due to the characteristics of nsk bearing steel, the requirements for smelting quality are much more stringent than those of ordinary industrial steels, such as chemical composition, purity, organization and structural uniformity of steel.
first, strict chemical composition requirements
general nsk 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 element over eutectoid steel. only the strict control of nsk bearing steel in the chemical composition of the content, can be obtained through the heat treatment process to meet the performance of nsk bearings and organization of hardness.
second, strict high-precision size requirements
rolling bearing steel requires a higher dimensional accuracy, this is because most of the nsk bearings parts have to be pressure forming. in order to save raw materials and improve labor productivity, the vast majority of nsk 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, which can not guarantee the product quality of nsk bearings parts, but also likely to cause damage to manufacturing equipment.
third, especially the strict purity requirements
the purity of steel refers to the amount of impurities contained in steel, the higher the purity of steel, the less the non-metallic inclusions. bearing steel in the oxide, silicate and other harmful impurities and nsk bearings early fatigue peeling off, nsk bearings have a great relationship to reduce the life. especially the most harmful brittle impurities, due to the processing process easily from the metal matrix peeling off, seriously affect the nsk imported bearings after finishing the appearance of quality.
fourth, strict low magnification organization and micro (high power) tissue 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 hard and brittle, harmful and brittle inclusions the same. mesh carbide reduces the impact toughness of steel, and the organization is not uniform, easy to deformation and cracking when quenching. the banded carbides affect the annealing and quenching tempering tissues as well as the contact fatigue strength.
fifth, external defects and internal defects are particularly stringent requirements
for nsk bearings, external defects include cracks, slag, burrs, scarring, scale, etc., internal defects include shrinkage, bubbles, white spots, severe loose and segregation. these defects for the processing of bearings, nsk bearings performance and life have a great impact, nsk bearings specifications clearly do not allow these defects.
sixth, particularly stringent requirements for carbide nonuniformity
nsk imported 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.
seventh, particularly stringent appearance decarburization requirements
nsk bearing specifications in the steel surface decarburization steel has a strict requirement, if the appearance of decarburized layer does not meet the requirements of the standard range, and in the heat treatment before the process did not remove all of them, then heat quenching the process is prone to quenching cracks, resulting in scrap parts.
eighth, other requirements
bearing steel material specifications also on the bearing steel smelting methods, oxygen content, annealing hardness, fracture, the remaining elements, spark inspection, delivery status, logo, etc. have strict requirements.
first, strict chemical composition requirements
general nsk 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 element over eutectoid steel. only the strict control of nsk bearing steel in the chemical composition of the content, can be obtained through the heat treatment process to meet the performance of nsk bearings and organization of hardness.
second, strict high-precision size requirements
rolling bearing steel requires a higher dimensional accuracy, this is because most of the nsk bearings parts have to be pressure forming. in order to save raw materials and improve labor productivity, the vast majority of nsk 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, which can not guarantee the product quality of nsk bearings parts, but also likely to cause damage to manufacturing equipment.
third, especially the strict purity requirements
the purity of steel refers to the amount of impurities contained in steel, the higher the purity of steel, the less the non-metallic inclusions. bearing steel in the oxide, silicate and other harmful impurities and nsk bearings early fatigue peeling off, nsk bearings have a great relationship to reduce the life. especially the most harmful brittle impurities, due to the processing process easily from the metal matrix peeling off, seriously affect the nsk imported bearings after finishing the appearance of quality.
fourth, strict low magnification organization and micro (high power) tissue 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 hard and brittle, harmful and brittle inclusions the same. mesh carbide reduces the impact toughness of steel, and the organization is not uniform, easy to deformation and cracking when quenching. the banded carbides affect the annealing and quenching tempering tissues as well as the contact fatigue strength.
fifth, external defects and internal defects are particularly stringent requirements
for nsk bearings, external defects include cracks, slag, burrs, scarring, scale, etc., internal defects include shrinkage, bubbles, white spots, severe loose and segregation. these defects for the processing of bearings, nsk bearings performance and life have a great impact, nsk bearings specifications clearly do not allow these defects.
sixth, particularly stringent requirements for carbide nonuniformity
nsk imported 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.
seventh, particularly stringent appearance decarburization requirements
nsk bearing specifications in the steel surface decarburization steel has a strict requirement, if the appearance of decarburized layer does not meet the requirements of the standard range, and in the heat treatment before the process did not remove all of them, then heat quenching the process is prone to quenching cracks, resulting in scrap parts.
eighth, other requirements
bearing steel material specifications also on the bearing steel smelting methods, oxygen content, annealing hardness, fracture, the remaining elements, spark inspection, delivery status, logo, etc. have strict requirements.
