Structural mechanism of reverse α → γ transformation and new functional properties of Fe-Ni austenitic alloys

The structure of the metastable austenite Fe-32%Ni alloy quenched for martensite and subjected to the alpha ->gamma transformation at slow heating (to 593-773 K) with the formation of a nanocrystalline austenite of different orientation was investigated. Electron diffraction analysis has revealed that a nickel-enriched nanocrystalline gamma-phase acquires ordered L1(0) superstructure. Together with the gamma-phase, there was detected the disperse epsilon-martensite with a hexagonal close-packed (hcp) lattice. Along with the realization of ordinary orientation relationships (ORs) of Kurdjumov-Sachs, between a matrix alpha-phase and an ordered gamma-phase in the sample of Fe-32%Ni alloy after slow heating to 773 K there have been established Headley-Brooks ORs. Cyclic transformation promotes the improvement of many functional properties of steels (strength, coercive force, controlled thermal expansion coefficient, and others).