Thick steel plate and production method therefor

Abstract

A thick steel plate including 0.02%-0.10% by mass C, 1.0%-2.0% by mass Mn, 0%-0.05% by mass Nb, 0%-0.05% by mass Ti, 0.01%-0.06% by mass Al, 0.1%-0.6% by mass Si, and 0.1%-0.6% by mass Cu. The total Si and Cu content is at least 0.3% by mass, with the remainder being iron and unavoidable impurities. The processed ferrite fraction is at least 50% by area ratio; the effective crystal grain size of crystal grains is no more than 30 [mu]m; the martensite-austenite mixed phase is no more than 5% by area ratio; and the dislocation density [rho] value measured by X-ray diffraction is 1.0 * 1014 m-2 -2.5 * 1015 m-2.

Description

technical field [0001] The present invention relates to a thick steel plate and its manufacturing method. Background technique [0002] In large-scale structures such as ships, buildings, bridges, and construction machinery, the size of the structure is advancing, and on the other hand, higher reliability is required for its structural members due to the magnitude of damage when damage occurs. The cause of damage to large structures has been known to be mostly fatigue fracture. Although various anti-fatigue fracture technologies have been developed, up to now, there are not many cases of damage caused by fatigue fracture. [0003] In general, fatigue fractures can be prevented in parts of large structures where fatigue damage is likely to occur, such as changing the shape of the part to a shape that is less likely to cause stress concentration, or using a high-strength steel plate for the part. However, when the strength of the steel sheet is too high, there is a problem th...

AI Technical Summary

Problems solved by technology

However, as described in Non-Patent Document 1 and Non-Patent Document 2, dislocation strengthening does little to improve the fatigue strength, and the aforementioned fatigue limit ratio is lowered.

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