Orientation relationship transition of nanometre sized interphase precipitated TiC carbides in Ti bearing steel

The objective of the present study was to investigate the crystallography and morphology of TiC particles in a titanium containing high strength low alloy (HSLA) steel that form during isothermal transformation at a temperature in the (alpha + gamma) phase field. The orientation relationships (ORs) were identified from selected area diffraction patterns (SADPs) and from moire fringes in high resolution transmission electron microscopy (HRTEM) lattice images. It was found that in the initial stages of the isothermal transformation, fine plate-like TiC particles develop and that these exhibit the Baker-Nutting (BN) OR with respect to the ferrite matrix. In the later stages of the transformation, however, coarser plate-like carbides are observed, and these adopt approximately the Nishiyama-Wassermann (NW) OR with respect to the ferrite matrix. The evidence indicates that OR transition is brought about simply by aging for a longer time at the transformation temperature, and also manifests a rotation of the precipitate during coarsening.