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Annealing Hardened steel

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  • Annealing Hardened steel

    As some of you know, I was boring and polishing stock A manifolds for B carburetors. I lost my bore plug, locater pin which I didn't consider really satisfactory. I don't have the access to steel I once had so I have to improvise. I was wondering what I had around that I could use when I saw an old sector gear that I missed on my last scrap drive. Aha! Sez I, and tried in the bore. It fit rather loosely, but with a wrap or two of tape to snug it up, it will work. I chopped the geared end off which gave me a piece of 1 1/8 round stock with a squared end. I checked the hardness with a file. OOOPPZ The file bounced off! It had to be annealed to cut. This is to make it fit a 3/4" Bridgeport Collet. I'll have to turn it down. Because of it's hardness and the interrupted cut due to the squared end it wasn't going to be easy. It had to be annealed, period. I figured that the gas barbecue would come in handy for this. I cranked it up to it's full heat and then I played a MAP gas torch over the shaft at the same time. Before long, it had gone through the heat colors, yellow, brown, dark blue, purple, then light blue and glowing red. I had a bucket of ashes ready to receive it and I let it cool for a few hours, tested it with a file and while it's still somewhat hard, it is workable.

  • #2
    Annealing temperature varies with different steels. For example, A-2 is a high carbon high chrome tool steel that reaches a hardness of Rc64 It is used when high wear resistance and stability is needed. To reach that hardness, you heat the steel to 1750 degrees, preferably in a controlled atmosphere furnace and allow it too cool in room temp air. If you decide you want that chunk of steel soft again, you must heat it to 1600 to 1650 degrees F, then cool it slowly (40 degrees per hour) When you get to 1000 degrees you can let it cool faster. Even lesser alloys, 4140, 6150 must been heated to 1500 degrees and cooled slowly. Your gas BBQ may reach over 1000 F. 1500 degrees will produce a bright red color. If you have access to a surface grinder and a spin fixture, that would be your best bet to grind that 3/4" diameter shank. Most home machinists use O-1 tool steel. It can be heated with an acetylene torch and quenched in a large metal bucket of oil.


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