Thick steel plate for high heat input welding with excellent shear property

Abstract

A plate steel that displays great HAZ toughness under high heat input weld and has excellent shearing property without shear fissure even if it is cut by a shearing press. The plate steel of the invention adjusts chemical components properly and meets formulae (1) and (2) and has tissue with bainite ratio that is above 95 area%. Average diameter of equivalent circle of a block size of the bainite is below 40 microns and a difference of a maximal diameter of equivalent circle of a block size of the bainite and the average diameter of equivalent circle is below 40 microns. [Ti]/[N] is more than or equal to 1.5 but less than or equal to 4.0 (1); X is more than or equal to 40 but less than or equal to 160 (2), X=500[C]+32[Si]+8[Mn]-9[Nb]+14[Cu]+17[Ni]-5[Cr]-25[Mo]-34[V], (in the formula, [] represents content (mass%) of each element.

Description

technical field [0001] The present invention relates to a thick steel plate suitable for welded structures such as ships and marine structures, and particularly relates to a steel plate having excellent toughness in the heat-affected zone (Heat Affected Zone: HAZ) after welding with high heat energy input and excellent shear properties. thick steel plate. Background technique [0002] In recent years, for example, container ships and the like have been increased in size, and thick steel plates having a plate thickness of 40 mm or more have been used. In order to efficiently weld such a thick steel plate, high heat input welding or ultra-high heat input welding (hereinafter represented by "high heat input welding") with a heat input of 40 kJ / mm or more is required. [0003] However, when high heat energy input welding is performed, the HAZ is heated to a high-temperature austenite region and then gradually cooled, so that the structure is coarsened, and there is a problem th...

AI Technical Summary

Problems solved by technology

When a shear crack occurs, it must be re-cut by off-line gas cutting to remove the cracked part, which will inevitably result in a significant extension of the construction period and increase in manufacturing costs.

However, the actual situation so far is that the technology that can effectively prevent such shear cracks has not been established

[0011] As a technique for preventing shear cracks, for example, Patent Document 5 proposes a technique of increasing the cooling rate after rolling (accelerated cooling) to adjust the segregation in the steel material to improve the shear property. , so there is a problem that the strength range that can be manufactured is limited, and it is not sufficient as a countermeasure against shear cracks

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