4. Structure Formation and Thermal Expansion Analysis of 0.6% Carbon-Containing Invar Alloy Crystallized at Different Cooling Rates

Qualitative and quantitative analysis of the distribution of structure components of Fe-Ni-Co carbon-containing invar alloy with 0.6%C has been performed. It has been shown that the cooling rate during crystallization affected volume percentage and dispersity of graphite. The alloy crystallized at a high cooling rate has demonstrated higher volume percentage and dispersity of graphite than the alloy crystallized at a low cooling rate. Both alloys have displayed similar behavior of the coefficient of thermal expansion. During the heating the constant values of thermal expansion were kept up to 200 °C. However, the minimal thermal expansion has been observed in the alloy crystallized at a high cooling rate. The explanation for that might be the following: the content of carbon into the γ-phase is lower in the alloy crystallized at a high cooling rate than in that crystallized at a low cooling rate. As thermal expansion is caused by γ-phase properties, the reduction of carbon into the γ-phase results in the minimal coefficient of thermal expansion.