Influence Mechanism Of Si On Carbide Formation In GCr15SiMo Bearing Steel

GCr15SiMo steel is a new type of steel with a large demand in the market,compared with GCr15 bearing steel,its content of Si and Mo elements has been improved,and the properties such as hardenability and elastic limit have also been improved.In order to improve the performance of bearing steel,researchers have carried out a lot of research starting from the process of controlling the carbide of bearing steel.In this thesis,the influence mechanism of Si content in steel on the carbide generation process of GCr15SiMo bearing steel is studied,so as to provide a theoretical basis for further improving the performance of bearing steel products by controlling carbide morphology.The GCr15SiMo steel samples with different Si contents obtained by smelting were detected and analyzed by scanning electron microscopy,XRD,energy spectrum and other means,and combined with the thermodynamic simulation software JMat Pro calculation,it was found that with the increase of Si content,the structure in GCr15SiMo bearing steel remained unchanged,and it was still lamellar pearlite and carbide,but the precipitation temperature of each phase changed,the precipitation temperature of cementite,ferrite,M₂（C,N）gradually increased,and austenite,M₂₃C₆,The precipitation temperature of M₇C₃gradually decreases.The increase of Si content makes the structure in cast bearing steel more uniform and dense,the spacing of lamellar pearlite sheets becomes smaller,and the hardness of the steel becomes larger.When the Si content reaches 0.74%,the structure is the most uniform and dense,the spacing between flaky pearlite sheets is the smallest,0.22μm,and the maximum hardness of the steel sample is 54.8 HRC.However,as the Si content continued to increase,the spacing of lamellar pearlite sheets did not continue to decrease,but increased,and the hardness began to decrease.Exploring the effects of austenitizing temperature and holding time on the carbides of GCr15SiMo steel,the optimal annealing process of GCr15SiMo steel is as follows:austenitizing temperature is 800°C and holding time is 30 min.At this time,the proportion of small particles of carbide in the bearing steel is the largest,and the large-size carbide almost disappears,and the spheroidization effect is the best.The research on the optimal isothermal spheroidization annealing process of GCr15SiMo steel samples with different Si content,combined with high-temperature confocal microscopy,it is found that with the increase of Si content,the carbide size of bearing steel becomes smaller,the number gradually increases,the spheroidization effect of bearing steel increases,the hardness decreases,and the carbide type will not change,which are M₂₃C₆,M₂（C,N）.When the Si content is 0.82%,there is almost no large-size sheet carbide in the steel,only a large number of small-size spherical structure,at this time the bearing steel obtains a complete global annealing structure,and the carbide in the steel is the smallest and the most evenly distributed.When the Si content in GCr15SiMo steel is controlled in the range of 0.74%～0.82%,it is conducive to controlling the morphology of carbide in steel and improving product performance.