Thick steel plate with excellent brittlement crevasse crack propagation halt characteristic and manufacturing method thereof

Abstract

The steel plate of the invention contains a C-grade chemical component and the balance of iron and unavoidable foreign substances, is formed by a structure of more than 95% of bainite by area on a prescribed position in the plate thickness direction. On a position from the surface by a depth of t/8-t/4 (t represents the plate thickness), an average diameter of granular equivalent circles is less than 8[Mu]m when a region enclosed by a greater horn grain boundary of two neighboring crystals with a more than 15 DEG azimuth error is used as a grain. By means of implementing the minuteness of the grain diameter, it is capable of obtaining the thick steel plate with an excellent brittlement crevasse crack propagation halt characteristic.

Description

technical field [0001] The present invention relates to a thick steel plate mainly used as a raw material for structural materials of ships and bridges, and in particular to a thick steel plate with improved properties of stopping the propagation of brittle cracks that have occurred, and a useful method for manufacturing such a thick steel plate Methods. Background technique [0002] In steel plates used in structures such as ships, buildings, storage tanks, marine structures, pipeline steel pipes, etc., in order to suppress brittle failure of structures, arrest characteristics (hereinafter referred to as "brittle cracks") are required. Propagation Stop Property"), which is the ability to suppress damage due to the propagation of brittle cracks. In recent years, along with the enlargement of structures, high-strength thick steel plates with a yield stress of 390 MPa or more and a plate thickness of 50 mm or more are frequently used. However, the brittle crack propagation s...

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