New technology and the development direction of the bearing steel
Bearing steel is mainly used in the manufacture of rolling bearings of rolling body and ring.
Due to bearing should have long life, high precision, low calorific value, recommend suite, high rigidity, low noise, high abrasion resistance and other characteristics, and therefore requires bearing steel should have: high hardness, uniform hardness, high elastic limit, high contact fatigue strength, must toughness, hardenability, bearing company in the atmosphere corrosion resistant performance of lubricant. In order to achieve the performance requirements, the uniformity of the chemical composition of bearing steel, non-metallic inclusion content and type, strict carbide particle size and distribution, decarburization, etc.
Bearing steel in general to develop in the direction of high quality, high performance and many varieties. According to the characteristics and application environment of bearing steel is divided into: high carbon chromium bearing steel, high temperature carburizing bearing steel, bearing steel special bearing, stainless bearing steel and special materials.
In order to adapt to high temperature, high speed, high load, corrosion resistant, radiation resistant engineering machinery bearing request, need to develop a series of new type of bearing steel with special performance. To decrease the oxygen content of bearing steel, the development of the vacuum smelting, esr, electron-beam remelting of bearing steel smelting technology. And bulk import bearings bearing steel smelting by electric arc furnace smelting, early developed into all kinds of smelting and refining outside the furnace.
At present, the use of early capacity greater than 60 tons + LF/VD and RH refining furnace, continuous casting and rolling process of bearing steel production, in order to achieve the purpose of high quality, high efficiency, low energy consumption. In terms of heat treatment process, from the car type furnace, bell type furnace developed into the continuous controlled atmosphere heat treatment of annealing furnace. At present, the longest continuous type heat treatment furnace is 150 m, processing production of bearing steel spheroidizing stable and uniform, the decarburization layer is small, low energy consumption.
Since the 1970 s, when economic development and industrial technology progress, application scope of bearing; And the development of international trade, and promote the internationalization of bearing steel standard and new technology, new technology and new equipment development and application of high efficiency, high quality and low cost of supporting technology and process equipment arises at the historic moment. Japan and Germany are built high cleanliness, high quality of bearing steel production line, make the output of steel increased rapidly, the quality of the steel and greatly improve the fatigue life. Japan and Sweden, production of bearing steel oxygen levels fall below 10 PPM. In the late 80 s, the advanced level of Japanese sanyo special steel company is a 5.4 PPM, achieved the level of vacuum remelting bearing steel.
Bearing contact fatigue life is sensitive to the uniformity of steel group. Improve cleanliness (reducing impurity elements and inclusion content in steel), non-metallic inclusions in steel and carbide tiny uniform distribution, can improve the contact fatigue life of bearing steel. Bearing steel using state organization should be tempered martensite matrix uniformly distributed on the fine carbide particles, such organizations can give the performance of the bearing steel needed. High carbon steel bearing the main alloy elements carbon, chromium, silicon, manganese, vanadium, etc.
How to get the ball organization is an important problem in bearing steel production, controlled rolling of cooling is one of the important production technology advanced bearing steel. By controlled rolling and cold rolling, quick to eliminate carbide network and obtain appropriate preparation group, bearing steel ball annealing can shorten the time, carbide, improve the fatigue life.
In recent years, Russia and Japan with low temperature rolling (below 800 ℃ ~ 850 ℃), using air cooling after rolling and annealing, short time or completely cancel the spheroidizing annealing process and they can get qualified bearing steel group. Bearing steel 650 ℃ temperature processing and new technology. If before the eutectoid steel or high carbon steel hot working with fine grained organization or in the process to form a fine grained, in melting temperature range (0.4 ~ 0.6), under a certain strain rate, exhibiting the plastic. U.S. naval institute (NSP) to 650 ℃ temperature of 52100 steel processing test showed that true strain under 650 ℃ 2.5 does not break. Therefore, likely to 650 ℃ temperature processing instead of high temperature processing and combining with spheroidizing annealing process, the simplified equipment and processes, to save energy and improve the quality.
On the side of heat treatment, improve the quality of spheroidizing annealing, small, uniform, spherical carbides, and shorten the annealing time or cancel the spheroidizing annealing process have the progress of research, namely the wire rod production by two organizations annealing, after drawing of 720 ℃ ~ 730 ℃ to 760 ℃ of recrystallization annealing annealing. So I can get a good low hardness, spheroidizing, no carbide network organization, the key to ensure the middle drawing degressive rate of 14% or higher. The process to improve the efficiency of the heat treatment furnace by 25% ~ 30%. Continuous spheroidizing annealing heat treatment technology is the development direction of bearing steel heat treatment.
All countries in the research and development of new type of bearing steel, expand application and instead of the traditional bearing steel. Such as rapid carburizing bearing steel, by changing the chemical composition to increase the speed of carburizing, including carbon content from the traditional 0.08% ~ 0.08% to 0.08%, carburizing time reduced from 7 hours and 30 minutes. High frequency quenching bearing steel is developed, with the common medium carbon steel or carbon manganese, chrome steel, to replace the ordinary bearing steel with high frequency quenching, simplify production process and reduce the cost, and improve the service life.