Influence of nitrogen and grain size on deformation behaviour of austenitic stainless steels

The present study concerns the deformation behaviour of two austenitic stainless steels (base composition corresponding to 316L) with two different nitrogen levels, 0.14 and 0.29 wt-% respectively. The influence of grain size on the mechanical properties has been investigated. The grain size dependence of the monotonic as well as the cyclic stress-strain curves were shown to follow a Hall-Petch type relationship. The influence of the grain size was found to be lower for the cyclic thanfor the mOnotonic yield stresses. The lower grain size sensitivity of the cyclic yield stresses can be explained by the successive breakdown of the planar slip mode during cyclic straining. For both static and cyclic deformation modes the dependence of grain size increases with higher nitrogen content. Dislocation structures of the various conditions were studied with transmission electron microscopy and related to the mechanical behaviour of the two materials.