Rolling bearing steel is mainly used in the manufacture of rolling elements and rings. Since the bearing should have a long life, high-precision, low heat, high speed, high rigidity, low noise, high wear resistance and other characteristics, thus requiring bearing steel should have: high hardness, uniform hardness, high elastic limit, high contact fatigue strength, toughness necessary, certain hardenability in atmospheric corrosion lubricant. To achieve the above performance requirements, bearing steel chemical composition uniformity, non-metallic inclusion content and type, carbide size and distribution of decarbonization and other demanding. Bearing steel development to quality, performance and overall direction of many varieties. Bearing steel according to the characteristics and application environments are divided into: carbon chromium bearing steel, carburizing bearing steel, high temperature bearing steel, stainless steel and special bearing special bearing materials.
To meet the high-temperature, high-speed, high load, corrosion, anti-radiation requirements, the need to develop a series of new bearing steel with special properties. To reduce the oxygen content of bearing steel, the development of vacuum smelting, remelting, electron beam remelting bearing steel smelting technology. And large quantities of bearing steel smelting by the arc melting, develop into all types of early outside plus refining furnace. Currently, the use of furnace capacity greater than 60 tons at the beginning + LF / VD or RH + casting + rolling bearing steel production process, in order to achieve high-quality, high efficiency, low energy consumption purposes. In terms of the heat treatment process, the car bottom furnace, bell furnace developed into a controlled atmosphere continuous annealing furnace heat treatment. Currently, continuous heat treatment furnace up to 150m, processing and production of steel ball bearings organizational stability and uniformity, decarbonization layer is small, low energy consumption.
Since the 1970s, along with economic development and industrial technological progress, expand the scope of application of the bearing; and the development of international trade, but also to promote the development and application of bearing steel to international standards and new technologies, new processes and new equipment, efficiency , high quality, low cost technology and process equipment supporting emerged. Japan and Germany etc built a high purity, high-quality bearing steel production line, the steel production increased rapidly, dramatically improving the quality and the fatigue life of the steel. Japan and Sweden, the oxygen content of bearing steel production dropped to below 10ppm. The late 1980s, Japan Sanyo Special Steel's advanced level of 5.4ppm, reached the level of vacuum remelting bearing steel.
Contact fatigue life of the bearing of the uniformity of the steel structure is very sensitive. Increase the cleanliness (reduce steel content of impurity elements and inclusions), prompting the non-metallic inclusions in steel and carbide fine and uniform distribution, can improve the contact fatigue life of the bearing steel. Organization bearing steel using state should be evenly distributed fine carbide particles tempered martensitic matrix, so organizations can give the required performance of the bearing steel. Carbon bearing steel main alloying elements carbon, chromium, silicon, manganese, vanadium.
How to get the ball bearing steel production organization is an important issue, controlled rolling and cooling is important advanced bearing steel production process. Through the controlled rolling or cold rolling fast eliminate network carbide, to get the right preparation tissue, can shorten bearing ball annealing time, refine carbides, improve fatigue life. In recent years, Russia and Japan, using low temperature controlled rolling (800 ℃ ~ 850 ℃ or less), plus air cooling after rolling a short anneal, or completely cancel spheroidizing, you can get a qualified organization bearing steel. Bearing steel 650 ℃ temperature processing is also new technology. Before eutectoid steel or high carbon steel having a thermal processing if the tissue or fine grain can be formed during processing of fine grains, then (0.4 to 0.6) within the range of the melting temperature, at a certain strain rate, exhibit superplasticity . US Naval Institute (NSP) for 52100 steel were 650 ℃ temperature processing tests showed that at 650 ℃ 2.5 true strain fracture does not occur. Therefore, it is possible to 650 ℃ temperature processing instead of processed and combined with the high temperature ball annealing process, which simplifies the equipment and processes, save energy, improve quality are important.
In the heat treatment terms, to improve the quality of ball annealing, to obtain small, uniform, spherical carbides and shortening the annealing time or cancel ball annealing process research progress has been made, namely, wire rod produced using the two organizations annealing, the drawing After 720 ℃ ~ 730 ℃ to 760 ℃ annealing recrystallization annealing organization. So you can get a low hardness, ball, and no carbide network organization, the key to ensure that the intermediate drawing reduction rate ≥14%. The process of heat treatment furnace efficiency increased by 25% to 30%. Continuous ball annealing technology is the development direction of bearing steel heat treatment.
