JP2004099951A - Steel sheet and electric resistance welded tube each having excellent corrosion resistance and used for fuel oil filler tube - Google Patents
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Abstract
Description
【０００１】
本発明は、ガソリンあるいはメタノール含有ガソリン等の燃料を供給する給油管の製造に適した鋼板および電縫鋼管に関する。
【０００２】
【従来の技術】
自動車等の燃料タンクの部品である燃料給油管に用いられる鋼管には、耐食性に優れたＺｎ系溶融めっき鋼板を素材とした電縫鋼管が広く用いられている。
近年、給油時のガソリンの蒸散防止や軽量化等を目的として、給油管は小径化される傾向にある。しかしながら給油機の寸法の関係から、給油口の口径は従来と変わっていない。このため、給油管本体の口径に対する給油口の口径の比率は大きくなる傾向にある。給油口はポンチ加工，張出し加工，バルジ加工等で電縫鋼管の管端を拡開することにより形成されるが、上記のように口径の比率が大きくなると、その他のフレア加工などを含めて、電縫鋼管に付与される加工歪みは、ますます大きくなる。このため、給油管用電縫鋼管には優れた拡管性が要求される。一般的に、拡管成形時に、鋼管の電縫溶接部近傍の欠陥を起点に割れが発生しやすいので、拡管性の更なる向上が求められている。
【０００３】
一方、給油管は、成型加工後に燃料タンクと溶接接合されるとともに、給油口のリテーナやブリーザーチューブ等、他の部品とも、溶接やろう付けによって接合されている。これらの他の部品との溶接接合において、接合部近傍に割れが生じやすい。特に、拡管等の加工条件が厳しくなった部分に溶接加工等が加わると、割れが著しく発生しやすくなる。このため、拡管等の成形加工の際に厳しい条件の成型加工が施された状態で溶接加工性に優れた給油管用電縫鋼管が求められている。
【０００４】
【発明が解決しようとする課題】
拡管成形において割れを生じた電縫鋼管の電縫溶接部近傍を詳細に調べたところ、溶接熱影響部ＨＡＺに微小なクラックが生成しており、このクラックを起点にして拡管成形時に大きな割れに進展することで、拡管性の低下を招いていることがわかった。また、上記微細クラックは結晶粒界に沿ったものであった。さらに、溶接加工において生じた給油管の割れを詳細に調べたところ、割れは熱影響部ＨＡＺに生成しており、また、粒界に沿った割れであった。
これらの現象から、拡管時の割れは、造管時の引張応力下において電縫溶接の熱で溶融したＺｎ金属が鋼管表面に接触し、結晶粒界に浸透することで生じ発展したものであり、溶接時の割れは、拡管等の厳しい加工で生じた引張残留応力下において溶接等の熱で溶融したＺｎ金属が鋼管表面に接触し、結晶粒界に浸透することで生じたもので、いずれも溶融金属脆化によるものと判断される。
【０００５】
以上の知見から、給油管用鋼管としては、まず電縫溶接時に溶融Ｚｎによる溶融金属脆化に対する抵抗のある素材鋼板を用いて優れた拡管性を有する電縫鋼管を得る必要があり、さらに拡管した後の溶接加工時に溶融Ｚｎによる溶融金属脆化に対する抵抗のある電縫鋼管を得る必要があることがわかる。
川崎製鉄技報２５（１９９３）ｐ２０には、溶融金属脆化を防止するために、低合金成分化や軟質化が有効であると紹介されている。しかしながら、給油管用鋼管には優れた加工性が要求されており、元々、加工性が良く、焼入れ性も低い鋼板が使用されている。このような鋼板を使用しても電縫溶接時に溶融金属脆化によるクラックが生成していることを考え合わせると、前記川崎技報で紹介されている低合金成分化や、Ｐ，Ｓ，Ｔｉ，Ｚｒ添加といった対応だけでは、給油管用鋼管の素材としては不十分である。
また、本出願人は、特開２００２−１１５７９３号公報で、Ｚｎ−Ａｌ−Ｍｇ合金めっき鋼板を素材とした電縫鋼管の溶接熱影響部に、溶融金属脆化に起因した割れが発生することを防止する技術に関する提案を行ったが、この技術は溶接手法を改良しようとするものであって、めっき原板そのものの改質までは検討していない。
本発明は、このような問題を解消すべく案出されたものであり、溶融Ｚｎによる溶融金属脆化を抑制することができる給油管用めっき電縫鋼管の素材を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明の耐食性に優れた燃料給油管用鋼板は、その目的を達成するため、質量％で、Ｃ：０．０００５〜０．１％，Ｓｉ：０．１％以下，Ｍｎ：０．０５〜２．０％，Ｐ：０．１％以下，Ｓ：０．０３％以下，Ｎ：０．０５％以下，ｓｏｌＡｌ：０．１％以下，Ｔｉ：０〜０．１０％（０％を含む）を含み、さらにＮ％≧１４／４８×Ｔｉ％、またはＴｉ％＝０の場合、［Ｂ］％＝Ｂ％−１１／１４（Ｎ％−１４／４８×Ｔｉ％）で、Ｎ％＜１４／４８×Ｔｉ％の場合、［Ｂ］％＝Ｂ％で表される有効Ｂ量［Ｂ］％が、［Ｂ］：０．０００１〜０．００８０％となるＢを含有し、残部が実質的にＦｅからなる鋼板を下地とし、その表面にＺｎ系溶融めっきが施されていることを特徴とする。
また、本発明の耐食性に優れた燃料給油管用電縫鋼管は、前記成分組成を有する鋼板を下地とし、その表面にＺｎ系溶融めっきが施されているめっき鋼板を素材として造管されていることを特徴とする。
【０００７】
【作用】
溶融金属脆化の現象による割れついて、これまでに多くの例が知られている。例えば、溶接加工した鋼材を溶融Ｚｎ浴に浸漬して溶融Ｚｎめっきを施す際に発生する熱溶融部ＨＡＺの割れなどがそれである。
溶融金属脆化の現象を防ぐための鋼材側の対策としては、▲１▼焼入れ性を抑制し、γ旧粒界を残さない、▲２▼粒界の脆化因子を取り除く、▲３▼粒界の結合力を上昇させる、▲４▼粒内・粒界の硬度差をなくして材料を軟質化する、▲５▼Ｚｎの粒界浸入を防ぐ、ことなどが知られている。
本発明者等は、Ｚｎ系溶融めっき鋼板を素材として電縫溶接した鋼管の熱影響部の溶融金属脆化と、電縫鋼管を拡管した後の溶接時の溶融金属脆化のメカニズムについて検討した。
【０００８】
その結果、Ｚｎ系溶融めっき鋼板を素材として電縫溶接した鋼管を拡管成形する際に熱影響部に発生する割れや、当該電縫鋼管を拡管した後の溶接接合時に発生する割れは、材料の強度の弱い部分で発生、進展していることがわかった。特に、粒界は界面エネルギーが高くなった部分であり、エネルギー的に不安定な部分であるので、粒界で割れが発生、進展しやすい。
Ｂは、粒界に偏析することによって界面エネルギーを下げ、エネルギー的に安定化させる効果があると考えられている。また、さらに粒界に集まったＢは、溶融状態のめっき金属が粒界を浸透していくのを防ぐ効果もあると考えられる。これらのことから、結果として、Ｂは粒界の結合力を高めるものと推定される。したがって、鋼中に適正量のＢを含有させることによって、溶融金属脆化を抑制できるものと考えられる。一方、過剰のＢは、鉄の硼化物等を形成して加工性を低下させる。特に拡管成形のような厳しい加工では、割れ発生の起点となる。
以上のことから、Ｂ含有量を調整することにより、耐溶融金属脆化性に優れ、かつ、拡管加工性にも優れた鋼板を得ることができることがわかった。
【０００９】
以下に、本発明のＺｎ系溶融めっき用下地鋼板の成分組成について説明する。なお、「％」表示は、いずれも「質量％」を示す。
Ｃ：０．０００５〜０．１％
Ｃは、材料強度を上昇させる作用を有している。しかしながら、過剰の含有は、炭化物を形成して延性を低下させるとともに、強度も上昇させて、結果的に溶融金属脆化を促進させることにもなる。したがって、Ｃ含有量は、０．０００５〜０．１％の範囲とする。
Ｓｉ：０．１％以下
Ｓｉは、固溶して強度を向上させるのに有効であるが、めっき性が低下する。したがってＳｉ含有量は０．１％以下とする。
【００１０】
Ｍｎ：０．０５〜２．０％
Ｍｎは、Ｓ起因の脆化を防止するとともに、強度向上に有効な元素である。しかしながら、過剰に含有させると加工性や溶接性を低下させたり、鋼材表面に濃化してめっき性に悪影響を及ぼす。したがって、Ｍｎ含有量は０．０５〜２．０％の範囲とする。
Ｐ：０．１％以下
Ｐは、延性に悪影響を及ぼすので、高加工性が要求される用途では少なくする必要がある。ただし、固溶して強度を上昇させる作用を有しているので、加工性やめっき性に悪影響を及ぼさない範囲内で含有させても良い。その上限は０．１％である。
【００１１】
Ｓ：０．０３％以下
Ｓは、熱間脆化の原因となり、加工性，耐食性を低下させる有害成分である。製造コストが許す限り、その含有量は少なくすべきで、本発明では０．０３％以下に規制する。
【００１２】
Ｎ：０．０５％以下
Ｎは、強度を上昇させる作用を有しているが、過剰に含有させると加工性を低下させるので低い方が好ましい。また、Ｂと結合して、耐溶融金属脆化性にとって有効なＢの有効量を減少させ、耐溶融金属脆化性を低下させることにもなるので低い方が好ましい。以上のことから、Ｎ含有量は０．０５％以下に限定する。
【００１３】
ｓｏｌ．Ａｌ：０．１％以下
Ａｌは、製鋼時に脱酸剤として有効である。しかしながら、過剰の添加は、鋼中に非金属介在物が増加し、加工性やめっき性を低下させることになる。したがって、その上限は、０．１％とする。
Ｔｉ：０〜０．１０％（０％を含む）
Ｔｉは、下地鋼の合金成分であるＣやＮを固定して成形性を改善する作用を有する。さらに、有効Ｂ量も確保できる。また、Ｔｉ添加により、下地鋼の結晶粒が微細化されて溶融金属脆化割れが低減される。しかし過剰の添加は、製造コスト上昇とともに、加工性の低下を招く。したがって、Ｔｉの含有量は０〜０．１０％とする（０％を含む）。
［Ｂ］：０．０００１〜０．００８０％
Ｂは、結晶粒界の結合力を高めて、溶融金属脆化の抑制に有効な合金成分で、本発明で最も重要な成分である。
Ｂは、鋼中のＮと結合してＢＮを形成してしまうと、溶融金属脆化の抑制効果がなくなる。一方、Ｔｉを含有している場合、鋼中のＮはＴｉによって固定されてＴｉＮとなり、その分、ＢＮの形成を抑制することができる。したがって、溶融金属脆化抑制に有効なＢ量［Ｂ］％は、鋼中Ｂ，Ｔｉ，およびＮ量によって、以下の式で表すことができる。
Ｎ％≧１４／４８×Ｔｉ％、または、Ｔｉ％＝０の場合、
［Ｂ］％＝Ｂ％−１１／１４（Ｎ％−１４／４８×Ｔｉ％）
Ｎ％＜１４／４８×Ｔｉ％の場合、
［Ｂ］％＝Ｂ％
溶融金属脆化抑制には、０．０００１％以上の［Ｂ］％が必要である。しかしながら過剰のＢは、鉄の硼化物等を形成して加工性を低下させることになるので、［Ｂ］％の上限は０．００８０％とする。
なお、上記式中、１４／４８×Ｔｉ％の項は、ＴｉＮの生成に消費されるＮ量で、Ｔｉ含有量とＴｉ，Ｎの原子量比から計算されるものである。また、１１／１４（Ｎ％−１４／４８×Ｔｉ％）の項は、ＢＮの生成に消費されるＢ量に関するものである。
【００１４】
上記のような成分組成を有する鋼板を下地にし、従来から行われているＺｎ系の溶融めっき，Ｚｎ−Ａｌ系の溶融めっきあるいはＺｎ−Ａｌ−Ｍｇ系の溶融めっきを施しためっき鋼板を得る。この鋼板を素材として、従来の高周波溶接法で造管すれば、所望特性を有する燃料給油管用電縫鋼管が得られる。
【００１５】
【実施例】
実施例１：
表１に示す化学成分をもった鋼を真空溶解にて溶製し、連続鋳造，熱間圧延，冷間圧延を経て、板厚１ｍｍの冷延板とした。この冷延板を７５０〜８００℃で３０秒還元焼鈍した後、Ｚｎ−６．４％Ａｌ−３．１％Ｍｇ合金めっき浴に浸漬して、めっき付着量９０ｇ／ｍ２のめっき鋼板を得た。得られためっき鋼板を用いて外径２５．４ｍｍの管を造管した。
拡管試験を下記の方法によって行った。造管した素管を、テーパー角１５度で外径３４．３，４１．９，４７．０，４９．５および５２．１ｍｍのポンチを順次用い、室温にて加工速度２００ｍｍ／分で拡管した。拡管率は、拡管率（％）＝｛（拡管後の直径）−（素管の直径）｝／（素管の直径）×１００で表されるが、上記ポンチを用いたときの各拡管率は、それぞれ３５．０，６５．０，８５．０，９４．０および１０５．１％であった。
それぞれの拡管率で拡管した後に、拡管部分の外見観察にて割れの有無を調査した。拡管試験は、各鋼種，各拡管率毎に４本の試験を行い、３本以上に割れがなかったものを合格とした。
【００１６】
試験結果を表１に併せて示す。なお、拡管試験の結果、その鋼種の最大の合格拡管率をＥｍａｘとした。
本発明鋼は、いずれもＥｍａｘ値が９４．９以上と、良好な拡管性を示していた。これに対してＢ１鋼はＣ含有量が多すぎたために、またＢ２，Ｂ４およびＢ５鋼はいずれも有効Ｂ量が少ないために、さらにＢ３鋼は逆に有効Ｂ量が多すぎたために、Ｅｍａｘ値が小さくなっており、拡管性が劣っていた。拡管率がＥｍａｘ値を超えていた拡管試験材では、溶融金属脆化によると思われる割れが発生していた。
【００１７】
実施例２：
実施例１と同様な方法により、表２に示す化学成分を有する冷延鋼板を原板とし、付着量９０ｇ／ｍ２のＺｎ−Ａｌ−Ｍｇ合金めっき鋼板を得た。得られためっき鋼板を用いて外径２５．４ｍｍの管を造管した。
そして造管した素管を、下記の方法で拡管した。すなわち、テーパー角１５度で外径３４．３，４１．９および４７．０ｍｍのポンチを順次用い、室温にて加工速度２００ｍｍ／分で拡管した。拡管率は、拡管率（％）＝｛（拡管後の直径）−（素管の直径）｝／（素管の直径）×１００で表されるが、上記ポンチを用いたときの各拡管率は、それぞれ３５．０，６５．０および８５．０％であった。
拡管後のパイプを、拡管部分端面の外周に沿ってアーク溶接にてビードオンを行った後、溶接部分の外見観察にて割れの有無を調査した。なお、溶接試験は、各鋼種，各拡管率毎に３本の試験を行なった。
【００１９】
試験結果を表２に併せて示す。
本発明鋼では、いずれも割れの発生はなかった。
これに対してＤ１およびＤ２鋼はいずれも有効Ｂ量が少ないために、またＤ３鋼はＣ含有量が多すぎたために、溶融金属脆化によると思われる割れが発生していた。さらに、Ｄ４鋼は、Ｂ量が過剰であったために加工性が悪く、円周溶接の前の拡管パイプに、拡管部分の外見観察にて割れの発生が認められた。
【００２０】
【発明の効果】
以上に説明したように、本発明によれば、Ｚｎ系溶融めっきが施されためっき鋼板を素材とし、電縫溶接され、さらに拡管加工されて燃料供給管として使用する際に、めっき原板として、Ｂ含有量を含有Ｎ量および含有Ｔｉ量との関係で調整して、適正量のＢを含有させたものを使用することにより、電縫溶接時や拡管加工時に、溶接熱影響部に発生しやすい溶融金属脆化に起因した割れや、拡管後燃料タンク等に溶接接合する際に発生しやすい溶融金属脆化に起因した割れの発生を抑制することが可能となった。
これにより、燃料供給管として、耐食性に優れるＺｎ系溶融めっき電縫鋼管を使用することができるので、信頼性と耐久性に優れた燃料供給管をコスト安く提供することが可能となった。[0001]
The present invention relates to a steel plate and an electric resistance welded steel pipe suitable for manufacturing a fuel supply pipe for supplying a fuel such as gasoline or gasoline containing methanol.
[0002]
[Prior art]
As a steel pipe used for a fuel supply pipe which is a component of a fuel tank of an automobile or the like, an electric resistance welded steel pipe made of a Zn-based hot-dip galvanized steel sheet having excellent corrosion resistance is widely used.
In recent years, oil supply pipes have tended to be reduced in diameter for the purpose of preventing gasoline transpiration and reducing weight during refueling. However, due to the size of the refueling machine, the diameter of the refueling port has not changed. For this reason, the ratio of the diameter of the oil supply port to the diameter of the oil supply pipe main body tends to increase. The refueling port is formed by expanding the pipe end of the ERW steel pipe by punching, overhanging, bulging, etc. However, if the diameter ratio increases as described above, The processing strain imparted to the ERW pipe becomes even greater. For this reason, excellent pipe expandability is required for the electric resistance welded steel pipe for the oil supply pipe. In general, at the time of pipe expansion forming, cracks tend to occur starting from a defect near an electric resistance welded portion of a steel pipe, so that further improvement in pipe expandability is required.
[0003]
On the other hand, the fuel filler pipe is welded and joined to the fuel tank after the molding process, and is also joined to other parts such as a fuel filler retainer and a breather tube by welding and brazing. In welding and joining with these other parts, cracks are likely to occur near the joint. In particular, when welding or the like is applied to a portion where the processing conditions such as pipe expansion are severe, cracks are easily generated. For this reason, an electric resistance welded steel pipe for an oil supply pipe which is excellent in welding workability in a state where molding processing under severe conditions is performed at the time of molding processing such as pipe expansion is demanded.
[0004]
[Problems to be solved by the invention]
A close examination of the vicinity of the ERW welded portion of the ERW steel pipe that had a crack in the expanded pipe forming revealed that minute cracks were formed in the weld heat affected zone HAZ. It has been found that progress has led to a decrease in expandability. The fine cracks were along the crystal grain boundaries. Further, when the cracks in the oil supply pipe generated in the welding process were examined in detail, the cracks were formed in the heat-affected zone HAZ and were along the grain boundaries.
From these phenomena, cracking at the time of pipe expansion was caused by Zn metal melted by the heat of ERW welding under the tensile stress at the time of pipe making coming into contact with the steel pipe surface and penetrating into the crystal grain boundaries and developing. Cracking during welding was caused by Zn metal melted by heat such as welding coming into contact with the steel pipe surface and penetrating into crystal grain boundaries under tensile residual stress generated by severe processing such as pipe expansion. Is also determined to be due to molten metal embrittlement.
[0005]
From the above findings, it is necessary to obtain an ERW steel pipe having excellent expandability by using a material steel sheet having resistance to molten metal embrittlement due to molten Zn during ERW welding as a steel pipe for oil supply pipe. It can be seen that it is necessary to obtain an electric resistance welded steel tube having resistance to molten metal embrittlement due to molten Zn at the time of subsequent welding.
Kawasaki Steel Technical Report 25 (1993) p20 states that low alloying and softening are effective in preventing molten metal embrittlement. However, excellent workability is required for a steel pipe for an oil supply pipe, and a steel sheet having good workability and low hardenability is originally used. Considering the fact that cracks due to molten metal embrittlement occur during ERW when using such a steel sheet, considering the low alloy composition introduced in the aforementioned Kawasaki Technical Bulletin, P, S, Ti The addition of Zr or Zr alone is not sufficient as a material for a steel pipe for an oil supply pipe.
In addition, the present applicant discloses in Japanese Patent Application Laid-Open No. 2002-115793 that cracks caused by molten metal embrittlement occur in a weld heat affected zone of an electric resistance welded steel pipe made of a Zn—Al—Mg alloy plated steel sheet. Although a proposal was made on a technique for preventing the occurrence of welding, this technique is intended to improve the welding method, and has not studied the modification of the original plate itself.
The present invention has been devised to solve such a problem, and an object of the present invention is to provide a material for a plated electric resistance welded steel pipe for an oil supply pipe that can suppress the embrittlement of molten metal due to molten Zn.
[0006]
[Means for Solving the Problems]
In order to achieve the object, the steel plate for fuel supply pipes excellent in corrosion resistance of the present invention is, in terms of mass%, C: 0.0005 to 0.1%, Si: 0.1% or less, and Mn: 0.05 to 2%. 0.0%, P: 0.1% or less, S: 0.03% or less, N: 0.05% or less, solAl: 0.1% or less, Ti: 0 to 0.10% (including 0%) When N% ≧ 14/48 × Ti% or Ti% = 0, [B]% = B% −11 / 14 (N% −14 / 48 × Ti%), and N% <14 In the case of / 48 × Ti%, the effective B amount [B]% expressed by [B]% = B% contains [B]: 0.0001 to 0.0080% of B, and the balance is substantially It is characterized in that a steel sheet made of Fe is used as a base and its surface is subjected to Zn-based hot-dip plating.
Further, the electric resistance welded steel pipe for a fuel supply pipe having excellent corrosion resistance of the present invention is formed by using a steel sheet having the above-described composition as a base, and using a plated steel sheet whose surface is subjected to Zn-based hot-dip plating as a raw material. It is characterized by the following.
[0007]
[Action]
Many examples of cracking due to the phenomenon of molten metal embrittlement have been known so far. For example, cracks in a hot-melt portion HAZ generated when a welded steel material is immersed in a molten Zn bath and subjected to hot-dip Zn plating.
As countermeasures on the steel side to prevent the phenomenon of molten metal embrittlement, (1) suppress hardenability, do not leave γ old grain boundaries, (2) remove embrittlement factors at grain boundaries, (3) grain It is known to increase the bonding force of the field, (4) soften the material by eliminating the hardness difference between the grains and the grain boundaries, and (5) prevent the penetration of Zn into the grain boundaries.
The present inventors studied the mechanism of molten metal embrittlement of the heat-affected zone of a steel tube welded by ERW using a Zn-based hot-dip coated steel sheet as a material and the mechanism of molten metal embrittlement during welding after expanding the ERW steel tube. .
[0008]
As a result, cracks that occur in the heat-affected zone when the ERW welded steel pipe is formed from a Zn-based hot-dip coated steel sheet as a material, and cracks that occur during welding and joining after the ERW steel pipe is expanded, It was found that it occurred and evolved in the weak part. In particular, the grain boundary is a portion where the interface energy is high and is a portion which is unstable in energy, so that cracks are easily generated and propagate at the grain boundary.
B is considered to have the effect of lowering the interface energy by segregating at the grain boundaries and stabilizing the energy. Further, it is considered that B further collected at the grain boundary has an effect of preventing the plated metal in a molten state from penetrating the grain boundary. From these facts, it is estimated that, as a result, B enhances the bonding force of the grain boundaries. Accordingly, it is considered that embrittlement of molten metal can be suppressed by including an appropriate amount of B in steel. On the other hand, excessive B forms iron borides and the like, thereby reducing workability. In particular, in severe processing such as pipe expansion, it becomes a starting point of crack generation.
From the above, it has been found that by adjusting the B content, it is possible to obtain a steel sheet that is excellent in the resistance to embrittlement of molten metal and that is also excellent in pipe expandability.
[0009]
Hereinafter, the composition of the Zn-based hot-dip galvanized steel sheet of the present invention will be described. In addition, all "%" display shows "mass%".
C: 0.0005 to 0.1%
C has the effect of increasing the material strength. However, an excessive content forms carbides and reduces ductility, and also increases strength, which in turn promotes molten metal embrittlement. Therefore, the C content is in the range of 0.0005 to 0.1%.
Si: 0.1% or less Si is effective for improving the strength by forming a solid solution, but reduces the plating property. Therefore, the Si content is set to 0.1% or less.
[0010]
Mn: 0.05-2.0%
Mn is an element that prevents embrittlement due to S and is effective for improving strength. However, if it is contained excessively, the workability and the weldability are reduced, or the steel is concentrated on the surface of the steel material to adversely affect the plating property. Therefore, the Mn content is in the range of 0.05 to 2.0%.
P: 0.1% or less P has an adverse effect on ductility, so it must be reduced in applications requiring high workability. However, since it has the effect of increasing the strength by solid solution, it may be contained within a range that does not adversely affect the workability and the plating property. The upper limit is 0.1%.
[0011]
S: 0.03% or less S is a harmful component that causes hot embrittlement and lowers workability and corrosion resistance. As far as the production cost permits, its content should be small, and in the present invention, it is regulated to 0.03% or less.
[0012]
N: 0.05% or less N has the effect of increasing the strength, but the N content is preferably as low as possible because the excessive content lowers the workability. Further, it is preferable that the amount of B is lower, because it combines with B to reduce the effective amount of B effective for molten metal embrittlement resistance and reduce the molten metal embrittlement resistance. From the above, the N content is limited to 0.05% or less.
[0013]
sol. Al: 0.1% or less Al is effective as a deoxidizing agent during steelmaking. However, excessive addition increases non-metallic inclusions in the steel, and reduces workability and plating properties. Therefore, the upper limit is set to 0.1%.
Ti: 0 to 0.10% (including 0%)
Ti has an effect of fixing C and N which are alloy components of the base steel and improving formability. Further, an effective B amount can be secured. Further, by the addition of Ti, the crystal grains of the base steel are refined, and the brittle crack of the molten metal is reduced. However, excessive addition causes an increase in production cost and a decrease in workability. Therefore, the content of Ti is set to 0 to 0.10% (including 0%).
[B]: 0.0001 to 0.0080%
B is an alloy component that increases the bonding strength of the crystal grain boundaries and is effective in suppressing the embrittlement of the molten metal, and is the most important component in the present invention.
When B combines with N in steel to form BN, the effect of suppressing molten metal embrittlement is lost. On the other hand, when Ti is contained, N in the steel is fixed by Ti to TiN, and the formation of BN can be suppressed accordingly. Therefore, the B content [B]% effective for suppressing molten metal embrittlement can be expressed by the following equation by the amounts of B, Ti, and N in steel.
When N% ≧ 14/48 × Ti% or Ti% = 0,
[B]% = B% -11 / 14 (N% -14 / 48 × Ti%)
When N% <14/48 × Ti%,
[B]% = B%
[B]% of 0.0001% or more is required for suppressing the embrittlement of molten metal. However, excessive B forms iron borides and the like, thereby reducing workability. Therefore, the upper limit of [B]% is made 0.0080%.
In the above equation, the term of 14/48 × Ti% is the amount of N consumed for the production of TiN, and is calculated from the Ti content and the atomic weight ratio of Ti and N. The term 11/14 (N% −14 / 48 × Ti%) relates to the amount of B consumed to generate BN.
[0014]
A steel sheet having the above-described composition is used as a base to obtain a plated steel sheet which has been subjected to conventional Zn-based hot-dip plating, Zn-Al-based hot-dip plating or Zn-Al-Mg-based hot-dip coating. If this steel plate is used as a raw material to form a pipe by a conventional high-frequency welding method, an ERW steel pipe for a fuel supply pipe having desired characteristics can be obtained.
[0015]
【Example】
Example 1
A steel having the chemical components shown in Table 1 was melted by vacuum melting, subjected to continuous casting, hot rolling, and cold rolling to obtain a cold-rolled sheet having a thickness of 1 mm. After the cold-rolled sheet was subjected to reduction annealing at 750 to 800 ° C. for 30 seconds, it was immersed in a Zn-6.4% Al-3.1% Mg alloy plating bath to obtain a plated steel sheet having a plating adhesion amount of 90 g / m 2. Was. A tube having an outer diameter of 25.4 mm was formed using the obtained plated steel sheet.
The pipe expansion test was performed by the following method. The tube thus formed was expanded at room temperature at a processing speed of 200 mm / min using a punch having a taper angle of 15 degrees and an outer diameter of 34.3, 41.9, 47.0, 49.5, and 52.1 mm. . The expansion rate is expressed by the expansion rate (%) = {(diameter after expansion) − (diameter of raw pipe)} / (diameter of raw pipe) × 100, and each expansion rate when using the punch described above. Was 35.0, 65.0, 85.0, 94.0 and 105.1%, respectively.
After expanding at each expansion ratio, the appearance of the expanded portion was inspected for cracks. In the pipe expansion test, four pipes were tested for each steel type and each pipe expansion rate, and those having no cracks in three or more pipes were judged as acceptable.
[0016]
The test results are shown in Table 1. As a result of tube expansion test was the maximum pass pipe expansion rate of the steel type and E max.
The present invention steel are all E max value and more than 94.9, indicating good expanded tube properties. On the other hand, the B1 steel had too much C content, the B2, B4 and B5 steels had too little effective B content, and the B3 steel had too much effective B content. The max value was small, and the expandability was poor. In the pipe expansion test material in which the pipe expansion ratio exceeded the Emax value, cracks which were considered to be caused by molten metal embrittlement occurred.
[0017]
Example 2:
In the same manner as in Example 1, a cold rolled steel sheet having the chemical components shown in Table 2 as the original plate, to obtain a Zn-Al-Mg alloy plated steel sheet of coating weight 90 g / m 2. A tube having an outer diameter of 25.4 mm was formed using the obtained plated steel sheet.
Then, the formed tube was expanded by the following method. That is, a punch having a taper angle of 15 degrees and outer diameters of 34.3, 41.9, and 47.0 mm was sequentially used, and the tube was expanded at a processing speed of 200 mm / min at room temperature. The expansion rate is expressed by the expansion rate (%) = {(diameter after expansion) − (diameter of raw pipe)} / (diameter of raw pipe) × 100, and each expansion rate when using the punch described above. Was 35.0, 65.0 and 85.0%, respectively.
After the expanded pipe was bead-on by arc welding along the outer circumference of the expanded pipe end face, the presence or absence of cracks was examined by observing the appearance of the welded part. In addition, three welding tests were performed for each steel type and each pipe expansion ratio.
[0019]
The test results are also shown in Table 2.
No cracking occurred in any of the steels of the present invention.
On the other hand, the D1 and D2 steels each had a small effective B content, and the D3 steel had an excessively high C content, so that cracks were thought to have been caused by molten metal embrittlement. Further, the D4 steel was inferior in workability due to the excessive amount of B, and cracks were observed in the expanded pipe before the circumferential welding in appearance observation of the expanded pipe.
[0020]
【The invention's effect】
As described above, according to the present invention, a zinc-based hot-dip plated steel sheet is used as a material, and is subjected to electric resistance welding and further expanded to be used as a fuel supply pipe. By adjusting the B content according to the relationship between the N content and the Ti content and using the one containing the proper amount of B, it is generated in the weld heat affected zone during electric resistance welding and pipe expansion. This makes it possible to suppress the occurrence of cracks caused by molten metal embrittlement that easily occurs and the occurrence of cracks caused by molten metal embrittlement that is likely to occur during welding and joining to a fuel tank or the like after pipe expansion.
As a result, a Zn-based hot-dip galvanized steel tube excellent in corrosion resistance can be used as the fuel supply pipe, so that a fuel supply pipe excellent in reliability and durability can be provided at low cost.
Claims (2)
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| JP2002261191A JP4126694B2 (en) | 2002-09-06 | 2002-09-06 | Steel plate and fuel-welded steel pipe for fuel supply pipes with excellent corrosion resistance |
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| JP2002261191A JP4126694B2 (en) | 2002-09-06 | 2002-09-06 | Steel plate and fuel-welded steel pipe for fuel supply pipes with excellent corrosion resistance |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006097129A (en) * | 2004-09-01 | 2006-04-13 | Nisshin Steel Co Ltd | Zn-al-mg alloy plated steel sheet having excellent hot dip metal embrittlement crack resistance |
| EP2407569A1 (en) * | 2009-03-10 | 2012-01-18 | Nisshin Steel Co., Ltd. | Zinc based alloy coated steel having superior resistance to liquid metal embrittlement and cracking |
| US11421294B2 (en) * | 2016-08-12 | 2022-08-23 | Posco | High strength steel sheet having excellent formability and manufacturing method thereof |
-
2002
- 2002-09-06 JP JP2002261191A patent/JP4126694B2/en not_active Expired - Fee Related
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006097129A (en) * | 2004-09-01 | 2006-04-13 | Nisshin Steel Co Ltd | Zn-al-mg alloy plated steel sheet having excellent hot dip metal embrittlement crack resistance |
| EP2407569A1 (en) * | 2009-03-10 | 2012-01-18 | Nisshin Steel Co., Ltd. | Zinc based alloy coated steel having superior resistance to liquid metal embrittlement and cracking |
| EP2407569A4 (en) * | 2009-03-10 | 2017-05-10 | Nisshin Steel Co., Ltd. | Zinc based alloy coated steel having superior resistance to liquid metal embrittlement and cracking |
| US11421294B2 (en) * | 2016-08-12 | 2022-08-23 | Posco | High strength steel sheet having excellent formability and manufacturing method thereof |
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| JP4126694B2 (en) | 2008-07-30 |
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