JP2004190086A - Resistance welded steel tube to be induction-hardened - Google Patents
Resistance welded steel tube to be induction-hardened Download PDFInfo
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【０００１】
【発明の属する技術分野】
この発明は、冷間成形加工後に高周波焼入れを施すことにより強度を上げて使用される鋼部品の素材となる高周波焼入れ用電気抵抗溶接鋼管に関し、例えば車両部品（自動車部品，二輪車部品，軌道車部品）用として好適な機械構造用電気抵抗溶接鋼管に関するものである。
【０００２】
【従来の技術】
近年、環境問題やエネルギ−問題等の観点から自動車車体等には厳しい軽量化対策が推し進められており、例えば自動車の足廻り部品等においてはその素材を棒綱から鋼管へ変換する状況に至っている。
このような自動車用部品（ラックバ−，ドライブシャフト，ステアリングシャフト，アクスルハウジング，ショックアブゾ−バ−，スタビライザ−，ドラッグリンク，タイロッド，バルブロッカ−シャフト等），自動二輪用部品（フロントフォ−ク等），自転車用部品，軌道車用部品，建設機械用部品，各種シリンダ−用部品，家具，その他の機械構造部品等の素材として用いられる機械構造用電気抵抗溶接鋼管（例えば電縫鋼管）は、一般に、目的とする部品形状への成形加工（冷間鍛造加工，転造，スウェ−ジング加工，プレス加工，曲げ加工，ハイドロフォ−ミング，爆発成形等）を施した後、高周波焼入れ処理による必要強度（硬度）の付与を行って使用に供している。
【０００３】
冷間成形加工後に高周波焼入れを施すことにより強度を上げて使用する鋼材では、焼入れによる十分な強度確保のためにＣ（炭素）の含有量を高くすることが必要であるが、Ｃ含有量が高くなると鋼材が硬くなって成形性が劣化するという問題があった。
【０００４】
なお、一般的に電気抵抗溶接鋼管の成形性を向上させるためにはＡｃ３変態点以上の温度で加熱・保持してから放冷する“焼きならし処理”が実施されるが、鋼の成分系によってはこの方法でも十分な成形性を得られない場合がある。
特に、高炭素綱を素材とする鋼管では上記焼きならし処理によっても十分な成形性を得られない場合が多く、そのため高炭素鋼の強度を低減する熱処理である球状化熱処理の適用が試みられてもいるが、この方法では熱処理工程に時間がかかり、そのため生産能率の面で著しい不利を伴う。その上、球状化熱処理を施した鋼材はＣがほぼ完全に球状化しているので、最終的に焼入れを実施する場合に焼きが入りにくいという問題や被削性が劣化するという問題があった。
【０００５】
例えば、特開２００１−１３１７０２号公報には、加工性に優れた冷間鍛造用電縫鋼管であるとして「Ｃ： ０．１〜 ０．５％（以降、 成分割合を表す％は質量％とする），Ｓｉ：０．０１〜 ０．５％，Ｍｎ： ０．１〜 ２．０％を含有すると共に、 必要に応じてＣｒ，Ｍｏ，Ｗ，Ｎｉ，Ｃｕ，Ｂ，Ｔｉ，Ｎｂ，Ｖ，Ｃａの１種以上をも含む化学組成の冷間鍛造用電縫鋼管」が開示されている。
しかし、この電縫鋼管は『組織中の炭化物で炭化物の占める割合が面積率にして３０％以下、 炭化物の球状化率が８０％以上で』としているように、球状化焼鈍による炭化物の球状化によって変形能に有害な層状炭化物を無くした鋼管であり、炭化物が球状化しているので材料の加工性は向上するが高周波焼入れ時に炭化物が固溶しにくく、そのため高周波焼入れによっては十分な強度を確保することができないので高周波焼入れ部品用としては不適当な材料であった。
【０００６】
ところで、特開２００１−３５５０４７号公報を見ると、冷間加工性と高周波焼入れ性に優れた高炭素電縫鋼管であるとして「Ｃ： ０．３〜 ０．８％，Ｓｉ：２％以下，Ｍｎ：３％以下を含有すると共に必要に応じてＣｒ，Ｍｏ，Ｗ，Ｎｉ，Ｃｕ，Ｂ，Ｔｉ，Ｎｂ，Ｖの１種以上をも含む電縫鋼管に、 温間での縮径圧延を施すことによってフェライト中に粒径が １．０μｍ以下のセメンタイトが微細分散した組織を有せしめて成る高炭素鋼管」が開示されている。
【０００７】
しかしながら、この鋼管は「Ｓｉ：２％以下，Ｍｎ：３％以下」と規定されているものの、その「実施例」欄や「添加量の説明」欄からも明らかなように焼入れ性を高めるために比較的高い添加量でＳｉ及びＭｎを含有させることを必要としたものである。そのため、高周波焼入れ前の材料強度が高くなるのを否めず、良好な加工性を確保するには温間｛（Ａｃ１変態点−５０℃）〜（Ａｃ１変態点）の温度域｝で縮径圧延を実施してフェライト中に粒径が １．０μｍ以下のセメンタイトが微細分散した組織を実現するという面倒な処理が不可欠となる。
【０００８】
その上、このような温間で縮径圧延を施すという処理だけでは電縫溶接部の硬化が残ってしまい、冷間成形加工用として満足できる材料であるとは言えなかった。
しかも、電縫溶接部の硬化を解消するためにＡｃ３変態点以上の温度域で後熱処理を実施すると、当該電縫鋼管ではその加工性が劣化してしまうという問題があった。
【０００９】
更に、この鋼管は「冷間加工性と高周波焼入れ性に優れた高炭素鋼管」であるとしているものの、その「実施例」欄の「表３−１」や「表３−２」からも確認できるように、高周波焼入れ性は「比較例（焼準）」の場合と同等か、むしろ「比較例（焼準）」の方が良好となる場合（製品管Ｎｏ．７と９、 １３と１５、 ３６と３８の比較）もあるので、必ずしも加工性と高周波焼入れ性が共に優れたものであるとは言い難かった。
【００１０】
【発明が解決しようとする課題】
このようなことから、本発明が目的としたのは、冷間加工時には良好な成形性を示すと共に、高周波焼入れにより車両部品等として満足できる高い強度を安定付与することができる高周波焼入れ用電気抵抗溶接鋼管の提供手段を確立することであった。
【００１１】
【課題を解決するための手段】
本発明者は、上記目的を達成すべく多くの試験を繰り返しながら研究を行った結果、次の知見を得ることができた。
ａ） 電気抵抗溶接鋼管を例えば車両部品に適用する場合には硬度でＨｖ５５０相当以上の強度が必要であり、焼入れによって鋼管にこのような高い強度を確保するためには相応量のＣを添加しなければならないが、Ｃ含有量が増量するにつれて鋼は硬くなって成形性は劣化し、焼入れ後の硬度Ｈｖ５５０以上が確保されるほどにＣ含有量を高めた場合には、焼入れ前の鋼管において、車両部品等への冷間成形を安定に実施できる“硬度Ｈｖ２００未満”の達成が困難となる。
【００１２】
ｂ） しかし、Ｃ含有量が比較的高い鋼材であっても、フェライト強化元素であるＳｉ，Ｍｎの含有量を抑制して鋼材の強度そのものを低減した場合には、“炭化物の球状化による強度低減”や“集合組織の調整によるｒ値の向上”に頼ることなく鋼材の成形性を改善することができる。
【００１３】
ｃ） なお、Ｍｎ含有量の低減はＭｎ偏析の抑制にもつながり、Ｍｎ偏析に起因した加工性（縮径，拡管等の加工性）の劣化はＭｎ含有量の低減によって顕著に軽減される。
即ち、熱間圧延鋼板を素材とした電気抵抗溶接鋼管（電縫溶接鋼管等）では、実用されている通常化学組成の機械構造用鋼材のものであるとフェライト強化元素であるＭｎの偏析が強く生じ、これによって加工性が劣化するだけでなく、Ｍｎ偏析はＣやＳｉの場合と比較すると高周波焼入れ時の加熱によっては拡散しにくいのでＭｎの負偏析部において局所的に焼入れ硬さが低下して高周波焼入れ後に硬さばらつきが発生し易い。なお、偏析を軽減するためには球状化焼鈍を施す必要があるが、球状化焼鈍を施したものはその後の焼入れ処理に“高周波焼入れ”を適用すると加熱が短時間であるので炭化物が完全に固溶せず、そのため焼入れ後に硬度低下が発生してしまう。
しかしながら、Ｍｎ含有量を低減すると、Ｍｎ偏析に起因した上記の問題が解決される上、溶接のままあるいは焼ならし後又は焼鈍後のフェライト＋パ−ライト組織でも軟質でかつ成形性に優れた鋼管が得られる。
【００１４】
ｄ） ところで、鋼材のＭｎ含有量を低減すると一般に焼入れ性が劣化するが、Ｂ添加あるいは必要により更にＣｒ添加をも実施することによってこの焼入れ性の低下を補償することが可能になる。
【００１５】
ｅ） また、一般に鋼材の焼入れでは昇温時間，均熱時間が長くなるほど熱歪による材料の変形が顕著となって元の寸法精度が損なわれやすく、そのため寸法精度が重視される部材では極く短時間で急速加熱して急冷する“高周波焼入れ”が有効であるが、急速加熱であって均熱時間も極めて短い場合には炭化物の拡散が十分になされずにオ−ステナイトへの炭化物の固溶が不十分となって炭化物が溶け残りやすくなり、結局は焼入れ後の強度が十分に得られないという問題が生じがちである。
しかし、予め焼ならし熱処理等により鋼材のフェライト面積率を下げてパ−ライトの面積率を上げておくと、高周波焼入れのような短時間の急速加熱，均熱によっても炭化物がオ−ステナイトに固溶しやすくなって、炭化物の溶け残りに起因した“焼入れ後の強度不足”の問題は解消される。
【００１６】
本発明は、上記知見事項等を基にして完成されたものであり、次の▲１▼〜▲４▼項に示す高周波焼入れ用電気抵抗溶接鋼管を提供するものである。
▲１▼ 質量割合にて
Ｃ：０．２０〜０．７０％，
Ｓｉ：０．１０％以下，
Ｍｎ： ０．１〜 １．０％，
Ａｌ： ０．００５〜０．０５％，
Ｎ： ０．００５％以下，
Ｂ： （１１／１４）Ｎ＊ ＋０．００１ 〜 （１１／１４）Ｎ＊ ＋０．００５ ，
Ｔｉ： ０．００５〜０．０５％
を含有すると共に残部はＦｅ及び不可避的不純物から成る鋼帯から製造された電気抵抗溶接鋼管であって、高周波焼入れ前の段階で鋼管断面の全肉厚においてフェライト面積率が６５％以下のフェライト・パ−ライトを主体とした組織を有して成ることを特徴とする、高周波焼入れ用電気抵抗溶接鋼管。
ここで、Ｎ＊ は、Ｎ＊ ＝Ｎ−（１４／４８）Ｔｉ ｛但し、 Ｎ−（１４／４８）Ｔｉ ≦０の場合にはＮ＊ ＝０｝とする。
▲２▼ 質量割合にて更にＣｒ：０．０２〜 ３．０％をも含有する鋼帯から製造されて成ることを特徴とする、前記▲１▼項記載の高周波焼入れ用電気抵抗溶接鋼管。
▲３▼ 高周波焼入れ前の段階での硬さがＨｖ２００以下であって高周波焼入れ後の硬さがＨｖ５５０以上である、前記▲１▼又は▲２▼項記載の高周波焼入れ用電気抵抗溶接鋼管。
▲４▼ 前記▲１▼乃至▲３▼項の何れかに記載の高周波焼入れ用高炭素綱電気抵抗溶接鋼管であって、車両部品に適用するための高周波焼入れ用電気抵抗溶接鋼管。
【００１７】
さて、本発明に係る高周波焼入れ用電気抵抗溶接鋼管（電縫鋼管等）は、造管に続いて、例えば「Ａｃ３変態点＋３０℃〜Ａｃ３変態点＋２００℃」の温度域に加熱・保持してから放冷する“焼ならし熱処理”を施す等といった簡易な手立てによって得ることができ、これにより鋼管の金属組織は“フェライト面積率が６５％以下のフェライト・パ−ライトが主体の組織”となって、硬さ（強度）をＨｖ２００以下にまで低下させることができる。
一般に、鋼の成形性はその強度（硬さ）が低いほど良好になることが知られているが、電気抵抗溶接鋼管を素材として車両部品等の構造部品を冷間で安定に成形加工するには鋼管の硬さ（強度）は少なくともＨｖ２００以下であることが望まれる。従って、硬さ（強度）がＨｖ２００以下の本発明に係る電気抵抗溶接鋼管は、成形加工に供する“構造部品の製造素材”として好ましい材料であると言える。
【００１８】
一方、本発明に係る高周波焼入れ用電気抵抗溶接鋼管は、Ｃ含有量が０．２０％以上であり、また特定量のＢ及びＴｉ並びに必要に応じて更にＣｒをも含有しているため、高周波焼入れ処理によって容易に高強度化することができる。
因みに、本発明に係る電気抵抗溶接鋼管を高周波焼入れすると、その硬さ（強度）は安定してＨｖ ５５０以上を示すようになり、車両部品等といった構造部品としての強度や耐摩耗性は十分となる。
なお、本発明に係る電気抵抗溶接鋼管では、「Ａｃ３変態点＋３０℃〜Ａｃ３変態点＋２００℃」の温度域に加熱・保持してから放冷する焼ならし熱処理が施されても、その焼き入れ性に何ら悪影響が及ぶものでないことは言うまでもない。
【００１９】
【発明の実施の形態】
以下、本発明において高周波焼入れ用電気抵抗溶接鋼管の化学組成や金属組織を前記の如くに限定した理由を説明する。
［Ａ］ 電気抵抗溶接鋼管の化学組成
ａ） Ｃ
Ｃは電気抵抗溶接鋼管の強度確保に有効な元素であり、焼き入れ後のマルテンサイト組織での強度（硬さ）はＣ含有量でほぼ決まる。そして、焼き入れ後のマルテンサイト組織において車両部品等といった構造部品として十分な強度や耐摩耗性を発揮するＨｖ ５５０以上の硬さ（強度）を確保するためには、機械構造用電気抵抗溶接鋼管の０．２０％以上のＣ含有量が必要である（より高い焼入れ硬さを得るためにＣ含有量は０．３０％以上とするのが望ましい）。一方、Ｃ含有量が高すぎると造管時の電気抵抗溶接部が硬くなり過ぎて製造が困難となるので、Ｃ含有量の上限は０．７０％としたが、より安定した電気抵抗溶接を行うためにはＣ含有量は０．６０％以下とするのが望ましい。
【００２０】
ｂ） Ｓｉ
Ｓｉはフェライトを固溶強化して鋼管の成形性を劣化させる元素であるため、良好な成形性を確保するためＳｉ含有量の上限を０．１０％として強度の上昇を抑える。好ましくは、Ｓｉ含有量は０．０５％以下に低減するのが良い。
【００２１】
ｃ） Ｍｎ
Ｍｎは鋼管の靱性・焼入れ性を改善する作用を有しているので、高周波焼入れ用電気抵抗溶接鋼管に必要な靱性・焼入れ性を確保すべくＭｎを ０．１％以上含有させることとしたが、Ｓｉと同様、Ｍｎにはフェライトを固溶強化する作用もあるので多すぎると材料の変形抵抗が大きくなる。従って、Ｍｎ含有量の上限は １．０％と定めたが、鋼管強度をより低くして成形性を改善し、またＭｎ偏析を極力低減するためには、Ｍｎ含有量は ０．５％以下とするのが望ましい。
【００２２】
ｄ） Ａｌ（ｓｏｌ．Ａｌ）
Ａｌは脱酸に必要な元素である上、鋼中のＮを固定して固溶Ｎによる降伏点伸びの回復を抑える作用を有しているので ０．００５％以上含有させることとしたが、過剰に添加すると鋼中にアルミナが増えて非金属介在物による溶接不良の原因となることから、その上限を０．０５％と定めた。
【００２３】
ｅ） Ｎ
Ｎは鋼材の耐時効性を最も劣化させる元素であって、少ないほど好ましい不純物元素であるが、鋼材の製造コストと悪影響の程度を考慮してＮ含有量の上限を０．００５ ％と定めた。
【００２４】
ｆ） Ｂ
Ｂは鋼材の焼入れ性を向上させるのに有効な元素であるが、鋼中のＮと結合すると焼入れ性の改善には寄与しなくなる。そのため、本発明ではＮと優先的に結合するＴｉの添加が共になされる。
Ｔｉと結合するＮの量は「 （１４／４８）Ｔｉ」となるので、「Ｎ＊ ＝Ｎ−（１４／４８）Ｔｉ 」とした場合に「Ｎ＊ ＞０」のときはＴｉと結合していないＮの量（Ｎ＊ ）とＢとが結合して焼入れに有効なＢが減少する。従って、焼入れ性に有効となるＢを確保するためにＢ含有量の下限は「 （１１／１４）Ｎ＊ ＋０．００１ 」と定めた。
また、Ｂ含有量が「 （１１／１４）Ｎ＊ ＋０．００５ 」を超えると鋼管の靱性が劣化することから、Ｂ含有量の上限は「 （１１／１４）Ｎ＊ ＋０．００５ 」と定めた。
なお、「Ｎ−（１４／４８）Ｔｉ ≦０」のときはＴｉと結合していないＮは実質上０となるので「Ｎ＊ ＝０」で表されることは言うまでもない。
【００２５】
ｇ） Ｔｉ
上述したように、ＴｉはＮとの親和性が強いためＢ添加を行った場合にＢＮが析出するのを抑制し、その結果としてＢが鋼中に固溶して焼き入れ性向上効果を発揮するのを助ける作用を発揮する。但し、Ｔｉ含有量が ０．００５％以下であるとＴｉ添加の効果が顕著でなく、一方、０．０５％を超えてＴｉを含有させてもＴｉ添加の効果は飽和してコスト高を招く。従って、Ｔｉ含有量は ０．００５〜０．０５％と定めたが、強度が上がり過ぎるのを防ぐにはＴｉ含有量を０．０３％以下に抑えるのが望ましい。
【００２６】
ｈ） Ｃｒ
Ｃｒも鋼材の焼入れ性を向上させるのに有効な元素であるので、本発明では必要に応じて含有させることとしたが、その含有量が０．０２％未満では焼入れ性向上効果は顕著化しない。一方、Ｃｒ含有量が多すぎると酸化物となって溶接不良が発生しやすくなるので、Ｃｒ含有量の上限を ３．０％と定めたが、より安定した電気抵抗溶接を行うためにはＣｒ含有量は １．０％以下に抑えることが望ましい。
【００２７】
［Ｂ］ 電気抵抗溶接鋼管の金属組成
先にも述べたように、高周波焼入れは寸法精度が重視される“鋼管を素材とする構造部材”に有効な焼入れ法であるが、炭化物の拡散が十分になされずにオ−ステナイトへの炭化物の固溶が不十分となって炭化物が溶け残りやすくなり、結局は焼入れ後の強度が十分に得られないという問題が生じがちである。しかしながら、本発明に係る鋼管のようなフェライト・パ−ライトを主体とした組織の鋼材（化学組成からして造管のままではフェライト・パ−ライトを主体とした組織となる）では、フェライト面積率を６５％以下に調整すると高周波焼入れにおけるような短時間の加熱でも炭化物の固溶が促進され、炭化物の溶け残りに起因した焼入れ後の強度不足を防止することができる。
従って、本発明に係る高周波焼入れ用電気抵抗溶接鋼管は「鋼管断面の全肉厚においてフェライト面積率が６５％以下のフェライト・パ−ライトを主体とした組織」を有するものと定めた。しかし、加熱開始から冷却完了までの時間が６０秒以下となるような急速加熱・急速冷却の高周波焼入れを実施する場合には、フェライト面積率を５０％以下に調整することが望ましい。
【００２８】
ここで、本発明で言う「フェライト・パ−ライトを主体とした組織」とは組織全体に占める「フェライト＋パ−ライト」の面積率が大半の組織であり、フェライト及びパ−ライト以外に面積率で０〜１０％程度のセメンタイト，０〜１％程度のベイナイト，０〜１％程度のマルテンサイトが含まれていても差し支えはない。
【００２９】
なお、「フェライト面積率が６５％以下のフェライト・パ−ライトを主体とした組織」が例えば「Ａｃ３変態点＋３０℃〜Ａｃ３変態点＋２００℃」の温度域に加熱して５〜３０分間保持してから放冷する“焼ならし熱処理”等の手立てによって実現できることは、先に説明した通りである。
なお、上記焼ならし熱処理は電気抵抗溶接部の硬化を解消する上でも有効な手段であり、この処理によれば鋼の強度がより低い状態であるフェライト，パ−ライト等が混在した組織状態が得られて綱中のＣ含有量が０．７０％以下であればＨｖ２５０以下を確保することができる。
【００３０】
また、鋼管強度の更なる低減を図るためには、成形加工前の段階で「Ａｃ１変態点〜（Ａｃ１変態点＋Ａｃ３変態点） ／２」の温度領域で１〜２０分間均熱した後空冷する熱処理を実施することが望ましい。
ところで、本発明に係る電気抵抗溶接鋼管は、高周波焼入れを施すことなく使用することも当然可能である。
続いて、本発明を実施例により更に具体的に説明する。
【００３１】
【実施例】
まず、表１に示す化学組成の鋼帯を準備し、これらの鋼帯から外径が３８．１ｍｍで肉厚が５．３ｍｍ の電縫鋼管を造管した。
【００３２】
【表１】
そして、造管後は、焼ならし及び高周波焼入れ等の次に示す２通りの処理を実施した。
工程１： 造管→焼ならし→高周波焼入れ，
工程２： 造管→焼ならし→抽伸（抽伸後の寸法：外径が３０ｍｍで肉厚が４．８ｍｍ ）→焼なまし→高周波焼入れ。
【００３４】
ここで、工程１及び工程２では共に、高周波焼入れ前に実施される車両部品等への冷間成形を想定し、造管後に焼ならし熱処理（Ａｃ３変態点＋３０℃〜Ａｃ３変態点＋２００℃の温度域に加熱して所定時間保持してから放冷）を実施して組織の調整を行うと同時に電縫溶接部の硬化の影響を消去した。
また、工程２では、焼ならし熱処理後に抽伸（冷間抽伸）を実施したことによって加工硬化が生じるので、抽伸後に焼なまし熱処理で材料を軟化させた。この際の焼なまし熱処理の条件は、材料の強度低減を図るのに効果的となる「Ａｃ１変態点〜（Ａｃ１変態点＋Ａｃ３変態点）／２」の温度領域で１０分間均熱してから放冷する条件とした。
【００３５】
なお、前記高周波焼入れ処理の直前の電縫鋼管から試験片を切り出し、その横断面について組織観察を行うと共に、組織観察で使用した試験片断面につきビッカ−ス硬さ（Ｈｖ１０ｋｇ）の測定も実施した。更に、高周波焼入れ処理後にも電縫鋼管から採取した試験片（横断面）についてビッカ−ス硬さ（Ｈｖ１０ｋｇ）を測定した。
表２に、造管から高周波焼入れまでの処理工程と組織観察並びに硬さ測定の結果を示す。
【００３６】
【表２】
表２に示される結果からも、本発明に係る電縫鋼管（高周波焼入れ前の電縫鋼管）は、焼入れ前には良好な冷間成形性の目安であるＨｖ２００以下の硬さ（強度）を示すものの、高周波焼入れによって車両部品等に望まれるＨｖ５５０以上を安定して確保できることが明らかである。
【００３８】
特に、試験番号２，５，９及び１２では、焼ならし時の均熱時間を長くしたためにフェライト面積率の減少が著しく、そのため焼入れ性が目立って向上し、高周波焼入れ後の硬さ上昇が際立っている。
また、試験番号３，６，１０及び１３では、抽伸後に焼なましを実施したことで高周波焼入れ前の硬さ低下が著しく、より優れた冷間成形性を示すことが明らかである。
【００３９】
これに対して、比較例である試験番号１６，１７及び１８では、電縫鋼管の化学組成が本発明の規定条件を満たしておらず、また焼入れ前の電縫鋼管におけるフェライト面積率も高いので、高周波焼入れ後の硬さが十分でない。
更に、比較例である試験番号１９及び２０では、電縫鋼管の化学組成が本発明の規定条件を満たしていないために高周波焼入れ前の硬さが高く、そのため冷間成形性が十分でないことは明らかである。
一方、比較例である試験番号２１では、化学組成は本発明の規定条件を満たしているものの、焼入れ前の電縫鋼管におけるフェライト面積率も高いので高周波焼入れ後の硬さが十分でない。
【００４０】
【発明の効果】
以上に説明した如く、この発明によれば、車両部品等といった機械構造部品への成形加工が容易で、加工後には高周波焼入れにより十分な強度上昇がなされる高周波焼入れ用電気抵抗溶接鋼管を提供することが可能になるなど、産業上有用な効果がもたらされる。[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric resistance welded steel pipe for induction hardening, which is used as a material of a steel part to be used with increased strength by performing induction hardening after cold forming, for example, for a vehicle part (automobile part, motorcycle part, rail car part). The present invention relates to an electric resistance welded steel pipe for a machine structure suitable for use in (1).
[0002]
[Prior art]
In recent years, strict measures to reduce the weight of automobile bodies and the like have been promoted from the viewpoint of environmental problems and energy problems. For example, in the case of undercarriage parts of automobiles, the materials have been converted from rods to steel pipes. .
Such automotive parts (rack bars, drive shafts, steering shafts, axle housings, shock absorbers, stabilizers, drag links, tie rods, valve rocker shafts, etc.), motorcycle parts (front forks, etc.) Electrical resistance welded steel pipes (for example, ERW steel pipes) for machine structures used as materials for parts for bicycles, parts for rail cars, parts for construction machines, parts for various cylinders, furniture, and other mechanical structure parts are generally used. After forming into the desired part shape (cold forging, rolling, swaging, pressing, bending, hydroforming, explosion molding, etc.), the required strength by induction hardening (Hardness) is provided for use.
[0003]
In steel materials used to increase strength by performing induction hardening after cold forming, it is necessary to increase the C (carbon) content in order to secure sufficient strength by quenching. When it becomes high, there is a problem that the steel material becomes hard and the formability deteriorates.
[0004]
Generally, in order to improve the formability of the electric resistance welded steel pipe, a “normalizing treatment” of heating and holding at a temperature of Ac 3 transformation point or higher and then allowing it to cool is performed. In some systems, this method may not provide sufficient moldability.
In particular, in steel pipes made of high carbon steel, sufficient formability cannot often be obtained even by the above normalizing treatment. Therefore, application of a spheroidizing heat treatment, which is a heat treatment for reducing the strength of high carbon steel, has been attempted. However, this method requires a long time for the heat treatment step, and thus has a significant disadvantage in terms of production efficiency. In addition, since C in the steel material subjected to the spheroidizing heat treatment is almost completely spheroidized, there is a problem that hardening hardly occurs and a machinability deteriorates when quenching is finally performed.
[0005]
For example, Japanese Patent Application Laid-Open No. 2001-131702 discloses that, as an ERW steel tube for cold forging having excellent workability, "C: 0.1 to 0.5% (hereinafter,% representing component ratio is mass%. ), Si: 0.01-0.5%, Mn: 0.1-2.0%, and if necessary, Cr, Mo, W, Ni, Cu, B, Ti, Nb, V , Ca ", an ERW steel tube for cold forging having a chemical composition containing at least one of Ca, Ca and the like.
However, in this ERW steel pipe, the spheroidization of carbides by spheroidizing annealing is described as "the proportion of carbides in the structure is 30% or less in terms of carbides and the spheroidization rate of carbides is 80% or more." This is a steel pipe that eliminates layered carbides that are harmful to deformability.Since carbides are spheroidized, workability of the material is improved, but carbides are less likely to form a solid solution during induction quenching. Therefore, the material was unsuitable for induction hardening parts.
[0006]
By the way, according to Japanese Patent Application Laid-Open No. 2001-355047, as a high carbon electric resistance welded steel tube having excellent cold workability and induction hardening properties, "C: 0.3 to 0.8%, Si: 2% or less, Mn: Reduced diameter rolling is performed on an ERW steel pipe containing not more than 3% and, if necessary, one or more of Cr, Mo, W, Ni, Cu, B, Ti, Nb and V. A high carbon steel pipe which has a structure in which cementite having a particle size of 1.0 μm or less is finely dispersed in ferrite by applying the same is disclosed.
[0007]
However, although this steel pipe is specified as “Si: 2% or less, Mn: 3% or less”, it is necessary to enhance the hardenability as is clear from the “Example” column and the “Description of added amount” column. Need to contain Si and Mn in relatively high amounts. Therefore, the material strength before induction hardening is unavoidably increased, and in order to ensure good workability, the material is shrunk in a temperature range of {(Ac 1 transformation point −50 ° C.) to (Ac 1 transformation point)}. It is indispensable to perform a troublesome treatment of performing diameter rolling to realize a structure in which cementite having a particle size of 1.0 μm or less is finely dispersed in ferrite.
[0008]
In addition, hardening of the electric resistance welded portion remains only by performing the diameter reduction rolling in such a warm state, and it cannot be said that the material is satisfactory for cold forming.
Moreover, when carrying out the post-heat treatment at a temperature range of not lower than Ac 3 transformation point in order to eliminate the curing of the electric resistance welding unit, the workability in the electric resistance welded steel pipe has a problem that deteriorates.
[0009]
Furthermore, although this steel pipe is said to be a "high carbon steel pipe excellent in cold workability and induction hardening properties", it was also confirmed from "Table 3-1" and "Table 3-2" in the "Example" column. In order to make it possible, the induction hardenability is equivalent to that of the “Comparative example (normalized)” or is better in the case of “Comparative example (normalized)” (product tubes Nos. 7 and 9, 13 and 15). , 36 and 38), it was not always possible to say that both workability and induction hardening were excellent.
[0010]
[Problems to be solved by the invention]
In view of the above, an object of the present invention is to provide an electric resistance for induction hardening that exhibits good formability at the time of cold working and can stably impart high strength satisfactory as a vehicle part or the like by induction hardening. The aim was to establish means for providing welded steel pipes.
[0011]
[Means for Solving the Problems]
The present inventor conducted research while repeating many tests in order to achieve the above object, and as a result, was able to obtain the following knowledge.
a) When applying an electric resistance welded steel pipe to, for example, a vehicle part, a strength equivalent to Hv550 or more in hardness is required. To secure such high strength to the steel pipe by quenching, an appropriate amount of C is added. However, as the C content increases, the steel becomes harder and the formability deteriorates, and when the C content is increased so that the hardness after quenching Hv 550 or more is ensured, the steel pipe before quenching In addition, it is difficult to achieve “hardness less than Hv200” which enables stable cold forming of vehicle parts and the like.
[0012]
b) However, even if a steel material has a relatively high C content, if the strength itself of the steel material is reduced by suppressing the contents of Si and Mn, which are ferrite strengthening elements, the "strength due to carbide spheroidization" The formability of the steel material can be improved without relying on "reduction" or "improvement of r value by adjusting texture".
[0013]
c) The reduction of the Mn content also leads to the suppression of Mn segregation, and the deterioration of the workability (workability such as diameter reduction and expansion of the tube) due to the Mn segregation is remarkably reduced by the reduction of the Mn content.
That is, in an electric resistance welded steel pipe made of a hot-rolled steel sheet (e.g., electric resistance welded steel pipe), segregation of Mn, which is a ferrite strengthening element, is strong when the steel is used for a machine structural steel having a normal chemical composition. This not only deteriorates the workability, but also causes the Mn segregation to be hardly diffused by heating during induction quenching as compared with the case of C or Si. Hardness variation is likely to occur after induction hardening. In order to reduce segregation, it is necessary to perform spheroidizing annealing. However, when spheroidizing annealing is performed, if "induction quenching" is applied to the subsequent quenching treatment, heating is performed in a short time, so that carbide is completely eliminated. They do not form a solid solution, so that a decrease in hardness occurs after quenching.
However, when the Mn content is reduced, the above-mentioned problem caused by Mn segregation is solved, and the ferrite + pearlite structure as welded or after normalizing or after annealing is soft and excellent in formability. A steel pipe is obtained.
[0014]
d) By the way, if the Mn content of the steel material is reduced, the hardenability generally deteriorates. However, it is possible to compensate for this decrease in hardenability by adding B or, if necessary, further adding Cr.
[0015]
e) Generally, in the quenching of steel, as the heating time and the soaking time become longer, the deformation of the material due to thermal strain becomes more remarkable, and the original dimensional accuracy is likely to be impaired. "Induction quenching", in which rapid heating and rapid cooling are performed in a short time is effective, but when rapid heating is performed and the soaking time is extremely short, diffusion of carbides is not sufficient and solidification of carbides in austenite is not sufficient. Insufficient dissolution causes carbides to easily remain undissolved, resulting in a problem that sufficient strength after quenching cannot be obtained.
However, if the area ratio of pearlite is increased by lowering the area ratio of ferrite of the steel material by normalizing heat treatment in advance, carbide can be converted to austenite even by short-time rapid heating and soaking such as induction hardening. It becomes easy to form a solid solution, and the problem of "insufficient strength after quenching" due to undissolved carbide is solved.
[0016]
The present invention has been completed based on the above findings and the like, and provides an electric resistance welded steel pipe for induction hardening described in the following items (1) to (4).
(1) C: 0.20 to 0.70% by mass ratio,
Si: 0.10% or less,
Mn: 0.1-1.0%,
Al: 0.005 to 0.05%,
N: 0.005% or less,
B: (11/14) N * + 0.001 to (11/14) N * + 0.005,
Ti: 0.005 to 0.05%
And the remainder is an electric resistance welded steel pipe manufactured from a steel strip composed of Fe and unavoidable impurities, and has a ferrite area ratio of 65% or less in the entire thickness of the steel pipe cross section before induction hardening. An electric resistance welded steel tube for induction hardening characterized by having a structure mainly composed of pearlite.
Here, N * is N * = N- (14/48) Ti {where N * = 0} when N- (14/48) Ti ≦ 0.
(2) The electric resistance welded steel pipe for induction hardening according to the above (1), characterized by being manufactured from a steel strip further containing Cr: 0.02 to 3.0% by mass.
(3) The electric resistance welded steel pipe for induction hardening according to the above (1) or (2), wherein the hardness before induction hardening is Hv200 or less and the hardness after induction hardening is Hv550 or more.
(4) The high carbon steel electric resistance welded steel tube for induction hardening according to any one of the above (1) to (3), which is applied to a vehicle part.
[0017]
By the way, the electric resistance welded steel pipe for induction hardening (such as an electric resistance welded steel pipe) according to the present invention is heated and held in a temperature range of, for example, “Ac 3 transformation point + 30 ° C. to Ac 3 transformation point + 200 ° C.” following pipe making. The steel pipe can be obtained by simple measures such as "normalizing heat treatment" in which it is left to cool, and the metallographic structure of the steel pipe is "a structure mainly composed of ferrite pearlite having a ferrite area ratio of 65% or less." And the hardness (strength) can be reduced to Hv200 or less.
In general, it is known that the lower the strength (hardness), the better the formability of steel. However, it is necessary to stably form cold-formed structural parts such as vehicle parts using electric resistance welded steel pipe as a material. It is desired that the hardness (strength) of the steel pipe is at least Hv200 or less. Therefore, it can be said that the electric resistance welded steel pipe according to the present invention having a hardness (strength) of Hv 200 or less is a preferable material as a “material for manufacturing structural parts” to be subjected to forming.
[0018]
On the other hand, the electric resistance welded steel pipe for induction hardening according to the present invention has a C content of 0.20% or more, and also contains specific amounts of B and Ti and, if necessary, further Cr. Strength can be easily increased by quenching.
By the way, when the electric resistance welded steel pipe according to the present invention is induction hardened, its hardness (strength) stably shows Hv 550 or more, and the strength and wear resistance as structural parts such as vehicle parts are not sufficient. Become.
In addition, in the electric resistance welded steel pipe according to the present invention, even if the normalizing heat treatment of heating and holding in the temperature range of “Ac 3 transformation point + 30 ° C. to Ac 3 transformation point + 200 ° C.” and then allowing it to cool is performed, It goes without saying that the hardenability has no adverse effect.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the reason why the chemical composition and the metal structure of the electric resistance welded steel pipe for induction hardening in the present invention are limited as described above will be described.
[A] Chemical composition of electric resistance welded steel pipe a) C
C is an element effective for securing the strength of the electric resistance welded steel pipe, and the strength (hardness) in the martensite structure after quenching is substantially determined by the C content. Then, in order to secure hardness (strength) of Hv 550 or more that exhibits sufficient strength and wear resistance as a structural component such as a vehicle component in a martensite structure after quenching, it is necessary to use an electric resistance welded steel pipe for a mechanical structure. Is required to be 0.20% or more (the C content is desirably 0.30% or more to obtain higher quench hardness). On the other hand, if the C content is too high, the electric resistance welded portion at the time of pipe making becomes too hard and production becomes difficult. Therefore, the upper limit of the C content is set to 0.70%. For this purpose, the C content is desirably 0.60% or less.
[0020]
b) Si
Since Si is an element that solid-solution strengthens ferrite and deteriorates the formability of a steel pipe, the upper limit of the Si content is set to 0.10% in order to secure good formability, thereby suppressing an increase in strength. Preferably, the Si content is reduced to 0.05% or less.
[0021]
c) Mn
Since Mn has the effect of improving the toughness and hardenability of steel pipes, Mn is added in an amount of 0.1% or more in order to secure the required toughness and hardenability of the electric resistance welded steel pipe for induction hardening. Like Si and Si, Mn also has the effect of solid-solution strengthening of ferrite, so if too much, the deformation resistance of the material will increase. Therefore, the upper limit of the Mn content is set to 1.0%. However, in order to improve the formability by lowering the strength of the steel pipe and to reduce Mn segregation as much as possible, the Mn content is 0.5% or less. It is desirable that
[0022]
d) Al (sol. Al)
Al is an element necessary for deoxidation, and has an effect of fixing N in steel and suppressing recovery of yield point elongation due to solid solution N. If added excessively, alumina increases in the steel and causes poor welding due to nonmetallic inclusions. Therefore, the upper limit is set to 0.05%.
[0023]
e) N
N is the element that most deteriorates the aging resistance of the steel material, and the smaller the amount, the more preferable the impurity element. However, the upper limit of the N content is set to 0.005% in consideration of the production cost and the degree of adverse effects of the steel material. .
[0024]
f) B
B is an element effective for improving the hardenability of the steel material, but does not contribute to the improvement of the hardenability when combined with N in the steel. Therefore, in the present invention, Ti that preferentially binds to N is added together.
Since the amount of N bonded to Ti is “(14/48) Ti”, when “N * = N− (14/48) Ti”, when “N * > 0”, the amount of N is bonded to Ti. The unreacted amount of N (N * ) and B combine to reduce the effective B for quenching. Therefore, the lower limit of the B content is determined as “(11/14) N * + 0.001” in order to secure B effective for hardenability.
If the B content exceeds "(11/14) N * + 0.005", the toughness of the steel pipe deteriorates. Therefore, the upper limit of the B content is set to "(11/14) N * + 0.005". Was.
It should be noted that when “N− (14/48) Ti ≦ 0”, N not bonded to Ti is substantially 0, and it is needless to say that “N * = 0”.
[0025]
g) Ti
As described above, since Ti has a strong affinity for N, it suppresses the precipitation of BN when B is added, and as a result, B forms a solid solution in steel and exhibits an effect of improving hardenability. It acts to help you. However, when the Ti content is 0.005% or less, the effect of the addition of Ti is not remarkable. On the other hand, even when the content of Ti exceeds 0.05%, the effect of the addition of Ti is saturated and the cost is increased. . Therefore, although the Ti content is set to 0.005 to 0.05%, it is desirable to suppress the Ti content to 0.03% or less in order to prevent the strength from increasing excessively.
[0026]
h) Cr
Since Cr is also an element effective in improving the hardenability of steel, it is included as necessary in the present invention, but if the content is less than 0.02%, the effect of improving hardenability does not become remarkable. . On the other hand, if the Cr content is too large, it becomes an oxide and welding failure is likely to occur. Therefore, the upper limit of the Cr content is set to 3.0%. The content is desirably suppressed to 1.0% or less.
[0027]
[B] Metal composition of electric resistance welded steel pipe As mentioned earlier, induction hardening is an effective quenching method for “structural members made of steel pipe” where dimensional accuracy is important, but diffusion of carbides is sufficient. However, the solid solution of the carbide in the austenite is insufficient, and the carbide tends to remain undissolved. As a result, the strength after quenching tends to be insufficient. However, in a steel material having a structure mainly composed of ferrite pearlite, such as the steel pipe according to the present invention (a structure mainly composed of ferrite pearlite if the pipe is formed as it is from the chemical composition), the ferrite area is reduced. When the rate is adjusted to 65% or less, solid solution of carbide is promoted even by heating for a short time as in induction hardening, and insufficient strength after quenching due to undissolved carbide can be prevented.
Therefore, the electric resistance welded steel pipe for induction hardening according to the present invention is determined to have "a structure mainly composed of ferrite pearlite having a ferrite area ratio of 65% or less in the entire wall thickness of the steel pipe section". However, when performing induction hardening of rapid heating and rapid cooling such that the time from the start of heating to the completion of cooling is 60 seconds or less, it is desirable to adjust the ferrite area ratio to 50% or less.
[0028]
Here, the term "structure mainly composed of ferrite / pearlite" as used in the present invention means a structure in which the area ratio of "ferrite + pearlite" in the whole structure is almost the entire structure, and the area ratio other than ferrite and pearlite. Cementite of about 0 to 10%, bainite of about 0 to 1%, and martensite of about 0 to 1% may be contained.
[0029]
The "structure mainly composed of ferrite pearlite having a ferrite area ratio of 65% or less" is heated, for example, to a temperature range of "Ac 3 transformation point + 30 ° C to Ac 3 transformation point + 200 ° C" for 5 to 30 minutes. What can be realized by means such as "normalizing heat treatment" of holding and then allowing to cool is as described above.
The above-mentioned normalizing heat treatment is also an effective means for eliminating the hardening of the electric resistance welded part. According to this treatment, the state of the structure where ferrite, pearlite, etc., in which the strength of steel is lower, is mixed. Is obtained, and if the C content in the rope is 0.70% or less, Hv 250 or less can be ensured.
[0030]
Further, in order to further reduce the strength of the steel pipe, the tube was soaked for 1 to 20 minutes in a temperature range of “Ac 1 transformation point to (Ac 1 transformation point + Ac 3 transformation point) / 2” before the forming process. It is desirable to carry out a heat treatment for air cooling afterwards.
By the way, the electric resistance welded steel pipe according to the present invention can naturally be used without induction hardening.
Next, the present invention will be described more specifically with reference to examples.
[0031]
【Example】
First, steel strips having the chemical compositions shown in Table 1 were prepared, and ERW steel pipes having an outer diameter of 38.1 mm and a wall thickness of 5.3 mm were formed from these steel strips.
[0032]
[Table 1]
After the pipe was formed, the following two processes such as normalizing and induction hardening were performed.
Process 1: Pipe making → normalizing → induction hardening,
Step 2: Pipe forming → normalizing → drawing (dimension after drawing: outer diameter is 30 mm and wall thickness is 4.8 mm) → annealing → induction hardening.
[0034]
Here, in both Step 1 and Step 2, cold forming of vehicle parts and the like performed before induction hardening is assumed, and normalizing heat treatment (Ac 3 transformation point + 30 ° C. to Ac 3 transformation point +200) is performed after pipe forming. The specimen was heated to a temperature range of ° C., held for a predetermined time, and then allowed to cool) to adjust the structure, and at the same time, the influence of the hardening of the ERW weld was eliminated.
In step 2, since the work hardening occurs by performing the drawing (cold drawing) after the normalizing heat treatment, the material was softened by the annealing heat treatment after the drawing. The annealing heat treatment condition at this time is soaking for 10 minutes in a temperature range of “Ac 1 transformation point to (Ac 1 transformation point + Ac 3 transformation point) / 2” which is effective for reducing the strength of the material. And then allowed to cool.
[0035]
In addition, a test piece was cut out from the ERW steel pipe immediately before the induction hardening treatment, and the cross section of the test piece was observed for structure, and the Vickers hardness (Hv 10 kg) of the test piece section used for the structure observation was also measured. . Further, Vickers hardness (Hv 10 kg) was measured for a test piece (cross section) taken from the ERW pipe even after the induction hardening treatment.
Table 2 shows the processing steps from pipe making to induction hardening, the results of microstructure observation, and the results of hardness measurement.
[0036]
[Table 2]
From the results shown in Table 2, the ERW steel pipe according to the present invention (the ERW steel pipe before induction hardening) has a hardness (strength) of Hv 200 or less before hardening, which is a measure of good cold formability. Although shown, it is clear that Hv550 or more desired for vehicle parts and the like can be stably secured by induction hardening.
[0038]
In particular, in Test Nos. 2, 5, 9 and 12, the soaking time during normalizing was prolonged, so that the area ratio of ferrite was remarkably reduced, so that the hardenability was remarkably improved and the hardness after induction hardening was increased. Stand out.
Further, in Test Nos. 3, 6, 10 and 13, it is clear that the hardness before the induction hardening is remarkably reduced by performing the annealing after the drawing, so that more excellent cold formability is exhibited.
[0039]
On the other hand, in Test Nos. 16, 17, and 18, which are comparative examples, the chemical composition of the ERW pipe does not satisfy the specified conditions of the present invention, and the ferrite area ratio in the ERW pipe before quenching is high. The hardness after induction hardening is not sufficient.
Further, in Test Nos. 19 and 20, which are comparative examples, the chemical composition of the ERW steel pipe did not satisfy the specified conditions of the present invention, so that the hardness before induction hardening was high, so that the cold formability was not sufficient. it is obvious.
On the other hand, in Test No. 21, which is a comparative example, although the chemical composition satisfies the specified conditions of the present invention, the ferrite area ratio in the ERW pipe before quenching is high, so that the hardness after induction hardening is not sufficient.
[0040]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an electric resistance welded steel pipe for induction hardening that can be easily formed into a machine structural part such as a vehicle part or the like, and has a sufficiently increased strength by induction hardening after the processing. Industrially useful effects, such as the ability to be used.
Claims (4)
Ｃ：０．２０〜０．７０％，
Ｓｉ：０．１０％以下，
Ｍｎ： ０．１〜 １．０％，
Ａｌ： ０．００５〜０．０５％，
Ｎ： ０．００５％以下，
Ｂ： （１１／１４）Ｎ＊ ＋０．００１ 〜 （１１／１４）Ｎ＊ ＋０．００５ ，
Ｔｉ： ０．００５〜０．０５％
を含有すると共に残部はＦｅ及び不可避的不純物から成る鋼帯から製造された電気抵抗溶接鋼管であって、高周波焼入れ前の段階で鋼管断面の全肉厚においてフェライト面積率が６５％以下のフェライト・パ−ライトを主体とした組織を有して成ることを特徴とする、高周波焼入れ用電気抵抗溶接鋼管。
ここで、Ｎ＊ は、Ｎ＊ ＝Ｎ−（１４／４８）Ｔｉ ｛但し、 Ｎ−（１４／４８）Ｔｉ ≦０の場合にはＮ＊ ＝０｝とする。C: 0.20 to 0.70% by mass ratio,
Si: 0.10% or less,
Mn: 0.1-1.0%,
Al: 0.005 to 0.05%,
N: 0.005% or less,
B: (11/14) N * + 0.001 to (11/14) N * + 0.005,
Ti: 0.005 to 0.05%
And the remainder is an electric resistance welded steel pipe manufactured from a steel strip composed of Fe and unavoidable impurities, and has a ferrite area ratio of 65% or less in the entire thickness of the steel pipe cross section before induction hardening. An electric resistance welded steel pipe for induction hardening characterized by having a structure mainly composed of pearlite.
Here, N * is N * = N− (14/48) Ti {where, when N− (14/48) Ti ≦ 0, N * = 0}.
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| JP2002358693A JP4038794B2 (en) | 2002-12-10 | 2002-12-10 | Electric resistance welded steel pipe for induction hardening |
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| JP4038794B2 JP4038794B2 (en) | 2008-01-30 |
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| WO2014119802A1 (en) * | 2013-01-31 | 2014-08-07 | Ｊｆｅスチール株式会社 | Electric-resistance-welded steel pipe |
| JP7188649B1 (en) * | 2022-02-10 | 2022-12-13 | 日本製鉄株式会社 | Electric resistance welded steel pipe for automobile parts, and method for manufacturing automobile parts |
| CN116103579A (en) * | 2023-02-27 | 2023-05-12 | 马鞍山钢铁股份有限公司 | Wear-resistant ERW welded steel pipe for concrete pump truck and manufacturing method thereof |
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2002
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| WO2014119802A1 (en) * | 2013-01-31 | 2014-08-07 | Ｊｆｅスチール株式会社 | Electric-resistance-welded steel pipe |
| CN104968821A (en) * | 2013-01-31 | 2015-10-07 | 杰富意钢铁株式会社 | Electric-resistance-welded steel pipe |
| EP2952601A4 (en) * | 2013-01-31 | 2016-02-17 | Jfe Steel Corp | Electric-resistance-welded steel pipe |
| JP5892267B2 (en) * | 2013-01-31 | 2016-03-23 | Ｊｆｅスチール株式会社 | ERW steel pipe |
| JP7188649B1 (en) * | 2022-02-10 | 2022-12-13 | 日本製鉄株式会社 | Electric resistance welded steel pipe for automobile parts, and method for manufacturing automobile parts |
| WO2023152906A1 (en) * | 2022-02-10 | 2023-08-17 | 日本製鉄株式会社 | Electric resistance welded steel pipe for automobile component, and method for manufacturing automobile component |
| CN116103579A (en) * | 2023-02-27 | 2023-05-12 | 马鞍山钢铁股份有限公司 | Wear-resistant ERW welded steel pipe for concrete pump truck and manufacturing method thereof |
| CN116103579B (en) * | 2023-02-27 | 2024-01-30 | 马鞍山钢铁股份有限公司 | Wear-resistant ERW welded steel pipe for concrete pump truck and manufacturing method thereof |
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