Jaz

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About Jaz

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    Fitness, engineering, guitar
  1. Forgive me if I just completely misunderstand and am being ignorant. Are you saying that you're wondering what to do once you quench your steel, in terms of keeping it at some "safety" temperature before you temper it (giving the oven time to cool down)? (or instead just use the kitchen oven as the heat treatment oven cools) I haven't really heard of this, from the information I've looked at, you don't need to keep your quenched steel at any temperature after you've quenched it, and you can wait as long as you want before tempering it. If cracking is going to occur, it will occur during the quench, not during the tempering process, and this is due to the stresses you mentioned, thermal stresses, etc. Now as far as I know when you temper your steel you are probably going to be moving into the recovery temperature range for the steel, where the residual stresses etc will be mostly eliminated from the quench, along with the carbon diffusion which makes the cementite grow coarser. So you shouldn't have to worry about what to do between the quench and temper stage. I may be completely wrong here, in which case I look forward to the learning experience haha, I know some of those steels you listed have "special" quirks with heat treatment.
  2. Hey thanks for the replies, I've been busy this last week and so I didn't get to see the comments until now. I asked my teacher the question about austenization and he reaffirmed that it depends on many variables, I forgot the exact number for an "average" steel that he gave me, it may have been 20m, or possibly 2h haha, so I can't remember which. Either way, he is a good guy, but his knowledge on this subject seemed sketchy, I'm pretty sure it doesn't take that long. In terms of doing experiments in the lab: The class isn't a metallurgy class by any means, its a materials class, and covers different topics relating to materials science, a few of the units we covered had information pertaining to blacksmithing, which I ate up :) We covered phase diagrams and calculations involving phase diagrams, knowing what phases are present and in what concentrations, and where, as well as the compositions of each phase (lever rule stuff). Strengthening mechanisms were covered as well, like why alloying elements add strength, grain boundary size, dislocation density etc. We did some stuff on phase transformations, which included the time temperature transformation curves etc. So in our labs we never get to do any real practical heat treating, since that is such a small part of the course. We did a lab where we performed tensile tests with different steels, and had a lab where we tested some different treated steels as well (it was pretty cool). Otherwise we did some fractography stuff in the last lab, which was really interesting. Our labs are always prepackaged, I could probably get some time with some of the machines if I really put some effort into it, like a hardness testing maching (don't we all wish we had one? :) ) as well as the microscopes and tensile test machines. Generally access is limited to people working on their fourth year design projects, as otherwise every guy who liked working with tools would be using the machines, and they are needed by the staff. If you guys have any theoretical questions or calculations you're interested in, feel free to ask. I understand the material we covered, but I know if I don't use it I'll lose it, so that would be an excellent way to keep me fresh, and also a way to learn the details better. Thanks again for the replies.
  3. Firstly, I haven't been on here in a long time. But summer is coming around and I want to get back to finishing my forge. Anyways. I'm a mechanical engineering student, and I've had quite a bit of course material relevant to metallurgy, but I still have a few practical questions. First of all, when Looking at a time temperature transformation phase diagram of eutectoid steel (0.76 wt % C), before cooling we always assume that the material is 100% austenite. If I have a piece of eutectoid steel, so with 100% pearlite microstructure, at room temperature, assuming negligable time to reach above the eutectoid temperature (~727C) how long does the specimen take to reach 100% austenite? I know it will depend on the size of the specimen, for this case assume its a typical size bowie. Looking at a phase diagram it's impossible to tell, since all the points on the phase diagram are based on the assumption of equilibrium being reached. Also, when hardening, is the general goal to have 100% martensite when quenched, I know this would result in the highest hardness, but I don't know what the typical procedure is in most cases. In my view it would seem simpler when tempering to know that you are starting out with 100% martensite than with say, 50% pearlite, 50% martensite. Since then you get into issues with the pearlite becoming coarser as diffusion accelerates, etc.