Effect of Al on the Cleanliness of the x% Al-7CrSiMnMoV Steel Produced by Scrap Steel

It is crucial for recycling scrap steel to effectively remove impurities such as sulfur and oxygen, which directly determine the characteristics of inclusions in steel liquid. This study attempts to investigate the effect of Al concentration on the cleanliness of x% Al-7CrSiMnMoV steel by directly smelting scrap steel. Impurities such as sulfur and oxygen, as well as alloying elements in steel, are investigated. Also, the evolution characteristics of inclusion in the x% Al-7CrSiMnMoV steel are evaluated. The results show that the oxygen concentration in steel liquid gradually decreases; however, the sulfur concentration in steel liquid first increases and then decreases as the aluminum concentration increases from 0.026% to 0.58%. A high-cleanliness 0.58% Al-7CrSiMnMoV steel with sulfur and oxygen concentrations of 0.0015% and 0.0018%, respectively, can be obtained. Additionally, the high Al-Ca-Mg-O and high Ca-Al-Mg-O contain S composite inclusions, and a small amount of fine Mn(Ca)S inclusions first form the high-Al-Ca-Mg-O composite inclusions with an aluminum concentration of 0.026%, then form the high-Al-Mg-O, Al-Mg-O-wrapped Mn(Ca)S, and a large number of fine MnS inclusions with an aluminum concentration of 0.11%; eventually, it forms Al-Mg-O-wrapped CaS as the Al concentrations continuously increase.