JPH06285534A - Descaling method for hot rolled steel plate - Google Patents

Abstract

PURPOSE:To nearly uniformly distribute the combined collision pressure of ejecting water from each of nozzles in the width direction of a steel plate with the value of pressure equal to or higher than a specific value and to smoothly distribute the combined amount of water when a hot rolled steel plate is descaled. CONSTITUTION:When the hot steel plate is rolled by a reversible hot rolling machine, the hot steel plate is manufactured by rolling several times descaling and cooling the steel plate. High pressure ejecting water ejected from plural nozzles is nearly uniformly distributed with a collision pressure equal to or higher than a specific value against the hot rolled steel plate in the width direction D. The pitch of nozzles L1 and ejecting angle theta1 are adjusted in compliance with the rolling conditions. Thus, the lap rate L2/L1 of high pressure ejecting water at the collision part on the hot rolled steel plate is determined and cooling capacity on the steel plate in the width direction is nearly uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a descaling method for preventing muscle cooling on a hot-rolled steel sheet caused by removing scale on the hot-rolled steel sheet with high-pressure jet water.

[0002]

2. Description of the Related Art Conventionally, descaling of a steel sheet with high-pressure water is performed by injecting high-pressure water onto a rolled steel sheet from a descaling nozzle, and the jet water causes the surface scale of the rolled material to float.
Moreover, the scale is blown off with high-pressure water to remove it. At this time, muscle cooling occurs due to the cooling of this high-pressure water. This muscle chill is recovered by providing a recovery time for each rolling pass and waiting for multiple heat from the high temperature portion existing in the center of the thickness of the rolled steel sheet, but satisfactory results cannot be obtained.

Therefore, during descaling of the hot rolled steel sheet, muscle coldness occurs corresponding to the lap portion where the jet water of the nozzle overlaps. When the steel sheet is rolled and forcedly cooled, the low temperature portion due to the muscle cooling is succeeded to the subsequent rolling step and affects the shape of the steel sheet. As a result, the rolled steel sheet has an uneven shape. In the traditional way,
The defective shape of the steel sheet is corrected by adding a step of correcting the shape to correct the shape of the steel sheet. However, since this correction process is performed after cooling, plastic deformation is added to the steel plate,
It causes variations in mechanical properties such as tensile strength, elongation and drawing of the steel sheet. Further, the increase in the number of steps causes an increase in the manufacturing cost of the steel sheet. Therefore, the shape correction process is not preferable in terms of quality and price of the rolled steel sheet.

Further, at present, when a tight-scale steel plate is manufactured from a thick steel plate, rolling is performed plural times at about 850 ° C. and descaling is performed before each rolling pass. This 85
Oxidation of the steel sheet in the temperature range of 0 ° C is extremely severe, and in order to prevent the generation of scale, the oxidation does not proceed to about 150.
It must be forcibly cooled to a temperature range of °. Therefore,
The conventional method of recovering muscle cold by waiting for the double heat of the steel sheet cannot be used.

Therefore, there is a need for a descaling method capable of uniformly descaling the surface of a steel sheet and preventing muscle coldness due to descaling.

[0006]

In the descaling of hot-rolled steel sheet, the muscle chill on the rolled steel sheet portion corresponding to the nozzle lap portion is caused by the non-uniformity of the amount of water jetted at the nozzle lap portion within the steel sheet width. Due to uniform distribution. Further, the descaling property is determined by the collision pressure of the jet water and the collision pressure distribution.

According to the present invention, in the descaling of hot rolled steel plate, the collision pressure of the water jet from each nozzle is set to a certain value or more so as to be distributed almost uniformly in the plate width direction, and the water jet from each nozzle in the steel plate width direction. The objective is to make the distribution of the synthetic jet water volume of 3 smooth and even.

[0008]

Means for Solving the Problems The above object of the present invention is to provide a hot rolled steel sheet which is rolled a plurality of times while performing descaling and cooling when rolling a high temperature steel sheet using a reversible hot rolling mill. In the manufacturing method, high-pressure jet water jetted from a plurality of nozzles toward the hot-rolled steel sheet for descaling is substantially evenly distributed in the sheet width direction at a collision pressure of a certain value or more, and the nozzle pitch L ₁ By adjusting the length L ₂ of the impinging portion of the jet water and the jet angle θ _{1 of the} nozzle according to the rolling conditions, the lap ratio L _{2 of the} high-pressure jet water at the impinging portion on the hot-rolled steel sheet is adjusted. It is achieved by a descaling method for a hot-rolled steel sheet, characterized in that / L ₁ is determined to make the cooling capacity of the hot-rolled steel sheet in the width direction substantially uniform.

[0009]

The descaling property in hot rolling is determined by the maximum impingement pressure (kg / cm ² ) of jet water on the steel surface. The collision pressure of the jetted water on the surface of the rolled steel sheet can be uniformly distributed in the width direction of the rolled steel sheet by providing the jet water with a lap portion. The surface temperature of the rolled steel sheet is determined by the cooling capacity h of water sprayed from the nozzle. According to Special Report No. 29 of "Forced Cooling of Steel" (edited by Japan Iron and Steel Institute, Thermo-Economic Technology Section, published in 1978), the cooling capacity h is generally proportional to the water density ρ 0.6 to the power of There is.

Log = 2.694 + 0.5964 × L
ogW-0.00179 × TS However, ρ: Water amount density (L / m ² min) TS: Steel plate surface temperature (° C.) The water jetted from the nozzle has a maximum pressure at the center of the nozzle and decreases outward from the center. Therefore, the low pressure portion can be eliminated by superimposing the water jets from the adjacent nozzles on the portion under a certain pressure. In the present invention, the lap width L ₃ is provided at the collision portion of the jet water by adjusting each nozzle pitch L ₁ . Further, a nozzle is used in which the sprayed water does not spread over the entire circumference of 360 ° and spreads at the nozzle spraying angle θ ₁ only in the rolling plate width direction. The collision portion length L ₂ is determined from the nozzle ejection angle θ ₁ and the nozzle height H. The lap ratio L ₂ / L ₁ of this high-pressure jet water is the nozzle pitch L ₁
And the collision portion length L ₂ . In the present invention, the cooling capacity h is determined by adjusting the amount W (L / cm min) of the water jet at the steel plate collision portion of the water jet. Furthermore, the lap rate L ₂
/ L ₁ , the nozzle pitch L ₁ , the nozzle height H, the collision portion length L ₂ and the nozzle injection angle θ ₁ are adjusted to make the cooling capacity h of the hot rolled steel sheet uniform. By adopting such a nozzle configuration, the collision pressure P at the jet water collision part on the steel plate surface
Distribute the distribution evenly, improve descaling,
Moreover, muscle cold can be prevented.

[0011]

EXAMPLES Table 1 shows the conventional method and the examples (1) to (1) of the present invention.
Describe the specifications and specific values of (3). 1A, 1B, and 1C of FIG. 1 show respective distributions of the impinging water pressure P and the injected water amount W in the direction of the rolled steel sheet width D according to the conventional method shown in Table 1. FIG. 2 shows a steel plate surface temperature TS distribution in the direction of the rolled steel plate width D performed by the conventional method. Figure 1 (B)
In the conventional method, the injection water amount W has a pointed portion in the water jet wrap portion, and the presence of the pointed portion causes muscle cooling, and as shown in FIG. A large temperature distribution occurred in the steel plate surface temperature TS.

[0012]

[Table 1]

In the embodiment (1) of the present invention, the nozzle injection angle θ
₁ is 64 °, nozzle pitch L ₁ is 150 mm, collision part length L ₂ is 500 mm, lap width L ₃ is 350 mm, and lap ratio L ₂ / L ₁ is 3.3. Is. FIG. 3A shows the nozzle pitch L ₁ , the collision portion length L ₂ and the lap width L ₃ of the embodiment (1) of the present invention, and FIG. 3B shows the rolled steel plate width D. Shows the distribution of the jet water amount W in the direction of, and FIG. 3 (B) shows the distribution of the jet pressure P of the jet water in the direction of the rolled steel plate width D.

Next, the embodiment (2) of the present invention will be described with reference to FIG.
Angle of incidence θ₁45 °, nozzle pitch L ₁150mm, collision
Part length L₂333 mm, lap width L₃183 mm
And lap rate L₂/ L₁Change to 2.2 and adjust to semi-strong cooling
It is a state. An embodiment of the present invention is shown in FIG.
Nozzle pitch L of (2)₁, Length of collision part L₂And luck
Width L₃FIG. 4B shows the direction of the rolled steel plate width D.
4 shows the distribution of the water injection amount W of the rolled steel, and FIG.
The distribution of the collision pressure P of the jet water in the direction of the plate width D is shown.

Further, in the embodiment (3) of the present invention, the nozzle jet angle θ ₁ is 25 °, the nozzle pitch L ₁ is 80 mm, the collision portion length L ₂ is 177 mm, and the wrap width L ₃ is 97 mm.
Also, the lap ratio L ₂ / L ₁ was changed to 1.2 and adjusted to a weakly cooled state. 5A shows the nozzle pitch L ₁ , the length L ₂ of the collision portion and the lap width L ₃ of the embodiment (3) of the present invention, and FIG. 5B shows the direction of the rolled steel plate width D. 5C shows the distribution of the jet water amount W, and FIG. 5C shows the distribution of the jet pressure P of the jet water in the direction of the rolled steel plate width D.

The region indicated by D in FIGS. 3 to 5 indicates the rolled steel plate width. As is clear from the results of the distributions of the injection water amount W and the collision pressure P in (B) and (C) of FIGS. 3 to 5, each of Examples (1) to (3) is the rolled steel plate width D. The distribution W of the injected water and the collision pressure P of the injected water in the indicated region were substantially uniform. Therefore, since the impinging pressure P of the jet water is almost uniform, the descaling property of the rolled steel sheet was uniform and good. FIG. 6 shows the rolled steel sheet width D according to the embodiment (3) of the present invention.
The steel plate surface temperature distribution in the direction of is shown. As shown in FIG. 6, the distribution W of the injected water was almost uniform, and muscle chilling did not occur at all.

[0017]

According to the descaling method of the present invention,
It is possible to preferably remove the scale of the hot-rolled steel sheet, and prevent uneven thickness of the rolled steel sheet in the sheet width direction and generation of waviness and bending (camber) in the longitudinal direction of the rolled steel sheet. This eliminates the step of correcting the shape of the steel sheet after rolling and cooling, so that the mechanical properties such as tensile strength, elongation and drawing of the steel sheet can be made uniform and improved. Further, the manufacturing cost of the steel sheet can be suppressed.

The descaling method of the present invention is suitable not only for production of ordinary thick and thin steel sheets, but also for production of tight-scale steel sheets that require forced cooling in a short time from the rolling temperature to a temperature range where oxidation does not proceed. Is.

[Brief description of drawings]

FIG. 1A shows a water amount and a collision pressure distribution of a nozzle alone, FIG. 1B shows a synthesized water amount distribution, and FIG. 1C shows a synthesized collision pressure distribution in a width direction of a rolled steel sheet according to a conventional technique.

FIG. 2 shows a distribution of a steel plate surface temperature in a width direction of a rolled steel plate according to a conventional technique.

FIG. 3 is a rolling plate widthwise sheet width direction according to the conditions of Example (1) of the present invention shown in Table 1, where (A) is the water amount and collision pressure distribution of the nozzle alone, (B) is the synthesized water amount distribution, ( C) shows the synthesized collision pressure distribution.

FIG. 4 is a rolled steel plate widthwise direction according to the conditions of Example (2) of the present invention shown in Table 1, where (A) is the water amount and collision pressure distribution of the nozzle alone, (B) is the synthesized water amount distribution, ( C) shows the synthesized collision pressure distribution.

5A and 5B, in the width direction of the rolled steel sheet according to the conditions of Example (3) of the present invention shown in Table 1, (A) is the water amount and collision pressure distribution of the nozzle alone, (B) is the synthesized water amount distribution, ( C) shows the synthesized collision pressure distribution.

FIG. 6 shows the temperature distribution in the width direction of the rolled steel sheet under the conditions of Example (3) of the present invention shown in Table 1.

[Explanation of symbols]

D: Rolled steel plate width L ₁ ... Nozzle pitch L ₂ ... Length of jet water collision part L ₃ ... Length of jet water lap portion L ₂ / L ₁ ... Lapping rate P ... Jet water collision pressure TS ... Steel plate surface temperature W ... Jetted water amount θ ₁ … Spread angle

Claims (1)

[Claims] 1. A method for producing a hot-rolled steel sheet, which comprises rolling multiple times while performing descaling and cooling when rolling a high-temperature steel sheet using a reversible hot rolling mill, wherein the hot-rolled steel sheet for descaling. The high-pressure jet water jetted from a plurality of nozzles toward the plate at a collision pressure of a certain value or more to be uniformly distributed in the plate width direction, and the pitch L _{1 of} the nozzles and the jet angle θ _{1 of the} nozzles are set as rolling conditions. By adjusting them together, the lap ratio L ₂ / L ₁ of the high-pressure jet water at the collision part on the hot-rolled steel sheet is determined, and the cooling capacity of the hot-rolled steel sheet in the plate width direction is made substantially uniform. A method for descaling a hot rolled steel sheet, comprising: