Abstract:The effect of solidification cooling rate on microstructure and room temperature tensile properties of equiaxed nickel-based cast superalloy K4750 were studied by designing shell insulation methods. Four types of insulation methods were designed, including: sand-filled, test bars without insulation felt, wrapped single-layer insulation felt and wrapped double-layer insulation felt, and the order of solidification cooling rate at the test bar of the shell is: test bars without insulation felt ≥ sand-filled > > wrapped single-layer insulation felt ≥ wrapped double-layer insulation felt. After standard heat treatment, the test bar with sand-filled shell has the highest room temperature tensile strength (1115MPa), the test bar without insulation felt is the seconed highest (1095MPa), and the single-layer insulation felt and the double-layer insulation felt are the worst (950MP and 952.5MPa respectively). OM, SEM and EBSD were used to characterise the microstructure of the alloy. The results show that the grains of sand-filled, test bars without insulation felt, single-layer insulation felt and double-layer insulation felt are equiaxed crystals, and the average grain sizes were 176μm, 167μm, 325μm and 315μm, respectively. Sand-filled and test bars without insulation felt alloys solidification cooling rate is faster, the formation of small equiaxed crystals more easily coordinated deformation in the stress conditions, solidification process to form the MC type primary carbide is finer and mainly in the form of blocks, which is conducive to inhibit the expansion of microvoids and cracks during deformation, significantly improving the tensile properties of the alloy at room temperature. On the contrary, single-layer insulation felt and double-layer insulation felt alloys solidification cooling rate is slower, the formation of large-size equiaxed crystals are not conducive to the coordinated deformation between the grains, and the precipitation of MC type primary carbide with large size and long strip shape promotes the emergence and expansion of holes and microcracks, which significantly reduces the strength and plasticity of the alloy at room temperature.