JP2009179844A - High tensile strength thick steel plate having excellent toughness in weld heat affected zone - Google Patents

High tensile strength thick steel plate having excellent toughness in weld heat affected zone Download PDF

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JP2009179844A
JP2009179844A JP2008019192A JP2008019192A JP2009179844A JP 2009179844 A JP2009179844 A JP 2009179844A JP 2008019192 A JP2008019192 A JP 2008019192A JP 2008019192 A JP2008019192 A JP 2008019192A JP 2009179844 A JP2009179844 A JP 2009179844A
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rem
less
insol
sulfide
steel plate
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Hidenori Nako
秀徳 名古
Yoshiomi Okazaki
喜臣 岡崎
Tetsushi Deura
哲史 出浦
Tomoko Sugimura
朋子 杉村
Hiromi Ota
裕己 太田
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Kobe Steel Ltd
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Kobe Steel Ltd
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Priority to KR1020080137115A priority patent/KR101082639B1/en
Publication of JP2009179844A publication Critical patent/JP2009179844A/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high tensile strength thick steel plate having excellent toughness in the weld heat affected zone in high heat input welding. <P>SOLUTION: The high tensile strength thick steel plate has a composition comprising, by mass, 0.02 to 0.12% C, 0 to 0.40% Si, 1.0 to 2.0% Mn, 0 to 0.03% P, 0 to 0.015% S, 0 to 0.050% Al, 0.005 to 0.100% Ti, 0.0002 to 0.0500% REM and/or 0.0003 to 0.0100% Ca, 0.0001 to 0.0500% Zr, 0.0020 to 0.0300% N and 0.0005 to 0.0100% O, and the balance Fe with inevitable impurities, in which the number of oxides present in the steel and having an equivalent circle diameter of <2 μm is ≥500 pieces/mm<SP>2</SP>, also, the number of oxides present in the steel and having an equivalent circle diameter of >5 μm is ≤5 pieces/mm<SP>2</SP>, and X value defined by formula (1): X=100×[insol Mn]/([insol REM]+[insol Ca]+0.05) from the concentrations of Mn, REM and Ca forming a compound in the steel is <10.0. In the formula, [insol Mn], [insol REM] and [insol Ca] denote the concentrations (mass%) of Mn, REM and Ca forming a compound in the steel, respectively. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、造船、建築等の分野において構造材として用いられ、大入熱溶接の適用に対し、溶接熱影響部（以下、「ＨＡＺ」と呼称する）の靭性に優れた溶接用高張力厚鋼板に関するものである。   The present invention is used as a structural material in the fields of shipbuilding, construction, and the like, and has high toughness for welding excellent in toughness of a weld heat affected zone (hereinafter referred to as “HAZ”) for application of high heat input welding. It relates to steel plates.

一般に、造船、建築等の分野において構造材として用いられる鋼材は、溶接施工により接合されることが多く、母材靭性に加えて、優れたＨＡＺ靭性を有することが必須とされる。   In general, steel materials used as structural materials in fields such as shipbuilding and construction are often joined by welding, and it is essential that they have excellent HAZ toughness in addition to base metal toughness.

近年、建築、造船分野における溶接構造物の大型化に伴い、板厚５０ｍｍ以上の厚鋼板の適用範囲が拡大しつつあり、溶接施工コスト低減の観点から、大入熱溶接が希求されている。しかしながら、一般に厚鋼板のＨＡＺは靭性劣化をきたしやすく、特に大入熱溶接において、その傾向はより顕著となる。すなわち、大入熱溶接においては、ＨＡＺは溶接時の加熱によって高温のオーステナイト域に保持された後に徐冷されるため、オーステナイト粒成長、オーステナイト粒界からの粗大粒界フェライト生成といった、組織粗大化がもたらされやすく、それに伴う靭性劣化が大きな課題となっている。   In recent years, with the increase in size of welded structures in the building and shipbuilding fields, the application range of thick steel plates with a thickness of 50 mm or more is expanding, and high heat input welding is desired from the viewpoint of reducing welding construction costs. However, in general, HAZ of thick steel plates is liable to deteriorate toughness, and the tendency becomes more remarkable particularly in high heat input welding. That is, in high heat input welding, since HAZ is gradually cooled after being held in a high temperature austenite region by heating during welding, the coarsening of the structure such as austenite grain growth and generation of coarse grain boundary ferrite from the austenite grain boundary. As a result, toughness deterioration associated with this is a major issue.

この課題に対し、ＨＡＺの靭性（以下、ＨＡＺ靭性と呼称する）を確保するための技術として、大きく分けて、酸化物、硫化物、あるいは窒化物といった介在物を利用したγ粒粗大化抑制技術、および粒内α変態促進技術が提案されている。前者は、鋼中に分散した介在物粒子がオーステナイト粒成長をピン止めすることで、高温加熱時のオーステナイト粒粗大化を抑制し、微細組織を得る技術であり、後者は、介在物を粒内α変態の起点として活用し、溶接終了後の徐冷過程における粒内α変態を促進することで、微細組織を得る技術である。   In response to this problem, as a technique for ensuring the toughness of HAZ (hereinafter referred to as HAZ toughness), γ grain coarsening suppression technology using inclusions such as oxides, sulfides, or nitrides can be roughly divided. , And intragranular α-transformation promotion techniques have been proposed. The former is a technique for suppressing the austenite grain coarsening during high-temperature heating by pinning austenite grain growth by inclusion particles dispersed in the steel, and the latter is a technique for obtaining a fine structure. It is a technique for obtaining a microstructure by utilizing the α transformation as a starting point and promoting intragranular α transformation in the slow cooling process after the end of welding.

従来、γ粒粗大化抑制、粒内α変態促進に有効な介在物として、主にＴｉＮが用いられてきた。例えば、特開２００１−２００３１号公報（特許文献１）には、組成を適切に制御したＴｉ−ＲＥＭ−Ｃａ−Ａｌ系酸化物、およびＴｉＮを利用したＨＡＺ靭性改善技術が提示されている。また、特開２００３−１６６０１７号公報（特許文献２）には、ＴｉＮによるγ粒粗大化抑制、Ｍｎ硫化物による粒内α変態促進を利用した技術が示されている。さらに、特開２００３−３２１７２８号公報（特許文献３）には、Ｍｇ酸化物を内包するＴｉＮによるγ粒粗大化抑制、ＭｎＣａＳによる粒内α変態促進を組み合わせ、高いＨＡＺ靭性を得る技術が提案されている。   Conventionally, TiN has been mainly used as an inclusion effective for suppressing γ grain coarsening and promoting intragranular α transformation. For example, Japanese Laid-Open Patent Publication No. 2001-20031 (Patent Document 1) proposes a HAZ toughness improving technique using Ti-REM-Ca-Al-based oxides with appropriately controlled compositions and TiN. Japanese Patent Application Laid-Open No. 2003-166017 (Patent Document 2) discloses a technique using suppression of γ grain coarsening by TiN and promotion of intragranular α transformation by Mn sulfide. Furthermore, Japanese Patent Laid-Open No. 2003-321728 (Patent Document 3) proposes a technique for obtaining high HAZ toughness by combining the suppression of γ grain coarsening by TiN containing Mg oxide and the promotion of intragranular α transformation by MnCaS. ing.

しかしながら、近年の溶接入熱増大傾向に対し、ＴｉＮは溶接時の消失・粗大化が進行しやすいため、安定したＨＡＺ靭性の確保が困難となりつつある。それに対し、γ粒粗大化抑制、粒内α変態促進に有効な介在物として、高温で安定な酸化物、硫化物、あるいは酸硫化物を用いた技術が提案され、数多くの検討がなされている。   However, in contrast to the recent trend of increasing welding heat input, TiN is prone to disappearance and coarsening during welding, making it difficult to ensure stable HAZ toughness. On the other hand, technologies using oxides, sulfides, or oxysulfides that are stable at high temperatures have been proposed as inclusions effective in suppressing γ grain coarsening and promoting intragranular α transformation, and many studies have been made. .

例えば、特開２００５−２０６９１０号公報（特許文献４）には、ＲＥＭ，Ｍｎ含有酸硫化物によりγ粒粗大化を抑制し、高いＨＡＺ靭性を得る技術が示されている。また、特開２００３−２８６５４０号公報（特許文献５）には、ＲＥＭを適切に制御することでＭｎ酸硫化物を微細に分散させ、γ粒粗大化を抑制する技術が提示されている。また、特開２００７−１００２１３号公報（特許文献６）には、ＲＥＭ、Ｚｒを含む酸化物を用いたγ粒粗大化抑制により、高いＨＡＺ靭性を得る技術が提案されている。また、特公平４−５４７３４号公報（特許文献７）には、ＲＥＭあるいはＣａの酸化物、硫化物にＢＮを析出させ、粒内α変態の起点とする技術が提案されている。
特開２００１−２００３１号公報 特開２００３−１６６０１７号公報 特開２００３−３２１７２８号公報 特開２００５−２０６９１０号公報 特開２００３−２８６５４０号公報 特開２００７−１００２１３号公報 特公平４−５４７３４号公報 For example, Japanese Patent Application Laid-Open No. 2005-206910 (Patent Document 4) discloses a technique for suppressing γ grain coarsening with REM and Mn-containing oxysulfides and obtaining high HAZ toughness. Japanese Patent Laid-Open No. 2003-286540 (Patent Document 5) proposes a technique for finely dispersing Mn oxysulfide by appropriately controlling REM and suppressing γ grain coarsening. Japanese Unexamined Patent Application Publication No. 2007-100133 (Patent Document 6) proposes a technique for obtaining high HAZ toughness by suppressing γ grain coarsening using an oxide containing REM and Zr. Japanese Patent Publication No. 4-54734 (Patent Document 7) proposes a technique in which BN is precipitated in an REM or Ca oxide or sulfide, and is used as a starting point of intragranular α transformation.
Japanese Patent Laid-Open No. 2001-20031 Japanese Patent Laid-Open No. 2003-166017 JP 2003-321728 A JP 2005-206910 A JP 2003-286540 A Japanese Patent Laid-Open No. 2007-1001000 Japanese Examined Patent Publication No. 4-54734

しかしながら、近年の溶接入熱増大に伴う最高加熱温度上昇、高温保持時間長時間化は、組織粗大化を助長すると同時に、溶接時のＨＡＺにおけるＭｎ硫化物溶解をもたらし、その後の冷却過程で再析出するＭｎ硫化物微細粒子が析出強化によりＨＡＺ硬度を上昇させることで、ＨＡＺ靭性低下の原因となる。そのため、従来の組織微細化技術だけでは、ＨＡＺ靭性向上の効果は限定的なものとならざるを得ず、より優れたＨＡＺ靭性を得る手段が望まれている。   However, the increase in the maximum heating temperature and the prolonged high-temperature holding time accompanying the recent increase in welding heat input promotes the coarsening of the structure and at the same time leads to Mn sulfide dissolution in the HAZ during welding and reprecipitation during the subsequent cooling process. The Mn sulfide fine particles that increase the HAZ hardness by precipitation strengthening cause a decrease in HAZ toughness. Therefore, the effect of improving the HAZ toughness is inevitably limited only by the conventional structure refinement technique, and a means for obtaining a better HAZ toughness is desired.

本発明は、上記問題に鑑みなされたもので、特に大入熱溶接において、優れたＨＡＺ靭性を有する溶接用高張力厚鋼板を提供することを目的とする。   The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-tensile steel plate for welding having excellent HAZ toughness particularly in high heat input welding.

本発明者らは、上記の課題を達成するため、γ粒粗大化抑制による組織微細化、微細Ｍｎ硫化物再析出抑制を同時に達成することで、優れたＨＡＺ靭性を得る手段について実験、検討を行った。その結果、鋳造プロセスを適切に制御することで、γ粒粗大化抑制に有効な、円相当径が２μｍより小さい酸化物を高密度で分散させることができ、さらに鋼中において化合物を形成するＭｎ、ＲＥＭ、Ｃａの濃度に基づいて、鋼中に存在するＭｎ硫化物量を表すパラメータ（後述するＸ値）を所定の値未満に制御することで、微細Ｍｎ硫化物再析出が抑制されることを見出した。本発明はかかる知見を基に完成されたものである。   In order to achieve the above-mentioned problems, the present inventors conducted experiments and examinations on means for obtaining excellent HAZ toughness by simultaneously achieving microstructure refinement by inhibiting γ grain coarsening and fine Mn sulfide reprecipitation inhibition. went. As a result, by appropriately controlling the casting process, it is possible to disperse an oxide having an equivalent circle diameter smaller than 2 μm at a high density, which is effective in suppressing γ grain coarsening, and to form a compound in steel. Based on the concentrations of REM and Ca, the parameter indicating the amount of Mn sulfide present in the steel (X value to be described later) is controlled to be less than a predetermined value to suppress the reprecipitation of fine Mn sulfide. I found it. The present invention has been completed based on such knowledge.

すなわち、本発明の溶接用高張力厚鋼板は、質量％（以下、「質量％」は単に「％」と記載する）で、
Ｃ ：０．０２〜０．１２％、
Ｓｉ：０．４０％以下（０％を含む）、
Ｍｎ：１．０〜２．０％、
Ｐ ：０．０３％以下（０％を含む）、
Ｓ ：０．０１５％以下（０％を含む）、
Ａｌ：０．０５０％以下（０％を含む）、
Ｔｉ：０．００５〜０．１００％、
ＲＥＭ：０．０００２〜０．０５００％及び／又はＣａ：０．０００３〜０．０１００％、
Ｚｒ：０．０００１〜０．０５００％
Ｎ ：０．００２０〜０．０３００％、
Ｏ ：０．０００５〜０．０１００％
を含有し、残部がＦｅおよび不可避的な不純物で構成される。組織的には、鋼中に存在する円相当径が２μｍより小さい酸化物が５００個／ｍｍ2 以上で、かつ円相当径が５μｍより大きい酸化物が５個／ｍｍ2 以下であり、鋼中において化合物を形成するＭｎ、ＲＥＭ、Ｃａの濃度から（１）式で定義されるＸ値が１０．０未満である。 That is, the high-tensile steel plate for welding of the present invention is in mass% (hereinafter, “mass%” is simply described as “%”),
C: 0.02 to 0.12%,
Si: 0.40% or less (including 0%),
Mn: 1.0-2.0%,
P: 0.03% or less (including 0%),
S: 0.015% or less (including 0%),
Al: 0.050% or less (including 0%),
Ti: 0.005 to 0.100%,
REM: 0.0002 to 0.0500% and / or Ca: 0.0003 to 0.0100%,
Zr: 0.0001 to 0.0500%
N: 0.0020 to 0.0300%,
O: 0.0005 to 0.0100%
The balance is composed of Fe and inevitable impurities. Organizationally, the number of oxides having an equivalent circle diameter of less than 2 μm existing in steel is 500 / mm 2 or more and the number of oxides having an equivalent circle diameter of more than 5 μm is 5 / mm 2 or less. The X value defined by the formula (1) is less than 10.0 based on the concentrations of Mn, REM, and Ca forming the compound.

また、上記基本成分にＡ群（Ｎｉ：０．０５〜１．５０％、Ｃｕ：０．０５〜１．５０％、Ｃｒ：０．０５〜１．５０％、Ｍｏ：０．０５〜１．５０％）、Ｂ群（Ｎｂ：０．００２〜０．１０％、Ｖ：０．００２〜０．１０％）、Ｂ：０．００１０〜０．００５０％の内、１種以上の元素を添加して下記(1) から(3) の化学組成とすることができる。
(1) 基本成分＋Ａ群から１種以上
(2) 基本成分又は上記(1) の成分＋Ｂ群から１種以上
(3) 基本成分、上記(1) 又は上記(2) の成分＋Ｂ Further, the above basic components include Group A (Ni: 0.05-1.50%, Cu: 0.05-1.50%, Cr: 0.05-1.50%, Mo: 0.05-1. 50%), Group B (Nb: 0.002-0.10%, V: 0.002-0.10%), B: 0.0010-0.0050%, one or more elements added Thus, the following chemical compositions (1) to (3) can be obtained.
(1) Basic component + 1 or more from Group A
(2) Basic component or one or more of component (1) above + Group B
(3) Basic component, component (B) above (1) or component (B) above + B

本発明の溶接用高張力厚鋼板によると、所定の鋼組成の下、円相当径で２μｍ未満の小径酸化物を用いてγ粒粗大化を抑制して組織微細化を図ると共に脆性破壊の起点となる円相当径で５μｍ超の大径酸化物の生成を抑制し、さらに微細Ｍｎ硫化物の再析出を抑制することができる化合物組成としたので、従来に比して大入熱溶接に対して優れたＨＡＺ靭性を備えたものとなる。   According to the high-strength thick steel plate for welding of the present invention, with a predetermined steel composition, a small-diameter oxide having an equivalent circle diameter of less than 2 μm is used to suppress the coarsening of γ grains and to refine the structure and to start the brittle fracture As a compound composition that can suppress the formation of large-diameter oxides with an equivalent circle diameter of more than 5 μm and further suppress the reprecipitation of fine Mn sulfide, And excellent HAZ toughness.

本発明の実施形態に係る溶接用高張力鋼板について、まず、その組織条件から以下詳細に説明する。
一般に、γ粒粗大化抑制に対しては、微細な介在物粒子を高密度に分散させる必要があり、粒子サイズが大きくなるにつれて、介在物粒子の個数密度が低下し、γ粒粗大化を抑制できなくなる。そこで、本発明者らは、十分なγ粒粗大化抑制効果が得られる介在物粒子サイズおよび個数密度を実験により求め、円相当径が２μｍより小さい酸化物を５００個／ｍｍ2 以上分散させることで、γ粒粗大化が抑制されることを見出した。円相当径が２μｍより小さい酸化物が５００個／ｍｍ2 より少ないと、必要なγ粒粗大化が得られなくなる。なお、円相当径が２μｍより小さい酸化物個数は、８００個／ｍｍ2 以上であることが好ましい。 First, the high-strength steel sheet for welding according to an embodiment of the present invention will be described in detail below from the structural conditions.
In general, to suppress γ grain coarsening, it is necessary to disperse fine inclusion particles at high density. As the particle size increases, the number density of inclusion particles decreases, and γ grain coarsening is suppressed. become unable. Accordingly, the present inventors have determined experimentally the inclusion particle size and number density at which a sufficient γ grain coarsening suppression effect can be obtained, and disperse 500 oxides / mm 2 or more of oxides having an equivalent circle diameter smaller than 2 μm. Thus, it was found that γ grain coarsening is suppressed. When the circle equivalent diameter of 2μm smaller oxide is less than 500 / mm 2, necessary γ grains coarsening can not be obtained. Note that the number of oxides having an equivalent circle diameter of less than 2 μm is preferably 800 / mm 2 or more.

また、ＨＡＺにおける微細Ｍｎ硫化物再析出を抑制する手段として、本発明者らは、Ｍｎ硫化物に比べより高温で安定なＲＥＭ硫化物及び／又はＣａ硫化物に着目し、鋼中において化合物を形成するＭｎ、ＲＥＭ、Ｃａの濃度から下記(1) 式のとおり定義されるＸ値を１０．０未満に制御することで、硫化物の主体がＣａ硫化物及び／又はＲＥＭ硫化物となり、ＨＡＺにおける微細Ｍｎ硫化物の再析出が抑制されることを見出した。
Ｘ＝100×［insol Ｍｎ］／（［insol ＲＥＭ］＋［insol Ｃａ］＋0.05）……(1)
但し、［insol Ｍｎ］、［insol ＲＥＭ］、［insol Ｃａ］は、それぞれ鋼中において化合物を形成するＭｎ、ＲＥＭ、Ｃａの濃度（％）を示す。 In addition, as a means of suppressing fine Mn sulfide reprecipitation in HAZ, the present inventors have focused on REM sulfide and / or Ca sulfide, which are stable at higher temperatures than Mn sulfide, and have added compounds in steel. By controlling the X value defined as the following formula (1) to less than 10.0 from the concentration of Mn, REM, and Ca to be formed, the main component of sulfide becomes Ca sulfide and / or REM sulfide, and HAZ It has been found that the reprecipitation of fine Mn sulfides in is suppressed.
X = 100 × [insol Mn] / ([insol REM] + [insol Ca] +0.05) (1)
However, [insol Mn], [insol REM], and [insol Ca] indicate the concentrations (%) of Mn, REM, and Ca that form compounds in the steel, respectively.

前記Ｘ値の表す技術的意味については以下のとおりである。Ｘ値は、鋼中に存在するＭｎ硫化物量を表現するパラメータである。Ｍｎ硫化物に対しては、一般的に、光学顕微鏡、あるいは走査型電子顕微鏡等を用いた組織観察により、Ｍｎ硫化物粒子の個数、またはサイズが評価される。しかしながら、本発明の成分系においては、Ｍｎ硫化物は単独で存在することが少なく、大多数が、ＲＥＭ硫化物、Ｃａ硫化物等との複合粒子として存在するため、組織観察によりＭｎ硫化物量を求めるのは困難である。よって、本発明では、Ｘ値によりＭｎ硫化物量を間接的に評価する手法を採用した。すなわち、Ｘ値が１０．０未満の時、化合物として存在するＭｎ量に対し、化合物として存在するＲＥＭ、Ｃａ量が十分確保されることで、硫化物の主体は高温でより安定なＲＥＭ硫化物、Ｃａ硫化物となり、ＨＡＺにおける微細Ｍｎ硫化物の再析出は抑制される。Ｘ値が１０．０以上となると、鋼中の硫化物の主体がＭｎ硫化物となり、微細Ｍｎ硫化物の再析出が十分に抑制されなくなる。なお、Ｘ値は８．０未満であることが望ましい。   The technical meaning of the X value is as follows. The X value is a parameter expressing the amount of Mn sulfide present in the steel. For Mn sulfide, the number or size of Mn sulfide particles is generally evaluated by structural observation using an optical microscope, a scanning electron microscope, or the like. However, in the component system of the present invention, Mn sulfide is rarely present alone, and most of the Mn sulfide is present as composite particles with REM sulfide, Ca sulfide, and the like. It is difficult to find. Therefore, in this invention, the method of indirectly evaluating the amount of Mn sulfide by the X value was adopted. That is, when the X value is less than 10.0, the amount of REM and Ca existing as a compound is sufficiently secured with respect to the amount of Mn present as a compound, so that the main component of sulfide is REM sulfide that is more stable at high temperatures. , Ca sulfide, and reprecipitation of fine Mn sulfide in HAZ is suppressed. When the X value is 10.0 or more, the main component of sulfide in the steel is Mn sulfide, and reprecipitation of fine Mn sulfide is not sufficiently suppressed. The X value is preferably less than 8.0.

良好なＨＡＺ靭性を得るためには、上記の微細酸化物分散、微細Ｍｎ硫化物再析出抑制に加え、鋼中に存在する、円相当径が５μｍより大きい酸化物を５個／ｍｍ2 以下に制御する必要がある。円相当径が５μｍより大きい酸化物が５個／ｍｍ2 を上回ると、これらの酸化物が脆性破壊の起点として作用し、靭性が悪化する。なお、円相当径が５μｍより大きい酸化物は、３個ｍｍ2 以下であることが好ましい。 In order to obtain good HAZ toughness, in addition to the above-mentioned fine oxide dispersion and fine Mn sulfide reprecipitation suppression, the number of oxides having an equivalent circle diameter larger than 5 μm in steel is 5 pieces / mm 2 or less. Need to control. When the number of oxides having an equivalent circle diameter larger than 5 μm exceeds 5 / mm 2 , these oxides act as starting points for brittle fracture, and the toughness deteriorates. The number of oxides having an equivalent circle diameter larger than 5 μm is preferably 3 mm 2 or less.

上記酸化物の分布、Ｘ値を得るには、鋳造工程において溶存酸素量、ＲＥＭ及び／又はＣａ、並びにＺｒの合金元素添加量、合金元素添加完了から鋳込み開始までの時間を以下のように制御する必要がある。すなわち、鋳造時において、Ｔｉ添加に先立ちＭｎ、Ｓｉ、Ａｌ等を添加し、Ｔｉ添加前の溶存酸素量を０．００２０〜０．０１００％に制御し、Ｔｉ添加前の溶存酸素量、硫黄量を基に、下記(2) 式から求まるＺ値が０．５８以上となるよう、ＲＥＭ及び／又はＣａ、並びにＺｒ添加量を決定したうえで、Ｔｉを添加した後に、ＲＥＭ及び／又はＣａ、並びにＺｒを添加し、さらに、これらの合金元素添加完了から鋳込み開始までの時間ｔ（ｍｉｎ）を下記(3) 式で定義される範囲に保ったうえで、鋳造時に凝固が進行する１４５０〜１５００℃の冷却時間を６０〜３００ｓに制御する。
Ｚ＝(3.5×([REM]＋[Ca])−0.7×[Ｏ]＋2.6×[Zr]＋0.3)／([S]＋0.5) ……(2)
3＋200×[Ｏ]×[Ｓ]／([REM]＋[Ca]) ＜ｔ＜60……(3)
なお、［Ｏ］、［Ｓ］はそれぞれ％で表される、Ｔｉ添加前の溶存Ｏ量、溶存Ｓ量であり、［ＲＥＭ］、［Ｃａ］、［Ｚｒ］はそれぞれ％で表される、ＲＥＭ、Ｃａ、Ｚｒの添加量である。 In order to obtain the above-mentioned oxide distribution and X value, the amount of dissolved oxygen, REM and / or Ca and Zr alloy elements added in the casting process, and the time from the completion of alloy element addition to the start of casting are controlled as follows. There is a need to. That is, at the time of casting, Mn, Si, Al, etc. are added prior to Ti addition, and the dissolved oxygen amount before Ti addition is controlled to 0.0020 to 0.0100%, and the dissolved oxygen amount and sulfur amount before Ti addition. Based on the above, after determining the amount of REM and / or Ca and Zr added so that the Z value obtained from the following formula (2) is 0.58 or more, after adding Ti, REM and / or Ca, In addition, Zr is added, and further, the time t (min) from the completion of the addition of these alloy elements to the start of casting is maintained within the range defined by the following formula (3), and solidification proceeds at the time of casting: 1450-1500 The cooling time at 0 ° C. is controlled to 60 to 300 s.
Z = (3.5 × ([REM] + [Ca]) − 0.7 × [O] + 2.6 × [Zr] +0.3) / ([S] +0.5) (2)
3 + 200 × [O] × [S] / ([REM] + [Ca]) <t <60 …… (3)
In addition, [O] and [S] are each expressed in%, and are dissolved O amount and dissolved S amount before addition of Ti, and [REM], [Ca], and [Zr] are each expressed in%. This is the amount of REM, Ca, Zr added.

鋳造時、Ｔｉ添加前の溶存酸素量が０．００２０％より少ないと、円相当径が２μｍより小さい酸化物の量を十分に確保できない。また、同溶存酸素量が０．０１００％より多い、あるいはＴｉに先立ちＲＥＭ及び／又はＣａ、並びにＺｒを添加すると、円相当径が５μｍより大きい酸化物の量が増加する、あるいは円相当径が２μｍより小さい酸化物の量が十分に得られなくなる。   At the time of casting, if the amount of dissolved oxygen before addition of Ti is less than 0.0020%, a sufficient amount of oxide having an equivalent circle diameter of less than 2 μm cannot be secured. Further, when the dissolved oxygen amount is more than 0.0100%, or when REM and / or Ca and Zr are added prior to Ti, the amount of oxide having an equivalent circle diameter larger than 5 μm is increased or the equivalent circle diameter is increased. A sufficient amount of oxide smaller than 2 μm cannot be obtained.

前記Ｚ値は、ＲＥＭ硫化物及び／又はＣａ硫化物の形成に寄与するＲＥＭ、Ｃａ、Ｓ量を考慮した値であり、Ｚ値が０．５８より小さいと、ＲＥＭ及び／又はＣａに対するＳの割合が高くなりすぎるため、より低温におけるＭｎ硫化物の生成量、あるいは固溶Ｓの増加を招き、ＨＡＺにおける微細Ｍｎ硫化物の再析出量が増加する。前記Ｚ値、ｔ（ｍｉｎ）の定義式に対し、式中の各係数は実験的に決定した。   The Z value is a value that takes into account the amount of REM, Ca, and S that contribute to the formation of REM sulfide and / or Ca sulfide. If the Z value is less than 0.58, the S value relative to REM and / or Ca Since the ratio becomes too high, the amount of Mn sulfide produced at a lower temperature or the amount of solute S is increased, and the amount of reprecipitation of fine Mn sulfide in HAZ increases. Each coefficient in the formula was experimentally determined with respect to the definition formula of the Z value and t (min).

また、合金元素添加完了から鋳込み開始までの時間ｔ（ｍｉｎ）が上記(3) 式の範囲から逸脱すると、十分なＨＡＺ靭性改善効果が得られなくなる。すなわち、ｔの値が３＋２００×［Ｏ］×［Ｓ］／（［ＲＥＭ］＋［Ｃａ］）以下となると、溶鋼中におけるＲＥＭ硫化物及び／又はＣａ硫化物の形成が十分に進行せず、微細Ｍｎ硫化物の再析出が十分抑制されなくなる。また、ｔの値が６０以上となると、酸化物の合体・成長により円相当径が５μｍより大きい酸化物が増加し、ＨＡＺ靭性低下の原因となる。   Further, if the time t (min) from the completion of addition of the alloy element to the start of casting deviates from the range of the above formula (3), a sufficient HAZ toughness improving effect cannot be obtained. That is, when the value of t is 3 + 200 × [O] × [S] / ([REM] + [Ca]) or less, the formation of REM sulfide and / or Ca sulfide in the molten steel does not proceed sufficiently, Reprecipitation of fine Mn sulfide is not sufficiently suppressed. On the other hand, when the value of t is 60 or more, oxides having an equivalent circle diameter larger than 5 μm increase due to coalescence / growth of oxides, which causes a reduction in HAZ toughness.

さらに、成分調整した溶湯を鋳型に鋳込み後、凝固までの間に１４５０〜１５００℃の温度域を通過する際の冷却時間が６０ｓより短いと、二次介在物としてＲＥＭ硫化物及び／又はＣａ硫化物が形成される時間が十分確保されないため、より低温におけるＭｎ硫化物生成量、あるいは固溶Ｓの増加を招き、ＨＡＺにおける微細Ｍｎ硫化物の再析出量が増加する。また、同冷却時間が３００ｓを超えると、凝固偏析による合金元素濃化域において円相当径が５μｍより大きい酸化物の形成が促進され、ＨＡＺ靭性低下をもたらす。   Further, if the cooling time for passing the temperature range of 1450 to 1500 ° C. is shorter than 60 s after casting the molten metal whose components are adjusted into the mold and before solidification, REM sulfide and / or Ca sulfide is used as a secondary inclusion. Since sufficient time for the formation of the product is not ensured, the amount of Mn sulfide produced at a lower temperature or the amount of solid solution S is increased, and the amount of reprecipitation of fine Mn sulfide in HAZ increases. On the other hand, when the cooling time exceeds 300 s, formation of an oxide having an equivalent circle diameter larger than 5 μm is promoted in the alloy element concentration region due to solidification segregation, resulting in a decrease in HAZ toughness.

次に、実施形態に係る溶接用高張力厚鋼板の化学組成の基本成分について説明する。
Ｃ：０．０２〜０．１２％
Ｃは、強度確保に必須の元素であり、含有量が０．０２％より少ないと必要な強度が得られないため、下限を０．０２％とした。また、含有量が０．１２％を超えると、硬質ＭＡ組織増加によるＨＡＺ靭性低下を招くため、上限を０．１２％とした。なお、好ましい下限は０．０４％、好ましい上限は０．１０％である。 Next, basic components of the chemical composition of the high-tensile thick steel plate for welding according to the embodiment will be described.
C: 0.02-0.12%
C is an element essential for securing the strength, and if the content is less than 0.02%, the required strength cannot be obtained, so the lower limit was made 0.02%. On the other hand, if the content exceeds 0.12%, the HAZ toughness decreases due to an increase in the hard MA structure, so the upper limit was made 0.12%. The preferred lower limit is 0.04%, and the preferred upper limit is 0.10%.

Ｓｉ：０．４０％以下（０％を含む）
Ｓｉは、固溶強化により強度を確保する元素であり、含有量が０．４０％を超えると、硬質ＭＡ組織（マルテンサイトと残留オーステナイトの混合組織）が増加し、ＨＡＺ靭性の低下を招くため、上限を０．４０％とした。なお、好ましくは０．３５％以下（０％を含む）である。 Si: 0.40% or less (including 0%)
Si is an element that secures strength by solid solution strengthening, and if the content exceeds 0.40%, a hard MA structure (mixed structure of martensite and residual austenite) increases and HAZ toughness decreases. The upper limit was made 0.40%. Note that the content is preferably 0.35% or less (including 0%).

Ｍｎ：１．０〜２．０％
Ｍｎは、強度確保に有効な元素であり、１．０％より少ないと必要な強度が得られないため、下限を１．０％とした。また、含有量が２．０％を超えると、ＨＡＺ強度の過大な上昇を招いてＨＡＺ靭性低下の原因となるため、上限を２．０％とした。なお、好ましい下限は１．４％、好ましい上限は１．８％である。 Mn: 1.0-2.0%
Mn is an element effective for securing the strength, and if it is less than 1.0%, the required strength cannot be obtained, so the lower limit was made 1.0%. Further, if the content exceeds 2.0%, the HAZ strength is excessively increased and the HAZ toughness is lowered, so the upper limit was made 2.0%. The preferred lower limit is 1.4% and the preferred upper limit is 1.8%.

Ｐ：０．０３％以下（０％を含む）
Ｐは、粒界偏析によって粒界破壊の原因となる不純物元素であり、含有量が０．０３％を超えると、ＨＡＺ靭性低下を招くため、上限を０．０３％とした。なお、好ましくは０．０２％以下（０％を含む）である。 P: 0.03% or less (including 0%)
P is an impurity element that causes grain boundary fracture due to grain boundary segregation. If the content exceeds 0.03%, the HAZ toughness is reduced, so the upper limit was made 0.03%. Note that the content is preferably 0.02% or less (including 0%).

Ｓ ：０．０１５％以下（０％を含む）
Ｓは、Ｍｎ硫化物として存在することで、ＨＡＺにおける微細Ｍｎ硫化物の再析出によるＨＡＺ靭性低下をもたらす元素であり、含有量が０．０１５％を超えると、Ｍｎ硫化物の再析出が抑制されなくなるため、上限を０．０１５％とした。なお、好ましくは０．０１２％以下（０％を含む）である。 S: 0.015% or less (including 0%)
S is an element that is present as Mn sulfide and causes HAZ toughness reduction due to reprecipitation of fine Mn sulfide in HAZ. When the content exceeds 0.015%, reprecipitation of Mn sulfide is suppressed. Therefore, the upper limit was made 0.015%. Note that the content is preferably 0.012% or less (including 0%).

Ａｌ：０．０５０％以下（０％を含む）
Ａｌは、鋳造時の脱酸に用いられる元素であり、含有量が０．０５０％を超えると、粗大酸化物を形成してＨＡＺ靭性低下を招くため、上限を０．０５０％とした。なお、好ましくは０．０４０％以下である。 Al: 0.050% or less (including 0%)
Al is an element used for deoxidation at the time of casting. When the content exceeds 0.050%, a coarse oxide is formed and the HAZ toughness is reduced, so the upper limit was made 0.050%. In addition, Preferably it is 0.040% or less.

Ｔｉ：０．００５〜０．１００％
Ｔｉは、ＲＥＭ、Ｚｒに先立ち添加されることで微細酸化物の形成に寄与する元素であり、含有量が０．００５％より少ないと、十分な効果が得られないため、下限を０．００５％とした。また、含有量が０．１００％を超えると、酸化物の粗大化によりＨＡＺ靭性低下を招くため、上限を０．１００％とした。なお、好ましい下限は０．０１０％、好ましい上限は０．０８０％であり、より好ましい上限は０．０６０％、更に好ましい上限は０．０５０％である。 Ti: 0.005 to 0.100%
Ti is an element that contributes to the formation of fine oxides by adding prior to REM and Zr. If the content is less than 0.005%, a sufficient effect cannot be obtained, so the lower limit is set to 0.005. %. Further, if the content exceeds 0.100%, the HAZ toughness is reduced due to the coarsening of the oxide, so the upper limit was made 0.100%. A preferred lower limit is 0.010%, a preferred upper limit is 0.080%, a more preferred upper limit is 0.060%, and a more preferred upper limit is 0.050%.

ＲＥＭ：０．０００２〜０．０５００％及び又はＣａ：０．０００３〜０．０１００％
ＲＥＭ（希土類元素）、Ｃａは、それぞれＲＥＭ硫化物、Ｃａ硫化物を形成することで、Ｍｎ硫化物量を減らし、微細Ｍｎ硫化物の再析出によるＨＡＺ靭性低下を抑制する。これらの効果を十分に得るためには、ＲＥＭで０．０００２％以上、Ｃａで０．０００３％以上含有させる必要がある。なお、好ましくは、ＲＥＭで０．０００５％以上、Ｃａで０．００１０％以上である。しかし、これら元素の含有量が過剰になると、粗大酸化物の形成によりＨＡＺ靭性が低下するため、ＲＥＭで０．０５００％以下、Ｃａで０．０１００％以下とする必要がある。なお、好ましくは、ＲＥＭで０．０４００％以下、Ｃａで０．００８０％以下である。 REM: 0.0002-0.0500% and / or Ca: 0.0003-0.0100%
REM (rare earth element) and Ca form REM sulfide and Ca sulfide, respectively, thereby reducing the amount of Mn sulfide and suppressing the reduction in HAZ toughness due to reprecipitation of fine Mn sulfide. In order to obtain these effects sufficiently, it is necessary to contain 0.0002% or more in REM and 0.0003% or more in Ca. Preferably, the REM content is 0.0005% or more, and the Ca content is 0.0010% or more. However, if the content of these elements is excessive, the HAZ toughness is lowered due to the formation of coarse oxides, so it is necessary to make 0.0500% or less in REM and 0.0100% or less in Ca. Preferably, the REM is 0.0400% or less, and the Ca is 0.0080% or less.

Ｚｒ：０．０００１〜０．０５００％
Ｚｒは、鋳造時において、Ｔｉ添加の後に添加されることで、円相当径が２μｍより小さい微細酸化物形成に寄与する元素であり、含有量が０．０００１％より少ないと、その効果が十分に得られなくなるため、下限を０．０００１％とした。また、含有量が０．０５００％より多いと、粗大酸化物、あるいは析出強化をもたらす微細な炭化物を形成して靭性低下を招くため、上限を０．０５００％とした。なお、好ましい下限は０．０００５％、好ましい上限は０．０４００％である。 Zr: 0.0001 to 0.0500%
Zr is an element that contributes to the formation of fine oxides with an equivalent circle diameter of less than 2 μm when added after the addition of Ti during casting. If the content is less than 0.0001%, the effect is sufficient. Therefore, the lower limit was made 0.0001%. Further, if the content is more than 0.0500%, coarse oxides or fine carbides that cause precipitation strengthening are formed and the toughness is reduced, so the upper limit was made 0.0500%. A preferred lower limit is 0.0005%, and a preferred upper limit is 0.0400%.

Ｎ：０．００２０〜０．０３００％
Ｎは、Ｔｉ窒化物を形成して靭性向上をもたらす元素であり、含有量が０．００２０％より少ないと、十分な効果が得られないため、下限を０．００２０％とした。また、含有量が０．０３００％を超えると、固溶Ｎとして歪時効による靭性低下をもたらすため、上限を０．０３００％とした。なお、好ましい下限は０．００３０％、好ましい上限は０．０２５０％であり、より好ましい上限は０．０２００％、更に好ましい上限は０．０１５０％である。 N: 0.0020 to 0.0300%
N is an element that forms Ti nitride to improve toughness, and if the content is less than 0.0020%, a sufficient effect cannot be obtained, so the lower limit was made 0.0020%. Moreover, when content exceeds 0.0300%, since the toughness fall by strain aging will be caused as solid solution N, the upper limit was made 0.0300%. The preferred lower limit is 0.0030%, the preferred upper limit is 0.0250%, the more preferred upper limit is 0.0200%, and the still more preferred upper limit is 0.0150%.

Ｏ：０．０００５〜０．０１００％
Ｏは、微細酸化物の生成に必須の元素であり、含有量が０．０００５％より低いと、十分な量の酸化物が得られないため、下限を０．０００５％とした。また、含有量が０．０１００％を超えると、酸化物の粗大化によりＨＡＺ靭性低下を招くため、上限を０．０１００％とした。なお、好ましい下限は０．００１０％、好ましい上限は０．００８０％である。 O: 0.0005 to 0.0100%
O is an essential element for the production of fine oxides. If the content is lower than 0.0005%, a sufficient amount of oxide cannot be obtained, so the lower limit was made 0.0005%. Further, if the content exceeds 0.0100%, the HAZ toughness is reduced due to the coarsening of the oxide, so the upper limit was made 0.0100%. A preferred lower limit is 0.0010%, and a preferred upper limit is 0.0080%.

上記基本成分に対して鋼板の機械的性質をより向上させるために、上記基本成分にＡ群（Ｎｉ：０．０５〜１．５０％、Ｃｕ：０．０５〜１．５０％、Ｃｒ：０．０５〜１．５０％、Ｍｏ：０．０５〜１．５０％）、Ｂ群（Ｎｂ：０．００２〜０．１０％、Ｖ：０．００２〜０．１０％）、Ｂ：０．００１０〜０．００５０％の１種以上を添加して下記(1) から(3) の組成（残部はＦｅおよび不可避的不純物）とすることができる。
(1) 基本成分＋Ａ群から１種以上
(2) 基本成分又は上記(1) の成分＋Ｂ群から１種以上
(3) 基本成分、上記(1) 又は(2) のいずれかの成分＋Ｂ In order to further improve the mechanical properties of the steel sheet with respect to the basic component, the basic component includes group A (Ni: 0.05 to 1.50%, Cu: 0.05 to 1.50%, Cr: 0). 0.05 to 1.50%, Mo: 0.05 to 1.50%), Group B (Nb: 0.002 to 0.10%, V: 0.002 to 0.10%), B: 0.0. One or more of 0010 to 0.0050% can be added to obtain the following compositions (1) to (3) (the balance being Fe and inevitable impurities).
(1) Basic component + 1 or more from Group A
(2) Basic component or one or more of component (1) above + Group B
(3) Basic component, component (B) above in either (1) or (2)

Ｎｉ、Ｃｕ、Ｃｒ、Ｍｏは、いずれも鋼材の高強度化に有効な元素であり、それぞれ、含有量が０．０５％より少ないと、その効果が十分に得られないため、下限を０．０５％とした。また、それぞれ、含有量が１．５０％を超えると、強度の過大な上昇を招いて、靭性低下をもたらすため、上限を１．５０％とした。なお、好ましい下限はそれぞれ０．１０％、好ましい上限はそれぞれ１．２０％である。   Ni, Cu, Cr, and Mo are all effective elements for increasing the strength of steel materials. If the content is less than 0.05%, the effect cannot be sufficiently obtained. 05%. In addition, when the content exceeds 1.50%, the strength is excessively increased and the toughness is reduced. Therefore, the upper limit is set to 1.50%. The preferred lower limit is 0.10%, and the preferred upper limit is 1.20%.

Ｎｂ、Ｖは、いずれも炭窒化物として析出することで、オーステナイト粒粗大化を抑制する元素であり、それぞれ、含有量が０．００２％より少ないと、その効果が十分に得られないため、下限を０．００２％とした。また、それぞれ、含有量が０．１０％を超えると、粗大炭窒化物として靭性低下を招くため、上限を０．１０％とした。なお、好ましい下限はそれぞれ０．００５％、好ましい上限は０．０８％である。   Nb and V are elements that suppress austenite grain coarsening by precipitating as carbonitrides, and if the content is less than 0.002%, the effect cannot be sufficiently obtained. The lower limit was made 0.002%. In addition, when the content exceeds 0.10%, the coarse carbonitride causes a reduction in toughness, so the upper limit was made 0.10%. The preferred lower limit is 0.005% and the preferred upper limit is 0.08%.

Ｂは、粒界フェライト生成を抑制することで、靭性を向上させる元素であり、含有量が０．００１０％より少ないと、その効果が十分に得られないため、下限を０．００１０％とした。また、含有量が０．００５０％より多いと、ＢＮとしてオーステナイト粒界に析出し、靭性低下を招くため、上限を０．００５０％とした。なお、好ましい下限は０．００１５％、好ましい上限は０．００４０％である。   B is an element that improves toughness by suppressing the formation of intergranular ferrite. If the content is less than 0.0010%, the effect cannot be sufficiently obtained, so the lower limit is made 0.0010%. . On the other hand, if the content is more than 0.0050%, BN precipitates at the austenite grain boundary and causes a decrease in toughness, so the upper limit was made 0.0050%. A preferred lower limit is 0.0015%, and a preferred upper limit is 0.0040%.

次に、上記溶接用高張力厚鋼板の製造方法について説明する。同厚鋼板の製造方法における特徴は鋳造工程にあり、これについてはすでに説明したので、以下、鋳造後の鋼塊に対する処理を簡単に説明する。上記鋳造プロセス、成分範囲等を満たして製造された鋳塊を、通常の熱間圧延手順に従い、圧延開始温度を１２００〜９００℃程度、圧延終了温度を９５０〜７５０℃程度として、圧延を終了したの後、室温〜５００℃程度の間の冷却停止温度まで冷却することで、厚鋼板が得られる。冷却終了後、さらにテンパー処理を施しても良い。なお、製造される厚鋼板の板厚については特に制限されないが、５０〜１２０mm程度が溶接用厚鋼板として求められており、本発明はかかる板厚であっても、優れたＨＡＺ靭性を得ることができる。   Next, the manufacturing method of the said high-tensile steel plate for welding is demonstrated. The feature of the method for producing the same steel plate is the casting process, which has already been described, and hereinafter, the processing for the steel ingot after casting will be briefly described. The ingot produced by satisfying the above casting process, component range, etc., was rolled according to a normal hot rolling procedure, with a rolling start temperature of about 1200 to 900 ° C. and a rolling end temperature of about 950 to 750 ° C. Then, a thick steel plate is obtained by cooling to the cooling stop temperature between room temperature and about 500 degreeC. A temper treatment may be further performed after the cooling. In addition, although it does not restrict | limit especially about the plate | board thickness of the steel plate manufactured, About 50-120mm is calculated | required as a steel plate for welding, and this invention obtains the outstanding HAZ toughness even if it is this plate | board thickness. Can do.

以下、実施例を挙げて本発明をより具体的に説明するが、本発明はかかる実施例により限定的に解釈されるものではない。   EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limitedly interpreted by this Example.

真空溶解炉（１５０ｋｇ）を用い、シリコン等の添加量を調整してＴｉ添加前の溶存酸素量を変化させ、Ｚ値を考慮しつつ、ＲＥＭ及び／又はＣａ、並びにＺｒ添加量を決定のうえ、一部のもの（表１の鋼Ｎｏ．２６）を除き、Ｔｉを添加した後、ＲＥＭ及び／又はＣａ、Ｚｒを添加し、合金元素添加完了から鋳込み開始までの時間ｔ（ｍｉｎ）、および成分調整した溶湯を鋳型に鋳込み後、凝固までの間に１４５０〜１５００℃の温度域を通過する際の冷却時間ｔ１（ｓ）を変化させて鋼を溶製し、得られた鋳塊を、圧延開始温度を９５０℃程度、最終圧延温度を８８０℃程度として熱間圧延を施し、厚さ８０ｍｍの厚鋼板を製造した。その組成を表１、表２に、Ｔｉ添加前の溶存酸素量［Ｏ］（％）、およびＺ値、(3) 式に基づき、下記(4) 式で表現されるｔ（ｍｉｎ）の許容下限値Ｙ、ｔ（ｍｉｎ）、ｔ１（ｓ）の各値を表３に示す。
Ｙ＝３＋２００×［Ｏ］×［Ｓ］／（［ＲＥＭ］＋［Ｃａ］）……(4)
なお、［Ｏ］、［Ｓ］ はそれぞれＴｉ添加前の溶存Ｏ量（％）、溶存Ｓ量（％）であり、［ＲＥＭ］、［Ｃａ］はそれぞれＲＥＭ、Ｃａの添加量（％）である。 Using a vacuum melting furnace (150 kg), adjust the amount of silicon added to change the amount of dissolved oxygen before adding Ti, and determine the amount of REM and / or Ca and Zr added while considering the Z value. , Except for some (steel No. 26 in Table 1), after adding Ti, add REM and / or Ca, Zr, time t (min) from completion of addition of alloy element to start of casting, and After casting the component-adjusted molten metal in the mold, the steel is melted by changing the cooling time t1 (s) when passing through the temperature range of 1450 to 1500 ° C. until solidification, and the resulting ingot is obtained. Hot rolling was performed at a rolling start temperature of about 950 ° C. and a final rolling temperature of about 880 ° C. to produce a thick steel plate having a thickness of 80 mm. The compositions are shown in Tables 1 and 2, and the amount of dissolved oxygen before adding Ti [O] (%), the Z value, and the allowable t (min) expressed by the following equation (4) based on the equation (3) Table 3 shows the lower limit values Y, t (min), and t1 (s).
Y = 3 + 200 × [O] × [S] / ([REM] + [Ca]) (4)
[O] and [S] are respectively the dissolved O amount (%) and the dissolved S amount (%) before Ti addition, and [REM] and [Ca] are respectively the addition amount (%) of REM and Ca. is there.

得られた各厚鋼板のｔ（板厚）／４位置において、化合物を形成するＭｎ、ＲＥＭ、Ｃａの濃度を測定し、Ｘ値を算出した。化合物を形成するＭｎの濃度については、ヨウ素メタノール法により測定を行った。また、化合物を形成するＲＥＭ、Ｃａの濃度については、電解液としてメタノール１００ｃｃ中にトリエタノールアミン２ｃｃとテトラメチルアンモニウムクロライド１ｇを含有する溶液を用いた電解抽出法により測定を行った。なお、残渣のろ過に際しては、ポアサイズ０．１μｍのフィルターを使用した。得られたＸ値を表３に示す。   At the position t (plate thickness) / 4 of each thick steel plate obtained, the concentrations of Mn, REM, and Ca forming the compound were measured, and the X value was calculated. About the density | concentration of Mn which forms a compound, it measured by the iodine methanol method. Further, the concentrations of REM and Ca forming the compound were measured by an electrolytic extraction method using a solution containing 2 cc of triethanolamine and 1 g of tetramethylammonium chloride in 100 cc of methanol as an electrolytic solution. A filter having a pore size of 0.1 μm was used for filtering the residue. The obtained X values are shown in Table 3.

また、得られた各厚鋼板のｔ（板厚）／４位置から試験片を切り出し、圧延方向および板厚方向に平行な断面（圧延面に垂直で圧延方向に沿った断面）を電界放射式走査型電子顕微鏡（装置名：SUPRA 35、Carl Zeiss社製）（以下、ＦＥ−ＳＥＭと呼称する）を用いて観察し、円相当径が２μｍより小さいの酸化物、および５μｍより大きい酸化物の個数密度を測定した。測定方法は以下のとおりである。   In addition, a test piece was cut out from each of the obtained thick steel plates at t (plate thickness) / 4 position, and a cross section parallel to the rolling direction and the plate thickness direction (cross section perpendicular to the rolling surface and along the rolling direction) was field emission type. Observed using a scanning electron microscope (device name: SUPRA 35, manufactured by Carl Zeiss) (hereinafter referred to as FE-SEM), an oxide having an equivalent circle diameter of less than 2 μm and an oxide of more than 5 μm The number density was measured. The measurement method is as follows.

まず、ＦＥ−ＳＥＭの観察倍率を５０００倍に設定し、０．００２４ｍｍ2 の面積を有する視野を無作為に２０視野選択し、各視野の画像を撮影した。同時に、各視野に含まれる、最大径２μｍ以下の個々の介在物粒子中央部をＦＥ−ＳＥＭ付属のＥＤＳにて測定し、構成元素に酸素が含まれる介在物粒子を酸化物と判定した。なお、最大径にして０．２μｍ以下の介在物粒子については、ＥＤＳ測定の信頼性が低いため、測定対象から除外した。そのうえで、得られた画像を、画像処理ソフト（ソフト名：Image-Pro Plus、Media Cybernetic社製）を用いた画像解析にかけ、これら酸化物のうち円相当径が２μｍより小さいものの個数密度Ｎ１（個／ｍｍ2 ）を算出した。Ｎ１の値を表３に示す。同様に、ＦＥ−ＳＥＭの観察倍率を１０００倍に設定し、０．０６ｍｍ2 の面積を有する２０視野から算出された、円相当径が５μｍより大きい酸化物の個数密度ＮＬ（個／ｍｍ2 ）の値を表３に示す。 First, the observation magnification of FE-SEM was set to 5000 times, 20 visual fields having an area of 0.0024 mm 2 were randomly selected, and images of each visual field were taken. At the same time, the central part of each inclusion particle having a maximum diameter of 2 μm or less included in each field of view was measured with EDS attached to the FE-SEM, and the inclusion particle containing oxygen as a constituent element was determined to be an oxide. Inclusion particles having a maximum diameter of 0.2 μm or less were excluded from the measurement target because of the low reliability of EDS measurement. After that, the obtained image was subjected to image analysis using an image processing software (software name: Image-Pro Plus, manufactured by Media Cybernetic). Among these oxides, the number density N1 (number of ones having an equivalent circle diameter of less than 2 μm) / Mm 2 ) was calculated. The value of N1 is shown in Table 3. Similarly, the number density NL (pieces / mm 2 ) of oxides having an equivalent circle diameter larger than 5 μm, calculated from 20 fields of view having an area of 0.06 mm 2 , with the observation magnification of FE-SEM set to 1000 times. Table 3 shows the values.

さらに、得られた各厚鋼板のｔ（板厚）／４位置から、圧延方向に対し平行に、シャルピー試験片（Ｖノッチ）を採取し、大入熱溶接時のＨＡＺ熱サイクルを模擬した、再現ＨＡＺ熱サイクルを施した際の靭性を評価した。上記再現ＨＡＺ熱サイクルは、試験片を１４００℃に加熱して６０ｓ間保持した後、８００〜５００℃の温度範囲を５００ｓかけて冷却したものである。シャルピー衝撃試験は、ＪＩＳ Ｚ ２２４２に準拠し、３本の試験片について−４０℃での衝撃吸収エネルギーｖＥ-40 （Ｊ）を測定した値の最小値ｖＥ-40(min)が１００Ｊを超えるものを、ＨＡＺ靭性に優れると評価した。ｖＥ-40(min)の値を表３に示す。 Furthermore, from the t (plate thickness) / 4 position of each thick steel plate obtained, a Charpy test piece (V notch) was sampled in parallel to the rolling direction, and the HAZ thermal cycle during large heat input welding was simulated, The toughness when subjected to reproducible HAZ thermal cycling was evaluated. The reproduced HAZ thermal cycle is a test piece heated to 1400 ° C. and held for 60 s, and then cooled in a temperature range of 800 to 500 ° C. over 500 s. The Charpy impact test conforms to JIS Z 2242, and the minimum value vE- 40 (min) of the measured values of impact absorption energy vE- 40 (J) at -40 ° C for three test pieces exceeds 100J. Was evaluated as having excellent HAZ toughness. Table 3 shows the value of vE -40 (min).

表１〜表３から明らかなとおり、発明例No. １〜２５は、厚鋼板の組成、鋳造プロセスを適切に制御したので、酸化物を適切な形態で分散させ、加えてＸ値を１０．０未満とすることに成功した。このため、組織微細化および微細Ｍｎ硫化物再析出抑制を達成することができ、ＨＡＺ靭性（ｖＥ-40(min)）において高い値が得られた。一方、比較例No. ２６〜４７では、Ｔｉ、ＲＥＭ、Ｚｒの添加順、Ｔｉ添加前の溶存酸素量［Ｏ］（％）、およびＺ値、合金元素添加完了から鋳込み開始までの時間ｔ（ｍｉｎ）、および鋳込み後、１４５０〜１５００℃の温度域を通過する際の冷却時間ｔ１（ｓ）、あるいは鋼の組成が適正な範囲から逸脱するなどし、規定の酸化物形態が得られないため、或いはＸ値が１０．０を超えたため、あるいは、おそらくは粗大介在物の増加、不純物の増加、過度の強化、固溶元素の粒界偏析などの理由により、発明例に比してＨＡＺ靭性がかなり低下している。 As apparent from Tables 1 to 3, Invention Examples Nos. 1 to 25 appropriately controlled the composition of the thick steel plate and the casting process, so that the oxide was dispersed in an appropriate form, and the X value was 10. Succeeded to make it less than 0. For this reason, microstructure refinement and fine Mn sulfide reprecipitation suppression can be achieved, and a high value was obtained in HAZ toughness (vE -40 (min)). On the other hand, in Comparative Examples Nos. 26 to 47, the order of addition of Ti, REM, and Zr, the amount of dissolved oxygen [O] (%) before Ti addition, and the time t ( min), and after casting, the cooling time t1 (s) when passing through the temperature range of 1450 to 1500 ° C., or the composition of the steel deviates from an appropriate range, and the prescribed oxide form cannot be obtained. Or because the X value exceeded 10.0, or perhaps because of increased coarse inclusions, increased impurities, excessive strengthening, grain boundary segregation of solid solution elements, etc. It has dropped considerably.

Figure 2009179844
Figure 2009179844

Figure 2009179844
Figure 2009179844

Figure 2009179844
Figure 2009179844

Claims (4)

質量％で、
Ｃ ：０．０２〜０．１２％、
Ｓｉ：０．４０％以下（０％を含む）、
Ｍｎ：１．０〜２．０％、
Ｐ ：０．０３％以下（０％を含む）、
Ｓ ：０．０１５％以下（０％を含む）、
Ａｌ：０．０５０％以下（０％を含む）、
Ｔｉ：０．００５〜０．１００％、
ＲＥＭ：０．０００２〜０．０５００％及び／又はＣａ：０．０００３〜０．０１００％、
Ｚｒ：０．０００１〜０．０５００％
Ｎ ：０．００２０〜０．０３００％、
Ｏ ：０．０００５〜０．０１００％
を含有し、残部がＦｅおよび不可避的な不純物で構成される鋼であって、鋼中に存在する円相当径が２μｍより小さい酸化物が５００個／ｍｍ2 以上で、かつ円相当径が５μｍより大きい酸化物が５個／ｍｍ2 以下であり、鋼中において化合物を形成するＭｎ、ＲＥＭ、Ｃａの濃度から（１）式で定義されるＸ値が１０．０未満である、大入熱溶接時の熱影響部の靭性に優れた溶接用高張力厚鋼板。
Ｘ＝100×［insol Ｍｎ］／（［insol ＲＥＭ］＋［insol Ｃａ］＋0.05）……(1)
但し、［insol Ｍｎ］、［insol ＲＥＭ］、［insol Ｃａ］は、それぞれ鋼中において化合物を形成するＭｎ、ＲＥＭ、Ｃａの濃度（質量％）を示す。 % By mass
C: 0.02 to 0.12%,
Si: 0.40% or less (including 0%),
Mn: 1.0-2.0%,
P: 0.03% or less (including 0%),
S: 0.015% or less (including 0%),
Al: 0.050% or less (including 0%),
Ti: 0.005 to 0.100%,
REM: 0.0002 to 0.0500% and / or Ca: 0.0003 to 0.0100%,
Zr: 0.0001 to 0.0500%
N: 0.0020 to 0.0300%,
O: 0.0005 to 0.0100%
In which the balance is Fe and inevitable impurities, and the equivalent circle diameter in the steel is 500 / mm 2 or more and the equivalent circle diameter is 5 μm or more. Large heat input, in which the number of larger oxides is 5 / mm 2 or less, and the X value defined by the formula (1) is less than 10.0 based on the concentration of Mn, REM, and Ca forming a compound in steel High strength thick steel plate for welding with excellent toughness of heat affected zone during welding.
X = 100 × [insol Mn] / ([insol REM] + [insol Ca] +0.05) (1)
However, [insol Mn], [insol REM], and [insol Ca] indicate the concentrations (mass%) of Mn, REM, and Ca that form compounds in the steel, respectively. さらに、質量％で、
Ｎｉ：０．０５〜１．５０％、
Ｃｕ：０．０５〜１．５０％、
Ｃｒ：０．０５〜１．５０％、
Ｍｏ：０．０５〜１．５０％、
のうち一種あるいは二種以上を含む、請求項１に記載した溶接用高張力厚鋼板。 Furthermore, in mass%,
Ni: 0.05-1.50%,
Cu: 0.05 to 1.50%,
Cr: 0.05 to 1.50%,
Mo: 0.05 to 1.50%,
The high-tensile thick steel plate for welding according to claim 1, comprising one or more of them. さらに、質量％で
Ｎｂ：０．００２〜０．１０％、
Ｖ ：０．００２〜０．１０％
のうち一種あるいは二種以上を含む、請求項１または２のいずれかに記載した溶接用高張力厚鋼板。 Furthermore, Nb by mass%: 0.002 to 0.10%,
V: 0.002-0.10%
The high-tensile steel plate for welding according to claim 1, comprising one or more of them. さらに、質量％で
Ｂ：０．００１０〜０．００５０％
を含む、請求項１から３のいずれか１項に記載した溶接用高張力厚鋼板。 Furthermore, B by mass%: 0.0010 to 0.0050%
The high-tensile thick steel plate for welding according to any one of claims 1 to 3, comprising:
JP2008019192A 2008-01-30 2008-01-30 High tensile strength thick steel plate having excellent toughness in weld heat affected zone Pending JP2009179844A (en)

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JP2010174314A (en) * 2009-01-28 2010-08-12 Kobe Steel Ltd Steel material excellent in toughness of weld heat-affected zone
WO2012099119A1 (en) * 2011-01-18 2012-07-26 株式会社神戸製鋼所 Steel material having superior toughness of welded heat-affected zone, and method for manufacturing same
WO2014045829A1 (en) 2012-09-19 2014-03-27 株式会社神戸製鋼所 Thick steel sheet having excellent welding heat-affected part toughness
WO2014148447A1 (en) * 2013-03-22 2014-09-25 株式会社神戸製鋼所 Steel material having superior toughness at welding heat affected zone

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010174314A (en) * 2009-01-28 2010-08-12 Kobe Steel Ltd Steel material excellent in toughness of weld heat-affected zone
WO2012099119A1 (en) * 2011-01-18 2012-07-26 株式会社神戸製鋼所 Steel material having superior toughness of welded heat-affected zone, and method for manufacturing same
JP2012162797A (en) * 2011-01-18 2012-08-30 Kobe Steel Ltd Steel excellent in toughness of weld heat affected zone and method for producing thereof
CN103328672A (en) * 2011-01-18 2013-09-25 株式会社神户制钢所 Steel material having superior toughness of welded heat-affected zone, and method for manufacturing same
EP2666880A1 (en) * 2011-01-18 2013-11-27 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Steel material having superior toughness of welded heat-affected zone, and method for manufacturing same
EP2666880A4 (en) * 2011-01-18 2015-02-25 Kobe Steel Ltd Steel material having superior toughness of welded heat-affected zone, and method for manufacturing same
CN103328672B (en) * 2011-01-18 2015-06-03 株式会社神户制钢所 Steel material having superior toughness of welded heat-affected zone, and method for manufacturing same
WO2014045829A1 (en) 2012-09-19 2014-03-27 株式会社神戸製鋼所 Thick steel sheet having excellent welding heat-affected part toughness
KR20150038664A (en) 2012-09-19 2015-04-08 가부시키가이샤 고베 세이코쇼 Thick steel sheet having excellent welding heat-affected part toughness
WO2014148447A1 (en) * 2013-03-22 2014-09-25 株式会社神戸製鋼所 Steel material having superior toughness at welding heat affected zone
EP2977479A4 (en) * 2013-03-22 2016-11-30 Kobe Steel Ltd Steel material having superior toughness at welding heat affected zone

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