Microstructure and mechanical properties of a high strength heat resistant bearing steel
Microstructure and mechanical properties of a new type of ultra-high strength bearing steel with optimized composition after heat treatment by different processes were studied by means of optical microscope(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),tensile test and Rockwell hardness tester.The results show that the tensile strength of the experimental steel increases and the yield strength decreases with the increase of solution temperature in the range of 1040-1080℃.After solution treatment at 1060 ℃ for 1 h by oil quenching and treatment by(cryogenic treatment at-73 ℃ for 2 h+tempering at 540 ℃ for 2 h)for twice,the tensile strength of the experimental steel reaches 1997 MPa,the yield strength reaches 1600 MPa,the elongation after fracture reaches 12％,and the reduction of area is 55％,which shows excellent strength and toughness.With the increase of solution temperature,the primary austenite grain size of the experimental steel increases gradually,from 19 μm increased to 50.9 μm,the content of undissolved carbide decreases obviously,and the content of retained austenite increases gradually.The increase of retained austenite is the main reason for the gradual decrease of yield strength.There are two different kinds of precipitates,M6C and Laves,in the experimental steel.Among them,the M6C carbide plays a role in refining grains in the solid solution stage,and the Laves phase uniformly precipitates during the tempering,which is the main strengthening mechanism for the experimental steel to obtain ultra-high strength.
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