等轴晶铸造镍基高温合金广泛用于航空发动机中低温热端部件，K492M 合金因凝固区间宽、浇注温度高易出现晶粒粗大、组织不均问题。 本文研究 Cr-Fe-Nb/Co-Fe-Nb 复合晶粒细化剂对 K492M 铸造高温合金显微组织与力学性能的影响规律，揭示了细晶强化机制，为该合金工程化应用提供组织调控依据。 结果表明，晶粒细化剂可显著细化K492M 合金的晶粒，其平均晶粒尺寸由 3 128.25 μm 减小到 297.59 μm，断面等轴晶比例由 60.28%提高到 94.06%，同时碳化物尺寸与含量、共晶组织含量也都有所降低，这是由于细化剂添加后形核质点增多，晶粒尺寸降低，减少了共晶和碳化物的生长空间，使得其长大受阻。另外，二次枝晶间距保持在同一水平范围内。进一步研究表明，细化剂添加可使K492M 合金在 760 ℃高温拉伸条件下的屈服强度从 690.38 MPa 提升至 978.76 MPa，抗拉强度从 941.25 MPa 提升至1 147.95 MPa，伸长率从 4.88%提升至 12.50%；760 ℃/662 MPa 条件下，合金持久寿命则从 35.88 h 提升至 110.99 h。 未加入细化剂的试样断口呈现出脆性断裂特征，且晶界区域应力集中显著，而加入细化剂的试样断口呈现出韧-脆混合断裂特征，晶界区域的位错密度也较原始试样显著降低。 因此，晶粒细化后，K492M 合金单位体积内的晶界面积上升，合金协调变形能力提高，促使了其强度和韧性的协同提升。

Equiaxed crystal cast nickel-based superalloys are widely used in the low-temperature hot-end components ofaeroengines. K492M superalloys, owing to their wide solidification range and high pouring temperature, are prone to coarsegrains and uneven microstructures. The effects of Cr-Fe-Nb/Co-Fe-Nb composite grain refiners on the microstructure andmechanical properties of K492M cast superalloys were studied, revealing the fine-grain strengthening mechanism andproviding a basis for controlling the microstructure of this alloy for engineering applications. The results show that thegrain refiners can significantly refine the grains of the K492M alloy, reducing the average grain size from 3 128.25 μm to297.59 μm and increasing the proportion of equiaxed grains in the cross-section from 60.28% to 94.06%. Moreover, thesize, content, and eutectic content of the carbides decrease. The reason is that the addition of the refiner increases thenumber of nucleation sites, reduces the grain size, and limits the growth space for eutectic structures and carbides,thereby hindering their growth. In addition, the second dendritic arm space remains at the same level with the addition ofgrain refiners. Further studies indicate that the addition of the refiner can increase the yield strength of the K492M alloy under 760 ℃ high-temperature tensile conditions from 690.38 MPa to 978.76 MPa, the tensile strength from 941.25 MPa to1 147.95 MPa, and the elongation from 4.88% to 12.50%; under 760 ℃/662 MPa creep conditions, the life increases from35.88 h to 110.99 h. The analysis shows that the fracture surfaces of samples without the refiner exhibit brittle fracturecharacteristics, with significant stress concentration at the grain boundaries, whereas samples with the refiner show mixedductile-brittle fracture characteristics, and the dislocation density in the grain boundary regions is reduced by an order ofmagnitude compared to that of the original samples. Therefore, after grain refinement, the grain boundary area per unitvolume of the K492M alloy increases, enhancing the ability of the superalloy to coordinate deformation and therebypromoting a synergistic improvement in both strength and toughness.