Effects of prior austenite deformation and non-metallic inclusions on the ferrite nucleation and grain refinement of two kinds of low-carbon steels have been studied. The ferrite nucleation on MnS and V(C,N) is observed. The combination of thermomechanical processes with adequate amounts of non-metallic inclusions formed in low-carbon steels could effectively refine the grain size and the microstructure. Ferrite nucleated on the single MnS or V(C,N) inclusions and complex MnS+V(C,N) inclusion. The proper addition of elements S and V could effectively promote the formation of ferrite and further refinement of ferrite grains. Effects of prior austenite deformation and non-metallic inclusions on the ferrite nucleation and grain refinement of two kinds of low-carbon steels have been studied. The ferrite nucleation on MnS and V (C, N) is observed. The combination of thermomechanical processes with Adequate amounts of non-metallic inclusions formed in low-carbon steels could effectively refine the grain size and the microstructure. Ferrite nucleated on the single MnS or V (C, N) inclusions and complex MnS + V (C, N) inclusion. proper addition of elements S and V could substantially promote the formation of ferrite and further refinement of ferrite grains.