Strengthening mechanisms and strain hardening behavior of 316L stainless steel manufactured by laser-based powder bed fusion

Kurzfassung

The microstructure-properties relations and strengthening mechanisms of additively manufactured 316L stainless steel is comprehensively investigated in this work. The orientation dependency and the strain hardening are studied by tensile testing of as-built specimens fabricated by laser-based powder bed fusion (LPBF) in different directions. The results are compared with those obtained for wrought material. The microstructure of the wrought and the LPBF materials are also comprehensively investigated. Equiaxed grains with random orientation and relatively uniform size (∽30 μm) are observed in the wrought material, where the LPBF samples showed columnar grains inside as well as fine equiaxed grains in the bottom of the molten pool. A bimodal grain size distribution, higher values of geometrically necessary dislocations density (∽25-32%) and lower fractions of high-angle grain boundaries (∽24-28%) is observed in LPBF 316L. A significant yield strength and considerable ultimate strength improvement without remarkable elongation decrease is obtained for the LPBF tensile specimens, resulting in a high strength-elongation balance (up to 26122 MPa%). Two-stage strain hardening is depicted in both wrought and LPBF samples. However, the LPBF samples illustrated lower strain hardening exponents in comparison with the wrought ones. The plastic region of true stress-strain curves is successfully predicted with two-stage Hollomon analysis results.