A. Carbon chromium steel
Commonly used bearing steel, high carbon chromium steel, it is characterized from the surface to the core hardenability to HRC58 ~ 66 so that the high hardness range, it is also known as hardened steel. This low steel prices, the most widely used worldwide. This steel is divided into chrome steel, chrome molybdenum steel, chromium, manganese silicon steel and chrome manganese molybdenum steel four categories in the national carbon chromium steel chromium content, since the 1960s to the 1970s, a certain increase in most countries will create rolling element of the original chromium content of low-carbon chromium steel (equivalent of the GCr6 steel) obsolete, and replaced by manufacturing the same ring of steel (equivalent to China GCrl5 steel), while countries bearing steel containing chromium large amount of biased standard range on the poor, there are slightly higher than its standard. YB (T), the new standard of Bearing Steel in China 1-80 will use the largest minimum bearing steel GCr15 containing chromium content from 1.30% to 1.40%. In addition, since the 1970s, some countries have to improve the molybdenum content in the bearing steel, or added new varieties to molybdenum bearing steel, in order to get a better hardenability and grain refinement.
Two. Carburizing bearing steel
Carburizing steel is the first steel bearing industry, is currently being developed. Carburizing bearing steel used to manufacture the bearing components under shock loading or vibration conditions, such as automotive, rolling stock, construction machinery, rolling mills and agricultural machinery and other bearing components. Steel: the carburized surface layer can be hardened and high-carbon chromium steel hardness and fatigue strength, core control within the hardness range of HRG35-40, and has sufficient ductility and good mechanical The strength of the surface to keep compressive stress state. Steel to meet this requirement, the bearings, impact resistance, surface easy to crack, even if the surface hardened layer micro-cracks, also not easy to be extended to the inner layer.
Carburizing bearing steel heat treatment process is complex and prone to brittle, soft spots, uneven, hardness, and other waste, and therefore higher cost. In order to ensure the strength of carburized bearing, the surface hardness of the carburized components, surface hardness distribution to the inner core hardness, the three are very important. Carburizing concentration to control the moderate, the higher the carbon content of the longer life expectancy, but within the allowed range of the retained austenite content, the plant because of high carbon content of retained austenite content. Bearing dimensional stability. In addition, in order to improve the hardenability, not too much to join a particular element should trace to join a variety of alloying elements.
3. The carbon bearing steel
Carburizing steel also can not adapt to the occasion to withstand greater impact, often used in carbon-manganese steel, chrome steel manufacturing bearing parts, components and a variety of size, not too high spiral roller requirements for low-speed large-scale hardness .
Some newly developed varieties of carbon steel, such as GCr15 bearing component manufacturing can be applied to small, medium and large variety of sizes, this is an expected wide range of application of promising steels. Its chemical composition and GCrl5 much the same, only the low carbon content, which is characterized by significantly improving the carbides in the steel uneven isotropic, uniform and fine spheroidized annealed structure, the microcrack difficult initiation and propagation, making the fatigue strength and crushing strength than GCr15, carbon less, the increase in the proportion of dislocation martensite, reduces the sensitivity of material defects, quenching hardness higher chromium content and GCr15, so its abrasion resistance, rust resistance and tempering stability, hardenability and a variety of mechanical properties and GCr15, and for the endurance of the vibration and shock loads, higher than GCr15, at the same time the technological properties of this steel is better production of steel and bearing manufacturing costs decrease bearing life has also increased, therefore a wide range of GCrl5 compete.
4. High-temperature bearing steel
(1) high temperature bearing steel
Modern technology such as nuclear power systems, jet engines and gas turbines, such as operating temperature often reached the number of Baidu, as well as thousands of degrees, apparently normal bearing steel can not be applied. Must use high-temperature bearing steel or other high temperature materials.
Generally considered more than 120 ° C temperature conditions, will be regarded as high-temperature working conditions, common bearing steel organizational change and yield strength decreased, the gradual loss of accuracy occurs; when the bearing operating temperature exceeds the tempering temperature of the bearing material, its hardness decline in operating temperature over 180 ℃, the hardness of a sharp decline, and soon early fatigue and wear.
Ensure that the central link in the bearing running accuracy and service life at high temperatures is to ensure that bearings with sufficient hardness and size and shape stability at high temperatures, high temperature bearing steel the following requirements:
1) high-temperature hardness of not lower than HRC 50 ~ 56; stability of the microstructure;
2) high temperature dimensional stability, temperature coefficient of expansion, no significant organizational change, and good creep resistance and residual stress;
3) good resistance to oxidation, the resulting oxide film and the substrate with a solid, good wear resistance and fatigue strength, good thermal shock resistance and can withstand rapid temperature changes, better thermal conductivity;
4) due as bearing steel, other material properties.
(2) high temperature bearing common steel
Low load situations, less than 180 ℃ can be commonly used bearing steel, high temperature tempering (160 ~ 300 ° C) to use, if the hardness does not comply, could be replaced by the Asian high-temperature bearing steel GCrSiWV operating temperature of this steel at 250 ℃ . Temperature about 300 ℃ can be Cr4Mo4V to adopt W6Cr4Mo5V2 below 538 ℃, over this temperature is used cobalt, chromium-based or molybdenum-based alloy bearings, titanium carbide, tungsten carbide and available when the temperature exceeds 81 ° C metal-ceramic materials, higher temperatures can be used such as zirconium oxide ceramic materials, the bearing of such material can withstand the highest operating temperature up to 1650 ℃.
Bearing steel corrosion
Several high-temperature bearing steel life compared to ordinary bearing steel has been incapable of corrosive media environment, it is necessary to use corrosion-resistant bearing steel to make bearings and parts thereof, for example, in hydraulic machinery in contact with water or water vapor in contact with acids and bases, chemical machinery, ships ships in contact with seawater; instrumentation bearings is also commonly used in corrosion-resistant steel, bearing a slight corrosion will affect the measurement accuracy and responsiveness; bearings in the food industry sometimes with corrosion-resistant steel, because of its bearing capability corrosion from corrosive substances caused by food contamination. Corrosion-resistant bearing steel can be divided into two categories: one is a martensitic stainless steel for applications requiring higher hardness occasions; a class of austenitic stainless steel for better corrosion resistance of occasions. The former is often added a considerable amount of molybdenum to replace part of the chromium to improve the performance of sea water corrosion resistance, low hardness of the latter, the load carrying capacity and service life is less than the former.
Many corrosion-resistant steel is also able to heat the two steels are often generic, but the goal is not the same, high temperature steel priority requirements of the stability of the high-temperature hardness and high temperature dimensional and shape accuracy, corrosion resistant steel focus requirement chemical stability. Modern technology requires bearings operate under high temperature, highly corrosive, non-lubricated conditions, such as bearings in the new atomic boiler to operate in the sodium solution, the above-mentioned high-temperature bearing steel can not meet this time required a special non-ferrous alloy or ceramic material manufacture of bearings.
Foreign commonly used corrosion resistant steel 140r4Mo has good acid and alkali, lower than the corrosion-resistant steel 440C only for the endurance of boiling dilute nitric acid, a strong resistance to sea water capacity SUS304 used to manufacture submersible pumps as well as the submarine in the bearing , but its hardness is somewhat low. Both steel to high temperature. 90r18Mo of high temperature and corrosion resistance are high, even work in the 400 ° C, the vapor of nitric acid or hydrochloric acid.
6. Low temperature bearing steel
In space technology, to provide liquid fuels for rocket turbopump bearings operating in liquid oxygen and liquid hydrogen. Temperature and equal to the liquefied gas. Common bearing steel in the martensite had the toughness is not ideal, and low temperature brittleness, such as for the low temperature of -5 to -200 ℃, and in fact due to air moisture condensation of water droplets and rust on the bearing surface, so should be stainless steel. General martensitic stainless steel at low temperature and cryogenic treatment, to ensure that their organization does not change. Steel manufactured in the liquid oxygen (boiling point -183 ° C) using SUS4400 radial ball bearings and cylindrical roller bearings made by running test results show that bearing no special exception in addition to some wear and tear of the rib surface can withstand up to the speed of 20000r/min , but this time bearing the cage must be used special materials. Resistance to low temperature bearing cage itself is also useful to stainless steel, commonly used austenitic SUS304 steel and the the Mahalanobis system SUS440V steel, the former is easy to process, use more.
In short, the key technology of low temperature resistance of bearing steel is that the low temperature brittleness and resistance to corrosion of the condensate, while Markov system SUS4400 can reach the surface hardness is HRC56 ~ 60 lower than the commonly used bearing steel, so the basic static load rating and basic dynamic load rating, or its useful life than the same basic model of the same sizes commonly used bearing steel bearing low, this must be noted.
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