JP4332974B2 - Manufacturing method of cold rolled steel strip for 3-piece can - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、高速製缶に適した３ピース缶用冷延鋼帯の製造方法に関するものである。
【０００２】
【従来の技術】
食缶や飲料缶等に用いられる３ピース缶には、熱間圧延鋼帯を酸洗し、冷間圧延し、焼鈍し、次いで調質圧延または二次圧延を行って冷延鋼帯とした後、鋼帯の表面に錫めっきを施したもの、ニッケルめっき後に錫めっきを施したもの、電解クロム酸処理を施したもの（ティンフリースチールあるいはＴＦＳ）、また、それらに有機樹脂フィルムがラミネートされたもの等の表面処理鋼板が用いられている。（以下、これらの表面処理の施されたものを含めて、３ピース缶用鋼帯または３ピース缶用冷延鋼板と記す。）
【０００３】
３ピース缶は、缶胴と蓋および底の部材から構成される。上記の３ピース缶用鋼板は、このうちの缶胴の素材として用いられる。缶胴は、前記の３ピース缶用鋼板の切り板またはコイルに塗装、印刷、あるいはフィルムをラミネートした後、１缶分の素材に相当する所定サイズの長方形ブランクにせん断し、ロールフォーミング加工によって筒状に丸め、端部を所定の幅で重ね合わせてその部分をワイヤーシーム溶接等の方法によって接合し、円筒状とすることで製造される。
【０００４】
ところで、近年、缶体の軽量化、素材コストの削減の観点から３ピース缶用鋼板のゲージダウンが強く求められ、板厚が従来にまして薄くなってきている。ゲージダウンした鋼板としては、焼鈍後に二次圧延を行う方法で製造されたＤＲ材が最も経済的な鋼板として用いられている。また、製造コスト低減の観点から、製缶の高速化が進行している。
【０００５】
こうした薄ゲージ化された素材の高速製缶において、ロールフォームされたブランクが搬送中に詰まる、いわゆるジャミングと呼ばれる不具合が顕在化している。すなわち、高速製缶ではロールフォームされたブランクを溶接機内で高速で搬送する必要があるが、ワイヤーシーム溶接ではロールフォームされたブランクの端部を所定の幅に精密にオーバーラップさせるため、ロールフォームされたブランクを極めて正確に設定された搬送ガイドによって拘束しつつ搬送する。この際、ロールフォームされたブランクの形状、すなわち巻幅やねじれ等が許容範囲以上に変動していると、精密に設定された搬送ガイド中でジャミングが発生する。この現象は、３ピース缶用冷延鋼帯の板厚がゲージダウンされ、溶接速度が高速になるに伴って、初めて顕在化した不具合である。
【０００６】
高速溶接に適した溶接缶胴用鋼板に関する技術としては、例えば、特開平７−１０９５２７号公報（以下、先行文献と記す。）に開示されたものがある。この先行文献に記載された技術は高速溶接でのラップ逃げを抑制することで、高速溶接性を確保するという技術思想に基づくものである。
【０００７】
【発明が解決しようとする課題】
しかしながら、こうしたラップ逃げは、鋼板特性よりはむしろ用いられる溶接機の装置設定に起因して生じることが多く、先行文献が開示された当時に比較して、さらに高速化（線速度１００ｍ／ｍｉｎ程度）された近年の高速溶接機の精密な装置設定では問題になりがたい事項を課題とするものであり、上述したような不具合を解消するものではない。
【０００８】
本発明は、かかる事情に鑑みてなされたものであって、薄ゲージ化するとともに溶接速度を高速化しても製缶に際してジャミング等の不具合を生じることのない３ピース缶用冷延鋼帯の製造方法を提供することを目的とする。
【０００９】
【課題を解決するための手段】
本発明者らは、高速溶接に適した３ピース缶用冷延鋼帯を製造する方法について鋭意検討を重ねた。その結果、高速製缶でのジャミングの発生は、熱延鋼帯の製造条件、特に仕上圧延出側温度と深く関係していることを見出した。
【００１０】
前述したように、３ピース缶の缶胴部は、３ピース缶用鋼板の切り板またはコイルに塗装、印刷、あるいはフィルムをラミネートした後、１缶分の素材に相当するサイズの長方形ブランクにせん断し、ロールフォーミング加工によって筒状に丸め、丸められた端部を所定の幅で重ね合わせ、その部分をワイヤーシーム溶接等の方法によって接合し、円筒状にすることで製造されるが、この際、ロールフォーミング条件は、前述したジャミング抑制の観点から、ロールフォーミング後のブランクの巻幅が一定になるように素材ロット毎に微調整される。しかし、板厚が薄くなるほどロールフォーミング後の巻幅は一定になりにくく、近年における素材の薄板厚化に伴い、巻幅の変動が極めて生じやすくなっている。また、近年の高速製缶においては、ジャミングを発生させないために要求されるロールフォーミングの巻幅の精度が非常に厳しい。したがって、ジャミングが発生しない巻幅の不均一の許容範囲が極めて小さく、極めてジャミングが発生しやすくなるものと考えられる。
【００１１】
一方、３ピース缶用鋼板のゲージダウンが進み、最終製品板厚が薄くなることに伴い、冷間圧延の負荷の低減のため、熱延仕上板厚も薄くする必要がある。このような熱延鋼帯の薄手化により、熱間圧延中の放熱が大きくなっており、仕上圧延出側温度ＦＴが熱延鋼帯の長手方向および幅方向で不均一になりやすくなっている。このようなＦＴの不均一は、熱延鋼帯の特性の不均一につながる。ジャミング発生頻度が熱延鋼帯の製造条件と関連するのは、こうした熱延鋼帯の特性の不均一の影響によるものであると考えられる。
【００１２】
従来は、単にＦＴをＡｒ３変態点以上、すなわちオーステナイト単相域で仕上圧延を終了すれば、熱延鋼帯の特性は比較的均一にすることができると考えられてきており、実際、比較的低速の製缶速度である場合は、巻幅の許容範囲は比較的広く、こうした条件で十分であった。しかし、今日のゲージダウンされた素材での高速製缶では、巻幅が不均一になりやすい上に、巻幅の許容範囲が極めて狭くなっているため、より厳密にＦＴを規定して熱延鋼帯の特性を均一化することが必要となるのである。
【００１３】
そこで本発明者らは、ゲージダウンされた素材の高速製缶を可能にするＦＴの規定条件を求めるべく、熱延鋼帯の仕上圧延出側温度とジャミング発生頻度との関係についてさらに検討を加えた結果、図１および図２の関係を見出した。
図１は、０．００３ｗｔ％のＣを含有する鋼を熱間圧延した際の、熱延鋼帯の幅方向中央部での仕上圧延出側温度の鋼帯全長にわたる間の変化ΔＦＴＣと、その熱延鋼帯から得た板厚０．１５ｍｍのＤＲ材である３ピース缶用冷延鋼帯を用いて、線速度１００ｍ／ｍｉｎの高速製缶に相当する条件で実験室的に評価されたジャミング発生頻度との関係を示したグラフである。この際、ロールフォーミング加工は、鋼帯の圧延方向が缶胴の周方向に直角になるようにして行った。図１に示すように、鋼帯の幅方向中央部での仕上圧延出側温度の鋼帯全長にわたる間の変化ΔＦＴＣを３０℃以下とすることで、実製缶において操業に支障をきたさないジャミング発生頻度とすることができる。
【００１４】
また、図２は、上記の熱延鋼帯のうちΔＦＴＣが３０℃であるものについて、鋼帯の幅方向中央部とエッジ部での仕上圧延出側温度の差ΔＦＴＥの最大値と、その熱延鋼帯から上記と同様にして得た３ピース缶用冷延鋼帯のジャミング発生頻度との関係を示したグラフである。図２に示すように、鋼帯の長手方向の全長にわたり、鋼帯の幅方向中央部とエッジ部での仕上圧延出側温度の差ΔＦＴＥを２０℃以下とすることで、実製缶において操業に支障をきたさないジャミング発生頻度とすることができる。
【００１５】
すなわち、本発明者らは、ジャミング発生については仕上圧延温度ＦＴよりも、熱延鋼帯の幅方向中央部での仕上圧延出側温度の鋼帯全長にわたる間の変化ΔＦＴＣと、熱延鋼帯の長手方向全長にわたる、幅方向中央部の仕上圧延出側温度と幅方向エッジ部での仕上圧延出側温度との差ΔＦＴＥが影響をおよぼし、これらの値を所定の範囲内とすることで高速製缶におけるジャミングの発生頻度を抑制することができることを新たに見出した。
【００１６】
本発明は上記知見に基づいてなされたものであって、以下の（１）〜（３）を提供する。
（１） 重量％で、Ｃ：０．００４０％以下、Ｓｉ：０．０５％以下、Ｍｎ：０．１〜０．７％、Ｐ：０．０５％以下、Ｓ：０．０３％以下、ｓｏｌ．Ａｌ：０．０２〜０．１２％、Ｎ：０．００３５％以下、残部がＦｅ及び不可避的不純物からなる連続鋳造スラブを調整し、
前記スラブをＡｒ ３ 変態点以上の温度域において圧下率７０％以上で粗圧延して粗バーとなし、
次いで前記粗バーの平坦度を矯正し、平坦度の矯正された前記粗バーを仕上圧延して熱延鋼帯とするにあたり、仕上圧延機の入側において、エッジヒーターによるエッジ部のみの加熱と、誘導加熱装置による幅方向全体の加熱とを行うことによって、前記粗バーの仕上圧延入側温度を調整し、
鋼帯の長手方向の全長および幅方向の全幅にわたり、仕上圧延出側温度がＡｒ３変態点以上９２０℃以下となり、
かつ、鋼帯の幅方向中央部での仕上圧延出側温度の、鋼帯の長手方向の全長にわたる変化が３０℃以下となり、
かつ、鋼帯の長手方向全長にわたり、鋼帯の幅方向中央部とエッジ部での仕上圧延出側温度の差が２０℃以下となるように、かつ、仕上板厚が２．４ｍｍ以下となるように仕上圧延を行い、
得られた熱延鋼帯を５４０〜６８０℃の温度でコイルに巻き取り、
次いで酸洗した後、冷間圧延し、焼鈍し、二次圧延し、板厚を０．１５ｍｍ以下とすることを特徴とする３ピース缶用冷延鋼帯の製造方法。
【００１７】
（２） 前記連続鋳造スラブは、さらに重量％で、Ｂ：０．０００３〜０．００３％を含有し、かつ、Ｂ／Ｎが重量比で０．５〜０．８であることを特徴とする前記（１）に記載の３ピース缶用冷延鋼帯の製造方法。
【００１８】
（３） 前記連続鋳造スラブは、さらに重量％で、Ｎｂ：０．０２１〜０．０５０％を含有し、かつ、Ｎｂ／Ｃが重量比で７．７超であることを特徴とする前記（１）または（２）に記載の３ピース缶用冷延鋼帯の製造方法。
【００２０】
なお、ロールフォーミング加工は、鋼帯の圧延方向を缶胴の周方向に平行な方向にする場合と、直角方向にする場合とがあり、それぞれにおいて適正な巻幅となるようにロールフォーミング装置を調整する必要があるが、上記ΔＦＴＣ、ΔＦＴＥを制御した場合には、ジャミング発生頻度に対して前記方向の影響はない。
【００２１】
【発明の実施の形態】
以下、本発明におけ冷延鋼帯の製造方法を、連続鋳造スラブの化学成分と、製造条件とに分けて、具体的に説明する。
１．化学成分
本発明における連続鋳造スラブの化学成分は、重量％で、Ｃ：０．００４０％以下、Ｓｉ：０．０５％以下、Ｍｎ：０．１〜０．７％、Ｐ：０．０５％以下、Ｓ：０．０３％以下、ｓｏｌ．Ａｌ：０．０２〜０．１２％、Ｎ：０．００３５％以下を含有する。また、鋼の組織均一性、焼き入れ性を向上する場合には、前記の化学成分に加えて、Ｂ：０．０００３〜０．００３％を含有し、かつ、Ｂ／Ｎが重量比で０．５〜０．８とする。さらに、鋼の時効性を向上させる場合には、前記いずれかの化学成分に加えて、Ｎｂ：０．０２１〜０．０５０％を含有し、かつ、Ｎｂ／Ｃが重量比で７．７超とする。以下、これらの限定理由について説明する。
【００２２】
Ｃ：０．００４０％以下
Ｃは、鋼板の強度を所望のレベルに調整するために有効な元素である。Ｃ含有量が０．００４０％を超えると、ゲージダウンした鋼板の製造方法として行われる二次圧延によって鋼板強度が過度に上昇し、ロールフォーミング加工での負荷を高めるため、０．００４０％以下とする。
【００２３】
Ｓｉ：０．０５％以下
Ｓｉは、意図的な添加を行わない場合にも不純物成分として鋼中に残留し、鋼板を脆化させ、耐食性を劣化させる元素であり、また、鋼板に電気めっきによる表面処理を施す場合には金属の電析に対しても悪影響を与える。これらの問題はＳｉ含有量が０．０５％を超えた場合に顕著になるため、Ｓｉ含有量は０．０５％以下とする。
【００２４】
Ｍｎ：０．１〜０．７％
Ｍｎは、鋼中ＳをＭｎＳとして析出させることによってスラブの熱間割れを防止するとともに、固溶強化元素として、Ｃによる強化を補う役割を果たす重要な元素である。本発明における連続鋳造スラブでは、Ｓを析出固定するためにＭｎを０．１％以上とする。一方、Ｍｎの多量の添加はゲージダウンによって低下する缶体強度を補う素材の強度確保には有効だが、過剰な強度上昇はロールフォーミング加工での負荷を高めるため、０．７％以下とする。
【００２５】
Ｐ：０．０５％以下
Ｐは、フェライト粒界に編析して粒界を脆化させる元素であり、その含有量は極力少ない方が好ましい。また、ＰはＭｎ以上に大きな強化能を有するため、Ｐの多量の添加はゲージダウンによって低下する缶体強度を補う素材の強度確保には有効だが、過剰な強度上昇はロールフォーミング加工での負荷を高める。これらを考慮してＰ含有量を０．０５％以下とする。
【００２６】
Ｓ：０．０３％以下
Ｓは、スラブの熱間割れを防止する観点から極力少ない方が望ましく、０．０３％以下とする。
【００２７】
ｓｏｌ．Ａｌ：０．０２〜０．１２％
Ａｌは、鋼中のＮと化合してＡｌＮとして析出するため、鋼中の固溶Ｎ量を調整するのに有効な元素である。こうした効果を発揮させるため、ｓｏｌ．Ａｌ含有量を０．０２％以上とする。一方、多量のＡｌを添加すると鋼板に電気めっきによる表面処理を施す場合には金属の電析対して悪影響を及ぼすため、ｓｏｌ．Ａｌ含有量を０．１２％以下とする。
【００２８】
Ｎ：０．００３５％以下
Ｎは、Ｃと同様に侵入型に固溶して鋼板の強度を調整するのに有効な元素である。しかし、Ｎ量が０．００３５％を超えると固溶Ｎ量が過剰に増大して時効性の劣化を招くとともに、鋼板の強度が過度に上昇してロールフォーミング加工での負荷を高めるため、０．００３５％以下とする。
【００２９】
Ｂ：０．０００３〜０．００３％、かつ、Ｂ／Ｎが重量比で０．５〜０．８
Ｂは、鋼中ＮをＡｌＮとなる前にＢＮとして析出させることにより巻取り後の熱延鋼帯の幅方向および長手方向の組織の均一性をさらに高める効果と、極低Ｃ化することで低下する溶接部の焼き入れ性を補う効果とを有しており、これらの効果が必要とされる場合に添加される。これらの効果を発揮させるためには０．０００３％以上の添加が必要であるが、０．００３％を超える過剰な添加を行ってもこれらの効果は飽和する。このため、Ｂを添加する場合にはその添加量を０．０００３〜０．００３％とする。また、Ｂを添加する場合には、Ｂ／Ｎを重量比で０．５〜０．８とする。Ｂ／Ｎが重量比で０．５未満ではＢＮが十分に析出せず、前述したＢＮ析出の効果が得られない。一方、Ｂ／Ｎが重量比で０．８を超えるとＢがＮに対して過剰となり、Ｂが結晶粒界に編析して固溶Ｃの粒界への編析を阻害し、鋼板の時効性の劣化を招く。
【００３０】
Ｎｂ：０．０２１〜０．０５０％、Ｎｂ／Ｃが重量比で７．７超
Ｎｂは、鋼中のＣをＮｂＣとして析出させ、鋼板を非時効として時効性を向上する効果を有する。このような効果を発揮させるためにはＮｂを０．０２１〜０．０５０％添加する必要がある。また、Ｎｂを添加する場合には、Ｎｂ／Ｃを重量比で７．７超とする。ＮｂとＣにこのような関係を満足させることにより、上述した効果を発揮させることができる。
【００３１】
なお、特性に悪影響をおよぼさない範囲で、上記以外の元素を添加してもよい。
【００３２】
２．製造条件
本発明においては、上記化学成分を有する鋼の連続鋳造スラブを調整し、前記スラブを粗圧延して粗バーとなし、次いで、前記粗バーを仕上圧延して熱間圧延鋼帯するにあたり、鋼帯の長手方向の全長および幅方向の全幅にわたり、仕上圧延出側温度がＡｒ３変態点以上９２０℃以下となり、かつ、鋼帯の幅方向中央部での仕上圧延出側温度の、鋼帯の長手方向の全長にわたる変化が３０℃以下となり、かつ、鋼帯の長手方向全長にわたり、鋼帯の幅方向中央部とエッジ部での仕上圧延出側温度の差２０℃以下になるように仕上圧延を行い、得られた熱延鋼帯を５４０〜６８０℃の温度でコイルに巻き取り、次いで酸洗した後、冷間圧延し、焼鈍し、二次圧延し、板厚を０．１５ｍｍ以下とする。
【００３３】
転炉溶製後の連続鋳造スラブは、再加熱することなく、または、スラブを一旦冷却してから加熱炉にて再加熱した後に、粗圧延して粗バーとする。スラブを再加熱してから粗圧延する場合、スラブの冷却温度および加熱温度は、冷延鋼帯の特性には影響をおよぼさないため、特に限定されない。
【００３４】
粗バーを仕上圧延して熱延鋼帯とするにあたり、鋼帯の幅方向中央部での仕上圧延出側温度の、鋼帯の長手方向の全長にわたる変化ΔＦＴＣが３０℃以下となるように仕上圧延を行うのは、図１に示したように、高速製缶におけるジャミング発生頻度を、実製缶において操業に支障をきたさないレベルまで抑えることができるからである。また、鋼帯の長手方向全長にわたり、鋼帯の幅方向中央部とエッジ部での仕上圧延出側温度の差ΔＦＴＥが２０℃以下になるように仕上圧延を行うのは、図２に示したように、ジャミング発生頻度をさらに低く抑制することができるからである。より好ましいΔＦＴＣとΔＦＴＥの値は、それぞれ２０℃以下、１５℃以下である。
【００３５】
仕上圧延出側温度ＦＴを、熱延鋼帯の長手方向の全長および全幅にわたってＡｒ３変態点以上９２０℃以下としたのは、仕上圧延出側温度ＦＴがＡｒ３変態点未満になると、加工歪みの残存するフェライト相の結晶粒が仕上圧延以降で粗大に粒成長して熱延鋼帯の結晶粒が混粒となり、鋼帯の不均一性が増大することでジャミング発生頻度が高まってしまい、９２０℃を超えると図３に示すようにスケール性欠陥により鋼帯の表面性状の劣化が著しいからである。図３は、仕上圧延出側温度ＦＴと、得られた熱延鋼帯表面に生じたスケール性欠陥の程度との関係を示すグラフである。図３より、仕上圧延出側温度ＦＴが９２０℃を超えるとスケール性欠陥により鋼帯の表面性状の劣化が顕著となることがわかる。
【００３６】
熱延鋼帯の仕上板厚を２．４ｍｍ以下とする場合には、ΔＦＴＣおよびΔＦＴＥを上記の範囲内とするために、上記化学成分を有する鋼スラブを粗圧延して粗バーとするにあたり、Ａｒ３変態点以上の温度域において圧下率７０％以上で粗圧延を行い、次いで前記粗バーの平坦度を矯正し、平坦度矯正された前記粗バーに対し、熱間仕上圧延機の入側において、エッジヒーターによるエッジ部のみの加熱と、誘導加熱装置による幅方向全体の加熱とを行うことによって、粗バーの仕上圧延入側温度を調整することが好ましい。
【００３７】
粗圧延をオーステナイト単相域であるＡｒ３変態点以上の温度域において７０％以上の圧下率で行うのは、オーステナイトの動的再結晶により、粗圧延後の組織の細粒化を図るためである。連続鋳造スラブは粗大な凝固組織を有しており、また、再加熱されたスラブも粗大なオーステナイト粒を呈しており、そのような組織のまま仕上圧延した場合には、仕上圧延後の熱延鋼帯のフェライト粒も過度に粗大化し不均一な組織となってしまう。このため、上記のように粗圧延を行うことでオーステナイト粒の細粒化をはかるとともに仕上圧延前の組織を均一化し、仕上圧延後の熱延鋼帯の組織を粒径の均一な整粒組織とする。
【００３８】
この場合の粗圧延は、スラブから粗バーにする過程での総圧下率が７０％以上であれば、連続圧延、リバース圧延等の複数パスの圧延であってもかまわない。また、粗圧延後の粗バー厚みが２０ｍｍ未満では温度低下が大きくなり後工程での粗バー全体加熱時の昇温量を大きくする必要が生じ、一方、粗圧延後の粗バー厚みが６０ｍｍ超では均一な温度分布とするために粗バー全体加熱時間を長くとる必要が生じるため、粗圧延後の粗バー厚は２０ｍｍ以上６０ｍｍ以下とすることが好ましい。
【００３９】
次いで、粗圧延後の粗バーの平坦度を矯正するのは、粗バーの平坦度が劣っていると、その後のエッジヒーター加熱および粗バー全体加熱の際に、表裏面、幅方向、長手方向に均一に加熱されずに、粗バーの温度分布が不均一となり、仕上圧延後の組織が不均一となるためである。粗バーの平坦度矯正を行うための装置は、特に限定されるものではなく、通常のレベラー等を用いることができる。
【００４０】
以上のようにして平坦度を矯正された粗バーに対し、エッジヒーターによるエッジ部のみの加熱と、誘導加熱装置による幅方向全体の加熱とを行い、粗バーの仕上圧延入側温度を調整することにより、仕上圧延出側温度のΔＦＴＣおよびΔＦＴＥを上記の範囲内とすることができる。なお、ここで幅方向全体の加熱を誘導加熱装置で行うのは、誘導加熱方式は、制御応答性が良好で、非接触で短時間での急速な加熱が可能なためである。
【００４１】
図４は、０．００３％のＣを含有する鋼の粗バーを板厚２．４ｍｍに仕上圧延した場合の熱延鋼帯長手方向各部における仕上圧延出側温度の変動を、エッジヒーターによる粗バーのエッジ部のみの加熱および粗バーの幅方向全体の加熱の双方を行った場合、エッジヒーターにより粗バーのエッジ部のみの加熱を行った場合、および加熱を行わない場合について示したグラフである。図４に示すように、熱延鋼帯の仕上圧延板厚を２．４ｍｍ以下とする場合、仕上圧延出側温度のΔＦＴＣおよびΔＦＴＥを上記の範囲内とするためには、エッジヒーターによる粗バーのエッジ部の加熱とあわせて、幅方向全体の加熱を行うことが必須である。
【００４２】
さらに、ΔＦＴＣおよびΔＦＴＥをより正確に制御するための方法としては、粗バーの少なくとも長手方向先端部の幅方向全体を加熱し、先端部の表面温度を４５℃以上昇温させることが有効である。
【００４３】
また、ΔＦＴＣおよびΔＦＴＥを制御する方法として、複数の粗バーを接合して仕上圧延する熱延連続化プロセスによる方法を用いることもできる。ただし、この方法は長大な設備を有するため製造コストの大幅な増大を招く場合もあり、必ずしも好ましくない。
【００４４】
以上のようにして仕上圧延された熱延鋼帯は５４０〜６８０℃で巻き取る。
仕上圧延後の巻取温度５４０℃未満では熱延鋼帯の粒成長が不十分となり、結晶組織が不均一となる。また、固溶Ｎが増大して過度の強度上昇を招く場合もある。一方、巻取温度が６８０℃を超えると熱延鋼帯の組織の一部が過度に粒成長し、粗大粒が発生し混粒となりやすく、ΔＦＴＣおよびΔＦＴＥを本発明の限定範囲にした効果が損なわれる。また、酸洗性が低下し、表面性状が劣化する。これらのことから、巻取温度は５４０〜６８０℃に限定する。より好ましい巻取温度の範囲は５６０〜６５０℃である。
【００４５】
その後、熱延鋼帯を酸洗、冷間圧延した後、焼鈍し、二次圧延する。
酸洗は、熱延鋼帯表面に生成した酸化物を除去する工程であり、この目的を達成しうる限り、広く行われている塩酸酸洗法、硫酸酸洗法等のいかなる方法も採用することができる。
冷延率は、３ピース缶用冷延鋼帯の最終製品板厚に応じて選択することができる。
焼鈍は、バッチ焼鈍、連続焼鈍のいずれも採用可能であるが、生産性の観点から連続焼鈍が好ましい。焼鈍温度は再結晶温度以上とすることが好ましい。
焼鈍後の鋼板は、二次圧延により０．１５ｍｍ以下の所定の板厚に仕上げる。本発明は、近年のゲージダウンされた鋼板で顕在化する高速製缶での不具合を回避することができる３ピース缶用冷延鋼帯を対象としているため、最終製品板厚を０．１５ｍｍ以下に限定する。二次圧延率は、１０％未満では形状制御が困難であり、３５％以上では調質圧延の負荷が増大する上、過度の強度上昇によりロールフォーミング加工での負荷が増大することから、１０％以上３５％以下とすることが好ましい。
【００４６】
その後、錫めっき、極薄錫めっき、錫−ニッケルめっき、ニッケルめっき、クロムめっき等の各種表面処理が施される。また、フィルムラミネート鋼板、プレコート鋼板の下地鋼板として用いる場合には、電解クロム酸処理鋼板すなわちＴＦＳが加工密着性の観点から最も望ましい。これらの表面処理鋼板は、鋼板単独のまま、あるいはポリエステル等の樹脂フィルムをラミネートしたフィルムラミネート鋼板、エポキシ等の塗料をコーティングしたプレコート鋼板としても使用することができる。さらに、必要に応じてこれらの鋼板に塗装、印刷等を行うことができる。
【００４７】
【実施例】
表１に示す化学成分を有する鋼を転炉溶製後に連続鋳造によりスラブとし、表２に示す粗圧延圧下率で粗圧延して粗バーとし、次いで、表２に示す粗バーの加熱条件、ΔＦＴＣ、ΔＦＴＥ、および熱延仕上厚の条件で仕上圧延を行って熱延鋼帯とし、６２０℃で巻き取った。その後、目標板厚に応じた圧下率で冷延し、均熱温度７５０℃の連続焼鈍を行い、１５％の圧下率で二次圧延して、表２に示す製品板厚の冷延鋼帯を得た。
次いで、得られた冷延鋼帯に電解クロム酸処理を施し、ＴＦＳとした後に、ポリエステルフィルムをラミネートした。
【００４８】
以上のようにして得られた鋼帯から、１缶分の素材に相当する所定サイズの長方形ブランクにせん断し、線速度１００ｍ／ｍｉｎの高速製缶に相当する条件でロールフォーム加工、ブランク搬送を行うことが可能な実験機によって、ジャミングの発生頻度を評価した。この際、ロールフォーム加工は、鋼帯の圧延方向が缶胴の周方向と直角になるようにした。ジャミング発生頻度の評価結果を表２に併せて示す
【００４９】
【表１】
【表２】
表２より、本発明例の冷延鋼帯では、いずれの場合もジャミング発生頻度が極めて低く抑えられており、高速製缶に適した特性の３ピース缶用冷延鋼帯が得られていることがわかる。これに対して、比較例では、ΔＦＴＣ、ΔＦＴＥが本発明の範囲を超えているため、いずれの場合もジャミング発生頻度が操業に支障をきたすレベルとなっており、高速製缶に適した特性を得ることができなかった。
【００５２】
【発明の効果】
以上のように、本発明によれば、近年のゲージダウンされた鋼板を用いた３ピース缶の高速製缶に適した３ピース缶用冷延鋼帯を得ることができる。また、鋼帯ロット毎でのロールフォーミング装置の条件設定の変更頻度も少なくて済む。これにより、ゲージダウンした素材を用いることによる素材コスト削減のメリット、高速製缶による生産性の向上によるメリット、ジャミング発生頻度の低減による操業の安定性のメリット等により、缶体の一層のコストダウンが可能になる。
【図面の簡単な説明】
【図１】０．００３ｗｔ％のＣを含有する鋼を熱間圧延した際の、熱延鋼帯の幅方向中央部での仕上圧延出側温度の鋼帯全長にわたる間の変化ΔＦＴＣと、その熱延鋼帯から得た板厚０．１５ｍｍのＤＲ材である３ピース缶用冷延鋼帯を用いて、線速度１００ｍ／ｍｉｎの高速製缶に相当する条件で実験室的に評価されたジャミング発生頻度との関係を示したグラフ。
【図２】図１のグラフに示した熱延鋼帯のうちΔＦＴＣが３０℃であるものについて、鋼帯の幅方向中央部とエッジ部での仕上圧延出側温度の差ΔＦＴＥと、その熱延鋼帯から得られた３ピース缶用冷延鋼帯のジャミング発生頻度との関係を示したグラフ。
【図３】仕上圧延温度ＦＴと、得られた熱延鋼帯表面に生じたスケール性欠陥の程度との関係を示すグラフ。
【図４】０．００３％のＣを含有する鋼の粗バーを板厚２．４ｍｍに仕上圧延した場合の熱延鋼帯長手方向各部における仕上圧延出側温度の変動を、エッジヒーターによる粗バーのエッジ部のみの加熱および粗バーの幅方向全体の加熱の双方を行った場合、エッジヒーターにより粗バーのエッジ部のみの加熱を行った場合、および加熱を行わない場合について示したグラフ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a cold rolled steel strip for a three-piece can suitable for high-speed can manufacturing.
[0002]
[Prior art]
For three-piece cans used for food cans and beverage cans, hot-rolled steel strips are pickled, cold-rolled, annealed, and then subjected to temper rolling or secondary rolling to form cold-rolled steel strips. Later, the surface of the steel strip was tin-plated, the surface was nickel-plated, tin-plated, the surface was subjected to electrolytic chromic acid treatment (tin-free steel or TFS), and an organic resin film was laminated to them Surface-treated steel sheets such as steel are used. (Hereinafter, the steel sheet for three-piece cans or the cold-rolled steel sheet for three-piece cans will be described including those subjected to these surface treatments.)
[0003]
The three-piece can is composed of a can body, a lid, and a bottom member. The steel plate for a three-piece can is used as a material for the can body. The can body is coated, printed, or laminated with a film on the cut plate or coil of the steel plate for a three-piece can, and then sheared into a rectangular blank of a predetermined size corresponding to the material of one can, and the tube is formed by roll forming. It is manufactured by rounding into a shape, overlapping the end portions with a predetermined width, and joining the portions by a method such as wire seam welding to form a cylindrical shape.
[0004]
By the way, in recent years, the gauge down of a steel plate for a three-piece can is strongly demanded from the viewpoint of reducing the weight of the can body and reducing the material cost, and the plate thickness has become thinner than before. As a gauge-down steel plate, DR material manufactured by a method of performing secondary rolling after annealing is used as the most economical steel plate. In addition, from the viewpoint of manufacturing cost reduction, the speed of can manufacturing is progressing.
[0005]
In such a high-speed can made of a thin gauge material, a problem called so-called jamming, in which a roll-formed blank is clogged during conveyance, has become apparent. That is, in high-speed cans, it is necessary to transport a roll-formed blank at a high speed in the welding machine, but in wire seam welding, the roll-formed blank is precisely overlapped to a predetermined width. The formed blank is transported while being restrained by a transport guide that is set very accurately. At this time, when the shape of the roll-formed blank, that is, the winding width, the twist, or the like fluctuates beyond an allowable range, jamming occurs in a precisely set conveyance guide. This phenomenon is a defect that has become apparent for the first time as the thickness of the cold rolled steel strip for a three-piece can is gauged down and the welding speed is increased.
[0006]
As a technique relating to a steel plate for a welding can body suitable for high-speed welding, for example, there is one disclosed in Japanese Patent Laid-Open No. 7-109527 (hereinafter referred to as a prior document). The technique described in this prior document is based on the technical idea of ensuring high-speed weldability by suppressing lap escape in high-speed welding.
[0007]
[Problems to be solved by the invention]
However, such lap relief often occurs due to the setting of the welding machine used rather than the steel plate characteristics, and is further increased in speed (linear speed of about 100 m / min) compared to the time when the prior literature was disclosed. However, the above-mentioned problems cannot be solved by the precise setting of high-speed welding machines in recent years, and the above-mentioned problems are not solved.
[0008]
The present invention has been made in view of such circumstances, and manufacture of a cold rolled steel strip for a three-piece can that does not cause defects such as jamming during can making even if the gauge is reduced and the welding speed is increased. It aims to provide a method.
[0009]
[Means for Solving the Problems]
The inventors of the present invention have made extensive studies on a method of manufacturing a cold rolled steel strip for a three-piece can suitable for high-speed welding. As a result, it has been found that the occurrence of jamming in a high-speed can is closely related to the production conditions of the hot-rolled steel strip, particularly the finish rolling exit temperature.
[0010]
As described above, the can body of a 3-piece can is coated, printed, or laminated on a cut plate or coil of a steel plate for a 3-piece can, and then sheared into a rectangular blank of a size corresponding to the material for one can. However, it is manufactured by rolling into a cylindrical shape by roll forming, overlapping the rounded ends with a predetermined width, and joining the portions by a method such as wire seam welding to form a cylindrical shape. The roll forming conditions are finely adjusted for each material lot so that the roll width of the blank after roll forming becomes constant from the viewpoint of jamming suppression described above. However, as the plate thickness decreases, the winding width after roll forming is less likely to be constant, and fluctuations in the winding width are extremely likely to occur with the recent reduction in the thickness of the material. In recent high-speed cans, the roll forming winding width accuracy required to prevent jamming is very strict. Therefore, it is considered that the allowable range of non-uniform winding width where jamming does not occur is extremely small, and jamming is very likely to occur.
[0011]
On the other hand, as the gauge of the three-piece can steel plate progresses and the final product thickness decreases, it is necessary to reduce the thickness of the hot rolled finish plate in order to reduce the cold rolling load. Due to such thinning of the hot-rolled steel strip, heat dissipation during hot rolling is increased, and the finish rolling exit temperature FT is likely to be non-uniform in the longitudinal direction and the width direction of the hot-rolled steel strip. . Such non-uniformity of FT leads to non-uniform characteristics of the hot-rolled steel strip. The fact that the frequency of jamming is related to the production conditions of the hot-rolled steel strip is thought to be due to the influence of the non-uniform properties of the hot-rolled steel strip.
[0012]
Conventionally, simply FT to Ar3It has been considered that the properties of the hot-rolled steel strip can be made relatively uniform if finish rolling is finished at the transformation point or higher, that is, in the austenite single-phase region, and in fact, the can-making speed is relatively low. In this case, the allowable range of the winding width was relatively wide, and these conditions were sufficient. However, in today's high-speed cans made of gauge-down materials, the winding width tends to be non-uniform and the allowable range of the winding width is extremely narrow. It is necessary to make the properties of the steel strip uniform.
[0013]
Therefore, the present inventors further examined the relationship between the finish rolling exit temperature of the hot-rolled steel strip and the jamming occurrence frequency in order to obtain the FT regulation conditions that enable high-speed can production of the gauge-down material. As a result, the relationship between FIG. 1 and FIG. 2 was found.
FIG. 1 shows the change ΔFTC between the length of the steel strip at the finish rolling at the center in the width direction of the hot-rolled steel strip when the steel containing 0.003 wt% C is hot-rolled, and Using a cold rolled steel strip for a three-piece can, which is a DR material having a thickness of 0.15 mm obtained from a hot rolled steel strip, it was evaluated in the laboratory under conditions equivalent to a high speed can with a linear velocity of 100 m / min. It is the graph which showed the relationship with the jamming occurrence frequency. At this time, the roll forming process was performed such that the rolling direction of the steel strip was perpendicular to the circumferential direction of the can body. As shown in FIG. 1, jamming that does not hinder the operation in the actual can by making the change ΔFTC between the entire length of the steel strip in the width direction center of the steel strip over the entire length of the steel strip to 30 ° C. or less. It can be the frequency of occurrence.
[0014]
Moreover, FIG. 2 shows the maximum value of the difference ΔFTE in the finish rolling exit temperature at the center and the width in the width direction of the steel strip, and the heat of the hot-rolled steel strip having ΔFTC of 30 ° C. It is the graph which showed the relationship with the jamming occurrence frequency of the cold rolled steel strip for 3 piece cans obtained from the rolled steel strip in the same manner as described above. As shown in FIG. 2, over the entire length in the longitudinal direction of the steel strip, the difference ΔFTE in the finish rolling exit temperature between the center portion in the width direction of the steel strip and the edge portion is set to 20 ° C. or less, so that the actual can can be operated. It is possible to set the frequency of jamming so as not to hinder.
[0015]
That is, for the occurrence of jamming, the present inventors have found that the change ΔFTC between the finish rolling temperature at the center in the width direction of the hot-rolled steel strip over the entire length of the steel strip and the hot-rolled steel strip for jamming. The difference ΔFTE between the finish rolling exit temperature at the center in the width direction and the finish rolling exit temperature at the edge in the width direction has an influence over the entire length in the longitudinal direction, and high speed is achieved by setting these values within a predetermined range. It has been newly found that the occurrence frequency of jamming in cans can be suppressed.
[0016]
The present invention has been made on the basis of the above findings, and the following (1) to (1)(3)I will provide a.
(1)% by weight, C: 0.0040% or less, Si: 0.05% or less, Mn: 0.1 to 0.7%, P: 0.05% or less, S: 0.03% or less, sol. Al: 0.02-0.12%, N: 0.0035% or lessThe balance consists of Fe and inevitable impuritiesAdjust the continuous casting slab,
The slabAr 3 In the temperature range above the transformation point, the rolling reduction is 70% or more.Rough rolling and rough bars and nothing,
Next, the flatness of the coarse bar was corrected, and the flatness was corrected.In finish rolling the rough bar to form a hot-rolled steel strip,On the entry side of the finish rolling mill, by adjusting only the edge part by the edge heater and heating the entire width direction by the induction heating device, the finish rolling entry side temperature of the rough bar is adjusted,
Over the entire length in the longitudinal direction and the entire width in the width direction of the steel strip, the finish rolling exit temperature is Ar.3The transformation point is 920 ° C. or higher,
And the change over the entire length in the longitudinal direction of the steel strip of the finish rolling outlet temperature at the center in the width direction of the steel strip is 30 ° C or less,
And over the entire length in the longitudinal direction of the steel strip, the difference in the finish rolling temperature at the center and the edge in the width direction of the steel strip is 20 ° C. or less.And the finishing plate thickness is 2.4mm or lessFinish rolling,
The obtained hot-rolled steel strip is wound around a coil at a temperature of 540 to 680 ° C.,
Next, after pickling, cold rolling, annealing, secondary rolling, and a sheet thickness of 0.15 mm or less, the manufacturing method of the cold rolled steel strip for 3 piece cans characterized by the above-mentioned.
[0017]
(2) The continuous cast slab is further characterized by containing, by weight, B: 0.0003 to 0.003%, and B / N is 0.5 to 0.8 by weight. The manufacturing method of the cold rolled steel strip for 3 piece cans as described in said (1).
[0018]
(3) The continuous cast slab further contains, by weight, Nb: 0.021 to 0.050%, and Nb / C is more than 7.7 by weight. The manufacturing method of the cold rolled steel strip for 3 piece cans as described in 1) or (2).
[0020]
The roll forming process may be performed in a case where the rolling direction of the steel strip is a direction parallel to the circumferential direction of the can body or a direction perpendicular to the can body. Although it is necessary to adjust, when the above-described ΔFTC and ΔFTE are controlled, there is no influence of the direction on the jamming occurrence frequency.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the manufacturing method of the cold-rolled steel strip according to the present invention will be specifically described by dividing it into chemical components of the continuously cast slab and manufacturing conditions.
1. Chemical composition
The chemical components of the continuously cast slab in the present invention are, by weight, C: 0.0040% or less, Si: 0.05% or less, Mn: 0.1 to 0.7%, P: 0.05% or less, S: 0.03% or less, sol. Al: 0.02 to 0.12%, N: 0.0035% or less is contained. Moreover, in order to improve the structure uniformity and hardenability of steel, in addition to the above chemical components, B: 0.0003 to 0.003% is contained, and B / N is 0 by weight. .5 to 0.8. Furthermore, when improving the aging property of steel, in addition to any one of the chemical components described above, Nb: 0.021 to 0.050% is contained, and Nb / C exceeds 7.7 by weight. And Hereinafter, these reasons for limitation will be described.
[0022]
C: 0.0040% or less
C is an element effective for adjusting the strength of the steel sheet to a desired level. When the C content exceeds 0.0040%, the steel sheet strength is excessively increased by secondary rolling performed as a gauge-down steel plate manufacturing method, and the load in roll forming is increased. To do.
[0023]
Si: 0.05% or less
Si is an element that remains in the steel as an impurity component even when not intentionally added, embrittles the steel sheet, and deteriorates the corrosion resistance. In addition, when the steel sheet is subjected to surface treatment by electroplating. It also has an adverse effect on metal electrodeposition. Since these problems become significant when the Si content exceeds 0.05%, the Si content is set to 0.05% or less.
[0024]
Mn: 0.1 to 0.7%
Mn is an important element that plays a role of supplementing strengthening by C as a solid solution strengthening element while preventing hot cracking of the slab by precipitating S in the steel as MnS. In the continuous cast slab in the present invention, Mn is 0.1% or more in order to precipitate and fix S. On the other hand, the addition of a large amount of Mn is effective in securing the strength of the material that can compensate for the strength of the can body, which is reduced by the gauge down, but excessive increase in strength increases the load in roll forming, so it is 0.7% or less.
[0025]
P: 0.05% or less
P is an element that is knitted into the ferrite grain boundary and embrittles the grain boundary, and its content is preferably as small as possible. Also, since P has a greater strengthening ability than Mn, adding a large amount of P is effective in securing the strength of the material that can compensate for the strength of the can, which is reduced by gauge down, but an excessive increase in strength is a burden in roll forming processing. To increase. Considering these, the P content is set to 0.05% or less.
[0026]
S: 0.03% or less
S is preferably as small as possible from the viewpoint of preventing hot cracking of the slab, and is 0.03% or less.
[0027]
sol. Al: 0.02 to 0.12%
Since Al combines with N in steel and precipitates as AlN, it is an effective element for adjusting the amount of solute N in steel. In order to exert such effects, sol. Al content shall be 0.02% or more. On the other hand, if a large amount of Al is added, the surface treatment by electroplating on the steel sheet has an adverse effect on the metal electrodeposition, so the sol. Al content shall be 0.12% or less.
[0028]
N: 0.0035% or less
N is an element effective for adjusting the strength of the steel sheet by dissolving in an interstitial form in the same manner as C. However, if the amount of N exceeds 0.0035%, the amount of solid solution N increases excessively, leading to deterioration of aging, and the strength of the steel sheet increases excessively, increasing the load in roll forming. .0035% or less.
[0029]
B: 0.0003 to 0.003%, and B / N is 0.5 to 0.8 by weight ratio
B has the effect of further increasing the uniformity of the structure in the width direction and the longitudinal direction of the hot-rolled steel strip after winding by precipitating N in the steel as BN before becoming AlN, and by reducing C to an extremely low level. It has the effect of supplementing the hardenability of the welded portion, and is added when these effects are required. In order to exhibit these effects, 0.0003% or more of addition is necessary, but even if excessive addition exceeding 0.003% is performed, these effects are saturated. For this reason, when adding B, the addition amount shall be 0.0003 to 0.003%. Moreover, when adding B, B / N shall be 0.5-0.8 by weight ratio. When B / N is less than 0.5 by weight, BN does not sufficiently precipitate, and the above-described BN precipitation effect cannot be obtained. On the other hand, when B / N exceeds 0.8 by weight, B becomes excessive with respect to N, and B is knitted to the crystal grain boundary to inhibit crystallization of solute C to the grain boundary. It causes deterioration of aging.
[0030]
Nb: 0.021 to 0.050%, Nb / C exceeds 7.7 by weight
Nb has the effect of precipitating C in the steel as NbC and improving the aging property by making the steel plate non-aging. In order to exert such an effect, it is necessary to add 0.021 to 0.050% of Nb. When Nb is added, Nb / C is made to exceed 7.7 by weight. By satisfying such a relationship between Nb and C, the above-described effects can be exhibited.
[0031]
In addition, elements other than those described above may be added as long as the characteristics are not adversely affected.
[0032]
2. Manufacturing conditions
In the present invention, by adjusting a continuous casting slab of steel having the above chemical components, the slab is roughly rolled to form a rough bar, and then the rough bar is finish-rolled to form a hot rolled steel strip. The finish rolling exit temperature is Ar over the entire length in the longitudinal direction of the belt and the entire width in the width direction.3The transformation temperature is not less than 920 ° C., and the change in the finish rolling outlet temperature at the center in the width direction of the steel strip is 30 ° C. or less over the entire length in the longitudinal direction of the steel strip. The finish rolling is performed so that the difference in finish rolling temperature at the center portion and the edge portion in the width direction of the steel strip is 20 ° C. or less, and the obtained hot rolled steel strip is wound around a coil at a temperature of 540 to 680 ° C. And then pickling, cold rolling, annealing, and secondary rolling to a thickness of 0.15 mm or less.
[0033]
The continuous cast slab after the melting of the converter is subjected to rough rolling without reheating or after the slab is once cooled and then reheated in a heating furnace to form a rough bar. In the case of rough rolling after reheating the slab, the cooling temperature and heating temperature of the slab are not particularly limited because they do not affect the properties of the cold-rolled steel strip.
[0034]
When the rough bar is finish-rolled into a hot-rolled steel strip, the finish rolling temperature at the center in the width direction of the steel strip is finished so that the change ΔFTC over the entire length in the longitudinal direction of the steel strip is 30 ° C. or less. As shown in FIG. 1, rolling is performed because the frequency of jamming in a high-speed can can be suppressed to a level that does not hinder the operation in the actual can. In addition, the finish rolling is performed so that the difference ΔFTE in the finish rolling outlet side temperature at the central portion and the edge portion in the width direction of the steel strip is 20 ° C. or less over the entire length in the longitudinal direction of the steel strip, as shown in FIG. This is because the jamming occurrence frequency can be further reduced. More preferable values of ΔFTC and ΔFTE are 20 ° C. or less and 15 ° C. or less, respectively.
[0035]
The finish rolling exit temperature FT is set to Ar over the entire length and width in the longitudinal direction of the hot-rolled steel strip.3The reason for setting the transformation point to 920 ° C. is that the finish rolling exit temperature FT is Ar3When the transformation point is below, the ferrite phase crystal grains with residual work strain grow coarsely after finish rolling, and the hot rolled steel strip crystal grains become mixed, increasing the non-uniformity of the steel strip. This is because the frequency of jamming increases, and when the temperature exceeds 920 ° C., the surface property of the steel strip is significantly deteriorated due to scale defects as shown in FIG. FIG. 3 is a graph showing the relationship between the finish rolling exit temperature FT and the degree of scale defects generated on the surface of the obtained hot-rolled steel strip. FIG. 3 shows that when the finish rolling exit temperature FT exceeds 920 ° C., the deterioration of the surface properties of the steel strip becomes significant due to the scale defect.
[0036]
When the finished sheet thickness of the hot-rolled steel strip is 2.4 mm or less, in order to make ΔFTC and ΔFTE within the above range, the steel slab having the above chemical components is roughly rolled into a rough bar. Ar3Rough rolling is performed at a reduction rate of 70% or more in a temperature range equal to or higher than the transformation point, and then the flatness of the rough bar is corrected. It is preferable to adjust the finishing rolling entry temperature of the rough bar by heating only the edge portion with an edge heater and heating the entire width direction with an induction heating device.
[0037]
Rough rolling is an austenite single-phase region Ar3The reason why the reduction is carried out at a reduction rate of 70% or more in the temperature range above the transformation point is to refine the structure after rough rolling by dynamic recrystallization of austenite. Continuously cast slabs have a coarse solidified structure, and reheated slabs also show coarse austenite grains. When such a structure is finished and rolled, hot rolling after finish rolling is performed. The ferrite grains of the steel strip also become excessively coarse and become a non-uniform structure. For this reason, the austenite grains are refined by rough rolling as described above, and the structure before finish rolling is made uniform, and the structure of the hot-rolled steel strip after finish rolling is sized with a uniform grain size. And
[0038]
The rough rolling in this case may be multi-pass rolling such as continuous rolling and reverse rolling as long as the total rolling reduction in the process of converting the slab into the rough bar is 70% or more. In addition, if the thickness of the rough bar after rough rolling is less than 20 mm, the temperature drop is large, and it is necessary to increase the temperature rise during heating of the entire rough bar in the subsequent process, while the thickness of the rough bar after rough rolling exceeds 60 mm. Then, in order to obtain a uniform temperature distribution, it is necessary to take a long heating time for the entire rough bar. Therefore, the thickness of the rough bar after rough rolling is preferably 20 mm or more and 60 mm or less.
[0039]
Next, to correct the flatness of the rough bar after rough rolling, if the flatness of the rough bar is inferior, the front and back surfaces, the width direction, and the longitudinal direction during the subsequent edge heater heating and rough bar heating This is because the temperature distribution of the coarse bar becomes non-uniform and the structure after finish rolling becomes non-uniform. The apparatus for correcting the flatness of the coarse bar is not particularly limited, and a normal leveler or the like can be used.
[0040]
For the rough bar whose flatness has been corrected as described above, only the edge portion is heated by the edge heater and the entire width direction is heated by the induction heating device to adjust the finish rolling entry temperature of the rough bar. Thus, ΔFTC and ΔFTE of the finish rolling outlet temperature can be set within the above range. The reason why the entire width direction is heated by the induction heating device is that the induction heating method has good control response and can be rapidly heated in a short time without contact.
[0041]
FIG. 4 shows the variation in the finish rolling temperature at each part in the longitudinal direction of the hot-rolled steel strip when the rough bar of steel containing 0.003% C is finish-rolled to a sheet thickness of 2.4 mm. This graph shows the case where only the edge portion of the bar and the entire width direction of the coarse bar are heated, the edge portion of the coarse bar is heated by the edge heater, and the case where the heating is not performed. is there. As shown in FIG. 4, when the finish rolled sheet thickness of the hot-rolled steel strip is 2.4 mm or less, in order to keep the ΔFTC and ΔFTE of the finish rolling outlet temperature within the above range, a rough bar by an edge heater is used. In addition to the heating of the edge portion, it is essential to heat the entire width direction.
[0042]
Further, as a method for more accurately controlling ΔFTC and ΔFTE, it is effective to heat at least the entire width direction of the front end portion in the longitudinal direction of the coarse bar and raise the surface temperature of the front end portion by 45 ° C. or more. .
[0043]
Further, as a method for controlling ΔFTC and ΔFTE, a method based on a hot rolling continuous process in which a plurality of rough bars are joined and finish-rolled can be used. However, this method has a long facility and may cause a significant increase in manufacturing cost, and is not always preferable.
[0044]
The hot-rolled steel strip finish-rolled as described above is wound up at 540 to 680 ° C.
If the coiling temperature after finish rolling is less than 540 ° C., the grain growth of the hot-rolled steel strip becomes insufficient and the crystal structure becomes non-uniform. Moreover, the solid solution N may increase to cause an excessive increase in strength. On the other hand, when the coiling temperature exceeds 680 ° C., a part of the structure of the hot-rolled steel strip grows excessively, coarse grains are easily generated and become mixed grains, and the effect of making ΔFTC and ΔFTE within the limited range of the present invention. Damaged. Moreover, pickling property falls and surface properties deteriorate. Therefore, the coiling temperature is limited to 540 to 680 ° C. A more preferable winding temperature range is 560 to 650 ° C.
[0045]
Thereafter, the hot-rolled steel strip is pickled and cold-rolled, and then annealed and secondary-rolled.
Pickling is a process for removing oxides generated on the surface of a hot-rolled steel strip, and any method such as a hydrochloric acid pickling method or a sulfuric acid pickling method that is widely used is adopted as long as this purpose can be achieved. be able to.
The cold rolling rate can be selected according to the final product sheet thickness of the cold rolled steel strip for a three-piece can.
As the annealing, both batch annealing and continuous annealing can be adopted, but continuous annealing is preferable from the viewpoint of productivity. The annealing temperature is preferably not less than the recrystallization temperature.
The steel plate after annealing is finished to a predetermined plate thickness of 0.15 mm or less by secondary rolling. Since the present invention is directed to a cold rolled steel strip for a three-piece can that can avoid problems with high-speed cans that are manifested in steel plates that have been gauged down in recent years, the final product thickness is 0.15 mm or less. Limited to. If the secondary rolling rate is less than 10%, shape control is difficult, and if it is 35% or more, the load of temper rolling increases, and the load in roll forming increases due to an excessive increase in strength. It is preferable to be 35% or less.
[0046]
Thereafter, various surface treatments such as tin plating, ultra-thin tin plating, tin-nickel plating, nickel plating, and chromium plating are performed. Moreover, when using as a base steel plate of a film laminated steel plate or a pre-coated steel plate, an electrolytic chromic acid-treated steel plate, that is, TFS is most desirable from the viewpoint of work adhesion. These surface-treated steel sheets can be used as a steel sheet alone, as a film-laminated steel sheet laminated with a resin film such as polyester, or as a pre-coated steel sheet coated with a paint such as epoxy. Furthermore, painting, printing, etc. can be performed on these steel plates as required.
[0047]
【Example】
Steel having the chemical composition shown in Table 1 is made into a slab by continuous casting after melting in the converter, and is roughly rolled into a rough bar at the rough rolling reduction shown in Table 2, and then the heating conditions for the coarse bar shown in Table 2, Finish rolling was performed under the conditions of ΔFTC, ΔFTE, and hot-rolled finish thickness to obtain a hot-rolled steel strip, which was wound at 620 ° C. Then, it is cold-rolled at a reduction ratio corresponding to the target sheet thickness, subjected to continuous annealing at a soaking temperature of 750 ° C., and secondary-rolled at a reduction ratio of 15%, and the cold-rolled steel strip having the product sheet thickness shown in Table 2 Got.
Next, the obtained cold-rolled steel strip was subjected to electrolytic chromic acid treatment to form TFS, and then a polyester film was laminated.
[0048]
The steel strip obtained as described above is sheared into a rectangular blank of a predetermined size corresponding to the material for one can, and roll foam processing and blank conveyance are performed under the conditions corresponding to a high-speed can made with a linear speed of 100 m / min. The frequency of jamming was evaluated by an experimental machine that can be used. At this time, the roll forming was performed such that the rolling direction of the steel strip was perpendicular to the circumferential direction of the can body. Table 2 also shows the evaluation results of the jamming occurrence frequency.
[0049]
[Table 1]
[Table 2]
From Table 2, in the cold-rolled steel strip of the example of the present invention, the frequency of jamming is suppressed to be extremely low in any case, and a cold-rolled steel strip for three-piece cans having characteristics suitable for high-speed cans is obtained. I understand that. On the other hand, in the comparative example, ΔFTC and ΔFTE exceed the range of the present invention, and in any case, the jamming frequency is at a level that hinders operation, and has characteristics suitable for high-speed cans. Couldn't get.
[0052]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a cold rolled steel strip for a three-piece can suitable for high-speed can-making of a three-piece can using a steel plate that has been gauged down in recent years. Moreover, the frequency of changing the condition setting of the roll forming apparatus for each steel strip lot can be reduced. As a result, the cost of the can body can be further reduced due to the benefits of reducing the material cost by using a gauge-down material, the benefits of improving the productivity of high-speed cans, and the operational stability of reducing the frequency of jamming. Is possible.
[Brief description of the drawings]
FIG. 1 shows the change ΔFTC between the length of the steel strip at the finish rolling at the center in the width direction of a hot-rolled steel strip when the steel containing 0.003 wt% C is hot-rolled, and Using a cold rolled steel strip for a three-piece can, which is a DR material having a thickness of 0.15 mm obtained from a hot rolled steel strip, it was evaluated in the laboratory under conditions equivalent to a high speed can with a linear velocity of 100 m / min. The graph which showed the relationship with jamming occurrence frequency.
FIG. 2 shows the difference ΔFTE in the finish rolling exit temperature between the center portion in the width direction of the steel strip and the edge portion of the hot-rolled steel strip shown in the graph of FIG. The graph which showed the relationship with the jamming occurrence frequency of the cold rolled steel strip for 3 piece cans obtained from the rolled steel strip.
FIG. 3 is a graph showing the relationship between the finish rolling temperature FT and the degree of scale defects generated on the surface of the obtained hot-rolled steel strip.
FIG. 4 shows fluctuations in the finish rolling temperature at each part in the longitudinal direction of the hot rolled steel strip when a rough bar of steel containing 0.003% C is finish-rolled to a thickness of 2.4 mm. The graph which showed the case where only the edge part of a bar and the heating of the whole width direction of a rough bar were performed, the case where only the edge part of a rough bar was heated with the edge heater, and the case where heating was not performed.
Claims (3)
前記スラブをＡｒ ３ 変態点以上の温度域において圧下率７０％以上で粗圧延して粗バーとなし、
次いで前記粗バーの平坦度を矯正し、平坦度の矯正された前記粗バーを仕上圧延して熱延鋼帯とするにあたり、仕上圧延機の入側において、エッジヒーターによるエッジ部のみの加熱と、誘導加熱装置による幅方向全体の加熱とを行うことによって、前記粗バーの仕上圧延入側温度を調整し、
鋼帯の長手方向の全長および幅方向の全幅にわたり、仕上圧延出側温度がＡｒ３変態点以上９２０℃以下となり、
かつ、鋼帯の幅方向中央部での仕上圧延出側温度の、鋼帯の長手方向の全長にわたる変化が３０℃以下となり、
かつ、鋼帯の長手方向全長にわたり、鋼帯の幅方向中央部とエッジ部での仕上圧延出側温度の差が２０℃以下となるように、かつ、仕上板厚が２．４ｍｍ以下となるように仕上圧延を行い、
得られた熱延鋼帯を５４０〜６８０℃の温度でコイルに巻き取り、
次いで酸洗した後、冷間圧延し、焼鈍し、二次圧延し、板厚を０．１５ｍｍ以下とすることを特徴とする３ピース缶用冷延鋼帯の製造方法。C: 0.0040% or less, Si: 0.05% or less, Mn: 0.1-0.7%, P: 0.05% or less, S: 0.03% or less, sol. Al: 0.02 to 0.12%, N: 0.0035% or less , the balance is a continuous cast slab consisting of Fe and inevitable impurities ,
The slab is roughly rolled at a reduction rate of 70% or more in a temperature range of Ar 3 transformation point or more to form a rough bar,
Next, the flatness of the rough bar is corrected, and when the rough bar having the corrected flatness is finish-rolled to form a hot-rolled steel strip, only the edge portion is heated by an edge heater on the entrance side of the finishing mill. , By adjusting the width of the coarse bar finish rolling by performing heating in the entire width direction with an induction heating device,
Over the entire length in the longitudinal direction and the entire width in the width direction of the steel strip, the finish rolling exit temperature is not less than the Ar 3 transformation point and not more than 920 ° C.,
And the change over the entire length in the longitudinal direction of the steel strip of the finish rolling outlet temperature at the center in the width direction of the steel strip is 30 ° C or less,
And over the entire length in the longitudinal direction of the steel strip, the difference in the finish rolling exit temperature at the center portion and the edge portion in the width direction of the steel strip is 20 ° C. or less , and the finished plate thickness is 2.4 mm or less. And finish rolling as
The obtained hot-rolled steel strip is wound around a coil at a temperature of 540 to 680 ° C.,
Next, after pickling, cold rolling, annealing, secondary rolling, and a sheet thickness of 0.15 mm or less, the manufacturing method of the cold rolled steel strip for 3 piece cans characterized by the above-mentioned.
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| JP2000041632A JP4332974B2 (en) | 2000-02-18 | 2000-02-18 | Manufacturing method of cold rolled steel strip for 3-piece can |
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| JP2000041632A JP4332974B2 (en) | 2000-02-18 | 2000-02-18 | Manufacturing method of cold rolled steel strip for 3-piece can |
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|---|---|---|---|
| JP2000041632A Expired - Fee Related JP4332974B2 (en) | 2000-02-18 | 2000-02-18 | Manufacturing method of cold rolled steel strip for 3-piece can |
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| JP5018843B2 (en) * | 2009-08-19 | 2012-09-05 | Ｊｆｅスチール株式会社 | Steel plate for high workability 3-piece welded can and manufacturing method thereof |
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| JP2001234248A (en) | 2001-08-28 |
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