Fatigue Behavior of Austenitic Stainless Steel 347 Fabricated via Wire Arc Additive Manufacturing

This study investigates the fatigue performance of wire arc additive manufactured (WAAM) SS 347 in different orientations. WAAM processed SS 347 plate features with grains mostly oriented in <001> and <101> crystallographic texture along the building direction (BD). Microstructure was mainly austenitic with a smaller fraction of ferrite. Tensile properties of the as-built SS 347 specimens were evaluated to understand the effect of orientation in regard to BD. Stress controlled fatigue tests were conducted at different stress amplitudes for samples in the horizontal direction (HD) and vertical direction (VD). The fatigue strength of as-built samples after sustaining 2×10⁶ cycles were 135 MPa and 128 MPa for VD and HD specimens, respectively. Fatigue strength was less for both the samples in different orientation than the wrought counterpart (~40%). The increase in tensile strength and decrease in fatigue strength is attributed to the presence of austenitic columnar grains with a smaller ferrite fraction less than 5% and noticed phase transformation along with local recrystallization as a result of remelting the former layers along the BD during deposition. The higher kernel average misorientation values confirm the degree of grain misorientation along the BD. The fatigue failure mode was ductile for HD and VD specimens with striations in the crack propagation region and micro-voids coalescence in the final fracture region.