Abstract
The influence of basicity and Al2O3 content of LF refining slag on T.[O] (total oxygen) as well as type, number and size of non-metallic inclusions in Al killed 60Si2MnA spring steel was investigated. The results showed that with the increase of slag basicity R(CaO/SiO2) or the decrease of Al2O3 content in slag, the T.[O], number and size of non-metallic inclusions decreased significantly. On the one hand, as the slag basicity increased, inclusions in steel were transformed from Al2O3–SiO2–CaO–MgO quaternary system to Al2O3–SiO2–CaO–MgO–CaS quinary system, which made the formation of voids between inclusions and steel matrix to decrease. Furthermore, thermodynamic calculations showed that CaS could only form in steel (R ≥ 3.4). Al2O3–SiO2–CaO–MgO came close to the compositions of the low melting point area, while Al2O3–SiO2–CaO–MgO–CaS deviated from this. On the other hand, as the Al2O3 content in slag increased, Al2O3–SiO2–CaO–MgO–CaS came close to the compositions of the low melting point area. In conclusion, the cleanness and fatigue life of 60Si2MnA spring steel had been improved by the increase of slag basicity or the decrease of Al2O3 content in slag.
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