WO2025258169A1 - Plating alloying facility, facility for manufacturing alloyed hot-dip galvanized steel sheet, plating alloying method, and method for manufacturing alloyed hot-dip galvanized steel sheet - Google Patents

Abstract

The present invention provides a plating alloying facility with which it is possible to efficiently heat a steel sheet regardless of the phase fraction of the steel sheet.　Provided is a plating alloying facility for heating and alloying a hot-dip metal-plated steel sheet, the plating alloying facility including: a phase fraction acquisition device for acquiring phase fraction information of the steel sheet; two or more types of induction heating devices that have different application directions of magnetic flux to the steel sheet; and a control device for controlling the two or more types of induction heating devices. The phase fraction acquisition device is installed on the upstream side of the induction heating devices in the conveyance direction of the steel sheet. The control device controls the two or more types of induction heating devices on the basis of the phase fraction information acquired by the phase fraction acquisition device.

Description

Galvannealing equipment, galvannealed steel sheet manufacturing equipment, galvannealing method, and galvannealed steel sheet manufacturing method

The present invention relates to plating alloying equipment that can perform uniform alloying heating in the width direction regardless of the phase fraction of the steel sheet, manufacturing equipment for galvannealed hot-dip galvannealed steel sheets, a plating alloying method, and a manufacturing method for galvannealed hot-dip galvannealed steel sheets.

In the production of automotive thin steel sheets, continuously cast slabs are subjected to significant deformation through hot rolling and cold rolling until they reach the final thickness. The subsequent annealing process restores the cold-worked structure, recrystallizes and grows grains, and controls the transformed structure, and together with the cooling process after annealing, the mechanical properties of the product are adjusted.

In recent years, there has been a demand for high-strength steel sheets to achieve both lightweight automobiles and crashworthiness. Since automobile body structural components are generally manufactured by press working, steel sheets that combine high strength with high formability are in demand. Zinc plating is often performed on materials for automotive parts to provide rust resistance. In particular, from the perspective of press workability, alloyed hot-dip galvanized steel sheets, in which zinc and iron are alloyed by heating after plating, are widely used.

To achieve high strength in steel sheets, a method is used in which the steel is heated in an annealing furnace from the region where ferrite and austenite coexist to the region where austenite is single-phase, and then the resulting austenite phase is rapidly cooled to utilize the martensite structure obtained. The alloying process of hot-dip galvanizing requires that the steel sheet be heated to a temperature controlled near the melting point of zinc, to a temperature range where the iron-zinc alloying reaction occurs.

Induction heating devices, particularly solenoid-type induction heating devices that apply magnetic flux in the longitudinal direction of the steel plate, are used as a heating method for alloying because they can heat up in a short time and have high temperature controllability. However, as mentioned above, the austenite phase (paramagnetic) fraction of steel plate increases as the strength of steel plate increases. Solenoid-type induction heating devices have a lower heating efficiency for paramagnetic materials. Fluctuations in the austenite phase fraction of the steel plate cause the coil voltage of solenoid-type induction heating devices to fluctuate suddenly, which poses a risk of damaging the device.

In response to this issue, Patent Document 1 discloses a continuous hot-dip galvanizing process that determines the austenite phase fraction from the results of measuring the magnetic properties of the steel sheet and suppresses sudden voltage fluctuations by controlling the output of an induction heating device installed downstream of the measurement location (e.g., an alloying furnace). Patent Document 2 discloses a continuous hot-dip galvanizing device for steel sheet that heats the steel sheet by combining a transverse induction heating device that applies magnetic flux perpendicular to the steel sheet with a solenoid induction heating device. Patent Document 2 claims that by combining a transverse induction heating device and a solenoid induction heating device, it is possible to improve the temperature uniformity across the width of the steel sheet.

Patent Document 3 discloses a method for measuring the proportion of austenite contained in a steel plate, in which the relative permeability of the steel plate is calculated based on the effective heat generation amount of the steel plate, which is calculated from the coil end voltage of an induction heating device, and the proportion of austenite in the steel plate is calculated from the reciprocal of the relative permeability of the steel plate.

Patent No. 6432645 Patent No. 6763261 JP 2017-67781 A

The continuous hot-dip galvanizing process disclosed in Patent Document 1 only uses a solenoid-type induction heating device, which poses the problem of not being able to heat steel sheets with a high austenite phase fraction, which is appropriate for high-strength steel sheets. Meanwhile, Patent Document 2 discloses the use of a transverse-type induction heating device, but does not disclose anything about its ability to heat steel sheets with a high austenite phase fraction. Therefore, Patent Document 2 poses the problem of not clarifying a method for efficiently heating steel sheets with a high austenite phase fraction.

In the method for measuring the austenite fraction disclosed in Patent Document 3, the austenite phase fraction is estimated from the relative magnetic permeability of the steel sheet, and the current value of the solenoid-type induction heating device is controlled. Because this control is feedback control, there is a delay in the control, and control accuracy decreases when the austenite phase fraction differs significantly at seams in the steel sheet, etc. Furthermore, because the alloying furnace only uses a solenoid-type induction heating device, there is also the issue that it cannot heat steel sheets with a high austenite phase fraction, which is necessary for high-strength steel sheets.

The present invention was made to solve these problems of the prior art. An object of the present invention is to provide a plating alloying equipment and a plating alloying method that can efficiently heat steel sheets regardless of the phase fraction of the steel sheets. Another object of the present invention is to provide a manufacturing equipment for galvannealed steel sheets and a manufacturing method for galvannealed steel sheets, which includes the plating alloying equipment and the plating alloying method.

The means for solving the above problems are as follows.
[1] A plating alloying facility that heats and alloys a hot-dip metal-plated steel sheet, the plating alloying facility comprising: a phase fraction acquisition device that acquires phase fraction information of the steel sheet; two or more types of induction heating devices that apply magnetic flux to the steel sheet in different directions; and a control device that controls the two or more types of induction heating devices, wherein the phase fraction acquisition device is installed upstream of the induction heating devices in the conveying direction of the steel sheet, and the control device controls the two or more types of induction heating devices based on the phase fraction information acquired by the phase fraction acquisition device.
[2] The plating alloying facility according to [1], wherein the phase fraction acquisition device inputs input data including a surface temperature of the steel sheet in continuous annealing facility into a phase fraction prediction model and outputs the phase fraction information to acquire the phase fraction information.
[3] The plating alloying equipment according to [1] or [2], wherein the control device inputs input data including the phase fraction information and the heating target temperature into a heating control model, outputs current values corresponding to the temperature rise amounts of each of the two or more types of induction heating devices, and sets the current values as heating conditions for each of the two or more types of induction heating devices.
[4] The plating alloying equipment according to [1] or [2], wherein the control device outputs a current value and a power supply frequency corresponding to the temperature rise of each of the two or more types of induction heating devices from a heating control model, and sets the current value and the power supply frequency as heating conditions for each of the two or more types of induction heating devices.
[5] A manufacturing facility for a galvannealed steel sheet, in which a continuous annealing facility, a hot-dip galvanizing facility, and the plating alloying facility according to any one of [1] to [4] are arranged in this order in the conveying direction of the steel sheet.
[6] A plating alloying method for heating and alloying a hot-dip metal-plated steel sheet, the plating alloying method comprising: a phase fraction acquisition step for acquiring phase fraction information of the steel sheet; a control step for feedforward controlling heating conditions of two or more types of induction heating devices with different magnetic flux application directions using the phase fraction information acquired in the phase fraction acquisition step; and a heating step for heating the steel sheet with the two or more types of induction heating devices.
[7] The plating alloying method according to [6], wherein in the phase fraction acquisition step, input data including a surface temperature of the steel sheet in continuous annealing equipment is input to a phase fraction prediction model, and the phase fraction information of the steel sheet is output to acquire the phase fraction information.
[8] The plating alloying method according to [6] or [7], wherein in the control step, input data including the phase fraction information and the heating target temperature is input to a heating control model, a current value for each of the two or more types of induction heating devices is output, and the current value is set as a heating condition for each of the two or more types of induction heating devices.
[9] In the control step, a current value and a power supply frequency corresponding to the temperature rise of each of the two or more types of induction heating devices are output from a heating control model, and the current value and the power supply frequency are set as heating conditions for each of the two or more types of induction heating devices. [10] The plating alloying method according to [6] or [11].
[10] A method for producing a galvannealed steel sheet, comprising: an annealing step of annealing the steel sheet; a hot-dip galvanizing step of hot-dip galvanizing the annealed steel sheet; and an alloying step of alloying the hot-dip galvanized coating by the plating alloying method according to any one of [6] to [9].

In the plating alloying equipment and plating alloying method of the present invention, a phase fraction acquisition device acquires phase fraction information of the steel sheet, and controls the heating conditions of two or more types of induction heating devices that apply magnetic flux to the steel sheet in different directions based on the phase fraction information. This makes it possible to heat the steel sheet using an induction heating device that is suited to the phase fraction of the steel sheet, making it possible to heat the steel sheet more efficiently than before, regardless of the phase fraction of the steel sheet.

FIG. 1 is a schematic diagram showing an example of the configuration of a manufacturing facility for a galvannealed steel sheet including a plating alloying facility according to a first embodiment. FIG. 2 is a schematic diagram showing an example of the configuration of a hot-dip galvanizing facility and a plating alloying facility. FIG. 3 is a schematic diagram showing an example of the configuration of the control device. FIG. 4 is a schematic diagram showing an example of the configuration of a manufacturing facility for a galvannealed steel sheet including a plating alloying facility according to the second embodiment. FIG. 5 is a schematic diagram showing an example of the configuration of plating alloying equipment. FIG. 6 is a schematic diagram showing an example of the configuration of the control device.

The present invention will now be described in detail through embodiments thereof. The following embodiments are intended to be preferred examples of the present invention, and the present invention is not limited to these embodiments in any way.

(First embodiment)
Fig. 1 is a schematic diagram showing a configuration example of a manufacturing facility 10 for a galvannealed steel sheet including a coating alloying facility 30 according to a first embodiment. Fig. 2 is a schematic diagram showing a configuration example of a hot-dip galvanizing facility 28 and a coating alloying facility 30. The coating alloying facility 30 and the manufacturing facility 10 for a galvannealed steel sheet according to the first embodiment will be described with reference to Figs. 1 and 2 .

The main components of the manufacturing equipment 10 for galvannealed steel sheets are a continuous annealing equipment 18, a hot-dip galvanizing equipment 28, and a plating alloying equipment 30. The continuous annealing equipment 18, the hot-dip galvanizing equipment 28, and the plating alloying equipment 30 are arranged in this order in the conveying direction X of the steel sheet S.

The steel sheet S is hot rolled or cold rolled to the specified thickness and wound into a coil, then unwound on a payoff reel 12 and transported in the X direction in Figure 1. The steel sheet S is joined together by a welder 14. The steel sheet S passes through a looper 16, which stores the steel sheet S for joining by the welder 14, and is transported to continuous annealing equipment 18.

Steel sheet S, transported to the continuous annealing equipment 18 at a temperature between room temperature and approximately 100°C, first enters the preheating zone 20 where it is heated to approximately 200°C. To improve heating efficiency, the preheating zone 20 uses the high-temperature exhaust gas generated in the heating zone 22.

The steel sheet S is then transported to the heating zone 22. Once transported to the heating zone 22, the steel sheet S is quickly heated to approximately 600-700°C to ensure the soaking time required for structure control in the next process, the soaking zone 24. A direct-fired heating furnace is preferably used as the heating method in the heating zone 22. This method has high heating capacity and allows for a small furnace volume. Furthermore, the direct-fired heating furnace method allows for the atmospheric composition to be changed by changing the fuel-to-air ratio, allowing for flexible control of the oxidation-reduction reaction on the surface of the steel sheet S to ensure galvanization in subsequent processes. For example, by setting the heating temperature in the heating zone 22 to 700°C or below, excessive oxidation of the surface of the steel sheet S can be suppressed.

The steel sheet S is then transported to the soaking zone 24. In the soaking zone 24, it is gently heated from the heating zone exit temperature to the target annealing temperature and held there. By gently heating in a temperature range from the heating zone exit temperature to below the A1 transformation point, recrystallization of the ferrite phase progresses, and the crystal grains that have been excessively refined by rolling can be appropriately coarsened.

In order to prevent the remaining unrecrystallized ferrite phase, it is preferable to ensure a residence time of approximately 20 to 60 seconds in the above temperature range. The residence time is controlled by the heating rate, and the heating rate from heating zone 22 until the annealing temperature is reached is preferably 10°C/s or less, and more preferably 5°C/s or less. By controlling the annealing temperature in a temperature range above the A1 transformation point, it is possible to adjust the proportion of ferrite phase and the austenite phase transformed from the ferrite phase, and in combination with the subsequent cooling, it becomes possible to control the mechanical properties of the product.

The heating method used in the soaking zone 24 is preferably radiant heating (radiant tube heating) using gas combustion, due to its high efficiency and heating uniformity. In addition, in order to stabilize the temperature of the steel sheet S near the exit of the soaking zone 24, it is preferable to use this heating method to keep the furnace temperature in the soaking zone 24 within the range of the target annealing temperature + 0 to 50°C, and more preferably within the range of the target annealing temperature + 5 to 20°C.

As shown in Figure 1, the soaking zone 24 may ensure the residence time within the furnace by moving the steel sheet S back and forth between transport rolls arranged above and below. The furnace structure itself may be one unit from the entrance to the exit, or the furnace shell may be separated into an adjustment zone, which heats the steel sheet from the recrystallization region to the annealing temperature, and a holding zone, which maintains the steel sheet at the annealing temperature. This allows the furnace volume of the soaking zone, which requires precise temperature control, to be reduced, thereby improving the temperature controllability of the soaking zone.

After being heated to the target annealing temperature in the soaking zone 24, the steel sheet S is transported to the cooling zone 26 and cooled. If the cooling rate in the cooling zone 26 is too slow, the austenite phase will transform into a pearlite phase or other phase, making it impossible to ensure sufficient strength. On the other hand, if the cooling rate in the cooling zone 26 is too fast, the risk of buckling deformation increases. For this reason, the cooling rate in the cooling zone 26 is preferably 5°C/s or more and 30°C/s or less. In order to prevent martensitic transformation from occurring upstream of the plating process and to transform some of the austenite phase into bainite, the cooling stop temperature is preferably above the martensitic transformation start temperature and below 550°C. A cooling stop temperature of 450°C or more and 550°C or less is more preferable.

In order to allow the bainite transformation to proceed sufficiently, it is preferable to hold the temperature for 1 to 100 seconds after reaching the cooling stop temperature, and it is even more preferable to hold the temperature for 20 to 50 seconds after reaching the cooling stop temperature. At this time, an electric heater may be provided to prevent excessive temperature drop of the steel sheet S during holding.

The cooling method used in the cooling zone 26 can be gas jet cooling, in which a compressed gas jet is collided with the steel sheet S; roll cooling, in which the steel sheet S is cooled by contact with a roll with a refrigerant running through it; water cooling using water jets; or mist cooling, in which compressed gas is mixed with tiny water droplets. In the first embodiment, gas jet cooling was used, which ensures the target cooling rate while preventing unstable temperature changes due to boiling and allows for highly accurate control of the cooling stop temperature.

A holding zone may be provided in the cooling zone 26 to change the cooling rate to control transformation during cooling or to ensure time to promote transformation after cooling is stopped. The cooling zone 26 may be divided into two cooling zones: a first cooling zone 26A and a second cooling zone 26B. After structural control is performed in the cooling zone 26, the steel sheet S is transported to the hot-dip galvanizing equipment 28. In this way, the steel sheet S is continuously annealed by passing through the preparatory zone 20, heating zone 22, soaking zone 24, and cooling zone 26. This annealing treatment in the preparatory zone 20, heating zone 22, soaking zone 24, and cooling zone 26 constitutes the annealing step in the manufacturing method of galvannealed steel sheet.

The hot-dip galvanizing equipment 28 uses a hot-dip galvanizing method in which the steel sheet S is immersed in a galvanizing bath 32 containing molten zinc. The hot-dip galvanizing equipment 28 has a gas wiping device 34 that scrapes off excess molten zinc, and a vibration damping device 36 that suppresses vibration of the steel sheet S. The vibration damping device 36 uses, for example, an electromagnetic vibration damping device that stabilizes the sheet passing position by the attractive force of electromagnets installed facing the front and back surfaces of the steel sheet S. The hot-dip galvanized steel sheet S is transported to the plating alloying equipment 30.

In the plating alloying equipment 30, the hot-dip galvanized steel sheet S is heated to 500-550°C to promote the Zn-Fe alloying reaction. The plating alloying equipment 30 according to the first embodiment includes a TF heating device 38 for heating the hot-dip galvanized steel sheet S, an LF heating device 40, a phase fraction meter 42, and a control device 44.

The TF heating device 38 and the LF heating device 40 are two types of induction heating type heating devices that apply magnetic flux to the steel sheet S in different directions. Induction heating type heating devices have high temperature controllability and responsiveness, and do not affect the plating surface of the steel sheet S. For this reason, it is preferable to use an induction heating type heating device as the heating device for the plating alloying equipment 30.

The TF heating device 38 is a transverse type induction heating device that heats the steel sheet S using a perpendicular magnetic flux method, in which the magnetic flux is perpendicular to the surface of the steel sheet S. In the TF heating device 38, an induction coil that covers the entire width of the steel sheet S is installed facing the steel sheet S, and magnetic flux is applied in a direction perpendicular to the surface of the steel sheet S. This generates an induced current that circulates around the magnetic flux, and the steel sheet S is heated by Joule heating caused by this induced current.

The LF heating device 40 is a solenoid-type induction heating device that heats the steel sheet S using a parallel magnetic flux method, in which the magnetic flux is parallel to the longitudinal direction of the steel sheet S. In the LF heating device 40, the steel sheet S is transported so that it passes through the induction coil, and the magnetic flux generated by the induction coil is applied in a direction parallel to the longitudinal direction of the steel sheet S. At this time, an induced current is generated on the steel sheet S side that circulates near the surface layer within the cross section in the width direction, and the steel sheet S is heated by Joule heating caused by this induced current.

The LF heating device 40 has the advantage that the strength of the induced current is nearly uniform across the width, making it less likely for temperature deviations to occur across the width. On the other hand, when the steel sheet S is a paramagnetic material (austenite phase), the LF heating device 40 has the problem that the area through which the induced current flows expands in the thickness direction, causing the induced currents flowing on the front and back surfaces of the steel sheet S to cancel each other out, resulting in a drastic reduction in heating efficiency.

In contrast, the TF heating device 38 does not cause such current cancellation, so it has the advantage of being able to heat the steel sheet S without reducing heating efficiency, even if it is a paramagnetic material. On the other hand, with the TF heating device 38, the induced current circulating within the surface of the steel sheet S concentrates at the edges of the steel sheet S, increasing the amount of heat generated at those edges. For this reason, the TF heating device 38 has the problem of low temperature uniformity in the width direction.

A known method for preventing overheating at the widthwise ends of the steel sheet S is to limit the range of magnetic flux application to the center in the widthwise direction by inserting an electromagnetic shield between the coil and the steel sheet S. However, even when this approach is taken, the TF heating device 38 has poorer temperature uniformity in the widthwise direction than the LF heating device 40, and there is also the problem of reduced heating efficiency due to the generation of magnetic flux that is not used to heat the steel sheet S.

In consideration of the advantages and disadvantages of the LF heating device 40 and the TF heating device 38, the plating alloying equipment 30 according to the first embodiment uses both the TF heating device 38 and the LF heating device 40 so that the steel sheet S can be heated efficiently and with a uniform temperature in the width direction regardless of the phase fraction of the steel sheet S. By using the TF heating device 38, the temperature at the ends of the steel sheet S, which has been lowered by the gas wiping device 34, can be increased, thereby improving the temperature uniformity in the width direction. Furthermore, by controlling the amount of heating of the steel sheet S by the TF heating device 38 and the LF heating device 40 based on the austenite phase fraction of the steel sheet S, the steel sheet S can be heated with high heating efficiency regardless of the austenite phase fraction.

The TF heating device 38 has a temperature control mechanism at the widthwise end, such as an electromagnetic shielding plate. However, the movable range of this control mechanism cannot cover the various widths of the steel sheet S. For this reason, it is preferable to install multiple TF heating devices 38 corresponding to the width of the steel sheet S being manufactured. The plating alloying equipment 30 according to the first embodiment also has a TF heating device 38A for wide widths and a TF heating device 38B for narrow widths as TF heating devices 38, making it possible to accommodate steel sheets S of various widths.

Similarly, in the LF heating device 40, the heating efficiency in the thickness direction changes depending on the power supply frequency used, so it is preferable to change the power supply frequency in accordance with the thickness of the steel sheet S being manufactured. Rather than controlling the power supply frequency via a circuit, it is also possible to prepare in advance two combinations of power supplies and coils with different power supply frequencies.

Next, the phase fraction meter 42 will be described. The phase fraction meter 42 measures the austenite phase fraction of the steel sheet S and obtains phase fraction information indicating the austenite phase fraction. This is the phase fraction acquisition step in the plating alloying method. The phase fraction meter 42 is preferably installed after the exit side of the soaking zone 24, where the phase fraction of the steel sheet S is roughly determined. Because the phase fraction meter 42 must obtain phase fraction information before plating alloying heating is performed, it must be installed just before the plating alloying equipment 30. Therefore, the phase fraction meter 42 may be installed downstream of the soaking zone 24 in the conveying direction of the steel sheet S and upstream of the plating alloying equipment 30 in the conveying direction of the steel sheet S. However, considering the environment and installation space around the measuring device and the possibility of partial transformation of the austenite phase during the cooling process, it is preferable to install the phase fraction meter 42 in the cooling zone 26. The phase fraction meter 42 is an example of a phase fraction acquisition device.

The phase fraction meter 42 may be a magnetic phase fraction measuring device composed of a drive coil that generates a magnetic field and a detection coil that measures the magnetic field that has passed through the steel sheet S, and may measure the austenite phase fraction of the steel sheet S. The phase fraction meter 42 may be a device that measures the austenite phase fraction from the diffraction peak intensity generated by irradiating the steel sheet S with X-rays. In the first embodiment, a magnetic phase fraction measuring device was used as the phase fraction meter 42 from the perspective of using it to control the induction heating device. However, the measurement method of the phase fraction meter 42 does not need to be particularly limited as long as it can measure the austenite phase fraction of the steel sheet S.

The phase fraction meter 42 measures the austenite phase fraction of the steel sheet S and outputs phase fraction information indicating the austenite phase fraction to the control device 44. The control device 44 controls the TF heating device 38 and the LF heating device 40 using the phase fraction information obtained from the phase fraction meter 42. Specifically, the control device 44 uses the phase fraction information to identify the current value and power supply frequency to be applied to the coils of the TF heating device 38 and the LF heating device 40, and sets these as the heating conditions for the steel sheet S by each heating device.

Next, the process computer 100 will be described. The process computer 100 is, for example, a general-purpose computer such as a workstation or personal computer. The process computer 100 is connected to each piece of equipment in the galvannealed steel sheet manufacturing facility 10 via wired or wireless connection, and controls the manufacturing process of the galvannealed steel strip. The process computer 100 also acquires quality information about the steel sheet S from a higher-level computer. The quality information about the steel sheet S includes, for example, information about the chemical composition of the steel sheet S, the hot rolling reduction, the cold rolling reduction, the sheet thickness, the sheet width, etc. The process computer 100 collects and stores the manufacturing conditions of each piece of equipment that makes up the galvannealed steel sheet manufacturing facility 10, as well as actual measurements taken by measuring instruments installed in each piece of equipment.

Next, the control device 44 that controls the TF heating device 38 and the LF heating device 40 will be described. Figure 3 is a schematic diagram showing an example configuration of the control device 44. The control device 44 is, for example, a general-purpose computer such as a workstation or personal computer. The control device 44 has a control unit 46, an input unit 48, an output unit 50, and a storage unit 52. The control unit 46 is, for example, a CPU, and functions as an acquisition unit 54 and a heating condition identification unit 56 by executing a program stored in the storage unit 52.

The input unit 48 is, for example, a keyboard, a touch panel integrated with a display, or the like. The output unit 50 is, for example, an LCD or CRT display, or the like. The storage unit 52 is, for example, an updatable flash memory, a built-in hard disk or a hard disk connected via a data communication terminal, an information recording medium such as a memory card, and a read/write device for the same. The storage unit 52 stores programs and data for realizing the functions of the control device 44. The target temperatures for heating the steel sheet S by the TF heating device 38 and the LF heating device 40 are stored in advance in the storage unit 52 by the operator via the input unit 48.

The storage unit 52 also stores a database 58 and a heating control model 60. The database 58 stores 20 or more, and more preferably 100 or more, data sets consisting of actual values for steel sheets S that have previously been heated and alloyed with high efficiency and uniformity in the width direction by the plating alloying equipment 30. Each of the above data sets is a set of the austenite phase fraction of the steel sheet S, the target heating temperature, and the actual current values of the TF heating device 38 and the LF heating device 40.

The heating control model 60 is a trained machine learning model that has been trained using the dataset stored in the database 58 as training data. The heating control model 60 is a trained machine learning model that takes input data including the austenite phase fraction of the steel sheet S and the target heating temperature as input, and outputs the current values of the TF heating device 38 and the LF heating device 40. The austenite phase fraction and target heating temperature of the steel sheet S affect the induction heating of the steel sheet S by the TF heating device 38 and the LF heating device 40. Therefore, by including this data in the input data, it becomes possible to predict with high accuracy the current value that will heat the steel sheet S with high efficiency and improve temperature uniformity in the width direction.

The input data for the heating control model 60 may include not only the austenite phase fraction of the steel sheet S and the target heating temperature, but also the component composition (mass %) of the steel sheet S, the cross-sectional shape (width dimension, thickness dimension), the manufacturing conditions of the steel sheet S before continuous annealing, and the continuous annealing conditions. In this case, the data set stored in the database 58 also includes this data.

The elemental composition (mass%) of the steel sheet S, its cross-sectional shape (width and thickness), the manufacturing conditions of the steel sheet S before continuous annealing, and the continuous annealing conditions all directly or indirectly affect the induction heating of the steel sheet S. Therefore, by including these data in the input data for the heating control model 60, it becomes possible to predict with high accuracy the current value that will heat the steel sheet S with high efficiency and improve temperature uniformity in the width direction. Furthermore, the output of the heating control model 60 may include not only the current values applied to the TF heating device 38 and the LF heating device 40, but also the power supply frequencies of the TF heating device 38 and the LF heating device 40.

Next, the processing performed by the acquisition unit 54 and heating condition identification unit 56 will be described. The acquisition unit 54 acquires phase fraction information indicating the austenite phase fraction of the steel sheet S from the phase fraction meter 42. The acquisition unit 54 outputs the acquired phase fraction information to the heating condition identification unit 56.

When the heating condition specification unit 56 acquires the phase fraction information of the steel sheet S, it reads out the heating target temperature and heating control model 60 from the storage unit 52. The heating condition specification unit 56 inputs the phase fraction information of the steel sheet S and the heating target temperature into the heating control model 60, which then outputs the current values of the TF heating device 38 and the LF heating device 40. The current values of the TF heating device 38 and the LF heating device 40 output in this manner are current values that can heat the steel sheet S to the heating target temperature with high efficiency, depending on the austenite phase fraction of the steel sheet S. The heating condition specification unit 56 specifies the output current values as the current values of the TF heating device 38 and the LF heating device 40. Whether the heating treatment is to be performed using TF heating device 38A or 38B is determined in advance based on the width dimension of the steel sheet S.

The heating condition specification unit 56 sets the specified current value as the heating condition for the TF heating device 38 and the LF heating device 40. In this way, the control device 44 feedforward controls the heating conditions for the TF heating device 38 and the LF heating device 40 based on the phase fraction information indicating the austenite phase fraction of the steel sheet S obtained by the phase fraction meter 42. This is the control step in the plating alloying method.

In the TF heating device 38 and the LF heating device 40, the steel sheet S is heated by applying a current of a set value to the coil. This is the heating step in the plating alloying method. As a result, the steel sheet S can be heated to the heating target temperature uniformly in the width direction with high efficiency, regardless of the austenite phase fraction. By heating the steel sheet S uniformly in the width direction with high efficiency to the heating target temperature in this manner, alloying can be carried out efficiently, and a high-quality galvannealed steel sheet with no alloying unevenness in the width direction can be manufactured. The phase fraction acquisition step, control step, and heating step in the plating alloying method, which alloy the hot-dip galvannealed coating, constitute the alloying step in the manufacturing method for galvannealed steel sheet.

The first embodiment of the present invention is not limited to the above embodiment and various modifications can be made. In the above embodiment, an example was described in which the control device 44 determines the current values of the TF heating device 38 and the LF heating device 40 using a heating control model, which is a trained machine learning model, but this is not limited to this. For example, the current values of the TF heating device 38 and the LF heating device 40 may be determined based on actual values, experimental values, or offline electromagnetic wave/heat transfer coupled analysis of steel sheets S previously alloyed in the plating alloying equipment 30, and the heating conditions of these devices may be feedforward controlled.

As mentioned above, if the austenite phase fraction is high, heating cannot be performed using the LF heating device 40. For this reason, the current value and current frequency of these devices may be determined so that the amount of heating by the TF heating device 38 increases and the amount of heating by the LF heating device 40 decreases as the austenite phase fraction increases. Similarly, since the TF heating device 38 can heat the widthwise ends of the steel sheet S, the current value of the TF heating device 38 may be determined according to the amount of temperature reduction at the widthwise ends of the steel sheet S caused by the gas wiping device 34.

Second Embodiment
Fig. 4 is a schematic diagram showing a configuration example of a manufacturing facility 110 for a galvannealed steel sheet including a coating alloying facility 80 according to a second embodiment. Fig. 5 is a schematic diagram showing a configuration example of the coating alloying facility 80. In the coating alloying facility 80 and the manufacturing facility 110 for a galvannealed steel sheet, the same components as those in the coating alloying facility 30 and the manufacturing facility 10 for a galvannealed steel sheet shown in Figs. 1 and 2 are designated by the same reference numerals, and redundant explanations will be omitted.

The galvannealed steel sheet manufacturing equipment 110 shown in Figure 4 differs from the galvannealed steel sheet manufacturing equipment 10 shown in Figure 1 in that it does not have a phase fraction meter 42, but has a thermometer 70 in the continuous annealing equipment 18 that measures the surface temperature of the steel sheet S. In the example shown in Figure 4, the thermometer 70 is provided at the connection between the soaking zone 24 and the cooling zone 26, but it is preferable that the thermometer 70 be provided at the connection between each zone of the continuous annealing equipment 18. In areas where the equipment length is long, such as the soaking zone 24, a thermometer 70 may also be provided inside the soaking zone 24 to check the temperature history along the way.

The temperature measurement method of the thermometer 70 is not particularly limited, but it is preferable that the thermometer 70 be a radiation thermometer that measures the temperature by detecting infrared rays emitted by the steel sheet S. However, because radiation thermometers are affected by the reflected infrared light from the surrounding furnace body, it is preferable to provide a cover (shielding tube) with a cooled inner surface between the measurement unit and the detection unit. A scanning type radiation thermometer may be used to measure the temperature distribution in the width direction of the steel sheet S. When using a scanning type radiation thermometer, it is preferable to provide a cooling tube in front of the thermometer to accurately measure the temperature at the end of the steel sheet S in the width direction.

On the other hand, since radiation thermometers are affected by the emissivity of the surface of the steel sheet S, a multi-reflection temperature measurement method that utilizes the wedge-shaped space between the furnace transport rolls and the steel sheet S may also be used. Due to the accuracy and stability of temperature measurement within the furnace, a multi-reflection thermometer was used for the thermometer 70 shown in Figure 4. Information on the surface temperature of the steel sheet S measured by the thermometer 70 is collected and stored by the process computer 100.

Next, a plating alloying equipment 80 according to a second embodiment will be described. The plating alloying equipment 80 according to the second embodiment includes a TF heating device 38, an LF heating device 40, and a control device 82. The control device 82 acquires the surface temperature of the steel sheet S in the continuous annealing equipment 18 measured by the thermometer 70 from the process computer 100, and acquires phase fraction information indicating the austenite phase fraction of the steel sheet S using input data including the surface data. The control device 82 uses the acquired phase fraction information of the steel sheet S to identify the current values to be applied to the coils of the TF heating device 38 and the LF heating device 40, and sets the identified current values as the heating conditions for the steel sheet S using each heating device.

Figure 6 is a schematic diagram showing an example configuration of the control device 82. In the control device 82 shown in Figure 6, the same components as those in the control device 44 are given the same reference numbers, and duplicate explanations will be omitted. The control device 82 differs from the control device 44 in that it has a control unit 84 and a storage unit 86.

The control unit 84 is, for example, a CPU, and functions as an acquisition unit 88, a phase fraction information acquisition unit 90, and a heating condition identification unit 56 by executing programs stored in the storage unit 86. The storage unit 86 is, for example, an updatable flash memory, a built-in hard disk or a hard disk connected via a data communication terminal, an information recording medium such as a memory card, and a read/write device for the same. The storage unit 86 stores programs and data for realizing the functions of the control unit 82. The target temperatures for heating the steel sheet S by the TF heating device 38 and the LF heating device 40 are stored in advance in the storage unit 86 by the operator via the input unit 48.

The storage unit 86 further stores a database 92, a phase fraction prediction model 94, and a heating control model 60. The database 92 stores 20 or more, and more preferably 100 or more, data sets, each of which is a set of the actual values of the surface temperature of the steel sheet S in the continuous annealing equipment 18 and the phase fraction of the steel sheet S, as training data for the phase fraction prediction model 94. Furthermore, 20 or more, and more preferably 100 or more, data sets, each of which is a set of the austenite phase fraction of the steel sheet S, the target heating temperature, and the actual values of the current values of the TF heating device 38 and the LF heating device 40, as training data for the heating control model 60, are also stored.

The phase fraction prediction model 94 is a trained machine learning model that has been trained using the dataset stored in the database 92 as training data. The phase fraction prediction model 94 is a trained machine learning model that receives input data including the surface temperature of the steel sheet S in the continuous annealing equipment 18, and outputs phase fraction information indicating the austenite phase fraction of the steel sheet S.

The input data for the phase fraction prediction model 94 may include not only the surface temperature of the steel sheet S in the continuous annealing equipment 18, but also the chemical composition of the steel sheet S and the manufacturing conditions of the steel sheet S in processes upstream of the continuous annealing. In this case, the data set stored in the database 92 also includes this data.

The surface temperature of the steel sheet S in the continuous annealing equipment 18 affects the austenite phase fraction of the steel sheet S after continuous annealing. Therefore, by including the surface temperature of the steel sheet S in the continuous annealing equipment 18 in the input data for the phase fraction prediction model 94, it becomes possible to predict the austenite phase fraction of the steel sheet S with high accuracy.

The input data for the machine learning model that outputs phase fraction information indicating the austenite phase fraction of steel sheet S may include the component concentrations of steel sheet S, the cross-sectional shape of steel sheet S, the continuous annealing conditions, and the manufacturing conditions of steel sheet S before continuous annealing. In this case, the data set stored in database 92 also includes this data.

The component concentrations of steel sheet S, the cross-sectional shape of the steel sheet, the continuous annealing conditions, and the manufacturing conditions of steel sheet S before continuous annealing affect the austenite phase fraction of steel sheet S after continuous annealing. Therefore, by including this data as input data for phase fraction prediction model 94, the austenite phase fraction of steel sheet S can be predicted with high accuracy.

Next, the processing performed by the acquisition unit 88 and the phase fraction information acquisition unit 90 will be described. The acquisition unit 88 acquires the surface temperature of the steel sheet S in the continuous annealing equipment 18 from the process computer 100. The acquisition unit 88 outputs the acquired surface temperature of the steel sheet S in the continuous annealing equipment 18 to the phase fraction information acquisition unit 90.

When the phase fraction information acquisition unit 90 acquires the surface temperature of the steel sheet S in the continuous annealing equipment 18, it reads out a phase fraction prediction model from the storage unit 86. The phase fraction information acquisition unit 90 inputs the surface temperature of the steel sheet S in the continuous annealing equipment 18 into the phase fraction prediction model, and outputs phase fraction information indicating the austenite phase fraction of the steel sheet S. In this way, the phase fraction information acquisition unit 90 acquires phase fraction information of the steel sheet S to be alloyed in the plating alloying equipment 80. The phase fraction information acquisition unit 90 outputs the acquired phase fraction information of the steel sheet S to the heating condition identification unit 56. The heating condition identification unit 56 uses the acquired phase fraction information of the steel sheet S to identify the current values of the TF heating device 38 and the LF heating device 40. The subsequent processing is the same as that of the control device 44 shown in Figure 3, so a description thereof will be omitted.

In this way, in the second embodiment, the control device 82 functions as a phase fraction acquisition device that acquires phase fraction information indicating the austenite phase fraction of the steel sheet S. In the second embodiment, an example has been described in which the control device 82 also functions as a phase fraction acquisition device that acquires phase fraction information of the steel sheet S, but this is not limited to this. The plating alloying equipment 80 may also have a separate phase fraction acquisition device that acquires phase fraction information indicating the austenite phase fraction of the steel sheet S using the phase fraction prediction model 94. In this case, the plating alloying equipment 80 can use the same control device as the control device 44 shown in FIG. 3.

The plating alloying equipment according to the first and second embodiments has been described using an example in which a hot-dip galvanized steel sheet S is heated and alloyed, but this is not limited to this. The plating alloying equipment according to the first and second embodiments is not limited to hot-dip galvanizing, and can also be applied to alloying processes for other hot-dip metal coatings. Regardless of the type of hot-dip metal coating used, the temperature of the widthwise ends is reduced by using a wiping device, and steel sheets S with a high austenite phase fraction cannot be heated by the LF heating device 40. For this reason, the plating alloying equipment according to the first and second embodiments can be applied not only to hot-dip galvanizing, but also to alloying processes for other hot-dip metal coatings, and similar effects can be obtained.

Furthermore, the plating alloying equipment according to the first and second embodiments has been described using an example in which the TF heating device 38 and the LF heating device 40 are used as two types of induction heating devices that apply magnetic flux to the steel sheet S in different directions, but this is not limited to this. The plating alloying equipment according to the first and second embodiments may further include an induction heating device that applies magnetic flux in a direction different from the TF heating device 38 and the LF heating device 40. In other words, the plating alloying equipment according to the first and second embodiments may simply include two or more types of induction heating devices that apply magnetic flux to the steel sheet S in different directions.

Next, an example will be described in which galvannealed steel sheets were manufactured using continuous annealing equipment equipped with the plating alloying equipment according to this embodiment. In this example, two types of steel sheets were used: a narrow material with a width of 800 mm and a wide material with a width of 1300 mm. Galvannealed steel sheets were manufactured using four types of steel sheets with different austenite phase fractions during galvanizing for these two widths.

Invention Example 1 is a manufacturing example in which a galvannealed hot-dip galvanized steel sheet was manufactured using the plating alloying equipment 30 shown in Figures 2 and 3. A TF heating device (narrow width), a TF heating device (wide width), and an LF heating device were used as induction heating devices, and each heating device was arranged in this order from upstream to downstream in the conveying direction of the steel sheet S. The galvannealed steel sheet was heated using these heating devices to manufacture a galvannealed hot-dip galvanized steel sheet. A phase fraction meter was installed in the cooling zone of the continuous annealing equipment to obtain information on the austenite phase fraction of the steel sheet during plating, and the austenite phase fraction information was used to control the current value, which is a heating condition for the TF heating device and LF heating device.

Invention Example 2 is a manufacturing example in which heating devices are arranged in the following order from upstream in the steel sheet conveying direction: LF heating device, TF heating device (for narrow width), and TF heating device (for wide width), and the hot-dip galvanized steel sheet is heated using these heating devices to produce an alloyed hot-dip galvanized steel sheet. In Invention Example 2, as in Invention Example 1, a phase fraction meter is installed in the cooling zone of the continuous annealing equipment to obtain information on the austenite phase fraction of the steel sheet during plating, and this austenite phase fraction information is used to control the current value, which is a heating condition for the TF heating device and LF heating device.

Invention Example 3 is a manufacturing example in which heating devices are arranged in the following order from upstream in the steel sheet conveying direction: TF heating device (narrow), LF heating device, and TF heating device (wide), and the hot-dip galvanized steel sheet is heated using these heating devices to produce an alloyed hot-dip galvanized steel sheet. In Invention Example 3, as in Invention Example 1, a phase fraction meter is installed in the cooling zone of the continuous annealing equipment to obtain information on the austenite phase fraction of the steel sheet during plating, and this austenite phase fraction information is used to control the current value, which is a heating condition for the TF heating device and LF heating device.

Invention Example 4 is a manufacturing example in which heating devices are arranged in the following order from upstream in the steel sheet conveying direction: TF heating device (for narrow width), TF heating device (for wide width), and LF heating device, and the hot-dip galvanized steel sheet is heated using these heating devices to produce an alloyed hot-dip galvanized steel sheet. In Invention Example 4, a phase fraction prediction model was used instead of a phase fraction meter to obtain phase fraction information for the steel sheet during plating. The input data and output data for the phase fraction prediction model used in Invention Example 4 are as follows:

Input data:
Steel plate composition (slab composition) (mass%)
Cooling start temperature in the hot rolling process (℃)
Cooling stop temperature (℃)
Coil winding temperature (℃)
Steel plate thickness (mm)
Sheet threading speed during continuous annealing (m/min)
Heating zone outlet temperature (℃)
Cooling start temperature (℃)
Cooling stop temperature (℃)
Output data:
Austenite phase fraction (%) of steel sheet during plating process

Among the above input data, the cooling start temperature, cooling stop temperature, and coil winding temperature in the hot rolling process are manufacturing conditions for steel sheet S before continuous annealing. The steel sheet thickness is the cross-sectional shape of the steel sheet. The sheet threading speed during continuous annealing is a continuous annealing condition. The heating zone exit temperature, cooling start temperature, and cooling stop temperature are the surface temperature of steel sheet S in the continuous annealing equipment.

The phase fraction prediction model is a trained machine learning model created by preparing 100 sets of data, each consisting of a set of the above input data and output data from past production results, and using these data as training data for machine learning. In invention example 4, this phase fraction prediction model was used to obtain phase fraction information indicating the austenite phase fraction of the steel sheet during plating. The obtained phase fraction information of the steel sheet was used to control the current value, which is a heating condition for the TF heating device and LF heating device. The heating conditions, temperature rise, input power, and temperature deviation in the width direction for invention examples 1 to 4 are shown in Table 1 below.

In Table 1 above, the temperature rise and input power are shown as a percentage of the reference value (100%), which is a gamma fraction of 100% in Example 1. In Table 1, gamma refers to the austenite phase. In the control methods, FF stands for feedforward control, and FB stands for feedback control. The temperature rise at the width center of a certain longitudinal position on the steel plate was used as the reference, and the percentage difference between the reference temperature rise and the maximum and minimum temperature rises in the width direction at the same longitudinal position was calculated for the entire longitudinal direction of the steel plate, and the maximum of these percentages was taken as the temperature deviation in the width direction. The above content is the same in Tables 2 to 4, which will be explained below.

In Example 1, the heating conditions of the TF heating device and LF heating device were feedforward controlled using the austenite phase fraction of the steel plate. As a result, in Example 1, the temperature rise was stable even for steel plate with a 100% austenite phase fraction, and the temperature deviation in the width direction was also reduced, confirming that uniform heating was possible in the width direction.

In Example 2, the heating conditions of the LF heating device and TF heating device were feedforward controlled using the austenite phase fraction of the steel plate. As a result, in Example 2, the temperature rise was stable, the input power was similar to that of Example 1, and the power efficiency and temperature deviation in the width direction were similar to that of Example 1. These results confirmed that in Example 2, the steel plate could be heated efficiently and uniformly in the width direction.

However, for steel sheets with a 100% austenite phase fraction, the LF heating device located upstream was unable to heat the steel sheets, causing the temperature to drop, resulting in a greater temperature rise in the TF heating device. For this reason, the steel sheets with a 100% austenite phase fraction in Example 2 were slightly worse in both power efficiency and width direction temperature deviation than the steel sheets with a 100% austenite phase fraction in Example 1.

In Example 3, the heating conditions of the LF heating device and TF heating device were feedforward controlled using the austenite phase fraction of the steel plate. As a result, in Example 3, the temperature rise was stable, the input power was about the same as in Example 1, and the power efficiency and temperature deviation in the width direction were about the same as in Example 1. These results confirmed that in Example 3, the steel plate S could be heated efficiently and uniformly in the width direction.

However, as with Inventive Example 2, the 1,300 mm wide steel plate with a 100% austenite phase fraction could not be heated by the TF heating device (narrow width) and LF heating device located upstream, causing the temperature of the steel plate to drop, resulting in a greater temperature rise in the TF heating device (wide width). For this reason, the 1,300 mm wide steel plate with a 100% austenite phase fraction in Inventive Example 3 had slightly worse power efficiency and width direction temperature deviation than the 1,300 mm wide steel plate with a 100% austenite phase fraction in Inventive Example 1.

In Example 4, the heating conditions for the LF heating device and TF heating device were feedforward controlled using the austenite phase fraction of the steel plate predicted using the phase fraction prediction model. As a result, it was confirmed that in Example 4, the temperature rise was stable, the input power was similar to that of Example 1, and the power efficiency and temperature deviation in the width direction were similar to that of Example 1. These results confirmed that the austenite phase fraction of the steel plate can be predicted with the same accuracy as the phase fraction meter in Example 1, even when using the phase fraction prediction model. It was confirmed that by controlling the heating conditions for the TF heating device and LF heating device using phase fraction information indicating the austenite phase fraction predicted by the phase fraction prediction model, the steel plate can be heated efficiently and uniformly in the width direction.

Next, we will explain Example 5 of the invention, in which the heating conditions for the TF heating device and LF heating device, namely the current value and power supply frequency, were controlled using the austenite phase fraction of the steel sheet. Example 5 of the invention is a manufacturing example in which the heating devices were arranged in the order of a TF heating device and an LF heating device from upstream in the steel sheet transport direction, and the steel sheet was heated using these heating devices to produce a galvannealed steel sheet. The width of the steel sheet was 1000 mm. In Example 5 of the invention, a phase fraction meter was installed in the cooling zone of the continuous annealing equipment to obtain information on the austenite phase fraction of the steel sheet during plating, and the austenite phase fraction information was used to feedforward control the heating conditions for the TF heating device and LF heating device, namely the current value and power supply frequency.

When heating steel plate using an induction heating device, the area through which the induced current flows varies depending on the power supply frequency and the austenite phase fraction. If the area through which the induced current flows is too wide relative to the thickness of the steel plate, the currents will cancel each other out, reducing heating efficiency. Therefore, to prevent a reduction in heating efficiency, the power supply frequency was changed according to the steel plate thickness and austenite phase fraction information to adjust the area through which the induced current flows. Specifically, the power supply frequency of the LF heating device was controlled so that the area through which the induced current flows was 20% or less of the plate thickness. The heating conditions, temperature rise, input power, and widthwise temperature deviation results for Example 5 of the invention are shown in Table 2 below. The power supply frequency in Table 2 indicates the power supply frequency of the LF heating device, and the power supply frequency of the TF heating device is fixed (1 kHz).

As shown in Table 2, by controlling the current value and power supply frequency according to the austenite phase fraction, the temperature rise in Example 5 was stable, the input power was about the same as in Example 1, and the power efficiency was also about the same as in Example 1. The temperature deviation in the width direction was smaller than in Example 1. These results confirm that by using the austenite phase fraction of the steel sheet to feedforward control the current value/power supply frequency, which are the heating conditions for the TF heating device and LF heating device, the steel sheet can be heated efficiently and uniformly in the width direction.

On the other hand, Comparative Examples 1 to 6 are manufacturing examples in which galvannealed steel sheets were produced using continuous annealing equipment equipped with conventional plating alloying equipment. Comparative Example 1 is a manufacturing example in which only an LF heating device was installed, and a galvannealed steel sheet was produced by heating the galvannealed steel sheet using this heating device until it reached the target heating temperature. In Comparative Example 1, a phase fraction meter was not installed, and information on the austenite phase fraction of the steel sheet was not obtained.

Comparative Example 2 is a manufacturing example in which only an LF heating device was installed, and the hot-dip galvanized steel sheet was heated using this heating device until it reached the target heating temperature. In Comparative Example 2, a phase fraction meter was installed in the cooling zone of the continuous annealing equipment to obtain phase fraction information indicating the austenite phase fraction of the steel sheet during plating, and the current value, which is a heating condition for the LF heating device, was feedforward controlled based on this phase fraction information.

Comparative Example 3 is a manufacturing example in which heating devices were arranged in the order of a TF heating device (narrow width) and a TF heating device (wide width) from the upstream side in the steel sheet conveying direction, and a galvannealed steel sheet was manufactured by heating using these heating devices. In Comparative Example 3, a phase fraction meter was not installed, and information on the austenite phase fraction of the steel sheet was not obtained.

Comparative Example 4 is a manufacturing example in which a TF heater (narrow width) and a TF heater (wide width) were arranged in this order from upstream in the steel sheet conveying direction, and a galvannealed steel sheet was produced by heating using these heaters. In Comparative Example 4, a phase fraction meter was installed in the cooling zone of the continuous annealing equipment to obtain phase fraction information indicating the austenite phase fraction of the steel sheet during plating, and the current value, which is the heating condition for the TF heater (narrow width) and TF heater (wide width), was feedforward controlled based on the phase fraction information.

Comparative Example 5 is a manufacturing example in which heating devices were arranged in the following order from upstream in the steel sheet conveying direction: TF heating device (for narrow width), TF heating device (for narrow width), and LF heating device, and the steel sheet was heated using these heating devices to produce a galvannealed steel sheet. In Comparative Example 5, a phase fraction meter was not installed, and phase fraction information indicating the austenite phase fraction of the steel sheet was not obtained, so the temperature rise amounts in the TF heating device and LF heating device were determined according to the target austenite phase fraction.

Comparative Example 6 is a manufacturing example in which heating devices were arranged in the following order from upstream in the steel sheet conveying direction: LF heating device, TF heating device (for narrow width), and TF heating device (for narrow width), and a galvannealed steel sheet was manufactured by heating using these heating devices. In Comparative Example 6, a phase fraction meter was not installed and information on the austenite phase fraction of the steel sheet was not obtained, so the temperature rise in the TF heating device and LF heating device was determined according to the target austenite phase fraction.

Comparative Example 7 is a manufacturing example in which heating devices were arranged in the following order from upstream in the steel sheet conveying direction: TF heating device (for narrow width), TF heating device (for narrow width), and LF heating device, and a galvannealed steel sheet was produced by heating using these heating devices. In Comparative Example 7, a phase fraction meter was installed downstream in the steel sheet conveying direction from the plating alloying equipment, and phase fraction information indicating the austenite phase fraction of the steel sheet was obtained. Based on the phase fraction information obtained by the phase fraction meter, the current value, which is a heating condition for the LF heating device, TF heating device (for narrow width), and TF heating device (for narrow width), was feedback controlled. The heating conditions, temperature rise, input power, and temperature deviation in the width direction for Comparative Examples 1 to 7 are shown in Tables 3 and 4 below.

In Comparative Example 1, an LF heating device was used, so steel sheets with an austenite phase fraction of 100% at the time of plating could not be heated, and the hot-dip galvanizing could not be alloyed. Because heating was performed using an LF heating device, more power was input than in Invention Example 1 for steel sheets with an austenite phase fraction of less than 100%, resulting in a significantly lower power efficiency than in Invention Example 1.

In Comparative Example 2, an LF heating device was used, which meant that steel sheets with a 100% austenite phase fraction at the time of plating could not be heated, and the hot-dip galvanizing could not be alloyed. In Comparative Example 2, the austenite phase fraction of the steel sheet was obtained, and this austenite phase fraction was used to control the current value, which is a pressure condition. As a result, less power was input than in Comparative Example 1, improving power efficiency; however, the input power was greater than in Invention Example 1, and power efficiency was significantly lower than in Invention Example 1.

In Comparative Example 3, a TF heating device was used, so steel sheets with a 100% austenite phase fraction at the time of plating could also be heated. However, because steel sheets with a low austenite phase fraction that can be heated with an LF heating device were also heated with a TF heating device, more power was input than in Invention Example 1 for steel sheets with an austenite phase fraction of less than 100%. As a result, power efficiency was significantly lower than in Invention Example 1 for steel sheets with an austenite phase fraction of less than 100%. Because heating was performed with a TF heating device, the temperature deviation in the width direction was larger for steel sheets with an austenite phase fraction of less than 100% than in Invention Example 1.

In Comparative Example 4, a TF heating device was also used, so it was possible to heat steel sheets with an austenite phase fraction of 100% at the time of plating. In Comparative Example 4, the austenite phase fraction of the steel sheet was obtained and used to control the current value, which is a pressing condition. However, since a TF heating device was used in Comparative Example 4, it was not affected by the austenite phase fraction of the steel sheet. As a result, the input power and temperature deviation in the width direction were the same as in Comparative Example 3, and the power efficiency was significantly lower than in Invention Example 1. Because heating was performed using a TF heating device, the temperature deviation in the width direction was larger than in Invention Example 1 for steel sheets with an austenite phase fraction of less than 100%.

In Comparative Example 5, a TF heating device and an LF heating device were used, so the amount of temperature rise using the upstream TF method was constant and not affected by phase fraction fluctuations. However, because heating was performed without obtaining austenite phase fraction information, the amount of temperature rise using the downstream LF method was unstable. As a result, the input power increased to raise the temperature to the target heating temperature, resulting in an input power greater than that of Invention Example 1.

In Comparative Example 6, an LF heating device and a TF heating device were used, but heating was performed without obtaining austenite phase fraction information, so heating by the upstream LF heating device was unstable. The insufficient temperature rise on the upstream side was compensated for by the downstream TF heating device, and heating to the target heating temperature was possible, but the amount of power input increased to increase the temperature rise in the TF heating device, and power efficiency was worse than in Invention Example 1. Because heating was performed using the downstream TF heating device, the temperature deviation in the width direction was larger than in Comparative Example 5 and Invention Example 1.

In Comparative Example 7, a TF heating device and an LF heating device were used, and it was possible to heat steel sheets with an austenite phase fraction of 100% at the time of plating. In Comparative Example 7, the austenite phase fraction was obtained, but because a phase fraction meter was installed downstream of the plating alloying equipment in the steel sheet transport direction and feedback control was performed, there was a delay in responding to changes in the phase fraction, and the amount of temperature rise was unstable, resulting in reduced power efficiency.

The results of Examples 1 to 5 and Comparative Examples 1 to 7 confirm that by using the plating alloying equipment of Examples 1 to 5, heating can be performed using an induction heating device suited to the phase fraction of the steel sheet, and that heating to the target heating temperature can be performed with less input power than in Comparative Examples 1 to 7. Furthermore, by heating using the plating alloying equipment of Examples 1 to 5, it was confirmed that the temperature deviation in the width direction of the steel sheet can be kept equal to or less than in Comparative Examples 1 to 7. These results confirm that by using the plating alloying equipment of this embodiment, it is possible to improve temperature uniformity in the width direction more efficiently than in the past, regardless of the phase fraction of the steel sheet. By using galvannealed hot-dip galvannealed steel sheet manufacturing equipment including such plating alloying equipment, it becomes possible to manufacture high-quality galvannealed steel sheet in which unevenness in the alloy with the zinc coating in the width direction of the steel sheet is suppressed.

10 Manufacturing equipment for galvannealed steel sheet 12 Payoff reel 14 Welder 16 Looper 18 Continuous annealing equipment 20 Preheating zone 22 Heating zone 24 Soaking zone 26 Cooling zone 28 Hot-dip galvanizing equipment 30 Galvanizing alloying equipment 32 Galvanizing bath 34 Gas wiping device 36 Vibration damping device 38 TF heating device 38A TF heating device for wide width 38B TF heating device for narrow width 40 LF heating device 42 Phase fraction meter 44 Control device 46 Control unit 48 Input unit 50 Output unit 52 Storage unit 54 Acquisition unit 56 Heating condition identification unit 58 Database 60 Heating control model 70 Thermometer 80 Galvanizing alloying equipment 82 Control device 84 Control unit 86 Storage unit 88 Acquisition unit 90 Phase fraction information acquisition unit 92 Database 94 Phase fraction prediction model 100 Process computer 110 Manufacturing equipment for galvannealed steel sheet

Claims (10)

A plating alloying facility for heating and alloying hot-dip metal-plated steel sheets,
a phase fraction acquisition device that acquires phase fraction information of the steel sheet;
two or more types of induction heating devices each having a different magnetic flux application direction to the steel sheet;
a control device for controlling the two or more types of induction heating devices;
and
the phase fraction acquisition device is installed upstream of the induction heating device in the conveying direction of the steel sheet,
The control device controls the two or more types of induction heating devices based on the phase fraction information acquired by the phase fraction acquisition device. The plating alloying equipment described in claim 1, wherein the phase fraction acquisition device acquires the phase fraction information by inputting input data including the surface temperature of the steel sheet in the continuous annealing equipment into a phase fraction prediction model and outputting the phase fraction information. The plating alloying equipment described in claim 1 or claim 2, wherein the control device inputs input data including the phase fraction information and the heating target temperature into a heating control model, outputs current values corresponding to the temperature rise amounts of each of the two or more types of induction heating devices, and sets the current values as the heating conditions for each of the two or more types of induction heating devices. The plating alloying equipment described in claim 1 or 2, wherein the control device outputs a current value and a power supply frequency corresponding to the temperature rise amount of each of the two or more types of induction heating devices from the heating control model, and sets the current value and power supply frequency as the heating conditions for each of the two or more types of induction heating devices. A manufacturing facility for galvannealed steel sheets, in which a continuous annealing facility, a hot-dip galvanizing facility, and a plating alloying facility according to any one of claims 1 to 4 are arranged in this order in the conveying direction of the steel sheets. A plating alloying method for alloying a hot-dip metal-plated steel sheet by heating the steel sheet, comprising:
a phase fraction acquisition step of acquiring phase fraction information of the steel sheet;
a control step of feedforward controlling heating conditions of two or more types of induction heating devices having different magnetic flux application directions using the phase fraction information acquired in the phase fraction acquisition step;
a heating step of heating the steel plate using the two or more types of induction heating devices;
A plating alloying method comprising: The plating alloying method according to claim 6, wherein, in the phase fraction acquisition step, input data including the surface temperature of the steel sheet in continuous annealing equipment is input into a phase fraction prediction model, and the phase fraction information of the steel sheet is output to acquire the phase fraction information. The plating alloying method according to claim 6 or 7, wherein in the control step, input data including the phase fraction information and the heating target temperature is input to a heating control model, current values for each of the two or more types of induction heating devices are output, and the current values are set as heating conditions for each of the two or more types of induction heating devices. The plating alloying method according to claim 6 or 7, wherein in the control step, a current value and a power supply frequency corresponding to the temperature rise amount of each of the two or more types of induction heating devices are output from the heating control model, and the current value and power supply frequency are set as the heating conditions for each of the two or more types of induction heating devices. an annealing step of annealing the steel sheet;
a hot-dip galvanizing step of hot-dip galvanizing the annealed steel sheet;
An alloying step of alloying the hot-dip galvanized coating according to any one of claims 6 to 9;
A method for producing a galvannealed steel sheet, comprising: