Effect of Top Slag with Low Basicity on Transformation Control of Inclusions in Spring Steel Deoxidized by Si and Mn

In order to study the effect of top slag with low basicity on transformation control of inclusions in spring steel deoxidized by Si and Mn, the optimum composition of CaO-SiO2-Al2O3-MgO slag system with low basicity was firstly calculated by FactSage. Then the industrial experiments were carried out based on the results of calculation. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to determine the morphology, size and composition of inclusions in spring steel. It is proved that MnS, CaO-SiO2-Al2O3-MgO and CaO-SiO2-Al2O3-MgO-MnS system inclusions are three major non-metallic inclusions in spring steel, and the transformation of inclusion compositions to plastic deformation can be achieved by controlling the binary basicity (CaO/SiO2 by mass percent) at the range of 1.0 to 1.19 and C/A (C/A = CaO/Al2O3 by mass percent) above 9 in top slag. In addition, along with the refining process, the average oxygen content in molten steel and the alumina content in inclusions both decrease, and the number of inclusions greater than 5 um gradually decreases. Finally, the inclusions in spring wire rod are controlled effectively.