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Controlled rolling and controlled cooling is an important production process for advanced bearing steel. Through the controlled rolling or rolling after the fast cooling eliminates the reticulated carbide, to obtain the appropriate preparatory organization, can shorten the bearing steel spheroid annealing time, refine the carbide, improve fatigue life. In recent years, Russia and Japan use low temperature control rolling (800 ℃ ~ 850 ℃ below), after rolling with air cooling plus a short period of annealing, or completely eliminate the spheroid annealing process, you can get qualified bearing steel organization.
Eutectic steel or high-carbon steel hot processing before if you have a fine grain organization or in the process of processing can form a fine grain, then in the (0.4 ~ 0. 6) melting temperature range, in a certain strain rate, showing superplasticity. The U.S. Naval Postgraduate School (NSP) conducted 650°C temperature processing tests on 5 2100 steel showed that true strain 2.5 at 650°C did not fracture. Therefore, it is possible to replace high-temperature processing with 650 ℃ temperature processing and combined with the spheroid annealing process, which is important to simplify the equipment and processes, energy savings, and improve quality.
In improving the quality of spheroid annealing, to obtain fine, uniform, spherical carbide and shorten the annealing time or eliminate the spheroid annealing process research has progressed, that is, the production of coils using two tissue annealing, 720 ℃ after drawing ~ 730 ℃ recrystallization annealing to 760 ℃ of tissue annealing. This can get low hardness, good spheroidization, no reticulated carbide organization, the key to ensure that the intermediate drawing surface reduction rate of ≥ 14%. The process makes the efficiency of the heat treatment furnace increased by 25% to 30%. Continuous spheroidized annealing heat treatment technology is the development direction of bearing steel heat treatment.
Expand the application and replace the traditional bearing steel. Such as fast carburizing bearing steel, by changing the chemical composition to improve the carburizing speed, where the carbon content from the traditional 0.08% to 0.20% to 0.45% or so, carburizing time from 7 hours to 30 minutes. The development of high-frequency quenching bearing steel, with ordinary medium-carbon steel or medium-carbon manganese, chromium steel, high-frequency heating and quenching to replace the ordinary bearing steel, both simplify the production process and reduce costs, and improve the service life. Japan developed GCr465, SCM465 fatigue life than the SUJ-2 2 to 4 times higher. As a result of high temperature, corrosion, lubrication conditions in the environment using more and more bearings, the past use of M50 (CrMo4V), 440C (9Cr18Mo) and other bearing steel can not meet the requirements, the urgent need to develop good processing performance, low cost, long fatigue life, can be suitable for different purposes and uses of bearing steel, such as high temperature carburizing steel M50NiL, easy to process stainless bearing steel 50X18M and ceramic bearing materials, etc.
