Tempering

It is a process that comes after hardening at a temperature under AC1 (steel). The martensitic structure obtained after hardening is to fragile, that's why every hardening is followed by tempering, which stabilize the martensite and relieve the tensions that appears after hardening and sometimes when is needed transform the martensite in bainite with a lower hardness but a high resilience and toughness(for steel, controlled atmosphere is usually not needed, but sometimes for higher temperatures (over 550°C), the nitrogen based atmosphere (N2, or N2+H2 under 5% - forming gas) are used. The tempering process for aluminums alloys is called aging and the result consists of compounds that increase the hardness and decrease the resilience of the material.

The tempering process is accomplished in the following furnaces: