Microstructural and tensile behavior of Fe-36%Ni alloy after cryorolling and subsequent annealing

In this paper, the microstructure and mechanical properties of Fe-36%Ni alloy after 90% reduction of cryorolling (CR) and subsequent annealing were investigated. The X-Ray diffraction (XRD) results indicated the existence of γ→α, phase transformation, and the measurement result of the α, volume fraction was 15%. Lath α, with average thickness of 29.3 nm was then observed by transmission electron microscope (TEM). After 90% reduction of CR, the ultimate strength (UTS) of the tested alloy was enhanced to 1100 MPa. This was mainly due to high density defects formation and α, transformation during CR. After annealing at 823 K for 5 min, TEM results revealed that a multimodal grain structure was produced, the UTS of the tested alloy was decreased to 830 MPa, total elongation (EL) was increased to 8%. With the increasing of annealing time, the recrystallized grains were gradually coarsened and the volume fraction was increased. The increase of ductility was accompanied by the significantly decrease of strength. The cryorolled Fe-36%Ni alloy was fully recrystallized after annealing at 823 K for 30 min. The grain size distribution indicated that nearly 62% of the grains were less than 3 µm and there were a few large grains more than 10 µm. The recrystallized sample exhibited a good mechanical property with a higher tensile strength of 550 MPa and total EL of 36%, which was probably due to the bimodal microstructure.