Precipitation behavior of inclusion-induced intra-granular ferrite in Ti-deoxided VN microalloyed steel

Precipitation behaviors of Ti-containing inclusions and inclusion-induced intragranular ferrite were investigated by thermodynamic calculations and laboratory experiments. The results show that there are six forms about position relations of inclusions to ferrite grains and pearlite grains. The effects of inclusion types and size on the inclusion-inducing ability were analyzed quantificationally by defining the index of inducing ability. It is indicated that the ability of Ti-containing complex oxide-inclusions inducing intragranular ferrite is the best, but that of Al₂O₃ is the worst. The optimal size of Ti-containing complex oxide-inclusions is 4 to 6μm and that of other inclusions is 2 to 4μm. Intra-granular ferrite is induced to precipitate by controlling the inclusion types and size, leading to grain refinement.