In another thread someone mentioned iron that shattered or broke when quenched.

What could cause this?

Thermal shock. Quench too aggressive.

Also possibly the iron was hammered too cold, or otherwise somehow a crack was forged into the iron. Could also be a combination of factors.

also certan types of steel will do this (air hardening tool steels come to mind) ive had this happen it wasnt a explotion but it did shatter!! i had a chizel that i made from s7 it was just below visable heat i thaught i could cool it down ... well it came apart in about 12 pieces...

Have you ever noticed how pop cans expand when frozen? This has to do with the molecules lining up or something, when something changes rapidly like that, any number of things can occur, and even if it does not break immediately, the first time an additional shock is applied, look out!! I spent 2 hours on a spring steel (coil) hold down as a new bs, and of course when it was done, I quenched it, first time I set it in the anvil, tapped it down, it lierally exploded into 4 pieces, it was at that exact moment that I remembered David Robinson's class that I had taken, and the fact that he always left his finished product sitting on the floor to cool, only quenching for tempering etc.. hard way to learn, (seems to be the only way for me) but valuable, I have never had that kind of problem again.

Have you ever noticed how pop cans expand when frozen? This has to do with the molecules lining up or something, ...

It has to do with water expanding when it freezes. Same reason ice floats.

Good Luck!

Water is very strange that way; iron does not go against the "cold things shrink, hot things expand" rule but does change when it goes through a phase change, which hardening involves.

I have an unknown piece of steel rod in the shop. I put it in the forge a while back thinking to make a tool from it as it is very hard. I forged it to a fish tail (making a hot cut chisel) and after I hardened it, it fractured into a buch of pieces, similar to a car windshield, but did not break apart. Further hammering on it cold will break off the little pieces though.

if ya put the wrong stel in water it will shatter say h13 or A2 they will tipicaly shater like a glass firecracker its not a good thing and it can punch a hole through a plastic 5gallon bucket no problem be careful and use the right quenchant with the right steel