JP4264299B2 - High strength steel for flash butt welding with excellent weld toughness and its welded structure - Google Patents
High strength steel for flash butt welding with excellent weld toughness and its welded structure Download PDFInfo
- Publication number
- JP4264299B2 JP4264299B2 JP2003162902A JP2003162902A JP4264299B2 JP 4264299 B2 JP4264299 B2 JP 4264299B2 JP 2003162902 A JP2003162902 A JP 2003162902A JP 2003162902 A JP2003162902 A JP 2003162902A JP 4264299 B2 JP4264299 B2 JP 4264299B2
- Authority
- JP
- Japan
- Prior art keywords
- flash butt
- toughness
- steel
- less
- butt welding
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Description
【０００１】
【発明の属する技術分野】
本発明はＴＳ４００ＭＰａ以上の鋼材をフラッシュバット溶接した際の溶接部靭性に優れた建築・土木用鋼材、その鋼構造物およびその製造方法に関するものであり、特に大断面の鋼材のフラッシュバット溶接に効果を発揮するものである。
【０００２】
【従来の技術】
従来、フラッシュバット溶接はラインパイプ、鉄道レール、チェーン、あるいは機械部品など比較的断面積の小さい部材に適用されていた。しかし、建築用大断面溶接に適したフラッシュバット溶接機および溶接方法が報告されている（例えば、特許文献１及び２参照）。これらの発明は溶接する大断面鋼材個々にクランプ（または反力版、反力帯）を取り付け、その間をアクチュエータで相互に連結し、各大断面鋼材へ給電用の電極を取り付けた後に、アクチュエータでフラッシュおよびアップセット工程に対して同期した変位制御により加圧することにより溶接することを特徴としている。しかも本溶接方法では大断面鋼材のフラッシュバット溶接に対して溶接機の小型化、軽量化が実現されており、現地溶接を可能にした発明も出てきている。
【０００３】
通常、鉄道レール、チェーン、あるいは機械部品などのフラッシュバット溶接部の材質特性に対しては、引張試験や曲げ試験などにより機械的特性が規格化されているが、溶接部の靭性に対しては厳格な要求がなされていなかった。これに対して、本発明の対象分野である建築分野では、たとえばＪＩＳ Ｇ ３１３６に規定されている建築構造用圧延鋼材（ＳＮ４９０など）の母材に対しては、靭性値としてｖＥ0≧２７Ｊが必要と明確に記載されている。近年、地震時の変形能付与の観点から、母材だけでなく溶接部の靭性も重要との認識が高まり、溶接部の靭性も十分に確保することが義務づけられる方向にある。しかしながら、現時点ではフラッシュバット溶接を行った場合の溶接部靭性を確保できる鋼材あるいは溶接方法については公表されるに至っていない。
【０００４】
なお、溶接部の引張試験や曲げ試験によって評価されるような材質特性（引張試験や曲げ試験等）を確保するための提案は既になされている（例えば、特許文献３及び４参照）。前者は鋼帯を中継ぎ溶接するためにシールドガスを使用するための装置であり、後者は高張力鋼のフラッシュバット溶接のために油を塗布し、溶接時に燃焼させて溶接部の酸化物の量および形態制御を実施したものである。しかし、このようなシールド装置は溶接物が大きくなると大規模なものとなり、現地溶接には不向きである。また、油の塗布に関しては燃焼を伴うため厳しい安全管理を必要とするなどの欠点がある。
【０００５】
以上のような背景から、現地溶接を可能とするようなフラッシュバット溶接に対して、しかも設備的な工夫を極力少なくできるような方策、換言すると、溶接後の材質特性の特に溶接部の靭性の優れた鋼材、その鋼構造物およびその製造方法が強く求められている。
【０００６】
【特許文献１】
特開２００１−２５９８４９号公報
【特許文献２】
特開２００１−２５９８５０号公報
【特許文献３】
実開昭５８−８５４８４号公報
【特許文献４】
特許第２８６４３３８号公報
【０００７】
【発明が解決しようとする課題】
フラッシュバット溶接は、高能率でしかも安定した溶接部を得ることから、土木、建築用途に利用されつつある。しかし、前述したようにフラッシュバット後の溶接線や溶接熱影響部において非常に低い靭性値を示す。
【０００８】
この原因として、下記の点が考えられる。すなわち、
（１） 通常のフラッシュバット溶接では溶接時に高能率性が要求されるため、短時間で溶接を完了する必要があり、他の溶接方法に比べて冷却速度が大きい。したがって、溶接部のミクロ組織において、硬化組織が生じやすくなり、これが靭性の劣化を招く。
【０００９】
（２） フラッシュバット溶接時には高温で溶接熱影響部が再加熱されるためγ粒が粗大化する。特に、溶接部が大断面になるとフラッシング時間が長くなるため粗大化の傾向はさらに強くなり、靭性の劣化が生じる。
【００１０】
したがって、本発明の目的は主として上記２点を解決し、フラッシュバット溶接後の溶接線およびＨＡＺの靭性を母材靭性と同等以上にできるフラッシュバット溶接用の溶接部高靭性高張力鋼材、フラッシュバット溶接構造物及びその製造方法を提供することにある。
【００１１】
【課題を解決するための手段】
本発明者らは上記課題を解決するために鋼材成分、溶接方法、溶接部組織、および靭性値の関係を詳細に調査した。その結果、以下の重要な知見を得るに至った。
【００１２】
（１） 溶接線（フラッシュバット溶接時に溶融し、冷却時に凝固する部分、約１００μｍの幅となる）のフェライト生成率が３０％以上になると母材に対する溶接線の硬化が抑えられる。これを実現させるためには、冷却速度を小さくする必要がある。
【００１３】
（２） 溶接線近傍のミクロ組織として細粒フェライトは靭性向上に有効である。しかし、フェライト粒が粗大化した場合、かえって劣化を招くので粒径の上限値の規定が必要である。
【００１４】
（３） Ｔｉ添加により溶接線のγ粒径が微細化する。さらに、Ｃａ、Ｍｇ、またはＲＥＭ、またはこれらを複合添加することにより細粒化が促進する。
【００１５】
以上の知見は次のように理解される。すなわち、大断面のフラッシュバット溶接の場合、通常の部材のフラッシュバット溶接と比較して入熱が高い。冷却速度が大きい場合には焼入れ性が高く、粗大な硬化相が増えることになる。それ故、冷却速度を小さく制御することはフェライト分率を増加させる作用を有している。４００ＭＰａ以上のフラッシュバット溶接鋼材では溶接線のフェライト分率が３０％以上になると硬化組織が減少し、顕著に靭性が向上する。この時のフェライトの種類については、靭性の劣化を招かない粒内フェライトやポリゴナルフェライトが望ましく、フェライトサイドプレートは靭性値の低下を招くので極力避ける必要がある。
【００１６】
また、フラッシュバット溶接は短絡時の抵抗溶接とフラッシング時のアーク溶接の両方の性質を持ち合わせた溶接である。一般に溶接熱影響部においては加熱γ粒の細粒化効果によってＴｉ添加鋼やＴｉ−Ｍｇ−Ｃａ添加鋼が良好な靭性値を示すことが広く知られている。一方、フラッシュバット溶接の溶接線ではＳｉ、Ｍｎ等を含めた元素が再酸化するため、Ｔｉ、Ｍｇ、Ｃａがγ粒のピニングに機能するかは不明であった。本発明者らが調査した結果、これらの元素がγ粒の成長に対しても十分にピニング作用をすることが確認できた。この理由としては、鋼板製造の鋳造凝固時に生成するＴｉ、Ｍｇ、Ｃａ酸化物が再酸化後においても微細なまま存在しているために、これらがγ粒のピニング粒子として働き、しかもこれらの酸化物の一部が溶接線近傍において粒内フェライトの生成サイトとしても有効に作用するため、ミクロ組織がより微細化するものと推定される。なお、フェライト粒が３０μｍ以下であれば良好な靭性値となることが確認できている。
【００１７】
本発明は、上記知見に基づいて完成したもので、その要旨とするところは下記の通りである。
【００１８】
（１） 鋼成分が質量％で、
Ｃ：０．０２〜０．２０％、
Ｓｉ：０．０１〜２．５％、
Ｍｎ：０．２５〜２．０％、
Ｐ：０．０３％以下、
Ｓ：０．０３％以下、
Ａｌ：０．００５％以下、
Ｔｉ：０．００５〜０．０５％
を含有し、残部鉄および不可避不純物からなることを特徴とするフラッシュバット溶接用の溶接部高靭性高張力鋼材。
【００１９】
（２）さらに鋼成分が質量％で
Ｃａ：０．０００５〜０．００５％、
Ｍｇ：０．０００５〜０．００５％、
ＲＥＭ：０．０００５〜０．００５％、
のうち１種または２種以上を含有することを特徴とする上記（１）記載のフラッシュバット溶接用の溶接部高靭性高張力鋼材。
（３） 鋼成分が質量％で、
Ｃ：０．０２〜０．２０％、
Ｓｉ：０．０１〜２．５％、
Ｍｎ：０．２５〜２．０％、
Ｐ：０．０３％以下、
Ｓ：０．０３％以下、
Ａｌ：０．０５％以下、
Ｔｉ：０．００５〜０．０５％
Ｍｇ：０．０００５〜０．００５％に、
さらに、
Ｃａ：０．０００５〜０．００５％、
ＲＥＭ：０．０００５〜０．００５％、
のうち１種または２種を含有し、残部鉄および不可避不純物からなることを特徴とするフラッシュバット溶接用の溶接部高靭性高張力鋼材。
【００２０】
（４） さらに鋼成分が質量％で
Ｎｂ：０．００５〜０．１％、
Ｎｉ：０．０５〜１．０％、
Ｃｕ：０．０５〜１．０％、
Ｃｒ：０．０５〜２．０％、
Ｍｏ：０．０５〜０．５０％、
Ｖ：０．００２〜０．５％、
Ｂ：０．０００５〜０．０１％
の１種または２種以上含有することを特徴とする上記（１）〜（３）のいずれかに記載のフラッシュバット溶接用の溶接部高靭性高張力鋼材。
【００２１】
（５） フラッシュバット溶接後の溶接線のフェライト生成率が３０％以上であることを特徴とする上記（１）〜（４）のいずれかに記載の鋼板を使用したフラッシュバット溶接構造物。
【００２２】
（６） フラッシュバット溶接後の溶接線のポリゴナルフェライト粒径が３０μｍ以下であることを特徴とする上記（５）記載のフラッシュバット溶接構造物。
【００２３】
（７） 溶接部靭性の優れたフラッシュバット溶接構造物の製造方法であって、上記（１）乃至（４）のいずれかに記載の成分を含有する鋼同士を溶接し、その冷却に際し、８００℃から５００℃までの間の冷却速度を６０℃／ｓ以下とすることを特徴とする上記（５）または（６）に記載のフラッシュバット溶接構造物およびその製造方法。
【００２４】
【発明の実施の形態】
以下、本発明を詳細に説明する。
【００２５】
４００ＭＰａ以上の鋼材をフラッシュバット溶接した場合には、その溶接線の組織がフェライト以外では硬化組織となるため、溶接部靭性が著しく損なわれる。従って、フラッシュバット鋼材の溶接線の組織としては、フェライト分率を３０％以上とする必要がある。また、フェライト粒径が大きいと脆性破壊の伝播に対する抵抗力が小さくなる。従って、フェライト粒径はその影響のない３０μｍ以下とする必要がある。
【００２６】
次に、本発明における溶接母材としてその鋼成分を以下の通りにすることが望ましい。
【００２７】
Ｃは０．０２％に満たないと鋼の強度が不足し、また製造技術面においてコストの増加を招く。そこでＣ量の下限値を０．０２％とした。一方、０．２％を超えると溶接部の硬度が上昇し靭性値を低下させる。そのため、Ｃ量は０．０２〜０．２％とした。
【００２８】
Ｓｉは脱酸上鋼に含まれる元素である。０．０１％未満ではその効果は少ない。一方、２．５％を超えて添加すると強度が高くなり靭性を低下させる。このため、上限値を２．５％とした。
【００２９】
Ｍｎは鋼の焼入性を向上させて強度を上昇させるのに有効である。これらの効果を得るためには、少なくとも０．２５％以上を添加する必要がある。一方、２．０％を超えると著しく硬化するため靭性が劣化する。このためＭｎの上限を２．０％とし、Ｍｎ量は０．２５〜２．０％の範囲とする。
【００３０】
Ｐは粒界に偏析し粒界脆化を起こしやすくするため、０．０３％以下にする必要がある。靭性確保の観点からは不純物元素であるＰは極力低減することが望ましい。
【００３１】
ＳもＰと同様に粒界に偏析し粒界脆化を起こしやすくするため、０．０３％以下にする必要がある。不純物元素であるＳは極力低減することが望ましい。
【００３２】
Ａｌは脱酸上鋼に含まれる元素であるため添加する必要がある。しかし、０．０５％超添加すると溶接部において粗大なＡｌ酸化物が生成するため靭性を低下させる。このため０．０５％以下とする。
【００３３】
Ｔｉは本発明の重要な元素の一つであり、ＴｉＯ2などの酸化物あるいはＴｉＮ、ＴｉＣなどのＴｉ析出物のピニング効果により熱処理時のγ粒径などを微細化する。この効果を得るためには０．００５％以上の添加が必要である。しかし、０．０５％超添加すると粗大なＴｉＮが多量に析出するため延性を劣化させる。このため、上限を０．０５％とする。
【００３４】
ＣａはＣａＳ（Ｏ）の生成により熱処理時のγ粒径などを微細化するのに有効な元素である。０．０００５％未満では効果がないため０．０００５％を下限値とした。しかし、０．００５％を超えると清浄度が低下するとともにＣａ介在物が粗大化し延性を低下させるため上限値を０．００５％とした。
【００３５】
ＭｇはＣａと同様に熱処理時のγ粒径などを微細化するのに有効な元素である。０．０００５％未満では効果がないため０．０００５％を下限値とした。しかし、０．００５％を超えると清浄度が低下するとともに介在物が粗大化し延性を低下させるため上限値を０．００５％とした。
【００３６】
ＲＥＭもＣａと同様に熱処理時のγ粒径などを微細化するために有効な元素である。０．０００５％未満では効果がないため０．０００５％を下限値とした。しかし、０．００５％を超えると清浄度が低下するとともにＲＥＭを含む介在物が粗大化し延性を低下するため上限値を０．００５％とした。
【００３７】
次に以下の元素も添加することによって機能の向上をはかることができる。
【００３８】
ＮｂはＮｂ析出物のピニング効果によりオーステナイト粒を微細化し、延性を向上させる。このためには０．００５％以上の添加が必要である。しかしながら、多量に添加しても効果が飽和し経済的に不利となるため０．１％を上限とする。このためＮｂの適正範囲を０．００５〜０．１％とする。
【００３９】
ＮｉはＣｕと同様に焼入性の向上させるために添加する。また、Ｃｕ脆化を抑制する効果もある。焼入性を向上させるためには０．０５％以上必要である。しかし、１．０％を超えるとその効果が飽和するため経済的に不利になる。このために上限値を１．０％とした。
【００４０】
Ｃｕは焼入性を向上させるために添加する。この効果を得るには０．０５％以上必要である。しかし、１．０％を超えると圧延時に熱間割れを引き起こしやすくなるため上限値を１．０％とした。
【００４１】
Ｃｒは固溶強化、焼入性向上させ強度を上昇させる。０．０５％以下ではこの効果が不十分である。しかし、２．０％を超えると強度が高くなり過ぎ、延性が低下する。このため上限値を２．０％とした。
【００４２】
Ｍｏは、鋼の強度を上昇させるためには少なくとも０．０５％以上添加しないとその効果は認められない。また、０．５０％を超えて添加するとフェライトの生成が抑制されるからその上限を０．５０％とする。そのため、Ｍｏの成分範囲を０．１０〜０．５０％までとした。
【００４３】
Ｖは炭窒化物を析出させγ粒を微細化し強度、延性を向上させる。この効果を得るには０．００２％以上の添加が必要である。しかし多量の添加では効果が飽和するため経済的に不利になる。このため上限値を０．５％とした。
【００４４】
Ｂは焼入性を向上させることで強度を向上する。また、優先的に粒界に偏析しＰ、Ｓ、Ｍｎ等の粒界偏析を抑制する粒界清浄効果のために靭性の劣化を抑える。このため、Ｂは０．０００５％を下限値とする。しかし、０．０１％を超えるとＦｅ23Ｂを析出しかえって靭性を劣化させる。このためＢの成分範囲を０．０００５〜０．０１％とする。
【００４５】
次に本発明の製造条件について説明する。
【００４６】
前記のように溶接部靭性を確保する溶接線の組織を制御で溶接線の組織をフェライト分率３０％以上とするためには、フラッシュバット溶接後の冷却速度を制御する必要がある。溶接後、８００〜５００℃の間の平均冷却速度が６０℃／ｓを超えるとフェライト分率が３０％未満となり硬化組織が増加する。このため８００〜５００℃の間の冷却速度を６０℃／ｓ以下にする必要がある。
【００４７】
【実施例】
以下本発明の実施例について説明する。表１の化学成分を有する鋼塊を熱間圧延および熱処理を行い鋼板とした。これらの鋼板を機械加工して試験材を作製した。この時の溶接部の面積は４０００〜５００００ｍｍ2とした。これらの鋼板をフラッシュバット溶接し溶接線のフェライト分率を測定した。フエライト分率はナイタールエッチング後溶接線１００μｍの幅を観察して決定した。溶接線溶接線はナイタールエッチにより他の部分より白色になる幅が約１００μｍのエリアである。フェライト分率、強度、および靭性値を表２に示す。
【００４８】
鋼１〜１０は本発明鋼であり、良好な靭性を示した。
【００４９】
鋼１１〜１６は鋼成分が適切でないため靭性値が確保できない。鋼１１ではＴｉ添加していないためフェライトが粗大となり靭性が低下した。鋼１２ではＴｉ量が多く靭性値が低下した。鋼１３ではＣａが高く、鋼１４ではＭｇ量が高いため靭性に有害な酸化物が多量に発生した。鋼１５ではＡｌが高くＡｌ酸化物の生成が顕著になり靭性値を低下させた。鋼１６の化学成分は本発明の請求範囲内にあるが、冷却速度が速くフェライト分率が低下したため靭性値が低下した。
【００５０】
【表１】
【表２】
【発明の効果】
本発明によると大断面のフラッシュバット溶接に対して高靭性のＦＢＷ（フラッシュバット溶接用鋼）鋼を得ることができ、工業的に非常に有用である。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a steel material for construction and civil engineering that has excellent weld toughness when flash butt welding of steel of TS400 MPa or more, a steel structure thereof, and a manufacturing method thereof, and is particularly effective for flash butt welding of a steel material having a large cross section. To demonstrate.
[0002]
[Prior art]
Conventionally, flash butt welding has been applied to members having a relatively small cross-sectional area, such as line pipes, railroad rails, chains, or machine parts. However, flash butt welders and welding methods suitable for large cross-section welding for construction have been reported (see, for example, Patent Documents 1 and 2). In these inventions, clamps (or reaction force plates, reaction belts) are attached to each large cross-section steel material to be welded, and the electrodes are connected to each other with an actuator, and power supply electrodes are attached to each large cross-section steel material. It is characterized by welding by applying pressure by displacement control synchronized with the flash and upset processes. In addition, in this welding method, the welding machine is reduced in size and weight compared to flash butt welding of a large-section steel material, and an invention that enables on-site welding has also come out.
[0003]
Usually, the material properties of flash butt welds such as railway rails, chains, or mechanical parts are standardized by tensile tests and bending tests, but for the toughness of welds. There were no strict requests. On the other hand, in the building field which is the subject field of the present invention, for example, vE 0 ≧ 27J as a toughness value for a base material of a rolled steel material for building structure (such as SN490) defined in JIS G 3136. It is clearly stated as necessary. In recent years, from the viewpoint of imparting deformability at the time of an earthquake, the recognition that not only the base metal but also the toughness of the welded portion is important is increasing, and it is in the direction that it is obliged to sufficiently ensure the toughness of the welded portion. However, at present, a steel material or a welding method that can ensure the weld toughness when flash butt welding is performed has not been disclosed.
[0004]
In addition, the proposal for ensuring the material characteristic (a tension test, a bending test, etc.) evaluated by the tensile test and the bending test of a welding part has already been made | formed (for example, refer patent document 3 and 4). The former is a device for using shield gas to weld steel strips, and the latter is oil applied for flash butt welding of high-strength steel and burned during welding to reduce the amount of oxide in the weld. And form control. However, such a shield device becomes large-scale when the welded material becomes large, and is not suitable for on-site welding. In addition, the application of oil has drawbacks such as requiring strict safety management because it involves combustion.
[0005]
Against the background as described above, it is possible to reduce the amount of equipment for flash butt welding that enables on-site welding, in other words, the material properties after welding, particularly the toughness of the weld. There is a strong demand for excellent steel materials, steel structures and manufacturing methods thereof.
[0006]
[Patent Document 1]
JP 2001-259849 A [Patent Document 2]
Japanese Patent Laid-Open No. 2001-259850 [Patent Document 3]
Japanese Utility Model Publication No. 58-85484 [Patent Document 4]
Japanese Patent No. 2864338 [0007]
[Problems to be solved by the invention]
Flash butt welding is being used for civil engineering and construction applications because it provides a highly efficient and stable weld. However, as described above, a very low toughness value is exhibited in the weld line after the flash butt and the weld heat affected zone.
[0008]
The following points can be considered as the cause. That is,
(1) Since normal flash butt welding requires high efficiency at the time of welding, it is necessary to complete the welding in a short time, and the cooling rate is higher than other welding methods. Therefore, a hardened structure is likely to be generated in the microstructure of the welded portion, which leads to deterioration of toughness.
[0009]
(2) During flash butt welding, the heat affected zone is reheated at a high temperature, so that the γ grains become coarse. In particular, when the welded portion has a large cross section, the flushing time becomes longer, so that the tendency of coarsening is further increased and toughness is deteriorated.
[0010]
Accordingly, the object of the present invention is to solve the above-mentioned two points, and to weld the high toughness steel material for flash butt welding, which can make the weld line after flash butt welding and the toughness of HAZ equal to or higher than the base material toughness, and flash bat. It is providing the welding structure and its manufacturing method.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have investigated in detail the relationship among steel material components, welding methods, welded portion structures, and toughness values. As a result, the following important findings were obtained.
[0012]
(1) When the ferrite generation rate of the weld line (the portion that melts during flash butt welding and solidifies during cooling, and has a width of about 100 μm) is 30% or more, hardening of the weld line to the base material is suppressed. In order to realize this, it is necessary to reduce the cooling rate.
[0013]
(2) As a microstructure near the weld line, fine-grained ferrite is effective in improving toughness. However, when the ferrite grains are coarsened, the deterioration of the ferrite grains is caused. Therefore, it is necessary to define the upper limit of the grain diameter.
[0014]
(3) The γ grain size of the weld line is refined by the addition of Ti. Further, fine addition is promoted by adding Ca, Mg, REM, or a combination thereof.
[0015]
The above knowledge is understood as follows. That is, in the case of flash butt welding of a large cross section, heat input is higher than that of flash butt welding of a normal member. When the cooling rate is high, the hardenability is high and the coarse cured phase increases. Therefore, controlling the cooling rate to be small has the effect of increasing the ferrite fraction. In a flash butt weld steel material of 400 MPa or more, when the ferrite fraction of the weld line is 30% or more, the hardened structure is reduced and the toughness is remarkably improved. Regarding the type of ferrite at this time, intragranular ferrite and polygonal ferrite that do not cause toughness deterioration are desirable, and the ferrite side plate causes a decrease in toughness value, so it is necessary to avoid it as much as possible.
[0016]
Further, flash butt welding is a welding having both properties of resistance welding at the time of short circuit and arc welding at the time of flushing. In general, it is widely known that Ti-added steel and Ti-Mg-Ca-added steel exhibit good toughness values due to the effect of refinement of heated γ grains in the weld heat affected zone. On the other hand, since elements including Si, Mn and the like are reoxidized in the weld line of flash butt welding, it is unclear whether Ti, Mg, and Ca function for γ grain pinning. As a result of investigation by the present inventors, it has been confirmed that these elements have a sufficient pinning effect on the growth of γ grains. The reason for this is that Ti, Mg and Ca oxides produced during the casting solidification of steel sheet production are still fine even after re-oxidation, and these act as pinning particles of γ grains, and these oxidations. It is estimated that the microstructure is further refined because part of the material effectively acts as a site for generating intragranular ferrite in the vicinity of the weld line. It has been confirmed that if the ferrite grains are 30 μm or less, a good toughness value is obtained.
[0017]
The present invention has been completed based on the above findings, and the gist thereof is as follows.
[0018]
(1) The steel component is mass%,
C: 0.02 to 0.20%,
Si: 0.01 to 2.5%,
Mn: 0.25 to 2.0%,
P: 0.03% or less,
S: 0.03% or less,
Al: 0.005% or less,
Ti: 0.005 to 0.05%
A high-toughness high-tensile strength steel material for flash butt welding characterized by comprising a balance iron and inevitable impurities .
[0019]
(2) Further, the steel component is in mass%, Ca: 0.0005 to 0.005%,
Mg: 0.0005 to 0.005%,
REM: 0.0005 to 0.005%,
1 type or 2 types or more are contained, The weld part high toughness high-tensile steel material for flash butt welding of the said (1) description characterized by the above-mentioned.
(3) The steel component is mass%,
C: 0.02 to 0.20%,
Si: 0.01 to 2.5%,
Mn: 0.25 to 2.0%,
P: 0.03% or less,
S: 0.03% or less,
Al: 0.05% or less,
Ti: 0.005 to 0.05%
Mg: 0.0005 to 0.005%,
further,
Ca: 0.0005 to 0.005%,
REM: 0.0005 to 0.005%,
A high-toughness high-tensile steel material for flash butt welding, which contains one or two of them and consists of the remaining iron and inevitable impurities.
[0020]
( 4 ) Further, the steel component is mass%, Nb: 0.005 to 0.1%,
Ni: 0.05 to 1.0%,
Cu: 0.05 to 1.0%,
Cr: 0.05-2.0%,
Mo: 0.05 to 0.50%,
V: 0.002 to 0.5%,
B: 0.0005 to 0.01%
One type or two or more types of the above-mentioned (1) to (3), the weld zone high toughness and high strength steel material for flash butt welding.
[0021]
( 5 ) A flash butt welded structure using the steel plate according to any one of (1) to ( 4 ) above, wherein the ferrite generation rate of the weld line after flash butt welding is 30% or more.
[0022]
( 6 ) The flash butt weld structure according to ( 5 ), wherein the polygonal ferrite particle size of the weld line after flash butt welding is 30 μm or less.
[0023]
( 7 ) A method for producing a flash butt welded structure with excellent weld zone toughness, wherein the steels containing the components according to any one of (1) to ( 4) above are welded together and cooled, and 800 The flash butt welded structure according to ( 5 ) or ( 6 ) above and a method for producing the same, wherein the cooling rate between 0 ° C. and 500 ° C. is 60 ° C./s or less.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0025]
When flash butt welding is performed on a steel material of 400 MPa or more, the weld line has a hardened structure other than ferrite, so that the weld zone toughness is significantly impaired. Accordingly, the structure of the weld line of the flash butt steel material needs to have a ferrite fraction of 30% or more. Further, when the ferrite grain size is large, the resistance to the propagation of brittle fracture becomes small. Therefore, the ferrite grain size needs to be 30 μm or less which does not affect the ferrite grain size.
[0026]
Next, it is desirable that the steel components of the welding base material in the present invention are as follows.
[0027]
If C is less than 0.02%, the strength of the steel is insufficient, and the cost is increased in terms of manufacturing technology. Therefore, the lower limit value of the C amount is set to 0.02%. On the other hand, if it exceeds 0.2%, the hardness of the welded portion increases and the toughness value decreases. Therefore, the C content is set to 0.02 to 0.2%.
[0028]
Si is an element contained in the deoxidized upper steel. If it is less than 0.01%, the effect is small. On the other hand, if added over 2.5%, the strength increases and the toughness decreases. For this reason, the upper limit value was set to 2.5%.
[0029]
Mn is effective in improving the hardenability of the steel and increasing the strength. In order to obtain these effects, it is necessary to add at least 0.25% or more. On the other hand, if it exceeds 2.0%, the toughness deteriorates because it hardens significantly. For this reason, the upper limit of Mn is set to 2.0%, and the amount of Mn is set to a range of 0.25 to 2.0%.
[0030]
P needs to be 0.03% or less in order to segregate at the grain boundary and easily cause embrittlement at the grain boundary. From the viewpoint of securing toughness, it is desirable to reduce P as an impurity element as much as possible.
[0031]
S, like P, segregates at the grain boundary and easily causes grain boundary embrittlement, so it is necessary to make it 0.03% or less. It is desirable to reduce S as an impurity element as much as possible.
[0032]
Since Al is an element contained in the deoxidized upper steel, it is necessary to add it. However, if added in excess of 0.05%, coarse Al oxide is generated in the welded portion, so the toughness is lowered. For this reason, it is 0.05% or less.
[0033]
Ti is one of the important elements of the present invention, and the γ grain size during heat treatment is refined by the pinning effect of oxides such as TiO 2 or Ti precipitates such as TiN and TiC. In order to obtain this effect, 0.005% or more must be added. However, if added over 0.05%, a large amount of coarse TiN precipitates, which deteriorates ductility. For this reason, the upper limit is made 0.05%.
[0034]
Ca is an element effective for reducing the γ grain size during heat treatment by the production of CaS (O). If it is less than 0.0005%, there is no effect, so 0.0005% was set as the lower limit. However, if it exceeds 0.005%, the cleanliness is lowered and the Ca inclusions are coarsened to reduce the ductility, so the upper limit is made 0.005%.
[0035]
Mg, like Ca, is an effective element for reducing the γ grain size during heat treatment. If it is less than 0.0005%, there is no effect, so 0.0005% was set as the lower limit. However, if it exceeds 0.005%, the cleanliness is lowered and inclusions are coarsened to reduce ductility, so the upper limit is set to 0.005%.
[0036]
REM is also an effective element for reducing the γ grain size during heat treatment, similar to Ca. If it is less than 0.0005%, there is no effect, so 0.0005% was set as the lower limit. However, when it exceeds 0.005%, the cleanliness is lowered, and inclusions including REM are coarsened to reduce ductility. Therefore, the upper limit is set to 0.005%.
[0037]
Next, the function can be improved by adding the following elements.
[0038]
Nb refines austenite grains by the pinning effect of Nb precipitates and improves ductility. For this purpose, 0.005% or more must be added. However, even if added in a large amount, the effect is saturated and economically disadvantageous, so 0.1% is made the upper limit. For this reason, the appropriate range of Nb is made 0.005 to 0.1%.
[0039]
Ni is added to improve the hardenability like Cu. It also has an effect of suppressing Cu embrittlement. In order to improve hardenability, 0.05% or more is necessary. However, if it exceeds 1.0%, the effect is saturated, which is economically disadvantageous. For this reason, the upper limit is set to 1.0%.
[0040]
Cu is added to improve hardenability. To obtain this effect, 0.05% or more is necessary. However, if it exceeds 1.0%, hot cracking is likely to occur during rolling, so the upper limit was made 1.0%.
[0041]
Cr increases solid strength by strengthening solid solution and improving hardenability. If it is 0.05% or less, this effect is insufficient. However, if it exceeds 2.0%, the strength becomes too high and the ductility decreases. For this reason, the upper limit value was set to 2.0%.
[0042]
In order to increase the strength of the steel, Mo is not effective unless it is added at least 0.05% or more. Further, if added over 0.50%, the formation of ferrite is suppressed, so the upper limit is made 0.50%. Therefore, the Mo component range is set to 0.10 to 0.50%.
[0043]
V precipitates carbonitride to refine γ grains and improves strength and ductility. To obtain this effect, 0.002% or more must be added. However, the addition of a large amount is economically disadvantageous because the effect is saturated. For this reason, the upper limit is set to 0.5%.
[0044]
B improves strength by improving hardenability. Moreover, the deterioration of toughness is suppressed because of the grain boundary cleaning effect that preferentially segregates at the grain boundaries and suppresses the grain boundary segregation of P, S, Mn and the like. For this reason, B sets 0.0005% as a lower limit. However, if it exceeds 0.01%, Fe 23 B is precipitated and the toughness is deteriorated. For this reason, the component range of B is made 0.0005 to 0.01%.
[0045]
Next, the manufacturing conditions of the present invention will be described.
[0046]
As described above, in order to control the structure of the weld line that ensures the toughness of the welded portion so that the structure of the weld line has a ferrite fraction of 30% or more, it is necessary to control the cooling rate after flash butt welding. After welding, when the average cooling rate between 800 and 500 ° C. exceeds 60 ° C./s, the ferrite fraction becomes less than 30% and the hardened structure increases. For this reason, the cooling rate between 800-500 degreeC needs to be 60 degrees C / s or less.
[0047]
【Example】
Examples of the present invention will be described below. Steel ingots having the chemical components shown in Table 1 were subjected to hot rolling and heat treatment to obtain steel plates. These steel plates were machined to produce test materials. The area of the welded portion at this time was set to 4000 to 50000 mm 2 . These steel plates were flash-butt welded and the ferrite fraction of the weld line was measured. The ferrite fraction was determined by observing the width of the weld line 100 μm after nital etching. The weld line is an area having a width of about 100 μm that becomes whiter than the other parts by nital etching. The ferrite fraction, strength, and toughness values are shown in Table 2.
[0048]
Steels 1 to 10 were steels of the present invention and exhibited good toughness.
[0049]
Steels 11 to 16 cannot secure a toughness value because the steel components are not appropriate. In Steel 11, since Ti was not added, ferrite became coarse and toughness decreased. In Steel 12, the amount of Ti was large and the toughness value was lowered. Steel 13 had a high Ca content, and steel 14 had a high Mg content, so a large amount of oxides harmful to toughness were generated. In Steel 15, Al was high and the formation of Al oxide was remarkable, resulting in a decrease in toughness. The chemical composition of steel 16 is within the claimed range of the present invention, but the toughness value was lowered because the cooling rate was fast and the ferrite fraction was lowered.
[0050]
[Table 1]
[Table 2]
【The invention's effect】
According to the present invention, FBW (flash butt welding steel) steel having high toughness can be obtained for flash butt welding with a large cross section, which is very useful industrially.
Claims (7)
Ｃ：０．０２〜０．２０％、
Ｓｉ：０．０１〜２．５％、
Ｍｎ：０．２５〜２．０％、
Ｐ：０．０３％以下、
Ｓ：０．０３％以下、
Ａｌ：０．００５％以下、
Ｔｉ：０．００５〜０．０５％
を含有し、残部鉄および不可避不純物からなることを特徴とするフラッシュバット溶接用の溶接部高靭性高張力鋼材。Steel component is mass%,
C: 0.02 to 0.20%,
Si: 0.01 to 2.5%,
Mn: 0.25 to 2.0%,
P: 0.03% or less,
S: 0.03% or less,
Al: 0.005% or less,
Ti: 0.005 to 0.05%
A high-toughness high-tensile strength steel material for flash butt welding characterized by comprising a balance iron and inevitable impurities .
Ｃａ：０．０００５〜０．００５％、
Ｍｇ：０．０００５〜０．００５％、
ＲＥＭ：０．０００５〜０．００５％、
のうち１種または２種以上を含有することを特徴とする請求項１記載のフラッシュバット溶接用の溶接部高靭性高張力鋼材。Furthermore, when the steel component is mass%, Ca: 0.0005 to 0.005%,
Mg: 0.0005 to 0.005%,
REM: 0.0005 to 0.005%,
The high toughness high toughness steel material for welded parts for flash butt welding according to claim 1, wherein one or more of them are contained.
Ｃ：０．０２〜０．２０％、
Ｓｉ：０．０１〜２．５％、
Ｍｎ：０．２５〜２．０％、
Ｐ：０．０３％以下、
Ｓ：０．０３％以下、
Ａｌ：０．０５％以下、
Ｔｉ：０．００５〜０．０５％
Ｍｇ：０．０００５〜０．００５％に、
さらに、
Ｃａ：０．０００５〜０．００５％、
ＲＥＭ：０．０００５〜０．００５％、
のうち１種または２種を含有し、残部鉄および不可避不純物からなることを特徴とするフラッシュバット溶接用の溶接部高靭性高張力鋼材。 Steel component is mass%,
C: 0.02 to 0.20%,
Si: 0.01 to 2.5%,
Mn: 0.25 to 2.0%,
P: 0.03% or less,
S: 0.03% or less,
Al: 0.05% or less,
Ti: 0.005 to 0.05%
Mg: 0.0005 to 0.005%,
further,
Ca: 0.0005 to 0.005%,
REM: 0.0005 to 0.005%,
A high-toughness high-tensile steel material for flash butt welding, which contains one or two of them and consists of the remaining iron and inevitable impurities.
Ｎｂ：０．００５〜０．１％、
Ｎｉ：０．０５〜１．０％、
Ｃｕ：０．０５〜１．０％、
Ｃｒ：０．０５〜２．０％、
Ｍｏ：０．０５〜０．５０％、
Ｖ：０．００２〜０．５％、
Ｂ：０．０００５〜０．０１％
の１種または２種以上含有することを特徴とする請求項１〜３のいずれかに記載のフラッシュバット溶接用の溶接部高靭性高張力鋼材。Furthermore, steel component is Nb: 0.005 to 0.1% by mass%,
Ni: 0.05 to 1.0%,
Cu: 0.05 to 1.0%,
Cr: 0.05-2.0%,
Mo: 0.05 to 0.50%,
V: 0.002 to 0.5%,
B: 0.0005 to 0.01%
One type or two or more types of these are contained, The weld part high toughness high-tensile steel material for flash butt welding according to any one of claims 1 to 3.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2003162902A JP4264299B2 (en) | 2003-06-06 | 2003-06-06 | High strength steel for flash butt welding with excellent weld toughness and its welded structure |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2003162902A JP4264299B2 (en) | 2003-06-06 | 2003-06-06 | High strength steel for flash butt welding with excellent weld toughness and its welded structure |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2004360048A JP2004360048A (en) | 2004-12-24 |
| JP4264299B2 true JP4264299B2 (en) | 2009-05-13 |
Family
ID=34054911
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2003162902A Expired - Fee Related JP4264299B2 (en) | 2003-06-06 | 2003-06-06 | High strength steel for flash butt welding with excellent weld toughness and its welded structure |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP4264299B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109112405A (en) * | 2018-09-13 | 2019-01-01 | 营口中车型钢新材料有限公司 | A kind of railroad train band steel and preparation method thereof |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104625373A (en) * | 2014-12-15 | 2015-05-20 | 贵州安大航空锻造有限责任公司 | Method for forming alpha-phase titanium alloy large-cross-section ring piece through flash welding |
-
2003
- 2003-06-06 JP JP2003162902A patent/JP4264299B2/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109112405A (en) * | 2018-09-13 | 2019-01-01 | 营口中车型钢新材料有限公司 | A kind of railroad train band steel and preparation method thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2004360048A (en) | 2004-12-24 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP5604842B2 (en) | Steel material for large heat input welding | |
| JP2008163446A (en) | Steel member for high heat input welding | |
| JP5958428B2 (en) | Manufacturing method of steel plates for high heat input welding | |
| TWI526545B (en) | Steel material for welding | |
| JP5999005B2 (en) | Low yield ratio high strength steel sheet with excellent weld heat affected zone toughness and method for producing the same | |
| JP5849892B2 (en) | Steel material for large heat input welding | |
| JP2009127104A (en) | Steel having excellent weld heat-affected zone toughness, and method for producing the same | |
| JP2006241510A (en) | Steel for high strength welded structure having excellent low temperature toughness in high heat input weld haz and its production method | |
| JP4901262B2 (en) | Thick steel plate with excellent toughness of heat affected zone | |
| JP2007023346A (en) | Method for producing high strength welded steel tube excellent in strain-aging characteristic | |
| JP4264299B2 (en) | High strength steel for flash butt welding with excellent weld toughness and its welded structure | |
| JP4433844B2 (en) | Method for producing high strength steel with excellent fire resistance and toughness of heat affected zone | |
| JP4264298B2 (en) | Large section flash butt welded structure with high toughness in the weld zone | |
| JP4105990B2 (en) | High strength welded structural steel with excellent low temperature toughness of large heat input weld HAZ and method for producing the same | |
| JP5720447B2 (en) | Steel sheet with excellent toughness of weld heat affected zone | |
| JP5509946B2 (en) | Steel sheet with excellent toughness of weld heat affected zone | |
| JP2010100909A (en) | High corrosion-resistant ferritic stainless steel sheet having excellent joint strength, for resistance spot welding | |
| JP4259374B2 (en) | High strength steel sheet with excellent low temperature toughness and weld heat affected zone toughness and method for producing the same | |
| JP3711948B2 (en) | Steel sheet pile excellent in toughness and weld properties and its manufacturing method | |
| JP4299743B2 (en) | High strength steel for high strength welded structure with excellent base metal toughness and super high heat input weld HAZ toughness, and its manufacturing method | |
| JP4105991B2 (en) | High strength welded structural steel with excellent high heat input weld HAZ toughness and method for producing the same | |
| JP3371712B2 (en) | Manufacturing method of earthquake resistant building steel with excellent fire resistance | |
| JP7260779B2 (en) | High strength steel plate for high heat input welding | |
| JP7272471B2 (en) | steel plate | |
| JP5458923B2 (en) | Welded joint with excellent brittle fracture resistance |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20050915 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20070517 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20070612 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20070810 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20090127 |
|
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20090216 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120220 Year of fee payment: 3 |
|
| R151 | Written notification of patent or utility model registration |
Ref document number: 4264299 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R151 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120220 Year of fee payment: 3 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120220 Year of fee payment: 3 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130220 Year of fee payment: 4 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130220 Year of fee payment: 4 |
|
| S531 | Written request for registration of change of domicile |
Free format text: JAPANESE INTERMEDIATE CODE: R313531 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130220 Year of fee payment: 4 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130220 Year of fee payment: 4 |
|
| S533 | Written request for registration of change of name |
Free format text: JAPANESE INTERMEDIATE CODE: R313533 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130220 Year of fee payment: 4 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20140220 Year of fee payment: 5 |
|
| S533 | Written request for registration of change of name |
Free format text: JAPANESE INTERMEDIATE CODE: R313533 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |
|
| LAPS | Cancellation because of no payment of annual fees |