Microstructural evolution of a steam-turbine rotor subjected to a water-quenching process: numerical simulation and experimental verification

Cr-Ni-Mo-V steam-turbine rotors have been widely used as key components in power plants. In this study, a coupled thermomechano-metallurgical model was proposed to simulate the phase transformation and transformation-induced plasticity (TRIP) of a 30Cr2Ni4MoV steam-turbine rotor during a water-quenching process, which was solved using a user defined material mechanical behavior (UMAT) subroutine in ABAQUS. The thermal dilation, heat generation from plastic work, transformation latent heat, phase transformation kinetics, and TRIP were considered in the model. The thermomechanical portion of the model was used to predict the evolution of temperature, strain, and residual stress in the rotor. The phase transformation that occurred during the quenching process was considered. Constitutive models of phase transformations (austenite to pearlite, austenite to bainite, and austenite to martensite) and TRIP were developed. Experimental data were adopted and compared with the predicted results to verify the accuracy of the model. This demonstrates that the model is reliable and accurate. Then, the model was utilized to predict the temperature variation, dimensional change, minimum austenitization time, residual stress, TRIP, and volume fractions of each phase. It is concluded that this model can be a useful computational tool in the design of heat-treatment routines of steam-turbine rotors.