JP2016047538A - Cooling method of steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling method for producing a steel plate having no configuration error, such as crook or curve, upon cooling the steel plate and having excellent flatness.SOLUTION: There is provided a cooling method for a steel plate 3 in which hot rolled steel plate 3 having high temperature is transported to a cooling device 2 comprising a plurality of cooling zones whose entrance/exit sides are partitioned with drainer rolls 5, and is cooled from the upper and lower surfaces. When the plurality of steel plates are continuously cooled, actual value of deformation ratio indicated by height difference in surfaces of the cooled steel plate 3, which is obtained by cooling one steel plate 3 of the plurality of steel plates 3 under a predetermined cooling condition, is defined as actual cooling deformation ratio. Upper/lower water volume ratio is corrected into corrected upper/lower water volume ratio so that the deformation ratio is less than the actual cooling deformation ratio when the upper/lower water volume ratio (upper/lower water volume ratio=upper surface cooling water volume density/lower surface cooling water volume density) under the predetermined cooling condition is defined as pre-correction upper/lower water volume ratio. A steel plate 3 to be cooled next to the one steel plate 3 is cooled under a cooling condition of the corrected upper/lower water volume ratio.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of cooling a hot-rolled high-temperature steel sheet in a cooling device having a plurality of cooling zones having upper and lower nozzles and capable of controlling the amount of water injected from the nozzles in the traveling direction of the steel sheet. Specifically, the present invention relates to a cooling method in which cooling water is supplied from the nozzle under specific conditions to the steel plate in the cooling device so that the flatness of the steel plate after cooling is high.

  In manufacturing the steel plate, controlled cooling is performed on the hot-rolled steel plate in order to ensure the mechanical properties required for the steel plate. This controlled cooling is performed by cooling the steel plate in a high temperature state after hot rolling to a predetermined cooling stop temperature at a predetermined cooling rate. In this cooling, the cooling rate and the cooling stop temperature are adjusted by the amount of cooling water, the cooling time, and the conveying speed of the steel plate. In this adjustment, the upper surface side water amount density and the lower surface side water amount density are controlled so that the temperatures of the upper surface and the lower surface of the steel plate during cooling are the same.

  In Patent Document 1, the amount of water supplied from above and below is adjusted so that the temperature of the upper and lower surfaces during cooling is the same according to the temperature from the front end to the tail end of the steel plate calculated in advance from the operating conditions during rolling. A method of changing during transport is disclosed. That is, in Patent Document 1, the relationship between the steel plate temperature and the optimum water and water ratio (the water and water ratio that provides the cooling ability so that the temperature drop on the upper and lower surfaces are the same) is obtained in advance, and according to this relationship, It is described that the amount of water supplied from above and below is changed during the conveyance of the steel sheet according to the steel sheet tip temperature and the steel sheet tail temperature.

  In Patent Document 2, when the upper surface of a steel plate having a thickness of 40 mm or more before finish rolling is cooled by a laminar flow and the lower surface is cooled by spraying, the water volume ratio between the upper and lower surfaces depends on the plate thickness (plate thickness (mm) / 30) A method of cooling a thick steel plate that is cooled within a range of ± 1.0 is disclosed.

  In addition, the water / water ratio in the controlled cooling of the steel sheet after hot rolling is generally set in advance based on the cooling conditions such as the dimensions of the steel sheet to be cooled, the steel sheet temperature at the end of rolling, the cooling water amount, and the cooling stop temperature. Is.

JP 2006-192489 A JP-A-6-142750

  Supply of cooling water in the cooling device is started before the completion of rolling of the steel sheet for the purpose of stabilizing the amount of supplied water. Accordingly, the water / water ratio at this time is set in advance based on the cooling conditions such as the size of the steel plate to be cooled, the steel plate temperature at the end of rolling, the amount of cooling water, and the cooling stop temperature.

  However, due to the influence of air temperature, water temperature, plate thickness, steel type, steel plate temperature, etc., the water / water ratio for producing a steel plate with excellent flatness changes. For this reason, even if the size of the steel plate to be cooled, the steel plate temperature at the end of rolling, and the like are the same, it is preferable to adjust the cooling conditions for each steel plate.

  An object of this invention is to provide the cooling method for manufacturing the steel plate which was excellent in flatness, without shape defects, such as a curvature and a bending, when cooling a steel plate.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, the amount of strain represented by the height difference in the steel sheet after completion of cooling when cooled under the predetermined cooling conditions was measured, and this value was regarded as the actual cooling strain amount, and the ratio of the amount of water and water in the above specified cooling conditions The amount of strain was measured so that the amount of distortion was smaller than the actual cooling strain amount when the condition of (upper and lower water amount ratio = upper surface side cooling water amount density / lower surface side cooling water amount density) was the pre-correction water amount ratio. It has been found that the above problems can be solved by correcting the ratio of the amount of water and water in the cooling of the next steel plate, and the present invention has been completed. More specifically, the present invention provides the following.

[1] In a method for cooling a steel sheet, the hot-rolled hot steel sheet is transported to a cooling device having a plurality of cooling zones partitioned on the entry and exit sides by a draining roll, and cooled from the upper and lower surfaces of the steel sheet.
When continuously cooling a plurality of steel plates, an actual measured value of the strain amount expressed by the height difference in the steel plate surface after cooling when one steel plate of the plurality of steel plates is cooled under a predetermined cooling condition is realized. When the cooling strain amount is set, and the vertical water amount ratio (upper and lower water amount ratio = upper surface side cooling water amount density / lower surface side cooling water amount density) under the predetermined cooling condition is set as the pre-correction upper and lower water amount ratio, the distortion is larger than the actual cooling strain amount. Correcting the water / water ratio to obtain a corrected water / water ratio, and cooling the steel sheet to be cooled next to the one steel sheet under the cooling condition of the corrected water / water ratio after the correction. Cooling method.

[2] The steel sheet cooling method according to claim 1, wherein the corrected water and water ratio is obtained from the pre-correction water and water ratio by the following formula (1).
Corrected water / water ratio = Water / water ratio before correction x (1-α x actual cooling strain) (1)
However, in Formula (1), (alpha) is a constant defined from actual measurement data.

  According to the present invention, the steel plate after cooling is excellent in flatness even if there is an influence of air temperature, water temperature, plate thickness, steel type, steel plate temperature and the like.

  In addition, in the present invention, the vertical flow rate ratio is controlled based on the strain after cooling, regardless of the plate thickness, the steel plate temperature, etc., so excellent flatness is achieved without giving detailed instructions for each plate thickness or surface temperature. Steel plate can be manufactured.

It is a figure which shows a general cooling device. It is a result which shows the state of the steel plate cooled on the cooling conditions before application of this invention. It is a result which shows the state of the steel plate cooled on the cooling conditions after this invention application.

  Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.

  First, an example of the cooling device will be described with reference to FIG. In FIG. 1, an example of the cooling device provided with the some cooling zone partitioned off with the draining roll is shown. The hot steel plate is conveyed through the cooling device, cooled in each cooling zone, and carried out of the cooling device (in the direction of the arrow in the drawing). In FIG. 1, 1 is a hot rolling mill, 2 is a cooling device, 3 is a steel plate, 4 is a table roll, 5 is a draining roll, 6 is an upper surface nozzle, and 7 is a lower surface nozzle.

  The upper surface nozzle 6 is generally a slit nozzle having a rectangular opening cross section in the steel plate width direction, and injects laminar flow cooling water so as to cover the upper surface of the steel plate in the steel plate conveyance direction. The lower surface nozzle 7 is generally a circular tube nozzle and is installed in a large number in the width and length directions of the steel plate, and injects cooling water toward the lower surface side of the steel plate. The draining roll 5 is a roll that cuts the cooling water sprayed from one upper surface nozzle 6 so as not to flow into the next cooling zone, and is installed immediately above the table roll 4. It is sandwiched. Therefore, one cooling zone consists of a space where the table rolls 4 face each other and the draining rolls 5 face each other.

  Although not shown in FIG. 1, a radiation thermometer that measures the temperature of the upper surface of the steel sheet and a fiber optic thermometer that measures the temperature of the lower surface of the steel sheet are installed on the inlet side and the outlet side of the cooling device. Furthermore, a distance meter (not shown) for measuring the height difference in the steel plate surface of the steel plate after completion of cooling is installed on the cooling device outlet side.

  Next, the cooling method of the present invention will be described. In the cooling method of the present invention, cooling is performed under a predetermined cooling condition, and after the cooling is completed, the height difference in the steel sheet surface is measured and used as an actual cooling strain amount, and the vertical water amount ratio (vertical water amount ratio = upper surface side cooling under the predetermined cooling condition). When the condition of (water density / lower surface side cooling water density) is the pre-correction water / water ratio, the water / water ratio is corrected so that the amount of distortion is smaller than the actual cooling distortion.

  The actual cooling strain amount may be an actual measurement value of the strain amount of the steel sheet cooled by adopting predetermined cooling conditions. The predetermined cooling condition may be determined by a general method. In the present invention, it is preferable to determine a predetermined cooling condition based on a cooling condition such as a planned steel sheet size, a steel sheet temperature at the end of rolling, a cooling water amount, and a cooling stop temperature. In the present invention, the strain amount is a strain amount represented by a difference in elevation in the steel plate surface. For example, the difference between the highest point and the lowest point in the steel plate surface is the strain amount. Moreover, since the said distortion arises by the difference in the cooling rate of the upper surface of a steel plate, and a lower surface, a steel plate will warp upward or downward. An upward warp is a shape in which the cross section in the width direction of the steel plate is convex downward, and a downward warp is a shape in which the cross section in the width direction of the steel plate is convex upward. The amount of distortion means the amount of warpage, and in the present invention, the amount of distortion is a negative value if warped, and a positive value if warped.

  The water / water ratio before correction means the water / water ratio in the predetermined cooling condition. In order to enhance the effect of the present invention, when determining the predetermined cooling condition, the condition of the water amount ratio is determined so that the cooling ability can be obtained so that the temperature drop amounts on the upper and lower surfaces are the same. It is preferable.

  The amount of strain after the cooling of the steel sheet cooled under the predetermined cooling condition is measured using a laser distance meter or the like. The distance to the steel plate is measured, and the height difference in the width direction of the steel plate is measured. In particular, the difference in height between the highest point and the lowest point in the width direction at an arbitrary position is defined as the amount of strain in the width direction. Further, a plurality of width direction strain amounts at arbitrary positions in the longitudinal direction of the steel sheet are measured. Of the amount of strain in the width direction at each position, the largest amount of strain in the width direction in the steel sheet is defined as the maximum amount of strain in the width direction. Here, it is preferable to measure the amount of strain in the width direction continuously over the whole. Moreover, let the value which averaged the width direction distortion amount in each width direction in the arbitrary positions of the longitudinal direction of a steel plate over the steel plate full length be a longitudinal direction average width direction distortion amount. The measurement of the strain amount is preferably performed near the outlet side of the cooling device because the actual cooling strain amount needs to be reflected in the cooling conditions after the subsequent steel plate.

  As described above, the strain amount of the steel sheet after completion of cooling is measured, and the vertical water amount ratio (vertical water amount ratio = upper surface side cooling water amount density / lower surface side cooling water amount density) is corrected so as to reduce the strain amount. For example, when the steel plate is warped, the cooling on the lower side of the steel plate is too stronger than the upper side, and therefore the correction is made so that the water amount ratio is larger. On the contrary, when the steel plate is warped, the cooling on the upper side of the steel plate is too strong than the lower side, and therefore the correction is made so that the ratio of the amount of water to water is smaller. The corrected water and sewage ratio may be corrected by adding or subtracting the correction amount that seems to be appropriate based on past results to the pre-correction water and sewage ratio according to the upper and lower warpage of the steel sheet after cooling. It may be determined by a method.

  The steel sheet is cooled at a plurality of water / water ratios, and the amount of strain after cooling is measured. Plotting the horizontal axis as the strain amount and the vertical axis as the water amount ratio, the slope of the straight line when approximated by a straight line is α. Here, α is a correction coefficient for the water / water ratio by the amount of distortion. Then, the upper and lower water ratio is corrected by the following equation (1).

Corrected water / water ratio = Water / water ratio before correction x (1-α x actual cooling strain) (1)
Further, the next steel plate is cooled at the corrected water / water ratio, and the correction of the water / water ratio is repeated if the amount of distortion of the steel plate after cooling is not sufficiently reduced.

  Further, as the amount of strain, any of the maximum width direction strain amount, the longitudinal direction average width direction strain amount, etc. may be used. However, since the width direction strain of the steel sheet is generally maximized at the tip of the steel sheet. It is most convenient and effective to use the maximum amount of strain in the width direction (generally the same as the amount of strain in the width direction at the tip of the steel plate in many cases).

  As described above, according to the present invention, in order to determine the conditions for reducing the strain amount based on the actual cooling strain amount, various effects such as air temperature, water temperature, sheet thickness, steel type, steel plate temperature are considered. Will be.

  In addition, in the present invention, the vertical flow rate ratio is controlled based on the strain after cooling, regardless of the plate thickness, the steel plate temperature, etc., so excellent flatness is achieved without giving detailed instructions for each plate thickness or surface temperature. Steel plate can be manufactured.

  By continuously deriving the corrected water and water ratio by the above method from the state of the steel plate that has been cooled one before, a steel plate having excellent flatness can be obtained even if the temperature or the like changes. “Continuously” means that the corrected water and water ratio may be derived from the state of the steel plate that has been cooled one time before, or every few or several tens of times before cooling. The corrected water and water ratio may be derived from the state of the steel sheet. In particular, when the change in temperature or the like is small, it is not necessary to derive the corrected water and water ratio every time.

  In the cooling method of the present invention, for example, the cooling device shown in FIG. 1 receives the strain amount measuring unit for measuring the strain amount of the steel sheet after cooling, and the measurement result in the strain amount measuring unit, This can be implemented by providing an electronic computer that calculates the water amount ratio and a water and water ratio control unit that controls the water and water ratio based on the result calculated by the computer.

  Based on the above results of the steel plate of 25.8 mm x 2206 mm x 8016 mm, based on the above results, cooling start temperature (740 ° C), cooling water amount (57.3 ton / min), cooling stop temperature (650 ° C) The water / water ratio of the steel plate considered to be optimal was 0.67.

  When controlled cooling of the steel sheet after hot rolling was performed under the above cooling conditions, it was warped and the maximum width direction strain amount was −9.0 mm (see FIG. 2). Hereinafter, the present invention was carried out with this strain amount as the actual cooling strain amount. FIG. 2 shows the strain distribution in the steel sheet measured using a laser displacement meter.

  From the measurement data of the water and water ratio and the maximum width direction strain until then, α in the formula (1) was determined to be 0.018. In the above formula (1), α = 0.018 was obtained to obtain the following formula (2).

Water / water ratio after correction = Water / water ratio before correction × (1−0.018 × actual cooling strain amount) (2)
Substituting 0.67 into the uncorrected water / water ratio before correction and substituting −9.0 into the actual cooling strain into the above equation (2), a corrected water / water ratio of 0.78 was obtained. When controlled cooling was performed at the same cooling start temperature and cooling stop temperature on a thick steel plate of the same size at this water / water ratio, the maximum strain in the width direction was 0.9 mm (in the same manner as in FIG. 2). FIG. 3 measured).

  As described above, it has been found that the amount of strain is reduced by correcting the water and water ratio based on the strain amount of the steel plate after cooling, that is, the steel plate has a high flatness.

DESCRIPTION OF SYMBOLS 1 Hot rolling mill 2 Cooling device 3 Steel plate 4 Table roll 5 Draining roll 6 Upper surface nozzle 7 Lower surface nozzle

Claims (2)

In the method of cooling a steel plate, the hot-rolled hot steel plate is conveyed to a cooling device having a plurality of cooling zones partitioned on the entry and exit sides by a draining roll, and cooled from the upper and lower surfaces of the steel plate.
When continuously cooling a plurality of steel plates, an actual measured value of the strain amount expressed by the height difference in the steel plate surface after cooling when one steel plate of the plurality of steel plates is cooled under a predetermined cooling condition is realized. When the cooling strain amount is set, and the vertical water amount ratio (upper and lower water amount ratio = upper surface side cooling water amount density / lower surface side cooling water amount density) under the predetermined cooling condition is set as the pre-correction upper and lower water amount ratio, the distortion is larger than the actual cooling strain amount. Correcting the water / water ratio to obtain a corrected water / water ratio, and cooling the steel sheet to be cooled next to the one steel sheet under the cooling condition of the corrected water / water ratio after the correction. Cooling method. The steel sheet cooling method according to claim 1, wherein the corrected water and water ratio is obtained from the pre-correction water and water ratio by the following formula (1).
Corrected water / water ratio = Water / water ratio before correction x (1-α x actual cooling strain) (1)
However, in Formula (1), (alpha) is a constant defined from actual measurement data.

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