Effects of Calcium Addition on Nonmetallic Inclusions in High‐Al Steel

To investigate the formation and evolution mechanism of inclusions in high‐Al steel, four lab‐scaled experiments are carried out with different calcium (Ca) contents. The Al 2 O 3 inclusions are modified to (CaO–Al 2 O 3 )–CaS after Ca addition. With the Ca content increased, the types of CA x ‐CaS inclusions are changed from CaS‐attached inclusions to CA x ‐wrapped inclusions. When the total calcium content (T.Ca) reached 29 ppm, the CA x –CaS inclusions are primarily distributed within the 50% liquidus in CaO–Al 2 O 3 –CaS ternary diagram. Some Al 2 O 3 inclusions are not completely modified with 7 ppm Ca addition. CaS and CaO–CaS inclusions are observed with a higher Ca addition. The modification of Al 2 O 3 by CaS and [Ca] occurs in CaS‐attached inclusions with a lower Ca addition. To clarify the formation of CaS, a new modification index for high‐Al steel is given based on the T.Ca/T.O index.