Superplastic deformation and cavitation of a 14CrMn stainless steel

Abstract

An experimental stainless steel containing 14Cr20Mn was found to exhibit moderate superplastic behaviour in the temperature range 800–1000 °C at strain rates of 10 −4–10 −3 −1. The strain rate sensitivity index was found to be insensitive to test temperatures between 825 and 875 °C but varied with strain rate, reaching a maximum of about 0.5 at 3 × 10 −4 s −1. A model is proposed to estimate the rate of grain growth that occurred during superplastic deformation in terms of static grain growth, which is a function of time and the activation energy of grain boundary self-diffusion, and strain-enhanced growth, which is a function of strain rate and volume self-diffusion. Cavitation accompanied superplastic deformation and increased with increasing local strain, increasing temperature and decreasing strain rate. The cavitation results were analysed using strain-based and time-based models. The latter gave a more consistent estimate of the cavities present in the prestrain condition.