YP690 N/mm2 Class Heavy Gauge Steel Plates with Low Temperature Toughness for Offshore Structures Manufactured by Continuous Casting, Forging and Rolling Process

摘要

YP690 N/mm~2 class heavy gauge steel plates with low temperaturetoughness for offshore structures have been developed. In thisdevelopment, annihilation of cast defects and microstructure control atthe mid-thickness are extremely important. JFE Steel established amanufacturing process which makes it possible to produce heavy thickplates from continuous casting slabs with a reduction ratio of around 2.The annihilation of cast defects can be achieved by the hot forgingprocess before hot rolling. An appropriate chemical composition wasrevealed in view of the optimum hardenability value and a sufficient Nicontent for excellent low temperature toughness. Plates with thicknessof 155 mm and 180 mm were successfully manufactured by applyingthe hot forging process and optimizing the chemical composition. As aresult, the developed steel plates satisfied the target properties and havereceived ABS and DNV approvals as EQ70 and E690 grades.Furthermore, the developed steels have already been manufacturedcommercially.