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  • Cast Iron welding: comments on welds

    I am building a custom exhaust, the space is very limted so I could not use a flange to bolt to the turbo, rather I had to weld directly to the cast iron flange on the turbo. I never welded on cast iron before so I was on use on hwo to go about it. I was talking to a number of people on the best means to weld it and took some from each of them. First I cleaned the cast iron phosphoric acid etch, washed it, then gorund down the surface to get it smoother, after used some isopropyl alcohol, then I heated it up to burn out some impurties, all I had was a B-tank so i am not sure if I got it hot enough.

    The materials used were cast iron, stainless steel 304 tubing and mild steel filler, argon back purge (figrured could not hurt) then covered it in sand. While tig welding I went thru a few tungsten's, it was spitting like crazy, would that be silicon, carbon, or other remaining foregin materials? Here is a couple pics of my results, is this what a cast iron weld looks like? Should do anything else?







  • #2
    From what little I know, I think you should have used a high nickel filler, like Ni99, which will help prevent the carbon in the cast mixing with the chromium in the stainless forming extremely brittle carbides.

    I think the stainless to cast weld may haunt you down the road especially with as hot as that flange is going to get, coupled with the engine vibration.
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    • #3
      Aggreed, I would think it will be a short lived weld. Hind sight is 20-20 but I would have made a flange as well instead of using the cast part. Or at least use and intermediate stub tube of mild steel welded to the cast flange, then somehow jointed to the stainless part.
      -Aaron
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      • #4
        Thanks guys, I am sure in the end thats its not going to last but worth a shot. Some told me to use NI rod, others mild steel. If I had the room I would have used a flange that bolted on to the flange I welded the tubing to, if you follow me. I only have about 1/8" clearance between the chassis and the exhaust, had to replace the studs with bolts.

        While I was welding I contcentrated the torch on the castiron, added the filler, kept feeding the filler as I brought the torch up to the stainless. I know its all molten, but thought it may help to "neutralize" the CI from the SS.

        Anything that could be done to help improve a durabilty? LOL

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        • #5
          There is actually.... cut off the stainless pipe, use a short piece of mild as aerometal said, weld the cast to the mild using NI99 filler (with pre/post heat) then weld the mild to the stainless using 309 or 312 filler. it's the only way you're going to have a durable weld that's not going to come back to haunt you IMHO....
          Last edited by bretsk2500; 11-02-2008, 02:26 PM.
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          • #6
            I think if you had done it just like you did only used 309 filler it would have been just fine and no worries...I have done this rod on cast iron a bunch on auto stuff. It works great if done in a cast iron type procedure (pre-heat, weld, post-heat)
            Mild on cast won't usually last very long at all but the tubo could even be cast steel and you may get lucky. I would say it is at least a higher grade than a normal exhaust manifold.
            A pic of the entire thing would help as well.

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            • #7
              Originally posted by FusionKing View Post
              I think if you had done it just like you did only used 309 filler it would have been just fine and no worries...I have done this rod on cast iron a bunch on auto stuff. It works great if done in a cast iron type procedure (pre-heat, weld, post-heat)
              Mild on cast won't usually last very long at all but the tubo could even be cast steel and you may get lucky. I would say it is at least a higher grade than a normal exhaust manifold.
              A pic of the entire thing would help as well.

              What if I were to grind some of it out, weld over it with 309? Or just cover it with 309?

              When you are asking the entire thing, what are you referring to?

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              • #8
                Originally posted by eyecandy View Post
                What if I were to grind some of it out, weld over it with 309? Or just cover it with 309?

                When you are asking the entire thing, what are you referring to?
                I was referrring to the rest of the part you welded, those are just close ups and I thot maybe we could tell more if you stepped back a bit...that was this morning tho. When I look at this pics now I'm thinking...why does he think that is cast iron??? It looks like it has been cut out and the #'s look stamped. If it is steel then you may be fine but 309 would'a been better to me still. Did you spark test it? Just wondering here.
                As for grinding and all, why not just do it over ? You won't do a "cap" and save it, if its cast. I'm thinking it ain't tho looking at the toes. Just my ramblin' thoughts

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                • #9
                  looks like a casting to me. I think the lines on the sides are from grinding a casting flash off rather than being punch pressed out or forged. Still might be cast steel.

                  1/8 body to header tube is real tight when you add in heat and there tends to be a lot of heat with turbos. Is there anything to burn near the tubing?
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                  • #10
                    Originally posted by Vicegrip View Post
                    1/8 body to header tube is real tight when you add in heat and there tends to be a lot of heat with turbos. Is there anything to burn near the tubing?
                    it is tight but doable if you use a nomex sheet...
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