Creep behavior of Fe–C alloys at high temperatures and high strain rates

The creep behavior of Fe–C alloys (1–1.8%C) has been studied at high temperatures (0.7–0.9Tm) and high strain rates (1–100 s−1). The dominant deformation resistance has been found to be climb-controlled dislocation creep and thus the creep rates are a function of elastic modulus, lattice diffusivity and stacking fault energy. The self-diffusion coefficient of iron in austenite was found to be solely a function of Tm/T and to vary as D=6.8×10−6 exp(−17Tm/T) m2 s−1. The Fe–C alloys were observed to have a high stacking fault energy which was unaffected by carbon and manganese. The stacking fault energy was observed to decrease with increasing concentrations of silicon, aluminum and chromium. At high stresses, deviation from power law behavior was accounted for by considering the contributions to diffusivity by dislocation pipe diffusion. The results have been used to develop a rate equation for these steels of varying composition that depends on only three material characteristics – alloy melting temperature, elastic modulus and stacking fault energy.