Microstructure and Non-Metallic Inclusion Modification in Steel Deoxidized by Complex Fe-Si-Mn-Al Alloy

This study evaluates the effects of semi-industrial and synthetic Fe–Si–Mn–Al deoxidizers on the microstructure, non-metallic inclusions, and hardness of St3 steel. Seven complex alloys with different Fe, Si, Mn, and Al contents were produced and compared with conventional FeSi–FeMn–Al deoxidizers. The steel samples were examined by optical microscopy and Rockwell hardness testing. Depending on the deoxidizer composition, ferrite–pearlite, bainitic, martensitic, and structurally heterogeneous regions were observed. The measured hardness ranged from 26 to 47 HRC. Porosity and dendritic heterogeneity remained in several samples. The results demonstrate that the composition of an Fe-Si-Mn-Al deoxidizer is associated with differences in optically observed microstructural characteristics and reported hardness. These findings provide an experimental basis for selecting complex deoxidizer compositions for further steelmaking studies.