JP2001129608A - Cooling method for hot rolling steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a useful cooling method and an useful cooling apparatus of a hot rolling steel for prevention of uneven defective products due to irregular cooling and the prevention of camber of far materials by control cooling of the hot rolling steel. SOLUTION: The position of the occurrence of the local super cooling of the breadth wise steel plate after control cooling is measured, and the hot rolling steel plate is cooled by a roll adjusted so that the surface roughness of the parts corresponding to the local position of the occurrence of the super cooling parts is the same with other parts or smaller than other parts. As to adjustment of the surface roughness of the rolling roller, the on-line-grinding- method is preferable. For prevention of chamber after for cutting the hot rolled steel plate is preferably cooled under control by use of a roll having a plurality of spots where the surface roughness differs from leach other as much as 10 μm or more in Rz in the breadth wise direction of the roll.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a controlled cooling process performed after finish rolling of a hot-rolled steel sheet. More specifically, the present invention relates to a cooling method that is effective for preventing flatness of a steel sheet caused by uneven cooling in controlled cooling and camber that is likely to occur in a strip material obtained by cutting a controlled cooled steel sheet.

2. Description of the Related Art Thick steel sheets are often controlled and cooled after hot rolling in order to realize high strength by using low alloy steel, and to produce high strength steel sheets with low cost and excellent weldability. Typical cooling start temperature in controlled cooling is 700 to 800 ° C
, And the cooling stop temperature is in the range of 400 to 600 ° C. In the production of a hot-rolled steel sheet by a hot strip mill, the same processing is performed after finish rolling. At the time of controlled cooling, a region where the temperature is locally low is often generated in the temperature distribution in the steel sheet width direction immediately after the cooling is stopped (hereinafter, simply referred to as “local overcooling”). It is extremely difficult to keep the production conditions uniform over the entire width direction in processes such as slab heating, hot rolling, and controlled cooling, especially for wide steel plates such as thick steel plates. And local supercooling are likely to occur. When the steel sheet in which local supercooling has occurred at the time of cooling stop is cooled to room temperature, residual stress is generated inside the steel sheet, which causes problems such as material variation and deterioration of flat shape. For example, in the case where the central part in the width direction is locally supercooled, even if the flattening process is performed by a hot leveler after the control cooling, even after cooling to room temperature, the flatness of the middle stretched shape becomes poor, and the end of the steel sheet is locally supercooled. When cooled, the shape becomes an ear wave even if similar processing is performed.
Further, when the portion that has been locally supercooled when the cooling is stopped is cut and cut, large transverse bending (camber) and poor flatness occur in the cut steel plate (hereinafter, also simply referred to as “strip”). As a result, it becomes difficult to process and weld the strip,
There is a need for a controlled cooling method that does not cause these defects. Among the causes of local overcooling and uneven cooling in the width direction of the steel sheet, uneven heating of the slab, which is a mechanical factor, cooling water retention on the top surface of the steel sheet, poor drainage, poor rolling shape, deformation during cooling, and control Poor water volume distribution during cooling can be solved by thorough equipment maintenance and optimization of operating conditions. Another major cause of local supercooling is uneven surface properties such as uneven surface roughness and scale of the steel sheet. Various techniques have been disclosed so far to prevent such poor cooling. For example, in Japanese Patent Application Laid-Open No. 1-284418, the surface roughness of the material to be rolled after rolling is adjusted to be not less than the vapor film thickness of the cooling medium, and within Ra to 10 to 30 μm, and the newly formed surface after rolling is adjusted. A uniform cooling method of cooling using a cooling medium after accelerated oxidation, and a roll grinding device provided near a rolling roll in the final pass of the hot rolling mill, and rolling by an oxidizing device provided behind the rolling roll in the final pass. A cooling method is disclosed in which the surface of the steel sheet is accelerated oxidized and then cooled. JP-A-7-290129 discloses a method for controlling a winding temperature of a hot-rolled steel sheet which is cooled and wound after hot finish rolling, wherein the surface roughness Ra of the hot-rolled steel sheet after hot finish rolling is 1.
A method for keeping the winding temperature constant by limiting the thickness to 0 to 1.5 μm is disclosed. Japanese Patent Application Laid-Open No. 7-314029 discloses a method of rolling from roll wear information depending on a roll chance in order to prevent non-uniform cooling in the width direction caused by surface roughness of a rolled material due to transfer of surface roughness of a roll. A method of estimating the cooling capacity in the width direction due to the material surface roughness and controlling the water distribution in the width direction based on this is disclosed.

However, the method described in Japanese Patent Application Laid-Open No. 1-284418 requires equipment for accelerating and oxidizing a new surface, which increases both equipment costs and operating costs. In the method described in JP-A-7-290129, it is necessary to limit the surface roughness to an extremely small value, so that rapid cooling is difficult, and there is a problem that the temperature at which the cooling is stopped is deviated. Further, in the method described in JP-A-7-314029, the effects of heating and primary rolling are complicated, the prediction model is incomplete, and it is difficult to control the water distribution in the width direction of the cooling device with high accuracy in terms of equipment. Therefore, the uniform cooling effect is not always sufficient. Further, the technology disclosed in each of the above publications is difficult to prevent supercooling that occurs locally in the width direction in particular, and the effect of preventing dimensional and shape defects of a strip obtained by cutting this is not sufficient. Did not. An object of the present invention is to solve these problems, and to control and cool hot-rolled steel sheets such as thick steel sheets and hot-rolled steel strips. An object of the present invention is to provide a method for cooling a hot-rolled steel sheet.

Means for Solving the Problems The present inventor has developed a steel sheet surface condition.
Effect on cooling rate and steel plate surface roughness
As a result of various studies on the adjustment method,
Such new knowledge was obtained. FIG. 1 shows an experiment conducted by the inventor.
This shows an example of the results.
Graph showing the relationship between steel sheet surface roughness and cooling rate
is there. In this experiment, a steel plate whose surface was adjusted to various roughness
A test piece was used and heated to 800 ° C. in vacuum
After that, spray the high pressure water spray on the surface under the same conditions,
Was measured for temperature change. Steel plate surface roughness is JISB-06
It is expressed by ten point average roughness (Rz) specified in 01.
Was. As shown in FIG. 1, as Rz increases, film boiling increases.
As the cooling rate during soaking increases, film boiling causes nuclei.
Transition temperature to boiling (quench point temperature, indicated by an arrow in the figure)
Shown) is higher. When cooling water hits the steel plate surface
A vapor film is generated at the steel plate interface, and in the initial stage of cooling (high temperature range)
It is cooled through the vapor film, but the vapor film
High temperature in areas with protrusions that are high enough to penetrate
The transition from film boiling to nucleate boiling also progresses in the
This is because nucleate boiling occurs. From this, Rz is large.
Early transition to rapid cooling in that area.
It can be seen that the cooling rate can be increased. FIG.
Is 75 thick steel plates with a thickness of 14 mm and a width of 4000 mm.
After hot rolling at 0 ° C, cooling water is sprayed uniformly in the width direction.
Immediately after cooling was stopped,
Temperature distribution in the width direction of the steel sheet (hereinafter simply referred to as “cooling stop temperature distribution”
And the surface roughness of a steel sheet cooled to room temperature.
FIG. As shown in FIG.
If the temperature is not uniform in the width direction, the cooling stop temperature distribution will be uneven.
And supercooling occurs locally in the area where Rz is large.
You can see that there is. FIG. 3 shows a controlled cooling according to the present invention.
Degree of supercooling ΔT in the subsequent widthwise temperature distribution _Two And surface roughness
9 is a graph illustrating an example of a relationship with a variation ΔRz. here
And the degree of supercooling ΔT is adjacent to the temperature distribution curve in the width direction.
ΔT means the temperature difference between the peak and the valley (unit: ° C), ΔT_Two Is cooling
The degree of supercooling after stopping is ΔT₁ Is the width direction before the start of control cooling
It shall represent the degree of supercooling measured from the temperature distribution. surface
The roughness variation ΔRz is the distribution of the surface roughness Rz in the width direction of the steel sheet.
Rz difference between adjacent peaks and valleys in the curve (unit is μ
m). As shown in FIG._Two And ΔRz
A good relationship was observed between the two, and ΔR
It can be seen that the adjustment of z is effective. Prior to controlled cooling
To predict the location of local supercooling in the width direction of the steel sheet,
By adjusting the surface roughness of the steel sheet
Therefore, it is possible to prevent local overcooling of the portion. Ma
Depending on the expected degree of supercooling,
Adjusting the height is also effective. Steel sheet surface roughness
The surface roughness of the tool is transferred. Generally, when transferring steel
The plate surface roughness is about 80% of the roll surface roughness. Follow
Adjustment of the steel sheet surface roughness is based on the expected width of the supercooled part.
Surface roughness at the axial position of the rolling roll corresponding to the
Adjustment and transfer of this to the steel sheet surface during rolling
It is. FIG. 4 shows a wide area where overcooling occurs locally when cooling is stopped.
Cooling stop temperature distribution and stripping when stripping thick steel plate
The position and the camber occurrence of the obtained strip are shown.
ΔT_j Is the fluctuation amount of the cooling stop temperature within each section (hereinafter simply referred to as
(Also referred to as "intra-section temperature deviation"). Strip steel plate
When the cooling stop temperature distribution in the strip is
To the left and right, and the residual stress in the
When the balance increases beyond the widthwise rigidity of the strip
Camber occurs. Articles j1, j2, j4 shown in FIG.
ΔT on the left and right in the width direction like j5_j Is 15-20 ° C or more
And the temperature distribution when cooling is stopped in the
Low asymmetric cooling temperature
An arc-shaped camber with the other end outward is generated.
I do. Whether the cooling stop temperature distribution is uniform in the strip,
Is ΔT as in Article j3_j Even if the width is wide
If the distribution is symmetric or nearly symmetric with respect to the
A good strip without chamber is obtained. From this,
(A) or (b) below
The described method is also suitable. (A) Control to maintain the temperature balance in the width direction of the strip
Cooling. For this purpose, there should be two or more supercooling sections in one section.
Control cooling or super cooling as it exists
The cooling stop temperature at which the interval between parts is less than 1/2 of the strip width
Controlled cooling is preferred so that a cloth is obtained. like this
Arbitrary position in the width direction by setting the cooling stop temperature distribution
The temperature balance in the width direction of the inside of the strip is greatly broken
To prevent camber after cutting.
can do. As a method of providing a supercooling section,
Hot rolling of steel sheets,
Alternate between high and low surface roughness areas
It is preferable to use a rolling roll provided in
You. A uniform table across the width of the steel sheet by online roll grinding
Surface roughening requires excessive capacity of equipment and is
Although not practical, grinding only desired parts as described above
If there is no such problem, it is economical and efficient
You can do it well. How to provide another supercooling section and
High pressure water or abrasive grease on the steel plate surface before cooling.
A mechanical impact on the desired area by spraying
Or apply a thermal shock to peel off the scale of the relevant part,
Further, a method of rapidly cooling the portion is also suitable. Scale
The interface between the steel plate and the steel plate surface is very uneven,
Surface roughness unevenness ΔRz is large in the area where
The part where the transition from film boiling to nucleate boiling begins
(Hereinafter simply referred to as "quench point")
Wear. In addition, steel plate by high pressure water or abrasive jet
Quench point at that part due to the direct cooling effect of the surface
You can also. (B) Stripping so that the temperature deviation within the strip is within the specified value
Control the cooling stop temperature at the location. As a method,
For example, make sure that the supercooling section comes to the scheduled cutting position.
Good. To produce local subcooling at the desired strip position
As described in (a), online roll grinding etc.
To partially grind the roll at the desired location
Increase the surface roughness of the part, transfer this to a steel plate and
Method of roughening the surface roughness of the steel plate of
The desired cooling is achieved by a local cooling method such as a spray nozzle upstream.
Local cooling of the location is also suitable. The present invention
Was completed based on the newly obtained knowledge of
The gist of the invention is that hot-rolled steel described in the following (1) to (3)
In the cooling method of the plate. (1) Controlled cooling of the hot-rolled steel sheet using a cooling device
A method of cooling a hot-rolled steel sheet,
Measure the location of local supercooling in the width direction and measure
Roll surface at the part corresponding to the location of the localized subcooling occurrence
Roughness equal to or less than other parts
Adjust the surface roughness of the rolling roll so that
Of hot-rolled steel sheet using rolling rolls
A method for cooling a hot-rolled steel sheet. (2) The adjustment of the surface roughness of the rolling roll is performed by a rolling line.
This is done by grinding the roll on
Cooling the hot-rolled steel sheet according to the above (1),
Method. (3) Controlly cool the hot-rolled steel sheet using a cooling device
A method of cooling a hot-rolled steel sheet,
In the opposite direction, a plurality of portions where the surface roughness differs by 10 μm or more in Rz
Controls hot-rolled steel sheet using rolling rolls
A method for cooling a hot-rolled steel sheet, comprising cooling.

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 5 is a partial conceptual diagram showing a configuration example of the cooling equipment according to the present invention. In FIG. 5, reference numeral 1 denotes a steel plate, reference numeral 2a denotes an output side width direction thermometer, reference numeral 2b denotes an entry side width direction thermometer, reference numeral 3 denotes a roll grinding device,
Reference numeral 5 denotes a control device, reference numeral 6 denotes a cooling device, reference numeral 7 denotes a finishing mill rolling roll, reference numeral 8 denotes a hot leveler, and reference numeral 9 denotes a finishing mill. The steel sheet 1 that has been finish-rolled by the finishing mill 9 is controlled and cooled by the cooling device 6. The width direction thermometer 2 is provided on the outlet side and / or the inlet side of the cooling device 6,
The temperature in the width direction of the steel sheet 1 is measured and output to the control device 5. The control device 5 recognizes the width direction temperature distribution pattern of the steel sheet 1 from the above width direction temperature, and based on the width direction temperature distribution, the width direction position of the local supercooling in the steel sheet width direction after the controlled cooling, or The cooling position and the degree of supercooling are determined, and this is used as a predicted value of the local supercooling of the steel sheet cooled after the measurement time, and the roll surface roughness necessary for eliminating supercooling stored in advance and the roll surface From the relationship between the roughness and the roll grinding conditions, the roll grinding conditions necessary for eliminating the local supercooling are determined, and a signal for grinding the position in the rolling roll width direction corresponding to the local supercooling occurrence position according to these conditions is output to the online roll. Output to the grinding device 3. FIG. 6 shows the degree of supercooling (Δ) of the steel sheet before controlled cooling when the thick steel sheet is controlled and cooled.
3 is a graph showing the relationship between T ₁ ) and the degree of supercooling (ΔT ₂ ) of the steel sheet after stopping the control cooling. As shown in FIG. 6, there is a correlation between the degrees of supercooling before and after the controlled cooling. This is because the lower the surface temperature of the steel sheet at the start of cooling, the sooner it reaches the quench point temperature after the start of cooling, so that rapid cooling is started earlier, and the lower the temperature of the steel sheet, the greater the heat transfer coefficient. By expanding. Therefore, the degree of supercooling may be determined based on the temperature distribution in the width direction when control cooling is stopped, or may be determined based on the temperature distribution in the width direction before control cooling is started. Although a known method can be applied to the online roll grinding method, it is desirable that the roll surface roughness can be changed online according to the degree of supercooling. For example, a roll grinding method in a stand disclosed in JP-A-60-207770 is disclosed. The method is preferred.
In this method, high-pressure water mixed with an abrasive is sprayed onto a portion to be polished of a rotating roll in a rolling mill stand to grind an arbitrary portion in a width direction (hereinafter, referred to as an “abrasive jet method”). ). However, it is not necessary to limit to this method, such as a method using a grinding wheel,
Other methods are acceptable. FIG. 7 is a schematic plan view showing the structure of the abrasive jet system and the arrangement thereof. FIG.
Reference numeral 11 denotes a nozzle unit, reference numeral 12 denotes a guide, reference numeral 13 denotes a support base, reference numeral 14 denotes a traverse motor, reference numeral 1
Reference numeral 5 denotes a nozzle approach motor, and reference numeral 16 denotes a nozzle tilting motor. There is one nozzle unit 11 on each side of the rolling roll, and a mixture of water and a grinding material such as iron powder is sprayed from the nozzle unit 11 onto the roll surface at high pressure. Each nozzle unit 11 is mounted on a support 13 mounted on a guide 12 provided in parallel with the roll axis, and can be moved to an arbitrary width direction position by a traverse motor 14. Nozzle unit 1
1 is a nozzle unit 11 by a nozzle approach motor 15
The distance between the roller and the roll surface can be adjusted, and the nozzle tilting motor 16 can adjust the injection angle with respect to the roll surface. The high-pressure water and the abrasive are supplied to the pipe 17,
The ink is supplied to the nozzle unit 11 through the nozzle 18. By controlling and operating the traverse motor 14, the nozzle approach motor 15, and the nozzle tilting motor 16, the roll surface in a desired area can be ground. FIG. 8 is a graph showing an example of the relationship between the abrasive material jetting conditions and the roll surface roughness in roll grinding by the abrasive jet method. The initial surface roughness of the roll is 40 to 50 in Rz.
μm. In FIG. 8, the abrasives A and B are both iron sand, but the abrasive A has a small particle size and the abrasive B has a large particle size. These abrasives were mixed with water, the injection amount of the abrasive was 6 kg / min, and the grinding time was 1 to 10 minutes. As shown in FIG. 8, the surface roughness after grinding was 1.5 to 2.5 μm for abrasive A and 27 to 33 μm for abrasive B. By adjusting the grinding conditions in this way, the surface roughness after polishing can be changed. When the local supercooling position in the width direction of the rolled steel sheet can be grasped in advance, or when the cutting position is determined, the change in the surface roughness of the rolling roll may be performed as an off-line operation. The method may be, for example, a method in which a work roll surface is ground to a desired state by a known method such as a roll lathe, and the work roll is mounted on a rolling mill and rolled. In the case where camber of the strip is prevented by maintaining the temperature balance in the strip width direction, controlled cooling is performed such that at least two or more supercooled portions are formed in each strip in the cooling stop temperature distribution. Alternatively, controlled cooling is performed so as to obtain a cooling stop temperature distribution in which the intervals at which the supercooling portions occur are less than 1/2 of the strip width. If there are at least two supercooled sections in the strip, the balance of residual stress in the strip width direction will not be significantly disrupted even if the strip temperature in the strip and the cutting position in the width direction fluctuate slightly, and the camber will If it does not exist, or if it occurs, the camber amount can be kept within an allowable range. As a method of providing the supercooling section, it is preferable to control-cool a steel sheet having a portion having a surface roughness different by 8 μm or more in Rz in the width direction. As can be seen from FIG. 8, if the variation in the surface roughness is 8 μm or more, a portion having a large surface roughness can be regarded as a local supercooling occurrence site. Preferably, a difference of 12 μm or more is provided. According to the method, since the transfer rate of the roll surface roughness to the steel plate surface roughness is about 80%, the surface roughness is 10% in Rz.
It is preferable to control and cool a hot-rolled steel sheet using a rolling roll having a plurality of portions having a difference of not less than 15 μm, preferably not less than 15 μm. For example, if a roll having a surface roughness of 10 μm or less in Rz and a portion of 25 μm or more in the width direction is used alternately, the steel sheet width direction position corresponding to the portion in which Rz is 25 μm or more is a supercooled portion. And R
A position in the width direction of the steel sheet facing a portion where z is 10 μm or less is a non-supercooled portion. In order to reliably obtain the supercooled portion, a portion having a large surface roughness (for example, a portion having Rz of 25 μm or more)
The width of each of the small portions (for example, the portion having Rz of 10 μm or less) is preferably 20 mm or more.

EXAMPLES (Example 1) A hot-rolled steel sheet was controlled and cooled using the apparatus shown in FIG. The equipment shown in FIG. 5 includes a finishing mill in which an abrasive jet type roll polishing device 3 is disposed in the vicinity of a rolling roll 1 and a cooling device provided with a width direction thermometer 2 on the outlet side and the inlet side downstream thereof. And a control device 6. First, as a conventional example, the thickness is 10 mm and the width is 40 mm.
A steel plate having a length of 00 mm and a length of 30,000 mm was hot-rolled by a conventional method without operating a roll polishing apparatus, subjected to controlled cooling for rapidly cooling from 750 ° C. to 500 ° C., and cooled to room temperature. At that time, the width direction temperature distribution of the steel sheet is measured by the width direction thermometer 2a on the cooling device outlet side, the result is output to the control device 5, and the control device 5 recognizes the width direction temperature distribution pattern of the steel sheet. The width direction position of the portion where the degree of supercooling was 10 ° C. or more was determined from the width direction temperature pattern.
Next, the required roll roll surface roughness is determined from the relationship between the degree of supercooling ΔT ₂ illustrated in FIG. 3 and the amount of surface roughness variation ΔRz required to eliminate the degree of supercooling ΔT ₂ previously stored from the past results. Then, the roll grinding conditions were determined so that the roll surface roughness was obtained, and a signal for grinding the position in the rolling roll width direction corresponding to the supercooled portion was output to the abrasive jet type roll polishing apparatus 3 according to the conditions. .
According to the signal, an abrasive jet type roll polishing device was used to grind the position corresponding to the widthwise supercooled portion of the rolling roll. Then, the second steel sheet of the same size is hot-rolled,
Controlled cooling from 50 ° C to 500 ° C,
Cooled to room temperature. At a later date, the first and second steel plates were cut into a width of 600 mm, and the camber of each strip was measured. FIG. 9 is a conceptual diagram showing a cooling stop temperature distribution when the second steel sheet is controlled and cooled, and a cut shape of a strip material obtained by cutting the steel sheet according to the embodiment of the present invention. As shown in FIG. 9, ΔT in the cooling stop temperature distribution was reduced by the method of the present invention, and each of the cambers after cutting was less than 3 mm / 10 m. FIG. 4 shows a conventional example, in which the cooling stop temperature distribution of the first steel sheet is shown.
It is a conceptual diagram which shows the cut shape of the strip which cut this steel plate. The effect of the present invention is apparent from comparison with FIG. 4 which is a conventional example. Separately, a large number of steel sheets having a width in the range of 3000 to 4500 mm were manufactured by a method of controlled roll cooling after online roll grinding by the same method of the present invention as described above. During that time, the flatness of the steel sheet before the stripping and the camber amount of the strip were measured, and the acceptance rates of these were investigated. As a conventional example, the flatness of the steel sheet before stripping and the camber amount of the strip were measured when the steel sheet and the strip having similar dimensions were rolled and rolled in a conventional manner without roll grinding and controlled and cooled. The pass rate in the conventional method was investigated. The flatness of the steel plate before stripping is 10m
The case where the hit wave height was 5 mm or less was regarded as the acceptable range, and the case where the camber of the strip was 3 mm / 10 m or less was regarded as good as described above. The results obtained are shown in Table 1.

[Table 1] As shown in Table 1, when cooled by the method of the present invention, the flatness passing rate of the steel sheet before the stripping was greatly improved, and the camber occurrence rate of the strip material from these was reduced to 1/3. (Embodiment 2) Using the same equipment as described in Embodiment 1, a roll was subjected to online roll grinding so that a portion having a surface roughness of 10 μm and a portion having a surface roughness of 35 μm alternately in Rz. Example 1
Controlled cooling was performed under the same conditions as described in (1). The interval between the 35 μm portions was about 230 mm. The dimensions of the steel plate are thickness 15mm, width 3000mm, length 20000m
m. At a later date, the steel sheet was cut into a width of 600 mm. Each section contained two to three supercooling sections. FIG.
FIG. 3 is a conceptual diagram showing a roll surface roughness of the above-mentioned rolling roll after online roll polishing, a cooling stop temperature distribution after controlled cooling, and a cut shape of a strip. As shown in FIG. 10, according to the method of the present invention, the temperature distribution in the cooling stop temperature distribution was controlled, and the camber after cutting was small, and a good strip was obtained.

According to the method for cooling a hot-rolled steel sheet of the present invention, localized supercooling can be efficiently prevented, so that a controlled-cooled steel sheet having good material and flat shape can be obtained. In addition, the method of the present invention is suitable for stably producing a strip having no dimensional defects or lateral bends when stripping a controlled cooled steel sheet, such as improving yield, improving rolling efficiency, and improving productivity. Great effect.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the steel sheet surface roughness and the cooling rate when high-pressure water is injected onto a high-temperature steel sheet to cool it.

FIG. 2 is a graph showing a temperature distribution in a width direction measured immediately after controlled cooling of a steel sheet controlled and cooled after finish rolling, in comparison with a surface roughness of the steel sheet.

FIG. 3 shows a width direction after controlled cooling according to the embodiment of the present invention.
Subcooling degree ΔT in temperature distribution _Two And variation in surface roughness ΔR
9 is a graph illustrating an example of a relationship with z.

FIG. 4 is a conceptual diagram illustrating a relationship between a cooling stop temperature distribution and a shape of a strip when a wide steel sheet locally supercooled in the width direction during controlled cooling is cut.

FIG. 5 is a partial conceptual view showing a configuration example of a steel plate rolling facility and a cooling facility according to the present invention.

FIG. 6 is a graph showing the relationship between the degree of supercooling of a steel sheet before control cooling (ΔT ₁ ) and the degree of supercooling of a steel sheet after control cooling is stopped (ΔT ₂ ).

FIG. 7 is a schematic plan view showing the structure of an abrasive jet system and the arrangement thereof.

FIG. 8 is a graph showing an example of a relationship between a grinding material ejection condition and a roll surface roughness in roll grinding by an abrasive jet method.

FIG. 9 is a conceptual diagram showing a cooling stop temperature distribution when controlled cooling of a hot-rolled steel sheet according to the local supercooling prevention method according to the embodiment of the present invention, and a cut shape of a strip obtained by cutting this steel sheet. It is.

FIG. 10 is a conceptual diagram showing a roll surface roughness after on-line roll polishing of a rolling roll, a cooling stop temperature distribution after controlled cooling, and a cut shape of a strip according to an embodiment of the present invention.

[Explanation of symbols]

1: steel plate 2: width direction thermometer 3: roll grinding device
5: Control device, 6: Cooling device, 7: Finishing mill rolling roll, 8: Hot leveler, 9: Finishing rolling mill, 11: Nozzle unit, 12: Guide, 13: Support base, 14: Motor for traverse, 15: Nozzle approach motor, 16: nozzle tilting motor, 17: pipe, 18: pipe.

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[Procedure amendment]

[Submission date] November 12, 1999 (1999.11.
12)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

[Title of the Invention] Method of cooling hot rolled steel sheet

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a controlled cooling process performed after finish rolling of a hot-rolled steel sheet. More specifically, the present invention relates to a cooling method that is effective for preventing flatness of a steel sheet caused by uneven cooling in controlled cooling and camber that is likely to occur in a strip material obtained by cutting a controlled cooled steel sheet.

[0002]

2. Description of the Related Art Thick steel sheets are often controlled and cooled after hot rolling in order to realize high strength by using low alloy steel, and to produce high strength steel sheets with low cost and excellent weldability. Typical cooling start temperature in controlled cooling is 700 to 800 ° C
, And the cooling stop temperature is in the range of 400 to 600 ° C. In the production of a hot-rolled steel sheet by a hot strip mill, the same processing is performed after finish rolling.

In controlled cooling, a region where the temperature is locally low is often generated in the temperature distribution in the width direction of the steel sheet immediately after the cooling is stopped (hereinafter, simply referred to as "local supercooling"). It is extremely difficult to keep the production conditions uniform over the entire width direction in processes such as slab heating, hot rolling, and controlled cooling, especially for wide steel plates such as thick steel plates. And local supercooling are likely to occur.

When the steel sheet in which local supercooling has occurred at the time of cooling stop is cooled to room temperature, a residual stress is generated inside the steel sheet, which causes problems such as a change in material and a deterioration in flat shape. For example, in the case where the central part in the width direction is locally supercooled, even if the flattening process is performed by a hot leveler after the control cooling, even after cooling to room temperature, the flatness of the middle stretched shape becomes poor, and the end of the steel sheet is locally supercooled. When cooled, the shape becomes an ear wave even if similar processing is performed.

[0005] Furthermore, when a portion that has been locally supercooled at the time of cooling stop is cut and cut, a large lateral bending (camber) and poor flatness occur in the cut steel sheet (hereinafter, also simply referred to as “strip”). . As a result, it becomes difficult to process and weld the strip, and there is a need for a controlled cooling method that does not cause these defects.

Among the causes of local overcooling and non-uniform cooling in the width direction of the steel sheet, non-uniform heating of the slab which is a mechanical factor, stagnant cooling water on the upper surface of the steel sheet, poor drainage, poor rolling shape, and cooling Deformation, poor water distribution during controlled cooling, etc.
It can be solved by thorough equipment maintenance and optimization of operating conditions.

Another major cause of local subcooling is that:
The surface properties of the steel sheet are uneven, such as uneven surface roughness and scale. Various techniques have been disclosed so far to prevent such poor cooling.

For example, Japanese Patent Application Laid-Open No. 1-284418 discloses that after rolling, the surface roughness of the material to be rolled is adjusted to be not less than the vapor film thickness of the cooling medium and within the range of 10 to 30 μm in terms of Ra. A uniform cooling method of accelerating oxidation of a newly formed surface and then cooling using a cooling medium, and a roll grinding device provided near a rolling roll in a final pass of a hot rolling mill, and an oxidation provided behind the rolling roll in the final pass. A cooling method is disclosed in which a steel sheet surface after rolling is accelerated oxidized by an apparatus and then cooled.

Japanese Patent Application Laid-Open No. Hei 7-290129 discloses a method for controlling a winding temperature of a hot-rolled steel sheet which is cooled and wound after hot finish rolling, and has a surface roughness R of the hot-rolled steel sheet after hot finish rolling.
A method is disclosed in which the winding temperature is kept constant by limiting a to 1.0 to 1.5 μm.

Japanese Patent Application Laid-Open No. 7-314029 discloses a roll wear depending on a roll chance in order to prevent uneven cooling in the width direction due to the surface roughness in the width direction of the rolled material due to the transfer of the surface roughness of the roll. A method of estimating the cooling capacity in the width direction due to the surface roughness of the rolled material from information and controlling the water flow distribution in the width direction based on this is disclosed.

[0011]

However, the method described in Japanese Patent Application Laid-Open No. 1-284418 requires equipment for accelerating and oxidizing a new surface, which increases both equipment costs and operating costs. In the method described in JP-A-7-290129, it is necessary to limit the surface roughness to an extremely small value, so that rapid cooling is difficult, and there is a problem that the temperature at which the cooling is stopped is deviated. Further, in the method described in JP-A-7-314029, the effects of heating and primary rolling are complicated, the prediction model is incomplete, and it is difficult to control the water distribution in the width direction of the cooling device with high accuracy in terms of equipment. Therefore, the uniform cooling effect is not always sufficient. Further, the technology disclosed in each of the above publications is difficult to prevent supercooling that occurs locally in the width direction in particular, and the effect of preventing dimensional and shape defects of a strip obtained by cutting this is not sufficient. Did not.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and to prevent poor flatness due to uneven cooling and camber of a strip when controlling and cooling a hot-rolled steel plate such as a thick steel plate or a hot-rolled steel strip. An object of the present invention is to provide an effective method for cooling a hot-rolled steel sheet.

[0013]

The present inventor has conducted various studies on the effects of the surface condition of the steel sheet on the cooling rate and a method for efficiently adjusting the surface roughness of the steel sheet. I got

FIG. 1 is a graph showing an example of an experimental result by the present inventor, and is a graph showing a relationship between a steel sheet surface roughness and a cooling rate when high-pressure water is sprayed on a high-temperature steel sheet. In this experiment, a steel plate specimen whose surface was adjusted to various roughnesses was used, heated to 800 ° C. in a vacuum, and then a high-pressure water spray was sprayed on the surface under the same conditions to change the temperature of the specimen. It was measured. The surface roughness of the steel sheet was represented by a ten-point average roughness (Rz) specified in JIS B-0601.

As shown in FIG. 1, as Rz increases, the cooling rate during film boiling cooling increases, and the transition temperature from film boiling to nucleate boiling (quenching point temperature, indicated by an arrow in the figure) increases. Has become. When the cooling water collides with the surface of the steel sheet, a vapor film is generated at the interface of the steel sheet, and is cooled through the vapor film in the initial stage of cooling (high temperature range), but the projection has a height enough to penetrate the vapor film on the surface of the steel sheet. This is because in a certain region, the transition from film boiling to nucleate boiling proceeds even in a high temperature region, and nucleate boiling occurs from the initial stage of cooling. From this, R
It can be seen that by increasing z, the region can be shifted to rapid cooling early and the cooling rate can be increased.

FIG. 2 shows a thickness: 14 mm and a width: 4000 m.
After hot rolling at 750 ° C. of a thick steel plate having a thickness of 500 m, cooling water is uniformly sprayed in the width direction to rapidly cool to 500 ° C., and the temperature distribution in the width direction of the steel plate immediately after cooling is stopped (hereinafter simply referred to as “cooling” Stop temperature distribution ") and the surface roughness of a steel sheet cooled to room temperature.

As shown in FIG. 2, when the surface roughness of the steel sheet is not uniform in the width direction, the cooling stop temperature distribution becomes uneven,
It can be seen that local supercooling occurs in the portion where Rz is large.

FIG. 3 shows the width after controlled cooling according to the present invention.
Degree of cooling ΔT in the direction temperature distribution _Two And surface roughness variation
It is a graph which shows an example of a relation with (DELTA) Rz. Subcool here
The rejection ΔT is the peak and valley adjacent to each other in the temperature distribution curve in the width direction.
Temperature difference (unit: ° C), ΔT_Two Is after cooling is stopped
The degree of supercooling of ΔT₁ Is the temperature in the width direction before the start of control cooling
It shall represent the degree of supercooling measured from the cloth. Surface roughness variation
The momentum ΔRz is the distribution curve of the surface roughness Rz in the steel sheet width direction.
Means the difference in Rz between adjacent peaks and valleys (unit: μm)
To taste. As shown in FIG._Two Good between and Rz
A favorable relationship was recognized, and ΔRz was adjusted to eliminate local supercooling.
Is effective.

Preventing local overcooling of a portion by predicting the location of local supercooling in the width direction of the steel plate prior to controlled cooling and adjusting the surface roughness of the steel plate before cooling. Can be. It is also effective to adjust the surface roughness of the steel sheet in that portion according to the estimated degree of supercooling.

The steel plate surface roughness is transferred to the surface roughness of the rolling roll. Generally, the surface roughness of the steel sheet during transfer is about 80% of the roll surface roughness. Therefore, the adjustment of the surface roughness of the steel sheet can be performed by adjusting the surface roughness of the position in the axial direction of the rolling roll corresponding to the predicted width direction position of the supercooled portion, and transferring this to the steel sheet surface during rolling. .

FIG. 4 shows a cooling stop temperature distribution, a cutting position, and a cambering state of the obtained strip when a wide steel plate that has been locally supercooled when the cooling is stopped is cut. ΔT _j is the fluctuation amount of the cooling stop temperature within each section (hereinafter,
Simply referred to as “intra-section temperature deviation”).

When cutting a steel sheet, the cooling stop temperature distribution in the strip is symmetrical with respect to the center in the width direction of the strip,
When the balance of the residual stress in the width direction of the strip becomes larger than the rigidity of the strip material in the width direction, camber occurs. As shown in strips j1, j2, j4, and j5 shown in FIG. 4, the left and right ΔT _j in the width direction is 15 to 20 ° C. or more, and the temperature distribution at the time of cooling stop in the strip width direction becomes extremely asymmetric. In this case, an arc-shaped camber having an arc-shaped portion with the lower end having the lower cooling stop temperature on the outside is generated.

If the cooling stop temperature distribution is uniform in the strip, or if the distribution is symmetrical or nearly symmetrical with respect to the center in the strip width direction even if ΔT _j is large, as in the case of strip j3, for example. A good strip without camber is obtained.

For this reason, the following method (a) or (b) is also suitable as a method for preventing camber of the strip.

(A) Control cooling is performed so as to maintain the temperature balance in the inner width direction. In order to achieve this, control cooling is performed so that there are two or more supercooling sections in one strip, or a cooling stop temperature distribution in which the intervals between the supercooling sections are less than 1/2 of the strip width is obtained. Controlled cooling is better. With such a cooling stop temperature distribution, even if the fiber is cut at an arbitrary position in the width direction, it is possible to prevent the temperature balance in the inner width direction from being largely collapsed and to prevent camber after the cutting. Can be.

As a method of providing the supercooling section, hot rolling of a target steel sheet is performed by a method such as online roll grinding using rolling rolls having portions having large and small surface roughness alternately. The method is preferred.

It is not practical to make the entire surface in the width direction of the steel sheet a uniform surface roughness by online roll grinding because it requires an excessive capacity of the apparatus. However, if only a desired portion is ground as described above, this is not possible. There is no such a problem, and it can be carried out efficiently and economically.

As another method of providing a supercooled portion, a mechanical impact or a thermal impact is applied to a desired portion by, for example, spraying high-pressure water or an abrasive jet onto the surface of the steel sheet before cooling, and the scale of the portion is cooled. Is also preferred. The interface between the scale and the steel sheet surface is highly uneven, and the surface roughness unevenness ΔRz increases at the part where the scale is peeled off from the steel sheet surface, and the part where the transition from film boiling to nucleate boiling starts (hereinafter simply referred to as “ Quenching point "). Also,
Due to the direct cooling effect of the steel sheet surface by high-pressure water or abrasive jet, that part can be set as a quench point.

(B) The cooling stop temperature at the cutting position is controlled so that the in-strip temperature deviation falls within a predetermined value. As a method thereof, for example, it is preferable that the supercooling section be located at the scheduled cutting position. In order to cause local supercooling at a desired cutting position, as described in (a), the roll of a desired portion is partially ground by, for example, online roll grinding to increase the surface roughness of the portion. However, a method of transferring this to a steel plate to roughen the surface roughness of the steel plate in the relevant portion, or a method of locally cooling a desired position by a local cooling method such as a spray nozzle upstream of the control cooling device is also suitable.

The present invention has been completed based on these newly obtained findings, and the gist of the present invention is as follows:
(3) The method for cooling a hot-rolled steel sheet according to (3).

(1) A method for cooling a hot-rolled steel sheet by controlling and cooling the hot-rolled steel sheet using a cooling device, wherein a position of occurrence of local supercooling in the width direction of the steel sheet after controlled cooling is measured. Then, the roll surface roughness of the portion corresponding to the measured local subcooling occurrence position is adjusted to be equal to or smaller than the other portions, and the rolling roll surface roughness is adjusted. A method for cooling a hot-rolled steel sheet, comprising cooling a hot-rolled steel sheet using a roll.

(2) The method for cooling a hot-rolled steel sheet according to (1), wherein the adjustment of the surface roughness of the roll is performed by grinding the roll on a rolling line. .

(3) A method of cooling a hot-rolled steel sheet by controlling and cooling the hot-rolled steel sheet using a cooling device, wherein a plurality of portions having a surface roughness different by 10 μm or more in Rz in the width direction of the rolling roll are provided. A method for cooling a hot-rolled steel sheet, wherein the hot-rolled steel sheet is controlled and cooled using a rolling roll provided at a location.

[0034]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 5 is a partial conceptual diagram showing a configuration example of the cooling equipment according to the present invention. In FIG. 5, reference numeral 1 denotes a steel plate, reference numeral 2a denotes an output side width direction thermometer, reference numeral 2b denotes an entry side width direction thermometer, reference numeral 3 denotes a roll grinding device,
Reference numeral 5 denotes a control device, reference numeral 6 denotes a cooling device, reference numeral 7 denotes a finishing mill rolling roll, reference numeral 8 denotes a hot leveler, and reference numeral 9 denotes a finishing mill.

The steel sheet 1 finish-rolled by the finishing mill 9 is controlled and cooled by the cooling device 6. Outlet side of the cooling device 6 and / or
Alternatively, a width direction thermometer 2 is provided on the entry side, and measures the width direction temperature of the steel sheet 1 and outputs the measured temperature to the control device 5.

The control device 5 recognizes the temperature distribution pattern in the width direction of the steel sheet 1 from the above-mentioned temperature in the width direction and, based on the temperature distribution in the width direction, the local position in the width direction of the local supercooling in the width direction of the steel sheet after controlled cooling. Or the supercooling position and the degree of subcooling,
This is a predicted value of the local supercooling of the steel sheet cooled after the measurement point, and the roll roll surface roughness necessary for eliminating supercooling stored in advance, and the relationship between the roll roll surface roughness and the roll grinding conditions. Then, a roll grinding condition necessary for eliminating the local supercooling is determined, and a signal for grinding the rolling roll width direction position corresponding to the local supercooling occurrence position is output to the online roll grinding device 3 in accordance with this condition.

FIG. 6 is a graph showing the relationship between the degree of supercooling (ΔT ₁ ) of the steel sheet before controlled cooling and the degree of supercooling (ΔT ₂ ) of the steel sheet after controlled cooling when the thick steel sheet is controlled and cooled. It is. As shown in FIG. 6, there is a correlation between the degrees of supercooling before and after the controlled cooling. This is because the lower the surface temperature of the steel sheet at the start of cooling, the sooner it reaches the quench point temperature after the start of cooling, so that rapid cooling is started earlier, and the lower the temperature of the steel sheet, the greater the heat transfer coefficient. By expanding. Therefore, the degree of supercooling may be determined based on the temperature distribution in the width direction when control cooling is stopped, or may be determined based on the temperature distribution in the width direction before control cooling is started.

Although a known method can be applied to the online roll grinding method, it is desirable that the roll surface roughness can be changed online according to the degree of supercooling.
The roll grinding method in a stand disclosed in JP-A-207770 is suitable. In this method, high-pressure water mixed with an abrasive is sprayed onto a portion to be polished of a rotating roll in a rolling mill stand to grind an arbitrary portion in a width direction (hereinafter, referred to as an “abrasive jet method”). ). However, it is not necessary to limit to this method, and another method such as a method using a grinding wheel may be used.

FIG. 7 is a schematic plan view showing the structure of the abrasive jet system and the arrangement thereof. Reference numeral 11 in FIG.
Reference numeral 12 denotes a guide, reference numeral 12 denotes a guide, reference numeral 13 denotes a support, reference numeral 14 denotes a traverse motor, reference numeral 15 denotes a nozzle approaching motor, and reference numeral 16 denotes a nozzle tilting motor.
There is one nozzle unit 11 on each side of the rolling roll, and a mixture of water and a grinding material such as iron powder is sprayed from the nozzle unit 11 onto the roll surface at high pressure.

Each of the nozzle units 11 has a support 1 mounted on a guide 12 provided in parallel with the roll axis.
3 and can be moved to any position in the width direction by the traverse motor 14. The distance between the nozzle unit 11 and the roll surface of the nozzle unit 11 can be adjusted by a nozzle approach motor 15,
The injection angle with respect to the roll surface can be adjusted by the nozzle tilting motor 16. High pressure water and abrasives
The liquid is supplied to the nozzle unit 11 via the pipes 17 and 18. Motor 14 for traverse, motor 1 for nozzle approach
5. The roll surface in a desired area can be ground by controlling and operating the nozzle tilting motor 16.

FIG. 8 is a graph showing an example of the relationship between the abrasive material jetting conditions and the roll surface roughness in the roll grinding by the abrasive jet method. The initial surface roughness of the roll was 40-50 μm in Rz. In FIG. 8, the abrasives A and B are both iron sand, but the abrasive A has a small particle size and the abrasive B has a large particle size. These abrasives were mixed with water, the injection amount of the abrasive was 6 kg / min, and the grinding time was 1 to 10 minutes.

As shown in FIG. 8, the surface roughness after grinding was 1.5 to 2.5 μm for the grinding material A and 27 to 3 μm for the grinding material B.
It was 3 μm. By adjusting the grinding conditions in this way, the surface roughness after polishing can be changed.

When the local supercooling position in the width direction of the rolled steel sheet can be grasped in advance, or when the cutting position is fixed, the change of the surface roughness of the rolling roll may be performed as an off-line operation. The method may be, for example, a method in which a work roll surface is ground to a desired state by a known method such as a roll lathe, and the work roll is mounted on a rolling mill and rolled.

When camber of the strip is prevented by maintaining the temperature balance in the strip width direction, controlled cooling is performed by forming at least two or more supercooled portions in each strip in the cooling stop temperature distribution. I do. Alternatively, controlled cooling is performed so as to obtain a cooling stop temperature distribution in which the intervals at which the supercooling portions occur are less than 1/2 of the strip width. If there are at least two supercooled sections in the strip, the balance of residual stress in the strip width direction will not be significantly disrupted even if the strip temperature in the strip and the cutting position in the width direction fluctuate slightly, and the camber will If it does not exist, or if it occurs, the camber amount can be kept within an allowable range.

As a method of providing a supercooling section, it is preferable to control and cool a steel sheet having a portion having a surface roughness different by 8 μm or more in Rz in the width direction. As can be seen from FIG. 8, if the variation in the surface roughness is 8 μm or more, a portion having a large surface roughness can be regarded as a local supercooling occurrence site. Preferably 1
It is preferable to provide a difference of 2 μm or more.

As the method, since the transfer ratio of the surface roughness of the rolling roll to the surface roughness of the steel sheet is about 80%, a rolling method having a plurality of portions where the surface roughness differs by 10 μm or more, preferably 15 μm or more in Rz. The rolled steel sheet is preferably controlled and cooled. For example, if the surface roughness is R
By using a roll having alternately in the width direction portions that are 10 μm or less and 25 μm or more in z, Rz
Is a supercooled portion corresponding to a portion where Rz is 25 μm or more, and a non-supercooled portion is a steel plate width direction position opposing a portion where Rz is 10 μm or less. In order to reliably obtain the supercooled portion, a portion having a large surface roughness (for example, a portion having an Rz of 25 μm or more) and a portion having a small surface roughness (for example, a Rz having a 10
m or less) is preferably 20 mm or more.

[0047]

EXAMPLES (Example 1) A hot-rolled steel sheet was controlled and cooled using the apparatus shown in FIG. The equipment shown in FIG. 5 includes a finishing mill in which an abrasive jet type roll polishing device 3 is disposed in the vicinity of a rolling roll 1 and a cooling device provided with a width direction thermometer 2 on the outlet side and the inlet side downstream thereof. And a control device 6.

First, as a conventional example, the thickness is 10 mm and the width is 4 mm.
000 mm and a length of 30,000 mm are hot-rolled by a conventional method without operating a roll polishing device, and the temperature is 750 ° C.
From 500 ° C. to 500 ° C., and cooled to room temperature. At that time, the width direction temperature distribution of the steel sheet is measured by the width direction thermometer 2a on the cooling device outlet side, the result is output to the control device 5, and the control device 5 recognizes the width direction temperature distribution pattern of the steel sheet. The width direction position of the portion where the degree of supercooling was 10 ° C. or more was determined from the width direction temperature pattern. Next, FIG. 3 stored in advance from the past results
The required roll surface roughness is determined from the relationship between the degree of supercooling ΔT ₂ and the amount of surface roughness variation ΔRz required to eliminate the degree of supercooling, and roll grinding is performed so that the roll surface roughness is obtained. The conditions were determined, and a signal for grinding the position in the width direction of the rolling roll corresponding to the supercooled portion was output to the abrasive jet type roll polishing apparatus 3 according to the conditions. According to the signal, an abrasive jet type roll polishing device was used to grind the position corresponding to the widthwise supercooled portion of the rolling roll. Thereafter, a second steel sheet having the same dimensions was hot-rolled, subjected to controlled cooling for rapidly cooling from 750 ° C. to 500 ° C., and cooled to room temperature. At a later date, the first and second steel plates were cut into a width of 600 mm, and the camber of each strip was measured.

FIG. 9 is a conceptual diagram showing a cooling stop temperature distribution when the second steel sheet is controlled and cooled, and a cut shape of the strip obtained by cutting the steel sheet according to the embodiment of the present invention.
As shown in FIG. 9, ΔT in the cooling stop temperature distribution was reduced by the method of the present invention, and each of the cambers after cutting was less than 3 mm / 10 m. FIG. 4 is a conceptual view showing a cooling stop temperature distribution of the first steel sheet and a cut shape of a strip obtained by cutting the steel sheet, which is shown as a conventional example. The effect of the present invention is apparent from comparison with FIG. 4 which is a conventional example.

Separately, a large number of steel sheets having a width in the range of 3000 to 4500 mm were manufactured by the method of online roll grinding by the same method of the present invention as described above, followed by controlled cooling. During that time, the flatness of the steel sheet before the stripping and the camber amount of the strip were measured, and the acceptance rates of these were investigated. As a conventional example, the flatness of the steel sheet before stripping and the camber amount of the strip were measured when the steel sheet and the strip having similar dimensions were rolled and rolled in a conventional manner without roll grinding and controlled and cooled. The pass rate in the conventional method was investigated. The flatness of the steel plate before stripping is 10m
The case where the hit wave height was 5 mm or less was regarded as the acceptable range, and the case where the camber of the strip was 3 mm / 10 m or less was regarded as good as described above. The results obtained are shown in Table 1.

[0051]

[Table 1]

As shown in Table 1, when cooled by the method of the present invention, the flatness acceptance rate of the steel sheet before the stripping was greatly improved, and the camber occurrence rate of the strip material from these was reduced to 1/3. (Embodiment 2) Using the same equipment as described in Embodiment 1, a roll was subjected to online roll grinding so that a portion having a surface roughness of 10 μm and a portion having a surface roughness of 35 μm alternately in Rz. Example 1
Controlled cooling was performed under the same conditions as described in (1). The interval between the 35 μm portions was about 230 mm. The dimensions of the steel plate are thickness 15mm, width 3000mm, length 20000m
m. At a later date, the steel sheet was cut into a width of 600 mm. Each section contained two to three supercooling sections.

FIG. 10 is a conceptual diagram showing the roll surface roughness of the above-mentioned rolling roll after online roll polishing, the cooling stop temperature distribution after controlled cooling, and the cut shape of the strip. FIG.
As shown in FIG. 0, according to the method of the present invention, the temperature distribution in the cooling stop temperature distribution was controlled, and the camber after cutting was small, and a good strip was obtained.

[0054]

According to the method for cooling a hot-rolled steel sheet of the present invention, localized supercooling can be efficiently prevented, so that a controlled-cooled steel sheet having good material and flat shape can be obtained. In addition, the method of the present invention is suitable for stably producing a strip having no dimensional defects or lateral bends when stripping a controlled cooled steel sheet, such as improving yield, improving rolling efficiency, and improving productivity. Great effect.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the steel sheet surface roughness and the cooling rate when high-pressure water is injected onto a high-temperature steel sheet to cool it.

FIG. 2 is a graph showing a temperature distribution in a width direction measured immediately after controlled cooling of a steel sheet controlled and cooled after finish rolling, in comparison with a surface roughness of the steel sheet.

FIG. 3 shows a width direction after controlled cooling according to the embodiment of the present invention.
Subcooling degree ΔT in temperature distribution _Two And variation in surface roughness ΔR
9 is a graph illustrating an example of a relationship with z.

FIG. 4 is a conceptual diagram illustrating a relationship between a cooling stop temperature distribution and a shape of a strip when a wide steel sheet locally supercooled in the width direction during controlled cooling is cut.

FIG. 5 is a partial conceptual view showing a configuration example of a steel plate rolling facility and a cooling facility according to the present invention.

FIG. 6 is a graph showing the relationship between the degree of supercooling of a steel sheet before control cooling (ΔT ₁ ) and the degree of supercooling of a steel sheet after control cooling is stopped (ΔT ₂ ).

FIG. 7 is a schematic plan view showing the structure of an abrasive jet system and the arrangement thereof.

FIG. 8 is a graph showing an example of a relationship between a grinding material ejection condition and a roll surface roughness in roll grinding by an abrasive jet method.

FIG. 9 is a conceptual diagram showing a cooling stop temperature distribution when controlled cooling of a hot-rolled steel sheet according to the local supercooling prevention method according to the embodiment of the present invention, and a cut shape of a strip obtained by cutting this steel sheet. It is.

FIG. 10 is a conceptual diagram showing a roll surface roughness after on-line roll polishing of a rolling roll, a cooling stop temperature distribution after controlled cooling, and a cut shape of a strip according to an embodiment of the present invention.

[Explanation of symbols] 1: steel plate, 2: width direction thermometer, 3: roll grinding device,
5: Control device, 6: Cooling device, 7: Finishing mill rolling roll, 8: Hot leveler, 9: Finishing rolling mill, 11: Nozzle unit, 12: Guide, 13: Support base, 14: Motor for traverse, 15: Nozzle approach motor, 16: nozzle tilting motor, 17: pipe, 18: pipe.

Claims (3)

[Claims] 1. A method for cooling a hot-rolled steel sheet in which a hot-rolled steel sheet is controlled and cooled by using a cooling device, wherein a position at which local supercooling occurs in a width direction of the steel sheet after the controlled cooling is measured. The roll roll surface roughness of the portion corresponding to the measured supercooling occurrence position is the same as the other portions, or the roll roll surface roughness is adjusted so as to be smaller than the other portions. A method for cooling a hot-rolled steel sheet, wherein the hot-rolled steel sheet is controlled and cooled using a cooling device. 2. The method for cooling a hot-rolled steel sheet according to claim 1, wherein the adjustment of the surface roughness of the rolling roll is performed by grinding the roll on a rolling line. 3. A method for cooling a hot-rolled steel sheet in which a hot-rolled steel sheet is controlled and cooled using a cooling device, wherein a plurality of portions having a surface roughness different by 10 μm or more in Rz in a width direction of a rolling roll are provided. A method for cooling a hot-rolled steel sheet, comprising controlling and cooling a hot-rolled steel sheet using a provided rolling roll.