Process for producing thick high-strength steel plate with excellent toughness of heat-affected zone in high heat input welding and thick high-strength steel plate with excellent toughness of heat-affected zone in high heat input welding

Abstract

Provided are a process for producing a thick high-strength steel plate having the satisfactory toughness of a heat-affected zone in high heat input welding and a thick high-strength steel plate obtained by the process. The process comprises heating a continuously cast slab to a temperature which is higher than 1,100 C but is 1,300 C or lower, subsequently rolling the slab at a steel surface temperature of 850 C or higher so as to result in a cumulative draft of 50% or more, and then cooling the slab from a steel surface temperature of 800 C or higher to 500 C or lower while applying accelerated cooling, the continuously cast slab having a given composition to which boron and vanadium have been added in combination, and the amount of residual oxygen (OTi) which remains after deoxidation with strong deoxidizing elements and can be removed with titanium, which is a weak deoxidizing element, the amount of effective boron (Bef) present in solution in the austenitic base that has not been transformed, and the carbon equivalent (Ceq) in the continuously cast slab being defined by respective expressions.

Description

technical field [0001] The present invention relates to a method of manufacturing a thick-walled high-strength steel plate excellent in brittle fracture propagation stop characteristics and high heat-affected zone (Heat Affected Zone: hereinafter also referred to as HAZ) toughness of high-energy-input welding, and a steel plate having excellent toughness in a high-energy-input welding heat-affected zone. Thick wall high strength steel plate. Background technique [0002] The requirements for welded structures in recent years include enlargement of structures, high safety against damage, high efficiency of welding during construction, and economical use of raw steel materials. Affected by such trends, the following requirements for steel plates used for welded structures are increasing: (1) high strength when the plate thickness is thick, (2) good HAZ toughness for large heat input welding, (3) low manufacturing costs, etc. [0003] Specifically, for steel plates used in hi...

AI Technical Summary

Problems solved by technology

Based on the above, the technology of using B in Patent Document 1 can be summarized as follows: in the direct quenching base metal and high heat input welding HAZ, the hardenability improvement effect produced by the solid solution of B in γ is used, and at the same time, in large In the HAZ of heat radiation welding, the hardenability reduction effect caused by the precipitation of B (here, BN) in γ is utilized

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