JP4453558B2 - Quality judgment method for continuous cast slabs - Google Patents

Description

  The present invention relates to a quality determination method for determining on-line the quality of a continuous cast slab cast by a slab continuous casting machine, and more particularly to a method for determining on-line the degree of segregation formed at the center of a slab. Is.

  In the final solidification part in the solidification process of steel, solute elements such as carbon, phosphorus and sulfur are concentrated in the unsolidified phase. When this concentrated molten steel flows, accumulates and solidifies, a component segregation part having a much higher concentration than the initial concentration is generated. When the steel solidifies, volume shrinkage occurs, and the molten steel is sucked along with the volume shrinkage. In the case of continuous casting, the steel is sucked and flows downstream in the drawing direction of the slab. Since there is not a sufficient amount of molten steel in the unsolidified phase at the end of solidification of a continuous cast slab, the concentrated molten steel between the dendritic trees, which is the final solidified part, flows and accumulates in the center of the slab. It solidifies, producing a so-called “center segregation”.

  Central segregation degrades the quality of steel products. For example, in line pipe materials for oil transportation and natural gas transportation, hydrogen-induced cracking (also referred to as “HIC”) occurs from the center segregation due to the action of sour gas, and it is also used for canned products for drinking water. In the deep drawn material, anisotropy appears in workability due to segregation of components. Therefore, many countermeasures for reducing the center segregation have been proposed from the casting process to the rolling process.

  Among them, as a means of reducing the center segregation of the slab at a low cost and effectively, a method of gradually reducing the unsolidified slab at a reduction amount corresponding to the solidification shrinkage of the slab at the end of solidification (hereinafter referred to as “ Has been proposed (for example, see Patent Document 1). Under this light pressure, the slab is gradually reduced with a light reduction amount commensurate with the amount of solidification shrinkage to reduce the volume of the unsolidified phase, and central segregation is performed without causing the flow of concentrated molten steel between dendrites. Therefore, the solidification completion position (also referred to as “crater end position”) of the slab is controlled within the range of the light pressure lower belt for casting. Here, the light lowering belt is a group of rolls for carrying out light lowering.

  By the way, slab cast slabs (hereinafter referred to as “slabs”) have a flat cross section, so that the solidification completion position is not uniform in the width direction, and the shape varies with time. It has been. If the solidification completion position is different in the slab width direction, the light reduction amount in the light reduction zone will be different in each position in the slab width direction, so the position where the light reduction amount is small, that is, the position where the solidification completion position is extended is sufficient. There are cases where the center segregation improvement effect cannot be obtained and the center segregation cannot be suppressed even if light reduction is performed.

  As described above, the center segregation of the slab is not constant in the casting direction and the width direction even if the light reduction is performed, and even the portion where the casting conditions have changed significantly deviates from the target level. Therefore, in order to determine the degree of center segregation, a sample for inspection is taken from a slab or rolled steel, and a macro test, component analysis test, Charpy test, etc. are performed to inspect the degree of center segregation of the slab. Judgment.

  These test methods are off-line inspection methods, and there is a drawback that feedback is delayed. Therefore, in Patent Document 2, the inventors of the present invention have performed casting by transmitting transverse wave ultrasonic waves to a slab cast by a continuous casting machine. It was proposed to detect the solidification completion position of the piece and to determine the quality of the slab based on the difference between the detected shortest solidification completion position and the detected longest solidification completion position. Here, the shortest solidification completion position is the solidification completion position at the shortest distance from the molten steel surface in the mold, and the longest solidification completion position is the solidification at the farthest distance from the molten steel surface in the mold. It is the completion position.

In Patent Document 2, the coagulation completion position is detected using a transverse wave ultrasonic wave. However, conventionally, various means for detecting the coagulation completion position have been proposed. For example, Patent Document 3 discloses a longitudinal wave. Transmitting the slab while scanning the ultrasonic wave and the transverse wave ultrasonic wave in the slab width direction, the propagation time of the longitudinal ultrasonic wave in the center part of the slab width direction, the solidified part and the unsolidified part in the slab width direction, The thickness of the unsolidified layer at the center position in the slab width direction based on the ratio of the transverse wave ultrasonic wave propagation time / longitudinal wave ultrasonic wave propagation time at the boundary position and the propagation velocity of the longitudinal wave ultrasonic wave in the solid and liquid phases In addition, in Patent Document 4, longitudinal wave waves and transverse wave ultrasonic waves are simultaneously transmitted through the slab, and the amplitude of the transmitted wave of the transverse wave ultrasonic wave and the transmitted wave of the longitudinal wave ultrasonic wave are transmitted. The ratio with the amplitude of the The method for determining the presence of the solidified layer has been proposed. Incidentally, the transverse wave ultrasonic wave has a property of transmitting only the solid phase and not the liquid phase, and Patent Documents 2 to 4 utilize this characteristic of the transverse wave.
JP 54-107831 A JP 2004-298916 A JP 54-115636 A Japanese Patent Laid-Open No. 62-148850

  However, the following problems remain in the prior art.

  In Patent Document 2, since it is only determined whether the coagulation completion position has reached the position where the electromagnetic ultrasonic transmitter and receiver are installed by utilizing the fact that the transverse wave does not pass through the liquid phase, It is impossible to know the solidification completion position simply by installing the transmitter and the receiver, and there is a problem that a large number of transmitters and receivers must be installed in the casting direction in order to know the solidification completion position. Also, when the solidification completion position is on the downstream side in the casting direction with respect to the installation position of the ultrasonic sensor, it is impossible to detect the solidification completion position because the transmission signal cannot be obtained by the method using the transverse wave. There is also a problem that it is impossible to make a determination.

  Patent Document 3 and Patent Document 4 are not related to the quality determination of a slab, but the methods of Patent Document 3 and Patent Document 4 have the following problems when detecting the solidification completion position. That is, in Patent Document 3, the liquid phase thickness is calculated using the propagation speed of the longitudinal wave in the solid phase and the liquid phase, but this propagation speed differs depending on the steel type. This propagation speed is not known for all steel types, so in order to calibrate the measured value obtained from the propagation time, for example, a metal rod is placed in the slab during casting, It is necessary to grasp the solid phase thickness by measuring the extent to which the wrinkles have been melted by cutting and polishing the implanted portion, and to adjust the calculated value obtained from the propagation time against this result. This work is laborious and costly, so it is practically impossible to calibrate all steel types. In addition, it is necessary to grasp the thickness of the slab at the measurement location, but since the slab having an unsolidified layer bulges, it is difficult to accurately and stably measure the thickness of the slab during casting. This is one of the causes of lowering. In Patent Document 4, since only the presence of the uncoagulated layer is determined from the ratio of the amplitude of the transmitted wave of the transverse ultrasonic wave and the amplitude of the transmitted wave of the longitudinal wave ultrasonic wave, a pair of transmitters and receivers are provided. It is impossible to know the solidification completion position simply by installing it, and in order to know the solidification completion position, a large number of transmitters and receivers must be installed in the casting direction.

  The present invention has been made in order to solve the above-described problems, and the object of the present invention is to eliminate the need for calibration by staking a slab into the slab, and to accurately determine the solidification completion position from only the measured value by the sensor. Using a solidification completion position detection device that can detect well, capture the shape of the solidification completion position in the slab width direction, and detect the degree of central segregation that changes in conjunction with the shape of the solidification completion position. To provide a quality determination method capable of accurately determining on-line based on the shape of a position.

  The present inventors have intensively studied and studied to solve the above problems. The examination and research results are explained below.

  First, the examination and research results on a solidification completion position detection device that can accurately detect the solidification completion position from only the measurement value by the sensor without requiring calibration by casting a slag into the slab will be described.

  As a result of repeated simulation of propagation time for the method of estimating the solid phase thickness from the propagation time of longitudinal wave ultrasonic waves in continuous cast slabs, in the conventional method, the dependence of the propagation speed of longitudinal wave ultrasound on the steel type and the casting It was found that the influence of the thickness of the piece is large, and it is impossible to measure with high accuracy unless these calibrations are performed. However, if the solidification completion position is downstream of the longitudinal wave ultrasonic sensor in the casting direction and the liquid phase is included in the propagation path of the ultrasonic wave, the propagation speed in the liquid phase is compared with the propagation speed in the solid phase. Therefore, the propagation time measured by the longitudinal wave ultrasonic sensor changes with high sensitivity according to the solid phase thickness, and the measured value of the solid phase thickness and the relative measurement accuracy of the solidification completion position derived from this solid phase thickness Was found to be extremely expensive.

  Therefore, as a method for calibrating the physical property values used when estimating the thickness of the solid phase from the propagation time of longitudinal ultrasonic waves, calibrating using the solidification completion position required when the transverse wave does not penetrate the liquid phase. It was investigated.

  Using a small steel ingot that was still unsolidified inside, a transverse wave ultrasonic wave was transmitted through the steel ingot while cooling it, and at the same time, the temperature of the steel ingot shaft was measured with a thermocouple. As a result, when an unsolidified phase is present inside the steel ingot, that is, when the solid phase ratio of the steel ingot axis is less than 1, the transverse wave ultrasonic wave cannot penetrate the steel ingot, and the steel ingot is in the axial direction. It was found that the transverse wave ultrasonic wave was transmitted through the steel ingot only when it solidified to the center, that is, when the solid phase ratio of the steel ingot axis became 1. Furthermore, it became clear that this property occurs independently of the steel type. Based on this property, the time when the transmission signal by the transverse wave ultrasonic sensor appears from the disappearance state or the point at which it disappears from the detection state is the solidification completion position and the transverse wave ultrasonic sensor's position regardless of the steel type and casting conditions. The knowledge that the absolute value measurement that the arrangement position matches can be obtained.

  Therefore, the relative measurement accuracy is excellent by calibrating the calculation formula for calculating the coagulation completion position from the propagation time of the longitudinal wave ultrasonic wave under the condition that the coagulation completion position is the arrangement position of the transverse wave ultrasonic sensor. It was found that the method for estimating the coagulation completion position using the propagation time of longitudinal ultrasonic waves can be used as a detection means excellent in absolute accuracy.

  Specifically, if the physical property value is determined so that the coagulation completion position calculated from the propagation time measured by the longitudinal wave ultrasonic sensor becomes the arrangement position of the transverse wave ultrasonic sensor, the coagulation completion position is determined by the propagation time. The calculated formula will be calibrated. Thereafter, the casting conditions are changed by, for example, further increasing the casting speed (hereinafter, the same meaning as “slab drawing speed”) by using a calculation formula for obtaining the solidification completion position from the calibrated propagation time in this way. It was found that the solidification completion position can be obtained with high accuracy.

  Here, the second transverse wave ultrasonic sensor is disposed downstream of the transverse wave ultrasonic sensor serving as the first calibration point in the casting direction, and the casting condition is such that the position of the second transverse wave ultrasonic sensor is the solidification completion position. The calibration accuracy of the solidification completion position was greatly improved by calibrating the calculation formula for calculating the solidification completion position.

  Next, the results of examination and research on the relationship between the shape in the slab width direction at the solidification completion position and center segregation will be described.

  The present inventors conducted a casting / rolling test using a small testing machine and investigated the relationship between the shape in the slab width direction at the solidification completion position and the center segregation in the slab and steel. The test uses a vacuum high-frequency melting furnace and the composition is C: 0.1 mass% (hereinafter referred to as “%”), Si: 0.3%, Mn: 1.3%, P: 0.005% , S: 0.005%, Ti: 0.01%, sol. Al: 0.04% medium carbon steel is melted, and a small test continuous casting machine (slab cross-sectional shape: width 800 mm, thickness 100 mm) , The mold powder is added into the mold, the gradient of the roll interval in the light pressure zone is set to two levels of 0.4 mm (level 1) and 0.9 mm (level 2) per meter, and the casting speed is 1.1 m. / Min. A slab full width sample for inspection was collected from the cast slab, and the slab after sampling was used for hot rolling. The light reduction zone is set in a range of 1.8 m to 6.0 m from the molten steel surface in the mold, and consists of a group of rolls having a diameter of 220 mm that can apply a reduction force to the slab.

  The solidification completion position in the slab width direction was detected using a solidification completion position detection apparatus (detailed description will be described later) provided with an ultrasonic sensor shown in FIG. The used ultrasonic sensor of the solidification completion position detecting device has a structure that can move in the slab width direction, and the solidification completion position in the entire slab width direction can be detected by a pair of ultrasonic sensors.

  The solidification completion position in the slab width direction detected by the solidification completion position detection device did not become flat, but had a concave and convex shape. In the present invention, the solidification completion position closest to the molten steel surface in the mold is referred to as the “shortest solidification completion position”, and conversely, the solidification completion position farthest from the molten steel surface in the mold is referred to as the “longest solidification completion position”. It was decided to organize and analyze. However, since the range from the slab short side to 100 mm is supercooled, this range was excluded from the range for determining the shortest solidification completion position.

  The shortest solidification completion position at level 1 (squeezing gradient = 0.4 mm / m) is 2.4 m from the molten steel surface, and the longest solidification completion position is 4.5 m from the molten steel surface. The distance from the position to the longest solidification completion position (hereinafter referred to as “solidification completion position / valley difference”) was 2.1 m. The longest solidification completion position is a position 110 mm from the short slab piece on the left side in the slab width direction position, and the shortest solidification completion position is a center part in the width direction of the slab, that is, a position of 1/2 width. there were. On the other hand, the shortest solidification completion position at level 2 (squeezing gradient = 0.9 mm / m) is 2.3 m from the molten steel surface, and the longest solidification completion position is 3.2 m from the molten steel surface. Completion position Yamatani difference was 0.9 m. The longest solidification completion position is 130 mm from the left slab short piece at the slab width direction position, and the shortest solidification completion position is the center part in the width direction of the slab, that is, a position of 1/2 width. .

  After collecting a full width sample from the cast slab, the slab was placed in a soaking furnace and held for 90 minutes, heated to 1250 ° C. in a soaking furnace, and then the maximum reduction rate was 20% within a range of 20%. A steel sheet was manufactured by hot rolling with a pass schedule of thickness → 80 mm thickness → 65 mm thickness → 45 mm thickness → 35 mm thickness → 30 mm thickness.

From the slab, chips are collected with a 5 mm diameter drill from three positions, the position corresponding to the longest solidification completion position of the slab, the 1/2 width position, and the 1/4 width position. Carbon was analyzed by an analyzer and the degree of segregation (C / C ₀ ) of carbon was investigated. The segregation degree (C / C ₀ ) is a value obtained by dividing the analysis value of carbon in each part by the carbon analysis value of a sample taken from molten steel, and the portion of positive segregation is the segregation degree (C / C ₀ ). The value becomes 1 or more, and on the contrary, the value of segregation degree (C / C ₀ ) becomes 1 or less in the negative segregation portion.

  The rolled steel sheet was subjected to the HIC test described in NACE Standard TM284-96. Specifically, from the three positions of the steel plate corresponding to the longest solidification completion position, 1/2 width position, and 1/4 width position of the slab, which is the position where the inspection sample was collected from the slab, 20 mm width, 30 mm A sample having a thickness of 100 mm was cut out and immersed in a 0.5% acetic acid solution in which 5% NaCl was dissolved for 96 hours, and the presence or absence of cracking was investigated. In the case of cracking, the case where the value of CLR shown in the following formula (1) was 2% or less was accepted, and the case where it exceeded it was regarded as unacceptable. However, in the formula (1), a is the generated crack length, W is the width of the inspected sample, and in the case of this sample, W is 20 mm.

Table 1 summarizes the solidification completion position length, the degree of segregation (C / C ₀ ), and the measurement results of the HIC test in the above test. In Table 1, the sample position of the slab is displayed with a negative value on the left side and a positive value on the right side with respect to the width direction center of the slab.

As is clear from Table 1, the segregation degree (C / C ₀ ) is the worst in the portion where the solidification completion position is most extended in both level 1 and level 2, and the HIC test of the steel plate is the most in that portion. It turned out to be bad. Further, from this result, it has been found that when evaluating the slab and the steel plate, it is necessary to evaluate at the site where the solidification completion position is the longest, that is, the site where the center segregation is the worst.

Further, when comparing Level 1 and Level 2, it was found that the segregation degree (C / C ₀ ) at the longest solidification completion position and the HIC test were the worst in the slab width direction, but the absolute values were different. did. That is, while the HIC test at the longest solidification completion position failed at level 1, it was acceptable at level 2, although it deteriorated compared to other parts. Comparing the solidification completion position difference between level 1 and level 2 is 2.1 m in level 1 and 0.9 m in level 2, which is why the central segregation at level 1 worsened compared to level 2 It was found that the level 1 was because the solidification completion position / valley difference became larger. That is, it has been found that it is possible to determine the quality of the slab based on the solidification completion position difference between the peaks and valleys.

The present invention has been made on the basis of the above examination results, and the quality determination method for a continuous cast slab according to the first invention is a method of transmitting a transverse wave ultrasonic wave to a continuous cast slab and transmitting the transmitted supersonic wave supersonic wave. A longitudinal ultrasonic wave sensor for receiving a sound wave, and a longitudinal position with respect to a continuous cast slab installed at the same position in the width direction of the slab away from the upstream side in the casting direction of the continuous casting machine. A longitudinal wave ultrasonic sensor that transmits a wave ultrasonic wave and receives the transmitted longitudinal wave ultrasonic wave, and a solidification for obtaining a solidification completion position of the slab using a calculation formula based on a reception signal received by the longitudinal wave ultrasonic sensor A vertical position at the time when it is confirmed that the arrangement position of the transverse wave ultrasonic sensor coincides with the solidification completion position of the slab by a change in intensity of the received signal of the transverse wave ultrasonic sensor. Signal from ultrasonic sensor As the solidification completion position calculated by the calculation formula based matches the position of the transverse ultrasonic wave sensor using the coagulation completion position detecting device in which the calculation formula is calibrated, the continuously cast slab slab width The solidification completion position in the direction is detected, and the quality of the slab is determined based on the difference between the detected shortest solidification completion position and the detected longest solidification completion position.

According to a second aspect of the present invention, there is provided a quality determination method for a continuous cast slab. The first transverse wave ultrasonic sensor transmits a transverse wave ultrasonic wave to the continuous cast slab and receives the transmitted transverse wave ultrasonic wave. Longitudinal wave transmitted and transmitted longitudinal wave ultrasonic waves to the continuous cast slab installed at the same position in the width direction of the slab away from the upstream position in the casting direction of the continuous casting machine. Transverse ultrasonic waves are transmitted to continuous cast slabs installed at the same position in the slab width direction downstream of the first transverse wave ultrasonic sensor and the first transverse wave ultrasonic sensor in the casting direction. And a second transverse wave ultrasonic sensor that receives the transmitted transverse wave ultrasonic wave, and a solidification completion position calculation unit that obtains a solidification completion position of the slab using a calculation formula based on the received signal received by the longitudinal wave ultrasonic sensor; The received signal of the first transverse wave ultrasonic sensor Calculated by the calculation formula based on a signal from the longitudinal wave ultrasonic sensor at the time when the change in the intensity that a first shear wave solidification completion position of the arrangement position and the slab of the ultrasonic sensor match is confirmed The solidification completion position to be matched with the arrangement position of the first transverse wave ultrasonic sensor, and the arrangement position of the second transverse wave ultrasonic sensor and the slab by the change in the intensity of the received signal of the second transverse wave ultrasonic sensor The solidification completion position calculated by the calculation formula based on the signal from the longitudinal wave ultrasonic sensor at the time when it is confirmed that the solidification completion position coincides with the arrangement position of the second transverse wave ultrasonic sensor. Consistently, using coagulation completion position detecting device in which the calculation formula is Tadashisa school, to detect the completion of solidification position of the slab width direction of the continuous casting slabs were detected and the detected shortest clotting completion position Longest coagulation It is characterized in that the quality determination of the slab on the basis of the difference between the completion position.

  The quality determination method for a continuous cast slab according to the third invention is characterized in that, in the first or second invention, the presence or absence of inspection in the slab or the steel material is further determined based on the quality determination. Is.

  The quality judgment method of the continuous cast slab according to the fourth invention is the third invention, wherein the inspection position of the slab or steel material is determined according to the shape of the solidification completion position when the inspection is performed on the slab or steel material. It is characterized by specifying.

  In the present invention, the same position in the slab width direction means a range in which it can be considered that there is almost no change in the casting direction at the solidification completion position. In slab continuous casting machines, the solidification completion position may differ in the width direction of the slab, so the solidification completion position detected by the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor is the same, or the solidification completion position Even if there is a change in the casting direction, it is necessary to arrange the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor within a range in the width direction where it can be considered that there is almost no difference in change. Specifically, when the shape in the slab width direction at the solidification completion position can be regarded as flat, it may be several hundred mm away, and conversely, the shape in the slab width direction at the solidification completion position is greatly changed. In some cases, it is necessary to make it within several tens of mm. This is because the wavelength of the ultrasonic wave used for this purpose is several tens of millimeters and the size of the sensor is about several tens of millimeters. Therefore, if the influence of diffraction is taken into consideration, it is regarded as the same position within several tens of millimeters. Because you can. Moreover, the same position of the continuous casting machine means that not only the slab width direction is the same position but also the same position in the casting direction. The same position in the casting direction means that the positions of the slab support roll gaps where the sensors are arranged are the same.

  According to the present invention, when the solidification completion position of the slab is detected by the transverse wave ultrasonic sensor, the solidification completion position obtained from the propagation time of the longitudinal ultrasonic wave measured by the longitudinal wave ultrasonic sensor is calibrated. It is possible to accurately detect the solidification completion position in the width direction of the slab from only the measured values of the transverse wave ultrasonic sensor and longitudinal wave ultrasonic sensor, without performing laborious calibration work such as hammering into the slab. Become. As a result, the shape of the slab width direction at the solidification completion position can be accurately grasped during casting under various casting conditions for all steel types, and the difference between the detected shortest solidification completion position and the longest solidification completion position Since the center segregation of the slab is determined online, even if the solidification completion position fluctuates during casting and the slab segregation changes, the portion where the segregation has deteriorated is not missed. Central segregation can be determined. In addition, it is possible to specify the inspection position in the slab and the steel material rolled from the slab based on the determination result, the number of inspections can be greatly reduced, and the inspection cost is greatly reduced, Supplying stable quality steel products is achieved. As a result, the center segregation of the slab can be reduced and the productivity can be improved by increasing the speed to the upper limit of the slab drawing speed, thereby producing an industrially beneficial effect.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. First, a first embodiment of a slab continuous casting machine in which a transverse wave ultrasonic sensor and a longitudinal wave ultrasonic sensor constituting a solidification completion position detection device are arranged at the same position will be described. FIG. 1 is a diagram showing a first embodiment of the present invention, and is a schematic side view of a slab continuous casting machine embodying the present invention.

  In FIG. 1, 1 is a slab, 2 is a solid phase part, 3 is a liquid phase part, and 4 is a solidification completion position. The molten steel injected into the mold 101 of the continuous casting machine is cooled by the mold 101 and is cast into the mold 101. The slab 1 having a solid phase part 2 formed in a part in contact with the solid part, the solid part 2 as a periphery, and an unsolidified liquid phase part 3 as an inside is formed of a plurality of pairs arranged opposite to the lower side of the mold 101. It is pulled out below the mold 101 while being supported by the slab support roll 102. A secondary cooling zone (not shown) in which a spray nozzle such as an air mist spray nozzle or a water spray nozzle that blows cooling water toward the surface of the slab 1 is disposed in the gap between the slab support rolls 102 adjacent to each other in the casting direction. The slab 1 is cooled in the secondary cooling zone while being drawn out downstream in the casting direction, and completely solidified to the center. The solidified position 4 is a position where the solidified portion is completely solidified. The slab 1 that has been solidified is cut to a predetermined length by a slab cutting machine 104 installed on the downstream side of the slab support roll 102, and is carried out as a slab 1A by a transport roll 103.

  A part of the slab support roll 102 is set such that a gap between opposing rolls (referred to as “roll interval”) is gradually narrowed toward the downstream side in the casting direction of the slab 1. A group of support rolls 102 that can apply a reduction force to the surface, that is, a light reduction belt 105 is installed. By reducing the slab 1 at the end of solidification, the flow of the concentrated molten steel based on the solidification shrinkage can be suppressed and the center segregation can be improved. What is necessary is just to set the gradient of the roll space | interval in this light reduction belt 105 to the grade from which the reduction speed of the slab 1 becomes the range of 0.6-1.5 mm / min. When the rolling speed is less than 0.6 mm / min, the effect of reducing segregation is small. On the other hand, when the rolling speed exceeds 1.5 mm / min, the concentrated molten steel is squeezed in the direction opposite to the casting direction, and the slab This is because negative segregation may be generated at the center. Moreover, 2-6 mm is sufficient for the total amount of rolling reduction.

  In the slab continuous casting machine having such a configuration, a solidification completion position detecting device for detecting the solidification completion position 4 of the slab 1 is arranged. The solidification completion position detecting device includes a transverse wave ultrasonic sensor composed of a transverse wave ultrasonic transmitter 6 and a transverse wave ultrasonic receiver 8 disposed opposite to each other with the slab 1 interposed therebetween, and a longitudinal wave disposed oppositely across the slab 1. An ultrasonic wave is sent to the slab 1 by supplying an electrical signal to the longitudinal wave ultrasonic sensor including the ultrasonic transmitter 7 and the longitudinal wave ultrasonic receiver 9, and the transverse wave ultrasonic transmitter 6 and the longitudinal wave ultrasonic transmitter 7. An ultrasonic transmission unit 5 that is an electric circuit for performing the processing, a transverse wave transmission intensity detection unit 10 for processing reception signals received by the transverse wave ultrasonic receiver 8 and the longitudinal wave ultrasonic receiver 9, and arrival of a coagulation completion position A detection unit 11, a longitudinal wave propagation time detection unit 12, and a coagulation completion position calculation unit 13 are provided. The ultrasonic waves transmitted by the transverse wave ultrasonic transmitter 6 and the longitudinal wave ultrasonic transmitter 7 are transmitted through the slab 1 and received by the transverse wave ultrasonic receiver 8 and the longitudinal wave ultrasonic receiver 9, respectively. Is converted to

  The transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor are attached to, for example, a pedestal that can move in the width direction of the slab 1, and the width of the slab 1 is obtained by moving the transmitter and the receiver in synchronization. The solidification completion position 4 at each position in the direction can be detected. In this case, the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor are also configured to move synchronously.

  The transverse wave transmission intensity detection unit 10 is an apparatus for detecting the intensity of the transverse wave ultrasonic signal received by the transverse wave ultrasonic receiver 8, and the coagulation completion position arrival detection unit 11 is detected by the transverse wave transmission intensity detection unit 10. It is an apparatus for determining whether the coagulation completion position 4 is upstream or downstream in the casting direction with respect to the arrangement position of the transverse wave ultrasonic transmitter 6 and the transverse wave ultrasonic receiver 8 from the change in the transmission signal of the transverse wave ultrasonic wave. . The longitudinal wave propagation time detection unit 12 is a device that detects the propagation time of longitudinal wave ultrasonic waves that pass through the slab 1 from the reception signal received by the longitudinal wave ultrasonic receiver 9, and is a coagulation completion position calculation unit. Reference numeral 13 denotes an apparatus for calculating and determining the coagulation completion position 4 from the propagation time of the longitudinal wave ultrasonic wave detected by the longitudinal wave propagation time detection unit 12. Here, the transverse wave transmission intensity detection unit 10, the coagulation completion position arrival detection unit 11, the longitudinal wave propagation time detection unit 12, and the coagulation completion position calculation unit 13 are calculated by a computer. Note that an ultrasonic signal amplifier and an A / D converter for taking a waveform into the computer are required between the transverse wave ultrasonic receiver 8 and the longitudinal wave ultrasonic receiver 9 and the computer. It is omitted inside. Moreover, in the coagulation completion position detection apparatus shown in FIG. 1, the transverse wave ultrasonic transmitter 6 and the longitudinal wave ultrasonic transmitter 7 are integrally configured, and similarly, the transverse wave ultrasonic receiver 8 and the longitudinal wave ultrasonic wave are formed. The receiver 9 is integrally formed.

  An example in which the transverse wave ultrasonic transmitter 6 and the longitudinal wave ultrasonic transmitter 7 and the transverse wave ultrasonic receiver 8 and the longitudinal wave ultrasonic receiver 9 are integrally configured will be described with reference to FIG. . FIG. 2 is a diagram illustrating the configuration and operation of an electromagnetic ultrasonic sensor for generating and detecting longitudinal and transverse ultrasonic waves at the same position.

  In FIG. 2, 31 is a magnet. This may be either a permanent magnet or an electromagnet, but a permanent magnet is preferred because the electromagnetic ultrasonic sensor can be miniaturized. Reference numeral 32 denotes a longitudinal wave coil, which is a pancake coil arranged so as to wind around the inner magnetic pole. On the other hand, 33 is a coil for transverse waves, which is a pancake coil arranged so as to overlap the magnetic pole surface. Reference numeral 34 denotes magnetic lines of force from the magnet 31. Reference numerals 35 and 36 denote eddy currents generated in the slab 1 from the longitudinal wave coil 32 and the transverse wave coil 33, respectively. The eddy current 35 and the eddy current 36 are transmitted from the ultrasonic transmission unit 5 to the longitudinal wave coil. It is generated when a high frequency current is passed through the coil 32 and the transverse wave coil 33.

  The eddy current 35 and the eddy current 36 generated in the slab 1 generate a Lorentz force between the eddy current 35 and the static magnetic field from the magnet 31 indicated by the lines of magnetic force 34, thereby generating a longitudinal wave ultrasonic wave 37 and a transverse wave ultrasonic wave 38. To do. The reception of ultrasonic waves is the reverse action of transmission, and the fact that the slab 1 in a static magnetic field vibrates due to ultrasonic waves, and that an eddy current is generated in the slab 1 by the longitudinal wave coil 32 and the transverse wave coil 33. It is to be detected, and the same configuration as the transmission can be used.

  In order to generate and detect longitudinal and transverse waves at the same position in the gap between adjacent slab support rolls of a continuous casting machine, a small electromagnetic that can be inserted into the gap between narrow rolls (generally 40 to 75 mm) An ultrasonic sensor is required. Electromagnetic ultrasonic sensors are well known, but no small electromagnetic ultrasonic sensor that can generate and detect longitudinal ultrasonic waves and transverse ultrasonic waves at the same location has been proposed. In the present invention, as shown in FIG. 2, by arranging the magnets 31 in the width direction of the slab 1, it is possible to provide three or more magnetic poles, and a narrow gap between the slab support rolls 102. In addition to inserting an electromagnetic ultrasonic sensor, longitudinal and transverse ultrasonic waves can be generated and detected at the same location. Further, by reducing the number of sensors installed, it is possible to reduce not only the installation cost but also the maintenance inspection cost.

  As a specific shape of this electromagnetic ultrasonic sensor, the area of the magnetic pole is preferably in the range of about 10 mm × 10 mm to 30 mm × 30 mm, and the interval of the magnetic pole is suitably in the range of about 5 mm to 30 mm. It is appropriate to have a magnetic force of 0.1 T or more. When a permanent magnet is used as the magnet 31, it is desirable to use a rare earth magnet, and the height may be about 20 mm to 100 mm. The number of turns of the coil is suitably in the range of about 10 to 100 turns. In addition, for the part where the coil protrudes from the magnetic pole in the casting direction, the sensor width in the casting direction can be narrowed by bending the coil. Therefore, it may be bent after protruding about 5 mm from the magnetic pole. The protruding width is about 3 mm, and the effect of preventing the sensitivity from being lowered is small, and if it is 10 mm or more, there is not much meaning in narrowing the width in the casting direction of the sensor, so about 3 mm to 10 mm is appropriate.

  When such an electromagnetic ultrasonic sensor is used, the specifications required for an electric circuit are generated and detected if the voltage of the transmission signal is about 1 kV or more (current is 20 A or more) and the gain of the receiving amplifier is 60 dB to 80 dB or more. The frequency of the transmission signal is suitably in the range of about 50 kHz to 150 kHz for the transverse wave and about 100 kHz to 400 kHz for the longitudinal wave. The transmission signal waveform may be a tone burst wave in which a sine wave is generated for a short time, or a modulation signal such as a chirp wave in which the amplitude or phase is changed within a predetermined time width.

  In addition, when the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor are arranged at the same position of the continuous casting machine, the electromagnetic ultrasonic sensor that always generates and detects the longitudinal wave ultrasonic wave and the transverse wave ultrasonic wave is used. There is no need, and if the arrangement interval between the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor is within a range in which it is considered that there is almost no change in the casting direction of the solidification completion position 4, it is specifically within several tens of mm. If so, the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor may be arranged separately.

  Hereinafter, a method for processing the received signal will be described. First, the operation of the transverse wave transmission intensity detector 10 will be described with reference to FIG.

  FIG. 3 is a diagram showing the operation of the transverse wave transmission intensity detection unit 10 and shows a received signal waveform corresponding to one transmission signal. The first wave in FIG. 3 is a signal in which the transmission signal leaks into the transverse wave ultrasonic receiver 8 electrically, and the second wave is a transmission signal of the transverse wave ultrasonic wave. Here, the time position at which the transmission signal of the transverse wave ultrasonic wave appears is roughly known from the thickness of the slab 1, the approximate temperature of the slab 1, and the propagation speed of the transverse wave ultrasonic wave. Is provided, and the maximum value of the signal in the gate is obtained. This processing can be easily realized by calculation processing by taking the waveform of the received signal into the computer by A / D conversion. As a method of taking the maximum value of the signal, either an absolute value based on 0 V or a peak-to-peak value may be used. Actually, since the transmission signal is repeated with a period of several tens of Hz to several hundreds of Hz, the transmission intensity of the transverse ultrasonic wave is obtained after averaging each waveform, or the transmission intensity of each waveform. It is effective to reduce the influence of fluctuation caused by noise.

  Next, the operation of the solidification completion position arrival detection unit 11 will be described with reference to FIG. FIG. 4 is a diagram showing an example of the operation of the solidification completion position arrival detection unit 11. The transverse wave ultrasonic wave sent from the transverse wave transmission intensity detection unit 10 while changing the casting conditions over several tens of minutes of continuous casting operation. It is the chart which detected the intensity | strength of the transmitted signal of.

  As shown in FIG. 4, the intensity of the transmitted signal of the transverse ultrasonic wave changes according to the change in the casting conditions of the continuous casting operation. In the range of A and B in FIG. 4, the intensity of the transmission signal is very small, and the coagulation completion position 4 is downstream in the casting direction from the arrangement position of the transverse wave ultrasonic transmitter 6 and the transverse wave ultrasonic receiver 8. Represents the state that exists. The coagulation completion position arrival detection unit 11 determines that the coagulation completion position 4 has passed the arrangement position of the transverse wave ultrasonic sensor when the intensity of the transmission signal crosses a predetermined determination threshold value. This determination threshold value may be either a predetermined fixed value or a fluctuation threshold value obtained by obtaining a noise level from a signal level in a time domain where a transmission signal of a transverse wave ultrasonic wave does not appear. . When the coagulation completion position arrival detection unit 11 determines that the coagulation completion position 4 has passed the arrangement position of the transverse wave ultrasonic sensor in this way, the coagulation completion position arrival detection unit 11 sends a timing signal to the coagulation completion position calculation unit 13.

  Next, the operation of the longitudinal wave propagation time detector 12 will be described with reference to FIG. FIG. 5 is a diagram illustrating the operation of the longitudinal wave propagation time detection unit 12, and is a diagram illustrating a waveform of a reception signal corresponding to one transmission signal. The first wave in FIG. 5 is a transmission signal that has leaked into the longitudinal wave ultrasonic receiver 9 electrically, and the second wave is a transmission signal of the longitudinal wave ultrasonic wave. Here, the longitudinal wave propagation time detector 12 detects the time from the transmission timing of the transmission signal to the appearance timing of the transmission signal of the longitudinal ultrasonic wave. As a method for detecting a transmission signal of longitudinal ultrasonic waves, as shown in FIG. 5, either the time when the threshold value is exceeded or the time when the maximum value in the gate is reached may be used. Similar to the transverse wave transmission intensity detection unit 10, this processing can be easily realized by calculation processing by taking the waveform of the received signal into the computer by A / D conversion. In practice, the transmission signal is repeated with a period of several tens of Hz to several hundreds of Hz, so that each waveform is averaged and then the propagation time of longitudinal ultrasonic waves is obtained, and the propagation of each waveform is performed. It is effective to reduce the influence of fluctuation due to noise by averaging time.

Finally, the operation of the coagulation completion position calculation unit 13 will be described with reference to FIG. FIG. 6 is a diagram illustrating the operation of the coagulation completion position calculation unit 13 in the first embodiment, and illustrates an approximate expression for calculating the coagulation completion position 4 from the propagation time of longitudinal wave ultrasonic waves. As the solidification completion position 4 is further downstream in the casting direction than the arrangement position of the longitudinal wave ultrasonic transmitter 7 and the longitudinal wave ultrasonic receiver 9, the thickness of the liquid phase portion 3 increases, and the propagation time becomes longer. Therefore, the propagation time and the distance from the molten steel surface 14 in the mold 101 to the solidification completion position 4 are approximately proportional to each other, and the relationship shown in FIG. 6 is shown. Therefore, in order to obtain the solidification completion position 4 from the propagation time, an approximate expression of a polynomial, for example, a linear expression shown in the following expression (2) may be used. In Equation (2), CE is the distance from the molten steel surface 14 in the mold to the solidification completion position 4, Δt is the propagation time of longitudinal ultrasonic waves, and a ₁ and a ₀ are polynomial coefficients.

In FIG. 6, a line indicated by A represents an approximate expression before calibration. Here, when the timing signal for determining the passage of the coagulation completion position 4 is sent from the coagulation completion position arrival detection unit 11 to the coagulation completion position calculation unit 13, the coagulation completion position calculation unit 13 transmits the longitudinal wave ultrasonic wave at that time. The propagation time (Δt ₁ ) is obtained, and further, the following formula (3) is set so that the distance (CE) from the molten steel surface 14 in the mold to the solidification completion position 4 matches the arrangement position of the transverse wave ultrasonic sensor. Is used to correct the coefficient (a ₀ ) in equation (2). However, in the expression (3), CE ₁ is the distance from the molten steel surface 14 in the mold to the position where the transverse ultrasonic sensor is arranged, and Δt ₁ is determined that the solidification completion position 4 has passed the arrangement position of the transverse wave ultrasonic sensor. It is the propagation time of the longitudinal ultrasonic wave at the time.

  As a result, the approximate expression for determining the solidification completion position 4 is calibrated, for example, after calibration indicated by B in FIG. After calibration, the solidification completion position 4 can be detected on-line during casting with high accuracy based on the propagation time of longitudinal ultrasonic waves using the approximate expression after calibration indicated by B.

  The calibration is performed only once every time a new steel type is cast, every time the solidification completion position 4 crosses the position of the transverse ultrasonic sensor during continuous casting operation, or at the discretion of the operator. Any suitable time may be used.

  As an electromagnetic ultrasonic sensor for generating and detecting longitudinal wave ultrasonic waves and transverse wave ultrasonic waves at the same position, the electromagnetic ultrasonic sensor shown in FIG. 2 has three magnetic poles. It can also be set as above. FIG. 7 is a diagram showing a configuration of an example in which four magnetic poles of an electromagnetic ultrasonic sensor for generating and detecting longitudinal wave ultrasonic waves and transverse wave ultrasonic waves at the same position are used. In FIG. 7, the longitudinal wave coil 32 and the transverse wave coil 33 that are actually arranged in an overlapping manner are drawn separately so that the arrangement with respect to the magnetic poles can be easily understood, and the left side of the drawing is for longitudinal waves. In the layout diagram of the coil 32, the right side is a layout diagram of the coil 33 for transverse waves. Similar to the electromagnetic ultrasonic sensor shown in FIG. 2, the longitudinal wave coil 32 is disposed so as to wrap around the inner magnetic pole, and the transverse wave coil 33 is disposed so as to overlap the magnetic pole surface. The number of magnetic poles is not limited to four and can be implemented even more. In this case, since the strength of the horizontal magnetic field with respect to the longitudinal wave coil 32 is increased, the sensitivity of longitudinal ultrasonic waves is increased and the generation / detection positions of the transverse ultrasonic waves and longitudinal ultrasonic waves are substantially equal. effective.

  By the way, when the coagulation completion position 4 is upstream of the position where the longitudinal wave ultrasonic sensor is disposed, all the longitudinal wave ultrasonic waves pass through the solid phase part 2. In addition, since the transverse wave ultrasonic waves are generated and detected at the same position as the longitudinal wave ultrasonic waves, they all pass through the solid phase part 2. The propagation time in this case depends on the propagation speed of the ultrasonic wave in the solid phase part 2. Since the propagation speed of the ultrasonic wave depends on the temperature of the solid phase part 2, the propagation time of the longitudinal wave ultrasonic wave and the transverse wave ultrasonic wave changes depending on the temperature of the slab 1. On the other hand, if the distance from the solidification completion position 4 to the electromagnetic ultrasonic sensor arrangement position is different, the temperature of the slab at the electromagnetic ultrasonic sensor arrangement position changes. That is, as the solidification completion position 4 becomes farther upstream from the position where the electromagnetic ultrasonic sensor is disposed, the temperature of the slab at the position where the electromagnetic ultrasonic sensor is disposed decreases. As the temperature of the slab is lower, the propagation speed of the ultrasonic wave increases, so the propagation time becomes shorter.

  Accordingly, even in the case where the solidification completion position 4 is upstream of the arrangement position of the longitudinal wave ultrasonic sensor, the relationship between the propagation time and the distance from the molten steel surface 14 to the solidification completion position 4 is shown in FIG. The trend is similar to that shown. However, compared with the case where the solidification completion position 4 is present downstream of the longitudinal wave ultrasonic sensor and the liquid phase part 3 is included in the propagation path, the liquid phase part 3 having a slower propagation speed than the solid phase part 2 is present. Since there is no influence, even if the solidification completion position 4 fluctuates in the casting direction, the influence of this fluctuation on the propagation time is small, and the fluctuation rate of the detected propagation time is small.

  Therefore, the calculation formula used when obtaining the coagulation completion position 4 from the propagation time is different depending on whether the coagulation completion position 4 exists on the upstream side of the longitudinal wave ultrasonic sensor or on the downstream side. Is preferred.

  Specifically, when the coagulation completion position 4 is upstream of the longitudinal wave ultrasonic sensor, a method using an empirical formula (formula as shown in FIG. 6) that directly links the propagation time and the coagulation completion position. Alternatively, any method of estimating the internal temperature or axial temperature of the slab from the propagation time and estimating the solidification completion position from the value may be used. On the other hand, when the coagulation completion position 4 is on the downstream side of the longitudinal wave ultrasonic sensor, a method using an empirical formula (expression as shown in FIG. 6) in which the propagation time and the coagulation completion position are directly linked, or propagation Any method of estimating the thickness of the solid phase portion 2 or the thickness of the liquid phase portion 3 from the time and estimating the solidification completion position from the value may be used. Even when an empirical formula as shown in FIG. 6 is used, the coefficients are different depending on whether the coagulation completion position 4 is upstream or downstream of the longitudinal wave ultrasonic sensor.

  In order to perform this, it is necessary to determine whether the coagulation completion position 4 is upstream or downstream of the arrangement position of the longitudinal wave ultrasonic sensor. Therefore, in this case, the coagulation completion position is determined. The arrival detection unit 11 also performs the following determination. That is, if the transmission intensity of the transverse wave ultrasonic wave is larger than the determination threshold value, the coagulation completion position 4 is determined to be upstream, and conversely if it is equal to or less than the determination threshold value, the coagulation completion position 4 is determined to be downstream. The signal is sent to the coagulation completion position calculation unit 13. The solidification completion position calculation unit 13 selects a calculation formula for calculating the solidification completion position 4 based on the result, and calculates the solidification completion position 4 using the selected calculation formula.

  In the continuous casting machine configured as described above, the quality determination method for the continuous cast slab according to the present invention is performed as follows.

  Molten steel is cast on the mold 101 through an immersion nozzle (not shown). The molten steel cast in the mold 101 is cooled by the mold 101 to form the solid phase part 2, and continuously drawn as a slab 1 having a liquid phase part 3 therein while being supported by the slab support roll 102. It is. The slab 1 is cooled in the secondary cooling zone while an appropriate amount of light reduction is added by the light reduction zone 105, the thickness of the solid phase portion 2 is increased, and solidification is eventually completed to the center portion. At that time, the position of the solidification completion position 4 is detected by the solidification completion position detection device.

  In this case, when casting to reduce the center segregation, it is desirable to control both the shortest solidification completion position and the longest solidification completion position within the range of the light pressure lowering band 105, and therefore the longest solidification completion position is lightly reduced. It is necessary to adjust the casting speed and the amount of secondary cooling water so as not to exceed the band 105. However, in the present invention, performing light reduction is not an essential condition, and casting may be performed without applying light reduction.

  From the detected solidification completion position 4 in the width direction of the slab, the shortest solidification completion position and the longest solidification completion position are obtained, and based on the difference between the longest solidification completion position and the shortest solidification completion position, that is, the solidification completion position mountain valley difference. Perform online quality assessment on slab center segregation. Specifically, the detected value of the solidification completion position ridge / valley difference is stored in a process computer (not shown) or the like every predetermined time, and the slab 1 is cut by the slab cutting machine 104 to obtain individual values. When it becomes the slab 1A, the maximum value among the solidification completion position and valley differences corresponding to the individual slabs 1A stored is determined as the solidification completion position and valley difference of the slab 1A. Furthermore, based on the quality determination result, it is possible to determine whether or not to inspect the slab 1A, for example, whether to inspect the slab 1A or a steel material obtained by rolling the slab 1A.

The determination of pass-fail based on the solidification completion position Yamatani difference, for example, whether or not to carry out the inspection, basically determines the threshold value by accumulating results. FIG. 8 is a diagram showing the relationship between the solidification completion position ridge-and-valley difference and the carbon segregation degree (C / C ₀ ) at the longest solidification completion position investigated by the present inventors and the like, as shown in FIG. In addition, the degree of segregation (C / C ₀ ) deteriorates as the solidification completion position / valley difference increases.

According to the experience of the present inventors, in the case of a slab with a normal center segregation criterion, the segregation degree (C / C ₀ ) is 1.3 or less if the solidification completion position ridge / valley difference is within 2 m. , Have confirmed that it is okay as a pass. In the case of passing, the operation is performed such that only the ½ width is inspected or the inspection is not performed in some cases. On the other hand, in the case of failure, in addition to the ½ width, an operation is performed such as inspecting the longest solidification completion position or the second longest solidification completion position. Of course, for a product that requires a stricter and higher quality level, the pass / fail criterion may be changed such that the solidification completion position / valley difference is within 1 m. In short, the degree of segregation (C / C ₀ ) that satisfies the required quality level is determined, and the solidification completion position and valley difference satisfying the degree of segregation (C / C ₀ ) may be used as a criterion.

  Usually, the position in the slab width direction of the shortest solidification completion position and the longest solidification completion position also changes during casting. However, when the slab 1 is cooled in a state where the spray nozzle is not clogged or the like, the shortest solidification completion position exists at the center of the slab width, and the longest solidification completion position has a slab thickness of about 250 mm. In some cases, it exists at a position about 200 mm away from the short side surface of the slab. For this reason, the solidification completion position shape is often W-shaped as shown in FIG. However, in this case, the solidification completion position shape is not an object on the left and right with respect to the center of the slab 1, and a difference occurs on the left and right in the width direction as shown in FIG. In such a case, in the present invention, the difference L1 in the figure, that is, the larger difference is used as the solidification completion position mountain-and-valley difference as a determination criterion.

  The slab 1 thus cast is cut by a slab cutting machine 104 to obtain a slab 1A. Each slab 1A is determined based on the solidification completion position and valley difference, and based on the determination result, a sample for inspection is taken from the slab 1A as necessary, and then transported to the next hot rolling step. The After hot rolling, an inspection sample is collected from the optimum location of the rolled steel material according to the determination result based on the solidification completion position difference between the peaks and valleys. If it is determined from the inspection result of the slab 1A that rolling is useless, the hot rolling is stopped and the slab 1A is subjected to a scrapping process.

  As described above, according to the present invention, since the center segregation of the slab 1 is determined online based on the solidification completion position / valley difference of the cast slab 1, the solidification completion position / valley difference fluctuates during casting. Even if the slab segregation changes, the center segregation can be determined quickly and reliably with high accuracy. Moreover, since it becomes possible to determine the presence or absence of the inspection implementation in the slab or the steel material rolled from the slab based on this determination result, the inspection can be performed efficiently and efficiently without waste. Can be maintained at a high level.

  Next, in the slab continuous casting machine in which the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor constituting the solidification completion position detection device are arranged at the same position in the slab width direction at two locations separated in the casting direction of the continuous casting machine. A second embodiment will be described. FIG. 10 is a diagram showing a second embodiment of the present invention, and is a schematic view of a slab continuous casting machine in which the present invention is implemented.

  In the second embodiment, as shown in FIG. 10, a transverse wave ultrasonic sensor comprising a transverse wave ultrasonic transmitter 6 and a transverse wave ultrasonic receiver 8, a longitudinal wave ultrasonic transmitter 7 and a longitudinal wave ultrasonic receiver. 9 longitudinal wave ultrasonic sensors are separately arranged at two locations in the casting direction. In this case, the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor need not be sensors that generate and detect longitudinal wave ultrasonic waves and transverse wave ultrasonic waves at the same position as shown in FIG. An ultrasonic sensor can be used. Of course, the electromagnetic ultrasonic sensor shown in FIG. 2 can also be used.

  However, in the slab continuous casting machine, the solidification completion position 4 may be different in the width direction of the slab 1, so the change in the casting direction of the solidification completion position 4 detected by the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor is different. It is necessary to arrange a transverse wave ultrasonic sensor and a longitudinal wave ultrasonic sensor within a range in the width direction that can be regarded as almost absent. Specifically, as described above, when the secondary cooling is appropriate and the shape in the width direction of the solidification completion position 4 can be regarded as flat, the width of the solidification completion position 4 may be several hundred mm apart. When the shape of the direction is greatly changed, it is necessary to be within several tens of mm. Therefore, in order to cope with any of them, it is necessary to be within several tens of mm. When the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor are moved in the width direction of the slab 1 to detect the solidification completion position 4 in the slab width direction, it is necessary to move in a state in which this relationship is maintained.

  In addition, since the detection accuracy is better as the distance between the arrangement position of the transverse wave ultrasonic sensor and the arrangement position of the longitudinal wave ultrasonic sensor is smaller, and the accuracy is worsened as the arrangement interval is wider, the arrangement interval may be within about 5 m. preferable. Further, as described above, the propagation time of the longitudinal wave ultrasonic wave detected by the longitudinal wave ultrasonic sensor changes sensitively when the liquid phase part 3 is included, so that the coagulation completion position 4 is at the longitudinal wave ultrasonic sensor. Therefore, the longitudinal wave ultrasonic sensor is preferably arranged upstream of the transverse wave ultrasonic sensor in the casting direction.

  Other configurations are the same as those of the first embodiment shown in FIG. 1, and the same portions are denoted by the same reference numerals, and the description thereof is omitted.

The operations of the transverse wave transmission intensity detection unit 10, the coagulation completion position arrival detection unit 11, the longitudinal wave propagation time detection unit 12, and the coagulation completion position calculation unit 13 are the same as those in the first embodiment, and the coagulation completion position arrival detection unit. When the timing signal of passage determination of the coagulation completion position 4 is sent from 11 to the coagulation completion position calculation unit 13, the coagulation completion position calculation unit 13 obtains the propagation time (Δt ₁ ) of the longitudinal ultrasonic wave at that time, and further The coefficient (a ₀ ) is corrected by the above-described equation (3) so that the distance (CE) from the molten steel surface 14 to the solidification completion position 4 becomes the arrangement position of the transverse ultrasonic sensor. After calibrating the polynomial for obtaining the solidification completion position 4, it is possible to accurately detect the solidification completion position 4 on-line during casting based on the propagation time of longitudinal ultrasonic waves by using the approximate expression after calibration. . Changing the calculation formula for calculating the coagulation completion position 4 according to the time of calibration and whether the coagulation completion position 4 is upstream of the longitudinal wave ultrasonic sensor is the first embodiment described above. This will be done in accordance with the explanation in.

  And the solidification completion position 4 in the slab width direction of the slab 1 during casting is detected by using the solidification completion position detection device having the above-described configuration, and the casting is performed based on the difference between the shortest solidification completion position and the longest solidification completion position. The quality of the piece 1 is determined. Since the quality judgment method and the quality-judged slab and the operation of the steel material rolled from the slab are the same as those in the first embodiment described above, description thereof will be omitted.

  In FIG. 10, the arrangement position of the transverse ultrasonic sensor is on the downstream side of the arrangement position of the longitudinal ultrasonic sensor, but it may be on the opposite upstream side. However, in this case, since the accuracy of detecting the coagulation completion position 4 upstream of the longitudinal wave ultrasonic sensor by the longitudinal wave ultrasonic sensor is not so high, after the arrival of the coagulation completion position 4 is detected by the transverse wave ultrasonic sensor. Considering the casting speed, it is desirable to calibrate the polynomial when it is expected that the solidification completion position 4 has reached the position where the longitudinal ultrasonic sensor is disposed. By doing so, high accuracy can be obtained.

  Finally, the second transverse wave ultrasonic sensor constituting the solidification completion position detecting device is arranged at the same position in the slab width direction, which is separated from the first transverse wave ultrasonic sensor on the downstream side in the casting direction. A third embodiment of the continuous casting machine will be described. FIG. 11 is a diagram showing a third embodiment of the present invention, and is a schematic view of a slab continuous casting machine in which the present invention is implemented.

  In the third embodiment, as shown in FIG. 11, the transverse wave ultrasonic transmitter 6, the transverse wave ultrasonic receiver 8, the longitudinal wave ultrasonic transmitter 7, and the longitudinal wave ultrasonic reception in the first embodiment example. The second transverse wave ultrasonic wave comprising a transverse wave ultrasonic transmitter 6A and a transverse wave ultrasonic receiver 8A downstream of the arrangement position of the electromagnetic ultrasonic sensor capable of generating and detecting the longitudinal wave ultrasonic wave and the transverse wave ultrasonic wave comprising the detector 9. A sonic sensor is installed. In this case, the second transverse wave ultrasonic sensor does not need to be a sensor that generates and detects the longitudinal wave ultrasonic wave and the transverse wave ultrasonic wave at the same position as shown in FIG. Can be used. Of course, the electromagnetic ultrasonic sensor shown in FIG. 2 can also be used. In order to avoid the influence of the change in the slab width direction of the solidification completion position 4, the second transverse wave ultrasonic sensor is a transverse wave ultrasonic sensor comprising a transverse wave ultrasonic transmitter 6 and a transverse wave ultrasonic receiver 8 ( (Hereinafter referred to as “first transverse wave ultrasonic sensor”) and the same position in the slab width direction. The received signal of the transverse wave ultrasonic receiver 8A is sent to the transverse wave transmission intensity detector 10A, and the signal of the transverse wave transmission intensity detector 10A is sent to the coagulation completion position arrival detector 11A. The transverse wave transmission intensity detection unit 10A and the coagulation completion position arrival detection unit 11A have the same functions as the transverse wave transmission intensity detection unit 10 and the coagulation completion position arrival detection unit 11 in the first embodiment described above, respectively. When the coagulation completion position 4 passes through the arrangement position of the second transverse wave ultrasonic sensor, the coagulation completion position arrival detection unit 11A sends a timing signal to the coagulation completion position calculation unit 13. When the first transverse wave ultrasonic sensor, the longitudinal wave ultrasonic sensor, and the second transverse wave ultrasonic sensor are moved in the width direction of the slab 1 to detect the solidification completion position 4 in the slab width direction, As described in the embodiment, it is necessary to move these sensors while maintaining the same position in the slab width direction.

  In addition, if the distance between the second transverse wave ultrasonic sensor and the first transverse ultrasonic sensor is too small, the calibration accuracy cannot be improved. The range of about 2 m to 10 m is appropriate. Other configurations are the same as those of the first embodiment shown in FIG. 1, and the same portions are denoted by the same reference numerals, and the description thereof is omitted.

  The operations of the transverse wave transmission intensity detection unit 10, the coagulation completion position arrival detection unit 11, and the longitudinal wave propagation time detection unit 12 are the same as those in the first embodiment, but the operation of the coagulation completion position calculation unit 13 is different. Hereinafter, the operation of the coagulation completion position calculation unit 13 will be described with reference to FIG.

  FIG. 12 is a diagram illustrating the operation of the coagulation completion position calculation unit 13 in the third embodiment, and illustrates an approximate expression for calculating the coagulation completion position 4 from the propagation time of longitudinal wave ultrasonic waves. Here, it is assumed that the coagulation completion position 4 is calculated from the propagation time of the longitudinal wave ultrasonic wave using the equation (2) as in the first embodiment. In FIG. 12, a line indicated by A represents an approximate expression before calibration.

Here, when the coagulation completion position arrival detection unit 11 sends a timing signal for determining the passage of the coagulation completion position 4 at the first transverse wave ultrasonic sensor position to the coagulation completion position calculation unit 13, the coagulation completion position calculation unit 13. Then, the propagation time (Δt ₁ ) of the longitudinal ultrasonic wave at that time is stored. Next, when the casting speed and the secondary cooling strength are changed to extend the solidification completion position 4 to the downstream side in the casting direction and the solidification completion position 4 passes the arrangement position of the second transverse wave ultrasonic sensor, the solidification completion position A timing signal for determining the passage of the coagulation completion position 4 is sent from the arrival detection unit 11A to the coagulation completion position calculation unit 13. The coagulation completion position calculation unit 13 obtains the propagation time (Δt ₂ ) of longitudinal ultrasonic waves at that time. Then, simultaneous equations of the following equations (4) and (5) are solved, and the constant (a ₁ ) and the constant (a ₀ ) of equation (2) are corrected. However, in the formulas (4) and (5), CE ₁ is the distance from the molten steel surface 14 in the mold to the position of the first transverse wave ultrasonic sensor, and Δt ₁ is the first transverse wave at the solidification completion position 4. Longitudinal ultrasonic wave propagation time when it is determined that the ultrasonic sensor has passed the arrangement position, CE ₂ is the distance from the molten steel surface 14 in the mold to the arrangement position of the second transverse ultrasonic sensor, Δt ₂ is It is the propagation time of longitudinal ultrasonic waves when it is determined that the coagulation completion position 4 has passed the arrangement position of the second transverse wave ultrasonic sensor.

  As a result, the approximate expression for obtaining the solidification completion position 4 is calibrated and becomes, for example, a line indicated by B in FIG. After calibration, the solidification completion position 4 can be detected on-line during casting with high accuracy based on the propagation time of longitudinal ultrasonic waves using the approximate expression after calibration indicated by B. In this case, the coagulation completion position 4 can be detected with higher accuracy than in the first embodiment. Changing the calculation formula for calculating the coagulation completion position 4 according to the time of calibration and whether the coagulation completion position 4 is upstream of the longitudinal wave ultrasonic sensor is the first embodiment described above. This will be done in accordance with the explanation in.

  And the solidification completion position 4 in the slab width direction of the slab 1 during casting is detected by using the solidification completion position detection device having the above-described configuration, and the casting is performed based on the difference between the shortest solidification completion position and the longest solidification completion position. The quality of the piece 1 is determined. Since the quality judgment method and the quality-judged slab and the operation of the steel material rolled from the slab are the same as those in the first embodiment described above, description thereof will be omitted.

  In addition, this invention is not limited to the range demonstrated above, In the range which does not deviate from the summary, it can be variously changed. For example, although the case where an electromagnetic ultrasonic sensor is used has been described in the above description, a method of bringing a piezoelectric vibrator into contact with water or a laser ultrasonic method may be used for transmission and reception of longitudinal ultrasonic waves. Also, it is useful to transmit by laser ultrasonic method and receive by electromagnetic ultrasonic method because the measurement sensitivity is increased.

  Furthermore, in the above embodiment, the transverse wave ultrasonic transmitter 6 and the transverse wave ultrasonic receiver 8 or the longitudinal wave ultrasonic transmitter 7 and the longitudinal wave ultrasonic receiver 9 are sandwiched between the slab 1. However, the transmitter and the receiver are arranged on the same surface of the slab 1 and are measured by the reflection method using echoes on the opposite surface of the slab 1. Also good. The ultrasonic sensor referred to in the present invention includes any of these forms. In the present invention, the calibration of the calculation formula for obtaining the solidification completion position from the propagation time may be performed at any plurality of positions in the slab width direction. In this way, if different calculation formulas are used at arbitrary multiple positions in the slab width direction, the influence of cooling unevenness and thickness fluctuation in the slab width direction is reduced, and the measurement accuracy is improved at each position. Can be improved.

  Moreover, although the case where the coagulation completion position 4 is directly obtained from the propagation time of the longitudinal wave ultrasonic wave using a linear equation has been described, a polynomial such as a quadratic equation or a cubic equation may be used. The thickness of the solid phase portion 2 may be obtained from the propagation time, and the solidification completion position may be obtained from the obtained thickness of the solid phase portion 2 and the casting speed.

  Furthermore, for electromagnetic ultrasonic sensors for generating and detecting longitudinal and transverse ultrasonic waves at the same position, the polarity of the magnetic pole of the sensor is not set up separately from the longitudinal and transverse wave coils. By alternately changing the longitudinal coil and the transverse coil, the same coil can be used.

It is a figure which shows the 1st Example of this invention. It is a figure which shows the structure and operation | movement of an electromagnetic ultrasonic sensor for generating and detecting a longitudinal wave ultrasonic wave and a transverse wave ultrasonic wave in the same position. It is a figure which shows operation | movement of a transverse wave transmission intensity detection part. It is a figure which shows an example of operation | movement of the coagulation completion position arrival detection part. It is a figure which shows operation | movement of a longitudinal wave propagation time detection part. It is a figure which shows operation | movement of the coagulation completion position calculating part in the example of 1st Embodiment. It is a figure which shows the structure which used the magnetic pole of the electromagnetic ultrasonic sensor for generating and detecting a longitudinal wave ultrasonic wave and a transverse wave ultrasonic wave in the same position as four. It is a figure which shows the relationship between the solidification completion position mountain valley difference in a longest solidification completion position, and a segregation degree. It is a figure which shows one example of the width direction shape of a coagulation completion position. It is a figure which shows the 2nd Example of this invention. It is a figure which shows the 3rd Embodiment of this invention. It is a figure which shows operation | movement of the coagulation completion position calculating part in the example of 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cast piece 2 Solid phase part 3 Liquid phase part 4 Solidification completion position 5 Ultrasonic transmission part 6 Transverse wave ultrasonic transmitter 7 Longitudinal wave ultrasonic transmitter 8 Transverse wave ultrasonic receiver 9 Longitudinal wave ultrasonic receiver 10 Transverse wave transmission intensity Detection unit 11 Solidification completion position arrival detection unit 12 Longitudinal wave propagation time detection unit 13 Solidification completion position calculation unit 14 Molten steel surface 31 Magnet 32 Longitudinal wave coil 33 Transverse wave coil 34 Magnetic field line 35 Eddy current 36 Eddy current 37 Longitudinal wave ultrasonic wave 38 Transverse ultrasonic wave 101 Mold 102 Casting support roll 103 Conveying roll 104 Casting cutting machine 105 Light pressure lower belt

Claims (4)

A transverse wave ultrasonic sensor that transmits a transverse wave ultrasonic wave to a continuous cast slab and receives the transmitted transverse wave ultrasonic wave , a slab separated from the arrangement position of the transverse wave ultrasonic sensor and the upstream side in the casting direction of the continuous casting machine A longitudinal wave ultrasonic sensor that transmits longitudinal wave ultrasonic waves to a continuous cast slab installed at the same position in the width direction and receives the transmitted longitudinal wave ultrasonic waves, and received by the longitudinal wave ultrasonic sensor A solidification completion position calculation unit that obtains a solidification completion position of the slab using a calculation formula based on the received signal, and the arrangement position of the transverse wave ultrasonic sensor and the slab by changing the intensity of the reception signal of the transverse wave ultrasonic sensor The solidification completion position calculated by the calculation formula based on the signal from the longitudinal wave ultrasonic sensor at the time when it is confirmed that the solidification completion position coincides with the arrangement position of the transverse wave ultrasonic sensor. Before Using a solidification completion position detector that calibrates the calculation formula, the solidification completion position in the slab width direction of the continuous cast slab is detected, and the difference between the detected shortest solidification completion position and the detected longest solidification completion position. The quality judgment method of the continuous cast slab characterized by performing quality judgment of a slab based on this. A first transverse wave ultrasonic sensor that transmits transverse wave ultrasonic waves to the continuous cast slab and receives the transmitted transverse wave ultrasonic waves, an arrangement position of the first transverse wave ultrasonic sensor, and a casting direction upstream side of the continuous casting machine installed at the same position of the slab width direction spaced a longitudinal ultrasonic wave sensor for receiving the transmitted and transmitted longitudinal ultrasonic wave and longitudinal wave ultrasonic waves to continuously cast slabs, the first shear wave A second transverse wave ultrasonic sensor, which is installed at the same position in the slab width direction downstream of the ultrasonic sensor in the casting direction, transmits transverse wave ultrasonic waves to the continuous cast slab and receives the transmitted transverse wave ultrasonic waves. And a solidification completion position calculation unit for obtaining a solidification completion position of the slab using a calculation formula based on the reception signal received by the longitudinal wave ultrasonic sensor, and the intensity of the reception signal of the first transverse wave ultrasonic sensor Of the first transverse wave ultrasonic sensor by the change of Solidification completion position calculated by the calculation formula based on a signal from the longitudinal wave ultrasonic sensor at the time the can and the solidification completion location of the location position and slab match was confirmed first transverse ultrasonic waves consistent with the arrangement position of the sensor, and, that the second transverse ultrasonic wave sensor solidification completion position of the arrangement position and the slab of the second transverse ultrasonic wave sensor by the change in the intensity of the received signal matches confirmed as the solidification completion position matches the position of the second transverse ultrasonic wave sensors based on the signal from the longitudinal wave ultrasonic sensor at the time calculated by the calculation formula, the formula is Tadashisa school The solidification completion position detection device is used to detect the solidification completion position in the slab width direction of the continuous cast slab, and the slab is based on the difference between the detected shortest solidification completion position and the detected longest solidification completion position. Judging the quality of Characterized the door, quality evaluation method of the continuous casting slab.   Furthermore, the quality determination method of the continuous casting slab of Claim 1 or Claim 2 which determines the presence or absence of inspection implementation in a slab or steel materials based on the said quality determination.   4. The method for determining the quality of a continuous cast slab according to claim 3, wherein the inspection position of the slab or the steel material is specified according to the shape of the solidification completion position when the slab or the steel material is inspected. .

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