Roller bearing life and reliability of the bearing steel with a large degree of quality is closely related. Due to the characteristics of bearing steel, the quality of smelting requirements than the general industrial steel to be much more stringent, such as steel chemical composition, purity, organization and uniformity.
First, strict chemical composition requirements
General bearing steel is mainly 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 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 the bearing steel in order to obtain the heat treatment process to meet the bearing performance of the organization and hardness.
Second, high-precision size requirements
Rolling bearing steel requires high dimensional accuracy of steel, this is because most of the bearing parts have to be pressure forming. In order to save material and improve labor productivity, the vast majority of bearing rings are forging molding, steel 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 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. Bearing steel in the oxide, silicate and other harmful inclusions are leading to early fatigue bearing off, significantly reduce the bearing life of the main reasons. In particular, the brittle inclusions are the most harmful, due to the process of easy to peel off from the metal matrix, seriously affecting the bearing parts after finishing the surface quality. Therefore, in order to improve the bearing life and reliability, it is necessary to reduce the content of inclusions in bearing steel.
Four, strict low magnification organization and micro (high power) organization requirements
Low magnification of bearing steel refers to the general loose, central loose and flat, micro (high power) organizations, including steel annealing organization, carbide mesh, ribbon and liquid chromatography. 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. Low and high power organization of the pros and cons of rolling bearing performance and service life have a great impact, so in the bearing material standards for low, high power organizations have strict requirements.
5, particularly stringent surface defects and internal defects requirements
For bearing steels, surface defects include cracks, slag, burrs, scarring, scale, etc., internal defects include shrinkage, bubbles, white spots, severe loose and segregation. These defects for the bearing processing, bearing performance and life have a great impact in the bearing material standard clearly does not allow these defects.
Six, particularly stringent requirements for carbide nonuniformity
In the bearing steel, if there is a serious distribution of carbides uneven, in the heat treatment process is likely to cause uneven organization and hardness, steel unevenness of the contact fatigue strength have a greater impact. In addition, the serious carbide non-uniformity is also easy to make the bearing parts in the quenching and cooling cracks, carbide unevenness will lead to lower bearing life Therefore, in the bearing material standards, different specifications of steel are clear special requirement.
Seven, particularly stringent surface decarburization requirements
In the bearing material standard on the steel surface decarburization layer has strict rules, if the surface decarburization layer beyond the standard range, and in the heat treatment before the process did not remove all of them, in the heat treatment quenching process Easy to produce quenching cracks, resulting in scrap parts.
Eight other requirements
In the bearing steel material standard also on the bearing steel smelting method, oxygen content, annealing hardness, fracture, residual elements, spark inspection, delivery status, logo, etc. have strict requirements
First, strict chemical composition requirements
General bearing steel is mainly 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 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 the bearing steel in order to obtain the heat treatment process to meet the bearing performance of the organization and hardness.
Second, high-precision size requirements
Rolling bearing steel requires high dimensional accuracy of steel, this is because most of the bearing parts have to be pressure forming. In order to save material and improve labor productivity, the vast majority of bearing rings are forging molding, steel 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 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. Bearing steel in the oxide, silicate and other harmful inclusions are leading to early fatigue bearing off, significantly reduce the bearing life of the main reasons. In particular, the brittle inclusions are the most harmful, due to the process of easy to peel off from the metal matrix, seriously affecting the bearing parts after finishing the surface quality. Therefore, in order to improve the bearing life and reliability, it is necessary to reduce the content of inclusions in bearing steel.
Four, strict low magnification organization and micro (high power) organization requirements
Low magnification of bearing steel refers to the general loose, central loose and flat, micro (high power) organizations, including steel annealing organization, carbide mesh, ribbon and liquid chromatography. 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. Low and high power organization of the pros and cons of rolling bearing performance and service life have a great impact, so in the bearing material standards for low, high power organizations have strict requirements.
5, particularly stringent surface defects and internal defects requirements
For bearing steels, surface defects include cracks, slag, burrs, scarring, scale, etc., internal defects include shrinkage, bubbles, white spots, severe loose and segregation. These defects for the bearing processing, bearing performance and life have a great impact in the bearing material standard clearly does not allow these defects.
Six, particularly stringent requirements for carbide nonuniformity
In the bearing steel, if there is a serious distribution of carbides uneven, in the heat treatment process is likely to cause uneven organization and hardness, steel unevenness of the contact fatigue strength have a greater impact. In addition, the serious carbide non-uniformity is also easy to make the bearing parts in the quenching and cooling cracks, carbide unevenness will lead to lower bearing life Therefore, in the bearing material standards, different specifications of steel are clear special requirement.
Seven, particularly stringent surface decarburization requirements
In the bearing material standard on the steel surface decarburization layer has strict rules, if the surface decarburization layer beyond the standard range, and in the heat treatment before the process did not remove all of them, in the heat treatment quenching process Easy to produce quenching cracks, resulting in scrap parts.
Eight other requirements
In the bearing steel material standard also on the bearing steel smelting method, oxygen content, annealing hardness, fracture, residual elements, spark inspection, delivery status, logo, etc. have strict requirements
