Flat products made of EN 1.4512 ferritic steel may present some defects after the hot rolling process, such as irregular jagged edges. In order to identify the origin of this type of defect to help their reduction, a study has been carried out considering the hot rolling conditions of flat bars made of EN 1.4512 steel. Many semi-empirical models regarding the microstructural evolution during hot deformation of austenitic stainless steels have been developed by many authors. On the contrary, no many studies have been performed about ferritic stainless steels. The main novelty of this work is in the development of a recrystallization and grain growth model applied to EN 1.4512 ferritic steel grade. The microstructural evolution of the ferritic grain size 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 introducing adequate equations. The results show that the defect can be produced by process conditions that trigger abnormal heating which induces an uncontrolled growth of the grain on the edges. The work-hardened grains undergo elongation during hot deformation but are not able to recrystallize. Consequently, these grains “squeezes” the surrounding recrystallized matrix towards the edges of the bar. Thus, on the edges occurs fractures that macroscopically manifest themselves as jagged edges.