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The use of vacuum exercise in aerospace
Source: Bearing network time: 2014-07-14
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In order to get used to the needs of high temperature, high speed, high load, corrosion resistance and radiation resistance; demand to develop a series of new bearing steels with special functions. In order to reduce the oxygen content of bearing steel; carry out vacuum exercise, electroslag remelting, electron beam weight The training skills of molten steel and other bearing steels. The training of large-volume bearing steels is smelted by electric arc furnaces; it is developed into various types of primary furnaces and furnaces. At present; the selection of capacity is greater than 60 tons of primary furnace + LF / VD or RH + continuous casting + Continuous rolling process produces bearing steel; in order to reach high quality, high power, low energy consumption. In the heat treatment process; from the bottom of the furnace, the cover furnace to the continuous controllable atmosphere annealing furnace heat treatment. Current; continuous heat treatment furnace The longest type is 150m; the spheroidization arrangement of the produced bearing steel is stable and uniform; the decarburization layer.
Since the 1970s, with the economic development and industrial skills advancement; the expansion of the use of bearings, and the development of international trade; has promoted the internationalization of bearing steel specifications and the development and application of new skills, new processes and new equipment; High-quality, low-cost supporting skills and process equipment came into being. Japan and Germany have built high-purity, high-quality bearing steel production lines; the steel output value is agile; steel quality and fatigue life is large The progress of the range. The oxygen content of bearing steel produced in Japan and Sweden fell below 10ppm. In the late 80s era; Japan's Shanyang Special Steel Company's leading level was 5.4ppm; reached the level of vacuum remelted bearing steel.
The contact fatigue life of the bearing is very sensitive to the uniformity of the steel arrangement. It improves the cleanliness (reduces the impurity elements and impurities in the steel); promotes the fine and uniform distribution of non-metallic impurities and carbides in the steel; can improve the bearing steel The fatigue life of the touch. The arrangement of the bearing steel should be such that the fine-grained carbide particles are evenly distributed on the tempered martensite matrix; this arrangement can give the bearing steel the required function. The primary in the high-carbon bearing steel Alloying elements are carbon, chromium, silicon, manganese, vanadium, etc.
How to obtain the spheroidization arrangement is an important issue in the production of bearing steel; controlled rolling and controlled cooling is an important production process of leading bearing steel. After controlled rolling or rapid cooling after rolling, the reticulated carbide is eliminated; suitable preparation arrangements can be obtained; Bearing steel spheroidizing annealing time; refine carbide; improve fatigue life. These years; Russia and Japan use low temperature controlled rolling (800 ° C ~ 850 ° C or less); after rolling, use air cooling plus short time annealing; or completely cancel the ball Annealing process; qualified bearing steel arrangement can be obtained. 650 °C temperature processing of bearing steel is also a new skill. If the eutectoid steel or high carbon steel has fine grain arrangement before thermal processing or can form fine grains during processing; Then in the (0. 4 ~ 0. 6) melting temperature scale; at a certain strain rate; superplasticity occurred. The US Naval Research Institute (NSP) marked 5 2100 steel at 650 ° C temperature processing experiments; at 650 ° C The true strain 2. 5 does not crack. Therefore, it is possible to replace the high temperature processing with 650 ° C temperature processing and combined with the spheroidizing annealing process; this is of great significance for simplifying equipment and processes, saving energy and improving quality.
In the aspect of heat treatment; progress has been made in improving the quality of spheroidizing annealing; obtaining fine, uniform, spherical carbides and shortening the annealing time or canceling the spheroidizing annealing process; that is, the wire rod production is selected twice to arrange annealing; After the 720 ° C ~ 730 ° C recrystallization annealing to 760 ° C arrangement annealing. This can get low hardness, good spheroidization, no network of carbide arrangements; the key to ensure that the central pull reduction rate ≥ 14%. The process improves the power of the heat treatment furnace by 25% to 30%. The continuous spheroidizing annealing heat treatment skill is the development direction of the bearing steel heat treatment.
Countries are researching and developing new type of bearing steel; expanding and replacing traditional bearing steels, such as fast carburizing bearing steels; modifying chemical composition to improve carburizing speed; the carbon content is 0.08% to 0. 20% progressed to about 0. 45%; carburization time was shortened from 7 hours to 30 minutes. Developed high-frequency hardened bearing steel; used medium carbon steel or medium carbon manganese, chrome steel; replaced by high frequency heating quenching Bearing steel; not only simplifies the production process but also reduces the cost; and improves the service life. The fatigue life of GCr465 and SCM465 developed in Japan is 2 to 4 times higher than that of SUJ 2. Because it is in a high temperature, corrosive and smooth environment. More and more bearings are used; the bearing steels such as M50 (CrMo4V) and 440C (9Cr18Mo) ​​used in the past have not been able to meet the demand; there is an urgent need for research and development, good processing, low cost, long life, and different intentions and uses. Bearing steel; such as high temperature carburized steel M50NiL, easy to process stainless bearing steel 50X18M and ceramic bearing materials.
Aligning the low hardenability of GCr15SiMn steel; China developed high hardenability and hardenability bearing steel GCr15SiMo; its hardenability HRC≥60; hardenability J60≥25mm. GCr15SiMo touch fatigue life L10 and L50 ratio GCr15Si Mn improved by 73% and 68%; under the same operating conditions; the bearing life of G015SiMo steel is twice that of GCr15SiMo steel. In these years, China has also developed GCr4 which can save energy, save resources and resist impact. Bearing steel. Compared with GCr15; GCr4 impact value improved by 66%~104%; cracking resistance improved by 67%; touch fatigue life L10 improved by 12%. GCr4 steel bearing used high temperature heating surface quenching heat treatment process. Comparison of GCr15 steel bearings; GCr4 steel bearing life is significantly improved; can be used for heavy-duty high-speed train bearings.
The bearing steel is mainly developed in the direction of high cleanliness and functional diversification. The cleanliness of the bearing steel is improved; especially the oxygen content in the steel is lowered; the life of the bearing can be significantly extended. The oxygen content is reduced from 28 ppm to 5 ppm. The fatigue life can be extended by an order of magnitude. In order to extend the life of the bearing steel; everyone has been committed to the development of the use of essential skills to reduce the oxygen content of the steel. Through unremitting efforts; the minimum oxygen content in the bearing steel has been 28ppm in the 1960s era dropped to 5ppm in the 90th era. At present, China can control the minimum oxygen content in bearing steel to about 10ppm. The bearing environment needs to change. Bearing steel needs to have functional diversification. Progress; demand for quasi-high temperature (below 200 ° C) bearing steel (usually based on the SUJ2 steel to improve the Si content, increase the V and Nb method to reach the softening and stability scale), corrosion applications; demand development Rust bearing steel, in order to simplify the process; should develop high-frequency hardened bearing steel and short-time carburized bearing steel, in order to meet the needs of aerospace; should develop high-temperature bearing steel .
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