JP3879207B2

JP3879207B2 - Manufacturing method of welded steel pipe

Info

Publication number: JP3879207B2
Application number: JP32097797A
Authority: JP
Inventors: 高明豊岡; 章依藤; 裕二橋本; 元晶板谷; 博之松井; 正徳西森
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 1997-11-21
Filing date: 1997-11-21
Publication date: 2007-02-07
Anticipated expiration: 2017-11-21
Also published as: JPH11151523A

Description

【０００１】
【発明の属する技術分野】
本発明は、鋼管の製造方法に関し、とくに、オープン管の両エッジ部を加熱し、衝合接合して製管された鋼管をさらに絞り圧延する溶接鋼管の製造方法に関する。
【０００２】
【従来の技術】
溶接鋼管は、鋼板または鋼帯を管状に成形しその継目を溶接したもので、小径から大径まで各種の製造方法によりつくられているが、主な製造方法として、電気抵抗溶接（電縫）、鍛接、電孤溶接によるものが挙げられる。
比較的小径鋼管用として極めて高い生産性を有する鍛接鋼管製造方法がある。この方法は、連続的に供給した鋼帯を加熱炉で1300℃程度に加熱したのち、成形ロールで管状に成形してオープン管とし、続いてオープン管の両エッジ部に高圧空気を吹きつけて端面のスケールオフを行い、ウェルディングホーンにより端面に酸素を吹きつけ、その酸化熱で端面を1400℃程度に昇温させてから鍛接ロールで両エッジ部端面を衝合させ固相接合して鋼管を製造する方法である（例えば、第３版鉄鋼便覧第III 巻（２）1056〜1092頁）。
【０００３】
しかし、この鍛接鋼管製造方法では、造管速度が速く生産性は高いが、
▲１▼端面のスケールオフが完全でないため、鍛接衝合部へのスケール噛込みが発生し、シーム部の強度が母材部に比べかなり劣る。
▲２▼帯鋼を高温に加熱するため、管表面にスケールが生成し表面肌が悪い。
などの欠点を有している。
【０００４】
一方、小径〜中径鋼管用としては、高周波誘導加熱を利用した電気抵抗溶接法（電気抵抗溶接鋼管、電縫管）が主として利用されている。この方法は、連続的に帯鋼を供給し、成形ロールで管状に成形してオープン管として、続いて高周波誘導加熱によりオープン管の両エッジ部端面を鋼の融点以上に加熱したのち、スクイズロールで両エッジ部端面を衝合溶接して鋼管を製造する方法である（例えば、第３版鉄鋼便覧第III 巻（２）1056〜1092頁）。
【０００５】
この電縫管では、
▲１▼オープン管は両エッジのみ接合時に融点以上とされる以外は冷間状態にある冷間製管のゆえに、孔型ロール等の製管工具と鋼帯とのスリップ疵の防止や成形荷重抑制等の措置を必要とするため生産能率が悪い。
▲２▼製品鋼管寸法に合わせた孔型ロールを用いなければならないことから小ロット多品種の鋼管製造には適していない。
などの問題があった。
【０００６】
このような鍛接鋼管製造方法あるいは電気抵抗溶接鋼管製造方法の問題点を解消するため、例えば、特開昭63-33105号公報には、電縫鋼管等の中空素管を冷間状態で３つのロールからなる孔形を複数個用いて圧延して外径縮小する鋼管の絞り圧延方法が提案されている。
しかし、この方法では、電縫鋼管等の中空素管を冷間状態で、絞り圧延を行うため、大きな圧延荷重に耐え得る大型の圧延機や、ロールとの焼付き防止のための潤滑圧延装置の設置を必要とするうえ、帯鋼をオープン管に成形するときの成形歪にさらに冷間絞り圧延による加工歪が重畳して材料の加工硬化が著しくなり、鋼管の伸びが低下し製管後熱処理工程を追加しなければならないという問題がある。また、冷間絞り圧延では、大幅な外径縮小、すなわち高絞りを行うと偏肉やロール疵が発生するという問題もあり、成形用孔型ロール寸法の大幅な統一ができにくいという問題もある。
【０００７】
また、特公平2-24606 号公報には、帯鋼をＡ₃ 変態点未満程度に加熱し、オープン管に成形したのち、高周波誘導加熱とスクイズロールによりオープン管の両縁部を溶接して母管とし、その後母管をＡ₃変態点以上に昇温し、管絞り圧延装置で所定の外径の製品管とする鋼管の製造方法が提案されている。図５はこの鋼管の製造方法を示す模式図であり、１は帯鋼、８は母管、16は製品管、２は帯鋼予熱炉、４は帯鋼加熱炉、24は母管加熱炉、21は絞り圧延装置、３は成形ロール群（成形加工装置）、９は誘導コイル、６はスクイズロール、11はビード切削機である。
【０００８】
しかし、この方法では、管全体を800 〜950 ℃程度の高温に加熱するため、新たなスケールロスを生じ歩留り低下に加えて、絞り圧延時にスケール噛込みを誘発し、表面疵の発生や表面肌が悪化するといった問題や、加熱炉の設置、加熱のための燃料費が増加するといったコスト増加の問題がある。
【０００９】
【発明が解決しようとする課題】
本発明は、上記した問題を有利に解決し、低圧延荷重で圧延でき、加工硬化を抑制し、しかも表面状態を悪化させずに、高強度高延性を有する鋼管を製造でき、高生産能率で小ロット多品種生産にも対応できる溶接鋼管の製造方法を提案することを目的とする。
【００１０】
【課題を解決するための手段】
本発明者らは、高強度で高延性を有する溶接鋼管を製造するために、鋭意検討した結果、加熱急冷処理を施した帯鋼から製造した鋼管に温間加工を施すことにより高延性が得られることを新たに知見した。本発明はこれら知見をもとに構成されたものである。
【００１１】
参考発明は、帯鋼を成形ロールで連続的に成形しオープン管とし、該オープン管の両エッジ部を融点以上に加熱し、スクイズロールで衝合接合し母管とし、ビード切削したのち、該母管を再加熱して絞り加工を施す溶接鋼管の製造方法において、前記帯鋼が熱間圧延工程で急冷処理を施されたものであり、前記絞り加工が200 〜700 ℃の温度範囲で行う温間絞り加工であることを特徴とする高強度高延性溶接鋼管の製造方法である。
【００１２】
本発明は、前記帯鋼の熱間圧延工程での急冷処理の代わりに、成形ロールでオープン管に成形する前に帯鋼に加熱急冷処理を施すものである。なお、本発明では、前記絞り加工は外径絞り率で５％以上の絞り加工とするのが好ましい。
また、本発明では、前記温間絞り加工は、２ロール以上のロールからなる複数スタンドの絞り圧延機により施されるのが好ましい。また、本発明では、前記ビード切削ののち、シーム部を冷却するのが好ましい。また、前記オープン管の両エッジ部の加熱は、誘導加熱、または通電による抵抗加熱、タングステンイナートガス溶接（TIG 溶接）、レーザービーム、電子ビーム、プラズマビーム、サブマージアーク溶接のうちのいずれかの方式により、行うのが好ましい。
【００１３】
また、本発明では、前記温間絞り加工のための加熱は、誘導加熱または、ガスあるいは重油を用いた加熱炉で行うのが好ましい。
また、本発明では、前記オープン管を700 ℃以下に予熱したのち、前記両エッジ部を加熱してもよい。
また、本発明は、帯鋼を払いだすアンコイラーと、先行する帯鋼と後行する帯鋼を接合する帯鋼接合装置と、帯鋼を貯えるルーパと、帯鋼を加熱急冷する帯鋼加熱急冷装置と、帯鋼を成形加工する成形ロール群からなる成形加工装置と、あるいはさらにオープン管を予熱する管体予熱装置と、誘導加熱コイルを有する誘導加熱装置と、オープン管を衝合接合するスクイズロールと、ビード切削機と、あるいはシーム冷却装置と、母管を加熱する母管誘導加熱装置あるいは加熱炉と、母管を絞り圧延する複数の絞り圧延機からなる絞り加工装置とを順次配列したことを特徴とする鋼管の製造設備列である。
【００１４】
【発明の実施の形態】
参考発明では、帯鋼は、熱間圧延工程で圧延後急冷され、マルテンサイト、ベーナイト等の急冷組織としたものが好適である。このような急冷組織とし、その後の温間加工と組合わせることにより高延性が確保できるのである。本発明では、前記熱間圧延工程で圧延後急冷の代わりに、成形ロールでオープン管に成形する前に帯鋼に加熱急冷処理を施し、急冷組織とする。この場合には、アンコイラーから払いだされた帯鋼を、加熱炉あるいは誘導加熱等によりＡc₃変態点以上に加熱したのち、急冷処理を施す。急冷処理の冷却手段は、水、ガス等の流体噴射が好ましい。
【００１５】
本発明に好適な帯鋼の化学組成は、重量％で、Ｃ：0.05〜0.19％、Si：0.01〜1.5 ％、Mn：0.5 〜3.5 ％を基本組成として必要に応じNi、Cr、Mo、Cu、Nb、Ｖ、Ti、Ｂ等の合金元素を添加してもよい。
Ｃは、焼入れ性を向上させる元素であり、マルテンサイト、ベイナイト等の急冷組織とするために必要である。このためには、0.05％以上の含有が必要であるが、0.19％を超えると溶接性が劣化するため、Ｃは0.05〜0.19％とするのが好ましい。
【００１６】
Siは、強度を向上させる元素であり、所望の強度を得るために、0.01％以上の含有が必要であるが、1.5 ％を超えると溶接性、加工性が劣化するため、Siは0.01〜1.5 ％とするのが好ましい。
Mnは、焼入れ性を向上させる元素であり、マルテンサイト、ベイナイト等の急冷組織とするために必要である。このためには、0.5 ％以上の含有が必要であるが、3.5 ％を超えると溶接性、加工性が劣化するため、Mnは0.5 〜3.5 ％とするのが好ましい。
【００１７】
その他、強度を高めるために、Ni、Cr、Mo、Cu、Nb、Ｖ、Ti、Ｂ等の合金元素を添加できるが、Niは２％以下、Crは１％以下、Moは２％以下、Cuは１％以下、Nbは0.1 ％以下、Ｖは0.3 ％以下、Tiは0.2 ％以下、Ｂは0.003 ％以下とするのが望ましい。
帯鋼は、アンコイラーから払いだされ、複数の成形ロールで連続的に成形されオープン管となる。成形は通常公知の複数の成形ロールによる加工方法が好適に適用できる。
【００１８】
ついで、オープン管の両エッジ部を融点以上に加熱する。
エッジ部の加熱は、エネルギー効率の観点から誘導コイルによる誘導加熱方式が好ましいが、通電による抵抗加熱、タングステンイナートガス溶接（ＴＩＧ溶接）、レーザービーム、電子ビーム、プラズマビーム、サブマージアーク溶接のうちのいずれかの方式により、行ってもよい。また、これら複数の加熱手段を併用してもよい。
【００１９】
エッジ部の加熱の前に、オープン管全体を700 ℃以下に予熱してもよい。予熱することにより、後に行うエッジ部加熱時にエッジ部とその近傍の母管との温度差を小さくし、エッジ部の温度及び温度分布を溶接時に適正に制御するために行う。予熱温度が700 ℃を超えるとオープン管表面に多量のスケールを形成し、鋼管の表面肌が劣化するため、700 ℃を予熱温度の上限とした。なお、200 ℃未満では、エッジ部近傍の温度、温度分布が適正とならないため、予熱温度は好ましくは200 〜700 ℃である。予熱方法は、加熱炉を用いる方法、誘導コイルを用いる誘導加熱方法、通電による抵抗加熱方法いずれも好適である。
【００２０】
両エッジ部を融点以上に加熱されたオープン管は、スクイズロールで両エッジ部を衝合され、溶接されて母管とされたのち、ビード切削される。
本発明では、ビード切削後の母管のシーム部近傍を冷却するのが好ましい。シーム部の冷却手段は、冷媒噴射ノズルによるのが好ましい。冷媒としては、水、低温エア等が使用できる。母管シーム部近傍は、オープン管エッジ部を溶接するために他の部位より高温に加熱されて、管周方向温度差が発生している。母管における管周方向温度差は、その後の絞り加工時に変形抵抗差を生じ、製品管に偏肉を生じやすくする。このため、母管シーム部を絞り加工前に冷却し、管周方向温度差を解消しておくのが好ましい。偏肉防止のためには、管周方向温度差は100 ℃以下とするのがよい。
【００２１】
ついで、本発明では、母管を再加熱し、200 〜700 ℃の温度範囲で外径絞り率で５〜60％の温間絞り加工を施し、所定の外径の製品管とする。温間絞り加工のため母管の再加熱方法は、とくに限定しないが、加熱炉、誘導コイル等を用いる加熱方法が好ましく、なかでも誘導コイルによる誘導加熱が好適である。
母管の再加熱は絞り加工温度が200 〜700 ℃の温間領域となるように加熱する。
【００２２】
絞り加工温度が200 〜700 ℃の温度範囲になるように加熱された母管は、２ロール以上の孔型ロール構造の複数スタンドの絞り圧延機により温間絞り加工を施される。絞り加工は、図２（ａ）〜（ｃ）に示す２ロール〜４ロールからなる孔型ロール構造の絞り圧延機を複数スタンド配設した絞り圧延機列で行われるのが好ましい。
【００２３】
また、絞り加工量は、外径絞り率で５％以上とするのが好ましい。外径絞り率が５％未満では、絞り圧延による延性向上効果が小さくなる。なお、外径絞り率の上限は、絞り圧延機の設備能力に依存して決定される。
また、絞り加工温度は200 〜700 ℃の温間領域とする。この温度範囲で絞り加工を施すことにより導入された加工歪と管材の前組織とが複合して、延性が著しく増加する。しかし、絞り加工温度が、200 ℃未満では、管材の加工硬化が著しく、延性が劣化し、さらに被圧延材の変形抵抗が高く圧延荷重が増大して、管表面にロールの焼付き疵が発生する。また、絞り加工温度が700 ℃を超えると圧延中に発生するスケールの噛み込み疵により管表面の粗さが増大し、表面肌が劣化する。
【００２４】
温間絞り加工を施された製品管は、空冷されるかあるいは水冷されて室温まで冷却される。得られた製品管は、切断機により所定の寸法に切断され、管矯正装置で矯正されるか、あるいは管矯正装置で矯正されたのちコイル状に巻き取られる。図１、図３に参考発明の、図２に本発明の、実施に好適な鋼管製造設備列を示す。
【００２５】
図１（ａ）においては、１は帯鋼、14は帯鋼を払いだすアンコイラ、15は先行する帯鋼の後端部と後行する帯鋼の先端部を接続する帯鋼接合装置、17は帯鋼を貯えるルーパ、３は成形ロール群からなる成形加工装置、７はオープン管、５はオープン管エッジ部を融点以上に加熱する誘導加熱装置、６はオープン管エッジ部を衝合接合するスクイズロール、８は母管、11は母管に形成されるビードを切削するビード切削機、10は絞り加工のための母管再加熱用の母管誘導加熱装置、21は母管に絞り加工を施す絞り圧延装置、18は製品管の切断機、16は製品管、19は管矯正装置、20は温度計である。
【００２６】
図１（ｂ）は、図１（ａ）の設備列のビード切削機11の出側にシーム冷却装置12を設けた鋼管製造設備列である。他の符号は図１（ａ）と同じとした。
図２は、図１（ａ）のルーパ17の出側に帯鋼を加熱する帯鋼加熱装置22ａと帯鋼を急冷する帯鋼急冷装置22ｂからなる帯鋼加熱急冷装置22を設けた鋼管製造設備列である。
【００２７】
図３は、図１（ｂ）の成形加工装置３の出側にオープン管を予熱する管体予熱装置23を設けた鋼管製造設備列である。
【００２８】
【実施例】
（参考例）
Ｃ：0.17wt％、Si：0.20wt％、Mn：1.30wt％、Cr：1.0 wt％の組成を有する鋼素材をFET800℃の熱間圧延により2.5 mm厚の鋼板とし、圧延終了後直ちに水冷し、急冷組織（マルテンサイト主体組織）としたのち巻き取りコイルとした。図１（ａ）の設備列を用いて、このコイルからアンコイラ14により払いだした帯鋼１を成形加工装置３によりオープン管７としたのち、誘導加熱装置５によりエッジ部を融点以上に加熱し、スクイズロール６により衝合接合し60.5mmφ×2.5mm 厚の母管とした。なお、接合時に形成したビードはビード切削機11により削除した。ビード切削後の母管の温度は350 ℃であった。その後、誘導コイル９により母管を加熱し、３ロール構造の絞り圧延機を20スタンド設置した絞り圧延装置21により25.4〜42.7mmφ×2.3mm の製品管16とした。このときの外径絞り率は29〜58％であった。
【００２９】
比較として、同一組成の鋼素材を2.5mm 厚の鋼板に熱間圧延し、熱間圧延のまま、水冷を行わずコイルに巻き取り、焼鈍処理（900 ℃焼鈍）を行った。このコイルを用いて、上記と同様な条件で製品管とし、比較例（No.A）とした。
従来例（No.B）として、同一組成の鋼素材を2.5mm 厚の鋼板に熱間圧延し、熱間圧延のまま、水冷を行わずコイルに巻き取り、上記と同様に、図１（ａ）の設備列を用いて、このコイルからアンコイラ14により払いだした帯鋼１を成形加工装置３によりオープン管７としたのち、誘導加熱装置５によりエッジ部を融点以上に加熱し、スクイズロール６により衝合接合し60.5mmφ×2.5mm 厚の母管とした。なお、接合時に形成したビードはビード切削機11により削除した。ビード切削後の母管の温度は50℃であった。その後、誘導加熱装置10による加熱を行わず、３ロール構造の絞り圧延機を８スタンド設置した絞り圧延装置21により外径絞り率29％の42.7mmφ×2.3mm の製品管16とした。
【００３０】
これら製品管の機械的性質、焼付きの有無、表面肌の粗さを表１に示す。
焼付きの有無は目視で、表面粗さは触針式表面粗さ計で製品管の長さ15×円周５mmについて測定しRmaxを求めた。
【００３１】
【表１】

【００３２】
表１から参考例は引張強さが700MPa以上、伸びが35％以上といずれも高く高強度高延性の鋼管で、表面肌も良好であることがわかる。これに対し、比較例は、延性、表面肌、強度、のいずれか１つが劣っている。
また、焼鈍した帯鋼を用いた比較例（No.A）では、引張強さが430MPaと強度が低い。また、冷間絞り加工を行う従来例では、伸びが14％と低い。また、参考例では、絞り圧延の荷重も低く、焼付も皆無であり、造管速度も従来例（No.B）に比べ2.6 〜4.5 倍となっている。
（実施例）
Ｃ：0.08wt％、Si：0.5wt ％、Mn：3.0wt ％、Cr：0.3 wt％、Nb：0.02wt％の組成を有する鋼素材を熱間圧延により2.0mm 厚の鋼板としたのち巻き取りコイルとした。図２の設備列を用いて、このコイルからアンコイラ14により払いだした帯鋼１を、加熱急冷装置22を通して、880 ℃に加熱後 350℃以下まで水冷して急冷組織（マルテンサイト主体組織）とする。その後、成形加工装置３によりオープン管７とし、誘導加熱装置５によりエッジ部を融点以上に加熱し、スクイズロール６により衝合接合し60.5mmφ×2.0mm 厚の母管とした。なお、接合時に形成したビードはビード切削機11により削除した。ビード切削後の母管の温度は50℃であった。その後、誘導コイル９により500 ℃に母管を加熱し、３ロール構造の絞り圧延機を16スタンド設置した絞り圧延装置21により31.8mmφ×1.8mm の製品管16とした。このときの絞り圧延温度は450 〜500 ℃で、外径絞り率は47％であった。
【００３３】
この製品管の機械的性質は、表２に示すように降伏強さが1240MPa 、引張強さが1380MPa 、伸びが29％であり、表面肌も良好な高強度高延性の鋼管であった。
【００３４】
【表２】

【００３５】
【発明の効果】
本発明によれば、低圧延荷重で圧延でき、表面状態を悪化させずに、高強度高延性を有する鋼管を高い生産性で製造でき、しかも母管サイズを統合することができ少ない母管サイズから多種類サイズの製品管の製造が可能となり、小ロット多品種生産にも対応できるという格別の効果を奏する。
【図面の簡単な説明】
【図１】参考発明の実施に好適な鋼管製造設備列の１例を示す模式図である。
【図２】本発明の実施に好適な鋼管製造設備列の１例を示す模式図である。
【図３】参考発明の実施に好適な鋼管製造設備列の１例を示す模式図である。
【図４】絞り圧延機のロール構造を示す説明図である。
【図５】従来の鋼管製造設備列の１例を示す模式図である。
【符号の説明】
１帯鋼
２帯鋼予熱炉
３成形加工装置
４帯鋼加熱炉
５誘導加熱装置
６スクイズロール
７オープン管
８母管
９誘導コイル
１０母管誘導加熱装置
１１ビード切削機
１２シーム冷却装置
１４アンコイラ
１５帯鋼接合装置
１６製品管
１７ルーパ
１８切断機
１９管矯正装置
２０温度計
２１絞り圧延装置
２２帯鋼加熱急冷装置
22ａ帯鋼加熱装置
22ｂ帯鋼急冷装置
２３管体予熱装置
２４母管加熱炉[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a steel pipe, and more particularly to a method for manufacturing a welded steel pipe in which both edge portions of an open pipe are heated and a steel pipe manufactured by abutting joining is further drawn and rolled.
[0002]
[Prior art]
Welded steel pipes are formed by forming a steel plate or steel strip into a tubular shape and welding its seam, and are made by various manufacturing methods from small to large diameters. , Forging and electric arc welding.
There is a forged steel pipe manufacturing method having extremely high productivity for a relatively small diameter steel pipe. In this method, a continuously supplied steel strip is heated to about 1300 ° C in a heating furnace, then formed into a tubular shape with a forming roll to form an open tube, and then high-pressure air is blown to both edges of the open tube. The end face is scaled off, oxygen is blown to the end face with a welding horn, the end face is heated to about 1400 ° C with the heat of oxidation, and the end faces of both edges are brought into contact with a forging roll and solid-phase bonded to a steel pipe (For example, 3rd Edition Steel Handbook, Volume III (2) 1056-1092).
[0003]
However, in this forged steel pipe manufacturing method, the pipe making speed is fast and the productivity is high.
(1) Since the scale-off of the end face is not complete, scale biting occurs in the forging contact portion, and the strength of the seam portion is considerably inferior to that of the base material portion.
(2) Since the steel strip is heated to a high temperature, scale is generated on the tube surface, and the surface skin is poor.
Have the disadvantages.
[0004]
On the other hand, for small to medium diameter steel pipes, an electric resistance welding method (electric resistance welded steel pipe, electric resistance welded pipe) using high-frequency induction heating is mainly used. In this method, a steel strip is continuously supplied and formed into a tubular shape with a forming roll to form an open tube. Subsequently, both end portions of the open tube are heated to a temperature higher than the melting point of the steel by high frequency induction heating, and then a squeeze roll. In this method, the end surfaces of both edge portions are abutted and welded to produce a steel pipe (for example, third edition Steel Handbook, Volume III (2) pages 1056-1092).
[0005]
In this electric pipe,
(1) Since the open pipe is a cold pipe that is in a cold state except that only the edges are joined at both edges, it prevents slip flaws between the pipe-making tool such as a hole roll and the steel strip, and the molding load. Production efficiency is poor because measures such as suppression are required.
{Circle around (2)} Since it is necessary to use a perforated roll that matches the size of the product steel pipe, it is not suitable for the production of many types of steel pipes in small lots.
There were problems such as.
[0006]
In order to solve such problems of the forged steel pipe manufacturing method or the electric resistance welded steel pipe manufacturing method, for example, Japanese Patent Laid-Open No. 63-33105 discloses three hollow element pipes such as ERW steel pipes in a cold state. A steel pipe drawing method has been proposed in which a plurality of hole shapes made of rolls are rolled to reduce the outer diameter.
However, in this method, hollow rolling tubes such as ERW steel tubes are cold-rolled in a cold state, so a large rolling mill capable of withstanding a large rolling load and a lubrication rolling device for preventing seizure with a roll. In addition, the work strain of the cold drawn rolling is superimposed on the forming strain when the strip steel is formed into an open tube, and the work hardening of the material becomes remarkable, and the elongation of the steel tube decreases and the pipe is There is a problem that a heat treatment step must be added. Further, in cold drawing rolling, there is a problem that when the outer diameter is greatly reduced, that is, when high drawing is performed, uneven thickness and roll wrinkles are generated, and there is also a problem that it is difficult to greatly unify the forming hole roll dimensions. .
[0007]
Further, Japanese Patent Kokoku 2-24606, heating the strip to the order of less than ₃ transformation point A, then molded into an open pipe, welding the edges of the open pipe by high-frequency induction heating and squeeze roll base and the tube, after which the substrate tube was raised above a ₃ transformation point, the production method of the steel pipe to a product pipe having a predetermined outer diameter tube reducing rolling devices have been proposed. FIG. 5 is a schematic diagram showing a method of manufacturing this steel pipe, wherein 1 is a steel strip, 8 is a master pipe, 16 is a product pipe, 2 is a steel strip preheating furnace, 4 is a steel strip heating furnace, and 24 is a master pipe heating furnace. , 21 is a drawing rolling device, 3 is a forming roll group (forming processing device), 9 is an induction coil, 6 is a squeeze roll, and 11 is a bead cutting machine.
[0008]
However, in this method, the entire tube is heated to a high temperature of about 800 to 950 ° C, which causes new scale loss and yield reduction. In addition, it induces scale biting during drawing rolling, generating surface flaws and surface skin. There are problems such as deterioration of the temperature, and problems of cost increase such as the installation of a heating furnace and an increase in fuel costs for heating.
[0009]
[Problems to be solved by the invention]
The present invention advantageously solves the above-mentioned problems, can be rolled at a low rolling load, suppresses work hardening, and can produce a steel pipe having high strength and high ductility without deteriorating the surface state, and has a high production efficiency. The purpose is to propose a method for manufacturing welded steel pipes that can be used for small-lot, multi-product production.
[0010]
[Means for Solving the Problems]
As a result of diligent studies to produce a welded steel pipe having high strength and high ductility, the present inventors have obtained high ductility by subjecting a steel pipe produced from a steel strip subjected to heating and quenching to warm working. It was newly discovered that The present invention is configured based on these findings.
[0011]
In the reference invention, a steel strip is continuously formed with a forming roll to form an open pipe, both edge portions of the open pipe are heated to a melting point or more, and a squeeze roll is used for abutting and joining to form a mother pipe. In the manufacturing method of a welded steel pipe in which a mother pipe is reheated and drawn, the steel strip is subjected to a rapid cooling process in a hot rolling process, and the drawing is performed in a temperature range of 200 to 700 ° C. A method for producing a high-strength, high-ductility welded steel pipe, characterized by warm drawing .
[0012]
This onset Ming, instead of quenching the hot rolling process of the steel strip, is intended to facilities heat quenching the strip prior to forming the open pipe at the forming roll. In the present invention, the drawing process is preferably a drawing process with an outer diameter drawing ratio of 5% or more.
Moreover, in this invention, it is preferable to perform the said warm drawing process with the multi-stand drawing mill which consists of a roll more than 2 rolls. In the present invention, it is preferable that the seam portion is cooled after the bead cutting. Further, the heating of both edge portions of the open tube is performed by any one of induction heating, resistance heating by energization, tungsten inert gas welding (TIG welding), laser beam, electron beam, plasma beam, and submerged arc welding. Preferably.
[0013]
In the present invention, the heating for the warm drawing process is preferably performed by induction heating or a heating furnace using gas or heavy oil.
In the present invention, both the edge portions may be heated after preheating the open pipe to 700 ° C. or lower.
The present invention also includes an uncoiler for discharging the steel strip, a steel strip joining device for joining the preceding steel strip and the subsequent steel strip, a looper for storing the steel strip, and a steel strip heating / quenching method for heating and cooling the steel strip. Squeeze that collides and joins an open tube, an apparatus, a forming device comprising a group of forming rolls for forming a steel strip, or a tube preheating device for preheating an open tube, an induction heating device having an induction heating coil A roll, a bead cutting machine, a seam cooling device, a mother tube induction heating device or a heating furnace for heating the mother tube, and a drawing device composed of a plurality of drawing mills for drawing and rolling the mother tube are sequentially arranged. It is the manufacturing equipment row | line | column of the steel pipe characterized by this.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In the reference invention, it is preferable that the steel strip is rapidly cooled after rolling in a hot rolling process and has a quenched structure such as martensite and bainite. A high ductility can be secured by combining such a rapidly cooled structure and subsequent warm working. In the present invention, instead of rolling after quench at the hot rolling step is subjected to heating and quenching treatment to the strip prior to forming the open pipe at the forming rolls, and rapidly cooled structure. In this case, the steel strip discharged from the uncoiler is heated to the Ac ₃ transformation point or higher by a heating furnace or induction heating, and then rapidly cooled. The cooling means for the rapid cooling treatment is preferably fluid injection such as water or gas.
[0015]
The chemical composition of the steel strip suitable for the present invention is, by weight, C: 0.05 to 0.19%, Si: 0.01 to 1.5%, Mn: 0.5 to 3.5% as the basic composition, if necessary, Ni, Cr, Mo, Cu , Nb, V, Ti, B and other alloy elements may be added.
C is an element that improves hardenability, and is necessary for forming a quenched structure such as martensite and bainite. For this purpose, a content of 0.05% or more is necessary, but if it exceeds 0.19%, the weldability deteriorates, so C is preferably 0.05 to 0.19%.
[0016]
Si is an element that improves the strength. In order to obtain a desired strength, it is necessary to contain 0.01% or more. However, if it exceeds 1.5%, weldability and workability deteriorate, so Si is 0.01 to 1.5%. % Is preferable.
Mn is an element that improves hardenability, and is necessary for forming a quenched structure such as martensite and bainite. For this purpose, it is necessary to contain 0.5% or more. However, if it exceeds 3.5%, weldability and workability deteriorate, so Mn is preferably 0.5 to 3.5%.
[0017]
In addition, alloy elements such as Ni, Cr, Mo, Cu, Nb, V, Ti, and B can be added to increase the strength, but Ni is 2% or less, Cr is 1% or less, Mo is 2% or less, It is desirable that Cu is 1% or less, Nb is 0.1% or less, V is 0.3% or less, Ti is 0.2% or less, and B is 0.003% or less.
The strip steel is dispensed from the uncoiler and is continuously formed by a plurality of forming rolls to form an open tube. For forming, a generally known processing method using a plurality of forming rolls can be suitably applied.
[0018]
Next, both edges of the open tube are heated to the melting point or higher.
The heating of the edge portion is preferably an induction heating method using an induction coil from the viewpoint of energy efficiency, but any of resistance heating by energization, tungsten inert gas welding (TIG welding), laser beam, electron beam, plasma beam, submerged arc welding This may be done by any method. Moreover, you may use these several heating means together.
[0019]
Before heating the edge part, the entire open tube may be preheated to 700 ° C. or lower. Preheating is performed in order to reduce the temperature difference between the edge portion and the mother pipe in the vicinity thereof when the edge portion is heated later, and to appropriately control the temperature and temperature distribution of the edge portion during welding. When the preheating temperature exceeds 700 ° C, a large amount of scale is formed on the surface of the open tube, and the surface of the steel pipe deteriorates. Therefore, 700 ° C was set as the upper limit of the preheating temperature. If the temperature is less than 200 ° C., the temperature and temperature distribution in the vicinity of the edge portion are not appropriate, so the preheating temperature is preferably 200 to 700 ° C. As the preheating method, any of a method using a heating furnace, an induction heating method using an induction coil, and a resistance heating method by energization are suitable.
[0020]
The open pipes whose both edge parts are heated to the melting point or higher are brought into contact with each other by a squeeze roll, welded to form a mother pipe, and then bead-cut.
In the present invention, it is preferable to cool the vicinity of the seam portion of the mother pipe after bead cutting. The cooling means for the seam portion is preferably a refrigerant injection nozzle. As the refrigerant, water, low-temperature air, or the like can be used. The vicinity of the mother pipe seam portion is heated to a higher temperature than other portions in order to weld the open pipe edge portion, and a temperature difference in the pipe circumferential direction is generated. The temperature difference in the pipe circumferential direction in the mother pipe causes a deformation resistance difference during the subsequent drawing process, and easily causes uneven thickness in the product pipe. For this reason, it is preferable to cool the mother pipe seam portion before drawing to eliminate the temperature difference in the pipe circumferential direction. In order to prevent uneven thickness, the temperature difference in the pipe circumferential direction should be 100 ° C or less.
[0021]
Next, in the present invention, the mother pipe is reheated and subjected to a warm drawing process of 5 to 60% at an outer diameter drawing ratio in a temperature range of 200 to 700 ° C. to obtain a product pipe having a predetermined outer diameter. The method for reheating the mother pipe for warm drawing is not particularly limited, but a heating method using a heating furnace, an induction coil or the like is preferable, and induction heating using an induction coil is particularly preferable.
The reheating of the mother pipe is performed so that the drawing temperature is in a warm region of 200 to 700 ° C.
[0022]
The mother pipe heated so that the drawing temperature is in a temperature range of 200 to 700 ° C. is subjected to warm drawing by a multi-stand drawing mill with a two-roll or more perforated roll structure. The drawing process is preferably performed in a drawing mill row in which a plurality of drawing mills having a hole-type roll structure composed of two to four rolls shown in FIGS.
[0023]
The drawing amount is preferably 5% or more in terms of the outer diameter drawing ratio. When the outer diameter drawing ratio is less than 5%, the effect of improving ductility by drawing is reduced. Note that the upper limit of the outer diameter drawing ratio is determined depending on the equipment capacity of the drawing mill.
The drawing temperature is a warm region of 200 to 700 ° C. The processing strain introduced by drawing in this temperature range is combined with the pre-structure of the tube material, and the ductility is remarkably increased. However, if the drawing temperature is less than 200 ° C, the work hardening of the tube material is remarkable, the ductility deteriorates, the deformation resistance of the rolled material is high, the rolling load increases, and roll seizure occurs on the tube surface. To do. On the other hand, when the drawing temperature exceeds 700 ° C., the roughness of the tube surface increases due to the bite of the scale generated during rolling, and the surface skin deteriorates.
[0024]
The product tube that has been subjected to warm drawing is cooled to room temperature by air cooling or water cooling. The obtained product tube is cut into a predetermined size by a cutting machine and corrected by a tube straightening device, or after being straightened by a tube straightening device and wound in a coil shape. Figure 1 shows the Reference Invention Figure 3, of the present invention in FIG. 2, the preferred steel pipe manufacturing equipment column to an.
[0025]
In FIG. 1 (a), 1 is a steel strip, 14 is an uncoiler for delivering the steel strip, 15 is a steel strip joining device for connecting the rear end of the preceding steel strip and the front end of the subsequent steel strip, 17 Is a looper for storing the steel strip, 3 is a forming apparatus comprising a group of forming rolls, 7 is an open pipe, 5 is an induction heating apparatus for heating the open pipe edge to the melting point or higher, and 6 is an abutting joint for the open pipe edge. Squeeze roll, 8 is a mother pipe, 11 is a bead cutting machine for cutting a bead formed on the mother pipe, 10 is a mother pipe induction heating device for reheating the mother pipe for drawing, and 21 is a drawing process on the mother pipe The drawing rolling device for applying 18, 18 is a product tube cutting machine, 16 is a product tube, 19 is a tube straightening device, and 20 is a thermometer.
[0026]
FIG.1 (b) is a steel pipe manufacturing equipment row | line | column which provided the seam cooling device 12 in the exit side of the bead cutting machine 11 of the equipment row | line | column of Fig.1 (a). Other reference numerals are the same as those in FIG.
FIG. 2 shows the production of a steel pipe provided with a steel strip heating and quenching device 22 comprising a steel strip heating device 22a for heating the steel strip and a steel strip quenching device 22b for quenching the steel strip on the exit side of the looper 17 in FIG. It is an equipment line.
[0027]
FIG. 3 shows a steel pipe manufacturing equipment line in which a tubular body preheating device 23 for preheating the open pipe is provided on the outlet side of the forming apparatus 3 in FIG.
[0028]
【Example】
( Reference example )
A steel material having a composition of C: 0.17 wt%, Si: 0.20 wt%, Mn: 1.30 wt%, Cr: 1.0 wt% was made into a 2.5 mm thick steel plate by hot rolling at FET 800 ° C, and water-cooled immediately after the end of rolling. Then, the coil was made into a winding coil after a rapid cooling structure (martensite-based structure). Using the equipment row in FIG. 1 (a), the steel strip 1 discharged from the coil by the uncoiler 14 is made into an open tube 7 by the molding apparatus 3, and then the edge portion is heated to the melting point or more by the induction heating apparatus 5. A squeeze roll 6 was used to make a 60.5 mmφ × 2.5 mm thick mother pipe. The bead formed at the time of joining was deleted by the bead cutting machine 11. The temperature of the mother pipe after bead cutting was 350 ° C. Thereafter, the mother pipe was heated by the induction coil 9, and the product pipe 16 having a diameter of 25.4 to 42.7 mmφ × 2.3 mm was obtained by the drawing rolling device 21 in which 20 three-roll drawing mills were installed. The outer diameter drawing ratio at this time was 29 to 58%.
[0029]
For comparison, a steel material having the same composition was hot-rolled into a 2.5 mm-thick steel plate, and was rolled into a coil without being water-cooled as it was hot-rolled and annealed (900 ° C. annealing). Using this coil, it was set as the product pipe on the same conditions as the above, and it was set as the comparative example (No. A).
As a conventional example (No. B), a steel material having the same composition was hot-rolled into a 2.5 mm-thick steel plate, wound in a coil without being water-cooled as it was hot-rolled, and similarly to the above, FIG. ), The steel strip 1 discharged from the coil by the uncoiler 14 is made into an open pipe 7 by the molding device 3, and the edge portion is heated to the melting point or more by the induction heating device 5, and the squeeze roll 6 To make a mother pipe of 60.5mmφ × 2.5mm thickness. The bead formed at the time of joining was deleted by the bead cutting machine 11. The temperature of the mother pipe after bead cutting was 50 ° C. Thereafter, heating by the induction heating device 10 was not performed, and a product tube 16 of 42.7 mmφ × 2.3 mm with an outer diameter drawing ratio of 29% was obtained by a drawing rolling device 21 in which eight three-roll drawing mills were installed.
[0030]
Table 1 shows the mechanical properties, the presence or absence of seizure, and the roughness of the surface skin of these product tubes.
The presence or absence of seizure was visually observed, and the surface roughness was measured with a stylus type surface roughness meter for a product tube length of 15 × circumference of 5 mm to determine Rmax.
[0031]
[Table 1]

[0032]
From Table 1, it can be seen that the reference examples are high strength and high ductility steel pipes with a tensile strength of 700 MPa or more and an elongation of 35% or more, and a good surface skin. In contrast, comparison examples, ductility, surface texture, strength, are inferior any one of.
Further, in the comparative example (No. A) using the annealed steel strip, the tensile strength is as low as 430 MPa. Further, in the conventional example in which cold drawing is performed, the elongation is as low as 14%. Moreover, in the reference example, the drawing rolling load is low, there is no seizure, and the pipe making speed is 2.6 to 4.5 times that of the conventional example (No. B).
( Example)
A steel material having a composition of C: 0.08 wt%, Si: 0.5 wt%, Mn: 3.0 wt%, Cr: 0.3 wt%, Nb: 0.02 wt% is hot rolled into a 2.0 mm thick steel plate and then wound. A coil was used. Using the equipment row in FIG. 2, the steel strip 1 delivered from the coil by the uncoiler 14 is heated to 880 ° C. through the heating and quenching device 22 and then water-cooled to 350 ° C. or less to form a rapid cooling structure (martensitic main structure). To do. Thereafter, the open tube 7 was formed by the molding device 3, the edge portion was heated to the melting point or more by the induction heating device 5, and abutting was joined by the squeeze roll 6 to obtain a mother tube of 60.5 mmφ × 2.0 mm thickness. The bead formed at the time of joining was deleted by the bead cutting machine 11. The temperature of the mother pipe after bead cutting was 50 ° C. Thereafter, the mother pipe was heated to 500 ° C. by the induction coil 9, and the product pipe 16 of 31.8 mmφ × 1.8 mm was formed by the drawing rolling device 21 in which 16 stands of a three-roll drawing mill were installed. The drawing rolling temperature at this time was 450 to 500 ° C., and the outer diameter drawing rate was 47%.
[0033]
As shown in Table 2, the mechanical properties of this product pipe were a high strength and high ductility steel pipe with a yield strength of 1240 MPa, a tensile strength of 1380 MPa, an elongation of 29%, and a good surface skin.
[0034]
[Table 2]

[0035]
【The invention's effect】
According to the present invention, a steel pipe having a high strength and high ductility can be manufactured with high productivity without being deteriorated in the surface condition, and can be rolled with a low rolling load, and the mother pipe size can be integrated with a small mother pipe size. Therefore, it is possible to manufacture various types of product pipes, and it has a special effect that it can be applied to small lots and many kinds of products.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of a steel pipe manufacturing equipment line suitable for carrying out the reference invention.
FIG. 2 is a schematic diagram showing an example of a steel pipe manufacturing equipment line suitable for carrying out the present invention.
FIG. 3 is a schematic diagram showing an example of a steel pipe manufacturing equipment line suitable for carrying out the reference invention.
FIG. 4 is an explanatory view showing a roll structure of a drawing mill.
FIG. 5 is a schematic view showing an example of a conventional steel pipe manufacturing equipment line.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Band steel 2 Band steel preheating furnace 3 Molding processing apparatus 4 Band steel heating furnace 5 Induction heating apparatus 6 Squeeze roll 7 Open pipe 8 Mother pipe 9 Induction coil 10 Mother pipe induction heating apparatus 11 Bead cutting machine 12 Seam cooling apparatus 14 Uncoiler 15 Steel strip joining device 16 Product pipe 17 Looper 18 Cutting machine 19 Pipe straightening device 20 Thermometer 21 Drawing rolling device 22 Steel strip heating and quenching device
22a Steel strip heating device
22b Steel strip quenching device 23 Tube preheating device 24 Mother tube heating furnace

Claims

A steel strip is continuously formed with a forming roll to form an open pipe, both edges of the open pipe are heated to the melting point or higher, and a squeeze roll is used for abutting and joining to form a mother pipe. the method of manufacturing a welded steel pipe subjected to processing, the steel strip is, has been into force the heating and quenching treatment prior to forming the open pipe at a molding roll, temperature at a temperature range of the drawing is 200 ~ 700 ° C. A method for producing a high-strength, high-ductility welded steel pipe, characterized by thinning .

The warm drawing is 2 method for producing a welded steel pipe according to claim 1, wherein it is intended to be applied by a plurality stand reducing mill comprising a roll or rolls.

After the bead cutting method of welding steel pipe according to claim 1 or 2, wherein the cooling the seam.

The heating of both edges of the open tube is performed by any one of induction heating, energization heating, tungsten inert gas welding, laser beam, electron beam, plasma beam, and submerged arc welding. Item 4. A method for producing a welded steel pipe according to any one of Items 1 to 3 .

The method for manufacturing a welded steel pipe according to any one of claims 1 to 4 , wherein the main pipe heating for the warm drawing is performed by induction heating or a heating furnace using gas or heavy oil.

The method for manufacturing a welded steel pipe according to any one of claims 1 to 5 , wherein the edge portions are heated after preheating the open pipe to 700 ° C or lower.

An uncoiler that dispenses the steel strip, a steel strip joining device that joins the preceding steel strip and the following steel strip, a looper that stores the steel strip, a steel strip heating and quenching device that heats and cools the steel strip, and a steel strip A forming device comprising a forming roll group for forming, or a tube preheating device for preheating an open tube, an induction heating device having an induction heating coil, a squeeze roll for abutting and joining open tubes, and a bead cutting machine Or a steel pipe characterized by sequentially arranging a seam cooling device, a mother pipe induction heating device or heating furnace for heating the mother pipe, and a drawing device comprising a plurality of drawing mills for drawing and rolling the mother pipe Manufacturing equipment column.