Martensite start temperature, written Ms, with Mf marking the martensite finish. Ms falls as carbon and most alloying elements rise: roughly 450 °C in a plain 0.2 percent carbon steel and closer to 200 °C at 1 percent carbon. Martensite forms progressively as the part cools below Ms, which is why marquenching holds parts just above it so surface and core can equalize before transformation begins.
Keep the marquench oil about 20 degrees over Ms or you start making martensite in the tank and lose the whole point.
Also heard as
- Ms point
- martensite start
Related terms
Martensite
The hard, needle-like phase that forms when austenite is quenched fast enough to trap its carbon.
Marquenching
Quenching steel into hot oil or salt just above Ms, holding to even out temperature, then air cooling.
Retained austenite
Austenite that fails to transform during the quench and survives at room temperature inside hardened steel.
Austempering
Quenching steel into a salt bath above Ms and holding it until the austenite fully transforms to bainite.