useualy to harden somthing its a rapid cooling proccess, Again I'm not to sure with alloy but the Idea is to lock molicul's in an ulterd state by cooling them as rapidly as posible and if it's cool slowly they return to there original state i.e. soft, and often if you go to a hardening mob they will chuck one'off's in with larg nummber job's and do it for cash.