I remember my first attempt at hardening some cable guide thimbles. No Idea what the steel was they had been made out of they came to me already cut to length all I had to do was machine a slight relief bevel to one end then heat quench and then temper.
So I heated one up then quenched it then picked it up to heat it again but dropped it on the floor it shattered like so much glass. Oops I'd say I had that one a little too hot before quenching. the rest of them I allowed to cool just a little before quenching then heated and tempered them all was good. But I'll never forget the look on the wife's face when she saw the dozen pieces of that shattered specimen