2019 Volume 91 Issue 4 Pages 201-207
In order to clarify the effect of inoculants containing zirconium on spheroidal graphite cast iron, systematic investigation was carried out from the solidification process to the metallographic structure, shrinkage property, and mechanical properties, and the mechanism bringing about the effect was examined from the microstructure.
The addition of the Fe-Si-Zr inoculant increases the stable eutectic temperature, and the differential curve angle at the end of solidification (θ) becomes small. As the graphite nodules in the microstructure increase, the shrinkage reduces. The mechanism of the improvement of the shrinkage property is considered to be due to the increased amount of graphite crystallized, particularly in the later stage of solidification. As for mechanical properties, the compatibility of tensile strength and elongation improved, and the wall-thickness sensitivity reduced. The mechanism for reducing the wall-thickness sensitivity is considered to be due to the suppression of ferritization around the graphite nodule by graphite crystallization in the late solidification region in which the carbide stabilizing elements are concentrated.
Though Fe-Si-Ti, Fe-Si-V, and Fe-Si-Nb inoculants also have the effect of increasing graphite nodules, Fe-Si-Zr inoculant has the most stable effect for the difference in molten metal characteristics.
