WEBVTT - One Stuff of Iron, The Other of Steel 0:00:04.400 --> 0:00:07.760 Welcome to text Uff, a production from my Heart Radio. 0:00:12.039 --> 0:00:14.840 Hey there, and welcome to text Stuff. I'm your host, 0:00:15.000 --> 0:00:17.840 John than Strickland. I'm an executive producer with I Heart 0:00:17.960 --> 0:00:22.000 Radio and I love all things tech and tech stuff. 0:00:22.040 --> 0:00:26.000 Listener Nick contacted me on Twitter and asked if I 0:00:26.079 --> 0:00:28.720 might do an episode to talk about the different kinds 0:00:28.760 --> 0:00:32.320 of steel, in the different grades of steel, and what 0:00:32.440 --> 0:00:35.680 makes one different from the next. Now. I have talked 0:00:35.720 --> 0:00:39.239 about steel a little bit in previous episodes, but it 0:00:39.320 --> 0:00:43.040 was always in relation to some other topic. For example, 0:00:43.360 --> 0:00:45.839 I did a couple of episodes with my friend Ariel 0:00:45.960 --> 0:00:49.320 about swords, and that included some stuff on steel. But 0:00:49.840 --> 0:00:52.360 I really want to dedicate a couple of episodes to 0:00:52.440 --> 0:00:55.760 this metal and why we have so many different classifications 0:00:55.760 --> 0:00:59.120 of it and what this classifications actually mean. But first 0:00:59.680 --> 0:01:02.240 let's get to some definitions and history. In fact, that's 0:01:02.280 --> 0:01:04.840 what this episode is going to be about, is sort 0:01:04.840 --> 0:01:10.320 of the history of steel making in general, because it's 0:01:10.360 --> 0:01:14.880 complicated stuff. And in the next episode will conclude with 0:01:15.000 --> 0:01:17.840 the history part and move on to the different types 0:01:17.880 --> 0:01:20.600 of steel. Now, if you take a look at the 0:01:20.720 --> 0:01:25.240 periodic table of elements, you'll notice that steel is not 0:01:25.560 --> 0:01:29.240 on it. And that's because steel isn't an element, it's 0:01:29.240 --> 0:01:33.120 an alloy, and alloy is a metal created from the 0:01:33.160 --> 0:01:38.840 combination of at least two metallic elements. And technically steel 0:01:39.040 --> 0:01:42.319 is an alloy of iron and carbon. But here's where 0:01:42.360 --> 0:01:45.479 it gets really confusing. All the iron we work with, 0:01:45.880 --> 0:01:49.520 the iron that's in our stuff like iron nails and stuff, 0:01:49.640 --> 0:01:52.400 all of that is really an alloy of iron and carbon. 0:01:52.920 --> 0:01:55.080 So this means that these episodes are really going to 0:01:55.120 --> 0:01:58.120 be not just about steel, but iron and how we 0:01:58.200 --> 0:02:01.400 learned how to work with iron. Now you might wonder 0:02:01.800 --> 0:02:05.280 why you'd bother making an alloy in the first place. 0:02:05.480 --> 0:02:08.560 Why would you not just use pure iron? Wouldn't that 0:02:08.560 --> 0:02:12.959 be easier? Well, it's because alloys can have different, more 0:02:13.120 --> 0:02:18.440 beneficial properties than the individual elements that combine together to 0:02:18.639 --> 0:02:22.280 make that alloy. So, in general, the reason we make 0:02:22.320 --> 0:02:25.720 alloys at all is to create materials that are stronger 0:02:25.880 --> 0:02:30.040 or lighter, or more resistant to corrosion or some other 0:02:30.120 --> 0:02:34.040 positive quality or combination thereof, compared to the metals we 0:02:34.160 --> 0:02:36.720 use to create the alloy. In the first place. Steel 0:02:37.160 --> 0:02:40.679 is superior to iron in many ways, which we will 0:02:40.760 --> 0:02:44.160 get into. But to really understand the development of steel, 0:02:44.480 --> 0:02:46.640 we have to take a closer look at the history 0:02:46.720 --> 0:02:50.880 of meta allergy in general. So for thousands of years, 0:02:51.000 --> 0:02:55.000 humanity relied primarily upon stone as a material for tools 0:02:55.040 --> 0:02:58.400 and weapons. And we have a name for this age, 0:02:58.840 --> 0:03:01.519 the flint stones. No way, I'm sorry, I just meant 0:03:01.520 --> 0:03:04.280 the Stone Age. But we can further divide the Stone 0:03:04.280 --> 0:03:08.160 Age into the Paleolithic or Old Stone Age, you know 0:03:08.160 --> 0:03:10.799 when everyone was listening to that, you know, real crappy music, 0:03:11.120 --> 0:03:14.840 and Neolithic or New Stone Age, which is what all 0:03:14.840 --> 0:03:20.160 the kids were listening to. Stone is plentiful. It's hard stuff, right, 0:03:20.240 --> 0:03:22.800 It's durable. Depending upon the type of stone, you could 0:03:22.800 --> 0:03:25.880 fashion it into sharp edges, and you could polish it up. 0:03:25.880 --> 0:03:30.000 You could make stuff like axes and spears, and so 0:03:30.040 --> 0:03:33.200 the ancestors of humans were using stone tools as far 0:03:33.320 --> 0:03:37.640 back as three million years ago, not earlier. I mentioned 0:03:37.800 --> 0:03:40.840 for thousands of years. But that wasn't to d emphasize 0:03:40.840 --> 0:03:43.120 how long we relied on stone, but rather just as 0:03:43.160 --> 0:03:45.200 a nod to how tricky it is to apply the 0:03:45.240 --> 0:03:50.440 word humans, because we're talking about you know, ancestors of 0:03:50.520 --> 0:03:53.560 humans as well. While stone could get the job done, 0:03:53.640 --> 0:03:57.800 it wasn't necessarily the best material for most jobs. It 0:03:57.920 --> 0:04:00.600 was brittle and heavy, and you could find yourself with 0:04:00.640 --> 0:04:03.520 a tool that had edges that were not as sharp 0:04:03.600 --> 0:04:06.720 after a few uses, or one that would break in 0:04:06.720 --> 0:04:10.520 a relatively short amount of time. Also, when we talk 0:04:10.600 --> 0:04:14.240 about stuff like the Stone Age and the Bronze Age 0:04:14.240 --> 0:04:16.120 and the Iron Age, we have to remember that these 0:04:16.240 --> 0:04:20.320 terms describe very broad eras that didn't actually have a 0:04:20.360 --> 0:04:25.920 definitive beginning and end. Some regions moved towards metallurgy much 0:04:25.960 --> 0:04:30.080 earlier than others, sometimes by as much as two thousand years. 0:04:30.440 --> 0:04:32.160 So I just don't want any of you thinking that, 0:04:32.440 --> 0:04:34.440 you know, a person went to bed on a Wednesday 0:04:34.560 --> 0:04:36.560 night when it was the Stone Age, and then they 0:04:36.560 --> 0:04:39.119 woke up Thursday morning and it was suddenly the Bronze Age. 0:04:39.560 --> 0:04:43.520 It's a little more subtle than that. Generally speaking, we 0:04:43.600 --> 0:04:46.359 think of the Bronze Age as beginning around three thousand 0:04:46.400 --> 0:04:49.280 b c E, and we think of it as ending 0:04:49.320 --> 0:04:52.560 as well. That depends on where you lived. If you 0:04:52.600 --> 0:04:56.320 lived in Mesopotamia, it ended sometime around twelve hundred b C. 0:04:56.760 --> 0:04:58.800 But if you were in Northern Europe you had to 0:04:58.800 --> 0:05:01.120 wait a little longer. It was closer to six hundred 0:05:01.160 --> 0:05:04.760 b c. E. Generally, the onset of the Bronze Age 0:05:04.839 --> 0:05:08.680 was brought about by trade, so the knowledge of how 0:05:08.800 --> 0:05:13.440 to produce bronze spread outward from the Mesopotamian area for 0:05:13.480 --> 0:05:16.599 the most part, so cultures first began to learn how 0:05:16.640 --> 0:05:20.960 to work with copper, and at first copper was fairly scarce. 0:05:21.000 --> 0:05:24.240 It just wasn't as readily available as different types of stone. 0:05:24.640 --> 0:05:28.080 But ancient people's developed mining and metallergy and created all 0:05:28.160 --> 0:05:30.840 sorts of stuff out of copper. But copper is not 0:05:31.080 --> 0:05:34.400 that great for tools. It's not terribly durable, it doesn't 0:05:34.400 --> 0:05:37.800 hold an edge very well. But by adding some tin 0:05:38.480 --> 0:05:42.520 to the copper t I N tin, mellergists could create 0:05:42.560 --> 0:05:47.799 a much stronger alloy bronze. This material made much better 0:05:47.880 --> 0:05:51.880 tools and weapons. Iron is even stronger, but the high 0:05:51.920 --> 0:05:54.760 melting point of iron meant that the tools humans had 0:05:54.800 --> 0:05:59.400 for me allergy weren't sufficient to make iron. The pods 0:05:59.520 --> 0:06:03.120 used to melt copper and tin couldn't withstand the temperatures 0:06:03.120 --> 0:06:06.560 you would need in order to smelt iron from iron. 0:06:06.560 --> 0:06:11.520 Ore the word smelt means to extract metal from ore, 0:06:11.839 --> 0:06:15.000 and or is a solid rock or sediment that contains 0:06:15.040 --> 0:06:18.040 one or more metals or minerals in it, So smelting 0:06:18.120 --> 0:06:21.880 is really about separating the metal from all the other 0:06:21.960 --> 0:06:24.560 stuff that's in that rock so that you can work 0:06:24.600 --> 0:06:26.440 with the metal. One of the things you had to 0:06:26.480 --> 0:06:30.680 deal with was iron oxide, which forms on the surface 0:06:30.720 --> 0:06:33.120 of iron exposed to air. Also, I should mention that 0:06:33.200 --> 0:06:36.719 iron oxide is actually an imprecise term, or rather it's 0:06:36.720 --> 0:06:40.120 a term for a bunch of different chemical compounds made 0:06:40.160 --> 0:06:43.279 up of iron and oxygen, and the iron oxide we 0:06:43.400 --> 0:06:47.920 know of as rust is just one form of that. Gradually, 0:06:48.040 --> 0:06:50.640 humans figured out how to build more robust forges and 0:06:50.680 --> 0:06:52.839 they could heat up or enough so that they could 0:06:52.839 --> 0:06:55.919 actually smelt iron, but it took some more time for 0:06:56.000 --> 0:07:00.120 anyone to really be able to reliably create steel. An 0:07:00.120 --> 0:07:05.720 exception was meteoric iron as an iron from space. Some 0:07:05.839 --> 0:07:09.840 meteorites contained alloys of iron and nickel, and the process 0:07:09.840 --> 0:07:13.560 of entering the Earth's atmosphere created enough heat to do 0:07:14.080 --> 0:07:17.360 essentially the smelting work for us. But this wasn't exactly 0:07:17.560 --> 0:07:20.840 plentiful stuff, so it's mostly used in small ornaments and 0:07:20.880 --> 0:07:23.520 things like that until we got more up to speed, 0:07:23.600 --> 0:07:27.000 like you might be say an Egyptian pharaoh with a 0:07:27.080 --> 0:07:31.600 meteoric iron dagger buried with you next to a gold dagger, 0:07:31.640 --> 0:07:34.560 because that's how valuable these things were. One of the 0:07:34.640 --> 0:07:37.320 things about iron that made it harder to work with 0:07:37.480 --> 0:07:40.840 is that it does oxidize rapidly upon contact with the air. 0:07:41.320 --> 0:07:45.160 Oxidization is a process in which a substance like an atom, 0:07:45.200 --> 0:07:49.200 an ion, or a molecule loses electrons in a chemical reaction. 0:07:49.600 --> 0:07:53.440 Now this does not necessarily involve oxygen, but oxygen is 0:07:53.480 --> 0:07:59.640 a pretty effective electron thief. Iron oxidizes pretty quickly. Oxidation 0:07:59.840 --> 0:08:04.800 is an exothermic reaction. Now that means that as a 0:08:04.840 --> 0:08:08.040 byproduct of this reaction there is a release of heat. 0:08:08.520 --> 0:08:12.080 So you can actually see the effects of oxidation on iron. 0:08:12.520 --> 0:08:15.480 It is what causes iron to rust. So iron in 0:08:15.520 --> 0:08:18.080 the presence of oxygen and water is going to rust. 0:08:18.800 --> 0:08:22.120 But even iron that's not actively rusting will have a 0:08:22.240 --> 0:08:25.320 layer of iron oxide on the surface of the iron itself. 0:08:26.040 --> 0:08:30.120 The process of oxidation is also pretty darn fast. If 0:08:30.160 --> 0:08:33.760 you were to expose a very small speck of iron 0:08:33.920 --> 0:08:37.120 to the air, it would oxidize and heat up and 0:08:37.160 --> 0:08:39.920 you would see a spark. So if you've got a 0:08:39.920 --> 0:08:42.679 lot of iron that's in a lump, you're gonna have 0:08:42.720 --> 0:08:46.080 more volume compared to surface area. Right, You've got more 0:08:46.120 --> 0:08:51.000 iron in the lump than is exposed on the surface, 0:08:51.360 --> 0:08:53.920 just because of the size. This is all about volume, 0:08:54.160 --> 0:08:56.679 and only the surface of the iron is oxidizing with 0:08:56.720 --> 0:08:58.320 the air because you know, the rest of the iron 0:08:58.520 --> 0:09:03.079 is shielded from the it's inside the lump. The heat 0:09:03.400 --> 0:09:07.440 from that oxidizing reaction, the oxidation will be able to 0:09:07.480 --> 0:09:10.319 dissipate into the rest of the lump of iron. Again, 0:09:10.320 --> 0:09:13.240 you've got that big volume of iron, so the heat 0:09:13.280 --> 0:09:16.960 from that process doesn't really amount too much in the 0:09:17.000 --> 0:09:20.040 grand scheme of the lump. But if you have a tiny, 0:09:20.080 --> 0:09:23.680 tiny speck of iron, well, now the ratio of surface 0:09:23.720 --> 0:09:27.120 area to volume has totally changed. There's very little volume 0:09:27.120 --> 0:09:30.480 in a tiny piece of iron. The surface will still 0:09:30.480 --> 0:09:34.199 react to oxygen, and there isn't so much iron inside 0:09:34.440 --> 0:09:37.440 the spec for the heat to dissipate so effectively. So 0:09:37.480 --> 0:09:41.080 the spec gets really hot, hot enough to glow. When 0:09:41.080 --> 0:09:43.800 someone uses a power grinder on iron and you see 0:09:43.800 --> 0:09:47.319 sparks fly, or they're using flint and steel, those sparks 0:09:47.320 --> 0:09:50.600 are tiny specks of iron oxidizing at a super fast rate. 0:09:51.320 --> 0:09:54.480 Iron oxide isn't the stuff we want, right, we want iron, 0:09:54.760 --> 0:09:58.920 So smelting helps us remove iron oxide and get iron instead. 0:09:59.040 --> 0:10:01.400 It goes through the set type of reaction we call 0:10:01.480 --> 0:10:05.640 this one reduction. Smelting also helps separate the iron from 0:10:05.720 --> 0:10:10.840 other impurities that could be in the ore, stuff like sulfur, phosphorous, silicon, 0:10:11.480 --> 0:10:16.040 things like that. Now, as far as the actual smelting process, that, 0:10:16.400 --> 0:10:19.360 as we will learn, evolved a great deal over time. 0:10:19.880 --> 0:10:24.760 The earliest furnaces used to smelt iron, we're called bloomer eyes. 0:10:25.320 --> 0:10:28.640 There's some great videos on YouTube that show how these 0:10:28.640 --> 0:10:32.400 bloomers worked. I highly recommend you guys go on YouTube 0:10:32.440 --> 0:10:35.480 and look up bloomery b l o O m e 0:10:35.679 --> 0:10:40.520 r Y because these videos are equal parts fascinating and terrifying. 0:10:40.679 --> 0:10:44.880 So typically, you would build a chimney like structure and 0:10:44.920 --> 0:10:47.640 you would use something like clay to make it. So 0:10:48.120 --> 0:10:52.800 imagine a a stack a chimney made of clay. You 0:10:52.840 --> 0:10:55.280 would have a little section in the very front that 0:10:55.320 --> 0:10:57.080 would be cut out like a door, but you would 0:10:57.120 --> 0:11:00.439 have a a piece of clay that fit into that. 0:11:00.960 --> 0:11:03.360 You would have at least one hole cut in the 0:11:03.400 --> 0:11:06.320 side of the chimney called a two year, and this 0:11:06.360 --> 0:11:09.360 would allow for more air circulation to go into the 0:11:09.440 --> 0:11:13.640 chamber of the bloomery. If you blue air into it, 0:11:13.679 --> 0:11:16.839 you would increase the temperature of the burn. So you 0:11:16.920 --> 0:11:21.800 would possibly have bellows attached to this, either operated by 0:11:21.880 --> 0:11:25.760 hand or later by having a water wheel turning a 0:11:25.800 --> 0:11:29.600 cam that would allow these bellows to open and close 0:11:29.640 --> 0:11:33.200 and thus blow air into the bloomery, or you might 0:11:33.280 --> 0:11:36.360 just be dependent upon the wind, which wouldn't be the 0:11:36.400 --> 0:11:39.720 most efficient way to make this stuff. You'd also typically 0:11:39.760 --> 0:11:42.880 have a hole towards the very bottom of the chimney 0:11:42.960 --> 0:11:45.840 that would allow you to draw off slag. This would 0:11:45.840 --> 0:11:49.960 be the the hot melted mixture of impurities, and you 0:11:50.120 --> 0:11:53.720 don't have to worry about melting off the iron having 0:11:53.720 --> 0:11:56.960 the iron pour out along with the slag, because that's 0:11:56.960 --> 0:11:59.560 just not going to happen. We're not talking about temperatures 0:11:59.640 --> 0:12:04.400 high enough to melt iron at this point. Conversely, the 0:12:04.600 --> 0:12:08.160 entire bloomery, if you didn't have this way of tapping 0:12:08.200 --> 0:12:10.960 it so that you can put get slag out, you 0:12:11.040 --> 0:12:14.480 might even have to push it over, which sounds incredibly 0:12:14.520 --> 0:12:17.319 dangerous to me, and then allow the molten slag to 0:12:17.320 --> 0:12:20.880 to pour out the top of it. Now, slag typically 0:12:20.960 --> 0:12:23.440 contains a little bit of iron in it as well, 0:12:23.800 --> 0:12:25.920 but for the most part you're talking about all the 0:12:25.960 --> 0:12:29.280 other stuff that you wanted to remove, leaving as much 0:12:29.280 --> 0:12:31.840 of the iron behind as possible. So you might have 0:12:31.960 --> 0:12:34.640 little chunks of iron in the slag, and thus you 0:12:34.720 --> 0:12:37.160 might want to keep the slag just in case has 0:12:37.200 --> 0:12:39.520 any iron in it in order to use in a 0:12:39.600 --> 0:12:44.360 future burn. But to facilitate the removal of slag, forgers 0:12:44.480 --> 0:12:47.040 or you know, smith's or metal or just however you 0:12:47.040 --> 0:12:50.120 want to call them, would typically add in a substance 0:12:50.400 --> 0:12:53.600 with a relatively low melting point that could help siphon 0:12:53.640 --> 0:12:56.640 out some of the impurities. That would act almost like 0:12:56.679 --> 0:12:58.880 a lubricant, if you can think of it that way, 0:12:59.400 --> 0:13:02.400 The bind with things and and be liquid in order 0:13:02.440 --> 0:13:05.360 to help coax more of those impurities to flow out. 0:13:05.480 --> 0:13:09.440 The stuff is called collectively flux, and flux can be 0:13:09.520 --> 0:13:12.440 made up of lots of different stuff, including sand or 0:13:12.480 --> 0:13:17.240 silica or limestone, but with ancient bloomer eyes, often the 0:13:17.280 --> 0:13:20.559 flux came from the material used to build the bloomery itself. 0:13:20.640 --> 0:13:23.920 It would just be leached out of the interior of 0:13:23.960 --> 0:13:27.599 the bloomery and become part of the mixture, so you 0:13:27.640 --> 0:13:30.960 didn't necessarily have to add more in the process of 0:13:31.000 --> 0:13:35.760 smelting and refining iron. This way is laborious. It involves 0:13:35.760 --> 0:13:38.880 getting the furnace really hot with a layer of charcoal 0:13:38.960 --> 0:13:42.600 at the base of the furnace. Then you add more 0:13:42.720 --> 0:13:45.880 charcoal to heat up the entirety of the furnace, and 0:13:45.920 --> 0:13:48.680 then you start adding in equal amounts of iron ore 0:13:48.760 --> 0:13:52.280 and charcoal every few minutes, and you alternate between them, um, 0:13:52.559 --> 0:13:54.640 but you add them both at around the same time. 0:13:54.720 --> 0:13:57.319 So you do, all right, let's put in a kilogram 0:13:57.360 --> 0:14:00.720 of iron ore and a kilogram of charcoal, and then 0:14:00.800 --> 0:14:03.160 after a few minutes another kilogram of iron or and 0:14:03.200 --> 0:14:06.040 another kilogram of charcoal. You have to keep doing this 0:14:06.160 --> 0:14:08.880 over and over and over again every few minutes for 0:14:09.000 --> 0:14:12.240 several hours. So these bloomerys couldn't get hot enough, as 0:14:12.280 --> 0:14:15.760 I said, to actually melt the iron ore outright. Instead, 0:14:16.040 --> 0:14:20.040 you would produce what was called a bloom thus bloomery. 0:14:20.080 --> 0:14:23.840 This would be a mass of hot iron and kind 0:14:23.840 --> 0:14:26.640 of you know, charcoal. Mixt year, the iron doesn't get 0:14:26.680 --> 0:14:29.040 hot enough to really melt, but it's hard enough to 0:14:29.080 --> 0:14:33.000 be kind of a spongy looking material that was somewhat 0:14:33.040 --> 0:14:35.240 malleable if you were to pull it out of the 0:14:35.240 --> 0:14:37.960 bloom moraine then hit it with a hammer. Managing this 0:14:38.040 --> 0:14:40.760 process is tricky because not only do you have to 0:14:41.000 --> 0:14:44.600 maintain that high level of heat, you also have to 0:14:44.600 --> 0:14:47.440 make sure that the two year remains clear of material. 0:14:47.520 --> 0:14:50.840 Remember that's the air channel, where air is either blowing 0:14:50.840 --> 0:14:53.240 in from the wind or you're forcing it in through 0:14:53.320 --> 0:14:56.560 something like a bellows. A lot of stuff can go 0:14:56.640 --> 0:15:00.360 wrong in this process, and even when everything goes corre directly, 0:15:00.400 --> 0:15:03.080 you might not end up with a great amount of iron, 0:15:03.200 --> 0:15:06.720 depending upon the quality of the ore itself. Once the 0:15:06.760 --> 0:15:11.080 process is done, it's time to retrieve the iron bloom. 0:15:11.120 --> 0:15:14.280 So you've tapped out the slag, You've let the slag 0:15:14.360 --> 0:15:19.000 run out. You pull the door off the furnace, assuming 0:15:19.040 --> 0:15:21.880 that or the bloomery, assuming that the bloomery has a door. 0:15:21.920 --> 0:15:24.640 You might even just break the bloomery open. Often these 0:15:24.640 --> 0:15:28.680 were just one use devices. You would construct one every 0:15:28.680 --> 0:15:31.200 time you want to do one of these, and uh 0:15:31.560 --> 0:15:34.400 you might have to break it apart anyway, because sometimes 0:15:34.400 --> 0:15:37.280 the iron bloom would be too large to fit through 0:15:37.320 --> 0:15:40.080 the door in the first place. Now the bloom will 0:15:40.120 --> 0:15:44.960 have absorbed some charcoal would be incorporated into it. Charcoal 0:15:44.960 --> 0:15:48.080 has a very high carbon content, and at higher temperatures, 0:15:48.440 --> 0:15:52.520 iron absorbs some of that carbon. This also lowers the 0:15:52.520 --> 0:15:55.280 melting point for iron a little bit, and that will 0:15:55.280 --> 0:15:58.920 become important later on. The charcoal needs to burn really 0:15:59.080 --> 0:16:02.440 thoroughly for of this process to really work, Otherwise you'll 0:16:02.440 --> 0:16:05.200 get chunks of charcoal that are too large, and you'll 0:16:05.280 --> 0:16:07.600 end up with iron that might have big chunks of 0:16:07.800 --> 0:16:10.360 unburned charcoal embedded in it, which is going to be 0:16:10.600 --> 0:16:12.800 harder to get rid of. But if the coals are 0:16:12.800 --> 0:16:16.520 the right size, the iron will absorb some carbon, but 0:16:16.720 --> 0:16:19.560 not all of it obviously. So now you've got a 0:16:19.640 --> 0:16:22.840 big old, porous lump of red hot iron with some 0:16:22.920 --> 0:16:26.800 carbon and maybe some charcoal. You've got some other stuff, 0:16:26.840 --> 0:16:29.480 and it some slag is still inside that, because again 0:16:29.480 --> 0:16:33.800 it's spongey, it's porous, so there will be slag contained 0:16:34.000 --> 0:16:38.160 inside this red hot bloom of iron. So what do 0:16:38.200 --> 0:16:40.480 you do then, Well, that stage the iron still isn't 0:16:40.560 --> 0:16:44.440 terribly useful, so you would have to reheat the mass 0:16:44.480 --> 0:16:46.960 so that it's malleable. You know, get it hot enough 0:16:47.000 --> 0:16:49.040 so that you can work it. Then you put it 0:16:49.040 --> 0:16:52.600 on an anvil and you start beating that iron bloom 0:16:52.640 --> 0:16:56.520 with a hammer. This compresses the mass. It forces the 0:16:56.600 --> 0:17:00.720 molten slag out of the lump to the surface of 0:17:00.760 --> 0:17:03.880 the iron. So remember I said it's like a sponge, 0:17:03.880 --> 0:17:07.280 it's porous. This is kind of like squeezing out a sponge. 0:17:07.520 --> 0:17:11.359 If you have a sponge that's absolutely saturated with water 0:17:11.760 --> 0:17:14.520 and you start to squeeze it, you force the water out. 0:17:14.760 --> 0:17:18.800 That's kind of what's happening when a blacksmith starts hammering 0:17:18.880 --> 0:17:22.400 an iron bloom with a hammer. You're forcing that slag 0:17:22.480 --> 0:17:25.399 out to the surface. You can watch videos of blacksmiths 0:17:25.440 --> 0:17:28.560 doing this process on YouTube. Again, it's fascinating. You're gonna 0:17:28.600 --> 0:17:32.679 see this sort of glowing orange mass of iron. But 0:17:32.760 --> 0:17:35.720 it will start to grow darker as it's getting hammered, 0:17:35.760 --> 0:17:38.400 not just because it's cooling off. I mean that is happening, 0:17:38.440 --> 0:17:41.280 but it's also growing darker because the slag is being 0:17:41.320 --> 0:17:44.640 forced towards the surface of the mass. So smith's need 0:17:44.720 --> 0:17:47.880 to hammer out the mass folded back in on itself 0:17:48.280 --> 0:17:51.800 and repeat this process over and over. Reheating it, hammering 0:17:51.800 --> 0:17:55.240 it out, folding it back on itself, welding it to itself, 0:17:55.280 --> 0:17:59.920 reheating it, hammering it out. This takes a lot of time, 0:18:00.600 --> 0:18:04.199 and you'll see that typically a relatively large bloom that 0:18:04.280 --> 0:18:07.320 you'll get out of a bloomery will ultimately reduce to 0:18:07.359 --> 0:18:10.680 a much smaller size once the smith has hammered out 0:18:11.040 --> 0:18:14.080 most of that slag, what is left is typically a 0:18:14.119 --> 0:18:17.680 hammered piece that is mostly iron with a very low 0:18:17.760 --> 0:18:22.280 carbon content less than point zero eight percent carbon compared 0:18:22.320 --> 0:18:25.719 to iron, and some other impurities are in there too. 0:18:26.080 --> 0:18:28.520 Because the smith had to work the mass by hand 0:18:28.560 --> 0:18:32.440 to produce this, we call it wrought iron w r 0:18:32.560 --> 0:18:37.120 o U g h T iron. That means worked iron. 0:18:37.640 --> 0:18:39.560 That we had to do work on it in order 0:18:39.560 --> 0:18:41.879 to make it this way. So once in a while, 0:18:42.280 --> 0:18:45.480 using this method of bloomery's you could produce steel. It 0:18:45.520 --> 0:18:48.960 wasn't necessarily predictable. You weren't necessarily going to be able 0:18:49.040 --> 0:18:51.919 to do it time and time again, but it did happen, 0:18:52.119 --> 0:18:56.320 and you'd be really happy whenever it did. Sometimes, however, 0:18:56.359 --> 0:19:00.880 that steel would be particularly hard but brittle. Gradually, mill 0:19:01.000 --> 0:19:04.320 Or just learned that by plunging very hot steel. We're 0:19:04.320 --> 0:19:08.680 talking about steel. This around nine degrees celsius into water. 0:19:09.040 --> 0:19:13.480 The cool steel's surface becomes extremely hard and brittle. But 0:19:14.160 --> 0:19:16.880 by reheating that steel to a temperature of around four 0:19:16.920 --> 0:19:20.760 hundred degrees celsius, in a process that was later called tempering, 0:19:21.119 --> 0:19:24.199 the material will become less brittle but still retain a 0:19:24.200 --> 0:19:28.760 lot of its hardness. So you would hear these terms 0:19:28.800 --> 0:19:32.879 by blacksmith talking about tempered steel. That's what they're referring to. 0:19:33.680 --> 0:19:36.520 But here's the thing. The process for making steel was 0:19:36.640 --> 0:19:40.000 imprecise and dependent on so many factors, including the quality 0:19:40.040 --> 0:19:42.919 of the ore being used to smelt the iron and 0:19:42.960 --> 0:19:45.920 the process to create the actual steel. It was hard 0:19:45.960 --> 0:19:48.840 to dial into the specific ratios you need to go 0:19:48.920 --> 0:19:53.080 from iron to steal in those times. So the concentration 0:19:53.119 --> 0:19:56.080 of carbon really determines what kind of metal you end 0:19:56.160 --> 0:19:58.359 up with. If you don't have enough carbon, you end 0:19:58.440 --> 0:20:01.960 up with wrought iron. If you have too much carbon, 0:20:02.000 --> 0:20:05.960 you end up with cast iron, two very different extremes. 0:20:06.359 --> 0:20:07.920 It's got to be just right, and for a couple 0:20:07.960 --> 0:20:10.040 of thousand years, that was pretty hard to do. Now, 0:20:10.040 --> 0:20:11.760 when we come back, I'll talk a bit about how 0:20:11.840 --> 0:20:15.760 humans figured out more effective ways to produce iron and steel. 0:20:16.000 --> 0:20:25.919 But first, let's take a quick break. We've looked at 0:20:25.960 --> 0:20:28.920 the oldest method of smelting iron with bloomers, and a 0:20:28.960 --> 0:20:32.480 bloomery gets the job done, but it's not terribly efficient. 0:20:32.720 --> 0:20:35.119 You have to pour in a lot of labor and 0:20:35.200 --> 0:20:38.440 a lot of iron ore and a lot of charcoal 0:20:38.840 --> 0:20:41.840 to get any results, and the bloom you produce still 0:20:41.880 --> 0:20:43.960 needs a lot of work to turn it into iron 0:20:44.000 --> 0:20:46.359 that can be put to any good use. So what 0:20:46.520 --> 0:20:48.720 was really needed was a better way to reduce the 0:20:48.800 --> 0:20:52.800 iron oxide and iron ore to iron, and one of 0:20:52.840 --> 0:20:54.920 the best ways to do that is to produce even 0:20:55.000 --> 0:20:58.200 higher amounts of heat. Now let's think about this chemically. 0:20:58.440 --> 0:21:01.359 I've mentioned that the oxidizing reaction is exothermic, but I 0:21:01.359 --> 0:21:03.239 haven't really talked about what's going on here at an 0:21:03.280 --> 0:21:07.679 atomic level. So with iron oxide, you've got iron and 0:21:07.760 --> 0:21:12.199 oxygen effectively bond with one another within a furnace. The 0:21:12.280 --> 0:21:15.439 intense heat and the presence of carbon allows for the 0:21:15.560 --> 0:21:20.439 separation of oxygen from iron. The oxygen instead bonds with 0:21:20.560 --> 0:21:24.520 the carbon forming carbon monoxide, which is an odorless and 0:21:24.720 --> 0:21:28.440 toxic gas. The carbon monoxide is happy to take on 0:21:28.480 --> 0:21:32.120 another oxygen atom as well, So at temperatures around six 0:21:32.359 --> 0:21:35.240 D nine D degrees celsius in a furnace, you'll end 0:21:35.320 --> 0:21:38.439 up with iron and carbon dioxide as well, not just 0:21:38.520 --> 0:21:43.280 carbon monoxide but carbon dioxide. The bloomers just weren't going 0:21:43.320 --> 0:21:45.320 to get the job done. They weren't going to get 0:21:45.320 --> 0:21:48.080 to those temperatures. So that brings us to the blast furnace. 0:21:48.720 --> 0:21:51.800 The bloomery produces a hot of lump iron. It gets 0:21:51.880 --> 0:21:54.520 hot enough to glow and it's malleable at that temperature, 0:21:54.520 --> 0:21:58.200 but it's not hot enough to melt. Blast furnaces can 0:21:58.240 --> 0:22:00.879 reach higher temperatures high end, so that you're not just 0:22:01.000 --> 0:22:05.440 reducing iron oxide to iron plus carbon monoxide or carbon dioxide. 0:22:05.800 --> 0:22:08.920 You're also getting a hot enough chamber so that you 0:22:08.960 --> 0:22:14.719 can melt the iron completely. You get molten iron liquid metal. 0:22:15.359 --> 0:22:18.480 So how is this possible? Well, first, blast furnaces are 0:22:18.680 --> 0:22:21.680 much bigger than bloomery's. They tend to have a chimney 0:22:21.720 --> 0:22:24.720 like structure, much like your typical bloomery, but instead of 0:22:24.720 --> 0:22:26.879 being made out of clay, they're usually made out of 0:22:26.920 --> 0:22:30.399 several layers of brick that form the chimney. Sometimes with 0:22:30.480 --> 0:22:34.439 other materials to provide both stability and often away for 0:22:34.560 --> 0:22:37.720 heat to dissipate. They can be a couple of stories tall, 0:22:37.880 --> 0:22:40.520 whereas a bloomery might only be a couple of meters tall, 0:22:40.640 --> 0:22:43.280 maybe three or four meters for the really big ones, 0:22:44.440 --> 0:22:47.560 and like a bloomery, blast furnaces have two years through 0:22:47.600 --> 0:22:51.080 which pumped air can enter into the furnace. The pumps 0:22:51.200 --> 0:22:54.159 or bellows could be operated by hand, but later on 0:22:54.200 --> 0:22:57.800 it was far more convenient to locate a furnace next 0:22:57.840 --> 0:23:01.000 to a source of flowing water and then use a 0:23:01.000 --> 0:23:03.920 water wheel to provide the power needed to pump the bellows. 0:23:04.000 --> 0:23:07.680 You are in effect blasting the combustion in the furnace 0:23:07.840 --> 0:23:11.879 with air. Thus you have a blast furnace. Unlike people, 0:23:12.119 --> 0:23:14.000 the water doesn't need to take a break, and the 0:23:14.000 --> 0:23:17.440 furnace could be kept at a high consistent temperature, assuming 0:23:17.480 --> 0:23:21.200 it was being fed with fuel regularly like a bloomery. 0:23:21.280 --> 0:23:24.840