JP4276574B2 - Thick steel plate with excellent toughness of heat affected zone - Google Patents

Thick steel plate with excellent toughness of heat affected zone Download PDF

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JP4276574B2
JP4276574B2 JP2004116908A JP2004116908A JP4276574B2 JP 4276574 B2 JP4276574 B2 JP 4276574B2 JP 2004116908 A JP2004116908 A JP 2004116908A JP 2004116908 A JP2004116908 A JP 2004116908A JP 4276574 B2 JP4276574 B2 JP 4276574B2
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明彦 児島
洋一 田中
譲 吉田
昌紀 皆川
学 星野
龍治 植森
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Nippon Steel Corp
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本発明は、大入熱溶接継手における溶接熱影響部(Heat Affected Zone:HAZ)の靭性に優れた厚手高強度鋼板に関するものである。本発明は、鉄鋼業において製造される厚鋼板に主に適用される。本発明は厚鋼板以外のH形鋼や鋼管などの鉄鋼製品へ適用することも可能である。本発明を適用した鋼板は、造船をはじめ、建築、橋梁、タンク、海洋構造物、ラインパイプなどの溶接構造物に使用され、溶接施工能率の高い大入熱溶接を施され、かつ、溶接部靭性の要求レベルが高い場合に好適である。   The present invention relates to a thick high-strength steel plate excellent in the toughness of a heat affected zone (HAZ) in a high heat input welded joint. The present invention is mainly applied to thick steel plates manufactured in the steel industry. The present invention can also be applied to steel products such as H-shaped steel and steel pipe other than thick steel plates. Steel plates to which the present invention is applied are used for shipbuilding, welding structures such as buildings, bridges, tanks, offshore structures, line pipes, etc., and are subjected to high heat input welding with high welding work efficiency, and welded parts It is suitable when the required level of toughness is high.

近年、造船に代表される溶接構造物に対する主要な要求は、構造の大型化、建造の高能率化、破壊に対する安全性向上である。このような動向を受け、溶接構造用鋼板には厚手化、高強度化、大入熱溶接化に対応しつつ、より一層の高いHAZ靭性が求められる。たとえば、近年急速な進化を遂げつつある大型コンテナ船に用いられる鋼板に対しては、50〜80mmの大きな厚みと390〜460MPa級の高い降伏強度を有しつつ、20kJ/mm以上の大きな溶接入熱量で高能率な1パス溶接を施した場合のHAZにおいて、−40℃という低温で高いシャルピー衝撃吸収エネルギーが要求される可能性がある。このように、母材の厚手高強度化を前提としたうえで、良好な大入熱溶接HAZ靭性を達成することが本発明の課題である。一般に、母材の厚手高強度化に伴って化学成分的な焼入性(たとえばCeq)が増加し、HAZが硬化するでHAZ靭性の確保が難しくなる。また、母材の厚手化に伴って1パス溶接時の溶接入熱量が増加し、HAZが受ける熱ダメージが大きくなって金属組織が粗大化し、HAZ靭性の確保が難しくなる。さらに、要求される靭性レベル(破壊吸収エネルーや靭性保証温度)が高度化することでHAZ靭性の確保がますます難しくなる。これら三つ要因が重畳することが、本発明が解決すべき課題の困難さである。   In recent years, major demands for welded structures typified by shipbuilding are to increase the size of structures, increase the efficiency of construction, and improve safety against destruction. In response to these trends, welded structural steel plates are required to have higher HAZ toughness while supporting thickening, high strength, and high heat input welding. For example, for steel plates used in large container ships that are undergoing rapid evolution in recent years, they have a large thickness of 50 to 80 mm and a high yield strength of 390 to 460 MPa class, and a large welding input of 20 kJ / mm or more. In HAZ when high-efficiency one-pass welding is performed with high heat, high Charpy impact absorption energy may be required at a low temperature of −40 ° C. As described above, it is an object of the present invention to achieve good large heat input welding HAZ toughness on the premise of increasing the thickness and strength of the base material. Generally, the hardenability (for example, Ceq) as a chemical component increases with increasing thickness and strength of the base material, and it becomes difficult to ensure HAZ toughness because the HAZ hardens. In addition, as the base metal becomes thicker, the amount of heat input during one-pass welding increases, the thermal damage that the HAZ receives increases, the metal structure becomes coarse, and it becomes difficult to ensure the HAZ toughness. Furthermore, as the required toughness level (destructive absorption energy and toughness guarantee temperature) increases, it becomes more difficult to ensure the HAZ toughness. The superposition of these three factors is the difficulty of the problem to be solved by the present invention.

厚手高強度鋼の大入熱溶接HAZ靭性に関する従来技術として、例えば、非特許文献1がある。ここに記載された技術は、CuやNiなどの有害元素の添加を控えて、炭素当量(Ceq)低減によって焼入性を低下させ、大入熱HAZ靭性を確保するものである。この技術は、母材の厚手高強度化を達成するために、圧延後の加速冷却を強化する必要があり、加速冷却設備の改造や新設などの設備投資が強いられる。さらに、このような技術で加速冷却工程に大きな負荷をかけても、溶融線近傍HAZの靭性保証温度は−20℃であり、−40℃のシャルピー衝撃特性が確保できることは示されていない。   For example, Non-Patent Document 1 is known as a conventional technique related to high heat input welding HAZ toughness of thick high-strength steel. The technology described here refrains from the addition of harmful elements such as Cu and Ni, reduces the hardenability by reducing the carbon equivalent (Ceq), and ensures high heat input HAZ toughness. This technology needs to enhance accelerated cooling after rolling in order to achieve thicker and higher strength of the base material, and is forced to invest in equipment such as remodeling or newly installing accelerated cooling equipment. Furthermore, even if a heavy load is applied to the accelerated cooling process with such a technique, the toughness guarantee temperature of the HAZ near the melting line is −20 ° C., and it is not shown that the Charpy impact characteristic of −40 ° C. can be secured.

以上の例のように、厚手高強度鋼板に高能率な大入熱溶接を適用したときのHAZ靭性を、要求される靭性レベルに応じて安定的に確保することが課題である。大型コンテナ船をはじめとする大型溶接構造物に対して、大入熱溶接HAZ靭性の優れた鋼板の提供が求められている。   As in the above example, it is a problem to stably ensure the HAZ toughness according to the required toughness level when high-efficiency large heat input welding is applied to the thick high-strength steel plate. For large welded structures such as large container ships, it is required to provide steel sheets with excellent high heat input weld HAZ toughness.

R&D神戸製鋼技報、Vol.52、No.1(Apr.2002)、p.2−5、「大型コンテナ船用大入熱溶接型YP355〜460MPa級鋼板および溶接材料」R & D Kobe Steel Engineering Reports, Vol. 52, no. 1 (Apr. 2002), p. 2-5, “High heat input welding type YP355-460 MPa class steel plate and welding material for large container ships”

本発明の第一の課題は、50〜80mmの厚みと390〜460MPa級の降伏強度を有し、20〜60kJ/mmの溶接入熱量で溶接されたHAZにおいて、−40℃でのシャルピー衝撃吸収エネルギー平均値が100J以上である、低C高Ni成分鋼板を提供することである。この課題は主に造船用鋼板を対象とする。本発明の第二の課題は、20〜100mmの厚みと325〜440MPa級の降伏強度を有し、50〜150kJ/mmの溶接入熱量で溶接されたHAZにおいて、0℃でのシャルピー衝撃吸収エネルギー平均値が100J以上である、高C低Ni成分鋼板を提供することである。この課題は主に建築用鋼板を対象とする。本発明を適用した鋼板は、造船や建築以外の各種の大型溶接構造物にも使用が可能であり、溶接施工能率の高い大入熱溶接を施した場合でも、良好なHAZ靭性を確保できることを目指す。   The first object of the present invention is to absorb Charpy impact at −40 ° C. in HAZ having a thickness of 50 to 80 mm and a yield strength of 390 to 460 MPa class and welded with a welding heat input of 20 to 60 kJ / mm. It is to provide a low C high Ni component steel sheet having an energy average value of 100 J or more. This subject is mainly for shipbuilding steel plates. The second subject of the present invention is the Charpy impact absorption energy at 0 ° C. in HAZ having a thickness of 20 to 100 mm and a yield strength of 325 to 440 MPa class and welded with a welding heat input of 50 to 150 kJ / mm. It is to provide a high C low Ni component steel sheet having an average value of 100 J or more. This subject is mainly intended for architectural steel plates. The steel sheet to which the present invention is applied can be used for various types of large welded structures other than shipbuilding and construction, and can ensure good HAZ toughness even when subjected to high heat input welding with high welding construction efficiency. aim.

本発明は、以下の通りの厚鋼板である。
(1)質量%で、C:0.03〜0.2%、Si:0.5%以下、Mn:0.5〜2%、P:0.015%以下、S:0.001〜0.005%、Al:0.001〜0.1%、V:0.02〜0.1%、N:0.001〜0.02%、O:0.001〜0.004%を含有し、Ca:0.0003〜0.005%、Mg:0.0003〜0.005%の一種以上を含有し、質量%を用いて計算される下記の式(1)を満たし、残部が鉄および不可避的不純物によって化学成分が構成され、Caまたは/およびMgを含む10〜500nmの酸化物または/および硫化物が1000個/mm以上存在することを特徴とする、大入熱溶接熱影響部の靭性に優れた厚鋼板。
(2)質量%で、C:0.03〜0.2%、Si:0.5%以下、Mn:0.5〜2%、P:0.015%以下、S:0.001〜0.005%、Al:0.001〜0.1%、V:0.02〜0.1%、N:0.001〜0.02%、O:0.001〜0.004%を含有し、Ca:0.0003〜0.005%、Mg:0.0003〜0.005%のうち、Mgの一種を、またはCaとMgの二種を含有し、さらにCu:0.05〜1%、Ni:0.05〜3%、Cr:0.05〜1%、Mo:0.05〜1%、Nb:0.003〜0.03%、Ti:0.003〜0.03%、B:0.0003〜0.003%の一種以上を含有し、質量%を用いて計算される下記の式(2)を満たし、残部が鉄および不可避的不純物によって化学成分が構成され、Mgを含む、またはMgおよびCaを含む10〜500nmの酸化物または/および硫化物が1000個/mm 以上存在することを特徴とする、大入熱溶接熱影響部の靭性に優れた厚鋼板。
The present invention is a thick steel plate as follows.
(1) By mass%, C: 0.03-0.2%, Si: 0.5% or less, Mn: 0.5-2%, P: 0.015% or less, S: 0.001-0 0.005%, Al: 0.001-0.1%, V: 0.02-0.1%, N: 0.001-0.02%, O: 0.001-0.004% , C a: from 0.0003 to 0.005%, Mg: comprise one or more from 0.0003 to 0.005%, satisfying the equation (1) below is calculated using the mass%, the remaining part A high heat input welding heat characterized in that a chemical component is formed by iron and inevitable impurities, and there are 1000 / mm 2 or more of oxides and / or sulfides of 10 to 500 nm containing Ca or / and Mg. A thick steel plate with excellent toughness in the affected area.
(2) By mass%, C: 0.03-0.2%, Si: 0.5% or less, Mn: 0.5-2%, P: 0.015% or less, S: 0.001-0 0.005%, Al: 0.001-0.1%, V: 0.02-0.1%, N: 0.001-0.02%, O: 0.001-0.004% Ca: 0.0003 to 0.005%, Mg: 0.0003 to 0.005%, containing one kind of Mg or two kinds of Ca and Mg, and further Cu: 0.05 to 1% Ni: 0.05-3%, Cr: 0.05-1%, Mo: 0.05-1%, Nb: 0.003-0.03%, Ti: 0.003-0.03%, B: contains one or more of 0.0003 to 0.003%, satisfies the following formula (2) calculated using mass%, and the balance is a chemical component due to iron and inevitable impurities Constructed, containing Mg, or oxides and / or sulfides of 10~500nm containing Mg and Ca are characterized by the presence 1000 / mm 2 or more, excellent in toughness of high heat input welding heat affected zone Thick steel plate.

0.05V ≦ N ≦ 0.27V…(1)
0.29Ti+0.15Nb+1.30B+0.05V ≦ N ≦ 0.29Ti+0.15Nb+1.30B+0.27V…(2)
0.05V ≦ N ≦ 0.27V (1)
0.29Ti + 0.15Nb + 1.30B + 0.05V ≦ N ≦ 0.29Ti + 0.15Nb + 1.30B + 0.27V (2)

本発明によって、50〜80mmの厚みと390〜460MPa級の降伏強度を有し、20〜60kJ/mmの溶接入熱量で溶接されたHAZにおいて、−40℃でのシャルピー衝撃吸収エネルギー平均値が100J以上である、低C高Ni成分鋼板(C<0.08%、Ni>0.5%)を提供することが可能となる。また、20〜100mmの厚みと325〜440MPa級の降伏強度を有し、50〜150kJ/mmの溶接入熱量で溶接されたHAZにおいて、0℃でのシャルピー衝撃吸収エネルギー平均値が100J以上である、高C低Ni成分鋼板(C≧0.08%、Ni≦1.0%)を提供することが可能となる。本発明を適用した鋼板は、造船や建築をはじめとする各種の溶接構造物に使用され、構造物の建造における高い溶接施工能率と、構造物の高い安全性・信頼性を両立することができる。   According to the present invention, the HAZ having a thickness of 50 to 80 mm and a yield strength of 390 to 460 MPa class and welded with a welding heat input of 20 to 60 kJ / mm has an average value of Charpy impact absorption energy at −40 ° C. of 100 J. It is possible to provide a low C high Ni component steel sheet (C <0.08%, Ni> 0.5%) as described above. In addition, in HAZ having a thickness of 20 to 100 mm and a yield strength of 325 to 440 MPa class and welded at a welding heat input of 50 to 150 kJ / mm, the Charpy impact absorption energy average value at 0 ° C. is 100 J or more. It is possible to provide a high C, low Ni component steel sheet (C ≧ 0.08%, Ni ≦ 1.0%). The steel plate to which the present invention is applied is used for various welded structures including shipbuilding and construction, and can achieve both high welding construction efficiency in construction of the structure and high safety and reliability of the structure. .

第一の課題である低C高Ni成分鋼板の大入熱溶接HAZ靭性を−40℃で保証するための技術を説明する。ここでのHAZ靭性に関する技術課題は二つである。一つ目の課題は、−40℃という低い試験温度に起因して脆性破壊が生じやすくなることである。二つ目の課題は、大入熱溶接に伴うHAZ組織の粗大化によって脆化することである。   A technique for assuring the high heat input HAZ toughness of the low-C, high-Ni steel sheet, which is the first problem, at -40 ° C will be described. There are two technical issues related to HAZ toughness. The first problem is that brittle fracture is likely to occur due to a test temperature as low as −40 ° C. The second problem is that the HAZ structure becomes brittle due to the coarsening of the HAZ structure accompanying high heat input welding.

一つ目の課題に対して、低温での脆性破壊には局部脆化相の存在とマトリックス(フェライト地)の靭性が大きく影響することから、C低減とNi増加を基本思想とする。C低減は局部脆化相であるC濃化相(セメンタイト、パーライト、MA:Martensite−Austenite constituent)の減少を、Ni増加は固溶Niによるマトリックス(フェライト相)の高靭化を意図する。この理由から、Cを0.08%未満に抑え、Niを0.5%よりも多く含有させる。   For the first problem, the brittle fracture at low temperature is greatly influenced by the presence of the local embrittlement phase and the toughness of the matrix (ferrite ground), so the basic idea is to reduce C and increase Ni. The C reduction is intended to reduce the C concentrated phase (cementite, pearlite, MA), which is a local embrittlement phase, and the Ni increase is intended to increase the toughness of the matrix (ferrite phase) due to solid solution Ni. For this reason, C is suppressed to less than 0.08% and Ni is contained in an amount of more than 0.5%.

二つ目の課題に対して、大入熱溶接においてHAZ組織を微細化する必要がある。鉄と鋼、第62年(1976)、第9号、p.1209−1218、「低炭素・低合金鋼のオーステナイト粒度に及ぼすTiNの分散状態の影響」に記載されているように、オーステナイト(γ)結晶粒の粗大化抑制を狙った析出物によるγ粒界移動のピン止め現象が有効である。この技術をさらに進化させたものとして、発明者らは特開2000−080436号に記載されているように、Mgを含有する超微細な酸化物を生成させてこれにTiNを複合析出させることでピン止めを強化する新しい技術を発明した。これらの技術によってHAZにおけるγ結晶粒粗大化を抑制すると、γ粒界から変態する粗大組織がγ細粒化に伴って微細化し、これらγ粒界変態組織の靭性への有害性が軽減される。HAZ組織を微細化するもう一つの手段は、γ粒内の析出物をフェライト変態核として活用する技術である。たとえば、特開昭60−245768号公報、特開昭60−152626号公報、特開昭63−210235号公報、特開平2−250917号公報に記載されているように、γ粒内の析出物からのフェラト変態が有効である。発明者らは先に示した特開2000−080436号において、Mgを含有する粗大な酸化物をフェライト変態核として活用し、ピン止め効果と組み合わせる技術を発明した。このような手段でピン止めによるγ細粒化効果と析出物からのγ粒内変態効果を組み合わせても、低C高Ni成分の厚手高強度鋼板を大入熱溶接したHAZにおいて、−40℃で100J以上の靭性を安定的に確保することは難しい。   For the second problem, it is necessary to refine the HAZ structure in high heat input welding. Iron and steel, 62nd year (1976), No. 9, p. 1209-1218, γ grain boundaries due to precipitates aimed at suppressing coarsening of austenite (γ) grains, as described in “Influence of TiN dispersion state on austenite grain size of low carbon / low alloy steel” The pinning phenomenon of movement is effective. As a further advancement of this technology, the inventors have produced an ultrafine oxide containing Mg and compositely precipitated TiN on this as described in JP-A-2000-080436. Invented a new technology to enhance pinning. When these techniques suppress the coarsening of γ grains in HAZ, the coarse structure transformed from the γ grain boundaries becomes finer as the γ grains become finer, and the harmfulness of these γ grain boundary transformed structures to the toughness is reduced. . Another means for refining the HAZ structure is a technique of utilizing precipitates in γ grains as ferrite transformation nuclei. For example, as described in JP-A-60-245768, JP-A-60-152626, JP-A-63-1210235, and JP-A-2-2501717, precipitates in γ grains Ferrat transformation from is effective. The inventors have invented a technique in which a coarse oxide containing Mg is utilized as a ferrite transformation nucleus and combined with a pinning effect in Japanese Patent Application Laid-Open No. 2000-080436 described above. Even if the γ grain refinement effect by pinning and the γ intragranular transformation effect from the precipitates are combined by such means, in a HAZ in which a thick high strength steel sheet having a low C and high Ni content is welded with high heat input, −40 ° C. Therefore, it is difficult to stably secure a toughness of 100 J or more.

そこで、本発明では大入熱溶接HAZ組織をさらに微細にすることを検討した。そして、ピン止め強化によるγ細粒化を基本技術として、冷却時のHAZにおいてγ粒界とγ粒内の両方にVNを析出させる技術を組み合わせることで、HAZ組織が一段と微細化できることを見出した。このときのHAZ組織の微細化は、γ粒界からの変態組織とγ粒内から変態組織に大別できるが、本発明ではγ粒界からの変態組織の微細化が特徴であり重要である。   Therefore, in the present invention, further study was made to further refine the high heat input welded HAZ structure. And, it was found that the HAZ structure can be further refined by combining the technique of precipitating VN in both the γ grain boundary and the γ grain in the HAZ at the time of cooling using γ fine graining by pinning strengthening as a basic technology. . The refinement of the HAZ structure at this time can be broadly divided into a transformation structure from the γ grain boundary and a transformation structure from the inside of the γ grain. In the present invention, the transformation structure from the γ grain boundary is characterized and important. .

本発明におけるγ粒界からの変態組織の微細化は、以下の四つの効果によって達成される。第一の効果は、ピン止めによるγ細粒化によってγ粒界の曲率が大きくなることで、γ粒界からの変態組織が生成して成長する過程で隣接する結晶粒との合体が困難となり、変態組織の粗大化が抑制されることである。第二の効果は、γ細粒化によってγ粒界の面積が増加することで、変態場所そのものが増えてγ粒界からの変態組織が微細化することである。第三の効果は、γ粒成長をピン止めしている粒子が変態場所として機能することでγ粒からの界変態組織が微細化することである。これら三つの効果は特開2000−080436号のような従来技術に既に織り込み済みである。そして、本発明の新規性である第四の効果は、γ粒界に析出したVNが優先的な変態場所として機能することで、γ粒界からの変態組織が微細化することである。この第四の効果は上記三つの効果に重畳することで増幅されるが、特に第三の効果であるピン止め粒子との相乗効果が大きい。γ粒界にピン止め粒子とVNが共存する形態として、複合と単独の二種類が存在することが明らかになった。γ粒界に存在するピン止め粒子にVNの複合した粒子は、変態促進能が極めて高く、一つの粒子から複数の変態組織を生成させる特殊な能力があることがわかった。   The refinement of the transformation structure from the γ grain boundary in the present invention is achieved by the following four effects. The first effect is that the curvature of the γ grain boundary increases due to the γ grain refinement by pinning, which makes it difficult to merge with adjacent crystal grains in the process of generating and growing the transformation structure from the γ grain boundary. The coarsening of the transformation structure is suppressed. The second effect is that the area of the γ grain boundary is increased by the γ grain refinement, whereby the transformation sites themselves are increased and the transformation structure from the γ grain boundary is refined. The third effect is that the grain transformation structure from the γ grains is refined by the particles that pin the growth of the γ grains functioning as transformation sites. These three effects have already been incorporated into the prior art such as Japanese Patent Laid-Open No. 2000-080436. And the 4th effect which is novel of this invention is that the transformation structure | tissue from a gamma grain boundary refines | miniaturizes because VN which precipitated to the gamma grain boundary functions as a preferential transformation place. This fourth effect is amplified by superimposing on the above three effects, but the synergistic effect with the pinning particles, which is the third effect, is particularly great. It has been clarified that there are two types of composites and singles as forms in which pinning particles and VN coexist at the γ grain boundary. It has been found that a particle in which VN is combined with pinning particles existing at the γ grain boundary has a very high transformation promoting ability and a special ability to generate a plurality of transformation structures from one particle.

このとき、ピン止め粒子が10nmよりも小さいと、これにVNが複合析出する頻度が激減するため、γ粒界におけるVN析出の効果が減少する。したがって、HAZの冷却時におけるγ粒界でのVN析出に先立ち、γ粒界に10nm以上の大きさのピン止め粒子を多数存在させておくことが重要である。一方、γ粒界に単独析出するVNからは概ね一つの変態組織が生成することがわかった。   At this time, if the pinning particles are smaller than 10 nm, the frequency of the composite precipitation of VN is drastically reduced, so that the effect of VN precipitation at the γ grain boundary is reduced. Therefore, it is important that a large number of pinning particles having a size of 10 nm or more exist at the γ grain boundary prior to VN precipitation at the γ grain boundary during cooling of the HAZ. On the other hand, it has been found that one transformation structure is generated from VN that precipitates alone at the γ grain boundary.

このように、γ粒界に存在する複合析出および単独析出のVNがγ粒界からの変態組織の微細化に大きく貢献していることを知見した。このように、本発明の特徴はγ粒界に存在する複合析出VNによる変態促進効果である。ピン止め現象を用いることなくγ粒を小さくした場合(たとえばHAZの加熱温度が低い場合)、γ粒界には単独析出したVNしか存在しないため、γ粒界からの変態組織の微細化効果は本発明より劣る結果となった。VNのもう一方の析出場所であるHAZのγ粒内においては、析出したVNを核としてフェライト変態が促され、これもHAZ組織微細化に貢献する。   Thus, it has been found that the composite precipitation and single precipitation VN existing at the γ grain boundary greatly contribute to the refinement of the transformation structure from the γ grain boundary. Thus, the feature of the present invention is the effect of promoting the transformation by the composite precipitation VN existing at the γ grain boundary. When the γ grain is made small without using the pinning phenomenon (for example, when the heating temperature of the HAZ is low), only the VN precipitated alone exists at the γ grain boundary, so the effect of refining the transformation structure from the γ grain boundary is The result was inferior to that of the present invention. In the HAZ γ grains, which is the other precipitation site of VN, ferrite transformation is promoted with the precipitated VN as a nucleus, which also contributes to the refinement of the HAZ structure.

以上説明したピン止めとVN析出との相乗効果を、低C高Ni成分の厚手高強度鋼板に組み合わせることで、大入熱溶接したHAZにおいて−40℃で100J以上の靭性を安定的に確保できる技術を発明した。   By combining the synergistic effect of pinning and VN precipitation described above with a thick, high-strength steel sheet having a low C and high Ni content, it is possible to stably secure a toughness of 100 J or more at −40 ° C. in HAZ subjected to high heat input welding. Invented technology.

次に、第二の課題である高C低Ni成分鋼板の大入熱溶接HAZ靭性を0℃で保証するための技術を説明する。ここでの主な技術課題はHAZ組織の微細化である。この場合はHAZ靭性の試験温度が0℃と比較的高いので、第一の課題のようにCを少なくしてNiを多くする必要性は小さい。本発明では経済的な見地から、許容される範囲でCを多くしてNiを少なくすることを前提とする。つまり、Cを0.08%以上に高め、Niを1.0%以下に抑えることで厚鋼板に経済性を付与する。高C化は建築用鋼板に要求される低降伏比の観点からも好ましい。この基本成分に上述したHAZ組織微細化技術、つまりピン止めとVN析出の相乗効果を組み合わせることで、大入熱溶接したHAZにおいて0℃で100J以上の靭性を安定的に確保できる技術を発明した。   Next, a technique for ensuring the high heat input welding HAZ toughness at 0 ° C. of the high C, low Ni component steel sheet, which is the second problem, will be described. The main technical issue here is the refinement of the HAZ structure. In this case, since the test temperature of the HAZ toughness is relatively high at 0 ° C., the necessity for increasing the Ni by decreasing the C as in the first problem is small. In the present invention, from an economic point of view, it is assumed that Ni is reduced by increasing C within an allowable range. That is, by increasing C to 0.08% or more and suppressing Ni to 1.0% or less, the thick steel plate is provided with economy. High C is also preferable from the viewpoint of the low yield ratio required for building steel sheets. By inventing the HAZ microstructure refinement technology described above, that is, the synergistic effect of pinning and VN precipitation, invented a technology that can stably secure a toughness of 100 J or more at 0 ° C. in HAZ subjected to high heat input welding. .

以上説明したように、本発明の肝心な点は、HAZ組織微細化を目的にしたピン止め効果とVN析出効果を同時に利用することである。これら二つの金属学的な効果を具体的に発現させるための方法を説明する。ピン止め効果については、従来のピン止め粒子であるTiNよりも熱的に安定な酸化物や硫化物を利用し、これらの粒子を鋼中に高密度に分散させるために微細化をはかる。そのために、CaやMgといったOやSと親和力の強い元素を利用する。溶鋼精錬においてSi、Mn、Alを添加して予備脱酸を行った後、CaやMgを添加して最終の脱酸と脱硫を行い、連続鋳造する。CaやMgの添加時期が不適切だと、大きさが500nmを超える粗大な酸化物や硫化物が多数生成し、10〜500nmの微細粒子を1000個/mm2以上確保できないため目的とするピン止め効果が得られない。また、CaやMgの添加量が不足すると、これらを含む酸化物や硫化物のピン止め粒子の個数と大きさの両方が減少して不足となり、ピン止め効果とVN析出効果が不十分となる。 As described above, the essential point of the present invention is to simultaneously use the pinning effect and the VN precipitation effect for the purpose of refining the HAZ structure. A method for specifically expressing these two metallurgical effects will be described. Regarding the pinning effect, oxides and sulfides that are more thermally stable than TiN, which is a conventional pinning particle, are used, and refinement is performed in order to disperse these particles in steel at a high density. For this purpose, elements having strong affinity for O and S such as Ca and Mg are used. In molten steel refining, Si, Mn, and Al are added for preliminary deoxidation, and then Ca and Mg are added for final deoxidation and desulfurization, and continuous casting is performed. If the addition time of Ca or Mg is inappropriate, a large number of coarse oxides and sulfides having a size exceeding 500 nm are generated, and it is not possible to secure 1000 particles / mm 2 or more of 10-500 nm fine particles. Stop effect cannot be obtained. Further, when the amount of Ca or Mg added is insufficient, both the number and size of pinning particles of oxides and sulfides containing these decrease and become insufficient, and the pinning effect and the VN precipitation effect become insufficient. .

次に、VN析出効果については、必要最低限のVN析出量を確保するために、VとNを適正に添加する必要がある。VとNの適正バランスは、次式(1)に示される。   Next, regarding the VN precipitation effect, it is necessary to add V and N appropriately in order to ensure the minimum amount of VN precipitation. The proper balance between V and N is shown in the following equation (1).

0.05V ≦ N ≦ 0.27V ・・・・・・・・・・・・・・ (1)
これはVより強力な窒化物形成元素が含まれない場合であり、添加されたVが少なくともその0.05倍のNと結合してVNを形成する必要があることを示す。しかし、Vと化学量論的に見合う0.27倍のNよりも過剰にNが含まれると、VNを形成して余ったNがマトリックスに固溶して脆化をもたらす。したがって、式(1)のバランスでVとNを添加する必要がある。Vよりも強力な窒化物形成元素であるTi、Nb、Bなどが添加される場合は、冷却時のHAZにおけるVNの析出に先立って、TiN、NbN、BNなどがγ相の高温側で析出することを考える必要がある。このような場合には、次式(2)に示すバランスでNを添加する必要がある。
0.29Ti+0.15Nb+1.30B+0.05V ≦ N ≦ 0.29Ti+0.15Nb+1.30B+0.27V ・・・・・・・・・・・・・・・ (2)
つまり、TiやNbやBと化学量論的に見合うNを差し引いた残りのNがVと結合できると考える。実際の窒化物の析出挙動は複雑であるが、本発明では式(1)や式(2)を目安にVN析出を制御すれば、工業的にHAZ組織を微細化できることを知見したのである。
0.05V ≤ N ≤ 0.27V (1)
This is the case when no nitriding element stronger than V is included, indicating that the added V needs to combine with at least 0.05 times N to form VN. However, if N is contained in excess of 0.27 times N which is stoichiometrically commensurate with V, the excess N formed by forming VN causes solid solution in the matrix and causes embrittlement. Therefore, it is necessary to add V and N in the balance of formula (1). When Ti, Nb, B or the like, which is a nitride forming element stronger than V, is added, TiN, NbN, BN, etc. are precipitated on the high temperature side of the γ phase prior to VN precipitation in the HAZ during cooling. You need to think about what to do. In such a case, it is necessary to add N in the balance shown in the following formula (2).
0.29Ti + 0.15Nb + 1.30B + 0.05V ≦ N ≦ 0.29Ti + 0.15Nb + 1.30B + 0.27V (2)
That is, it is considered that the remaining N obtained by subtracting N that is stoichiometrically compatible with Ti, Nb, or B can be combined with V. The actual precipitation behavior of nitrides is complicated, but in the present invention, it has been found that the HAZ structure can be refined industrially by controlling the VN precipitation based on the formulas (1) and (2).

以下に化学成分の限定理由について詳細に説明する。   The reason for limiting the chemical components will be described in detail below.

Cは厚手母材の強度と靭性を確保するために0.03%以上必要であり、これが下限である。−40℃のような低温で大入熱溶接HAZ靭性を確保する場合は、Cを0.08%未満に抑える必要がある。0℃のような比較的高い温度で大入熱溶接HAZ靭性を確保する場合は、Cを0.08%以上に高めても問題ないから、経済性と低降伏比の観点からできるだけ高いC量が望まれる。しかしながら、Cが0.2%を超えるとたとえ0℃でも良好なHAZ靭性を確保することは難しいから、これが上限である。   C is required to be 0.03% or more in order to ensure the strength and toughness of the thick base material, and this is the lower limit. When securing high heat input welding HAZ toughness at a low temperature such as −40 ° C., C needs to be suppressed to less than 0.08%. When securing high heat input HAZ toughness at a relatively high temperature such as 0 ° C., there is no problem even if C is increased to 0.08% or more. Therefore, the C content is as high as possible from the viewpoint of economy and low yield ratio. Is desired. However, if C exceeds 0.2%, it is difficult to ensure good HAZ toughness even at 0 ° C., so this is the upper limit.

Siは脱酸元素および強化元素として有効であるが、0.5%を超えるとHAZ靭性が大きく劣化するためこれが上限である。SiはMA生成を助長して大入熱溶接HAZ靭性を劣化させる傾向があるため、本発明ではできるだけ少ないほうが好ましい。   Si is effective as a deoxidizing element and strengthening element, but if it exceeds 0.5%, the HAZ toughness is greatly deteriorated, so this is the upper limit. Since Si tends to promote MA generation and deteriorate high heat input welding HAZ toughness, it is preferably as small as possible in the present invention.

Mnは厚手母材の強度と靭性を経済的に確保するために0.5%以上必要である。ただし、2%を超えてMnを添加すると、中心偏析の有害性が顕著となってこの部分の母材とHAZの靭性が劣化するため、これが上限である。   Mn is required to be 0.5% or more in order to economically secure the strength and toughness of the thick base material. However, if Mn is added in excess of 2%, the hazard of central segregation becomes significant, and the toughness of the base material and HAZ in this portion deteriorates, so this is the upper limit.

Pは不純物元素であり、HAZ靭性を安定的に確保するために0.015%以下に低減する必要がある。   P is an impurity element and needs to be reduced to 0.015% or less in order to stably secure the HAZ toughness.

SはHAZにおけるピン止めの観点から、CaやMgを含む微細な硫化物を生成して有用であるため、0.001%以上必要である。Sが0.001%未満ではピン止め粒子である硫化物の個数と大きさが不足する。しかし、Sが0.005%を超えて含まれると粗大な硫化物が生成して母材やHAZの靭性を損なうため、これが上限である。   From the viewpoint of pinning in HAZ, S is useful because it produces fine sulfides containing Ca and Mg, so 0.001% or more is necessary. If S is less than 0.001%, the number and size of sulfides as pinning particles are insufficient. However, when S exceeds 0.005%, coarse sulfides are generated and the toughness of the base material and HAZ is impaired, so this is the upper limit.

Alは脱酸を担い、不純物元素であるOを0.004%以下に低減するために必要である。Al以外にもMnやSiも脱酸に寄与するが、たとえこれらの元素が添加される場合でも、0.001%以上のAlがないと安定的にOを0.004%以下に抑えることは難しい。ただし、Alが0.1%を超えると、アルミナ系の粗大酸化物やそのクラスターが生成し、母材とHAZの機械的性質が損なわれるため、これが上限である。   Al is necessary for deoxidation and to reduce O, which is an impurity element, to 0.004% or less. In addition to Al, Mn and Si also contribute to deoxidation, but even when these elements are added, if 0.001% or more Al is not present, O can be stably suppressed to 0.004% or less. difficult. However, if Al exceeds 0.1%, an alumina-based coarse oxide or cluster thereof is generated, and the mechanical properties of the base material and the HAZ are impaired, so this is the upper limit.

V は本発明で最も重要である。大入熱溶接の遅い冷却速度に起因してHAZ冷却時にγ粒界とγ粒内にVNが析出し、これが変態場所として機能することで変態組織の微細化をもたらす。そのために必要な下限のVは0.02%である。Vが0.1%を超えるとHAZの析出硬化が顕著となってHAZ靭性が劣化し、溶接性も損なわれる。したがって、これが上限である。   V is most important in the present invention. Due to the slow cooling rate of high heat input welding, VN precipitates in the γ grain boundaries and γ grains during HAZ cooling, and this functions as a transformation site, resulting in refinement of the transformation structure. The lower limit V required for this is 0.02%. When V exceeds 0.1%, precipitation hardening of HAZ becomes remarkable, HAZ toughness deteriorates, and weldability is also impaired. Therefore, this is the upper limit.

Nは本発明で重要である。VNを生成させるために、Vの下限に合わせて少なくとも0.001%のNが必要である。しかし、Nが0.02%を超えると連続鋳造における鋳片表面割れが顕著となるため、これが上限である。Vとその他の窒化物形成元素に合わせてVN析出量を制御するために式(1)、式(2)を満たす必要がある。これらの式に対してNが不足すると変態核としてのVNが不足し、Nが過剰であると固溶Nによってマトリクスが脆化する。   N is important in the present invention. In order to generate VN, N of at least 0.001% is required in accordance with the lower limit of V. However, if N exceeds 0.02%, slab surface cracks in continuous casting become significant, so this is the upper limit. In order to control the amount of VN precipitation according to V and other nitride forming elements, it is necessary to satisfy the expressions (1) and (2). When N is insufficient with respect to these formulas, VN as a transformation nucleus is insufficient, and when N is excessive, the matrix is embrittled by solid solution N.

Oはピン止め粒子である10〜500nmの酸化物を1000個/mm2以上確保するために0.001%以上必要である。Oが0.001%未満では、ピン止め粒子である酸化物の個数と大きさが不足する。しかし、Oが0.004%を超えると酸化物の一部が粗大化して母材とHAZの靭性が損なわれるため、これが上限である。 O is required to be 0.001% or more in order to secure 1000 / mm 2 or more of oxide of 10 to 500 nm as pinning particles. If O is less than 0.001%, the number and size of oxides as pinning particles are insufficient. However, if O exceeds 0.004%, part of the oxide is coarsened and the toughness of the base material and the HAZ is impaired, so this is the upper limit.

Ca、Mgは本発明で重要である。先に説明した溶鋼への添加順序を考慮して一方あるいは両方を0.0003%以上添加することで、CaやMgを含有する10〜500nmの酸化物や硫化物を1000個/mm2以上確保することができる。CaやMgが0.0003%未満では、ピン止め粒子である酸化物や硫化物の個数と大きさが不足する。しかし、それぞれ0.005%以上の多量添加は酸化物や硫化物の粗大化をまねき、所定の分散状態を確保できず、さらには経済性も失うため、これが上限である。 Ca and Mg are important in the present invention. Considering the order of addition to the molten steel described above, adding one or both of 0.0003% or more ensures that 1000 or more oxides / sulfides containing Ca and Mg are contained at 1000 pieces / mm 2 or more. can do. If Ca and Mg are less than 0.0003%, the number and size of oxides and sulfides as pinning particles are insufficient. However, addition of a large amount of 0.005% or more leads to coarsening of oxides and sulfides, and a predetermined dispersion state cannot be ensured. Further, the cost is lost, so this is the upper limit.

Cu、Cr、Mo、Nb、Tiは板厚に応じて母材の強度と靭性を確保するために添加される。これらの元素が効果を発揮する下限は、Cu、Cr、Moについては0.05%であり、NbとTiについては0.003%である。ただし、これらの元素が多すぎるとHAZ靭性や溶接性が劣化するため、上限をもうける必要がある。Cu、Cr、Moの上限は1%であり、NbとTiの上限は0.03%である。   Cu, Cr, Mo, Nb, and Ti are added to ensure the strength and toughness of the base material according to the plate thickness. The lower limit of the effect of these elements is 0.05% for Cu, Cr and Mo, and 0.003% for Nb and Ti. However, if there are too many of these elements, the HAZ toughness and weldability deteriorate, so an upper limit must be provided. The upper limit of Cu, Cr, and Mo is 1%, and the upper limit of Nb and Ti is 0.03%.

Niは大入熱溶接HAZ靭性の保証温度に応じて使い分けられる。−40℃のような低温でHAZ靭性を確保する場合は、C低減と併せてNiを0.05%以上に高めてマトリックスを高靭化する必要がある。しかしながらNiが3%を超えると厚鋼板として経済性を大きく損なうため、これが上限である。0℃のような比較的高い温度でHAZ靭性を確保する場合は、C増加と併せてNiを1.0%以下に低めても問題ないから、経済性の観点からできるだけ低いNi量が望まれる。   Ni is selectively used according to the guaranteed temperature of high heat input HAZ toughness. In order to ensure HAZ toughness at a low temperature such as −40 ° C., it is necessary to increase Ni to 0.05% or more in combination with C reduction to make the matrix highly tough. However, if Ni exceeds 3%, the economical efficiency of the steel plate is greatly impaired, so this is the upper limit. When securing HAZ toughness at a relatively high temperature such as 0 ° C., there is no problem even if Ni is lowered to 1.0% or less in combination with an increase in C. Therefore, a Ni amount as low as possible is desired from the viewpoint of economy. .

Bは厚手母材の製造において焼入性を高めて強度と靭性の確保に寄与する。この効果を発揮するためには、0.0003%以上のBが必要である。ただし、Bが0.003%を超えると溶接性が劣化する恐れがあるため、これが上限である。   B contributes to securing strength and toughness by increasing hardenability in the production of thick base materials. In order to exhibit this effect, 0.0003% or more of B is necessary. However, if B exceeds 0.003%, the weldability may deteriorate, so this is the upper limit.

次に、本発明を適用した鋼板の製造方法の例を説明する。鉄鋼業の製鋼工程において、Si、Mn、Alを溶鋼に添加して予備脱酸を行った後、CaやMgを添加して最終の脱酸と脱硫を行い、連続鋳造によって鋳片を造る。鋳造時の冷却途中あるいは冷却後に鋼片を再加熱し、厚板圧延によって所定の厚みの鋼板を造り、圧延後に空冷するか、あるいは水冷する。水冷途中で水冷を停止して空冷することもある。冷却後に適当な熱処理を行うことで、母材の強度と靭性を調整する。   Next, the example of the manufacturing method of the steel plate to which this invention is applied is demonstrated. In the steelmaking process of the steel industry, Si, Mn, and Al are added to molten steel, and after preliminary deoxidation, Ca and Mg are added to perform final deoxidation and desulfurization, and a slab is produced by continuous casting. The steel slab is reheated during or after cooling at the time of casting, a steel plate having a predetermined thickness is produced by thick plate rolling, and air-cooled or water-cooled after rolling. In the middle of water cooling, water cooling may be stopped and air cooling may be performed. The strength and toughness of the base material are adjusted by performing an appropriate heat treatment after cooling.

製鋼工程で溶鋼の脱酸、脱硫手順と化学成分を制御して連続鋳造によって鋼片を作製し、これを再加熱して厚板圧延によって20〜100mm厚みの鋼板とし、空冷あるいは水冷を行った。必要に応じて熱処理を施し、降伏強度が340〜480MPa級である厚鋼板を製造した。表1に鋼の化学成分とピン止め粒子個数を、表2に鋼板の機械的性質と1パス溶接継手のHAZ靭性を示す。成分は低C高Ni系と高C低Ni系に大別される。ピン止め粒子の個数は、次のような方法で測定した。鋼板の任意の場所から抽出レプリカ資料を作成し、これを透過型電子顕微鏡(TEM)を用いて10000〜50000倍で1000μm2以上の面積を観察し、対象となる10〜500nmの大きさのCaまたは/およびMgを含む酸化物または/および硫化物の個数を測定し、単位面積あたりの個数に換算した。このとき、これらの酸化物や硫化物に析出物が複合析出している場合も測定の対象となる。また、酸化物と硫化物が複合して酸硫化物となっていても測定の対象となる。低C高Ni成分鋼板についてはエレクトロガス溶接法を用いて図1に示すような突合せ継手を作製した。高C低Ni成分鋼板については、エレクトロスラグ溶接法を用いて図2に示すようなT字継手を作製した。ともに1パスの大入熱溶接継手である。図1と図2に示す要領で、溶解融線(FL)から1mm離れたHAZ、あるいはFLにノッチを入れ、−40℃あるいは0℃でシャルピー衝撃試験を行った。表2にHAZ靭性を示す。ここでのシャルピー衝撃試験はJIS Z 2242に準拠し、JIS Z 2202のVノッチ試験片を用いた。 A steel piece was produced by continuous casting by controlling the deoxidation and desulfurization procedures and chemical components of the molten steel in the steel making process, and this was reheated to obtain a steel plate having a thickness of 20 to 100 mm by thick plate rolling, and air cooling or water cooling was performed. . Heat treatment was performed as necessary to produce a thick steel plate having a yield strength of 340 to 480 MPa. Table 1 shows the chemical composition of the steel and the number of pinning particles, and Table 2 shows the mechanical properties of the steel sheet and the HAZ toughness of the one-pass welded joint. Ingredients are broadly classified into low C high Ni system and high C low Ni system. The number of pinning particles was measured by the following method. An extraction replica material is created from an arbitrary place on the steel plate, and this is observed using a transmission electron microscope (TEM) at a magnification of 10,000 to 50,000 times and an area of 1000 μm 2 or more, and the target Ca is 10 to 500 nm in size. Alternatively, the number of oxides and / or sulfides containing Mg was measured and converted to the number per unit area. At this time, even in the case where precipitates are complexly deposited on these oxides and sulfides, they are also subject to measurement. Moreover, even if an oxide and a sulfide are combined to form an oxysulfide, it is an object of measurement. A butt joint as shown in FIG. 1 was produced by using an electrogas welding method for the low C high Ni component steel sheet. About the high C low Ni component steel plate, the T-shaped joint as shown in FIG. 2 was produced using the electroslag welding method. Both are high-heat input welded joints with one pass. As shown in FIGS. 1 and 2, a notch was made in HAZ or FL 1 mm away from melt melting line (FL), and a Charpy impact test was performed at −40 ° C. or 0 ° C. Table 2 shows the HAZ toughness. The Charpy impact test here was based on JIS Z 2242, and a JIS Z 2202 V-notch test piece was used.

鋼1〜14は本発明鋼であり、鋼の化学成分と粒子分散状態が適正に制御されているため、−40℃あるいは0℃で100Jを超える良好なHAZ靭性が達成されている。一方、鋼13〜20は比較鋼であり、鋼の化学成分や粒子分散状態が適正でないために、HAZ靭性が不十分である。鋼13と鋼17はVが少ないために、鋼14と鋼18はNが少ないために、HAZにおけるVN析出量が不十分となり、HAZ組織の微細化が不十分で靭性が低下している。鋼15と鋼19はVNは十分に生成してHAZ組織が微細化されるものの、Nが多すぎるために固溶N脆化が原因でHAZ靭性が低下している。鋼16と鋼20はVNは十分い生成しているものの、CaやMgが添加されていないためにピン止め粒子である酸化物や硫化物の個数が不足し、HAZのγ粒が粗大化して靭性が低下している。   Steels 1 to 14 are steels of the present invention, and the chemical composition and particle dispersion state of the steel are appropriately controlled, so that a good HAZ toughness exceeding 100 J is achieved at -40 ° C or 0 ° C. On the other hand, the steels 13 to 20 are comparative steels, and the HAZ toughness is insufficient because the chemical components and the particle dispersion state of the steel are not appropriate. Since the steel 13 and the steel 17 have a small V, the steel 14 and the steel 18 have a small N, so the amount of VN precipitation in the HAZ is insufficient, the HAZ structure is not sufficiently refined, and the toughness is reduced. In Steel 15 and Steel 19, although VN is sufficiently generated and the HAZ structure is refined, the HAZ toughness is lowered due to the solid solution N embrittlement because N is too much. Steel 16 and Steel 20 generate a sufficient amount of VN, but because Ca and Mg are not added, the number of pinning particles such as oxides and sulfides is insufficient, and HAZ γ grains are coarsened. Toughness is reduced.

低C高Ni成分鋼板のエレクトロガス溶接突合せ継手におけるシャルピー試験片の採取要領を示す図である。It is a figure which shows the extraction | collection point of the Charpy test piece in the electrogas welding butt joint of a low C high Ni component steel plate. 高C低Ni成分鋼板のエレクトロスラグ溶接T字継手におけるシャルピー試験片の採取要領を示す図である。It is a figure which shows the extraction | collection point of the Charpy test piece in the electroslag welding T-shaped joint of a high C low Ni component steel plate.

Claims (2)

質量%で、
C :0.03〜0.2%、
Si:0.5%以下、
Mn:0.5〜2%、
P :0.015%以下、
S :0.001〜0.005%、
Al:0.001〜0.1%、
V :0.02〜0.1%、
N :0.001〜0.02%、
O :0.001〜0.004%
を含有し、
Ca:0.0003〜0.005%、
Mg:0.0003〜0.005%
の一種以上を含有し、質量%を用いて計算される式(1)を満たし、残部が鉄および不可避的不純物によって化学成分が構成され、Caまたは/およびMgを含む10〜500nmの酸化物または/および硫化物が1000個/mm2以上存在することを特徴とする、大入熱溶接熱影響部の靭性に優れた厚鋼板。
0.05V ≦ N ≦ 0.27V ・・・・・・・・ (1)
% By mass
C: 0.03-0.2%,
Si: 0.5% or less,
Mn: 0.5-2%
P: 0.015% or less,
S: 0.001 to 0.005%,
Al: 0.001 to 0.1%,
V: 0.02 to 0.1%,
N: 0.001 to 0.02%,
O: 0.001 to 0.004%
Containing
Ca: 0.0003 to 0.005%,
Mg: 0.0003 to 0.005%
An oxide of 10 to 500 nm that contains one or more of the following, satisfies the formula (1) calculated using mass%, the remainder is composed of iron and unavoidable impurities, and contains Ca or / and Mg: / And a thick steel plate excellent in toughness of a heat-affected zone with high heat input welding, characterized in that 1000 / mm 2 or more of sulfides are present.
0.05V ≤ N ≤ 0.27V (1)
質量%で、
C :0.03〜0.2%、
Si:0.5%以下、
Mn:0.5〜2%、
P :0.015%以下、
S :0.001〜0.005%、
Al:0.001〜0.1%、
V :0.02〜0.1%、
N :0.001〜0.02%、
O :0.001〜0.004%
を含有し、
Ca:0.0003〜0.005%、
Mg:0.0003〜0.005%
うち、Mgの一種を、またはCaとMgの二種を含有し、さらに
Cu:0.05〜1%、
Ni:0.05〜3%、
Cr:0.05〜1%、
Mo:0.05〜1%、
Nb:0.003〜0.03%、
Ti:0.003〜0.03%、
B :0.0003〜0.003%
一種以上を含有し、質量%を用いて計算される式(2)を満たし、残部が鉄および不可避的不純物によって化学成分が構成され、Mgを含む、またはMgおよびCaを含む10〜500nmの酸化物または/および硫化物が1000個/mm以上存在することを特徴とする、大入熱溶接熱影響部の靭性に優れた厚鋼板。
0.29Ti+0.15Nb+1.30B+0.05V ≦ N ≦ 0.29Ti+0.15Nb+1.30B+0.27V ・・・・・・・・ (2)
% By mass
C: 0.03-0.2%,
Si: 0.5% or less,
Mn: 0.5-2%
P: 0.015% or less,
S: 0.001 to 0.005%,
Al: 0.001 to 0.1%,
V: 0.02 to 0.1%,
N: 0.001 to 0.02%,
O: 0.001 to 0.004%
Containing
Ca: 0.0003 to 0.005%,
Mg: 0.0003 to 0.005%
Among them, it contains one kind of Mg, or two kinds of Ca and Mg , and further Cu: 0.05 to 1%,
Ni: 0.05-3%,
Cr: 0.05 to 1%,
Mo: 0.05 to 1%
Nb: 0.003 to 0.03%,
Ti: 0.003 to 0.03%,
B: 0.0003 to 0.003%
The chemical component is composed of iron and inevitable impurities, and the balance is 10 to 500 nm including Mg or Ca and Mg and Ca. A thick steel plate excellent in toughness of a high heat input welding heat-affected zone, characterized in that oxides and / or sulfides are present at 1000 pieces / mm 2 or more.
0.29Ti + 0.15Nb + 1.30B + 0.05V ≦ N ≦ 0.29Ti + 0.15Nb + 1.30B + 0.27V (2)
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