Do the physical properties of 4340HT (249-301 BHN) chage when torched? - Page 2
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  1. #21
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    I wonder what the hardness would be if the parts were simply retempered.

    As for the high hardness, I expect the self quench is a much more severe quench than using a quenching medium.

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    It shouldn't do the rest of the part any harm to have them re-tempered to the same temperature that was used for the original heat treat spec.

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    Quote Originally Posted by doug925 View Post
    UPDATE:

    The parts arrived, and were hardness tested in the gouged out surface, and at the top of the counterbore diameter.
    The result was Rc65 or higher!
    I didn't think that 4340 would get anywhere near that high, even with the extra carbon from the lance.

    The parts were picked up, and the PO is on hold until my customer decides on the annealing/re-heat treating.

    Doug.
    Anneal, glass bead blast (to not close up any cracks) and then at least dye penetrant inspect, or magnaflux.

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    Quote Originally Posted by gbent View Post
    . . . depends on the skill of the guy with the torch. But since he tore up the seat, I'm guessing the skill level wasn't high. . .
    Well, how would you torch the head off a large diameter bolt in a 2 5/8" deep counterbore without damaging the seat? (This is an honest question. I'm always looking for tips & technique).

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    Quote Originally Posted by digger doug View Post
    Anneal, glass bead blast (to not close up any cracks) and then at least dye penetrant inspect, or magnaflux.
    If (other) Doug cuts at least 1/8" below the last of the flame damage, shouldn't that wipe out any likely cracks? It wouldn't hurt to do a NDT on the seat before reinstallation, but the area under the bolt is compressively loaded, and that tends to not be a crack initiation/propagation risk.

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    Don't know how you are going to fixture this. My thought is to treat the affected area as torch cut slag. When I saw that alloy and a torch used I had a bad feeling about this project. Woodpecker lips is the term I remember from this sort of situation.
    Any chance of using some sort of grinding to get through the first layer? Grinding stuff can be pretty cheap, and maybe even shaped to get it close enough to cut to finish later. Pilot/sleeve in the through hole? Maybe that idea is crazy, dunno.
    Good luck!

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    Quote Originally Posted by Milland View Post
    If (other) Doug cuts at least 1/8" below the last of the flame damage, shouldn't that wipe out any likely cracks? It wouldn't hurt to do a NDT on the seat before reinstallation, but the area under the bolt is compressively loaded, and that tends to not be a crack initiation/propagation risk.
    That's quite an assumption, one that I wouldn't want to take.

  10. #28
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    Quote Originally Posted by Gordon Heaton View Post
    Well, how would you torch the head off a large diameter bolt in a 2 5/8" deep counterbore without damaging the seat? (This is an honest question. I'm always looking for tips & technique).
    Very carefully. I have seen guys who can torch a threaded stud out of a hole and not nick the threads. The secret is controlling the heat transfer between the two parts. It may take several pauses to let everything cool down. Better bet is to drill the head off the bolt

    Dennid

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    Quote Originally Posted by eaglemike View Post
    Woodpecker lips is the term I remember from this sort of situation.
    Any chance of using some sort of grinding to get through the first layer?
    The gouges in the seat, are almost 1/2" deep in some parts.
    I did recommend re-tempering, or anneal / normalize / heat treat as a quick, and fairly inexpensive process. (compared to grinding or attempting to machine in place.)

    If I had a horizontal mill, and some Greenleaf or Kennametal, ceramic button inserts, and the mill to run them, I would attempt....

    Doug.

  12. #30
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    Quote Originally Posted by Modelman View Post
    Very carefully. I have seen guys who can torch a threaded stud out of a hole and not nick the threads. The secret is controlling the heat transfer between the two parts. It may take several pauses to let everything cool down. Better bet is to drill the head off the bolt Dennid
    I've done that myself, but not on a 2 1/2" bolt. There had to be a significant thread depth, and that would require a lot of heat and movement of the flame. Just seems like size matters.


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