Microstructure and mechanical properties of heavy section ductile iron castings: experimental and numerical evaluation of effects of cooling rates

This paper focuses on the development of experimental relationships between the microstructure and mechanical properties of a sand cast ductile iron and on the design of a direct ‘in mould’ thermal analysis system for heavy section castings. The casting system was developed in order to obtain different thermal modules, and it has been studied by numerical simulation. The microstructure was estimated through numerical models implemented in a commercial casting simulation code and validated by comparing simulated and experimental data obtained from more than 2000 optical micrographs considering nodularity, density and size of nodules, fractions of graphite, ferrite and pearlite. Empirical relationships between the microstructure and mechanical properties were developed and then implemented in the simulation software in order to evaluate the local mechanical properties. The results of hardness and tensile tests carried out on samples extracted from the castings showed good accordance between predicted and measured mechanical properties.