Orientation-dependent deformation micro-mechanism and failure analysis of SS 316 under tensile and cyclic load

摘要

In the present investigation, the effect of crystallographic texture on deformation and failure mechanism of austenitic stainless steel 316 (SS 316) during monotonic tension and stress control cyclic (also known as fatigue) deformation has been correlated with the statistical aspect of microstructural defects structure and deformation microstructure. The monotonic tension and fatigue behavior for 0 and 45-deg orientation of the loading axis with respect to the rolling direction of hot rolled and annealed SS 316 sheet has been determined at room temperature using a servo-hydraulic universal testing machine. The Synchrotron X-ray diffraction technique has been used to measure the deformation texture in the specimens subjected to monotonic tension and cyclic deformation. Also, line profile analysis of synchrotron data including peak shift due to stacking fault has been carried out to estimate orientation dependent micro-strain and overall dislocation density for two different mode of loading. The result shows isotropic tensile property while strong anisotropy in fatigue property. The isotropic tensile behavior has been attributed to the strengthening of G/B texture component which enhances twinning activity in 45-deg orientation. Thus, the combined activity of slip and twinning leads to almost similar strain hardening and tensile ductility of SS 316. On the other hand, during stress controlled cyclic loading strengthening of soft cube texture component via cross slip activity suppresses twinning in 45-deg orientation, thus reducing fatigue crack propagation resistance leading to the shorter fatigue life of 45-deg orientation compared to 0-deg orientation.