Distribution and diffusion of carbon atoms during deformation of undercooled austenite in medium carbon steel

The distribution and diffusion of carbon atoms during deformation of undercooled austenite in the medium carbon steel were investigated by means of uniaxial hot compression simulation experiment, SEM, XRD and thermomagnetic methods. The experimental results showed that the effective diffusion coefficient of the carbon atoms during dynamic transformation of undercooled austenite increased significantly compared with that during the isothermal transformation at the same temperature, as a result the completion of ferrite and pearlite transformation was shortened. During the subsequent spheroidization process of lamellae pearlite, high density dislocations and vacancies introduced during hot deformation promoted the diffusion of the carbon atoms, therefore the cementite spheroidization kinetics was accelerated dramatically as compared to isothermal annealing treatment. The dissolution, re-precipitation of cementite, and supersaturation of carbon inside the ferrite grains were confirmed. The supersaturated carbon atoms were not located at interstitial sites within the iron lattices homogeneously, but highly segregated at ferrite grain boundaries and dislocation cores.