Tempering is a metal treatment process. After hardening, the meal piece need to re-heating to an appropriate temperature, hold this temperature degree for a while, and then slowly or rapidly cooled. Generally, tempering is used to reduce or eliminate the stress of hardened steel, or to reduce its hardness and strength, to improve ductility or toughness. According to different requirements for the meal piece, there are three different types of tempering which are Low Temperature Tempering, Medium Temperature Tempering, High Temperature Tempering. When increasing the temperature of tempering, the hardness and strength decreased, the ductility or toughness increased gradually.
The characteristic after tempering including:
1.Got martensite, bainite, residual austenite unbalanced ( ie instability) organization.
2.Bigger internal stress
3.After quenching, the mechanical properties of the metal piece can not meet the requirements. Therefore, tempering is necessary to improve the organizational stability and enhance the mechanical properties.
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