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Thread: Welding stainless to mild steel

  1. #1
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    Welding stainless to mild steel

    To tig thin SS to mild steel would ER70-2 rod or one of the stainless 308,309 or 316 be a better choice for filler rod. It is thin tubing for exhaust system so looking for the least brittle joint so it is less likely to crack.

    Thank you.

  2. #2
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    Re: Welding stainless to mild steel

    Canoecruiser,
    Thanks man.
    I found some .040 SS I had in a tube here. Can't remember the grade and the thin rods aren't stamped but I got it done and think it will be plenty strong.

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    Re: Welding stainless to mild steel

    My go to filler for steel to stainless is ER312. The general rule of thumb if it is steel to steel, steel to stainless steel, or stainless steel of unknown composition, then 312 is a wise choice. 309 is a close second.
    Weld like a "WELDOR", not a wel-"DERR"
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    Re: Welding stainless to mild steel

    @ shovelon - 312 is solid. Ever experience any cracking issues with the filler on steel-to-SS apps for service temperatures above 800F? Know a few fabricators in motorsports who prefer 309 for high temp applications. 312 does wet out nicely.
    Last edited by ManoKai; 07-25-2016 at 05:14 PM.
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    Re: Welding stainless to mild steel

    Quote Originally Posted by ManoKai View Post
    @ shovelon - 312 is solid. Ever experience any cracking issues with the filler on steel-to-SS apps for service temperatures above 800F? Know a few fabricators in motorsports who prefer 309 for high temp applications. 312 does wet out nicely.
    Not yet. I have had more cracking issues with 309, and 312 solved it. Especially when I don't know the alloy. I got to a point where I just gave up on 309L.
    Weld like a "WELDOR", not a wel-"DERR"
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    Re: Welding stainless to mild steel

    Quote Originally Posted by ManoKai View Post
    @ shovelon - 312 is solid. Ever experience any cracking issues with the filler on steel-to-SS apps for service temperatures above 800F? Know a few fabricators in motorsports who prefer 309 for high temp applications. 312 does wet out nicely.
    In the boiler industry we weld our dissimilar metal(carbon to stainless) with Inconel. 309 went out years ago due to cracking issues. One thing that helps with 309 welds was the development of the EPRI (electric power research institute) prep. Look up EPRI, some good reading

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    Re: Welding stainless to mild steel

    Quote Originally Posted by Showdog75 View Post
    In the boiler industry we weld our dissimilar metal(carbon to stainless) with Inconel. 309 went out years ago due to cracking issues. One thing that helps with 309 welds was the development of the EPRI (electric power research institute) prep. Look up EPRI, some good reading
    Good information on the inconel. The cracking was fusion line cracking due to carbon dilution from the carbon steel with the 309? Would EPRI recommend inconel alloy 625?

    Here is a good read on the subject. https://nickelinstitute.org/~/Media/...als_14018_.pdf
    Weld like a "WELDOR", not a wel-"DERR"
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    Re: Welding stainless to mild steel

    @ Showdog75 - Thanks for the f/b. Quite familiar with EPRI. Great group. What grades of SS are you welding? What grade of Inconel? Boiler service temps/pressure? Know Inconel 740H and Haynes 282 is used to by the Oak Ridge Boys for ASME tubes operating at 1500F.

    @ shovelon - that's a 25yr old paper. The documents calls out 309 filler for mild to stainless for temps above 800F. What Showdog75 is saying is that ASME experiences proved that 309 is filla non grata for welding mild to SS. Check out this presentation, Matls for A-USC Steam Boilers. 740H's 3pts of C and 25pts of Cr Alloy 740 give it great resistance to oxidation, carburization, and sulfidation.
    Last edited by ManoKai; 07-26-2016 at 10:57 PM.
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  9. #9
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    Re: Welding stainless to mild steel

    310 is also good. It's about 25% chrome and 20% nickel, which makes it very ductile.

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