JP2004298888A

JP2004298888A - Method and device for manufacturing hot-rolled steel strip

Info

Publication number: JP2004298888A
Application number: JP2003092118A
Authority: JP
Inventors: Satoshi Kamioka; 悟史上岡; Toru Minote; 徹簑手
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2003-03-28
Filing date: 2003-03-28
Publication date: 2004-10-28

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method and a manufacturing device of a hot-rolled steel strip which stably satisfy two contrary requirements that a material to be rolled is cooled between rolling stands in order to suppress the generation of secondary scale and the temperature of the steel strip is not lowered too much in order to secure the finishing temperature of rolling for obtaining a required material. <P>SOLUTION: In the manufacturing method of the hot-rolled steel strip in which the finish rolling of the material to be rolled is performed while cooling the material to be rolled with cooling water between a plurality of rolling stands which comprise a finishing mill, at least one of (a) and (b) is performed. (a) Y/X ≥ 0.2 ( Where, Y is a distance between the starting position of cooling and a rolling stand on the upstream side of the position and X is a distance between the rolling stands. ). (b) Regions where the surface temperature of the material to be rolled is relatively higher in accordance with rolling conditions are preferentially cooled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、仕上圧延中に生成する２次スケールに起因して発生する熱延鋼帯の表面欠陥を防止することができる熱延鋼帯の製造方法および製造装置に関するものである。
【０００２】
【従来の技術】
仕上圧延機で熱延鋼帯を製造する際には、仕上圧延に先立って、デスケーリング装置により、被圧延材の表面に生成したスケールの除去が行われる。しかし、このデスケーリング装置にてデスケーリングを行った直後から被圧延材表面の酸化が始まり、いわゆる２次スケールが生成される。この２次スケールは、仕上圧延により被圧延材の表面に押し込まれるなどして熱延鋼帯の表面欠陥の原因となる。
【０００３】
２次スケールに起因して発生する熱延鋼帯の表面欠陥を防止するため、２次スケールの生成を抑制するための技術が、従来から多数示されている。その中のひとつが、仕上圧延スタンド間で被圧延材を冷却し２次スケールの生成を抑制する方法である。
【０００４】
このうち、仕上圧延スタンド間の鋼板表面積の５０％以上７０％以下の範囲に、単位面積当りの噴射量が１００〜３００ｃｃ／ｃｍ^２／ｍｉｎの冷却水を、鋼板の板幅全幅に噴射する技術が知られている。（例えば、特許文献１参照。）。
【０００５】
【特許文献１】
特開平１０−１８０３３８号公報
【０００６】
【発明が解決しようとする課題】
一般的に熱延鋼帯を製造する際には、フェライト変態を開始する前に仕上圧延を終了してなければ材質が劣化するため、圧延仕上温度をフェライト変態開始温度以上に管理しなければならない。しかし、上記のように２次スケールの生成を抑制するために圧延スタンド間で被圧延材の冷却を行うと、所望の温度より過度に温度が低下して、圧延仕上温度をフェライト変態開始温度以上に確保できなくなる恐れがある。
【０００７】
このように圧延仕上温度を確保することと、２次スケールの生成を抑制するために圧延スタンド間で被圧延材を冷却することとは一般に相反する要求であって、圧延スタンド間の冷却方法および冷却装置には高い制御精度が必要とされる。
【０００８】
特許文献１に示されている冷却方式は、単位面積あたり噴射量が１００〜３００ｃｃ／ｃｍ^２／ｍｉｎと小さく、沸騰状態の変動が大きくなりやすいという問題がある。例えば、冷却されている鋼板の広い範囲が、安定した膜沸騰状態から突然核沸騰状態に遷移すると、冷却能が高くなって急激に温度が下がり圧延仕上温度が確保できなくなるといった問題が起こりうる。しかるに、ここには沸騰状態の時間的、空間的な変動に関する示唆は一切されていない。
【０００９】
本発明は、上記のような従来技術の問題点を解決し、２次スケールの生成を抑制するために圧延スタンド間で被圧延材を冷却すること、所要の材質を得るための熱延鋼帯の圧延仕上温度を確保するために鋼帯の温度を余り下げ過ぎないという、相反する２つの要求を安定して満たすことのできる熱延鋼帯の製造方法および製造装置を提供することを目的とする。
【００１０】
【課題を解決するための手段】
このような目的を達成するために、安定した冷却制御を行い、必要な部分のみを冷却するという観点から、本発明の特徴は以下の通りである。
【００１１】
（１）仕上圧延機を構成する複数の圧延スタンド間で、被圧延材を冷却水で冷却しつつ、被圧延材の仕上圧延を行う熱延鋼帯の製造方法において、下記（ａ）または（ｂ）の少なくとも１つを行うことを特徴とする熱延鋼帯の製造方法。
【００１２】
（ａ）被圧延材の冷却が行われる各圧延スタンド間において、冷却開始位置とその上流側の圧延スタンドとの距離Ｙが、圧延スタンド間距離Ｘに対して、下記（１）式を満足する。
【００１３】
Ｙ／Ｘ≧０．２ …（１）
（ｂ）少なくとも１つの圧延スタンド間において、被圧延材の上面または下面の少なくとも一方と対向して、被圧延材の通板方向に沿って複数の冷却装置を設け、複数の冷却装置を選択的に作動させること、または／および複数の冷却装置からの冷却水の噴射量を調整することにより、圧延条件に応じて被圧延材の表面温度が相対的に高くなる領域を優先的に冷却する。
【００１４】
（２）仕上圧延機を構成する複数の圧延スタンド間で、被圧延材を冷却水で冷却しつつ、被圧延材の仕上圧延を行う熱延鋼帯の製造装置であって、被圧延材の冷却が行われる各圧延スタンド間において、冷却開始位置とその上流側の圧延スタンドとの距離Ｙが、圧延スタンド間距離Ｘに対して、下記（１）式を満足するように、被圧延材を冷却する冷却装置が設けられていることを特徴とする熱延鋼帯の製造装置。
【００１５】
Ｙ／Ｘ≧０．２・・・（１）
（３）少なくとも１つの圧延スタンド間において、被圧延材の上面または下面の少なくとも一方と対向して、被圧延材の通板方向に沿って複数の冷却装置が設けられており、該複数の冷却装置を選択的に作動させることができ、または／および複数の冷却装置の冷却水の噴射量を調整することができることを特徴とする熱延鋼帯の製造装置。
【００１６】
【発明の実施の形態】
図１および図２は本発明の熱延鋼帯の製造装置の一実施形態を示す説明図で、図１は全体側面図、図２は圧延スタンド間の側面図である。
【００１７】
図１に示す熱延鋼帯の製造装置は、７基の圧延スタンドで構成される仕上圧延機１と、この仕上圧延機１の圧延スタンド間に設置される上下面各２基ずつの冷却装置２と、仕上圧延機入側温度計３と、仕上圧延機出側温度計４とからなる。
【００１８】
次に図２に示す熱延鋼帯の製造装置は、ある圧延スタンド間の側面図であって、各２列の冷却装置２ａおよび２ｂを被圧延材の上下面に設置した例であり、３は仕上圧延機入側温度計、４は仕上圧延機出側温度計、５は制御装置である。
【００１９】
前記冷却装置２は、第１スタンドと第２スタンド間、第２スタンドと第３スタンド間、および第３スタンドと第４スタンド間にのみ設けられている。
【００２０】
前記制御装置５は、冷却水の温度を調整する温度調整手段を有して冷却水を高温化できる。
【００２１】
さらに、仕上圧延機入側温度計３や仕上圧延機出側温度計４、または、図示しない圧延スタンド間温度計で検出された被圧延材の表面温度の結果より、冷却装置２ａおよび２ｂを選択的に作動させたり、冷却装置２ａおよび２ｂの冷却水噴射量を制御する機能を有する装置とする。
【００２２】
本発明では、仕上圧延機を構成する複数の圧延スタンド間で、被圧延材を冷却水で冷却しつつ、被圧延材の仕上圧延を行う熱延鋼帯の製造方法において、下記（ａ）または（ｂ）の少なくとも１つを行う。
【００２３】
（ａ）被圧延材の冷却が行われる各圧延スタンド間において、冷却開始位置とその上流側の圧延スタンドとの距離Ｙが、圧延スタンド間距離Ｘに対して、下記（１）式を満足する。
【００２４】
Ｙ／Ｘ≧０．２ …（１）
（ｂ）少なくとも１つの圧延スタンド間において、被圧延材の上面または下面の少なくとも一方と対向して、被圧延材の通板方向に沿って複数の冷却装置を設け、複数の冷却装置を選択的に作動させること、または／および複数の冷却装置からの冷却水の噴射量を調整することにより、圧延条件に応じて被圧延材の表面温度が相対的に高くなる領域を優先的に冷却する。
【００２５】
以下に（ａ）、（ｂ）について説明する。
【００２６】
（ａ）図２は、被圧延材の冷却が行われる各圧延スタンド間において、冷却開始位置とその上流側の圧延スタンドとの距離Ｙと圧延スタンド間距離Ｘの関係を示す。
【００２７】
また、図３は、被圧延材の表面温度と図２に示す圧延スタンド１ａからの距離との関係を示す被圧延材表面温度分布図である。圧延ロールとの接触による抜熱のため、被圧延材の表面温度は圧延終了直後に最も低く、その後は被圧延材の表面温度は板厚中心部からの復熱により上昇する。圧延スタンド間における冷却は、スケール生成量の少ない復熱過程の低温域で被圧延材の表面を冷却しても効果は小さく、復熱がある程度進行したところから始めるべきである。本発明者等は、実用的な仕上圧延条件のもとで被圧延材の表面温度の数値シミュレーションを行い、Ｙ／Ｘを０．２以上にすればよいことを見出した。
【００２８】
そこで、被圧延材の冷却が行われる各圧延スタンド間において、冷却開始位置とその上流側の圧延スタンドとの距離Ｙが、圧延スタンド間距離Ｘに対して、Ｙ／Ｘ≧０．２となるように、被圧延材を冷却する冷却装置が設けられている。
【００２９】
（ｂ）さらに、数値シミュレーションの結果、発明者等は、圧延スタンド間における被圧延材の表面温度履歴に、図４に示すような、２種類の類型があることを見出した。図４の実線で示される一つの類型は、被圧延材の復熱が完了する前に次の圧延スタンド１ｂに被圧延材が進行する場合である。この類型は、比較的板厚の厚い、第１〜第３スタンド間において起こりやすく、次の圧延スタンドに進行する直前で被圧延材の表面温度は最も高くなる。一方、図４の点線で示される他の類型は、被圧延材の復熱が圧延スタンド間にて完了し、その後は放射などにより被圧延材の表面温度が下がる場合である。このような表面温度履歴は、比較的板厚の小さい、第３スタンド以降で起こりやすい。
【００３０】
図２は、被圧延材の上下面ともに２つの冷却装置を備えた一例である。この２つの冷却装置を選択的に作動させること、または／および複数の冷却装置からの冷却水の噴射量を調整することにより、圧延条件に応じて被圧延材の表面温度が相対的に高くなる領域を優先的に冷却する。そこで、図２の例では第１〜第３スタンドの圧延スタンド間では、圧延スタンド１ｂに近い側の冷却装置２ｂを優先的に使用して、図４に示す区間Ｂの領域を優先的に冷却する。また第３スタンド以降では、圧延スタンド１ａに近い側の冷却装置２ａを優先的に使用して、図４に示す区間Ａの領域を優先的に冷却する。
【００３１】
しかしながら、圧延条件によっては、どちらの冷却装置を先に使用すべきかが変わることがある。仕上圧延機入側温度計３で測定した被圧延材の温度や、仕上圧延条件をもとに、圧延スタンド間の被圧延材表面温度を予測するモデルを具備し、予測計算結果をもとに使用する冷却装置を変えるような制御を行うことが好ましい。あるいは、過去の操業データをもとに、圧延条件ごとに、冷却装置の使用パターンをテーブル化しておき、それを使用することも有効である。
【００３２】
【発明の効果】
本発明によると、仕上圧延中の被圧延材表面を、安定的かつ効率的に冷却することができる。その結果、表面欠陥の低減と、圧延仕上温度の確保を両立させることが可能となり、熱延鋼帯の品質向上に有効である。
【図面の簡単な説明】
【図１】本発明の熱延鋼帯の製造装置の一実施形態を示す全体側面図
【図２】本発明の熱延鋼帯の製造装置の一実施形態を示すある圧延スタンド間の側面図
【図３】被圧延材の表面温度と、図２に示す圧延スタンド１ａからの距離との関係を示す被圧延材表面温度分布図
【図４】被圧延材の表面温度と、図２に示す圧延スタンド１ａからの距離との関係を示す被圧延材表面温度分布図
【符号の説明】
１仕上圧延機
１ａ圧延スタンド
１ｂ圧延スタンド
２冷却装置
３仕上圧延機入側温度計
４仕上圧延機出側温度計
５制御装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for manufacturing a hot-rolled steel strip capable of preventing surface defects of a hot-rolled steel strip caused by a secondary scale generated during finish rolling.
[0002]
[Prior art]
When a hot-rolled steel strip is manufactured by a finish rolling mill, scales formed on the surface of the material to be rolled are removed by a descaling device prior to finish rolling. However, immediately after the descaling is performed by the descaling device, oxidation of the surface of the material to be rolled starts, and a so-called secondary scale is generated. The secondary scale is pressed into the surface of the material to be rolled by finish rolling and causes surface defects of the hot-rolled steel strip.
[0003]
Many techniques for suppressing the formation of the secondary scale in order to prevent surface defects of the hot-rolled steel strip caused by the secondary scale have been conventionally shown. One of them is a method of cooling the material to be rolled between the finishing rolling stands and suppressing the formation of the secondary scale.
[0004]
Among them, a technique of injecting cooling water having an injection amount per unit area of 100 to 300 cc / cm ² / min over the entire width of the steel sheet in a range of 50% or more and 70% or less of the surface area of the steel sheet between the finish rolling stands. It has been known. (For example, refer to Patent Document 1).
[0005]
[Patent Document 1]
JP 10-180338 A
[Problems to be solved by the invention]
Generally, when producing a hot-rolled steel strip, if the finish rolling is not completed before starting the ferrite transformation, the material will deteriorate, so the rolling finish temperature must be controlled to be equal to or higher than the ferrite transformation start temperature. . However, when the material to be rolled is cooled between rolling stands in order to suppress the formation of secondary scale as described above, the temperature is excessively lowered from a desired temperature, and the rolling finish temperature is increased to a ferrite transformation start temperature or more. May not be able to be secured.
[0007]
Securing the rolling finish temperature in this way and cooling the material to be rolled between the rolling stands to suppress the formation of the secondary scale are generally contradictory requirements, and a method of cooling between the rolling stands and High control accuracy is required for the cooling device.
[0008]
The cooling method disclosed in Patent Document 1 has a problem that the injection amount per unit area is as small as 100 to 300 cc / cm ² / min, and the fluctuation of the boiling state is likely to be large. For example, when a wide range of a cooled steel sheet suddenly transitions from a stable film boiling state to a nucleate boiling state, a problem may occur in which the cooling capacity is increased, the temperature is rapidly decreased, and the rolling finish temperature cannot be secured. However, there is no suggestion here about the temporal and spatial fluctuations of the boiling state.
[0009]
The present invention solves the above-mentioned problems of the prior art, and cools a material to be rolled between rolling stands to suppress generation of a secondary scale, and a hot-rolled steel strip for obtaining a required material. To provide a method and an apparatus for manufacturing a hot-rolled steel strip which can stably satisfy two contradictory requirements that the temperature of the steel strip is not excessively lowered in order to secure the finishing temperature of the steel strip. I do.
[0010]
[Means for Solving the Problems]
In order to achieve such an object, the features of the present invention are as follows from the viewpoint of performing stable cooling control and cooling only necessary parts.
[0011]
(1) In a method for producing a hot-rolled steel strip in which a material to be rolled is finish-rolled while cooling the material to be rolled with cooling water between a plurality of rolling stands constituting a finishing mill, the following (a) or ( A method for producing a hot-rolled steel strip, wherein at least one of b) is performed.
[0012]
(A) Between the rolling stands where the material to be rolled is cooled, the distance Y between the cooling start position and the upstream rolling stand satisfies the following formula (1) with respect to the distance X between the rolling stands. .
[0013]
Y / X ≧ 0.2 (1)
(B) Between at least one rolling stand, a plurality of cooling devices are provided along the sheet passing direction of the material to be rolled in opposition to at least one of the upper surface and the lower surface of the material to be rolled, and the plurality of cooling devices are selectively provided. And / or by adjusting the injection amount of the cooling water from the plurality of cooling devices, a region where the surface temperature of the material to be rolled becomes relatively high in accordance with the rolling conditions is preferentially cooled.
[0014]
(2) An apparatus for manufacturing a hot-rolled steel strip, which finish-rolls a material to be rolled while cooling the material to be rolled with cooling water between a plurality of rolling stands constituting a finishing mill. Between the rolling stands where the cooling is performed, the material to be rolled is set such that the distance Y between the cooling start position and the upstream rolling stand satisfies the following expression (1) with respect to the distance X between the rolling stands. An apparatus for manufacturing a hot-rolled steel strip, comprising a cooling device for cooling.
[0015]
Y / X ≧ 0.2 (1)
(3) A plurality of cooling devices are provided between at least one rolling stand and at least one of the upper surface and the lower surface of the material to be rolled along the direction in which the material to be rolled passes. An apparatus for manufacturing a hot-rolled steel strip, wherein the apparatus can be selectively operated and / or the injection amount of cooling water of a plurality of cooling apparatuses can be adjusted.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
1 and 2 are explanatory views showing an embodiment of a hot-rolled steel strip manufacturing apparatus according to the present invention. FIG. 1 is an overall side view, and FIG. 2 is a side view between rolling stands.
[0017]
The apparatus for manufacturing a hot-rolled steel strip shown in FIG. 1 includes a finishing mill 1 having seven rolling stands, and two cooling devices each of upper and lower surfaces installed between the rolling stands of the finishing mill 1. 2, a finishing rolling mill inlet thermometer 3, and a finishing rolling mill outlet thermometer 4.
[0018]
Next, the apparatus for manufacturing a hot-rolled steel strip shown in FIG. 2 is a side view between certain rolling stands, in which two rows of cooling devices 2a and 2b are installed on the upper and lower surfaces of a material to be rolled. Is a thermometer on the inlet side of the finishing mill, 4 is a thermometer on the outlet side of the finishing mill, and 5 is a controller.
[0019]
The cooling device 2 is provided only between the first stand and the second stand, between the second stand and the third stand, and only between the third stand and the fourth stand.
[0020]
The control device 5 has a temperature adjusting means for adjusting the temperature of the cooling water, and can increase the temperature of the cooling water.
[0021]
Further, the cooling devices 2a and 2b are selected based on the result of the surface temperature of the material to be rolled detected by the finishing-rolling machine inlet-side thermometer 3, the finishing-rolling machine outlet-side thermometer 4, or the unillustrated thermometer between rolling stands. It is a device having a function of controlling the cooling water injection amount of the cooling devices 2a and 2b in a controlled manner.
[0022]
According to the present invention, in a method for producing a hot-rolled steel strip in which a material to be rolled is finish-rolled while cooling the material to be rolled with cooling water between a plurality of rolling stands constituting a finishing mill, the following (a) or Perform at least one of (b).
[0023]
(A) Between the rolling stands where the material to be rolled is cooled, the distance Y between the cooling start position and the upstream rolling stand satisfies the following formula (1) with respect to the distance X between the rolling stands. .
[0024]
Y / X ≧ 0.2 (1)
(B) Between at least one rolling stand, a plurality of cooling devices are provided along the sheet passing direction of the material to be rolled in opposition to at least one of the upper surface and the lower surface of the material to be rolled, and the plurality of cooling devices are selectively provided. And / or by adjusting the injection amount of the cooling water from the plurality of cooling devices, a region where the surface temperature of the material to be rolled becomes relatively high in accordance with the rolling conditions is preferentially cooled.
[0025]
Hereinafter, (a) and (b) will be described.
[0026]
(A) FIG. 2 shows the relationship between the cooling start position and the distance Y between the cooling start position and the upstream rolling stand and the distance X between the rolling stands between the rolling stands where the material to be rolled is cooled.
[0027]
FIG. 3 is a distribution temperature diagram of the material to be rolled, showing the relationship between the surface temperature of the material to be rolled and the distance from the rolling stand 1a shown in FIG. Due to heat removal due to contact with the rolling roll, the surface temperature of the material to be rolled is lowest immediately after the end of rolling, and thereafter, the surface temperature of the material to be rolled rises due to reheating from the center of the sheet thickness. Cooling between the rolling stands has a small effect even if the surface of the material to be rolled is cooled in a low-temperature region of the recuperation process in which the amount of generated scale is small, and should be started after the recuperation has progressed to some extent. The present inventors performed numerical simulation of the surface temperature of the material to be rolled under practical finish rolling conditions, and found that Y / X should be 0.2 or more.
[0028]
Thus, the distance Y between the cooling start position and the upstream rolling stand between the rolling stands where the material to be rolled is cooled is Y / X ≧ 0.2 with respect to the distance X between the rolling stands. Thus, a cooling device for cooling the material to be rolled is provided.
[0029]
(B) Further, as a result of the numerical simulation, the inventors have found that there are two types of surface temperature histories of the material to be rolled between the rolling stands as shown in FIG. One type shown by a solid line in FIG. 4 is a case where the material to be rolled advances to the next rolling stand 1b before the reheating of the material to be rolled is completed. This type is likely to occur between the first to third stands, which are relatively thick, and the surface temperature of the material to be rolled becomes highest immediately before proceeding to the next rolling stand. On the other hand, another type shown by the dotted line in FIG. 4 is a case where the reheating of the material to be rolled is completed between the rolling stands, and thereafter, the surface temperature of the material to be rolled is lowered by radiation or the like. Such a surface temperature history is likely to occur in the third stand and thereafter, where the plate thickness is relatively small.
[0030]
FIG. 2 is an example in which two cooling devices are provided on both the upper and lower surfaces of the material to be rolled. By selectively operating these two cooling devices or / and adjusting the injection amount of the cooling water from the plurality of cooling devices, the surface temperature of the material to be rolled becomes relatively high according to the rolling conditions. Cool the area preferentially. Therefore, in the example of FIG. 2, between the rolling stands of the first to third stands, the cooling device 2b closer to the rolling stand 1b is preferentially used to preferentially cool the area of the section B shown in FIG. I do. In the third and subsequent stands, the cooling device 2a on the side closer to the rolling stand 1a is preferentially used to preferentially cool the area of the section A shown in FIG.
[0031]
However, depending on the rolling conditions, which cooling device should be used first may change. A model for predicting the surface temperature of the material to be rolled between the rolling stands based on the temperature of the material to be rolled measured by the finishing thermometer 3 and the finish rolling conditions, and based on the prediction calculation results It is preferable to perform control to change the cooling device to be used. Alternatively, it is also effective to tabulate the use pattern of the cooling device for each rolling condition based on the past operation data and use the table.
[0032]
【The invention's effect】
According to the present invention, the surface of a material to be rolled during finish rolling can be cooled stably and efficiently. As a result, it is possible to achieve both reduction of surface defects and securing of the rolling finish temperature, which is effective in improving the quality of the hot-rolled steel strip.
[Brief description of the drawings]
FIG. 1 is an overall side view showing an embodiment of a hot-rolled steel strip manufacturing apparatus according to the present invention. FIG. 2 is a side view showing an embodiment of a hot-rolled steel strip manufacturing apparatus according to the present invention. FIG. 3 is a distribution diagram of the surface temperature of the material to be rolled, showing the relationship between the surface temperature of the material to be rolled and the distance from the rolling stand 1a shown in FIG. 2; Rolled material surface temperature distribution diagram showing the relationship with the distance from the rolling stand 1a.
DESCRIPTION OF SYMBOLS 1 Finishing rolling machine 1a Rolling stand 1b Rolling stand 2 Cooling device 3 Finishing rolling mill inlet thermometer 4 Finishing rolling mill outlet thermometer 5 Control device

Claims

In a method for producing a hot-rolled steel strip in which a material to be rolled is finish-rolled while cooling the material to be rolled with cooling water between a plurality of rolling stands constituting a finishing mill, the following (a) or (b) A method for producing a hot-rolled steel strip, wherein at least one is performed.
(A) Between the rolling stands where the material to be rolled is cooled, the distance Y between the cooling start position and the upstream rolling stand satisfies the following formula (1) with respect to the distance X between the rolling stands. .
Y / X ≧ 0.2 (1)
(B) Between at least one rolling stand, a plurality of cooling devices are provided along the sheet passing direction of the material to be rolled in opposition to at least one of the upper surface and the lower surface of the material to be rolled, and the plurality of cooling devices are selectively provided. And / or by adjusting the injection amount of the cooling water from the plurality of cooling devices, a region where the surface temperature of the material to be rolled becomes relatively high in accordance with the rolling conditions is preferentially cooled.

An apparatus for manufacturing a hot-rolled steel strip that performs finish rolling of a material to be rolled while cooling the material to be rolled with cooling water between a plurality of rolling stands constituting a finish rolling mill, wherein the material to be rolled is cooled. The cooling Y for cooling the material to be rolled is such that the distance Y between the cooling start position and the upstream rolling stand between the rolling stands with respect to the distance X between the rolling stands satisfies the following expression (1). An apparatus for producing a hot-rolled steel strip, wherein the apparatus is provided.
Y / X ≧ 0.2 (1)

A plurality of cooling devices are provided along at least one of the upper and lower surfaces of the material to be rolled along the direction in which the material to be rolled passes between at least one rolling stand, and the plurality of cooling devices are selected. An apparatus for producing a hot-rolled steel strip, wherein the apparatus can be operated in a controlled manner and / or the injection amount of cooling water of a plurality of cooling apparatuses can be adjusted.