Evolution of inclusions during refining in low carbon Al-killed steel produced by BOF-LF-CSP process

Intensive steel samples were taken from industrial beats at various time in a ladle furnace during BOF-LF-CSP process. The compositions, size distribution and change in number of inclusions in the samples were statistically analyzed by using an ASPEX scanning electron microscope. It is found that the number density and area fraction of inclusions in the samples sharply increase after Al addition. Then the number density has little changes while the area fraction obviously decreases during the period between 20 min-refining and soft blowing before Ca treatment. At the end of refining, the inclusions are mainly MgO-Al₂O₃ spinels containing little amounts of CaO. Both the number density and area fraction increase after Ca treatment, and the typical inclusions at this moment are calcium-aluminates and CaS due to excessive Ca treatment.