Lath boundary thin-film martensite in acicular ferrite ultralow carbon pipeline steels

Modern pipeline technology for the production of oil and gas pipeline steels is aiming at achieving high strength and toughness. An experimental acicular ferrite (AF) ultralow carbon pipeline steel was investigated to correlate the microstructural characteristic of the steel to its strength and toughness behavior at the present work. The experimental result indicated that the AF ultralow carbon pipeline steel can well satisfy the high strength and toughness requirement. By comparing with the AF conventional carbon pipeline steel, the AF ultralow carbon pipeline steel possesses much higher additional toughness. In addition to having the conventional microstructural characteristics of the AF microstructure, the AF ultralow carbon pipeline steels were observed to present a layer of thin martensite film at the lath boundaries of the AF microstructure. Increasing in toughness of the AF ultralow carbon pipeline steel was analyzed to be related to the lath boundary thin films as well as its microstructural characteristics.