Quality Requirements For Bearing Steel

1. Quality requirements for bearing steel. Rolling bearing to tensile, compression, bending, shear, alternating and other complex stress states and high stress values, high speed, long time work. Therefore, in the production process, there are many quality control inspection items of bearing steel, the control scope is narrow, the production process is strict and complex, and certain tooling equipment, inspection means and certain level of villain technology are required. In order to ensure that bearings have good performance and high life, the quality requirements for bearing steel are as follows:

(1) Chemical composition: chemical composition is the most essential factor of bearing steel. The physical, chemical, mechanical properties and metallographic structure of steel are determined by the chemical composition. Changing the chemical composition will change the basic properties of steel. Therefore, the chemical composition of bearing steel must conform to the allowable range specified in the standard.

(2) Internal quality: it can be divided into macro quality and micro quality.

Macro quality: Bearing steel is not allowed to have white spots, shrinkage holes, slag inclusion, civilian metals, cracks, overburning, subcutaneous bubbles and other defects. The internal segregation and porosity of bearing steel are required to be controlled within a certain range. In short, the interior of the bearing steel should be dense, and no visible defects should be allowed to split the steel matrix.

Microscopic quality: The internal organization of bearing steel should be uniform and the purity should be high.

The internal structure of bearing steel refers to carbide strip, carbide network, carbide liquid out and annealed structure. Carbide is one of the main components of bearing steel, is objective existence, how to make the distribution of carbide uniform, dispersed, fine, is one of the important issues to improve the quality of bearing steel. In recent years, the main manufacturers of bearing steel have adopted high temperature diffusion treatment, new controlled rolling technology and continuous annealing furnace equipment. Even so, the distribution of carbides is still not ideal. Therefore, their permissible scope and level of control are specified in the standard.

The purity of bearing steel refers to the degree of contamination of non-metallic inclusions on steel. Non-metallic inclusions are the main substances of bearing steel matrix, which destroy the continuity of the matrix and are one of the main causes of early fatigue and spalling of bearings. Therefore, the less non-metallic inclusion is required in bearing steel, the better. In order to limit and control the presence of non-metallic inclusions in steel, strict grade control is carried out on them in the standard. In addition to using electric furnace smelting and electroslag remelting, manufacturers also use electric furnace smelting and refining, vacuum deoxidation, argon blowing treatment, outside the furnace powder treatment, trying to reduce the oxygen content of steel to less than 20ppm.

(3) Surface quality: the forming methods of bearing parts, including forging, turning and cold stamping, etc. According to different forming methods, the surface quality of steel has different requirements. In general, bearing steel surface shall not have cracks, folding, cracking, scarring and slag inclusion. For cold drawing steel for cold stamping, in addition to the above defects, the surface should be clean, no corrosion, pitting and other defects. Bearing steel surface shall not have serious decarbonization phenomenon, according to the different requirements of bearing parts forming process, in the standard, there are different restrictions on the depth of decarbonization layer on the surface of different varieties of steel.

(4) Size tolerances: According to the forming process of bearing parts and the production process of steel, the size tolerances of various varieties and specifications of bearing steel are specified in the standards. Dimensional tolerance of forged steel is generally in accordance with GB908-72 standard, dimensional tolerance of hot-rolled steel is in accordance with GB702-86, cold-drawn steel is in accordance with GB905-82 standard, and cold-drawn steel wire is in accordance with YB245-64 standard.