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  1. #1

    Default "No-PreHeat" Cast Iron Repair Technique

    Goodafternoon, everyone!!

    So, this is the latest of my Cast Iron welding videos... I repaired a "crack" in a transmission housing without any kind of a preheat, or a post-heat:

    Basically, Cast Iron cracks when it's heated and/or cooled rapidly, hence the reason why its usually pre-heated and allowed to cool slowly, but theres a chance that you can get around this by just not getting it very hot...

    I used a Nickel-99 electrode to make welds under 1" in length, which I then peened and allowed to cool completely, so that I could run my fingers directly over the weld, at which point I ran another short weld using the "back-stepping" technique, and repeated...

    This is a technique that can be used with any of the main electric arc welding processes... I've seen it done with TIG using stainless filler, and I've heard of people having success with it running MIG , again with stainless filler...

    Its just a little technique that I heard of, and had to try, I made a video about it and just thought i'd share... Doesnt seem like a bad way to weld a cracked engine block or something along those lines...

    Well, hope you guys like the video... Have a great week, everyone!!

  2. #2
    Join Date
    Jul 2010


    Quote Originally Posted by ChuckE2009 View Post
    Basically, Cast Iron cracks when it's heated and/or cooled rapidly, hence the reason why its usually pre-heated and allowed to cool slowly, but theres a chance that you can get around this by just not getting it very hot...
    Someone correct me if I'm wrong, but my understanding is that one of the reasons cast iron cracks after welding it with normal steel electrodes is because some of the carbon in the cast iron (which has more carbon than even high-carbon steel) dissolves into the weld deposit, in effect creating a "high-carbon steel" weld deposit.

    If the surrounding cast iron isn't pre-heated and post-heated, this "high carbon steel" weld deposit is effectively "quenched" by the surrounding cast iron, which quickly draws the heat out of the weld deposit.

    This "quenching" causes the weld deposit to get much harder and less ductile than normal mild steel, and when everything shrinks after the welding is done, the lack of ductility in the weld deposit causes cracks.

    This is one of the reasons nickel electrodes are used ... because nickel is far more ductile than cast iron or even mild steel, and because adding carbon from the cast iron into the (mostly nickel) weld deposit doesn't have the same hardening effect as with a normal steel electrode.

    Anyway, long story short, pre-heat and post-heat is probably always going to be the better bet...IMHO.

    Again, I'm far from an expert, so if this isn't accurate, someone please correct/clarify. And thanks for posting up ChuckE2009, your videos are great...

  3. #3


    Yes, I don't doubt that mild steel electrodes are far from an ideal way to weld cast iron (even tho I've welded it with 7018 before), but these are expensive nickel electrodes, Ni-99s to be exact, which helps with it.

    Im sure cracking is caused in part by what you describe, but its also largly because cast iron doesnt bend... It can't "distort" from heat input like mild steel can, thus then you weld it and dont manage the heat input, it "pulls" the weld apart just from stress.

  4. #4


    I think the point of the video wasn't how to do it the 'best' way when one had all the right equipment, etc. but how one could perform this task in less than ideal conditions when the immediate need was present.

    Keep 'em coming Lance! Once more the only thing I find wrong with your videos is there aren't enough of them. :-) I don't know what I'd do without you and Jody at weldingtipsandtricks.
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  5. #5
    Join Date
    Sep 2005
    Salem ,Ohio


    I do it 2-3 times a week. The rod specs set whether it needs preheat or not. I don't just use any old flea market rod or old rods from an old shop i get quality rods and most of them don't require preheat but i do cool it as slow as i can with insulation. I have had an ad on CL for months and get all kinds of different parts to fix....Bob
    Bob Wright, Grandson of Tee Nee Boat Trailer Founder
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  6. #6
    Join Date
    Mar 2011


    Always has been to two schools of thought concerning welding cast, hot & fast or slow & cool, nothing new here.
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  7. #7
    Join Date
    Oct 2009


    Cast iron cracks, especially on something like a cast iron engine block because the material around the weld is constrained. When the weld is made the material is superheated and expands (you can't weld it cold, your arc is around 2500 degrees) this expanding material has no where to grow so instead the material thickens, as it cools back down the thickened material tries to go back its original shape and pulls the surrounding material causing a crack.
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  8. #8
    Join Date
    Sep 2012
    seaford de


    I have tried the utp 55, and 99. And lots of other techniques. The very best I have found that I always use is tig weld silicon bronze. Its a bit too hard to drill but if your just repairing cracks...try it. I guarantee you'll never use anything else

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