Two full tempering cycles with a complete cool in between. During the first temper, retained austenite in tool steels and carburized parts can transform to fresh, untempered martensite as the part cools, and the second temper relieves and toughens it. High-speed and high-alloy tool steels routinely get two or three tempers, and many aerospace specs require double tempering for high-strength steels.
M2 gets a triple temper at 1,025, cool to room temp between each one or don't bother.
Also heard as
- double temper
- triple temper
- multiple tempering
Related terms
Tempering
Reheating hardened steel below its lower critical temperature to trade some hardness for toughness.
Retained austenite
Austenite that fails to transform during the quench and survives at room temperature inside hardened steel.
Secondary hardening
A rise in hardness when certain alloy steels are tempered around 500 to 600 °C, from fine alloy carbides.
Sub-zero treatment
Chilling hardened steel well below room temperature to turn retained austenite into martensite.