Abstract: Effect of addition of 4.6%Mo on high-temperature (500 ℃) long-term mechanical properties and microstructure evolution of a heat-resistant bearing steel was studied by means of universal material testing machine, Rockwell hardness tester and scanning electron microscope. The results show that the addition of 4.6%Mo improves the decreasing trend of tensile strength and hardness of the tested bearing steel without Mo addition under 500 ℃ long-term tempering. After tempering for 100 h, the tensile strength and the hardness of 4.6Mo steel show an upward trend, and the yield strength begins to decrease when the tempering time is 80 h. During the entire tempering process, the percentage reduction of area of 0Mo steel shows an overall trend of first decreasing and then increasing, reaching a minimum value of 43.60% after tempering for 80 h. The percentage reduction of area of 4.6Mo steel does not show significant change within the tempering time range of 0-50 h, and then decreases, reaching a maximum value of 62.16% after tempering for 0 h and a minimum value of 51.84% after tempering for 80 h. With the extension of tempering time, the number and size of Fe₃C phase in the 0Mo tested steel decrease, while the size of M₂₃C₆ phase increases, growing from 25-42 nm after tempering for 10 h to 167-333 nm after tempering for 100 h. As the tempering time increases, there is no significant change in the size of M₂C phase in the 4.6Mo tested steel, but the quantity increases, however, the quantity of M₂₃C₆ phase does not change significantly, but the size increases slightly. The addition of Mo has a significant impact on the nucleation and growth mechanism of carbides, which can improve the tempering stability of the tested steel.

Key words: heat-resistant bearing steel, high-temperature long-term mechanical properties, microstructure evolution, thermal stability