Experimental investigation of in-situ microstructural transformations in wire arc additively manufactured maraging 250-grade steel

Wire arc additive manufacturing (WAAM) is suitable for near-net-shaped manufacturing of large-scale components due to compelling factors such as high deposition rates and low feedstock costs. These factors notwithstanding, an understanding of the process-structure-property relations is necessary for the industrial use of this manufacturing process. However, the thermal cycles and heat accumulation in the WAAM process can result in different microstructural transformations. These complexities make it non-trivial to establish the process-structure-property relations. Hence, the objective of this work is to understand the various aspects of microstructure evolution in an as-fabricated material. A suite of characterization techniques, including optical microscopy, scanning electron microscopy, and electron backscatter diffraction were utilized to characterize a wire arc additively manufactured maraging steel 250 thin wall. The characterization findings show grain refinement and variation in precipitation categories and volumetric fraction as a function of the height of the thin wall. These variations are then qualitatively related to the thermal conditions during fabrication. Overall, findings from this work shed light on the impact of thermal cycles and heat accumulation on the microstructure evolution in as-fabricated maraging steel 250.