Effects of Thermal History on Solidification Structure, d-Ferrite Retention, and Microhardness Gradients in WAAM-Fabricated ۳۱۶L Stainless Steel

Additive manufacturing (AM) of metals has emerged as a transformative approach for producing complex components, with Wire Arc Additive Manufacturing (WAAM) and Selective Laser Melting (SLM) representing two prominent techniques. In this study, austenitic stainless steel ۳۱۶L was fabricated using GMAW-based WAAM to investigate the influence of thermal history on microstructural evolution and mechanical properties. The as-fabricated WAAM walls exhibited a dual-phase microstructure composed of y-austenite and ۸.۵% retained ۸-ferrite, consistent with FA (ferritic-austenitic) solidification predicted by the Schaeffler diagram. Columnar dendritic grains predominantly grew opposite to the heat flow direction, and no carbide precipitates or manufacturing defects such as cracks, pores, or lack of fusion were observed. Microhardness measurements revealed a gradual decrease from the bottom to the top layers, attributed to thermal accumulation, reduced cooling rates, and grain coarsening. Comparatively, SLM-produced ۳۱۶L exhibits fully austenitic microstructures or minimal ۸-ferrite (<۱-۲%), characterized by ultrafine cellular/dendritic y-austenite, higher hardness (۲۲۰-۲۸۰ HV), and more uniform spatial distribution due to extremely rapid solidification and high cooling rates. The observed differences between WAAM and SLM highlight the role of process-specific thermal gradients and solidification kinetics in determining phase constitution, grain morphology, and mechanical performance. Overall, the findings highlight the strong relationship between thermal history, microstructural evolution, and mechanical response in Wire Arc Additive Manufactured ۳۱۶L stainless steel components.

کلیدواژه ها:

Wire Arc Additive Manufacturing ، ۳۱۶L Stainless Steel ، Microstructure ، Mechanical Properties ، Microhardness