NUMERICAL MODELING OF PHASE TRANSFORMATION IN DUAL PHASE (DP) STEEL AFTER HOT ROLLING AND LAMINAR COOLING

摘要

Continuous development of the automotive industry is associated with the search for construction materials that combine high strength with good plastic properties and which allow improvement of the process technology. DP steels meet the high requirements for materials currently used in the automotive industry. Production of DP steels is a very complex process requiring precise control of technological parameters during thermo-mechanical treatment. Design of these processes can be significantly improved by the numerical models of phase transformations occurring in the DP steels. The main aim of this work is multiscale modeling of the austenite decomposition intoferrite, bainite, and martensite in processes of laminar cooling. Partial differential diffusion equation of carbon diffusion is solved with a moving boundary (Stefan problem). The solution was performed in the real microstructure of austenite, which was obtained using the electron microscope image and digital material representation. The developed model based on finite element modeling (FEM) solution of a diffusion equation allows one to determine phase volume fractions, grain size, and carbon segregation before the front of transformation in fluctuating temperature conditions. Results of numerical simulations were used for development of the relationship between microstructure and mechanical properties of DP steel strips.