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Heat treating/Welding question

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  • Heat treating/Welding question

    I have two 4140 square blocks 1.25" X 4". I need to join/weld them end to end to make an 8" block. Currently they are annealed. Should I weld first, then heat treat, grind, or wait until they're heat treated? I know the risk of warping at the joint, but which way poses the least risk?

  • #2
    Heat treating includes processes such as annealing, hardening, normalizing, stress relieving, tempering, and others. If by "heat treating" you mean hardening, then you should weld the two pieces together before hardening. Welding hardened steel is a virtual guarantee of cracking the material due to stress in the heat effected zone.


    • #3
      You're gonna have a big discontinuitty in the weld zone that may or may not accept heat treating depending on filler metal. Regardless of filler metal you will still have the welded microstructure interrupting the grain of the parent metal. I you wish to merely join the two hunks of metal all you have to sweat is selecting a suitable filler metal. If you wish the weld to have as heat treated properties comparable to the parent metal, then you have a weld engineering problem on your hands.

      There are weld electrondes and filler metal suitable for 4340 but they are expensive for those that deliver full properties and I would imagine 10 lb is the minimum quantity sold. Figure $50 to $100 for 10 lb of stuff for a weld joint that won't heat treat the same as the parent metal.

      You could prep and forge weld. That's an autonomous weld indistinguishable from the parent metal and if done right will accept full heat treatment.

      I bet finding a contiguous piece is looking like a better alternative, huh??
      Last edited by Forrest Addy; 02-22-2012, 04:21 AM.


      • #4
        I would weld (with 4140 filler), then stress relieve. Straighten it on a press if necessary. Then heat treat.

        Originally posted by Forrest Addy
        That's an autonomous weld indistinguishable from the parent metal
        "autogenous" (fusion) weld . I don't think even an experienced blacksmith would recommend forge welding it
        Last edited by lazlo; 02-22-2012, 11:21 AM.
        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


        • #5
          Thanks guys. I wasn't really interested in having the filler material wind up with the same RC after hardening, but rather something that will survive the hardening process without a great deal of warping. I just need a reasonably parallel block, so it'll wind up on the surface grinder after hardening.

          I have a batch of chuck stops heading to the heat shop already, so I thought I might just throw this contraption in with 'em, but then again if it's gonna cause a bunch of problems, who needs hardened parallel blocks anyway?