JP2021113765A - Method for estimating average film thickness of oxide film - Google Patents

Abstract

To provide a method for estimating an average film thickness of an oxide film more easily and more accurately by removing influence of background radiation from a radiation rate.SOLUTION: The present invention relates to a method for estimating an average film thickness of an oxide film formed on a steel plate during oxide processing, the method including the steps of: calculating an apparent radiation rate from temperatures measured by a plate thermometer and a radiation temperature meter for measuring the temperature of the surface of a steel plate and by a cooling plate for preventing background radiation; correcting the apparent radiation rate; and estimating the average film thickness of the oxide film from the radiation rate after the correction step.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for estimating the average film thickness of an oxide film.

As high-strength steel sheets used for automobile bodies and the like, surface-treated steel sheets having rust-preventive properties, among them, hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets having excellent rust preventive properties are known. As the hot-dip galvanized steel sheet, a strip-shaped steel sheet obtained by hot-rolling and cold-rolling a slab is generally used as a base steel sheet, and this base steel sheet is recrystallized and annealed in a reducing furnace in a reducing atmosphere, and then recrystallized. Manufactured by hot dip galvanizing.

In such a high-strength steel plate, it is effective to add Si, Mn, etc. in order to increase the strength. However, when the steel sheet contains Si or Mn, oxidation proceeds even in a reducing atmosphere containing reducing hydrogen gas in which iron does not oxidize, and an oxide of Si or Mn is formed on the surface of the steel sheet. Since the wettability between the hot-dip zinc and the steel sheet is lowered by this oxide during the plating treatment, the plating adhesion is likely to be lowered when the base steel sheet to which Si, Mn or the like is added is used.

As a method for improving the plating adhesion of the base steel sheet to which Si, Mn, etc. are added, a manufacturing method by a redox method using an annealing furnace having an oxidation zone and a reduction zone has been put into practical use. In this manufacturing method, an iron oxide film is formed on the surface of the steel sheet, and the oxide film is reduced in a reducing atmosphere containing hydrogen, and then plating treatment is performed.

In this redox method, the average film thickness of the oxide film is important in order to ensure the plating adhesion. If the oxide film is too thin, the oxides of Si and Mn are not sufficiently covered by the oxide film, and the amount of iron reduced from the oxide film is insufficient, so that the oxides of Si and Mn remain on the surface of the steel plate. It will be easier. On the other hand, if the average film thickness of the oxide film is too large, plating peeling is likely to occur. Therefore, it is necessary to properly control the average film thickness of the oxide film.

As a method for estimating the average film thickness of the oxide film, a method for estimating the average film thickness of the oxide film based on the relationship between the (spectral) emissivity and the average film thickness of the oxide film has been proposed (Japanese Patent Laid-Open No. 7-270130). See Gazette). In this conventional method for estimating the average film thickness of an oxide film, the spectral radiance is detected at a specific wavelength in the far infrared region where the emissivity changes according to the film thickness of the oxide film, and the emissivity at this specific wavelength is obtained. , The average film thickness of the oxide film is estimated from the relationship between the emissivity measured in advance and the average film thickness of the oxide film.

In this conventional estimation method, the relationship between the emissivity and the average film thickness of the oxide film changes due to background radiation, but this background radiation changes under the influence of the type of steel sheet, oxidation conditions, etc. Difficult to control.

Japanese Unexamined Patent Publication No. 7-270130

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a method for accurately and easily estimating the average film thickness of an oxide film by removing the influence of background radiation from the emissivity. ..

The invention made to solve the above problems is a method for estimating the average thickness of an oxide film formed on a steel plate during an oxidation treatment, which is a plate thermometer and a radiation thermometer for measuring the temperature of the surface of the steel plate, and a background. A step of calculating the apparent emissivity from the temperature measured by the plate thermometer and the radiation thermometer using a cooling plate that suppresses radiation, a step of correcting the apparent emissivity, and a step of correcting the apparent emissivity, and after the correction step. It is provided with a step of estimating the average film thickness of the oxide film from the emissivity of.

In the method for estimating the average film thickness of the oxide film, background radiation is first suppressed by using a cooling plate. Further, in the method for estimating the average film thickness of the oxide film, background radiation that cannot be suppressed even by using a cooling plate is removed by correcting the emissivity in the correction step, so that the oxide film can be accurately and easily suppressed. The average film thickness can be estimated.

ここで、εは補正後の放射率、ε’は上記見かけの放射率、ａは酸化処理条件により定まる定数である。 In the above correction step, the following formula (1) may be used for the correction. As described above, since the following formula (1) is used for the correction in the above correction step, the average film thickness of the oxide film can be estimated more easily.

Here, ε is the corrected emissivity, ε'is the apparent emissivity, and a is a constant determined by the oxidation treatment conditions.

It is advisable to use a plurality of radiation thermometers having different wavelengths. The sensitivity of the corrected emissivity to the average film thickness of the oxide film changes depending on the wavelength of the radiation thermometer. Therefore, by estimating the average film thickness using a wavelength having high sensitivity according to the average film thickness of the oxide film, it is possible to improve the estimation accuracy of the average film thickness of the oxide film.

As described above, by using the method for estimating the average thickness of the oxide film of the present invention, the influence of background radiation can be removed from the emissivity, and the average thickness of the oxide film can be estimated accurately and easily. ..

FIG. 1 is a flow chart showing a method for estimating the average film thickness of an oxide film according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an oxidation zone used in the method for estimating the average film thickness of the oxide film of FIG. FIG. 3 is a graph for explaining the relationship between the emissivity and the oxide film thickness. FIG. 4 is a schematic cross-sectional view showing the layout of the experimental apparatus used in the examples. FIG. 5 is a graph showing the relationship between the emissivity of the radiation thermometer used in the examples and the average film thickness of the oxide film. FIG. 6 is a graph showing the correlation of the emissivity with the reference value in the examples. FIG. 7 is a graph showing the correlation of the emissivity with the reference value in the comparative example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

The method for estimating the average thickness of the oxide film shown in FIG. 1 is a method for estimating the average thickness of the oxide film formed on the steel sheet during the oxidation treatment, and includes a calculation step S1, a correction step S2, and an estimation step S3. Be prepared.

<Oxidation furnace>
The method for estimating the average film thickness of the oxide film can be used to estimate the average film thickness of the oxide film produced in the oxidation zone 1 of the annealing furnace used in the redox method as shown in FIG. The oxide zone 1 has a roll 11, and the strip-shaped steel plate M charged from the oxide zone inlet 1a is fed by the roll 11 and sent out from the oxide zone outlet 1b.

The oxidation zone 1 has, for example, a direct flame burner 12, and the direct flame burner 12 oxidizes the surface of the steel sheet M to form an iron oxide film on the surface of the steel sheet M. By using the direct flame burner 12 in this way, the oxygen concentration can be adjusted by controlling the air ratio, and the film thickness of the oxide film can be easily controlled. Further, since the heating rate of the steel sheet M can be increased, the furnace length of the oxide zone 1 can be shortened to save space in the heating furnace, or the feeding rate of the steel sheet M can be increased to improve the manufacturing efficiency. can.

The steel sheet M to be used in the method for estimating the average film thickness of the oxide film is preferably a base steel sheet to which Si, Mn, P, Al and the like are added. When improving the plating adhesion of a steel sheet to a base steel sheet to which these elements are added, the average film thickness of the oxide film is particularly important for ensuring the plating adhesion, and the average film thickness of the oxide film is particularly important. The thickness estimation method can be preferably used.

When Si is added to the steel sheet M, the lower limit of the Si content is preferably 0.3% by mass, more preferably 1.0% by mass. On the other hand, the upper limit of the Si content is preferably 3.0% by mass, more preferably 2.5% by mass. If the Si content is less than the above lower limit, other alloying elements are required in order to achieve both strength and workability, which may increase the manufacturing cost. On the contrary, when the Si content exceeds the above upper limit, the formation of the oxide film is suppressed, so that the plating adhesion may be lowered by the Si oxide.

Further, the steel sheet M may contain C, Cr, Ti, S and the like in addition to the above-mentioned Si, Mn and the like. The rest of the steel sheet M is iron and unavoidable impurities.

The lower limit of the average film thickness of the oxide film formed in the oxide zone 1 is preferably 0.1 μm, more preferably 0.3 μm. On the other hand, the upper limit of the average film thickness of the oxide film is preferably 1.1 μm, more preferably 0.8 μm. If the average film thickness of the oxide film is less than the above lower limit, the effect of improving the plating adhesion may be insufficient. On the contrary, when the average film thickness of the oxide film exceeds the above upper limit, the oxide film is unnecessarily thick, the reduction time in the reduction zone following the oxide zone 1 becomes long, and the production efficiency may be lowered.

As shown in FIG. 2, as a method for estimating the average film thickness of the oxide film, a plate thermometer 13 and a radiation thermometer 14 for measuring the temperature of the surface of the steel plate M and a cooling plate 15 for suppressing background radiation are used.

The plate thermometer 13 is a thermometer capable of directly measuring the temperature of the surface of the steel sheet M without being affected by the amount of radiation. As the plate thermometer 13, a known thermometer such as a thermocouple, a contact thermometer, or a roll multiple plate thermometer can be used.

The plate thermometer 13 may be arranged so as to measure the temperature of the steel plate M at a position within 1 m, more preferably within 0.5 m, from the measurement position of the radiation thermometer 14 described later. From the viewpoint of temperature consistency, the plate thermometer 13 preferably measures the same surface as the surface of the steel plate M measured by the radiation thermometer 14, but when it is difficult to arrange the plate thermometer 13, as shown in FIG. It is also possible to measure on the surface opposite to the surface of the steel plate M measured by the radiation thermometer 14.

The radiation thermometer 14 is a thermometer that measures the intensity of infrared rays or visible light emitted from an object and converts it into the temperature of the object. Specifically, the radiation thermometer 14 collects infrared rays emitted from an object with a lens, and converts the amount of light into temperature by a detection element. The detection element is warmed when it absorbs infrared rays, and generates an electric signal according to the warmed temperature. Alternatively, as the detection element, an element that outputs an output due to the photoelectric effect due to light energy can also be used.

As shown in FIG. 2, the radiation thermometer 14 is composed of, for example, a thermometer main body 14a and a measuring cylinder 14b. One end side of the measuring cylinder 14b is located inside the oxide zone 1, and the other end side is located outside the oxide zone 1. Further, the measuring cylinder 14b is arranged so that at least one end side thereof is surrounded by the cooling plate 15. The radiation thermometer main body 14a is arranged on the other end side of the measuring cylinder 14b, that is, outside the oxide zone 1, and is configured so that the radiation thermometer 14 can measure the surface of the steel plate M via the measuring cylinder 14b.

The spot diameter (the diameter of the range that the radiation thermometer 14 collects) on the steel plate M surface of the radiation thermometer 14 is determined by the distance between the radiation thermometer 14 and the steel plate M surface and the measurement angle of the radiation thermometer 14. For example, it is 5 mm or more and 30 mm or less.

In the method for estimating the average film thickness of the oxide film, it is preferable to use a plurality of radiation thermometers 14 having different wavelengths. The sensitivity of the corrected emissivity to the average film thickness of the oxide film depends on the wavelength of the radiation thermometer 14. Therefore, by estimating the average film thickness using a wavelength having high sensitivity according to the average film thickness of the oxide film, it is possible to improve the estimation accuracy of the average film thickness of the oxide film.

When a plurality of radiation thermometers 14 are used, it is preferable to measure the same spot on the surface of the steel sheet M. Therefore, as the upper limit of the number of radiation thermometers 14 used, 5 is preferable, and 4 is more preferable. If the number of radiation thermometers 14 used exceeds the above upper limit, it may be difficult to arrange a plurality of radiation thermometers 14 so as to measure the same spot. On the contrary, as the lower limit of the number of radiation thermometers 14 used, two are preferable, and three are more preferable. If the number of radiation thermometers 14 used is less than the above lower limit, the effect of using a plurality of radiation thermometers 14 may be insufficient.

The wavelength of the radiation thermometer 14 is appropriately determined according to the average film thickness of the oxide film to be measured, and is selected from, for example, a range of 0.8 μm or more and 15 μm or less. When a plurality of radiation thermometers 14 are used, their wavelengths are determined so that the region where the corrected emissivity with respect to the average film thickness of the oxide film is highly sensitive is different in each radiation thermometer 14. The wavelength can be selected according to the type of the detection element of the radiation thermometer 14. For example, when three radiation thermometers 14 are used, for example, a Si detection element (wavelength: 1 μm), an InSb detection element (wavelength: 5 μm), and a thermopile detection element (wavelength: 11 μm) are used as each detection element. Can be done.

The cooling plate 15 is, for example, an annular shape, and is provided along the outer wall of the furnace so as to surround the radiation thermometer 14. As shown in FIG. 2, a part of the cooling plate 15 may be located in the furnace. The cooling plate 15 can suppress the background radiation entering the radiation thermometer 14. As the cooling plate 15, for example, a water cooling plate can be used.

When the cooling plate 15 is annular, the lower limit of the outer diameter of the cooling plate 15 is preferably 100 mm, more preferably 130 mm. On the other hand, the upper limit of the outer diameter of the cooling plate 15 is preferably 300 mm, more preferably 200 mm. If the outer diameter of the cooling plate 15 is less than the above lower limit, the effect of suppressing background radiation may be insufficient. On the contrary, if the outer diameter of the cooling plate 15 exceeds the above upper limit, the cooling plate 15 may become unnecessarily large in order to improve the effect of suppressing background radiation. The outer diameter of the cooling plate 15 is preferably increased as the distance from the surface of the steel plate M to the cooling plate 15 is larger, and the outer diameter of the cooling plate 15 is four times the distance from the surface of the steel plate M to the cooling plate 15. It should be 6 times or more and 6 times or less.

The lower limit of the separation distance (measurement distance) from the surface of the steel plate M to the cooling plate 15 is preferably 50 mm, more preferably 100 mm. On the other hand, as the upper limit of the measurement distance, 300 mm is preferable, and 200 mm is more preferable. If the measurement distance is less than the above lower limit, the cooling plate 15 may come into contact with the steel plate M and the steel plate M may be scratched. On the contrary, when the measurement distance exceeds the upper limit, the background radiation easily enters the measurement cylinder 14b of the radiation thermometer 14, so that the measurement accuracy of the radiation thermometer 14 may decrease.

<Calculation process>
In the calculation step S1, the apparent emissivity ε'is calculated from the temperatures measured by the plate thermometer 13 and the radiation thermometer 14.

The amount of infrared rays emitted from an object differs depending on the material and surface condition of the object even if the object has the same temperature. In the radiation thermometer 14, since the temperature of an object is measured from the amount of infrared rays emitted from the object, it is necessary to correct the ratio of this radiation depending on the object, and this ratio is called "emissivity". The emissivity takes a value in the range of 0 or more and 1 or less, and is 1 for an ideal blackbody, and 0 for an ideal blackbody that completely reflects or transmits infrared rays (for example, air).

On the other hand, since the plate thermometer 13 directly measures the temperature of an object, the emissivity is such that the measured temperature indicated by the radiation thermometer 14 in consideration of the emissivity is equal to the measured temperature indicated by the plate thermometer 13. By calculation, the emissivity of the object to be measured can be determined.

In the method for estimating the average thickness of the oxide film, the cooling plate 15 is used to suppress the background radiation entering the radiation thermometer 14, but this background radiation cannot be completely removed. The emissivity calculated as described above includes not the emissivity of the measurement object alone but the background radiation entering the radiation thermometer 14. That is, the emissivity calculated in this calculation step S1 is an "apparent emissivity ε'" having an error from the true value.

<Correction process>
In the correction step S2, the apparent emissivity ε'is corrected.

ここで、εは補正後の放射率、ε’は上記見かけの放射率、ａは酸化処理条件により定まる定数である。 In the correction step S2, the following equation (1) is used for correction. As described above, since the following formula (1) is used for the correction in the correction step S2, the average film thickness of the oxide film can be estimated more easily.

Here, ε is the corrected emissivity, ε'is the apparent emissivity, and a is a constant determined by the oxidation treatment conditions.

Hereinafter, the reason why the emissivity can be corrected by the above equation (1) will be described in detail.

ここで、Ｇ：射度、ε：放射率、Ｌ_ｂ：黒体放射エネルギー、Ｔ：温度、Ｃ：指向性放射率係数、Ｆ：形態係数を表す。また、添え字は、１：鋼板Ｍ、２：冷却板１５、３：背景放射面を指す。 In addition to the energy radiated from the measurement point (measurement spot) on the surface of the steel plate M to be measured, the radiation thermometer 14 receives the reflected energy from the surroundings (background radiation and the cooling plate 15). Therefore, when the radiation transmission calculation formula is established on the three surfaces of the measurement spot, the background radiation surface, and the cooling plate surface, the following formula (2) is obtained.

Here, G: Emissivity, ε: Emissivity, L _b : Blackbody radiation energy, T: Temperature, C: Directivity emissivity coefficient, F: View factor. The subscripts refer to 1: steel plate M, 2: cooling plate 15, 3: background radiation surface.

The background radiation surface is a virtual surface and can be set to _{ε 3 = 1.} Solving for G ₁ from this and the equation (2), the following equation (3) is obtained.

On the other hand, for the radiation thermometer 14, there is a relationship of _{G 1} = ε _m L _b (T _m ) using the _{emissivity ε m.} Further, since the cooling plate 15 is sufficiently large and can be approximated to F21≈0, the following equation (4) can be obtained by solving _{ε 1 from these and the above equation (3).} The subscript m refers to a radiation thermometer.

Here, the emissivity epsilon ₁ of the black body radiation thermometer 14 apparent to radiant energy in the case of not removing the background radiation 'is, epsilon _1' is represented by _{= L b (T m) /} L b (T 1) Therefore, multiplying ε 1'by the inverse number on the right side (L _b (T ₁ ) / L _b (T _m )) gives _1. By transforming the above equation (4) using this, the following (5) is obtained.

Further, by using the constant a defined by the following equation (6), it can be transformed as in the following equation (7).

The equation (7) ε _m ε _{1 'is} calculated by the calculating process S1 "emissivity apparent epsilon' represent ', epsilon ₁ is from represents the epsilon true emissivity of the steel sheet M, the above-mentioned formula ( The emissivity can be corrected in 1). The constant a can be obtained experimentally in advance. Specifically, the procedure is as follows. _{The apparent emissivity ε'(= ε m} ε ₁ ') obtained from the measurement results of the plate thermometer 13 and the radiation thermometer 14 is calculated. In addition, the average film thickness of the oxide film obtained from the measurement result is obtained. _{From the average film thickness of this oxide film, the true emissivity ε 1} is obtained from the relationship between the average film thickness and the emissivity of the oxide film analyzed in advance by another method, and the above equation (7) is established. a can be determined.

The value of a is determined depending on the oxidation treatment conditions such as the temperature of the steel plate M, the furnace temperature, and the layout of the measuring instruments (plate thermometer 13, radiation thermometer 14 and cooling plate 15). That is, if these oxidation treatment conditions are the same, the value of a can be diverted.

<Estimation process>
In the estimation step S3, the average film thickness of the oxide film is estimated from the emissivity after the correction step S2.

The emissivity ε calculated in the correction step S2 changes according to the average thickness of the oxide film, for example, as shown in FIG. Therefore, if the emissivity ε is known, the average film thickness of the oxide film can be estimated.

For example, in the case of the relationship shown in FIG. 3, the accuracy is high when measuring an oxide film having an average thickness of 0.2 μm or more and 0.8 μm or less, in which the change (sensitivity) of the emissivity ε with respect to the average thickness of the oxide film is large. This region of high accuracy differs depending on the wavelength of the radiation thermometer 14 even if the oxidation treatment conditions are the same. Therefore, when a plurality of radiation thermometers 14 having different wavelengths are used, the average film thickness of the oxide film in a wide range can be maintained by properly using the measurement results of the plurality of radiation thermometers 14 according to the high accuracy. Can be estimated accurately.

<Advantage>
In the method for estimating the average film thickness of the oxide film, background radiation is suppressed by first using the cooling plate 15. Further, in the method for estimating the average thickness of the oxide film, the background radiation that cannot be suppressed even by using the cooling plate 15 is removed by correcting the emissivity in the correction step S2, so that the oxidation is accurate and easy. The average film thickness can be estimated.

[Other Embodiments]
The present invention is not limited to the above embodiment.

In the above embodiment, the case of using the oxide film in the oxidation-reduction method has been described, but the method for estimating the average thickness of the oxide film of the present invention is not limited to this, and is formed on the steel plate by another method. It is also possible to estimate the average thickness of the oxide film.

In the above embodiment, the case where the above-mentioned formula (1) is used for the correction in the correction step has been described, but the correction can be performed by another calculation formula. For example, in the above equation (5), the directional emissivity coefficient C and the view factor F can be specified and corrected.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Example]
An experiment was conducted in which the steel sheet was oxidized and the average thickness of the oxide film was estimated from the change in the emissivity of the steel sheet. The layout of the apparatus used in the examples is shown in FIG. This experimental apparatus includes a cooling chamber 2 and a heating chamber 3 so that the steel plate M can move back and forth between the two chambers.

As the plate temperature gauge, a thermocouple (not shown) was welded to the steel plate M and used. As the radiation thermometer 14, three types of thermometers having different wavelengths were used. The wavelengths used were 1 μm (Si detection element), 5 μm (InSb detection element), and 11 μm (thermopile detection element). The spot diameter of the radiation thermometer 14 on the surface of the steel plate M was 10 mm, and the measurement distance of the radiation thermometer 14 from the surface of the steel plate M was 50 mm. The relationship between the emissivity of these three types of radiation thermometers 14 and the average film thickness of the oxide film is shown in FIG. Further, as the cooling plate 15, a water cooling plate (diameter 139.8 mm) was used. The view factors of this experimental device are shown in Table 1.

[Comparison example]
In the comparative example, the apparatus used in the example from which the cooling plate 15 was removed was used. The view factors of this experimental device are shown in Table 1.

[Experimental procedure]
The experiment was carried out according to the following procedure using the above-mentioned two experimental devices. First, the steel plate M to which the thermocouple was welded was installed in the cooling chamber 2. Next, the steel plate M was pulled up to the heating chamber 3 and heated by the direct flame burner 12. At this time, since the temperature of the steel plate M can be measured by the thermocouple (plate thermometer) and the radiation thermometer, the emissivity from the steel plate M can be estimated according to the flow shown in FIG.

After heating for a predetermined time, the steel plate M was pulled down to the cooling chamber 2 and cooled. After cooling, the steel sheet M was taken out and the average film thickness of the oxide film was analyzed. Using the emissivity determined from this average film thickness and the graph shown in FIG. 5 as a reference, the emissivity estimated during heating was compared. The average thickness of the oxide film is estimated in the oxide film by analyzing the oxygen concentration in the oxide film in the depth direction using a glow discharge emission analyzer (GDOES) in addition to the analysis by the cross-sectional SEM photograph. The thickness at which the oxygen concentration (for example, 10% by mass) was observed was specified by a method of determining the oxide film thickness.

This experiment was carried out using 6 steel plates M of the same type.

[result]
The results when the apparatus of the example is used are shown in FIG. Further, FIG. 7 shows the results when the apparatus of the comparative example was used. The straight lines shown in FIGS. 6 and 7 connect the points where the estimated emissivity and the reference value match.

From the results of FIG. 6, since the background radiation is removed by correcting the emissivity by the method of estimating the average film thickness of the oxide film using the cooling plate, the average film thickness of the oxide film can be estimated accurately. I understand. On the other hand, the result of FIG. 7 shows that the estimation accuracy of the average film thickness of the oxide film is low. It is considered that the background radiation is too large to remove the background radiation sufficiently because the cooling plate is not used.

By using the method for estimating the average thickness of the oxide film of the present invention, the influence of background radiation can be removed from the emissivity, and the average thickness of the oxide film can be estimated accurately and easily.

1 Oxidation zone 1a Inlet 1b Outlet 11 Roll 12 Direct fire burner 13 Plate thermometer 14 Radiation thermometer 14a Thermometer body 14b Measuring cylinder 15 Cooling plate 2 Cooling chamber 3 Heating chamber

Claims (3)

A method for estimating the average film thickness of an oxide film formed on a steel sheet during an oxidation treatment.
Using a plate thermometer and radiation thermometer that measure the temperature of the surface of the steel plate, and a cooling plate that suppresses background radiation,
The process of calculating the apparent emissivity from the temperature measured by the plate thermometer and the radiation thermometer, and
The process of correcting the apparent emissivity and
A method for estimating the average film thickness of an oxide film, which comprises a step of estimating the average film thickness of the oxide film from the emissivity after the above correction step. The method for estimating the average film thickness of an oxide film according to claim 1, wherein the following formula (1) is used for correction in the correction step.

Here, ε is the corrected emissivity, ε'is the apparent emissivity, and a is a constant determined by the oxidation treatment conditions. The method for estimating the average film thickness of an oxide film according to claim 1 or 2, wherein a plurality of radiation thermometers having different wavelengths are used.

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