Energetics of plastic deformation of metastable austenitic stainless steel

The change in the internal energy during uniaxial tensile deformation of austenitic stainless steels EN 1.4301 (AISI 304) and EN 1.4318 (AISI 301LN) was determined by measuring the extent of gamma ->alpha'-martensite transformation and the temperature increase of the samples. From the results the fraction of the stored energy of cold work and the free energy change related to the strain-induced gamma ->alpha'-martensite transformation were determined. The fraction of stored energy varied around 0.4. With the metastable steel grades the free energy change related to the gamma ->alpha'-martensite transformation was found to vary between -98 MJ/m(3) and -206 MJ/m(3) depending on the austenite stability of the steel. Furthermore, the magnitude of the mechanical driving force was estimated by comparing the results with the free energy change of thermally induced transformation.