JP3898809B2 - Method for producing ERW steel pipe having excellent formability and high ductility - Google Patents
Method for producing ERW steel pipe having excellent formability and high ductility Download PDFInfo
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- JP3898809B2 JP3898809B2 JP28642697A JP28642697A JP3898809B2 JP 3898809 B2 JP3898809 B2 JP 3898809B2 JP 28642697 A JP28642697 A JP 28642697A JP 28642697 A JP28642697 A JP 28642697A JP 3898809 B2 JP3898809 B2 JP 3898809B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、成形性の優れた高延性を有する電縫鋼管の製造法に関するものである。
【０００２】
【従来の技術】
欧米において、自動車の軽量化と部品点数削減によるコストダウン狙いでハイドロフォ−ム技術の実用化が進みつつあり、日本においても次世代自動車生産技術の中核の一つとして積極的な取り組みが進みつつある。ハイドロフォ−ム用の材料は成形に耐え得る良好な延性を有することが重要な要素である。これまで同程度の強度でありながら延性を向上させる、すなわち強度−延性バランスの向上を目的とした研究開発が数多く行われてきた。過去において、飛躍的に強度−延性バランスを向上させたのは、フェライトとマルテンサイトの混合組織からなるいわゆる二相鋼である。例えば、特開昭５１−１２３１７号公報に熱延後急冷することにより得られる二相鋼の技術、特公昭５７−４５４５４号公報には連続焼鈍により得られる技術がある。現在、二相鋼はその優れた特性を生かし、自動車用等の材料の軽量化用途として注目されている。
【０００３】
【発明が解決しようとする課題】
炭素鋼の強度を向上させるためには、炭素含有量を増加させるのが最も簡単であるが、炭素量が増すと、伸びや絞り等の延性が低下し、また、溶接性が劣化する。一方、炭素鋼を特別な熱処理によってフェライトマトリックスに第二相を分散させ二相組織にすることで強度を確保しつつ延性が優れ、良好な強度−伸びバランスが得られる。本発明は成形性の優れた高延性を有する電縫鋼管を提供するものである。
【０００４】
【課題を解決するための手段】
その発明の要旨とするところは、重量％で、
Ｃ ：０．０５〜０．２５％、
Ｓｉ：０．６％以下、
Ｍｎ：０．２０〜２．００％、
Ａｌ：０．００５〜０．０５０％、
Ｎ ：０．００３６％以下
を含有し、残部Ｆｅおよび不可避不純物よりなる鋼帯を管状に成形し、この管状鋼帯のエッジ部を高周波溶接により素管を成形し、溶接後フェライト＋オ−ステナイト二相域加熱温度（変態温度Ａｃ1 〜Ａｃ3 ）で３０分以下加熱保持し、その後５〜３０℃／秒の冷却速度で冷却することを特徴とするＴＳ３９０〜４３０Ｎ／ｍｍ2 の成形性の優れた高延性を有する電縫鋼管の製造法である。
【０００５】
【発明の実施の形態】
以下に、本発明の成形性の優れた高延性を有する電縫鋼管の製造法について詳細に説明する。
本発明における化学成分、高周波溶接後の電縫鋼管の熱処理条件の限定理由について説明する。はじめに化学成分の限定理由について説明する。
Ｃは強度増加に有効な元素であるが、適量の第二相の組織を生成させ強度を確保するためその下限を０．０５％とした。Ｃが多いと強度が高くなり過ぎ延性が低下し良好な成形性が得られない。よって、優れた強度−延性バランスを得るためにその上限を０．２５％とした。
【０００６】
Ｓｉは脱酸および強度増加に有効な元素であり、Ｓｉが多くなると鋼の脆化をまねき強度−延性バランスの劣化を招くことからその上限を０．６％とした。
Ｍｎは鋼の強度、靱性を確保する上で不可欠な元素であり、Ｍｎが少ないと強度が不足するためその下限を０．２０％とした。Ｍｎが多いと強度が高くなり過ぎ、靱性および延性の劣化を招くことからその上限を２．００％とした。
【０００７】
Ａｌは、脱酸のため必要であるが、過剰に添加するとＡｌ2 Ｏ3 を中心とした脱酸生成物が鋼中に残存する量が増える。特に本発明の場合のように電縫鋼管に用いられる場合、溶接部での巨大な介在物は致命的欠陥となるので、その上限を０．０５％とした。
鋼中のＮを固定することによって固溶Ｎによる降伏点伸びの回復を抑える作用があり、この作用は０．００５％未満のＡｌでは発揮されないため、その下限を０．００５％とした。
Ｎは鋼の耐時効性を最も劣化させる元素であり、含有量が少ないほど好ましく、その上限を０．００３６％以下とした。
【０００８】
次に本発明鋼の高周波溶接後の電縫鋼管の熱処理条件について説明する。
上記に説明した含有成分および含有割合の鋼帯を従来法と同様の方法で溶接を行い素管を形成した後、この素管をフェライト＋オ−ステナイト二相域加熱温度（変態温度Ａｃ1 〜Ａｃ3 ）で３０分以下加熱保持し、その後５〜３０℃／秒の冷却速度で冷却する。加熱温度がＡｃ1 より低いとオ−ステナイトの逆変態が起こらず、その後の冷却条件でも複合組織が得られず良好な強度−延性バランスは得られない。一方、加熱温度がＡｃ3 より高い場合には完全にオ−ステナイト化されてしまうためにＣの農化が起こらず組織が粗大化するため強度−延性バランスが劣化する。したがって、加熱温度はＡｃ1 〜Ａｃ3 とした。
【０００９】
二相域加熱温度域においてα−Ｆｅ中のＣは３０分で十分オ−ステナイト中へ拡散できることから３０分以下の加熱保持時間とした。二相域加熱温度(変態温度Ａｃ1 〜Ａｃ3 )域に加熱したあとの冷却速度はいかにして初析フェライトを細粒にし、かつ低温変態生成物を微細分散するかが問題となることから冷却速度を５〜３０℃／秒とした。本発明のように特定の成分系でフェライト＋オ−ステナイト二相域熱処理することで高度で複雑な成形にも十分耐え得る電縫鋼管が得られる。
【００１０】
【実施例】
表１に化学成分、熱処理条件、機械的特性を示す。表１のＮｏ１〜６は本発明法を示し、Ｎｏ７〜１２は比較法を示す。表１から明らかなように本発明法にしたがって製造した鋼管は優れた強度−延性バランスを有する。これに対して比較法は熱処理条件が適切でなく、本発明法に比較して強度−延性バランスが劣る。
【００１１】
【表１】
【発明の効果】
本発明により成形性の優れた高延性を有する電縫鋼管が安定して製造できるようになった。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an electric resistance welded steel pipe having excellent formability and high ductility.
[0002]
[Prior art]
In Europe and the United States, hydroform technology is being put into practical use with the aim of reducing costs by reducing the weight of automobiles and reducing the number of parts. In Japan, active efforts are being made as one of the core of next-generation automobile production technologies. is there. It is an important factor that the material for the hydroform has good ductility that can withstand molding. There have been many researches and developments aimed at improving ductility while maintaining the same strength, that is, improving the strength-ductility balance. In the past, what has greatly improved the strength-ductility balance is a so-called duplex steel composed of a mixed structure of ferrite and martensite. For example, Japanese Patent Application Laid-Open No. 51-12317 discloses a duplex stainless steel technique obtained by rapid cooling after hot rolling, and Japanese Patent Publication No. 57-45454 discloses a technique obtained by continuous annealing. Currently, duplex stainless steels are attracting attention as applications for reducing the weight of materials for automobiles, etc., taking advantage of their excellent characteristics.
[0003]
[Problems to be solved by the invention]
In order to improve the strength of the carbon steel, it is easiest to increase the carbon content. However, when the carbon content increases, the ductility such as elongation and drawing decreases, and the weldability deteriorates. On the other hand, carbon steel is dispersed by a special heat treatment to disperse the second phase in the ferrite matrix to form a two-phase structure, thereby ensuring excellent strength and excellent balance between strength and elongation. The present invention provides an ERW steel pipe having excellent ductility and high ductility.
[0004]
[Means for Solving the Problems]
The gist of the invention is weight percent,
C: 0.05 to 0.25%,
Si: 0.6% or less,
Mn: 0.20 to 2.00%,
Al: 0.005 to 0.050%,
N: A steel strip containing 0.0036% or less and the balance of Fe and inevitable impurities is formed into a tubular shape, and an edge portion of the tubular steel strip is formed by high-frequency welding, and after welding, ferrite + austenite The moldability of TS390 to 430 N / mm 2 , characterized in that it is heated and held for 30 minutes or less at a two-phase region heating temperature (transformation temperatures Ac 1 to Ac 3 ) and then cooled at a cooling rate of 5 to 30 ° C./second. This is a method for producing an ERW steel pipe having excellent high ductility.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Below, the manufacturing method of the ERW steel pipe which has the high ductility which was excellent in the moldability of this invention is demonstrated in detail.
The reasons for limiting the chemical components and heat treatment conditions of the ERW steel pipe after high frequency welding in the present invention will be described. First, the reasons for limiting chemical components will be described.
C is an element effective for increasing the strength, but the lower limit was made 0.05% in order to generate an appropriate amount of the second phase structure and ensure the strength. If the amount of C is large, the strength becomes too high and the ductility is lowered, and good moldability cannot be obtained. Therefore, in order to obtain an excellent strength-ductility balance, the upper limit is made 0.25%.
[0006]
Si is an element effective for deoxidation and strength increase. When Si is increased, the steel becomes brittle and the strength-ductility balance is deteriorated, so the upper limit was made 0.6%.
Mn is an element indispensable for ensuring the strength and toughness of steel. If the amount of Mn is small, the strength is insufficient, so the lower limit was made 0.20%. If the amount of Mn is large, the strength becomes too high and the toughness and ductility are deteriorated, so the upper limit was made 2.00%.
[0007]
Al is necessary for deoxidation, but if it is added in excess, the amount of deoxidation products centered on Al 2 O 3 remaining in the steel increases. In particular, when used for ERW steel pipes as in the case of the present invention, enormous inclusions in the welds become fatal defects, so the upper limit was made 0.05%.
By fixing N in the steel, there is an effect of suppressing the recovery of the yield point elongation due to solute N. Since this effect is not exhibited with less than 0.005% Al, the lower limit was made 0.005%.
N is an element that most deteriorates the aging resistance of steel, and the smaller the content, the better . The upper limit is set to 0.0036% or less.
[0008]
Next, heat treatment conditions for the ERW steel pipe after high frequency welding of the steel of the present invention will be described.
The steel strip having the above-described components and content ratios was welded in the same manner as in the conventional method to form a raw pipe, and then this raw pipe was heated to a ferrite + austenite two-phase region heating temperature (transformation temperature Ac 1 to Ac 3 ) is heated and held for 30 minutes or less, and then cooled at a cooling rate of 5 to 30 ° C./second. The heating temperature is lower than the Ac 1 O - reverse transformation austenite does not occur, good strength is not obtained composite structure in the subsequent cooling conditions - not available ductility balance. On the other hand, when the heating temperature is higher than Ac 3 , it is completely austenitic, so that C is not agricultural and the structure is coarsened, so that the strength-ductility balance is deteriorated. Therefore, the heating temperature was set to Ac 1 to Ac 3 .
[0009]
In the two-phase region heating temperature region, C in α-Fe can be sufficiently diffused into austenite in 30 minutes, so the heating and holding time was set to 30 minutes or less. Because the cooling rate after heating to the two-phase region heating temperature (transformation temperature Ac 1 to Ac 3 ) region is how to refine the pro-eutectoid ferrite and finely disperse the low-temperature transformation product. The cooling rate was 5 to 30 ° C./second. As in the present invention, an electric resistance welded steel pipe that can sufficiently withstand sophisticated and complex forming can be obtained by heat treatment of ferrite + austenite two-phase region with a specific component system.
[0010]
【Example】
Table 1 shows chemical components, heat treatment conditions, and mechanical properties. Nos. 1 to 6 in Table 1 show the method of the present invention, and Nos. 7 to 12 show comparative methods. As is apparent from Table 1, the steel pipe produced according to the method of the present invention has an excellent strength-ductility balance. In contrast, the heat treatment conditions of the comparative method are not appropriate, and the strength-ductility balance is inferior to that of the method of the present invention.
[0011]
[Table 1]
【The invention's effect】
According to the present invention, an ERW steel pipe having excellent ductility and high ductility can be stably produced.
Claims (1)
Ｃ ：０．０５〜０．２５％、
Ｓｉ：０．６％以下、
Ｍｎ：０．２０〜２．００％、
Ａｌ：０．００５〜０．０５０％、
Ｎ ：０．００３６％以下
を含有し、残部Ｆｅおよび不可避不純物よりなる鋼帯を管状に成形し、この管状鋼帯のエッジ部を高周波溶接により素管とし、溶接後フェライト＋オ−ステナイト二相域加熱温度（変態温度Ａｃ1 〜Ａｃ3 ）で３０分以下加熱保持し、その後５〜３０℃／秒の冷却速度で冷却することを特徴とするＴＳ３９０〜４３０Ｎ／ｍｍ2 の成形性の優れた高延性を有する電縫鋼管の製造法。% By weight
C: 0.05 to 0.25%,
Si: 0.6% or less,
Mn: 0.20 to 2.00%,
Al: 0.005 to 0.050%,
N: A steel strip containing 0.0036% or less and the balance Fe and inevitable impurities is formed into a tubular shape, and the edge portion of the tubular steel strip is formed into a blank by high-frequency welding, and after welding, ferrite + austenite two-phase Heating and holding at a zone heating temperature (transformation temperature Ac 1 to Ac 3 ) for 30 minutes or less, and then cooling at a cooling rate of 5 to 30 ° C./second is excellent in moldability of TS390 to 430 N / mm 2 A method for manufacturing ERW steel pipes with high ductility.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP28642697A JP3898809B2 (en) | 1997-10-20 | 1997-10-20 | Method for producing ERW steel pipe having excellent formability and high ductility |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP28642697A JP3898809B2 (en) | 1997-10-20 | 1997-10-20 | Method for producing ERW steel pipe having excellent formability and high ductility |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11124631A JPH11124631A (en) | 1999-05-11 |
| JP3898809B2 true JP3898809B2 (en) | 2007-03-28 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP28642697A Expired - Fee Related JP3898809B2 (en) | 1997-10-20 | 1997-10-20 | Method for producing ERW steel pipe having excellent formability and high ductility |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3898809B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5753781B2 (en) * | 2008-07-11 | 2015-07-22 | アクティエボラゲット・エスコーエッフ | Method for manufacturing steel components, weld lines, welded steel components, and bearing components |
-
1997
- 1997-10-20 JP JP28642697A patent/JP3898809B2/en not_active Expired - Fee Related
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| Publication number | Publication date |
|---|---|
| JPH11124631A (en) | 1999-05-11 |
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