Bearing steel smelting quality of the basic requirements

The service life and reliability of the rolling bearing and largely has close relation with the quality of bearing steel smelting. Due to the nature of 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 bearing steel general control under,65%1. Only strict control of the bearing steel chemical composition, can through the heat treatment process to satisfy the bearing performance of the organization and hardness. Second, the size of the high precision demands of rolling bearing steel steel dimension precision is higher, this is because most of the bearing parts, it takes pressure molding. In order to save material and improve labor productivity, the vast majority of 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 ensure the quality of bearing parts, 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. Harmful oxide and silicate inclusions in bearing steel bearing early fatigue is the main cause of peeling, significantly reduce the bearing life. Especially brittle inclusion most harmful, because in the process of peeling off easily from the metal substrate, seriously affect the quality of bearing parts after finishing surface. Therefore, in order to improve the service life and reliability of the bearing, must reduce the content of inclusions in bearing steel. Four, 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. 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, high quality of performance and service life of rolling bearing has a great influence, so, in standard bearing materials have strict requirements on low and high power organization. Five, particularly strict surface flaws and internal requirements for 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 the processing, the bearing performance and life of bearing has a great influence, explicitly stipulated in the standard bearing materials don't allow these defects. Six, particularly strict carbide inhomogeneity requirements in 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, serious inhomogeneity carbide bearing parts during quenching cooling could produce cracks, carbide non-uniformity also can reduce the service life of bearing, therefore, in the bearing material standard, with different specifications of the steel have clear special requirements. Seven, particularly strict requirements on the bearing surface decarburization layer material standard of the decarburization layer of the steel surface has strict rules, 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 for bearing steel in bearing steel material standard of smelting method, hardness, fracture, oxygen content and annealing residual elements, spark test, delivery status, identity, and so on have strict requirements.