Suppression of strain-induced precipitation of NbC by epitaxial growth of NbC on pre-existing TiN in Nb-Ti microalloyed steel

Absence of strain-induced precipitation of NbC is observed in a conventional hot rolled Nb-Ti microalloyed X90 strip. Quantitative analysis using transmission electron microscopy and 3D atom probe tomography indicates that epitaxial growth of NbC on pre-existing TiN particles with a short inter-particle spacing of 300±65nm suppresses the occurrence of strain-induced precipitation of NbC on dislocations. The model for predicting kinetics of strain-induced precipitation of NbC on dislocations is incorporated into a criterion for the end of nucleation of strain-induced precipitation to estimate the effects of process parameters on suppression of strain-induced precipitation of NbC. TiN particle inter-spacing is identified as a key parameter influencing the precipitation behavior of NbC during thermomechanical controlled processing. TiN-NbC composite precipitates offer an alternative approach to strain-induced precipitation of NbC for high temperature processing of Nb microalloyed steels with high toughness. The significance and possible implication of the TiN-NbC composite precipitate engineering are discussed.