The properties of NSK needle roller bearings material:
Due to the characteristics of NSK imported bearing steel, the quality of smelting is much stricter than that of general industrial steel, such as the chemical composition, purity, microstructure and structural uniformity of steel.
First, strict chemical composition requirements of NSK needle roller bearings
Generally, NSK needle roller bearings are mainly high-carbon chromium bearing steels, that is, hypereutectoid steels containing about 1% of carbon, adding about 1.5% of chromium, and containing a small amount of manganese and silicon. Only by strictly controlling the chemical composition of NSK imported bearing steel can the structure and hardness satisfying the performance of NSK needle roller bearings can be obtained through the heat treatment process.
Second, strict high precision dimensional requirements of NSK needle roller bearings
NSK needle roller bearings require higher dimensional accuracy because most NSK needle roller bearings are pressure molded. In order to save raw materials and increase labor productivity, most NSK needle roller bearings are forged, steel balls are cold-rolled or hot-rolled, and small-sized rollers are cold-formed. If the dimensional accuracy of the steel is not high, the size and weight of the blank cannot be accurately calculated, so that the product quality of the NSK needle roller bearings is not guaranteed, and the manufacturing equipment is easily damaged.
Third, particularly strict purity requirements of NSK needle roller bearings
The purity of steel refers to the amount of impurities contained in the steel. The higher the purity, the less non-metallic inclusions in the steel. The content of harmful impurities such as oxides and silicates in bearing steel has a great relationship with the early fatigue spalling of NSK bearings and the life expectancy of NSK needle roller bearings. In particular, brittle impurities are the most harmful, and it is easy to peel off from the metal substrate during processing of NSK needle roller bearings, which seriously affects the appearance quality of NSK needle roller bearings after finishing.
Fourth, strict low-fold tissue and microscopic (high magnification) tissue requirements of NSK needle roller bearingsThe low-magnification structure of the bearing steel refers to general looseness, center looseness and flatness, and the microscopic (high-power) structure includes annealed structure of steel, carbide mesh, ribbon and liquid analysis. Carbide liquid is hard and brittle, and the hazard is the same as brittle inclusions. Reticulated carbide reduces the impact toughness of steel and makes the structure uneven, which is easily deformed and cracked during quenching. Banded carbides affect annealing and quenched tempered structures and contact fatigue strength.
Fifth, external and internal defects, particularly stringent requirements of NSK needle roller bearings
For NSK imported 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. These defects have a great influence on the processing of the bearing, the performance and life of the NSK needle roller bearings, and the NSK needle roller bearings data specification clearly stipulates that these defects are not allowed.
Sixth, particularly stringent carbide non-uniformity requirements of NSK needle roller bearings
In the NSK imported bearing steel, if the serious carbide distribution is uneven, the microstructure and hardness are easily uneven during the heat treatment process, and the structural heterogeneity of the steel has a great influence on the contact fatigue strength.
Seventh, particularly stringent surface decarburization requirements of NSK needle roller bearings
NSK needle roller bearings have strict regulations on the decarburization layer of steel. If the decarburization layer does not meet the scope of the standard and has not been removed during the processing NSK needle roller bearings before heat treatment, then it is treated at heat. Quenching cracks are likely to occur during the quenching process, resulting in the scrapping of parts of the NSK needle roller bearings.
Eighth, other requirements of NSK needle roller bearings
The bearing steel material specification also has strict requirements on the smelting method of bearing steel, oxygen content, annealing hardness, fracture, residual elements, spark inspection, delivery status, and marking.
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