The Deal With Steel

What's inside those rocks? We found two material we can use to build things and or make weapons to poke each other with. We talked about smelting and furnaces and the refining processes, and we ended that episode with a very brief explanation of what an electrical arc furnace is. Today, we're going to start off by going into a bit more detail about how the electrical arc furnace actually works to refine iron, and then we'll move on to talk

about the different types of steel, including the famous Damascus steel. Now, as I said in the previous episode, the electrical arc furnace generates high temperatures through the creation of an electrical arc. But that description isn't terribly satisfying, is it. How does it create the electrical arc what makes it so hot? Well, in that last episode I mentioned, Sir Humphrey Davy invented

the arc lamp using a pair of carbon electrodes. He used a couple of thousand battery cells and connected one electrode to the positive terminal and one to the negative terminal. Then he brought these two electrodes in contact with one another. This formed a circuit. So not only could electricity flow through this completed path, but also the negative carbon electrode

began to attract particles from the positive carbon electrode. In other words, material from the positively charged electrode was literally moving over to the negatively charged one and pulling the electrodes apart slowly allows an electrical arc to form between the two electrodes. It seems like electricity is still traveling between one and the other even though there is no longer a physical path. So if it's seemingly passing through the air itself, how is that even possible? Is there

an enormous difference in electric potential between the rods? Is the voltage super high? Remember voltage is like water pressure, right, It's how hard the current is being pushed through a circuit. But no, that's not the case. The voltage doesn't have to be super high, although typically we're talking about more than forty five volts for arc lamps and sometimes more

than a hundred volts for electrical arc applications. But when the two electrodes make contact with one another, there is a lot of atomic movement at the point of contact. Atomic movement means lots of stuff, but one thing we can think about is heat. Hot atoms move around a lot, cold atoms don't. In fact, there are some who say that absolute zero or zero kelvin isn't just the bottom end of how cold temperatures can get, but represents a

total lack of atomic movement. This heat is enough to boil off some atoms from the solid carbon electrodes and it forms a gas. That gas is still capable of conducting an electric charge, and it does so. Thus you get a plasma and ionized gas. So what we have here is a plasma generator with a bright electrical arc

passing through it. There's a lot more science than this that we could talk about, such as ionization and stuff, but the important thing for us is that by bringing these electrodes in contact with one another and then separating them from each other slightly, you get a very hot, very bright electrical arc. This would end up being basic technology behind some of the earliest electric lights before incandescent bulbs. They were used for street lighting and for movie projectors

and search lights. The light they produce is incredibly bright. It's bright enough to hurt your eyes if you look straight at it, and they also emit ultra violet light, so you wouldn't want to look at them directly or be around and unshielded electrical arc for a really long time. Fortunately, good old playing glass doesn't allow ultra violet light to pass through it, so with a glass lens you can actually block that pesky UV radiation. Our lamps aren't that

common these days. I mean, there are still some out there, but electrical arcs are still used for lots of stuff. Old time listeners to the show might remember that one of my first articles for the website how Stuff works dot com was on a technology called plasma waste converters. These facilities use a plasma torch, which is a sin a variation of what I've already been talking about with arc lamps, to gasify or to liquefy garbage. Essentially, anything

that's carbon based gets gasified. It's it's turned into gas. Anything that's not carbon based gets heated up so much that it becomes molten. Well, electrical arc furnaces use this same basic technology in order to make steel. Your typical electrical arc furnace has a cylindrical vessel, right This is the base of the furnace. This is what holds the charge. In other words, the raw material you're using. This vessel has an interior lining of refractory material designed to reflect

heat back into the chamber. The melted material, called helpfully the melt, will gather at the bottom of the furnace. And this is really dense stuff right now we're talking about steel. So the slag, as in the other materials, the impurities that were also part of the charge. Typically it's stuff you don't want. Tends to float in a layer above the steel melt, and it can be drawn out through a slag door. At a certain height on the chamber. Towards the bottom of the furnace is a

tap hole. It's kind of the drain for the furnace, and this is the hole through which molten steel will flow. And then it's collected in another vessel called the ladle. So you have a ladle is essentially a special kind of bucket that's underneath this tap hole. The open up

the tap hole and the molten steel comes out. And typically these furnaces are mounted on platforms that have a hydraulic lifting arm below them that can extend so it tilts the entire furnace to get every last delicious drop of molten steel out, although honestly they don't always take every drop out. In fact, some furnaces specifically leave some and steel behind to help with future UH steel production.

The furnace is removable lid, which is really more of a roof because these things are usually several meters in diameter. They're huge anyway. This removable lid typically has three electrodes which extend down into the chamber. The electrodes make contact with the charge and the furnace operator filips the switch to send electricity through these electrodes. Current flows from the

electrodes to the charge. UH The electrodes are typically made out of graphite, so a type of carbon, and the electrodes just like the old carbon electrodes that Sir Humphrey Davy used, they begin to ionize and they form a plasma gas and that allows this electrical arc to form. Power continues to go to the electrodes to perpetuate the arc because in this case, this process does not depend upon the chemical process oxidation, which was what was generating

heat with stuff like basic oxygen uh processes. Now, it's not like electrical arc furnaces are the new norm. In fact, they're responsible for only about a quarter of the world's steel production. Most of the rest is still produced through basic oxygen furnaces. And the steel that electrical arc furnaces produces typically has a higher carbon content than the kind

that is produced by those other furnaces. And we have to remember carbon content and steel affects the metals properties like hardness and how malleable versus brittle it is and the melting point for the metal. The more carbon, the harder the surface of the metal tends to be, the more brittle it will be, and the lower the melting point will be. One drawback to electrical arc furnaces is that they can introduce nitrogen into the steel alloy, and

nitrog can make steel more brittle. So to deal with that the furnace operators can blow in other gases to react with the nitrogen, thus neutralizing it, or carbon monoxide can be used for this purpose or other other techniques included shorter bursts of the electrical arc so you're not

producing so much nitrogen. Often electrical arc furnaces will use scrap steel as part of the charge material, so the input you're putting into the furnace in order to get steel at the end, it might involve shredded or scrapped steel from other stuff, but they can also bring in things like iron from blast furnaces to it doesn't have to be scrap steel, and it can involve other materials

as well. Scrap steel can contain other stuff in it, typically referred to as residuals, stuff like nickel, copper, chromium, tin, and other stuff which you may or may not actually want in your final product, and you may have to draw that off separately. And that's generally how electrical arc furnaces work. It's a different approach, not just in technique but in the actual physics involved, but the end result

is the production of steel. So let's talk a bit about the different kinds of steel and what they all do and what makes them different. But we're going to start with a legendary type of steel, Damascus steel. And to talk about this, we have to go way back before anyone had ever considered using an electrical arc furnace. So, beginning sometime around five Common era, sword makers in the Middle East began to create weapons that were known for

their sharpness, for their durability, and for their beauty. They could hold an edge really well, they stood up to a lot of abuse, and they had these intricate wavy patterns on the surface of the metal itself. And legend stated that a sword made from that kind of steel could be sharpened to the point where it could cut a feather in half while the feathers floating in the air. Or similarly, if you were to drop a silk scarf, you could cut it in half before it hit the ground.

So sharp these these swords could be because of that that incredible metal. But there's some complications to this story. First, the legend also states that sword makers lost this ability sometime in the eighteenth or nineteenth century, that the entire method of producing weapons of this quality was lost to time. It seemed as though people just forgot how to make weapons this way, and sword makers could still make weapons. In fact, they could still make weapons that had wavy

patterns in the metal. More on that in a second. But they didn't possess the legendary hardness and edge holding capabilities of those earlier weapons. So how did that knowledge die out so suddenly? What was so special about the weapons? Well, one reason this is so confusing is that name Damascus Steel. It is a little bit misleading because it makes it sound as though the steel for the legendary pieces of

arms and armor all came from Damascus. The city of Damascus is in Syria, and that region does have iron mines, But the steel they were using to make these particularly strong weapons probably didn't come from the Middle East, at least not most of it. Most of it came from India. See, Damascus was an incredibly important trade city in the Middle Ages.

All sorts of merchants passed through that city trading goods, and some of those goods included steel forged from iron that had been mined far away in India and then refined into steel in India. So they were actually bringing steel ingots, or more fittingly, steel cakes to Damascus, and this particular type of steel is more accurately called woots steel w O O t Z. This steal happened to have a low concentration of an impurity that gave Damascus

steel that particularly vibrant, wavy pattern and strength. It was vanadium. As it turns out, there is a mine in Jordan's that also produces iron ore with a similar amount of vanadium in it, So at least some Damascus steel may have originally come from the Middle East, with most of

the rest being imported from India. The process for making the steel itself involved smelting iron ore using a bloomery, which remember it doesn't melt the iron, it just heats it up to a glowing, hot, spongy mass that you didn't have to work with a hammer. But then after the iron bloom, which is what you call the lump that you create at the end of the bloomery process, after the iron bloom cooled, then they would crush it up and put the little pieces of the iron bloom

into a crucible. And along with that iron bloom they would put some green leaves, uh some crushed glass, and maybe some charcoal in there. Before they would seal the crucible up so it's completely sealed, and they would then put that into a furnace. And because the crucible sealed, no oxygen gets into this process, so combustion cannot happen. Remember, for combustion to happen, you need heat, you need fuel, and you need an oxidizer. It doesn't combust the material

inside heats up to very high temperatures. The leaves release hydrogen as they heat up, which facilitates the absorption of carbon into the iron. And as iron absorbs carbon, the melting point for the iron decreases, and that allowed these ancient blacksmiths to actually work with molten iron. They weren't just heating up a lump anymore. Now the iron was melting into a molten liquid. The glass also melts, becoming a cap over the iron. Because the glass is less

dense than the iron, it floats on top. That further protected the iron from being exposed to the air prematurely. And the charcoal serves not just as a source of some carbon, but also as a way to neutralize any oxygen that was being released in the process. The result was an ingot or cake of high carbon steel. A skilled blacksmith would take that steel, and through a long process of reheating the steel and cooling it, would then

prepare it for forging. Forging would involve heating the metal enough so that it would become malleable when struck with a hammer, and these are all dependent on specific temperature ranges.

So the blacksmith would get that metal hot enough, put it into on an anivil, work it with a hammer, work the metal into a long sword blank, for example, which would then be further worked into the sword itself, and the steel's composition, combined with the sword maker's technique, is what would create those intricate patterns on the blades.

The patterns were made in part because the vanadium was in that iron and carbides or the carbon compounds, and the blade itself provided the strength and hardness needed to create very sharp, durable weapons. But then there's another way of creating those patterns. I alluded to it earlier. It's called pattern folding. This is a totally different technique, and the patterns in pattern folded weapons are not exactly identical to those of true Damascus steel, but they are still

very pretty, so they were kind of sought after. But this is a technique in which a blacksmith would take iron from different blooms. Thus, these different chunks of iron have different concentrations of carbon in them, so some of them may be low carbon, some of them may be high carbon. And they would hammer out these various pieces

of iron into strips. They would heat these strips up together so they would reach this very high temperature, and then would start to hammer those together to weld these different layers of metal together. Are so you've got these different concentrations of carbon in different strips of iron all getting welded together, and they would fold it and weld it again, folded and welded again, and this would create

that sort of pattern. Look, because you're actually looking at different concentrations of carbon in iron, it's that's what's causing the pattern. It's not the nature of the iron itself. And because you were using this approach where you're hammering it out and you're never melting the iron, you couldn't get as pure a version of steel as you would with the crucible. The crucible would allow all the slag

to rise to the top of the crucible. You know, everything turns into liquid, so you could just pour the slag off, but you couldn't do that with this approach because you never melted the iron, so you had to work it with a hammer, and it would never be as pure as true Damascus steel would, so you and not get a weapon of the same quality as one that was a true Damascus steel sword made by an

actual master sword maker. Damascus steel, the real stuff died out largely because industrialization brought about mass production and steel, and that lowered the demand for the more artisan approach and the process of working the steel, which included very many steps. It was typically passed down through oral tradition, not written down anywhere, so it was gradually forgotten because there was no call to make that steal, so no

one was passing down that knowledge. More recently, modern blacksmiths have been working with different approaches to replicate the forging of Damascus steel, largely based on some very educated guesses as to how it must have happened, and they've made a lot of progress, largely through trial and error. But it all starts with having the right type of steal from the right type of iron ore. When we come back, we're gonna talk about some modern classifications of steel and

what that all means. But first, let's take a quick break. So how many types of steel are there? Well, golly, that really depends upon whom you ask. I know that is a lame answer, but it's true. Some people will divide steel into four broad categories. Uh. Those broad categories could be plane, carbon steel, alloy steel, tool steel, and stainless steel. Some say alloy steel and low alloy steel instead of tool steel. And the reason why you get all these different terms for the same basic stuff is

because it all depends on your point of view. It's just like what obi Wan said. The site mead Metals classifies steel into carbon, alloy, stainless, and tool. But Thomas, which is an industrial sourcing company, so it's a company that helps manufacturing companies find sources for the raw materials they need, they classify it as carbon alloy, low alloy, and stainless. Uh. Meanwhile, the home Stratosphere site breaks it

down to twenty six different types. And then you have various standards associations like s a E International s a E originally stood for Society of Automotive Engineers or the American Iron and Steel Institute or ai s I. Those are just two in the United States. You also have other ones in other countries, like British standards in the UK. You have International Organization for Standardization lots of these different groups,

and they have thousands of different grades for steel. So what does this tell us, Well, it tells us there's an incredible amount of variability in the different types of steel people have made over the years, and that creating standards is tricky. If your standard is Lucy goosey and each grade of steel covers a fairly wide range of qualities like hardness or flexibility, or percentage of carbon or percentage of other alloys, you really end up with some

real problems. So let's say that you've got a standardization system where you've got pretty wide grades to cover a spectrum of steel. But you're in charge of making steel girders, and so you're looking for a specific grade of steel, and the problem is that because it covers a spectrum, some of the girders you make might be stronger than others. Some might be better at standing up to really strong compression forces, and others are not. And that ain't great.

You really want all that steel to be of similar hardness, similar strength. You really need it all to be consistent. So it really is necessary to break down steel into thousands of grades so that when it comes to actually manufacturing and selling the stuff, companies can make sure they are getting the raw materials they need to do whatever

the job necessary is. But the downside is there's no way for me to do an episode about every single grade of steel, as it would be a billion hours long, and a lot of it would just be repeating seemingly arbitrary designations between two very similar but technically distinct types of steel, and that is just too much. But I will go over some of the classification strategies though, and what it all means. So let's start with some of the broader categories and we can drill down from there. Uh.

And we're gonna go with carbon steel first. Now quickly, just as a reminder, we're gonna be talking about carbon steel and alloy steel. Things like that steel itself is an alloy, so that makes these designations confusing, right, And more than that, steel is an alloy of iron and carbon, so that makes it even more confusing. Why do you

have carbon steel versus alloy steel? I mean, if all steel has carbon in it, and if all steel is an alloy, what do those designations even mean well, all of these steels are still alloys, and all of them still have carbon in them, But what really differentiates them is how much carbon each type of steel contains, and whether or not the steel has a significant amount of

other stuff in it besides iron and carbon. Other factors also make a difference, such as how slowly or rapidly the steel cools in the manufacturing process, or how long the steel has been held at specific temperatures, or whether it's been heat treated. These processes all have their own names. To cool steel quickly is to quench it, which typically

hardens steel. A sword maker might quench a sword to give the exterior a harder surface while the interior, which will cool more slowly because it's not being bosed to the water, retains a more flexible core. As a result, to avoid making a sword to brittle, the sword maker would temper the blade. That involves heating the sword back up again, but below the critical temperature at which the sword maker would you know, heat the blade in order

to work it. So it's not as hot that it would be malleable, but it's hotter than it had been. So it gets really complicated, right, and it's all about creating the right crystalline structure for steel, and I'll get more into that towards the end of this episode. For now, let's take a closer look at some of those categories. So carbon steel that is mostly iron and carbon with only trace amounts of other elements in the mix. It's also by far the most common type of steel produced

around the world. And we can also break down carbon steel into three large subcategories. Low carbon steel sometimes also called mile steel, this can contain up to point three percent carbon. Then you've got medium carbon steels, this contains between point three and point six percent carbon. And then you get high carbon steels, which have more than point six percent carbon, typically not much more than one percent.

You might go up as high as two point five percent for some types, but beyond that is unusual, not unheard of, but unusual. So even within these subcategories, you see there is variation. Right, low carbon or mild steel is the easiest to work and shape all of the three subcategories because it doesn't have as much carbon in it. Remember, you add carbon, the the steel becomes harder. That also means it's harder to shape. Now, low carbon steel has

high ductility, which I haven't really talked about. Ductility is the ability of a material to be plastically deformed under ten style stresses without fracturing. Tensile stresses are those placed on a material that tends to elongate the material. I think of it as a kind of tug of war kind of stress. Right, You've got people pulling on either end of a rope, those are ten sile stresses on

that rope a pulling stress. Deforming means to change shape, so a material with high ductility will stretch, becoming thinner without breaking apart. And that also means that low carbon steel can be drawn into wires. This involves passing the steel through a series of dyes, and these are kind of like metal blocks that have a hole in the middle of them. And the hole is of a diameter that's slightly smaller than what the steel is that you're passing through it. So you narrow the end of the

steel so it'll go through this hole. You connect it to some really powerful machine that pulls that steal through and the steel elongates. Rather than gets more dense and keeps the same density, it just it elongates and gets thinner. And you do this several times, and each time you're doing it, you're typically going a little smaller with the following dye, and you eventually create wire this way, and you do this until you reach the gauge or a

thickness of the wire that you want to produce. Besides wire, low carbon steel can be used to make stuff like pipes or automobile body parts, and some construction materials. They're also used in processes that require machining or welding. Then we move to medium carbon steels. These are less ductile, but they are also more hard than low carbon steels. They have greater hardness. They're often used for gear parts like crank shafts and axles and stuff like that, or

in machinery parts where hardness is an important requirement. When you get to the upper ranges of medium carbon steel, meaning you're getting closer to high carbon steel, and you're working with a metal strong enough to be used in tools like screw drivers and pliers and that kind of thing. So keep in mind, like I said earlier, each of these types of steel has a range within it. They're not all equal. But moving on up we get onto high carbon steel, we get into the territory of the

hardest of the carbon steels. It's also the least ductal and least malleable, meaning it's the most brittle and and it's the most difficult to shape. This stuff can be used for rails, for wear resistant plates, for high strength bars, and that kind of thing. It's also sometimes used in the production of knives. It's hardness makes it really valuable for that purpose. They're even processes that can produce steels with a really high carbon content around two and a

half percent. Remember, everything we've talked about from this point has been steel with a carbon content of around one percent or less. These knives can be sharpened to a very fine edge, but they will lose that edge fairly quickly over time and require sharpening. But high carbon steel also has a very low resistance to corrosion, so if you get high carbon steel near water, it can rust

pretty quickly. So while you can find cutlery made of high carbon steel, it's far more common to encounter knives and silverware made out of a different kind of steel, and that is stainless steel. All right, how about we shift over to stainless steel for a few minutes. We already know that stainless steel has carbon in it, otherwise

it wouldn't be steel. But what makes it stainless, Well, stainless is a type of alloy steel And again, yes, steel all on its own is an alloy with iron and carbon, but in this case we're talking about alloy with another metal added to it. So what is our addition to our favorite iron carbon combo. Well, it's chromium, and that typically ends up making up between ten and twenty percent of the overall composition of stainless steel. Other metals and materials are typically in that alloy as well,

including nickel, and then you get stainless steel. And chromium is a hard, brittle metal. It's also incredibly resistant to corrosion, and it's specifically that property that comes in awfully handy when you're producing a steel alloy. Stainless steel resists corrosive effects, and so there are types of stainless steel that are really handy for stuff like cutlery or containers that hold

corrosive materials. It's also pretty strong stuff, or at least it can be, because there are different types of stainless steel, just as there are different types of carbon steel, and the grades of stainless steel depend on many factors, not just how much carbon and chromium are in the alloy, but also stuff like nickel, copper, silicon, aluminum, and even

the process of making the steel itself. All of these can affect the various aspects of the stainless steel, including its hardness, its resistance to corrosion, its heat resistance, and more. There are lots of different steel alloys, and each creates a different kind of steel with properties that are sought after for specific applications. Steel that works great for one

purpose might not be ideal for another. But luckily, because metallurgists have a lot of time on their hands, I mean, they've done so much work experimenting with different alloys that we can produce a lot of different kinds of steel, and there's probably a kind that's going to be ideal for whatever purpose you have in minds let's go over a few of them. Tungsten is a dull silver metal sometimes it's called wolfram that one of tungsten's properties is

a very high melting point. So if you make an alloy of steel with tungsten and you get toungusten steel, you get a really tough, hard metal that can withstand incredible temperatures, and for that reason, engineers rely on tungsten steel for stuff like rocket engine nozzles. I mean, you don't want your engine melting off your launch vehicle when

you're headed off to space. After all. Tungsten steel is a go to for applications that involve high temperatures, but it may also be combined with other metals like nickel or iron for the production of turbine blades. Nickel steel is another alloy and is a pretty common one. It's one of the alloys that works best for heat treated steel, as it decreases the amount of distortion in the steel when it has been quenched, you know, when it's been

cooled very quickly. That also boosts steels strength while not trading off on ductility, so you can get very strong steel. There's still ductal Like chromium, nickel resists corrosion. It's one of the reasons why it's frequently a component in stainless steel. Then there's manganese. Manganese steel typically has between eleven and fourteen percent manganese in it. Manganese steel is quite hard

and it resists where and tear. It's frequently used in railway tracks and heavy duty applications that encounter lots of mechanical forces, like parts for rock crushers, for example, or cement mixers and you know other seriously tough machines. Next, we come to a medal we mentioned earlier in this episode, vanadium. Vanadium steel is resistant to corrosion. It's also got some shock absorption qualities. It's used in the automobile industry and

parts meant to distribute shock and vibration. It's also a common material in pipes and tubes, mint for carrying corrosive chemicals, and it is often used as a bonding material to bring steel and titanium into b f F territory. Get your titanium steel. I've got more to say on different types of steel, but Gali, I need to steal myself with some tea. My voice is giving out. We'll be right back. In the last section, when I was talking

about stainless steel, I mentioned chromium. But making matters more confusing is that there are chromium steel alloys that are not stainless steel. In addition to corrosion resistance, chromium can give steel a boost in high temperature strength, and it's also a more elastic alloy with greater tensile strength. It's used in automobile manufacturing and frequently is the steel that

you find for safes. Sometimes chromium and vanadium while tag team with steel and create a chromium vanadium steel alloy, and this alloy has got high tensile strength, and it's suitable for stuff like vehicular frames and gears, that kind of thing. Aluminium steel there's another alloy that I need

to touch on, So that is a thing. Aluminium boosts steel's ability to reflect heat, and aluminium is much much lighter than steel, So an aluminium steel alloy results in a type of steel that's lighter than most other kinds, and it's used in all sorts of applications, from packaging to energy production to the automotive industry. Cobalt steel, like nickel steel, is tough and stands up well too high temperatures.

It's frequently used to produce high speed cutting tools. Cobalt steel is also ferro magnetic, and uh oh, that reminds me. One of the things I haven't really talked about much in these episodes is magnetism. With certain temperatures, iron is ferro magnetic. Now those temperatures involved pretty much all the temperatures that you and I would ever experience. If we were to experience the temperatures above which iron no longer

as ferro magnetic, we would be in trouble. See those high temperatures beyond what is called the Curi point, iron isn't nearly as faro magnetic. It will react weakly to magnetic fields. Now that temperature is pretty high. We're talking seven seventy degrees celsius for pure iron, but other stuff can affect the cury point for steel, and some alloys are downright diamagnetic, which means they're not magnetic at all.

To get into why something can sometime as be magnetic and at other temperatures it's not as magnetic, and in certain alloys it's not magnetic at all would require a full blown dive into quantum physics and the crystalline structure of iron, and I'm just not prepared to get into that. I ain't got enough coffee in this house to take care of that. But the important thing to remember is that steals magnetic nature depends heavily on which alloy you're talking about. One alloy that is on the high end

for magnetic force is silicon steel. This stuff is used in lots of electromagnetic components, stuff like electrical transformers, relays, motors, that kind of thing. If you've got a steel permanent magnet, chances are it's made out of silicon steel alloy. Now it's time for you to cross your fingers for me, because it's time for me to attempt to say the word molybdenum. Adding molybdenum to steal and making an alloy

improves steels well debility as well as its toughness. It's also more resistant to corrosion, and it is a common material for structural steel, particularly around what would otherwise be really corrosive environments, like anything having to do with the ocean. So if you were building, say, uh, like an oil drilling rig out on the ocean, you're probably using molybdenum in your steel alloy. And that's pretty much it for

the major alloys. Now, keep in mind, each of the kinds I mentioned have their own grades of steel, and the qualities I mentioned are are general in nature. So while one maybe harder than steel typically is you know, just carbon steel, the grade to which it is harder is dependent upon multiple factors. I guess I should really

briefly go over tool steels. These are also alloy steels, but of course they get their own designation and their own subcategories because categorizing stuff is hard, and these steels typically include a larger amount of materials like vanadium and tongue sten. These have greater resistance to wear and tear. They have increased hardness and toughness over typical alloys, and tool steels typically have a carbon content between point five and one percent. They put us put them closer to

the high carbon steel category. You can break this down into six subcategories, cold work, hot work, shock resistant, water hardening, and dealer's choice. No way, I'm sorry, I'm I'm in special purpose. The names give you a big hand about what's going on here. Some of these steel types are best if you need to work within very hot or

very cold materials or environments. Water hardened steel is a type that is water quenched when produced, and it's pretty similar to high carbon steel in a lot of ways. But that's kind of the down and dirty approach to tool steel. But what is it about steel grades? What's the story there? Well, it helps if we focus on one set of standards and explain from there. So for the purposes of this podcast, we're gonna go with the

s a E steel grade designations. This system grew out from the nineteen forties as various engineers and drafts people and architects and metallurgists and all these folks were getting together and trying to catalog all the different types of steel and the specific qualities to those specific types, including

the differences within a specific group of steel. And the s a E system uses a four digit code to designate steel so that you really know what you're dealing with the first two digits of that four digit code tells you which alloying element is present in the steel and to what degree. The first digit indicates the alloying element, the second indicates the presence of major elements. So here's

how the first digits shake out. If the first digit in that four digit code is a one, then the type of steel that's being talked about is a carbon steel, so there are no other major trace elements in that steel, or at least not beyond trace amounts. If the first number is a two, then you're talking about a nickel

steel alloy. Three would be nickel chromium steel, four is molybdenum steel, five is chromium steel, six is chromium vanadium steel, seven is tungsten steel, eight is nickel chromium vanadium steel, and nine is silicon manganese steel. So that first digit tells you a lot, and then the last two digits in that four digit code tell you how much carbon is in the steel, and it's all in point zero

one increments. So if you saw a code that said ten forty two steel, that would mean you've got carbon steel with a carbon percentage of point for two, so you would have a type of medium carbon steel in other words. But sometimes these four digit codes go and make things more confusing. They throw a le are in there, so you might see something like twelve L fourteen, So

what the heck does that mean? If the twelve means it's a carbon based steel with some other element in it, and fourteen tells you there's point one four carbon in it, was the L. The letter L indicates the addition of some other material to the steel alloy. L specifically refers to lead, so adding lead to the alloy would improve the machine ability of the steel. The letter B is a similar thing, it could appear in the middle of a code, but B stands for boron that improves steel's hardness.

Other letters might be found at the very front of the code. So if you see the letter M, that stands for merchant quality, meaning the steel is suitable for non critical parts of machinery or structures. The letter E before a code would indicate that the steel is suitable for electric furnaces. If the code has the letter H at the end, that would mean the steel meets harden

ability limits. And then you have other coding systems entirely, so that works for S A E. But the AI S I coding system also includes three digit designations for different classifications of stainless steel, and the first digit in those three digits ranges between two and five. You don't have any one hundred series, but two hundred to five hundred series that indicates whether the stainless steel is forritic, austinitic,

or martensitic. So what is that? What? Well? It all has to do with that crystalline structure of stainless steel, which in turn will dictate certain properties of that steel. And I've avoided talking about this because it's hard to talk about, but here we go. So crystals only form as molten steel or molten iron cools. As the material cools, it's lidifies, and it forms a type of lattice that's

the crystalline structure. Now that that lattice includes a very small amount of carbon, and we're talking about just point zero to five or less, we call it fairte. And fairite has a cubic body crystal structure, and there's an iron atom at the center of this crystal that has one iron atom at each corner. There's just not much room for carbon to fit in there. Ferretic steel is susceptible to corrosion. It's not particularly strong or particularly hard,

so it's not really used very much. Austinitic steel contains a form of iron called austinite, and this has a different crystalline structure. It's slightly more conducive to absorbing carbon. So to make austinite you have to heat faeryte up to really high temperatures like n twelve degrees celsius, at which point the crystalline structure shifts. But it doesn't break apart and become molten. It doesn't liquefy. You're still solid.

It's just the crystal structure changes and at that temperature the steel can absorb more carbon, but needs additional additives like manganese and nickel in order to maintain that crystalline structure when it starts to cool down. This type of stainless steel is much more resistant to corrosion, and it's used in stuff like stainless steel, screws, Martin sidic stainless steel has Martin site in it, and that clears everything up right. So Martin site is another form of crystallized iron,

and you create it by taking austinite. You heat up the austinite, then you cool it rapidly through quenching. So when you do this, when the austinite cools down very quickly relatively speaking, it prevents those carbon atoms from getting the boot from the austinite. Right, Because remember I said that you had to add in stuff or for austinite to maintain that crystalline structure. One other thing you could do is cool it really fast, and then you prevent

the austinite from converting back into fairite. There are a lot of other differences between these types austinitics. Stainless steels can't be heat treated, for example, but Martin Siddik stainless steel can be. This also means that the different types

of stainless steel are good for different applications. There's so much more we could go into, including stuff like prolite, which is important with some of those Damascus blades I talked about in the beginning of this episode, but it really gets fairly far out of the realm of tech stuff. The interesting thing I find about steel is that there really are so many different kinds of it, and all of them have different qualities that make them great for

certain and sometimes incredibly specific applications. I have a greater appreciation for that now. It's about way more than just heating up a lump of metal until it's glowing and then whacking at it with the hamlets. Far more nuanced than that, and that ends our discussion about iron and

steel and why there are so many different grades. I mean, honestly, it's because these different variations of steel have different enough properties that you got to be aware of it before you start buying it in bulk and using it to create stuff you would hate to create or to order steal that is hard to work with. For example, if you wanted to have something that was really easy to mold into different shapes. You'd really be stuck there. So

the gradations are important. They're just difficult to really get your mind wrapped around. If you guys have any suggestions for future topics that I should cover here on tech Stuff, reach out to me on Twitter or Facebook. To handle for both of those is text Stuff H s W, and I'll talk to you again really soon. Text Stuff is an I Heart Radio production. For more podcasts from my Heart Radio, visit the i Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.