JP3796133B2 - Thick steel plate cooling method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thick steel plate cooling method and apparatus for controlling and cooling a thick steel plate in a thick steel plate manufacturing process.
[0002]
[Prior art]
Recently, in the manufacture of thick steel plates, the strength and weldability of the steel plates have been improved by controlled cooling after finish rolling. In the controlled cooling, in order to obtain uniform material characteristics and flatness, it is necessary to perform cooling so that the temperature distribution in the plate width direction is uniform. For this reason, many cooling methods have been proposed. For example, a cooling method according to JP-A-6-328118, JP-A-6-330155 or JP-A-7-256331 is known.
[0003]
In the cooling method disclosed in JP-A-6-328118, a high-strength steel is produced by cooling a thick steel plate by a control cooling device after rolling, and a descaling device or other device is used during or before rolling. Utilizing it, the scale removal range in the steel sheet width direction is controlled, and further, the scale residual thickness is controlled, thereby changing the width direction heat transfer coefficient of the steel sheet surface to make the steel sheet shape and material after cooling uniform. .
[0004]
The cooling method disclosed in Japanese Patent Application Laid-Open No. 6-330155 controls the thickness of the scale on the steel sheet by adjusting the pressure of high-pressure water in a scale removing device attached to the rolling mill in the controlled cooling of the thin-walled steel sheet. Thus, the mechanical properties in the longitudinal direction of the steel sheet are made uniform by controlling the heat transfer coefficient of the steel sheet surface.
[0005]
Furthermore, the cooling method disclosed in Japanese Patent Application Laid-Open No. 7-256331 is a controlled cooling method of a thick steel plate that obtains a uniform material and good steel plate flatness in the plate width direction, and on the surface of the thick steel plate during hot rolling. Disclosed is a method for measuring a scale thickness distribution and cooling after controlling the water injection position and the amount of water to be injected so that the measured value matches the target value of the scale thickness distribution on the surface of the steel plate. ing.
[0006]
However, any of the cooling methods described above ignores an increase in the amount of scale that grows during controlled cooling after rolling, and the scale that grows after rolling due to contact between the steel plate surface and the table roller during conveyance. The scale thickness cannot be controlled as intended before the controlled cooling device, such as the occurrence of peeling. In addition, when control cooling is performed after correction is performed after rolling, scale peeling occurs after rolling in the correction apparatus, and the scale thickness distribution tends to vary.
[0007]
[Problems to be solved by the invention]
The present invention seeks to provide a thick steel plate cooling method and apparatus capable of improving the flatness of the steel plate shape and making the material uniform.
[0008]
[Means for Solving the Problems]
The method of cooling a thick steel plate according to the present invention is a method of cooling a thick steel plate after finish rolling in a thick steel plate manufacturing process. When performing control cooling after finish rolling, descaling is performed after more than 5 seconds before control cooling. Do. This is to remove the scale layer by performing descaling before performing the control cooling. If the time from descaling to control cooling exceeds 5 seconds, when about 5 seconds have elapsed and control cooling is performed after the scale becomes 1 μm or more, there may be an advantage in terms of the material of the steel sheet. Because.
[0009]
In the above thick steel plate cooling method, when performing control cooling after finishing rolling, descaling is performed within 20 seconds before control cooling. This is because, even if this descaling is performed, if the time until the controlled cooling is longer than a certain length, the removed scale layer grows, and the scale varies due to scale peeling during running on the roller table. This is because non-uniform cooling occurs.
[0010]
In the steel plate cooling method, descaling is performed after finish rolling and hot straightening, and then controlled cooling is performed. Since the descaling is performed after the hot straightening, a part of the scale is peeled off by the hot straightening, and the scale peeling becomes easy in the descaling. Further, by allowing a predetermined time from descaling to controlled cooling, the temperature distribution becomes uniform due to reheating of the steel sheet surface. As a result, the thick steel plate is uniformly cooled in the controlled cooling.
[0011]
In the steel plate cooling method, descaling is performed after finish rolling, and then control cooling is performed after hot straightening. Since descaling is performed before hot straightening, the occurrence of scale wrinkles during hot straightening can be suppressed. This scale wrinkle occurs as follows. The scale that grows after rolling and during hot straightening partially peels due to contact between the steel plate surface and the table roller, vibration, and the like during conveyance from the rolling mill to the straightening machine. The unevenness due to the variation in scale thickness generated at this time is transferred to the surface of the steel sheet when passing through the hot straightening machine, and scale wrinkles are generated. Furthermore, by allowing a predetermined time from descaling to controlled cooling, the temperature distribution becomes uniform due to reheating of the steel sheet surface. As a result, the thick steel plate is uniformly cooled in the controlled cooling.
[0012]
In the thick steel plate cooling method, only the edge portion of the thick steel plate may be descaled. Since the edge portion tends to be supercooled compared to the central portion, it is also effective to descal only the edge portion.
[0013]
The steel plate cooling device of the present invention is a device that performs controlled cooling in a steel plate manufacturing facility, and uses a finishing rolling mill, a hot straightening device, a descaling device, a steel plate temperature measurement device, and a steel plate temperature measurement result based on a steel plate temperature measurement result. Control cooling devices for cooling are sequentially arranged.
With this device arrangement, the cooling method of the present invention can be effectively implemented. The steel plate temperature measuring device can be installed between the finish rolling mill and the hot straightening machine, or between the hot straightening machine and the descaling device.
[0014]
The steel plate cooling device of the present invention is a device that performs controlled cooling in a steel plate manufacturing facility, and uses a finish rolling mill, a descaling device, a hot straightening device, a steel plate temperature measurement device, and a steel plate temperature measurement result based on the steel plate temperature measurement result. Control cooling devices for cooling are sequentially arranged.
With this device arrangement, the cooling method of the present invention can be effectively implemented. The steel plate temperature measuring device can be installed between the finish rolling mill and the descaling device, or between the descaling device and the hot straightening machine.
[0015]
The steel plate cooling device of the present invention is a control cooling device that cools a steel plate based on a finishing rolling mill, a descaling device, a steel plate temperature measuring device, and a steel plate temperature measurement result in a device row that performs controlled cooling in a steel plate manufacturing facility. Are sequentially arranged.
With this device arrangement, the cooling method of the present invention can be effectively implemented. The steel plate temperature measuring device can be installed between the finish rolling mill and the descaling device, or between the descaling device and the control cooling device.
[0016]
In the steel plate cooling device, the distance L between the descaling device and the control cooling device is 20 (s) · v (m / s) ≧ L (m) ≧ 5 (s) · v (m / s) ( However, it is desirable that v is a plate passing speed of the thick steel plate. With such an interval, the time from descaling to control cooling is 5 to 20 seconds .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an example of equipment for carrying out the thick steel plate cooling method of the present invention. As shown in FIG. 1, a hot straightening device (roller leveler) 12 and a descaling device 14 are arranged adjacent to the hot rolling device 10 after the finishing mill 10. The descaling device 14 is a high pressure water spray type. A control cooling device 18 is arranged at an interval L on the exit side of the descaling device 14. The distance L between the descaling device 14 and the control cooling device 18 satisfies the relationship of 20 (s) · v (m / s) ≧ L (m) ≧ 5 (s) · v (m / s). desirable. A steel plate temperature measurement device 16 is disposed between the descaling device 14 and the control cooling device 18. The steel plate temperature measuring device 16 uses a radiation thermometer, and measures the steel plate surface temperature. The control cooling device 18 adjusts the cooling rate and the cooling stop temperature of the steel plate 1 based on the measurement result of the steel plate surface temperature. In addition, a heating furnace, a roughing mill, etc. (all are not shown) are arrange | positioned as a main apparatus in the upstream of the finishing mill 10.
[0018]
In the thick steel plate cooling method of the present invention, descaling is performed at least 1 second before the controlled cooling. The reason is as follows.
[0019]
Descaling removes the scale and eliminates variations in scale thickness distribution (scale unevenness). If there is unevenness in the scale, the steel sheet cannot be cooled uniformly.
[0020]
Descaling that injects high-pressure water is also a powerful cooling device. As shown in FIG. 6, the descaling high-pressure water jet usually provides an overlapping portion in the water jet collision in order to reliably perform descaling. As a result, as shown in FIG. 7, the descaling water jet overlapping portion is different from the nozzle jet collision portion in the steel plate surface temperature. If controlled cooling is performed while maintaining the temperature distribution, the temperature difference will increase. Therefore, in order to make the temperature distribution uniform by reheating the steel sheet surface, after descaling, control cooling is performed after a predetermined time to achieve uniform cooling. FIG. 8 (a) shows the steel plate surface temperature distribution without descaling, and FIG. 8 (b) shows the steel plate surface temperature distribution with a predetermined time after descaling. FIG. 8 shows that in the latter case, the steel plate surface temperature distribution is substantially uniform.
[0021]
The predetermined time is preferably more than 5 seconds. If it is less than 1 s, the reheating of the steel sheet surface is not sufficient, and a temperature distribution may remain. When the predetermined time is 2 s or longer, the heat can be reliably recovered. Furthermore, when the time after descaling is 1 second or longer, the scale grows. In the controlled cooling, the cooling rate when there is no scale layer is slower than when the scale layer is about 30 μm, for example. Therefore, when controlled cooling is performed after about 5 seconds have passed and the scale has reached 1 μm or more, the cooling rate of the steel sheet will be improved compared to when it is about 1 second, which may be advantageous in terms of the material of the steel sheet. is there.
[0022]
In the thick steel plate cooling method of the present invention, descaling is performed within 20 seconds of control cooling. The reason is as follows.
Descaling removes the scale and eliminates variations in scale thickness distribution (scale unevenness). If there is unevenness in the scale, the steel sheet cannot be cooled uniformly.
[0023]
Even after descaling, the steel plate temperature is high before controlled cooling, and the scale grows and grows thick. In order to make the temperature distribution after the controlled cooling uniform, it is necessary to perform the controlled cooling in a state where even if the scale grows, the grown thickness is small, and even if part of the scale is peeled off, the temperature unevenness is small. The present inventors have examined the conditions under which such non-uniformity cannot occur by various experiments and the like. As a result, if controlled cooling is performed within 20 seconds after descaling, the scale layer grown after descaling is developed. It has been found that even when the amount of growth is small, and even if part of the film is peeled off by a roller table or the like, temperature non-uniformity during controlled cooling can be suppressed within an allowable range. The result is shown in FIG . As shown in FIG. 9 , after 20 seconds after descaling. The temperature variation after controlled cooling increases and the product rejection rate increases. Thus, by removing the unevenness of the scale generated on the surface of the steel plate, uniform cooling can be performed, and the material and plate shape are also uniform.
[0024]
In addition, in order to determine at the time of descaling at this time, the distance between the nozzle and the steel plate is 180 under the conditions of a water pressure of 10 MPa, an amount of water per nozzle, 10 liters per minute, and a descaling water injection spread angle of 37 degrees. , 200, 220 mm. As a result, when the distance between the nozzle and the steel plate was 200 mm or more, the effect of uniform cooling decreased. That is, the distance between the nozzle and the steel plate is preferably less than 200 mm. In descaling, in general, the higher the water pressure, the greater the amount of water per nozzle, the smaller the descaling water jet spread angle, and the closer the distance between the steel plate and the nozzle, the higher the ability to remove the scale. Are known. It is also known that the ability to remove scale significantly decreases as the distance between the nozzle and the steel plate increases. Therefore, if the descaling condition is such that the ability to remove the scale is stronger than the condition used this time, the uniform cooling effect can be expected. At this time, generally referred to as descaling incident angle, angle between the vertical direction forming surface and the steel sheet descaling water jets were carried out at 0 and 15 degrees. There was not much influence of this incident angle.
[0025]
The hot straightening device 12 corrects the shape defect of the thick steel plate 1 after finish rolling to flatten the steel plate, and peels a part of the scale or assists the scale peeling by descaling. FIG. 3 shows a state where the scale 5 is peeled off by hot correction and the steel plate surface 2 is exposed. For example, the peeled scale has a thickness of 10 to 40 μm, a width of 50 to 300 mm, and a length of about 100 to 10,000 mm. FIG. 4 shows that when the descaling is performed after hot correction, the scale thickness is smaller, that is, the scale peeling is larger than when no hot correction is performed. This is because a part of the scale is peeled off by the hot straightening, and a fine crack is generated on the scale by the hot straightening, and the scale peeling by the high-pressure water spray becomes easy.
[0026]
FIG. 2 shows another example of equipment for carrying out the thick steel plate cooling method of the present invention. As shown in FIG. 2, a descaling device 14 and a hot straightening device (roller leveler) 12 are disposed adjacent to the finishing mill 10. The descaling device 14 is a high pressure water spray type. A control cooling device 18 is arranged at an interval L on the exit side of the descaling device 14. During this interval L, the hot straightening device 12 is arranged. The distance L between the descaling device 14 and the control cooling device 18 satisfies the relationship of 20 (s) · v (m / s) ≧ L (m) ≧ 5 (s) · v (m / s). desirable. A steel plate temperature measuring device 16 is disposed between the hot straightening device 12 and the control cooling device 18. The steel plate temperature measuring device 16 uses a radiation thermometer, and measures the steel plate surface temperature. The control cooling device 18 adjusts the cooling rate and the cooling stop temperature of the steel plate 1 based on the measurement result of the steel plate surface temperature. In addition, a heating furnace, a roughing mill, etc. (all are not shown) are arrange | positioned as a main apparatus in the upstream of the finishing mill 10.
[0027]
In the steel plate cooling method of the present invention, as described above, the effect of facilitating the scale peeling of the hot straightening device cannot be enjoyed. However, as shown in FIG. The occurrence of drought can be suppressed.
Also in this method, as shown in FIG. 8 (b), the effect of making the steel plate surface temperature distribution substantially uniform can be obtained.
[0028]
FIG. 10 shows another example of equipment for carrying out the thick steel plate cooling method of the present invention. As shown in FIG. 10 , a descaling device 14 is disposed after the finishing mill 10. The descaling device 14 is a high pressure water spray type. A control cooling device 18 is arranged at an interval L on the exit side of the descaling device 14. The distance L between the descaling device 14 and the control cooling device 18 satisfies the relationship of 20 (s) · v (m / s) ≧ L (m) ≧ 5 (s) · v (m / s). desirable. A steel plate temperature measurement device 16 is disposed between the descaling device 14 and the control cooling device 18. The steel plate temperature measuring device 16 uses a radiation thermometer, and measures the steel plate surface temperature. The control cooling device 18 adjusts the cooling rate and the cooling stop temperature of the steel plate 1 based on the measurement result of the steel plate surface temperature. In addition, a heating furnace, a roughing mill, etc. (all are not shown) are arrange | positioned as a main apparatus in the upstream of the finishing mill 10.
[0029]
In the thick steel plate cooling method of the present invention, as described above, the effect of correcting the shape of the steel plate before controlled cooling by the hot straightening device cannot be obtained. For this reason, the tail end of the steel sheet, that is, the part that exits the finishing mill at the end of the steel sheet part, the shape is bad in some cases, the cooling uniformity may be disturbed, but in the majority of the steel sheet, Also in this method, as shown in FIG. 8 (b), the effect of making the steel plate surface temperature distribution substantially uniform can be obtained.
[0030]
The steel plate edge portion tends to be supercooled compared to the central portion. In order to cool uniformly, it is also effective to descal only the edge portion of the steel plate by utilizing the fact that the scale has a higher heat transfer coefficient than the steel plate surface. The width of the steel plate edge portion to be descaled is about 50 to 200 mm depending on the width of the steel plate.
[0032]
【The invention's effect】
As described above, by adopting the method for cooling a thick steel plate according to the present invention, the steel plate temperature can be made uniform, and the resulting flatness of the steel plate shape can be improved and the material can be made uniform. . Furthermore, when the time from descaling to the start of forced cooling is more than 5 seconds as compared to about 1 second, the cooling rate is improved, which may be advantageous in terms of the material of the steel sheet.
[Brief description of the drawings]
FIG. 1 is one of configuration diagrams of equipment for carrying out a method of cooling a thick steel plate of the present invention.
FIG. 2 is a structural diagram of equipment for carrying out the thick steel plate cooling method of the present invention.
FIG. 3 is a drawing schematically showing a scale peeling state by hot correction.
FIG. 4 is a graph showing a difference in scale thickness after descaling depending on whether or not hot correction is performed.
FIG. 5 is a graph showing a difference in scale wrinkle generation depending on whether or not hot correction is performed.
FIG. 6 is a plan view schematically showing a state of a descaling water jet collision.
FIG. 7 is a diagram showing a steel plate temperature change due to a difference in descaling water jet collision.
8A is a graph showing a steel plate surface temperature distribution when descaling is not performed, and FIG. 8B is a graph showing a steel plate surface temperature distribution when a predetermined time is left after descaling.
FIG. 9 is a diagram showing a change in product rejection rate when the time from descaling to control cooling changes.
FIG. 10 is one of the structural views of equipment for carrying out the thick steel plate cooling method of the present invention.

Claims (7)

In the method of cooling a thick steel plate after finish rolling in the thick steel plate manufacturing process, when performing control cooling after finish rolling, descale should be performed after more than 5 seconds and within 20 seconds before control cooling. Thick steel plate cooling method characterized. The method for cooling a thick steel plate according to claim 1, wherein in the method for cooling the thick steel plate after finish rolling in the thick steel plate manufacturing step, descaling is performed after finish rolling and hot straightening, and then controlled cooling is performed . The method of cooling a thick steel plate according to claim 1 , wherein in the method of cooling the thick steel plate after finish rolling in the thick steel plate manufacturing process, the descaling is performed after the finish rolling , and then the control cooling is performed after hot straightening . The thick steel plate cooling method according to claim 1, wherein only the edge portion of the thick steel plate is descaled. In the equipment row that performs controlled cooling in the thick steel plate manufacturing facility, a finish rolling mill, a hot straightening device, a descaling device, a steel plate temperature measuring device, and a control cooling device that cools the steel plate based on the steel plate temperature measurement result are sequentially arranged. The distance L between the descaling device and the control cooling device is 20 (s) · v (m / s) ≧ L (m) ≧ 5 (s) · v ( m / s) satisfying the condition of thick steel plate cooling device. In the equipment row that performs controlled cooling in the thick steel plate manufacturing facility, the finish rolling mill, descaling device, hot straightening device, steel plate temperature measuring device, and control cooling device that cools the steel plate based on the steel plate temperature measurement result are arranged in sequence. The distance L between the descaling device and the control cooling device is 20 (s) · v (m / s) ≧ L (m) ≧ 5 (s) · v ( m / s) satisfying the condition of thick steel plate cooling device. In the equipment row that performs controlled cooling in the thick steel plate manufacturing facility, the finish rolling mill, descaling device, steel plate temperature measuring device, and control cooling device that cools the steel plate based on the steel plate temperature measurement result are arranged in order , and descaling The distance L between the apparatus and the control cooling apparatus is 20 (s) · v (m / s) ≧ L (m) ≧ 5 (s) · v (m / s) with respect to the sheet passing speed v. Thick steel plate cooling device characterized by satisfying conditions .

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