Quenching device, quenching method, and method for manufacturing a metal plate

Abstract

Suppresses deviations in the shape of the metal plate that occur during quenching. The quenching device (1) for a metal plate cools while conveying the metal plate (S) and comprises a cooling tank (11) that stores a cooling fluid (CF) and cools the metal plate (S) by immersing it, a restraining roll (20) installed in the cooling tank (11) that conveys the metal plate (S) cooled by the cooling tank (11) while restraining it in the thickness direction, a water level regulator (30) that adjusts the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11), and a position control device (40) that controls the operation of the water level regulator (30) to adjust the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11).

Description

Technology Field

[0001] The present invention relates to a quenching apparatus and a quenching method for performing annealing while continuously conveying a metal plate, and a method for manufacturing a metal plate. Background Technology

[0002] In a continuous annealing facility that performs annealing while continuously conveying metal plates, metal plates are formed by cooling after heating and causing a phase transformation. In particular, the demand for thin-walled high-strength steel (high-tensile) is increasing in the automotive industry with the aim of achieving both lightweighting of the vehicle body and crash safety. When manufacturing high-strength steel, technology for rapidly cooling the steel plate becomes important. Water quenching is known as one of the technologies with the fastest cooling rate for metal plates. In the water quenching method, quenching of the metal plate is performed by simultaneously immersing a heated metal plate in water and spraying cooling water onto the metal plate through a quench nozzle installed in the water.

[0003] During the quenching of a metal plate, shape defects such as warping or wavy deformation occur in the metal plate. This is caused by thermal shrinkage resulting from the rapid cooling of the metal plate by a cooling fluid. In particular, when the temperature of the metal plate changes from the temperature Ms at which martensitic transformation begins to the temperature Mf at which martensitic transformation ends, rapid thermal shrinkage and transformation expansion occur simultaneously.

[0004] Therefore, various methods have been proposed to prevent shape defects of metal plates during quenching (see, for example, Patent Documents 1 and 2). Patent Document 1 proposes a method of restraining a metal plate by a pair of restraining rolls formed in a cooling fluid when the temperature of the metal plate is in the range from (TMs+150) (°C) to (TMf-150) (°C), where the temperature of the Ms point at which the martensite transformation of the metal plate begins is TMs (°C) and the temperature of the Mf point at which the martensite transformation ends is TMf (°C).

[0005] Patent Document 2 discloses a method for cooling a metal plate by spraying water from a plurality of water jet nozzles onto the surface of the metal plate, wherein the metal plate is constrained by a constraining roll, and the distance between the metal plate and the constraining roll is controlled by movable masking. In addition, similar to Patent Document 1, a method is proposed in which the metal plate is passed through a constraining roll at a temperature of (TMs+150) (°C) to (TMf-150) (°C), where the temperature at the Ms point at which the martensite transformation of the metal plate begins is TMs (°C) and the temperature at the Mf point at which the martensite transformation ends is TMf (°C). Prior art literature

[0006] Japanese Patent Publication No. 6094722, Japanese Published Patent Application No. 2019-90106 The problem to be solved

[0007] However, in the method described in Patent Document 1, depending on the manufacturing conditions of the metal plate, the location where the temperature of the metal plate is in the range of (TMs+150) (°C) to (TMf-150) (°C) changes. Because of this, the restraining roll cannot restrain the metal plate at the location where the temperature of the metal plate is (TMs+150) (°C) to (TMf-150) (°C), and there may be cases where deviations occur in the shape of the metal plate.

[0008] In the method described in Patent Document 2, water colliding with the movable masking falls due to gravity and interferes with the water sprayed from the water jet nozzle at the bottom of the movable masking, thereby making the cooling capacity of the metal plate unstable. Additionally, since masking occurs at each nozzle, the cooling capacity changes stepwise (discontinuously), and as a result, the position where the temperature of the metal plate becomes (TMs+150) (°C) to (TMf-150) (°C) becomes unstable, and deviations in the shape of the metal plate may occur.

[0009] The present invention was made to solve these problems and aims to provide a quenching device, a quenching method, and a method for manufacturing a metal plate product that can suppress deviations in the shape of a metal plate that occur during quenching. means of solving the problem

[0010] [1] A quenching device for a metal plate that cools while conveying a metal plate, comprising: a cooling tank that stores a cooling fluid and immerses the metal plate to cool it; a restraining roll installed in the cooling tank that conveys the metal plate cooled by the cooling tank while restraining it in the thickness direction; a water level regulator that adjusts the height of the fluid surface of the cooling fluid in the cooling tank, which is the cooling start position of the metal plate; and a position control device that controls the operation of the water level regulator to control the height of the fluid surface of the cooling fluid in the cooling tank.

[0011] [2] A quenching device for a metal plate described in [1], having a plurality of nozzles installed in the cooling tank and spraying the cooling fluid onto the metal plate to cool it.

[0012] [3] The above-described level regulator has a quenching device of a metal plate as described in [1] or [2], which has a quenching tank connected to the cooling tank and has a supply source that supplies the cooling fluid to the quenching tank and a dam that controls the discharge of the cooling fluid from the quenching tank, and adjusts the height of the fluid surface of the cooling fluid in the cooling tank by adjusting the amount of the cooling fluid stored in the quenching tank.

[0013] [4] The position control device adjusts the height of the fluid surface of the cooling fluid in the cooling tank to adjust the cooling start position of the metal plate so that the restraining roll restrains the metal plate at the position where the metal plate reaches the target temperature. [1] to [3] A quenching device for a metal plate described in any one of [1] to [3].

[0014] [5] A quenching device for a metal plate described in [4], wherein the temperature at the Ms point where the martensite transformation of the metal plate begins is TMs (°C) and the temperature at the Mf point where the martensite transformation ends is TMf (°C), and the target temperature is set to a temperature range of (TMs+150) (°C) to (TMf-150) (°C).

[0015] [6] The position control device sets the distance from the cooling start position to the restraint roll based on the conveying speed of the metal plate, the cooling start temperature of the metal plate at the time of cooling start by the cooling tank, the target temperature, and the cooling speed of the metal plate, and adjusts the height of the fluid surface of the cooling fluid in the cooling tank to the set distance [4] or [5] quenching device for a metal plate.

[0016] [7] The position control device is a quenching device for a metal plate described in [6], wherein the distance d (mm) from the cooling start position to the restraining roll is calculated using Equation (1) when the conveying speed of the metal plate is v (mm / s), the cooling start temperature is T1 (°C), the target temperature is T2 (°C), and the cooling speed of the metal plate by the cooling bath is CV (°C / s).

[0017] d = (T1-T2)×v / CV (1)

[0018] [8] The position control device described above is a quenching device for a metal plate as described in [7], wherein the cooling rate CV is set as CV = α / t by the coefficient α representing the cooling condition of the metal plate and the plate thickness t of the metal plate.

[0019] [9] A quenching device for a metal plate described in [2], wherein the distance between the fluid surface of the cooling fluid in the cooling tank and the collision location of the fluid stream from the nozzle on the metal plate is 30 mm or more and 2000 mm or less.

[0020]

[10] A method for quenching a metal plate while cooling it by conveying the metal plate, wherein the metal plate is immersed in a cooling tank containing a cooling fluid, and the height of the fluid surface of the cooling fluid in the cooling tank is set as the cooling start position to cool the metal plate, and the height of the fluid surface of the cooling fluid in the cooling tank is adjusted so that the metal plate is restrained by a restraining roll at the position where the metal plate is at the target temperature.

[0021]

[11] A method for quenching a metal plate as described in

[10] , wherein the temperature at the Ms point where the martensite transformation of the metal plate begins is TMs (°C) and the temperature at the Mf point where the martensite transformation ends is TMf (°C), and the target temperature is set to a temperature range of (TMs+150) (°C) to (TMf-150) (°C).

[0022]

[12] A method for quenching a metal plate described in

[10] or

[11] , wherein the height of the fluid surface of the cooling fluid is adjusted based on the conveying speed of the metal plate, the cooling start temperature of the metal plate at the start of cooling, the target temperature, and the cooling speed of the metal plate, and the distance from the cooling start position to the restraining roll is set, and the height of the fluid surface of the cooling fluid in the cooling tank is adjusted to the set distance.

[0023]

[13] A method for quenching a metal plate described in

[12] , wherein the distance from the cooling start position to the restraining roll by the cooling bath is calculated using Equation (1), where v (mm / s) is the conveying speed of the metal plate, T1 (°C) is the cooling start temperature, T2 (°C) is the target temperature, and CV (°C / s) is the cooling speed of the metal plate.

[0024] d = (T1-T2)×v / CV (1)

[0025]

[14] The above cooling rate CV is set as CV = α / t by the coefficient α representing the cooling conditions of the metal plate and the plate thickness t of the metal plate

[13] , in the quenching method of the metal plate described in

[13] .

[0026]

[15] A method for manufacturing a metal plate using the quenching method of a metal plate described in any one of

[10] ~

[14] .

[0027]

[16] A method of manufacturing a metal plate by performing any of the following on a metal plate obtained by the method described in

[15] : hot-dip galvanizing, electro-galvanizing, or alloying hot-dip galvanizing.

[0028]

[17] A method for quenching a metal plate as described in

[10] , wherein the cooling fluid is sprayed from a nozzle installed in the cooling tank to cool the metal plate, and the distance between the fluid surface of the cooling fluid in the cooling tank and the collision position of the fluid stream from the nozzle on the metal plate is 30 mm or more and 2000 mm or less. Effects of the invention

[0029] According to the present invention, during the quenching of a metal plate, the operation of a water level regulator is controlled to adjust the height of the fluid surface of the cooling fluid in the cooling tank, which is the cooling start position, thereby controlling the distance from the cooling start position to the restraining roll. This allows for the suppression of deviations in the shape of the metal plate that occur during quenching. Brief explanation of the drawing

[0030] FIG. 1 is a schematic diagram showing a quenching device related to an embodiment of the present invention. Figure 2 is a schematic diagram showing an example of the water level regulator of Figure 1. Figure 3 is a schematic diagram showing an example of the definition of the amount of bending of a metal plate. Figure 4 is a graph showing the relationship between the return speed and the target temperature in the example of the present invention. Figure 5 is a graph showing the relationship between the conveying speed and the amount of bending of the metal plate in the example of the present invention. Figure 6 is a graph showing the relationship between the return speed and the target temperature in Comparative Example 1. Figure 7 is a graph showing the relationship between the return speed and the amount of bending of the metal plate in Comparative Example 1. Figure 8 is a graph showing the relationship between the return speed and the target temperature in Comparative Example 2. Figure 9 is a graph showing the relationship between the return speed and the amount of bending of the metal plate in Comparative Example 2. Specific details for implementing the invention

[0031] An embodiment of the present invention will be described based on the drawings. FIG. 1 is a schematic diagram showing a quenching device related to an embodiment of the present invention. In addition, the quenching device (1) of FIG. 1 is applied to a cooling facility formed on the exit side of the cracking zone of a continuous annealing furnace, for example, to perform quenching of steel as a metal plate (S). The quenching device (1) of FIG. 1 for a metal plate comprises a cooling device (10) for cooling the metal plate (S) and a restraining roll (20) for restraining the cooled metal plate (S) in the thickness direction.

[0032] The cooling device (10) cools a metal plate (S) using a cooling fluid (CF) and is equipped with a cooling tank (11) that stores the cooling fluid (CF) and a plurality of nozzles (12) installed in the cooling tank (11) that spray the cooling fluid (CF) onto the surface of the metal plate (S). Water is stored in the cooling tank (11) as the cooling fluid (CF), and, for example, the metal plate (S) is immersed in the conveying direction (BD) from the upper surface of the cooling tank (11). Additionally, a sink roll (2) that changes the conveying direction of the metal plate (S) is installed in the cooling tank (11).

[0033] A plurality of nozzles (12) are formed, for example, slit nozzles, and are installed on each of the two sides of the metal plate (S) along the conveying direction of the metal plate (S). Accordingly, the metal plate (S) is cooled by the cooling fluid (CF) in the cooling tank (11) and the cooling fluid (CF) sprayed from the plurality of nozzles (12). In this way, by using both the cooling tank (11) and the plurality of nozzles (12) to cool the metal plate (S), the boiling state of the surface of the metal plate (S) is stabilized, and uniform shape control can be performed.

[0034] Additionally, although the case of water quenching using water as the cooling fluid (CF) is illustrated, cooling using oil or an ionic fluid as the cooling fluid (CF) may also be used. Furthermore, although the case in FIG. 1 is illustrated as having multiple nozzles (12) installed in the cooling tank (11), the cooling method is not limited to this as long as it is a method capable of cooling the metal plate (S) within a preset temperature range. For example, the metal plate (S) may be cooled using only the cooling tank (11) without using nozzles (12).

[0035] The restraining rolls (20) restrain the metal plate (S) cooled by the cooling device (10) in the thickness direction and are fixed to each side of the metal plate (S) inside the cooling tank (11). In addition, in FIG. 1, a pair of restraining rolls (20) are installed facing each other, but if they are to restrain, they may be installed at positions offset along the conveying direction. Also, FIG. 1 illustrates the case where a pair of restraining rolls (20) are installed, but they are not limited to a single pair and may be installed in multiple pairs or multiple rolls. In that case, the entire pair of restraining rolls may be position-controlled collectively.

[0036] Here, the quenching of the metal plate (S) is performed by immersing the metal plate (S) in the cooling fluid (CF) stored in the cooling tank (11). Accordingly, the cooling start position (SP) of the metal plate (S) changes according to the water level of the cooling tank (11). Thus, the metal quenching device (1) has the function of changing the cooling start position (SP) by changing the height of the fluid surface of the cooling tank (11).

[0037] A metal quenching device (1) is equipped with a level regulator (30) that adjusts the height of the fluid surface of the cooling fluid (CF) contained in the cooling tank (11), and a position control device (40) that controls the operation of the level regulator (30). FIG. 2 is a schematic diagram showing an example of the level regulator (30) of FIG. 1. The level regulator (30) of FIG. 2 has a regulating tank (31) that stores the cooling fluid (CF), a supply source (32) that supplies the cooling fluid (CF) to the regulating tank (31), and a dike (33) that controls the discharge of the cooling fluid (CF) within the regulating tank (31). The adjustment tank (31) and the cooling tank (11) are connected by a discharge pipe (34) through which a cooling fluid (CF) is discharged from the cooling tank (11) and a supply pipe (35) that supplies the cooling fluid (CF) to the cooling tank (11). In addition, in order to prevent boiling or hindering spraying from the nozzle (12), it is preferable that the discharge pipe (34) and the supply pipe (35) be formed below the fluid surface. Furthermore, the discharge pipe (34) and the supply pipe (35) may be integrated.

[0038] The height of the fluid level of the adjustment tank (31) and the cooling tank (11) is adjusted by the fluid flowing back and forth through the discharge pipe (34) and the supply pipe (35) so that they become equal by atmospheric pressure. Accordingly, for example, the height of the fluid level of the adjustment tank (31) can be adjusted by monitoring the height of the fluid level of the adjustment tank (31) and adjusting the amount of fluid stored in the adjustment tank (31). In addition, the cooling start position (SP) can be adjusted by this. Specifically, when the cooling start position (SP) is raised, cooling fluid (CF) is supplied into the adjustment tank (31) from the supply source (32), and the amount of fluid stored increases. Accordingly, the height of the fluid level of the cooling tank (11), that is, the cooling start position (SP), is raised. When the cooling start position (SP) is lowered, the dam (33) moves, so that the dam (33) descends, and the cooling fluid (CF) in the adjustment tank (31) overflows from the dam (33), thereby discharging the cooling fluid (CF) from the adjustment tank (31). Consequently, the height of the fluid surface of the cooling tank (11), i.e., the cooling start position (SP), is lowered.

[0039] In addition, the water level regulator (30) is not limited to the configuration of FIG. 2 and may be equipped with a pump for supplying and discharging cooling fluid (CF) to the cooling tank (11), or the height of the fluid level may be adjusted by immersing or removing an object of a volume determined at the time of design into the adjustment tank (31). Considering the precision and responsiveness of the management of the cooling fluid (CF), such as liquid temperature or contamination, and the adjustment of the height of the fluid level, it is preferable to connect the adjustment tank (31) to the cooling tank (11) along with the drainage by the pump described above, and to adjust the fluid level of the cooling tank (11) by adjusting the amount of water stored in the adjustment tank (31).

[0040] The position control device (40) is composed of hardware resources such as a computer and controls the water level regulator (30) to control the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11). In particular, the position control device (40) controls the operation of the water level regulator (30) to adjust the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11) so that the metal plate (S) is constrained at a position (RP) where it reaches a target temperature. Here, the target temperature is preferably set to a temperature range of (TMs+150) (°C) to (TMf-150) (°C), where the temperature of the Ms point at which the martensite transformation of the metal plate (S) begins is TMs (°C) and the temperature of the Mf point at which the martensite transformation ends is TMf (°C). Thus, at a location where rapid thermal shrinkage and transformation expansion occur simultaneously in the metal plate (S), the deformation of the metal plate (S) can be restrained by the restraining roll (20), thereby suppressing the deformation of the metal plate (S) during quenching.

[0041] The position control device (40) calculates the distance d from the target cooling start position (SP) of the metal plate (S) by the cooling fluid (CF) to the target temperature position (RP), and adjusts the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11) based on the calculated distance d. At this time, the position control device (40) calculates the distance d using the conveying speed v (mm / s) of the metal plate (S), the cooling start temperature T1 (°C), the target temperature T2 (°C), and the cooling speed CV (°C / s) of the metal plate (S) by the cooling device (10). In addition, the above parameters may be obtained sequentially from the set values ​​of the process computer or actual operation values, or may be measured using a speed sensor or a temperature sensor, etc. The cooling start temperature T1 (°C) refers to the temperature at which cooling of the metal plate (S) begins, specifically, the temperature of the metal plate (S) immediately before the cooling start position (SP). For example, based on the cooling condition of the metal plate (S) up to the cooling start position (SP) or the quenching device (1), the temperature of the metal plate (S) just before reaching the cooling start position (SP) can be calculated. Specifically, the temperature of the metal plate (S) is measured by a non-contact type thermometer at the exit side of the cracking zone of the continuous annealing furnace. Then, based on that temperature and the temperature drop due to natural cooling of the metal plate (S) up to reaching the quenching device (1), the temperature of the metal plate (S) just before or at the time of reaching the cooling start position (SP) can be calculated. The temperature drop due to natural cooling of the metal plate (S) described above can be determined in advance through experiment. Target temperature T2 refers to the target value of the temperature of the metal plate (S) at the position (RP) where the metal plate (S) is restrained by the restraining roll (20).

[0042] Specifically, the relationship between distance d and cooling rate CV (°C / s) is expressed by the following equation (1).

[0043] CV = (T1-T2) / (d / v)

[0044] d = (T1-T2)×v / CV … (1)

[0045] The cooling rate CV (°C / s) can be expressed by the following equation (2) using a coefficient α (°C·mm / s) representing cooling conditions such as nozzle shape, type of cooling fluid (CF) being sprayed, temperature, and amount of spray, and the thickness t of the metal plate (S).

[0046] CV = α / t … (2)

[0047] (1) If equation (2) is substituted into equation (1), the distance d can be expressed by equation (3) below.

[0048] d = (T1-T2)×v×t / α… (3)

[0049] In the position control device (40), a cooling rate CV (°C / s) or α (°C·mm / s) obtained in advance through experiments or numerical analysis is stored. Then, the position control device (40) calculates a distance d using equation (1) or equation (3) and adjusts the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11) so as to restrain the metal plate (S) at the calculated distance d. In addition, the cooling rate CV is a value determined according to the plate thickness, etc., and for a plate thickness of 1 to 2 mm, the cooling rate CV = 1000 to 2000 (°C / s) and α = 500 to 2000 (°C·mm / s). Therefore, in the position control device (40), the cooling rate CV may be set to 1500 (°C / s), which is the middle of the above range. In this case, α may be treated as an intermediate value of 1250 (°C·mm / s). In this way, the cooling condition α obtained by the cooling rate CV and plate thickness t described above and equation (2) may be set.

[0050] If the height of the fluid surface can be changed, it is possible to change the initial cooling rate CV of the metal plate (S) by combining low-speed cooling by simply immersing the metal plate (S) in the fluid with rapid cooling by the nozzle (12). In the cooling section by the nozzle (12) that sprays the fluid, a high cooling rate CV is obtained by destroying the vapor film formed on the surface of the metal plate (S) by boiling through the fluid stream. On the other hand, in the cooling section by simply immersing the metal plate (S) in the fluid, the surface of the metal plate (S) becomes covered with a vapor film, resulting in a film boiling state, and heat transfer between the fluid and the metal plate (S) is inhibited by the vapor film. Therefore, the cooling rate CV is reduced. By using this low-speed cooling by film boiling, not only is stress caused by rapid temperature changes suppressed, but the metal plate (S) at the beginning of cooling can be cooled more uniformly, thereby reducing temperature deviation. Because of this, it is possible to suppress the shape deformation of the metal plate (S) and obtain a metal plate (S) with a flatter shape.

[0051] For this reason, when simply immersing a metal plate (S) in a fluid and cooling by a nozzle (12) are used in combination, it is preferable that the height of the liquid surface be higher than the position where the fluid stream from the nozzle (12) strikes the metal plate (S). The range of the height of the fluid surface from the nozzle (12), that is, the distance between the fluid surface and the nozzle (12), is preferably 30 mm or more and 2000 mm or less, for example.

[0052] When the fluid surface is closer to the collision position of the fluid stream than the lower limit of the above distance of 30 mm, the fluid surface fluctuates due to the influence of the fluid stream from the nozzle (12). Specifically, because periodic up-and-down movement of the fluid surface occurs, the cooling capacity for the metal plate (S) is not stable. As a result, the temperature (constraint temperature) at the point where the metal plate (S) is constrained by the constraining roll (20) fluctuates, and there is a possibility that periodic shape changes of the metal plate (S) may occur.

[0053] The upper limit of the above distance is preferably determined appropriately according to the metallurgical properties of the metal plate (S), the conveying speed (v), the cooling speed CV, etc. Generally, in order to obtain desired metal properties by liquid quenching, rapid cooling in the transformation temperature range is required. Therefore, considering that the conveying speed range in the general metal plate quenching process is 10 m / min to 600 m / min, it is not desirable for the above upper limit to exceed 2000 mm. This is because if the upper limit exceeds 2000 mm, there is a high possibility that sufficient cooling capacity for the metal plate (S) in the transformation temperature range will not be obtained. Therefore, the distance between the fluid surface and the nozzle (12) is preferably 30 mm or more and 2000 mm or less. Furthermore, in order to stabilize the fluid surface more and obtain an effective cooling speed, it is more desirable for the distance to be 50 mm or more and 1000 mm or less.

[0054] With reference to FIG. 1, the quenching method and the method for manufacturing a metal plate according to the present invention will be described. First, while conveying the metal plate (S), the metal plate (S) is cooled by a cooling device (10), and quenching of the metal plate (S) is performed. At this time, at the position (RP) where the metal plate (S) reaches the target temperature T2, the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11) is adjusted so as to restrain the metal plate (S) from both sides in the thickness direction of the metal plate (S). Specifically, in the position control device (40), a distance d is calculated using the above equation (1) or equation (3), and the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11) is adjusted so as to restrain the metal plate (S) at the calculated distance d position. In addition, the adjustment of the fluid surface height can be performed sequentially even while the metal plate (S) is being quenched. For example, the position control device (40) may calculate the distance d and adjust the height of the fluid surface at the timing when the return speed v is changed.

[0055] The conveying speed of the metal plate (S) varies even for a single metal plate (S) (in one coil). Therefore, it is also desirable to be able to move the height of the fluid surface up and down while restraining the metal plate (S) with the restraining roll (20), as this can improve the yield of the decelerating parts, such as the leading edge and trailing edge of the metal plate (S). Alternatively, the position control device (40) may calculate the distance d and adjust the height of the fluid surface at set intervals.

[0056] According to the above embodiment, the operation of the water level regulator (30) is controlled to adjust the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11), which is the cooling start position (SP). By doing so, the metal plate (S) at the target temperature T2 can be restrained by the restraining roll (20) regardless of the manufacturing conditions of the metal plate (S). As a result, in a continuous annealing facility, shape defects of the metal plate (S) caused by the manufacturing conditions of the metal plate (S) during quenching can be suppressed.

[0057] That is, the temperature of the metal plate (S) being conveyed to the quenching device (1) varies depending on the manufacturing conditions of the metal plate (S), such as the conveying speed v, the cooling start temperature T1 of the metal plate (S), and the thickness t of the metal plate (S). Therefore, if the distance d is set to be constant regardless of the manufacturing conditions, the temperature of the metal plate (S) when it reaches the restraining roll (20) will also vary.

[0058] In order to resolve this problem, in short, it was found that adjusting the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11) is effective in accurately controlling the shape of the metal plate (S) at different optimal temperature positions depending on the manufacturing conditions. By adjusting the height of the fluid surface of the cooling fluid (CF) in the cooling tank (11), the metal plate (S) can be constrained within the target temperature range even if the manufacturing conditions change.

[0059] In particular, it is possible to reduce the complex and non-uniform irregular shape that occurs when the microstructure expands in volume due to martensitic transformation during rapid cooling of the metal plate (S). Therefore, the deformation suppression effect is particularly greater when the metal plate (S) is a high-strength steel plate (high-tensile). Specifically, it is desirable to apply this to the manufacture of steel plates with a tensile strength of 580 MPa or more. The upper limit of the tensile strength is not specifically limited, but as an example, it should be 2000 MPa or less. Examples of the above high-strength steel plates (high-tensile) include high-strength cold-rolled steel plates, and hot-dip galvanized steel plates, electro-galvanized steel plates, and alloyed hot-dip galvanized steel plates that have undergone surface treatment.

[0060] In addition, as a specific example of the composition of the high-strength steel plate, in mass%, C is 0.04% or more and 0.35% or less, Si is 0.01% or more and 2.50% or less, Mn is 0.80% or more and 3.70% or less, P is 0.001% or more and 0.090% or less, S is 0.0001% or more and 0.0050% or less, sol.Al is 0.005% or more and 0.065% or less, optionally, at least one of Cr, Mo, Nb, V, Ni, Cu, and Ti is 0.5% or less each, additionally optionally, B and Sb are 0.01% or less each, and the remainder is Fe and unavoidable impurities. In addition, the metal plate is not limited to a steel plate and may be a metal plate other than a steel plate.

[0061] Example 1

[0062] An embodiment of the present invention is described. As an example of the present invention, quenching was performed on a high-tensile cold-rolled steel sheet (hereinafter referred to as "steel sheet") with a tensile strength of 1470 MPa, having a plate thickness t of 1.0 mm and a plate width of 1000 mm, using a quenching device (1) related to the embodiment of the present invention. As the composition of the steel sheet with a tensile strength of 1470 MPa, in mass%, C was 0.20%, Si 1.0%, Mn 2.3%, P 0.005%, and S 0.002%. The temperature TMs of the Ms point of the steel sheet is 300 ℃, and the temperature TMf of the Mf point is 250 ℃. Therefore, the target temperature T2 of the steel plate when passing through the restraining roll (20) should be set to be in the range of 450 ℃ to 100 ℃. In this embodiment, the target temperature T2 was set to 400 ℃. Also, the cooling start temperature T1 was set to 800 ℃. The temperature of the cooling fluid (CF) was approximately 30 ℃, and the cooling rate CV was set to 1500 (℃ / s).

[0063] As a change in manufacturing conditions, the conveying speed v was varied between 1000 mm / s and 3000 mm / s, and based on Equation (1), the distance d (mm) was controlled to d = 267 mm to 800 mm in accordance with the change in conveying speed v. Ten steel plates were collected at intervals of 100 m in the longitudinal direction (i.e., the same direction as the conveying direction of the steel plate) after cooling, and the amount of bending of each steel plate was investigated. FIG. 3 is a schematic diagram showing an example of the definition of the amount of bending. As shown in FIG. 3, the amount of bending was defined as the height from the ground plane to the highest position when the steel plate is placed on a horizontal plane.

[0064] FIG. 4 is a graph showing the relationship between the conveying speed v and the target temperature in the example of the present invention, and FIG. 5 is a graph showing the relationship between the conveying speed v and the amount of bending of the metal plate in the example of the present invention. As shown in FIG. 4, even when the conveying speed v changes, the temperature (°C) of the steel plate when passing through the restraining roll (20) becomes 400±25°C by adjusting the height of the fluid surface of the cooling fluid (CF) according to the conveying speed v and changing the distance d. That is, even when the conveying speed v changes, the temperature (°C) of the steel plate when passing through the restraining roll (20) can be controlled within the range of the target temperature T2 (450°C to 100°C). As a result, as shown in FIG. 5, the amount of bending of the steel plate is reduced to 10 mm or less. By doing so, the deviation, which is the difference between the maximum and minimum values ​​of the bending amount, was suppressed to 4.2 mm.

[0065] FIG. 6 is a graph showing the relationship between the return speed v and the target temperature in Comparative Example 1, and FIG. 7 is a graph showing the relationship between the return speed v and the amount of bending of the metal plate in Comparative Example 1. In Comparative Example 1, the distance d (mm) from the cooling start position to the restraining roll (20) was kept constant at d = 400 mm, and other conditions were kept the same as those in the present invention example.

[0066] In Comparative Example 1, as shown in FIG. 6, the temperature (°C) of the steel plate passing through the restraining roll (20) varied significantly depending on the conveying speed v (mm / s) and could not be controlled. Consequently, under conditions other than v = 1000 mm / s and v = 1500 mm / s, the temperature (°C) of the steel plate passing through the restraining roll (20) deviated from the target temperature T2, which is 450°C to 100°C. As a result, as shown in FIG. 7, under conditions other than v = 1000 mm / s and v = 1500 mm / s, the amount of bending of the steel plate was all 10 mm or more, and the deformation suppression effect of the steel plate was insufficient. Consequently, the deviation, which is the difference between the maximum and minimum values ​​of the amount of bending, increased to 10.3 mm.

[0067] FIG. 8 is a graph showing the relationship between the return speed v and the target temperature in Comparative Example 2, and FIG. 9 is a graph showing the relationship between the return speed v and the amount of bending of the metal plate (S) in Comparative Example 2. In Comparative Example 2, as shown in Patent Document 2, the distance d was controlled by controlling the cooling start position by moving the movable masking while keeping the restraining roll (20) fixed. The steel plate was manufactured with the other conditions being the same as those of the present invention.

[0068] As shown in FIG. 8, in Comparative Example 2, the temperature (°C) of the steel plate passing through the restraining roll (20) varied significantly regardless of the conveying speed v (mm / s) and could not be controlled. Consequently, under all conditions, the temperature (°C) of the steel plate passing through the restraining roll (20) deviated from the target temperature T2, which is 450°C to 100°C. Furthermore, as shown in FIG. 9, under all conditions, there were steel plates with a bending amount exceeding 10 mm, and the deformation suppression effect of the steel plate was insufficient. As a result, the deviation, which is the difference between the maximum and minimum values ​​of the bending amount, increased to 9.2 mm.

[0069] The embodiments of the present invention are not limited to the above embodiments, and various modifications may be added. For example, the above embodiments are exemplified for cases where the target temperature T2 is (TMs+150) (°C) to (TMf-150) (°C), but are not limited thereto. In terms of ensuring freedom of processing in subsequent processes or operation, for example, if it is sufficient that there is no deviation in the shape of the metal plate (S), such as the amount of warping, the target temperature T2 does not need to be limited to (TMs+150) (°C) to (TMf-150) (°C).

[0070] In this case, while keeping in mind the processing in the subsequent process and the securing of the degree of freedom of operation, a target temperature T2 is predetermined by considering the predicted shape (e.g., amount of bending). In addition, the distance d from the cooling start position to the restraining roll (20) is controlled by adjusting the position of the restraining roll (20). In this way, the temperature of the metal plate (S) when passing through the restraining roll (20) is set to the predetermined target temperature T2, and the deviation of the shape of the metal plate (S), that is, the amount of bending of the metal plate (S) defined in FIG. 3, is made to be within 4 mm.

[0071] Additionally, although the example is given in which the position of the restraining roll (20) is fixed, the restraining roll (20) may be configured to move in the longitudinal direction of the metal plate (S), that is, in the conveying direction of the metal plate (S). That is, the quenching device (1) of the metal plate (S) may be equipped with a roll moving device that moves the restraining roll (20), for example, made of a motor. In this case, the distance d is controlled by both the height of the fluid surface of the cooling fluid (CF) and the position of the restraining roll (20). Thus, for example, when one wants to increase the distance d, the distance d can be quickly adjusted by moving the restraining roll (20) in the conveying direction of the metal plate (S) while increasing the height of the fluid surface. Alternatively, precise control of the distance d can be performed, such as by adjusting the approximate distance d by the water level adjuster (30) and adjusting the distance d by adjusting the position of the restraint roll (20).

[0072] Example 2

[0073] Quenching of the steel plate was performed under the same manufacturing conditions as in Example 1, except that the conveying speed v was varied between 1000 mm / s and 2500 mm / s, and the distance between the fluid surface and the collision position of the fluid stream from the nozzle (12) on the steel plate in the vertical direction (hereinafter referred to as the collision position) was varied between 0 mm and 400 mm. Table 1 shows the results of verifying the relationship between the height of the fluid surface and the collision position in Example 2. In addition, the collision position is the position where a straight line drawn from the center of the nozzle (12) in the direction of fluid injection intersects the surface of the steel plate. In addition, the presence or absence of a change in the shape of the steel plate in the longitudinal direction (i.e., the same direction as the conveying direction of the steel plate) was performed by visual inspection under a sufficiently bright fluorescent light during the exit inspection.

[0074]

[0075] As shown in Table 1, in Reference Examples 1 to 3, where the distance between the fluid surface and the collision position is 0 mm to 20 mm, a variation was observed in which the bending shape of the steel plate periodically changed between upward bending and downward bending in the conveying direction of the steel plate. Furthermore, upward bending refers to the deformation such that the central part of the steel plate in the width direction becomes convex upward compared to both ends. Downward bending refers to the deformation such that, conversely to upward bending, both ends of the steel plate in the width direction become convex upward compared to the central part.

[0076] In addition, in Reference Examples 1 to 3, the maximum bending amount in the width direction of the steel plates taken every 100 m showed a tendency to be slightly higher compared to Examples 1 to 5 of the present invention.

[0077] In Examples 1 to 5 of the present invention, where the distance between the fluid surface and the collision position was 30 mm or more, no periodic bending variation in the longitudinal direction of the steel plate was observed. In addition, the maximum amount of bending in the width direction of the steel plate taken every 100 m showed a tendency to decrease with increasing distance and conveying speed v. That is, in Examples 1 to 5 of the present invention, by setting the height of the fluid surface to be 30 mm or more higher than the collision position of the fluid stream from the nozzle, the initial cooling of the steel plate could be slow cooling. This allowed the stress caused by rapid thermal shrinkage to be reduced, thereby suppressing deformation of the steel plate's shape and reducing the amount of bending of the steel plate. Explanation of the symbols

[0078] 1 : Quenching device for metal plates 10: Cooling device 11: Cooling tank 12: Nozzle 20: Restraint Roll 30 : Water level regulator 40: Position control device BD: Return direction CF: Cooling fluid S : Metal plate

Claims

Claim 1 A quenching device for a metal plate that cools while conveying a metal plate comprises: a cooling tank that stores a cooling fluid and cools the metal plate by immersing it; a restraining roller installed in the cooling tank that conveys the metal plate cooled by the cooling tank while restraining it in the thickness direction; a water level regulator that adjusts the height of the fluid surface of the cooling fluid in the cooling tank, which is the cooling start position of the metal plate; and a position control device that controls the operation of the water level regulator to control the height of the fluid surface of the cooling fluid in the cooling tank. The water level regulator comprises a control tank that stores the cooling fluid and is connected to the cooling tank to allow the cooling fluid to flow between them; a supply source that supplies the cooling fluid to the control tank; and a dike configured to be vertically movable and controls the discharge of the cooling fluid from the control tank by moving vertically. The position control device adjusts the amount of the cooling fluid stored in the control tank by moving the dike vertically so that the restraining roller restrains the metal plate at the position where the metal plate reaches a target temperature, thereby controlling the amount of the cooling fluid in the cooling tank A metal plate quenching device for adjusting the height of the fluid surface of the above cooling fluid. Claim 2 A quenching device for a metal plate according to claim 1, further comprising a plurality of nozzles installed within the cooling tank and spraying the cooling fluid onto the metal plate to cool it. Claim 3 delete Claim 4 delete Claim 5 A quenching apparatus for a metal plate according to claim 1, wherein the temperature of the Ms point at which the martensite transformation of the metal plate begins is TMs (°C) and the temperature of the Mf point at which the martensite transformation ends is TMf (°C), and the target temperature is set to a temperature range of (TMs+150) (°C) to (TMf-150) (°C). Claim 6 A quenching device for a metal plate according to claim 1 or 5, wherein the position control device sets the distance from the cooling start position to the restraining roll based on the conveying speed of the metal plate, the cooling start temperature of the metal plate at the time of cooling start by the cooling tank, the target temperature, and the cooling speed of the metal plate, and adjusts the height of the fluid surface of the cooling fluid in the cooling tank so as to be the set distance. Claim 7 In claim 6, the position control device is a quenching device for a metal plate, wherein the distance d (mm) from the cooling start position to the restraining roll is calculated using Equation (1), where v (mm / s) is the conveying speed of the metal plate, T1 (°C) is the cooling start temperature, T2 (°C) is the target temperature, and CV (°C / s) is the cooling speed of the metal plate by the cooling bath. d = (T1-T2)×v / CV (1) Claim 8 In claim 7, the position control device is a quenching device for a metal plate, wherein the cooling rate CV is set as CV = α / t by a coefficient α representing the cooling condition of the metal plate and the plate thickness t of the metal plate. Claim 9 A quenching device for a metal plate according to claim 2, wherein the distance between the fluid surface of the cooling fluid in the cooling tank and the collision position of the fluid stream from the uppermost nozzle among the plurality of nozzles on the metal plate is 30 mm or more and 2000 mm or less, and the collision position is a position where the center axis of the uppermost nozzle intersects the surface of the metal plate. Claim 10 A method for quenching a metal plate while cooling it while conveying the metal plate, wherein the metal plate is immersed in a cooling tank in which a cooling fluid is stored, and the height of the fluid surface of the cooling fluid in the cooling tank is set as the cooling start position to perform cooling of the metal plate, wherein the cooling fluid is stored so that the metal plate is restrained by a restraining roll at a position in which the metal plate is at a target temperature in the cooling tank, and further wherein the height of the fluid surface of the cooling fluid in the cooling tank is adjusted by adjusting the amount of the cooling fluid stored in the adjustment tank by moving a dike provided in an adjustment tank connected to the cooling tank so that the cooling fluid can flow between the cooling tank and the adjustment tank. Claim 11 A method for quenching a metal plate according to claim 10, wherein the temperature of the Ms point at which the martensite transformation of the metal plate begins is TMs (°C) and the temperature of the Mf point at which the martensite transformation ends is TMf (°C), and the target temperature is set to a temperature range of (TMs+150) (°C) to (TMf-150) (°C). Claim 12 A method for quenching a metal plate according to claim 10, wherein the height of the fluid surface of the cooling fluid is adjusted by setting a distance from the cooling start position to the restraining roll based on the conveying speed of the metal plate, the cooling start temperature of the metal plate at the start of cooling, the target temperature, and the cooling speed of the metal plate, and adjusting the height of the fluid surface of the cooling fluid in the cooling tank so that the set distance is achieved. Claim 13 A quenching method for a metal plate according to claim 12, wherein the distance from the cooling start position by the cooling bath to the restraining roll is calculated using Equation (1), where v (mm / s) is the conveying speed of the metal plate, T1 (°C) is the cooling start temperature, T2 (°C) is the target temperature, and CV (°C / s) is the cooling speed of the metal plate. d = (T1-T2)×v / CV (1) Claim 14 A quenching method for a metal plate according to claim 13, wherein the cooling rate CV is set as CV = α / t by a coefficient α representing the cooling conditions of the metal plate and the plate thickness t of the metal plate. Claim 15 A method for manufacturing a metal plate using a quenching method for a metal plate described in any one of claims 10 to 14. Claim 16 A method for manufacturing a metal plate, wherein any one of hot-dip galvanizing, electro-galvanizing, or alloying hot-dip galvanizing is performed on a metal plate obtained by the method described in claim 15. Claim 17 A method for quenching a metal plate according to claim 10, wherein the cooling fluid is sprayed onto the metal plate from a plurality of nozzles installed in the cooling tank to cool it, and the distance between the fluid surface of the cooling fluid in the cooling tank and the collision position of the fluid stream from the uppermost nozzle among the plurality of nozzles on the metal plate is 30 mm or more and 2000 mm or less, and the collision position is a position where the center axis of the uppermost nozzle intersects the surface of the metal plate.

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