Austempering:

The component to be hardened is initialy austenised and after that quenched into a lead or salt bath held at just over the martensite transformation temperature. The component is held in the bath till the bainite transformation is finished. This is after such removed from the bath and cooled in air to room temperature. The bainite consequently produced is somewhat softer than martensite of similar carbon content and distortion is minimum. The austempered steel also has enhanced shock resistance and low notch sensitivity. The procedure of austempering is depicted in following figure. Austempering is often restricted to section thickness of 20 millimeter. Austempering is appropriate to a few plain carbon steel and needs facility of molten salt bath. It may be observed a disadvantages over tempering and quenching.

Figure: Austempering represented on the TTT Curve