High quality of the NTN bearing smelting requirements for material

The quality of the rolling bearing large level and quality of the NTN bearing steel are closely linked. Due to the nature of NTN bearing steel is, 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. Chromium heat treatment can improve performance, increase the hardenability, uniformity, tempering stability, and can improve the anti-corrosion properties of steel and grinding performance. 65%, after quenching can increase the residual austenite in the steel, reduce hardness and dimensional stability, increase the inhomogeneity of carbide lower impact toughness and fatigue strength of steel. To this end, the chromium content of high carbon chromium NTN bearing steel general control in 1. Less than 65%. Only strict control of chemical composition in NTN bearing steel, can only through the heat treatment process for meet the NTN bearing performance of the organization and hardness. Second, strictly the size of the high precision demands NTN bearing steel rolling size precision, this is because most of the NTN bearing parts, it takes pressure molding. In order to save raw materials and improve labor productivity, the vast majority of NTN 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, which can guarantee NTN bearing parts of the product quality, 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 NTN bearing early fatigue spalling, NTN bearing life reduce very much. Brittle most harmful impurities, in particular, because in the process of peeling off easily from the metal substrate, the serious influence NTN bearing after finishing the appearance quality. Therefore, in order to improve the service life and reliability of the NTN bearing, must reduce the content of impurities in NTN bearing steel. 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. Low, high quality of rolling NTN bearing quality has a great influence, therefore, NTN bearing manufacturing specifications have strict requirements on low and high power organization. Fifth, external defects and internal defects especially strict requirements for NTN bearing steel, 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 NTN bearing processing, NTN bearing performance and life has a great influence, NTN bearing material in the specification are not allowed to. These defects are clearly defined. Sixth, particularly strict carbide inhomogeneity NTN bearing steel, 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. In addition, the serious carbide inhomogeneity is easy to make NTN bearing parts during quenching crack, carbide inhomogeneity will results in the decrease of NTN bearing of life, therefore, NTN bearing material specification, for different specifications of the steel have clear special requirements. The decarburization layer 7, especially strict appearance requirements NTN bearing material specification for steel surface decarburization layer has strict rules, 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.