Abstract: Decarburization of non-oriented electrical steel in the two-phase region is a known method to acquire a columnar ferrite structure which may effectively ameliorate the microstructure homogeneity of materials. In this paper,the growth process of columnar grains was analyzed from the kinetics point of view. The results show that the columnar structure formation involves two stages:nucleation and directed growth. Directed growth is a sort of interface migration process caused by both reaction-diffusion and recrystallization growth,and fits a parabolic law. The growth rate and the annealing temperature do not show a monotonic functional relationship,but the growth rate reaches a maximal value when the temperature is 900℃. At last,we get the size constraint condition of columnar nuclei on the basis of the derived growth rate formula,which may present some significance for guiding the design of relevant decarburization parameters in industrial production.