Role of Scan Strategies and Heat Treatment on Grain Structure Evolution in Fe-Si Soft Magnetic Alloys made by Laser – Powder Bed Fusion

A major goal in printing soft magnetic Fe-Si steels using additive manufacturing is to take advantage of the potential for complex geometric designs and site-specific grain control. One major step in the processing of these alloys is understanding how processing parameters might impact how the as-built microstructure responds to annealing (i.e. the annealing response). The impact of scan strategy on the annealing response for thin wall geometries is specifically explored. Two scan strategies were explored for a thin wall geometry that produced a strongly columnar grain structure and equiaxed grain structure. Samples from both scan strategies annealed at 1200 °C showed a marked difference in annealing response with the more equiaxed sample seeing full recrystallization and grain growth, while the more columnar grain structure saw little change in microstructure. After analysis through characterization techniques and thermal-mechanical simulations Differences in internal energy within the grains were ruled out because calculated GND density values were similar for both samples. The formation of secondary particles was ruled out as a contributing factor due to the type of oxide formations and their size. It was concluded that the contributing factor to the difference in the annealing response were a difference in the resulting grain size and the density of high angle grain boundaries. These two differences were largely attributed to differences in the thermal gradient conditions due to grains preferentially growing in the direction of the steepest thermal gradient. • Different scan strategies result in different microstructures for thin wall samples printed in Soft magnetic Fe-3Si Steel. • Differences in resulting microstructure between samples can be attributed to differences in the resulting thermal gradient. • Annealing of samples show that the sample with a higher number of equiaxed grains saw faster grain growth. • Similar geometric necessary dislocation (GND) densities were noted for the as-built samples but not the annealed samples. • Differences in annealing response is attributed to differences in grain size and density of high angle grain boundaries.