Research On Hot Deformation Behavior And Grain Evolution Of As-cast SA508-3 Steel

Heavy forgings are usually forged by large ingots. Because there are much defects in large ingots and the formation has multi-pass, multi-reductions and heterogeneous deformation characteristics, coarse grain or heterogeneous structure occurs easily in forgings, which seriously weaken products’ mechanical properties and performance. Thus, it is critical to research on refinement and homogenization of steel. This paper centers about as-cast SA508-3 steel and researches on hot deformation mechanical behavior, dynamic recrystallization(DRX) and grain evolution through physical experiments and numerical simulations. The main methods and findings are briefly listed as follows.Based on Gleeble isothermal hot-compression of as-cast SA508-3 steel, the flow stress constitutive equations, DRX kinematic model and grain evolution model were established and verified. These models were successfully integrated into DEFORM software. It is found that in low temperature as-cast coarse grain has higher flow stress compared with forged fine grain in strain hardening stage, because the former one has poor deformation compatibility and numerous deformation twining.Combined with upsetting experiments and processing map(PM), grain size and heterogeneity evolution with temperature, strain rate and strain were obtained, and the optimistic hot working conditions for refinement and homogenization of as-cast SA508-3 steel were identified.The kinetics of DRX for as-cast coarse grain is briefly analyzed based on experimental data, and it is found that as-cast coarse grain starts earlier for that some boundary has high-energy or deformation concentration, and ends later than homogeneous structure with the same average grain size. For three kinds of structures with different initial grain size, their necessary strains for DRX accomplishment were obtained.