Effects of annealing temperature and holding time in the isothermal annealing process on microstructure of C-Mn steel were studied by means of optical microscope. And the influence on ferrite recrystallization,widmanstatten and troostite phase transformation was analyzed. The results indicate that ferrite recrystallization is mainly happened when the heating temperature is at less than 750 ℃. With the increasing of annealing temperature and holding time,the degree of ferrite recrystallization is increased,b...