Microstructural characterization of super duplex stainless steel fabricated using WAAM technique

Abstract

In the present work, Robotic CMT based multilayered wall of super duplex stainless steel (SDSS) comprising 75 layers was fabricated using wire arc additive manufacturing (WAAM) technique. Microstructural studies were performed on different regions of the WAAM wall. Various morphologies of austenite namely, Widmanstätten austenite (WA), intragranular austenite (IGA), grain boundary austenite (GBA), and secondary austenite (SA) were observed in almost all the layers of the SDSS wall. Widmanstätten austenite (WA) was predominant in the top region of the wall while intragranular austenite (IGA) was leading in the transition region along with secondary austenite (SA). Secondary austenite was found in the bottom region of wall. Such transformation of different phases with different morphologies resulted into microhardness variation across different regions of the wall. The bottom region was 11.8% harder and the middle region was 5.85% harder than the top region of the wall. Based upon these results such as a close variation of microhardness across different regions, accompanied by sound quality and thermal stability of the WAAM wall, the welding procedure as reported in this work, can be recommended for industrial applications involving fabricating SDSS structures.