JP3643319B2

JP3643319B2 - Continuously cast enamel steel sheet excellent in workability, enamel adhesion, foam resistance, sunspot resistance, and tear resistance, and a method for producing the same

Info

Publication number: JP3643319B2
Application number: JP2001166569A
Authority: JP
Inventors: 英邦村上; 哲西村; 正芳末廣; 志郎佐柳
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2000-12-22
Filing date: 2001-06-01
Publication date: 2005-04-27
Anticipated expiration: 2021-06-01
Also published as: JP2002249850A

Description

【０００１】
【発明の属する技術分野】
本発明はほうろう特性（耐泡・黒点性、密着性、耐つまとび性）及び加工特性の優れたほうろう用鋼板及びその製造方法に関し、特に連続鋳造によって得ることを特徴とするものである。
【０００２】
【従来の技術】
従来、ほうろう用鋼板は、キャップド鋼またはリムド鋼を造塊し、分塊、熱延、冷延の後にオープンコイル焼鈍法によって脱炭し、更に脱窒焼鈍し、炭素や窒素を数１０ｐｐｍ以下に減少させることによって製造されてきた。しかし、このようにして製造されたほうろう用鋼板は造塊、分塊法によって製造する点や脱炭脱窒焼鈍が必要なことや、製造コストが高いという欠点があった。
【０００３】
そこでこれらの欠点を克服すべく、連続鋳造法によるほうろう用鋼板製造技術が開発された。今日のほうろう用鋼板は、製造コストの低減をはかるべく、この連続鋳造法によって製造されるのが通常である。その１例として、例えば特開平０７−１６６２９５号公報に高酸素鋼を連続鋳造してほうろう用鋼板を得る技術が開示されている。しかしこの技術によるほうろう用鋼板は、ほうろう特性が劣り、複雑な形状の深絞り加工製品には適用できない。
【０００４】
そこで、本発明者らは鋭意研究を重ねた結果、つまとび性、深絞り性に優れたほうろう用鋼板について特願平１１−１９８６７８号（特開２０００−２６８４３号公報）で出願した。しかしながら、この技術による鋼板は、安定して高いｒ値が得られることと、ほうろう泡、黒点性が純Ａｌレス高酸素鋼と同等レベル以上であることとの両立が達成できていない。
【０００５】
【発明が解決しようとする課題】
本発明は前述したほうろう用鋼板の問題点を克服し、深絞り性指標のｒ値が高く、非時効性の１回かけほうろう耐泡・黒点性、密着性、耐つまとび性が優れた連続鋳造ほうろう用鋼板及びその製造法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明は、従来の鋼板、鋼板製造法の欠点を克服するために種々の検討を重ねて得られたもので、ほうろう用鋼板の加工性及びほうろう特性について、下記のような主要元素についての化学組成、製造条件、更に通常の工業プロセスにおいて鋼中に不可避的に含有されると考えられる微量元素の影響を検討した結果、（１）〜（６）の項目を知見した。
【０００７】
化学組成：
Ｃ：０．０００５〜０．００５５％
Ｍｎ：０．０５〜０．５％
Ｏ：０．００２〜０．０７％
Ｎｂ：０〜０．０６％
Ｖ：０〜０．０７％
Ｃｕ：０．０８％以下
Ｓｉ：０．１２％以下
Ｐ：０．００５％〜０．０２５％
Ｓ：０．０３５％以下
Ａｌ：０．０００２〜０．０１５％
Ｎ：０．０００５〜０．００６５％
製造条件：
加熱温度：１２５０〜１０５０℃
仕上温度：７５０〜９５０℃
巻取温度：５００〜８００℃
冷間圧延率：５０％以上
焼鈍：６５０〜８５０℃×１〜３００分
ほうろう性：
酸洗、Ｎｉ処理を行った後、膜厚：１００μｍの１回かけほうろう処理を行い、つまとび性、泡・黒点性表面欠陥、密着性を調査した。
（１）深絞り性はＣ量が低いほど、酸素量が低いほど良好になる。
（２）深絞り性はＣ：０．００２５％以下で、Ｎｂを０．００５％以上添加すれば、高いｒ値が得られる。
（３）時効性はＣ：０．００２５％以下、Ｖ：０．００５％以上、Ｎｂ：０．００５％以上添加の条件を満足すれば、焼鈍条件によらず小さく抑えられる。
（４）つまとび性と良い相関のある水素透過時間は酸素、Ｍｎ、Ｖ、Ｎｂ量に影響され、これらの元素は添加量が多いほど水素透過時間が長くなる。
（５）水素透過時間と深絞り性は通常は一方を向上させるともう一方が劣化する関係にあるが、上記のようにＭｎ、Ｎｂ、Ｖ、Ｏを制御した鋼でも特にＡｌ量を特定の範囲内に制御することで両特性とも良好になる。
（６）通常の工業的な製鋼製造プロセスにおいて不可避的に含有されると考えられる微量元素については含有量の合計について本発明の効果を阻害しない上限の含有量が存在する。
【０００８】
本発明は以上の事実に基づき完成したもので、その発明の要旨は以下の通りである。
【０００９】
質量％で、
Ｃ：０．００２５％以下、
Ｍｎ：０．０５〜０．４％、
Ｓｉ：０．０１５％以下、
Ａｌ：０．００３〜０．０１％、
Ｎ：０．００４５％以下、
Ｏ：０．０１５〜０．０５５％、
Ｐ：０．０１５％以下、
Ｓ：０．０２５％以下、
Ｃｕ：０．０１５〜０．０４５％、
Ｎｂ：０．０３１〜０．０５５％、好ましくは０．０４２〜０．０５５％、
Ｖ：０．００５〜０．０５５％、好ましくは０．０３〜０．０５５％
を含有し、更に不可避的または必要に応じＡｓ、Ｔｉ、Ｂ、Ｎｉ、Ｓｅ、Ｃｒ、Ｔａ、Ｗ、Ｍｏ、Ｓｎの１種以上を合計で０．０２％以下含有し、残部がＦｅ及び不可避的不純物からなることを特徴とする、加工性、ほうろう密着性、耐泡・黒点性及び耐つまとび性に優れた連続鋳造ほうろう用鋼板である。そして、製造条件としてはこの鋼成分の連続鋳造鋳片を仕上温度８００℃以上、巻取温度６００〜８００℃で熱間圧延し、冷延率６０％以上で冷間圧延したのち、再結晶温度以上の温度で焼鈍することを特徴とするものである。
【００１０】
【発明の実施の形態】
以下に本発明について詳述する。
【００１１】
まず、鋼組成について詳述する。
【００１２】
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、時効を抑制し、かつ高いｒ値を得るために０．００２５％以下にする必要がある。好ましい範囲は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。
【００１３】
Ｓｉはほうろう特性を阻害するので、０．０１５％以下にする必要がある。好ましい範囲は良好なほうろう特性を得る点から０．００５％以下である。
【００１４】
Ｍｎは酸素、Ａｌ、Ｖ、Ｎｂ添加量と関連してほうろう特性に影響する重要な成分である。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量が高くなるとほうろう密着性が悪くなり、泡や黒点が発生しやすくなるため、Ｍｎ量の上限を０．４％に特定した。なお、好ましくはＭｎの上限は、０．１７％である。
【００１５】
酸素はつまとび性、加工性に直接に影響すると同時に、Ａｌ、Ｍｎ、Ｎｂ、Ｖ量と関連してほうろう密着性、耐泡・黒点性に影響する。これらの効果を発揮するには０．０１５％は必要である。一方、酸素量が高くなると酸素が高いことにより直接に加工性を劣化させると共に、Ｎｂ、Ｖ添加効率を低め間接的に加工性、時効性を悪くするので、上限を０．０５５％に特定した。
【００１６】
Ａｌは、脱酸元素であり、ほうろう特性としてのつまとび性を良好にするためには、鋼中の酸素を適正量鋼材中に酸化物として存在させることが望ましいが、加工性の観点からは過剰の酸化物として存在すると加工性を劣化させる。本発明鋼では酸化物の形態を制御し、つまとび性と加工性の両立を図るため酸素量のみならずＭｎ、Ｎｂ、Ｖ量、そしてＡｌ量の制御が重要である。
【００１７】
Ｎｂ、Ｖを含有する鋼における加工性（ｒ値）と耐つまとび性に及ぼすＡｌ含有量の影響を図１に示す。両特性を共に最良の状態にするにはＡｌを０．００３〜０．０１％とすることが極めて望ましく、これにより鋼中酸化物の形態が好ましく制御され非常に良好な耐つまとび性と非常に良好な加工性の両立が可能となる。
【００１８】
ＮはＣと同様に侵入型固溶元素であり、０．００４５％を超えると、Ｎｂ、Ｖを添加しても加工性が劣化すると共に非時効性鋼板の製造が出来なくなる。この理由から、Ｎの上限を０．００４５％に特定した。下限は特に限定する必要がないが、現在の製鋼技術では０．００１％以下に溶製するのはコストがかかるため、コストの面から望ましい下限値は０．００１％になる。
【００１９】
Ｐは含有量が０．０１５％超だとほうろう前処理時の酸洗速度を速め、泡・黒点の原因となるスマットを増加させる。したがって、本発明ではＰ含有量を０．０１５％以下に特定した。Ｐ量を０．０１５％未満とすることで、泡・黒点の大幅な改善が実現できる。そのメカニズムは、定かではないが以下のように推定している。Ｐは粒界偏析を生じやすい元素であり、ＦｅＰ化合物を生成する。このＦｅＰ化合物は酸洗時にスマット等を生成させるため、泡・黒点を発生させやすい。そのため、Ｐ量を０．０１５％以下に制御して、ＦｅＰ化合物の生成を抑制することが必要である。Ｐ量が０．０１５％超となると粒界のＰ濃度が増加してＦｅＰ化合物が生成しやすくなる。そうするとＦｅＰ化合物によって、酸洗時に粒界とマトリックスの電位の差により局部電池が発生し、局所的に酸洗速度が速まる。その過程でスマットが著しく発生する。これらの酸洗時のスマット発生を抑制するためには、粒界偏析Ｐを押さえてＦｅＰ化合物の発生を極力少なくすることが極めて重要である。
【００２０】
Ｓはほうろう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、０．０２５％以下とする必要がある。
【００２１】
Ｖは本発明の重要な構成要件の一つである。ＶはＮを固定し、Ｎによる深絞り性の劣化、時効による伸び低下によるプレス加工性の低下を防止する。また、添加したＶの一部は鋼中酸素と結合して酸化物となり、つまとび防止に有効な働きをすると同時に、つまとび発生を抑えるのに必要な酸素量を低くし、間接的な加工性の向上効果も有する。この結果は、０．００５％以上のＶを含有すれば得ることができるが、効果を顕著にし著しく良好な特性を得るには０．０３％以上とすることが好ましい。一方、Ｖ添加量が多くなるとほうろう密着性、耐泡・黒点性が劣化するので、上限を０．０５５％とした。
【００２２】
Ｎｂも本発明の重要な元素である。ＮｂはＣを固定し、深絞り性を向上せしめると共に、非時効化する。また、添加したＮｂは鋼中酸素と結合し酸化物を形成し、つまとび防止に有効な働きをする。この効果は、０．０３１％以上のＮｂを含有すれば得ることができるが、効果を顕著にし著しく良好な特性を得るには０．０４２％以上とすることが好ましい。しかし、添加量が高すぎると密着性、耐泡・黒点性が劣化するので上限を０．０５５％に特定した。
【００２３】
Ｃｕはほうろう前処理時の酸洗速度を抑制する働きがあることが良く知られている。本発明ではＣｕの働きを引き出すため０．０１５％は必要である。本発明はＮｂ、Ｖを添加し、固溶Ｃ、Ｎが極めて少ないので酸洗抑制作用が強すぎると低酸洗時間域での密着性が低下するため、上限を０．０４５％に特定した。
【００２４】
その他の不可避的不純物は、材質特性、ほうろう特性に悪影響を及ぼすので低くすることが望ましいが、Ａｓ、Ｔｉ、Ｂ、Ｎｉ、Ｓｅ、Ｃｒ、Ｔａ、Ｗ、Ｍｏ、Ｓｎについては１種以上の合計で０．０２％以下であれば特に本発明の効果を阻害するものではない。言い換えれば、上記の範囲内であれば本発明で想定しているメリット以外の製造上または品質上のメリットを期待して積極的に添加することも可能である。
【００２５】
次に、製造方法について開示した請求項３の発明について説明する。本発明にかかる鋼スラブは連続鋳造で製造されるが、インゴット−分塊圧延法で製造しても本発明の特徴は損なわない。引き続いて熱間圧延されるが、加熱温度によって本発明の特徴は影響されないので、加熱温度は通常行われている１０５０℃〜１２５０℃の範囲で実施している。熱延仕上り温度は８００℃以上であれば、何℃でも良いが、熱延操業性からＡｒ_３点温度以上であることが望ましい。巻き取り温度も良好な加工性を得たいときは熱延終了後直ちに５０℃以下の冷却を行うと良い。
【００２６】
冷間圧延は深絞り性の良好な鋼板を得るために６０％以上を必要とする。特に深絞り性を必要とする場合には、７５％以上とすることが好ましい。
【００２７】
焼鈍は箱焼鈍でも連続焼鈍でも本発明の特徴は変わらなく、再結晶温度以上であれば本発明の特徴を発揮する。特に本発明の特徴である深絞り性が優れ、ほうろう特性が良好という特徴を顕現させるには連続焼鈍が好ましい。箱焼鈍では６５０〜６７０℃で、連続焼鈍では７００〜８００℃で主に実施することができる。
【００２８】
以上、説明したように本発明の化学組成からなる鋼板、及び発明による製造条件で製造した鋼板は、連続鋳造法による鋳片によるものであっても従来の脱炭キャップド鋼と同等以上にプレス加工性が優れ、直接１回かけのほうろうでも、泡・黒点欠陥が発生しにくく、優れたほうろう密着性を有するほうろう用鋼板である。また、直接１回かけ以外の用途のバスタブ、ケトル等でも、その特性を発揮し、なんら変わることがない。
【００２９】
【実施例】
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に示す製造条件で、熱間圧延、冷間圧延、焼鈍を行った。引き続き１．０％の調質圧延を行った後、機械的特性及びほうろう特性を調査した。調査結果を表２に併せて示した。
【００３０】
機械特性は、焼鈍後、１．０％の調質圧延後の鋼板をＪＩＳ５号試験片に加工し、引張り試験、ｒ値、時効指数を調査した。時効指数は引張試験において１０％の予歪を付与した材料についての１００℃×６０分の時効前後の耐力の差で示した。
【００３１】
ほうろう特性は表３に示した工程で評価した。ほうろう特性の内、泡・黒点の表面特性は酸洗時間を２０分と長い条件を選び、その評価は次の通り表示した。
◎：発生なし、○：少し発生、×：発生多い
【００３２】
また、ほうろう密着性は酸洗時間が３分と短い条件で評価した。ほうろう密着性は通常行われているＰ．Ｅ．Ｉ．密着試験方法（ＡＳＴＭＣ３１３−５９）では密着性に差がでないため、２ｋｇの球頭の重りを１ｍ高さから落下させ、変形部のほうろう剥離状態を１６９本の触診針で計測し、未剥離部分の面積率で評価した。
【００３３】
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１回かけ用の釉薬を施釉、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つぎのとおり表示した。
【００３４】
表２の結果から明らかなように、本発明の鋼板はｒ値、Ｅｌ値が良好であり、かつ耐時効性も良好で、ほうろう特性も優れたほうろう用鋼板である．一方、比較例で示した鋼板は、材料特性もしくはほうろう特性のいずれか一方、または双方の特性が劣っている。すなわち、化学組成及び化学組成間の密着な関係が本発明範囲をはずれると材質、ほうろう特性の優れた鋼板が得られない。
【００３５】
【表１】

【００３６】
【表２】

【００３７】
【表３】

【００３８】
【発明の効果】
本発明のほうろう用鋼板は、従来使用されているプレス成形性の良好なＴｉ添加鋼と同等、またはそれ以上の深絞り性を有し、さらにほうろう用鋼板として必要な耐泡・黒点性、ほうろう密着性、表面特性のすべてを満たしている。特にＴｉ添加鋼で問題のあった泡・黒点欠陥を克服し、連続鋳造法によって製造されている高酸素鋼のように脱炭または脱炭脱窒焼鈍ではなく、連続焼鈍、または箱焼鈍を行ってもプレス成形性、耐時効性の優れた鋼板が製造できるので、焼鈍に要するコストの低減も大きく、工業的異議は大きい。
【図面の簡単な説明】
【図１】Ｎｂ−Ｖ鋼の耐つまとび性と加工性に及ぼすＡｌの影響を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel plate for enamel having excellent enamel characteristics (foam resistance / spot resistance, adhesion, resistance to picking) and processing characteristics, and a method for producing the same, and is characterized by being obtained by continuous casting.
[0002]
[Prior art]
Conventionally, steel plates for enamel are ingots of capped or rimmed steel, decarburized by open coil annealing after splitting, hot rolling, and cold rolling, and further denitrifying annealing, and carbon and nitrogen are several tens ppm or less. Has been manufactured by reducing to. However, the enameled steel sheet produced in this way has the disadvantages of being produced by the ingot-making and splitting method, requiring decarburization and denitrification annealing, and the production cost being high.
[0003]
Therefore, in order to overcome these drawbacks, a steel sheet manufacturing technology for enamel by a continuous casting method was developed. Today's enamel steel plates are usually produced by this continuous casting method in order to reduce production costs. As an example, for example, Japanese Patent Application Laid-Open No. 07-166295 discloses a technology for obtaining a steel plate for enamel by continuously casting high oxygen steel. However, enameled steel sheets using this technique have poor enamel characteristics and cannot be applied to deep-drawn products with complex shapes.
[0004]
Therefore, as a result of intensive studies, the present inventors have filed an application for Japanese Patent Application No. 11-198678 (Japanese Patent Application Laid-Open No. 2000-26843) regarding a steel plate for enamel that is excellent in toughness and deep drawability. However, the steel plate according to this technique cannot achieve both the stable high r value and the enamel foam and black spot properties being equal to or higher than those of pure Al-less high oxygen steel.
[0005]
[Problems to be solved by the invention]
The present invention overcomes the problems of the enamel steel plate described above, has a high deep drawability index r value, and is a non-aging single-time enameled foam / black spot resistance, adhesion, and resistance to continuation. It aims at providing the steel plate for cast enamel and its manufacturing method.
[0006]
[Means for Solving the Problems]
The present invention has been obtained through various studies to overcome the drawbacks of conventional steel sheets and steel sheet manufacturing methods. The workability and enamel characteristics of enamel steel sheets are as follows. As a result of examining the effects of trace elements considered to be inevitably contained in steel in a normal industrial process, as a result of the composition, production conditions, items (1) to (6) were found.
[0007]
Chemical composition:
C: 0.0005 to 0.0055%
Mn: 0.05 to 0.5%
O: 0.002 to 0.07%
Nb: 0 to 0.06%
V: 0 to 0.07%
Cu: 0.08% or less Si: 0.12% or less P: 0.005% to 0.025%
S: 0.035% or less Al: 0.0002 to 0.015%
N: 0.0005 to 0.0065%
Manufacturing conditions:
Heating temperature: 1250-1050 ° C
Finishing temperature: 750-950 ° C
Winding temperature: 500-800 ° C
Cold rolling rate: 50% or more Annealing: 650-850 ° C. x 1 to 300 minutes
After pickling and Ni treatment, the film was subjected to a single enamel treatment with a film thickness of 100 μm, and the picking property, foam / spot surface defect and adhesion were investigated.
(1) The deep drawability is better as the C content is lower and the oxygen content is lower.
(2) The deep drawability is C: 0.0025% or less, and a high r value can be obtained by adding 0.005% or more of Nb.
(3) Aging can be suppressed to a small value regardless of the annealing conditions if the conditions of C: 0.0025% or less, V: 0.005% or more, and Nb: 0.005% or more are satisfied.
(4) The hydrogen permeation time that has a good correlation with the toughness is affected by the amounts of oxygen, Mn, V, and Nb, and the hydrogen permeation time becomes longer as the amount of these elements added increases.
(5) The hydrogen permeation time and deep drawability are usually related to the deterioration of the other when improved, but the steel with Mn, Nb, V, O controlled as described above has a specific Al content. By controlling within the range, both characteristics are improved.
(6) About the trace element considered to be inevitably contained in a normal industrial steelmaking production process, there is an upper limit content that does not impair the effects of the present invention with respect to the total content.
[0008]
The present invention has been completed based on the above facts, and the gist of the present invention is as follows.
[0009]
% By mass
C: 0.0025% or less,
Mn: 0.05 to 0.4%,
Si: 0.015% or less,
Al: 0.003 to 0.01%,
N: 0.0045% or less,
O: 0.015-0.055%,
P: 0.015% or less,
S: 0.025% or less,
Cu: 0.015-0.045%,
Nb: 0.031 to 0.055%, preferably 0.042 to 0.055%,
V: 0.005-0.055%, preferably 0.03-0.055%
In addition, it is inevitable or contains 0.02% or less in total of one or more of As, Ti, B, Ni, Se, Cr, Ta, W, Mo, Sn if necessary, with the balance being Fe and inevitable It is a steel sheet for continuous casting enamel that is excellent in workability, enamel adhesion, foam resistance, sunspot resistance, and tear resistance. And as manufacturing conditions, this steel component continuous cast slab is hot-rolled at a finishing temperature of 800 ° C. or more and a coiling temperature of 600 to 800 ° C., and cold-rolled at a cold rolling rate of 60% or more, and then the recrystallization temperature. It is characterized by annealing at the above temperature.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
[0011]
First, the steel composition will be described in detail.
[0012]
Conventionally, it is known that the lower the C, the better the workability. However, in the present invention, in order to suppress aging and obtain a high r value, it is necessary to make it 0.0025% or less. A preferable range is 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.
[0013]
Since Si hinders enamel characteristics, it must be 0.015% or less. A preferable range is 0.005% or less from the viewpoint of obtaining good enamel characteristics.
[0014]
Mn is an important component that affects enamel characteristics in relation to the amounts of oxygen, Al, V, and Nb added. At the same time, it is an element that prevents hot brittleness caused by S during hot rolling. In the present invention containing oxygen, 0.05% or more is required. On the other hand, when the amount of Mn increases, the enamel adhesion deteriorates and bubbles and black spots are likely to be generated. Therefore, the upper limit of the amount of Mn is specified to be 0.4%. In addition, Preferably the upper limit of Mn is 0.17%.
[0015]
Oxygen directly affects the tensile properties and workability, and at the same time affects the enamel adhesion, foam resistance and sunspot properties in relation to the amounts of Al, Mn, Nb and V. In order to exert these effects, 0.015% is necessary. On the other hand, when the oxygen amount is high, the workability is directly deteriorated due to the high oxygen content, and the Nb and V addition efficiency is lowered to indirectly deteriorate the workability and aging, so the upper limit is specified to 0.055%. .
[0016]
Al is a deoxidizing element, and in order to improve the toughness as an enamel characteristic, it is desirable that oxygen in the steel be present as an appropriate amount of oxide in the steel, but from the viewpoint of workability. When it exists as an excess oxide, workability is deteriorated. In the steel of the present invention, it is important to control not only the amount of oxygen but also the amounts of Mn, Nb, V, and Al in order to control the form of oxides and achieve both balance and workability.
[0017]
FIG. 1 shows the influence of the Al content on the workability (r value) and the resistance to slip in steels containing Nb and V. In order to achieve the best of both characteristics, it is highly desirable that Al is 0.003 to 0.01%, and thus the form of the oxide in the steel is preferably controlled, and very good anti-tacking properties and extremely high In addition, it is possible to achieve both good workability.
[0018]
N is an interstitial solid solution element like C, and if it exceeds 0.0045%, even if Nb and V are added, workability deteriorates and it becomes impossible to manufacture a non-aged steel sheet. For this reason, the upper limit of N is specified as 0.0045%. The lower limit is not particularly limited, but it is costly to melt to 0.001% or less in the current steelmaking technology. Therefore, a desirable lower limit is 0.001% in terms of cost.
[0019]
If the P content exceeds 0.015%, the pickling speed during enamel pretreatment is increased, and the smut that causes bubbles and black spots is increased. Therefore, in the present invention, the P content is specified to be 0.015% or less. By making the amount of P less than 0.015%, it is possible to realize significant improvement of bubbles and black spots. The mechanism is not clear but is estimated as follows. P is an element that easily causes grain boundary segregation, and produces an FeP compound. Since this FeP compound generates smut and the like during pickling, it tends to generate bubbles and black spots. Therefore, it is necessary to control the amount of P to 0.015% or less to suppress the formation of the FeP compound. If the amount of P exceeds 0.015%, the P concentration at the grain boundary increases and an FeP compound is likely to be formed. Then, a local battery is generated by the FeP compound due to the difference between the grain boundary and the matrix potential during pickling, and the pickling speed is locally increased. In the process, smut is remarkably generated. In order to suppress the occurrence of smuts during pickling, it is extremely important to suppress the generation of FeP compounds by suppressing the grain boundary segregation P.
[0020]
S increases the amount of smut during pickling during enamel pretreatment and facilitates the generation of bubbles and black spots. Therefore, S needs to be made 0.025% or less.
[0021]
V is one of the important constituent elements of the present invention. V fixes N and prevents deterioration of deep drawability due to N and reduction of press workability due to a decrease in elongation due to aging. In addition, part of the added V combines with oxygen in the steel to form an oxide, which works effectively to prevent tripping, and at the same time lowers the amount of oxygen necessary to prevent tripping and indirectly processing. It also has an effect of improving properties. This result can be obtained if it contains 0.005% or more of V, but it is preferably 0.03% or more in order to make the effect remarkable and obtain remarkably good characteristics. On the other hand, since the enamel adhesion and the bubble resistance / spot resistance deteriorate as the V addition amount increases, the upper limit was made 0.055%.
[0022]
Nb is also an important element of the present invention. Nb fixes C, improves deep drawability and is non-aging. Further, the added Nb combines with oxygen in the steel to form an oxide, which works effectively for preventing the twisting. This effect can be obtained if it contains 0.031 % or more of Nb, but it is preferably 0.042% or more in order to make the effect remarkable and to obtain remarkably good characteristics. However, if the addition amount is too high, the adhesion and the bubble resistance / spot resistance deteriorate, so the upper limit was specified to 0.055%.
[0023]
It is well known that Cu has a function of suppressing the pickling rate during enamel pretreatment. In the present invention, 0.015% is necessary to bring out the function of Cu. In the present invention, Nb and V are added, and since solid solution C and N are very small, if the pickling inhibiting action is too strong, the adhesiveness in the low pickling time range is lowered, so the upper limit is specified as 0.045%. .
[0024]
Other inevitable impurities adversely affect material characteristics and enamel characteristics, so it is desirable to make them low, but As, Ti, B, Ni, Se, Cr, Ta, W, Mo, Sn are a total of one or more. If it is 0.02% or less, the effect of the present invention is not particularly impaired. In other words, as long as it is within the above range, it is possible to positively add it in anticipation of merit in manufacturing or quality other than the merit assumed in the present invention.
[0025]
Next, the invention of claim 3 which discloses the manufacturing method will be described. Although the steel slab according to the present invention is manufactured by continuous casting, the characteristics of the present invention are not impaired even when manufactured by the ingot-slab rolling method. Although it is subsequently hot-rolled, since the characteristics of the present invention are not affected by the heating temperature, the heating temperature is usually in the range of 1050 ° C. to 1250 ° C. As long as the hot rolling finish temperature is 800 ° C. or higher, any temperature may be used, but from the viewpoint of hot rolling operability, Ar ₃ point temperature or higher is desirable. When it is desired to obtain good workability at the coiling temperature, it is preferable to cool to 50 ° C. or less immediately after the end of hot rolling.
[0026]
Cold rolling requires 60% or more in order to obtain a steel sheet with good deep drawability. Especially when deep drawability is required, it is preferably 75% or more.
[0027]
Whether the annealing is box annealing or continuous annealing, the characteristics of the present invention are not changed, and the characteristics of the present invention are exhibited as long as the recrystallization temperature is exceeded. In particular, continuous annealing is preferable in order to reveal the features of the present invention that the deep drawability is excellent and the enamel characteristics are good. It can be mainly carried out at 650 to 670 ° C. for box annealing and 700 to 800 ° C. for continuous annealing.
[0028]
As described above, the steel plate having the chemical composition of the present invention and the steel plate manufactured under the manufacturing conditions according to the present invention are pressed to the same level or higher than the conventional decarburized capped steel even if the steel plate is manufactured by a continuous casting method. It is a steel plate for enamel that has excellent workability, is less likely to generate bubbles and black spots even when directly enameled, and has excellent enamel adhesion. In addition, even in bathtubs, kettles, etc., for applications other than direct one-time use, they exhibit their characteristics and do not change at all.
[0029]
【Example】
The continuous cast slabs having various chemical compositions shown in Table 1 were subjected to hot rolling, cold rolling, and annealing under the manufacturing conditions shown in Table 2. Subsequently, 1.0% temper rolling was performed, and then the mechanical characteristics and enamel characteristics were investigated. The survey results are also shown in Table 2.
[0030]
As for mechanical properties, a steel sheet after temper rolling of 1.0% after annealing was processed into a JIS No. 5 test piece, and a tensile test, an r value, and an aging index were investigated. The aging index is shown by the difference in proof stress before and after aging at 100 ° C. for 60 minutes for the material given 10% pre-strain in the tensile test.
[0031]
The enamel characteristics were evaluated by the process shown in Table 3. Of the enamel characteristics, the surface characteristics of bubbles and black spots were selected under conditions where the pickling time was as long as 20 minutes, and the evaluation was indicated as follows.
◎: No occurrence, ○: Little occurrence, ×: Many occurrences [0032]
The enamel adhesion was evaluated under conditions where the pickling time was as short as 3 minutes. Enamel adhesion is usually performed by P.I. E. I. In the adhesion test method (ASTM C313-59), since there is no difference in adhesion, the weight of a 2 kg ball head 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 part was evaluated.
[0033]
As for the resistance to pickling, 3 sheets of steel plate are pickled for 3 minutes, pretreated without Ni dipping, directly applied with glaze for one time, dried, and placed in a firing furnace with a dew point of 50 ° C and 850 ° C. After charging for a minute and firing, a accelerating test was conducted for 10 hours in a constant temperature bath at 160 ° C., and the occurrence state of the pulverization was visually determined and displayed as follows.
[0034]
As is apparent from the results in Table 2, the steel sheet of the present invention is a steel sheet for enamel having good r and El values, good aging resistance and excellent enamel characteristics. On the other hand, the steel sheet shown in the comparative example is inferior in either the material characteristics or the enamel characteristics, or both characteristics. That is, if the close relationship between the chemical composition and the chemical composition is out of the scope of the present invention, a steel plate having excellent material and enamel characteristics cannot be obtained.
[0035]
[Table 1]

[0036]
[Table 2]

[0037]
[Table 3]

[0038]
【The invention's effect】
The enamel steel sheet of the present invention has a deep drawability equivalent to or better than that of a Ti-added steel having a good press formability that has been used in the past, and also has the necessary bubble resistance and black spot resistance as an enamel steel sheet. Satisfies all adhesion and surface properties. Overcoming bubble and sunspot defects, which were particularly problematic with Ti-added steels, are not decarburized or decarburized and denitrified as in the case of high-oxygen steels produced by continuous casting, but continuous annealing or box annealing is performed. However, since a steel sheet excellent in press formability and aging resistance can be produced, the cost required for annealing is greatly reduced, and industrial objection is great.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing the influence of Al on the tensile resistance and workability of Nb-V steel.

Claims

% By mass
C: 0.0025% or less,
Mn: 0.05 to 0.4%,
Si: 0.015% or less,
Al: 0.003 to 0.01%,
N: 0.0045% or less,
O: 0.015-0.055%,
P: 0.015% or less,
S: 0.025% or less,
Cu: 0.015-0.045%,
Nb: 0.031 to 0.055%,
V: 0.005-0.055%
A steel sheet for continuous casting enamel that is excellent in workability, enamel adhesion, foam resistance, sunspot resistance, and tear resistance, characterized in that it contains Fe and the balance is inevitable impurities.

% By mass
C: 0.0025% or less,
Mn: 0.05 to 0.4%,
Si: 0.015% or less,
Al: 0.003 to 0.01%,
N: 0.0045% or less,
O: 0.015-0.055%,
P: 0.015% or less,
S: 0.025% or less,
Cu: 0.015-0.045%,
Nb: 0.042 to 0.055%,
V: 0.03-0.055%
A steel sheet for continuous casting enamel that is excellent in workability, enamel adhesion, foam resistance, sunspot resistance, and tear resistance, characterized in that it contains Fe and the balance is inevitable impurities.

The steel component continuous cast slab according to claim 1 or 2 is hot-rolled at a finishing temperature of 800 ° C or higher and a coiling temperature of 600 to 800 ° C, cold-rolled at a cold rolling rate of 60% or higher, and then re-rolled. A method for producing a steel sheet for continuous cast enamel, which is excellent in workability, enamel adhesion, foam resistance / spot resistance and toughness resistance, characterized by annealing at a temperature equal to or higher than the crystal temperature.