Castability of molten steel and cleanliness of slab for high strength low alloy steel without calcium treatment

Abstract

Calcium treatment is an important parameter in solving nozzle clogging during continuous casting of Al containing steel. In this study, the process of slag washing was optimised in order to control the compositions of the refining slag. The results showed that the total oxygen (T[O]) content in the casting slab could be controlled to 13–23 ppm and the nitrogen ([N]) content to 21–47 ppm. The total number of macroinclusions in the slab was also reduced to 9·82 mg 10 kg⁻¹ of steel. The typical size of microinclusions in the steel without calcium treatment was <5 μm in the MgO–Al₂O₃, SiO₂–Al₂O₃ systems, and only a small amount of Al₂O₃ was found. The rolled metals therefore met the quality and performance requirements of a high strength low alloy steel for engineering applications. Thus, by eliminating the need for calcium treatment, production costs could be reduced significantly, and the cleanliness of the molten steel could be improved.

Keywords:

• Calcium treatment
• Refining slag
• Castability
• High strength low alloy steel