Effects of Heat Treatment on the Coefficient of Linear Thermal Expansion of Low-Expansion Cast Iron

The average coefficient (α) of Iinear thermal expansion of low-expansion flake and spheroidal graphite cast irons with 35 mass % Ni-1.8 mass % C-1.2 mass % Si, subjected to heat treatment under different conditions, was measured in the temperature range from 323 K to 773 K. When the cast irons were subjected to solution treatment or annealing at the temperature range from 873 K to 1373 K for 3.6 ks, the values of α at 373 K decreased with elevating the heat treatment temperature. The cast irons annealed at 1273 K for 3.6∼360 ks showed a decrease in the value of α at 373 K with increasing the holding time. It was concluded that such a decrease in α was caused by the homogenization of nickel in austenite.