Effect of Minor Alloying Elements on the Mean Thermal Expansion Coefficient of Fe-36% Ni Invar Alloy

The effects of single addition (C, B<0.02%, Al<0.1%, others<0.5%) of various minor alloying elements such as C, Si, Mn, Cr, Mo, Cu, Nb, Ti, V, Al, W and B in 36%Ni base alloy on thermal expansion and Curie temperature (Tc) were investigated.The results obtained are as follows :(1) Thermal expansion coefficient between 30°C and 100°C (α30100°C) increases with increase in the content of all these alloying elements. The magnitude of the effect of alloying elements on α30100°Cwas evaluated quantitatively. α300400°Cincreases also with increase in the content of these alloying elernents except B and Cu.(2) It is found that α 30100°C of 36%Ni alloys with Tc lower than that of the base alloy tends to decrease with rise in Tc. On the other hand α30100°C of the alloys with Tc higher than that of the base alloy tends to increase with rise in Tc.(3) Relation between α 30100°C and the mean number of valence electrons per atom (e/a) is classified into 3 groups which depend on number of valence electrons of alloying elements. α30100°C in each group has good relation to e/a.