Enhanced ductility in harmonic structure designed SUS316L produced by high energy ball milling and hot isostatic sintering

The objective of the present study is to optimize the mechanical properties of commercial SUS316L stainless steel through harmonic structure design. The harmonic structured SUS316L compacts were fabricated by a process including high energy ball milling and subsequent hot isostatic pressing. Although the harmonic structured compacts had a bimodal grain size distribution, our investigations showed that both hardness and yield strength still well resembled the Hall-Petch relationship. A great combination of high yield strength and improved uniform elongation can be achieved simultaneously in the harmonic structured SUS316L compacts (σy=695 MPa, εu=27.1%). The improved ductility was attributed to both the strain hardening induced by the coarse-grained structure and the extra strain hardening caused by the peculiar macroscopic network of ultrafine-grained structure. It was suggested that core grain size of approximately 1.2 µm and shell volume fraction of approximately 50-60% were the optimized harmonic structure design for austenite stainless steel.