Investigation of primary phases in Ce-containing heat-resistant steel electroslag remelting ingots

Strong carbide-forming elements（e. g., Nb, Ti） in ferrite/martensite（F/M） heat-resistant steels tend to form coarse primary phases during the solidification of molten steel, which significantly impairs the steels′ creep and fatigue properties. Therefore, modulating the composition and size of these primary phases is crucial for enhanc‑ing the mechanical properties of such steels. Numerous studies have confirmed that both electroslag remelting（ESR） and rare earth modification are well-established methods for regulating the primary phase in steel. There is a lock of relevant research on the effect of the combined oution of the two on the primary phases of liquaation in F/M heat-resistant steel. This study investigates the precipitation behavior of secondary phases in Ce-containing 10 Cr1 Si F/M steel following electroslag remelting（ESR）. Scanning electron microscopy（SEM） and ASPEX automated SEM were employed to conduct statistical analysis on the primary phases in the ESR ingot of this steel. The results reveal three dominant precipitates across different positions of the ingot（i. e., top, bottom, center, and edge）,namely black spherical rare earth oxide CeAlO₃, polygonal nitride TiN, and acicular/striated carbide NbC. Their maximum number densities are（29. 1±6. 14）×10¹⁰,（1. 42±0. 29）×10¹⁰,（2. 15±0. 99）×10¹⁰/m³, respectively. Among these precipitates, NbC exhibits the largest size（about 3 μm）, whereas TiN and the rare earth oxide（CeAlO₃） have comparable sizes of approximately 2. 0 μm, and 1. 5 μm, respectively. Furthermore, the primary phases exhibit diverse structural configurations, including bilayer structures（TiN-NbC, CeAlO₃-Al₂O₃）, three-layer structures（CeAlO₃-Al₂O₃-NbC）, and four-layer structures（CeAlO₃-Al₂O₃-TiN-NbC）. Thermodynamic calcula‑tions and misfit theory were applied to clarify the formation mechanism of these multi-layered structures. Owing to the slag-metal reaction and element segregation during solidification, CeAlO₃, Al₂O₃, TiN, and NbC are sequen‑tially formed in the molten steel. The interfacial relationships among these precipitated phases exhibit a certain degree of matching, and heterogeneous nucleation occurs between the primary phases, thereby promoting the for‑mation of various core-shell structures. This study provides an experimental foundation for understanding and regu‑lating secondary phases in rare earth-containing heat-resistant steels.