Acicular ferritic microstructure of a low-carbon Mn-Mo-Nb microalloyed pipeline steel

The transformations during continuous cooling and isothermal processes, the effects of hot deformation and the morphology of the final microstructure of a low-carbon Mn-Mo-Nb microalloyed pipeline steel designed for acicular ferrite microstructure were investigated. The results show that there are three independent “C” curves for isothermal phase transformation, i.e., TTT diagram, of low-carbon microalloyed steel, namely, polygonal ferrite-pearlite transformation “C” curve, the massive ferrite transformation “C” curve and the bainitic transformation “C” curve, respectively. Hot deformation accelerates acicular ferrite transformation and refines the steel's matrix. The microstructure of acicular ferrite for pipeline steels was discussed.