JP3872537B2

JP3872537B2 - Method for producing hot-rolled steel sheet with good surface properties and pickling properties

Info

Publication number: JP3872537B2
Application number: JP06513196A
Authority: JP
Inventors: 隆彰中村; 稔小寺
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1996-02-28
Filing date: 1996-02-28
Publication date: 2007-01-24
Anticipated expiration: 2016-02-28
Also published as: JPH09235622A

Description

【０００１】
【発明の属する技術分野】
本発明は連続熱間圧延設備において、移動する鋼板の先行鋼板後端部と、これに続く後行鋼板先端部を接合し、複数の鋼板を連続して圧延するいわゆる熱延連続化プロセスによる表面性状と酸洗性の良好な熱延鋼板の製造方法に関する。
【０００２】
【従来の技術】
従来の鋼板の連続熱間圧延は、スラブ毎での圧延を行うため鋼板の先端部と後端部は、鋼板が仕上圧延機を出た後に巻取られるまでの間においては、無張力状態のいわゆる、非定常部とならざるを得なかった。このため、この部分に該当する鋼板は擦り傷、形状不良、板幅不良、板厚不良等の鋼板表面品位および形状品位の劣化は避けられなかった。
また、上記形状品位の変化は鋼板の材質についても大きく影響し、冷却時の冷却ムラにより機械的性質（引張特性等）が大きくばらつき、定常部分に比し良好な鋼板が得られなかった。そのため、不良部分の除去により鋼板歩留りの低下と共に、精整通板を必要とする等の作業付加があった。
【０００３】
また材質については、通板性等の操業上の観点からコイル（圧延された鋼板はスラブ単位に粗圧延後はコイルボックス内にて巻かれ、また仕上圧延後は巻取機によって巻取られてコイル状となるので、以下単にコイルと称す）長手方向（圧延方向）で圧延速度が異なるため、単一コイル内であっても圧延温度等の熱延条件が変化し、機械的性質の変動が生じていた。
また、熱延鋼板表面上に発生する黒皮スケールと呼ばれる鉄の酸化被膜（以下単にスケールと称す）についても定常部と非定常部とでは、前記のごとき圧延条件の変化によりその生成形態にも差異が生じていた。
【０００４】
このような状況下において、近年複数の粗圧延後のシートバー（以下、粗バーと称す）を順次接合して、連続して所定の速度で熱間圧延処理する、いわゆる熱延連続化プロセスが試みられている。
この熱延連続化プロセスは、一般に、粗バーを供給する工程、この粗バーの先端と後端を切断する工程、走行しながら先行粗バーの後端部と、後行粗バーの先端部を、各々クランプして突き合わせて接合する工程、複数のスタンドで該圧延用鋼板を所定の圧延スケジュールで、所定のサイズに仕上げる熱間仕上圧延工程、熱間仕上圧延工程を出た鋼板を冷却し巻取る工程、熱間仕上圧延工程と巻取り工程との間にあって、鋼板を所定の重量または長さ単位で切断する走間切断分割工程とから構成されている。
【０００５】
このための粗バーの接合方法としては、各種の提案がなされており、例えば、特開平４−２８８９０６号公報には、先行材と後行材の端面接触領域を幅方向の少なくとも両端部域となるよう切断加工を施し、加熱と搬送速度を調整し両縁部近傍に圧縮応力を発生させて相互に密着させることが開示されており、また、特開平５−１０４１０７号公報では、先行材と後行材の端面幅方向両端部同士を圧延前に熱間溶接した後、幅方向中央の未接合部を圧延によって熱間圧接する方法が提案されている。また、特公平５−６２０３５号公報では、長手方向で先行圧延材の後端部と後行圧延材の先端部を重ね合わせて切断し、切断面に直角に圧縮力を加えることにより、新生面同士の結合領域を拡げスケールの除去なしで両金属板を溶着し、厚み方向で全面接触して強固に結合する方法が提案されている。
【０００６】
一方、発生したスケールの処理法としては、高い加工度の加工に供される鋼板あるいは加工後塗装される鋼板では黒皮スケールの脱スケール処理が施されており、この脱スケール処理法としてはショットブラスト法、酸洗法等があるが、脱スケールの完全化の点から酸洗法が一般に用いられている。
近年酸洗工程のスピード化、酸洗液使用量の低減等が要請されているが、加工性確保のために前述の高温でのコイル巻取を行った熱延鋼板ではスケール厚が厚く、酸への溶解速度もそのスケールの厚さに原因して遅いため、酸洗速度が極端に低下していた。
【０００７】
そこで、酸洗工程での生産能率向上を図った酸洗性に優れた加工用熱延鋼板の製造方法として特公平７−７４３７６号公報の提案がある。この技術は熱間圧延ラインにおいて、粗圧延後の被圧延材に１１００℃以下Ａｒ₃ 点以上の温度域で曲げ加工を施し、かつ上記温度域に１０秒以上保持した後、該被圧延材に仕上圧延を施し、該仕上圧延後の熱延鋼板をただちに２０℃／ｓ以上の冷却速度で冷却して６００℃以下で巻取ることを特徴とし、これに加え粗圧延後の被圧延材に施す曲げ加工が、板厚ｔと曲げ径Ｄの比ｔ／Ｄを０．０１以上とするものである。
【０００８】
【発明が解決しようとする課題】
熱延連続化プロセスについて、その手段は上記のごとく種々の提案がなされているが、鋼板の材質面からの検討については一部なされているのみで、完全なる対策については多くの開発の余地が残されており、従来での鋼板の先・後端部における材質不良部を完全に解消するまでには到っていない。
また、同様に生成スケールの減少対策については熱延連続化プロセスの採用により、その効果を確認することはなされておらず、前記した熱延鋼板でのスケール生成量およびスケールの均一性に多くの問題を残していた。
【０００９】
本発明は工場出荷時のコイル表面の脱スケールを容易に行うことができる熱延鋼板を対象とするもので、本発明対象の熱延鋼板は通常製造される鋼板を全て含むが、特に高Ｓｉ材のＳｉスケールは、熱延鋼板表面上に縞模様を形成し、脱スケール性が悪く、表面性状不良の原因となっていた。
本発明はこのような従来法でのスケール生成量の減少およびコイル内でのスケール生成量のばらつきを解消した表面性状と酸洗性の良好な熱延鋼板の製造方法を提供することを目的とするものである。
【００１０】
【課題を解決するための手段】
本発明は上記課題を解決するためになされたものであって、その手段は下記の通りである。
（１）重量％で、
Ｃ：≦０．２０％
Ｓｉ：≦２．５０％
Ｍｎ：≦２．５％
Ｐ：≦０．０２５％
Ｓ：≦０．０２５％
とし、残部Ｆｅと不可避的不純物からなる鋼片を、１１５０℃以下の温度域で加熱し、粗圧延後にコイルボックス内で粗バーの巻取り、巻戻しにより表面に３％以上の歪みを歪速度０．１（ｓ^-1）以上で付与した後、先行の前記粗バーの後端と後行の前記粗バーの先端を接合し、デスケーリングを行って仕上圧延機へ供給し、熱間仕上圧延することを特徴とする表面性状と酸洗性の良好な熱延鋼板の製造方法。
【００１１】
（２）重量％で、
Ｃ：≦０．２０％
Ｓｉ：≦２．５０％
Ｍｎ：≦２．５％
Ｐ：≦０．０２５％
Ｓ：≦０．０２５％
とし、残部Ｆｅと不可避的不純物からなる鋼片を加熱し、１１５０℃以下の温度域で加熱し、粗圧延後にコイルボックス内で粗バーの巻取り、巻戻しにより表面に３％以上の歪みを歪速度０．１（ｓ^-1）以上で付与した後、先行の前記粗バーの後端と後行の前記粗バーの先端を接合し、０．２ｋｇｆ／ｍｍ^２以上の張力を付与し、かつデスケーリングを行って仕上圧延機へ供給し、熱間仕上圧延することを特徴とする表面性状と酸洗性の良好な熱延鋼板の製造方法。
【００１２】
（３）重量％で、
Ｃ：≦０．２０％
Ｓｉ：≦２．５０％
Ｍｎ：≦２．５％
Ｐ：≦０．０２５％
Ｓ：≦０．０２５％に加え、
Ｎｂ：≦０．０６０％
Ｔｉ：≦０．１００％
Ｖ：≦０．０８０％
Ｃａ：≦０．００６０％のいずれか１種または２種以上を含み、残部Ｆｅと不可避的不純物からなる鋼片を加熱し、粗圧延後にコイルボックス内で粗バーの巻取り、巻戻しにより表面に３％以上の歪みを歪速度０．１（ｓ^-1）以上で付与した後、先行の前記粗バーの後端と後行の前記粗バーの先端を接合し、デスケーリングを行って仕上圧延機へ供給し、熱間仕上圧延することを特徴とする表面性状と酸洗性の良好な熱延鋼板の製造方法。
【００１３】
（４）重量％で、
Ｃ：≦０．２０％
Ｓｉ：≦２．５０％
Ｍｎ：≦２．５％
Ｐ：≦０．０２５％
Ｓ：≦０．０２５％に加え、
Ｎｂ：≦０．０６０％
Ｔｉ：≦０．１００％
Ｖ：≦０．０８０％
Ｃａ：≦０．００６０％のいずれか１種または２種以上を含み、残部Ｆｅと不可避的不純物からなる鋼片を加熱し、粗圧延後にコイルボックス内で粗バーの巻取り、巻戻しにより表面に３％以上の歪みを歪速度０．１（ｓ^-1）以上で付与した後、先行の前記粗バーの後端と後行の前記粗バーの先端を接合し、０．２ｋｇｆ／ｍｍ^２以上の張力を付与し、かつデスケーリングを行って仕上圧延機へ供給し、熱間仕上圧延することを特徴とする表面性状と酸洗性の良好な熱延鋼板の製造方法。
【００１４】
【発明の実施の形態】
本発明は鋼板の圧延を熱延連続化プロセスで行うことを目的とし、それにより従来の圧延で発生していた鋼板の先・後端部での特に表面品位（スケール生成）の劣化を回避すると共に、鋼板定常部を含む鋼板コイル内でのスケール生成量のばらつきを防ぐところに主眼があり、組成としては通常の熱延鋼板に用いられている主要元素を含み、これに加えてその目的に応じ例えば高強度、高靱性、高耐食性等の特性を発揮する元素の添加を行うことができる。
また、鋼種についての制約もなく通常のアルミキルド鋼、またはアルミ−シリコン−キルド鋼等が対象となる。
【００１５】
本発明が対象としている鋼の成分は通常の熱延鋼板として使用されているもので、その好ましい含有限度は以下の通りである。
Ｃは強度を向上するための成分であるが、０．２０ｗｔ％を超えると溶接性や低温靱性が劣化する。従って、その含有量は０．２０ｗｔ％以下である。
Ｓｉは脱酸剤として有効であり、また強度向上の元素でもある。さらには鋼中のフェライトの生成を促進し、炭化物の生成を抑制することにより残留オーステナイトを確保する作用を有する。しかし、その含有量は２．５ｗｔ％を超えるとその効果は飽和し、かえって溶接性の劣化、また鋳造鋳片での割れ発生の原因ともなる。従って、その含有量は２．５０ｗｔ％以下である。
【００１６】
Ｍｎは強度、靱性を向上させるために有効な成分であるが、２．５０ｗｔ％を超えると溶接性が劣化する。従って、その含有量は２．５ｗｔ％以下である。
Ｐは低温靱性を劣化させ、溶接時に高温割れを発生させることがあることから、その含有量は０．０２５ｗｔ％以下とする。ただし、鋼板表面のスケール疵（赤スケール）防止の観点からは０．０１０〜０．０２０％が好ましい。
ＳはＭｎと結合してＡ系介在物を生じて、靱性、延性を劣化させることからその含有量は０．０２５ｗｔ％以下である。
【００１７】
さらに、本発明においては、上記の主要成分組成例に加えて、Ｎｂ，Ｔｉ，Ｖ，Ｃａのうちから選んだ１種または２種以上を含有してもよい。
Ｎｂは微量添加で大幅に強度を上昇させ、かつ、固溶Ｎによる歪時効によって靱性の劣化を防止する好ましい成分であるが、０．０６０ｗｔ％を超えると飽和する。従って、その含有量は０．０６０ｗｔ％以下である。
ＴｉはＮｂと同様、微量添加で大幅に強度を上昇させ、制御圧延との相乗効果により靱性を向上させる好ましい成分であるが、０．１００ｗｔ％を超えると飽和する。従って、その含有量は０．１００ｗｔ％以下である。
Ｖは微量添加で大幅な強度の向上が期待できる成分であるが、０．０８０ｗｔ％を超えて含有するとその効果は飽和し、溶接性が劣化する。従って、上限は０．０８０ｗｔ％である。
Ｃａは介在物の形態制御により、低温靱性、延性に好ましいばかりでなく、セパレーション対策としても好ましい成分である。しかし、０．００６０ｗｔ％を超えて含有すると、溶接性、および靱性の劣化をまねく。従って、上限は０．００６０ｗｔ％である。
【００１８】
前述のように本発明対象の熱延鋼板は通常製造される鋼板を全て含むが、特に高Ｓｉ熱延鋼板のＳｉスケール対策について、その防止効果は大きい。このＳｉスケールの発生は加熱炉での鋼片加熱時にＳｉとＦｅの酸化物（ＦｅＯ＋Ｆｅ₂ ＳｉＯ₄ ）が生成し、粒子間の粒界に入り込み、根を張った状態となり、この結果、熱延鋼板表面上にこれが縞模様となって表れる。このＳｉスケールは脱スケール性が悪く、表面性状不良の原因となっている。
次に、本発明の熱延連続化プロセスを工程順にその特徴部分と、その効果および熱延条件の限定理由について以下に説明する。
【００１９】
図１は本発明を実施するための設備配置の一例を示した図であり、まず、加熱炉でのスラブ加熱であるが、本発明においてはスケール生成量を抑制する意味合いからも、特殊添加元素を添加しない場合は加熱温度を低温の１１５０℃以下とし、１次スケールの発生を極力少なくする。
これは、粗圧延後の粗バー同士の先・後端部を溶接する以前、すなわち粗圧延以降において粗バーを巻取り、コイル状となして保熱を行うコイルボックスを有しているため、いたずらに加熱温度を上昇させる必要がなく、これによって後述するように材質的にも低温加熱による効果を享受できる。
【００２０】
加熱炉から抽出されたスラブは粗バーに圧延され、コイルボックスにてコイル状に巻取られ、通常１０数秒間保熱されてコイルの全長にわたる均一な保熱が行われる（特に粗圧延での圧延先端の局部的な温度低下部は、粗圧延後コイル内に巻込まれることにより復熱し均一な温度となる）。この時の温度低下は１℃／ｓｅｃ以内の極めて微々たる温度しか降下しない。
その後コイルは巻戻されて、その先・後端部は溶接面切断シャーにおいて切断され、切断面が整えられる。このようにコイルボックスにおいては粗バーの巻取り、巻戻しが行われるためコイルに歪加工が加わる。その量は３％以上の表面歪みを歪速度０．１（ｓ^-1）以上で付与することができ、コイル表面のスケールに亀裂が入り、これが起点となり１次スケールの剥離性が向上する。
【００２１】
また、後述するように本発明では、コイルボックス内で巻戻された粗バーは、次工程の走間接合装置により接合され、一体ものとなり仕上圧延機内へ送られるので、コイルボックス内を出た粗バーは、コイルボックスと仕上圧延機間を一定の時間で通過することができ、粗バーには０．２ｋｇｆ／ｍｍ² 以上の張力を均一に加えることができる。
この結果、粗バーの表面状態は全長に亘って均等な状況下となるので、脱スケール面では、コイル内で異なった処置を採ることなく、ほぼ同一な処理条件下でデスケーリングを行うことができる。
【００２２】
溶接面切断シャーにおいて、先・後端部を切断された粗バーは接合台車上の走間接合装置（走間接合装置については特に限定しないので、ここでは特に触れない。また、接合方法についても種々の方法が考えられるが、レーザー溶接方法が好ましい）により先行材の後端部と後行材の先端部が接合され、仕上圧延機で圧延されるため、最初の粗バーの先端部と最後の粗バーの後端部を除いた部分は仕上圧延において圧延端のない圧延ができる。また、仕上圧延機までの間も粗バーには速度の変化がなく一定速度で走行し、コイルにかかる張力も絶えず安定しており、コイル表面の任意の位置における、冷却条件（水量、圧力等）が一定となり、ばらつきのないデスケーリングが行われ、従前のようなスケールムラが発生しない。
さらに、ピンチロール後のシャーにより鋼板接合部を走行切断して巻取機にてコイルを巻取るため、従前コイル先・後端部で発生していたタング状、またはフィッシュテール状の形状不良部分が皆無となる。従って、従前の精整通板による形状不良部分の矯正、および先・後端部分を含んだ形状不良部の切捨てが不必要となり、精整工程の省略、成品歩留りの向上が達成できる。
【００２３】
以上、本発明の設備上での特徴部分の説明とそれによってもたらされる効果についての説明を行ったが、本発明においては従前の工程によって得られる鋼板に比し最も大きな効果の違いは本発明を実施することによって、熱延鋼板表面上のスケール生成を抑制することができ、かつ、生成したスケールが薄くコイル全長にわたって均一な厚みをもつことができることになったものである。それに加えて鋼板の品質特性のばらつき、すなわちコイル内のばらつきが著しく低下し、均一で安定した材質の成品が得られるという効果も有する。
また、本発明においては、コイル内の変動量についても触れたが、これらの値は当然少ない方が好ましい。しかし、従前の圧延法では前述のようにこのばらつきは避け得なかった。
【００２４】
本発明では、最近の鋼板製造技術の急速な進歩に伴い、鋳片での偏析の改善、圧延での制御圧延の向上と相まって熱延連続化プロセスを採用することにより、これらコイル内の材質のばらつきも少なくすることができ、さらには本発明の目的でもあるスケール生成量の変動も極く小さい範囲内に抑制することができるようになったものである。
スケール生成を抑制するために規制した圧延条件等は、連続圧延プロセスの実施によって得られた実績から、その許容範囲を導き出したものである。
この結果によって、同一ロット内ではどの位置に該当する鋼板であっても、その部位を配慮することなく略同一の条件で脱スケール処理を行うことができるようになった。
【００２５】
【実施例】
以下、本発明における前述の効果を実施例によって具体的かつ、詳細に説明する。
本発明は殆ど全ての鋼種に適用できるので３種を選んで鋼板の化学組成を表１に示した。
【００２６】
【表１】

【００２７】
この３種の鋼種から鋳造されたスラブを本発明によって表２に示す条件で鋼板に圧延し、圧延された成品について各鋼種毎に同一ロット（１回の圧延単位で鋼板が接合されて連続圧延されたもの）内からコイル２本（ただし、最先端、最後端コイル以外）をランダムに抽出し、コイル全長から５個所（非定常部に該当する先・後端部および定常部に該当する中央部から均等距離を置いた３個所の部分）から試料を採取した。
【００２８】
【表２】

【００２９】
この試料についてスケールの生成状況の調査をそれぞれ行った。またコイル内での材質特性を表３に示した（本発明ではスケール生成状況に主体があるので、機械的性質についてはその数を減じた）。なお、比較のために従来方法で圧延した鋼板についても同様に表２に圧延条件を表３にスケール生成状況と材質の調査結果を示した。
表３中Δとあるのはコイル内の変動（ばらつき）を示したもので、最大値−最小値で表した。
【００３０】
【表３】

【００３１】
表３から明らかなように、本発明によればスケール生成においてスケール厚みが薄くなっており、コイル内においてもその差が少なく、均一で薄いスケールとなっていることがわかる。
【００３２】
【発明の効果】
本発明によれば、熱間圧延鋼板でのスケール生成量が少なく（薄い）、かつコイル内においてもその厚みに差がなく、例えば酸洗による脱スケール時間が短くて済み、通板速度の増加が可能となり、酸洗性の良好な鋼板が得られるようになった。
【図面の簡単な説明】
【図１】本発明を実施するための設備配置の一例を示す図[0001]
BACKGROUND OF THE INVENTION
In the present invention, in a continuous hot rolling facility, the surface by a so-called hot rolling continuation process in which a leading end of a preceding steel plate of a moving steel plate and a leading end of a subsequent steel plate are joined and a plurality of steel plates are continuously rolled. The present invention relates to a method for producing a hot-rolled steel sheet having good properties and pickling properties.
[0002]
[Prior art]
In conventional continuous hot rolling of steel plates, rolling is performed for each slab, so that the front and rear ends of the steel plates are in a tension-free state until the steel plates are wound after they exit the finish rolling mill. It had to be a so-called unsteady part. For this reason, the steel plate corresponding to this portion cannot avoid deterioration of the surface quality and shape quality of the steel plate such as scratches, shape defects, plate width defects, plate thickness defects, and the like.
In addition, the change in the shape and quality greatly affects the material of the steel sheet, and mechanical properties (tensile properties, etc.) vary greatly due to uneven cooling during cooling, and a steel sheet that is better than the steady part cannot be obtained. For this reason, the removal of the defective part has resulted in a reduction in the yield of the steel sheet and the addition of operations such as requiring a precision plate.
[0003]
The material is coiled from the operational point of view, such as threadability (rolled steel sheets are wound in slabs in a coil box after rough rolling, and after finish rolling, they are wound by a winder. Since it is coiled, the rolling speed is different in the longitudinal direction (rolling direction). Therefore, the hot rolling conditions such as the rolling temperature change even within a single coil, and the mechanical properties vary. It was happening.
In addition, the iron oxide film called black skin scale (hereinafter simply referred to as “scale”) generated on the surface of the hot-rolled steel sheet is also formed in the steady state and the unsteady part due to changes in rolling conditions as described above. There was a difference.
[0004]
Under such circumstances, a so-called hot rolling continuation process in which a plurality of rough-rolled sheet bars (hereinafter referred to as rough bars) are sequentially joined and hot-rolled continuously at a predetermined speed in recent years. Has been tried.
This hot rolling continuous process generally includes a step of supplying a rough bar, a step of cutting the front end and the rear end of the rough bar, and the rear end of the preceding rough bar and the front end of the subsequent rough bar while traveling. , A process of clamping and butting each other, a hot finish rolling process in which the steel sheet for rolling is finished to a predetermined size on a predetermined rolling schedule with a plurality of stands, and the steel sheet that has undergone the hot finish rolling process is cooled and wound It is between the process of taking, the hot finishing rolling process, and the winding process, and is composed of a running cutting and dividing process of cutting the steel sheet by a predetermined weight or length unit.
[0005]
For this purpose, various proposals have been made as a method for joining the rough bars. For example, in Japanese Patent Laid-Open No. 4-288906, the end surface contact areas of the preceding material and the following material are defined as at least both end regions in the width direction. It is disclosed that a cutting process is performed, heating and conveying speed are adjusted, compressive stress is generated in the vicinity of both edges, and they are brought into close contact with each other. A method has been proposed in which both end portions in the widthwise direction of the succeeding material are hot-welded before rolling, and then the unjoined portion in the center in the widthwise direction is hot-welded by rolling. In Japanese Patent Publication No. 5-62035, the rear end portion of the preceding rolled material and the front end portion of the subsequent rolled material are overlapped and cut in the longitudinal direction, and a compressive force is applied at right angles to the cut surface, so A method has been proposed in which both of the metal plates are welded without expanding the bonding area without removing the scale, and are firmly bonded by contacting the entire surface in the thickness direction.
[0006]
On the other hand, as a treatment method for the generated scale, a steel plate that is subjected to processing at a high degree of processing or a steel plate that is coated after processing is subjected to a scale removal treatment of the black skin scale. There are a blasting method, a pickling method, and the like, but the pickling method is generally used from the viewpoint of complete descaling.
In recent years, speeding of the pickling process and reduction of the amount of pickling solution have been requested. However, in order to ensure workability, the hot-rolled steel sheet that has been coiled at the above-mentioned high temperature has a large scale thickness, Since the rate of dissolution in water was also slow due to the thickness of the scale, the pickling rate was extremely reduced.
[0007]
Therefore, Japanese Patent Publication No. 7-74376 proposes a method for producing a hot-rolled steel sheet for processing excellent in pickling performance that improves the production efficiency in the pickling process. In this hot rolling line, the material to be rolled is subjected to bending in a temperature range of 1100 ° C. or lower and an Ar ₃ point or higher in the hot rolled line, and held in the temperature range for 10 seconds or longer. The hot-rolled steel sheet after finish rolling is immediately cooled at a cooling rate of 20 ° C./s or more and wound at 600 ° C. or less. In addition to this, it is applied to the material to be rolled after rough rolling. The bending process is such that the ratio t / D of the plate thickness t and the bending diameter D is 0.01 or more.
[0008]
[Problems to be solved by the invention]
As described above, various proposals have been made for the hot rolling continuous process, but only a part of the study from the material aspect of the steel sheet has been made, and there is much room for development for complete measures. It remains, and it has not yet reached the point where the defective material portions at the front and rear ends of the conventional steel plate are completely eliminated.
Similarly, the measures for reduction of the production scale have not been confirmed by adopting the hot rolling continuous process, and there is a large amount of scale generation and scale uniformity in the hot rolled steel sheet described above. I left a problem.
[0009]
The present invention is intended for hot-rolled steel sheets that can be easily descaled on the coil surface at the time of shipment from the factory, and the hot-rolled steel sheets subject to the present invention include all steel sheets that are normally manufactured, but particularly high Si. The Si scale of the material formed a striped pattern on the surface of the hot-rolled steel sheet, resulting in poor descaling properties and a cause of poor surface properties.
It is an object of the present invention to provide a method for producing a hot-rolled steel sheet with good surface properties and pickling properties that eliminates the reduction in the amount of scale produced in the conventional method and the variation in the amount of scale produced in the coil. To do.
[0010]
[Means for Solving the Problems]
The present invention has been made to solve the above-described problems, and the means thereof is as follows.
(1) By weight%
C: ≦ 0.20%
Si: ≦ 2.50%
Mn: ≦ 2.5%
P: ≦ 0.025%
S: ≦ 0.025%
The steel piece composed of the remaining Fe and inevitable impurities is heated in a temperature range of 1150 ° C. or less, and after rough rolling, a coarse bar is wound in the coil box, and the surface is strained by 3% or more by unwinding. After applying at 0.1 (s ⁻¹ ) or more, the rear end of the preceding coarse bar and the front end of the subsequent coarse bar are joined, descaled and supplied to the finishing mill , method for producing a good hot-rolled steel sheet front surface characteristics and pickling you characterized in that the upper rolling.
[0011]
(2) By weight%
C: ≦ 0.20%
Si: ≦ 2.50%
Mn: ≦ 2.5%
P: ≦ 0.025%
S: ≦ 0.025%
The steel piece consisting of the remainder Fe and inevitable impurities is heated and heated in a temperature range of 1150 ° C. or less, and after rough rolling, the surface is strained by 3% or more by winding and unwinding the coarse bar in the coil box. After applying at a strain rate of 0.1 (s ⁻¹ ) or more, the rear end of the preceding coarse bar and the front end of the subsequent coarse bar are joined, and a tension of 0.2 kgf / mm ² or more is applied, and fed to the mill finish performing descaling method for producing a good hot-rolled steel sheet front surface characteristics and pickling you, characterized in that the upper rolling specification hot.
[0012]
(3) By weight%
C: ≦ 0.20%
Si: ≦ 2.50%
Mn: ≦ 2.5%
P: ≦ 0.025%
S: In addition to ≦ 0.025%,
Nb: ≦ 0.060%
Ti: ≦ 0.100%
V: ≦ 0.080%
Ca: ≦ 0.0060% of any one or two or more types, the steel piece consisting of the remainder Fe and inevitable impurities is heated, and after rough rolling, the surface is obtained by winding and unwinding a rough bar in a coil box After applying a strain of 3% or more to a strain rate of 0.1 (s ^-1 ) or more, the rear end of the preceding coarse bar and the front end of the subsequent coarse bar are joined, and descaling is performed. supplied to the rolling mill, the manufacturing method of a good hot-rolled steel sheet front surface characteristics and pickling you, characterized in that the upper rolling specification hot.
[0013]
(4) By weight%
C: ≦ 0.20%
Si: ≦ 2.50%
Mn: ≦ 2.5%
P: ≦ 0.025%
S: In addition to ≦ 0.025%,
Nb: ≦ 0.060%
Ti: ≦ 0.100%
V: ≦ 0.080%
Ca: ≦ 0.0060% of any one or two or more types, the steel piece consisting of the remainder Fe and inevitable impurities is heated, and after rough rolling, the surface is obtained by winding and unwinding a rough bar in a coil box After applying a strain of 3% or more at a strain rate of 0.1 (s ⁻¹ ) or more, the rear end of the preceding coarse bar and the front end of the subsequent coarse bar are joined, and 0.2 kgf / mm ² grant more tension, and descaling supplied to the finish rolling mill performs manufacturing method of a good hot-rolled steel sheet front surface characteristics and pickling you, characterized in that the upper rolling specification hot.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The object of the present invention is to perform the rolling of a steel sheet by a hot rolling continuous process, thereby avoiding deterioration of surface quality (scale generation) particularly at the front and rear ends of the steel sheet, which has occurred in conventional rolling. In addition, the main point is to prevent variation in the amount of scale generation in the steel sheet coil including the steel plate stationary part, and the composition includes the main elements used in normal hot-rolled steel sheets. Accordingly, for example, an element exhibiting characteristics such as high strength, high toughness, and high corrosion resistance can be added.
Moreover, there is no restriction on the steel type, and ordinary aluminum killed steel, aluminum-silicon-killed steel, or the like is targeted.
[0015]
The components of steel targeted by the present invention are those used as ordinary hot-rolled steel sheets, and the preferred content limits are as follows.
C is a component for improving the strength, but if it exceeds 0.20 wt%, the weldability and the low temperature toughness deteriorate. Therefore, the content is 0.20 wt% or less.
Si is effective as a deoxidizer and is an element for improving strength. Furthermore, it has the effect | action which ensures a retained austenite by promoting the production | generation of the ferrite in steel and suppressing the production | generation of a carbide | carbonized_material. However, when the content exceeds 2.5 wt%, the effect is saturated, and on the contrary, the weldability is deteriorated and cracks are generated in the cast slab. Therefore, the content is 2.50 wt% or less.
[0016]
Mn is an effective component for improving strength and toughness, but if it exceeds 2.50 wt%, the weldability deteriorates. Therefore, the content is 2.5 wt% or less.
P degrades the low temperature toughness and may cause high temperature cracks during welding, so its content is set to 0.025 wt% or less. However, from the viewpoint of preventing scale wrinkles (red scale) on the steel sheet surface, it is preferably 0.010 to 0.020%.
Since S combines with Mn to produce A-based inclusions and deteriorates toughness and ductility, the content is 0.025 wt% or less.
[0017]
Furthermore, in this invention, in addition to said main component composition example, you may contain 1 type, or 2 or more types selected from Nb, Ti, V, and Ca.
Nb is a preferred component that greatly increases the strength when added in a small amount and prevents deterioration of toughness by strain aging due to solid solution N, but saturates when it exceeds 0.060 wt%. Therefore, the content is 0.060 wt% or less.
Ti, like Nb, is a preferred component that significantly increases the strength when added in a small amount and improves toughness due to a synergistic effect with controlled rolling, but saturates when it exceeds 0.100 wt%. Therefore, the content is 0.100 wt% or less.
V is a component that can be expected to significantly improve the strength by addition of a small amount, but if it exceeds 0.080 wt%, the effect is saturated and weldability deteriorates. Therefore, the upper limit is 0.080 wt%.
Ca is not only preferable for low-temperature toughness and ductility by controlling the form of inclusions, but is also a preferable component as a countermeasure against separation. However, if the content exceeds 0.0060 wt%, weldability and toughness deteriorate. Therefore, the upper limit is 0.0060 wt%.
[0018]
As described above, the hot-rolled steel sheet according to the present invention includes all the steel sheets that are normally produced, but the prevention effect is particularly great for measures against Si scale in high-Si hot-rolled steel sheets. The generation of this Si scale generates a Si and Fe oxide (FeO + Fe ₂ SiO ₄ ) during heating of the steel slab in the heating furnace, enters the grain boundary between the particles, and becomes a rooted state. This appears as a striped pattern on the steel plate surface. This Si scale has a poor descaling property, which causes poor surface properties.
Next, the hot rolling continuation process of the present invention will be described below in the order of its features, the effects thereof, and the reasons for limiting the hot rolling conditions.
[0019]
FIG. 1 is a diagram showing an example of an equipment arrangement for carrying out the present invention. First, slab heating in a heating furnace is performed, but in the present invention, a special additive element is also used from the viewpoint of suppressing the amount of scale generation. When not added, the heating temperature is set to a low temperature of 1150 ° C. or lower, and the generation of primary scale is minimized.
This has a coil box that winds the rough bar before coiling the front and rear ends of the rough bars after rough rolling, that is, after the rough rolling, and keeps the heat in a coil shape. There is no need to unnecessarily increase the heating temperature, and as a result, the effects of low-temperature heating can be enjoyed in terms of material as will be described later.
[0020]
The slab extracted from the heating furnace is rolled into a rough bar, wound in a coil shape in a coil box, and normally kept warm for 10 seconds or more to perform uniform heat retention over the entire length of the coil (particularly in rough rolling). The local temperature-decreasing portion at the rolling tip is reheated by being wound into the coil after the rough rolling, and becomes a uniform temperature). The temperature drop at this time falls only very slightly within 1 ° C./sec.
Thereafter, the coil is rewound, and the front and rear ends thereof are cut by a welding surface cutting shear to adjust the cut surface. In this way, in the coil box, the coarse bar is wound and rewound, so that distortion processing is applied to the coil. The amount can impart a surface strain of 3% or more at a strain rate of 0.1 (s ⁻¹ ) or more, and cracks are generated in the scale of the coil surface, which becomes the starting point and improves the peelability of the primary scale.
[0021]
Further, as will be described later, in the present invention, the coarse bar that has been rewound in the coil box is joined by the running joint device in the next process and is fed into the finishing mill as a single unit. The coarse bar can pass between the coil box and the finishing mill in a certain time, and a tension of 0.2 kgf / mm ² or more can be uniformly applied to the coarse bar.
As a result, the surface state of the coarse bar is uniform over the entire length, and therefore, descaling can be performed on the descaling surface under almost the same processing conditions without taking different measures in the coil. it can.
[0022]
In the welding surface cutting shear, the rough bar whose front and rear end portions have been cut is not particularly touched here because it is not particularly limited as to the running joint device on the joining carriage. Various methods are conceivable, but the laser welding method is preferred), so that the rear end of the preceding material and the front end of the subsequent material are joined together and rolled in a finish rolling mill. The portion excluding the rear end of the rough bar can be rolled without a rolling end in finish rolling. In addition, the coarse bar runs at a constant speed with no change in speed until the finishing mill, and the tension applied to the coil is constantly stable. Cooling conditions (water volume, pressure, etc.) at any position on the coil surface ) Is constant, non-variable descaling is performed, and conventional scale unevenness does not occur.
In addition, because the steel plate joint is run and cut by the shear after the pinch roll and the coil is wound by the winder, the tongue-shaped or fishtail-shaped defective portion that has occurred at the front and rear end portions of the previous coil There will be no. Accordingly, it is not necessary to correct the shape defect portion by using the conventional finishing plate and to cut off the shape defect portion including the front and rear end portions, and it is possible to achieve the omission of the adjusting step and the improvement of the product yield.
[0023]
As mentioned above, although the description of the characteristic part on the installation of this invention and the effect brought about by it was performed, in this invention, the biggest difference of the effect compared with the steel plate obtained by the previous process is the present invention. By carrying out, scale generation on the surface of the hot-rolled steel sheet can be suppressed, and the generated scale can be thin and have a uniform thickness over the entire length of the coil. In addition, the variation in the quality characteristics of the steel sheet, that is, the variation in the coil is remarkably reduced, and there is an effect that a uniform and stable product can be obtained.
In the present invention, the fluctuation amount in the coil is also mentioned, but it is naturally preferable that these values are small. However, this variation cannot be avoided in the conventional rolling method as described above.
[0024]
In the present invention, with the recent rapid progress of steel plate manufacturing technology, by adopting a hot rolling continuous process combined with improvement of segregation in slab and improvement of controlled rolling in rolling, the material in these coils can be improved. The variation can be reduced, and furthermore, the fluctuation of the scale generation amount, which is the object of the present invention, can be suppressed within a very small range.
The rolling conditions and the like regulated to suppress the scale generation are derived from the permissible range based on the results obtained by the continuous rolling process.
As a result, the descaling process can be performed under substantially the same conditions regardless of the position of the steel sheet corresponding to any position in the same lot.
[0025]
【Example】
The above-described effects of the present invention will be described specifically and in detail with reference to examples.
Since the present invention can be applied to almost all steel types, the chemical composition of the steel plate is shown in Table 1 by selecting three types.
[0026]
[Table 1]

[0027]
The slab cast from these three types of steel is rolled into a steel plate under the conditions shown in Table 2 according to the present invention, and the rolled product is continuously rolled by joining the same lot for each steel type (the steel plate is joined in one rolling unit). Two coils (except for the most advanced and rearmost coils) are randomly extracted from the inside of the coil, and five points from the total length of the coil (the front / rear end corresponding to the unsteady part and the center corresponding to the steady part) Samples were taken from three parts) at an equal distance from the part.
[0028]
[Table 2]

[0029]
Each sample was examined for the scale generation status. In addition, the material characteristics in the coil are shown in Table 3 (in the present invention, the number of the mechanical properties is reduced because the scale is generated mainly). For comparison, the steel sheet rolled by the conventional method was similarly shown in Table 2 with the rolling conditions and Table 3 with the scale generation status and the investigation results of the materials.
“Δ” in Table 3 indicates the fluctuation (variation) in the coil, and is represented by the maximum value-minimum value.
[0030]
[Table 3]

[0031]
As is apparent from Table 3, according to the present invention, the scale thickness is reduced in the generation of the scale, and the difference is small even in the coil, and it can be seen that the scale is uniform and thin.
[0032]
【The invention's effect】
According to the present invention, the amount of scale generation in the hot rolled steel sheet is small (thin), and there is no difference in the thickness in the coil. For example, the descaling time by pickling is short, and the plate passing speed is increased. As a result, a steel plate with good pickling properties can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of equipment layout for carrying out the present invention.

Claims

% By weight
C: ≦ 0.20%
Si: ≦ 2.50%
Mn: ≦ 2.5%
P: ≦ 0.025%
S: ≦ 0.025%
The steel piece composed of the remaining Fe and inevitable impurities is heated in a temperature range of 1150 ° C. or less, and after rough rolling, a coarse bar is wound in the coil box, and the surface is strained by 3% or more by unwinding. After applying at 0.1 (s ⁻¹ ) or more, the rear end of the preceding coarse bar and the front end of the subsequent coarse bar are joined, descaled and supplied to the finishing mill , method for producing a good hot-rolled steel sheet front surface characteristics and pickling you characterized in that the upper rolling.

% By weight
C: ≦ 0.20%
Si: ≦ 2.50%
Mn: ≦ 2.5%
P: ≦ 0.025%
S: ≦ 0.025%
The steel piece consisting of the remainder Fe and inevitable impurities is heated and heated in a temperature range of 1150 ° C. or less, and after rough rolling , the surface is strained by 3% or more by winding and unwinding the coarse bar in the coil box. After applying at a strain rate of 0.1 (s ⁻¹ ) or more, the rear end of the preceding coarse bar and the front end of the subsequent coarse bar are joined, and a tension of 0.2 kgf / mm ² or more is applied, and fed to the mill finish performing descaling method for producing a good hot-rolled steel sheet front surface characteristics and pickling you, characterized in that the upper rolling specification hot.

% By weight
C: ≦ 0.20%
Si: ≦ 2.50%
Mn: ≦ 2.5%
P: ≦ 0.025%
S: In addition to ≦ 0.025%,
Nb: ≦ 0.060%
Ti: ≦ 0.100%
V: ≦ 0.080%
Ca: ≦ 0.0060% of any one or two or more types, the steel piece consisting of the remainder Fe and inevitable impurities is heated, and after rough rolling, the surface is obtained by winding and unwinding a rough bar in a coil box After applying a strain of 3% or more to a strain rate of 0.1 (s ^-1 ) or more, the rear end of the preceding coarse bar and the front end of the subsequent coarse bar are joined, and descaling is performed. supplied to the rolling mill, the manufacturing method of a good hot-rolled steel sheet front surface characteristics and pickling you, characterized in that the upper rolling specification hot.

% By weight
C: ≦ 0.20%
Si: ≦ 2.50%
Mn: ≦ 2.5%
P: ≦ 0.025%
S: In addition to ≦ 0.025%,
Nb: ≦ 0.060%
Ti: ≦ 0.100%
V: ≦ 0.080%
Ca: ≦ 0.0060% of any one or two or more types, the steel piece consisting of the remainder Fe and inevitable impurities is heated, and after rough rolling, the surface is obtained by winding and unwinding a rough bar in a coil box 3% or more strain strain rate 0.1 (s ^-1) after the application of the above, and bonding the crude bar tip of the trailing and end after said coarse bars of the prior, 0.2 kgf / mm ² grant more tension, and descaling supplied to the finish rolling mill performs manufacturing method of a good hot-rolled steel sheet front surface characteristics and pickling you, characterized in that the upper rolling specification hot.