JP2004351501A - Method and equipment for cooling of hot rolled metal sheet, and high tension hot rolled steel sheet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling method and cooling equipment for a hot rolled metal sheet with a uniform coiling temperature distribution in the width direction, and a high tension hot rolled steel sheet with a small variation of yield strength in the width direction. <P>SOLUTION: A steel material containing 0.01-0.2% of C, 0.01-1.5% of Si, 0.1-3% of Mn, ≤0.04% of P, ≤0.02% of S, ≤0.1% of Al and ≤0.005% of N is subjected to roughing and finishing rolling to produce a hot rolled steel sheet. While cooling in the cooling zone, the proximity of both width edges of the steel sheet is masked from cooling water supplied, and the cooling water of the masked portion is shifted from the proximity of both width edges to the center side of the width to cool the specific region intensively. Thus, the high tension hot rolled steel sheet with small variation in the yield strength is produced, which has the yield strength difference between the maximum and the minimum of not larger than 30 MPa in the region from 20mm in both width edges to the width center. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００５４】
仕上圧延機１８で仕上圧延された熱延鋼板１は、ついで冷却ゾーン２２で巻取り温度まで冷却した。なお、熱延鋼板の目標強度は、引張強さ：４００ 〜１０００ＭＰａ （許容：−５０ＭＰａ 、＋４０ＭＰａ ）とした。
冷却ゾーン２２での冷却は、図５に示すように、テーブルローラ３を配列したランアウトテーブルを通過する間に、上下に設置された複数のヘッダ４、４１から冷却水を供給して行った。上部のヘッダ４は円管状のノズル５を熱延鋼板１の幅方向に並べたパイプラミナーヘッダであり、棒状の冷却水を鋼板１の幅方向に５０ｍｍピッチで多数供給する。上下ヘッダとも円管状のノズル５を鋼板１の幅方向に５０ｍｍピッチで４０本設置し、搬送方向に６ヘッダを１組として共通元配管につなぎ配設したものを１つの水冷ゾーンとして扱い、これを２０ゾーン設ける構成とした。また、上部ヘッダ４と熱延鋼板１の間には、図１および図２に示される構造、形状の遮蔽体６および移動機構７を配設して、両幅エッジに供給される冷却水を遮蔽する（両幅エッジをエッジマスキングする）とともに、特定領域に遮蔽した冷却水を供給した。遮蔽体６は、移動機構７により熱延鋼板の幅方向に移動可能に取り付けられており、各水冷ゾーンごとに遮蔽体６の位置を変更した。なお、従来例として、図１３に示す従来の遮蔽体も使用した。なお、以下、遮蔽体および移動機構を含めエッジマスキング装置ともいう。
【００５５】
冷却方法は表２に示す次の３種類とした。
【００５６】
【表２】

【００５７】
（Ａ）適用例
水冷ゾーンＮｏ．２〜Ｎｏ．４、Ｎｏ．６〜Ｎｏ．８、Ｎｏ．１０ 〜Ｎｏ．１２ 、Ｎｏ．１４ 〜Ｎｏ．１６ 、Ｎｏ．１８ には、図１および図２に示す構造の遮蔽体６および移動機構７を有するエッジマスキング装置を設置し、熱延鋼板１の両幅エッジ付近に供給される冷却水を遮蔽するとともに、遮蔽された冷却水を熱延鋼板１の両幅エッジ付近よりも幅中央側に落下させた。なお、各水冷ゾーンで、遮蔽体の位置を変更し、熱延鋼板の両幅エッジにせり出す遮蔽体の幅を４０〜１８０ｍｍ の間で変化させた。一方、水冷ゾーンＮｏ．１、Ｎｏ．５、Ｎｏ．９、Ｎｏ．１３ 、Ｎｏ．１７ 、Ｎｏ．１９ 、Ｎｏ．２０ には、図１３に示す構造の遮蔽体（従来例）を設置し、水冷ゾーンＮｏ．１のみ、熱延鋼板１の両幅エッジで幅中央側にせり出す幅（遮蔽体のせり出し幅）が７０ｍｍとなるように遮蔽体６を設定してエッジマスキングを行った。他の冷却ゾーンでは遮蔽体は熱延鋼板の外側に留め、遮蔽体のせり出しは無しとした。なお、この水冷ゾーンのパターンは、図６のエッジマスキング効果に関する結果をもとに、巻取り温度の幅方向分布が均一になるように、さらに実験を加えて得られたものである。
（Ｂ）従来例１
各水冷ゾーンともエッジマスキング装置を使用しない例とした。
（Ｃ）従来例２
各水冷ゾーンに図１３に示す構造のエッジマスキング装置を設置し、奇数番目の水冷ゾーン合計１０ゾーンで、遮蔽体のせり出し幅が交互に１００ｍｍ あるいは７０ｍｍとなるように遮蔽体６を設置してエッジマスキングを行なった。一方、偶数番目の水冷ゾーンでは遮蔽体のせり出し幅を零とし、エッジマスキング無しとした。
【００５８】
上記した（Ａ）〜（Ｃ）の冷却方法で冷却したのちに、得られた熱延鋼板の巻取り温度の幅方向分布の一例を図７に示す。幅方向の巻取り温度分布は、幅中央に対し線対称となっており、図７では幅中央から片側の幅エッジにかけての右側半分の温度分布を示した。
適用例の巻取り温度の幅方向温度分布曲線Ａ（実線）は、遮蔽体６により冷却水が遮蔽された領域の直下部には冷却水が供給されないから、従来この部分で生じていた過冷却を抑制することができ、熱延鋼板の幅エッジから２０ｍｍの位置の温度が幅中央より２３℃低いだけにとどまり、また、遮蔽体６で遮蔽された冷却水を集中的に両幅エッジから１２０ｍの位置に供給したため、その位置の温度も幅中央に比べて３５℃高くなっただけであった。図７から、本発明の冷却方法（適用例）によれば、均一な幅方向温度分布となることがわかる。
【００５９】
一方、従来例１の幅方向温度分布曲線Ｂ（一点鎖線）は、熱延鋼板の両幅エッジ付近が他の部分と比べて局部的に過冷却となり、熱延鋼板の幅エッジから２０ｍｍの位置での温度は、幅中央の温度よりも１３３ ℃も低くなっている。また、従来例２の幅方向温度分布曲線Ｃ（破線）は、遮蔽体６により冷却水が遮蔽された領域の直下部には冷却水が供給されないから、従来この部分で生じていた過冷却を抑制することができ、熱延鋼板の幅エッジから２０ｍｍの位置の温度は幅中央より３３℃低いだけにとどまっているが、両幅エッジから１００ｍｍ の位置の温度は幅中央に比べて９８℃高くなっている。
【００６０】
つぎに、上記した冷却方法で冷却した熱延鋼板から、短冊状の試験片（幅：２０ｍｍ）を採取し、引張試験片に加工して引張試験を実施し、降伏強さＹＳ、引張強さＴＳ、伸びＥｌを測定した。なお、使用した引張試験片はＪＩＳ Ｚ２２０１ に規定されるＪＩＳ ５ 号試験片に準じ平行部：１８ｍｍ幅、平行部長さ：６０ｍｍ（ＧＬ：５０ｍｍ）とし、引張方向を熱延鋼板の圧延長さ方向とした。また、引張試験片は、試験片幅中央が、熱延鋼板幅エッジから、２０ｍｍ間隔で所定の位置（幅エッジから２０ｍｍ、４０ｍｍ等）となるように採取した。得られた結果を図８〜図１０に示す。
【００６１】
本発明例の冷却方法（Ａ）で冷却された表１中に示す鋼Ｎｏ．Ｄの組成を有する熱延鋼板では、遮蔽体６により冷却水が遮蔽され、図７で示したように幅エッジから２０ｍｍの位置の温度は幅中央より２３℃低いだけにとどまったため、図８に示すようにＴＳ：５５４ＭＰａ、ＹＳ：４７１ＭＰａ（図８の最右端のプロット）となっている。このため、耳切り代は、エッジドロップなど材質とは関係のない条件で決められ、両幅エッジとも２０ｍｍ（合計４０ｍｍ）となり、歩留まりは９６％となった。また、遮蔽体６を熱延鋼板の幅中央に向けせり出す幅を４０〜１８０ｍｍ の間で段階的に変えるようにしたから、図７に示すように、両幅エッジから１２０ｍｍ の位置の巻取り温度が幅中央に比べて３５℃高くなっただけであり、図８に示すように、幅エッジから２０ｍｍの位置から幅中央側の全領域での、ＴＳの変動（最大と最小の差）は３５ＭＰａ 、ＹＳの変動は２８ＭＰａ となり、幅方向における強度変動が少ない熱延鋼板となっている。
【００６２】
一方、従来例１の冷却方法（Ｂ）で冷却された熱延鋼板では、両幅エッジでマスキングを行わなかったため、図７で示したように幅エッジから２０ｍｍの位置の巻取り温度は幅中央よりも１３３ ℃も低くなっており、ＴＳ：６１８ＭＰａ、ＹＳ：５１９ＭＰａとなっている。両幅エッジとも、硬すぎて製品に要求されるＥｌ：２４％を確保できない領域：６０ｍｍを耳切り代として切り捨てざるをえなかったため、製品の歩留まりは８８％となった。また、図７に示すように、両幅エッジから１２０ｍｍ の位置の巻取り温度は、幅中央に比べて８３℃高く、ＴＳ：４９０ＭＰａ、ＹＳ：４１１ＭＰａとなっている。図９に示すように、両幅エッジの硬すぎる領域（合計１２０ｍｍ ）を耳切り代として切り捨てた後も、ＴＳの変動（最大と最小の差）は４０ＭＰａ 、ＹＳの変動は幅方向で４５ＭＰａ もあり、幅方向における強度変動が大きな熱延鋼板となっている。
【００６３】
また、従来例２の冷却方法（Ｃ）で冷却された熱延鋼板では、遮蔽体６により冷却水が遮蔽され、従来この部分で生じていた過冷却を抑制することができ、図７に示すように、幅エッジから２０ｍｍの位置の温度は幅中央より３３℃低いだけにとどまったため、ＴＳ：５６０ＭＰａ、ＹＳ：４７０ＭＰａとなっている。。これよりも幅中央側の材質が良好であったので、耳切り代はエッジドロップなど材質とは関係のない条件で決められ、両幅エッジとも２０ｍｍ（合計４０ｍｍ）となり、歩留まりは９６％となった。
【００６４】
なお、両幅エッジから１２０ｍｍ の位置の巻取り温度は、幅中央に比べて９６℃高くなり、ＴＳ：４８２ＭＰａ、ＹＳ：４０４ＭＰａであった。図１０に示すように、幅エッジから２０ｍｍの位置から幅中央側の全領域での、ＴＳの変動（最大と最小の差）は７８ＭＰａ 、ＹＳの変動は６６ＭＰａ となり、幅方向の強度変動が大きな熱延鋼板となっている。
つぎに、仕上圧延終了後、上記した（Ａ）〜（Ｃ）の冷却方法で冷却した熱延鋼板について、さらに仕上圧延後の熱延鋼板先端からの長さで２００ ｍの位置で、鋼板の幅方向全域にわたり２０ｍｍピッチで、短冊状（幅：１８ｍｍ）の試験片を採取し、引張試験片に加工して引張試験を実施し、降伏強さＹＳ、引張強さＴＳ、伸びＥｌを測定した。なお、使用した引張試験片は平行部：１８ｍｍ幅、平行部長さ：６０ｍｍ（ＧＬ：５０ｍｍ）とし、引張方向を熱延鋼板の圧延長さ方向とした。また、引張試験片は、試験片幅中央が、熱延鋼板幅エッジから、２０ｍｍ間隔で所定の位置（幅エッジから２０ｍｍ、４０ｍｍ等）となるように採取した。得られた結果を表３に示す。表３では、各位置で得られた、降伏強さ、引張強さ、伸びのうちの、最大値、最小値、およびそれらの差を記した。
【００６５】
【表３】

【００６６】
【表４】

【００６７】
本発明の冷却方法を適用した熱延鋼板（適用例）では、鋼板の幅方向での強度変動を確実に少なくすることができる。一方、本発明の範囲を外れる従来例では、幅方向での強度変動が大きく、プレス加工時のスプリングバックの発生量が鋼板部位により違うなどの問題が生じる可能性が大きいことがわかる。また、熱延鋼板の幅中央側に遮蔽した冷却水を集中的に供給できる水冷ゾーンを少なくとも１つ以上設けることにより、熱延鋼板の幅方向の強度変動は確実に小さくすることができることがわかる。
【００６８】
なお、ここで示した本発明例では、鋼板の幅方向外側に冷却水を落下させる形式のエッジマスキング装置（例えば、図１３）をいくつかの水冷ゾーンに設置したが、この形式のエッジマスキング装置は必ずしも併設する必要はない。遮蔽した冷却水を鋼板幅中央側に集中的に供給できるエッジマスキング装置を設置するだけで、遮蔽板が鋼板の幅中央に向けせり出した領域の直下ではエッジマスキングを行なったのと同様な効果が得られるためである。また、ここで示した本発明例の冷却方法では、両幅エッジにせり出し量を調整して設置された遮蔽板により遮蔽された冷却水が集中的に供給される特定領域を各水冷ゾーンごとに鋼板のエッジ側から中央側に順次変化させた例を示したが、本発明はこれに限定されるものではないことはいうまでもない。
【００６９】
また、本発明の実施例では、図１１に示した熱間圧延ライン１００ を利用したが、本発明はこれに限定されるものではなく、図１２に示すような、薄スラブを連続鋳造し、粗圧延を経ずに直接仕上圧延する、熱間圧延ライン２００ のような他のタイプの熱間圧延ラインにも適用可能なことはいうまでもない。
【００７０】
【発明の効果】
以上説明したように、本発明によれば、巻取り温度が熱延金属板の幅方向で均一となり、幅方向に降伏強さの変動が少なく、幅方向に均一な品質を有する高張力熱延鋼板を容易にしかも安価に製造でき、産業上格段の効果を奏する。また、本発明によれば、プレス加工など後工程における歩留まりが改善されるという効果もある。
【図面の簡単な説明】
【図１】本発明の冷却装置の一例を模式的に示す正面図である。
【図２】本発明の冷却装置の一例を模式的に示す平面図である。
【図３】本発明の冷却装置の一例を模式的に示す平面図である。
【図４】本発明の冷却装置の一例を模式的に示す正面図である。
【図５】本発明の冷却装置の一例を模式的に示す側面図である。
【図６】冷却ゾーンの１ゾーンあたりの幅方向各位置の温度変化におよぼすエッジマスキング、エッジマスキング＋特定領域冷却の影響の一例を示すグラフである。
【図７】巻取り温度の幅方向分布の比較を示すグラフである。
【図８】冷却方法（Ａ）で冷却した場合の引張特性の幅方向分布を示すグラフである。
【図９】冷却方法（Ｂ）で冷却した場合の引張特性の幅方向分布を示すグラフである。
【図１０】冷却方法（Ｃ）で冷却した場合の引張特性の幅方向分布を示すグラフである。
【図１１】熱間圧延ラインの一例を模式的に示す説明図である。
【図１２】熱間圧延ラインの一例を模式的に示す説明図である。
【図１３】従来のエッジマスキング装置を模式的に示す説明図である。
【図１４】従来の熱延鋼板巻取り温度の幅方向分布の一例を示す説明図である。
【図１５】従来の熱延金属板冷却における冷却水の流れを模式的に示す説明図である。
【図１６】熱延金属板における抜熱状態を模式的に示す説明図である。
【符号の説明】
１ 熱延金属板（熱延鋼板、鋼板）
３ テーブルローラ
４ ヘッダ（上部ヘッダ）
４１ 下部ヘッダ
５ ノズル
５１ 下部ノズル
６ 遮蔽体
６ａ 溝状穴
６ｂ 蝶番
６ｃ ウインチ（釣り上げ機構）
７ 温度計
７ａ 仕上出側温度計
７ｂ、７ｃ 幅方向温度計
７ｄ 巻取り温度計
８ 被圧延材
１０ 加熱炉
１２ 粗圧延機
１３ ワークロール
１４ クロップシャ
１６ デスケーリング装置
１８ 仕上圧延機
１９ ワークロール
２０ スラブ連続鋳造設備
２２ 冷却ゾーン
２４ コイラー
５０ 制御装置
７０ プロセスコンピュータ
８０ ビジネスコンピュータ
１００ 、２００ 熱間圧延ライン[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and a device for cooling a hot-rolled metal sheet, and more particularly to a high-tensile hot-rolled steel sheet having a sheet width of 500 mm or more, which suppresses fluctuations in yield strength in the width direction, and a method for manufacturing the same. The steel sheet in the present invention includes a steel strip.
[0002]
[Prior art]
Hot rolling refers to heating a metal material to a few hundred to a few hundred degrees, extracting it on a hot rolling line, rotating the roll while pinching it with a pair of rolls, and stretching it thinly. Many hot rolling lines are of the type called 3/4 continuous. An example of this type of hot rolling line is shown in FIG. In the hot rolling line 100, usually, a heating furnace 10, a plurality of rough rolling mills 12, a crop shear 14, a descaling device 16, a finishing mill 18, a cooling zone 22, a coiler (winding device) 24 is arranged. In the hot rolling line 100 of this type, the rough rolling mill 12 often has four rolling mills, some of which (one in many cases) perform reciprocating rolling, and the remaining rolling mills perform unidirectional rolling. In many cases, for this reason, three out of four units are unidirectionally rolled, and are therefore referred to as a 3/4 continuous type. The 3/4 continuous type includes, for example, a type in which three rough rolling mills 12 are provided and one or two of them are unidirectional.
[0003]
In the example of the hot rolling line 100 shown in FIG. 11, there are three rough rolling mills, and two of them perform reciprocating rolling. Although not shown, a number of table rollers are provided between the respective equipments, and thereby the material 8 to be rolled is conveyed. The group of table rollers in the cooling zone 22 may be particularly called a run-out table. Since a plurality of the rough rolling mills 12 and the finishing rolling mills 18 are provided, the initials of Rougher (rough rolling mill) and Finisher (finishing rolling mill) are respectively taken, and the numbers of the respective stands are assigned. R2, R3, F1, F2 ... F7, etc. Similarly, there are also a plurality of coilers 24, which are abbreviated as DC1, DC2, etc., by giving a machine number.
[0004]
In recent years, a hot rolling line for continuously casting thin slabs and directly finishing and rolling without rough rolling has also been provided. An example of such a hot rolling line 200 is shown in FIG.
In order to impart a desired metallurgical property to the metal plate after hot finish rolling (hereinafter also including a metal strip), a cooling plate is usually provided on a run-out table for transporting the metal plate from the hot finish rolling mill to the coiler. A cooling device is provided as the zone 22. The metal sheet passes through a cooling zone 22, is cooled to a desired winding temperature, and is wound by a coiler 24. Water is usually used as a cooling medium. For example, in the case of a hot-rolled steel sheet, the winding temperature is very important for providing a desired material, and needs to be controlled with high accuracy.
[0005]
In the cooling zone 22, a cooling device for cooling the upper surface of the metal plate is a device which has a large cooling capacity and facilitates maintenance of the device, which is called a pipe laminator and which drops rod-shaped cooling water onto the upper surface of the metal plate. Is often used. On the other hand, in cooling the lower surface of the metal plate, various cooling devices such as a spray and a pipe laminator are used, and the cooling is not constant.
[0006]
Conventionally, in cooling a hot-rolled metal plate, it has been considered desirable to make the distribution of the cooling water flow rate in the width direction of the hot-rolled metal plate constant so that the hot-rolled metal plate is uniformly cooled in the width direction. . Therefore, the direction of the cooling water injected from each nozzle is constant, and the flow rate of the cooling water injected from each nozzle is also constant. It is common to arrange a plurality of units in the cooling zone. However, conventionally, it is known that the vicinity of both width edges of the hot-rolled metal plate is locally cooled better than other portions. In addition, the vicinity of both width edges of the hot-rolled metal plate generally refers to a region of, for example, approximately 50 mm by approximately 50 mm from the uppermost edge of both widths of the hot-rolled metal plate to a maximum of 80 mm.
[0007]
In the vicinity of both width edges of the hot-rolled metal sheet, the winding temperature is locally lowered due to the local cooling, and the desired material cannot be obtained in that region in many cases. It is generally cut off in the next step of the purification line or the like.
In order to reduce the margin for trimming as much as possible, for example, in Patent Document 1, an end (edge) of a thick steel plate (hot-rolled metal plate 1) is shielded by a shielding gutter 6, and a nozzle is inserted through an upper header 4. As shown in FIG. 13, a part of the cooling water W supplied from 5 is dropped outside the both width ends (edges) of the thick steel plate (hot-rolled metal plate 1). A method and apparatus for cooling a steel sheet have been proposed. The device described in Patent Literature 1 is called a so-called edge masking device. By using this device, supercooling near both width edges of a thick steel plate is suppressed, and the width direction of a thick steel plate (hot rolled metal plate) is reduced. It is stated that the temperature distribution can be made uniform, and mechanical variations and distortion of thick steel plates (hot-rolled metal plates) can be prevented.
[0008]
Further, in Patent Document 2, a cooling zone for cooling the upper surface of the steel sheet is divided into a plurality of zones, and cooling water is injected into each of the divided zones so as to form a laminar flow in a strip shape in the traveling direction of the steel sheet. There has been proposed a cooling method of a steel sheet in which a water injection position of a cooling zone near an edge portion in a width direction of a steel sheet is shifted to a downstream side in a traveling direction of the steel sheet from a water injection position in a center part of the steel sheet in a width direction to cool the steel sheet. According to the technique described in Patent Literature 2, cooling can be uniformly performed along the width direction of the steel sheet, and variation in material and deformation of the steel sheet are reduced. Also, various proposals have been made in Patent Literature 3, Patent Literature 4, and the like in order to perform uniform cooling in the width direction of the steel sheet.
[0009]
[Patent Document 1]
JP-A-58-32511
[Patent Document 2]
JP-A-11-57836
[Patent Document 3]
JP-A-11-267736
[Patent Document 4]
JP 2002-263724 A
[0010]
[Problems to be solved by the invention]
However, in recent years, a demand for a metal plate having a uniform material in the width direction has been increasing more and more. Therefore, in addition to the temperature control in the longitudinal direction of the metal plate, the temperature control in the width direction has become important, and the inlet / outlet side of the cooling zone 22 has the width center of the hot rolled metal plate conventionally provided. In addition to a thermometer for measuring the temperature of the hot rolled metal sheet in the width direction, installing a width direction thermometer, etc. And deal with it. Particularly in recent years, in the production of high-strength steel sheets, which have been increasingly required for quality in order to reduce the weight of automobiles, etc., in order to produce uniform and high-quality metal sheets in the width direction, the winding temperature in the width direction has to be increased. Control is important.
[0011]
In the hot rolling of a high-tensile steel sheet, the rolling load particularly in the finish rolling increases, and therefore, the torque of the electric motor for rotating and driving the work roll of each rolling mill also increases, and a large amount of electric power is required. Because the power of the electric motor of the rolling mill is limited, the hot finish rolling of high strength steel sheets requires a lower rolling speed than the hot finish rolling of low carbon steel sheets and ultra low carbon steel sheets with relatively low strength. Has become commonplace.
[0012]
However, when the rolling speed was reduced and the width direction temperature distribution of the steel sheet after finish rolling was measured using a width direction thermometer, the temperature distribution was almost smooth in the width direction of the steel sheet on the exit side of the finishing mill. Nevertheless, before being wound after being cooled in the cooling zone, the temperature distribution tends to have an M-shaped shape as shown in FIG. That is, it was found that when the rolling speed was low, there was a problem that the uniformity of the winding temperature in the steel sheet width direction was lost. Here, the M-shaped temperature distribution as shown in FIG. 14 means that the temperature at the center of the width of the steel sheet is minimal, the temperature increases as approaching the width edge, shows a peak, and further approaches the width edge. And the temperature distribution in the width direction such that the temperature sharply decreases.
[0013]
According to the investigation by the present inventor, the region where the steel plate temperature locally increases and shows a peak is a region corresponding to a position of 100 to 200 mm from both width edges of the steel plate, and the temperature difference from the center of the width of the steel plate. In some cases, the temperature was 80 ° C. or more, depending on the rolling speed and the level of the winding temperature. It was also found that the peak position (d: distance from both edges of the steel sheet) of the M-shaped temperature distribution shape was substantially constant even when the width of the steel sheet changed.
[0014]
In the related arts described in Patent Documents 1 to 4, it is possible to suppress the vicinity of the width edge of the hot-rolled metal plate from being locally cooled more easily than other portions. However, the M-shaped temperature distribution of the winding temperature in the width direction of the hot-rolled metal sheet cannot be suppressed.
The present invention provides a method for cooling a hot-rolled metal sheet and a cooling apparatus therefor, which eliminate the above-described conventional M-shaped temperature distribution in the width direction of the hot-rolled metal sheet and provide a uniform winding temperature distribution in the width direction. The primary purpose is to make proposals. A second object of the present invention is to propose a high-strength hot-rolled steel sheet having a small variation in yield strength in the width direction and a method for producing the same.
[0015]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present inventors have first studied diligently about the reason why the temperature distribution in the width direction of a hot-rolled metal sheet cooled by cooling water in a cooling zone after finish rolling is generated.
The cooling water that cools the lower surface of the hot-rolled metal plate is supplied by being sprayed toward the hot-rolled metal plate and then falls by gravity. For this reason, if the same nozzles are installed at equal intervals in the width direction of the hot-rolled metal plate, temperature unevenness rarely occurs in the width direction of the hot-rolled metal plate. On the other hand, the cooling water W that cools the upper surface of the hot-rolled metal plate 1 falls from the nozzle 5 onto the hot-rolled metal plate 1 and then flows over the hot-rolled metal plate 1 and from both edges to the run-out table. drop down. During this time, a complicated interference flow is created on the hot-rolled metal plate 1.
[0016]
When the pipe laminar type rod-shaped cooling water W is dropped onto the upper surface of the hot-rolled metal plate 1 from the header 4 via the nozzle 5, the flow of the cooling water formed on the hot-rolled metal plate 1 is schematically shown. As shown in FIG. The cooling water that has collided with the hot-rolled metal sheet 1 flows downstream in the transport direction (the direction of the arrow A) while being carried along with the transport of the hot-rolled metal sheet 1. The cooling water that has flowed downstream in the transport direction is blocked by walls formed by the cooling water W that falls on the downstream side in the transport direction, and thus flows in the width direction of the hot-rolled metal plate 1 (in the direction of arrow B). When the flows in the two directions A and B become stronger to some extent, the force of the falling cooling water W to break the water film formed by these flows and reach the surface of the hot-rolled metal plate 1 becomes insufficient. Become like That is, the area where the falling cooling water W comes into direct contact with the hot-rolled metal plate 1, that is, a so-called black spot, is reduced, and the cooling capacity is reduced.
[0017]
Here, the flow rate of the cooling water carried on the hot-rolled metal plate 1 from the upstream along the transport direction does not depend on the position in the width direction of the hot-rolled metal plate 1. On the other hand, since the cooling water after falling flows right and left, the flow rate of the flow in the width direction decreases toward the center of the width of the hot-rolled metal sheet 1, and the flow rate of the flow in the width direction increases as approaching both width edges, It is largest at both width edges. In other words, the flow in the B direction becomes stronger as it approaches both width edges of the hot-rolled metal plate 1, so that the falling cooling water is less likely to directly contact the metal plate 1, and the cooling capacity is reduced. Therefore, it is considered that the winding temperature is locally increased as the width edge is approached, except for a region where the winding temperature is locally reduced near the both width edges. The reason why the winding temperature locally decreases near the both width edges is that, as shown in FIG. 16, heat is removed from only two surfaces in the other region, whereas heat is removed from three surfaces in both width edges. It is inferred that this is due to
[0018]
In this way, it is considered that the temperature distribution in the width direction of the hot-rolled metal sheet cooled in the cooling zone after the finish rolling becomes uneven. It has been found that the non-uniformity of the temperature distribution is greatly affected by the rolling speed and becomes significant when the rolling speed is approximately 10 m / s or less. In addition, the unevenness of the temperature distribution in the width direction of the hot-rolled metal sheet becomes larger as the target value of the winding temperature is lower, that is, as the temperature drop when cooling the upper surface of the hot-rolled metal sheet is larger. Further, when the winding temperature is lower than 500 ° C., the temperature drop locally becomes large, the vicinity of both width edges of the hot-rolled metal sheet and the center area of the width of the hot-rolled metal sheet become the transition boiling temperature range. Therefore, the non-uniformity of the temperature distribution generated in the width direction of the hot-rolled metal plate is further increased. Therefore, a metal plate of a type in which the temperature drop is large because the target value of the winding temperature is low, specifically, particularly, is cooled to a low temperature such that the winding temperature is lower than 500 ° C. to refine the ferrite structure. In the case of a high-strength steel sheet or the like that obtains high strength by heating, there has been a problem that the unevenness of the temperature distribution generated in the width direction of the steel sheet is further increased, and the material variation in the width direction of the steel sheet is increased.
[0019]
From the above, the present inventor performed edge masking to reduce the temperature drop of both width edges, and shielded by edge masking, in order to eliminate the unevenness of the temperature distribution in the width direction of the hot-rolled metal sheet. By supplying the cooling water to the width center side from both the width edges and enhancing the cooling at the width center side from both the width edges, he came to think that the peak of the M-shaped temperature distribution was leveled.
[0020]
The present invention has been completed based on the above findings, with further investigations. That is, the present invention for achieving the above object is as follows.
The first invention is
(1) In a method for cooling a hot-rolled metal sheet, in which a cooling zone cools an upper surface of the hot-rolled metal sheet after completion of hot finish rolling, the hot-rolled metal sheet is supplied near both width edges of the hot-rolled metal sheet. A method for cooling a hot-rolled metal sheet, comprising shielding cooling water, and supplying the shielded cooling water to the width center side of the hot-rolled metal sheet near both width edges thereof. The present invention
(2) A hot-rolled metal sheet cooling device that is installed in a cooling zone on the downstream side of the hot-finish rolling mill in the metal sheet conveying direction and cools the upper surface of the hot-rolled metal sheet conveyed after finish rolling, A plurality of headers disposed above the hot-rolled metal plate to supply cooling water; and a plurality of headers each of which is disposed at an interval in the width direction of the hot-rolled metal plate on each of the plurality of headers. A plurality of nozzles for supplying cooling water to the upper surface, a part of the cooling water supplied from the plurality of nozzles is shielded from both width edge sides of the hot-rolled metal plate, and the shielded cooling water is It is characterized by comprising: a shield for supplying the width-centered side of the hot-rolled metal plate closer to the width than the vicinity of both width edges; and a moving mechanism for moving the shield in the width direction of the hot-rolled metal plate. Cooling equipment for hot rolled metal sheets
It is.
[0021]
In addition, the third present invention,
(3) In mass%, C: 0.01 to 0.2%, Si: 0.01 to 1.5%, Mn: 0.1 to 3%, P: 0.04% or less, S: 0. Contains not more than 02%, not more than 0.1% of Al, not more than 0.005% of N, and has a composition consisting of the balance of Fe and unavoidable impurities, and has a maximum yield strength from the width edges of 20 mm to the width center. A high-strength hot-rolled steel sheet, wherein the difference between the value and the minimum value is 30 MPa or less.
(4) In (3), in addition to the above composition, in mass%, Cu: 0.01 to 1.0%, Cr: 0.01 to 1.0%, Ni: 0.01 to 1.0%. %, Mo: 0.01 to 1.0%, Ti: 0.01 to 0.2%, Nb: 0.01 to 0.2%, V: 0.01 to 0.1%. A high-strength hot-rolled steel sheet comprising one or more kinds.
It is. In addition, the fourth present invention,
(5) In the method for producing a hot-rolled steel sheet by subjecting a steel material to hot rolling including rough rolling and finish rolling, wherein the steel material is mass%, C: 0.01 to 0.2%. , Si: 0.01 to 1.5%, Mn: 0.1 to 3%, P: 0.04% or less, S: 0.02% or less, Al: 0.1% or less, N: 0.005 % Of a steel material having a composition of not more than 0.1%, and cooling the upper surface of the hot-rolled steel sheet with cooling water after the finish rolling, shielding cooling water supplied near both width edges of the hot-rolled steel sheet, The method is characterized in that the shielded cooling water is supplied to the width center side of the hot-rolled steel sheet from the vicinity of both width edges, and the difference between the maximum value and the minimum value of the yield strength from both width edges 20 mm to the width center is 30 MPa. The following is a method for producing a high-tensile hot-rolled steel sheet.
It is.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
First, a method for cooling a hot-rolled metal plate according to the first invention will be described.
In the cooling method of the present invention, as shown in FIG. 5, after the hot finish rolling, the surface of the hot rolled metal sheet 1 conveyed by the conveying rolls 3 is cooled on the exit side of the final stand of the hot finish rolling mill 18. Cooling is performed in zone 22 with cooling water. At this time, in the present invention, the cooling water W supplied near the both width edges of the upper surface of the hot-rolled metal plate 1 is shielded by the shielding body 6, and the shielded cooling water is supplied near the both width edges of the hot-rolled metal plate 1. To the width center side. This situation is schematically shown in FIG.
[0023]
In FIG. 1, the shielding body 6 is formed in a gutter shape so that the shielded cooling water can be supplied to a specific place C through the groove-shaped hole 6a. As a result, similarly to the conventional edge masking device, it is possible to suppress local supercooling near both width edges of the hot-rolled metal plate 1 and to reduce local supercooling near the both width edges of the hot-rolled metal plate 1. (A specific location C: including an M-shaped temperature distribution peak) can be intensively cooled, and unevenness of the temperature distribution in the width direction can be suppressed. In the present invention, the method of cooling the lower surface of the hot-rolled metal plate does not need to be particularly limited. Any ordinary cooling method, such as injecting cooling water from nozzles 51 installed at equal intervals in the width direction of the hot-rolled metal plate 1 via the header 41, can be applied.
[0024]
Next, a description will be given of a hot rolled metal plate cooling device suitable for use in the first invention, which is the second invention.
As shown in FIG. 5, the cooling device for hot-rolled metal sheets of the present invention includes a plurality of cooling devices (a plurality of zones) on the exit side of the hot finishing rolling mill 18, that is, in the cooling zone 22 on the downstream side in the hot-rolled metal sheet conveying direction. The upper surface of the hot rolled metal sheet 1 that is installed and conveyed after the finish rolling is cooled by supplying cooling water from the nozzle 5 via the header 4. Needless to say, a cooling device of a different type from the cooling device for the upper surface (the present invention) may be provided for cooling the lower surface of the hot-rolled metal plate. FIG. 5 illustrates a cooling device of a type in which cooling water is jetted from a nozzle 51 attached to a header 41 to the lower surface of the hot-rolled metal plate for cooling the lower surface of the hot-rolled metal plate. It is not limited.
[0025]
An example of the apparatus for cooling a hot-rolled metal plate of the present invention is schematically shown in FIG. 1 in a front view and schematically in a plan view in FIG.
The apparatus for cooling a hot-rolled metal plate according to the present invention includes a plurality of headers 4, a plurality of nozzles 5 arranged on the header 4, a shield 6, and a shield moving mechanism 7. The header 4 is provided above the upper surface of the hot-rolled metal sheet 1 conveyed by the conveying rolls 3 and supplies cooling water. As shown in FIG. 2, a plurality of headers 4 are provided in the transport direction. In each header 4, a plurality of nozzles 5 are arranged at intervals in the width direction of the hot-rolled metal plate, and supply cooling water to the upper surface of the hot-rolled metal plate. Although the type of the nozzle 5 is not particularly limited, it is preferable to use a tubular shape in which a pipe laminar is formed from the viewpoint of easiness of device design, versatility of parts, cost, and the like.
[0026]
In the present invention, of the cooling water supplied to the upper surface of the hot-rolled metal plate 1 from the nozzle 5, the cooling water supplied to both width edges of the hot-rolled metal plate 1 is reduced to a predetermined length in the transport direction. Shields 6 are provided on both width edge sides of the hot-rolled metal plate 1 for shielding over the entire width. Further, the shielding body 6 in the present invention is formed in a gutter shape so that the blocked cooling water can be supplied to the width center side from the vicinity of both width edges, and corresponds to an M-shaped temperature peak of the hot-rolled metal plate 1. It is preferable to have a groove-shaped hole 6a so as to be able to collectively supply a desired specific region (region C in FIG. 1) having a width of 50 to 100 mm including a portion and preferably extending symmetrically on both sides in the width direction. Thereby, the shielded cooling water can be intensively supplied to a desired specific area of the hot-rolled metal plate 1 with high accuracy, and the temperature distribution in the width direction can be made uneven. For example, the interval between nozzles in the width direction of the hot-rolled metal plate is 50 mm, the width of the gutter-shaped shield 6 is 300 mm, the width of the bottom groove-shaped hole 6a is 50 mm, and the shielded cooling water W is hot-rolled. If the cooling water W is supplied to a specific region on the upper surface of the metal plate 1, the flow rate of the cooling water W per unit area is doubled, and the cooling capacity is increased.
[0027]
Note that the width of the groove-shaped hole 6a can be changed according to the width of a desired specific region to be intensively cooled. Further, the planar shape of the shield 6 may be changed from a rectangle as shown in FIG. 2 to a trapezoid or a triangle (not shown) shown in FIG. The shield 6 having a trapezoidal or triangular planar shape is provided with a groove-shaped hole 6a having a constant width at the bottom formed in a gutter shape, similarly to the rectangular shape. Thus, similarly to the case where the width of the groove-shaped hole 6a is changed, it is possible to change the width of a desired specific region to be intensively cooled.
[0028]
Further, the cooling device of the present invention includes a moving mechanism 7 that enables the shield 6 to move in the width direction of the hot-rolled metal plate 1. Thus, the shield 6 can be set at a desired position in the width direction. By supplying the shielded cooling water to a desired specific area of the hot-rolled metal sheet 1 to locally cool strongly and increase the temperature drop, a new unexpected flow occurs, and It is possible to assume that the cooling unevenness (non-uniformity of the temperature distribution) has not been eliminated. However, even in such a case, by providing the moving mechanism 7 and changing the position of the shield 6, In many cases, uneven cooling can be eliminated.
[0029]
The type of the moving mechanism 7 in the present invention is not particularly limited as long as the shield 6 can be moved forward or backward in the width direction of the hot-rolled metal plate 1. As the moving mechanism 7, for example, a screwing mechanism of a screw and a nut can be exemplified. According to this screwing mechanism, for example, a nut is disposed on the shield 6, and the screw is rotated forward or backward to move the shield 6 forward or backward in the width direction of the hot-rolled metal plate 1. It becomes possible. It is preferable that the moving mechanism 7 is provided so that the shields 6 and 6 can move synchronously and symmetrically in the width direction.
[0030]
In addition, as another moving mechanism, a servomotor, a hydraulic cylinder, or the like can be exemplified. Further, the moving mechanism 7 may be the mechanism shown in FIG. In the example of the moving mechanism shown in FIG. 4, one end of the shield 6 is rotatably installed on a fixed object (not shown) via a hinge 6b or the like, and the shield 6 is usually suspended vertically. Only when the cooling water W is shielded, the other end of the shielding body 6 may be a mechanism for catching a winch or the like by a catching mechanism 6c capable of catching and catching. Needless to say, the moving mechanism in the present invention is not limited to the moving mechanism described above.
[0031]
In the present invention, the moving mechanism 7 controls the movement of the shield 6 in the width direction of the hot-rolled metal plate so that the cooling water shielded by the shield 6 can be intensively supplied to a desired area. Information on the width of the hot-rolled metal plate 1 is obtained from the business computer 90 shown in FIG. 11 via the process computer 70, and based on this information, the moving mechanism 7 is operated by a command from the control device 50. Thus, it is preferable to control the shield 6 so as to be set at a predetermined position in the width direction of the hot-rolled metal plate 1. In addition, before the end of the hot-rolled metal sheet 1 is still wound around the coiler 24, or before the tail end of the hot-rolled metal sheet 1 passes through the finishing mill 18 and is wound on the coiler 24, the hot-rolled metal sheet 1 1 is easy to meander, the width of the hot-rolled metal plate 1 is detected by a width gauge (not shown) installed on the exit side of the finishing mill 18 or on the entrance side of the coiler 24, and in the meandering direction, The shield 6 may be controlled in real time so as to be shifted in the width direction of the hot-rolled metal plate 1 by the moving mechanism 7 by the meandering amount. In addition, the shield 6 may be shifted in the width direction of the hot-rolled metal plate 1 by an amount corresponding to the meandering amount other than the front end and the tail end of the hot-rolled metal plate 1.
[0032]
Next, the hot-rolled steel sheet (3 mm thick × 1000 mm width) obtained by performing the finish rolling at the finish rolling exit side temperature of 880 ° C. by the cooling method using the cooling device of the present invention shown in FIGS. The effect of the present invention will be described by taking cooling as an example. At the time of cooling, both width edges 100 mm of the hot-rolled steel sheet were edge-masked by the shield 6, and the hot-rolled steel sheet 1 was spread symmetrically in the width direction including a portion corresponding to the peak of the M-shaped temperature distribution. The cooling water was intensively supplied to a desired specific region having a width of 50 mm and having a width of 50 mm. In addition, as a comparison, both width edges of 100 mm were shielded by a shield, and the shielded cooling water was allowed to fall outside the both width edges of the hot-rolled steel sheet. In addition, the same operation was performed when no shield was used. The temperature change at each position in the steel sheet width direction per water cooling zone is determined based on the case where the shield is not used (the edge masking is not performed), and is shown in FIG.
[0033]
From FIG. 6, in the case of the conventional masking of 100 mm 2 of the edge (dotted line: conventional example), the supercooling of the 100 mm 2 of the edge is alleviated, and there is a temperature rise of 10 ° C. as compared with the case where the edge masking is not performed. I understand. On the other hand, by applying the cooling method of the present invention (masking of the edge 100 mm 2 + specific partial cooling: application example of the present invention), the supercooling is alleviated at the edge 100 mm 2, and 10 ° C. as in the conventional edge masking only. In addition to the temperature rise, the shielded cooling water is dropped and supplied intensively to the center in the width direction, so that in the area of 100 to 150 mm from the width edge, the maximum compared to the case where edge masking is not performed It can be seen that there is a temperature drop of 25 ° C.
[0034]
As described above, according to the cooling method of the present invention, the temperature in the width direction, which has conventionally been M-shaped, can be increased in the width edge portion and the temperature in the peak position can be decreased. A uniform temperature distribution can be obtained in the width direction.
Next, by applying the above-described method for cooling a hot-rolled metal sheet of the present invention, a high-tensile hot-rolled steel sheet having a high tensile strength of 400 MPa or more and a small variation in yield strength in the width direction is obtained. A method for producing a high-tensile hot-rolled steel sheet to be produced will be described.
[0035]
The high-strength hot-rolled steel sheet of the present invention is obtained by subjecting a steel material having a predetermined composition to hot rolling including rough rolling and finish rolling to obtain a hot-rolled steel sheet, and then finishing the hot-rolled steel sheet after finish rolling as described above. It is manufactured by applying the cooling method of the invention.
The steel material used in the present invention is obtained by refining a molten steel produced by a converter, an electric furnace, or the like, preferably by a known refining method such as further degassing by VOD or the like to obtain a predetermined composition, and then continuously casting. A slab or the like cast by a known casting method such as that described above can be used. It goes without saying that the method of manufacturing the steel material is not limited to the above-described method.
[0036]
The steel material used in the present invention is mass%, C: 0.01 to 0.2%, Si: 0.01 to 1.5%, Mn: 0.1 to 3%, P: 0.04%. In the following, S: 0.02% or less, Al: 0.1% or less, N: 0.005% or less, or further mass%, Cu: 0.01 to 1.0%, Cr: 0. 01 to 1.0%, Ni: 0.01 to 1.0%, Mo: 0.01 to 1.0%, Ti: 0.01 to 0.2%, Nb: 0.01 to 0.2% , V: one or more selected from 0.01% to 0.1%, and preferably has a composition comprising the balance of Fe and unavoidable impurities. The reasons for the composition limitation are as follows. Hereinafter, mass% in the composition is simply described as%.
[0037]
C: 0.01-0.2%
C is contained in an amount of 0.01% or more to increase the strength. However, if the content exceeds 0.2%, the weldability deteriorates. For this reason, C is limited to the range of 0.01 to 0.2%. In addition, from the viewpoint of further improving strength and weldability, the content is preferably set to 0.03 to 0.18%.
[0038]
Si: 0.01 to 1.5%
Si is contained in an amount of 0.01% or more to improve cold workability such as pressing. However, if the content exceeds 1.5%, a scale that is difficult to peel occurs on the surface layer of the steel slab of the steel sheet during heating for hot rolling, and does not peel even after descaling, and the surface quality of the product is reduced. Getting worse. For this reason, Si was limited to the range of 0.01 to 1.5%. From the viewpoint of further improving the cold workability and the descaling property, the content is preferably set to 0.1 to 1.0%.
[0039]
Mn: 0.1 to 3%
Mn is contained in an amount of 0.1% or more to increase the strength. However, even if the content exceeds 3%, the effect is saturated, but the effect of improving the hardenability increases, and even a slight change in the cooling conditions (for example, the difference between immediately below the laminar water (black spot) and the other ones) causes This leads to fluctuations in the strength of the hot-rolled steel products. For this reason, Mn was limited to the range of 0.1 to 3%. Incidentally, the content is preferably 1.5% or less.
[0040]
P: 0.04% or less
P is an element that increases the strength and may be contained in an unavoidable content (about 0.008%) or more as necessary. However, if contained in a large amount, the steel sheet is embrittled. %.
S: 0.02% or less
S forms sulfides in the steel and lowers the ductility of the steel, so that it is preferable to make S as low as possible. In the present invention, S is limited to 0.02% or less.
[0041]
Al: 0.1% or less
Al is an element that effectively acts as a deoxidizing agent, and it is preferable to contain it in an amount of 0.001% or more. However, if it exceeds 0.1%, the amount of inclusions increases, the cleanliness is deteriorated, and heat is reduced. The surface of the product after the cold rolling is easily cracked or flawed. For this reason, Al was limited to 0.1% or less.
[0042]
N: 0.005% or less
It is desirable to reduce N as much as possible in order to secure materials such as ductility and r value, but if it is 0.005% or less, almost satisfactory characteristics can be obtained. For this reason, N is limited to 0.005% or less.
In the present invention, in addition to the basic composition described above, Cu: 0.01 to 1.0%, Cr: 0.01 to 1.0%, Ni: 0.01 to 1.0%, Mo: 0.1 to 1.0%. One or two selected from 01 to 1.0%, Ti: 0.01 to 0.2%, Nb: 0.01 to 0.2%, V: 0.01 to 0.1% The above can be contained. Cu, Cr, Ni, Mo, Ti, Nb, and V are all elements that increase the strength, and can be selectively contained as necessary.
[0043]
Cu: 0.01 to 1.0%
Cu is preferably contained in an amount of 0.01% or more in order to improve the strength. However, if it is contained in excess of 1.0%, cracks or flaws may occur on the product surface after hot rolling. It will be easier. Therefore, Cu is preferably limited to 1.0% or less.
Cr: 0.01 to 1.0%
Cr is preferably contained in an amount of 0.01% or more in order to improve the strength, but if it exceeds 1.0%, it hardens and deteriorates cold workability such as pressing. Therefore, the content of Cr is preferably limited to 0.01 to 1.0%.
[0044]
Ni: 0.01 to 1.0%
Ni is an element that improves the strength and the toughness, and such an effect is recognized at a content of 0.01% or more, but the effect is saturated even if the content exceeds 1.0%, The effect corresponding to the content cannot be expected, which is economically disadvantageous. For this reason, Ni is preferably limited to the range of 0.01 to 1.0%.
[0045]
Mo: 0.01 to 1.0%
Mo is preferably contained in an amount of 0.01% or more in order to improve the strength, but if it exceeds 1.0%, the toughness is reduced. For this reason, Mo is preferably limited to the range of 0.01 to 1.0%.
Ti: 0.01 to 0.2%
Ti is an element that forms carbides, nitrides, and carbonitrides, increases strength, and improves toughness. Such an effect is recognized when the content is 0.01% or more. On the other hand, if the content exceeds 0.2%, both strength and toughness decrease. For this reason, Ti was limited to the range of 0.01 to 0.2%.
[0046]
Nb: 0.01 to 0.2%
Like Nb, Nb is an element that forms carbides or nitrides, increases strength and improves toughness, and such an effect is recognized at a content of 0.01% or more. On the other hand, if the content exceeds 0.2%, both strength and toughness decrease. For this reason, Nb was limited to the range of 0.01 to 0.2%.
[0047]
V: 0.01 to 0.1%
V is preferably contained at 0.01% or more in order to improve the strength. On the other hand, if the content exceeds 1.0%, the toughness decreases. For this reason, V is preferably limited to the range of 0.01 to 0.1%.
The balance other than the components described above is Fe and inevitable impurities.
[0048]
Heating a steel material containing the above-mentioned basic composition or an element that further increases the strength, without heating, or when heating at a temperature higher than the temperature at which hot rolling can be performed, or without heating for a short time After furnace holding, hot rolling including rough rolling and finish rolling is performed to obtain a hot-rolled steel sheet having a predetermined size. After the finish rolling, cooling water is supplied to the surface of the hot-rolled steel sheet after the finish rolling in a cooling zone provided on the exit side of the finishing mill to cool the steel sheet. The cooling method uses the cooling device of the present invention exemplified in FIGS. 1 to 5 to shield cooling water supplied to both width edges of the hot-rolled steel sheet, and to block the shielded cooling water from the vicinity of both width edges. The method for cooling a hot-rolled metal sheet of the present invention, in which the hot-rolled metal sheet is also supplied to the width center side, is applied.
[0049]
In the cooling zone 22 installed on the outlet side of the finishing mill 18, a plurality of headers 4 and 41 are arranged in the direction of transport of the hot-rolled steel sheet, divided into a plurality of water cooling zones, and cooled in each water cooling zone. It is preferable to adjust the conditions so that a desired winding temperature distribution can be obtained. For example, the total length of the water-cooling zone for supplying the cooling water is calculated based on the measurement value of the finishing-side thermometer 7a and the transport speed pattern of the steel sheet 1. That is, when the temperature of the steel plate 1 before cooling is the same, the total length of the water cooling zone for supplying the cooling water in the transport direction is adjusted so as to reach a desired temperature according to the increase or decrease in the transport speed. Furthermore, when the temperature of the steel plate 1 before cooling rises or falls, it is preferable to further adjust the total length of the water cooling zone for supplying the cooling water in the transport direction by a corresponding amount. Further, feedback control for increasing or decreasing the total length in the transport direction of the water cooling zone for supplying the cooling water may be performed based on the difference between the target winding temperature and the value measured by the winding thermometer 7c.
[0050]
In addition, the edge masking by the shield 6 and the intensive supply of the cooling water to the specific area need not always be applied to the entire water cooling zone, so that the target winding temperature can be obtained and the width distribution of the winding temperature is uniform. It is preferable to adjust for each water cooling zone so that
This suppresses local supercooling near both width edges of the hot-rolled steel sheet, and locally increases the temperature near the width center near the both width edges (the peak position of the M-shaped temperature distribution is reduced). The specific area C) can be intensively cooled, the distribution of the winding temperature in the width direction is made uniform, the tensile strength: 400 MPa or more, and the maximum yield strength from the both width edges 20 mm to the center of the width. A high-strength hot-rolled steel sheet having a uniform characteristic with a small variation in yield strength in the width direction and a difference between the value and the minimum value of 30 MPa or less can be obtained.
[0051]
Hereinafter, the present invention will be described in more detail with reference to Examples.
[0052]
【Example】
A steel material having the composition shown in Table 1 was melted in a converter, and was made into a steel material (slab) by a continuous casting method. Next, these slabs were charged into a heating furnace 10 using a hot rolling line 100 shown in FIG. 11 and heated to about 1200 ° C., and then were subjected to a hot rolling steel sheet (3 mm) by a rough rolling mill 12 and a finishing rolling mill 18. (Thickness x 1000 mm width). The finish-rolling exit temperature was 835 to 883 ° C. Further, the width distribution of the finish-rolling exit temperature of the hot-rolled steel sheet 1 immediately after the finish rolling measured by the width-direction thermometer 7b disposed on the exit side of the finish exit-side thermometer 7a shown in FIG. It is confirmed that the temperature is almost uniform except for the uppermost edge and the temperature fluctuation is at most about 10 to 15 ° C.
[0053]
[Table 1]

[0054]
The hot-rolled steel sheet 1 finish-rolled by the finish rolling mill 18 was then cooled in a cooling zone 22 to a winding temperature. The target strength of the hot-rolled steel sheet was set to a tensile strength of 400 to 1000 MPa (permissible: -50 MPa, +40 MPa).
As shown in FIG. 5, the cooling in the cooling zone 22 was performed by supplying cooling water from a plurality of headers 4 and 41 provided vertically while passing through a run-out table in which the table rollers 3 were arranged. The upper header 4 is a pipe laminar header in which cylindrical nozzles 5 are arranged in the width direction of the hot-rolled steel sheet 1, and supplies a large number of rod-shaped cooling waters at a pitch of 50 mm in the width direction of the steel sheet 1. The upper and lower headers are each provided with 40 tubular nozzles 5 at 50 mm pitch in the width direction of the steel plate 1, and a set of 6 headers connected in the conveying direction to a common base pipe is treated as one water cooling zone. Are provided in 20 zones. In addition, between the upper header 4 and the hot-rolled steel sheet 1, a shield 6 and a moving mechanism 7 having the structure and shape shown in FIGS. 1 and 2 are arranged to supply cooling water supplied to both width edges. In addition to shielding (edge masking of both width edges), shielding water was supplied to a specific area. The shield 6 was attached so as to be movable in the width direction of the hot-rolled steel sheet by the moving mechanism 7, and the position of the shield 6 was changed for each water cooling zone. As a conventional example, a conventional shield shown in FIG. 13 was also used. Hereinafter, the masking device including the shield and the moving mechanism is also referred to as an edge masking device.
[0055]
The following three cooling methods shown in Table 2 were used.
[0056]
[Table 2]

[0057]
(A) Application example
Water cooling zone No. 2-No. 4, no. 6-No. 8, No. 10 -No. 12, no. 14 -No. 16, no. 18, an edge masking device having a shield 6 and a moving mechanism 7 having the structure shown in FIGS. 1 and 2 is installed to shield cooling water supplied near both width edges of the hot-rolled steel sheet 1 and to shield the cooling water. The cooled water dropped from the vicinity of both width edges of the hot-rolled steel sheet 1 toward the width center. In each water cooling zone, the position of the shield was changed, and the width of the shield protruding to both width edges of the hot-rolled steel sheet was changed between 40 and 180 mm. On the other hand, the water cooling zone No. 1, No. 5, no. 9, No. 13, no. 17, No. 19, no. 20 is provided with a shield (conventional example) having the structure shown in FIG. In the case of Sample No. 1, only the shield 6 was set so that the width of the hot-rolled steel sheet 1 at both width edges protruding toward the center of the width (extension width of the shield) was 70 mm, and edge masking was performed. In the other cooling zones, the shield was fixed to the outside of the hot-rolled steel sheet, and there was no protrusion of the shield. The pattern of the water-cooled zone was obtained based on the result of the edge masking effect shown in FIG. 6 and further experimented so that the distribution of the winding temperature in the width direction became uniform.
(B) Conventional example 1
In each of the water cooling zones, an example in which the edge masking device is not used is used.
(C) Conventional example 2
An edge masking device having the structure shown in FIG. 13 is installed in each of the water cooling zones, and the shields 6 are installed so that the overhang width of the shields is alternately 100 mm or 70 mm in a total of 10 odd-numbered water cooling zones. Masking was performed. On the other hand, in the even-numbered water-cooled zones, the protruding width of the shield was set to zero, and no edge masking was performed.
[0058]
FIG. 7 shows an example of the distribution in the width direction of the winding temperature of the obtained hot-rolled steel sheet after cooling by the cooling methods (A) to (C) described above. The winding temperature distribution in the width direction is line-symmetric with respect to the width center, and FIG. 7 shows a right half temperature distribution from the width center to one width edge.
The temperature distribution curve A (solid line) of the winding temperature in the width direction of the application example shows that the cooling water is not supplied immediately below the region where the cooling water is shielded by the shield 6, so that the supercooling which has conventionally occurred in this portion The temperature at the position 20 mm from the width edge of the hot-rolled steel sheet is only 23 ° C. lower than the center of the width, and the cooling water shielded by the shield 6 is concentrated 120 m from both width edges. , The temperature at that position was only 35 ° C. higher than at the center of the width. FIG. 7 shows that the cooling method (application example) of the present invention has a uniform temperature distribution in the width direction.
[0059]
On the other hand, the temperature distribution curve B in the width direction of the conventional example 1 (dashed-dotted line) indicates that the vicinity of both width edges of the hot-rolled steel sheet is locally supercooled as compared with the other portions, and the position 20 mm from the width edge of the hot-rolled steel sheet. Is 133 ° C. lower than the temperature at the center of the width. Further, the width direction temperature distribution curve C (broken line) of Conventional Example 2 indicates that the cooling water is not supplied to the area directly below the area where the cooling water is shielded by the shield 6, so that the supercooling which has conventionally occurred in this area is not performed. The temperature at the position 20 mm from the width edge of the hot-rolled steel sheet is only 33 ° C. lower than the center of the width, but the temperature at the position 100 mm from both width edges is 98 ° C. higher than the center of the width. Has become.
[0060]
Next, a strip-shaped test piece (width: 20 mm) was sampled from the hot-rolled steel sheet cooled by the cooling method described above, processed into a tensile test piece and subjected to a tensile test, and the yield strength YS and the tensile strength were measured. TS and elongation El were measured. The tensile test piece used was a parallel part: 18 mm width and parallel part length: 60 mm (GL: 50 mm) in accordance with JIS No. 5 test piece specified in JIS Z2201, and the tensile direction was the direction of the elongation of the hot-rolled steel sheet. And Moreover, the tensile test piece was sampled so that the center of the test piece width was at a predetermined position (20 mm, 40 mm, etc. from the width edge) at an interval of 20 mm from the width edge of the hot-rolled steel sheet. The obtained results are shown in FIGS.
[0061]
The steel No. shown in Table 1 cooled by the cooling method (A) of the present invention example. In the hot-rolled steel sheet having the composition of D, the cooling water is shielded by the shield 6, and as shown in FIG. 7, the temperature at the position 20 mm from the width edge was only 23 ° C. lower than the center of the width. As shown, TS: 554 MPa and YS: 471 MPa (the rightmost plot in FIG. 8). For this reason, the trimming margin was determined under conditions unrelated to the material such as edge drop, and both edges were 20 mm (total 40 mm), and the yield was 96%. Further, since the width of the shield 6 protruding toward the center of the width of the hot-rolled steel sheet was changed stepwise between 40 and 180 mm, as shown in FIG. Is only 35 ° C. higher than the width center, and as shown in FIG. 8, the TS variation (the difference between the maximum and minimum) in the entire region from the position 20 mm from the width edge to the width center is 35 MPa. , YS is 28 MPa, and the hot-rolled steel sheet has little strength fluctuation in the width direction.
[0062]
On the other hand, in the hot-rolled steel sheet cooled by the cooling method (B) of Conventional Example 1, since the masking was not performed at both width edges, as shown in FIG. 133 ° C. lower than that, and TS: 618 MPa and YS: 519 MPa. Both edges were too hard and the area required for the product El: 24% could not be secured: 60 mm had to be cut off as a margin, so the product yield was 88%. As shown in FIG. 7, the winding temperature at a position 120 mm from both edges is 83 ° C. higher than the center of the width, and is 490 MPa for TS and 411 MPa for YS. As shown in FIG. 9, even after a region where both width edges are too hard (total 120 mm 2) is discarded as a margin, a variation in TS (the difference between the maximum and minimum) is 40 MPa, and a variation in YS is 45 MPa in the width direction. There is a hot-rolled steel sheet having a large variation in strength in the width direction.
[0063]
Further, in the hot-rolled steel sheet cooled by the cooling method (C) of the conventional example 2, the cooling water is shielded by the shielding body 6, so that the supercooling which has conventionally occurred in this portion can be suppressed. As described above, the temperature at the position 20 mm from the width edge was only 33 ° C. lower than the center of the width, so that TS: 560 MPa and YS: 470 MPa. . Since the material on the center side of the width was better than this, the edge trimming margin was determined under conditions unrelated to the material such as edge drop, and both width edges were 20 mm (40 mm in total), and the yield was 96%. Was.
[0064]
The winding temperature at a position 120 mm from both edges was 96 ° C higher than the center of the width, and was 482 MPa for TS and 404 MPa for YS. As shown in FIG. 10, in the entire region from the position 20 mm from the width edge to the center of the width, the variation in TS (difference between maximum and minimum) is 78 MPa, the variation in YS is 66 MPa, and the intensity variation in the width direction is large. It is a hot rolled steel sheet.
Next, after the finish rolling, the hot-rolled steel sheet cooled by the cooling method described in (A) to (C) above was further subjected to a 200 m-long position from the tip of the hot-rolled steel sheet after finish rolling. Strip-shaped (width: 18 mm) test pieces were sampled at a pitch of 20 mm over the entire width direction, processed into tensile test pieces and subjected to a tensile test, and the yield strength YS, tensile strength TS, and elongation El were measured. . The tensile test piece used had a parallel portion: 18 mm width and a parallel portion length: 60 mm (GL: 50 mm), and the tensile direction was the direction in which the hot-rolled steel sheet was elongated. Moreover, the tensile test piece was sampled so that the center of the test piece width was at a predetermined position (20 mm, 40 mm, etc. from the width edge) at an interval of 20 mm from the width edge of the hot-rolled steel sheet. Table 3 shows the obtained results. Table 3 shows the maximum value, the minimum value, and the difference among the yield strength, tensile strength, and elongation obtained at each position.
[0065]
[Table 3]

[0066]
[Table 4]

[0067]
In the hot-rolled steel sheet (application example) to which the cooling method of the present invention is applied, the fluctuation in strength in the width direction of the steel sheet can be reliably reduced. On the other hand, in the conventional example out of the range of the present invention, it can be seen that there is a large possibility that the strength varies greatly in the width direction and the amount of springback generated during the press working differs depending on the steel plate portion. In addition, it can be seen that by providing at least one or more water-cooling zones capable of intensively supplying the shielded cooling water to the width center side of the hot-rolled steel sheet, fluctuations in the strength of the hot-rolled steel sheet in the width direction can be reliably reduced. .
[0068]
In the example of the present invention shown here, an edge masking device of a type in which the cooling water is dropped to the outside in the width direction of the steel plate (for example, FIG. 13) is installed in some water cooling zones. Does not necessarily need to be installed. Just by installing an edge masking device that can supply shielded cooling water intensively to the center of the steel sheet width, an effect similar to that obtained by performing edge masking directly under the area where the shield plate protrudes toward the center of the steel sheet width is achieved. It is because it is obtained. Further, in the cooling method of the present invention example shown here, a specific region in which the cooling water shielded by the shielding plate installed by adjusting the amount of protrusion at both width edges is intensively supplied is provided for each water cooling zone. Although an example is shown in which the steel sheet is sequentially changed from the edge side to the center side, it goes without saying that the present invention is not limited to this.
[0069]
Further, in the embodiment of the present invention, the hot rolling line 100 shown in FIG. 11 was used. However, the present invention is not limited to this, and as shown in FIG. It is needless to say that the present invention can be applied to other types of hot rolling lines, such as a hot rolling line 200, which performs finish rolling directly without going through rough rolling.
[0070]
【The invention's effect】
As described above, according to the present invention, the winding temperature becomes uniform in the width direction of the hot-rolled metal sheet, the fluctuation of the yield strength in the width direction is small, and the high-tension hot-rolling material having uniform quality in the width direction is obtained. Steel plates can be manufactured easily and inexpensively, and this has a remarkable industrial effect. Further, according to the present invention, there is also an effect that the yield in a post-process such as press working is improved.
[Brief description of the drawings]
FIG. 1 is a front view schematically showing one example of a cooling device of the present invention.
FIG. 2 is a plan view schematically showing an example of the cooling device of the present invention.
FIG. 3 is a plan view schematically showing an example of the cooling device of the present invention.
FIG. 4 is a front view schematically showing an example of the cooling device of the present invention.
FIG. 5 is a side view schematically showing one example of the cooling device of the present invention.
FIG. 6 is a graph showing an example of the influence of edge masking, edge masking + specific area cooling on a temperature change at each position in the width direction per cooling zone.
FIG. 7 is a graph showing a comparison of the distribution of the winding temperature in the width direction.
FIG. 8 is a graph showing the distribution of tensile properties in the width direction when cooled by the cooling method (A).
FIG. 9 is a graph showing a width direction distribution of tensile properties when cooled by a cooling method (B).
FIG. 10 is a graph showing a width direction distribution of tensile properties when cooled by a cooling method (C).
FIG. 11 is an explanatory view schematically showing an example of a hot rolling line.
FIG. 12 is an explanatory view schematically showing an example of a hot rolling line.
FIG. 13 is an explanatory diagram schematically showing a conventional edge masking device.
FIG. 14 is an explanatory view showing an example of a conventional distribution of a hot-rolled steel sheet winding temperature in a width direction.
FIG. 15 is an explanatory view schematically showing a flow of cooling water in the conventional hot-rolled metal plate cooling.
FIG. 16 is an explanatory view schematically showing a heat removal state of a hot-rolled metal plate.
[Explanation of symbols]
1 Hot rolled metal sheet (hot rolled steel sheet, steel sheet)
3 Table roller
4 header (top header)
41 Lower header
5 nozzles
51 Lower nozzle
6 Shield
6a Slotted hole
6b hinge
6c winch (fishing mechanism)
7 Thermometer
7a Finishing thermometer
7b, 7c Width thermometer
7d winding thermometer
8 Rolled material
10 heating furnace
12 Rough rolling mill
13 Work Roll
14 Kropsha
16 Descaling device
18 Finishing mill
19 Work Roll
20 Slab continuous casting equipment
22 Cooling zone
24 coiler
50 Control device
70 Process computer
80 Business Computer
100, 200 hot rolling line

Claims (5)

In the method for cooling a hot-rolled metal sheet, in which the upper surface of the metal sheet after hot finish rolling is cooled by cooling water in a cooling zone, the cooling water supplied near both width edges of the hot-rolled metal sheet is shielded. Supplying the shielded cooling water to the width center side of the hot rolled metal plate from the vicinity of both width edges. A hot-rolled metal sheet cooling device that is installed in a cooling zone on the downstream side of the hot-finish rolling mill in the metal sheet transport direction and cools an upper surface of the hot-rolled metal sheet to be transported after the finish rolling, A plurality of headers arranged above the metal plate to supply cooling water, and each of the plurality of headers is arranged at an interval in the width direction of the hot-rolled metal plate and provided on an upper surface of the hot-rolled metal plate. A plurality of nozzles for supplying cooling water, a part of the cooling water supplied from the plurality of nozzles is shielded from both width edge sides of the hot-rolled metal plate, and the shielded cooling water is supplied to the hot-rolled metal. A hot-rolled metal, comprising: a shield that supplies the shield to the width center side from the vicinity of both width edges of the plate; and a moving mechanism that enables the shield to move in the width direction of the hot-rolled metal plate. Board cooling device. mass%, C: 0.01 to 0.2%, Si: 0.01 to 1.5%, Mn: 0.1 to 3%, P: 0.04% or less, S: 0.02% or less , Al: 0.1% or less, N: 0.005% or less, has a composition consisting of the balance Fe and unavoidable impurities, and has a maximum value and a minimum value of the yield strength from both width edges 20 mm to the center of the width. A high-strength hot-rolled steel sheet having a difference in value of 30 MPa or less. In addition to the above composition, in mass%, Cu: 0.01 to 1.0%, Cr: 0.01 to 1.0%, Ni: 0.01 to 1.0%, Mo: 0.01 to 1.0% 1.0%, Ti: 0.01-0.2%, Nb: 0.01-0.2%, V: 0.01-0.1% The high-strength hot-rolled steel sheet according to claim 3, which is contained. In a method for producing a hot-rolled steel sheet by subjecting a steel material to hot rolling including rough rolling and finish rolling to obtain a hot-rolled steel sheet, the steel material is mass%, C: 0.01 to 0.2%, Si: 0.01 to 1.5%, Mn: 0.1 to 3%, P: 0.04% or less, S: 0.02% or less, Al: 0.1% or less, N: 0.005% or less. When cooling the upper surface of the hot-rolled steel sheet with cooling water after the finish rolling, the cooling water supplied near both width edges of the hot-rolled steel sheet is shielded, and the shielded cooling is performed. The difference between the maximum value and the minimum value of the yield strength from the both width edges 20 mm to the width center is 30 MPa or less, wherein water is supplied to the width center side of the hot rolled steel sheet from the vicinity of both width edges. Manufacturing method for high-strength hot-rolled steel sheet.

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