Film manufacturing method, object manufacturing method, oxide film manufacturing method, and plated steel manufacturing method

Abstract

The film manufacturing method of the present invention includes a spectral reflectance calculation step of calculating a spectral reflectance from reflected light obtained by light being reflected by the film, an information calculation step of calculating, from the calculated spectral reflectance, information regarding the number of spectral reflectance extreme values and the wavelength positional relationship of the extreme values within a predetermined wavelength range, and a control step of controlling the film formation conditions based on the calculated information.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a film, a method for manufacturing an object, a method for manufacturing an oxide film, and a method for manufacturing a plated steel material. [Background technology]

[0002] Conventionally, when manufacturing an object by forming a film on its surface, the thickness of the film can be important. Interferometry, which utilizes the interference of light and is relatively easy to install and inexpensive, is often used to measure the thickness of a film formed on the surface of an object. In interferometry, light is incident on an object having a film formed on a substrate or on the film itself. The incident light, reflected from the film surface, and the light that passes through the film and is reflected by the substrate or the bottom of the film and emerges from the film surface, interfere with each other, resulting in a unique spectral reflectance corresponding to the film thickness. The film thickness can then be measured by analyzing the spectral reflectance. Methods for evaluating film thickness from the spectral reflectance obtained by interferometry include those disclosed in Patent Documents 1, 2, and 3, for example.

[0003] For example, Patent Document 1 discloses a method for measuring film thickness by expressing the change in spectral reflectance due to light interference as a two-wavelength ratio of reflectance in order to obtain an oxide layer suitable for improving plating characteristics. In the method disclosed in Patent Document 1, a sample considered to be the measurement target is prepared in advance, and the film thickness of the sample and the reflectance ratio at two specific wavelengths in the infrared region are measured. Then, in the method disclosed in Patent Document 1, a relationship between the reflectance ratio and film thickness is created from the measurement results, and accurate film thickness is measured from the specific two-wavelength ratio of reflectance actually measured online. Patent Document 2 also discloses a method for measuring oxide films formed during hot rolling and the cooling process after hot rolling using interferometry. In the method disclosed in Patent Document 2, continuous oxide film thickness measurements are performed on a steel sheet during strip threading based on the relationship between pre-measured film thickness and spectral reflectance. Patent Document 3 also discloses a method that uses an interferometry film thickness measurement device to accurately measure film thickness even when the film structure cannot be identified. In the method disclosed in Patent Document 3, the theoretical reflectance for the expected film structure is acquired in advance, and the film thickness is determined by determining the correlation between the measured reflectance and the theoretical reflectance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-202968 [Patent Document 2] Japanese Patent Application Publication No. 10-206125 [Patent Document 3] Japanese Patent Application Publication No. 11-160028 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the method of Patent Document 1, when measuring the film thickness from the spectral reflectance of the film to be measured and controlling it to an appropriate thickness to improve plating characteristics, it is necessary to determine the relationship between film thickness and spectral reflectance in advance using samples with known film thicknesses and to create a relationship between the reflectance ratio at two wavelengths and film thickness. Similarly, in the method of Patent Document 2, in order to measure film thickness from spectral reflectance, it is necessary to determine the relationship between spectral reflectance and film thickness in advance. To determine this relationship in advance, it is necessary to prepare samples consisting of the same composition, different film thickness, and the same base object as the film to be measured, or to prepare samples by sampling an object on which the film to be measured is formed from the production line. However, if it is not possible to prepare samples with the same composition as the film to be measured and different film thicknesses, it is impossible to determine the relationship between film thickness and reflectance spectrum in advance. For example, in the process using a direct-fire heating furnace used in the steelmaking process exemplified in Patent Document 1, it is not possible to sample during the process. Furthermore, because the actual film composition is unknown, it is not possible to perform sample measurements in advance to obtain the relationship between oxide film thickness and reflectance spectrum. Furthermore, in the method of Patent Document 3, when the film structure cannot be specified, the film thickness can only be measured for a relatively simple and predictable film structure, so the film thickness cannot be measured when the details of the film structure are unknown. Therefore, the film thickness cannot be evaluated from the measured reflectance spectrum, and a film with an appropriate film thickness range cannot be produced.

[0006] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a method for manufacturing a film, a method for manufacturing an object, a method for manufacturing an oxide film, and a method for manufacturing plated steel material, which are capable of manufacturing a film suitable for subsequent processes or products even if the thickness of the film cannot be measured accurately. [Means for solving the problem]

[0007] In order to solve the above problems and achieve the objectives, (1) The method for manufacturing a film according to the present invention includes a spectral reflectance calculation step for calculating a spectral reflectance from reflected light obtained by light being reflected by a film; an information calculation step for calculating, from the calculated spectral reflectance, information relating to the number of extreme values of the spectral reflectance and the wavelength positional relationship of the extreme values within a predetermined wavelength range; and a control step for controlling the film formation conditions based on the calculated information.

[0008] (2) In the film manufacturing method of the present invention, in the invention (1) above, the controlled formation conditions are one or more, and are formation conditions in a process before the spectral reflectance calculation step and / or formation conditions in a process after the information calculation step.

[0009] (3) A method for manufacturing an object according to the present invention includes a film formation step of forming a film on the surface of the object by the film manufacturing method according to the invention of (1) or (2) above.

[0010] (4) A method for producing an oxide film according to the present invention includes an annealing step for forming an oxide film on a surface of a steel sheet, the annealing step including: a spectral reflectance calculation step for calculating a spectral reflectance from reflected light obtained by light being reflected by the formed oxide film; an information calculation step for calculating, from the calculated spectral reflectance, information relating to the number of extreme values of the spectral reflectance and the wavelength positional relationship of the extreme values within a predetermined wavelength range; and a control step for controlling conditions for forming the oxide film based on the calculated information.

[0011] (5) The method for manufacturing plated steel material of the present invention is a method for manufacturing plated steel material having a plating film on the surface of the plated steel material, and includes an annealing process for forming an oxide film on the surface of the plated steel material and reducing the formed oxide film, and a plating process for forming the plating film on the plated steel material after the annealing process. The annealing process includes the following steps: a spectral reflectance calculation step for calculating a spectral reflectance from reflected light obtained by light being reflected on an oxide film formed on the surface of the plated steel material; an information calculation step for calculating, from the calculated spectral reflectance, information regarding the number of extreme values of the spectral reflectance and the wavelength positional relationship of the extreme values within a predetermined wavelength range; and a control step for controlling the formation conditions of the oxide film in a process before the spectral reflectance calculation step and / or controlling the reduction conditions of the oxide film in a process after the information calculation step, based on the calculated information. [Effects of the Invention]

[0012] The film manufacturing method, object manufacturing method, oxide film manufacturing method, and plated steel manufacturing method according to the present invention have the advantage of being able to manufacture a film suitable for subsequent processes or products even if the thickness of the film cannot be measured accurately. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a manufacturing facility using a film thickness evaluation device according to an embodiment. [Figure 2] FIG. 2 is a diagram showing a schematic configuration of a film thickness evaluation device according to an embodiment. [Figure 3] FIG. 3 is a graph showing the time change of the air ratio, the time change of the strip temperature, and the time change of the wavelength position of the extreme value as the change of the spectral reflectance. [Figure 4] FIG. 4 is a diagram showing the relationship between the range of oxide film thickness, the spectral reflectance, and the wavelength positional relationship of the extreme values. [Figure 5] FIG. 5 is a diagram showing a schematic configuration of a film thickness evaluation device according to the first modification. [Figure 6]FIG. 6 is a graph showing the change over time in the air ratio, the change over time in the strip temperature, and the change over time in the wavelength position of the extreme value. [Figure 7] FIG. 7 is a diagram showing the relationship between the oxide film thickness range in a predetermined wavelength range, the spectral reflectance, and the wavelength position relationship of the extreme value (criterion 1 and criterion 2), in which the T6 region is added to the relationship shown in FIG. [Figure 8] FIG. 8 is a diagram showing the relationship between the oxide film thickness range, the spectral reflectance, and the evaluation criteria in a predetermined wavelength range, in which the region corresponding to the T6 region is designated as the T6-1 region and the T6-2 region is added as a new T6 region, in comparison with FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the film manufacturing method, object manufacturing method, oxide film manufacturing method, and plated steel manufacturing method according to the present invention will be described, but the present invention is not limited to these embodiments.

[0015] The present embodiment will be described taking a plated steel material, specifically a hot-dip galvanized steel sheet, as an example of an object manufactured using the manufacturing method described in this embodiment.

[0016] In recent years, high-tensile hot-dip galvanized steel sheets (hereinafter referred to as "high-tensile GA steel sheets"), which use high-tensile steel sheets as thick plates, have been used in some automotive components. Furthermore, various high-tensile GA steel sheets, i.e., steel sheets with different strength values, are selected depending on the components used. In the production of high-tensile GA steel sheets, easily oxidizable elements such as Si and Mn are added to the steel sheet to improve strength. These easily oxidizable elements are selectively oxidized on the steel sheet surface during the annealing process in the production process of hot-dip galvanized steel sheets, and are known to adversely affect the coating properties when the steel sheet surface is coated with a coating in the coating process that follows the annealing process. Specifically, the oxidation of elements such as Si and Mn can result in oxides of elements in the steel being formed on the steel sheet surface, which can cause uncoated areas.

[0017] On the other hand, direct-fired heating furnaces, which are often installed in the first half of the annealing process, offer significant economic benefits, such as compact equipment, improved steel sheet threading, and superior thermal response characteristics. They also offer advantages such as ensuring good galvanization and raising the limits on the addition of elements such as Si and Mn. Direct-fired heating furnaces are divided into multiple zones, and combustion patterns can be set for each zone according to the load. In the multiple zones, oxidation-promoting heating or reduction heating is performed continuously, and the combustion time is controlled for each zone according to the load. As a result, the steel to be plated reaches a temperature of several hundred degrees Celsius or higher at the outlet of the heating furnace. The steel to be plated, which has been rapidly heated in a short time, is sent to a radiant tube heating furnace, which is often installed in the second half of the annealing process, where it is annealed to reduce the surface layer before being introduced into the plating process.

[0018] As mentioned above, preventing the oxidation of easily oxidizable elements is a key factor in the production of high-tensile GA steel sheets. High-tensile GA steel sheets of 590 MPa or higher contain large amounts of Si and Mn, so preventing the oxidation of easily oxidizable elements by heating in a direct-fire furnace is an effective means of improving galvanizability. In a direct-fire furnace, a thick oxide film is formed on the surface of the steel to be plated by increasing the air ratio during burner heating. Oxygen supplied from the thick oxide film formed on the surface of the steel to be plated oxidizes easily oxidizable elements such as Si and Mn inside the steel, suppressing surface oxidation and improving galvanizing properties. Here, the air ratio during burner heating refers to the ratio of the amount of air supplied to the amount of air that reacts appropriately with the gas.

[0019] Currently, the relationship between coating properties and direct-fired heating furnace conditions is investigated for each amount of Si and Mn added, optimizing the air ratio and burner flame intensity. However, this method cannot completely prevent the occurrence of uncoated areas due to the large fluctuations in process volume in the actual hot-dip galvanized steel sheet manufacturing process, the occurrence of burner clogging, flame abnormalities, and gas composition fluctuations. Therefore, to improve the final coating properties of high-tensile GA steel, it is important to understand the amount of oxidation in the oxide layer formed after the direct-fired heating furnace. However, the harsh environment at the exit of the annealing furnace makes direct measurement of the amount of oxidation difficult. Therefore, we decided to measure the oxide film thickness and control it within an appropriate range (hereinafter referred to as oxide film thickness) to prevent uncoated areas. Furthermore, because the amount of easily oxidizable elements added to high-tensile GA steel varies depending on its material properties, such as strength, the thickness of the oxide layer formed is likely to vary for each high-tensile GA steel with different material properties.

[0020] For this reason, although it would be useful to directly measure the oxide film thickness, due to production line restrictions it is not possible to sample the plated steel material with an oxide film formed on its surface, making it difficult to determine the actual structure and composition of the film that has formed.

[0021] Below, we will explain a method for producing a film that uses interference spectroscopy, which is inexpensive and easy to handle, and starts with forming an oxide film thickness on the surface of the steel material to be plated at the outlet of a direct-fire heating furnace in an appropriate range so that no bare spots occur.

[0022] As a result of extensive research, the present inventors discovered that, within a given wavelength range, information regarding the number of spectral reflectance extreme values and the wavelength positional relationship of the extreme values correlates with the air ratio, strip temperature, and the occurrence of non-plating. The inventors then came to the conclusion that this information can be used to control film formation. Therefore, in the film manufacturing method according to the present embodiment, this information is used to control film formation as an alternative to conventional film thickness control. The reason this information can be used as an alternative to film thickness control is that it can be assumed that there is a correlation between the air ratio, strip temperature, and the occurrence of non-plating and the thickness of the film formed. Theoretically, this can be explained by film interference.

[0023] In the film manufacturing method according to the embodiment, information regarding the number of spectral reflectance extrema and the wavelength positional relationship of the extrema is calculated from the spectral reflectance calculated from the reflected light obtained by reflecting light from the film in a predetermined wavelength range. Then, in the film manufacturing method according to the embodiment, the thickness of the film is estimated based on the calculated information from interference film theory, and the film formation conditions are controlled. Furthermore, the information is not limited to the number of spectral reflectance extrema and the wavelength positional relationship of the extrema. That is, the information also includes multiple thickness ranges arranged in order of thickness, such as the T1 to T5 regions described below with reference to FIG. 4. The multiple thickness ranges are estimated, for example, from the film interference and set by applying the thickness order. The information also includes multiple thickness ranges, such as A [nm] to B [nm], B [nm] to C [nm], and C [nm] to D [nm]. The thickness ranges are, for example, converted values obtained by simulation using related materials with compositions similar to the film to be formed.

[0024] FIG. 1 is a diagram showing the schematic configuration of a manufacturing facility using a film thickness evaluation device 3 according to an embodiment. The manufacturing facility shown in FIG. 1 includes a direct-fire heating furnace 2 for annealing a traveling thin-plate steel material 1 to be plated, and a film thickness evaluation device 3 for evaluating the film thickness of an oxide film formed on the surface of the steel material 1 to be plated. The direct-fire heating furnace 2 is covered with refractory material and includes an inner furnace roll 4, a measurement window 5, a burner 6, and an inner furnace roll 7. The steel material 1 to be plated is suspended between multiple inner furnace rolls and can travel along a linear path provided within the direct-fire heating furnace 2 from top to bottom in FIG. 1. Multiple burners 6 are installed in the direct-fire heating furnace 2 in a portion corresponding to the linear path, along the transport direction of the steel material 1 to be plated. The multiple burners 6 are installed facing each other across the steel material 1 to enable annealing with burner flames on both the front and back surfaces of the steel material 1 to be plated. The linear path of the direct-fire heating furnace 2 is divided into a first zone Z1, a second zone Z2, a third zone Z3, and a fourth zone Z4, which are multiple zones in which the air ratio, gas composition, and burner flame intensity can be specified as annealing conditions. The surface of the steel material 1 to be plated is heated by burners 6 installed in each of the first zone Z1 to the fourth zone Z4, thereby forming an oxide film on the surface of the steel material 1 to be plated.

[0025] The film thickness evaluation device 3 is disposed downstream of the fourth zone Z4 in the linear path of the direct-fire heating furnace 2 in the running direction of the steel material 1 to be plated, at the exit of the direct-fire heating furnace 2. Note that in FIG. 1, for example, one film thickness evaluation device 3 is installed on one side (front surface) of the steel material 1 to be plated so that the film thickness on one side (front surface) of the steel material 1 to be plated can be evaluated, but this is not limited to this. For example, a film thickness evaluation device 3 may be installed on each of the front and back surfaces of the steel material 1 to be plated so that the film thickness on both sides (front and back surfaces) of the steel material 1 to be plated can be evaluated. Furthermore, multiple film thickness evaluation devices 3 may be installed in the width direction of the steel material 1 to be plated.

[0026] 2 is a diagram showing a schematic configuration of a film thickness evaluation device 3 according to the embodiment. The film thickness evaluation device 3 according to the embodiment includes a detection unit 31, a calculation unit 32, a light guide 33, a detector 34, a shutter 35, an instrumentation air introduction unit 36, a light source unit 37, an optical fiber 38, a halogen light source 39, a xenon light source 310, and a database 321.

[0027] The detection unit 31 is a unit that detects reflected light and emitted light within a specific wavelength range. The detection unit 31 is provided with a light guide 33 and a detector 34. The light source unit 37 is a unit that includes a halogen light source 39 and a xenon light source 310, which are light sources for generating light with an intensity within a specific wavelength range. Specifically, the light source unit 37 is composed of two types of light sources, the halogen light source 39 and the xenon light source 310, to provide intensity over the entire wavelength range of 400 nm to 1050 nm. The halogen light source 39 and the xenon light source 310 are connected to the light guide 33 provided in the detection unit 31 by an optical fiber 38. Note that the light source for the light source unit 37 is preferably selected based on the element characteristics of the detection unit 31 (detector 34), and it is not necessary to use two types of light sources.

[0028] The light guide 33 is positioned so that irradiated light L1 can be incident on the surface of the steel material 1 to be plated through a measurement window 5 provided in the furnace wall of the direct-fire heating furnace 2. The detector 34 is also positioned so that specularly reflected light L2 from the surface of the steel material 1 to be plated can be acquired. The detector 34 is, for example, one with a measurable wavelength range of 400 nm to 1050 nm, but one capable of measuring other wavelength ranges may also be used. In the detection unit 31, the film thickness measurement position P1 is set on the surface of the steel material 1 at the portion where the steel material 1 is wrapped around the in-furnace roll 4 to suppress the influence of fluctuations in the specularly reflected light L2 due to vibration of the steel material 1 to be plated. The detection unit 31 irradiates the irradiated light L1 from the light guide 33 through the measurement window 5 onto the measurement position P1 on the surface of the steel material 1 to be plated, and the specularly reflected light L2 reflected at the measurement position P1 is measured by the detector 34.

[0029] The calculation unit 32 converts the spectrum of the reflected light intensity measured by the detector 34 into a reflectance spectrum to evaluate the film thickness.

[0030] The detection unit 31 preferably has an instrumentation air inlet 36 for introducing air into the housing of the detection unit 31 to prevent heat transfer to the light guide 33 and the detector 34 in a high-temperature environment and to prevent dust from affecting the precision equipment. The light source unit 37 also has an instrumentation air inlet 36 for introducing air into the housing of the light source unit 37 to prevent heat transfer to the halogen light source 39 or the xenon light source 310 in a high-temperature environment and to prevent dust from affecting the precision equipment. The calculation unit 32 may be installed in a location remote from the direct-fire heating furnace 2. The calculation unit 32 may also be connected to the detector 34 via a network. For example, the calculation unit 32 may be installed in an external server, and the detector 34 and the external server may be configured to communicate via a network. The detector 34 may access the calculation unit 32 on the external server, and the calculation unit 32 may perform processing. In these cases, the calculation unit 32 does not need to have an instrumentation air inlet. On the other hand, when the calculation unit 32 is installed near the direct flame heating furnace 2, it is preferable that the calculation unit 32 has an instrumentation air inlet for introducing air into the housing thereof, similar to the detection unit 31 and the light source unit 37.

[0031] In the film thickness evaluation device 3 according to the embodiment, the detection unit 31 and the light source unit 37 are provided separately, which makes it possible to reduce the weight of the detection unit 31 and to easily adjust the angle of the detection unit 31 when installing it.

[0032] As shown in Figure 1, the film thickness evaluation device 3 according to this embodiment measures the steel material 1 to be plated immediately after it has been heated by burners 6 in each of multiple zones Z1, Z2, Z3, and Z4, i.e., immediately after an oxide film has formed on the surface. The steel material 1 to be plated immediately after the oxide film has formed is red-hot at several hundred degrees Celsius. Therefore, when the specularly reflected light L2 incident from the light guide 33 and reflected by the steel sheet surface is measured by the detector 34, the measurement also includes light emitted from the red-hot steel material 1 to be plated.

[0033] Therefore, by closing the shutter 35, which is provided in the detection unit 31 and can be opened and closed, to block the irradiated light L1 irradiated from the light guide 33 toward the surface of the steel material 1, it becomes possible to instantaneously measure only the radiated light from the steel material 1 by the detector 34. On the other hand, when the shutter 35 is open, the irradiated light L1 irradiated from the light guide 33 is incident on the surface of the steel material 1, so that the specularly reflected light L2 and radiated light from the surface of the steel material 1 are simultaneously measured by the detector 34. The calculation unit 32 then subtracts the spectral radiated light intensity measured immediately before with the shutter 35 closed from the spectral reflected light intensity and spectral radiated light intensity measured with the shutter 35 open, to obtain the spectral reflection intensity of the specularly reflected light L2 that takes into account the influence of the radiated light from the red-hot steel material 1.

[0034] In this way, the film thickness evaluation device 3 measures the spectral reflection intensity that is not affected by the radiated light from the plated steel material 1 by intermittently irradiating the surface of the plated steel material 1 with the irradiated light L1 using the shutter 35. The film thickness evaluation device 3 then measures the spectral reflectance by calculating in the calculation unit 32 the ratio between the spectral reflection intensity of the base steel sheet that does not have an oxide film formed on its surface, which has been measured in advance, and the measured spectral reflection intensity that takes into account the influence of the radiated light.

[0035] Next, an example of a method for manufacturing a film in an appropriate film thickness range (target film thickness range) using interference spectroscopy according to the embodiment will be described.

[0036] The film manufacturing method according to the embodiment includes a spectral reflectance calculation step, an information calculation step, and a control step. In the spectral reflectance calculation step, the spectral reflectance intensity is calculated from the reflected light obtained by light reflecting off the film. In the information calculation step, information regarding the number of spectral reflectance extreme values and the wavelength positional relationship of the extreme values is calculated from the calculated spectral reflectance within a predetermined wavelength range. In the control step, film formation conditions are controlled based on the information regarding the calculated number of spectral reflectance extreme values and the wavelength positional relationship of the extreme values. The formation conditions controlled in this control step may be one or more, and may be formation conditions in a process prior to the spectral reflectance calculation step and / or formation conditions in a process subsequent to the information calculation step. Examples of the formation conditions include the air ratio, gas composition, and burner flame intensity in each of multiple zones Z1, Z2, Z3, and Z4 in the linear path of the direct-fire heating furnace 2.

[0037] Conventionally, to measure film thickness using interferometry, samples consisting of the same composition, different film thicknesses, and the same base object must be prepared in advance, or samples must be prepared by sampling objects with the film to be measured formed on their surfaces from the production line. The relationship between film thickness and reflectance must then be clarified using the prepared samples. However, in the case of the present embodiment, samples cannot be sampled in advance immediately after passing through the direct-fired heating furnace 2. This makes it impossible to use actual samples or prepare samples that simulate the actual samples. As a result, the exact film thickness cannot be determined from the measured reflectance, making it impossible to produce oxide films within the appropriate film thickness range.

[0038] As a result of extensive research, the inventors of the present application have discovered that even if it is not possible to prepare a sample in advance and measure the true film thickness, it is possible to produce a film within an appropriate film thickness range by clarifying the relationship between the spectral reflectance measured online and the film thickness at which that spectral reflectance is obtained.

[0039] In interference spectroscopy, it is known that as the film thickness increases, the frequency of the spectral reflectance increases, the interval between the wavelength positions of the extreme values in the measurement wavelength range decreases, and the wavelength positions of the extreme values of the spectral reflectance shift to longer wavelengths. Similarly, in interference spectroscopy, it is known that as the film thickness decreases, the frequency of the spectral reflectance decreases, and the wavelength positions of the extreme values shift to shorter wavelengths. Therefore, if it is possible to constantly measure the wavelength positions of specific extreme values in the measurement wavelength range, it is possible to determine whether the film thickness increases or decreases based on the wavelength positions of specific extreme values in the measurement wavelength range, and the relationship between spectral reflectance and film thickness can be clarified.

[0040] On the other hand, when actually constructing and installing the device, the measurement wavelength range is almost always limited due to cost issues, making it difficult to continuously measure the wavelength position of a specific extremum. Therefore, we conducted an experiment in which the film thickness was increased and decreased, and observed the changes in the extremum of the spectral reflectance with increasing and decreasing film thickness in the measurement wavelength range. As a result, we found that there is a characteristic relationship between the wavelength position of the extremum measured within a specific wavelength range and a certain range of film thickness. Below, we will explain the content and results of the actual experiment we conducted.

[0041] To investigate the conditions for oxide film formation and changes in spectral reflectance, as well as the occurrence of unplated areas in the subsequent plating process, the air ratio was continuously changed in each of multiple zones Z1, Z2, Z3, and Z4 in the linear path of the direct-fired heating furnace 2 shown in Figure 1. The thickness of the oxide film formed on the surface of the steel material 1 to be plated was continuously changed as the steel material traveled along the linear path of the direct-fired heating furnace 2, and the spectral reflectance at that time was measured using a film thickness evaluation device 3. Note that the burner flame intensity was adjusted to keep the temperature of the steel material 1 to be plated (hereinafter referred to as the sheet temperature) constant, but it is not possible to keep the sheet temperature completely constant, and this is thought to have some effect on the oxide film thickness.

[0042] 3 is a graph showing the time change in the air ratio, the time change in the strip temperature, and the time change in the wavelength position of the extreme value as a change in spectral reflectance. The strip temperature was measured using a radiation thermometer (not shown) at the temperature measurement position on the surface of the plated steel material 1 wound around the inner furnace roll 7 located downstream of the inner furnace roll 4.

[0043] In addition, to detect the wavelength positions of extrema, we calculated the rate of change of the spectral reflectance measured over a specified wavelength range and detected the wavelength positions where the rate of change changes from positive to negative as the wavelength positions of extrema. However, because the measured spectral reflectance contains noise, it is difficult to detect the desired extrema simply by calculating the rate of change, resulting in false detection of extrema. Therefore, we used polynomial curve approximation as preprocessing for the measured spectral reflectance. Polynomial curve approximation here involves finding the coefficients of a polynomial that minimizes the sum of the squares of the differences between the data points and the polynomial value. While we used a 10th-order polynomial in this study, polynomials of other orders can also be used. We created approximation polynomials of several orders and selected the order that best approximates the measured spectral reflectance. Although we used polynomial curve approximation in this study, taking a moving average of the spectral reflectance is also an effective preprocessing method. On the other hand, with moving averages, increasing the number of average data points can reduce false detection of extreme values due to small noise, but having a large number of average data points can result in extreme values being overlooked when the peak intensity of a specific extreme value is small or the interval between extreme values is short. Conversely, having a small number of average data points makes it easier to detect extreme values even when the peak intensity of a specific extreme value is small or the interval between extreme values is short, but it has the disadvantage of being more susceptible to noise. Furthermore, the specified wavelength range was set to 400 nm to 1050 nm, which is a range that allows easy capture of reflected light from an oxide film. Thus, the specified wavelength range can be appropriately selected so that the spectral reflectance of the film to be measured can be easily measured.

[0044] In the graph of FIG. 3 showing the change in wavelength position of extrema over time, a cross mark indicates a single minimum extrema in a given wavelength range. The graph also plots a circle mark when there are two extrema in the measured wavelength range, with the shortest wavelength being the minimum. The graph also plots a square mark when there are two extrema in the measured wavelength range, with the shortest wavelength being the maximum. The graph also plots a triangle mark when there are three extrema in the measured wavelength range, with the shortest wavelength being the minimum. The graph reveals that the number of extrema and their wavelength positional relationship change within the wavelength range of 400 nm to 1050 nm as the air ratio increases or decreases, i.e., as the oxide film thickness on the surface of the plated steel material 1 increases or decreases, the wavelength positional relationship of the extrema shifts. Specifically, as the air ratio decreases from 13:47 to 14:07, the number of extrema and their wavelength positional relationship change as follows: In other words, the number of extrema and their wavelength positional relationship change as the extrema shift toward the shorter wavelength side, from two extrema (minimum on the short wavelength side), to three extrema (minimum on the short wavelength side), to two extrema (maximum on the short wavelength side), to one minimum. Then, around 14:00, the extrema shift toward the longer wavelength side, resulting in two extrema (maximum on the short wavelength side), and then they shift again toward the shorter wavelength side, resulting in one minimum and two extrema (minimum on the short wavelength side). The shift of the extrema toward the longer wavelength side around 14:00 is due to an increase in the sheet temperature, and it is estimated that the oxide film thickness increased slightly at this time.

[0045] From these results, it is estimated that information regarding the number of extrema and the wavelength positional relationship of the extrema is correlated with the film thickness (film thickness). The 13:47 and 14:07 films are estimated to have significantly different air ratios and significantly different oxide film thicknesses, but they are similar in that they have the number of extrema and a minimum on the short wavelength side. However, as the film thickness increases, the frequency of the spectral reflectance increases, making it possible to distinguish between extrema (minima) and extrema (maxima) based on the distance between their wavelength positions. Even if there is only one extrema, it is possible to distinguish between them based on the half-width of the extrema or the range of wavelength positions that the extrema can take.

[0046] The inventors also created Figure 4 based on the results and findings of Figure 3. Figure 4 shows the relationship between the oxide film thickness range, spectral reflectance, and wavelength positional relationship of extrema within a given wavelength range. The oxide film thickness range here is estimated based on the aforementioned air ratio, the aforementioned strip temperature, and the occurrence of non-plated films in the subsequent plating process. In Figure 4, the range of a given oxide film thickness is divided into regions T1, T2, T3, T4, and T5 in order of estimated thinnest film thickness. Figure 4 also shows the actually measured spectral reflectance, the number of extrema in the measured wavelength range, and the wavelength positional relationship of the extrema, corresponding to each of the T1, T2, T3, T4, and T5 regions. In Figure 4, regions T1 to T5 provide information regarding the number of extrema in the spectral reflectance and the wavelength positional relationship of the extrema, which can be used to control film formation, etc. In the case of Figure 4, it is expected that information regarding the number of extreme values and the wavelength positional relationship of the extreme values will be correlated with the above-mentioned film thickness range based on the air ratio, sheet temperature, and the occurrence of non-plating.

[0047] In the case of the relationship in FIG. 4, in order to evaluate the oxide film thickness range (region T1 to T5) from the wavelength positional relationship of the spectral reflectance extrema, the wavelength positional relationship of the extrema is provided with two types of information: judgment criterion 1 and judgment criterion 2. Judgment criterion 1 is information regarding the number of extrema and the wavelength positional relationship of the extrema (arrangement order of the extrema). As will be described later, judgment criterion 1 has information for all regions from region T1 to region T5. Judgment criterion 2 is information regarding the distance between extrema, which is one of the wavelength positional relationships of the extrema. As will be described later, judgment criterion 2 has information for oxide film thickness range regions for which information is available and oxide film thickness range regions for which information is not available.

[0048] In Figure 4, after determining Criterion 1, which is one of the wavelength position relationships of extreme values, if Criterion 2 exists, the oxide film thickness range of the spectral reflectance can be evaluated by determining Criterion 2. Furthermore, if there are Criteria 3, 4, ..., the oxide film thickness range is evaluated by determining the criteria in order from the smallest number.

[0049] In the T1 region, there are two extrema in the measured wavelength range, with the shortest wavelength being the minimum, the wavelength positional relationship of the extrema being minimum → maximum, and the wavelength positional interval between the extrema (minimum) and maximum is greater than 350 [nm]. Therefore, criterion 1 for the wavelength positional relationship of the extrema is set to "minimum → maximum," and criterion 2 is set to "extrema interval > 350 [nm]." In the T2 region, there is one extrema in the measured wavelength range. In the T3 region, there are two extrema in the measured wavelength range, with the shortest wavelength being the maximum, and the wavelength positional relationship of the extrema is maximum → minimum. In the T4 region, there are three extrema in the measured wavelength range, with the shortest wavelength being the minimum, and the wavelength positional relationship of the extrema is minimum → maximum → minimum. In the T5 region, there are two extreme values in the measurement wavelength range, with the short wavelength side being the minimum, and the wavelength position relationship of the extreme values is minimum → maximum, with the wavelength position interval between the extreme values (minimum) and (maximum) being 350 nm or less.

[0050] Then, such estimated oxide film thickness range (T1 region, T2 region, T3 region, T4 region, T5 region), the number of extrema, and the wavelength positional relationship of the extrema are created in advance as a database as information on the number of extrema of the spectral reflectance and the wavelength positional relationship of the extrema. This previously created database is used, for example, as database 321 provided in the calculation unit 32 of the film thickness evaluation device 3. As a result, the calculation unit 32 can determine the oxide film thickness range (T1 region, T2 region, T3 region, T4 region, T5 region) from the number of extrema in the measurement wavelength range and the wavelength positional relationship of the extrema using the spectral reflectance measured by the detection unit 31 and the database 321. Note that the database 321 is not limited to being provided in the calculation unit 32 of the film thickness evaluation device 3. For example, the database 321 may be provided in an external server. The film thickness evaluation device 3 and the external server may be configured to be able to communicate with each other via a network, and the film thickness evaluation device 3 may access the database 321 of the external server to determine the oxide film thickness range in the calculation unit 32. In addition, in a predetermined wavelength range, the information relating to the number of spectral reflectance extrema and the wavelength positional relationship of the extrema may be applied as a converted value simulated using a related substance similar to the film composition, instead of a code as in the above-described T1 to T5 regions. In this case, a database is created with the range of converted values as the oxide film thickness range. Furthermore, the information relating to the number of spectral reflectance extrema and the wavelength positional relationship of the extrema may be the number of spectral reflectance extrema and the wavelength positional relationship of the extrema. Either method may be selected as appropriate, taking into consideration the size of the database and the load on the manufacturing equipment.

[0051] Additionally, during the above experiment, plated steel materials 1 were also prepared, each estimated to have a different oxide film thickness, by lowering the air ratio in each of the multiple zones Z1, Z2, Z3, and Z4 in the linear path of the direct-fire heating furnace 2 during the first half of the annealing process. The oxide films on the surfaces of these plated steel materials 1 were reduced during the second half of the annealing process, and then a coating was applied to the surface of the plated steel materials 1 during the plating process. The occurrence of surface defects was also investigated. This enabled us to investigate the relationship between regions T1 to T5 (i.e., information regarding the number of spectral reflectance extrema and the wavelength positional relationship of these extrema within a given wavelength range) and the occurrence of surface defects during the plating process performed after the annealing process. As a result, it was found that surface defects occurred on the surface of the plated steel materials 1 in the oxide film thickness ranges where the number of extrema and the wavelength positional relationship of the extrema corresponding to regions T1 and T2 appeared. From these results, it is possible to create a database of regions T1 to T5 that are expected to form during normal manufacturing (i.e., information on the number of spectral reflectance extreme values and the wavelength positional relationship of the extrema within a predetermined wavelength range) and the occurrence of unplated areas. This database is used as database 321 provided in calculation unit 32 of film thickness evaluation device 3. Below, we will explain a method for producing an oxide film using information on the number of spectral reflectance extreme values and the wavelength positional relationship of the extrema within a predetermined wavelength range to prevent unplated areas from occurring on the surface of plated steel material 1.

[0052] To produce hot-dip galvanized steel sheets with good surfaces free of uncoated spots, the oxide film thickness must not fall below a certain level (T1 and T2 regions) in the direct-fire heating furnace 2. Therefore, once the T3 region is confirmed, the flow rates of gas and air used for burner combustion are increased in each of the multiple zones Z1, Z2, Z3, and Z4 in the linear path of the direct-fire heating furnace 2 to strengthen the burner flame intensity and control the oxide film thickness to fall into the T4 region. This reduces the occurrence of uncoated spots.

[0053] Furthermore, if the region where the occurrence of non-plating can be suppressed is region T5, then the burner flame intensity in the linear path of the direct-fired heating furnace 2 can be maintained. Furthermore, although not necessary in this embodiment, if the oxide film is to be formed so that the thickness does not exceed a certain value, the upper limit of the oxide film thickness range is also determined through prior experiments. It is then preferable to form the oxide film by controlling the burner flame intensity in the linear path of the direct-fired heating furnace 2 so that the number of extrema in a predetermined wavelength range and the wavelength positional relationship of the extrema do not exceed the upper limit of the oxide film thickness range. In these cases, feedback control is performed on the direct-fired heating furnace 2 using information regarding the number of extrema of spectral reflectance and the wavelength positional relationship of the extrema within the predetermined wavelength range.

[0054] Furthermore, for example, when it is desired to set more detailed thresholds in the T3 region based on information relating to the number of spectral reflectance extreme values and the wavelength positional relationship of the extreme values in a predetermined wavelength range, it is preferable to create a database of wavelength positions of arbitrary extreme values in the T3 region based on the results of a previous experiment, and then set thresholds for the wavelength positions of arbitrary extreme values in the T3 region.

[0055] Furthermore, the above experiment should be performed for each steel type, and if the number of extreme values in the measurement wavelength range and the wavelength positional relationship of the extreme values change depending on the steel type, a database should be created for each steel type and used for each steel type.

[0056] Furthermore, when manufacturing hot-dip galvanized steel sheets, an oxide film is formed on the surface of the steel material 1 to be plated in a direct-fire heating furnace 2 in the first half of the annealing process, and then the steel material 1 is radiantly heated in a reducing atmosphere in a radiant tube heating furnace in the second half of the annealing process. This radiant heating step is performed after the control step. This converts the oxide film formed on the surface of the steel material 1 from an iron oxide layer to a reduced iron layer, and simultaneously, oxygen supplied from the iron oxide layer internally oxidizes the additive elements inside the steel sheet. As a result, the surface of the steel material 1 is covered only with a reduced iron layer that has good wettability with zinc. Information regarding the number of spectral reflectance extrema in a predetermined wavelength range and the wavelength positional relationship of the extrema can also be used in the radiant heating step, which is the next step after the direct-fire heating furnace 2. For example, the relationship between the furnace temperature in the radiant furnace and the surface condition (whether all iron oxide has been converted to reduced iron) is investigated in each of the different oxide film thickness regions T1, T2, T3, T4, and T5 formed in the direct-fire heating furnace 2. Then, when the oxide film is thick, such as in region T5, the furnace temperature of the radiant furnace is increased to control the reduction and thereby change the amount of reduction of the oxide film on the plated steel material 1 after measuring the film thickness range.

[0057] (Variation 1) Next, modified examples of the film thickness evaluation device 3 according to the embodiment will be described. Fig. 5 is a diagram showing a schematic configuration of the film thickness evaluation device 3 according to Modification 1. The configuration of the film thickness evaluation device 3 according to Modification 1 is basically the same as the configuration of the film thickness evaluation device 3 shown in Fig. 2, but it further includes a reference light measurement unit 311. Here, the base steel sheet described in the above paragraph

[0034] , on whose surface an oxide film is not formed, is called the reference measurement sample, and the spectral reflection intensity measured with the reference measurement sample used when calculating the spectral reflectance is called the reference light.

[0058] The reference light measurement unit 311 shown in Figure 5 is composed of a light guide 331, a detector 341, a reference measurement sample 312, and an instrumentation air inlet 361. The optical system of the reference light measurement unit 311 is designed so that light emitted from the light guide 331 of the reference light measurement unit 311 is measured by the detector 34 through specular reflection from the reference measurement sample 312. In Figure 5, the light emitted from the light source unit 37 passes through an optical fiber 38 and is branched into the detection unit 31 and the light guides 33, 331 of the reference light measurement unit 311, respectively, and is configured so that light can be emitted from each of the light guides 33, 331.

[0059] In paragraph

[0034] above, a reference light is measured in advance and used to measure the spectral reflectance. However, depending on the light source, the filament deteriorates over time, causing the light emission intensity of the light source to decay. This creates a problem: the light emission intensity spectrum of the light source changes over time. This decay in emission intensity may not be constant across all wavelengths, but may vary depending on the wavelength. Therefore, if a reference light measured in advance is used to calculate the spectral reflectance, if the emission intensity spectrum of the light source after the filament deteriorates differs from the reference light measured in advance, an incorrect spectral reflectance will be measured. In particular, when using two or more types of light sources, as in Variation 1, the filaments have different lifespans and deterioration patterns, and the filament replacement times also differ. Therefore, it is difficult to predict and respond to the decay pattern of the emission intensity spectrum over time, and it is difficult to measure a reference light in advance that takes the effects of decay into account.

[0060] Therefore, in the film thickness evaluation device 3 according to the first modification, by providing a reference light measurement unit 311 as shown in FIG. 5, the reference light can be measured at any timing and updated as needed. Therefore, in the spectral reflectance measurement described in paragraphs

[0032] to

[0034] above, fluctuations in the light source emission intensity spectrum can be accommodated, and the spectral reflectance can be calculated accurately. The timing for measuring and updating the reference light may be the same as the timing for measuring the spectral reflection intensity from the steel material to be plated in the detection unit 31, or may be once every few hours. Because the emission spectral intensity does not significantly attenuate over a period of several seconds, accurate spectral reflectance measurement can be performed even if the reference light is updated once every few hours.

[0061] (Variation 2) Next, we will explain a modified example of the database of spectral reflectance and oxide film thickness range in the film manufacturing method according to the embodiment. In Modification 2, in order to obtain data reproducibility, an additional experiment similar to that described in paragraph

[0041] above was conducted in which the air ratio was changed in multiple zones Z1, Z2, Z3, and Z4 in the linear path of the direct-fire heating furnace 2 shown in FIG. 1. In this experiment, the temperature of the steel sheet was intentionally increased by slowing down the line speed, resulting in a thicker oxide film. The experimental results are shown in FIG. 6 as a graph showing the change in air ratio over time, a graph showing the change in sheet temperature over time, and a graph showing the change in wavelength position of the extremum over time.

[0062] In the graph shown in Figure 6, which shows the change over time in the wavelength position of the extremum, there are three extremums in a predetermined wavelength range, and the extremum on the shortest wavelength side is plotted with a triangle mark when it is the smallest. Also, in this graph, there are two extremums in the measured wavelength range, and the extremum on the shortest wavelength side is plotted with a square mark when it is the largest. Also, in this graph, there are two extremums in the measured wavelength range, and the extremum on the shortest wavelength side is plotted with a circle when it is the smallest. Also, in this graph, there are three extremums in a predetermined wavelength range, and the extremum on the shortest wavelength side is plotted with a diamond when it is the largest.

[0063] The graph clearly shows the wavelength position relationship of the extrema, which corresponds to the T6 region, which is thicker than the T5 region in Figure 4. Specifically, the strip temperature begins to rise around 12:11 in Figure 6. Accordingly, the wavelength position relationship of the extrema corresponding to the T5 region transitions to a "maximum → minimum → maximum" wavelength position relationship of extrema, where there are three extrema in the measured wavelength range, with the shortest wavelength being the maximum. Based on this result, we determined that Criterion 1 corresponds to the T6 region, which is thicker than the T5 region, which is the "maximum → minimum → maximum" oxide thickness range. Therefore, we added the T6 region to the relationship shown in Figure 4 and created new relationships (Criterion 1 and Criterion 2) between the oxide thickness range, spectral reflectance, and wavelength position relationship of extrema within a specified wavelength range. The new relationships are shown in Figure 7.

[0064] In the case of the relationship in Figure 7, the wavelength position relationship of the extrema has two types of information: judgment criterion 1 and judgment criterion 2. Both judgment criterion 1 and judgment criterion 2 are the same as those in Figure 4. Judgment criterion 1 is information regarding the number of extrema and the wavelength position relationship of the extrema (the order in which the extrema are arranged). Judgment criterion 2 is information regarding the distance between extrema, which is one of the wavelength position relationships of the extrema. Judgment criterion 1 has information in all oxide film thickness range regions, while judgment criterion 2 exists in some oxide film thickness range regions with information and some oxide film thickness range regions without information. For the spectral reflectance of the newly added T6 region, only judgment criterion 1 exists, and judgment criterion 1 for the T6 region has three extrema in the measurement wavelength range, with the extrema on the short wavelength side being the maximum, and the wavelength position relationship of the extrema is "maximum → minimum → maximum."

[0065] As in FIG. 4, the T1 to T6 regions in FIG. 7 can be used to control film formation as information on the wavelength positional relationship (criterion) of the spectral reflectance extrema. In FIG. 7, criterion 1, which is one of the wavelength positions of the extrema, is determined, as in paragraph

[0047] above. After determining criterion 1, if there is another criterion for the wavelength positional relationship of the extrema, criterion 2, the oxide film thickness range can be evaluated by determining criterion 2. Furthermore, if there are criteria 3, 4, ..., the criteria with the lowest number are determined in order to evaluate the oxide film thickness range.

[0066] (Variation 3) Next, we will explain another example of a modified database of spectral reflectance and oxide film thickness range in the film manufacturing method according to the embodiment. In Figure 6 shown in Modification 2 above, in the middle of the continuous wavelength position relationship of "maximum → minimum → maximum" around 12:11, a "minimum → maximum" (extremum interval > 350 [nm]) was confirmed in the wavelength position relationship of extreme values corresponding to the T1 region. It is unnatural that the wavelength position relationship of extreme values in the T1 region appears for just a moment in the continuous wavelength position relationship of "maximum → minimum → maximum" corresponding to the oxide film thickness range in the T6 region without any significant change in the sheet temperature or air ratio. Therefore, when we investigated the spectral reflectance that appears around 12:11 and is judged to be "minimum to maximum (extremum interval > 350 [nm])" which corresponds to the T1 region, we found that the spectral reflectance has a shape in which the amplitude due to interference of the spectral reflectance corresponding to the T6 region is crushed. Furthermore, when we investigated the amplitude crushing phenomenon described above, we found that the amplitude due to interference of the measured spectral reflectance is reduced due to the presence of unevenness in film thickness, the roughness of the base steel sheet on which the oxide film is formed, and the deviation of specular reflection due to sheet vibration of the flowing steel sheet.

[0067] From this, it is predicted that the spectral reflectance determined to be "minimum to maximum (extremum interval > 350 [nm])" corresponding to the T1 region observed around 12:11 in Figure 6 is actually a spectral reflectance corresponding to the T6 region. In this way, when the amplitude of the spectral reflectance is reduced, the current method of determining extrema described in paragraph

[0043] above will determine that the spectral reflectance with reduced amplitude that actually corresponds to the T6 region is a spectral reflectance with a wavelength position relationship that corresponds to the T1 region.

[0068] Therefore, we defined the spectral reflectance determined to have a wavelength positional relationship of "maximum → minimum → maximum" as the T6-1 region, which corresponds to the T6 region. Furthermore, we defined the spectral reflectance of "minimum → maximum (extremum interval > 350 [nm])" as the T6-2 region, which corresponds to the T6 region, even though it is actually predicted to be in the T6 region. Repeated online experiments revealed that it is possible to determine whether a spectral reflectance is in the T1 region or the T6-2 region by using the two criteria of the wavelength positional relationship of the extrema and the extrema interval, as well as evaluating whether the reflectance difference between extrema is greater than or equal to 0.2 or less. This is presumably because the amplitude of spectral reflectance in the T6-2 region is reduced, which reduces the reflectance difference between extrema, making it easier for the reflectance difference between extrema of spectral reflectance in the T1 region to be different.

[0069] Based on the above findings, the inventors of the present invention have newly created a relationship between the oxide film thickness range, the spectral reflectance, and the evaluation criteria in a predetermined wavelength range. The newly created relationship is shown in Figure 8. In Figure 8, the region corresponding to the T6 region is designated as the T6-1 region, and a new T6 region, the T6-2 region, is added to Figure 7. Furthermore, a new evaluation criterion 3 is added to Figure 7.

[0070] In the case of the relationship shown in FIG. 8, the wavelength positional relationship of the extrema includes two types of information: criterion 1 and criterion 2. Criterion 1 and criterion 2 are the same as those shown in FIGS. 4 and 7. Criterion 1 is information regarding the number of extrema and the wavelength positional relationship of the extrema (the order in which the extrema are arranged). Criterion 2 is information regarding the distance between the extrema, which is one of the wavelength positional relationships of the extrema. Criterion 1 has information for all oxide thickness range regions, while criterion 2 exists in some oxide thickness range regions with and without information. Criterion 3 is a new criterion added in FIG. 8 and is information regarding the reflectance difference between the extrema. As with criterion 2, criterion 3 exists in some oxide thickness range regions with and without information. In FIG. 8, the oxide thickness range of the spectral reflectance is evaluated by the following method: criterion 1 is judged, then, if criterion 2 is present, criterion 2 is judged. Then, if criterion 3 is present, criterion 3 is judged.

[0071] In this way, in Modification 3, a database such as that shown in Fig. 8 is created in advance using information on the shape of the spectral reflectance, such as not only the positional relationship of the extreme values but also the difference in reflectance between the extreme values of the spectral reflectance. The created database makes it possible to manufacture the oxide film described in paragraphs

[0051] to

[0056] above, which can address the issue of the collapse of the amplitude of the spectral reflectance due to unevenness in film thickness and deviation of regular reflection. [Industrial Applicability]

[0072] The present invention can provide a method for manufacturing a film, a method for manufacturing an object, a method for manufacturing an oxide film, and a method for manufacturing plated steel material, which can manufacture a film suitable for subsequent processes or products even if the thickness of the film cannot be measured accurately. [Explanation of symbols]

[0073] 1. Steel to be plated 2 Direct-fire heating furnace 3 Film thickness evaluation equipment 4 Furnace roll 5 Measurement window 6 burners 7 Furnace Roll 31 Detection unit 32 Arithmetic section 33,331 Light Guide 34,341 detectors 35 Shutter 36,361 Instrument air introduction section 37 Light source section 38 Optical Fiber 39 Halogen light source 310 Xenon Light Source 311 Reference light measurement section 312 Reference Measurement Sample 321 databases

Claims

1. a spectral reflectance calculation step of calculating a spectral reflectance from reflected light obtained by light being reflected by the film; an information calculation step of calculating, from the calculated spectral reflectance, information regarding the number of extreme values of the spectral reflectance and the wavelength positional relationship of the extreme values within a predetermined wavelength range; a control step of controlling a formation condition related to a film thickness of the film based on a comparison between the calculated information and predetermined information related to the number of the extremums and the wavelength positional relationship of the extremums; Equipped with A method for manufacturing a film, wherein information regarding the film thickness and information regarding the number of extrema and the wavelength positional relationship of the extrema are associated in advance.

2. The information regarding the wavelength positional relationship of the extrema includes at least information regarding the order of the extrema, out of information regarding the order of the extrema and information regarding the distances between the extrema. A method for producing the membrane of claim 1.

3. The predetermined information regarding the number of extreme values and the wavelength positional relationship of the extreme values is The information includes a plurality of pieces of information relating to the number of the extrema and the wavelength positional relationship of the extrema, Information regarding the number of the plurality of extrema and the wavelength positional relationship of the extrema is arranged in order of thickness by estimating the thickness of the film from a film interference theory. A method for producing the membrane of claim 1.

4. The predetermined information regarding the number of extreme values and the wavelength positional relationship of the extreme values is It is pre-related to the formation conditions to be controlled, A method for producing the membrane of claim 1.

5. The formation conditions to be controlled are: one or more, and Formation conditions in a process before the spectral reflectance calculation step and / or formation conditions in a process after the information calculation step; The method for producing a film according to any one of claims 1 to 4, wherein

6. A method for manufacturing an object, comprising a film formation step of forming a film on a surface of the object by the film manufacturing method according to any one of claims 1 to 4.

7. A method for manufacturing an object, comprising a film formation step of forming a film on the surface of the object by the film manufacturing method described in claim 5.

8. An annealing process is provided to form an oxide film on the surface of the steel sheet. The annealing step includes: a spectral reflectance calculation step of calculating a spectral reflectance from reflected light obtained by light being reflected by the formed oxide film; an information calculation step of calculating, from the calculated spectral reflectance, information regarding the number of extreme values of the spectral reflectance and the wavelength positional relationship of the extreme values within a predetermined wavelength range; a control step of controlling a formation condition related to a thickness of the oxide film based on a comparison between the calculated information and predetermined information related to the number of the extrema and the wavelength positional relationship of the extrema; Including, A method for manufacturing an oxide film, wherein information regarding the thickness of the oxide film and information regarding the number of extrema and the wavelength positional relationship of the extrema are associated in advance.

9. A method for producing a plated steel product having a plating film on the surface of the plated steel product, comprising: an annealing step of forming an oxide film on the surface of the plated steel material and reducing the formed oxide film; a plating step of forming the plating film on the steel material to be plated after the annealing step; Equipped with The annealing step includes: a spectral reflectance calculation step of calculating a spectral reflectance from reflected light obtained by light being reflected by the oxide film formed on the surface of the steel material to be plated; an information calculation step of calculating, from the calculated spectral reflectance, information regarding the number of extreme values of the spectral reflectance and the wavelength positional relationship of the extreme values within a predetermined wavelength range; a control step of controlling a formation condition related to the thickness of the oxide film in a process before the spectral reflectance calculation step and / or controlling a reduction condition related to the thickness of the oxide film in a process after the information calculation step, based on a comparison between the calculated information and predetermined information related to the number of the extreme values and the wavelength positional relationship of the extreme values; Including, A method for manufacturing a plated steel product, wherein information about the thickness of the oxide film and information about the number of extrema and the wavelength positional relationship of the extrema are associated in advance.

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