Martempering (also called marquenching, step quenching, or interrupted quenching) is a specialized heat treatment process designed to reduce distortion and cracking risk while achieving high hardness in steel parts. This process is particularly valuable for larger parts with thick or dramatically variable cross sections where tolerances are critical.

During martempering, parts are heated to austenitizing temperatures and then quenched into molten salt baths held just above the material’s martensite start point—generally around 350°F, depending on the alloy. Parts are held in this quench just long enough for the core and surface temperatures to equalize. They’re then pulled from the quench and further cooled in still air at room temperature.

This controlled approach promotes the formation of martensite (the hardest form steel can take) while significantly reducing the stress that causes warping and cracking in traditional quenching processes. 

Parts that respond best to martempering: bearings, gears, tooling, dies, and shafts—especially those made from high-quality, highly-hardenable steels where dimensional precision is paramount.