JP3698088B2

JP3698088B2 - Manufacturing method of hot-rolled steel strip

Info

Publication number: JP3698088B2
Application number: JP2001329554A
Authority: JP
Inventors: 徹簔手; 勝三宅; 善道日野; 祥三東; 貞和升田
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2001-10-26
Filing date: 2001-10-26
Publication date: 2005-09-21
Anticipated expiration: 2016-02-20
Also published as: JP2002178005A

Description

【０００１】
この発明は、連続熱間圧延機において圧延された熱延鋼帯の長さ方向の温度分布を均一となし、長さ方向の材質のばらつきが少ない品質の優れた熱延鋼帯を歩留り高く製造するための熱延鋼帯の製造方法に関するものである。
【０００２】
【従来の技術】
一般に、熱延鋼帯は、加熱炉においてスラブを所定温度に加熱し、加熱されたスラブを粗圧延機で所定厚さに圧延して粗バーとなし、次いで、粗バーを、複数基のスタンドからなる連続仕上圧延機において仕上圧延して所定厚さの熱延鋼帯とし、この熱延鋼帯を、ランアウトテーブル上の冷却スタンドにおいて冷却した後、コイラーで巻取ることにより製造される。
【０００３】
このような熱延鋼帯の製造過程において、熱延鋼帯の長さ方向に不均一な温度分布が発生する。即ち、粗圧延機で圧延された粗バーの、仕上圧延機入側における温度は、粗バーの長さ方向に均一ではなく、その後部に至るほど低くなる。その理由は、粗圧延機で圧延された粗バーが、粗圧延機を出てから仕上圧延機に入るまでの時間が、粗バーの後部ほど長いことに起因している。
【０００４】
このような仕上圧延機に入る粗バーの長さ方向の温度差を補償する手段として、従来、仕上圧延機で圧延される粗バーの圧延速度を一定とせず、仕上圧延機に粗バーの先端部が入ってから、その圧延速度を高める「ズーミング」と称する方法が行われている。
【０００５】
仕上圧延機による粗バーの仕上圧延を、上述した「ズーミング」により行うことによって、粗バーの仕上圧延に要する時間は、粗バーの前部よりも後部の方が短くなる。その結果、仕上圧延機によって仕上圧延される粗バーの、圧延ロールとの接触による抜熱および放射による温度低下は、粗バーの後部ほど小になり、且つ、圧延ロールの圧下によって生ずる加工発熱は、粗バーの後部ほど大になる。従って、仕上圧延機によって仕上圧延された熱延鋼帯の、圧延機出側における温度分布は、鋼帯の先端部が低く、その後端部に至るほど高くなる。
【０００６】
仕上圧延機によって仕上圧延された熱延鋼帯は、ランアウトテーブル上の冷却スタンドにおいて冷却された後、コイラーで巻取られるが、その際、巻取り温度を一定にする観点から、熱延鋼帯の冷却速度を、冷却水のオンオフやその流量調整によって一定となるように制御している。
【０００７】
【発明が解決しようとする課題】
しかしながら、上述した「ズーミング」による温度補償だけで、熱延鋼帯の圧延仕上温度を鋼帯長さ方向に均一にすることはできず、また、「ズーミング」により鋼帯の移動速度が変化するため、冷却スタンドにおける冷却水の流量調整だけで、冷却速度を一定に保つことは困難である。
【０００８】
更に、「ズーミング」によって圧延仕上温度を高めるためには、仕上圧延機の駆動モーターに大きなパワーを必要とし、圧延荷重も大きくなるために、板クラウンの変動やロール肌荒れを引き起こすおそれが生ずる。
【０００９】
圧延条件やランアウトテーブル上での冷却速度は、熱延鋼帯の材質に影響を与える。特に、炭素鋼の場合には、フェライト変態開始温度（Ａｒ₃温度）付近の冷却速度によって、変態生成物の種類や粒径が変わり、最終的な製品の材質に大きな影響を及ぼす。
【００１０】
前述した従来の製造方法においては、熱延鋼帯の長さ方向に圧延仕上温度が不均一な温度分布を持つこと、および、「ズーミング」によってランアウトテーブル上での熱延鋼帯の移動速度が変化することから、冷却水の流量制御のみによって、熱延鋼帯の長さ方向全体にわたり、一定の冷却速度を得ることは極めて困難であり、そのため、熱延鋼帯の材質がばらつき、製品歩留りが低下する問題が生ずる。
【００１１】
従って、この発明の目的は、上述した問題を解決し、熱延鋼帯の仕上圧延機入側温度、仕上圧延条件およびランアウトテーブル上での冷却速度を、熱延鋼帯の長さ方向にわたり一定に保ち、均一な材質の熱延鋼帯を歩留り高く製造し得る方法を提供することにある。
【００１２】
【課題を解決するための手段】
本発明者等は、上述した観点から、仕上圧延機入側温度、仕上圧延条件およびランアウトテーブル上での冷却速度を、熱延鋼帯の長さ方向全体について一定に保つ方法を開発すべく鋭意研究を重ねた。その結果、仕上圧延機で圧延される粗バーの温度がその長さ方向に均一になるように、仕上圧延機入側において粗バーを加熱し、仕上圧延機での粗バーの圧延速度およびランアウトテーブル上での冷却速度を一定にすれば、均一な材質の熱延鋼帯を歩留り高く製造し得ることを知見した。
【００１３】
この発明は、上記知見に基づいてなされたものであって、下記を特徴とするものである。
【００１４】
請求項１記載の発明は、スラブを粗圧延機によって粗圧延して粗バーとし、次いで、粗圧延された粗バーを熱間仕上圧延機によって仕上圧延して熱延鋼帯とした後、冷却スタンドによって冷却して熱延鋼帯を製造する際に、粗圧延された前記粗バーを、前記熱間仕上圧延機の入側に設けられた誘導加熱装置によって、その長さ方向に均一な温度になるように加熱し、このように均一に加熱された前記粗バーを、一定速度で前記熱間仕上圧延機に通して仕上圧延を行い、次いで、一定速度で前記冷却スタンドに通して冷却する熱延鋼帯の製造方法において、熱間仕上圧延機出側温度計および巻取り温度計を設け、仕上圧延を行った後、一定速度で前記冷却スタンドに通し、前記熱間仕上圧延機出側温度計の位置から前記巻取り温度計の位置まで前記熱延鋼帯が進む間の平均冷却速度を均一にして冷却することに特徴を有するものである。
【００１５】
請求項２記載の発明は、スラブを粗圧延機によって粗圧延して粗バーとし、次いで、粗圧延された粗バーを熱間仕上圧延機によって仕上圧延して熱延鋼帯とした後、冷却スタンドによって冷却して熱延鋼帯を製造する際に、粗圧延された前記粗バーを、前記熱間仕上圧延機の入側に設けられた誘導加熱装置によって、その長さ方向に均一な温度になるように加熱し、このように均一に加熱された前記粗バーを、一定速度で前記熱間仕上圧延機に通して仕上圧延を行い、次いで、一定速度で前記冷却スタンドに通して冷却する熱延鋼帯の製造方法において、仕上圧延機出側温度計および巻取り温度計を設け、仕上圧延を行った後、一定速度で前記冷却スタンドに通し、且つ、前記冷却スタンドでの冷却水量を制御することなく、一定の水量で冷却を行い、前記熱間仕上圧延機出側温度計および前記巻取り温度計によって温度計測し、均一な冷却速度で冷却したことを確認することに特徴を有するものである。
【００１６】
請求項３記載の発明は、請求項１または２記載の発明において、粗圧延された粗バーを、前記誘導加熱装置によって、その長さ方向の温度のばらつきが約１０℃以内の均一な温度になるように加熱することに特徴を有し、請求項４記載の発明は、請求項１から３の何れか１つに記載の発明において、前記熱延鋼帯の長さ方向の引張強度のばらつきが約５％以下であることに特徴を有し、請求項５記載の発明は、請求項１から４の何れか１つに記載の発明において、前記熱延鋼帯の長さ方向の引張強度のばらつきが約２ｋｇ／ｍｍ ^２以下であることに特徴を有するものである。
【００１７】
【発明の実施の形態】
図１は、この発明の方法を示す連続熱間圧延ラインの概略説明図である。図１に示すように、粗圧延機１、複数スタンドからなる連続熱間仕上圧延機５、冷却スタンド８およびコイラー１０がこの順序で配置されている。７はランアウトテーブルである。仕上圧延機５の入側には、粗圧延機１によって粗圧延された粗バー２を加熱するための加熱装置３が設けられている。４は仕上圧延機入側温度計、６は仕上圧延機出側温度計、９は巻取り温度計である。
【００１８】
粗圧延機１で圧延された粗バー２は、仕上圧延機５の入側に設置された加熱装置３により、図２に部分概略平面図で示すように、その幅方向全体にわたり加熱される。その際、仕上圧延機入側温度計４により測定された粗バー２の温度が加熱装置３にフィードバックされ、粗バー２の長さ方向に均一な温度に加熱されるように、加熱装置３による粗バー２の加熱温度が制御される。このような加熱装置３として、誘導加熱装置を使用すれば、制御応答性がよく、仕上圧延機５の入側における粗バー２の温度を、その長さ方向全長にわたって一定温度に加熱することができる。
【００１９】
このようにして、仕上圧延機５の入側における粗バー２の温度が、その長さ方向に一定に保たれる結果、従来のように、仕上圧延機５で仕上圧延される粗バー２の圧延速度を、粗バー２の先端部が入ってから高める「ズーミング」を行う必要はなくなる。
【００２０】
従って、粗バー２の仕上圧延を、その長さ方向に一定の速度で行うことが可能になり、仕上圧延に要する時間は、粗バー２の長さ方向に均一になって、圧延ロールとの接触による抜熱および放射による温度低下、ならびに、圧延ロールの圧下によって生ずる加工発熱も均一になる。従って、仕上圧延機出側温度計６で測定された圧延仕上温度は一定になって、仕上圧延後の熱延鋼帯のオーステナイト組織を、その長さ方向に均一にすることができる。
【００２１】
更に、仕上圧延機５を出てランアウトテーブル７上の冷却スタンド８で連続的に冷却される熱延鋼帯の移動速度も一定になるので、冷却スタンド８での冷却水量を制御する必要はなく、一定の水量で冷却を行い、熱延鋼帯の長さ方向の冷却速度および巻取温度を均一に保つことが可能になる。
【００２２】
【実施例】
次に、この発明の方法を、実施例により更に説明する。加熱炉において、１２６０℃の温度に加熱された、厚さ２２６mm、幅１０５０mm、長さ９２００mmの寸法の炭素鋼からなるスラブを、図１に示す粗圧延機１において８７％の圧下率により粗圧延し、粗圧延された粗バーを、この発明の方法により、仕上圧延機入側温度計４によって測定された温度が、粗バーの長さ方向に均一になるように誘導加熱装置３において加熱した。
【００２３】
次いで、誘導加熱装置３により均一な温度に加熱された粗バーを、７スタンドからなる連続熱間仕上圧延機５に一定速度で通して、９５％の圧下率により仕上圧延し、仕上圧延された熱延鋼帯を冷却スタンド８において、仕上圧延機出側温度計６の位置から巻取り温度計９の位置まで、熱延鋼帯が進む間の平均冷却速度が１７℃/secと熱延鋼帯の長さ方向について均一な冷却速度で冷却した後、コイラー１０で巻き取った。かくして、板厚１．６mm、幅１０５０mmの熱延鋼帯を調製した。
【００２４】
図３に、仕上圧延機入側温度計４によって測定された粗バーの長さ方向の温度分布を黒丸印で示す。比較のために、従来方法により、粗圧延機１において粗圧延された粗バーを誘導加熱装置３において加熱せず、直ちに連続熱間仕上圧延機５に通したときの、仕上圧延機入側温度計４によって測定された粗バーの長さ方向の温度分布を白丸印で示す。
【００２５】
図３から明らかなように、従来法の場合の粗バーの温度は、先端部が約１０８０℃、後端部が約９５０℃であって、大きな差が生じていたのに対し、本発明方法の場合の粗バーの温度分布は、その先端部から後端部に至るまで、約１０７０〜１０８０℃でほぼ均一であった。
【００２６】
図４は、仕上圧延され次いで冷却された熱延鋼帯の、最先後端部を除く部分から長さ方向に均等に１０箇所よりサンプルを採取し、引張り試験を行ったときの、引張り強度の最大値および最小値を、本発明方法の場合と従来方法の場合とで比較して示すグラフである。
【００２７】
図４から明らかなように、従来方法の場合の引張り強度のばらつきは約５ｋｇ／ｍｍ²で大きいのに対し、本発明方法の場合の引張り強度のばらつきは、約２ｋｇ／ｍｍ²程度で極めて小さく、その長さ方向に均一な材質の熱延鋼帯を製造することができた。
【００２８】
【発明の効果】
以上述べたように、この発明の方法によれば、熱延鋼帯の仕上圧延機入側温度、仕上圧延条件およびランアウトテーブル上での冷却速度を、熱延鋼帯の長さ方向にわたり一定に保ち、均一な材質の熱延鋼帯を歩留り高く製造することができる、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】この発明の方法を示す連続熱間圧延ラインの概略説明図である。
【図２】加熱装置部分の概略平面図である。
【図３】仕上圧延機入側における粗バーの長さ方向温度分布を、本発明法の場合と従来法の場合とで比較して示すグラフである。
【図４】熱延鋼帯の引張り強度のばらつきを、本発明法の場合と従来法の場合とで比較して示すグラフである。
【符号の説明】
１：粗圧延機
２：粗バー
３：加熱装置
４：仕上圧延機入側温度計
５：連続熱間仕上圧延機
６：仕上圧延機出側温度計
７：ランアウトテーブル
８：冷却スタンド
９：巻取り温度計
１０：コイラー[0001]
This invention makes the temperature distribution in the length direction of the hot-rolled steel strip rolled in a continuous hot rolling mill uniform, and produces high-quality hot-rolled steel strip with high quality with little variation in the material in the length direction. The present invention relates to a method for manufacturing a hot-rolled steel strip.
[0002]
[Prior art]
Generally, a hot-rolled steel strip is obtained by heating a slab to a predetermined temperature in a heating furnace and rolling the heated slab to a predetermined thickness with a roughing mill to form a rough bar. The hot-rolled steel strip having a predetermined thickness is finish-rolled in a continuous finish rolling mill consisting of the following, and the hot-rolled steel strip is cooled in a cooling stand on a run-out table and then wound by a coiler.
[0003]
In the manufacturing process of such a hot-rolled steel strip, a non-uniform temperature distribution occurs in the length direction of the hot-rolled steel strip. That is, the temperature of the rough bar rolled by the roughing mill on the entrance side of the finishing mill is not uniform in the length direction of the roughing bar, and decreases toward the rear part. The reason is that the time from the rough bar rolled by the rough rolling mill to the finish rolling mill after leaving the rough rolling mill is longer in the rear part of the rough bar.
[0004]
As a means of compensating for the temperature difference in the length direction of the rough bar entering such a finishing mill, conventionally, the rolling speed of the rough bar rolled by the finishing mill is not constant, and the end of the rough bar is fed to the finishing mill. After entering the part, a method called “zooming” is performed to increase the rolling speed.
[0005]
By performing the above-described “zooming” for the finish rolling of the rough bar by the finish rolling mill, the time required for the finish rolling of the rough bar is shorter at the rear portion than at the front portion of the coarse bar. As a result, the heat removal due to contact with the rolling roll and the temperature drop due to radiation of the rough bar that is finish-rolled by the finishing mill becomes smaller at the rear of the rough bar, and the processing heat generated by the rolling of the rolling roll is reduced. The rear part of the coarse bar becomes larger. Therefore, the temperature distribution of the hot-rolled steel strip that has been finish-rolled by the finish rolling mill on the outlet side of the rolling mill is lower at the leading end of the steel strip and higher at the rear end.
[0006]
The hot-rolled steel strip that has been finish-rolled by the finish rolling mill is cooled in a cooling stand on the run-out table and then wound up by a coiler. In this case, from the viewpoint of keeping the winding temperature constant, The cooling rate is controlled to be constant by turning on / off the cooling water and adjusting its flow rate.
[0007]
[Problems to be solved by the invention]
However, it is not possible to make the rolling finish temperature of the hot-rolled steel strip uniform in the length direction of the steel strip only by temperature compensation by the above-mentioned “zooming”, and the moving speed of the steel strip changes due to “zooming”. Therefore, it is difficult to keep the cooling rate constant only by adjusting the flow rate of the cooling water in the cooling stand.
[0008]
Further, in order to increase the rolling finishing temperature by “zooming”, a large power is required for the drive motor of the finishing mill and the rolling load becomes large, which may cause fluctuations in the sheet crown and roll roughness.
[0009]
The rolling conditions and the cooling rate on the run-out table affect the material of the hot-rolled steel strip. In particular, in the case of carbon steel, the type and particle size of the transformation product change depending on the cooling rate near the ferrite transformation start temperature (Ar ₃ temperature), which greatly affects the material of the final product.
[0010]
In the conventional manufacturing method described above, the rolling finish temperature has a non-uniform temperature distribution in the length direction of the hot-rolled steel strip, and the movement speed of the hot-rolled steel strip on the run-out table is reduced by “zooming”. Therefore, it is extremely difficult to obtain a constant cooling rate over the entire length of the hot-rolled steel strip by controlling the flow rate of the cooling water. Problem arises.
[0011]
Accordingly, the object of the present invention is to solve the above-mentioned problems and to keep the hot rolling steel strip entry side temperature, finishing rolling conditions and the cooling rate on the runout table constant over the length of the hot rolling steel strip. It is to provide a method capable of producing a hot rolled steel strip of a uniform material with a high yield.
[0012]
[Means for Solving the Problems]
From the above-mentioned viewpoints, the present inventors have earnestly developed a method for keeping the finishing mill entry side temperature, finishing rolling conditions, and the cooling rate on the runout table constant over the entire length of the hot-rolled steel strip. Repeated research. As a result, the rough bar is heated on the inlet side of the finishing mill so that the temperature of the rough bar rolled in the finishing mill is uniform in the length direction, and the rolling speed and runout of the rough bar in the finishing mill are performed. It was found that if the cooling rate on the table is kept constant, a hot-rolled steel strip made of a uniform material can be produced with a high yield.
[0013]
The present invention has been made on the basis of the above findings and is characterized by the following.
[0014]
In the invention according to claim 1, the slab is roughly rolled by a roughing mill to form a rough bar, and then the rough rolled rough bar is finish-rolled by a hot finish rolling mill to form a hot-rolled steel strip, followed by cooling. When producing a hot-rolled steel strip by cooling with a stand, the rough bar is subjected to a uniform temperature in the length direction by an induction heating device provided on the entry side of the hot finish rolling mill. The coarse bar thus heated uniformly is passed through the hot finish rolling mill at a constant speed, and then rolled through the cooling stand at a constant speed. In the method for producing a hot-rolled steel strip, a hot finish rolling mill delivery-side thermometer and a winding thermometer are provided, and after finishing rolling, the hot-finishing steel strip is passed through the cooling stand at a constant speed, and the hot finish rolling mill delivery side From the position of the thermometer to the position of the winding thermometer Those having features that serial hot-rolled steel strip is cooled to a uniform average cooling rate during traveling.
[0015]
In the invention of claim 2, the slab is roughly rolled by a roughing mill to form a rough bar, and then the rough rolled rough bar is finish-rolled by a hot finish rolling mill to form a hot-rolled steel strip, followed by cooling. When producing a hot-rolled steel strip by cooling with a stand, the rough bar is subjected to a uniform temperature in the length direction by an induction heating device provided on the entry side of the hot finish rolling mill. The coarse bar thus heated uniformly is passed through the hot finish rolling mill at a constant speed, and then rolled through the cooling stand at a constant speed. In the method for producing a hot-rolled steel strip, a finishing rolling mill exit-side thermometer and a winding thermometer are provided, and after finishing rolling, the steel sheet is passed through the cooling stand at a constant speed, and the amount of cooling water in the cooling stand is determined. Cool with a constant amount of water without control Was carried out, the temperature measured by the hot finish rolling mill exit side thermometer and the winding thermometer, and has a particular feature to make sure that the cooling at a uniform cooling rate.
[0016]
According to a third aspect of the present invention, in the first or second aspect of the present invention, the rough-rolled rough bar is brought to a uniform temperature with a temperature variation in the length direction within about 10 ° C. by the induction heating device. so as to have a feature to be heated, an invention according to claim 4, wherein, in the invention according to any one of claims 1 to 3, the variation in the length direction of the tensile strength of the hot rolled steel strip The invention according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 4, the tensile strength in the length direction of the hot-rolled steel strip. It is characterized in that the variation of is 2 kg / mm ² or less .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic explanatory view of a continuous hot rolling line showing the method of the present invention. As shown in FIG. 1, a rough rolling mill 1, a continuous hot finishing rolling mill 5 composed of a plurality of stands, a cooling stand 8, and a coiler 10 are arranged in this order. 7 is a run-out table. A heating device 3 for heating the rough bar 2 roughly rolled by the rough rolling mill 1 is provided on the entry side of the finishing mill 5. 4 is a finishing mill entry side thermometer, 6 is a finishing mill exit side thermometer, and 9 is a winding thermometer.
[0018]
The rough bar 2 rolled by the rough rolling mill 1 is heated over the entire width direction by a heating device 3 installed on the entrance side of the finish rolling mill 5 as shown in a partial schematic plan view in FIG. At that time, the temperature of the rough bar 2 measured by the finishing mill entry-side thermometer 4 is fed back to the heating device 3 and is heated to a uniform temperature in the length direction of the rough bar 2 by the heating device 3. The heating temperature of the coarse bar 2 is controlled. If an induction heating device is used as such a heating device 3, the control responsiveness is good, and the temperature of the coarse bar 2 on the entry side of the finish rolling mill 5 can be heated to a constant temperature over its entire length in the length direction. it can.
[0019]
In this way, the temperature of the coarse bar 2 on the entry side of the finish rolling mill 5 is kept constant in the length direction thereof. As a result, the coarse bar 2 to be finish-rolled by the finish rolling mill 5 as in the conventional manner. There is no need to perform “zooming” to increase the rolling speed after the end of the coarse bar 2 enters.
[0020]
Therefore, the finish rolling of the rough bar 2 can be performed at a constant speed in the length direction, and the time required for the finish rolling becomes uniform in the length direction of the rough bar 2, Heat removal due to contact and temperature drop due to radiation, and processing heat generated by rolling of the rolling roll are also uniform. Therefore, the rolling finishing temperature measured by the finishing mill exit-side thermometer 6 becomes constant, and the austenite structure of the hot-rolled steel strip after finish rolling can be made uniform in the length direction.
[0021]
Furthermore, since the moving speed of the hot-rolled steel strip that is continuously cooled by the cooling stand 8 on the run-out table 7 after leaving the finishing mill 5 is also constant, there is no need to control the amount of cooling water in the cooling stand 8. Cooling with a constant amount of water makes it possible to maintain a uniform cooling rate and coiling temperature in the length direction of the hot-rolled steel strip.
[0022]
【Example】
Next, the method of the present invention will be further described with reference to examples. A slab made of carbon steel having a thickness of 226 mm, a width of 1050 mm, and a length of 9200 mm heated to a temperature of 1260 ° C. in a heating furnace is roughly rolled with a reduction ratio of 87% in the rough rolling machine 1 shown in FIG. Then, the roughly rolled rough bar was heated by the induction heating device 3 so that the temperature measured by the finishing mill entry side thermometer 4 was uniform in the length direction of the rough bar by the method of the present invention. .
[0023]
Next, the rough bar heated to a uniform temperature by the induction heating device 3 was passed through a continuous hot finish rolling mill 5 consisting of 7 stands at a constant speed, and finished and rolled at a reduction rate of 95%. The hot-rolled steel strip is cooled at an average cooling rate of 17 ° C./sec during the course of the hot-rolled steel strip from the position of the finisher rolling mill thermometer 6 to the position of the coiling thermometer 9 in the cooling stand 8. After cooling at a uniform cooling rate in the length direction of the band, it was wound up by a coiler 10. Thus, a hot rolled steel strip having a thickness of 1.6 mm and a width of 1050 mm was prepared.
[0024]
In FIG. 3, the temperature distribution in the length direction of the coarse bar measured by the finishing mill entry-side thermometer 4 is indicated by black circles. For comparison, when the rough bar roughly rolled in the roughing mill 1 is not heated in the induction heating device 3 by the conventional method, and immediately passed through the continuous hot finish rolling mill 5, the inlet temperature of the finishing mill is measured. The temperature distribution in the length direction of the coarse bars measured by the total 4 is indicated by white circles.
[0025]
As apparent from FIG. 3, the temperature of the coarse bar in the case of the conventional method was about 1080 ° C. at the front end portion and about 950 ° C. at the rear end portion. In this case, the temperature distribution of the coarse bar was substantially uniform at about 1070 to 1080 ° C. from the front end portion to the rear end portion.
[0026]
Fig. 4 shows the tensile strength of a hot-rolled steel strip that has been finish-rolled and then cooled, when a sample is taken from 10 locations evenly in the length direction from the portion excluding the rearmost end, and a tensile test is performed. It is a graph which compares and shows the maximum value and the minimum value in the case of the method of the present invention and the case of the conventional method.
[0027]
As apparent from FIG. 4, the variation in tensile strength in the case of the conventional method is large at about 5 kg / mm ² , whereas the variation in tensile strength in the case of the method of the present invention is extremely high at about 2 kg / mm ^2. It was possible to produce a hot-rolled steel strip that was small and uniform in the length direction.
[0028]
【The invention's effect】
As described above, according to the method of the present invention, the temperature at the entrance to the finish rolling mill of the hot rolled steel strip, the finish rolling conditions, and the cooling rate on the run-out table are made constant over the length direction of the hot rolled steel strip. An industrially useful effect can be obtained, in which a hot rolled steel strip made of a uniform material can be produced with a high yield.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory diagram of a continuous hot rolling line showing the method of the present invention.
FIG. 2 is a schematic plan view of a heating device portion.
FIG. 3 is a graph showing the temperature distribution in the length direction of the rough bar on the entrance side of the finishing mill in comparison with the method of the present invention and the conventional method.
FIG. 4 is a graph showing the variation in tensile strength of a hot-rolled steel strip in comparison with the method of the present invention and the conventional method.
[Explanation of symbols]
1: Coarse rolling mill 2: Coarse bar 3: Heating device 4: Finishing mill entry side thermometer 5: Continuous hot finishing mill 6: Finishing mill exit side thermometer 7: Runout table 8: Cooling stand 9: Winding Thermometer 10: Coiler

Claims

The slab is roughly rolled by a roughing mill to form a rough bar, and then the rough rolled rough bar is finish-rolled by a hot finish rolling mill to form a hot-rolled steel strip, and then cooled by a cooling stand to be hot-rolled steel When manufacturing the strip, the rough bar that has been roughly rolled is heated so as to have a uniform temperature in its length direction by an induction heating device provided on the entry side of the hot finish rolling mill. In the method of manufacturing a hot-rolled steel strip, the coarse bar heated uniformly as described above is subjected to finish rolling through the hot finishing mill at a constant speed, and then cooled through the cooling stand at a constant speed . ,
A hot finish rolling mill outlet thermometer and a winding thermometer are provided, and after finishing rolling, the rolling temperature is passed through the cooling stand at a constant speed, and the winding temperature is measured from the position of the hot finishing mill outlet thermometer. A method for producing a hot-rolled steel strip, wherein the hot-rolled steel strip is cooled at a uniform average cooling rate while the hot-rolled steel strip proceeds to a total position.

The slab is roughly rolled by a roughing mill to form a rough bar, and then the rough rolled rough bar is finish-rolled by a hot finish rolling mill to form a hot-rolled steel strip, and then cooled by a cooling stand to be hot-rolled steel When manufacturing the strip, the rough bar that has been roughly rolled is heated so as to have a uniform temperature in its length direction by an induction heating device provided on the entry side of the hot finish rolling mill. In the method of manufacturing a hot-rolled steel strip, the coarse bar heated uniformly as described above is subjected to finish rolling through the hot finishing mill at a constant speed, and then cooled through the cooling stand at a constant speed. ,
A finishing rolling mill delivery-side thermometer and a winding thermometer are provided, and after finishing rolling, it is passed through the cooling stand at a constant speed, and the amount of cooling water at the cooling stand is not controlled, and the amount of water is constant. A method for producing a hot-rolled steel strip , comprising cooling, measuring the temperature with the hot-end rolling mill outlet thermometer and the winding thermometer, and confirming cooling at a uniform cooling rate .

The rough bar which is roughly rolled is heated by the induction heating device so that the temperature variation in the length direction becomes a uniform temperature within about 10 ° C. Manufacturing method of hot-rolled steel strip.

The method for producing a hot-rolled steel strip according to any one of claims 1 to 3, wherein a variation in tensile strength in the length direction of the hot-rolled steel strip is about 5% or less .

The method for producing a hot-rolled steel strip according to any one of claims 1 to 4, wherein a variation in tensile strength in the length direction of the hot-rolled steel strip is about 2 kg / mm ² or less .