NTN Bearing steel smelting quality basic requirements

NTN Bearing steel smelting quality basic requirements

       Closely related smelting quality rolling bearing life and reliability NTN largely NTN bearing steel. Since NTN bearing steel with the characteristics of the smelting quality requirements are much stricter than the general steel industry, such as steel chemical composition, purity, organization and uniformity.

First, the chemical composition of the strict requirements

Usually NTN carbon chromium bearing steel is mainly NTN Bearing steel, carbon content that is about 1%, about 1.5% of chromium is added, and a small amount of manganese, silicon element eutectoid steel. Chromium heat treatment can improve performance, increase hardenability, microstructure uniformity, tempering stability, but also can improve the rust resistance and grinding performance steel. But when the chromium content exceeds 1.65%, it will increase the retained austenite after quenching, reduce the hardness and dimensional stability, increased carbide inhomogeneity, reducing steel toughness and fatigue strength. To this end, high-carbon chromium bearing steel NTN amount of chromium containing the general control of 1,65% or less. Only strict control of NTN Bearing steel chemical composition, in order to be satisfied NTN Bearing performance microstructure and hardness through heat treatment process.

Second, the size precision requirements

NTN Bearing steel rolling steel higher dimensional accuracy, because most NTN Bearing parts to go through pressure molding. In order to save material and improve labor productivity, the vast majority of NTN bearing rings are formed through forging, cold heading steel ball is the result of hot-rolled or shaped, small-size roller is formed through cold forging. If the dimensional accuracy of the steel is not high, it can not accurately calculate the sizes of materials and weight, but can not guarantee the quality of products NTN bearing parts, are likely to cause damage to equipment and tooling.

Third, particularly stringent purity requirements

Purity steel refers to the number of non-metallic inclusions contained in the steel, the higher the purity, the less non-metallic inclusions in steel. NTN Bearing steel oxides, silicates and other harmful inclusions lead to early fatigue spalling NTN Bearing, mainly due to a significant reduction NTN bearing life. Especially brittle inclusions most harmful, because the easily peeled off from the metal substrate in the process, seriously affecting the quality of NTN bearing parts surface after finishing. Therefore, in order to improve the life and reliability of NTN bearings, NTN bearings must reduce the amount of steel inclusions.

Fourth, strict macrostructure and microstructure (high power) organizational requirements

NTN Bearing Steel low magnification refers to the general loose, center porosity and flat analysis, microscopy (high magnification) organizations, including organizations annealing steel, carbide mesh, ribbon and fluid analysis and the like. Eliquation carbide hard and brittle, it's the same dangers and brittle inclusions. Reduce the impact of network carbide toughness, uneven and make organization easier in quenching deformation and cracking. Carbide strip annealing and quenching and tempering influence organizations and contact fatigue strength. Low, the merits of high-powered organization has a great influence on the rolling NTN bearing performance and service life, so in NTN standard bearing materials for low, high-powered organization has strict requirements.

Fifth, particularly stringent requirements for surface defects and internal defects

NTN Bearing steels for surface defects including cracks, slag, burrs, scarring, oxide and other internal defects include craters, bubbles, white point, severe osteoporosis and segregation. These defects for NTN Bearing processing, NTN Bearing performance and life have a great impact in the NTN standard bearing materials clearly do not allow the emergence of these defects.

Sixth, the carbide of particularly stringent requirements

In NTN Bearing steels, carbide if severe uneven distribution of the heat treatment process likely to cause non-uniform microstructure and hardness of the steel inhomogeneity have a greater impact on the contact fatigue strength. In addition, severe carbide heterogeneity also easy to make NTN bearing parts crack when quenching, carbide heterogeneity will result in reduced bearing life NTN Therefore, NTN standard bearing materials, different specifications of steel are clear special requirements.

Seven, particularly stringent requirements for surface decarburization

In NTN standard bearing materials for steel surface decarburization layer has strict rules, if the surface carbon layer outside the specified range of the standard, and in the process before the heat treatment in its entirety and not removed, then the heat treatment and quenching process it is easy to produce quenching cracks, resulting in scrapped parts.

Eight other requirements

In NTN Bearing steel smelting method also standard NTN Bearing steel, oxygen content, annealed hardness, fracture, residual elements, spark test, delivery status, identification and other strict requirements.