Marquenching

Very massive parts, or those having varied dimensional characteristics, may benefit from this process to avoid cracking and ensure uniform hardness results.

Marquenching is also known as stepped quenching or interrupted quenching.  Marquenching is a method by which the stresses and strains generated during the quenching of a steel component can be controlled. In this process, the steel is heated above the upper critical point (above the transformation range) and then quenched in a salt, oil, or lead bath kept at a temperature of 300 °F - 575 °F. The workpiece is held at this temperature above the martensite start (Ms) point for enough time to allow the center to cool to the same temperature as the surface. After that, it is cooled in air or oil to room temperature.  The steel is then tempered. 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.