On critical deformation of dynamic recrystallization of steam turbine low pressure rotor steel 26Cr2Ni4MoV

The Steel 26Cr2Ni4MoV is adopted to manufacture low-pressure steam turbine rotors generally. However, hybrid crystals tend to occur in real production. Thermo-torsion method was adopted to investigate the dynamic recrystallization of Steel 26Cr2Ni4MoV when the strain rate was 0.04S^-1 and the deformation temperature was 800°C, 900°C, 1000°C and 1100°C, respectively. The critical strain was obtained when the Steel 26Cr2Ni4MoV dynamic recrystallization happens. Thermo-torsion testing results show that the dynamic recrystallization tended to occur when the temperature was high. The critical strain was 0.21 when the temperature was 1100°C, but the maximum equivalent strain in real production of rotors forgings was 0.18, still smaller than the critical strain, which was necessary for the generation of dynamic recrystallization. Therefore, it is hard for dynamic recrystallization to happen in real production of rotors forgings. Fine and even crystals can be obtained through the static recrystallization after forging.