JPH09300003A - Method for rolling hot rolled steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a hot rolled steel strip of a homogeneous material at high yield by keeping the temp. of the hot rolled steel strip on the inlet side of a finishing mill, finish roll-condition and cooling rate constant in the length direction of the hot rolled steel strip. SOLUTION: A slab heated to a prescribed temp. is rough rolled with a roughing mill 1, the rough-rolled rough bar is coiled in a coil box 3 and thermally insulated. Next, by passing the rough bar which is thermally insulated in this manner through a continuous hot rolling mill 5 at constant speed, finish rolling is executed and, by passing the hot rolled steel strip to which finish rolling is executed through a cooling stand at constant speed and cooling it, the hot rolled steel strip of the homogeneous material is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a uniform temperature distribution in the length direction of a hot-rolled steel strip rolled by a continuous hot rolling mill and has excellent quality with little variation in the material in the length direction. The present invention relates to a method for rolling a hot-rolled steel strip for producing a rolled steel strip with a high yield.

[0002]

2. Description of the Related Art Generally, a hot-rolled steel strip is manufactured by heating a slab to a predetermined temperature in a heating furnace, rolling the heated slab to a predetermined thickness with a rough rolling machine to form a coarse bar, and then forming a coarse bar. By finishing rolling with a continuous finishing rolling mill consisting of multiple stands to form a hot-rolled steel strip with a predetermined thickness, cooling this hot-rolled steel strip at a cooling stand on a runout table, and then winding it with a coiler. Manufactured.

In the process of manufacturing such a hot rolled steel strip,
The temperature of the rough bar rolled by the rough rolling mill on the entry side of the finish rolling mill is not uniform in the length direction of the rough rolling mill, and becomes lower toward the rear part thereof. The reason is that the time from when the rough bar rolled by the rough rolling mill exits the rough rolling mill to when it enters the finishing rolling mill is longer in the rear part of the rough bar. A non-uniform temperature distribution occurs along the length of the strip.

As a means for compensating for the temperature difference in the lengthwise direction of the rough bar entering the finish rolling mill, conventionally, the rolling speed of the rough bar rolled by the finish rolling mill is not constant but the rough rolling is performed by the finish rolling mill. A method called "zooming" is used to increase the rolling speed of the bar after it is inserted.

By performing the finish rolling of the rough bar by the finish rolling machine by the above-mentioned "zooming", the time required for finish rolling of the rough bar is shorter in the rear part than in the front part of the rough bar. As a result, the rough bar finish-rolled by the finish rolling mill, the heat removal due to the contact with the rolling rolls and the temperature decrease due to the radiation are smaller toward the rear part of the rough bar, and the processing heat generated by the reduction of the rolling rolls is not generated. The larger the rear part of the coarse bar, the larger. Therefore, the temperature distribution of the hot-rolled steel strip finish-rolled by the finish rolling mill on the outlet side of the rolling mill is low at the leading end of the steel strip and becomes higher toward the trailing end.

The hot-rolled steel strip finish-rolled by the finish rolling mill is cooled on a run-out table and then wound up by a coiler. At that time, from the viewpoint of keeping the winding temperature constant, the hot-rolled steel strip is wound. The cooling rate is controlled to be constant by turning the cooling water on and off and adjusting its flow rate.

[0007]

However, the rolling finish temperature of the hot rolled steel strip cannot be made uniform in the length direction of the steel strip only by temperature compensation by the above-mentioned "zooming". In addition, since the steel strip moving speed on the runout table changes due to "zooming", in order to keep the cooling speed constant,
It must be controlled according to the change in the moving speed of the steel strip, but this is practically difficult.

Further, in order to increase the rolling finish temperature by "zooming", a large power is required for the drive motor of the finishing rolling mill, and the rolling load is also increased, which may cause fluctuations in the plate crown and roughening of the roll surface. Occurs.

[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 grain size of the transformation product change depending on the cooling rate near the ferrite transformation start temperature (Ar ₃ temperature), which has a great influence on the final product material.

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 hot-rolled steel strip on the runout table is subjected to "zooming". Since the moving speed changes,
It is extremely difficult to obtain a constant cooling rate over the entire length of the hot-rolled steel strip only by controlling the flow rate of the cooling water. Therefore, the material of the hot-rolled steel strip varies and the product yield decreases. Occurs.

Therefore, an object of the present invention is to solve the above-mentioned problems and to determine the temperature of the hot-rolled steel strip on the finish rolling mill side, the conditions for finish rolling, the cooling rate on the run-out table, and the length of the hot-rolled steel strip. (EN) It is intended to provide a method capable of manufacturing a hot-rolled steel strip of a uniform material with a high yield by keeping it constant in all directions.

[0012]

From the above-mentioned viewpoints, the inventors of the present invention have determined that the temperature at the entrance of the finish rolling mill, the conditions for the finish rolling, and the cooling rate on the run-out table are determined for the entire length of the hot-rolled steel strip. We have conducted extensive research to develop a method of keeping it constant. As a result, a coil box was installed between the rough rolling machine and the finishing rolling machine of the continuous hot rolling line, and the rough bar coming out of the rough rolling machine was wound in the coil box and kept warm, thereby finishing the rolling machine. If finish rolling is performed by preventing the temperature drop due to the waiting time before entering, it is possible to finish rolling at a constant speed without compensating for the temperature difference due to "zooming" as in the past. It was found that the inlet side temperature, finish rolling condition and cooling rate on the run-out table can be kept constant along the length of the hot rolled steel strip, and the hot rolled steel strip of uniform material can be manufactured with high yield.

The present invention has been made on the basis of the above-mentioned findings. The slab heated to a predetermined temperature is roughly rolled by a rough rolling mill, and then the rough rolled rough bar is continuously hot-finished by a rolling mill. After finishing rolling by, by the method of rolling a hot rolled steel strip to produce a hot rolled steel strip having a predetermined thickness by cooling with a cooling stand, a coil box is provided on the inlet side of the continuous hot finish rolling mill, The rough rolled rough bar is wound in the coil box and kept warm, and then the rough bar wound and kept warm in the coil box is fed at a constant speed to the continuous hot finish rolling mill and the cooling stand. It is characterized in that it is continuously finish-rolled by passing through.

[0014]

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 finish rolling mill 5 including a plurality of stands, a cooling stand 8 and a coiler 10 are arranged in this order. 7 is a runout table.

The coil box 3 is provided on the entrance side of the finish rolling mill 5.
Is provided. The coil box 3 has a heat retaining function by a heat insulating material, a heating device, etc., and a coarse bar winder (not shown) is provided in the box. 4 is a thermometer on the inlet side of the finishing rolling mill, 6 is a thermometer on the outlet side of the finishing rolling mill, and 9 is a winding thermometer.

The rough bar 2 rolled by the rough rolling mill 1 is guided to a coil box 3 provided on the entrance side of the finishing rolling mill 5, and wound by a winding machine provided in the coil box 3. Be kept warm. The rough bar 2 that has been wound and kept warm is then guided to the finish rolling machine 5 by the reverse rotation of the winder, the driving of the table roller, etc., and finish rolling is performed.

In this way, since the coarse bar is kept warm in the coil box 3 during the waiting time until the rough bar is finish-rolled, its temperature does not decrease and is kept constant over the entire length. To be done. Therefore, there is no need to perform "zooming" in which the rolling speed of the rough bar 2 finish-rolled by the finish rolling mill 5 is increased after the tip of the rough bar 2 is inserted as in the conventional case.

As a result, the finish rolling of the rough bar 2 can be performed at a constant speed in the lengthwise direction, and the time required for finish rolling becomes uniform in the lengthwise direction of the rough bar 2.
The heat removal due to contact with the rolling rolls and the temperature decrease due to radiation, and the processing heat generated by the rolling of the rolling rolls are also uniform. Therefore, the rolling finishing temperature measured by the finishing side thermometer 6 becomes constant, and the austenite structure of the hot rolled steel strip after finishing rolling can be made uniform in the length direction.

Further, since the moving speed of the hot rolled steel strip that exits the finish rolling mill 5 and is continuously cooled by the cooling stand 8 on the runout table 7 is also constant, the amount of cooling water in the cooling stand 8 is controlled. It is not necessary to perform cooling with a constant amount of water, and it becomes possible to keep the cooling rate in the length direction of the hot-rolled steel strip and the winding temperature uniform.

Further, the winding of the rough bar by the winding machine in the coil box 3 is not affected by the finish rolling speed, so that the speed can be increased. Therefore, as a result of the retention time of the coarse bar on the run-out table 7 being shortened, the temperature decrease in the entire line can be suppressed. The moving speed of the rough bar from the coil box 3 to the finishing rolling mill 5 is controlled by the rolling speed of the finishing rolling mill 5 and becomes slower.
The position of is preferably as close to the finish rolling mill 5 as possible.

[0021]

Next, the method of the present invention will be further described with reference to examples. In a heating furnace, a slab made of carbon steel having a thickness of 226 mm, a width of 1000 mm and a length of 9150 mm, which was heated to a temperature of 1260 ° C., was used as a rough rolling mill 1 shown in FIG.
In the coil box 3 provided on the inlet side of the finish rolling mill 5, the rough bar is roughly rolled by a rolling reduction of 87% in accordance with the method of the present invention.
Then, it is passed through a continuous hot finishing mill 5 consisting of 7 stands at a constant speed to finish rolling at a reduction rate of 95%, and the hot rolled steel strip subjected to finish rolling is uniformly distributed in the cooling stand 8 in its length direction. After cooling at the cooling rate, it was wound by the coiler 10. Thus, the plate thickness is 1.6 mm and the width is 100
A 0 mm hot rolled steel strip was prepared.

The surface temperature difference between the leading end and the trailing end of the rough bar when wound in the coil box 3 by the above-described method of the present invention was examined, and in the case of the conventional method, that is, the finish rolling of the rough bar was performed in a "Z-".
On the entry side of the finishing mill when
The surface temperature difference between the front end and the rear end of the rough bar is compared with FIG.
It was shown to.

As is apparent from FIG. 2, in the case of the conventional method, the surface temperature difference between the leading end portion and the rear end portion of the rough bar is 65 ° C., whereas in the case of the method of the present invention, the above temperature difference. Is only 15
° C. This temperature difference between the front and rear ends is due to the waiting time after rough rolling and before finish rolling, and indicates that the coil box according to the method of the present invention has a great effect of retaining heat during winding.

The temperature distribution in the longitudinal direction of the rough bar on the entry side of the finish rolling mill when the rolling was carried out by the method of the present invention and the conventional method described above was shown in FIG. As is clear from FIG.
In the case of the conventional method, the temperature difference between the front end portion and the rear end portion of the rough bar was about 70 ° C, but in the case of the method of the present invention, it was less than about 10 ° C, and the temperature difference was extremely small.

Further, the finishing temperature distribution in the length direction of the hot-rolled steel strip when rolled by the method of the present invention and the conventional method was examined and shown in FIG. As is clear from FIG. 4, the finishing temperature distribution in the case of the method of the present invention was substantially uniform within about 810 ° C. from the leading end to the trailing end.

As described above, according to the present invention, at the time of rolling a hot-rolled steel strip, the temperature at the finish rolling mill entrance side of the rough bar rolled by the rough rolling mill can be made uniform in the length direction. As a result, the finishing rolling speed and the cooling speed on the run-out table are made uniform, so that a hot-rolled steel strip made of a homogeneous material can be manufactured with high yield.

[0027]

As described above, according to the method of the present invention, the temperature of the hot-rolled steel strip on the finishing rolling mill side, the finish-rolling conditions, and the cooling rate on the run-out table are determined by the length of the hot-rolled steel strip. A hot rolled steel strip made of a uniform material can be manufactured at a high yield while keeping it constant over the entire length in the depth direction, which is an industrially useful effect.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a comparison between the surface temperature difference between the leading end portion and the trailing end portion of the rough bar on the entry side of the finishing mill between the method of the present invention and the conventional method.

FIG. 3 is a diagram showing a comparison of temperature distributions in the longitudinal direction of the rough bar on the entry side of the finishing rolling mill between the method of the present invention and the conventional method.

FIG. 4 is a view showing comparison of finishing temperature distributions in the length direction of a hot rolled steel strip between the method of the present invention and the conventional method.

[Explanation of symbols]

 1 Rough rolling mill 2 Rough bar 3 Coil box 4 Finishing rolling mill inlet side thermometer 5 Continuous hot finishing rolling mill 6 Finishing rolling mill outlet side thermometer 7 Runout table 8 Cooling stand 9 Winding thermometer 10 Coiler

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sadakazu Masuda 1-2, Marunouchi, Chiyoda-ku, Tokyo Day Steel Pipe Co., Ltd. (72) Yutaka Mihara 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Date Inside the Steel Pipe Co., Ltd. (72) Inventor Naoko Eda 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Date Inside the Steel Pipe Co., Ltd. (72) Takuma Terauchi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Date Main Steel Pipe Co., Ltd.

Claims (1)

[Claims] 1. A slab heated to a predetermined temperature is roughly rolled by a rough rolling mill, and then the rough rolled rough bar is finish-rolled by a continuous hot finish rolling mill and then cooled by a cooling stand. In a method of rolling a hot-rolled steel strip for producing a hot-rolled steel strip having a thickness, a coil box is provided on the inlet side of the continuous hot finish rolling mill, and the rough-rolled rough bar is wound in the coil box. It is characterized in that it is taken and kept warm, and then the rough bar wound and kept warm in the coil box is continuously finish-rolled at a constant speed through the continuous hot finish rolling mill and the cooling stand. A method for rolling hot-rolled steel strip.