Comparative Assessment on the Hot Deformation Behaviour of 9Cr-1Mo Steel with 1Cr-1Mo Steel

Hot forged 1Cr-1Mo and 9Cr-1Mo steels are being progressively used in the making of the turbine rotors of steam power plants. Forging of these steels requires precise control of processing parameters (i.e. strain, strain rate and temperature) for a defect free product. In line with the above mentioned applications, a comparative study to analyze the hot deformation behavior of both the steels was carried out in the temperature domain of 850-1050 degrees C with varying strain rate (0.001-0.1 s(-1)) by compression test data obtained from Gleeble 3800 (R) thermomechanical simulator up to true strain of 0.69. The flow stress behavior of hot compressed specimens was analyzed by using material constants, activation energy and formulated Zener-Hollomon parameter. Critical conditions for dynamic recrystallization (DRX) of both the steels were calculated with the help of a mathematical model developed by Poliak and Jonas. Further, the variations in critical conditions were correlated with the Zener-Hollomon parameter. For both the steels, the current study also focused on the comparison of dynamically recrystallized austenite (X-DRX) volume fraction with respect to true strain by applying the concept of Avrami equation. Finally, to validate the kinetics of DRX and softening mechanism, the microstructural evaluation and characterization have been carried out using optical and electron microscopy.

Automated summary

Hot forged 1Cr-1Mo and 9Cr-1Mo steels are increasingly used in turbine rotor manufacturing for steam power plants, requiring precise control of processing parameters for defect-free products. A comparative study analyzed the hot deformation behavior of both steels, determining flow stress behavior, activation energy, Zener-Hollomon parameter, and critical conditions for dynamic recrystallization. The study also focused on the comparison of dynamically recrystallized austenite volume fraction with respect to true strain. Microstructural evaluation and characterization were conducted to validate the kinetics of DRX and softening mechanism.