High-strength steel plate with superior crack arrestability

Abstract

The present invention provides high strength thick steel plate superior in crack arrestability, high in strength, free of deterioration of HAZ toughness, and free of anisotropy, that steel plate containing, by mass%, C: 0.03 to 0.15%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.0%, P: 0.02%, S: 0.01%, Al: 0.001 to 0.1%, Ti: 0.005 to 0.02%, Ni: 0.15 to 2%, and N: 0.001 to 0.008% and having a balance of iron and unavoidable impurities as chemical components, having a microstructure of a ferrite and / or pearlite structure with bainite as a matrix phase, and having an average circle equivalent diameter of crystal grains with a crystal misorientation angle of 15 DEG or more of 15 [mu]m or less in the regions of 10% of plate thickness from the front and rear surfaces and of 40 [mu]m or less in the other region including the center part of plate thickness.

Description

technical field [0001] The present invention relates to a high-strength thick steel plate excellent in arrestability. Background technique [0002] For the thick steel plates used in structures such as shipbuilding, buildings, storage tanks, marine structures, and pipelines, in order to suppress the brittle failure of the structure, the arrestability (the ability to stop the propagation of brittle failure) is required as the ability to inhibit the propagation of brittle failure. performance). In recent years, along with the increase in size of structures, the use of high-strength thick steel plates with a yield stress of 390 MPa to 500 MPa and a plate thickness of 40 to 100 mm has increased. However, generally speaking, the strength has an opposite tendency to the plate thickness, and the above-mentioned crack arrestability decreases as the plate thickness increases. Therefore, for high-strength thick steel plates, a technique for improving crack arrestability is desired. ...

AI Technical Summary

Problems solved by technology

[0008] The above technique of controlling the grain size uses soft ferrite as the parent phase, so it is difficult to produce a high-strength and thick steel plate

[0009] Moreover, in the technique of controlling the above-mentioned brittle second phase, the martensite is dispersedly distributed in the ferrite, so the brittle crack occurrence characteristics are remarkably deteriorated

In addition, since ferrite is used as the parent phase, it is difficult to produce a high-strength and thick steel plate similar to the above.

[0010] In addition, in the technique of controlling the above-mentioned texture, ultra-low carbon steel is used, the structure is bainite single-phase, and a uniform texture in the thickness direction of the plate is developed, so the crack arrestability cannot be greatly improved.

In addition, the load required for steelmaking to obtain ultra-low carbon steel is also extremely large

Images