JP5104247B2 - Manufacturing method of continuous cast slab - Google Patents

Description

  The present invention relates to a method for producing a continuous cast slab, and more specifically, the measured value of the mold copper plate temperature during casting is compared with the defect detection result by the defect detection device, and the detected defects on the surface portion of the slab are reduced. Therefore, the present invention relates to a method for producing a slab by a continuous casting machine while changing a magnetic field application condition of a magnetic field generator for applying a magnetic field in a mold and adjusting a flow of molten steel in the mold.

In continuous casting of steel, molten steel is discharged into a mold at a high speed via an immersion nozzle, and a molten steel flow is generated in the mold due to this discharge flow. It is known that the molten steel flow in the mold has a great influence on the surface properties of the slab. For example, when the surface flow velocity of the molten steel surface in the mold (hereinafter referred to as “meniscus”) is too fast, or when vertical vortices occur in the meniscus due to collisions of molten steel flows in different directions, The added mold powder is caught in the molten steel and captured by the solidified shell. On the contrary, when the surface flow velocity of the meniscus is too slow, the deoxidation product such as Al ₂ O ₃ present in the molten steel and the cleaning effect at the solidified shell interface of Ar gas bubbles are reduced, and Al ₂ O ₃ Deoxidation products such as Ar gas bubbles are trapped in the solidified shell. When the mold powder, deoxidation product, and Ar gas bubbles trapped in the solidified shell of the slab, that is, the slab surface layer, are rolled without removing them in the mold, It becomes a surface flaw defect and decreases the yield of thin steel sheet products.

  Therefore, in order to prevent the occurrence of defects in the surface portion of the slab, many methods for evaluating the surface properties by controlling or monitoring the molten steel flow in the mold have been proposed.

  For example, in Patent Document 1, a plurality of temperature measuring elements are arranged in the width direction on the back side of the long side copper plate of the mold for continuous casting, and the temperature distribution in the width direction of the long side copper plate is measured. Of the magnetic field intensity of the magnetic field generator attached to the mold, the slab drawing speed, the immersion nozzle immersion depth, and the amount of Ar blown into the immersion nozzle so that the difference between the maximum value and the minimum value is 12 ° C. or less It has been proposed to adjust any one or more of these. Further, in Patent Document 1, the molten steel flow velocity in the mold in front of each measurement point is calculated from the mold long side copper plate temperature, and the difference between the maximum value and the minimum value of the calculated molten steel flow velocity is 0.25 m / sec or less. Thus, it is also proposed to adjust any one or two or more of the magnetic field strength of the magnetic field generator, the slab drawing speed, the immersion depth of the immersion nozzle, and the amount of Ar blown into the immersion nozzle. .

  In Patent Document 2, the mold copper plate temperature or the heat flow rate at each point in the width direction of the continuous casting mold is measured and the distribution in the mold width direction is monitored, and the distribution state in the mold width direction is large in time. A surface defect detection method for determining that vertical cracks have occurred on the surface of a slab when changed is proposed.

In Patent Document 3, a plurality of temperature measuring elements are arranged in the width direction on the back side of the long side copper plate of the continuous casting mold to measure the mold copper plate temperature at each position in the long side width direction of the mold, and from the measured mold copper plate temperature. Obtain the molten steel flow velocity at each measurement point. If the obtained molten steel flow velocity value is less than 0.13 m / sec, it is determined that a defect in the physical properties of the slab surface has occurred, and the portion is removed by cutting. It has been proposed to do.
International Publication No. 2000/51763 Japanese Patent Laid-Open No. 2-151356 JP 2005-262305 A

  According to the above Patent Documents 1 to 3 and the like, the occurrence of defects in the slab surface layer portion has been greatly reduced. However, Patent Documents 1 to 3 have the following problems.

  That is, in Patent Documents 1 to 3, a threshold value is set for the temperature difference in the width direction of the mold copper plate, the temporal change in temperature distribution, or the molten steel flow velocity value, and the occurrence of a defect in the slab surface layer is determined using the threshold value as a boundary. However, in setting this threshold, it is set based on the casting results under the most common casting conditions in the continuous casting machine, that is, based on average data. It is. Even with the same continuous casting machine, if the drawing speed of the slab or the size of the slab changes, the discharge flow rate from the immersion nozzle changes, and the flow of molten steel in the mold naturally changes. Should be changed. Furthermore, if the continuous casting machine to be used is changed, the mold structure is also different, and therefore, it is considered that the absolute value of the mold copper plate temperature itself changes.

  Therefore, in the above-mentioned Patent Documents 1 to 3, the defect occurrence threshold is set excessively severely, and even though no defect occurs, unnecessary casting conditions and unnecessary slab maintenance work are forced. In certain casting conditions, the threshold value is inappropriate, so that a surface layer defect may be missed. In other words, we accurately grasp the molten steel flow in the mold under the casting conditions where the defect occurred, clarify the cause of the defect from the grasped molten steel flow, and modify the flow in the mold to prevent the occurrence of similar defects. However, Patent Documents 1 to 3 do not pursue that much.

  The present invention has been made in view of such circumstances, the purpose of which is to grasp the defects generated in the slab surface layer portion, grasp the molten steel flow in the mold at the time of occurrence of the defects, A method for producing a continuous cast slab capable of producing a continuous cast slab having few defects in the surface layer portion by ascertaining the cause of the occurrence of defects by attaching these together, thereby preventing the occurrence of similar defects. Is to provide.

  The method for producing a continuous cast slab according to the first invention for solving the above-mentioned problem is that a plurality of temperature measuring elements are arranged in a mold to measure the mold copper plate temperature during continuous casting, and the measured mold copper plate temperature Is stored in the storage device, the defect of the surface layer portion of the cast slab is detected by the defect detection device, the detection result of the defect by the defect detection device, the measured value of the mold copper plate temperature stored in the storage device, Based on the above, the magnetic field application condition of the magnetic field generator for controlling the flow of molten steel in the mold is changed.

  According to a second aspect of the present invention, there is provided the method for manufacturing a continuous cast slab according to the first aspect, wherein the defect detection device includes a surface state information input device for inputting surface state information of the slab, and ultrasonically detects defects in the slab. A flaw detection ultrasonic device for flaw detection, a flaw detection result obtained by the flaw detection ultrasonic device, and surface state information of the slab input to the surface state information input device are input, and the surface state of the slab that is input A defect determination processing device that removes the data of the non-flat portion position of the slab from the flaw detection result based on the information and uses the flaw detection result after removing the data of the non-flat portion position as defect inspection information of the slab. It is characterized by comprising.

  According to a third aspect of the present invention, there is provided a method for producing a continuous cast slab according to the second aspect, wherein the flaw detection ultrasonic device includes a transmitting piezoelectric vibrator for transmitting a creeping wave to the slab, and the slab. A first ultrasonic flaw detector and / or a receiving piezoelectric type vibrator that receives a creeping wave reflected by a defect existing in a position different from a transmission position, and / or ultrasonic waves on a slab A transmission piezoelectric transducer for transmitting, a reception piezoelectric transducer for receiving ultrasonic waves reflected by defects present in the slab, and an acoustic separator that acoustically isolates between transmission and reception of ultrasonic waves The ultrasonic flaw detector is provided.

  According to the present invention, when a defect occurs in the slab surface layer portion, this defect is detected by the defect detection device, and the measured value of the mold copper plate temperature at the time when the defect occurs is stored in the storage device. Therefore, the flow of molten steel in the mold that caused the occurrence of defects is grasped from the measured values of the mold copper plate temperature, and based on these, the molten steel flow in the mold is magnetically applied so that the detected defects do not occur again. Since the correction is made by the generator, it is possible to stably produce a continuous cast slab with few defects on the surface layer portion with a continuous casting machine, and there are industrially advantageous effects such as improvement in yield and shortening of delivery time.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a flow diagram showing a flow from a continuous casting process of a slab manufactured according to the present invention to a heating furnace of a hot rolling process, and FIG. FIG. 1 (B) is a flow chart when detecting the wrinkles of the skin after removing the scale of the skin without removing the scarf), and FIG. It is a flow figure when detecting the flaw of this welding surface or a grinding surface.

  As shown in FIG. 1, in the present invention, the scale of the slab skin is removed by shot blasting or the like in the middle of the conveyance process of conveying the slab manufactured in the continuous casting process to the heating furnace in the hot rolling process. Or, the slab surface layer is cut by hot scurfer or cold scurfer, or ground by a grinder or shaper, etc., or the scale is removed, or the cut surface or grinder by hot scurfer, etc. The ground surface is checked by a defect detection device such as an optical surface flaw detection device, a magnetic particle flaw detection device, an ultrasonic flaw detection device, or an eddy current sensor to investigate the presence or absence of defects. When a defect is detected, the information is fed back to the continuous casting process.

  In the continuous casting process, the temperature of the mold copper plate is measured and stored for the purpose of monitoring the flow of molten steel in the mold, and the defect information of the slab surface layer fed back and the mold copper plate at the time when the defect occurs are fed back. Compare the temperature, that is, the molten steel flow in the mold, identify the cause of the detected defect, and change the molten steel flow in the mold using the magnetic field generator so that the detected defect will not occur again. To do. In order to monitor the molten steel flow in the mold, it is necessary to measure at least the mold copper plate temperature in the mold width direction, but by measuring the mold copper plate temperature in the mold casting direction (longitudinal direction) together with the mold width direction. Thus, it becomes possible to monitor the molten steel flow in the mold with higher accuracy.

  The slab in which the defect is detected in the defect detection process is charged into a heating furnace in the hot rolling process after the defect detected by a spot scurfer, a grinder, or a hot scurfer is removed. The slab in which no defect is detected in the defect detection process is inserted into the heating furnace of the hot rolling process as it is.

  In recent years, environmental measures and energy measures for preventing global warming have been questioned. From that viewpoint, it is desirable to effectively use the heat of a slab cast by a continuous casting machine. It is preferable to carry out the process from charging to heating furnace charging while the slab is hot or warm. Here, the hot state is defined as an average slab temperature of about 400 ° C. or higher, and the warm state is defined as an average temperature of about 200 ° C. or higher. The slab heated at a predetermined temperature and for a predetermined time in a heating furnace in the hot rolling process is hot rolled to produce a hot rolled steel material.

  Hereinafter, the present invention will be described in the order of steps. In addition, here, an example in which the slab is charged into a heating furnace while being in a hot piece state will be described, but the present invention is also applied to a case where the slab is in a warm state or a cold state according to the case of the hot piece state. Apply.

  2 and 3 show a slab continuous casting machine suitable for carrying out the present invention. FIG. 2 is a schematic side view of a vertical bending type slab continuous casting machine, and FIG. 3 is a schematic front sectional view showing details of a mold part of the slab continuous casting machine shown in FIG.

  As shown in FIG. 2, a slab continuous casting machine 1 is provided with a mold 5 for cooling the molten steel 11, and a molten steel supplied from a ladle (not shown) at a predetermined position above the mold 5. A tundish 2 for relaying 11 to the mold 5 is installed. On the other hand, below the mold 5, a plurality of pairs of slab support rolls including a support roll 6, a guide roll 7 and a pinch roll 8 are arranged. Among these, the pinch roll 8 is a drive roll for drawing the slab 12 at the same time as supporting the slab 12. A secondary cooling zone in which a spray nozzle (not shown) such as a water spray nozzle or an air mist spray nozzle is arranged in the gap between the slab support rolls adjacent in the casting direction is configured. The slab 12 is cooled while being drawn out by cooling water sprayed from (also referred to as “secondary cooling water”). On the downstream side of the slab support roll, a plurality of transport rolls 9 for transporting the cast slab 12 are installed. Above the transport roll 9, a predetermined slab 12 is cast from the slab 12 to be cast. A gas cutting machine 10 for cutting the length slab 12a is arranged.

  Further, as shown in FIG. 3, an upper nozzle 18 is provided at the bottom of the tundish 2, and a sliding nozzle 3 including a fixed plate 19, a sliding plate 20 and a rectifying nozzle 21 is connected to the upper nozzle 18. Further, on the lower surface side of the sliding nozzle 3, an immersion nozzle 4 having a discharge hole 22 in the lower part is arranged, and a molten steel outflow hole 23 from the tundish 2 to the mold 5 is formed.

  The mold 5 includes a pair of mold long-side copper plates 16 facing each other and a pair of mold short-side copper plates 17 disposed inside the mold long-side copper plate 16. Is provided with a magnetic field generator 27 for controlling the flow of the molten steel 11 by applying an electromagnetic field to the internal space of the mold 5. The magnetic field generated by the magnetic field generator 27 may be a DC static magnetic field, an AC moving magnetic field, or a magnetic field in which a DC static magnetic field and an AC moving magnetic field are superimposed. What is necessary is just to arrange | position according to the effect anticipated in the generator 27. FIG.

  The DC static magnetic field is a device having a function of applying an electromagnetic braking force to the moving molten steel 11 in the direction opposite to the direction of the molten steel 11, and the AC moving magnetic field applies the molten steel 11 in the direction of the moving magnetic field. The device has a function of moving, and the DC / AC superimposed magnetic field is a device having both functions. The magnetic field intensity of the magnetic field generator 27 is controlled by the magnetic field intensity controller 30. In this case, in FIG. 2, the magnetic field generator 27 is shown as one in the slab width direction, but is divided into two or more places with the center in the mold width direction as a boundary, and each of the magnetic field intensity control devices is independently provided. Thirty signals may be input. Moreover, although the magnetic field generator 27 is installed in the vicinity of the discharge hole 22 of the immersion nozzle 4, the magnetic field generator 27 is arranged at an optimal position according to the function of the magnetic field generator 27 such as the vicinity of the meniscus 25 and the lower end portion of the mold 5. And Furthermore, in FIG. 3, only one stage of the magnetic field generator 27 is installed in the casting direction, but two or more stages may be arranged in the casting direction.

  A plurality of holes are provided in the back surface of the long mold copper plate 16 along the width direction of the long mold copper plate 16, and serve as measurement points 28 for measuring the copper plate temperature of the long mold copper plate 16. A temperature measuring element 29 is disposed at each measurement point 28 so that the tip thereof is in contact with the long copper plate 16 of the mold. In this case, the distance from the molten steel side surface of the mold long side copper plate 16 to the tip of the temperature measuring element 29 is preferably set to 16 mm or less in order to accurately grasp the change in the molten steel flow rate every moment as the change in the copper plate temperature. . Further, the distance from the meniscus 25 to the measurement point 28 is set to 10 mm or more so as not to be affected by temperature fluctuations caused by the vertical movement of the meniscus 25 during casting, and the long side copper plate temperature of the mold due to a change in molten steel flow In order to accurately grasp the amount of change, the thickness is preferably set to 135 mm or less. Furthermore, in order to accurately grasp the temperature distribution of the mold long side copper plate 16 in the mold width direction, the interval between the adjacent measurement points 28 is preferably set to 200 mm or less. The temperature measuring element 29 may be of any type as long as it can measure temperature with an accuracy of ± 1 ° C. or higher among thermocouples and resistance temperature measuring elements.

  The other end of the temperature measuring element 29 is connected to a zero point compensator (not shown), and an electromotive force signal output from the temperature measuring element 29 is input to the storage device 31 via the zero point compensator. The storage device 31 converts the electromotive force signal into a current signal and stores it as measurement data. Further, the storage device 31 has casting conditions such as the slab drawing speed when the copper plate temperature is measured, the magnetic field strength of the magnetic field generator 27, the immersion depth of the immersion nozzle 4, and the amount of Ar blown into the immersion nozzle. It is input from the process computer 33 that controls the continuous casting operation, and is stored together with the measured value of the copper plate temperature. A data analysis device 32 is installed in connection with the storage device 31. The data analysis device 32 uses the measurement data input from the storage device 31, for example, the slab drawing speed and the temperature difference in the mold width direction. Various analyzes such as the relationship are possible.

  Since the mold copper plate temperature changes in relation to the molten steel flow immediately before the mold copper plate, specifically, the mold copper plate temperature increases as the molten steel flow velocity immediately before the mold copper plate increases. Therefore, the mold copper plate temperature is increased in the width direction of the mold 5. By measuring, it is possible to grasp the molten steel flow and its distribution in the mold.

  In the slab continuous casting machine 1 configured as described above, molten steel 11 is poured into a tundish 2 from a ladle (not shown), a predetermined amount of molten steel 11 is retained in the tundish 2, and then the molten steel retained in the tundish 2. 11 through the molten steel outflow hole 23, the discharge flow 24 of the molten steel 11 is directed from the discharge hole 22 provided in the lower part of the immersion nozzle 4 and immersed in the molten steel 11 in the mold toward the short side copper plate 17 of the mold. Inject into the mold 5. The molten steel 11 injected into the mold 5 is cooled by the mold 5 to form a solidified shell 13, and as a cast piece 12 having an unsolidified phase 14 therein, a support roll 6 and a guide roll 7 provided below the mold 5. And while being supported by the pinch roll 8, it is continuously pulled out below the mold 5 by the driving force of the pinch roll 8. While the slab 12 passes through these slab support rolls, it is cooled by the secondary cooling water in the secondary cooling zone, the thickness of the solidified shell 13 is increased, and solidification to the inside is completed at the solidification completion position 15. . The slab 12 is cut by the gas cutter 10 to become a slab 12a. While the slab 12 is drawn, the position of the meniscus 25 of the mold 5 is set to a substantially constant position, and a mold powder 26 that functions as a heat retaining agent, a lubricant, an antioxidant, etc. is added on the meniscus 25.

  During the casting, the storage device 31 sequentially stores the mold long side copper plate temperature measured by the temperature measuring element 29. However, storing all the mold long side copper plate temperatures to be measured is disadvantageous because the storage capacity increases, and the temporal change in the mold long side copper plate temperature is not as great as the left, so at intervals of 10 seconds to several tens of seconds. You may memorize it. In this casting, when the casting is the first casting, the magnetic field generator 27 may or may not apply a magnetic field. However, after the present invention is applied, a magnetic field is applied under a predetermined predetermined magnetic field application condition.

  The slab 12a manufactured in this way and stored with other casting conditions such as the mold long side copper plate temperature and slab drawing speed is transported to the heating furnace of the next hot rolling process in a hot state. The

  During the transfer process, the surface, back and side surfaces of the slab 12a in the hot state are treated by shot blasting or the like on a transfer roller table or at an appropriate place such as a dedicated surface layer maintenance place. Remove the scale of the skin, or slab the surface, back and side surfaces of the slab 12a in the hot state with a hot scurfer or cold scurfer, or with a grinder, shaper or milling cutter Grind. In the present invention, the reason for removing the scale of the slab skin is to remove the adhered scale to facilitate detection of flaws, and the reason for cutting or grinding the slab surface layer is the slab surface layer. This is to make the defects present in the part obvious. In the case of performing cutting or grinding, in order to reveal defects, the thickness of cutting or grinding is preferably 1 mm to 4 mm from the as-cast slab skin, and the defects present in the slab surface layer portion In order to make the material appear, the entire surface of the slab 12a is subjected to hot-cutting or grinding.

  Next, the skin of the slab 12a from which the scale has been removed, or the cut or ground surface of the slab 12a is provided with an optical surface defect detection device, a magnetic particle inspection device, an ultrasonic inspection device, an eddy current sensor, and the like. An inspection is performed using a defect detection device, and the presence or absence of a defect is investigated. As the defect detection device, it is preferable to use an optical surface defect detection device using a CCD camera or a defect detection device equipped with an ultrasonic flaw detection device because rapid inspection is possible and detection accuracy is high.

  However, the surface of the slab 12a, in particular, the surface of the slab 12a from which the scale has been removed, has a recess such as an oscillation mark. When a defect is detected by an ultrasonic flaw detector, this recess is Detection accuracy deteriorates due to disturbance. Therefore, when detecting a defect using the defect detection apparatus provided with the ultrasonic flaw detection apparatus, in order to avoid the influence of the unevenness | corrugation of the surface of the slab 12a, the ultrasonic flaw detection type defect detection apparatus shown in FIG. It is preferable to use it. FIG. 4 is a configuration diagram of an ultrasonic flaw detection type defect detection apparatus suitable for carrying out the present invention.

  In FIG. 4, reference numeral 34 denotes a first flaw detection ultrasonic sensor, 35 denotes a second flaw detection ultrasonic sensor, 36 denotes a surface state measurement sensor, 37 denotes a driving device, and 38 denotes a first flaw detection ultrasonic transmission. , 39 is a second flaw detection ultrasonic transmission unit, 40 is a first flaw detection ultrasonic reception unit, 41 is a second flaw detection ultrasonic reception unit, 42 is a surface state measurement unit, and 43 is an A / D. A conversion unit, 44 is a computer, 45 is a flaw detection condition input unit, and 46 is an output unit.

  The first flaw detection ultrasonic sensor 34 and the second flaw detection ultrasonic sensor 35 transmit and receive ultrasonic waves by using an ultrasonic acoustic coupling method with the surface of the slab 12a as a material to be inspected as a local water immersion method. . Based on the set values input by the flaw detection condition input unit 45, the calculator 44 includes a drive device 37, a first flaw detection ultrasonic transmission unit 38, a second flaw detection ultrasonic transmission unit 39, and an A / D conversion. The unit 43 is controlled to perform measurement by scanning the first flaw detection ultrasonic sensor 34, the second flaw detection ultrasonic sensor 35, and the surface state measurement sensor 36 with respect to the slab surface. As a scanning method, a two-way scan (for example, an XY scan) or a one-way scan may be appropriately selected according to a site where flaw detection is desired.

  At this time, the first flaw detection ultrasonic sensor 34, the second flaw detection ultrasonic sensor 35, and the surface state measurement sensor 36 may be housed in the same sensor head for flaw detection at the same time, or separate sensor heads. It is possible to carry out flaw detection by driving separately. Further, the surface state measuring sensor 36 may be used for measurement at different locations or lines before and after the flaw detection by the first flaw detection ultrasonic sensor 34 or the second flaw detection ultrasonic sensor 35.

  Further, the scanning method does not drive each sensor, but it may be possible to scan the slab 12a as a material to be inspected while being conveyed by a roll or the like, and each sensor is driven while the slab 12a is being conveyed. The scanning method is not limited as long as the range to be flawed can be scanned.

  When a flaw detection gate is set immediately after the dead zone of the material to be inspected using a normal single probe (a method in which ultrasonic transmission and reception are performed with the same piezoelectric vibrator), the surface of the material to be inspected is detected. If even a slight dent, for example, a dent of about 0.1 mm, is present, the reflected ultrasonic wave leaks into the defect detection gate, resulting in erroneous detection due to the dent in most of the flaw detection range. . For this reason, the effective flaw detection area with respect to the flaw detection range becomes extremely small, and the inspection object cannot be correctly evaluated.

Therefore, in the ultrasonic flaw detection type defect detection apparatus used in the present invention, two types of ultrasonic sensors made difficult to be affected by unevenness on the surface of the inspection material are arranged, and the depth d _X1 mm from directly below the surface of the inspection material. The first flaw detection ultrasonic sensor 34 detects flaws, and the second flaw detection ultrasonic sensor 35 detects flaws deeper than the depth d _X1 (up to the depth d _X2 ). Although a method of combining the two sensors will be described here, only one of them may be used according to the state of the material to be inspected. That is, the measurement conditions and the combination of these sensors may be appropriately determined according to the depth range in which the defect to be detected exists from the surface of the inspection object. For example, if a defect from the surface to the depth d _X1 is to be inspected, only the first flaw detection ultrasonic sensor 34 is required, and if a defect from the depth d _X1 to d _X2 is to be inspected, Only the second ultrasonic sensor 35 for flaw detection may be used. If a defect from the surface to d _X2 is inspected, both ultrasonic sensors are required.

  The first flaw detection ultrasonic sensor 34 will be described in detail with reference to FIG. The first flaw detection ultrasonic sensor 34 transmits a creeping wave to a material to be inspected and receives a creeping wave reflected by a defect existing in the material to be inspected at a position different from the transmission position. In this way, noise caused by the surface roughness of the material to be inspected can be suppressed, and minute defects existing immediately below the surface of the material to be inspected can be detected with high detection capability. FIG. 5 is a diagram showing an embodiment of the first flaw detection ultrasonic sensor 34.

  In the ultrasonic flaw detection method shown in FIG. 5, the acoustic coupling method with the surface of the slab 12a is a water immersion method, and transmission and reception of creeping waves are made to the transmitting piezoelectric transducer 47 and the receiving piezoelectric transducer 48. Do it separately. The angle Φ1 between the transmitting piezoelectric vibrator 47 and the material to be inspected is a creeping wave in which the ultrasonic wave transmitted from the transmitting piezoelectric vibrator 47 has a refraction angle of about 75 ° to 90 ° inside the inspected material. The angle Φ2 between the receiving piezoelectric vibrator 48 and the surface of the material to be inspected is set so as to propagate and receive a creeping wave having a refraction angle of 75 ° to 90 °. Reference numeral 50 in FIG. 5 is a defect existing in the slab 12a.

  At this time, an angle Φ1 with the inspection material surface of the transmitting piezoelectric vibrator 47 and an angle Φ2 with the inspection material surface of the receiving piezoelectric vibrator 48 are set to different angles. By setting the angle Φ1 and the angle Φ2 in this way, as shown in FIG. 5, the centers of the transmitted and received ultrasonic beams can be crossed at a certain surface depth, and the focal point can be formed. The detection ability in the vicinity of the focal point can be enhanced.

  As shown in FIG. 5, the transmitting piezoelectric vibrator 47 and the receiving piezoelectric vibrator 48 are arranged in a tandem arrangement. In order to facilitate the arrangement, it is preferable that the intersection of the transmission and reception beams inside the inspection material, the incident position and the radiation position of the ultrasonic wave are on the same straight line, but the present invention is not limited to this. With the arrangement shown in FIG. 5, the receiving piezoelectric vibrator 48 faces in a significantly different direction with respect to the incident position of the transmission beam. Therefore, even if there is a beam spread and the transmission beam spreads around the incident position and is scattered by the surface roughness, the surface echo is not easily received by the receiving piezoelectric transducer 48. Further, since the propagation path of the ultrasonic wave in the inspection material can be shortened, it is possible to strongly receive the signal of the defect echo. As a result, noise due to surface roughness can be reduced and the signal-to-noise ratio (S / N) can be improved.

  Furthermore, a surface that slightly propagates to the receiving piezoelectric vibrator 48 side by installing an acoustic separator 49 between the transmitting piezoelectric vibrator 47 and the receiving piezoelectric vibrator 48. Scattering noise can be shielded and S / N can be further improved.

  Next, the second ultrasonic inspection sensor 35 will be described in detail with reference to FIG. The second ultrasonic sensor 35 for flaw detection performs transmission / reception of ultrasonic waves by using different piezoelectric vibrators, and installs an acoustic isolation plate 53 between the piezoelectric vibrations to be transmitted / received. The reflected wave is hardly received or a surface wave with a small amplitude is received, so that a defect in the surface layer can be detected with better S / N. Here, the surface layer defect is an internal defect near the surface or a crack at the surface, but the “crack” refers to a surface defect in which the gap is very narrowly adhered. FIG. 6 is a diagram showing an embodiment of the second flaw detection ultrasonic sensor 35.

  In the ultrasonic flaw detection method shown in FIG. 6, the acoustic coupling method with the surface of the slab 12a is the water immersion method, the angle between the transmitting piezoelectric vibrator 51 and the surface of the inspection object is θ1, and the receiving piezoelectric vibration. The angle between the child 52 and the surface of the material to be inspected is θ2, and ultrasonic waves are transmitted and received. At this time, the angles θ1 and θ2 and the transmission piezoelectric wave are set so that the centers of ultrasonic beams for transmitting and receiving ultrasonic waves intersect at a preset depth position to form a focal point and enhance the detection ability in the vicinity of the focal point. The distance between the mold vibrator 51 and the receiving piezoelectric vibrator 52 is set.

  An acoustic separator 53 is disposed between the transmitting piezoelectric transducer 51 and the receiving piezoelectric transducer 52 to acoustically separate transmission and reception of ultrasonic waves. In order to prevent any reflected wave from the surface of the material to be inspected from being received, it is preferable that the distance between the tip of the acoustic separator 53 and the surface of the material to be inspected be as small as possible.

  Further, the shape of the tip of the acoustic separator 53 is set so that the reflected wave from the material to be inspected is difficult to be reflected, and the reflected wave from the surface of the material to be inspected is reflected by the tip of the acoustic separator 53 and scattered. It is preferable that the scattered wave is not received. This also applies to the acoustic separator 49 described above.

  For example, in the example of FIG. 7A, the shape of the tip is sharpened in order to reduce the reflection area at the tip of the acoustic separators 49 and 53. At this time, the thickness t of the tip is set to be equal to or less than the wavelength so that it is difficult to reflect, and is preferably equal to or less than half of the wavelength.

  In the example of FIG. 7B, the acoustic separators 49 and 53 are shaped so that the receiving side surface is perpendicular to the material to be inspected and the transmitting side surface is at an acute angle θ3 with respect to the receiving side surface. Reflected waves generated at the tips of the separators 49 and 53 are reflected to the transmission side. Since the shapes of the tip portions of the acoustic separators 49 and 53 are determined in this way, even if the echo reflected from the surface of the material to be inspected is reflected by the acoustic separators 49 and 53, the receiving piezoelectric vibrator 48 and The S / N can be increased without almost entering the receiving piezoelectric vibrator 52.

  Also, as shown in FIG. 8, by providing an air layer or a discontinuous portion inside the acoustic separators 49 and 53, it is possible to reduce the ultrasonic waves that pass through the acoustic separators 49 and 53 from the transmission side. , S / N can be reduced.

  Note that the acoustic coupling method of the first flaw detection ultrasonic sensor 34 and the second flaw detection ultrasonic sensor 35 is a so-called water immersion method (total immersion method, local immersion method, jet water) that uses water. In addition to the immersion method, a gap method or a direct contact method using acrylic resin or the like, and further water or oil can be used.

  A first inspection ultrasonic transmission unit 38 drives a transmission piezoelectric vibrator 47 disposed in the first ultrasonic inspection sensor 34 to transmit ultrasonic waves through water, and a material to be inspected. The reflected wave from the inside is received by the receiving piezoelectric vibrator 48 arranged in the first flaw detection ultrasonic sensor 34, and the received reflected wave is filtered by the first flaw detection ultrasonic receiving unit 40. Amplification is performed and the data is captured by the computer 44 via the A / D converter 43, and the computer 44 calculates an ultrasonic instruction.

  In addition, the second ultrasonic inspection transmitter 35 drives the transmission piezoelectric vibrator 51 disposed in the second ultrasonic inspection sensor 35 to transmit ultrasonic waves through water, The reflected wave from the inside of the inspection material is received by the receiving piezoelectric transducer 52 arranged in the second flaw detection ultrasonic sensor 35, and the received reflected wave is received by the second flaw detection ultrasonic receiving unit 41. Filtering and amplification are performed and captured by the computer 44 via the A / D converter 43, and the computer 44 calculates an ultrasonic instruction.

  Waveforms detected by the first flaw detection ultrasonic sensor 34 and the second flaw detection ultrasonic sensor 35 are further subjected to synchronous addition averaging, aperture synthesis, and the like by a DSP (Digital Signal Processor) attached inside or outside the computer 44. The ultrasonic instruction may be determined after performing digital signal processing, or the ultrasonic instruction may be calculated by an analog circuit.

  Further, the computer 44 inputs not only the measurement data of the first flaw detection ultrasonic sensor 34 and the second flaw detection ultrasonic sensor 35 but also the measurement data of the surface condition measurement sensor 36, and compares the results. Thus, it has a role as a defect determination processing device that accurately determines internal defects and surface defects of the material to be inspected, and also has a function of the defect determination processing device described below.

  The calculator 44 performs full-wave rectification of the signal waveform on the reception signal input by the A / D converter 43, and calculates the maximum value Fp of the signal amplitude within a preset gate range. At this time, the maximum value Fp Is determined to have ultrasonic indication (internal defect or surface defect exists) when Fp> Fth is satisfied with respect to the preset Fth, and if not, ultrasonic inspection is not indicated (no defect). Along with the position information, it is recorded in a recording device or the like installed inside or outside the computer 44.

  A distance meter is used as the surface state measurement sensor 36 and the surface state measurement unit 42 for detecting a dent on the surface of the material to be inspected, which is a surface state information input device. As the distance meter, various distance meters such as a laser distance meter or an ultrasonic distance meter are used, and the distance from the distance meter to the surface of the material to be inspected is measured by this distance meter. The data value which is the surface state information calculated and output by the surface state measuring unit 42 is converted into digital data by the A / D conversion unit 43 or serial communication for directly connecting the computer 44 and the surface state measuring unit 42. The data is taken into the computer 44 by GPIB communication or the like, and the final defect is determined by the defect determination processing function of the computer 44. The value taken into the computer 44 is recorded in a recording device installed outside or inside the computer 44 together with measurement position information on the material to be inspected.

  The computer 44 inputs the distance information once recorded, and calculates the presence / absence of a dent (dent instruction) as surface condition information on the material to be inspected. Specifically, at an arbitrary position P of the material to be inspected, a distance Sp (measured value of the distance meter) from the distance meter to the surface of the material to be inspected is set to a preset threshold value (reference value) Sth, Sth <Sp When satisfying, it is determined that there is a dent (concave), and when not satisfying, it is determined that there is no dent.

  And it was calculated from the dent position on the surface of the material to be inspected calculated from the measurement data by the surface state measurement sensor 36 and the measurement data by the first flaw detection ultrasonic sensor 34 and the second flaw detection ultrasonic sensor 35. A dent is detected at the same position as the ultrasonic indication position by comparing the ultrasonic indication position (position determined to have a defect) (first flaw detection ultrasonic sensor 34 or second flaw detection ultrasonic wave). When the position of the defect detected by the sensor 35 coincides with the dent position detected by the surface state measurement sensor 36), the ultrasonic instruction is excluded and only the position that is highly likely to be a defect is excluded. Create the remaining data. As a result, an instruction determined to be “defective”, which may be erroneously detected, is caused by the fact that ultrasonic reflected waves from the surface are mixed into the gate for detecting defects due to dents during ultrasonic flaw detection. It is excluded and an accurate defect indication can be output.

  The created data is output to the output unit 46, and quality of the material to be inspected can be determined based on the data.

  As a surface state information input device, instead of the surface state measurement sensor 36 and the surface state measurement unit 42, the surface state of the material to be inspected is inspected by visual observation by an inspector to detect the dent position, and this surface A surface state inspection result input unit for inputting state information may be provided and connected to the computer 44. In the present invention, the “surface state information input device” may be a surface state measuring device itself such as the surface state measuring sensor 36, a terminal for inputting information data of the surface state measuring device, or for communication. It includes an input device such as an I / F and a surface condition inspection result input unit for inputting information on the above-described visual inspection. Further, although the example using a distance meter as the surface state measurement sensor 36 has been described, the present invention is not limited to this, and for example, a convex portion or a concave portion of a material to be inspected such as a light cutting method or a method of measuring distortion of a projection pattern by image processing A three-dimensional shape measuring apparatus capable of measuring the surface shape such as the above may be used. Furthermore, the output unit 46 does not output only the data of the defect instruction (position, defect type, degree, etc.) excluding the position where the dent is detected, but dents as necessary in the defect instruction data before the exclusion. It is also possible to output the detected indication and the dent detection position together, or simultaneously output the size and depth of the defect estimated from the ultrasonic signal together with the defect indication. Good.

  As described above, in the ultrasonic flaw detection type defect detection apparatus having the above-described configuration, the surface of the inspection object is obtained by using the first flaw detection ultrasonic sensor 34 and / or the second flaw detection ultrasonic sensor 35. In addition to suppressing false detection due to slight dents, the surface state information of the surface state measurement sensor 36 is used to remove deeper dent positions. It becomes feasible to correctly evaluate a material to be inspected with a poor surface state, and is a defect detection apparatus that is extremely suitable for carrying out the present invention.

  If a defect is detected by the defect detection device, the identification number of the slab 12a where the defect has occurred, the position of the defect occurrence, the number of defects, etc. are transmitted from the defect detection device via the process computer 33 and the storage device 31 to the data analysis device 32. Sent to. The data analyzer 32 displays the detected defect data in comparison with the mold long side copper plate temperature corresponding to the slab portion of the defect and other casting conditions, and at the same time, compares and detects these data. Analyze and display the relationship between the generated defects and casting conditions.

  Based on the data displayed on the data analysis device 32, the operator changes the magnetic field application condition of the magnetic field generation device 27 via the magnetic field strength control device 30 so that the detected defect does not occur again. In this case, if the magnetic field application conditions are changed frequently, the molten steel flow may not be controlled and may diverge. Therefore, the magnetic field application is performed at a certain interval, for example, every time one charge is cast. It is preferable to change the conditions. If the defect does not disappear even if the magnetic field application condition is changed, or if another type of defect occurs, the magnetic field application condition is changed according to the above. This change in the magnetic field application conditions is performed in accordance with casting conditions such as the size of the slab 12 and the slab drawing speed, and is applied under conditions where the casting conditions such as the size of the slab 12 and the slab drawing speed are different. do not do.

  The slab 12a in which the defect is detected in the defect detection process is inserted into a heating furnace of the hot rolling process after the defect detected by a spot scurfer, a grinder, or a hot scurfer is removed, and the defect detection process The slab 12a, in which no defect is detected, is charged in a hot state in a heating furnace in a hot rolling process.

  As described above, according to the present invention, when a defect occurs in the surface layer portion of the slab 12a, the defect is detected by the defect detection device, and from the mold long side copper plate temperature at the time when the defect occurs. The molten steel flow situation in the mold is grasped, and the molten steel flow in the mold is corrected by the magnetic field generator 27 so that the defects detected based on these conditions are not generated again. Can be stably produced by a continuous casting machine.

  A slab slab having a thickness of 250 mm and a width of 1650 mm was cast in a slab continuous casting machine provided with a magnetic field generator for applying an AC moving magnetic field. The entire surface of the resulting slab was subjected to a 2 mm thickness cut from the skin using a hot scurfer, and the cut surface was inspected with a defect detection device using a CCD camera system. As a result, a defect was detected in one slab.

  The occurrence position of the defect is shown in FIG. The defects are a position of about 4 m and a position of about 7 m from the bottom side (lower side in the casting direction) of the slab having a length of about 10 m, and in the width direction of the slab, 0.4 m to the south side from the center of the slab width. It occurred at a position 0.8 m away. The mold long side copper plate temperature distribution corresponding to a position of about 4 m from the slab bottom side at this time is shown in FIG. As apparent from FIG. 10, the mold long side copper plate temperature decreased at the site where the defect occurred, and it was confirmed that the flow rate of the molten steel was insufficient at the site where the defect occurred. The slab drawing speed at that time was 2.2 m / min.

  Therefore, when the slab thickness is 250 mm, the slab width is 1650 mm, and the slab drawing speed is around 2.2 m / min, an AC moving magnetic field is applied so that the molten steel is stirred horizontally in the mold by the magnetic field generator. The operating conditions were changed to apply. As a result, when a slab slab having a thickness of 250 mm and a width of 1650 mm was cast at a slab drawing speed of 2.2 m / min, no similar defects occurred thereafter.

  A slab slab having a thickness of 250 mm and a width of 1650 mm was cast in a slab continuous casting machine provided with a magnetic field generator for applying an AC moving magnetic field. The entire surface of the resulting slab was shot blasted to remove the scale of the slab skin, and then the slab surface was inspected with an ultrasonic flaw detection apparatus shown in FIG. As a result, a defect was detected in one slab.

  The occurrence position of the defect is shown in FIG. The defects are a position of about 3 m and a position of about 5 m from the bottom side (lower side in the casting direction) of the slab having a length of about 10 m. In the width direction of the slab, the defect is 0.5 m to the south side from the center of the slab width. It occurred at a position 0.7 m away. The mold long side copper plate temperature distribution corresponding to a position of about 3 m from the slab bottom side at this time is shown in FIG. As apparent from FIG. 12, the mold long side copper plate temperature decreased at the site where the defect occurred, and it was confirmed that the flow rate of the molten steel was insufficient at the site where the defect occurred. The slab drawing speed at that time was 2.2 m / min.

  Therefore, when the slab thickness is 250 mm, the slab width is 1650 mm, and the slab drawing speed is around 2.2 m / min, an AC moving magnetic field is applied so that the molten steel is stirred horizontally in the mold by the magnetic field generator. The operating conditions were changed to apply. As a result, when a slab slab having a thickness of 250 mm and a width of 1650 mm was cast at a slab drawing speed of 2.2 m / min, no similar defects occurred thereafter.

It is a flowchart which shows the flow from the continuous casting process of the slab manufactured by this invention to the heating furnace of a hot rolling process. 1 is a schematic side view of a slab continuous casting machine suitable for carrying out the present invention. It is a front cross-sectional schematic diagram which shows the detail of the casting_mold | template part of the slab continuous casting machine shown in FIG. 1 is a configuration diagram of an ultrasonic flaw detection type defect detection apparatus suitable for carrying out the present invention. It is a figure which shows embodiment of the 1st ultrasonic sensor for a flaw shown in FIG. It is a figure which shows embodiment of the 2nd ultrasonic sensor for flaw detection shown in FIG. It is the schematic which shows the shape of an acoustic separator. It is the schematic which shows the other shape of an acoustic separator. It is a figure which shows the generation | occurrence | production position of the defect in Example 1. FIG. It is a figure which shows the mold long side copper plate temperature distribution when the defect shown in FIG. 9 generate | occur | produces. It is a figure which shows the generation | occurrence | production position of the defect in Example 2. FIG. It is a figure which shows mold long side copper plate temperature distribution when the defect shown in FIG. 11 generate | occur | produces.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Slab continuous casting machine 2 Tundish 3 Sliding nozzle 4 Immersion nozzle 5 Mold 6 Support roll 7 Guide roll 8 Pinch roll 9 Conveyance roll 10 Gas cutting machine 11 Molten steel 12 Slab 13 Solidified shell 14 Unsolidified phase 15 Solidification completion position 16 Mold Long side copper plate 17 Mold short side copper plate 18 Upper nozzle 19 Fixed plate 20 Sliding plate 21 Rectification nozzle 22 Discharge hole 23 Molten steel outflow hole 24 Discharge flow 25 Meniscus 26 Mold powder 27 Magnetic field generator 28 Measurement point 29 Temperature measuring element 30 Magnetic field strength Control device 31 Storage device 32 Data analysis device 33 Process computer 34 First flaw detection ultrasonic sensor 35 Second flaw detection ultrasonic sensor 36 Surface state measurement sensor 37 Drive device 38 First flaw detection ultrasonic transmission unit 39 Second ultrasonic inspection transmission DESCRIPTION OF SYMBOLS 40 1st ultrasonic detector for flaw detection 41 2nd ultrasonic receiver for flaw detection 42 Surface state measurement part 43 A / D conversion part 44 Computer 45 Flaw detection condition input part 46 Output part 47 Piezoelectric vibrator for transmission 48 Reception Piezoelectric vibrator 49 Acoustic separator 50 Defect 51 Transmitter piezoelectric vibrator 52 Receiver piezoelectric vibrator 53 Acoustic separator

Claims (3)

A plurality of temperature measuring elements are arranged in the mold to measure the mold copper plate temperature during continuous casting, and the measured mold copper plate temperature is stored in the storage device, and the defect detection device detects defects in the surface layer portion of the cast slab. detected by, against a detection result and the measured value of the mold copper plate temperatures are stored before Symbol storage defect by the defect detection apparatus, based on measurements of the mold copper plate temperature at the time generated the detected defect In order to control the flow of molten steel in the mold so that the molten steel flow situation in the mold that caused the defect is grasped and the molten steel flow situation in the mold does not match the molten steel flow situation at the time of the occurrence of the defect. A method for producing a continuous cast slab, comprising adjusting a magnetic field application condition of the magnetic field generator. The defect detection apparatus includes:
A surface state information input device for inputting surface state information of a slab;
A flaw detection ultrasonic device for ultrasonic flaw detection of slab defects;
The flaw detection result obtained by the flaw detection ultrasonic device and the surface condition information of the slab input to the surface condition information input device are input, and the cast result is obtained from the flaw detection result based on the input surface condition information of the slab. Defect determination processing device that removes the data of the non-flat portion position of the piece, and uses the flaw detection result after removing the data of the non-flat portion position as defect inspection information of the slab,
The manufacturing method of the continuous cast slab of Claim 1 characterized by the above-mentioned. The flaw detection ultrasonic apparatus comprises:
A transmitting piezoelectric vibrator for transmitting a creeping wave to the slab, and a receiving piezoelectric vibrator for receiving a creeping wave reflected by a defect present in the slab at a position different from the transmission position; A first ultrasonic flaw detector having and / or
A piezoelectric transducer for transmission that transmits ultrasonic waves to the slab, a piezoelectric transducer for reception that receives ultrasonic waves reflected by defects present in the slab, and an acoustic that acoustically isolates transmission and reception of ultrasonic waves A second ultrasonic flaw detector having a separator,
The manufacturing method of the continuous cast slab of Claim 2 characterized by the above-mentioned.

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