High-tensile steel sheet excellent in low-temperature toughness and method for producing the same

Abstract

A high-tensile-strength steel plate having both high strength and excellent low-temperature toughness is provided. This steel plate satisfies a prescribed chemical composition, and has a CEQ value (mass%) of 0.345 to 0.428 as defined by formula (1) and a value of 2080 or more as defined by formula (2). Further, the microstructure of the steel plate at a position of t / 4 (wherein t is plate thickness) is a ferrite / pearlite mixed structure wherein the mean equivalent-circle diameter of the ferrite grains is controlled to 7.0m or less. CEQ = [C]+[Mn] / 6+([Cr]+[Mo]+[V]) / 5+([Cu]+[Ni]) / 15 ··· (1) = 2.90×{602781.57-(1154×CEQ-3.25)2}1 / 2 / 0.963+400×[Ni] ··· (2)

Description

technical field [0001] The present invention relates to a high-tensile steel sheet excellent in low-temperature toughness and a method for producing the same. In particular, it relates to a technology for improving the low-temperature toughness of such a high-tensile steel sheet used in an environment exposed to low temperature, such as a pressure vessel, a ship, and an ocean structure. Background technique [0002] Steel plates (high-tensile steel plates) used in the construction of pressure vessels, ships, and marine structures are required to have high strength, toughness at low temperatures (low temperature toughness) and excellent weldability. In particular, in recent years, higher toughness at extremely low temperatures has been demanded from the viewpoint of safety. [0003] In order to improve the toughness of the steel sheet, it is preferable to control the addition amount of the alloy elements as much as possible, but it becomes difficult to ensure the strength in...

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Problems solved by technology

A large number of steel sheets containing Ni have been proposed so far, but in reality, as represented by 3.5% Ni steel and 9% Ni steel, the effect cannot be fully exerted unless a large amount of Ni is contained.

On the other hand, regarding a steel sheet containing a small amount of Ni of about 1 to 2%, for example, it is proposed in Patent Document 1, but even if it satisfies high strength, it still cannot satisfy toughness at low temperature, and it is difficult to satisfy both strength and low temperature toughness.

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