JP2007100213A - Steel having excellent toughness in weld heat-affected zone and manufacturing method therefor - Google Patents

Steel having excellent toughness in weld heat-affected zone and manufacturing method therefor Download PDF

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JP2007100213A
JP2007100213A JP2006160998A JP2006160998A JP2007100213A JP 2007100213 A JP2007100213 A JP 2007100213A JP 2006160998 A JP2006160998 A JP 2006160998A JP 2006160998 A JP2006160998 A JP 2006160998A JP 2007100213 A JP2007100213 A JP 2007100213A
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steel material
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steel
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JP4825057B2 (en
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Tetsushi Deura
哲史 出浦
Tomoko Sugimura
朋子 杉村
Hideaki Suito
英昭 水渡
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Kobe Steel Ltd
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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
    • C22C38/06—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
    • C22C38/001—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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper

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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)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel having excellent toughness in the weld heat-affected zone, and to provide a manufacturing method therefor. <P>SOLUTION: The steel has a composition comprising, by mass, 0.01 to 0.2% C, ≤0.5% (excluding 0%) Si, ≤2.5% (excluding 0%) Mn and ≤0.01% (excluding 0%) N, satisfying ≤0.02% (including 0%) P, ≤0.015% (including 0%) S and ≤0.01% (including 0%) Al, further comprising 0.001 to 0.1% rare earth metals and/or 0.0003 to 0.02% Ca, and 0.001 to 0.05% Zr, respectively, and also comprising the oxide of rare earth metals and/or Cao, and ZrO<SB>2</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、橋梁や高層建造物、船舶などに使用される鋼材を溶接するにあたり、熱影響を受ける部位（以下、「溶接熱影響部」または「ＨＡＺ」ということがある）での靭性を改善した鋼材およびその製法に関するものである。   The present invention improves the toughness at the part affected by heat (hereinafter, sometimes referred to as “welding heat affected zone” or “HAZ”) when welding steel materials used in bridges, high-rise buildings, ships, etc. The present invention relates to a steel material and its manufacturing method.

橋梁や高層建造物、船舶などに使用される鋼材に要求される特性は、近年益々厳しくなっており、とりわけ良好な靭性が求められている。これらの鋼材は、一般的に溶接にて接合されることが多いが、特にＨＡＺは溶接時に熱影響を受けて靭性が劣化しやすいという問題がある。この靭性劣化は溶接時の入熱量が大きくなるほど顕著に現れ、その原因は溶接時の入熱量が大きくなるとＨＡＺの冷却速度が遅くなり、焼入性が低下して粗大な島状マルテンサイトを生成することにあると考えられている。従ってＨＡＺの靭性を改善するには、溶接時の入熱量を極力抑えればよい。その一方で、溶接作業効率を高めるうえでは、例えばエレクトロガスアーク溶接法やフラックス−銅バッキング溶接法などの大入熱溶接法の採用が望まれる。   The properties required for steel materials used in bridges, high-rise buildings, ships and the like have become increasingly severe in recent years, and particularly good toughness is required. In general, these steel materials are often joined by welding. In particular, HAZ has a problem that the toughness is easily deteriorated due to thermal influence during welding. This toughness deterioration becomes more prominent as the heat input during welding increases, and the cause is that the larger the heat input during welding, the slower the cooling rate of the HAZ, and the lower the hardenability and the generation of coarse island martensite. It is thought that there is to do. Therefore, in order to improve the toughness of the HAZ, the heat input during welding should be suppressed as much as possible. On the other hand, in order to increase the welding work efficiency, it is desired to employ a high heat input welding method such as an electrogas arc welding method or a flux-copper backing welding method.

そこで大入熱溶接法を採用した場合でもＨＡＺ靭性の劣化を抑制する鋼材が既に提案されている。例えば特許文献１には、鋼材中に微細なＴｉＮを分散再析出させることで、大入熱溶接を行なったときのＨＡＺで生じるオーステナイト粒の粗大化を抑制し、ＨＡＺ靭性の劣化を抑えた鋼材が提案されている。しかし本発明者らが検討したところ、溶接金属が１４００℃以上の高温になると、ＨＡＺのうち特に溶接金属に近接した部位（以下、「ボンド部」ということがある）において溶接時に受ける熱によって上記ＴｉＮが固溶消失してしまい、靭性劣化を抑えることができないことが分かった。   Therefore, steel materials that suppress the deterioration of HAZ toughness even when the high heat input welding method is adopted have already been proposed. For example, Patent Document 1 discloses a steel material in which fine TiN is dispersed and reprecipitated in the steel material to suppress coarsening of austenite grains generated in the HAZ when high heat input welding is performed, and deterioration in HAZ toughness is suppressed. Has been proposed. However, as a result of investigations by the present inventors, when the weld metal reaches a high temperature of 1400 ° C. or higher, the above-described heat is received by the heat received during welding at a portion of the HAZ that is particularly close to the weld metal (hereinafter sometimes referred to as “bond portion”). It was found that TiN disappeared from the solid solution and toughness deterioration could not be suppressed.

一方、特許文献２には、母材とＨＡＺの靭性を向上させる技術として、鋼材に含まれる酸化物と窒化物の存在形態を制御することが開示されている。この文献には、ＴｉとＺｒを組み合わせて使用することにより、微細な酸化物と窒化物を生成させて母材とＨＡＺの靭性を向上させること、こうした微細な酸化物と窒化物を生成させるには、ＴｉとＺｒをこの順で添加すればよいことが開示されている。しかし本発明者らが検討したところ、ＨＡＺの靭性を更に高めるには、酸化物量を増やせばよいことが判明したが、上記特許文献２に開示されている技術において、酸化物量を増やすためにＴｉやＺｒを多量に添加すると、ＴｉやＺｒなどの炭化物を形成し、鋼材（母材）の靭性が却って低下することが分かった。   On the other hand, Patent Document 2 discloses controlling the form of oxides and nitrides contained in steel as a technique for improving the toughness of the base material and the HAZ. In this document, Ti and Zr are used in combination to produce fine oxides and nitrides to improve the toughness of the base material and HAZ, and to produce such fine oxides and nitrides. Discloses that Ti and Zr may be added in this order. However, as a result of studies by the present inventors, it has been found that the oxide amount should be increased in order to further increase the toughness of the HAZ. However, in the technique disclosed in Patent Document 2, the Ti content is increased in order to increase the oxide amount. It has been found that when a large amount of Zr or Zr is added, carbides such as Ti and Zr are formed, and the toughness of the steel (base material) is decreased.

ところで本発明者らは、溶接時に高温の熱影響を受けた場合でもＨＡＺの靭性が劣化しない鋼材を特許文献３に先に提案している。この鋼材は、Ｌａ2Ｏ3−ＳｉＯ2系酸化物やＣｅ2Ｏ3−ＳｉＯ2系酸化物、Ｌａ2Ｏ3−Ｃｅ2Ｏ3−ＳｉＯ2系酸化物などの複合酸化物を鋼材中に分散させたものであり、この複合酸化物は、溶鋼中では液状で存在するため鋼中に微細分散し、しかも溶接時には熱影響を受けても固溶消失しないため、ＨＡＺの靭性を向上させる。そしてこの文献には、上記複合酸化物を生成させるために、溶存酸素量を調整した溶鋼へＬａやＣｅを添加し、次いでＳｉを添加すればよいことを開示している。また、この文献には鋼材にＴｉを含有させて鋼材組織中にＴｉＮを析出させることによってＨＡＺの靭性を更に高めることを開示している。そしてこうしたＴｉＮを生成させるには、上記複合酸化物が生成した溶鋼へＴｉを添加すればよいことを開示している。
特公昭５５−２６１６４号公報 特開２００３−２１３３６６号公報 特開２００５−４８２６５号公報 By the way, the present inventors have previously proposed a steel material in which the HAZ toughness does not deteriorate even when subjected to high-temperature heat effects during welding. This steel material is composed of complex oxides such as La 2 O 3 —SiO 2 oxide, Ce 2 O 3 —SiO 2 oxide, and La 2 O 3 —Ce 2 O 3 —SiO 2 oxide in the steel material. Since this composite oxide exists in liquid steel in a liquid state, it is finely dispersed in the steel, and since the solid solution does not disappear even if it is affected by heat during welding, the toughness of the HAZ is improved. And in this document, in order to produce | generate the said complex oxide, La and Ce should just be added to the molten steel which adjusted the amount of dissolved oxygen, and then Si may be added. Further, this document discloses that the toughness of HAZ is further enhanced by adding Ti to the steel material and precipitating TiN in the steel material structure. And in order to produce | generate such TiN, what is necessary is just to add Ti to the molten steel which the said complex oxide produced | generated.
Japanese Patent Publication No.55-26164 JP 2003-213366 A JP 2005-48265 A

本発明者らは、特許文献３として先に開示した技術に対して、上記組成の複合酸化物以外の組成の酸化物に注目し、上記特許文献３とは異なる組成の酸化物を鋼材中に分散させることによってＨＡＺの靭性を高めることができないかについて検討を重ねた。即ち、本発明の目的は、上記特許文献３で提案した鋼材とは異なる組成の酸化物を鋼材中に分散させることによって、ＨＡＺ（溶接熱影響部）の靭性に優れた鋼材およびその製法を提供することにある。   The present inventors pay attention to an oxide having a composition other than the composite oxide having the above composition with respect to the technique disclosed above as Patent Document 3, and an oxide having a composition different from that of Patent Document 3 is incorporated into the steel material. Investigations were made as to whether the toughness of the HAZ could be increased by dispersing. That is, the object of the present invention is to provide a steel material excellent in HAZ (welding heat affected zone) toughness and a method for producing the same by dispersing an oxide having a composition different from that proposed in Patent Document 3 in the steel material. There is to do.

本発明者らは、上記特許文献３で提案した成分系とは異なる組成の鋼材について、溶接熱影響部の靭性を高めるべく検討を重ねてきた。その結果、ＲＥＭおよび／またはＣａと、Ｚｒを鋼材に複合添加することによって、該鋼材に含まれる全酸化物の組成を測定したときに、ＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2が含有するように調整すれば、溶接熱影響部の靭性を高めることができること、またこうした成分系に更にＴｉを複合添加することによって、前記鋼材に含まれる全酸化物の組成を測定したときに、Ｔｉ酸化物を含有するように調整すれば、溶接熱影響部の靭性が一層向上することを見出し、本発明を完成した。 The inventors of the present invention have repeatedly studied to improve the toughness of the heat affected zone of the steel material having a composition different from that of the component system proposed in Patent Document 3. As a result, when the composition of all oxides contained in the steel material was measured by adding REM and / or Ca and Zr to the steel material, the REM oxide and / or CaO and ZrO 2 contained. If adjusted so that the toughness of the weld heat affected zone can be increased, and when the composition of all oxides contained in the steel material is measured by further adding Ti to such a component system, Ti It has been found that the toughness of the weld heat affected zone can be further improved by adjusting to contain an oxide, and the present invention has been completed.

即ち、上記課題を解決することのできた本発明に係る鋼材とは、Ｃ：０．０１〜０．２％（「質量％」の意味。以下同じ）、Ｓｉ：０．５％以下（０％を含まない）、Ｍｎ：２．５％以下（０％を含まない）、およびＮ：０．０１％以下（０％を含まない）を含み、Ｐ：０．０２％以下（０％を含む）、Ｓ：０．０１５％以下（０％を含む）、およびＡｌ：０．０１％以下（０％を含む）を満足すると共に、更に、ＲＥＭ：０．００１〜０．１％および／またはＣａ：０．０００３〜０．０２％と、Ｚｒ：０．００１〜０．０５％を夫々含有し、且つ該鋼材に含まれる全酸化物の組成を測定したときに、酸化物としてＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2を含有する点に要旨を有する。 That is, the steel material according to the present invention that has solved the above problems is C: 0.01 to 0.2% (meaning “mass%”; the same applies hereinafter), Si: 0.5% or less (0%) ), Mn: not more than 2.5% (not including 0%), and N: not more than 0.01% (not including 0%), P: not more than 0.02% (including 0%) ), S: 0.015% or less (including 0%), and Al: 0.01% or less (including 0%), and REM: 0.001 to 0.1% and / or When the composition of all oxides contained in the steel material was measured when Ca: 0.0003 to 0.02% and Zr: 0.001 to 0.05%, respectively, oxidation of REM as an oxide It has a gist in that it contains a product and / or CaO and ZrO 2 .

前記鋼材は、該鋼材に含まれる全酸化物の組成を測定し、合計を１００％としたときに、ＲＥＭの酸化物および／またはＣａＯの合計が５％以上で、ＺｒＯ2が５％以上を満足することが好ましい。 The steel material measures the composition of all oxides contained in the steel material, and when the total is 100%, the total of REM oxide and / or CaO is 5% or more, and ZrO 2 is 5% or more. It is preferable to satisfy.

前記鋼材は、更に他の元素として、Ｔｉ：０．０８％以下（０％を含まない）を含むと共に、前記鋼材に含まれる全酸化物の組成を測定したときに、Ｔｉ酸化物を含有することが好ましく、Ｔｉを含むことによって溶接熱影響部の靭性を一層向上させることができる。前記鋼材がＴｉを含む場合には、全酸化物の組成を測定したときに、酸化物としてＴｉ酸化物が０．３％以上を満足することが好ましい。   The steel material further contains Ti: 0.08% or less (not including 0%) as another element, and also contains a Ti oxide when the composition of all oxides contained in the steel material is measured. Preferably, the toughness of the weld heat affected zone can be further improved by including Ti. When the steel material contains Ti, it is preferable that the Ti oxide satisfies 0.3% or more as an oxide when the composition of all oxides is measured.

前記鋼材は、更に他の元素として、Ｃｕ：２％以下（０％を含まない）、Ｎｉ：３．５％以下（０％を含まない）、Ｃｒ：３％以下（０％を含まない）、Ｍｏ：１％以下（０％を含まない）、Ｎｂ：０．２５％以下（０％を含まない）、Ｖ：０．１％以下（０％を含まない）、およびＢ：０．００５％以下（０％を含まない）よりなる群から選ばれる１種以上の元素を含むものが好ましく、こうした元素を含有することで母材の強度を高めることができる。なお、前記鋼材の残部は、Ｆｅおよび不可避不純物であってもよい。   The steel material further includes, as other elements, Cu: 2% or less (not including 0%), Ni: 3.5% or less (not including 0%), Cr: 3% or less (not including 0%) Mo: 1% or less (not including 0%), Nb: 0.25% or less (not including 0%), V: 0.1% or less (not including 0%), and B: 0.005 % Containing at least one element selected from the group consisting of% or less (not including 0%) is preferred, and the strength of the base material can be increased by containing such elements. The balance of the steel material may be Fe and inevitable impurities.

本発明に係る鋼材は、例えば溶存酸素量を０．００２０〜０．０１０％の範囲に調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素とＺｒを添加すれば製造できる。上記鋼材が特にＴｉを含む場合には、溶存酸素量を０．００２０〜０．０１０％の範囲に調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、ＴｉとＺｒを添加することが好ましい。この場合には、上記溶存酸素量を調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素とＺｒを添加するに先立って、Ｔｉを添加することが好ましい。   The steel material according to the present invention can be manufactured, for example, by adding at least one element selected from the group consisting of REM and Ca and Zr to molten steel whose dissolved oxygen content is adjusted to a range of 0.0020 to 0.010%. . When the steel material contains Ti in particular, at least one element selected from the group consisting of REM and Ca, Ti, and Zr to a molten steel whose dissolved oxygen content is adjusted to a range of 0.0020 to 0.010%. Is preferably added. In this case, it is preferable to add Ti prior to adding at least one element selected from the group consisting of REM and Ca and Zr to the molten steel in which the amount of dissolved oxygen is adjusted.

本発明によれば、ＲＥＭおよび／またはＣａと、Ｚｒを鋼材に複合添加することによって、該鋼材に含まれる全酸化物の組成を測定したときに、ＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2を含有するように調整しているため、上記特許文献３で提案した鋼材とは異なる組成の酸化物を鋼材中に分散させて溶接熱影響部（ＨＡＺ）の靭性を改善することができる。特に本発明で規定する上記酸化物は、１４００℃レベルの高温に達しても鋼材中に固溶消失しないため、本発明の鋼材を溶接する際に、小〜中入熱溶接に限らず、大入熱溶接においても溶接熱影響部（ＨＡＺ）の靭性劣化を防止できる。 According to the present invention, when REM and / or Ca and Zr are combined and added to a steel material, the composition of all oxides contained in the steel material is measured, and then the REM oxide and / or CaO and ZrO since the adjusted to contain 2, an oxide of a different composition than the steel proposed in the Patent Document 3 can improve the toughness of the heat affected zone is dispersed in the steel (HAZ). In particular, the oxide defined in the present invention does not disappear in the steel material even when reaching a high temperature of 1400 ° C. Therefore, when welding the steel material of the present invention, not only small to medium heat input welding, but large Even in heat input welding, it is possible to prevent toughness deterioration of the weld heat affected zone (HAZ).

本発明の鋼材は、合金元素として特にＲＥＭおよび／またはＣａと、Ｚｒを夫々含有するところに特徴があり、該鋼材に含まれる全酸化物の組成を測定したときに、酸化物としてＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2を含有するところに特徴がある。 The steel material of the present invention is particularly characterized in that it contains REM and / or Ca and Zr as alloy elements, respectively. When the composition of all oxides contained in the steel material is measured, the oxidation of REM as an oxide is performed. And / or CaO and ZrO 2 .

まず、本発明の鋼材が含有する酸化物について説明する。本発明の鋼材は、該鋼材に含まれる全酸化物の組成を測定したときに、ＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2を含有するものである。鋼材に含まれる全酸化物の組成を測定したときに、ＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2を含有することにより、ＲＥＭやＣａ、Ｚｒを夫々単独添加して酸化物を形成し、ＨＡＺの靭性を改善する場合よりも鋼材に対する各元素の添加量を低減することができる。しかも鋼材中に上記酸化物あるいは複合酸化物を鋼材中に組み合わせて含有させれば、鋼材中に含有する全酸化物の絶対量を増大させることができる。従ってＲＥＭやＣａ、Ｚｒを過剰に添加して鋼材（母材）の靭性劣化の原因となるＲＥＭの硫化物やＣａの硫化物、或いはＺｒの炭化物が生成するのを防止できるため、母材の靭性劣化を抑えつつＨＡＺの靭性を向上させることができる。 First, the oxide contained in the steel material of the present invention will be described. The steel material of the present invention contains REM oxide and / or CaO and ZrO 2 when the composition of all oxides contained in the steel material is measured. When the composition of the total oxide contained in the steel material is measured, REM and / or CaO and ZrO 2 are included to form an oxide by adding REM, Ca, and Zr, respectively, The amount of each element added to the steel can be reduced as compared with the case where the HAZ toughness is improved. And if the said oxide or composite oxide is combined and contained in steel materials in steel materials, the absolute amount of all the oxides contained in steel materials can be increased. Therefore, it is possible to prevent the formation of REM sulfide, Ca sulfide, or Zr carbide that causes toughness deterioration of steel materials (base materials) by excessively adding REM, Ca, or Zr. The toughness of the HAZ can be improved while suppressing toughness deterioration.

また、後記の実施例から明らかなように、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを添加する直前の溶存酸素量を適切に制御すれば、ＲＥＭやＣａ、Ｚｒの添加量をある程度多くしても酸化物を確実に形成させることができるため、ＲＥＭの硫化物やＣａの硫化物、或いはＺｒの炭化物が生成することはない。そしてこうした酸化物は、溶接時に熱影響を受けて１４００℃レベルの高温になっても固溶消失しないため、溶接時のＨＡＺにおいてオーステナイト粒の粗大化を防止することができ、その結果としてＨＡＺの靭性劣化を防止できる。   Further, as is clear from the examples described later, if the amount of dissolved oxygen immediately before adding Zr and at least one element selected from the group consisting of REM and Ca is appropriately controlled, REM, Ca, and Zr Even if the addition amount is increased to some extent, an oxide can be formed reliably, so that REM sulfide, Ca sulfide, or Zr carbide is not generated. These oxides are affected by heat during welding and do not lose their solid solution even at a high temperature of 1400 ° C., so that the austenite grains can be prevented from coarsening in the HAZ during welding. Toughness degradation can be prevented.

本発明の鋼材は、（ａ）ＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2を含有するか、あるいは（ｂ）ＲＥＭおよび／またはＣａと、Ｚｒを含む複合酸化物を含有するか、（ｃ）ＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2を含有すると共に、ＲＥＭおよび／またはＣａと、Ｚｒを含む複合酸化物を含有するものであればよい。ＲＥＭおよび／またはＣａと、Ｚｒを含む複合酸化物とは、例えばＲＥＭとＺｒを含む複合酸化物、ＣａとＺｒを含む複合酸化物、ＲＥＭとＣａとＺｒを含む複合酸化物などが挙げられる。 The steel material of the present invention contains (a) an oxide of REM and / or CaO and ZrO 2 , or (b) a composite oxide containing REM and / or Ca and Zr, or (c ) Any oxide containing REM and / or CaO and ZrO 2 and any composite oxide containing REM and / or Ca and Zr may be used. Examples of the composite oxide containing REM and / or Ca and Zr include a composite oxide containing REM and Zr, a composite oxide containing Ca and Zr, and a composite oxide containing REM, Ca, and Zr.

本発明の鋼材は、上述した酸化物の他に、更にＴｉ酸化物を含有することが好ましい。即ち、前記鋼材に含まれる全酸化物の組成を測定したときに、Ｔｉ2Ｏ3やＴｉ3Ｏ5，ＴｉＯ2を含有するものであればよい。Ｔｉ酸化物を含有することで、鋼材中に分散する酸化物量を更に増大させることができるため、ＨＡＺの靭性を一層向上させることができる。 The steel material of the present invention preferably further contains a Ti oxide in addition to the oxides described above. That is, any material containing Ti 2 O 3 , Ti 3 O 5 , or TiO 2 when the composition of all oxides contained in the steel material is measured. By containing the Ti oxide, the amount of oxide dispersed in the steel material can be further increased, so that the toughness of the HAZ can be further improved.

上記Ｔｉ酸化物は、鋼材中に単独酸化物（Ｔｉ2Ｏ3やＴｉ3Ｏ5，ＴｉＯ2）として含有されていてもよいし、例えば上記複合酸化物（即ち、ＲＥＭとＺｒを含む複合酸化物、ＣａとＺｒを含む複合酸化物、ＲＥＭとＣａとＺｒを含む複合酸化物）に包含されて複合酸化物として含有されていてもよい。 The Ti oxide may be contained in the steel material as a single oxide (Ti 2 O 3 , Ti 3 O 5 , TiO 2 ) or, for example, the composite oxide (that is, composite oxide containing REM and Zr). Or a composite oxide containing Ca and Zr, and a composite oxide containing REM, Ca and Zr).

上記鋼材は、該鋼材に含まれる全酸化物の組成を測定し、合計を１００％としたときに、ＲＥＭの酸化物および／またはＣａＯの合計が５％以上で、ＺｒＯ2が５％以上を満足することが好ましい。この理由はＨＡＺの靭性向上に寄与する酸化物量を確保するためである。ＲＥＭの酸化物および／またはＣａＯの合計は１０％以上であることが好ましく、より好ましくは１５％以上、更に好ましくは２０％以上である。一方、ＺｒＯ2は１０％以上であることが好ましく、より好ましくは１５％以上、更に好ましくは２０％以上である。 The above steel material has a composition of all oxides contained in the steel material, and when the total is 100%, the total of REM oxides and / or CaO is 5% or more, and ZrO 2 is 5% or more. It is preferable to satisfy. The reason for this is to ensure the amount of oxide that contributes to the improvement of HAZ toughness. The total of REM oxides and / or CaO is preferably 10% or more, more preferably 15% or more, and still more preferably 20% or more. On the other hand, ZrO 2 is preferably 10% or more, more preferably 15% or more, and further preferably 20% or more.

上記鋼材がＴｉ酸化物を含有する場合は、該鋼材に含まれる全酸化物の組成を測定したときに、Ｔｉ酸化物が０．３％以上を満足することが好ましい。より好ましくは１％以上、更に好ましくは３％以上、特に好ましくは５％以上、最も好ましくは１０％以上である。なお、Ｔｉ酸化物は、鋼材中でＴｉ2Ｏ3やＴｉ3Ｏ5，ＴｉＯ2として存在するが、鋼材に含まれる全酸化物の組成を測定し、全てのＴｉ酸化物をＴｉ2Ｏ3として換算した値が、上記範囲を満足していればよい。 When the steel material contains Ti oxide, it is preferable that the Ti oxide satisfies 0.3% or more when the composition of all oxides contained in the steel material is measured. More preferably, it is 1% or more, more preferably 3% or more, particularly preferably 5% or more, and most preferably 10% or more. The Ti oxide exists as Ti 2 O 3 , Ti 3 O 5 , and TiO 2 in the steel material. The composition of all oxides contained in the steel material is measured, and all Ti oxides are converted into Ti 2 O 3. As long as the value converted as follows satisfies the above range.

本発明の鋼材は、該鋼材に含まれる全酸化物の組成を測定したときに、ＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2およびＴｉ酸化物（Ｔｉ2Ｏ3）の合計が５５％以上である。これらの酸化物の合計が５５％未満では、ＨＡＺの靭性向上に寄与する酸化物量が不足し、ＨＡＺの靭性を充分に改善できない。より好ましくは６０％以上、更に好ましくは６５％以上である。 When the composition of the total oxide contained in the steel material of the present invention is measured, the total of the REM oxide and / or CaO and the ZrO 2 and Ti oxide (Ti 2 O 3 ) is 55% or more. It is. If the total of these oxides is less than 55%, the amount of oxide contributing to the improvement of HAZ toughness is insufficient, and the toughness of HAZ cannot be sufficiently improved. More preferably, it is 60% or more, More preferably, it is 65% or more.

なお、全酸化物の組成の残りの成分は特に限定されないが、例えばＳｉＯ2やＡｌ2Ｏ3、ＭｎＯであればよい。ＳｉＯ2やＡｌ2Ｏ3、ＭｎＯ以外の「その他」の成分は５％未満であることが好ましい。 The remaining components of the total oxide composition are not particularly limited, but may be, for example, SiO 2 , Al 2 O 3 , or MnO. The “other” component other than SiO 2 , Al 2 O 3 and MnO is preferably less than 5%.

鋼材に含まれる酸化物の組成は、鋼材の断面を例えばＥＰＭＡ（Electron Probe X-ray Micro Analyzer；電子線マイクロプローブＸ線分析計）で観察し、観察視野内に認められる介在物を定量分析すれば測定できる。ＥＰＭＡの観察は、例えば加速電圧を２０ｋＶ，試料電流を０．０１μＡ，観察視野面積を１〜５ｃｍ2とし、介在物の中央部での組成を特性Ｘ線の波長分散分光により定量分析する。 The composition of the oxide contained in the steel material is determined by observing the cross section of the steel material with, for example, EPMA (Electron Probe X-ray Micro Analyzer) and quantitatively analyzing the inclusions observed in the observation field. Can be measured. In the observation of EPMA, for example, the acceleration voltage is 20 kV, the sample current is 0.01 μA, the observation visual field area is 1 to 5 cm 2, and the composition at the center of the inclusion is quantitatively analyzed by wavelength dispersion spectroscopy of characteristic X-rays.

分析対象とする介在物の大きさは、最大径が０．２μｍ以上のものとし、分析個数は少なくとも１００個とする。   The size of inclusions to be analyzed is a maximum diameter of 0.2 μm or more, and the number of analyzes is at least 100.

分析対象元素は、Ａｌ，Ｍｎ，Ｓｉ，Ｔｉ，Ｚｒ，Ｃａ，Ｌａ，ＣｅおよびＯとし、既知物質を用いて各元素のＸ線強度と元素濃度の関係を予め検量線として求めておき、分析対象とする介在物から得られたＸ線強度と前記検量線から分析対象とする介在物に含まれる元素濃度を定量し、酸素含量が５％以上の介在物を酸化物とする。但し、一つの介在物から複数の元素が観測された場合には、それらの元素の存在を示すＸ線強度の比から各元素の単独酸化物に換算して酸化物の組成を算出する。そして本発明の鋼材では、こうして個々の酸化物について得られた定量結果を平均したものを酸化物の平均組成とする。   The analysis target elements are Al, Mn, Si, Ti, Zr, Ca, La, Ce, and O. Using a known substance, the relationship between the X-ray intensity and the element concentration of each element is obtained in advance as a calibration curve. From the X-ray intensity obtained from the inclusions to be measured and the calibration curve, the element concentration contained in the inclusions to be analyzed is quantified, and inclusions having an oxygen content of 5% or more are defined as oxides. However, when a plurality of elements are observed from one inclusion, the composition of the oxide is calculated in terms of a single oxide of each element from the ratio of X-ray intensity indicating the presence of these elements. And in the steel material of this invention, what averaged the quantitative result obtained about each oxide in this way is made into the average composition of an oxide.

次に、本発明の鋼材（母材）における成分組成について説明する。本発明の鋼材は、ＲＥＭ：０．００１〜０．１％および／またはＣａ：０．０００３〜０．０２％と、Ｚｒ：０．００１〜０．０５％を含有するところに特徴がある。こうした範囲を定めた理由は以下の通りである。   Next, the component composition in the steel material (base material) of the present invention will be described. The steel material of the present invention is characterized in that it contains REM: 0.001 to 0.1% and / or Ca: 0.0003 to 0.02% and Zr: 0.001 to 0.05%. The reasons for setting these ranges are as follows.

ＲＥＭ、ＣａおよびＺｒは、鋼材中にＲＥＭの酸化物やＣａＯ、ＺｒＯ2、或いは複合酸化物を形成してＨＡＺの靭性向上に寄与する元素である。本発明の鋼材では、ＲＥＭとＣａは夫々単独で、或いは併用できる。 REM, Ca, and Zr are elements that contribute to improving the toughness of HAZ by forming REM oxide, CaO, ZrO 2 , or a composite oxide in the steel material. In the steel material of the present invention, REM and Ca can be used alone or in combination.

ＲＥＭは、０．００１％以上含有させるべきであり、好ましくは０．００６％以上、より好ましくは０．０１０％以上である。しかし過剰に添加すると、ＲＥＭの硫化物が生成して母材の靭性が劣化するため、０．１％以下に抑えるべきである。好ましくは０．０９％以下であり、より好ましくは０．０８％以下とする。なお、本発明において、ＲＥＭとは、ランタノイド元素（ＬａからＬｎまでの１５元素）およびＳｃ（スカンジウム）とＹ（イットリウム）を含む意味であり、これらの元素のなかでも、Ｌａ、ＣｅおよびＹよりなる群から選ばれる少なくとも１種の元素を含有することが好ましく、より好ましくはＬａおよび／またはＣｅを含有するのがよい。   REM should be contained in an amount of 0.001% or more, preferably 0.006% or more, and more preferably 0.010% or more. However, if added excessively, sulfide of REM is generated and the toughness of the base material deteriorates, so it should be suppressed to 0.1% or less. Preferably it is 0.09% or less, More preferably, it is 0.08% or less. In the present invention, REM means a lanthanoid element (15 elements from La to Ln) and Sc (scandium) and Y (yttrium). Among these elements, La, Ce and Y It is preferable to contain at least one element selected from the group consisting of, and more preferably La and / or Ce.

Ｃａは、０．０００３％以上含有させるべきであり、好ましくは０．０００５％以上、より好ましくは０．０００８％以上である。しかし過剰に添加すると、粗大なＣａの硫化物が生成して母材の靭性が劣化するため、０．０２％以下に抑えるべきである。好ましくは０．０１５％以下であり、より好ましくは０．０１％以下とする。   Ca should be contained in an amount of 0.0003% or more, preferably 0.0005% or more, and more preferably 0.0008% or more. However, if excessively added, coarse Ca sulfide is generated and the toughness of the base material deteriorates, so it should be suppressed to 0.02% or less. Preferably it is 0.015% or less, More preferably, you may be 0.01% or less.

Ｚｒは、０．００１％以上含有させるべきであり、好ましくは０．００３％以上、より好ましくは０．００５％以上である。しかし過剰に添加すると、粗大なＺｒの炭化物が生成して母材の靭性が劣化するため、０．０５％以下に抑えるべきである。好ましくは０．０４％以下であり、より好ましくは０．０３％以下とする。   Zr should be contained in an amount of 0.001% or more, preferably 0.003% or more, and more preferably 0.005% or more. However, if added excessively, coarse Zr carbide is generated and the toughness of the base material deteriorates, so it should be suppressed to 0.05% or less. Preferably it is 0.04% or less, More preferably, it is 0.03% or less.

本発明の鋼材は、ＲＥＭおよび／またはＣａと、Ｚｒを含むほか、基本元素として、Ｃ：０．０１〜０．２％、Ｓｉ：０．５％以下（０％を含まない）、Ｍｎ：２．５％以下（０％を含まない）およびＮ：０．０１％以下（０％を含まない）を含むものである。このような範囲を定めた理由は以下の通りである。   The steel material of the present invention contains REM and / or Ca and Zr, and as basic elements, C: 0.01 to 0.2%, Si: 0.5% or less (excluding 0%), Mn: 2.5% or less (not including 0%) and N: 0.01% or less (not including 0%). The reason for setting such a range is as follows.

Ｃは、鋼材（母材）の強度を確保するために欠くことのできない元素であり、こうした効果を発揮させるには、０．０１％以上含有させる必要がある。Ｃは、０．０２％以上含有させることが好ましく、より好ましくは０．０３％以上とする。しかし０．２％を超えると、溶接時にＨＡＺに島状マルテンサイトを多く生成してＨＡＺの靭性劣化を招くばかりでなく、溶接性にも悪影響を及ぼす。従ってＣは０．２％以下、好ましくは０．１８％以下、より好ましくは０．１５％以下に抑える必要がある。   C is an element indispensable for securing the strength of the steel material (base material), and in order to exert such an effect, it is necessary to contain 0.01% or more. C is preferably contained in an amount of 0.02% or more, more preferably 0.03% or more. However, if it exceeds 0.2%, a lot of island martensite is generated in the HAZ at the time of welding to cause deterioration of the toughness of the HAZ, and also has an adverse effect on the weldability. Therefore, C must be suppressed to 0.2% or less, preferably 0.18% or less, more preferably 0.15% or less.

Ｓｉは、脱酸作用を有すると共に鋼材（母材）の強度向上に寄与する元素である。こうした効果を有効に発揮させるには、０．０２％以上含有させることが好ましく、より好ましくは０．０５％以上、更に好ましくは０．１％以上含有させるのがよい。しかし０．５％を超えると、鋼材（母材）の溶接性や母材靭性が劣化するため、０．５％以下に抑える必要がある。好ましくは０．４５％以下であり、より好ましくは０．４％以下に抑える。なお、ＨＡＺに高靭性が求められる場合には、Ｓｉは０．３％以下に抑えるのがよい。より好ましくは０．０５％以下であり、更に好ましくは０．０１％以下である。但し、このようにＳｉ含有量を抑えるとＨＡＺの靭性は向上するが、強度は低下する傾向がある。   Si is an element that has a deoxidizing action and contributes to improving the strength of the steel (base material). In order to exhibit such an effect effectively, it is preferable to contain 0.02% or more, more preferably 0.05% or more, and still more preferably 0.1% or more. However, if it exceeds 0.5%, the weldability and base material toughness of the steel (base material) deteriorate, so it is necessary to keep it to 0.5% or less. Preferably it is 0.45% or less, More preferably, it restrains to 0.4% or less. In addition, when high toughness is required for HAZ, Si is preferably suppressed to 0.3% or less. More preferably, it is 0.05% or less, More preferably, it is 0.01% or less. However, when the Si content is suppressed in this way, the toughness of the HAZ is improved, but the strength tends to decrease.

Ｍｎは、鋼材（母材）の強度向上に寄与する元素であり、こうした効果を有効に発揮させるには、０．５％以上含有させることが好ましい。より好ましくは０．７％以上、更に好ましくは０．８％以上含有させるのがよい。しかし２．５％を超えると、鋼材（母材）の溶接性を劣化させるため２．５％以下に抑える必要がある。好ましくは２．３％以下であり、より好ましくは２％以下に抑えるのがよい。   Mn is an element that contributes to improving the strength of the steel material (base material), and it is preferable to contain 0.5% or more in order to effectively exhibit these effects. More preferably 0.7% or more, still more preferably 0.8% or more. However, if it exceeds 2.5%, the weldability of the steel (base material) is deteriorated, so it is necessary to keep it to 2.5% or less. The content is preferably 2.3% or less, and more preferably 2% or less.

Ｎは、窒化物（例えば、ＺｒＮやＴｉＮなど）を析出する元素であり、該窒化物は溶接時にＨＡＺに生成するオーステナイト粒の粗大化を防止してフェライト変態を促進するため、ＨＡＺの靭性を向上させるのに寄与する。こうした効果を有効に発揮させるには、０．００２％以上含有させることが好ましく、より好ましくは０．００３％以上である。Ｎは多いほどオーステナイト粒の微細化が促進されるため、ＨＡＺの靭性向上に有効に作用する。しかし０．０１％を超えると、固溶Ｎ量が増大して母材の靭性が劣化する。従ってＮは０．０１％以下に抑える必要があり、好ましくは０．００９％以下、より好ましくは０．００８％以下とする。   N is an element that precipitates nitrides (for example, ZrN and TiN), and the nitrides prevent austenite grains formed in the HAZ during welding and promote ferrite transformation, so that the toughness of the HAZ is increased. Contributes to improvement. In order to exhibit such an effect effectively, it is preferable to make it contain 0.002% or more, More preferably, it is 0.003% or more. The more N, the more refined austenite grains are promoted, which effectively works to improve the toughness of HAZ. However, if it exceeds 0.01%, the amount of solute N increases and the toughness of the base material deteriorates. Therefore, N must be suppressed to 0.01% or less, preferably 0.009% or less, more preferably 0.008% or less.

本発明の鋼材は、上記元素を含むほか、Ｐ：０．０２％以下（０％を含む）、Ｓ：０．００８％以下（０％を含む）およびＡｌ：０．０１％以下（０％を含む）を満足するものである。このような範囲を定めた理由は以下の通りである。   The steel material of the present invention contains the above elements, P: 0.02% or less (including 0%), S: 0.008% or less (including 0%), and Al: 0.01% or less (0%) Is satisfied). The reason for setting such a range is as follows.

Ｐは、偏析し易い元素であり、特に鋼材中の結晶粒界に偏析して靭性を劣化させる。従ってＰは０．０２％以下に抑制する必要があり、好ましくは０．０１８％以下、より好ましくは０．０１５％以下とする。   P is an element that easily segregates, and particularly segregates at a grain boundary in the steel material to deteriorate toughness. Therefore, P must be suppressed to 0.02% or less, preferably 0.018% or less, more preferably 0.015% or less.

Ｓは、Ｍｎと結合して硫化物（ＭｎＳ）を生成し、母材の靭性や板厚方向の延性を劣化させる有害な元素である。またＳは、ＬａやＣｅと結合してＬａＳやＣｅＳを生成し、酸化物の生成を阻害する。従ってＳは０．０１５％以下に抑えるべきであり、好ましくは０．０１２％以下、より好ましくは０．００８％以下、特に０．００６％以下とする。   S is a harmful element that combines with Mn to produce sulfide (MnS) and degrades the toughness of the base material and the ductility in the thickness direction. S combines with La and Ce to form LaS and CeS and inhibits the formation of oxides. Therefore, S should be suppressed to 0.015% or less, preferably 0.012% or less, more preferably 0.008% or less, and particularly 0.006% or less.

Ａｌは、脱酸力の強い元素であり、過剰に添加すると酸化物を還元して所望の酸化物を生成し難くなる。従ってＡｌは０．０１％以下に抑える必要があり、好ましくは０．００９０％以下、より好ましくは０．００８０％以下とする。   Al is an element having a strong deoxidizing power, and when added in excess, the oxide is reduced and it becomes difficult to produce a desired oxide. Therefore, Al must be suppressed to 0.01% or less, preferably 0.0090% or less, more preferably 0.0080% or less.

本発明の鋼材は、上記元素を含有するものであるが、更に他の元素として、Ｔｉ：０．０８％以下（０％を含まない）を含むことが好ましい。こうした範囲を定めた理由は以下の通りである。   The steel material of the present invention contains the above elements, but it is preferable that Ti: 0.08% or less (not including 0%) is further contained as another element. The reasons for setting these ranges are as follows.

Ｔｉは、鋼材中にＴｉＮなどの窒化物やＴｉ酸化物を生成してＨＡＺの靭性向上に寄与する元素である。こうした効果を有効に発揮させるには、Ｔｉは０．００５％以上含有させることが好ましく、より好ましくは０．００７％以上、更に好ましくは０．０１％以上とする。しかし過剰に添加すると鋼材（母材）の靭性を劣化させるため、０．０８％以下に抑えるべきである。好ましくは０．０７％以下であり、より好ましくは０．０６％以下とする。   Ti is an element that contributes to improving the toughness of the HAZ by generating a nitride such as TiN or Ti oxide in the steel material. In order to exert such an effect effectively, Ti is preferably contained in an amount of 0.005% or more, more preferably 0.007% or more, and further preferably 0.01% or more. However, if added excessively, the toughness of the steel (base material) is deteriorated, so it should be suppressed to 0.08% or less. Preferably it is 0.07% or less, More preferably, it is 0.06% or less.

本発明の鋼材は、強度を高めるために、Ｃｕ：２％以下（０％を含まない）、Ｎｉ：３．５％以下（０％を含まない）、Ｃｒ：３％以下（０％を含まない）、Ｍｏ：１％以下（０％を含まない）、Ｎｂ：０．２５％以下（０％を含まない）、Ｖ：０．１％以下（０％を含まない）およびＢ：０．００５％以下（０％を含まない）よりなる群から選ばれる１種以上の元素、を含有することも有効である。こうした範囲を定めた理由は以下の通りである。   In order to increase the strength of the steel material of the present invention, Cu: 2% or less (not including 0%), Ni: 3.5% or less (not including 0%), Cr: 3% or less (including 0%) No), Mo: 1% or less (not including 0%), Nb: 0.25% or less (not including 0%), V: 0.1% or less (not including 0%) and B: 0. It is also effective to contain one or more elements selected from the group consisting of 005% or less (not including 0%). The reasons for setting these ranges are as follows.

Ｃｕは、鋼材を固溶強化させる元素であり、こうした効果を有効に発揮させるには、０．０５％以上含有させることが好ましい。より好ましくは０．１％以上であり、更に好ましくは０．２％以上である。特に０．６％以上含有させると、固溶強化のほか、時効析出強化も発揮し、大幅な強度向上が可能となる。しかし２％を超えて含有させると、鋼材（母材）の靭性を低下させるため、Ｃｕは２％以下に抑えるのがよい。好ましくは１．８％以下であり、より好ましくは１．６％以下とする。   Cu is an element for solid solution strengthening of the steel material, and in order to exhibit such an effect effectively, it is preferable to contain 0.05% or more. More preferably, it is 0.1% or more, More preferably, it is 0.2% or more. In particular, when 0.6% or more is contained, in addition to solid solution strengthening, aging precipitation strengthening is also exhibited, and a significant improvement in strength becomes possible. However, if the content exceeds 2%, the toughness of the steel material (base material) is lowered, so Cu should be suppressed to 2% or less. Preferably it is 1.8% or less, More preferably, you may be 1.6% or less.

Ｎｉは、鋼材の強度を高めると共に、鋼材の靭性を向上させるのに有効に作用する元素であり、こうした作用を発揮させるには、０．０５％以上含有させることが好ましい。より好ましくは０．１％以上であり、更に好ましくは０．２％以上とする。Ｎｉは多いほど好ましいが、高価な元素であるため経済的観点から３．５％以下に抑えることが好ましい。より好ましくは３．３％以下であり、更に好ましくは３％以下とする。   Ni is an element that effectively acts to increase the strength of the steel material and improve the toughness of the steel material. In order to exert such an effect, Ni is preferably contained in an amount of 0.05% or more. More preferably, it is 0.1% or more, More preferably, it is 0.2% or more. The more Ni, the better. However, since it is an expensive element, it is preferable to suppress it to 3.5% or less from an economical viewpoint. More preferably, it is 3.3% or less, More preferably, it is 3% or less.

Ｃｒを添加して強度を高めるには、０．０１％以上含有させることが好ましい。より好ましくは０．０２％以上、更に好ましくは０．０３％以上である。しかし３％を超えると溶接性が劣化するため、Ｃｒは３％以下に抑えることが好ましい。より好ましくは１．５％以下であり、更に好ましくは１％以下とする。   In order to increase the strength by adding Cr, the content is preferably 0.01% or more. More preferably it is 0.02% or more, and still more preferably 0.03% or more. However, if it exceeds 3%, weldability deteriorates, so Cr is preferably suppressed to 3% or less. More preferably, it is 1.5% or less, More preferably, it is 1% or less.

Ｍｏを添加して強度を高めるには、０．０１％以上含有させるのが望ましい。より好ましくは０．０２％以上であり、更に好ましくは０．０３％以上含有させるのが推奨される。但し、１％を超えると溶接性を悪化させるためＭｏは１％以下とするのが好ましい。より好ましくは０．９％以下であり、更に好ましくは０．８％以下に抑えるのが推奨される。   In order to increase the strength by adding Mo, it is desirable to contain 0.01% or more. More preferably, the content is 0.02% or more, and further preferably 0.03% or more is recommended. However, if it exceeds 1%, the weldability deteriorates, so Mo is preferably 1% or less. More preferably, it is 0.9% or less, and more preferably 0.8% or less.

Ｎｂを添加して強度を高めるには、０．００５％以上含有させるのが好ましい。より好ましくは０．０１％以上であり、更に好ましくは０．０３％以上である。しかし０．２５％を超えると炭化物（ＮｂＣ）が析出して母材の靭性を劣化させるので、Ｎｂは０．２５％以下に抑えるのが好ましい。より好ましくは０．２３％以下であり、更に好ましくは０．２％以下とする。   In order to increase the strength by adding Nb, it is preferable to contain 0.005% or more. More preferably, it is 0.01% or more, More preferably, it is 0.03% or more. However, if it exceeds 0.25%, carbide (NbC) precipitates and deteriorates the toughness of the base material, so Nb is preferably suppressed to 0.25% or less. More preferably, it is 0.23% or less, and still more preferably 0.2% or less.

Ｖを添加して強度を高めるには、０．００５％以上含有させるのが望ましい。より好ましくは０．０１％以上、更に好ましくは０．０３％以上含有させるのがよい。しかし０．１％を超えると溶接性が悪化する共に、母材の靭性が劣化するため、Ｖは０．１％以下とするのが好ましい。より好ましくは０．０８％以下、更に好ましくは０．０６％以下に抑えるのがよい。   In order to increase the strength by adding V, it is desirable to contain 0.005% or more. More preferably 0.01% or more, still more preferably 0.03% or more. However, if it exceeds 0.1%, the weldability deteriorates and the toughness of the base material deteriorates, so V is preferably 0.1% or less. More preferably, it is 0.08% or less, and more preferably 0.06% or less.

Ｂは、鋼材の強度を高めると共に、溶接時に加熱されたＨＡＺが冷却される過程において鋼中のＮと結合してＢＮを析出し、オーステナイト粒内からのフェライト変態を促進させる。こうした効果を有効に発揮させるには、０．０００３％以上含有させるのが好ましい。より好ましくは０．０００５％以上であり、更に好ましくは０．０００８％以上とする。しかし０．００５％を超えると鋼材（母材）の靭性を劣化させるためＢは０．００５％以下とするのが好ましい。より好ましくは０．００４％以下であり、更に好ましくは０．００３％以下とするのがよい。   B increases the strength of the steel material and, in the process of cooling the HAZ heated during welding, combines with N in the steel to precipitate BN and promote ferrite transformation from within the austenite grains. In order to exhibit such an effect effectively, it is preferable to contain 0.0003% or more. More preferably it is 0.0005% or more, and still more preferably 0.0008% or more. However, if it exceeds 0.005%, the toughness of the steel (base material) is deteriorated, so B is preferably 0.005% or less. More preferably, it is 0.004% or less, and further preferably 0.003% or less.

本発明の鋼材は、上記元素を必須成分として含有するものであり、残部はＦｅおよび不可避不純物（例えば、ＭｇやＡｓ，Ｓｅなど）であってもよい。   The steel material of the present invention contains the above elements as essential components, and the balance may be Fe and inevitable impurities (for example, Mg, As, Se, etc.).

次に、本発明の鋼材を製造するに当たり、好適に採用できる製法について説明する。本発明の鋼材は、例えば溶存酸素量を０．００２０〜０．０１０％の範囲に調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを添加すれば製造できる。   Next, a production method that can be suitably employed in producing the steel material of the present invention will be described. The steel material of the present invention can be manufactured, for example, by adding at least one element selected from the group consisting of REM and Ca and Zr to molten steel whose dissolved oxygen content is adjusted to a range of 0.0020 to 0.010%. .

即ち、溶存酸素量を適切に制御した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを複合添加すれば、所定の酸化物を生成させることができる。このとき上記溶存酸素量が０．００２０％未満では、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを複合添加しても、酸素量不足になるため、ＨＡＺの靭性向上に寄与する酸化物量を確保することができず、しかも酸化物を形成できなかったＲＥＭやＣａが硫化物を形成したり、Ｚｒが炭化物を形成して母材の靭性を劣化する。上記元素を複合添加する前の溶存酸素量は、０．００２５％以上に調整することが好ましく、より好ましくは０．００３０％以上である。しかし溶存酸素量が０．０１０％を超えていると、溶鋼中の酸素量が多すぎるため、溶鋼中の酸素と上記元素の反応が激しくなって溶製作業上好ましくないばかりか、粗大なＲＥＭの酸化物やＣａの酸化物と、ＺｒＯ2を生成する。従って溶存酸素量は０．０１０％以下に抑えるべきであり、好ましくは０．００８％以下、より好ましくは０．００７％以下とする。 That is, a predetermined oxide can be generated by adding Zr in combination with at least one element selected from the group consisting of REM and Ca to molten steel in which the amount of dissolved oxygen is appropriately controlled. At this time, if the amount of dissolved oxygen is less than 0.0020%, even if Zr is added in combination with at least one element selected from the group consisting of REM and Ca, the amount of oxygen becomes insufficient, so the HAZ toughness is improved. REM or Ca, which could not secure the amount of contributing oxides and could not form oxides, formed sulfides, or Zr formed carbides, deteriorating the toughness of the base material. The amount of dissolved oxygen before adding the above elements is preferably adjusted to 0.0025% or more, and more preferably 0.0030% or more. However, if the amount of dissolved oxygen exceeds 0.010%, the amount of oxygen in the molten steel is too large, and the reaction between the oxygen in the molten steel and the above elements becomes violent, which is not preferable for melting work, and is also a coarse REM. And ZrO 2 are produced. Therefore, the amount of dissolved oxygen should be suppressed to 0.010% or less, preferably 0.008% or less, more preferably 0.007% or less.

上記ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを複合添加した後は、合金元素を添加して鋼材の成分を調整すればよい。   After at least one element selected from the group consisting of REM and Ca and Zr are added in combination, an alloy element may be added to adjust the components of the steel material.

なお、上記溶存酸素量を調整した溶鋼へ上記元素を添加するに当たっては、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを複合添加すればよく、例えばＲＥＭとＣａを複合添加する場合には、（ａ）溶存酸素量を調整した溶鋼へＲＥＭとＣａとＺｒを添加した後、合金元素を添加して鋼材の成分を調整してもよいし、（ｂ）溶存酸素量を調整した溶鋼へＲＥＭ（あるいはＣａ）とＺｒを添加した後、Ｃａ（あるいはＲＥＭ）以外の合金元素を添加して鋼材の成分を調整し、次いでＣａ（あるいはＲＥＭ）を添加してもよい。   In addition, when adding the said element to the molten steel which adjusted the amount of dissolved oxygen, what is necessary is just to compound-add at least 1 sort (s) of elements selected from the group which consists of REM and Ca, for example, REM and Ca are compounded. In order to do this, (a) after adding REM, Ca, and Zr to the molten steel in which the amount of dissolved oxygen is adjusted, the alloy elements may be added to adjust the components of the steel material, and (b) the amount of dissolved oxygen is adjusted. After adding REM (or Ca) and Zr to the adjusted molten steel, an alloy element other than Ca (or REM) may be added to adjust the components of the steel material, and then Ca (or REM) may be added.

上記溶存酸素量を調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを複合添加する手順は特に限定されず、例えば（ａ）ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素を添加した後に、Ｚｒを添加してもよいし、（ｂ）Ｚｒを添加した後に、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素を添加してもよいし、（ｃ）ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを同時に複合添加してもよい。ＲＥＭとＣａを複合添加する場合には、（ｄ）ＲＥＭ（あるいはＣａ）を添加した後に、Ｚｒを添加し、次いでＣａ（あるいはＲＥＭ）を添加してもよいし、（ｅ）ＲＥＭとＣａとＺｒを同時に複合添加してもよい。   The procedure for adding at least one element selected from the group consisting of REM and Ca and Zr to the molten steel with the dissolved oxygen content adjusted is not particularly limited. For example, (a) selected from the group consisting of REM and Ca Zr may be added after at least one element is added, or (b) at least one element selected from the group consisting of REM and Ca may be added after adding Zr. (C) At least one element selected from the group consisting of REM and Ca and Zr may be simultaneously added in combination. When REM and Ca are added in combination, (d) REM (or Ca) may be added, then Zr may be added, and then Ca (or REM) may be added. (E) REM and Ca Zr may be combined and added simultaneously.

本発明の鋼材がＴｉを含む場合におけるＴｉの添加順序は特に限定されず、溶存酸素量を調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを複合添加した後に、（ａ）鋼材の成分調整する際に併せてＴｉを添加してもよいし、（ｂ）鋼材の成分調整した後に、Ｔｉを添加してもよい。好ましくは溶存酸素量を調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、ＴｉとＺｒを添加するのが好ましい。この場合には、溶存酸素量を調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素とＺｒを添加するに先立って、Ｔｉを添加するのがよい。溶存酸素量を調整した溶鋼へ、Ｔｉを添加すれば、まずＴｉ酸化物を形成するが、Ｔｉ酸化物は溶鋼との界面エネルギーが小さいため、形成されたＴｉ酸化物のサイズは微細になる。次いでＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを複合添加することによってＲＥＭの酸化物やＣａＯ、ＺｒＯ2が、上記Ｔｉ酸化物を生成核として成長するため、結果的に粒子の個数が増大し、オーステナイト粒の粗大化抑制効果が大きくなる。 The order of addition of Ti in the case where the steel material of the present invention contains Ti is not particularly limited, and at least one element selected from the group consisting of REM and Ca and Zr are added in combination to the molten steel in which the amount of dissolved oxygen is adjusted. Later, (a) Ti may be added when adjusting the components of the steel material, or (b) Ti may be added after adjusting the components of the steel material. Preferably, at least one element selected from the group consisting of REM and Ca, and Ti and Zr are added to the molten steel in which the amount of dissolved oxygen is adjusted. In this case, it is preferable to add Ti prior to adding at least one element selected from the group consisting of REM and Ca and Zr to the molten steel in which the amount of dissolved oxygen is adjusted. If Ti is added to the molten steel in which the amount of dissolved oxygen is adjusted, a Ti oxide is first formed. However, since the Ti oxide has a small interface energy with the molten steel, the size of the formed Ti oxide becomes fine. Then, by adding Zr in combination with at least one element selected from the group consisting of REM and Ca, the REM oxide, CaO, and ZrO 2 grow using the Ti oxide as a production nucleus. The number of particles increases, and the effect of suppressing coarsening of austenite grains increases.

ところで、転炉や電気炉で一次精錬された溶鋼中の溶存酸素量は、通常０．０１０％を超えている。そこで本発明の製法では、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを複合添加する前、或いはＴｉを添加する前に、溶鋼中の溶存酸素量を上記範囲に調整する必要がある。溶存酸素量を調整する方法としては、例えばＲＨ式脱ガス精錬装置を用いて真空Ｃ脱酸する方法や、ＳｉやＭｎ，Ｔｉ，Ａｌなどの脱酸性元素を添加する方法などが挙げられ、勿論これらの方法を適宜組み合わせて溶存酸素量を調整しても良い。また、ＲＨ式脱ガス精錬装置の代わりに、取鍋加熱式精錬装置や簡易式溶鋼処理設備などを用いて溶存酸素量を調整しても良い。この場合、真空Ｃ脱酸による溶存酸素量の調整はできないため、溶存酸素量の調整にはＳｉ等の脱酸性元素を添加する方法を採用すれば良い。Ｓｉ等の脱酸性元素を添加する方法を採用するときは、転炉から取鍋へ出鋼する際に脱酸性元素を添加しても構わない。   By the way, the amount of dissolved oxygen in molten steel primarily refined in a converter or electric furnace usually exceeds 0.010%. Therefore, in the manufacturing method of the present invention, the amount of dissolved oxygen in the molten steel is adjusted to the above range before adding Zr in combination with at least one element selected from the group consisting of REM and Ca, or before adding Ti. There is a need. Examples of the method for adjusting the amount of dissolved oxygen include a method of vacuum C deoxidation using an RH type degassing refining device, a method of adding a deacidifying element such as Si, Mn, Ti, Al, etc. The amount of dissolved oxygen may be adjusted by appropriately combining these methods. Moreover, you may adjust the amount of dissolved oxygen using a ladle heating type refining apparatus, a simple molten steel processing facility, etc. instead of the RH type degassing refining apparatus. In this case, since the amount of dissolved oxygen cannot be adjusted by vacuum C deoxidation, a method of adding a deacidifying element such as Si may be employed to adjust the amount of dissolved oxygen. When employing a method of adding a deoxidizing element such as Si, the deoxidizing element may be added when steel is removed from the converter to the ladle.

溶鋼へ添加するＲＥＭやＣａ，Ｚｒ，Ｔｉの形態は特に限定されず、例えば、ＲＥＭとして、純Ｌａや純Ｃｅ，純Ｙなど、或いは純Ｃａ，純Ｚｒ，純Ｔｉ、更にはＦｅ−Ｓｉ−Ｌａ合金，Ｆｅ−Ｓｉ−Ｃｅ合金，Ｆｅ−Ｓｉ−Ｃａ合金，Ｆｅ−Ｓｉ−Ｌａ−Ｃｅ合金，Ｆｅ−Ｃａ合金，Ｎｉ−Ｃａ合金などを添加すればよい。また、溶鋼へミッシュメタルを添加してもよい。ミッシュメタルとは、セリウム族希土類元素の混合物であり、具体的には、Ｃｅを４０〜５０％程度，Ｌａを２０〜４０％程度含有している。但し、ミッシュメタルには不純物としてＣａを含むことが多いので、ミッシュメタルがＣａを含む場合は本発明で規定する範囲を満足する必要がある。   The form of REM, Ca, Zr, Ti added to the molten steel is not particularly limited. For example, as REM, pure La, pure Ce, pure Y, or pure Ca, pure Zr, pure Ti, and further Fe-Si- A La alloy, Fe—Si—Ce alloy, Fe—Si—Ca alloy, Fe—Si—La—Ce alloy, Fe—Ca alloy, Ni—Ca alloy, or the like may be added. Moreover, you may add misch metal to molten steel. Misch metal is a mixture of cerium group rare earth elements, and specifically contains about 40 to 50% of Ce and about 20 to 40% of La. However, since misch metal often contains Ca as an impurity, when the misch metal contains Ca, the range specified in the present invention must be satisfied.

こうして成分調製して得られた溶鋼は、常法に従って連続鋳造してスラブとした後、常法に従って熱間圧延すればよい。   The molten steel obtained by preparing the components in this manner may be continuously cast according to a conventional method to form a slab, and then hot rolled according to a conventional method.

こうして得られた本発明に係る鋼材は、例えば橋梁や高層建造物、船舶などの構造物の材料として使用でき、小〜中入熱溶接はもとより、大入熱溶接においても溶接熱影響部の靭性劣化を防ぐことができる。   The steel material according to the present invention obtained in this way can be used as a material for structures such as bridges, high-rise buildings, ships, etc., and the toughness of the weld heat affected zone not only in small to medium heat input welding but also in large heat input welding. Deterioration can be prevented.

以下、本発明を実施例によって更に詳細に説明するが、下記実施例は本発明を限定する性質のものではなく、前・後記の趣旨に適合し得る範囲で適当に変更して実施することも可能であり、それらはいずれも本発明の技術的範囲に含まれる。   Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

実験例１
溶銑を２４０トン転炉で一次精錬した後、該転炉から取鍋へ出鋼し、成分調整および温度調整しながら二次精錬を行った。ここで、取鍋では、下記表１に示す脱酸方法で、下記表１に示す溶存酸素量に調整した。その後、下記表１に示す順序で元素を添加した。次いで必要に応じて残りの合金元素を添加して最終的に下記表２に示す組成に調整した。なお、二次精錬にはＲＨ式脱ガス精錬装置等を用いて脱Ｈや脱Ｓなどを行なった。 Experimental example 1
After the hot metal was first refined in a 240-ton converter, the steel was removed from the converter into a ladle and subjected to secondary refining while adjusting the components and adjusting the temperature. Here, in the ladle, the amount of dissolved oxygen shown in Table 1 below was adjusted by the deoxidation method shown in Table 1 below. Thereafter, the elements were added in the order shown in Table 1 below. Subsequently, the remaining alloying elements were added as necessary to finally adjust the compositions shown in Table 2 below. In the secondary refining, dehydrogenation and desulfurization were performed using an RH type degassing refining apparatus.

下記表１に成分調整の手順、脱酸方法、溶存酸素量を夫々示す。また下記表２には、成分調整後の鋼材の成分組成を示す。なお、下記表１において、ＬａはＦｅ−Ｌａ合金の形態で、ＣｅはＦｅ−Ｃｅ合金の形態で、ＲＥＭはＬａを５０％程度とＣｅを２５％程度含有するミッシュメタルの形態で、ＣａはＮｉ−Ｃａ合金、またはＣａ−Ｓｉ合金、またはＦｅ−Ｃａ圧粉体の形態で、ＺｒはＺｒ単体で、ＴｉはＦｅ−Ｔｉ合金の形態で、夫々添加した。但し、下記表２中「−」は元素を添加していないことを示している。また「未満」は元素を添加していないが不可避的に含まれていたため、定量限界以下の範囲で検出されたことを意味している。   Table 1 below shows the component adjustment procedure, deoxidation method, and dissolved oxygen amount. Table 2 below shows the component composition of the steel material after component adjustment. In Table 1 below, La is in the form of Fe-La alloy, Ce is in the form of Fe-Ce alloy, REM is in the form of misch metal containing about 50% La and about 25% Ce, and Ca is In the form of Ni-Ca alloy, Ca-Si alloy, or Fe-Ca green compact, Zr was added in the form of Zr alone, and Ti was added in the form of Fe-Ti alloy. However, "-" in the following Table 2 indicates that no element is added. “Less than” means that the element was detected within the range below the limit of quantification because no element was added but it was inevitably contained.

Figure 2007100213
Figure 2007100213

Figure 2007100213
Figure 2007100213

成分調整後の溶鋼を、連続鋳造機でスラブに鋳造し、該スラブのＤ／４（但し、Ｄはスラブの厚み）位置における横断面からサンプルを切り出した。切り出されたサンプル表面を島津製作所製「ＥＰＭＡ−８７０５（装置名）」を用いて６００倍で観察し、最大径が０．２μｍ以上の析出物について成分組成を定量分析した。観察条件は、加速電圧を２０ｋＶ，試料電流を０．０１μＡ，観察視野面積を１〜５ｃｍ2，分析個数を１００個とし、特性Ｘ線の波長分散分光により析出物中央部での成分組成を定量分析した。分析対象元素は、Ａｌ，Ｍｎ，Ｓｉ，Ｔｉ，Ｚｒ，Ｃａ，Ｌａ，ＣｅおよびＯとし、既知物質を用いて各元素の電子線強度と元素濃度の関係を予め検量線として求めておき、次いで、前記析出物から得られた電子線強度と前記検量線からその析出物の元素濃度を定量した。 The molten steel after component adjustment was cast into a slab with a continuous casting machine, and a sample was cut out from a cross section at a D / 4 (where D is the thickness of the slab) position of the slab. The cut sample surface was observed 600 times using “EPMA-8705 (device name)” manufactured by Shimadzu Corporation, and the component composition of the precipitate having a maximum diameter of 0.2 μm or more was quantitatively analyzed. The observation conditions are an acceleration voltage of 20 kV, a sample current of 0.01 μA, an observation visual field area of 1 to 5 cm 2 , and an analysis number of 100, and the component composition at the center of the precipitate is determined by wavelength dispersion spectroscopy of characteristic X-rays. analyzed. The analysis target elements are Al, Mn, Si, Ti, Zr, Ca, La, Ce, and O, and a relationship between the electron beam intensity and the element concentration of each element is obtained in advance using a known substance as a calibration curve. The element concentration of the precipitate was determined from the electron beam intensity obtained from the precipitate and the calibration curve.

得られた定量結果のうち酸素含量が５％以上の析出物を酸化物とし、平均したものを酸化物の平均組成とした。全酸化物の平均組成を下記表３に示した。なお、Ｔｉ酸化物およびＲＥＭの酸化物は、金属元素をＭで表すと、鋼材中にＭ2Ｏ3やＭ3Ｏ5，ＭＯ2の形態で存在するが、全ての酸化物をＭ2Ｏ3に換算し、組成を測定した。また、一つの介在物から複数の元素が観測された場合には、それらの元素の存在を示すＸ線強度の比から各元素の単独酸化物に換算して酸化物の組成を算出した。 Of the obtained quantitative results, a precipitate having an oxygen content of 5% or more was defined as an oxide, and the average was defined as the average composition of the oxide. The average composition of all oxides is shown in Table 3 below. The Ti oxide and REM oxide are present in the form of M 2 O 3 , M 3 O 5 , and MO 2 in the steel material when the metal element is represented by M, but all oxides are M 2 O. Converted to 3 , the composition was measured. When a plurality of elements were observed from one inclusion, the composition of the oxide was calculated in terms of a single oxide of each element from the ratio of X-ray intensity indicating the presence of these elements.

上記サンプル表面をＥＰＭＡで観察した結果、観察された酸化物は、ＲＥＭおよび／またはＣａとＺｒを含む複合酸化物、或いは更にＴｉを含む複合酸化物が大半であったが、単独酸化物としてＲＥＭの酸化物、ＣａＯ、ＺｒＯ2、Ｔｉ2Ｏ3も生成していた。 As a result of observing the sample surface with EPMA, most of the observed oxides were REM and / or a composite oxide containing Ca and Zr, or a composite oxide containing Ti. These oxides, CaO, ZrO 2 and Ti 2 O 3 were also produced.

次に、溶接時に熱影響を受けるＨＡＺの靭性を評価するために、大入熱溶接を模擬して下記に示す溶接再現試験を行なった。溶接再現試験は、スラブから切り出したサンプル全体が１４００℃になる様に加熱し、この温度で５秒間保持した後、冷却して行った。冷却速度は、８００℃から５００℃への冷却時間が３００秒となるように調整した。   Next, in order to evaluate the toughness of HAZ which is affected by heat during welding, a welding reproduction test shown below was performed by simulating high heat input welding. The welding reproduction test was performed by heating the entire sample cut out from the slab to 1400 ° C., holding at this temperature for 5 seconds, and then cooling. The cooling rate was adjusted so that the cooling time from 800 ° C. to 500 ° C. was 300 seconds.

冷却後のサンプルの衝撃特性は、Ｖノッチシャルピー試験して−４０℃における吸収エネルギー（ｖＥ-40）を測定して評価した。ｖＥ-40が１５０Ｊ以上のものを合格（ＨＡＺ靭性良好）とする。測定結果を下記表３に示す。 The impact characteristics of the sample after cooling were evaluated by measuring the absorbed energy (vE -40 ) at -40 ° C by a V-notch Charpy test. When vE- 40 is 150 J or more, it is regarded as acceptable (haz toughness is good). The measurement results are shown in Table 3 below.

Figure 2007100213
Figure 2007100213

表２〜３から次のように考察できる。Ｎｏ．１〜１４は、本発明で規定する要件を満足する例であり、鋼材にＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2を含有しているため、溶接熱影響部の靭性が良好な鋼材が得られている。特に、Ｎｏ．１０〜１４は、鋼材中にＣｅ2Ｏ3やＬａ2Ｏ3および／またはＣａＯと、ＺｒＯ2、更にはＴｉ2Ｏ3が生成しているため、溶接熱影響部の靭性が格段に向上している。 It can be considered as follows from Tables 2-3. No. Nos. 1 to 14 are examples that satisfy the requirements defined in the present invention. Since the steel material contains REM oxide and / or CaO and ZrO 2 , a steel material having good toughness in the weld heat affected zone is obtained. Has been obtained. In particular, no. In Nos. 10 to 14, Ce 2 O 3 , La 2 O 3 and / or CaO, ZrO 2 , and further Ti 2 O 3 are generated in the steel material, so the toughness of the weld heat affected zone is greatly improved. ing.

一方、Ｎｏ．１５〜２３は、本発明で規定するいずれかの要件を外れる例である。特に、Ｎｏ．１５〜２２は、鋼材にＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2の何れか一方を含有していないため、溶接熱影響部の靭性が劣っている。Ｎｏ．２３は、Ｍｎ量が本発明で規定する範囲から外れており、また溶存酸素量も少ない。 On the other hand, no. 15 to 23 are examples that do not meet any of the requirements defined in the present invention. In particular, no. Since Nos. 15 to 22 do not contain any one of REM oxide and / or CaO and ZrO 2 in the steel material, the toughness of the weld heat affected zone is inferior. No. In No. 23, the amount of Mn is out of the range defined in the present invention, and the amount of dissolved oxygen is small.

実験例２
上記実験例１で得られたＮｏ．６，１２，１９のスラブを、熱間圧延して厚み３０ｍｍの鋼板を得た。 Experimental example 2
No. obtained in Experimental Example 1 above. Six, 12, and 19 slabs were hot-rolled to obtain a steel plate having a thickness of 30 mm.

得られた鋼板の圧延方向に対して垂直な断面を、島津製作所製「ＥＰＭＡ−８７０５（装置名）」を用いて６００倍で観察し、最大径が０．２μｍ以上の析出物の成分組成を定量分析した。観察条件は、加速電圧を２０ｋＶ，試料電流を０．０１μＡ，観察視野面積を３〜５ｃｍ2，分析個数を１００個とし、特性Ｘ線の波長分散分光により析出物中央部での成分組成を上記実験例１と同じ手順で定量分析した。なお、観察位置は、鋼板のＤ／４（但し、Ｄは鋼板の厚み）位置とした。 The cross section perpendicular to the rolling direction of the obtained steel sheet was observed at 600 times using “EPMA-8705 (device name)” manufactured by Shimadzu Corporation, and the component composition of precipitates having a maximum diameter of 0.2 μm or more was observed. Quantitative analysis was performed. The observation conditions are as follows: the acceleration voltage is 20 kV, the sample current is 0.01 μA, the observation visual field area is 3 to 5 cm 2 , the number of analysis is 100, and the component composition at the center of the precipitate is determined by wavelength dispersion spectroscopy of characteristic X-rays. Quantitative analysis was performed in the same procedure as in Experimental Example 1. The observation position was the D / 4 position of the steel sheet (where D is the thickness of the steel sheet).

得られた定量結果のうち酸素含量が５％以上の析出物を酸化物とし、平均したものを酸化物の平均組成とした。全酸化物の平均組成を下記表４に示した。なお、一つの介在物から複数の元素が観測された場合には、それらの元素の存在を示すＸ線強度の比から各元素の単独酸化物に換算して酸化物の組成を算出した。   Of the obtained quantitative results, a precipitate having an oxygen content of 5% or more was defined as an oxide, and the average was defined as the average composition of the oxide. The average composition of all oxides is shown in Table 4 below. When a plurality of elements were observed from one inclusion, the composition of the oxide was calculated in terms of the X-ray intensity ratio indicating the presence of these elements, converted to a single oxide of each element.

ＥＰＭＡで観察した結果、観察された酸化物は、ＲＥＭおよび／またはＣａとＺｒを含む複合酸化物、或いは更にＴｉを含む複合酸化物が大半であったが、単独酸化物としてＲＥＭの酸化物、ＣａＯ、ＺｒＯ2、Ｔｉ2Ｏ3も生成していた。 As a result of observation by EPMA, the observed oxide was mostly a composite oxide containing REM and / or Ca and Zr, or a composite oxide further containing Ti, but the oxide of REM as a single oxide, CaO, ZrO 2 and Ti 2 O 3 were also generated.

次に、溶接時に熱影響を受けるＨＡＺの靭性を評価するために、大入熱溶接を模擬して下記に示す溶接再現試験を行なった。溶接再現試験は、上記鋼板から切り出した試験片を、全体が１４００℃になる様に加熱し、この温度で５秒間保持した後、冷却して行った。冷却速度は、８００℃から５００℃への冷却時間が３００秒となるように調整した。   Next, in order to evaluate the toughness of HAZ which is affected by heat during welding, a welding reproduction test shown below was performed by simulating high heat input welding. The welding reproduction test was performed by heating a test piece cut out from the steel plate so that the whole was 1400 ° C., holding at this temperature for 5 seconds, and then cooling. The cooling rate was adjusted so that the cooling time from 800 ° C. to 500 ° C. was 300 seconds.

冷却後の試験片の衝撃特性は、Ｖノッチシャルピー試験して−４０℃における吸収エネルギー（ｖＥ-40）を測定して評価した。ｖＥ-40が１５０Ｊ以上のものを合格（ＨＡＺ靭性良好）とする。測定結果を下記表４に示す。 The impact characteristics of the specimen after cooling were evaluated by measuring the absorbed energy (vE- 40 ) at -40 ° C by V-notch Charpy test. When vE- 40 is 150 J or more, it is regarded as acceptable (haz toughness is good). The measurement results are shown in Table 4 below.

下記表４と上記表３から明らかなように、鋼板から切り出した試験片の衝撃特性は、スラブから切り出したサンプルの衝撃特性とほぼ同程度であり、熱間圧延してもＨＡＺ靭性は変化しないことが分かる。   As is clear from Table 4 and Table 3 above, the impact properties of the test piece cut out from the steel plate are almost the same as those of the sample cut out from the slab, and the HAZ toughness does not change even when hot-rolled. I understand that.

Figure 2007100213
Figure 2007100213

Claims (9)

Ｃ ：０．０１〜０．２％（「質量％」の意味。以下同じ）、
Ｓｉ：０．５％以下（０％を含まない）、
Ｍｎ：２．５％以下（０％を含まない）、および
Ｎ ：０．０１％以下（０％を含まない）を含み、
Ｐ ：０．０２％以下（０％を含む）、
Ｓ ：０．０１５％以下（０％を含む）、および
Ａｌ：０．０１％以下（０％を含む）を満足すると共に、
更に、
ＲＥＭ：０．００１〜０．１％および／またはＣａ：０．０００３〜０．０２％と、
Ｚｒ：０．００１〜０．０５％を夫々含有し、且つ
酸化物としてＲＥＭの酸化物および／またはＣａＯと、ＺｒＯ2を含有することを特徴とする溶接熱影響部の靭性に優れた鋼材。 C: 0.01 to 0.2% (meaning “mass%”; the same shall apply hereinafter),
Si: 0.5% or less (excluding 0%),
Mn: 2.5% or less (not including 0%), and N: 0.01% or less (not including 0%),
P: 0.02% or less (including 0%),
S: 0.015% or less (including 0%) and Al: 0.01% or less (including 0%),
Furthermore,
REM: 0.001-0.1% and / or Ca: 0.0003-0.02%,
A steel material excellent in toughness of the weld heat affected zone, characterized by containing Zr: 0.001 to 0.05%, respectively, and containing REM oxide and / or CaO and ZrO 2 as oxides. 前記ＲＥＭの酸化物および／またはＣａＯの合計が５％以上で、前記ＺｒＯ2が５％以上を満足するものである請求項１に記載の鋼材。 The steel material according to claim 1, wherein the total of the REM oxide and / or CaO is 5% or more and the ZrO 2 satisfies 5% or more. 前記鋼材が、更に他の元素として、Ｔｉ：０．０８％以下（０％を含まない）を含むと共に、酸化物としてＴｉ酸化物を含有するものである請求項１または２に記載の鋼材。   The steel material according to claim 1 or 2, wherein the steel material further contains, as another element, Ti: 0.08% or less (not including 0%) and a Ti oxide as an oxide. 前記Ｔｉ酸化物が０．３％以上を満足するものである請求項３に記載の鋼材。   The steel material according to claim 3, wherein the Ti oxide satisfies 0.3% or more. 前記鋼材が、更に他の元素として、
Ｃｕ：２％以下（０％を含まない）、
Ｎｉ：３．５％以下（０％を含まない）、
Ｃｒ：３％以下（０％を含まない）、
Ｍｏ：１％以下（０％を含まない）、
Ｎｂ：０．２５％以下（０％を含まない）、
Ｖ ：０．１％以下（０％を含まない）、および
Ｂ ：０．００５％以下（０％を含まない）
よりなる群から選ばれる１種以上の元素を含むものである請求項１〜４のいずれかに記載の鋼材。 The steel material is still another element,
Cu: 2% or less (excluding 0%),
Ni: 3.5% or less (excluding 0%),
Cr: 3% or less (excluding 0%),
Mo: 1% or less (excluding 0%),
Nb: 0.25% or less (excluding 0%),
V: 0.1% or less (not including 0%), and B: 0.005% or less (not including 0%)
The steel material according to any one of claims 1 to 4, comprising at least one element selected from the group consisting of: 残部がＦｅおよび不可避不純物からなるものである請求項１〜５のいずれかに記載の鋼材。   The steel material according to any one of claims 1 to 5, wherein the balance is made of Fe and inevitable impurities. 請求項１〜６のいずれかに記載の鋼材を製造する方法であって、
溶存酸素量を０．００２０〜０．０１０％の範囲に調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、Ｚｒを添加することを特徴とする溶接熱影響部の靭性に優れた鋼材の製法。 A method for producing the steel material according to any one of claims 1 to 6,
The weld heat-affected zone is characterized by adding at least one element selected from the group consisting of REM and Ca and Zr to molten steel whose dissolved oxygen content is adjusted to a range of 0.0020 to 0.010%. A manufacturing method for steel with excellent toughness. 請求項３〜６のいずれかに記載の鋼材を製造する方法であって、
溶存酸素量を０．００２０〜０．０１０％の範囲に調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素と、ＴｉとＺｒを添加することを特徴とする溶接熱影響部の靭性に優れた鋼材の製法。 A method for producing the steel material according to any one of claims 3 to 6,
Welding heat effect characterized by adding at least one element selected from the group consisting of REM and Ca, and Ti and Zr to molten steel whose dissolved oxygen content is adjusted to a range of 0.0020 to 0.010%. A method of manufacturing steel with excellent toughness of the part. 上記溶存酸素量を調整した溶鋼へ、ＲＥＭおよびＣａよりなる群から選ばれる少なくとも１種の元素とＺｒを添加するに先立って、Ｔｉを添加する請求項８に記載の製法。   The method according to claim 8, wherein Ti is added to the molten steel with the dissolved oxygen content adjusted before adding at least one element selected from the group consisting of REM and Ca and Zr.
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