Are 40 rear axle housings cast iron?

[mdemeglio]

Anyone ever hear a loud CRACK when welding a 40 axle housing?

I was welding perches on the rear axle housing the other night and within about 5 seconds I heard a huge "crack" - happened on both sides and I was being very careful to keep the heat under control (short beads, 120A). I figured for sure I would see a crack somewhere from the heat but didn't..

Any thoughts? I might try to fill it with water and see if anything leaks out - it's just the bare housing - no cracks are visible to the naked eye though.

 

[mtweller]

I cranked on mine when welding the perches - 240V max setting. The housing is cast steel. Not sure what that crack might be???

R