High strength steel plate having excellent brittle crack arrestability and method for manufacturing same

Abstract

Provided are a high strength steel plate having excellent brittle crack arrestability and a method for manufacturing the same. A steel plate, which contains C, Si, Mn, Al, P, S and N each in a definite amount, satisfies the requirement Ceq (=C+Mn / 6+(Cu+Ni) / 15+(V+Mo+Cr) / 5) being 0.34-0.49% inclusive, and may further contain, if required, one or more members selected from among Nb, Ti, Cu, Ni, Cr, Mo, V, Ca, B and REM, wherein a region with an aggregate tissue, said region having an X-ray diffraction intensity ratio according to plane (211) in a plane parallel to the surface of the steel plate of 1.0 or greater, is disposed within at least 1 / 3 of the sheet thickness including the central part of the sheet thickness, the bainite fraction at the central part of the sheet thickness is 80% or greater, and the Charpy fracture transition temperature at a position of 1 / 4 of the sheet thickness is -40 DEG C or lower. The method according to the present invention comprises hot rolling a steel material in such a manner that the cumulative rolling reduction ratio is at least 50% within a temperature range at the central part of the sheet thickness from (Ar3+60) DEG C to Ar3 inclusive, and then cooling to 450 DEG C or lower at a cooling speed of 4.0 DEG C / s or higher.

Description

technical field [0001] The present invention relates to high brittle crack arrestability (brittle crack arrestability) which is suitable as a thick steel plate exceeding 50 mm in plate thickness and is used in large structures such as ships, marine structures, low-temperature storage tanks, and building / civil structures. High strength steel plate and its manufacturing method. Background technique [0002] For large-scale structures such as ships, marine structures, cryogenic storage tanks, and architectural / civil structures, accidents caused by brittle fractures have a great impact on the economy and the environment, so it is usually required to improve safety For steel materials used, toughness and brittle crack propagation stopping properties at operating temperatures are required. [0003] Ships such as container ships and bulk carriers use high-strength thick-walled materials for the outer plate of the ship's hull in their structures. In other words, the brittle crack ...

AI Technical Summary

Problems solved by technology

[0011] However, the steel materials with excellent brittle crack propagation arresting properties described in Patent Documents 1 and 2 obtained a specific structure by cooling only the surface layer of the steel material and then reheating, and performing processing during the reheating. It is difficult to control, especially for thick-walled materials with a plate thickness exceeding 50mm, it is a process that places a large load on rolling and cooling equipment

Images