With increasingly stringent demands for superalloys in the aerospace field, conventional composition optimization approaches have reached their performance ceiling. It has become increasingly difficult to significantly improve the performance of superalloys by adjusting the ratios of primary elements. Rare earth elements serve as important microalloying additives, and the addition of trace amounts can profoundly influence the microstructure and properties of superalloys. Industrial-scale 1 t vacuum induction melting was employed to prepare K465 master alloy ingots. The rare earth elements cerium (Ce) and yttrium (Y) were added during the smelting process to enhance the performance of this cast superalloy. Microstructural characterization was performed via optical microscopy (OM) on both the as-cast and solution-treated samples, whereas scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS) was employed to analyse the microstructure systematically. The room-temperature tensile properties and high-temperature stress rupture performance after solution treatment were examined via a universal testing machine and a creep testing machine. These findings indicate that the addition of rare earth elements (Ce and Y) did not alter the phase constitution of the alloy, which is mainly composed of γ matrix phase, γ′ phase, (γ+γ′) eutectic phase, and carbides. The master alloy exhibits a room-temperature tensile strength of 887 MPa with 4.0% elongation and demonstrates high-temperature stress rupture lifetimes of 88 h and 30 min at 975 ℃/225 MPa.