Effect of heat treatment on thin wall of bimetallic austenitic steel fabricated through wire arc additive manufacturing (WAAM)

Abstract

Wire and Arc Additive Manufacturing (WAA M) enables the fabrication of complex geometrical features and intricate components. SS316L is favoured for its superior corrosion resistance and mechanical strength. However, WAA M-fabricated SS316L components are prone to hot cracking due to their fully austenitic microstructure. Conversely, SS309, with its higher ferritic content, has shown potential in mitigating hot cracking when alloyed with SS316L. In this study, bimetallic SS316L-SS309 thin wall was fabricated using WAA M and subjected to heat treatments at 400°C, 950°C, and 1200°C, each for a duration of two hours, to investigate the resultant effects on microstructural evolution and mechanical properties. The as-built specimens exhibited δ-ferrite dendrites within an austenitic (γ) matrix, with finer grain structures compared to heat-treated samples. Minimal changes were observed in microstructure and mechanical properties at 400°C, while treatments at 950°C and 1200°C resulted in a significant reduction in ultimate tensile strength (UTS), accompanied by nearly double the elongation for samples treated at 1200°C relative to their as-deposited counterparts whereas 14.3% reduction in UTS, Whereas the hardness decrease by 25-35 HV. This study highlights the impact of heat treatment on the microstructural stability and mechanical performance of WAA M-fabricated thin bimetallic austenitic steel structures.