuse me, horizontal. In this case, they are vertical. And then here they are again horizontal and vertical, okay, etc. And so the reason is you cannot make the, if you have two rolls, yes, you cannot make the, and you start with a big section, yes, you cannot make the final section, yes, by doing a circular, changing the section in a circular manner. And the reason is, is because you're rolling basically, right? So if you're rolling things, they will tend to assume this shape, yes. And so the way it works, you basically have oval shapes, yes, as you do the reduction of the section. There are many steps, many more steps in the deformation. This is a case which would be a more old-fashioned case where you have a blooming mill. Remember, that's where you have a heavier section such as ingots or you have a bloom. So nowadays, because of the continuous casting, lots of this blooming is not necessary anymore. You can just basically cast directly the bar, yes, or the billet in the right size. Okay, so that reduces the amounts, the number of stands that you need to have, okay? Here you can see, and the evolution can be quite dramatic. This is, for instance, an example here where it goes oval, square, oval. Yes, it depends very much on the technology that's installed. And this is an example here where you go from oval round, oval round, yes. But the basic point being that you don't go from the starting situation, which may be a square billet, to the end situation via continuous diameter reduction. You go through these non-rectangular sections, yes. Okay, it's not the case when, of course, you, towards the end of the process, where your product usually has to have a very perfect round or square. I'm only talking here about round shapes, but if you need square shapes, it's the same thing. So there, and that's what happens in the finishing mill, yes, you have five or six stands, maybe more, where you generate the final shape, the final required shape. And in this case, your stands will make, in this case, the circular sections, yes. And you can have two high round passes, like this one, or three roll round passes, like this one here. Okay, so you've got, and here, these, in the finishing mill, when you have these three roll reducing and sizing blocks that we call them, we don't really call them stands. The, you have the rolls are oriented in Y positions and anti-Y positions, yes. So as to have, see, when you, when you roll, every time you roll like this, you will always have a little bit of material that will be squeezed out. And so, and that is why the, you usually turn, you go from a vertical to a horizontal situation or from a Y situation to anti-Y situation, because in the next stand, in the next stand, you'll be doing the rolling this way, yeah. You'll be doing the rolling this way, okay. And so here, of course, you'll have a, still a little bit of material that you, you don't, this material doesn't really get squeezed out, it's just, because it's an opening, it doesn't get reduced, yes. Some people think this material gets kind of, gets pushed out from between the rolls, that's not really what happens, it's just you don't roll it, so it's not reducing, yeah. So, and so this squeezing out is reduced a lot and also, and it's even better with these three roll reducing and sizing blocks, yes. And this is an example of how things look like, okay. And this is a typical example here, it's a slightly older setup and you can see there are one, two, three, one, two, three, four, five, about five of these blocks, yes. The company that makes those is very famous, yes, because it basically owns the technology for these three roll reducing and sizing blocks, and it's called Cox from Germany. And it's, and so that's very often the type of equipment that you find at the end of a bar or wire mill. Again here we won't go into this, but obviously you understand that we have a section, a material that has this kind of section, yes, and you have to turn it into maybe something that's just a few millimeters or in diameter, right. So things become very, very long, yes, in a bar or mill, yes, very long. And so, and you go from one stand to another stand to another stand. So there'll be, you remember when we talked about the hot strip mill, you always have problems, you know problems, but you have to deal with the fact that you may have tension, yes, between the both, and you need to have, of course, constant mass throughput, yes. If one mill produces more, has a higher velocity, exit velocity, then the next mill has an entry velocity, you're going to accumulate material in your mill, and you end up with cobbles, yes, and it can be pretty horrible when this happens, because you get this very high temperature spaghetti all over the place, yes. And once it's cooled, you have to remove it and cut it up, it's a terrible loss of time. So these mills, and I'll show you an example of this in a moment, do take this into consideration for the processing. So, of course, when you make bar, the section is much larger than in, this is a larger section, yes, you don't need as many stands, in fact, you may just have a few roughing stands. So for instance, if you make a round bar mill, we'll have heating furnace, you can have a blooming mill, perhaps, yes, but you will have then going to a roughing mill, an intermediate mill, and a finishing mill can be one mill position, with different stands, where the bar goes back and forth till it's got the right section. So typically machine structural parts that are based on these bars will be produced this way. In a wire mill, of course, we have much smaller reductions, larger reductions, excuse me, so you go from heating furnace, there may or may not be this reversing rougher that's similar to this one, yes. That depends on what we start with, yes, and then you go through the intermediate mill and wire rod blocks where all the stands are in tandem, okay. So again, I want to mention the fact that all these mills, the material comes in, goes through one stand, goes through another stand, and so how do you manage the material flow, the mass flow through the line, yes. Nowadays, what is being done is tension free rolling, yes. You basically have something that's reminiscent of a looper, a looper between the rolling stands of a finishing mill, yes. So, and in this case, the loop that you have is such that you eliminate the tension. So there is no tension between the wire, yes, between the stands. So this way, we are able to provide at the exit a constant exit velocity, yes, it's constant. It's constant, this exit velocity is constant, and that is rather important because of the heat treatment or the cooling that's being done after the finishing mill. This heat treatment requires a constant exit speed for the cooling bed, or for the cooling bed is basically the name we use for the run-out equivalent of the run-out table in the hot strip mill, the cooling bed. And this exit speed must be synchronized with one part that, you'll see that in a moment what it looks like, the part that puts down the wire on the cooling bed, and that's a laying head, laying head. And that's a rather slow equipment, it's not really able to respond to exit velocity changes, yes. So it's critical to keep the exit velocity constant. A wire mill can make a very large, not only a wide selection of diameters, but a very large number of diameters, yes. So for instance, this is an example here of a situation where a wire mill can make sections going from about 19 millimeters to 75 millimeters, yes. And so you can see the ranges, the actual ranges of the actual diameters that it can make, yes. Now the way it makes it is by combining different stands, yes, and in these stands having different types of rolls, yes. So there is a very large number of rolls that you need to manage in these wire and bar mills, yes. It's not like a hot strip mill where you always have the same work roll and backup roll for a certain stand. Here it depends on what you're going to produce, yes. So for instance here you can see in this mill, in this particular mill you have oval and round changes, yes. And if you want to make, say, the exit rougher diameter is 115 millimeters, so about 10 centimeters, and you want to make a 35 millimeter wire out of this, well this is the sequence that will have to be mounted, yes. So, okay. So that means that you have to set up the mill for specific products, yes. Now you realize, of course, that when you're making a wire, yes, there's only one wire that goes through the line, right. So if you make small wire, the productivity is low, okay. So for products, very often that's what you have to live with because you need to make products with certain specifications in terms of the dimensions. If they ask you to make a five or one centimeter diameter bar, it shouldn't be 1.3 or sometimes one, it's got to be that dimension, yes. So there's not much you can do, but there are products which are commodity products, yes, where the demands are less, yes. And where you can, and of course the costs, the prices are much less, so there it's important to increase productivity, yes. And so there are possibilities to do this, for instance, if you have a rebar, for instance, commodity product, yes, there are units that will allow you to make three bars or more bars in parallel. This is an example here where you have about a centimeter large rebar, yes, and it's produced here in this unit that's split, it's a bar splitting unit, yes. And you enter with something that looks like this, yes, and after this unit it's split in these rebars, yes. And so the amount of material you produce, the amount of bars you produce per unit of time is increased, yes. That allows you, but of course you can only use it for large production volumes, smaller rebar sizes, and obviously we're talking about commodity products here. Temperature control, as always, very important with steel, certainly carbon steels, yes. So typically a typical mill temperature profile will be reheating at 1100 for 20 minutes, so remember that slabs in the hot strip mill are two hours at 1250, yes. This is much shorter, one of the reasons is of course that these billets are much smaller than these huge slabs, yes, okay. And the temperature decreases slowly as you go through the line, yes. You end up with relatively simple rules when it comes, and we'll discuss those when it comes to how you cool the wire after it's being produced. So we'll see, first you have a cooling from the deformation temperature to about 910, yes, and then you do what's called Stelmore cooling, yes, to typically 570. And we'll see that that temperature is the temperature that we like to carry out the pearlite transformation, yes, and then you air cool the material. Again, as always in a steel hot production area, the temperature is not homogeneous at the surface and the interior of the material. So if you look at the surface, you get the blue profile here. So you have the roughing mill, the intermediate mill, yes, and every time you go through the mill, you get cooling from the mill, yes. So the surface is cool. At the very center of the material, it's a very different story. Every time you pass through the deformation stages, you get heating, the material heats up in the center, yes. So that when you get out of the mills, the surface temperature increases again, yes, and this is the actual, say, average temperature. So at the end, when you come to having to do the transformation, yes, you will have to apply cooling, and these are these cooling stages, yes. That are used at the exit of the wire after the exit from the mill. Okay, so why do we need to do this? Well, first of all, the wire steels that we make are very often steels that contain, or where pearlite is a very important constituent, yes. And so let's just make, we'll go into details in the products, but one of the products that are being made with wire are what we call cold-heading steels, cold-heading quality steels, CHQ, or steel for fasteners. Bolts are fasteners, nails are fasteners, yes. So typically have 0.3 to 0.5 carbon in these steels, yes. So when you cool this steel, let's say 0.4, yes, you cool this steel, what you get, of course, it's discontinuous cooling. So you get, this is your cooling curve, yes, you get the CCT diagram, yes, and you see that the transformation, if you do a slow cooling, transformation starts at 7, there is a transformation that starts at 700, yes. And if I use a high cooling rate of 50, the transformation is starting around 600 degrees C, yes. So temperatures that are much lower than what the phase diagram tells you, okay. If you look at the temperature now, yes, in the wire, yes, you see that when the transformation starts here, at these red lines, yes, and this would be for this temperature here, you see that the temperature, the transformation starts, the temperature increases, yes. And this phenomenon is called recolescence, yes, and it's basically the heat of transformation that's released, and that gives you a slight increase in the temperature, yes. And then what happens in terms of the transformation, yes, well first, you can see here, of course, as soon as we pass the E3 temperature, yes, there is, you can form some ferrites, and that's what happens, you form some initial amount of ferrite, yes. But the bulk of the transformation here, going from here to here, is the perlite transformation, and 80% of the microstructure will be, more than 80% in this particular case, will be perlite. So the fast cooling and the low transformation temperatures are very important for wire products, because that gives us the best microstructure for strength, yes. So there are different ways you can do this, let's say for instance you do the cooling with forced air, which would be about 10 degrees per second, or you can do the cooling in a metal bath, for instance lead, lead bath, lead doesn't react with steel, and you can use it as a cooling medium, yes. It also has a very low melting temperature, yes, so you can basically heat it up, and the advantage is it doesn't evaporate, yes, it doesn't alloy with the steel, and it's a very good heat conductor, so you can cool your steel to the temperature of your bath very nicely. So this is what you get if you cool your steel in lead, 20 degrees per second, forced air, yes, and you can look at the strength that you get for the same material, yes, when you do the transformation in this lead or in the forced air cooling. So the mean temperature for transformation, the mean temperature transformation in forced air is around 640, in the lead, yes, it's around 600 or lower, yes. Very often this treatment in lead is called patenting, it's basically using lead as a low temperature cooling medium with a high cooling rate, and you see that we can achieve an impressive increase in strength just by doing the transformation at higher rates and lower temperatures, okay. So that is one method that is used by the steel maker to increase strength, yes, is transformation at lower temperatures, yes, and higher cooling rates, yeah. When the products are made, yes, we can also increase the strength even further by reducing, continuing to reduce the interlaminar spacing of the pearlite, yes, and that's done by deformation, yes, so if you take one of these materials, let's go back, for instance, you see here forced air cooling, lead patenting, gives me about 10 cell strength around a thousand, yeah, around a thousand, so that would be somewhere here, yes. If I draw this material, yes, I get an increase in strength, in strength of course, and I get a reduction, a refinement of the pearlite, and you can see here very large increase in strength, almost three times, starting from a thousand, you get close to three giga Pascal, and it's also important to have a very small starting microstructure to do this, okay. So how do you actually carry this out, this transforming all this wire that comes out up to 100 meters per second, how do you do the transformation, how do you manage this? Well, there's a clever way in which it's being done, with this piece of equipment here, yes, the wire comes in as a wire, yes, and this machine turns it into a spiral, yes, spiral shaped wire, so instead of having straight wire, it now comes out as a spiral, yes, you can see it coming out of the machine, this laying head as a spiral, and then you put it down on a cooling table, yes, and you can see here these are all, this is the wire that's laid down, yes, on a cooling table, so this is the top view of the, this cooling table, and you see here the rings of the wire, yes, and it's carried by a conveyor chain that takes it along over the cooling section. The cooling section itself, view from the side, so you can see here you have these rings, yes, that are put on top of each other, and below, so it's open, yes, it's open, this conveyor belt is open, and you have fans that blow air through it, yes. And so that will give you a cooling, you can control the cooling by having a cover, yes, put a cover on top of the rings so that the cooling rate is less, yes, it's, right, and so we can adjust the cooling rate on this table, yes, this is the picture here, this is the laying head, this is the ring wires, as they go on the wire rings, as they are on the conveyor belt, and here you see this, the covers, the covers here, that you can put down over this, over your cooling section to decrease the cooling rate, yes, and so as the wire cools down, yes, of course it's not red anymore, red hot anymore, and at the end we can form these coils, yes, by putting them over this cone here, yes, and for final cooling, and then you can make these coils of wire. So this is for how you produce wire, yes, but in the case of bar, the amount of deformation, the amount of reduction is much smaller, yes, and the little bit shift in emphasis when you make bar, certainly bar, for instance, bright bar, such as the one you see here, so again you start with heating the billets, you force them, or usually you roll them, yes, so that they have the right general dimensions, yes, they're usually then annealed and pre-aligned, yes, then we have bar peeling, yes, again this is not for all kinds of bars, not for rebars, for instance, for bright bars that are used in machine parts, yes, or motors, yes, the bar peeling you remove oxide, skin, generally the chilled skin is because the outer side may have cooled down faster and be, for instance, martensitic, so you want to remove it, also may want to remove surface cracks so that you can achieve dimensional accuracy and high surface finish. The bars are very many applications that have to be very straight, so you have to straighten them, and then in many applications you also want to the ends, the quality of the ends of the bar has to be assured, you have certain finishes, so we're talking about chamfering and end-facing, I'll show you an example. For bars are typically fully tested ultrasonically, so to detect cracks and imperfections inside the material, then marked, and if it's required by the application there may even be the final grinding of the bar to get high quality surfaces. So you have to imagine these bars that come out of the mill, they will pass through, first pass through a unit that does the peeling, yes, and I don't have really good picture of the process, but basically these bar enter the peeling machine and there is a turning head in the peeling machine with carbide tools, that will remove, it turns, it spins around, and it removes at very high speed, it removes all these surface layer basically, removes oxide, etc. And it gives you very high, again, dimensional quality. And some of the bars will require drawing, so lengthening, so you can lengthen the bar and get reduction in section this way. You can have straight drawing, you can have them by spinning, or you can basically draw the rods, yes. When you do this drawing, so you basically have a circular tool with cylindrical tool with a hole in, yes, you pass your wire or your bar through it, yes, and when you do this, it's very, it's of critical importance, yes, that the force with which you pull, and in particular the angle here, the angle of the tool is chosen very carefully. Why is that? Because if you don't do this, you get what are called chevron defects in the bar. So these are chevron defects, and which you can basically see these are cracks, internal cracks. So the bar looks perfect from the outside, but internally you have these chevron defects. And the chevron defects occur for the following reason, in bars, no? Because when we are reducing bars, the diameter of the bars, you have plastic deformation inside the die, yes. And if the plastic deformation zone, yes, does not reach to the center of the bar, yes. So if there is a part of the bar that does not deform, we call this the dead zone, yes. So in the dead zone, there is no deformation, yes. Well, then this part deforms, and this part deforms, and the dead zone will crack, basically, yes. Obviously because it doesn't become longer, yes, it should crack, it will crack. And this depends very much on this angle here of the drawing die, and the amount of deformation that we give, yes. And so if the angle is very small, of course, we get safe situation, yes. If the angle is very large, very steep, like in this case, then we get shaving, that's also not very good, yes. And so what you need to have, and you also want to avoid this intermediate stage where you have a dead zone, a dead zone, deformation dead zone, where you start making chevron marks, okay. Straightening and finishing of the ends of the bars is very important, yes. So this is, so you have chamfering machines which will change the ends of the bar, for instance, in this case, it's a tube, or, yes, and the end finishing here, the end, yes, it has to be, of course, flat and of high quality. The straightening happens, is done in special straightening machines, yes. This is what it looks like, you have the bars straightening machines. If you have round bars, you typically have a pair of rolls that are shaped, yes. You can see they're not flat, they're shaped like this, yes. And this one is shaped like this, and they're crossed, yes. So when the bar passes through, it turns, it does two things, it turns, and it's being slightly bent when it goes through these rolls, yes. In order to keep it in place, if I look from the front, yes, there are guides, yes. So the bar is basically getting little amounts of deformations back and forth so that it becomes straight. And there are similar types of equipment for, if your bar is a square bar, yes, another round bar, you have profile straighteners, yes. Okay, very important for bars, yes, and profiles, is that you need to test them. You need to test them to check the internal quality. We've just seen that you have the chevron marks. The chevron marks are absolutely not visible from outside, from the outer side. So you need to do a surface quality of your material, so you have to make sure there are no cracks, for instance, at the surface, yes. And you do this with eddy current testing. That's the most common method, is eddy current testing. You can also do it with automatic visual inspection, otherwise you have to do it, there has to be an inspector who will actually inspect all the tubes, or the bars. The production rates are too high for one person to do this, but you can do this with a computer who will recognize, so you will take images of the product as it comes out, and analyze the images and make reports about the defects it's detected, yes. The other method is eddy current testing, electrical nature, and both of these methods, because you can automate them, are very popular lately. And then when it comes to the internal inspection, you cannot use eddy currents testing, because eddy current testing is only sensitive to surface defects. And of course visual inspection, whether it's a person or a camera, or with a camera, it's the same thing, you can only see the exterior. So with ultrasonic testing, yes, you can do internal inspection, yes. And nowadays you have, for instance, these new probes, phase array probes, you can basically test 100% of your production, yes, and make sure that there are no internal defects, in particular that there are no things like chevron marks. Right, so bar and rods, interpass times and strain rates can be very high, deformation rates, yes. I'm going to talk about this too much. With wire and bar roll, there is absolutely no reason why you cannot use alternative or newer processing methods when you do the deformation at high temperatures. So yes, you can do standard rolling or normalizing rolling or thermo-mechanical rolling of these steels, yes. And again, and use concepts like the ones we use for a thermo-mechanical processing of strip, you can apply these concepts to wire and bar products, okay. So we've discussed this at length and there's no difference in the approach. Let's have a look now at some products, specific products. So in, when we come to wire products, these are the five groups of applications which are the most important one, tire cord steel, cold-heading quality steel, spring steel, bearing steel and free-cutting steel. And what is important in each application is strength, yes, certainly in the two top ones. But in an application like spring steels, its fatigue is extremely important, yes. And in case of bearing steels and spring steels, cleanliness is extremely important. You don't want to have material failure due to non-metallic inclusions. And the last application, free-cutting steel, that's where you make small steel parts, yes. You have the requirement of machinability is important. Let me just to wrap up this part and say a few things about bars, yes. So bars we're talking about, heavier sections, yes. So these are typical applications. You have shafts, yes. Typical example here is a forged crankshaft, yes. You have gears, yes. This is gear for transmission of the car, yes. You have induction-harnable steels that are used in treated condition. For instance, this bar there. There's an application stabilizing bars are used for the steering of all vehicles, trucks and cars, yes. So there are usually bars that are hot-formed and quenched. And then we also have heavy springs, yes. So applications such as these, very heavy springs such as railroad cars, yes. Okay, so we'll talk about these in more detail when we meet next Tuesday. Thank you. Thank you.
 Railroad cars.  Very heavy springs.  Okay.  So let's just have a quick view of the wire mill part.  In an integrated steel plant, you will, of course,  use steel from high purity steel coming from blast furnace and basic oxygen, B.O.F. furnace.  And then you go to continuous casting.  There it depends what your continuous castor can do.  If it makes blooms, you usually need to turn these into billets,  square or round billets via a blooming mill and billet mill.  Or you make, if you have a castor that can make multi-strand circular or square billets,  you of course don't need to do the blooming.  And you go straight to the reheating furnace.  Now, depending on the product, there will be more or less care taken of the surface of these billets.  So if the application requires it, you will, for instance, do ultrasound testing of your billet.  You'll be looking for defects in the structure that are not visible, slightly below the surface.  And you can also do billet conditioning. That means you basically remove oxides and surface defects  and decarburization layers on top of your billet so you have a perfectly conditioned billet.  Now, these billets then go into the reheating furnace.  And similarly to what we've seen for strip mills, although it looks different, of course,  you do a roughing mill and then an intermediate mill and a finishing mill.  And in the case of wire, we have this special cooling table, which we'll be discussing in a moment,  where you do the transformation. That would be the equivalent of, say, the run-out table  and the cooling in the run-out table for hot strip mill.  So let's have a look at what production levels we have here.  Yes. Typical, the reheating furnace will have capacities of around 100 tons, 8,200 tons per hour,  the amount of steel that is being processed.  The yearly production of a normal wire and bar production is usually from 350 to 500 tons,  1,000 tons per year, so typically about a little less than half a million tons a year.  The billets that we use to start are 12 to 18 centimeter in section.  Rolling speeds depends, of course, on the type of product you make.  If you make very small wire, yes, the rolling speed at the exit will be very high, 100 meters per second.  If you make bar, yes, or bar in coil, this bar that's the section of which is small enough,  so you can still coil it, yes, 20 meters per second.  Well, typical products that are made are wire rod, bar in coil, and bar.  Bar being, it's too thick and the application doesn't allow you to bend it.  And typical section diameters, so wire, typically wire rod would be 5 millimeters to 20 millimeters.  Yes, the bar in coil 14 to 60 millimeters, about 6 centimeters, yes,  and the round bars is that you don't bend, depends on the application again.  If the section can be smaller than the bar in coil, of course,  it's just what the application demands, whether you can coil it or not.  Typical volume of a wire and bar production unit is that you don't make one single type of product in general.  So it's kind of spread out over, about 50 percent goes into wire rod, yes,  and then bars are either in coil or not in coil, and there it's about half and half, half will be,  coil half will be just straight bars, yes.  What's also important here is that these production units do not necessarily make only carbon steels,  yes, they can also be involved in producing other types of steels.  So typically the majority of the products will be carbon steels,  but you may find wire and bar steel production units which produce also the same products,  the same type of products, but stainless, using stainless steels, yes.  So there is more variation in the type of compositions that you use, okay.  So the basic layout is, as I said, the reheating furnace,  here's a picture of the reheating furnace, yes.  The billets come in at one side, come out through this much smaller, of course, exit port, yes.  The reheated billets come out and then they go through a roughing mill, a roughing mill.  And we'll see in a moment that the roughing, the process of rolling wire and bar products  goes through special mills, yes, with alternating vertical and horizontal stands, yes.  The roughing mill, intermediate mill, and then the finishing.  And then you have lines that will do the transformation, excuse me,  the cooling of a straight bar on a cooling bed.  If you have bars in coils or wires, you will have the wire rods are usually,  heat treated as they come out of the finisher,  and the bars in coil can be heat treated or transformed after that.  So this is here the finisher, yes.  And so you can see the section of the product decreasing as you go through the unit.  This is an intermediate part of a wire and bar mill.  And you can see here that you see the rolls are, in this case, a vertical, horizontal, excuse me, horizontal.  In this case, they are vertical.  And then here they are again horizontal and vertical, okay, etc.  And so the reason is you cannot make the, if you have two rolls, yes, you cannot make the,  and you start with a big section, yes, you cannot make the final section, yes,  by doing a circular, changing the section in a circular manner.  And the reason is, is because you're rolling basically, right?  So if you're rolling things, they will tend to assume this shape, yes.  And so the way it works, you basically have oval shapes, yes,  as you do the reduction of the section.  There are many steps, many more steps in the deformation.  This is a case which would be a more old-fashioned case where you have a blooming mill.  Remember, that's where you have a heavier section such as ingots or you have a bloom.  So nowadays, because of the continuous casting, lots of this blooming is not necessary anymore.  You can just basically cast directly the bar, yes, or the billet in the right size.  Okay, so that reduces the amounts, the number of stands that you need to have, okay?  Here you can see, and the evolution can be quite dramatic.  This is, for instance, an example here where it goes oval, square, oval.  Yes, it depends very much on the technology that's installed.  And this is an example here where you go from oval round, oval round, yes.  But the basic point being that you don't go from the starting situation,  which may be a square billet, to the end situation via continuous diameter reduction.  You go through these non-rectangular sections, yes.  Okay, it's not the case when, of course, you, towards the end of the process,  where your product usually has to have a very perfect round or square.  I'm only talking here about round shapes, but if you need square shapes, it's the same thing.  So there, and that's what happens in the finishing mill, yes, you have five or six stands,  maybe more, where you generate the final shape, the final required shape.  And in this case, your stands will make, in this case, the circular sections, yes.  And you can have two high round passes, like this one, or three roll round passes, like this one here.  Okay, so you've got, and here, these, in the finishing mill, when you have these three roll reducing  and sizing blocks that we call them, we don't really call them stands.  The, you have the rolls are oriented in Y positions and anti-Y positions, yes.  So as to have, see, when you, when you roll, every time you roll like this,  you will always have a little bit of material that will be squeezed out.  And so, and that is why the, you usually turn, you go from a vertical to a horizontal situation  or from a Y situation to anti-Y situation, because in the next stand,  in the next stand, you'll be doing the rolling this way, yeah.  You'll be doing the rolling this way, okay.  And so here, of course, you'll have a, still a little bit of material that you,  you don't, this material doesn't really get squeezed out, it's just, because it's an opening, it doesn't get reduced, yes.  Some people think this material gets kind of, gets pushed out from between the rolls, that's not really what happens,  it's just you don't roll it, so it's not reducing, yeah.  So, and so this squeezing out is reduced a lot and also, and it's even better with these three roll reducing and sizing blocks, yes.  And this is an example of how things look like, okay.  And this is a typical example here, it's a slightly older setup and you can see there are one, two, three, one, two, three, four, five,  about five of these blocks, yes.  The company that makes those is very famous, yes, because it basically owns the technology for these three roll reducing and sizing blocks,  and it's called Cox from Germany.  And it's, and so that's very often the type of equipment that you find at the end of a bar or wire mill.  Again here we won't go into this, but obviously you understand that we have a section,  a material that has this kind of section, yes, and you have to turn it into maybe something that's just a few millimeters or in diameter, right.  So things become very, very long, yes, in a bar or mill, yes, very long.  And so, and you go from one stand to another stand to another stand.  So there'll be, you remember when we talked about the hot strip mill, you always have problems,  you know problems, but you have to deal with the fact that you may have tension, yes, between the both,  and you need to have, of course, constant mass throughput, yes.  If one mill produces more, has a higher velocity, exit velocity, then the next mill has an entry velocity,  you're going to accumulate material in your mill, and you end up with cobbles, yes,  and it can be pretty horrible when this happens, because you get this very high temperature spaghetti all over the place, yes.  And once it's cooled, you have to remove it and cut it up, it's a terrible loss of time.  So these mills, and I'll show you an example of this in a moment, do take this into consideration for the processing.  So, of course, when you make bar, the section is much larger than in, this is a larger section, yes,  you don't need as many stands, in fact, you may just have a few roughing stands.  So for instance, if you make a round bar mill, we'll have heating furnace,  you can have a blooming mill, perhaps, yes, but you will have then going to a roughing mill,  an intermediate mill, and a finishing mill can be one mill position, with different stands,  where the bar goes back and forth till it's got the right section.  So typically machine structural parts that are based on these bars will be produced this way.  In a wire mill, of course, we have much smaller reductions, larger reductions, excuse me,  so you go from heating furnace, there may or may not be this reversing rougher that's similar to this one, yes.  That depends on what we start with, yes, and then you go through the intermediate mill  and wire rod blocks where all the stands are in tandem, okay.  So again, I want to mention the fact that all these mills, the material comes in, goes through one stand,  goes through another stand, and so how do you manage the material flow, the mass flow through the line, yes.  Nowadays, what is being done is tension free rolling, yes.  You basically have something that's reminiscent of a looper,  a looper between the rolling stands of a finishing mill, yes.  So, and in this case, the loop that you have is such that you eliminate the tension.  So there is no tension between the wire, yes, between the stands.  So this way, we are able to provide at the exit a constant exit velocity, yes, it's constant.  It's constant, this exit velocity is constant, and that is rather important because of the heat treatment  or the cooling that's being done after the finishing mill.  This heat treatment requires a constant exit speed for the cooling bed,  or for the cooling bed is basically the name we use for the run-out equivalent of the run-out table in the hot strip mill,  the cooling bed.  And this exit speed must be synchronized with one part that, you'll see that in a moment what it looks like,  the part that puts down the wire on the cooling bed, and that's a laying head, laying head.  And that's a rather slow equipment, it's not really able to respond to exit velocity changes, yes.  So it's critical to keep the exit velocity constant.  A wire mill can make a very large, not only a wide selection of diameters, but a very large number of diameters, yes.  So for instance, this is an example here of a situation where a wire mill can make sections going from about 19 millimeters to 75 millimeters, yes.  And so you can see the ranges, the actual ranges of the actual diameters that it can make, yes.  Now the way it makes it is by combining different stands, yes, and in these stands having different types of rolls, yes.  So there is a very large number of rolls that you need to manage in these wire and bar mills, yes.  It's not like a hot strip mill where you always have the same work roll and backup roll for a certain stand.  Here it depends on what you're going to produce, yes.  So for instance here you can see in this mill, in this particular mill you have oval and round changes, yes.  And if you want to make, say, the exit rougher diameter is 115 millimeters, so about 10 centimeters,  and you want to make a 35 millimeter wire out of this, well this is the sequence that will have to be mounted, yes.  So, okay.  So that means that you have to set up the mill for specific products, yes.  Now you realize, of course, that when you're making a wire, yes, there's only one wire that goes through the line, right.  So if you make small wire, the productivity is low, okay.  So for products, very often that's what you have to live with because you need to make products with certain specifications in terms of the dimensions.  If they ask you to make a five or one centimeter diameter bar, it shouldn't be 1.3 or sometimes one, it's got to be that dimension, yes.  So there's not much you can do, but there are products which are commodity products, yes, where the demands are less, yes.  And where you can, and of course the costs, the prices are much less, so there it's important to increase productivity, yes.  And so there are possibilities to do this, for instance, if you have a rebar, for instance, commodity product, yes,  there are units that will allow you to make three bars or more bars in parallel.  This is an example here where you have about a centimeter large rebar, yes, and it's produced here in this unit that's split, it's a bar splitting unit, yes.  And you enter with something that looks like this, yes, and after this unit it's split in these rebars, yes.  And so the amount of material you produce, the amount of bars you produce per unit of time is increased, yes.  That allows you, but of course you can only use it for large production volumes, smaller rebar sizes, and obviously we're talking about commodity products here.  Temperature control, as always, very important with steel, certainly carbon steels, yes.  So typically a typical mill temperature profile will be reheating at 1100 for 20 minutes, so remember that slabs in the hot strip mill are two hours at 1250, yes.  This is much shorter, one of the reasons is of course that these billets are much smaller than these huge slabs, yes, okay.  And the temperature decreases slowly as you go through the line, yes.  You end up with relatively simple rules when it comes, and we'll discuss those when it comes to how you cool the wire after it's being produced.  So we'll see, first you have a cooling from the deformation temperature to about 910, yes, and then you do what's called Stelmore cooling, yes, to typically 570.  And we'll see that that temperature is the temperature that we like to carry out the pearlite transformation, yes, and then you air cool the material.  Again, as always in a steel hot production area, the temperature is not homogeneous at the surface and the interior of the material.  So if you look at the surface, you get the blue profile here.  So you have the roughing mill, the intermediate mill, yes, and every time you go through the mill, you get cooling from the mill, yes.  So the surface is cool.  At the very center of the material, it's a very different story.  Every time you pass through the deformation stages, you get heating, the material heats up in the center, yes.  So that when you get out of the mills, the surface temperature increases again, yes, and this is the actual, say, average temperature.  So at the end, when you come to having to do the transformation, yes, you will have to apply cooling, and these are these cooling stages, yes.  That are used at the exit of the wire after the exit from the mill.  Okay, so why do we need to do this?  Well, first of all, the wire steels that we make are very often steels that contain, or where pearlite is a very important constituent, yes.  And so let's just make, we'll go into details in the products, but one of the products that are being made with wire are what we call cold-heading steels,  cold-heading quality steels, CHQ, or steel for fasteners.  Bolts are fasteners, nails are fasteners, yes.  So typically have 0.3 to 0.5 carbon in these steels, yes.  So when you cool this steel, let's say 0.4, yes, you cool this steel, what you get, of course, it's discontinuous cooling.  So you get, this is your cooling curve, yes, you get the CCT diagram, yes, and you see that the transformation, if you do a slow cooling,  transformation starts at 7, there is a transformation that starts at 700, yes.  And if I use a high cooling rate of 50, the transformation is starting around 600 degrees C, yes.  So temperatures that are much lower than what the phase diagram tells you, okay.  If you look at the temperature now, yes, in the wire, yes, you see that when the transformation starts here, at these red lines, yes,  and this would be for this temperature here, you see that the temperature, the transformation starts, the temperature increases, yes.  And this phenomenon is called recolescence, yes, and it's basically the heat of transformation that's released, and that gives you a slight increase in the temperature, yes.  And then what happens in terms of the transformation, yes, well first, you can see here, of course, as soon as we pass the E3 temperature, yes,  there is, you can form some ferrites, and that's what happens, you form some initial amount of ferrite, yes.  But the bulk of the transformation here, going from here to here, is the perlite transformation, and 80% of the microstructure will be,  more than 80% in this particular case, will be perlite.  So the fast cooling and the low transformation temperatures are very important for wire products, because that gives us the best microstructure for strength, yes.  So there are different ways you can do this, let's say for instance you do the cooling with forced air, which would be about 10 degrees per second,  or you can do the cooling in a metal bath, for instance lead, lead bath, lead doesn't react with steel, and you can use it as a cooling medium, yes.  It also has a very low melting temperature, yes, so you can basically heat it up, and the advantage is it doesn't evaporate, yes,  it doesn't alloy with the steel, and it's a very good heat conductor, so you can cool your steel to the temperature of your bath very nicely.  So this is what you get if you cool your steel in lead, 20 degrees per second, forced air, yes, and you can look at the strength that you get for the same material, yes,  when you do the transformation in this lead or in the forced air cooling.  So the mean temperature for transformation, the mean temperature transformation in forced air is around 640, in the lead, yes, it's around 600 or lower, yes.  Very often this treatment in lead is called patenting, it's basically using lead as a low temperature cooling medium with a high cooling rate,  and you see that we can achieve an impressive increase in strength just by doing the transformation at higher rates and lower temperatures, okay.  So that is one method that is used by the steel maker to increase strength, yes, is transformation at lower temperatures, yes, and higher cooling rates, yeah.  When the products are made, yes, we can also increase the strength even further by reducing, continuing to reduce the interlaminar spacing of the pearlite, yes,  and that's done by deformation, yes, so if you take one of these materials, let's go back, for instance, you see here forced air cooling, lead patenting,  gives me about 10 cell strength around a thousand, yeah, around a thousand, so that would be somewhere here, yes.  If I draw this material, yes, I get an increase in strength, in strength of course, and I get a reduction, a refinement of the pearlite,  and you can see here very large increase in strength, almost three times, starting from a thousand, you get close to three giga Pascal,  and it's also important to have a very small starting microstructure to do this, okay.  So how do you actually carry this out, this transforming all this wire that comes out up to 100 meters per second,  how do you do the transformation, how do you manage this?  Well, there's a clever way in which it's being done, with this piece of equipment here, yes, the wire comes in as a wire, yes,  and this machine turns it into a spiral, yes, spiral shaped wire, so instead of having straight wire, it now comes out as a spiral, yes,  you can see it coming out of the machine, this laying head as a spiral, and then you put it down on a cooling table, yes,  and you can see here these are all, this is the wire that's laid down, yes, on a cooling table, so this is the top view of the,  this cooling table, and you see here the rings of the wire, yes, and it's carried by a conveyor chain that takes it along over the cooling section.  The cooling section itself, view from the side, so you can see here you have these rings, yes, that are put on top of each other,  and below, so it's open, yes, it's open, this conveyor belt is open, and you have fans that blow air through it, yes.  And so that will give you a cooling, you can control the cooling by having a cover, yes, put a cover on top of the rings so that the cooling rate is less,  yes, it's, right, and so we can adjust the cooling rate on this table, yes, this is the picture here, this is the laying head, this is the ring wires,  as they go on the wire rings, as they are on the conveyor belt, and here you see this, the covers, the covers here, that you can put down over this,  over your cooling section to decrease the cooling rate, yes, and so as the wire cools down, yes, of course it's not red anymore, red hot anymore,  and at the end we can form these coils, yes, by putting them over this cone here, yes, and for final cooling, and then you can make these coils of wire.  So this is for how you produce wire, yes, but in the case of bar, the amount of deformation, the amount of reduction is much smaller, yes,  and the little bit shift in emphasis when you make bar, certainly bar, for instance, bright bar, such as the one you see here,  so again you start with heating the billets, you force them, or usually you roll them, yes, so that they have the right general dimensions, yes,  they're usually then annealed and pre-aligned, yes, then we have bar peeling, yes, again this is not for all kinds of bars, not for rebars, for instance, for bright bars that are used in machine parts, yes,  or motors, yes, the bar peeling you remove oxide, skin, generally the chilled skin is because the outer side may have cooled down faster and be, for instance, martensitic,  so you want to remove it, also may want to remove surface cracks so that you can achieve dimensional accuracy and high surface finish.  The bars are very many applications that have to be very straight, so you have to straighten them, and then in many applications you also want to the ends,  the quality of the ends of the bar has to be assured, you have certain finishes, so we're talking about chamfering and end-facing, I'll show you an example.  For bars are typically fully tested ultrasonically, so to detect cracks and imperfections inside the material, then marked, and if it's required by the application there may even be the final grinding of the bar to get high quality surfaces.  So you have to imagine these bars that come out of the mill, they will pass through, first pass through a unit that does the peeling, yes,  and I don't have really good picture of the process, but basically these bar enter the peeling machine and there is a turning head in the peeling machine with carbide tools,  that will remove, it turns, it spins around, and it removes at very high speed, it removes all these surface layer basically, removes oxide, etc.  And it gives you very high, again, dimensional quality. And some of the bars will require drawing, so lengthening, so you can lengthen the bar and get reduction in section this way.  You can have straight drawing, you can have them by spinning, or you can basically draw the rods, yes.  When you do this drawing, so you basically have a circular tool with cylindrical tool with a hole in, yes, you pass your wire or your bar through it, yes,  and when you do this, it's very, it's of critical importance, yes, that the force with which you pull, and in particular the angle here, the angle of the tool is chosen very carefully.  Why is that? Because if you don't do this, you get what are called chevron defects in the bar.  So these are chevron defects, and which you can basically see these are cracks, internal cracks.  So the bar looks perfect from the outside, but internally you have these chevron defects.  And the chevron defects occur for the following reason, in bars, no?  Because when we are reducing bars, the diameter of the bars, you have plastic deformation inside the die, yes.  And if the plastic deformation zone, yes, does not reach to the center of the bar, yes.  So if there is a part of the bar that does not deform, we call this the dead zone, yes.  So in the dead zone, there is no deformation, yes.  Well, then this part deforms, and this part deforms, and the dead zone will crack, basically, yes.  Obviously because it doesn't become longer, yes, it should crack, it will crack.  And this depends very much on this angle here of the drawing die, and the amount of deformation that we give, yes.  And so if the angle is very small, of course, we get safe situation, yes.  If the angle is very large, very steep, like in this case, then we get shaving, that's also not very good, yes.  And so what you need to have, and you also want to avoid this intermediate stage where you have a dead zone,  a dead zone, deformation dead zone, where you start making chevron marks, okay.  Straightening and finishing of the ends of the bars is very important, yes.  So this is, so you have chamfering machines which will change the ends of the bar, for instance, in this case, it's a tube,  or, yes, and the end finishing here, the end, yes, it has to be, of course, flat and of high quality.  The straightening happens, is done in special straightening machines, yes.  This is what it looks like, you have the bars straightening machines.  If you have round bars, you typically have a pair of rolls that are shaped, yes.  You can see they're not flat, they're shaped like this, yes.  And this one is shaped like this, and they're crossed, yes.  So when the bar passes through, it turns, it does two things, it turns, and it's being slightly bent when it goes through these rolls, yes.  In order to keep it in place, if I look from the front, yes, there are guides, yes.  So the bar is basically getting little amounts of deformations back and forth so that it becomes straight.  And there are similar types of equipment for, if your bar is a square bar, yes, another round bar, you have profile straighteners, yes.  Okay, very important for bars, yes, and profiles, is that you need to test them.  You need to test them to check the internal quality.  We've just seen that you have the chevron marks.  The chevron marks are absolutely not visible from outside, from the outer side.  So you need to do a surface quality of your material, so you have to make sure there are no cracks, for instance, at the surface, yes.  And you do this with eddy current testing.  That's the most common method, is eddy current testing.  You can also do it with automatic visual inspection, otherwise you have to do it, there has to be an inspector who will actually inspect all the tubes, or the bars.  The production rates are too high for one person to do this, but you can do this with a computer who will recognize, so you will take images of the product as it comes out,  and analyze the images and make reports about the defects it's detected, yes.  The other method is eddy current testing, electrical nature, and both of these methods, because you can automate them, are very popular lately.  And then when it comes to the internal inspection, you cannot use eddy currents testing, because eddy current testing is only sensitive to surface defects.  And of course visual inspection, whether it's a person or a camera, or with a camera, it's the same thing, you can only see the exterior.  So with ultrasonic testing, yes, you can do internal inspection, yes.  And nowadays you have, for instance, these new probes, phase array probes, you can basically test 100% of your production, yes, and make sure that there are no internal defects,  in particular that there are no things like chevron marks.  Right, so bar and rods, interpass times and strain rates can be very high, deformation rates, yes.  I'm going to talk about this too much.  With wire and bar roll, there is absolutely no reason why you cannot use alternative or newer processing methods when you do the deformation at high temperatures.  So yes, you can do standard rolling or normalizing rolling or thermo-mechanical rolling of these steels, yes.  And again, and use concepts like the ones we use for a thermo-mechanical processing of strip, you can apply these concepts to wire and bar products, okay.  So we've discussed this at length and there's no difference in the approach.  Let's have a look now at some products, specific products.  So in, when we come to wire products, these are the five groups of applications which are the most important one,  tire cord steel, cold-heading quality steel, spring steel, bearing steel and free-cutting steel.  And what is important in each application is strength, yes, certainly in the two top ones.  But in an application like spring steels, its fatigue is extremely important, yes.  And in case of bearing steels and spring steels, cleanliness is extremely important.  You don't want to have material failure due to non-metallic inclusions.  And the last application, free-cutting steel, that's where you make small steel parts, yes.  You have the requirement of machinability is important.  Let me just to wrap up this part and say a few things about bars, yes.  So bars we're talking about, heavier sections, yes.  So these are typical applications.  You have shafts, yes.  Typical example here is a forged crankshaft, yes.  You have gears, yes.  This is gear for transmission of the car, yes.  You have induction-harnable steels that are used in treated condition.  For instance, this bar there.  There's an application stabilizing bars are used for the steering of all vehicles, trucks and cars, yes.  So there are usually bars that are hot-formed and quenched.  And then we also have heavy springs, yes.  So applications such as these, very heavy springs such as railroad cars, yes.  Okay, so we'll talk about these in more detail when we meet next Tuesday.  Thank you.  Thank you.
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Railroad cars. Very heavy springs. Okay. So let's just have a quick view of the wire mill part. In an integrated steel plant, you will, of course, use steel from high purity steel coming from blast furnace and basic oxygen, B.O.F. furnace. And then you go to continuous casting. There it depends what your continuous castor can do. If it makes blooms, you usually need to turn these into billets, square or round billets via a blooming mill and billet mill. Or you make, if you have a castor that can make multi-strand circular or square billets, you of course don't need to do the blooming. And you go straight to the reheating furnace. Now, depending on the product, there will be more or less care taken of the surface of these billets. So if the application requires it, you will, for instance, do ultrasound testing of your billet. You'll be looking for defects in the structure that are not visible, slightly below the surface. And you can also do billet conditioning. That means you basically remove oxides and surface defects and decarburization layers on top of your billet so you have a perfectly conditioned billet. Now, these billets then go into the reheating furnace. And similarly to what we've seen for strip mills, although it looks different, of course, you do a roughing mill and then an intermediate mill and a finishing mill. And in the case of wire, we have this special cooling table, which we'll be discussing in a moment, where you do the transformation. That would be the equivalent of, say, the run-out table and the cooling in the run-out table for hot strip mill. So let's have a look at what production levels we have here. Yes. Typical, the reheating furnace will have capacities of around 100 tons, 8,200 tons per hour, the amount of steel that is being processed. The yearly production of a normal wire and bar production is usually from 350 to 500 tons, 1,000 tons per year, so typically about a little less than half a million tons a year. The billets that we use to start are 12 to 18 centimeter in section. Rolling speeds depends, of course, on the type of product you make. If you make very small wire, yes, the rolling speed at the exit will be very high, 100 meters per second. If you make bar, yes, or bar in coil, this bar that's the section of which is small enough, so you can still coil it, yes, 20 meters per second. Well, typical products that are made are wire rod, bar in coil, and bar. Bar being, it's too thick and the application doesn't allow you to bend it. And typical section diameters, so wire, typically wire rod would be 5 millimeters to 20 millimeters. Yes, the bar in coil 14 to 60 millimeters, about 6 centimeters, yes, and the round bars is that you don't bend, depends on the application again. If the section can be smaller than the bar in coil, of course, it's just what the application demands, whether you can coil it or not. Typical volume of a wire and bar production unit is that you don't make one single type of product in general. So it's kind of spread out over, about 50 percent goes into wire rod, yes, and then bars are either in coil or not in coil, and there it's about half and half, half will be, coil half will be just straight bars, yes. What's also important here is that these production units do not necessarily make only carbon steels, yes, they can also be involved in producing other types of steels. So typically the majority of the products will be carbon steels, but you may find wire and bar steel production units which produce also the same products, the same type of products, but stainless, using stainless steels, yes. So there is more variation in the type of compositions that you use, okay. So the basic layout is, as I said, the reheating furnace, here's a picture of the reheating furnace, yes. The billets come in at one side, come out through this much smaller, of course, exit port, yes. The reheated billets come out and then they go through a roughing mill, a roughing mill. And we'll see in a moment that the roughing, the process of rolling wire and bar products goes through special mills, yes, with alternating vertical and horizontal stands, yes. The roughing mill, intermediate mill, and then the finishing. And then you have lines that will do the transformation, excuse me, the cooling of a straight bar on a cooling bed. If you have bars in coils or wires, you will have the wire rods are usually, heat treated as they come out of the finisher, and the bars in coil can be heat treated or transformed after that. So this is here the finisher, yes. And so you can see the section of the product decreasing as you go through the unit. This is an intermediate part of a wire and bar mill. And you can see here that you see the rolls are, in this case, a vertical, horizontal, excuse me, horizontal. In this case, they are vertical. And then here they are again horizontal and vertical, okay, etc. And so the reason is you cannot make the, if you have two rolls, yes, you cannot make the, and you start with a big section, yes, you cannot make the final section, yes, by doing a circular, changing the section in a circular manner. And the reason is, is because you're rolling basically, right? So if you're rolling things, they will tend to assume this shape, yes. And so the way it works, you basically have oval shapes, yes, as you do the reduction of the section. There are many steps, many more steps in the deformation. This is a case which would be a more old-fashioned case where you have a blooming mill. Remember, that's where you have a heavier section such as ingots or you have a bloom. So nowadays, because of the continuous casting, lots of this blooming is not necessary anymore. You can just basically cast directly the bar, yes, or the billet in the right size. Okay, so that reduces the amounts, the number of stands that you need to have, okay? Here you can see, and the evolution can be quite dramatic. This is, for instance, an example here where it goes oval, square, oval. Yes, it depends very much on the technology that's installed. And this is an example here where you go from oval round, oval round, yes. But the basic point being that you don't go from the starting situation, which may be a square billet, to the end situation via continuous diameter reduction. You go through these non-rectangular sections, yes. Okay, it's not the case when, of course, you, towards the end of the process, where your product usually has to have a very perfect round or square. I'm only talking here about round shapes, but if you need square shapes, it's the same thing. So there, and that's what happens in the finishing mill, yes, you have five or six stands, maybe more, where you generate the final shape, the final required shape. And in this case, your stands will make, in this case, the circular sections, yes. And you can have two high round passes, like this one, or three roll round passes, like this one here. Okay, so you've got, and here, these, in the finishing mill, when you have these three roll reducing and sizing blocks that we call them, we don't really call them stands. The, you have the rolls are oriented in Y positions and anti-Y positions, yes. So as to have, see, when you, when you roll, every time you roll like this, you will always have a little bit of material that will be squeezed out. And so, and that is why the, you usually turn, you go from a vertical to a horizontal situation or from a Y situation to anti-Y situation, because in the next stand, in the next stand, you'll be doing the rolling this way, yeah. You'll be doing the rolling this way, okay. And so here, of course, you'll have a, still a little bit of material that you, you don't, this material doesn't really get squeezed out, it's just, because it's an opening, it doesn't get reduced, yes. Some people think this material gets kind of, gets pushed out from between the rolls, that's not really what happens, it's just you don't roll it, so it's not reducing, yeah. So, and so this squeezing out is reduced a lot and also, and it's even better with these three roll reducing and sizing blocks, yes. And this is an example of how things look like, okay. And this is a typical example here, it's a slightly older setup and you can see there are one, two, three, one, two, three, four, five, about five of these blocks, yes. The company that makes those is very famous, yes, because it basically owns the technology for these three roll reducing and sizing blocks, and it's called Cox from Germany. And it's, and so that's very often the type of equipment that you find at the end of a bar or wire mill. Again here we won't go into this, but obviously you understand that we have a section, a material that has this kind of section, yes, and you have to turn it into maybe something that's just a few millimeters or in diameter, right. So things become very, very long, yes, in a bar or mill, yes, very long. And so, and you go from one stand to another stand to another stand. So there'll be, you remember when we talked about the hot strip mill, you always have problems, you know problems, but you have to deal with the fact that you may have tension, yes, between the both, and you need to have, of course, constant mass throughput, yes. If one mill produces more, has a higher velocity, exit velocity, then the next mill has an entry velocity, you're going to accumulate material in your mill, and you end up with cobbles, yes, and it can be pretty horrible when this happens, because you get this very high temperature spaghetti all over the place, yes. And once it's cooled, you have to remove it and cut it up, it's a terrible loss of time. So these mills, and I'll show you an example of this in a moment, do take this into consideration for the processing. So, of course, when you make bar, the section is much larger than in, this is a larger section, yes, you don't need as many stands, in fact, you may just have a few roughing stands. So for instance, if you make a round bar mill, we'll have heating furnace, you can have a blooming mill, perhaps, yes, but you will have then going to a roughing mill, an intermediate mill, and a finishing mill can be one mill position, with different stands, where the bar goes back and forth till it's got the right section. So typically machine structural parts that are based on these bars will be produced this way. In a wire mill, of course, we have much smaller reductions, larger reductions, excuse me, so you go from heating furnace, there may or may not be this reversing rougher that's similar to this one, yes. That depends on what we start with, yes, and then you go through the intermediate mill and wire rod blocks where all the stands are in tandem, okay. So again, I want to mention the fact that all these mills, the material comes in, goes through one stand, goes through another stand, and so how do you manage the material flow, the mass flow through the line, yes. Nowadays, what is being done is tension free rolling, yes. You basically have something that's reminiscent of a looper, a looper between the rolling stands of a finishing mill, yes. So, and in this case, the loop that you have is such that you eliminate the tension. So there is no tension between the wire, yes, between the stands. So this way, we are able to provide at the exit a constant exit velocity, yes, it's constant. It's constant, this exit velocity is constant, and that is rather important because of the heat treatment or the cooling that's being done after the finishing mill. This heat treatment requires a constant exit speed for the cooling bed, or for the cooling bed is basically the name we use for the run-out equivalent of the run-out table in the hot strip mill, the cooling bed. And this exit speed must be synchronized with one part that, you'll see that in a moment what it looks like, the part that puts down the wire on the cooling bed, and that's a laying head, laying head. And that's a rather slow equipment, it's not really able to respond to exit velocity changes, yes. So it's critical to keep the exit velocity constant. A wire mill can make a very large, not only a wide selection of diameters, but a very large number of diameters, yes. So for instance, this is an example here of a situation where a wire mill can make sections going from about 19 millimeters to 75 millimeters, yes. And so you can see the ranges, the actual ranges of the actual diameters that it can make, yes. Now the way it makes it is by combining different stands, yes, and in these stands having different types of rolls, yes. So there is a very large number of rolls that you need to manage in these wire and bar mills, yes. It's not like a hot strip mill where you always have the same work roll and backup roll for a certain stand. Here it depends on what you're going to produce, yes. So for instance here you can see in this mill, in this particular mill you have oval and round changes, yes. And if you want to make, say, the exit rougher diameter is 115 millimeters, so about 10 centimeters, and you want to make a 35 millimeter wire out of this, well this is the sequence that will have to be mounted, yes. So, okay. So that means that you have to set up the mill for specific products, yes. Now you realize, of course, that when you're making a wire, yes, there's only one wire that goes through the line, right. So if you make small wire, the productivity is low, okay. So for products, very often that's what you have to live with because you need to make products with certain specifications in terms of the dimensions. If they ask you to make a five or one centimeter diameter bar, it shouldn't be 1.3 or sometimes one, it's got to be that dimension, yes. So there's not much you can do, but there are products which are commodity products, yes, where the demands are less, yes. And where you can, and of course the costs, the prices are much less, so there it's important to increase productivity, yes. And so there are possibilities to do this, for instance, if you have a rebar, for instance, commodity product, yes, there are units that will allow you to make three bars or more bars in parallel. This is an example here where you have about a centimeter large rebar, yes, and it's produced here in this unit that's split, it's a bar splitting unit, yes. And you enter with something that looks like this, yes, and after this unit it's split in these rebars, yes. And so the amount of material you produce, the amount of bars you produce per unit of time is increased, yes. That allows you, but of course you can only use it for large production volumes, smaller rebar sizes, and obviously we're talking about commodity products here. Temperature control, as always, very important with steel, certainly carbon steels, yes. So typically a typical mill temperature profile will be reheating at 1100 for 20 minutes, so remember that slabs in the hot strip mill are two hours at 1250, yes. This is much shorter, one of the reasons is of course that these billets are much smaller than these huge slabs, yes, okay. And the temperature decreases slowly as you go through the line, yes. You end up with relatively simple rules when it comes, and we'll discuss those when it comes to how you cool the wire after it's being produced. So we'll see, first you have a cooling from the deformation temperature to about 910, yes, and then you do what's called Stelmore cooling, yes, to typically 570. And we'll see that that temperature is the temperature that we like to carry out the pearlite transformation, yes, and then you air cool the material. Again, as always in a steel hot production area, the temperature is not homogeneous at the surface and the interior of the material. So if you look at the surface, you get the blue profile here. So you have the roughing mill, the intermediate mill, yes, and every time you go through the mill, you get cooling from the mill, yes. So the surface is cool. At the very center of the material, it's a very different story. Every time you pass through the deformation stages, you get heating, the material heats up in the center, yes. So that when you get out of the mills, the surface temperature increases again, yes, and this is the actual, say, average temperature. So at the end, when you come to having to do the transformation, yes, you will have to apply cooling, and these are these cooling stages, yes. That are used at the exit of the wire after the exit from the mill. Okay, so why do we need to do this? Well, first of all, the wire steels that we make are very often steels that contain, or where pearlite is a very important constituent, yes. And so let's just make, we'll go into details in the products, but one of the products that are being made with wire are what we call cold-heading steels, cold-heading quality steels, CHQ, or steel for fasteners. Bolts are fasteners, nails are fasteners, yes. So typically have 0.3 to 0.5 carbon in these steels, yes. So when you cool this steel, let's say 0.4, yes, you cool this steel, what you get, of course, it's discontinuous cooling. So you get, this is your cooling curve, yes, you get the CCT diagram, yes, and you see that the transformation, if you do a slow cooling, transformation starts at 7, there is a transformation that starts at 700, yes. And if I use a high cooling rate of 50, the transformation is starting around 600 degrees C, yes. So temperatures that are much lower than what the phase diagram tells you, okay. If you look at the temperature now, yes, in the wire, yes, you see that when the transformation starts here, at these red lines, yes, and this would be for this temperature here, you see that the temperature, the transformation starts, the temperature increases, yes. And this phenomenon is called recolescence, yes, and it's basically the heat of transformation that's released, and that gives you a slight increase in the temperature, yes. And then what happens in terms of the transformation, yes, well first, you can see here, of course, as soon as we pass the E3 temperature, yes, there is, you can form some ferrites, and that's what happens, you form some initial amount of ferrite, yes. But the bulk of the transformation here, going from here to here, is the perlite transformation, and 80% of the microstructure will be, more than 80% in this particular case, will be perlite. So the fast cooling and the low transformation temperatures are very important for wire products, because that gives us the best microstructure for strength, yes. So there are different ways you can do this, let's say for instance you do the cooling with forced air, which would be about 10 degrees per second, or you can do the cooling in a metal bath, for instance lead, lead bath, lead doesn't react with steel, and you can use it as a cooling medium, yes. It also has a very low melting temperature, yes, so you can basically heat it up, and the advantage is it doesn't evaporate, yes, it doesn't alloy with the steel, and it's a very good heat conductor, so you can cool your steel to the temperature of your bath very nicely. So this is what you get if you cool your steel in lead, 20 degrees per second, forced air, yes, and you can look at the strength that you get for the same material, yes, when you do the transformation in this lead or in the forced air cooling. So the mean temperature for transformation, the mean temperature transformation in forced air is around 640, in the lead, yes, it's around 600 or lower, yes. Very often this treatment in lead is called patenting, it's basically using lead as a low temperature cooling medium with a high cooling rate, and you see that we can achieve an impressive increase in strength just by doing the transformation at higher rates and lower temperatures, okay. So that is one method that is used by the steel maker to increase strength, yes, is transformation at lower temperatures, yes, and higher cooling rates, yeah. When the products are made, yes, we can also increase the strength even further by reducing, continuing to reduce the interlaminar spacing of the pearlite, yes, and that's done by deformation, yes, so if you take one of these materials, let's go back, for instance, you see here forced air cooling, lead patenting, gives me about 10 cell strength around a thousand, yeah, around a thousand, so that would be somewhere here, yes. If I draw this material, yes, I get an increase in strength, in strength of course, and I get a reduction, a refinement of the pearlite, and you can see here very large increase in strength, almost three times, starting from a thousand, you get close to three giga Pascal, and it's also important to have a very small starting microstructure to do this, okay. So how do you actually carry this out, this transforming all this wire that comes out up to 100 meters per second, how do you do the transformation, how do you manage this? Well, there's a clever way in which it's being done, with this piece of equipment here, yes, the wire comes in as a wire, yes, and this machine turns it into a spiral, yes, spiral shaped wire, so instead of having straight wire, it now comes out as a spiral, yes, you can see it coming out of the machine, this laying head as a spiral, and then you put it down on a cooling table, yes, and you can see here these are all, this is the wire that's laid down, yes, on a cooling table, so this is the top view of the, this cooling table, and you see here the rings of the wire, yes, and it's carried by a conveyor chain that takes it along over the cooling section. The cooling section itself, view from the side, so you can see here you have these rings, yes, that are put on top of each other, and below, so it's open, yes, it's open, this conveyor belt is open, and you have fans that blow air through it, yes. And so that will give you a cooling, you can control the cooling by having a cover, yes, put a cover on top of the rings so that the cooling rate is less, yes, it's, right, and so we can adjust the cooling rate on this table, yes, this is the picture here, this is the laying head, this is the ring wires, as they go on the wire rings, as they are on the conveyor belt, and here you see this, the covers, the covers here, that you can put down over this, over your cooling section to decrease the cooling rate, yes, and so as the wire cools down, yes, of course it's not red anymore, red hot anymore, and at the end we can form these coils, yes, by putting them over this cone here, yes, and for final cooling, and then you can make these coils of wire. So this is for how you produce wire, yes, but in the case of bar, the amount of deformation, the amount of reduction is much smaller, yes, and the little bit shift in emphasis when you make bar, certainly bar, for instance, bright bar, such as the one you see here, so again you start with heating the billets, you force them, or usually you roll them, yes, so that they have the right general dimensions, yes, they're usually then annealed and pre-aligned, yes, then we have bar peeling, yes, again this is not for all kinds of bars, not for rebars, for instance, for bright bars that are used in machine parts, yes, or motors, yes, the bar peeling you remove oxide, skin, generally the chilled skin is because the outer side may have cooled down faster and be, for instance, martensitic, so you want to remove it, also may want to remove surface cracks so that you can achieve dimensional accuracy and high surface finish. The bars are very many applications that have to be very straight, so you have to straighten them, and then in many applications you also want to the ends, the quality of the ends of the bar has to be assured, you have certain finishes, so we're talking about chamfering and end-facing, I'll show you an example. For bars are typically fully tested ultrasonically, so to detect cracks and imperfections inside the material, then marked, and if it's required by the application there may even be the final grinding of the bar to get high quality surfaces. So you have to imagine these bars that come out of the mill, they will pass through, first pass through a unit that does the peeling, yes, and I don't have really good picture of the process, but basically these bar enter the peeling machine and there is a turning head in the peeling machine with carbide tools, that will remove, it turns, it spins around, and it removes at very high speed, it removes all these surface layer basically, removes oxide, etc. And it gives you very high, again, dimensional quality. And some of the bars will require drawing, so lengthening, so you can lengthen the bar and get reduction in section this way. You can have straight drawing, you can have them by spinning, or you can basically draw the rods, yes. When you do this drawing, so you basically have a circular tool with cylindrical tool with a hole in, yes, you pass your wire or your bar through it, yes, and when you do this, it's very, it's of critical importance, yes, that the force with which you pull, and in particular the angle here, the angle of the tool is chosen very carefully. Why is that? Because if you don't do this, you get what are called chevron defects in the bar. So these are chevron defects, and which you can basically see these are cracks, internal cracks. So the bar looks perfect from the outside, but internally you have these chevron defects. And the chevron defects occur for the following reason, in bars, no? Because when we are reducing bars, the diameter of the bars, you have plastic deformation inside the die, yes. And if the plastic deformation zone, yes, does not reach to the center of the bar, yes. So if there is a part of the bar that does not deform, we call this the dead zone, yes. So in the dead zone, there is no deformation, yes. Well, then this part deforms, and this part deforms, and the dead zone will crack, basically, yes. Obviously because it doesn't become longer, yes, it should crack, it will crack. And this depends very much on this angle here of the drawing die, and the amount of deformation that we give, yes. And so if the angle is very small, of course, we get safe situation, yes. If the angle is very large, very steep, like in this case, then we get shaving, that's also not very good, yes. And so what you need to have, and you also want to avoid this intermediate stage where you have a dead zone, a dead zone, deformation dead zone, where you start making chevron marks, okay. Straightening and finishing of the ends of the bars is very important, yes. So this is, so you have chamfering machines which will change the ends of the bar, for instance, in this case, it's a tube, or, yes, and the end finishing here, the end, yes, it has to be, of course, flat and of high quality. The straightening happens, is done in special straightening machines, yes. This is what it looks like, you have the bars straightening machines. If you have round bars, you typically have a pair of rolls that are shaped, yes. You can see they're not flat, they're shaped like this, yes. And this one is shaped like this, and they're crossed, yes. So when the bar passes through, it turns, it does two things, it turns, and it's being slightly bent when it goes through these rolls, yes. In order to keep it in place, if I look from the front, yes, there are guides, yes. So the bar is basically getting little amounts of deformations back and forth so that it becomes straight. And there are similar types of equipment for, if your bar is a square bar, yes, another round bar, you have profile straighteners, yes. Okay, very important for bars, yes, and profiles, is that you need to test them. You need to test them to check the internal quality. We've just seen that you have the chevron marks. The chevron marks are absolutely not visible from outside, from the outer side. So you need to do a surface quality of your material, so you have to make sure there are no cracks, for instance, at the surface, yes. And you do this with eddy current testing. That's the most common method, is eddy current testing. You can also do it with automatic visual inspection, otherwise you have to do it, there has to be an inspector who will actually inspect all the tubes, or the bars. The production rates are too high for one person to do this, but you can do this with a computer who will recognize, so you will take images of the product as it comes out, and analyze the images and make reports about the defects it's detected, yes. The other method is eddy current testing, electrical nature, and both of these methods, because you can automate them, are very popular lately. And then when it comes to the internal inspection, you cannot use eddy currents testing, because eddy current testing is only sensitive to surface defects. And of course visual inspection, whether it's a person or a camera, or with a camera, it's the same thing, you can only see the exterior. So with ultrasonic testing, yes, you can do internal inspection, yes. And nowadays you have, for instance, these new probes, phase array probes, you can basically test 100% of your production, yes, and make sure that there are no internal defects, in particular that there are no things like chevron marks. Right, so bar and rods, interpass times and strain rates can be very high, deformation rates, yes. I'm going to talk about this too much. With wire and bar roll, there is absolutely no reason why you cannot use alternative or newer processing methods when you do the deformation at high temperatures. So yes, you can do standard rolling or normalizing rolling or thermo-mechanical rolling of these steels, yes. And again, and use concepts like the ones we use for a thermo-mechanical processing of strip, you can apply these concepts to wire and bar products, okay. So we've discussed this at length and there's no difference in the approach. Let's have a look now at some products, specific products. So in, when we come to wire products, these are the five groups of applications which are the most important one, tire cord steel, cold-heading quality steel, spring steel, bearing steel and free-cutting steel. And what is important in each application is strength, yes, certainly in the two top ones. But in an application like spring steels, its fatigue is extremely important, yes. And in case of bearing steels and spring steels, cleanliness is extremely important. You don't want to have material failure due to non-metallic inclusions. And the last application, free-cutting steel, that's where you make small steel parts, yes. You have the requirement of machinability is important. Let me just to wrap up this part and say a few things about bars, yes. So bars we're talking about, heavier sections, yes. So these are typical applications. You have shafts, yes. Typical example here is a forged crankshaft, yes. You have gears, yes. This is gear for transmission of the car, yes. You have induction-harnable steels that are used in treated condition. For instance, this bar there. There's an application stabilizing bars are used for the steering of all vehicles, trucks and cars, yes. So there are usually bars that are hot-formed and quenched. And then we also have heavy springs, yes. So applications such as these, very heavy springs such as railroad cars, yes. Okay, so we'll talk about these in more detail when we meet next Tuesday. Thank you. Thank you.
processed. The yearly production of a normal wire are wire rod, bar in coil, and bar. Bar being, through the unit. This is an intermediate part of is not homogeneous at the surface and the yes. So if there is a part of the bar that does