JP4569093B2 - Method for detecting solidification completion position of continuous cast slab - Google Patents

Description

  The present invention relates to a method for detecting a solidification completion position of a continuous cast slab being cast by a continuous casting machine.

  In continuous casting of steel, it is extremely important to determine at which position in the slab the solidification completion position (also referred to as “crater end position”) of the continuous cast slab. This is because detecting the solidification completion position greatly contributes to the improvement of the productivity and quality of the slab.

  For example, when the casting speed is increased in order to improve productivity, the solidification completion position moves to the downstream side in the casting direction of the slab. When the solidification completion position exceeds the range of the slab support roll, the slab swells due to static iron pressure (hereinafter referred to as “bulging”), and in the case of deterioration of the internal quality or huge bulging, it was said that the casting was stopped. A problem occurs. Further, in the light reduction operation for improving the quality by reducing the center segregation of the slab, it is necessary to control the casting speed and the amount of secondary cooling water so that the solidification completion position is located in the light reduction zone.

  In addition, since the cross section of the slab slab is flat, it is known that the solidification completion position is not uniform in the width direction of the slab and the shape varies with time. The shape of the solidification completion position that varies in the width direction is also a major factor that determines the quality and productivity of the slab.

  For example, even in the light reduction operation using the above-described light reduction zone, in order to stably reduce the center segregation of the slab, it is necessary to make the solidification completion position uniform in the width direction of the slab. is there. When the solidification completion position is different in the slab width direction, the reduction amount in the light reduction zone is different in each position in the slab width direction, and a sufficient center segregation improvement effect cannot be obtained at a position where the reduction amount is small. In addition, when the casting speed is maximized for improving productivity or direct rolling, the stretched portion of the solidification completion position may exceed the range of the slab support roll, In this case, problems such as deterioration of internal quality due to bulging occur. Direct feed rolling is a technique in which a hot slab cast by a continuous casting machine is hot-rolled after auxiliary heating.

  In order to meet these demands, it is necessary to measure the solidification state of the slab online. Therefore, various methods for determining the solidification state of the slab have been proposed. Many methods using the transmission intensity of shear waves have been proposed. The shear wave has the property of transmitting only the solid phase and not transmitting when the liquid phase is present. If the transverse wave is transmitted in the thickness direction of the slab and a signal transmitted through the slab is detected, it is completely solidified. This is because it can be determined that an unsolidified layer remains if no signal is obtained.

For example, Patent Document 1 discloses an apparatus that scans a transverse wave ultrasonic wave transmitter and receiver in the slab width direction and detects the shape of a solidification completion position in the slab width direction. Further, in Patent Document 2, as means for improving the measurement system of the transverse wave ultrasonic wave transmitted through the slab, the intensity of the transmitted transverse wave ultrasonic wave is corrected based on the distance between the transmitter and the receiver and the slab, and the correction is made. An apparatus for determining a coagulation state based on the strength obtained is disclosed.
Japanese Patent Laid-Open No. Sho 62-144851 Japanese Patent Laid-Open No. 11-83814

  However, the devices proposed in Patent Document 1 and Patent Document 2 are devices that determine whether coagulation is completed or uncoagulated, and by using these devices, at the position where the device is disposed. Although the solidification state can be determined, the solidification completion position changes greatly in the casting direction due to changes in casting conditions such as casting speed and secondary cooling strength, so in order to grasp the solidification completion position even if the casting conditions are changed In addition, it is necessary to arrange a large number of sensors having a pair of transmitter and receiver in the casting direction. Therefore, in practice, in order to reduce the equipment cost due to the arrangement of a large number of sensors, the number of sensors arranged is limited to detect the solidification completion position only for specific casting conditions, or the sensor installation interval is increased. Therefore, it was forced to reduce the detection accuracy.

  The present invention has been made in view of the above circumstances, and its object is to reduce the solidification completion position that varies depending on the casting conditions and the steel type when detecting the solidification completion position of the slab using transverse wave ultrasonic waves. To provide a method for detecting a coagulation completion position, which can be detected with high accuracy by the number of sensors installed.

A solidification completion position detection method for a continuous cast slab according to a first aspect of the present invention for solving the above-described problem includes a transmission sensor that transmits a transverse wave of electromagnetic ultrasonic waves and a reception sensor that receives the transmitted transverse wave. Two or more electromagnetic ultrasonic sensors are installed at the same position in the width direction of the continuous casting machine but at a distance in the casting direction. First, the position of the electromagnetic ultrasonic sensor on the upstream side is the solidification completion position of the slab. Measure the propagation time of the transverse wave that passes through the slab with the downstream electromagnetic ultrasonic sensor in the state adjusted to the casting condition to be, and obtain the average temperature in the thickness direction of the slab from the measured propagation time, Calculated by heat transfer using the solidification completion position detected by the electromagnetic ultrasonic sensor and the average temperature in the thickness direction of the slab determined by the downstream electromagnetic ultrasonic sensor. Slab The average temperature of the end position and the slab in the thickness direction, to coincide with the electromagnetic ultrasonic sensor at an average temperature of the measured coagulation completion position and the slab in the thickness direction, to calibrate the heat transfer calculations, the calibration Are repeatedly performed under different steel types, different casting speeds, and different secondary cooling strengths, and a database of relational expressions between the solidification completion position and the average temperature in the thickness direction of the slab is constructed in advance for each casting condition, then, said database previously constructed on the basis of the average of the thickness direction temperature at the downstream side of the electromagnetic ultrasonic sensor by determined from the propagation time of the shear wave that will be measured cast piece, to estimate the clotting completion position of the slab It is characterized by.

  The solidification completion position detection method for a continuous cast slab according to a second invention is the first invention, wherein the transmitting sensor and the receiving sensor move in synchronization with the width direction of the continuous casting machine, The solidification completion position in the entire width direction can be detected.

  According to the present invention, two or more electromagnetic ultrasonic sensors that transmit and receive a transverse wave of electromagnetic ultrasonic waves are installed in the casting direction of the continuous casting machine. Since the average temperature is calculated, and the average temperature in the slab thickness direction obtained in this way is estimated in advance against the database of the relationship between the casting conditions and the average temperature in the thickness direction of the slab, the solidification completion position is estimated. By simply installing at least two electromagnetic ultrasonic sensors per strand of the continuous casting machine, it is possible to detect the solidification completion position of the slab with high accuracy. As a result, it is possible to reduce the center segregation of the slab and improve the productivity by increasing the casting speed up to the upper limit of the casting speed, thereby providing an industrially beneficial effect.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic view of a slab continuous casting machine embodying the present invention.

  As shown in FIG. 1, a slab continuous casting machine 1 is provided with a mold 2 for injecting and solidifying molten steel, and a plurality of sets of a pair of opposing rolls are provided below the mold 2. The slab support roll 3 is installed, and on the downstream side of the slab support roll 3, a plurality of transport rolls 4 are positioned above the transport roll 4 and synchronized with the casting speed of the slab 13. A gas cutter 5 is installed. The slab support roll 3 includes a first cooling zone 7a, 7b, a second cooling zone 8a, 8b, a third cooling zone 9a, 9b, and a fourth cooling zone 10a from directly under the mold 2 toward the downstream side. A secondary cooling zone 6 comprising cooling zones divided into a total of 8 of 10b is installed. In each cooling zone of the secondary cooling zone 6, a plurality of spray nozzles (not shown) for air mist spray or water spray are installed, and secondary cooling water is provided from the spray nozzle to the surface of the slab 13. Is sprayed. In each cooling zone, the cooling zone on the upper surface side of the slab continuous casting machine 1 is indicated by a, the cooling zone on the lower surface side is indicated by b, and the total number of cooling zones is 8 in FIG. However, the slab continuous casting machine 1 may be divided into several parts depending on the length of the slab continuous casting machine 1, and the entire range of the slab support roll 3 may be a secondary cooling zone.

  In the gap between the slab support rolls 3 on the downstream side of the secondary cooling zone 6, a transmission sensor 11 (11 a, 11 b) that constitutes a part of the solidification state determination device that detects the solidification completion position 16 of the slab 13, In addition, three receiving sensors 12 (12a, 12b) are installed in the casting direction. The transmission sensors 11, 11 a, 11 b and the reception sensors 12, 12 a, 12 b are installed at the same position in the width direction of the slab continuous casting machine 1. In FIG. 1, the electromagnetic ultrasonic sensors having a pair of the transmission sensor 11 and the reception sensor 12 are installed at three locations in the casting direction. However, the number of installation is not limited to three. Any number is acceptable. However, since the installation cost increases as the number of installations increases, two or three locations are sufficient in the present invention.

  The solidification state determination device includes an electromagnetic ultrasonic sensor including a transmission sensor 11 and a reception sensor 12 that are opposed to each other with a slab 13 interposed therebetween, and a transmission output system (not shown) that outputs a transmission signal to the transmission sensor 11. ) And a reception processing system (not shown) for processing the reception signal received by the reception sensor 12. The transmission sensor 11 and the reception sensor 12 are attached to a mounting base (not shown) that is movable in the width direction of the slab 13, and the transmission sensor 11 and the reception sensor 12 move in synchronization. Thus, the solidification completion position 16 can be detected over the entire width of the slab 13. That is, since it can move in the width direction of the slab 13, the situation of the solidification completion position 16 in the slab width direction can be grasped.

  The transmission sensor 11 transmits a transmission signal as a transverse electromagnetic ultrasonic wave, and the reception sensor 12 receives a transmission signal of the electromagnetic ultrasonic wave that has passed through the slab 13. FIG. 2 shows examples of transmitted transmission signals and received transmission signals. FIG. 2A shows a case where a transmission signal is transmitted when the slab 13 is completely solidified, and the transmission signal passes through the slab 13 and a transmission signal is received by the receiving sensor 12. . The time until the reception sensor 12 receives the transmission signal after the transmission sensor 11 transmits the transmission signal is the propagation time of the transverse wave that penetrates the slab 13. On the other hand, FIG. 2 (B) is a case where a transmission signal is transmitted when the unsolidified layer 15 is present inside the slab 13, and the transmission signal cannot penetrate the unsolidified layer 15, The receiving sensor 12 cannot receive a transmission signal. In FIG. 2, the portion surrounded by a circle is the transmitted signal.

  There is a correlation between the propagation time of the transverse wave passing through the slab 13 and the temperature of the slab 13. FIG. 3 is a diagram showing a result of investigation by the present inventors on the relationship between the temperature of a slab and the speed of a transverse wave passing through the slab in a continuous cast slab heated uniformly using a heating furnace. . As shown in FIG. 3, the transmission speed of the transverse wave in the slab becomes slower as the temperature of the slab becomes higher. Accordingly, even if the surface temperature of the slab 13 is the same, the propagation time becomes longer because the average temperature in the thickness direction of the slab 13 is high immediately after the slab 13 is solidified, whereas the solidification completion position At a position away from 16 on the downstream side in the casting direction, the average temperature in the thickness direction of the slab 13 is lowered, and the propagation time is shortened.

Here, when the temperature distribution in the thickness direction of the slab 13 obtained by heat transfer calculation is represented by T (x), the sound velocity of the transverse wave at each position in the thickness direction of the slab 13 is represented by C (T (x)). The Accordingly, the average temperature (Tav) in the thickness direction of the slab 13 whose temperature distribution in the thickness direction is T (x) is expressed by the following equation (1), and the propagation time of the transverse wave that passes through the slab 13 ( t _d ) is expressed by the following equation (2). However, in the formulas (1) and (2), d is the thickness of the slab 13.

FIG. 4 shows the relationship between the average temperature (Tav) in the thickness direction of the slab thus obtained and the propagation time (t _d ) of the transverse wave in the slab having a thickness (d) of 235 mm. As shown in FIG. 4, by measuring the propagation time of the shear wave (t _d) by coagulation determination device, it can determine the average temperature in the thickness direction of the slab 13 based on the measured propagation times (t _d) it can. In this case, since the transmission sensor 11 and the reception sensor 12 can move in synchronization with the width direction of the slab 13, the slab 13 is determined from the propagation time (t _d ) at each position in the width direction of the slab 13. The average temperature in the thickness direction can be obtained.

  The slab continuous casting machine 1 embodying the present invention has such a configuration. In the slab continuous casting machine 1 having such a configuration, the method for detecting the solidification completion position 16 according to the present invention is as follows. carry out.

  Molten steel is cast into the mold 2 through an immersion nozzle (not shown). The molten steel cast in the mold 2 is cooled in the mold 2 to form a solidified shell 14, and continuously cast downward while being supported by the slab support roll 3 as a slab 13 having an unsolidified layer 15 therein. Pulled out. While the slab 13 passes through the slab support roll 3, it is cooled in the secondary cooling zone 6 to increase the thickness of the solidified shell 14 and eventually complete the solidification to the center.

  In the method for detecting the solidification completion position 16 according to the present invention, the average temperature in the thickness direction of the slab 13 is determined from the propagation time of the transverse electromagnetic ultrasonic wave during the casting of the slab 13, and is obtained beforehand by heat transfer calculation. Further, the solidification completion position 16 is estimated from the average temperature in the thickness direction of the slab 13 obtained from the propagation time using the relational expression between the average temperature in the thickness direction of the slab 13 and the solidification completion position 16. The heat transfer calculation result is calibrated in advance based on the measurement value obtained by the solidification state determination device, and the solidification completion position 16 is estimated based on the calibrated heat transfer calculation result.

  The average temperature is calibrated as follows. First, in FIG. 1 where the position of the electromagnetic ultrasonic sensor on the upstream side, that is, the electromagnetic ultrasonic sensor is installed at three locations, the position where the transmission sensor 11 and the reception sensor 12 are installed, or the transmission sensor. The casting speed and the secondary cooling strength are adjusted so that the position where 11a and the receiving sensor 12a are installed is the solidification completion position 16. This can be adjusted by receiving a transmission signal that has not been received by the reception sensor (12 or 12a) as a transmission signal or by not receiving a transmission signal that has been received.

  Under the casting conditions in which the position of the upstream electromagnetic ultrasonic sensor coincides with the solidification completion position 16, the solidification state of the slab 13 is obtained from heat transfer calculation. Then, the solidification completion position 16 obtained by the heat transfer calculation is compared with the solidification completion position 16 (the position of the sensors 11 and 12 or the position of the sensors 11a and 12a) detected by the solidification state determination device. The average temperature in the thickness direction of the slab 13 obtained by thermal calculation is compared with the average temperature in the thickness direction of the slab 13 obtained from the propagation time of the transverse wave measured by the downstream solidification state determination device. The thermal calculation result is calibrated with the value detected by the solidification state determination device.

  FIG. 5 shows an example of this calibration. FIG. 5 shows an example in which the coagulation completion position 16 is aligned with the position where the transmission sensor 11 and the reception sensor 12 are installed, and the propagation time is measured by the transmission sensor 11a and the reception sensor 12a. . FIG. 5 shows that the average temperature (broken line) in the thickness direction of the slab 13 obtained by heat transfer calculation is higher than the measurement points (two circles in the figure) measured by the solidification state determination device. The example which calibrated the average temperature of the thickness direction by calculation to the temperature shown as a continuous line based on two measured values by the solidification state determination apparatus is shown. In this case, the solidification completion position 16 calculated by the heat transfer calculation is calibrated to the upstream side based on the detection result of the solidification state determination device.

  As described above, in the present invention, the result of the heat transfer calculation is calibrated by the measurement points by the solidification state determination device in at least two places in the casting direction, so the solidification state obtained from the heat transfer calculation is the actual solidification state. It will be very similar.

  This calibration is repeatedly performed under different steel types, different casting speeds, and different secondary cooling strengths, and a database of the relationship between casting conditions and the average temperature in the thickness direction of the slab 13 is constructed. When calibrating, in order to match the solidification completion position 16 and the installation position of the electromagnetic ultrasonic sensor, the installation position of the electromagnetic ultrasonic sensor may be moved up and down in the casting direction.

  During continuous casting of the slab 13, the propagation time of the transverse wave is measured by the solidification state determination device provided with the transmission sensor 11 and the reception sensor 12, and is measured by the database constructed as described above and the solidification state determination device. The solidification completion position 16 of the slab 13 is estimated by comparing with the measured data. For example, when there is a coagulation completion position 16 between the installation position of the transmission sensor 11 and the installation position of the transmission sensor 11a, the reception sensor 12 cannot receive a transmission signal, and the reception sensor 12a and the reception sensor 12b. Then, a transmission signal is received. The average temperature in the thickness direction of the slab 13 is obtained from the propagation time in the receiving sensor 12a and the receiving sensor 12b, and the obtained average temperature is compared with a database constructed in advance, and the average temperature in the thickness direction corresponding to the time of completion of solidification is obtained. The position is defined as the coagulation completion position 16.

  Changes in the solidification completion position 16 according to the width direction of the slab 13, that is, the solidification completion position 16, are obtained by moving the electromagnetic ultrasonic sensors installed apart from each other in the casting direction in synchronization with the width direction of the slab 13. The shape in the width direction can be detected.

  Based on the detected solidification completion position 16 in the slab width direction, for example, when light reduction is performed on the slab 13 to reduce center segregation, the solidification completion position 16 is a light reduction band (not shown). If the solidification completion position 16 is extended to the outlet side of the slab continuous casting machine 1 in order to maximize the productivity of the slab continuous casting machine 1, the solidification completion position 16 is supported by the slab. The casting is performed by adjusting the casting speed and the secondary cooling strength so as not to deviate from the roll. And the slab 13 cast in this way is cut | disconnected by the gas cutting machine 5, and the slab 13a is obtained.

  As described above, according to the present invention, it is possible to accurately detect the solidification completion position 16 of the slab 13 only by installing at least two electromagnetic ultrasonic sensors per strand of the slab continuous casting machine 1. It becomes. As a result, the center segregation of the slab 13 can be reduced, and the productivity can be improved by increasing the casting speed up to the upper limit of the casting speed. This provides an industrially beneficial effect.

  In addition, although the said description was performed regarding the slab continuous casting machine 1, application of this invention is not restricted to the slab continuous casting machine 1, It applies to a Bloom continuous casting machine and a billet continuous casting machine according to the said description. be able to.

  Low carbon steel and medium carbon steel having the composition shown in Table 1 were cast using a slab continuous casting machine (machine length: 42 m) shown in FIG. The cross-sectional size of the slab was 235 mm in thickness and 1340 to 2000 mm in width, and was cast at a casting speed of 1.8 to 2.6 m / min.

  During this casting, a solidification completion position was detected by a solidification state determination device. For comparison, the heat transfer calculation result is not calibrated based on the measurement result of the solidification state determination device, but the thickness direction average temperature by the solidification state determination device and the thickness direction average temperature by the heat transfer calculation result are A method of obtaining the solidification completion position was also carried out by comparing (Comparative Example). The actual solidification completion position is confirmed by a method in which a plurality of metal rods that reach the center of the slab are driven in the casting direction of the slab, and after solidification is completed, the presence or absence of an unsolidified layer is checked from the presence or absence of melting of the implanted metal rod did. The melting point of the metal slag is matched to the melting point of the molten steel to be investigated. The range where the metal smelt is melted is the range where the unsolidified layer remains, and the range where it is not melted is the fully solidified range. Table 2 also shows the detection result of the solidification completion position and the actual measurement result by driving the metal rod. The solidification completion position shown in Table 2 is indicated by the distance (m) from the molten steel surface in the mold.

  As shown in Table 2, in the comparative example, the difference from the solidification completion position detected by driving the metal rod is 0.8 to 1.5 m, whereas in the present invention example, the difference is detected by driving the metal rod. The difference from the completed solidification completion position was within 0.3 m, and it was confirmed that the solidification completion position could be detected with high accuracy by the method of the present invention.

It is the schematic of the slab continuous casting machine which implemented this invention. It is a figure which shows the example of the transmitted signal transmitted and the transmitted signal received, (A) is a case where a transmission signal is transmitted when it is in a completely solidified state, (B) is an uncoagulated layer inside This is a case where a transmission signal is transmitted in a state of being engaged. It is a figure which shows the relationship between the temperature of a slab, and the speed of the transverse wave which passes a slab. It is a figure which shows the relationship between the average temperature of the thickness direction of slab, and the propagation time of a transverse wave. It is a figure which shows the example which calibrates the heat-transfer calculation result with the value detected by the solidification state determination apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Slab continuous casting machine 2 Mold 3 Slab support roll 4 Conveyance roll 5 Gas cutting machine 6 Secondary cooling zone 11 Transmitting sensor 12 Receiving sensor 13 Cast slab 14 Solidified shell 15 Unsolidified layer 16 Solidification completion position

Claims (2)

Electromagnetic ultrasonic sensor consisting of a transmission sensor that transmits a transverse wave of electromagnetic ultrasonic waves and a reception sensor that receives the transmitted transverse wave are positioned at the same position in the width direction of the continuous casting machine but at a distance from the casting direction. 2 or more places in
First, in a state where the position of the electromagnetic ultrasonic sensor on the upstream side is adjusted under the casting conditions to be the solidification completion position of the slab, the propagation time of the transverse wave that passes through the slab is measured by the electromagnetic ultrasonic sensor on the downstream side, Find the average temperature in the thickness direction of the slab from the measured propagation time,
The casting conditions calculated by heat transfer calculation using the solidification completion position detected by the upstream electromagnetic ultrasonic sensor and the average temperature in the thickness direction of the slab determined by the downstream electromagnetic ultrasonic sensor. the average temperature of the coagulation completion position and the slab in the thickness direction of the slab under the said to match the electromagnetic ultrasonic sensor at an average temperature of the coagulation completion position and the slab in the thickness direction is measured, heat transfer calculations Calibrate the
This calibration is repeatedly performed under different steel types, different casting speeds, and different secondary cooling strengths, and a database of relational expressions between the solidification completion position and the average temperature in the thickness direction of the slab is built in advance for each casting condition. And
Then, said database previously constructed on the basis of the average of the thickness direction temperature at the downstream side of the electromagnetic ultrasonic sensor by determined from the propagation time of the shear wave that will be measured cast piece, to estimate the clotting completion position of the slab A method for detecting the complete solidification position of a continuously cast slab characterized by   The transmission sensor and the reception sensor move in synchronization with the width direction of the continuous casting machine, and can detect a solidification completion position in the entire width direction of the slab. 4. A method for detecting a complete solidification position of a continuous cast slab described in 1.

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