Vermicularity window of vermicular graphite cast iron and new vermicularity criterion

By adjusting the dosages of the inoculant and the vermiculizer respectively, the graphite morphology, vermicularity, thermal conductivity, and internal friction parameters of the vermicular graphite cast iron (VGI) were systematically studied. The results show that there is a synergistic regulatory relationship between the graphite vermicularity in the cast iron and the dosages of the inoculant and the vermiculizer. For different vermicularity ranges, there are different dosage windows for the inoculant and the vermiculizer. Among them, the window for the vermiculizer is relatively narrow, while that for the inoculant is relatively wide. In addition, there exists a critical graphite vermicularity window of 80%–85% within which the thermal conductivity drops sharply, indicating that the thermal conductivity can serve as an effective criterion for evaluating the graphite vermicularity. When the thermal conductivity decreases to below 40 W·m −1 ·K −1 , the graphite vermicularity is generally no higher than 80%. The graphite vermicularity can be determined by the change rate of the internal friction with the strain amplitude d( Q −1 )/dγ under low strain amplitude, or by the peak internal friction Q −1 max at high strain amplitude.