High Strength and Ductility of Additively Manufactured 316L Stainless Steel Explained

Structure-property relationships of an additively manufactured 316L stainless steel were explored. A scanning electron microscope and electron backscattered diffraction (EBSD) analysis revealed a fine cellular-dendritic (0.5 to 2 mu m) substructure inside large irregularly shaped grains (similar to 100 mu m). The cellular structure grows along the aOE (c) 100 > crystallographic directions. However, texture analysis revealed that the main aOE (c) 100 > texture component is inclined by similar to 15 deg from the building direction. X-ray diffraction line profile analysis indicated a high dislocation density of similar to 1 x 10(15) m(-2) in the as-built material, which correlates well with the observed EBSD microstructure and high-yield strength, via the traditional Taylor hardening equation. Significant variations in strain hardening behavior and ductility were observed for the horizontal (HB) and vertical (VB) built samples. Ductility of HB and VB samples measured 49 and 77 pct, respectively. The initial growth texture and subsequent texture evolution during tensile deformation are held responsible for the observed anisotropy. Notably, EBSD analysis of deformed samples showed deformation twins, which predominately form in the grains with aOE (c) 111 > aligned parallel to the loading direction. The VB samples showed higher twinning activity, higher strain hardening rates at high strain, and therefore, higher ductility. Analysis of annealed samples revealed that the observed microstructures and properties are thermally stable, with only a moderate decrease in strength and very similar levels of ductility and anisotropy, compared with the as-built condition.