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The most common material for bearings is bearing steel. […]
The most common material for bearings is bearing steel. The internal structure of the bearing, the uniformity of chemical composition, the non-metallic inclusions, the size and distribution of carbide particles, and the degree of decarburization are very strict. Otherwise, these defects will significantly shorten the bearing. The service life and applicability of materials. For bearing material requirements, tell you where you can analyze it.
1. Purity of bearing steel Fatigue spalling of bearing parts is related to non-metallic inclusions in steel, especially oxides. This is because when the rolling bearing rotates, the contact surface of the bearing parts is under the action of impulse load, and the non-metallic inclusions cause partial destruction of the continuity of the steel matrix structure, causing internal stress concentration, plastic deformation around the non-metallic inclusions, and the formation of micro-cracks .
In addition, the amount of gas (oxygen, nitrogen, hydrogen) in the bearing steel is also an important indicator of purity. The oxygen dissolved in the steel precipitates with the decrease of temperature and forms oxide inclusions with aluminum, calcium, silicon, manganese and other elements. Nitrogen forms very dispersed aluminum nitride inclusions and coarser titanium nitride and titanium carbonitride in the steel. Inclusions, when the aggregated hydrogen atoms combine to form hydrogen molecules, a great pressure is generated. Once the strength limit of the steel is exceeded, internal cracks will occur and white spots will be formed. Reducing the gas content is an important part of improving the purity of bearing steel.
The main bearing steel manufacturers in my country have successively built and put into production ultra-high-power electric arc furnaces in recent years, using advanced eccentric furnace bottom tapping technology and performing secondary refining to reduce the oxygen content in the steel to about 10×10-6, which is the lowest in some cases. The oxygen content drops to (4~3)×10-6. The secondary refining ratio also reaches 100%. Therefore, the number of inclusions in the steel has been better controlled.
2. Uniformity of bearing steel
The uniformity of bearing steel refers to the uniformity of chemical composition and the uniformity of carbides. Steel ingot structure, ingot weight, casting temperature, ingot casting method, etc. affect the distribution of chemical components in steel. The heating process of steel ingots and billets before hot working, the termination temperature of steel hot working and subsequent cooling methods, and the spheroidizing annealing process affect the uniformity of carbides. According to the shape and distribution of the carbide inhomogeneity in the bearing steel on the microstructure and the reason for its formation, it can be divided into liquefied carbides, banded carbides and network carbides. The harmfulness of liquefied carbides is equivalent to The inclusions in the steel and the band-shaped carbides are rated 3~4 grades, which can reduce the fatigue life of the steel by 30%. The increase of network carbide by one level can reduce the life of the bearing by 1/3, and the size of the carbide particles directly or indirectly affects the life of the bearing. The rating levels of liquefied carbides, banded carbides, and networked carbides are indicators to measure the uniformity of carbides.
3. The dimensional accuracy and surface quality of steel
Improving the dimensional accuracy of steel not only increases the utilization rate of bearing materials, but also reduces unnecessary cutting. Some steel mills adopt short-stress line and high-rigidity rolling mills, and the deviation of steel cross-section size is greatly reduced. For round steel with a diameter of less than 30mm, the diameter deviation can reach about 0.3mm.
The life and reliability of the bearing are related to the structural design of the bearing, the materials used, the hot and cold processing technology and equipment, installation and use conditions and other factors. Among them, the material and heat treatment are one of the main factors that affect the life and feasibility of the bearing. Due to the influence of materials and heat treatment processes, factors such as low material strength, poor purity, unreasonable orientation of the fiber structure of metal materials, low hardness, inappropriate forging ratio, large residual stress and other factors can easily damage the bearing. The impact of foreign steel quality on bearing life accounted for about 50% in the 1950s and 1960s, and it was reduced to 1/3 in the 1980s. In my country, currently affected by technology and equipment, the quality of bearing steel material accounts for about 60% of bearing life. Therefore, for bearing manufacturers, choosing qualified and high-quality bearing materials is also one of the key factors to improve bearing life.