Oriented thermomechanical hardening and recrystallization of high-carbon steels

Abstract

Recrystallization of austenite in high-carbon steels after light (ɛ = 20–25%) deformation is not a uniform process because of the nonuniform and localized character of the deformation of austenite grains. The largest increase in the average grain size of austenite in steel ShKh15 takes place during the first 1.5 min of post-deformation annealing, and the grain growth rate is much faster in the transverse than in the longitudinal direction. As a result of recrystallization processes during HTMT of high-carbon steels, their strength and ductility are sometimes reduced below the level recorded for quench-hardened and tempered specimens. Recrystallization during HTMT leads to a reduction in the degree of anisotropy of mechanical properties determined in tests under direct and inverse loads. The results of mechanical tests show, however, that oriented inclusions and a striated structure confer a considerable degree of anisotropy on the properties of recrystallized specimens. The reduction of quasi-brittle strength of martensite after HTMT (followed by recrystallization) is to a large degree attributable to the oriented growth of recrystallized grains; this relation is described by Eq. (2). The reduction in ductility is associated with the reduced quasi-brittle strength of martensite formed from recrystallized austenite.