Theory of mobile dislocation density: Application to the deformation of 304 stainless steel

Abstract

Tensile and creep deformation of 304 stainless steel have been studied at room temperature in a soft tensile machine. The strain-stress curve shows a long inelastic transient, over nearly two hundred megapascals, in which the slope and the strain rate increase by about a factor of 3. Creep is characterized by large creep strain, transient strain rate, and a weak stress dependence. The stress rate applied during loading, on the other hand, has a strong effect on the subsequent creep. These results, in combination with earlier studies, have suggested a new model for the evolution of mobile dislocation density. Mobile dislocations are injected into the sample as a consequence of the increase of stress; the dislocations move under the influence of an effective stress over a statistical mean free path and then are trapped in a network. The effects of trapping are reduced mobile density, strain hardening, and a decrease in the effective stress. Application of the model provides a quantitative prediction of the principal experimental results.