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Basic requirements for exercise quality of NTN bearing steel
Source: China Bearing Network Time: 2014-01-25
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First, the strict chemical composition requirements NTN bearing steel is mainly high carbon chromium NTN bearing steel; that is, the carbon content is about 1%; participate in about 1.5% of chromium; and is rich in a small number of manganese, silicon Steel analysis. Chromium can improve heat treatment function, improve hardenability, arrange uniformity, tempering stability; and can improve the anti-rust function and grinding function of steel. But when the chromium content exceeds 1.65%; Adding retained austenite in steel; reducing hardness and dimensional stability; adding carbide non-uniformity; reducing steel impact toughness and fatigue strength. For this reason; chromium content in high carbon chromium NTN bearing steel is usually controlled at 1 65% or less. As long as the chemical composition of the NTN bearing steel is strictly controlled; the order and hardness of the satisfactory NTN bearing function can be obtained through the heat treatment process.
Second, the high-precision scale demand rolling NTN bearing steel demand steel scale accuracy is higher; this is because most NTN bearing parts have to be formed by pressure. In order to save data and improve labor productivity; most NTN bearing rings are Through the forming of the casting; the steel ball is formed by cold heading or hot rolling; the small-scale roller is also formed by cold heading. If the dimensional accuracy of the steel is not high; the cutting scale and component cannot be accurately calculated; and the NTN cannot be ensured. The quality of the bearing parts; also the formation of equipment and mold damage.
Third, the unique and strict purity requirements The purity of steel refers to the number of non-metallic inclusions in the steel; the higher the purity; the less non-metallic inclusions in the steel. The oxide and silicic acid in NTN bearing steel Harmful inclusions such as salt are the main reason for the early exhaustion of NTN bearings and the significant decrease in the life of NTN bearings. The uniqueness is the most damage to brittle inclusions; it is simply removed from the metal substrate during processing; severely affecting NTN bearing parts The quality of the finished surface after processing. Therefore; in order to improve the service life and reliability of NTN bearings; it is necessary to reduce the content of inclusions in NTN bearing steel.
Fourth, strict low-order arrangement and microscopic (high-power) arrangement requirements NTN bearing steel low-order arrangement refers to usually loose, intermediate loose and flat analysis; microscopic (high-power) arrangement includes steel annealing arrangement, carbide mesh, Banding and liquid precipitation, etc. Carbide liquid is hard and brittle; its damaging is the same as brittle inclusions. Reticulated carbides reduce the impact toughness of steel; and make it unevenly arranged; simple deformation and cracking during quenching. Strip carbide affects annealing and quenching and tempering arrangements and touch fatigue strength. The low and high magnification arrangements have a great influence on the function and service life of the tumble NTN bearing; therefore; in the NTN bearing data specification, low, High-powered arrangements have strict demands.
5. Unique and severe external defects and internal defects. For NTN bearing steel; external defects include cracks, slag inclusions, burrs, crusting, oxide scales, etc.; internal defects include shrinkage cavities, bubbles, white spots, severe looseness and Segregation, etc. These shortcomings have a great influence on the processing of NTN bearings, the function and lifespan of NTN bearings; the clear rules in the NTN bearing data specification do not allow these shortcomings to be presented.
Sixth, the unique and strict carbide non-uniformity demand in NTN bearing steel; if it presents a severe uneven carbide dispersion; then in the heat treatment process is simply formed arrangement and hardness unevenness; steel arrangement unevenness Touch fatigue strength has a greater impact. Others; severe carbide inhomogeneity also makes NTN bearing parts crack when quenching and cooling; carbide inhomogeneity will also lead to a decrease in the life of NTN bearings; In the bearing data specification; there are clear and unique requirements for different specifications of steel.
Seven, unique and strict appearance of decarburization layer requirements In the NTN bearing data specification, there are strict rules on the decarburization layer of steel; if the outer decarburization layer exceeds the normative rule scale; and it is not in the processing process before heat treatment Completely removed; in the heat treatment quenching process, quenching cracks occur simply; the formation of parts is invalid.
8. Other requirements In the NTN bearing steel data specification, there are strict requirements for the training methods, oxygen content, annealing hardness, fracture, residual elements, spark inspection, delivery status, and marking of NTN bearing steel.
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