Untempered martensitic steel, while very hard, is too brittle to be useful for most applications. A method for alleviating this problem is called tempering.

Tempering consists of heating steel below the lower critical temperature to impart some toughness. 

Age Hardening  •  Anneal for Machining  •  Full Anneal  •  Post Weld Heat Treating (Code Stress Relieve) 
Temper Modify  •  Stress Relieve  •  Temper Anneal