Optimization of inclusion removal in spring steel with Rb2O-containing refining slag

High-performance valve spring steel requires exceptional fatigue resistance, which is critically limited by non-metallic inclusions. Optimizing refining slag composition is a key metallurgical approach to control inclusions and enhance steel cleanliness. In this work, the effect of Rb 2 O-containing refining slag on inclusion removal in spring steel was systematically investigated. The results demonstrated that when the addition of Rb 2 O was 7.5 wt%, the refining slag exhibited the optimal inclusion removal effect in steel. As the Rb 2 O content rose from 0 to 10 wt%, the free oxygen ions (O 2− ) generated by the ionization of Rb 2 O depolymerized the complex units in the [SiO 4 ] structure into simple units, leading to a decrease in viscosity of slag. Meanwhile, the surface tension of the refining slag initially declined and then rose, reaching its minimum at 7.5 wt%. The rise in the number of anionic groups reduced the total ion moment of the slag, thereby causing an initial decrease in surface tension. Nevertheless, excessive Rb 2 O addition will cause a surplus of O 2− , resulting in an increase in surface tension. The reduction in surface tension of slag contributes more significantly to inclusion removal efficiency than the decrease in viscosity. Consequently, adding an appropriate amount of Rb 2 O improves the physicochemical properties of the slag and accelerates inclusion removal kinetics. This work provides theoretical guidance for producing high-strength valve spring steel with high cleanliness.