Commonly used various types of bearing steel

Source: China Bearing Network Time: 2013-03-10

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1. The high-carbon chrome steel commonly used bearing steel is high-carbon chrome steel; it is characterized by the high hardness scale from the appearance to the core quenching to HRC58-66; it is also called completely hardened steel. This steel is cheap; in the world It is widely used in scale. This steel is divided into four categories: chrome steel, chrome molybdenum steel, chrome manganese silicon steel and chromium manganese molybdenum steel. From the 1960s to the 1970s, the chromium content in high carbon chromium steels in various countries has It must be increased; most countries will make the roll of the original high chromium content of high-carbon chromium steel (suitable for GCr6 steel used in China) to abandon it; instead, the same steel type used to make the ferrule (appropriate for China) The GCrl5 steel); and the practice of bearing steel in various countries, the chromium content is mostly biased to the difference in its standard size; there is also slightly higher than its specifications. China's new bearing steel specification YB (T) 180 will also use the largest bearing The minimum chromium content of steel GCr15 increased from 1.30% to 1.40%. In addition; from the 1970s; some countries increased the amount of molybdenum in bearing steel; or increased the new type of bearing steel containing molybdenum; Find better hardenability and refine grains.
2. Carburized bearing steel Carburizing steel is the earliest steel type used in the bearing industry; it was being carried out at the time. Carburized bearing steel is used to make bearing components that operate under impact load or oscillation conditions; for example, automobiles, rolling stock, construction machinery; Bearing components for rolling mills and agricultural machinery. The demand for this steel is that the carburized outer skin can be hardened to have the same hardness and fatigue strength as high carbon chromium steel; the core is manipulated within the hardness scale of HRG35 40; Satisfy tolerance and outstanding inductive mechanical strength; appearance of compressive stress state. Steel that meets this demand; bearing is resistant to impact; surface is not easy to crack; even if the hard surface of the surface is cracked, it is not easy to expand to the inner layer.
The heat treatment process of carburized bearing steel is disordered; the simple occurrence of brittleness, soft spots, and unequal hardness of waste products; therefore, the cost is higher. To ensure the strength of carburized bearings; the hardness of the carburized components; the hardness distribution of the surface layer to the inner layer and the core Hardness; all three are important. The carburizing concentration should be moderately controlled; the higher the carbon content, the longer the life expectancy; but it should be within the agreed scale of the retained austenite content; because the carbon content is high; the remaining austenite content is also Gaochang. Bearing scale stability is poor. Other; in order to improve hardenability; should not participate in too much of an element; should participate in a variety of alloying elements.
3. Medium carbon bearing steels can not be used to accept more impact and carburized steel; often use medium carbon manganese steel, chrome steel and other bearing parts; mostly low-speed large hardness requirements and components of various scales Spiral roller, etc.
Some of the newly developed medium carbon steel types such as GCr15 can be used in the production of large, medium and small bearing components of various scales; this is a promising steel grade that is expected to be widely used. Its chemical composition is roughly the same as that of GCrl5; It has only a low carbon content; it is characterized by a significant improvement in the anisotropy of carbides in the steel; a uniform and fine spheroidizing annealing arrangement is obtained; microcracks are difficult to germinate and expand; and the fatigue strength and crushing strength are higher than GCr15; because the carbon content is small; the proportion of dislocation martensite increases; the sensitivity to the data defects is reduced; the quenching hardness can be higher; the chromium content is the same as GCr15; so its wear resistance; rust prevention Saturation, tempering stability; hardenability and a variety of mechanical properties and GCr15; and the endurance with respect to oscillation and impact load; higher than GCrl5; together with the steel's process function; steel production and bearing production costs Reduced; the life of the bearing has also increased; so it can compete with GCrl5 on a large scale.
4. High temperature bearing steel
(1) Demand for bearing steels operating at high temperatures Modern operating conditions such as nuclear power systems, jet engines, and gas turbines often operate in the range of hundreds of degrees and thousands of degrees; significant common bearing steels cannot be used. It is necessary to use High temperature bearing steel or other high temperature data.
It is usually considered to exceed the temperature condition of 120 Â° C; it is considered to be a high temperature operation condition; at this moment, the bearing steel will usually change the arrangement and the yield strength will decrease; the accuracy will gradually decrease, and when the bearing operating temperature exceeds the bearing data tempering temperature; the hardness is remarkable. Reduced; the hardness decreases sharply when the operating temperature exceeds 180 Â°C; it quickly shows early fatigue and wear.
The central part of ensuring the accuracy and life of the bearing at high temperatures is to ensure that the bearing has a satisfactory hardness and dimensional stability at high temperatures; therefore, the following requirements are required for high temperature bearing steel:
1) The hardness at high temperature is not lower than HRC50ï½ž56, and the metallographic arrangement is stable.
2) Excellent stability at high temperature scale; temperature expansion coefficient. Swinging é‚¢ æ·–æ©¹æµ è±¢ æ·–æ©¹æµ è±¢ æµ”æ¹« æµ”æ¹« æµ”æ¹« èŒ«å¾Š èŒ«å¾Š èŒ«å¾Š å˜¤ å˜¤ Ï€ Î± ..
3) Good oxidation resistance; the formed oxide film is strong with the matrix; and the wear resistance and fatigue strength are good; the thermal shock resistance is good; the temperature change can be satisfactorily tested; the thermal conductivity is better,
4) Other data characteristics that should be available as bearing steel.
(2) The common steel for high temperature bearings is in the low load case below 180 Â°C; the common bearing steel can be used for high temperature tempering (160~300 Â°C); if the hardness is not suitable, the sub-high temperature bearing steel GCrSiWV can be used; The working temperature of steel is about 250 Â°C. Cr4Mo4V can be used at temperatures around 300 Â°C; W6Cr4Mo5V2 can be used below 538 Â°C; beyond this temperature, bearings are made of cobalt-based, chromium-based or molybdenum-based alloys; At Â°C, cermet materials such as titanium carbide and tungsten carbide can be used; ceramic materials such as zirconia can be used at higher temperatures; bearings with such materials can accept a maximum operating temperature of up to 1650 Â°C.
5 Corrosion-resistant bearing steels The lifespan of several high-temperature bearing steels is compared to the corrosive medium environment in which the bearing steel can no longer be used; the bearing and its parts are made of corrosion-resistant bearing steel; for example, in the touch of water or water vapor In hydraulic machinery; in chemical machinery that touches acid and alkali; in ships that touch seawater, the bearings in the instrumentation are also made of corrosion-resistant steel; because the bearings are slightly corroded, they will affect their measurement accuracy and response sensitivity. Bearings in the food industry are sometimes made of corrosion-resistant steel; because it expects bearing corrosion; no corrosive substances cause food contamination. Corrosion-resistant bearing steel can be divided into two categories: one is martensitic stainless steel Where the hardness is high, one type is austenitic stainless steel; it is used in places where there is a need for better corrosion resistance. The former often adds an appropriate amount of molybdenum to replace some of the chromium; to improve the function of seawater corrosion resistance; The hardness is low; the load carrying capacity and the service life are less than the former.
Many corrosion-resistant steels are also high-temperature; two steels are common; but the guidelines are different; high-temperature steels require high-temperature hardness and high-temperature scale and shape accuracy; and corrosion-resistant steels require chemical stability. Modern skill requires bearings to operate under high temperature, high corrosive, and non-smooth conditions; for example, bearings in new atomic boilers must be operated in sodium solution; the above high temperature bearing steels are not customary; special non-ferrous alloy or ceramic materials are required. Made a bearing.
The commonly used corrosion-resistant steel 140r4Mo has good acid and alkali resistance; the endurance of dilute nitric acid is only lower than that of corrosion-resistant steel 440C; while SUS304 is very resistant to seawater; it is commonly used to make submersible pumps and even submarines. Bearing; but its hardness is somewhat low. These two steels also have high temperature. 90r18Mo has high temperature resistance and corrosion resistance; it can even work in steam of 400 Â°C nitric acid or hydrochloric acid.
6. Low temperature bearing steel is used in aerospace skills; turbo pump bearings that supply liquid fuel to rockets are operated in liquid oxygen and liquid hydrogen. The temperature and liquefied gas are flat. Because there is usually a martensitic arrangement in the bearing steel; the original tolerance is not ambition It has low temperature brittleness; for low temperature of 5 ~ 200 Â°C; in practice, it will rust due to moisture in the air condensing water droplets on the bearing surface; therefore, stainless steel should be used. Generally, the martensitic stainless steel is subjected to low temperature cryogenic treatment; The arrangement does not change. The experimental results of the radial ball bearing and the cylindrical roller bearing made of SUS4400 steel in liquid oxygen (boiling point 183 Â° C) show that the bearing has no special abnormalities except for the flank appearance; The rotational speed of 20000r/min; however, the cage of the bearing must be made of special materials. The cage of the low temperature resistant bearing itself is also made of stainless steel; the commonly used SUS304 steel of the austenitic system and the SUS440V steel of the martensitic system. The former is easy to process; more applications.
The key to the low-temperature bearing steel is the low-temperature brittleness and the corrosion resistance of the condensed water; while the Martensitic SUS4400 can reach a hardness of HRC 56-60; lower than the common bearing steel; therefore its fundamental additional static load and fundamental Additional dynamic load; perhaps its lifespan is lower than the common bearing steel bearings of the same type of standard type; this is necessary to pay attention to.

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