Using an intermediate nanocrystalline γ phase for producing austenitic steels with a controllable thermal expansion coefficient

The metastable austenitic iron alloy with 31.3 wt % Ni (N31) has been used to show the possibility of the formation of a nickel-concentration inhomogeneity in a fine-grained austenite due to an α → γ trans-formation under the condition of a preliminary formation of a nickel-enriched intermediate nanocrystalline γ phase. The thermal expansion coefficients (TECs) in the range of −100 to +300°C have been estimated in concentrationally inhomogeneous steel N31 after various heat treatments. The conditions necessary to ensure the possibility of controlling the TEC in wide limits have been found.