JP4648804B2 - Cooling method for high temperature steel sheet - Google Patents

Description

  The present invention relates to a method for cooling a hot-rolled high-temperature steel sheet, and more particularly to a cooling method for performing uniform cooling in the sheet thickness direction of the steel sheet.

In recent years, as a manufacturing process for thick steel plates, on-line controlled cooling is performed in which a high-temperature steel plate immediately after hot rolling is water-cooled by a cooling device provided on the rear surface of the rolling mill. According to this method, high strength and high toughness can be imparted to the steel sheet, the alloy elements can be reduced and heat treatment can be omitted, and the cost can be reduced.
However, in the continuous cooling usually performed in the water cooling of the steel sheet, the cooling rate is different between the surface layer part and the center part in the steel sheet thickness direction, and the cooling rate of the steel sheet surface layer part is compared with the cooling rate of the sheet thickness center part. Since it is large, there is a temperature difference between the surface layer portion and the central portion, which causes a problem.
For example, because the surface layer part is compressed and tensile residual stress is generated inside, deformation occurs during processing such as deformation of the steel sheet, cutting and welding of the steel sheet, and transformation of the surface layer part is compared to the center part. As a result, non-uniform materials such as differences in mechanical properties such as strength and hardness between the surface layer portion and the center portion are caused.

In order to solve these problems, Patent Document 1 discloses a method for manufacturing a steel sheet with a small residual stress. When manufacturing a steel sheet by performing water cooling after hot rolling, water cooling / air cooling is performed multiple times as a single process. Proposed so-called intermittent cooling, in which the air cooling process is repeated to cool to a predetermined water cooling end temperature.
Further, in Patent Document 2, in order to uniformly cool a high-temperature steel sheet without cooling, the cooling zone is divided into a plurality of cooling blocks in the steel sheet transfer direction, and the cooling of the steel sheet in each cooling block by cooling water is nucleate boiling. A so-called intermittent cooling method is proposed in which the cooling rate of the steel sheet is controlled by controlling the cooling rate of the steel sheet by performing on-off control in units of blocks or a plurality of cooling blocks.
Further, in Patent Document 3, in order to produce a high-tensile steel plate having a small material difference in the plate thickness direction, hot rolling is finished at (Ar ₃ −50) ° C. or higher, and the steel plate surface temperature is (Ar ₃ −50). ) Cooling at a cooling rate of the steel sheet surface of 20 ° C./s or more and 50 ° C./s or less from a temperature range of 0 ° C. or more to a temperature range of ((Ar ₃ −300) ° C. to (Ar ₃ −150) ° C. A method of cooling to an average steel plate temperature of 650 ° C. at an average cooling rate of 12 ° C./s or more is proposed.

JP-A-4-371519 Japanese Patent No. 3287254 JP 2000-119746 A

However, in the method of Patent Document 1, the cooling rate of the surface layer portion decreases due to intermittent cooling in which air cooling and water cooling are alternately repeated, and the temperature difference between the surface layer portion and the central portion is reduced, but the influence on the cooling rate of the central portion is not affected. Not considered. When the cooling rate of the surface layer is simply reduced, the cooling rate of the steel sheet as a whole is lowered, and the influence on productivity is inevitable. In addition, simple intermittent cooling cannot control the cooling rate of the surface layer portion, that is, the material of the surface layer portion.
Further, in the method of Patent Document 2, intermittent cooling is performed by turning on and off each cooling block, and although the temperature difference between the surface layer and the central part can be reduced, the influence on the cooling rate of the central part is not taken into consideration. Similarly, if the temperature difference is reduced, the cooling rate of the steel sheet as a whole is lowered, and the influence on the material and productivity is inevitable.
Further, in the technique of this document, the water density of the cooling water for each block is set according to the temperature of the steel plate so that the nucleate boiling state is maintained over the entire cooling surface. It does not consider the viewpoint.
In the method of Patent Document 3, the material difference in the sheet thickness direction is reduced by changing the cooling rate of the steel sheet surface in the cooling process between the front stage and the rear stage, but the temperature difference between the surface layer part and the center part still exists, The difference has not been fully resolved.

In this way, by performing intermittent cooling, the temperature difference between the surface layer and the center and the difference in cooling rate are reduced, and the difference in material and residual stress resulting from this is reduced. Although it is possible, if the difference in cooling rate is made excessively small, the cooling rate of the central part is affected and the cooling rate of the entire steel sheet is suppressed. Accordingly, there is a problem that the steel plate material and productivity cannot be secured.
In view of the above-described conventional state, the present invention can reduce the temperature difference in the plate thickness direction of the steel plate while ensuring the cooling rate of the central portion when cooling the high temperature steel plate, and obtain uniform cooling and material. It is an object of the present invention to provide a cooling control method that can be used.

The present invention has been made to solve the above problems, and the gist of the present invention is as follows.
(1) A method of cooling a hot-rolled high-temperature steel sheet, which sets a cooling zone necessary for cooling the steel sheet in a continuous cooling pattern and the water density of each cooling zone, and cools the high-temperature steel sheet. In this case, a management temperature range that is a temperature range in which the cooling rate in the central portion and the surface layer portion of the steel sheet should be managed, and a cooling rate lower limit value and a cooling rate upper limit value in the central portion of the steel sheet in this management temperature range, respectively. Set,
In each cooling zone in which the steel sheet falls within this control temperature range, it becomes the control temperature range when cooling with the water density set in the continuous cooling pattern based on the steel sheet temperature history up to the cooling zone before the cooling zone. Calculate the cooling rate of the center and surface layer of the steel plate between the cooling zone and the cooling zone,
When the calculated cooling rate of the central portion is equal to or higher than the set cooling rate lower limit value of the central portion, and the calculated cooling rate of the surface layer portion is equal to or lower than the cooling rate upper limit value of the surface layer portion, the cooling zone The water density of the water is set in the continuous cooling pattern,
The calculated cooling rate of the central portion of the steel sheet is less than the set cooling rate lower limit value of the central portion, or the calculated cooling rate of the surface layer portion of the steel sheet is the set upper limit value of the surface layer cooling rate. If it exceeds
The cooling zone and the intermittent cooling pattern in which the water density is zero or the next cooling zone that is smaller than the cooling zone are combined , and the cooling rate of the central part of the steel sheet is equal to or higher than the cooling rate lower limit value of the set central part. There, and the cooling rate of the surface layer portion of the hot steel plate, characterized in that cooling by setting those said cooling zone and water density of the next cooling zone cooling rate upper limit that Do the following surface layer portion described above set Cooling method.

(2) Regarding the water density of the cooling zone and the next cooling zone, the cooling rate at the center of the steel sheet is equal to or higher than the set cooling rate lower limit of the center, and the cooling rate of the surface layer is the setting. If a solution that is lower than the upper limit of the cooling rate of the surface layer portion is not obtained, the cooling zone and the next cooling zone are further sequentially switched to the downstream cooling zone of the next cooling zone. combination, the cooling rate lower limit or more central cooling rate of the center portion of the steel plate has the set, and those the cooling cooling rate of the surface layer portion of the steel sheet that Do the following cooling speed upper limit of the surface layer portion which is the setting The method for cooling a high-temperature steel sheet according to (1), wherein water density in the zone, the next cooling zone, and the cooling zone downstream of the next cooling zone is set and cooled.

  According to the method of the present invention, in the cooling of the high-temperature steel plate, the temperature difference between the surface layer portion and the central portion of the steel plate can be reduced while maintaining the cooling rate of the whole steel plate, that is, the average cooling rate, so While securing the material, it is possible to suppress the hardening of the surface layer portion and efficiently produce a steel plate having a uniform material in the thickness direction.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 7 is a schematic diagram showing an example of a cooling facility for carrying out the present invention.
On the rear surface of the rolling mill 1, a pair of table rolls 2 and draining rolls 3 are arranged in the traveling direction of the steel plate 7 (arrow →) as a pair in the vertical direction, and in the gap in the traveling direction of the table rolls 2 and draining rolls 3. A cooling device 4 is provided at the top and bottom, and a plurality of cooling zones 9 are formed. In this example, the cooling device 4 includes a spray nozzle 6 attached to the cooling water header 5 and a flow rate adjusting valve 7 for adjusting the cooling water amount to the water supply header.
The cooling water is supplied from a water supply pipe (not shown) to the cooling water header 5 through the flow rate adjusting valve 7 and sprayed from the spray nozzle 6 onto the upper and lower surfaces of the steel plate 8 to cool the steel plate. Needless to say, the cooling device is not limited to the spray system, and the cooling zone can be configured by a single or a combination of a slit nozzle and a pipe nozzle.

1 and 2 are diagrams showing a flow for performing cooling setting in the cooling method of the present invention.
For the cooling of the high-temperature steel sheet of the present invention, first, (i) the cooling conditions necessary for the high-temperature steel sheet after rolling, that is, the cooling zone i to be used (i = 1 to N), and the water amount density Wi ( m ³ / m ² .min). This is to set the cooling conditions such as the number of water cooling zones and the water density of each water cooling zone on the premise that continuous cooling (hereinafter also referred to as a continuous cooling pattern) is performed, as in normal cooling control. Yes, the finishing rolling temperature, the required cooling rate (center), the cooling start temperature, the cooling stop temperature, and the plate thickness and cooling of the target steel plate, which are set in advance to ensure the predetermined material and productivity at the center of the steel plate It is calculated and set based on measured values or calculated values such as water temperature.

In the present invention, further, (ii) from the viewpoint of ensuring uniformity in the thickness direction of the steel sheet, a temperature range in which it is determined that management of a temperature difference or a cooling rate difference between the center portion and the surface layer portion is necessary. Set the control temperature range of the steel sheet. The control temperature range may be set using the temperature of the center or surface layer of the steel sheet or the average temperature as an index, but in the following description, it is assumed that the temperature of the surface layer is set as an index. That is, the management start temperature X (° C.) and the management end temperature Y (° C.) of the surface layer portion are set. Furthermore, a cooling rate lower limit value α (° C./sec) of the central portion between the X and Y temperatures and a cooling rate upper limit value β (° C./sec) of the surface layer portion are set. X, Y and α, β are considered in the temperature range in consideration of the difference in material such as hardness due to the temperature difference between the central portion and the surface layer portion when cooling at each cooling rate, and the difference in residual stress, A temperature at which these differences are within an allowable range or a cooling rate is set. These cooling rates can be set based on performance data in a conventional operation or simulation of materials and cooling rates, and X and Y may have a width.
In the present invention, the surface layer portion means a range from the surface of the plate thickness to 1 mm.

  After rolling, cooling is started at a water density set on the premise of a continuous cooling pattern, and the cooling history up to that point, that is, the temperature of the surface layer part of the steel sheet is controlled to the above-described management temperature of the surface layer part by cooling to the previous cooling zone ( X) After the temperature is reached, the water density is set by the following procedure for each cooling zone thereafter. Hereinafter, this cooling zone will be described as the N cooling zone or later, for example.

First, 1) Based on the cooling history until the steel sheet reaches the N water cooling zone, the water density W _N (m ³ / m ² · min) of the water cooling zone set on the premise of the continuous cooling pattern set in (i) above. The cooling rate α ′ (° C./sec) at the center when cooled and the cooling rate β ′ (° C./sec) at the surface layer are calculated and estimated.
Next, 2) whether the calculated cooling rate α ′ of the central part is equal to or higher than the set cooling rate lower limit value α of the central part, and the calculated cooling rate β ′ of the surface layer part is the set surface layer part. It is determined whether or not the cooling rate upper limit value β is equal to or less than that, that is, whether α ′ ≧ α and β ′ ≦ β.
That is, when α ′ <α, a predetermined material cannot be obtained, and when β ′> β, the material of the surface layer portion is deteriorated or the material in the thickness direction is not uniform and the steel plate is deformed. To do.

Next, 3) the calculated cooling rates α ′ and β ′ of the central portion and the surface layer portion are respectively in the relationship between the set lower limit value α of the central portion cooling rate and the upper cooling rate value β of the surface layer portion. When the relationship 2) is satisfied, the N zone is set to be cooled at the water density W _N (m ³ / m ² · min) set in the continuous cooling pattern of (i). Thereafter, returning to 1), the cooling rate and water density of the next (N + 1) cooling zone are calculated and set.

If the cooling rates α ′ and β ′ of the central part and the surface layer calculated in 4) and 2) are the lower limit value α of the cooling rate of the central part and the upper limit of the cooling rate β of the surface part as set in 2) above, When the relationship is not satisfied, the cooling zone and the next cooling zone are combined, and the average cooling rates α ′ and β of the center portion and the surface layer portion of the steel plate in the cooling including the cooling zone and the next cooling zone are combined. In the relationship between the central portion cooling rate lower limit value α set in i) and the surface layer cooling rate upper limit value β, α ′ ≧ α, β ′ ≦ β so that the cooling zone and the next Surface layer cooling rate controlled cooling is performed to set the water density in the cooling zone.
As described later, this surface layer cooling rate controlled cooling is performed by combining the cooling zone and the next cooling zone or a cooling zone downstream of the next cooling zone, and the center of the steel plate in these cooling zones. In relation to the cooling rate lower limit value α of the central part and the cooling rate upper limit value β of the surface layer part, the average cooling rates α ′ and β ′ of the part and the surface layer part are set in i), α ′ ≧ α, β ′ ≦ β It goes without saying that the water density of the cooling zone and the next cooling zone, or further downstream cooling zone can be set so that

Although it does not specifically limit as a surface layer cooling rate control cooling method, It is also preferable to employ | adopt an intermittent cooling pattern which is illustrated below. That is, a cooling pattern (hereinafter referred to as intermittent cooling pattern I) is set so that the subsequent N + 1 cooling zone, that is, the next N + 1 cooling zone is an air cooling zone (water density zero), and 5) the next N + 1 cooling zone is air cooled. Considering the recuperation of the steel sheet when the zone is made, the average cooling rate α ′ _I (° C./sec), β ′ _I of the central portion and the surface layer portion in the cooling including the N cooling zone and the next N + 1 cooling zone (° C./sec) satisfies α ′ _I , ≧ α, and β ′ _I ≦ β in the relationship between the lower limit value α of the cooling rate at the center portion set in i) and the upper cooling rate value β of the surface layer portion. Thus, the average cooling rates α ′ _I (° C./sec) and β ′ _I (° C./sec) of the central portion and the surface layer portion are set.

Next, 6) the water density W _NI (m ³ / m ² · min) in the N zone for obtaining the above-described cooling rates α ′ _I and β ′ _I is calculated.
7) It is determined whether the obtained water density W _NI is within the range of the water density W _Nc (m ³ / m ² · min) of the cooling facility capacity of the N cooling zone.

8) When the water density W _NI is within the water density range of the cooling facility capacity of the N water cooling zone, the water density of the N zone is set to the W _NI , and the next N + 1 cooling zone is the air cooling zone. The intermittent cooling pattern I is set to (water density W _{N + 1I} = 0).
Thereafter, returning to (1), the above procedure is repeated, and the cooling rate of the next (N + 2) cooling zone is calculated and set in one of the N cooling zones.

If the water density W _NI obtained in 9) and 7) exceeds the water density range W _Nc of the cooling facility capacity of the N water cooling zone, the N + 1 cooling zone next to the N cooling zone is not set as the air cooling zone. The N + 1 cooling zone is cooled as a water density that includes at least the water density (W _NI -W _Nc ) (m ³ / m ² · min) in excess of the cooling facility capacity in the N cooling zone (also described as a weak cooling zone) Select a cooling pattern (hereinafter referred to as intermittent cooling pattern II).

10) Considering the recuperation of the steel sheet in the N + 1 cooling zone (which becomes the weak cooling zone), the average cooling rate α ′ _II of the central portion and the surface layer portion in the cooling including the N cooling zone and the next N + 1 cooling zone (° C./sec), β ′ _II (° C./sec) is the relationship between the cooling rate lower limit value α of the central part and the cooling rate upper limit value β of the surface layer set in i), α ′ _II ≧ α, and The average cooling rates α ′ _II and β ′ _II of the central part and the surface layer part are set so that β ′ _II ≦ β.

Next, 11) water density W _{N + 1II} (m ³ / m ² · min) in the N + 1 cooling zone for obtaining the cooling rates α ′ _II and β ′ _II is calculated. At this time, the water density in the N cooling zone is W _NII (m ³ / m ² · min) = (W _Nc ).
The water density W _{N + 1II} in the N + 1 cooling zone is not _{limited to} the water density exceeding the equipment capacity of the N cooling zone, and the water density ΔW (m ³ / m Needless to say, ² min) can be added. That is, W _{N + 1II} = ((W _NI −W _Nc ) + ΔW)), where ΔW includes 0.

12) The above water density W _NII = W _Nc , W _{N + 1II} = ((W _NI −W _Nc ) + ΔW)) is set as the water density of the N cooling zone and the N + 1 cooling zone.
Thereafter, returning to 1), in one of the N cooling zones, 1) to 12) are repeated in the same manner for the next N + 2 cooling zone, the cooling rate of the cooling zone is calculated, and the water density is set.

In the above 1) to 12), when the cooling rates α ′, β ′, α ′ _I , β ′ _I , α ′ _II , β ′ _II satisfying the above relationship for predetermined α, β are not obtained, A cooling pattern in which the cooling zone and the next cooling zone are further combined with the cooling zone downstream of the next cooling zone in order, and similarly α ′, β ′, α ′ _I, β ′ _I, α ′ _{If II and} β ′ _II are obtained and the solution is still not obtained, the water amount density Wi set in the continuous cooling pattern is set as the water amount density in the cooling zone.

  In this way, the water density in the cooling zone is sequentially determined by the procedure from 1) to 12) until the temperature of the surface layer as the management temperature of the steel sheet reaches the management end temperature (Y) ° C. After the temperature reaches the management end temperature (Y) ° C., each subsequent cooling zone is set to the water density Wi set in the initial continuous cooling pattern and cooled to the cooling end temperature.

  As described above, in order to maintain the productivity of steel sheet cooling and to reduce the temperature difference between the surface layer portion and the center portion of the steel plate, the material in the thickness direction such as the residual stress difference, and the shape deviation, Set the control temperature range where the cooling rate should be managed, and the cooling rate of the surface layer and center part within this control temperature range, and in each cooling zone where the steel sheet is within this control temperature range, the cooling before the cooling zone Based on the cooling history up to the zone, when cooling with the water density set in the continuous cooling pattern in the cooling zone, the cooling rate of the central part and the surface layer part from the cooling zone that is the management temperature range to the cooling zone The calculated cooling rate of the central part is equal to or higher than the lower limit of the cooling rate of the central part set above, and the calculated cooling rate of the surface layer is equal to or lower than the upper limit of the cooling speed of the surface layer set above. In this case, the water volume density of the cooling zone remains set in the continuous cooling pattern, and the calculated cooling rate of the central portion is less than the lower limit value of the central cooling rate set above or the calculated cooling of the surface layer portion. When the speed exceeds the set cooling rate upper limit of the surface layer portion, the cooling zone and the next cooling zone are combined, and the cooling rate at the center of the steel sheet is equal to or higher than the set cooling rate lower limit of the center. In addition, surface layer cooling rate controlled cooling is performed in which the water density of the cooling zone and the next cooling zone is set and cooled so that the cooling rate of the surface layer portion is equal to or less than the set upper cooling rate value of the surface layer portion.

  In this surface layer cooling rate control cooling, preferably, the cooling zone and the next cooling zone in which the water density is zero or smaller than the cooling zone, or the cooling zone and the next cooling zone are combined. In addition, a cooling pattern in which cooling zones further downstream of the next cooling zone are sequentially combined, and the cooling rate at the center of the steel sheet when cooled as such a cooling pattern is the lower limit of the cooling rate at the set center. The cooling zone in the cooling pattern, the water density in the next cooling zone, or further, the next cooling zone, so that the cooling rate of the surface layer portion is equal to or greater than the upper limit cooling rate of the set surface layer portion. Set the water density in the cooling zone downstream of.

  By doing this, the cooling rate at the center can be set by a continuous cooling pattern, in other words, while maintaining the overall cooling rate, the difference in cooling rate between the center and the surface layer can be reduced, and material properties and production can be reduced. It is possible to obtain a steel sheet having a small material difference between the surface layer portion and the central portion and a small residual stress difference without impairing the properties.

In the present invention, the intermittent cooling pattern is distinguished from the continuous cooling pattern. In all cooling zones where the continuous cooling pattern is used for cooling, a water amount density that is substantially constant or gradually decreases is set. whereas being intermittent cooling pattern, often water density difference between adjacent cooling zone are largely different, for example, 1 / 5-1 / 10 of the water flow rate before and after the cooling zone (m ³ / m ² · min) or less water density is often set.

  Next, FIGS. 3 and 4 are diagrams showing an example of setting the water density in each cooling zone in the cooling control method of the present invention. FIG. 3 (a) shows the whole cooling, and FIGS. 3 (b) and (c). ) And FIGS. 4A and 4B show setting examples of the water density for each cooling zone. 4A and 4B show setting examples of water density in other cooling zones following FIGS. 3B and 3C.

  As described above, from the viewpoint of ensuring the material and productivity of the steel plate, first, the cooling pattern for the entire steel plate is set in FIG. That is, a cooling zone necessary for cooling in a continuous cooling pattern from the cooling start temperature (900 ° C.) to the cooling end temperature (200 ° C.) and the water density of each cooling zone are set. 3 and 4, the cooling zones No. 1 to No. No. 19 is used. The water density after the 13th zone is no. 1 to No. It is set smaller than up to 12 zones.

  In addition, the water volume density of these cooling zones and each water cooling zone is the predetermined material of the steel plate, the preset finishing rolling temperature, the required cooling rate (center part), the cooling start temperature, the cooling stop temperature, and the target steel plate. Calculated and set based on the plate thickness, cooling water temperature, and the like.

Furthermore, the management start temperature X (° C.) and the management end temperature Y (° C.) of the surface layer where it is determined that the temperature difference between the center and the surface layer should be managed, and cooling of the center between the X and Y temperatures A speed lower limit value α (° C./sec) and a surface layer cooling rate upper limit value β (° C./sec) are set.
As described above, X, Y, α, and β are within the allowable range of material differences mainly including residual stress difference and hardness difference caused by temperature difference due to cooling rate difference between the center part and the surface layer part. Is set according to the thickness, composition, cooling conditions, and the like of the steel sheet.

As shown in (b) of FIG. 1-No. Since the temperature of the surface layer portion of the steel sheet does not reach the control start temperature X until the 4th cooling zone, the water volume density in these cooling zones is the water volume density W _1-4 set in the continuous cooling pattern in FIG. Set to.

No. at which the temperature of the surface layer part becomes the management start temperature X For the 5th and subsequent cooling zones, the water density is set according to the flow shown in 1) to 12) of FIGS. 1 and 2 so that the cooling rate of the central portion and the surface layer satisfies the predetermined condition.
No. No. 4 steel plate after passing through the cooling zone. The cooling rates α ′ and β ′ of the central part and the surface layer part are calculated and estimated when cooling is performed with the water density W ₅ set in the above-described continuous cooling pattern for the five cooling zones, and this is expressed as α ′ ≧ α, β ′ ≦ If β, no. The water density in the 5 cooling zone is set to the water density W ₅ set in the continuous cooling pattern. However, in the case of FIG. 3B, the cooling rate of the central part and the surface layer part is the above relationship α ′. Since ≧ α and β ′ ≦ β are not satisfied, intermittent cooling is performed.

That is, no. 5 Cooling zone is water-cooled. An intermittent cooling pattern I in which six cooling zones are air-cooled, and the average cooling rates α ′ _I and β ′ _I in both the central and surface cooling zones are α ′ _I ≧ α and β ′ _I ≦ β No. _{'I, beta'} to calculate the _I, the average cooling rate alpha _{'I, beta'} to the _I No. 6 when the cooling zone is air-cooled (W _6I = 0). Calculate the water density W _5I of the 5 cooling zones and set the water density.

In addition, No. set as the intermittent cooling pattern I. If the water density W _5I of the 5 cooling zone exceeds the cooling facility capacity W _5C of the cooling zone, as will be described later, the next cooling zone in which the excess (W _5I -W _5C ) is first air-cooled, that is, No . The intermittent cooling pattern II (weak cooling zone) set as at least the water density W _6II of the six cooling zones.

FIG. 7, no. The example which sets the water quantity density in 8 cooling zones is shown. No. Steel plate temperature obtained by cooling history up to 6 cooling zones, No. 6 based on the temperature of the center part and the surface layer part of the steel sheet after cooling in the 6 cooling zone. The cooling rate of the center portion and the surface layer portion when cooling with the water density W ₇ set in the continuous cooling pattern in the 7 cooling zones (that is, the average cooling rate of the No. 5 to No. 7 cooling zones) α ′ and β ′ are calculated and estimated. If α ′ ≧ α and β ′ ≦ β, No. The water density in the 7 cooling zone is set to the water density W ₇ set in the continuous cooling pattern. However, in the case of FIG. 3C as well, as in the case of FIG. The cooling rate of the part does not satisfy the above relationships α ′ ≧ α and β ′ ≦ β. The intermittent cooling pattern I is performed with the 8 cooling zone as an air cooling zone.

  No. in the intermittent cooling pattern I in FIG. 7, no. The water density of the 8 cooling zone is set as described in No. 1 above. 5, no. Since it is the same as the 6 cooling zone setting method, the description is omitted to avoid duplication.

FIG. 9, no. The example which sets the water amount density of 10 cooling zones is shown. No. Steel plate temperature obtained by cooling history up to 8 cooling zones, No. 8 based on the temperature of the center part and the surface layer part of the steel sheet after cooling in the cooling zone. Cooling rate of the center part and the surface layer part when cooling with the water density W ₉ set in the continuous cooling pattern in the 9 cooling zone (meaning the average cooling rate from No. 5 to No. 9 cooling zone) α ', Β' is calculated and estimated. If α ′ ≧ α and β ′ ≦ β, then No. The water density in the 7 cooling zone is set to the water density W ₇ set in the continuous cooling pattern. However, in the case of FIG. 4A as well, as in the case of FIG. The cooling rate of the part does not satisfy the above relationships α ′ ≧ α and β ′ ≦ β. The intermittent cooling pattern I with the 10 cooling zone as the air cooling zone is performed.

  No. in the intermittent cooling pattern I in FIG. 9, no. The setting of the water amount density in the 10 cooling zone is as described in No. 1 above. 7, no. Since it is the same as the setting method of 8 cooling zones, description is abbreviate | omitted in order to avoid duplication.

By the way, as shown in FIG. 9, no. In the intermittent cooling pattern in the 10 cooling zone, no. The water density W _{9I in the} 9 cooling zone is considerably large. In this example, no. It is assumed that the water density W _9I of the 9 cooling zones is within the equipment capacity.
However, as described above, this water density W _9I is No. When the water capacity density W _9c of the cooling facility capacity of the 9 cooling zone is exceeded, as shown in FIG. 5, the excess (W9 _I -W _9c ) was initially air-cooled. The intermittent cooling pattern II is a weak cooling zone set at least as a water density of 10. That is, FIG. 5 is a diagram showing a setting example of the water density of the intermittent cooling pattern II provided with the weak cooling zone.

In this way, when the intermittent cooling pattern II is set, no. 9, no. 10, respectively in the cooling zone water density _{W 9II (= W 9c),} it means the average cooling rate until the average cooling rate (Nanba5～nanba10 cooling zone of the central portion and surface layer portion of the case of cooling with _{W 10II} become) α _{'II, β' II is, α 'II ≧ α, β} ' so as to satisfy the relation of _II ≦ _β, No. 10 the amount of water density _{W 10II} cooling zone, for example, as _{W 10II} added water density [Delta] w besides excess _{= ((W9 I -W 9c)} + Δw), to adjust, to set. Note that ΔW may be 0 as described above.

As shown in FIG. The temperature of the surface layer at the time of leaving the 10 cooling zone is in the vicinity of the management end temperature Y. Therefore, after No. 11 cooling zone, it cools with the water density _W12-19 set with the continuous cooling pattern.
As described above, the cooling rates α ′, β ′, α ′ _I , β ′ _I , α ′ _II , β ′ _II satisfying the above relationship with respect to predetermined α and β in the control temperature range of the surface layer portion as described above. Is not obtained, a cooling pattern in which the cooling zone and the next cooling zone are further sequentially combined with a cooling zone downstream of the next cooling zone, and similarly α ′, β ′, α ′ _I , β If ' _I , α' _II and β ' _II are obtained and the solution is still not obtained, the water amount density Wi set in the continuous cooling pattern is set as the water amount density in the cooling zone.
These water density densities can be set by simulation or the like using an online computer provided in an online cooling device.

Hereinafter, the present invention will be described in more detail with reference to examples.
A simulation was performed on an as-rolled steel plate, which is problematic because of the difference in material between the surface layer and the center of the steel plate.
The plate thickness is 85 mm, the cooling start temperature is 900 ° C., the cooling stop temperature is 550 ° C., and when the conventional cooling is performed using six cooling zones, the management start temperature of the surface layer is 850 ° C., and the management end temperature is 550 ° C. As described above, the cooling rate of the surface layer portion and the center portion of the steel plate when the intermittent cooling is performed by dividing the six cooling zones into 22 cooling zones and setting the water density for each cooling zone of the present invention. Each was obtained by simulation.

The cooling history is shown in FIG. (A) shows the case of the cooling method which performed the conventional continuous cooling, (b) shows the case of the cooling method which performed the intermittent cooling of this invention.
As can be seen from FIG. 6, in the conventional method, the average cooling rate of the surface layer portion (average of No. 1 to 6 zones) is 44 ° C./sec and the average cooling rate of the central portion is 6 ° C./sec. In the method of the present invention, the average cooling rate of the surface layer portion (average of No. 1 to 22 zones) is 25 ° C./sec, and the average cooling rate of the central portion is 5 ° C./sec. According to this, it can be seen that the cooling rate at the surface layer is significantly reduced as compared with the conventional cooling method, while the cooling rate at the center is almost the same.
Therefore, according to the cooling method of the present invention, the material at the central portion of the plate thickness is sufficiently secured, the hardening of the surface layer is suppressed, the material has a more homogeneous material, and the residual stress difference is reduced, so that it can be reduced during processing. It can be seen that a steel plate with little deformation can be obtained.

  According to the method of the present invention, the cooling rate of the surface layer during cooling is greatly reduced, while the cooling rate of the central part is heat conduction limited, so the cooling rate is hardly affected, The material can be secured. Therefore, it is possible to obtain a steel plate having an excellent material and shape in the plate thickness direction without impairing the material and productivity.

It is a flowchart which shows the cooling method of this invention. It is a flowchart which shows the cooling method of this invention following FIG. It is a figure which shows the setting of the water density of each cooling zone in the cooling method of this invention, (a) shows the whole cooling, (b), (c) shows the setting example in each cooling zone. It is a figure which shows the setting of the water amount density of each cooling zone in the cooling method of this invention, (a), (b) shows the example of a setting in the cooling zone following FIG.3 (c). It is a figure which shows the setting of the water amount density of each cooling zone by the cooling control method of this invention, and shows the other example of a setting of Fig.4 (a). It is a figure which shows the cooling history in the intermittent cooling in the Example of this invention, (a) shows the conventional continuous cooling method, (b) shows the case by the cooling method of this invention, respectively. It is a schematic diagram showing an example of cooling equipment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling machine 2 Table roll 3 Draining roll 4 Cooling device 5 Cooling water header 6 Spray nozzle 7 Flow control valve 8 Steel plate 9 Cooling zone

Claims (2)

A method of cooling a hot-rolled high-temperature steel sheet, setting a cooling zone and water density of each cooling zone necessary for cooling the steel sheet in a continuous cooling pattern, and cooling a high-temperature steel sheet, Set the management temperature range that is the temperature range that should manage the cooling rate in the central part and the surface layer part of the steel sheet, the cooling rate lower limit value of the central part of the steel sheet and the cooling rate upper limit value of the surface layer part in this management temperature range,
In each cooling zone in which the steel sheet falls within this control temperature range, it becomes the control temperature range when cooling with the water density set in the continuous cooling pattern based on the steel sheet temperature history up to the cooling zone before the cooling zone. Calculate the cooling rate of the center and surface layer of the steel plate between the cooling zone and the cooling zone,
When the calculated cooling rate of the central portion is equal to or higher than the set cooling rate lower limit value of the central portion, and the calculated cooling rate of the surface layer portion is equal to or lower than the cooling rate upper limit value of the surface layer portion, the cooling zone The water density of the water is set in the continuous cooling pattern,
The calculated cooling rate of the central portion of the steel sheet is less than the set cooling rate lower limit value of the central portion, or the calculated cooling rate of the surface layer portion of the steel sheet is the set upper limit value of the surface layer cooling rate. If it exceeds
The cooling zone and the intermittent cooling pattern in which the water density is zero or the next cooling zone that is smaller than the cooling zone are combined , and the cooling rate of the central part of the steel sheet is equal to or higher than the cooling rate lower limit value of the set central part. There, and the cooling rate of the surface layer portion of the hot steel plate, characterized in that cooling by setting those said cooling zone and water density of the next cooling zone cooling rate upper limit that Do the following surface layer portion described above set Cooling method. Regarding the water density of the cooling zone and the next cooling zone, the cooling rate of the central part of the steel sheet is equal to or higher than the set cooling rate lower limit value of the central part, and the cooling rate of the surface layer part is the set surface layer part. If a solution that is less than or equal to the cooling rate upper limit value is not obtained, the cooling zone and the next cooling zone are further combined with a cooling zone downstream of the next cooling zone in order, the cooling rate of the center portion is the set center portion of the cooling rate lower limit or more, those the cooling zone and the cooling rate of the surface layer portion of the steel sheet that Do the following cooling speed upper limit of the surface layer portion which is the setting The cooling method for a high-temperature steel sheet according to claim 1 , wherein the cooling is performed by setting the water density in the cooling zone downstream of the next cooling zone and the next cooling zone.

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