JP5151090B2 - Structural high-strength thick steel plate with excellent brittle crack propagation stopping characteristics and method for producing the same - Google Patents

Structural high-strength thick steel plate with excellent brittle crack propagation stopping characteristics and method for producing the same Download PDF

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JP5151090B2
JP5151090B2 JP2006222859A JP2006222859A JP5151090B2 JP 5151090 B2 JP5151090 B2 JP 5151090B2 JP 2006222859 A JP2006222859 A JP 2006222859A JP 2006222859 A JP2006222859 A JP 2006222859A JP 5151090 B2 JP5151090 B2 JP 5151090B2
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公宏 西村
伸一 鈴木
隆二 村岡
恒久 半田
伸夫 鹿内
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JFE Steel Corp
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Description

本発明は、船舶、海洋構造物、低温貯蔵タンク、建築・土木構造物等の大型構造物に使用される脆性亀裂伝播停止特性に優れた、板厚50mm以上の高強度厚鋼板およびその製造方法に関する。   The present invention is a high-strength steel plate having a thickness of 50 mm or more, excellent in brittle crack propagation stopping characteristics, and used for large structures such as ships, marine structures, low-temperature storage tanks, and construction / civil engineering structures, and a method for producing the same. About.

船舶、海洋構造物、低温貯蔵タンク、建築・土木構造物等の大型構造物においては、脆性破壊に伴う事故が経済や環境に及ぼす影響が大きいため、安全性の向上が常に求められている。   In large structures such as ships, offshore structures, low-temperature storage tanks, and construction / civil engineering structures, accidents associated with brittle fractures have a large impact on the economy and the environment, and therefore safety is always required to be improved.

従って、この様な構造物に使用される鋼材に対しては、低温靭性が要求されることが多く、最近では、不慮の事故等で構造物に亀裂が発生した場合においても破壊に至ることを防止する観点から、低温における脆性亀裂伝播停止特性が要求されている。   Therefore, steel materials used in such structures are often required to have low temperature toughness, and recently, even if a crack occurs in the structure due to an accident, etc. From the viewpoint of prevention, brittle crack propagation stop characteristics at low temperatures are required.

一般に、鋼板の脆性亀裂伝播停止特性は高強度あるいは厚肉材ほど劣化する傾向がある。このため、コンテナ船やバルクキャリアーなどの船舶においてはその構造上、船体外板に高強度の厚肉材を使用される場合が多く、船舶の安全性確保の点から材料に対する脆性亀裂伝播停止特性の要求も一段と高度化している。   In general, the brittle crack propagation stopping property of a steel sheet tends to deteriorate as the strength or thickness of the steel sheet increases. For this reason, vessels such as container ships and bulk carriers often use high-strength thick materials for the outer skin of the hull because of their structure. The demand for this is also becoming more sophisticated.

鋼材の脆性亀裂伝播停止特性を向上させる手段として、従来からNi含有量を増加させる方法が知られており、液化天然ガス(LNG)の貯槽タンクにおいては、9%Ni鋼が商業規模で使用されている。しかし、Ni量の増加はコストの大幅な上昇を余儀なくさせるため、LNG貯槽タンク以外の用途には適用が難しい。   As a means of improving the brittle crack propagation stopping characteristics of steel materials, a method of increasing the Ni content has been conventionally known. In a LNG storage tank, 9% Ni steel is used on a commercial scale. ing. However, since the increase in the amount of Ni necessitates a significant increase in cost, it is difficult to apply to applications other than the LNG storage tank.

一方、LNGのような極低温まで至らない、船舶やラインパイプに使用される鋼板の板厚が50mm未満の比較的薄手の鋼材に対しては、TMCP法により細粒化を図り、低温靭性を向上させて、優れた脆性亀裂伝播停止特性を付与することができる。   On the other hand, for thin steel materials with a plate thickness of less than 50 mm, such as LNG, which does not reach extremely low temperatures and are used for ships and line pipes, fine graining is performed by the TMCP method to achieve low temperature toughness. It can be improved to give excellent brittle crack propagation stopping properties.

近年、合金コストを上昇させることなく、鋼材の表層部の組織を超微細化する技術が、脆性亀裂伝播停止特性を向上させる手段として提案されている。例えば、特許文献1では、脆性亀裂が伝播する際に、鋼材表層部に発生するシアリップ(塑性変形領域)が脆性亀裂伝播停止特性の向上に効果があることに着目し、シアリップ部分の結晶粒を微細化させて、伝播する脆性亀裂が有する伝播エネルギーを吸収させる方法が開示されている。   In recent years, a technique for making the structure of the surface layer portion of a steel material ultrafine without increasing the alloy cost has been proposed as a means for improving the brittle crack propagation stop characteristic. For example, in Patent Document 1, when a brittle crack propagates, the shear lip (plastic deformation region) generated in the steel surface layer portion is effective in improving the brittle crack propagation stop characteristic, and the crystal grains of the shear lip portion are changed. A method is disclosed in which the propagation energy possessed by the brittle cracks that are propagated by miniaturization is absorbed.

この製造方法としては、熱間圧延後の制御冷却により表層部分をAr変態点以下に冷却し、その後制御冷却を停止して表層部分を変態点以上に復熱させる工程を1回以上繰り返して行い、この間に鋼材に圧下を加えることにより、繰り返し変態させ又は加工再結晶させて、表層部分に超微細なフェライト組織又はベイナイト組織を生成させるものである。 As this manufacturing method, the process of cooling the surface layer portion below the Ar 3 transformation point by controlled cooling after hot rolling, and then stopping the controlled cooling to reheat the surface layer portion above the transformation point is repeated once or more. During this time, by rolling down the steel material, it is repeatedly transformed or processed and recrystallized to generate an ultrafine ferrite structure or bainite structure in the surface layer portion.

さらに、特許文献2では、フェライト−パーライトを主体のミクロ組織とする鋼材において脆性亀裂伝播停止特性を向上させるには、両表面部は円相当粒径:5μm以下、アスペクト比:2以上のフェライト粒を有するフェライト組織を50%以上有する層で構成し、フェライト粒径のバラツキを抑えることが重要であることが開示されている。   Further, in Patent Document 2, in order to improve the brittle crack propagation stop property in a steel material mainly composed of ferrite-pearlite, both surface portions have ferrite grains having a circle-equivalent grain size of 5 μm or less and an aspect ratio of 2 or more. It is disclosed that it is important to configure a layer having a ferrite structure having 50% or more to suppress variation in ferrite grain size.

バラツキを抑える方法として仕上げ圧延中の1パス当りの最大圧下率を12%以下にすることで局所的な再結晶現象が抑制されるとしている。しかし、上述の発明は、鋼材表層部のみを一旦冷却した後に復熱させ、かつ復熱中に加工を加えることによって、脆性亀裂伝播停止特性に効果のある組織を得るものであり、実生産規模では制御が容易ではないと考えられるプロセスである。また、板厚が50mm以上の厚肉材での記載もないため、厚肉材への適用は不明である。   As a method for suppressing variation, the local recrystallization phenomenon is suppressed by setting the maximum rolling reduction per pass during finish rolling to 12% or less. However, in the above-mentioned invention, only the steel surface layer part is once cooled and then reheated, and by adding processing during recuperation, a structure effective for brittle crack propagation stop characteristics is obtained. It is a process that is considered difficult to control. Moreover, since there is no description with a thick material with a plate thickness of 50 mm or more, application to a thick material is unknown.

このような問題を解決する方法として、特許文献3において、フェライト結晶粒の微細化のみならずフェライト結晶粒内に形成されるサブグレインに着目しTMCP法の延長技術が提供されている。   As a method for solving such a problem, Patent Document 3 provides a technique for extending the TMCP method by paying attention to subgrains formed in ferrite crystal grains as well as miniaturization of ferrite crystal grains.

具体的には、板厚30〜40mmにおいて、鋼板表層の冷却および復熱などの複雑な温度制御を必要とせずに、(a)微細なフェライト結晶粒を確保する圧延条件、(b)鋼材板厚の5%以上の部分に微細フェライト組織を生成する圧延条件、(c)微細フェライトに集合組織を発達させるとともに加工(圧延)により導入した転位を熱的エネルギーにより再配置しサブグレインを形成させる圧延条件、(d)形成した微細なフェライト結晶粒と微細なサブグレイン粒の粗大化を抑制する冷却条件、によって脆性亀裂伝播停止特性を向上させる方法を提供している。しかし、板厚50mm以上の厚肉材での記載がなく、板厚50mm以上の厚肉材において所定の脆性亀裂伝播停止特性が得られるかどうか不明である。   Specifically, in a plate thickness of 30 to 40 mm, without requiring complicated temperature control such as cooling and recuperation of the steel sheet surface layer, (a) rolling conditions for securing fine ferrite crystal grains, (b) steel plate Rolling conditions for generating a fine ferrite structure in a portion of 5% or more of the thickness, (c) A texture is developed in the fine ferrite, and dislocations introduced by processing (rolling) are rearranged by thermal energy to form subgrains. The present invention provides a method for improving brittle crack propagation stop characteristics by rolling conditions and (d) cooling conditions for suppressing coarsening of formed fine ferrite crystal grains and fine subgrain grains. However, there is no description with a thick material having a thickness of 50 mm or more, and it is unclear whether a predetermined brittle crack propagation stop characteristic can be obtained with a thick material having a thickness of 50 mm or more.

一方、制御圧延において、変態したフェライトに圧下を加えて集合組織を発達させることにより、脆性亀裂伝播停止特性を向上させる方法も知られている。鋼材の破壊面上にセパレーションを板厚方向と平行な方向に生ぜしめ、脆性亀裂先端の応力を緩和させることにより、脆性破壊に対する抵抗を高める方法である。   On the other hand, in controlled rolling, a method of improving the brittle crack propagation stopping property by applying a reduction to a transformed ferrite to develop a texture is also known. This is a method of increasing resistance to brittle fracture by causing separation on the fracture surface of the steel material in a direction parallel to the plate thickness direction to relieve stress at the tip of the brittle crack.

例えば、特許文献4では、制御圧延により(110)面X線強度比を2以上とし、かつ円相当径20μm以上の粗大粒を10%以下とすることにより、耐脆性破壊特性を向上させている。   For example, in Patent Document 4, the brittle fracture resistance is improved by controlling the rolling to have a (110) plane X-ray intensity ratio of 2 or more and coarse grains having an equivalent circle diameter of 20 μm or more to 10% or less. .

また、特許文献5では継手部の脆性亀裂伝播停止性能の優れた溶接構造用鋼として、板厚内部においての圧延面での(100)面のX線面強度比が1.5以上を有することを特徴とする鋼板が開示されている。その原理はこの集合組織発達による応力負荷方向と亀裂伝播方向の角度のずれであるとしている。   Moreover, in patent document 5, as a steel for welded structures excellent in the brittle crack propagation stop performance of a joint part, the X-ray surface strength ratio of the (100) plane at the rolled surface in the plate thickness has 1.5 or more. A steel sheet featuring the above is disclosed. The principle is that the difference between the stress loading direction and the crack propagation direction is due to the texture development.

しかし、本技術においても、最大板厚は50mmの記載があるのみで、50mmを超える板厚の記載はなく、より厚肉への適用が困難と予想される。また、後述する板厚方向の亀裂伝播に対しての特性が全く検証されていない。
特開平4−141517号公報 特開2002−256375号公報 特許第3467767号公報 特許第3548349号公報 特開平6−207241号公報
However, even in this technique, there is only a description of the maximum plate thickness of 50 mm, there is no description of a plate thickness exceeding 50 mm, and it is expected that application to thicker wall is more difficult. Moreover, the characteristic with respect to the crack propagation of the plate | board thickness direction mentioned later is not verified at all.
JP-A-4-141517 JP 2002-256375 A Japanese Patent No. 3467767 Japanese Patent No. 3548349 JP-A-6-207241

一方、最近の6,000TEUを越える大型コンテナ船では鋼板の板厚は50mm以上で、板厚効果により破壊靱性が低下することに加え、溶接入熱もより大きくなるため、溶接部の破壊靭性が一層低下する傾向にある。   On the other hand, in recent large container ships exceeding 6,000 TEU, the plate thickness of the steel plate is 50 mm or more, and the fracture toughness is lowered due to the plate thickness effect. In addition, the weld heat input becomes larger, so the fracture toughness of the welded portion is reduced. There is a tendency to further decrease.

最近、このような厚肉大入熱溶接継手では、溶接部から発生した脆性亀裂は母材側に反れずに直進し、骨材等の鋼板母材部でも停止しない可能性があることが実験的に示され(山口ら:「超大型コンテナ船の開発 ― 新しい高強度極厚鋼板の実用 ―」,日本船舶海洋工学会誌,3,(2005),P70.)、50mm以上の板厚の鋼板を適用した船体構造の安全確保の上で大きな問題となっている。   Recently, in such a thick-walled high heat input welded joint, an experiment has been conducted that a brittle crack generated from a welded portion may go straight without warping to the base metal side and may not stop even in a steel plate base material such as an aggregate. (Yamaguchi et al .: "Development of ultra-large container ship-practical application of new high-strength ultra-thick steel plate"), Journal of Japan Society of Marine Science and Technology, 3, (2005), P70.), Steel plate with a thickness of 50 mm or more It is a big problem in ensuring the safety of the hull structure to which is applied.

造船分野でのコンテナ船やバルクキャリヤーなどの強力甲板部構造では、ウエブ材(ハッチコーミング)にT字継手によりフランジ材(甲板)が溶接された様な構造になっている。脆性破壊はウエブ材の大入熱溶接部での進展が想定されるわけであるが、この場合、フランジ材では亀裂は板厚方向の進展となる。   In the shipbuilding field, a strong deck structure such as a container ship or a bulk carrier has a structure in which a flange material (deck) is welded to a web material (hatch combing) by a T-shaped joint. The brittle fracture is assumed to progress in the high heat input weld of the web material. In this case, the crack in the flange material progresses in the plate thickness direction.

つまり、一般に厚鋼板で脆性亀裂伝播を問題とする場合は、図1に示す様に亀裂は板厚方向に対し垂直な方向へ進展する亀裂を扱うものであり、ESSO試験等の標準的な試験で評価される。しかし、T字継手のフランジ材では図2の様に板厚方向の亀裂進展となる。   In other words, in general, when brittle crack propagation is a problem in thick steel plates, as shown in FIG. 1, cracks deal with cracks that propagate in a direction perpendicular to the plate thickness direction. It is evaluated with. However, in the flange material of the T-shaped joint, the crack progresses in the plate thickness direction as shown in FIG.

前述した様に、図1に示す如く進展する脆性亀裂伝播停止特性を向上させることを意図した先行技術は多く、板厚が50mm未満の比較的薄い板厚においては十分な効果を発揮すると考えられるが、板厚が50mm以上の厚肉材において、十分な脆性亀裂伝播停止特性を工業的な規模で安定して得ることは難しいと考えられる。   As described above, there are many prior arts intended to improve the brittle crack propagation stopping property that progresses as shown in FIG. 1, and it is considered that a sufficient effect is exhibited at a relatively thin plate thickness of less than 50 mm. However, it is considered difficult to stably obtain sufficient brittle crack propagation stopping characteristics on an industrial scale in a thick material having a plate thickness of 50 mm or more.

さらに、先行技術に係る鋼板は図2に示す板厚方向の亀裂停止性能に優れるかどうかが検証されておらず、課題が残されている。   Furthermore, it has not been verified whether the steel plate according to the prior art is excellent in the crack stopping performance in the plate thickness direction shown in FIG.

そこで本発明は、板厚50mm以上の厚鋼板において、圧延条件を最適化し、板厚方向での集合組織を制御することにより、板厚方向の脆性亀裂伝播停止特性に優れる高強度厚鋼板を、工業的に極めて簡易的なプロセスで安定して得る製造方法を提供することを目的とする。   Therefore, in the present invention, in a thick steel plate having a thickness of 50 mm or more, by optimizing the rolling conditions and controlling the texture in the thickness direction, a high strength thick steel plate having excellent brittle crack propagation stop characteristics in the thickness direction, An object of the present invention is to provide a production method which can be stably obtained by an industrially very simple process.

本発明者らは、上記課題の達成に向けて鋭意研究を重ねた結果、以下に述べるように、板厚方向に進展する脆性亀裂に対し、優れた伝播停止特性を有する高強度厚鋼板および当該鋼板を安定して得る製造方法の発明を完成するに至った。   As a result of intensive studies aimed at achieving the above-mentioned problems, the present inventors, as will be described below, with respect to brittle cracks that progress in the thickness direction, a high-strength thick steel plate having excellent propagation stop characteristics and the It came to complete the invention of the manufacturing method which obtains a steel plate stably.

すなわち、板厚50mm以上の厚鋼板での板厚方向の脆性亀裂伝播停止特性に及ぼす集合組織の影響を詳細に調べた結果、板厚中央部における圧延面での(100)面X線強度比が2.0以上で、かつ板厚1/4部における圧延面での(110)面X線強度比が1.5以上とすることにより、板厚方向に亀裂が突入する初期段階で亀裂停止性能を発揮させ、その後の亀裂の進展を抑制することができ、板厚50mm以上の厚鋼板で優れた脆性亀裂伝播停止特性が得られることを見出した。   That is, as a result of examining in detail the influence of the texture on the brittle crack propagation stop characteristics in the thickness direction of a thick steel plate having a thickness of 50 mm or more, the (100) plane X-ray intensity ratio at the rolling surface in the central portion of the thickness Is 2.0 or more, and the (110) plane X-ray intensity ratio at the rolling surface at a thickness of 1/4 part is 1.5 or more, so that cracks stop at the initial stage when cracks enter the plate thickness direction. It has been found that the performance can be exhibited, the subsequent progress of cracks can be suppressed, and excellent brittle crack propagation stopping characteristics can be obtained with a thick steel plate having a thickness of 50 mm or more.

さらに、その集合組織を実現するための熱間圧延プロセスとして、板厚中央部がAr点以下Ar点−60℃以上の温度範囲における累積圧下率を30%以上とすれば良いことを見出した。本発明はこれらの知見に基づくものであり、次の技術を提供する。
1.鋼組成が、質量%で、C:0.03〜0.20%、Si:0.03〜0.5%、Mn:0.5〜2.0%、Al:0.005〜0.08%、P:0.03%以下,S:0.01%以下、N:0.0050%以下を含有し、残部がFeおよび不可避的不純物からなり、板厚中央部における圧延面での(100)面X線強度比が2.0以上、かつ板厚1/4部における圧延面での(110)面X線強度比が1.5以上の集合組織を有する、板厚方向の脆性亀裂伝播停止特性に優れた板厚1/4部におけるシャルピー破面遷移温度がー30℃以下である板厚50mm以上の構造用高強度厚鋼板。
2.鋼組成が、さらに、質量%で、Ti:0.005〜0.03%、Nb:0.005〜0.05%、Cu:0.01〜0.5%、Ni:0.01〜1.0%、Cr:0.01〜0.5%、Mo:0.01〜0.5%、V:0.001〜0.1%、B:0.003%以下、Ca:0.005%以下、REM:0.01%以下のいずれか1種、または2種以上を含有することを特徴とするに記載の板厚方向の脆性亀裂伝播停止特性に優れた板厚1/4部におけるシャルピー破面遷移温度がー30℃以下である板厚50mm以上の構造用高強度厚鋼板。
3.またはに記載の組成を有する鋼素材を、900〜1200℃の温度に加熱し、板厚中央部の温度がAr点以上の温度で累積圧下率30%以上、板厚中央部の温度がAr点以下Ar点―60℃以上の温度域において累積圧下率30%以上の圧延を行った後、2℃/s以上の冷却速度にて600℃以下まで冷却することを特徴とする板厚方向の脆性亀裂伝播停止特性に優れた板厚1/4部におけるシャルピー破面遷移温度がー30℃以下である板厚50mm以上の構造用高強度厚鋼板の製造方法。
Furthermore, as a hot rolling process for realizing the texture, it has been found that the cumulative reduction ratio in the temperature range where the central portion of the plate thickness is Ar 3 points or less, Ar 3 points to 60 ° C. or more, should be 30% or more. It was. The present invention is based on these findings and provides the following techniques.
1. Steel composition is mass%, C: 0.03-0.20%, Si: 0.03-0.5%, Mn: 0.5-2.0%, Al: 0.005-0.08 %, P: 0.03% or less, S: 0.01% or less, N: 0.0050% or less, with the balance being Fe and unavoidable impurities (100 ) Brittle crack propagation in the thickness direction having a texture with a plane X-ray intensity ratio of 2.0 or more and a (110) plane X-ray intensity ratio of 1.5 or more at the rolled surface at a thickness of 1/4. A structural high-strength steel plate having a thickness of 50 mm or more and a Charpy fracture surface transition temperature at ¼ part having a thickness of ¼ ° C., which is excellent in stopping properties.
2. Steel composition is further mass%, Ti: 0.005-0.03%, Nb: 0.005-0.05%, Cu: 0.01-0.5%, Ni: 0.01-1 0.0%, Cr: 0.01-0.5%, Mo: 0.01-0.5%, V: 0.001-0.1%, B: 0.003% or less, Ca: 0.005 % or less, REM: 0.01% or less of any one, or ¼ of the sheet thickness parts having excellent brittle crack propagation stop characteristics of thickness direction according to contain two or more to 1, wherein A structural high-strength thick steel sheet having a Charpy fracture surface transition temperature of −30 ° C. or less and a thickness of 50 mm or more.
3. The steel material having the composition described in 1 or 2 is heated to a temperature of 900 to 1200 ° C., the temperature at the center of the plate thickness is 3 points or more at Ar, the cumulative rolling reduction is 30% or more, and the temperature at the center of the plate thickness. Is rolled at a cumulative reduction rate of 30% or more in a temperature range of Ar 3 points or less, Ar 3 points -60 ° C. or more, and then cooled to 600 ° C. or less at a cooling rate of 2 ° C./s or more. A method for producing a structural high-strength thick steel plate having a thickness of 50 mm or more with a Charpy fracture surface transition temperature of -30 ° C. or less at a thickness of ¼ part having excellent brittle crack propagation stopping characteristics in the thickness direction.

本発明によって製造される厚鋼板は、板厚位置での集合組織が適切に制御されており、板厚方向の脆性亀裂伝播停止特性に優れる。特に、板厚50mm以上の厚物材をフランジに用いた溶接構造物において、ウエブから進展してきた脆性亀裂をフランジ部で停止されることが可能となり、産業上極めて有用である。   In the thick steel plate produced by the present invention, the texture at the plate thickness position is appropriately controlled, and the brittle crack propagation stopping property in the plate thickness direction is excellent. In particular, in a welded structure using a thick material having a plate thickness of 50 mm or more as a flange, a brittle crack that has progressed from the web can be stopped at the flange portion, which is extremely useful industrially.

例えば、造船分野ではコンテナ船、バルクキャリアーの強力甲板部構造においてハッチサイドコーミングに接合される甲板部材へ本鋼板を適用することにより船舶の安全性向上に寄与するとこ大である。 For example, in the shipbuilding container vessels, which contributes Toko filtrate Univ improve safety of the ship by applying the present steel plate to deck member to be joined to the hatch side coaming in strength deck section structure of the bulk carrier.

本発明では、1.板厚内部の集合組織、2.鋼の組成、3.製造条件を規定する。
1.板厚内部の集合組織
板厚方向に進展する亀裂伝播に対して亀裂伝播停止特性を向上させるため、その板厚中央部に圧延面に平行に(100)面を、かつ板厚の1/4の位置には(110)面を発達させ、板厚中央部における圧延面での(100)面X線強度比を2.0以上とし、かつ板厚1/4部における圧延面での(110)面X線強度比が1.5以上の集合組織とする。
In the present invention, 1. Texture inside the plate thickness; 2. steel composition; Define manufacturing conditions.
1. Texture inside the plate thickness In order to improve the crack propagation stop property against the crack propagation progressing in the plate thickness direction, the (100) plane is parallel to the rolling surface at the center of the plate thickness, and 1/4 of the plate thickness. The (110) plane is developed at the position, the (100) plane X-ray intensity ratio at the rolled surface at the center of the plate thickness is 2.0 or more, and the (110) plane at the rolled surface at the 1/4 thickness portion is (110). ) The texture has a plane X-ray intensity ratio of 1.5 or more.

板厚中央部で(100)面を発達させると、亀裂進展方向に対し垂直にへき開面が集積しているため、進展方向に垂直に微細なクラックが発生し亀裂進展の抵抗となるからである。   This is because when the (100) plane is developed at the center of the plate thickness, the cleavage planes are accumulated perpendicular to the crack propagation direction, so that fine cracks are generated perpendicular to the propagation direction and resistance to crack propagation. .

溶接部から板表面に脆性亀裂が突入した場合、亀裂は初期段階としてまず板厚1/4部に突入する。従って、板厚1/4部では(110)面が発達している方が好ましい。この理由については必ずしも明らかになったわけではないが、亀裂突入直後の亀裂伝播エネルギーの吸収能力が高いものと考えられる。   When a brittle crack enters the plate surface from the welded portion, the crack first enters the plate thickness ¼ part as an initial stage. Therefore, it is preferable that the (110) plane is developed at the 1/4 thickness portion. Although the reason for this is not necessarily clarified, it is considered that the ability to absorb crack propagation energy immediately after entering the crack is high.

ここで、(100)面X線強度比とは、対象材の(100)結晶面の集積度を表す数値で、対象材の(200)反射のX線回折強度と集合組織のないランダムな標準試料からの(200)反射のX線回折強度の比のことであり、(110)面X線強度比とは対象材の(110)結晶面の集積度を表す数値で、対象材の(110)反射のX線回折強度と集合組織のないランダムな標準試料からの(110)反射のX線回折強度の比のことである。   Here, the (100) plane X-ray intensity ratio is a numerical value indicating the degree of integration of the (100) crystal plane of the target material, and is a random standard having no (200) reflection X-ray diffraction intensity and texture of the target material. This is the ratio of the X-ray diffraction intensity of (200) reflection from the sample. The (110) plane X-ray intensity ratio is a numerical value representing the degree of integration of the (110) crystal plane of the target material and (110) of the target material. ) The ratio of the X-ray diffraction intensity of reflection and the X-ray diffraction intensity of (110) reflection from a random standard sample without texture.

また、母材靭性についても、ある程度の特性を有することが亀裂の進展を抑制するための前提となるので、本発明が開示する鋼板では板厚1/4部におけるシャルピー破面遷移温度は−30℃以下と規定する。シャルピー破面遷移温度の低下は、破面単位の微細化によって達成されるが、後述する成分、圧延条件等の調整によってその特性を得ることが可能である。   Further, as for the base metal toughness, it is a premise for suppressing the progress of cracks to have a certain level of characteristics, so in the steel sheet disclosed by the present invention, the Charpy fracture surface transition temperature at ¼ part thickness is −30. It is defined as ℃ or less. The reduction of the Charpy fracture surface transition temperature is achieved by making the fracture surface unit finer, but it is possible to obtain the characteristics by adjusting the components, rolling conditions and the like described later.

板厚方向に亀裂が進展する場合、特性の異なる領域を亀裂が進展するわけであるが、実際の溶接構造物を想定した場合、亀裂の先端は広がりをもち亀裂伝播停止性能を支配する要因はより複雑になるため、板厚方向の集合組織分布も重要になってくるものと考えられる。   When cracks propagate in the plate thickness direction, cracks propagate in regions with different characteristics.However, assuming an actual welded structure, the crack tip has a spread and the factors governing crack propagation stopping performance are Since it becomes more complicated, it is considered that the texture distribution in the thickness direction is also important.

上述した集合組織は、化学成分と製造条件を適正な条件とした場合に得られるため、本発明では規定する。   The texture described above is obtained in the present invention because it is obtained when the chemical components and manufacturing conditions are set to appropriate conditions.

2.化学成分
本発明は、溶接構造用厚鋼板として使用される厚鋼板で、引張強さが490MPa以上、板厚1/4部におけるシャルピー破面遷移温度が−30℃以下の靭性を有する厚鋼板に対するものであり、そのためには以下の化学成分からなることが好ましい。
説明において%は質量%とする。
2. Chemical component The present invention is a thick steel plate used as a thick steel plate for welded structures, and has a toughness with a tensile strength of 490 MPa or more and a Charpy fracture surface transition temperature at ¼ part of the plate thickness of -30 ° C or less. For that purpose, it is preferably composed of the following chemical components.
In the description,% is mass%.

C:0.03〜0.20%
Cは鋼の強度を向上する元素であり、本発明では、所望の強度を確保するためには0.03%以上の含有を必要とするが、0.20%を超えると、溶接性が劣化するばかりか靭性にも悪影響がある。このため、Cは、0.03〜0.20%の範囲に規定した。なお、好ましくは0.05〜0.15%である。
C: 0.03-0.20%
C is an element that improves the strength of steel. In the present invention, it is necessary to contain 0.03% or more in order to ensure a desired strength, but if it exceeds 0.20%, the weldability deteriorates. As well as adversely affecting toughness. For this reason, C was specified in the range of 0.03 to 0.20%. In addition, Preferably it is 0.05 to 0.15%.

Si:0.03〜0.5%
Siは脱酸元素として、また、鋼の強化元素として有効であるが、0.03%未満の含有量ではその効果がない。一方、0.5%を越えると鋼の表面性状を損なうばかりか靭性が極端に劣化する。従ってその添加量を0.03%以上、0.5%以下とする。
Si: 0.03-0.5%
Si is effective as a deoxidizing element and as a strengthening element for steel, but if its content is less than 0.03%, it has no effect. On the other hand, if it exceeds 0.5%, not only the surface properties of the steel are impaired, but also the toughness is extremely deteriorated. Therefore, the addition amount is set to 0.03% or more and 0.5% or less.

Mn:0.5〜2.0%
Mnは、強化元素として添加する。0.5%より少ないとその効果が十分でなく、2.0%を超えると溶接性が劣化し、鋼材コストも上昇するため、0.5%以上、2.0%以下とする。
Mn: 0.5 to 2.0%
Mn is added as a strengthening element. If the content is less than 0.5%, the effect is not sufficient. If the content exceeds 2.0%, the weldability deteriorates and the steel material cost increases, so the content is made 0.5% or more and 2.0% or less.

Al:0.005〜0.08%
Al:Alは、脱酸剤として作用し、このためには0.005%以上の含有を必要とするが、0.08%を超えて含有すると、靭性を低下させるとともに、溶接した場合に、溶接金属部の靭性を低下させる。このため、Alは、0.005〜0.08%の範囲に規定した。なお、好ましくは、0.02〜0.04%である。
Al: 0.005 to 0.08%
Al: Al acts as a deoxidizer, and for this purpose, it needs to contain 0.005% or more. However, if it contains more than 0.08%, the toughness is lowered and when welding is performed, Reduces the toughness of the weld metal. For this reason, Al was specified in the range of 0.005 to 0.08%. In addition, Preferably, it is 0.02 to 0.04%.

N:0.0050%以下
Nは、鋼中のAlと結合し、圧延加工時の結晶粒径を調整し、鋼を強化するが、0.0050%を超えると靭性が劣化するため、0.0050%以下とする。
N: 0.0050% or less N combines with Al in the steel, adjusts the crystal grain size at the time of rolling, and strengthens the steel. However, if it exceeds 0.0050%, the toughness deteriorates. 0050% or less.

P,S
P,Sは、鋼中の不可避不純物であるが、Pは0.03%を超え、Sは0.01%を超えると靭性が劣化するため、それぞれ、0.03%以下、0.02%以下が望ましい。
P, S
P and S are unavoidable impurities in the steel, but P exceeds 0.03%, and if S exceeds 0.01%, the toughness deteriorates. Therefore, 0.03% or less and 0.02%, respectively. The following is desirable.

以上が本発明の基本成分組成であるが、更に特性を向上させるため、Nb,Ti,Cu,Ni,Cr,Mo,V,B,Ca,REMの一種または二種以上を含有することが可能である。   The above is the basic component composition of the present invention. In order to further improve the characteristics, it is possible to contain one or more of Nb, Ti, Cu, Ni, Cr, Mo, V, B, Ca, and REM. It is.

Nb:0.005〜0.05%
Nbは、NbCとしてフェライト変態時あるいは再加熱時に析出し、高強度化に寄与する。また、オーステナイト域の圧延において未再結晶域を拡大させる効果をもち、フェライトの細粒化に寄与するので、靭性の改善にも有効である。その効果を得るためには0.005%以上の添加が必要であるが0.05%を超えて添加すると、粗大なNbCが析出し逆に、靭性の低下を招くのでその上限は0.05%とするのが好ましい。
Nb: 0.005 to 0.05%
Nb precipitates as NbC at the time of ferrite transformation or reheating, and contributes to the increase in strength. In addition, it has the effect of expanding the non-recrystallized region in rolling in the austenite region, and contributes to the refinement of ferrite, so it is also effective in improving toughness. In order to obtain the effect, 0.005% or more of addition is necessary, but if added over 0.05%, coarse NbC precipitates and conversely causes a decrease in toughness, so the upper limit is 0.05. % Is preferable.

Ti:0.005〜0.03%、
Tiは微量の添加により、窒化物、炭化物、あるいは炭窒化物を形成し、結晶粒を微細化して母材靭性を向上させる効果を有する。その効果は0.005%以上の添加によって得られるが、0.03%を超える含有は、母材および溶接熱影響部の靭性を低下させるので、Tiは、0.005〜0.03%の範囲にするのが好ましい。
Ti: 0.005 to 0.03%,
Ti has the effect of forming nitrides, carbides, or carbonitrides by adding a small amount, and refining crystal grains to improve the base material toughness. The effect is obtained by addition of 0.005% or more, but the content exceeding 0.03% lowers the toughness of the base metal and the weld heat affected zone, so Ti is 0.005 to 0.03%. The range is preferable.

Cu,Ni、Cr、Mo
Cu,Ni、Cr、Moはいずれも鋼の焼入れ性を高める元素である。圧延後の強度アップに直接寄与するとともに、靭性、高温強度、あるいは耐候性などの機能向上のために添加するが、過度の添加は靭性や溶接性を劣化させるため、それぞれ上限を0.5%、1.0%、0.5%、0.5%とする。逆に添加量が0.01%未満であるとその効果が現れないため、0.01%以上の添加とする。
Cu, Ni, Cr, Mo
Cu, Ni, Cr, and Mo are all elements that enhance the hardenability of steel. It contributes directly to strength improvement after rolling, and is added to improve functions such as toughness, high-temperature strength, or weather resistance, but excessive addition degrades toughness and weldability, so the upper limit is 0.5% respectively. 1.0%, 0.5%, 0.5%. On the contrary, if the addition amount is less than 0.01%, the effect does not appear, so 0.01% or more is added.

V:0.001〜0.1%
Vは、V(CN)として析出強化により、鋼の強度を向上する元素であり、0.001%以上含有してもよいが、0.10%を超えて含有すると、靭性を低下させる。このため、Vは、0.001〜0.10%の範囲の添加とする。
V: 0.001 to 0.1%
V is an element that improves the strength of the steel by precipitation strengthening as V (CN), and may be contained in an amount of 0.001% or more, but if it exceeds 0.10%, the toughness is lowered. Therefore, V is added in the range of 0.001 to 0.10%.

B:0.003%以下
Bは微量で鋼の焼き入れ性を高める元素として添加してもよい。しかし、0.003%を超えて含有すると溶接部の靭性を低下させるので、Bは0.003%以下の添加とする。
B: 0.003% or less B may be added as an element that enhances the hardenability of steel in a small amount. However, if contained over 0.003%, the toughness of the welded portion is lowered, so B is added at 0.003% or less.

Ca:0.005%以下、REM:0.01%以下
Ca,REMは溶接熱影響部の組織は微細化し靭性を向上させる、添加しても本発明の効果が損なわれることはないので必要に応じて添加してもよい。しかし、過度に添加すると、粗大な介在物を形成し母材の靭性を劣化させるので、添加量の上限をそれぞれ0.005%、0.01%とするのが好ましい。
Ca: 0.005% or less, REM: 0.01% or less Ca, REM is necessary because the structure of the weld heat-affected zone is refined to improve toughness, and even if added, the effect of the present invention is not impaired. It may be added accordingly. However, if added excessively, coarse inclusions are formed and the toughness of the base material is deteriorated. Therefore, it is preferable to set the upper limit of the addition amount to 0.005% and 0.01%, respectively.

3.製造条件
上記の化学成分と集合組織を有する厚鋼板は、優れた板厚方向の脆性亀裂伝播停止特性を有し、次に示す製造工程が適当である。
3. Manufacturing Conditions A thick steel plate having the above chemical components and texture has excellent brittle crack propagation stopping characteristics in the thickness direction, and the following manufacturing process is appropriate.

まず、上記した組成の溶鋼を、転炉等で溶製し、連続鋳造等で鋼素材(スラブ)とする。
ついで、鋼素材を、900〜1200℃の温度に加熱してから熱間圧延を行う。
First, molten steel having the above composition is melted in a converter or the like, and is made into a steel material (slab) by continuous casting or the like.
Next, hot rolling is performed after the steel material is heated to a temperature of 900 to 1200 ° C.

加熱温度が900℃以下であると、圧延能率が低下し、加熱温度が1200℃以上であるとオーステナイト粒が粗大化し、靭性の低下を招くばかりか、酸化ロスが顕著となり、歩留が低下するので、加熱温度は900〜1200℃とする。   When the heating temperature is 900 ° C. or lower, the rolling efficiency is lowered, and when the heating temperature is 1200 ° C. or higher, the austenite grains are coarsened and the toughness is lowered, and the oxidation loss becomes remarkable and the yield is lowered. Therefore, heating temperature shall be 900-1200 degreeC.

靭性の観点から好ましい加熱温度の範囲は1000〜1150℃であり、より好ましくは1000〜1050℃である。   The range of preferable heating temperature from a viewpoint of toughness is 1000-1150 degreeC, More preferably, it is 1000-1050 degreeC.

熱間圧延は板厚中央部の温度がAr点以上で累積圧下率を30%以上とすることが好ましい。累積圧下率が30%未満であると、オーステナイトの細粒化が十分でなく、靭性が向上しないばかりか、目的とする集合組織の分布が得られない。 In the hot rolling, it is preferable that the temperature at the central portion of the plate thickness is Ar 3 point or higher and the cumulative rolling reduction is 30% or higher. If the cumulative rolling reduction is less than 30%, the austenite is not sufficiently refined and the toughness is not improved, and the desired texture distribution cannot be obtained.

次に、板厚中央部の温度がAr点以下Ar点―60℃以上の温度域において累積圧下率30%以上の圧延を行う。この圧延工程は所望の集合組織を有する鋼板を得るための肝要なプロセスである。 Next, rolling is performed at a cumulative reduction ratio of 30% or more in a temperature range where the temperature at the center of the plate thickness is Ar 3 points or less, Ar 3 points to 60 ° C. or more. This rolling process is an essential process for obtaining a steel sheet having a desired texture.

板厚50mm以上の厚鋼板に対して、この圧延を行うことにより、板厚中央部における圧延面での(100)面X線強度比が2.0以上で、かつ板厚1/4部における圧延面での(110)面X線強度比が1.5以上の集合組織を得ることができる。   By performing this rolling on a thick steel plate having a thickness of 50 mm or more, the (100) plane X-ray intensity ratio at the rolling surface in the central portion of the thickness is 2.0 or more and the thickness is ¼ part. A texture having a (110) plane X-ray intensity ratio on the rolled surface of 1.5 or more can be obtained.

Ar点以下で圧延を行わなければ、板厚中央部の圧延面での(100)面X線強度比2.0以上を得ることができず、板厚中央部の温度がAr点以下Ar点―60℃以上の温度域において累積圧下率30%以上の圧延を行わなければ、板厚1/4部における圧延面での(110)面X線強度比が1.5以上の集合組織を得ることができない。 If rolling is not performed at Ar 3 points or less, a (100) plane X-ray intensity ratio of 2.0 or more at the rolling surface at the center of the plate thickness cannot be obtained, and the temperature at the center of the plate thickness is Ar 3 or less. Ar 3 points—A set having a (110) plane X-ray intensity ratio of 1.5 or more at the rolling surface at a thickness of 1/4 part unless rolling is performed at a cumulative reduction ratio of 30% or higher in a temperature range of 60 ° C. or higher. I can't get an organization.

ここで、温度域をAr点以下Ar点―60℃以上と規定したが、このことはAr点―60℃以下の圧延を行うことを制限するものではない。圧延温度が規定の温度域より低下しても規定する温度域で30%以上の累積圧下がおこなわれていればよい。 Here, the temperature range is defined as Ar 3 points or less, Ar 3 points −60 ° C. or more, but this does not limit the rolling of Ar 3 points −60 ° C. or less. Even if the rolling temperature falls below the specified temperature range, it is sufficient that the cumulative reduction of 30% or more is performed in the specified temperature range.

圧延が終了した鋼板は2℃/s以上の冷却速度にて600℃以下まで冷却する。2相域圧延によって導入された加工集合組織が再結晶するのを防ぐためであり、圧延後には鋼板を低温まで冷却する必要がある。   The rolled steel sheet is cooled to 600 ° C. or lower at a cooling rate of 2 ° C./s or higher. This is to prevent reworking of the work texture introduced by the two-phase rolling, and it is necessary to cool the steel sheet to a low temperature after rolling.

冷却速度が2℃/s未満では求める集合組織が得られないばかりか、鋼板の強度も低下するので、冷却速度は2℃/s以上とする。冷却停止温度は600℃より高いと冷却停止後にも再結晶が進行して所望の集合組織が得られないので冷却停止温度は600℃以下とすることが好ましい。   When the cooling rate is less than 2 ° C./s, not only the desired texture is obtained, but also the strength of the steel sheet is lowered, so the cooling rate is set to 2 ° C./s or more. If the cooling stop temperature is higher than 600 ° C., recrystallization proceeds even after the cooling stop and a desired texture cannot be obtained. Therefore, the cooling stop temperature is preferably 600 ° C. or lower.

表1に示す各組成の溶鋼を、転炉で溶製し、連続鋳造法で鋼素材(スラブ)とした(鋼記号A〜T)。これらスラブ(鋼素材:280mm厚)を用いて、表2に示す圧延条件にて板厚50〜70mmに熱間圧延して、同じく表2に示す条件で、冷却を行いNo.1〜29の供試鋼を得た。   Molten steel of each composition shown in Table 1 was melted in a converter and used as a steel material (slab) by a continuous casting method (steel symbols A to T). Using these slabs (steel material: 280 mm thick), the steel sheet was hot-rolled to a thickness of 50 to 70 mm under the rolling conditions shown in Table 2. 1 to 29 test steels were obtained.

Figure 0005151090
Figure 0005151090

Figure 0005151090
Figure 0005151090

これらの厚鋼板について、板厚の1/4部よりΦ14のJIS14A号試験片を採取し、引張試験を行い、降伏点(YS)、引張強さ(TS)を測定した。また、板厚の1/4部よりJIS4号衝撃試験片を採取し、シャルピー試験を行って、破面遷移温度(vTrs)を求めた。板厚1/4部におけるシャルピー破面遷移温度がー30℃以下のものを本発明範囲内とした。 About these thick steel plates, the JIS14A test piece of (PHI) 14 was extract | collected from 1/4 part of plate | board thickness, the tensile test was done, and the yield point (YS) and the tensile strength (TS) were measured. Further, a JIS No. 4 impact test piece was sampled from ¼ part of the plate thickness, and a Charpy test was performed to determine the fracture surface transition temperature (vTrs). The Charpy fracture surface transition temperature at ¼ part of the plate thickness was within the range of the present invention within −30 ° C.

また、鋼板の集合組織を評価するため、板厚中央部における圧延面での(100)面X線強度比と、板厚1/4部における圧延面での(110)面X線強度比を測定した。   Further, in order to evaluate the texture of the steel sheet, the (100) plane X-ray intensity ratio at the rolling surface at the center part of the plate thickness and the (110) plane X-ray intensity ratio at the rolling surface at the ¼ part plate thickness are It was measured.

次に、これらの厚鋼板の板厚方向の脆性亀裂伝播停止特性を評価するため、完全溶け込みT字型の溶接継手を作製した。作製したT字型溶接継手を用いて、図3に示す十字型ESSO試験片を作製し、脆性亀裂伝播停止試験(ESSO試験)に供した。図3(a)は正面図、図3(b)は側面図を示す。   Next, in order to evaluate the brittle crack propagation stop characteristics in the plate thickness direction of these thick steel plates, complete penetration T-shaped welded joints were produced. Using the produced T-shaped welded joint, a cross-shaped ESSO test piece shown in FIG. 3 was produced and subjected to a brittle crack propagation stop test (ESSO test). 3A is a front view, and FIG. 3B is a side view.

試験は応力24kgf/mm、温度−10℃の条件にて実施した、ウエブ材の機械ノッチに打撃を与え脆性亀裂を発生させて、ウエブ材と溶接金属を貫通した脆性亀裂が評価する母材で停止するか否かを調査した。 The test was carried out under the conditions of stress 24 kgf / mm 2 and temperature −10 ° C. The base material that was hit by the mechanical notch of the web material to generate a brittle crack and evaluated the brittle crack that penetrated the web material and the weld metal. We investigated whether or not to stop at.

表2に十字型ESSO試験の結果を併せて示す。板厚中央部と1/4部における集合組織が本発明の範囲である供試鋼板の場合、脆性亀裂は停止した。一方、板厚1/4部におけるシャルピー破面遷移温度がー30℃を超えるものは、もともと靭性が劣るので脆性亀裂は停止せず、板厚を貫通した。製造条件が本発明範囲外で、鋼板の集合組織が本発明の規定を満たさない鋼板では脆性亀裂は停止せず、板厚を貫通した。   Table 2 also shows the results of the cross-shaped ESSO test. In the case of the test steel sheet in which the texture in the center part of the plate thickness and the quarter part is within the scope of the present invention, the brittle cracks stopped. On the other hand, when the Charpy fracture surface transition temperature at ¼ part of the plate thickness exceeded −30 ° C., the toughness was originally inferior, so the brittle crack did not stop and penetrated the plate thickness. In a steel sheet in which the production conditions were outside the scope of the present invention and the texture of the steel sheet did not satisfy the provisions of the present invention, the brittle crack did not stop and penetrated the thickness.

厚鋼板の脆性亀裂伝播を説明する模式図Schematic diagram explaining brittle crack propagation in thick steel plate T形隅肉継手における脆性亀裂伝播を説明する模式図で(a)はT形隅肉継手、(b)はフランジにおける脆性亀裂伝播を説明する模式図。The schematic diagram explaining the brittle crack propagation in a T type fillet joint, (a) is a T type fillet joint, (b) is the schematic diagram explaining the brittle crack propagation in a flange. 十字型ESSO試験片形状を説明する図。The figure explaining a cross-shaped ESSO test piece shape.

符号の説明Explanation of symbols

1 鋼板
2 ウエブ材
3 フランジ材
4 溶接部
a 脆性亀裂
b 機械ノッチ
c 仮付け溶接
DESCRIPTION OF SYMBOLS 1 Steel plate 2 Web material 3 Flange material 4 Welded part a Brittle crack b Machine notch c Tack welding

Claims (3)

鋼組成が、質量%で、C:0.03〜0.20%、Si:0.03〜0.5%、Mn:0.5〜2.0%、Al:0.005〜0.08%、P:0.03%以下,S:0.01%以下、N:0.0050%以下を含有し、残部がFeおよび不可避的不純物からなり、板厚中央部における圧延面での(100)面X線強度比が2.0以上、かつ板厚1/4部における圧延面での(110)面X線強度比が1.5以上の集合組織を有する、板厚方向の脆性亀裂伝播停止特性に優れた板厚1/4部におけるシャルピー破面遷移温度がー30℃以下である板厚50mm以上の構造用高強度厚鋼板。   Steel composition is mass%, C: 0.03-0.20%, Si: 0.03-0.5%, Mn: 0.5-2.0%, Al: 0.005-0.08 %, P: 0.03% or less, S: 0.01% or less, N: 0.0050% or less, with the balance being Fe and unavoidable impurities (100 ) Brittle crack propagation in the thickness direction having a texture with a plane X-ray intensity ratio of 2.0 or more and a (110) plane X-ray intensity ratio of 1.5 or more at the rolled surface at a thickness of 1/4. A structural high-strength steel plate having a thickness of 50 mm or more and a Charpy fracture surface transition temperature at ¼ part having a thickness of ¼ ° C., which is excellent in stopping properties. 鋼組成が、さらに、質量%で、Ti:0.005〜0.03%、Nb:0.005〜0.05%、Cu:0.01〜0.5%、Ni:0.01〜1.0%、Cr:0.01〜0.5%、Mo:0.01〜0.5%、V:0.001〜0.1%、B:0.003%以下、Ca:0.005%以下、REM:0.01%以下のいずれか1種、または2種以上を含有することを特徴とする請求項に記載の板厚方向の脆性亀裂伝播停止特性に優れた板厚1/4部におけるシャルピー破面遷移温度がー30℃以下である板厚50mm以上の構造用高強度厚鋼板。 Steel composition is further mass%, Ti: 0.005-0.03%, Nb: 0.005-0.05%, Cu: 0.01-0.5%, Ni: 0.01-1 0.0%, Cr: 0.01-0.5%, Mo: 0.01-0.5%, V: 0.001-0.1%, B: 0.003% or less, Ca: 0.005 % or less, REM: 0.01% or less of any one, or to contain two or more, characterized in claim 1 a thickness excellent brittle crack propagation stop characteristics of thickness direction according to 1 / Structural high-strength thick steel plate having a thickness of 50 mm or more and a Charpy fracture surface transition temperature at 4 parts of -30 ° C. or lower. 請求項1またはに記載の組成を有する鋼素材を、900〜1200℃の温度に加熱し、板厚中央部の温度がAr点以上の温度で累積圧下率30%以上、板厚中央部の温度がAr点以下Ar点―60℃以上の温度域において累積圧下率30%以上の圧延を行った後、2℃/s以上の冷却速度にて600℃以下まで冷却することを特徴とする板厚方向の脆性亀裂伝播停止特性に優れた板厚1/4部におけるシャルピー破面遷移温度が−30℃以下である板厚50mm以上の構造用高強度厚鋼板の製造方法。 The steel material having the composition according to claim 1 or 2 is heated to a temperature of 900 to 1200 ° C., and the temperature of the central portion of the plate thickness is 3 or more points of Ar, the cumulative rolling reduction is 30% or more, the central portion of the plate thickness. After rolling at a cumulative reduction rate of 30% or more in a temperature range of Ar 3 points or less, Ar 3 points to 60 ° C. or more, and cooling to 600 ° C. or less at a cooling rate of 2 ° C./s or more. A method for producing a structural high-strength thick steel plate having a thickness of 50 mm or more with a Charpy fracture surface transition temperature at ¼ part having a thickness of ¼ ° C. excellent in brittle crack propagation stopping characteristics in the thickness direction.
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