Ferrite formation and its effect on deformation mechanism of wire arc additive manufactured 308 L stainless steel

Abstract Wire arc additive manufacturing (WAAM) with many superior characteristics, such as high deposition rate, low cost, free shape, and environmental friendliness has attracted much attention and will be used in the nuclear industry. A 308 L stainless steel plate with 40 deposited layers was manufactured by WAAM and further treated into solution treatment status in this work. A ferrite formation model was proposed based on the detailed microstructural characterization at different layers where the consistently large columnar austenite grains and small ferrite grains with different shapes including skeletal, lathy and granular coexisted. Furthermore, monotonic tensile tests with the specimens extracted from the top, middle and bottom layers of the WAAM plate were carried out to evaluate the mechanical properties, and relatively consistent strength was revealed. Moreover, an interrupted test was performed to investigate the role of ferritic and austenitic phases on the deformation mechanisms of the WAAM material under monotonic tensile loading. It was shown that the deformation behavior was primarily controlled by the single slip and double slip of dislocations of austenitic matrix and ferrite, and the lathy ferritic grains and austenitic grains dominated the fracture behavior.