Effect of Tempering Temperature on Microstructure and Mechanical Properties of Cr-Ni-Mo-V Rotor Steel

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.