Steel melts at about 2500 F. Aluminum and magnesium at about 1250 F. I have never seen steel burn, but I have seen magnesium and aluminum burn. Quite a sight. New engine blocks are a bit of a nightmare for firefighters. Basically, if yer gonna put water on a burning block, you'd better have enough to KEEP putting water on that block until the temperature is lowered below its ignition point or it can and sometimes does explode. The 'shrapnel' from that can cause serious injury/death.