The Ball several tempering methods and the time control skills

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Tempering
When the Ball full-quenching into martensite and then heated to 150 ° C-170 ° C tempering with increasing tempering temperature, change its internal organizational structure is divided into four phases:bearings high speed
1) decomposition of the martensite; 2) residual austenite transformation; 3) carbides shift; the gathering grew 4) changes in the e-phase state, and carbides.
Secondary hardening: to form in the tempering temperature zones of the fourth stage (about 500 ~ 550 ℃) when the steel contains more carbide forming elements, of alloy cementite or special carbide. Of these carbide precipitation, will once again raise the hardness, called secondary hardening image.
Tempering purpose: to reduce or eliminate the quenching stress, improve toughness and ductility, hardness, strength, ductility and toughness, fit to meet the performance requirements of the steel ball.
1 carbon steel tempered characteristics
 Mechanical properties, after tempering of the quenched steel is often the hardness measured. Along the workpiece cross-section, in case of not completely hardenability hardness difference with t he improvement of the tempering temperature and tempering time prolonged gradually decreases. The alloy steel tempering characteristics, similar to the basic and carbon steel. Can not simply tempering M parameter to characterize the degree of secondary hardening steel.special bearing
2 low-temperature tempering
Low-temperature tempering, also known as "stress relief tempering". The tempering temperature range of 150-250 degrees Celsius, and the tempered martensite after tempering. Steel having high hardness and high wear resistance, but the internal stress and reduce brittleness. Parts of the carburized and surface hardening, the hardness after tempering is generally 58-64HRC.
3. Tempering time
Tempering time workpiece cross-section should include the heating time required to achieve the tempering temperature evenly and press M parameters to achieve the requirements of the the tempering hardnes s of time to complete the organizational changes required, considering the elimination of internal stress, you still should consider tempering temperature under stress relaxation time.steel ball bearing
Stress relaxation-based cryogenic tempering time longer than the tabulated data, up to tens of hours long. Secondary hardening high-alloy steel, tempering time should be based the carbide transformation process determined by experiments. When contain more residual austenite, and rely on secondary quenching eliminate, should also determine the a tempered number of times.