JP5531852B2 - Method for determining refrigerant flow rate - Google Patents

Description

  The present invention relates to a method for determining a refrigerant flow rate and a steel sheet cooling apparatus capable of rapidly cooling a steel sheet.

  Steel materials used for automobiles, structural materials, etc. are required to have excellent mechanical properties such as strength, workability, and toughness. It is effective to reduce the size. Therefore, many manufacturing methods for obtaining a hot rolled steel sheet having fine crystal grains have been sought. Further, if the crystal grains are refined, it is possible to produce a high-strength hot-rolled steel sheet having excellent mechanical properties even if the addition amount of the alloy element is reduced.

  As a method of refining crystal grains of hot-rolled steel sheet, particularly in the latter stage of hot finish rolling, high-pressure rolling is performed to refine austenite grains and accumulate rolling strain in the grains, after cooling (or after transformation) And the like, and the like. From the viewpoint of suppressing the recrystallization and recovery of austenite grains and promoting ferrite transformation, it is effective to cool the steel sheet to a predetermined temperature or less in a short time after rolling. In other words, in order to manufacture hot rolled steel sheets with fine crystal grains, it is effective to install a cooling device that can cool faster than before, followed by hot finish rolling, and rapidly cool the rolled steel sheet. It is.

Regarding such a steel sheet cooling device, for example, Patent Document 1 includes an upper surface side / lower surface side nozzle box having a plurality of spray nozzles for injecting water onto the upper and lower surfaces of a thick steel plate that passes between a pair of restraining rolls. A technology related to a cooling apparatus for thick steel plates is described. In Patent Document 1, a plurality of types of spray nozzles are disclosed, and the influence of water on the plate on cooling is also studied. Patent Document 2 discloses a slab continuous casting method in which a slab short side surface is cooled with high-pressure spray water having a collision pressure of 5 × 10 ⁻³ MPa or more in a secondary cooling zone of a continuous casting machine. . Further, in Patent Document 3, when cooling a cooled plate such as a high-temperature steel plate hot-rolled in a line such as a hot rolling line with a cooling device, the cooling water staying on the cooled plate to be cooled is A technique related to a draining method and apparatus for discharging water and air by fluid injection is disclosed. Patent Document 4 discloses a steel sheet cooling device that can reduce cooling unevenness.

JP 2006-35311 A JP 2005-177841 A JP 2002-121616 A JP 2006-35233 A

  However, when the technique disclosed in Patent Document 1 is used to rapidly cool the steel sheet by causing the coolant jetted from the nozzle toward the steel sheet to collide with the steel sheet surface, the on-board water tends to stay on the upper surface of the steel sheet. Since it is difficult to rapidly cool the steel sheet even if the refrigerant is simply sprayed onto the steel sheet where the on-board water is retained, it is difficult to rapidly cool the steel sheet even using the technique disclosed in Patent Document 1. There was a problem. Further, when the technique disclosed in Patent Document 2 is simply applied to cooling of a steel plate after rolling, there is a problem that water on the plate tends to stay and it is difficult to rapidly cool the steel plate. These problems are difficult to solve even if the techniques of Patent Documents 1 to 4 are combined.

  Therefore, an object of the present invention is to provide a refrigerant flow rate determination method and a steel plate cooling device capable of rapidly cooling a steel plate even when water on the plate is retained.

The present inventor conducted research on the production of hot-rolled steel sheets having ultrafine crystal grains (hereinafter sometimes referred to as “ultrafine grain steel”), and obtained the following knowledge.
(1) As shown in FIG. 1, after rolling in a temperature range of Ar3 point or higher and completing cooling to 720 ° C. within 0.2 seconds, the crystal grains can be further refined. .
(2) In order to finish cooling at 100 ° C. from 820 ° C. to 720 ° C., for example, at an Ar3 point or higher, within 0.2 seconds after rolling, it is necessary to perform rapid cooling at a cooling rate of 600 ° C./s or higher. .
(3) There is a correlation between the pressure (surface pressure) at which the cooling water sprayed onto the steel plate collides with the steel plate and the cooling rate of the steel plate (see FIG. 2), and the pressure at which the cooling water collides with the steel plate is increased. By making it, it becomes possible to increase the cooling rate of a steel plate. Therefore, in order to perform rapid cooling at a cooling rate of 600 ° C./s or higher, it is necessary to set the pressure at which high-pressure jet water injected toward the steel plate collides to 3.5 kPa or higher. In addition, the “average cooling rate of the steel plate” in FIG. 2 is a cooling rate at a depth of ¼ depth in the plate thickness direction when the high-pressure jet water is uniformly collided with the upper and lower surfaces of the 3 mm thick steel plate. Further, the “pressure at which the high-pressure jet water collides with the steel sheet” in FIG. 2 is a pressure that collides with one surface of the steel sheet, and is an “average collision pressure Ps” described later.

  As described above, in order to produce a fine-grained steel, it is necessary to rapidly cool after rolling at a cooling rate of 600 ° C./s or more. On the other hand, the present inventors believe that it is effective to use a flat spray nozzle (sometimes referred to as a “fan-shaped nozzle”) that forms a fan-shaped jet and has an appropriate spread and penetration force for cooling the steel sheet. The invention according to Patent Document 4 has been completed so far. However, in such rapid cooling, a large amount of refrigerant is injected onto the steel plate in a state in which a large number of nozzles are arranged in the width direction and the conveying direction of the steel plate, so that the refrigerant injected onto the steel plate tends to stay on the upper surface of the steel plate. Such refrigerant staying on the plate (hereinafter sometimes referred to as “water on the plate”) reduces the collision force of the spray on the steel plate, so it is assumed that the injection amount of the refrigerant is simply increased. Street quenching capacity may not be achieved. Then, in order to specify the conditions at the time of rapid cooling of the steel plate using a flat spray nozzle, the relationship between the height of the water on the plate and the pressure (surface pressure) at which the cooling water collides with the steel plate was investigated. The contents are shown below.

  A schematic diagram of the experimental apparatus is shown in FIG. Clean water pressurized by a plunger pump was sprayed from a nozzle (flat spray nozzle), and the collision pressure at an acrylic collision surface (600 mm square) having a pressure measurement hole was measured. The distance H between the center point of the cooling water jet and the collision surface (hereinafter sometimes referred to as “injection distance H”) was 300 mm. The apex angle α of the cooling water jet injected from the nozzle (hereinafter sometimes referred to as “jet apex angle α”) is approximately 37π / 180 rad, and the water supply pressure Pn to the nozzle (hereinafter referred to as “nozzle pressure”). The flow rate Q of cooling water injected from the nozzle when the pressure is 1.5 MPa (hereinafter, the flow rate of cooling water injected from the nozzle may be referred to as “nozzle flow rate”) is 33.5 L / min. Met. In order to model on-board water retention, an acrylic weir is installed around the collision surface so that excess on-board water overflows to the outside, and the height of the on-board water level Hw ( In the following, the “water height on the plate” may be referred to)). The liquid level height Hw was set to 0 to 450 mm (5 types of 0 mm, 100 mm, 200 mm, 300 mm, and 450 mm). Pressure measurement holes with a diameter of 1 mm were formed on the collision surface at a pitch of 10 mm, connected to an acrylic pipe with an inner diameter of 10 mm with a touch tube, and the water column was read. Only the dynamic pressure was read by setting the position of the water surface on the plate to 0 kPa. In addition, the impact pressure distribution in the thickness direction was also measured by moving the impact surface in the thickness direction of the spray.

  4 and 5 are diagrams showing the influence of the liquid level height on the collision pressure distribution, and are the results when the nozzle pressure is 1.5 MPa and the injection distance H is 300 mm. 4A is Hw = 0 mm, FIG. 4B is Hw = 100 mm, FIG. 4C is Hw = 200 mm, FIG. 5A is Hw = 300 mm, and FIG. 5B is Hw = 450 mm. Is the result of the case. As shown in FIGS. 4A to 4C, when Hw is 200 mm or less, the shape of the portion with high collision pressure (hereinafter, sometimes referred to as “collision pressure shape”) is substantially oval. It became a shape. In contrast, as shown in FIGS. 5A and 5B, when Hw was 300 mm or more, the collision pressure shape approached a circle. Therefore, it has been found that under the present experimental conditions, when the Hw is 300 mm or more, it becomes difficult to obtain the cooling characteristics by the flat spray nozzle. Moreover, the maximum value of the collision pressure was halved at Hw = 200 mm, and was minimum when Hw = 300 mm.

  6 and 7 are diagrams showing the influence of the nozzle pressure on the collision pressure distribution immediately below the nozzle, and are the results when the injection distance H = 300 mm. 6A is Hw = 0 mm, FIG. 6B is Hw = 100 mm, FIG. 6C is Hw = 200 mm, FIG. 7A is Hw = 300 mm, and FIG. 7B is Hw = 450 mm. Is the result of the case. As shown in FIGS. 6A to 6C, when Hw is 200 mm or less, two impact pressure peaks are recognized, and a substantially trapezoidal distribution is obtained. As shown in FIG. 7B and FIG. 7B, when Hw is 300 mm or more, there is only one peak of the collision pressure, and the distribution is mountain-shaped. Therefore, from the results of FIGS. 6 and 7, it has been found that under the present experimental conditions, it becomes difficult to obtain the cooling characteristics by the flat spray nozzle when the Hw is 300 mm or more. Further, as shown in FIGS. 6A to 7B, the maximum collision pressure is almost proportional to the nozzle pressure at all liquid level heights, and the shape of the collision pressure distribution is the liquid level height. Were the same (similar) regardless of nozzle pressure.

  Table 1 shows the nozzle pressure, nozzle flow rate, average flow density, and average collision pressure Ps for the nozzle pressures of 0.5 MPa, 1.0 MPa, and 1.5 MPa in the above-described collision pressure distribution test.

Here, the average collision pressure Ps is the collision pressure of the spray when there is no water on the plate (Hw = 0 mm), and the force (collision force) of the cooling water that has collided with the jet collision effective area is used as the jet collision effective. It is a value that can be calculated by dividing by the area of the area, and is a value calculated by the rearrangement formula (formula E) described below. FIG. 8 shows the concept of the jet collision effective area, the injection distance H, the jet apex angle α, and the major axis length Ls of the refrigerant jet collision area. As shown in FIG. 8, in the jet collision effective area, the length of one side is the major axis length Ls (= 2 × H × tan (α / 2)) of the refrigerant jet collision area, and the length of the other side. Is defined by a rectangle having a jet collision width of 40 mm (± 20 mm width on both sides of the center line of the refrigerant jet collision area).

<Definition of long axis length Ls of refrigerant jet collision area>
The major axis length Ls of the refrigerant jet collision area shown in FIG. 8 is such that, when a plurality of nozzles are arranged in the width direction of the steel plate, a uniform cooling capacity distribution is obtained in the width direction of the steel plate as described below. It is the length that becomes the standard for doing. FIG. 9 is a diagram showing a form of a refrigerant jet collision area formed by a refrigerant jetted from a nozzle array provided in a steel plate cooling device of the present invention, which will be described later, colliding with the upper surface of the steel plate. The left-right direction in FIG. 9 is the width direction of the steel sheet, and a part of the refrigerant jet collision area formed on the upper surface of the steel sheet by the refrigerant injected from the three nozzle rows is extracted and shown. FIG. 9 shows a state in which all the points in the width direction of the steel plate pass twice through the refrigerant jet collision area formed by the refrigerant injected from one nozzle row. The pitch Np [m], the twist angle β [rad], the major axis length Ls [m] of the refrigerant jet collision area, and the adjacent jet interval Jd [m] are also shown. In this case, by adjusting the major axis length Ls of the refrigerant jet collision area so that Ls = Np × 2 / cos β, all the points in the width direction of the steel plate are exactly the refrigerant jet collision area in each nozzle row. It will pass through twice, and a uniform cooling capacity distribution will be obtained.

  FIG. 10 shows the result of measuring the flow rate distribution when the nozzle used in the above-described experiment is ejected with a nozzle pressure of 1.5 MPa and an ejection distance H = 300 mm. As shown in FIG. 11, the flow distribution is such that a plurality of 10 mm-wide slit-shaped measuring rods are arranged in the width direction of the steel sheet (long axis direction of the refrigerant jet collision area), and cooling water is deposited on each measuring rod for 1 minute. The amount of was measured and determined. As can be seen from FIG. 10, in the nozzle used in the experiment, a substantially uniform flow distribution is obtained at a width of about ± 60 mm in the center in the width direction of the steel sheet, but on both sides, the flow distribution decreases almost linearly toward the outside. Become.

  As the major axis length Ls of the refrigerant jet collision area, for example, as shown in FIG. 10, the flow rate decreases linearly when the average flow rate in the uniform flow distribution region at the center in the width direction of the steel sheet is Qm. The positions of Qm / 2 in the regions on both sides can be defined as both ends of the major axis of the refrigerant jet collision area, and the length between them can be defined as Ls. In this case, Ls = 200 mm in the measurement example of FIG. However, the definition method of Ls is not limited to this example as long as it is determined for the purpose of obtaining a uniform cooling capacity distribution when arranging a plurality of nozzles in the width direction of the steel plate as described above. The definition method may be changed depending on the shape of the flow distribution obtained from the nozzle to be used.

<Introduction of collision pressure control type>
In order to create a collision pressure arrangement formula for the case where there is no water on the plate, the experimental apparatus shown in FIG. 3 is used, the water height on the plate Hw = 0 mm, the injection distance H = 300 to 800 mm, and the nozzle flow rate Q = 33.5 to 134L. / Min, nozzle pressure Pn = 0.75 to 1.5 MPa, jet apex angle α = 15π / 180 to 40π / 180 rad, the experiment was performed by changing the nozzle and injection conditions, and the vertical axis represents the average collision pressure Ps [kPa] ] Are shown in FIG. 12 as a result of taking the product of the flow density Ws [m ³ / (m ² · min)] and the nozzle pressure Pn to the 0.5th power on the horizontal axis. The average collision pressure Ps in FIG. 12 is, for example, a value obtained by averaging the collision pressure distribution measurement results shown in FIG. 4A within the jet collision effective region defined in FIG. Further, the flow rate density Ws of the refrigerant in FIG. 12 is a value obtained by dividing the nozzle flow rate Q by the area As [m ² ] of the jet collision effective area, that is,
Ws = Q / (1000 × As) (Formula A)
As = 2 × H / 1000 × tan (α / 2) × 40/1000 (Formula B)
It is.

From FIG. 12, it was found that the average collision pressure Ps can be arranged by the following formula C using the flow density Ws and the nozzle pressure Pn as parameters.
Ps = 0.589 × Ws × Pn ^0.5 (Formula C)
From the formulas A, C, and B, the following formulas D and E are obtained.
Ps = 0.589 × Q / (1000 × As) × Pn ^0.5 (Formula D)
= 0.689 × Q / (80 × H / 1000 × tan (α / 2)) × Pn ^0.5
... (Formula E)

  Here, the width of the jet collision effective area is set to ± 20 mm on both sides of the center line of the refrigerant jet collision area regardless of the nozzle injection condition. This is the spray injection condition assumed to be used in the cooling device according to the present invention. Therefore, it is considered that the spray collision range is at least within ± 20 mm on both sides of the center line of the refrigerant jet collision area, that is, in evaluating the influence of the refrigerant jet on the penetration capacity and cooling characteristics of the water on the plate. This is because it is considered sufficient to consider the range of ± 20 mm on both sides of the center line of the refrigerant jet collision area. In addition, the collision width slightly changes depending on the nozzle specifications and injection conditions, but the amount of change is affected by the type of nozzle (thick jet film thickness type, thin type, etc.). This is because it is very difficult, and if the width of the average range is changed depending on the injection conditions and the nozzle type, the arrangement becomes very complicated and it is considered that it is not suitable for the purpose of use in industrial performance evaluation.

  Here, a method of quantitatively organizing the influence of the water height on the plate on the collision pressure distribution shape determined from the above-described collision pressure distribution measurement results of FIGS. That is, the jet flow from the nozzle penetrates the water on the plate, and in order to maintain the magnitude and distribution of the collision pressure even under the water on the plate, the collision pressure of the jet is sufficiently higher than the hydrostatic pressure of the plate water. The ratio of the average impinging pressure of the jet and the hydrostatic pressure of the water on the plate was arranged as a parameter.

The hydrostatic pressure Ph [kPa] in each case of Hw of 100 mm, 200 mm, and 300 mm uses water as the refrigerant, so the density of water ρ [kg / m ³ ] = 1000, and the gravitational acceleration g = 9.81 [m] / S ² ]
Ph = ρ × g × Hw / 1000/1000
= 9.81 × Hw / 1000 (Formula F)
Can be obtained. That is, when Hw = 100 mm, Ph = 0.98 kPa, when Hw = 200 mm, Ph = 1.96 kPa, when Hw = 300 mm, Ph = 2.94 kPa, and when Hw = 450 mm, Ph = 4.41 kPa. Become. Table 2 shows values obtained by dividing the average collision pressure Ps at each nozzle pressure of 0.5 MPa, 1 MPa, and 1.5 MPa shown in Table 1 by the hydrostatic pressure Ph at each Hw (the numbers in the upper row of each column).

  The three symbols at the bottom of each column in Table 2 are the determination results regarding (i) uniformity, (ii) collision length, and (iii) average collision pressure in order from the left, and the collision pressure distribution measurement in FIGS. 6 and 7 is performed. Judging from the results, the following criteria were used.

(I) Uniformity: When Hw = 0 mm in FIG. 6A, a collision pressure peak occurs at a position in the width direction distance of 50 mm and −50 mm, and the variation of the collision pressure is −15 mm between −50 mm and 50 mm. %, And an almost uniform distribution is obtained. Therefore, the criteria for uniformity when Hw> 0 mm were set as follows.
○: Collision pressure variation between width direction distances -50mm to 50mm within ± 15% ×: Collision pressure variation between width directions distance -50mm to 50mm exceeds ± 15%

(Ii) Collision length: When Hw = 0 mm in FIG. 6A, the collision pressure is distributed to the outside of the collision pressure width direction distance −100 mm to 100 mm. Therefore, the criteria for the collision length are as follows.
○: Collision pressure distribution range outside width direction distance −100 mm to 100 mm ×: Collision pressure distribution range inside width direction distance −100 mm to 100 mm

(Iii) Average collision pressure: The average collision pressure at a distance in the width direction of −50 mm to 50 mm was relatively compared with the case of Hw = 0 mm, and the criterion for the cooling capacity was as follows.
A: Increased when the average collision pressure is Hw = 0 mm. O: Same as that when the average collision pressure is Hw = 0 mm. X: About 1/2 or less when the average collision pressure is Hw = 0 mm.

  From Table 2, in the case of Ps / Ph <1.0, compared with the case of Hw = 0 mm, the collision pressure distribution variation (decrease in uniformity), the collision length, and the average collision pressure as a whole are reduced. It is considered that the cooling water jetted from the nozzles cannot sufficiently penetrate the plate water. Further, when 1.0 <Ps / Ph <2.0, the collision length is decreased and the average collision pressure is decreased. On the other hand, in the case of Ps / Ph> 2.0, it can be seen that the distribution of performance equal to or higher than that in the case of Hw = 0 mm is obtained for the uniformity, the collision length, and the average collision pressure. That is, in the case of Ps / Ph <2.0, at least one of an increase in collision pressure distribution variation (decrease in uniformity), a decrease in collision length, and a decrease in average collision pressure occurs, and a flat spray nozzle is used. It is difficult to obtain the cooling uniformity and the high cooling ability that are the features of the conventional cooling. Therefore, it was suggested from Table 2 that at least Ps / Ph> 2.0 is required to perform rapid cooling when producing fine-grained steel. On the other hand, from Table 2, when Ps / Ph> 3.0, the collision pressure can be increased more than when there is no water on the plate, and further cooling can be promoted.

  As described above, by setting Ps / Ph> 2.0, it is possible to maintain the collision pressure distribution with the same performance as when there is no water on the plate even when water on the plate is generated. Further, by setting Ps / Ph> 3.0, it is possible to further increase the collision pressure as compared with the case where there is no water on the plate. On the other hand, as shown in FIG. 2 in the test results thus far, there is a correlation between the collision pressure of the high-pressure jet and the cooling ability. If an average collision pressure of 3.5 kPa or more can be secured, a steel plate with a thickness of 3 mm is 600 ° C. It is possible to achieve rapid cooling of 1000 ° C./s or more if an average collision pressure of / s or more and 8 kPa or more can be secured. Therefore, even if a large amount of on-board water is generated due to high flow density, Ps / Ph> 2.0, preferably Ps / Ph> 3.0, and an average of 3.5 kPa or more in the absence of on-board water By realizing the injection conditions for obtaining the collision pressure, it is possible to realize uniform cooling at a cooling rate of 600 ° C./s or more.

From the above investigation, the present inventors obtained the following knowledge.
1) When the cooling water is sprayed onto the steel sheet with the nozzle pressure kept constant, the pressure at which the cooling water sprayed onto the steel sheet collides with the steel sheet when the liquid surface height Hw of the plate water exceeds the threshold (collision pressure) The reduction of becomes remarkable.
2) Maintaining a collision pressure distribution with the same performance as when there is no board water by injecting the ratio Ps / Ph of the average collision pressure Ps to the hydrostatic pressure Ph of board water exceeding 2.0. Is possible.
3) Further, by injecting so that Ps / Ph exceeds 3.0, it is possible to increase the collision pressure as compared with the case where there is no water on the plate, and it is possible to further promote cooling.
4) Therefore, in order to rapidly cool the steel sheet in which the on-board water stays, a refrigerant satisfying Ps / Ph> 2.0, preferably Ps / Ph> 3.0 may be injected from the nozzle.
In addition to the above findings 1) to 4), the present inventors have also obtained the following findings.
5) The triangular shape of the refrigerant jet formed by both ends of the major axis of the refrigerant jet collision area formed by the collision of the refrigerant jet injected from the nozzle toward the steel plate with the steel plate and the center point of the refrigerant jet The apex angle (jet apex angle α) at the center point increases monotonously as the pressure of the refrigerant supplied to the nozzle (hereinafter, sometimes referred to as “nozzle pressure”) increases to a constant value (maximum value). ) And the nozzle pressure is set to 0.3 MPa or more, it is possible to suppress the reduction margin of the jet flow apex angle within 10% from the maximum value. By suppressing the reduction margin of the jet apex angle α, it becomes possible to cool the steel plate uniformly, so the nozzle pressure is preferably 0.3 MPa or more.
The present invention has been completed based on these findings. The present invention will be described below.

In the present invention , the maximum value of the flow rate of the refrigerant that can be supplied to the nozzle is Q _U [L / min], and the distance between the center point of the refrigerant jet injected from the tip of the nozzle toward the steel plate and the surface of the steel plate is H [Mm], the apex angle at the center point of the triangular coolant jet formed by the both ends of the major axis of the coolant jet collision area formed by the coolant jet colliding with the steel plate and the center point of the coolant jet α [ rad], the angle formed between the center line of the refrigerant jet and the perpendicular of the surface of the steel plate is γ [rad], the pressure of the refrigerant supplied to the nozzle is Pn [MPa], and the nozzle is injected from the tip of the nozzle toward the steel plate When the flow rate density of the refrigerant is Wd [m ³ / (m ² · min)], and the maximum value of the plate width of the steel sheet to which quenching with the refrigerant can be applied is Wp [m], Q _U Is a method for determining the refrigerant flow rate.
17.2 × Q _U / {2 × H × tan (α / 2) / cos γ} × Pn ^0.5
> 2 × 0.319 × Wd ^0.667 × Wp ^0.69 (Formula 1)

  Here, the “major axis of the refrigerant jet collision area” refers to the longer axis of the refrigerant jet collision area as shown in FIG. 13 when the refrigerant jet collision area is in the shape of a band or an ellipse. . On the other hand, when the refrigerant jet collision area is circular and the major axis and the minor axis have the same length, the diameter of the refrigerant jet collision area is referred to. Further, the flow density Wd is defined by an expression S or an expression S ′ described later.

In the present invention, the flow rate of the refrigerant supplied to the nozzle can be controlled within a predetermined flow rate control range, the maximum value of the flow rate control range is set to the above Q _U, and the minimum value of the flow rate control range is set to Q _L [L / min], Q _L is preferably determined so as to satisfy the following formula 2.
9.4 × Q _L / {2 × H × tan (α / 2) / cosγ}
≧ 2 × 0.319 × Wd ^0.667 × Wp ^0.69 (Expression 2)

  Here, the above equation 2 is an equation arranged by substituting 0.3 for Pn of the above equation 1. In other words, in the above formula 1, the formula 2 expresses that it is preferable to control the nozzle flow rate while suppressing the reduction margin of the jet apex angle α by setting Pn to 0.3 MPa or more.

In the above present invention, that the Q _U is determined so as to satisfy the following equation 3 preferred.
17.2 × Q _U / {2 × H × tan (α / 2) / cos γ} × Pn ^0.5
> 3 × 0.319 × Wd ^0.667 × Wp ^0.69 (Formula 3)

In the present invention, the maximum value Q _U of the flow rate of the refrigerant that can be supplied to the nozzle is determined so as to satisfy Equation 1. Here, since the left side of Equation 1 corresponds to the average collision pressure Ps and 0.319 × Wd ^0.667 × Wp ^{0.69 on} the right side of Equation 1 corresponds to Ph, Equation 1 satisfies Ps> 2 × Ph. It can also be expressed. That is, in the present invention , Q _U is determined such that the ratio Ps / Ph between the average collision pressure Ps and the hydrostatic pressure Ph of the on-plate water exceeds 2.0. Therefore, according to the present invention, it is possible to provide a method for determining a refrigerant flow rate that can rapidly cool a steel plate even when water on the plate is retained. In the present invention, the steel sheet is rapidly cooled while the flow rate is controlled within a range where the maximum value becomes Q _U by setting Pn to 0.3 MPa or more, so that the reduction margin of the jet apex angle α is always suppressed to within 10%. As a result, it becomes easy to uniformly cool the steel sheet and control the temperature immediately after the rapid cooling (quenching stop temperature) with high accuracy. Furthermore, by Ps / Ph is Q _U to exceed the 3.0 is determined, it is possible to enhance the impact pressure than without the plate clean water, it is possible to achieve a further cooling promoting .

It is a figure which shows the relationship between the required time for cooling to 720 degreeC, and the ferrite particle size obtained. It is a figure which shows the relationship between the steel plate surface collision pressure of high pressure jet water, and the average cooling rate of a steel plate. It is a figure explaining the form of an experimental apparatus. It is a figure which shows the influence of the liquid level height which gives to collision pressure distribution. It is a figure which shows the influence of the liquid level height which gives to collision pressure distribution. It is a figure which shows the influence of the nozzle pressure which acts on the collision pressure distribution right under a nozzle. It is a figure which shows the influence of the nozzle pressure which acts on the collision pressure distribution right under a nozzle. It is a figure explaining the concept of a jet collision effective area. It is a figure explaining the refrigerant | coolant jet collision area | region formed in the surface of a steel plate. It is a figure which shows the measurement method of flow volume distribution, and the definition method of the major axis length of a refrigerant | coolant jet collision area. It is a figure which shows the measuring method of flow volume distribution. It is a figure which shows the relationship between the flow volume density Ws of a refrigerant | coolant, the nozzle pressure Pn, and the average collision pressure Ps. Injection distance H [m], jet apex angle α [rad], refrigerant jet center line, refrigerant jet center point, refrigerant jet collision area, refrigerant jet collision area center line, and refrigerant jet layer and long axis of additional recording It is a figure which defines length Ls. FIG. 13 (a) is a diagram showing a case where the refrigerant is jetted vertically, and FIG. 13 (b) shows that the refrigerant jet is placed so that the center line of the refrigerant jet forms an angle γ (≠ 0) with the perpendicular to the surface of the steel sheet. It is a figure which shows the case where it injects. It is a figure which shows the board water and the steel plate divided | segmented into the block shape for every nozzle. It is a front view explaining the test apparatus for verification of a board water height distribution calculation result. It is XVI-XVI sectional drawing of FIG. It is a figure which shows the comparison with the board | substrate water height distribution measured with the test apparatus of FIG.15 and FIG.16, and the board | substrate water height distribution calculated | required by calculation. It is a figure which shows the relationship between the flow rate density Wd and the board top water height Hw. It is a figure explaining the cooling device which quenches the steel plate immediately after rolling, and the apparatus arrange | positioned around it. It is a figure which shows the temperature distribution measurement result of the width direction immediately after a rapid cooling stop.

  Embodiments of the present invention will be described below.

1. The method for determining the coolant flow rate determination method invention of the refrigerant flow rate, the maximum value Q _U supply to the refrigerant flow rate to the nozzle is determined so as to satisfy the following equation G.
17.2 × Q _U / {2 × H × tan (α / 2)} × Pn ^0.5 > 2 × Ph (Formula G)
In Formula G, H [mm] is the distance (injection distance) between the center point of the refrigerant jet injected from the tip of the nozzle toward the steel plate and the surface of the steel plate, and α [rad] is injected from the nozzle. The apex angle (jet apex angle) at the center point of the triangular refrigerant jet formed by both ends of the major axis of the refrigerant jet collision zone formed by the collision of the refrigerant jet against the steel plate and the center point of the refrigerant jet is there. Pn [MPa] is the pressure of the refrigerant supplied to the nozzle (nozzle pressure), and Ph [kPa] is the hydrostatic pressure of the refrigerant on the upper surface of the steel plate (hydrostatic pressure of water on the plate). In addition, since the thickness of the steel plate which is the application object of the rapid cooling process by the cooling device of the steel plate of this invention mentioned later is the range of 2-6 mm normally, and the steel plate thickness is sufficiently small with respect to the injection distance H, the above-mentioned injection | pouring for convenience. The definition of the distance H may be substituted by “the distance between the center point of the refrigerant jet and the pass line”.

FIG. 13 is a diagram for defining the injection distance H [m] and the jet apex angle α [rad] in the equation G. The central point of the refrigerant jet is the base point in the direction in which the droplets that make up the refrigerant jet that radiates from the spray nozzle are scattered, and is usually several mm to several tens of mm from the tip of the nozzle. It is in the position. FIG. 13A shows a form in which the refrigerant is injected vertically so that the center line of the refrigerant jet is parallel to the perpendicular to the surface of the steel sheet (hereinafter sometimes referred to as “vertical blowing”). FIG. 13B shows a case where the refrigerant is injected such that the center line of the refrigerant jet forms an angle γ (≠ 0) with the perpendicular to the surface of the steel sheet (hereinafter “obliquely blown”). It is a figure which shows. As shown in FIG. 13A, “2 × H × tan (α / 2)” in the above formula G is the major axis length Ls [mm] of the refrigerant jet collision area formed on the steel plate surface. is there. That is, the formula G defines the conditions to be satisfied by Q _U when blowing vertically refrigerant. Therefore, in consideration of the case where the refrigerant is blown vertically (when γ = 0) and the case where the refrigerant is blown obliquely (when γ ≠ 0), in the present invention, Q _U is determined so as to satisfy the following formula H: Just do it.
17.2 × Q _U / {2 × H × tan (α / 2) / cos γ} × Pn ^0.5 > 2 × Ph
... (Formula H)
The configurations shown in FIGS. 13A and 13B are cases where the center line of the refrigerant jet and the center line of the refrigerant jet collision area are orthogonal to each other. However, for example, when the nozzle is tilted at an angle γ facing the rolling mill in the conveying direction and at the same time twisted at a predetermined angle β with respect to the plate width direction as shown in FIG. 9, the center line of the refrigerant jet and the refrigerant jet collision The angle at which the center line of the area intersects is not a right angle. In this case, strictly speaking, the major axis length Ls of the refrigerant jet collision area is slightly longer than the value calculated by “2 × H × tan (α / 2) / cos γ” of the above formula H. However, when the direction angle γ is as small as about 15 ° or less, even if Ls is calculated by “2 × H × tan (α / 2) / cos γ”, the error is sufficiently small. Absent. If the angle of directivity γ is greater than 15 ° and the error cannot be ignored, the increase rate of Ls is calculated geometrically, corrected by multiplying the injection distance H in equation H by the increase rate of Ls, and then the equation H It is desirable to use

In addition, the coolant sprayed on the upper surface of the steel sheet flows on the steel sheet from the center of the sheet width toward both sides in the width direction of the steel sheet and is discharged outward from both ends in the width direction of the steel sheet. Height increases. That is, the through-water penetration ability by the refrigerant jet injected from the nozzle is the lowest at the center of the plate width. The hydrostatic pressure Ph on the plate at the center of the plate width can be arranged by the flow density Wd [m ³ / (m ² · min)] and the plate width Wp [m]. In the present invention, the following formula 1 is satisfied. Q _U can be determined.
17.2 × Q _U / {2 × H × tan (α / 2) / cos γ} × Pn ^0.5
> 2 × 0.319 × Wd ^0.667 × Wp ^0.69 (Formula 1)

In the above formula G, formula H, and formula 1, the left side corresponds to the average collision pressure Ps. Therefore, when determining the maximum flow rate Q _U so as to satisfy these equations, such that the ratio Ps / Ph with hydrostatic pressure Ph of the average impact pressure Ps and the plate clean water is more than 2.0, to determine the Q _U Can do. Here, as described above, when Ps / Ph exceeds 2.0, it is possible to rapidly cool the steel sheet in which the on-board water is retained. Therefore, the formula G, wherein H and, by determining the maximum flow rate Q _U so as to satisfy the formula 1, according to the present invention, capable of rapidly cooling the steel sheet even if the plate clean water staying A method for determining the refrigerant flow rate can be provided. Further, the maximum flow rate Q is set so as to satisfy the following formula 3 in which the right side of the formula 1 is changed to 3 × 0.319 × Wd ^0.667 × Wp ^0.69 , that is, Ps / Ph exceeds 3.0. By determining _U , the collision pressure can be increased as compared with the case where there is no water on the plate, so that further cooling can be promoted.
17.2 × Q _U / {2 × H × tan (α / 2)} × Pn ^0.5
> 3 × 0.319 × Wd ^0.667 × Wp ^0.69 (Formula 3)

<Collision pressure calculation method>
Below, the meaning of the calculation formula of average collision pressure Ps is demonstrated. Since the collision force F [kN] of the refrigerant jet to the steel plate is theoretically equal to the momentum of the refrigerant jet injected from the nozzle per unit time, it can be obtained by the following formula I.
F = ρ × Q / (1000 × 60) × V / 1000 (Formula I)
Here, Q: nozzle flow rate [L / min], ρ: refrigerant density [kg / m ³ ], and V: jet velocity [m / s] at the nozzle outlet. Moreover, V is calculated | required by the following formula | equation J from the law of kinetic energy conservation.
V = C × (2 × Pn × 10 ⁶ / ρ) ^0.5 (Formula J)
Here, C is the loss factor [−] of the nozzle.

In a steel cooling device, water is usually used as a refrigerant. Therefore, assuming that ρ = 1000, a theoretical formula (the following formula K) for the collision force F can be obtained from Formula I and Formula J.
F = 0.745 × C × Q / 1000 × Pn ^0.5 (Formula K)

On the other hand, assuming that the collision force due to the spray jet is all added within the jet collision effective area,
Ps = F / As
= 0.745 x C x Q / (1000 x As) x Pn ^0.5 (Formula L)
It becomes. From Formula D and Formula L,
C = 0.925 (Formula M)
It becomes. From Formula L, Formula M, and Formula B Ps = 0.745 × C × Q / (1000 × As) × Pn ^0.5
= 0.745 x 0.925 x Q
/ (2 × H × tan (α / 2) × 40/1000) × Pn ^0.5
= 17.2 × Q / (2 × H × tan (α / 2)) × Pn ^0.5 (Formula N)
It becomes.

<Calculation method of water distribution on board>
Below, the calculation method of the width direction distribution of board water height is demonstrated.
As shown in FIG. 14, considering the case where nozzles are arranged at equal intervals over the entire width direction of the steel sheet and the cooling water is injected, the water on the board is divided into blocks for each nozzle, and the center in the width direction of the steel sheet is symmetrical. As the block numbers i = 0 to N in order from the end side (N: the number of nozzles existing on the half width of the steel plate), the plate water height of the block (i) is h (i) [m], the width direction When the flow velocity flowing through the nozzle is v (i) [m / s], the interval between the nozzle rows in the transport direction is Sr [m], and the cooling water injection width is Wn [m] (= plate width Wp), the incompressible flow From the energy conservation law
h (n) = h (n−1) + {(v (i−1) ² −v (i) ² )
+ Cd × Wn / 2 / (N + 1) × ((v (i−1) + v (i)) / 2) ² } / (2 × g) (formula O)
v (i) = (N−i) × Q / (1000 × 60 × h (i) × Sr) (Formula P)
Is true. Here, Cd [m ⁻¹ ] is 1.0 as a pressure loss coefficient of the widthwise flow.

The relationship between the flow velocity v (0) and h (0) of the water flowing down from the edge of the plate is
v (0) = Cf × (2 × g × h (0) / 2) ^0.5 (Formula Q)
It can be expressed as. Here, Cf [−] is a flow coefficient when water overflows from the weir and flows down, and is set to 0.6. V (0) and h (0) are obtained by setting i = 0 in the formulas Q and P, and then the initial value of h (i) (i = 1 to N) is set to h (0).
(A) v (i) using equation P (i = 1 to N), and
(B) Calculation of h (i) (i = 1 to N) using equation O,
Is repeated until the change in the calculation results of (a) and (b) becomes sufficiently small, the plate height distribution h (i) can be obtained.

  FIG. 15 and FIG. 16 show a test apparatus that has performed a test for verifying the above-described on-board water height distribution calculation result. The left-right direction in FIG. 15 and the back / near direction in FIG. 16 are the width direction of the steel sheet. 15 is a front view of the test apparatus, and FIG. 16 is a cross-sectional view taken along the line XVI-XVI of FIG. In FIG. 15, the direction of water flow is indicated by arrows. On the lower surface (nozzle surface) of the header to which the water supply pipe is connected and can inject cooling water, 62 mm pitch × 25 rows = 1550 mm in the width direction of the steel plate, 54 mm pitch × 6 rows in the direction perpendicular to the width direction (depth direction) = A total of 25 × 6 = 150 drill hole nozzles with an inner diameter of 6 mm are provided in a lattice shape over a range of 324 mm. Further, a steel plate having a width of 1550 mm and a depth of 750 mm was installed 150 mm below the nozzle surface of the header, and a columnar jet flow was sprayed onto the steel plate. In order to measure the water height distribution on the steel plate at this time, side walls of the acrylic plate were provided in three directions in total, one on both sides of the steel plate in the depth direction and on the width direction of the steel plate, and the other side in the width direction of the steel plate. The water on the plate only flows out from the outside. In this case, it can be considered that the open side in the width direction of the steel plate corresponds to the end of the steel plate, and the side wall side corresponds to the center of the plate width of the steel plate having a double plate width from the symmetry of the flow. It is possible to measure the on-board water height distribution when the cooling water is jetted in the entire width direction (cooling water jet width Wn = plate width Wp = 3.1 m). Side walls are also provided before and after the depth direction, and the interval between them is 750 mm. Since the nozzle rows are 6 rows in the depth direction, the interval between the nozzle rows is 750 ÷ 6 = 125 mm on average (Sr = 0 in Formula P) .125m).

  The reason why the drilled nozzle is used in the test apparatus shown in FIGS. 15 and 16 is that the surrounding air is relatively small in the water on the plate and the water on the plate can be accurately measured. It is. When the flat spray nozzle used in the apparatus according to the present invention is used as the cooling nozzle and when the drill hole nozzle is used, the jet forms of the individual nozzles are different. The jets of the individual nozzles that collided with each other once spread radially, collided between adjacent nozzles, risen, and flow out to the end in the width direction of the steel sheet through the gaps between the nozzle jets. The rough cooling water flow seen in (1) is the same, and it is considered that the on-board water height distribution can be roughly predicted by the above-described calculation method regardless of the nozzle type.

FIG. 17 shows a comparison between the on-board water height distribution measured by the test apparatus shown in FIGS. 15 and 16 and the on-board water height distribution calculated by the above-described method. The vertical axis | shaft of FIG. 17 is board water height Hw [mm], and a horizontal axis is the width direction position x [m]. The header flow rate Qh [m ³ / min] is Qh = 1.0, 3.0, as the flow rate when the injection width Wn is 3.1 m width (twice the flow rate actually passed through the header in the test). Tests and calculations were performed for the case of changing to 5.5. In FIG. 17, the test results are symbols of ○ (Qh = 1.0), Δ (Qh = 3.0), and □ (Qh = 5.5), and the calculation result is a dotted line (Qh = 1.0). , A broken line (Qh = 3.0) and a solid line (Qh = 5.5). As shown in FIG. 17, it can be seen that the on-board water height distribution obtained by the test can be accurately simulated by calculation.

In FIG. 18, when the plate width Wp [m] is 0.9 to 1.8, the flow rate density Wd [m ³ / (m) when cooling water is injected over the entire plate width (Wn = Wp). ² · min)] and the calculation result of the relationship between the plate water height Hw [mm] at the plate width center where the plate water height is the highest, ○ (Wp = 0.9), □ (Wp = 1. 2), Δ (Wp = 1.5), and ◇ (Wp = 1.8). The vertical axis | shaft of FIG. 18 is board water height Hw [mm], and a horizontal axis | shaft is flow volume density Wd [m < ³ > / (m < ² > * min)]. In FIG. 18, the result calculated by the following formula R for each plate width is shown by four types of curves.
Hw = 32.5 × Wd ^0.667 × Wp ^0.69 (Formula R)
Here, Wd is Qn = 2 × N × Q, Wp = 2 × N × where Qn [m ³ / min] is the flow rate of cooling water per nozzle row and Np [m] is the nozzle pitch in the width direction of the steel plate. From Np
Wd = Qn / (Wp × Sr) (Formula S)
= Q / (Np × Sr) (Formula S ′)
Is required.
As shown in FIG. 18, it can be seen that the on-board water height Hw at the center of the plate width can be arranged by the formula R.

Further, since the hydrostatic pressure Ph [kPa] on the steel plate generated by the water on the plate having the height Hw is obtained by Formula F, by substituting Formula R into Formula F, the hydrostatic pressure Ph [kPa] at the center of the plate width is ,
Ph = 0.319 × Wd ^0.667 × Wp ^0.69 (Formula T)
Is required.

2. Steel Plate Cooling Device As shown in FIG. 9, the cooling device of the present invention includes a plurality of nozzles that form an oblong refrigerant jet collision area on the upper surface of the steel plate, and the plurality of nozzles are predetermined in the width direction of the steel plate. Nozzle rows are configured by being arranged at an interval Np. Generally, two or more nozzle rows are provided at a predetermined interval Sr in the conveying direction of the steel plate (direction perpendicular to the width direction of the steel plate). By cooling the steel plate by injecting the coolant from the plurality of nozzles provided in the steel plate cooling device, the steel plate can be uniformly cooled. Furthermore, the maximum value Q _U [L / min] of the refrigerant flow rate that can be supplied to each nozzle provided in the steel sheet cooling device of the present invention is determined so as to satisfy any one of the above formulas 1 to 3. . By maximum value Q _U of the refrigerant flow rate is determined in this way, it becomes possible to quench the steel sheet plate clean water staying. Therefore, according to the present invention, it is possible to provide a steel plate cooling device capable of rapidly cooling the steel plate in which the on-board water stays, and the refrigerant jet collision area is configured as shown in FIG. Thus, it is possible to provide a steel plate cooling device capable of uniformly and rapidly cooling a steel plate in which water on the plate is retained.
In addition, when the number of nozzle rows is only one, water on the plate is not normally formed. For example, only one row of nozzles is arranged in the vicinity of the work roll exit side of the finish rolling mill, and the nozzle is inclined to the work roll side. When obliquely blowing, most of the refrigerant that has collided with the steel sheet flows to the work roll side and is dammed in a form sandwiched between the work roll and the refrigerant jet, so that on-plate water may be formed. In this case, for convenience, the nozzle row interval Sr in the transport direction is set, for example, from the position where the interval in the direction perpendicular to the steel plate between the work roll surface and the steel plate surface is 20 mm from the center line of the refrigerant jet shown in FIG. As the distance to the “collision center line of the nozzle row” formed by connecting the intersections of the steel plate surfaces, the flow rate density Wd is calculated by the formula S or the formula S ′ so as to satisfy any of the formulas 1 to 3 above. The maximum value Q _U [L / min] of the refrigerant flow rate that can be supplied to each nozzle can be determined. The nozzle row interval Sr is determined from “the position where the interval in the direction perpendicular to the steel plate between the work roll surface and the steel plate surface is 20 mm” because the interval is 20 mm or less (between the work roll and the steel plate). This is because it is considered that substantially no refrigerant can be trapped in the gap).

Also, as shown in FIG. 12, there is a correlation between the refrigerant flow density and the average collision pressure Ps, and the average collision pressure Ps can be increased as the refrigerant flow density is increased. FIG. 12 shows measured data when there is no water on the plate. The maximum value Q _U [L / min] of the refrigerant flow rate that can be supplied to each nozzle provided in the steel plate cooling device of the present invention is expressed by the above equation 1. -By determining so that either of the said Formula 3 may be satisfy | filled, even when board water is formed with an actual machine, it becomes possible to maintain the collision pressure shown in FIG. By setting the flow rate density of the refrigerant to 10 m ³ / (m ² · min) or more, the average collision pressure is also obtained in the range of nozzle pressure (0.3 to 2.0 MPa) used in the normal steel plate cooling device from the above formula C. Can be set to 3.5 kPa or more, and in that case, it is possible to realize a rapid cooling ability of 600 ° C./s or more from FIG. Therefore, in the steel plate cooling apparatus of the present invention, it is easy to rapidly cool the steel plate by setting the flow rate density of the refrigerant to 10 m ³ / (m ² · min) or more.

The steel plate cooling device of the present invention changes the flow rate of cooling water injected between nozzles so that a predetermined flow rate distribution is formed in the width direction in at least one or more nozzle rows, and at least one or more nozzle rows. In the nozzle, the maximum value Q _U [L / min] of the flow rate of the cooling water that can be supplied is determined so as to satisfy any one of the above formulas 1 to 3. By adopting such a configuration, for example, nozzles with different flow rates at the same nozzle pressure are used so that the flow rate of cooling water sprayed from the nozzle near the center of the width where water on the plate is most likely to collect is larger than the nozzles at both ends. The maximum flow rate of cooling water that can be arranged and at least supplied to the nozzle near the center of the width is set so as to satisfy any of the above formulas 1 to 3, so that the water on the plate near the center becomes high. It is possible to prevent the cooling ability from being lowered compared to the portion and to perform uniform cooling in the width direction.

For each case shown in Table 3 below, the above equation N is used to calculate the collision pressure Ps when there is no water on the plate, and the above equation T is used to calculate Ph when the plate width Wp is 1.6 m. These ratios Ps / Ph were calculated. Table 3 shows the experimental conditions (experimental conditions 1 to 6), Table 4 shows the results of experimental condition 1, Table 5 shows the results of experimental condition 2, Table 6 shows the results of experimental condition 3, Table 6 shows the results of experimental condition 4. Table 7 shows the results of the experimental condition 5 in Table 8, and Table 9 shows the results of the experimental condition 6. In Table 3, the nozzle flow rate Q [L / min] in the row described as 0.3 MPa is the nozzle flow rate Q [L / min] when the nozzle pressure is 0.3 MPa, and is described as 1.5 MPa. The nozzle flow rate Q [L / min] in the row is the nozzle flow rate Q [L / min] when the nozzle pressure is 1.5 MPa. Table 3 also shows the result of nozzle clogging. In Tables 4 to 9, when Ps> 3Ph, the determination is ◎, when 3Ph ≧ Ps> 2Ph, the determination is ○, and when Ps ≦ 2Ps, the determination is ×. The maximum value of the nozzle pressure Pn that can be set under the experimental conditions 1 to 6 is 2.0 MPa, and the nozzle pressure can be controlled in the range of 0.3 to 2.0 MPa. The theoretical nozzle diameter Dt [mm] in Table 3 is considered to be the diameter when the hole cross section is circular at the position where the inner diameter of the nozzle hole is minimum, and is calculated by the following formula U.
Dt = (4 / π × Qo / 60 / (2 × Po / ρ) ^0.5 ) ^0.5 (Formula U)
Here, Po [MPa] is the reference nozzle pressure (0.3 MPa in Table 3), and Qo [L / min] is the nozzle flow rate when the nozzle pressure is the reference nozzle pressure.

  As shown in Table 4, under experimental condition 1, Ps ≦ 2Ph was obtained when the nozzle pressure Pn was 0.7 MPa or less. On the other hand, when the nozzle pressure Pn was 1.0 to 1.5 MPa, Ps> 2Ph, and a collision pressure distribution having the same performance as that obtained when there was no water on the plate was obtained. Further, when the nozzle pressure Pn was 2.0 MPa, Ps> 3Ph, and a higher cooling ability was obtained than when there was no water on the plate. That is, in the experimental condition 1, the range of the nozzle pressure at which a collision pressure distribution with a performance equal to or better than the case where there is no water on the plate is obtained is 1.0 MPa ≦ Pn ≦ 2.0 MPa, and the upper limit value and lower limit value of Pn The ratio was 2. Therefore, under the experimental condition 1, it is difficult to control the nozzle pressure over a wide range.

  As shown in Table 5, under experimental condition 2, Ps ≦ 2Ph when the nozzle pressure Pn was 0.5 MPa or less. On the other hand, when the nozzle pressure Pn was 0.7 to 1.0 MPa, Ps> 2Ph, and a collision pressure distribution having the same performance as that obtained when no water on the plate was present was obtained. Further, when the nozzle pressure Pn was 1.5 to 2.0 MPa, Ps> 3Ph, and a higher cooling ability was obtained than when no water was on the plate. That is, in the experimental condition 2, the range of the nozzle pressure at which a collision pressure distribution with a performance equal to or better than the case without water on the plate is obtained is 0.7 MPa ≦ Pn ≦ 2.0 MPa, and the upper limit value and the lower limit value of Pn The ratio was about 2.86. Therefore, the experimental condition 2 was able to control the nozzle pressure over a wider range than the experimental condition 1.

  As shown in Table 6, under experimental condition 3, Ps ≦ 2Ph was obtained when the nozzle pressure Pn was 0.3 MPa. On the other hand, when the nozzle pressure Pn was 0.5 to 0.7 MPa, Ps> 2Ph, and a collision pressure distribution having the same performance as that obtained when there was no water on the plate was obtained. Further, when the nozzle pressure Pn was 1.0 to 2.0 MPa, Ps> 3Ph, and a higher cooling ability was obtained than when no water was on the plate. That is, in the experimental condition 3, the range of the nozzle pressure at which a collision pressure distribution with a performance equal to or higher than that in the case where there is no water on the plate is obtained is 0.5 MPa ≦ Pn ≦ 2.0 MPa, and the upper limit value and the lower limit value of Pn The ratio to was 4. Therefore, the experimental condition 3 was able to control the nozzle pressure in a wider range than the experimental condition 2.

  As shown in Table 7, in the experimental condition 4, even when the nozzle pressure Pn is 0.3 MPa, Ps> 2Ph, and the collision pressure having the same or better performance than the case where there is no water on the plate within the current nozzle pressure control range. A distribution was obtained. Specifically, when the nozzle pressure Pn was 0.3 to 0.5 MPa, Ps> 2Ph, and a collision pressure distribution having the same performance as that obtained when there was no water on the plate was obtained. In addition, when the nozzle pressure Pn was 0.7 to 2.0 MPa, Ps> 3Ph, and a higher cooling ability was obtained than when there was no water on the plate. That is, in the experimental condition 4, the range of the nozzle pressure at which the collision pressure distribution having the same or better performance as that in the case where there is no water on the plate is obtained is 0.3 MPa ≦ Pn ≦ 2.0 MPa, and the upper limit value and the lower limit value of Pn The ratio was about 6.67. Therefore, the experimental condition 4 was a condition in which the nozzle pressure could be controlled over a wide range, and the steel sheet was easier to cool than the experimental condition 3.

  As shown in Table 8, under the experimental condition 5, even when the nozzle pressure Pn is 0.3 MPa, Ps> 2Ph, and the collision pressure having the same or better performance than the case where there is no water on the plate within the current nozzle pressure control range. A distribution was obtained. Specifically, when the nozzle pressure Pn was 0.3 MPa, Ps> 2Ph, and a collision pressure distribution having the same performance as that obtained when there was no water on the plate was obtained. Further, when the nozzle pressure Pn was 0.5 to 2.0 MPa, Ps> 3Ph, and a higher cooling ability was obtained than when no water was on the plate. That is, in the experimental condition 5, the range of the nozzle pressure at which the collision pressure distribution having the same or better performance as that without water on the plate is obtained is 0.3 MPa ≦ Pn ≦ 2.0 MPa, and the upper limit value and lower limit value of Pn The ratio was about 6.67. Moreover, in the experimental condition 5, the range of the nozzle pressure that satisfies Ps> 3Ph is wider than in the experimental condition 4. Therefore, the experimental condition 5 was a condition in which the nozzle pressure could be controlled over a wide range, and the steel sheet was more easily cooled than the experimental condition 4.

  As shown in Table 9, under the experimental condition 6, even when the nozzle pressure Pn is 0.3 MPa, Ps> 3Ph, and within this nozzle pressure control range, higher cooling ability is obtained than when there is no water on the plate. It was. That is, in the experimental condition 6, the range of the nozzle pressure at which a collision pressure distribution with a performance equal to or better than the case where there is no water on the plate is obtained is 0.3 MPa ≦ Pn ≦ 2.0 MPa, and the upper limit value and the lower limit value of Pn The ratio was about 6.67. Moreover, in the experimental condition 6, the range of the nozzle pressure that satisfies Ps> 3Ph is wider than in the experimental condition 5. Therefore, the experimental condition 6 was a condition in which the nozzle pressure could be controlled over a wide range, and the steel sheet was more easily cooled than the experimental condition 5.

  Generally, the finishing plate thickness, finishing temperature, temperature immediately after quenching (quenching stop temperature), and finishing speed, which is the plate feeding speed during quenching, vary depending on the type of steel produced, and the header (nozzle row) to be used depends on these manufacturing conditions. Although the number is controlled, the quenching stop temperature is within the target range (for example, the target quenching stop temperature ± 10 ° C) due to disturbance factors such as fluctuations in cooling water temperature, finishing temperature, and surface properties of the steel sheet. There is a case that does not enter. In such a case, if control is performed with only the number of headers to be used (injection ON / OFF for each header), depending on the conditions, the quenching stop temperature may change by 20-30 ° C just by turning ON / OFF one header. It becomes difficult to finely control the quenching stop temperature. In such a case, for example, a means for adjusting the cooling amount by reducing the nozzle pressure for 2-3 headers from the outlet side among the headers to be used is effective.

  The cooling capacity is proportional to the 0.6th power of the collision pressure as shown in FIG. Further, if the nozzles are the same, the nozzle flow rate Q is proportional to the 0.5th power of the nozzle pressure Pn, and the collision pressure Ps is proportional to the nozzle pressure Pn from Expression D. Therefore, the cooling capacity is proportional to the 0.6th power of the nozzle pressure Pn. Therefore, if the maximum nozzle pressure is 2.0 MPa, the cooling capacity per header can be adjusted to about 2/3 if the nozzle pressure can be halved to 1.0 MPa, and can be adjusted to about 1/2 if it can be reduced to 0.7 MPa. In addition, the rapid cooling stop temperature can be controlled in steps of about 10 ° C., and the rapid cooling stop temperature control can be performed.

  As described above, under the experimental condition 1, by setting the nozzle pressure Pn to 1.0 MPa or more, the collision pressure distribution having the same performance as that in the case of satisfying the above formula 1 and no water on the plate was obtained. Moreover, the said Formula 1 was satisfy | filled by setting the nozzle pressure Pn to 0.7 MPa or more in the experimental condition 2, and setting the nozzle pressure Pn to 0.5 MPa or more in the experimental condition 3, respectively. Moreover, in the experimental conditions 4-6, the said Formula 1 was satisfy | filled by setting the nozzle pressure Pn to 0.3 Mpa or more. Furthermore, in the experimental condition 1, by setting the nozzle pressure Pn to 2.0 MPa, a higher cooling ability was obtained than when there was no water on the plate. Similarly, in the experimental conditions 2, 3, 4, 5, and 6, the nozzle pressure Pn is set to 1.5 MPa or more, 1.0 MPa or more, 0.7 MPa or more, 0.5 MPa or more, and 0.3 MPa or more, respectively. As a result, higher cooling performance was obtained than when there was no water on the plate. In addition, in the experimental conditions 4 to 6, the ratio between the upper limit value and the lower limit value of the nozzle pressure at which the collision pressure distribution with the same or better performance as the case without water on the plate was obtained exceeded 5, so the nozzle pressure was reduced. Thus, it becomes easy to control the cooling capacity per header, and it becomes easy to control the quenching stop temperature with high accuracy. Moreover, in the experimental conditions 3-6, since the theoretical nozzle diameter was 6 mm or more, nozzle clogging did not occur. On the other hand, since the nozzle diameter was less than 6 mm in the experimental conditions 1 and 2, nozzle clogging occurred. In other words, nozzle clogging could be prevented by using a nozzle having a theoretical nozzle diameter of 6 mm or more. By preventing the occurrence of nozzle clogging, it becomes easy to cool the steel plate uniformly. From the viewpoint of making the steel plate uniformly coolable, use a nozzle having a theoretical nozzle diameter of 6 mm or more. Is preferred.

Next, a test (quenching test) for rapidly cooling the hot-rolled steel sheet immediately after rolling was performed. The apparatus used for the test is shown in a simplified manner in FIG. In FIG. 19, the steel plate 1 is conveyed from the left side to the right side (the direction from the hot rolling finish rolling mill 2 to the draining roll 5), and in FIG. 19, some reference numerals are omitted. In the rapid cooling test, immediately after the work rolls 2a, 2b of the hot rolling finishing mill 2, the header of the cooling device 3 is arranged in 30 rows (3a, 3a,...) On the upper surface side of the steel plate 1 and 24 rows (3c, 3c, ...), arranged in the conveying direction of the steel sheet 1, and a test for rapidly cooling the hot-rolled steel sheet 1 immediately after rolling was performed. As for the nozzle specifications / injection conditions, tests were conducted for the experimental conditions 1 to 6 shown in Table 3. Note that a pump with a discharge pressure of 2.0 MPa was used as the water supply source, and the maximum value of the nozzle pressure Pn was set to 1.5 MPa under all the experimental conditions in consideration of pressure loss generated in the water supply pipe on the way. Thus, the maximum flow rate _{Q U} that can be supplied to the nozzle at each experimental condition, the nozzle flow rate Q in 1.5MPa shown in Table 3.
The header pitch in the transport direction (the transport direction nozzle pitch Sr in Table 3) was set as shown in Table 3 as much as possible. However, in order to ensure the plate-passability on the lower surface of the steel plate 1, the transport is about 1300 mm pitch and 300 mm in diameter. The rolls 4, 4, and 4 are arranged, and the header pitch is widened by 300 mm between the headers 3c and 3c with the transport roll 4 sandwiched therebetween. For the headers 3a, 3a, 3c, and 3c in the first row and the second row that are closest to the work rolls 2a and 2b (the upstream side in the transport direction), Inclined toward the work rolls 2a and 2b so that rapid cooling can be started from near the bottom dead center of the work roll 2a in contact with the upper surface and the top dead center of the work roll 2b in contact with the lower surface of the steel plate 1. The opposite angle γ was 30 ° in the first row and 15 ° in the second row. Moreover, the draining rolls 5 and 5 were installed in the upper surface side and lower surface side of the steel plate 1 at the exit side of the cooling device 3, and the draining roll 5 installed in the upper surface side was able to raise / lower up and down. Further, between the nozzles 3b, 3b,... On the upper surface side of the steel plate 1 and the pass line, and between the nozzles 3d, 3d,. In order to prevent the steel plate from colliding with the nozzles 3d, 3d,..., And to ensure the plate-passability at the tip of the steel plate, the upper guide plates 6, 6,. The upper guide plates 6, 6,... And the lower guide plates 7, 7,... Are provided with injection holes through which the cooling water injected from the nozzles 3 b, 3 b,. It has been. Further, the lower guide plates 7, 7,... Are supplied with cooling water sprayed from the lower surface side nozzles 3 d, 3 d,... And collected between the lower guide plates 7, 7,. A discharge hole for discharging downward from between (3c, 3c,...) Is also provided.
For the lower surface side nozzles 3d, 3d,..., The cooling water sprayed on the lower surface of the steel plate is discharged downward from the discharge holes provided in the lower guide plates 7, 7,. Like 3b,..., It is not always necessary to ensure the flow rate and nozzle pressure necessary to penetrate the water on the plate. However, it is desirable that the cooling capacities of the upper and lower surfaces be as equal as possible, and if the impact pressure received from the cooling water jet is greatly different between the upper and lower surfaces of the steel plate 1, the steel plate 1 is deformed and the upper guide plates 6, 6, ... or rubbing against the lower guide plates 7, 7,..., And the surface of the steel plate 1 may be crushed, so the flow rate and nozzle pressure of the lower surface side nozzles 3 d, 3 d,. It is desirable that the size be approximately the same as 3b,. Therefore, in this test, the flow rate, the nozzle pressure, and the nozzle pitch in the width direction of the lower surface side nozzles 3d, 3d,... Were made equal to the upper surface side nozzles 3b, 3b,.
Moreover, the rolling conditions of the steel sheet 1 subjected to the rapid cooling test are as follows: the finishing plate thickness is 3.2 mm, the plate width is 1600 mm, the finishing temperature is 890 ° C., the finishing speed is 600 m / min, and the quenching stop temperature of the cooling device 3 is The target value was 650 ° C.

  In the case of the experimental condition 1 shown in Table 3, the steel plate 1 could be rapidly cooled at a cooling rate of 840 ° C./s by setting the nozzle pressure Pn to 1.5 MPa. Even if cooling water is injected from the nozzles 3b, 3b,... And the nozzles 3d, 3d,... Connected to the headers 3a, 3a,. The steel sheet 1 could not be rapidly cooled to 0 ° C. Therefore, it was necessary to reduce the finishing speed to 250 m / min, and the rolling efficiency was greatly reduced.

  Further, in the case of the experimental condition 2 shown in Table 3, the steel plate 1 could be rapidly cooled at a cooling rate of 970 ° C./s by setting the nozzle pressure Pn to 1.5 MPa. , And the nozzles 3b, 3b,... And nozzles 3d, 3d,... Connected to the 24 headers 3c, 3c,. The steel sheet 1 could not be rapidly cooled to 650 ° C. Therefore, it was necessary to reduce the finishing speed to 400 m / min, and the rolling efficiency was greatly reduced. Furthermore, in the case of the experimental condition 3 shown in Table 3, the steel plate 1 can be rapidly cooled at a cooling rate of 1100 ° C./s by setting the nozzle pressure Pn to 1.5 MPa. , And the nozzles 3b, 3b,... And nozzles 3d, 3d,... Connected to the headers 3a, 3a,. The steel plate 1 could be rapidly cooled.

  Further, in the case of the experimental condition 4 shown in Table 3, the steel plate 1 can be rapidly cooled at a cooling rate of 1270 ° C./s by setting the nozzle pressure Pn to 1.5 MPa. , And the nozzles 3b, 3b,... And the nozzles 3d, 3d,... Connected to the headers 3c, 3c,..., Respectively, to rapidly cool the steel plate 1 to the target 650 ° C. did it. Further, in the case of the experimental condition 5 shown in Table 3, the steel plate 1 can be rapidly cooled at a cooling rate of 1370 ° C./s by setting the nozzle pressure Pn to 1.5 MPa, and the headers 3a in the upper and lower 14 rows from the top. , And the nozzles 3b, 3b,... And the nozzles 3d, 3d,... Connected to the headers 3c, 3c,..., Respectively, to rapidly cool the steel plate 1 to the target 650 ° C. did it. In experimental condition 5, even when the nozzle pressure Pn was set to 0.3 MPa, the target cooling rate of 600 ° C./s necessary for producing ultrafine-grained steel could be achieved. In the case of the experimental condition 6 shown in Table 3, the steel plate 1 can be rapidly cooled at a cooling rate of 1520 ° C./s by setting the nozzle pressure Pn to 1.5 MPa. , And the nozzles 3b, 3b,... And the nozzles 3d, 3d,... Connected to the headers 3c, 3c,..., Respectively, to rapidly cool the steel plate 1 to the target 650 ° C. did it. In experimental condition 6, even when the nozzle pressure Pn was set to 0.3 MPa, the target cooling rate of 600 ° C./s necessary for producing ultrafine-grained steel could be achieved.

The temperature in the width direction of the steel sheet 1 immediately after stopping the rapid cooling using a thermometer (not shown) provided on the outlet side of the rapid cooling equipment 3 (cooling device 3) in FIG. Distribution was measured. FIG. 20A shows a temperature distribution measurement result in the case of the experimental condition 5, and FIG. 20B shows a temperature distribution measurement result in the case of the experimental condition 2. Since the quenching stop temperature has a great influence on the mechanical properties of the product after quenching, it is necessary to keep it within a predetermined range (650 ± 10 ° C. in this embodiment), but the temperature unevenness in the heating furnace during heating, The rapid cooling start temperature (finishing temperature) fluctuates in the longitudinal direction of the steel sheet 1 due to changes in the air cooling time before rolling, changes in the rolling speed, etc., so the flow rate is controlled according to fluctuations in the finishing temperature at some nozzles during rapid cooling. It is necessary to perform temperature control. In the case of the experimental condition 5 and the experimental condition 2, both of the upper and lower headers 3a, 3a,... And the headers 3c, 3c,. The nozzle pressure Pn of the nozzles 3b, 3b,... And the nozzles 3d, 3d,... Connected to the headers 3a, 3a,. By adjusting the interval, the flow rate was controlled and the quenching stop temperature was controlled. In other words, by reducing the nozzle pressure Pn from the maximum of 1.5 MPa to 0.3 MPa, the cooling capacity can be adjusted to about 2/5 while suppressing the decrease in the jet apex angle to within 10% from the maximum value. A wide range of cooling capacity control is possible.
In the case of the experimental condition 5, in the whole range where the nozzle pressure Pn is 0.3 to 1.5 MPa, a collision pressure distribution having the same performance as that in the case where there is no water on the plate is obtained, and it is possible to uniformly cool rapidly. . On the other hand, in the case of the experimental condition 2, when the nozzle pressure Pn is in the range of 0.3 to 0.5 MPa, the collision pressure is significantly attenuated by the water on the plate, and uneven cooling occurs during rapid cooling. As a result, as shown in FIG. 20A, in the case of the experimental condition 5, the temperature variation in the width direction of the steel sheet 1 can be suppressed within the target ± 10 ° C., and the steel sheet 1 can be uniformly and rapidly cooled. It has become possible. On the other hand, as shown in FIG. 20B, in the case of the experimental condition 2, the fine temperature fluctuation due to the nozzle pitch became more remarkable. Further, as shown in FIG. 17, since the height distribution on the plate is higher on the center side in the width direction than on the end side, the cooling capacity decrease is larger on the center side of the width, and the end portion compared to the width center portion. The tendency of the temperature of the side to decrease becomes remarkable. For this reason, the temperature variation in the width direction of the steel plate 1 could not be suppressed to within the target ± 10 ° C., and the steel plate 1 could not be uniformly cooled rapidly.

  The method for determining the refrigerant flow rate and the steel sheet cooling apparatus of the present invention can be used for manufacturing a hot-rolled steel sheet having ultrafine crystal grains. Moreover, the hot-rolled steel sheet having ultrafine crystal grains can be used as a material used for applications such as automobiles, household appliances, machine structures, and buildings.

DESCRIPTION OF SYMBOLS 1 ... Steel plate 2 ... Hot rolling finishing rolling mill 3 ... Cooling device 3a, 3c ... Header 3b, 3d ... Nozzle 4 ... Conveyance roll 5 ... Draining roll 6 ... Upper guide plate 7 ... Lower guide plate

Claims (3)

The maximum value of the flow rate of the refrigerant that can be supplied to the nozzle is Q _U [L / min], and the distance between the center point of the refrigerant jet injected from the tip of the nozzle toward the steel plate and the surface of the steel plate is H [mm. ], The apex angle at the center point of the triangular coolant jet formed by the both ends of the major axis of the coolant jet collision area formed by the coolant jet colliding with the steel plate and the center point of the coolant jet is α [Rad], an angle formed by the center line of the refrigerant jet and the perpendicular of the surface of the steel plate is γ [rad], the pressure of the refrigerant supplied to the nozzle is Pn [MPa], and the tip of the nozzle is When the flow density of the refrigerant injected toward the steel plate is Wd [m ³ / (m ² · min)], and the maximum value of the plate width of the steel plate to which quenching by the refrigerant is applicable is Wp [m] The Q _U is determined so as to satisfy Equation 1 below. A method for determining the refrigerant flow rate.
17.2 × Q _U / {2 × H × tan (α / 2) / cos γ} × Pn ^0.5
> 2 × 0.319 × Wd ^0.667 × Wp ^0.69 (Formula 1) And controllable in flow rate a predetermined flow control range of the refrigerant supplied to the nozzle, the maximum value of the flow rate control range and the Q _U, the minimum value of the flow rate control range Q _L and _[L / min] The method for determining the refrigerant flow rate according to claim 1, wherein the Q _L is determined so as to satisfy the following formula 2.
9.4 × Q _L / {2 × H × tan (α / 2) / cosγ}
≧ 2 × 0.319 × Wd ^0.667 × Wp ^0.69 (Expression 2) Wherein Q _U, characterized in that is determined so as to satisfy the following equation 3, the method for determining the flow rate of refrigerant according to claim 1 or 2.
17.2 × Q _U / {2 × H × tan (α / 2) / cos γ} × Pn ^0.5
> 3 × 0.319 × Wd ^0.667 × Wp ^0.69 (Formula 3)