JP7464143B2 - Quenching device, quenching method, and method of manufacturing metal plate - Google Patents

Description

The present invention relates to a quenching apparatus and a quenching method for annealing a metal plate while continuously transporting the metal plate, and a method for manufacturing a metal plate.

In a continuous annealing facility where metal sheets are annealed while being continuously transported, the metal sheets are heated and then cooled to cause a phase transformation, thereby forming a metal sheet structure. In particular, in the automotive industry, there is an increasing demand for thin-walled high-tensile steel sheets (hi-tensile) in order to achieve both weight reduction and crashworthiness of the car body. When manufacturing high-tensile steel sheets, a technique for rapidly cooling the steel sheet is important. Water quenching is known as one of the techniques that can cool metal sheets at the fastest rate. In the water quenching method, the heated metal sheet is immersed in water, and at the same time, cooling water is sprayed onto the metal sheet from a quench nozzle installed in the water, thereby quenching the metal sheet.

During quenching of a metal sheet, defects in shape such as warping and wavy deformation occur in the metal sheet. This is due to thermal contraction of the metal sheet caused by rapid cooling. In particular, when the temperature of the metal sheet 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 simultaneously.

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

Patent Document 2 discloses that, when performing a quenching method in which water is sprayed from a plurality of water spray nozzles onto the surface of a metal plate to cool it, the metal plate is constrained by a constraining roll while a movable masking is used to control the distance between the constraining roll and the position at which cooling of the metal plate by a cooling fluid starts.Furthermore, similar to Patent Document 1, a method is proposed in which, when the temperature of the Ms point at which the martensitic transformation of the metal plate starts is TMs (°C) and the temperature of the Mf point at which the martensitic transformation ends is TMf (°C), the metal plate is passed through the constraining roll 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 sheet is in the range of (TMs+150) (°C) to (TMf-150) (°C) changes depending on the manufacturing conditions of the metal sheet. For this reason, the restraining rolls cannot restrain the metal sheet at the position where the temperature of the metal sheet is in the range of (TMs+150) (°C) to (TMf-150) (°C), and there is a possibility that variation occurs in the shape of the metal sheet.

In the method described in Patent Document 2, water that collides with the movable masking falls due to gravity and interferes with the water jetted from the water jet nozzles at the bottom of the movable masking, making the cooling capacity of the metal plate unstable. In addition, because masking is performed for each nozzle, the cooling capacity changes stepwise (discontinuously), and as a result, the position where the temperature of the metal plate is between (TMs+150) (°C) and (TMf-150) (°C) becomes unstable, which may cause variation in the shape of the metal plate.

The present invention has been made to solve these problems, and aims to provide a hardening device and hardening method, as well as a manufacturing method for metal plate products, that can control the temperature of a metal plate at the position where the metal plate is restrained with high precision and suppress variation in the shape of the metal plate that occurs during hardening.

[1] A metal plate quenching apparatus that cools a metal plate while transporting the metal plate, the metal plate quenching apparatus comprising: a cooling device that cools the metal plate being transported; a constraint roll that transports the metal plate cooled by the cooling device while constraining it in a thickness direction; a roll moving device that moves the constraint roll along the transport direction of the metal plate; and a movement control device that controls the operation of the roll moving device to adjust the position of the constraint roll.
[2] The metal plate quenching apparatus according to [1], wherein the cooling device has a plurality of nozzles that spray a cooling fluid onto the metal plate to cool it.
[3] The metal plate quenching apparatus according to [1] or [2], wherein the cooling device has a cooling tank in which the metal plate is immersed and cooled.
[4] The metal plate quenching device according to any one of [1] to [3], wherein the movement control device controls the operation of the roll movement device and positions the constraint roll so that the constraint roll constrains the metal plate at a position where the metal plate reaches a target temperature.
[5] The metal plate quenching device according to [4], wherein the target temperature is set in a temperature range of (TMs+150) (°C) to (TMf-150) (°C), where TMs (°C) is the temperature of the Ms point at which the martensitic transformation of the metal plate starts, and TMf (°C) is the temperature of the Mf point at which the martensitic transformation ends.
[6] The metal plate quenching device according to [4] or [5], wherein the movement control device sets a distance from a position where cooling by the cooling device starts to the restraint roll based on the conveying speed of the metal plate, the cooling start temperature of the metal plate when cooling by the cooling device starts, the target temperature, and the cooling rate of the metal plate, and moves the position of the restraint roll so that the set distance is achieved.
[7] The metal plate quenching device according to [6], wherein the movement control device calculates a distance d (mm) from the cooling start position to the restraint roll using equation (1), where v (mm/s) is a conveying speed of the metal plate, T1 (°C), T2 (°C), and CV (°C/s) is a cooling rate of the metal plate by the cooling device.
d = (T1 - T2) x v / CV (1)
[8] The metal plate quenching device according to [7], wherein the movement control device has a cooling rate CV set as CV=α/t, where α is a coefficient indicating the cooling conditions of the metal plate and t is a plate thickness of the metal plate.
[9] A method for quenching a metal plate in which the metal plate is cooled while being transported, wherein when the cooled metal plate is constrained in the thickness direction by constraining rolls, the constraining rolls are moved along a transport direction so as to constrain the metal plate at a position where the metal plate is at a target temperature.
[10] The method for quenching a metal plate according to [9], wherein the target temperature is set in a temperature range of (TMs+150) (°C) to (TMf-150) (°C), where TMs (°C) is the temperature of the Ms point at which martensitic transformation of the metal plate starts, and TMf (°C) is the temperature of the Mf point at which martensitic transformation ends.
[11] The method for quenching a metal plate according to [9] or [10], wherein the movement of the restraining roll is performed by setting a distance from a cooling start position to the restraining roll based on a conveying speed of the metal plate, a cooling start temperature of the metal plate at the start of cooling, the target temperature, and a cooling rate of the metal plate, and moving the restraining roll to the set distance.
[12] The quenching method of the metal plate according to [11], wherein the distance d (mm) from the cooling start position to the constraining roll is calculated by 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 rate of the metal plate is CV (°C/s).
d = (T1 - T2) x v / CV (1)
[13] The method for quenching a metal plate according to [12], wherein the cooling rate CV is set as CV=α/t, where α indicates a cooling condition of the metal plate and t is a thickness of the metal plate.
[14] A method for producing a high-strength cold-rolled steel sheet, using the method for quenching a metal sheet according to any one of [9] to [13].
[15] A method for producing a high-strength steel sheet, comprising subjecting the high-strength steel sheet obtained by the method according to [14] to any one of hot-dip galvanizing, electrogalvanizing, and galvannealing.

According to the present invention, when quenching a metal plate, the position of the restraint roll is adjusted along the transport direction of the metal plate in accordance with the temperature of the metal plate, thereby controlling the distance from the cooling start position to the restraint roll, thereby suppressing variation in the shape of the metal plate that occurs during quenching.

FIG. 1 is a schematic diagram showing a hardening device according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing an example of the definition of the amount of warping of a metal plate. 13 is a graph showing the relationship between the transport speed and the target temperature in an example of the present invention. 10 is a graph showing the relationship between the conveying speed and the amount of warping of a metal plate in an example of the present invention. 13 is a graph showing the relationship between the conveying speed and the target temperature in Comparative Example 1. 13 is a graph showing the relationship between the conveying speed and the amount of warping of the metal plate in Comparative Example 1. 13 is a graph showing the relationship between the conveying speed and the target temperature in Comparative Example 2. 13 is a graph showing the relationship between the conveying speed and the amount of warping of the metal plate in Comparative Example 2. 10A and 10B are diagrams illustrating the movement of a restraining roll and a nozzle in another example of a hardening device according to an embodiment of the present invention.

An embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram showing a quenching apparatus according to an embodiment of the present invention. The quenching apparatus 1 of Fig. 1 is for quenching a steel material as a metal sheet S, for example, and is applied to a cooling facility provided on the outlet side of a soaking zone of a continuous annealing furnace. The quenching apparatus 1 for a metal sheet S of Fig. 1 includes a cooling device 10 for cooling the metal sheet S, and a restraining roll 20 for restraining the cooled metal sheet S in the thickness direction.

The cooling device 10 cools the metal sheet S using a cooling fluid CF, and includes a cooling tank 11 that stores the cooling fluid CF, and a plurality of nozzles 12 that are installed in the cooling tank 11 and spray the cooling fluid CF onto the surface of the metal sheet S. Water is stored in the cooling tank 11 as the cooling fluid CF, and the metal sheet S is immersed in the cooling tank 11 from its upper surface in the conveying direction BD, for example. Note that a sink roll 2 that changes the conveying direction of the metal sheet S is installed in the cooling tank 11.

The multiple nozzles 12 are, for example, quench nozzles, and are installed on both sides of the metal sheet S along the conveying direction of the metal sheet S. Thus, the metal sheet S is cooled by the cooling fluid CF in the cooling tank 11 and the cooling fluid CF sprayed from the multiple nozzles 12. In this way, by cooling the metal sheet S using both the cooling tank 11 and the multiple nozzles 12, the boiling state on the surface of the metal sheet S can be stabilized and uniform shape control can be performed.

Although the example shows a case where water quenching is performed using water as the cooling fluid CF, oil cooling using oil as the cooling fluid CF may be used. In addition, although the example shows a case where multiple nozzles 12 are installed in the cooling tank 11 in Fig. 1, the cooling method is not limited to this as long as it is a method that can cool the metal plate S to a desired temperature range. For example, the metal plate S may be cooled only by the cooling tank 11, or may be cooled only by the multiple nozzles 12.

When the nozzle 12 is installed in the cooling tank 11, the distance between the metal plate S and the nozzle 12 is important in rapid cooling by liquid quenching. Since rapid cooling is performed by breaking up the vapor film generated by the boiling phenomenon with a liquid jet, it is desirable to install the nozzle 12 close to the metal plate S. The distance between the tip of the nozzle 12 and the metal plate S is preferably 10 mm or more and 150 mm or less. If it is less than 10 mm, there is a possibility that the deformed and fluttering metal plate S may come into contact with the nozzle 12. Also, if it exceeds 150 mm, the effect of breaking up the vapor film becomes weak, and it may be difficult to ensure sufficient cooling capacity.

The restraint rolls 20 restrain the metal sheet S cooled by the cooling device 10 in the thickness direction, and are installed on both sides of the metal sheet S in the cooling tank 11. In Fig. 1, a pair of restraint rolls 20 are installed facing each other, but they may be installed at positions shifted along the conveying direction as long as they restrain the metal sheet S. In Fig. 1, a case where a pair of restraint rolls 20 is installed is illustrated, but multiple pairs of restraint rolls 20 may be installed along the conveying direction.

In addition, the roll diameter of the constraint roll 20 is preferably 50 mm or more and 300 mm or less, in view of the correlation between roll rigidity and deflection due to the constraint stress. The material of the constraint roll 20 is not limited. When a general steel roll is used as the constraint roll 20 and the roll diameter is less than 50 mm, the roll rigidity is insufficient, and it becomes difficult to apply a uniform constraint force to the metal sheet S due to deflection, and there is a possibility of breakage. In addition, when the roll diameter is larger than 300 mm, the section where the jet from the nozzle 12 does not reach the metal sheet S becomes long, and the destruction of the steam film becomes insufficient, and there is a possibility of a decrease in cooling capacity.

The restraining roll 20 is installed so as to be movable along the conveying direction of the metal sheet S. Here, the conveying direction refers to the direction in which the metal sheet S is conveyed. Specifically, the hardening device 1 for the metal sheet S includes a roll moving device 30 for moving the restraining roll 20 and a movement control device 40 for controlling the movement of the restraining roll 20. The roll moving device 30 includes a known driving means such as a motor, and is configured to move the restraining roll 20 along the conveying direction of the metal sheet S in the conveying direction BD of the metal sheet S or in the opposite direction to the conveying direction BD. Specifically, the roll moving device 30 can be suitably manufactured by combining mechanical parts such as a power jack, a screw-type lifting device using a screw mechanism or a gear mechanism, and a Linear Motion Guide (LM guide) that utilizes rolling and has low resistance. FIG. 1 shows an example in which the roll moving device 30 is configured using a screw-type lifting device. The restraining roll 20 is rotatably attached to one end of an L-shaped arm 31. The other end of the arm 31 is provided with a screw portion 32, another screw portion that engages with the screw portion 32, and a drive means (not shown) for driving the other screw portion. The drive means is fixed to a fixed portion (not shown). Therefore, when the other screw portion rotates due to torque generated by the drive means, the arm 31 moves in a direction parallel to the conveying direction BD.

If the driving means is immersed in the liquid, maintenance of the driving means may become difficult. Therefore, the driving means is preferably installed above the liquid level of the cooling tank 11. In addition, the driving means is preferably installed in a space that is shielded from the inside of the furnace where the temperature becomes high.

The roll moving device 30 may have a function of moving the restraining roll 20 in the thickness direction of the metal sheet S to restrain and release the restraint of the metal sheet S. In addition, any method may be used as long as it is possible to move the metal sheet S, but an electric type is more preferable in consideration of responsiveness.

The movement control device 40 is composed of hardware resources such as a computer, and controls the movement of the constraint roll 20. In particular, the movement control device 40 controls the operation of the roll movement device 30, and positions the constraint roll 20 so that the metal sheet S is constrained at a position RP where the target temperature is reached. Here, the target temperature is preferably set in a temperature range of (TMs+150) (°C) to (TMf-150) (°C), where TMs (°C) is the temperature of the Ms point at which the martensitic transformation of the metal sheet S starts, and TMf (°C) is the temperature of the Mf point at which the martensitic transformation ends. This allows the constraint roll 20 to constrain the deformation of the metal sheet S at a position where the metal sheet S undergoes rapid thermal contraction and transformation expansion at the same time, and suppresses the deformation of the metal sheet S during quenching.

The movement control device 40 calculates a distance d from the cooling start position SP of the metal sheet S by the cooling fluid CF to the position RP at which the target temperature is reached for constraining by the constraining rolls 20, and moves the constraining rolls 20 based on the calculated distance d. At this time, the movement control device 40 calculates the distance d using the conveying speed v (mm/s) of the metal sheet S, the cooling start temperature T1 (°C), the target temperature T2 (°C) for constraining by the constraining rolls 20, and the cooling speed CV (°C/s) of the metal sheet S by the cooling device 10. Here, the cooling start temperature T1 is the temperature of the metal sheet S immediately before the cooling start position SP where cooling of the metal sheet S is started by the cooling fluid CF. For example, the temperature immediately before the cooling start position SP can be calculated based on the cooling state of the metal sheet S until it reaches the cooling start position SP or the quenching device 1. Specifically, the temperature of the metal sheet S is measured by a non-contact type thermometer at the exit 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 that temperature and the temperature drop due to natural cooling of the metal sheet S until it reaches the quenching device 1. The temperature drop due to natural cooling of the metal sheet S described above can be obtained in advance by experiment. The above parameters may be sequentially obtained from the set values of a process computer or the operation record values, or may be actually measured using a speed sensor, a temperature sensor, or the like.

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) x v / CV (1)

The cooling rate CV (°C/s) can be expressed by the following equation (3) using a coefficient α (°C·mm/s) indicating cooling conditions such as the nozzle shape, or the type, temperature, and amount of cooling fluid CF sprayed, and the plate thickness t of the metal plate S.

CV=α/t (2)

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

d = (T1 - T2) x v x t / α ... (3)

The movement control device 40 stores the cooling rate CV (°C/s) or α (°C·mm/s) obtained in advance by experiments, numerical analysis, or the like. The movement control device 40 then obtains the distance d using formula (1) or formula (3), and moves the restraining roll 20 so as to restrain the metal sheet S at the position of the obtained distance d. The cooling rate CV is a value determined according to the sheet thickness, etc., and for a sheet 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 movement control device 40, the cooling rate CV may be set to 1500 (°C/s), which is in the middle of the above range. In this case, α may be treated as the middle value of 1250 (°C·mm/s). In this way, the cooling condition α obtained by the above-mentioned cooling rate CV, sheet thickness t, and formula (2) may be set.

The quenching method and the manufacturing method of the metal sheet S of the present invention will be described with reference to FIG. 1. First, the metal sheet S is cooled by the cooling device 10 while being transported, and the metal sheet S is quenched. At this time, the constraint roll 20 moves along the transport direction so as to constrain the thickness direction of the metal sheet S that has reached the target temperature T2 at the position RP. At this time, the movement control device 40 calculates the distance d using the above formula (1) or formula (3), and moves the constraint roll 20 so as to constrain the metal sheet S at the position of the calculated distance d. The movement of the constraint roll 20 can be performed sequentially even during the quenching of the metal sheet S. For example, the movement control device 40 may calculate the distance d and move the constraint roll 20 at the timing when the transport speed v is changed.

The conveying speed of the metal sheet S varies even for one metal sheet S (within one coil). For this reason, if the metal sheet S can be moved in the conveying direction or the reverse direction while being restrained by the restraining rolls 20, this is more preferable because it can improve the yield caused by defective shapes in the parts of the metal sheet S that are decelerated, such as the leading and trailing ends. Alternatively, the movement control device 40 may calculate the distance d and move the restraining rolls 20 for each set period.

The movement distance of the constraining roll 20 for adjusting the constraining roll 20 to the constraining position RP of the metal sheet S based on the distance d can be estimated to be about 10 mm to 150 mm in reality. As shown in FIG. 1, when the nozzles 12 are installed in the cooling tank 11, the constraining roll 20 may be raised and lowered between the nozzles 12 with the interval between the nozzles 12 widened in advance to about 10 mm to 150 mm. In addition, for example, rapid cooling by liquid jet has a cooling capacity of about 1000° C./sec, and when the running speed of the metal sheet S is 60 m/min (=1000 mm/sec), the temperature changes by about 100° C. over a distance of 100 mm. In other words, if the constraining roll 20 can be raised and lowered in the range of 10 mm to 150 mm, the temperature of the constrained metal sheet S can be adjusted to about 10° C. to 150° C., and the above-mentioned movement distance of the constraining roll 20 is a sufficient control adjustment range in reality.

Here, a case where the constraining roll 20 is moved more than in the above-mentioned example will be described. When the composition, thickness, conveying speed, etc. of the metal sheet S change significantly, it is necessary to move the constraining roll 20 by 150 mm or more in order to position the constraining roll 20 at the constraining position RP of the metal sheet S. A configuration for moving the constraining roll 20 by 150 mm or more will be described. FIG. 9 is a diagram showing another example of a quenching device according to an embodiment of the present invention. The quenching device 50 shown in FIG. 9 includes a nozzle moving device 60 for moving the nozzle 12 in addition to the roll moving device 30 for moving the constraining roll 20. The nozzle moving device 60 is disposed on both sides of the metal sheet S, as shown in FIG. 9(A). The nozzle moving device 60 is configured to move the nozzle 12 along the metal sheet S and to move the nozzle 12 closer to and away from the metal sheet S. In the example shown in FIG. 9, the constraining rolls 20 on both sides of the metal sheet S are offset in the vertical direction.

As shown in Fig. 9, the nozzle moving device 60 includes a lifting device 62 that moves the cooling pipes 61 connected to each of the nozzles 12 in the vertical direction of the cooling device 10, and a slider 63 that moves the lifting device 62 toward and away from the metal plate S. The lifting device 62 is configured to be able to lift and lower each of the multiple cooling pipes 61 independently of each other. The lifting device 62 and the slider 63 may be conventionally known. Also, a control device (not shown) is provided that controls the driving of the lifting device 62 and the slider 63.

Next, the operation of the quenching device 50 shown in FIG. 9 will be described. When the constraint roll 20 is moved upward from the position shown in FIG. 9A, the constraint roll 20 and the nozzle 12 located above it interfere with each other. Therefore, first, the nozzle 12 is separated from the metal sheet S by the slider 63 in the width direction of the cooling device 10 (left and right direction in FIG. 9). That is, the nozzle 12 is moved to retract from the constraint roll 20. The interval between the metal sheet S and the tip of the nozzle 12 after the nozzle 12 is separated from the metal sheet S is set to an interval at which the constraint roll 20 and the tip of the nozzle 12 do not contact each other. In this state, the constraint roll 20 is moved upward or downward. FIG. 9 illustrates the case where it is moved upward. That is, the constraint roll 20 is moved to a position RP suitable for the target temperature T2 of the metal sheet S. FIG. 9B illustrates this state.

In the state shown in FIG. 9(B), the restraining roll 20 and the nozzle 12 are adjacent to each other in the width direction of the cooling tank 11. Therefore, the nozzle 12 adjacent to the restraining roll 20 in the width direction is moved to the lower side of the restraining roll 20 by the lifting device 62 as shown in FIG. 9(B). This prevents the restraining roll 20 and the nozzle 12 from interfering with each other in either the vertical direction or the width direction. FIG. 9(C) shows this state. Next, the slider 63 moves each nozzle 12 closer to the metal sheet S, and the interval between them is set to and maintained at a preset interval. In this way, the movement of the restraining roll 20 is completed. FIG. 9(D) shows this state.

9(D), the interval between the nozzles 12 may be widened to about 10 mm to 150 mm, and the restraining rolls 20 may be moved by about 10 mm to 150 mm in this state to adjust to the above-mentioned position RP, in a manner similar to the example shown in Fig. 1. Furthermore, if the cooling capacity allows, the widened interval between the metal sheet S and the nozzles 12 may be maintained so that the restraining rolls 20 can move by 150 mm or more.

According to the above embodiment, by installing the constraint rolls 20 movably along the conveyance direction, the distance from the cooling start position to the constraint rolls 20 can be controlled, and the metal sheet S at the target temperature T2 can be constrained by the constraint rolls 20 regardless of the manufacturing conditions of the metal sheet S. As a result, in the continuous annealing equipment, it becomes possible to suppress shape defects of the metal sheet S caused by the manufacturing conditions of the metal sheet S during quenching.

That is, the temperature of the metal sheet S transported to the quenching device 1 varies depending on the manufacturing conditions of the metal sheet, such as the transport speed v, the cooling start temperature T1 of the metal sheet S, and the thickness t of the metal sheet S. Therefore, if the distance d is set to a constant value regardless of the manufacturing conditions, the temperature of the metal sheet S when it reaches the constraint rolls 20 will also vary.

To solve this problem, it was found that in order to accurately control the shape at an optimal temperature position that differs depending on the manufacturing conditions, it is effective to change the position of the restraining roll 20. By moving the restraining roll 20 itself, it is possible to restrain the metal sheet S within the desired temperature range even if the manufacturing conditions change, without causing instability in the cooling form.

In particular, it is possible to reduce the complex and uneven uneven shape that occurs when the martensitic transformation occurs during the quenching of the metal sheet S and the structure expands in volume. Therefore, when the metal sheet S is a high-strength steel sheet (hi-tensile), the deformation suppression effect is particularly large. Specifically, it is preferable to apply it to the manufacture of a steel sheet having a tensile strength of 580 MPa or more. The upper limit of the tensile strength is not particularly limited, but as an example, it may be 2000 MPa or less. The above-mentioned high-strength steel sheet (hi-tensile) includes a high-strength cold-rolled steel sheet, and a hot-dip galvanized steel sheet, an electrolytic galvanized steel sheet, an alloyed hot-dip galvanized steel sheet, etc., which are obtained by subjecting the high-strength cold-rolled steel sheet to surface treatment.

Specific examples of the composition of the high-strength steel plate include, in mass%, C of 0.04% to 0.35%, Si of 0.01% to 2.50%, Mn of 0.80% to 3.70%, P of 0.001% to 0.090%, S of 0.0001% to 0.0050%, sol.Al of 0.005% to 0.065%, and optionally, at least one of Cr, Mo, Nb, V, Ni, Cu, and Ti is 0.5% or less, and further optionally, B and Sb are 0.01% or less, with the balance being Fe and unavoidable impurities. The metal plate S is not limited to a steel plate, and may be a metal plate other than a steel plate.

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

As a change in the manufacturing conditions, the conveying speed v was changed between 1000 and 3000 mm/s, and the distance d (mm) was controlled to d = 267 to 800 m according to the change in the conveying speed v based on the formula (1). Ten steel sheets after cooling were sampled at intervals of 100 m in the longitudinal direction (i.e., the same direction as the conveying direction of the steel sheet), and the amount of warping of each steel sheet was investigated. Figure 2 is a schematic diagram showing an example of the definition of the amount of warping. As shown in Figure 2, the amount of warping was defined as the height from the ground surface to the highest point when the steel sheet was placed on a horizontal surface.

Fig. 3 is a graph showing the relationship between the conveying speed v and the target temperature in the example of the present invention, and Fig. 4 is a graph showing the relationship between the conveying speed v and the warpage of the steel sheet as the metal sheet S in the example of the present invention. As shown in Fig. 3, even if the conveying speed v changes, the temperature (°C) when passing through the restraining roll 20 could be controlled to the target temperature of 400±25°C by moving the restraining roll 20 according to the conveying speed v to change the distance d. As a result, as shown in Fig. 4, the warpage of the steel sheet was reduced to 10 mm or less in all cases. As a result, the variation in the warpage, i.e., the difference between the maximum value and the minimum value, was suppressed to 4.2 mm.

Fig. 5 is a graph showing the relationship between the conveying speed v and the target temperature in Comparative Example 1, and Fig. 6 is a graph showing the relationship between the conveying speed v and the warpage of the steel sheet as the metal sheet S in Comparative Example 1. As Comparative Example 1, a quenching device with a fixed constraining roll 20 as in Patent Document 1 was used, and the other conditions were the same as those in the above-mentioned Example of the present invention. In Comparative Example 1, the distance d (mm) from the cooling start position to the constraining roll 20 was fixed at d = 400 mm.

In Comparative Example 1, as shown in FIG. 5, the temperature (°C) when passing through the restraining rolls changed significantly depending on the conveying 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) when passing through the restraining rolls 20 was out of the range of 450°C to 100°C. As a result, as shown in FIG. 6, under conditions other than v = 1000 mm/s and v = 1500 mm/s, the warpage of the steel sheet was 10 mm or more in all cases, and the deformation suppression effect was insufficient. As a result, the variation, which is the difference between the maximum and minimum values of the warpage, became large at 10.3 mm.

Fig. 7 is a graph showing the relationship between the conveying speed v and the target temperature in Comparative Example 2, and Fig. 8 is a graph showing the relationship between the conveying speed v and the warpage of the steel sheet as the metal sheet S in Comparative Example 2. In Comparative Example 2, as shown in Patent Document 2, the restraining roll 20 was fixed and the movable masking was moved to control the distance d depending on the cooling start position. The other conditions were the same as those of the present invention, and the above high-tensile cold-rolled steel sheet was manufactured.

As shown in Fig. 7, in Comparative Example 2, regardless of the manufacturing condition of the steel sheet, namely the conveying speed v (mm/s), the temperature (°C) when passing through the constraining roll 20 changed significantly and could not be controlled. Therefore, under all conditions, the temperature (°C) when passing through the constraining roll was out of the range of 450°C to 100°C. Then, as shown in Fig. 8, the warpage of the steel sheet was 10 mm or more, and the deformation suppression effect was insufficient. As a result, the variation in the warpage (the difference between the maximum value and the minimum value) was large, at 9.2 mm.

The embodiment of the present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above embodiment, the target temperature T2 is exemplified as being between (TMs+150) (°C) and (TMf-150) (°C), but is not limited thereto. In terms of ensuring the flexibility of processing and operation in the post-process, for example, if there is no variation in the shape of the metal sheet S, such as the amount of warping, the target temperature T2 does not have to be limited to (TMs+150) (°C) and (TMf-150) (°C).

In this case, a target temperature T2 is determined in advance in consideration of the predicted shape (e.g., the amount of warping) while keeping in mind the treatment in the subsequent process and ensuring the freedom of operation, and the distance d from the cooling start position to the constraining roll 20 is controlled by adjusting the position of the constraining roll 20. Then, the temperature of the metal sheet S when passing through the constraining roll 20 is set to the predetermined temperature T2, so that the shape (e.g., the amount of warping) of the metal sheet S becomes approximately the same, for example, the variation in the amount of warping defined in Fig. 2 is within 4 mm.

Furthermore, the number of constraining rolls 20 is not limited to one, but may be multiple pairs or multiple rolls. In that case, the positions of the entire constraining roll pair may be controlled collectively, or a mechanism may be provided to control the position or opening/closing of each of the multiple constraining rolls.

Reference Signs List 1: Metal plate quenching device 10: Cooling device 11: Cooling tank 12: Nozzle 20: Restraining roll 30: Roller moving device 40: Movement control device BD: Transport direction CF: Cooling fluid S: Metal plate

Claims (14)

A metal plate quenching device that cools a metal plate while transporting the metal plate,
a cooling device having a plurality of nozzles for injecting a cooling fluid onto the metal plate being conveyed to cool the metal plate;
A restraining roll that conveys the metal plate cooled by the cooling device while restraining it in a thickness direction;
a roll moving device that moves the restraining roll along a conveying direction of the metal plate;
a movement control device that controls the operation of the roll moving device to adjust the position of the restraining roll;
A nozzle moving device that moves the plurality of nozzles,
the nozzle moving device includes a lifting device that lifts and lowers cooling pipes that are connected to the plurality of nozzles, respectively, along the transport direction independently of each other;
a slider for moving the nozzles toward and away from the metal plate ;
The slider is a metal plate hardening device that can move the multiple nozzles to a position where the restraint roll and the multiple nozzles overlap each other in the conveying direction, and a position where they do not overlap each other . The metal plate quenching device according to claim 1, wherein the cooling device has a cooling tank in which the metal plate is immersed and cooled. The metal plate quenching device according to claim 1, wherein the movement control device controls the operation of the roll movement device and positions the restraining roll so that the restraining roll restrains the metal plate at a position where the metal plate reaches a target temperature. The metal plate quenching device according to claim 3, wherein the target temperature is set in the temperature range of (TMs+150) (°C) to (TMf-150) (°C), where TMs (°C) is the temperature of the Ms point at which the martensitic transformation of the metal plate starts, and TMf (°C) is the temperature of the Mf point at which the martensitic transformation ends. The metal plate quenching device according to claim 3 or 4, wherein the movement control device sets the distance from the cooling start position of the cooling device to the restraining roll based on the conveying speed of the metal plate, the cooling start temperature of the metal plate when cooling by the cooling device starts, the target temperature, and the cooling speed of the metal plate, and moves the position of the restraining roll so that the set distance is reached. 6. The metal plate quenching device according to claim 5, wherein the movement control device calculates a distance d (mm) from the cooling start position to the restraint roll using equation (1), where v (mm/s) is a conveying speed of the metal plate, T1 (°C) is a cooling start temperature, T2 (°C) is a target temperature, and CV (°C/s) is a cooling rate of the metal plate by the cooling device.
d = (T1 - T2) x v / CV (1) The metal plate quenching device according to claim 6, wherein the cooling rate CV is set as CV=α/t in the movement control device, where α is a coefficient indicating the cooling conditions of the metal plate, and t is the thickness of the metal plate. A method for quenching a metal plate, comprising the steps of:
a cooling fluid is sprayed from a plurality of nozzles onto the metal plate to cool it, and the metal plate cooled by the cooling fluid is restrained in a thickness direction by a restraining roll, the restraining roll is moved along a conveying direction of the metal plate so as to restrain the metal plate at a position where the metal plate is at a target temperature,
The method for hardening a metal plate includes moving the constraining roll along the conveying direction, thereby moving, among the plurality of nozzles, any nozzle that interferes with the constraining roll to the opposite side to the direction in which the constraining roll moves. The method for hardening a metal plate according to claim 8, wherein the target temperature is set in the temperature range of (TMs+150) (°C) to (TMf-150) (°C), where TMs (°C) is the temperature of the Ms point at which the martensitic transformation of the metal plate starts, and TMf (°C) is the temperature of the Mf point at which the martensitic transformation ends. The movement of the restraining roll is performed by setting a distance from a cooling start position to the restraining roll based on a conveying speed of the metal sheet, a cooling start temperature of the metal sheet at the start of cooling, the target temperature, and a cooling speed of the metal sheet;
9. The method for quenching a metal plate according to claim 8, wherein the quenching is performed by moving the restraining rolls to a set distance. 11. The method for quenching a metal plate according to claim 10, wherein a distance d (mm) from the cooling start position to the constraining roll is calculated by Equation (1) where v (mm/s) is a conveying speed of the metal plate, T1 (°C) is a cooling start temperature, T2 (°C) is a target temperature, and CV (°C/s) is a cooling rate of the metal plate.
d = (T1 - T2) x v / CV (1) The method for hardening a metal plate according to claim 11, wherein the cooling rate CV is set as CV=α/t, where α is a coefficient indicating the cooling conditions of the metal plate, and t is the thickness of the metal plate. A method for manufacturing a metal plate using the method for quenching a metal plate described in any one of claims 8 to 12. A method for manufacturing a metal sheet, comprising the steps of: subjecting the metal sheet obtained by the method according to claim 13 to a hot-dip galvanizing treatment, an electrolytic galvanizing treatment, or an alloyed hot-dip galvanizing treatment.

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