Evolution of Microstructure and Mechanical Properties of Ultra-High-Strength Heat-Resistant Bearing Steel During Long-Term Aging at 500 °C

In this study, various testing methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Electron Backscatter Diffraction (EBSD), and high-resolution transmission electron microscopy (HRTEM), were utilized to examine the effects of aging time on the microstructure and mechanical properties of ultra-high-strength heat-resistant bearing steel. The findings revealed that as the aging time progressed, the tensile strength, yield strength, and elongation exhibited an initial increase followed by a decline. Specifically, after 50 h of aging, the tensile strength and yield strength peaked at 2133 MPa and 1874 MPa, respectively. Calculations indicated that precipitation strengthening was the primary contributor to the strength, accounting for 1311 MPa. During the aging process, the martensite laths underwent coarsening, broadening from 202 nm to 306.5 nm, while the residual austenite remained relatively stable. Additionally, dislocations underwent annihilation, resulting in a decrease in dislocation density to 4.84 x 1011/cm2 at 100 h. As the aging time continued to increase, both M6C and M2C phases gradually coarsened. Notably, the number of M2C phases increased, and they transformed from an acicular shape to a spherical shape at 100 h.