Phase Transformation and Properties Under Different Quenching mediums of an X120 Pipeline Steel

摘要

The microstructure, CVN toughness and micro-hardness of an X120 pipeline steel were investigated by metalloscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) etc. It showed that the microstructure evolved from lathe martensite, lathe bainite to granular bainite and polygonal ferrite, the size of M-A islands increased. With cooling velocity increasing, the CVN toughness at -20°C was fluctuating, and reaching its peak in the steel cooled in oil had the best toughness, while the steel cooled in furnace was brittle at -20°C. With cooling velocity decreasing, the micro-hardness of the steel decreased, whereas, the micro-hardness of the steel cooled in furnace increased slightly.