Evaluating the Effects of Scan Strategy on AM Annealed Fe-3Si steel through Understanding of Solidification Conditions and Thermal Stresses

Soft magnetic steels have seen recent adoption in additive manufacturing (AM) due to the prospect of reducing eddy currents and hysteresis losses through leveraging of complex geometries and microstructural control. An annealing step will be a significant step for these alloys produced in AM to increase grain size and further reduce hysteresis losses. In this study, thin wall Fe-3Si samples were produced using laser powder bed fusion (L-PBF) using two different scan strategies, with a subset of samples annealed at 1200°C for 5 minutes. The effects of the two different scan strategies on microstructure in the as-built and annealed samples were analyzed through EBSD where it was found that the scan strategy does have an effected on annealed microstructure. Thermal simulations using OpenFoam were used to rationalize the differences in microstructure formation between the two scan strategies for the as-built scan strategies by looking at the thermal gradients and solidification velocity, while explanations on why there is a difference in resulting annealed microstructure was made by looking at the grain orientation, size and misorientation. Further, thermal-mechanical simulations were conducted using Abaqus to see if differences in the resulting elastic and plastic strains due to differences in thermal stresses related to the two difference scan strategies could be a mechanism causing differences in annealed microstructure to occur.