Microstructure, Mechanical Properties and Fracture Toughness of SS 321 Stainless Steel Manufactured Using Wire Arc Additive Manufacturing

In this study, a multi-layered wall was fabricated using Wire Arc Additive Manufacturing (WAAM) process using ER321 filler wire to evaluate the static and dynamic mechanical properties. The micrographs of WAAM processed SS 321 revealed the existence of columnar and equiaxed dendrites along the building direction, and recrystallization of grains was observed due to the re-melting of former layers. The microstructure was dominantly austenitic with a small fraction of ferrite (FN) within the austenitic matrix. Comparable tensile properties were noticed for as-deposited SS 321 WAAM samples in comparison to wrought grade. This is attributed to the presence of equiaxed and columnar dendritic microstructure with a formation of residual delta ferrites along the build direction. The hardness gradually reduced from the bottom (250 HV) to the top (199 HV) region in WAAM SS 321 wall due to the difference in microstructure with varying ferrite fractions (5.9 to 3.6 FN). The fracture toughness of wrought SS 321 and WAAM processed SS 321 was 162 kJ/m(2) and 153 kJ/m(2). The manufacturing techniques influenced the fracture behaviour and were confirmed from the J-R curves obtained from the strain energy rate required to initiate the crack growth. This study demonstrates the potential of WAAM technology for the fabrication of free-form structural components with comparable mechanical properties and fracture toughness in comparison to wrought alloy.