JPH0665722B2 - Cooling method for hot steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for cooling a steel sheet, and more specifically, it can prevent nonuniformity of steel sheet strength and defective shape by cooling after hot rolling or the like. The present invention relates to a method for cooling a hot steel sheet.

(Prior Art) A hot-rolled steel sheet after working or treatment such as hot rolling needs to be cooled to a predetermined temperature without causing a problem in its material and shape.

Therefore, conventionally, as cooling equipment for cooling the hot steel sheet, an upper surface cooling device and a lower surface cooling device are provided on the downstream side of the hot rolling mill, and the flow control is performed with respect to the hot steel sheet sent by the transport roller. Cooling water was sprayed from above and below via the valve. At that time, the cooling water flow rate is adjusted by measuring the upper surface temperature of the hot steel plate with a thermometer installed above the line on the inlet side of the cooling equipment, and setting the cooling water flow rate corresponding to this measured value to the upper and lower surfaces. The structure of supplying and injecting from a cooling device has been adopted.

However, there are various quality sizes of hot steel sheets that are transported, and despite different processing or treatment history,
Since only the upper surface temperature is measured and the amount of cooling water is controlled, it is not possible to correct the variation between the upper surface temperature and the lower surface temperature of the hot steel sheet. There is a problem that the mechanical properties of the steel sheet become non-uniform, etc.

The present invention eliminates the above-mentioned drawbacks of the prior art, prevents the steel sheet shape defect after cooling that occurs due to the steel sheet surface temperature difference between the upper surface side and the lower surface side of the hot steel sheet, and improves the mechanical properties of the steel sheet. It is an object of the present invention to provide a cooling method capable of preventing nonuniformity.

(Means for Solving Problems) In order to achieve the above-mentioned object, a method for cooling a hot steel sheet according to the present invention includes a hot steel sheet from both sides by an upper surface cooling device and a lower surface cooling device having a plurality of cooling zones. When cooling all at once, the surface temperature of the steel plate on the upper surface side and the steel plate surface temperature on the lower surface side are measured immediately before cooling, and considering the temperature difference, the upper surface side cooling set beforehand from the operation schedule for each cooling zone. While maintaining the total of the water flow rate and the cooling water flow rate on the lower surface side,
It is characterized in that the cooling is performed by correcting the water amount ratio with respect to the upper and lower surface side cooling water flow rates.

The present invention will be described in detail below based on examples.

(Embodiment) FIG. 1 shows an example of the structure of a hot steel plate cooling apparatus used for carrying out the present invention.

In the figure, 1 is a rolling mill, 9 is a conveying roller, and the sent hot steel plate 8 is conveyed to the cooling equipment by the conveying roller 9.

The cooling equipment has an upper surface cooling device 2 and a lower surface cooling device 3 with a conveyance line narrowed, each cooling device is divided into a plurality of cooling zones, and each cooling zone has upper and lower flow control for flow control. Valves 4 and 5 are provided.

An upper surface thermometer 6 and a lower surface thermometer 7 are installed on the upstream side of the cooling equipment (that is, on the rolling mill side) with the transfer line interposed therebetween.

In such a cooling facility, the hot steel plate 8 rolled by the rolling mill 1 is transported to the cooling devices 2 and 3 by the transport roller 9, and at that time, heat is applied by the upper surface thermometer 6 and the lower surface thermometer 7. The surface temperatures of the upper surface and the lower surface of the steel sheet 8 are measured for a certain period of time and input to the correction calculator 10.

The correction calculator 10 calculates the average of the obtained plural data, and calculates the average temperature of the upper surface (Tu · avg) and the average temperature of the lower surface (Tu
l · avg). Then, the temperature difference is calculated by the following equation ΔT = Tu · avg−Tl · avg. Next, the correction coefficient ε ₁ = f ₁ (ΔT−ΔT ₀ ) for the temperature difference ΔT ₀ between the upper surface and the lower surface in standard operation.
Is calculated, and the upper surface side cooling water flow rate and the lower surface side cooling water flow rate to be corrected are calculated by the following equations (1) and (2). The water amount ratio R ₀ (upper surface water amount / lower surface water amount) under standard operating conditions is given by the following equation.

R ₀ = a ₀ + a ₁ W + a ₂ W ² Here, W is the average of the upper surface water amount and the lower surface water amount, and a ₀ , a ₁ , and a ₂ are coefficients.

Here, SVu ′: Upper surface side cooling water flow rate after correction of the zone SVl ′: 〃 〃 Lower surface side 〃 SVu: 〃 Upper surface side before correction 〃 SVl: 〃 〃 Lower surface side 〃 Correction output is input to the flow controller 11. And the upper flow regulator 4
And the lower flow control valve 5 is adjusted so that the required cooling water flow rate is supplied to the upper surface and the lower surface of the hot steel plate 8.

Example 1 Next, the results of concretely cooling the steel sheet after hot rolling by the conventional method and the method of the present invention are shown. The cooling conditions and the like are as follows, and the method of the present invention used the cooling device having the configuration shown in FIG.

(Cooling conditions and results of the conventional method) Steel plate size (mm): 25t x 3200w x 10,000 to 15,000l Cooling method: Transfer the steel plate into the cooling device so that the tail part is about 1m out of the device, and then inject water. (Cooling with simultaneous water injection).

Transfer rate: 0.65 ± 0.05m / s Cooling start surface temperature: Upper surface… 775 ± 30 ℃ Lower surface… 795 ± 30 ℃ Total water volume: Upper surface… 1962m ³ / h Lower surface… 3238m ³ / h Cooling stop temperature: 550 ± 30 ℃ Cooling Subsequent steel plate shape: average rank 0.46 The average rank is an average value when the warp of the steel plate is divided into ranks 0 to 5, and the larger the value, the larger the warp.

(Cooling conditions and results of the method of the present invention) Steel plate size (mm): 25t × 3200 × 10,000 to 15,000l Cooling method: Simultaneous water injection cooling Transfer rate: 0.65 ± 0.05 m / s Cooling start surface temperature: Top surface… 775 ± 30 ° C. Lower surface… 795 ± 30 ℃ Total water amount: Upper surface… 1962 ± 40m ³ / h Lower surface… 3238 ± 40m ³ / h Cooling stop temperature: 550 ± 30 ℃ Steel plate shape after cooling: Average rank 0.26 Various depending on the above cooling conditions FIG. 3 shows the distribution of the steel sheet shape after cooling, which was obtained by cooling the steel sheets having the sizes of 4 and statistically investigated. The steel plate size (mm) is 9 to 51t x
It is 2,000-4,600wx-35,000l. From the figure, it can be seen that the steel sheet shape after cooling can be improved according to the method of the present invention.

In the first embodiment, the total sum of the upper surface side cooling water flow rate before correction and the lower surface side cooling water flow rate is the same as that after correction, and the ratio between the upper surface side cooling water flow rate and the lower surface side cooling water flow rate is However, as shown in FIG. 2, the required cooling zone among the cooling zones 1 to N is changed according to the temperature difference and the like. (For example, the first zone (* 1), the second zone (* 2)) can be corrected, and other cooling zones can be configured to control the cooling water flow rate according to the setting as in the conventional case. it can. Although the correction coefficient ε is a function of (ΔT−ΔT ₀ ), it may be a function of only ΔT.

Embodiment 2 FIG. 2 shows an example of the construction of a hot steel plate cooling device for carrying out another embodiment of the present invention.

In the figure, 1 is a rolling mill, 9 is a conveying roller, and the sent hot steel plate 8 is conveyed to the cooling equipment by the conveying roller 9.

The cooling equipment has an upper surface cooling device 2 and a lower surface cooling device 3 with a conveyance line narrowed, each cooling device is divided into a plurality of cooling zones, and each cooling zone has upper and lower flow control for flow control. Valves 4 and 5 are provided.

An upper surface thermometer 6 and a lower surface thermometer 7 are installed on the upstream side of the cooling equipment (that is, on the rolling mill side) with the conveyance line narrowed.

In such a cooling facility, the hot steel plate 8 rolled by the rolling mill 1 is transported to the cooling devices 2 and 3 by the transport roller 9, and at that time, heat is applied by the upper surface thermometer 6 and the lower surface thermometer 7. The surface temperatures of the upper surface and the lower surface of the steel sheet 8 are measured for a certain period of time and input to the correction calculator 10.

The correction calculator 10 calculates the average of the obtained plural data, and calculates the average temperature of the upper surface (Tu · avg) and the average temperature of the lower surface (Tu
l · avg). Then, the temperature difference is calculated by the following equation ΔT = Tu · avg−Tl · avg. Next, the correction coefficient ε ₂ = f ₂ (ΔT = ΔT ₀ ) for the temperature difference ΔT ₀ between the upper surface and the lower surface in standard operation.
Is calculated, and the upper surface side cooling water flow rate and the lower surface side cooling water flow rate to be corrected are calculated by the following equations (3) and (4). The water amount ratio R ₀ (bottom face water amount / top face water amount) under standard operating conditions is given by the following equation.

R ₀ = a ₀ + a ₁ W + a ₂ W ² Here, W is the average of the upper surface water amount and the lower surface water amount, and a ₀ , a ₁ , and a ₂ are coefficients.

Where SVu′i: Upper surface side cooling water flow rate after correction of the zone SVl′i: 〃 〃 Lower surface side 〃 SVui: 〃 Upper surface side before correction 〃 〃 Lower surface side 〃 i: Water quantity correction target It is the divided cooling zone number.

The corrected output is input to the flow control device 11 and the upper flow control valve 4
And the lower flow control valve 5 is adjusted, and the desired cooling water flow rate is supplied to the upper surface and the lower surface of the hot steel plate 8.

In this embodiment, the total of the upper surface side cooling water flow rate before correction and the lower surface side cooling water flow rate is the same as the corrected total sum, and the ratio of the upper surface side cooling water flow rate and the lower surface side cooling water flow rate is It is configured to change, and while maintaining the cooling rate in the cooling zone that gives the required mechanical properties in the steel plate by making the total amount the same before and after the correction, the front and back surfaces of the plate thickness of the steel plate It is possible to provide a uniform temperature distribution of

FIG. 4 shows the distribution of the steel sheet shape after cooling, which was statistically investigated by cooling steel sheets of various sizes similar to those of Example 1 shown in FIG. 3 using the cooling device of this configuration. The cooling conditions of the conventional method and the method of the present invention are the same as those in the first embodiment. However, in this embodiment, the first zone 13 and the second zone 14 of the cooling zones 12 shown in FIG. 2 were corrected.

As is clear from FIG. 4, according to the method of the present invention, the shape of the steel sheet after cooling can be significantly improved.

The correction coefficient ε used in the above embodiment is shown in FIG. This ε is represented by a function f (ΔT−ΔT ₀ ) of ΔT ₀ and the actual temperature difference ΔT when the plate thickness is 30 mm and the average water amount density is 0.2 m ³ / min · m ² . The functional expressions f ₁ and f ₂ in each of the above-described embodiments are simply distinguished for each embodiment, and in reality, the functional expression f (ΔT−
ΔT ₀ ) was used.

Regarding the correction coefficient ε, for example, as shown in FIG. 5, the function f in standard operation is experimentally determined for each plate thickness or each plate thickness group, or each average water amount density or each average water amount density group. Prepare a large number (f ₁ , f ₂ ...) In advance, select a function f that matches the actual plate thickness or average water density in actual operation,
It is practical to use the correction coefficient ε based on the function f.

(Effects of the Invention) As described in detail above, according to the present invention, the upper surface and the lower surface of the hot steel plate are kept in consideration of the difference in the measured surface temperature between the upper surface and the lower surface while maintaining the total flow rate of the cooling water. Since the water amount ratio with respect to the lower surface side cooling water flow rate is corrected, it is possible to effectively eliminate the defective shape of the hot steel sheet after completion of cooling. Also, of course, it means that cooling is performed uniformly,
The mechanical properties of the steel sheet are also stable.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a hot steel plate cooling device used for implementing the present invention, FIG. 2 is a diagram showing another configuration example, and FIG. 3 is a steel plate shape after cooling according to the first embodiment of the present invention. FIG. 4 is a diagram showing the distribution of the steel sheet shape after cooling according to Example 2, and FIG. 5 is a functional formula f (ΔT−ΔT ₀ ) of the correction coefficient ε used in Example. FIG. 1 ... Rolling mill, 2 ... Top cooling device, 3 ... Bottom cooling device, 4 ... Upper flow control valve, 5 ... Lower flow control valve, 6 ... Top thermometer, 7 ... Bottom thermometer, 8 ... Hot steel plate, 9 ... Conveying roller, 10 ... Correction calculator, 11 ... Flow control device, 12 ... Cooling zone, 13 ... First zone, 14 ... Second zone.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshinori Kishimoto 8-53 Shinnobe Kitamachi, Beppu Town, Kakogawa City, Hyogo Prefecture (72) Inventor Akinori Otomo 3-2 Takamaru, Tarumi-ku, Kobe City, Hyogo Prefecture (56) Reference Reference JP-A-59-185501 (JP, A) JP-A-62-112732 (JP, A)

Claims (2)

[Claims] 1. When simultaneously cooling a hot steel sheet from both sides with an upper surface cooling device and a lower surface cooling device having a plurality of cooling zones, immediately before cooling, the steel plate surface temperature on the upper surface side and the steel plate surface temperature on the lower surface side are measured. However, in consideration of the temperature difference, while maintaining the total of the upper surface side cooling water flow rate and the lower surface side cooling water flow rate preset from the operation schedule for each cooling zone, A method for cooling a hot steel sheet, comprising cooling by correcting a water amount ratio. 2. The upper surface cooling device and the lower surface cooling device are divided into zones, and when the hot steel sheet is successively cooled from the tip in the moving direction by the cooling device, at least one cooling zone is provided. The method according to claim 1, wherein the water amount ratio with respect to the upper and lower surface side cooling water flow rates is corrected.