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Thread: 76 R75/6 Subframe

  1. #1
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    76 R75/6 Subframe

    The right side diagonal leg on my subframe is slightly bent and I would like to straighten it. What is the drill for cooling the steel after it has been heated in order to best preserve its strength? Thanks

  2. #2
    Administrator 20774's Avatar
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    Someone will correct me, but it's either quenching or annealing.

    http://en.wikipedia.org/wiki/Quenching
    http://en.wikipedia.org/wiki/Annealing_(metallurgy)

    But after reading the annealing site, I think you want to quench it.
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  3. #3
    Curmudgeon nrpetersen's Avatar
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    Assuming it is a fully heat treated aircraft steel alloy like 4130 (and not just normalized 4130), you might be best off just cold or warm working it. To do a full re-heat treat would require you to get it to about 1500 degF, quench it in water (which makes it full hard but potentially brittle), and anneal it to perhaps 900 degF (which will give it some ductility).

    Or you could just assume that the bent portion is already annealed from production 30 years ago, and just cold work it back to being straight. A lot of 4130 light aircraft parts are simply cold or warm formed, and not fully hardened. The only exceptions might be the engine mount, and even that would still be unusual for most light aircraft.

    You really don't want to start heat treating steel without knowing what you are doing. If it was mine (and I know some things about heat treating) I'd cold work it - maybe using a torch if necessary, but not letting it get to any near-red temperatures. Chrome moly steel (~4130) is really good stuff but you don't want to get it too hard or it can get brittle.
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

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