JP3681712B2 - High carbon steel wire rod excellent in drawability and manufacturing method thereof - Google Patents
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Description
【０００１】
【発明が属する技術分野】
本発明は、タイヤの補強用鋼線、ＰＣ鋼線、ロープ用鋼線などの高強度鋼線の素材として乾式伸線に供される高炭素鋼線材およびその製造方法に関する。
【０００２】
【従来の技術】
高強度鋼線は、熱間圧延によって製造された高炭素鋼線材を必要な線径に伸線加工することによって製造される。タイヤのスチールコード、ベルトコードなどのように細線に伸線加工される線材では、伸線時に断線すると、生産性が著しく阻害されるため、良好な伸線性が求められる。従来、かかる良好な伸線性を得るため、熱間圧延後、熱延線材を水冷し、衝風冷却することによって線材組織を微細パーライトにし、さらに乾式伸線工程の途中で１〜２回中間パテンティングを施すことが行われている。
【０００３】
しかし、近年、高炭素鋼線にはより細い線径が求められており、また生産性の向上の観点から中間パテンティングを省略することが望まれている。このため、高炭素鋼線材にはより優れた耐断線性が要求されており、さらにダイスの寿命を向上させることも生産性向上の観点から求められている。
【０００４】
かかる要求に対して、特公平３−６０９００号公報には、高炭素鋼線材のＣ当量に応じて引張強さとパーライト中の粗パーライト（５００倍の顕微鏡下で識別可能なパーライト）の割合を適正値に制御することにより、また特開２０００−６３９８７号公報には、パーライトの平均コロニー径を１５０μm 以下とし、平均ラメラ間隔を０．１〜０．４μm とすることにより、伸線性を向上させる技術が紹介されている。前記コロニーとは、パーライトのラメラの方向が揃った領域をいい、このコロニーの複数によってフェライト結晶方位が一定の領域であるノジュール（ブロックともいう。）が形成される。なお、熱間圧延後の線材は、上記公報に記載されているように、水冷により巻き取り温度を調節し、引き続きステルモア調整冷却装置により衝風量を調整することにより製造される。
【０００５】
【発明が解決しようとする課題】
しかしながら、前者の技術では、ラメラ間隔の粗い粗パーライトが１０〜３０％程度存在するため、ダイス寿命の改善が図られるものの、伸線中の断線に対する抵抗性が不足し、十分な伸線性が得られていない。一方、後者の技術においてもラメラ間隔を０．１〜０．４μm とある程度粗くすることでダイス寿命を改善することができるが、ラメラ間隔を上記のように粗くした結果、平均コロニー径が実施例に開示されているように４０μm 程度に止まっており、やはり十分な耐断線性が得られているとは言えない。
【０００６】
なお、製鉄研究第２９５号（ｐ５２−６３、１９７８年、新日本製鐵株式会社発行の技報）には、断線の防止には極端なラメラ間隔の粗大化の抑制やパーライトブロック（ノジュール）サイズの粗大化の抑制が有効であることが示されているが、供試鋼としてＣｒを１〜２wt％を含むＣｒ添加高炭素鋼線材に基づく結果であり、またダイス寿命の観点を考慮して論じられたものではなく、ダイス寿命を考慮した伸線性に対してラメラ間隔とノジュールサイズとの関係について明らかにされていない。
【０００７】
本発明はかかる問題に鑑みなされたもので、乾式伸線に供される高炭素鋼線材であって、乾式伸線における耐断線性およびダイス寿命に優れた、優れた伸線性を有する高炭素鋼線材およびその製造方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明者は、ダイス寿命の向上のためにはパーライトのラメラ間隔をある程度広くし、線材の強度を下げることが必須であるとの認識の下、如何に断線を抑制、防止するかについて研究したところ、結晶粒として物理的意味のあるパーライトのノジュールの平均粒径をある値以下に微細化することで、比較的広いラメラ間隔のパーライト組織であっても耐断線性が大幅に向上し、優れた伸線性が得られることを知見し、本発明を完成するに至った。
【０００９】
すなわち、本発明の高炭素鋼線材は、乾式伸線に供される高炭素鋼線材であって、化学成分がmass％で、
Ｃ：０．６〜１．０％、
Ｓｉ：０．１〜１．５％、
Ｍｎ：０．３〜０．９％、
Ｐ：０．０２％以下、
Ｓ：０．０３％以下、
Ｎ：０．００５％以下、
残部Ｆｅおよび不可避的不純物からなり、あるいはさらに
Ｎｂ：０．０２０〜０．０５０％、
Ｖ：０．０５〜０．２０％
の１種または２種以上を含み、組織が９５面積％以上のパーライトを有し、パーライトの平均ノジュール径Ｐが３０μm 以下、平均ラメラ間隔Ｓが１００ｎｍ以上で、かつＰをμm 、Ｓをｎｍで表したとき下記Ｆ式がＦ＞０となる範囲内とされたものである。さらに、上記組成において、Ａｌを０．０３５％以下含有させることができ、特にＮ：０．００１５〜０．００５０％で、かつＡｌ：０．０３０％以下を含有させるようにするとよい。
Ｆ＝３５０．３／√Ｓ＋１３０．３／√Ｐ−５１．７
【００１０】
また、本発明の高炭素鋼線材の製造方法は、前記化学成分の鋼片を仕上温度１０５０〜８００℃で熱間圧延を行い、仕上圧延終了後直ちに５０℃／ｓ以上の冷却速度にて９５０〜７５０℃の範囲内の温度に冷却し、引き続き５〜２０℃／ｓ以上の冷却速度にて６２０〜６８０℃の範囲内の温度に冷却した後、２℃／ｓ以下の冷却速度にて２０秒以上冷却し、あるいはその後さらに引き続いて５℃／ｓ以上の冷却速度にて３００℃以下まで冷却する方法である。
【００１１】
【発明の実施の形態】
まず、本発明の高炭素鋼線材の化学成分（以下、単位はmass％）の限定理由について説明する。
Ｃ：０．６〜１．０％
Ｃは強度を確保するための基本元素であり、０．６％未満では初析フェライトが生成し過ぎてパーライト主体の組織にならず、強度も低下する。一方、１．０％超では初析セメンタイトが生成して、伸線性を阻害するようになる。
【００１２】
Ｓｉ：０．１〜１．５％
Ｓｉは脱酸作用と固溶強化により強度を高める作用を有する。０．１％未満と少な過ぎるとこれらの効果が不足し、一方１．５％を超えて高過ぎるとフェライトを固溶強化し過ぎて加工性を阻害する。
【００１３】
Ｍｎ：０．３〜０．９％
Ｍｎは脱酸作用と固溶強化による強度向上作用を有する。含有量が０．３％未満と少な過ぎるとこれらの作用が不足し、一方０．９％超ではフェライトを固溶強化しすぎて加工性を阻害するようになる。また、偏析が生じ易い元素であり、添加量が多いと偏析により組織が不均−となり、伸線性が阻害される。
【００１４】
Ｐ：０．０２％以下
Ｐは不純物元素であり、少ないほど好ましい。特にフェライトを固溶強化するため、伸線性の劣化への影響が大きいので、本発明では０．０２％以下に止める。
【００１５】
Ｓ：０．０３％以下
Ｓも不純物元素であり、介在物ＭｎＳを生成して伸線性を阻害するため、０．０３％以下に止める。
【００１６】
Ｎ：０．００５％以下
Ｎも不純物元素であり、フェライトに固溶して、伸線時の発熱により時効硬化させ、伸線性の低下への影響が大きいため、少ないほど好ましく、０．００５％以下に止める。
【００１７】
本発明の高炭素鋼線材は、典型的には上記成分および残部Ｆｅを本質的成分とし、その他不可避的不純物からなるが、上記本質的成分の作用、効果を損なわない範囲で他の成分を添加してもよく、さらに線材の特性をより向上させる元素を添加してもよい。例えば、下記のＮｂ、Ｖの１種以上を必要に応じて添加することができる。
【００１８】
Ｎｂ：０．０２０〜０．０５０％、Ｖ：０．０５〜０．２０％
これらの元素はオーステナイトの回復、再結晶、粒成長を抑制する作用を有する。これによりパーライト変態が促進され、引張強さＴＳの低下、ノジュールサイズの微細化を促進することができ、伸線性が向上する。Ｎｂが０．０２０％未満、Ｖが０．０５％未満では前記作用が過少であるため、各々下限を０．０２０％、０．０５％とする。一方、Ｎｂが０．０５０％超、Ｖが０．２０％超では過度の析出強化により伸線性が返って低下するので、各々上限を０．０５０％、０．２０％とする。Ｖは添加により焼き入れ性向上効果も有するが、上記添加範囲では強度は過大にならず、伸線性も劣化しない。
【００１９】
さらにまた、前記本質的成分からなる組成、あるいはさらにＮｂ、Ｖを添加した組成において、Ａｌを０．０３５％以下含有させても伸線性が劣化することはないが、特にＮ：０．００１５〜０．００５０％で、かつＡｌ：０．０３０％以下含有させることで伸線性をより向上させることができる。
Ａｌを微量添加することで、ＡｌＮを析出させ、圧延線材のノジュールサイズをより微細に維持することが可能となる。ノジュールサイズをより微細化することで、伸線加工性がより向上し、より高い速度での伸線が可能となる。このとき、この効果を有効に発揮させるには、Ａｌを０．００６％以上添加することが好ましい。もっとも、Ａｌ添加系の高炭素鋼線は、タイヤコードやソーワイヤのような直径０．５mm以下の極細鋼線にまで加工すると、Ａｌを主成分とした不可避的な介在物がカッピー断線の起点となるため、かえって伸線性を阻害する。従って、Ａｌの微量添加は、鋼線の直径が０．５mm超のサイズの場合に適用することが好ましい。また、Ａｌを添加し過ぎても、ＡｌＮが析出し過ぎて、高い伸線速度における伸線性の向上が果たせないようになるため、Ａｌの含有量の上限は０．０３０％とすることが好ましい。なお、Ａｌを添加する場合、ＡｌＮの適量析出のために、鋼中に含有されるＮ量を０．００１５％以上に調節する必要がある。このようにＡｌ量およびＮ量を適切にコントロールすることで、適量のＡｌＮを析出させることができ、高速伸線により適した鋼線材を得ることができる。
【００２０】
次に、本発明の高炭素鋼線材の組織について説明する。
まず、組織と伸線性、ダイス寿命との関係について説明し、本発明の組織限定理由について説明する。
【００２１】
ダイス寿命を長くするためには、線材（圧延材）の強度を低下させる必要がある。引張強さＴＳ（ＭＰａ）はラメラ間隔Ｓ（μm ）によって決まり、下記の関係があることが知られている。したがって、ダイス寿命を伸ばすには、平均ラメラ間隔Ｓを大きくすることが重要である。
ＴＳ＝σ0＋ＫＳ-1/2
ここで、σ0、Ｋは定数である。
一方、歪（減面率）の小さい伸線初期には、ノジュール単位でパーライトの回転が起こり、ラメラが伸線方向に平行になるように回転する。このときラメラ間隔が粗いと円滑に回転することが困難であるため、ポイドが発生しやすくなる。ボイドが発生すると、これが起点となってカッピー断線と呼ばれる破断を引き起こし易くなり、伸線性が低下する。
【００２２】
従来の製造方法は、ラメラ間隔を広くするため、圧延後、水冷した線材を衝風冷却する際に、衝風量を絞り込んで製造していた。これによって、ラメラ間隔の広いパーライトを生成させることができるが、必然的にノジュールのサイズも大きくなり、強度の低下によるダイス寿命の向上と、ノジュールの微細化による伸線性の向上との両立が困難であった。なお、衝風量の制御においては、衝風量をゼロとするような特殊な制御は行われていない。
【００２３】
本発明では、後述するように、熱延後の冷却段階で衝風量をゼロとする冷却工程を含む冷却条件にて冷却することで、パーライトのラメラ間隔を広く維持しながら、ノジュールのサイズを飛躍的に微細化することに成功したものである。ノジュールが十分微細であれば、ラメラ間隔が広くても、伸線時にノジュールの回転が円滑に生じ、ポイドの発生ひいてはカッピー断線の発生が抑制される。このため、低強度ながら優れた伸線性を備え、より高速で伸線しても断線が生じることがなく、しかもダイス寿命の低下を防止することができる。
【００２４】
具体的組織条件として、まず組織中のパーライトの面積割合は多いほど望ましく、９５面積％以上とされる。パーライト以外の組織（フェライト、ベイナイト）が５％超であると伸線性が低下し、またフェライトは強度を低下させるため、最終製品（鋼線）の強度が出ないようになる。
【００２５】
前記パーライトはその平均ノジュール径が３０μm 以下とされる。３０μm 超では伸線の際にノジュールの円滑な回転が起きにくくなり、その分、断線し易くなり、伸線性の大幅な向上が期待できない。また、パーライトの平均ラメラ間隔は１００ｎｍ以上、好ましくは１５０ｎｍ以上とされる。１００ｎｍ未満では強度が必然的に高くなり、ダイス寿命が低下するようになる。一方、平均ラメラ間隔の上限は、下記Ｆ式がＦ＞０となる範囲内とされる。Ｆ式は、後述の実施例によって求められたものであり、ラメラ間隔を広くしたとき、その強度低下による断線発生傾向をノジュールの微細化によって相殺することができる限界を定める式であり、Ｆ＞０の範囲であれば断線を抑制しつつ、ラメラ間隔の拡張によりダイス寿命の向上を図ることができる。
Ｆ＝３５０．３／√Ｓ＋１３０．３／√Ｐ−５１．７
但し、Ｓは平均ラメラ間隔（ｎｍ）、Ｐは平均ノジュール径（μm ）
【００２６】
次に、本発明の高炭素鋼線材の工業的生産に適した製造方法について説明する。
上記化学成分の高炭素鋼を溶製後、連続鋳造により、あるいはその鋼塊を分塊圧延により鋼片（ビレット）を作製し、これを必要に応じて加熱後、仕上温度を１０５０〜８００℃として熱間圧延を終了する。仕上温度を１０５０℃以下の低温にすることによりオーステナイトの回復、再結晶、粒成長を抑制して強度低下を抑制し、ノジュールを微細化することができる。仕上温度の下限は低温過ぎると圧延機への負荷が過大となるため、８００℃以上、好ましくは９００℃以上とするのがよい。
【００２７】
仕上げ圧延後の冷却条件は、本発明において特に重要であり、図１を参照して詳細に説明する。なお、図１中、破線はパーライトのラメラ間隔を広くする際に採られる従来の冷却パタンを示すものであり、一様に冷却速度を遅くして冷却するため、ノジュール径を小さくすることに限界があり、ダイス寿命の向上と耐断線性との両立に限度があった。図１中の実線が本発明の冷却パターンであり、低強度と高耐断線性とを備えた前記パーライト組織を実現するものである。
【００２８】
仕上圧延後、直ちに、第１段冷却として、５０℃／ｓ以上の冷却速度にて９５０〜７５０℃の範囲内の温度まで急冷する。この第１段冷却によって、オーステナイトの回復、再結晶、粒成長を抑制して、線材の強度を低下させ、パーライトのノジュールを微細化する。第１段冷却の停止温度は、後述する第２段冷却の際にスケールを適度に生成させて、脱スケール性を確保するために規定される。スケールと伸線性とは密接な関連があり、脱スケール性が悪いと、残存スケールが多くなり、線材の表面性状が悪化し、ダイスとの摩擦が増加するため、ダイス寿命が低下し、また伸線性も低下するようになる。このため、適切なスケールを生成させるべく、第１段冷却の急冷停止温度を７５０〜９５０℃の範囲内に定める。７５０℃未満の温度まで冷却するとスケールが成長せず、脱スケールがし難くなる。一方、９５０℃超ではスケールが厚くなり過ぎるために、返って脱スケールが難くなる。また、９５０℃超では、その後の冷却過程で高温に曝される時間が長くなるため、オーステナイト粒が粒成長してしまい、微細ノジュールが得られないようになる。この第１段冷却は典型的には熱延後の線材を水冷することにより実施することができる。
【００２９】
次に、第２段冷却として、５〜２０℃／ｓの冷却速度にて６２０〜６８０℃の範囲内の温度に冷却する。冷却速度が５℃／ｓ未満では６８０℃よりも高い温度でパーライト変態が生じる。６８０℃超では、パーライトの核生成頻度が非常に低い状態での変態となる。このため生成するパーライト核の数が非常に少なく、少数のパーライトが成長することになり、ノジュールサイズが粗大化し、伸線性が低下する。一方、冷却速度が２０℃／ｓ超では、第２段冷却の際にスケールが成長しないようになるため、脱スケール性が悪化する。また、６２０℃未満まで冷却すると、ラメラ間隔が狭くなり、強度が高くなり過ぎてダイス磨耗が増加する。一方、６８０℃超では、高い温度域でパーライト変態が起こるため、上記のように伸線性が低下するようになる。この第２段冷却は、典型的には衝風冷却を行い、その風量を調整することにより実施することができる。
【００３０】
第２段冷却に引き続いて第３段冷却として２℃／ｓ以下の冷却速度にて２０秒以上保持する。この冷却により、第２段冷却後のある程度低い温度で保持された状態でパーライト変態が進行する。このため、パーライトの変態核が数多く生成し、ノジュールが微細化する。２℃／ｓ超の冷却速度あるいは２０秒未満の保持時間では、その後の温度低下が速く、低い温度領域でパーライト変態するようになり、パーライトのラメラ間隔が狭くなって強度が上昇し、ダイス寿命を悪化させる。この第３段冷却は、衝風量を必ずしもゼロにする必要はないが、典型的には衝風を所定時間止めて衝風量をゼロとし、パーライト変態の際の発熱を利用することによって実行することができる。
【００３１】
さらに、第３段冷却の後、好ましくは第４段冷却として、５℃／ｓ以上で３００℃以下の温度まで冷却するのがよい。かかる冷却により、スケール性状が改良され、伸線性がより向上する。冷却停止温度が３００℃超では、スケールの剥離を招き、新生面に新たに非常に薄いスケールが発生して脱スケールが困難になる。また、５℃／ｓ未満の冷却速度では、３００℃以下まで冷却するのに時間がかかり、生産性が非常に悪くなる。
【００３２】
以下、実施例を挙げて、本発明をより具体的に説明するが、本発明はかかる実施例によって限定的に解釈されるものではない。
【００３３】
【実施例】
［実施例Ａ］
本発明の成分を満足する下記高炭素鋼を転炉で溶製し、その鋼塊を分解圧延して１５５mm角のビレットを作製し、１１５０℃程度に加熱後、熱間圧延を行い、直径５．５mmの線材を得た。熱延線材を８８０〜１１００℃に設定した大気加熱炉、５８０〜６９０℃に保持した流動層に連続して通線し、線材の組織をパーライトに変態させた。この際、加熱温度、通線速度を変化させることにより、オーステナイト粒径を１０〜２００μm に制御した。流動層の温度により若干変化するが、オーステナイト粒径が小さい場合にはノジュール径が小さくなり、オーステナイト粒径が大きい場合にはノジュール径も大きくなる。一方、ラメラ間隔は流動層の温度が高ければ広くなり、低くければ狭くなる。これら温度を種々設定することにより、ラメラ間隔とノジュール径が種々異なる線材を実験室的に作製した。
【００３４】
上記の線材を用いてパーライトの面積率、平均ノジュール径、平均ラメラ間隔および引張試験により引張強さが測定された。
パーライト面積率は、線材を切断して横断面を鏡面研磨した試料を硝酸とエタノールの混合溶液でエッチングし、線材の表面と中心との間の中央位置における組織をＳＥＭ（走査型電子顕微鏡、倍率１０００）によって観察することによって求められた。
また、平均ノジュール径は、上記と同様にして試料を調整し、光学顕微鏡（倍率１００）にて組織観察を行い、フェライト粒度の測定方法（ＪＩＳＧ０５５２）に準拠して粒度番号Ｇを小数点以下第１位まで求め、次の式によってμm の単位に換算することによって求められた。
ノジュール径（μm ）＝１０×２(10-G)/2
一方、平均ラメラ間隔は、上記と同様に鏡面研磨し、上記と同様の方法でエッチングした試料の前記中央位置をＳＥＭで観察し、１０視野で５０００倍の写真を撮影し、各視野の写真を用いて視野内で最も、あるいはそれに次いで微細である３点でラメラに直角に線分を引き、その線分の長さとそれを横切るラメラの数からラメラ間隔を求め、すべての線分のラメラ間隔を平均することによって求められた。
【００３５】
さらにまた、上記線材の伸線性が以下のように実際に線材を伸線することによって評価された。線材は塩酸中に浸漬されてスケールが完全に除去された後、燐酸塩を線材表面に形成させる潤滑処理が行われ、その後、多段式の乾式伸線機で直径１．０mmまで伸線された。伸線は、最終伸線速度が３００ｍ／min の通常速度領域での通常伸線と、その２倍の６００ｍ／min での高速伸線とが行われた。伸線性の評価は、耐断線性については線材１００トン当たりの断線の有無によって評価された。さらに、断線が生じなかった線材についてダイスへの影響が調べられ、伸線後の表面性状（ダイス荒れによる表面傷が観察されなかった場合：○、断続的に軽微な表面傷が観察された場合：△、連続的な表面傷が観察された場合：×）とダイス寿命（ダイスが割れることなく摩耗もほとんど生じなかった場合：○、ダイスが割れなかったものの軽微な摩耗が生じた場合：△、摩耗が著しく、ダイスが割れた場合：×）とが評価された。
【００３６】
これらの測定結果、観察結果を表１に併せて示す。表１には前記Ｆ式によって算出した値（Ｆ値）も併記した。また、平均ラメラ間隔と平均ノジュール径と伸線速度６００ｍ／min における総合判定との関係を整理したグラフを図２に示す。前記Ｆ式は、同図において総合判定の○（図２中◎）および△（図２中○）と、×（図２中●）との境界線を求めることによって決定されたものであり、図中に実線により示される。
【００３７】
【表１】
表１より、平均ラメラ間隔、平均ノジュール径、Ｆ値が本発明条件を満足する試料No. １〜１７（発明例）では、通常伸線、高速伸線のいずれの場合でも良好な結果を得た。特に平均ラメラ間隔が１５０ｎｍ以上かつＦ値が適正なNo. ４〜１７では伸線性が非常に優れている。一方、試料No. ２１〜３６は比較例であり、No. ３１はパーライト量が過少であり、平均ラメラ間隔が１００ｎｍよりも狭いため、通常伸線においても表面性状が悪く、またダイスに割れが生じた。他のものでは、Ｆ値がＦ＜０となっており、通常伸線では問題がないものもあったが、高速伸線では全て断線してしまい、伸線性の劣化が著しい。
【００３９】
［実施例Ｂ］
下記表２に記載した種々の成分の鋼を用いて、実施例Ａと同様に、パーライト組織を有する直径５．５mmの熱間圧延線材を製作し、実施例Ａと同様に、引張強さ、パーライト面積率、平均ラメラ間隔、平均ノジュール径を測定し、伸線性を評価した。Ａｌを含有する試料線材の伸線性については、より一層条件の厳しい、最終伸線速度が８００ｍ／min での高速伸線をも実施し、評価した。
それらの結果を表３に示す。
【００４０】
【表２】
【表３】
表３より、発明例のNo. １〜９は、本発明の成分、パーライト組織条件を満足しており、通常伸線、高速伸線のいずれの場合でも良好な結果を得た。これに対して、比較例のNo. ２１，２２はＮｂ、Ｖのいずれかが規定量を超えて多量に添加されており、これらの元素による析出強化によって強度が非常に高くなり、通常伸線ではNo. ２２は断線しなかったものの、高速伸線では全て伸線途中で断線し、伸線性に劣る。
また、Ａｌ、Ｎをバランスよく含有した発明例のNo. ３０〜３２は伸線速度が８００ｍ／min の高速伸線であっても良好な伸線性を示した。一方、Ａｌは含有するもののＮ量が極めて少ないNo. ４０やＡｌ量が多過ぎるNo. ４２では、伸線速度：６００ｍ／min までは良好な伸線性を示したものの、伸線速度：８００ｍ／min では断線を生じた。また、Ａｌを含有するものの、Ｎが０．００５５％含有するNo. ４１はＮ量が多すぎて伸線性が劣化している。
【００４３】
［実施例Ｃ］
本発明の成分を満足する下記高炭素鋼を連続鋳造によりビレットを作製し、表４に示した仕上温度にて直径５．５mmの線材に熱間圧延し、この線材を熱延後直ちに図１に示す冷却曲線および表４に示す冷却速度、冷却停止温度、冷却時間に従って冷却した。第１段冷却は水冷により、第２段および第４段冷却は衝風冷却により、第３段冷却は衝風を停止して冷却速度を調整した。
・鋼組成（残部Ｆｅ、単位mass％）
Ｃ：０．８１６％、Ｓｉ：０．１５％、Ｍｎ：０．４６％、
Ｐ：０．００７％、Ｓ：０．００５％、Ｎ：０．００２５％
このようにして得られた線材を用いて、実施例Ａと同様にして、引張強さ、パーライト面積率、平均ラメラ間隔、平均ノジュール径を測定し、伸線性を評価した。それらの結果を表５に示す。
【００４４】
【表４】
【表５】
表５より、本発明の製造条件に従って熱間圧延、冷却を行った発明例No. １〜１１は、いずれも平均ラメラ間隔、平均ノジュール径、これらの値から求められるＦ値がそれぞれ本発明条件を満足しており、良好な伸線性が得られることが確認された。
【００４７】
一方、比較例については、No. ２１は圧延温度が１０５０℃を超えており、このため平均ノジュール径が大きく、Ｆ＜０となり、高速伸線の際に断線した。No. ２２は仕上げ圧延直後の第１段冷却の冷却速度が３５℃／ｓと遅いために平均ノジュール径が大きく、Ｆ＜０となり、高速伸線の際に断線した。No. ２３は第１段冷却の冷却停止温度が９２３℃と９００℃を超えているために平均ノジュール径が粗大化し、Ｆ＜０となり、またスケールが厚くなって脱スケール性が悪化したため、高速伸線で断線した。No. ２４は第２段冷却の冷却速度が２９℃／ｓと速いため、スケールが十分に成長せず、このため脱スケール性が悪化したため、高速伸線時に断線した。No. ２５は第２段冷却の停止温度が６９５℃と高く、このため第３段冷却の開始温度が６８０℃を超えるため、ラメラ間隔は十分広いが、ノジュールの微細化が不足して、Ｆ＜０となり、高速伸線時に断線した。No. ２６は、第２段冷却の停止温度が６１０℃と低すぎるため、またNo. ２７は第３段冷却の冷却速度が２．８℃／ｓと速すぎるため、ラメラ間隔が狭くなり過ぎて平均ラメラ間隔が１００ｎｍを下回り、強度が高くなり過ぎ、高速伸線時に断線した。またNo. ２８は第３段冷却の冷却時間が短すぎるため、第３段冷却の際に高温域で十分にパーライト変態が進行せず、その後の第４段冷却中の低温域にてパーライト変態が進行したため、平均ラメラ間隔が１００ｎｍを下回り、強度が過大となって、高速伸線時に断線した。また、No. ２９は第２段冷却〜第４段冷却を段階的に行うことなく一様の冷却速度にて冷却した従来の製造条件に対応した例であり、平均ラメラ間隔は広いが、平均コロニー径が４０μm 程度に微細化されたものの、平均ノジュール径はかなり大きいレベルに止まっており、このため高速伸線時に断線が生じた。
【００４８】
［実施例Ｄ］
下記鋼組成の高炭素鋼を用いて、実施例Ｃと同様に連続鋳造によりビレットを作製し、表６に示した仕上温度にて直径５．５mmの線材に熱間圧延した。その後、得られた線材の冷却速度を実施例Ｃと同様の方法で調節して、製造条件が伸線性に及ぼす影響を調べた。その結果を表７に示す。
・鋼組成（残部Ｆｅ，単位mass％）
Ｃ：０．７９０％、Ｓｉ：０．１８％、Ｍｎ：０．３８％、Ｐ：０．００６％、
Ｓ：０．００９％、Ｎ：０．００３５％、Ａｌ：０．０１８％
【００４９】
【表６】
【表７】
表７より、本発明の製造条件に従って熱間圧延、冷却を行った発明例の試料No. １〜３は、ＡｌおよびＮを適量含有するものであるので、伸線速度が８００ｍ／min まで良好な伸線特性が得られた。一方、比較例の試料No. １１は、熱間圧延仕上温度が１０５０℃を超え、かつ第１段冷却の冷却停止温度が９５０℃を超えているため、平均のノジュール径が大きくなり、Ｆ値が負となり、伸線時に断線した。また、比較例の試料No. １２は第２段冷却の冷却速度が５℃／ｓ未満であり、かつその冷却停止温度も６８０℃を超えているため、平均のノジュール径が粗大化し、Ｆ値が負となって、伸線時に断線した。
【００５２】
【発明の効果】
本発明の高炭素鋼線材は、所定成分の下、９５面積％以上のパーライトを有し、パーライトの平均ラメラ間隔を１００ｎｍ以上としてダイス寿命の向上を図る一方、従来ラメラ間隔を広げる製造条件の下では不可能であった領域まで平均ノジュール径を微細化したので、乾式伸線における断線の発生を抑制しつつ、強度の上昇を抑えてダイス寿命の向上を図ることができ、優れた伸線性を備える。
【図面の簡単な説明】
【図１】本発明の高炭素鋼線材の製造における熱延後の冷却工程を示す冷却線図である。
【図２】実施例における平均ノジュール径および平均ラメラ間隔と伸線性との関係を示すグラフである。[0001]
[Technical field to which the invention belongs]
The present invention is a material for high-strength steel wires such as tire reinforcing steel wires, PC steel wires, and steel wires for ropes.Used for dry drawingThe present invention relates to a high carbon steel wire and a method for producing the same.
[0002]
[Prior art]
A high-strength steel wire is produced by drawing a high carbon steel wire produced by hot rolling to a required wire diameter. For wire rods that are drawn into fine wires, such as tire steel cords and belt cords, if wire breakage occurs during wire drawing, productivity is significantly hindered, and thus good wire drawing properties are required. Conventionally, in order to obtain such good drawability, after hot rolling, the hot-rolled wire is water-cooled and blast-cooled to make the wire structure fine pearlite,DryIntermediate patenting is performed once or twice during the wire drawing process.
[0003]
However, in recent years, thinner wire diameters are required for high carbon steel wires, and it is desired to omit intermediate patenting from the viewpoint of improving productivity. For this reason, the high carbon steel wire is required to have better disconnection resistance, and further to improve the life of the die is also required from the viewpoint of productivity improvement.
[0004]
In response to such requirements, Japanese Patent Publication No. 3-60900 discloses an appropriate ratio of tensile strength and coarse pearlite in pearlite (perlite identifiable under a 500-fold microscope) according to the C equivalent of high carbon steel wire rod. In addition, JP 2000-63987 A discloses a technique for improving the drawability by setting the average colony diameter of pearlite to 150 μm or less and the average lamella spacing to 0.1 to 0.4 μm. Has been introduced. The colony refers to a region where the directions of pearlite lamella are aligned, and a nodule (also referred to as a block) having a constant ferrite crystal orientation is formed by a plurality of colonies. As described in the above publication, the wire rod after hot rolling is manufactured by adjusting the winding temperature by water cooling and subsequently adjusting the amount of blast by a stealmore adjusting cooling device.
[0005]
[Problems to be solved by the invention]
However, in the former technique, there is about 10 to 30% of coarse pearlite having a rough lamella spacing, so that the die life is improved, but the resistance to disconnection during wire drawing is insufficient, and sufficient wire drawing property is obtained. It is not done. On the other hand, even in the latter technique, the die life can be improved by roughening the lamella spacing to some extent as 0.1 to 0.4 μm. As a result of roughening the lamella spacing as described above, the average colony diameter is However, it cannot be said that sufficient disconnection resistance is obtained.
[0006]
In addition, in Steelmaking Research No. 295 (p52-63, technical report published by Nippon Steel Co., Ltd. in 1978), in order to prevent disconnection, suppression of excessive lamellar spacing and pearlite block (nodule) size Although it is shown that the suppression of the coarsening of the steel is effective, it is a result based on a Cr-added high carbon steel wire containing 1 to 2 wt% of Cr as a test steel, and considering the viewpoint of the die life It is not discussed, and the relationship between lamella spacing and nodule size is not clarified for wire drawing considering die life.
[0007]
The present invention has been made in view of such problems,A high carbon steel wire used for dry drawing, in dry drawingAn object of the present invention is to provide a high carbon steel wire rod having excellent wire drawability and excellent wire breakage resistance and die life, and a method for producing the same.
[0008]
[Means for Solving the Problems]
The present inventor researched how to suppress and prevent disconnection with the recognition that it is essential to widen the lamella spacing of pearlite to some extent and reduce the strength of the wire to improve the die life. However, by reducing the average particle size of pearlite nodules, which have physical meaning as crystal grains, to less than a certain value, even with a pearlite structure with a relatively wide lamellar spacing, the breakage resistance is greatly improved and excellent. As a result, it has been found that the wire drawing property can be obtained, and the present invention has been completed.
[0009]
That is, the high carbon steel wire of the present invention isIt is a high carbon steel wire used for dry drawing,Chemical composition is mass%,
C: 0.6-1.0%
Si: 0.1 to 1.5%,
Mn: 0.3-0.9%
P: 0.02% or less,
S: 0.03% or less,
N: 0.005% or less,
The balance Fe and inevitable impurities, or
Nb: 0.020 to 0.050%,
V: 0.05-0.20%
The pearlite has a pearlite of 95 area% or more, the average nodule diameter P of pearlite is 30 μm or less, the average lamella spacing S is 100 nm or more, P is μm, and S is nm. When expressed, the following formula F is within the range where F> 0. Further, in the above composition, Al can be contained in an amount of 0.035% or less, and in particular, N: 0.0015 to 0.0050% and Al: 0.030% or less may be contained.
F = 350.3 / √S + 130.3 / √P-51.7
[0010]
Moreover, the manufacturing method of the high carbon steel wire rod of this invention hot-rolls the steel slab of the said chemical component at the finishing temperature of 1050-800 degreeC, and immediately after completion | finish of finish rolling, 950 with the cooling rate of 50 degreeC / s or more. After cooling to a temperature in the range of ˜750 ° C., followed by cooling to a temperature in the range of 620 to 680 ° C. at a cooling rate of 5 to 20 ° C./s or more, 20 at a cooling rate of 2 ° C./s or less. It is a method of cooling to 300 ° C. or lower at a cooling rate of 5 ° C./s or more after that.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
First, the reasons for limiting the chemical components (hereinafter, the unit is mass%) of the high carbon steel wire of the present invention will be described.
C: 0.6 to 1.0%
C is a basic element for securing the strength. If it is less than 0.6%, pro-eutectoid ferrite is generated too much to form a pearlite-based structure, and the strength also decreases. On the other hand, if it exceeds 1.0%, pro-eutectoid cementite is formed and the wire drawing property is inhibited.
[0012]
Si: 0.1 to 1.5%
Si has the effect of increasing strength through deoxidation and solid solution strengthening. If the content is too small, such as less than 0.1%, these effects are insufficient. On the other hand, if the content is too high, exceeding 1.5%, the ferrite is strengthened by solid solution and the workability is impaired.
[0013]
Mn: 0.3 to 0.9%
Mn has a deoxidizing action and a strength improving action by solid solution strengthening. If the content is too low, less than 0.3%, these effects are insufficient. On the other hand, if it exceeds 0.9%, the ferrite is strengthened by solid solution and the workability is impaired. Further, it is an element that is easily segregated, and if the amount added is large, the structure becomes uneven due to segregation, and the drawability is hindered.
[0014]
P: 0.02% or less
P is an impurity element and is preferably as small as possible. In particular, since the solid solution strengthening of ferrite has a great influence on the deterioration of the wire drawing property, it is limited to 0.02% or less in the present invention.
[0015]
S: 0.03% or less
S is also an impurity element, and the inclusion MnS is generated to inhibit the drawability. Therefore, the content is limited to 0.03% or less.
[0016]
N: 0.005% or less
N is also an impurity element, and is solid-solved in ferrite and age-hardened by heat generation at the time of wire drawing, and since it has a large influence on the reduction of wire drawing property, the smaller the amount, the better.
[0017]
The high carbon steel wire rod of the present invention typically comprises the above components and the balance Fe as essential components, and other inevitable impurities, but other components are added within a range that does not impair the functions and effects of the above essential components. Alternatively, an element that further improves the properties of the wire may be added. For example, one or more of the following Nb and V can be added as necessary.
[0018]
Nb: 0.020 to 0.050%, V: 0.05 to 0.20%
These elements have a function of suppressing austenite recovery, recrystallization, and grain growth. As a result, the pearlite transformation is promoted, the reduction of the tensile strength TS and the refinement of the nodule size can be promoted, and the drawability is improved. If Nb is less than 0.020% and V is less than 0.05%, the effect is too small.0.020% And 0.05%. On the other hand, if Nb exceeds 0.050% and V exceeds 0.20%, the wire drawing property is reduced due to excessive precipitation strengthening, so the upper limit is made 0.050% and 0.20%, respectively. V has an effect of improving hardenability by addition, but the strength does not become excessive and the drawability does not deteriorate in the above addition range.
[0019]
Furthermore, in the composition consisting of the above-mentioned essential components, or in the composition to which Nb and V are further added, even if Al is contained in an amount of 0.035% or less, the drawability does not deteriorate, but particularly N: 0.0015 to By containing 0.0050% and Al: 0.030% or less, the drawability can be further improved.
By adding a small amount of Al, it becomes possible to precipitate AlN and maintain the nodule size of the rolled wire rod more finely. By making the nodule size finer, wire drawing workability is further improved, and wire drawing at a higher speed becomes possible. At this time, in order to exhibit this effect effectively, it is preferable to add Al 0.006% or more. However, when an Al-added high carbon steel wire is processed into an ultrafine steel wire with a diameter of 0.5 mm or less, such as a tire cord or saw wire, the inevitable inclusions containing Al as the main component are Therefore, the wire drawing is inhibited. Therefore, it is preferable to apply a small amount of Al when the diameter of the steel wire is more than 0.5 mm. In addition, even if Al is added excessively, AlN is precipitated too much to improve the drawability at a high drawing speed, so the upper limit of the Al content is preferably 0.030%. . In addition, when adding Al, it is necessary to adjust N amount contained in steel to 0.0015% or more for precipitation of an appropriate amount of AlN. By appropriately controlling the amount of Al and the amount of N in this manner, an appropriate amount of AlN can be precipitated, and a steel wire suitable for high-speed wire drawing can be obtained.
[0020]
Next, the structure of the high carbon steel wire of the present invention will be described.
First, the relationship between the structure, the drawability, and the die life will be described, and the reason for limiting the structure of the present invention will be described.
[0021]
In order to increase the die life, it is necessary to reduce the strength of the wire (rolled material). It is known that the tensile strength TS (MPa) is determined by the lamellar spacing S (μm) and has the following relationship. Therefore, in order to extend the die life, it is important to increase the average lamella spacing S.
TS = σ0+ KS-1/2
Where σ0, K are constants.
On the other hand, in the initial stage of wire drawing with a small strain (area reduction rate), pearlite rotates in units of nodules, and the lamella rotates so as to be parallel to the wire drawing direction. At this time, if the lamella spacing is rough, it is difficult to rotate smoothly, so that voids are likely to occur. When a void is generated, it becomes a starting point, and it is easy to cause a break called a “coppy disconnection”, and the drawability is lowered.
[0022]
In the conventional manufacturing method, in order to widen the lamella spacing, when the water-cooled wire rod is blast-cooled after rolling, the blast volume is reduced. This makes it possible to generate pearlite with wide lamella spacing, but inevitably the size of the nodules increases, making it difficult to achieve both improved die life due to reduced strength and improved drawability due to smaller nodules. Met. In the control of the blast volume, no special control is performed so that the blast volume is zero.
[0023]
In the present invention, as will be described later, by cooling under cooling conditions including a cooling process in which the amount of blast is zero in the cooling stage after hot rolling, the size of the nodules jumps while maintaining a wide pearlite lamella spacing. Succeeded in miniaturization. If the nodules are sufficiently fine, even if the lamella spacing is wide, the nodules are smoothly rotated during wire drawing, and the generation of voids and, in turn, the occurrence of coupling breaks is suppressed. For this reason, although it has low strength, it has excellent wire drawing properties, and even if it is drawn at a higher speed, disconnection does not occur, and a reduction in die life can be prevented.
[0024]
As a specific tissue condition, first, it is desirable that the area ratio of pearlite in the tissue is as large as possible. If the structure (ferrite, bainite) other than pearlite is more than 5%, the wire drawability is lowered, and the ferrite lowers the strength, so that the strength of the final product (steel wire) is prevented.
[0025]
The pearlite has an average nodule diameter of 30 μm or less. If it exceeds 30 μm, smooth rotation of the nodules is difficult to occur during wire drawing, and accordingly, wire breakage is likely to occur, and a significant improvement in wire drawability cannot be expected. The average lamella spacing of pearlite is 100 nm or more, preferably 150 nm or more. If the thickness is less than 100 nm, the strength is inevitably increased, and the die life is reduced. On the other hand, the upper limit of the average lamella interval is set within a range where F> 0 is F> 0. Formula F is obtained by the examples described later, and is a formula that defines a limit that can cancel out the tendency of disconnection due to a decrease in strength when the lamella spacing is widened by making nodules finer, and F> If it is in the range of 0, the die life can be improved by expanding the lamella spacing while suppressing disconnection.
F = 350.3 / √S + 130.3 / √P-51.7
Where S is the average lamella spacing (nm) and P is the average nodule diameter (μm).
[0026]
Next, the manufacturing method suitable for industrial production of the high carbon steel wire of this invention is demonstrated.
After melting the high-carbon steel having the above chemical components, a billet is produced by continuous casting or by ingot rolling of the steel ingot, and after heating this as necessary, the finishing temperature is set to 1050 to 800 ° C. The hot rolling is finished. By setting the finishing temperature to a low temperature of 1050 ° C. or less, it is possible to suppress austenite recovery, recrystallization, and grain growth, thereby suppressing a decrease in strength and miniaturizing nodules. If the lower limit of the finishing temperature is too low, the load on the rolling mill will be excessive, so that it is 800 ° C or higher, preferably 900 ° C or higher.
[0027]
The cooling conditions after finish rolling are particularly important in the present invention, and will be described in detail with reference to FIG. In FIG. 1, the broken line indicates a conventional cooling pattern taken when the pearlite lamella spacing is widened, and the cooling rate is uniformly slowed down so that the nodule diameter is limited. Therefore, there is a limit to the balance between the improvement of the die life and the resistance to disconnection. The solid line in FIG. 1 is the cooling pattern of the present invention, and realizes the pearlite structure having low strength and high disconnection resistance.
[0028]
Immediately after the finish rolling, the first stage cooling is rapidly cooled to a temperature in the range of 950 to 750 ° C. at a cooling rate of 50 ° C./s or more. This first stage cooling suppresses austenite recovery, recrystallization, and grain growth, lowers the strength of the wire, and refines the pearlite nodules. The stop temperature of the first stage cooling is defined in order to appropriately generate a scale during the second stage cooling described later and to ensure descalability. Scale and drawability are closely related.If the descalability is poor, the remaining scale increases, the surface quality of the wire deteriorates, and friction with the die increases, resulting in a decrease in die life and elongation. The linearity also decreases. For this reason, in order to generate an appropriate scale, the rapid cooling stop temperature of the first stage cooling is set within a range of 750 to 950 ° C. When cooled to a temperature of less than 750 ° C., the scale does not grow and descaling becomes difficult. On the other hand, if it exceeds 950 ° C., the scale becomes too thick, so that it becomes difficult to remove the scale. On the other hand, when the temperature exceeds 950 ° C., the time of exposure to a high temperature in the subsequent cooling process becomes long, so that austenite grains grow and fine nodules cannot be obtained. This first stage cooling can typically be carried out by water cooling the wire after hot rolling.
[0029]
Next, as the second stage cooling, cooling is performed at a cooling rate of 5 to 20 ° C./s to a temperature in the range of 620 to 680 ° C. When the cooling rate is less than 5 ° C./s, pearlite transformation occurs at a temperature higher than 680 ° C. Above 680 ° C., transformation takes place with a very low pearlite nucleation frequency. For this reason, the number of pearlite nuclei to be generated is very small, and a small number of pearlite grows, the nodule size becomes coarse, and the drawability deteriorates. On the other hand, when the cooling rate exceeds 20 ° C./s, the scale does not grow during the second stage cooling, so the descaling property is deteriorated. Moreover, when it cools to less than 620 degreeC, a lamella space | interval will become narrow and intensity | strength will become high too much and die wear will increase. On the other hand, when the temperature exceeds 680 ° C., pearlite transformation occurs in a high temperature range, so that the drawability is lowered as described above. This second stage cooling can be performed by typically performing blast cooling and adjusting the air volume.
[0030]
Subsequent to the second stage cooling, the third stage cooling is maintained for 20 seconds or more at a cooling rate of 2 ° C./s or less. By this cooling, the pearlite transformation proceeds while being kept at a somewhat low temperature after the second stage cooling. For this reason, a lot of pearlite transformation nuclei are generated, and the nodules are refined. At a cooling rate of over 2 ° C / s or a holding time of less than 20 seconds, the subsequent temperature drop is rapid, and pearlite transformation occurs in a low temperature region, the pearlite lamella spacing is narrowed, the strength is increased, and the die life is increased. Worsen. This third stage cooling is not necessarily required to reduce the blast amount to zero, but is typically performed by stopping the blast for a predetermined time to make the blast amount zero, and using the heat generated during the pearlite transformation. Can do.
[0031]
Furthermore, after the third stage cooling, it is preferable to cool to a temperature not lower than 5 ° C./s and not higher than 300 ° C. as the fourth stage cooling. Such cooling improves the scale properties and further improves the drawability. When the cooling stop temperature is higher than 300 ° C., scale peeling occurs, and a very thin scale is newly generated on the new surface, making it difficult to descal. Further, at a cooling rate of less than 5 ° C./s, it takes time to cool down to 300 ° C. or less, and the productivity becomes very poor.
[0032]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limitedly interpreted by this Example.
[0033]
【Example】
[Example A]
The following high carbon steel satisfying the components of the present invention is melted in a converter, the steel ingot is cracked and rolled to produce a 155 mm square billet, heated to about 1150 ° C., hot-rolled, and diameter 5 A 5 mm wire was obtained. The hot-rolled wire was continuously passed through an atmospheric heating furnace set at 880 to 1100 ° C. and a fluidized bed maintained at 580 to 690 ° C. to transform the structure of the wire into pearlite. At this time, the austenite particle size was controlled to 10 to 200 μm by changing the heating temperature and the line speed. Although it varies slightly depending on the temperature of the fluidized bed, the nodule diameter decreases when the austenite particle size is small, and the nodule diameter increases when the austenite particle size is large. On the other hand, the lamellar interval becomes wider when the temperature of the fluidized bed is higher and becomes narrower when the temperature of the fluidized bed is lower. By setting these temperatures in various ways, wires with different lamella spacing and nodule diameter were produced in the laboratory.
[0034]
Tensile strength was measured by the pearlite area ratio, average nodule diameter, average lamellar spacing, and tensile test using the above wire.
The pearlite area ratio is obtained by etching a sample obtained by cutting a wire and mirror-polishing the cross section with a mixed solution of nitric acid and ethanol, and analyzing the structure at the central position between the surface and the center of the wire with an SEM (scanning electron microscope, magnification) 1000).
In addition, the average nodule diameter was adjusted in the same manner as described above, and the structure was observed with an optical microscope (magnification 100). It was calculated by converting to the unit of μm by the following formula.
Nodule diameter (μm) = 10 × 2(10-G) / 2
On the other hand, the average lamella spacing was mirror-polished in the same manner as described above, and the central position of the sample etched by the same method as above was observed with an SEM. Use a line segment perpendicular to the lamella at the three points that are the finest in the field of view, or the next finest, and find the lamella interval from the length of the line segment and the number of lamellas that cross it. Was obtained by averaging.
[0035]
Furthermore, the drawability of the wire was evaluated by actually drawing the wire as follows. The wire was immersed in hydrochloric acid and the scale was completely removed, followed by a lubrication treatment for forming phosphate on the surface of the wire. Thereafter, the wire was drawn to a diameter of 1.0 mm with a multistage dry wire drawing machine. . For wire drawing, normal wire drawing in a normal speed region where the final wire drawing speed was 300 m / min and high-speed wire drawing at 600 m / min which was twice that of the normal wire drawing were performed. The evaluation of wire drawability was evaluated based on the presence or absence of wire breakage per 100 tons of wire. Furthermore, the influence on the die was investigated for the wire that did not break, and the surface properties after wire drawing (when surface damage due to roughing of the die was not observed: ○, when slight surface damage was observed intermittently : △, when continuous surface scratches are observed: ×) and die life (when the die does not crack and wear hardly occurs: ○, when the die does not crack but slight wear occurs: △ In the case where the wear was remarkable and the die was cracked, x) was evaluated.
[0036]
These measurement results and observation results are also shown in Table 1. Table 1 also shows values (F values) calculated by the F formula. Further, FIG. 2 shows a graph in which the relationship between the average lamella spacing, the average nodule diameter, and the comprehensive determination at the drawing speed of 600 m / min is arranged. The formula F is determined by obtaining a boundary line between ○ (◎ in FIG. 2) and Δ (○ in FIG. 2) and × (● in FIG. 2) of the comprehensive judgment in FIG. Indicated in the figure by a solid line.
[0037]
[Table 1]
From Table 1, sample Nos. 1 to 17 (invention examples) in which the average lamella spacing, average nodule diameter, and F value satisfy the conditions of the present invention give good results in both normal wire drawing and high-speed wire drawing. It was. In particular, Nos. 4 to 17 having an average lamella spacing of 150 nm or more and an appropriate F value have excellent wire drawing properties. On the other hand, Samples Nos. 21 to 36 are comparative examples, and No. 31 has an excessive amount of pearlite, and the average lamella spacing is narrower than 100 nm. Therefore, the surface properties are poor even in normal wire drawing, and the die is cracked. occured. Others had an F value of F <0 and there was no problem with normal wire drawing. However, high-speed wire drawing was all broken, and the wire drawing property was significantly deteriorated.
[0039]
[Example B]
Using steels having various components described in Table 2 below, a hot rolled wire rod having a pearlite structure and a diameter of 5.5 mm was produced in the same manner as in Example A. As in Example A, the tensile strength, The pearlite area ratio, the average lamella spacing, and the average nodule diameter were measured to evaluate the drawability. The wire drawability of the sample wire containing Al was evaluated by carrying out high-speed wire drawing at a final wire drawing speed of 800 m / min even more severe.
The results are shown in Table 3.
[0040]
[Table 2]
[Table 3]
From Table 3, Nos. 1 to 9 of the inventive examples satisfy the components of the present invention and the pearlite structure conditions, and good results were obtained in both cases of normal wire drawing and high-speed wire drawing. On the other hand, in Comparative Examples No. 21 and 22, either Nb or V is added in a large amount exceeding the specified amount, and the strength is very high due to precipitation strengthening by these elements. Then, although No. 22 did not break, in high-speed wire drawing, all were broken in the middle of wire drawing, and the wire drawing property was inferior.
In addition, Nos. 30 to 32 of the invention examples containing Al and N in a well-balanced manner showed good wire drawing even when the wire drawing speed was 800 m / min. On the other hand, No. 40 containing Al but having a very small amount of N and No. 42 containing too much Al showed good wire drawing until a drawing speed of 600 m / min, but a drawing speed of 800 m / min. In min, disconnection occurred. Moreover, although No. 41 which contains Al but 0.0055% of N contains too much N amount, wire drawing property has deteriorated.
[0043]
[Example C]
A billet is produced by continuous casting of the following high carbon steel satisfying the components of the present invention, and hot-rolled to a wire having a diameter of 5.5 mm at the finishing temperature shown in Table 4. It cooled according to the cooling curve shown in Table 4 and the cooling rate, cooling stop temperature, and cooling time shown in Table 4. The first stage cooling was performed by water cooling, the second stage cooling and the fourth stage cooling were performed by blast cooling, and the third stage cooling was stopped by adjusting the cooling rate.
-Steel composition (remainder Fe, unit mass%)
C: 0.816%, Si: 0.15%, Mn: 0.46%,
P: 0.007%, S: 0.005%, N: 0.0025%
Using the wire thus obtained, the tensile strength, the pearlite area ratio, the average lamella spacing, and the average nodule diameter were measured in the same manner as in Example A to evaluate the wire drawing property. The results are shown in Table 5.
[0044]
[Table 4]
[Table 5]
From Table 5, Invention Example Nos. 1 to 11 in which hot rolling and cooling were performed according to the production conditions of the present invention are all average lamella spacing, average nodule diameter, and F values determined from these values, respectively. It was confirmed that good drawability was obtained.
[0047]
On the other hand, as for the comparative example, No. 21 had a rolling temperature exceeding 1050 ° C., and thus the average nodule diameter was large, F <0, and the wire was broken during high-speed drawing. In No. 22, the cooling rate of the first stage cooling immediately after finish rolling was as slow as 35 ° C./s, so the average nodule diameter was large, F <0, and the wire was broken during high-speed drawing. In No. 23, since the cooling stop temperature of the first stage cooling exceeds 923 ° C and 900 ° C, the average nodule diameter becomes coarse, F <0, and the scale becomes thick and the descaling property deteriorates. Disconnected by wire drawing. In No. 24, the cooling rate of the second stage cooling was as fast as 29 ° C./s, so that the scale did not grow sufficiently. For this reason, the descalability was deteriorated, and therefore, the wire was broken at the time of high-speed drawing. No. 25 has a high second-stage cooling stop temperature of 695 ° C., and therefore the third-stage cooling start temperature exceeds 680 ° C., so that the lamella spacing is sufficiently wide, but nodule refinement is insufficient, and F <0 and the wire was broken during high-speed drawing. In No. 26, the stop temperature of the second stage cooling is too low at 610 ° C., and in No. 27, the cooling speed of the third stage cooling is too high at 2.8 ° C./s, so that the lamella interval becomes too narrow. The average lamella spacing was less than 100 nm, the strength was too high, and the wire was broken during high-speed drawing. In No. 28, since the cooling time of the third stage cooling is too short, the pearlite transformation does not proceed sufficiently in the high temperature region during the third stage cooling, and the pearlite transformation in the low temperature region during the subsequent fourth stage cooling. Therefore, the average lamella spacing was less than 100 nm, the strength was excessive, and the wire was broken during high-speed wire drawing. In addition, No. 29 is an example corresponding to the conventional manufacturing conditions in which cooling is performed at a uniform cooling rate without performing the second-stage cooling to the fourth-stage cooling step by step. Although the colony diameter was refined to about 40 μm, the average nodule diameter remained at a considerably large level, and thus disconnection occurred at the time of high-speed drawing.
[0048]
[Example D]
Billets were produced by continuous casting in the same manner as in Example C using high carbon steel having the following steel composition, and hot rolled into a wire having a diameter of 5.5 mm at the finishing temperature shown in Table 6. Thereafter, the cooling rate of the obtained wire was adjusted in the same manner as in Example C, and the influence of the production conditions on the wire drawing property was examined. The results are shown in Table 7.
-Steel composition (remainder Fe, unit mass%)
C: 0.790%, Si: 0.18%, Mn: 0.38%, P: 0.006%,
S: 0.009%, N: 0.0035%, Al: 0.018%
[0049]
[Table 6]
[Table 7]
From Table 7, sample Nos. 1 to 3 of the inventive examples that were hot-rolled and cooled in accordance with the production conditions of the present invention contain appropriate amounts of Al and N, so the wire drawing speed is good up to 800 m / min. A good wire drawing characteristic was obtained. On the other hand, the sample No. 11 of the comparative example has a hot rolling finish temperature exceeding 1050 ° C. and the cooling stop temperature of the first stage cooling exceeds 950 ° C., so that the average nodule diameter becomes large and F value Became negative and disconnected during wire drawing. Further, Sample No. 12 of the comparative example has a cooling rate of the second stage cooling of less than 5 ° C./s and its cooling stop temperature exceeds 680 ° C., so that the average nodule diameter becomes coarse and F value Became negative and disconnected during wire drawing.
[0052]
【The invention's effect】
The high carbon steel wire of the present invention has 95% by area or more of pearlite under a predetermined component, and is intended to improve the die life by setting the average lamella spacing of pearlite to 100 nm or more. Since the average nodule diameter has been reduced to a region that was impossible,In dry drawingWhile suppressing the occurrence of disconnection, it is possible to improve the die life by suppressing an increase in strength, and has excellent wire drawing properties.
[Brief description of the drawings]
FIG. 1 is a cooling diagram showing a cooling process after hot rolling in the production of a high carbon steel wire of the present invention.
FIG. 2 is a graph showing the relationship between the average nodule diameter and the average lamella spacing and the wire drawing in the examples.
Claims (6)
Ｃ：０．６〜１．０％、
Ｓｉ：０．１〜１．５％、
Ｍｎ：０．３〜０．９％、
Ｐ：０．０２％以下、
Ｓ：０．０３％以下、
Ｎ：０．００５％以下、
残部Ｆｅおよび不可避的不純物からなり、組織が９５面積％以上のパーライトを有し、パーライトの平均ノジュール径Ｐが３０μm 以下、平均ラメラ間隔Ｓが１００ｎｍ以上で、かつＰをμm 、Ｓをｎｍで表したとき下記Ｆ式がＦ＞０となる範囲内にある、伸線性に優れた高炭素鋼線材。
Ｆ＝３５０．３／√Ｓ＋１３０．３／√Ｐ−５１．７ It is a high carbon steel wire used for dry wire drawing, and its chemical composition is mass%.
C: 0.6-1.0%
Si: 0.1 to 1.5%,
Mn: 0.3-0.9%
P: 0.02% or less,
S: 0.03% or less,
N: 0.005% or less,
It consists of the balance Fe and inevitable impurities, the structure has pearlite of 95 area% or more, the average nodule diameter P of pearlite is 30 μm or less, the average lamella spacing S is 100 nm or more, P is μm, and S is nm. A high carbon steel wire rod excellent in wire drawability within the range where the following formula F is F> 0.
F = 350.3 / √S + 130.3 / √P-51.7
Ｎｂ：０．０２０〜０．０５０％、
Ｖ：０．０５〜０．２０％
の１種または２種以上を含む請求項１に記載した高炭素鋼線材。further,
Nb: 0.020 to 0.050%,
V: 0.05-0.20%
The high carbon steel wire according to claim 1, comprising one or more of the above.
Ａｌ：０．０３５％以下を含む請求項１または２に記載した高炭素鋼線材。further,
The high carbon steel wire according to claim 1 or 2, comprising Al: 0.035% or less.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| JP2002166615A JP3681712B2 (en) | 2001-06-28 | 2002-06-07 | High carbon steel wire rod excellent in drawability and manufacturing method thereof |
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| Application Number | Priority Date | Filing Date | Title |
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| JP2001196066 | 2001-06-28 | ||
| JP2001-196066 | 2001-06-28 | ||
| JP2002166615A JP3681712B2 (en) | 2001-06-28 | 2002-06-07 | High carbon steel wire rod excellent in drawability and manufacturing method thereof |
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| JP2003082434A JP2003082434A (en) | 2003-03-19 |
| JP3681712B2 true JP3681712B2 (en) | 2005-08-10 |
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| JP2002166615A Expired - Fee Related JP3681712B2 (en) | 2001-06-28 | 2002-06-07 | High carbon steel wire rod excellent in drawability and manufacturing method thereof |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007139234A1 (en) | 2006-06-01 | 2007-12-06 | Nippon Steel Corporation | High-ductility high-carbon steel wire |
| KR100970788B1 (en) * | 2006-10-12 | 2010-07-16 | 신닛뽄세이테쯔 카부시키카이샤 | High strength steel sheet for good wire drawability property and the method thereof |
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| EP1674588B1 (en) | 2004-12-22 | 2010-02-10 | Kabushiki Kaisha Kobe Seiko Sho | High carbon steel wire material having excellent wire drawability and manufacturing process thereof |
| JP4836121B2 (en) * | 2006-01-13 | 2011-12-14 | 株式会社神戸製鋼所 | Method for producing high carbon steel wire rod excellent in wire drawability |
| JP2007327084A (en) * | 2006-06-06 | 2007-12-20 | Kobe Steel Ltd | Wire rod having excellent wire drawability and its production method |
| WO2011055746A1 (en) | 2009-11-05 | 2011-05-12 | 新日本製鐵株式会社 | High-carbon steel wire material with excellent processability |
| JP5503515B2 (en) * | 2010-12-15 | 2014-05-28 | 株式会社神戸製鋼所 | High carbon steel wire rod excellent in dry drawing and method for producing the same |
| JP5783067B2 (en) * | 2011-01-28 | 2015-09-24 | 新日鐵住金株式会社 | Wire mesh |
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| WO2016021556A1 (en) | 2014-08-08 | 2016-02-11 | 新日鐵住金株式会社 | High carbon steel wire having excellent drawability |
| JP2017101296A (en) * | 2015-12-02 | 2017-06-08 | 株式会社神戸製鋼所 | Hot rolled wire excellent in hydrogen blistering resistance |
| CN115287545B (en) * | 2022-08-29 | 2023-07-14 | 盐城市联鑫钢铁有限公司 | Q195L cold heading steel wire rod for fastener and preparation method thereof |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007139234A1 (en) | 2006-06-01 | 2007-12-06 | Nippon Steel Corporation | High-ductility high-carbon steel wire |
| KR100970788B1 (en) * | 2006-10-12 | 2010-07-16 | 신닛뽄세이테쯔 카부시키카이샤 | High strength steel sheet for good wire drawability property and the method thereof |
| US8308875B2 (en) | 2006-10-12 | 2012-11-13 | Nippon Steel Corporation | High-strength wire rod excellent in drawing characteristics and method of manufacturing the same |
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| Publication number | Publication date |
|---|---|
| JP2003082434A (en) | 2003-03-19 |
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