Investigation of Soft Magnetic Material Fe-6.5Si Fracture Obtained by Additive Manufacturing

Abstract

The freeform capability additive manufacturing (AM) technique and the magnetic efficiency of Fe-6.5Si steel have the potential for the development of electromechanical component designs with thin body sections. Moreover, the directional anisotropy of the material, which is formed during growth, improves the magnetic and electrical properties of Fe-6.5 wt%Si. We obtained the range of optimal technological modes of Laser Power Bed Fusion process (volume energy density (VED) of 100–140 J/mm3, scanning speed of 750–500 mm/s) to produce the samples from Fe-6.5 wt%Si powder, but even at the best of them cracks may appear. The optical microscopy and SEM with EDX analysis of the laser-fabricated structures are applied for investigation of this phenomena. We detected a carbon content at the boundaries of the cracks. This suggests that one of the reasons for the crack formation is the presence of Fe3C in the area of the ordered α’FeSi (B2)+Fe3Si(D03) phases. Quantitative analysis based on crack initiation criteria (CIC) showed that the safe level of internal stresses in terms of the CIC criteria in the area of discontinuities is exceeded by almost 190%. Local precipitates of carbides in the area of cracks are explained by the heterogeneity and high dynamics of temperature fields, as well as the transfer of substances due to Marangoni convection, which, as a result, contributes to a significant segregation of elements and the formation of precipitate phases.