Effect of refining slag system with different basicities on the inclusion in spring steel

    The existence of non-deformable inclusions with large size is one of the major factors that cause the fatigue failure of spring 

steel. To optimize the composition, morphology and distribution of inclusions in high grade spring steel 55SiCr, two LF refining 

processes were carried out when two kinds of refining slag system with different basicities were designed and employed in steel

 making process. Total oxygen content, the size and composition of inclusions in spring steel were analyzed with oxygen-nitrogen 

analyzer and EPMA. It is concluded that refining slag with lower basicity makes the composition of inclusions in spring steel 

approaching to the plastifying zone with low melting points in ternary system of A12O3-SiO2-CaO, but is unfavourable for the 

removal and control of inclusions with larger size. The slag with higher basicity contributes to the formation of inclusions with 

smaller and even size, but increases Al2O3 content in inclusions. Refining slag with higher basicity is beneficial for deeply-

deoxidation to achieve high purity steer, at the same time, reoxidation of molten steel during continuous casting process should be 

prevented.