On the origin of the tensile flow stress in the stainless steel AISI 316L at 300 K: Back stress and effective stress

The tensile behaviour of a polycrystal austenitic stainless steel at 0.2T(m) is discussed in terms of back and effective stresses with the help of qualitative and quantitative TEM observations. Particular attention is given to the transition between stages I and II which occurs at a plastic strain equal to 1.5%. The effective stress evolution can be interpreted as a competition process between the increase of mobile dislocation density and dislocation interactions and an annihilation process. The main purpose of this work is to provide a basis for separating the two different contributions of the back stress, namely the intragranular back stress X-intra arising from the heterogeneous dislocation distribution inside the grains and the intergranular back stress component X-inter resulting from plastic strain incompatibilities between grains. Moreover, it is shown that the latter contribution is dominant at small strains (stage I), whereas the former one is more important subsequently (stages II and III), when cross-slip and multiple slip occur. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. An rights reserved.