Abstract: Effect of annealing on microstructure, grain boundary distribution, thermal expansion and mechanical properties of hot-rolled Fe-36%Ni invar alloy was investigated by means of backscattered electron diffraction (EBSD), scanning electron microscope (SEM), thermal expansion test, hardness test and tensile test. The results show that the hot-rolled alloy has a single austenite structure with low coefficient of thermal expansion (CTE). When the annealing temperature increases from 600 ℃ to 900 ℃, the recrystallization ratio of the alloy increases and a large number of ∑3 twin boundaries form, the small angle grain boundaries gradually change to large angle grain boundaries, the CTE and the strength gradually decreases, and the plasticity increases. After annealing at 900 ℃ for 10 min, the alloy completely recrystallizes and accompanies by a large amount of annealing twins, the tensile strength and yield strength of the alloy are 401 MPa and 243 MPa, respectively, the elongation is 55.8%, and the lowest CTE of 0.89×10^-6℃^-1 is obtained.

Key words: Fe-36%Ni invar alloy, annealing, microstructure, strength, coefficient of thermal expansion