Anisotropic plasticity and damage of additively manufactured 316L stainless steel by multiscale approach

Stainless steel 316L produced by laser powder bed fusion (L-PBF) technique exhibits distinctly patterned microstructures due to directional rapid cooling of successive layers. Thus, its tensile properties are highly anisotropic depending on applied build strategies that often led to inferior performance compared to conventional 316L steel. In this work, a multiscale modeling approach was proposed for more precisely describing effects of complex printed microstructure characteristics on local and overall deformation behaviors of the steel. Micro-scale models incorporated grain morphologies and crystallographic textures developed in different melt pools. Hereby, the strain gradient crystal plasticity (CP) model was used to thoroughly reveal anisotropic stress-strain responses which were primarily driven by crystallographic features. Subsequently, a meso-scale model was employed to elucidate the heterogeneous deformation occurring at the melt pool boundaries, particularly in relation to the specified scanning patterns. Homogenized stress-strain properties of each meso-scale region were obtained from the micro-scale models in conjunction with the Hill48 yield criterion. Furthermore, the Hosford-Coulomb ductile damage model was defined on the meso-scale for representing crack initiations at crucial sites of the melt pools. The model showed that the grain configurations of 45°/0°/45° and −90°/0°/90° in melt pools strongly governed the anisotropic strain hardening behavior of printed samples. Local stress incompatibilities induced by grain and melt pool arrangements according to the defined scanning strategies resulted in different strain localizations and following damages. The approach can further serve as a framework for 3D printed material designs requiring more accurate microstructure-properties relationships.