Development of High Density Parts in the Low-Alloy, High-Performance Steel AF9628 Using Laser Powder Bed Fusion

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A process parameter development study was performed in order to determine the printability of a low-alloy, high-performance steel, AF9628, using laser powder bed fusion. A weld track study was performed using 40 distinct laser power and speed combinations in order to determine which combinations produced acceptable conduction welds that would yield high-quality parts. Ten combinations with three distinct hatch spacing values were selected to create cylindrical specimens for porosity studies. Eight out of the ten combinations resulted in parts that were 99.5% dense. Two combinations that produced 99.9% dense parts were used to create tensile specimens. Tensile testing revealed that the ultimate tensile strength (UTS) for as-printed specimens manufactured using both of the processing conditions was significantly higher (24%) than the literature values for wrought AF9628. Heat-treating the specimens reduced their UTS values, but they still exceeded the literature value by 8%. Hardness measurements indicate that the Vickers hardness is approximately 10% lower for the as-printed specimens when compared to the literature value for wrought AF9628, while it is at least 6% greater for the heat-treated specimens than the wrought AF9628. Electron backscatter diffraction results showed that the as-printed microstructure exhibited features typical of the martensitic transformation in quench-and-temper steels.


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Materials Science and Engineering: A