Thick steel plate

Abstract

The invention provides a thick steel plate, which is excellent in HAZ toughness during the large energy welding process. The characteristics of the thick steel plate satisfy the following chemical composition by mass% except oxygen constituent elements: Ti> 10%, A1<20%, 5 % <ca<40 % and 5 % <REM<50 %, 5 %<zr<40 % of at least any one of oxide, which satisfies the following formula (1) and (2). (1)Measured by an equivalent circle diameter gauge, the number of the oxide below 2 mu m is 200 / mm < 2 > or more. (2) Measured by an equivalent circle diameter, the number of the oxide over 2 mu m is 100 / mm < 2 > or less.

Description

technical field [0001] The present invention relates to thick steel plates used in welded structures such as bridges, high-rise buildings, and ships. More specifically, it relates to the toughness of welding heat-affected zones (hereinafter referred to as "HAZ") during high-energy-input welding. Excellent thick steel plate. Background technique [0002] In recent years, properties required for steel materials used in welded structures such as bridges, high-rise buildings, and ships tend to become more stringent as these welded structures increase in size. In particular, among the many properties required, the requirements for toughness tend to be more stringent. [0003] Steel materials used in welded structures and the like have a problem that the toughness of the HAZ formed by the influence of heat at the time of welding joins tends to deteriorate. The deterioration of the HAZ toughness tends to be more pronounced as the heat input during welding is larger. Therefore, in...

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Problems solved by technology

However, the technology described in this patent document 11 is not a technology that focuses on HAZ toughness when performing high heat input welding such that the heat input is 100 kJ / mm or more.

In addition, Patent Document 12 also proposes a technique for achieving a low yield ratio of a steel sheet having a tensile strength of 590 MPa or more by dispersing oxide-based inclusions and ensuring a certain amount of ferrite. But the line energy of the object is small

[0013] As explained above, with regard to ensuring the HAZ toughness when carrying out high heat input welding such as 100kJ / mm or more of heat input, it is necessary to make other characteristics (improvement of strength and toughness of the base material or further lower yield ratio) at the same time. Improved technology, underdeveloped status quo

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