Development of ultra-high strength linepipes with dual-phase microstructure for high strain application

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Development of ultra-high strength linepipes with dual-phase microstructure for high strain application

Ishikawa, Nobuyuki / Shikanai, Nobuo / Kondo, Joe

Extensive studies to develop high strength linepipes with higher deformability have been conducted. One of the key technologies for improving deformability is dual-phase microstructural control. Steel plate with ferrite-bainite microstructure can be obtained by applying thermo-mechanical controlled processing, TMCP, combined with controlled rolling and accelerated cooling process. Low-carbon boron-free steels were used to enable the ferrite formation during cooling after controlled rolling, and the accelerated cooling process with ultimate cooling rate enabled achieving high strength of up to X120 grade. Heat Treatment On-line Process, 'HOF', was also applied subsequently after accelerated cooling in order to improve Charpy energy of the base material. Trial production of X120 high deformability linepipe was conducted by applying dual-phase microstructural control.