| The effects of the holding temperature, heating rate and nickel content on the formation of the send phase were investigated for the ductile cast iron having ferrite matrix. In order to vary the heating rate, specimens were prepared from 1 to l0㎜ in thickness and nickel was added up to 1% to study the effect of nickel content. The main results obtained from this study were as follows; 1. Austenitizing velocity increased with high holding temperature and rapid heating rate but decreased with nickel amount. 2. Incubation period decreased with high holding temperature, rapid heating rate, and high nickel content. 3. Radius of the second phase formed by the graphite diffusion into ferrite matrix increased by the rapid heating but decreased by addition of nickel. 4. Uniform spheroidal second phase was formed when the specimen were held at high temperature and heated rapidly to the high temperature. 5. The discrepancies between Paxton-Judd model and this study were mainly arised from the condition of the holding temperature, the carbon, and the impurities. 6. After rapid increase of the hardness in early stage, the hardness increased slowly with the amount of the second phase. |
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