Abstract: Aimed at the abnormal fracture of K418 superalloy ingots during secondary induction remelting, a systematic investigation was carried out through macroscopic morphology observation, microscopic analysis of fracture, metallographic examination, and energy-dispersive spectroscopy (EDS). The results reveal that the fracture surface of the fractured ingot exhibits the characteristics of high-stress overload fracture, with shrinkage porosity defects at the core area, and the crack propagated radially outward from the core. The γ' phase at the edge of the ingot was dissolved and then precipitated, while the core remains as cast, indicating significant temperature gradient during induction heating. The skin effect led to the uneven distribution of axial and radial temperature, and the superposition of compound thermal stresses is the main cause of the fracture of the ingot. As a stress concentration source, the shrinkage porosity defects in the ingot core significantly reduced the effective bearing capacity of the material. In addition, the fracture location is spatially related to the distribution of the magnetic induction lines of the induction coil. Based on the effect mechanism of temperature gradient and thermal stress, it is recommended to adjust the heating rate and optimize the arrangement of the induction coil to reduce the thermal stress level. The present work provides reference for the optimization of the process parameters of induction remelting of superalloys.