| 简介 |
PROBLEM TO BE SOLVED : To provide a steel plate which has a low yield ratio and excellent brittle crack generation resistance, and is suitable for a high strength line pipe having a pipe thickness of ≥20 mm and a tensile strength of >600 MPa, and to provide a method for producing the same.
SOLUTION : The steel is composed of a Cu-Ni-Nb-Ti system as the fundamental component system and, as necessary, comprises one or two kinds selected from Mo, Cr, V, B, Ca, rare earth metals, Zr and Mg, and the balance Fe with inevitable impurities, and in which the Vickers hardness Hvm of the central part in the plate thickness part satisfies Hvm≤1.05 Hva to the average Hva of the Vickers hardness in the plate thickness direction, a microstructure is essentially composed of bainite, and insular martensite is dispersed in the bainite at an area ratio of 5 to 15% as a second phase. The steel having the above composition is reheated to a specified temperature, is subjected to hot rolling including a cumulative draft of ≥30% in the temperature range of ≤1, 000 to ≥950°C, is subjected to accelerated cooling after the completion of the rolling, is reheated to a specified temperature, and is air-cooled.
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