In this paper, we investigated the effects of the matrix and precipitates in Cr-Ni-Mo-V rotor steel on its mechanical properties after water quenching and tempering (450–700 °C). The results indicate that the microstructure and mechanical properties of the steel can be significantly adjusted by changing the tempering temperature. An excellent combination of tensile strength (1028.608 MPa) and elongation (19%) was obtained upon tempering at 650 °C. This is attributed to the martensite lath with a high dislocation density, solid solution strengthening and the strengthening effect of spherical Mo₂C and VC particles. At a tempering temperature of 550 °C, the precipitation and development of rod-shaped Fe₃Mo₃C resulted in a considerable drop in strength. At 650 °C, the dissolution of Fe₃Mo₃C and dispersion precipitation of Mo₂C and VC led to a large rise in strength. At 700 °C, the coarsening of Mo₂C and VC, together with the recrystallization of the martensite lath, resulted in a loss in strength. Meanwhile, as the tempering temperature was increased from 450 °C to 700 °C, the tensile fracture characteristics of Cr-Ni-Mo-V rotor steel gradually changed from cleavage fractures to dimple fractures.

The influence of tempering temperature on the microstructure and mechanical properties of Cr–Ni–Mo–V rotor steel for large rotors was investigated. The microstructure was characterized by scanning electron microscope, transmission electron microscope and X-ray diffraction, and the mechanical properties were tested by uniaxial tensile test. The results show that as the tempering temperature increases from 450 ℃ to 700 ℃, the strength of Cr–Ni–Mo–V rotor steel first decreases, then increases and then decreases again, and the plasticity gradually increases. The main reason is that with the increase of tempering temperature, the gradual recovery and recrystallization of lat martensite lead to a decrease in dislocation density in the matrix, and the carbide gradually changes from a large number of rod-shaped continuous Fe3Mo3C distribution to a spherical Mo2C and VC distribution, resulting in Fe3Mo3C precipitation and resolution, and dispersion precipitation of Mo2C and VC. Therefore, the change in strength is mainly influenced by the balance between the strengthening of the solid solution, the strengthening of the precipitation and the strengthening of the dislocation in the matrix.