Abstract: In consideration of the influence of irregular inclusions to the nucleation of acicular ferrite, building the nucleation model whose base phase and precipitated phase are normal triple prism. Theoretical analysis reveals that not only spherical inclusions can induce acicular ferrite to nucleation, but also irregular inclusions with corner angle. The smaller of the wetting angle, the easier of the acicular ferrite to nucleation. When the side corner of the base phase is between 75°－120°, the irregular inclusions induce the acicular ferrite to nucleation easily.

Key words: acicular ferrite, irregular inclusions, mathematical model, normal triple prism