Tempering

Operation method:
The quenched steel is reheated to a temperature below Ac1, and after being kept warm, it is cooled in air or oil, hot water and water.

Features:
1. Reduce or eliminate internal stress after quenching and reduce deformation and cracking of the workpiece.
2. Adjust the hardness, improve the plasticity and toughness, and obtain the mechanical properties required for the work.
3. Stabilize the workpiece size.

Application:
1. Keep the steel high temperature and wear resistance after quenching with low temperature tempering, and use medium temperature tempering to maintain high impact toughness and plasticity when increasing the elasticity and yield strength of steel under certain toughness conditions. Mainly, when there is sufficient strength, temper with high temperature.
2. The general steel should be avoided at 230~280 degrees, and the stainless steel should be tempered between 400~450 degrees, because there will be a temper brittleness.

Cold treatment

Operation method:
The quenched steel is cooled to -60 to -80 degrees or lower in a low temperature medium (such as dry ice, liquid nitrogen), and the temperature is uniform and then taken out to room temperature.

Features:
1. The whole or most of the retained austenite in the hardened steel is converted into martensite, thereby improving the hardness, strength, wear resistance and fatigue limit of the steel.
2. Stabilize the structure of the steel to stabilize the shape and size of the steel.

Application:
1. After quenching, the steel should be cold treated immediately and then tempered at low temperature to eliminate internal stress during low temperature cooling.
2. Cold treatment is mainly applied to compact tools, gauges and compact parts made of alloy steel.

Carburization

Operation method:
The steel is placed in a carburizing medium, heated to 900-950 degrees and insulated to obtain a carburized layer of a certain concentration and depth on the steel surface.

Features:
Improve the surface hardness, wear resistance and fatigue strength of steel parts, and the heart remains in a tough state.

Application:
1. For low carbon steel and low alloy steel parts with a carbon content of 0.15% to 0.25%, the depth of the carburized layer is generally 0.5 to 2.5 mm.
2. After carburizing, quenching must be carried out to obtain martensite on the surface to achieve the purpose of carburizing.