Commonly used rolling bearing steels include high-carbon chromium bearing steel, carburized bearing steel, corrosion-resistant bearing steel, high-temperature bearing steel, antimagnetic bearing steel, stainless bearing steel and medium carbon alloy steel.
1. High carbon chromium bearing steel
High-carbon chromium bearing steel is a high-carbon alloy steel containing chromium 1.30 ～ 1.65%. Its characteristics are: the microstructure after heat treatment is relatively uniform and stable, the hardness is high and uniform, the wear resistance is good, the contact fatigue strength is high, and it has good Dimensional stability and corrosion resistance. After spheroidizing annealing, its cutting performance is good, and the price is relatively cheap. This kind of steel can meet the requirements of bearings operating under general working conditions.
High carbon chromium bearing steel has high contact fatigue strength and wear resistance, and is widely used in the world. The most commonly used grades are GCr 15, GCr15SiMn, GCr15SiMo, GCr18Mo. However, because some bearings require good toughness in the core and high strength on the surface, limited hardenable bearing steels have also been developed. Bearings made of high carbon steel chromium bearing steel are generally suitable for operating temperatures in the range of -40 to 130 degrees, and oil and grease lubrication are normal. Can meet the requirements of general machinery.
2. Carburized bearing steel
Carburized bearing steel is the support of various mechanical parts, and its working environment may be ultra-high temperature, ultra-low temperature, strong (slightly) vacuum, or it may be strong impact, high wear and ultra-high speed. The carburized steel used for manufacturing bearing parts is mainly low carbon steel and high quality low carbon alloy structural steel. Bearing parts made of this type of steel, after carburizing, quenching, tempering and other heat treatment processes, the surface has a high hardness (hardness ≥ HRC60) and a certain wear resistance and high contact fatigue strength, and the heart The department has good toughness, a certain strength and hardness.
Carburized steel is the earliest steel grade used in the bearing industry and is currently developing. It is suitable for manufacturing bearings that work under impact load conditions and bearings with larger sizes. For example, bearing components for automobiles, rolling stock, construction machinery, steel rolling mills and agricultural machinery. The requirements for this kind of steel are: the carburized surface layer can be hardened to have the same hardness and fatigue strength as high carbon chromium steel, the core is controlled within the hardness range of HRG35-40, and has sufficient toughness and good comprehensive machinery Strength, the surface retains the state of compressive stress.
3. Corrosion-resistant bearing steel
Comparison of the life of several high-temperature bearing steels In the environment of corrosive media where ordinary bearing steels are no longer competent, it is necessary to use corrosion-resistant bearing steels to manufacture bearings and their parts, such as in hydraulic machines that are exposed to water or water vapor. Acid and alkali chemical machinery, in ships and ships that are exposed to sea water; bearings in instrumentation are also commonly made of corrosion-resistant steel, because slight corrosion of bearings will affect their measurement accuracy and response sensitivity; bearings in the food industry Sometimes it is also made of corrosion-resistant steel, because it hopes that the bearing can be resistant to corrosion, so that there is no corrosive substances that cause food contamination.
Corrosion-resistant bearing steel, also known as stainless steel, is not easily oxidized when working in a corrosive medium. Commonly used corrosion-resistant bearing steel is divided into two major categories of austenitic stainless steel (1Cr18Ni9Ti), which is used for occasions requiring better corrosion resistance, and martensitic stainless steel (9Cr18, 9Cr18Mo, Cr15Mo4), which is used for higher hardness Occasions. Corrosion-resistant bearing steel is used to manufacture bearing parts that work in corrosive environments such as the chemical industry and the food industry and at low temperatures, as well as some instruments and instrument bearings that require low friction.
4. High temperature bearing steel
Modern technologies such as nuclear power systems, jet engines, and gas turbines often operate at temperatures of hundreds to thousands of degrees. Obviously, ordinary bearing steel cannot be used. High temperature bearing steel or other high temperature resistant materials must be used. It is generally considered that the temperature condition exceeding 120 ° C is considered to be a high-temperature working condition. At this time, the ordinary bearing steel will undergo a structural change and a decrease in yield strength, and the accuracy will gradually lose; when the bearing working temperature exceeds the bearing material tempering temperature, its hardness is obvious The hardness drops sharply when the working temperature exceeds 180 ° C, and early fatigue and wear soon appear.
The central link to ensure the accuracy and service life of bearings at high temperatures is to ensure that the bearings have sufficient hardness and stability of size and shape at high temperatures, so high-temperature bearing steels need to meet higher requirements:
1) The hardness is not lower than HRC50 ^ 56 at high temperature; the metallographic structure is stable;
2) Good dimensional stability at high temperature, small temperature expansion coefficient, no significant structural changes, good creep resistance, and small residual stress;
3) Good oxidation resistance, the generated oxide film is firmly combined with the substrate, and has good wear resistance and fatigue strength, good thermal shock resistance, can withstand rapid temperature changes, and good thermal conductivity.
For bearings operating at 150 to 250 ° C, if the rings and rolling elements are still made of ordinary high-carbon chromium bearing steel, special requirements must be placed on the tempering temperature of the steel, which should generally be higher than the working temperature at 50 ° C Perform tempering. Bearing steel that has been tempered according to the above requirements can work normally at 250 ° C, but due to the decrease in hardness after tempering, the bearing life is reduced.
Therefore, when the operating temperature is higher than 250 ℃, high temperature bearing steel must be used. In addition to the performance of general bearing steel, high temperature bearing steel should also have certain high temperature hardness and high temperature wear resistance and high temperature contact fatigue strength. It is also resistant to oxidation, impact resistance and high temperature dimensional stability. High temperature bearing steel is mainly made of high speed steel and high chromium martensitic stainless steel. For bearings with complex structure and strong impact load, high temperature carburized steel can also be used.