Effect of Bismuth on Microstructure and Properties of Ductile Iron

This study explores the effect of bismuth on ductile iron to enhance its mechanical properties and to prevent the formation of chunky graphite. Various heats of ductile iron were produced with varying bismuth (0.000–0.010 wt%Bi). Microscopic examinations, Brinell hardness tests, and tension tests were conducted to characterize the samples. The results indicate that Bi influences the microstructure, nodule count, hardness, and tensile strength of the ductile iron, with optimal amount of Bi (0.005–0.007 wt%Bi) depending on section thickness. Bi prevented the carbide formation and increased the nodule count, leading to improved mechanical properties. In addition, the study demonstrated that Ce/Bi values of 1.29–1.60 were corresponding levels that showed optimal microstructure and properties. Thermal analysis demonstrated the inoculation effect of Bi addition by shifting TE_low and TE_high toward the stable eutectic temperature. Electron Probe Microanalysis (EPMA) results showed that Bi oxide and sulfide were found at the graphite cores as heterogeneous nucleation sites during solidification.