Ferrite nucleation potency of non-metallic inclusions in medium carbon steels

Abstract In recent years, there has been renewed interest in the role of non-metallic inclusions in controlling the microstructure of steels. The potency of various inclusions and precipitates such as SiO 2 , MnO·SiO 2 , MnS, Al 2 O 3 , Ti 2 O 3 and VN for the nucleation of intragranular ferrite has been examined in the present study. Among them, single SiO 2 , MnO·SiO 2 , Al 2 O 3 , TiN and MnS particles seem to be inert to the nucleation of intragranular ferrite under the present experimental condition. Ti 2 O 3 particles in a Mn-containing steel are very effective for the nucleation of intragranular ferrite, being (Ti,Mn) 2 O 3 particles by absorbing Mn atoms from a steel matrix. On the other hand, Ti 2 O 3 particles in a Mn-free steel are not effective. MnS and Al 2 O 3 particles in high nitrogen steels containing vanadium also appear to be potent for the nucleation of intragranular ferrite. The decrease in transformation temperature causes a change in the morphology of intragranular ferrite from idiomorphic ferrite to acicular ferrite.