Submerged arc additive manufacturing of duplex stainless steel: Effect of intrinsic heat treatment on microstructure, mechanical properties and pitting resistance

Abstract

In the additive manufacturing of duplex stainless steel (DSS), thermal cycle and material mismatch frequently result in the imbalance between austenite and ferrite and properties deterioration. Due to the limitations of heat input and forming conditions during the wire arc additive manufacturing (WAAM) process, the improvement of the deposition efficiency faces significant challenges. In this study, submerged arc additive manufacturing (SAAM) with high deposition efficiency is utilized for the fabrication of 2209 DSS with heat inputs of 1.3 kJ/mm, 1.5 kJ/mm, 2.0 kJ/mm and 2.4 kJ/mm. The unique intrinsic heat treatment (IHT) inherent to SAAM is investigated, revealing its significant impact on the microstructure, mechanical properties, and corrosion resistance. Under the high heat input and large width-to-thickness ratio of SAAM, the deposited metal undergoes two remelting processes and multiple reheating processes. This IHT induced nitrogen loss and austenite transformation in the deposited metal, resulting in the formation of interlayer and intralayer zones with different austenite morphology. As the heat input increases, nitrogen loss intensifies and the change of travel speed alters the molten pool morphology, resulting in an increase in cooling rate. These lead to a reduction in austenite content, reaching its lowest value of 63.7 % at the heat input of 2.0 kJ/mm. Subsequently, further increases in heat input result in an increase in austenite content. The yield strength of these components is all higher than the 2205 DSS hot-rolled plates. The pitting corrosion resistance of these components decreases as heat input increases, but remains superior to that of 2205 DSS hot-rolled plates.