Austempering

The component to be hardened is primary austenised and after that quenched into a lead or salt bath held at just above the martensite transformation temperature. The component is held in the bath till the bainite transformation is completed. This is then eliminated from the bath and cooled in air to room temperature. The bainite so produced is somewhat softer than martensite of similar carbon content & distortion is minimum. Also the austempered steel has improved shock resistance and low notch sensitivity. The procedure of austempering is depicted in Figure. Austempering is often limited to section thickness of 20 mm. Austempering is applicable to a few plain carbon steel and needs facility of molten salt bath. This might be regarded a disadvantages over quenching & tempering.

                                                   Figure: Austempering Shown on the TTT Curve