Method for manufacturing plated steel sheet and apparatus for manufacturing plated steel sheet

Abstract

To provide a method for producing a plated steel sheet by which the plated steel sheet can be produced in a satisfactory surface state.SOLUTION: A method for manufacturing a plated steel sheet includes a heating step of heating a steel sheet by injecting gas toward the steel sheet, and a plating step of plating the heated steel sheet. The method for manufacturing a plated steel sheet includes a manufacturing condition acquisition step of acquiring a manufacturing condition of the plated steel sheet, an oxide film thickness acquisition step of acquiring a thickness of an oxide film formed on a surface of the steel sheet in the heating step of the steel sheet, a water vapor amount determination step of determining an amount of water vapor contained in the gas based on the manufacturing condition acquired in the manufacturing condition acquisition step and the thickness of the oxide film acquired in the oxide film thickness acquisition step, and a component ratio setting step of setting a component ratio of the gas according to the amount of water vapor. In the heating step, the steel sheet is heated by spraying the gas having the component ratio set in the component ratio setting step to the steel sheet.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for producing a plated steel sheet by plating a steel sheet heated by gas injection. [Background technology]

[0002] Coated steel sheets are manufactured in facilities that include an annealing furnace in which a heating zone, a soaking zone, and a cooling zone are arranged in that order, and a hot-dip galvanizing tank adjacent to the cooling zone. To increase the tensile strength of coated steel sheets, solid-solution strengthening elements such as Si and Mn are added. Solid-solution strengthening elements are more easily oxidized than Fe. Therefore, when a steel sheet is heated in the heating zone of an annealing furnace, the solid-solution strengthening elements concentrate on the surface of the steel sheet and oxidize. The presence of oxides of solid-solution strengthening elements on the surface of the steel sheet can lead to a problem of deterioration in the quality of the coating.

[0003] In order to improve the quality of such coating, Patent Document 1 discloses that the front and back sides of a steel sheet are heated with flames sprayed from slit burners in a direct-fire heating furnace having an oxidation zone and a reduction zone. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO 24 / 014372 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, a slit burner is installed in a direct-fired heating furnace having an oxidation zone operated at an air ratio of 1 or more and a reduction zone operated at an air ratio of less than 1. The air ratio fluctuates during the manufacturing process. This makes it difficult to form an oxide film with a consistent thickness. For example, if the oxide film thickness is insufficient, silicon oxides, manganese oxides, etc. may be present on the surface of the steel sheet, preventing the plating from adhering properly, i.e., a satisfactory plating appearance may not be obtained. Furthermore, if the oxide film thickness is excessive, the oxide film may peel off, resulting in the formation of a defect known as "pickup" on the plated steel sheet.

[0006] The present invention has been made in view of the above problems, and has an object to provide a method for producing a plated steel sheet that can produce a plated steel sheet with a good surface condition. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention has the following features.

[0008] [1] A method for producing a plated steel sheet, comprising: a heating step of injecting gas toward a steel sheet to heat the steel sheet; and a plating step of plating the heated steel sheet, a manufacturing condition acquisition step of acquiring manufacturing conditions of the plated steel sheet; an oxide film thickness obtaining step of obtaining a thickness of an oxide film formed on the surface of the steel sheet in the heating step; a water vapor amount determination step of determining an amount of water vapor contained in the gas based on the manufacturing conditions acquired in the manufacturing condition acquisition step and the oxide film thickness acquired in the oxide film thickness acquisition step; a component ratio setting step of setting a component ratio of the gas in accordance with the amount of water vapor determined in the amount of water vapor determination step, In the heating step, the gas having the component ratio set in the component ratio setting step is sprayed onto the steel sheet to heat the steel sheet. [2] The method for producing a plated steel sheet according to [1], wherein the gas containing 30% by volume or more of water vapor and less than 5% by volume of oxygen is injected in the heating step. [3] The method for producing a plated steel sheet according to [1] or [2], wherein in the heating step, the gas is injected at a flow velocity of 3 to 53 m / s. [4] An apparatus for manufacturing a plated steel sheet, comprising: a heating section that injects gas toward a steel sheet to heat the steel sheet; and a plating section that applies plating to the heated steel sheet, a manufacturing condition acquisition unit that acquires manufacturing conditions of the steel plate; an oxide film thickness acquisition unit that acquires the thickness of an oxide film formed on the steel sheet; a water vapor amount determination unit that determines the amount of water vapor contained in the gas based on the manufacturing conditions and the thickness of the oxide film; a component ratio setting unit that sets a component ratio of the gas in accordance with the amount of water vapor, The heating unit heats the steel sheet by injecting the gas adjusted by the component ratio setting unit onto the steel sheet. [Effects of the Invention]

[0009] According to the method for producing a plated steel sheet of the present invention, the amount of water vapor contained in the gas is determined based on the production conditions of the plated steel sheet and the thickness of the oxide film formed on the plated steel sheet, and the gas components are adjusted according to the amount of water vapor. The gas thus adjusted is then sprayed onto the steel sheet to heat the steel sheet. By heating the steel sheet in this manner, an oxide film with a stable thickness can be formed. Therefore, it is possible to produce a plated steel sheet with a good surface condition. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a plated steel sheet manufacturing apparatus. [Figure 2] FIG. 2 is an explanatory diagram showing the configuration of the heating zone in FIG. [Figure 3] FIG. 2 is an explanatory view showing a state in which gas is injected onto a steel plate. [Figure 4] FIG. 2 is a functional block diagram of a heating control unit in FIG. [Figure 5] FIG. 4 is a flow chart showing heating control by a heating control unit. [Figure 6] 1 is a graph showing the relationship between the temperature of the steel sheet on the outlet side of the heating zone and the thickness of the oxide film. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows a plated steel sheet manufacturing apparatus 100. The plated steel sheet manufacturing apparatus 100 of Fig. 1 has a supply unit 10 that supplies a steel sheet.

[0012] The supply section 10 has a payoff reel 11 that unfolds the coiled steel sheet, and an inlet looper 12 that holds the steel sheet supplied from the payoff reel 11.

[0013] The coated steel sheet manufacturing apparatus 100 has a heating section 20 that heats the steel sheet. The heating section 20 has a preheating zone 21 that preheats the steel sheet that has passed through the inlet looper 12, a heating zone 22 that heats the steel sheet preheated in the preheating zone 21 to a target temperature range, and a soaking zone 23 that maintains the temperature of the steel sheet heated in the heating zone 22. Each of the preheating zone 21, the heating zone 22, and the soaking zone 23 has a heating means such as a heater that heats the steel sheet.

[0014] The plated steel sheet manufacturing apparatus 100 has a first cooling section 30 that cools the steel sheet heated in the heating section 20. The first cooling section 30 has cooling means that cools the steel sheet. The cooling means is not particularly limited, and may be, for example, a water-cooling cooling device, an air-cooling cooling device, or the like.

[0015] The plated steel sheet manufacturing apparatus 100 has a plating tank 40 as a plating section that performs plating treatment on the steel sheet. Molten metal is stored in the plating tank 40. The molten metal is not particularly limited, but zinc, for example, is used.

[0016] The plated steel sheet manufacturing apparatus 100 has an alloying section 50 that promotes alloying of iron and molten metal in the steel sheet that has passed through the plating tank 40. The alloying section 50 has heating means such as a heater that heats the steel sheet to a desired temperature.

[0017] The plated steel sheet manufacturing apparatus 100 has a second cooling section 60 that cools the steel sheet that has passed through the alloying section 50. The second cooling section 60 has cooling means that cools the steel sheet. The cooling means is not particularly limited, and for example, a water-cooling cooling device, an air-cooling cooling device, etc. can be used.

[0018] The plated steel sheet manufacturing apparatus 100 has a heating control unit 70 that controls the heating mode of the steel sheet in the heating zone 22. The heating control unit 70 is connected to, for example, the heating unit 20 so that they can communicate data with each other. The heating control unit 70 controls the heating mode in the heating unit 20.

[0019] 2 shows the configuration of the heating zone 22. As shown in Fig. 2, the heating zone 22 has a conveying path 24 that conveys the steel sheet S toward the soaking zone 23. The conveying path 24 is surrounded by a wall portion 25.

[0020] The wall portion 25 is provided with injection ports 26 that inject gas toward the steel sheet S. A plurality of injection ports 26 are arranged along the extension direction of the conveying path 24. The injection ports 26 are preferably arranged so that gases injected from adjacent injection ports 26 in the extension direction do not interfere with each other. For example, the arrangement interval between adjacent injection ports 26 in the extension direction may be 3 to 10 times the opening width of the injection ports 26 in the extension direction of the conveying path 24.

[0021] Wall 25 is provided with measuring unit 27 that measures the amount of water vapor in the gas injected from nozzle 26. Measuring unit 27 is not particularly limited, but a dew point meter, for example, can be used. The amount of water vapor in the gas can be calculated, for example, from data measured by measuring unit 27 using the humidity measurement method specified in JIS Z 8806:2001. Measuring unit 27 is preferably provided corresponding to nozzle 26.

[0022] Fig. 3 shows an aspect in which gas is injected onto the steel sheet S. As shown in Fig. 3, the injection port 26 is formed in the shape of a slit across the width direction of the steel sheet S. The length of the injection port 26 in the width direction of the steel sheet is preferably 2 to 200 times the opening width of the injection port 26 in the extension direction of the conveying path 24. By forming the injection port 26 in this manner, it is possible to inject gas uniformly in the width direction of the steel sheet S. This makes it possible to suppress temperature variations in the width direction of the steel sheet S.

[0023] Each of the injection ports 26 is connected to a pipe 28 through which gas is supplied. Further, a gas supply unit 29 that adjusts the gas components is connected to the pipe 28. Each of the gas supply units 29 is connected to a heating control unit 70 so as to be able to communicate with the heating control unit 70. Each of the gas supply units 29 is provided with a valve (not shown) that adjusts the amount of gas supplied. The valve is, for example, configured by an electromagnetic valve, and the opening degree of which can be adjusted in response to a command from the heating control unit 70.

[0024] The gas injected from the injection port 26 is, for example, a mixed gas in which a plurality of gases are mixed. An example of such a mixed gas is a mixture of coke oven by-product gas, hydrogen gas, and air. The mixed gas is not limited to this embodiment, and may be, for example, a mixture of hydrogen and air, or a mixture of superheated steam and preheated nitrogen. The gas injected from the injection port 26 is not limited to such a mixed gas, and may be, for example, superheated steam.

[0025] Fig. 4 shows functional blocks of the heating control unit 70. As shown in Fig. 4, the heating control unit 70 has an input / output unit 71 that is an interface with external devices, a memory unit 72 that stores various data, and a control unit 73 that controls the operation of the heating control unit 70. The input / output unit 71, memory unit 72, and control unit 73 are connected to each other via a bus 74 so that they can communicate data with each other.

[0026] Input / output unit 71 is connected to be able to communicate data with measurement unit 27 and gas supply unit 29. In addition, input / output unit 71 is connected to be able to communicate data with input unit 81 that inputs data and display unit 82 that displays data output from heating control unit 70.

[0027] The input unit 81 is not particularly limited as long as it is an input device that can input data, and for example, an input device such as a keyboard, a mouse, or a touch panel can be used.

[0028] The display unit 82 is not particularly limited as long as it is a display device capable of displaying data, and examples thereof include a liquid crystal display.

[0029] The storage unit 72 is a writable nonvolatile memory such as an EPROM. The storage unit 72 is not particularly limited, and may be, for example, a storage device such as an HDD or SSD. The storage unit 72 stores measurement data measured by the measurement unit 27, manufacturing conditions of the plated steel sheet, the thickness of the oxide film formed on the steel sheet, index data recording the relationship between the oxide film thickness and the amount of water vapor, and the like. The oxide film is a film formed by iron oxide.

[0030] The manufacturing conditions of the plated steel sheet include the thickness (mm) and width (mm) of the steel sheet, the temperature of the steel sheet on the entry side of the heating zone 22 and the temperature of the steel sheet on the exit side, and the chemical composition of the steel sheet. The chemical composition of the steel sheet includes, for example, the content of magnetic iron and the content of silicon.

[0031] The thickness (nm) of an oxide film formed on a steel sheet is determined according to the manufacturing conditions of the steel sheet. The oxide film thickness is input by, for example, an operator using the input unit 81. The oxide film thickness is determined based on, for example, performance data. In addition to being input by an operator, the oxide film thickness may also be determined using an oxide film thickness prediction model that is machine-learned using the manufacturing conditions of the steel sheet as explanatory variables and the oxide film thickness as a target variable.

[0032] The oxide film thickness is determined taking into consideration the concentration of Si oxide and Mn oxide on the surface of the steel sheet. The oxide film thickness can be set, for example, depending on the C, Si, and Mn contents of the steel sheet. Specifically, when the steel sheet contains 0.115% C, 1.4% Si, and 1.9% Mn, the oxide film thickness can be determined to be 300 nm.

[0033] The oxide film thickness is preferably 200 nm or more and less than 500 nm. By making the oxide film thickness 200 nm or more, it is possible to prevent Si and Mn that have remained inside the steel sheet from concentrating on the surface after the reduced iron layer is formed on the steel sheet, thereby obtaining appropriate plating properties. Furthermore, by making the oxide film thickness less than 500 nm, it is possible to sufficiently reduce the iron oxide and prevent the iron oxide from peeling off from the steel sheet in the soaking zone 23.

[0034] The control unit 73 is a computer including a CPU. The control unit 73 controls the operation of the heating control unit 70. The control unit 73 has a manufacturing condition acquisition unit 73a that acquires manufacturing conditions for the plated steel sheet and an oxide film thickness acquisition unit 73b that acquires the thickness of an oxide film formed on the plated steel sheet. The control unit 73 has a water vapor amount determination unit 73c that determines the amount of water vapor contained in the gas and a component ratio setting unit 73d that sets the component ratio of the gas injected from the injection port 26.

[0035] The functions of the manufacturing condition acquisition unit 73 a, the oxide film thickness acquisition unit 73 b, the water vapor amount determination unit 73 c, and the component ratio setting unit 73 d are realized by executing programs stored in the storage unit 72.

[0036] The manufacturing condition acquisition unit 73a reads out from the storage unit 72 and acquires the manufacturing conditions of the steel plate.

[0037] The oxide film thickness obtaining unit 73b obtains the oxide film thickness by reading it from the storage unit 72.

[0038] The water vapor amount determining unit 73c determines the amount of water vapor contained in the gas based on the manufacturing conditions acquired by the manufacturing condition acquiring unit 73a and the oxide film thickness acquired by the oxide film thickness acquiring unit 73b.

[0039] The component ratio setting unit 73d sets the component ratio of the gas in accordance with the amount of water vapor determined by the water vapor amount determining unit 73c. ​​Specifically, the component ratio setting unit 73d determines, for example, the amount of water generated when hydrogen atoms contained in the gas are burned, i.e., the amount of water vapor.

[0040] For example, when a mixed gas of coke oven by-product gas (hereinafter also referred to as C gas) and hydrogen gas is ejected, the component ratio setting unit 73d calculates the volume fraction of each gas after the reaction, assuming that all hydrocarbons contained in the C gas are converted to CO2 or HO. Based on the result, the component ratio setting unit 73d adjusts the amount of hydrogen gas to be mixed so that the water vapor fraction is 50%. The component ratio setting unit 73d sets the gas component ratio so that the calculated amount of water vapor matches the amount of water vapor determined by the water vapor amount determination unit 73c.

[0041] Fig. 5 shows a flow of the method for manufacturing a plated steel sheet. As shown in Fig. 5, the manufacturing condition acquisition unit 73a reads out the manufacturing conditions of the steel sheet from the storage unit 72 and executes a manufacturing condition acquisition step (step S01).

[0042] The oxide film thickness obtaining unit 73b reads the oxide film thickness of the steel plate from the storage unit 72 and executes an oxide film thickness obtaining step (step S02).

[0043] The water vapor amount determination unit 73c determines the amount of water vapor contained in the gas using the manufacturing conditions acquired in the manufacturing condition acquisition step of step S01 and the oxide film thickness acquired in the oxide film thickness acquisition step of step S02, and executes the water vapor amount determination step (step S03).

[0044] The component ratio setting unit 73d sets the component ratio of the gas in accordance with the amount of water vapor determined in the water vapor amount determining step of step S03, and executes the component ratio setting step (step S04).

[0045] The component ratio setting unit 73d sets the component ratio of the gas so that the gas contains 30% or more by volume of water vapor when injected from the injection port 26. When the gas contains 30% or more by volume of water vapor, the rate at which an oxide film is formed on the steel sheet can be increased, and the oxide film can be formed in a short time, thereby improving production efficiency.

[0046] Furthermore, the component ratio setting unit 73d may set the gas component ratio so that the oxygen content when injected from the injection port 26 is, for example, 0% by volume or more and less than 5% by volume. By setting the gas component ratio in this manner, it is possible to prevent the formation of an oxide film containing pores. This makes it possible to prevent the oxide film from peeling off and the formation of a defect known as pick-up.

[0047] The component ratio setting unit 73d adjusts the amount of gas supplied from the gas supply unit 29 so that the component ratio is the one set in the component ratio setting step of step S04, thereby executing the adjustment step (step S05).

[0048] The component ratio setting unit 73d performs the heating step by injecting the gas from the injection port 26 at the component ratio of the gas adjusted in the adjustment step of step S05 (step S06). During the heating step of step S06, the component ratio setting unit 73d may inject the gas by setting the gas flow velocity to, for example, 3 m / s or more and 53 m / s or less.

[0049] By setting the gas flow velocity to 3 m / s or more, the steel sheet can be heated appropriately while maintaining the sheet passing speed, making it possible to maintain production efficiency. Furthermore, by setting the gas flow velocity to 50 m / s or less, vibration of the steel sheet caused by gas injection can be suppressed, thereby suppressing the occurrence of shape defects in the steel sheet.

[0050] Furthermore, the temperature of the gas when it is injected from the injection nozzle 26 should be 1000°C or higher and 2000°C or lower. By injecting the gas from the injection nozzle 26 at a temperature of 1000°C or higher, the heating rate of the steel sheet can be maintained, and the production efficiency of the plated steel sheet can be maintained. Furthermore, by injecting the gas from the injection nozzle 26 at a temperature of 2000°C or lower, the cost of the equipment for heating the gas can be minimized.

[0051] Next, a plating step is performed (step S07) to plate the steel sheet heated in the heating step of step S06.

[0052] Fig. 6 is a graph showing the relationship between the temperature of the steel sheet at the exit of the heating zone 22 and the thickness of the oxide film. In the graph shown in Fig. 6, the temperature of the steel sheet at the exit of the heating zone 22 is used as the manufacturing condition of the steel sheet. In the graph shown in Fig. 6, the thickness of the oxide film relative to the temperature of the steel sheet is shown for each amount of water vapor contained in the gas.

[0053] The water vapor amount determination unit 73c determines the water vapor amount using the graph shown in Fig. 6, i.e., the index data. For example, when the acquired oxide film thickness is 300 nm and the temperature of the steel sheet on the outlet side of the heating zone 22 is 700°C, the water vapor amount determination unit 73c determines the water vapor amount by setting the water vapor amount contained in the gas to 50% by volume.

[0054] If there is a difference between the amount of water vapor measured by the measuring unit 27 and the amount of water vapor determined by the water vapor amount determining unit 73c, the gas component ratio may be adjusted according to the magnitude of the difference. For example, if the difference is equal to or greater than a predetermined threshold, the component ratio setting unit 73d may adjust the gas component ratio so that the amount of water vapor measured by the measuring unit 27 approaches the determined amount of water vapor. The threshold may be set to an amount at which the influence of the amount of water vapor begins to have a noticeable effect on the environment, and may be set to, for example, 5% by volume.

[0055] 6, the temperature of the steel sheet on the outlet side of the heating zone 22 is used as the manufacturing condition. The manufacturing conditions are not limited to this, and may be, for example, at least one of the thickness (mm) and width (mm) of the steel sheet, the temperature of the steel sheet on the inlet side of the heating zone 22, the temperature of the steel sheet on the outlet side of the heating zone 22, and the chemical composition of the steel sheet.

[0056] As described above, according to the method for producing a plated steel sheet of the present invention, the amount of water vapor contained in the gas is determined based on the production conditions of the plated steel sheet and the thickness of the oxide film formed on the plated steel sheet, and the gas components are adjusted according to the amount of water vapor. The gas thus adjusted is then sprayed onto the steel sheet S to heat the steel sheet S. By heating the steel sheet S in this manner, an oxide film with a stable thickness can be formed. This makes it possible to produce a plated steel sheet with a good surface condition.

[0057] In this embodiment, an example has been described in which the injection port 26 is formed in a slit shape. The shape of the injection port 26 is not particularly limited as long as the gas can be injected in a uniform manner in the width direction of the steel sheet S. For example, the injection port may be formed by arranging a plurality of cylindrical nozzles along the width direction of the steel sheet S. Even in this case, the same effects as those of the above-mentioned embodiment can be obtained.

[0058] In the present embodiment, an example has been described in which the manufacturing conditions for the steel sheet are acquired from the storage unit 72. However, the acquisition of the manufacturing conditions for the steel sheet is not limited to this, and the manufacturing conditions for the steel sheet may be acquired from an external device. For example, the manufacturing conditions for the steel sheet may be acquired from a computer or the like that controls the operation of the plated steel sheet manufacturing apparatus 100. [Example]

[0059] The gas was ejected from the nozzle to heat the steel sheet, and the pickup occurrence was confirmed. In the test, the temperature of the steel sheet on the exit side of the heating zone was set to 700°C.

[0060] Samples Nos. 1 to 17 were prepared by varying the gas components ejected from the nozzle, the adjustment of the gas component ratio, the nozzle shape, the amount of water vapor, the gas flow rate, and the thickness of the oxide film. The values ​​for Test Nos. 1 to 17 are shown in Table 1. Whether or not the gas component ratio was adjusted is indicated in Table 1 as "Whether or not controlled."

[0061] The evaluation was carried out on the plating appearance in the width direction of the steel sheet, the plating appearance in the length direction of the steel sheet, and the occurrence of pick-up defects. The occurrence of pick-up defects was evaluated on a three-point scale: "◎", "◯", and "×".

[0062] The plating appearance was evaluated according to the following criteria. ◎: No plating or uneven alloying ○: Slight bare spots or slight alloying irregularities ×: Significant bare spots or significant uneven alloying

[0063] Pick-up defects were evaluated according to the following criteria. ◎: No extrusion scratches are visible ○: Slight extrusion scratches are visible ×: Extrusion scratches are clearly visible

[0064] The shape was evaluated according to the following criteria. ◎: No defects in shape due to wavy edges or other issues across the entire steel plate (Ear waves, etc., good) ○: Minor shape defects are observed in some parts of the steel plate, but the standard is met. (A slight amount of ear waves was detected, but the standard was met.) ×: Defective shape throughout the steel plate (There are ripples all over the steel plate, which does not meet the standards.)

[0065] [Table 1]

[0066] Test No. 12, in which the gas component ratio was not adjusted, was evaluated as "X" because a pickup defect occurred.

[0067] In contrast, in Test Nos. 1 to 11, 13 to 15, and 17, in which the gas component ratio was adjusted, the pickup defects all met the criteria, and the evaluation was "Excellent" or "Good."

[0068] In particular, Test Nos. 1 to 11, 14, 15, and 17, in which the shape of the ejection port was formed in a slit shape, were evaluated as "Excellent" for pick-up defects.

[0069] Test No. 17 is an example in which the gas component ratio was adjusted. In Test No. 17, the amount of water vapor was less than in the other invention examples, so the oxide film thickness was thin and no pickup defects occurred, but slight alloying unevenness occurred in the plating appearance in the longitudinal direction of the steel strip.

[0070] On the other hand, Test No. 16 is an example in which the gas component ratio was not adjusted. Although no pickup defects were observed in Test No. 16, the oxide film thickness on the steel sheet surface was thin, and coating defects occurred over the entire steel strip, so the evaluation was "X" in both the width direction and the length direction.

[0071] In tests Nos. 1 to 11, 13, 14, 16, and 17, in which the gas flow rate was set to 2 to 53 m / s, the steel sheet did not vibrate and the occurrence of defective shape of the steel sheet was suppressed. On the other hand, in tests Nos. 12 and 15, although the coating quality was good, the gas flow rate was too high, causing the steel sheet to vibrate and resulting in shape evaluations of "×" and "◯." [Explanation of symbols]

[0072] 100 Steel plate manufacturing equipment 20 Heating section 26 Nozzle 40 Plating Department 73a Manufacturing condition acquisition department 73b Oxide film thickness acquisition section 73c Water vapor amount determination unit 73d Composition Ratio Setting Department

Claims

1. A method for producing a plated steel sheet, comprising: a heating step of injecting gas toward a steel sheet to heat the steel sheet; and a plating step of plating the heated steel sheet, a manufacturing condition acquisition step of acquiring manufacturing conditions of the plated steel sheet; an oxide film thickness obtaining step of obtaining a thickness of an oxide film formed on the surface of the steel sheet in the heating step; a water vapor amount determination step of determining an amount of water vapor contained in the gas based on the manufacturing conditions acquired in the manufacturing condition acquisition step and the oxide film thickness acquired in the oxide film thickness acquisition step; a component ratio setting step of setting a component ratio of the gas in accordance with the amount of water vapor determined in the amount of water vapor determination step, In the heating step, the gas having the component ratio set in the component ratio setting step is sprayed onto the steel sheet to heat the steel sheet.

2. 2. The method for producing a plated steel sheet according to claim 1, wherein the gas containing 30% by volume or more of water vapor and less than 5% by volume of oxygen is injected in the heating step.

3. The method for producing a plated steel sheet according to claim 1 or 2, wherein in the heating step, the gas is injected at a flow velocity of 3 to 53 m / s.

4. An apparatus for manufacturing a plated steel sheet, comprising: a heating section that injects gas toward a steel sheet to heat the steel sheet; and a plating section that applies plating to the heated steel sheet, a manufacturing condition acquisition unit that acquires manufacturing conditions of the steel plate; an oxide film thickness acquisition unit that acquires the thickness of an oxide film formed on the steel sheet; a water vapor amount determination unit that determines the amount of water vapor contained in the gas based on the manufacturing conditions and the thickness of the oxide film; a component ratio setting unit that sets a component ratio of the gas in accordance with the amount of water vapor, The heating unit heats the steel sheet by injecting the gas adjusted by the component ratio setting unit onto the steel sheet.

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