Hot Deformation Behavior and Thermal Processing Map of 630°C Ultra-Supercritical Rotor Steel

The isothermal hot compression experiments of 630°C ultra-supercritical rotor steel were performed using Thermecmastor-Z thermal simulation testing machine. The deformation behavior of the steel was studied at temperatures ranging from 950–1250°C and strain rate of 0.01–0.5 s^–1. The results indicate that the flow stress of the steel increases as the deformation temperature decreases and the strain rate increases. The flow stress curves of the steel can be categorized into two types: dynamic recovery and dynamic recrystallization (DRX). The activation energy of hot deformation of the steel was calculated to be 528 584 J/mol, and a high temperature plastic constitutive equation of the steel was established. The calculated flow stress values are in good agreement with the experimental results. The thermal processing map of the steel under strain of 0.9 was established. After analyzing the microstructural characteristics following thermal deformation, it was found that the steel showed improved deformation behavior at temperatures ranging from 1050–1175°C and strain rates of 0.01–0.5 s^–1. The typical microstructural characteristics in these safe zones include equiaxed and fine DRXed grains.