High quality NSK bearing import smelting requirements for material

NSK import is bearing steel, due to the requirement of smelting quality is much more strict than general industrial steel, such as chemical composition of steel, purity, organization and structure uniformity, etc. About 5% of chromium and contains a small amount of manganese and silicon hypereutectoid steel. Only strictly control the import of NSK bearing steel in the content of chemical composition, can only through the heat treatment process for NSK import bearing performance meet the structure and hardness. Second, strictly the size of the high precision demands of rolling bearing steel dimension precision is higher, this is because most import NSK bearing parts, it takes pressure molding. In order to save raw materials and improve labor productivity, the vast majority of NSK import bearing ring forging forming, steel ball is through cold heading or hot forming, small size of the roller is also through the cold heading forming. If the size of the steel precision is not high, will not be able to accurately calculate the expected size and weight, to ensure the quality of NSK bearing parts of products to be imported, also easy to cause the damage of the manufacturing equipment. Third, particularly strict purity requirements the purity of steel is refers to the amount of impurity content in the steel, the higher the purity, the less the non-metallic inclusions in steel. Bearing steel in the content of harmful impurities such as oxides, silicates and import NSK bearing NSK import bearing life early fatigue spalling, reduce very much. Brittle most harmful impurities, in particular, because in the process of peeling off easily from the metal substrate, the serious influence NSK bearing import after finishing appearance quality. Fourth, the strict macrostructure and microstructure, At high magnification) Organization for bearing steel macrostructure is refers to the general loose, loose and flat center, microscopy ( At high magnification) Organizations including steel annealing, carbide mesh, strip and liquid chromatography. Carbide liquid chromatography were hard and brittle, harmfulness and brittle inclusion are the same. Carbide network to reduce the impact toughness of steel, and the organization is not uniform, easy to deformation and cracking when the quenching. Banded carbide annealing and quenching tempering and contact fatigue strength. Fifth, external defects and internal defects especially strict requirements for NSK bearing steel imports, external defects including cracks, slag inclusion, burr, scarring, scale, etc. , internal defects including shrinkage cavity, bubbles, white spots, such as severe osteoporosis and segregation. These defects for processing, NSK bearings imported bearing performance and life has a great influence, NSK bearing import data in the specification are not allowed to. These defects are clearly defined. Sixth, particularly strict carbide inhomogeneity NSK bearing steel imports, in demand if there is a serious uneven distribution of carbide, is in the process of heat treatment is likely to cause tissue and uneven hardness, the organization of the steel inhomogeneity has a larger effect on contact fatigue strength. The decarburization layer 7, especially strict appearance requirements NSK bearing import data in the specification there are strict rules of the decarburization layer of steel appearance, if the decarburization layer appearance does not conform to the scope of the provisions of the standard, and before the heat treatment process, and there is no clear away all the, in the heat treatment quenching is likely to happen in the process of quenching crack, cause scrap parts. Eighth, other requirements for bearing steel in bearing steel material specification smelting method, hardness, fracture, oxygen content and annealing residual elements, spark test, delivery status, identity, and so on have strict requirements.