Microstructural characteristics, mechanical properties and corrosion performance of super austenitic stainless steel 904L produced by wire arc additive manufacturing

Abstract

This study involves the fabrication of a super austenitic stainless steel 904 L thin wall using wire arc additive manufacturing (WAAM) technology. The microstructure, mechanical properties, and localized corrosion performance of WAAM-processed 904 L were investigated. The average surface roughness varied between 22.43 and 28.51 µm due to the presence of delineations in the wall. Microstructural analysis revealed the presence of equiaxed, columnar, and elongated dendrites along the building direction (BD) of the as-deposited wall. Secondary phases were not noticed in the as-deposited wall due to repeated thermal cycles. Energy-dispersive X-ray spectroscopy (EDS) analysis confirmed the uniform dissolution of elements such as Ni, Cr, and Mo within the austenitic matrix. The hardness mapping in WAAM 904 L indicated the variation at the top, middle, and bottom regions and was 220 ± 11 HV, 235 ± 9 HV, and 260 ± 8 HV, respectively. The tensile test outcomes of WAAM 904 L specimens at 0°, 45°, and 90° orientation showed lower anisotropy and observed maximum tensile properties in the horizontal direction (0 °), i.e., YS= 312 ± 12 MPa, UTS= 658 ± 24 MPa & %E = 36 ± 1.5%. The mode of fracture was ductile in nature, with dimples and microvoids. The Potentiodynamic polarization (PDP) tests in 3.5% NaCl solution highlighted the formation of stable passive film on the surface of the as-produced 904 L specimens, and superior resistance to pitting corrosion was noticed. Electrochemical impedance measurements revealed the stability of WAAM specimens and showed a similar trend to PDP outcomes. The degree of sensitization (DOS) of the WAAM 904 L samples was lower, and the corrosion rate ranged between 0.07 and 0.70 mils per year (mpy).