Effect of Yttrium Content on the Transformation of Inclusions in a Si–Mn-Killed Stainless Steel

Laboratory experiments were performed to study the transient evolution of inclusions in Si–Mn-killed stainless steels with additions of 60 and 360 ppm yttrium using low- and high-oxygen yttrium-containing ferroalloys. With the increase of the yttrium content in the steel, the evolution path of inclusions was CaO–Al2O3–SiO2–MnO → Y2O3–Al2O3–SiO2(–CaO–MnO) → Y2O3 and YS → Y2O3. The YS inclusion was generated as a transient product in the steel with 360 ppm yttrium addition using high-oxygen yttrium-containing ferroalloys. With the addition of 60 ppm yttrium, initial larger CaO–Al2O3–SiO2–MnO inclusions were modified to smaller liquid Y2O3–Al2O3–SiO2(–CaO–MnO) inclusions, resulting in a smaller diameter of inclusions. After the addition of 360 ppm yttrium, initial liquid CaO–Al2O3–SiO2–MnO inclusions were modified to small solid Y2O3-rich inclusions, lowering the average diameter of inclusions. Then, the size of inclusions in the steel increased due to the collision of solid inclusions.