Large volume heat inputing in the welding tie-in tenacity excellent thick steel plate

Abstract

PROBLEM TO BE SOLVED: To provide a high strength thick steel plate in a class of 590 to 780 MPa which has excellent welded joint toughness (HAZ toughness) even when subjected to high heat input welding.

SOLUTION: Specified components of a thick steel plate, in particular, the total content of C, Mn, Cu and Ni are controlled by a specified parameter, the average number of fine Ti-containing oxides with a mean particle diameter of 0.05 to 1 μm is controlled to ≥10,000 pieces/cm<SP>2</SP>, and also the average number of coarse Ti-containing oxides with a mean particle diameter of ≥2 μm is controlled to ≤2,000 pieces/cm<SP>2</SP>. Thus, even in a high strength thick steel plate in a class of 590 to 780 MPa, the toughness of the whole region of the HAZ in high heat input welding including, in particular, the weld heat affected zone in the vicinity of 3 to 5 mm from a melting line whose toughness is apt to decrease is remarkably improved.

COPYRIGHT: (C)2006,JPO&NCIPI

Description

technical field [0001] The present invention relates to a thick steel plate with excellent toughness of welded joints with large heat input, and relates to a high-strength thick steel plate of 590-780 MPa level which can also exhibit excellent toughness of welded joints during high heat input welding. Background technique [0002] Conventionally, in order to ensure the HAZ toughness of thick steel plates, attempts have been made to ensure that the structure is refined by forming ferrite from within the grain during cooling of the HAZ portion by dispersing Ti-containing oxides in the base metal. HAZ toughness. [0003] For example, in Patent Document 1, it is described that by precipitating either or both of Ti oxide or a composite of Ti oxide and Ti nitride with a thickness of 0.1 to 3.0 μm, the coarse-grained region of the HAZ portion The γ→α transformation during cooling is controlled to generate intragranular ferrite, thereby improving the HAZ toughness. [0004] In Pat...

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Problems solved by technology

[0006] However, among these technologies, it is difficult to say that excellent HAZ toughness can b

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