Abstract: The ferrite in twinroll cast strips with different P contents was analyzed by the observation of the microstructure. The results showed that the volume fraction of ferrite in the cast strip was obviously more than that in the cast billet with the same P content. In a cast strip， the volume fraction of ferrite in the surface layer was less than that in the center area， and the ferrite in the surface layer was reduced with the reduction of the P content. The morpology of the ferrite in the cast strip was gradually transformed from the acicular form into the polygonal form with smooth surface with the increase of the P content. Through the theoretical analysis， it was shown that the rapid cooling favored ferrite stabilizing in steels， and the polygonal ferrite with smooth surface directly precipitated from the liquid steel while the acicular ferrite precipitated from the solid austenite.

Key words: subrapid solidification, twinroll cast strip, P content, volume fraction, morphology