Evolution and Multidimensional Characterization of Non-metallic Inclusions in Steel: An Industrial Study

The evolution of non-metallic inclusions (NMIs) in the industrial production process of 42CrMo4 medium carbon alloy steel was analyzed by 3D-XRM and 2D methods. The results show that, as refining proceeds, the single-existing Al₂O₃ inclusions are transformed into Al₂O₃-CaO and CaS (MgO)-Al₂O₃-CaO. During the steel refining process, slag particles were entrapped into the molten steel and reacted with the relevant elements. As a result, these particles were eventually incorporated into the billet as large-sized inclusions with a composition similar to that of the refining slag. The MnS precipitation behavior of the non-final composition of the molten steel during solidification throughout the refining process was revealed by experiments and theoretical calculations. Meanwhile, MnS is prone to non-homogeneous nucleation and precipitation on the surface of Al₂O₃ in the late stage of refining, which is crucial for the modification of MnS and Al₂O₃. Meanwhile, 3D-XRM technology has successfully performed non-destructive characterization of industrial samples to obtain three-dimensional feature information of inclusions in steel. In combination with traditional 2D characterization and destructive 3D characterization, the data information for the NMIs study can be further expanded.