Investigation of microstructural and corrosion behavior of 316LSi structure developed by wire arc additive manufacturing

Abstract

SS316LSi austenitic stainless steel thin wall was deposited using wire arc additive manufacturing technology, which is known for its high deposition rate and effective material utilization. The optical micrograph revealed the formation of vermicular δ-ferrite, dispersed in the austenite matrix in the deposited wall. The X-ray diffraction patterns confirmed the formation of γ-austenite, δ-ferrite, and chromium carbide (Cr23C6) phases. The SEM and energy dispersive spectroscopy study exhibited the formation of intergranular precipitates. In the magnetic study, ferrite number was found from 3 to 7 in a different portion of the wall which revealed the formation of the ferromagnetic δ-ferrite phase. The Cr and Ni equivalent ratio, 1.66, ferrite number, and presence of vermicular δ-ferrite in the microstructure showed that ferrite austenite can be the mode of solidification in the alloy. The preferred grain growth direction was determined by electron backscattered diffraction analysis to be < 001 > orientation along the build-up direction. In the potentiodynamic polarization and double loop electrochemical potentiodynamic reactivation study, the corrosion rate and intergranular corrosion were correlated to the amount of δ-ferrite and Cr23C6 respectively. The degree of sensitization confirmed that the amount of Cr23C6 formed is least in the lowermost and highest in the central portion of the deposited wall.