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 degrees 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 rim. Finish rolling at 850 degrees C produced weak texture, alpha-fibre and gamma-fibre intensified with the decrease in finish rolling temperature to 800 degrees C. Intensities of the beneficial texture components such as, {554}< 225 > and {332}< 113 > also reached the highest value at 800 degrees C. Ferrite deformation texture i.e. alpha-fibre dominated at 750 degrees 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 (405-507 MPa), moderate tensile strength (515-586 Mi3a) 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 degrees C) in the sub-size sample. The above strength - ductility - toughness combination boosts the potentiality of developed steel for the pipeline application.