Critical Conditions for Dynamic Recrystallization of Hot Deformed 1 wt% Chromium - 1 wt% Molybdenum Rotor Steel

Abstract

A medium carbon 1 wt% Chromium and 1 wt% Molybdenum low-alloy steel is an important material for making of rotors of turbines. Its hot forging requires precise control of temperature, strain, and strain rate for defect-free forging. In a view of this, this steel was subjected to a hot compression test in a thermomechanical simulator, Gleeble 3800®. Hot compression was carried out at temperatures of 900°C, 1,000°C, and 1,100°C. At each temperature four strain rates, i.e., 0.001 s−1, 0.01 s−1, 0.1 s−1 and 1 s−1, were used. Constitutive equations were used to analyze hot flow behavior, material constants, and activation energy. A mathematical model developed by Poliak and Jonas has been used to determine critical condition parameters like critical stress (σc), critical strain (εc), peak stress (σp), and peak strain (εp). For dynamic recrystallization (DRX), the variation of strain hardening rate up to steady state stress (σss), steady state strain (εss), and volume fraction of DRX (XDRX), with the help of Avrami-type models, have been discussed. Zener Hollomon parameters (Z) explained in terms of strain rate and steady state that flow stress (σss) has been expressed. Microstructures at different hot deformation conditions have been reported and explained.