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Rean Lubbe

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  1. So onto the next part, just wrapping a mild steel blank in a container (i use a piece of pipe) will work fine, but please note that this whole thing will not produce the best blade ever. The reason I did it for this was two fold - First, I liked the patterning in the wrought iron, and wanted a knife with that pattern. So carburising then folding a bunch of times to yet the carbon homogenous (an even spread of it throughout the blade) didn't appeal as it would make the pattern a lot finer, and I liked it the way it was. Second was that I didn't know any better at the time. It definitely works, but you end up with a blade that has an absolute outside that is probably like 2% carbon (waaay too much) and that gets less as it goes deeper. So it's really difficult to figure out exactly how to heat treat it because depending how deep you've ground, there's different amounts of carbon. It works, but it's not close to modern steel. On the cemetite part, the reason for the fancy word being used often in knife steel metallurgy is because most if the other stuff in steel (chromium, tungsten, vanadium, molybdenum etc.) will also form carbide, so people use it to specifically refer to iron carbide. Would you like me to go into steel being a solution (like salt dissolved in water), or have I hit the preach limit? Again, please know I'm not trying to be a condescending A-hole, and I expect you know most of what I said there allready. It's just easy to misunderstand a small part of something, and then the whole thing doesn't make much sense
  2. Hey @Carlos Lara There's a fair bit here, so here goes. I'll try to explain the whole concept a bit more - thanks for the interrest. You probably know most of this allready, but it's easy to get some misconceptions about things that bite you in the butt later when you know enough about something that there's just one part that was missed and it completely throws the thing off. Long story short im not trying to be condenscending by going into basics, just running through the whole thing from the ground up. When the blade broke, I polished it and etched it with ferric chloride (its an acid that leaves a black patina, but discolours steel more or less depending on what state it's in, if it has carbon in it and has been hardened it leaves a deep black colour - martensite, has carbon but isn't hardened often leaves a fuzzy grey - pearlite, and if it doesn't have much carbon in it tends not to do much - ferrite). So my steel isn't actually that colour, it just had a patina applied so I could see where I had carbon and where it had hardened. People usually do this to make a hamon in a blade more visible as well. Onto the carburizing part, it doesn't make it harder or anything else and isn't a heat treatment like case hardening, it just adds more carbon. That's it, the end. It's just something you would do to turn a very low carbon steel (or iron in my case - the definition of steel is just iron with enough carbon in it, when people talk about iron in this context they just mean it doesn't have enough carbon to be called steel) into steel that can be hardened. Onto case hardening as a heat treatment: it literally just means hardening the outer part of something (its case). You could do this in the way I did it by adding carbon to the outer part through cementation (the technique of having your low carbon stuff in a very carbon monoxide rich environment at high heat for a good while, the carbon gets absorbed and forms "cementite" which is just a fancy word for iron carbide) and then heat treating it the normal way: heat it up, quench it, temper it. When you do it this way only the outer shell gets hardened because only the outer shell has carbon. Another way is to take a shallow hardening steel like 1095 and just heat treat it normally, it needs to go from hot to cold *really* fast to harden. So what happens is that the outer bit cools down fast enough to harden, but because the inner part cooled more slowly, being way on the inside, it didn't harden. That way you also get something that only has the outer part hardened. The third way is the one you'd usually find in a kobuse katana, where you wrap some high carbon steel around a core of lower carbon stuff and weld them together. Then only the outer part would harden since only the outer part has enough carbon. So "case hardening" is the heat treatment, and we can make it happen a couple of different ways, while "carburizing" is only adding the carbon, and in this case was done specifically with cementation. More to come, but I gotta take my daughter to extra math class
  3. Hey @Carlos Lara Sorry for not writing you a reply yet, I definitely will. It'll probably be a lengthy one.
  4. @David Weaver I'm in South Africa, so our selection isn't nearly as good as either the states or Europe. The only big thing we have going for us is that the country isn't that big and it's pretty centralized in the middle (and smallest) province, so things are relatively close by. Bohler's south african branch is about 60 miles from where I live. There's about 3 sources for silver steel here, but all buy from the same importer, and thus have the same batches, so if mine is dodgy I expect ill just go back to my standard of 52100. I'm a bit surprised you get such good results with W1, we don't get an equivalent here so I can only go on hearsay and reading, but doesn't it have massive fluctuation in carbon content? IMO, you can't go wrong with 52100 for cost vs performance and reliability. I have to ask, what do you do to get those results? I also push the boundaries of "best practice" a little, but use a thermostat controlled kiln. Personally I soak at the high end of recommended temp, then just before I take it out to quench I push an extra 15 degrees celcius (takes around 20 seconds for the kiln to get to it). The reasoning behind it being that it takes a bit of time for grain to grow, which I want to avoid, and the time-frame is short enough that i don't see any grain growth, but the little extra heat makes a noticeable difference. Please note I don't do this for anything above 0.8 carbon, as I've learned the hard way that brittle plate martensite is indeed a thing. Thus the asking how you get those
  5. @Jerrod Miller nope, ill give it a look right now, thanks! *edited* ok, I've read through it. Thanks a bunch, that makes sense. I had it at welding heat which would be around 1100 celcius for almost two hours, so 1.6mm sounds in the right area. I have to admit the error function math is a bit beyond me, but I will tackle it and attempt to understand to the point where I can run my own equations. Thanks very much again for that. I have a couple of questions regarding the calculation if you don't mind. I expect the purpose of the calculation is to predict the carbon percentage at a specific point, meaning that in the example the area at 1.5mm depth would have 0.8%C, as opposed to an average carbon content and a penetration depth, meaning that there would be an average of 0.8 in the carburized area and the area would extend up to 1.5mm. Is this correct?
  6. I cannot thank you enough for all this info. I recently got some silver steel and was looking for some decent info on HT seeing as the min/max terraces on both chrome and manganese seemed pretty wide. This is my first post, been lurking for quite a while. @David Weaver I have to say I'm surprised that there would be graphitization, I would have expected you'd need a lot more silica for that to happen. My knowledge on it isn't enough to say though, and what you said about being intentional for self lubricating properties makes sense, surely it could be managed if was the purpose of the exercise. @Alan Longmire I've had some experience with carbon migration, and know it's supposed to be very quick (if memory serves Verhoeven also mentions it in his book on HT) but I have found it to be notably less in practical terms. I expect the rate mentioned is for moving randomly, being if you had one carbon atom how much would it move around (potentially back and forth), not what distance would it cover. And that a hellova lot of movement can be done without much actual diffusion taking place (for instance from a high carbon to low carbon area). The reason I say this is because I case hardened a wrought iron blade, putting it in a canister with calcium carbonate and fine charcoal, and shoved it into the forge when I was welding up some billets. It spent about 2 hours at more than 1000 celcius in there. Following the carbon diffusion diagrams it should have been pretty uniform carbon distribution. Unfortunately the blade cracked in the quench (full water quench, and outsude couple of micron would have been close to cast iron I expect. Live and learn). I took the opportunity to polish and etch to see how deep my carbon penetration was, and is was notably shallower than I expected. Calipers said 1.6mm for the dark parts (extremely thick blade. Spine was around 5.2mm). I figured it may have just been the fact that its a very shallow hardening steel (being from wrought iron and all) and that what I was seeing was martensite, with the core still having carbon, just not showing on the etch since it hadn't hardened, but grinding past the black layer showed a drastic reduction in sparking on the grinder. I'm sure that the diffusion rate is scientifically correct, but I believe translating it into practical terms of how much diffusion took place to be less predictable.
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