JP2000096142A - Method for reducing steel tube - Google Patents

Method for reducing steel tube

Info

Publication number
JP2000096142A
JP2000096142A JP10267106A JP26710698A JP2000096142A JP 2000096142 A JP2000096142 A JP 2000096142A JP 10267106 A JP10267106 A JP 10267106A JP 26710698 A JP26710698 A JP 26710698A JP 2000096142 A JP2000096142 A JP 2000096142A
Authority
JP
Japan
Prior art keywords
less
rolling
cooling
point
reducing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
JP10267106A
Other languages
Japanese (ja)
Other versions
JP3785828B2 (en
Inventor
Takaaki Toyooka
高明 豊岡
Akira Yorifuji
章 依藤
Masanori Nishimori
正徳 西森
Motoaki Itaya
元晶 板谷
Yuji Hashimoto
裕二 橋本
Yoshitomo Okabe
能知 岡部
Masahiko Morita
正彦 森田
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JFE Steel Corp
Original Assignee
Kawasaki Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kawasaki Steel Corp filed Critical Kawasaki Steel Corp
Priority to JP26710698A priority Critical patent/JP3785828B2/en
Publication of JP2000096142A publication Critical patent/JP2000096142A/en
Application granted granted Critical
Publication of JP3785828B2 publication Critical patent/JP3785828B2/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Classifications

    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing a steel tube which is capable of imparting excellent ductility and collision impact resistant characteristic to the steel tube without requiring large-scale process modification. SOLUTION: A blank having a chemical composition consisting of 0.005 to 0.30% C, 0.01 to 3.0% Si, 0.01 to 2.0% Mn and 0.001 to 0.10% Al and consisting of the balance Fe and inevitable impurities is worked to tube stock and thereafter, (1) this tube stock is subjected to reducing to a diameter reduction rate of >=10% at 950 deg.C to Ar3 point. (2) The cooling down to the Ar1 point or below is executed and thereafter, (3) the tube stock is subjected to reducing to a diameter reduction rate of >=20% at an Ac1 point to 400 deg.C. The reducing at 950 deg.C or over is recommended to precede (1).

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【0001】(用語の定義) 化学組成に係る%:重量%。 縮径率:ある一連のパスによる絞り圧延において、圧延
前、圧延後の管外径をそれぞれD0 、D1 とすれば、該
絞り圧延による縮径率rは、式r=(D0 −D 1 )/D
0 で表される(%を付すときはこの式の値を100 倍す
る)。なお、単パス圧延の縮径率を、とくに「縮径率/
パス」と記す。
(Definition of terms)% related to chemical composition:% by weight. Diameter reduction: rolling in a series of passes
Before and after rolling,0, D1Then,
The diameter reduction ratio r by the reduction rolling is represented by an equation r = (D0-D 1) / D
0(When adding%, multiply the value of this formula by 100
). In addition, the diameter reduction rate of the single-pass rolling is,
Path ".

【0002】φ,T:例えばφ100 mm×T6.0 mmは、管
の外径が100 mmで肉厚が6.0 mmの意である。 std. :例えば10std.は、レデューサのスタンド数が10
スタンドの意である。
Φ, T: For example, φ100 mm × T6.0 mm means that the outer diameter of the tube is 100 mm and the wall thickness is 6.0 mm. std .: For example, 10std. means that the reducer has 10 stands.
Stand stands for.

【0003】[0003]

【発明の属する技術分野】本発明は、鋼管の絞り圧延方
法に関し、特に、鋼管に優れた機械的性質を付与できる
絞り圧延方法に関する。
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing and rolling steel pipes, and more particularly to a method for reducing and rolling steel pipes with excellent mechanical properties.

【0004】[0004]

【従来の技術】鋼材の強度を増加させるためには、Mn、
Si等の合金元素の添加や、さらに、制御圧延、制御冷
却、焼入れ焼戻し等の熱処理あるいは、Nb、V等の析出
硬化型元素の添加などが利用されている。しかし、鋼材
には、強度のみでなく延性・靱性が高いことが必要で、
以前から、強度と延性・靱性がバランスよく向上した鋼
材が要望されている。
2. Description of the Related Art In order to increase the strength of steel, Mn,
Addition of alloy elements such as Si, heat treatment such as controlled rolling, controlled cooling, quenching and tempering, and addition of precipitation hardening elements such as Nb and V are utilized. However, steel materials need to have high ductility and toughness as well as strength.
For some time, there has been a demand for a steel material in which strength, ductility, and toughness are improved in a well-balanced manner.

【0005】結晶粒の微細化は、強度、延性・靱性を共
に向上させうる数少ない手段として重要である。結晶粒
を微細化する方法としては、オーステナイト粒の粗大化
を防止して、微細オーステナイトからオーステナイト−
フェライト変態を利用しフェライト粒を微細化する方
法、加工によりオーステナイト粒を微細化しフェライト
粒を微細化する方法、あるいは焼入れ焼戻し処理による
マルテンサイト、下部べイナイトを利用する方法などが
ある。
[0005] Refinement of crystal grains is important as a few means capable of improving both strength, ductility and toughness. As a method for refining crystal grains, coarse austenite grains are prevented, and fine austenite is converted to austenite-.
There are a method of making ferrite grains fine by utilizing ferrite transformation, a method of making austenite grains fine by working to make ferrite grains fine, and a method of using martensite and lower bainite by quenching and tempering.

【0006】なかでも、オーステナイト域における強加
工とそれに続くオーステナイト−フェライト変態により
フェライト粒を微細化する制御圧延が、鋼材製造に広く
利用されている。また、微量のNbを添加しオーステナイ
ト粒の再結晶を抑制してフェライト粒を一層微細化する
ことも行われている。オーステナイトの未再結晶温度域
で加工を施すことにより、オーステナイト粒が伸長して
粒内に変形帯が生成し、この変形帯からフェライト粒が
生成して、フェライト粒が一層微細化される。さらにフ
ェライト粒を微細化するために、加工の途中あるいは加
工後に冷却を行う工程、すなわち制御冷却も利用される
ようになっている。
Above all, controlled rolling in which ferrite grains are refined by strong working in the austenite region and subsequent austenite-ferrite transformation is widely used in steel production. Further, a small amount of Nb is added to suppress recrystallization of austenite grains to further refine ferrite grains. By processing in the austenite non-recrystallization temperature range, the austenite grains elongate and deformed bands are formed in the grains, and ferrite grains are generated from the deformed bands, and the ferrite grains are further refined. In order to further refine the ferrite grains, a step of cooling during or after the processing, that is, a controlled cooling is also used.

【0007】[0007]

【発明が解決しようとする課題】しかしながら、上記方
法では、最近強く要望されている高安全性自動車に適し
た構成部材としての耐衝突衝撃特性を高めた鋼管を製造
するうえで、設備の改造等を含む大幅な工程改造が必要
となり、コスト面で限界があった。本発明は、かかる問
題を有利に解決し、大幅な工程改造を要さず、鋼管に優
れた延性及び耐衝突衝撃特性を付与せしめ得る鋼管の絞
り圧延方法を提供することを目的とする。
However, according to the above-mentioned method, in order to manufacture a steel pipe having a high impact-resistant property as a component member suitable for a highly-safety automobile which has been strongly demanded recently, it is necessary to modify equipment. And significant process remodeling was required, and there was a limit in cost. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for reducing the diameter of a steel pipe, which can advantageously solve such a problem and can impart excellent ductility and impact resistance to the steel pipe without requiring significant process modification.

【0008】[0008]

【課題を解決するための手段】本発明者らは、延性に優
れた高強度鋼管を高造管速度で生産できる鋼管製造プロ
セスについて鋭意検討した結果、特定組成の素管を、あ
る限られた条件で熱間絞り圧延後オーステナイトをフェ
ライト−パーライトまたはべイナイトまたはマルテンサ
イトまたはこれらの混合に変態させ更に温間絞り圧延す
ることにより、ミクロ組織がフェライト粒径2μm以下
の微細かつ均一なフェライト、セメンタイト組織にな
り、高強度でかつ延性・靱性に優れる鋼管が得られるこ
とを見いだし、以下に述べる本発明をなした。
The present inventors have conducted intensive studies on a steel pipe manufacturing process capable of producing a high-strength steel pipe excellent in ductility at a high pipe-forming speed. After hot-rolling under the conditions, austenite is transformed into ferrite-pearlite, bainite, martensite, or a mixture thereof, and further hot-rolled, whereby the microstructure has a fine and uniform ferrite or cementite having a ferrite grain size of 2 μm or less. The present inventors have found that a steel pipe having a high strength and excellent ductility and toughness can be obtained, and the present invention described below has been made.

【0009】すなわち本発明は、C:0.005 〜0.30%、
Si:0.01〜3.0 %、Mn:0.01〜4.0%、Al:0.001 〜0.1
0%を含有し、残部Fe及び不可避的不純物からなる化学
組成を有する素材を素管に加工した後、950 ℃〜Ar3
で縮径率10%以上の絞り圧延を行い、次いでAr1 点以下
まで冷却を行い、次いでAc1 点〜400 ℃で縮径率20%以
上の絞り圧延を行うことを特徴とする鋼管の絞り圧延方
法である。
That is, according to the present invention, C: 0.005 to 0.30%;
Si: 0.01 to 3.0%, Mn: 0.01 to 4.0%, Al: 0.001 to 0.1
After processing a raw material containing 0% and having a chemical composition consisting of the balance Fe and unavoidable impurities into a raw tube, reduction rolling is performed at 950 ° C. to Ar 3 points with a diameter reduction ratio of 10% or more, and then Ar 1 point perform cooling to below, and then a reducing rolling process of a steel pipe, which comprises carrying out the reducing rolling radial contraction rate of 20% or more at Ac 1 point to 400 ° C..

【0010】本発明では、前記素材を素管に加工した
後、950 ℃〜Ar3 点で縮径率10%以上の前記絞り圧延を
行う前に、950 ℃超で縮径率10%以上の絞り圧延を行う
ことが好ましい。また、本発明では、前記素材の化学組
成(以下、単に組成ともいう)にさらに、Cu:1%以
下、Ni:2%以下、Cr:2%以下、Mo:1%以下のうち
から選ばれた1種又は2種以上、および/または、Nb:
0.1 %以下、V:0.3 %以下、Ti:0.2 %以下、B:0.
004 %以下のうちから選ばれた1種又は2種以上、およ
び/または、REM :0.02%以下、Ca:0.01%以下のうち
から選ばれた1種又は2種が付加されてもよい。
In the present invention, after the raw material is processed into a raw tube, before the reduction rolling at a temperature of 950.degree. C. to three points of Ar at 10% or more, the reduction at a temperature exceeding 950.degree. C. is 10% or more. It is preferable to perform reduction rolling. In the present invention, the chemical composition of the material (hereinafter, also simply referred to as composition) is further selected from among Cu: 1% or less, Ni: 2% or less, Cr: 2% or less, and Mo: 1% or less. And / or Nb:
0.1% or less, V: 0.3% or less, Ti: 0.2% or less, B: 0.
One or two or more selected from 004% or less and / or one or two selected from REM: 0.02% or less and Ca: 0.01% or less may be added.

【0011】[0011]

【発明の実施の形態】本発明では、特定組成になる鋼を
素材として用いるが、素材を素管(鋼管)に加工する手
段(造管法)は特に限定されない。高周波電流を利用し
た電気抵抗溶接法(素管名称:電縫鋼管)、オープン管
両エッジ部を固相圧接温度域に加熱し圧接接合する固相
圧接法(素管名称:固相圧接鋼管)、鍛接法(素管名
称:鍛接鋼管)、およびマンネスマン式穿孔圧延法(素
管名称:継目無鋼管)いずれも好適に使用できる。
DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, steel having a specific composition is used as a raw material, but there is no particular limitation on means (tube forming method) for processing the raw material into a raw pipe (steel pipe). Electric resistance welding method using high-frequency current (base pipe name: ERW steel pipe), solid-state pressure welding method in which both ends of open pipe are heated to the solid-state pressure welding temperature range and pressure-welded (base pipe name: solid-state pressure-welded steel pipe) , Forged welding method (base pipe name: forged steel pipe) and Mannesmann piercing and rolling method (base pipe name: seamless steel pipe) can be suitably used.

【0012】次に、素材の組成の限定理由を説明する。 C:0.005 〜0.30% Cは、基地中に固溶あるいは炭化物として析出し、鋼の
強度を増加させる元素であり、また、硬質な第2相とし
て析出した微細なセメンタイトが延性(一様伸び)向上
に寄与する。所望の強度を確保し、第2相として析出し
たセメンタイト等による延性向上の効果を得るために
は、Cは0.005 %以上、より好ましくは0.04%以上、の
含有を必要とするが、0.30%を超えて含有すると強度が
高くなりすぎ延性が劣化する。このようなことから、C
は0.005 〜0.30%の範囲に限定した。なお、より好まし
い範囲は0.04〜0.30%である。
Next, the reasons for limiting the composition of the material will be described. C: 0.005 to 0.30% C is an element which increases the strength of steel by being precipitated as a solid solution or carbide in the matrix, and fine cementite precipitated as a hard second phase has ductility (uniform elongation). Contribute to improvement. In order to secure the desired strength and obtain the effect of improving ductility due to the cementite or the like precipitated as the second phase, the content of C must be 0.005% or more, more preferably 0.04% or more. If the content exceeds this, the strength becomes too high and the ductility deteriorates. Because of this, C
Is limited to the range of 0.005 to 0.30%. In addition, a more preferable range is 0.04 to 0.30%.

【0013】Si:0.01〜3.0 % Siは、脱酸元素として作用するとともに、基地中に固溶
し鋼の強度を増加させる。この効果は、0.01%以上、好
ましくは0.1 %以上、の含有で認められるが、3.0 を超
える含有は延性を劣化させる。このことから、Siは0.01
〜3.0 %の範囲に限定した。なお、耐疲労特性を向上さ
せるには、Siは1.5 %以下とするのが好ましい。1.5 %
を超えると介在物を生成するため、耐疲労特性が劣化す
る。よって、好ましいのは0.1 〜1.5 %の範囲である。
Si: 0.01-3.0% Si acts as a deoxidizing element and forms a solid solution in the matrix to increase the strength of steel. This effect is observed at a content of 0.01% or more, preferably 0.1% or more, but a content of more than 3.0 deteriorates the ductility. From this, Si is 0.01
Limited to the range of ~ 3.0%. In order to improve the fatigue resistance, the content of Si is preferably set to 1.5% or less. 1.5%
If the ratio exceeds the range, inclusions are generated, and the fatigue resistance is deteriorated. Therefore, the preferred range is 0.1 to 1.5%.

【0014】Mn:0.01〜4.0 % Mnは、鋼の強度を増加させる元素であり、本発明では第
2相としてのセメンタイトの微細析出を促進させる。0.
01%未満では、所望の強度が確保できないうえ、セメン
タイトの微細析出が阻害される。また、4.0 %を超える
と、強度が増加しすぎて延性が劣化する。このため、Mn
は0.01〜4.0 %の範囲に限定した。なお、強度−伸びバ
ランスの観点から、Mnは0.2 〜1.3 %の範囲が好まし
く、より好ましくは0.6 〜1.3 %の範囲である。
Mn: 0.01 to 4.0% Mn is an element that increases the strength of steel, and promotes fine precipitation of cementite as the second phase in the present invention. 0.
If it is less than 01%, desired strength cannot be ensured and fine precipitation of cementite is hindered. On the other hand, if it exceeds 4.0%, the strength is excessively increased and ductility is deteriorated. For this reason, Mn
Was limited to the range of 0.01 to 4.0%. From the viewpoint of strength-elongation balance, Mn is preferably in the range of 0.2 to 1.3%, more preferably in the range of 0.6 to 1.3%.

【0015】Al:0.001 〜0.10% Alは、結晶粒径を微細化する作用を有している。結晶粒
微細化のためには、少なくとも0.001 %以上の含有を必
要とするが、0.10%を超えると酸化物系介在物量が増加
し清浄度が劣化する。このため、Alは0.001 〜0.10%の
範囲に限定した。なお、好ましくは0.015 〜0.06%であ
る。
Al: 0.001% to 0.10% Al has the effect of reducing the crystal grain size. To refine the crystal grains, the content must be at least 0.001% or more. However, if the content exceeds 0.10%, the amount of oxide-based inclusions increases and the cleanliness deteriorates. For this reason, Al was limited to the range of 0.001 to 0.10%. Incidentally, the content is preferably 0.015 to 0.06%.

【0016】上記した素材鋼管の基本組成に加えて、つ
ぎに述べる合金元素群を単独あるいは複合して添加して
もよい。 Cu:1%以下、Ni:2%以下、Cr:2%以下、Mo:1%
以下のうちから選ばれた1種又は2種以上 Cu、Ni、Cr、Moはいずれも強度を増加させる元素であ
り、必要に応じ1種または2種以上を添加できる。これ
ら元素は、変態点を低下させ、フェライト粒あるいは第
2相を微細化する効果を有している。しかし、Cuは多量
添加すると熱間加工性が劣化するため、1%を上限とし
た。Niは強度増加とともに靱性をも改善するが2%を超
えて添加しても効果が飽和しコスト高になるため、2%
を上限とした。Cr、Moは多量添加すると溶接性、延性が
劣化するうえコスト高となるため、それぞれ2%、1%
を上限とした。なお、好ましくはCu:0.1 〜0.6 %、N
i:0.1 〜1.0 %、Cr:0.1 〜1.5 %、Mo:0.05〜0.5
%である。
In addition to the above-described basic composition of the material steel pipe, a group of alloy elements described below may be added alone or in combination. Cu: 1% or less, Ni: 2% or less, Cr: 2% or less, Mo: 1%
One or more selected from the following Cu, Ni, Cr, and Mo are all elements that increase the strength, and one or more of them can be added as necessary. These elements have the effect of lowering the transformation point and miniaturizing the ferrite grains or the second phase. However, the hot workability deteriorates when a large amount of Cu is added, so the upper limit is 1%. Ni improves toughness with increasing strength, but adding more than 2% saturates the effect and increases cost, so 2%
Was set as the upper limit. If large amounts of Cr and Mo are added, the weldability and ductility will deteriorate and the cost will increase.
Was set as the upper limit. Preferably, Cu: 0.1-0.6%, N
i: 0.1 to 1.0%, Cr: 0.1 to 1.5%, Mo: 0.05 to 0.5
%.

【0017】Nb:0.1 %以下、V:0.3 %以下、Ti:0.
2 %以下、B:0.004 %以下のうちから選ばれた1種ま
たは2種以上 Nb、V、Ti、Bは、炭化物、窒化物または炭窒化物とし
て析出し、結晶粒の微細化と高強度化に寄与する元素で
あり、特に高温に加熱される接合部を有する鋼管では、
接合時の加熱過程での粒の微細化や、冷却過程でフェラ
イトの析出核として作用し、接合部の硬化を防止する効
果もあり、必要に応じ1種または2種以上添加できる。
しかし、多量添加すると、溶接性、靱性とも劣化するた
め、Nbは0.1 %、Vは0.3 %、Tiは0.2 %、Bは0.004
%をそれぞれ上限とした。なお、好ましくはNb:0.005
〜0.05%、V:0.05〜0.1 %、Ti:0.005 〜0.10%、
B:0.0005〜0.002 %である。
Nb: 0.1% or less, V: 0.3% or less, Ti: 0.
2% or less, B: one or two or more selected from 0.004% or less Nb, V, Ti, and B precipitate as carbides, nitrides, or carbonitrides, resulting in finer grains and higher strength. Element, which contributes to the formation of
There is also an effect of miniaturizing grains in a heating process at the time of joining and a precipitation nucleus of ferrite in a cooling process to prevent hardening of a joined portion, and one or more kinds can be added as necessary.
However, when added in large amounts, both weldability and toughness deteriorate, so that Nb is 0.1%, V is 0.3%, Ti is 0.2%, and B is 0.004%.
% Was the upper limit. Preferably, Nb: 0.005
~ 0.05%, V: 0.05 ~ 0.1%, Ti: 0.005 ~ 0.10%,
B: 0.0005 to 0.002%.

【0018】REM :0.02%以下、Ca:0.01%以下のうち
から選ばれた1種または2種 REM 、Caは、いずれも介在物の形状を調整し加工性を向
上させる作用を有しており、さらに、硫化物、酸化物ま
たは硫酸化物として析出し、接合部を有する鋼管での接
合部の硬化を防止する作用をも有し、必要に応じ1種以
上添加できる。REM が0.02%を超え、あるいは、Caが0.
01%を超えると介在物が多くなりすぎ清浄度が低下し、
延性が劣化する。なお、REM が0.004 %未満、Caが0.00
1 %未満ではこの作用による効果が少ないため、REM :
0.004 %以上、Ca:0.001 %以上とするのが好ましい。
One or two types of REM and Ca selected from REM: 0.02% or less and Ca: 0.01% or less, both have an effect of adjusting the shape of inclusions and improving workability. Further, it has a function of preventing sulphate, oxide or sulphate from being precipitated and hardening of a joint in a steel pipe having a joint, and one or more kinds thereof can be added as necessary. REM exceeds 0.02% or Ca is 0.
If it exceeds 01%, the amount of inclusions becomes too large and the cleanliness decreases,
Ductility deteriorates. REM is less than 0.004% and Ca is less than 0.004%.
Below 1%, the effect of this effect is small, so REM:
The content is preferably 0.004% or more and Ca: 0.001% or more.

【0019】素材組成における上記成分元素以外の組成
部分(残部)は、Feおよび不可避的不純物からなる。不
可避的不純物としては、N:0.010 %以下、O:0.006
%以下、P:0.025%以下、S:0.020 %以下が許容さ
れる。 N:0.010 %以下 Nは、Alと結合して結晶粒を微細化するに必要な量、0.
010 %までは許容できるが、それ以上の含有は延性を劣
化させるため、0.010 %以下に低減するのが好ましい。
なお、より好ましくは、Nは0.002 〜0.006 %である。
The composition portion (remaining portion) other than the above component elements in the material composition is composed of Fe and unavoidable impurities. As inevitable impurities, N: 0.010% or less, O: 0.006%
% Or less, P: 0.025% or less, S: 0.020% or less. N: 0.010% or less N is an amount necessary for bonding with Al and refining crystal grains.
Up to 010% is acceptable, but more than 10% will reduce ductility, so it is preferred to reduce it to 0.010% or less.
More preferably, N is 0.002 to 0.006%.

【0020】O:0.006 %以下 Oは、酸化物として清浄度を劣化させるため、できるだ
け低減するのが好ましいが、0.006 %までは許容でき
る。 P:0.025 %以下 Pは、粒界に偏析し、靱性を劣化させるため、できるだ
け低減するのが好ましいが、0.025 %までは許容でき
る。
O: 0.006% or less O degrades cleanliness as an oxide, so it is preferable to reduce O as much as possible, but up to 0.006% is acceptable. P: 0.025% or less P segregates at grain boundaries and degrades toughness, so it is preferable to reduce P as much as possible, but up to 0.025% is acceptable.

【0021】S:0.020 %以下 Sは、硫化物を増加し清浄度を劣化させるため、できる
だけ低減するのが好ましいが、0.020 %までは許容でき
る。次に、本発明の絞り圧延工程について説明する。絞
り圧延は、3ロール式の絞り圧延機(レデューサ)によ
り行うのが好ましいが、3ロール式に限定されるもので
はない。レデューサは複数のスタンドをタンデムに配置
した連続圧延可能なものがよい。スタンド数は被圧延管
のレデューサ入側および出側での目標寸法により適宜定
められる。
S: not more than 0.020% S is preferably reduced as much as possible because it increases sulfides and deteriorates cleanliness. However, S is allowable up to 0.020%. Next, the reduction rolling step of the present invention will be described. The reduction rolling is preferably performed by a three-roll type reduction mill (reducer), but is not limited to the three-roll type. The reducer is preferably one that can be continuously rolled with a plurality of stands arranged in tandem. The number of stands is appropriately determined according to the target dimensions at the reducer entrance side and exit side of the rolled tube.

【0022】本発明では、上記組成を有する素材を素管
に加工した後、950 ℃〜Ar3 点で縮径率10%以上の絞り
圧延(熱間低温域圧延という)を行い、次いでAr1 点以
下まで冷却(中間冷却という)を行い、次いでAc1 点〜
400 ℃で縮径率20%以上の絞り圧延(温間圧延という)
を行う。より好ましくは、加工後の素管に、熱間低温域
圧延に先行して、950 ℃超で縮径率10%以上の絞り圧延
(熱間高温域圧延という)を行う。
[0022] In the present invention, after processing the material having the above composition to the base tube, subjected to radial contraction rate of 10% or more reducing rolling (called hot cold region rolling) at 950 ° C. to Ar 3 point, then Ar 1 Cooling to below the point (intermediate cooling), then Ac 1 point ~
Rolling at 400 ° C with diameter reduction of 20% or more (called warm rolling)
I do. More preferably, the hot-rolled tube is subjected to drawing rolling at a temperature exceeding 950 ° C. and a diameter reduction rate of 10% or more (hereinafter referred to as hot high-temperature rolling) prior to hot low-temperature rolling.

【0023】図1は、本発明の絞り圧延方法を示す模式
図であり、図中、、、は、熱間低温域圧延、中
間冷却、温間圧延、熱間高温域圧延にそれぞれ対応する
工程を示す。工程(熱間低温域圧延)は、変態前のオ
ーステナイト組織を微細化するために必要なプロセスで
ある。工程での温度が950 ℃を超えると、オーステナ
イトの再結晶・粒成長が促進され、以後の工程、で
微細なフェライト−パーライト組織にすることが困難に
なる。また、この温度がAr3 点未満になると、圧延中に
析出したフェライトが優先的に加工され未変態オーステ
ナイト部分の加工量が不十分となる結果、組織が不均一
になる。このことから、工程の温度域は950℃〜Ar3
点に限定される。また、工程での縮径率が10%に満た
ないと、オーステナイト粒を十分に微細化させることが
できないため、工程での縮径率は10%以上に限定され
る。
FIG. 1 is a schematic view showing a drawing rolling method according to the present invention. In FIG. 1, the symbols indicate steps corresponding to hot low-temperature rolling, intermediate cooling, warm rolling, and hot high-temperature rolling, respectively. Is shown. The process (hot low-temperature rolling) is a process necessary for refining the austenite structure before transformation. If the temperature in the step exceeds 950 ° C., recrystallization and grain growth of austenite are promoted, and it becomes difficult to obtain a fine ferrite-pearlite structure in the subsequent steps. If this temperature is lower than the Ar 3 point, the ferrite precipitated during rolling is preferentially processed, and the amount of processing of the untransformed austenite portion becomes insufficient. As a result, the structure becomes uneven. From this, the temperature range of the process is 950 ° C. to Ar 3
Limited to points. If the diameter reduction rate in the step is less than 10%, the austenite grains cannot be sufficiently refined, so that the diameter reduction rate in the step is limited to 10% or more.

【0024】また、工程(熱間高温域圧延)を工程
に先行させることにより、工程に入る材料のオーステ
ナイト粒径をさらに細粒にすることができる。しかし、
縮径率10%未満ではこの更なるオーステナイト細粒化効
果がほとんど得られないため、工程は、縮径率10%以
上に限定される。なお、工程を工程と区別するため
に950 ℃超としたが、工程先行付加による前記効果は
1100℃超えではそれほど顕著でないため、工程は950
℃超1100℃以下の温度域にて行うのがよい。
In addition, by performing the step (hot high-temperature rolling) before the step, the austenite grain size of the material entering the step can be further reduced. But,
If the diameter reduction ratio is less than 10%, this further austenite grain-reducing effect is hardly obtained, so that the process is limited to the diameter reduction ratio of 10% or more. In order to distinguish the process from the process, the temperature was set to be higher than 950 ° C.
Above 1100 ° C, the process is 950
It is preferable to carry out in a temperature range of more than 1 ° C. and 1100 ° C.

【0025】なお、素材を素管に加工する造管法によっ
ては、加工後の材料温度が直ちには工程あるいは工程
の圧延温度域に入らない場合があるが、高温側に外れ
ているときには空冷あるいは強制冷却(水スプレー冷
却、衝風冷却、ミスト冷却等)により、低温側に外れて
いるときには加熱(輻射加熱、高周波加熱等)により、
材料温度をこの圧延温度域にもってくることが容易であ
る。
Depending on the pipe forming method for processing the raw material into a raw tube, the material temperature after processing may not immediately enter the process or the rolling temperature range of the process. By forced cooling (water spray cooling, blast cooling, mist cooling, etc.), when it is off the low temperature side, heating (radiant heating, high frequency heating, etc.)
It is easy to bring the material temperature to this rolling temperature range.

【0026】工程(中間冷却)は、工程で形成した
微細なオーステナイト組織をフェライト−パーライト組
織に変態させるために必要なプロセスである。Ar3 点以
上からAr1 点以下まで冷却することにより、マルテンサ
イト変態あるいはべイナイト変態を起こさせずにフェラ
イト−パーライト組織とすることができる。なお、本発
明における素材組成では、Ar3 点〜Ar1 点間の平均冷却
速度は、200 ℃/min以下とするのが望ましい。中間冷却
終了温度はAr1 点以下の範囲で任意に選択できるが、生
産性及び省エネルギーの観点からすればAr1 点直下とす
るのが好ましい。
The step (intermediate cooling) is a process necessary for transforming the fine austenite structure formed in the step into a ferrite-pearlite structure. By cooling from the Ar 3 point or more to the Ar 1 point or less, a ferrite-pearlite structure can be obtained without causing martensite transformation or bainite transformation. In the material composition according to the present invention, the average cooling rate between Ar 3 point and Ar 1 point is desirably 200 ° C./min or less. The intermediate cooling end temperature can be arbitrarily selected within a range of not more than the Ar 1 point. However, from the viewpoint of productivity and energy saving, it is preferable to set the temperature immediately below the Ar 1 point.

【0027】工程(温間圧延)は、フェライトに十分
な加工歪を導入して粒径2μm以下にまで組織の微細化
を達成するために必要なプロセスである。ここでの温度
がAc 1 点を超えると部分的にオーステナイト変態が生じ
るため組織が不均一になりやすい。また、400 ℃未満で
絞り圧延すると、青熱脆性により脆化して圧延中に材料
が破断するおそれがある。また、加工硬化が大きくなっ
て焼付きが発生しやすく、製品での延性も低下する。こ
のため、工程の温度域はAc1 点〜400 ℃に限定され
る。また、縮径率20%未満の絞り圧延では、フェライト
粒径を2μm以下に微細化することができないため、縮
径率は20%以上に限定される。なお、フェライトの再結
晶を促進させてより細粒化させる観点から、工程で
は、少なくともいずれかの圧延パスの縮径率/パスを6
%以上とするのが望ましい。
The step (warm rolling) is sufficient for ferrite
Refinement of microstructure to 2μm or less in particle diameter by introducing various processing strains
Is the process required to achieve Temperature here
Is Ac 1Beyond the point, austenite transformation occurs partially
Therefore, the tissue tends to be uneven. In addition, at less than 400 ° C
During rolling, the material becomes brittle due to blue embrittlement and
May be broken. In addition, the work hardening increases
And seizure easily occurs, and the ductility of the product also decreases. This
Therefore, the temperature range of the process is Ac1Limited to ~ 400 ° C
You. In the case of reduction rolling with a diameter reduction ratio of less than 20%, ferrite
Since the particle size cannot be reduced to 2 μm or less,
The diameter ratio is limited to 20% or more. In addition, ferrite reconnection
From the viewpoint of promoting crystallization and making finer grains,
Means that at least one rolling pass has a diameter reduction ratio / pass of 6
% Is desirable.

【0028】工程終了時の材料温度が直ちには工程
の圧延温度域に入らない場合、加熱(輻射加熱、高周波
加熱等)または空冷もしくは強制冷却(水スプレー冷
却、衝風冷却、ミスト冷却等)を行うことにより、材料
温度をこの圧延温度域にもってくることができる。
If the material temperature at the end of the process does not immediately fall within the rolling temperature range of the process, heating (radiant heating, high frequency heating, etc.) or air cooling or forced cooling (water spray cooling, impingement cooling, mist cooling, etc.) By doing so, the material temperature can be brought to this rolling temperature range.

【0029】[0029]

【実施例】表1に組成を示す鋼A,B,C,F,G,
H,I,Kを素材として、表2に示す素管(φ146.0 mm
×T5.5 mm)に加工(造管)し、これら素管に、多スタ
ンド・タンデム配置の3ロール式レデューサを用い以下
の条件で工程→→を連続実施して製品を得た。
EXAMPLE Steels A, B, C, F, G, whose compositions are shown in Table 1 are shown below.
Using H, I and K as raw materials, the raw tubes shown in Table 2 (φ146.0 mm
× T5.5 mm), and the process was continuously performed on these blanks using a three-roll reducer in a multi-stand tandem arrangement under the following conditions to obtain products.

【0030】 工程:φ62.0mm×T5.0 mm(開始925 ℃,終了850 ℃,22std.) 工程:冷却速度60℃/min,580 ℃終了 工程:φ25.4mm×T4.5 mm(開始700 ℃,終了655 ℃,16std.) 圧延速度(最終スタンド出側)400 m/min なお、工程に付記した管寸法はその工程での仕上寸法で
ある(以下同じ)。
Step: φ62.0 mm × T5.0 mm (start 925 ° C., end 850 ° C., 22std.) Step: cooling rate 60 ° C./min, end 580 ° C. Step: φ25.4 mm × T4.5 mm (start 700 ℃, end 655 ° C, 16std.) Rolling speed (outside of the last stand) 400 m / min The pipe dimensions given in the process are the finished dimensions in the process (the same applies hereinafter).

【0031】また、表1に組成を示す鋼D,E,J,
F,Lを素材として、表2に示す素管(φ192.0 mm×T
12.0mm)に加工(造管)し、これら素管に、多スタンド
の3ロール・レデューサを用い以下の条件で工程→
→→を連続実施して製品を得た。 工程:φ 158.0mm×T12.0mm(開始1025℃,終了975 ℃,18std.) 工程: φ71.5mm×T11.0mm(開始930 ℃,終了875 ℃,24std.) 工程:冷却速度40℃/min,560 ℃終了 工程: φ33.0mm×T10.0mm(開始680 ℃,終了645 ℃,18std.) 圧延速度(最終スタンド出側)500 m/min ここで、表2中素管の欄に「固相」と記した固相圧接鋼
管は、熱延鋼帯を600℃に予熱炉で予熱後、複数の成形
ロールで連続的に管状に成形し、その継ぎ目部を誘導加
熱により、1000℃に予熱後未溶融温度域の1450℃まで加
熱し、スクイズロールによりアプセットすることにより
造管された。「SML」と記した継目無鋼管は、連続鋳
造製ビレットを加熱しマンネスマンマンドレルミルにて
穿孔圧延することにより造管された。「ERW」と記し
た電縫鋼管は、熱延鋼帯を複数の成形ロールで連続的に
管状に成形しその継ぎ目部を誘導加熱により溶融温度域
に加熱後スクイズロールによりアプセットする常法によ
り造管された。
Table 1 shows steels D, E, J,
Using F and L as raw materials, pipes shown in Table 2 (φ192.0 mm × T
12.0mm), and process these tubes using a multi-stand 3-roll reducer under the following conditions.
The product was obtained by continuously performing →→. Process: φ158.0mm × T12.0mm (start 1025 ° C, end 975 ° C, 18std.) Process: φ71.5mm × T11.0mm (start 930 ° C, end 875 ° C, 24std.) Process: cooling rate 40 ° C / min , End at 560 ° C Process: φ33.0mm × T10.0mm (start 680 ° C, end 645 ° C, 18std.) Rolling speed (finish stand exit side) 500m / min Phase, the pre-heated hot-rolled steel strip is heated to 600 ° C in a preheating furnace, and then continuously formed into a tube with multiple forming rolls.The joint is preheated to 1000 ° C by induction heating. Thereafter, the tube was heated to an unmelting temperature range of 1450 ° C., and the tube was formed by upsetting with a squeeze roll. A seamless steel pipe marked "SML" was produced by heating a continuous cast billet and piercing and rolling the billet using a Mannes mandrel mill. An ERW steel pipe marked "ERW" is manufactured by a conventional method in which a hot-rolled steel strip is continuously formed into a tubular shape by using a plurality of forming rolls, the joint is heated to a melting temperature range by induction heating, and then upset by a squeeze roll. Was tubed.

【0032】なお、造管後の素管は一旦常温に冷却さ
れ、誘導加熱により工程あるいは工程の温度域に加
熱された。工程での冷却にはミスト冷却が採用され
た。工程から工程に至る間の材料は誘導加熱により
加熱された。絞り圧延後の製品について、引張特性、衝
突衝撃特性、フェライト粒径を調査した結果を、比較の
ために一部の素材を造管後工程のみによって製品とし
たもの、および造管のみによって製品としたものについ
て前記同様に調査した結果と併せて表2に示す。
The tube after the tube was formed was once cooled to room temperature, and heated to a process or a temperature range of the process by induction heating. Mist cooling was adopted for cooling in the process. The material from step to step was heated by induction heating. For the product after drawing rolling, the results of the investigation of the tensile properties, impact impact properties, and ferrite grain size were compared. The results are shown in Table 2 together with the results of the same investigation.

【0033】引張試験にはJIS 11号試験片を用い、伸び
の値は、試験片サイズ効果を考慮して、換算式El=El
0(√(a0/a))0.4(ここに、El0 :実測伸び,a0:定数29
2mm2,a :試験片断面積(mm2) )による換算値で評価し
た。衝突衝撃特性は、歪速度 2000s-1の高速引張試験を
行い、得られた応力−歪曲線から歪量30%までの吸収エ
ネルギーを求め、衝突衝撃吸収エネルギーとして評価し
た。(衝突衝撃特性は、実際に自動車が衝突する時の歪
速度1000〜 2000s-1における材料の変形エネルギーで代
表され、この値が大きいほど同特性が優れる。)表2よ
り、造管のみによる製品ではフェライト粒が9μm以上
と大きく、温間圧延(工程)によりかなり小さくする
ことができるが、最小でも3μm超の粒径にとどまるの
に対し、本発明に従い熱間低温域圧延(工程)→中間
冷却(工程)→温間圧延(工程)を順次行うと、製
品のフェライト粒が2μm以下に微細化し、さらに熱間
低温域圧延(工程)に先立って熱間高温域圧延(工程
)を行うとそれが1μm以下へとさらに微細化し、そ
の結果、強度がより高くしかも延性及び耐衝突衝撃特性
の格段に優れた鋼管が得られることが明らかである。
For the tensile test, a JIS No. 11 test piece was used, and the value of elongation was calculated in consideration of the size effect of the test piece by the conversion formula El = El.
0 (√ (a 0 / a)) 0.4 (where, El 0 : measured elongation, a 0 : constant 29
2 mm 2 , a: Evaluation value was calculated based on the converted value of the test piece cross-sectional area (mm 2 ). The impact impact characteristics were determined by performing a high-speed tensile test at a strain rate of 2000 s −1 , obtaining the absorbed energy up to a strain amount of 30% from the obtained stress-strain curve, and evaluating it as the impact impact absorbed energy. (Collision impact characteristics are represented by the deformation energy of the material at a strain rate of 1000 to 2000 s -1 when a vehicle actually collides. The larger the value, the better the characteristics.) From Table 2, it can be seen that only products made from pipes are used. Ferrite grains are as large as 9 μm or more and can be considerably reduced by warm rolling (process). However, the grain size is at least 3 μm or more at the minimum. When cooling (process) → warm rolling (process) is sequentially performed, the ferrite grains of the product are refined to 2 μm or less, and hot high-temperature rolling (process) is performed prior to hot low-temperature rolling (process). It is apparent that the fineness is further reduced to 1 μm or less, and as a result, a steel pipe having higher strength and excellent in ductility and impact resistance is obtained.

【0034】本発明を実施するには、既存のレデューサ
に簡単な加熱手段(誘導加熱装置等)や冷却手段(ミス
ト冷却装置等)を付加するだけでよいから、大幅な工程
改造を伴うことなく、高い生産性を維持することができ
る。
In order to carry out the present invention, it is only necessary to add a simple heating means (such as an induction heating apparatus) or a cooling means (such as a mist cooling apparatus) to an existing reducer. , High productivity can be maintained.

【0035】[0035]

【表1】 [Table 1]

【0036】[0036]

【表2】 [Table 2]

【0037】[0037]

【発明の効果】かくして本発明によれば、大幅な工程改
造を要さずに、フェライト粒を2μm以下に微細化させ
ることができ、延性及び耐衝突衝撃特性の格段に優れた
鋼管が高能率で生産できるという優れた効果を奏する。
As described above, according to the present invention, it is possible to reduce the size of ferrite grains to 2 μm or less without significantly modifying the process, and to obtain a highly efficient steel pipe having excellent ductility and impact resistance. It has an excellent effect that it can be produced at

【図面の簡単な説明】[Brief description of the drawings]

【図1】本発明の絞り圧延方法を示す模式図である。FIG. 1 is a schematic view showing a reduction rolling method of the present invention.

───────────────────────────────────────────────────── フロントページの続き (72)発明者 西森 正徳 愛知県半田市川崎町1丁目1番地 川崎製 鉄株式会社知多製造所内 (72)発明者 板谷 元晶 愛知県半田市川崎町1丁目1番地 川崎製 鉄株式会社知多製造所内 (72)発明者 橋本 裕二 愛知県半田市川崎町1丁目1番地 川崎製 鉄株式会社知多製造所内 (72)発明者 岡部 能知 愛知県半田市川崎町1丁目1番地 川崎製 鉄株式会社知多製造所内 (72)発明者 森田 正彦 岡山県倉敷市水島川崎通1丁目(番地な し) 川崎製鉄株式会社水島製鉄所内 Fターム(参考) 4K032 AA01 AA02 AA04 AA05 AA08 AA11 AA12 AA14 AA16 AA17 AA19 AA22 AA23 AA24 AA26 AA27 AA29 AA31 AA32 AA35 AA36 AA40 BA03 CB02 CC01 CC02  ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masanori Nishimori 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Inside the Chita Works of Kawasaki Steel Works (72) Inventor Motoaki Itani 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Yuji Hashimoto 1-1-1 Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Nochika Okabe 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Address Kawasaki Steel Co., Ltd. Chita Works (72) Inventor Masahiko Morita 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Pref. AA14 AA16 AA17 AA19 AA22 AA23 AA24 AA26 AA27 AA29 AA31 AA32 AA35 AA36 AA40 BA03 CB02 CC01 CC02

Claims (3)

【特許請求の範囲】[Claims] 【請求項1】 C:0.005 〜0.30%、Si:0.01〜3.0
%、Mn:0.01〜4.0 %、Al:0.001 〜0.10%を含有し、
残部Fe及び不可避的不純物からなる化学組成を有する素
材を素管に加工した後、950 ℃〜Ar3 点で縮径率10%以
上の絞り圧延を行い、次いでAr1 点以下まで冷却を行
い、次いでAc1 点〜400 ℃で縮径率20%以上の絞り圧延
を行うことを特徴とする鋼管の絞り圧延方法。
1. C: 0.005 to 0.30%, Si: 0.01 to 3.0
%, Mn: 0.01 to 4.0%, Al: 0.001 to 0.10%,
After processing the raw material having a chemical composition consisting of the balance Fe and unavoidable impurities into a raw tube, performing reduction rolling at a reduction ratio of 10% or more at 950 ° C. to Ar 3 points, and then cooling to Ar 1 point or less, then reducing rolling process of a steel pipe, which comprises carrying out the reducing rolling radial contraction rate of 20% or more at Ac 1 point to 400 ° C..
【請求項2】 前記素材を素管に加工した後、950 ℃〜
Ar3 点で縮径率10%以上の前記絞り圧延を行う前に、95
0 ℃超で縮径率10%以上の絞り圧延を行う請求項1記載
の方法。
2. After processing the raw material into a raw tube, the raw material is heated to 950 ° C.
Before performing the above-mentioned reduction rolling with a diameter reduction ratio of 10% or more at three points of Ar, 95%
2. The method according to claim 1, wherein the reduction rolling is performed at a reduction ratio of 10% or more at a temperature exceeding 0 ° C.
【請求項3】 前記素材の化学組成にさらに、Cu:1%
以下、Ni:2%以下、Cr:2%以下、Mo:1%以下のう
ちから選ばれた1種又は2種以上、および/または、N
b:0.1 %以下、V:0.3 %以下、Ti:0.2 %以下、
B:0.004 %以下のうちから選ばれた1種又は2種以
上、および/または、REM :0.02%以下、Ca:0.01%以
下のうちから選ばれた1種又は2種が付加された請求項
1または2記載の方法。
3. The chemical composition of the material further includes Cu: 1%
Hereinafter, one or more selected from Ni: 2% or less, Cr: 2% or less, Mo: 1% or less, and / or N
b: 0.1% or less, V: 0.3% or less, Ti: 0.2% or less,
B: one or more selected from 0.004% or less and / or one or two selected from REM: 0.02% or less and Ca: 0.01% or less. 3. The method according to 1 or 2.
JP26710698A 1998-09-21 1998-09-21 Steel pipe drawing method Expired - Fee Related JP3785828B2 (en)

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JP3785828B2 JP3785828B2 (en) 2006-06-14

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JP2002294405A (en) * 2001-04-02 2002-10-09 Nippon Steel Corp Steel tube superior in formability and the production method for the same
WO2002103070A1 (en) * 2001-06-14 2002-12-27 Kawasaki Steel Corporation Method for producing steel pipe having high ductility
WO2002103069A1 (en) * 2000-01-28 2002-12-27 Kawasaki Steel Corporation Steel pipe having high formability and method for production thereof
EP1816225A1 (en) * 2004-11-26 2007-08-08 JFE Steel Corporation Steel pipe having excellent electromagnetic properties and process for producing the same
KR100878731B1 (en) * 2001-05-31 2009-01-14 제이에프이 스틸 가부시키가이샤 Welded steel pipe having excellent hydroformability and method for making the same
US7591914B2 (en) * 2000-01-28 2009-09-22 Jfe Steel Corporation High-workability steel pipe and method of producing same

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US7591914B2 (en) * 2000-01-28 2009-09-22 Jfe Steel Corporation High-workability steel pipe and method of producing same
WO2002103069A1 (en) * 2000-01-28 2002-12-27 Kawasaki Steel Corporation Steel pipe having high formability and method for production thereof
WO2001096624A1 (en) * 2000-06-14 2001-12-20 Kawasaki Steel Corporation High carbon steel pipe excellent in cold formability and high frequency hardenability and method for producing the same
JP4567907B2 (en) * 2001-04-02 2010-10-27 新日本製鐵株式会社 Steel pipe excellent in hydroformability and manufacturing method thereof
JP2002294405A (en) * 2001-04-02 2002-10-09 Nippon Steel Corp Steel tube superior in formability and the production method for the same
KR100878731B1 (en) * 2001-05-31 2009-01-14 제이에프이 스틸 가부시키가이샤 Welded steel pipe having excellent hydroformability and method for making the same
WO2002103070A1 (en) * 2001-06-14 2002-12-27 Kawasaki Steel Corporation Method for producing steel pipe having high ductility
EP1816225A1 (en) * 2004-11-26 2007-08-08 JFE Steel Corporation Steel pipe having excellent electromagnetic properties and process for producing the same
EP1816225A4 (en) * 2004-11-26 2009-03-25 Jfe Steel Corp Steel pipe having excellent electromagnetic properties and process for producing the same
US7942984B2 (en) 2004-11-26 2011-05-17 Jfe Steel Corporation Steel pipe with good magnetic properties and method of producing the same

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