Void initiation at TiN precipitates in IF steels during tensile deformation

An experimental study on interstitial free (IF) steel sheets was performed with the objective to determine the micromechanism(s) governing the void initiation caused by cubic titanium nitride, TiN, particles during tensile deformation. Void initiation was characterized using optical and scanning electron microscopy on samples that were deformed to various elongations. Moreover the development of the particle deformation zone was critically assessed using electron backscatter diffraction (EBSD) technique. It was observed that voids are nucleated in TiN particles by particle fragmentation and particle–matrix decohesion. In the initial stages of deformation the stresses generated within the TiN particles promote the fragmentation of the weakest particles. In the later stages of plastic strain internal stresses of the particles are relaxed by substructural formation of the ferrite matrix and hence the fragmentation rate is reduced. However, stress concentration sites such as particle corners promote particle–matrix decohesion which becomes the predominant void nucleation mechanism at higher strains.