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Technical Mig weld cast iron?

Discussion in 'The Hokey Ass Message Board' started by blowby, Jun 2, 2016.

  1. blowby
    Joined: Dec 27, 2012
    Posts: 8,306

    from Nicasio Ca

    Many say no, some say yes. This guy does a nice job on an exhaust manifold with SS wire, skip to the 10 minute mark to see the actual welding. I myself mig welded a toilet flange buried in a concrete slab a few years ago, so far successfully holding up under the tremendous strain I subject it to.


    Hnstray likes this.
  2. I'm not saying its right.... but about 10 years ago I took my old snap on mig welder and welded up a crack in the block of a friends boat. 350 block that was cracked from a freeze plug down the side of the block. I ground the crack open, heated it up with a torch and then welded it up with my mig welder. We figured what was there to lose? it ran good, just leaked water from not being winterized right and cracked the block, and it was that or swap the motor. This was basically free. Not saying it was the right way or if I even did it right way to weld cast iron. but its still holding after 10 years.
    el Scotto, Atwater Mike and Hnstray like this.
  3. sunbeam
    Joined: Oct 22, 2010
    Posts: 5,607


    I've had better luck welding cast with stainless than nickel.
  4. HAMB Metallurgist here, welding cast iron is tough because of the high carbon content. The issue is you get iron carbides (very hard and brittle) that form near the fusion line. When the weld cools, it shrinks and pulls at the fusion line. Since the iron carbides have little ductility, you get cracking.

    The high pre-heat and slow cooling help. So does peening the weld, as it helps reduce those shrinkage stresses, but must be done very quick after welding. The use of more ductile filler (stainless steel as in hte OP's example) also helps. There is no easy sure-fire solution.
    williebill, 302GMC and kevinwalshe like this.

  5. Atwater Mike
    Joined: May 31, 2002
    Posts: 10,800

    Atwater Mike

    Amen...I've arc welded it with nickel rod. (the '60s, when information was taken on the run...)
    Grind out a furrow; heat with oxy/acet, then weld the furrow: Big block Chev exh manifolds, 'tilted' the outlets. Worked for a few years, then the customer bought headers...
  6. I have a Lincoln "mini" mig and filled a couple of holes in my exhaust manifolds by pre-heating with a small propane bottle/torch.
  7. I think preheating is the key. Welded quite a few exhaust manifolds with a mig, and so far they are hanging out. It seems like it's common with guys running turbos to cut and relocate flanges on exhaust manifolds. They might have some insight.

    Sent from my SM-S920L using H.A.M.B. mobile app
  8. I would imagine that the stainless wire has a fairly high nickel content which would help. Having done a good bit of structural welding with core wire I discovered that you can get wire in a lot of different alloys and strengths. I would not doubt that you could buy wires that is the same as ni-rod if you looked.

    I personally am pretty set in my ways and still prefer to stick weld cast, or braze it with brass filler is I don't have access to a stick welder.

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