Forging a Sword (Part 3): Heat Treatment

This was the state of play, the blades were now shaped. Tom's, you can see, was just three inches longer, but this made a huge difference to the way it handled. And I could tell our swords apart at a glance from the other end of the workshop. This is not the first time I've ever tried to forge a sword. This is in fact the second. The first time was many years ago when I was 17 years old at school, and I managed to get hold of a car leaf spring. And I thought, wow, I could forge a sword out of that. And my metalwork teacher let me use the forge. And so I had it like this, heating in the coals, and I was going to beat it on an anvil and turn it into a sword. I had not a lot of idea about what I was doing, I wasn't particularly confident, but hell, I was going to give it a go. But it went wrong. I got almost nowhere, because as I was heating my leaf spring, Katie Arnanda, yes, Katie Arnanda, you if you're watching, Katie Arnanda came to the door to the metal workshop, which was right next to the forge, and started talking to me. Now, Katie was distractingly good-looking, and I left it in for too long. And when it came out, when it came out, it looked like a flipping sparkler. It looked like this. Katie, do you remember? It looked like this, didn't it? And I put it on the anvil thinking, oh no, what do I do, what do I do? And I hit it, and it broke and fell in two. And a glowing bit of orange metal landed on the floor, and someone who was visiting, her dog, walked out and just didn't tread on the hot bit, thank goodness, and went out. And the half of the sword I had left, I thought, what do I do with this? Didn't know what I was doing, and I plunged it into a bucket of water. Huge amount of steam blinded me, and then, to my amazement, there was a dry bucket there. I boiled a bucket of water dry, and I said to my metalwork teacher, uh, now what do I do? And he took one look at it and said, ah, no, that's it, it's over, it's all gone crystalline, it's stuffed. And we didn't find another leaf spring, and that was it, that was the end. Katie, that was the end of my first sword, but this sword will not suffer the same fate, no. We fetched in an extra-long heater from outside, as well as this old gas cylinder filled with vegetable oil. It was time for some heat treatment. Now, we started, if you remember, with a rectangular section bar, and there's pretty much not a molecule of that bar now that is where it started off. Everything has been drawn out, and bashed in, and bevelled, and so forth. And so, there's no part of the surface of this which was the surface of that bar. So, it's covered in scale at the moment. We're going to take the scale off as part of the preparation for the next stage. It's going to go into this, which is a long burner with five gas jets, that's going to sit on the, the sword is going to sit on this firebrick bed here. We've got to get that nice and flat, because if it doesn't lie flat on that, then as this heats, it can settle down or onto that warped surface and itself warp. The idea of this thing is we can heat the whole sword all at once, and that will, all going well, even out all the stresses, because we've been heating this, heating this up in little, little bits. So, this bit expands as it heats relative to its neighbouring bit, and where, where the join between the fast expanding part is, and it's colder neighbour, their stresses can build up. And then we've been whacking the hot bits with hammers, and that, of course, shifts metal around and, again, builds up all sorts of stresses. So, there are all sorts of stresses and strains in this that we don't know about. It's unpredictable. So, what we're trying to do now is even everything out, heat it all up to a temperature and let the whole metal relax and even out, and average out all the stresses, so there's no particularly stress point, because the next thing we can do after that is temper it, which involves plunging it into this big bath of oil. It's just like cooking oil, quite ordinary oil. It's going to go in, tip down like that, not the tang, and that's quite a heat shock. And if there is some bit where there's a big build-up of stress, and you then stress it loads more by suffering it, getting it to suffer this heat shock, you can then do serious damage to it. So, we don't want that. So, we're going to even it out, get it relaxed, and then temper it. I scraped off the scale with a motorised tool. Yes, not exactly medieval, but neither was having no apprentices to do it for me, and not having the plague. I don't like this. I see now why you asked me to step back. I had to shift the blades back and forth to get an even heat, because the spots of temperature immediately under the five burners were hotter than in between. We got the steel blades hot enough to recrystallise, and then let the stresses even out as they slowly cooled. This process is called normalisation, which is similar to annealing, but that takes hours. At the end of normalisation, the steel is fairly soft for steel, and all the stresses from hammering and deforming the crystals were, in theory, gone. The next process is a bit nerve-wracking. It's perhaps the most critical one. This is the quenching. I'm going to be taking my sword, and it will go in there and get extremely hot, and then I have to take it out from there. I'll put it onto its edge like that, so that it supports its own weight a bit better, bring it towards me, wearing tongs. It'll be very, very hot, slightly hotter than it needs to be for the quench, because it'll be cooling the instant it gets out, and all going well, once I've finally got it in position, it'll be down to the ideal temperature. With a second pair of tongs, all held in thickly gloved hands, I will then support its weight, bring it to the vertical without bending it, because it'll be very dangerously soft at this point, and then, in one swift movement, I dunk it into this oil here, quenching it. I then bring it up and down a bit, which speeds up the quenching movement. If I were to move it that way, like a paddle, the friction on the weight of the oil could actually warp it again. This will have the effect of hardening it, which is what you want on a sword blade, so that it can hold an edge, and so forth. But I won't be dunking in the tang, because we don't want that to go brittle. It then comes out, it's still very hot, and I will then hand over to Tom, because he's enormously more experienced than I am, and he will, if he sees any warp in it, very quickly get rid of that warp. He'll have about 15 seconds to get rid of the warp, otherwise we'll be in trouble. So, it's an important part of the process of getting a really good sword, but a bit nerve-wracking. But I thought that, you know, I really want to go through this, because it's such a critical part of the whole process. I can't really say I've forged a sword unless I've done the quench myself. I've had a rehearsal with a cold sword, and I'm going to watch Tom do his first, and then it'll be my turn. This time, we heat the sword hot enough such that the carbon in it goes into solution, and then we quench it and cool it so fast, that the carbon doesn't have time to come out of the solution and form perlite. Instead, it stays in the steel and hardens it. The outside of the sword cools fastest and goes hardest. If you were to cool it too fast by, for instance, dunking it in water, then the whole thing would go brittle right the way through. Saint Dunstan, patron saint of smiths, do not fail me now. I grab, I turn, I slide horizontally, I support in the middle, I bring vertical, get rid of one, bring up, straight down. Hold for a second, flame on, start waggling up and down, just touching the tang. Okay, the flame's off already. You tell me when. There's still a bit of glow in the tang. Tell me when. Suddenly, the workshop smelled like a chip shop. Okay, now. It's still going. Thank you, sir. You're welcome. Ah, I'm glad they didn't chicken out of that. So then, after it cooled again, I washed off the oil and salted it. It was all covered in scale again. This would have to come off. That's the thing I use. Ah, you have to lock it back before pushing it. You didn't tell me. It's not something I was really aware of. I needed the blade shiny because I needed to be able to see the exact colour of the surface of the steel to be able to judge its temperature in the next stage, the tempering. Tom went first to show me the way. Using a blowtorch, a little bit of the blade is heated until it turns what smiths call straw, the golden brown colour you see appearing here. Then, to avoid overheating, the next bit of the blade is heated to the same colour, and as this happens, conducted heat further increases the temperature of the bit just heated, which then turns blue. The blue follows you down the blade. You have to be very vigilant. Get any one bit too hot and there'll be a soft patch in the blade. Will I set fire to my socks? Now, I think what really upset me was that Katie actually found it funny, and there are some things that are difficult to forgive. Anyway, I now have a blue sword. It won't stay blue. It's been made blue so that I know that I've heated it to the right temperature. It may look really cool. You may think, oh, he's made a blue sword. That's great. That's really cool. I want one like that. But no, it's not going to stay blue. It'll be, it'll finish polished into a silvery sheen like a proper knight's sword. Yes! Had it failed that test, it would have cracked. So, it's a good test. Or stayed bent. Or stayed, oh yeah, or stayed bent. True, true. And it's, it has got a little bit of a wonk in it actually, you know. There. But that wonk was there before. That's not where I put my knee. So, it didn't come from what I just did. Huzzah! Hooray!