Maps of structural states for the optimization of hot-working regimes of steels

The structural-state maps (SSM) drawn in the "temperature-strain rate" coordinates are proposed to outline the temperature-rate fields of the dynamic polygonization and recrystallization that occur upon hot working of steels and to quantitatively estimate the steel structure. The SSMs are constructed for a certain degree of deformation and a certain initial grain size. The principal quantitative characteristics are the isolines of equal fractions of dynamically recrystallized volumes, equal sizes of dynamically recrystallized grains, and equal subgrain sizes. The dynamic recrystallization temperature increases with decreasing rate and degree of steady-stage deformation, increasing initial grain size, increasing stacking-fault energy, decreasing carbon content, and increasing degree of alloying. The SSMs were used to develop the thermomechanical treatment regimes providing the formation of polygonized structure in low-carbon and medium-carbon tool steels; austenitic, ferritic, and austenitic-ferritic corrosion-resistant steels; acid electrical ferritic silicon steels. The polygonized structure of the high-temperature phase not only increases the strength of these materials in the final structural state, hut also improves the processing and service characteristics of most steels.