JP3617477B2

JP3617477B2 - Method for producing cold-rolled steel sheet with excellent degreasing and chemical conversion properties

Info

Publication number: JP3617477B2
Application number: JP2001219606A
Authority: JP
Inventors: 隆人横手; 文弘齋田; 耕一田谷; 明宏三沢
Original assignee: Sumitomo Metal Industries Ltd
Current assignee: Nippon Steel Corp
Priority date: 2001-07-19
Filing date: 2001-07-19
Publication date: 2005-02-02
Anticipated expiration: 2021-07-19
Also published as: JP2003033802A

Description

【０００１】
【発明が属する技術分野】
本発明は表面にめっきや塗装などを施して使用される冷延鋼板の製造方法に関する。
【０００２】
【従来の技術】
鋼板製品としての冷延鋼板は、製鉄工場から出荷される際、発錆防止のため通常は表面に防錆油が塗布された状態になっている。この鋼板を使用する自動車メーカや家電製品メーカなどでは、所要形状の部品に加工成形後、ほとんどの場合塗装あるいはめっきなど施して表面を被覆し最終製品とする。この鋼板表面に塗装やめっきを施すときに、被覆物ができるだけ十分かつ均一に密着できるよう防錆油などの油脂分を脱脂し、塗装の場合はさらに下地層形成のため化成処理がおこなわれる。
【０００３】
脱脂が十分できたかどうかは、通常表面の水濡れ面積率で評価され、同じ条件で脱脂処理が実施された場合、この水濡れ面積率が高いほど冷延鋼板としては脱脂性、さらには化成処理性が良好であると判断される。同様な防錆油が塗布されているとき、脱脂性は塗布量が少ないほどよいが、塗布量が少なくなると当然のことながら発錆の危険が増してくる。このため、鋼板を出荷する際には発錆を抑止できる最小限の範囲で防錆油が塗布されており、脱脂性改善のための防錆油塗布量低減は困難である。
【０００４】
冷延鋼板は、平坦度修正など形状の改善やストレッチャストレイン発生防止のため、焼鈍後の出荷に際し、調質圧延が施される。調質圧延には多くの場合調質圧延液が使用されるが、調質圧延の直後防錆油の塗布がおこなわれるので、調質圧延液は防錆油に混合してもその防錆性、脱脂性、化成処理性に悪影響をおよぼさないようなものが選定される。
【０００５】
調質圧延に圧延液を使用しないドライ圧延法があり、この場合は防錆油の影響だけを考えればよいが、ロール摩耗の増大や疵発生が多くなり生産能率が低いので特定の用途に限られている。また調質圧延液に防錆性のすぐれたものを適用し、より防錆性を向上させることもおこなわれているが、この場合粘性変化によって異物が混入しやすくなり、表面疵が増加する傾向がある。
【０００６】
このように、防錆油および調質圧延液に対しその種類やその組成、それらの組み合わせ等の検討が種々おこなわれてきた。しかし冷延鋼板を使用する出荷先からの脱脂性改善に対する要望は強く、その上、ときには点状の脱脂不良を発生することもあり、防錆性を損なうことのない脱脂性向上に対し、より一層十分な対応が必要である。
【０００７】
【発明が解決しようとする課題】
本発明の目的は、防錆油の塗布量を変えることなく脱脂性および化成処理性を向上させた冷延鋼板の製造方法の提供にある。
【０００８】
【課題を解決するための手段】
本発明者らは、防錆油塗布量を一定にして、冷延鋼板の脱脂性および化成処理性、すなわち脱脂処理後の水濡れ面積率を向上させるべく種々検討をおこなった。調質圧延液や防錆油の組成変更や添加剤の選定による改善についてはすでに数多くの検討がなされている。そこで本発明者は、主として調質圧延液の使用方法に着目し調査をおこなった。
【０００９】
調質圧延液にはほぼ１００％有機質の油性のものと、水溶性有機質や無機質を混ぜた水溶液のものとがあるが、調質圧延の作業条件、防錆油塗布、出荷先での処理条件等を考えて、水溶性有機質の水溶液を用いることにした。有機質としてはカルボン酸系の有機物にスルフォン酸塩など界面活性剤やアミン塩などの防錆剤が加わったのもである。多くの場合、このような調質圧延液を用いた圧延では、圧延直後に鋼板表面に付着した有機質分は１００ｍｇ／ｍ^２を超えている。
【００１０】
有機質の濃度を種々変えた調質圧延液にて、圧延液の供給方法なども変えて調質圧延後の鋼板表面の有機質付着量を変化させ、これらの鋼板に一定量の防錆油を塗布し、脱脂性および化成処理性を調査した。その結果、有機質付着量を少なくすると、ドライ圧延に近づきロールのダル面の摩耗が激しくなるなど圧延の作業性を低下させ、その上脱脂性がよくないことがわかった。しかし、有機質付着量を増していくと、脱脂性が劣化してくるばかりでなく、有機質のガム化が生じやすくなり、ロール表面への異物付着による押し込み疵や鋼板表面の汚れが生じてくる傾向がある。これらの結果から、圧延作業性と脱脂性の点で、最適の有機質付着量があることが明らかになった。
【００１１】
この有機質の付着量は、調質圧延後の鋼板の表面粗さに大きく依存し、粗さの値が大きいほど増加する。冷延鋼板の場合、一般的にダル仕上げといわれる鋼板の表面粗さはＲａにて０．５〜１．５μｍ、ブライト仕上げでは０．１〜０．３μｍであるので、このダル仕上げ面鋼板までの表面粗さを対象に、上述の最適有機質付着量を得るための、調質圧延液の濃度や圧延中における供給方法等を検討した。
【００１２】
冷延鋼板を連続焼鈍法にて処理する場合、化成処理性や防錆性の改善のため、フラッシュめっきと称する微量のＮｉを付着させることがある。このＮｉフラッシュめっきは、出荷先における脱脂処理後の水濡れ面積率に大きく影響することがあるので、上述の調質圧延における最適有機質付着量の範囲での影響を調査した。その結果、Ｎｉ付着量の上限値を設定することにより、脱脂性および化成処理性のすぐれた鋼板になることが確認できた。
【００１３】
さらに、この調質圧延における有機質の付着量を最適の範囲に管理することは、点状脱脂不良の防止にも有効であることがわかった。点状脱脂不良とは、連続焼鈍炉を通過させた後の冷延鋼板製品にて、出荷先での成形品の脱脂後、表面に局所的な脱脂不良部分の散在が検出される現象である。
【００１４】
これは鋼板が連続焼鈍炉内を通過する際、鋼板表面に小さな凹み疵が作られ、この疵は多くの場合調質圧延によって平滑化されるが、疵の状態によってはその内部に調質圧延液が入り込み、それが元になって出荷先での点状脱脂不良が現れるとされている。この対策として、防錆油の塗布量を低減することが有効であるが、鋼板の発錆のため十分には低減できない。
【００１５】
鋼板の凹み疵の多くは、加熱帯や均熱帯など鋼板の温度が最も高くなる部位における、鋼板通過と共に堆積してくるハースロール表面のビルドアップといわれる突起物によると考えられている。ビルドアップの形成は炉の操業上避け難いが、ハースロールの表面粗さにより、形成のされ方が変わるとされている。そこで、加熱帯、均熱帯および徐冷帯のハースロールの表面粗さを変えてみると、調質圧延前の鋼板表面で検出される凹み疵の大きさが変化した。そして凹み疵の大きさが小さくなると、点状脱脂不良が減少することがわかった。このことから、ハースロールの表面粗さを低下させ、その上で前述の調質圧延における有機質の付着量を最適の範囲とすると、上記の点状脱脂不良が大幅に低減できることも確認できた。
【００１６】
以上のように、出荷の際に塗布する防錆油の量は変えずに調質圧延による圧延液の残存量を管理することによって、鋼板の脱脂性および化成処理性を大幅に改善できることが明らかになった。そこで、この効果を再現性よく実現するための諸条件についてさらに検討を進め、本発明を完成させることができた。本発明の要旨は次のとおりである。
【００１７】
(1) 焼鈍後に調質圧延を施して、表面粗さがＲ a で 0.5 〜 1.5 μｍである冷延鋼板を製造する方法であって、1〜15％の水溶性有機質を含む調質圧延液を用いて調質圧延を行い、圧延後の鋼板表面に調質圧延液の有機質を20〜80mg／m^２付着させることを特徴とする脱脂性および化成処理性にすぐれた冷延鋼板の製造方法。
【００１８】
(2) 焼鈍後に調質圧延を施して、表面粗さがＲ a で 1.5 μｍ以下で、Ｎｉの付着量が 15mg ／ m ^２以下である冷延鋼板を製造する方法であって、1〜15％の水溶性有機質を含む調質圧延液を用いて調質圧延を行い、圧延後の鋼板表面に調質圧延液の有機質を20〜80mg／m^２付着させることを特徴とする脱脂性および化成処理性にすぐれた冷延鋼板の製造方法。
【００１９】
(3) 連続焼鈍後に調質圧延を施して、表面粗さがＲ a で 1.5 μｍ以下である冷延鋼板を製造する方法であって、表面粗さがＲ a で 8 μ m 以下であるハースロールを用いて連続焼鈍を行い、1〜15％の水溶性有機質を含む調質圧延液を用いて調質圧延を行い、圧延後の鋼板表面に調質圧延液の有機質を20〜80mg／m^２付着させることを特徴とする脱脂性および化成処理性にすぐれた冷延鋼板の製造方法。
【００２０】
【発明の実施の形態】
本発明の製造方法は、表面粗さがＲａ１．５μｍ以下である冷延鋼板に適用する。一般にダル仕上げといわれる冷延鋼板の表面粗さは、Ｒａ０．５〜１．５μｍ、ブライト仕上げでは０．１〜０．３μｍであり、これらの鋼板を対象とするからであるが、表面粗さＲａが１．５μｍを超えるようになると、調質圧延液の付着量が増し、鋼板の脱脂性が低下する傾向を示すためでもある。
【００２１】
この表面粗さの製品鋼板を調質圧延するときに、調質圧延液として水溶性の有機質を１〜１５％（重量％）含む水溶液を使用し、調質圧延後の鋼板表面にこの調質圧延液に含まれていた有機質が、２０〜８０ｍｇ／ｍ^２付着しているものとする。
【００２２】
調質圧延液に含まれる有機質は、たとえば潤滑効果のある脂肪族や芳香族のカルボン酸、アルキルアリールスルフォン酸などの界面活性剤、防錆効果のあるアミン系化合物などである。これらの有機質の調質圧延液中の濃度が１％未満では、潤滑効果がなくロールのダルの摩耗が増し再々研磨する必要が生じてくる。しかし１５％を超える含有量になると、圧延後の鋼板表面への有機質付着量が増し、出荷先での脱脂性を悪くする。
【００２３】
調質圧延後の鋼板表面に付着する有機質は、２０〜８０ｍｇ／ｍ^２とする。これは付着量が２０ｍｇ／ｍ^２を下回るようになると圧延の潤滑性の低下や、製品鋼板の防錆性が低下するからであり、８０ｍｇ／ｍ^２を超えると出荷先での脱脂性が低下するばかりでなく、ロール表面に粘着物が堆積し押し込み疵などが増加してくるからである。
【００２４】
調質圧延液の有機質としてＭＫ−５５（出光興産社製調質圧延剤）を用い、濃度と圧延ロールへの供給方法とを変えて圧延後の鋼板表面への有機質付着量を変え、防錆油はＳＫ（出光興産社製防錆油）を用いて塗布量を１．０〜１．５ｇ／ｍ^２のほぼ一定として、鋼板の脱脂性と防錆性とを調査した。
【００２５】
脱脂性については脱脂剤ＦＣ−４４８０（日本パーカライズ社製鋼板洗浄剤）を２０ｇ／Ｌ溶解した４５℃の水溶液にて３０秒間のスプレイ洗浄をおこない、水洗してから３０秒放置後、水濡れ面積率を測定した。結果の例を図１（ａ）に示すが、水濡れ面積率は調質圧延液の有機質付着が多くても少なくても悪くなる傾向を示した。
【００２６】
防錆性については、防錆油塗布後表面にＣｌイオンを２０ｐｐｍ含む水滴を垂らした後、６週間室内に放置し、発生した錆の観察から錆の発生の小さいものほど大きい値となるよう１〜４の評点を付した。結果の例を図１（ｂ）に示す。
【００２７】
図１（ａ）および図１（ｂ）からわかるように、水濡れ面積率が十分高くかつ防錆評価点の高い調質圧延液の有機質の付着量範囲は、２０〜８０ｍｇ／ｍ^２の範囲である。
【００２８】
製品鋼板の表面粗さＲａと、調質圧延液の濃度および有機質付着量との関係を調べた結果を図２に示す。表面粗さＲａが大きくなるほど、そして調質圧延液の濃度が高くなるほど、有機質の付着量は増加の傾向を示している。表面粗さＲａが１．５μｍ以下である鋼板にて、付着量を２０〜８０ｍｇ／ｍ^２とするためには、調質圧延液の濃度は１〜１５％とするのが望ましいことがわかる。
【００２９】
Ｎｉのフラッシュめっきをおこなった鋼板の場合、Ｎｉの付着量は１５ｍｇ／ｍ^２以下とする。これは、１５ｍｇ／ｍ^２以下とすれば、上述の表面粗さがＲａで１．５μｍ以下である鋼板にて、圧延後の鋼板表面に調質圧延液の有機質を２０〜８０ｍｇ／ｍ^２付着させることによって、すぐれた脱脂性と防錆性とを有する鋼板にすることができるからである。
【００３０】
フラッシュめっきにより付着したＮｉは、蛍光Ｘ線分析法（ＸＰＳ）にて調べてみると、鋼板表面にて金属ＮｉとＮｉ−Ｏ（酸化Ｎｉまたは水酸化Ｎｉ）とが混在する状態になっている。防錆油塗布後の脱脂性について検討の結果、図３に示すようにＮｉ−ＯとなっているＮｉの原子比率（以下Ｎｉ−Ｏ比率とする）が増すと、脱脂性すなわち水濡れ性が低下することがわかった。良好な水濡れ性を得るためには、Ｎｉ−Ｏ比率が、７．５原子％以下である必要がある。
【００３１】
一方、Ｎｉの付着量とＮｉ−Ｏ比率との関係を調べてみると、図４に示すようにＮｉの付着量がが増すとＮｉ−Ｏ比率が大きくばらつくようになることがわかった。これから、安定してＮｉ−Ｏ比率を低くし、そして７．５原子％以下とするためには、Ｎｉの付着量を１５ｍｇ／ｍ^２以下とするのがよいことが明らかである。ただし、Ｎｉのフラッシュめっきをおこなうことにより得られる化成処理性や防錆性の改善効果は、Ｎｉがほとんど検出されない場合でも認められるが、望ましいのは付着量が少なくとも３ｍｇ／ｍ^２以上である。フラッシュめっきでのＮｉ付着量については、めっき電流を増減することにより容易に制御できる。
【００３２】
表面粗さＲａが１．５μｍ以下である鋼板にて、付着量を２０〜８０ｍｇ／ｍ^２とすることは、点状脱脂不良の低減にも有効である。とくに連続焼鈍炉の加熱帯、均熱帯、徐冷帯等の高温部分にて用いられるハースロールの表面粗さは、Ｒａで８μｍ以下とすることによって、より一層この点状脱脂不良を抑止することができる。
【００３３】
連続焼鈍設備にて調質圧延直前の鋼板表面に見出される凹み疵欠陥のうち、径が０．１ｍｍ以上で深さ１０μｍ以上の欠陥について、径と深さとの積の値でその大きさを表すこととし、この凹み欠陥の大きさと調質圧延および防錆油塗布後の鋼板の点状脱脂不良との関係を調査した。結果を図５に示すが、凹み疵が大きくなると点状脱脂不良の発生頻度が急激に増加する。この場合、調質圧延後の鋼板表面における調質圧延液の有機質の付着量を２０〜８０ｍｇ／ｍ^２とすると、凹み疵の径と深さとの積が、４０×１０００μｍ^２以下であれば、点状脱脂不良の発生率はほぼ零にすることができた。
【００３４】
そこで、炉内の高温部分のハースロールの粗さと、焼鈍後の鋼板に見出される凹み疵の径と深さとの積の関係を調べてみると、図６の結果が得られた。この図から、凹み疵の径と深さとの積を、４０×１０００μｍ^２以下とするには、ハースロールの表面粗さＲａを８μｍ以下にすればよいことがわかる。
【００３５】
このように、炉内の高温部分のハースロールの表面粗さをＲａにて８μｍ以下とし、前述のように圧延後鋼板表面の調質圧延液の有機分の付着量を２０〜８０ｍｇ／ｍ^２とすれば、表面粗さがＲａで１．５μｍ以下の鋼板の、点状脱脂不良をほぼ完全に抑止することができる。
【００３６】
調質圧延後鋼板表面における調質圧延液の有機分付着量を２０〜８０ｍｇ／ｍ^２とすることができるのであれば、その方法はとくには限定しないが、例えば図７に模式的に示すように、圧延ロールの出側から圧延液溜まり受けに調質圧延液を供給すれば、バックアップロールとの接触によってワークロールに面に付着する調質圧延液が絞られ、鋼板表面への有機分の付着量を上記範囲に制御することが可能である。
【００３７】
【実施例】
〔実施例１〕
表１に示すようにＮｉのフラッシュめっきの有無、製品の表面粗さ、調質圧延液等を変え、冷延鋼板製品を製造した。この場合、調質圧延の圧下率を０．６％の一定とし、圧延後の防錆油はＳＫ（出光興産社製）を用い塗布量は１．０〜１．５ｇ／ｍ^２のほぼ一定とした。製品の表面粗さは調質圧延ロールにて調整し、調質圧延液の有機質はＭＫ−５５（出光興産社製）を用い、無機調質圧延液の場合はＲＳ２１０（出光興産社製）とした。調質圧延液は図７に示した圧延ロールの出側から圧延液溜まり受けに供給する方法とし、圧延液の濃度を変えることにより、鋼板表面の有機質の付着量を変えた。
【００３８】
【表１】

【００３９】
鋼板表面の有機質付着量は、イオン交換水と濾紙を用いて鋼板表面を洗浄し、ごみを除去した洗浄液について吸光度を測定して、あらかじめ作成しておいた有機質による検量線との比較から洗浄液の濃度を測定し、洗浄液量と被測定鋼板表面積とから付着量を求めた。
【００４０】
防錆油塗布後の脱脂性は、脱脂剤ＦＣ−４４８０（日本パーカライジング社製鋼板洗浄剤）を２０ｇ／Ｌ溶解した４５℃の水溶液にて３０秒間のスプレイ洗浄をおこない、水洗してから３０秒放置後、水濡れ面積率を測定した。化成処理性は、ＰＢＬ３０２０（日本パーカライジング社製化成処理剤）を用い、所定の温度、時間にて処理をおこない、化成結晶状態のＳＥＭによる観察および被膜付着量から良否を判断した。
【００４１】
調査した結果を合わせて表１に示す。本発明にて定めるの鋼板表面粗さがＲａにて１．５μｍ以下で、調質圧延液の有機質の付着量が２０〜８０ｍｇ／ｍ^２である試番２および試番１２はすぐれた脱脂性を有していることが明らかである。試番５は本発明範囲ではあるが、Ｎｉの付着量が多すぎたためか脱脂性がやや劣る結果になった。なお化成処理性については、脱脂性が良好である場合は、いずれも良好な結果を示していた。
【００４２】
〔実施例２〕
連続焼鈍炉の加熱帯、均熱帯および徐冷帯のハースロールに対して、その表面粗さを同時に変え、その際の調質圧延直前における鋼板の凹み疵を観察し、調質圧延後の鋼板表面における調質圧延液の有機質の付着量、防錆油塗布後の脱脂性を評価した。この場合ハースロールの表面粗さはＲａで０．１、２、８および１０μｍの４種とした。凹み疵は調質圧延前にて鋼板から１００ｍｍ角の試片を切り出して、凹み疵の存在を確認した後、ＳＥＭ観察および３次元粗さ計を用いて、凹み疵の大きさと深さを測定した。
【００４３】
製品の表面粗さはＲａで１．０μｍとし、調質圧延条件は実施例１と同じで、圧延後の表面の有機質付着量は実施例１と同様圧延液の有機質濃度の変更にて変え、その他の調質圧延条件、防錆油塗布および脱脂性の評価方法等はすべて実施例１と同様にした。
【００４４】
表２にハースロールの表面粗さ、調質圧延後の有機質付着量、凹み疵、製品の脱脂性評価をまとめて示す。ここで、凹み疵は大きさが０．１ｍｍから１．５ｍｍ程度のものであり、明確な形を示さないものもあるが、その場合は円形に近似して直径を求めた。深さは１０〜５０μｍのものが大半であった。この凹み疵については、採取試片において観察された凹み疵の中で、最大のものの大きさと大きさが０．１ｍｍ以上で深さが１０μｍ以上のものの個数を示した。脱脂性評価については、点状脱脂不良の評価を示した。
【００４５】
【表２】

【００４６】
この表２の結果から、ハースロールの表面粗さがＲａで８μｍ以下であれば、凹み疵の大きさおよび数は共に相対的に小さく、同様な大きさや数の凹み疵であれば、調質圧延液の有機質付着量が本発明範囲の３０〜５０ｍｇ／ｍ^２である試番１５、１８および２１は点状脱脂不良が抑止されることがわかる。ただし、試番２４は本発明範囲の例であるが、ハースロールの表面粗さが粗かったため、点状脱脂不良を十分抑止できなかった。
【００４７】
【発明の効果】
本発明によれば、工場出荷から部品への成形使用までの間の、発錆を抑止するための防錆油を低減することなく、成形部品の脱脂性を向上させた冷延鋼板を製造することができる。このように防錆と脱脂とを両立させることは、冷延鋼板製品使用時の品質の信頼性を大きく向上させる効果がある。
【図面の簡単な説明】
【図１】調質圧延液の有機質の鋼板面付着量と、防錆油塗布後の鋼板の脱脂後水濡れ面積率および防錆性との関係を示す図である。
【図２】鋼板表面粗さおよび調質圧延液の濃度と、有機質の鋼板表面付着量との関係を示す図である。
【図３】Ｎｉフラッシュめっき中のＮｉ−Ｏ比率と、調質圧延後防錆油塗布した鋼板の水濡れ率との関係を示す図である。
【図４】Ｎｉ付着量とＮｉ−Ｏ比率との関係を示す図である。
【図５】鋼板表面の凹み疵の大きさと、調質圧延後防錆油塗布した鋼板の点状脱脂不良発生率との関係を示す図である。
【図６】連続焼鈍炉のハースロールの表面粗さと、凹み疵の大きさとの関係を示す図である。
【図７】調質圧延時の圧延液の供給方法の例を示す模式図である。
【符号の説明】
１鋼板
２ワークロール
３バックアップロール
４圧延液
５圧延液供給用ポンプ[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for producing a cold-rolled steel sheet that is used with a surface plated or painted.
[0002]
[Prior art]
When a cold-rolled steel sheet as a steel sheet product is shipped from a steel factory, the surface is usually coated with a rust-preventing oil to prevent rusting. In automobile manufacturers and household appliance manufacturers that use this steel sheet, after processing and forming parts of the required shape, in most cases, coating or plating is applied to cover the surface to obtain the final product. When coating or plating on the surface of the steel sheet, oil and fat such as rust preventive oil is degreased so that the coating can be adhered as sufficiently and uniformly as possible, and in the case of coating, a chemical conversion treatment is performed to form a base layer.
[0003]
Whether or not degreasing is sufficient is usually evaluated by the surface wetted area ratio of the surface, and when the degreasing treatment is carried out under the same conditions, the higher the wetted area ratio, the more degreased the cold rolled steel sheet, and further the chemical conversion treatment Is judged to be good. When the same rust preventive oil is applied, the degreasing property is better as the coating amount is smaller. However, as the coating amount decreases, the risk of rusting naturally increases. For this reason, when shipping steel sheets, the rust preventive oil is applied to the minimum extent that can prevent rusting, and it is difficult to reduce the amount of rust preventive oil applied to improve the degreasing property.
[0004]
Cold-rolled steel sheets are subjected to temper rolling at the time of shipment after annealing in order to improve the shape such as flatness correction and prevent the occurrence of stretcher strain. In many cases, temper rolling is used for temper rolling, but rust preventive oil is applied immediately after temper rolling, so even if temper rolling fluid is mixed with rust preventive oil, its rust resistance Those that do not adversely affect the degreasing and chemical conversion properties are selected.
[0005]
There is a dry rolling method that does not use rolling liquid for temper rolling.In this case, it is only necessary to consider the effect of rust-preventing oil, but it is limited to specific applications because roll wear increases and wrinkles increase and the production efficiency is low. It has been. In addition, temper rolling liquids with excellent rust prevention properties are applied to improve rust prevention properties, but in this case, foreign matter tends to be mixed due to viscosity changes, and surface defects tend to increase. There is.
[0006]
As described above, various studies have been made on the types, compositions, combinations thereof, and the like of the rust preventive oil and the tempered rolling fluid. However, there is a strong demand for improvement in degreasing properties from customers who use cold-rolled steel sheets, and in addition, there are cases where point-like degreasing defects occur, and in order to improve degreasing properties without impairing rust prevention, More sufficient measures are required.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing a cold-rolled steel sheet having improved degreasing properties and chemical conversion properties without changing the coating amount of rust preventive oil.
[0008]
[Means for Solving the Problems]
The present inventors have made various studies in order to improve the degreasing and chemical conversion properties of cold-rolled steel sheets, that is, the water-wetting area ratio after degreasing, with a constant amount of rust-preventing oil applied. Many studies have already been made on the improvement of the composition of temper rolling liquid and rust preventive oil and the improvement by selecting additives. Therefore, the present inventor conducted an investigation mainly focusing on the method of using the temper rolling liquid.
[0009]
There are two types of temper rolling liquids, one that is almost 100% organic oil and the other that is a mixture of water-soluble organic and inorganic substances. The working conditions of temper rolling, the application of rust prevention oil, and the processing conditions at the shipping destination. In view of the above, it was decided to use a water-soluble organic aqueous solution. As organic substances, surfactants such as sulfonates and rust preventives such as amine salts are added to carboxylic acid organic substances. In many cases, in the rolling using such a temper rolling solution, the organic matter adhering to the steel sheet surface immediately after rolling exceeds 100 mg / m ² .
[0010]
With temper rolling liquids with various organic concentrations, the amount of organic adhesion on the steel sheet surface after temper rolling is changed by changing the supply method of the rolling liquid, and a certain amount of rust preventive oil is applied to these steel sheets. The degreasing and chemical conversion properties were investigated. As a result, it was found that when the organic adhesion amount was reduced, the workability of the rolling was lowered, such as the dull surface of the roll approaching the dry rolling, and the degreasing property was not good. However, as the amount of organic adhesion increases, not only the degreasing property deteriorates, but also organic gumming tends to occur, and indentation flaws and dirt on the steel sheet surface due to adhesion of foreign matter to the roll surface tend to occur. There is. From these results, it has been clarified that there is an optimum organic adhesion amount in terms of rolling workability and degreasing properties.
[0011]
The organic adhesion amount greatly depends on the surface roughness of the steel sheet after temper rolling, and increases as the roughness value increases. In the case of a cold-rolled steel sheet, the surface roughness of the steel sheet, generally called dull finish, is 0.5 to 1.5 μm in Ra, and 0.1 to 0.3 μm in bright finish. In consideration of the surface roughness, the concentration of the tempered rolling liquid and the supply method during rolling were studied in order to obtain the above-mentioned optimum organic adhesion amount.
[0012]
When a cold-rolled steel sheet is processed by a continuous annealing method, a small amount of Ni called flash plating may be adhered in order to improve chemical conversion treatment properties and rust prevention properties. Since this Ni flash plating may greatly affect the water wetted area ratio after degreasing treatment at the shipping destination, the influence in the range of the optimum organic adhesion amount in the above-mentioned temper rolling was investigated. As a result, it was confirmed that by setting the upper limit value of the Ni adhesion amount, the steel sheet was excellent in degreasing and chemical conversion properties.
[0013]
Furthermore, it has been found that managing the organic adhesion amount in the temper rolling within the optimum range is effective in preventing the point-like degreasing failure. Poor degreasing is a phenomenon in which local degreasing portions are detected on the surface of a cold-rolled steel sheet product after passing through a continuous annealing furnace after degreasing the molded product at the shipping destination. .
[0014]
This is because when the steel sheet passes through the continuous annealing furnace, a small dent crease is made on the surface of the steel sheet, and this crease is often smoothed by temper rolling. It is said that the liquid enters and causes point-like degreasing defects at the shipping destination. As a countermeasure, it is effective to reduce the coating amount of the rust preventive oil, but it cannot be sufficiently reduced due to rusting of the steel sheet.
[0015]
Many of the steel plate pits are thought to be due to protrusions called build-up on the surface of the hearth roll that accumulates with the passage of the steel plate in the region where the temperature of the steel plate is highest, such as a heating zone and a soaking zone. Build-up formation is difficult to avoid in the operation of the furnace, but the way it is formed is said to change depending on the surface roughness of the hearth roll. Therefore, when the surface roughness of the hearth rolls in the heating zone, the soaking zone and the slow cooling zone was changed, the size of the dents detected on the surface of the steel plate before the temper rolling changed. And when the magnitude | size of the dent wrinkles became small, it turned out that a point-like degreasing defect reduces. From this fact, it was also confirmed that the above-described point-like degreasing failure can be greatly reduced by reducing the surface roughness of the hearth roll and setting the organic adhesion amount in the temper rolling described above to the optimum range.
[0016]
As described above, it is clear that the degreasing and chemical conversion properties of steel sheets can be greatly improved by managing the remaining amount of rolling fluid by temper rolling without changing the amount of rust preventive oil applied at the time of shipment. Became. Therefore, further studies were made on various conditions for realizing this effect with good reproducibility, and the present invention could be completed. The gist of the present invention is as follows.
[0017]
(1) A method for producing a cold-rolled steel sheet having a surface roughness Ra of 0.5 to 1.5 μm by temper rolling after annealing and comprising 1 to 15% of water-soluble organic material. A method for producing a cold-rolled steel sheet having excellent degreasing and chemical conversion properties, characterized in that temper rolling is performed using 20 to 80 mg / m ² of organic material of the temper rolling liquid on the surface of the steel sheet after rolling. .
[0018]
(2) A method for producing a cold-rolled steel sheet having a surface roughness Ra of 1.5 μm or less and a Ni adhesion amount of 15 mg / m ² or less by applying temper rolling after annealing. Degreasing and chemical conversion, characterized in that temper rolling is performed using a temper rolling liquid containing 1% water-soluble organic matter, and the organic matter of the temper rolling liquid is adhered to the rolled steel sheet surface at 20 to 80 mg / m ^2. A method for producing cold-rolled steel sheets with excellent processability.
[0019]
(3) subjected to a temper rolling after the continuous annealing, the surface roughness A method of manufacturing a cold-rolled steel sheet is 1.5 [mu] m or less in R a, surface roughness is not more than 8 mu m in R a Haas Continuous annealing is performed using a roll, temper rolling is performed using a temper rolling liquid containing 1 to 15% water-soluble organic matter, and the organic content of the temper rolling liquid is 20 to 80 mg / m on the surface of the steel sheet after rolling. ^{2. A} method for producing a cold-rolled steel sheet having excellent degreasing properties and chemical conversion properties, characterized by adhering.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
The production method of the present invention is applied to a cold-rolled steel sheet having a surface roughness of Ra 1.5 μm or less. This is because the surface roughness of cold-rolled steel sheet, generally called dull finish, is 0.5 to 1.5 μm Ra and 0.1 to 0.3 μm in bright finish, and these steel sheets are targeted. When Ra exceeds 1.5 μm, the adhesion amount of the temper rolling liquid increases and the degreasing property of the steel sheet tends to decrease.
[0021]
When temper rolling a product steel sheet with this surface roughness, an aqueous solution containing 1 to 15% (wt%) water-soluble organic substance is used as the temper rolling liquid, and this tempering is performed on the surface of the steel sheet after temper rolling. It is assumed that 20 to 80 mg / m ^{2 of} organic matter contained in the rolling liquid is attached.
[0022]
Examples of organic substances contained in the temper rolling liquid include surfactants such as aliphatic and aromatic carboxylic acids having a lubricating effect and alkylaryl sulfonic acids, and amine compounds having a rust preventive effect. If the concentration of these organic tempered rolling liquids is less than 1%, there is no lubricating effect, wear of the roll dal increases, and it becomes necessary to grind again. However, if the content exceeds 15%, the organic adhesion amount on the steel sheet surface after rolling increases, and the degreasing property at the shipping destination is deteriorated.
[0023]
The organic matter that adheres to the surface of the steel sheet after temper rolling is set to 20 to 80 mg / m ² . This is because when the adhesion amount is less than 20 mg / m ² , the lubricity of the rolling is lowered and the rust prevention property of the product steel plate is lowered, and when it exceeds 80 mg / m ² , the degreasing property at the shipping destination is lowered. Not only does this occur, but sticky material accumulates on the roll surface, increasing the amount of indentation and the like.
[0024]
Using MK-55 (Idemitsu Kosan Co., Ltd.'s temper rolling agent) as the organic material of the temper rolling liquid, changing the concentration and supply method to the rolling roll, changing the amount of organic matter adhered to the steel sheet surface after rolling, and preventing rust The oil was SK (rust prevention oil manufactured by Idemitsu Kosan Co., Ltd.), and the coating amount was set to be substantially constant at 1.0 to 1.5 g / m ² , and the degreasing property and rust prevention property of the steel sheet were investigated.
[0025]
For degreasing properties, spray cleaning is performed for 30 seconds with an aqueous solution of 45 ° C. in which 20 g / L of a degreasing agent FC-4480 (steel plate cleaner manufactured by Nihon Parkerize Co., Ltd.) is dissolved. The area ratio was measured. An example of the results is shown in FIG. 1 (a), and the water-wetting area ratio showed a tendency to deteriorate even if the organic adhesion of the temper rolling liquid was large or small.
[0026]
About antirust property, after applying a water drop containing 20 ppm of Cl ions on the surface after applying antirust oil, leave it indoors for 6 weeks, and from the observation of the generated rust, the smaller the rust occurrence, the larger the value 1 A rating of ~ 4 was affixed. An example of the result is shown in FIG.
[0027]
As can be seen from FIG. 1 (a) and FIG. 1 (b), the organic adhesion amount range of the tempered rolling liquid having a sufficiently high water-wetting area ratio and a high rust prevention evaluation point is a range of 20 to 80 mg / m ² . It is.
[0028]
FIG. 2 shows the results of examining the relationship between the surface roughness Ra of the product steel sheet, the concentration of the temper rolling solution, and the amount of organic adhesion. As the surface roughness Ra is increased and the concentration of the temper rolling liquid is increased, the organic adhesion amount tends to increase. It can be seen that, in a steel sheet having a surface roughness Ra of 1.5 μm or less, the concentration of the temper rolling liquid is preferably 1 to 15% in order to make the adhesion amount 20 to 80 mg / m ² .
[0029]
In the case of a steel plate subjected to flash plating of Ni, the amount of Ni attached is 15 mg / m ² or less. If this is 15 mg / m ² or less, the surface roughness of the steel sheet with Ra of 1.5 μm or less is 20 to 80 mg / m ² of organic material of the temper rolling liquid on the steel plate surface after rolling. It is because it can be set as the steel plate which has the outstanding degreasing property and rust prevention property by making it.
[0030]
When the Ni adhering by flash plating is examined by fluorescent X-ray analysis (XPS), the surface of the steel sheet is in a state where metal Ni and Ni—O (Ni oxide or Ni hydroxide) are mixed. . As a result of the study on the degreasing property after the application of the rust preventive oil, when the atomic ratio of Ni that is Ni-O (hereinafter referred to as Ni-O ratio) is increased as shown in FIG. It turns out that it falls. In order to obtain good water wettability, the Ni—O ratio needs to be 7.5 atomic% or less.
[0031]
On the other hand, when the relationship between the adhesion amount of Ni and the Ni—O ratio was examined, it was found that as the adhesion amount of Ni increased, the Ni—O ratio varied greatly as shown in FIG. From this, it is clear that in order to stably reduce the Ni—O ratio and to make it 7.5 atomic% or less, it is preferable to make the amount of Ni deposited 15 mg / m ² or less. However, the improvement effect of chemical conversion treatment property and rust prevention property obtained by performing flash plating of Ni is recognized even when Ni is hardly detected, but it is desirable that the adhesion amount is at least 3 mg / m ² or more. The Ni adhesion amount in flash plating can be easily controlled by increasing or decreasing the plating current.
[0032]
In a steel sheet having a surface roughness Ra of 1.5 μm or less, setting the adhesion amount to 20 to 80 mg / m ² is also effective in reducing point-like degreasing defects. In particular, the surface roughness of the hearth roll used in high-temperature parts such as the heating zone, soaking zone, and slow cooling zone of a continuous annealing furnace should further suppress this point-like degreasing defect by setting the Ra to 8 μm or less. Can do.
[0033]
Of the dent defects found on the surface of the steel sheet immediately before temper rolling in a continuous annealing facility, the size of the defect having a diameter of 0.1 mm or more and a depth of 10 μm or more is represented by the product of the diameter and the depth. In particular, the relationship between the size of the dent defect and the point-like degreasing failure of the steel sheet after temper rolling and rust prevention oil application was investigated. A result is shown in FIG. 5, and when the dent wrinkles become large, the occurrence frequency of the point-like degreasing failure increases rapidly. In this case, if the organic adhesion amount of the temper rolling liquid on the steel sheet surface after temper rolling is 20 to 80 mg / m ² , the product of the diameter and depth of the dents is 40 × 1000 μm ² or less, The incidence of point-like degreasing failure could be almost zero.
[0034]
Therefore, when the relationship between the product of the roughness of the hearth roll in the high-temperature portion in the furnace and the diameter and depth of the dents found in the steel sheet after annealing was examined, the result of FIG. 6 was obtained. From this figure, it is understood that the surface roughness Ra of the hearth roll should be 8 μm or less in order to make the product of the diameter and depth of the ridges 40 × 1000 μm ² or less.
[0035]
Thus, the surface roughness of the hearth roll at the high-temperature portion in the furnace is set to 8 μm or less in Ra, and the adhesion amount of the organic component of the temper rolling liquid on the surface of the steel sheet after rolling is 20 to 80 mg / m ^{2 as described above.} If so, the point-like degreasing failure of the steel sheet having a surface roughness Ra of 1.5 μm or less can be almost completely prevented.
[0036]
The method is not particularly limited as long as the organic content adhesion amount of the temper rolling liquid on the surface of the temper rolled steel sheet after temper rolling can be ²⁰ to 80 mg / m ^2. For example, as schematically shown in FIG. In addition, if the tempered rolling fluid is supplied to the rolling fluid reservoir receiver from the exit side of the rolling roll, the tempered rolling fluid adhering to the surface of the work roll due to contact with the backup roll is squeezed, and the organic content on the steel sheet surface is reduced. It is possible to control the adhesion amount within the above range.
[0037]
【Example】
[Example 1]
As shown in Table 1, cold rolled steel sheet products were manufactured by changing the presence or absence of Ni flash plating, the surface roughness of the product, the temper rolling liquid, and the like. In this case, the rolling reduction of the temper rolling is constant at 0.6%, the rust prevention oil after rolling is SK (made by Idemitsu Kosan Co., Ltd.), and the coating amount is substantially constant at 1.0 to 1.5 g / m ² . It was. The surface roughness of the product is adjusted with a temper rolling roll, and the organic material of the temper rolling liquid is MK-55 (made by Idemitsu Kosan Co., Ltd.). In the case of an inorganic tempered rolling liquid, RS210 (made by Idemitsu Kosan Co., Ltd.) did. The temper rolling liquid was supplied to the rolling liquid pool receiver from the exit side of the rolling roll shown in FIG. 7, and the amount of organic adhesion on the steel sheet surface was changed by changing the concentration of the rolling liquid.
[0038]
[Table 1]

[0039]
The amount of organic adhesion on the surface of the steel sheet was determined by washing the surface of the steel sheet with ion-exchanged water and filter paper, measuring the absorbance of the cleaning liquid from which debris was removed, and comparing it with a calibration curve prepared in advance using organic substances. The concentration was measured, and the amount of adhesion was determined from the amount of cleaning liquid and the surface area of the steel plate to be measured.
[0040]
The degreasing property after the application of rust-preventing oil is 30 seconds after performing spray cleaning for 30 seconds with a 45 ° C. aqueous solution in which 20 g / L of a degreasing agent FC-4480 (steel plate cleaning agent manufactured by Nihon Parkerizing Co., Ltd.) is dissolved. After standing, the water wetted area ratio was measured. The chemical conversion treatment was performed using PBL3020 (Chemical conversion treatment agent manufactured by Nippon Parkerizing Co., Ltd.) at a predetermined temperature and time, and the quality was judged from the SEM observation of the chemical conversion crystal state and the coating adhesion amount.
[0041]
The survey results are shown together in Table 1. Sample No. 2 and No. 12 in which the surface roughness of the steel sheet defined by the present invention is 1.5 μm or less in Ra and the organic adhesion amount of the temper rolling liquid is 20 to 80 mg / m ² are excellent degreasing properties. It is clear that Although test number 5 was within the scope of the present invention, the degreasing property was slightly inferior because of the excessive amount of Ni deposited. In addition, about chemical conversion treatment property, when the degreasing property was favorable, all showed the favorable result.
[0042]
[Example 2]
Change the surface roughness of the continuous annealing furnace heating zone, soaking zone and slow cooling zone at the same time, and observe the dents in the steel plate immediately before temper rolling. The organic adhesion amount of the temper rolling liquid on the surface and the degreasing property after applying the rust preventive oil were evaluated. In this case, the surface roughness of the hearth roll was Ra, 0.1, 2, 8, and 10 μm. For dent wrinkles, a 100 mm square specimen is cut out from a steel plate before temper rolling, and after confirming the presence of dent wrinkles, the size and depth of the dent wrinkles are measured using SEM observation and a three-dimensional roughness meter. did.
[0043]
The surface roughness of the product is Ra of 1.0 μm, the temper rolling conditions are the same as in Example 1, and the amount of organic adhesion on the surface after rolling is changed by changing the organic concentration of the rolling liquid as in Example 1, Other temper rolling conditions, application of rust preventive oil, evaluation method of degreasing properties, and the like were all the same as in Example 1.
[0044]
Table 2 summarizes the surface roughness of the hearth roll, the organic adhesion amount after temper rolling, the dents, and the degreasing evaluation of the product. Here, the size of the ridges is about 0.1 mm to 1.5 mm, and some of them do not show a clear shape. In that case, the diameter was obtained by approximating a circle. Most of the depth was 10 to 50 μm. As for the dent folds, among the dent ridges observed in the collected specimens, the maximum size and the number of those having a size of 0.1 mm or more and a depth of 10 μm or more are shown. About degreasing property evaluation, the evaluation of the point-like degreasing defect was shown.
[0045]
[Table 2]

[0046]
From the results shown in Table 2, if the surface roughness of the hearth roll is 8 μm or less in Ra, both the size and number of the ridges are relatively small. It turns out that the dotted | punctate degreasing defect is suppressed by the trial numbers 15, 18, and 21 whose organic adhesion amount of a rolling liquid is 30-50 mg / m < ² > of the range of this invention. However, although the trial number 24 is an example of the scope of the present invention, since the surface roughness of the hearth roll was rough, the point-like degreasing failure could not be sufficiently suppressed.
[0047]
【The invention's effect】
According to the present invention, a cold-rolled steel sheet with improved degreasing properties of a molded part is manufactured without reducing rust preventive oil for inhibiting rusting from factory shipment to use for molding on the part. be able to. Thus, coexistence of rust prevention and degreasing has the effect of greatly improving the reliability of the quality when using cold-rolled steel sheet products.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the amount of organic steel sheet surface adhering to a temper rolling solution, the wetted area ratio after degreasing of a steel sheet after application of rust-preventive oil, and rust resistance.
FIG. 2 is a graph showing the relationship between the steel sheet surface roughness and the concentration of the temper rolling liquid and the amount of organic steel sheet surface adhesion.
FIG. 3 is a graph showing the relationship between the Ni—O ratio during Ni flash plating and the water wetting rate of a steel sheet coated with anti-rust oil after temper rolling.
FIG. 4 is a diagram showing the relationship between the amount of deposited Ni and the Ni—O ratio.
FIG. 5 is a diagram showing the relationship between the size of the dents on the surface of the steel sheet and the occurrence rate of defective spot degreasing of the steel sheet coated with rust preventive oil after temper rolling.
FIG. 6 is a diagram showing the relationship between the surface roughness of the hearth roll of the continuous annealing furnace and the size of the dents.
FIG. 7 is a schematic diagram showing an example of a method for supplying a rolling fluid during temper rolling.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steel plate 2 Work roll 3 Backup roll 4 Rolling liquid 5 Rolling liquid supply pump

Claims

A method of producing a cold-rolled steel sheet having a surface roughness Ra of 0.5 to 1.5 μm by temper rolling after annealing , using a temper rolling liquid containing 1 to 15% of water-soluble organic matter. A method for producing a cold-rolled steel sheet having excellent degreasing and chemical conversion properties, characterized by performing temper rolling and adhering ²⁰ to 80 mg / m ² of organic material of the temper rolling liquid to the surface of the steel sheet after rolling.

A method for producing a cold-rolled steel sheet having a surface roughness Ra of 1.5 μm or less and a Ni adhesion amount of 15 mg / m ² or less by temper rolling after annealing, comprising 1 to 15% water perform temper rolling using a temper rolling solution containing sex organic, the organic nature temper rolling fluid on the surface of the steel sheet after rolling to degreasing and chemical conversion treatability, characterized in that to 20 to 80 mg / m ² adhesion Excellent cold-rolled steel plate manufacturing method.

Subjected to continuous annealing after temper rolling, surface roughness A method of manufacturing a cold-rolled steel sheet is 1.5 [mu] m or less in R a, with a hearth roll surface roughness is less than 8 mu m in R a Continuous annealing is performed, temper rolling is performed using a temper rolling liquid containing 1 to 15% of water-soluble organic matter, and 20 to 80 mg / m ² of organic material of the temper rolling liquid is adhered to the surface of the rolled steel sheet. A method for producing a cold-rolled steel sheet having excellent degreasing properties and chemical conversion properties.