The recrystallization behaviours of two Nb steels (0.023Nb and 0.07Nb) were investigated under isothermal conditions. This was done using double twist torsion tests carried out in the temperature range of 850 to 1100degC, together with strain rates of 0.02 to 10 s~-1, and interpasstimes of 0.05 to 100 seconds. Various strains were also studied, ranging from a little less than the critical strain for dynamic recrystallization, epsilon_c, to the steady state strain for dynamic recrystallization, epsilon_ss. The experimental results show that, for a given interpass interval, the amount of fractional softening increases linearly with strain unitl a transition strian (epsilon_T) is reached. after which the amount of fractional softening remains constant. It was observed that at strains above epsilon_T, the kinetics of recrystallization are independent of strain, weakly dependent on temperature, and strongly dependent on strain rate. A kinetics model of metadynaic recrystallization was derived from the experimental data; it takes into account the effects of the deformation parameters and of the Nb in solution.
展开▼
