Abstract Scope |
Microstructure-processing-property relationships are the foundation for understanding the physical metallurgy of welding and additive manufacturing. In this work, the microstructural development of laser powder bed fusion 316L was characterized from the as-built stage and after post processing. Variations in microstructure due to differences in processing were studied to understand variations in mechanical properties. Laser powder bed fusion components in type 316L stainless steel were produced by 5 suppliers with different powder lots and machine types. From the components, mechanical testing and microstructural characterization samples were taken. Mechanical testing included room and elevated temperature tensile, and charpy testing. Optical and SEM imaging was used for microstructural analysis. Two post processing conditions were tested: HIP followed by solution anneal, and only solution anneal. The as-built primary solidification mode varied between primary ferrite and primary austenite, depending on processing parameters and powder composition. Mixed primary solidification mode was also predominant in some samples, and the primary ferrite areas in those mixed regions were indicative of a potential solid-state massive transformation to austenite. As-built primary austenite microstructures developed fully recrystallized wrought-like microstructures after solution annealing and showed lower yield strengths. The mixed solidification mode microstructures did not fully recrystallize after solution annealing and showed higher yield strengths. The microstructure characterization showed variations in primary solidification mode that led to differing response to post processing and mechanical properties. Further work is needed to understand this variation in response to heat treatment. |