MARTEMPERING PROCESS IN HEAT TREATMENT :

Martempering or interrupted quenching is a hardening operation that produces martensite. It is not tempering. In this method the steel is heated to the hardening temperature and then quenched in a medium, usually in a salt bath, having a temperature, just above that where martensite starts to form (usually from 150*C to 300*C). The article is held until it reaches the temperature of the medium but not long enough to austenite decomposition. It is then cooled further to room temperature in air and sometimes in oil. The austenite is transformed to martensite during the last period of cooling to room temperature. This treatment will provide a structure of martensite and retained austenite in the hardened steel.

Martempering has the following advantages over the conventional quenching :

1. Less volume changes occur due to the presence of a large amount of retained austenite.

2. Less warping since the transformations occur almost simultaneously in all parts of the article.

3. Less danger of quenching cracks appearing in the article.

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