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In order to improve the ifling ability of large complex thin wal castings, the pouring temperature should be increased, but this wil result in the grain coarsening. To overcome this problem, two kinds of grain refiners of Co-Fe-Nb and Cr-Fe-Nb tary alloys, which contain high stability compound particles, were prepared. The effects of the reifners on the as-cast structures and tensile properties of the K4169 superaloy with different casting conditions were studied by analyzing specimens 110 mm long and 20 mm in diameter. Results showed that the mixture addition of the two reifners in the melt of K4169 can reduce the columnar grain region and decrease the equiaxed grain size greatly. After reifnement, the amount of Laves phase decreases and its morphology changes from island to blocky structure. The carbides in the ifne grain samples are ifne and dispersive. Meanwhile, the porosity in specimens is decreased due to grain reifnement. As a result, the yield strength, ultimate strength and the elongation of the specimens are increased. The grain reifnement mechanisms are also discussed.