One Stuff of Iron, The Other of Steel

was always in relation to some other topic. For example, I did a couple of episodes with my friend Ariel about swords, and that included some stuff on steel. But I really want to dedicate a couple of episodes to this metal and why we have so many different classifications of it and what this classifications actually mean. But first let's get to some definitions and history. In fact, that's what this episode is going to be about, is sort of the history of steel making in general, because it's

complicated stuff. And in the next episode will conclude with the history part and move on to the different types of steel. Now, if you take a look at the periodic table of elements, you'll notice that steel is not on it. And that's because steel isn't an element, it's an alloy, and alloy is a metal created from the combination of at least two metallic elements. And technically steel is an alloy of iron and carbon. But here's where

it gets really confusing. All the iron we work with, the iron that's in our stuff like iron nails and stuff, all of that is really an alloy of iron and carbon. So this means that these episodes are really going to be not just about steel, but iron and how we learned how to work with iron. Now you might wonder why you'd bother making an alloy in the first place. Why would you not just use pure iron? Wouldn't that

be easier? Well, it's because alloys can have different, more beneficial properties than the individual elements that combine together to make that alloy. So, in general, the reason we make alloys at all is to create materials that are stronger or lighter, or more resistant to corrosion or some other positive quality or combination thereof, compared to the metals we use to create the alloy. In the first place. Steel is superior to iron in many ways, which we will

get into. But to really understand the development of steel, we have to take a closer look at the history of meta allergy in general. So for thousands of years, humanity relied primarily upon stone as a material for tools and weapons. And we have a name for this age, the flint stones. No way, I'm sorry, I just meant

the Stone Age. But we can further divide the Stone Age into the Paleolithic or Old Stone Age, you know when everyone was listening to that, you know, real crappy music, and Neolithic or New Stone Age, which is what all the kids were listening to. Stone is plentiful. It's hard stuff, right, It's durable. Depending upon the type of stone, you could fashion it into sharp edges, and you could polish it up.

You could make stuff like axes and spears, and so the ancestors of humans were using stone tools as far back as three million years ago, not earlier. I mentioned for thousands of years. But that wasn't to d emphasize how long we relied on stone, but rather just as a nod to how tricky it is to apply the word humans, because we're talking about you know, ancestors of humans as well. While stone could get the job done,

it wasn't necessarily the best material for most jobs. It was brittle and heavy, and you could find yourself with a tool that had edges that were not as sharp after a few uses, or one that would break in a relatively short amount of time. Also, when we talk about stuff like the Stone Age and the Bronze Age and the Iron Age, we have to remember that these terms describe very broad eras that didn't actually have a

definitive beginning and end. Some regions moved towards metallurgy much earlier than others, sometimes by as much as two thousand years. So I just don't want any of you thinking that, you know, a person went to bed on a Wednesday night when it was the Stone Age, and then they woke up Thursday morning and it was suddenly the Bronze Age. It's a little more subtle than that. Generally speaking, we think of the Bronze Age as beginning around three thousand b c E, and we think of it as ending

as well. That depends on where you lived. If you lived in Mesopotamia, it ended sometime around twelve hundred b C. But if you were in Northern Europe you had to wait a little longer. It was closer to six hundred b c. E. Generally, the onset of the Bronze Age was brought about by trade, so the knowledge of how to produce bronze spread outward from the Mesopotamian area for the most part, so cultures first began to learn how to work with copper, and at first copper was fairly scarce.

It just wasn't as readily available as different types of stone. But ancient people's developed mining and metallergy and created all sorts of stuff out of copper. But copper is not that great for tools. It's not terribly durable, it doesn't hold an edge very well. But by adding some tin to the copper t I N tin, mellergists could create a much stronger alloy bronze. This material made much better

tools and weapons. Iron is even stronger, but the high melting point of iron meant that the tools humans had for me allergy weren't sufficient to make iron. The pods used to melt copper and tin couldn't withstand the temperatures you would need in order to smelt iron from iron.

Ore the word smelt means to extract metal from ore, and or is a solid rock or sediment that contains one or more metals or minerals in it, So smelting is really about separating the metal from all the other stuff that's in that rock so that you can work with the metal. One of the things you had to deal with was iron oxide, which forms on the surface

of iron exposed to air. Also, I should mention that iron oxide is actually an imprecise term, or rather it's a term for a bunch of different chemical compounds made up of iron and oxygen, and the iron oxide we know of as rust is just one form of that. Gradually, humans figured out how to build more robust forges and they could heat up or enough so that they could actually smelt iron, but it took some more time for anyone to really be able to reliably create steel. An

exception was meteoric iron as an iron from space. Some meteorites contained alloys of iron and nickel, and the process of entering the Earth's atmosphere created enough heat to do essentially the smelting work for us. But this wasn't exactly plentiful stuff, so it's mostly used in small ornaments and things like that until we got more up to speed, like you might be say an Egyptian pharaoh with a meteoric iron dagger buried with you next to a gold dagger,

because that's how valuable these things were. One of the things about iron that made it harder to work with is that it does oxidize rapidly upon contact with the air. Oxidization is a process in which a substance like an atom, an ion, or a molecule loses electrons in a chemical reaction. Now this does not necessarily involve oxygen, but oxygen is a pretty effective electron thief. Iron oxidizes pretty quickly. Oxidation

is an exothermic reaction. Now that means that as a byproduct of this reaction there is a release of heat. So you can actually see the effects of oxidation on iron. It is what causes iron to rust. So iron in the presence of oxygen and water is going to rust. But even iron that's not actively rusting will have a layer of iron oxide on the surface of the iron itself.

The process of oxidation is also pretty darn fast. If you were to expose a very small speck of iron to the air, it would oxidize and heat up and you would see a spark. So if you've got a lot of iron that's in a lump, you're gonna have more volume compared to surface area. Right, You've got more iron in the lump than is exposed on the surface, just because of the size. This is all about volume, and only the surface of the iron is oxidizing with the air because you know, the rest of the iron

is shielded from the it's inside the lump. The heat from that oxidizing reaction, the oxidation will be able to dissipate into the rest of the lump of iron. Again, you've got that big volume of iron, so the heat from that process doesn't really amount too much in the grand scheme of the lump. But if you have a tiny, tiny speck of iron, well, now the ratio of surface area to volume has totally changed. There's very little volume

in a tiny piece of iron. The surface will still react to oxygen, and there isn't so much iron inside the spec for the heat to dissipate so effectively. So the spec gets really hot, hot enough to glow. When someone uses a power grinder on iron and you see sparks fly, or they're using flint and steel, those sparks are tiny specks of iron oxidizing at a super fast rate. Iron oxide isn't the stuff we want, right, we want iron, So smelting helps us remove iron oxide and get iron instead.

It goes through the set type of reaction we call this one reduction. Smelting also helps separate the iron from other impurities that could be in the ore, stuff like sulfur, phosphorous, silicon, things like that. Now, as far as the actual smelting process, that, as we will learn, evolved a great deal over time. The earliest furnaces used to smelt iron, we're called bloomer eyes. There's some great videos on YouTube that show how these

bloomers worked. I highly recommend you guys go on YouTube and look up bloomery b l o O m e r Y because these videos are equal parts fascinating and terrifying. So typically, you would build a chimney like structure and you would use something like clay to make it. So imagine a a stack a chimney made of clay. You would have a little section in the very front that would be cut out like a door, but you would have a a piece of clay that fit into that.

You would have at least one hole cut in the side of the chimney called a two year, and this would allow for more air circulation to go into the chamber of the bloomery. If you blue air into it,

you would increase the temperature of the burn. So you would possibly have bellows attached to this, either operated by hand or later by having a water wheel turning a cam that would allow these bellows to open and close and thus blow air into the bloomery, or you might just be dependent upon the wind, which wouldn't be the most efficient way to make this stuff. You'd also typically have a hole towards the very bottom of the chimney

that would allow you to draw off slag. This would be the the hot melted mixture of impurities, and you don't have to worry about melting off the iron having the iron pour out along with the slag, because that's just not going to happen. We're not talking about temperatures

high enough to melt iron at this point. Conversely, the entire bloomery, if you didn't have this way of tapping it so that you can put get slag out, you might even have to push it over, which sounds incredibly dangerous to me, and then allow the molten slag to to pour out the top of it. Now, slag typically contains a little bit of iron in it as well, but for the most part you're talking about all the other stuff that you wanted to remove, leaving as much

of the iron behind as possible. So you might have little chunks of iron in the slag, and thus you might want to keep the slag just in case has any iron in it in order to use in a future burn. But to facilitate the removal of slag, forgers or you know, smith's or metal or just however you want to call them, would typically add in a substance with a relatively low melting point that could help siphon

out some of the impurities. That would act almost like a lubricant, if you can think of it that way, The bind with things and and be liquid in order to help coax more of those impurities to flow out. The stuff is called collectively flux, and flux can be made up of lots of different stuff, including sand or silica or limestone, but with ancient bloomer eyes, often the flux came from the material used to build the bloomery itself.

It would just be leached out of the interior of the bloomery and become part of the mixture, so you didn't necessarily have to add more in the process of smelting and refining iron. This way is laborious. It involves getting the furnace really hot with a layer of charcoal

at the base of the furnace. Then you add more charcoal to heat up the entirety of the furnace, and then you start adding in equal amounts of iron ore and charcoal every few minutes, and you alternate between them, um, but you add them both at around the same time. So you do, all right, let's put in a kilogram of iron ore and a kilogram of charcoal, and then after a few minutes another kilogram of iron or and

another kilogram of charcoal. You have to keep doing this over and over and over again every few minutes for several hours. So these bloomerys couldn't get hot enough, as I said, to actually melt the iron ore outright. Instead, you would produce what was called a bloom thus bloomery. This would be a mass of hot iron and kind

of you know, charcoal. Mixt year, the iron doesn't get hot enough to really melt, but it's hard enough to be kind of a spongy looking material that was somewhat malleable if you were to pull it out of the bloom moraine then hit it with a hammer. Managing this process is tricky because not only do you have to maintain that high level of heat, you also have to make sure that the two year remains clear of material.

Remember that's the air channel, where air is either blowing in from the wind or you're forcing it in through something like a bellows. A lot of stuff can go wrong in this process, and even when everything goes corre directly, you might not end up with a great amount of iron, depending upon the quality of the ore itself. Once the process is done, it's time to retrieve the iron bloom. So you've tapped out the slag, You've let the slag

run out. You pull the door off the furnace, assuming that or the bloomery, assuming that the bloomery has a door. You might even just break the bloomery open. Often these were just one use devices. You would construct one every time you want to do one of these, and uh you might have to break it apart anyway, because sometimes the iron bloom would be too large to fit through the door in the first place. Now the bloom will

have absorbed some charcoal would be incorporated into it. Charcoal has a very high carbon content, and at higher temperatures, iron absorbs some of that carbon. This also lowers the melting point for iron a little bit, and that will

become important later on. The charcoal needs to burn really thoroughly for of this process to really work, Otherwise you'll get chunks of charcoal that are too large, and you'll end up with iron that might have big chunks of unburned charcoal embedded in it, which is going to be harder to get rid of. But if the coals are the right size, the iron will absorb some carbon, but not all of it obviously. So now you've got a big old, porous lump of red hot iron with some

carbon and maybe some charcoal. You've got some other stuff, and it some slag is still inside that, because again it's spongey, it's porous, so there will be slag contained inside this red hot bloom of iron. So what do you do then, Well, that stage the iron still isn't terribly useful, so you would have to reheat the mass so that it's malleable. You know, get it hot enough so that you can work it. Then you put it on an anvil and you start beating that iron bloom

with a hammer. This compresses the mass. It forces the molten slag out of the lump to the surface of the iron. So remember I said it's like a sponge, it's porous. This is kind of like squeezing out a sponge. If you have a sponge that's absolutely saturated with water and you start to squeeze it, you force the water out. That's kind of what's happening when a blacksmith starts hammering an iron bloom with a hammer. You're forcing that slag out to the surface. You can watch videos of blacksmiths

doing this process on YouTube. Again, it's fascinating. You're gonna see this sort of glowing orange mass of iron. But it will start to grow darker as it's getting hammered, not just because it's cooling off. I mean that is happening, but it's also growing darker because the slag is being forced towards the surface of the mass. So smith's need to hammer out the mass folded back in on itself

and repeat this process over and over. Reheating it, hammering it out, folding it back on itself, welding it to itself,

reheating it, hammering it out. This takes a lot of time, and you'll see that typically a relatively large bloom that you'll get out of a bloomery will ultimately reduce to a much smaller size once the smith has hammered out most of that slag, what is left is typically a hammered piece that is mostly iron with a very low carbon content less than point zero eight percent carbon compared to iron, and some other impurities are in there too.

Because the smith had to work the mass by hand to produce this, we call it wrought iron w r o U g h T iron. That means worked iron. That we had to do work on it in order to make it this way. So once in a while, using this method of bloomery's you could produce steel. It wasn't necessarily predictable. You weren't necessarily going to be able to do it time and time again, but it did happen, and you'd be really happy whenever it did. Sometimes, however,

that steel would be particularly hard but brittle. Gradually, mill Or just learned that by plunging very hot steel. We're talking about steel. This around nine degrees celsius into water. The cool steel's surface becomes extremely hard and brittle. But by reheating that steel to a temperature of around four hundred degrees celsius, in a process that was later called tempering, the material will become less brittle but still retain a lot of its hardness. So you would hear these terms

by blacksmith talking about tempered steel. That's what they're referring to. But here's the thing. The process for making steel was imprecise and dependent on so many factors, including the quality of the ore being used to smelt the iron and the process to create the actual steel. It was hard to dial into the specific ratios you need to go from iron to steal in those times. So the concentration of carbon really determines what kind of metal you end

up with. If you don't have enough carbon, you end up with wrought iron. If you have too much carbon, you end up with cast iron, two very different extremes. It's got to be just right, and for a couple of thousand years, that was pretty hard to do. Now, when we come back, I'll talk a bit about how humans figured out more effective ways to produce iron and steel.

But first, let's take a quick break. We've looked at the oldest method of smelting iron with bloomers, and a bloomery gets the job done, but it's not terribly efficient. You have to pour in a lot of labor and a lot of iron ore and a lot of charcoal to get any results, and the bloom you produce still needs a lot of work to turn it into iron

that can be put to any good use. So what was really needed was a better way to reduce the iron oxide and iron ore to iron, and one of the best ways to do that is to produce even higher amounts of heat. Now let's think about this chemically. I've mentioned that the oxidizing reaction is exothermic, but I haven't really talked about what's going on here at an atomic level. So with iron oxide, you've got iron and

oxygen effectively bond with one another within a furnace. The intense heat and the presence of carbon allows for the separation of oxygen from iron. The oxygen instead bonds with the carbon forming carbon monoxide, which is an odorless and toxic gas. The carbon monoxide is happy to take on another oxygen atom as well, So at temperatures around six D nine D degrees celsius in a furnace, you'll end up with iron and carbon dioxide as well, not just

carbon monoxide but carbon dioxide. The bloomers just weren't going to get the job done. They weren't going to get to those temperatures. So that brings us to the blast furnace. The bloomery produces a hot of lump iron. It gets hot enough to glow and it's malleable at that temperature, but it's not hot enough to melt. Blast furnaces can reach higher temperatures high end, so that you're not just reducing iron oxide to iron plus carbon monoxide or carbon dioxide.

You're also getting a hot enough chamber so that you can melt the iron completely. You get molten iron liquid metal. So how is this possible? Well, first, blast furnaces are much bigger than bloomery's. They tend to have a chimney like structure, much like your typical bloomery, but instead of being made out of clay, they're usually made out of several layers of brick that form the chimney. Sometimes with other materials to provide both stability and often away for

heat to dissipate. They can be a couple of stories tall, whereas a bloomery might only be a couple of meters tall, maybe three or four meters for the really big ones, and like a bloomery, blast furnaces have two years through which pumped air can enter into the furnace. The pumps or bellows could be operated by hand, but later on it was far more convenient to locate a furnace next to a source of flowing water and then use a water wheel to provide the power needed to pump the bellows.

You are in effect blasting the combustion in the furnace with air. Thus you have a blast furnace. Unlike people, the water doesn't need to take a break, and the furnace could be kept at a high consistent temperature, assuming it was being fed with fuel regularly like a bloomery. Metal orgists would feed a blast furnace by pouring iron ore fuel and flux down into a chimney like furnace from the top of it. A description of a typical blast furnace says that to charge a furnace that is

to prepare it for the process of smelting iron. First, workers called fillers would empty around twenty baskets of charcoal into the furnace through the top. The bottom of the furnace would be lit, and so you would have combustion going on inside the furnace, and the hot gases created from that combustion would start heating up the charcoal that

was further up the stack. Soon the heat would reach a stage where the heat of rising gas would be enough for the whole smelting process would start as soon as you start pouring charges in through the top, and a charge at this point is that mixture of iron ore, charcoal and flux. So after they get this started with those twenty baskets full of charcoal, they would add in around oh, I don't know, seven hundred pounds of iron ore, followed by limestone. So within half an hour the charge

level would have sunk down by about ten ft. So you're looking at this chimney that was effectively full of material. Now that material has sunk in ten ft because of that combustion and and the conversion of these solids into gases and slag. So then you would add in more iron ore, more charcoal, more limestone, and then a bit more iron ore at the end, and you repeat that process every so often as the furnace burns down, working in shive to keep the furnace working the entire time.

You know, you have to keep on going because if you lose this, if you let the furnace go cold, then that's a whole thing and you have to start all over. Essentially. Inside the furnace, you've got a few different areas. So if we were looking at a cross section of a furnace at the very base, we would see a section that's called the crucible. This is the bottom interior part of the furnace. This is where the molten iron will eventually collect more on that in a second.

Above the crucible is an area called the bosch b O s H. This is where the furnace temperatures get hot enough to reduce iron oxide and ultimately melt iron into molten iron. Above the bosch, you've got the stack, which is where all your charges are. The intense heat in the furnace increases as you get lower down into it, allowing for this chemical reaction for iron oxide to reduce to iron and as iron got hotter, it melts, and because it's so heavy, it's so dense, it sinks to

the very bottom of the blast furnace. Because just because the iron has gone from solid to liquid doesn't mean it's no longer dense. It still is. And the slag that is all the impurities that were in the iron ore plus stuff like the flux that you're adding in UH typically again in the form of limestone, would float on top of the layer of iron because it's it's

not as dense. So it's kind of like when you mix water and oil together, the denser material is going to be at the bottom, right, So taps near the base of the furnace. These are pipes that lead into the furnace would allow mel or just to tap off the slag and also to drain out the molten iron. Now that molten iron would typically follow a channel from the tap and go down the channel and flow into

molds on either side of the channel. So while a blacksmith would have to work a bloom for ages and a bloomery in order to turn it into a bar, a blast furnace produces liquid iron that then flows into molds and just cools into bars big labor saver there right well. In addition, while blue Morays use charcoal as a fuel of choice and blast furnaces, once charcoal became scarce because people were cutting down all the forests, they

started to move toward coke. Now, I don't mean the soft drink instead, I mean the carbon rich fuel that we produce by heating either oil or coal in a chamber that doesn't have air in it. Now, if you don't have air in a chamber and you add heat, you cannot have combustion. Combustion or fire needs three things, right. You need fuel, you need heat, and you need an oxidizer, of which oxygen is one. But if you're burning something or heating something in a chamber that has no air,

you can't really burn it. You can only heat it up. And in this case you can convert stuff like coal or oil into coke. The higher temperatures inside a blast furnace would allow the iron inside it to absorb more carbon than you would find in a bloomery. I think of it kind of like how I think of how sugar will dissolve into hot tea much more readily than it would in cold tea. Chemically, we're not talking about identical processes here. I don't want to make you think

that it's exactly the same thing. It's just sort of an analogy I use. Also, it's a reminder that if you want to make sweet ice tea, you don't do it by dumping sugar in a cold glass of tea. Don't don't try that stuff around me. I'm from the South, but this is tech stuff, not simple syrup stuff. So I'll get back on topic whether the blast furnace is

using charcoal or coke as a fuel. In the end, you produce molten iron which can be tapped to run into that channel and it splits off into those molds down the length of the channel, forming bars of iron. Somewhere along the way, someone thought that this channel with the mold that split off to either side kind of looked a bit like a sow, as in a female pig suckling her piglets. And so the name for this

type of iron is called pig iron. If you've ever heard of pig iron, this is where he gets his name. He gets his name because of those channels that ran from the blast furnace and split off into these molds for pig iron. Bars. Pig iron typically isn't an end goal in of itself. It's a starting point for metalworking. So the production of pig iron is really about taking the stuff that comes out of the ground, whether from bogs or mines or whatever, and separating the metal from

most of the other stuff it's stuck to. But pig iron still has a lot of impurities in it and way too much carbon for most uses. Remember, carbon hardens iron, but it also makes it way more brittle. Often pig iron has too many impurities and too high a carbon content to be used as cast iron. Cast iron has between two point one and four carbon in it, and pig iron can have more than that. It also can contain other impurities like manganese, sulfur, silicon, and phosphorus, and

those things affect the qualities of iron as well. If there are high levels of impurities, iron workers will heat the pig iron in another type of furnace quite similar to a blast furnace, and adding other components to help remove some of those impurities, to combine and form another form of slag, and to tap that slag and move the carbon percentage lower. In the same process, liquid cast iron, which is you know that high carbon content iron with

fewer impurities than your general pig iron is liquid. Cast iron can be poured into casts to form stuff, thus its name. So if you want to make a cast iron skillet, first you had created cast out of something like sand, so you would carve out the shape of a cast iron skillet that way. It's essentially a skillet shaped cavity inside a sand block. And then you would pour molten cast iron into that sand block, and you would allow it to cool inside the sand block and set.

After doing so, you can break the cast open and you've got yourself a cast iron skillet, though you'd still have to do a few more steps to treat it before you could actually use it as a skillet. But the big problem with this type of iron is that once it has cooled, you can't easily heat it up and work it again, meaning shape it. You can't really, you know, heat it up and hammer it and knock

it into a new shape. The iron is just too brittle wrought iron, which has a much lower percentage of carbon. In fact, wrought iron typically has less carbon in it than steel does. It is much more easily worked if reheated, so there needed to be a pro says to refine pig iron to get rid of some of that carbon and some of the other impurities if you wanted to make wrought iron or steel on a much more efficient

sort of mass production kind of basis. Because as it stands, you could make cast iron pretty easily, but wrought iron was still hard to do. You were typically still using bloomer eas and those just didn't produce on very large scales. One advancement in iron working that made this possible was the development of special forges called fineries and chaferies, each

of which did something special. So the finery forge was where a finer this is the person working at the forge, would take pig iron and they would put it into a smallish furnace. The finer would use bellows, usually water powered bellows, to blast more air on the pig iron as it was being reheated inside this furnace. This would cause an oxidation reaction. It would remove some of the carbon,

which would vent out as carbon monoxide. It would combine with the oxygen that was being blown into the furnace, or you might even get carbon dioxide, and this would leave more pure iron behind. So you're kind of leaching out some of the carbon of the pig iron, bringing it closer to the type of iron you would find in a bloom in a bloomery from centuries earlier, and

this was typically called a half bloom. The finer would then remove this half bloom and then another forgeman would take the half bloom and place it on an anvil under a water powered trip hammer. What the heck is a trip hammer. Well, imagine you've got a lever, okay, like a see saw, but you don't have the pivot in the middle of this lever. It's closer to one

side than the other. So on the long end of the lever, which would typically be in the down position because it's heavier, you have the hammer, and on the short end you have that connected close to a cam. Cam is a wheel in this case, it's got some projections on it and those projections can make contact with the short end of the lever. So as the wheel turns, it pushes down on that short end of the lever and it starts to lift the other side. So the

hammer goes up in the air. But as the cam continues to rotate, it eventually rotates to a point where it loses contact with the short end of the lever. It's like if you were to push down on a seesaw and then pull your hand away very quickly. So the trip hammer starts to strike the half bloom and does so several times, pushing out impurities that are otherwise trapped inside the iron, just as the blacksmith would with

the bloom from a Bloomery. The process has to happen several times, so the half bloom has to be reheated and then hammered again and again until it can finally be forged into a bar of wrought iron called an and coney. The end coney would then be put into the chaffery. Chaffery is a hearth style furnace, and the bars would undergo reheating before being hammered out into de

carbonized iron. While this would bring us back to a similar kind of iron produced by Bloomery's, the process was still more efficient from a labor standpoint, particularly with the use of water power, so you could do it faster than you would if you were to use the old Bloomery method. When we come back, we'll move on to some other developments in iron and steel production. But first let's take another quick break. We've talked a lot about iron, and by wie, I mean i've talked a lot about iron.

What about steel? So, steel has a carbon content that typically puts it between wrought iron and cast iron. Wrought iron generally has less carbon than steel. Cast iron has more carbon than steel. The carbon content and steel affects the steel's weight, hardness, and melting point, as well as it's malleability versus brittleness. But if pig iron has too much carbon in it and wrought iron has too little

iron in it, how do you make steel? Well? Typically, in days of your you'd have to take wrought iron billets. You can think of those as just iron bars for simplicity sake, and you would put them in clay pots along with some charcoal. So layer of iron bars, layer of charcoal, layer of iron bars, layer of charcoal all the way to the top. And then you would close these clay pots so that they were essentially airtight, and you put them into a large kiln called a cementation furnace.

You would fire up the kiln and it would heat up all the clay pots filled with these mixtures of iron and charcoal, and it would cause the heated iron to absorb some of the carbon that was in that charcoal. And in case you're keeping track, yes, we've talked about a process in which you add carbon to iron oxide and you get a high carbon iron called pig iron. You then refine that in a finery and a chaffery to produce a low carbon type of iron called wrought iron.

And then you use the wrought iron and add carbon back into it in order to get steel, which does sound pretty crazy, right, like a very laborious process to go from iron ore to steal. To make it even more complicated, this kiln heating process was typically done multiple times, with the iron reforged after heating and then put back into pots with charcoal. Again, this was to ensure homogeneity

throughout the metal. You wanted that carbon to be distributed evenly throughout the iron as much as possible so that you would have really consistent iron. During the heating process, one of the byproducts was once again carbon monoxide. The forming of carbon monoxide gas would cause blisters to form on the surface of the metal inside these pots, so we came to call this type of metal blister steel.

We call this process a carburization process, which means to use a heat treatment process in which iron is absorbing carbon in order to become steel, or you might use it with steel itself in order to make a more

high carbon form of steel. So if you want to make steel around this time, it either involved a decent amount of luck so that you were using a bloomery and the iron bloom you produce just happen to have the right amount of carbon and lack of impurities in it to qualify as steel, or you need to go through a series of refinement processes from smelting or into pig iron, to refining the pig iron wrought iron, to refining the wrought iron and too steel and making wrought

iron this way took a long time too. Then a fellow named Henry Court came along in sevent four. Court found that by heating pig iron in a furnace at temperatures high enough to melt it, because remember pig iron has a lower melting point than other kinds of iron, and then by stirring this mixture in the presence of oxidizing substances, he could produce wrought iron much more efficiently

than the old finery forge process. This new process was called puddling, or since I'm from the South, I'm gonna call it pudlin. This process was one in which the iron wouldn't actually be in contact with the fuel, and most of the other versions you're putting the iron ore

in the same chamber where the fuel is burning. Not with puddling, the puddler what that's what they were called, would use these really long iron tools to reach into the furnace bed and violently stir the semi molten pig iron, and the stirring action would help separate the iron from the impurities, and in the process of oxidizers, it would really help create that separation. This was done repeatedly with the puddler eventually removing this ball of refined iron from

the furnace using really long tools. And the key thing about this process is that even with the constant stirring and vigorous stirring of the puddler, it was much faster than using a finery where you were putting those pots inside a furnace over and over again, and you could produce wrought iron relatively fast, and it would become one of the important contributors towards the Industrial Revolution as a result, because wrought iron was desperately needed for big construction jobs,

you know, like building railroads. Still, steel production was more limited, with most of it being made in the form of blister steel. An Englishman named Benjamin Huntsman further refined steelmaking by taking blister steel and melting it inside clay crucibles and incredibly hot furnaces reaching temperatures around six degrees celsius it's about twenty degrees fahrenheit, and then the molten steel could be poured into casts, much like cast iron could be,

but with the benefits of steel. The next big development in steel production came in eighteen fifty six thanks to English inventor Henry Bessemer. Now to be totally fair, Bessemer was one of a few people to suss this out. There was also an American named William Kelly who came up with the general same idea independently. Bessemer was trying to find a means to produce steel and greater quantities and at lower expense. His approach, which he called the

manufacture of iron without fuel, sounds kind of terrifying, honestly. First, you take molten pig iron yikes. So when a process begins with molten hot metal, you know you're getting into some hardcore engineering. But next you blow oxygen through the molten iron mix. The oxygen reacts with the impurities in the pig iron and effectively creates oxides that end up as slag, and the slag just gets tapped off separately

from the iron itself. The oxidizing reactions were exothermic, so they generated eat that provided heat that could be harnessed to keep this iron from solidifying, so the reaction would help sustain itself this way, the result was the rapid production of steel, very low carbon steel. Other inventors and middle are just figured out that by adding some other

stuff like manganese, iron and carbon into the mix. So yes, once again we are adding carbon, the carbon content of the steel could be increased while remaining impurities like sulfur could be neutralized. The resulting steel was a much more pure version than the typical kind produced in older methods, and it could be made quickly and cheaply. For the first time in history, steel was easy enough to manufacture to make it a viable material for stuff like construction.

The one impurity that the original Bessemer converter wasn't really good at removing was phosphorus, which was unfortunate as that stuff was fairly common in the iron ore of Europe. Sydney Gilchrist Thomas invented the variation of the Bessemer converter that incorporated limestone that helped strip phosphorus from the iron mix.

And it did have one other problem this approach, which is that the original converters would introduce small amounts of nitrogen into the iron ore, thus introducing an impurity making the iron a little more brittle. This was hard to correct for it was hard to get a pure source

of oxygen at this point in history. In the mid nineteenth century, William or Wilhelm Siemens, who was German but was living in Englands or right back to Old Blighty, tried something new that would create an alternative to the Bessemer converter. He rigged up a furnace so that the escaping hot gases from the furnace would heat up a chamber filled with a lattice of bricks so the bricks

would absorb this heat. Then he would change the flow of air so that the incoming air used to feed the furnace would first pass through these bricks lattices, and that would preheat the incoming air and you would get hotter furnace temperatures as a result, So it was essentially creating a hot blower versus a cold blower. Unlike the best of our process, Wilhelm's furnace, called an open hearth furnace,

was slow. But while it wasn't as fast as a Bessemer converter, it allowed for far more precision when you were making the steel, so the quality control was much better. The end product was molten steel, so you could even cast that into ingots right away. The open hearth furnaces could take steel scraps as a charge, thus cutting down on waste. So let's say you make some steel it's

not as good quality as you would like. You could put it in an open hearth furnace and it could be used as a charge to create your next batch of steel that could be better. It could also process pig iron. It became a popular method of steel making for a century. Alright, we're getting into the home stretch of this steel making episode. In night, a Swiss inventor named Robert Durer improved upon the Bestimer converter from a century earlier. He invented a process called basic oxygen steel making.

It's not using basic oxygen, it does use a highly pure form of oxygen. Rather, the term basic actually refers to the use of chemically base materials, again for the purposes of removing impurities that are in pig iron. Like the Bestimer process, basic oxygen steel making forces oxygen through molten pig iron, but the process is totally wicked. So imagine you've got a big container that's lined with a refractory material, meaning it it reflects heat back into the

chamber itself. This container is called the ladle. Inside the ladle, you pour molten pig iron. Suspended over the pig iron inside the ladle is what is called an oxygen lance. So imagine a pipe through which ultra pure oxygen can blast out, hitting the molten pig iron at supersonic speeds. The lance itself has to be actively cool to typically water cooled, to keep it from overheating from the intense

heat from this furnace. The oxygen reacts with the impurities, thus you get oxidation and it creates heat through that reaction, and the heat sustains the temperature needed to keep the furnace in action, it becomes sustaining. So in many ways, it's a more advanced version of the best Americ converter. And this became a new method for making steel efficiently, with fewer impurities and at a faster rate than open

hearth furnaces. All right, we've got one more method to talk about, or at least to introduce, and we'll really talk about it more in the next episode, and then we'll also explore about all the different types of steel like Nick had asked. So, the final type of furnace I need to mention here is the electric arc furnace, and it heats up the materials inside the furnace the charge through an electric arc rather than by burning some

sort of fuel. Back in the early nineteenth century, Sir Humphrey Davy created an electric arc between two carbon electrodes. In fact, we had electric arc lamps before we had the incandescent light bulb, and these things were terrifying too. They generate a light by by creating this electric arc between two electrodes, very high voltage electric arc. And it didn't take very long before someone thought, huh, I wonder if there's enough energy in that electric arc to you know,

melt metal like iron. This is the same basic technology that would go into electric arc welders. While using an electric arc was effective early on, it was also inefficient and expensive, which made it less viable as a means of mass producing steel. And there's a lot more of tech to go into with that, but I think that's

enough for today's episode. In our next episode, we'll pick back up with electric arc furnaces, talk about how they really work, and then finally we'll talk about the different classications of steel and what they all mean, including maybe a discussion about Damascus steel, because that stuff is largely misunderstood, so we'll cover that in the next episode. Two. Uh. If you guys have suggestions for things I should cover in future episodes of tech Stuff, let me know. Send

me a message on Twitter or Facebook. The handle for both is tech Stuff hs W, and I'll talk to you again really soon. Text Stuff is an I Heart Radio production. For more podcasts from I Heart Radio, visit the i Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.