JP3189732B2 - Cooling method for hot steel sheet and cooling device for hot steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for uniformly cooling a hot-rolled high-temperature steel sheet, and more particularly to a method and an apparatus for uniformly cooling front and rear ends of a steel sheet.

[0002]

2. Description of the Related Art In recent years, hot-rolled high-temperature steel sheets are often subjected to strong cooling immediately after rolling, with the aim of increasing strength by quenching heat treatment and reducing costs by reducing alloys.
This cooling is generally performed while a hot steel sheet after rolling is passed on-line, and the steel sheet is cooled by pouring cooling water from above and below while being transported in a horizontal state.

[0003] At this time, it is important to adjust and control the amount of water so that the cooling in the plate width direction and the plate longitudinal direction is performed equally on average.

Normally, cooling of a steel sheet immediately after rolling is performed by flowing laminar cooling water having a substantially rectangular cross section in the conveying direction of the steel sheet from a laminar nozzle having a slit shape.

The cooling method and the cooling device are described in, for example, Japanese Utility Model Laid-Open No. 58-4209, and Japanese Patent Publication No. 3-1040.
And Japanese Patent Publication No. 7-8373.

The technique disclosed in Japanese Utility Model Laid-Open Publication No. 58-4209 discloses a method in which flat laminar cooling water is dropped from a slit laminar nozzle provided between draining rolls, and the steel sheet is cooled by the water flow. Is the way.

[0007] Further, the technique disclosed in Japanese Patent Publication No. 3-10407 supplies cooling water to the vicinity of the center of two draining rolls and causes the cooling water to collide with the steel sheet. This is a method of cooling the steel plate before and after the collision point with cooling water flowing in the traveling direction.

The technique disclosed in Japanese Patent Publication No. 7-8373 discloses a technique in which cooling water flows from a slit-shaped nozzle provided in the vicinity of a draining roll or a steel plate in the traveling direction of the plate, and the next draining roll is rotated. This is a method of eliminating suction in the vicinity.

[0009]

However, both of these methods have the following problems.

Japanese Utility Model Application Laid-Open No. 58-4209 and
In the technology disclosed in Japanese Patent No. 10407, the cooling water contacts the steel plate only when the tip of the moving steel plate reaches just below the nozzle from which the cooling water is jetted, and then the cooling water flows upstream from the collision point of the steel plate. The water that flows back and downstream, and the back-flowed water reaches the upstream draining rolls, and starts steady cooling only when it reaches the upstream side.

Also, at the stage where the rear end of the steel sheet has passed through the cooling device, the cooling water no longer reaches the steel sheet after the rear end of the steel sheet has passed just below the nozzle, and cooling is not performed. As described above, these methods cause insufficient cooling at the leading and trailing ends of the plate.

In the technique disclosed in Japanese Patent Publication No. 7-8373, cooling water is not supplied onto the steel plate after the rear end of the plate has passed just below the cooling water injection nozzle. Insufficient cooling at the ends.

As described above, the conventional steel sheet cooling apparatus has a problem that the rear end of the steel sheet is insufficiently cooled.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. When a hot-rolled high-temperature steel plate is cooled by jetting cooling water from a slit nozzle from the front end to the rear end of the plate. It is an object of the present invention to provide a cooling method and a cooling device in which cooling water is always supplied in the same manner to enable uniform cooling.

[0015]

SUMMARY OF THE INVENTION The object of the present invention is to convey a high-temperature steel sheet while constraining it with a plurality of sets of upper and lower restraining rolls. A method for cooling a steel sheet, comprising: cooling a first slit nozzle that discharges cooling water along the upper surface of the steel sheet toward the downstream side in the steel sheet conveyance direction, near the downstream side of the upper constraining roll on the upstream side in the steel sheet conveyance direction. A second slit nozzle for discharging water along the upper surface of the steel sheet toward the upstream side in the steel sheet transport direction is provided near the upstream side of the upper constraining roll on the downstream side in the steel sheet transport direction, and the tip portion of the steel sheet is provided. When cooling, only the first slit nozzle is used, and when cooling the rear end portion of the steel sheet, only the second slit nozzle is used. Solved That.

According to this method, when the leading end of the steel sheet passes through the cooling equipment, the cooling water is supplied from the first slit nozzle installed near the upper constraining roll on the upstream side in the sheet conveying direction. Cooling can be started from the tip of the steel sheet.

When the rear end of the steel sheet passes through the cooling equipment, the cooling water from the first slit nozzle does not flow on the steel sheet. However, in this case, since the cooling water from the second slit nozzle installed near the upper constraining roll on the downstream side of the steel sheet transport direction is supplied onto the steel sheet, the rear end of the steel sheet is effectively cooled. be able to.

When cooling the central portion of the steel sheet, either the first or second slit nozzle may be used.

In the present specification, the "front end portion of the steel sheet" refers to a front portion including a range in which the cooling water of the second slit nozzle does not fall on the steel sheet, and "a rear end portion of the steel sheet".
The term “rear” means a rear portion including a range in which the cooling water of the first slit nozzle does not drop onto the steel plate.

The above method comprises a first slit nozzle provided near the upstream side of the upper constraining roll on the upstream side in the steel sheet transport direction and discharging cooling water along the upper surface of the steel sheet toward the downstream side in the steel sheet transport direction. A second slit nozzle that is provided near the upstream side of the upper constraining roll on the downstream side in the steel sheet transport direction, and discharges cooling water along the upper surface of the steel sheet toward the upstream side in the steel sheet transport direction; And the second slit
It can be implemented by a cooling device for hot steel plates having a cooling water shut-off valve for selectively using a nozzle .

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram illustrating an example of equipment according to an embodiment of the present invention. In FIG. 1, 1 is a steel plate, 2 is an upper roll, 3 is a lower roll, and a steel plate 1 is an upper roll 2.
It is cooled while being constrained by being sandwiched between the lower roll 3. Reference numeral 4 denotes a slit nozzle provided on the upstream side in the transport direction of the steel plate 1, reference numeral 5 denotes its header, and reference numeral 6 denotes its skirt. Reference numeral 7 denotes a slit nozzle provided on the downstream side in the transport direction of the steel sheet 1, reference numeral 8 denotes a header thereof, and reference numeral 9 denotes a skirt portion thereof. Cooling water to each of the slit nozzles 4 and 7 is supplied from a cooling water main pipe 12 through cooling water cutoff valves 10 and 11, respectively. Reference numeral 13 denotes a circular tube nozzle, which cools the lower surface of the steel plate by injecting cooling water. Each slit nozzle 4, 7
The skirt portions 6 and 9 have an elongated rectangular cross section with a width of about 5 m and a slit gap of about 5 mm, for example, and are seamlessly connected to the headers 5 and 8 in the width direction.

The cooling water flowing out of the upstream slit nozzle 4 uniformly flows along the upper surface of the steel sheet 1 to the downstream side in the transport direction of the steel sheet 1 and cools the steel sheet 1. The cooling water flowing out of the downstream side slit nozzle 7 flows uniformly along the upper surface of the steel sheet 1 to the upstream side in the transport direction of the steel sheet 1 and cools the steel sheet 1.

FIG. 2 shows an embodiment of the cooling method according to the present invention.
This will be described with reference to FIG. 2, the same elements as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 2A shows a state immediately after the leading end of the steel plate 1 has entered the cooling device. The tip of the steel plate 1 has not yet reached the position of the downstream slit nozzle 7. In this state, the cooling water cutoff valve 10 is opened, the cooling water cutoff valve 11 is closed, and only the upstream slit nozzle 4 is used.

The tip of the steel plate 1 is already in the slit nozzle 4
The cooling water from the slit nozzle 4 flows to the downstream side along the upper surface of the steel sheet 1, and normal cooling is performed.

FIG. 2B is a diagram showing the positional relationship at the time when the leading end portion of the steel sheet 1 has passed the positions of the rolls 2 and 3 on the downstream side. In this embodiment, at this time, the cooling water cutoff valve 11 is opened, and then the cooling water cutoff valve 10 is closed to shut off the cooling water from the upstream slit nozzle 4. Then, the cooling water is discharged from the downstream slit nozzle 7, flows upstream along the upper surface of the steel plate 1, and collides with the cooling water from the upstream slit nozzle 4. Subsequent cooling,
This is performed by cooling water from the downstream slit nozzle 7.

FIG. 2C shows the positional relationship when the rear end of the steel sheet 1 comes to a position outside the drop point of the cooling water from the upstream rolls 2 and 3 and the upstream slit nozzle 4. FIG. Also at this time, since the cooling is performed by the cooling water from the downstream slit nozzle 7, the cooling of the rear end portion of the steel sheet 1 is also performed as usual.

In the above description, the slit nozzle to be used is switched to the downstream slit nozzle 7 immediately after the leading end of the steel sheet 1 has passed the rolls 2 and 3 on the downstream side, and the downstream is also used for cooling the central portion. Although the side slit nozzle 7 was used, the switching timing of the slit nozzles 4 and 7 was set to the timing when the rear end of the steel plate 1 approached the upstream rolls 2 and 3 and the central portion of the steel plate 1 was set to the upstream slit nozzle 4. May be used.

At the switching timing of the slit nozzles 4 and 7, the two coolants collide with each other on the steel plate 1 and the flow reverses thereafter. As a result of the investigation, the uneven cooling caused by this was observed. Did not.

[0031]

【Example】

(Example) Using the equipment shown in FIG. 1, cooling of a high-temperature steel sheet was carried out by the method shown in FIG. In this example, the pitch between the upper and lower rolls was 1500 mm.
The width of the slit nozzles 4 and 7 was 5 m, and the gap between the slits was 5 mm. The cooling water amount is the cooling water shutoff valve 10,
When 11 was open, it was 1500 liters / min per meter width. On the other hand, the lower surface was cooled by cooling water jetted from circular nozzles 13 arranged in a staggered manner at a pitch of 100 mm.

In this cooling device, a steel plate width 430 immediately after rolling is applied.
0mm, length 18m, thickness 40mm, initial temperature 840 ° C
At a speed of 5 mpm for cooling. The temperature of each part at the stage of reheating after cooling is 500 ± 15 ° C,
In particular, insufficient cooling did not occur at the rear end of the plate. This steel sheet was cooled to room temperature on the cooling floor, but no distortion such as warpage occurred. The hardness in the longitudinal direction of the plate was measured. As a result, there was no unevenness in the firing, the hardness distribution was uniform, and there was little variation in the material. Therefore, there was no downgrade of the rear end of the plate due to the material being out of specification, and the product yield was 100%.

(Comparative Example) Using the same cooling device as in the example,
Cooling was performed over the entire range of the steel sheet 1 using only the upstream slit nozzle 4. Other conditions were the same as those of the example.

The temperature of each part of the steel sheet at the stage of recuperation after cooling was 500 to 570 ° C., especially at the rear end of the steel sheet, where the cooling was insufficient, and the rear end was 570 ° C. After cooling, the hardness in the longitudinal direction of the plate was measured. As a result, the rear end of the plate had a portion with low hardness due to uneven baking, and the material had large variations.
As a result, the material was out of specification at the rear end of the plate,
m had to be truncated. The product yield was 97%.

[0035]

As described above, according to the present invention, when the tip of the steel sheet passes through the cooling equipment, the first slit nozzle installed near the downstream side of the upper constraining roll on the upstream side in the sheet conveying direction. Since the cooling water is supplied from the cooling device, the cooling can be started from the tip of the steel plate. When the rear end of the steel sheet passes through the cooling equipment, the cooling water from the second slit nozzle installed near the upstream side of the upper constraining roll on the downstream side in the sheet conveying direction is supplied onto the steel sheet. Can effectively cool the rear end.

Accordingly, the front and rear ends of the steel sheet can be uniformly cooled, so that there is no material defect caused by unevenness in the longitudinal direction of the steel sheet, and the yield of the product is improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of equipment according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a cooling method according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Upper roll 3 Lower roll 4 Upstream slit nozzle 5 Header 6 Skirt part 7 Downstream slit nozzle 8 Header 9 Skirt part 10 Cooling water shutoff valve 11 Cooling water shutoff valve 12 Cooling water main pipe 13 Round pipe nozzle

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoneaki Fujita 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-62-196337 (JP, A) JP-A Sho 62-260022 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 45/02 320 C21D 9/52 102

Claims (2)

(57) [Claims] 1. A method for cooling a high-temperature steel sheet by conveying a high-temperature steel sheet while constraining the high-temperature steel sheet by a plurality of sets of upper and lower restraining rolls, and cooling the high-temperature steel sheet by injecting cooling water from above and below during the conveyance. A first slit nozzle for discharging water along the upper surface of the steel sheet toward the downstream side in the steel sheet transport direction is provided near the downstream side of the upper restraining roll on the upstream side in the steel sheet transport direction, and the cooling water is directed toward the upstream side in the steel sheet transport direction. A second slit nozzle for discharging along the upper surface of the steel sheet is provided in the vicinity of the upstream side of the upper restraining roll on the downstream side in the steel sheet conveyance direction, respectively,
Only the first slit nozzle is used to cool the front end of the steel sheet, and the second slit nozzle is used to cool the rear end of the steel sheet.
A method for cooling a high-temperature steel sheet, wherein only a slit nozzle is used. 2. A first slit nozzle which is provided near the downstream side of the upper constraining roll on the upstream side in the steel sheet transport direction and discharges cooling water along the upper surface of the steel sheet toward the downstream side in the steel sheet transport direction; A second slit nozzle which is provided near the upstream side of the upper constraining roll on the downstream side in the transport direction and discharges cooling water along the upper surface of the steel sheet toward the upstream side in the transport direction of the steel sheet.
And the first slit nozzle and the second slit nozzle
A cooling device for a high-temperature steel plate, comprising a cooling water shut-off valve that can be selectively used .