Multiscale Simulation on Casting Process and Analysis of Structurally Sensitive Regions of K4169 Superalloy Casing

To address the challenges of high misrun risk, severe shrinkage porosity tendency and inhomogeneous grain microstructure induced by the large-area thin walls, radial hollow support plates and abrupt section transitions of K4169 superalloy casing, an investment casting model of a K4169 casing was established via ProCAST software, and the cellular automata-finite element(CAFE) macro-micro coupled method was adopted to simulate filling and solidification, shrinkage porosity, equivalent stress and grain structure. The inner ring, outer ring, radial support plates and root junctions of inner and outer rings were selected as typical regions. The spatial distribution laws of macroscopic shrinkage porosity defects, thermal history and microstructures were comprehensively compared to identify structurally sensitive regions of the casting and the ideas for process optimization were proposed. The results show that the bottom gating process with pouring temperature of 1500 ℃, mould preheating temperature of 1000 ℃ and pouring time of 5 s can realize stable and complete mould filling. Thin-walled regions solidify firstly, while the gating system and thick connecting hot spot areas solidify at a later stage. With the cutoff threshold of 1.8% shrinkage porosity for screening, no continuous shrinkage porosity bands exist in the casting, and discrete porosity spots are mainly distributed at the concave areas around the inner ring holes, the ends of radial support plates and their root transition zones. High values of solidification equivalent stress concentrate at the junctions with abrupt section changes between support plates and rings, and the high-risk regions of shrinkage porosity do not completely overlap with stress concentration zones spatially. The grain size distribution varies significantly among different characteristic regions. The outer ring possesses the finest grains with an average equivalent grain diameter of 1.387 mm, and the proportion of grains larger than 5 mm is merely 0.198%. The radial support plates exhibit the most prominent long tail of coarse grains, with an average equivalent grain diameter of 1.562 mm and a 0.827% fraction of grains exceeding 5 mm. Secondary dendrite arm spacing (SDAS) shows a strong positive correlation with solidification time, yet its distribution is asynchronous with grain size distribution. Regions with shrinkage porosity, high stress, coarse grains and large SDAS do not fully overlap spatially. The radial support plates and their roots bear multiple defect risks, making them the primary structurally sensitive zones. Concave areas around the inner ring holes serve as local sensitive sites for shrinkage porosity, and dendrite coarsening in the outer ring needs to be controlled. Accordingly, regulation schemes are proposed from the perspectives of feeding design, differentiated heat dissipation, mould shell heat preservation and structural fillet optimization. Meanwhile, experimental verification routes involving CT inspection and EBSD metallographic characterization are planned. This study constructs an evaluation system integrating multi-scale simulation and statistics of typical sub-regions, which can provide simulation support for defect suppression, microstructure regulation and safety assessment of similar casing castings.