Fatigue and tensile deformation behaviors of laser powder bed fused 304L austenitic stainless steel

Abstract

Unique microstructure equilibrium state induced by the laser powder bed fusion (LPBF) process endows the deposited metallic parts with excellent mechanical properties. However, the microstructure evolution of LPBF metallic materials during fatigue deformation and its influence on fatigue properties remain still unclear. This paper systematically investigated the microstructural evolution and deformation behavior of LPBF 304L austenitic stainless steel (ASS) during tensile and fatigue testing. Experimental results indicated that LPBF 304L ASS exhibited superior tensile and fatigue properties compared with its annealed counterparts, which could be attributed to different deformation mechanisms. The superior tensile properties were commonly attributed to the regulation of cell walls on the dislocation flow. Many fine α′-martensite particles were distributed in the γ-austenite matrix grains of fatigue-fractured LPBF 304L ASS, indicating the occurrence of martensitic transformation during cyclic deformation. The cell walls with strong chemical misfits and high coherent internal stress might provide the non-parallel lattice shear forces for α′-martensite nucleation during cyclic deformation. The martensitic transformation could inhibit the cyclic softening and postpone the strain localization, thus contributing to the remarkable prolongation of the steady stage and the significant improvement of fatigue lifetime. Collectively, this study established the microstructural evolution role in regulating the tensile and fatigue deformation of LPBF 304L ASS.