Microstructural administered mechanical properties and corrosion behaviour of wire plus arc additive manufactured SS 321 plate

Abstract

Wire plus arc additive manufacturing (WAAM) technology with higher deposition rate and efficient material utilization was employed to fabricate a stainless steel 321 (SS 321) wall for the first time. In this work, the microstructural characteristics, mechanical properties and corrosion performance of as-built SS 321 were evaluated. The micrographs confirmed the presence of columnar and equiaxed dendrites along the building direction, and recrystallization of grains was noticed due to the re-melting of former layers. The microstructure was dominantly austenite with a small fraction of ferrite within the austenitic matrix. Better tensile properties were noticed for as-printed SS 321 WAAM samples in-comparison to wrought counterpart. This is corroborated to the equiaxed and columnar dendritic microstructure with small fraction of ferrite (FN). The hardness decreased from bottom (247 HV) to top (196 HV) region in SS 321 WAAM plate and is attributed to the microstructural difference with varying amount of ferrite (6.3 to 3.7 FN). The impact strength of samples in the horizontal and vertical direction was 116  ±  2 J and 114  ±  2.5 J respectively, and is comparable with the wrought AISI 321 (123  ±  1.5 J). The reduction in impact toughness is attributed to the ferrite (<6.3 FN) fraction. Polarization curves and Nyquist plots elucidate the excellent pitting resistance of SS 321 WAAM specimens, and the corrosion rate was less than 1 mils per year (mpy). Corrosion cracks were absent, and the passive film formation in the WAAM specimens were compact and highly stable for corrosive environments.