JP4402886B2

JP4402886B2 - Steel plate for enamel with extremely excellent enamel adhesion, its manufacturing method, and enamel product

Info

Publication number: JP4402886B2
Application number: JP2003017745A
Authority: JP
Inventors: 英邦村上; 良久高田
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2003-01-27
Filing date: 2003-01-27
Publication date: 2010-01-20
Anticipated expiration: 2023-01-27
Also published as: JP2004225150A

Description

【０００１】
【発明の属する技術分野】
本発明は、ホーロー前処理が簡易にも関わらず、ホーロー性、特に良好なホーロー密着性を発揮するホーロー用鋼板及びその製造方法並びにその使用方法に関する。
【０００２】
【従来の技術】
ホーロー用鋼板を用いたホーロー製品の製造においては金属である鋼板とガラスであるホーロー皮膜をより強固に接合するために鋼板とホーロー層の界面に存在するＮｉの有効性が知られており、一般的にはホーロー釉薬を鋼板に掛ける前にＮｉフラッシュと呼ばれるＮｉ含有溶液中に鋼板を浸漬し鋼板表面にＮｉを析出させる手法がとられている。また、単に密着性を向上させるだけでなく、ホーロー前に行われる酸洗やＮｉフラッシュといった工程を省略するため鋼板の製造工程においてＮｉをめっきする方法も例えば特許文献１等に開示されている。しかし、これらの技術では浸漬処理工程やめっき工程によるコスト増、生産性低下を引き起こすだけでなく、これらの処理に使用される溶液の廃棄において環境への悪影響も懸念されている。
【０００３】
【特許文献１】
特許第１３２０７７２号公報
【０００４】
【発明が解決しようとする課題】
本発明は、ホーロー釉薬を掛ける前にホーロー用鋼板の表面にＮｉを高濃度に存在させる方法において、成分および製造条件をトータルに最適化することで、従来のホーロー用鋼板でホーロー密着性を向上させるために必要とされていたＮｉ処理を省略した場合にもＮｉ処理を行った鋼板と同等以上の密着性を付与するとともに、従来のＮｉ処理工程を適用した場合に問題となる廃液処理の問題を軽減または完全に回避することを目的とする。
【０００５】
【課題を解決するための手段】
本発明者らは、前記目的を達成すべく種々実験し検討を重ねてきた。即ち、本発明はＣ：０．００４０％以下、Ｎｉ：０．３０〜８．０％、Ｓｉ：０．５％以下、Ｍｎ：０．０５〜０．９５％、Ｐ：０．２０％以下、Ｓ：０．００８０％以下、Ａｌ：０．００８５％以下、Ｃｕ：８．０％以下、Ｏ：０．００５〜０．０４５％、Ｎ：０．０１００％以下を基本成分として含有する鋼材を熱処理するにあたり、表面に生成する酸化スケールの状態を適度に制御することでホーロー釉薬を掛ける前の鋼板の表面にＮｉ濃化部を形成させ、ホーロー密着性を向上させるものである。その要旨は次のとおりである。
【０００７】
（１）質量％で、Ｃ：０．００４０％以下、Ｎｉ：０．３０〜８．０％、Ｓｉ：０．５％以下、Ｍｎ：０．０５〜０．９５％、Ｐ：０．２０％以下、Ｓ：０．０８０％以下、Ａｌ：０．００８５％以下、Ｃｕ：８．０％以下、Ｏ：０．００５〜０．０５５％、Ｎ：０．０１００％以下を含有し、残部Ｆｅ及び不可避的不純物からなり、鋼材表面にＮｉ濃度が鋼中の平均Ｎｉ含有量の２．５倍以上となっているＮｉ濃化部を有することを特徴とするホーロー密着性が著しく優れたホーロー用鋼板。
【０００８】
（２）質量％で、Ｃ：０．００２０％以下、Ｎｉ：０．３０〜８．０％、Ｓｉ：０．０５０％以下、Ｍｎ：０．０５〜０．９５％、Ｐ：０．０５％以下、Ｓ：０．０３０％以下、Ａｌ：０．００４９％以下、Ｃｕ：８．０％以下、Ｏ：０．００５〜０．０４５％、Ｎ：０．００４９％以下を含有し、残部Ｆｅ及び不可避的不純物からなり、鋼材表面にＮｉ濃度が鋼中の平均Ｎｉ含有量の２．５倍以上となっているＮｉ濃化部を有することを特徴とするホーロー密着性が著しく優れたホーロー用鋼板。
【０００９】
（３）質量％で、Ｃ：０．００１５％以下、Ｎｉ：０．５０〜８．０％、Ｓｉ：０．０１０％以下、Ｍｎ：０．０５〜０．９５％、Ｐ：０．０１５％以下、Ｓ：０．０１０〜０．０２０％、Ａｌ：０．００４９％以下、Ｃｕ：８．０％以下、Ｏ：０．００５〜０．０４５％、Ｎ：０．００４０％以下を含有し、残部Ｆｅ及び不可避的不純物からなり、鋼材表面にＮｉ濃度が鋼中の平均Ｎｉ含有量の２．５倍以上となっているＮｉ濃化部を有することを特徴とするホーロー密着性が著しく優れたホーロー用鋼板。
【００１０】
（４）質量％で、さらに、Ｎｂ：０．１０％以下、Ｖ：０．１０％以下、Ｂ：０．０１０％以下の１種または２種以上を含有することを特徴とする（１）〜（３）のいずれかの項に記載のホーロー密着性が著しく優れたホーロー用鋼板。
【００１１】
（５）質量％で、さらにＣａ：０．２％以下を含有することを特徴とする（１）〜（４）のいずれかの項に記載のホーロー密着性が著しく優れたホーロー用鋼板。
【００１３】
（６）半製品を含めた鋼板製造工程の少なくとも一時期において鋼材表面にＮｉ濃度が鋼中の平均Ｎｉ含有量の２．５倍以上となっているＮｉ濃化部が存在し、そのＮｉ濃化部について、成分が質量％でＮｉ：２０％以上、鋼板厚さ方向の厚みが０．０１μｍ以上、鋼板表面の被覆率が５％以上の条件のうち少なくとも一つを満足し、鋼板製造後も、鋼板表面に残存していることを特徴とする（１）〜（５）のいずれかの項に記載のホーロー密着性が著しく優れたホーロー用鋼板。
【００１４】
（７）熱延およびそれに続く酸洗後の鋼材において、鋼材表面にＮｉ濃度が鋼中の平均Ｎｉ含有量の２．５倍以上となっているＮｉ濃化部が存在し、そのＮｉ濃化部について、成分が質量％でＮｉ：２０％以上、鋼板厚さ方向の厚みが０．０１μｍ以上、鋼板表面の被覆率が５％以上の条件のうち少なくとも一つを満足し、鋼板製造後も、鋼板表面に残存している（１）〜（５）のいずれかの項に記載のホーロー密着性が著しく優れたホーロー用鋼板。
【００１５】
（８）（１）〜（５）のいずれかの項に記載の成分の鋼を、熱延スラブ加熱における熱履歴において１１００℃以上１４００℃以下での保持時間が２０分以上４００分以下、熱延仕上げ圧延後冷延前のコイル熱履歴において６５０℃以上９００℃以下での保持時間が２０分以上６００分以下、冷間圧延後のコイルの熱履歴において７５０℃以上９５０℃以下での保持時間が２０秒以上４００分以下、の条件のうち少なくとも一つを満足し、Ｎｉを含有する雰囲気中での処理を行うことなく鋼材表面にＮｉ濃度が鋼中の平均Ｎｉ含有量の２．５倍以上となっているＮｉ濃化部を有せしめることを特徴とするホーロー密着性が著しく優れたホーロー用鋼板の製造方法。
【００１６】
（９）熱延スラブ加熱における熱履歴において１１００℃以上１４００℃以下での保持時間を２０分以上４００分以下とすることで熱延スラブ加熱中のスケール生成厚さを０．２mm以上とする、熱延仕上げ圧延後冷延前のコイル熱履歴において６５０℃以上９００℃以下での保持時間を２０分以上６００分以下とすることで熱延コイル巻取り中のスケール生成厚さを０．２μｍ以上とする、冷間圧延後の焼鈍での温度履歴を７５０℃以上９５０℃以下での保持時間を２０秒以上４００分以下とすることで冷延後焼鈍中のスケール生成厚さを０．０２μｍ以上とする、の条件のうち少なくとも一つを満足している（７）記載のホーロー密着性が著しく優れたホーロー用鋼板の製造方法。
【００１８】
（１０）前記冷間圧延後のコイルの熱処理を露点が０℃以上の雰囲気中で行うことを特徴とする（８）記載のホーロー密着性が著しく優れたホーロー用鋼板の製造方法。
【００１９】
（１１）（１）〜（７）のいずれかの項に記載のホーロー用鋼板を使用し、ホーロー釉薬を掛ける前までの全製造工程においてＮｉを含有する雰囲気中での表面処理工程を経ることがないことを特徴とするホーロー製品の製造方法。
【００２０】
（１２）（１）〜（７）のいずれかの項に記載のホーロー用鋼板を使用し、ホーロー釉薬を掛ける前に酸洗工程を経ることがないことを特徴とするホーロー製品の製造方法。
【００２１】
【発明の実施の形態】
以下詳細に説明する。各成分元素の含有量は質量％である。
【００２２】
Ｃは従来から低いほど加工性が良好となることが知られているが、本発明では、良好な耐時効性、加工性およびホーロー性を得るために０．００４０％以下にする必要がある。好ましい範囲は０．００２０％以下、さらに好ましくは０．００１５％以下である。下限は特に限定する必要がないが、Ｃ量を低めると製鋼コストを高めるので実用的な下限は０．０００５％である。
【００２３】
Ｎｉは本発明の目的が鋼材表面を鋼板製造工程またはホーロー製品製造工程において適当に酸化させ酸化スケールを形成させることで鋼中に含有されたＮｉをスケールと鋼の界面に濃化させ、その後の酸洗等の脱スケール工程を経ても鋼表面にＮｉ濃化部位を残存させることが主旨であることから本発明においては必須の元素である。その含有量は通常のホーロー用鋼板で不可避的に含有される可能性がある０．０５％程度以下では本発明の効果は殆ど検知されないため、積極的に添加する必要がある。上記効果を得るには０．３０％以上の添加が必要で、好ましくは０．５０％以上、１．０％以上添加すれば著しい効果が得られる。２．０％以上の添加では効果は飽和する傾向が見られる。過剰な添加は合金コストの点からも好ましくはないが、同時にホーローと鋼の反応の不均一が大きくなり黒点などのホーロー欠陥を生じやすくなるとともに加工性の面からの悪影響も見られるようになるため、上限を８．０％とする。好ましくは５．０％以下で、３．０％以下でも十分な効果を得ることができる。
【００２４】
Ｓｉはホーロー性を阻害するので、あえて添加する必要はなく少ないほど好ましいが、高強度化を補う意味で上限を０．５％として添加することは可能である。通常程度以上のホーロー性を確実に確保するには０．０５０％以下、さらに好ましくは０．０１０％以下である。
【００２５】
Ｍｎは酸素、Ｓ量と関連してホーロー性に影響する成分である。同時に熱間圧延時にＳに起因する熱間脆性を防止する元素で、酸素を多く含む本発明では０．０５％以上が必要である。一方、Ｍｎ量が高くなるとホーロー密着性が悪くなり、泡や黒点が発生しやすくなるため上限を０．９５％とする。
【００２６】
Ｐは含有量を高めることで高強度化を達成できるが、本発明では高強度化は主としてＣｕからなる金属相の微細分散により達成が可能であり、ホーロー時の泡、黒点などの欠陥を抑制するために低い方が好ましい。含有量が０．２０％を超えると材料を顕著に脆化させ製造が困難となる。好ましくは０．０５％以下、良好なホーロー性を確保するには、０．０１５％以下にすることが好ましい。
【００２７】
Ｓはホーロー前処理の酸洗時にスマット量を増やし、泡・黒点を発生しやすくするので、０．０８０％以下、好ましくは０．０３０％以下とする。しかし過度に低くなるとスマット量が少なくなりすぎホーロー密着性が劣化する場合があるので、さらに好ましい範囲として０．０１０〜０．０２０％とする。
【００２８】
Ａｌはあまり多く含有させると鋼中Ｏを限定範囲内に制御することができなくなる。また、Ａｌ窒化物がホーロー焼成中の水分と反応してガスを発生し泡欠陥の原因となりやすいため好ましくない。このため含有量を０．００８５％以下、好ましくは０．００４９％以下に限定する。
【００２９】
Ｃｕは本発明鋼ではＮｉについで重要な元素である。Ｃｕは鋼板の製造工程において酸化スケールの形成に伴いＮｉと同様にスケールと鋼材の界面に濃化し、その後もＮｉと同様に鋼材表面に残存しホーロー密着性に影響を及ぼす。ただし、Ｎｉとは異なりＣｕ単独では本発明の効果を得ることができないばかりか鋼板の表面疵を増大させホーローの泡欠陥、黒点を増大させる場合がある。この原因は明確ではないが、Ｃｕ単独で本発明のようなスケール生成に伴う濃化現象を活用した場合、Ｃｕ濃化部が溶融し鋼材の粒界部と粒界でない部位での差が顕著になり過剰な濃淡が表面疵の原因となるまでに形成されるとともにＣｕ濃化部位がスケールと鋼の界面の全面を覆うようになり、ホーローのぬれ性を低下させるためと思われる。ただし、従来添加されている０．０５％程度以下の含有Ｃｕは上記のような悪影響もほとんど見られず、従来と同様にホーロー前の酸洗処理において酸洗スマットの形成を介してホーロー密着性に好ましい効果を有する。
【００３０】
さらに本発明のように多量のＮｉを含む場合に、本発明で活用するスケール界面への濃化現象を適用した場合には上記のＣｕ単独添加の場合の悪影響も見られなくなると同時に、Ｎｉの濃化形態に好ましい影響を及ぼす。ＣｕとＮｉが共存することによる効果の原因は明確ではないが、以下のように考えられる。ＣｕとＮｉが共存すると両元素が同様にスケールと鋼の界面に濃化し互いに固溶するため濃化部位の溶融温度が上昇し上記のようなＣｕ単独の場合の悪影響が消失する。このため濃化部位は適当な鋼表面の全面を覆うことなく適当な間隔で島状に形成されると同時に鋼の粒界等に起因する不均一も解消される。さらに、その後の温度低下に伴い、ＣｕとＮｉが混じった濃化部位はＣｕ濃化部とＮｉ濃化部に分離し、それぞれが有するホーロー密着性への好ましい効果が有効に作用するものと考えられる。Ｎｉの含有を前提としたＣｕ含有量の上限は８．０％、好ましくは５．０％以下、さらに好ましくは３．０％以下で、Ｃｕが本来有する酸洗スマットの生成を介した密着性の向上効果を考慮した好ましい範囲は０．０２〜２．０％である。
【００３１】
Ｏはつまとび性に直接に影響すると同時に、Ｍｎ量と関連してホーロー密着性、耐泡・黒点性に影響する。これらの効果を発揮するには０．００５％は必要である。一方、Ｏ量が過度に高くなると製鋼時の生産性を低下させるとともに鋼板の加工性を悪くするので、上限を０．０５５％に特定する。好ましい範囲は０．０１０〜０．０４５％である。
【００３２】
Ｎは時効性・耐泡・黒点性の観点からは少ないほど好ましいが、適当な窒化物形成元素の添加によりその害を低減することが可能である。０．０１００％以上では窒化物を形成させたとしても良好な特性を得ることができなくなるためこれを上限とする。好ましくは０．００４９％以下、さらに好ましくは０．００４０％以下である。
【００３３】
酸化物形成元素であり酸化物形態制御の観点からホーロー性に大きな影響を与え、また炭窒化物形成元素で時効性および加工性の向上が期待できる元素としてＮｂ，Ｖ，Ｂがあるが、いずれも過度な添加はホーロー性を劣化させることから、Ｎｂ：０．１０％以下、Ｖ：０．１０％以下，Ｂ：０．０１０％以下とする。
【００３４】
また、鉱石やスクラップなどから不可避的に含まれる程度の量に加え様々な目的で微量元素を添加しても本発明の効果は何ら損なわれるものではない。この場合もコストやホーロー性の兼ね合いからＣａを０．２％以下添加してもよい。
【００３５】
前記成分を含む鋼は、通常のホーロー用鋼板と同様に転炉で溶製され、連続鋳造でスラブとされ、ついで熱間圧延、酸洗、冷間圧延、焼鈍などの工程で製造される。これらの工程の中で脱炭工程などを経ることも本発明の効果を何ら損なうものではない。また通常の工程ではなく熱延工程を省略する薄スラブＣＣなどの工程によって製造しても問題ない。
【００３６】
本発明の特徴とするＮｉ濃化部位を鋼板表面に形成するには以下のような熱履歴を経ることが望ましい。それは製品板を製造する過程において、熱延スラブ加熱における熱履歴において１１００℃以上での保持時間が２０分以上、熱延仕上げ圧延後冷延前の熱処理におけるコイル熱履歴において６５０℃以上での保持時間が２０分以上、冷間圧延後の熱処理におけるコイルの熱履歴において７５０℃以上での保持時間が２０秒以上、の条件のうち少なくとも一つを満足することである。熱延スラブ加熱条件において、温度は好ましくは１２００℃以上、さらに好ましくは１２５０℃以上、時間は好ましくは４０分以上、さらに好ましくは６０分以上である。熱延仕上げ圧延後冷延前の熱処理におけるコイル熱履歴において、温度は好ましくは７００℃以上、さらに好ましくは７５０℃以上、時間は好ましくは４０分以上、さらに好ましくは６０分以上である。冷間圧延後の熱処理におけるコイルの熱履歴において、温度は好ましくは８００℃以上、さらに好ましくは８５０℃以上、時間は好ましくは４０秒以上、さらに好ましくは６０秒以上である。
【００３７】
これらの温度および時間は基本的に高温、長時間で発明効果が顕著になるが、過度な高温、長時間条件においてはＮｉ濃化部位が量的に過度になりホーロー焼成時の溶融釉薬の鋼板への濡れ性を低下させホーロー密着性を低下させる場合がる。また、鋼板の結晶組織や結晶方位に機械特性の面から好ましからざる影響を及ぼす場合もある。上限を熱延スラブ加熱条件について、温度は１４００℃以下、時間は４００分以下、熱延仕上げ圧延後冷延前の熱処理におけるコイル熱履歴について、温度は９００℃以下、時間は６００分以下、冷間圧延後のコイルの熱履歴について、温度は９５０℃以下、時間は４００分以下が望ましい。
【００３８】
なお、これら温度、時間条件は鋼材全体に及ぶものではなく、熱処理中の鋼材表面のみがこの条件にあれば本発明の目的は過不足なく達成される。これらの温度および時間条件はスケール生成量およびその質さらには界面に形成される濃化部位中の元素の拡散などを適当に制御するため選択されるが、その条件は熱処理中の雰囲気にも大きく影響される。酸化挙動は特に雰囲気中の水分量に影響されるが、特に冷延鋼板において最終製品に近い冷間圧延後のコイルの熱処理は露点０℃以上の雰囲気中で行うことが好ましい。
【００３９】
これらの工程を経て鋼材表面のＮｉ濃化部位が形成されるが、その濃化状況を規定する一つの指標として、酸化時のスケール厚さを用いることは本発明の効果を制御するのに有効な手段の一つである。熱延スラブ加熱中のスケール生成厚さが０．２mm以上、熱延コイル巻取り中のスケール生成厚さが０．２μｍ以上、冷延後焼鈍中のスケール生成厚さが０．０２μｍ以上、の条件のうち少なくとも一つを満足した酸化が行われることでＮｉの鋼材表面での濃化状態が好ましく制御される。これらの条件のうち２つを同時に満足することで発明の効果がさらに顕著になり、さらに好ましくはすべての条件を満足する場合であることは言うまでもない。
【００４０】
熱延スラブ加熱中のスケール生成厚さは好ましくは１mm以上、さらに好ましくは２mm以上、熱延コイル巻取り中のスケール生成厚さは好ましくは１μｍ以上、さらに好ましくは２μｍ以上、冷延後焼鈍中のスケール生成厚さは好ましくは０．１μｍ以上、さらに好ましくは０．２μｍ以上である。この厚さについても過度な場合にはＮｉ濃化部位の状態に悪影響を及ぼすとともに、鋼板の表面性状を劣化させ表面疵の原因にもなるため好ましい上限として熱延スラブ加熱中のスケール生成厚さは１０mm以下、熱延コイル巻取り中のスケール生成厚さは１０μｍ以下、冷延後焼鈍中のスケール生成厚さは１μｍ以下とする。
【００４１】
これらの熱履歴により鋼板の表面にＮｉ濃化部が形成されるが、注意を要するのは、熱処理は条件によっては濃化部位を溶体化し消失させてしまう場合もあることである。例えば、スラブ加熱時にＮｉ濃化部が形成されても、冷延、焼鈍後の熱処理がスケール形成が全く起きない条件であれば高温での保持により表面に濃化したＮｉは濃度勾配に起因した拡散のため単調に母材中に溶けていき、濃化部のＮｉ濃度は単調に低下し、ついには消失してしまう。この条件はＮｉ濃化の程度やその後の熱履歴さらには雰囲気などが複雑に関係しているため本発明で一律に限定することは困難であるが、技術常識の拡散理論等を用いることでＮｉ濃化部の残存を適切な範囲に制御することは何ら困難を伴うことなく可能である。また、理論的な考察をせずとも適当な試行の後に、経験的に適当な範囲を設定することは当業者であれば容易に行うことができる。
【００４２】
このようにして鋼板表面に形成される組成変動で重要なのは主としてＮｉの濃化である。Ｎｉ濃化部は一般的には鋼中の平均Ｎｉ含有量よりＮｉの濃度が高い部分を言うが、本発明ではホーロー密着性に及ぼす効果や測定ばらつき等を考慮し、Ｎｉ濃度が鋼中の平均Ｎｉ含有量の２．５倍以上となっている部位をＮｉ濃化部と定義する。この濃化は電子顕微鏡、Ｘ線分析、電子線分析、イオン分析等の最新の解析機器で十分に観測が可能なものである。もちろん化学分析などこれ以外の方法によっても同定が可能なものである。
【００４３】
測定データを検討する際には、測定領域の面積のみならず表面から分析する場合には測定領域の深さも考慮してＮｉ濃度を決定する必要があるのは言うまでも無い。特に注意を有するのは例えば表面にＮｉ１００％の皮膜が形成されていてもそれが非常に薄い場合、表面から電子線やＸ線を用いた解析機器で成分分析を行うと皮膜を透過し母材部も含めた領域の成分が検出されるためＮｉ含有量としては低い定量値が得られるような場合である。本発明では空間的に十分に微小な領域に限定した解析が必要である。もちろん、上の事例のようにＮｉが濃化していない領域まで含めた広い領域を平均した定量値においてさえも本発明で規定する定量値、例えばＮｉ２０％以上、を満足する場合はその成分値を採用しても構わない。
【００４４】
また、濃化の程度によっては例えば冷延前に濃化部位が確認できた場合でも、冷延率等によっては鋼材とともに濃化部位が非常に薄く延伸してしまい、通常の解析機器では検知が困難になる場合も想定される。このため、本発明においてはホーロー釉薬を掛ける直前の鋼板ばかりではなく、鋼板製造の全工程の１つ、例えば酸洗前後の熱延鋼板や熱延スラブ加熱中のスラブ等、半製品におけるＮｉ濃化部位について、その少なくとも１つの工程で条件を満足すれば本発明の範囲とする。
【００４５】
本発明ではこのＮｉ濃化部について、成分が質量％でＮｉ：２０％以上、鋼板厚さ方向の厚みが０．０１μｍ以上、鋼板表面の被覆率が５％以上の条件のうち少なくとも一つを満足するものとする。これらの条件のうち２つを同時に満足することで発明の効果がさらに顕著になり、さらに好ましくはすべての条件を満足する場合であることは言うまでも無い。被覆率については十分に微小な面積のＮｉ濃度の定量を行い、１０００点以上の測定データについて本発明の規定を満足するＮｉ濃化部の面積比率で定義する。特に通常のホーロー用冷延鋼板またはホーロー用熱延鋼板では酸洗後の状態でこの濃化部位の検出をすることは本発明の効果を規定するのに都合がよい。
【００４６】
Ｎｉ濃化部のより好ましい形態については、成分が質量％でＮｉ：３０％以上、さらに好ましくは５０％以上、鋼板厚さ方向の厚みが０．０５μｍ以上、さらに好ましくは０．１μｍ以上、鋼板表面の被覆率が２０％以上、さらに好ましくは４０％以上である。このうち、特に成分についてはＮｉ１００％でもかまわないし、通常、Ｎｉ以外は主としてＦｅとなるが、上述のようにＣｕの他、Ｓｉ，Ｐ，Ａｌ，Ｍｎなど鋼中元素を含有することは本発明の効果を何ら損ねるものではなく、ＣｏやＭｏなど、ホーロー密着性に好ましい場合があることが報告されている元素を含有することで発明の効果が向上することも期待できる。また、厚さについては上述のように鋼板製造工程によっては非常に薄くなり、検出が困難な場合も想定されるが、０でなければ原理上、本発明の効果を得ることができる。また、表面被覆率には適当な領域が存在し、高すぎてもホーロー釉薬の濡れ性が低下し密着性を阻害する場合がある。被覆率の上限は９５％、好ましくは８０％以下である。
【００４７】
本発明を適用することにより、通常行われているＮｉフラッシュやＮｉめっきなどのＮｉ処理を完全に省略することが可能で、本発明効果のみでも通常程度の密着性の付与が可能であるため通常行われるホーロー掛け前の酸洗工程でさえも完全に省略することも可能となる。また、Ｎｉ処理や酸洗を行う場合には、処理液濃度の低減や処理時間の短時間化などの効果を得ることができ、通常のＮｉ処理や酸洗と併用することで密着性を格段に向上させることができる。
【００４８】
用途は特に限定されるものではなく、台所用品または衛生用品等通常のホーロー用途の他、建材、化学工業製品などホーロー製品が使用される全ての用途に適用される。
【００４９】
また、本発明の対象となる鋼板は板厚や熱延鋼板、冷延鋼板の種類など本発明で規定していない製造法に関わらずその効果を得ることができ、またホーローの密着性を向上する目的以外でＮｉを実質的に含まない雰囲気での処理を行うことも可能である。
【００５０】
また本発明の適用は、本発明で記述されていないホーロー用鋼板に具備させることが好ましい特性、例えば加工性等にはなんら悪影響を及ぼすものではない。
【００５１】
【実施例】
＜実施例１＞
表１に示した種々の化学組成からなる連続鋳造スラブを表２に示す条件で熱間圧延、冷間圧延、焼鈍を行い、圧下率１％の調質圧延を施し板厚１．２mmのホーロー用鋼板を得た。得られた鋼板を表３に示した工程でホーロー処理しホーロー処理後のホーロー性を評価した。一部の材料については表３の内の酸洗およびＮｉ処理を省略してホーロー性を評価した。Ｎｉ処理を省略した場合は中和処理も省略した。ホーロー前処理の省略については表２中に記す。
【００５２】
酸洗を行ったものについては、ホーロー性の内、泡・黒点の表面特性は酸洗時間が２０分と長い条件を選び、その目視で評価した。ホーロー密着性は酸洗時間が３分と短い条件で評価した。ホーロー密着性は通常行われているＰ．Ｅ．Ｉ．密着試験方法（ＡＳＴＭＣ３１３−５９）では密着性に差が出にくいため、２kgの球頭の重りを１ｍ高さから落下させ、変形部のホーロー剥離状態を１６９本の触診針で計測し、未剥離部分の面積率で評価した。耐つまとび性は３枚の鋼板を酸洗時間３分、Ｎｉ浸漬なしの前処理を施し、直接一回かけ用釉薬を施釉、乾燥を行い、露点５０℃で８５０℃の焼成炉に３分間装入して焼成した後、１６０℃の恒温槽中に１０時間入れるつまとび促進試験を行い、目視でつまとび発生状況を判定した。
【００５３】
各種特性を表２に示す。表２の結果から明らかなように、本発明によりホーロー密着性が格段に向上し、かつホーロー性も良好な優れたホーロー用鋼板を得ることができる。
【００５４】
【表１】

【００５５】
【表２】

【００５６】
【表３】

【００５７】
＜実施例２＞
表４に示した種々の化学組成からなるスラブを実験室にて溶解、鋳造した４０mm厚のスラブを電気炉を用い表５に示す条件で熱延スラブ加熱を行い、４．０mmの仕上げ板厚で熱間圧延の後、酸洗し、次いで０．５mmまで冷間圧延し、続けて７０％Ｎ２＋３０％Ｈ２、露点−２０℃の雰囲気中で８００℃１分の焼鈍を行い、さらに圧下率１％の調質圧延を施しホーロー用鋼板を得た。得られた鋼板を表６に示した工程でホーロー処理しホーロー処理後のホーロー性を評価した。また酸洗およびＮｉ処理を簡省略したものについてもホーロー性を評価した。Ｎｉ処理を省略した場合は中和処理も省略した。
【００５８】
ホーロー性の内、泡・黒点の表面特性は目視で評価した。ホーロー密着性は通常行われているＰ．Ｅ．Ｉ．密着試験方法（ＡＳＴＭＣ３１３−５９）では密着性に差が出にくいため、２kgの球頭の重りを１．５ｍ高さから落下させ、変形部のホーロー剥離状態を１６９本の触診針で計測し、未剥離部分の面積率で評価した。耐つまとび性は調質圧延ままの鋼板をアルカリ脱脂後、＃２４０エメリー紙研磨した後、以下に示す定電位酸化法による水素透過時間により評価した。定電位酸化法は鋼板の片面（Ａ面）を５％Ｈ₂ ＳＯ₄ ＋２ｇ／ｌのＡｌ₂ Ｏ₅ 溶液に浸漬し、もう一方の面（Ｂ面）を０．５ＮのＮａＯＨ溶液に浸漬しておき、Ａ面側溶液中でプラチナ電極との間で０．０６Ａ／cm² の電流密度で鋼板Ａ面をカソードとして溶液中の水素イオンを還元し鋼板中に原子状水素を侵入させ、鋼板を透過し鋼板Ｂ面側より溶液中に溶け出す水素イオンをＢ面側溶液中の別のプラチナ電極との間で鋼板Ｂ面をアノードとして生じるアノーディック電流の変化により観察し、水素が鋼板を透過するまでの時間により鋼板の耐水素透過性を評価した。この時間は通常Ｔ値と呼ばれ、この時間が長いほど耐水素透過性が高いことになり、鋼板の耐つまとび性が良好となる。
【００５９】
各種特性を図１、図２および図３に示す。この結果から明らかなように、本発明によりホーロー前処理条件によらずホーロー密着性が格段に向上し、またホーロー前処理を簡省略した場合にも良好な密着性が得られることがわかる。さらに本発明においてはつまとびの指標となるＴ値も良好である。また、図２、図３の全条件で泡・黒点は見られなかった。
【００６０】
【表４】

【００６１】
【表５】

【００６２】
【表６】

【００６３】
【発明の効果】
本発明のホーロー用鋼板は、良好な加工性を有し、さらにホーロー用鋼板として必要な耐つまとび性、ホーロー密着性、表面特性のすべてを満たしている。特にホーロー密着性を高めるため通常のホーロー用鋼板で行われるＮｉ処理や酸洗の簡省略が可能となるためコスト低減、生産性の向上が可能となると共に、Ｎｉ処理や酸洗に伴う廃液処理による環境汚染問題を解消できる。
【図面の簡単な説明】
【図１】鋼板のＮｉ含有量と熱延条件とホーロー密着性の関係を示す図である。
【図２】鋼板のＮｉ含有量とホーロー前処理条件とホーロー密着性の関係を示す図である。
【図３】鋼板のＮｉ含有量とホーロー前処理条件とＴ値の関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a steel plate for enamel that exhibits enamelability, particularly good enamel adhesion, despite its simple enamel pretreatment, a method for producing the same, and a method for using the same.
[0002]
[Prior art]
In the manufacture of enamel products using enamel steel plates, the effectiveness of Ni present at the interface between the enamel plate and enamel layer is known in order to more firmly join the enamel steel plate and the metal enamel steel plate. Specifically, before the enamel glaze is applied to the steel sheet, a technique is adopted in which the steel sheet is immersed in a Ni-containing solution called Ni flash to precipitate Ni on the steel sheet surface. Further, for example, Patent Document 1 discloses a method of plating Ni in a manufacturing process of a steel sheet in order to omit steps such as pickling and Ni flash performed before enameling as well as simply improving adhesion. However, these techniques not only cause an increase in cost and a decrease in productivity due to the immersion treatment process and the plating process, but there is also a concern about an adverse effect on the environment in the disposal of the solution used for these treatments.
[0003]
[Patent Document 1]
Japanese Patent No. 1320772
[0004]
[Problems to be solved by the invention]
The present invention improves the enamel adhesion of conventional enamel steel plates by optimizing the components and manufacturing conditions in a method that allows Ni to be present in a high concentration on the enamel steel surface before enamel enameling. Even when the Ni treatment that is required for the purpose of the treatment is omitted, the same level of adhesion as that of the steel plate subjected to the Ni treatment is given, and the problem of waste liquid treatment that becomes a problem when the conventional Ni treatment process is applied. The purpose is to reduce or completely avoid.
[0005]
[Means for Solving the Problems]
  The present inventors have conducted various experiments and studies in order to achieve the above object. That is, the present invention is C: 0.0040% or less, Ni:0.30-8.0%, Si: 0.5% or less, Mn: 0.05-0.95%, P: 0.20% or less, S: 0.0080% or less, Al:0.0085%Hereinafter, when heat-treating a steel material containing Cu: 8.0% or less, O: 0.005 to 0.045%, N: 0.0100% or less as basic components, the state of oxide scale generated on the surface is moderate. By controlling this, a Ni-enriched portion is formed on the surface of the steel plate before the enamel glaze is applied, and the enamel adhesion is improved. The summary is as follows.
[0007]
  (1) By mass%, C: 0.0040% or less, Ni: 0.30 to 8.0%, Si: 0.5% or less, Mn: 0.05 to 0.95%, P: 0.20 %: S: 0.080% or less, Al: 0.0085% or less, Cu: 8.0% or less, O: 0.005 to 0.055%, N: 0.0100% or less, the balance From Fe and inevitable impuritiesThe Ni concentration part where the Ni concentration is 2.5 times or more of the average Ni content in the steel.A steel plate for enamel with extremely excellent enamel adhesion.
[0008]
  (2) By mass%, C: 0.0020% or less, Ni: 0.30 to 8.0%, Si: 0.050% or less, Mn: 0.05 to 0.95%, P: 0.05 %: S: 0.030% or less, Al: 0.0049% or less, Cu: 8.0% or less, O: 0.005 to 0.045%, N: 0.0049% or less, the balance From Fe and inevitable impuritiesThe Ni concentration part where the Ni concentration is 2.5 times or more of the average Ni content in the steel.A steel plate for enamel with extremely excellent enamel adhesion.
[0009]
  (3) By mass%, C: 0.0015% or less, Ni: 0.50-8.0%, Si: 0.010% or less, Mn: 0.05-0.95%, P: 0.015 %: S: 0.010 to 0.020%, Al: 0.0049% or less, Cu: 8.0% or less, O: 0.005 to 0.045%, N: 0.0040% or less And the balance Fe and inevitable impuritiesThe Ni concentration part where the Ni concentration is 2.5 times or more of the average Ni content in the steel.A steel plate for enamel with extremely excellent enamel adhesion.
[0010]
  (4) In mass%,Nb: 0.10% or less, V: 0.10% or less, B: 0.010% or less(1) to (1) characterized by containing one or more of3) A steel plate for enamel that is extremely excellent in enamel adhesion according to any one of items 1).
[0011]
  (5) Mass%,Ca: 0.2% or less(1) to () characterized by containing4)A steel plate for enamel, which is remarkably excellent in enamel adhesion according to any one of the above items.
[0013]
  (6) At least one part of the steel plate manufacturing process including semi-finished productsNi concentration is more than 2.5 times the average Ni content in steelThere is a Ni-concentrated part, and the Ni-concentrated part has a component of mass%, Ni: 20% or more, a thickness in the steel sheet thickness direction of 0.01 μm or more, and a steel sheet surface coverage of 5% or more. Satisfy at least one of themEven after steel plate manufacture, it remains on the steel plate surface.It is characterized by (1)-(5) A steel plate for enamel that is extremely excellent in enamel adhesion according to any one of items 1).
[0014]
  (7) In steel after hot rolling and subsequent pickling,Ni concentration is more than 2.5 times the average Ni content in steelThere is a Ni-concentrated part, and the Ni-concentrated part has a component of mass%, Ni: 20% or more, a thickness in the steel sheet thickness direction of 0.01 μm or more, and a steel sheet surface coverage of 5% or more. Satisfy at least one of themEven after steel plate manufacture, it remains on the steel plate surface.(1) to (5) A steel plate for enamel that is extremely excellent in enamel adhesion according to any one of items 1).
[0015]
  (8) (1) to (5)The holding time at 1100 ° C. or higher and 1400 ° C. or lower in the heat history in hot rolling slab heating is 20 minutes or longer and 400 minutes or shorter, and the holding time at 650 ° C. or higher and 900 ° C. or lower in the coil heat history before cold rolling after hot rolling finish rolling. Satisfying at least one of the conditions of 20 minutes or more and 600 minutes or less, and the holding time at 750 ° C. or more and 950 ° C. or less in the thermal history of the coil after cold rolling is 20 seconds or more and 400 minutes or less,On the surface of steel without treatment in an atmosphere containing NiNi concentration is more than 2.5 times the average Ni content in steelThe manufacturing method of the steel plate for enamels which is excellent in enamel adhesion characterized by having a Ni concentration part.
[0016]
  (9)In the heat history in hot rolling slab heating, the holding time at 1100 ° C. or higher and 1400 ° C. or lower is set to 20 minutes or longer and 400 minutes or shorter.Scale formation thickness during hot-rolled slab heatingThe0.2mm or moreTo,By keeping the holding time at 650 ° C. or more and 900 ° C. or less in the coil heat history after hot rolling finish rolling and before cold rolling at 20 minutes or more and 600 minutes or less.Scale formation thickness during hot rolling coil windingThe0.2μm or moreTo,By setting the temperature history in annealing after cold rolling to 750 ° C. or higher and 950 ° C. or lower to 20 seconds or longer and 400 minutes or shorter.Scale formation thickness during annealing after cold rollingThe0.02μm or moreToSatisfy at least one of the conditions (7) A method for producing a steel plate for enamel, which is remarkably excellent in enamel adhesion.
[0018]
  (10) Heat treatment of the coil after the cold rolling is performed in an atmosphere having a dew point of 0 ° C. or higher.(8) As describedA method for producing a steel plate for enamel with extremely excellent enamel adhesion.
[0019]
  (11) (1)-(7The steel plate for enamel according to any one of the above items is used, and the surface treatment step in an atmosphere containing Ni is not performed in all manufacturing steps until the enamel glaze is applied.RuLowProductManufacturing method.
[0020]
  (12) (1)-(7The steel plate for enamel described in any one of the above items is used, and the pickling process is not performed before the enamel glaze is applied.RuLowProductManufacturing method.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
This will be described in detail below. The content of each component element is mass%.
[0022]
Conventionally, it is known that the lower C is, the better the workability is. However, in the present invention, it is necessary to make it 0.0040% or less in order to obtain good aging resistance, workability and enamelability. The preferred range is 0.0020% or less, more preferably 0.0015% or less. The lower limit is not particularly limited, but a practical lower limit is 0.0005% because lowering the C content increases the steelmaking cost.
[0023]
  The purpose of the present invention is to enrich the Ni contained in the steel at the interface between the scale and the steel by appropriately oxidizing the steel surface in the steel plate manufacturing process or enamel product manufacturing process to form an oxidized scale, This is an essential element in the present invention because the main purpose is to leave Ni-concentrated sites on the steel surface even after a descaling step such as pickling. Since the effect of the present invention is hardly detected when the content is about 0.05% or less, which may be unavoidably contained in ordinary steel plates for enamel, it is necessary to add it positively. To obtain the above effect0.30%The above addition is necessary,Preferably 0.50% or more,If 1.0% or more is added, a remarkable effect is obtained. If the addition is 2.0% or more, the effect tends to be saturated. Excessive addition is not preferable from the viewpoint of alloy cost, but at the same time, the heterogeneity of the reaction between enamel and steel becomes large, and enamel defects such as black spots are likely to occur, and there is an adverse effect on workability. Therefore, the upper limit is set to 8.0%. Preferably, it is 5.0% or less, and a sufficient effect can be obtained even if it is 3.0% or less.
[0024]
Since Si hinders the enamel property, it is preferable that it is not necessary to add it. In order to ensure the enamel property above the normal level, it is 0.050% or less, more preferably 0.010% or less.
[0025]
Mn is a component that affects the enamel property in relation to oxygen and S content. At the same time, it is an element that prevents hot brittleness caused by S during hot rolling, and 0.05% or more is required in the present invention containing a large amount of oxygen. On the other hand, if the amount of Mn increases, the enamel adhesion deteriorates and bubbles and black spots are likely to be generated. Therefore, the upper limit is made 0.95%.
[0026]
P can be increased in strength by increasing the content, but in the present invention, the increase in strength can be achieved by fine dispersion of a metal phase mainly composed of Cu and suppresses defects such as bubbles and black spots during enamel. Therefore, the lower one is preferable. When the content exceeds 0.20%, the material is remarkably embrittled and it becomes difficult to manufacture. Preferably it is 0.05% or less, and 0.015% or less is preferable in order to ensure good enamel performance.
[0027]
S increases the amount of smut during pickling in the enamel pretreatment and easily generates bubbles and black spots. Therefore, the content is set to 0.080% or less, preferably 0.030% or less. However, if the amount is too low, the amount of smut becomes too small and the enamel adhesion may be deteriorated. Therefore, a more preferable range is 0.010 to 0.020%.
[0028]
  If too much Al is contained, O in the steel cannot be controlled within the limited range. In addition, Al nitride reacts with moisture during enamel firing, generating gas and causing bubble defects, which is not preferable. For this reason, the content0.0085%Hereinafter, it is preferably limited to 0.0049% or less.
[0029]
Cu is an important element next to Ni in the steel of the present invention. Cu is concentrated at the interface between the scale and the steel material in the same way as Ni in the manufacturing process of the steel plate, as is the case with Ni, and then remains on the steel surface like Ni and affects the enamel adhesion. However, unlike Ni, Cu alone cannot provide the effects of the present invention, and may increase the surface defects of the steel sheet and increase enamel bubble defects and black spots. The cause of this is not clear, but when the concentration phenomenon accompanying the scale formation as in the present invention is utilized with Cu alone, the Cu concentration portion melts and the difference between the grain boundary portion of the steel material and the portion that is not the grain boundary is remarkable. It seems that excessive darkness is formed until the surface becomes a cause of surface defects, and the Cu concentration part covers the entire surface of the interface between the scale and the steel, thereby reducing the wettability of the enamel. However, Cu containing 0.05% or less, which has been added conventionally, has almost no adverse effects as described above, and in the same manner as in the past, enamel adhesion through the formation of pickling smut in the pickling treatment before enamel. It has a favorable effect.
[0030]
Further, when a large amount of Ni is contained as in the present invention, when the concentration phenomenon at the scale interface utilized in the present invention is applied, the above-described adverse effect of adding Cu alone is not observed, and at the same time It has a favorable effect on the concentrated form. The cause of the effect of coexistence of Cu and Ni is not clear, but is considered as follows. When Cu and Ni coexist, both elements are similarly concentrated at the interface between the scale and the steel and are dissolved in each other, so that the melting temperature of the concentrated portion is increased and the adverse effects of Cu alone as described above disappear. For this reason, the concentrated portion is formed in an island shape at an appropriate interval without covering the entire surface of the appropriate steel surface, and at the same time, nonuniformity caused by the grain boundary of the steel is eliminated. Further, as the temperature is lowered thereafter, the concentrated portion where Cu and Ni are mixed is separated into a Cu concentrated portion and a Ni concentrated portion, and the preferable effect on the enamel adhesion of each is considered to work effectively. It is done. The upper limit of the Cu content premised on the Ni content is 8.0%, preferably 5.0% or less, more preferably 3.0% or less, and adhesion through the formation of pickling smut inherent to Cu. A preferable range considering the improvement effect is 0.02 to 2.0%.
[0031]
O directly affects the pick-up property, and at the same time affects the enamel adhesion, the bubble resistance and the sunspot property in relation to the amount of Mn. In order to exert these effects, 0.005% is necessary. On the other hand, if the amount of O is excessively high, productivity at the time of steelmaking is lowered and workability of the steel sheet is deteriorated, so the upper limit is specified as 0.055%. A preferred range is from 0.010 to 0.045%.
[0032]
N is preferably as small as possible from the viewpoint of aging, foam resistance, and sunspot properties, but the harm can be reduced by adding an appropriate nitride-forming element. If it is 0.0100% or more, even if a nitride is formed, good characteristics cannot be obtained, so this is the upper limit. Preferably it is 0.0049% or less, More preferably, it is 0.0040% or less.
[0033]
  It is an oxide-forming element that greatly affects enamelability from the viewpoint of oxide form control, and is an element that can be expected to improve aging and workability with carbonitride-forming elementsNb, V, BHowever, Nb: 0.10% or less, since excessive addition deteriorates enamel characteristics in any case.V: 0.10% or less, B: 0.010% or lessAnd
[0034]
  Further, the addition of trace elements for various purposes in addition to the amount inevitably contained from ore and scrap does not impair the effects of the present invention. Again, this is because of cost and enamel balanceYou may add 0.2% or less of Ca.
[0035]
The steel containing the above components is melted in a converter in the same manner as a normal enamel steel plate, made into a slab by continuous casting, and then manufactured by processes such as hot rolling, pickling, cold rolling, and annealing. The effects of the present invention are not impaired at all by going through a decarburization step or the like among these steps. Moreover, there is no problem even if it is manufactured by a process such as a thin slab CC which omits the hot rolling process instead of the normal process.
[0036]
  In order to form the Ni-concentrated site, which is a feature of the present invention, on the surface of the steel sheet, it is desirable to undergo the following thermal history. In the process of producing a product plate, the heat history in hot-rolled slab heating has a holding time of 1100 ° C or higher for 20 minutes or longer, after hot-rolling finish rolling and before cold rolling.In heat treatmentIn coil heat history, holding time at 650 ° C. or higher is 20 minutes or longer, after cold rollingIn heat treatmentIn the thermal history of the coil, at least one of the conditions that the holding time at 750 ° C. or more is 20 seconds or more is satisfied. In the hot-rolled slab heating conditions, the temperature is preferably 1200 ° C. or higher, more preferably 1250 ° C. or higher, and the time is preferably 40 minutes or longer, more preferably 60 minutes or longer. After hot rolling finish rolling and before cold rollingIn heat treatmentIn the coil heat history, the temperature is preferably 700 ° C. or more, more preferably 750 ° C. or more, and the time is preferably 40 minutes or more, more preferably 60 minutes or more. After cold rollingIn heat treatmentIn the thermal history of the coil, the temperature is preferably 800 ° C. or higher, more preferably 850 ° C. or higher, and the time is preferably 40 seconds or longer, more preferably 60 seconds or longer.
[0037]
  These temperatures and times are basically high, and the effect of the invention becomes prominent at a long time. However, at excessively high temperatures and a long time, the Ni-concentrated site becomes quantitatively excessive and the steel sheet of molten glaze during enamel firing It may reduce the wettability to water and lower the enamel adhesion. In addition, the crystal structure and crystal orientation of the steel sheet may be undesirably influenced from the viewpoint of mechanical properties. The upper limit is about hot-rolled slab heating conditions, the temperature is 1400 ° C. or less, the time is 400 minutes or less, after hot-rolling finish rolling and before cold rollingIn heat treatmentRegarding the coil heat history, the temperature is preferably 900 ° C. or less, the time is 600 minutes or less, and the heat history of the coil after cold rolling is preferably 950 ° C. or less and the time is 400 minutes or less.
[0038]
  These temperature and time conditions do not extend to the entire steel material, and the object of the present invention can be achieved without excess or deficiency if only the surface of the steel material during heat treatment is in this condition. These temperature and time conditions are selected in order to appropriately control the amount of scale produced and its quality, as well as the diffusion of elements in the concentrated sites formed at the interface, but the conditions are also great for the atmosphere during heat treatment. Affected. Oxidation behavior is particularly affected by the moisture content in the atmosphere, but especially after cold rolling near the final product in cold-rolled steel sheets.The heat treatment of the coilIt is preferable to carry out in an atmosphere having a dew point of 0 ° C. or higher.
[0039]
Ni concentration sites on the steel surface are formed through these steps, but using one of the scale thicknesses during oxidation as an index for defining the concentration status is effective in controlling the effect of the present invention. It is one of the means. The scale generation thickness during hot-rolling slab heating is 0.2 mm or more, the scale generation thickness during hot-rolling coil winding is 0.2 μm or more, and the scale generation thickness during annealing after cold rolling is 0.02 μm or more. By performing oxidation that satisfies at least one of the conditions, the concentrated state of Ni on the steel surface is preferably controlled. It goes without saying that satisfying two of these conditions at the same time makes the effect of the invention more remarkable, and more preferably satisfies all the conditions.
[0040]
The scale generation thickness during hot rolling slab heating is preferably 1 mm or more, more preferably 2 mm or more, and the scale generation thickness during hot rolling coil winding is preferably 1 μm or more, more preferably 2 μm or more, during annealing after cold rolling. The scale generation thickness of is preferably 0.1 μm or more, more preferably 0.2 μm or more. If this thickness is excessive, it will adversely affect the state of the Ni-concentrated site, and the surface properties of the steel sheet will deteriorate and cause surface flaws. Is 10 mm or less, the scale generation thickness during winding of the hot-rolled coil is 10 μm or less, and the scale generation thickness during annealing after cold rolling is 1 μm or less.
[0041]
Although the Ni concentrated portion is formed on the surface of the steel sheet due to these thermal histories, it should be noted that the heat treatment may cause the concentrated portion to be dissolved and disappear depending on conditions. For example, even if a Ni-concentrated portion is formed during slab heating, if the heat treatment after cold rolling and annealing does not cause any scale formation, Ni concentrated on the surface by holding at a high temperature is caused by a concentration gradient. Due to the diffusion, it melts monotonously in the base material, and the Ni concentration in the concentrated portion monotonously decreases and eventually disappears. This condition is complicated by the degree of Ni concentration, the subsequent heat history, and the atmosphere, so it is difficult to limit it uniformly in the present invention. It is possible to control the remaining thickening portion within an appropriate range without any difficulty. Also, a person skilled in the art can easily set an appropriate range empirically after an appropriate trial without theoretical consideration.
[0042]
Thus, Ni concentration is mainly important in the composition variation formed on the surface of the steel sheet. The Ni-concentrated portion generally refers to a portion where the Ni concentration is higher than the average Ni content in the steel, but in the present invention, considering the effect on the enamel adhesion and measurement variation, the Ni concentration is in the steel. A portion that is 2.5 times or more the average Ni content is defined as a Ni-enriched portion. This concentration can be sufficiently observed with the latest analysis equipment such as electron microscope, X-ray analysis, electron beam analysis, ion analysis and the like. Of course, identification is possible by other methods such as chemical analysis.
[0043]
Needless to say, when examining measurement data, it is necessary to determine the Ni concentration in consideration of not only the area of the measurement region but also the depth of the measurement region when analyzing from the surface. Particular attention should be paid, for example, when a Ni 100% film is formed on the surface, but it is very thin. When component analysis is performed from the surface with an analytical instrument using an electron beam or X-ray, the film is transmitted through the film. This is a case where a low quantitative value is obtained as the Ni content because the components in the region including the part are detected. In the present invention, analysis limited to a spatially sufficiently small region is necessary. Of course, when the quantitative value defined in the present invention, for example, Ni 20% or more, is satisfied even in the quantitative value obtained by averaging a wide region including the region where Ni is not concentrated as in the above example, the component value is set to You may adopt.
[0044]
Also, depending on the degree of concentration, for example, even if a concentrated part can be confirmed before cold rolling, depending on the cold rolling rate, etc., the concentrated part may be stretched very thin together with the steel material, and detection is possible with ordinary analytical equipment. It may be difficult. For this reason, in the present invention, not only the steel plate immediately before the enamel glaze is applied, but also one of all the steps of steel plate production, for example, hot rolled steel plate before and after pickling and slab during hot rolling slab heating, etc. If the condition is satisfied in at least one step of the chemical site, the scope of the present invention is set.
[0045]
In the present invention, for this Ni-concentrated portion, at least one of the conditions in which the component is mass%, Ni is 20% or more, the thickness in the steel sheet thickness direction is 0.01 μm or more, and the coverage of the steel sheet surface is 5% or more. Satisfied. It goes without saying that satisfying two of these conditions at the same time makes the effects of the invention more remarkable, more preferably satisfying all of the conditions. The coverage is determined by quantitatively determining the Ni concentration in a sufficiently small area, and the measurement data of 1000 points or more is defined by the area ratio of the Ni-concentrated portion that satisfies the provisions of the present invention. In particular, in a normal enamel cold-rolled steel sheet or enameled hot-rolled steel sheet, it is convenient to define the effect of the present invention to detect this concentrated portion after pickling.
[0046]
As for a more preferable form of the Ni-enriched portion, the component is mass%, Ni: 30% or more, more preferably 50% or more, and the thickness in the steel sheet thickness direction is 0.05 μm or more, more preferably 0.1 μm or more. The surface coverage is 20% or more, more preferably 40% or more. Among these, the component may be Ni 100%, and normally, except Ni, it is mainly Fe. However, as described above, it contains the elements in steel such as Si, P, Al, Mn in addition to Cu. The effect of the invention can be expected to be improved by containing an element that has been reported to be preferable for enamel adhesion, such as Co or Mo. As described above, the thickness may be very thin depending on the steel plate manufacturing process as described above, and it may be difficult to detect the thickness. However, if the thickness is not 0, the effect of the present invention can be obtained in principle. Moreover, there exists an appropriate area | region in the surface coverage, and even if it is too high, the wettability of enamel glaze will fall and it may inhibit adhesiveness. The upper limit of the coverage is 95%, preferably 80% or less.
[0047]
By applying the present invention, it is possible to completely omit the Ni treatment such as Ni flash or Ni plating that is normally performed, and it is possible to provide a normal degree of adhesion only by the effect of the present invention. Even the pickling step before enameling that is performed can be omitted completely. In addition, when Ni treatment or pickling is performed, effects such as reduction in the concentration of the treatment solution and shortening of the treatment time can be obtained. Can be improved.
[0048]
The use is not particularly limited, and it is applicable to all uses in which enamel products such as building materials and chemical industrial products are used in addition to ordinary enamel uses such as kitchenware and sanitary products.
[0049]
In addition, the steel plate that is the subject of the present invention can obtain the effect regardless of the manufacturing method not specified in the present invention, such as the thickness, hot-rolled steel plate, and cold-rolled steel plate, and improves enamel adhesion. It is also possible to perform the treatment in an atmosphere that does not substantially contain Ni for purposes other than the purpose.
[0050]
In addition, the application of the present invention does not adversely affect the characteristics, for example, the workability, which are preferably included in the enamel steel plate not described in the present invention.
[0051]
【Example】
<Example 1>
  Continuously cast slabs with various chemical compositions shown in Table 1 are hot rolled, cold rolled and annealed under the conditions shown in Table 2, subjected to temper rolling with a reduction ratio of 1%, and enamel with a thickness of 1.2 mm A steel plate was obtained. The obtained steel sheet was subjected to enamel treatment in the steps shown in Table 3, and the enamel properties after enamel treatment were evaluated. For some materialsTable 3Of these, pickling and Ni treatment were omitted, and the enamel characteristics were evaluated. When the Ni treatment was omitted, the neutralization treatment was also omitted. Refer to the table for omitting enamel pre-processing.2Write inside.
[0052]
About the thing which pickled, the surface property of a bubble and a black spot selected the long pickling time as 20 minutes among enamel characteristics, and evaluated it visually. The enamel adhesion was evaluated under conditions where the pickling time was as short as 3 minutes. The enamel adhesion is generally performed by P.I. E. I. In the adhesion test method (ASTM C313-59), it is difficult to make a difference in adhesion, so a 2 kg ball head weight is dropped from a height of 1 m, and the enamel peeling state of the deformed part is measured with 169 palpation needles. The area ratio of the peeled portion was evaluated. As for the resistance to picking up, 3 sheets of steel plate are pickled for 3 minutes, pre-treated without Ni dipping, directly applied with glaze for one time, dried, and placed in a 850 ° C firing furnace with a dew point of 50 ° C for 3 minutes. After charging and firing, a accelerating test was performed for 10 hours in a constant temperature bath at 160 ° C., and the occurrence of the squeezing was judged visually.
[0053]
Various characteristics are shown in Table 2. As is apparent from the results in Table 2, according to the present invention, it is possible to obtain an excellent enamel steel plate with enormous improvement in enamel adhesion and good enamel capability.
[0054]
[Table 1]

[0055]
[Table 2]

[0056]
[Table 3]

[0057]
<Example 2>
A slab having various chemical compositions shown in Table 4 was melted and cast in a laboratory, and a 40 mm-thick slab was heated in an electric furnace under the conditions shown in Table 5, and the finished plate thickness was 4.0 mm. After hot rolling, pickling and then cold rolling to 0.5 mm, followed by annealing at 800 ° C. for 1 minute in an atmosphere of 70% N2 + 30% H 2 and dew point −20 ° C., and a reduction rate of 1 % Temper rolling was performed to obtain a steel plate for enamel. The obtained steel sheet was enameled in the steps shown in Table 6, and the enamelability after enamelling was evaluated. Moreover, the enamel property was evaluated also about what abbreviate | omitted pickling and Ni process. When the Ni treatment was omitted, the neutralization treatment was also omitted.
[0058]
Of the enamel properties, the surface characteristics of bubbles and black spots were evaluated visually. The enamel adhesion is generally performed by P.I. E. I. With the adhesion test method (ASTM C313-59), it is difficult to make a difference in adhesion. The weight of a 2 kg ball head is dropped from a height of 1.5 m, and the enamel peeling state of the deformed part is measured with 169 palpation needles. The area ratio of the unpeeled part was evaluated. The tensile resistance was evaluated by hydrogen permeation time by a constant potential oxidation method shown below after polishing a temper rolled steel sheet with alkali degreasing and polishing # 240 emery paper. In the constant potential oxidation method, one side (A side) of the steel sheet is 5% H.₂ SO_Four +2 g / l Al₂ O_Five Immerse in the solution, and immerse the other side (B side) in a 0.5N NaOH solution, 0.06 A / cm between the platinum electrode in the A side solution.² The hydrogen ion in the solution is reduced with the current density of steel plate A as the cathode, atomic hydrogen is allowed to penetrate into the steel plate, and hydrogen ions that permeate the steel plate and dissolve into the solution from the steel plate B surface side are contained in the B surface side solution. The hydrogen permeation resistance of the steel sheet was evaluated by the time until hydrogen permeated through the steel sheet. This time is usually referred to as a T value, and the longer this time, the higher the hydrogen permeation resistance, and the better the steel sheet resistance.
[0059]
Various characteristics are shown in FIG. 1, FIG. 2 and FIG. As is apparent from the results, it can be seen that the present invention significantly improves the enamel adhesion regardless of the enamel pretreatment conditions, and that good adhesion can be obtained even when the enamel pretreatment is simply omitted. Furthermore, in the present invention, the T value that serves as an index of picking is also good. Also, no bubbles / spots were observed under all conditions shown in FIGS.
[0060]
[Table 4]

[0061]
[Table 5]

[0062]
[Table 6]

[0063]
【The invention's effect】
The steel plate for enamel of the present invention has good workability and further satisfies all of the resistance to squeezing, the adhesion to the enamel and the surface characteristics necessary for the steel plate for enamel. In particular, Ni treatment and pickling performed on ordinary steel plates for enameling can be easily omitted to increase enamel adhesion, thus reducing costs and improving productivity, and waste liquid treatment accompanying Ni treatment and pickling. Can solve environmental pollution problems.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the Ni content of a steel sheet, hot rolling conditions, and enamel adhesion.
FIG. 2 is a diagram showing the relationship between the Ni content of a steel sheet, enamel pretreatment conditions, and enamel adhesion.
FIG. 3 is a diagram showing the relationship between the Ni content of steel sheets, enamel pretreatment conditions, and T values.

Claims

In mass%, C: 0.0040% or less, Ni: 0.30-8.0%, Si: 0.5% or less, Mn: 0.05-0.95%, P: 0.20% or less, S: 0.080% or less, Al: 0.0085% or less, Cu: 8.0% or less, O: 0.005 to 0.055%, N: 0.0100% or less, the remainder Fe and inevitable impurities Ri Do from enamel steel sheet for the enamel adhesion was significantly better characterized by having a Ni-concentrated portion is Ni concentration steel material surface has a 2.5 times or more the average content of Ni in the steel .

In mass%, C: 0.0020% or less, Ni: 0.30 to 8.0%, Si: 0.050% or less, Mn: 0.05 to 0.95%, P: 0.05% or less, S: 0.030% or less, Al: 0.0049% or less, Cu: 8.0% or less, O: 0.005 to 0.045%, N: 0.0049% or less, balance Fe and inevitable impurities Ri Do from enamel steel sheet for the enamel adhesion was significantly better characterized by having a Ni-concentrated portion is Ni concentration steel material surface has a 2.5 times or more the average content of Ni in the steel .

In mass%, C: 0.0015% or less, Ni: 0.50 to 8.0%, Si: 0.010% or less, Mn: 0.05 to 0.95%, P: 0.015% or less, S: 0.010-0.020%, Al: 0.0049% or less, Cu: 8.0% or less, O: 0.005-0.045%, N: 0.0040% or less, remainder Ri Do Fe and inevitable impurities, Ni concentration enamel adhesion characterized by having a Ni-concentrated portion which is 2.5 times or more the average Ni content in the steel is remarkably excellent in the steel surface Steel plate for enamel.

The composition further comprises one or more of Nb: 0.10% or less, V: 0.10% or less, and B: 0.010% or less. A steel plate for enamel, which is remarkably excellent in enamel adhesion according to any one of the items.

5. The steel plate for enamel, which is remarkably excellent in enamel adhesion according to claim 1, further comprising Ca: 0.2% or less in mass%.

In at least one stage of the steel plate manufacturing process including the semi-finished product, there is a Ni concentrated portion where the Ni concentration is 2.5 times or more of the average Ni content in the steel on the steel surface, Ni component in terms of mass%: 20% or more, the steel sheet thickness direction of the thickness of 0.01μm or more, and satisfies at least one of the coverage of the steel sheet surface is 5% or more conditions, even after steel sheet production, the steel sheet surface The enamel steel sheet according to any one of claims 1 to 5 , wherein the enamel adhesion is remarkably excellent.

In the steel material after hot rolling and subsequent pickling, there is a Ni concentrated portion where the Ni concentration is 2.5 times or more of the average Ni content in the steel on the steel surface, Ni component in terms of mass%: 20% or more, the steel sheet thickness direction of the thickness of 0.01μm or more, and satisfies at least one of the coverage of the steel sheet surface is 5% or more conditions, even after steel sheet production, the steel sheet surface The steel plate for enamels which is remarkably excellent in the enamel adhesion according to any one of claims 1 to 5 .

The steel having the component according to any one of claims 1 to 5 is cooled after hot-rolling finish rolling in a heat history in hot-rolled slab heating at a time of 1100 ° C or higher and 1400 ° C or lower for 20 to 400 minutes. In the coil heat history before rolling, the holding time at 650 ° C. or more and 900 ° C. or less is 20 minutes or more and 600 minutes or less, and in the heat history of the coil after cold rolling, the holding time at 750 ° C. or more and 950 ° C. or less is 20 seconds or more and 400 Satisfy at least one of the following conditions: Ni concentration on the steel surface is 2.5 times or more of the average Ni content in the steel without treatment in an atmosphere containing Ni The manufacturing method of the steel plate for enamels which is excellent in enamel adhesion characterized by having a Ni concentration part.

And 0.2mm or more scale formation thickness in hot rolling a slab heated by the holding time at 1100 ° C. or higher 1400 ° C. or less in the heat history of hot-rolled slab heating than 400 minutes or more 20 minutes, hot rolling finish and above 0.2μm scale formation thickness in hot rolling coiling by a holding time at 650 ° C. or higher 900 ° C. or less and 600 minutes or less than 20 minutes in the rolling after cold-rolled before the coil heat history, and above 0.02μm scale formation thickness in cold rolling after annealing by the holding time at below 950 ° C. 750 ° C. or higher temperature history in annealing after cold rolling and less 400 minutes or 20 seconds, The manufacturing method of the steel plate for enamels in which the enamel adhesion is remarkably excellent according to claim 7, wherein at least one of the above conditions is satisfied.

The method for producing a steel plate for enamel having a significantly improved enamel adhesion according to claim 8, wherein the heat treatment of the coil after the cold rolling is performed in an atmosphere having a dew point of 0 ° C or higher.

It uses the steel plate for enamel according to any one of claims 1 to 7, and does not go through a surface treatment step in an atmosphere containing Ni in all manufacturing steps before applying enamel glaze. and the sulfo Ro product method of manufacturing.

Using enamel steel plate according to any one of claims 1 to 7, characterized and sulfo Ro product manufacturing method of the never undergo pickling before applying the enamel glaze.