Process Parameter Optimization of Directed Energy Deposited QT17-4+ Steel

The feasibility of using argon-atomized QT 17-4+ stainless steel powder for directed energy deposition (DED) additive manufacturing is studied. The QT 17-4+ steel is a novel martensitic steel designed based on the compositional modification of the standard 17-4 precipitation-hardened (PH) stainless steel. This modification aims to achieve better mechanical properties of as-deposited components compared to the heat-treated wrought 17-4PH steel. In this study, QT 17-4+ steel powder is used for DED, for the first time. The influence of laser power, laser scan speed, powder feed rate, and hatch overlap on the density is studied. The central composite design is used to determine the experimental matrix of these factors. The response surface methodology is used to obtain the empirical statistical prediction model. Both columnar and equiaxed parent austenite grain structures are observed. X-ray diffraction analyses reveal a decrease in the percentage of retained austenite from 19% in the powder to 5% after DED. The microhardness of the DED processed sample in the as-deposited state is slightly higher than that of wrought 17-4PH steel either solution-annealed or H900-aged. A higher 0.2% yield strength, a lower ultimate tensile strength, and lower elongation are observed for the vertically printed test sample, when compared to the horizontal one.