Good point also Mr Slater.
A clean,properly perpared surface,That can be TEMPERATURE CONTROLLED before and AFTER the welding process is key.
Ideally,an oven to do the work inside would be wonderfull,but I know this aint fitting inside most ovens ,especially fully assembled.lol .
I have had real good luck doing "barn" repairs using an acetylene torch to heat the work area up before welding and helping to gradually bring down the tempurature afterwards. TOO quick of a cool down period causes problems.But Overheating the work area is also bad. cast will bust if cooled too quickly.(NEVER EVER "quench" with water afterwards.)
I am still curious to see what he is actually needing welded yet.That would help me determine on how to go about it.