Study On Spheroidizing Process Of High Carbon Si - Mn Steel And Its Effect On Microstructure And Properties

Recently, with the fast development of car and machinery automation industry, the use of all kinds of bearings increased rapidly and the performance was required to be more comprehensive. Purity is an importance factor in the study of bearing steel. Under the present equipment and smelting technology, it has been able to obtain high purity of bearing steel case. It has been demonstrated that the performance and service life of high carbon silicon manganese steel can be improved by improve the carbide morphology and size uniformity. The high carbon silicon manganese steel was investigated as experimental material in this paper. A systematic research has been done to study the isothermal spheroidzing annealing process and its influence on the microstructure and mechanical properties of high temperature tempering. By images software statistical analysis has been done for spheroidizing carbide and high temperature tempering undissolved carbide including number、particle size and size uniformity to characterize the spheroidizing quality and microstructure genetic. These results can provide the theoretic foundation for strength and toughness influenced by morphology, size and uniformity of carbide of GCr15SiMn bearing steel.The results showed that it has important influence on the spheroidizing carbide and high temperature tempering undissolved carbide morphology, the size of the number, size and uniformity by changing the heating temperature, heating time, isothermal temperature and isothermal time during isothermal spheroidizing annealing process.With the increase of the heating temperature, the number of fine granular carbides increased, austenite composition was homogenized and the chance of lamellar carbide increases. When the heating temperature was 770℃, the spherical was cementite fine dispersion and the roundness and size uniformity was the best. With the extension of the heating time, the number and particle size of carbides decreased but the roundness and size uniformity was improved. When the heating time was 6h, the spherical cementite was fine dispersion and the roundness and size uniformity was the best.With the increase of isothermal temperature, the average particle size, the variance of particle size and the roundness first decreased then increased but the number of carbide first increased then decrease. The lamellar carbide production appeared mainly due to the temperature of pearlite transformation zone. When the isothermal temperature was 700℃, the spherical cementite was fine dispersion and the roundness and size uniformity was the best. With the extension of the isothermal time, the carbide change rule of the average particle size, the variance of particle size, the roundness and the number same to isothermal temperature. When the isothermal time was 4h, the spherical cementite was fine dispersion and the roundness and size uniformity was the bestAfter heating at 770℃ for 6h and isothermal process at 700℃ for 4h, the steel was then heated at 830℃ for 1h followed by oil quenching, tempered at 600℃ for 2h. It obtained good strength and toughness comprehensive performance with fine particle size, high roundness and good size uniformity undissolved carbide.