Defect Reduction in Ferritic Stainless Steels through Modelling Plastic Deformation and Metallurgical Evolution

Steel products made of ferritic steel can show some defects, such as jagged edges, following the hot rolling process. Aiming to identify the origin of this type of defect in order to help their reduction, an in-depth study has been carried out considering the hot rolling conditions of flat bars made of EN 1.4512 steel. A wide number of references to austenitic stainless steel can be found in literature: almost all the semi-empirical models describing the microstructural evolution during hot deformation refer to austenitic stainless steel. In this work, a comprehensive model for recrystallization and grain growth of the ferritic stainless steel grade EN 1.4512 is proposed, enriching the literature and works regarding ferritic stainless steels. Thermomechanical and metallurgical models have been implemented. The microstructural evolution and the damage of the material were calculated through the coupling of metallurgical and damage models. In the thermomechanical simulations of the roughing passes, three granulometry levels (PFGS) and three heating furnace temperatures were considered. The ferritic grain evolution metallurgical model was obtained by introducing apposite equations. The results highlight that the defect could be produced by process conditions that spark abnormal heating and consequently uncontrolled growth of the grains. The work-hardened grains undergo elongation during hot deformation without recrystallizing. Those grains “squeeze” the surrounding recrystallized grains towards the edges. Thus, on the edges occurs a series of cracks that macroscopically manifest themselves as jagged edges.