Oxidation mechanism and microstructure evolution of invar alloy with high temperature annealing process

The high temperature oxidation behavior of Fe–36Ni Invar alloy in the forged billet stage and hot rolled rod stage in the compressed air atmosphere has been systematically studied. The results show that the oxide layer can be divided into the external oxide layer composed of Fe2O3, Fe3O4 and NiO, and the inner transition oxide layer composed of FeO, Fe2O3, Fe3O4 and NiO. In addition, hot rolled rod samples treated by solution and rolling have higher oxidation resistance. The mechanism of O diffusion during oxidation is analyzed, and it is found that the O atom adsorbed on the surface of the substrate diffuses into the grain along the grain boundary. The grain boundary is the optimal path for O diffusion to the interior of the material, which results in the degree of intergranular oxidation of the alloy being greater than the degree of intragranular oxidation. In summary, the oxidation resistance of Invar alloy can be improved by proper solution treatment and avoiding the formation of grain boundary cracks during production.