WEBVTT - The Deal With Steel 0:00:04.400 --> 0:00:07.760 Welcome to text Stuff, a production from I Heart Radio. 0:00:12.160 --> 0:00:15.000 Hey there, and welcome to tech Stuff. I'm your host, 0:00:15.160 --> 0:00:18.280 Jonathan Strickland. I'm an executive producer with I Heart Radio 0:00:18.360 --> 0:00:21.440 and I love all things tech and we are continuing 0:00:21.600 --> 0:00:25.840 our episodes about iron and steel today. So in the 0:00:25.880 --> 0:00:29.000 previous episode, I covered the history of our use of 0:00:29.040 --> 0:00:32.120 iron and how we learned how to refine it into 0:00:32.159 --> 0:00:36.200 something you know, actually useful. To go from hard stuff. 0:00:36.280 --> 0:00:39.839 What's inside those rocks? We found two material we can 0:00:39.920 --> 0:00:43.040 use to build things and or make weapons to poke 0:00:43.080 --> 0:00:47.360 each other with. We talked about smelting and furnaces and 0:00:47.479 --> 0:00:51.600 the refining processes, and we ended that episode with a 0:00:51.720 --> 0:00:56.320 very brief explanation of what an electrical arc furnace is. Today, 0:00:56.320 --> 0:00:58.640 we're going to start off by going into a bit 0:00:58.680 --> 0:01:02.640 more detail about how the electrical arc furnace actually works 0:01:03.040 --> 0:01:05.720 to refine iron, and then we'll move on to talk 0:01:05.800 --> 0:01:11.840 about the different types of steel, including the famous Damascus steel. Now, 0:01:11.959 --> 0:01:15.600 as I said in the previous episode, the electrical arc 0:01:15.640 --> 0:01:20.000 furnace generates high temperatures through the creation of an electrical arc. 0:01:20.280 --> 0:01:24.160 But that description isn't terribly satisfying, is it. How does 0:01:24.200 --> 0:01:28.160 it create the electrical arc what makes it so hot? Well, 0:01:28.200 --> 0:01:31.880 in that last episode I mentioned, Sir Humphrey Davy invented 0:01:31.920 --> 0:01:35.800 the arc lamp using a pair of carbon electrodes. He 0:01:35.959 --> 0:01:39.480 used a couple of thousand battery cells and connected one 0:01:39.520 --> 0:01:43.400 electrode to the positive terminal and one to the negative terminal. 0:01:43.680 --> 0:01:47.760 Then he brought these two electrodes in contact with one another. 0:01:48.400 --> 0:01:51.480 This formed a circuit. So not only could electricity flow 0:01:51.560 --> 0:01:55.480 through this completed path, but also the negative carbon electrode 0:01:55.520 --> 0:01:59.560 began to attract particles from the positive carbon electrode. In 0:01:59.600 --> 0:02:04.600 other words, material from the positively charged electrode was literally 0:02:04.720 --> 0:02:08.360 moving over to the negatively charged one and pulling the 0:02:08.400 --> 0:02:13.200 electrodes apart slowly allows an electrical arc to form between 0:02:13.240 --> 0:02:17.560 the two electrodes. It seems like electricity is still traveling 0:02:17.760 --> 0:02:20.000 between one and the other even though there is no 0:02:20.080 --> 0:02:24.799 longer a physical path. So if it's seemingly passing through 0:02:24.800 --> 0:02:28.280 the air itself, how is that even possible? Is there 0:02:28.320 --> 0:02:31.720 an enormous difference in electric potential between the rods? Is 0:02:31.760 --> 0:02:35.800 the voltage super high? Remember voltage is like water pressure, right, 0:02:35.840 --> 0:02:39.960 It's how hard the current is being pushed through a circuit. 0:02:40.040 --> 0:02:43.160 But no, that's not the case. The voltage doesn't have 0:02:43.240 --> 0:02:46.480 to be super high, although typically we're talking about more 0:02:46.520 --> 0:02:50.200 than forty five volts for arc lamps and sometimes more 0:02:50.240 --> 0:02:54.639 than a hundred volts for electrical arc applications. But when 0:02:54.639 --> 0:02:57.480 the two electrodes make contact with one another, there is 0:02:57.520 --> 0:03:00.320 a lot of atomic movement at the point of contact. 0:03:00.600 --> 0:03:02.920 Atomic movement means lots of stuff, but one thing we 0:03:02.960 --> 0:03:06.919 can think about is heat. Hot atoms move around a lot, 0:03:07.320 --> 0:03:10.399 cold atoms don't. In fact, there are some who say 0:03:10.440 --> 0:03:13.600 that absolute zero or zero kelvin isn't just the bottom 0:03:13.680 --> 0:03:15.920 end of how cold temperatures can get, but represents a 0:03:15.919 --> 0:03:20.360 total lack of atomic movement. This heat is enough to 0:03:20.520 --> 0:03:25.400 boil off some atoms from the solid carbon electrodes and 0:03:25.480 --> 0:03:29.240 it forms a gas. That gas is still capable of 0:03:29.280 --> 0:03:32.760 conducting an electric charge, and it does so. Thus you 0:03:32.840 --> 0:03:37.120 get a plasma and ionized gas. So what we have 0:03:37.240 --> 0:03:41.000 here is a plasma generator with a bright electrical arc 0:03:41.040 --> 0:03:43.960 passing through it. There's a lot more science than this 0:03:44.080 --> 0:03:46.640 that we could talk about, such as ionization and stuff, 0:03:46.640 --> 0:03:49.560 but the important thing for us is that by bringing 0:03:49.600 --> 0:03:53.720 these electrodes in contact with one another and then separating 0:03:53.760 --> 0:03:56.360 them from each other slightly, you get a very hot, 0:03:56.640 --> 0:04:00.480 very bright electrical arc. This would end up being basic 0:04:00.560 --> 0:04:06.000 technology behind some of the earliest electric lights before incandescent bulbs. 0:04:06.040 --> 0:04:09.160 They were used for street lighting and for movie projectors 0:04:09.160 --> 0:04:13.840 and search lights. The light they produce is incredibly bright. 0:04:13.880 --> 0:04:16.080 It's bright enough to hurt your eyes if you look 0:04:16.120 --> 0:04:20.040 straight at it, and they also emit ultra violet light, 0:04:20.560 --> 0:04:22.839 so you wouldn't want to look at them directly or 0:04:22.920 --> 0:04:27.960 be around and unshielded electrical arc for a really long time. Fortunately, 0:04:28.560 --> 0:04:31.919 good old playing glass doesn't allow ultra violet light to 0:04:31.920 --> 0:04:34.800 pass through it, so with a glass lens you can 0:04:34.839 --> 0:04:39.600 actually block that pesky UV radiation. Our lamps aren't that 0:04:39.680 --> 0:04:42.679 common these days. I mean, there are still some out there, 0:04:42.760 --> 0:04:46.039 but electrical arcs are still used for lots of stuff. 0:04:46.240 --> 0:04:48.520 Old time listeners to the show might remember that one 0:04:48.520 --> 0:04:51.720 of my first articles for the website how Stuff works 0:04:51.760 --> 0:04:56.520 dot com was on a technology called plasma waste converters. 0:04:57.000 --> 0:04:59.880 These facilities use a plasma torch, which is a sin 0:05:00.200 --> 0:05:02.640 a variation of what I've already been talking about with 0:05:02.760 --> 0:05:09.719 arc lamps, to gasify or to liquefy garbage. Essentially, anything 0:05:09.760 --> 0:05:14.640 that's carbon based gets gasified. It's it's turned into gas. 0:05:15.040 --> 0:05:17.640 Anything that's not carbon based gets heated up so much 0:05:17.680 --> 0:05:22.040 that it becomes molten. Well, electrical arc furnaces use this 0:05:22.240 --> 0:05:26.760 same basic technology in order to make steel. Your typical 0:05:26.839 --> 0:05:31.800 electrical arc furnace has a cylindrical vessel, right This is 0:05:32.200 --> 0:05:36.279 the base of the furnace. This is what holds the charge. 0:05:36.440 --> 0:05:39.960 In other words, the raw material you're using. This vessel 0:05:40.279 --> 0:05:45.000 has an interior lining of refractory material designed to reflect 0:05:45.040 --> 0:05:51.080 heat back into the chamber. The melted material, called helpfully 0:05:51.120 --> 0:05:54.560 the melt, will gather at the bottom of the furnace. 0:05:55.000 --> 0:05:57.560 And this is really dense stuff right now we're talking 0:05:57.560 --> 0:06:02.320 about steel. So the slag, as in the other materials, 0:06:02.320 --> 0:06:05.600 the impurities that were also part of the charge. Typically 0:06:05.600 --> 0:06:08.839 it's stuff you don't want. Tends to float in a 0:06:08.960 --> 0:06:12.680 layer above the steel melt, and it can be drawn 0:06:12.720 --> 0:06:16.760 out through a slag door. At a certain height on 0:06:16.880 --> 0:06:20.480 the chamber. Towards the bottom of the furnace is a 0:06:20.520 --> 0:06:23.520 tap hole. It's kind of the drain for the furnace, 0:06:24.080 --> 0:06:28.120 and this is the hole through which molten steel will flow. 0:06:28.560 --> 0:06:31.560 And then it's collected in another vessel called the ladle. 0:06:31.680 --> 0:06:34.320 So you have a ladle is essentially a special kind 0:06:34.360 --> 0:06:37.599 of bucket that's underneath this tap hole. The open up 0:06:37.640 --> 0:06:39.840 the tap hole and the molten steel comes out. And 0:06:39.920 --> 0:06:44.400 typically these furnaces are mounted on platforms that have a 0:06:44.560 --> 0:06:48.760 hydraulic lifting arm below them that can extend so it 0:06:48.880 --> 0:06:52.880 tilts the entire furnace to get every last delicious drop 0:06:52.920 --> 0:06:56.680 of molten steel out, although honestly they don't always take 0:06:56.760 --> 0:06:59.880 every drop out. In fact, some furnaces specifically leave some 0:07:00.200 --> 0:07:05.279 and steel behind to help with future UH steel production. 0:07:05.800 --> 0:07:09.720 The furnace is removable lid, which is really more of 0:07:09.760 --> 0:07:13.720 a roof because these things are usually several meters in diameter. 0:07:13.800 --> 0:07:19.800 They're huge anyway. This removable lid typically has three electrodes 0:07:19.880 --> 0:07:24.680 which extend down into the chamber. The electrodes make contact 0:07:24.800 --> 0:07:28.040 with the charge and the furnace operator filips the switch 0:07:28.360 --> 0:07:32.320 to send electricity through these electrodes. Current flows from the 0:07:32.360 --> 0:07:36.040 electrodes to the charge. UH The electrodes are typically made 0:07:36.040 --> 0:07:38.880 out of graphite, so a type of carbon, and the 0:07:38.920 --> 0:07:43.560 electrodes just like the old carbon electrodes that Sir Humphrey 0:07:43.600 --> 0:07:47.760 Davy used, they begin to ionize and they form a 0:07:47.760 --> 0:07:50.760 plasma gas and that allows this electrical arc to form. 0:07:51.120 --> 0:07:53.880 Power continues to go to the electrodes to perpetuate the 0:07:53.960 --> 0:07:58.400 arc because in this case, this process does not depend 0:07:58.520 --> 0:08:03.000 upon the chemical process oxidation, which was what was generating 0:08:03.040 --> 0:08:09.440 heat with stuff like basic oxygen uh processes. Now, it's 0:08:09.480 --> 0:08:13.320 not like electrical arc furnaces are the new norm. In fact, 0:08:13.360 --> 0:08:16.520 they're responsible for only about a quarter of the world's 0:08:16.560 --> 0:08:19.440 steel production. Most of the rest is still produced through 0:08:19.520 --> 0:08:24.680 basic oxygen furnaces. And the steel that electrical arc furnaces 0:08:24.680 --> 0:08:29.360 produces typically has a higher carbon content than the kind 0:08:29.560 --> 0:08:33.600 that is produced by those other furnaces. And we have 0:08:33.679 --> 0:08:38.760 to remember carbon content and steel affects the metals properties 0:08:39.080 --> 0:08:42.760 like hardness and how malleable versus brittle it is and 0:08:43.000 --> 0:08:47.280 the melting point for the metal. The more carbon, the 0:08:47.360 --> 0:08:49.400 harder the surface of the metal tends to be, the 0:08:49.440 --> 0:08:52.000 more brittle it will be, and the lower the melting 0:08:52.040 --> 0:08:55.960 point will be. One drawback to electrical arc furnaces is 0:08:56.000 --> 0:08:59.559 that they can introduce nitrogen into the steel alloy, and 0:08:59.640 --> 0:09:03.800 nitrog can make steel more brittle. So to deal with 0:09:03.840 --> 0:09:07.000 that the furnace operators can blow in other gases to 0:09:07.080 --> 0:09:11.319 react with the nitrogen, thus neutralizing it, or carbon monoxide 0:09:11.960 --> 0:09:16.080 can be used for this purpose or other other techniques 0:09:16.080 --> 0:09:19.080 included shorter bursts of the electrical arc so you're not 0:09:19.160 --> 0:09:23.000 producing so much nitrogen. Often electrical arc furnaces will use 0:09:23.120 --> 0:09:27.080 scrap steel as part of the charge material, so the 0:09:27.120 --> 0:09:29.160 input you're putting into the furnace in order to get 0:09:29.160 --> 0:09:32.640 steel at the end, it might involve shredded or scrapped 0:09:32.679 --> 0:09:36.280 steel from other stuff, but they can also bring in 0:09:36.920 --> 0:09:40.360 things like iron from blast furnaces to it doesn't have 0:09:40.480 --> 0:09:44.440 to be scrap steel, and it can involve other materials 0:09:44.440 --> 0:09:47.800 as well. Scrap steel can contain other stuff in it, 0:09:47.840 --> 0:09:53.080 typically referred to as residuals, stuff like nickel, copper, chromium, tin, 0:09:53.280 --> 0:09:55.600 and other stuff which you may or may not actually 0:09:55.640 --> 0:09:57.959 want in your final product, and you may have to 0:09:58.040 --> 0:10:01.880 draw that off separately. And that's generally how electrical arc 0:10:01.920 --> 0:10:05.439 furnaces work. It's a different approach, not just in technique 0:10:05.480 --> 0:10:08.400 but in the actual physics involved, but the end result 0:10:08.520 --> 0:10:11.199 is the production of steel. So let's talk a bit 0:10:11.240 --> 0:10:13.319 about the different kinds of steel and what they all 0:10:13.360 --> 0:10:15.360 do and what makes them different. But we're going to 0:10:15.440 --> 0:10:20.440 start with a legendary type of steel, Damascus steel. And 0:10:20.520 --> 0:10:23.080 to talk about this, we have to go way back 0:10:23.120 --> 0:10:26.960 before anyone had ever considered using an electrical arc furnace. So, 0:10:27.080 --> 0:10:31.480 beginning sometime around five Common era, sword makers in the 0:10:31.480 --> 0:10:35.679 Middle East began to create weapons that were known for 0:10:35.840 --> 0:10:39.040 their sharpness, for their durability, and for their beauty. They 0:10:39.040 --> 0:10:41.920 could hold an edge really well, they stood up to 0:10:42.000 --> 0:10:45.360 a lot of abuse, and they had these intricate wavy 0:10:45.440 --> 0:10:49.440 patterns on the surface of the metal itself. And legend 0:10:49.480 --> 0:10:52.120 stated that a sword made from that kind of steel 0:10:52.200 --> 0:10:55.160 could be sharpened to the point where it could cut 0:10:55.240 --> 0:10:58.280 a feather in half while the feathers floating in the air. 0:10:58.640 --> 0:11:01.600 Or similarly, if you were to drop a silk scarf, 0:11:01.600 --> 0:11:03.880 you could cut it in half before it hit the ground. 0:11:04.000 --> 0:11:07.760 So sharp these these swords could be because of that 0:11:07.760 --> 0:11:13.880 that incredible metal. But there's some complications to this story. First, 0:11:14.200 --> 0:11:18.040 the legend also states that sword makers lost this ability 0:11:18.240 --> 0:11:22.120 sometime in the eighteenth or nineteenth century, that the entire 0:11:22.480 --> 0:11:25.959 method of producing weapons of this quality was lost to time. 0:11:26.720 --> 0:11:28.640 It seemed as though people just forgot how to make 0:11:28.679 --> 0:11:31.840 weapons this way, and sword makers could still make weapons. 0:11:31.920 --> 0:11:34.440 In fact, they could still make weapons that had wavy 0:11:34.480 --> 0:11:37.200 patterns in the metal. More on that in a second. 0:11:37.600 --> 0:11:41.160 But they didn't possess the legendary hardness and edge holding 0:11:41.200 --> 0:11:45.880 capabilities of those earlier weapons. So how did that knowledge 0:11:45.920 --> 0:11:49.439 die out so suddenly? What was so special about the weapons? Well, 0:11:50.040 --> 0:11:54.760 one reason this is so confusing is that name Damascus Steel. 0:11:55.040 --> 0:11:58.280 It is a little bit misleading because it makes it 0:11:58.320 --> 0:12:01.800 sound as though the steel for the legendary pieces of 0:12:02.080 --> 0:12:05.839 arms and armor all came from Damascus. The city of 0:12:05.920 --> 0:12:10.280 Damascus is in Syria, and that region does have iron mines, 0:12:10.840 --> 0:12:13.800 But the steel they were using to make these particularly 0:12:13.800 --> 0:12:17.800 strong weapons probably didn't come from the Middle East, at 0:12:17.840 --> 0:12:22.480 least not most of it. Most of it came from India. See, 0:12:22.760 --> 0:12:27.480 Damascus was an incredibly important trade city in the Middle Ages. 0:12:27.600 --> 0:12:31.320 All sorts of merchants passed through that city trading goods, 0:12:31.440 --> 0:12:35.000 and some of those goods included steel forged from iron 0:12:35.080 --> 0:12:37.959 that had been mined far away in India and then 0:12:38.000 --> 0:12:41.480 refined into steel in India. So they were actually bringing 0:12:41.760 --> 0:12:47.040 steel ingots, or more fittingly, steel cakes to Damascus, and 0:12:47.120 --> 0:12:50.840 this particular type of steel is more accurately called woots 0:12:50.880 --> 0:12:55.480 steel w O O t Z. This steal happened to 0:12:55.480 --> 0:13:00.000 have a low concentration of an impurity that gave Damascus 0:13:00.200 --> 0:13:06.760 steel that particularly vibrant, wavy pattern and strength. It was vanadium. 0:13:06.800 --> 0:13:09.880 As it turns out, there is a mine in Jordan's 0:13:10.120 --> 0:13:13.400 that also produces iron ore with a similar amount of 0:13:13.480 --> 0:13:18.200 vanadium in it, So at least some Damascus steel may 0:13:18.200 --> 0:13:21.760 have originally come from the Middle East, with most of 0:13:21.760 --> 0:13:25.360 the rest being imported from India. The process for making 0:13:25.360 --> 0:13:29.679 the steel itself involved smelting iron ore using a bloomery, 0:13:30.320 --> 0:13:32.760 which remember it doesn't melt the iron, it just heats 0:13:32.760 --> 0:13:36.080 it up to a glowing, hot, spongy mass that you 0:13:36.120 --> 0:13:39.080 didn't have to work with a hammer. But then after 0:13:39.160 --> 0:13:41.800 the iron bloom, which is what you call the lump 0:13:42.360 --> 0:13:45.000 that you create at the end of the bloomery process, 0:13:45.040 --> 0:13:48.080 after the iron bloom cooled, then they would crush it 0:13:48.200 --> 0:13:51.800 up and put the little pieces of the iron bloom 0:13:51.840 --> 0:13:55.760 into a crucible. And along with that iron bloom they 0:13:55.760 --> 0:14:00.320 would put some green leaves, uh some crushed glass, and 0:14:00.520 --> 0:14:03.600 maybe some charcoal in there. Before they would seal the 0:14:03.640 --> 0:14:07.240 crucible up so it's completely sealed, and they would then 0:14:07.320 --> 0:14:10.800 put that into a furnace. And because the crucible sealed, 0:14:10.880 --> 0:14:16.040 no oxygen gets into this process, so combustion cannot happen. Remember, 0:14:16.080 --> 0:14:20.000 for combustion to happen, you need heat, you need fuel, 0:14:20.200 --> 0:14:24.360 and you need an oxidizer. It doesn't combust the material 0:14:24.400 --> 0:14:27.960 inside heats up to very high temperatures. The leaves release 0:14:28.080 --> 0:14:31.280 hydrogen as they heat up, which facilitates the absorption of 0:14:31.360 --> 0:14:35.880 carbon into the iron. And as iron absorbs carbon, the 0:14:35.960 --> 0:14:39.400 melting point for the iron decreases, and that allowed these 0:14:39.560 --> 0:14:42.960 ancient blacksmiths to actually work with molten iron. They weren't 0:14:43.040 --> 0:14:45.680 just heating up a lump anymore. Now the iron was 0:14:45.760 --> 0:14:51.080 melting into a molten liquid. The glass also melts, becoming 0:14:51.480 --> 0:14:54.760 a cap over the iron. Because the glass is less 0:14:54.800 --> 0:14:57.480 dense than the iron, it floats on top. That further 0:14:57.560 --> 0:15:00.720 protected the iron from being exposed to the air prematurely. 0:15:01.240 --> 0:15:03.800 And the charcoal serves not just as a source of 0:15:03.840 --> 0:15:06.080 some carbon, but also as a way to neutralize any 0:15:06.120 --> 0:15:09.520 oxygen that was being released in the process. The result 0:15:10.000 --> 0:15:14.120 was an ingot or cake of high carbon steel. A 0:15:14.200 --> 0:15:17.560 skilled blacksmith would take that steel, and through a long 0:15:17.720 --> 0:15:21.640 process of reheating the steel and cooling it, would then 0:15:21.680 --> 0:15:25.240 prepare it for forging. Forging would involve heating the metal 0:15:25.600 --> 0:15:28.520 enough so that it would become malleable when struck with 0:15:28.560 --> 0:15:32.480 a hammer, and these are all dependent on specific temperature ranges. 0:15:33.040 --> 0:15:36.240 So the blacksmith would get that metal hot enough, put 0:15:36.280 --> 0:15:39.160 it into on an anivil, work it with a hammer, 0:15:39.280 --> 0:15:42.360 work the metal into a long sword blank, for example, 0:15:42.920 --> 0:15:46.920 which would then be further worked into the sword itself, 0:15:47.200 --> 0:15:50.880 and the steel's composition, combined with the sword maker's technique, 0:15:51.280 --> 0:15:54.240 is what would create those intricate patterns on the blades. 0:15:54.360 --> 0:15:57.560 The patterns were made in part because the vanadium was 0:15:57.720 --> 0:16:02.200 in that iron and carbides or the carbon compounds, and 0:16:02.240 --> 0:16:05.080 the blade itself provided the strength and hardness needed to 0:16:05.120 --> 0:16:09.760 create very sharp, durable weapons. But then there's another way 0:16:09.760 --> 0:16:12.120 of creating those patterns. I alluded to it earlier. It's 0:16:12.120 --> 0:16:16.760 called pattern folding. This is a totally different technique, and 0:16:16.800 --> 0:16:21.320 the patterns in pattern folded weapons are not exactly identical 0:16:21.480 --> 0:16:24.760 to those of true Damascus steel, but they are still 0:16:24.840 --> 0:16:27.520 very pretty, so they were kind of sought after. But 0:16:27.600 --> 0:16:30.240 this is a technique in which a blacksmith would take 0:16:30.280 --> 0:16:35.240 iron from different blooms. Thus, these different chunks of iron 0:16:35.320 --> 0:16:39.040 have different concentrations of carbon in them, so some of 0:16:39.080 --> 0:16:41.880 them may be low carbon, some of them may be 0:16:42.040 --> 0:16:46.000 high carbon. And they would hammer out these various pieces 0:16:46.040 --> 0:16:49.280 of iron into strips. They would heat these strips up 0:16:49.320 --> 0:16:53.200 together so they would reach this very high temperature, and 0:16:53.240 --> 0:16:57.480 then would start to hammer those together to weld these 0:16:57.520 --> 0:17:00.760 different layers of metal together. Are so you've got these 0:17:00.760 --> 0:17:05.120 different concentrations of carbon in different strips of iron all 0:17:05.240 --> 0:17:09.320 getting welded together, and they would fold it and weld 0:17:09.400 --> 0:17:13.399 it again, folded and welded again, and this would create 0:17:13.800 --> 0:17:16.560 that sort of pattern. Look, because you're actually looking at 0:17:16.640 --> 0:17:21.680 different concentrations of carbon in iron, it's that's what's causing 0:17:21.720 --> 0:17:24.960 the pattern. It's not the nature of the iron itself. 0:17:25.760 --> 0:17:29.920 And because you were using this approach where you're hammering 0:17:29.960 --> 0:17:33.680 it out and you're never melting the iron, you couldn't 0:17:33.680 --> 0:17:37.119 get as pure a version of steel as you would 0:17:37.119 --> 0:17:40.879 with the crucible. The crucible would allow all the slag 0:17:41.000 --> 0:17:43.159 to rise to the top of the crucible. You know, 0:17:43.200 --> 0:17:45.679 everything turns into liquid, so you could just pour the 0:17:45.720 --> 0:17:50.600 slag off, but you couldn't do that with this approach 0:17:50.600 --> 0:17:54.119 because you never melted the iron, so you had to 0:17:54.119 --> 0:17:56.119 work it with a hammer, and it would never be 0:17:56.160 --> 0:18:00.040 as pure as true Damascus steel would, so you and 0:18:00.240 --> 0:18:04.480 not get a weapon of the same quality as one 0:18:04.560 --> 0:18:07.080 that was a true Damascus steel sword made by an 0:18:07.119 --> 0:18:12.520 actual master sword maker. Damascus steel, the real stuff died 0:18:12.520 --> 0:18:16.959 out largely because industrialization brought about mass production and steel, 0:18:17.400 --> 0:18:21.120 and that lowered the demand for the more artisan approach 0:18:21.640 --> 0:18:25.080 and the process of working the steel, which included very 0:18:25.080 --> 0:18:28.320 many steps. It was typically passed down through oral tradition, 0:18:28.440 --> 0:18:31.919 not written down anywhere, so it was gradually forgotten because 0:18:32.280 --> 0:18:34.600 there was no call to make that steal, so no 0:18:34.640 --> 0:18:39.520 one was passing down that knowledge. More recently, modern blacksmiths 0:18:39.560 --> 0:18:42.720 have been working with different approaches to replicate the forging 0:18:42.800 --> 0:18:47.240 of Damascus steel, largely based on some very educated guesses 0:18:47.280 --> 0:18:49.439 as to how it must have happened, and they've made 0:18:49.480 --> 0:18:52.000 a lot of progress, largely through trial and error. But 0:18:52.160 --> 0:18:54.960 it all starts with having the right type of steal 0:18:55.480 --> 0:18:59.040 from the right type of iron ore. When we come back, 0:18:59.359 --> 0:19:02.800 we're gonna talk about some modern classifications of steel and 0:19:02.840 --> 0:19:05.879 what that all means. But first, let's take a quick break. 0:19:13.480 --> 0:19:18.399 So how many types of steel are there? Well, golly, 0:19:18.520 --> 0:19:21.399 that really depends upon whom you ask. I know that 0:19:21.720 --> 0:19:24.480 is a lame answer, but it's true. Some people will 0:19:24.560 --> 0:19:29.440 divide steel into four broad categories. Uh. Those broad categories 0:19:29.440 --> 0:19:34.840 could be plane, carbon steel, alloy steel, tool steel, and 0:19:34.960 --> 0:19:39.600 stainless steel. Some say alloy steel and low alloy steel 0:19:39.840 --> 0:19:43.520 instead of tool steel. And the reason why you get 0:19:43.560 --> 0:19:46.399 all these different terms for the same basic stuff is 0:19:46.440 --> 0:19:49.240 because it all depends on your point of view. It's 0:19:49.280 --> 0:19:53.199 just like what obi Wan said. The site mead Metals 0:19:53.240 --> 0:19:59.040 classifies steel into carbon, alloy, stainless, and tool. But Thomas, 0:19:59.160 --> 0:20:02.560 which is an industrial sourcing company, so it's a company 0:20:02.560 --> 0:20:06.640 that helps manufacturing companies find sources for the raw materials 0:20:06.640 --> 0:20:11.200 they need, they classify it as carbon alloy, low alloy, 0:20:11.320 --> 0:20:16.080 and stainless. Uh. Meanwhile, the home Stratosphere site breaks it 0:20:16.119 --> 0:20:19.920 down to twenty six different types. And then you have 0:20:20.119 --> 0:20:24.520 various standards associations like s a E International s a 0:20:24.600 --> 0:20:28.600 E originally stood for Society of Automotive Engineers or the 0:20:28.600 --> 0:20:32.120 American Iron and Steel Institute or ai s I. Those 0:20:32.119 --> 0:20:34.159 are just two in the United States. You also have 0:20:34.280 --> 0:20:37.360 other ones in other countries, like British standards in the UK. 0:20:37.600 --> 0:20:43.040 You have International Organization for Standardization lots of these different groups, 0:20:43.080 --> 0:20:47.440 and they have thousands of different grades for steel. So 0:20:47.480 --> 0:20:49.920 what does this tell us, Well, it tells us there's 0:20:49.960 --> 0:20:53.199 an incredible amount of variability in the different types of 0:20:53.200 --> 0:20:56.320 steel people have made over the years, and that creating 0:20:56.359 --> 0:21:00.280 standards is tricky. If your standard is Lucy goosey and 0:21:00.720 --> 0:21:04.119 each grade of steel covers a fairly wide range of 0:21:04.200 --> 0:21:08.720 qualities like hardness or flexibility, or percentage of carbon or 0:21:08.760 --> 0:21:11.600 percentage of other alloys, you really end up with some 0:21:11.680 --> 0:21:15.520 real problems. So let's say that you've got a standardization 0:21:15.720 --> 0:21:19.680 system where you've got pretty wide grades to cover a 0:21:20.160 --> 0:21:26.080 spectrum of steel. But you're in charge of making steel girders, 0:21:26.160 --> 0:21:29.080 and so you're looking for a specific grade of steel, 0:21:29.480 --> 0:21:32.240 and the problem is that because it covers a spectrum, 0:21:32.280 --> 0:21:35.160 some of the girders you make might be stronger than others. 0:21:35.200 --> 0:21:39.280 Some might be better at standing up to really strong 0:21:39.359 --> 0:21:42.960 compression forces, and others are not. And that ain't great. 0:21:43.280 --> 0:21:49.480 You really want all that steel to be of similar hardness, 0:21:49.560 --> 0:21:53.040 similar strength. You really need it all to be consistent. 0:21:53.480 --> 0:21:56.720 So it really is necessary to break down steel into 0:21:56.800 --> 0:21:59.800 thousands of grades so that when it comes to actually 0:21:59.840 --> 0:22:03.480 manufacturing and selling the stuff, companies can make sure they 0:22:03.480 --> 0:22:06.840 are getting the raw materials they need to do whatever 0:22:07.000 --> 0:22:10.520 the job necessary is. But the downside is there's no 0:22:10.560 --> 0:22:13.000 way for me to do an episode about every single 0:22:13.080 --> 0:22:16.520 grade of steel, as it would be a billion hours long, 0:22:16.760 --> 0:22:20.840 and a lot of it would just be repeating seemingly 0:22:20.960 --> 0:22:25.879 arbitrary designations between two very similar but technically distinct types 0:22:25.920 --> 0:22:29.399 of steel, and that is just too much. But I 0:22:29.440 --> 0:22:32.600 will go over some of the classification strategies though, and 0:22:32.640 --> 0:22:35.600 what it all means. So let's start with some of 0:22:35.640 --> 0:22:39.560 the broader categories and we can drill down from there. Uh. 0:22:39.560 --> 0:22:44.680 And we're gonna go with carbon steel first. Now quickly, 0:22:45.359 --> 0:22:47.600 just as a reminder, we're gonna be talking about carbon 0:22:47.680 --> 0:22:52.159 steel and alloy steel. Things like that steel itself is 0:22:52.240 --> 0:22:56.399 an alloy, so that makes these designations confusing, right, And 0:22:56.560 --> 0:23:00.600 more than that, steel is an alloy of iron and carbon, 0:23:01.000 --> 0:23:03.040 so that makes it even more confusing. Why do you 0:23:03.080 --> 0:23:06.680 have carbon steel versus alloy steel? I mean, if all 0:23:06.680 --> 0:23:09.280 steel has carbon in it, and if all steel is 0:23:09.320 --> 0:23:14.120 an alloy, what do those designations even mean well, all 0:23:14.160 --> 0:23:17.760 of these steels are still alloys, and all of them 0:23:17.800 --> 0:23:20.400 still have carbon in them, But what really differentiates them 0:23:20.440 --> 0:23:24.800 is how much carbon each type of steel contains, and 0:23:25.320 --> 0:23:28.080 whether or not the steel has a significant amount of 0:23:28.240 --> 0:23:32.200 other stuff in it besides iron and carbon. Other factors 0:23:32.240 --> 0:23:35.720 also make a difference, such as how slowly or rapidly 0:23:35.800 --> 0:23:39.080 the steel cools in the manufacturing process, or how long 0:23:39.119 --> 0:23:42.320 the steel has been held at specific temperatures, or whether 0:23:42.359 --> 0:23:46.360 it's been heat treated. These processes all have their own names. 0:23:46.600 --> 0:23:50.040 To cool steel quickly is to quench it, which typically 0:23:50.119 --> 0:23:54.080 hardens steel. A sword maker might quench a sword to 0:23:54.160 --> 0:23:57.520 give the exterior a harder surface while the interior, which 0:23:57.800 --> 0:24:00.600 will cool more slowly because it's not being bosed to 0:24:00.720 --> 0:24:03.960 the water, retains a more flexible core. As a result, 0:24:04.680 --> 0:24:07.800 to avoid making a sword to brittle, the sword maker 0:24:07.920 --> 0:24:11.600 would temper the blade. That involves heating the sword back 0:24:11.680 --> 0:24:15.040 up again, but below the critical temperature at which the 0:24:15.080 --> 0:24:18.080 sword maker would you know, heat the blade in order 0:24:18.119 --> 0:24:20.520 to work it. So it's not as hot that it 0:24:20.520 --> 0:24:24.960 would be malleable, but it's hotter than it had been. 0:24:25.359 --> 0:24:28.960 So it gets really complicated, right, and it's all about 0:24:29.240 --> 0:24:33.240 creating the right crystalline structure for steel, and I'll get 0:24:33.280 --> 0:24:36.840 more into that towards the end of this episode. For now, 0:24:36.920 --> 0:24:39.960 let's take a closer look at some of those categories. 0:24:40.000 --> 0:24:43.679 So carbon steel that is mostly iron and carbon with 0:24:43.720 --> 0:24:47.719 only trace amounts of other elements in the mix. It's 0:24:47.760 --> 0:24:50.720 also by far the most common type of steel produced 0:24:50.760 --> 0:24:53.560 around the world. And we can also break down carbon 0:24:53.680 --> 0:24:58.920 steel into three large subcategories. Low carbon steel sometimes also 0:24:59.040 --> 0:25:03.399 called mile steel, this can contain up to point three 0:25:03.520 --> 0:25:08.160 percent carbon. Then you've got medium carbon steels, this contains 0:25:08.200 --> 0:25:12.040 between point three and point six percent carbon. And then 0:25:12.080 --> 0:25:15.200 you get high carbon steels, which have more than point 0:25:15.280 --> 0:25:19.560 six percent carbon, typically not much more than one percent. 0:25:20.000 --> 0:25:22.080 You might go up as high as two point five 0:25:22.080 --> 0:25:26.080 percent for some types, but beyond that is unusual, not 0:25:26.680 --> 0:25:31.000 unheard of, but unusual. So even within these subcategories, you 0:25:31.080 --> 0:25:35.240