Jim, you generally need to have some idea of what cast iron material you are trying toweld. Some are unweldable. Most cast irons are grey cast iron, and as long as it is a clean casting, this can be welded quite well.
If you can give a high pre-heat, then this is the best way to go. Pre-heat to around 500°C and weld with either C/Steel rods (E7018) or better with Ni based consumables specially made for welding cast iron. (e.g. ENi-CI)
If high pre-heats are not feasible, (Under these circumstances brazing is often also not feasible.) then perform the welding using the Ni based consumables with low heat inputs. The HAZ will be brittle, but if you keep the heat input low, then the HAZ is very narrow and does not result in such a big problem.
Hope this helps
Regards
Niekie Jooste
Hello Jim,
If the pipe is Durite (chilled cast iron) it really isn't weldable. If it's not Durite there are several oprtions. The best process to use in regards to getting a homogenous weld w/o leaks is the hot process torch. It combines the benefits of brazing with the advantages of Ni filler metal. Proper prep is critical here. No corners can be cut.
There are of course the Ni/Fe electrodes in various form and the arc brazing electrodes. The Al bronze electrodes provide good ductility and high tensile strength. The Al bronze SMAW electrodes run similar to Al SMAW electrodes so expect to move rather quickly.
HTH,
Steve
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