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The service life and reliability of rolling bearings are closely related to the quality of smelting of imported bearings. Due to the characteristics of imported bearing steel, the quality of smelting requirements than the general industrial steel to be much more stringent, such as the chemical composition of steel, purity, organization and uniformity.
Strict chemical composition requirements
General imports of steel is mainly imported high-carbon chromium bearing steel, that is about 1% carbon content, adding about 1.5% of chromium, and contains a small amount of manganese, silicon over eutectoid steel. Chromium can improve the heat treatment performance, improve the hardenability, uniformity of the organization, tempering stability, but also can improve the anti-rust properties of steel and grinding performance. However, when the chromium content exceeds 1.65%, quenching will increase the retained austenite in steel, reduce the hardness and dimensional stability, increase the carbide heterogeneity, reduce the impact toughness and fatigue strength of steel. To this end, high-carbon chromium bearing steel in the chromium content is generally controlled at 1,65% or less. Only by strictly controlling the chemical composition of imported bearing steel in order to obtain through the heat treatment process to meet the performance of imported bearings and hardness. Second, high-precision size requirements
Rolling imported bearings steel requirements of high dimensional accuracy, this is because most of the imported bearing parts have to be pressure forming. In order to save materials and improve labor productivity, the vast majority of imported bearing rings are through forging molding, the ball is cold heading or hot rolling molding, small size of the roller is also cold heading forming. If the steel size accuracy is not high, it can not accurately calculate the size and weight of the material, but can not guarantee the quality of imported bearing parts, but also likely to cause damage to equipment and mold.
Three, especially the strict requirements of the purity
Steel's purity refers to the amount of non-metallic inclusions contained in the steel, the higher the purity, the less the non-metallic inclusions in the steel. Imports of bearing steel oxides, silicates and other harmful inclusions are leading to early fatigue bearing peeling off, significantly reduce the main reasons for the life of imported bearings. Especially the most harmful brittle inclusions, due to the process of easy to peel off from the metal matrix, seriously affecting the imported bearing parts after finishing the surface quality. Therefore, in order to improve the service life and reliability of imported bearings, it is necessary to reduce the content of inclusions in imported bearing steel.
Four, strict low magnification organization and micro (high power) organization requirements
Low magnification of imported bearing steel refers to the general loose, central loose and flat body, micro (high power), including steel annealing organization, carbide mesh, ribbon and liquid. Carbide liquid is hard and brittle, and its hazards are the same as those of brittle inclusions. Mesh carbide reduces the impact toughness of steel and makes it inhomogeneous, prone to deformation and cracking during quenching. The banded carbides affect the annealing and quenching tempering tissues as well as the contact fatigue strength. The advantages and disadvantages of low and high power organizations have a great influence on the performance and service life of rolling bearings. Therefore, there are strict requirements for low and high power organizations in the standard of imported bearing materials.
5, particularly stringent surface defects and internal defects requirements
For imported bearing steel, surface defects include cracks, slag, burrs, scarring, scale, etc., internal defects include shrinkage, bubbles, white spots, severe loose and segregation. These defects for the import of imported bearings, bearing performance and life have a great impact in the import bearing material standards clearly do not allow these defects.


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