Austempering is a hardening process for carbon steel parts that uses a high temperature molten salt solution (at 500 to 800 ^oF) as a quench medium rather than oil or water (at 50 to 250 ^oF).  The benefits of austempering include less distortion of the parts in quenching and a microstructure with certain mechanical advantages compared to oil or water quenching.  Austempering is typically performed on carbon and alloy steel stampings, steel springs, and ductile iron castings.  Most stampings and springs are austempered in continuous furnaces, while most castings are treated in batch furnaces.

 An intermediate process between conventional oil quenching and austempering is martempering.  In this case the parts are quenched in special hot oil (at 350 to 450 ^oF) to produce a typical quench and temper microstructure, but with less distortion or risk of cracking for the treated part.  Martempering is often performed in batch furnaces on high hardenability alloy and tool steels and on parts with cross sections in excess of six inches.  The process is sometimes used with continuous hardening furnaces on small metal stampings that might otherwise be oil quenched or austempered.