During uniaxial hot compression for a
medium carbon steel, the deformation induced ferrite (DIF) appeared when deformed temperatures
lower than Ad3(786℃). The volume fraction of DIF increases with decreasing
deformation temperature, especially when deformed temperatures lower than 750℃ the volume fraction of DIF increases significantly, which is far beyond the equilibrium ferrite fraction of 54%. With the increase of DIF, more and more carbon atoms were rejected into the boundaries of ferrite and interfaces of ferrite/untransformed austenite. During isothermal holding below A1(719℃) temperature just after deformation, supercooled austenite would decompose to different structures in three different ways: when the deformation temperature is higher than Ad3,conventional ferrite-lamellar pearlite structure was obtained; when the deformation temperature is lower than Ad3 whereas higher than Ar3(645℃), retained austenite transformed to ferrite-lamellar or degenerated pearlite-grain boundary cementite; when the deformation temperature decreased to just above Ad3, a microstructure different from lamellar pearlite was obtained, which consisted of fine cementite particle and ferrite.