JP3661434B2 - Controlled cooling method for hot rolled steel sheet - Google Patents

Controlled cooling method for hot rolled steel sheet Download PDF

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JP3661434B2
JP3661434B2 JP25376898A JP25376898A JP3661434B2 JP 3661434 B2 JP3661434 B2 JP 3661434B2 JP 25376898 A JP25376898 A JP 25376898A JP 25376898 A JP25376898 A JP 25376898A JP 3661434 B2 JP3661434 B2 JP 3661434B2
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cooling
steel sheet
temperature
hot
steel
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JP2000084612A (en
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洋 木部
晃夫 藤林
正之 堀江
悟史 上岡
伸一 鈴木
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Jfeスチール株式会社
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Description

【0001】
【発明の属する技術分野】
この発明は、熱間圧延鋼板の制御冷却方法に関するもので、特に厚鋼板の制御冷却方法に関するものである。
【0002】
【従来の技術】
近年、厚鋼板の製造プロセスとして、オンライン制御冷却法の適用が拡大している。これは、圧延直後の熱間鋼板をオンラインで冷却する方法で、高強度、高靭性の付与といった効果の他、合金元素の低減、省熱処理などのコスト削減効果も得られる。
【0003】
しかしながら、一般に圧延後の熱間鋼板は、温度分布、板形状、表面性状等が必ずしも均一でないため、冷却中に鋼板内に冷却むらが発生しやすく、冷却後の鋼板に変形、残留応力、材質不均一等が生じ、品質不良や操業上のトラブルを招いている。そこで、鋼板の冷却むらの発生を抑えるために、これまで数多くの均一冷却方法が提案されている。
【0004】
圧延後の熱間鋼板の板形状を予め平坦にすることによって、板変形に起因する冷却むらを防止する方法として、特開昭54−124864号公報には、熱間圧延機の直後に設けられた第1のホットレベラーで鋼板を矯正後、このレベラーの直後に設けられた冷却装置で冷却を行い、更に、第2のホットレベラーで矯正して平坦な鋼板を得る技術が開示されている(以下、「 先行技術1」 という)。
【0005】
一方、冷却中に発生する温度むらを冷却中に緩和する方法として、特開昭62−289316号公報には、冷却を2段に分け、前段冷却で鋼板表面温度を100℃以上低下させ、引き続き、後段冷却で所定の温度まで冷却することにより、板幅方向の温度差を減少させる方法が開示されている(以下、「 先行技術2」 という)。
【0006】
また、特開平7−284836号公報には、同じく二段冷却法において、前段冷却と後段冷却との間で一旦冷却を停止し、鋼板表面温度が復熱して750〜650℃になるように前段冷却を調整し、後段冷却では所望の冷却水量で冷却を行うことによって、板内温度の均一性を向上させる方法が開示されている(以下、「 先行技術3」 という)。
【0007】
【発明が解決しようとする課題】
ところが、先行技術1に示される方法では、鋼板の形状によって引き起こされる冷却むらを解消することはできるが、冷却前の鋼板の温度分布、表面粗さ、スケール形状などによって発生する冷却むらを防止することはできず、仮に冷却後ホットレベラーで鋼板を平坦にしても、室温まで空冷される途中で、冷却むらに起因した変形が再び発生してしまう。
【0008】
先行技術2に示される方法では、前段冷却時に鋼板内に冷却むらや変形が発生すると、引き続き行なわれる後段冷却で、温度むらや変形は積算され、更に拡大するといった問題が発生する。
【0009】
また、先行技術3に示される方法では、図7に示すような、前段冷却ゾーンa、復熱ゾーンbおよび後段冷却ゾーンcを有する冷却設備において、前段冷却ゾーンで冷却した後、復熱後の鋼板表面温度を750〜650℃とし、更に、後段冷却すると、復熱させないで続けて冷却した場合に比べ、温度むらは減少するが、前段冷却終了時の鋼板内の変態進行状態が必ずしも均一でないため、復熱過程で変形が発生し、それが、後段冷却時の冷却むらの原因になってしまう問題があった。図7において、1は鋼板、2はテーブルロール、3、4は冷却ノズル、5はエアノズルである。
【0010】
従って、本発明の目的は、これら従来の問題を解決し、冷却中に発生する温度むらや変形を低減し、冷却後に平坦度の良好な鋼板が得られる冷却方法を提供することにある。特に、前段冷却終了時の鋼板内の変態進行状態の不均一の影響を低減し、後段冷却で、均一な冷却を可能にすることにある。
【0011】
【課題を解決するための手段】
請求項1記載の発明は、熱間圧延鋼板の制御冷却方法において、冷却を途中で一旦停止し、次いで、熱間矯正し、次いで、再び前記冷却の冷却速度と同一の冷却速度で冷却することに特徴を有するものである。
【0012】
請求項2記載の発明は、熱間矯正するときの鋼板温度がAr3 −150℃以上Ar3 −20℃以下の範囲であることに特徴を有するものである。
請求項3記載の発明は、熱間矯正するときの鋼板の変態率が5%以上75%以下の範囲であることに特徴を有するものである。
【0013】
【発明の実施の形態】
次に、この発明の実施の形態を図面を参照しながら説明する。
一般に、高温鋼板を冷却すると、膜沸騰、遷移沸騰および核沸騰を通過して低温に到達するが、鋼板表面温度が遷移沸騰領域の場合、冷却開始時に温度が高い部分は、温度が低い部分に比べて熱流束が小さいため冷却が遅れるのに対し、温度が低い部分は、逆に熱流束が大きいため冷却が促進される。その結果、両者の温度差は拡大することになる。連続的に冷却を行っていく限り、遷移沸騰中にこの局所的な温度むらは積算され、拡大していき、冷却後の鋼板に、平坦度不良の他、残留応力や材質むらを生じさせることになる。
【0014】
これに対し、冷却を一旦停止し、鋼板を板厚および板幅の両方向に渡って復熱させると、低温部と高温部との差が減少し、再び冷却する際の鋼板の温度むらを減少させることができる。ただし、復熱過程で温度むらは減少するものの、冷却中に発生した温度むらに起因する変形が復熱中に発生する。これは、鋼板内部の変態進行状態が均一ではないためで、鋼板温度と鋼の伸び計の値との関係を示す図1に示すように、変態の進行状態によって、鋼の伸び計の値が異なることから説明される。即ち、鋼板内で局所的に変態の進行状態が異なると、その部分で冷却に伴う収縮量が異なるため、冷却後変形となって現れるのである。従って、一旦冷却を停止して復熱させたとしても、前段冷却によって発生した変形によって、後段冷却時に変形に起因する冷却むらが発生し、最終的な鋼板の温度分布は不均一となってしまう。
【0015】
本発明者らは、 前段冷却時に発生する温度むらを復熱により減少させると同時に、前段冷却時に発生する変形を熱間矯正によって除去することによって、引き続き行なわれる後段冷却を均一に行い、最終冷却後の鋼板の温度むらを抑制し、平坦度に優れた鋼板が得られることを見出して、本発明を完成したものである。
【0016】
更に、本発明者らは、熱間矯正するときの鋼板温度と、冷却後の鋼板の温度むらとの関係を仔細に調査し調査したところ、熱間矯正時の鋼板温度が特定の範囲において、冷却後の鋼板の温度むらが著しく向上することを見出した。図2は、板厚25mmの鋼板を900℃から20℃/sの冷却速度で種々の温度まで冷却した後、熱間矯正し、更に、20℃/sの冷却速度で500℃まで冷却したときの、熱間矯正したときの鋼板温度と冷却後の鋼板の温度むらとの関係を示すグラフである。ここで、鋼板の温度むらは、鋼板の板幅方向の変形量の、板長に対する割合で示した。図2から、鋼板の温度むらは、鋼板温度がAr3 (Ar3 変態点)−150℃以上Ar3 −20℃以下の範囲で特に低減することが分かった。これは、鋼板温度がAr3 −150℃以上Ar3 −20℃以下の範囲で、復熱による温度むら低減効果と、熱間矯正による変形矯正効果とが相乗的に働き、後段の冷却時の冷却むらが低減したことによると考えられる。これに対し、鋼板平均温度がAr3 −20℃より高い場合、即ち、前段冷却で変態が余り進んでいない場合は、後段冷却時に発生する変形および冷却むらが共に大きいため、最終冷却後の鋼板の温度分布が不均一になってしまうものと考えられる。また、鋼板平均温度がAr3 −150℃より低い場合は、前段冷却で変態が進行しているため、後段冷却で発生する変形は小さいものの、前段冷却時に発生した温度むらが大きく、前段冷却停止後の復熱中に緩和しきれず、最終冷却後に温度むらとして残ってしまうためと考えられる。
【0017】
また、図3に、熱間矯正時の鋼板平均温度と変態率との関係を示す。図3から、図2で示した冷却後の鋼板の温度均一性が向上する変態率の範囲が、5%以上75%以下であることが分かる。同様の傾向は、他の鋼種、板厚、冷却速度においても認められた。
【0018】
また、本発明では、前段冷却と後段冷却との間に熱間矯正することを構成要件としているが、もちろん、必要に応じて、冷却前あるいは冷却後に熱間矯正しても良い。
【0019】
【実施例】
以下に、実施例を用いて本発明を更に詳細に説明する。
[実施例1]
図4は、この発明の実施例1に係る冷却装置の側面断面図である。冷却装置は、前段冷却装置8と後段冷却装置9とに別れ、その中間にホットレベラー7が配置されている。
【0020】
冷却装置は、テーブルロール2単位で分割され、上面には水切りロール6が設置されている。上面および下面の冷却方式は、共に冷却ノズル3、4によるスプレー冷却である。
【0021】
図4において、圧延機で圧延された熱間鋼板1は、テーブルロール2により搬送され制御冷却装置に運ばれる。このとき、本図では図示していないが、制御冷却装置に入る前に、更に、別のホットレベラーによって予め圧延歪みを除去すると更に良い。制御冷却装置に運ばれた鋼板1は、前段冷却装置8で冷却された後、ホットレベラー7で熱間矯正され、引き続き、後段冷却装置9で目標停止温度まで冷却される。冷却速度、冷却停止温度は、前段冷却装置8と後段冷却装置9の水量と鋼板1の搬送速度とによりコントロールされる。熱間矯正時の鋼板温度は、ホットレベラー7の前面(図4においてホットレベラー7の左側)の放射温度計によって、変態率は超音波を使った変態率計で測定した。
【0022】
表1に、供試材として、化学成分が重量%で、C:0. 13wt.%、Si:0.35wt.%、Mn:1.35wt.%、Nb:0.01wt.%含有する鋼を、加熱炉で1150℃まで加熱した後、熱間圧延により板厚25mm、板幅3000mm、板長12000mmの鋼板とした後、種々の条件で冷却したときの、冷却後の鋼板の温度分布を調べた結果を示す。
【0023】
【表1】
【0024】
本発明に従って冷却を2回に分け、冷却の間に熱間矯正した場合と、熱間矯正をしなかった場合、更に、1回の冷却で目標停止温度まで冷却した場合とを比較した。ここで、冷却後の鋼板の温度分布は、鋼板面内の最高温度と最低温度との差で示した。この値が低いほど、温度むらは小さく、温度均一性が良好であることを意味する。表1から、本発明実施例1〜7は、比較例8、9の連続冷却や二段冷却に比べ、冷却後の鋼板の温度分布が良好で、冷却均一性が向上していることが分かる。
【0025】
[実施例2]
図5は、この発明の実施例2に係る冷却装置の側面断面図である。ホットレベラー7は、冷却装置10の前面(図5において冷却装置10の左側)に置かれている。冷却装置10は、テーブルロール2単位で分割され、上面には水切りロール6が設置されている。冷却ノズル3、4による、上面の冷却方式はパイプラミナー、下面の冷却方式はスプレー冷却である。
【0026】
圧延された熱間鋼板1は、ホットレベラー7で矯正された後、引き続き冷却装置10で所定の温度まで冷却される。その後、鋼板1はラインを逆送して冷却装置10を通過した後、再び熱間矯正され変形を除去した後、再び冷却装置10で目標とする停止温度まで冷却される。本実施例は、実施例1に比べ、能率は低下するが、ホットレベラー1台で冷却前および冷却途中の熱間矯正が可能である上、前段冷却条件と後段冷却条件とを完全に独立して設定できる。
【0027】
この設備を用い、供試材として、化学成分が、C:0.12wt.%、Si:0.36wt.%、Mn:1.30wt.%、Nb:0.012wt.%含有する鋼を、加熱炉で1150℃まで加熱した後、熱間圧延により板厚12mm、板幅4000mm、板長18000mmの鋼板とした後、冷却開始温度800℃、最終冷却停止温度500℃で冷却した。
【0028】
本発明に従って冷却を2回に分け、冷却速度30℃/sで前段冷却後、700℃で熱間矯正し、引き続き冷却速度30℃/sで後段冷却した場合、冷却後の鋼板の温度分布は9℃であった。
【0029】
これに対し、冷却速度30℃/sで前段冷却後、熱間矯正をせず、そのまま、冷却速度30℃/sで後段冷却した場合、冷却後の鋼板の温度分布は36℃であった。更に、冷却速度30℃/sの連続冷却で500℃まで冷却した場合、冷却後の鋼板の歪量は60℃であった。
【0030】
この結果から、本発明例は、比較例の連続冷却や二段冷却に比べ、冷却後の鋼板の温度むらが小さく、冷却均一性が向上していることが分かる。
[実施例3]
図6は、この発明の実施例3に係る冷却装置の側面断面図である。ホットレベラー7は、冷却装置10の後面(図6において冷却装置10の右側)に設置されている。冷却装置10はテーブルロール2単位で分割され、上面には水切りロール6が設置されている。冷却ノズル3、4による、上面の冷却方式はスリットラミナー、下面の冷却方式は噴水冷却である。
【0031】
圧延された熱間鋼板1は、冷却装置10で所定の温度まで冷却された後、熱間矯正される。その後、鋼板1はラインを逆送し、再び冷却装置10で目標とする停止温度まで冷却される。
【0032】
この設備を用い、供試材として、化学成分が、C:0.14wt.%、Si:0.33wt.%、Mn:1. 42wt.%含有する鋼を、加熱炉で1150℃まで加熱した後、熱間圧延により板厚40mm、板幅2000mm、板長8000mmの鋼板とした後、冷却開始温度800℃、最終冷却停止温度500℃で冷却した。
【0033】
本発明に従って冷却を2回に分け、冷却速度15℃/sで前段冷却後、680℃で熱間矯正し、引き続き冷却速度15℃/sで後段冷却した場合、冷却後の鋼板の温度分布は6℃であった。
【0034】
これに対し、冷却速度15℃/sで前段冷却後、熱間矯正をせず、そのまま冷却速度15℃/sで後段冷却した場合、冷却後の鋼板の歪量は31℃であった。更に、冷却速度15℃/sの連続冷却で500℃まで冷却した場合、冷却後の鋼板の歪量は52℃であった。
【0035】
この結果からも、本発明例は比較例の連続冷却や二段冷却に比べ、冷却後の鋼板の温度むらが小さく、冷却均一性が向上していることが分かる。
【0036】
【発明の効果】
以上説明したように、この発明によれば、冷却によって発生する温度むらを低減し、冷却後の鋼板の平坦度を向上させることができ、これによって、冷却後の鋼板の再矯正や手入れが不必要となる他、材質のばらつきを抑え、歩留まりを向上させることが可能となり、かくして、工業上有用な効果がもたらされる。
【図面の簡単な説明】
【図1】鋼板温度と鋼の伸び計の値との関係を示すグラフである。
【図2】熱間矯正時の鋼板温度と冷却後の鋼板の温度むらとの関係を示すグラフである。
【図3】熱間矯正時の鋼板温度と変態率との関係を示すグラフである。
【図4】この発明の実施例1に係る冷却装置の側面断面図である。
【図5】この発明の実施例2に係る冷却装置の側面断面図である。
【図6】この発明の実施例3に係る冷却装置の側面断面図である。
【図7】従来の二段冷却装置の説明図である。
【符号の説明】
1:鋼板
2:テーブルロール
3:冷却ノズル
4:冷却ノズル
5:エアノズル
6:水切りロール
7:ホットレベラー
8:前段冷却装置
9:後段冷却装置
10:冷却装置
a:前段冷却ゾーン
b:復熱ゾーン
c:後段冷却ゾーン
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a controlled cooling method for hot-rolled steel sheets, and particularly to a controlled cooling method for thick steel sheets.
[0002]
[Prior art]
In recent years, the application of the on-line controlled cooling method has expanded as a manufacturing process of thick steel plates. This is a method for online cooling of a hot-rolled steel sheet immediately after rolling. In addition to the effects of imparting high strength and high toughness, cost reduction effects such as reduction of alloy elements and heat treatment can be obtained.
[0003]
However, in general, a hot-rolled steel sheet after rolling is not necessarily uniform in temperature distribution, plate shape, surface properties, etc., so that uneven cooling is likely to occur in the steel sheet during cooling, and deformation, residual stress, and material of the steel sheet after cooling are likely to occur. Non-uniformity has occurred, leading to poor quality and operational problems. Therefore, in order to suppress the occurrence of uneven cooling of the steel sheet, many uniform cooling methods have been proposed so far.
[0004]
As a method for preventing uneven cooling due to plate deformation by flattening the plate shape of a hot-rolled steel plate after rolling, JP 54-124864 A is provided immediately after a hot rolling mill. In addition, a technique is disclosed in which a steel sheet is straightened with a first hot leveler, cooled by a cooling device provided immediately after the leveler, and further straightened with a second hot leveler to obtain a flat steel sheet ( Hereinafter referred to as “prior art 1”).
[0005]
On the other hand, as a method of mitigating the temperature unevenness generated during cooling, Japanese Patent Application Laid-Open No. 62-289316 discloses that cooling is divided into two stages, and the steel sheet surface temperature is lowered by 100 ° C. or more in the preceding stage cooling, and subsequently A method of reducing the temperature difference in the plate width direction by cooling to a predetermined temperature by subsequent cooling is disclosed (hereinafter referred to as “Prior Art 2”).
[0006]
Japanese Patent Application Laid-Open No. 7-284836 similarly discloses that in the two-stage cooling method, the cooling is temporarily stopped between the former stage cooling and the latter stage cooling so that the steel sheet surface temperature is reheated to 750 to 650 ° C. A method of improving the uniformity of the temperature in the plate by adjusting the cooling and performing the cooling with a desired amount of cooling water in the subsequent cooling is disclosed (hereinafter referred to as “prior art 3”).
[0007]
[Problems to be solved by the invention]
However, the method shown in Prior Art 1 can eliminate the uneven cooling caused by the shape of the steel sheet, but prevents the uneven cooling caused by the temperature distribution, surface roughness, scale shape, etc. of the steel sheet before cooling. Even if the steel plate is flattened with a hot leveler after cooling, deformation due to uneven cooling occurs again during air cooling to room temperature.
[0008]
In the method shown in the prior art 2, if uneven cooling or deformation occurs in the steel sheet during the pre-cooling, the uneven temperature or deformation is accumulated and further expanded in the subsequent post-cooling.
[0009]
Further, in the method shown in Prior Art 3, in the cooling facility having the front cooling zone a, the recuperation zone b and the rear cooling zone c as shown in FIG. When the steel sheet surface temperature is set to 750 to 650 ° C. and the latter stage cooling is performed, the temperature unevenness is reduced as compared with the case where the cooling is continued without reheating, but the transformation progress state in the steel sheet at the end of the first stage cooling is not necessarily uniform. Therefore, there is a problem that deformation occurs in the recuperation process, which causes cooling unevenness at the time of subsequent cooling. In FIG. 7, 1 is a steel plate, 2 is a table roll, 3, 4 is a cooling nozzle, and 5 is an air nozzle.
[0010]
Accordingly, an object of the present invention is to provide a cooling method that solves these conventional problems, reduces temperature unevenness and deformation that occur during cooling, and provides a steel sheet with good flatness after cooling. In particular, it is intended to reduce the influence of non-uniformity of the transformation progress state in the steel sheet at the end of the pre-stage cooling, and to enable uniform cooling by the post-stage cooling.
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, in the controlled cooling method for hot-rolled steel sheets, cooling is temporarily stopped halfway, then hot-corrected, and then cooled again at the same cooling rate as the cooling rate. It has the characteristics.
[0012]
The invention described in claim 2 is characterized in that the temperature of the steel sheet when hot straightening is in the range of Ar 3 −150 ° C. or higher and Ar 3 −20 ° C. or lower.
The invention according to claim 3 is characterized in that the transformation rate of the steel sheet when hot straightening is in the range of 5% to 75%.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
Generally, when a high-temperature steel sheet is cooled, it passes through film boiling, transition boiling, and nucleate boiling to reach a low temperature, but when the steel sheet surface temperature is in the transition boiling region, the high temperature part at the start of cooling is changed to the low temperature part. On the other hand, cooling is delayed because the heat flux is small, whereas cooling is promoted at the low temperature portion because the heat flux is large. As a result, the temperature difference between the two increases. As long as the cooling is continuously performed, this local temperature unevenness will be accumulated and expanded during the transition boiling, causing the steel sheet after cooling to have residual flatness and material unevenness in addition to poor flatness. become.
[0014]
On the other hand, once cooling is stopped and the steel sheet is reheated in both the plate thickness and width directions, the difference between the low temperature part and the high temperature part is reduced, and the temperature unevenness of the steel sheet during cooling is reduced. Can be made. However, although the temperature unevenness is reduced during the recuperation process, deformation due to the temperature unevenness generated during cooling occurs during the recuperation. This is because the state of transformation inside the steel sheet is not uniform, and the value of the steel extensometer depends on the state of transformation as shown in FIG. It is explained from the difference. That is, if the progress of transformation is locally different within the steel sheet, the amount of shrinkage accompanying cooling is different in that portion, and thus appears as deformation after cooling. Therefore, even if the cooling is once stopped and the heat is recovered, the deformation generated by the pre-stage cooling causes uneven cooling due to the deformation during the post-stage cooling, and the temperature distribution of the final steel sheet becomes non-uniform. .
[0015]
The inventors of the present invention reduced the temperature unevenness generated during the first stage cooling by recuperation, and at the same time, removed the deformation generated during the first stage cooling by hot straightening, so that the subsequent second stage cooling was performed uniformly and the final cooling was performed. The present invention has been completed by finding that a steel plate with excellent flatness can be obtained by suppressing the temperature unevenness of the steel plate later.
[0016]
Furthermore, the present inventors carefully investigated and investigated the relationship between the steel plate temperature when hot straightening and the temperature unevenness of the steel plate after cooling, and the steel plate temperature during hot straightening was in a specific range, It has been found that the temperature unevenness of the steel sheet after cooling is significantly improved. FIG. 2 shows a case where a steel plate having a thickness of 25 mm is cooled to various temperatures at a cooling rate of 900 ° C. to 20 ° C./s, then hot-corrected, and further cooled to 500 ° C. at a cooling rate of 20 ° C./s. It is a graph which shows the relationship between the steel plate temperature when hot-correcting, and the temperature nonuniformity of the steel plate after cooling. Here, the temperature unevenness of the steel sheet is shown as a ratio of the deformation amount in the sheet width direction of the steel sheet to the sheet length. From FIG. 2, it was found that the temperature unevenness of the steel sheet was particularly reduced in the range where the steel sheet temperature was Ar 3 (Ar 3 transformation point) −150 ° C. or higher and Ar 3 −20 ° C. or lower. This is because, when the steel sheet temperature is in the range of Ar 3 −150 ° C. or higher and Ar 3 −20 ° C. or lower, the effect of reducing temperature unevenness due to recuperation and the effect of correcting deformation due to hot correction work synergistically. This is thought to be due to a reduction in uneven cooling. On the other hand, when the average temperature of the steel sheet is higher than Ar 3 -20 ° C., that is, when the transformation is not so advanced in the former stage cooling, both the deformation and the cooling unevenness that occur during the latter stage cooling are large. It is considered that the temperature distribution of the film becomes non-uniform. In addition, when the average temperature of the steel sheet is lower than Ar 3 -150 ° C., since the transformation has progressed in the pre-stage cooling, the deformation that occurs in the post-stage cooling is small, but the temperature unevenness that occurs during the pre-stage cooling is large, and the pre-stage cooling is stopped. This is thought to be because it cannot be alleviated during the subsequent recuperation and remains as uneven temperature after the final cooling.
[0017]
FIG. 3 shows the relationship between the steel sheet average temperature and the transformation rate during hot straightening. FIG. 3 shows that the range of the transformation rate in which the temperature uniformity of the steel sheet after cooling shown in FIG. 2 is improved is 5% or more and 75% or less. Similar trends were observed for other steel types, sheet thicknesses, and cooling rates.
[0018]
Further, in the present invention, hot correction is performed between the pre-cooling and the post-cooling, but of course, hot correction may be performed before or after cooling as needed.
[0019]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[Example 1]
FIG. 4 is a side sectional view of the cooling device according to Embodiment 1 of the present invention. The cooling device is divided into a front cooling device 8 and a rear cooling device 9, and a hot leveler 7 is arranged in the middle.
[0020]
A cooling device is divided | segmented by the table roll 2 units, and the draining roll 6 is installed in the upper surface. The cooling method for the upper surface and the lower surface is spray cooling by the cooling nozzles 3 and 4.
[0021]
In FIG. 4, the hot steel plate 1 rolled by the rolling mill is conveyed by the table roll 2 and carried to the control cooling device. At this time, although not shown in the figure, it is further preferable to remove the rolling distortion by another hot leveler before entering the control cooling device. The steel plate 1 conveyed to the control cooling device is cooled by the pre-stage cooling device 8, hot-corrected by the hot leveler 7, and subsequently cooled to the target stop temperature by the rear-stage cooling device 9. The cooling rate and the cooling stop temperature are controlled by the amount of water in the pre-stage cooling device 8 and the post-stage cooling device 9 and the conveyance speed of the steel plate 1. The steel sheet temperature during hot straightening was measured with a radiation thermometer on the front surface of the hot leveler 7 (left side of the hot leveler 7 in FIG. 4), and the transformation rate was measured with a transformation rate meter using ultrasonic waves.
[0022]
Table 1 shows that as a test material, the chemical component is wt%, and C: 0.13 wt. %, Si: 0.35 wt. %, Mn: 1.35 wt. %, Nb: 0.01 wt. % Steel is heated to 1150 ° C. in a heating furnace, and then hot rolled to form a steel sheet having a plate thickness of 25 mm, a plate width of 3000 mm, and a plate length of 12000 mm, and then cooled under various conditions. The result of examining the temperature distribution of is shown.
[0023]
[Table 1]
[0024]
According to the present invention, the cooling was divided into two times, and the case where hot correction was performed during cooling, the case where hot correction was not performed, and the case where cooling was performed to the target stop temperature by one cooling were compared. Here, the temperature distribution of the steel plate after cooling is shown by the difference between the highest temperature and the lowest temperature in the steel plate surface. The lower the value, the smaller the temperature unevenness and the better the temperature uniformity. From Table 1, it can be seen that Examples 1 to 7 of the present invention have a better temperature distribution of the steel sheet after cooling and improved cooling uniformity compared to the continuous cooling and two-stage cooling of Comparative Examples 8 and 9. .
[0025]
[Example 2]
FIG. 5 is a side sectional view of a cooling device according to Embodiment 2 of the present invention. The hot leveler 7 is placed on the front surface of the cooling device 10 (the left side of the cooling device 10 in FIG. 5). The cooling device 10 is divided in units of two table rolls, and a draining roll 6 is installed on the upper surface. The cooling method of the upper surface by the cooling nozzles 3 and 4 is a pipe laminator, and the cooling method of the lower surface is spray cooling.
[0026]
The rolled hot steel sheet 1 is straightened by the hot leveler 7 and subsequently cooled to a predetermined temperature by the cooling device 10. After that, the steel plate 1 is fed back through the line and passes through the cooling device 10. Then, the steel plate 1 is hot-corrected again to remove deformation, and then cooled again to the target stop temperature by the cooling device 10. Although the efficiency of the present embodiment is lower than that of the first embodiment, hot correction before and during cooling is possible with one hot leveler, and the pre-cooling conditions and the post-cooling conditions are completely independent. Can be set.
[0027]
Using this equipment, the chemical component C: 0.12 wt. %, Si: 0.36 wt. %, Mn: 1.30 wt. %, Nb: 0.012 wt. % Steel was heated to 1150 ° C. in a heating furnace, and after hot rolling to a steel plate having a plate thickness of 12 mm, a plate width of 4000 mm, and a plate length of 18000 mm, a cooling start temperature of 800 ° C. and a final cooling stop temperature of 500 ° C. Cooled down.
[0028]
According to the present invention, when the cooling is divided into two times, after pre-cooling at a cooling rate of 30 ° C./s, hot-corrected at 700 ° C., and subsequently cooled at the cooling rate of 30 ° C./s, the temperature distribution of the steel sheet after cooling is It was 9 ° C.
[0029]
On the other hand, after pre-cooling at a cooling rate of 30 ° C./s, hot correction was not performed, and when the subsequent cooling was performed at a cooling rate of 30 ° C./s, the temperature distribution of the steel sheet after cooling was 36 ° C. Furthermore, when it cooled to 500 degreeC by the continuous cooling of the cooling rate 30 degreeC / s, the distortion amount of the steel plate after cooling was 60 degreeC.
[0030]
From these results, it can be seen that the inventive example has less temperature unevenness of the steel sheet after cooling and improved cooling uniformity as compared with the continuous cooling or two-stage cooling of the comparative example.
[Example 3]
FIG. 6 is a side sectional view of a cooling device according to Embodiment 3 of the present invention. The hot leveler 7 is installed on the rear surface of the cooling device 10 (on the right side of the cooling device 10 in FIG. 6). The cooling device 10 is divided in units of two table rolls, and a draining roll 6 is installed on the upper surface. The cooling method of the upper surface by the cooling nozzles 3 and 4 is slit laminar, and the cooling method of the lower surface is fountain cooling.
[0031]
The rolled hot steel sheet 1 is hot-corrected after being cooled to a predetermined temperature by the cooling device 10. Thereafter, the steel sheet 1 is fed back through the line and cooled again to the target stop temperature by the cooling device 10.
[0032]
Using this equipment, the chemical component C: 0.14 wt. %, Si: 0.33 wt. %, Mn: 1.42 wt. % Steel is heated to 1150 ° C. in a heating furnace, and then hot rolled to form a steel plate having a plate thickness of 40 mm, a plate width of 2000 mm, and a plate length of 8000 mm, followed by a cooling start temperature of 800 ° C. and a final cooling stop temperature of 500 ° C. Cooled down.
[0033]
According to the present invention, when the cooling is divided into two times, after pre-cooling at a cooling rate of 15 ° C./s, hot-corrected at 680 ° C., and then subsequently cooled at a cooling rate of 15 ° C./s, the temperature distribution of the steel sheet after cooling is It was 6 ° C.
[0034]
On the other hand, after pre-cooling at a cooling rate of 15 ° C./s, hot correction was not performed, and when post-cooling was performed at a cooling rate of 15 ° C./s as it was, the strain of the steel sheet after cooling was 31 ° C. Furthermore, when it cooled to 500 degreeC by the continuous cooling of the cooling rate of 15 degree-C / s, the distortion amount of the steel plate after cooling was 52 degreeC.
[0035]
Also from this result, it can be seen that the inventive example has less temperature unevenness of the cooled steel sheet and improved cooling uniformity compared to the continuous cooling and two-stage cooling of the comparative example.
[0036]
【The invention's effect】
As described above, according to the present invention, temperature unevenness generated by cooling can be reduced, and the flatness of the steel plate after cooling can be improved, thereby preventing re-correction and care of the steel plate after cooling. In addition to the necessity, it is possible to suppress the variation of the material and improve the yield, and thus to provide an industrially useful effect.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between a steel plate temperature and a steel extensometer value.
FIG. 2 is a graph showing the relationship between the steel sheet temperature during hot straightening and the temperature unevenness of the steel sheet after cooling.
FIG. 3 is a graph showing the relationship between the steel sheet temperature and the transformation rate during hot straightening.
FIG. 4 is a side sectional view of the cooling device according to Embodiment 1 of the present invention.
FIG. 5 is a side sectional view of a cooling apparatus according to Embodiment 2 of the present invention.
FIG. 6 is a side sectional view of a cooling device according to Embodiment 3 of the present invention.
FIG. 7 is an explanatory diagram of a conventional two-stage cooling device.
[Explanation of symbols]
1: Steel plate 2: Table roll 3: Cooling nozzle 4: Cooling nozzle 5: Air nozzle 6: Draining roll 7: Hot leveler 8: Pre-stage cooling device 9: Rear-stage cooling device 10: Cooling device a: Pre-stage cooling zone b: Recuperation zone c: Rear cooling zone

Claims (3)

  1. 熱間圧延鋼板の制御冷却方法において、冷却を途中で一旦停止し、次いで、熱間矯正し、次いで、再び前記冷却の冷却速度と同一の冷却速度で冷却することを特徴とする、熱間圧延鋼板の制御冷却方法。In the controlled cooling method of a hot rolled steel sheet, the hot rolling is characterized in that the cooling is temporarily stopped halfway, then hot straightened, and then cooled again at the same cooling rate as the cooling rate of the cooling. Controlled cooling method for steel sheet.
  2. 熱間矯正するときの鋼板温度がAr3−150℃以上Ar3−20℃以下の範囲であることを特徴とする、請求項1記載の方法。The method according to claim 1, wherein the temperature of the steel sheet when hot straightening is in the range of Ar 3 -150 ° C to Ar 3 -20 ° C.
  3. 熱間矯正するときの鋼板の変態率が5%以上75%以下の範囲であることを特徴とする請求項1または2記載の方法。  The method according to claim 1 or 2, wherein the transformation rate of the steel sheet when hot straightening is in the range of 5% to 75%.
JP25376898A 1998-09-08 1998-09-08 Controlled cooling method for hot rolled steel sheet Expired - Fee Related JP3661434B2 (en)

Priority Applications (1)

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CN100464886C (en) * 2003-06-13 2009-03-04 杰富意钢铁株式会社 Device and method for controllably cooling thick steel plate
KR100715264B1 (en) * 2003-06-13 2007-05-04 제이에프이 스틸 가부시키가이샤 Device and method for controllably cooling thick steel plate
JP5058652B2 (en) * 2007-03-29 2012-10-24 新日本製鐵株式会社 Manufacturing method of thick steel plate with excellent low temperature toughness of base metal and weld heat affected zone
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