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Annealing steel The change at the high temp where it becomes non-magnetic is a phase change. The ferrite changes to austenite which is a completely new configuration of the iron atoms. The crystal structure changes from a "body-centered cubic structure" to a "face-centered cubic structure". When this happens, the carbon is free to migrate as if in solution and it finds new places to reside. When quenched from this temp, the austenite changes to martensite, a smaller, hard, wear resistant structure, and traps the carbon creating a highly stressed but very hard matrix. Subsequent tempering reduces stresses and "softens" the steel --up to a point. For full annealing, you need to reach that critical temperature and let it cool very slowly (as you've apparently done.) Be aware of the de-carburized skin that you've created with all this heating in air. When the steel is at the high temperature the carbon atoms are moving freely about and when one of them hits the surface it runs off with the first oxygen slut it bumps into (they're so seductive). Gone forever. So diy heat treating usually creates an unhardenable layer on the steel. Be prepared to grind that layer off, down to the good stuff, after tempering. Is the ruining by grinding just moving to a less hard, but still hard spot on that continuum? Yes. When it's time to harden, how long do you have after you take the steel from the fire -- how quickly will it cool down? I don't want to oil soak it inside the house, and it will take 30 seconds or so to get outside. Is it worth an ash bucket for that length of time? Unless you really *want* the divorce (and the insurance claim for the total loss), do this outside. Wear gloves that will resist fire, face/eye protection and keep a fire extinguisher handy. Move quickly from the heat to the quench (you really don't want to be running around with a piece of glowy metal). Ron Hock |
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