JP2009138255A - High tensile strength thick steel plate for welding, having excellent toughness in heat-affected zone at large heat-input welding - Google Patents
High tensile strength thick steel plate for welding, having excellent toughness in heat-affected zone at large heat-input welding Download PDFInfo
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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、大入熱溶接における、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 heat-affected zone (hereinafter referred to as “HAZ”) in high heat input welding, and is a high-tensile steel plate for welding. It is about.
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、溶接によって必要な形状に接合される。そのため、これらの鋼材は、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。 Generally, a steel material used as a structural material in the fields of shipbuilding, construction, and the like is joined to a necessary shape by welding. Therefore, these steel materials are required to have excellent HAZ toughness in addition to the base material 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、溶接施工効率向上および施工コスト低減を目的として、大入熱溶接が求められている。大入熱溶接においては、ＨＡＺは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、加熱時のオーステナイト粒の成長、徐冷時におけるオーステナイト粒界からの粗大粒界フェライトの生成といった、組織の粗大化に伴う靭性の劣化が生じやすい。このため、大入熱溶接においては特にＨＡＺの靭性（以下、「ＨＡＺ靭性」と呼称する。）を高い水準に保つ技術が必要とされている。 In recent years, with the increase in the size of welded structures in the construction and shipbuilding fields, the range of application of thick steel plates with a thickness of 50 mm or more is expanding, and high heat input welding is required to improve welding efficiency and reduce construction costs. It has been. In high heat input welding, since HAZ is gradually cooled after being held in a high temperature austenite region by heating, growth of austenite grains during heating, generation of coarse grain boundary ferrite from austenite grain boundaries during slow cooling, etc. In addition, deterioration of toughness due to coarsening of the structure tends to occur. For this reason, in high heat input welding, a technique for maintaining the toughness of HAZ (hereinafter referred to as “HAZ toughness”) at a high level is particularly required.
ＨＡＺ靭性を確保するために用いられる技術は、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変態促進技術に大別される。すなわち、前者は、介在物のピン止め効果により、溶接による高温加熱時のγ粒粗大化を抑制し、微細組織を得る技術であり、後者は、溶接終了後の冷却過程において、介在物を起点とした粒内α変態を促進し、微細組織を得る技術である。 Techniques used to ensure HAZ toughness are broadly classified into γ grain coarsening suppression techniques using inclusions such as oxides, sulfides, and nitrides, and intragranular α transformation promotion techniques. In other words, the former is a technique for obtaining a fine structure by suppressing the coarsening of γ grains during high-temperature heating by welding due to the pinning effect of inclusions, and the latter is the origin of inclusions in the cooling process after the end of welding. This technology promotes the intragranular α transformation and obtains a fine structure.
γ粒粗大化抑制によるＨＡＺ靭性改善を意図した技術として、例えば、特開２００５−２０６９１０号公報（特許文献１）には、ＲＥＭ、Ｍｎ含有酸硫化物によりγ粒の粗大化を抑制し、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２）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３）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。さらに、特開２００７−４６０９６号公報（特許文献４）には、Ｃａ酸化物によるγ粒粗大化抑制、ＲＥＭ、Ｚｒによる硫化物制御によりＨＡＺ靭性を改善する技術が提示されている。 As a technique intended to improve HAZ toughness by suppressing γ grain coarsening, for example, in JP 2005-206910 A (Patent Document 1), REM, Mn-containing oxysulfide suppresses γ grain coarsening and is high. Techniques for obtaining HAZ toughness are shown. Japanese Patent Application Laid-Open No. 2003-286540 (Patent Document 2) proposes a technique for finely dispersing Mn oxysulfide by appropriately controlling REM to suppress γ grain coarsening. Japanese Unexamined Patent Application Publication No. 2007-100133 (Patent Document 3) proposes a technique for obtaining high HAZ toughness by suppressing γ grain coarsening using an oxide containing REM and Zr. Furthermore, Japanese Patent Application Laid-Open No. 2007-46096 (Patent Document 4) proposes a technique for improving HAZ toughness by suppressing γ grain coarsening by Ca oxide, and sulfide control by REM and Zr.
また、粒内α変態促進によるＨＡＺ靭性改善を意図した技術として、例えば、特開昭６１−２５３３４４号公報（特許文献５）には、ＴｉＮなどに複合析出したＢＮをα変態の核として利用し、ＨＡＺ靭性を改善させる技術が示されている。また、特開平７−２５２５８６号公報（特許文献６）には、ＴｉおよびＲＥＭの複合酸化物上にＭｎＳを析出させ、粒内α変態の起点として作用させることで、高いＨＡＺ靭性を得る技術が提示されている。 Further, as a technique intended to improve HAZ toughness by promoting intragranular α transformation, for example, JP-A-61-253344 (Patent Document 5) uses BN compositely precipitated in TiN or the like as the nucleus of α transformation. Techniques for improving HAZ toughness are shown. Japanese Patent Laid-Open No. 7-252586 (Patent Document 6) discloses a technique for obtaining high HAZ toughness by precipitating MnS on a composite oxide of Ti and REM and acting as an origin of intragranular α transformation. Presented.
さらに、γ粒粗大化抑制および粒内α変態促進の両者を利用した組織微細化技術として、例えば、特開平１１−２７９６８４号公報（特許文献７）には、酸化物を起点としたＴｉＮによりγ粒の粗大化を抑制し、Ｔｉ、ＭｇおよびＡｌを含有する酸化物を起点とした粒内α変態の促進により、組織微細化を達成し、ＨＡＺ靭性を改善する技術が提案されている。また、特開２００１−２００３１号公報（特許文献８）には、組成を適切に制御したＴｉ−ＲＥＭ−Ｃａ−Ａｌ系酸化物、およびＴｉＮを利用した技術が提示されている。また、特許３７３３８９８号公報（特許文献９）には、ＴｉＮによりγ粒の粗大化を抑制し、ＭｎＳによる粒内α変態の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１０）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。
しかしながら、従来、ＨＡＺ靭性確保手段として主に用いられてきたＴｉＮに対し、近年の溶接入熱の増大は、溶接時のＴｉＮ粒子の消失や粗大化をもたらし、十分な組織微細化を困難なものとしている。また、ＴｉＮに比べ高温で安定な酸化物あるいは硫化物といった介在物を利用した、γ粒粗大化抑制、粒内α変態促進による組織微細化技術については、γ粒粗大化抑制および粒内α変態促進に同時に寄与する酸硫化物を分散させることが困難である。さらに、粒内α変態促進に有効な酸硫化物として、α相と良好な格子整合性を有する酸硫化物などが提案されているものの、格子整合性のみに着目した場合、得られるＨＡＺ靭性は限定されたものとなる。 However, in contrast to TiN, which has been mainly used as a means for ensuring HAZ toughness, the recent increase in welding heat input causes disappearance and coarsening of TiN particles during welding, making it difficult to sufficiently refine the structure. It is said. In addition, γ grain coarsening suppression and intragranular α transformation promotion using inclusions such as oxides or sulfides that are stable at high temperatures compared to TiN, γ grain coarsening suppression and intragranular α transformation It is difficult to disperse oxysulfides that simultaneously contribute to the promotion. Furthermore, although oxysulfides having good lattice matching with the α phase have been proposed as oxysulfides effective for promoting intragranular α transformation, when attention is focused only on lattice matching, the obtained HAZ toughness is It will be limited.
本発明は、かかる問題に鑑みなされたもので、高温で不安定なＴｉＮを用いることなく、γ粒粗大化抑制および粒内α変態促進を同時に達成して、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 such problems, and without using TiN that is unstable at high temperatures, achieves suppression of γ grain coarsening and promotion of intragranular α transformation at the same time, and has high HAZ toughness. It aims at providing a tension steel plate.
本発明者らは、上記の課題を達成するために、高温で安定な酸化物、硫化物、あるいは酸硫化物を利用したγ粒粗大化抑制、粒内α変態促進効果を相乗的に作用させることで、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、鋳造から圧延前の再加熱にかけてのプロセスを制御することで、円相当径で２μｍ未満の小さい酸化物を高密度で分散させることにより、γ粒粗大化を有効に抑制することができ、さらに円相当径で２μｍ以上の特定組成の酸硫化物を適切に分散させることにより、粒内α変態も同時に大幅に促進されることを見出した。本発明はかかる知見に基づいて完成されたものである。 In order to achieve the above-described problems, the present inventors synergistically act to suppress γ grain coarsening and promote intragranular α transformation using oxides, sulfides, or oxysulfides that are stable at high temperatures. Thus, experiments and examinations were conducted on means for obtaining excellent HAZ toughness. As a result, by controlling the process from casting to reheating before rolling, it is possible to effectively suppress coarsening of γ grains by dispersing small oxides with an equivalent circle diameter of less than 2 μm at high density. Furthermore, it was found that by appropriately dispersing an oxysulfide having a specific circle equivalent diameter of 2 μm or more, the intragranular α-transformation is also greatly promoted. The present invention has been completed based on such findings.
すなわち、本発明の大入熱時のＨＡＺ靭性に優れた溶接用高張力厚鋼板は、化学組成が質量％（以下、「質量％」は単に「％」と表記することがある。）で、
Ｃ ：０．０２〜０．１２％、
Ｓｉ：０．４０％以下（０％を含む）、
Ｍｎ：１．０〜２．０％、
Ｐ ：０．０３０％以下（０％を含む）、
Ｓ ：０．００１〜０．０２５％、
Ａｌ：０．０５０％以下（０％を含む）、
Ｔｉ：０．００５〜０．１００％、
ＲＥＭ：０．０００１〜０．０５００％、
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からなり、円相当径で２μｍ未満の酸化物が分散して５００個／ｍｍ2 以上含有され、円相当径で２μｍ以上の酸硫化物が分散して４０〜１０００個／ｃｍ2 含有される。そして、前記円相当径で２μｍ以上の酸硫化物を形成するＲＥＭ、Ｚｒ、Ｃａ、Ｍｎ、Ｍｇ、Ａｌ、Ｓｉの所定酸化物をそれぞれＲＥＭ2Ｏ3、ＺｒＯ2 、ＣａＯ、ＭｎＯ、ＭｇＯ、Ａｌ2Ｏ3、ＳｉＯ2 とし、前記酸硫化物を形成する元素の内のある元素の平均濃度に（当該元素の所定酸化物の分子量／当該元素の原子量）を掛けて算出した値を当該元素の酸化物換算値というとき、前記酸硫化物を形成する前記各元素の平均濃度（質量％）に基づいて算出した前記各元素の酸化物換算値と酸硫化物中のＳの平均濃度の合計値に対するＲＥＭの酸化物換算値、Ｍｎの酸化物換算値およびＳ濃度の割合がそれぞれ、ＲＥＭの酸化物換算値：１０％以上、Ｍｎの酸化物換算値：２０％以下、Ｓ：３〜２０％とされたものである。なお、本発明において、酸化物とは酸素を含む介在物の総称を意味し、酸素に加えて硫黄を含む酸硫化物もその範疇に含まれる。また、円相当径とは、組織観察面に現れた介在物粒子の断面の面積に相当する円を想定したとき、その相当円の直径を意味する。
That is, the high-tensile thick steel plate for welding excellent in HAZ toughness at the time of large heat input according to the present invention has a chemical composition of mass% (hereinafter, “mass%” may be simply expressed as “%”).
C: 0.02 to 0.12%,
Si: 0.40% or less (including 0%),
Mn: 1.0-2.0%,
P: 0.030% or less (including 0%),
S: 0.001 to 0.025%,
Al: 0.050% or less (including 0%),
Ti: 0.005 to 0.100%,
REM: 0.0001-0.0500%
Zr: 0.0001 to 0.0500%,
N: 0.0020 to 0.0300%,
O: 0.0005 to 0.0100% is contained,
The balance is made of Fe and inevitable impurities, oxides having an equivalent circle diameter of less than 2 μm are dispersed and contained in an amount of 500 / mm 2 or more, and oxysulfides having an equivalent circle diameter of 2 μm or more are dispersed to form 40 to 1000 Contained / cm 2 . Then, predetermined oxides of REM, Zr, Ca, Mn, Mg, Al, and Si that form an oxysulfide having an equivalent circle diameter of 2 μm or more are respectively replaced with REM 2 O 3 , ZrO 2 , CaO, MnO, MgO, and Al. 2 O 3 , SiO 2, and the value calculated by multiplying the average concentration of an element among the elements forming the oxysulfide by (the molecular weight of the predetermined oxide of the element / the atomic weight of the element) When referred to as an oxide equivalent value, the total value of the oxide equivalent value of each element calculated based on the average concentration (% by mass) of each element forming the oxysulfide and the average concentration of S in the oxysulfide The REM oxide conversion value, the Mn oxide conversion value, and the S concentration ratio with respect to the REM are respectively the REM oxide conversion value: 10% or more, the Mn oxide conversion value: 20% or less, and the S: 3-20%. It is said that. In the present invention, the oxide means a generic name of inclusions containing oxygen, and oxysulfides containing sulfur in addition to oxygen are also included in the category. The equivalent circle diameter means the diameter of the equivalent circle when a circle corresponding to the cross-sectional area of the inclusion particles appearing on the tissue observation surface is assumed.
また、上記基本成分にＣａ：０．０００３〜０．０１００％、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(4) の化学組成とすることができる。
(1) 基本成分＋Ｃａ
(2) 基本成分又は上記(1) の成分＋Ａ群から１種以上
(3) 基本成分、上記(1) 又は上記(2) の成分＋Ｂ群から１種以上
(4) 基本成分、上記(1) 、上記(2) 又は上記(3) の成分＋Ｂ
Moreover, Ca: 0.0003-0.0100%, A group (Ni: 0.05-1.50%, Cu: 0.05-1.50%, Cr: 0.05-1. 50%, Mo: 0.05 to 1.50%), Group B (Nb: 0.002 to 0.10%, V: 0.002 to 0.10%), B: 0.0010 to 0.0050 %, The chemical composition of (1) to (4) below can be obtained by adding one or more elements.
(1) Basic component + Ca
(2) Basic component or one or more of component (1) above + Group A
(3) Basic component, one or more of the above components (1) or (2) + group B
(4) Basic component, component (B) above (1), (2) or (3) above
また、化学成分として前記Ｃａを含有させたとき、前記円相当径で２μｍ未満の酸化物の内、酸素を除いて酸化物を構成する元素の割合が質量％でＴｉ：１０％以上、ＲＥＭ：５〜５０％、Ｚｒ：５％以上、Ｃａ：５〜４０％である酸化物が３００個／mm2 以上とすることが好ましい。 Further, when Ca is contained as a chemical component, the ratio of elements constituting the oxide excluding oxygen in the equivalent circle diameter of less than 2 μm is 10% by mass, Ti: 10% or more, REM: It is preferable that the oxide which is 5 to 50%, Zr: 5% or more, and Ca: 5 to 40% is 300 pieces / mm 2 or more.
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、鋼中に円相当径で２μｍ未満の小さな酸化物が分散して５００個／ｍｍ2 以上含有し、ＲＥＭ、Ｍｎの酸化物換算値およびＳ濃度の割合が、ＲＥＭの酸化物換算値：１０％以上、Ｍｎの酸化物換算値：２０％以下、Ｓ：３〜２０％の酸硫化物であって、円相当径で２μｍ以上の酸硫化物が鋼中に分散して４０〜１０００個／ｃｍ2 含有するので、２μm 未満の小さな酸化物の分散によるγ粒の粗大化抑制と、所定組成の２μm 以上の酸硫化物の分散による粒内α変態の促進との協働により組織微細化が促進され、これにより大入熱溶接に対しても優れた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, under a predetermined steel composition, small oxides having an equivalent circle diameter of less than 2 μm are dispersed in the steel and contained at least 500 pieces / mm 2 , and oxidation of REM and Mn The equivalent value of the product and the ratio of the S concentration are REM oxide equivalent value: 10% or more, Mn oxide equivalent value: 20% or less, S: 3-20% oxysulfide, and the equivalent circle diameter Since oxysulfides of 2 μm or more are dispersed in the steel and contain 40 to 1000 / cm 2, γ-grain coarsening is suppressed by dispersion of small oxides of less than 2 μm, and oxysulfides of 2 μm or more having a predetermined composition. The refinement of the structure is promoted in cooperation with the promotion of the intragranular α transformation due to the dispersion of the dispersion, and this provides excellent HAZ toughness for large heat input welding.
以下に、本発明の溶接用高張力厚鋼板について、γ粒の粗大化抑制に寄与する鋼中の酸化物のサイズと分布密度、粒内α変態の促進に寄与する酸硫化物の組成、サイズおよび分布密度、並びに鋼組成について順次説明する。 Below, regarding the high-tensile thick steel plate for welding of the present invention, the size and distribution density of oxides in the steel that contribute to the suppression of coarsening of γ grains, the composition and size of oxysulfides that contribute to the promotion of intragranular α transformation The distribution density and steel composition will be described in turn.
一般に、γ粒粗大化抑制には、比較的微細な介在物粒子の高密度分散が有効であり、粒子サイズが大きくなるにつれて、γ粒粗大化は十分抑制されなくなる。そこで、本発明者らは、γ粒粗大化抑制に有効な介在物粒子サイズを実験によって検討したところ、円相当径にして２μｍより小さい酸化物を、５００個／ｍｍ2 以上、好ましくは８００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。円相当径にして２μｍより小さい酸化物が５００個／ｍｍ2 より少ないと、γ粒粗大化が十分に抑制されなくなる。 In general, high-density dispersion of relatively fine inclusion particles is effective for suppressing γ grain coarsening, and as the particle size increases, γ grain coarsening is not sufficiently suppressed. Therefore, the present inventors examined the inclusion particle size effective in suppressing the coarsening of the γ grains by experiments, and found that the number of oxides having an equivalent circle diameter of less than 2 μm was 500 / mm 2 or more, preferably 800. It was found that γ grain coarsening is suppressed by dispersing at least / mm 2 . When 2μm smaller oxide in the equivalent circle diameter is less than 500 / mm 2, gamma grains coarsening is not sufficiently suppressed.
ところで、化学組成として所定量のＣａを含有させると、円相当径が２μm 未満の酸化物（以下、「微細酸化物」という場合がある。）にも不可避的にＣａが含有されるようになる。このようなＣａ含有微細酸化物は、単にγ粒の粗大化抑制効果だけでなく、粒内α変態促進効果をも奏するようになり、ＨＡＺ靭性をより向上させることができる。特に、前記Ｃａ含有微細酸化物を構成する元素（但し、酸素を除く。）の割合を質量％でＴｉ：１０％以上、ＲＥＭ：５〜５０％、Ｚｒ：５％以上、Ｃａ：５〜４０％に制御することにより、粒内α変態促進効果がより促進され、さらにかかる組成比のＣａ含有微細酸化物を３００個／mm2 以上、好ましくは３５０個／mm2 以上鋼中に存在させることにより、優れた粒内α変態促進効果が得られ、さらにＨＡＺ靭性を向上させることができる。 By the way, when a predetermined amount of Ca is contained as a chemical composition, Ca is inevitably contained in an oxide having an equivalent circle diameter of less than 2 μm (hereinafter sometimes referred to as “fine oxide”). . Such a Ca-containing fine oxide not only has an effect of suppressing the coarsening of γ grains but also has an effect of promoting intragranular α transformation, and can further improve the HAZ toughness. In particular, the proportion of the elements constituting the Ca-containing fine oxide (excluding oxygen) in terms of mass% is Ti: 10% or more, REM: 5-50%, Zr: 5% or more, Ca: 5-40 %, The effect of promoting intragranular α transformation is further promoted, and more than 300 / mm 2 , preferably 350 / mm 2 or more of Ca-containing fine oxide having such a composition ratio is present in the steel. Thus, an excellent effect of promoting intragranular α-transformation can be obtained, and further, HAZ toughness can be improved.
鋼材にＣａを添加し、あるいはさらに酸化物を構成する元素の割合を上記のように適切に制御することで、Ｃａ含有微細酸化物に粒内α変態促進効果が付与されるメカニズムについて必ずしも明らかではないが、次のように推測される。すなわち、Ｃａ非添加時に、微細酸化物の主体となるＲＥＭ酸化物は、α相との界面エネルギーが高く、粒内α変態促進効果が低いのに対し、Ｃａを添加し、微細酸化物にＣａを含ませ、あるいはさらにＣａ含有微細酸化物を構成する元素の割合を上記のように調整することで、界面エネルギーが低下し、粒内α変態促進効果が高まり、さらに、このような組成のＣａ含有微細酸化物を所定個数密度以上生成させることにより、前記効果がより有効に発現するようになるものと考えられる。 It is not always clear about the mechanism by which Ca-containing fine oxides are imparted with an intragranular α-transformation promoting effect by adding Ca to the steel material or appropriately controlling the ratio of elements constituting the oxide as described above. There is not, but it is guessed as follows. That is, when Ca is not added, the REM oxide, which is the main component of the fine oxide, has high interfacial energy with the α phase and low intragranular α transformation promotion effect, whereas Ca is added to the fine oxide to form Ca. Or by further adjusting the ratio of the elements constituting the Ca-containing fine oxide as described above, the interfacial energy is reduced, and the intragranular α-transformation promoting effect is enhanced. It is considered that the above effect is more effectively exhibited by generating the contained fine oxide at a predetermined number density or more.
また、粒内α変態を促進する因子として、本発明者らは、酸硫化物とγ相との熱膨張差により、酸硫化物周囲のγ相に導入される熱膨張歪に着目し、酸硫化物サイズが円相当径にして２μｍ以上の時、これら熱膨張歪が十分に導入されることで、歪誘起の粒内α変態が促進されることを見出した。さらに、これら酸硫化物の組成を以下のとおり制御することで、α相と良好な格子整合性を有するＲＥＭ硫化物が、酸硫化物表面に形成され、ＲＥＭ硫化物とα相との良好な格子整合性による粒内α変態促進効果が、歪導入による効果と相乗的に作用することで、粒内α変態が大幅に促進されることを見出した。 Further, as a factor for promoting the intragranular α transformation, the present inventors have focused on the thermal expansion strain introduced into the γ phase around the oxysulfide due to the difference in thermal expansion between the oxysulfide and the γ phase. It has been found that when the sulfide size is 2 μm or more in the equivalent circle diameter, the strain-induced intragranular α transformation is promoted by sufficiently introducing these thermal expansion strains. Furthermore, by controlling the composition of these oxysulfides as follows, a REM sulfide having good lattice matching with the α phase is formed on the surface of the oxysulfide, and a good relationship between the REM sulfide and the α phase. It has been found that the intragranular α-transformation promoting effect due to lattice matching acts synergistically with the effect of strain introduction, whereby the intragranular α-transformation is greatly promoted.
まず、鋼中の酸硫化物の組成を説明するに際し、その表現方法について説明する。本発明においては、鋼中の酸硫化物組成を直感的に捉えやすいよう、酸硫化物を構成するＲＥＭ、Ｚｒ、Ｃａ、Ｍｎ、Ｍｇ、Ａｌ、Ｓｉの各元素について、ＲＥＭ2Ｏ3、ＺｒＯ2 、ＣａＯ、ＭｎＯ、ＭｇＯ、Ａｌ2Ｏ3、ＳｉＯ2 をそれらの元素の所定酸化物とし、ＥＰＭＡで測定される酸硫化物中の前記各元素の平均濃度に（当該元素の所定酸化物の分子量／当該元素の原子量）を掛け、それぞれの元素の酸化物換算値を算出したうえで、上記７元素の酸化物換算値および酸硫化物中のＳ濃度の合計値に対する、ＲＥＭの酸化物換算値、Ｍｎの酸化物換算値およびＳ濃度の割合により、酸硫化物組成を表現した。なお、Ｍｇは不可避不純物として存在するものである。また、鋼中の酸硫化物を構成する主要元素として、上記元素の他にＴｉが挙げられるが、Ｔｉは窒化物としても存在し得るため、ＥＰＭＡ測定に際し酸硫化物を構成するもののみを検出することは困難である。よって、酸化物換算値の算出に際し、Ｔｉを計算より除外した。 First, in describing the composition of oxysulfide in steel, the expression method will be described. In the present invention, REM 2 O 3 , ZrO for each element of REM, Zr, Ca, Mn, Mg, Al, and Si constituting the oxysulfide so that the oxysulfide composition in the steel can be easily grasped intuitively. 2 , CaO, MnO, MgO, Al 2 O 3 , SiO 2 are the predetermined oxides of these elements, and the average concentration of each element in the oxysulfide measured by EPMA (the predetermined oxide of the element) (Molecular weight / Atomic weight of the element), and the oxide equivalent value of each element is calculated. Then, the oxide equivalent value of REM with respect to the oxide equivalent value of the above seven elements and the total value of S concentration in the oxysulfide The oxysulfide composition was expressed by the value, the Mn oxide equivalent value, and the ratio of the S concentration. Mg exists as an inevitable impurity. In addition to the above elements, Ti can be cited as the main element that constitutes oxysulfides in steel, but since Ti can also exist as nitrides, only those constituting oxysulfides are detected during EPMA measurement. It is difficult to do. Therefore, Ti was excluded from the calculation when calculating the oxide conversion value.
上記表現による酸硫化物の組成の一例を示す。ＥＰＭＡ測定により得られた酸硫化物中の平均濃度（質量％）が、Ｃｅ＝１７．１％、Ｌａ＝７．９％、Ｚｒ＝８．０％、Ｃａ＝０．１％、Ｍｎ＝７．６％、Ｍｇ＝０．２％、Ａｌ＝３．５％、Ｓｉ＝２．７％、Ｓ＝５．９％のとき、ＣｅのＣｅ2Ｏ3に基づく酸化物換算値は、（１７．１×Ｃｅ2Ｏ3の分子量／Ｃｅの原子量）＝２０．１であり、同様に、各元素の酸化物換算値は、Ｌａの酸化物換算値＝９．３、Ｚｒの酸化物換算値＝１０．８、Ｃａの酸化物換算値＝０．２、Ｍｎの酸化物換算値＝９．８、Ｍｇの酸化物換算値＝０．３、Ａｌの酸化物換算値＝６．６、Ｓｉの酸化物換算値＝５．９と算出される。これら酸化物換算値とＳ濃度との合計６８．９より、例えばＲＥＭ（ＣｅとＬａの合計）の酸化物換算値の割合は、ＲＥＭ（ＣｅとＬａの合計）の酸化物換算値＝４２．６％と算出される。 An example of the composition of the oxysulfide according to the above expression is shown. The average concentration (mass%) in the oxysulfide obtained by EPMA measurement was Ce = 17.1%, La = 7.9%, Zr = 8.0%, Ca = 0.1%, Mn = 7. When 0.6%, Mg = 0.2%, Al = 3.5%, Si = 2.7%, and S = 5.9%, the oxide conversion value based on Ce 2 O 3 of Ce is (17 0.1 × Ce 2 O 3 molecular weight / Ce atomic weight) = 20.1. Similarly, the oxide equivalent value of each element is the oxide equivalent value of La = 9.3, the oxide equivalent value of Zr = 10.8, Ca oxide equivalent value = 0.2, Mn oxide equivalent value = 9.8, Mg oxide equivalent value = 0.3, Al oxide equivalent value = 6.6, Si The oxide equivalent value is calculated as 5.9. From the total of 68.9 of these oxide conversion values and S concentration, for example, the ratio of the oxide conversion values of REM (total of Ce and La) is the oxide conversion value of REM (total of Ce and La) = 42. Calculated as 6%.
円相当径にして２μｍ以上の酸硫化物について、その組成を構成するＲＥＭ、ＭｎおよびＳについて、ＲＥＭ2Ｏ3およびＭｎＯについてのＲＥＭ、Ｍｎの酸化物換算値およびＳ濃度の割合を、ＲＥＭの酸化物換算値：１０％以上、Ｍｎの酸化物換算値：２０％以下、Ｓ：３〜２０％に保つことで、α相と良好な格子整合性を有するＲＥＭ硫化物が、酸硫化物表面に形成され、ＲＥＭ硫化物とα相との良好な格子整合性による粒内α変態促進効果と、歪導入による効果とが相乗的に作用し、粒内α変態が大幅に促進される。酸硫化物中のＲＥＭあるいはＭｎの各酸化物換算値、あるいはＳ濃度の割合が、前記の範囲を逸脱すると、α相と良好な格子整合性を有するＲＥＭ硫化物が、酸硫化物表面に適切な形態で形成されず、粒内α変態促進効果が低下する。ＲＥＭ、Ｍｎの各酸化物換算値およびＳの好ましい割合は、ＲＥＭの酸化物換算値：１５％以上、Ｍｎの酸化物換算値：１５％以下、Ｓ：５〜１５％である。 For REM, Mn, and S constituting the composition of an oxysulfide having an equivalent circle diameter of 2 μm or more, the REM, MnO equivalent value and the ratio of S concentration of REM 2 O 3 and MnO Oxide conversion value: 10% or more, Mn oxide conversion value: 20% or less, S: 3 to 20% S, REM sulfide having good lattice matching with α phase is the surface of oxysulfide The effect of promoting intragranular α transformation due to good lattice matching between the REM sulfide and the α phase and the effect of introducing strain act synergistically, and intragranular α transformation is greatly promoted. When the REM or Mn oxide equivalent value in the oxysulfide or the ratio of the S concentration deviates from the above range, the REM sulfide having good lattice matching with the α phase is suitable for the oxysulfide surface. The effect of promoting intragranular α transformation is reduced. The REM and Mn oxide equivalent values and the preferred ratio of S are REM oxide equivalent value: 15% or more, Mn oxide equivalent value: 15% or less, and S: 5 to 15%.
また、上記酸硫化物の円相当径が２μｍより小さいと、酸硫化物の周囲のγ相に、十分な歪が導入されず、やはり粒内α変態促進効果が低下する。これら酸硫化物の粒内α変態促進によるＨＡＺ靭性改善効果を十分に得るためには、これら酸硫化物を４０〜１０００個／ｃｍ2 、好ましくは５０〜８００個／ｃｍ2 の密度で分散させる必要がある。該酸硫化物個数が４０個／ｃｍ2 を下回ると、十分な粒内α変態が得られず、ＨＡＺ靭性向上につながらない。また、１０００個／ｃｍ2 を上回ると、脆性破壊を助長するようになり、ＨＡＺ靭性に悪影響をもたらす。 If the equivalent circle diameter of the oxysulfide is smaller than 2 μm, sufficient strain is not introduced into the γ phase around the oxysulfide, and the intragranular α transformation promoting effect is also lowered. In order to sufficiently obtain the HAZ toughness improving effect by promoting intragranular α transformation of these oxysulfides, these oxysulfides are dispersed at a density of 40 to 1000 / cm 2 , preferably 50 to 800 / cm 2 . There is a need. When the number of oxysulfides is less than 40 / cm 2 , sufficient intragranular α-transformation cannot be obtained, and the HAZ toughness cannot be improved. On the other hand, when it exceeds 1000 / cm 2 , brittle fracture is promoted, and the HAZ toughness is adversely affected.
次に、本発明の厚鋼板の化学組成およびその成分限定理由を説明する。単位は質量％である。
Ｃ：０．０２〜０．１２％
Ｃは、鋼材の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（マルテンサイト及びオーステナイトの混合組織）の増加による靭性低下を招くため、上限を０．１２％とした。好ましい下限は０．０４％、好ましい上限は０．１０％である。
Next, the chemical composition of the steel plate of the present invention and the reasons for limiting its components will be described. The unit is mass%.
C: 0.02-0.12%
C is an element essential for ensuring the strength of the steel material. If the content is less than 0.02%, the required strength cannot be obtained, so the lower limit was made 0.02%. Further, if the content exceeds 0.12%, the toughness decreases due to an increase in the hard MA structure (mixed structure of martensite and austenite), so the upper limit was made 0.12%. A preferred lower limit is 0.04% and a preferred upper limit is 0.10%.
Ｓｉ：０．４０％以下（０％を含む）
Ｓｉは、固溶強化により、鋼材の強度を確保する元素であり、含有量が０．４０％より多いと、硬質ＭＡ組織の増加によりＨＡＺ靭性低下を招くため、上限を０．４０％とした。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 the strength of the steel material by solid solution strengthening. If the content is more than 0.40%, the HAZ toughness is reduced due to an increase in the hard MA structure, so the upper limit was made 0.40%. . Preferably, it is 0.35% or less (including 0%).
Ｍｎ：１．０〜２．０％
Ｍｎは、強度確保に必須の元素であり、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靭性の低下の原因となるため、上限を２．０％とした。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 essential for securing 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%. A preferred lower limit is 1.4% and a preferred upper limit is 1.8%.
Ｐ：０．０３０％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０．０３０％を超えると、ＨＡＺ靭性の低下を招くため、上限を０．０３０％とした。好ましくは０．０２％以下（０％を含む）である。
P: 0.030% or less (including 0%)
P is an impurity element that causes grain boundary fracture due to grain boundary segregation. If the content exceeds 0.030%, the HAZ toughness is reduced, so the upper limit was made 0.030%. Preferably, it is 0.02% or less (including 0%).
Ｓ：０．００１〜０．０２５％
Ｓは、ＲＥＭ硫化物の生成に必須の元素であり、含有量が０．００１％より少ないと、十分なＲＥＭ硫化物が得られないため、下限を０．００１％とした。また、含有量が０．０２５％を超えると、ＲＥＭ量にかかわらず固溶Ｓの粒界偏析により靭性が低下するため、上限を０．０２５％とした。好ましい下限は０．００２％、好ましい上限は０．０２０％である。
S: 0.001 to 0.025%
S is an essential element for the production of REM sulfide. If the content is less than 0.001%, sufficient REM sulfide cannot be obtained, so the lower limit was made 0.001%. Further, if the content exceeds 0.025%, the toughness decreases due to segregation of the solid solution S regardless of the amount of REM, so the upper limit was made 0.025%. A preferred lower limit is 0.002% and a preferred upper limit is 0.020%.
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靭性の低下を招くため、上限を０．０５０％とした。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. If the content exceeds 0.050%, a coarse oxide is formed and the HAZ toughness is lowered, so the upper limit was made 0.050%. Preferably it is 0.040% or less.
Ｔｉ：０．００５〜０．１００％
Ｔｉは、後述するように、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靭性の低下を招くため、上限を０．１００％とした。好ましい下限は０．０１０％、好ましい上限は０．０８０％である。
Ti: 0.005 to 0.100%
As will be described later, Ti is an element that contributes to the formation of fine oxides by being added prior to REM and Zr. If the content is less than 0.005%, a sufficient effect cannot be obtained. The lower limit was made 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% and a preferred upper limit is 0.080%.
ＲＥＭ（希土類元素）：０．０００１〜０．０５００％
ＲＥＭは、ＲＥＭ硫化物の生成に必須の元素であり、含有量が０．０００１％より少ないと、ＲＥＭ硫化物が十分に生成しないため、下限を０．０００１％とした。また、含有量が０．０５００％を超えると、固溶ＲＥＭの粒界偏析によりＨＡＺ靭性の低下を招くため、上限を０．０５００％とした。好ましい下限は０．０００５％、好ましい上限は０．０４００％である。
REM (rare earth element): 0.0001 to 0.0500%
REM is an essential element for the production of REM sulfide. If the content is less than 0.0001%, REM sulfide is not sufficiently produced, so the lower limit was made 0.0001%. On the other hand, if the content exceeds 0.0500%, the HAZ toughness is reduced due to the grain boundary segregation of the solid solution REM, so the upper limit was made 0.0500%. A preferred lower limit is 0.0005% and a preferred upper limit is 0.0400%.
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、円相当径で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。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 oxide with an equivalent circle diameter of less than 2 μm by adding after Ti addition during casting, and its effect is sufficient when the content is less than 0.0001%. 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。好ましい下限は０．００３０％、好ましい上限は０．０２５０％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%. A preferred lower limit is 0.0030% and a preferred upper limit is 0.0250%.
Ｏ：０．０００５〜０．０１００％
Ｏは、酸化物の生成に必須の元素であり、含有量が０．０００５％より少ないと、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靭性の低下を招くため、上限を０．０１００％とした。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 element essential for the formation of oxides, and if the content is less 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%.
さらにまた、鋼材の機械的性質をより向上させるため、上記基本成分にＣａ：０．０００３〜０．０１００％、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(4) の化学組成（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＋Ｃａ
(2) 基本成分又は上記(1) の成分＋Ａ群から１種以上
(3) 基本成分、上記(1) 又は上記(2) の成分＋Ｂ群から１種以上
(4) 基本成分、上記(1) 、上記(2) 又は上記(3) の成分＋Ｂ
Furthermore, in order to further improve the mechanical properties of the steel material, the above basic components include Ca: 0.0003 to 0.0100%, Group A (Ni: 0.05 to 1.50%, Cu: 0.05 to 1). .50%, Cr: 0.05-1.50%, Mo: 0.05-1.50%), Group B (Nb: 0.002-0.10%, V: 0.002-0.10) %) And B: 0.0010% to 0.0050% or more of the following chemical compositions (1) to (4) (the balance being Fe and inevitable impurities) can be obtained.
(1) Basic component + Ca
(2) Basic component or one or more of component (1) above + Group A
(3) Basic component, one or more of the above components (1) or (2) + group B
(4) Basic component, component (B) above (1), (2) or (3) above
Ｃａは、円相当径にして２μｍより小さい酸化物に対し、粒内α変態促進効果向上に有効な元素であり、含有量が０．０００３％より少ないと、その効果が十分に得られないため、下限を０．０００３％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靭性の低下を招くため、上限を０．０１００％とした。好ましい下限は０．００１０％、好ましい上限は０．００８０％である。 Ca is an element effective for improving the effect of promoting intragranular α transformation with respect to an oxide having an equivalent circle diameter of less than 2 μm. If the content is less than 0.0003%, the effect cannot be sufficiently obtained. The lower limit was made 0.0003%. 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%.
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、靭性の低下をもたらすため、上限を１．５０％とした。好ましくは、下限が０．２０％で、上限が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%. Preferably, the lower limit is 0.20% and the 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。好ましくは、下限が０．００５％で、上限が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%. Preferably, the lower limit is 0.005% and the 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％とする。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、靭性の低下を招くため、上限を０．００５０％とする。好ましくは、下限が０．００１５％で、上限が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 is made 0.0050%. Preferably, the lower limit is 0.0015% and the upper limit is 0.0040%.
次に、本発明の溶接用高張力厚鋼板の製造について説明する。この製造において、上記円相当径が２μm 未満の微細酸化物、２μm 以上の酸硫化物の分散組織を形成するには、鋳造から圧延前の再加熱にかけての製造条件が重要である。
上記微細酸化物、酸硫化物の分散を得るためには、まず、本発明厚鋼板の鋼組成からＴｉ、ＲＥＭ、Ｚｒ、Ｃａ、Ｏを除く他の成分がほぼ上記鋼組成になるようにベース鋼を溶製し、Ｍｎ添加後のベース鋼に対して、脱酸元素であるＳｉ、Ａｌ等を添加することで、Ｔｉ添加前の溶存酸素量を０．００２０〜０．０１００質量％に制御する。そして、Ｔｉ添加前の溶存酸素量、Ｓ量を基に、下式から求まるＺ値を０．５８以上となるよう、ＲＥＭおよびＺｒ添加量を決定したうえで、Ｔｉを添加した後に、ＲＥＭ、Ｚｒを添加し、Ｃａを添加する場合はＴｉ添加後にＲＥＭ、Ｚｒ添加し、さらにその後にＣａを添加して本発明に係る所定組成の鋼を溶製し、鋳造する。
Ｚ＝（３．５×［ＲＥＭ］−０．７×［Ｏ］＋２．６×［Ｚｒ］＋０．３）／（［Ｓ］＋０．５）
なお、［Ｏ］、［Ｓ］はそれぞれＴｉ添加前の溶存Ｏ量、Ｓ量（共に質量％）であり、［ＲＥＭ］、［Ｚｒ］はそれぞれＲＥＭ、Ｚｒの添加量（質量％）である。
Next, production of the high-tensile thick steel plate for welding according to the present invention will be described. In this production, the production conditions from casting to reheating before rolling are important in order to form a fine oxide having a circle equivalent diameter of less than 2 μm and a dispersed structure of oxysulfide of 2 μm or more.
In order to obtain the dispersion of the fine oxides and oxysulfides, first, a base is formed so that the other components excluding Ti, REM, Zr, Ca, and O from the steel composition of the thick steel plate of the present invention have almost the above steel composition. By melting steel and adding Si, Al, etc. as deoxidizing elements to the base steel after Mn addition, the amount of dissolved oxygen before Ti addition is controlled to 0.0020-0.0100 mass% To do. Then, based on the amount of dissolved oxygen before addition of Ti and the amount of S, the REM and Zr addition amounts are determined so that the Z value obtained from the following formula is 0.58 or more, and after adding Ti, REM, When Zr is added and Ca is added, REM and Zr are added after Ti is added, and then Ca is added to melt and cast a steel having a predetermined composition according to the present invention.
Z = (3.5 × [REM] −0.7 × [O] + 2.6 × [Zr] +0.3) / ([S] +0.5)
[O] and [S] are the dissolved O amount and S amount (both mass%) before addition of Ti, respectively, and [REM] and [Zr] are the addition amount (mass%) of REM and Zr, respectively. .
Ｔｉ添加前の溶存酸素量が０．００２０％より少ないと、円相当径で２μｍより小さい酸化物が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またはＺｒを添加すると、粗大酸化物が形成され、やはり円相当径で２μｍより小さい酸化物が十分に得られない。Ｚ値は、ＲＥＭ硫化物形成に寄与するＲＥＭ、Ｓ量を考慮した値であり、Ｚ値が０．５８より小さいと、ＲＥＭに対するＳの割合が高くなりすぎるため、固溶Ｓが生じて靭性の劣化をもたらす。なお、Ｚ値の計算式中の各元素量の係数は実験的に決定した。 If the amount of dissolved oxygen before addition of Ti is less than 0.0020%, an oxide having an equivalent circle diameter of less than 2 μm cannot be secured sufficiently. Further, when the dissolved oxygen amount is more than 0.0100%, or when REM or Zr is added prior to Ti, a coarse oxide is formed, and an oxide having an equivalent circle diameter of less than 2 μm cannot be obtained sufficiently. The Z value is a value that takes into account the amount of REM and S that contribute to REM sulfide formation. If the Z value is less than 0.58, the ratio of S to REM becomes too high, so that solid solution S is generated and toughness is generated. Cause deterioration. In addition, the coefficient of each element amount in the calculation formula of Z value was determined experimentally.
Ｃａを添加する場合、円相当径で２μm 未満のＣａ含有微細酸化物であって、その構成元素（但し、酸素を除く。）の割合をＴｉ：１０％以上、ＲＥＭ：５〜５０％、Ｚｒ：５％以上、Ｃａ：５〜４０％に制御すると共にかかる組成のＣａ含有微細酸化物を鋼中に３００個／mm2 以上分散させるには、下記(1) および(2) の制御を行う必要がある。なお、上記構成元素割合の組成を有するＣａ含有微細酸化物は、下記(1) および(2) の制御を行わなくても、Ｔｉ添加後にＣａを添加することで鋼中に一定数生成するが、下記(1) 、(2) の制御を行うことで所定構成元素割合のＣａ含有微細酸化物の個数を３００個／mm2 以上に増やすことができ、粒内α変態促進効果を著しく向上させることができるようになる。
(1) Ｔｉ添加後にＲＥＭ、Ｚｒ添加し、さらにその後にＣａを添加する。
(2) Ｃａ添加から鋳込み開始までの時間ｔ（min ）を下記式によって定まる最小鋳込み時間（許容下限値）ｔｍ（min ）の経過後（ｔｍ＜ｔ）に鋳込む。式中の[Ｃａ]、[ＲＥＭ]はそれぞれ質量％で表されるＣａ、ＲＥＭの添加量である。
ｔｍ＝８−１．８×[Ｃａ]／（[ＲＥＭ]＋０．０１）
When Ca is added, it is a Ca-containing fine oxide with an equivalent circle diameter of less than 2 μm, and the proportion of its constituent elements (excluding oxygen) is Ti: 10% or more, REM: 5-50%, Zr : 5% or more, Ca: 5 to 40%, and in order to disperse 300 pieces / mm 2 or more of the Ca-containing fine oxide having such a composition in steel, the following controls (1) and (2) are performed. There is a need. The Ca-containing fine oxide having the composition of the above constituent elements is produced in a certain number in the steel by adding Ca after the addition of Ti, even without controlling the following (1) and (2). By controlling the following (1) and (2), the number of Ca-containing fine oxides having a predetermined constituent element ratio can be increased to 300 pieces / mm 2 or more, and the intragranular α transformation promotion effect is remarkably improved. Will be able to.
(1) Add REM and Zr after adding Ti, and then add Ca.
(2) The time t (min) from the addition of Ca to the start of casting is cast after the minimum casting time (allowable lower limit value) tm (min) determined by the following formula (tm <t). [Ca] and [REM] in the formula are addition amounts of Ca and REM expressed in mass%, respectively.
tm = 8−1.8 × [Ca] / ([REM] +0.01)
上記(1) のようにＣａ添加タイミングを制御する理由は以下のとおりである。Ｃａは酸化物生成能が高いため、Ｔｉ、ＲＥＭ、Ｚｒに先立ちＣａを添加すると、微細酸化物の主体がＣａ酸化物となり、構成元素割合がＴｉ：１０％以上、ＲＥＭ：５〜５０％、Ｚｒ：５％以上、Ｃａ：５〜４０％の範囲内の組成を有する、高い粒内α変態能を示すＣａ含有微細酸化物が規定個数（３００個／mm2 ）を満たさないようになる。このため、ＣａはＲＥＭ、Ｚｒの後に添加する必要がある。 The reason for controlling the Ca addition timing as in (1) above is as follows. Since Ca has a high oxide-forming ability, when Ca is added prior to Ti, REM, and Zr, the main component of the fine oxide is Ca oxide, and the constituent element ratio is Ti: 10% or more, REM: 5-50%, A Ca-containing fine oxide having a composition in the range of Zr: 5% or more and Ca: 5-40% and exhibiting high intragranular α-transforming ability does not satisfy the specified number (300 / mm 2 ). For this reason, Ca needs to be added after REM and Zr.
また、上記(2) のようにＣａ添加から鋳込み開始までの時間を制御する理由は以下のとおりである。ｔｍは、微細酸化物へのＣａ溶け込み時間を制御するためのパラメータである。Ｃａを最後に添加しても、微細酸化物の組成が規定範囲に達するためには、微細酸化物にＣａが溶け込む時間が必要である。この微細酸化物へのＣａ溶け込み時間を確保するために、Ｃａ添加から鋳込み開始までの時間を制御することが必要になる。Ｃａの溶け込み時間に対しては、Ｃａに次いで酸化物生成能の高いＲＥＭが大きな影響を与えるため、Ｃａ添加量に対してＲＥＭ添加量が多いほど、Ｃａ溶け込みに必要な時間が長くなる。このため、ｔｍを規定する式で示されるとおり、Ｃａ添加量が少ない、あるいはＲＥＭ添加量が多いほどｔｍは大きい値を取る。ＲＥＭ添加量が極めて少ない場合でもＣａ溶け込みにはある程度時間が必要であるため、ｔｍ式の分母にはＲＥＭ添加量に０．０１の定数項が加算されている。なお、ｔｍの計算式中の各元素量の係数は実験的に決定したものである。 The reason for controlling the time from the addition of Ca to the start of casting as in (2) is as follows. tm is a parameter for controlling the Ca dissolution time in the fine oxide. Even when Ca is added last, in order for the composition of the fine oxide to reach the specified range, it takes time for Ca to dissolve in the fine oxide. In order to secure the Ca dissolution time in the fine oxide, it is necessary to control the time from the addition of Ca to the start of casting. Since the REM with the highest oxide generation ability has a great influence on the Ca soaking time, the time required for the Ca soaking becomes longer as the REM adding amount is larger than the Ca adding amount. For this reason, as shown by the equation that defines tm, tm takes a larger value as the Ca addition amount decreases or the REM addition amount increases. Even when the amount of REM added is extremely small, a certain amount of time is required for Ca dissolution, so that a constant term of 0.01 is added to the amount of REM added to the denominator of the tm formula. In addition, the coefficient of each element amount in the calculation formula of tm is determined experimentally.
鋳造後の溶鋼の冷却については、凝固が進行する１４５０〜１５００℃の冷却時間を６０〜３００ｓに制御し、加えて、圧延前の再加熱において、最高加熱温度１０５０〜１２００℃の間に保ち、かつ、加熱開始から圧延開始までの時間を２ｈｒ以上とする。 For cooling of the molten steel after casting, the cooling time of 1450-1500 ° C. at which solidification proceeds is controlled to 60-300 s. In addition, in reheating before rolling, the maximum heating temperature is maintained between 1050-1200 ° C., And the time from a heating start to the rolling start shall be 2 hr or more.
鋳造時の１４５０〜１５００℃の冷却時間が６０ｓより短いと、酸硫化物表面に十分な量のＲＥＭ硫化物が形成されず、必要な粒内α変態が得られない。また、同冷却時間が３００ｓを超えると、酸化物の粗大化を招き、靭性低下の原因となる。さらに、圧延前の再加熱において、最高加熱温度が１０５０℃より低い、あるいは加熱開始から圧延開始までの時間が２ｈｒより短いと、ＲＥＭ硫化物が十分に成長せず、必要な粒内α変態が得られない。一方、最高加熱温度が１２００℃を超えると、ＲＥＭ硫化物の生成量が十分に確保できなくなり、必要な粒内α変態が得られないようになる。 When the cooling time of 1450-1500 ° C. during casting is shorter than 60 seconds, a sufficient amount of REM sulfide is not formed on the surface of oxysulfide, and the necessary intragranular α transformation cannot be obtained. On the other hand, if the cooling time exceeds 300 s, the oxide becomes coarse and causes a decrease in toughness. Furthermore, in the reheating before rolling, when the maximum heating temperature is lower than 1050 ° C., or when the time from the start of heating to the start of rolling is shorter than 2 hr, the REM sulfide does not grow sufficiently, and the necessary intragranular α transformation occurs. I can't get it. On the other hand, if the maximum heating temperature exceeds 1200 ° C., a sufficient amount of REM sulfide cannot be secured, and the necessary intragranular α transformation cannot be obtained.
上記の条件により冷却し、再加熱した鋳造片は、通常の低炭素鋼の熱間圧延に従って、圧延開始温度を１１００〜９００℃程度、圧延終了温度を９５０〜７５０℃程度とし、圧延を終了する。圧延終了後、例えば２〜１５℃／ｓ程度の冷却速度にて、室温〜５００℃程度の間の冷却停止温度まで冷却すればよい。冷却終了後、さらにテンパー処理を施してもよい。 The cast piece that has been cooled and reheated under the above conditions is subjected to a normal low carbon steel hot rolling with a rolling start temperature of about 1100 to 900 ° C and a rolling end temperature of about 950 to 750 ° C, and the rolling is completed. . What is necessary is just to cool to the cooling stop temperature between about room temperature and about 500 degreeC after the completion | finish of rolling at the cooling rate of about 2-15 degreeC / s, for example. You may perform a temper process after completion | finish of cooling.
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、Ｍｎを添加後の溶鋼にＳｉ等を添加して溶存酸素量を制御し、Ｚ値を考慮しつつ、ＲＥＭ、Ｚｒ添加量を決定のうえ、一部のもの（表２の鋼Ｎｏ．３６）を除いて、Ｔｉを添加した後、ＲＥＭ、Ｚｒを添加し、さらにＣａを添加するものについては、一部のもの（表１の鋼Ｎｏ．１２）を除いて、ＲＥＭ、Ｚｒ添加の後にＣａを添加して表１および表２の鋼を溶製した。鋼Ｎｏ．１２についてはＲＥＭ、Ｚｒ添加に先立ちＣａを添加した。Ｃａを添加したものについては、Ｃａ添加から鋳込み開始までの時間ｔ（ｍｉｎ）を制御しつつ、これらの溶鋼を鋳造して１４５０〜１５００℃の冷却時間ｔ１（ｓ）を変化させて凝固させた。このようにして鋳造したスラブを、圧延前の再加熱における最高加熱温度Ｔｍ（℃）、加熱開始から圧延開始までの時間ｔ２（ｈｒ）を変化させて加熱し、スラブを加熱した後引き続いて圧延開始温度を９５０℃程度、最終圧延温度を８８０℃程度として熱間圧延を施し、圧延終了後、冷却速度約５℃／ｓで水冷し、厚さ８０ｍｍの厚鋼板を製造した。製造過程における、Ｔｉ添加前の溶存酸素量［Ｏ］（％）、Ｚ値、ｔ（ｍｉｎ）、前記ｔの制御基準となる最小鋳込み時間（許容下限値）ｔｍ、ｔ１（ｓ）、Ｔｍ（℃）、ｔ２（ｈｒ）の各値を表３、表４に示す。 Use a vacuum melting furnace (150 kg), add Si, etc. to the molten steel after adding Mn to control the dissolved oxygen amount, and determine the REM and Zr addition amounts while taking into account the Z value. Except (Steel No. 36 in Table 2), after adding Ti, REM and Zr are added, and Ca is further added except for some (Steel No. 12 in Table 1). Then, after addition of REM and Zr, Ca was added to melt the steels in Tables 1 and 2. Steel No. For No. 12, Ca was added prior to the addition of REM and Zr. About what added Ca, while controlling time t (min) from Ca addition to casting start, these molten steel was cast and it was made to solidify by changing the cooling time t1 (s) of 1450-1500 degreeC. . The slab cast in this manner is heated while changing the maximum heating temperature Tm (° C.) in reheating before rolling and the time t2 (hr) from the start of heating to the start of rolling, and then the slab is heated and subsequently rolled. Hot rolling was performed at a starting temperature of about 950 ° C. and a final rolling temperature of about 880 ° C., and after completion of rolling, water cooling was performed at a cooling rate of about 5 ° C./s to produce a thick steel plate having a thickness of 80 mm. In the manufacturing process, dissolved oxygen amount [O] (%) before addition of Ti, Z value, t (min), minimum casting time (allowable lower limit value) tm, t1 (s), Tm (which is a control standard of the t) C) and t2 (hr) are shown in Tables 3 and 4.
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、円相当径で２μｍ以下の酸化物の個数密度を以下の要領で測定した。 A test piece was cut out from each of the obtained thick steel plates at t (plate thickness) / 4 position, and a field emission scanning was performed on the cross section parallel to the rolling direction and the plate thickness direction (cross section perpendicular to the rolling surface and along the rolling direction). Observation was made using a scanning electron microscope (device name: SUPRA 35, manufactured by Carl Zeiss) (hereinafter referred to as FE-SEM), and the number density of oxides having an equivalent circle diameter of 2 μm or less was measured 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）を用いて画像解析を行い、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、表４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 included in each field of view and having a maximum diameter of 2 μm or less was measured with an 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 image processing software (software name: Image-Pro Plus, manufactured by Media Cybernetic), and the number density N1 of these oxides having a circle equivalent diameter of less than 2 μm ( Piece / mm 2 ) was calculated. Tables 3 and 4 show the values of N1.
また、Ｃａを含む鋼については、上記Ｎ１個／ｍｍ2 の酸化物のうち、構成する元素の割合が、酸素を除き、Ｔｉ：１０％以上、ＲＥＭ：５〜５０％、Ｚｒ：５％以上、Ｃａ：５〜４０％である酸化物をＥＤＳ測定により判定し、円相当径で２μｍより小さい酸化物で、構成する元素の割合が上記の酸化物の個数密度Ｎｓ（個／ｍｍ2 ）を算出した。Ｎｓの値も表３、表４に併記した。なお、酸化物組成のＥＤＳ測定時に検出されるＦｅは、母相Ｆｅの影響を受けていると考えられるため、測定より除外した。 Also, the steels including Ca, among the oxides of the N1 pieces / mm 2, the ratio of elements constituting the, except oxygen, Ti: 10% or more, REM: 5~50%, Zr: 5% or more , Oxide of Ca: 5 to 40% is determined by EDS measurement, and the equivalent circle diameter is less than 2 μm, and the ratio of the constituent elements is the number density Ns of oxides (pieces / mm 2 ). Calculated. The values of Ns are also shown in Tables 3 and 4. Note that Fe detected during the EDS measurement of the oxide composition is considered to be affected by the parent phase Fe and thus excluded from the measurement.
また、同様に、得られた各厚鋼板のｔ（板厚）／４位置で、圧延方向および板厚方向に平行な断面を、ＥＰＭＡ装置（装置名：ＥＰＭＡ−８７０５、島津製作所製）を用いて観察し、ＲＥＭの酸化物換算値：１０％以上、Ｍｎの酸化物換算値：２０％以下、Ｓ：３〜２０％を満足する、円相当径で２μｍ以上の酸硫化物の個数密度を以下の要領で測定した。 Similarly, using the EPMA apparatus (apparatus name: EPMA-8705, manufactured by Shimadzu Corp.), a cross section parallel to the rolling direction and the sheet thickness direction at t (plate thickness) / 4 position of each thick steel plate obtained. The number density of oxysulfides with an equivalent circle diameter of 2 μm or more, which satisfies REM oxide conversion value: 10% or more, Mn oxide conversion value: 20% or less, and S: 3-20%. The measurement was performed as follows.
まず、ＥＰＭＡ装置の観察倍率を２００倍に設定し、４ｍｍ×８ｍｍの観察視野内に存在する、円相当径が２μｍ以上である介在物粒子について、質量％で表される平均組成の定量分析を行った。得られた分析結果から、ＯおよびＳが含まれる介在物粒子を酸硫化物と判定し、個々の酸硫化物に含まれるＲＥＭ（Ｃｅ、Ｌａ） 、Ｚｒ、Ｃａ、Ｍｎ、Ｍｇ、Ａｌ、Ｓｉの平均濃度を基に、ＲＥＭ2Ｏ3、ＺｒＯ2 、ＣａＯ、ＭｎＯ、ＭｇＯ、Ａｌ2Ｏ3、ＳｉＯ2 に対する前記各元素の酸化物換算値を算出し、これらの酸化物換算値と酸硫化物中のＳの平均濃度の合計値Σを求めた後、ＲＥＭ、Ｍｎの各酸化物換算値およびＳの平均濃度をΣで規格化した（除した）値を算出し、得られた値（割合）が、ＲＥＭの酸化物換算値：１０％以上、Ｍｎの酸化物換算値：２０％以下、Ｓ：３〜２０％を満足する酸硫化物の個数密度Ｎ２（個／ｃｍ2 ）を算出した。Ｎ２の値を表３、表４に示す。 First, the EPMA apparatus observation magnification is set to 200 times, and quantitative analysis of the average composition expressed in mass% is performed for inclusion particles present in the observation field of 4 mm × 8 mm and having an equivalent circle diameter of 2 μm or more. went. From the obtained analysis results, inclusion particles containing O and S are determined as oxysulfides, and REM (Ce, La), Zr, Ca, Mn, Mg, Al, Si contained in each oxysulfide is determined. On the basis of the average concentration of REM 2 O 3 , ZrO 2 , CaO, MnO, MgO, Al 2 O 3 and SiO 2 , oxide equivalent values of the respective elements are calculated, and these oxide equivalent values and oxysulfides After obtaining the total value Σ of the average concentration of S in the product, the REM and Mn oxide equivalent values and the average concentration of S were normalized (divided) by Σ, and the obtained value ( The oxysulfide number density N2 (pieces / cm 2 ) satisfying the following ratio: REM oxide equivalent value: 10% or more, Mn oxide equivalent value: 20% or less, and S: 3-20% did. Tables 3 and 4 show the values of N2.
次に、得られた各厚鋼板から、溶接継手作製用試験片を採取し、各試験片のＨＡＺのシャルピー衝撃試験を以下の要領で実施した。各溶接継手作製用試験片に、Ｖ開先を加工し、入熱量５０ｋＪ／ｍｍにてエレクトロガスアーク溶接を施し、溶接継手を得た。これら溶接継手より、溶接金属部近傍のＨＡＺに切欠を加工したシャルピー衝撃試験片を採取し、試験温度−４０℃にてシャルピー衝撃試験を実施し、得られた吸収エネルギーｖＥ-40 （Ｊ）を測定した。ｖＥ-40 （Ｊ）が１８０Ｊを超えるものは、ＨＡＺ靭性に優れると評価することができる。得られたｖＥ-40の値を表３、表４に併せて示す。 Next, test pieces for producing welded joints were collected from each of the obtained thick steel plates, and a HAZ Charpy impact test of each test piece was performed as follows. Each weld joint preparation test piece was processed with a V groove and subjected to electrogas arc welding at a heat input of 50 kJ / mm to obtain a welded joint. From these welded joints, Charpy impact test pieces with notches formed in the HAZ near the weld metal part were collected, and Charpy impact tests were conducted at a test temperature of −40 ° C., and the obtained absorbed energy vE −40 (J) was obtained. It was measured. Those having vE -40 (J) exceeding 180 J can be evaluated as having excellent HAZ toughness. The obtained vE- 40 values are shown in Tables 3 and 4 together.
表１〜４から明らかなとおり、発明例の試料Ｎｏ．１〜３５は、厚鋼板の組成、鋳造および圧延前の再加熱プロセスを適切に制御したので、円相当径が２μｍ未満の小さい酸化物、および円相当径２μｍ以上の酸硫化物、さらにＣａを添加した試料では円相当径で２μｍより小さい酸化物で、Ｔｉ：１０％以上、ＲＥＭ：５〜５０％、Ｚｒ：５％以上、Ｃａ：５〜４０％である酸化物を分散させることに成功し、ＨＡＺ靭性において高い値が得られている。
一方、比較例の試料Ｎｏ．３６は、鋳造時においてＴｉ添加に先立ち、ＲＥＭ、Ｚｒを添加したため、円相当径が２μｍより小さい酸化物が十分に存在せず、ＨＡＺ靭性が低下している。また、比較例の試料Ｎｏ．３７〜４１、５８は発明成分範囲を満足するものの、製造条件（Ｔｉ添加前の溶存酸素量、Ｚ値、鋳造後の冷却過程における１４５０〜１５００℃の冷却時間ｔ１、圧延前の再加熱における最高加熱温度Ｔｍ、加熱開始から圧延開始までの時間ｔ２のいずれか）が適切でないため、また試料No. ４２〜５６は製造条件は適切であるが、鋼の組成が適正な範囲から逸脱したため、No. ５７は両者が適切でないため、規定の酸化物、および酸硫化物形態が得られなかったか、あるいはおそらく粗大介在物の増加、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、ＨＡＺ靭性が低下している。
As is clear from Tables 1 to 4, Sample No. 1 to 35, since the composition of the thick steel plate, the reheating process before casting and rolling were appropriately controlled, a small oxide with an equivalent circle diameter of less than 2 μm, an oxysulfide with an equivalent circle diameter of 2 μm or more, and further Ca In the added sample, an oxide having an equivalent circle diameter of less than 2 μm and succeeding in dispersing an oxide with Ti: 10% or more, REM: 5-50%, Zr: 5% or more, Ca: 5-40% However, a high value is obtained in the HAZ toughness.
On the other hand, Sample No. In No. 36, since REM and Zr were added prior to the addition of Ti at the time of casting, an oxide having an equivalent circle diameter of less than 2 μm was not sufficiently present, and HAZ toughness was lowered. In addition, sample No. Although 37 to 41 and 58 satisfy the invention component range, the production conditions (dissolved oxygen amount before addition of Ti, Z value, cooling time t1 of 1450 to 1500 ° C. in the cooling process after casting, maximum in reheating before rolling) Any of heating temperature Tm and time t2 from the start of heating to the start of rolling) is not appropriate, and sample Nos. 42 to 56 have appropriate manufacturing conditions, but the composition of the steel deviated from an appropriate range. 57 is not suitable for both, so the prescribed oxide and oxysulfide forms could not be obtained, or possibly increased coarse inclusions, increased impurities, excessive strengthening, grain boundary segregation of solid solution elements, etc. For reasons, the HAZ toughness is reduced.
Claims (6)
Ｃ ：０．０２〜０．１２％、
Ｓｉ：０．４０％以下（０％を含む）、
Ｍｎ：１．０〜２．０％、
Ｐ ：０．０３０％以下（０％を含む）、
Ｓ ：０．００１〜０．０２５％、
Ａｌ：０．０５０％以下（０％を含む）、
Ｔｉ：０．００５〜０．１００％、
ＲＥＭ：０．０００１〜０．０５００％、
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からなり、
円相当径で２μｍ未満の酸化物が分散して５００個／ｍｍ2 以上含有され、
円相当径で２μｍ以上の酸硫化物が分散して４０〜１０００個／ｃｍ2 含有され、
前記円相当径で２μｍ以上の酸硫化物を形成するＲＥＭ、Ｚｒ、Ｃａ、Ｍｎ、Ｍｇ、Ａｌ、Ｓｉの所定酸化物をそれぞれＲＥＭ2Ｏ3、ＺｒＯ2 、ＣａＯ、ＭｎＯ、ＭｇＯ、Ａｌ2Ｏ3、ＳｉＯ2 とし、前記酸硫化物を形成する元素の内のある元素の平均濃度に（当該元素の所定酸化物の分子量／当該元素の原子量）を掛けて算出した値を当該元素の酸化物換算値というとき、前記酸硫化物を形成する前記各元素の平均濃度（質量％）に基づいて算出した前記各元素の酸化物換算値と酸硫化物中のＳの平均濃度の合計値に対するＲＥＭの酸化物換算値、Ｍｎの酸化物換算値およびＳ濃度の割合がそれぞれ、ＲＥＭの酸化物換算値：１０％以上、Ｍｎの酸化物換算値：２０％以下、Ｓ：３〜２０％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。 Chemical composition is mass%,
C: 0.02 to 0.12%,
Si: 0.40% or less (including 0%),
Mn: 1.0-2.0%,
P: 0.030% or less (including 0%),
S: 0.001 to 0.025%,
Al: 0.050% or less (including 0%),
Ti: 0.005 to 0.100%,
REM: 0.0001-0.0500%
Zr: 0.0001 to 0.0500%,
N: 0.0020 to 0.0300%,
O: 0.0005 to 0.0100% is contained,
The balance consists of Fe and inevitable impurities,
An oxide having an equivalent circle diameter of less than 2 μm is dispersed and contained at 500 pieces / mm 2 or more,
An oxysulfide having an equivalent circle diameter of 2 μm or more is dispersed and contained in an amount of 40 to 1000 / cm 2 .
The predetermined oxides of REM, Zr, Ca, Mn, Mg, Al, and Si that form an oxysulfide having an equivalent circle diameter of 2 μm or more are respectively REM 2 O 3 , ZrO 2 , CaO, MnO, MgO, and Al 2 O. 3 , SiO 2, and the value calculated by multiplying the average concentration of an element among the elements forming the oxysulfide by (molecular weight of the predetermined oxide of the element / atomic weight of the element) is the oxide of the element When referred to as a conversion value, REM for the total value of the oxide conversion value of each element calculated based on the average concentration (% by mass) of each element forming the oxysulfide and the average concentration of S in the oxysulfide The oxide conversion value of Mn, the oxide conversion value of Mn, and the ratio of S concentration are respectively REM oxide conversion value: 10% or more, Mn oxide conversion value: 20% or less, and S: 3-20%. Excellent toughness of heat-affected zone during high heat input welding High strength thick steel plate for welding.
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, 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 steel plate for welding according to any one of claims 1 to 3, comprising one or more of them.
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から４のいずれか１項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 any one of claims 1 to 4, comprising one or more of them.
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Cited By (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2011038180A (en) * | 2009-07-15 | 2011-02-24 | Kobe Steel Ltd | Steel member having excellent toughness in weld heat affected zone, and method for producing the same |
| JP2011074403A (en) * | 2009-09-16 | 2011-04-14 | Jfe Steel Corp | Steel for high heat input welding |
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| JP2011127220A (en) * | 2009-11-18 | 2011-06-30 | Kobe Steel Ltd | Method for manufacturing steel member excellent in toughness at weld heat-affected zone |
| JP2011241461A (en) * | 2010-05-20 | 2011-12-01 | Kobe Steel Ltd | Thick steel plate excellent in toughness of weld heat-affected zone |
| JP2012046815A (en) * | 2010-08-30 | 2012-03-08 | Kobe Steel Ltd | METHOD FOR PRODUCING Zr-CONTAINING STEEL |
| JP2012092422A (en) * | 2010-09-29 | 2012-05-17 | Kobe Steel Ltd | Thick steel plate excellent in toughness of weld heat-affected zone |
| JP2012092425A (en) * | 2010-09-29 | 2012-05-17 | Kobe Steel Ltd | Thick steel plate 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 |
| CN103103440A (en) * | 2011-11-14 | 2013-05-15 | 株式会社神户制钢所 | Steel plate with excellent toughness in heat-affected zone |
| JP2013213273A (en) * | 2012-03-09 | 2013-10-17 | Kobe Steel Ltd | Thick steel plate superior in ultra-low temperature toughness |
| JP2013234381A (en) * | 2012-04-13 | 2013-11-21 | Kobe Steel Ltd | Thick steel plate with excellent cryogenic toughness |
| 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 |
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| JP2016079461A (en) * | 2014-10-17 | 2016-05-16 | 株式会社神戸製鋼所 | Thick steel plate for tank excellent in the toughness of weld heat affected zone |
| JP2018016890A (en) * | 2017-09-26 | 2018-02-01 | 株式会社神戸製鋼所 | Thick steel sheet for tank excellent in toughness of hot affected zone |
| EP3282028A4 (en) * | 2015-04-10 | 2018-11-07 | Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) | Steel sheet for high strength line pipe with excellent low temperature toughness and steel pipe for high strength line pipe |
| KR20200076387A (en) | 2018-12-19 | 2020-06-29 | 주식회사 포스코 | Ultra thick structural steel having superior brittle crack initiation resistance and method of manufacturing the same |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP5883257B2 (en) * | 2011-09-13 | 2016-03-09 | 株式会社神戸製鋼所 | Steel material excellent in toughness of base metal and weld heat-affected zone, and manufacturing method thereof |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2007247004A (en) * | 2006-03-16 | 2007-09-27 | Kobe Steel Ltd | Low yield ratio high tensile steel having excellent toughness of weld heat-affected zone and manufacturing method therefor |
| JP2007247005A (en) * | 2006-03-16 | 2007-09-27 | Kobe Steel Ltd | Steel having excellent toughness of weld heat-affected zone and excellent base metal toughness and method for manufacturing the same |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1946862B (en) * | 2004-04-07 | 2012-08-29 | 新日本制铁株式会社 | Thick high strength steel plate having excellent low temperature toughness in welding heat affected zone caused by high heat input welding |
| JP4311740B2 (en) * | 2004-10-27 | 2009-08-12 | 株式会社神戸製鋼所 | Thick steel plate with high heat input welded joint toughness |
| JP4825057B2 (en) * | 2005-09-12 | 2011-11-30 | 株式会社神戸製鋼所 | Steel with excellent toughness of weld heat affected zone and its manufacturing method |
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2008
- 2008-03-03 JP JP2008051670A patent/JP5201665B2/en not_active Expired - Fee Related
- 2008-11-07 CN CN2008101748813A patent/CN101435051B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007247004A (en) * | 2006-03-16 | 2007-09-27 | Kobe Steel Ltd | Low yield ratio high tensile steel having excellent toughness of weld heat-affected zone and manufacturing method therefor |
| JP2007247005A (en) * | 2006-03-16 | 2007-09-27 | Kobe Steel Ltd | Steel having excellent toughness of weld heat-affected zone and excellent base metal toughness and method for manufacturing the same |
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| JP2011038180A (en) * | 2009-07-15 | 2011-02-24 | Kobe Steel Ltd | Steel member having excellent toughness in weld heat affected zone, and method for producing the same |
| JP2011074403A (en) * | 2009-09-16 | 2011-04-14 | Jfe Steel Corp | Steel for high heat input welding |
| JP2011127220A (en) * | 2009-11-18 | 2011-06-30 | Kobe Steel Ltd | Method for manufacturing steel member excellent in toughness at weld heat-affected zone |
| JP2011117057A (en) * | 2009-12-07 | 2011-06-16 | Kobe Steel Ltd | Thick steel plate having superior toughness at weld heat-affected zone and superior uniformity of strength |
| JP2011241461A (en) * | 2010-05-20 | 2011-12-01 | Kobe Steel Ltd | Thick steel plate excellent in toughness of weld heat-affected zone |
| JP2012046815A (en) * | 2010-08-30 | 2012-03-08 | Kobe Steel Ltd | METHOD FOR PRODUCING Zr-CONTAINING STEEL |
| JP2012092422A (en) * | 2010-09-29 | 2012-05-17 | Kobe Steel Ltd | Thick steel plate excellent in toughness of weld heat-affected zone |
| JP2012092425A (en) * | 2010-09-29 | 2012-05-17 | Kobe Steel Ltd | Thick steel plate excellent in toughness of weld heat-affected zone |
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| 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 |
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| CN103103440A (en) * | 2011-11-14 | 2013-05-15 | 株式会社神户制钢所 | Steel plate with excellent toughness in heat-affected zone |
| JP2013213273A (en) * | 2012-03-09 | 2013-10-17 | Kobe Steel Ltd | Thick steel plate superior in ultra-low temperature toughness |
| JP2013234381A (en) * | 2012-04-13 | 2013-11-21 | Kobe Steel Ltd | Thick steel plate with excellent cryogenic toughness |
| 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 |
| EP2977479A4 (en) * | 2013-03-22 | 2016-11-30 | Kobe Steel Ltd | Steel material having superior toughness at welding heat affected zone |
| JP2014185364A (en) * | 2013-03-22 | 2014-10-02 | Kobe Steel Ltd | Steel material excellent in toughness of welded heat affected zone |
| 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 |
| JP2014214371A (en) * | 2013-04-30 | 2014-11-17 | 株式会社神戸製鋼所 | Steel sheet excellent in sour resistance and haz toughness |
| JP2016079461A (en) * | 2014-10-17 | 2016-05-16 | 株式会社神戸製鋼所 | Thick steel plate for tank excellent in the toughness of weld heat affected zone |
| EP3282028A4 (en) * | 2015-04-10 | 2018-11-07 | Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) | Steel sheet for high strength line pipe with excellent low temperature toughness and steel pipe for high strength line pipe |
| JP2018016890A (en) * | 2017-09-26 | 2018-02-01 | 株式会社神戸製鋼所 | Thick steel sheet for tank excellent in toughness of hot affected zone |
| KR20200076387A (en) | 2018-12-19 | 2020-06-29 | 주식회사 포스코 | Ultra thick structural steel having superior brittle crack initiation resistance and method of manufacturing the same |
Also Published As
| Publication number | Publication date |
|---|---|
| CN101435051B (en) | 2011-04-20 |
| CN101435051A (en) | 2009-05-20 |
| JP5201665B2 (en) | 2013-06-05 |
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