Discontinuous Deformation Modes of a Nitrogen-Stabilized Austenitic Steel

Abstract

The instability of plastic flow at low temperatures appears to be quite a general phenomenon of many metallic materials. Several theories have been advanced to account for this effect: strain-induced phase transformations¹ and twins,² avalanche-like barrier crossing by dislocation pile-ups and their sudden multiplication under the action of the load,³ and thermal instability of deformation resulting from a large temperature dependence of the flow stress coupled with low specific heat.^4–6 This last “thermal model” is commonly given as the cause for discontinuous yielding. However, the detailed mechanism has not been definitely explained. Particularly, the considerable localized plastic flow that must have occurred before the temperature rises⁷ can by no means be ruled out, and the available experimental results are quite contradictory.