Deformation behavior during hot torsion of an ultrahigh carbon steel containing 1.3 wt.% C

The torsion behavior of an ultrahigh carbon steel containing 1.3 wt.% C has been studied at high strain rates (2-26 s(-1)) and high temperatures (900-1200degreesC). Adiabatic heating strongly affects the shape of the stress-strain curves. Grain size measurements at strains of epsilon = 2 and epsilon = 5 reveal that the austenite grain size does not change between these two strains and is finer than the initial austenite grain size. This is an indication that a recrystallization process took place in the interval of strains between epsilon(peak) and epsilon = 2 and that the deformation state associated to the strains of epsilon = 2 and epsilon = 5 can be considered as steady state. Stress-strain rate relations have been analysed for epsilon(peak), epsilon = 2 and epsilon = 5. It has been found that data obtained at epeak correlate well with a lattice diffusion-controlled dislocation creep process. On the other hand, analysis of the stress-strain rate relations found at the steady state indicated that the deformation occurs by the contribution of two independent mechanisms: grain boundary sliding controlled by pipe diffusion and slip creep controlled by lattice diffusion.