Static and dynamic strain aging at high temperatures in 304 stainless steel

Commercial 304 austenitic stainless steel was deformed at high temperatures, The experiments involved 2-hit hot compression and multi-pass hot torsion testing; the experimental variables included strain rate, temperature and interpass time. The relationship between these variables and the degree of interpass softening produced unexpected results. Specifically, the normal effect of temperature on the static softening kinetics was reversed at intermediate interpass times: the fractional softening decreased with increasing temperature for these times. The diffusion kinetics and segregation mechanics of the substitutional impurities in the material, combined with the experimental results, suggest that the temporary non-equilibrium segregation of phosphorus (and/or sulphur) to dislocations is responsible for the observed behaviour. Additionally, the observed trend in strain rate sensitivity with increasing deformation temperature indicates that dynamic strain aging was taking place.