Modern Steel Products (2014) - Standards, Ironmaking: lecture 7
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Cooman, Bruno C. de
Professor de Cooman finishes his lecture on "Standards" and begins one on ironmaking using the blast furnace. This is a part of a course of lectures by Professor Bruno de Cooman, of the Graduate Institute of Ferrous Technology, POSTECH, Republic of Korea.
 Standards. And we had talked about some basics of the Japanese and the European standards, which are very widely used internationally. So when we closed on Monday, excuse me, Tuesday, we had gone through the basics of the European normalization schemes for steels. And now we come to the US normalization of steel grates. As I had told you earlier in the US, the impact of professional engineering societies on standardizations of materials in general and steel in particular is very large. So it's a bit different from situation in, for instance, Japan or Europe, where government agencies have a big impact also to homogenize the approach. So you won't find this in the American standards. And depending on whether you become an engineer in a company, depending on the clients you have, they will be ordering steels. If they do this using American standards, they will use different standards depending on the application. Let's have a look. But there is American Iron and Steel Institute, which has standards which are widely used across many industries to specify steel grates. And they are very closely tied with the Society of Automotive Engineers. Automotive industry is a very big user of steel products, so it makes sense that they streamlined their approach to normalization. So they basically use a very simple scheme with four numerical symbols, or alphanumeric symbols, four or five. So they always look like x, x, y, y, y, because these digits refer to something different. So the first digits are a reference to the major alloying elements. And so they define the various types of steels you have, basically three types. Plain carbon, carbon manganese steels, two more hardenable grades, which contain substantial alloying elements. Carbon steels with less than 1.65 manganese, 0.6 silicon and 0.6 copper will look like this. They will all start with a 1, x, y, y. So plain carbon steels of this type here, 1, x, y, y, are divided in subclasses. So the 0 means that you have a low manganese content, less than 1%. If it's a 1 instead of a 0, it doesn't mean anything in relation to the manganese. It just means that it's resulphurized. It contains 0.1% of sulfur. If it's got 0.2, yes, it means that it's resulphurized, and it also has refosphorized. It's got a higher phosphorus content to make them easily more machinable. If it's got a 3, then we're back to specification related to manganese. It means that the manganese range goes from 1.6 to 1.9% of manganese, and if it goes to 5, you would think it would be related to a higher percentage of manganese, and it's from 1 to 1.6% of manganese. So there is no logic, not necessarily logic in the numbering, in this numbering. So it's a little bit frustrating, and you usually have to go back through the tables to find out what specifically is referred to. So that's a little bit frustrating. Luckily, the last two digits, or three digits, yy or yyy, define the approximate carbon concentration times 100. So, for instance, an xx number of 40 means approximately 0.4% of carbon, and if you have xx100, yes, so number number 100, means approximately 1% of carbon. So you can basically divide your steels into low-carbon steels, medium-carbon steels, and high-carbon steels. So low-carbon less than 0.2%, 0.2 to 0.5% are medium-carbon steels, and high-carbon steels are more than half a percent. That is, in the US, in North America, a very, very common way of referring to steels, low-carbon, medium-carbon, or engineering steel and high-carbon. So it's kind of good to remember that what people mean when they say high-carbon. In the US, it means more than half a percent. It doesn't mean 1%. It could be 1%, but it could be as low as half a percent. And then, if the steel contains important alloying elements, there is an extra letter inserted between second and third digit. So sometimes you have five symbols, but one of them is not necessarily a number. If it's a B, for instance, it means it's a boron added steel. If it contains lead, yes, L, instead of a P, which you would expect from the chemical symbol, it's L. So that is also indicated. All right? That's the other direction. Quite a challenge to find your way in this numbering. So obviously, I don't expect you to learn this, but I do provide you with some starting knowledge about this approach used by AISIS-AE standards. So first of all, the way you have to look at it, the way it's structured, the material steels are divided in low alloy steels and high alloy steels. When we meet alloy steels, there's nothing about the carbon. Alloying means adding chromium moly. It doesn't say anything about the carbon. So what are high alloy steels? With the high alloy steels in AISIS standards, that means corrosion resistance, chromium, high chromium, high nickel steels, basically stainless steels. So let's just focus on what we say. We call low alloy steels. They are divided in these three big groups, low carbon, less than 0.2, medium carbon, 0.2 to 0.6, and high carbon, 0.6 to... There's a few typos. So this should be 0.5 and then 0.6, higher than 0.5. So if you could change this to 0.5, maybe... Then you know that up to 0.5, it's a medium carbon seal and then from over there, it's... We call it high carbon steels. And so in each case, you have a plain carbon version. That's just a steel where the main alloying element is carbon. And so because they're not alloyed, all the numbers... So there are no alloying additions. It doesn't mean that there are no specifications about the levels of certain elements. But in principle, you don't make alloying additions. We'll see when we talk about steel making. Usually you have to... Even if you make a very simple grade, you need to have the right composition for all the elements that are specified in the center. So you may very well have added some manganese just to get the right levels. But in principle, it's not an addition to achieve anything peculiar, specific. So they all start with 1, 0 because there's no alloying additions. And then the other number that's of importance is the two last digits. So this means 0.1% of carbon, 0.4% of carbon, 0.95% of carbon. And of course, you can have this type of steels where you do alloy. For instance, at HSLA steels, you add micro alloying additions. So different number. It's just to make you feel good. I know a few numbers because they're common. But this one, you would tell me, ask me what it is. Precisely. I wouldn't be able to tell you. I would have to look it up. But anyway, so this is for instance, a micro. This group here is very important. These are all the engineering steels. So they usually start with a 4 or a 5 or 6 or 8 numbers. So I know when I see this, it's an engineering steel. So it could be heat treated, usually used in the quenched and tempered states. And the highly alloyed steels, same thing. Lots of carbon and alloying additions. So why would you do this? For instance, if I make martensite here, it's going to be much softer martensite than in this case. That would be for instance, one of the reasons that you would do this. And you can see this in the applications. Here, for instance, these kind of things will be used to make, for instance, pressure vessel steels. Here, we'll make parts that go into construction of motors, pistons, gears, other wear resistance parts in machineries. These are kind of steels, yes. And here, drills, tools, saw, dyes, etc. Okay. So, right, and here you have a number of... So this list is put together. These are very common AISI grades, yes. These grades are very common. And you can see, so the two top ones are plain carbon steels, no alloying, so they start with 1, 0. As soon as you get the 1 here, you probably remember that means that you've added sulfur, yes. So it's a resulphurized steels. The 5 here means it's manganese added, okay? As soon as you don't have this one anymore, you know you're into alloyed grades, yes. Excuse me. Alloyed grades and higher carbon. So for instance, this one is a well-known grade name for steels that we make ball bearings with. Ball bearings are often made with this. This is a very well-offer used engineering steel. So these are pretty important. So you can see here that if I look at this carefully, I can see for instance that 5, 5, I look at the composition, yes, of the... so the important alloying elements as you know are chrome, molly, nickel, et cetera. You can see here that with the 5, 1, 5, 1, I have... I only have chrome, yes. So the 5,000 series usually refers to steels where the only addition is chromium, yes. You can see that in this case, for instance, the 8,620, I have nickel, I have added chrome, and I have added molybdenum. So these numbers will refer to the more complex alloying additions. Let's have a look here. Okay. So here I know it's a plain carbon steel because of this one here, right? Same here. Here I have the one on the second place, so resulphurized. Here I have a 5 on the second place, high manganese steel. These numbers here, 41, 43, 51, 52, you know, there's no logic to it, but these numbers refer to the type of alloy steels. One for this is chrome alloyed, chrome nickel moly alloyed. Is it nickel alloyed? Yes. So if you want to add this, you can do this. And this is the actual list, yes. So if you want to know what, for instance, 88 means, you can see it's a nickel chrome moly alloy, okay? And you see typical levels, yes. But if it's a 5, it's only chromium, yes. Now I want you to look at your table, yes, and there are some typos. So the 5OXX is mistyped. There's nickel, something, something. So if you go on the line, chromium steels, 5OXX, it says something with nickel, I think, if you look carefully. And there's another one that, I think that 52, it should be this, high chrome and high carbon. Okay? And sometimes, you know, I do have to say things can be quite confusing. For instance, you would think that the nickel, originally the silicon steels, the high silicon steels, would be all with 90s, yes. But you actually have nickel chrome molybdenum steels that also start with the same numbers. Why is that? Because with this approach, you quickly run out of numbers. So it's not a very logical thing, but if you know vaguely how it works, you can identify the grades. But for specific grades, you will have to go back to the either table like this or, of course, by the actual standards. Okay? Okay, so in the US, there was also something that's called the universal numbering system. And that's basically, all materials have a number. Basically, well, a digit, one digit followed by one letter, excuse me, followed by a five digit number, yes. So any time there is a steel, yes, a new steel being developed, it gets a number, right? So the number itself doesn't make much sense. You know, it doesn't say anything, it's just a number. New steel comes in, new number, okay? There is a little bit of a subdivision in the numbering, yes, and that's in the letter. So G, S, T, D, H. So G stands for just, it's a plain carbon steel or it's an alloy steel. S, if it's specifically for heat or corrosion application, resistant application. T for tool steels. D for specific mechanical properties, usually meaning drawing applications. And H for hardenable steels. This system is very rarely used. Some people use it. It's even more mysterious what the number means because the numbers are just given to steel as they are being developed, yes. So it's not very much used, but you should know about this, that if you ever come across it, it's the universal numbering system number, yes. Now, having said this, in North America, you have AISI, yes, and you have a lot of other professional organizations that have their own specifications. So AISI itself has designations for stainless steels, yes, which takes into account the ferritic stainless steels, austenitic stainless steels, martensitic stainless steel, precipitation hardened stainless steels, yes. And that does not refer, the numbers there also don't refer to the composition or the carbon level, yes. So that's, for instance, 304, yes, is a, we call them, a 300 series stainless steel, yes. And any stainless steel that is, the 300 series austenitic, yes. If it's ferritic, it's a 400 number, yes. And sometimes these numbers are followed by letters such as L, which L doesn't mean lead in this case, in this case it means low for low carbon. So the 304 is a very, very common 1810, 18 chrome, 10% nickel, austenitic stainless steels, and it, the L means it has a reduced, a low carbon content to provide adequate weldability or formability properties depending on the situation, okay. So that is, that also very widely used across the world, yes. So even, even the GIST standards use this numbering system. So if you see stainless steels with, you know, 400, you know, it's a ferritic, if it's, for instance, a 439 is a ferritic stainless steel, a 321, you know, it's an austenitic steel. It may be, obviously, a special one, but it's an austenitic steel, right. You, I'm sure you've heard about ASTM. ASTM is a, so it stands for American Society for Testing and Materials, yes. So in the, in the name itself, it says testing and materials. So very often, these specifications, yes, will, will, you will have, in this specification, will have steel specifications and testing methods for these steels, yes. That's why ASTM test methods, test procedure are very widely used, yes, because they allow engineers to do the same tests, you know, in China and Japan according to the same rules, right. So we can compare our data, you know. And it's, and it also defines the grades, yes. And so that means there is an application element to the, the test and the grade, you know. So, so we have ASTM classification where the focus is on steel, the type of steel product application, yes. You will have information about composition and properties. And very often, you can recognize these grades because they are preceded, it's a number preceded by the letter A, yes. So for instance, for structural steels, you know, you will have A36, A36, very common structural steel. That means some, you know, steel you make buildings with, you know. If it's for ships, A131, for Bridget, A709, there's no logic, don't look for logic in the numbers, okay. But if you come across a grade that, you know, doesn't look like a European grade name, it doesn't look like an SAE grade name, but it starts with a good chance that it's an ASTM specification. And so you'd think that would be enough for Americans to deal with, but, you know, as there are many other societies that bring out their own specification for steels, yes. For instance, the American Association of, I have to read it myself, State Highway and Transportation Officials, they have specification for steels in bridge construction, yes. The ASME is a very important engineering society when it comes to ASME, American Society of Mechanical Engineers, for pressure vessels, pressure vessel steel. America is a, as American engineering has a big impact on petroleum and gas technology. So this is a very important society when it comes to pressure vessel, piping steels, etc. API, yes, also related to petroleum and gas industry, but there to the tubing, yes. The line pipes in the offshore platforms, they, society which has a lot of standards in this, yes. So there are specifications for line pipes are usually according to the American Petroleum Institute, yes. AMS is for aerospace, aerospace, material, aerospace, material specifications, yes. And the military is also a huge consumer of equipment, yes. And obviously the equipment is according to specifications. And those ones you can recognize when, because it says, Mell, they start with Mell. So you know it's a military grade steel, for instance. For instance, when the military makes orders, vehicles for troops in the battlefield, they usually have plates to protect the, against explosions, yes. So the steels that are used like this are not just any steel. They're very well specified steels according to these military specifications. Right, and then perhaps I just want to finish, but I'm not going to talk about it. There are also ISO, ISO is an international body of standardization, International Standardization Office, yes. And they also have standardized, many, many things, not only steels, but they have standardized steel grades. And they're basically based on the composition of the steels. They consider base steels, unalloyed steels, alloyed steels, unalloyed special steels. You can read this. You will very rarely come across these specifications, yes. So I usually skip it because it's not used. But it's really important for you to know about these Japanese and North American and the European specifications, because they really, you come across them very often and everywhere. Right, when you are an engineer in a plant, yes. And you have to do something according to specification. Your company should buy the specifications, the standards, yes. You should not read an article and say, well, here it says that AISI 439 should have this much titanium, yes. So that's not, okay, specifications you have to buy them. Your company has to own them, yes, because if there is ever a problem, it turns out you don't even know the specifications or own them, you know, that's not very professional. So usually you buy these things, yes. You don't steal them from Internet or you don't copy them from somebody else. So they cost some money, of course, but your company should have this. It's part of quality aspects of steelmaking. You should own the standards. It's very easy to buy via Internet. So don't, right. So again, so I hope I've been able to show you that standards can be useful, yes. And also show you that a lot of impact of professional engineering societies and trade association and government into these, the steel standards. So the physical metallurgy is sometimes very hard to, you know, to find, but it's there behind it, yes. And the reason why we use this is because it's for reasons of quality, reliability, and also interchangeability. And interchangeability in today's very large international trade is extremely important, right. And the standards are not just about chemical compositions, right. They'll also go into properties, yes, mechanical properties, dimensions, yes, dimensions. And I want to close by saying that even though we have standards, yes, it's very well possible that in your professional activities, you will be making steels not according to AISI or ASTM or some Europeena, but according to the specification of your client. So sometimes large consumers of steel such as big car makers, Toyota, GM, you have to make their steel, yes, according to their specifications, yes. So you also have this kind of situations, yes. All right. So that was for the standards. And now we will continue with some few more basics related to products. Where is it? Stooped otherwise. Okay. There we go. We will now have to say a few words about steelmaking. We have a TIFT, like a chairs, lots of them, on steelmaking. And the thing with these courses is of course they deal with steelmaking and the blast furnace and slags and et cetera. Very often not necessarily in connection with products. But so in this case, I'm not giving this type of introduction, what I will be focusing on is a few technological things you should know to understand the further processing of the steels, yes. And some things that are really important for specific products. So it's a very light introduction to iron and steelmaking essentials. So we're just going to review the essentials. And so we'll look at the black's furnace, we'll look at the electric arc furnace. That's where our iron comes from, basically. You have some understanding of the liquid part of the manufacturing process. And the impact of this liquid part of the processing on the microstructure and composition of the steels. It's also important to know that this liquid part has a big impact, yes. Because that's basically where you make your chemistry, yes. That's where you, you know, when we talk about chemistry and composition, that's where it's made, yes, in the liquid part. And as soon as you cast the steel, there's no more going back, yes, there's no more going back. So it's interesting to know a few things about how this alloying is being done, basically. So we'll say a few words about this. And I'll try to convey the idea that steelmaking is not something simple, yes. Getting the composition right of a steel is not done in a simple way. It takes some effort, yes, to get the right chemistry. And it's important for you to know this, because if you work in engineering and, for instance, a bar mel, for instance, you know, you may not be aware of defects that you see that are caused by the liquid part of the process. Okay, so let's start. So what we're basically going to talk about, yes, is this here, yes, in the flow of material flow to make products in steel plants, we start with steelmaking, yes. And before that, the electric arc furnace or the blast furnace, yes. And then the continuous casting or the ingot casting. And then the material gets in the solid state and then gets processed to different products. Okay, so let's have a look here and say a few words about the ways we make our steels. And actually, we start, we either start with a blast furnace or a variety of variants on the blast furnace. But by and large, most steel makers make iron from ore using the blast furnace. So in the blast furnace, what do we do? We, it's a big reactor. And the top we load iron ore, coke and limestone. These are the basic things, yeah. And at the bottom, yes, we get out molten iron and molten slag. So the molten iron is, so iron, not steel, right? Not steel. The slag contains or should contain all what we call impurities. So what else happens here? Well, this big reactor is operating at high temperature. So there is a lining inside that's refractory lining, yes. And inside, we have charged this, the iron ore, the coke and the limestone in layers, yes, in layers. So we alternate coke layers with iron ore, yes. And in order to get the reaction of iron reduction, iron oxide reduction going, we blow in air, heated air, yes, at the bottom here via these, this big pipe here that has connections to the furnace via tubes, yeah, which we call two years. Okay, some details here. First of all, what we load is not usually, is not usually coal. It's coal that has been treated, metallurgical coal that has been turned into coke. So it's hard and it has mechanical properties. So it doesn't collapse and it doesn't contain gaseous compounds. Okay, same with the iron ore. Iron ore, we don't use iron ore as such, very little of it. We center the iron ore usually. So again, so we have a very strong lumps of material, yes, with the right permeability, yes, and the right strength, so it doesn't collapse at high heat, yeah, and the correct dimensions. So the flow of gas is good through the blast furnace. And with the heated air here, we can also inject coal powder to decrease the amount of coke we add at the top here. So what happens? We generate heat in this converter, basically, it is a reactor, excuse me, by one exothermic reaction which is burning of carbon. C plus O is CO2. So this reactor produces a lot of CO2. And then we reduce the oxide to metal. And we use for the reduction of the oxide, we use CO gas which is made in the furnace, and we use carbon, yes, and these are the reactions here. Fe2O3 going to iron, and then Fe2O3 being reduced in steps to iron by carbon. All these reactions are endothermic, they pick up heat, you need heat for that, okay? So you absolutely need coal combustions to make the blast furnace work. There's other important reactions that happen is purifications. All our, the ore material we add contains not only our iron oxide, but also silica, alumina, yes, etc. We need to separate this from our metal, and we do this with, by adding lime. Lime is basically calcium oxide, yes. And the calcium oxide reacts with silica and alumina to form a liquid slag, and it's an oxide, yes, and so it has a very low density compared to the iron, so it floats on top and we can remove them. We can separate the two phases. All right, some little detail here, some numbers first. 9,000 tons per day, modern blast furnace produced 9,000 tons. That means 2.5 million tons of iron per year, yes. Blast furnaces operate around the clock every day for many, many years. 10 years, 15 years, depending on the wear of the lining, yes, on the inside. Where does the ore come from, yes? Well, iron can be mined many places, yes, but most of iron ore comes from high iron oxide content minerals, yes. And so they come from mainly countries like Australia, Brazil, yes, which have very high, they have ores with very high iron contents. And one of the minerals is, are these banded iron formations, yes, which this is what the mineral looks like. You can see the iron oxide, this is the red layers, yes, and this is where they are made. So they were very, made billions of years ago. Originally, we did not have on earth oxygen, yes, and the oceans contain a lot of iron, yes, which was dissolved and there's no oxygen in the air. However, when we started getting living organisms, we changed CO2 into oxygen, yes. Suddenly, we had, due to photosynthesis, we started to having oxygen in the water, yes. And this was then transformed, this oxygen in the water reacted with the iron, yes, and just formed deposits of hematite and magnetite. And because they're deposited in water, they form these layers and they alternate with silica-rich layers. And this is why there's always intimately mixed with other minerals, yes, and that's the reason why you need these slags to remove these other oxides that you don't need to have in the steel. But this is important here because minerals that are in the ore will also be reduced to a certain level, yes. There will always be some silicon in your steels because that's in the ore. The same thing, there will always be some manganese in your steel because it's very often associated with iron in your iron ores, yes. Now, the steel that, excuse me, the iron that's been made, yes, contains high levels of carbon, high levels of phosphorus, and high levels of sulfur. Now, carbon in itself, we don't mind. We've seen when we talked about standards that you need carbon for many steels to achieve strength. But in a blast furnace iron, yes, the levels are very high, 4%. So you can't really use this material because it's basically a cast iron, yes, it's very brittle. So you need to remove the carbon, the sulfur and the phosphorus, the sulfur and the phosphorus because they are very strong and brittle agents, yes. And the levels of sulfur and phosphorus are too high for most applications, so you remove them. So how does this work? So you do this in a, the desulfurization to start with, you do this in a pretreatment. So the material that comes out of the blast furnace is desulfurized and the decarburization and the phosphorization is done in the converter. And the, this is usually called the BOF converter, basic oxygen furnace, BOF. Right, so BOF is basically a reactor, yes, a reactor where you put in the iron. This iron will contain about 4% of carbon. After the treatment in the BOF, it will be 100 to 500 ppm of carbon. So it's a huge reduction of the carbon content. How is this reduced, this level, by blowing oxygen on the surface of your iron and by injecting gas through the bottom of this BOF? Again, all this carbon is turned into CO2, so you produce a lot of CO2. And this production of CO2 is very exothermic reaction, so you will need to have a refractory brick lined converter. And usually that is magnesium brick lining, which contains a little bit of carbon. It has mechanical stability and chemical stability is also important. Chemical stability towards the liquid metal, but also chemical stability towards the slag that you form. Okay, let's see a few numbers about the converter. Typically 150 to 350 tons of metal can be, 350 is a very large one, 150 is on the smaller side, but typical sizes are 250, 250 to 75. That's what you usually see, that's an industry standard. Tap to tap time, that means the time it takes to make 250 tons of steel is between 20 and 25 minutes. So it's a very high rate of production. How long do you blow typically? Well, of these 20 to 25 minutes, about 15 minutes are spent blowing. Blowing meaning carrying out the decarburization. So what you do is you have oxygen top blowing, and you have bottom stirring. Bottom stirring means you inject gas in the bottom, and usually this gas is oxygen and argon. The oxygen will just do the decarburization, and the argon is used to stir up the bath. And this is very important, no alloying additions. The BOF is not an alloying, you don't do any alloying. If anything, you remove a lot of elements, not only carbon. To say here an example, we come in not only with high carbon, but also with high silicon, 0.8 silicon, almost 1% of silicon, half a percent of manganese, 600 ppm of sulfur, 350 ppm of carbon. So the temperature that you have by the time you go from the blast furnace into the basic oxygen furnace, the BOF, is about 1450 degrees. That's much lower than the solidification temperature of iron, which is close to 1600. So you've noticed that there's no added heat in this. There's enough heat produced by the burning of the carbon. So this is what you have in terms of the steel coming out. You have 500 to 800 ppm of carbon. That's important that you remember this number. You have about 0.01% of silicon. You have about 0.15% of manganese. So even an unalloyed low carbon steel will always have at least 0.15% of manganese, not 0% of manganese. So sulfur, 350, so about half of this, and phosphorus is reduced to about 100 ppm. Remember that number? That is typically the lowest level you can get in terms of phosphorus. The phosphorus is actually removed effectively in the BOF, and that's the kind of level that you can get in the regular steel. In addition to this, you have about 40 ppm of nitrogen, usually low hydrogen or no hydrogen, and low residuals. When steel makers talk about residuals, they mean things like antimony, tin, bismuth, copper. And the temperature is a staggering 1700 degrees Celsius, so it's very hot. The reaction is very hot. The slag that you get out is a slag with very high CAO content and also very high FEO content. This is very typical of a BOF slag, so it's a very high bacissity slag. The reason why we have this is because it's here underneath, is to ensure that you remove as much phosphorus as possible. For those who have taken steel metallurgy courses, the slag has to be oxidizing and have a high bacissity. You need to oxidize the phosphorus and be able to trap the phosphorus in the slag. SiO2 is in the slag, MGO is in the slag. The MGO in the slag is from the lime, from the lime that we use to make the slag. If you ever work in a or visit a steel plant, there are many variants of the process. Most of the modern BOFs combine top blowing and bottom blowing technologies. You have what we call combined blowing. Most of the BOFs nowadays look like this. You have both combined nitrogen, argon, or oxygen and argon bottom blowing and a top blowing of oxygen. What happens during the steel composition changes? The temperature increases and the composition of the slag changes. Let's have a look here at the carbon-silicon and phosphorus content of the steel. This is for the steel. What we see is that the carbon level decreases. The silicon level decreases very quickly. The silicon removal is very easy in the BOF. Carbon is also very easy. You do have a lot more carbon, so it takes a longer time. The phosphorus initially decreases a little bit, then it stays flat until... At this stage, about three-fourths through the process, the amount of carbon in the steel has dropped considerably. You start oxidizing the iron. This iron oxide goes into the slag. This makes it possible for the slag to absorb P2O5, phosphorus oxide. That's where you start decreasing the phosphorus level. The FEO content in the slag is necessary for an efficient phosphorus removal. Of course, it results in some loss of iron to the slag. Meanwhile, the temperature has gone from 1,300 to 1,400 to 1,600. Very high temperatures. We have other techniques to make steels. That's basically by melting old steel. That technology is electric arc furnaces. Electric arc furnace technologies are usually associated with smaller steel companies. Companies like Posco, Nippon Steel, Arcelor, and Metell are big companies. They make 40-50 million tons of steel, close to 100 million tons of steel per year. Most of the steel they make is new steel. They use ore to make iron, pig iron, and then turn it into steel. Many companies use old steel, recycled steel, recycled steel, and they use electric arc furnace to make steel. Steelmaking from recycled scrap steel, we have the electric arc furnace. You melt scrap metal and you already make chemical composition when you do this. Something you don't do in the BUF. Usually, two steps. You have an electric arc furnace where you melt the scrap metal, you add ferro alloys and other additions, and in the second step you adjust the composition. This may involve oxygen also. Let's have a look at this electric arc furnace. There are many different technologies, but nowadays you have what we call low-cost high-performance electric arc furnaces. These are the specifics of these electric arc furnaces. Diameters are circular furnaces, about 4 to 8 meters of diameter. The weight of steel is typically 50 to 150. Nowadays, industries are about 120, 150 is on the larger size, 125. The electric power is with 125 mega volt amperes, transformers, and we use alternating current. There is a big difference between making new steel and using scrap. When you make new steel, you make a lot of CO2. You become a major source of CO2. When you use an electric arc furnace, all the heating comes from the electricity. You don't emit CO2. There is an environmental impact to the use of electric arc furnaces. There are also burners. You use a foaming slag, a special slag that foams. Basically by injecting a mixture of carbon and oxygen into the slag. You have about 30 heats a day with an electric arc furnace. The production is about 3,600 tons per day. The tap-to-tap time is about 50 minutes. An electric arc furnace will produce 120 tons of steel. A BOF produces 250 tons every half an hour. It's a big difference. You produce a lot more steel in a BOF situation than with an electric arc furnace. This is what it looks like. You have these electrodes here that make an arc with the steel surface. That melts the metal. Then you have a slag on top of the steel. You can separate them both. Nowadays, when you pour the steel, you pour it from below. It's called an eccentric bottom tapping. You can easily separate the steel from the slag. You don't want to have slag inclusions in your steel. That's very bad. Here are some numbers. I'll close. What are the typical inputs in an electric arc furnace? These electrodes are made from graphite. They do burn in the atmosphere. We have scrap metal goes into the electric arc furnace. Limb or dolomite. Limb is CO and dolomite is a mixture of CO and MGO. That will form the slag. As I said, make a foaming slag. We'll need to inject oxygen and carbon. What do we get? We put in about 1,000 kilos of scrap here. We put more than 1,000 kilos. This is referring to a ton. What you get out is what you put in. You put in about a ton of scrap. You get out a ton of steel. You use a few kilograms of electrode. About 30 kilos of lime. About 20-25 kilos of oxygen. Natural gas, coal and refractories. This is what you get out. For every ton of steel, you get about 100 kilos of slag. We'll finish here. Thank you for your attention. you you
 Standards.  And we had talked about some basics of the Japanese and the European standards,  which are very widely used internationally.  So when we closed on Monday, excuse me, Tuesday, we had gone through the basics of the European normalization schemes for steels.  And now we come to the US normalization of steel grates.  As I had told you earlier in the US, the impact of professional engineering societies on standardizations of materials in general and steel in particular is very large.  So it's a bit different from situation in, for instance, Japan or Europe, where government agencies have a big impact also to homogenize the approach.  So you won't find this in the American standards. And depending on whether you become an engineer in a company, depending on the clients you have, they will be ordering steels.  If they do this using American standards, they will use different standards depending on the application.  Let's have a look.  But there is American Iron and Steel Institute, which has standards which are widely used across many industries to specify steel grates.  And they are very closely tied with the Society of Automotive Engineers. Automotive industry is a very big user of steel products, so it makes sense that they streamlined their approach to normalization.  So they basically use a very simple scheme with four numerical symbols, or alphanumeric symbols, four or five.  So they always look like x, x, y, y, y, because these digits refer to something different.  So the first digits are a reference to the major alloying elements.  And so they define the various types of steels you have, basically three types.  Plain carbon, carbon manganese steels, two more hardenable grades, which contain substantial alloying elements.  Carbon steels with less than 1.65 manganese, 0.6 silicon and 0.6 copper will look like this.  They will all start with a 1, x, y, y.  So plain carbon steels of this type here, 1, x, y, y, are divided in subclasses.  So the 0 means that you have a low manganese content, less than 1%.  If it's a 1 instead of a 0, it doesn't mean anything in relation to the manganese.  It just means that it's resulphurized. It contains 0.1% of sulfur.  If it's got 0.2, yes, it means that it's resulphurized, and it also has refosphorized.  It's got a higher phosphorus content to make them easily more machinable.  If it's got a 3, then we're back to specification related to manganese.  It means that the manganese range goes from 1.6 to 1.9% of manganese,  and if it goes to 5, you would think it would be related to a higher percentage of manganese,  and it's from 1 to 1.6% of manganese.  So there is no logic, not necessarily logic in the numbering, in this numbering.  So it's a little bit frustrating, and you usually have to go back through the tables  to find out what specifically is referred to.  So that's a little bit frustrating.  Luckily, the last two digits, or three digits, yy or yyy,  define the approximate carbon concentration times 100.  So, for instance, an xx number of 40 means approximately 0.4% of carbon,  and if you have xx100, yes, so number number 100,  means approximately 1% of carbon.  So you can basically divide your steels into low-carbon steels,  medium-carbon steels, and high-carbon steels.  So low-carbon less than 0.2%, 0.2 to 0.5% are medium-carbon steels,  and high-carbon steels are more than half a percent.  That is, in the US, in North America,  a very, very common way of referring to steels, low-carbon, medium-carbon,  or engineering steel and high-carbon.  So it's kind of good to remember that what people mean when they say high-carbon.  In the US, it means more than half a percent.  It doesn't mean 1%.  It could be 1%, but it could be as low as half a percent.  And then, if the steel contains important alloying elements,  there is an extra letter inserted between second and third digit.  So sometimes you have five symbols,  but one of them is not necessarily a number.  If it's a B, for instance, it means it's a boron added steel.  If it contains lead, yes, L, instead of a P,  which you would expect from the chemical symbol, it's L.  So that is also indicated.  All right?  That's the other direction.  Quite a challenge to find your way in this numbering.  So obviously, I don't expect you to learn this,  but I do provide you with some starting knowledge  about this approach used by AISIS-AE standards.  So first of all, the way you have to look at it,  the way it's structured,  the material steels are divided in low alloy steels and high alloy steels.  When we meet alloy steels, there's nothing about the carbon.  Alloying means adding chromium moly.  It doesn't say anything about the carbon.  So what are high alloy steels?  With the high alloy steels in AISIS standards,  that means corrosion resistance, chromium, high chromium,  high nickel steels, basically stainless steels.  So let's just focus on what we say.  We call low alloy steels.  They are divided in these three big groups,  low carbon, less than 0.2, medium carbon, 0.2 to 0.6,  and high carbon, 0.6 to...  There's a few typos.  So this should be 0.5 and then 0.6, higher than 0.5.  So if you could change this to 0.5, maybe...  Then you know that up to 0.5, it's a medium carbon seal  and then from over there, it's...  We call it high carbon steels.  And so in each case, you have a plain carbon version.  That's just a steel where the main alloying element is carbon.  And so because they're not alloyed, all the numbers...  So there are no alloying additions.  It doesn't mean that there are no specifications about the levels of certain elements.  But in principle, you don't make alloying additions.  We'll see when we talk about steel making.  Usually you have to...  Even if you make a very simple grade, you need to have the right composition  for all the elements that are specified in the center.  So you may very well have added some manganese just to get the right levels.  But in principle, it's not an addition to achieve anything peculiar, specific.  So they all start with 1, 0 because there's no alloying additions.  And then the other number that's of importance is the two last digits.  So this means 0.1% of carbon, 0.4% of carbon, 0.95% of carbon.  And of course, you can have this type of steels where you do alloy.  For instance, at HSLA steels, you add micro alloying additions.  So different number.  It's just to make you feel good.  I know a few numbers because they're common.  But this one, you would tell me, ask me what it is.  Precisely.  I wouldn't be able to tell you.  I would have to look it up.  But anyway, so this is for instance, a micro.  This group here is very important.  These are all the engineering steels.  So they usually start with a 4 or a 5 or 6 or 8 numbers.  So I know when I see this, it's an engineering steel.  So it could be heat treated, usually used in the quenched and tempered states.  And the highly alloyed steels, same thing.  Lots of carbon and alloying additions.  So why would you do this?  For instance, if I make martensite here, it's going to be much softer martensite than in this case.  That would be for instance, one of the reasons that you would do this.  And you can see this in the applications.  Here, for instance, these kind of things will be used to make, for instance, pressure vessel steels.  Here, we'll make parts that go into construction of motors, pistons, gears, other wear resistance parts in machineries.  These are kind of steels, yes. And here, drills, tools, saw, dyes, etc.  Okay.  So, right, and here you have a number of...  So this list is put together. These are very common AISI grades, yes.  These grades are very common.  And you can see, so the two top ones are plain carbon steels, no alloying, so they start with 1, 0.  As soon as you get the 1 here, you probably remember that means that you've added sulfur, yes.  So it's a resulphurized steels.  The 5 here means it's manganese added, okay?  As soon as you don't have this one anymore, you know you're into alloyed grades, yes.  Excuse me.  Alloyed grades and higher carbon.  So for instance, this one is a well-known grade name for steels that we make ball bearings with.  Ball bearings are often made with this.  This is a very well-offer used engineering steel.  So these are pretty important.  So you can see here that if I look at this carefully, I can see for instance that 5, 5, I look at the composition, yes,  of the... so the important alloying elements as you know are chrome, molly, nickel, et cetera.  You can see here that with the 5, 1, 5, 1, I have... I only have chrome, yes.  So the 5,000 series usually refers to steels where the only addition is chromium, yes.  You can see that in this case, for instance, the 8,620, I have nickel, I have added chrome, and I have added molybdenum.  So these numbers will refer to the more complex alloying additions.  Let's have a look here.  Okay. So here I know it's a plain carbon steel because of this one here, right?  Same here. Here I have the one on the second place, so resulphurized.  Here I have a 5 on the second place, high manganese steel.  These numbers here, 41, 43, 51, 52, you know, there's no logic to it, but these numbers refer to the type of alloy steels.  One for this is chrome alloyed, chrome nickel moly alloyed. Is it nickel alloyed? Yes.  So if you want to add this, you can do this.  And this is the actual list, yes.  So if you want to know what, for instance, 88 means, you can see it's a nickel chrome moly alloy, okay?  And you see typical levels, yes.  But if it's a 5, it's only chromium, yes.  Now I want you to look at your table, yes, and there are some typos.  So the 5OXX is mistyped. There's nickel, something, something.  So if you go on the line, chromium steels, 5OXX, it says something with nickel, I think, if you look carefully.  And there's another one that, I think that 52, it should be this, high chrome and high carbon.  Okay?  And sometimes, you know, I do have to say things can be quite confusing.  For instance, you would think that the nickel, originally the silicon steels, the high silicon steels, would be all with 90s, yes.  But you actually have nickel chrome molybdenum steels that also start with the same numbers.  Why is that? Because with this approach, you quickly run out of numbers.  So it's not a very logical thing, but if you know vaguely how it works, you can identify the grades.  But for specific grades, you will have to go back to the either table like this or, of course, by the actual standards.  Okay?  Okay, so in the US, there was also something that's called the universal numbering system.  And that's basically, all materials have a number.  Basically, well, a digit, one digit followed by one letter, excuse me, followed by a five digit number, yes.  So any time there is a steel, yes, a new steel being developed, it gets a number, right?  So the number itself doesn't make much sense.  You know, it doesn't say anything, it's just a number.  New steel comes in, new number, okay?  There is a little bit of a subdivision in the numbering, yes, and that's in the letter.  So G, S, T, D, H. So G stands for just, it's a plain carbon steel or it's an alloy steel.  S, if it's specifically for heat or corrosion application, resistant application.  T for tool steels.  D for specific mechanical properties, usually meaning drawing applications.  And H for hardenable steels.  This system is very rarely used.  Some people use it.  It's even more mysterious what the number means because the numbers are just given to steel as they are being developed, yes.  So it's not very much used, but you should know about this, that if you ever come across it, it's the universal numbering system number, yes.  Now, having said this, in North America, you have AISI, yes,  and you have a lot of other professional organizations that have their own specifications.  So AISI itself has designations for stainless steels, yes,  which takes into account the ferritic stainless steels, austenitic stainless steels, martensitic stainless steel,  precipitation hardened stainless steels, yes.  And that does not refer, the numbers there also don't refer to the composition or the carbon level, yes.  So that's, for instance, 304, yes, is a, we call them, a 300 series stainless steel, yes.  And any stainless steel that is, the 300 series austenitic, yes.  If it's ferritic, it's a 400 number, yes.  And sometimes these numbers are followed by letters such as L, which L doesn't mean lead in this case,  in this case it means low for low carbon.  So the 304 is a very, very common 1810, 18 chrome, 10% nickel, austenitic stainless steels,  and it, the L means it has a reduced, a low carbon content to provide adequate weldability  or formability properties depending on the situation, okay.  So that is, that also very widely used across the world, yes.  So even, even the GIST standards use this numbering system.  So if you see stainless steels with, you know, 400, you know, it's a ferritic,  if it's, for instance, a 439 is a ferritic stainless steel, a 321, you know, it's an austenitic steel.  It may be, obviously, a special one, but it's an austenitic steel, right.  You, I'm sure you've heard about ASTM. ASTM is a, so it stands for American Society for Testing and Materials, yes.  So in the, in the name itself, it says testing and materials.  So very often, these specifications, yes, will, will, you will have, in this specification,  will have steel specifications and testing methods for these steels, yes.  That's why ASTM test methods, test procedure are very widely used, yes,  because they allow engineers to do the same tests, you know, in China and Japan according to the same rules, right.  So we can compare our data, you know.  And it's, and it also defines the grades, yes.  And so that means there is an application element to the, the test and the grade, you know.  So, so we have ASTM classification where the focus is on steel, the type of steel product application, yes.  You will have information about composition and properties.  And very often, you can recognize these grades because they are preceded, it's a number preceded by the letter A, yes.  So for instance, for structural steels, you know, you will have A36, A36, very common structural steel.  That means some, you know, steel you make buildings with, you know.  If it's for ships, A131, for Bridget, A709, there's no logic, don't look for logic in the numbers, okay.  But if you come across a grade that, you know, doesn't look like a European grade name,  it doesn't look like an SAE grade name, but it starts with a good chance that it's an ASTM specification.  And so you'd think that would be enough for Americans to deal with, but, you know,  as there are many other societies that bring out their own specification for steels, yes.  For instance, the American Association of, I have to read it myself, State Highway and Transportation Officials,  they have specification for steels in bridge construction, yes.  The ASME is a very important engineering society when it comes to ASME,  American Society of Mechanical Engineers, for pressure vessels, pressure vessel steel.  America is a, as American engineering has a big impact on petroleum and gas technology.  So this is a very important society when it comes to pressure vessel, piping steels, etc.  API, yes, also related to petroleum and gas industry, but there to the tubing, yes.  The line pipes in the offshore platforms, they, society which has a lot of standards in this, yes.  So there are specifications for line pipes are usually according to the American Petroleum Institute, yes.  AMS is for aerospace, aerospace, material, aerospace, material specifications, yes.  And the military is also a huge consumer of equipment, yes.  And obviously the equipment is according to specifications.  And those ones you can recognize when, because it says, Mell, they start with Mell.  So you know it's a military grade steel, for instance.  For instance, when the military makes orders, vehicles for troops in the battlefield,  they usually have plates to protect the, against explosions, yes.  So the steels that are used like this are not just any steel.  They're very well specified steels according to these military specifications.  Right, and then perhaps I just want to finish, but I'm not going to talk about it.  There are also ISO, ISO is an international body of standardization, International Standardization Office, yes.  And they also have standardized, many, many things, not only steels, but they have standardized steel grades.  And they're basically based on the composition of the steels.  They consider base steels, unalloyed steels, alloyed steels, unalloyed special steels.  You can read this.  You will very rarely come across these specifications, yes.  So I usually skip it because it's not used.  But it's really important for you to know about these Japanese and North American and the European specifications,  because they really, you come across them very often and everywhere.  Right, when you are an engineer in a plant, yes.  And you have to do something according to specification.  Your company should buy the specifications, the standards, yes.  You should not read an article and say, well, here it says that AISI 439 should have this much titanium, yes.  So that's not, okay, specifications you have to buy them.  Your company has to own them, yes, because if there is ever a problem,  it turns out you don't even know the specifications or own them, you know, that's not very professional.  So usually you buy these things, yes.  You don't steal them from Internet or you don't copy them from somebody else.  So they cost some money, of course, but your company should have this.  It's part of quality aspects of steelmaking. You should own the standards.  It's very easy to buy via Internet.  So don't, right.  So again, so I hope I've been able to show you that standards can be useful, yes.  And also show you that a lot of impact of professional engineering societies and trade association and government into these, the steel standards.  So the physical metallurgy is sometimes very hard to, you know, to find, but it's there behind it, yes.  And the reason why we use this is because it's for reasons of quality, reliability, and also interchangeability.  And interchangeability in today's very large international trade is extremely important, right.  And the standards are not just about chemical compositions, right.  They'll also go into properties, yes, mechanical properties, dimensions, yes, dimensions.  And I want to close by saying that even though we have standards, yes, it's very well possible that in your professional activities,  you will be making steels not according to AISI or ASTM or some Europeena, but according to the specification of your client.  So sometimes large consumers of steel such as big car makers, Toyota, GM, you have to make their steel, yes, according to their specifications, yes.  So you also have this kind of situations, yes.  All right.  So that was for the standards.  And now we will continue with some few more basics related to products.  Where is it?  Stooped otherwise.  Okay.  There we go.  We will now have to say a few words about steelmaking.  We have a TIFT, like a chairs, lots of them, on steelmaking.  And the thing with these courses is of course they deal with steelmaking and the blast furnace and slags and et cetera.  Very often not necessarily in connection with products.  But so in this case, I'm not giving this type of introduction, what I will be focusing on is a few technological things you should know to understand the further processing of the steels, yes.  And some things that are really important for specific products.  So it's a very light introduction to iron and steelmaking essentials.  So we're just going to review the essentials.  And so we'll look at the black's furnace, we'll look at the electric arc furnace.  That's where our iron comes from, basically.  You have some understanding of the liquid part of the manufacturing process.  And the impact of this liquid part of the processing on the microstructure and composition of the steels.  It's also important to know that this liquid part has a big impact, yes.  Because that's basically where you make your chemistry, yes.  That's where you, you know, when we talk about chemistry and composition, that's where it's made, yes, in the liquid part.  And as soon as you cast the steel, there's no more going back, yes, there's no more going back.  So it's interesting to know a few things about how this alloying is being done, basically.  So we'll say a few words about this.  And I'll try to convey the idea that steelmaking is not something simple, yes.  Getting the composition right of a steel is not done in a simple way.  It takes some effort, yes, to get the right chemistry.  And it's important for you to know this, because if you work in engineering and, for instance, a bar mel, for instance,  you know, you may not be aware of defects that you see that are caused by the liquid part of the process.  Okay, so let's start.  So what we're basically going to talk about, yes, is this here, yes, in the flow of material flow to make products in steel plants,  we start with steelmaking, yes.  And before that, the electric arc furnace or the blast furnace, yes.  And then the continuous casting or the ingot casting.  And then the material gets in the solid state and then gets processed to different products.  Okay, so let's have a look here and say a few words about the ways we make our steels.  And actually, we start, we either start with a blast furnace or a variety of variants on the blast furnace.  But by and large, most steel makers make iron from ore using the blast furnace.  So in the blast furnace, what do we do? We, it's a big reactor.  And the top we load iron ore, coke and limestone. These are the basic things, yeah.  And at the bottom, yes, we get out molten iron and molten slag.  So the molten iron is, so iron, not steel, right? Not steel.  The slag contains or should contain all what we call impurities.  So what else happens here? Well, this big reactor is operating at high temperature.  So there is a lining inside that's refractory lining, yes.  And inside, we have charged this, the iron ore, the coke and the limestone in layers, yes, in layers.  So we alternate coke layers with iron ore, yes.  And in order to get the reaction of iron reduction, iron oxide reduction going, we blow in air, heated air, yes, at the bottom here  via these, this big pipe here that has connections to the furnace via tubes, yeah, which we call two years.  Okay, some details here. First of all, what we load is not usually, is not usually coal.  It's coal that has been treated, metallurgical coal that has been turned into coke.  So it's hard and it has mechanical properties. So it doesn't collapse and it doesn't contain gaseous compounds.  Okay, same with the iron ore. Iron ore, we don't use iron ore as such, very little of it.  We center the iron ore usually. So again, so we have a very strong lumps of material, yes, with the right permeability, yes,  and the right strength, so it doesn't collapse at high heat, yeah, and the correct dimensions.  So the flow of gas is good through the blast furnace.  And with the heated air here, we can also inject coal powder to decrease the amount of coke we add at the top here.  So what happens? We generate heat in this converter, basically, it is a reactor, excuse me,  by one exothermic reaction which is burning of carbon. C plus O is CO2.  So this reactor produces a lot of CO2.  And then we reduce the oxide to metal.  And we use for the reduction of the oxide, we use CO gas which is made in the furnace, and we use carbon, yes,  and these are the reactions here. Fe2O3 going to iron, and then Fe2O3 being reduced in steps to iron by carbon.  All these reactions are endothermic, they pick up heat, you need heat for that, okay?  So you absolutely need coal combustions to make the blast furnace work.  There's other important reactions that happen is purifications.  All our, the ore material we add contains not only our iron oxide, but also silica, alumina, yes, etc.  We need to separate this from our metal, and we do this with, by adding lime.  Lime is basically calcium oxide, yes.  And the calcium oxide reacts with silica and alumina to form a liquid slag, and it's an oxide, yes,  and so it has a very low density compared to the iron, so it floats on top and we can remove them.  We can separate the two phases.  All right, some little detail here, some numbers first.  9,000 tons per day, modern blast furnace produced 9,000 tons.  That means 2.5 million tons of iron per year, yes.  Blast furnaces operate around the clock every day for many, many years.  10 years, 15 years, depending on the wear of the lining, yes, on the inside.  Where does the ore come from, yes?  Well, iron can be mined many places, yes, but most of iron ore comes from high iron oxide content minerals, yes.  And so they come from mainly countries like Australia, Brazil, yes, which have very high,  they have ores with very high iron contents.  And one of the minerals is, are these banded iron formations, yes, which this is what the mineral looks like.  You can see the iron oxide, this is the red layers, yes, and this is where they are made.  So they were very, made billions of years ago.  Originally, we did not have on earth oxygen, yes, and the oceans contain a lot of iron, yes, which was dissolved and there's no oxygen in the air.  However, when we started getting living organisms, we changed CO2 into oxygen, yes.  Suddenly, we had, due to photosynthesis, we started to having oxygen in the water, yes.  And this was then transformed, this oxygen in the water reacted with the iron, yes, and just formed deposits of hematite and magnetite.  And because they're deposited in water, they form these layers and they alternate with silica-rich layers.  And this is why there's always intimately mixed with other minerals, yes, and that's the reason why you need these slags to remove these other oxides that you don't need to have in the steel.  But this is important here because minerals that are in the ore will also be reduced to a certain level, yes.  There will always be some silicon in your steels because that's in the ore.  The same thing, there will always be some manganese in your steel because it's very often associated with iron in your iron ores, yes.  Now, the steel that, excuse me, the iron that's been made, yes, contains high levels of carbon, high levels of phosphorus, and high levels of sulfur.  Now, carbon in itself, we don't mind.  We've seen when we talked about standards that you need carbon for many steels to achieve strength.  But in a blast furnace iron, yes, the levels are very high, 4%.  So you can't really use this material because it's basically a cast iron, yes, it's very brittle.  So you need to remove the carbon, the sulfur and the phosphorus, the sulfur and the phosphorus because they are very strong and brittle agents, yes.  And the levels of sulfur and phosphorus are too high for most applications, so you remove them.  So how does this work?  So you do this in a, the desulfurization to start with, you do this in a pretreatment.  So the material that comes out of the blast furnace is desulfurized and the decarburization and the phosphorization is done in the converter.  And the, this is usually called the BOF converter, basic oxygen furnace, BOF.  Right, so BOF is basically a reactor, yes, a reactor where you put in the iron.  This iron will contain about 4% of carbon.  After the treatment in the BOF, it will be 100 to 500 ppm of carbon.  So it's a huge reduction of the carbon content.  How is this reduced, this level, by blowing oxygen on the surface of your iron and by injecting gas through the bottom of this BOF?  Again, all this carbon is turned into CO2, so you produce a lot of CO2.  And this production of CO2 is very exothermic reaction, so you will need to have a refractory brick lined converter.  And usually that is magnesium brick lining, which contains a little bit of carbon.  It has mechanical stability and chemical stability is also important.  Chemical stability towards the liquid metal, but also chemical stability towards the slag that you form.  Okay, let's see a few numbers about the converter. Typically 150 to 350 tons of metal can be,  350 is a very large one, 150 is on the smaller side, but typical sizes are 250, 250 to 75.  That's what you usually see, that's an industry standard.  Tap to tap time, that means the time it takes to make 250 tons of steel is between 20 and 25 minutes.  So it's a very high rate of production.  How long do you blow typically? Well, of these 20 to 25 minutes, about 15 minutes are spent blowing.  Blowing meaning carrying out the decarburization.  So what you do is you have oxygen top blowing, and you have bottom stirring.  Bottom stirring means you inject gas in the bottom, and usually this gas is oxygen and argon.  The oxygen will just do the decarburization, and the argon is used to stir up the bath.  And this is very important, no alloying additions. The BOF is not an alloying, you don't do any alloying.  If anything, you remove a lot of elements, not only carbon.  To say here an example, we come in not only with high carbon, but also with high silicon, 0.8 silicon, almost 1% of silicon,  half a percent of manganese, 600 ppm of sulfur, 350 ppm of carbon.  So the temperature that you have by the time you go from the blast furnace into the basic oxygen furnace, the BOF,  is about 1450 degrees. That's much lower than the solidification temperature of iron, which is close to 1600.  So you've noticed that there's no added heat in this. There's enough heat produced by the burning of the carbon.  So this is what you have in terms of the steel coming out. You have 500 to 800 ppm of carbon.  That's important that you remember this number. You have about 0.01% of silicon.  You have about 0.15% of manganese.  So even an unalloyed low carbon steel will always have at least 0.15% of manganese, not 0% of manganese.  So sulfur, 350, so about half of this, and phosphorus is reduced to about 100 ppm.  Remember that number? That is typically the lowest level you can get in terms of phosphorus.  The phosphorus is actually removed effectively in the BOF, and that's the kind of level that you can get in the regular steel.  In addition to this, you have about 40 ppm of nitrogen, usually low hydrogen or no hydrogen, and low residuals.  When steel makers talk about residuals, they mean things like antimony, tin, bismuth, copper.  And the temperature is a staggering 1700 degrees Celsius, so it's very hot. The reaction is very hot.  The slag that you get out is a slag with very high CAO content and also very high FEO content.  This is very typical of a BOF slag, so it's a very high bacissity slag.  The reason why we have this is because it's here underneath, is to ensure that you remove as much phosphorus as possible.  For those who have taken steel metallurgy courses, the slag has to be oxidizing and have a high bacissity.  You need to oxidize the phosphorus and be able to trap the phosphorus in the slag.  SiO2 is in the slag, MGO is in the slag. The MGO in the slag is from the lime, from the lime that we use to make the slag.  If you ever work in a or visit a steel plant, there are many variants of the process.  Most of the modern BOFs combine top blowing and bottom blowing technologies.  You have what we call combined blowing. Most of the BOFs nowadays look like this.  You have both combined nitrogen, argon, or oxygen and argon bottom blowing and a top blowing of oxygen.  What happens during the steel composition changes?  The temperature increases and the composition of the slag changes.  Let's have a look here at the carbon-silicon and phosphorus content of the steel.  This is for the steel. What we see is that the carbon level decreases.  The silicon level decreases very quickly.  The silicon removal is very easy in the BOF. Carbon is also very easy.  You do have a lot more carbon, so it takes a longer time.  The phosphorus initially decreases a little bit, then it stays flat until...  At this stage, about three-fourths through the process, the amount of carbon in the steel has dropped considerably.  You start oxidizing the iron.  This iron oxide goes into the slag. This makes it possible for the slag to absorb P2O5, phosphorus oxide.  That's where you start decreasing the phosphorus level.  The FEO content in the slag is necessary for an efficient phosphorus removal.  Of course, it results in some loss of iron to the slag.  Meanwhile, the temperature has gone from 1,300 to 1,400 to 1,600.  Very high temperatures.  We have other techniques to make steels.  That's basically by melting old steel. That technology is electric arc furnaces.  Electric arc furnace technologies are usually associated with smaller steel companies.  Companies like Posco, Nippon Steel, Arcelor, and Metell are big companies.  They make 40-50 million tons of steel, close to 100 million tons of steel per year.  Most of the steel they make is new steel.  They use ore to make iron, pig iron, and then turn it into steel.  Many companies use old steel, recycled steel, recycled steel, and they use electric arc furnace to make steel.  Steelmaking from recycled scrap steel, we have the electric arc furnace.  You melt scrap metal and you already make chemical composition when you do this.  Something you don't do in the BUF.  Usually, two steps. You have an electric arc furnace where you melt the scrap metal,  you add ferro alloys and other additions, and in the second step you adjust the composition.  This may involve oxygen also.  Let's have a look at this electric arc furnace.  There are many different technologies, but nowadays you have what we call low-cost high-performance electric arc furnaces.  These are the specifics of these electric arc furnaces.  Diameters are circular furnaces, about 4 to 8 meters of diameter.  The weight of steel is typically 50 to 150.  Nowadays, industries are about 120, 150 is on the larger size, 125.  The electric power is with 125 mega volt amperes, transformers, and we use alternating current.  There is a big difference between making new steel and using scrap.  When you make new steel, you make a lot of CO2.  You become a major source of CO2.  When you use an electric arc furnace, all the heating comes from the electricity.  You don't emit CO2.  There is an environmental impact to the use of electric arc furnaces.  There are also burners.  You use a foaming slag, a special slag that foams.  Basically by injecting a mixture of carbon and oxygen into the slag.  You have about 30 heats a day with an electric arc furnace.  The production is about 3,600 tons per day.  The tap-to-tap time is about 50 minutes.  An electric arc furnace will produce 120 tons of steel.  A BOF produces 250 tons every half an hour.  It's a big difference.  You produce a lot more steel in a BOF situation than with an electric arc furnace.  This is what it looks like.  You have these electrodes here that make an arc with the steel surface.  That melts the metal.  Then you have a slag on top of the steel.  You can separate them both.  Nowadays, when you pour the steel, you pour it from below.  It's called an eccentric bottom tapping.  You can easily separate the steel from the slag.  You don't want to have slag inclusions in your steel.  That's very bad.  Here are some numbers.  I'll close.  What are the typical inputs in an electric arc furnace?  These electrodes are made from graphite.  They do burn in the atmosphere.  We have scrap metal goes into the electric arc furnace.  Limb or dolomite.  Limb is CO and dolomite is a mixture of CO and MGO.  That will form the slag.  As I said, make a foaming slag.  We'll need to inject oxygen and carbon.  What do we get?  We put in about 1,000 kilos of scrap here.  We put more than 1,000 kilos.  This is referring to a ton.  What you get out is what you put in.  You put in about a ton of scrap.  You get out a ton of steel.  You use a few kilograms of electrode.  About 30 kilos of lime.  About 20-25 kilos of oxygen.  Natural gas, coal and refractories.  This is what you get out.  For every ton of steel, you get about 100 kilos of slag.  We'll finish here.  Thank you for your attention.  you  you
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