Influence of Carbon and Nickel Segregation on Thermal Expansion Coefficient of 35mass%Ni Cast Iron

The thermal expansion coefficient of 35mass%Ni austenite cast iron is 3.0 X 106 /K to 4.0 X 106 /K and becomes larger in three times than that of Inver aloy. Therefore, we first discuss the influence of carbon content on the thermal expansion coefficient using the carburized samples, and then, the effect of Ni segregation using the cast samples with different graphite morphology. In addition, the influence of the cooling rate, namely nickel segregation distance, on the thermal expansion coefficient is investigated by changing the thickness of the cast samples. As the result, the influence of carbon on the thermal expansion coefficient is not so significant. Spheroidal graphite iron is not suitable for annealing due to the large segregation distance. In addition, the thermal expansion coefficient of thin cast sample decreases faster than that of the thick one by annealing. The thermal expansion coefficient of 35mass%Ni austenite cast iron can be decreased to 2.0 x 10u /K, by fully annealing to decrease in the Ni segregation, regardless of the addition of Co.