Formation and Evolution of DS-Type Inclusions in 15-5PH Stainless Steel

15-5PH stainless steel castings are key components in fracturing trucks. However, DS-type inclusions can lead to fatigue failure of the material. To elucidate formation mechanism large-size inclusions, evolution, growth, and aggregation during vacuum oxygen decarburization, ladle refining, casting were studied. The results show that with sizes larger than 20 μm CaO–Al2O3–SiO2–MgO–CaS composite inclusions. After Si–Al additions degassing, typical spinel or Al2O3. Ca–Si treatment, liquid dual-phase Al2O3–CaO–SiO2–MgO. During solidification process, due segregation S decrease solubility, final became Al2O3–CaO–SiO2–MgO–CaS. For optimal performance castings, slag refractory composition control also necessary because [Mg] contents mainly come from lining.