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K4750 alloy is a new cast nickel-based superalloy with excellent mechanical properties at 700-750℃ and is expected to replace K4169 alloy. However, the tensile plasticity of K4750 alloy at room temperature fluctuates, and the relationship among room temperature tensile properties, solidification microstructure, and casting parameters is still unclear for this alloy. In this work, several K4750 alloy test bars were prepared with various casting temperatures and shell cooling conditions, and tested at room temperature by uniaxial tension. Sensitivity of the alloy"s room temperature tensile properties to changes in casting temperature and shell cooling rate was evaluated, and the mechanism was elucidated by microstructure characterization. Results show that the grain size of alloy drops significantly with decreasing casting temperature, and the yield strength of alloy slightly increases while the plasticity remains stable. When cooling rate of the shell decreases, the fracture elongation of alloy decreases significantly at room temperature. This is mainly because the cooling condition of mold shell significantly affects the precipitation characteristics of MC carbides. When the cooling rate is low, MC carbides tend to precipitate at grain boundaries in coarse and strip-like shapes. MC carbides are prone to internal cracks under stress, accelerating the intergranular failure of material and reducing the plasticity of alloy. In order to optimize the tensile properties of K4750 alloy at room temperature, more attention should be paid to the cooling rate of mold shell after casting and the precipitation morphology of intergranular carbides, prohibiting the formation of coarse intergranular carbides to improve the grain boundary plasticity of alloy.