Application of hot deformation structure state maps to scheduling thermomechanical processing of steels

To determine temperature and strain rate ranges for dynamic polygonization and recrystallization under hot deformation conditions and to quantitatively evaluate the resultant structure, structure state maps (SSM) are plotted in coordinates "temperature - strain rate" for given strain and initial grain size. SSM describe strain rate dependencies of temperatures corresponding to the onset and to 100 % of dynamic recrystallization, lines of equal values of dynamically recrystallized grain size, subgrain size and dynamic recrystallization volume fraction. Temperature threshold for dynamic recrystallization increases in higher extent than that for static recrystallization with decreasing strain rate and strain at the steady state deformation, increasing initial grain size and stacking fault energy, decreasing carbon content and alloying with Si, Cr, Mo, Co and especially V and Nb. On the SSM basis, schedules have been developed for thermomechanical processing of structural low-and medium-carbon steels (rolled strips and sheets), austenitic, ferritic and austenitic-ferritic stainless steels (sections, sheets, tubes), high speed tool steels, electric silicon steels (bands) with resultant polygonized structure.