Macro and micro simulation of microstructure evolution in discontinuous thermal deformation of large forging parts

Abstract

Several modeling methods of microstructure evolution in the hot working process of typical large forging materials were summarized. Taking the microstructure evolution law of nuclear power steel SA508-3 in the whole process from heating to forging as the research content, phenomenological mathematical models which could reflect the physical characteristics of microstructure evolution were established. Taking the low carbon steel SS400 as the research object, the new identification method of nucleation parameters and the dislocation-related nucleation model were proposed, and the cellular automaton model suitable for predicting the dynamic recrystallization behavior of this material was developed. Taking low-pressure rotor steel 30Cr2Ni4MoV as the research object, according to the combination of theoretical modeling, numerical simulation and experimental research and the macro and micro interaction law among strain-dislocation density-recrystallization-flow stress, the cellular automaton simulation method of microstructure evolution in the processes including austenite grain could growth-deformation-recovery-dynamic recrystallization-meta-dynamic recrystallization-static recrystallization was established, which could be used to simulate the microstructure evolution of multi-pass hot compression. Taking stainless steel 316LN for nuclear power as the research object, by introducing the idea of multilevel cellular space into the traditional cellular automaton simulation framework and formulating cellular state transformation rules in recrystallization and data transfer rules between different levels of cellular spaces, the multilevel cellular automaton model for simulating the dynamic recrystallization was constructed. The established multilevel cellular automaton model includes a full-field multilevel grain topological deformation module and a multilevel recrystallized nucleation module, and this model was verified. The industrial application cases of new technological derelopment for nuclear large steam generator and water chamber head forming were introduced. Furthermore, combining with the cellular automaton model of multi-pass, the multi-scale digital simulation system for discontinuous deformation of hot forging was integrated to simulate the microstructure evolution of multi-step and multi-pass drawing process.