JP3856940B2

JP3856940B2 - Hot-bending metal strip and its manufacturing method

Info

Publication number: JP3856940B2
Application number: JP09405298A
Authority: JP
Inventors: 正章高岸; 芳信日高
Original assignee: Dai Ichi High Frequency Co Ltd
Current assignee: Dai Ichi High Frequency Co Ltd
Priority date: 1998-03-23
Filing date: 1998-03-23
Publication date: 2006-12-13
Anticipated expiration: 2018-03-23
Also published as: JPH11267763A

Description

【０００１】
【発明の属する技術分野】
本発明は、鋼管やＨ形鋼等の金属条材の長手方向の一部区間を熱間曲げ加工して形成した熱間曲げ金属条材及びその製造方法に関し、例えば、石油及びガス輸送配管等の保安要請の特に高い用途に使用するのに好適な熱間曲げ金属管体及びその製造方法に関する。
【０００２】
【従来の技術】
従来、曲げ部と直線部を有する金属管体の製造方法としては、直線状の管体の長手方向の所望区間を熱間曲げ加工する方法が一般的であり、また、その熱間曲げ加工は、直線状の金属管体の長手方向の狭幅領域を、それを取り囲むように配置した誘導コイルで塑性変形容易な赤熱状態に加熱して加熱部を形成し、該加熱部に曲げモーメントを付与して曲げ変形させ、その直後に冷却して変形を終了させながら、前記誘導コイルを金属管体に対して長手方向に相対的に移動させることによって加熱部を金属管体の長手方向に移動させる操作を順次進めて所望区間全体を曲げ変形させるという方法で行っていた。
【０００３】
【発明が解決しようとする課題】
ところが、上記した熱間曲げ加工方法で製造した曲げ加工管体は、熱間曲げ加工の際に加熱された領域（以下加熱領域という）と加熱されなかった領域（以下非加熱領域という）との境界部分（以下熱境界部という）の強度（耐力、引張強さなど）が他の領域に比べて低下する傾向にあった。この強度低下は大きくなく、また、狭い領域で生じており、管体による通常の流体輸送時に輸送圧力によって管体にかかる応力に対して問題となるようなものではないが、前記石油、ガス輸送配管などにおいても埋設して使用する場合が多く、特に大地震時には管体に大きい曲げ応力や引張応力がかかることから、昨今は、上記した曲げ加工管体の熱境界部の強度にも関心が及ぶようになってきた。
【０００４】
そこで、本発明者等は熱間曲げ加工管体の熱境界部の強度が低下する理由を検討し、次のような結果を得た。図８において、管体（ＡＰＩ−Ｘ６５、外径６１５ｍｍ、肉厚２０．２ｍｍのＵＯＥ鋼管）１を、図示位置にセットした誘導コイル２で赤熱状態に加熱し、その後、誘導コイル２を管体１に対して相対的に矢印Ａ方向に移動させて曲げ加工を行った後、その管体１の実肉部分（実際に肉を有する部分。管の場合は管壁）を切断して金属組織を観察したところ、図示したように、３つの部分１ａ、１ｂ、１ｃに分かれていることが認められた。因みに、曲げ加工の際の管体１の管軸方向に対する最高加熱温度分布は曲線３で示すようになっていた。管体１の断面における第一の部分１ａは、曲げ加工のために高温に加熱され、曲げ変形直後に冷却水で急冷されたことにより焼入れ状態となった領域であり、以下高温加熱部という。この高温加熱部１ａの金属組織はベーナイト＋フェライトであり、高強度となっていた。第二の部分１ｂは、全く加熱されないか又は伝熱によって昇温するが最高温度が７００°Ｃ程度以下の部分であり、以下非加熱部という。この非加熱部１ｂは管体製造時の圧延組織（アシキュラーなフェライト＋パーライト）を維持しており、この部分でも、高強度となっている。第三の部分１ｃは、高温加熱部１ａからの伝熱によって、最高温度が７５０〜８５０°Ｃ程度に昇温し、Ａｃ₁〜Ａｃ₃の二相域を履歴した部分であり、その金属組織が、球状を呈するポリゴナルなフェライト＋パーライトとなり、硬度が低く（図８の曲線４参照）且つ強度も低くなっていた。以下、この部分１ｃを軟化部という。この軟化部１ｃと高温加熱部１ａとの境界（以下熱影響ラインという）６及び軟化部１ｃと非加熱部１ｂとの境界７は肉厚を直角に横切る形となっており、換言すれば、軟化部１ｃは高温加熱部１ａと非加熱部１ｂの間に介在する形で肉厚方向に生じていた。このように熱境界部に肉厚方向に伸びる軟化部１ｃが存在するため、その軟化部１ｃの幅が５〜１０ｍｍ程度と狭いにも係わらず、管体１の管軸方向の強度が低くなっていたと推定される。
【０００５】
上記したように熱境界部の管軸方向強度の低下傾向は軟化部１ｃによって生じているので、問題解決には軟化部を無くせばよく、そのためには、軟化部を熱処理することが考えられる。しかしながら、軟化部のみを熱処理しても、熱処理を施した領域の両端部に新たな軟化部が形成されてしまい、解決策とはならない。そこで、曲げ加工操作と、管体の直線部の全長（非加熱部１ｂ及び軟化部１ｃとなる部分）を曲げ加工区間と同一熱履歴となるように連続的に熱処理する操作を一連的に行うことも必要に応じて行われる。しかしながら、直線部を熱処理する分、操作も工数も増えて、生産性が低下しコスト高となるという問題が生じる。
【０００６】
上記した問題点は管以外の金属条材についても生じている。
【０００７】
本発明はかかる問題点に鑑みてなされたもので、従来熱境界部に生じていた強度低下を、熱処理を行うことなく低減し、熱境界部の強度を大きくした熱間曲げ金属条材並びにその製造方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明は、熱間曲げ加工の際の加熱領域と非加熱領域の境界部分すなわち熱境界部に生じる軟化部による、条材軸線方向の強度低下を低減するため、熱影響ラインに沿って生じる軟化部を肉厚方向に対して傾斜させると共にその傾斜角度を、軟化部のどの位置で肉厚方向に切断した断面にも軟化部のみならず高温加熱部、非加熱部の少なくとも一方が存在するように定めたものである。このように熱影響ラインに沿って生じる軟化部を肉厚方向に対して傾斜させたことにより、金属条材を軟化部の任意の位置で肉厚方向（条材軸線に直角方向）に切断した断面には、強度の小さい軟化部のみならず、強度の大きい高温加熱部、非加熱部の少なくと一方が存在することとなり、全体としての条材軸線方向の強度が、軟化部のみの場合に比べて大きくなる。かくして、熱境界部における条材軸線方向の強度低下を低減し、強度を大きくできる。
【０００９】
【発明の実施の形態】
本発明の熱間曲げ金属条材は、直線状の金属条材の長手方向の一部区間に熱間曲げ加工を施したものにおいて、その曲げ始め部分と曲げ終わり部分の少なくとも一方における熱間曲げ加工の際の加熱領域と非加熱領域との境界部分に熱影響ラインに沿って生じる軟化部を肉厚方向に対して傾斜させると共にその傾斜角度を、軟化部のどの位置で肉厚方向に切断した断面にも軟化部のみならず高温加熱部、非加熱部の少なくとも一方が存在するように定めていることを特徴とする。本発明の対象とする金属条材の形態は任意であり、例えば、丸形鋼管、角形鋼管等の鋼管、Ｈ形鋼、Ｔ形鋼、Ｕ形鋼（又はＣ形鋼）、Ｌ形鋼等の形鋼、棒状或いは板状の鋼材等を挙げることができる。特に、埋設配管は大地震により液状化現象が起こったときなどに過大な力がかかる恐れがあることから、埋設配管に使用する管体には本発明を適用することが好ましい。鋼材以外の金属条材も加熱を経て大なり小なり軟化するので、本発明の適用対象とすることができる。
【００１０】
以下、図面を参照して本発明を更に詳細に説明する。図１は、長手方向の一部区間に熱間曲げ加工を施した本発明の金属条材１１の熱境界部における実肉部分（条材１１が管の場合には管壁、Ｈ形鋼、Ｌ形鋼等の場合にはウェブやフランジ）の断面を示すものである。図１において、金属条材１１は、曲げ加工のために高温に加熱され且つ強制冷却されて焼入れ状態となった高温加熱部１１ａと、加熱温度が低いため条材製造時の金属組織を維持している非加熱部１１ｂと、両者間に生じる軟化部１１ｃを有しているが、高温加熱部１１ａと非加熱部１１ｂとの境界に形成される熱影響ライン１６を肉厚方向に対して傾斜させている。この構成により、軟化部１１ｃも肉厚方向に対して傾斜している。このため、金属条材１１を軟化部１１ｃの任意の位置で肉厚方向（条材軸線に直角方向）に切断した断面（例えば、Ａ−Ａ断面）には、強度の小さい軟化部１１ｃのみならず、強度の大きい高温加熱部１１ａ及び／又は非加熱部１１ｂが存在する。従って、金属条材１１の断面全体としての条材軸線方向の強度は、図８に示す従来例のように、軟化部１ｃのみしか存在しない場合に比べて、大幅に向上しており、熱境界部の強度を大きくできる。
【００１１】
ここで、熱境界部の条材軸線方向の強度は、傾斜角θを大きくするほど向上するが、その他にも、金属条材１１の肉厚と軟化部１１ｃの幅（熱影響ラインに直角方向の寸法）の比率も向上度合に関係する。従って、傾斜角θの選定に当たっては、金属条材１１の肉厚及び軟化部１１ｃの幅も考慮して定めるが、傾斜角θの大体の目安としては、２５°以上に設定することが好ましく、更には、４５°以上に設定することが一層好ましい。
【００１２】
熱間曲げ金属条材において、熱境界部は熱間曲げ加工の開始位置に存在するのみならず、曲げ加工の終了位置にも存在している。本発明は、これらの開始位置及び終了位置の両方に適用することが最も好ましいが、必要に応じていずれか一方のみに適用してもよい。
【００１３】
次に、本発明の熱間曲げ加工金属条材の製造方法を説明する。上記した熱影響ライン１６は、熱履歴における最高加熱温度が焼入れ可能な最低温度であった位置に形成されるので、金属条材の曲げ始めの部分などの加熱開始位置或いは曲げ終わりの部分などの加熱終了位置において、焼入れを生じる最低温度の等温線が肉厚方向に対して傾斜するような温度分布を形成させればよい。このような温度分布の形成は、実肉部分の片面に対する予熱、後熱の適宜取り入れ、加熱手段による加熱温度パターンの選定、冷却の適宜取り入れ等によって行うことが可能であり、中でも、実肉部分片面側と反対面側とで加熱開始時の冷却開始位置及び加熱終了時の赤熱開始位置に差をつけることにより容易に上記等温線を肉厚方向に対して傾斜させることができ、好ましい。
【００１４】
更に具体的に説明すると、本発明方法の一つの実施の形態は加熱開始部に関するものであって、直線状の金属条材の長手方向の狭幅領域を赤熱状態に加熱して加熱部を形成し、該加熱部に曲げモーメントを付与して曲げ変形させ、その直後に冷却しながら前記加熱部を金属条材の長手方向に移動させて、長手方向の所望区間を熱間曲げ加工する方法において、加熱開始時に、前記金属条材の実肉部分を片面側から加熱し、同時にその加熱領域内に加熱開始側から食い込ませる形で、反対面側に配した冷却手段によって反対面側から冷却媒体を吹き付けることにより、前記実肉部分内における反対面側の冷却前線の位置を片面側よりも加熱終了側にずらして、前記等温線を肉厚方向に対して傾斜させることを特徴とする。そして、この構成により、加熱開始位置における熱境界部の熱影響ラインを肉厚方向に対して傾斜させることができる。
【００１５】
また、他の実施の形態は加熱終了部に関するものであって、直線状の金属条材の長手方向の狭幅領域を赤熱状態に加熱して加熱部を形成し、該加熱部に曲げモーメントを付与して曲げ変形させ、その直後に冷却しながら前記加熱部を金属条材の長手方向に移動させて、長手方向の所望区間を熱間曲げ加工する方法において、加熱終了時に、前記金属条材の実肉部分を片面側から加熱し、同時にその加熱領域内に加熱終了側から食い込ませる形で、反対面側に配した冷却手段によって反対面側から冷却媒体を吹き付けることにより、前記実肉部分内における反対面側の赤熱前線の位置を片面側よりも加熱開始側にずらして、前記等温線を肉厚方向に対して傾斜させることを特徴とする。そして、この構成により、加熱終了位置における熱境界部の熱影響ラインを肉厚方向に対して傾斜させることができる。
【００１６】
上記した方法を金属管に対して適用する場合には、金属管を外面側から誘導コイルで加熱し、本発明方法固有の上記冷却については、内面側から冷却媒体を吹き付けて冷却する構成とすることが、実施するための設備構成を簡単にできるので好ましい。なお、この場合、曲げ開始から終了に至る間の曲げ変形直後の冷却については、上記本発明方法に係る上記冷却と併せて内面側から行っても良く、或いは、又、通常通り外面側から行っても良く、更には、厚肉管の場合など両面側から行うようにしてもよい。
【００１７】
【実施例】
以下、本発明を、金属条材が鋼管である場合に適用した実施例を説明する。図２は本発明の一実施例による熱間曲げ加工鋼管（金属条材）２１を示す概略断面図である。この熱間曲げ加工鋼管２１は、直線状の鋼管の長手方向の一部区間を９０°に熱間曲げ加工して形成した曲げ部２１Ａと、その両端に続く直管部２１Ｂ、２１Ｃを有している。そして、その曲げ部２１Ａの全域（ハッチングで示す領域）は曲げ加工により焼入れされた状態となっており、その両端にそれぞれ熱影響ライン２２、２３が生じている。この熱影響ライン２２、２３はそれぞれ、肉厚方向に対して傾斜しており、これによって軸線方向の強度低下が小さくなっている。
【００１８】
次に、上記した熱間曲げ加工鋼管２１の製造方法及びそれに用いる装置を説明する。図３は熱間曲げ加工を行う装置の概略断面図であり、３１は支点Ｏを中心に旋回可能に設けられた旋回アーム、３２は旋回アーム３１に取り付けられ、曲げ加工すべき鋼管２１を把持するクランプ、３４は鋼管２１の長手方向の狭幅領域を赤熱状態に加熱する誘導コイルであり、加熱領域のクランプ３２側の端部に冷却水等の冷却媒体３５を吹き付ける冷却手段を備えている。この誘導コイル３４は、支点Ｏを通り且つ直線状の鋼管２１の軸線に直角な曲げ基準面Ｐ−Ｐ上に配置されている。３６は鋼管２１の端部を把持するテールクランプであり、図示しない駆動装置によって鋼管２１を軸線方向に矢印Ｂで示す方向に移動させる構成となっている。
【００１９】
３８は鋼管２１内に位置するように挿入された冷却装置である。この冷却装置３８は鋼管２１の内面全周に冷却水等の冷却媒体３９を鋼管２１の軸線に対して、図３に示すように右方向に傾斜させて吹き付けることができ、また、図６に示すように左方向にも傾斜させて吹き付けることができる構成となっている。冷却装置３８は支持部材４０によって保持されており、その支持部材４０には冷却装置３８を鋼管２１の軸線方向の所望位置に移動させるための移動機構（図示せず）が連結されている。
【００２０】
次に、上記構成の装置を用いた曲げ加工方法を説明する。まず、図３に示す状態に、曲げ加工前の直線状の鋼管２１をセットする。次いで、誘導コイル３４に通電して鋼管２１の加熱を開始すると共にその加熱領域の端部に冷却媒体３５を吹き付け、同時に、鋼管２１の内側に位置する冷却装置３８からも冷却媒体３９を鋼管２１の内面に吹き付ける。ここで、冷却装置３８により冷却媒体３９を吹き付けて冷却する領域は、図４に拡大して示すように、鋼管２１の実肉部分を外面側から誘導コイル３４で加熱する際の加熱領域内に曲げ開始側（即ち加熱開始側、矢印Ｂ側）から食い込んだ領域とし、赤熱状態の加熱部４１の内面側での冷却開始位置を外面側よりも曲げ終了側（即ち加熱終了側、矢印Ｃ側）にずらしている。かくして、加熱開始部における赤熱状態の加熱部４１の等温線４２、４２ａ、４２ｂ等は肉厚方向に対して傾斜した状態となる。
【００２１】
図３において、誘導コイル３４で加熱を開始し、加熱部４１が曲げ加工を行うための所定の温度に達すると、テールクランプ３６による鋼管２１の矢印Ｂ方向の移動を開始する。これにより、旋回アーム３１によって鋼管２１に曲げモーメントが付与され、鋼管２１は加熱部４１のところで曲げ変形し、且つ曲げ変形を生じた直後の部分が冷却媒体３５で冷却固化される。そして、図５に示すように、鋼管２１が矢印Ｂ方向の移動を続け、それによって旋回アーム３１が旋回することにより、鋼管２１が連続的に熱間曲げ加工される。なお、曲げ開始時以外には、鋼管２１の内側に配置された冷却装置３８による冷却媒体の鋼管内面への吹き付けは行っても、行わなくてもよい。
【００２２】
熱間曲げ加工が進行し、図６に示すように、鋼管２１の曲げ加工すべき区間の後端が誘導コイル３４による加熱領域に接近した時点で、鋼管２１の内部の冷却装置３８が冷却媒体３９の鋼管内面への吹き付けを開始する。この時の冷却装置３８により冷却媒体３９を吹き付けて冷却する領域は、図７に拡大して示すように、鋼管２１の実肉部分を外面側から誘導コイル３４で加熱する際の加熱領域内に曲げ終了側（即ち加熱終了側、矢印Ｃ側）から食い込んだ領域、すなわち、赤熱開始側の一部領域とし、加熱部４１の内面側での赤熱開始位置４１ｂを外面側の赤熱開始位置４１ａよりも曲げ開始側（即ち加熱開始側、矢印Ｂ側）にずらしている。かくして、曲げ終了部における加熱部４１の等温線４３、４３ａ、４３ｂ等は肉厚方向に対して傾斜した状態となるので、この加熱部４１が、鋼管２１の曲げ加工すべき区間の後端に達する迄この状態を維持させる。そして、所定の曲げ加工が行われた時点で、テールクランプ３６による鋼管２１の移動及び誘導コイル３４による加熱を停止し、曲げ加工を終了する。以上の工程により、図２に示すように、曲げ部２１Ａと、その両端に続く直管部２１Ｂ、２１Ｃを有した構成の曲げ鋼管２１が製造される。なお、図３〜図７の各図において、冷却媒体３５、３９を斜めに吹き付けているのは、対象面上の一線を境として、その一方側の領域を冷やし、他方側の領域を冷やさないようにするためであって上記一線は言わば冷却前線である。冷却領域の規制は冷却前線とすべき線上にエアを噴射することによっても行える。
【００２３】
以上の工程において、曲げ加工の開始時即ち加熱開始時には、図４に示すように、赤熱状態に加熱した加熱部４１の加熱開始側の端部には、肉厚方向に対して傾斜した等温線４２、４２ａ、４２ｂが形成されており、また、曲げ加工の終了時即ち加熱終了時にも、図７に示すように、赤熱状態に加熱した加熱部４１の加熱終了側の端部には、肉厚方向に対して傾斜した等温線４３、４３ａ、４３ｂが形成されている。しかして、熱影響ライン２２、２３は、これらの等温線４２、４２ａ、４２ｂ又は等温線４３、４３ａ、４３ｂに平行に生じることから、曲げ部２１Ａの両端に、肉厚方向に対して傾斜した熱影響ライン２２、２３が生じることになる。
【００２４】
ここで、図４における等温線４２、４２ａ、４２ｂの傾斜、或いは図７における等温線４３、４３ａ、４３ｂの傾斜の度合は、冷却媒体３９の吹き付けにより冷却される領域の前線を鋼管２１の軸線方向に移動させることにより、或いは冷却媒体の吹き付け量を増減させて冷却効果を変化させること等により調整可能である。従って、これらの調整によって熱影響ライン２２、２３の傾きを所望のように調整できる。
【００２５】
なお、上記実施例では、誘導コイル３４を曲げ基準面Ｐ−Ｐ上に常時位置させる構成としているが、本発明はこの構成に限らず、曲げ加工の開始時及び終了時に誘導コイル３４を移動させる場合にも適用可能である。例えば、図２に示すような曲げ鋼管において、曲げ部２１Ａの両端の直管部に移行する部分の曲率をなだらかに変化させるため、曲げ開始時には、図３において誘導コイル３４を曲げ基準面Ｐ−Ｐより右方向に離れた所望位置に位置させ、その状態で熱間曲げ加工を開始すると共に誘導コイル３４を曲げ基準面Ｐ−Ｐに向かって移動させ、曲げ基準面Ｐ−Ｐに達した後は、その位置に停止させて曲げ加工を継続し、曲げ終了時には、誘導コイル３４を図６に示す位置から左方向に離れた所望位置まで順次移動させて曲げ加工を終了するという曲げ方法（ぼかし曲げ）が知られており、この場合にも本発明を適用可能である。また、曲げ部２１Ａの両端の直管部を適当な長さだけ熱処理するため、曲げ開始前に、図３において誘導コイル３４を曲げ基準面Ｐ−Ｐより右方向に離れた位置に位置させ、その位置で加熱を開始すると共に誘導コイル３４を曲げ基準面Ｐ−Ｐに向かって移動させて鋼管の熱処理を行い、曲げ基準面Ｐ−Ｐに達した後は、その位置に停止させて曲げ加工を行い、曲げ終了時には、誘導コイル３４を図６に示す位置から左方向に所望量だけ移動させて熱処理を行うという方法も知られており、この場合にも本発明を適用可能である。いずれの場合においても、誘導コイル３４による加熱開始時及び加熱終了時にはそれぞれ、図４、図７に示すように内面側からの冷却媒体３９の吹き付けによる冷却によって、等温線４２、４３を肉厚方向に対して傾斜させればよい。
【００２６】
次に、図３に示す装置を用いて、鋼管に対して曲げ加工を行った結果を表１に示す。使用した鋼管は、グレード；ＡＰＩ−Ｘ６５のものであり、これを曲げ半径が３ＤＲ（Ｄは鋼管外径）及び５ＤＲとなるように曲げ加工した。得られた曲げ加工鋼管の曲げ開始側の熱境界部（直管部と曲げ部の境界部分）を切断して断面を観察し、熱影響ラインの傾斜角θ（図１参照）を測定した。また、その熱境界部が標点間の中央となるように試験片を切り出し、ＪＩＳ１２Ｃ号の試験片とした。この試験片について、鋼管の長手方向引張試験を行い、耐力、引張強さ及び伸びを測定した。これらの結果を表１に示す。更に、比較のため、曲げ半径が５ＤＲとなるように曲げ加工した曲げ加工鋼管の直管部及び曲げ部についても、同様の引張試験を行ったので、その結果を表１に示す。
【００２７】
【表１】

【００２８】
表１から分かるように、熱影響ラインを肉厚方向に対して傾斜させることにより、耐力、引張強さが増加しており、特に、傾斜角θを４７°以上とした場合にその効果が顕著に現れ、直管部や曲げ部にほぼ匹敵するような強度特性となっていた。
【００２９】
【発明の効果】
以上のように、本発明の熱間曲げ加工金属条材は、曲げ加工時の熱境界部に生じる熱影響ラインに沿って生じる軟化部を肉厚方向に対して傾斜させたことにより、その熱境界部に生じる軟化部による条材軸線方向の強度低下を少なくできており、換言すれば、熱境界部の条材軸線方向の強度が従来に比べて大きくなっており、その結果、埋設配管や建築物の構造体として使用し、大地震などで過大な力が作用した際の耐久性のレベルが向上するという効果を有している。
【００３０】
また、本発明方法は、金属条材の熱間曲げ加工を行う場合に、前記金属条材の実肉部分を片面側から加熱し、加熱開始時に或いは加熱終了時に、加熱領域内の特定領域に反対面側から冷却媒体を吹き付けるという簡便な手段によって、前記実肉部分内における等温線を肉厚方向に対して傾斜させて、得られた曲げ加工金属条材の加熱開始部或いは加熱終了部における熱境界部の熱影響ラインを肉厚方向に対して傾斜させる構成としたので、熱境界部の強度低下を低減した曲げ加工金属条材を安価に製造できるという効果を有している。
【図面の簡単な説明】
【図１】本発明の熱間曲げ加工金属条材の熱境界部を示す概略断面図
【図２】本発明の一実施例による熱間曲げ加工鋼管の概略断面図
【図３】図２に示す熱間曲げ加工鋼管を製造する曲げ加工装置の概略断面図
【図４】図３に示す装置において、加熱開始時の鋼管の実肉部分及びその周辺を示す概略断面図
【図５】図３に示す装置を、曲げ加工の途中の状態で示す概略断面図
【図６】図３に示す装置を、曲げ加工の終了時の状態で示す概略断面図
【図７】図６における鋼管の実肉部分及びその周辺を示す概略断面図
【図８】従来の熱間曲げ加工鋼管の熱境界部の概略断面図及びその部分の熱履歴及び表面硬度を示すグラフ
【符号の説明】
１１金属条材
１１ａ高温加熱部
１１ｂ非加熱部
１１ｃ軟化部
１６熱影響ライン
２１熱間曲げ加工鋼管（金属条材）
２１Ａ曲げ部
２１Ｂ直管部
２２、２３熱影響ライン
３１旋回アーム
３２クランプ
３４誘導コイル
３５冷却媒体
３６テールクランプ
３８冷却装置
３９冷却媒体
４０支持部材
４１加熱部
４２、４２ａ、４２ｂ等温線
４３、４３ａ、４３ｂ等温線[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot-bending metal strip formed by hot-bending a partial section in the longitudinal direction of a metal strip such as a steel pipe or H-shaped steel, and a manufacturing method thereof, for example, oil and gas transport pipes, etc. The present invention relates to a hot-bending metal tube suitable for use in a particularly high security requirement and a method for manufacturing the same.
[0002]
[Prior art]
Conventionally, as a method of manufacturing a metal tube having a bent portion and a straight portion, a method of hot bending a desired section in the longitudinal direction of a straight tube is generally used. The heating coil is formed by heating the narrow area in the longitudinal direction of the straight metal tube to a red-hot state that is easily plastically deformed by an induction coil arranged so as to surround it, and a bending moment is applied to the heating coil. Then, the heating part is moved in the longitudinal direction of the metal tube by moving the induction coil relative to the metal tube in the longitudinal direction while bending and deforming immediately after cooling. It was performed by a method in which the operation was sequentially advanced and the entire desired section was bent and deformed.
[0003]
[Problems to be solved by the invention]
However, the bent tube manufactured by the above-described hot bending method has a region heated during hot bending (hereinafter referred to as a heated region) and a region not heated (hereinafter referred to as a non-heated region). The strength (proof strength, tensile strength, etc.) of the boundary portion (hereinafter referred to as the thermal boundary portion) tended to decrease compared to other regions. This decrease in strength is not large and occurs in a narrow region, and does not cause a problem with respect to the stress applied to the pipe body due to the transport pressure during normal fluid transport by the pipe body. In many cases, pipes are also buried and used, and since large bending stresses and tensile stresses are applied to the pipes, especially in the event of a large earthquake, recently there is an interest in the strength of the thermal boundary part of the bent pipes described above. It has come to reach.
[0004]
Therefore, the present inventors examined the reason why the strength of the thermal boundary portion of the hot-bending tube was lowered, and obtained the following results. In FIG. 8, a tubular body (API-X65, UOE steel pipe having an outer diameter of 615 mm and a wall thickness of 20.2 mm) 1 is heated to a red hot state by an induction coil 2 set at the illustrated position, and then the induction coil 2 is tubular. After the bending process is performed by moving in the direction of arrow A relative to 1, the actual part of the pipe body 1 (the part that actually has meat; in the case of a pipe, the pipe wall) is cut to form a metal structure. As shown in the figure, it was recognized that the three parts 1a, 1b and 1c were separated. Incidentally, the maximum heating temperature distribution with respect to the tube axis direction of the tube body 1 at the time of bending was as shown by a curve 3. The first portion 1a in the cross section of the tube body 1 is a region that is heated to a high temperature for bending and quenched by cooling water immediately after bending deformation, and is hereinafter referred to as a high temperature heating portion. The metal structure of the high-temperature heating part 1a was bainite + ferrite and had high strength. The second portion 1b is a portion that is not heated at all or is heated by heat transfer but has a maximum temperature of about 700 ° C. or less, and is hereinafter referred to as a non-heated portion. The non-heated portion 1b maintains a rolled structure (acicular ferrite + pearlite) at the time of manufacturing the tubular body, and this portion also has high strength. The third portion 1c is a portion in which the maximum temperature is raised to about 750 to 850 ° C. by heat transfer from the high temperature heating section 1a, and the two-phase region of Ac _{1 to} Ac ₃ is historyd. However, it became polygonal ferrite + pearlite having a spherical shape, and had low hardness (see curve 4 in FIG. 8) and low strength. Hereinafter, this portion 1c is referred to as a softened portion. The boundary (hereinafter referred to as a heat affected line) 6 between the softened portion 1c and the high temperature heating portion 1a and the boundary 7 between the softened portion 1c and the non-heated portion 1b have a shape that crosses the wall at right angles. The softening part 1c was generated in the thickness direction in a form interposed between the high temperature heating part 1a and the non-heating part 1b. As described above, since the softened portion 1c extending in the thickness direction is present at the thermal boundary portion, the strength of the tubular body 1 in the tube axis direction is lowered although the width of the softened portion 1c is as narrow as about 5 to 10 mm. It is estimated that
[0005]
As described above, the tendency of the strength in the tube axis direction of the thermal boundary portion to decrease is caused by the softened portion 1c. Therefore, the softened portion may be eliminated in order to solve the problem. For this purpose, it is conceivable to heat treat the softened portion. However, even if only the softened portion is heat-treated, new softened portions are formed at both ends of the heat-treated region, which is not a solution. Therefore, the bending operation and the operation of continuously heat-treating the entire length of the straight portion of the tube (the portion that becomes the non-heating portion 1b and the softening portion 1c) so as to have the same thermal history as the bending processing section are performed. Things are done as needed. However, the amount of operations and man-hours increases as the straight portion is heat-treated, resulting in a problem that productivity is lowered and cost is increased.
[0006]
The above-mentioned problems have arisen for metal strips other than pipes.
[0007]
The present invention has been made in view of such problems, and reduces the strength reduction that has conventionally occurred in the thermal boundary portion without performing a heat treatment, and increases the strength of the thermal boundary portion and the hot-bending metal strip and its An object is to provide a manufacturing method.
[0008]
[Means for Solving the Problems]
The present invention, by softening unit occurring in the boundary portion or thermal boundary portion of the heating area and the unheated area when hot bending, to reduce the decrease in strength of the elongated member axially occurs along the heat-affected line softened the Rutotomoni its inclination angle is inclined with respect to the thickness direction parts, high temperature heating unit not only softened portion in cross section cut in the thickness direction at any position of the softened portion, at least one of the non-heated part is present It is determined as follows. Cut thus softening portion occurring along the heat-affected line by which is inclined with respect thickness direction, the metal strip material in the thickness direction at an arbitrary position of the softened portion (perpendicular to the strip member axis) In the cross section, not only the softened part with low strength, but also at least one of the high-temperature heated part and non-heated part with high strength exists, and the overall strength in the axial direction of the strip is only the softened part. Larger than Thus, it is possible to reduce the strength reduction in the strip axis direction at the thermal boundary portion and increase the strength.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The hot-bending metal strip of the present invention is obtained by subjecting a part of the linear metal strip in the longitudinal direction to hot bending, and hot bending at at least one of the bending start portion and the bending end portion. the Rutotomoni its inclination angle is inclined softening portion occurring along the heat-affected line relative thickness direction in the boundary portion between the heating area and the unheated area during processing, the thickness direction at any position of the softened portion The cut cross section is defined so that not only the softened portion but also at least one of the high temperature heating portion and the non-heating portion exists . The form of the metal strip targeted by the present invention is arbitrary. For example, steel pipes such as round steel pipes and square steel pipes, H-shaped steels, T-shaped steels, U-shaped steels (or C-shaped steels), L-shaped steels, etc. The shape steel, rod-shaped or plate-shaped steel materials, etc. can be mentioned. In particular, it is preferable to apply the present invention to the pipe used for the buried pipe because the buried pipe may be subjected to an excessive force when a liquefaction phenomenon occurs due to a large earthquake. Since metal strips other than steel also soften to a greater or lesser extent through heating, they can be applied to the present invention.
[0010]
Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 shows the actual part of the thermal boundary portion of the metal strip 11 of the present invention that has been subjected to hot bending in a section in the longitudinal direction (when the strip 11 is a pipe, the pipe wall, H-section steel, In the case of L-shaped steel or the like, a cross section of a web or a flange) is shown. In FIG. 1, a metal strip 11 maintains a metal structure at the time of manufacturing the strip material because the metal strip 11 is heated to a high temperature for bending and is forcedly cooled to be in a quenched state and a heating temperature is low. The non-heating part 11b and the softening part 11c generated between the two are inclined, but the heat-affected line 16 formed at the boundary between the high-temperature heating part 11a and the non-heating part 11b is inclined with respect to the thickness direction. I am letting. With this configuration, the softened portion 11c is also inclined with respect to the thickness direction. For this reason, in the cross section (for example, AA cross section) which cut | disconnected the metal strip 11 in the thickness direction (perpendicular to a strip axis) in the arbitrary positions of the softening part 11c, if only the softening part 11c with small intensity | strength is used. However, there is a high-temperature heating part 11a and / or a non-heating part 11b with high strength. Accordingly, the strength in the axial direction of the strip as the entire cross section of the metal strip 11 is greatly improved as compared with the case where only the softened portion 1c exists as in the conventional example shown in FIG. The strength of the part can be increased.
[0011]
Here, the strength in the strip axis direction of the thermal boundary portion increases as the inclination angle θ increases, but in addition, the thickness of the metal strip 11 and the width of the softened portion 11c (perpendicular to the heat affected line). Ratio) is also related to the degree of improvement. Accordingly, in selecting the inclination angle θ, the thickness of the metal strip 11 and the width of the softened portion 11c are determined in consideration, but as a rough standard of the inclination angle θ, it is preferable to set it to 25 ° or more, Furthermore, it is more preferable to set the angle to 45 ° or more.
[0012]
In the hot-bending metal strip, the thermal boundary portion exists not only at the start position of the hot bending process but also at the end position of the bending process. The present invention is most preferably applied to both the start position and the end position, but may be applied to only one of them as necessary.
[0013]
Next, the manufacturing method of the hot bending metal strip of this invention is demonstrated. Since the above-described heat-affected line 16 is formed at a position where the maximum heating temperature in the thermal history was the lowest temperature that can be quenched, the heating start position such as the bending start portion or the bending end portion of the metal strip material, etc. What is necessary is just to form the temperature distribution which the isothermal line of the minimum temperature which produces quenching inclines with respect to the thickness direction at the heating end position. Such a temperature distribution can be formed by preheating the single side of the actual meat part, appropriately incorporating post-heat, selecting a heating temperature pattern by a heating means, appropriately incorporating cooling, etc. It is preferable that the isotherm can be easily inclined with respect to the thickness direction by making a difference between the cooling start position at the start of heating and the red heat start position at the end of heating on one side and the opposite side.
[0014]
More specifically, one embodiment of the method of the present invention relates to a heating start part, and a heating part is formed by heating a narrow region in the longitudinal direction of a linear metal strip to a red hot state. In the method of hot bending a desired section in the longitudinal direction by applying a bending moment to the heating portion to cause bending deformation, and immediately moving the heating portion in the longitudinal direction of the metal strip while cooling. The cooling medium disposed on the opposite surface side is cooled from the opposite surface side by the cooling means disposed on the opposite surface side in such a manner that the actual meat portion of the metal strip is heated from one surface side at the start of heating and is simultaneously encroached into the heating region from the heating start side. By spraying, the isothermal line is inclined with respect to the thickness direction by shifting the position of the cooling front on the opposite surface side in the actual meat portion from the one surface side to the heating end side. And by this structure, the heat influence line of the thermal boundary part in a heating start position can be inclined with respect to the thickness direction.
[0015]
Further, another embodiment relates to a heating end portion, and heats a narrow region in a longitudinal direction of a linear metal strip in a red hot state to form a heating portion, and a bending moment is applied to the heating portion. In the method of hot bending the desired section in the longitudinal direction by moving the heating part in the longitudinal direction of the metal strip while cooling immediately after being applied, the metal strip is heated at the end of heating. The actual meat portion is heated from one side and simultaneously blown into the heating area from the heating end side by spraying a cooling medium from the opposite surface side by cooling means disposed on the opposite surface side. The isotherm is inclined with respect to the thickness direction by shifting the position of the red hot front on the opposite surface side to the heating start side from the one surface side. And by this structure, the heat influence line of the thermal boundary part in a heating end position can be inclined with respect to the thickness direction.
[0016]
When the above-described method is applied to a metal tube, the metal tube is heated by an induction coil from the outer surface side, and the cooling unique to the method of the present invention is cooled by blowing a cooling medium from the inner surface side. It is preferable because the equipment configuration for carrying out can be simplified. In this case, the cooling immediately after the bending deformation from the start to the end of bending may be performed from the inner surface side together with the cooling according to the method of the present invention, or from the outer surface side as usual. Further, it may be performed from both sides, such as in the case of a thick-walled tube.
[0017]
【Example】
Hereinafter, the Example which applied this invention when a metal strip is a steel pipe is described. FIG. 2 is a schematic cross-sectional view showing a hot bent steel pipe (metal strip) 21 according to an embodiment of the present invention. This hot-bending steel pipe 21 has a bending part 21A formed by hot-bending a partial section in the longitudinal direction of a straight steel pipe at 90 °, and

straight pipe parts

21B and 21C that are connected to both ends thereof. ing. And the whole area (area | region shown by hatching) of the bending part 21A is the state hardened by the bending process, and the

heat influence lines

22 and 23 have arisen in the both ends, respectively. Each of the heat-affected

lines

22 and 23 is inclined with respect to the thickness direction, thereby reducing the strength reduction in the axial direction.
[0018]
Next, a method for manufacturing the hot-bending steel pipe 21 described above and an apparatus used therefor will be described. FIG. 3 is a schematic cross-sectional view of an apparatus for performing hot bending, wherein 31 is a turning arm provided so as to be turnable around a fulcrum O, 32 is attached to the turning arm 31 and holds a steel pipe 21 to be bent. The clamp 34 is an induction coil that heats the narrow-width region in the longitudinal direction of the steel pipe 21 to a red-hot state, and includes a cooling unit that blows a cooling medium 35 such as cooling water on the end of the heating region on the clamp 32 side. . The induction coil 34 is disposed on a bending reference plane PP that passes through the fulcrum O and is perpendicular to the axis of the straight steel pipe 21. Reference numeral 36 denotes a tail clamp that holds the end portion of the steel pipe 21 and is configured to move the steel pipe 21 in the direction indicated by the arrow B in the axial direction by a driving device (not shown).
[0019]
Reference numeral 38 denotes a cooling device inserted so as to be located in the steel pipe 21. The cooling device 38 can spray a cooling medium 39 such as cooling water to the entire circumference of the inner surface of the steel pipe 21 so as to be inclined rightward with respect to the axis of the steel pipe 21 as shown in FIG. As shown, it is configured to be able to spray while tilting to the left. The cooling device 38 is held by a support member 40, and a movement mechanism (not shown) for moving the cooling device 38 to a desired position in the axial direction of the steel pipe 21 is connected to the support member 40.
[0020]
Next, a bending method using the apparatus having the above configuration will be described. First, the straight steel pipe 21 before bending is set in the state shown in FIG. Next, the induction coil 34 is energized to start heating the steel pipe 21 and the cooling medium 35 is sprayed onto the end of the heating region. At the same time, the cooling medium 39 is also supplied from the cooling device 38 located inside the steel pipe 21. Spray on the inside. Here, as shown in an enlarged view in FIG. 4, the region where the cooling medium 38 blows and cools the cooling medium 39 is within a heating region when the actual part of the steel pipe 21 is heated by the induction coil 34 from the outer surface side. It is set as the area which has digged in from the bending start side (that is, the heating start side, arrow B side), and the cooling start position on the inner surface side of the heating part 41 in the red hot state is the bending end side (that is, heating end side, arrow C side) from the outer surface side. ). Thus, the isotherms 42, 42a, 42b, etc. of the heating part 41 in the red hot state at the heating start part are inclined with respect to the thickness direction.
[0021]
In FIG. 3, heating is started by the induction coil 34, and when the heating unit 41 reaches a predetermined temperature for bending, the movement of the steel pipe 21 in the arrow B direction by the tail clamp 36 is started. As a result, a bending moment is applied to the steel pipe 21 by the swivel arm 31, the steel pipe 21 is bent and deformed at the heating portion 41, and the portion immediately after the bending deformation is cooled and solidified by the cooling medium 35. As shown in FIG. 5, the steel pipe 21 continues to move in the direction of the arrow B, whereby the turning arm 31 turns, whereby the steel pipe 21 is continuously subjected to hot bending. Note that, other than at the start of bending, the cooling medium 38 disposed on the inner side of the steel pipe 21 may or may not be sprayed onto the inner surface of the steel pipe.
[0022]
When the hot bending progresses and the rear end of the section of the steel pipe 21 to be bent approaches the heating area by the induction coil 34 as shown in FIG. 6, the cooling device 38 inside the steel pipe 21 moves to the cooling medium. Start spraying 39 on the inner surface of the steel pipe. The region where the cooling medium 39 is blown and cooled by the cooling device 38 at this time is within the heating region when the real part of the steel pipe 21 is heated by the induction coil 34 from the outer surface side as shown in FIG. A region digging in from the bending end side (that is, the heating end side, the arrow C side), that is, a partial region on the red heat start side, and the red heat start position 41b on the inner surface side of the heating unit 41 from the red heat start position 41a on the outer surface side. Is also shifted to the bending start side (that is, the heating start side, arrow B side). Thus, since the

isothermal lines

43, 43a, 43b, etc. of the heating part 41 at the bending end part are inclined with respect to the thickness direction, the heating part 41 is at the rear end of the section of the steel pipe 21 to be bent. This state is maintained until it reaches. When the predetermined bending process is performed, the movement of the steel pipe 21 by the tail clamp 36 and the heating by the induction coil 34 are stopped, and the bending process is finished. Through the above steps, as shown in FIG. 2, a bent steel pipe 21 having a configuration including a bent portion 21A and

straight pipe portions

21B and 21C following both ends thereof is manufactured. In addition, in each figure of FIGS. 3-7, the

cooling mediums

35 and 39 are sprayed diagonally, the area | region of one side is cooled on the boundary on the object surface, and the area | region of the other side is not cooled. For this purpose, the above-mentioned line is the cooling front. The cooling region can also be regulated by injecting air onto the line that should be the cooling front.
[0023]
In the above process, at the start of bending, that is, at the start of heating, as shown in FIG. 4, an isotherm inclined toward the thickness direction is formed at the heating start side end of the heating unit 41 heated to a red hot state. 42, 42a, 42b are formed, and at the end of the bending process, that is, at the end of heating, as shown in FIG. Isothermal lines 43, 43a, 43b inclined with respect to the thickness direction are formed. Thus, the heat-affected

lines

22 and 23 are generated in parallel to the isotherms 42, 42a and 42b or the

isotherms

43, 43a and 43b, so that they are inclined with respect to the thickness direction at both ends of the bent portion 21A. Heat-affected

lines

22 and 23 are generated.
[0024]
Here, the inclination of the isotherms 42, 42 a, 42 b in FIG. 4 or the inclination of the

isotherms

43, 43 a, 43 b in FIG. 7 depends on the axis of the steel pipe 21 in the region cooled by the blowing of the cooling medium 39. It can be adjusted by moving in the direction or by changing the cooling effect by increasing or decreasing the amount of cooling medium sprayed. Therefore, the inclination of the heat affected

lines

22 and 23 can be adjusted as desired by these adjustments.
[0025]
In the above embodiment, the induction coil 34 is always positioned on the bending reference plane PP, but the present invention is not limited to this configuration, and the induction coil 34 is moved at the start and end of bending. It is also applicable to cases. For example, in a bent steel pipe as shown in FIG. 2, in order to gently change the curvature of the portion that transitions to the straight pipe portion at both ends of the bent portion 21A, the induction coil 34 in FIG. After being positioned at a desired position away from P in the right direction and starting the hot bending process in this state, the induction coil 34 is moved toward the bending reference plane PP and reaches the bending reference plane PP. Stops at that position and continues the bending process, and at the end of the bending process, the induction coil 34 is sequentially moved from the position shown in FIG. 6 to a desired position leftward to end the bending process (blurring). (Bending) is known, and in this case, the present invention can be applied. Further, in order to heat the straight pipe portions at both ends of the bent portion 21A by an appropriate length, the induction coil 34 is positioned at a position away from the bending reference plane PP in the right direction in FIG. Heating is started at that position, and the induction coil 34 is moved toward the bending reference plane PP to heat-treat the steel pipe, and after reaching the bending reference plane PP, it is stopped at that position and bent. At the end of bending, a method is also known in which the induction coil 34 is moved leftward from the position shown in FIG. 6 by a desired amount and heat treatment is performed. In this case, the present invention is also applicable. In any case, at the start of heating by the induction coil 34 and at the end of heating, as shown in FIGS. 4 and 7, the

isotherms

42 and 43 are formed in the thickness direction by cooling by blowing the cooling medium 39 from the inner surface side. Can be inclined with respect to.
[0026]
Next, Table 1 shows the results of bending the steel pipe using the apparatus shown in FIG. The steel pipe used was of grade; API-X65, and was bent so that the bending radius was 3DR (D is the outer diameter of the steel pipe) and 5DR. A thermal boundary portion (boundary portion between the straight tube portion and the bent portion) on the bending start side of the obtained bent steel pipe was cut and the cross section was observed, and the inclination angle θ (see FIG. 1) of the heat affected line was measured. Further, a test piece was cut out so that the thermal boundary portion was in the center between the gauge points, and a test piece of JIS 12C was obtained. About this test piece, the longitudinal direction tensile test of the steel pipe was done, and yield strength, tensile strength, and elongation were measured. These results are shown in Table 1. Further, for comparison, the same tensile test was performed on the straight pipe portion and the bent portion of the bent steel pipe bent to have a bending radius of 5DR, and the results are shown in Table 1.
[0027]
[Table 1]

[0028]
As can be seen from Table 1, the yield strength and the tensile strength are increased by inclining the heat-affected line with respect to the thickness direction, particularly when the inclination angle θ is 47 ° or more. The strength characteristics were almost comparable to those of straight pipes and bent parts.
[0029]
【The invention's effect】
As described above, the hot-bending metal strip of the present invention has its heat produced by inclining the softened portion that occurs along the heat-affected line generated at the thermal boundary portion during bending with respect to the thickness direction. The strength reduction in the strip axis direction due to the softened portion at the boundary portion can be reduced, in other words, the strength in the strip axis direction of the thermal boundary portion is larger than before, and as a result, Used as a building structure, it has the effect of improving the level of durability when an excessive force is applied in a major earthquake.
[0030]
Further, in the method of the present invention, when hot bending of the metal strip material is performed, the actual meat portion of the metal strip material is heated from one side, and at the start of heating or at the end of heating, it is applied to a specific region within the heating region. By a simple means of spraying the cooling medium from the opposite surface side, the isotherm in the actual meat portion is inclined with respect to the thickness direction, and the obtained bent metal strip material is heated at the heating start portion or at the heating end portion. Since the heat-affected line at the thermal boundary portion is inclined with respect to the thickness direction, the bent metal strip having reduced strength reduction at the thermal boundary portion can be manufactured at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a thermal boundary portion of a hot-bending metal strip of the present invention. FIG. 2 is a schematic cross-sectional view of a hot-bending steel pipe according to an embodiment of the present invention. 4 is a schematic cross-sectional view of a bending apparatus for producing the hot-bending steel pipe shown in FIG. 4. FIG. 4 is a schematic cross-sectional view showing the actual part of the steel pipe at the start of heating and its periphery in the apparatus shown in FIG. Fig. 6 is a schematic cross-sectional view showing the apparatus shown in Fig. 6 in a state in the middle of bending. Fig. 6 is a schematic cross-sectional view showing the device shown in Fig. 3 in a state at the end of bending. Fig. 7 Fig. 8 is a schematic cross-sectional view showing a portion and its periphery. Fig. 8 is a schematic cross-sectional view of a thermal boundary portion of a conventional hot-bending steel pipe, and a graph showing the thermal history and surface hardness of the portion.
DESCRIPTION OF SYMBOLS 11 Metal strip 11a High temperature heating part 11b Non-heating part 11c Softening part 16 Heat influence line 21 Hot-bending steel pipe (metal strip)
21A Bending part 21B

Straight pipe part

22, 23 Heat affected line 31 Swivel arm 32 Clamp 34 Inductive coil 35 Cooling medium 36 Tail clamp 38 Cooling device 39 Cooling medium 40 Support member 41 Heating part 42, 42a,

42b Isotherm

43, 43a, 43b isotherm

Claims

In a hot-bending metal strip that has been subjected to hot-bending in a part of the longitudinal direction of the linear metal strip, a heating region during hot-bending in at least one of the bending start portion and the bending end portion soften and the Rutotomoni its inclination angle is inclined softening portion occurring along the heat-affected line in a boundary portion with respect to the thickness direction of the non-heating regions, even cross section cut in the thickness direction at any position of the softened portion A hot-bending metal strip characterized in that at least one of a high-temperature heating part and a non-heating part exists in addition to the part .

The hot-bending metal strip according to claim 1, wherein the softened portion generated along the heat-affected line has an inclination of 45 ° or more with respect to the thickness direction.

A narrow region in the longitudinal direction of the linear metal strip is heated to a red hot state to form a heating portion, a bending moment is applied to the heating portion to cause bending deformation, and immediately after cooling the heating portion is cooled. In the method of hot bending a desired section in the longitudinal direction by moving in the longitudinal direction of the metal strip, at the start of heating, from the cooling start position on one side where the heating means is arranged in the actual meat portion of the metal strip In the hot bending, the isothermal line at the start of heating in the actual meat portion is inclined with respect to the thickness direction by starting cooling on the opposite surface side at a position shifted to the heating end side. Manufacturing method of metal strip.

A narrow region in the longitudinal direction of the linear metal strip is heated to a red hot state to form a heating portion, a bending moment is applied to the heating portion to cause bending deformation, and immediately after cooling the heating portion is cooled. In the method of hot bending a desired section in the longitudinal direction by moving in the longitudinal direction of the metal strip, at the end of heating , a part of the actual portion of the metal strip on the red hot start side of the heating area by the heating means The region is cooled from the side opposite to the side on which the heating means is disposed, and the red hot start position on the side opposite to the side on which the heating means is disposed of the actual meat portion of the metal strip is defined as the heating means. The hot bend is characterized in that the isotherm at the end of heating in the actual meat portion is inclined with respect to the thickness direction by shifting to the bending start side from the red hot start position on the side where the Manufacturing method of metal strip.

The metal strip is a metal tube, and the method according to claim 3 or 4 is carried out in a configuration in which induction heating is performed from the outer surface side of the metal tube and cooling is performed by blowing a cooling medium from the inner surface side. The manufacturing method of the hot bending metal strip.