Dynamic gamma ->alpha transformation during hot deformation in iron-nickel-carbon alloys

Fe-6mass%Ni-(0.0008 similar to 0.29)mass%C alloys were hot-deformed in tors ion at 600-720 degrees C (above the cooling transformation start temperatur es A(r3)) after austenitization. An in-situ X-ray diffraction study reveale d that gamma-->alpha transformation occurred during deformation in a wide r ange of condition, even above A(3)(p) (paraequilibrium gamma-->alpha transf ormation temperature). Corresponding to this transformation, apparent decre ase in deformation stress from that expected for austenite was observed. Mi crostructural study of the specimens quenched after the deformation showed that a large amount of fine-grained ferrite was formed due to the deformati on. The analysis of deformation stress and chemical driving-force of the tr ansformation indicated that the transformation occurred in order to reduce the total energy of deformed material since the deformation of energy of ex was revealed to be considerably smaller than that of gamma and the amount of deformation energy saved by the transformation was shown to be much grea ter than the chemical energy consumed by the transformation at the tested t emperatures.