Tempering
When the ball full quenching into martensite and then heated to 150 ° C-170 ° C tempering, with the tempering temperature increases, according to their internal organizational structure changes, in four stages:
1) martensite decomposition;
2) the transformation of retained austenite;
3) the transformation of carbides;
4) e-phase changes in the status and carbide accumulating and growing.
Secondary hardening: when steel contains more carbon atoms in the stage tempering fourth temperature zone (approximately 500 ~ 550 ° C) the formation of alloy cementite or special carbide. Carbide precipitation, will again raise the hardness, known as secondary hardening image.
Tempering Objective: To reduce or eliminate the quenching stress, improve toughness and ductility, hardness, strength, ductility and toughness of the appropriate co-ordination to meet the performance requirements of the ball.
Tempering characteristics of a carbon steel
The mechanical properties after the quench, often to measure the hardness. In the case of not fully hardenability along the workpiece cross-section hardness difference gradually decreases with the extension of the improvement of the tempering temperature and tempering time. Tempering characteristics of alloy steel, the basic carbon steel similar. Is different, but a secondary hardening steel can not be simply tempered with M parameters to characterize the degree of
(2) low-temperature tempering
The low-temperature tempering, also known as the Elimination of stress tempering. Tempering temperature range 150-250 ° C tempered martensite after tempering. The steel has high hardness and high wear resistance, lower internal stress and brittleness. Carburizing and hardening the surface of the parts, the hardness after tempering is generally 58-64HRC.
(3) tempering time
Tempering time should include the workpiece cross-section evenly reach the tempering temperature required heating time and tempering hardness completion of organizational changes in the time required by M parameters to meet the requirements, if you consider the elimination of internal stress, you still should consider tempering temperature the stress relaxation time.
Stress relaxation-based low-temperature tempering time should be longer than the tabular data, long up to tens of hours. Secondary hardening alloy steel, tempering time should be determined by experiments based on carbide transformation process. Contain more residual austenite by secondary quenching eliminate, but also to determine the tempering times.
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