WO2023026774A1

WO2023026774A1 - Quench-hardening apparatus, quench-hardening method, and metal sheet manufacturing method

Info

Publication number: WO2023026774A1
Application number: PCT/JP2022/029365
Authority: WO
Inventors: 宗司吉本; 弘和小林
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2021-08-24
Filing date: 2022-07-29
Publication date: 2023-03-02
Also published as: KR20240035543A; EP4372106A1; CN117836436A; JPWO2023026774A1

Abstract

The present invention addresses the problem of suppressing unevenness in the shape of a metal sheet, generated when performing quench hardening thereof.　A metal-sheet quench-hardening apparatus (1) cools a metal sheet (S) while conveying said metal sheet and includes: a cooling bath (11) that stores a cooling fluid (CF) and in which the metal sheet (S) is immersed and cooled; a restraint roll (20) that is installed in the cooling bath (11) and that conveys the metal sheet (S) that has been cooled by the cooling bath (11) while restraining said metal sheet in the thickness direction; a liquid-level adjuster (30) that adjusts the height of a fluid surface of the cooling fluid (CF) in the cooling bath (11); and a position controller (40) that controls the operation of the liquid-level adjuster (30) to adjust the height of the fluid surface of the cooling fluid (CF) in the cooling bath (11).

Description

Quenching apparatus, quenching method, and method for manufacturing metal plate

The present invention relates to a quenching apparatus, a quenching method, and a method of manufacturing a metal plate that perform annealing while continuously conveying the metal plate.

In a continuous annealing facility where metal sheets are annealed while being continuously transported, the metal sheets are built in by phase transformation caused by cooling the metal sheets after heating. Especially in the automobile industry, the demand for thin high-strength steel sheets (high-tensile steel) is increasing for the purpose of achieving both weight reduction and collision safety. When manufacturing high-strength steel sheets, a technique for rapidly cooling the steel sheets is important. A water quenching method is known as one of the techniques with the fastest cooling rate for a metal plate. In the water quenching method, a heated metal plate is immersed in water and at the same time cooling water is sprayed onto the metal plate from a quench nozzle provided in the water, thereby quenching the metal plate.

When the metal plate is quenched, shape defects such as warping and wavy deformation occur in the metal plate. This is due to thermal contraction or the like due to the metal plate being quenched by the cooling liquid. In particular, when the temperature of the metal plate changes from the temperature Ms at which martensitic transformation starts to the temperature Mf at which martensitic transformation ends, rapid thermal contraction and transformation expansion occur at the same time.

Therefore, conventionally, various methods have been proposed to prevent shape defects of metal plates during quenching (see Patent Documents 1 and 2, for example). In Patent Document 1, when the temperature at the Ms point where the martensitic transformation of the metal plate starts is TMs (°C) and the temperature at the Mf point where the martensitic transformation ends is TMf (°C), the temperature of the metal plate is ( A method has been proposed in which a metal plate is constrained by a pair of constraining rolls provided in a cooling liquid in the range of TMs+150) (°C) to (TMf-150) (°C).

In Patent Document 2, when performing a quenching method in which water is jetted from a plurality of water jet nozzles onto the surface of a metal plate to cool it, the metal plate is restrained by restraint rolls, and the metal plate is cooled by a cooling fluid using a movable mask. It is disclosed to control the distance between the cooling start position and the constraining roll. Furthermore, as in Patent Document 1, when the temperature at the Ms point where the martensitic transformation of the metal plate starts is TMs (° C.) and the temperature at the Mf point where the martensitic transformation ends is TMf (° C.), the metal plate is ( A technique has been proposed in which the film is passed through restraint rolls at a temperature of TMs+150) (° C.) to (TMf−150) (° C.).

Japanese Patent No. 6094722 JP 2019-90106 A

However, in the method described in Patent Document 1, the position where the temperature of the metal plate falls within the range of (TMs+150) (°C) to (TMf-150) (°C) changes depending on the manufacturing conditions of the metal plate. For this reason, the constraining rolls cannot constrain the metal plate at a position where the temperature of the metal plate is (TMs+150)(°C) to (TMf-150)(°C), which may cause variations in the shape of the metal plate. be.

In the method described in Patent Document 2, the water that collides with the movable masking falls due to gravity and interferes with the water that is jetted from the water jetting nozzle at the bottom of the movable masking, thereby destabilizing the cooling ability of the metal plate. Become. In addition, since each nozzle is masked, the cooling capacity changes stepwise (discontinuously), and as a result, the temperature of the metal plate becomes (TMs+150) (°C) to (TMf-150) (°C). The position may become unstable and the shape of the metal plate may vary.

The present invention has been made to solve such problems, and provides a quenching apparatus, a quenching method, and a method of manufacturing a metal plate product that can suppress variations in the shape of a metal plate that occur during quenching. for the purpose.

[1] A metal plate quenching apparatus that cools a metal plate while it is conveyed, comprising: a cooling tank in which a cooling fluid is stored and the metal plate is immersed and cooled; a constraining roll that conveys the metal plate cooled by by constraining it in the thickness direction, and a water level adjuster 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 for controlling the height of the fluid surface of the cooling fluid in the cooling tank by controlling the operation of the water level adjuster.
[2] The apparatus for quenching a metal plate according to [1], further comprising a plurality of nozzles installed in the cooling tank for cooling the metal plate by injecting the cooling fluid.
[3] The water level adjuster stores the cooling fluid, and controls an adjustment tank connected to the cooling tank, a supply source to the adjustment tank, and discharge of the cooling fluid from the adjustment tank. The weir according to [1] or [2], wherein the height of the fluid surface of the cooling fluid in the cooling tank is adjusted by adjusting the storage amount of the cooling fluid in the adjustment tank. Quenching equipment for metal plates.
[4] The position control device adjusts the height of the fluid surface of the cooling fluid in the cooling tank so that the constraining roll constrains the metal plate at a position where the metal plate reaches the target temperature. 1] The apparatus for hardening a metal plate according to any one of [3].
[5] The target temperature is (TMs+150), where TMs (° C.) is the temperature at the Ms point where the martensitic transformation of the metal plate starts, and TMf (° C.) is the temperature at the Mf point where the martensitic transformation ends. (° C.) to (TMf-150) (° C.).
[6] The position control device controls the distance from the cooling start position to the restraint roll, the conveying speed of the metal plate, the cooling start temperature of the metal plate at the start of cooling by the cooling tank, and the target temperature. and the cooling rate of the metal plate, and adjust the height of the fluid surface of the cooling fluid in the cooling tank so that the set distance is reached. The metal according to [4] or [5] Plate quenching equipment.
[7] The position control device has a conveying speed of the metal plate of v (mm/s), a cooling start temperature of T1 (°C), a target temperature of T2 (°C), and cooling of the metal plate by the cooling bath. The metal plate quenching apparatus according to [6], wherein the distance d (mm) from the cooling start position to the constraining roll is determined by the formula (1), where CV (° C./s) is the speed.
d=(T1-T2)×v/CV (1)
[8] Described in [7], wherein in the position control device, the cooling rate CV is set as CV=α/t by a coefficient α indicating a cooling condition of the metal plate and a plate thickness t of the metal plate. metal plate quenching equipment.
[9] The metal plate according to [2], wherein the distance between the liquid surface of the cooling fluid in the cooling tank and the collision position of the liquid jet from the nozzle on the metal plate is 30 mm or more and 2000 mm or less. Quenching equipment.
[10] A method of quenching a metal plate in which the metal plate is cooled while being transported, 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 measured. is the cooling start position, and the metal plate is cooled at the position where the metal plate is at the target temperature, and the cooling fluid in the cooling bath is restrained by the restraining rolls at the position where the metal plate is at the target temperature. A metal plate quenching method that adjusts the height of the fluid surface.
[11] The target temperature is (TMs + 150), where TMs (°C) is the temperature at the Ms point where the martensitic transformation of the metal plate starts, and TMf (°C) is the temperature at the Mf point where the martensitic transformation ends. (° C.) to (TMf-150) (° C.).
[12] The height of the fluid surface of the cooling fluid is adjusted according to 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. Based on this, the distance from the cooling start position to the constraining roll is set, and the height of the fluid surface of the cooling fluid in the cooling tank is adjusted so as to achieve the set distance. A method of quenching a metal plate.
[13] The distance from the cooling start position of the cooling tank to the constraining roll is v (mm/s) for the conveying speed of the metal plate, T1 (°C) for the cooling start temperature, and T2 (°C) for the target temperature. , where the cooling rate of the metal plate is CV (° C./s), the distance d (mm) from the cooling start position to the restraint roll is obtained by formula (1). Method.
d=(T1-T2)×v/CV (1)
[14] The method of hardening a metal plate according to [13], wherein the cooling rate CV is set as CV=α/t by a coefficient α indicating the cooling condition of the metal plate and a plate thickness t of the metal plate. .
[15] A method for producing a high-strength cold-rolled steel sheet, using the metal plate quenching method according to any one of [10] to [14].
[16] A method for producing a high-strength steel sheet, wherein the high-strength steel sheet obtained by the method described in [15] is subjected to any one of hot-dip galvanizing treatment, electro-galvanizing treatment, or galvannealing treatment.
[17] Cooling the metal plate by injecting the cooling fluid from a nozzle installed in the cooling tank, and liquid jet flow from the nozzle on the liquid surface of the cooling fluid in the cooling tank and the metal plate The method of quenching a metal plate according to [10], wherein the distance between the collision position of is 30 mm or more and 2000 mm or less.

According to the present invention, during quenching of a metal plate, by controlling the operation of the water level adjuster to adjust the height of the fluid surface of the cooling fluid in the cooling tank, which is the cooling start position, the cooling start position is restrained. You can control the distance to the roll. As a result, variations in the shape of the metal plate that occur during quenching can be suppressed.

It is a mimetic diagram showing a quenching device concerning an embodiment of the present invention. FIG. 2 is a schematic diagram showing an example of the water level adjuster of FIG. 1; It is a schematic diagram which shows an example of the definition of the curvature amount of a metal plate. It is a graph which shows the relationship between the conveyance speed and target temperature in the example of this invention. It is a graph which shows the relationship between the conveyance speed and the curvature amount of a metal plate in the example of this invention. 7 is a graph showing the relationship between the conveying speed and the target temperature in Comparative Example 1. FIG. 7 is a graph showing the relationship between the conveying speed and the warp amount of the metal plate in Comparative Example 1. FIG. 9 is a graph showing the relationship between the conveying speed and the target temperature in Comparative Example 2. FIG. 9 is a graph showing the relationship between the conveying speed and the amount of warpage of the metal plate in Comparative Example 2. FIG.

An embodiment of the present invention will be described based on the drawings. FIG. 1 is a schematic diagram showing a hardening apparatus according to an embodiment of the present invention. The quenching apparatus 1 shown in FIG. 1 is for quenching a steel material, for example, as a metal sheet S, and is applied to a cooling facility provided on the delivery side of a soaking zone of a continuous annealing furnace. A metal plate quenching apparatus 1 shown in FIG. 1 includes a cooling device 10 that cools a metal plate S, and restraint rolls 20 that restrain the cooled metal plate S in the thickness direction.

The cooling device 10 cools the metal plate S using the cooling fluid CF. and a plurality of nozzles 12 for jetting. Water is stored in the cooling tank 11 as a cooling fluid CF. For example, the metal plate S is immersed from the upper surface of the cooling tank 11 in the transport direction BD. A sink roll 2 for changing the conveying direction of the metal plate S is installed in the cooling tank 11 .

The plurality of nozzles 12 are, for example, slit nozzles or the like, and are installed on both sides of the metal plate S along the conveying direction of the metal plate S. Therefore, the metal plate S is cooled by the cooling fluid CF in the cooling tank 11 and the cooling fluid CF jetted from the plurality of nozzles 12 . By cooling the metal plate S using both the cooling bath 11 and the plurality of nozzles 12 in this manner, the boiling state of the surface of the metal plate S is stabilized, and uniform shape control can be performed.

Although the case of water quenching using water as the cooling fluid CF is exemplified, cooling using oil or an ionic liquid as the cooling fluid CF is also possible. In addition, FIG. 1 illustrates a case where a plurality of nozzles 12 are installed in the cooling tank 11, but if the method can cool the metal plate S within a preset temperature range, this cooling method can be used. Not limited. For example, the metal plate S may be cooled only by the cooling bath 11 without using the nozzle 12 .

The constraining rolls 20 constrain the metal plate S cooled by the cooling device 10 in the thickness direction, and are fixed to both surfaces of the metal plate S in the cooling tank 11 . In FIG. 1, a pair of restraint rolls 20 are installed so as to face each other, but they may be installed at positions shifted along the conveying direction as long as they restrain. Further, although FIG. 1 illustrates a case where one pair of restraint rolls 20 is installed, the number of restraint rolls 20 is not limited to one pair, and a plurality of pairs or a plurality of rolls may be provided. In that case, the entire binding roll pair may be collectively position-controlled.

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 bath 11 . Therefore, the cooling start position SP of the metal plate S varies depending on the water level of the cooling tank 11. FIG. Therefore, the metal quenching apparatus 1 has a function of changing the cooling start position SP by changing the height of the fluid surface of the cooling bath 11 .

The metal quenching device 1 includes a water level adjuster 30 that adjusts the height of the cooling fluid CF contained in the cooling bath 11 and a position control device 40 that controls the operation of the water level adjuster 30 . FIG. 2 is a schematic diagram showing an example of the water level regulator 30 of FIG. The water level regulator 30 of FIG. 2 includes an adjustment tank 31 that stores the cooling fluid CF, a supply source 32 that supplies the cooling fluid CF to the adjustment tank 31, and a weir 33 that controls discharge of the cooling fluid CF from the adjustment tank 31. and The adjustment bath 31 and the cooling bath 11 are connected by a discharge pipe 34 through which the cooling fluid CF is discharged from the cooling bath 11 and a supply pipe 35 through which the cooling fluid CF is supplied to the cooling bath 11 . Moreover, in order not to interfere with the boiling phenomenon and the injection from the nozzle 12, it is preferable that the discharge pipe 34 and the supply pipe 35 are provided below the liquid surface. Furthermore, the discharge pipe 34 and the supply pipe 35 may be integrated.

The heights of the fluid surfaces of the adjustment tank 31 and the cooling tank 11 are adjusted by the movement of the fluid through the discharge pipe 34 and the supply pipe 35 so that they are the same due to the atmospheric pressure. Therefore, the height of the fluid level of the cooling tank 11 can be adjusted by adjusting the storage amount of the adjustment tank 31 while monitoring the height of the fluid level of the adjustment tank 31, for example. In addition, this makes it possible to adjust the cooling start position SP. Specifically, when the cooling start position SP is raised, the cooling fluid CP is supplied from the supply source 32 into the adjustment tank 31 to increase the storage amount. Along with this, the height of the liquid surface in the cooling tank 11, that is, the cooling start position SP increases. When the cooling start position SP is lowered, the weir 33 is moved, that is, the weir 33 is lowered, and the cooling fluid CP in the adjustment tank 31 overflows from the weir 33, causing the cooling fluid CP to flow out of the adjustment tank 31. Ejected. Along with this, the height of the liquid surface in the cooling bath 11, that is, the cooling start position SP is lowered.

In addition, the water level adjuster 30 is not limited to the configuration of FIG. The height of the liquid surface may be adjusted by immersing or removing the object. Considering the accuracy and responsiveness of the management of the cooling fluid CF such as liquid temperature or dirt and the adjustment of the liquid surface height, in addition to the above-described drainage by the pump, the cooling tank 11 is connected to the adjustment tank 31 for adjustment. It is preferable to adjust the liquid level of the cooling bath 11 by adjusting the storage volume of the bath 31 .

The position control device 40 consists of hardware resources such as a computer, and controls the water level adjuster 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 adjuster 30, and adjusts 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 the position RP where the target temperature is reached. adjust. Here, the target temperature is defined as (TMs+150)( ° C.) to (TMf-150) (° C.). As a result, the deformation of the metal plate S can be restrained by the restraining rolls 20 at the position where the metal plate S undergoes rapid thermal contraction and transformation expansion at the same time, and deformation of the metal plate S during quenching can be restrained. can.

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 position RP at which the target temperature is reached, and controls the cooling fluid in the cooling tank 11 based on the calculated distance d. Adjust the height of the CF fluid surface. At this time, the position control device 40 controls the conveying speed v (mm/s) of the metal plate S, the cooling start temperature T1 (°C), the target temperature T2 (°C), the cooling speed CV (°C) of the metal plate S by the cooling device 10, /s) to calculate the distance d. 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, temperature sensor, or the like. The cooling start temperature T1 (° C.) means the temperature at which cooling of the metal plate S is started, specifically the temperature of the metal plate S immediately before the cooling start position SP. For example, the temperature of the metal plate S immediately before reaching the cooling start position SP can be calculated based on the cooling state of the metal plate S up to the cooling start position SP and the hardening device 1 . Specifically, the temperature of the metal sheet S is measured with a non-contact type thermometer on the delivery side of the soaking zone of the continuous annealing furnace. Then, the temperature of the metal sheet S immediately before or at the time of reaching the cooling start position SP can be calculated based on the temperature and the amount of temperature decrease due to the natural cooling of the metal sheet S until it reaches the quenching device 1. can. The amount of temperature decrease due to the natural cooling of the metal plate S described above can be obtained in advance by experiments. The target temperature T2 means a target value of the temperature of the metal plate S at the position RP where the metal plate S is constrained by the constraining rolls 20 .

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

CV = (T1-T2)/(d/v)
d=(T1−T2)×v/CV (1)

The cooling rate CV (°C/s) is determined by the nozzle shape or the coefficient α (°C mm/s) indicating the cooling conditions such as the type, temperature, and injection amount of the cooling fluid CF to be jetted, and the thickness of the metal plate S. It can be represented by the following formula (3) using t.

CV = α/t (2)

By substituting the formula (2) into the formula (1), the distance d can be expressed by the following formula (3).

　　　d=(T1-T2)×v×t/α (3)

The position control device 40 stores the cooling rate CV (°C/s) or α (°C·mm/s) obtained in advance through experiments, numerical analysis, or the like. Then, the position control device 40 obtains the distance d using the formula (1) or (3), and adjusts the cooling fluid CF in the cooling tank 11 so as to constrain the metal plate S at the position of the obtained distance d. Adjust the height of the fluid surface. The cooling rate CV is a value determined according to the plate thickness, etc. 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). is. 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 manner, the cooling condition α obtained by the above-described cooling rate CV, plate thickness t, and equation (2) may be set.

If the height of the liquid surface can be changed, the initial cooling rate CV of the metal plate S can be changed by combining slow cooling by simply immersing the metal plate S in the liquid and rapid cooling by the nozzle 12. It is possible to change. In the cooling section by the nozzles 12 that inject liquid, a high cooling rate CV is obtained by destroying the vapor film formed on the surface of the metal plate S due to boiling by the liquid jet. On the other hand, in the cooling section where the metal plate S is simply immersed in liquid, the surface of the metal plate S is covered with a vapor film, causing film boiling, and heat transfer between the liquid and the metal plate S is affected by the vapor film. inhibited. Therefore, the cooling rate CV decreases. By using this slow cooling by film boiling, not only can the stress caused by rapid temperature change be suppressed, but also the metal plate S in the early stages of cooling can be cooled more uniformly, and temperature variations can be reduced. Therefore, it is possible to suppress shape deformation of the metal plate S and obtain a metal plate S with a flatter shape.

For this reason, when simply immersing the metal plate S in liquid and cooling by the nozzles 12 are used in combination, the height of the liquid surface is the position at which the liquid jet from the nozzles 12 collides with the metal plate S. preferably higher than The range of the height of the liquid surface from the nozzle 12, that is, the distance between the liquid surface and the nozzle 12 is preferably, for example, 30 mm or more and 2000 mm or less.

When the liquid surface is closer to the collision position of the liquid jet than 30 mm, which is the lower limit of the distance, the liquid surface fluctuates under the influence of the liquid jet from the nozzle 12 . Specifically, the cooling ability for the metal plate S is not stable because the liquid surface periodically moves up and down. As a result, the temperature (restraining temperature) at the location where the metal plate S is restrained by the restraining rolls 20 may fluctuate, and the shape of the metal plate S may change periodically.

It is preferable that the upper limit of the distance is appropriately determined according to the metallurgical properties of the metal plate S, the transport speed v, the cooling speed CV, and the like. In general, rapid cooling in the transformation temperature range is required to obtain desired metallic properties by liquid quenching. Therefore, considering that the conveying speed range in a general metal plate quenching treatment process is 10 m/min to 600 m/min, it is not preferable that the upper limit exceeds 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 cannot be obtained. Therefore, the distance between the liquid surface and the nozzle 12 is preferably 30 mm or more and 2000 mm or less. Furthermore, it is more preferably 50 mm or more and 1000 mm or less in order to stabilize the liquid surface more and obtain an effective cooling rate.

The quenching method and the metal plate manufacturing method of the present invention will be described with reference to FIG. First, the metal plate S is cooled by the cooling device 10 while being transported, and the metal plate S is quenched. At this time, the height of the fluid surface of the cooling fluid CF in the cooling tank 11 is adjusted so that the metal plate S is constrained from both sides in the thickness direction of the metal plate S at the position RP where the metal plate S reaches the target temperature T2. be done. Specifically, in the position control device 40, the distance d is calculated using the above formula (1) or formula (3), and the cooling tank 11 is moved so as to constrain the metal plate S at the position of the calculated distance d. The height of the fluid surface of the cooling fluid CF inside is adjusted. Note that the adjustment of the height of the fluid surface can be performed successively 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 transport speed v is changed.

The transport speed of the metal plate S fluctuates even for one metal plate S (within one coil). Therefore, if the height of the fluid surface can be moved up and down while the metal plate S is restrained by the restraining rolls 20, the yield of the decelerating portions such as the front end and the tail end of the metal plate S can be improved, which is more preferable. Alternatively, the position control device 40 may calculate the distance d and adjust the height of the fluid surface for each set period.

According to the above embodiment, the operation of the water level adjuster 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. Thereby, the metal sheet S at the target temperature T2 can be restrained by the restraining rolls 20 regardless of the manufacturing conditions of the metal sheet S. As a result, in the continuous annealing equipment, it is possible to suppress shape defects of the metal sheet S due to manufacturing conditions of the metal sheet S that occur during quenching.

That is, the temperature of the metal plate S conveyed to the hardening apparatus 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 constant regardless of the manufacturing conditions, the temperature of the metal sheet S when it reaches the restraining rolls 20 also varies.

In order to solve this problem, that is, to accurately control the shape of the metal plate S at the optimum temperature position that varies depending on the manufacturing conditions, the height of the fluid surface of the cooling fluid CF in the cooling bath 11 can be adjusted. found to be effective. By adjusting the height of the fluid surface of the cooling fluid CF in the cooling bath 11, the metal plate S can be restrained within the target temperature range even if the manufacturing conditions change.

In particular, it is possible to reduce the complex and non-uniform uneven shape that occurs when the structure expands in volume due to martensitic transformation during rapid cooling of the metal plate S. Therefore, when the metal plate S is a high-strength steel plate (high-tensile steel), the effect of suppressing deformation is particularly large. Specifically, it is preferably applied to the production of steel sheets having a tensile strength of 580 MPa or more. Although the upper limit of the tensile strength is not particularly limited, it may be 2000 MPa or less as an example. The high-strength steel sheets (high-tensile steel) include high-strength cold-rolled steel sheets, hot-dip galvanized steel sheets, electro-galvanized steel sheets, alloyed hot-dip galvanized steel sheets, and the like.

In addition, as a specific example of the composition of the high-strength steel sheet, in mass%, C is 0.04% or more and 0.35% or less, Si is 0.01% or more and 2.50% or less, and 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, if necessary, at least one of Cr, Mo, Nb, V, Ni, Cu, and Ti is 0.5% or less, and if necessary , B, and Sb are each 0.01% or less, and the balance is Fe and unavoidable impurities. In addition, the metal plate is not limited to the steel plate, and may be a metal plate other than the steel plate.

An embodiment of the present invention will be described. As an example of the present invention, using the quenching apparatus 1 according to the above-described embodiment of the present invention, a high-strength cold-rolled steel sheet (hereinafter referred to as a steel sheet) having a thickness t of 1.0 mm and a width of 1000 mm and a tensile strength of 1470 MPa ) was quenched. The composition of the steel sheet with a tensile strength of 1470 MPa is, in mass%, 0.20% C, 1.0% Si, 2.3% Mn, 0.005% P, and 0.002% S. bottom. The temperature TMs at the Ms point of the steel sheet is 300°C, and the temperature TMf at the Mf point is 250°C. Therefore, the target temperature T2 of the steel sheet when passing through the constraining rolls 20 may be set within the range of 450.degree. C. to 100.degree. In this embodiment, the target temperature T2 is set at 400.degree. Also, the cooling start temperature T1 was set to 800°C. The temperature of the cooling fluid CF was approximately 30° C., and the cooling rate CV was set at 1500 (° C./s).

As a change in the manufacturing conditions, the conveying speed v is changed between 1000 mm / s and 3000 mm / s, and based on the formula (1), the distance d (mm) is adjusted to d = 267 mm to 800 mm according to the change in the conveying speed v. controlled. Ten sheets of the cooled steel sheet were sampled every 100 m in the longitudinal direction (that is, the same direction as the conveying direction of the steel sheet), and the amount of warpage of each steel sheet was investigated. FIG. 3 is a schematic diagram showing an example of the definition of the amount of warpage. As shown in FIG. 3, the amount of warp was defined as the height from the contact surface to the highest position when the steel plate was placed on a horizontal surface.

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 warp amount of the metal plate in the example of the present invention. As shown in FIG. 4, even if the conveying speed v changes, the height of the fluid surface of the cooling fluid CF is adjusted according to the conveying speed v to change the distance d. The temperature (°C) of the steel plate was 400±25°C. That is, even if the conveying speed v changed, the temperature (° C.) of the steel sheet when passing through the restraining rolls 20 could 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 warpage of all the steel sheets was reduced to 10 mm or less. As a result, the variation, which is the difference between the maximum value and the minimum value of the amount of warpage, was suppressed to 4.2 mm.

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

In Comparative Example 1, as shown in FIG. 6, the temperature (°C) of the steel sheet when passing through the restraining rolls 20 greatly changed depending on the transport speed v (mm/s), and could not be controlled. Therefore, under conditions other than v = 1000 mm/s and v = 1500 mm/s, the temperature (°C) of the steel sheet when passing through the restraint roll 20 is outside the range of 450°C to 100°C, which is the target temperature T2. . As a result, as shown in FIG. 7, under conditions other than v=1000 mm/s and v=1500 mm/s, the amount of warpage of the steel sheets was all 10 mm or more, and the effect of suppressing deformation of the steel sheets was insufficient. As a result, the variation, which is the difference between the maximum value and the minimum value of the amount of warpage, increased to 10.3 mm.

FIG. 8 is a graph showing the relationship between the transport speed v and the target temperature in Comparative Example 2, and FIG. 9 is a graph showing the relationship between the transport speed v and the warp amount 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 moving the movable masking while the restraint roll 20 was fixed and controlling the cooling start position. Other conditions were the same as in the present invention example to produce the above steel plate.

As shown in FIG. 8, in Comparative Example 2, the temperature (° C.) of the steel sheet when passing through the restraint roll 20 changed greatly regardless of the conveying speed v (mm/s), and could not be controlled. . Therefore, under all conditions, the temperature (° C.) of the steel sheet when passing through the restraining rolls 20 sometimes deviated from the range of 450° C. to 100° C., which is the target temperature T2. Further, as shown in FIG. 9, under all conditions, there were steel sheets with a warpage amount exceeding 10 mm or more, and the effect of suppressing deformation of the steel sheets was insufficient. As a result, the variation, which is the difference between the maximum value and the minimum value of the amount of warpage, increased to 9.2 mm.

The embodiments of the present invention are not limited to the above embodiments, and various modifications can be made. For example, in the above embodiment, the target temperature T2 is (TMs+150) (° C.) to (TMf−150) (° C.), but is not limited to this. From the point of view of post-process processing and ensuring flexibility of operation, for example, if there is no variation in the shape of the metal plate S such as the amount of warpage, the target temperature T2 is set to (TMs + 150) (°C) ~ ( It may not be limited to TMf-150) (°C).

In this case, the target temperature T2 is determined in advance, taking into account the expected shape (for example, the amount of warpage) while keeping in mind the degree of freedom of processing and operation in the post-process. Further, by adjusting the position of the constraining roll 20, the distance d from the cooling start position to the constraining roll 20 is controlled. In this way, the temperature of the metal plate S when passing through the restraining rolls 20 is set to the predetermined temperature T2, and the shape of the metal plate S, that is, the variation in the amount of warp of the metal plate S defined in FIG. It should be within

Furthermore, although the case where the position of the constraining roll 20 is fixed is illustrated, the constraining 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 apparatus 1 for the metal plate S may include a roll moving device for moving the constraining roll 20 made up of, for example, 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 constraining rolls 20 . As a result, for example, when the distance d is desired to be increased, the distance d can be quickly adjusted by moving the constraining roll 20 in the conveying direction of the metal plate S while increasing the height of the fluid surface. Alternatively, the distance d can be precisely controlled, for example, by roughly adjusting the distance d with the water level adjuster 30 and finely adjusting the distance d by adjusting the position of the restraint rolls 20 .

The conveying speed v is changed between 1000 mm/s and 2500 mm/s, and the distance between the liquid surface and the collision position of the liquid jet from the nozzle 12 on the steel plate in the vertical direction (hereinafter referred to as the collision position) The steel plate was quenched under the same manufacturing conditions as in Example 1, except that the was changed between 0 mm and 400 mm. Table 1 shows the results of verification of the relationship between the liquid level height and the collision position in Example 2. The collision position is a position where a straight line drawn from the center of the nozzle 12 in the direction of liquid injection intersects the surface of the steel plate. Further, presence or absence of change in the shape of the steel sheet in the longitudinal direction (that is, the same direction as the conveying direction of the steel sheet) was visually inspected under a sufficiently bright fluorescent lamp in the inspection on the delivery side.

As shown in Table 1, in Reference Examples 1 to 3 in which the distance between the liquid surface and the collision position is 0 mm to 20 mm, the steel sheet warps upward and downward in the conveying direction. A change was seen. The term "upward warpage" means that the center portion of the steel plate in the width direction deforms so as to be more convex upward than both end portions. Contrary to upward warping, downward warping means that both ends in the width direction of the steel plate are deformed so as to project upward from the central portion.

In addition, in Reference Examples 1 to 3, the maximum amount of warp in the width direction of the steel plate sampled every 100 m tended to be slightly higher than in Examples 1 to 5 of the present invention.

In Examples 1 to 5 of the present invention, in which the distance between the liquid surface and the collision position was 30 mm or more, no periodic variation in warpage in the longitudinal direction of the steel plate was observed. Also, the maximum amount of warp in the width direction of the steel plate sampled every 100 m tended to decrease as the distance and the conveying speed v increased. That is, in Examples 1 to 5 of the present invention, the initial cooling of the steel sheet could be slow cooling by setting the liquid level higher than the collision position of the liquid jet from the nozzle by 30 mm or more. As a result, the stress due to rapid thermal contraction can be reduced, the shape deformation of the steel sheet can be suppressed, and the amount of warpage of the steel sheet can be reduced.

1 Metal plate quenching device 10 Cooling device 11 Cooling tank 12 Nozzle 20 Constrained roll 30 Water level adjuster 40 Position control device BD Conveying direction CF Cooling fluid S Metal plate

Claims

A metal plate quenching apparatus that cools a metal plate while conveying it,
a cooling tank that stores a cooling fluid and cools the metal plate by immersing it;
a constraining roll installed in the cooling tank for conveying the metal plate cooled by the cooling tank while constraining it in the thickness direction;
a water level adjuster 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;
a position control device for controlling the operation of the water level adjuster to control the height of the fluid surface of the cooling fluid in the cooling bath;
A metal plate quenching device.
The apparatus for quenching a metal plate according to claim 1, further comprising a plurality of nozzles installed in the cooling bath for cooling the metal plate by injecting the cooling fluid.
The water level regulator stores the cooling fluid, and includes an adjustment tank connected to the cooling tank, a supply source to the adjustment tank, and a weir controlling discharge of the cooling fluid from the adjustment tank. 3. The apparatus for hardening a metal plate according to claim 1, 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. .
The position control device adjusts the height of the fluid surface of the cooling fluid in the cooling bath so that the constraining roll constrains the metal plate at a position where the metal plate reaches a target temperature. The metal plate quenching apparatus according to any one of claims 1 to 3, wherein the cooling start position of is adjusted.
The target temperature is (TMs + 150) (°C), where TMs (°C) is the temperature at the Ms point at which the martensitic transformation of the metal plate starts, and TMf (°C) is the temperature at the Mf point at which the martensitic transformation ends. 5. The apparatus for quenching a metal plate according to claim 4, wherein the temperature is set within a temperature range of ~(TMf-150)(°C).
The position control device controls the distance from the cooling start position to the constraining roll, the conveying speed of the metal plate, the cooling start temperature of the metal plate at the start of cooling by the cooling tank, the target temperature, and the 6. The apparatus for hardening a metal plate according to claim 4 or 5, wherein the height of the fluid surface of the cooling fluid in the cooling bath is set based on the cooling rate of the metal plate and adjusted so as to achieve the set distance.
The position control device sets the conveying speed of the metal plate to v (mm/s), the cooling start temperature to T1 (°C), the target temperature to T2 (°C), and the cooling speed of the metal plate by the cooling bath to CV. 7. The apparatus for quenching a metal plate according to claim 6, wherein the distance d (mm) from the cooling start position to the restraint roll is obtained by formula (1), where (° C./s).
d=(T1-T2)×v/CV (1)
8. The metal plate according to claim 7, wherein the cooling rate CV is set as CV=α/t in the position control device by a coefficient α indicating the cooling condition of the metal plate and a plate thickness t of the metal plate. quenching equipment.
3. The apparatus for hardening a metal plate according to claim 2, wherein the distance between the liquid surface of the cooling fluid in the cooling tank and the collision position of the liquid jet from the nozzle on the metal plate is 30 mm or more and 2000 mm or less.
A metal plate quenching method for cooling while conveying the metal plate,
The metal plate is immersed in a cooling tank containing a cooling fluid, and the metal plate is cooled using the height of the fluid surface of the cooling fluid in the cooling tank as a cooling start position,
A method of quenching a metal plate, wherein the height of the fluid surface of the cooling fluid in the cooling tank is adjusted so that the metal plate is constrained by constraining rolls at a position where the metal plate is at a target temperature.
The target temperature is (TMs + 150) (°C), where TMs (°C) is the temperature at the Ms point at which the martensitic transformation of the metal plate starts, and TMf (°C) is the temperature at the Mf point at which the martensitic transformation ends. 11. The method of hardening a metal plate according to claim 10, wherein the temperature is set within a range of ~(TMf-150)(°C).
The adjustment of the height of the fluid surface of the cooling fluid is 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, Set the distance from the cooling start position to the restraint roll,
12. The method of hardening a metal plate according to claim 10, wherein the height of the fluid surface of the cooling fluid in the cooling tank is adjusted so as to achieve a set distance.
The distance from the cooling start position by the cooling tank to the constraining roll is v (mm/s) for the conveying speed of the metal plate, T1 (° C.) for the cooling start temperature, T2 (° C.) for the target temperature, and T2 (° C.) for the target temperature. 13. The method of quenching a metal plate according to claim 12, wherein the distance d (mm) from the cooling start position to the constraining roll is obtained by formula (1), where CV (° C./s) is the cooling rate of the plate.
d=(T1-T2)×v/CV (1)
14. The method of hardening a metal plate according to claim 13, wherein the cooling rate CV is set as CV=α/t by a coefficient α indicating the cooling condition of the metal plate and the plate thickness t of the metal plate.
A method for producing a high-strength cold-rolled steel sheet using the method for quenching a metal plate according to any one of claims 10 to 14.
A method for producing a high-strength steel sheet, wherein the high-strength steel sheet obtained by the method according to claim 15 is subjected to hot-dip galvanizing treatment, electro-galvanizing treatment, or hot-dip alloying galvanizing treatment.
The cooling fluid is jetted from a nozzle installed in the cooling tank to the metal plate to cool the metal plate, and the collision position of the liquid surface of the cooling fluid in the cooling tank and the liquid jet from the nozzle on the metal plate 11. The method of hardening a metal plate according to claim 10, wherein the distance between is 30 mm or more and 2000 mm or less.