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

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

[0001] The present invention relates to a plating alloying equipment capable of uniformly alloying heating in the width direction regardless of the phase fraction of the steel sheet, a manufacturing equipment for a galvannealed steel sheet, a plating alloying method, and a manufacturing method for a galvannealed steel sheet.

[0002] In the production of automotive steel sheets, continuously cast slabs are subjected to significant deformation by 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 also controls the transformed structure. This, combined with the cooling process after annealing, adjusts the mechanical properties of the product.

[0003] In recent years, high-strength steel sheets have been required 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 required. Galvanized steel sheets are often used as materials for automobile parts to provide rust resistance. In particular, galvannealed steel sheets, in which zinc and iron are alloyed by heating after plating, are widely used from the perspective of press workability.

[0004] To achieve high strength in steel sheets, a method is used in which the steel sheet is heated in an annealing furnace from the coexistence region of ferrite and austenite to the single-phase region of austenite, and then the resulting austenite phase is rapidly cooled to obtain a martensite structure.The alloying process of hot-dip galvanizing requires that the steel sheet be heated to a temperature near the melting point of zinc, up to a temperature range where the iron-zinc alloying reaction proceeds.

[0005] As a heating means for alloying, induction heating devices, particularly solenoid-type induction heating devices that apply magnetic flux in the longitudinal direction of steel sheets, are used because they can heat steel sheets in a short time and have high temperature controllability. However, as mentioned above, the austenite phase (paramagnetic) fraction of steel sheets is increasing as the strength of steel sheets increases. Solenoid-type induction heating devices have a lower heating efficiency for paramagnetic materials. Solenoid-type induction heating devices also have the risk of being damaged because the coil voltage fluctuates rapidly depending on the austenite phase fraction of the steel sheet.

[0006] To address this issue, Patent Document 1 discloses a continuous hot-dip galvanizing process in which the austenite phase fraction is determined from the results of measuring the magnetic properties of the steel sheet, and sudden voltage fluctuations are suppressed 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 apparatus 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 states that combining the transverse induction heating device and the solenoid induction heating device can improve the temperature uniformity in the width direction of the steel sheet.

[0007] Patent Document 3 discloses a method for measuring the proportion of austenite contained in a steel sheet, in which the relative permeability of the steel sheet is calculated based on the effective heat generation amount of the steel sheet calculated from the coil end voltage of an induction heating device, and the proportion of austenite in the steel sheet is calculated from the reciprocal of the relative permeability of the steel sheet.

[0008] Japanese Patent No. 6432645 Japanese Patent No. 6763261 Japanese Patent Application Laid-Open No. 2017-67781

[0009] The continuous hot-dip galvanizing process disclosed in Patent Document 1 uses only a solenoid-type induction heating device, and therefore has the problem of not being able to heat steel sheets with a high austenite phase fraction corresponding to high-strength steel sheets. On the other hand, Patent Document 2 discloses the use of a transverse-type induction heating device, but does not disclose anything about the ability to heat steel sheets with a high austenite phase fraction. Therefore, Patent Document 2 has the problem of not disclosing a method for efficiently heating steel sheets with a high austenite phase fraction.

[0010] 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 a solenoid-type induction heating device is controlled. This control is a feedback control, which causes a delay in the control, and the control accuracy decreases when the austenite phase fraction differs significantly at the seam of the steel sheet, etc. Furthermore, since the alloying furnace only uses a solenoid-type induction heating device, there is also the problem that it cannot heat steel sheets with a high austenite phase fraction corresponding to high-strength steel sheets.

[0011] The present invention has been made to solve the problems of the prior art. An object of the present invention is to provide a galvannealing equipment and a galvannealing method that can efficiently heat a steel sheet regardless of the phase fraction of the steel sheet. Another object of the present invention is to provide a galvannealed steel sheet manufacturing equipment and a galvannealed steel sheet manufacturing method that include the galvannealing equipment and the galvannealing method.

[0012] Means for solving the above problems are as follows. [1] A plating and alloying facility that heats and alloys a hot-dip metal-plated steel sheet, the plating and 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 a 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 and alloying facility according to [1], wherein the phase fraction acquisition device inputs input data including a surface temperature of the steel sheet in a continuous annealing facility into a phase fraction prediction model and acquires the phase fraction information by outputting the phase fraction information. [3] The plating alloying facility 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, causes current values ​​corresponding to the temperature rises of each of the two or more types of induction heating devices to be output, and sets the current values ​​as heating conditions for each of the two or more types of induction heating devices. [4] The plating alloying facility according to [1] or [2], wherein the control device outputs current values ​​and power supply frequencies corresponding to the temperature rises of each of the two or more types of induction heating devices from the heating control model, and sets the current values ​​and power supply frequencies as heating conditions for each of the two or more types of induction heating devices. [5] A manufacturing facility for galvannealed steel sheets, wherein 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 a 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 the 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 acquired by outputting it. [8] The plating alloying method according to [6] or [7], wherein, in the control step, input data including the phase fraction information and a heating target temperature is input to a heating control model, and a current value for each of the two or more types of induction heating devices is output, and the current value is set as the heating condition for each of the two or more types of induction heating devices. [9] The plating alloying method according to [6] or [7], wherein, 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 the heating control model, and the current value and the power supply frequency are set as the heating condition for each of the two or more types of induction heating devices.

[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].

[0013] In the plating alloying equipment and plating alloying method according to the present invention, a phase fraction acquisition device acquires information on the phase fraction of a steel sheet, and based on the phase fraction information, the heating conditions of two or more types of induction heating devices that apply magnetic flux to the steel sheet in different directions are controlled. This makes it possible to heat the steel sheet using an induction heating device that is suitable for the phase fraction of the steel sheet, thereby making it possible to heat the steel sheet more efficiently than before, regardless of the phase fraction of the steel sheet.

[0014] Fig. 1 is a schematic diagram showing an example of the configuration of a manufacturing facility for galvannealed steel sheets including a coating 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 coating alloying facility. Fig. 3 is a schematic diagram showing an example of the configuration of a control device. Fig. 4 is a schematic diagram showing an example of the configuration of a manufacturing facility for galvannealed steel sheets including a coating alloying facility according to a second embodiment. Fig. 5 is a schematic diagram showing an example of the configuration of a coating alloying facility. Fig. 6 is a schematic diagram showing an example of the configuration of a control device.

[0015] The present invention will be specifically described below through embodiments of the present invention. The following embodiments are preferred examples of the present invention, and the present invention is not limited to these embodiments.

[0016] (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 .

[0017] The manufacturing equipment 10 for galvannealed steel sheets mainly comprises a continuous annealing equipment 18, a hot-dip galvanizing equipment 28, and a coating alloying equipment 30. The continuous annealing equipment 18, the hot-dip galvanizing equipment 28, and the coating alloying equipment 30 are arranged in this order with respect to the conveying direction X of the steel sheet S.

[0018] The steel sheet S is hot rolled or cold rolled to a predetermined thickness and wound into a coil, and then unwound by a payoff reel 12 and transported in the X direction in Fig. 1. The steel sheet S is joined by a welder 14. The steel sheet S passes through a looper 16 that stores the steel sheet S to be joined by the welder 14, and is transported to continuous annealing equipment 18.

[0019] The steel sheet S, which is transported to the continuous annealing facility 18 at a temperature between room temperature and about 100°C, first enters the preheating zone 20 and is heated to about 200°C. In the preheating zone 20, a method is adopted in which high-temperature exhaust gas generated in the heating zone 22 is utilized to improve heating efficiency.

[0020] The steel sheet S is then transported to the heating zone 22. The steel sheet S transported to the heating zone 22 is quickly heated to approximately 600 to 700°C in order to ensure the soaking time required for microstructure control in the soaking zone 24 in the next process. A direct-fired heating furnace is preferably used as the heating method in the heating zone 22. The direct-fired heating furnace 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 varying the fuel-to-air ratio, thereby flexibly controlling the oxidation-reduction reaction on the surface of the steel sheet S to ensure galvanic properties in subsequent processes. For example, by setting the heating temperature in the heating zone 22 to 700°C or less, excessive oxidation of the surface of the steel sheet S can be suppressed.

[0021] Thereafter, the steel sheet S is transported to the soaking zone 24. In the soaking zone 24, the steel sheet S is slowly heated from the heating zone outlet temperature to the target annealing temperature and held therein. By slowly heating in a temperature range from the heating zone outlet temperature to below the A1 transformation point, recrystallization of the ferrite phase progresses, and crystal grains that have been excessively refined by rolling can be appropriately coarsened.

[0022] To suppress the remaining unrecrystallized ferrite phase, it is preferable to ensure a residence time in the above temperature range of about 20 to 60 seconds. The residence time is controlled by the heating rate, and the heating rate from the 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 fraction of ferrite phase and the austenite phase transformed from the ferrite phase, and by combining this with the subsequent cooling, it becomes possible to control the mechanical properties of the product.

[0023] Because of its high efficiency and high heating uniformity, it is preferable to adopt a radiant heating method using gas combustion (radiant tube heating) as the heating method in the soaking zone 24. In addition, in order to stabilize the temperature of the steel sheet S near the outlet of the soaking zone 24, it is preferable to set the furnace temperature in the soaking zone 24 within a range of the target annealing temperature +0 to 50°C, and more preferably within a range of the target annealing temperature +5 to 20°C, by this heating method.

[0024] The soaking zone 24 may ensure the residence time in the furnace by reciprocating the steel sheet S between transport rolls arranged above and below it, as shown in Figure 1. The furnace itself may be structured as a single unit from the entrance to the exit, or the furnace shell may be separated into an adjustment zone that heats the steel sheet from the recrystallization region to the annealing temperature and a holding zone that 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.

[0025] 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 the like, 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 galvanizing process and to transform a portion of the austenite phase into the bainite phase, the cooling stop temperature is preferably not less than the martensitic transformation start temperature and not more than 550°C. The cooling stop temperature is more preferably not less than 450°C and not more than 550°C.

[0026] In order to allow the bainite transformation to proceed sufficiently, the steel sheet S is preferably held at the cooling stop temperature for 1 second to 100 seconds, more preferably for 20 seconds to 50 seconds, after the cooling stop temperature is reached. At this time, an electric heater may be provided to prevent an excessive decrease in temperature of the steel sheet S during holding.

[0027] 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 through which a coolant passes, water cooling using a water jet, or mist cooling, in which compressed gas is mixed with fine water droplets. In the first embodiment, gas jet cooling is used, which can ensure a target cooling rate while preventing unstable temperature changes due to boiling and allowing for highly accurate control of the cooling stop temperature.

[0028] A holding zone may be provided in the cooling zone 26 for the purpose of changing the cooling rate to control transformation during cooling or ensuring 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 microstructure control is performed in the cooling zone 26, the steel sheet S is transported to hot-dip galvanizing equipment 28. In this manner, the steel sheet S is continuously annealed by passing through the preparatory zone 20, the heating zone 22, the soaking zone 24, and the cooling zone 26. The annealing treatment in the preparatory zone 20, the heating zone 22, the soaking zone 24, and the cooling zone 26 constitutes the annealing step in the manufacturing method of a galvannealed steel sheet.

[0029] The hot-dip galvanizing equipment 28 employs 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 may be, for example, an electromagnetic vibration damping device that stabilizes the sheet threading 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 a plating alloying equipment 30.

[0030] In the plating alloying equipment 30, the hot-dip galvanized steel sheet S is heated to 500 to 550°C to cause a Zn—Fe alloying reaction to proceed. The plating alloying equipment 30 according to the first embodiment includes a TF heating device 38 that heats the hot-dip galvanized steel sheet S, an LF heating device 40, a phase fraction meter 42, and a control device 44.

[0031] The TF heating device 38 and the LF heating device 40 are two types of induction heating type heating devices that differ in the direction of application of magnetic flux to the steel sheet S. 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 of the plating alloying equipment 30.

[0032] 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.

[0033] 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 as to pass 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, circulating near the surface layer in the cross section in the width direction, and the steel sheet S is heated by Joule heating caused by this induced current.

[0034] The LF heating device 40 has the advantage that the strength of the induced current is almost uniform in the width direction, making it difficult for temperature deviation to occur in the width direction. On the other hand, when the steel sheet S is a paramagnetic material (austenite phase), the LF heating device 40 has a problem in that the region through which the induced current flows expands in the thickness direction, and the induced currents flowing on the front and back surfaces of the steel sheet S cancel each other out, resulting in an extreme decrease in heating efficiency.

[0035] In contrast, the TF heating device 38 has the advantage that such current cancellation does not occur, and therefore the steel sheet S can be heated without reducing heating efficiency even if it is a paramagnetic material. On the other hand, in the TF heating device 38, the induced current circulating within the surface of the steel sheet S concentrates at the end of the steel sheet S, increasing the amount of heat generated at the end. For this reason, the TF heating device 38 has the problem of low temperature uniformity in the width direction.

[0036] As a means for suppressing overheating at the widthwise ends of the steel sheet S, a method is known in which an electromagnetic shielding plate is inserted between the coil and the steel sheet S to limit the range in which the magnetic flux is applied to the center in the widthwise direction. However, even if such a measure is taken, the TF heating device 38 has a problem in that it has inferior temperature uniformity in the widthwise direction compared to the LF heating device 40, and in that heating efficiency is reduced due to the generation of magnetic flux that is not used in heating the steel sheet S.

[0037] Taking into account 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 efficiently heated and the temperature thereof can be uniform in the width direction regardless of the phase fraction of the steel sheet S. By using the TF heating device 38, the temperature of the end portion 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.

[0038] The TF heater 38 has a temperature control mechanism at the width direction end, such as an electromagnetic shielding plate. However, the movable range of the control mechanism cannot cover the various widths of the steel sheet S. For this reason, it is preferable to install a plurality of TF heaters 38 corresponding to the widths of the steel sheets S to be manufactured. The plating alloying equipment 30 according to the first embodiment also has a TF heater 38A for wide widths and a TF heater 38B for narrow widths as the TF heaters 38, so that it can accommodate steel sheets S of various widths.

[0039] 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 to be manufactured. Instead of controlling the power supply frequency in a circuit, two combinations of power supplies and coils with different power supply frequencies may be prepared in advance.

[0040] 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. Since the phase fraction meter 42 needs to obtain phase fraction information before plating alloying heating, it needs to 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 conveyance direction of the steel sheet S and upstream of the plating alloying equipment 30 in the conveyance 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.

[0041] The phase fraction meter 42 may be a device that measures the austenite phase fraction of the steel sheet S using a magnetic phase fraction measurement device that is configured with 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. The phase fraction meter 42 may be a device that measures the austenite phase fraction based on the diffraction peak intensity generated by irradiating the steel sheet S with X-rays. In the first embodiment, a magnetic phase fraction measurement device is used as the phase fraction meter 42 from the perspective of using it to control an induction heating device. However, the measurement method of the phase fraction meter 42 is not particularly limited as long as it can measure the austenite phase fraction of the steel sheet S.

[0042] 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 acquired 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.

[0043] Next, the process computer 100 will be described. The process computer 100 is, for example, a general-purpose computer such as a workstation or a personal computer. The process computer 100 is connected to each piece of equipment in the manufacturing facility 10 for galvannealed steel sheets by wire or wirelessly, and controls the manufacturing process of the galvannealed steel strip. The process computer 100 also acquires quality information of the steel sheet S from a higher-level computer. The quality information of the steel sheet S includes, for example, information on the chemical composition of the steel sheet S, the hot rolling reduction rate, the cold rolling reduction rate, the sheet thickness, the sheet width, etc. The process computer 100 collects and stores the manufacturing conditions of each piece of equipment constituting the manufacturing facility 10 for galvannealed steel sheets and actual measured values ​​measured by measuring instruments provided in each piece of equipment.

[0044] Next, the control device 44 that controls the TF heating device 38 and the LF heating device 40 will be described. Fig. 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 a 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 or the like, and functions as an acquisition unit 54 and a heating condition identification unit 56 by executing a program stored in the storage unit 52.

[0045] 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 therefor. The storage unit 52 stores programs and data for realizing each function 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 an operator via the input unit 48.

[0046] The storage unit 52 further 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 made up of actual values ​​of steel sheets S that have been previously heated and alloyed with high efficiency and uniformity in the width direction in the plating alloying equipment 30. The above data sets are data sets each consisting of a set of the austenite phase fraction of the steel sheet S, the heating target temperature, and actual values ​​of the current values ​​of the TF heating device 38 and the LF heating device 40.

[0047] The heating control model 60 is a trained machine learning model that has been trained using the data set stored in the database 58 as training data. The heating control model 60 is a trained machine learning model that receives input data including the austenite phase fraction of the steel sheet S and the target heating temperature, and outputs the current values ​​of the TF heating device 38 and the LF heating device 40. The austenite phase fraction and the 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 these data in the input data, it becomes possible to predict with high accuracy the current value that can heat the steel sheet S with high efficiency and improve the temperature uniformity in the width direction.

[0048] The input data for the heating control model 60 may include not only the austenite phase fraction and the heating target temperature of the steel sheet S, 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.

[0049] 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 directly or indirectly affect the induction heating of the steel sheet S. Therefore, by including these data in the input data of the heating control model 60, it becomes possible to predict with high accuracy the current value that can heat the steel sheet S with high efficiency and improve the 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.

[0050] Next, a description will be given of the processing executed by the acquisition unit 54 and the heating condition specification unit 56. 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 specification unit 56.

[0051] When the heating condition specifying unit 56 acquires the phase fraction information of the steel sheet S, it reads out the heating target temperature and the heating control model 60 from the storage unit 52. The heating condition specifying unit 56 inputs the phase fraction information of the steel sheet S and the heating target temperature into the heating control model 60, and causes it to output current values ​​for the TF heating device 38 and the LF heating device 40. The current values ​​for 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 according to the austenite phase fraction of the steel sheet S. The heating condition specifying unit 56 specifies the output current values ​​as the current values ​​for the TF heating device 38 and the LF heating device 40. Whether the TF heating device 38A or 38B is used for the heat treatment is determined in advance based on the width dimension of the steel sheet S.

[0052] The heating condition specifying 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 acquired by the phase fraction meter 42. This is the control step in the plating alloying method.

[0053] 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 current 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 performed efficiently, and a high-quality galvannealed steel sheet without alloying unevenness in the width direction can be manufactured. The phase fraction acquisition step, control step, and heating step in the plating alloying method constitute the alloying step in the manufacturing method of a galvannealed steel sheet.

[0054] 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 has been described in which the control device 44 specifies the current values ​​of the TF heating device 38 and the LF heating device 40 using a heating control model that 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 a steel sheet S that has previously been alloyed in the plating alloying equipment 30, and the heating conditions of these devices may be feedforward controlled.

[0055] As described above, if the austenite phase fraction is high, heating cannot be performed by 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 width direction end portions of the steel sheet S, the current value of the TF heating device 38 may be determined depending on the amount of temperature decrease at the width direction end portions of the steel sheet S caused by the gas wiping device 34.

[0056] 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.

[0057] The manufacturing equipment 110 for galvannealed steel sheets shown in Fig. 4 differs from the manufacturing equipment 10 for galvannealed steel sheets shown in Fig. 1 in that it does not have a phase fraction meter 42, but has a thermometer 70 for measuring the surface temperature of the steel sheet S in the continuous annealing equipment 18. In the example shown in Fig. 4, the thermometer 70 is provided at the junction between the soaking zone 24 and the cooling zone 26, but it is preferable that the thermometer 70 be provided at the junction between each zone in the continuous annealing equipment 18. In a portion where the equipment length is long, such as the soaking zone 24, the thermometer 70 may also be provided inside the soaking zone 24 in order to check the temperature history along the way.

[0058] The temperature measurement method of the thermometer 70 is not particularly limited, but the thermometer 70 is preferably a radiation thermometer that measures the temperature by detecting infrared rays emitted by the steel sheet S. However, since the radiation thermometer is 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 a scanning type radiation thermometer is used, it is preferable to provide a cooling tube in front of the thermometer to accurately measure the temperature of the end parts of the steel sheet S in the width direction.

[0059] On the other hand, since the radiation thermometer is affected by the emissivity of the surface of the steel sheet S, a multi-reflection type temperature measurement method utilizing the wedge-shaped space between the in-furnace transport roll and the steel sheet S may be adopted. In view of the accuracy and stability of temperature measurement inside the furnace, a multi-reflection type thermometer was used as 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.

[0060] 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 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 by each heating device.

[0061] Fig. 6 is a schematic diagram showing an example of the configuration of the control device 82. In the control device 82 shown in Fig. 6, the same components as those in the control device 44 are given the same reference numerals, and duplicated 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.

[0062] 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 specification unit 56 by executing a program 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 information recording medium. The storage unit 86 stores programs and data for realizing each function of the control device 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 an operator via the input unit 48.

[0063] 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, preferably 100 or more, data sets, each of which is a set of actual values ​​of the surface temperature of the steel sheet S and the phase fraction of the steel sheet S in the continuous annealing equipment 18, as training data for the phase fraction prediction model 94. Furthermore, the database 92 also stores 20 or more, preferably 100 or more, data sets, each of which is a set of actual values ​​of the austenite phase fraction of the steel sheet S, the heating target temperature, and the current values ​​of the TF heating device 38 and the LF heating device 40, as training data for the heating control model 60.

[0064] The phase fraction prediction model 94 is a trained machine learning model that has been trained using the data set 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 as input and outputs phase fraction information that indicates the austenite phase fraction of the steel sheet S.

[0065] 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.

[0066] 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 of the phase fraction prediction model 94, it becomes possible to predict the austenite phase fraction of the steel sheet S with high accuracy.

[0067] The input data of the machine learning model that outputs phase fraction information indicating the austenite phase fraction of the steel sheet S may include the component concentrations of the steel sheet S, the cross-sectional shape of the steel sheet S, the continuous annealing conditions, and the manufacturing conditions of the steel sheet S before continuous annealing. In this case, the data set stored in the database 92 also includes this data.

[0068] The component concentrations of the steel sheet S, the cross-sectional shape of the steel sheet S, the continuous annealing conditions, and the manufacturing conditions of the steel sheet S before continuous annealing affect the austenite phase fraction of the steel sheet S after continuous annealing. Therefore, by including these data in the input data of the phase fraction prediction model 94, it becomes possible to predict the austenite phase fraction of the steel sheet S with high accuracy.

[0069] Next, a description will be given of the processing executed by the acquisition unit 88 and the phase fraction information acquisition unit 90. 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.

[0070] 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 the 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 specification unit 56. The heating condition specification unit 56 uses the acquired phase fraction information of the steel sheet S to specify 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 FIG. 3 , and therefore description thereof will be omitted.

[0071] As described above, 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 limiting. 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 .

[0072] 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 limiting. The plating alloying equipment according to the first and second embodiments can be applied not only to hot-dip galvanizing but also to alloying treatments of other hot-dip metal coatings. Regardless of the type of hot-dip metal coating used, the temperature of the widthwise end portions is reduced by using a wiping device, and a steel sheet 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 treatments of other hot-dip metal coatings, and similar effects can be obtained.

[0073] Furthermore, in the plating alloying equipment according to the first embodiment and the second embodiment, an example has been described in which the equipment includes the TF heating device 38 and the LF heating device 40 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 embodiment and the second embodiment 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. That is, the plating alloying equipment according to the first embodiment and the second embodiment may only need to include two or more types of induction heating devices that apply magnetic flux to the steel sheet S in different directions.

[0074] Next, an example will be described in which a galvannealed steel sheet was produced using a continuous annealing facility having a plating alloying facility according to this embodiment. In the example, two types of steel sheet were used: a narrow material with a sheet width of 800 mm and a wide material with a sheet width of 1300 mm. For these two types of steel sheet widths, four types of steel sheet with different austenite phase fractions during hot-dip galvanizing were used to produce galvannealed steel sheets.

[0075] Invention Example 1 is a production example in which a galvannealed steel sheet was produced 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 the heating devices were arranged in this order from the upstream side with respect to the conveying direction of the steel sheet S. The galvannealed steel sheet was heated with these heating devices to produce a galvannealed steel sheet. A phase fraction meter was installed in the cooling zone of the continuous annealing equipment to obtain austenite phase fraction information 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 the LF heating device.

[0076] Inventive Example 2 is a production example in which heating devices are arranged in the order of an LF heating device, a TF heating device (for narrow width), and a TF heating device (for wide width) from the upstream side with respect to the conveying direction of the steel sheet, and a hot-dip galvanized steel sheet is heated with these heating devices to produce an alloyed hot-dip galvanized steel sheet. In Inventive Example 2, as in Inventive Example 1, a phase fraction meter is provided in the cooling zone of the continuous annealing equipment to obtain austenite phase fraction information of the steel sheet during galvanizing, and the austenite phase fraction information is used to control the current value, which is a heating condition for the TF heating device and the LF heating device.

[0077] Inventive Example 3 is a production example in which heating devices were arranged in the order of a TF heating device (narrow), an LF heating device, and a TF heating device (wide) from the upstream side with respect to the conveying direction of the steel sheet, and a hot-dip galvanized steel sheet was heated with these heating devices to produce an alloyed hot-dip galvanized steel sheet. In Inventive Example 3, as in Inventive Example 1, a phase fraction meter was provided in the cooling zone of the continuous annealing equipment to obtain austenite phase fraction information of the steel sheet during galvanizing, and the austenite phase fraction information was used to control the current value, which is a heating condition for the TF heating device and the LF heating device.

[0078] Inventive Example 4 is a manufacturing example in which heating devices are arranged in the following order from the upstream side with respect to the conveying direction of the steel sheet: a TF heating device (for narrow width), a TF heating device (for wide width), and an LF heating device, and the hot-dip galvanized steel sheet is heated by these heating devices to produce an alloyed hot-dip galvanized steel sheet. In Inventive Example 4, a phase fraction prediction model was used instead of a phase fraction meter to obtain phase fraction information of the steel sheet during coating. The input data and output data of the phase fraction prediction model used in Inventive Example 4 are as follows:

[0079] Input data: Steel sheet composition (slab composition) (mass%) Cooling start temperature in hot rolling process (°C) Cooling stop temperature (°C) Coiling temperature (°C) Steel sheet thickness (mm) Sheet passing speed during continuous annealing (m / min) Heating zone exit temperature (°C) Cooling start temperature (°C) Cooling stop temperature (°C) Output data: Austenite phase fraction of steel sheet during plating process (%)

[0080] Of the above input data, the cooling start temperature, cooling stop temperature, and coiling temperature in the hot rolling process are manufacturing conditions of the steel sheet S before continuous annealing. The thickness of the steel sheet is the cross-sectional shape of the steel sheet. The sheet passing speed during continuous annealing is a continuous annealing condition. The heating zone exit temperature, cooling start temperature, and cooling stop temperature are the surface temperatures of the steel sheet S in the continuous annealing equipment.

[0081] The phase fraction prediction model is a trained machine learning model created by preparing 100 sets of data, each set consisting of the above-mentioned input data and output data from past production results, and using these sets of data as training data for machine learning. In 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 the LF heating device. The heating conditions, temperature rise, input power, and temperature deviation in the width direction for Examples 1 to 4 are shown in Table 1 below.

[0082]

[0083] In Table 1 above, the temperature rise and input power are shown as a percentage of the γ fraction of 100% in Example 1 (100%). γ in Table 1 refers to the austenite phase. FF in the control method refers to feedforward control, and FB refers to feedback control. The temperature rise at the width center at a certain longitudinal position on the steel plate was used as a reference, and the percentage of the 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 described below.

[0084] In Example 1, the heating conditions of the TF heater and the LF heater were feedforward controlled using the austenite phase fraction of the steel sheet. As a result, in Example 1, it was confirmed that the temperature rise was stable even for a steel sheet with an austenite phase fraction of 100%, and the temperature deviation in the width direction was also small, enabling uniform heating in the width direction.

[0085] In Inventive Example 2, the heating conditions of the LF heater and the TF heater were feedforward controlled using the austenite phase fraction of the steel sheet. As a result, in Inventive Example 2, the temperature rise was stable, the input power was similar to that of Inventive Example 1, and the power efficiency and temperature deviation in the width direction were similar to that of Inventive Example 1. These results confirmed that Inventive Example 2 was able to heat the steel sheet efficiently and uniformly in the width direction.

[0086] However, for the steel sheet with an austenite phase fraction of 100%, the LF heating device located upstream was unable to heat the steel sheet, causing the temperature of the steel sheet to drop, and the temperature rise in the TF heating device was increased. As a result, the steel sheet with an austenite phase fraction of 100% in Example 2 was slightly worse in both power efficiency and width direction temperature deviation than the steel sheet with an austenite phase fraction of 100% in Example 1.

[0087] In Inventive Example 3, the heating conditions of the LF heater and the TF heater were feedforward controlled using the austenite phase fraction of the steel sheet. As a result, in Inventive Example 3, the temperature rise was stable, the input power was similar to that of Inventive Example 1, and the power efficiency and temperature deviation in the width direction were similar to that of Inventive Example 1. From these results, it was confirmed that Inventive Example 3 was able to heat the steel sheet S efficiently and uniformly in the width direction.

[0088] However, as in Inventive Example 2, the steel plate having an austenite phase fraction of 100% and a width of 1,300 mm could not be heated by the TF heating device (narrow width) and LF heating device arranged upstream, resulting in a drop in the temperature of the steel plate and a large temperature rise in the TF heating device (wide width). As a result, the steel plate having an austenite phase fraction of 100% and a width of 1,300 mm in Inventive Example 3 was slightly worse in both power efficiency and width direction temperature deviation than the steel plate having an austenite phase fraction of 100% and a width of 1,300 mm in Inventive Example 1.

[0089] In Example 4, the heating conditions of the LF heater and the TF heater were feedforward controlled using the austenite phase fraction of the steel sheet 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. From these results, it was confirmed that the austenite phase fraction of the steel sheet can be predicted with the same accuracy as the phase fraction meter of Example 1, even when the phase fraction prediction model is used. It was confirmed that the steel sheet can be heated efficiently and uniformly in the width direction by controlling the heating conditions of the TF heater and the LF heater using phase fraction information indicating the austenite phase fraction predicted by the phase fraction prediction model.

[0090] Next, Example 5 will be described in which the heating conditions of the TF heater and the LF heater, i.e., the current value and the power supply frequency, were controlled using the austenite phase fraction of the steel sheet. Example 5 is a manufacturing example in which a TF heater and an LF heater were arranged in this order from the upstream side with respect to the conveyance direction of the steel sheet, and the steel sheet was heated using these heaters to produce a galvannealed steel sheet. The width of the steel sheet was 1000 mm. In Example 5, a phase fraction meter was installed in the cooling zone of the continuous annealing equipment to obtain austenite phase fraction information of the steel sheet during galvanizing, and the austenite phase fraction information was used to feedforward control the heating conditions of the TF heater and the LF heater, i.e., the current value and the power supply frequency.

[0091] When heating a steel sheet using an induction heating device, the region through which the induced current flows varies depending on the power supply frequency and the austenite phase fraction. If the region through which the induced current flows is too wide relative to the thickness of the steel sheet, the currents cancel each other out, resulting in reduced heating efficiency. Therefore, to prevent a reduction in heating efficiency, the region through which the induced current flows was adjusted by changing the power supply frequency according to the steel sheet thickness and austenite phase fraction information. Specifically, the power supply frequency of the LF heating device was controlled so that the region through which the induced current flows was 20% or less of the sheet thickness. The heating conditions, temperature rise, input power, and widthwise temperature deviation results for Example 5 are shown in Table 2 below. The power supply frequency in Table 2 indicates the power supply frequency of the LF heating device, while the power supply frequency of the TF heating device is fixed (1 kHz).

[0092]

[0093] As shown in Table 2, by controlling the current value and power supply frequency in accordance with the austenite phase fraction, the temperature rise in Example 5 was stable, the input power was similar to that of Example 1, and the power efficiency was similar to that of Example 1. The temperature deviation in the width direction was smaller than that of Example 1. These results confirmed that the steel sheet can be heated efficiently and uniformly in the width direction by using the austenite phase fraction of the steel sheet to perform feedforward control of the current value / power supply frequency, which are the heating conditions of the TF heating device and the LF heating device.

[0094] On the other hand, Comparative Examples 1 to 6 are production examples in which galvannealed steel sheets were produced using continuous annealing equipment having a conventional plating alloying device. Comparative Example 1 is a production example in which only an LF heating device was provided, and a galvannealed steel sheet was heated to a target heating temperature using this heating device to produce a galvannealed steel sheet. In Comparative Example 1, a phase fraction meter was not installed, and austenite phase fraction information of the steel sheet was not obtained.

[0095] Comparative Example 2 is a manufacturing example in which only an LF heating device was provided and the hot-dip galvanized steel sheet was heated by this heating device until the target heating temperature was reached. In Comparative Example 2, a phase fraction meter was provided in the cooling zone of the continuous annealing equipment to obtain phase fraction information indicating the austenite phase fraction of the steel sheet during galvanizing, and the current value, which is a heating condition of the LF heating device, was feedforward controlled based on the phase fraction information.

[0096] Comparative Example 3 is a production example in which a TF heating device (narrow width) and a TF heating device (wide width) were arranged in this order from the upstream side with respect to the conveying direction of the steel sheet, and a galvannealed steel sheet was produced by heating with 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.

[0097] Comparative Example 4 is a production example in which a TF heater (narrow width) and a TF heater (wide width) were arranged in this order from the upstream side with respect to the conveyance direction of the steel sheet, and a galvannealed steel sheet was produced by heating using these heaters. In Comparative Example 4, a phase fraction meter was provided in the cooling zone of the continuous annealing equipment to obtain phase fraction information indicating the austenite phase fraction of the steel sheet during galvanizing, and the current value, which was a heating condition for the TF heater (narrow width) and the TF heater (wide width), was feedforward controlled based on the phase fraction information.

[0098] Comparative Example 5 is a production example in which heating devices were arranged in the following order from the upstream side with respect to the conveying direction of the steel sheet: a TF heating device (for narrow width), a TF heating device (for narrow width), and an LF heating device, and a galvannealed steel sheet was produced by heating with these heating devices. 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 the LF heating device were determined depending on the target austenite phase fraction.

[0099] Comparative Example 6 is a production example in which heating devices were arranged in the following order from the upstream side with respect to the conveying direction of the steel sheet: an LF heating device, a TF heating device (for narrow width), and a TF heating device (for narrow width), and a galvannealed steel sheet was produced by heating with 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 amounts in the TF heating device and LF heating device were determined according to the target austenite phase fraction.

[0100] 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 provided downstream in the steel sheet conveying direction from the plating alloying equipment to obtain phase fraction information indicating the austenite phase fraction of the steel sheet. Based on the phase fraction information obtained by the phase fraction meter, the current value, which is the 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.

[0101]

[0102]

[0103] In Comparative Example 1, an LF heating device was used, so a steel sheet having an austenite phase fraction of 100% at the time of plating could not be heated, and hot-dip galvanizing could not be performed. Because heating was performed using an LF heating device, the input power was greater than that in Invention Example 1 for steel sheets having an austenite phase fraction of less than 100%, and the power efficiency was significantly lower than that in Invention Example 1.

[0104] In Comparative Example 2, an LF heating device was used, so a steel sheet with an austenite phase fraction of 100% at the time of plating could not be heated, and hot-dip galvanizing could not be performed. In Comparative Example 2, the austenite phase fraction of the steel sheet was obtained, and the current value, which is a pressing condition, was controlled using the austenite phase fraction. As a result, the input power was less than in Comparative Example 1, improving power efficiency, but the input power was more than in Invention Example 1, and power efficiency was significantly lower than in Invention Example 1.

[0105] In Comparative Example 3, a TF heater was used, and therefore it was possible to heat steel sheets with an austenite phase fraction of 100% at the time of plating. However, because a steel sheet with a low austenite phase fraction that can be heated with an LF heater was also heated with a TF heater, the input power was greater than that of Invention Example 1 for steel sheets with an austenite phase fraction of less than 100%. As a result, the power efficiency was significantly lower for steel sheets with an austenite phase fraction of less than 100% than for Invention Example 1. Because heating was performed with a TF heater, the temperature deviation in the width direction was greater than that of Invention Example 1 for steel sheets with an austenite phase fraction of less than 100%.

[0106] Since a TF heater was also used in Comparative Example 4, 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 the current value, which is a pressing condition, was controlled using that austenite phase fraction. However, since a TF heater was used in Comparative Example 4, it was not affected by the austenite phase fraction of the steel sheet. Therefore, 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 heater, 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%.

[0107] In Comparative Example 5, since a TF heating device and an LF heating device were used, the temperature rise rate in the upstream TF method was constant and not affected by phase fraction fluctuations, but since heating was performed without acquiring austenite phase fraction information, the temperature rise rate in the downstream LF method was not stable. As a result, the input power increased to raise the temperature to the heating target temperature, and the input power was higher than in Invention Example 1.

[0108] In Comparative Example 6, an LF heating device and a TF heating device were used, but heating was performed without acquiring austenite phase fraction information, so heating by the upstream LF heating device was unstable. Although heating to the target heating temperature was possible by compensating for the insufficient temperature rise by the upstream TF heating device with the downstream TF heating device, the amount of input power increased to increase the temperature rise by the TF heating device, and power efficiency was worse than in Invention Example 1. Because heating was performed with the downstream TF heating device, the temperature deviation in the width direction was larger than in Comparative Example 5 and Invention Example 1.

[0109] In Comparative Example 7, a TF heating device and an LF heating device were used, and it was possible to heat a steel sheet having 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 provided 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.

[0110] From the results of Examples 1 to 5 and Comparative Examples 1 to 7, it was confirmed that by using the plating alloying equipment of Examples 1 to 5, heating was possible with an induction heating device suitable for the phase fraction of the steel sheet, and heating to the target heating temperature was possible with less input power than in Comparative Examples 1 to 7. Furthermore, it was confirmed that by heating using the plating alloying equipment of Examples 1 to 5, the temperature deviation in the width direction of the steel sheet could be made equal to or less than that in Comparative Examples 1 to 7. From these results, it was confirmed that by using the plating alloying equipment of this embodiment, it is possible to improve the temperature uniformity in the width direction more efficiently than in the past, regardless of the phase fraction of the steel sheet. By using a galvannealed steel sheet manufacturing facility including such plating alloying equipment, it is possible to realize the production of high-quality galvannealed steel sheets in which unevenness in the alloy with the zinc coating in the width direction of the steel sheet is suppressed.

[0111] 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

1. A plating alloying apparatus that heats molten metal-plated steel sheets to form an alloy, A phase fraction acquisition device for acquiring phase fraction information of the steel plate, Two or more induction heating devices with different directions of magnetic flux application to the steel plate, A control device for controlling the two or more induction heating devices, It has, The phase fraction acquisition device is installed upstream of the induction heating device in the direction of transporting the steel plate. The control device controls the two or more induction heating devices based on the phase fraction information obtained by the phase fraction acquisition device, in a plating alloying facility.

2. The plating alloying equipment according to 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.

3. The plating alloying equipment according to claim 1 or 2, wherein the control device inputs input data including the phase fraction information and the target heating temperature to a heating control model, outputs a current value corresponding to the heating amount of each of the two or more induction heating devices, and sets the current value to the heating conditions of each of the two or more induction heating devices.

4. The plating alloying equipment according to claim 1 or 2, wherein the control device outputs a current value and a power supply frequency corresponding to the respective heating amount of the two or more induction heating devices from a heating control model, and sets the current value and power supply frequency to the respective heating conditions of the two or more induction heating devices.

5. A manufacturing facility for alloyed hot-dip galvanized steel sheets, wherein a continuous annealing facility, a hot-dip galvanizing facility, and a plating alloying facility according to claim 1 or claim 2 are arranged in this order in the direction of transporting the steel sheet.

6. A manufacturing facility for alloyed hot-dip galvanized steel sheets, wherein a continuous annealing facility, a hot-dip galvanizing facility, and the plating alloying facility described in claim 3 are arranged in this order in the direction of transporting the steel sheet.

7. A manufacturing facility for alloyed hot-dip galvanized steel sheets, wherein a continuous annealing facility, a hot-dip galvanizing facility, and the plating alloying facility described in claim 4 are arranged in this order in the direction of transporting the steel sheet.

8. A plating alloying method in which a molten metal-plated steel sheet is heated to form an alloy, A phase fraction acquisition step for acquiring phase fraction information of the steel plate, A control step that uses the phase fraction information obtained in the phase fraction acquisition step to feedforward control the heating conditions of two or more induction heating devices with different magnetic flux application directions, A heating step of heating the steel plate with the two or more induction heating devices, A method for plating and alloying, including the above.

9. The method for plating alloys according to claim 8, wherein in the phase fraction acquisition step, input data including the surface temperature of the steel sheet in a continuous annealing facility 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.

10. The plating alloying method according to claim 8 or 9, wherein in the control step, input data including the phase fraction information and the target heating temperature is input to a heating control model, the current values ​​of each of the two or more induction heating devices are output, and the current values ​​are set as the heating conditions for each of the two or more induction heating devices.

11. The plating alloying method according to claim 8 or 9, wherein the control step involves outputting a current value and a power supply frequency corresponding to the respective heating amount of the two or more induction heating devices from a heating control model, and setting the current value and power supply frequency to the respective heating conditions of the two or more induction heating devices.

12. The annealing step of annealing the steel plate, A hot-dip galvanizing step in which an annealed steel plate is hot-dip galvanized, The alloying step of alloying the hot-dip galvanized plating using the plating alloying method according to claim 8 or claim 9, A method for manufacturing alloyed hot-dip galvanized steel sheets, including the method described above.

13. The annealing step of annealing the steel plate, A hot-dip galvanizing step in which an annealed steel plate is hot-dip galvanized, The alloying step of alloying the hot-dip galvanized plating in the plating alloying method according to claim 10, A method for manufacturing alloyed hot-dip galvanized steel sheets, including the method described above.

14. The annealing step of annealing the steel plate, A hot-dip galvanizing step in which an annealed steel plate is hot-dip galvanized, The alloying step of alloying the hot-dip galvanized plating in the plating alloying method according to claim 11, A method for manufacturing alloyed hot-dip galvanized steel sheets, including the method described above.