JP3243994B2 - Hot rolled steel strip rolling method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled steel strip having a material uniform in the longitudinal direction, wherein the finishing temperature of a hot-rolled steel strip rolled in a continuous hot rolling mill is made uniform over its length. The present invention relates to a method for manufacturing a belt.

[0002]

2. Description of the Related Art Generally, in a hot-rolled steel strip, a slab is heated to a predetermined temperature in a heating furnace, and the heated slab is rolled to a predetermined thickness by a rough rolling mill to form a coarse bar. By finishing rolling in a continuous finishing rolling mill consisting of a plurality of stands to form a hot-rolled steel strip having a predetermined thickness, the hot-rolled steel strip is cooled in a cooling stand on a run-out table, and then wound up by a coiler. Manufactured.

In the process of producing such a hot-rolled steel strip,
An uneven temperature distribution occurs in the length direction of the hot-rolled steel strip. That is, the temperature of the coarse bar rolled by the rough rolling mill on the entrance side of the finish rolling mill is not uniform in the length direction of the rough bar, but becomes lower toward the rear. The reason is that the time required for the coarse bar rolled by the rough rolling mill to leave the rough rolling mill and to enter the finishing rolling mill is longer toward the rear of the rough bar.

As means for compensating for the temperature difference in the length direction of the rough bar entering the finishing mill, conventionally, the rolling speed of the rough bar rolled by the finishing mill is not fixed, and the roughing bar is roughened. After the tip of the bar enters, a method called "zooming" is used to increase the rolling speed.

[0005] By performing the finish rolling of the rough bar by the finishing mill by the above-mentioned "zooming", the time required for the finish rolling of the rough bar is shorter at the rear portion than at the front portion of the rough bar. As a result, the temperature drop due to heat release and radiation of the rough bar that is finish-rolled by the finish rolling machine due to contact with the rolling roll becomes smaller toward the rear of the rough bar, and the processing heat generated by the reduction of the rolling roll is reduced. Larger at the rear of the coarse bar. Therefore, the temperature distribution on the exit side of the rolling mill of the hot-rolled steel strip that has been finish-rolled by the finishing mill, the tip of the steel strip tends to be low and the rear end tends to be high, and the temperature distribution of the hot-rolled steel strip Can be uniformed in its length direction.

[0006]

SUMMARY OF THE INVENTION In continuous hot rolling of a slab made of carbon steel, from the viewpoint of securing the material, the rolling finishing temperature in the finishing mill is made higher than the ferrite transformation start temperature (Ar ₃ temperature). There is a need. When ferrite transformation occurs during rolling, the properties such as strength, ductility, and toughness of the steel strip may deteriorate due to growth of ferrite grains and accumulation of strain in the ferrite.

Therefore, of the hot-rolled steel strip which has been finish-rolled,
The part where the rolling finish temperature could not be maintained higher than the Ar ₃ temperature becomes a defective product, and the product yield decreases.
In actual operation, in order to keep the rolling finish temperature at the Ar ₃ temperature or higher over the entire width of the hot-rolled steel strip, a target finish temperature is set, and rolling is performed so that the roll finish temperature becomes the target finish temperature.

When the temperature difference in the longitudinal direction of the coarse bar is compensated for by the "zooming" method of increasing the rolling speed after the leading end of the rough bar enters the finishing mill, the rolling speed is accelerated to a predetermined speed. Thereafter, the rolling finish temperature of the hot-rolled steel strip can be raised to a target finish temperature or higher.

However, during the period from when the leading end of the coarse bar enters the finishing mill to when the rolling speed is increased to a predetermined speed, the rolling finishing temperature of the hot-rolled steel strip is not adjusted to the target finishing temperature. It cannot be increased any more, and it is lower than other parts. In the case of a thin steel strip having a thickness of 1.6 mm or less, such a low-temperature portion extends over a wide area of about 30% from its tip.

Thus, in the finish rolling of the hot-rolled steel strip,
With the conventional "zooming" method, it is difficult to keep the rolling finish temperature uniform over the entire length of the hot-rolled steel strip, and particularly in the case of a thin steel strip having a thickness of 1.6 mm or less, The rolling finish temperature could not be raised above the target finish temperature over a wide range of about 30% from the tip end, resulting in a reduction in product yield.

As means for solving the above-mentioned problem, Japanese Patent Application Laid-Open No. 7-155822 discloses that a leading end of a coarse bar rolled by a rough rolling mill is supplied to a leading side of a finishing rolling mill by an electric heating device. A method of directly increasing the temperature of the tip portion by heating (hereinafter referred to as Prior Art 1) is disclosed. However, in the prior art 1, since the coarse bar is directly heated by electric current, there is a problem that a spark is generated during energization, a part of the coarse bar is melted, and a flaw is generated.

Further, Japanese Patent Application Laid-Open Nos. Hei 4-33715 and Hei 4-190916 disclose a method of heating a longitudinal end portion of a coarse bar by a heater (hereinafter referred to as prior art 2). . However, the method of prior art 2 is:
Only the longitudinal end of the coarse bar is heated, and the longitudinal direction of the coarse bar is not heated over a wide range.

[0013] Accordingly, an object of the present invention is to solve the above-mentioned problems and, in the finish rolling of a hot-rolled steel strip, to raise the rolling finish temperature to a predetermined temperature or higher over the entire length direction of the hot-rolled steel strip and uniformly. An object of the present invention is to provide a method that can maintain a hot-rolled steel strip of a homogeneous material at a high yield without being flawed by heating.

[0014]

SUMMARY OF THE INVENTION In view of the above-mentioned viewpoints, the inventors of the present invention, in the finish rolling of a hot-rolled steel strip, raise the rolling finish temperature to a predetermined temperature or more over the entire length direction of the hot-rolled steel strip. We worked diligently to develop a method that can maintain uniformity. As a result, after the leading end of the rough bar enters the finishing mill, until the rolling speed is sufficiently accelerated to a predetermined temperature by "zooming", the leading end of the rough bar is induction-heated at the finishing rolling mill entry side. If heated by the equipment, the rolling finishing temperature in the finishing mill can be made uniform in the length direction of the hot-rolled steel strip, and no flaws or the like are generated by heating. It has been found that the belt can be manufactured with high yield.

[0015] The present invention has been made based on the above findings. According to the first aspect of the present invention, a slab heated to a predetermined temperature is roughly rolled by a rough rolling mill, and then the roughly rolled coarse bar is rolled. When finish rolling by a continuous hot finish rolling mill, the rolling speed of the coarse bar in the finish rolling machine is accelerated after the leading end of the coarse bar enters the finish rolling mill, a method of rolling a hot-rolled steel strip. In the finish
The induction heating device provided on the entry side of the rolling mill
When the end is detected, the induction heating device
The heating of the coarse bar by
The coarse bar is heated by the induction heating device.
It is characterized by stopping .

[0016] The invention according to claim 2 is a method according to claim 2, wherein
When the rough bar is heated by the induction heating device.
Performing zooming in the finishing mill without heating,
The rolling finish temperature on the exit side of the finishing mill exceeds the target finish temperature
It is characterized by the fact that it is the first time .

[0017]

FIG. 1 is a schematic explanatory view of a continuous hot rolling line showing a method of the present invention. As shown in FIG. 1, a rough rolling mill 1, an induction heating device 4, and a continuous hot finishing mill 6 including a plurality of stands are arranged in this order. Numeral 3 is a coarse bar tip detector for detecting the tip of the coarse bar 2 coarsely rolled by the rough rolling mill 1 provided on the entrance side of the induction heating device 4, 5 is a thermometer on the entrance side of the finishing mill, 7 Is a thermometer on the exit side of the finishing mill.

The rough bar 2 rolled by the rough rolling mill 1 is covered by an induction heating device 4 installed on the entrance side of the finishing rolling mill 6 over the entire width thereof as shown in a partial schematic plan view in FIG. Heated.

The rough bar 2 roughly rolled by the rough rolling mill 1
Is detected by the detector 3 provided on the entry side of the induction heating device 4, the induction heating device 4 is turned on, and the heating of the rough bar 2 is started by the induction heating device 4. The heated coarse bar 2 is guided to a continuous hot finishing mill 6 for finish rolling, and the rolling speed of the finishing mill 6 at that time is as follows:
It is advanced by "zooming" after the leading end of the coarse bar 2 enters, and the time required for finish rolling of the coarse bar is shorter at the rear part than at the front part of the coarse bar. When the rolling speed of the finishing mill is accelerated to a predetermined speed and the rolling finishing temperature becomes equal to or higher than the target temperature, the heating of the rough bar 2 by the induction heating device 4 is stopped.

In this manner, until the rolling speed of the hot-rolled steel strip to be finish-rolled by zooming in the finishing mill 6 is increased to a predetermined speed, that is, until the rolling finishing temperature reaches the target temperature. Since the compensation is performed by the heating of the rough bar by the induction heating device 4, the temperature becomes a uniform temperature equal to or higher than the target finishing temperature over the entire length direction of the hot-rolled steel strip, and a hot-rolled steel strip of a uniform material can be manufactured.

[0021]

Next, the method of the present invention will be further described with reference to examples. In a heating furnace, heated to a temperature of 1280 ° C., thickness 226 mm, width 1050 mm, length 920
A slab made of carbon steel having a size of 0 mm is roughly rolled in a rough rolling mill 1 shown in FIG. 1 at a rolling reduction of 96%, and then, in a continuous hot finishing rolling mill 6 consisting of 7 stands, a rolling reduction of 96%. Finish rolling. Finishing mill 6
The rolling speed was accelerated by "zooming" after the tip of the rough bar 2 was inserted. When the tip of the rough bar 2 roughly rolled in the rough rolling mill 1 is detected by the detector 3 provided on the inlet side of the induction heating device 4, the induction heating device 4 is turned on, and the induction heating device is turned on. 4, heating of the coarse bar 2 was started.

FIG. 3 shows the relationship between the peripheral speed of the roll and the rolling time in the final stand of the finishing mill 6. By "zooming" described above, a roll peripheral speed of the rolling mill 6 finish with time is advanced, and reaches the maximum roll circumferential velocity t ₀ is determined from the operating conditions, and thereafter becomes a constant velocity.

The time t ₁ at which the peripheral speed of the final stand roll of the finishing mill 6 described above and the temperature of the hot-rolled steel strip detected by the thermometer 7 on the exit side of the finishing mill satisfy appropriate conditions (see FIG. (When the white circle graph exceeds the target finishing temperature), the induction heating device 4 was turned off. Therefore, thereafter, the rough bar is not heated by the induction heating device 4 and the time required for finish rolling of the rough bar is shortened by “zooming” of the finishing mill 6, and as a result, the finish rolling is performed by the finishing mill 6. The temperature distribution in the length direction of the hot rolled steel strip became uniform.

FIG. 4 shows a temperature distribution in the longitudinal direction of the hot-rolled steel strip measured by the exit thermometer 7 on the finishing mill. As shown by the black circles in FIG. 4, the rolling finishing temperature was uniform over the length direction of the hot-rolled steel strip, and the target finishing temperature or higher could be secured. The time t ₁ switching off the induction heating device 4 described above, Ri Tokidea the graph of white circles in FIG. 4 exceeds the target finishing temperature of the hot rolled strip, predetermined
You.

On the other hand, in the conventional case in which the heating is not performed at the entrance of the finishing mill but is performed only by "zooming" of the finishing mill 6, as shown by a white circle in FIG. The portion of about 30% from the tip was lower than the target finishing temperature determined from the Ar ₃ temperature, and the material deteriorated.

In particular, in the case of a thin steel strip having a thickness of 1.6 mm or less, there has conventionally been a problem that the rolling finish temperature becomes lower than Ar _{3 in the} vicinity of the tip of the steel strip, so that the yield decreases. However, according to the method of the present invention, after the leading end of the rough bar enters the finishing mill, until the rolling speed is sufficiently accelerated by "zooming", the guide provided on the entrance side of the finishing mill. Since the rolling finish temperature is compensated by heating by the heating device 4, the rolling finish temperature near the steel strip tip does not become Ar ₃ or lower, and the product yield can be improved.

The hot-rolled steel strip thus finish-rolled is cooled at a cooling stand at about 17 ° C./sec.
Wound with a coiler. Thus, a thickness of 1.2 mm and a width of 1
A 050 mm hot-rolled steel strip of a uniform material in the length direction could be produced.

[0028]

As described above, according to the method of the present invention, in the finish rolling of the hot-rolled steel strip, the rolling finish temperature is raised to a predetermined temperature or more over the entire length direction of the hot-rolled steel strip; Can be kept constant over its length,
It has become possible to manufacture a hot-rolled steel strip with a small thickness, which could not be manufactured because a rolling finish temperature higher than the Ar ₃ temperature could not be secured. In addition, by using the induction heating device, the controllability is improved, and the generation of flaws due to sparks which may be caused by the electric heating does not occur, and the reheating temperature for the slab to be roughly rolled can be reduced. Many industrially useful effects are provided.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a continuous hot rolling line showing a method of the present invention.

FIG. 2 is a schematic plan view of a heating device portion.

FIG. 3 is a graph showing a relationship between a peripheral speed of a roll and a rolling time in a final stand of a finishing mill.

FIG. 4 is a graph showing a temperature distribution of a finish rolling temperature in a length direction of a hot-rolled steel strip.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rough rolling mill 2 Coarse bar 3 Coarse bar tip detector 4 Induction heating device 5 Finishing rolling mill entrance thermometer 6 Continuous hot finishing rolling mill 7 Finishing rolling mill exit thermometer

────────────────────────────────────────────────── ─── Continuing on the front page (72) Shozo Higashi, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Sadaka Masuda 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (56) References JP-A-61-119328 (JP, A) JP-A-59-56911 (JP, A) JP-A-57-119492 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 1/26 B21B 37/76 B21B 45/00

Claims (2)

(57) [Claims] 1. A slab heated to a predetermined temperature is roughly rolled by a rough rolling mill, and then, when the rough-rolled rough bar is finish-rolled by a continuous hot finish rolling mill, the rough bar in the finishing mill is rolled. In the method of rolling a hot-rolled steel strip, the rolling speed of the rough bar is accelerated after the leading end portion of the rough bar enters the finishing mill, the induction heating device provided on the entrance side of the finishing mill includes the roughing bar.
When the arrival of the bar tip is detected,
Start heating the coarse bar with a heating device, and during acceleration,
And, at a predetermined time, before the induction heating device
A method for rolling a hot-rolled steel strip, wherein the heating of the coarse bar is stopped . 2. The method according to claim 1, wherein the predetermined time is a time when the coarse bar
Without heating by the induction heating device.
Performing zooming with the upper rolling mill, and
2. The method for rolling a hot-rolled steel strip according to claim 1, wherein the time at which the finishing temperature exceeds the target finishing temperature .