Characterisation of microstructure, texture and mechanical properties in ultra low-carbon Ti-B microalloyed steels

In the present study, thermo-mechanical controlled processing followed by water quenching has been utilised to produce ultra low-carbon microalloyed steel in a laboratory scale. The variation in microstructure and corresponding mechanical properties at the selected range of finish rolling temperatures (FRT), (850–750 °C) has been evaluated. The microstructures of the steels consisted of polygonal ferrite, acicular ferrite as well as granular bainite with the average ferrite grain sizes less than 5 μm. Finish rolling at 850°C produced weak texture. α-fibre and γ-fibre intensified with the decrease in finish rolling temperature to 800°C. Intensities of the beneficial texture components such as, {554}<225> and {332}<113> also reached the highest value at 800°C. Ferrite deformation texture i.e. α-fibre dominated at 750°C FRT. The characteristic ferrite — bainite microstructure with fine ferrite grain size and uniform distribution of fine TiC particles (< 50 nm) resulted in high yield strength (405–507MPa), moderate tensile strength (515–586 MPa) and high total elongation (19–22%) for the selected range of finish rolling temperatures. Fairly good impact toughness value in the range of 63–74J was obtained at subzero temperature (−40 °C) in the sub-size sample. The above strength — ductility — toughness combination boosts the potentiality of developed steel for the pipeline application.