Hot deformation characteristics of as-cast high-Cr ultra-super-critical rotor steel with columnar grains

摘要

Isothermal hot compression tests of as-cast high-Cr ultra-super-critical (USC) rotor steel with columnar grains perpendicular to the compression direction were carried out in the temperature range from 950 to 1250A degrees C at strain rates ranging from 0.001 to 1 s(-1). The softening mechanism was dynamic recovery (DRV) at 950A degrees C and the strain rate of 1 s(-1), whereas it was dynamic recrystallization (DRX) under the other conditions. A modified constitutive equation based on the Arrhenius model with strain compensation reasonably predicted the flow stress under various deformation conditions, and the activation energy was calculated to be 643.92 kJa (TM) mol(-1). The critical stresses of dynamic recrystallization under different conditions were determined from the work-hardening rate (theta)-flow stress (sigma) and -a,theta/a,sigma-sigma curves. The optimum processing parameters via analysis of the processing map and the softening mechanism were determined to be a deformation temperature range from 1100 to 1200A degrees C and a strain-rate range from 0.001 to 0.08 s(-1), with a power dissipation efficiency eta greater than 31%.