Speaker 1: Welcome to text Stuff, a production from I Heart Radio.
Speaker 1: Hey there, and welcome to tech Stuff. I'm your host,
Speaker 1: Jonathan Strickland. I'm an executive producer with I Heart Radio
Speaker 1: and I love all things tech and we are continuing
Speaker 1: our episodes about iron and steel today. So in the
Speaker 1: previous episode, I covered the history of our use of
Speaker 1: iron and how we learned how to refine it into
Speaker 1: something you know, actually useful. To go from hard stuff.
Speaker 1: What's inside those rocks? We found two material we can
Speaker 1: use to build things and or make weapons to poke
Speaker 1: each other with. We talked about smelting and furnaces and
Speaker 1: the refining processes, and we ended that episode with a
Speaker 1: very brief explanation of what an electrical arc furnace is. Today,
Speaker 1: we're going to start off by going into a bit
Speaker 1: more detail about how the electrical arc furnace actually works
Speaker 1: to refine iron, and then we'll move on to talk
Speaker 1: about the different types of steel, including the famous Damascus steel. Now,
Speaker 1: as I said in the previous episode, the electrical arc
Speaker 1: furnace generates high temperatures through the creation of an electrical arc.
Speaker 1: But that description isn't terribly satisfying, is it. How does
Speaker 1: it create the electrical arc what makes it so hot? Well,
Speaker 1: in that last episode I mentioned, Sir Humphrey Davy invented
Speaker 1: the arc lamp using a pair of carbon electrodes. He
Speaker 1: used a couple of thousand battery cells and connected one
Speaker 1: electrode to the positive terminal and one to the negative terminal.
Speaker 1: Then he brought these two electrodes in contact with one another.
Speaker 1: This formed a circuit. So not only could electricity flow
Speaker 1: through this completed path, but also the negative carbon electrode
Speaker 1: began to attract particles from the positive carbon electrode. In
Speaker 1: other words, material from the positively charged electrode was literally
Speaker 1: moving over to the negatively charged one and pulling the
Speaker 1: electrodes apart slowly allows an electrical arc to form between
Speaker 1: the two electrodes. It seems like electricity is still traveling
Speaker 1: between one and the other even though there is no
Speaker 1: longer a physical path. So if it's seemingly passing through
Speaker 1: the air itself, how is that even possible? Is there
Speaker 1: an enormous difference in electric potential between the rods? Is
Speaker 1: the voltage super high? Remember voltage is like water pressure, right,
Speaker 1: It's how hard the current is being pushed through a circuit.
Speaker 1: But no, that's not the case. The voltage doesn't have
Speaker 1: to be super high, although typically we're talking about more
Speaker 1: than forty five volts for arc lamps and sometimes more
Speaker 1: than a hundred volts for electrical arc applications. But when
Speaker 1: the two electrodes make contact with one another, there is
Speaker 1: a lot of atomic movement at the point of contact.
Speaker 1: Atomic movement means lots of stuff, but one thing we
Speaker 1: can think about is heat. Hot atoms move around a lot,
Speaker 1: cold atoms don't. In fact, there are some who say
Speaker 1: that absolute zero or zero kelvin isn't just the bottom
Speaker 1: end of how cold temperatures can get, but represents a
Speaker 1: total lack of atomic movement. This heat is enough to
Speaker 1: boil off some atoms from the solid carbon electrodes and
Speaker 1: it forms a gas. That gas is still capable of
Speaker 1: conducting an electric charge, and it does so. Thus you
Speaker 1: get a plasma and ionized gas. So what we have
Speaker 1: here is a plasma generator with a bright electrical arc
Speaker 1: passing through it. There's a lot more science than this
Speaker 1: that we could talk about, such as ionization and stuff,
Speaker 1: but the important thing for us is that by bringing
Speaker 1: these electrodes in contact with one another and then separating
Speaker 1: them from each other slightly, you get a very hot,
Speaker 1: very bright electrical arc. This would end up being basic
Speaker 1: technology behind some of the earliest electric lights before incandescent bulbs.
Speaker 1: They were used for street lighting and for movie projectors
Speaker 1: and search lights. The light they produce is incredibly bright.
Speaker 1: It's bright enough to hurt your eyes if you look
Speaker 1: straight at it, and they also emit ultra violet light,
Speaker 1: so you wouldn't want to look at them directly or
Speaker 1: be around and unshielded electrical arc for a really long time. Fortunately,
Speaker 1: good old playing glass doesn't allow ultra violet light to
Speaker 1: pass through it, so with a glass lens you can
Speaker 1: actually block that pesky UV radiation. Our lamps aren't that
Speaker 1: common these days. I mean, there are still some out there,
Speaker 1: but electrical arcs are still used for lots of stuff.
Speaker 1: Old time listeners to the show might remember that one
Speaker 1: of my first articles for the website how Stuff works
Speaker 1: dot com was on a technology called plasma waste converters.
Speaker 1: These facilities use a plasma torch, which is a sin
Speaker 1: a variation of what I've already been talking about with
Speaker 1: arc lamps, to gasify or to liquefy garbage. Essentially, anything
Speaker 1: that's carbon based gets gasified. It's it's turned into gas.
Speaker 1: Anything that's not carbon based gets heated up so much
Speaker 1: that it becomes molten. Well, electrical arc furnaces use this
Speaker 1: same basic technology in order to make steel. Your typical
Speaker 1: electrical arc furnace has a cylindrical vessel, right This is
Speaker 1: the base of the furnace. This is what holds the charge.
Speaker 1: In other words, the raw material you're using. This vessel
Speaker 1: has an interior lining of refractory material designed to reflect
Speaker 1: heat back into the chamber. The melted material, called helpfully
Speaker 1: the melt, will gather at the bottom of the furnace.
Speaker 1: And this is really dense stuff right now we're talking
Speaker 1: about steel. So the slag, as in the other materials,
Speaker 1: the impurities that were also part of the charge. Typically
Speaker 1: it's stuff you don't want. Tends to float in a
Speaker 1: layer above the steel melt, and it can be drawn
Speaker 1: out through a slag door. At a certain height on
Speaker 1: the chamber. Towards the bottom of the furnace is a
Speaker 1: tap hole. It's kind of the drain for the furnace,
Speaker 1: and this is the hole through which molten steel will flow.
Speaker 1: And then it's collected in another vessel called the ladle.
Speaker 1: So you have a ladle is essentially a special kind
Speaker 1: of bucket that's underneath this tap hole. The open up
Speaker 1: the tap hole and the molten steel comes out. And
Speaker 1: typically these furnaces are mounted on platforms that have a
Speaker 1: hydraulic lifting arm below them that can extend so it
Speaker 1: tilts the entire furnace to get every last delicious drop
Speaker 1: of molten steel out, although honestly they don't always take
Speaker 1: every drop out. In fact, some furnaces specifically leave some
Speaker 1: and steel behind to help with future UH steel production.
Speaker 1: The furnace is removable lid, which is really more of
Speaker 1: a roof because these things are usually several meters in diameter.
Speaker 1: They're huge anyway. This removable lid typically has three electrodes
Speaker 1: which extend down into the chamber. The electrodes make contact
Speaker 1: with the charge and the furnace operator filips the switch
Speaker 1: to send electricity through these electrodes. Current flows from the
Speaker 1: electrodes to the charge. UH The electrodes are typically made
Speaker 1: out of graphite, so a type of carbon, and the
Speaker 1: electrodes just like the old carbon electrodes that Sir Humphrey
Speaker 1: Davy used, they begin to ionize and they form a
Speaker 1: plasma gas and that allows this electrical arc to form.
Speaker 1: Power continues to go to the electrodes to perpetuate the
Speaker 1: arc because in this case, this process does not depend
Speaker 1: upon the chemical process oxidation, which was what was generating
Speaker 1: heat with stuff like basic oxygen uh processes. Now, it's
Speaker 1: not like electrical arc furnaces are the new norm. In fact,
Speaker 1: they're responsible for only about a quarter of the world's
Speaker 1: steel production. Most of the rest is still produced through
Speaker 1: basic oxygen furnaces. And the steel that electrical arc furnaces
Speaker 1: produces typically has a higher carbon content than the kind
Speaker 1: that is produced by those other furnaces. And we have
Speaker 1: to remember carbon content and steel affects the metals properties
Speaker 1: like hardness and how malleable versus brittle it is and
Speaker 1: the melting point for the metal. The more carbon, the
Speaker 1: harder the surface of the metal tends to be, the
Speaker 1: more brittle it will be, and the lower the melting
Speaker 1: point will be. One drawback to electrical arc furnaces is
Speaker 1: that they can introduce nitrogen into the steel alloy, and
Speaker 1: nitrog can make steel more brittle. So to deal with
Speaker 1: that the furnace operators can blow in other gases to
Speaker 1: react with the nitrogen, thus neutralizing it, or carbon monoxide
Speaker 1: can be used for this purpose or other other techniques
Speaker 1: included shorter bursts of the electrical arc so you're not
Speaker 1: producing so much nitrogen. Often electrical arc furnaces will use
Speaker 1: scrap steel as part of the charge material, so the
Speaker 1: input you're putting into the furnace in order to get
Speaker 1: steel at the end, it might involve shredded or scrapped
Speaker 1: steel from other stuff, but they can also bring in
Speaker 1: things like iron from blast furnaces to it doesn't have
Speaker 1: to be scrap steel, and it can involve other materials
Speaker 1: as well. Scrap steel can contain other stuff in it,
Speaker 1: typically referred to as residuals, stuff like nickel, copper, chromium, tin,
Speaker 1: and other stuff which you may or may not actually
Speaker 1: want in your final product, and you may have to
Speaker 1: draw that off separately. And that's generally how electrical arc
Speaker 1: furnaces work. It's a different approach, not just in technique
Speaker 1: but in the actual physics involved, but the end result
Speaker 1: is the production of steel. So let's talk a bit
Speaker 1: about the different kinds of steel and what they all
Speaker 1: do and what makes them different. But we're going to
Speaker 1: start with a legendary type of steel, Damascus steel. And
Speaker 1: to talk about this, we have to go way back
Speaker 1: before anyone had ever considered using an electrical arc furnace. So,
Speaker 1: beginning sometime around five Common era, sword makers in the
Speaker 1: Middle East began to create weapons that were known for
Speaker 1: their sharpness, for their durability, and for their beauty. They
Speaker 1: could hold an edge really well, they stood up to
Speaker 1: a lot of abuse, and they had these intricate wavy
Speaker 1: patterns on the surface of the metal itself. And legend
Speaker 1: stated that a sword made from that kind of steel
Speaker 1: could be sharpened to the point where it could cut
Speaker 1: a feather in half while the feathers floating in the air.
Speaker 1: Or similarly, if you were to drop a silk scarf,
Speaker 1: you could cut it in half before it hit the ground.
Speaker 1: So sharp these these swords could be because of that
Speaker 1: that incredible metal. But there's some complications to this story. First,
Speaker 1: the legend also states that sword makers lost this ability
Speaker 1: sometime in the eighteenth or nineteenth century, that the entire
Speaker 1: method of producing weapons of this quality was lost to time.
Speaker 1: It seemed as though people just forgot how to make
Speaker 1: weapons this way, and sword makers could still make weapons.
Speaker 1: In fact, they could still make weapons that had wavy
Speaker 1: patterns in the metal. More on that in a second.
Speaker 1: But they didn't possess the legendary hardness and edge holding
Speaker 1: capabilities of those earlier weapons. So how did that knowledge
Speaker 1: die out so suddenly? What was so special about the weapons? Well,
Speaker 1: one reason this is so confusing is that name Damascus Steel.
Speaker 1: It is a little bit misleading because it makes it
Speaker 1: sound as though the steel for the legendary pieces of
Speaker 1: arms and armor all came from Damascus. The city of
Speaker 1: Damascus is in Syria, and that region does have iron mines,
Speaker 1: But the steel they were using to make these particularly
Speaker 1: strong weapons probably didn't come from the Middle East, at
Speaker 1: least not most of it. Most of it came from India. See,
Speaker 1: Damascus was an incredibly important trade city in the Middle Ages.
Speaker 1: All sorts of merchants passed through that city trading goods,
Speaker 1: and some of those goods included steel forged from iron
Speaker 1: that had been mined far away in India and then
Speaker 1: refined into steel in India. So they were actually bringing
Speaker 1: steel ingots, or more fittingly, steel cakes to Damascus, and
Speaker 1: this particular type of steel is more accurately called woots
Speaker 1: steel w O O t Z. This steal happened to
Speaker 1: have a low concentration of an impurity that gave Damascus
Speaker 1: steel that particularly vibrant, wavy pattern and strength. It was vanadium.
Speaker 1: As it turns out, there is a mine in Jordan's
Speaker 1: that also produces iron ore with a similar amount of
Speaker 1: vanadium in it, So at least some Damascus steel may
Speaker 1: have originally come from the Middle East, with most of
Speaker 1: the rest being imported from India. The process for making
Speaker 1: the steel itself involved smelting iron ore using a bloomery,
Speaker 1: which remember it doesn't melt the iron, it just heats
Speaker 1: it up to a glowing, hot, spongy mass that you
Speaker 1: didn't have to work with a hammer. But then after
Speaker 1: the iron bloom, which is what you call the lump
Speaker 1: that you create at the end of the bloomery process,
Speaker 1: after the iron bloom cooled, then they would crush it
Speaker 1: up and put the little pieces of the iron bloom
Speaker 1: into a crucible. And along with that iron bloom they
Speaker 1: would put some green leaves, uh some crushed glass, and
Speaker 1: maybe some charcoal in there. Before they would seal the
Speaker 1: crucible up so it's completely sealed, and they would then
Speaker 1: put that into a furnace. And because the crucible sealed,
Speaker 1: no oxygen gets into this process, so combustion cannot happen. Remember,
Speaker 1: for combustion to happen, you need heat, you need fuel,
Speaker 1: and you need an oxidizer. It doesn't combust the material
Speaker 1: inside heats up to very high temperatures. The leaves release
Speaker 1: hydrogen as they heat up, which facilitates the absorption of
Speaker 1: carbon into the iron. And as iron absorbs carbon, the
Speaker 1: melting point for the iron decreases, and that allowed these
Speaker 1: ancient blacksmiths to actually work with molten iron. They weren't
Speaker 1: just heating up a lump anymore. Now the iron was
Speaker 1: melting into a molten liquid. The glass also melts, becoming
Speaker 1: a cap over the iron. Because the glass is less
Speaker 1: dense than the iron, it floats on top. That further
Speaker 1: protected the iron from being exposed to the air prematurely.
Speaker 1: And the charcoal serves not just as a source of
Speaker 1: some carbon, but also as a way to neutralize any
Speaker 1: oxygen that was being released in the process. The result
Speaker 1: was an ingot or cake of high carbon steel. A
Speaker 1: skilled blacksmith would take that steel, and through a long
Speaker 1: process of reheating the steel and cooling it, would then
Speaker 1: prepare it for forging. Forging would involve heating the metal
Speaker 1: enough so that it would become malleable when struck with
Speaker 1: a hammer, and these are all dependent on specific temperature ranges.
Speaker 1: So the blacksmith would get that metal hot enough, put
Speaker 1: it into on an anivil, work it with a hammer,
Speaker 1: work the metal into a long sword blank, for example,
Speaker 1: which would then be further worked into the sword itself,
Speaker 1: and the steel's composition, combined with the sword maker's technique,
Speaker 1: is what would create those intricate patterns on the blades.
Speaker 1: The patterns were made in part because the vanadium was
Speaker 1: in that iron and carbides or the carbon compounds, and
Speaker 1: the blade itself provided the strength and hardness needed to
Speaker 1: create very sharp, durable weapons. But then there's another way
Speaker 1: of creating those patterns. I alluded to it earlier. It's
Speaker 1: called pattern folding. This is a totally different technique, and
Speaker 1: the patterns in pattern folded weapons are not exactly identical
Speaker 1: to those of true Damascus steel, but they are still
Speaker 1: very pretty, so they were kind of sought after. But
Speaker 1: this is a technique in which a blacksmith would take
Speaker 1: iron from different blooms. Thus, these different chunks of iron
Speaker 1: have different concentrations of carbon in them, so some of
Speaker 1: them may be low carbon, some of them may be
Speaker 1: high carbon. And they would hammer out these various pieces
Speaker 1: of iron into strips. They would heat these strips up
Speaker 1: together so they would reach this very high temperature, and
Speaker 1: then would start to hammer those together to weld these
Speaker 1: different layers of metal together. Are so you've got these
Speaker 1: different concentrations of carbon in different strips of iron all
Speaker 1: getting welded together, and they would fold it and weld
Speaker 1: it again, folded and welded again, and this would create
Speaker 1: that sort of pattern. Look, because you're actually looking at
Speaker 1: different concentrations of carbon in iron, it's that's what's causing
Speaker 1: the pattern. It's not the nature of the iron itself.
Speaker 1: And because you were using this approach where you're hammering
Speaker 1: it out and you're never melting the iron, you couldn't
Speaker 1: get as pure a version of steel as you would
Speaker 1: with the crucible. The crucible would allow all the slag
Speaker 1: to rise to the top of the crucible. You know,
Speaker 1: everything turns into liquid, so you could just pour the
Speaker 1: slag off, but you couldn't do that with this approach
Speaker 1: because you never melted the iron, so you had to
Speaker 1: work it with a hammer, and it would never be
Speaker 1: as pure as true Damascus steel would, so you and
Speaker 1: not get a weapon of the same quality as one
Speaker 1: that was a true Damascus steel sword made by an
Speaker 1: actual master sword maker. Damascus steel, the real stuff died
Speaker 1: out largely because industrialization brought about mass production and steel,
Speaker 1: and that lowered the demand for the more artisan approach
Speaker 1: and the process of working the steel, which included very
Speaker 1: many steps. It was typically passed down through oral tradition,
Speaker 1: not written down anywhere, so it was gradually forgotten because
Speaker 1: there was no call to make that steal, so no
Speaker 1: one was passing down that knowledge. More recently, modern blacksmiths
Speaker 1: have been working with different approaches to replicate the forging
Speaker 1: of Damascus steel, largely based on some very educated guesses
Speaker 1: as to how it must have happened, and they've made
Speaker 1: a lot of progress, largely through trial and error. But
Speaker 1: it all starts with having the right type of steal
Speaker 1: from the right type of iron ore. When we come back,
Speaker 1: we're gonna talk about some modern classifications of steel and
Speaker 1: what that all means. But first, let's take a quick break.
Speaker 1: So how many types of steel are there? Well, golly,
Speaker 1: that really depends upon whom you ask. I know that
Speaker 1: is a lame answer, but it's true. Some people will
Speaker 1: divide steel into four broad categories. Uh. Those broad categories
Speaker 1: could be plane, carbon steel, alloy steel, tool steel, and
Speaker 1: stainless steel. Some say alloy steel and low alloy steel
Speaker 1: instead of tool steel. And the reason why you get
Speaker 1: all these different terms for the same basic stuff is
Speaker 1: because it all depends on your point of view. It's
Speaker 1: just like what obi Wan said. The site mead Metals
Speaker 1: classifies steel into carbon, alloy, stainless, and tool. But Thomas,
Speaker 1: which is an industrial sourcing company, so it's a company
Speaker 1: that helps manufacturing companies find sources for the raw materials
Speaker 1: they need, they classify it as carbon alloy, low alloy,
Speaker 1: and stainless. Uh. Meanwhile, the home Stratosphere site breaks it
Speaker 1: down to twenty six different types. And then you have
Speaker 1: various standards associations like s a E International s a
Speaker 1: E originally stood for Society of Automotive Engineers or the
Speaker 1: American Iron and Steel Institute or ai s I. Those
Speaker 1: are just two in the United States. You also have
Speaker 1: other ones in other countries, like British standards in the UK.
Speaker 1: You have International Organization for Standardization lots of these different groups,
Speaker 1: and they have thousands of different grades for steel. So
Speaker 1: what does this tell us, Well, it tells us there's
Speaker 1: an incredible amount of variability in the different types of
Speaker 1: steel people have made over the years, and that creating
Speaker 1: standards is tricky. If your standard is Lucy goosey and
Speaker 1: each grade of steel covers a fairly wide range of
Speaker 1: qualities like hardness or flexibility, or percentage of carbon or
Speaker 1: percentage of other alloys, you really end up with some
Speaker 1: real problems. So let's say that you've got a standardization
Speaker 1: system where you've got pretty wide grades to cover a
Speaker 1: spectrum of steel. But you're in charge of making steel girders,
Speaker 1: and so you're looking for a specific grade of steel,
Speaker 1: and the problem is that because it covers a spectrum,
Speaker 1: some of the girders you make might be stronger than others.
Speaker 1: Some might be better at standing up to really strong
Speaker 1: compression forces, and others are not. And that ain't great.
Speaker 1: You really want all that steel to be of similar hardness,
Speaker 1: similar strength. You really need it all to be consistent.
Speaker 1: So it really is necessary to break down steel into
Speaker 1: thousands of grades so that when it comes to actually
Speaker 1: manufacturing and selling the stuff, companies can make sure they
Speaker 1: are getting the raw materials they need to do whatever
Speaker 1: the job necessary is. But the downside is there's no
Speaker 1: way for me to do an episode about every single
Speaker 1: grade of steel, as it would be a billion hours long,
Speaker 1: and a lot of it would just be repeating seemingly
Speaker 1: arbitrary designations between two very similar but technically distinct types
Speaker 1: of steel, and that is just too much. But I
Speaker 1: will go over some of the classification strategies though, and
Speaker 1: what it all means. So let's start with some of
Speaker 1: the broader categories and we can drill down from there. Uh.
Speaker 1: And we're gonna go with carbon steel first. Now quickly,
Speaker 1: just as a reminder, we're gonna be talking about carbon
Speaker 1: steel and alloy steel. Things like that steel itself is
Speaker 1: an alloy, so that makes these designations confusing, right, And
Speaker 1: more than that, steel is an alloy of iron and carbon,
Speaker 1: so that makes it even more confusing. Why do you
Speaker 1: have carbon steel versus alloy steel? I mean, if all
Speaker 1: steel has carbon in it, and if all steel is
Speaker 1: an alloy, what do those designations even mean well, all
Speaker 1: of these steels are still alloys, and all of them
Speaker 1: still have carbon in them, But what really differentiates them
Speaker 1: is how much carbon each type of steel contains, and
Speaker 1: whether or not the steel has a significant amount of
Speaker 1: other stuff in it besides iron and carbon. Other factors
Speaker 1: also make a difference, such as how slowly or rapidly
Speaker 1: the steel cools in the manufacturing process, or how long
Speaker 1: the steel has been held at specific temperatures, or whether
Speaker 1: it's been heat treated. These processes all have their own names.
Speaker 1: To cool steel quickly is to quench it, which typically
Speaker 1: hardens steel. A sword maker might quench a sword to
Speaker 1: give the exterior a harder surface while the interior, which
Speaker 1: will cool more slowly because it's not being bosed to
Speaker 1: the water, retains a more flexible core. As a result,
Speaker 1: to avoid making a sword to brittle, the sword maker
Speaker 1: would temper the blade. That involves heating the sword back
Speaker 1: up again, but below the critical temperature at which the
Speaker 1: sword maker would you know, heat the blade in order
Speaker 1: to work it. So it's not as hot that it
Speaker 1: would be malleable, but it's hotter than it had been.
Speaker 1: So it gets really complicated, right, and it's all about
Speaker 1: creating the right crystalline structure for steel, and I'll get
Speaker 1: more into that towards the end of this episode. For now,
Speaker 1: let's take a closer look at some of those categories.
Speaker 1: So carbon steel that is mostly iron and carbon with
Speaker 1: only trace amounts of other elements in the mix. It's
Speaker 1: also by far the most common type of steel produced
Speaker 1: around the world. And we can also break down carbon
Speaker 1: steel into three large subcategories. Low carbon steel sometimes also
Speaker 1: called mile steel, this can contain up to point three
Speaker 1: percent carbon. Then you've got medium carbon steels, this contains
Speaker 1: between point three and point six percent carbon. And then
Speaker 1: you get high carbon steels, which have more than point
Speaker 1: six percent carbon, typically not much more than one percent.
Speaker 1: You might go up as high as two point five
Speaker 1: percent for some types, but beyond that is unusual, not
Speaker 1: unheard of, but unusual. So even within these subcategories, you
Speaker 1: see there is variation. Right, low carbon or mild steel
Speaker 1: is the easiest to work and shape all of the
Speaker 1: three subcategories because it doesn't have as much carbon in it. Remember,
Speaker 1: you add carbon, the the steel becomes harder. That also
Speaker 1: means it's harder to shape. Now, low carbon steel has
Speaker 1: high ductility, which I haven't really talked about. Ductility is
Speaker 1: the ability of a material to be plastically deformed under
Speaker 1: ten style stresses without fracturing. Tensile stresses are those placed
Speaker 1: on a material that tends to elongate the material. I
Speaker 1: think of it as a kind of tug of war
Speaker 1: kind of stress. Right, You've got people pulling on either
Speaker 1: end of a rope, those are ten sile stresses on
Speaker 1: that rope a pulling stress. Deforming means to change shape,
Speaker 1: so a material with high ductility will stretch, becoming thinner
Speaker 1: without breaking apart. And that also means that low carbon
Speaker 1: steel can be drawn into wires. This involves passing the
Speaker 1: steel through a series of dyes, and these are kind
Speaker 1: of like metal blocks that have a hole in the
Speaker 1: middle of them. And the hole is of a diameter
Speaker 1: that's slightly smaller than what the steel is that you're
Speaker 1: passing through it. So you narrow the end of the
Speaker 1: steel so it'll go through this hole. You connect it
Speaker 1: to some really powerful machine that pulls that steal through
Speaker 1: and the steel elongates. Rather than gets more dense and
Speaker 1: keeps the same density, it just it elongates and gets thinner.
Speaker 1: And you do this several times, and each time you're
Speaker 1: doing it, you're typically going a little smaller with the
Speaker 1: following dye, and you eventually create wire this way, and
Speaker 1: you do this until you reach the gauge or a
Speaker 1: thickness of the wire that you want to produce. Besides wire,
Speaker 1: low carbon steel can be used to make stuff like
Speaker 1: pipes or automobile body parts, and some construction materials. They're
Speaker 1: also used in processes that require machining or welding. Then
Speaker 1: we move to medium carbon steels. These are less ductile,
Speaker 1: but they are also more hard than low carbon steels.
Speaker 1: They have greater hardness. They're often used for gear parts
Speaker 1: like crank shafts and axles and stuff like that, or
Speaker 1: in machinery parts where hardness is an important requirement. When
Speaker 1: you get to the upper ranges of medium carbon steel,
Speaker 1: meaning you're getting closer to high carbon steel, and you're
Speaker 1: working with a metal strong enough to be used in
Speaker 1: tools like screw drivers and pliers and that kind of thing.
Speaker 1: So keep in mind, like I said earlier, each of
Speaker 1: these types of steel has a range within it. They're
Speaker 1: not all equal. But moving on up we get onto
Speaker 1: high carbon steel, we get into the territory of the
Speaker 1: hardest of the carbon steels. It's also the least ductal
Speaker 1: and least malleable, meaning it's the most brittle and and
Speaker 1: it's the most difficult to shape. This stuff can be
Speaker 1: used for rails, for wear resistant plates, for high strength bars,
Speaker 1: and that kind of thing. It's also sometimes used in
Speaker 1: the production of knives. It's hardness makes it really valuable
Speaker 1: for that purpose. They're even processes that can produce steels
Speaker 1: with a really high carbon content around two and a
Speaker 1: half percent. Remember, everything we've talked about from this point
Speaker 1: has been steel with a carbon content of around one
Speaker 1: percent or less. These knives can be sharpened to a
Speaker 1: very fine edge, but they will lose that edge fairly
Speaker 1: quickly over time and require sharpening. But high carbon steel
Speaker 1: also has a very low resistance to corrosion, so if
Speaker 1: you get high carbon steel near water, it can rust
Speaker 1: pretty quickly. So while you can find cutlery made of
Speaker 1: high carbon steel, it's far more common to encounter knives
Speaker 1: and silverware made out of a different kind of steel,
Speaker 1: and that is stainless steel. All right, how about we
Speaker 1: shift over to stainless steel for a few minutes. We
Speaker 1: already know that stainless steel has carbon in it, otherwise
Speaker 1: it wouldn't be steel. But what makes it stainless, Well,
Speaker 1: stainless is a type of alloy steel And again, yes,
Speaker 1: steel all on its own is an alloy with iron
Speaker 1: and carbon, but in this case we're talking about alloy
Speaker 1: with another metal added to it. So what is our
Speaker 1: addition to our favorite iron carbon combo. Well, it's chromium,
Speaker 1: and that typically ends up making up between ten and
Speaker 1: twenty percent of the overall composition of stainless steel. Other
Speaker 1: metals and materials are typically in that alloy as well,
Speaker 1: including nickel, and then you get stainless steel. And chromium
Speaker 1: is a hard, brittle metal. It's also incredibly resistant to corrosion,
Speaker 1: and it's specifically that property that comes in awfully handy
Speaker 1: when you're producing a steel alloy. Stainless steel resists corrosive effects,
Speaker 1: and so there are types of stainless steel that are
Speaker 1: really handy for stuff like cutlery or containers that hold
Speaker 1: corrosive materials. It's also pretty strong stuff, or at least
Speaker 1: it can be, because there are different types of stainless steel,
Speaker 1: just as there are different types of carbon steel, and
Speaker 1: the grades of stainless steel depend on many factors, not
Speaker 1: just how much carbon and chromium are in the alloy,
Speaker 1: but also stuff like nickel, copper, silicon, aluminum, and even
Speaker 1: the process of making the steel itself. All of these
Speaker 1: can affect the various aspects of the stainless steel, including
Speaker 1: its hardness, its resistance to corrosion, its heat resistance, and more.
Speaker 1: There are lots of different steel alloys, and each creates
Speaker 1: a different kind of steel with properties that are sought
Speaker 1: after for specific applications. Steel that works great for one
Speaker 1: purpose might not be ideal for another. But luckily, because
Speaker 1: metallurgists have a lot of time on their hands, I mean,
Speaker 1: they've done so much work experimenting with different alloys that
Speaker 1: we can produce a lot of different kinds of steel,
Speaker 1: and there's probably a kind that's going to be ideal
Speaker 1: for whatever purpose you have in minds let's go over
Speaker 1: a few of them. Tungsten is a dull silver metal
Speaker 1: sometimes it's called wolfram that one of tungsten's properties is
Speaker 1: a very high melting point. So if you make an
Speaker 1: alloy of steel with tungsten and you get toungusten steel,
Speaker 1: you get a really tough, hard metal that can withstand
Speaker 1: incredible temperatures, and for that reason, engineers rely on tungsten
Speaker 1: steel for stuff like rocket engine nozzles. I mean, you
Speaker 1: don't want your engine melting off your launch vehicle when
Speaker 1: you're headed off to space. After all. Tungsten steel is
Speaker 1: a go to for applications that involve high temperatures, but
Speaker 1: it may also be combined with other metals like nickel
Speaker 1: or iron for the production of turbine blades. Nickel steel
Speaker 1: is another alloy and is a pretty common one. It's
Speaker 1: one of the alloys that works best for heat treated steel,
Speaker 1: as it decreases the amount of distortion in the steel
Speaker 1: when it has been quenched, you know, when it's been
Speaker 1: cooled very quickly. That also boosts steels strength while not
Speaker 1: trading off on ductility, so you can get very strong steel.
Speaker 1: There's still ductal Like chromium, nickel resists corrosion. It's one
Speaker 1: of the reasons why it's frequently a component in stainless steel.
Speaker 1: Then there's manganese. Manganese steel typically has between eleven and
Speaker 1: fourteen percent manganese in it. Manganese steel is quite hard
Speaker 1: and it resists where and tear. It's frequently used in
Speaker 1: railway tracks and heavy duty applications that encounter lots of
Speaker 1: mechanical forces, like parts for rock crushers, for example, or
Speaker 1: cement mixers and you know other seriously tough machines. Next,
Speaker 1: we come to a medal we mentioned earlier in this episode, vanadium.
Speaker 1: Vanadium steel is resistant to corrosion. It's also got some
Speaker 1: shock absorption qualities. It's used in the automobile industry and
Speaker 1: parts meant to distribute shock and vibration. It's also a
Speaker 1: common material in pipes and tubes, mint for carrying corrosive chemicals,
Speaker 1: and it is often used as a bonding material to
Speaker 1: bring steel and titanium into b f F territory. Get
Speaker 1: your titanium steel. I've got more to say on different
Speaker 1: types of steel, but Gali, I need to steal myself
Speaker 1: with some tea. My voice is giving out. We'll be
Speaker 1: right back. In the last section, when I was talking
Speaker 1: about stainless steel, I mentioned chromium. But making matters more
Speaker 1: confusing is that there are chromium steel alloys that are
Speaker 1: not stainless steel. In addition to corrosion resistance, chromium can
Speaker 1: give steel a boost in high temperature strength, and it's
Speaker 1: also a more elastic alloy with greater tensile strength. It's
Speaker 1: used in automobile manufacturing and frequently is the steel that
Speaker 1: you find for safes. Sometimes chromium and vanadium while tag
Speaker 1: team with steel and create a chromium vanadium steel alloy,
Speaker 1: and this alloy has got high tensile strength, and it's
Speaker 1: suitable for stuff like vehicular frames and gears, that kind
Speaker 1: of thing. Aluminium steel there's another alloy that I need
Speaker 1: to touch on, So that is a thing. Aluminium boosts
Speaker 1: steel's ability to reflect heat, and aluminium is much much
Speaker 1: lighter than steel, So an aluminium steel alloy results in
Speaker 1: a type of steel that's lighter than most other kinds,
Speaker 1: and it's used in all sorts of applications, from packaging
Speaker 1: to energy production to the automotive industry. Cobalt steel, like
Speaker 1: nickel steel, is tough and stands up well too high temperatures.
Speaker 1: It's frequently used to produce high speed cutting tools. Cobalt
Speaker 1: steel is also ferro magnetic, and uh oh, that reminds me.
Speaker 1: One of the things I haven't really talked about much
Speaker 1: in these episodes is magnetism. With certain temperatures, iron is
Speaker 1: ferro magnetic. Now those temperatures involved pretty much all the
Speaker 1: temperatures that you and I would ever experience. If we
Speaker 1: were to experience the temperatures above which iron no longer
Speaker 1: as ferro magnetic, we would be in trouble. See those
Speaker 1: high temperatures beyond what is called the Curi point, iron
Speaker 1: isn't nearly as faro magnetic. It will react weakly to
Speaker 1: magnetic fields. Now that temperature is pretty high. We're talking
Speaker 1: seven seventy degrees celsius for pure iron, but other stuff
Speaker 1: can affect the cury point for steel, and some alloys
Speaker 1: are downright diamagnetic, which means they're not magnetic at all.
Speaker 1: To get into why something can sometime as be magnetic
Speaker 1: and at other temperatures it's not as magnetic, and in
Speaker 1: certain alloys it's not magnetic at all would require a
Speaker 1: full blown dive into quantum physics and the crystalline structure
Speaker 1: of iron, and I'm just not prepared to get into that.
Speaker 1: I ain't got enough coffee in this house to take
Speaker 1: care of that. But the important thing to remember is
Speaker 1: that steals magnetic nature depends heavily on which alloy you're
Speaker 1: talking about. One alloy that is on the high end
Speaker 1: for magnetic force is silicon steel. This stuff is used
Speaker 1: in lots of electromagnetic components, stuff like electrical transformers, relays, motors,
Speaker 1: that kind of thing. If you've got a steel permanent magnet,
Speaker 1: chances are it's made out of silicon steel alloy. Now
Speaker 1: it's time for you to cross your fingers for me,
Speaker 1: because it's time for me to attempt to say the
Speaker 1: word molybdenum. Adding molybdenum to steal and making an alloy
Speaker 1: improves steels well debility as well as its toughness. It's
Speaker 1: also more resistant to corrosion, and it is a common
Speaker 1: material for structural steel, particularly around what would otherwise be
Speaker 1: really corrosive environments, like anything having to do with the ocean.
Speaker 1: So if you were building, say, uh, like an oil
Speaker 1: drilling rig out on the ocean, you're probably using molybdenum
Speaker 1: in your steel alloy. And that's pretty much it for
Speaker 1: the major alloys. Now, keep in mind, each of the
Speaker 1: kinds I mentioned have their own grades of steel, and
Speaker 1: the qualities I mentioned are are general in nature. So
Speaker 1: while one maybe harder than steel typically is you know,
Speaker 1: just carbon steel, the grade to which it is harder
Speaker 1: is dependent upon multiple factors. I guess I should really
Speaker 1: briefly go over tool steels. These are also alloy steels,
Speaker 1: but of course they get their own designation and their
Speaker 1: own subcategories because categorizing stuff is hard, and these steels
Speaker 1: typically include a larger amount of materials like vanadium and
Speaker 1: tongue sten. These have greater resistance to wear and tear.
Speaker 1: They have increased hardness and toughness over typical alloys, and
Speaker 1: tool steels typically have a carbon content between point five
Speaker 1: and one percent. They put us put them closer to
Speaker 1: the high carbon steel category. You can break this down
Speaker 1: into six subcategories, cold work, hot work, shock resistant, water hardening,
Speaker 1: and dealer's choice. No way, I'm sorry, I'm I'm in
Speaker 1: special purpose. The names give you a big hand about
Speaker 1: what's going on here. Some of these steel types are
Speaker 1: best if you need to work within very hot or
Speaker 1: very cold materials or environments. Water hardened steel is a
Speaker 1: type that is water quenched when produced, and it's pretty
Speaker 1: similar to high carbon steel in a lot of ways.
Speaker 1: But that's kind of the down and dirty approach to
Speaker 1: tool steel. But what is it about steel grades? What's
Speaker 1: the story there? Well, it helps if we focus on
Speaker 1: one set of standards and explain from there. So for
Speaker 1: the purposes of this podcast, we're gonna go with the
Speaker 1: s a E steel grade designations. This system grew out
Speaker 1: from the nineteen forties as various engineers and drafts people
Speaker 1: and architects and metallurgists and all these folks were getting
Speaker 1: together and trying to catalog all the different types of
Speaker 1: steel and the specific qualities to those specific types, including
Speaker 1: the differences within a specific group of steel. And the
Speaker 1: s a E system uses a four digit code to
Speaker 1: designate steel so that you really know what you're dealing
Speaker 1: with the first two digits of that four digit code
Speaker 1: tells you which alloying element is present in the steel
Speaker 1: and to what degree. The first digit indicates the alloying element,
Speaker 1: the second indicates the presence of major elements. So here's
Speaker 1: how the first digits shake out. If the first digit
Speaker 1: in that four digit code is a one, then the
Speaker 1: type of steel that's being talked about is a carbon steel,
Speaker 1: so there are no other major trace elements in that steel,
Speaker 1: or at least not beyond trace amounts. If the first
Speaker 1: number is a two, then you're talking about a nickel
Speaker 1: steel alloy. Three would be nickel chromium steel, four is
Speaker 1: molybdenum steel, five is chromium steel, six is chromium vanadium steel,
Speaker 1: seven is tungsten steel, eight is nickel chromium vanadium steel,
Speaker 1: and nine is silicon manganese steel. So that first digit
Speaker 1: tells you a lot, and then the last two digits
Speaker 1: in that four digit code tell you how much carbon
Speaker 1: is in the steel, and it's all in point zero
Speaker 1: one increments. So if you saw a code that said
Speaker 1: ten forty two steel, that would mean you've got carbon
Speaker 1: steel with a carbon percentage of point for two, so
Speaker 1: you would have a type of medium carbon steel in
Speaker 1: other words. But sometimes these four digit codes go and
Speaker 1: make things more confusing. They throw a le are in there,
Speaker 1: so you might see something like twelve L fourteen, So
Speaker 1: what the heck does that mean? If the twelve means
Speaker 1: it's a carbon based steel with some other element in it,
Speaker 1: and fourteen tells you there's point one four carbon in it,
Speaker 1: was the L. The letter L indicates the addition of
Speaker 1: some other material to the steel alloy. L specifically refers
Speaker 1: to lead, so adding lead to the alloy would improve
Speaker 1: the machine ability of the steel. The letter B is
Speaker 1: a similar thing, it could appear in the middle of
Speaker 1: a code, but B stands for boron that improves steel's hardness.
Speaker 1: Other letters might be found at the very front of
Speaker 1: the code. So if you see the letter M, that
Speaker 1: stands for merchant quality, meaning the steel is suitable for
Speaker 1: non critical parts of machinery or structures. The letter E
Speaker 1: before a code would indicate that the steel is suitable
Speaker 1: for electric furnaces. If the code has the letter H
Speaker 1: at the end, that would mean the steel meets harden
Speaker 1: ability limits. And then you have other coding systems entirely,
Speaker 1: so that works for S A E. But the AI
Speaker 1: S I coding system also includes three digit designations for
Speaker 1: different classifications of stainless steel, and the first digit in
Speaker 1: those three digits ranges between two and five. You don't
Speaker 1: have any one hundred series, but two hundred to five
Speaker 1: hundred series that indicates whether the stainless steel is forritic, austinitic,
Speaker 1: or martensitic. So what is that? What? Well? It all
Speaker 1: has to do with that crystalline structure of stainless steel,
Speaker 1: which in turn will dictate certain properties of that steel.
Speaker 1: And I've avoided talking about this because it's hard to
Speaker 1: talk about, but here we go. So crystals only form
Speaker 1: as molten steel or molten iron cools. As the material cools,
Speaker 1: it's lidifies, and it forms a type of lattice that's
Speaker 1: the crystalline structure. Now that that lattice includes a very
Speaker 1: small amount of carbon, and we're talking about just point
Speaker 1: zero to five or less, we call it fairte. And
Speaker 1: fairite has a cubic body crystal structure, and there's an
Speaker 1: iron atom at the center of this crystal that has
Speaker 1: one iron atom at each corner. There's just not much
Speaker 1: room for carbon to fit in there. Ferretic steel is
Speaker 1: susceptible to corrosion. It's not particularly strong or particularly hard,
Speaker 1: so it's not really used very much. Austinitic steel contains
Speaker 1: a form of iron called austinite, and this has a
Speaker 1: different crystalline structure. It's slightly more conducive to absorbing carbon.
Speaker 1: So to make austinite you have to heat faeryte up
Speaker 1: to really high temperatures like n twelve degrees celsius, at
Speaker 1: which point the crystalline structure shifts. But it doesn't break
Speaker 1: apart and become molten. It doesn't liquefy. You're still solid.
Speaker 1: It's just the crystal structure changes and at that temperature
Speaker 1: the steel can absorb more carbon, but needs additional additives
Speaker 1: like manganese and nickel in order to maintain that crystalline
Speaker 1: structure when it starts to cool down. This type of
Speaker 1: stainless steel is much more resistant to corrosion, and it's
Speaker 1: used in stuff like stainless steel, screws, Martin sidic stainless
Speaker 1: steel has Martin site in it, and that clears everything
Speaker 1: up right. So Martin site is another form of crystallized iron,
Speaker 1: and you create it by taking austinite. You heat up
Speaker 1: the austinite, then you cool it rapidly through quenching. So
Speaker 1: when you do this, when the austinite cools down very
Speaker 1: quickly relatively speaking, it prevents those carbon atoms from getting
Speaker 1: the boot from the austinite. Right, Because remember I said
Speaker 1: that you had to add in stuff or for austinite
Speaker 1: to maintain that crystalline structure. One other thing you could
Speaker 1: do is cool it really fast, and then you prevent
Speaker 1: the austinite from converting back into fairite. There are a
Speaker 1: lot of other differences between these types austinitics. Stainless steels
Speaker 1: can't be heat treated, for example, but Martin Siddik stainless
Speaker 1: steel can be. This also means that the different types
Speaker 1: of stainless steel are good for different applications. There's so
Speaker 1: much more we could go into, including stuff like prolite,
Speaker 1: which is important with some of those Damascus blades I
Speaker 1: talked about in the beginning of this episode, but it
Speaker 1: really gets fairly far out of the realm of tech stuff.
Speaker 1: The interesting thing I find about steel is that there
Speaker 1: really are so many different kinds of it, and all
Speaker 1: of them have different qualities that make them great for
Speaker 1: certain and sometimes incredibly specific applications. I have a greater
Speaker 1: appreciation for that now. It's about way more than just
Speaker 1: heating up a lump of metal until it's glowing and
Speaker 1: then whacking at it with the hamlets. Far more nuanced
Speaker 1: than that, and that ends our discussion about iron and
Speaker 1: steel and why there are so many different grades. I mean, honestly,
Speaker 1: it's because these different variations of steel have different enough
Speaker 1: properties that you got to be aware of it before
Speaker 1: you start buying it in bulk and using it to
Speaker 1: create stuff you would hate to create or to order
Speaker 1: steal that is hard to work with. For example, if
Speaker 1: you wanted to have something that was really easy to
Speaker 1: mold into different shapes. You'd really be stuck there. So
Speaker 1: the gradations are important. They're just difficult to really get
Speaker 1: your mind wrapped around. If you guys have any suggestions
Speaker 1: for future topics that I should cover here on tech Stuff,
Speaker 1: reach out to me on Twitter or Facebook. To handle
Speaker 1: for both of those is text Stuff H s W,
Speaker 1: and I'll talk to you again really soon. Text Stuff
Speaker 1: is an I Heart Radio production. For more podcasts from
Speaker 1: my Heart Radio, visit the i Heart Radio app, Apple Podcasts,
Speaker 1: or wherever you listen to your favorite shows.