The ordinary bearing steel

 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.

Japan developed GCr465, SCM465 fatigue life of 2 ~ 4 times higher than SUJ - 2. Due to the high temperature, corrosion, lubrication conditions under the environment of using bearing more and more, the use of M50 (CrMo4V) and 440 c (9 cr18mo) bearing steel can not meet the use requirement, be badly in need of development of processing performance is good, low cost and long fatigue life, can suitable for different purposes of bearing steel, such as high temperature carburizing steel M50NiL, easy processing 50 x18m stainless bearing steel and ceramic bearing material, etc. For GCr15SiMn steel hardenability low vulnerability, our country has developed high hardenability and hardenability bearing steel GCr15SiMo, its hardenability HRC 60 or higher, hardenability J60 25 mm or more. L10 GCr15SiMo contact fatigue life and L50 respectively 73% and 68% higher than that of GCr15SiMn, under the same conditions of use, made of G015SiMo steel bearing life is GCr15SiMo steel twice. In recent years, our country has also developed can save energy, save resources and impact resistant GCr4 bearing steel. Compared with GCr15 GCr4 impact value increased by 66% ~ 66%, the fracture toughness increased by 67%, L10 contact fatigue life increased by 12%. GCr4 bearing steel with high temperature heating and surface hardening heat treatment process. Compared with the hardening GCr15 bearing steel, GCr4 steel bearing's life has improved significantly, can be used to override high-speed train bearing. The bearing steel is mainly to develop in the direction of diversification and performance with high degree of cleanliness, two. Improve the cleanliness of bearing steel, reduce the oxygen content in the steel, in particular, can obviously prolong the life of bearing. Oxygen content by 28 PPM down to 5 PPM, the fatigue life could be extended by one order of magnitude. In order to prolong the service life of bearing steel, people over the years has been committed to the development and application to reduce the oxygen content in the steel refining technology.

Through unremitting efforts, low oxygen content in bearing steel has been reduced from 28 PPM in the 1960 s to 90 s of 5 PPM. At present, the minimum oxygen content of bearing steel can be controlled at about 10 PPM. Bearing used changes in the environment for the diversification of bearing steel must have a performance. Such as device speed increases, the need to use (below 200 ℃) quasi high temperature bearing steel (usually using in SUJ2 steel on the basis of the increase of Si content, add V and Nb methods to achieve the purpose of the softening resistance and stable size); Corrosion applications, the need to develop stainless bearing steel; In order to simplify the process, should develop high frequency quenching and short-term carburizing bearing steel bearing steel; In order to meet the needs of aerospace, should develop high temperature bearing steel.