Intragranular Ferrite Formed in a V–Ti–N Medium‐Carbon Steel Containing MnS Inclusions

Abstract

This paper studies the formation of intragranular ferrite in a V–Ti–N medium‐carbon steel containing MnS inclusions. The (Ti, V)(C, N) particles precipitating on MnS inclusions are confirmed to be the main nucleation sites of intragranular ferrite. Because of the small lattice mismatch and low‐energy ferrite/V(C, N) interphase boundary, the vanadium‐rich edge of (Ti, V)(C, N) particles increases the nucleation potency of intragranular ferrite. The interphase of MnS inclusions and austenite provides suitable sites for (Ti, V)(C, N) particles to grow big enough to reach the critical size for intragranular ferrite nucleation. Furthermore, the efficiency of the formation of intragranular ferrite starts to increase rapidly when the length of MnS inclusions decreases to less than 10 µm. The shape of intragranular ferrite is also significantly influenced by the length of MnS inclusions. In addition, the intragranular ferrite is confirmed to have a new type of orientation relationship with the particles precipitating in liquid phase, which indicates that the orientation relationship between the intragranular ferrite and (Ti, V)(C, N) particles is not sole, but diversified.