Plastic behaviour of austenitic stainless steel at low temperature

The Uni-axial tensile strength test was used for loading austenitic stainless steel of type 304 at different temperatures below room temperature (from 77 K to 300 K). The relation between austenite stability and work hardening, as affected by testing temperature, is discussed in terms of the relationship between the strain-induced martensitic transformation, which occurs during plastic deformation, and the dislocation slip in austenite. In stress-strain curves that assume the Ludwik equation sigma = sigma(upsilon) + k epsilon(n), where sigma is the true stress and epsilon the true plastic strain, a meaningful way to analyze work hardening is by plotting log d sigma/d epsilon against log epsilon. A significant aspect is the variation of the work hardening rate d sigma/d epsilon with the true plastic strain at different temperatures. The changes in work hardening behavior which provoked up to three deformation stages, may be associated with different micro-structural processes. The martensitic transformation may be regarded as a deformation process that competes with the usual slip process. The investigation of these stages within the plastic range gives a qualitative picture of how different factors, such as the degree of deformation, temperature and chemical composition of austenite affect the austenite-martensite transformation.