| In China, with the development of high-end equipment manufacturing industry and the attention to the small size and light weight of the bearing components, the quality of the bearing steel GCr15 products used in bearing manufacturing has been demanded higher,especially in controlling the grade of network carbide. Though advanced equipments and new technology have been used in bearing steel production process, the precipitation of network carbide in bearing steel has still not been effectively solved. Combined with the actual situation of a certain steel mill, a study on the control of network carbide in bearing steel is carried out, using laboratory simulations, field tests and temperature field simulations. The main research contents and results of the present work are included as the following:(1) Thermal simulation of the continuous cooling process of GCr15 bearing steel after hot-rolling was performed by MMS-200 multifunction thermo-mechanical simulator in the laboratory. The results showed that cooling rate and deformation temperature had an important influence on the morphology of secondary carbide in grain boundary. With the increase of cooling rate, the precipitation of network carbide could be inhibited; with the decrease of deformation temperature, the secondary carbide appeared broken off.(2) With the aid of the commercial FE software MSC.Marc, the temperature field simulation results for Φ23mm and Φ40mm bearing steel in rapid cooling process were got.A analysis of the existing cooling process was conducted according to simulated temperature and cooling rate in different sites of cross section. The simulated results of temperature were in good agreement with measurements.(3) A analysis of the primary and secondary impacts of controlled cooling process parameters for Φ40mm bearing steel bars was conducted using orthogonal design method and finite element simulation. The impact trend of various parameters to test index was discussed, while a most sensitivity factor, the length of water cooling zone, was determined with the use of variance analysis, which provided a reference to the optimization of water cooling process in production line.(4) With pre-water cooling device applied in field trials, low temperature rolling was achieved by adjusting the water pressure in pre-water cooling device. With the increase of the water pressure, the grade of network carbide decreased.(5) A segmented secondary cooling process was proposed for high-temperature bearing steel. With the aid of the FE software MSC.Marc, temperature field of GCr15 bearing steel of different specifications in segmented secondary cooling process was got.The results showed that the cooling rate of different sites of high-temperature bearing steel cross section was reach to the cooling rate require of restraining network carbide and residual austenite transforming to pearlite absolutely, which achieved the purpose of water cooling process optimization. |
