JP3572784B2 - Hot-rolled steel sheet excellent in slidability and mold galling resistance and method for producing the same - Google Patents
Hot-rolled steel sheet excellent in slidability and mold galling resistance and method for producing the same Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、熱延後、酸洗および塗油して使用される熱延鋼板とその製造方法に関するものであって、とくに摺動性と耐型かじり性とを兼ね備えた特性を有し、プレス等の成形加工用の使途に好適な熱延鋼板およびその製造方法に関するものである。
【０００２】
【従来の技術】
熱延鋼板は、連続鋳造法あるいは造塊法によって得た鋼片を熱間圧延することによって製造される。こうして製造された熱延鋼板は、一部は冷延鋼板用の圧延素材として使用され、また他の一部は熱延のままで加工用として使用される。
さて、最近、自動車分野などにおいては、製品コストを低減させる方策として、従来では冷延鋼板が用いられたプレス部位を、より低コストの熱延鋼板に置き替えようとする傾向が増えてきた。
このような、冷延鋼板に代替するための熱延鋼板の製造技術は、例えば、特開昭５９−７６８２３号公報、特開昭４−１３６１２２号公報などに提案されている。
【０００３】
上記特開昭５９−７６８２３号公報に開示の方法は、Ｃ，Ｍｎ，Ｐ量を規定した鋼を、熱延後６００ ℃以上で３時間以上の熱処理を行い、酸洗後、１ 〜５％で調質圧延を行う薄手の熱延鋼板の製造法である。また、前記特開平４−１３６１２２号公報に開示の方法は、Ｃ 、Ｍｎ量を規定した鋼をＡｒ３変態点以上で圧延し、酸洗工程を経た後に５ 〜２０％の調質圧延を行い、板厚０．８ 〜２．０ｍｍ とする極薄熱延鋼板の製造方法である。
【０００４】
【発明が解決しようとする課題】
しかしながら、これら従来の熱延鋼板は、安価ではあるもののそのプレス加工性は冷延鋼板には遠く及ばないのが実情であった。このように、従来の技術によって製造した熱延鋼板の加工性が劣る大きな理由として、製品の表面粗さが粗い（Ｒａ：１．５μｍ程度）ために、摺動性が劣ることが挙げられる。
すなわち、自動車用の鋼板として理想的な表面粗さは、プレス加工時の摺動性の向上（摩擦係数の低減）の観点から、Ｒａ：０．８ μｍ以下、Ｒｍａｘ ： ４．０μｍ以下であるのに対し、従来の技術では、熱延鋼板の表面粗さはどうしてもこれよりも大きくなり、加工に耐えうる熱延鋼板を製造することができなかったのである。その上、表面粗さが粗いと、プレス成形し塗装した後の表面外観が劣るという問題も招いていた。
【０００５】
ところで、このように表面性状が劣る熱延鋼板の表面粗さを低減するための手段として、焼鈍後の冷延鋼板に一般的に採用されている、調質圧延を適用することが考えられる。
しかし、この場合には、粗度の大きな熱延鋼板を調質圧延で無理矢理粗度調整すると、その分高圧下が必要となり、延性の低下が避けられない。そして、この延性の低下は、通常の熱延鋼板の製造工程において、酸洗効率を向上させるために行われる、調質圧延あるいはレベラーを用いた酸洗前処理によって引き起こされる延性の低下と重畳して、一層の延性低下をもたらすという問題があった。
また、鋼板表面をこのような方法で低粗度の表面にした場合、従来の熱延鋼板では粗度が粗いため問題とならなかった、耐型かじり性が低下するという問題が新たに出現した。例えば、従来の技術を駆使して低粗度を達成した熱延鋼板を、冷延鋼板の代替に使用した場合に、プレス加工後のビード部やコーナー部のように大きな荷重がかかる個所で耐型かじり性が低下していた。
【０００６】
上述したように、従来の技術では、摺動性と耐型かじり性とを共に満たした、プレス加工に耐えるような熱延鋼板を製造することができなかった。
そこで、本発明の主たる目的は、従来の熱延鋼板が抱えている上述した問題を解消した、摺動性および耐型かじり性に優れる新規な熱延鋼板を提供することにある。
本発明の他の目的は、摺動特性としての摩擦係数が０．１３以下であって、しかも耐型かじり性が良好な熱延鋼板を提供することにある。
本発明のさらに他の目的は、上記各熱延鋼板を、熱間粗圧延工程と熱間仕上げ圧延工程との間で超高圧のデスケーリングを適用することにより、有利に製造する方法を提供することにある。
【０００７】
【課題を解決するための手段】
発明者らは、上記目的を達成すべく、まず、摺動性の改善（摩擦係数の低減）について、仕上圧延に先立って行うデスケーリング条件に着目して鋭意研究を重ねた結果、これまでに用いられたことのないような超高圧のデスケーリングを適用することが、鋼板表面の表面粗さを低下、摺動性の改善の向上に極めて有効であることを知見した。
また、熱延鋼板の型かじりが、冷延鋼板に比べ発生しやすくなるという現象は、冷延鋼板では焼鈍中の元素濃化により鋼板表面に表面濃化層が存在し、耐型かじり性に有利に作用するのに対し、酸洗処理を経た熱延鋼板では鋼板表面に地鉄がそのまま露出した状態となり、摺動性は良好でも金型との焼きつきのようなかじりを引き起こすことによるものである考えた。この現象は、延性改善に一般的に採用される、鋼の極低炭素化を目指した場合に、一層顕著になることを意味する。
この型かじり性の改善についても、発明者らは多くの実験を重ねた。その結果、素材成分と製造条件を適正に制御して得られた鋼板の表面に、極圧添加剤を含有する潤滑油膜を形成することにより、有利に耐型かじり性を改善できることを知見した。
本発明は、上述した知見に立脚するものであり、その要旨構成は下記のとおりである。
【０００８】
（１） 鋼組成が、
Ｃ：０．０１ｗｔ％以下、 Ｍｎ：０．０５〜０．５ ｗｔ％、
Ｐ：０．０１ｗｔ％以下、 Ｓ：０．０１ｗｔ％以下、
ｓｏｌ Ａｌ：０．０１〜０．１０ｗｔ％、Ｎ：０．００４ ｗｔ％以下
を含有し、残部はＦｅおよび不可避的不純物よりなり、少なくとも一方の面の表面粗さがＲａ ：０．８ μｍ以下およびＲｍａｘ ：４．０ μｍ以下である鋼板の上面に、硫黄濃度にして０．０５〜５ｗｔ％の硫黄系極圧添加剤およびりん濃度にして０．０５〜５ｗｔ％のりん系極圧添加剤から選ばれるいずれか１種または２種を含む、４０℃における動粘度が５〜３０ ｃＳｔである防錆油の層を０．５ 〜５ｇ／ｍ２ の付着量で形成してなることを特徴とする摺動性および耐型かじり性に優れる熱延鋼板。
【０００９】
（２） 鋼組成が、
Ｃ：０．０１ｗｔ％以下、 Ｍｎ：０．０５〜０．５ ｗｔ％、
Ｐ：０．０１ｗｔ％以下、 Ｓ：０．０１ｗｔ％以下、
ｓｏｌ Ａｌ：０．０１〜０．１０ｗｔ％、Ｎ：０．００４ ｗｔ％以下
を含み、かつ
Ｔｉ：０．１０ｗｔ％以下、 Ｎｂ：０．１０ｗｔ％以下
およびＢ：０．０１ｗｔ％以下
のうちから選ばれるいずれか１種または２種以上を含有し、残部はＦｅおよび不可避的不純物よりなり、少なくとも一方の面の表面粗さがＲａ ：０．８ μｍ以下およびＲｍａｘ ：４．０ μｍ以下である鋼板の上面に、硫黄濃度にして０．０５〜５ｗｔ％の硫黄系極圧添加剤およびりん濃度にして０．０５〜５ｗｔ％のりん系極圧添加剤から選ばれるいずれか１種または２種を含む、４０℃における動粘度が５〜３０ ｃＳｔである防錆油の層を０．５ 〜５ｇ／ｍ２ の付着量で形成してなることを特徴とする摺動性および耐型かじり性に優れる熱延鋼板。
【００１０】
（３） Ｃ：０．０１ｗｔ％以下、Ｍｎ：０．０５〜０．５ ｗｔ％、Ｐ：０．０１ｗｔ％以下、Ｓ：０．０１ｗｔ％以下、ｓｏｌ Ａｌ：０．０１〜０．１０ｗｔ％、Ｎ：０．００４ ｗｔ％以下を含有し、残部はＦｅおよび不可避的不純物よりなる鋼スラブを、熱間粗圧延し、得られたシートバーの少なくとも一方の面に、衝突圧２５ｋｇｆ／ｃｍ２ 以上の超高圧デスケーリングを施し、次いで熱間仕上げ圧延を行い、７００ ℃以下で巻き取り、酸洗を行い、その後、少なくとも前記デスケーリング側の面に、硫黄濃度にして０．０５〜５ｗｔ％の硫黄系極圧添加剤およびりん濃度にして０．０５〜５ｗｔ％のりん系極圧添加剤から選ばれるいずれか１種または２種を含む、４０℃における動粘度が５〜３０ ｃＳｔである防錆油を０．５ 〜５ｇ／ｍ２ の付着量で塗油することを特徴とする熱延鋼板の製造方法。
【００１１】
（４） Ｃ：０．０１ｗｔ％以下、Ｍｎ：０．０５〜０．５ ｗｔ％、Ｐ：０．０１ｗｔ％以下、Ｓ：０．０１ｗｔ％以下、ｓｏｌ Ａｌ：０．０１〜０．１０ｗｔ％、Ｎ：０．００４ ｗｔ％以下を含み、かつＴｉ：０．１０ｗｔ％以下、Ｎｂ：０．１０ｗｔ％以下およびＢ：０．０１ｗｔ％以下のうちから選ばれるいずれか１種または２種以上を含有し、残部はＦｅおよび不可避的不純物よりなる鋼スラブを、熱間粗圧延し、得られたシートバーの少なくとも一方の面に、衝突圧２５ｋｇｆ／ｃｍ２ 以上の超高圧デスケーリングを施し、次いで熱間仕上げ圧延を行い、７００ ℃以下で巻き取り、酸洗を行い、少なくとも前記デスケーリング側の面に、硫黄濃度にして０．０５〜５ｗｔ％の硫黄系極圧添加剤およびりん濃度にして０．０５〜５ｗｔ％のりん系極圧添加剤から選ばれるいずれか１種または２種を含む、４０℃における動粘度が５〜３０ ｃＳｔである防錆油を０．５ 〜５ｇ／ｍ２ の付着量で塗油することを特徴とする熱延鋼板の製造方法。
【００１２】
（５） 上記（１） 〜（４） の各発明において、硫黄系極圧添加剤とりん系極圧添加剤とを複合添加する場合には、防錆油中の（硫黄＋りん）含有量を０．０５〜５ｗｔ％の範囲にするのが好適である。
【００１３】
【発明の実施の形態】
本発明の鋼成分について以下に説明する。
Ｃ：0.01wt％以下
Ｃは、多量に含有すると鋼中にセメンタイトを多量に生成し、延性の劣化を引き起こすので好ましくない。このため、Ｃ含有量の上限は0.01wt％とする。好ましくは0.004wt％以下とする。なお、現在の製鋼技術ではその量を0.0005wt％以下に低下させるには多大なコストを必要とするので、下限は0.0005wt％に止めるのがよい。
【００１４】
Ｓｉ：０．０２ｗｔ％以下
Ｓｉは、多量に含有すると延性の低下を引き起こすので、その上限を０．０２ｗｔ％とする。
【００１５】
Ｍｎ：０．０５〜２．０ ｗｔ％
Ｍｎは、熱間加工時の脆化の原因となる固溶ＳをＭｎＳとして無害化するために必要であるが、その添加量が多過ぎると延性の低下を引き起こす。したがって、その添加量を０．０５〜２．０ ｗｔ％とする。
【００１６】
Ｐ：０．０１ｗｔ％以下
Ｐは、本発明において特に有害な元素である。後述するように、防錆油中に添加されている極圧添加剤は、プレス加工時の局部的な温度上昇により鋼板表面で反応し、固形潤滑膜を形成することにより、耐型かじり性を改善する効果を発揮する。鋼中のＰ含有量が多いと、鋼板表面にあらかじめＰが存在することになり反応性を阻害する。なぜなら、Ｐは特に表面偏析しやすい元素であるので、プレス成形中の変形、温度上昇等により、鋼板表面に出現しやすく、そのため極圧添加剤の反応性を阻害するのである。従って、その含有量は極圧添加剤の効果を確保するうえから、上限を０．０１ｗｔ％とする。なお、０．００１ ｗｔ％以下に低減すると製鋼上のコストが著しく増大するので、Ｐの下限は０．００１ ｗｔ％とするのが好ましい。
【００１７】
Ｓ：０．０１ｗｔ％以下
Ｓは、本発明においてＰと同様に有害な元素である。後述するように， 防錆油中に添加されている極圧添加剤はプレス加工時の局部的な温度上昇により鋼板表面で反応し、固形潤滑膜を形成することにより、耐型かじり性を改善する効果を発揮する。鋼中のＳ量が多いと、鋼板表面にあらかじめＰが存在することになり反応性を阻害する。Ｓも、Ｐと同様に表面偏析しやすい元素であるので、プレス成形中の変形、温度上昇等により、鋼板表面に出現しやすく、極圧添加剤の反応性を阻害する。従って、その含有量は極圧添加剤の効果を確保するうえから、上限を０．０１ｗｔ％とする。なお、Ｓ含有量を０．００１ ｗｔ％以下に低減すると製鋼上のコストが著しく増大するので、その下限は０．００１ ｗｔ％とするのが好ましい。
【００１８】
ｓｏｌ Ａｌ：０．０１〜０．１０ｗｔ％
Ａｌは、脱酸剤として添加されるが、ｓｏｌ Ａｌ量で０．０１ｗｔ％に満たないと効果がなく、一方、０．１０ｗｔ％を超えて添加してもコストアップとなるばかりか鋼の脆化を招くので、０．０１〜０．１０ｗｔ％とする。
【００１９】
Ｎ：０．００４ ｗｔ％以下
Ｎは、Ｃと同様に鋼中に多量に含有すると延性を低下させるため好ましくないので、その上限を０．００４ ｗｔ％とする。なお、Ｎ含有量を０．００１ ｗｔ％以下に低減するためには、製鋼上の著しいコスト高を招くので、その下限は０．００１ ｗｔ％とするのが好ましい。
【００２０】
Ｔｉ：０．１０ｗｔ％以下
Ｔｉは、炭窒化物を形成することにより、固溶Ｃ，Ｎを低減し、伸び、ｒ値の向上に寄与する元素であるが、多量に添加するとスケールの剥離に起因するスケール疵の発生を招くので、０．１０ｗｔ％以下の範囲で添加する。なお、添加量が余りに少ないと前記効果も期待できないので、０．００５ ｗｔ％以上添加するのが好ましい。
【００２１】
Ｎｂ：０．１０ｗｔ％以下
Ｎｂは、炭窒化物を形成することにより、固溶Ｃ，Ｎを低減し、伸び、ｒ値の向上に寄与する元素であるが、多量に添加するとスケールの剥離に起因するスケール疵の発生を招くので、０．１０ｗｔ％以下の範囲で添加する。なお、添加量が余りに少ないと前記効果も期待できないので、０．００３ ｗｔ％以上添加するのが好ましい。
【００２２】
Ｂ：０．０１ｗｔ％以下
Ｂは、Ｃ，Ｎ量の低下、特にＣ＋Ｎで０．０００５ｗｔ％以下に低減した場合に問題となる粒界脆化を抑制する効果があるが、０．０１ｗｔ％を超えて添加すると鋼の延性を低下させるので、０．０１ｗｔ％以下の範囲で添加する。なお、添加量が余りに少ないと前記効果も期待できないので、０．０００２ｗｔ％以上添加するのが好ましい。
【００２３】
次に、本発明方法における製造条件について、限定理由を含めて説明する。
熱延前の鋼スラブの加熱は、完全な溶体化処理がなされればよく、Ａｃ３点以上に加熱されればよい。具体的には通常のスラブ加熱温度範囲である１０５０〜１３００℃が適する。なお、鋳造後に鋼スラブの大幅な温度低下を伴うことなく、熱延前の温度がＡｃ３点以上を確保できる場合には、鋳造後直接圧延を行ってもよい。
【００２４】
上記加熱に次いで、粗圧延および仕上げ圧延よりなる熱間圧延を行う。また、この粗圧延と仕上げ圧延の間で超高圧水によるデスケーリングを行う。
熱間圧延の圧延条件は、特に定めないが、超高圧デスケーリングのもとで酸洗効率のよい薄スケール鋼板を製造するため、粗圧延は（Ａｒ３点＋１００ ℃）〜（Ａｒ３点＋５０℃）の範囲で終了し、高圧デスケーリング後に、圧下率８０％以上、圧延終了温度Ａｒ３点以上の条件で仕上げ圧延するのが好ましい。
粗圧延を（Ａｒ３点＋１００ ℃）〜（Ａｒ３点＋５０℃）の範囲で終了させるのは、粗圧延終了温度が（Ａｒ３点＋１００ ℃）を超えると鋼板の表層がγ域の状態となるため、強度が高くなり、この後に引き続き行われる高圧デスケーリングによる粗度調整が行い難くなるためである。一方、（Ａｒ３点＋５０℃）よりも低くすると、デスケーリング中にα変態が進行して強度が上昇し、粗度調整が行いにくくなるためである。
また、仕上げ圧延の圧下率を８０％以上とするのは、圧下率が８０％未満であると、圧延によるスケールの伸展が不十分となり、薄スケールが達成できにくいからである。さらに、仕上げ温度をＡｒ３点以上とするのは、Ａｒ３未満の温度で圧延すると、圧延による加工組織が製品としての熱延鋼板に残り、延性が小さくなる可能性があるからである。
【００２５】
上記の粗圧延と仕上げ圧延との間で超高圧のデスケーリングを施す。このデスケーリングは、本発明において特に重要な工程であり、粗圧延で得られたシートバーの少なくとも一方の面に、鋼板面での衝突圧を２５ｋｇｆ／ｃｍ２ 以上、好ましくは３０ｋｇｆ／ｃｍ２ 以上の範囲の超高圧とする必要がある。衝突圧が、２５ｋｇｆ／ｃｍ２ 未満では、仕上げ圧延後に酸洗、調質圧延を行っても表面粗さと延性とをともに高レベルに維持することが困難になるからである。
因に、従来の高圧デスケーリングにおける衝突圧は１．０〜４．０ｋｇｆ／ｃｍ２ 程度であり、本発明では、その約１０倍に当たる超高圧を採用することで、従来技術の下では期待されていなかった特有の作用効果を発現したものと思われる。
【００２６】
なお、デスケーリング時の鋼板表面での上記衝突圧ｐは、一般に、ノズルの吐出圧Ｐおよび吐出量Ｑ、鋼板表面とノズルとの間の距離Ｈから次式により求めることができる。（「鉄と鋼」１９９１ ｖｏｌ．７７ Ｎｏ．９ ｐ１１４５０参照）
ｐ＝５．６４ＰＱ／Ｈ２
ただし、ｐ：鋼板表面での衝突圧（ＭＰａ）
Ｐ：吐出圧（ＭＰａ）
Ｑ：吐出量（リットル／ｓｅｃ）
Ｈ：鋼板表面とノズルとの間の距離（ｃｍ）
【００２７】
デスケーリング後、上述したような、常法による仕上げ圧延を行い、巻き取る。この巻取温度が、 ７００℃を超えると特にコイル端部において巻取後のスケール成長が著しくなり、薄スケールとすることができなくなる。なお、鋼板形状の点から、巻取温度の下限は４５０ ℃とするのが好ましい。
【００２８】
上述したような熱間圧延と巻取処理を行った後の熱延鋼板に、常法に従い、酸洗を施す。ここで、酸洗は通常の、酸洗前に伸び率０．５ ％〜３％の調質圧延あるいはテンションレベラによるメカニカルデスケーリング、形状調整等を行う工程を含むものである。本発明法で得られる熱延後の鋼板のスケールは極めて薄く、かつ素材が軟質なため、この酸洗前に行う調質圧延による粗度調整が有効であり、所定の粗度に調整できる。また、用いる酸洗液としては、例えば５０℃−２０ ％の塩酸等を使用すればよい。
【００２９】
以上説明した製造方法により、鋼板の表面状態をＲａ ： ０．８μｍ以下およびＲｍａｘ ： ４．０μｍ以下に制御することができ、これにより摩擦係数の減少が可能となり、摺動性が改善される。これらの表面粗さの両特性のいずれか一方でも上記範囲を逸脱すると、目標とする摩擦係数が得られなくなる。したがって、本発明における熱延、酸洗後の鋼板の表面粗さは、Ｒａ ： ０．８μｍ以下およびＲｍａｘ ： ４．０μｍ以下の範囲とする。
【００３０】
さらに、酸洗、水洗が終了した鋼板についてその表面に防錆油を塗油する。ここで本発明における防錆油の役割は非常に重要である。従来、熱延鋼板に塗油される防錆油は、鋼板が使用されるまでの防錆効果のみ有する、基油に防錆剤が添加された程度の防錆油であった。しかし本発明における防錆油は、この従来の防錆油に極圧添加剤を添加することにより、鋼板の粗度調整だけでは解決できない型かじりを解消する。
【００３１】
本発明に用いる防錆油の基油としては、通常用いられる鉱物油、常温で液体の油脂および合成エステルから選ばれる１種または２種以上とする。また添加剤として、以下に述べる極圧添加剤を添加することを必須とする。また、この防錆油には通常の熱延鋼板用防錆油で添加されているような、スルフォン酸塩、カルボン酸塩、石油酸化ワックス等の防錆剤に加え、酸化防止剤、油性向上剤、水置換剤等の添加剤を加えてもよい。
上記極圧添加剤としては硫黄系、りん系の極圧添加剤を用いる。極圧剤の効果は、プレス加工時の局部的な温度上昇により化学分解して工具、鋼板と反応し、硫黄系化合物の場合硫化鉄系の、りん化合物の場合りん化鉄やりん酸鉄系の固体潤滑膜を形成することにより潤滑性を向上させ、耐型かじり性を改善することにある。
【００３２】
硫黄系の極圧添加剤としては、例えばジベンジルサルファイド等のポリサルファイド類、硫化油脂類が好ましく、りん系極圧添加剤としてはトリクレジルフォスフェートのようなホスフェート類あるいはトリブチルフォスファイトのようなホスファイト類、アルキルりん酸エステル類が好ましい。
また、これらの添加量は、硫黄系極圧添加剤の場合には、硫黄濃度として０．０５〜５ｗｔ％、りん系極圧添加剤の場合には、りん濃度として０．０５〜５ｗｔ％とする必要がある。極圧添加剤の添加量が０．０５ｗｔ％未満では極圧性が不十分となり、添加量が上記添加量を超えると、オイルステインと呼ばれる鋼板表面の変色が発生する恐れがあるからである。
これらの極圧添加剤の効果は１種でも２種の複合でも得られるが、２種の極圧添加剤を併用すると一層効果が期待され好ましい。なお、２種の極圧添加剤を併用する場合には、（硫黄濃度＋りん濃度）で５ｗｔ％以下の範囲で添加することが好ましい。
【００３３】
本発明に用いる防錆油の動粘度は４０℃で５〜３０ ｃＳｔとする。動粘度が余りに大きいと、プレス後に施される脱脂工程での洗浄除去性を確保できなくなるので、４０℃での動粘度を３０ ｃＳｔ以下、好ましくは２０ ｃＳｔ以下とする必要がある。また、動粘度が余りに小さいと、プレス加工時の潤滑性を満足に発揮させることができなくなるため、４０℃での動粘度を５ ｃＳｔ以上、好ましくは１０ ｃＳｔ以上とする必要がある。
【００３４】
極圧添加剤を含有する防錆油を、超高圧デスケーリングを施した鋼板の少なくとも一方の面に、０．５ 〜５ｇ／ｍ２ の付着量で塗油し、油膜を形成する。
油膜の付着量が０．５ ｇ／ｍ２ 未満では、摩擦係数の低減効果が十分でなく、また塗布量の制御も困難である。一方５ｇ／ｍ２ を超えて塗油しても、効果が飽和するばかりか、巻き取りコイルやシートの梱包後に防錆油の外部への流出、需要家における脱脂性や接着性の低下の原因を招きやすい。したがって防錆油の付着量は０．５ 〜５ｇ／ｍ２ 、好ましくは１〜２ｇ／ｍ２ の範囲とする。
【００３５】
以上説明した製造方法により、表面粗さをＲａ ： ０．８μｍ以下およびＲｍａｘ ： ４．０μｍ以下に制御した鋼板の表面に、適正な特性を有する防錆油の油膜が所定の付着量で形成され、これによって摺動性と型かじり性とを兼備した熱延鋼板を製造することが可能になる。
【００３６】
【実施例】
表１に示す成分組成の極低炭素鋼スラブを、１２００℃に加熱後、９７０ ℃で粗圧延して、３０ｍｍのシートバーとし、その両面に、表２に示す条件でデスケーリングを施し、その後、７パス、終了温度９２０ ℃（Ａｒ３＝９００ 〜９１０ ℃）、最終板厚１．２ ｍｍに仕上げ圧延し、５５０ ℃で巻き取った。この鋼帯を、酸洗槽の入り側で、伸び率２％で調質圧延し、メカニカルデスケーリング、形状矯正を行ったのち、５０℃、２０％塩酸の条件で酸洗を行った。
得られた鋼帯の両面に対し、防錆油を片面当りの付着量が１．５ ｇ／ｍ２ になるよう塗油した。なお、防錆油としては、ＩＳＯ ＶＧ１５の鉱油を基油とし、極圧添加剤の条件を下記のように変えて実験した。
・油Ａ；硫黄系極圧剤 ジベンジルジサルファイド 硫黄濃度＝１．３ ｗｔ％
・油Ｂ；りん系極圧剤 トリクレジルフォスフェート りん濃度＝０．４ ｗｔ％
・油Ｃ；硫黄系極圧剤＋りん系極圧剤 ジベンジルジサルファイド＋トリクレジルフォスフェート 硫黄濃度＋りん濃度＝０．８ ｗｔ％
・油Ｄ；極圧剤無添加
なお、これらの防錆油の動粘度は、いずれも４０℃で１４〜１６ ｃＳｔであった。
【００３７】
このようにして製造した熱延鋼板について摩擦係数（摺動性）および型かじり性を調査した。これら特性の測定方法は次に方法に従った。
・摩擦係数：ＪＩＳ Ｇ４４０４ にある冷間金型用鋼ＳＫＤ１１ 製の治具を用い、平均面圧１ ｋｇｆ／ｍｍ２ 、引き抜き速度１００ ｍｍ／ｓｅｃ として求めた。
・耐型かじり性：ＪＩＳ Ｇ４４０４ にある冷間金型用鋼ＳＫＤ１１ 製の治具を用い、平均面圧２０ ｋｇｆ／ｍｍ２ 、引き抜き速度１００ ｍｍ／ｓｅｃ の条件で、治具で供試材を押しつけ、１００ ｍｍの距離を引き抜く摺動試験により、目視によるかじりが発生するまでの繰り返し数から積算距離を求めた。この積算距離が長いものほど良好な耐型かじり性を有するものであるとして評価した。これらの結果を併せて表２に示す。
【００３８】
【表１】
【表２】
表１、２から明らかなように、本発明による熱延鋼板は、いずれもＲａが０．８ μｍ以下およびＲｍａｘ が ４．０μｍ以下であり、摩擦係数は０．１３以下、耐かじり性試験における摺動距離も９０ ｃｍ 以上を示しており、摺動性、耐型かじり性ともに優れていることがわかった。
なお極圧添加剤を含む油膜に関しては上記実験は１例に過ぎず、本発明で限定した条件を満たすものであれば、市販のいかなる防錆油でもよいことも確認した。
【００４１】
【発明の効果】
以上説明したように、本発明によれば摺動性、耐型かじり性ともに優れる熱延鋼板を得ることが可能となる。
したがって本発明によれば、これまでプレス成形用材料として用いられてきた冷延鋼板の一部を、この発明による熱延鋼板で代替えさせることが可能となり、自動車部材等の低コスト化に大きく貢献できる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hot-rolled steel sheet which is used after pickling and oiling after hot rolling, and a method for producing the hot-rolled steel sheet. TECHNICAL FIELD The present invention relates to a hot-rolled steel sheet suitable for use in forming and the like and a method for producing the same.
[0002]
[Prior art]
A hot-rolled steel sheet is manufactured by hot rolling a slab obtained by a continuous casting method or an ingot-making method. A part of the hot-rolled steel sheet thus manufactured is used as a rolling material for a cold-rolled steel sheet, and another part is used as it is for hot-rolling for processing.
In recent years, in the field of automobiles and the like, as a measure for reducing product cost, there has been an increasing tendency to replace a press portion in which a cold-rolled steel sheet is conventionally used with a lower-cost hot-rolled steel sheet.
Such a technology for manufacturing a hot-rolled steel sheet in place of a cold-rolled steel sheet has been proposed in, for example, JP-A-59-76823 and JP-A-4-136122.
[0003]
The method disclosed in the above-mentioned JP-A-59-76823 discloses a method in which a steel having specified amounts of C, Mn, and P is subjected to a heat treatment at 600 ° C. or more after hot rolling for 3 hours or more, and after pickling, 1 to 5%. This is a method for producing a thin hot-rolled steel sheet that is subjected to temper rolling in. Further, in the method disclosed in Japanese Patent Application Laid-Open No. 4-136122, a steel having a specified amount of C and Mn is rolled at an Ar 3 transformation point or higher, and after a pickling step, a temper rolling of 5 to 20% is performed. And a thickness of 0.8 to 2.0 mm.
[0004]
[Problems to be solved by the invention]
However, although these conventional hot-rolled steel sheets are inexpensive, their press workability is far from that of cold-rolled steel sheets. As described above, one of the major reasons why the workability of the hot-rolled steel sheet manufactured by the conventional technique is inferior is that the surface roughness of the product is rough (Ra: about 1.5 μm), so that the sliding property is inferior.
That is, the ideal surface roughness as a steel sheet for an automobile is Ra: 0.8 μm or less and Rmax: 4.0 μm or less from the viewpoint of improving the slidability during press working (reducing the friction coefficient). On the other hand, in the conventional technology, the surface roughness of the hot-rolled steel sheet is inevitably greater than this, and it has not been possible to produce a hot-rolled steel sheet that can withstand processing. In addition, if the surface roughness is rough, there has been a problem that the surface appearance after press molding and coating is inferior.
[0005]
By the way, as a means for reducing the surface roughness of a hot-rolled steel sheet having such poor surface properties, temper rolling, which is generally adopted for a cold-rolled steel sheet after annealing, may be applied.
However, in this case, if the hot-rolled steel sheet having a large roughness is forcibly adjusted for the roughness by temper rolling, it is necessary to reduce the ductility by a correspondingly high pressure, which is inevitable. This decrease in ductility is superimposed on the decrease in ductility caused by temper rolling or pretreatment for pickling using a leveler, which is performed to improve pickling efficiency in a normal hot-rolled steel sheet manufacturing process. Thus, there is a problem that the ductility is further reduced.
In addition, when the surface of the steel sheet is made to have a low roughness by such a method, a problem that the conventional hot-rolled steel sheet has a rough surface has no problem because the roughness is rough, and the resistance to mold galling decreases. . For example, when a hot-rolled steel sheet that has achieved low roughness using conventional technology is used as a substitute for a cold-rolled steel sheet, it can withstand heavy loads such as beads and corners after pressing. Mold seizure was reduced.
[0006]
As described above, with the conventional technology, it was not possible to manufacture a hot-rolled steel sheet that satisfies both the slidability and the anti-galling property and that can withstand press working.
Accordingly, a main object of the present invention is to provide a novel hot-rolled steel sheet which is excellent in slidability and mold galling resistance and which solves the above-mentioned problems of the conventional hot-rolled steel sheet.
Another object of the present invention is to provide a hot-rolled steel sheet having a friction coefficient of 0.13 or less as a sliding property and having good anti-galling properties.
Still another object of the present invention is to provide a method for advantageously producing each of the above hot-rolled steel sheets by applying ultra-high pressure descaling between a hot rough rolling step and a hot finish rolling step. It is in.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have first conducted intensive research on improving the slidability (reducing the coefficient of friction) by focusing on the descaling conditions performed prior to finish rolling. It has been found that application of ultrahigh-pressure descaling, which has never been used, is extremely effective in reducing the surface roughness of the steel sheet surface and improving the slidability.
In addition, the phenomenon that mold galling of hot-rolled steel sheets tends to occur more easily than that of cold-rolled steel sheets is due to the fact that cold-rolled steel sheets have a surface-concentrated layer on the steel sheet surface due to elemental enrichment during annealing. On the other hand, in the hot-rolled steel sheet that has been pickled, the base iron is exposed as it is on the steel sheet surface, and even though the sliding property is good, it causes galling like seizure with the mold. I thought. This phenomenon means that it is more remarkable when aiming for ultra-low carbon steel, which is generally employed for improving ductility.
The inventors have conducted many experiments on the improvement of the mold galling. As a result, they found that forming a lubricating oil film containing an extreme pressure additive on the surface of a steel sheet obtained by appropriately controlling the material components and manufacturing conditions can advantageously improve the mold galling resistance.
The present invention is based on the above findings, and the gist configuration thereof is as follows.
[0008]
(1) The steel composition is
C: 0.01 wt% or less, Mn: 0.05-0.5 wt%,
P: 0.01 wt% or less, S: 0.01 wt% or less,
sol Al: 0.01 to 0.10 wt%, N: 0.004 wt% or less, the balance consists of Fe and unavoidable impurities, and the surface roughness of at least one surface is Ra: 0.8 μm or less. And Rmax: a sulfur-based extreme pressure additive having a sulfur concentration of 0.05 to 5 wt% and a phosphorus-based extreme pressure additive having a phosphorus concentration of 0.05 to 5 wt% on the upper surface of a steel sheet having a particle size of 4.0 μm or less. Characterized in that a rust-preventive oil layer having a kinematic viscosity at 40 ° C. of 5 to 30 cSt containing one or two selected from the group consisting of 0.5 to 5 g / m 2 is formed. Hot rolled steel sheet with excellent sliding properties and mold galling resistance.
[0009]
(2) The steel composition is
C: 0.01 wt% or less, Mn: 0.05-0.5 wt%,
P: 0.01 wt% or less, S: 0.01 wt% or less,
sol Al: 0.01 to 0.10 wt%, N: 0.004 wt% or less, and Ti: 0.10 wt% or less, Nb: 0.10 wt% or less, and B: 0.01 wt% or less It contains one or more selected ones, and the balance consists of Fe and unavoidable impurities, and the surface roughness of at least one surface is Ra: 0.8 μm or less and Rmax: 4.0 μm or less. Any one or two selected from a sulfur-based extreme pressure additive having a sulfur concentration of 0.05 to 5 wt% and a phosphorus-based extreme pressure additive having a phosphorus concentration of 0.05 to 5 wt% on the upper surface of the steel sheet. A rust-preventive oil layer having a kinematic viscosity at 40 ° C. of 5 to 30 cSt at an adhesion amount of 0.5 to 5 g / m 2 . Hot rolled steel sheet with excellent performance.
[0010]
(3) C: 0.01 wt% or less, Mn: 0.05 to 0.5 wt%, P: 0.01 wt% or less, S: 0.01 wt% or less, sol Al: 0.01 to 0.10 wt% , N: 0.004 wt% or less, the balance being hot rough rolling of a steel slab consisting of Fe and unavoidable impurities, and applying an impact pressure of 25 kgf / cm 2 on at least one surface of the obtained sheet bar. The above ultra-high pressure descaling is performed, followed by hot finish rolling, winding at a temperature of 700 ° C. or less, pickling, and then, at least on the descaling side, a sulfur concentration of 0.05 to 5 wt%. Having a kinematic viscosity at 40 ° C. of 5 to 30 cSt containing at least one selected from a sulfur-based extreme pressure additive and a phosphorus-based extreme pressure additive having a phosphorus concentration of 0.05 to 5 wt%. 0.5 to rust preventive oil method for manufacturing a hot-rolled steel sheet, which comprises coating the oil at a coverage of g / m 2.
[0011]
(4) C: 0.01 wt% or less, Mn: 0.05 to 0.5 wt%, P: 0.01 wt% or less, S: 0.01 wt% or less, sol Al: 0.01 to 0.10 wt% , N: 0.004 wt% or less, and Ti: 0.10 wt% or less, Nb: 0.10 wt% or less, and B: 0.01 wt% or less. The steel slab containing Fe and unavoidable impurities is subjected to hot rough rolling, and at least one surface of the obtained sheet bar is subjected to ultra-high pressure descaling with an impact pressure of 25 kgf / cm 2 or more. Hot finish rolling, winding at 700 ° C. or lower, pickling, and at least the surface of the descaling side having a sulfur-based extreme pressure additive of 0.05 to 5 wt% and a phosphorus concentration of 0.05 to 5 wt%. 0.05-5 comprising any one or two substituents selected from t% of the phosphorus-based extreme pressure additive, at a coverage of a rust-preventive oil 0.5 to 5 g / m 2 kinematic viscosity of 5 to 30 cSt at 40 ° C. A method for producing a hot-rolled steel sheet, comprising applying oil.
[0012]
(5) In each of the above inventions (1) to (4), when a sulfur-based extreme pressure additive and a phosphorus-based extreme pressure additive are added in combination, the (sulfur + phosphorus) content in the rust preventive oil Is preferably in the range of 0.05 to 5 wt%.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The steel composition of the present invention will be described below.
C: not more than 0.01 wt% C is not preferable because a large amount of C generates a large amount of cementite in steel and causes deterioration of ductility. For this reason, the upper limit of the C content is set to 0.01 wt%. Preferably, it is 0.004 wt% or less. It should be noted that since the current steelmaking technology requires a great deal of cost to reduce the amount to 0.0005 wt% or less, the lower limit is preferably limited to 0.0005 wt%.
[0014]
Si: not more than 0.02 wt% Since a large amount of Si causes a decrease in ductility, the upper limit is made 0.02 wt%.
[0015]
Mn: 0.05-2.0 wt%
Mn is necessary to detoxify solid solution S, which causes embrittlement during hot working, as MnS. However, an excessive amount of Mn causes a decrease in ductility. Therefore, the addition amount is set to 0.05 to 2.0 wt%.
[0016]
P: 0.01 wt% or less P is a particularly harmful element in the present invention. As will be described later, the extreme pressure additive added to the rust-preventive oil reacts on the steel sheet surface due to a local temperature increase during press working, and forms a solid lubricating film, thereby improving the mold galling resistance. It has the effect of improving. If the P content in the steel is large, P is present on the surface of the steel sheet in advance, which impairs the reactivity. This is because P is an element that is particularly liable to be segregated on the surface, and is likely to appear on the surface of the steel sheet due to deformation during press forming, temperature rise, and the like, and thus impairs the reactivity of the extreme pressure additive. Therefore, the upper limit of the content is set to 0.01 wt% in order to secure the effect of the extreme pressure additive. If the content is reduced to 0.001 wt% or less, the cost for steelmaking is significantly increased. Therefore, the lower limit of P is preferably set to 0.001 wt%.
[0017]
S: 0.01 wt% or less S is a harmful element like P in the present invention. As described later, the extreme pressure additive added to the rust-preventive oil reacts on the steel sheet surface due to local temperature rise during press working, and forms a solid lubricating film to improve mold galling resistance. It has the effect of doing. If the amount of S in the steel is large, P is pre-existing on the surface of the steel sheet, thereby inhibiting the reactivity. S is also an element that is easily segregated on the surface like P, so that it is likely to appear on the steel sheet surface due to deformation, temperature rise, etc. during press forming, and impairs the reactivity of the extreme pressure additive. Therefore, the upper limit of the content is set to 0.01 wt% in order to secure the effect of the extreme pressure additive. If the S content is reduced to 0.001 wt% or less, the cost for steelmaking is significantly increased. Therefore, the lower limit is preferably set to 0.001 wt%.
[0018]
sol Al: 0.01 to 0.10 wt%
Although Al is added as a deoxidizing agent, it has no effect unless the amount of sol Al is less than 0.01 wt%. On the other hand, adding more than 0.10 wt% not only increases the cost but also makes the steel brittle. Therefore, the content is set to 0.01 to 0.10 wt%.
[0019]
N: 0.004 wt% or less N, like C, is not preferable if it is contained in a large amount in steel because ductility is lowered, so the upper limit is made 0.004 wt%. In order to reduce the N content to 0.001 wt% or less, a significant increase in steelmaking cost is caused. Therefore, the lower limit is preferably set to 0.001 wt%.
[0020]
Ti: 0.10 wt% or less Ti is an element that reduces solid solution C and N by forming carbonitride and contributes to improvement of elongation and r value. Therefore, it is added in a range of 0.10 wt% or less, since it causes the generation of scale flaws. If the amount is too small, the above effect cannot be expected, so it is preferable to add 0.005 wt% or more.
[0021]
Nb: 0.10 wt% or less Nb is an element that reduces solid solution C and N by forming carbonitrides and contributes to improvement of elongation and r value. Therefore, it is added in a range of 0.10 wt% or less, since it causes the generation of scale flaws. Note that if the amount is too small, the above effect cannot be expected, so it is preferable to add 0.003 wt% or more.
[0022]
B: 0.01 wt% or less B has an effect of suppressing grain boundary embrittlement, which is a problem when the amount of C and N is reduced, particularly when C + N is reduced to 0.0005 wt% or less. If added in excess, the ductility of the steel will be reduced, so it is added in a range of 0.01 wt% or less. Note that if the amount is too small, the above effect cannot be expected, so it is preferable to add 0.0002 wt% or more.
[0023]
Next, the manufacturing conditions in the method of the present invention will be described including the reasons for limitation.
The heating of the steel slab before hot rolling may be performed by a complete solution treatment, and may be performed by heating to three or more Ac points. Specifically, a temperature range of 1050 to 1300 ° C. which is a normal slab heating temperature range is suitable. In addition, if the temperature before hot-rolling can secure 3 or more Ac before hot rolling without drastic temperature decrease of the steel slab after casting, direct rolling may be performed after casting.
[0024]
Subsequent to the heating, hot rolling consisting of rough rolling and finish rolling is performed. In addition, descaling by ultra-high pressure water is performed between the rough rolling and the finish rolling.
The rolling conditions of the hot rolling are not particularly defined, but in order to produce a thin-scale steel sheet with high pickling efficiency under ultra-high pressure descaling, rough rolling is performed at (Ar 3 points + 100 ° C.) to (Ar 3 points + 50). C), and after high-pressure descaling, it is preferable to perform finish rolling under the conditions of a rolling reduction of 80% or more and a rolling end temperature Ar of 3 points or more.
Rough rolling (Ar 3 point +100 ° C.) ~ to terminate a range of (Ar 3 point + 50 ° C.), the surface layer of the steel sheet when the rough rolling termination temperature exceeds (Ar 3 point +100 ° C.) and the state of the γ region Therefore, the strength is increased, and it is difficult to perform the roughness adjustment by the high-pressure descaling performed subsequently. On the other hand, if the temperature is lower than (Ar 3 points + 50 ° C.), α transformation proceeds during descaling, the strength increases, and it becomes difficult to adjust the roughness.
The reason why the rolling reduction of the finish rolling is set to 80% or more is that if the rolling reduction is less than 80%, the expansion of the scale by rolling becomes insufficient, and it is difficult to achieve a thin scale. Furthermore, the reason why the finishing temperature is set to the Ar 3 point or more is that when rolling is performed at a temperature lower than Ar 3 , a work structure by rolling remains on a hot-rolled steel sheet as a product, and ductility may be reduced.
[0025]
Ultra-high pressure descaling is performed between the rough rolling and the finish rolling. This descaling is a particularly important step in the present invention, at least one surface of the sheet bar obtained by the rough rolling, the impact pressure of the steel plate surface 25 kgf / cm 2 or more, preferably 30 kgf / cm 2 or more It is necessary to have an ultra-high pressure in the range. If the impact pressure is less than 25 kgf / cm 2 , it is difficult to maintain both the surface roughness and the ductility at a high level even if pickling and temper rolling are performed after finish rolling.
Incidentally, the collision pressure in the conventional high-pressure descaling is about 1.0 to 4.0 kgf / cm 2 , and in the present invention, by employing an ultra-high pressure that is about 10 times that of the collision pressure, it is expected under the prior art. It is thought that the specific action and effect that had not been achieved were exhibited.
[0026]
In general, the collision pressure p on the steel sheet surface at the time of descaling can be obtained by the following equation from the discharge pressure P and discharge amount Q of the nozzle, and the distance H between the steel sheet surface and the nozzle. (Refer to "Iron and Steel" 1991 vol. 77 No. 9 p11450)
p = 5.64PQ / H 2
Here, p: collision pressure on the steel sheet surface (MPa)
P: discharge pressure (MPa)
Q: Discharge rate (liter / sec)
H: distance between steel plate surface and nozzle (cm)
[0027]
After descaling, finish rolling is performed by a conventional method as described above, and the film is wound. If the winding temperature exceeds 700 ° C., scale growth after winding becomes remarkable, especially at the coil end, and it becomes impossible to obtain a thin scale. From the viewpoint of the shape of the steel sheet, the lower limit of the winding temperature is preferably set to 450 ° C.
[0028]
The hot-rolled steel sheet that has been subjected to the above-described hot rolling and winding treatment is subjected to pickling according to a conventional method. Here, the pickling includes ordinary steps of performing temper rolling at an elongation of 0.5% to 3% or mechanical descaling by a tension leveler and shape adjustment before pickling. Since the scale of the hot-rolled steel sheet obtained by the method of the present invention is extremely thin and the material is soft, the roughness adjustment by temper rolling before this pickling is effective and can be adjusted to a predetermined roughness. As the pickling solution to be used, for example, hydrochloric acid at 50 ° C.-20% may be used.
[0029]
By the manufacturing method described above, the surface state of the steel sheet can be controlled to Ra: 0.8 μm or less and Rmax: 4.0 μm or less, whereby the friction coefficient can be reduced and the slidability is improved. If any one of these characteristics of the surface roughness deviates from the above range, a target friction coefficient cannot be obtained. Therefore, the surface roughness of the steel sheet after hot rolling and pickling in the present invention is in the range of Ra: 0.8 μm or less and Rmax: 4.0 μm or less.
[0030]
Further, a rust-preventive oil is applied to the surface of the steel plate that has been pickled and washed. Here, the role of the rust preventive oil in the present invention is very important. Conventionally, the rust-preventive oil applied to the hot-rolled steel sheet is a rust-preventive oil having only a rust-preventive effect until the steel sheet is used and having a rust-preventive agent added to the base oil. However, the rust preventive oil in the present invention eliminates mold galling that cannot be solved only by adjusting the roughness of the steel sheet by adding an extreme pressure additive to the conventional rust preventive oil.
[0031]
The base oil of the rust preventive oil used in the present invention is one or more selected from mineral oils, oils and fats which are liquid at ordinary temperature, and synthetic esters which are usually used. In addition, it is essential to add an extreme pressure additive described below as an additive. In addition to this rust preventive oil, in addition to the rust preventive agents such as sulfonate, carboxylate, petroleum oxidized wax, etc., which are added with the normal rust preventive oil for hot-rolled steel sheets, an antioxidant and an oil improve You may add additives, such as an agent and a water displacement agent.
As the extreme pressure additives, sulfur-based and phosphorus-based extreme pressure additives are used. The effect of the extreme pressure agent is that it chemically decomposes due to the local temperature rise during press working and reacts with tools and steel sheets.For sulfur compounds, iron sulfide is used.For phosphorus compounds, iron phosphide and iron phosphate are used. The purpose of the present invention is to improve the lubricity by forming a solid lubricating film and improve the anti-galling property.
[0032]
As sulfur-based extreme pressure additives, for example, polysulfides such as dibenzyl sulfide, and sulfurized fats and oils are preferable, and as phosphorus-based extreme pressure additives, phosphates such as tricresyl phosphate or tributyl phosphite. Phosphites and alkyl phosphates are preferred.
The amount of these additives is 0.05 to 5 wt% as sulfur concentration in the case of sulfur-based extreme pressure additives, and 0.05 to 5 wt% as phosphorus concentration in the case of phosphorus-based extreme pressure additives. There is a need to. If the amount of the extreme pressure additive is less than 0.05 wt%, the extreme pressure property becomes insufficient, and if the amount exceeds the above amount, discoloration of the steel sheet surface called oil stain may occur.
The effect of these extreme pressure additives can be obtained by one kind or two kinds of composites, but it is more preferable to use two kinds of extreme pressure additives in combination because they are more effective. When two types of extreme pressure additives are used in combination, it is preferable to add them in a range of (sulfur concentration + phosphorus concentration) of 5 wt% or less.
[0033]
The kinematic viscosity of the rust preventive oil used in the present invention is 5 to 30 cSt at 40 ° C. If the kinematic viscosity is too large, it is not possible to ensure the cleaning and removability in the degreasing step performed after pressing, so the kinematic viscosity at 40 ° C. needs to be 30 cSt or less, preferably 20 cSt or less. On the other hand, if the kinematic viscosity is too small, the lubricity at the time of press working cannot be sufficiently exhibited, so that the kinematic viscosity at 40 ° C. needs to be 5 cSt or more, preferably 10 cSt or more.
[0034]
A rust-preventive oil containing an extreme pressure additive is applied to at least one surface of the steel plate subjected to ultra-high pressure descaling at an adhesion amount of 0.5 to 5 g / m 2 to form an oil film.
When the amount of the oil film adhered is less than 0.5 g / m 2 , the effect of reducing the coefficient of friction is not sufficient, and it is difficult to control the amount of application. On the other hand, even if the oil is applied in excess of 5 g / m 2 , the effect is not only saturated, but also the rust preventive oil leaks out after the winding coil or the sheet is packed, and causes the degreasing property and the adhesion property to be reduced in the consumer. Easy to invite. Therefore, the amount of the rust-preventive oil to be applied is in the range of 0.5 to 5 g / m 2 , preferably 1 to 2 g / m 2 .
[0035]
According to the manufacturing method described above, an oil film of rust-preventive oil having appropriate properties is formed on the surface of a steel sheet whose surface roughness is controlled to 0.8 μm or less and Rmax: 4.0 μm or less with a predetermined adhesion amount. This makes it possible to manufacture a hot-rolled steel sheet having both slidability and mold galling.
[0036]
【Example】
The ultra-low carbon steel slab having the composition shown in Table 1 was heated to 1200 ° C, and then roughly rolled at 970 ° C to form a 30 mm sheet bar. Both surfaces were descaled under the conditions shown in Table 2, , 7 pass, end temperature 920 ℃ (Ar 3 = 900 ~910 ℃), finish rolled to a final sheet thickness 1.2 mm, was wound at 550 ° C.. This steel strip was subjected to temper rolling at an elongation of 2% on the entry side of the pickling tank, subjected to mechanical descaling and shape correction, and then pickled at 50 ° C. and 20% hydrochloric acid.
Rust-preventive oil was applied to both sides of the obtained steel strip so that the amount of adhesion per side was 1.5 g / m 2 . In addition, the experiment was conducted by using a mineral oil of ISO VG15 as a base oil and changing the conditions of the extreme pressure additive as follows.
Oil A: sulfur-based extreme pressure agent dibenzyl disulfide sulfur concentration = 1.3 wt%
Oil B: Phosphorus extreme pressure agent tricresyl phosphate Phosphorus concentration = 0.4 wt%
Oil C: sulfur-based extreme pressure agent + phosphorus-based extreme pressure agent dibenzyl disulfide + tricresyl phosphate Sulfur concentration + phosphorus concentration = 0.8 wt%
Oil D; no extreme pressure agent added The kinematic viscosity of each of these rust preventive oils was 14 to 16 cSt at 40 ° C.
[0037]
With respect to the hot-rolled steel sheet manufactured in this manner, the friction coefficient (sliding property) and the mold galling property were examined. The measuring method of these characteristics followed the method.
Coefficient of friction: Determined by using a jig made of steel SKD11 for cold mold according to JIS G4404, with an average surface pressure of 1 kgf / mm 2 and a drawing speed of 100 mm / sec.
-Resistance to die galling: Using a jig made of steel SKD11 for cold mold according to JIS G4404, the test material was tested with a jig under the conditions of an average surface pressure of 20 kgf / mm 2 and a drawing speed of 100 mm / sec. The accumulated distance was determined from the number of repetitions until visual galling occurred by pressing and pulling out a distance of 100 mm. The longer the integrated distance was, the better the anti-galling property was evaluated. Table 2 also shows these results.
[0038]
[Table 1]
[Table 2]
As is clear from Tables 1 and 2, all of the hot-rolled steel sheets according to the present invention have a Ra of 0.8 μm or less and an Rmax of 4.0 μm or less, a friction coefficient of 0.13 or less, and a galling resistance test. The sliding distance was 90 cm or more, and it was found that both the sliding property and the anti-galling property were excellent.
The above experiment was only one example of an oil film containing an extreme pressure additive, and it was confirmed that any commercially available rust-preventive oil may be used as long as it satisfies the conditions defined in the present invention.
[0041]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a hot-rolled steel sheet having both excellent slidability and mold galling resistance.
Therefore, according to the present invention, it is possible to replace a part of the cold-rolled steel sheet that has been used as a material for press forming with the hot-rolled steel sheet according to the present invention, which greatly contributes to cost reduction of automobile parts and the like. it can.
Claims (4)
Ｃ：０．０１ｗｔ％以下、 Ｍｎ：０．０５〜０．５ ｗｔ％、
Ｐ：０．０１ｗｔ％以下、 Ｓ：０．０１ｗｔ％以下、
ｓｏｌ Ａｌ：０．０１〜０．１０ｗｔ％、Ｎ：０．００４ ｗｔ％以下
を含有し、残部はＦｅおよび不可避的不純物よりなり、少なくとも一方の面の表面粗さがＲａ ：０．８ μｍ以下およびＲｍａｘ ：４．０ μｍ以下である鋼板の上面に、硫黄濃度にして０．０５〜５ｗｔ％の硫黄系極圧添加剤およびりん濃度にして０．０５〜５ｗｔ％のりん系極圧添加剤から選ばれるいずれか１種または２種を含む、４０℃における動粘度が５〜３０ ｃＳｔである防錆油の層を０．５ 〜５ｇ／ｍ２ の付着量で形成してなることを特徴とする摺動性および耐型かじり性に優れる熱延鋼板。Steel composition,
C: 0.01 wt% or less, Mn: 0.05-0.5 wt%,
P: 0.01 wt% or less, S: 0.01 wt% or less,
sol Al: 0.01 to 0.10 wt%, N: 0.004 wt% or less, the balance consists of Fe and unavoidable impurities, and the surface roughness of at least one surface is Ra: 0.8 μm or less. And Rmax: a sulfur-based extreme pressure additive having a sulfur concentration of 0.05 to 5 wt% and a phosphorus-based extreme pressure additive having a phosphorus concentration of 0.05 to 5 wt% on the upper surface of a steel sheet having a particle size of 4.0 μm or less. Characterized in that a rust-preventive oil layer having a kinematic viscosity at 40 ° C. of 5 to 30 cSt containing one or two selected from the group consisting of 0.5 to 5 g / m 2 is formed. Hot rolled steel sheet with excellent sliding properties and mold galling resistance.
Ｃ：０．０１ｗｔ％以下、 Ｍｎ：０．０５〜０．５ ｗｔ％、
Ｐ：０．０１ｗｔ％以下、 Ｓ：０．０１ｗｔ％以下、
ｓｏｌ Ａｌ：０．０１〜０．１０ｗｔ％、Ｎ：０．００４ ｗｔ％以下
を含み、かつ
Ｔｉ：０．１０ｗｔ％以下、 Ｎｂ：０．１０ｗｔ％以下
およびＢ：０．０１ｗｔ％以下
のうちから選ばれるいずれか１種または２種以上を含有し、残部はＦｅおよび不可避的不純物よりなり、少なくとも一方の面の表面粗さがＲａ ：０．８ μｍ以下およびＲｍａｘ ：４．０ μｍ以下である鋼板の上面に、硫黄濃度にして０．０５〜５ｗｔ％の硫黄系極圧添加剤およびりん濃度にして０．０５〜５ｗｔ％のりん系極圧添加剤から選ばれるいずれか１種または２種を含む、４０℃における動粘度が５〜３０ ｃＳｔである防錆油の層を０．５ 〜５ｇ／ｍ２ の付着量で形成してなることを特徴とする摺動性および耐型かじり性に優れる熱延鋼板。Steel composition,
C: 0.01 wt% or less, Mn: 0.05-0.5 wt%,
P: 0.01 wt% or less, S: 0.01 wt% or less,
sol Al: 0.01 to 0.10 wt%, N: 0.004 wt% or less, and Ti: 0.10 wt% or less, Nb: 0.10 wt% or less, and B: 0.01 wt% or less It contains one or more selected ones, and the balance consists of Fe and unavoidable impurities, and the surface roughness of at least one surface is Ra: 0.8 μm or less and Rmax: 4.0 μm or less. Any one or two selected from a sulfur-based extreme pressure additive having a sulfur concentration of 0.05 to 5 wt% and a phosphorus-based extreme pressure additive having a phosphorus concentration of 0.05 to 5 wt% on the upper surface of the steel sheet. A rust-preventive oil layer having a kinematic viscosity at 40 ° C. of 5 to 30 cSt at an adhesion amount of 0.5 to 5 g / m 2 . Excellent hot rolled steel sheet.
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|---|---|---|---|
| JP05144196A JP3572784B2 (en) | 1996-03-08 | 1996-03-08 | Hot-rolled steel sheet excellent in slidability and mold galling resistance and method for producing the same |
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|---|---|---|---|
| JP05144196A JP3572784B2 (en) | 1996-03-08 | 1996-03-08 | Hot-rolled steel sheet excellent in slidability and mold galling resistance and method for producing the same |
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| CN102041444A (en) * | 2010-12-21 | 2011-05-04 | 南阳汉冶特钢有限公司 | Low-carbon low-silicon high-quality carbon structural steel and production method thereof |
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