JP5303887B2 - Heat treatment method for ERW steel pipe - Google Patents
Heat treatment method for ERW steel pipe Download PDFInfo
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- JP5303887B2 JP5303887B2 JP2007248672A JP2007248672A JP5303887B2 JP 5303887 B2 JP5303887 B2 JP 5303887B2 JP 2007248672 A JP2007248672 A JP 2007248672A JP 2007248672 A JP2007248672 A JP 2007248672A JP 5303887 B2 JP5303887 B2 JP 5303887B2
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- 238000010438 heat treatment Methods 0.000 title claims description 111
- 229910000831 Steel Inorganic materials 0.000 title claims description 72
- 239000010959 steel Substances 0.000 title claims description 72
- 238000000034 method Methods 0.000 title claims description 17
- 230000006698 induction Effects 0.000 claims description 62
- 230000009466 transformation Effects 0.000 claims description 25
- 238000004458 analytical method Methods 0.000 claims description 18
- 230000004907 flux Effects 0.000 claims description 12
- 238000012546 transfer Methods 0.000 claims description 10
- 230000005672 electromagnetic field Effects 0.000 claims description 8
- 238000003466 welding Methods 0.000 description 11
- 238000001816 cooling Methods 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 6
- 238000012360 testing method Methods 0.000 description 6
- 238000005520 cutting process Methods 0.000 description 4
- 238000009863 impact test Methods 0.000 description 4
- 229910001563 bainite Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 238000000137 annealing Methods 0.000 description 2
- 238000013459 approach Methods 0.000 description 2
- 239000011324 bead Substances 0.000 description 2
- 239000012141 concentrate Substances 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000010606 normalization Methods 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
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Description
本発明は、電縫鋼管に係り、とくに溶接部の加工性、靭性の向上を目的とした、高精度、高効率の電縫鋼管溶接部の熱処理方法に関する。 The present invention relates to an electric resistance welded steel pipe, and more particularly, to a highly accurate and highly efficient heat treatment method for an electric resistance welded steel pipe weld for the purpose of improving workability and toughness of the weld.
通常、電縫鋼管５は、図１に示すように、コイル状の鋼帯１を、アンコイラー６、レベラー７を介し、ロール成形機２により管状に成形したのち、板端面を突き合せて、高周波溶接機３で電縫溶接し、ビード部切削機８によりビードを切削され、さらにはサイザー９により所定の径に調整され、管切断機10により所定長さに切断された鋼管として製造されている。この電縫溶接では、突き合わせ部に高周波溶接機（誘導加熱装置）３で高周波電流を流し、ジュール熱を集中させて突き合わせ部を溶融しスクイズロール４で圧着して、溶接部を形成し、電縫鋼管５とする。形成された溶接部は、急速加熱されかつ急速冷却されるため、母材（鋼帯）と異なる組成、組織、強度を有し、加工性、靭性、さらには耐食性が他の部位（母材）に比べて低下した状態となっている。溶接部の加工性、靭性、耐食性を管の他の部位（母材）と同等以上とするために、一般的に、シームアニールと称して、電縫鋼管溶接部に熱処理を施すことが行なわれている。
Usually, as shown in FIG. 1, the electric resistance welded
電縫鋼管溶接部に施す熱処理は、図２に示すように、電縫鋼管製造ラインのスクイズロール４の出側に、設置されたシームアニーラ１１により行われているのが一般的である。このシームアニーラ１１には、管外面長手方向に誘導コイルを設けた高周波誘導加熱手段を複数スタンド配置し、溶接部およびその周辺に誘導電流を発生させて加熱する誘導加熱装置が、通常、用いられている。
As shown in FIG. 2, the heat treatment applied to the ERW steel pipe welded portion is generally performed by a
しかし、この種のシームアニーラでは、溶接部の加熱が管外面のみからの加熱となるため、管肉厚方向に温度分布が生じる。とくに厚肉の電縫鋼管では、管の内外面の温度差が増大し、管溶接部の肉厚全体を所望の温度に均一に加熱することが難しいという問題がある。
このような問題に対し、管内部まで充分に加熱するために、高周波誘導加熱手段の投入電力を増加し、誘導電流を増加させると、管外面の温度が高くなりすぎて、結晶粒が粗大化し、かえって靭性が低下する場合がある。また、造管速度を極低速とし、シームアニーラによる加熱後の伝熱時間を十分に確保して、管内外面の温度差を低減する方法では、誘導加熱手段を直列に多数基配置した長尺の設備とする必要があり、設備費が増大するとともに、投入電力量が増加し、ランニングコストの増加を招くことになる。また、造管速度を極低速とすると、電縫溶接部に欠陥が増加しやすくなり、溶接部特性の低下を招くという問題もある。また、造管時のトラブルにより製造ラインが停止した場合には、設備が長尺であるために電縫溶接部の不均一が増加し、歩留りが低下するという問題もある。
However, in this type of seam annealer, the heating of the welded part is only from the outer surface of the pipe, and thus a temperature distribution occurs in the pipe thickness direction. In particular, a thick ERW steel pipe has a problem that the temperature difference between the inner and outer surfaces of the pipe increases, and it is difficult to uniformly heat the entire thickness of the welded portion of the pipe to a desired temperature.
In order to sufficiently heat the inside of the tube to such a problem, if the input power of the high-frequency induction heating means is increased and the induction current is increased, the temperature of the outer surface of the tube becomes too high and the crystal grains become coarse. On the contrary, the toughness may decrease. In addition, a long facility with a large number of induction heating means arranged in series is a method for reducing the temperature difference between the inner and outer surfaces of the pipe by ensuring a sufficiently low heat transfer time after heating by the seam annealer at a very low pipe forming speed. As a result, the equipment cost increases, the amount of input power increases, and the running cost increases. In addition, when the pipe making speed is extremely low, there is a problem that defects are easily increased in the electric seam welded portion, and the welded portion characteristics are deteriorated. In addition, when the production line is stopped due to troubles during pipe making, the equipment is long, so there is a problem that non-uniformity of the ERW welds increases and the yield decreases.
このような問題に対し、例えば、特許文献１には、厚肉電縫鋼管溶接部に高周波誘導加熱装置で、溶接部外面温度が（Ａc３点＋100℃）〜（Ａc３点＋300℃）となるように加熱する第１回目の焼ならしと、引続いて溶接部外面温度がＡc１点以下に降下した時点で、Ａc１点〜（Ａc３点＋100℃）の温度範囲となるように加熱する第２回目の焼ならし・焼なましとからなる熱処理を行なう厚肉電縫鋼管の製造方法が記載されている。この技術によれば、複雑でしかも処理時間の長い工程を付加することなく、溶接部靭性の極めて優れた厚肉電縫鋼管を製造できるとしている。 For such a problem, for example, Patent Document 1 discloses that the outer surface temperature of a welded portion is (Ac 3 points + 100 ° C.) to (Ac 3 points + 300 ° C.) with a high-frequency induction heating device in a thick-walled electric-welded steel pipe welded portion. When the first normalization is performed and the outer surface temperature of the welded portion subsequently decreases to 1 point or less of Ac, the temperature range is from 1 point to 3 points (Ac 3 points + 100 ° C). A method for manufacturing a thick-walled electric-welded steel pipe is described in which a heat treatment consisting of second normalizing and annealing is performed. According to this technique, a thick ERW steel pipe having extremely excellent weld toughness can be manufactured without adding a complicated and long processing time.
また、特許文献２には、厚肉電縫鋼管溶接部に高周波誘導加熱装置で、溶接部内面の温度が（Ａc３点＋50℃）以上となるように加熱する第１回目の加熱と、第１回目の加熱後水冷または空冷によって外面温度が被加熱材のベイナイト変態終了温度以下まで冷却し、ついでＡc３変態域が第１回目の加熱・冷却によるベイナイト組織の発生領域をカバーしうる温度で、かつベイナイト組織が発生する温度以下まで加熱する第２回目の加熱とからなる熱処理を施す、厚肉電縫鋼管の熱処理方法が記載されている。この技術によれば、複雑でしかも処理時間の長い工程を付加することなく、溶接部靭性に優れた厚肉電縫鋼管を製造できるとしている。
特許文献１に記載された技術では、第１回目の加熱後に所定の温度以下まで冷却するが、しかし、この温度が高く未変態のオーステナイトが残存して、第２回目の加熱後の冷却時に低温変態生成物に変態するため、所望の靭性向上が得られないという問題があった。
また、特許文献１、２に記載された技術では、第１回目の加熱後に冷却することから、熱処理設備を長くする必要があり、設備費の増大を招くとともに、非効率な製造となり、製造コスト（ランニングコスト）の増大を招くという問題がある。また、さらに冷却速度が水温、気温により微妙に変化するため、第１回加熱後の冷却時の到達温度を、精度よく一定の所望温度とすることが難しく、安定して十分な靭性の向上が得られにくいという問題があった。
In the technique described in Patent Document 1, cooling is performed to a predetermined temperature or lower after the first heating. However, this temperature is high and untransformed austenite remains, and the temperature is low during cooling after the second heating. There is a problem that the desired toughness improvement cannot be obtained due to transformation into a transformation product.
Further, in the techniques described in Patent Documents 1 and 2, since the cooling is performed after the first heating, it is necessary to lengthen the heat treatment equipment, resulting in an increase in equipment costs, inefficient production, and production costs. There is a problem of increasing the (running cost). In addition, since the cooling rate slightly changes depending on the water temperature and air temperature, it is difficult to accurately achieve the desired temperature at the time of cooling after the first heating, and it is possible to stably improve sufficient toughness. There was a problem that it was difficult to obtain.
本発明は、かかる従来技術の問題を解決し、電縫鋼管溶接部の靭性向上を効率よく、かつ安定して達成できる電縫鋼管溶接部の熱処理方法を提案することを目的とする。 The object of the present invention is to solve the problems of the prior art and to propose a heat treatment method for an ERW steel pipe weld that can efficiently and stably achieve improvement in toughness of the ERW steel pipe weld.
本発明者らは、上記した目的を達成するため、溶接部靭性を向上できる熱処理を効率よく施せる加熱パターンについて鋭意研究した。その結果、Ａc3変態点到達までの加熱パターンが重要であることに思い至った。そして更なる研究により、本発明者らは、管溶接部外面温度がＡc3変態点を超えるまでは、各加熱手段の出側における管溶接部外面温度を、該各加熱手段の一つ前の加熱手段の出側における管溶接部外面温度より常に高くなる加熱パターンとすることがよいことを見出した。このような加熱パターンとすることにより、管溶接部外面温度が徐々に目標温度に近づき、それに伴い管溶接部内面側の温度も効率よく上昇させることができ、したがって、熱処理設備の長さを短くでき、投入電力が少なくてすみ、製造コスト（ランニングコスト）の低減が可能となることを知見した。 In order to achieve the above-described object, the present inventors diligently studied a heating pattern that can efficiently perform heat treatment capable of improving weld toughness. As a result, it came to mind that the heating pattern until reaching the Ac 3 transformation point is important. And by further studies, the present inventors found that until the tube weld the outer surface temperature exceeds Ac 3 transformation point, the pipe welds the outer surface temperature at the exit side of the heating means, before one of the respective heating means It has been found that a heating pattern that is always higher than the outer surface temperature of the pipe weld on the outlet side of the heating means is preferable. By adopting such a heating pattern, the outer surface temperature of the welded portion of the pipe gradually approaches the target temperature, and accordingly, the temperature on the inner surface side of the welded portion of the tube can be efficiently increased. It was possible to reduce the input power and reduce the manufacturing cost (running cost).
ついで、本発明者らは、管溶接部外面温度がＡc3変態点を超えたのちの、電縫鋼管溶接部の加熱方法について、電磁場解析および伝熱解析を利用し、さらには各種加熱方法について電縫鋼管温度を実測して、鋭意研究した。その結果、シームアニーラの高周波誘導加熱手段により発生した磁束は、キュリー点以上に加熱された領域を迂回する傾向があり、そのため、キュリー点以上に加熱された領域では磁束の集中が少なくなる。そのため、キュリー点以上に加熱された領域ではそれ以外の領域に比べ温度上昇が少なくなる。したがって、外面から加熱する電縫鋼管のシームアニーラの場合には、管溶接部外面側をキュリー点以上の適正温度に保持しておけば、管溶接部外面側の温度上昇が抑制され、管溶接部中央部、管溶接部内面側に磁束が集中し、効率よく加熱できることを知見した。さらに、本発明者らは、管溶接部中央部から管溶接部内面側を目標温度まで効率よく加熱するために、誘導加熱手段の周波数を１００〜２００００Hzの範囲とすることが好ましいことを思い至った。これらを組合せることにより初めて、誘導加熱装置（シームアニーラ）の長さを短くしても、管溶接部外面側を過加熱することなく、また管溶接部内面側の加熱不足を生じることなく、溶接部の充分な加熱が可能で、溶接部靭性に優れた電縫鋼管を、安価にしかも安定して製造できるという知見を得た。 Next, the present inventors use electromagnetic field analysis and heat transfer analysis for the heating method of the ERW steel pipe welded portion after the outer surface temperature of the pipe welded portion exceeds the Ac 3 transformation point, and further various heating methods. The temperature of the ERW pipe was measured and researched earnestly. As a result, the magnetic flux generated by the high-frequency induction heating means of the seam annealer tends to bypass the region heated above the Curie point, and therefore the concentration of magnetic flux is reduced in the region heated above the Curie point. Therefore, the temperature rise is less in the region heated to the Curie point or higher than in the other regions. Therefore, in the case of a seam annealer for ERW steel pipes heated from the outer surface, if the outer surface side of the pipe weld is kept at an appropriate temperature above the Curie point, the temperature rise on the outer surface of the pipe weld is suppressed, It has been found that magnetic flux concentrates on the inner side of the central part and the pipe welded part and can be heated efficiently. Furthermore, the present inventors have come up with the idea that it is preferable to set the frequency of the induction heating means in the range of 100 to 20000 Hz in order to efficiently heat the inner side of the pipe weld from the center of the pipe weld to the target temperature. It was. For the first time by combining these, even if the length of the induction heating device (Seam Annealer) is shortened, welding is performed without overheating the outer surface of the pipe welded part and without causing insufficient heating of the inner surface of the pipe welded part. It was found that an electric resistance welded steel pipe capable of sufficiently heating the part and excellent in welded part toughness can be manufactured at low cost and stably.
本発明は上記した知見に基づいて、さらに検討を加えて完成されたものである。すなわち、本発明の要旨はつぎのとおりである。
（１）管外面長手方向に誘導コイルを配置した高周波誘導加熱手段を複数スタンド、直列に配置した高周波誘導加熱装置に、電縫鋼管を送給し外面から該電縫管溶接部の熱処理を行なう電縫鋼管溶接部の熱処理方法であって、前記高周波誘導加熱手段の各スタンドの出側に前記電縫鋼管溶接部の外面温度が計測可能な温度計を配置し、前記電縫鋼管溶接部の外面温度が該電縫鋼管溶接部のＡc3変態点を超えるまでは、前記高周波誘導加熱手段の各スタンドの出側における該電縫鋼管溶接部の外面温度を、該各スタンドの一つ前のスタンド出側における該電縫鋼管溶接部の外面温度より高くなるように前記高周波誘導加熱手段の投入電力を調整して加熱し、前記電縫鋼管溶接部の外面温度がＡc3変態点を超えたのちは、その後の各スタンドの高周波誘導加熱手段では、電磁場解析および伝熱解析により、磁束が電縫鋼管溶接部内面近傍に集中するように、該高周波誘導加熱手段の使用周波数を設定し、さらに前記電縫鋼管溶接部の外面温度の適正温度を電磁場解析および伝熱解析により磁束が電縫鋼管溶接部内面近傍に集中するように前記高周波誘導加熱手段の使用周波数に対応して設定して、前記高周波誘導加熱手段の使用周波数および投入電力を調整し、前記電縫鋼管溶接部の外面温度を前記設定されたキュリー点以上の適正温度に保持しながら該電縫鋼管溶接部の内面を加熱することを特徴とする電縫鋼管溶接部の熱処理方法。
The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) A plurality of high-frequency induction heating means having induction coils arranged in the longitudinal direction of the pipe outer surface are supplied to a plurality of high-frequency induction heating devices arranged in series, and the electric resistance welded steel pipe is fed from the outer surface to heat-treat the electric-welded pipe welded portion. A heat treatment method for an ERW steel pipe welded portion, wherein a thermometer capable of measuring the outer surface temperature of the ERW steel pipe welded portion is disposed on the exit side of each stand of the high-frequency induction heating means , Until the outer surface temperature exceeds the Ac 3 transformation point of the ERW steel pipe welded portion, the outer surface temperature of the ERW steel pipe welded portion on the outlet side of each stand of the high-frequency induction heating means Heating was performed by adjusting the input power of the high frequency induction heating means so as to be higher than the outer surface temperature of the ERW steel pipe welded portion on the stand exit side, and the outer surface temperature of the ERW steel pipe welded portion exceeded the Ac 3 transformation point. Later, the height of each subsequent stand A wave induction heating means, the electromagnetic field analysis and heat transfer analysis, such a magnetic flux is concentrated in the electric resistance welded steel pipe weld near the inner surface, set the frequency used in the high-frequency induction heating means, further the outer surface of the electric resistance welded steel pipe weld and setting magnetic flux proper temperature of the electromagnetic field analysis and heat transfer analysis corresponds to the frequency used in the high frequency induction heating means so as to focus on electric resistance welded steel pipe weld near the inner surface, the use of the high frequency induction heating means Adjusting the frequency and input power and heating the inner surface of the ERW steel pipe welded portion while maintaining the outer surface temperature of the ERW steel pipe welded portion at an appropriate temperature equal to or higher than the set Curie point. Heat treatment method for steel pipe welds.
（２）（１）において前記電縫鋼管溶接部の内面をＡc3変態点以上の温度に加熱することを特徴とする電縫鋼管溶接部の熱処理方法。 (2) heat treatment method of the electric resistance welded steel pipe welds, characterized by heating the internal surface of the electric resistance welded steel pipe welds Ac 3 transformation point or above the temperature in (1).
本発明によれば、電縫鋼管溶接部の靭性向上を安価で、効率よく、かつ安定して達成でき、産業上格段の効果を奏する。また、本発明によれば、誘導加熱装置（シームアニーラ）の長さが短くでき、熱処理が効率よく行え、投入電力を低減でき、製造コスト（ランニングコスト）を低減できるという効果もある。 According to the present invention, improvement in toughness of an ERW steel pipe welded portion can be achieved inexpensively, efficiently and stably, and there is a remarkable industrial effect. Further, according to the present invention, the length of the induction heating device (seam annealer) can be shortened, heat treatment can be performed efficiently, input power can be reduced, and manufacturing costs (running costs) can be reduced.
本発明で使用する電縫鋼管は、通常、図１に示すように、鋼帯１をロール成形機２により連続的に管状に成形したのち、板端面を突き合せて、高周波溶接機３で突き合わせ部を溶融しスクイズロール４で圧着して、溶接部を形成し、電縫鋼管５とする。
本発明では、対象とする電縫鋼管を、高周波誘導加熱手段が複数スタンド、直列に配置された高周波誘導加熱装置に送給し、該電縫鋼管の溶接部の熱処理を行なう。ここで使用する高周波誘導加熱装置11は、図２（a）に示すように、スクイズロール７の出側に配設することが、生産性向上の観点から好ましい。本発明で使用する高周波誘導加熱装置11は、図２（ｂ）に示すように、高周波誘導加熱手段11aを複数基（複数スタンド）、直列に配置した構成とする。また、高周波誘導加熱手段11aは、被加熱体である電縫鋼管の管外面長手方向に誘導コイルを有し、管外面から溶接部およびその周辺に誘導電流を発生させて、溶接部を局部加熱可能な構成とする。なお、各高周波誘導加熱手段11aの出側には、電縫鋼管溶接部の外面温度が計測可能な温度計12を配置することが好ましい。また、各高周波誘導加熱手段11aは、所望の周波数に随時適合可能なように周波数可変装置（図示せず）を備えることが好ましい。
As shown in FIG. 1, the ERW steel pipe used in the present invention is usually formed into a tubular shape by a roll forming machine 2 continuously after forming a steel strip 1, and the plate end faces are butted together by a high-frequency welding machine 3. The part is melted and pressure-bonded with a squeeze roll 4 to form a welded part, which is referred to as an
In the present invention, the target ERW steel pipe is fed to a high frequency induction heating apparatus in which a plurality of high frequency induction heating means are arranged in series, and heat treatment is performed on the welded portion of the ERW steel pipe. As shown in FIG. 2A, the high-frequency
本発明における加熱パターンは、電縫鋼管溶接部（以下、管溶接部ともいう）の外面温度がその鋼管溶接部のＡc3変態点を超えるまでは、高周波誘導加熱手段の各スタンドの出側における電縫鋼管溶接部の外面温度を、該各スタンドの一つ前のスタンド出側における該外面温度より高くなるように各スタンドで加熱するパターンとする。管溶接部の外面温度がＡc3変態点を超えるまでの各スタンドでは、高周波誘導加熱手段の周波数、投入電力量はとくに限定する必要はないが、外面側が効率よく目標温度に到達できるように調整することが好ましい。なお、管溶接部の外面温度は、当該スタンド出側に設置された温度計により計測するものとする。これにより、管溶接部の外面温度を、スタンドごとに上下させることなく、徐々にその目標加熱温度に近づくように効率よく上昇でき、高周波誘導加熱手段のスタンド数を少なくすることができ、高周波誘導加熱手段への投入電力量も少なくすることができる。また、加熱と同時に熱伝導が加わるため、管溶接部の内面側の温度を効率よく上昇でき、管溶接部内面の目標加熱温度に早期に到達することができるようになる。 The heating pattern in the present invention is such that the outer surface temperature of the ERW steel pipe welded portion (hereinafter also referred to as the pipe welded portion) exceeds the Ac 3 transformation point of the steel pipe welded portion at the exit side of each stand of the high frequency induction heating means. The outer surface temperature of the welded portion of the ERW steel pipe is set to a pattern in which heating is performed at each stand so as to be higher than the outer surface temperature at the stand exit side immediately before each stand. In each stand where the outer surface temperature of the pipe weld exceeds the Ac 3 transformation point, the frequency of the high-frequency induction heating means and the input power amount do not need to be particularly limited, but are adjusted so that the outer surface side can reach the target temperature efficiently. It is preferable to do. In addition, the outer surface temperature of a pipe welding part shall be measured with the thermometer installed in the said stand exit side. As a result, the outer surface temperature of the pipe welded portion can be efficiently increased so as to gradually approach the target heating temperature without raising or lowering each stand, and the number of stands of the high-frequency induction heating means can be reduced. The amount of power input to the heating means can also be reduced. Moreover, since heat conduction is added simultaneously with heating, the temperature on the inner surface side of the pipe welded portion can be increased efficiently, and the target heating temperature of the inner surface of the tube welded portion can be reached early.
管溶接部の外面温度が、Ａc3変態点を超えた以降の各スタンドでは、管溶接部の外面温度がＡc3変態点を超えるまでの各スタンドに比べて少ない投入電力量に調整して管溶接部の外面温度をキュリー点以上の適正温度に保持しながら、電磁場解析および伝熱解析により、磁束が管溶接部内面に集中するように、高周波誘導加熱手段の周波数を、好ましくは、１００〜２００００Hzの範囲内の周波数に設定して、加熱する。キュリー点未満の温度に保持された領域に比べ、キュリー点以上に保持された領域では磁束の集中が少なくなるため、本発明では、管溶接部の外面温度をキュリー点以上の適正温度に保持しながら、加熱する。これにより、管溶接部の外面側の加熱が抑制され、内面側が効率よく加熱され、管溶接部の内外温度差を低減することができる。なお、管溶接部の外面温度の適正温度とは、電磁場解析および伝熱解析により、管溶接部外面の到達温度と使用する高周波誘導加熱手段の周波数との関係で、管肉厚方向の磁束発生状態を計算し、磁束が最も集中する位置を求め、その位置が管溶接部内面近傍となるように、使用する周波数に対応して設定した温度である。 The external surface temperature of the pipe welds, each stand after exceeding the Ac 3 transformation point, the external surface temperature of the tube weld is adjusted to less input power amount in comparison with the stand up more than Ac 3 transformation point tube The frequency of the high-frequency induction heating means is preferably 100 to so that the magnetic flux concentrates on the inner surface of the welded portion of the tube by the electromagnetic field analysis and the heat transfer analysis while maintaining the outer surface temperature of the welded portion at an appropriate temperature above the Curie point. Set to a frequency in the range of 20000 Hz and heat. In the present invention, the outer surface temperature of the pipe weld is maintained at an appropriate temperature above the Curie point because the concentration of magnetic flux is less in the region held above the Curie point compared to the region maintained at a temperature below the Curie point. While heating. Thereby, the heating of the outer surface side of a pipe welding part is suppressed, the inner surface side is heated efficiently, and the internal and external temperature difference of a pipe welding part can be reduced. In addition, the appropriate temperature of the outer surface temperature of the pipe welded part is the relationship between the reached temperature of the outer surface of the pipe welded part and the frequency of the high-frequency induction heating means used by electromagnetic field analysis and heat transfer analysis. The temperature is set according to the frequency to be used so that the position is calculated, the position where the magnetic flux is most concentrated is obtained, and the position is in the vicinity of the inner surface of the pipe weld.
また、高周波誘導加熱手段の周波数が100Hz未満では、効果の高い渦電流を誘起させることが難しく、一方、20000Hzを超える周波数では、内面側に充分に磁束が集中できなくなる。このため、管溶接部の外面温度が、Ａc3変態点を超えた以降の各スタンドでは、高周波誘導加熱手段の周波数は100〜20000Hzの範囲内の周波数に設定することが好ましい。なお、本発明では、管溶接部の内面の温度が、目標加熱温度であるＡc3変態点を超える温度となるまで、１スタンドまたは複数スタンドで上記したように高周波誘導加熱手段の周波数を、好ましくは、100〜20000Hzの範囲内に設定して加熱する。管溶接部の内面温度は、実測、および／または、例えば非特許文献（鉄と鋼、vol93、No.5(2007)、P373〜378）に記載の伝熱解析および電磁場解析によって求めるものとする。 If the frequency of the high-frequency induction heating means is less than 100 Hz, it is difficult to induce a highly effective eddy current. On the other hand, if the frequency exceeds 20000 Hz, the magnetic flux cannot be sufficiently concentrated on the inner surface side. Therefore, the external surface temperature of the pipe welds, each stand after exceeding the Ac 3 transformation point, the frequency of the high frequency induction heating means is preferably set to a frequency in the range of 100～20000Hz. In the present invention, the frequency of the high-frequency induction heating means is preferably set as described above for one stand or a plurality of stands until the temperature of the inner surface of the pipe weld reaches a temperature exceeding the Ac 3 transformation point that is the target heating temperature. Set the temperature within the range of 100-20000Hz and heat. The inner surface temperature of the welded portion of the pipe is obtained by actual measurement and / or heat transfer analysis and electromagnetic field analysis described in, for example, non-patent literature (iron and steel, vol93, No.5 (2007), P373-378). .
質量％で、0.05％C−0.2％Si−1.4％Mn系の熱延鋼帯（Ａc3変態点：860℃）を、図１に示すような、アンコイラー６、レベラー７、ロール成形機２、高周波溶接機３、スクイズロール４、サイザー９等を有する造管機で、電縫鋼管（外径600φmm×肉厚25.4mm）とした。ついで、これら電縫鋼管を被処理材として、図２に示すような、高周波誘導加熱装置（シームアニーラ）11を用いて、管溶接部の熱処理を行なった。なお、使用した高周波誘導加熱装置（シームアニーラ）11は、７スタンドの高周波誘導加熱手段11aを配し、各スタンド出側に管溶接部外面温度測定用の温度計12を配置した。これら温度計12を用いて、各スタンド出側の管溶接部外面温度を測定した。
（従来例）
まず、被処理材の管溶接部外面の到達温度が目標の880℃となるように、各スタンドの投入電力を、従来どおり各スタンドの効率がほぼ均等になるように調整して、熱処理を行なった結果、５スタンドで管溶接部外面温度が目標温度に到達した。外面温度が目標温度に到達したのちはその温度を保持した。ついで、その後のスタンドで同様に熱処理を行った結果、さらに２スタンドの加熱で管溶接部の内面温度が目標のＡc3変態点を超える880℃に到達した。すなわち、合計７スタンドの高周波誘導加熱手段の利用で、管溶接部外面および内面を目標温度に到達させることができた。
（本発明例）
高周波誘導加熱装置（シームアニーラ）11の各スタンド出側の管溶接部の外面温度が、Ａc3変態点（860℃）を超えるまでは、該各スタンドの一つ前のスタンド出側の管溶接部外面温度より高くなるように、各スタンドの投入電力を調整して、被処理材に熱処理を施した結果、４スタンドで管溶接部外面温度が目標の880℃に到達した。管溶接部の外面温度がＡc3変態点を超えたのちのスタンドでは、管溶接部外面温度を、伝熱解析および電磁場解析から得た、管溶接部内面側に磁束が最も集中する管溶接部外面温度（キュリー点以上）となるように、高周波誘導加熱手段11aの使用周波数および投入電力を調整して、被処理材に熱処理を施した。その結果、1スタンドの追加のみで、管溶接部内面の温度がＡc3変態点を超える目標の880℃に到達した。すなわち、合計5スタンドの高周波誘導加熱手段の利用で、管溶接部外面および内面を目標温度に到達させることができた。
A 0.05% C-0.2% Si-1.4% Mn hot-rolled steel strip (Ac 3 transformation point: 860 ° C.) in mass%, as shown in FIG. 1, an uncoiler 6,
(Conventional example)
First, heat treatment is performed by adjusting the input power of each stand so that the efficiency of each stand is substantially equal as before, so that the ultimate temperature of the outer surface of the welded part of the material to be processed will be the target 880 ° C. As a result, the outer surface temperature of the pipe welded portion reached the target temperature with 5 stands. After the outer surface temperature reached the target temperature, the temperature was maintained. Subsequently, as a result of heat treatment in the same manner in the subsequent stands, the inner surface temperature of the pipe weld reached 880 ° C. exceeding the target Ac 3 transformation point by heating the two stands. That is, by using a total of seven high-frequency induction heating means, the outer surface and the inner surface of the pipe welded part could reach the target temperature.
(Example of the present invention)
Until the outer surface temperature of the tube welded part on the outlet side of each stand of the high-frequency induction heating device (Seam Annealer) 11 exceeds the Ac 3 transformation point (860 ° C), the pipe welded part on the outlet side of the previous stand of each stand The power applied to each stand was adjusted so as to be higher than the outer surface temperature, and the material to be treated was heat treated. As a result, the outer surface temperature of the pipe welded part reached the target of 880 ° C. in four stands. The stand after the external surface temperature of the pipe weld exceeds the Ac 3 transformation point, the tube weld external surface temperature, were obtained from the heat transfer analysis and electromagnetic analysis, the pipe weld flux is most concentrated in the tube weld inner surface The material to be treated was heat-treated by adjusting the operating frequency and input power of the high-frequency induction heating means 11a so that the external surface temperature (curie point or higher) was reached. As a result, with the addition of only one stand, the temperature of the inner surface of the pipe weld reached the target of 880 ° C., which exceeds the Ac 3 transformation point. That is, by using a total of five high-frequency induction heating means, the outer surface and the inner surface of the welded part of the pipe could reach the target temperature.
ついで、上記のような熱処理を施された電縫鋼管の管溶接部からシャルピー衝撃試験片を採取して、管溶接部の靭性を調査した。試験方法はつぎのとおりとした。
（１）シャルピー衝撃試験
得られた電縫鋼管の溶接部から、JIS Z 2242の規定に準拠して、衝撃試験片（Ｖノッチ試験片）を採取した。試験片の採取位置は、管長手方向の異なる10箇所で、試験片長さ方向を管周方向に平行とし、試験片ノッチ位置を溶接部中心として、管溶接部外面側および内面側からそれぞれ１本ずつ採取した。これら試験片を用いて、JIS Z 2242の規定に準拠して、試験温度：−46℃でシャルピー衝撃試験を実施し、吸収エネルギーおよび脆性破面率を求めた。得られた値を算術平均し、平均値を求めた。得られた結果を表１に示す。
Next, a Charpy impact test piece was taken from the pipe welded part of the ERW steel pipe subjected to the heat treatment as described above, and the toughness of the pipe welded part was investigated. The test method was as follows.
(1) Charpy impact test An impact test piece (V-notch test piece) was collected from the welded portion of the obtained ERW steel pipe in accordance with the provisions of JIS Z 2242. The test specimens were collected at 10 locations in the pipe longitudinal direction, with the test specimen length direction parallel to the pipe circumferential direction, and the test specimen notch position at the center of the welded section, one from the outer side and the inner side of the pipe welded part. Collected one by one. Using these test pieces, a Charpy impact test was performed at a test temperature of −46 ° C. in accordance with the provisions of JIS Z 2242 to determine the absorbed energy and the brittle fracture surface ratio. The obtained values were arithmetically averaged to obtain an average value. The obtained results are shown in Table 1.
本発明例では、従来例に比べ少ないスタンド数の高周波誘導加熱手段の利用で管溶接部の内外面をＡc3変態点（860℃）を超える目標温度に到達でき、本発明によれば、高周波誘導加熱手段のスタンド数を低減することが可能となる。
また、本発明例では、吸収エネルギー値が高く、脆性破面率が低く靭性に優れた管溶接部となっており、信頼性の高い製品管となっている。一方、従来例では、吸収エネルギー値が低く、脆性破面率が高く溶接部靭性が低下して、信頼性の低い製品管となっている。
In the present invention example, it is possible to reach the target temperature exceeding the Ac 3 transformation point (860 ° C.) on the inner and outer surfaces of the pipe welded portion by using high frequency induction heating means having a smaller number of stands than in the conventional example. It is possible to reduce the number of the induction heating means.
Moreover, in the example of this invention, it is a pipe weld part with a high absorbed energy value, a low brittle fracture surface ratio, and excellent toughness, resulting in a highly reliable product pipe. On the other hand, in the conventional example, the absorbed energy value is low, the brittle fracture surface ratio is high, and the weld zone toughness is lowered, resulting in a product pipe with low reliability.
１ 鋼帯
２ ロール成形機
３ 高周波溶接機
４ スクイズロール
５ 鋼管（電縫鋼管）
６ アンコイラ
７ レベラー
８ ビード切削機
９ サイザー
１０ 管切断機
１１ シームアニーラ（高周波誘導加熱装置）
１１ａ 高周波誘導加熱手段
１２ 温度計
1 Steel strip 2 Roll forming machine 3 High frequency welding machine 4
6
11a High-frequency induction heating means 12 Thermometer
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