Influence of heat input on the evolution of δ-ferrite grain morphology of SS308L fabricated using WAAM-CMT

Abstract

Wire-arc additive manufacturing (WAAM) is acquiring impetus for fabricating medium-complexity and large metallic components owing to its high material deposition with faster building rates. Austenitic stainless steels are commonly used among the numerous materials processed by WAAM and microstructural study of single walled components has been widely researched in the past. In this paper, manual cold metal transfer (CMT) welding is used to produce WAAM samples of SS308L austenitic stainless steel with SS304 as a substrate. Detailed microstructural studies with grain morphology of δ-ferrite based on heat input at various layers fabricated using WAAM-CMT are mainly explored. Results showed that the concentration of γ-austenite drops as heat input increases, but δ-ferrite and micro-inclusions increase. Within δ-ferrite, lathy ferrite morphology evolves into faceted morphology while vermicular evolves into a globular (spheroidized) ferrite morphology as heat input increases. The grain morphology pattern repeats itself for each layer as moving along the building direction, resulting in a repetitive heterogenous grain morphology with nearly identical chemical compositions.