Novel insight into graphite morphology evolution in large-section ductile iron bearing seats and the influence on mechanical properties with the guidance of phase diagram calculation and Finite Element Method

This study investigates the formation mechanism of graphite distortion in large-section ductile iron bearing seats and its impact on mechanical properties. Combining CALPHAD thermodynamic calculations with Finite Element Method (FEM) simulations, the graphite morphology evolution and its effects on mechanical performance are analyzed. CALPHAD results show that increasing Mg content from 0.03 wt% to 0.06 wt% expands the (FCC + Graphite + Liquid) phase temperature range from 7.25 °C to 15.14 °C, indicating Mg's role in inhibiting flake graphite formation. Experimental data reveal that flake graphite cast iron exhibits tensile strength and elongation of 351.7 MPa and 6.1 %, respectively, compared to 455.3 MPa and 22.3 % for spheroidal graphite cast iron. FEM simulations using Abaqus under a loading speed of 3 mm/min indicate that when the tensile direction is parallel to flake graphite, the material has a tensile strength of 408.2 MPa and an elongation of 21.1 %. Conversely, cracks initiate and propagate through flake graphite regions when the tensile direction is perpendicular, leading to brittle fracture behavior. These findings provide theoretical support for optimizing ductile iron production processes and enhancing casting quality.