EFFECTIVENESS OF EX-SITU HEAT TREATMENT OF L-PBF AM 17-4PH STAINLESS STEEL SPECIMENS INTENTIONALLY EXPOSED TO DIFFERENT AS-BUILT THERMAL HISTORIES

The presented research demonstrates the effectiveness of H900 heat treatment in eliminating microstructural and mechanical property differences between additively manufactured 17-4PH stainless steel samples of varying thermal histories. For this effort, 17-4PH stainless steel was manufactured using laser-based powder bed fusion on an EOS M280 machine in two geometries: ASTM Standard E8 subsize rectangular tensile specimen geometry with thicknesses of 2mm and 6mm. Thermal histories were manipulated by adding secondary laser passes on each layer at varying levels of reduced power. All samples were heat treated after the build following H900 procedures. Mechanical performance was evaluated with uniaxial quasi-static tensile testing and Vickers microhardness measurements. Metallography was examined qualitatively with optical and electron microscopy as well as quantitatively through electron backscatter diffraction. No statistically significant mechanical property or microstructural differences were discovered, suggesting a successful ex-situ heat treatment.