High-strength steel having excellent brittle crack arrestability and welding part brittle crack initiation resistance, and production method therefor

Abstract

The present invention provides a high-strength steel and a production method therefor, the high-strength steel: comprising, in wt %, C: 0.05-0.09%, Mn: 1.5-2.0%, Ni: 0.3-0.8%, Nb: 0.005-0.04%, Ti: 0.005-0.04%, Cu: 0.1-0.5%, Si: 0.05-0.3%, Al: 0.005-0.05%, P: 100 ppm or less, S: 40 ppm or less, and a remainder made up by Fe and other inevitable impurities; having a center part microstructure comprising, in area %, 70% or more of acicular ferrite and 10% or more of pearlite, wherein the equivalent circular diameter of the pearlite is 15 μm(micrometers) or less; having, in a 2 mm or less subsurface region, a microstructure comprising, in area %, 30% or more of one type or more among ferrite and a remainder made up by bainite, martensite, and pearlite; and having a welding heat affected zone, which is formed when welding, that comprises, in area %, 5% or less of a martensite-austenite constituent.

Description

TECHNICAL FIELD[0001]The present disclosure relates to a high-strength steel material having excellent brittle crack arrestability and welding zone brittle crack initiation resistance, and to a method of manufacturing the same.BACKGROUND ART[0002]Recently, there has been demand for the development of ultra-thick steel sheets having high strength properties in consideration of the design requirements of structures to be used in the shipping, maritime, architectural, and civil engineering fields, domestically and internationally.[0003]In a case in which high-strength steel is included in the design of a structure, economic benefits may be obtained due to reductions in the weight of structures while processing and welding operations may be easily undertaken using a steel sheet having a relatively reduced thickness.[0004]In general, in the case of high-strength steel, due to a reduction in a reduction ratio when thick steel plates are manufactured, sufficient deformation may not be perf...

AI Technical Summary

Benefits of technology

[0030]According to an aspect of the present disclosure, a high-strength steel material having a relatively high level of yield strength, as well as excellent brittle crack arrestability and welding zone brittle crack initiation resistance may be provided.

Problems solved by technology

In general, in the case of high-strength steel, due to a reduction in a reduction ratio when thick steel plates are manufactured, sufficient deformation may not be performed, as compared with a thin steel sheet.

Thus, microstructures of thick steel plates may be coarse, so that low temperature properties on which grain sizes have the most significant effect may be degraded.

However, in a case in which microstructures become coarse, a phenomenon in which brittle crack arrestability is significantly degraded may occur.

Thus, it may be difficult to improve brittle crack arrestability of an ultra-thick high-strength steel material.

However, such technologies may contribute to refining a structure of a surface portion, but may not solve a problem in which impact toughness is degraded due to coarsening of structures other than that of the surface portion.

Thus, such technologies may not be fundamental countermeasures to brittle crack arrestability.

In general, since, in the case of high-strength steel, the microstructure in a HAZ includes low temperature transformation ferrite having high strength, such as bainite, there is a limitation in which HAZ properties, in detail, toughness, are significantly reduced.

Thus, it maybe difficult to improve brittle crack initiation resistance of a high-strength steel material.

However, the effort partially contributes to forming impact toughness through refining a structure, but does not have a great effect on reducing a fraction of martensite-austenite having a significant influence on reducing brittle crack initiation resistance.

However, in the case of a HAZ, in which an effect of tempering disappears due to thermal history, it is impossible to apply brittle crack initiation resistance.

However, in this case, it may be difficult to secure a specific level of strength.

Thus, there is a limitation in which economic efficiency is deteriorated.

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