Molten steel temperature measuring method and molten steel temperature measuring device

Abstract

To provide a molten steel temperature measuring method for measuring a temperature of molten steel that can measure the temperature of molten steel in response to disturbances such as fluctuations in an atmosphere in a vacuum tank or a liquid level of the molten steel.SOLUTION: A molten steel temperature measuring method for measuring a temperature of molten steel in a vacuum chamber in which molten steel is refined under reduced pressure, includes: an imaging step of imaging a surface of the molten steel in the vacuum chamber to generate image data; a luminance information acquisition step of acquiring luminance information from the image data; an operation parameter acquisition step of acquiring operation parameters of refining; a correction step of correcting brightness information to post-correction brightness information using the operation parameters; and a calculation step of calculating a molten steel temperature using the post-correction brightness information.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and device for measuring the temperature of molten steel. [Background technology]

[0002] In secondary refining facilities, which are the final process of steel refining, conventionally, the temperature of molten steel is measured by immersing an immersion type temperature measuring probe equipped with a thermocouple in the molten steel in the ladle during the refining process. If the immersion type temperature measuring probe is immersed in the molten steel or slag for a long time, it will be severely eroded and damaged, so it cannot measure the molten steel temperature continuously. For this reason, the immersion type temperature measuring probe measures the molten steel temperature intermittently, and the molten steel temperature is adjusted by predicting the temperature change from the measurement results.

[0003] As described above, in the past, the temperature of molten steel was measured discontinuously, so that when a phenomenon accompanied by a large drop in temperature occurred, such as when a metal that had been adhering to the inside of a vacuum tank fell into the molten steel, it was difficult to detect the temperature drop early and take action. If the detection of a temperature drop is delayed, the amount of oxygen required to heat the molten steel increases, so the processing time becomes longer. As a result, the supply of molten steel to the continuous casting machine cannot keep up, and continuous casting may be interrupted, which may cause a major operational problem.

[0004] Therefore, techniques for continuously measuring the temperature of molten iron such as molten steel have been proposed. For example, Patent Document 1 discloses a technique for continuously measuring the temperature of molten iron by immersing a ceramic-coated continuous thermometer or immersion thermocouple into the molten iron in a cylindrical furnace through a measurement hole penetrating the side wall of the furnace. Patent Document 2 discloses a technique for continuously measuring the temperature of molten steel by penetrating the side wall of a refining vessel and immersing a temperature measuring element made of a thermocouple covered with a cermet protective tube into the molten steel.

[0005] However, in the above-mentioned technology of measuring temperature by immersing a temperature sensor with a thermocouple inside in molten steel, it is necessary to use expensive refractories to prevent wear of the protective tube caused by slag and molten steel. Even if the refractory performance is improved, wear of the protective tube is not completely eliminated, and the temperature sensor will eventually need to be replaced due to the wear of the protective tube, which raises the problem of increased refining costs.

[0006] For these reasons, technologies capable of measuring the temperature of molten steel without contacting the molten steel have also been developed. Patent Document 3 discloses a technology for continuously measuring the temperature of molten steel circulating inside the vacuum chamber of an RH vacuum degassing apparatus using a radiation thermometer installed on the side wall of the vacuum chamber. Patent Document 4 discloses a technology for measuring the temperature of molten steel using a two-color thermometer, in which the wavelength used for temperature measurement by the two-color thermometer is changed depending on the maximum atmospheric pressure in the vacuum chamber. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 5-39516 [Patent Document 2] JP 2010-243171 A [Patent Document 3] JP 2018-109633 A [Patent Document 4] Patent Publication No. 2022-29570 Summary of the Invention [Problem to be solved by the invention]

[0008] In the techniques disclosed in Patent Documents 1 and 2, it is difficult to continuously measure the temperature of the molten steel circulating inside the vacuum tank due to wear of the protective tube as described above. In the technique disclosed in Patent Document 3, a radiation thermometer capable of non-contact temperature measurement is used, so that the temperature of the molten steel can be continuously measured. However, a radiation thermometer measures the temperature of an object using the intensity of infrared rays (wavelength: in the range of 0.7 to 400 μm) emitted from the object, and therefore has the problem that a large error occurs in the measured temperature value due to the influence of the object's emissivity.

[0009] In the technology disclosed in Patent Document 4, the accuracy of the temperature measurement value by the two-color thermometer decreases when the atmospheric pressure in the vacuum chamber exceeds a certain value, so the wavelength used for temperature measurement by the two-color thermometer is changed according to the maximum atmospheric pressure in the vacuum chamber. However, fluctuations in the liquid level of the molten steel in the vacuum chamber can cause the focusing lens of the radiation thermometer to go out of focus, which results in large fluctuations in the temperature measurement value, leaving room for improvement.

[0010] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method and device for measuring the temperature of molten steel that can measure the temperature of molten steel in response to disturbances such as fluctuations in the atmosphere inside a vacuum vessel or the level of the molten steel. [Means for solving the problem]

[0011] The means for solving the above problems are as follows. [1] A method for measuring the temperature of molten steel in a vacuum tank in which molten steel is refined under reduced pressure, comprising: an imaging step of imaging a surface of molten steel in the vacuum tank to generate image data; a luminance information acquisition step of acquiring luminance information from the image data; an operation parameter acquisition step of acquiring operation parameters for the refining; a correction step of correcting the luminance information to corrected luminance information using the operation parameters; and a calculation step of calculating the molten steel temperature using the corrected luminance information. [2] The method for measuring the temperature of molten steel according to [1], wherein in the imaging step, visible light in a wavelength range of 0.4 to 0.8 μm is received to generate image data. [3] The method for measuring molten steel temperature according to [1] or [2], wherein the atmospheric pressure in the vacuum chamber is 0.5 kPa or less. [4] The method for measuring molten steel temperature according to any one of [1] to [3], wherein in the operational parameter acquisition step, an atmospheric pressure in the vacuum chamber and a gas exhaust flow rate from within the vacuum chamber are acquired as the operational parameters. [5] The method for measuring the temperature of molten steel according to [4], wherein in the correction step, the luminance information is corrected to corrected luminance information using the atmospheric pressure and the gas exhaust flow rate. [6] A molten steel temperature measuring device that measures the temperature of molten steel in a vacuum tank in which molten steel is refined under reduced pressure, the molten steel temperature measuring device having an imaging unit that images a surface of molten steel in the vacuum tank and generates image data, a luminance information acquisition unit that acquires luminance information from the image data, an operation parameter acquisition unit that acquires operation parameters for the refining, a correction unit that corrects the luminance information to corrected luminance information using the operation parameters, and a calculation unit that calculates the molten steel temperature using the corrected luminance information. [7] The molten steel temperature measuring device according to [6], wherein the imaging unit receives visible light in a wavelength range of 0.4 to 0.8 μm and generates image data. [8] The molten steel temperature measuring device according to [6] or [7], wherein the operational parameter acquisition unit acquires the atmospheric pressure in the vacuum chamber and the gas exhaust flow rate from within the vacuum chamber as the operational parameters. [9] The molten steel temperature measuring device according to [8], wherein the correction unit corrects the luminance information to corrected luminance information using an atmospheric pressure in the vacuum chamber and a gas exhaust flow rate from the vacuum chamber. Effect of the Invention

[0012] In the molten steel temperature measuring method and device according to the present invention, the luminance information of the molten steel surface is corrected using operational parameters to obtain corrected luminance information, and the molten steel temperature is calculated using the corrected luminance information. This makes it possible to measure the molten steel temperature in response to disturbances such as fluctuations in the atmosphere in the vacuum vessel and the level of the molten steel, and thus makes it possible to measure the molten steel temperature in the vacuum vessel with higher accuracy than ever before. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an RH vacuum degassing facility including a molten steel temperature measuring device according to this embodiment. [Diagram 2] FIG. 2 is a schematic diagram of the imaging section and its surroundings. [Diagram 3] FIG. 3 is a diagram illustrating a configuration example of a temperature analysis device. [Figure 4] FIG. 4 is a schematic diagram showing an image divided into a plurality of regions. [Diagram 5] FIG. 5 is a graph showing the relationship between the wavelength of the emitted light in the imaging section and the relative spectral luminance. [Figure 6] FIG. 6 is a graph showing the relationship between luminance information and blackbody temperature. [Figure 7] FIG. 7 is a diagram showing a flow of the method for measuring the temperature of molten steel according to this embodiment. [Figure 8] FIG. 8 is a graph showing the measurement results of the molten steel temperature in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be specifically described below through the embodiments of the present invention. The following embodiments are preferred examples of the present invention, and the present invention is not limited to these embodiments.

[0015] In the following embodiment, a molten steel temperature measuring method and a molten steel temperature measuring device according to the present embodiment will be described using an example in which the method and device are applied to an RH vacuum degassing device that is widely used as a refining facility for refining molten steel under reduced pressure. Fig. 1 is a cross-sectional schematic diagram showing an RH vacuum degassing facility 100 including a molten steel temperature measuring device according to the present embodiment.

[0016] The RH vacuum degassing facility 100 includes an RH vacuum degassing apparatus 10 and a molten steel temperature measuring device 12. The RH vacuum degassing apparatus 10 includes a ladle 14, a vacuum vessel 16, a top blowing lance 18, a duct 20, a vacuum exhaust device 22, a vacuum level measuring device 24, an exhaust gas flowmeter 26, and a process computer 28. The ladle 14 contains molten steel 30, the upper layer of which is covered with slag 32.

[0017] The vacuum vessel 16 is provided above the ladle 14. The vacuum vessel 16 is composed of an upper vessel 34 and a lower vessel 36. The upper vessel 34 is provided with a raw material inlet 38. An up-side immersion tube 40 and a down-side immersion tube 42 are provided below the lower vessel 36, and a reflux gas inlet tube 44 is provided on the up-side immersion tube 40. The top blowing lance 18 is a device for adding oxygen gas and flux to the molten steel 30 in the vacuum vessel 16 by blowing them, and is provided on the top of the vacuum vessel 16 so that it can move up and down inside the vacuum vessel 16. A duct 20 is connected to the inside of the vacuum vessel 16. The inside of the vacuum vessel 16 is depressurized by exhausting the gas inside with a vacuum exhaust device 22 connected via the duct 20.

[0018] In the RH vacuum degassing apparatus 10, the ladle 14 containing the molten steel 30 is raised by a lifting device (not shown) to immerse the up-side submerged pipe 40 and the down-side submerged pipe 42 in the molten steel 30 in the ladle 14. In this state, the inside of the vacuum vessel 16 is evacuated by the vacuum exhaust device 22 connected to the duct 20 to reduce the pressure inside the vacuum vessel 16, and reflux gas is blown into the up-side submerged pipe 40 from the reflux gas blowing pipe 44. When the pressure inside the vacuum vessel 16 is reduced, the molten steel 30 in the ladle 14 rises in proportion to the difference between the atmospheric pressure and the atmospheric pressure inside the vacuum vessel 16, and flows into the vacuum vessel 16. At the same time, due to the gas lift effect of the reflux gas blown from the reflux gas blowing pipe 44, the molten steel 30 in the ladle rises up the up-side submerged pipe 40 together with the reflux gas and flows into the vacuum vessel 16, and then a reflux is formed that returns to the ladle 14 via the down-side submerged pipe 42. The molten steel 30 is exposed to a reduced pressure atmosphere in the vacuum chamber 16, and due to the difference in equilibrium based on the pressure difference between atmospheric pressure and the reduced pressure ambient pressure, hydrogen and nitrogen in the molten steel 30 move to the atmosphere in the vacuum chamber 16, and dehydrogenation and denitrogenation reactions of the molten steel 30 proceed.

[0019] The vacuum exhaust device 22 includes a booster 46, an ejector 48, and a condenser 50, and controls the atmosphere inside the vacuum chamber 16. The ejector 48 ejects steam from a nozzle and exhausts it using a diffuser. The booster 46 is an ejector that operates on the high vacuum side, and is arranged in multiple stages to increase the degree of vacuum inside the vacuum chamber 16. The condenser 50 condenses the steam and removes dust. The water condensed in the condenser 50 is stored in a hot well (water tank). The vacuum exhaust device 22 is also connected to a dust separator, gas cooler, dust exhaust unit, etc., not shown.

[0020] A vacuum gauge 24 is provided between the vacuum exhaust device 22 and the vacuum chamber 16. The vacuum gauge 24 may be a Bourdon tube vacuum gauge, a liquid column differential vacuum gauge, a diaphragm vacuum gauge, a Pirani vacuum gauge, a thermocouple vacuum gauge, or a quartz friction vacuum gauge, which measure pressure. In this embodiment, the vacuum gauge 24 is, for example, an absolute pressure transmitter EJX310J manufactured by Yokogawa Electric Corporation.

[0021] In the absolute pressure transmitter, when pressure is applied to the diaphragm, the pressure receiving part deforms, and the oscillator in the pressure receiving part operates, thereby continuously measuring pressure. The absolute pressure transmitter converts the measured absolute pressure into an analog or digital current signal and outputs it. The vacuum gauge 24 outputs the continuously measured atmospheric pressure in the vacuum chamber 16 to the process computer 28. As the vacuum gauge 24, it is preferable to use a gauge that can measure pressures in the range from atmospheric pressure to about 0.1 kPa.

[0022] The exhaust gas flow meter 26 is connected to the vacuum exhaust device 22 and continuously measures the flow rate of the exhaust gas exhausted by the exhaust device from inside the vacuum chamber 16. The exhaust gas flow meter 26 outputs the continuously measured exhaust gas flow rate to the process computer 28.

[0023] The RH vacuum degassing apparatus 10 may further include an exhaust gas concentration meter, a gas analyzer, and / or a dew point meter. The exhaust gas concentration meter is connected to the vacuum exhaust apparatus 22 and measures the concentrations of exhaust gas components, such as the CO gas concentration, the CO2 gas concentration, and the O2 gas concentration, contained in the exhaust gas. The gas analyzer and the dew point meter are also connected to the vacuum exhaust apparatus 22 and measure or estimate the amount of water vapor contained in the exhaust gas. When the exhaust gas concentration meter, the gas analyzer, and / or the dew point meter are provided, the exhaust gas component concentrations and the amount of water vapor measured by these measuring devices are also output to the process computer 28.

[0024] The process computer 28 collects information obtained by various sensors provided in the RH vacuum degassing apparatus 10, and controls the operations of the top blowing lance 18, the vacuum exhaust device 22, and other components of the RH vacuum degassing apparatus 10 so that the molten steel 30 can be refined under set operating conditions. The process computer 28 is also connected to a temperature analysis device 52, which will be described later, and is configured so that the temperature analysis device 52 can obtain the operating data collected by the process computer 28.

[0025] The molten steel temperature measuring device 12 has an imaging unit 54 and a temperature analysis device 52. The imaging unit 54 images the surface of the molten steel 30 in the vacuum tank 16 through a monitoring hole 56 provided in the upper part of the vacuum tank 16 to generate image data. The image data generated by the imaging unit 54 is transmitted to the temperature analysis device 52 through a communication cable 58.

[0026] When the temperature analysis device 52 receives the image data from the imaging unit 54, it obtains luminance information from the image data. The temperature analysis device 52 also obtains refining operation parameters from the process computer 28, and corrects the luminance information using the operation parameters to obtain corrected luminance information. The temperature analysis device 52 calculates the molten steel temperature in the vacuum vessel 16 using the corrected luminance information. In this manner, the temperature analysis device 52 calculates the molten steel temperature in the RH vacuum degassing device 10.

[0027] Next, the imaging unit 54 will be described. Fig. 2 is a schematic diagram of the imaging unit 54 and its surroundings. The imaging unit 54 captures images of the surface of the molten steel 30 in the vacuum tank 16 through the monitoring hole 56 at predetermined intervals to generate image data. The imaging unit 54 sets the exposure time to, for example, 20 to 40 ms, and generates image data continuously at intervals according to the exposure time. The exposure time may be set appropriately within a time range in which the brightness value in the image data captured and generated by the imaging unit 54 does not become saturated. After generating the image data, the imaging unit 54 transmits the image data to the temperature analysis device 52.

[0028] It is preferable that the imaging unit 54 images the surface of the molten steel 30 in the vacuum tank 16 when the atmospheric pressure in the vacuum tank 16 is 0.5 kPa or less. If the atmospheric pressure in the vacuum tank 16 exceeds 0.5 kPa, scattering of the radiated light by the atmospheric gas and dust in the vacuum tank 16 increases, causing fluctuations in the brightness value of the image data captured and generated by the imaging unit 54, which reduces the measurement accuracy of the molten steel temperature, and this is not preferable. For this reason, imaging of the surface of the molten steel 30 by the imaging unit 54 may be started under the condition that the atmospheric pressure in the vacuum tank 16 is determined by the process computer 28 and the atmospheric pressure is 0.5 kPa or less.

[0029] Heat-resistant glass is provided in the observation hole 56 provided in the upper part of the vacuum chamber 16. The heat-resistant glass used is one that transmits radiation with a wavelength of 0.8 μm or less irradiated from inside the vacuum chamber 16. The material of the heat-resistant glass is, for example, borosilicate glass or quartz glass. Materials such as barium fluoride, calcium fluoride, zinc sulfide, zinc selenide, and germanium are used for the heat-resistant glass.

[0030] For example, borosilicate glass attenuates radiation with a wavelength exceeding 2 μm and blocks radiation with a wavelength of 3 μm or more. Quartz glass attenuates radiation with a wavelength exceeding 4 μm and blocks radiation with a wavelength of 5 μm or more. Heat-resistant glass such as barium fluoride, calcium fluoride, and zinc sulfide attenuates radiation with a wavelength of 10 μm or more. If such heat-resistant glass is provided in the monitoring hole 56, it is difficult to receive radiation from the surface of the molten steel 30 in the vacuum chamber 16 and measure the intensity of the radiation, even if a radiation thermometer that receives infrared rays is placed outside the vacuum chamber 16. For this reason, it is preferable to use a camera that can receive visible light in the wavelength range of 0.4 to 0.8 μm and generate image data for the imaging unit 54 of the molten steel temperature measuring device 12 according to this embodiment.

[0031] The monitoring hole 56 may be provided with a rotating plate 60. The rotating plate 60 has a notch in a part of a disk-shaped member, and is configured so that the rotating plate 60 rotates. The rotating plate 60 is provided to prevent scattered metal from adhering to the heat-resistant glass of the monitoring hole 56. In addition, the rotating plate 60 opens when the imaging unit 54 images the molten steel 30 in the vacuum chamber 16, and closes when the image is not being captured. This makes it possible to protect the imaging unit 54 from radiant heat from the molten steel 30.

[0032] The imaging unit 54 is only required to be able to capture radiation in the visible light wavelength band and to receive visible light with a wavelength of 0.4 to 0.8 μm. Therefore, a general-purpose digital camera can be used that can receive radiation in a wavelength range of 0.4 to 1.0 μm, which includes visible light in the wavelength range of 0.4 to 0.8 μm and partially includes the infrared wavelength range, and generate color image data. The imaging unit 54 is, for example, a digital camera having a commercially available CCD (Charge Coupled Devices) image sensor or CMOS (Complementary Metal Oxide Semiconductor) image sensor.

[0033] A monochrome digital camera that generates monochrome image data may be used as the imaging unit 54. In this case, the image captured by the CCD camera or CMOS camera has a brightness value (for example, 256 levels) specified for each pixel arranged two-dimensionally.

[0034] In this way, in the molten steel temperature measuring device 12 according to this embodiment, a camera capable of capturing visible light with a wavelength of 0.4 to 0.8 μm can be used as the imaging unit 54. Therefore, the molten steel temperature can be measured with a cheaper device configuration compared to a radiation thermometer such as infrared thermography that captures images using infrared rays.

[0035] Furthermore, when the surface of the molten steel 30 in the vacuum tank 16 is imaged from outside the vacuum tank 16, the heat-resistant glass provided in the monitoring hole 56 may block wavelengths in the infrared region, and in this case, the measurement error of the molten steel temperature will be large when using thermography with an infrared camera. In contrast, the heat-resistant glass provided in the monitoring hole 56 transmits visible light in the wavelength region of 0.4 to 0.8 μm, so that there is an effect that no disturbance is caused to the image acquired through the heat-resistant glass provided in the monitoring hole 56. Furthermore, the monitoring hole 56 may be equipped with a monitoring camera (ITV) that monitors the state of the molten steel in the vacuum tank 16, and by making the monitoring camera function as the imaging unit 54, it becomes possible to measure the temperature of the molten steel in the vacuum tank 16 without providing an additional camera.

[0036] Next, the temperature analysis device 52 will be described. Fig. 3 is a diagram showing a schematic configuration example of the temperature analysis device 52. The temperature analysis device 52 is, for example, a general-purpose computer such as a workstation or a personal computer. The temperature analysis device 52 has a control unit 62, an input unit 64, an output unit 66, and a storage unit 68.

[0037] The control unit 62 is, for example, a CPU, and executes various programs stored in the storage unit 68 to cause the control unit 62 to function as a luminance information acquisition unit 70, an operation parameter acquisition unit 72, a correction unit 74, and a calculation unit 76. The input unit 64 is, for example, a keyboard, a touch panel integrally provided with a display, or the like. The output unit 66 is, for example, an LCD or CRT display, or the like. The storage unit 68 is, for example, an information recording medium such as an updatable flash memory, a built-in hard disk or a hard disk connected via a data communication terminal, or a memory card, and a read / write device for the information recording medium. The storage unit 68 stores programs and data used to measure the molten steel temperature. The storage unit 68 also stores a formula for correcting the luminance information to corrected luminance information and a formula for calculating the molten steel temperature from the corrected luminance information.

[0038] Next, a description will be given of the processes executed by the luminance information acquisition unit 70, the operation parameter acquisition unit 72, the correction unit 74, and the calculation unit 76. Upon receiving the image data generated by the imaging unit 54, the luminance information acquisition unit 70 performs a luminance information acquisition step and acquires luminance information from the image data. Here, the luminance information acquired by the luminance information acquisition unit 70 is a luminance value representative of the molten steel temperature in the vacuum tank 16 extracted from the image data.

[0039] In the image data, a luminance value is specified for each pixel arranged two-dimensionally, and in this embodiment, the luminance value of each coordinate (x, y) is represented as "luminance I(x, y)." In the luminance information acquisition step, the luminance information acquisition unit 70 acquires, for example, the maximum value of the luminance I(x, y) of the image data as the luminance information.

[0040] Slag and oxides are present on the surface of the molten steel 30 in the vacuum tank 16. Therefore, at positions on the surface of the molten steel 30 where slag or oxides are present, the intensity of the emitted light is reduced due to the influence of the slag or oxides, and the luminance I(x, y) becomes small. Therefore, by using the maximum value of the luminance I(x, y) of the image data, it becomes possible to acquire luminance information related to the temperature of the molten steel 30 which is less influenced by the slag or oxides. However, instead of being limited to the maximum value of the luminance I(x, y) in the acquired image data, the luminance information acquisition unit 70 may acquire, as the luminance information, the average value of the 5th to 10th largest luminance I(x, y) in the image data.

[0041] FIG. 4 is a schematic diagram showing an image divided into a plurality of regions. The luminance information acquisition unit 70 may divide the pixels in the image sensor into a plurality of regions like the image divided into a plurality of regions shown in FIG. 4, calculate the average value of the luminance I(x, y) for each region, and acquire the maximum value of these average values ​​as the luminance information. Furthermore, the luminance information acquisition unit 70 may generate a plurality of image data in a predetermined time, acquire the maximum value of the luminance I(x, y) for each of the plurality of image data, and acquire the average value of these maximum values ​​as the luminance information. By acquiring the average value of the maximum luminance in a plurality of consecutive image data (for example, 5 to 50 pieces) as the luminance information, the luminance information acquisition unit 70 can acquire luminance information with reduced measurement noise.

[0042] The operation parameter acquisition unit 72 executes an operation parameter acquisition step to acquire the refining operation parameters from the process computer 28. The refining operation parameters are operation conditions for setting and controlling the gas atmosphere in the vacuum chamber 16 in the RH vacuum degassing apparatus 10.

[0043] The brightness value of the image data captured and generated by the imaging unit 54 varies depending on the amount of atmospheric gas and dust generated in the vacuum chamber 16 at the time of capturing the image. In addition, the surface condition of the molten steel 30 changes depending on the refining operation conditions. This change in the surface condition causes the intensity of the light emitted from the surface of the molten steel 30 to vary, and therefore the brightness value of the image data also varies. Therefore, the operation parameter acquisition unit 72 acquires the refining operation parameters in order to correct the brightness information so as to reduce the influence of the atmospheric gas, dust, and surface condition of the molten steel 30. This makes it possible to reduce the influence of the atmospheric gas, dust, and surface condition of the molten steel 30 contained in the brightness information, thereby improving the measurement accuracy of the temperature of the molten steel 30.

[0044] As the refining operation parameters, it is preferable to use operation parameters related to the gas atmosphere in the vacuum tank 16. As the operation parameters related to the gas atmosphere in the vacuum tank 16, it is preferable to use one or more parameters selected from, for example, the atmospheric pressure in the vacuum tank 16, the flow rate of exhaust gas exhausted from the vacuum tank 16 by the exhaust device, the CO gas concentration contained in the exhaust gas, the CO2 gas concentration contained in the exhaust gas, the O2 gas concentration contained in the exhaust gas, and the amount of water vapor in the vacuum tank 16. By correcting using these parameters of the vacuum exhaust device 22 as the refining operation parameters, it is possible to reduce the influence of disturbance due to the atmospheric gas in the vacuum tank 16 until the radiation from the surface of the molten steel 30 reaches the imaging unit 54.

[0045] In addition to the operational parameters of the vacuum exhaust device 22, the flow rates of the reflux gas (Ar flow rate, N2 flow rate) blown from the reflux gas blowing pipe 44 into the interior of the upflow side immersion tube 40 may be used as operational parameters related to the gas atmosphere in the vacuum chamber 16. This is because the surface of the molten steel 30 fluctuates depending on the reflux gas flow rate, and this fluctuation causes a fluctuation in the intensity of the radiated light from the surface of the molten steel 30. For this reason, the operational parameter acquisition unit 72 may acquire the flow rates of the reflux gas (Ar flow rate, N2 flow rate) for the purpose of correcting this fluctuation.

[0046] Furthermore, the furnace idle time before refining the molten steel 30 under reduced pressure, the processing time of the previous charge, the cumulative amount of molten iron processed, etc. may be used as the refining operation parameters. These values ​​affect the temperature of the refractory material constituting the vacuum vessel 16, and the temperature of the refractory material affects the brightness of the image data generated by the imaging unit 54. In order to reduce this effect, the operation parameter acquisition unit 72 may acquire the furnace idle time before refining, the processing time of the previous charge, and the cumulative amount of molten iron processed.

[0047] In this embodiment, the operation parameter acquisition unit 72 acquires, as refining operation parameters, the atmospheric pressure in the vacuum tank 16 when the surface of the molten steel 30 is imaged by the imaging unit 54 and the flow rate of exhaust gas exhausted from the vacuum tank 16 by the vacuum exhaust device 22. Since these operation parameters have a significant effect on the brightness value of the image data generated by the imaging unit 54, the measurement accuracy of the temperature of the molten steel 30 is greatly improved by correcting the brightness information using the atmospheric pressure in the vacuum tank 16 and the flow rate of exhaust gas exhausted from the vacuum tank 16.

[0048] The correction unit 74 executes the correction step to correct the luminance information to the corrected luminance information using the operation parameters acquired in the operation parameter acquisition step. The correction unit 74 may correct the luminance information to the corrected luminance information, for example, using the operation parameter p and the following formula (1) and formula (3) described later.

[0049] Irm = Ir + ΔIr(p) (1) In the above formula (1), Irm is the corrected luminance information (au), Ir is the luminance information (au), and ΔIr(p) is a correction term (au) that corrects the luminance information Ir using the operational parameter p. By calculating the corrected luminance information Irm in this manner, the influence of the gas atmosphere in the vacuum chamber 16 on the luminance information Ir is reduced, and this makes it possible to measure the luminance of the synchrotron radiation emitted from the surface of the molten steel 30 with high accuracy.

[0050] The correction term ΔIr(p) used in the above formula (1) is a correction term expressed as a function of the operation parameter p. The correction term ΔIr(p) is a correction term that corrects the influence of the operation parameter p on the luminance information Ir. For example, if the ambient pressure y1 in the vacuum chamber 16 and the exhaust gas flow rate y2 exhausted from the vacuum chamber 16 are acquired as the operation parameter p, the parameters of a multiple regression equation (linear regression equation) in which the luminance information Ir acquired in the luminance information acquisition step is used as the objective variable and the ambient pressure y1 in the vacuum chamber 16 and the exhaust gas flow rate y2 exhausted from the vacuum chamber 16 are used as explanatory variables are specified. The parameters k1 and k2 of the multiple regression equation are luminance correction parameters that indicate the influence of the ambient pressure y1 and the exhaust gas flow rate y2 on the luminance information Ir. The linear regression equation for the luminance information Ir can be expressed by the following formula (2).

[0051] Ir = k1 × y1 + k2 × y2 + k3 (2) In the above formula (2), Ir is the luminance information (au), y1 is the atmospheric pressure (kPa), y2 is the exhaust gas flow rate (kg / h), k1 and k2 are luminance correction parameters determined by multiple regression analysis, and k3 is a constant (au) determined by multiple regression analysis.

[0052] The correction term ΔIr(p) can be expressed by the following equation (3) using luminance correction parameters k1 and k2. ΔIr(p)=-k1×y1-k2×y2 (3) It should be noted that the constant k3 is included in the luminance information Ir acquired in the luminance information acquisition step in the above equation (1), and is therefore not included in the above equation (3) expressing the correction term ΔIr(p).

[0053] Regarding the operation parameter p used in the multiple regression analysis, a large number of refining operation parameters are acquired from the process computer 28, and the operation parameter p having a large luminance correction parameter identified by the multiple regression analysis and a large influence on the luminance information Ir is identified in advance. Then, the above formulas (3) and (1) including the luminance correction parameters k1 and k2 for the operation parameter p identified by the multiple regression analysis are stored in the storage unit 68 in advance.

[0054] When the correction unit 74 acquires the operation parameter p, it reads out the above formula (3) including the luminance correction parameters k1, k2 from the storage unit 68, and calculates the correction term ΔIr(p) using the above formula (3) and the operation parameter p. When the correction unit 74 calculates the correction term ΔIr(p), it reads out the above formula (1) from the storage unit 68, and calculates the corrected luminance information Irm using the above formula (1), the correction term ΔIr(p), and the luminance information Ir. In this way, the correction unit 74 corrects the luminance information Ir to the corrected luminance information Irm.

[0055] According to the inventors' study, for the luminance information Ir specified from the image data generated by the imaging unit 54, the atmospheric pressure y1 in the vacuum chamber 16 and the exhaust gas flow rate y2 exhausted from the vacuum chamber 16 are operational parameters that have large luminance correction parameters and have a large influence on the luminance information Ir. For this reason, it is preferable that the operational parameters p acquired by the operational parameter acquisition unit 72 include the atmospheric pressure in the vacuum chamber 16 and the gas exhaust flow rate for exhausting the atmospheric gas from the vacuum chamber 16.

[0056] The luminance information Ir used in the multiple regression analysis is acquired as time-series data using the imaging unit 54 and the luminance information acquisition unit 70, and stored in the storage unit 68. The number of acquired data used in the multiple regression analysis is preferably 20 to 10,000. If the number of acquired data is less than 20, the accuracy of the parameters of the regression equation may decrease, which is not preferable. Moreover, even if the number of acquired data exceeds 10,000, the accuracy of the parameters of the regression equation is hardly improved, and the load of data acquisition increases, which is not preferable.

[0057] The calculation unit 76 executes a calculation step and calculates the molten steel temperature using the corrected luminance information Irm. The luminance information Ir determined from the image data of the surface of the molten steel 30 in the vacuum tank 16 is correlated with the molten steel temperature. For this reason, a relational expression showing the correspondence between the corrected luminance information Irm and the molten steel temperature is determined in advance, and the corrected luminance information Irm is converted to the molten steel temperature using the relational expression. The relational expression showing the correspondence between the corrected luminance information Irm and the molten steel temperature is determined in advance and stored in the storage unit 68.

[0058] Incidentally, the luminance in the image data generated by the imaging unit 54 is information obtained by converting the radiation emitted from the surface of the molten steel 30 in accordance with the spectral sensitivity characteristics of the camera. Fig. 5 is a graph showing the relationship between the wavelength of the radiation light in the imaging unit 54 and the relative spectral luminance.

[0059] For example, when a CCD camera that captures a monochrome image with a sensitivity wavelength range of 0.4 to 1.0 μm receives radiation emitted from a black body at a temperature of 1600° C., the radiation is converted into a wavelength-spectral relative luminance spectrum shown in FIG. 5. The luminance of the image data captured and generated by the imaging unit 54 corresponds to the integral value (area shown in FIG. 5) of the spectral relative luminance in the sensitivity wavelength range. Therefore, the relationship between the luminance of the camera and the black body temperature can be specified by determining the wavelength-spectral relative luminance spectrum for each black body temperature according to the spectral sensitivity characteristics of the camera used. In addition, depending on the heat-resistant glass used for the monitoring hole 56, a part of the wavelength range of infrared rays exceeding 0.8 μm is attenuated. In this case, the wavelength-spectral relative luminance spectrum can be obtained by taking into account the attenuation by the monitoring hole 56.

[0060] Fig. 6 is a graph showing the relationship between luminance information and blackbody temperature. As shown in Fig. 6, when molten steel is refined under reduced pressure using the RH vacuum degassing apparatus 10, a linear relationship is established between the luminance value of image data captured and generated by the imaging unit 54 and the molten steel temperature, at least if the molten steel temperature is within a range of 1550°C to 1610°C. Furthermore, according to the inventors' studies, it was found that a roughly linear relationship is established between the luminance value of image data captured and generated by the imaging unit 54 and the molten steel temperature, at least within a range of 1550°C to 1750°C. Therefore, the molten steel temperature can be calculated using the corrected luminance information Irm and the following formula (4).

[0061] T = a × Irm + b (4) In the above formula (4), T is the molten steel temperature (°C), Irm is the corrected luminance information (au), and a and b are temperature conversion parameters determined based on the relationship between the luminance of the radiation light radiated from a black body and the temperature shown in FIG. 6.

[0062] In this embodiment, the above formula (4) including the temperature conversion parameters a and b is specified in advance and stored in the storage unit 68. This allows the calculation unit 76 to calculate the molten steel temperature T using the corrected luminance information Irm and the above formula (4). The calculation unit 76 may also cause the output unit 66 to display the calculated molten steel temperature T. In this manner, the molten steel temperature measuring device 12 according to this embodiment measures the molten steel temperature in the vacuum tank 16.

[0063] As another embodiment of the calculation step, the relationship between the corrected luminance information Irm and the molten steel temperature T may be estimated online. In the method in which the constants a and b used in the formula (4) are specified offline in advance as described above, a change in emissivity due to a fluctuation in the refining operation parameters becomes a disturbance, and the measurement accuracy of the molten steel temperature T may decrease.

[0064] In response to this, by specifying the relationship between the corrected luminance information Irm and the molten steel temperature T online, even if the refining operation parameters fluctuate, it is possible to suppress a decrease in the measurement accuracy of the molten steel temperature T. The relationship between the corrected luminance information Irm and the molten steel temperature T is assumed to be as shown in the following formula (5), similar to the above formula (4).

[0065] T = c × Irm + d (5) In the above formula (5), T is the molten steel temperature (°C), Irm is the corrected luminance information (au), and c and d are temperature conversion parameters that are determined online during operation of the RH vacuum degasser.

[0066] Specifically, when refining the molten steel 30 under reduced pressure (for example, the atmospheric pressure in the vacuum tank 16 is 0.5 kPa or less), batch temperature measurement may be performed using a lance equipped with a thermocouple. Therefore, the temperature conversion parameters c and d are determined online by multiple regression analysis so that the molten steel temperature obtained by the batch temperature measurement coincides with the molten steel temperature T calculated by equation (5).

[0067] In addition, in an operation using the RH vacuum degassing apparatus 10, the temperature of the refractory in the vacuum vessel 16 and the corrected luminance information Irm obtained by the treatment charge of the molten steel may fluctuate. For this reason, when multiple (two or more) batch temperature measurements are performed in the same treatment charge, the temperature conversion parameter c in the above formula (5) is determined from the ratio of the difference ΔTm between the molten steel temperatures Tm measured in the multiple batch temperature measurements and the difference ΔI between the corrected luminance information Irm obtained at the same timing. Then, at the timing of the first batch temperature measurement of the treatment charge in which the molten steel temperature is measured, it is preferable to determine the temperature conversion parameter d in the formula (5) using the molten steel temperature Tm measured in the batch temperature measurement, the corrected luminance information Irm obtained at the same timing, and the temperature conversion parameter c determined above. As a result, after the first batch temperature measurement is completed, the constants c and d in the formula (5) are determined, so that in the subsequent refining process, the molten steel temperature T can be continuously measured using the formula (5) determined online.

[0068] Fig. 7 is a diagram showing a flow of the method for measuring the temperature of molten steel according to this embodiment. The flow of the method for measuring the temperature of molten steel according to this embodiment will be described with reference to Fig. 7. The process shown in Fig. 7 is started, for example, when the temperature analysis device 52 is started and the input unit 64 receives an instruction from the operator to start measuring the temperature of molten steel.

[0069] The imaging unit 54 captures an image of the surface of the molten steel 30 in the vacuum chamber 16 and generates image data (step S101). The imaging unit 54 transmits the generated image data to the temperature analysis device 52. This step is the imaging step.

[0070] The luminance information acquisition unit 70 acquires luminance information Ir from the image data (step S102). The luminance information acquisition unit 70 acquires, for example, the maximum value of luminance included in the image data as the luminance information Ir. This step is a luminance information acquisition step. The luminance information acquisition unit 70 outputs the acquired luminance information to the correction unit 74.

[0071] The operation parameter acquisition unit 72 acquires refining operation parameters from the process computer 28 (step S103). The operation parameters acquired by the operation parameter acquisition unit 72 are operation parameters p that have a large influence on the luminance information Ir, for example, the atmospheric pressure in the vacuum chamber 16 and the flow rate of the exhaust gas exhausted by the vacuum exhaust device 22. This step is the operation parameter acquisition step. The operation parameter acquisition unit 72 outputs the acquired operation parameters p to the correction unit 74. Note that the operation parameter acquisition step may be performed before the luminance information acquisition step.

[0072] When the correction unit 74 acquires the luminance information Ir and the operation parameter p, it reads out the above formula (3) from the storage unit 68 and calculates the correction term ΔIr(p). Furthermore, after calculating ΔIr(p), the correction unit 74 reads out the above formula (1) from the storage unit 68 and corrects the luminance information Ir to corrected luminance information Irm using the formula (1) and the correction term ΔIr(p) (step S104). This step is the correction step. The correction unit 74 outputs the corrected luminance information Irm to the calculation unit 76.

[0073] When the calculation unit 76 acquires the corrected luminance information Irm, the calculation unit 76 reads out the above formula (4) from the storage unit 68 and calculates the molten steel temperature T (step S105). This step is the calculation step. The calculation unit 76 may cause the output unit 66 to display the calculated molten steel temperature T.

[0074] The calculation unit 76 determines whether or not an instruction to end the measurement of the molten steel temperature has been received from the operator (step S106). If the input unit 64 has not received an instruction to end the measurement of the molten steel temperature from the operator, the calculation unit 76 determines that the instruction to end the measurement has not been received (step S106: No), returns the process to step S101, and repeats the processes from step S101 to step S105 again. By repeating the processes from step S101 to step S105 in this manner, the molten steel temperature in the vacuum tank 16 can be continuously measured. The measurement period of the molten steel temperature is, for example, 0.1 to 10.0 seconds.

[0075] On the other hand, when the input unit 64 receives an instruction from the operator to end the measurement of the molten steel temperature, the calculation unit 76 determines that the instruction to end the measurement has been received (step S106: Yes), and ends the flow of the method for measuring the molten steel temperature shown in Fig. 7. In this way, the method for measuring the molten steel temperature according to this embodiment can continuously measure the temperature of the molten steel refined in the vacuum tank 16 in the refining process in which the molten steel is refined under reduced pressure.

[0076] According to the molten steel temperature measuring device and measuring method of the embodiment, image data of the surface of the molten steel 30 in the vacuum tank 16 is generated using a camera that receives visible light in a wavelength range of 0.4 to 0.8 μm and generates image data as the imaging unit 54, and luminance information representative of the molten steel temperature is obtained from the image data. This allows the use of an inexpensive camera, and even if heat-resistant glass such as borosilicate glass or quartz glass is used in the monitoring hole 56, attenuation of the radiated light due to the heat-resistant glass can be suppressed. Then, the influence of the state of the atmospheric gas in the vacuum tank 16 on the luminance information is corrected using the operation parameters, and the molten steel temperature in the vacuum tank is measured using the correlation between the luminance information and the temperature. This allows the molten steel temperature to be measured with high accuracy under reduced pressure, and in the refining process in which the molten steel is refined under reduced pressure, deviations in the molten steel temperature can be suppressed, thereby improving the production efficiency and yield of the refining equipment. EXAMPLES

[0077] Next, an embodiment in which the molten steel temperature in the vacuum tank 16 was continuously measured using the RH vacuum degassing equipment 100 shown in FIG. 1 will be described. In the embodiment, a monochrome CCD camera capable of receiving radiation in a wavelength range of 0.4 to 1.0 μm and generating monochrome image data was used as the imaging unit 54 that images the surface of the molten steel 30 in the vacuum tank 16 and generates image data. In the imaging step using the monochrome CCD camera, the surface of the molten steel 30 was imaged with an exposure time of 40 ms to generate 25 pieces of image data per second. In the luminance information acquisition step, the maximum luminance value identified from each image data was identified, and the average value of the 25 luminance values ​​was taken as the luminance information Ir. In this way, in the luminance information acquisition step, the luminance information Ir was acquired every second.

[0078] In the operation parameter acquisition step in the embodiment, the atmospheric pressure P (kPa) in the vacuum chamber 16 and the gas exhaust flow rate V (kg / h) for exhausting the atmospheric gas from the vacuum chamber 16 were acquired from the process computer 28 as the operation parameters of the refining. The atmospheric pressure P in the vacuum chamber 16 was measured using the vacuum level measuring instrument 24 and collected by the process computer 28. The operation parameter acquisition unit 72 acquired the actual value of the atmospheric pressure in the vacuum chamber 16 from the process computer 28. In addition, the gas exhaust flow rate of the atmospheric gas exhausted from the vacuum chamber 16 was measured using the exhaust gas flow meter 26 and collected by the process computer 28. The operation parameter acquisition unit 72 acquired the actual value of the exhaust gas flow rate from the process computer 28.

[0079] On the other hand, prior to the continuous measurement of the molten steel temperature in the embodiment, luminance correction parameters k1, k2 that the operational parameters, atmospheric pressure P and exhaust gas flow rate V, give to the luminance information Ir acquired in the luminance information acquisition step were specified in advance. Here, the luminance correction parameters k1, k2 of the atmospheric pressure P and exhaust gas flow rate V with respect to the luminance information Ir were specified by performing multiple regression analysis with the luminance information Ir acquired in the luminance information acquisition step as the objective variable and the atmospheric pressure P and exhaust gas flow rate V as explanatory variables. The luminance correction parameters were k1=-0.8 (1 / Pa) and k2=-0.2 (h / g).

[0080] Next, equation (5) was assumed as the conversion equation (calibration curve) to be used in the calculation step, and temperature conversion parameters c and d were specified. Specifically, batch temperature measurement using a lance equipped with a thermocouple was carried out two or more times in the same processing charge under reduced pressure conditions where the atmospheric pressure in the vacuum chamber 16 was 0.5 kPa or less, and actual data was obtained. Using this actual data, the temperature conversion parameter c in equation (5) above was specified from the ratio of the difference ΔTm in the molten steel temperature Tm measured in multiple batch temperature measurements to the difference ΔI in the corrected luminance information Irm obtained at the same timing. The temperature conversion parameter c was 0.065(m 2The temperature conversion parameter d was determined using the same performance data and a temperature conversion parameter c = 0.065. The temperature conversion parameter d was 1685 (K).

[0081] Using the brightness correction parameters and temperature conversion parameters thus specified, the temperature of molten steel in a vacuum tank in a refining facility that refines molten steel under reduced pressure was measured. Fig. 8 is a graph showing the measurement results of the molten steel temperature in the example. In Fig. 8, the horizontal axis represents the processing time (s) and the vertical axis represents the molten steel temperature (°C).

[0082] The solid line in Fig. 8 represents the molten steel temperature calculated by correcting the luminance information to corrected luminance information using the luminance correction parameter, and then using the above formula (5) including the corrected luminance information and the temperature conversion parameter. On the other hand, the dotted line in Fig. 8 represents the molten steel temperature calculated by using the above formula (5) without carrying out the correction step and using the luminance information as it is. Also, the circles in Fig. 8 represent the time and molten steel temperature measured in batches using a lance equipped with a thermocouple.

[0083] As shown in Fig. 8, the correction step is performed to correct the luminance information to corrected luminance information, and the corrected temperature calculated using the corrected luminance information shows significantly smaller fluctuations in the molten steel temperature than the pre-correction temperature calculated using the luminance information alone. This result confirms that correcting the luminance information to corrected luminance information makes it possible to deal with disturbances due to fluctuations in the atmosphere in the vacuum tank 16 and the liquid level of the molten steel 30, thereby making it possible to reduce fluctuations in the molten steel temperature. In addition, the corrected temperature matches the molten steel temperature measured in batches, confirming that the molten steel temperature in the vacuum tank 16 can be measured with high accuracy.

[0084] Since the molten steel temperature can be measured with such high accuracy, the molten steel temperature can be continuously monitored by continuous measurement, and even if the molten steel temperature suddenly drops significantly during the degassing process of the molten steel, the drop can be detected early and dealt with. In this embodiment, the molten steel temperature was also continuously monitored, and it was confirmed that the molten steel temperature gradually dropped from 1674°C to 1658°C, and the molten steel temperature could be controlled so that it was within the range of 1655 to 1665°C, which is the target end point temperature of the molten steel set in advance as an operating condition, and a stable refining process was realized.

[0085] On the other hand, when the molten steel temperature was measured by executing the calculation step using the brightness information and the above formula (5) without applying the correction step, the fluctuation of the molten steel temperature became very large. This is considered to be because the influence of disturbances corresponding to the state of the gas atmosphere in the vacuum tank 16, which is included in the brightness of the image data, could not be eliminated, and this resulted in the large fluctuation of the molten steel temperature. When the fluctuation of the molten steel temperature is so large, the molten steel temperature cannot be controlled to the end point target temperature of the molten steel, which is set in advance as an operating condition based on the molten steel temperature, and therefore a stable refining process cannot be realized. [Explanation of symbols]

[0086] 10 RH vacuum degasser 12. Molten steel temperature measuring device 14 Ladle 16 Vacuum chamber 18 Top blowing lance 20 Duct 22 Vacuum exhaust device 24 Vacuum measuring device 26 Exhaust gas flow meter 28 Process Computer 30 Molten Steel 32 Slug 34 Upper tank 36 Lower tank 38 Raw material input port 40 Upward side immersion tube 42 Descending dip tube 44 Circulation gas inlet pipe 46 Booster 48 Ejector 50 Capacitor 52 Temperature analysis device 54 Imaging unit 56 Monitoring hole 58 Communication Cable 60 Rotating Plate 62 Control section 64 Input section 66 Output section 68 Storage area 70 Luminance information acquisition section 72 Operational Parameter Acquisition Section 74 Correction section 76 Calculation section 100 RH vacuum degassing equipment

Claims

1. A method for measuring a molten steel temperature in a vacuum vessel in which molten steel is refined under reduced pressure, comprising the steps of: an imaging step of imaging a surface of molten steel in the vacuum chamber to generate image data; a luminance information acquisition step of acquiring luminance information from the image data; An operation parameter acquisition step of acquiring operation parameters of the refining; a correction step of correcting the luminance information to corrected luminance information using the operation parameters; a calculation step of calculating a molten steel temperature using the corrected luminance information; A method for measuring the temperature of molten steel, comprising:

2. The method for measuring the temperature of molten steel according to claim 1, wherein in the imaging step, visible light in a wavelength range of 0.4 to 0.8 μm is received to generate image data.

3. 3. The method for measuring the temperature of molten steel according to claim 1, wherein an atmospheric pressure in the vacuum chamber is 0.5 kPa or less.

4. 3. The method for measuring the temperature of molten steel according to claim 1, wherein in the operation parameter acquisition step, an atmospheric pressure in the vacuum vessel and a gas exhaust flow rate from within the vacuum vessel are acquired as the operation parameters.

5. The method for measuring a molten steel temperature according to claim 3 , wherein in the operation parameter acquisition step, an atmospheric pressure in the vacuum vessel and a gas exhaust flow rate from within the vacuum vessel are acquired as the operation parameters.

6. The method for measuring the temperature of molten steel according to claim 4 , wherein in the correcting step, the luminance information is corrected to corrected luminance information using the atmospheric pressure and the gas exhaust flow rate.

7. The method for measuring the temperature of molten steel according to claim 5 , wherein in the correcting step, the luminance information is corrected to corrected luminance information using the atmospheric pressure and the gas exhaust flow rate.

8. A molten steel temperature measuring device for measuring the temperature of molten steel in a vacuum vessel in which molten steel is refined under reduced pressure, comprising: an imaging unit that images a surface of the molten steel in the vacuum chamber and generates image data; a luminance information acquisition unit for acquiring luminance information from the image data; An operation parameter acquisition unit that acquires operation parameters of the refining; a correction unit that corrects the luminance information to corrected luminance information using the operation parameters; a calculation unit for calculating a molten steel temperature using the corrected luminance information; A device for measuring the temperature of molten steel.

9. The molten steel temperature measuring device according to claim 8, wherein the imaging unit receives visible light in a wavelength range of 0.4 to 0.8 μm and generates image data.

10. The molten steel temperature measuring device according to claim 8 or claim 9, wherein the operation parameter acquisition unit acquires, as the operation parameters, an atmospheric pressure in the vacuum chamber and a gas exhaust flow rate from the vacuum chamber.

11. The molten steel temperature measuring device according to claim 10 , wherein the correction unit corrects the luminance information to corrected luminance information using an atmospheric pressure in the vacuum chamber and a gas exhaust flow rate from the vacuum chamber.

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