Coupled Visco-Plastic Thermo-Mechanical Models of Steel Solidification

Coupled thermo-mechanical models based on highly nonlinear elastic visco-plastic constitutive laws are applied to simulate simultaneous development of temperature and stress that occurs during steel solidification in continuous casting processes. The efficient and robust local visco-plastic integration scheme [Koric 2006] is implemented into both implicit and explicit FE commercial software ABAQUS/Standard and ABAQUS/Explicit via user defined subroutines VUMAT and UMAT. The models are first verified with a semi-analytical solution [Weiner 1963], and later they are applied to simulate 2D and 3D transverse sections of a thin slab caster under realistic operating conditions as they move down the mold. The execution times of the implicit and explicit parallel solvers performing some of these highly computationally demanding analyses are benchmarked on the latest high performance computing platforms. INTRODUCTION: Continuous casting is the process by which over 90% of steel is produced today. The harsh environment and extreme temperatures make experimenting and taking measurements difficult, and so many numerical models have been developed over the years, mostly using implicit finite element methods. The few seconds the steel spends in the mold are often the most critical, given the large number of possible defects related to initial solidification. The quality of continuously cast products is constantly improving, but there is still a significant amount of modeling work needed to minimize the amount of defects and to maximize the productivity. Numerical modeling of the thermo-mechanical behavior of the shell presents a large number of computational difficulties, such as the integration of the highly nonlinear visco-plastic constitutive laws, treatment of liquid/mushy zone, treatment of latent heat, accounting for the temperature dependence of material properties, contact between the solidified shell and mold surfaces, and coupling between the heat transfer and stress analysis. A new approach is proposed here to link a cost-effective explicit time integration solution method on the global level with an efficient and robust implicit integration scheme to integrate the highly-nonlinear viscoplastic equations at the local level. The explicit and traditionally-favored implicit FE numerical methods for solidification problems are compared and the advantages that the explicit FE formulation exhibits for this class of difficult, coupled contact problems are demonstrated. PROCEDURES, RESULTS AND DISCUSSION: Inertial effects are negligible in solidification problems, so using the static mechanical equilibrium as the governing Plasticity ’09 Conference, St. Thomas, Jan. 3-8, 2009.