Linepipe with the dual-phase steel of bainite and dispersed MA (martensite-austenite constituent) phases has been applied for many pipelines in the seismic and permafrost regions which require higher deformability of the linepipes. Bainite-MA dual-phase microstructure exhibits excellent deformability and high strength up to Grade X100. Finely dispersed MA phases in the bainitic matrix also show strong resistance to microscopic crack initiation and propagation, resulting in good toughness of the base metal. This paper introduces metallurgical features of the bainite-MA type dual-phase steel with exploring microscopic deformation and fracture behaviors.

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