The mechanism of intragranular ferrite formed on Ti-rich (Ti,V)(C,N) precipitates in the coarse heat affected zone of a V–N–Ti microalloyed steel

• Increasing nitrogen contents promote polygonal ferrite and acicular ferrite forming.
• The undissolved Ti-core was nucleation sites of V-rich cap.
• Intragranular ferrite formed on Ti-rich (Ti,V)(C,N) as V-rich cap increased nucleation potency.

The effect of Ti-rich (Ti,V)(C,N) precipitates on the evolution of intragranular ferrite in the coarse grain heated effected zone (CGHAZ) of V–N–Ti steel was systematically investigated via transmission electron microscopy. The coarse grain boundary ferrite, bainite, and ferritic side-plates in simulated CGHAZ were replaced by polygonal ferrite and acicular ferrite, when the nitrogen content was increased from 0.0044 wt% to 0.0094 wt%. In addition, the undissolved Ti-rich core acted as a nucleation site for the V-rich cap; the cap reached the critical size at which nucleation of intragranular ferrite occurs nucleation size of intragranular ferrite with the aid of the core. Owing to a cap-induced increase in the nucleation potency, the intragranular ferrite have formed on the Ti-rich (Ti,V)(C,N) hold the Baker-Nutting orientation relationship ((001)IGF//(001)(Ti,V)(C,N), [110]IGF//[100](Ti,V)(C,N)).