Study On Evolution Law And Mechanical And Fatigue Properties Of Carbide In High Alloy Bearing

The carbides evolution of low carbon Cr-Co-Mo-Ni high alloy bearing steel were studied based on qualitative and quantitative methods. The carbides under different cryogenic temperature、carbides evolution under different temperature and carbides in carburizing layer have the influence on rotating fatigue performence of steel were researched and carbides grew up theory was discussed, then the relationship between carbides and mechanical properties were studied.(1) The steel was did heat treatment using different cryogenic temperature and the carbides in it were researched. The results show that the steel had M6C and M2C carbides, The process in -196℃ cryogennic increased M2C nucleation of steel and make the steel yield strength increase, after tempering, M2C grew up to 35.7 nm and the yield strength of steel decreased.(2) The testing steel after a reasonable heat treatment was insulated 100 h at different temperatures to research heating temperature had impact on carbides evolution and mechanical properties of steel. The results show that hardness、yield strength and tensile strength of steel increaseed after decreasing, hardness、yield strength and tensile strength droped the lowest point 35.3 HRC、895 MPa and 1197 MPa, impact energy reached highest point 107 J under 750℃. The size of M23C6 and M6C increased gradually, the effect of second phase strengthening reduced to make mechanical propertity decrease, then the mechanical properties decreased because of the alloy elements spreading to matrix lead to solid solution strengthening.(3) The testing steel after a reasonable heat treatment was put in 700℃ and 960℃ for a long time to heat respectively, holding time had influence on carbides and mechanical properties was researched. The results show that insulating 100 h under 700℃, the hardness falled 2.5 HRC, in the heating process the highest impact energy was 66 J, highest yield strength was 895 MPa, lowest tensile strength was 1195 MPa. The main carbides in the steel were M6C and M23C6, the critical curing radius was 0.25μm, the curing rate of M6C was 0.112μm/h1/3 between 5 h and 20 h and matained 0.061μm/h1/3 between 20 h and 100 h, the curing rate of M23C6 reached the lowest point 0.014μm/h1/3 in 50 h. The steel had M6C After 960℃ heat preservation for a long time, the diameter increased 0.05μm. The steel was insulated from 10 h to 20 h, M2C had the effect of enhancing the matrix to make the hardness and break elongation increase rapidly, at the same time M6C grew in grain boundary decreasing impact energy quickly.(4) putting the roating bending fatigue specimens after carburizing in domestic PQ1-6 type rotating bending fatigue testing for rotating bending fatigue test, carbides in carburizing layer had effect on performance of rotating bending fatigue was researched. The results show that the cracking in carburizing layer near the surface caused by carbides was 86% and in caiburizing layer surface caused by carbides was 40%, the cracks spreaded along M23C6.