Thermal Stability and Section Sensitivity of Ni and Cu Alloyed Austempered Ductile Iron

This study emphasizes the formation of microstructure and its impact on the thermal stability of high-quality cast iron, specifically austempered ductile iron (ADI). The role of the initial heat treatment stage, namely the austenitization process, in determining structural stability and homogeneity of the investigated ADI castings was examined. Additionally, the issue of the presence of unstable high-carbon austenite was addressed. Experiments were conducted on castings with varying wall thicknesses ranging from 3 to 12.5 mm under different austenitization temperatures between 800°C and 900°C. X-ray diffraction (XRD) analyses were performed on test castings over a temperature range from -260°C to 450°C to study structural parameters, including phase fractions, lattice parameters, stresses within the microstructure, and crystal lattice expansion. Additionally, mechanical properties under both static and dynamic conditions were analyzed. It was demonstrated that achieving a homogeneous structure, free of unstable austenite strongly depends on heat treatment parameters, especially the austenitization stage. Furthermore, thin-walled castings showed improved structural homogeneity and stability compared to reference castings. The present work also aims to develop strategies for enhancing structural stability in ADI castings to maintain microstructural homogeneity and high thermal stability. Acknowledgments This research was conducted within Horizon Europe Project No. 101159771 — NetCastPL4.0