超高強度高変形ラインパイプの開発

摘要

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, "HOP," 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.%ミクロ組織の2相組織化技術を活用して高変形能を有する高強度ラインパイプの開発を行った。ホウ素を含有しない成分を用い，鋼板製造過程での制御圧延-加速冷却条件を高精度に制御することにより，フェライト-ベイナイト2相組織を得ることが可能であり，APIX120グレード（API：アメリカ石油協会）の高強度と変形能が両立できた。また，加速冷却後のオンライン熱処理（HOP：Heat Treatment On-line Process）の適用によって，フェライト-ベイナイト2相鋼において高いシヤルピー吸収エネルギーを可能とした。UOEプロセスによりX120ラインパイプを実製造し，高強度と高い変形能を確認した。