JP2009191330A - Electric resistance steel tube - Google Patents
Electric resistance steel tube Download PDFInfo
- Publication number
- JP2009191330A JP2009191330A JP2008034807A JP2008034807A JP2009191330A JP 2009191330 A JP2009191330 A JP 2009191330A JP 2008034807 A JP2008034807 A JP 2008034807A JP 2008034807 A JP2008034807 A JP 2008034807A JP 2009191330 A JP2009191330 A JP 2009191330A
- Authority
- JP
- Japan
- Prior art keywords
- steel pipe
- mass
- electric resistance
- hardness
- less
- 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.)
- Pending
Links
Images
Abstract
Description
本発明は、電縫鋼管に関し、特に、自動車の足廻り部材や構造部材等で使用される電縫鋼管に関する。 The present invention relates to an electric resistance welded steel pipe, and more particularly to an electric resistance welded steel pipe used for an undercarriage member or a structural member of an automobile.
近年、自動車の軽量化に伴い、種々の部品において中空化の提案がなされている。特に、自動車の足廻り部材の一つであるスタビライザーでは、丸棒から鋼管への変更が急速に進んでいる。その一方で、スタビライザーは、高速走行時に車体の走行安定性を確保する重要な部材であるため、自動車の高出力化に伴い、スタビライザーに要求される繰返し応力が高まっている。従って、スタビライザーには高応力下での疲労寿命を向上させることが望まれている。 In recent years, with the reduction in weight of automobiles, proposals for hollowing out various parts have been made. In particular, in a stabilizer that is one of suspension members of an automobile, a change from a round bar to a steel pipe is rapidly progressing. On the other hand, the stabilizer is an important member for ensuring the running stability of the vehicle body at the time of high speed running, and therefore, the repeated stress required for the stabilizer is increased with the increase in the output of the automobile. Therefore, it is desired for the stabilizer to improve the fatigue life under high stress.
中空化したスタビライザー（以下、「中空スタビライザー」という）の疲労寿命を向上させる方法としては、ショットピーニングにより圧縮残留応力を付与する方法が知られている。しかし、ショットピーニングによる方法は、鋼管の外表面では容易に適用することができるものの、鋼管の内表面では適用することが工業的に難しいという問題がある。そのため、薄肉の電縫鋼管を用いて製造した薄肉の中空スタビライザーでは、高い繰返し応力に十分に対応できていない。そこで、鋼管肉厚ｔと鋼管外径Ｄとの比（ｔ／Ｄ）を大きくした厚肉の電縫鋼管を用いて厚肉の中空スタビライザーを製造することにより、鋼管の内表面にかかる応力を低減させている。ここで、電縫鋼管を厚肉化する場合、造管時やスタビライザーへの成形時において素材表面に大きな歪が加わるため、素材となる鋼板には高い加工性が要求される。
一方、鋼管の内表面の強化方法として、鋼管の内表面に浸炭硬化層を形成する方法も知られている（例えば、特許文献１参照）。しかし、この強化方法は、電縫鋼管の溶接ビード部分を肉厚方向で安定的に強化することが困難であると共に、鋼管製造後に塗布型浸炭組成物を内表面に塗布、乾燥する工程が必要となるため、製造コストが上昇するという問題がある。さらに、この強化方法では、焼入れ温度及び加熱時間を厳密に管理することも必要となる。
As a method for improving the fatigue life of a hollow stabilizer (hereinafter referred to as “hollow stabilizer”), a method of applying compressive residual stress by shot peening is known. However, although the method by shot peening can be easily applied to the outer surface of the steel pipe, it is industrially difficult to apply to the inner surface of the steel pipe. Therefore, a thin hollow stabilizer manufactured using a thin ERW steel pipe cannot sufficiently cope with high cyclic stress. Therefore, by producing a thick hollow stabilizer using a thick ERW steel pipe with a large ratio (t / D) between the steel pipe wall thickness t and the steel pipe outer diameter D, the stress applied to the inner surface of the steel pipe is reduced. It is reduced. Here, when increasing the thickness of the electric resistance welded steel pipe, a large strain is applied to the surface of the material at the time of pipe making or forming into a stabilizer.
On the other hand, a method of forming a carburized hardened layer on the inner surface of the steel pipe is also known as a method for strengthening the inner surface of the steel pipe (see, for example, Patent Document 1). However, in this strengthening method, it is difficult to stably strengthen the weld bead portion of the ERW steel pipe in the thickness direction, and a process of applying and drying the coating type carburizing composition on the inner surface after manufacturing the steel pipe is required. Therefore, there is a problem that the manufacturing cost increases. Further, in this strengthening method, it is necessary to strictly control the quenching temperature and the heating time.
中空スタビライザー等で使用される電縫鋼管は、鋼板を造管することによって製造することができるが、造管溶接の凝固時に、固相と液相との間で元素の分配が生じ、凝固した固相中の炭素量が液相中の炭素量に比べて大幅に低下する。そのため、電縫鋼管の溶接ビード部分では、中空スタビライザーを製造する際に焼入れ性が低下し、焼入れ硬さが母材部分と比較して低い部分が生成する。その結果、軟質の溶接ビード部が疲労破壊の起点となり、中空スタビライザーの疲労特性が低下する。
また、中空スタビライザーの製造において電縫鋼管に焼入れを行う際（すなわち、調質熱処理を行う際）には、高温に加熱された電縫鋼管を水等の冷媒により冷却するが、電縫鋼管の外表面からの冷却のみであるため、内表面側の冷却速度が外表面側の冷却速度に比べて低くなり、焼入れ不良が生じ易い。そのため、特に、電縫鋼管の内表面の溶接ビード部分では、焼入れ硬さが最も低くなる。
ERW steel pipes used in hollow stabilizers and the like can be manufactured by making steel sheets, but when pipe welding is solidified, element distribution occurs between the solid and liquid phases and solidifies. The amount of carbon in the solid phase is significantly reduced compared to the amount of carbon in the liquid phase. Therefore, in the weld bead portion of the electric resistance welded steel pipe, the hardenability is lowered when the hollow stabilizer is manufactured, and a portion having a lower quenching hardness than the base material portion is generated. As a result, the soft weld bead portion becomes the starting point of fatigue failure, and the fatigue characteristics of the hollow stabilizer are reduced.
When the ERW steel pipe is quenched in the manufacture of the hollow stabilizer (that is, when the tempering heat treatment is performed), the ERW steel pipe heated to a high temperature is cooled with a coolant such as water. Since the cooling is only from the outer surface, the cooling rate on the inner surface side is lower than the cooling rate on the outer surface side, and a quenching failure is likely to occur. Therefore, the quenching hardness is lowest at the weld bead portion on the inner surface of the ERW steel pipe.
上述のように、自動車の足廻り部材の一つである中空スタビライザーでは、疲労特性が重要視されるため、中空スタビライザー用鋼管として、疲労特性に優れた構造用合金鋼鋼管を使用することが考えられる。しかし、構造用合金鋼鋼管は、合金添加によって製造コストの上昇に繋がるという問題がある。
そこで、疲労特性に優れた中空スタビライザーを与える電縫鋼管として、所定の化学組成を有する電縫鋼管をオーステナイト領域まで加熱し、熱間絞り圧延機にて縮径圧延した後、焼入れ処理を施した電縫鋼管が提案されている（例えば、特許文献２参照）。この電縫鋼管は、縮径圧延を施すことで、溶接によって低炭素化した部分へ炭素が拡散し、溶接ビード部分の硬度低下を防止することができると考えられる。
As mentioned above, in hollow stabilizers, which are one of the suspension members of automobiles, fatigue characteristics are regarded as important, so it is considered to use structural alloy steel pipes with excellent fatigue characteristics as steel pipes for hollow stabilizers. It is done. However, the structural alloy steel pipe has a problem that the addition of the alloy leads to an increase in manufacturing cost.
Therefore, as an ERW steel pipe giving a hollow stabilizer with excellent fatigue characteristics, an ERW steel pipe having a predetermined chemical composition was heated to the austenite region, reduced in diameter by a hot drawing mill, and then quenched. An electric resistance steel pipe has been proposed (see, for example, Patent Document 2). The electric resistance welded steel pipe is considered to be capable of preventing the hardness of the weld bead portion from being reduced by reducing the diameter of the weld bead by diffusing the carbon into the portion that has been reduced in carbon by welding.
しかしながら、特許文献２の電縫鋼管は、縮径圧延を行うためにオーステナイト領域まで加熱する必要があると共に、熱歪による歪を防止して直管とするために伸管加工による矯正も必要となる。そのため、特許文献２の電縫鋼管は、製造コストが上昇すると共に、生産性も悪いという問題がある。さらに、特許文献２の電縫鋼管では、オーステナイト領域まで加熱した際に、表面脱炭やスケール疵の発生等の表面品質の低下が生じる恐れもある。
本発明は、上記のような問題を解決するためになされたものであり、製造コストを抑えつつ生産性良く製造し得ると共に、加工性及び調質熱処理後の疲労特性に優れる電縫鋼管を提供することを目的とする。
However, the ERW steel pipe of
The present invention has been made in order to solve the above-described problems, and provides an electric-welded steel pipe that can be manufactured with high productivity while suppressing manufacturing costs, and that is excellent in workability and fatigue characteristics after temper heat treatment. The purpose is to do.
本発明者等は、上記課題を解決すべく鋭意検討を重ねた結果、鋼成分の化学組成及び金属組織を総合的且つ適正に調整することで、縮径圧延を行わなくても電縫鋼管を容易且つ効率的に製造することができると共に、電縫鋼管の加工性及び調質熱処理後の疲労特性を向上させ得ることを見出した。
すなわち、本発明の電縫鋼管は、Ｃ：０．１５〜０．３０質量％、Ｓｉ：０．３０質量％以下、Ｍｎ：１．０〜２．０質量％、Ｐ：０．０３０質量％以下、Ｓ：０．０１０質量％以下、Ｃｒ：０．２〜１．５質量％、Ｔｉ：０．００５〜０．０３質量％、ｓｏｌ．Ａｌ：０．００５〜０．１０質量％、Ｎ：０．０１０質量％以下、及びＢ：０．００１０〜０．００７０質量％を含み、残部がＦｅ及び不可避的不純物からなると共に、以下の式で示されるＸ及びＹの値がそれぞれＸ＜８及びＹ＞３００を満たす化学組成をもち、且つフェライトとパーライトとの混合組織又はフェライトとセメンタイトとの混合組織を有することを特徴とする。
Ｘ＝３Ｃ＋１．５Ｍｎ＋２Ｃｒ＋１２０Ｓ＋９０Ｔｉ
Ｙ＝２０Ｃ＋２５０Ｍｎ＋３５Ｃｒ＋３５０Ｂ
As a result of intensive studies to solve the above-mentioned problems, the present inventors have adjusted the chemical composition and metal structure of the steel components comprehensively and appropriately, thereby allowing the ERW steel pipe to be manufactured without reducing diameter rolling. It has been found that it can be produced easily and efficiently, and the workability of the ERW steel pipe and the fatigue characteristics after the temper heat treatment can be improved.
That is, the ERW steel pipe of the present invention has C: 0.15-0.30 mass%, Si: 0.30 mass% or less, Mn: 1.0-2.0 mass%, P: 0.030 mass%. Hereafter, S: 0.010 mass% or less, Cr: 0.2-1.5 mass%, Ti: 0.005-0.03 mass%, sol. Al: 0.005 to 0.10% by mass, N: 0.010% by mass or less, and B: 0.0010 to 0.0070% by mass, with the balance being Fe and inevitable impurities, It has a chemical composition satisfying X <8 and Y> 300, respectively, and has a mixed structure of ferrite and pearlite or a mixed structure of ferrite and cementite.
X = 3C + 1.5Mn + 2Cr + 120S + 90Ti
Y = 20C + 250Mn + 35Cr + 350B
本発明によれば、製造コストを抑えつつ生産性良く製造し得ると共に、加工性及び調質熱処理後の疲労特性に優れる電縫鋼管を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, while being able to manufacture with sufficient productivity, suppressing manufacturing cost, the electric-resistance-welded steel pipe which is excellent in workability and the fatigue characteristic after tempering heat processing can be provided.
調質熱処理後の疲労特性の低下は、上述したとおり、造管溶接の凝固時に炭素量が大幅に低下した溶接ビード部を起点とする疲労破壊に起因するので、この疲労特性を向上させるには、溶接ビード部での疲労破壊を防止することが重要である。溶接ビード部を起点とする疲労破壊を防止するためには、通電加熱焼入れや高周波焼入れ等による調質熱処理を電縫鋼管に施した後に、溶接ビード部の金属組織を焼入組織（マルテンサイト）とし、硬さを確保する必要がある。このような見地に基づき、加工性と調質熱処理後の疲労特性の双方を両立すべく電縫鋼管の化学組成及び金属組織を設計した。 As described above, the deterioration of the fatigue characteristics after the tempering heat treatment is caused by the fatigue fracture starting from the weld bead portion in which the carbon content is greatly reduced during solidification of pipe welding. It is important to prevent fatigue failure at the weld bead. In order to prevent fatigue failure starting from the weld bead, the tempering heat treatment by electric heating quenching or induction quenching is applied to the ERW steel pipe, and then the metal structure of the weld bead is quenched (martensite). It is necessary to secure hardness. Based on such a viewpoint, the chemical composition and the metal structure of the ERW steel pipe were designed to achieve both workability and fatigue characteristics after temper heat treatment.
以下、本発明の電縫鋼管における化学組成及び金属組織について詳細に説明する。
本発明の電縫鋼管は、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｒ、Ｔｉ、ｓｏｌ．Ａｌ、Ｎ、Ｂを含み、残部がＦｅ及び不可避的不純物からなる。これらの成分の中でも、Ｃ、Ｔｉ、Ｍｎ、Ｃｒ、Ｓの上限は加工性の観点から規制され、Ｃ、Ｍｎ、Ｃｒの下限は熱処理の観点から規制される。また、Ｂ、Ｔｉは焼入性の改善に有効な成分である。
Hereinafter, the chemical composition and metal structure in the ERW steel pipe of the present invention will be described in detail.
The electric resistance welded steel pipe of the present invention includes C, Si, Mn, P, S, Cr, Ti, sol. Including Al, N, and B, the balance is made of Fe and inevitable impurities. Among these components, the upper limit of C, Ti, Mn, Cr, and S is regulated from the viewpoint of workability, and the lower limit of C, Mn, and Cr is regulated from the viewpoint of heat treatment. B and Ti are effective components for improving hardenability.
Ｃ：０．１５〜０．３０質量％
Ｃは、自動車の構造部材として必要な硬さを確保するために重要な成分であり、０．１５質量％以上のＣを含有させることで所望の硬さが得られる。しかし、０．３０質量％を超える多量のＣを含有させると、焼入性及び焼入硬さは十分確保されるが、電縫鋼管の曲げ加工性が著しく低下する。
C: 0.15-0.30 mass%
C is an important component for ensuring the hardness necessary for a structural member of an automobile, and a desired hardness can be obtained by containing 0.15% by mass or more of C. However, when a large amount of C exceeding 0.30% by mass is contained, the hardenability and quenching hardness are sufficiently ensured, but the bending workability of the ERW steel pipe is remarkably lowered.
Ｓｉ：０．３０質量％以下
Ｓｉは、延性に対する影響が大きい成分の１つである。Ｓｉを過剰に含有させると固溶強化作用によってフェライトが硬化し、成形加工時に割れ発生の原因となる。また、Ｓｉ含有量が増加すると、電縫鋼管の素材である鋼板の製造工程で鋼板表面にスケール疵が発生する傾向を示し、表面品質の低下を招く。さらに、造管溶接時にペネトレータが生成し、溶接欠陥となる。そのため、Ｓｉ含有量の上限は０．３質量％とする必要がある。
Si: 0.30 mass% or less Si is one of the components having a great influence on ductility. If Si is contained excessively, the ferrite is hardened by the solid solution strengthening action, which causes cracking during the molding process. Moreover, when Si content increases, it shows the tendency for a scale flaw to generate | occur | produce on the steel plate surface in the manufacturing process of the steel plate which is a raw material of an ERW steel pipe, and causes the fall of surface quality. Furthermore, a penetrator is generated at the time of pipe making welding, resulting in a welding defect. Therefore, the upper limit of the Si content needs to be 0.3% by mass.
Ｍｎ：１．０〜２．０質量％
Ｍｎは、焼入れ加熱後の冷却過程でフェライト変態を抑制し、比較的遅い冷却速度でもマルテンサイト主体の組織にすることにより、鋼材の焼入れ性を高める成分である。また、Ｍｎは、強靭化にも有効な成分である。しかし、１．０質量％未満のＭｎ含有量では、焼入れ性が大幅に低下し、冷却中にパーライト、上部ベイナイト等の高温生成物が形成され、自動車の構造部材として必要な焼入れ硬さが得られなくなる。逆に、２．０質量％を超える多量のＭｎを含有させると、フェライトが硬化し、電縫鋼管の曲げ加工性が劣化する。
Mn: 1.0 to 2.0% by mass
Mn is a component that suppresses the ferrite transformation in the cooling process after quenching heating and makes the steel material a martensite-based structure even at a relatively slow cooling rate, thereby improving the hardenability of the steel material. Mn is an effective component for toughening. However, when the Mn content is less than 1.0% by mass, the hardenability is significantly lowered, and high-temperature products such as pearlite and upper bainite are formed during cooling, and the quenching hardness necessary as a structural member of an automobile is obtained. It becomes impossible. On the contrary, when a large amount of Mn exceeding 2.0 mass% is contained, the ferrite is hardened and the bending workability of the ERW steel pipe is deteriorated.
Ｐ：０．０３０質量％以下
Ｐは、延性や靭性を劣化させる成分であり、０．０３０質量％を超えるＰを含有させると、焼入れ後に旧オーステナイト粒界の靭性が劣化し、疲労特性が低下する。そのため、Ｐ含有量の上限は０．０３０質量％とする必要がある。
P: 0.030% by mass or less P is a component that deteriorates ductility and toughness. If P exceeding 0.030% by mass is included, the toughness of prior austenite grain boundaries deteriorates after quenching, and the fatigue characteristics decrease. To do. Therefore, the upper limit of the P content needs to be 0.030% by mass.
Ｓ：０．０１０質量％以下
Ｓは、電縫鋼管の曲げ加工性を支配する極めて重要な成分である。すなわち、Ｓは、ＭｎＳ系の介在物を生成し、特に局部的な延性を劣化させる。曲げ加工では、生成したＭｎＳが破断の起点になり、割れが発生し易くなる。そのため、Ｓ含有量の上限は０．０１０質量％以下、好ましくは０．００５質量％以下とする必要がある。
S: 0.010 mass% or less S is an extremely important component that governs the bending workability of the electric resistance welded steel pipe. That is, S produces MnS-based inclusions and deteriorates local ductility. In the bending process, the generated MnS becomes the starting point of fracture, and cracks are likely to occur. Therefore, the upper limit of the S content needs to be 0.010% by mass or less, preferably 0.005% by mass or less.
Ｃｒ：０．２〜１．５質量％
Ｃｒは、焼入れ性の改善に有効な成分であり、０．２質量％以上の含有量でＣｒの添加効果が顕著になる。０．２質量％未満のＣｒ含有量では、硬さが不足するだけでなく、焼入れ時の冷却速度依存性が大きくなるため、焼入れ硬さが不安定になり易い。逆に、１．５質量％を超える多量のＣｒを含有させると、焼入れ前の曲げ加工性が著しく劣化する。
Cr: 0.2-1.5 mass%
Cr is a component effective for improving hardenability, and the effect of adding Cr becomes remarkable when the content is 0.2% by mass or more. When the Cr content is less than 0.2% by mass, not only the hardness is insufficient, but also the dependency on the cooling rate at the time of quenching increases, so that the quenching hardness tends to become unstable. On the other hand, when a large amount of Cr exceeding 1.5% by mass is contained, the bending workability before quenching is remarkably deteriorated.
Ｔｉ：０．００５〜０．０５質量％
Ｔｉは、溶鋼の脱酸調整に添加される成分であり、脱窒作用を有する。また、Ｔｉは、鋼板に固溶しているＮを窒化物として固定するので、焼入れ性を改善する有効Ｂ量を高めることができる。さらに、Ｔｉは、炭窒化物を形成し、焼入れ加熱時に結晶粒の粗大化を防止する作用を有する。これらの作用を安定して得るためには、０．００５質量％以上のＴｉ含有量が必要である。しかし、０．０５質量％を超える多量のＴｉを含有させると、経済的に不利になるだけでなく、曲げ加工性を劣化させる原因ともなる。
Ti: 0.005 to 0.05 mass%
Ti is a component added to adjust the deoxidation of molten steel, and has a denitrification action. Further, Ti fixes N dissolved in the steel sheet as a nitride, so that the effective B amount for improving the hardenability can be increased. Furthermore, Ti has a function of forming carbonitrides and preventing coarsening of crystal grains during quenching heating. In order to stably obtain these actions, a Ti content of 0.005% by mass or more is necessary. However, if a large amount of Ti exceeding 0.05% by mass is contained, not only is it economically disadvantageous, but it also causes a deterioration in bending workability.
ｓｏｌ．Ａｌ（酸可溶性Ａｌ）：０．００５〜０．１０質量％
ｓｏｌ．Ａｌは、溶鋼の脱酸剤として使用される成分であり、Ｎを固定する作用も有する。このような作用は、０．００５質量％以上のｓｏｌ．Ａｌ含有量で顕著になる。しかし、０．１０質量％を超える多量のｓｏｌ．Ａｌを含有させると、鋼板の清浄度が損なわれ、表面疵が発生し易くなり、表面品質を低下させる原因となる。
sol. Al (acid-soluble Al): 0.005 to 0.10% by mass
sol. Al is a component used as a deoxidizer for molten steel, and also has an effect of fixing N. Such an effect is achieved when the sol. It becomes remarkable with the Al content. However, a large amount of sol. When Al is contained, the cleanliness of the steel sheet is impaired, surface flaws are easily generated, and the surface quality is deteriorated.
Ｎ：０．０１０質量％以下
Ｎは、Ｔｉと結合してＴｉＮを形成し、焼入れ加熱時の結晶粒微細化に有効な成分である。しかし、Ｎ含有量が０．０１０質量％を超えると、延性が低下する。また、過剰なＮはＢと結合し、焼入れ性の改善に有効なＢ量を消費する。そのため、Ｎ含有量の上限は０．０１０質量％とする必要がある。
N: 0.010% by mass or less N is a component that combines with Ti to form TiN and is effective in refining crystal grains during quenching heating. However, when the N content exceeds 0.010% by mass, the ductility decreases. Excess N combines with B and consumes an amount of B effective for improving hardenability. Therefore, the upper limit of the N content needs to be 0.010% by mass.
Ｂ：０．００１０〜０．００７０質量％
Ｂは、ごく微量の添加で鋼材の焼入れ性を大幅に向上させる成分である。また、Ｂは、粒界の歪みエネルギーを低下させることによって粒界を強化する作用を有する。従って、自動車の構造部材として必要な硬さを安定して得るためにも必要な成分である。このようなＢの添加効果は、０．００１０質量％以上の含有量で顕著になる。しかし、０．００７０質量％を超えるＢを添加しても、その効果が飽和し、逆に靭性を劣化させてしまう。
B: 0.0010 to 0.0070% by mass
B is a component that greatly improves the hardenability of the steel material by adding a very small amount. Moreover, B has the effect | action which strengthens a grain boundary by reducing the distortion energy of a grain boundary. Therefore, it is a component necessary for stably obtaining the hardness required as a structural member of an automobile. Such an effect of addition of B becomes remarkable when the content is 0.0010% by mass or more. However, even if B exceeding 0.0070 mass% is added, the effect is saturated and the toughness is deteriorated.
各成分の含有量が上記範囲を満足する場合であっても、ＭｎＳ系介在物、フェライト硬さ、セメンタイトやパーライト等の量が複雑に関連して電縫鋼管の曲げ加工性に多大な影響を及ぼす。そこで、様々な化学組成をもつ電縫鋼管を作製し、化学組成と曲げ加工性との関係について検討した結果、曲げ加工性がＣ、Ｍｎ、Ｃｒ、Ｓ及びＴｉの含有量と密接に関連していることを見出し、曲げ加工性の指標として下記の式を得た。
Ｘ＝３Ｃ＋１．５Ｍｎ＋２Ｃｒ＋１２０Ｓ＋９０Ｔｉ
上記の式で示されるＸ値が８未満である場合、引張伸びが向上し、曲げ加工による部品製造の際に要求される曲げ加工性が得られる。一方、Ｘ値が８以上である場合、所望の曲げ加工性が得られない。
Even if the content of each component satisfies the above range, the amount of MnS inclusions, ferrite hardness, cementite, pearlite, etc. are related in a complex manner and have a great influence on the bending workability of ERW steel pipes. Effect. Therefore, as a result of preparing ERW steel pipes with various chemical compositions and examining the relationship between chemical composition and bending workability, bending workability is closely related to the contents of C, Mn, Cr, S and Ti. The following formula was obtained as an index of bending workability.
X = 3C + 1.5Mn + 2Cr + 120S + 90Ti
When the X value represented by the above formula is less than 8, the tensile elongation is improved, and the bending workability required when manufacturing a part by bending is obtained. On the other hand, when the X value is 8 or more, desired bending workability cannot be obtained.
同様に、様々な化学組成をもつ電縫鋼管を作製し、化学組成と焼入性及び焼入硬さとの関係について検討した結果、焼入性がＣ、Ｍｎ、Ｃｒ及びＢの含有量と密接に関連し、また、焼入硬さがＣ及びＭｎの含有量と密接に関連していることを見出し、焼入性及び焼入硬さの指標として下記の式を得た。
Ｙ＝２０Ｃ＋２５０Ｍｎ＋３５Ｃｒ＋３５０Ｂ
上記の式で示されるＹ値が３００を超える場合、溶接ビード部において良好な焼入性及び焼入硬さが安定して得られる。一方、Ｙ値が３００以下である場合、所望の焼入性及び焼入硬さが得られない。
Similarly, ERW steel pipes with various chemical compositions were prepared, and the relationship between the chemical composition, hardenability and quenching hardness was examined. As a result, the hardenability was closely related to the contents of C, Mn, Cr and B. Moreover, it discovered that quenching hardness was closely related with content of C and Mn, and obtained the following formula as an index of hardenability and quenching hardness.
Y = 20C + 250Mn + 35Cr + 350B
When the Y value indicated by the above formula exceeds 300, good hardenability and hardened hardness can be stably obtained in the weld bead portion. On the other hand, when the Y value is 300 or less, desired hardenability and hardenability cannot be obtained.
本発明の電縫鋼管は、フェライトとパーライトとの混合組織又はフェライトとセメンタイトとの混合組織を有する。ベイナイトやマルテンサイトのような組織が存在すると、曲げ加工時に割れの起点となるため好ましくない。
このような混合組織は、上記成分を適正量で配合した鋼を溶製してスラブに連鋳した後、仕上温度８５０〜９５０℃、冷却速度１０〜７０℃／秒、巻取温度５００〜６５０℃の条件で、常法にて熱間圧延を施した後、必要に応じて冷間圧延や焼鈍を施すことによって発現させることができる。特に、より厳しい曲げ加工が施される場合には、焼鈍を施してフェライトとセメンタイトとの混合組織を発現させることが好ましい。
The ERW steel pipe of the present invention has a mixed structure of ferrite and pearlite or a mixed structure of ferrite and cementite. The presence of a structure such as bainite or martensite is not preferable because it becomes a starting point of cracking during bending.
Such a mixed structure is obtained by melting steel containing the above components in appropriate amounts and continuously casting it on a slab, then finishing temperature 850 to 950 ° C., cooling
本発明の電縫鋼管は、上記のような圧延処理を施した鋼板をロール成形することにより連続的に造管して製造することができる。ここで、造管溶接方法としては、特に限定されることはなく、高周波溶接、ＴＩＧ溶接、レーザー溶接等の公知方法を用いることができる。ここで、本発明の電縫鋼管における鋼管外径Ｄや鋼管肉厚ｔは、用途等にあわせて適宜調整すればよいが、中空スタビライザーに用いる場合には、鋼管外径Ｄが１０〜４５ｍｍ、鋼管肉厚ｔが１〜７ｍｍであることが好ましい。
このようにして製造される本発明の電縫鋼管は、縮径圧延を行う必要がないので、製造コストを抑えつつ生産性良く製造することができる。
The electric resistance welded steel pipe of the present invention can be manufactured by continuously forming a steel sheet subjected to the rolling process as described above by roll forming. Here, it does not specifically limit as a pipe making welding method, Well-known methods, such as high frequency welding, TIG welding, and laser welding, can be used. Here, the steel pipe outer diameter D and the steel pipe wall thickness t in the ERW steel pipe of the present invention may be appropriately adjusted according to the use etc., but when used for a hollow stabilizer, the steel pipe outer diameter D is 10 to 45 mm, The steel pipe wall thickness t is preferably 1 to 7 mm.
Since the ERW steel pipe of the present invention thus manufactured does not need to be reduced in diameter, it can be manufactured with high productivity while suppressing the manufacturing cost.
以下、実施例により本発明を詳細に説明するが、これらによって本発明が限定されるものではない。
表１及び２の化学組成（ただし、残部は、Ｆｅ及び不可避的不純物からなる）をもつ各鋼を転炉で出鋼し、連続鋳造法でスラブとした後、表１及び２の条件にて熱間圧延を施し、板厚６ｍｍの熱延鋼板を作製した。次に、熱延鋼板を酸洗した後、幅８０ｍｍのスリットコイルとし、高周波溶接方法にて溶接することで鋼管外径２８．６ｍｍ、鋼管肉厚６ｍｍの電縫鋼管を製造した。
EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by these.
Each steel having the chemical composition shown in Tables 1 and 2 (with the balance consisting of Fe and inevitable impurities) is produced in a converter and made into a slab by a continuous casting method. Hot rolling was performed to produce a hot-rolled steel sheet having a thickness of 6 mm. Next, after pickling the hot-rolled steel sheet, a slit coil having a width of 80 mm was formed and welded by a high-frequency welding method to produce an electric-welded steel pipe having a steel pipe outer diameter of 28.6 mm and a steel pipe wall thickness of 6 mm.
得られた電縫鋼管について以下の評価を行った。
（１）曲げ加工性
曲げ加工性は、電縫鋼管を長さ５００ｍｍに切り出した後、曲げ半径２ＤＲ(Ｄ＝鋼管外径)にて回転引き曲げを行い、種々の観点から評価した。この評価において、曲げ部の外径減少率が５％未満で割れがない場合を評価点５、曲げ部の外径減少率が５〜１０％で割れがない場合を評価点４、曲げ部の外径減少率が１０％を超える場合を評価点３、割れが発生した場合を評価点２、破断した場合を評価点１として５段階評価で表した。
（２）引張伸び
引張伸びは、ＪＩＳ Ｚ ２２０１に定める１１号試験片を用い、引張試験により評価した。
The following evaluation was performed about the obtained ERW steel pipe.
(1) Bending workability Bending workability was evaluated from various viewpoints by cutting an ERW steel pipe into a length of 500 mm and then rotating and bending it with a bending radius of 2DR (D = outer diameter of steel pipe). In this evaluation, when the outer diameter reduction rate of the bent portion is less than 5% and there is no crack, the evaluation point is 5, and when the outer diameter reduction rate of the bent portion is 5 to 10% and there is no crack, the evaluation point is 4. When the outer diameter reduction rate exceeds 10%, the evaluation score is 3, the evaluation is 2 when the crack is generated, and the evaluation is 1 when the fracture occurs.
(2) Tensile elongation Tensile elongation was evaluated by a tensile test using No. 11 test piece defined in JIS Z 2201.
次に、調質熱処理後の電縫鋼管の疲労特性を調査するため、電縫鋼管に焼入れ焼戻しを行い、この電縫鋼管における溶接ビード部及び母材部の硬さ、並びに耐久性について評価した。ここで、焼入れは、電縫鋼管を、通電加熱方法を用いて１１００℃まで加熱した後、水冷槽に浸漬して冷却することにより行った。また、焼戻しは、均熱温度３５０℃、均熱時間３０分の条件下で行った。
硬さ及び耐久性については以下のようにして評価した。
（３）硬さ（ＨＶ）
硬さ（ＨＶ）は、溶接ビード部及び母材部において、ビッカース硬さ試験機を用い、試験荷重を５００ｇとして評価した。また、溶接ビード部の焼戻し硬さが低下しているか否かを確認するために、母材部のビッカース硬さ（ＨＶ）と溶接ビード部のビッカース硬さ（ＨＶ）との差ΔＨＶを計算により求めた。
（４）耐久性
耐久性は、ねじり試験により、電縫鋼管に付与する応力を７００ＭＰａとして疲労破壊の起点を評価した。この評価において、溶接ビードを起点として疲労破壊しなければ疲労特性として良好であると判断した。
上記（１）〜（４）の評価結果について表３に示す。
Next, in order to investigate the fatigue characteristics of the ERW steel pipe after the tempering heat treatment, the ERW steel pipe was quenched and tempered, and the hardness and durability of the weld bead part and the base metal part in this ERW steel pipe were evaluated. . Here, quenching was performed by heating the ERW steel pipe to 1100 ° C. using an electric heating method and then cooling it by immersing it in a water-cooled tank. The tempering was performed under conditions of a soaking temperature of 350 ° C. and a soaking time of 30 minutes.
Hardness and durability were evaluated as follows.
(3) Hardness (HV)
Hardness (HV) was evaluated using a Vickers hardness tester at a weld bead portion and a base metal portion, with a test load of 500 g. Further, in order to confirm whether or not the tempering hardness of the weld bead portion is reduced, the difference ΔHV between the Vickers hardness (HV) of the base metal portion and the Vickers hardness (HV) of the weld bead portion is calculated. Asked.
(4) Durability Durability was evaluated by a torsion test, with the stress applied to the ERW steel pipe being 700 MPa. In this evaluation, it was judged that the fatigue characteristics were good unless fatigue fracture occurred from the weld bead.
It shows in Table 3 about the evaluation result of said (1)-(4).
表３に示されるように、本発明例（鋼種１〜２５）の電縫鋼管では、優れた曲げ加工性及び引張伸びを示した。また、本発明例の電縫鋼管では、焼入れ焼戻し後の溶接ビード部と母材部との間の硬度差が３０以下と小さく、溶接ビード部及び母材部の両方が安定して高い焼戻し硬さを示した。さらに、本発明例の電縫鋼管では、溶接ビード部が疲労破壊の起点とならず、調質熱処理後に優れた疲労特性を示した。
一方、比較例（鋼種２６〜３６）では、曲げ加工性及び引張伸びが悪いか、又は焼入れ焼戻し後の溶接ビード部と母材部との間の硬度差（ΔＨＶ）が大きく、溶接ビード部が疲労破壊の起点となった。特に、本発明の電縫鋼管における各成分の含有量を満足していても、Ｘ値が所定の範囲外であると、曲げ加工性が悪いことが鋼種３２及び３３の結果からわかる。また、本発明の電縫鋼管における各成分の含有量を満足していても、Ｙ値が所定の範囲外であると、焼入れ焼戻し後の溶接ビード部と母材部との間の硬度差（ΔＨＶ）が大きく、溶接ビード部が疲労破壊の起点となることが鋼種３１の結果からわかる。
As shown in Table 3, the ERW steel pipes of the present invention examples (
On the other hand, in comparative examples (steel types 26 to 36), bending workability and tensile elongation are poor, or the hardness difference (ΔHV) between the weld bead portion and the base metal portion after quenching and tempering is large, and the weld bead portion is It became the starting point of fatigue failure. In particular, even when the content of each component in the ERW steel pipe of the present invention is satisfied, it can be seen from the results of the steel types 32 and 33 that the bending workability is poor when the X value is outside the predetermined range. In addition, even if the content of each component in the ERW steel pipe of the present invention is satisfied, if the Y value is out of the predetermined range, the hardness difference between the weld bead part after quenching and tempering and the base material part ( It can be seen from the results for steel grade 31 that ΔHV) is large and the weld bead is the starting point for fatigue failure.
次に、上記結果を基に、曲げ加工性の評価点とＸ値との関係を図１に、曲げ加工性の評価点と引張伸びとの関係を図２に、溶接ビード部と母材部との間の硬度差（ΔＨＶ）とＹ値との関係を図３に示す。
図１に示されるように、Ｘ値が８未満であると、曲げ加工性の評価点が４以上（すなわち、曲げ部の外径減少率が１０％以下で割れがないもの）となり、曲げ加工性が向上する。一方、Ｘ値が８以上であると、曲げ加工性の評価点が３以下（すなわち、曲げ部の外径減少率が１０％を超えるか、割れや破断が生じるもの）となり、曲げ加工性が低下する。
図２に示されるように、引張伸びが２４％以上であると、曲げ加工性の評価点が４以上（すなわち、曲げ部の外径減少率が１０％以下で割れがないもの）となり、特に、引張伸びが２８％以上であると、曲げ加工性の評価点が５（すなわち、曲げ部の外径減少率が５％未満で割れがないもの）となり、曲げ加工性が向上する。一方、引張伸びが２４％未満であると、曲げ加工性の評価点が３以下（すなわち、曲げ部の外径減少率が１０％を超えるか、割れや破断が生じるもの）となり、曲げ加工性が低下する。
図３に示されるように、Ｙ値が３００よりも大きいと、溶接ビード部と母材部との間の硬度差（ΔＨＶ）が３０以下となり、溶接ビード部及び母材部の両方が安定して高い焼戻し硬さを示し、溶接ビード部が疲労破壊の起点とならなくなる。一方、Ｙ値が３００以下であると、溶接ビード部と母材部との間の硬度差（ΔＨＶ）が大きくなり、溶接ビード部を起点とする疲労破壊が生じる。
以上の結果からわかるように、本発明の電縫鋼管は、製造コストを抑えつつ生産性良く製造し得ると共に、加工性及び調質熱処理後の疲労特性に優れている。
Next, based on the above results, the relationship between the evaluation point of bending workability and the X value is shown in FIG. 1, the relationship between the evaluation point of bending workability and tensile elongation is shown in FIG. 2, and the weld bead portion and the base material portion. FIG. 3 shows the relationship between the hardness difference (ΔHV) and the Y value.
As shown in FIG. 1, when the X value is less than 8, the evaluation point of bending workability is 4 or more (that is, the outer diameter reduction rate of the bent portion is 10% or less and there is no crack), and bending work is performed. Improves. On the other hand, when the X value is 8 or more, the evaluation point of bending workability is 3 or less (that is, the outer diameter reduction rate of the bent portion exceeds 10%, or cracking or breaking occurs), and the bending workability is improved. descend.
As shown in FIG. 2, when the tensile elongation is 24% or more, the evaluation point of bending workability is 4 or more (that is, the outer diameter reduction rate of the bent portion is 10% or less and there is no crack). When the tensile elongation is 28% or more, the evaluation point of bending workability is 5 (that is, the outer diameter reduction rate of the bent portion is less than 5% and there is no crack), and the bending workability is improved. On the other hand, if the tensile elongation is less than 24%, the evaluation point of bending workability becomes 3 or less (that is, the outer diameter reduction rate of the bending part exceeds 10%, or cracking or breaking occurs), and the bending workability. Decreases.
As shown in FIG. 3, when the Y value is larger than 300, the hardness difference (ΔHV) between the weld bead part and the base metal part becomes 30 or less, and both the weld bead part and the base metal part are stabilized. High tempering hardness, and the weld bead becomes the starting point of fatigue failure. On the other hand, if the Y value is 300 or less, the hardness difference (ΔHV) between the weld bead portion and the base metal portion becomes large, and fatigue failure starts from the weld bead portion.
As can be seen from the above results, the electric resistance welded steel pipe of the present invention can be manufactured with high productivity while suppressing the manufacturing cost, and is excellent in workability and fatigue characteristics after tempering heat treatment.
Claims (3)
Ｘ＝３Ｃ＋１．５Ｍｎ＋２Ｃｒ＋１２０Ｓ＋９０Ｔｉ
Ｙ＝２０Ｃ＋２５０Ｍｎ＋３５Ｃｒ＋３５０Ｂ C: 0.15-0.30 mass%, Si: 0.30 mass% or less, Mn: 1.0-2.0 mass%, P: 0.030 mass% or less, S: 0.010 mass% or less Cr: 0.2-1.5% by mass, Ti: 0.005-0.03% by mass, sol. Al: 0.005 to 0.10% by mass, N: 0.010% by mass or less, and B: 0.0010 to 0.0070% by mass, with the balance being Fe and inevitable impurities, An electric resistance welded steel pipe having a chemical composition satisfying X <8 and Y> 300, respectively, and having a mixed structure of ferrite and pearlite or a mixed structure of ferrite and cementite .
X = 3C + 1.5Mn + 2Cr + 120S + 90Ti
Y = 20C + 250Mn + 35Cr + 350B
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2008034807A JP2009191330A (en) | 2008-02-15 | 2008-02-15 | Electric resistance steel tube |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2008034807A JP2009191330A (en) | 2008-02-15 | 2008-02-15 | Electric resistance steel tube |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JP2009191330A true JP2009191330A (en) | 2009-08-27 |
Family
ID=41073615
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2008034807A Pending JP2009191330A (en) | 2008-02-15 | 2008-02-15 | Electric resistance steel tube |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2009191330A (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011021510A1 (en) | 2009-08-20 | 2011-02-24 | シャープ株式会社 | Display device |
| KR101359141B1 (en) * | 2009-12-29 | 2014-02-05 | 주식회사 포스코 | Welded steel pipe for automobile and manufacturing method of the same |
| EP2952601A4 (en) * | 2013-01-31 | 2016-02-17 | Jfe Steel Corp | Electric-resistance-welded steel pipe |
| JP2019131842A (en) * | 2018-01-29 | 2019-08-08 | 日鉄日新製鋼株式会社 | Steel pipe |
| WO2020003720A1 (en) * | 2018-06-27 | 2020-01-02 | Ｊｆｅスチール株式会社 | Electric-resistance-welded steel pipe for producing hollow stabilizer, hollow stabilizer, and method for producing same |
| JP2022510381A (en) * | 2019-05-21 | 2022-01-26 | サムウォンスティール カンパニー，リミテッド | A steel material for springs to omit the tempering process and a spring manufacturing method using this steel material |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6013025A (en) * | 1983-07-05 | 1985-01-23 | Nippon Steel Corp | Production of electric welded steel pipe having low yield point and high strength |
| JP2003193198A (en) * | 2001-12-26 | 2003-07-09 | Sumitomo Pipe & Tube Co Ltd | Electric resistance welded tube for machine structure and heat treatment method therefor |
| JP2005076047A (en) * | 2003-08-28 | 2005-03-24 | Jfe Steel Kk | Method for manufacturing hollow stabilizer superior in fatigue resistance |
-
2008
- 2008-02-15 JP JP2008034807A patent/JP2009191330A/en active Pending
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6013025A (en) * | 1983-07-05 | 1985-01-23 | Nippon Steel Corp | Production of electric welded steel pipe having low yield point and high strength |
| JP2003193198A (en) * | 2001-12-26 | 2003-07-09 | Sumitomo Pipe & Tube Co Ltd | Electric resistance welded tube for machine structure and heat treatment method therefor |
| JP2005076047A (en) * | 2003-08-28 | 2005-03-24 | Jfe Steel Kk | Method for manufacturing hollow stabilizer superior in fatigue resistance |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011021510A1 (en) | 2009-08-20 | 2011-02-24 | シャープ株式会社 | Display device |
| KR101359141B1 (en) * | 2009-12-29 | 2014-02-05 | 주식회사 포스코 | Welded steel pipe for automobile and manufacturing method of the same |
| EP2952601A4 (en) * | 2013-01-31 | 2016-02-17 | Jfe Steel Corp | Electric-resistance-welded steel pipe |
| JP2019131842A (en) * | 2018-01-29 | 2019-08-08 | 日鉄日新製鋼株式会社 | Steel pipe |
| WO2020003720A1 (en) * | 2018-06-27 | 2020-01-02 | Ｊｆｅスチール株式会社 | Electric-resistance-welded steel pipe for producing hollow stabilizer, hollow stabilizer, and method for producing same |
| JPWO2020003720A1 (en) * | 2018-06-27 | 2020-07-02 | Ｊｆｅスチール株式会社 | ERW steel pipe for manufacturing hollow stabilizers, hollow stabilizers, and manufacturing methods thereof |
| JP2022510381A (en) * | 2019-05-21 | 2022-01-26 | サムウォンスティール カンパニー，リミテッド | A steel material for springs to omit the tempering process and a spring manufacturing method using this steel material |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP6465249B2 (en) | ERW steel pipe for high-strength thin-walled hollow stabilizer and method for manufacturing the same | |
| JP6225026B2 (en) | Hollow stabilizer, steel pipe for hollow stabilizer and method for producing the same | |
| KR101321681B1 (en) | Hollow member and method for manufacturing same | |
| JP6452454B2 (en) | Rolled material for high strength spring and wire for high strength spring | |
| JP4381355B2 (en) | Steel having excellent delayed fracture resistance and tensile strength of 1600 MPa class or more and method for producing the molded product thereof | |
| JP6212473B2 (en) | Rolled material for high-strength spring and high-strength spring wire using the same | |
| JP2008202124A (en) | Steel wire for high-strength spring, high-strength spring and method for manufacturing them | |
| JP6065120B2 (en) | High carbon hot rolled steel sheet and manufacturing method thereof | |
| JP6065121B2 (en) | High carbon hot rolled steel sheet and manufacturing method thereof | |
| JP2009191330A (en) | Electric resistance steel tube | |
| JP4859240B2 (en) | Manufacturing method of ERW steel pipe for hollow stabilizer | |
| JPH11236644A (en) | Steel for induction hardening excellent in high strength characteristic and low heat treating strain characteristic and its production | |
| JP6034605B2 (en) | Boron-added steel for high strength bolts and high strength bolts with excellent delayed fracture resistance | |
| JP6796472B2 (en) | Hollow member and its manufacturing method | |
| JP2009235499A (en) | Method for manufacturing hollow stabilizer | |
| JP4728884B2 (en) | Induction contour hardened steel and induction contour hardened parts with excellent low cycle fatigue characteristics | |
| JP4500246B2 (en) | Steel pipe for machine structural member and manufacturing method thereof | |
| JP6747623B1 (en) | ERW steel pipe | |
| JP4828321B2 (en) | Induction hardened steel and induction hardened parts with excellent low cycle fatigue properties | |
| JP7229827B2 (en) | Manufacturing method of high carbon steel sheet | |
| JP5505264B2 (en) | Induction contour hardened steel and induction contour hardened parts with excellent low cycle fatigue characteristics | |
| JP2006265703A (en) | Steel for case hardening having excellent crystal grain coarsening resistance and cold workability and method for producing the same | |
| JPH10259447A (en) | Steel plate for drive plate excellent in form-rollability | |
| JP5633426B2 (en) | Steel for heat treatment | |
| JP2005220415A (en) | Method for producing b-added low alloy steel showing excellent toughness as quenched state |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Effective date: 20110214 Free format text: JAPANESE INTERMEDIATE CODE: A621 |
|
| A711 | Notification of change in applicant |
Effective date: 20110516 Free format text: JAPANESE INTERMEDIATE CODE: A711 |
|
| A521 | Written amendment |
Effective date: 20110516 Free format text: JAPANESE INTERMEDIATE CODE: A821 |
|
| A977 | Report on retrieval |
Effective date: 20121228 Free format text: JAPANESE INTERMEDIATE CODE: A971007 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20130115 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20130314 |
|
| A02 | Decision of refusal |
Effective date: 20130514 Free format text: JAPANESE INTERMEDIATE CODE: A02 |