Effect of low basicity refining slag on evolution and removal of oxide inclusions in 55SiCrA spring steel

The laboratory experiments, thermodynamic analysis, dynamic analysis, and industrial trials were carried out to investigate the influence of refining slag on the evolution and removal of oxide inclusions in 55SiCrA spring steel. The reduction in basicity and Al₂O₃ content in refining slag can reduce the [Al]_s content in the molten steel, which is conducive to the control of the low melting point of inclusions. However, the refining slag with excessively low basicity transfers the oxygen element to molten steel and increases the Al₂O₃ content in inclusions, which is harmful to the control of inclusions. According to the chemical compositions of inclusions and refining slag in laboratory experiments, their physical parameters were calculated. The maximum separation ratio and the moving time of inclusions to reach the maximum separation ratio (t_max) of inclusions under different laboratory experimental conditions were studied. The maximum separation ratio of inclusions is positively correlated with the overall wettability (cosθ_IMS) among the slag, steel, and inclusions. The maximum separation ratio of inclusions obtained by laboratory experiments is between 85% and 91%. The t_max decreases with the decline in basicity and Al₂O₃ content of refining slag, but excessively low basicity will increase the t_max. The basicity of refining slag in the range of 0.88–0.97 and the content of Al₂O₃ less than 6% is not only conducive to reducing the content of Al₂O₃ and the melting point of inclusions but also beneficial to removing the inclusions to the slag. The slag system shows good metallurgical results in industrial trials.