Heavy plate excellent in haz toughness

Abstract

The invention provides a thick steel plate which has a great HAZ toughness even processing the super high heat energy welding above 40kJ / mm; the toughness of the parent material, the extending rate, the intensity and extending rate balance are also great. The thick steel plate also has a great material anisotropy and low temperature toughness of the parent material. The thick steel plate contains C: 0.030-0.10%, Si: below 1.0%, Mn:0.8-2.0%, P: below 0.03%, S: below 0.01%, Al: 0.01-0.10%, Nb: below 0.035%, Ti: 0.015-0.03%, B: 0.0010-0.0035, N: 0.0050-0.01%, Cu: 0-2.0%, Ni: 0-2.0%, Cr: 0-1%, Mo:0-0.5% and V: 0-0.1%; the invention satisfies the following formulas (1) (2): [Ti] / [N] is more than or equal to 1.5 and less than or equal to 4 (1); the area rate of the residual austenite is 2-10%; the average equivalent circle of the island-shaped martensite (MA) is below 3.0 um; or the average equivalent circle of the old austenite crystal is below 100 um; the flat rate (long diameter / short diamater) is below 2.5.

Description

Thick steel plate with excellent HAZ toughness technical field The present invention relates to thick steel plates applicable to welded structures such as ships and marine structures, and relates to the heat-affected zone (Heat Affected Zone, HAZ) after welding even if the ultra-high heat energy input welding of the preferred heat input is 40kJ / mm or more. ) toughness is also excellent thick steel plate. In addition, it also relates to a thick steel plate excellent in base material toughness, elongation, and strength-elongation balance, or a thick steel plate with less material anisotropy and excellent low-temperature base material toughness. Background technique In recent years, container ships and marine structures have been increased in size, and thick steel plates with a plate thickness of 60 mm or more have been adopted. In order to efficiently weld such a thick steel plate, it is required to have excellent HAZ toughness even in ultra-high heat input welding with a h...

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Problems solved by technology

In addition, in Patent Document 7, the cumulative reduction of the austenite non-recrystallization region is reduced to 60% or less, and the rolling is completed at the non-recrystallization temperature of austenite -80°C or higher, thereby reducing the sound anisotropy. opposite sex

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