JP2002178004A - Hot rolling equipment and method for hot rolled steel strip - Google Patents

Abstract

(57) [Summary] [Problem] By combining rapid cooling and slow cooling, ferrite grains can be sufficiently refined.
A hot rolling method and equipment for a hot-rolled steel strip capable of accurately controlling an intermediate temperature (or a cooling stop temperature). A slab is formed into a rough bar by a rough rolling mill, and the rough bar is finish-rolled by a finishing rolling mill to form a hot-rolled steel strip, and then is transported on a hot run table and wound by a winder. In the method of rolling a steel strip, between the final stand of the roughing mill and the final stand of the finishing mill, a heating step of heating the rough bar over the entire width direction, and between the first stand of the finishing mill and the winding machine, A cooling step including rapid cooling of the finish-rolled hot-rolled steel strip with at least one or more cooling devices at 200 ° C./s or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a hot rolling method and a hot rolling facility for producing a hot-rolled steel strip.

[0002]

2. Description of the Related Art The production of a hot-rolled steel strip by a conventional hot strip mill is performed as follows. A slab having a predetermined temperature, which has been reheated in a slab heating furnace or sent directly to a rolling process after continuous casting, is roughly rolled into a rough bar by a rough rolling mill, and the rough bar is further processed into a finishing mill. And hot rolled steel strip. The hot rolled steel strip is sprayed with cooling water in a plurality of cooling banks while being transported onto the hot run table, cooled to a predetermined temperature, and then wound up by a coiler.

[0003] The temperature control of the hot-rolled steel strip on the hot-run table is performed by controlling the finishing temperature of the rolled steel sheet measured from the end of the finish rolling to the start of the hot-run cooling, the intermediate temperature measured during the hot-run cooling, and the hot-run cooling. This is done by controlling the winding temperature measured from the end to the winding by the coiler.

[0004] In the production of a hot-rolled steel strip, it is extremely important to secure a rolling finish temperature equal to or higher than a ferrite transformation start temperature in order to obtain a good material. However, due to the difference in the waiting time of the finish rolling, the temperature of the coarse bar on the entrance side of the finishing mill is high at the front end and lower as approaching the rear end. In order to correct this temperature distribution, in the conventional hot rolling method, accelerated rolling is performed to finish the rolling speed as the finish rolling progresses.

[0005] The intermediate temperature is managed as the temperature in the ferrite nose in CCT or as an index for controlling the precipitation of some high-tensile materials. In particular,
The cooling rate from the austenitic region to the ferrite nose in CCT is a very important factor that substantially determines the ferrite grain size of the hot-rolled steel strip. The higher the cooling rate from the rolling finishing temperature to the intermediate temperature, the finer the ferrite grains and the better the workability of the material. As a hot-run cooling method, a pipe laminar or a spray is usually used. The cooling rate is 100 ° C./s or less, corresponding to slow cooling. The crystal grain size of the material obtained by such a cooling method,
From the viewpoint of workability, it cannot be said that it has been miniaturized to an ideal level. On the other hand, in the perforated jet cooling system described in JP-A-53-127313 and JP-A-61-179814, a cooling rate of 200 ° C./s is realized. It is considered that if the porous flow cooling device is employed for hot run cooling, the crystal grain size of the hot-rolled steel strip can be further reduced.

[0006] The winding temperature is also strictly controlled in order to control deposits such as aluminum nitride. Cooling from the intermediate temperature to the winding temperature is also usually performed by slow cooling using a pipe laminar or spray.

[0007]

In order to reduce the crystal grain size of the hot-rolled steel strip to an ideal level and produce a hot-rolled steel strip of uniform material, hot-run cooling after finishing rolling is completed. It is necessary to precisely control the rolling finish temperature measured before starting, the winding temperature measured after finishing hot-run cooling and winding to the coiler, and the intermediate temperature measured during hot-run cooling. There is.

[0008] Usually, the control of the rolling finish temperature is performed by accelerated finish rolling. However, this method controls the amount of heat dissipated from the material to be rolled during finish rolling, and controls the temperature of the material to be rolled itself. However, there is a problem that the accuracy is not sufficient. In addition, when the finish accelerated rolling is used, the cooling speed is also difficult because the conveying speed of the hot-rolled steel strip changes every moment. There is a difficulty in the accuracy of the intermediate temperature and the winding temperature.

It is used for conventional hot run cooling.
In a pipe laminar or a spray, there is a problem that a cooling rate from a rolling finishing temperature to an intermediate temperature is low and ferrite grains are not sufficiently refined.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hot rolling device capable of sufficiently reducing the size of ferrite grains by using a rapid cooling device such as a perforated jet cooling device. An object of the present invention is to provide a method and equipment for hot rolling a steel strip.

On the other hand, rapid cooling makes it difficult to control the intermediate temperature (or the cooling stop temperature). If the intermediate temperature is too low, the nose of ferrite goes too far and the nose of bainite is formed, and bainite is formed. However, a further object of the present invention is to accurately control the intermediate temperature (or cooling stop temperature) by combining a rapid cooling device with a slow cooling device. It is an object of the present invention to provide a hot-rolled steel strip hot-rolling method and equipment capable of forming a hot-rolled steel strip.

[0012]

Means for Solving the Problems In order to solve the above-mentioned problems, a hot rolling method and a hot rolling facility of the present invention are constituted as follows.

(1) The slab is formed into a rough bar by a rough rolling mill, and the rough bar is finish-rolled by a finishing mill to form a hot-rolled steel strip.
Then, in a method of rolling a hot-rolled steel strip that is conveyed on a hot run table and wound by a winder, between the final stand of the rough rolling mill and the final stand of the finishing mill, heating is performed to heat the coarse bar over the entire width direction. And a cooling step including a rapid cooling of 200 ° C./s or more of the hot-rolled steel strip that has been finish-rolled between the first stand and the winder of the finish rolling mill with at least one or more cooling devices. A method for rolling a hot-rolled steel strip.

(2) The method for rolling a hot-rolled steel strip according to (1), wherein the cooling step includes slow cooling at a rate of 100 ° C./s or less.

(3) A steel strip temperature is detected on at least one of the inlet side and the outlet side of the cooling device group, and the difference between the steel strip temperature at each location and a predetermined target temperature is within ± 30 ° C. The method for rolling a hot-rolled steel strip according to (1) or (2), wherein the temperature is controlled by the heating device and the cooling device.

(4) A rough rolling mill for rough-rolling a slab to form a rough bar, a finishing rolling mill for finishing-rolling a rough bar to form a hot-rolled steel strip, a hot run table for transporting the hot-rolled steel strip, and a hot-rolled steel In a hot rolling facility equipped with a winder for winding a belt, a heating device for heating a rough bar or a hot-rolled steel strip over the entire width direction is provided between a final stand of the rough rolling machine and a winder, and finish rolling is performed. Between the mill and the winder,
A hot rolling facility for a hot-rolled steel strip, comprising one or more rapid cooling devices for rapidly cooling at a cooling rate of not less than ° C / s.

(5) 100 ° C /
(4) The hot rolling equipment for hot-rolled steel strip according to (4), further comprising a slow cooling device for cooling at a cooling rate of not more than s.

(6) The above-mentioned rapid cooling device is disposed on the lower surface side through the upper surface cooling device and the steel band transfer path, by injecting cooling water to the upper surface of the hot-rolled steel strip to cool it. The hot-rolled steel according to (4) or (5), further comprising a lower surface cooling means for injecting cooling water to the lower surface of the rolled steel strip to cool the steel strip, and a draining means at least on an outlet side thereof. Strip hot rolling equipment.

(7) The hot-rolled steel strip according to (6), wherein the upper surface cooling means is provided with means for freely moving up and down and having a space between the steel strip and the upper and lower surface cooling devices close to +100 mm or less. Hot rolling equipment.

[0020]

FIG. 1 is a schematic side view showing an example of an embodiment of the present invention. A slab having a predetermined temperature is applied to a rough rolling mill 1.
And rough-rolled into a rough bar. After the coarse bar is heated over the entire width direction by the solenoid-type induction heating device 2, it is finish-rolled by the finish-rolling machine 4 to be a hot-rolled steel strip. The hot-rolled steel strip is cooled to a predetermined temperature by the rapid cooling device 6 and the slow cooling device 7 while being transported on the hot run table, and then wound by the coiler 10. The finish-rolling machine inlet-side thermometer 3 measures the finish temperature of the rough bar on the finish-rolling machine side, and the finish-rolling machine outlet-side thermometer 5 measures the rolling finish temperature of the hot-rolled steel strip. The intermediate thermometer 8 measures the temperature during cooling of the hot-rolled steel strip,
Is a means for measuring the winding temperature of the hot-rolled steel strip.

Normally, due to the difference in the waiting time for finish rolling, the temperature at the entrance of the roughing bar to the finish rolling mill is highest at the front end and decreases as approaching the rear end. In the conventional hot strip mill, there is no means for compensating for the temperature drop of the coarse bar in the line, so finish accelerated rolling has been performed. This method uses the fact that the amount of heat dissipated from the material to be rolled during the finish rolling becomes smaller as the rolling speed increases, thereby making the longitudinal distribution of the rolling finish temperature of the hot-rolled steel strip uniform. However, since the temperature of the material to be rolled is not controlled, there is a problem that accuracy is not sufficient. To solve this problem, the hot rolling equipment of the present invention includes a solenoid-type induction heating device 2 that heats a rough bar over the entire width direction between a rough rolling mill and a finishing rolling mill. By directly heating the coarse bar, the accuracy of the rolling finishing temperature can be improved.

If the coarse bar is heated to make the longitudinal distribution of the temperature on the entrance side of the finishing mill uniform, the finishing temperature can be uniform in the longitudinal direction of the hot-rolled steel strip even if the finish rolling is performed at a constant speed. Become. Even when the rough bar heating and the finish accelerated rolling are used together, the acceleration can be reduced as compared with the case where the rough bar heating is not performed. If the time change of the conveying speed of the hot-rolled steel strip is small, the temperature control of the hot-rolled steel strip in hot run cooling becomes easy.

The reason why the heating device of the present invention is the solenoid type induction heating device 2 is as follows. In order to provide a predetermined temperature distribution in the longitudinal direction of the material to be rolled, a high degree of control response is required for the heating device. Therefore, an electromagnetic heating method is desirable. In the current technology, the electric heating method and the induction heating method are known, but in the electric heating method, there is a fear that a surface flaw occurs in the rolled material due to the occurrence of spark,
Induction heating should be used. Further, there are two types of induction heating systems: a transverse flux type and a solenoid type. Either method can be used, but the transverse flux type induction heating method tends to overheat the edge of the material to be rolled, and the structure of the inductor is complicated and the equipment tends to be expensive. Therefore, the solenoid type induction heating system 2 should be used.

FIG. 1 shows an example in which two solenoid-type induction heating devices 2 are installed.
The number of the solenoid type induction heating devices 2 may be any, due to restrictions on the installation space and the like. Further, the place where the material to be rolled is heated is not limited to between the rough rolling mill 1 and the finishing rolling mill 4. The same effect can be obtained even if a solenoid-type induction heating device is provided between the stands of the finishing mill 4. In addition, performing the temperature compensation of the edge portion using the edge heater does not hinder the embodiment of the present invention.

In order to achieve the main object of the present invention, that is, to refine the ferrite structure of the hot-rolled steel strip, the cooling rate when the temperature of the hot-rolled steel strip crosses the ferrite transformation start temperature (Ar3 temperature). Needs to be 200 ° C./s or more.
Therefore, the cooling rate of the rapid cooling device 6 of the present invention is 200
C./s or more is required. As an example of a cooling means capable of realizing such a cooling rate, an upper surface cooling means for injecting cooling water to the upper surface of the hot-rolled steel strip to cool it, and disposed on a lower surface side via the upper surface cooling means and the steel strip conveying path. In addition, there is an upper and lower surface perforated jet system provided with a lower surface cooling means for injecting cooling water to the lower surface of the hot-rolled steel strip to cool it.

FIG. 2 schematically shows the rapid cooling device 6. This apparatus comprises a jet cooling device 6 arranged between a plurality of pairs of transport rolls 63 and draining rolls 61 above and below a hot-rolled steel strip, respectively.
2a and 62b are arranged, and a barge device 64 is provided on each of the entrance side and the exit side.

FIG. 3 is a plan view of the perforated jet cooling device 62a as viewed from above. This apparatus has a perforated plate nozzle, and this perforated plate nozzle has a vertical nozzle having a diameter of 5 mm or less arranged such that the distance between the nearest holes is 50 mm or less. By spraying a large number of jets from the perforated plate nozzle onto the hot-rolled steel strip, a temperature of 200 ° C /
s or higher cooling rates are possible. Close the perforated plate nozzle to a distance of 100 mm or less from the hot-rolled steel strip,
By spraying the jet at [kgf / cm ² ] or more, interference between adjacent nozzles is almost eliminated, and the hot-rolled steel strip can be cooled by utilizing only the portion having a high cooling capacity immediately below the jet. The heat transfer coefficient at this time is 1000
It reaches 0 [kcal / cm ² / ° C.] or more. Since there is almost no interference between adjacent jets, uniform cooling is possible in the width direction of the hot-rolled steel strip.

The transport roll 63 shown in FIG. 2 may be the same as that of the other portion of the hot run table. Perforated jet cooling device 62 on the lower side of hot-rolled steel strip 62
a and 62b can be installed between the existing transport rolls 63, or in some cases, some of the transport rolls 63 can be pulled out and inserted there. Drain roll 6
Numeral 1 is provided to prevent water from flowing out before and after the rapid cooling device 6 and to limit the length of the wet edge. If the cooling water is blown out in the vertical direction as in the porous jet cooling device 62a of FIG. 2, a water riding area is generated between the draining roll 61 and the porous jet cooling device 62a, and the control accuracy is deteriorated. Let it. Inclined outer hard hole nozzles, such as perforated jet cooling device 62b, are effective in reducing the water riding area. The purge device 15 is provided to remove cooling water leaking from between the draining roll 12 or the transport roll 14 and the hot-rolled steel strip, and is effective in improving cooling accuracy.

The material of the hot-rolled steel sheet or the cold-rolled steel sheet obtained by cold rolling the hot-rolled steel sheet has an important influence on the rolling finishing temperature, the intermediate temperature during the two-stage cooling, and the winding temperature. is there. The hot rolling equipment according to the present invention includes a finish-rolling mill outlet thermometer 5, an intermediate thermometer 6, and a winding thermometer 7. Based on the temperature of the hot-rolled steel strip measured by the respective thermometers, the solenoid-type induction heating device 2, the finishing mill 4, or the cooling facilities 6, 7 are controlled. Among the materials of the heat / cooling steel plate, those that are easily affected by the temperature during hot run cooling are the workability (γ value, elongation) of soft materials such as IF steel and low carbon steel, and the strength and ductility of the high-tensile steel. In order to make these characteristics uniform in the longitudinal and width directions of the steel strip, the difference between the target temperature and the rolling finish temperature, intermediate temperature, and winding temperature should be within ± 30 ° C (more preferably, within ± 20 ° C). Need to be controlled to fit.

Although such a temperature control can be performed only by the rapid cooling device 6, it is more preferable to provide the slow cooling device 7 in order to increase the control accuracy of the cooling end temperature.

FIG. 4 shows an example of the slow cooling device 7. The components are a spray 72, a transport roll 73, a draining roll 7
1. Barge device 74. The components other than the spray 72 are the same as those of the rapid cooling device 6 including the purpose. Spray 72
Has a lower cooling capacity than the porous jet cooling devices 62a and 62b, and the cooling rate of the hot-rolled steel strip is at most 100 ° C./s. It is of course possible to use another means such as laminar flow for slow cooling of the hot-rolled steel strip.

FIG. 1 shows an example in which the rapid cooling device 6 and the slow cooling device 7 are combined. The rapid cooling device 6, the slow cooling device 7, the rapid cooling device 6, and the slow cooling device 7 are arranged in this order. However, the present invention is not limited to this, and the arrangement, the number, and the like can be arbitrarily set according to the purpose. For example, FIGS. 9 to 11 show examples in which the rapid cooling device 6 and the conventional cooling device 20 are combined.
9 shows an example in which the rapid cooling device 6 is arranged before the conventional cooling devices 20... FIG. 10 shows an example in which the rapid cooling device 6 is arranged before and after the conventional cooling devices 20. This is an example in which a quenching device 6 is arranged after. In the present invention, the slow cooling device 7 can be further arranged as appropriate in the arrangement shown in FIGS.

Next, the method for rolling a hot-rolled steel strip according to the present invention will be described. Up to the point where the slab at a predetermined temperature is roughly rolled into a rough bar, the process is the same as the conventional rolling method. The coarse bar is heated over the entire width direction by the solenoid-type induction heating device 2 to give a predetermined temperature distribution in the longitudinal direction. The compensation of the temperature distribution in the longitudinal direction of the coarse bar by the solenoid type induction heating device 2 includes the uniformity of the temperature distribution in which the temperature decreases in the longitudinal direction due to the waiting time for finish rolling, the removal of skid marks, and the like. Is included. Here, the predetermined temperature distribution may be rephrased as a temperature distribution in which the rolling finish temperature is uniform in the longitudinal direction of the hot-rolled steel strip. The difference between the rolling finish temperature and the target rolling finish temperature is ± 3
It is desirable that the temperature be within 0 ° C. Of course, the rolling finish temperature detected by the finish-rolling mill outlet thermometer 5 is reflected in the control of the solenoid-type induction heating device 2. Finishing accelerated rolling is
It may or may not be performed, but by heating the coarse bar, the acceleration can be reduced as compared to a case where the coarse bar is not heated. The time change of the conveying speed of the hot-rolled steel strip is small, which is advantageous for the cooling control as described above.

The hot-run cooling of the hot-rolled steel strip is performed by using the rapid cooling device 6 and the slow cooling device 7 together. The cooling control includes a rolling finish temperature measured by a finishing mill output thermometer 5, an intermediate temperature measured by an intermediate thermometer 8, a winding temperature measured by a winding thermometer 9, and conveyance of a hot-rolled steel strip. Speed is taken into account.
The difference between the intermediate temperature and the winding temperature from the target temperature is ± 30
It is desirable that the temperature be within ° C. When such temperature control is performed using only the rapid cooling device 6, the cooling device is subdivided to perform on / off control, or the water pressure of the header is adjusted. If the slow cooling device 7 is used, delicate temperature control can be performed, so that such a complicated method is not required.

By applying the present invention, the conventional hot strip mill could not be manufactured. It is possible to produce a material having extremely excellent workability. Longitudinal direction,
A hot-rolled steel strip or a cooled steel strip having a uniform material in the width direction can be manufactured, so that the yield can be improved and the trust of customers can be obtained.

[0036]

EXAMPLES (Example 1: Refinement of ferrite structure)
In the temperature history of hot-rolled cold-rolled steel sheets (soft materials such as IF steel and low-carbon steel and high-tensile steel), the cooling rate when passing the ferrite transformation start temperature on a hot run table is determined by the refinement of the ferrite structure. Has a great effect on In order to refine the ferrite grains, the cooling rate at this time may be increased. Refining the ferrite grains increases the strength of the material, so that alloy elements such as manganese can be reduced, and manufacturing costs can be reduced. Further, there is an effect of improving the material such as a balance between strength and ductility and a balance between strength and hole expandability. When the cooling rate exceeds 200 ° C./s, the effect of refining ferrite grains does not increase even if the cooling rate is further increased. Cooling rate is 2
It is sufficient to keep the temperature at 00 ° C./s or more.

The difference ΔT between the ferrite transformation start temperature and the rapid cooling end temperature is an important factor. If ΔT exceeds 200 ° C., acicular ferrite is generated, and the material (workability) is rather deteriorated. ΔT is desirably 100 ° C. or more and 150 ° C. or less. 200 ° C / s
It is not always easy to control ΔT within such a narrow range at the rapid cooling rate described above. In order to meet such difficult requirements, the present invention particularly includes a slow cooling step. FIG. 5 compares the cooling curves of the hot-rolled steel strip of the present invention and the prior art on the CCT diagram. By placing the perforated jet cooling device immediately after the finishing mill, as shown in FIG. 1, a cooling pattern as shown in the cooling curve according to the invention of FIG. 5 is possible. The perforated jet cooling device is 2
It is fully possible to achieve a cooling rate of 00 ° C./s or more. However, the cooling stop temperature (intermediate temperature) can be kept within ± 30 ° C. only by the rapid cooling device. However, in order to improve the control accuracy of the cooling end temperature, the finishing thermometer output side thermometer 5 and the intermediate thermometer are used. 8, a slow cooling device 7 is installed, and fine control of the intermediate temperature can be performed by the slow cooling device 7.

The heating is performed by a solenoid type induction heating device so that the temperature on the entrance side of the finishing mill becomes uniform in the longitudinal direction of the rough bar, so that the rolling finishing temperature F corresponding to the cooling start temperature is obtained.
Variation of T can be reduced. Further, when performing finish rolling at a constant speed or performing accelerated finish rolling, the acceleration can be reduced. as a result,
The time change of the conveying speed of the hot-rolled steel strip becomes small, and the cooling control becomes easy. In the present embodiment, the cooling amount means the difference between the rolling finishing temperature and the intermediate temperature. Usually, since the rolling finish temperature FT is controlled just above the ferrite transformation start temperature, the cooling amount can be considered to be almost the same as ΔT in FIG. The cooling capacity required to make ΔT a certain value is proportional to the transport speed. FIG. 6 schematically shows this relationship. If the coarse bar is heated by the solenoid-type induction heating device, the amount of change in the transport speed can be reduced, so that the control amount of the cooling capacity for controlling ΔT can be reduced.

(Example 2: Production of DP steel) In a conventional hot strip mill, it is difficult to produce some special materials such as DP steel. This will be described using DP steel as an example. D
P steel is a composite structure steel composed of ferrite and martensite. The temperature history on the hot run table when producing DP steel with a hot strip mill is represented by CCT.
It is shown in FIG. The hot-rolled steel strip after the finish rolling was started from the rolling finish temperature FT, and “water cooling 1” using some of the cooling banks on the side close to the finish rolling mill was performed, and the water in the cooling bank was stopped. By three cooling processes of “air cooling” and “air cooling 2” using some cooling banks on the side near the coiler, it is cooled to the winding temperature CT and wound around the coiler. Important factors in controlling the material properties of DP steel are the following two points. (1) The finish temperature of rolling is set to be equal to or higher than the ferrite transformation start temperature, and (2) The ferrite transformation time is lengthened to some extent. However, these requirements are conflicting. To raise the rolling finish temperature, the finish rolling speed may be increased. This is because the amount of heat lost by the material to be rolled during finish rolling is reduced. However, when the finish rolling speed increases, the speed at which the hot-rolled steel strip passes on the hot run table increases, and as a result, the time available for ferrite transformation decreases. Conversely, if the finish rolling speed is reduced, it is easy to secure the ferrite transformation time, but the rolling finish temperature will decrease. As described above, since two contradictory conditions must be satisfied, the yield of DP steel is low in a hot rolling process using a normal cooling method, and the manufacturable range of the plate thickness and width is limited.

Therefore, as shown in FIG. 1, a solenoid-type induction heating device 2 is provided between the rough rolling mill 1 and the finishing rolling mill 4, and between the finishing thermometer 5 and the intermediate thermometer 8, and between the rough rolling mill 1 and the finishing rolling mill 4. Consider the production of DP steel by a hot rolling facility equipped with a rapid cooling device 6 between a thermometer 8 and a winding thermometer 9. If the coarse bar is heated by the solenoid type induction heating device 2, it is easy to secure the finishing temperature of the rolling, and the finishing rolling speed can be reduced. As a result, the conveying speed of the hot-rolled steel strip on the hot run table becomes slow, and the air cooling time can be saved.
As described in the first embodiment, the acceleration can be reduced by heating the rough bar with the solenoid-type induction heating device 2 also in the case of performing the finish accelerated rolling. In addition, by using the rapid cooling device 6, the time required for “water cooling 1” and “water cooling 2” in FIG. 7 is reduced, and the air cooling time can be increased as shown in FIG. In addition, the rapid cooling of “water cooling 1” makes it possible to reduce the size of ferrite and to produce a DP steel excellent in strength-ductility balance. The fine adjustment of the cooling stop temperature and CT of “water cooling 1” is performed by the slow cooling device 7.
By using this method, deterioration of the material due to supercooling can be prevented.

By the above effects, the uniform material D
P steel can be manufactured, and the yield is also improved. By heating the rough bar, the finish rolling load can be reduced, and the manufacturable range of the width and the thickness can be expanded.

[0042]

According to the method and the hot rolling equipment for hot-rolled steel strip of the present invention, the temperature of the hot-rolled steel strip on the hot run table can be accurately controlled, and the material can be made uniform and the yield can be improved. Can be expected. Further, a cooling pattern which cannot be obtained by the conventional technology can be obtained, and the material of the hot-rolled steel sheet and the cold-rolled steel sheet can be dramatically improved. Further, since the finish rolling load is reduced, the manufacturable range of the width and the plate thickness is expanded.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a hot rolling facility of the present invention.

FIG. 2 is a schematic side view showing a rapid cooling device of the present invention.

FIG. 3 is a top view of the perforated jet cooling device of the present invention.

FIG. 4 is a schematic side view showing a slow cooling device of the present invention.

FIG. 5 is a view showing a cooling pattern for refining ferrite grains.

FIG. 6 is a diagram illustrating a relationship between a transport speed and a required cooling capacity.

FIG. 7 is a diagram showing a cooling pattern when producing DP steel.

FIG. 8 is a diagram comparing a cooling pattern when manufacturing DP steel between a conventional technique and the present invention.

FIG. 9 is a diagram showing an example of the equipment arrangement of the present invention.

FIG. 10 is a diagram showing another example of the equipment arrangement of the present invention.

FIG. 11 is a diagram showing still another example of the equipment arrangement of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Rough rolling mill, 2 ... Solenoid type induction heating apparatus, 3 ... Finishing rolling mill entrance side thermometer, 4 ... Finishing rolling mill, 5 ... Finishing rolling mill exit side thermometer, 6 ... Rapid cooling device, 7 ... Slow cooling Apparatus, 8: Intermediate thermometer, 9: Winding thermometer, 10: Coiler (winding machine), 61: Draining roll, 62a, b: Porous jet cooling device, 63: Conveying roll, 64: Draining purge, 71 ... Draining roll, 72: Spray, 73: Conveyance roll, 74: Draining purge.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Sadanori Imada 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Shozo Ikemune 1-2-1, Marunouchi, Chiyoda-ku, Tokyo No. Nippon Kokan Co., Ltd. (72) Yoshimichi Hino, Inventor 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Japan Nippon Kokan Co., Ltd. (72) Inventor Shogo Tomita 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Japan F-term (reference) 4E002 AD02 AD04 BA01 BD03 BD07 BD08 CB01

Claims (7)

[Claims] A slab is formed into a rough bar by a rough rolling mill, and the rough bar is finish-rolled by a finishing rolling mill to form a hot-rolled steel strip.
In the method of rolling a hot-rolled steel strip conveyed on a hot run table and wound by a winder, a heating step of heating a coarse bar over the entire width direction between a final stand of a rough rolling mill and a final stand of a finishing mill. Between the first stand of the finish rolling mill and the winder, the finish-rolled hot-rolled steel strip is cooled by at least one or more cooling devices.
A cooling step including rapid cooling at 0 ° C./s or more. 2. The method of rolling a hot-rolled steel strip according to claim 1, wherein the cooling step includes slow cooling at 100 ° C./s or less. 3. A steel strip temperature is detected on at least one of an inlet side and an outlet side of the cooling device group, and a difference between the steel strip temperature at each point and a predetermined target temperature is within ± 30 ° C. 3. The method for rolling a hot-rolled steel strip according to claim 1, wherein the temperature is controlled by the heating device and the cooling device. 4. A rough rolling machine for roughly rolling a slab to form a rough bar, a finish rolling mill for finishing rolling a rough bar to form a hot-rolled steel strip,
In hot rolling equipment equipped with a hot run table for transporting hot rolled steel strip and a winder for winding hot rolled steel strip, a rough bar or hot rolled steel strip is placed between the final stand of the rough rolling mill and the winder. A heating device for heating the entire width direction is provided, and the material to be rolled is placed between a finish rolling mill and a winder.
A hot rolling facility for a hot-rolled steel strip, comprising one or more rapid cooling devices for rapidly cooling at a cooling rate of not less than ° C / s. 5. The hot rolling equipment for hot-rolled steel strip according to claim 4, further comprising a slow cooling device for cooling at a cooling rate of 100 ° C./s or less together with the rapid cooling device. 6. The rapid cooling device is arranged on an upper surface cooling means for injecting cooling water to an upper surface of the hot-rolled steel strip to cool it, and disposed on a lower surface side through the upper surface cooling means and the steel strip conveying path. The heat of a hot-rolled steel strip according to claim 4 or 5, further comprising a lower surface cooling means for injecting cooling water to a lower surface of the steel strip to cool the steel strip, and a draining means at least on an outlet side thereof. Rolling equipment. 7. The hot rolled steel strip according to claim 6, wherein said upper surface cooling means is provided with means capable of moving up and down and having a space between the steel strip and the upper and lower surface cooling devices close to +100 mm or less. Rolling equipment.