JP6666740B2 - Grain boundary oxidation detector and grain boundary oxidation detection method - Google Patents

Description

  The present invention relates to a grain boundary oxidation detection device and a grain boundary oxidation detection method.

  For example, when a steel sheet is manufactured by hot rolling (hot rolling) a high-strength steel containing Si or the like, a black-scale scale made of an oxide is formed on an outer surface, and a ground iron inside the scale is formed. Oxidation of the surface grain boundaries may form grain boundary oxides. It is known that such a grain boundary oxide, when present in the final product of a high-strength cold-rolled steel sheet, causes deterioration in chemical conversion treatment.

  The scale and grain boundary oxide layer of the hot-rolled steel sheet (a layer of crystal grains around which grain boundary oxides are formed, which may include particulate matter on which oxides are precipitated) can be removed by pickling. . Therefore, a method has been proposed in which the time for pickling is determined in accordance with the thickness of the scale and the grain boundary oxide layer to ensure the removal of the scale and grain boundary oxide (Japanese Patent Application Laid-Open No. 2013-237924). )reference.

  As described above, the method of removing the grain boundary oxide layer from the hot-rolled steel sheet is known, but in the steel sheet production line, the removal of the grain boundary oxide layer is confirmed, that is, the presence or absence of the residual grain boundary oxide is confirmed. No effective means has been proposed for the method.

JP 2013-237924 A

  In view of the above disadvantages, an object of the present invention is to provide a grain boundary oxidation detection device and a grain boundary oxidation detection method that can determine the presence or absence of grain boundary oxide on the surface of a hot-rolled steel sheet after pickling.

  The invention made in order to solve the above-mentioned problem is a device for detecting grain boundary oxidation of a hot-rolled steel sheet after pickling, comprising: a first radiation thermometer; And a mechanism for determining the presence or absence of grain boundary oxides based on the measured temperature of the first radiation thermometer and the measured temperature of the second thermometer. This is a grain boundary oxidation detector.

  Since the grain boundary oxidation detector includes a first radiation thermometer and a second thermometer capable of measuring the temperature of the hot-rolled steel sheet after pickling regardless of the thermal emissivity, the second boundary thermometer can be used depending on the presence or absence of a grain boundary oxidation layer. The relationship between the measurement temperature of the first radiation thermometer and the measurement temperature of the second radiation thermometer changes. Thereby, the grain boundary oxidation detecting device is configured such that when the parameter calculated based on the measurement temperature of the first radiation thermometer and the measurement temperature of the second thermometer falls within a predetermined range, It can be determined that the object has been removed. Therefore, the grain boundary oxidation detector can relatively accurately determine the presence or absence of grain boundary oxide on the surface of the hot-rolled steel sheet after pickling.

  The determination mechanism may perform the determination based on the emissivity of the hot-rolled steel sheet obtained from the measurement temperature of the first radiation thermometer and the measurement temperature of the second thermometer. Thus, by calculating the emissivity of the hot-rolled steel sheet and comparing it with the emissivity of the hot-rolled steel sheet after pickling obtained in advance, it is possible to improve the determination accuracy of the grain boundary oxide.

  The determination mechanism may make the determination based on a difference between the measured temperature of the first radiation thermometer and the measured temperature of the second thermometer. As described above, by performing the determination based on the difference between the measurement temperature of the first radiation thermometer and the measurement temperature of the second thermometer, the presence or absence of the grain boundary oxide can be relatively easily determined.

  The set value of the thermal emissivity of the first radiation thermometer is preferably 0.5 or more and 0.9 or less. By setting the set value of the thermal emissivity of the first radiation thermometer within the above range, when there is no grain boundary oxide layer on the surface of the Si-containing high-strength steel sheet, the measurement temperature of the first radiation thermometer and the second temperature Since the measurement temperature of the gauge substantially matches, the presence or absence of grain boundary oxides of the Si-containing high-strength steel sheet can be determined relatively accurately.

  The measurement center wavelength of the first radiation thermometer is preferably 4 μm or more and 14 μm or less. As described above, by setting the measurement center wavelength of the first radiation thermometer within the above range, the thermal emissivity depending on the presence or absence of a grain boundary oxide layer having a thickness of about 5 μm to 10 μm formed on the Si-containing high-strength steel sheet. Is relatively large, the presence or absence of grain boundary oxides can be determined more accurately.

  The second thermometer may be a radiation thermometer using multiple reflection. As described above, since the second thermometer is a radiation thermometer utilizing multiple reflection, the apparent thermal emissivity of the hot-rolled steel sheet after pickling can be reduced to about 1 regardless of the presence of scale or grain boundary oxide. The temperature of the hot-rolled steel sheet after pickling can be detected relatively accurately by the amount of radiation. Thereby, the presence or absence of the grain boundary oxide can be more accurately determined.

  The second thermometer may be a contact thermometer. As described above, since the second thermometer is a contact thermometer, the temperature of the hot-rolled steel sheet after pickling can be detected relatively accurately, so that the presence or absence of grain boundary oxides can be more accurately determined. Can be.

  The second thermometer is a temperature-controllable reference plate installed opposite to the pickled hot-rolled steel sheet, and radiation emitted from the pickled hot-rolled steel sheet and reflected by the reference plate A radiation temperature sensor for detecting the amount of light, and a temperature calculated from the detected value of the radiation temperature sensor by adjusting the temperature of the reference plate and a value obtained by converting the amount of radiation of the reference plate to the temperature of the black body. A control unit for calculating the temperature of the hot-rolled steel sheet after pickling from the detection value of the radiation temperature sensor. As described above, since the second thermometer includes the reference plate, the radiation temperature sensor, and the control unit, the temperature of the hot-rolled steel sheet after pickling can be measured relatively accurately regardless of the thermal emissivity. Therefore, the presence or absence of the grain boundary oxide can be more accurately determined.

  The second thermometer detects a radiation amount having a center wavelength different from that of the first radiation thermometer, and calculates a temperature of the hot-rolled steel sheet based on a ratio with the radiation amount detected by the first radiation thermometer. It may be. As described above, the second thermometer detects the amount of radiation having a center wavelength different from that of the first radiation thermometer, and determines the temperature of the hot-rolled steel sheet based on the ratio with the amount of radiation detected by the first radiation thermometer. By calculating the temperature, the temperature of the hot-rolled steel sheet after pickling can be measured relatively accurately regardless of the thermal emissivity as a so-called two-color thermometer, and the presence or absence of grain boundary oxides can be measured more accurately. Can be determined.

  The determination mechanism may correct the influence of the ambient temperature of the measurement environment on the measurement temperature of the first radiation thermometer. As described above, by correcting the influence of the ambient temperature on the measurement temperature of the first radiation thermometer, it is possible to improve the determination accuracy of the presence or absence of the grain boundary oxide.

  Another invention made in order to solve the above-mentioned problem is a method for detecting grain boundary oxidation of a hot-rolled steel sheet after pickling, wherein the first radiation thermometer detects the intergranular oxidation of the hot-rolled steel sheet after pickling. Measuring the second temperature of the hot-rolled steel sheet after pickling with a second thermometer capable of measuring the temperature regardless of the heat emissivity; and measuring the first temperature and the second temperature. Determining the presence or absence of grain boundary oxides based on the temperature of the grain boundary oxide.

  The grain boundary oxidation detection method includes the steps of: when a parameter calculated based on a first temperature measured by a first radiation thermometer and a second temperature measured by a second thermometer falls within a predetermined range; It can be determined that it has been removed. Therefore, the grain boundary oxidation detection method can relatively accurately determine the presence or absence of grain boundary oxides on the surface of the hot-rolled steel sheet after pickling.

  Note that “measureable” means that the difference between the measured temperature and the actual temperature is 5 ° C. or less, preferably 3 ° C. or less in absolute value.

  The grain boundary oxidation detecting device and the grain boundary oxidation detecting method of the present invention can determine the presence or absence of grain boundary oxide on the surface of a hot-rolled steel sheet after pickling.

It is a mimetic diagram showing the partial composition of the steel plate manufacturing device provided with the grain boundary oxidation detecting device of one embodiment of the present invention. It is a schematic diagram which shows the partial structure of the steel plate manufacturing apparatus provided with the grain boundary oxidation detection apparatus of embodiment different from FIG. 1 of this invention. It is a schematic diagram which shows the partial structure of the steel plate manufacturing apparatus provided with the grain boundary oxidation detection apparatus of embodiment different from FIG. 1 and FIG. 2 of this invention. It is a schematic diagram which shows the partial structure of the steel plate manufacturing apparatus provided with the grain boundary oxidation detection apparatus of embodiment different from FIG. 1 thru | or FIG. 3 of this invention. 5 is a graph showing measurement results in Example 1 of the present invention. 6 is a graph showing measurement results in Example 2 of the present invention. 9 is a graph showing measurement results in Example 3 of the present invention. 13 is a graph showing measurement results in Example 4 of the present invention.

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

[First embodiment]
The steel sheet manufacturing apparatus of FIG. 1 includes a transport roller 1 that continuously transports a strip-shaped hot-rolled steel sheet S in a longitudinal direction, and stores an acidic liquid upstream of the transport roller 1 to convert the transported hot-rolled steel sheet S into an acidic liquid. A pickling tank 2 to be immersed, and a grain boundary oxidation detecting device 3 according to the first embodiment of the present invention for detecting grain boundary oxidation on the surface of the hot-rolled steel sheet S downstream of the transport roller 1 are provided.

<Hot rolled steel sheet>
Although there is no particular limitation on the hot-rolled steel sheet S, a Si (silicon) -containing high-strength steel sheet or the like that has a high demand for detection of grain boundary oxides is assumed. Specific examples of such a Si-containing high-strength steel sheet include a Si-rich Mn-containing steel containing 1.0% by mass or more of Si and 1.5% by mass or more of Mn (manganese).

  The lower limit of the average surface temperature of the hot-rolled steel sheet S at the time when the grain boundary oxidation detector 3 detects grain boundary oxidation is preferably 40 ° C, more preferably 50 ° C. On the other hand, the upper limit of the average surface temperature of the hot-rolled steel sheet S upon detection of the grain boundary oxidation is preferably 300 ° C, more preferably 200 ° C. When the average surface temperature of the hot-rolled steel sheet S at the time of detection of the above-mentioned grain boundary oxidation is less than the above lower limit, the detection accuracy of the grain boundary oxide by the grain boundary oxidation detection device 3 utilizing the measurement error of the thermometer will be described later. It may be insufficient. Conversely, when the average surface temperature of the hot-rolled steel sheet S at the time of detection of the grain boundary oxidation exceeds the above upper limit, there is a possibility that grain boundary oxides may be generated even after the detection of the grain boundary oxidation.

<Grain boundary oxidation detector>
The grain boundary oxidation detector 3 includes a first radiation thermometer 4 in which the value of the thermal emissivity of the measurement target is set in advance, and a second temperature capable of measuring the temperature of the hot-rolled steel sheet S regardless of the thermal emissivity. And a determination mechanism 6 for determining the presence or absence of grain boundary oxides based on the measurement temperature of the first radiation thermometer 4 and the measurement temperature of the second thermometer 5, and a thermometer for measuring the ambient temperature of the measurement environment. 12 mainly.

(1st radiation thermometer)
The first radiation thermometer 4 includes a radiation light amount sensor that detects a light amount (brightness of radiation light) of radiation light in a predetermined wavelength region among radiation lights radiated from a region within a certain field of view of the hot-rolled steel sheet S, A conversion unit for converting the detection value of the radiation light amount sensor into a temperature (a temperature obtained from the radiation light amount assuming that the hot-rolled steel sheet S is a black body), and measuring by dividing this temperature by a preset heat emissivity. And a correction unit that calculates a first temperature as a value. The first radiation thermometer 4 is arranged at a position where the transport roller 1 does not enter the field of view. It is preferable that the first radiation thermometer 4 can set the thermal emissivity.

  The lower limit of the measurement center wavelength of the first radiation thermometer 4 is preferably 4 μm, more preferably 8 μm. On the other hand, the upper limit of the measurement center wavelength of the first radiation thermometer 4 is preferably 14 μm, more preferably 12 μm. When the measurement center wavelength of the first radiation thermometer 4 is less than the above lower limit or exceeds the above upper limit, the thermal emissivity of the hot-rolled steel sheet S at the measurement wavelength becomes small, and the detection accuracy of the grain boundary oxide is insufficient. Could be.

  The upper limit of the thermal emissivity preset in the first radiation thermometer 4 is preferably 0.9, and more preferably 0.8. When the thermal emissivity preset in the first radiation thermometer 4 exceeds the above upper limit, the change in the measurement value of the first radiation thermometer 4 due to the presence or absence of the grain boundary oxide becomes small, and thus the first radiation thermometer 4 Since the rate of change of the difference between the measurement values of the second thermometer 4 and the second thermometer 5 becomes small, the detection accuracy of the grain boundary oxide may be insufficient.

  The thermal emissivity preset in the first radiation thermometer 4 is an average of the hot rolled steel sheet S when the grain boundary oxides of the hot rolled steel sheet S are completely removed by pickling in the pickling tank 2. The absolute value of the error from the average thermal emissivity is preferably set to be 0.1 or less, more preferably 0.05 or less so as to substantially match the thermal emissivity. The average thermal emissivity of the hot-rolled steel sheet S when the grain boundary oxide is completely removed by pickling differs depending on the composition of the hot-rolled steel sheet S, but in the case of the high Si high Mn-containing steel, it is 0.5%. It is considered to be not less than 0.8 and not more than 0.8.

  Therefore, when the hot-rolled steel sheet S is a high Si high Mn-containing steel, the lower limit of the thermal emissivity preset in the first radiation thermometer 4 is preferably 0.5, and more preferably 0.6. On the other hand, in the above case, the upper limit of the thermal emissivity preset in the first radiation thermometer 4 is preferably 0.8, and more preferably 0.7. When the heat emissivity set in the first radiation thermometer 4 is less than the above lower limit when the hot-rolled steel sheet S is a high Si high Mn-containing steel, the heat when the scale layer is present on the surface of the hot-rolled steel sheet S Since it is close to the emissivity (about 0.3 to 0.4), when the scale layer remains, it may be erroneously recognized that the grain boundary oxidation has been removed. Conversely, if the heat emissivity set in the first radiation thermometer 4 exceeds the upper limit when the hot-rolled steel sheet S is a high Si high Mn-containing steel, the first radiation thermometer based on the presence or absence of grain boundary oxides When the rate of change of the difference between the measurement values of the fourth thermometer 4 and the second thermometer 5 decreases, the accuracy of determining the grain boundary oxide may be insufficient.

(2nd thermometer)
The second thermometer 5 is a radiation thermometer having a configuration similar to that of the first radiation thermometer 4, and makes the apparent thermal emissivity of the hot-rolled steel sheet S close to 1 using multiple reflection. Thus, the thermometer is capable of relatively accurately measuring the temperature (surface temperature) of the hot-rolled steel sheet S regardless of the actual amount of radiation of the hot-rolled steel sheet S. Specifically, the second thermometer 5 is a radiation thermometer whose measurement error of the temperature of the hot-rolled steel sheet S is 5 ° C. or less, preferably 3 ° C. or less, more preferably 2 ° C. or less.

  More specifically, the second thermometer 5 is formed between the hot-rolled steel sheet S and the transport roller 1 having a surface temperature substantially equal to that of the hot-rolled steel sheet S by sufficiently contacting the hot-rolled steel sheet S. The amount of radiation emitted from the wedge-shaped portion is detected. With this configuration, the radiated light emitted from the hot-rolled steel sheet S and the transport roller 1 is repeatedly reflected between the hot-rolled steel sheet S and the transport roller 1 and is incident on the second thermometer 5, whereby the hot-rolled steel sheet S and the transport roller 1 are hot-rolled. The apparent thermal emissivity of the steel sheet S and the transport roller 1 becomes a value close to 1, for example, exceeding 0.9.

  Therefore, the second thermometer 5 can relatively accurately measure the temperature of the hot-rolled steel sheet S regardless of the actual heat emissivity of the hot-rolled steel sheet S and the transport roller 1. As described above, by using the second thermometer 5 using multiple reflection, the configuration of the grain boundary oxidation detector can be simplified, and the influence of the temperature measurement on the hot-rolled steel sheet S can be extremely reduced.

(Thermometer)
The thermometer 12 measures the ambient temperature of the measurement environment of the first radiation thermometer 4 and the second thermometer 5. As the thermometer 12, a known thermometer can be used.

(Judgment mechanism)
The determination mechanism 6 determines the presence or absence of grain boundary oxidation of the hot-rolled steel sheet S based on the measurement value (measurement temperature) of the first radiation thermometer 4 and the measurement value (measurement temperature) of the second thermometer 5.

  As the determination mechanism 6, a microcomputer or the like that receives an electric signal indicating a measurement value of the first radiation thermometer 4 and the second thermometer 5 is used.

  As a specific method of determining the grain boundary oxidation, (1) the grain boundary oxidation is determined based on the emissivity of the hot-rolled steel sheet obtained from the measurement temperature of the first radiation thermometer 4 and the measurement temperature of the second thermometer 5. A first method of determining the presence or absence, and (2) a second method of determining the presence or absence of grain boundary oxidation based on the difference between the measurement temperature of the first radiation thermometer 4 and the measurement temperature of the second thermometer 5 Can be applied. Hereinafter, each method will be described.

(1) First Method In this method, first, from the first temperature T1 [K] measured by the first radiation thermometer 4 and the second temperature T2 [K] measured by the second thermometer 5 For example, the spectral radiance L [W · sr ⁻¹ · m ⁻² ] at each measurement temperature is obtained based on the following equation (1).

In the above formula (1), lambda measurement center wavelength of the first radiation thermometer 4 [m], T is a constant temperature T2, _{C 1} of the first temperature T1 or the second is represented by the following formula (2) [W · m ² ] and C ₂ are constants [m · K] represented by the following equation (3).
C ₁ = c ² h = 5.9548 × 10 ⁻¹⁷ [W · m ² ] (2)
C ₂ = ch / k = 0.014388 [m · K] (3)
Here, c is the speed of light in vacuum (2.9972458 × 10 ⁸ [m / s]), h is Planck's constant (6.6256 × 10 ⁻³⁴ [J · s]), and k is Boltzmann's constant (1 .38054 × 10 ^-23 [J / K]).

Next, the spectral radiance L1 at the first temperature T1 obtained from the above equation (1), the spectral radiance L2 at the second temperature T2, the set thermal emissivity ε1 of the first radiation thermometer 4, and Is used to determine the emissivity ε2 of the hot-rolled steel sheet from the following equation (4).
ε2 = ε1 × L1 / L2 (4)

  Finally, the emissivity ε2 obtained from the above equation (4) is compared with the predicted emissivity ε0 of the hot-rolled steel sheet, and if the difference (ε2−ε0) between the two is within the set range, the grain boundary oxidation will not occur. It is determined that there is no grain boundary, and if this difference is out of the set range, it is determined that there is grain boundary oxidation.

  Since the emissivity ε0 has a judgment tolerance, the lower limit of the setting range of the difference (ε2−ε0) is preferably −0.1, and more preferably −0.05. On the other hand, the upper limit of the setting range of the difference (ε2−ε0) is preferably 0.3, and more preferably 0.1.

  In the first method, the determination mechanism 6 may include a device that displays both the calculated emissivity ε2 and the predicted emissivity ε0. By displaying ε2 and ε0 at the same time in this way, the operator can make a judgment visually or the like. Note that the predicted emissivity ε0 may be a value having a width. In addition, the emissivity ε0 is determined or predicted in advance by a test or the like for each condition such as a steel type based on the amount of Si, a coil winding temperature, and the like, and data prepared as a table linked to such information can be suitably used. .

(2) Second Method In this method, the difference between the measured temperature of the first radiation thermometer 4 and the measured temperature of the second thermometer 5 is calculated, and the absolute value of the calculated temperature difference is equal to or less than a preset threshold. When it is determined that there is no grain boundary oxidation in the hot-rolled steel sheet S.

  The lower limit of the threshold is preferably 2%, more preferably 3%, even more preferably 4% of the temperature measured at the Celsius temperature of the second thermometer 5 (the actual temperature of the hot-rolled steel sheet S). On the other hand, the upper limit of the threshold is preferably 15% of the temperature measured by the second thermometer 5, more preferably 10%, and still more preferably 7%. When the threshold is less than the lower limit, there is a possibility that the measurement error of the first radiation thermometer 4 and the second thermometer 5 may result in erroneous determination that the grain boundary oxide is present even though the grain boundary oxide is removed. is there. Conversely, if the threshold value exceeds the upper limit, there is a possibility that the grain boundary oxidation is erroneously determined to have been eliminated despite the insufficient removal of the grain boundary oxide layer from the hot-rolled steel sheet S.

  In addition, the determination mechanism 6 may correct the influence of the ambient temperature of the measurement environment on the measurement temperature of the first radiation thermometer 4. Since the first radiation thermometer 4 is affected by the ambient temperature of the surrounding environment (the temperature measured by the thermometer 12), by correcting the numerical value used for the judgment in accordance with the ambient temperature, the first radiation thermometer 4 can more accurately perform the grain boundary oxidation. Presence or absence can be determined.

A specific correction method will be described below. The difference ΔL (= L1′−L1) between the spectral radiance L1 corresponding to the first temperature T1 measured by the first radiation thermometer 4 and the spectral radiance L1 ′ considering the influence of the ambient temperature is as follows. It can be expressed as equation (5). In the following equation (5), Lb is the spectral radiance at the ambient temperature Tb [° C.] at the measurement center wavelength of the first radiation thermometer 4, and is obtained by the above equation (1).
ΔL = (1−ε2) × Lb (5)

  The difference ΔL may be obtained by measuring the spectral radiance of a steel sheet having a stable emissivity and a small amount of Si while changing the ambient temperature a plurality of times.

  By correcting the spectral radiance L1 corresponding to the first temperature T1 with this ΔL, the determination accuracy of the determination mechanism 6 can be increased. When the second method is used as the determination method, the accuracy can be improved by back-calculating the corrected first temperature T1 'from the spectral radiance L1' considering the influence of the ambient temperature.

<Advantages>
In the grain boundary oxidation detection device, the determination mechanism 6 determines the particle set in the first radiation thermometer 4 based on the difference between the measurement temperature of the first radiation thermometer 4 and the measurement temperature of the second thermometer 5. It is detected that the thermal emissivity assuming removal of the field oxide layer is substantially equal to the thermal emissivity of the surface of the hot-rolled steel sheet S, that is, that the grain boundary oxide layer has been removed from the hot-rolled steel sheet S. Therefore, the grain boundary oxidation detection device can relatively accurately determine the presence or absence of grain boundary oxide on the surface of the hot-rolled steel sheet S.

[Second embodiment]
The steel sheet manufacturing apparatus of FIG. 2 includes a transport roller 1 that continuously transports a strip-shaped hot-rolled steel sheet S in a longitudinal direction, and an acidic solution stored upstream of the transport roller 1 to convert the transported hot-rolled steel sheet S into an acidic solution. A pickling tank 2 for immersing and pickling, a grain boundary oxidation detector 3a according to the second embodiment of the present invention for detecting grain boundary oxidation on the surface of the hot-rolled steel sheet S upstream of the transport roller 1, and measurement It mainly comprises a thermometer 12 for measuring the ambient temperature of the environment.

  The configuration of the hot-rolled steel sheet S, the transport roller 1, the pickling tank 2, and the thermometer 12 in the steel sheet manufacturing apparatus of FIG. Since it is the same as the total 12, a duplicate description will be omitted.

<Grain boundary oxidation detector>
The grain boundary oxidation detector 3a includes a first radiation thermometer 4 in which the value of the thermal emissivity of the measurement object is set in advance, and a second temperature capable of measuring the temperature of the hot-rolled steel sheet S regardless of the thermal emissivity. And a determination mechanism 6 for determining the presence or absence of grain boundary oxides based on the measurement temperature of the first radiation thermometer 4 and the measurement temperature of the second thermometer 5a.

  The configuration of the first radiation thermometer 4 and the determination mechanism 6 in the grain boundary oxidation detector 3a is the same as the configuration of the first radiation thermometer 4 and the determination mechanism 6 in the grain boundary oxidation detector 3 of the steel sheet manufacturing apparatus in FIG. Therefore, a duplicate description will be omitted. That is, the grain boundary oxidation detector 3a is the same as the grain boundary oxidation detector 3 of FIG. 1 except that the configuration and the temperature detection method of the second thermometer 5a are different from those of the second thermometer 5 of FIG. To work.

(2nd thermometer)
The second thermometer 5a is a contact-type thermometer that directly measures the temperature of the hot-rolled steel sheet S by contacting the hot-rolled steel sheet S. As the contact-type thermometer constituting the second thermometer 5a, for example, a thermocouple or the like can be used. Further, it is preferable that the second thermometer 5 a be disposed outside the field of view of the first radiation thermometer 4, and as close as possible to the field of view of the first radiation thermometer 4.

  As described above, by using a contact-type thermometer as the second thermometer 5a, the temperature of the hot-rolled steel sheet S can be relatively accurately detected. Can be determined relatively accurately.

[Third embodiment]
The steel sheet manufacturing apparatus in FIG. 3 includes a transport roller 1 that continuously transports a strip-shaped hot-rolled steel sheet S in a longitudinal direction, an acid solution stored upstream of the transport roller 1, and the transported hot-rolled steel sheet S turned into an acidic liquid. A pickling tank 2 for immersing and pickling, a grain boundary oxidation detecting device 3b according to the second embodiment of the present invention for detecting grain boundary oxidation of the surface of the hot-rolled steel sheet S upstream of the transport roller 1, and measurement It mainly comprises a thermometer 12 for measuring the ambient temperature of the environment.

  The configuration of the hot-rolled steel sheet S, the transport roller 1, the pickling tank 2, and the thermometer 12 in the steel sheet manufacturing apparatus of FIG. Since it is the same as the total 12, a duplicate description will be omitted.

<Grain boundary oxidation detector>
The grain boundary oxidation detector 3b includes a first radiation thermometer 4 in which the value of the thermal emissivity of the measurement target is set in advance, and a second temperature capable of measuring the temperature of the hot-rolled steel sheet S regardless of the thermal emissivity. And a determination mechanism 6 for determining the presence or absence of grain boundary oxides based on the measurement temperature of the first radiation thermometer 4 and the measurement temperature of the second thermometer 5b.

  The configuration of the first radiation thermometer 4 and the determination mechanism 6 in the grain boundary oxidation detector 3b is the same as the configuration of the first radiation thermometer 4 and the determination mechanism 6 in the grain boundary oxidation detector 3 of the steel sheet manufacturing apparatus in FIG. Therefore, a duplicate description will be omitted. That is, the grain boundary oxidation detector 3b is the same as the grain boundary oxidation detector 3 of FIG. 1 except that the configuration and the temperature detection method of the second thermometer 5b are different from those of the second thermometer 5 of FIG. To work.

(2nd thermometer)
The second thermometer 5b is a reference plate thermometer having a reference plate 7, a radiation temperature sensor 8, and a control unit 9. The reference plate 7 is installed to face the hot-rolled steel sheet S and is configured to be capable of controlling the temperature. The radiation temperature sensor 8 detects the amount of radiation radiated from the hot-rolled steel sheet S and reflected by the reference plate 7. The control unit 9 controls the radiation temperature when the temperature calculated from the detected value of the radiation temperature sensor 8 by adjusting the temperature of the reference plate 7 matches the value obtained by converting the amount of radiation of the reference plate 7 into the temperature of the black body. The temperature of the hot-rolled steel sheet S is calculated from the value detected by the sensor 8. It is preferable that the second thermometer 5b is disposed outside the visual field of the first radiation thermometer 4 and as close as possible to the visual field of the first radiation thermometer 4.

  The radiation temperature sensor 8 detects the total light amount of the radiation light from the hot-rolled steel sheet S and the reflected light of the radiation light from the reference plate 7 on the hot-rolled steel sheet S. Therefore, by making the temperature calculated from the detection value of the radiation temperature sensor 8 and the value obtained by converting the amount of radiation of the reference plate 7 into the temperature of the black body coincide, the detection value of the radiation temperature sensor 8 and the hot rolled steel sheet S The temperature matches. In this manner, the second thermometer 5b can relatively accurately measure the temperature of the hot-rolled steel sheet S regardless of the thermal emissivity of the hot-rolled steel sheet S. The presence or absence of the field oxide can be determined relatively accurately.

[Fourth embodiment]
The steel sheet manufacturing apparatus in FIG. 4 includes a transport roller 1 that continuously transports a strip-shaped hot-rolled steel sheet S in a longitudinal direction, and stores an acidic liquid upstream of the transport roller 1 to convert the transported hot-rolled steel sheet S into an acidic liquid. A pickling tank 2 for immersing and pickling, a grain boundary oxidation detection device 3c according to the second embodiment of the present invention for detecting grain boundary oxidation of the surface of the hot-rolled steel sheet S upstream of the transport roller 1, and measurement It mainly comprises a thermometer 12 for measuring the ambient temperature of the environment.

  The configuration of the hot-rolled steel sheet S, the transport roller 1, the pickling tank 2, and the temperature in the steel sheet manufacturing apparatus of FIG. Since it is the same as the total 12, a duplicate description will be omitted.

<Grain boundary oxidation detector>
The grain boundary oxidation detection device 3c includes a first radiation thermometer 4 in which the value of the thermal emissivity of the measurement object is set in advance, and a second temperature capable of measuring the temperature of the hot-rolled steel sheet S regardless of the thermal emissivity. And a determination mechanism 6 for determining the presence or absence of grain boundary oxides based on the measurement temperature of the first radiation thermometer 4 and the measurement temperature of the second thermometer 5c.

  The configuration of the first radiation thermometer 4 and the determination mechanism 6 in the grain boundary oxidation detection device 3c is the same as the configuration of the first radiation thermometer 4 and the determination mechanism 6 in the grain boundary oxidation detection device 3 of the steel sheet manufacturing apparatus in FIG. Therefore, a duplicate description will be omitted. That is, the grain boundary oxidation detector 3c is the same as the grain boundary oxidation detector 3 of FIG. 1 except that the configuration and the temperature detection method of the second thermometer 5c are different from those of the second thermometer 5 of FIG. To work.

(2nd thermometer)
The second thermometer 5c includes a radiation temperature sensor 10 that detects a radiation amount having a center wavelength different from that of the first radiation thermometer, a radiation amount detected by the radiation temperature sensor 10, and a radiation amount detected by the first radiation thermometer 4. And a calculator 11 for calculating the temperature of the hot-rolled steel sheet S based on the ratio of the hot-rolled steel sheet S and functions as a so-called two-color thermometer. It is preferable that the second thermometer 5c be disposed so that its visual field overlaps or approaches the visual field of the first radiation thermometer 4. Further, it is preferable that the first radiation thermometer 4 and the second thermometer 5c are arranged so as not to be in the field of view of each other.

  The center wavelength of the radiation detected by the radiation temperature sensor 10 is not particularly limited, but may be, for example, 0.8 μm or more and 1.6 μm or less.

  As described above, by calculating the temperature of the hot-rolled steel sheet S based on the ratio between the amount of radiation detected by the radiation temperature sensor 10 and the amount of radiation detected by the first radiation thermometer 4, the heat radiation of the hot-rolled steel sheet S is calculated. Regardless of the ratio, the temperature of the hot-rolled steel sheet S can be measured relatively accurately. Therefore, the grain boundary oxidation detecting device 3c can relatively accurately determine the presence or absence of grain boundary oxides in the hot-rolled steel sheet S.

[Embodiment of a method for detecting grain boundary oxidation]
The method for detecting grain boundary oxidation according to one embodiment of the present invention is a hot rolled steel sheet after pickling with a first radiation thermometer that sets a thermal emissivity according to a hot rolled steel sheet after removal of grain boundary oxides by pickling. Measuring the second temperature of the hot-rolled steel sheet after pickling with a second thermometer capable of measuring the temperature regardless of the thermal emissivity; Determining the presence or absence of grain boundary oxides based on the second temperature.

  As the first radiation thermometer used in the grain boundary oxidation detection method, the same one as the first radiation thermometer 4 of the first to fourth embodiments of the above-described grain boundary oxidation detection device can be used. As the second thermometer used in the grain boundary oxidation detection method, the second thermometers 4, 4a, 4b, and 4c of the first to fourth embodiments of the grain boundary oxidation detection device of the above embodiment are used. The same one can be used.

  The determination step in the method for detecting grain boundary oxidation is a first method for determining the presence or absence of grain boundary oxidation based on the emissivity of the hot-rolled steel sheet obtained from the first temperature and the second temperature, or And a second method for determining the presence or absence of grain boundary oxidation based on the difference between the second temperature and the second temperature.

  The details of the first method and the second method, and the determination thresholds in these methods are the same as those described for the determination mechanism 6 in the above-described first to fourth embodiments. That is, this determination step may be performed using the determination mechanism 6 of the first to fourth embodiments of the grain boundary oxidation detection device. This determination step may be performed by an operator manually calculating the emissivity or the temperature difference.

[Other Embodiments]
The above embodiments do not limit the configuration of the present invention. Therefore, in the above embodiment, it is possible to omit, replace, or add the components of each part of the embodiment based on the description of the present specification and common technical knowledge, and all of them are interpreted as belonging to the scope of the present invention. Should.

  The second thermometer in the grain boundary oxidation detection device and the second thermometer used in the grain boundary oxidation detection method are not limited to those having the configuration of the above embodiment, regardless of the thermal emissivity of the hot-rolled steel sheet. Any thermometer that can measure the surface temperature of the hot-rolled steel sheet after pickling may be used. For example, the second thermometer may be a radiation thermometer that utilizes multiple reflections between members other than the transport rollers and the hot-rolled steel sheet after pickling.

  Further, a plurality of first radiation thermometers or second thermometers in the grain boundary oxidation detection device may be respectively provided to obtain the first temperature or the second temperature from the plurality of measured temperatures. .

  In addition, the determination mechanism of the grain boundary oxidation detection device determines that the difference between the measurement value (first temperature) of the first radiation thermometer and the measurement value (second temperature) of the second thermometer is less than a predetermined lower limit. If the lower limit is in the range up to the upper limit where the absolute value is different, it may be determined that there is no grain boundary oxide. Specifically, when the heat emissivity set in the first radiation thermometer is different from the heat emissivity of the hot-rolled steel sheet from which grain boundary oxides have been removed, when the hot-rolled steel sheet has no grain boundary oxide layer, Since the theoretical value of the difference between the first temperature and the second temperature is a value other than zero, a range centered on this theoretical value may be set as a range where it is determined that there is no grain boundary oxide.

  Further, in the grain boundary oxidation detection device, a thermometer is not essential, and it is not always necessary to correct the influence of the ambient temperature of the measurement environment on the measurement temperature of the first radiation thermometer.

  Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not to be construed as being limited based on the description of the examples.

<Example 1>
As Example 1, a hot-rolled steel sheet having a pickling time different from 30 seconds, 60 seconds, 90 seconds, 120 seconds, 150 seconds, 180 seconds, and 200 seconds by an apparatus having a configuration similar to the steel sheet manufacturing apparatus shown in FIG. The first temperature and the second temperature were measured, and the difference was calculated.

  The surface of the hot-rolled steel sheet after pickling was observed with a microscope to confirm the degree of removal of the grain boundary oxide layer. In the hot-rolled steel sheets having the pickling times of 30 seconds and 60 seconds, the grain boundary oxide layer was hardly removed, and the scale remained on the grain boundary oxide layer. In the hot-rolled steel sheets with pickling times of 90 seconds and 120 seconds, the grain boundary oxide layer was partially removed, but the grain boundary oxide remained. Hot-rolled steel sheets with pickling times of 150 seconds, 180 seconds and 200 seconds had substantially all of the grain boundary oxides removed.

(Hot rolled steel sheet)
As the hot-rolled steel sheet, a high-strength steel containing 1.4% by mass of Si was rolled at 600 ° C. after hot rolling. The temperature of the hot-rolled steel sheet at the time of detecting grain boundary oxidation after the pickling (measuring the first temperature and the second temperature) was set to 80 ° C. ± 2 ° C. In addition, the temperature of the hot-rolled steel sheet at the time of detection was measured using a thermocouple “K-CERAC” manufactured by Duplex.

(1st radiation thermometer)
As the first radiation thermometer, “CS-40TAC” (measurement wavelength range: 8 μm to 14 μm) manufactured by Optex was used, and the thermal emissivity was set to 0.65.

(2nd thermometer)
As the second thermometer, the same radiation thermometer as the first radiation thermometer was used with the thermal emissivity set to 0.95.

<Example 2>
As Example 2, a test for detecting grain boundary oxidation was performed using an apparatus having a configuration similar to the steel sheet manufacturing apparatus shown in FIG. The same hot-rolled steel plate and first radiation thermometer as in Example 1 were used.

(2nd thermometer)
As the second thermometer, a thermocouple “K-CERAC” manufactured by Duplex was used.

<Example 3>
As Example 3, a test for detecting grain boundary oxidation was performed using an apparatus having a configuration similar to the steel sheet manufacturing apparatus shown in FIG. The same hot-rolled steel plate and first radiation thermometer as in Example 1 were used.

(2nd thermometer)
The configuration of the second thermometer used was a “CS-40TAC” (Optics) (measurement wavelength range: 8 μm to 14 μm) as a radiation temperature sensor, and a sufficiently large flat plate provided with an electric heater as a reference plate.

<Example 4>
As Example 4, a test for detecting grain boundary oxidation was performed using an apparatus having a configuration similar to the steel sheet manufacturing apparatus shown in FIG. The same hot-rolled steel sheets as in Example 1 were used at different temperatures. The first radiation thermometer used was the same as that used in Example 1.

(Hot rolled steel sheet)
The same hot-rolled steel sheet as in Example 1 was used, but the temperature of the hot-rolled steel sheet at the time of measurement was set at 250 ° C. ± 2 ° C.

(2nd thermometer)
As the second thermometer, "FTC6-P200-100R" (measurement wavelength range from 0.8 μm to 1.6 μm) manufactured by Japan Sensor Co., Ltd. was used. The second temperature was calculated by setting the ratio of the radiance of the hot-rolled steel sheet at the measurement center wavelength of the second thermometer to the radiance of the hot-rolled steel sheet at the measurement center wavelength of the first radiation thermometer to 2546.

<Evaluation>
5 to 8 show the relationship between the pickling time and the temperature difference between the first temperature and the second temperature in Examples 1 to 4.

  As shown in the figures, in any of the examples, when the pickling time was short and scale was present on the surface of the hot-rolled steel sheet, the difference between the first temperature and the second temperature was large, As the boundary oxide layer is removed, the difference between the first temperature and the second temperature becomes smaller. When the grain boundary oxide layer is completely removed, the difference between the first temperature and the second temperature becomes almost zero. lost. Note that the difference between the first temperature and the second temperature in the case where the pickling time is sufficiently long and the grain boundary oxide layer is considered to be completely removed is attributed to a measurement error of the thermometer. Conceivable.

  Therefore, in consideration of this measurement error, in the first to third embodiments, the absolute value of the difference between the first temperature and the second temperature is, for example, 5 ° C. or less (6.3% of the second temperature). It is considered appropriate to determine that the grain boundary oxide layer has been completely removed from the hot-rolled steel sheet when the following condition is satisfied. On the other hand, in the case of Example 4 in which the steel sheet temperature is high, when the absolute value of the difference between the first temperature and the second temperature is, for example, 15 ° C. or less (6.0% or less of the second temperature), heat is applied. It is considered appropriate to determine that the grain boundary oxide layer has been completely removed from the rolled steel sheet.

<Example 5>
By using an apparatus having a configuration similar to that of the steel sheet manufacturing apparatus shown in FIG. 1, as a first radiation thermometer and a second thermometer, "CS-40TAC" (measurement wavelength range: 8 μm to 14 μm) of OPTEX Co., Ltd. A temperature measurement was performed. The thermal emissivity of the first thermometer was set to 0.65, and the thermal emissivity of the second thermometer was set to 0.95. As the hot-rolled steel sheet, a high-strength steel containing 2.0% by mass of Si was rolled at 600 ° C. after hot rolling. From the measured temperature T1 of the first radiation thermometer and the measured temperature T2 of the second thermometer, the emissivity ε2 of the hot-rolled steel sheet is calculated backward, and the difference (ε2−ε0) from the predicted emissivity ε0 of the hot-rolled steel sheet is calculated. If it was less than -0.1, it was determined that grain boundary oxidation remained (presence), and if it was -0.1 or more and 0.3 or less, it was determined that grain boundary oxidation did not remain (no). Further, in addition to the determination based on the emissivity, the determination of the remaining grain boundary oxidation was also visually performed. These measurements and judgments were performed three times using different hot-rolled steel sheets. Table 1 shows the results.

  As shown in Table 1, the same result as the visual determination was obtained by the determination using the emissivity difference (ε2−ε0).

<Example 6>
By using an apparatus having a configuration similar to the steel sheet manufacturing apparatus shown in FIG. 1, a grain boundary oxide layer is formed using "CS-40TAC" (measurement wavelength range: 8 to 14 [mu] m) as a first radiation thermometer and a second thermometer. The temperature of a mild steel material in which no cracks occurred was measured. This mild steel material is considered to have a substantially constant surface emissivity after pickling. The thermal emissivity of the first thermometer was set to 0.65, and the thermal emissivity of the second thermometer was set to 0.95. The ambient temperature Tb was also measured. From the measured temperature T1 of the first radiation thermometer and the measured temperature T2 of the second thermometer, the emissivity ε2 of the steel material was calculated back. The emissivity ε2 ′ was calculated by correcting the emissivity ε2 using the ambient temperature Tb. These measurements and calculations were performed three times using different steel materials. Table 2 shows the results.

  As shown in Table 2, the emissivity .epsilon.2 before correction was large in three measurements and the maximum difference was 0.08, but the emissivity .epsilon.2 'after correction was small and the maximum difference was small. 0.03. Therefore, by correcting the emissivity using the ambient temperature Tb, the presence or absence of the grain boundary oxide can be more accurately determined.

  INDUSTRIAL APPLICABILITY The grain boundary oxidation detecting device and the grain boundary oxidation detecting method of the present invention are suitably used for confirming removal of a grain boundary oxide layer particularly in the production of a Si-containing high-strength steel sheet.

S Hot-rolled steel sheet 1 Conveying roller 2 Pickling tank 3, 3a, 3b, 3c Grain boundary oxidation detector 4 First radiation thermometer 5, 5a, 5b, 5c Second thermometer 6 Judgment mechanism 7 Reference plate 8 Radiation temperature sensor 9 control unit 10 radiation temperature sensor 11 calculation unit 12 thermometer

Claims (10)

A device for detecting grain boundary oxidation of a hot-rolled steel sheet after pickling,
A first radiation thermometer that can set the value of the thermal emissivity of the hot-rolled steel sheet after the pickling, and can measure the temperature of the hot-rolled steel sheet after the pickling ;
A second thermometer capable of measuring the temperature of the hot-rolled steel sheet after the pickling, regardless of the thermal emissivity,
A mechanism for determining the presence or absence of grain boundary oxides based on the measurement temperature of the first radiation thermometer and the measurement temperature of the second thermometer ,
Intergranular oxidation detection device setting value of the thermal emissivity of the first radiation thermometer is characterized in der Rukoto 0.5 to 0.9.   The grain boundary oxidation detector according to claim 1, wherein the determination mechanism makes the determination based on the emissivity of the hot-rolled steel sheet obtained from the measured temperature of the first radiation thermometer and the measured temperature of the second thermometer.   2. The grain boundary oxidation detector according to claim 1, wherein the determination mechanism makes the determination based on a difference between a temperature measured by the first radiation thermometer and a temperature measured by the second thermometer. 3. 4. The grain boundary oxidation detector according to claim 1 , wherein a measurement center wavelength of the first radiation thermometer is 4 μm or more and 14 μm or less. The grain boundary oxidation detector according to any one of claims 1 to 4 , wherein the second thermometer is a radiation thermometer using multiple reflection. The grain boundary oxidation detector according to any one of claims 1 to 4 , wherein the second thermometer is a contact thermometer. The second thermometer is
A temperature-controllable reference plate installed opposite to the hot-rolled steel sheet after the pickling,
A radiation temperature sensor that detects the amount of radiation radiated from the hot-rolled steel sheet after the pickling and reflected by the reference plate,
The acid calculated from the detected value of the radiation temperature sensor when the temperature calculated from the detected value of the radiation temperature sensor by adjusting the temperature of the reference plate and the value obtained by converting the amount of radiation of the reference plate into the temperature of the black body match. intergranular oxidation detecting device as claimed in any one of claims 4 and a control unit for calculating the temperature of the hot-rolled steel sheet after pickling. The second thermometer detects a radiation amount having a center wavelength different from that of the first radiation thermometer, and calculates a temperature of the hot-rolled steel sheet based on a ratio with the radiation amount detected by the first radiation thermometer. The grain boundary oxidation detector according to any one of claims 1 to 4 , wherein The determination mechanism, grain boundary oxidation detecting apparatus according to any one of claims 1 to 8 for correcting the influence of by the ambient temperature of the measurement environment to measure the temperature of the first radiation thermometer. A method for detecting grain boundary oxidation of a hot-rolled steel sheet after pickling,
Measuring the first temperature of the hot-rolled steel sheet after pickling by a first radiation thermometer in which the value of the thermal emissivity of the hot-rolled steel sheet after pickling is set ;
Measuring a second temperature of the hot-rolled steel sheet after pickling by a second thermometer capable of measuring the temperature regardless of the thermal emissivity;
Determining the presence or absence of grain boundary oxides based on the first temperature and the second temperature ;
Intergranular oxidation detection method setting value of the thermal emissivity of the first radiation thermometer is characterized in der Rukoto 0.5 to 0.9.

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