Influence of the grain orientation and δ-ferrite on the cyclic deformation behavior of an austenitic CrNi steel manufactured by wire and arc additive manufacturing

In contrast to most additive manufacturing processes, Wire and Arc Additive Manufacturing enables the production of big metallic components, as it offers sufficient building rates and dimension limits. As the larger dimensions and higher building rates lead to other thermal conditions compared to other, more frequently used additive manufacturing processes, a sound analysis of the resulting microstructure and the corresponding mechanical properties is required. As shown in the presented work for the austenitic stainless steel X1CrNi19-9 (AISI 308L; DIN EN-ISO: 1.4316), the process-induced microstructure features textured austenite grains with intragranular δ-ferrite dendrites, both arranged in dependency with the building direction. Thus, the monotonic and cyclic deformation behavior was analyzed for three different orientations of the loading direction to the building direction, i.e., parallel (vertical), 45° and perpendicular (horizontal). The presented results reveal a strong anisotropy in elastic and plastic deformation behavior. Due to the preferential orientation of the austenite grains, the 45° orientation led to a higher stiffness, a more pronounced plastic deformability and a higher cyclic hardening potential, when compared to the other orientations. Because of this, at lower stress amplitudes the 45° orientation shows a higher fatigue life than the vertical and horizontal orientation. However, besides the texture also the grain elongation and the orientation of the δ-ferrite dendrites towards the loading direction influence the plastic deformation processes. This results in higher monotonic strength for the horizontal orientation in relation to the vertically oriented specimens.