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Discussion Starter #1
Quick question. I've been collecting parts kits and build tools for years now and am finally getting around to getting started. One question is on heat treating. I don't have a kiln so mapp torch is my method for heat treating. I've noticed that most tutorials suggest after the initial heat and quench to reheat to about 750 degrees and allow to cool. Ak-builder suggests baking in the oven at 400 degrees for an hour for the 2nd stage. Is one method better or will both work?
 

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I was wondering the same thing. My limited understanding of heat treating steel is the idea of heating it until it is bright red and quenching it in either water or oil. This is supposed to make it very hard, but also brittle. This is followed by heating it until it turns blue, or maybe just begins to show dull red, and then allowing it to cool in the air. This is to anneal it and give it toughness, rather than remaining hard and brittle.

When I went to school, one of the projects in the shop was to make a center punch on a lathe. We then heated in bright red and quenched, followed by the annealing process. We didn't have a kiln or a way of measuring the temperature. The instructor gauged our work by the color of the metal.

I was wondering if the AK Builder instruction using 400 degrees F in an oven for one hour accomplished the annealing by using a lower temperature for a longer period. Perhaps someone with some knowledge in metallurgy can give us a better explanation.


abukamoon
 

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Ok and I'm assuming you've had good results with the oven/ broil method? This seems like a pretty critical step so I'm trying not to F it up.
 

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No problems as of yet. It should be getting the metal to the 600-700 degree point in there. Once it been tempered, it even has a different sound to it when struck.
 

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All depends on what steel alloy the reciever is made of. A general rule of thumb when heat treating non-stainless tool steels is to get the steel bright cherry red. The iron and carbon molecules will "unhook" from each other at about 1500-1600 degrees F. When this happens the bright orange steel will become non-magnetic,use a speaker magnet glued to a dowel or something to test, if the magnet sticks, go hotter, increase heat until the magnet will not atract the steel then quench in oil. this a cheap and surefire way of knowing the steel is hot enough to quench. as far as tempering temperature, IMO 400 degrees is not hot enough, I temper my blades at 400 and they yield about 55 to 58 rockwell C. This is too brittle for a receiver
IMO. The steel should be "tough" rather than "hard", judging color of the oxidation layer is fairly accurate. When tempering, clean the steel very well until it is shiny and run it up to 450 or so degrees, the color range will go from straw or a golden color which is hard and brittle to pinkish which is less hard but tougher, to a bluish color which is slightly hard and rather tough, then a deep peacock blue which is spring temper, kinda hard but very tough. This is where I would stop if I were doing a receiver. Your mileage may vary.
 
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