In this process, steel is heated above the upper critical point (above the transformation range) and then quenched in a hot-oil, molten-salt, or molten-lead bath kept at a temperature of 150-300 °C.
In this process, austenite is transformed to martensite by step quenching, at a rate fast enough to avoid the formation of ferrite, pearlite, or bainite.
The metal part is then removed from the bath and cooled in air to room temperature to permit the austenite to transform to martensite.
Martempering is a method by which the stresses and strains generated during the quenching of a steel component can be controlled.
In martempering, steel is heated to above the critical range to make it all austenite.