NTN bearing steel smelting quality of the basic requirements

Service life and reliability of the rolling NTN bearing largely with NTN bearing steel smelting quality have a close relationship. 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 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% when, after quenching can increase the retained 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 under,65%1. Only strict control of the NTN bearing steel chemical composition, can satisfy the NTN bearing performance of the organization through heat treatment process and hardness. Second, the size of the high precision demands NTN bearing steel rolling steel dimension precision is higher, this is because most of the NTN bearing parts, it takes pressure molding. In order to save material and improve labor productivity, the vast majority of NTN bearing ring have been 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, and cannot guarantee the NTN bearing parts of the product quality, also easy to cause damage of equipment and dies. Three, particularly strict purity requirements of steel purity refers to contain nonmetallic inclusion in steel, the higher the purity, the less the non-metallic inclusions in steel. NTN bearing harmful oxide and silicate inclusions in steel is causing NTN bearing early fatigue spalling, significantly reduce the main reason for the NTN bearing life. Especially brittle inclusion most harmful, because in the process of peeling off easily from the metal substrate, the serious influence NTN bearing parts surface quality after finishing. Therefore, in order to improve the service life and reliability of the NTN bearing, must reduce the content of inclusions in the NTN bearing steel. Four, the strict macrostructure and microstructure, At high magnification) Organization for NTN 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. The dangers of carbide liquid chromatography were hard and brittle, it is the same as the brittle inclusion. Carbide network to reduce the impact toughness of steel, and made it the organization is not uniform, easy to deformation and cracking during quenching. Banded carbide annealing and quenching tempering and contact fatigue strength. Low and high power quality for performance and service life of rolling NTN bearing has a great influence, so in NTN bearing material standards have strict requirements on low and high power organization. Five, particularly strict surface defects and internal defects requirements for NTN bearing steel, surface 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, explicitly stipulated in the standard NTN bearing materials don't allow these defects. Six, particularly strict carbide inhomogeneity requirements in NTN bearing steel, if there is a serious uneven distribution of carbide, is in the process of heat treatment process is easy 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 lead to decrease as a result, NTN bearing life in NTN bearing material standard, the different specifications of the steel have clear special requirements. Seven, particularly strict surface decarburization layer requirements in NTN bearing material standard has strict rules on steel surface decarburization layer, if the surface decarburization layer beyond the prescribed scope of the standard, and before the heat treatment process, and there is no clear away all the, is in the process of heat treatment quenching is prone to quenching crack, cause scrap parts. Eight, other requirements in NTN bearing steel material standard of NTN bearing steel smelting method, hardness, fracture, oxygen content and annealing residual elements, spark test, delivery status, identity, and so on have strict requirements.