LOW YIELD RATIO HIGH STRENGTH AND HIGH TOUGHNESS STEEL PLATE, METHOD FOR PRODUCING LOW YIELD RATIO HIGH STRENGTH AND HIGH TOUGHNESS STEEL PLATE, AND STEEL PIPE

摘要

PROBLEM TO BE SOLVED: To provide a low yield ratio high strength and high toughness steel plate showing high toughness in such a manner that Charpy impact absorption energy at -20°C is 200 J or higher, and having a low yield ratio of 85%, and in which the low yield ratio and high toughness can be made consistent even in the case of API 5L×80 or higher.;SOLUTION: Provided is a low yield ratio high strength and high toughness steel plate having a steel structure made of bainite and island martensite, and having a steel structure where the area ratio of the island martensite is 2 to 15%, the number of the island martensite having a major axis of 3.5 μm or higher is 0.010 pieces/μm² or lower by number density, in which yield ratio is 85% or lower and Charpy impact absorption energy at -20°C is 200 J or higher.;COPYRIGHT: (C)2016,JPO&INPIT