Abstract: Medium carbon steel (0.36% C) was thermo-mechanically deformed and subsequent controlled cooled (TMCP) to obtain refined microstructure with spheroidized cementite. It was found that ferrite grain size reduced with decreasing deformation temperature or increasing deformation strain. Owing to deformation induced ferrite transformation (DIFT), ultra-fine ferrite grain size of about 2~3μm could be obtained for the steel deformed just above Ar3 temperature. The volume fraction of DIF enhanced with decreasing deformation temperature or increasing deformation strain, especially when deformed temperature lowered than 750℃ the volume fraction of DIF increased significantly, which is far beyond the equilibrium ferrite fraction of 54%. The results indicated that a fairly spheroidized microstructure could be gained for steel deformed at low temperature and high strain and then controlled cooling.