dissimular metals welding

[JOHN R. TIPTON]

I AM TRYING TO WELD SOME STEERING BOXES MADE OF A CAST STEEL OR CAST IRON AND WE ARE PUTTING A 1020 MILD STEEL FITTING ONT OIT. WE ARE HELICARING ITAND WONDER WHICH ROD WE SHOULD USE. WE WHERE TOLD THAT UTEKTIC 680 WAS AN EXCELLENT ROD FOR THIS AND WONDER WQHAT YOU THINK ABOUT THAT AND ALSO IF WE SHOULD BE PREHEATING THE PART.

THANKS

JOHN R. TIPTON

[Kevin Disney]

John,

Had to do some research on your question concerning welding cast iron and mild steel. I will try to make this brief as possible, because there was quite a bit of information available. I will list this in sequence –

Preparation – if the casting is used it may be necessary to heat the area to be welded up to 750 F for a short period or at a lower temperature (400 F) for an hour, to decompose any oil or grease that has penetrated the casting.
Preheating – it is general accepted that a preheat of at least 400 F is preferred. A softer and more ductile weld is obtained if the casting is preheated and cooled very slowly. Wrap the casting in a fireproof material immediately after welding.
Welding Process – HeliArc (TIG) would be my choice, but wire (MIG) should also be adequate. Use low currents.
Filler Metal – There are several choices here. The use of a high nickel wire (ERNi) seams to be the most common. The addition of nickel to the weld reduces the hardening of the weld, use a normal weave technique. An alternate would be stainless steel wire (ER309).
Bead Shrinkage and Stresses – steel shrinks more than cast iron, so when the weld bead cools residual stresses can cause cracking. To minimize this problem you weld in short lengths, 15-30 sec. then wait a few minutes. Another way is to peen the weld before it has a chance to cool and contract, using a ½” to ¾” ball peen hammer.
Postweld Treatment – None, just wrap up and cool slowly.