Exploring Selective Laser Melting Processing Strategies for ASTM F139 Stainless Steel

This study examines the influence of powder characteristics and laser powder bed fusion (LPBF) processing parameters on the microstructure and mechanical performance of ASTM F139 stainless steel fabricated from powders supplied by two manufacturers. Feedstock powders were characterized with respect to chemical composition, particle size distribution, morphology, density, and flowability. Cubic and tensile specimens were produced using different combinations of laser power, scan speed, hatch spacing, and scanning strategy. The fabricated components were evaluated by density and porosity measurements, surface roughness analysis, optical and electron microscopy, hardness testing, and tensile characterization in both horizontal and vertical build orientations. Powder flowability and packing density were found to strongly influence consolidation behaviour, with improved flow characteristics promoting higher densification and reduced porosity. Scanning strategy also affected defect formation, and a 67° interlayer rotation produced lower porosity than the conventional 0°/90° pattern. An optimal processing window was identified at a laser power of 212 W, scan speed of 1600 mm s−1, hatch spacing of 0.07 mm, and layer thickness of 30 μm, yielding components with ~1% porosity, surface roughness below 15 μm, and a density of 7.65 g cm−3 (>95% of the theoretical density). Under these conditions, horizontally built specimens exhibited an ultimate tensile strength of 612 ± 43 MPa and a yield strength of 544 ± 37 MPa, exceeding the corresponding values obtained for vertically built specimens. Microstructural characterization revealed a refined cellular austenitic structure associated with epitaxial grain growth during solidification, while fractographic analysis indicated predominantly ductile failure through microvoid coalescence. The results establish clear process–structure–property relationships in LPBF-fabricated ASTM F139 stainless steel and demonstrate that the combined optimization of powder quality, scan strategy, and energy input enables the production of near-full-density components.