JP2000176543A - Detection and production of steel plate, and treating equipment for hot-rolled steel plate and producing equipment for cold-rolled steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect the defect, to facilitate the judgement of a cause, to obtain the correspondence to the defect at early time and to improve the yield and the quality of a steel plate by continuously executing the flaw detection on the defect in the steel plate during conveying after hot-rolling. SOLUTION: Plural ultrasonic line sensors 26 are successively disposed along the width direction of the hot-rolled steel plate 15 at wider than the width of the steel plate, and transmitting parts 26a and receiving parts 26b are supported with a U-shaped frame body 30. In this way, the whole width of the conveying hot-rolled steel plate 15 can be detected with few detecting parts. The reason why the transmitting parts 26a and the receiving parts 26b are disposed as the zigzag state, is because the whole surface in the width direction of the hot-rolled steel plate 15 while avoiding the unnecessary interference between the adjacent sensors 26 can be detected. Desirably, the flaw detection in a pickling process after hot-rolling is executed, or the shape of the steel plate is corrected to the flat before executing the flaw detection, or the flaw detection is continuously executed on the defect in the steel plate during conveying before cold-rolling since hot-rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of a hot-rolled steel sheet or a cold-rolled steel sheet, and more particularly, to a method of inspecting a steel sheet characterized by detecting defects in the steel sheet and utilizing the flaw detection information, and a manufacturing method thereof. The present invention relates to equipment for processing hot-rolled steel sheets and equipment for producing cold-rolled steel sheets.

[0002]

2. Description of the Related Art Conventionally, defect inspection for a cold-rolled steel sheet has been performed by:
It has been performed while continuously transporting (passing) a processing line after cold rolling, for example, a steel strip unwound in a refining process. The reason why the process is performed in the processing line after cold rolling is that the inspection can be performed immediately before the product is shipped, so that the shipping decision can be made.In other words, the emphasis was on quality assurance of the final product, and the surface generated in the cold rolling process etc. This is to enable detection of defects and the like.

[0003]

However, after the cold rolling, the flow of the manufacturing process is divided by the plating method or the like, so that it is necessary to install a flaw detector for each corresponding line, which increases the cost. .

[0004] Further, even if a defect is detected, the diversion destination of the cold rolled steel sheet is limited in the detection on the downstream side. For example, if the defect is found after refinement to the product dimensions, the sheet after the inspection is inspected. Since it was not possible to change the destination, it became scrap material,
The yield decline was large and uneconomical.

[0005] Feeding back the cause of the defect to the upstream process is an extremely labor- and time-consuming operation. In other words, in the past, after a defect was found or pointed out, a defect sample was ordered and the cause was clarified.However, the number of steps from the inspection position to the process that caused the defect occurred increased. It is difficult or troublesome to identify the cause of the problem because many products are interposed and the order of in-process products is changed according to the processing timing of each line. Response to defects (measures)
It is also conceivable to install a flaw detector on the cold rolling mill exit side before splitting into each processing line, but the detection speed of the flaw detector could not catch up with the speed of the plate, so it was realized. Have difficulty.

On the other hand, defect inspection in the production of hot rolling is conventionally sufficiently performed by extracting and inspecting a hot-rolled product for quality assurance, and is generally sufficient. The necessity and advantage of conducting defect inspections were not particularly pointed out. (This is because until recently, flaw detection methods that enable high-precision full-width, full-length, high-speed inspection of hot-rolled steel sheets were not provided until recently. Also play a role). However, since demands for more efficient and trouble-free operation of hot-rolled steel sheets are increasing in consumers, quality assurance through full inspection rather than probable assurance is considered desirable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a steel plate inspection and production which can easily take a countermeasure against a steel plate defect and can respond to the steel plate defect at an early stage. It is an issue.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention according to claim 1 provides a method for continuously manufacturing a hot-rolled steel sheet with respect to defects in the steel sheet being conveyed after hot rolling. An object of the present invention is to provide a method for inspecting a hot-rolled steel sheet, which performs flaw detection.

Next, the invention according to a second aspect is characterized in that the flaw detection is performed in a pickling step in a facility having a pickling step after hot rolling, with respect to the configuration according to the first aspect. It is assumed that. Next, the invention described in claim 3 is characterized in that, in the configuration described in claim 1 or 2, the shape of the steel sheet is corrected to be flat before performing the flaw detection.

Next, the invention described in claim 4 is characterized in that the above-described flaw detection is performed by an ultrasonic flaw detection apparatus, in contrast to the configurations described in claims 1 to 3. Next, the invention described in claim 5 is characterized in that, when producing a cold-rolled steel sheet, after hot rolling and before cold rolling, a flaw is continuously detected for defects in the steel sheet being conveyed. An object of the present invention is to provide a method for inspecting a cold-rolled steel sheet.

Next, the invention described in claim 6 is characterized in that the above-mentioned flaw detection is performed in a pickling step after hot rolling, with respect to the configuration described in claim 5. Next, the invention described in claim 7 is characterized in that the shape of the steel plate is corrected to be flat before performing the flaw detection with respect to the configuration described in claim 5 or 6. Here, the higher the flatness is, the better, but it is effective enough to be achieved by a normal leveler or the like.

Next, the invention described in claim 8 is characterized in that the above-described flaw detection is performed by an ultrasonic flaw detector in the structure according to any one of claims 5 to 7. is there. Next, in the invention according to claim 9, when manufacturing a hot-rolled steel sheet, after hot rolling, the steel sheet is continuously inspected for defects in the steel sheet being conveyed, and the flaw detection is performed based on the flaw detection information by the flaw detection. An object of the present invention is to provide a method for manufacturing a hot-rolled steel sheet, wherein a process condition on an upstream side of a position is corrected.

According to a tenth aspect of the present invention, in the configuration described in the ninth aspect, the flaw detection is performed by the method for inspecting a hot-rolled steel sheet according to any one of the second to fourth aspects. It is characterized by the following. Next, the invention according to claim 11, when manufacturing a cold-rolled steel sheet, after hot rolling and before cold rolling, perform continuous flaw detection for defects in the steel sheet being conveyed, and the flaw detection information by the flaw detection The present invention provides a method for manufacturing a cold-rolled steel sheet, wherein a process condition on the upstream side of the flaw detection position is corrected based on the above.

Next, according to a twelfth aspect of the present invention, when manufacturing a cold-rolled steel sheet, after hot rolling and before cold rolling, the steel sheet is continuously inspected for defects in the sheet being transported, and the flaw detection is performed. The present invention provides a method for manufacturing a cold-rolled steel sheet, characterized in that process conditions downstream of the flaw detection position are corrected or determined based on flaw detection information.

[0015] Next, in the invention according to claim 13, when manufacturing a cold-rolled steel sheet, after hot rolling and before cold rolling, the steel sheet is continuously inspected for defects in the steel sheet being conveyed. The present invention provides a method for manufacturing a cold-rolled steel sheet, comprising determining a processing line for a steel sheet after cold-rolling based on flaw detection information obtained by the method.

Next, a fourteenth aspect of the present invention provides a configuration according to any one of the eleventh to thirteenth aspects,
The flaw detection is performed by the method for inspecting a cold-rolled steel sheet according to any one of claims 6 to 8. Next, the invention as set forth in claim 15 is characterized in that a processing device for hot-rolled hot-rolled steel sheets is provided with a flaw detector for continuously detecting flaws in the conveyed hot-rolled steel sheets. An object of the present invention is to provide processing equipment for hot-rolled steel sheets.

The equipment for processing a hot-rolled steel sheet is literally equipment for processing a hot-rolled steel sheet. In equipment for producing a cold-rolled steel sheet, the equipment is disposed after hot rolling and before cold rolling. Equipment for manufacturing hot-rolled steel sheets,
Equipment from hot rolling to before hot rolled product shipment.

Next, a sixteenth aspect of the present invention is characterized in that, in addition to the configuration of the fifteenth aspect, a shape correcting means is arranged upstream of the flaw detector. Next, a seventeenth aspect of the present invention is characterized in that, in addition to the configuration of the fifteenth or sixteenth aspect, tension applying means is arranged upstream and downstream of the flaw detector.

Next, the invention as set forth in claim 18 differs from the configuration as set forth in any of claims 15 to 17 in that
The flaw detector is arranged in the pickling process. Next, the invention described in claim 19 is based on the configuration described in any one of claims 15 to 18,
The flaw detection device is an ultrasonic flaw detection device.

[0020] Next, according to a twentieth aspect of the present invention, in a facility for manufacturing a cold-rolled steel sheet provided with a hot rolling mill and a cold rolling mill, the cold rolling mill is provided between the hot rolling mill and the cold rolling mill. An object of the present invention is to provide a cold-rolled steel sheet manufacturing facility, which is provided with an ultrasonic flaw detector for continuously detecting flaws in a conveyed steel sheet.

Although there are many types of defects in steel sheets, extrinsic defects that occur after the completion of hot rolling include abrasions, indentations,
It is limited to surface defects such as biting of dust or discoloration, and can be detected only by surface inspection after cold rolling (annealing). Therefore, the flaw inspection for a steel sheet in a hot-rolled steel sheet can be sufficiently substituted for the flaw detection after cold rolling.

The defects targeted by the present invention include internal defects due to inclusions and the like, and inclusions such as slivers, scabs, scale flaws and gouges, or inclusions (including iron oxides). Refers to surface defects that are involved, for example. Although all of these defects can be detected by the method of the present invention, it goes without saying that the inspection may be limited to a specific defect.

Based on such knowledge, the present invention detects a defect in a steel strip between hot rolling and cold rolling before cold rolling. As a result, almost all internal defects and surface defects can be detected by a concentrated flaw detection in one place. In addition, between the hot rolling step and the cold rolling step, there is usually a pickling step of a hot-rolled steel sheet. In this pickling step, the conveying speed of the steel sheet is controlled by a hot rolling step or a cold rolling step. In view of the fact that the transfer speed is slower than the transfer speed and the degree of freedom of the transfer speed is relatively large, the pickling step is preferable as the installation position of the flaw detector. Furthermore, if the flaw detection device is configured to perform flaw detection in water, that is, to perform flaw detection in water, the entrance side of the pickling tank is suitable because the steel plate immersed in water does not need to be dried.

Further, by correcting the shape of the steel plate to be flat prior to the flaw detection, the flaw detection is continuously performed on the flat steel plate, so that the detection accuracy over the entire width is improved. Further, since the scale and the attached matter on the brittle outermost surface of the hot-rolled steel strip usually fall off by a forcing means such as a tension leveler, there is also an effect that foreign matter is less likely to be deposited on a water tank for flaw detection. Further, when the flaw detection is performed in a state where the tension is applied, the flatness of the steel plate at the time of the flaw detection is further improved, and the fluctuation of the pass line hardly occurs, so that the detection accuracy is further improved.

Further, as a flaw detector capable of continuously detecting a steel sheet (steel strip) which is rewound and continuously conveyed over the entire width, there are a flaw detector using a leakage magnetic flux method and a flaw detector using ultrasonic waves. Conceivable. However, despite the fact that the hot-rolled steel sheet is thicker than the cold-rolled sheet,
When the steel sheet becomes thicker, the ratio of (defect cross-sectional area / steel cross-sectional area) becomes smaller, and it becomes difficult for magnetic flux to leak to the surface. In addition, since the leakage magnetic flux attenuates rapidly in inverse proportion to the distance from the surface of the steel sheet, it is necessary to control the vertical fluctuation of the pass line of the steel sheet to within ± 0.1 mm. Must be controlled within 0.5 mm, and it is difficult to apply continuous flaw detection in a steel sheet being transported, particularly in a state where the transport speed is high. Further, there is a problem that there are many noise factors. In addition to the problems of the detection accuracy, the leakage magnetic flux method has a disadvantage that almost no information on the shape of the detected defect can be obtained.

For this reason, the flaw detection for the hot-rolled steel sheet may be thick, and in the case of the non-contact type, the gap between the surface of the steel sheet and the detecting portion can be made wider than the leakage magnetic flux method. An ultrasonic flaw detector is preferred. Here, as the ultrasonic flaw detection apparatus, a plate wave UT method, a focused beam UT method, and a reflection type flaw detection method in a transmission type arrangement (hereinafter, also referred to as an ultrasonic line sensor) can be considered.

The plate wave UT method detects a flaw by rolling a tire-type acoustic probe (detection unit) into contact with the surface of a steel sheet, but has a dead zone in the thickness direction and is a contact type. It is necessary to adjust the contact pressure of the tire to the surface, the tire bounces, and so on.The transport speed of the steel sheet is limited to a very low range, and it is virtually impossible to continuously detect a wide range of hot rolled steel strips. Impossible. Also, there is a fear that the tires burst.

In this regard, the focused beam UT method and the ultrasonic line sensor do not have the above-mentioned problem because the inspection is performed in a non-contact manner. That is, the influence of the pass line fluctuation at the time of transporting the steel sheet is small and advantageous. . Here, the focused beam UT method is used for defect detection of a thick plate or a welded part, and the theory has been established. However, as compared with an ultrasonic line sensor, an ultrasonic beam is converged in a point shape (for example, 1 mmφ), so that a number of probes (detection units) corresponding to a flaw detection area is required, and the number of parts for flaw detection is reduced. As the number increases, the flaw detection efficiency decreases. Another drawback is that a dead zone is formed immediately below the steel sheet surface.

In view of the above, of the ultrasonic flaw detector, the ultrasonic line for performing the reflection type flaw detection in a non-contact and transmissive arrangement (where a transmission section and a reception section are arranged with a steel plate interposed therebetween) is provided. Those using a sensor are preferable. Here, the configuration and principle of the ultrasonic line sensor are disclosed by the present inventors in Japanese Patent Application Laid-Open No. Hei 7-253414, Japanese Patent Application No. 9-240932, and the like. A band-like ultrasonic beam is transmitted, and the beam is received by a receiving unit including a plurality of rectangular ultrasonic transducers arranged in the width direction of the band. That is, a line-focus type transmission array probe (transmission unit) with the steel strip conveyed in between
And the line focus type receiving array probe (receiving unit) are arranged in an opposed arrangement (the direction of the arrangement is the width direction of the test material), and an internal defect caused by the ultrasonic wave transmitted from the transmitting array probe. The reflected wave is received by the receiving array probe arranged opposite to the transmitting array probe, thereby detecting the internal defect of the test sample without a dead zone just below the front and back surfaces (see FIGS. 3 and 4). The reflection type flaw detection in the transmission type arrangement is performed by transmitting a 0.5 round-trip transmitted wave T1 transmitted from the transmission array probe and arriving at the reception array probe by reciprocating 0.5 times of the test material, and substantially 1.5 times of the test material. The reflected waves F1 and F2 from the defect appearing between the 1.5 reciprocating transmitted waves that reciprocate and reach the receiving array probe are extracted by the gate circuit.
The internal defect is detected assuming that there is a defect reflected wave (see FIG. 5).

Further, since this line sensor has a wide range in which a single detecting portion can detect a flaw, it is preferable for detecting a steel sheet being conveyed. Note that the flaw detection by the ultrasonic flaw detector is preferably performed in a liquid in order to maintain good acoustic coupling between the ultrasonic probe and the steel plate, that is, to increase detection accuracy.

Further, the present invention provides a method for removing defects in a process after hot rolling and before cold rolling (after hot rolling in the case of manufacturing a hot-rolled steel sheet), which is an upper process and before the production process is divided. Perform detection. For this reason, in order to detect a defect early and at a position close to the position where the cause of the defect occurs, it is easy to take measures to correct the cause and to cope with the defect early.

In addition, by performing flaw detection before cold rolling where each cold-rolled steel sheet is diverted, processing of the cold-rolled steel sheet according to the defect is performed by changing downstream process conditions for each steel sheet based on the flaw detection information. It is possible to appropriately select the processing line of the cold rolled steel sheet to be sorted after the cold rolling according to the defect situation.

[0033]

Next, a first embodiment of the present invention will be described with reference to the drawings. The present embodiment relates to a facility for manufacturing a cold-rolled steel sheet. The equipment, from the upstream side,
Blast furnace-Converter-(Degassing equipment)-Continuous casting equipment-(Slab storage)-Hot rolling-Pickling process of hot rolled steel sheet-Cold rolling process-Continuous annealing process-(Secondary cold rolling and box Annealing process-)
The processing line after cold rolling (continuous annealing step-temper rolling step-refinement step) is divided into a plurality of processing lines according to the final product. The processing line after the cold rolling step is an example, and depending on the type of the cold-rolled steel sheet, for example, there may be a step such as a plating step.

In the pickling step of the hot-rolled steel sheet, for example, as shown in FIG. 1, the payoff reel 1, the shear 2, the welding machine 3, the entrance looper 4, the entrance bridle roll 5, the tension leveler 6 from the upstream side. Outlet bridle roll 7, pickling tank 8, rinsing tank 9, drying device 10, outlet looper 11,
Each equipment is arranged in the order of the trimmer 12, the shear 13, and the coiler 14, and the hot-rolled hot-rolled steel sheet is rewound to perform the pickling treatment.

In this embodiment, an ultrasonic flaw detector 20 is provided between the tension leveler 6 and the outgoing bridle roll 7 on the entrance side of the pickling tank 8, as shown in FIG. I have. Here, the tension leveler 6 is
Cracking is applied to the scale on the surface of the hot-rolled steel sheet 15 to promote the cleaning with acid in the pickling tank 8, and also has the function of correcting and flattening the shape of the plate before flaw detection, and Also serves as a shape correction means. In addition, the flaw detector 20
The bridle rolls 5 and 7 before and after have a function of applying a tensile force in the longitudinal direction to the plate at the flaw detection position. That is, the tension leveler 6 and the bridle rolls 5 and 7 form a part of the flaw detection equipment together with the ultrasonic flaw detection apparatus 20.

The configuration of the flaw detection equipment will be described. An upstream bridle roll 5, a tension leveler 6, a liquid tank 21 containing water 22, and a downstream bridle roll 7 are arranged from the upstream side to the downstream side. ing. In addition, a rust preventive or the like for preventing rust of the hot-rolled steel sheet 15 is added to the water 22 in the liquid tank 21.

The first transport roll 2 is located on the entry side of the liquid tank 21.
2, the transport path of the hot-rolled steel sheet 15 is changed vertically downward by the first transport roll 22 and the second transport roll 23 completely immersed in water, and the hot rolled steel sheet 15 is guided into the water in the liquid tank 21.
The transport direction of the hot-rolled steel sheet 15 immersed in water is bent in the horizontal direction by the second and third transport rolls 23 and 24 that are completely immersed in water, and subsequently the third transport roll 24 and the upper surface of the water are bent upward. The transport direction is bent in the vertical direction by the third transport roll 24 located, and the third transport roll 24 exits the water, that is, from the liquid tank 21. Subsequently, the hot-rolled steel sheet 15 is
The downstream bridle roll 7 side, that is, the pickling tank 8
Guided to the side. Here, the first and fourth transport rolls 2
The reason why the rolls 2 and 25 are each composed of two rolls is that the height of the conveying path of the hot-rolled steel sheet 15 is once increased so that the hot-rolled steel sheet 15 can be guided into the liquid tank 21. Not necessarily.

An ultrasonic line sensor 26 as a detection unit of the ultrasonic flaw detector 20 is disposed between the second transport roll 23 and the third transport roll 24. The flaw detection method of the ultrasonic line sensor 26 is disclosed in Japanese Patent Laid-Open No. 7-25341.
As shown in FIG. 3 which is a conceptual diagram based on the principle described in Japanese Patent Publication No. 4 and the like, a transmitting unit 26a and a receiving unit 26b each formed of a one-dimensional array type probe sandwich a hot-rolled steel plate 15 therebetween. The hot-rolled steel sheets 15 are arranged to face each other in the thickness direction. In FIG. 3, reference numeral 27 indicates a line focus beam, and reference numeral 28 indicates a reception beam.

The ultrasonic line sensor 2 configured as described above
4, a plurality of transmitters 26a and receivers 26b are continuously arranged along the width direction of the hot-rolled steel sheet 15 and larger than the width of the steel sheet. 30
It is supported by. Accordingly, it is possible to detect a defect in the entire width of the hot-rolled steel sheet 15 conveyed by a small number of detecting units. Here, the arrangement of the transmission units 26a and the reception units 26b in a staggered manner enables inspection of the entire width direction of the hot-rolled steel sheet 15 while avoiding unnecessary interference between the adjacent sensors 26. That's why. Note that the receiving unit 26b may be arranged on the upper side, and the transmitting unit 26a may be arranged on the lower side, or may be arranged upside down as appropriate.

Each sensor 26 is connected to the flaw detector main body 31. In the flaw detector main unit 31, the 0.5 reciprocating transmitted wave T1 transmitted from the transmitting unit 26a and reciprocating the hot-rolled steel plate 15 by 0.5 in the thickness direction to reach the receiving unit 26b and the hot-rolled steel plate 1
When the reflected waves F1 and F2 from the defect appearing between the reflected wave F1 and the reflected wave F1 and the reflected wave F2 reaching the receiving unit 26b after reciprocating 1.5 times in the plate thickness direction and reaching the receiving unit 26b are extracted by a gate circuit, Detects that there is a defect reflected wave and detects an internal defect. The detected internal defect information is supplied to, for example, an operation unit or a control unit in an upper process or a lower process.

A ringer roll 32 serving as a liquid squeezing means for squeezing water adhering to the steel plate 15 is disposed between the third transport roll 24 and the fourth transport roll 25 at a position close to the water surface. In addition, a liquid receiver 33 is disposed between the ringer roll 32 and the water surface to receive the liquid falling from the hot-rolled steel plate 15 and prevent the liquid from directly colliding with the water surface. The liquid receiver 33 may be above the water surface 22a, or may be in contact with the water 22 in the liquid tank 21. Further, the water received by the liquid receiver 33 is gently poured into the liquid tank 21.
It may be returned to the inside water 22 or may be discharged to the liquid tank 21. Further, in FIG. 2, a container-like liquid receiver 33 is shown, but a flat plate member such as a shielding plate may be used.

In the above-described cold rolled steel sheet manufacturing equipment, when hot-rolled steel sheet 15 is subjected to pickling treatment, it is continuously flaw-detected while being conveyed before the pickling.
That is, the hot-rolled steel sheet 15 before hot-rolling and before pickling is conveyed in a state where the upstream bridle roll 5 and the downstream bridle roll 7 apply a tension in the longitudinal direction, and is immersed in the water 22 in the liquid tank 21. Before that, it is continuously flattened by the tension leveler 6. Subsequently, the hot-rolled steel sheet 15 is immersed in the water in the liquid tank 21 by the transport rolls 22 to 25, and while moving horizontally in the water, the line sensor 26 of the transmission type ultrasonic flaw detector 20 continuously detects internal defects. An inspection is performed.

In addition, despite the fact that the flaws are detected in a concentrated manner at one place, almost all the defects to be detected can be detected. Here, in the present embodiment, in order to prevent the detection accuracy from deteriorating due to bubbles, the hot-rolled steel sheet 15 enters the water perpendicular to the water surface, and the generation of bubbles when the hot-rolled steel sheet 15 is immersed is minimized. In addition, the water adhering to the hot-rolled steel sheet 15 coming out of the water is squeezed by the ringer roll 32 near the surface of the water, and the liquid is reliably dropped from the ringer roll 32 installation height. The liquid that has fallen from the hot rolled steel plate 15 above the water surface is prevented from directly colliding with the water surface to prevent bubbles from being generated by the liquid that falls from the hot-rolled steel plate 15 (see FIG. 5).
Since the falling liquid is received by the liquid receiver 33, the ringer roll 32 is not necessarily required.
At the same time, in order to prevent water from being conveyed to the downstream process, and by lowering the falling height of the liquid, there is an effect that the splash of the liquid that has collided with the liquid receiver 33 is reduced.

In the flaw detection using ultrasonic waves of the present embodiment, since the detection unit 26 of the ultrasonic flaw detection apparatus 20 employs a non-contact and transmission type reflection type flaw detection method,
By eliminating the dead zone just below the surface, it is possible to detect defects of the hot-rolled steel sheet 15 being conveyed at a predetermined speed while securing predetermined detection accuracy, and by using the line sensor 26, the width direction of the hot-rolled steel sheet 15 can be detected. Even when the entire width is to be inspected, the number of the detection units (sensors 26) can be reduced.

Further, the detection accuracy is improved by performing the flaw detection in water, and the generation of bubbles due to the hot-rolled steel sheet 15 entering the water and moving upward from the water surface is minimized. Erroneous detection is prevented, and the detection accuracy is further improved. Since the transport rolls that are in contact with water are all submerged in water, the entrapment of bubbles due to the rotation of the transport rolls is reduced. Here, the flaw detector 20
Is not limited to the vertical direction, so that the transport path of the flaw detection position of the hot-rolled steel sheet 15 in water may not be horizontal. However, from the viewpoint of preventing adverse effects of air bubbles, it is preferable to detect flaws at the position farthest from the water surface.

Further, before the inspection, the hot-rolled steel sheet 15 is inspected in a state where it is straightened and tension is applied.
The hot-rolled steel sheet 15 becomes flatter, and thus, the flaw detection of the defect of the hot-rolled steel sheet 15 is performed with higher accuracy. Here, the tension leveler 6 and the bridle rolls 5 and 7 are not necessarily required, but without the tension leveler 6 or the like, the flatness of the hot-rolled steel sheet 15 at the flaw detection position is deteriorated and the detection accuracy is reduced. descend. The shape correcting means is not limited to the tension leveler 6, and for example, a temper rolling mill or the like may be used. Also, if the bridle rolls 5 and 7 are manually provided with tension, other known means may be used. In this embodiment, the hot-rolled steel sheet 15 is immersed in water 22 in order to increase the detection accuracy of flaw detection. However, since it is on the entrance side of the pickling tank 8, there is no need for a means for particularly drying the hot-rolled steel sheet 15 after the flaw detection. When the flaw detector 20 is disposed on the entrance side of the pickling tank 8, the tension leveler 6 is usually disposed on the entrance side of the pickling tank 8 as described above, so that the flaw detector 20 is separately provided. It is not necessary to provide a shape correcting means for the purpose. Further, in the pickling step, the inlet side of the pickling tank 8 is the most suitable because the transport speed is the most stable.

By employing such flaw detection equipment, full width continuous flaw detection is possible even under a high-speed sheet passing speed of about 300 to 1000 m / min. In the above embodiment, in order to improve the detection accuracy, the water immersion method using a water tank in which the rolls are fully immersed is adopted, but the invention is not limited to such a flaw detection method. For example, as shown in FIG.
A different water immersion method using two pairs of air rolls 23 'and 24' for sealing the water (liquid) while conveying the steel strip may be used. Further, a flaw detection method in the atmosphere or atmosphere that does not collapse can be adopted.

Further, instead of the line sensor 26, an ultrasonic flaw detector using a focused beam UT method may be employed. However, the number of probes (detection units) increases, which may complicate the device configuration and lower the detection accuracy. Also,
In the above-described embodiment, an example in which flaw detection equipment is provided in the pickling process is described. However, if it is between hot rolling and cold rolling, another position such as a trimmer or a cold-rolling entrance equipment is provided. May be provided with the flaw detection equipment. For example, in FIG. 6, which is the entrance equipment of the tandem cold rolling mill, the flaw detection equipment may be interposed at a portion K on the exit side of the welding machine 40 (the flaw detection equipment is not shown). In FIG. 6, reference numeral 41 denotes a payoff reel,
Reference numeral 42 denotes a looper, and reference numeral 43 denotes a cold rolling mill.

The equipment of the present embodiment is a manufacturing equipment for a cold-rolled steel sheet. However, even when the hot-rolled steel sheet 15 before cold rolling is shipped as a product, as described above, the hot-rolled steel sheet 15 can be used. Since the quality control of the steel sheet 15 is performed, it is not necessary to separately provide a defect inspection facility for the hot-rolled steel sheet.

The presence or absence of scratches after cold rolling is checked by
As before, if necessary, before product shipment. Hot rolled steel sheet 15
The same applies to the case of shipment. (Example) In the above-mentioned cold rolled steel sheet manufacturing equipment, a steel sheet containing 0.3 inclusions per ton (0.005 per square meter) was inspected by the flaw detection equipment, and as a result, the recognition rate was almost 100%. It was confirmed that defect inclusions could be detected at a ratio of.

Here, when flaw detection is performed in a state where tension is not applied by the bridle rolls 5 and 7, the recognition rate is reduced to about 99.5%, and when the tension leveler 6 is not used, the recognition rate is reduced. The rate dropped to about 99.0%. For comparison, a steel sheet containing 0.3 inclusions per ton as in the prior art without a flaw detection equipment in the above pickling process was used in a refining process before product shipment. When a defect was inspected by the flaw detection apparatus 20, the recognition rate of the defect was about 80 to 98% due to reasons such as the inability to distinguish it from electrical noise.

As described above, it can be understood that the defect can be detected with high accuracy by detecting the defect based on the present invention. In addition, detection can be performed at one place and at an early stage. next,
A second embodiment will be described with reference to the drawings. The same reference numerals are given to the same equipment and devices as those in the first embodiment, and the detailed description thereof will be omitted.

The second embodiment is a facility for manufacturing a hot-rolled steel sheet 15 and has the same apparatus configuration as the first embodiment up to the pickling step. A refining process is arranged. That is, it is composed of blast furnace-converter- (degassing treatment equipment) -continuous casting equipment- (slab storage) -hot rolling-pickling process of hot-rolled steel sheet-refining process.

The other structures, operations and effects are the same as those of the first embodiment. That is, even when the hot-rolled steel sheet 15 is shipped as a product, defects in the steel sheet can be detected with high accuracy, and quality control can be performed with high accuracy. The installation of the flaw detection equipment is not limited to the pickling step, and may be separately provided between the pickling step and the refining step.

Next, a third embodiment will be described with reference to the drawings. The same reference numerals are given to the same equipment and devices as those in the first embodiment, and the detailed description thereof will be omitted.
The present embodiment relates to a cold rolled steel sheet manufacturing facility,
With the same equipment configuration as that of the first embodiment, between the hot rolling and the cold rolling, such as the pickling step and the cold rolling incoming equipment, the flaw detection equipment is used to perform the hot rolling with high precision as described above. Steel plate 15
Detect defects at

For example, for a defect caused by a (non-metallic) inclusion detected by flaw detection in advance, the shape, size, amount, etc. of the flaw are investigated, and the cause is determined for each form of the inclusion based on the investigation result (flaw detection information). After identifying, which defect type is currently occurring is determined, and the specified steelmaking conditions (especially casting conditions) are corrected so as to reduce or eliminate the corresponding defect type. The casting conditions are, for example, a slab casting position, a casting speed, a casting temperature, a used flux, and the like, and other steelmaking conditions include oxygen in steel,
There is a degassing time. As an example, inclusions are mainly classified into a plurality of forms based on the shape, and the form to which the current defect belongs is determined, and a countermeasure corresponding to each is set in the operating conditions of the continuous casting equipment (and degassing equipment). To reflect. As a result, the hot-rolled steel sheet 15
In addition, in the cold-rolled steel sheet, the continuous occurrence rate of the coil having the same defect is quickly and almost eliminated.

In this embodiment, since the flaw detection is performed before the steel sheet is diverted to each line, the defect can be detected efficiently, and the defect is detected in a process close to a casting process or the like where the defect is generated. In addition, since measures can be taken early to take countermeasures and the cause of the defect can be easily specified, the countermeasures based on the flaw detection information as described above can be easily performed.

For example, in the case of equipment for manufacturing steel plates for cans, conventionally, the discovery of defects, such as internal defects due to inclusions, which is the object of the present invention, is performed by inspection of the original plating sheet and surface It was discovered and pointed out for the first time after inspecting treated steel sheets, and then conducting can manufacturing in the can manufacturing process. As a result, even if a discovery or indication is received, in order to take countermeasures, we will order a defect sample, estimate the cause, review the manufacturing process history of the defective product, find the defect condition and take measures Therefore, it takes time and effort to elucidate the cause and determine countermeasures.Many steel plates manufactured during that time are downgraded, and in order to replenish them, the original process production plan must be reconfigured and reproduced. And the economic blow was enormous.

On the other hand, in the present embodiment, the process of manufacturing a cold-rolled steel sheet such as a steel sheet for cans is an inspection method at the stage of the hot-rolled steel sheet 15 having a large thickness, which is an upper step. It is possible to detect the presence of a defective steel sheet, and to send the flaw detection information to the upper steelmaking and hot rolling process at an early stage, that is, with a small number of defective sheets, and immediately determine the cause and countermeasures. Can take.

Further, since the process condition causing the defect and the flaw detection position are close to each other, it is easy to specify the cause. Moreover, the ultrasonic flaw detector 20 using the line sensor 26 employed in the present embodiment can also obtain detailed information on the position where the defect is generated and the shape and size of the defect, so that the cause and countermeasure can be taken immediately.

(Embodiment) The following inspection and determination were first performed when using the ultrasonic flaw detector 20 to feed back the flaw detection information to the upper process. In the following description, the steel sheet for cans is assumed as the cold-rolled steel sheet,
It is not limited to steel plates for cans.

First, a sample is taken from the position of the hot-rolled steel sheet 15 indicated by the ultrasonic flaw detector 20, a cross section in the rolling direction and a cross section in the width direction are observed with a microscope, and the following three types are determined according to the type of defect and the generation process. , And go back to the generation process, 3
Causes and measures were linked for each type of classification.

That is, scale flaws generated during hot rolling (Scale; ISIJ TR009-1980)
The Iron and Steel Institute of Japan), and Hege (Scab), Gouge generated after the hot finishing mill,
Sliver generated by steelmaking-continuous casting (Sliver) and Skin Inclusion (Skin Inclusi)
on)). This result was compared with the flaw detection information, that is, the mixing position, shape, and size of the hot-rolled steel sheet 15 in the width direction and the length width direction of the defect, and used as a process standard.

In the following description, a case will be described in which inclusion defects occurring in steelmaking-continuous casting are targeted. As shown in Table 1 below, the tolerance of defective cans caused by steel sheet material for cans in the can making process is extremely strict. In order to remove defective cans from the can-making line, even if the line is stopped and restored manually by human intervention, the rate of defective cans remains at 10%.
The lower limit was about 0 ppm.

[0065]

[Table 1] In order to respond to the demand for a further reduction in the defect rate, the characteristics of the line sensor type ultrasonic flaw detector 20 for non-metallic inclusions that were difficult to detect and classify as defects with the conventional flaw detectors such as the leakage magnetic flux method As a result of conducting research with the help of, the inclusions can be detected and classified as follows, and the early detection can prevent the occurrence of a large number of problems.

Here, the steel sheet for cans is very severe compared to steel sheets for automobiles and the like, and both canning speed and filling speed are 1000 times.
As described above, the productivity is high at cans / minute or more, and the contents are also for food. As described above, the generation control of defective cans is very strict, and research and improvement have been promoted conventionally.

The following operating conditions were set in order to suppress the occurrence of defective cans. That is, low carbon Al killed steel (C <0.10 wt%, Al <0.15
wt%) in the production of continuous cast slabs.
With a 0t bottom-blowing converter, the reaction inside the furnace was leveled with strong stirring,
By shortening the reaction time in the furnace, the iron oxide (T, F
e) was reduced and the steel was blown and melted to reduce the amount of oxygen in the steel. In tapping, the slag detector detects slag outflow and the slag stopper minimizes slag outflow. Instead of converter slag, synthetic slag was added to the molten steel surface for heat retention and the like.

Subsequently, if necessary, vacuum degassing treatment is performed to adjust the amount of C and increase the cleanliness of the molten steel,
1 was added, followed by addition of a carbide-forming element and a nitride-forming element as required. Using a vertical bending type continuous casting machine having a large capacity 70 tons tundish each of which is advantageous for removing nonmetallic inclusions,
In order to promote the flotation and separation of inclusions, weirs were provided in the tundish, and the time required to reach the mold from the ladle was increased, so that the inclusions were coarsened and floated.

This is because even if the nonmetallic inclusions that pose a problem in quality are 100 μmφ, the floating speed is as low as 0.3 m / min. However, it reaches the mold in a short time along the bottom of the tundish, and there is not enough time for coalescing coarse separation / floating separation.

The molten steel temperature was maintained at a high temperature of 1500 ° C. or more in order to promote the coalescence of the inclusions and the flotation separation. At this time, the extremely small one of about 30 μmφ cannot be expected to float and separate as it is, so the molten steel temperature is increased,
It is important to make the coalescing coarse. If the diameter is about 40 μmφ or more, floating separation is expected by securing the floating time.

Further, the oxygen concentration in the atmosphere in the tundish was replaced with argon gas from the start of injection for the purpose of preventing atmospheric oxidation, and the operation was continued at 0.5% or less. The molten steel flows from the ladle to the tundish and then to the mold, where it solidifies and finishes.In order to prevent atmospheric oxidation, each joint is replaced with argon gas to prevent atmospheric oxidation. At the same time, refractory nozzles have been used, and argon gas has been blown into molten steel for the purpose of preventing clogging of inclusions in the nozzles.

In the mold, a mold powder having a large viscosity and an excellent ability to absorb inclusions was used in order to suppress fluctuations in the molten metal level. If the inclusion absorption capacity is poor, Al ₂ O ₃ floating on the molten steel surface with the flow of the molten steel remains without being absorbed by the mold powder, flows from the meniscus portion along the side surface of the slab, and is captured by the solidification front. . For this reason, along with the optimization of the powder component, the molten steel temperature was maintained at a high temperature of 1560 ° C. or higher, and the absorption capacity of Al ₂ O ₃ was increased.

Further, depending on the discharge shape of the immersion nozzle, for example, the balance of the jet flow velocity from the nozzle is poor, and if the flow velocity into the mold is strong, the inclusions are carried together and trapped in the solidified layer, The flow of the high-temperature molten steel decreases, the temperature of the molten metal decreases, and inclusions are trapped. Conversely, if the flow of the high-temperature molten steel to the molten metal surface is strong, the fluctuations in the molten metal surface become large, and the fluctuations bring in inclusions in the downward flow. Also, if the jet flow velocity from the immersion nozzle is large, the surface of the molten metal immediately above the discharge port becomes negative pressure, and the powder that has absorbed Al ₂ O ₃ is brought down and captured.

An immersion nozzle that satisfies the above constraints was designed and confirmed by a water model experiment. In operation, a vortex-type mold level controller is used to reduce the level fluctuation by up to 20
In order to be able to cast while controlling the thickness to mm, the molten steel flow in the mold was made normal, and an immersion nozzle with an appropriate discharge shape was used so that inclusions were not trapped in the solidified layer. In addition, the electromagnetic brake is effectively used to prevent the molten steel flow from penetrating deeply, and a slab having a slab thickness of 260 mm and a large cross section of 1300 mm is cast at a casting speed of 1.0 m / min or more. Slabs were manufactured with defect specifications.

As described above, a continuous cast slab for a steel plate for cans manufactured by controlling the casting conditions so as to minimize defects caused by inclusions was subjected to hot rolling to a thickness of 2 mmt. After that, as described above, an inspection is performed by water immersion ultrasonic testing arranged on the entry side of the hydrochloric acid pickling tank 8, a sample is collected from the corrugated portion of the steel sheet, and the presence of nonmetallic inclusions is observed by a cross-sectional microscope. After confirming the position (depth), shape and size, EPM
A analysis was performed to confirm the composition of the nonmetallic inclusions, and to clarify the cause in light of the casting conditions for continuous casting.

Further, after taking appropriate countermeasures against the cause, the inspection was conducted again with the flaw detector 20, and if the cause was clarified and the countermeasure was confirmed to be appropriate, the flaw detection information (defect hot-rolled steel sheet) 15 were arranged in the width direction and the length width direction. Such research was repeated over several hundred cases as needed, and as a result, as shown in FIG. 7, defect forms due to inclusions could be classified into three types, and the shape at the time of slab was classified for each classification. Could be associated.

Thus, for a two-piece can steel plate,
Non-metallic inclusions are mixed in the plate despite the strict control of the casting conditions for continuous casting, but the inclusion defects are detected after hot rolling, and the composition and size of the non-metallic inclusions Can be roughly divided into three types as shown in FIG.
The relationship with the cause of occurrence and the frequency of occurrence could be clarified from the correspondence with the manufacturing history.

Here, the classification A of nonmetallic inclusions has the highest mixing frequency of about 70% and is super-hard, so it is used in hot rolling, cold rolling, temper rolling, and can forming. Even if ironing, stretch draw molding or stretch ironing molding is performed, it does not break and does not expand, so it retains the shape mixed with the slab, so high strength and ultra-thin steel plate and can processing In the process of processing to about 40 to 60 μm, it becomes a pinhole defect or a minute crack defect in a neck-in processed portion, and its frequency is large, and a countermeasure has been desired. In addition, the inclusions of this class A, after hot rolling,
It is detected as a spherical body having a diameter (X, Y) of about 30 to 50 μmmφ (see FIG. 7).

This Al_TwoO_ThreeSystem inclusions are refined in a converter.
To convert the finished molten steel composition to Al-killed steel,
Vacuum degassing during or after tapping
In addition to adding metal Al to deoxidize oxygen in steel,
In order to obtain the necessary mechanical properties as a steel sheet for cans,
It is necessary to leave 0.01% by weight or more of Al.
Low-carbon Al-killed steel
And finish. Deoxidation products generated by this deoxidation treatment
Is Al_TwoO_ThreeIt is the main cause of system inclusions, and
0.01% by weight or more of Al in steel before solidification by casting
And oxides on the steel surface
Al as long as supplied or reacted_TwoO _ThreeInclusions increase
Add. For example, when tapping molten steel in a converter into a ladle
And a small amount of converter slag
Escapes into the ladle. Even if it ’s a very small amount,
If slabs are manufactured by using slabs,
You. In particular, low carbon Al killed steel is
To blow, supply a large amount of pure oxygen into the steel bath,
It is necessary to decarbonize carbon as CO, and as a result,
And the iron oxide in the slag
(T, Fe) increases, fluidity is good,
Can easily flow into the ladle. Slag itself remains
And the defect of Class B described later,
Inclusions also increase during oxidation. Also, in the continuous casting process
Is shut off the atmosphere, but still leaked and supplied
If the operation continues without recognizing the situation, it will be reoxidized
To increase. Al_TwoO_ThreeSystem inclusions are numbers when generated
It is as small as μmφ and large if it is the same size
It does not cause harm, but the molten steel temperature is over 1500 ℃
Al_TwoO_ThreeThe grains aggregate and coalesce and enlarge. That
The mechanism attaches to the inner wall of the immersion nozzle in addition to the merging of inclusions.
Size that causes harm in the can making process
30 to 50 μmφ. Al on the inner wall of the immersion nozzle
_TwoO_ThreeOperation while flowing Ar gas so that particles do not adhere
Although it does, a slight amount of adhesion is inevitable. as a result,
This is a problem as a steel plate for cans.

From the above research results, when non-metallic inclusions of Class A were detected, the casting conditions were adjusted so that the amount of oxygen in the steel at the time of tapping was reduced and the amount of deoxidation products was reduced. Fix it. The confirmation can be made when the ratio of the amount of soluble Al to the weight of metallic Al added to the molten steel is 25% or more. Insoruburu Al which was left as Soruburu Al is adapted to Al ₂ O ₃ inclusions.
In addition, it was made possible by directly inspecting the device to see if air had flowed in, and by strictly controlling the results of the slag detector to see if the amount of slag mixed in was large.

Incidentally, in addition to Al-killed steel, Si-killed, T-
In recent years, one-killed steel or a combination thereof has been used. In this case, A type Al ₂ O ₃ type inclusions decrease, but the ratio of B type, C type and the like increases. In addition, in the non-metallic inclusion class B, the mixing frequency is as low as about 20%, but because of the hardness, hot rolling, cold rolling, temper rolling,
And, even if ironing, stretch draw molding or stretch ironing molding in can making is performed, it is processed to a high-strength ultra-thin steel plate and can making up to about 100 μm in order to expand without being divided. In the process, flange cracking defects occurred, and the frequency was high, and measures were desired. The inclusions belonging to the category B have a major axis Y of 100 to 300 μm and a minor axis X of 50 to 50 μm after hot rolling.
It is detected as a flat, substantially elliptical shape of about 150 μmm (see FIG. 7).

The origin of the CaO—Al ₂ O ₃ inclusions is that the converter slag is finely suspended in molten steel or the tundish flux is also suspended in the molten steel.
Deoxidized product A while being reduced by Al in molten steel
It is agglomerated with l ₂ O ₃ .

From the above research results, when non-metallic inclusions of class B are detected, it is necessary to improve the class A and to inject molten steel from the ladle into the tundish so as not to suspend the tundish flux. Confirm that the refractory nozzle is set near the bottom of the tundish, and then improve the casting condition by changing the casting conditions so that it is set deeper.

The classification C of the non-metallic inclusions has a mixing frequency of about 1
Although it is as low as 0%, it is soft, so if it is subjected to hot rolling, cold rolling, temper rolling, and ironing, stretching draw molding or stretch ironing in can making, it will be broken / cut and spread. In order to process high-strength ultra-thin steel sheets and cans, the body wall cracks in the process of processing the sheet thickness up to about 100 μm, and even if the frequency is low, the defective cans must be removed. Since the can-making operation could not be continued, the can-making line had to be stopped, and measures were desired. In addition, the inclusions belonging to the class C have a long diameter Y as a whole after hot rolling.
Is detected as a shape having a gap inside, leaving a substantially elliptical flat plate-like shape having a length of 300 μmm or more and a minor axis X of 150 μmm or more (see FIG. 7).

This CaO—SiO ₂ —Al ₂ O ₃ —Na
Origin of ₂ O-based inclusions are those mold flux that suspended finely in steel are aggregated combined with Al ₂ O ₃ of deoxidation products. From the above research results, when non-metallic inclusions of class C are detected, the same improvement as that of class A and the measurement values of the eddy current mold level control device are confirmed, and the casting level is reduced to reduce the level fluctuation. The problem can be solved by changing the conditions.

As described above, based on the flaw detection information detected by the flaw detector 20 arranged in the pickling process, whether the current defect is classified into any of A to C and how much the current defect is generated By correcting the process conditions by taking the above measures for each classification, appropriate measures can be taken for defects at an early stage, and the occurrence of the same defective coils in product coils is reduced early and significantly, thereby improving the yield. , The rejection rate was greatly reduced.

Here, in the above embodiment, an inclusion which is a defect generated by casting conditions is targeted, and the process conditions in the casting process upstream of the flaw detection position are corrected based on the flaw detection information, so that an early response is possible. However, the present invention is not limited to this. For example, as described above, hot rolling conditions (heating / cooling conditions, rolling conditions, etc.) and inclusions to be detected
The relationship with the form of crack defects (scale flaws, scabs, gouges, etc.) is investigated in advance, and the defects are classified based on the form. To detect defects in the hot-rolled steel sheet 15 and feed back to the process conditions of the hot-rolling line and pickling line based on the flaw detection information of hot-rolling defects such as scale flaws and scab flaws. By correcting the conditions and the like, early response to a defect may be achieved. Here, if flaw detection is performed at the cold-rolling entrance equipment, a defect (a gouge defect or the like) occurring near the pay-off reel on the cold-rolling entrance side can also be detected, and early action can be taken.

Next, a fourth embodiment will be described. Note that the same equipment and devices as those in the third embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The fourth embodiment is a manufacturing facility for a hot-rolled steel sheet 15 and has the same apparatus configuration as the third embodiment up to the pickling step, but has a refinement step downstream of the pickling step. Is arranged. That is, it is composed of blast furnace-converter- (degassing treatment equipment) -continuous casting equipment- (slab storage) -hot rolling-pickling process of hot-rolled steel sheet-refining process.

The other structures, operations and effects are the same as those of the third embodiment. That is, even when the hot-rolled steel sheet 15 is shipped as a product, the steel sheet defect is dealt with at an early stage, the continuous occurrence rate of hot coils having the same defect almost disappears, and the yield in the production of the hot-rolled steel sheet 15 is reduced. Improvement and quality improvement.

Next, a fifth embodiment will be described. In addition, the same reference numerals are given to the same facilities and devices as those in the above embodiments, and detailed description thereof will be omitted. The present embodiment relates to a cold-rolled steel sheet manufacturing facility having the same equipment as the first embodiment, and manufactures a steel sheet for cans having strict quality as a target cold-rolled steel sheet.

In the present embodiment, as described above, the flaw detection information detected in the pickling step or the like of the hot-rolled steel sheet 15 before the steel sheet is diverted to each line, for example, the size and amount of inclusions are detected.
Based on the flaw detection information, a cold rolling processing line after cold rolling is selected, and cold rolling conditions and the like are determined and changed.

As a result, an appropriate destination according to the defect state of the steel sheet can be determined in advance, and cold rolling can be performed under appropriate cold rolling conditions according to each steel sheet. As a result, the quality of the cold-rolled steel sheet can be improved. , And the yield is improved. For example, slabs (unsteady slabs) near the start and end of continuous casting, which had been difficult to apply in the past due to the risk of inclusion of inclusions greater than a predetermined amount, also have an appropriate destination immediately after cold rolling. (Cold-rolling processing line according to steel type) can be determined, so that it can be applied to steel plates for cans.

(Examples) Based on the average number of inclusions per square meter detected in the pickling step, the steel sheets are classified into 1 to 6 ranks according to the degree of defects as shown in Table 2, and each rank is Correspondingly, processing was performed by changing the application destination of the cold rolling processing line.

In addition, the rolling reduction of the primary cold rolling, the annealing temperature, the rolling reduction of the temper rolling (or the secondary cold rolling), and the like were determined according to the product specifications. After annealing, the DR material was temper rolled (1
%, And the hardness is increased by performing secondary cold rolling (reducing the thickness and securing the hardness by reducing the pressure by several percent to several tens of percent) instead of adjusting the hardness and shape by light reduction of about%. In order to increase the hardness, it is possible to decrease the annealing temperature or increase the rolling reduction of temper rolling (or secondary cold rolling). However, the components may differ depending on the grade (hardness). The diversion is convenient.

An example of diversion is shown below. Diversion Example 1: When a hot-rolled steel sheet to be applied to a T3 grade (thickness: 0.20 mm) can steel sheet of rank 3 was inspected for flaws in a pickling line, an average of 0.025 pieces / m ² was obtained. Inclusions were detected. Therefore, referring to the order status, etc., it was decided to divert to T3 class of rank 4 (plate thickness 0.20 mm). The processing lines such as cold rolling, annealing, and temper rolling, and the cold rolling reduction were not changed, but with the change in the hardness grade, the annealing temperature was raised by 30 ° C., and the elongation of temper rolling was reduced to 0. .3% down.

Diversion Example 2: T5 class of rank 1 (thickness of 0.2
When a hot-rolled steel sheet to be applied to a 5 mm) steel sheet for cans was inspected for flaws in an acid pickling line, an average of 0.003 inclusions / m ² was detected. Therefore, referring to the order situation, etc., it was decided to convert to rank 9 DR9 class (thickness 0.16 mm), and the planned annealing line was a continuous annealing furnace and a continuous annealing furnace from an integrated line of temper rolling mill-DR rolling. The line was changed to an integrated line, and the cold rolling reduction, refining temperature, etc. were also changed according to the target material.

[0097]

[Table 2] Here, in Table 2, the two-piece can is a steel plate having a can thickness of about 0.1 mm, which has been processed by a can maker after shipping, such as drawing (drawing, deep drawing). Also, the three-piece can
Since the can is formed as it is by cylindrical molding and welding, it is a steel plate whose can thickness is almost the same as the product can thickness. The positive pressure can
Since the contents are used under high internal pressure such as carbonated beverages, the can thickness is thin. The negative pressure can is subjected to a retort sterilization treatment (described later) or the like after vacuum encapsulation, and is used at an internal pressure equal to or lower than the atmospheric pressure. Also, T1 to T6, DR8 to DR1 as product grades
There is 0, and the higher the number, the higher the hardness.

Based on the flaw detection information obtained before the cold rolling based on the above Table 2, the cold rolling processing line of each steel sheet and the processing conditions after the cold rolling were appropriately changed in accordance with the degree of the defect. The yield in steel grades has improved, and the steel plate as a product as a whole has increased by 20% or more.

[0099]

As described above, when the present invention is employed, it is possible to accurately detect defects in cold-rolled steel sheets and hot-rolled steel sheets. Further, the cause of the defect can be easily identified, and the defect can be dealt with at an early stage, so that the yield of the cold-rolled steel sheet and the hot-rolled steel sheet is improved and the quality of the steel sheet is also improved.

Further, even in the case of shipping at the stage of a hot-rolled steel sheet in a cold-rolled steel sheet manufacturing facility, sufficient quality control can be performed. Furthermore, in the production of cold-rolled steel sheets, it is possible to detect defects by flaw detection at one place, simplify the flaw detection equipment, and to understand the defect status of each steel sheet before cold rolling, By being redirected to the cold rolling processing line suitable for the steel sheet, the scrap material is reduced, the yield of the cold rolled steel sheet is improved, and the quality of the steel sheet is also improved.

This method uses another metal plate, for example, A
The same effect was exhibited even when employed in the process of forming a 1 or Cu strip.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing equipment for a pickling step according to an embodiment of the present invention.

FIG. 2 is a view showing a flaw detection equipment according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a line sensor according to the embodiment of the present invention.

FIG. 4 is a diagram related to an array of line sensors according to the embodiment of the present invention.

FIG. 5 is a diagram illustrating the principle of a line sensor.

FIG. 6 is a diagram illustrating cold-rolling mill entry-side equipment.

FIG. 7 is a diagram showing classification of nonmetallic inclusions.

FIG. 8 is a diagram illustrating another example of the water immersion method for the flaw detection method.

[Explanation of symbols]

 5 Inlet bridle roll 6 Tension leveler 7 Outlet bridle roll 15 Hot rolled steel plate 20 Flaw detector 21 Liquid tank 22 Water 22-25 Transport roll 26 Line sensor (detector) 31 Flaw detector main body

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Teruhiro Saito 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Chiba Works of Kawasaki Steel Co., Ltd. (72) Inventor Toshihiko Chino 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (72) Inventor Susumu Okada 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba (72) Inventor Hideo Kuguminato 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture F-term (reference) 2G047 AA07 AB04 AD03 BB06 EA13 EA16 4E002 AA02 AD01 AD05 AD06 BC03 BD02 BD03 BD08 BD10 CA16 CB03 4K053 PA02 PA12 SA06 SA18 TA02 TA03 TA16 TA18 XA50 YA30

Claims (20)

[Claims] 1. A method for inspecting a hot-rolled steel sheet, comprising, after producing hot-rolled steel sheet, continuously detecting defects in the steel sheet being conveyed after hot rolling. 2. The method for inspecting a hot-rolled steel sheet according to claim 1, wherein the flaw detection is performed in a pickling step in a facility provided with a pickling step after hot rolling. 3. The method for inspecting a hot-rolled steel sheet according to claim 1, wherein the shape of the steel sheet is corrected to be flat before performing the flaw detection. 4. The method for inspecting a hot-rolled steel sheet according to claim 1, wherein the flaw detection is performed by an ultrasonic flaw detector. 5. A method for inspecting a cold-rolled steel sheet, wherein, when manufacturing a cold-rolled steel sheet, flaw detection of a steel sheet being conveyed is continuously performed after hot rolling and before cold rolling. 6. The method according to claim 5, wherein the flaw detection is performed in a pickling step after hot rolling. 7. The method for inspecting a cold-rolled steel sheet according to claim 5, wherein the shape of the steel sheet is corrected to be flat before performing the flaw detection. 8. The method for inspecting a cold-rolled steel sheet according to claim 5, wherein the flaw detection is performed by an ultrasonic flaw detector. 9. During the production of a hot-rolled steel sheet, after hot rolling, the steel sheet is continuously inspected for defects in the sheet being conveyed,
A method for manufacturing a hot-rolled steel sheet, comprising correcting a process condition upstream of a flaw detection position based on flaw detection information by the flaw detection. 10. The method for manufacturing a hot-rolled steel sheet according to claim 9, wherein the flaw detection is performed by the inspection method for a hot-rolled steel sheet according to any one of claims 2 to 4. 11. When manufacturing a cold-rolled steel sheet, after hot rolling and before cold rolling, the steel sheet is continuously inspected for defects in the steel sheet being conveyed. A method for manufacturing a cold-rolled steel sheet, wherein the process conditions on the upstream side are also modified. 12. When a cold-rolled steel sheet is manufactured, after hot rolling and before cold rolling, the steel sheet is continuously inspected for defects in the steel sheet being conveyed. A method for manufacturing a cold-rolled steel sheet, further comprising correcting or determining process conditions on the downstream side. 13. When manufacturing a cold-rolled steel sheet, after hot rolling and before cold rolling, the steel sheet is continuously inspected for defects in the steel sheet being conveyed. A method for producing a cold-rolled steel sheet, comprising: determining a processing line for the steel sheet. 14. The cold rolling according to claim 11, wherein the flaw detection is performed by the method for inspecting a cold rolled steel sheet according to any one of claims 6 to 8. Steel plate manufacturing method. 15. A hot-rolled steel sheet processing facility, characterized in that a hot-rolled hot-rolled steel sheet processing equipment is provided with a flaw detector for continuously detecting flaws in a conveyed hot-rolled steel sheet. 16. The hot-rolled steel sheet processing equipment according to claim 15, wherein a shape correcting means is arranged upstream of the flaw detector. 17. The equipment for processing a hot-rolled steel sheet according to claim 15, wherein tension applying means is arranged upstream and downstream of the flaw detector. 18. The hot-rolled steel sheet processing equipment according to claim 15, wherein the flaw detector is disposed in an acid pickling step. 19. The equipment for processing a hot-rolled steel sheet according to claim 15, wherein the flaw detector is an ultrasonic flaw detector. 20. A manufacturing apparatus for a cold-rolled steel sheet provided with a hot rolling mill and a cold rolling mill, wherein defects in the steel sheet conveyed between the hot rolling mill and the cold rolling mill are continuously detected. A cold rolled steel sheet manufacturing facility, wherein an ultrasonic flaw detector for flaw detection is provided.