JP3551129B2 - Manufacturing method and manufacturing equipment for hot rolled steel strip - Google Patents

Manufacturing method and manufacturing equipment for hot rolled steel strip Download PDF

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JP3551129B2
JP3551129B2 JP2000152371A JP2000152371A JP3551129B2 JP 3551129 B2 JP3551129 B2 JP 3551129B2 JP 2000152371 A JP2000152371 A JP 2000152371A JP 2000152371 A JP2000152371 A JP 2000152371A JP 3551129 B2 JP3551129 B2 JP 3551129B2
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rolled
stands
stand
steel strip
hot
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JP2001334306A (en
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保 佐々木
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Nippon Steel Corp
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Sumitomo Metal Industries Ltd
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Description

【0001】
【発明の属する技術分野】
本発明は、熱延鋼帯の製造方法および製造設備に関する。詳しくは、本発明は、表面性状に優れ、かつ、機械的特性に優れた熱延鋼帯の製造方法および製造設備に関する。
【0002】
【従来の技術】
一般に、熱延鋼帯は、所定温度に加熱したスラブを粗圧延機で粗圧延して被圧延材となし、この被圧延材の表面に高圧水を噴射してスケールを除去した後、複数のスタンドを有する仕上圧延機で仕上圧延を施して製造される。
【0003】
仕上圧延機出側における熱延鋼帯の温度(以下、仕上温度ともいう)は、熱延鋼帯の機械的性質に大きく影響を及ぼす。したがって、所期の機械的性質を確保するために、仕上温度の下限値(以下、仕上下限温度ともいう)が定められている。
【0004】
ところで、上記熱延鋼帯の製造において、被圧延材は高温状態で搬送、圧延されるため、被圧延材の表面には酸化スケールが生成する。この酸化スケールは酸化鉄を主成分とするものであるが、金属酸化物を含むこともある。
【0005】
このような酸化スケール(以下、単にスケールともいう)が被圧延材の表面に存在したまま、熱間圧延をおこなうと、圧延時にスケールが表面に押し込まれて表面疵が発生する。特に、近年は、熱延鋼帯の機械的性質の改善に伴い、その利用範囲の拡大から、高い表面品質へのニーズが高まり、スケール原因の表面品質劣化防止が重要となっている。例えば、冷延代替熱延鋼板として、板厚が2mm以下で、SPHDクラス以上の機械的性質を有し、かつ、表面性状の良好な熱延鋼帯が要求されている。
【0006】
スケール原因の表面品質劣化防止策として、特開平6−269840号公報や特開平10−128423号公報には、仕上圧延機の入側で鋼板表面を加熱後、高圧水によるデスケーリングを行い、直ちに仕上圧延する方法が開示されている。
【0007】
【発明が解決しようとする課題】
しかしながら、上記公報に開示された方法においても、特に板厚の薄い熱延鋼帯を圧延する場合に、微細な2次スケールの残存により表面疵が発生することがあり、高い表面品質のニーズを満足することができない。
【0008】
一方、2次スケール対策として、スタンド間の通過時間が長く、圧延負荷も大きい仕上圧延機の上流スタンドのスタンド間で高圧水によるデスケーリングを行う方法が考えられる。しかしながら、スタンド間で高圧水を噴射するデスケーリングを行うと、特に、板厚の薄い熱延鋼帯を圧延する場合に、被圧延材の温度低下が大きく、仕上下限温度の確保が難しく、所期の機械的性質が得られないことがある。
【0009】
したがって、従来の技術では、仕上板厚が2mm以下で、SPHDクラス以上の機械的性質を有し、かつ、表面性状に優れた熱延鋼帯を安定して圧延するのが困難であった。
【0010】
本発明の課題は、表面疵の発生を抑制し、かつ、SPHDクラス以上の機械的性質を得るために必要な仕上下限温度の確保を可能とした熱延鋼帯の製造方法および製造設備を提供することにある。
【0011】
【課題を解決するための手段】
本発明者は、上記課題を解決するため、種々検討を行い、以下の知見を得た。
(a)仕上圧延前で被圧延材の幅方向全体を加熱する加熱処理を施すことにより、仕上下限温度の確保が可能となる。しかしながら、被圧延材の温度上昇により、仕上圧延機のスタンド間でスケールの生成が大きくなり、特に、隣接するスタンド間における被圧延材の通過時間が長い上流側スタンドにおける圧延の際に表面疵が発生しやすい。
【0012】
(b)上記通過時間が1秒以上となるスタンド間で、被圧延材の表面に高圧水を噴射するスケール除去を行うことにより、上記表面疵の発生が抑制される。
(c)従って、仕上圧延前で被圧延材の幅方向全体を加熱する加熱処理と、隣接するスタンド間における被圧延材の通過時間が1秒以上となる仕上圧延機のスタンド間で被圧延材の表面に高圧水を噴射するスケール除去を行うことにより、仕上下限温度の確保と表面疵の発生の抑制が可能となり、SPHDクラス以上の機械的性質を備え、かつ、表面性状に優れた熱延鋼帯を製造することができる。
【0013】
(d)前記通過時間が2秒以上となると、スタンド間で生成するスケール量の増加により、高Si鋼や高Mn鋼などの熱延鋼帯では、スタンド間でのスケール除去が不十分となることがある。
【0014】
(e)スタンド間の上流側スタンド出口で被圧延材の表面に水を噴射して被圧延材の表面を冷却することにより、スタンド間で生成するスケールの量を減少させることができる。
【0015】
(f)従って、スタンド間でのスケール除去を行い、更に、仕上圧延機においてスタンド間の通過時間が2秒以上となる全てのスタンド間における上流側スタンド出口で被圧延材に低圧水を噴射し被圧延材の表面を冷却することにより、高Si鋼や高Mn鋼などの熱延鋼帯の圧延でも、表面疵の発生を抑制することができる。
【0016】
本発明は、上記知見に基づき完成されたもので、その要旨は以下のとおりである
【0017】
)上流から下流に向かって、粗圧延機、加熱装置、デスケーリング装置および仕上圧延機を順次備え、前記粗圧延機でスラブに粗圧延を施して被圧延材とし、次いで、前記加熱装置で前記被圧延材の幅方向全体を加熱した後、前記デスケーリング装置で高圧水を噴射して被圧延材のスケールを除去し、その後、複数のスタンドを備えた前記仕上圧延機で仕上圧延を施して熱延鋼帯を製造する方法であって、前記仕上圧延機の隣接するスタンド間における被圧延材の通過時間が1秒以上となる少なくとも1つのスタンド間で高圧水を噴射して被圧延材のスケールを除去するとともに、前記通過時間が2秒以上となる全てのスタンド間における上流側スタンド出口に冷却装置を設け、該冷却装置で被圧延材の表面を水冷却することを特徴とする熱延鋼帯の製造方法。
)前記通過時間が1秒以上となる複数のスタンド間に、スタンド間デスケーリング装置を設け、被圧延材の仕上板厚の目標値と仕上下限温度の目標値に応じて、前記スタンド間デスケーリング装置の使用基数を調整することを特徴とする(1) に記載の熱延鋼帯の製造方法。
【0018】
)上流から下流に向かって、スラブに粗圧延を施して被圧延材とするための粗圧延機、前記被圧延材の幅方向全体を加熱するための加熱装置、高圧水を噴射して被圧延材のスケールを除去するためのデスケーリング装置および、複数のスタンドを有し、仕上圧延を施すための仕上圧延機を順次備える熱延鋼帯の製造設備であって、さらに、前記仕上圧延機の隣接するスタンド間における被圧延材の通過時間が1秒以上となるスタンド間で高圧水を噴射して被圧延材のスケールを除去するためのスタンド間デスケーリング装置と、前記通過時間が2秒以上となるスタンド間における上流側スタンド出口に設けられて、被圧延材の表面を水冷却するための冷却装置とを備えることを特徴とする熱延鋼帯の製造設備。

【0019】
本発明は、仕上板厚が2mm以下の冷延代替鋼板として利用可能な熱延鋼帯の製造方法に好適である。また、上記(3)項に記載の発明は、Siの含有量が高い高Si含有鋼の熱延鋼帯やMnの含有量が高い高Mn含有鋼の熱延鋼帯の製造に好適である。
【0020】
【発明の実施の形態】
本発明の実施の形態を添付図面を参照して説明する。
図1は、本発明を実施する熱間圧延設備の一例の要部を模式的に示す概要図である。
【0021】
図1に示すように、この熱間圧延設備は、加熱装置1、加熱装置2ならびに7基のスタンド(上流から下流に向かってF1スタンド〜F7スタンド)からなる仕上圧延機5を備え、更に、F1スタンドの入側に設けたデスケーリング装置すなわち仕上前デスケーリング装置4と、F1スタンド〜F5スタンドの各スタンド間に設けたデスケーリング装置すなわちスタンド間デスケーリング装置6a,6b,6c,6dと、F1スタンド〜F3スタンドの各スタンド間に設けた冷却装置8a,8bとを備える。符号3はクロップシャー、7は仕上温度計で、10は被圧延材、11は熱延鋼帯である。なお、以下、仕上前デスケーリング装置およびスタンド間デスケーリング装置によるスケール除去をそれぞれ仕上前デスケーリング、スタンド間デスケーリングといい、冷却装置による冷却をスタンド間冷却ともいう。
【0022】
所定温度に加熱されたスラブは、1基以上のスタンドで構成される粗圧延機で粗圧延を施されて被圧延材10(以下、粗バ−ともいう)となる。次いで、図1に示すように、この粗バー10は、ローラテーブル上を搬送されて、F1スタンドの前に設置された加熱装置1および加熱装置2で所定温度に加熱された後、クロップシャー3で必要に応じて粗バー10の先端と後端を切断され、その後、仕上前デスケーリング装置4で高圧水を表面に噴射してスケールが除去され、仕上圧延機5で仕上圧延されて所定厚さの熱延鋼帯11となる。
【0023】
加熱装置1は粗バー10の幅方向全体を加熱する全幅加熱装置で、例えば、ソレノイド型誘導加熱装置が用いられる。加熱装置2は幅端部を加熱するエッジ加熱装置で、例えば、誘導加熱方式の加熱装置が用いられる。図1では、加熱装置1の下流に加熱装置2を配置しているが、加熱装置2を加熱装置1の上流に設けてもよい。但し、仕上温度確保の観点から、温度降下の大きい幅端部を効率的に昇温するために、図1に示すように、加熱装置2は加熱装置1の下流に設置するのがよい。
【0024】
加熱装置1と加熱装置2による被圧延材の加熱では、長手方向と幅方向の全ての領域の仕上温度が製品である熱延鋼帯の機械的性質に応じて定まる仕上下限温度以上となるように、仕上前デスケーリングやスタンド間デスケーリング、スタンド間冷却による温度降下も考慮して加熱装置1と加熱装置2とを組み合わせて被圧延材の昇温が行われる。以下、加熱装置1と加熱装置2による被圧延材の温度上昇量を昇温量という。
【0025】
図2は、被圧延材の昇温量と、F7スタンド出側の熱延鋼帯の温度すなわち仕上温度の長手方向の変化の一例を示すグラフで、図2(a)は昇温量の変化を、図2(b)は仕上温度の変化を、横軸に長手方向の位置を粗バー長さで換算して示す。
【0026】
図2(a)、(b)に示すように、被圧延材の昇温量を長手方向に調節することにより、仕上温度を長手方向にほぼ均一に制御することができる。なお、以下、長手方向における昇温量の最大値を最大昇温量という。
【0027】
被圧延材の昇温量は幅中央部に比べ幅方向端部が大きく、かつ、仕上圧延機入側での幅方向温度分布も幅中央部に比べ幅方向端部で高くなるように加熱することが望ましい。これは、高圧水の噴射による被圧延材の温度降下が幅端部で大きくなるからである。
【0028】
仕上前デスケーリング装置としては、慣用の高圧水噴射式のデスケーリング装置でよく、例えば、吐出圧力が5〜20MPa程度の能力を有する装置とされる。なお、高圧水噴射時の被圧延材の温度降下を小さくするには、圧力を高め、噴射する水量を小さくするのがよい。
【0029】
仕上前デスケーリング装置でスケールを除去された粗バーはF1スタンドから、順次、仕上圧延を施されが、その際、粗バー表面に形成したスケールを除去するため、スタンド間デスケーリング装置で高圧水を噴射する。図1の実施形態では、F1スタンド〜F5スタンドの各スタンド間にスタンド間デスケーリング装置6a〜6dを設ける場合を示したが、隣接するスタンド間を被圧延材が通過する時間すなわち通過時間が1秒以上となる少なくとも1つのスタンド間で高圧水を噴射してスケールの除去を行えばよい。
【0030】
被圧延材の表面に形成するスケールは、仕上板厚や仕上温度によって種々異なる。すなわち、仕上板厚が薄くなるほど、また、仕上温度が高くなるほど、スケールは生成しやすい。したがって、スタンド間デスケーリング装置を複数のスタンド間に設け、仕上板厚と仕上温度に応じて、スタンド間デスケーリング装置の使用基数を調整することが望ましい。
【0031】
例えば、仕上板厚と仕上温度に応じ、更に鋼種ごとにスタンド間デスケーリング装置の使用基数ならびにスケール除去を行うスタンド間を予め決定し、これをテーブル化しておき、このテーブルに基づいてスタンド間デスケーリングを行えばよい。
【0032】
隣接するスタンド間の通過時間が増加すると、スタンド間で生成するスケールの量が増加するため、高圧水の噴射によるスタンド間でのスケール除去が不十分となり、特に、Siの含有量が高い高Si含有鋼やMnの含有量が高い高Mn鋼などの熱延鋼板では、表面疵が発生しやすい。
【0033】
従って、隣接するスタンド間の通過時間が2秒以上となる全てのスタンド間における上流側スタンド出口に冷却装置を設け、この冷却装置で被圧延材に冷却水を噴射し被圧延材の表面を冷却するのが望ましい。図1の実施形態では、通過時間が2秒以上となるF1スタンド〜F3スタンドの各スタンド間に冷却装置8a、8bを設けた。なお、冷却水の吐出圧力は2MPa程度以下でよい。
【0034】
通過時間が2秒以上となるスタンド間で被圧延材の表面を冷却することにより、スタンド間で生成するスケールの量を抑制することが可能となり、高圧水の噴射によるスタンド間でのスケール除去の効果が向上する。従って、上記スタンド間で被圧延材の表面を冷却することにより、表面性状が良好な高Si鋼や高Mn鋼の熱延鋼板の製造が可能となる。
【0035】
なお、実施形態の説明では、被圧延材の加熱装置として、全幅加熱装置である加熱装置1とエッジ加熱装置である加熱装置2を備えた熱間圧延設備を用いた。しかし、本発明はこの形態に限定されず、加熱装置として全幅加熱装置のみを備える熱間圧延設備にたいしても同様に適用される。
【0036】
【実施例】
(実施例1)
図1に示す基本構成の熱間圧延設備により、板厚30mm、板幅1250mmの粗バーを仕上圧延して、板厚1.2〜1.8mmの熱延鋼帯とした。鋼種は低炭素鋼である。仕上下限温度はSPHDクラスの機械的性質の熱延鋼帯を得るために必要となる820℃とSPHEクラスの機械的特性の熱延鋼帯を得るために必要となる840℃のいずれかに設定した。
【0037】
誘導加熱方式の加熱装置1,2を用い、仕上温度が仕上下限温度〜仕上下限温度+20℃の範囲となるように長手方向に粗バーの昇温量を制御しながら粗バーの幅方向全体を加熱した。
【0038】
F1〜F5の各スタンド間に設けた高圧水噴射式のスタンド間デスケーリング装置6a〜6dの少なくとも1つのスタンド間デスケーリング装置を用いて被圧延材の表面に高圧水を噴射した。すなわち、表1に示す隣接するスタンド間における被圧延材の通過時間に基づき、その通過時間が1秒以上となる少なくとも1つのスタンド間で高圧水を噴射してスケールを除去した。高圧水の吐出圧力は14MPaとした。
【0039】
【表1】

Figure 0003551129
比較例として、粗バーの加熱無し、かつ、スタンド間デスケーリング無しの条件(比較例1、4)と、粗バーの加熱有り、かつ、スタンド間デスケーリング無しの条件(比較例2、3、5)でも実施した。
【0040】
F7スタンド出側に設けた仕上温度計7で仕上温度を熱延鋼帯の全長に渡って測定して仕上温度の最低値を求めるとともに、熱延鋼帯の表面性状を調査した。
表2に、仕上温度の最低値と、熱延鋼帯の表面性状を比較例とともに示す。なお、同表で、最大昇温量とは、加熱装置1、2による粗バー加熱の際の長手方向における粗バーの昇温量の最大値を指す。
【0041】
【表2】
Figure 0003551129
表2に示すように、本発明例は、いずれもスケール疵発生率が5%未満で、かつ、全長に渡り仕上下限温度820℃の確保が可能であった。従って、本発明方法により、表面性状が良好で、機械的性質がSPHDクラス以上の特性を有する熱延鋼帯の製造が可能であることが判った。
【0042】
比較例では、スケール疵発生率が5%以上で表面性状が不良であった。更に、比較例1は、仕上温度が820℃未満となる部位があり、この部位ではSPHDクラス以上の機械的特性を有する熱延鋼帯が得られないことが判った。
(実施例2)
図1に示す基本構成の熱間圧延設備により、板厚30mm、板幅1250mmの粗バーを板厚1.4mmの熱延鋼帯とした。鋼種は高Si含有鋼(Si:0.3質量%)である。仕上下限温度はSPHDクラス以上の機械的性質の特性を有する熱延鋼帯を得るために必要となる830℃とした。
【0043】
実施例1と同様に誘導加熱方式の加熱装置1、2で仕上温度が仕上下限温度〜仕上下限温度+20℃の範囲となるように長手方向に粗バーの昇温量を制御しながら粗バーの幅方向全体を加熱した。次いで、仕上前デスケーリング装置で高圧水を噴射してスケール除去を行い、その後仕上げ圧延を施した。
【0044】
仕上圧延に際しては、F1スタンド〜F4スタンドの各スタンド間に設けたスタンド間デスケーリング装置6a〜6cの少なくとも1つのデスケーリング装置を用い、表1に示す通過時間が1秒以上となるF1スタンド〜F4スタンドの各スタンド間の少なくとも1つのスタンド間で高圧水を噴射してスケールを除去した。高圧水の吐出圧力は14MPaとした。
【0045】
更に、本発明例2では、上記スケール除去を行うとともに、通過時間が2秒以上となるスタンド間、すなわちF1スタンドとF2スタンドのスタンド間ならびにF2スタンドとF3スタンドのスタンド間におけるそれぞれの上流側スタンドの出口に設けた冷却装置8a、8bで冷却水を噴射して被圧延材の表面を冷却した。なお、冷却水の吐出圧力は2MPaとした。
【0046】
比較例として、スタンド間デスケーリング無し、かつ、スタンド間冷却無し、の条件でも実施した。
実施例1と同様に、F7スタンド出側に設けた仕上温度計7で仕上温度を熱延鋼帯の全長に渡って測定して仕上温度の最低値を求めるとともに、熱延鋼帯の表面性状を調査した。
【0047】
表3に、仕上温度の最低値と、熱延鋼帯の表面性状を比較例とともに示す。
【0048】
【表3】
Figure 0003551129
表3に示すように、本発明例は、表面性状が良好で、仕上温度830℃以上の確保が可能であることが判った。特に、スタンド間冷却を実施した本発明例2では、スケール疵の発生がなく表面性状は極めて良好であった。一方、比較例は表面性状が不良であった。
【0049】
【発明の効果】
本発明によれば、特に、板厚が2mm以下の薄い熱延鋼板の圧延に際し、熱延鋼帯の表面に発生するスケール疵が抑制され、かつ高い仕上温度も確保できる。したがって、表面性状に優れ、かつSPHDクラス以上の機械的特性を有する熱延鋼帯の製造が可能になる。また、本発明によれば、スタンド間で被圧延材を冷却することにより、スタンド間で生成するスケールの量が抑制され、表面性状に優れた高Si鋼や高Mn鋼の熱延鋼帯の製造が可能となる。
【図面の簡単な説明】
【図1】本発明を実施する熱間圧延設備の一例の要部を模式的に示す概要図である。
【図2】被圧延材の昇温量と、F7スタンド出側の熱延鋼帯の温度すなわち仕上温度の長手方向の変化の一例を示すグラフで、(a)は昇温量の変化を、(b)は仕上げ温度の変化である。
【符号の説明】
1、2:加熱装置、3:クロップシャー、
4:仕上前デスケーリング装置、
5:仕上圧延機、
6a〜6d:スタンド間デスケーリング装置、
7:仕上温度計、8a、8b:冷却装置、
10:被圧延材(粗バー)、11:熱延鋼帯。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and a facility for manufacturing a hot-rolled steel strip. More specifically, the present invention relates to a method and a facility for manufacturing a hot-rolled steel strip having excellent surface properties and excellent mechanical properties.
[0002]
[Prior art]
In general, the hot-rolled steel strip is formed into a material to be rolled by roughly rolling a slab heated to a predetermined temperature with a rough rolling mill, and after removing scale by injecting high-pressure water onto the surface of the material to be rolled, a plurality of strips are formed. It is manufactured by performing finish rolling with a finishing mill having a stand.
[0003]
The temperature of the hot-rolled steel strip on the exit side of the finishing mill (hereinafter, also referred to as finishing temperature) greatly affects the mechanical properties of the hot-rolled steel strip. Therefore, a lower limit of the finishing temperature (hereinafter, also referred to as a finishing lower limit temperature) is determined in order to secure desired mechanical properties.
[0004]
By the way, in the production of the hot-rolled steel strip, since the material to be rolled is transported and rolled in a high temperature state, an oxide scale is generated on the surface of the material to be rolled. This oxide scale is mainly composed of iron oxide, but may contain metal oxide.
[0005]
When hot rolling is performed while such an oxide scale (hereinafter, also simply referred to as a scale) is present on the surface of a material to be rolled, the scale is pushed into the surface during rolling and surface flaws are generated. In particular, in recent years, with the improvement of the mechanical properties of the hot-rolled steel strip, the range of its use has been expanded, and the need for high surface quality has increased, and prevention of surface quality deterioration due to scale has become important. For example, as a cold-rolled alternative hot-rolled steel sheet, a hot-rolled steel strip having a sheet thickness of 2 mm or less, having mechanical properties of SPHD class or higher, and having good surface properties is required.
[0006]
As measures for preventing surface quality deterioration due to scale, JP-A-6-269840 and JP-A-10-128423 disclose that after heating a steel sheet surface at the entrance of a finishing rolling mill, descaling with high-pressure water is immediately performed. A method of finish rolling is disclosed.
[0007]
[Problems to be solved by the invention]
However, even in the method disclosed in the above publication, particularly when a hot-rolled steel strip having a small thickness is rolled, surface defects may be generated due to the remaining fine secondary scale, and the need for high surface quality is reduced. I cannot be satisfied.
[0008]
On the other hand, as a measure against secondary scale, a method of performing descaling with high-pressure water between stands of an upstream stand of a finishing mill having a long passage time between stands and a large rolling load can be considered. However, when descaling by injecting high-pressure water between stands is performed, particularly in the case of rolling a hot-rolled steel strip having a small thickness, the temperature of the material to be rolled is greatly reduced, and it is difficult to secure a minimum finishing temperature. Mechanical properties may not be obtained.
[0009]
Therefore, in the prior art, it was difficult to stably roll a hot-rolled steel strip having a finish plate thickness of 2 mm or less, having mechanical properties of SPHD class or higher, and having excellent surface properties.
[0010]
An object of the present invention is to provide a method and apparatus for manufacturing a hot-rolled steel strip capable of suppressing the occurrence of surface flaws and ensuring a minimum finishing temperature necessary for obtaining mechanical properties of SPHD class or higher. Is to do.
[0011]
[Means for Solving the Problems]
The present inventor has conducted various studies in order to solve the above problems, and has obtained the following findings.
(A) By performing a heat treatment for heating the entire width of the material to be rolled before the finish rolling, it is possible to secure a finish lower limit temperature. However, due to a rise in the temperature of the material to be rolled, scale generation is increased between stands of the finishing mill, and particularly, surface flaws occur during rolling on the upstream stand where the passage time of the material to be rolled between adjacent stands is long. Likely to happen.
[0012]
(B) By removing the scale by spraying high-pressure water onto the surface of the material to be rolled between stands where the passage time is 1 second or longer, the generation of the surface flaws is suppressed.
(C) Therefore, a heat treatment for heating the entire width of the material to be rolled before finish rolling, and a material to be rolled between the stands of the finishing mill where the passage time of the material to be rolled between adjacent stands is 1 second or more. By removing the scale by injecting high-pressure water onto the surface of the surface, it is possible to secure the minimum finishing temperature and suppress the occurrence of surface flaws. Steel strip can be manufactured.
[0013]
(D) When the passing time is 2 seconds or more, scale removal between stands becomes insufficient in a hot-rolled steel strip such as a high Si steel or a high Mn steel due to an increase in the amount of scale generated between stands. Sometimes.
[0014]
(E) By spraying water on the surface of the material to be rolled at the outlet of the upstream stand between the stands to cool the surface of the material to be rolled, the amount of scale generated between the stands can be reduced.
[0015]
(F) Therefore, scale removal between stands is performed, and further, low-pressure water is sprayed on the material to be rolled at the outlet of the upstream stand between all stands in the finishing mill where the passage time between stands is 2 seconds or more. By cooling the surface of the material to be rolled, generation of surface flaws can be suppressed even when rolling a hot-rolled steel strip such as a high Si steel or a high Mn steel.
[0016]
The present invention has been completed based on the above findings, and the gist is as follows .
[0017]
( 1 ) A rough rolling mill, a heating device, a descaling device, and a finishing rolling machine are sequentially provided from upstream to downstream, and the slab is subjected to rough rolling by the rough rolling machine to obtain a material to be rolled, and then the heating device After heating the entire width of the material to be rolled in, the high-pressure water is injected by the descaling device to remove the scale of the material to be rolled, and thereafter, finish rolling is performed by the finishing mill having a plurality of stands. Applying a high-pressure water jet between at least one stand where the passage time of the material to be rolled between adjacent stands of the finishing mill is 1 second or more. While removing the scale of the material, a cooling device is provided at the outlet of the upstream stand between all the stands where the passing time is 2 seconds or more, and the surface of the material to be rolled is water-cooled by the cooling device. Manufacturing method of hot-rolled steel strip that.
( 2 ) An inter-stand descaling device is provided between a plurality of stands where the passing time is 1 second or more, and the stand-to-stand de-scaling device is provided in accordance with a target value of a finished plate thickness of a material to be rolled and a target value of a lower limit temperature of the finish method for producing characterized (1) hot-rolled steel strip according to claim adjusting the use radix descaling device.
[0018]
( 3 ) From the upstream to the downstream, a rough rolling machine for subjecting the slab to rough rolling to obtain a material to be rolled, a heating device for heating the entire width direction of the material to be rolled, and high-pressure water being injected. A descaling apparatus for removing scale of a material to be rolled, and a hot-rolled steel strip manufacturing facility having a plurality of stands and a finishing mill for sequentially performing finish rolling, further comprising the finish rolling An inter-stand descaling device for injecting high-pressure water between stands where the passage time of the material to be rolled between adjacent stands of the mill is 1 second or more to remove the scale of the material to be rolled; A hot-rolled steel strip manufacturing facility, comprising: a cooling device provided at an outlet of an upstream stand between stands which is longer than one second and for cooling a surface of a material to be rolled with water.

[0019]
INDUSTRIAL APPLICABILITY The present invention is suitable for a method for producing a hot-rolled steel strip that can be used as a cold-rolled alternative steel sheet having a finished plate thickness of 2 mm or less. Further, the invention described in the above item (3) is suitable for producing a hot-rolled steel strip of a high Si-containing steel having a high Si content or a hot-rolled steel strip of a high Mn-containing steel having a high Mn content. .
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram schematically showing a main part of an example of a hot rolling facility for carrying out the present invention.
[0021]
As shown in FIG. 1, the hot rolling equipment includes a heating device 1, a heating device 2, and a finishing mill 5 including seven stands (F1 stand to F7 stand from upstream to downstream). A descaling device provided on the entry side of the F1 stand, that is, a pre-finishing descaling device 4, and a descaling device provided between the stands of the F1 stand to the F5 stand, that is, inter-stand descaling devices 6a, 6b, 6c, 6d; Cooling devices 8a and 8b are provided between stands F1 to F3. Reference numeral 3 denotes a crop shear, 7 denotes a finishing thermometer, 10 denotes a material to be rolled, and 11 denotes a hot-rolled steel strip. Hereinafter, scale removal by the pre-finishing descaling device and the inter-stand descaling device will be referred to as pre-finishing descaling and inter-stand descaling, respectively, and cooling by the cooling device will also be referred to as inter-stand cooling.
[0022]
The slab heated to a predetermined temperature is subjected to rough rolling by a rough rolling mill including one or more stands to become a material to be rolled 10 (hereinafter, also referred to as a rough bar). Next, as shown in FIG. 1, the coarse bar 10 is conveyed on a roller table and heated to a predetermined temperature by a heating device 1 and a heating device 2 installed in front of an F1 stand. If necessary, the leading and trailing ends of the coarse bar 10 are cut off, and then high-pressure water is sprayed on the surface by the pre-finishing descaling device 4 to remove scale, and is finished and rolled by the finishing mill 5 to a predetermined thickness. The hot rolled steel strip 11 is obtained.
[0023]
The heating device 1 is a full-width heating device for heating the entire width direction of the rough bar 10, and for example, a solenoid-type induction heating device is used. The heating device 2 is an edge heating device for heating the width end portion, and for example, an induction heating type heating device is used. In FIG. 1, the heating device 2 is disposed downstream of the heating device 1, but the heating device 2 may be provided upstream of the heating device 1. However, from the viewpoint of ensuring the finishing temperature, in order to efficiently raise the temperature of the width end having a large temperature drop, the heating device 2 is preferably installed downstream of the heating device 1 as shown in FIG.
[0024]
In the heating of the material to be rolled by the heating device 1 and the heating device 2, the finishing temperature in all the regions in the longitudinal direction and the width direction is equal to or higher than the finishing lower limit temperature determined according to the mechanical properties of the hot-rolled steel strip as a product. In addition, the temperature of the material to be rolled is increased by combining the heating device 1 and the heating device 2 in consideration of the descaling before finishing, the descaling between stands, and the temperature drop due to the cooling between stands. Hereinafter, the amount of temperature rise of the material to be rolled by the heating device 1 and the heating device 2 is referred to as a temperature rise amount.
[0025]
FIG. 2 is a graph showing an example of a change in the heating amount of the material to be rolled and a change in the temperature of the hot-rolled steel strip on the exit side of the F7 stand, that is, a finishing temperature, in the longitudinal direction. FIG. 2B shows the change in the finishing temperature by converting the position in the longitudinal direction on the horizontal axis into the value of the coarse bar length.
[0026]
As shown in FIGS. 2A and 2B, the finishing temperature can be controlled substantially uniformly in the longitudinal direction by adjusting the amount of temperature rise of the material to be rolled in the longitudinal direction. Hereinafter, the maximum value of the heating amount in the longitudinal direction is referred to as the maximum heating amount.
[0027]
The material to be rolled is heated so that the temperature increase amount at the width direction end is larger than the width center portion, and the width direction temperature distribution at the finishing mill entry side is higher at the width direction end portion than at the width center portion. It is desirable. This is because the temperature drop of the material to be rolled due to the injection of high-pressure water increases at the width end.
[0028]
The pre-finishing descaling device may be a conventional high-pressure water injection type descaling device, for example, a device having a discharge pressure of about 5 to 20 MPa. In order to reduce the temperature drop of the material to be rolled during high-pressure water injection, it is preferable to increase the pressure and reduce the amount of water to be injected.
[0029]
The coarse bar from which the scale has been removed by the pre-finishing descaling device is subjected to finish rolling sequentially from the F1 stand. At this time, in order to remove the scale formed on the surface of the rough bar, high-pressure water is used by the inter-stand descaling device. Inject. In the embodiment of FIG. 1, the case where the inter-stand descaling devices 6 a to 6 d are provided between the F1 stand to the F5 stand is shown. The scale may be removed by injecting high-pressure water between at least one stand for more than one second.
[0030]
The scale flaws formed on the surface of the material to be rolled vary depending on the finished plate thickness and the finished temperature. That is, the smaller the finished plate thickness and the higher the finishing temperature, the more easily scale flaws are generated. Therefore, it is desirable to provide a stand-to-stand descaling device between a plurality of stands, and to adjust the number of bases of the stand-to-stand descaling device according to the finishing plate thickness and the finishing temperature.
[0031]
For example, according to the finishing plate thickness and the finishing temperature, the number of units of the stand-to-stand descaling device and the stand between which the scale is to be removed are determined in advance for each steel type, and this is tabulated, and the stand-to-stand data is determined based on this table. You only need to scale.
[0032]
As the passage time between adjacent stands increases, the amount of scale generated between stands increases, so that scale removal between stands by injection of high-pressure water becomes insufficient, and particularly, high Si content is high. Hot-rolled steel sheets such as steel containing steel and high Mn steel having a high Mn content tend to have surface defects.
[0033]
Therefore, a cooling device is provided at the outlet of the upstream stand between all the stands where the passage time between adjacent stands is 2 seconds or more, and the cooling device injects cooling water to the material to be rolled to cool the surface of the material to be rolled. It is desirable to do. In the embodiment of FIG. 1, the cooling devices 8a and 8b are provided between the F1 stand to the F3 stand where the passage time is 2 seconds or longer. Note that the discharge pressure of the cooling water may be about 2 MPa or less.
[0034]
By cooling the surface of the material to be rolled between stands having a passage time of 2 seconds or more, the amount of scale generated between stands can be suppressed, and scale removal between stands by jetting high-pressure water can be achieved. The effect is improved. Therefore, by cooling the surface of the material to be rolled between the stands, it becomes possible to manufacture a hot-rolled steel sheet of high Si steel or high Mn steel having good surface properties.
[0035]
In the description of the embodiment, a hot rolling facility including a heating device 1 as a full width heating device and a heating device 2 as an edge heating device is used as a heating device for a material to be rolled. However, the present invention is not limited to this mode, and is similarly applied to a hot rolling facility having only a full-width heating device as a heating device.
[0036]
【Example】
(Example 1)
A rough bar having a thickness of 30 mm and a width of 1250 mm was finish-rolled by a hot rolling facility having a basic configuration shown in FIG. 1 to obtain a hot-rolled steel strip having a thickness of 1.2 to 1.8 mm. The steel type is low carbon steel. The minimum finishing temperature is set to either 820 ° C required to obtain a hot-rolled steel strip having mechanical properties of SPHD class or 840 ° C required to obtain a hot-rolled steel strip having mechanical properties of SPHE class. did.
[0037]
Using the induction heating type heating devices 1 and 2, the entire coarse bar width direction is controlled while controlling the amount of temperature rise of the coarse bar in the longitudinal direction so that the finishing temperature is in the range of the lower finishing temperature to the lower finishing temperature + 20 ° C. Heated.
[0038]
High-pressure water was sprayed on the surface of the material to be rolled using at least one of the stand-to-stand descaling devices 6a to 6d of the high-pressure water injection type provided between the stands F1 to F5. That is, based on the passage time of the material to be rolled between the adjacent stands shown in Table 1, high-pressure water was injected between at least one stand having a passage time of 1 second or more to remove scale. The discharge pressure of the high-pressure water was 14 MPa.
[0039]
[Table 1]
Figure 0003551129
As a comparative example, the condition without heating of the coarse bar and no descaling between stands (Comparative Examples 1 and 4) and the condition with heating of the coarse bar and no descaling between stands (Comparative Examples 2, 3 and 4) 5) was also carried out.
[0040]
The finishing temperature was measured over the entire length of the hot-rolled steel strip by the finishing thermometer 7 provided on the exit side of the F7 stand to determine the minimum value of the finishing temperature, and the surface properties of the hot-rolled steel strip were investigated.
Table 2 shows the minimum value of the finishing temperature and the surface properties of the hot-rolled steel strip together with comparative examples. In the table, the maximum amount of temperature rise refers to the maximum value of the amount of temperature rise of the coarse bar in the longitudinal direction during heating of the coarse bar by the heating devices 1 and 2.
[0041]
[Table 2]
Figure 0003551129
As shown in Table 2, in each of the examples of the present invention, the scale flaw occurrence rate was less than 5%, and the minimum finishing temperature of 820 ° C could be secured over the entire length. Therefore, it was found that the method of the present invention can produce a hot-rolled steel strip having good surface properties and mechanical properties of SPHD class or higher.
[0042]
In the comparative example, the scale defect generation rate was 5% or more and the surface properties were poor. Furthermore, in Comparative Example 1, it was found that there was a portion where the finishing temperature was lower than 820 ° C., and a hot rolled steel strip having mechanical properties of SPHD class or higher could not be obtained at this portion.
(Example 2)
Using the hot rolling equipment having the basic configuration shown in FIG. 1, a rough bar having a thickness of 30 mm and a width of 1250 mm was converted into a hot-rolled steel strip having a thickness of 1.4 mm. The steel type is a high Si content steel (Si: 0.3% by mass). The finishing lower limit temperature was set to 830 ° C. necessary to obtain a hot-rolled steel strip having mechanical properties of SPHD class or higher.
[0043]
In the same manner as in Example 1, while controlling the amount of heating of the coarse bar in the longitudinal direction, the heating temperature of the coarse bar is controlled by the induction heating type heating devices 1 and 2 so that the finishing temperature is in the range of the lower finishing temperature to the lower finishing temperature + 20 ° C. The entire width was heated. Next, high-pressure water was injected with a pre-scaling descaling device to remove scale, and then finish rolling was performed.
[0044]
At the time of finish rolling, at least one of the inter-stand descaling devices 6a to 6c provided between the stands of the F1 stand to the F4 stand is used, and the passing time shown in Table 1 is 1 second or more. High pressure water was injected between at least one stand between each stand of the F4 stand to remove scale. The discharge pressure of the high-pressure water was 14 MPa.
[0045]
Further, in Example 2 of the present invention, the above-described scale removal is performed, and the respective upstream stands between the stands where the passage time is 2 seconds or more, that is, between the stands of the F1 stand and the F2 stand and between the stands of the F2 stand and the F3 stand. The cooling water was injected by the cooling devices 8a and 8b provided at the outlets to cool the surface of the material to be rolled. Note that the discharge pressure of the cooling water was 2 MPa.
[0046]
As a comparative example, the test was performed under the conditions of no descaling between stands and no cooling between stands.
In the same manner as in Example 1, the finishing temperature was measured over the entire length of the hot-rolled steel strip by the finishing thermometer 7 provided on the exit side of the F7 stand to determine the minimum value of the finishing temperature, and the surface properties of the hot-rolled steel strip were measured. investigated.
[0047]
Table 3 shows the minimum value of the finishing temperature and the surface properties of the hot-rolled steel strip together with comparative examples.
[0048]
[Table 3]
Figure 0003551129
As shown in Table 3, it was found that the examples of the present invention had good surface properties and could secure a finishing temperature of 830 ° C. or higher. In particular, in Example 2 of the present invention in which inter-stand cooling was performed, no scale flaw was generated and the surface properties were extremely good. On the other hand, the comparative example was poor in surface properties.
[0049]
【The invention's effect】
According to the present invention, in particular, when rolling a thin hot-rolled steel sheet having a thickness of 2 mm or less, scale flaws generated on the surface of the hot-rolled steel strip are suppressed, and a high finishing temperature can be secured. Therefore, it becomes possible to produce a hot-rolled steel strip having excellent surface properties and mechanical properties equal to or higher than the SPHD class. Further, according to the present invention, by cooling the material to be rolled between the stands, the amount of scale generated between the stands is suppressed, and the hot rolled steel strip of high Si steel or high Mn steel having excellent surface properties is obtained. Manufacturing becomes possible.
[Brief description of the drawings]
FIG. 1 is a schematic diagram schematically showing a main part of an example of a hot rolling facility for carrying out the present invention.
FIG. 2 is a graph showing an example of a change in a heating amount of a material to be rolled and a temperature of a hot-rolled steel strip on an exit side of an F7 stand, that is, a change in a finishing temperature in a longitudinal direction. (B) is a change in the finishing temperature.
[Explanation of symbols]
1, 2: heating device, 3: crop shear,
4: Descaling device before finishing
5: finishing mill
6a to 6d: descaling device between stands,
7: finishing thermometer, 8a, 8b: cooling device,
10: Rolled material (rough bar), 11: Hot rolled steel strip.

Claims (3)

上流から下流に向かって、粗圧延機、加熱装置、デスケーリング装置および仕上圧延機を順次備え、前記粗圧延機でスラブに粗圧延を施して被圧延材とし、次いで、前記加熱装置で前記被圧延材の幅方向全体を加熱した後、前記デスケーリング装置で高圧水を噴射して被圧延材のスケールを除去し、その後、複数のスタンドを備えた前記仕上圧延機で仕上圧延を施して熱延鋼帯を製造する方法であって、前記仕上圧延機の隣接するスタンド間における被圧延材の通過時間が1秒以上となる少なくとも1つのスタンド間で高圧水を噴射して被圧延材のスケールを除去するとともに、前記通過時間が2秒以上となる全てのスタンド間における上流側スタンド出口に冷却装置を設け、該冷却装置で被圧延材の表面を水冷却することを特徴とする熱延鋼帯の製造方法。From the upstream to the downstream, a rough rolling mill, a heating device, a descaling device, and a finishing rolling machine are sequentially provided, and the slab is roughly rolled by the rough rolling machine to obtain a material to be rolled, and then, the slab is heated by the heating device. After heating the entire width of the rolled material, high-pressure water is sprayed by the descaling device to remove the scale of the material to be rolled, and then subjected to finish rolling by the finish rolling mill having a plurality of stands to be heated. A method for producing a rolled steel strip, wherein high-pressure water is injected between at least one stand where the passage time of a material to be rolled between adjacent stands of the finishing mill is 1 second or more, and the scale of the material to be rolled is produced. And a cooling device is provided at the outlet of the upstream stand between all the stands where the passage time is 2 seconds or more, and the surface of the material to be rolled is cooled with water by the cooling device. Method of manufacturing a band. 前記通過時間が1秒以上となる複数のスタンド間に、スタンド間デスケーリング装置を設け、被圧延材の仕上板厚の目標値と仕上下限温度の目標値に応じて、前記スタンド間デスケーリング装置の使用基数を調整することを特徴とする請求項1に記載の熱延鋼帯の製造方法。An inter-stand descaling device is provided between a plurality of stands having the passing time of 1 second or more, and the inter-stand descaling device is provided in accordance with a target value of a finished plate thickness of a material to be rolled and a target value of a lower limit temperature of finishing. The method for producing a hot-rolled steel strip according to claim 1, wherein the number of bases used is adjusted. 上流から下流に向かって、スラブに粗圧延を施して被圧延材とするための粗圧延機、前記被圧延材の幅方向全体を加熱するための加熱装置、高圧水を噴射して被圧延材のスケールを除去するためのデスケーリング装置および、複数のスタンドを有し、仕上圧延を施すための仕上圧延機を順次備える熱延鋼帯の製造設備であって、さらに、前記仕上圧延機の隣接するスタンド間における被圧延材の通過時間が1秒以上となるスタンド間で高圧水を噴射して被圧延材のスケールを除去するためのスタンド間デスケーリング装置と、前記通過時間が2秒以上となるスタンド間における上流側スタンド出口に設けられて、被圧延材の表面を水冷却するための冷却装置とを備えることを特徴とする熱延鋼帯の製造設備。From upstream to downstream, a rough rolling machine for subjecting the slab to rough rolling to obtain a material to be rolled, a heating device for heating the entire width of the material to be rolled, and a material to be rolled by injecting high-pressure water A descaling device for removing scale, and a hot-rolled steel strip manufacturing facility having a plurality of stands and sequentially including a finish rolling mill for performing finish rolling, further comprising: A stand-to-stand descaling device for injecting high-pressure water between stands where the passage time of the material to be rolled between the stands is 1 second or more to remove the scale of the material to be rolled; A hot-rolled steel strip manufacturing facility, comprising: a cooling device that is provided at an outlet of an upstream stand between stands to cool a surface of a material to be rolled with water.
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