Process for producing thick high-strength steel plate excellent in brittle fracture arrestability and toughness of zone affected by heat in large-heat-input welding and thick high-strength steel plate

Abstract

A process for producing a thick high-strength steel plate which comprises cooling a continuous-casting slab containing, in terms of mass%, 0.05-0.12% carbon, up to 0.3% silicon, 1-2% manganese, up to 0.015% phosphorus, up to 0.005% sulfur, 0.0003-0.003% boron, 0.01-0.15% vanadium, 0.001-0.1% aluminum, 0.005-0.02% titanium, 0.002-0.01% nitrogen, and up to 0.004% oxygen, with the remainder being iron and incidental impurities, to a temperature lower than Ar3 by at least 200 DEG C, subsequently heating the slab again to 950-1,100 DEG C, then roughly rolling the continuous-casting slab at 900 DEGC or higher so as to result in a cumulative draft of 30% or more, subsequently conducting finish rolling at 700 DEG C or higher to a cumulative draft of 50% or more under such conditions that the temperature at which the finish rolling is initiated and the temperature at which the finish rolling is terminated each is not higher than the temperature represented by the expression {-0.5x(slab heatingtemperature ( DEG C)) + 1,325} ( DEG C) to thereby form a rolled plate, and then rapidly cooling the rolled plate to 500 DEG C or lower to obtain a steel plate. The continuous-casting slab has an amount of boron present in the form of solution in the austenitic raw material before transformation {effective boron amount: Bef (%)} of 0% or smaller in terms of calculated value and has a carbon equivalent (Ceq) in the range of 0.32-0.42%.

Description

technical field [0001] The present invention relates to a method of manufacturing a thick-walled high-strength steel sheet excellent in brittle fracture propagation stop characteristics and toughness of a heat-affected zone (Heat Affected Zone: hereinafter sometimes referred to as HAZ) under high heat input welding (high heat input welding), and brittle A thick-walled high-strength steel plate with excellent fracture propagation stop characteristics and high heat input welded heat-affected zone toughness. The thick-walled high-strength steel plate of the present invention is mainly used in ships such as large container ships, and can also be used in other welded structures such as buildings, bridges, tanks, and marine structures. [0002] This application claims the priority of Japanese Patent Application No. 2007-315840 filed on December 6, 2007, and uses the content thereof here. Background technique [0003] Recent demands of welded structures represented by ships includ...

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Problems solved by technology

Furthermore, from the viewpoint of (2) above, when the refinement of the γ structure before transformation in TMCP is pursued, the hardenability decreases and the strength decreases. Therefore, between the above requirement (1) and the above requirement (2), opposing interests

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