JP5692305B2 - Thick steel plate with excellent heat input welding characteristics and material homogeneity, and its manufacturing method - Google Patents

Thick steel plate with excellent heat input welding characteristics and material homogeneity, and its manufacturing method Download PDF

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JP5692305B2
JP5692305B2 JP2013171932A JP2013171932A JP5692305B2 JP 5692305 B2 JP5692305 B2 JP 5692305B2 JP 2013171932 A JP2013171932 A JP 2013171932A JP 2013171932 A JP2013171932 A JP 2013171932A JP 5692305 B2 JP5692305 B2 JP 5692305B2
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善明 村上
善明 村上
長谷 和邦
和邦 長谷
亮 荒尾
亮 荒尾
遠藤 茂
茂 遠藤
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    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/002Bainite

Description

本発明は、船舶、海洋構造物、建築、鋼管分野などの各種鋼構造物に使用され、特に大入熱溶接が適用される厚鋼板およびその製造方法として好適なものに関する。   The present invention relates to a steel plate that is used in various steel structures such as ships, offshore structures, architecture, and steel pipe fields, and that is particularly suitable as a manufacturing method thereof to which large heat input welding is applied.

船舶、海洋構造物、建築、鋼管等の分野で使用される鋼構造物は、溶接接合により所望の形状の構造物に仕上げられるのが一般的である。したがって、これらの構造物は、安全性を確保する観点から、使用される鋼材の基本となる母材特性、すなわち強度、靱性、伸びの確保に加えて、溶接部の特性、主に継手強度、継手靱性にも優れていることが要請されている。   Generally, steel structures used in the fields of ships, offshore structures, architecture, steel pipes, etc. are finished into structures of a desired shape by welding. Therefore, from the viewpoint of ensuring safety, these structures are based on the base material characteristics that are the basis of the steel materials used, that is, in addition to ensuring strength, toughness, and elongation, as well as characteristics of welds, mainly joint strength, There is a demand for excellent joint toughness.

さらに、近年では、上記船舶や鋼構造物は大型化する傾向にあるため、使用される鋼材も高強度化や厚肉化が要望される一方で、鋼材重量の大幅な増加による調達コスト増加を抑制するという観点も注目されている。このため、適用する鋼板の強度・板厚が過大にならないような設計を取り入れ、且つ溶接施工には、サブマージアーク溶接やエレクトロガス溶接、エレクトロスラグ溶接などの高能率で大入熱の溶接方法を適用し、全体的な製造コストの合理化を指向するようになってきている。具体的には、上述の大入熱溶接の適用を前提として、強度や板厚がさほど過大でない、強度クラスとしては引張強さで550〜750N/mm級程度まで、板厚が50mm以下の鋼板の適用拡大が見込まれている。 Furthermore, in recent years, the ships and steel structures tend to be larger, so that the steel materials used are required to have higher strength and thickness, while the procurement cost has increased due to a significant increase in steel weight. The viewpoint of suppression is also attracting attention. For this reason, a design that prevents the strength and thickness of the steel sheet to be applied from being excessive is adopted, and for welding work, a high-efficiency, high-heat-input welding method such as submerged arc welding, electrogas welding, or electroslag welding is used. It has become more oriented towards streamlining overall manufacturing costs. Specifically, assuming the application of large heat input welding described above, not very excessive strength and thickness, until secondary approximately 550~750N / mm in tensile strength as a strength class, the thickness is below 50mm Application of steel sheets is expected to expand.

一般的に上記強度クラス、板厚の厚鋼板は、鋼板の特性の向上や合金元素の削減、さらには熱処理の省略などを目的として、制御圧延と加速冷却を組み合わせた、所謂TMCP技術により製造される。TMCP技術は高冷却速度が確保出来るため、比較的低成分で母材強度を確保可能という利点がある。その一方で、鋼板内部に比べて鋼板の表面が急冷されるため、鋼板内部に比べて鋼板表面近傍の硬さが高くなり、板厚方向の硬さ分布にばらつきが生じることがある。また、加速冷却が鋼板全面に渡って均一でない場合もあり、鋼板内の材質均一性、具体的には鋼板の伸び特性への影響が懸念される。   In general, thick steel plates with the above strength classes and thicknesses are manufactured by the so-called TMCP technology that combines controlled rolling and accelerated cooling for the purpose of improving the properties of steel plates, reducing alloy elements, and omitting heat treatment. The Since the TMCP technology can secure a high cooling rate, there is an advantage that the strength of the base material can be secured with a relatively low component. On the other hand, since the surface of the steel plate is rapidly cooled compared to the inside of the steel plate, the hardness in the vicinity of the steel plate surface is higher than that inside the steel plate, and the hardness distribution in the thickness direction may vary. In addition, accelerated cooling may not be uniform over the entire surface of the steel sheet, and there is a concern about the influence on the material uniformity within the steel sheet, specifically the elongation characteristics of the steel sheet.

上記の問題を解決するため、従来からTMCP技術の一環として種々の解決策が提案されており、例えば特許文献1には、加速冷却に際して、冷却速度を3〜12℃/sという比較的低い冷却速度に制御することにより、板厚中心部に対する表面の硬さ上昇を抑える方法が、また、特許文献2には、冷却過程で、フェライトが析出する温度域で待機を行うことにより、鋼板の組織をフェライトとベイナイトの2相組織とし、表層と板厚中心部の硬さの差を低減した、板厚方向の材質差が小さい鋼板の製造方法が開示されている。さらに、鋼板表面のスケール性状と鋼板の加速冷却時の冷却速度に着目した視点から、特許文献3,4には、冷却直前にデスケーリングを行うことにより、スケール性状に起因した冷却むらを低減し、鋼板形状を改善する方法が開示されている。これらの技術はいずれも、材質均一性を担保すると共に、結晶粒を微細化することによる高靭化も同時に達成出来る技術と解釈される。   In order to solve the above problems, various solutions have been proposed as part of the TMCP technology. For example, Patent Document 1 discloses a relatively low cooling rate of 3 to 12 ° C./s for accelerated cooling. By controlling the speed, a method of suppressing the increase in surface hardness with respect to the center portion of the plate thickness is disclosed in Patent Document 2, and in the cooling process, the structure of the steel plate is obtained by waiting in the temperature range where ferrite precipitates. Has a two-phase structure of ferrite and bainite, and a method for manufacturing a steel sheet having a small material difference in the thickness direction in which the difference in hardness between the surface layer and the thickness center portion is reduced is disclosed. Furthermore, from the viewpoint of paying attention to the scale properties of the steel sheet surface and the cooling rate during accelerated cooling of the steel sheet, Patent Documents 3 and 4 reduce the uneven cooling due to the scale characteristics by performing descaling immediately before cooling. A method for improving the steel plate shape is disclosed. All of these techniques are interpreted as techniques capable of ensuring material uniformity and simultaneously achieving high toughness by refining crystal grains.

一方で、上述したように鋼板の溶接施工には施工効率の高い大入熱溶接が適用される傾向にあるが、大入熱溶接により形成される溶接熱影響部(HAZ[Heat Affected Zone]とも言う)においては、上述した各種制御圧延・加速冷却プロセスによる結晶粒微細化効果が消失してしまうことによる継手靱性の低下や、継手軟化域の形成による継手強度の低下が同時に発生し、それらを併せて解決する対策が求められる。   On the other hand, as described above, high heat input welding with high construction efficiency tends to be applied to the welding work of the steel sheet, but the welding heat affected zone (HAZ [Heat Affected Zone]) formed by high heat input welding is also known. )) Joint toughness due to the disappearance of the grain refinement effect by the various controlled rolling / accelerated cooling processes described above and joint strength reduction due to the formation of the joint softening region occur simultaneously. Measures to resolve together are also required.

中でも広く知られている対策としては、溶接中の高温域で比較的安定なTiNを鋼中に微細分散させることによりオーステナイト粒の粗大化を抑制する技術や、特許文献5に記載の如く、鋼中に適量のTi,Bを添加させることにより、継手低温靱性の低下を補填する方法がある。   Among them, as a widely known measure, a technique for suppressing austenite grain coarsening by finely dispersing TiN, which is relatively stable in a high temperature range during welding, as described in Patent Document 5, There is a method of compensating for the decrease in joint low temperature toughness by adding appropriate amounts of Ti and B therein.

さらに、特許文献6に記載の如く、鋼中のNb添加量を最適化することにより、鋼板の高強度化と継手特性、特にHAZ靱性の両立を図る方法が開示されている。しかしながら、文献5、および6に代表される大入熱溶接対策手法が、鋼板材質の均質性に及ぼす影響は検証されていない。   Furthermore, as described in Patent Document 6, a method is disclosed in which the Nb addition amount in the steel is optimized to achieve both high strength of the steel sheet and joint characteristics, particularly HAZ toughness. However, the effect of the high heat input welding countermeasure techniques represented by Documents 5 and 6 on the homogeneity of the steel sheet material has not been verified.

特公平7−116504号公報Japanese Patent Publication No.7-116504 特許第3911834号公報Japanese Patent No. 3911834 特開平9−57327号公報JP-A-9-57327 特許第3796133号公報Japanese Patent No. 3796133 特開2005−2476号公報JP 2005-2476 A 特開2011−074448号公報JP 2011-074448 A

本発明は、上記の現状に鑑み開発されたもので、大入熱溶接継手部に要求される諸特性を具備させると共に、鋼板の板厚方向および板幅方向の硬さのばらつきを軽減することにより鋼板の材質、特にその全厚伸び特性を向上させた板厚50mm以下の厚鋼板を、その有利な製造方法と共に提供することにある。   The present invention was developed in view of the above-described present situation, and has various characteristics required for a high heat input welded joint, and reduces variations in hardness in the plate thickness direction and the plate width direction of the steel plate. Therefore, it is to provide a thick steel plate having a thickness of 50 mm or less with improved material properties, particularly its total thickness elongation characteristic, together with its advantageous manufacturing method.

本発明は上記課題を解決するため、大入熱溶接対策としての成分設計適正化に加えて、鋼板内の材質均質性を向上させるための製造条件の検討、および所定の均質性を満足させるために具備されるべき材質閾値に関して数多くの実験・検討を行った後に得られたものである。すなわち本発明は、
1.質量%で、C:0.030〜0.080%、Si:0.01〜0.10%、Mn:1.20〜2.40%、P:0.008%以下、S:0.0005〜0.0040%、Al:0.005〜0.080%、Nb:0.003〜0.040%、Ti:0.003〜0.040%、N:0.0030〜0.0100%、B:0.0003〜0.0030%を含有し、残部がFeおよび不可避的不純物からなる成分組成を有し、かつ、板厚方向と板幅方向のそれぞれでのビッカース硬さ(HV)の変動幅:ΔHVが30以下であることを特徴とする大入熱溶接特性と材質均質性に優れた厚鋼板。
2.更に、質量%で、Cu:1.00%以下、Ni:1.00%以下、Cr:1.00%以下、Mo:0.50%以下、V:0.10%以下の1種または2種以上を含有することを特徴とする1に記載の大入熱溶接特性と材質均質性に優れた厚鋼板。
3.更に、質量%で、Ca:0.0005〜0.0050%、Zr:0.001〜0.020%、REM:0.001〜0.020%の1種または2種以上を含有することを特徴とする1または2に記載の大入熱溶接特性と材質均質性に優れた厚鋼板。
4.1乃至3のいずれか一つに記載の成分組成の鋼素材を1000〜1300℃に加熱後、熱間圧延し、鋼板表面での噴射流の衝突圧が1MPa以上の条件で噴射流を鋼板表面に衝突させることによりデスケーリングを行い、その後、直ちに、鋼板の平均冷却速度:10℃/s以上、鋼板の平均冷却停止温度:200〜600℃で加速冷却を行うことを特徴とする板厚方向と板幅方向のそれぞれでのビッカース硬さ(HV)の変動幅:ΔHVが30以下であることを特徴とする大入熱溶接特性と材質均質性に優れた厚鋼板の製造方法。
5.加速冷却停止後、Ac1変態点以下で焼き戻すことを特徴とする4記載の厚鋼板の製造方法。
In order to solve the above-mentioned problems, the present invention, in addition to optimizing the component design as a measure against large heat input welding, to examine the manufacturing conditions for improving the material homogeneity in the steel sheet, and to satisfy the predetermined homogeneity It was obtained after many experiments and examinations regarding the material threshold value to be included in That is, the present invention
1. In mass%, C: 0.030 to 0.080%, Si: 0.01 to 0.10%, Mn: 1.20 to 2.40%, P: 0.008% or less, S: 0.0005 -0.0040%, Al: 0.005-0.080%, Nb: 0.003-0.040%, Ti: 0.003-0.040%, N: 0.0030-0.0100%, B: 0.0003 to 0.0030% contained, the remainder having a component composition consisting of Fe and inevitable impurities, and fluctuations in Vickers hardness (HV) in each of the plate thickness direction and the plate width direction Width: A thick steel plate excellent in high heat input welding characteristics and material homogeneity, wherein ΔHV is 30 or less.
2. Further, by mass%, Cu: 1.00% or less, Ni: 1.00% or less, Cr: 1.00% or less, Mo: 0.50% or less, V: 0.10% or less, or 1 or 2 2. A thick steel plate excellent in high heat input welding characteristics and material homogeneity according to 1, characterized by containing at least a seed.
3. Furthermore, it contains one or more of Ca: 0.0005 to 0.0050%, Zr: 0.001 to 0.020%, REM: 0.001 to 0.020% in mass%. A thick steel plate having excellent high heat input welding characteristics and material homogeneity as described in 1 or 2.
The steel material having the composition described in any one of 4.1 to 3 is heated to 1000 to 1300 ° C. and then hot-rolled, and the jet flow is performed under the condition that the collision pressure of the jet flow on the steel plate surface is 1 MPa or more. The descaling is performed by colliding with the steel plate surface, and then accelerated cooling is immediately performed at an average cooling rate of the steel plate of 10 ° C./s or more and an average cooling stop temperature of the steel plate of 200 to 600 ° C. Vickers hardness (HV) fluctuation width in each of the thickness direction and the plate width direction: ΔHV is 30 or less, A method for producing a thick steel plate excellent in high heat input welding characteristics and material homogeneity.
5. 5. The method for producing a thick steel plate according to 4, wherein after accelerating cooling is stopped, tempering is performed below the Ac1 transformation point.

本発明によれば、材質均質性と大入熱溶接継手特性の両者に優れた厚鋼板とその製造方法が得られ、産業上極めて有用である。   According to the present invention, a thick steel plate excellent in both material homogeneity and high heat input weld joint characteristics and a method for producing the same can be obtained, which is extremely useful industrially.

以下、本発明の限定条件を説明する。なお、化学成分における%は全て質量%とする。
C:0.030〜0.080%
Cは、鋼材の強度を高める元素であり、構造用鋼として必要な強度を確保するためには、0.030%以上の添加が必要である。一方、0.080%を超えると、大入熱溶接HAZ中に島状マルテンサイトが生成し易くなるため、上限は0.080%とする。好ましくは、0.040〜0.070%の範囲である。
Hereinafter, the limiting conditions of the present invention will be described. In addition, all% in a chemical component shall be the mass%.
C: 0.030 to 0.080%
C is an element that increases the strength of the steel material, and 0.030% or more of addition is necessary in order to ensure the strength necessary for structural steel. On the other hand, if it exceeds 0.080%, island martensite is likely to be generated in the high heat input welding HAZ, so the upper limit is made 0.080%. Preferably, it is 0.040 to 0.070% of range.

Si:0.01〜0.10%
Siは、鋼を溶製する際の脱酸剤として添加される元素であり、0.01%以上の添加が必要である。しかし、0.10%を超えると、大入熱溶接HAZ中に島状マルテンサイトが生成し、靱性の低下を招きやすくなる。よって、Siは0.01〜0.10%の範囲とする。
Si: 0.01-0.10%
Si is an element added as a deoxidizer when melting steel, and it is necessary to add 0.01% or more. However, if it exceeds 0.10%, island martensite is generated in the high heat input welding HAZ, and the toughness is liable to be lowered. Therefore, Si is taken as 0.01 to 0.10% of range.

Mn:1.20〜2.40%
MnはCと同様に、鋼板母材の強度を高める元素であり、構造用鋼として必要な強度を確保するために、1.20%以上の添加が必要である。また他の合金成分に比較して安価であることから、積極的な添加が有効であるが、2.40%を超えると焼入性が過剰となり、母材靱性が低下するとともに溶接性を損なう。従ってMn量は1.20〜2.40%とする。好ましくは1.50%〜2.20%の範囲である。
Mn: 1.20 to 2.40%
Mn, like C, is an element that enhances the strength of the steel plate base material, and it needs to be added in an amount of 1.20% or more in order to ensure the strength necessary for structural steel. Moreover, since it is inexpensive compared with other alloy components, aggressive addition is effective. However, if it exceeds 2.40%, the hardenability becomes excessive, the base metal toughness is lowered and the weldability is impaired. . Therefore, the Mn content is 1.20 to 2.40%. Preferably it is 1.50% to 2.20% of range.

P:0.008%以下
Pは不純物として鋼中に含有される元素の一つであるが、鋼板母材および、大入熱HAZ部の靱性を低下させるため、0.008%以下とする。素材溶製時の経済性を考慮した上で可能な範囲で低減することが好ましい。
P: 0.008% or less P is one of the elements contained in steel as an impurity, but is 0.008% or less in order to reduce the toughness of the steel plate base material and the high heat input HAZ part. It is preferable to reduce as much as possible in consideration of economics at the time of melting the material.

S:0.0005〜0.0040%
SはPと同様不純物として鋼中に含有される元素の一つであるが、Pと異なり、MnSやCaS、REM−Sなどの硫化物として存在した場合にフェライトの生成核となり、大入熱HAZ部靱性を向上させる効果を現す。この効果は0.0005%以上の添加で有効である。一方で過剰の添加は多量の硫化物生成を招き、母材靱性を低下させるようになる。従って、S量は0.0005〜0.0040%の範囲とする。
S: 0.0005 to 0.0040%
Like P, S is one of the elements contained in steel as an impurity, but unlike P, when it exists as sulfides such as MnS, CaS, and REM-S, it becomes a nucleus of ferrite formation, resulting in a large heat input. The effect of improving the toughness of the HAZ part is exhibited. This effect is effective when 0.0005% or more is added. On the other hand, excessive addition leads to a large amount of sulfide formation, and lowers the base material toughness. Therefore, the S amount is in the range of 0.0005 to 0.0040%.

Al:0.005〜0.080%
Alは、鋼の脱酸のために添加される元素であり、0.005%以上含有させる必要がある。一方で、0.080%を超えて添加すると、介在物量が過剰となり、母材の靱性を低下させる。従って、Alは0.005〜0.080%の範囲とする。好ましくは0.010〜0.060%とする。
Al: 0.005-0.080%
Al is an element added for deoxidation of steel, and it is necessary to contain 0.005% or more. On the other hand, if added over 0.080%, the amount of inclusions becomes excessive and the toughness of the base material is lowered. Therefore, Al is made 0.005 to 0.080% of range. Preferably, the content is 0.010 to 0.060%.

Nb:0.003〜0.040%
Nbは、添加により未再結晶温度域を拡大させる効果を有し、鋼板母材の強度靱性を確保するのに有効な元素である。しかし、0.003%未満の添加では上記効果が小さく、一方で0.040%を超えて添加すると、大入熱溶接HAZに島状マルテンサイトを生成させ、靱性を低下させる。このため、Nbは0.003〜0.040%の範囲とする。好ましくは、0.005〜0.025%の範囲である。
Nb: 0.003-0.040%
Nb has an effect of expanding the non-recrystallization temperature region by addition, and is an element effective for ensuring the strength toughness of the steel plate base material. However, if the addition is less than 0.003%, the above effect is small. On the other hand, if the addition exceeds 0.040%, island martensite is generated in the high heat input welding HAZ, and the toughness is lowered. For this reason, Nb is taken as 0.003 to 0.040% of range. Preferably, it is 0.005 to 0.025% of range.

Ti:0.003〜0.040%
Tiは、凝固時にTiNとして析出し、特に溶接熱影響部のオーステナイト粒の粗大化を抑制し、且つ、フェライトの変態核となるなど、大入熱溶接HAZの高靭化に極めて有用な元素である。この効果を得るためには、0.003%以上の添加が必要である一方で、0.040%を超えて添加すると、析出したTiNが粗大化し、上記効果が得られにくくなる。よって、Tiは、0.003〜0.040%の範囲とする。好ましくは、0.005〜0.025%の範囲である。
Ti: 0.003-0.040%
Ti precipitates as TiN during solidification, and is an extremely useful element for increasing the toughness of high heat input weld HAZ, particularly suppressing the coarsening of austenite grains in the weld heat affected zone and becoming a transformation nucleus of ferrite. is there. In order to obtain this effect, addition of 0.003% or more is necessary. On the other hand, if the addition exceeds 0.040%, the precipitated TiN becomes coarse and the above effect is hardly obtained. Therefore, Ti is taken as 0.003 to 0.040% of range. Preferably, it is 0.005 to 0.025% of range.

N:0.0030〜0.0100%
Nは、上述したTiNの生成、また、後述するB窒化物の形成に必要な元素であり、本発明において最も重要な元素の一つである。これらの窒化物を大入熱溶接HAZ部において生成させ、靱性向上に有効に寄与させるためには、0.0030%以上含有させる必要がある。一方で、0.0100%を超えて添加すると、溶接入熱条件によってはTiNが溶解する領域における固溶N量が増加し、溶接HAZ部の靱性を低下させる場合がある。従って、Nは、0.0030〜0.0100%の範囲とする。好ましくは、0.0040〜0.0070%の範囲である。
N: 0.0030 to 0.0100%
N is an element necessary for the formation of TiN described above and the formation of B nitride described later, and is one of the most important elements in the present invention. In order to generate these nitrides in the high heat input welded HAZ part and effectively contribute to the improvement of toughness, it is necessary to contain 0.0030% or more. On the other hand, if added over 0.0100%, depending on the welding heat input conditions, the amount of solute N in the region where TiN dissolves may increase, and the toughness of the welded HAZ part may be reduced. Therefore, N is set to a range of 0.0030 to 0.0100%. Preferably, it is 0.0040 to 0.0070% of range.

B:0.0003〜0.0030%
Bは固溶状態で存在する場合は粒界に偏在して焼入性を確保し、母材強度の確保に寄与すると共に、B窒化物として存在する場合はフェライト核として作用し、大入熱溶接HAZ靱性を高める効果の両方に寄与する、本発明で最も重要な元素の一つである。含有量が0.0003%未満では前者の効果が得られず、また、0.0030%を超えて添加するとB窒化物を上回る固溶Bが多量に存在することになり、大入熱溶接HAZ靱性を低下させる。従ってBは0.0003〜0.0030%の範囲とする。
B: 0.0003 to 0.0030%
When B exists in a solid solution state, it is unevenly distributed at grain boundaries to ensure hardenability and contribute to ensuring the strength of the base material, and when it exists as B nitride, it acts as a ferrite nucleus and has a large heat input. It is one of the most important elements in the present invention that contributes to both the effects of increasing welded HAZ toughness. If the content is less than 0.0003%, the former effect cannot be obtained. If the content exceeds 0.0030%, a large amount of solid solution B exceeding B nitride exists, and high heat input welding HAZ. Reduce toughness. Therefore, B is in the range of 0.0003 to 0.0030%.

本発明の基本成分組成は以上で、残部がFeおよび不可避的不純物からなるが、更に所望の特性を向上させる場合は、Cu、Ni、Cr、Mo、V、Ca、Zr、REMの1種または2種以上を選択元素として添加することができる。   The basic component composition of the present invention is as described above, and the balance is composed of Fe and unavoidable impurities. In order to further improve desired characteristics, one of Cu, Ni, Cr, Mo, V, Ca, Zr, and REM is used. Two or more kinds can be added as selective elements.

Cu:1.00%以下
Cuは強度を増加させるために添加することができる元素であるが、1.00%を超えて添加すると、熱間脆性により鋼板母材表面の性状を劣化させるため、添加する場合、その量は1.00%以下の範囲とすることが好ましい。
Cu: 1.00% or less Cu is an element that can be added in order to increase the strength, but if added over 1.00%, the properties of the surface of the steel sheet base material deteriorate due to hot brittleness. When added, the amount is preferably in the range of 1.00% or less.

Ni:1.00%以下
Niは母材の強度を増加させつつ靭性も向上させることが可能な元素である。1.00%を超えて添加した場合、効果が飽和するとともに経済的に不利となるため、添加する場合、その量は1.00%以下の範囲とすることが好ましい。
Ni: 1.00% or less Ni is an element capable of improving the toughness while increasing the strength of the base material. When added over 1.00%, the effect is saturated and economically disadvantageous, so when added, the amount is preferably in the range of 1.00% or less.

Cr:1.00%以下
Crは強度を増加させるために有効な元素であるが、1.00%を超えて添加すると、母材靭性を劣化させるため、添加する場合、その量は1.00%以下の範囲とすることが好ましい。
Cr: 1.00% or less Cr is an effective element for increasing the strength. However, if added over 1.00%, the base metal toughness is deteriorated, so when added, the amount is 1.00. % Or less is preferable.

Mo:0.50%以下
Moは母材強度を増加するのに有効な元素であるが、0.50%を超えて添加すると、著しく靭性を劣化させるとともに経済性を損なうため、添加する場合、その量は0.50%以下の範囲とすることが好ましい。
Mo: 0.50% or less Mo is an element effective for increasing the strength of the base metal. However, if added over 0.50%, the toughness is significantly deteriorated and the economy is impaired. The amount is preferably in the range of 0.50% or less.

V:0.10%以下
Vは母材強度を増加するのに有効な元素であるが、0.10%を超えて添加すると、著しく靭性を劣化させるため、添加する場合、その量は0.10%以下の範囲とすることが好ましい。
V: 0.10% or less V is an element effective for increasing the strength of the base metal. However, if added over 0.10%, the toughness is remarkably deteriorated. A range of 10% or less is preferable.

Ca:0.0005〜0.0050%、Zr:0.001〜0.020%およびREM:0.001〜0.020%
Ca、Zr、REMは鋼中のSを固定して鋼板の靭性を向上させる効果があり、強い硫化物形成元素であるCaは0.0005%以上で、また、ZrおよびREMに関しては0.001%以上の添加でそれぞれ効果が得られる。しかしながら、Ca、Zr、REMのそれぞれの量が0.0050%、0.020%、0.020%を超えて添加すると鋼中の介在物量が増加し靭性をかえって劣化させる。従って、これらの元素を添加する場合、Caは0.0005〜0.0050%、Zrは0.001〜0.020%、REMは0.001〜0.020%の範囲とすることが好ましい。
Ca: 0.0005-0.0050%, Zr: 0.001-0.020% and REM: 0.001-0.020%
Ca, Zr, and REM have the effect of fixing S in the steel to improve the toughness of the steel sheet. Ca, which is a strong sulfide-forming element, is 0.0005% or more, and 0.001 for Zr and REM. The effect can be obtained by adding more than%. However, if the amount of each of Ca, Zr, and REM exceeds 0.0050%, 0.020%, and 0.020%, the amount of inclusions in the steel increases and the toughness is deteriorated. Therefore, when these elements are added, it is preferable that Ca is 0.0005 to 0.0050%, Zr is 0.001 to 0.020%, and REM is 0.001 to 0.020%.

板厚方向および板幅方向のそれぞれでのビッカース硬さ(HV)の変動幅:ΔHVが30以下
本規定は、本発明内でも最も重要な要件の一つで有り、材質の均質性、特に母鋼板全厚の伸び特性に多大な影響を及ぼす。板厚方向および板幅方向のそれぞれでのビッカース硬さ(HV)の変動幅(ΔHV)が30超えである鋼板は、母鋼板の引張試験時にその硬さが相対的に低位となる部位で優先的にくびれが生じるため、全厚の伸び特性が著しく低下する。このため、硬さの変動幅(ばらつき)はビッカース硬度で30以下の範囲、望ましくは20以下とする。このような鋼板を鋼板内の材質均質性に優れた鋼板とする。硬さ試験方法は実施例において詳述する。
Vickers hardness (HV) fluctuation range in each of the plate thickness direction and the plate width direction: ΔHV is 30 or less This specification is one of the most important requirements in the present invention. It has a great influence on the elongation characteristics of the full thickness of the steel sheet. Steel plates with a fluctuation range (ΔHV) of more than 30 in the Vickers hardness (HV) in each of the plate thickness direction and the plate width direction are given priority in areas where the hardness is relatively low during the tensile test of the base plate. Since the constriction occurs, the elongation characteristic of the entire thickness is remarkably deteriorated. For this reason, the fluctuation range (variation) of the hardness is set to a range of 30 or less, preferably 20 or less in terms of Vickers hardness. Such a steel plate is a steel plate excellent in material homogeneity in the steel plate. The hardness test method will be described in detail in Examples.

上記成分組成を有する鋼を、転炉あるいは電気炉等の常法の方法を用いて溶製し、連続鋳造法あるいは造塊法等の常法の工程により、鋼板製造のためのスラブなどの鋼素材とすることが好ましい。以下、本発明で規定する鋼板製造条件の限定理由に関して説明する。本発明における鋼材温度は、鋼材の表面と中心部(板厚の1/2部)の平均温度とする。   Steels such as slabs for the production of steel sheets are produced by melting steels having the above-described composition using conventional methods such as converters or electric furnaces, and using conventional processes such as continuous casting or ingot casting. It is preferable to use a raw material. Hereinafter, the reason for limiting the steel sheet manufacturing conditions defined in the present invention will be described. The steel material temperature in the present invention is the average temperature of the steel material surface and the center (1/2 part of the plate thickness).

加熱温度:1000〜1300℃
鋳造後のスラブなどの鋼素材は、室温まで冷却した後、あるいは高温の状態のままで、加熱炉に装入し、鋼素材温度を1000℃以上とする。鋼素材の加熱温度は、主にNb炭窒化物を溶解せしめ、固溶Nbを十分に確保する観点から下限を1000℃とした。また、鋼素材温度が1300℃を超える場合、加熱時のオーステナイト粒の粗大化が起こり母材靱性に悪影響を及ぼすため上限は1300℃とした。なお、望ましい鋼素材温度は1000〜1250℃、より望ましくは1050〜1200℃である。
Heating temperature: 1000-1300 ° C
A steel material such as a slab after casting is charged into a heating furnace after being cooled to room temperature or in a high temperature state, and the steel material temperature is set to 1000 ° C. or higher. The lower limit of the heating temperature of the steel material was set to 1000 ° C. from the viewpoint of mainly dissolving Nb carbonitride and ensuring sufficient solid solution Nb. In addition, when the steel material temperature exceeds 1300 ° C., the austenite grains become coarse during heating and adversely affect the base material toughness, so the upper limit is set to 1300 ° C. In addition, desirable steel raw material temperature is 1000-1250 degreeC, More desirably, it is 1050-1200 degreeC.

未再結晶温度域において累積圧下率40%以上の圧延
加熱された鋼スラブは、再結晶温度域での熱間圧延後、未再結晶温度域にて制御圧延を行う。再結晶温度域における圧延は、加熱時のオーステナイト粒を微細化するために実施することが好ましく、1パス以上、好ましくは累積圧下率20%以上行うのが望ましい。この再結晶温度域での熱間圧延後に未再結晶温度域において実施する制御圧延はその圧下率が小さい場合、所定の母材靱性を得ることが出来ない。このため、未再結晶温度域における圧延の累積圧下率の下限を40%と規定する。また、圧下率は高い方が好ましいが、工業的には80%程度が上限となる。
The steel slab that is rolled and heated with a cumulative reduction ratio of 40% or more in the non-recrystallization temperature range is subjected to controlled rolling in the non-recrystallization temperature range after hot rolling in the recrystallization temperature range. Rolling in the recrystallization temperature region is preferably performed in order to refine the austenite grains at the time of heating, and it is desirable to perform one pass or more, preferably 20% or more of the cumulative rolling reduction. When the rolling reduction in the non-recrystallization temperature range after the hot rolling in the recrystallization temperature range is small, the predetermined base material toughness cannot be obtained. For this reason, the lower limit of the rolling rolling reduction ratio in the non-recrystallization temperature region is defined as 40%. Moreover, although the one where a rolling reduction is higher is preferable, about 80% becomes an upper limit industrially.

なお、再結晶温度域の下限温度は、鋼組成のほか、結晶粒径や加工履歴や歪量などの影響を受けるが、概ね800〜950℃の範囲にある。事前に予備試験をして調査することにより、前記下限温度を推測することができる。   The lower limit temperature of the recrystallization temperature range is influenced by the crystal grain size, processing history, strain amount, etc. in addition to the steel composition, but is generally in the range of 800 to 950 ° C. By conducting a preliminary test and investigating in advance, the lower limit temperature can be estimated.

また、圧延終了温度は組織の均一性の観点から、Ar3変態点以上であることが好ましい。   Moreover, it is preferable that rolling completion temperature is more than Ar3 transformation point from a viewpoint of the uniformity of structure | tissue.

加速冷却前のデスケーリングの実施
加速冷却の直前に高衝突圧の噴射流を鋼板表面に衝突させることによるデスケーリングを行う。鋼板内の材質均一性に優れた厚鋼板とするためには、鋼板内の硬さのばらつきを低減することが必要であり、特に鋼板内部の強度を保ちながら、表層部の硬さのばらつきを抑制することが重要である。
Implementation of descaling before accelerated cooling Descaling is performed by causing a high collision pressure jet stream to collide with the steel plate surface immediately before accelerated cooling. In order to make a thick steel plate with excellent material uniformity within the steel plate, it is necessary to reduce the variation in hardness within the steel plate, and in particular, while maintaining the strength inside the steel plate, the variation in hardness of the surface layer is reduced. It is important to suppress.

圧延後の鋼板においては、圧延前および圧延中のデスケーリング等により幅方向にスケールの厚さにむらが生じることがある。また、スケールが厚い場合には、部分的にスケールの剥離が生じることがある。圧延後の冷却の際に、スケール厚さにばらつきがあると、その厚さに応じて鋼板表面の冷却速度も変化し、その冷却速度に応じて鋼板表面の硬さも変化する。鋼板を高強度化するためには、加速冷却時の冷却速度を大きくすることが有効であるが、高冷却速度での冷却では表層硬さに及ぼすスケール厚さの影響が顕著になるため、スケール厚さにむらがあると硬さのばらつきが増大して鋼板内の材質均一性が劣化する。   In a steel sheet after rolling, unevenness in the thickness of the scale may occur in the width direction due to descaling or the like before rolling and during rolling. Further, when the scale is thick, the scale may be partially peeled off. If the scale thickness varies during cooling after rolling, the cooling rate of the steel sheet surface changes according to the thickness, and the hardness of the steel sheet surface also changes according to the cooling rate. To increase the strength of steel sheets, it is effective to increase the cooling rate during accelerated cooling, but the effect of scale thickness on the surface hardness becomes significant when cooling at a high cooling rate. If the thickness is uneven, the variation in hardness increases and the material uniformity in the steel sheet deteriorates.

本発明では、加速冷却の直前に高衝突圧の噴射流によるデスケーリングを実施し、スケール厚さを冷却速度に大きな差が生じない、15μm以下まで均一に薄くする。すなわち、加速冷却後の鋼板のスケール厚さを15μm以下とした場合に、板厚方向の硬さのばらつきがΔHV30以下、且つ板幅方向の硬さのばらつきも同様にΔHV30以下となる。   In the present invention, the descaling by the high collision pressure jet flow is performed immediately before the acceleration cooling, and the scale thickness is uniformly thinned to 15 μm or less without causing a large difference in the cooling rate. That is, when the scale thickness of the steel sheet after accelerated cooling is 15 μm or less, the hardness variation in the plate thickness direction is ΔHV30 or less, and the hardness variation in the plate width direction is also ΔHV30 or less.

加速冷却直前の鋼板のスケール厚みを測定することは困難であるが、加速冷却前のスケール厚みは加速冷却後のスケール厚みによって推定することができ、冷却後の鋼板のスケール厚みが15μm以下となるように冷却直前にデスケーリングを行うことによって、所望の効果が得られることが解明された。冷却直前での高衝突圧の噴射流によるデスケーリングによって、高冷却速度下での強度と鋼板内の材質均一性を両立することができる。   Although it is difficult to measure the scale thickness of the steel plate immediately before accelerated cooling, the scale thickness before accelerated cooling can be estimated by the scale thickness after accelerated cooling, and the scale thickness of the steel plate after cooling is 15 μm or less. Thus, it has been clarified that the desired effect can be obtained by performing descaling immediately before cooling. By descaling by the jet flow of high impact pressure immediately before cooling, both strength at high cooling speed and material uniformity in the steel sheet can be achieved.

デスケーリング圧(鋼板表面での噴射流の衝突圧):1MPa以上
本発明では、冷却後の鋼板のスケール厚みが15μm以下となるように加速冷却の直前に鋼板表面での噴射流の衝突圧が1MPa以上となる条件でデスケーリングを行う。鋼板表面での噴射流の衝突圧が1MPa未満では、デスケーリングが不十分でスケールむらが生じる場合があり、表層硬さのばらつきが生じるため、噴射流の衝突圧は1MPa以上とする。デスケーリングは高圧水を用いて行うが、鋼板表面での噴射流の衝突圧が1MPa以上であれば、他の噴射流を用いても問題はない。より好ましくは2MPa以上である。
Descaling pressure (impact pressure of jet flow on steel plate surface): 1 MPa or more In the present invention, the impact pressure of jet flow on the steel plate surface immediately before accelerated cooling is such that the scale thickness of the steel plate after cooling is 15 μm or less. Descaling is performed under conditions of 1 MPa or more. If the collision pressure of the jet flow on the surface of the steel sheet is less than 1 MPa, the descaling may be insufficient and unevenness in scale may occur, resulting in variations in surface hardness. Therefore, the collision pressure of the jet flow is 1 MPa or more. Although descaling is performed using high-pressure water, there is no problem even if another jet flow is used as long as the collision pressure of the jet flow on the steel plate surface is 1 MPa or more. More preferably, it is 2 MPa or more.

鋼板の平均冷却速度:10℃/s以上
デスケーリング後の加速冷却は、鋼板の強度を確保するために実施されるが、鋼板表層部の材質均質性を同時に担保する条件を選択する必要がある。鋼板の平均冷却速度が10℃/s未満の場合、デスケ−リングされた表層面であっても表層域の冷却が不均一となり、鋼板内部との硬さのばらつきが大きくなる。このため、平均冷却速度は10℃/s以上に規定する。また、より好ましい平均冷却速度は15℃/s以上である。なお、冷却開始温度は、得られる金属組織の均一性の観点から、理想的にはAr3変態点以上であることが好ましいが、例えば板厚が薄い場合などにおいては、圧延完了からデスケーリングを経て、加速冷却設備に搬送される間に温度低下が起こり、冷却開始温度がAr3変態点を下回る場合がある。この影響が本発明の目的とするところの硬さの均質性を阻害しないためには、加速冷却開始温度は、圧延終了温度〜(圧延終了温度−30℃)の範囲内であることが望ましい。
Average cooling rate of steel plate: 10 ° C./s or more Accelerated cooling after descaling is carried out in order to ensure the strength of the steel plate, but it is necessary to select conditions that simultaneously ensure the material homogeneity of the steel plate surface layer part. . When the average cooling rate of the steel sheet is less than 10 ° C./s, even in the descaled surface layer, the cooling of the surface layer region becomes non-uniform, and the variation in hardness with the inside of the steel plate becomes large. For this reason, an average cooling rate is prescribed | regulated to 10 degrees C / s or more. A more preferable average cooling rate is 15 ° C./s or more. It should be noted that the cooling start temperature is ideally not less than the Ar3 transformation point from the viewpoint of the uniformity of the obtained metal structure. For example, when the plate thickness is thin, the descaling is performed after completion of rolling. In some cases, the temperature is lowered while being transported to the accelerated cooling facility, and the cooling start temperature is lower than the Ar3 transformation point. In order that this influence does not hinder the homogeneity of hardness as the object of the present invention, it is desirable that the accelerated cooling start temperature is within the range of the rolling end temperature to (rolling end temperature −30 ° C.).

冷却停止温度:鋼板平均温度で200〜600℃
加速冷却は、ベイナイト変態の温度域である200〜600℃まで冷却し、所定の強度が得られるミクロ組織に鋼板内部を変態(本発明ではベイナイト変態)させる。冷却停止温度が600℃を超えると、ベイナイト変態が不完全であり、十分な強度が得られない。また、冷却停止温度が200℃未満では、特に表層部において一部マルテンサイトや島状マルテンサイト(MA)が生成し、鋼板内の材質均一性が得られず全厚の伸び特性が低下する。このため、加速冷却の冷却停止温度は鋼板平均温度で200〜600℃とする。所望の強度靭性が得られるように加速冷却停止後、Ac1変態点以下で焼き戻しても良い。Ac1変態点は下式によって求めることができる。但し、式において、各元素記号は各元素の含有量(質量%)を示す。
Ac1 =751−26.6C+17.6Si−11.6Mn−169Al−23Cu−23Ni+24.1Cr+22.5Mo+233Nb−39.7V−5.7Ti−895B
Cooling stop temperature: 200 to 600 ° C. at the average steel plate temperature
In the accelerated cooling, cooling is performed to 200 to 600 ° C., which is a temperature range of bainite transformation, and the inside of the steel sheet is transformed (bainite transformation in the present invention) into a microstructure capable of obtaining a predetermined strength. When the cooling stop temperature exceeds 600 ° C., the bainite transformation is incomplete and sufficient strength cannot be obtained. If the cooling stop temperature is less than 200 ° C., part of martensite or island martensite (MA) is generated particularly in the surface layer portion, and material uniformity in the steel sheet cannot be obtained, resulting in a reduction in the elongation characteristics of the entire thickness. For this reason, the cooling stop temperature of accelerated cooling is set to 200 to 600 ° C. in terms of the average steel plate temperature. It may be tempered at the Ac1 transformation point or lower after the accelerated cooling is stopped so as to obtain desired strength toughness. The Ac1 transformation point can be obtained by the following equation. However, in the formula, each element symbol indicates the content (% by mass) of each element.
Ac1 = 751-26.6C + 17.6Si-11.6Mn-169Al-23Cu-23Ni + 24.1Cr + 22.5Mo + 233Nb-39.7V-5.7Ti-895B

以下、本発明の効果を実施例により詳細に説明する。表1に示す組成の鋼を転炉で溶製後、連続鋳造法でスラブ(鋼素材)とし、表2に示す制御圧延、加速冷却条件により20〜50mm厚の鋼板を作製した。なお、表1において、鋼番号1〜10が本発明の実施例であり、鋼番号11〜15は、成分組成のいずれかが本発明の範囲外となる比較例である。また、表2において、鋼番号に続く枝番Aは本発明によるところの制御圧延・冷却条件によるものであり、枝番B1・B2は製造条件のいずれかが本発明の範囲外となる比較例である。   Hereinafter, the effects of the present invention will be described in detail with reference to examples. Steels having the compositions shown in Table 1 were melted in a converter and then made into slabs (steel materials) by a continuous casting method, and steel plates having a thickness of 20 to 50 mm were produced by controlled rolling and accelerated cooling conditions shown in Table 2. In Table 1, steel numbers 1 to 10 are examples of the present invention, and steel numbers 11 to 15 are comparative examples in which any of the component compositions falls outside the scope of the present invention. In Table 2, the branch number A following the steel number is based on the controlled rolling / cooling conditions according to the present invention, and the branch numbers B1 and B2 are comparative examples in which any of the manufacturing conditions is outside the scope of the present invention. It is.

上記組成ならびに製造工程を経て製造された厚鋼板について、平行部幅25mmの全厚引張試験片を採取して、JIS Z 2241(1998)の規定に準拠して引張試験を実施し、引張強さ(以下TSと記載する)および全厚伸び(全伸び)を求めた。なお、本発明はその対象として高強度鋼板を想定しているため、その強度目標をTS:550N/mm以上とし、全厚伸び値は一般的に同強度クラスの鋼材に対して要求される20%以上を目標とした。 About the thick steel plate manufactured through the above-mentioned composition and manufacturing process, a full thickness tensile test piece having a parallel part width of 25 mm is sampled and subjected to a tensile test in accordance with the provisions of JIS Z 2241 (1998). (Hereinafter referred to as TS) and total thickness elongation (total elongation) were determined. Since the present invention assumes a high-strength steel plate as the object, the strength target is TS: 550 N / mm 2 or more, and the total thickness elongation value is generally required for steel materials of the same strength class. The target was 20% or more.

また、上記の全厚引張試験における伸び値と、鋼板の硬さばらつき値の相関を明らかにするために、圧延方向に直角な断面について、JIS Z 2244に準拠して、ビッカース硬さを測定し、板厚方向の硬さ分布と板幅方向の硬さ分布を求めた。板厚方向については、1mmピッチで全厚の硬さを測定し、板幅方向については、20mmピッチで全幅の硬さを測定した。なお、板幅方向の硬さは、表層1mm位置(表層から1mm内側の位置)、t/4位置(板厚1/4位置)、t/2位置(板厚中心部)で測定したが、いずれの鋼板も表層1mm位置において硬さのばらつきが最大を示したので、板幅方向の硬さのばらつきは表層1mm位置で評価した。なお、硬さ測定時の試験荷重は10kgf(98N)で一定とした。   Further, in order to clarify the correlation between the elongation value in the full thickness tensile test and the hardness variation value of the steel sheet, Vickers hardness was measured in accordance with JIS Z 2244 for a cross section perpendicular to the rolling direction. The hardness distribution in the plate thickness direction and the hardness distribution in the plate width direction were determined. For the plate thickness direction, the hardness of the entire thickness was measured at a pitch of 1 mm, and for the plate width direction, the hardness of the full width was measured at a pitch of 20 mm. In addition, although the hardness in the plate width direction was measured at the surface layer 1 mm position (position 1 mm inside from the surface layer), t / 4 position (plate thickness 1/4 position), t / 2 position (plate thickness center), Since all the steel sheets showed the largest variation in hardness at the surface layer of 1 mm, the variation in hardness in the plate width direction was evaluated at the surface layer of 1 mm. In addition, the test load at the time of hardness measurement was made constant at 10 kgf (98 N).

さらに、大入熱溶接HAZの靭性を評価するため、上記厚鋼板から、幅80mm×長さ80mm×厚み15mmの試験片を採取し、1450℃に加熱後、800〜500℃を250secで冷却する熱処理を付与した後、2mmVノッチシャルピー試験片を各3本採取して、上記と同様にしてシャルピー衝撃試験を行った。なお、衝撃試験温度は−40℃とし、その靱性目標を−40℃における吸収エネルギー平均値(以下vE−40℃と記載する)で50J以上とした。   Furthermore, in order to evaluate the toughness of the high heat input welding HAZ, a test piece having a width of 80 mm, a length of 80 mm and a thickness of 15 mm is taken from the thick steel plate, heated to 1450 ° C., and then cooled to 800 to 500 ° C. in 250 seconds. After the heat treatment, three 2 mm V notch Charpy test pieces were collected and subjected to the Charpy impact test in the same manner as described above. The impact test temperature was −40 ° C., and the toughness target was 50 J or more in terms of the average absorbed energy at −40 ° C. (hereinafter referred to as vE-40 ° C.).

表4に、上記の鋼板母材特性ならびに大入熱溶接HAZ靱性評価結果を示す。板厚方向と板幅方向のそれぞれでのビッカース硬さ(HV)の変動幅:ΔHVが30以下で、TS:550N/mm以上、全厚伸び値:20%以上を母材評価が良好とした。本発明例である鋼番号1〜10かつ枝番Aにおいては、母材ならびに大入熱溶接HAZ特性とも良好な値が得られているのに対して、鋼番号1〜10かつ枝番B1・B2においては、化学成分規定は本発明の範囲内であるため大入熱HAZ特性は満足するものの、製造条件が範囲外であるため母材の特性が劣り、一方で、鋼番号11〜15(枝番AおよびB1・B2)においては、成分範囲が本発明の範囲外であるために、大入熱溶接HAZ部の靱性が劣っている。 Table 4 shows the steel plate base material characteristics and the high heat input welding HAZ toughness evaluation results. Vickers hardness (HV) fluctuation width in each of the plate thickness direction and the plate width direction: ΔHV is 30 or less, TS: 550 N / mm 2 or more, total thickness elongation value: 20% or more did. In steel numbers 1 to 10 and branch number A, which are examples of the present invention, good values are obtained for both the base material and high heat input welding HAZ characteristics, whereas in steel numbers 1 to 10 and branch numbers B1 and B2. Although the chemical composition definition is within the scope of the present invention, the high heat input HAZ characteristics are satisfied, but the manufacturing conditions are out of the range, so the characteristics of the base material are inferior. On the other hand, steel numbers 11 to 15 (branch numbers) In A and B1 and B2), since the component range is outside the range of the present invention, the toughness of the high heat input HAZ part is inferior.

Claims (5)

質量%で、C:0.030〜0.080%、Si:0.01〜0.10%、Mn:1.20〜2.40%、P:0.008%以下、S:0.0005〜0.0040%、Al:0.005〜0.080%、Nb:0.003〜0.040%、Ti:0.003〜0.040%、N:0.0030〜0.0100%、B:0.0003〜0.0030%を含有し、残部がFeおよび不可避的不純物からなる成分組成を有し、かつ、板厚方向と板幅方向のそれぞれでのビッカース硬さ(HV)の変動幅:ΔHVが30以下であることを特徴とする大入熱溶接特性と材質均質性に優れた厚鋼板。   In mass%, C: 0.030 to 0.080%, Si: 0.01 to 0.10%, Mn: 1.20 to 2.40%, P: 0.008% or less, S: 0.0005 -0.0040%, Al: 0.005-0.080%, Nb: 0.003-0.040%, Ti: 0.003-0.040%, N: 0.0030-0.0100%, B: 0.0003 to 0.0030% contained, the remainder having a component composition consisting of Fe and inevitable impurities, and fluctuations in Vickers hardness (HV) in each of the plate thickness direction and the plate width direction Width: A thick steel plate excellent in high heat input welding characteristics and material homogeneity, wherein ΔHV is 30 or less. 更に、質量%で、Cu:1.00%以下、Ni:1.00%以下、Cr:1.00%以下、Mo:0.50%以下、V:0.10%以下の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1に記載の大入熱溶接特性と材質均質性に優れた厚鋼板。   Further, by mass%, Cu: 1.00% or less, Ni: 1.00% or less, Cr: 1.00% or less, Mo: 0.50% or less, V: 0.10% or less, or 1 or 2 The thick steel plate excellent in high heat input welding characteristics and material homogeneity according to claim 1, comprising at least a seed. 更に、質量%で、Ca:0.0005〜0.0050%、Zr:0.001〜0.020%、REM:0.001〜0.020%の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1または2に記載の大入熱溶接特性と材質均質性に優れた厚鋼板。   Furthermore, it contains one or more of Ca: 0.0005 to 0.0050%, Zr: 0.001 to 0.020%, REM: 0.001 to 0.020% in mass%. The thick steel plate excellent in high heat input welding characteristics and material homogeneity according to claim 1 or 2. 請求項1乃至3のいずれか一つに記載の成分組成の鋼素材を1000〜1300℃に加熱後、熱間圧延し、鋼板表面での噴射流の衝突圧が1MPa以上の条件で噴射流を鋼板表面に衝突させることによりデスケーリングを行い、その後、直ちに、鋼板の平均冷却速度:10℃/s以上、鋼板の平均冷却停止温度:200〜600℃で加速冷却を行うことを特徴とする板厚方向と板幅方向のそれぞれでのビッカース硬さ(HV)の変動幅:ΔHVが30以下であることを特徴とする大入熱溶接特性と材質均質性に優れた厚鋼板の製造方法。   The steel material having the component composition according to any one of claims 1 to 3 is heated to 1000 to 1300 ° C and then hot-rolled, and the jet flow is performed under a condition that the collision pressure of the jet flow on the steel plate surface is 1 MPa or more. The descaling is performed by colliding with the steel plate surface, and then accelerated cooling is immediately performed at an average cooling rate of the steel plate of 10 ° C./s or more and an average cooling stop temperature of the steel plate of 200 to 600 ° C. Vickers hardness (HV) fluctuation width in each of the thickness direction and the plate width direction: ΔHV is 30 or less, A method for producing a thick steel plate excellent in high heat input welding characteristics and material homogeneity. 加速冷却停止後、Ac1変態点以下で焼き戻すことを特徴とする請求項4記載の厚鋼板の製造方法。   The method for producing a thick steel plate according to claim 4, wherein after the accelerated cooling is stopped, tempering is performed at a temperature equal to or lower than the Ac1 transformation point.
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