JP2005059060A - Method for manufacturing cold-rolled steel strip and surface treated steel strip having reduced surface flaw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a cold-rolled steel strip and a surface treated steel strip with surface flaws reduced by preventing belt-like patterns and line flaws after cold rolling which are caused by removing surface flaws. <P>SOLUTION: In the manufacturing method of the cold-rolled steel strip and the surface treated steel strip by which the surface flaws on the surface and back faces of a hot-rolled steel strip are detected with a defect detecting device, surface flaw parts are removed on the basis of this detected signal with a defect removing device installed on the downstream side of the defect detecting device while conveying the steel strip, the steel strip is reduced to a prescribed thickness by cold rolling and, after that, treatments such as annealing and plating are performed, the rolling conditions of the cold rolling of the steel strip are adjusted in accordance with the surface roughness before the cold rolling of the surface flaw removed part where the surface flaws are removed with the defect removing device. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to steelmaking inclusions present in the surface layer of a hot rolled steel strip, which is the original sheet of the cold rolled steel strip, or cold caused by defects in the surface of the hot rolled steel strip such as a thread. Cold surface with less surface defects that are removed in advance before cold rolling and detoxified by cold rolling. Surface defects generated in rolled steel strip or surface-treated steel strip plated on cold rolled steel strip are removed in advance. The present invention relates to a method for producing a rolled steel strip and a surface-treated steel strip.

  Usually, a cold rolled steel strip is obtained by reducing a slab formed by casting into a hot rolled steel strip having a predetermined thickness in a hot rolling process, and then performing a batch pickling process or pickling process and thereafter In the pickling cold rolling composite line in which the cold rolling process is continuous, the oxide scale layer on the surface of the hot rolled steel strip is dissolved and removed with a strong acid such as hydrochloric acid, and then multiple times in the cold rolling process. The thickness is reduced to a cold-rolled steel strip having a predetermined thickness through a rolling pass. Thereafter, the cold-rolled steel strip is annealed in a continuous annealing line, and the material is adjusted by temper rolling. In addition, depending on applications such as automobile outer plate materials and edible cans, surface treatment such as galvanization and tin plating is performed after annealing in order to improve the corrosion resistance.

  However, cold-rolled steel strips or surface-treated steel strips are caused by the cast slab itself, caused by the hot rolling process (hereinafter, caused by the cast slab itself and the hot rolling process) Various types of surface defects such as pickling, cold rolling, and self-lineability in the surface treatment process have occurred. In this way, it is important to fundamentally cut off the generation of surface defects that have a variety of generation factors. A method of removing it in the process and detoxifying it has also been proposed.

  For example, on the entry side of the cold rolling mill, surface defects existing in the cold rolled original sheet, especially wrap-like defects called scabs, are detected, and only the shave portion is cut inline based on this detection information. A removal method is disclosed (for example, see Patent Document 1). In this proposal, a cutting tool, a milling type rotary cutting device, an ultrasonic cutting device, or the like is used as a cutting means, and the surface layer of the cold rolled original sheet is removed over a depth of 200 μm or more immediately before the cold rolling mill group. It is said that it is preferable. Moreover, in this cutting apparatus, the defect which has generate | occur | produced on the whole plate surface is enabled by performing a width direction feed using a ball screw etc. FIG. At that time, the cutting traces partially generated on the surface of the steel strip completely disappear due to the thickness reduction in the cold rolling process immediately after that.

  In addition, the position and size of defects on the front and back surfaces of the steel strip are detected and stored at the discharge side of the pickling tank of the batch type pickling line, and the information is stored, and then the rolling mill inlet side of the batch type cold rolling line A method for removing surface defects based on the detected defect information has been proposed (for example, see Patent Document 2).

In addition, a method for detecting color unevenness generated in the pickling process with a sensor and removing the color unevenness using a grinding roll immediately before cold rolling based on this detection information is disclosed. (For example, refer to Patent Document 3). In this proposal, a special treatment facility such as a subsequent rinsing tank and a dryer facility is attached to the grinding roll, and the grinding powder generated by grinding is treated to make it harmless.
JP 2001-191206 A Japanese Patent Laid-Open No. 61-219403 JP-A-6-15338

  As a result of earnestly examining the technology for detecting and partially removing the surface defects of the hot-rolled steel strip before the cold rolling and detoxifying the surface defects, the present inventors have found that important techniques not disclosed in the prior art are important. Focused on technical issues. The important technical problem is that, depending on the surface roughness after removal of defects (hereinafter referred to as removed portion roughness) and the rolling conditions of cold rolling, the portion where defects have not been removed after cold rolling (hereinafter referred to as non-removal) Since the surface gloss of the removal portion is different from that of the removal portion, the removal portion remains as a belt-like pattern. Further, when the removal portion roughness is excessive, not only the strip-shaped pattern but also a linear wrinkle parallel to the defect removal direction is generated in the strip-shaped pattern. Band-like patterns and linear wrinkles are also generated in the surface-treated steel strip that has been annealed and surface-treated using such a cold-rolled steel strip as a base material. These strip-like patterns and linear wrinkles impair the appearance of the steel strip surface.

  Among the above-described conventional technologies, in Patent Document 1, the removed portion roughness is set to Ra 0.5 to 5.0 μm. The basis for this is to prevent the occurrence of a band-like pattern by making the defect removed portion and the non-removed portion have the same surface roughness, but according to the study by the present inventors, the defect removed portion and the non-removed portion have the same surface roughness. However, depending on the cold rolling conditions, a strip-shaped pattern remains.

  Moreover, in patent document 2, the removal part roughness and the cold rolling method are not described at all.

  Further, in Patent Document 3, as in Patent Document 1, the removed portion roughness is set to Ra 0.7 to 2.0 μm in order to make the defect removed portion and the non-removed portion have the same surface roughness. No mention is made regarding rolling conditions.

  As described above, the problem to be solved by the present invention is to prevent the strip-like pattern and the linear wrinkles generated by removing the surface defects that are not mentioned in the prior art at all, and to reduce the surface defects. It is providing the manufacturing method of a cold-rolled steel strip and a surface treatment steel strip.

  As a result of diligent examination of the present defect removal technology, the present inventors have found that the strip-shaped pattern after cold rolling generated by removing surface defects before cold rolling has minute recesses in the defect removing portion after cold rolling. It was found that the cause was remaining. In cold rolling, it is known that rolling oil is sealed in minute recesses and minute recesses called oil pits remain.

  1A and 1B are schematic diagrams for explaining a belt-like pattern generation mechanism, where FIG. 1A is a surface state of a steel strip after surface defect removal (before cold rolling), and FIG. 1B is a cold rolling of the steel strip after surface defect removal. The subsequent surface condition is shown. In the non-removed part, micro-recesses due to the surface roughness after pickling are randomly present on the steel strip surface and become the starting point of oil pits, so micro-recesses after cold rolling are also randomly present on the steel strip surface. . On the other hand, in the removal portion, the minute recesses are parallel to the processing direction (surface defect removal direction) and in the form of a broken line and serve as the starting point of the oil pit, so the minute recesses after cold rolling are also parallel to the processing direction and It exists in the form of a broken line. Thus, the non-removed part and the removed part differ in the distribution form of the minute recesses after the cold rolling. Furthermore, the depth and size of the minute recesses are also different. Such a difference in the minute recesses as an aggregate affects the light reflection state, so that the removed portion appears as a belt-like pattern.

  In order to eliminate the difference between these minute recesses, it is effective to erase the minute recesses. In order to erase the minute recesses, dry rolling without using rolling oil is effective, but it is not realistic from the viewpoint of rolling load and roll wear. Therefore, it is difficult to eliminate the difference between the above-described minute irregularities. It is.

  Therefore, the present inventors do not erase the difference in the micro unevenness between the non-removed part and the removed part by erasing the micro recessed part, but separate the entire surface of the cold rolled steel strip from the cold rolling final stand. By providing the micro unevenness, it is possible to prevent the micro unevenness difference between the non-removed portion and the removed portion from becoming obvious after cold rolling, thereby causing the strip shape due to the micro unevenness between the non-removed portion and the removed portion. The idea was to conceal the pattern and to solve the problem of strip pattern generation.

  Generally, in the final stand of a cold rolling mill, the steel strip surface may be roughened by a roll called a dull roll. Here, the dull roll is a roll in which random minute irregularities are formed in the circumferential direction and the axial direction by shot blasting, electric discharge machining, etc., and when rolling with a dull roll, the random minute irregularities of the roll will be on the surface of the steel strip. As shown in FIG. 2, fine irregularities are imparted to the surface of the steel strip after cold rolling.

  The degree of unevenness transfer to the steel strip depends on the rolling conditions and the material properties of the steel strip, and increases as the rate decreases under high pressure. However, the main purpose of roughening the steel strip surface with a dull roll in the above-mentioned final stand is to prevent slipping during steel strip conveyance in the next process. In general, (the steel strip surface roughness Ra after rolling) ) / (Roll surface roughness Ra) × 100 As a roughness transfer rate, only minimum light roughening for preventing slip of about 20 to 30% is performed.

  As a result of examination by experiment, in order to conceal the minute unevenness difference between the removed part and the non-removed part and prevent the occurrence of the strip pattern, the final stand is a planar element with respect to the unevenness to be given to the entire steel strip. Considering the contact area ratio (hereinafter referred to as contact area ratio) of the work roll and steel strip surface roughness after cold rolling (hereinafter referred to as cold rolled steel strip surface roughness), which is an element in the depth direction It has been found that it is impossible to solve the problem even if only one of the conditions is satisfied. In addition, since the form of the micro unevenness | corrugation in a removal part also changes with removal part roughness, the rolling conditions in the last stand required for concealing the micro unevenness | corrugation difference of a removal part and a non-removal part differ with removal part roughness.

  Further, it was found that the linear wrinkles occur when the removed portion roughness is about Ra 4 μm or more, and the deep concave portions derived from the defect removed portion remain even after rolling. In this case as well, in principle, it is possible to conceal the deep concave portions remaining after rolling by optimizing the rolling conditions of the final stand of the cold rolling in the same manner as the strip pattern. However, since the depth after cold rolling of such a wire rod is very deep, in order to conceal this, more severe rolling conditions are necessary than to conceal the strip pattern, so as an actual operation Will be difficult.

  Thus, as a result of further intensive studies, the present inventors have found that linear wrinkles can be reduced by optimizing the rolling conditions of the upstream stand for cold rolling. This is because, by rolling with a rough roll at the upstream stand, the mitigation effect by dividing the deep concave portion of the defect removal part, and the surface of the steel strip with the rough roll of the upstream stand, as in the case of the strip pattern This is due to the effect of concealing the deep concave portion derived from the defect removal portion due to the concavities and convexities imparted to the whole.

  As the application stand, it is most effective to use the most upstream stand with relatively small deformation resistance, but when the removal depth is deep, the contact surface pressure between the roll and the steel strip is low in the most upstream stand. The effect may not be sufficient. In such a case, a sufficient effect can be obtained by implementing both the most upstream stand and the next stand.

  The present invention has been made based on these findings and has the following characteristics.

(1) A surface defect is detected by detecting a surface defect on the front and back surfaces of a hot-rolled steel strip using a defect detection device, and transporting the steel strip by a defect removal device installed downstream of the defect detection device based on this detection signal. In the method of manufacturing a cold-rolled steel strip that is subjected to treatment such as annealing and plating, and a surface-treated steel strip, the thickness is reduced to a predetermined thickness by cold rolling,
According to the surface roughness before the cold rolling of the surface defect removal portion from which the surface defects have been removed by the defect removing apparatus, the rolling conditions of the cold rolling of the steel strip are adjusted, A method for producing few cold-rolled steel strips and surface-treated steel strips.

  (2) According to the surface roughness before cold rolling of the surface defect removing portion, the rolling condition of the final stand in the cold rolling of the steel strip is adjusted. A method for producing few cold-rolled steel strips and surface-treated steel strips.

  (3) Final in the cold rolling of the steel strip so that the surface roughness after cold rolling of the surface defect removal part and the contact area ratio between the steel strip surface and the work roll of the final stand are within the appropriate range determined in advance. The method for producing a cold-rolled steel strip and a surface-treated steel strip with few surface defects according to (2), wherein the rolling conditions on the stand are adjusted.

  (4) The rolling condition at the final stand in the cold rolling of the steel strip is characterized by adjusting the work roll roughness of the final stand and the rolling reduction of the final stand, as described in (2) or (3) Of cold-rolled steel strip and surface-treated steel strip with few surface defects.

  (5) According to the surface roughness before cold rolling of the surface defect removing portion, the uppermost stand in the cold rolling of the steel strip, or the rolling conditions of the uppermost stand and the next stand are adjusted. The manufacturing method of the cold-rolled steel strip with few surface defects in any one of (2) thru | or (4), and a surface treatment steel strip.

  (6) The uppermost stand in the cold rolling of the steel strip, or the rolling conditions of the uppermost stand and the next stand, the work roll roughness and the rolling reduction of the uppermost stand are adjusted for the uppermost stand. And, for the next stand, the work roll roughness and the rolling reduction of the next stand are adjusted, and the cooling with few surface defects according to any one of (2) to (5) is performed. Manufacturing method of steel strip and surface-treated steel strip.

  As described above, according to the present invention described above, it is generated due to steel-making inclusions or defects on the surface of the steel strip that are present in the surface layer of the hot-rolled steel strip that is the original sheet of the cold-rolled steel strip. Surface defects that occur in cold-rolled steel strips or surface-treated steel strips plated on cold-rolled steel strips can be reduced by removing them with a defect removal device, Since the strip-like pattern and the linear wrinkle after cold rolling are also prevented, it is possible to manufacture a cold-rolled steel strip and a surface-treated steel strip with few surface defects.

  In the method of the present invention, not only the defective part exposed on the surface of the steel strip, but also the steel strip including the defective part present in the surface layer of the steel without being exposed on the surface of the hot rolled steel strip. Detection and removal of a defective portion existing in the surface-surface layer portion is performed. Therefore, the “surface defect” of the hot-rolled steel strip detected and removed in the method of the present invention means “a defect exposed on the surface of the steel strip” or “the surface of the steel strip without being exposed. `` Defects existing in the surface layer of the steel strip '' or `` Defects exposed on the surface of the steel strip and the defects present in the surface layer of the steel strip without being exposed on the surface of the steel strip It means "defects existing on the surface of the steel strip-surface layer".

  FIG. 3 is a diagram showing an example of the structure of a production line for steel strips used in the practice of the present invention, in which a pickling line and a pickling plate are reduced in thickness to a predetermined thickness and a series of cold rolling mills are continuously used. The example of a principal part structure of a cold-rolling composite line is shown. In FIG. 3, 1 is a defect detection device, 2 is a defect removal device, 3 is a defect removal position control computer, 4 is a pickling tank, 5 is a cold rolling mill group, 6 is a steel strip, 7 is an uncoiler, and 8 is a coiler. , 9 is a tracking roll, and 10 is a bridle roll. A plurality of defect removal apparatuses 2 are installed in the width direction of both surfaces of the steel strip, and a grinding wheel is used as the defect grinding means.

  In the steel strip production line in FIG. 3, surface defects on the front and back surfaces of the steel strip 6 are detected by the defect detection device 1 disposed opposite to both surfaces of the steel strip on the entry side of the pickling tank 4. The detection method of the defect detection device 1 is not particularly limited, and may be an optical method or an image processing method, but in terms of reliably detecting, for example, a heddle existing under the surface layer of a hot-rolled steel strip, Magnetic type sensors such as eddy current type and magnetic flux leakage type are desirable. The defect detection apparatus using this magnetic sensor uses, for example, an apparatus that detects a surface defect portion by detecting a change in AC magnetic flux generated due to a surface defect at the same time as performing AC excitation of a steel strip. be able to.

  The detection signal of the surface defect is taken into the defect removal position control computer 3 and then the size and occurrence position of the defect are analyzed, and a plurality of defect removal apparatuses 2 installed in the plate width direction are analyzed for each defect. On the other hand, the operation timing of the defect removal apparatus 2 such as movement in the plate width direction, cutting, and cutting is calculated. The signal is transmitted to each defect removing device 2, and the position in the transport direction is accurately measured by the tracking roll 9, and the movement in the plate width direction and the vertical direction (cutting direction) are performed at the commanded operation timing. To remove defects.

  Since it is necessary to determine the work roll roughness and rolling reduction of the final stand of the cold rolling mill group 5, the roughness of the defect removing portion is investigated in advance. When removing the defects, the generated debris and powder are removed by a chip receiver, a suction duct, or the like. The removal scraps and removal powder remaining on the surface of the steel strip without being removed by these are completely removed by passing through the pickling tank 4. The steel strip 6 is reduced in thickness to a predetermined thickness by a cold rolling mill group 5 continuously installed behind the pickling tank 4 and wound around a coiler 8.

  In the final stand of the cold rolling mill group 5, a work roll having a roughness capable of preventing the occurrence of a strip-like pattern is loaded with respect to the removed portion roughness investigated in advance. If the roughness of the removed portion investigated in advance is about Ra 4 μm or more, a linear wrinkle is generated. Therefore, the wrinkle can be erased from the uppermost stream stand of the cold rolling mill group 5 or the uppermost stream stand and the next stand. Load a rough work roll.

  The method for determining the work roll roughness and rolling reduction at the final stand of the cold rolling mill group is as follows. With respect to various removed portion roughnesses, the presence or absence of strip-like patterns after cold rolling in the case of rolling with various combinations of work roll roughness and rolling reduction ratio of the final stand was examined in rolling experiments. FIG. 4 shows the experimental results, and Table 1 shows the rolling conditions.

  In order to prevent the occurrence of strip-like patterns due to the difference in micro unevenness between the defect removal part and the non-removal part, the contact area ratio that is a planar element and the cold-rolled steel strip that is an element in the depth direction are used. It is necessary to consider the surface roughness, and the combination of these can prevent the occurrence of a band-like pattern. The concealment critical curve representing the boundary of the region where the occurrence of the band-like pattern can be prevented is shown in the figure. The upper region of the concealment critical curve is a region where no band pattern is generated. Here, the contact area ratio is the contact area ratio between the work roll and the steel strip surface at the final stand.

  The contact area ratio was measured by observing the cold rolled steel strip with an optical microscope. Generally, in a cold-rolled steel strip that has been rolled with a dull roll at the final stand, the location where the small convex portion of the dull roll contacts the cold-rolled steel strip has a characteristic surface form. It is easy to determine whether or not. Furthermore, a dimple occurred locally at the contact portion with the small convex portion of the dull roll, and when the cold rolled steel strip surface was observed with an optical microscope, the optical microscope was in contact with the dull roll because the depth of field was shallow. The part looks dark. Therefore, if the surface of the cold rolled steel strip is observed and photographed with an optical microscope and analyzed by image processing or the like, it is possible to measure the contact area ratio between the steel strip and the roll at the final stand. . The surface roughness of the cold rolled steel strip was measured with a two-dimensional stylus roughness meter. The difference in surface roughness between the removed part and the non-removed part is slight just before the final stand, and there is no difference in general surface roughness parameters, so the cold rolled steel strip surface roughness is the removed part, Either surface roughness of the non-removal part may be used.

  This result shows that even if the contact area ratio with the steel strip surface is close to 100%, the strip pattern remains if the uneven depth provided by the dull roll does not reach the fine uneven depth of the steel strip surface. ing. On the other hand, even if the surface roughness of the cold rolled steel strip is extremely increased, the strip pattern remains if the contact area ratio is small.

  In addition, from the above results, the conditions of the work roll roughness and reduction rate of the final cold rolling stand are adjusted within the upper region of the concealment critical curve obtained according to the surface roughness before cold rolling of the surface defect removal portion. By doing this, it can be seen that the occurrence of a band-like pattern can be prevented after cold rolling.

  The surface roughness and the contact area ratio of the cold rolled steel strip are affected by the geometric contact state between the roll and the steel strip in the final stand and the material properties of the steel strip. First, factors affecting the state of geometric contact mainly include the roll roughness of the final stand and the rolling reduction of the final stand. Further, factors affecting the material properties of the steel strip include the total rolling reduction in cold rolling and the steel type.

  Therefore, considering these effects, the total roll reduction ratio of cold rolling and the combination of the work roll roughness of the final stand and the roll reduction ratio of the final stand for steel strips with different defect removal roughness for each steel type. Is subjected to cold rolling, and the presence or absence of a band pattern after cold rolling is investigated. And the work roll roughness of the last stand which does not generate a strip | belt-shaped pattern after cold rolling, and the rolling reduction of the last stand are previously calculated | required with respect to the defect removal part roughness. Then, when the steel strip is cold-rolled, the rolling conditions of the final stand are adjusted according to the defect-removed portion roughness. Specifically, the roughness of the work roll of the final stand and the rolling reduction of the final stand are obtained in advance. The condition is adjusted so as not to generate a strip pattern after cold rolling.

  Further, in the above, for the surface defect removing portion, the steel strip surface roughness after cold rolling and the contact area ratio with the work roll of the final rolling stand are investigated, and the defect removing portion roughness is shown in FIG. As shown in a) to (c), a concealment critical curve showing the boundary (lower limit) of the appropriate range of the steel strip surface roughness after cold rolling and the contact area ratio after cold rolling, which can prevent the occurrence of a strip pattern after cold rolling. , And the combination of the roughness of the work roll of the final stand and the rolling reduction of the final stand within the appropriate range. And, when the steel strip is cold-rolled, according to the defect-removed part roughness, the surface roughness after the cold rolling of the surface defect-removed part and the contact area ratio are within the appropriate range determined in advance. The rolling conditions at the final stand in the cold rolling of the belt are adjusted. Specifically, the combination of the roughness of the work roll of the final stand and the rolling reduction of the final stand is concealed as shown in FIGS. Adjust to the condition in the region above the critical curve. Moreover, as factors that influence the geometric contact state, the roll diameter of the final stand, the roll material, and the final stand entry side plate thickness can be considered, so it is more preferable to consider these influences.

  The rolling conditions at the final stand that are necessary to prevent the occurrence of strip-shaped patterns differ depending on the roughness of the removed part, and the combination of roll roughness and rolling reduction of the final stand to prevent the occurrence of the strip-shaped pattern for a certain removed part roughness Is innumerable. These determination methods will be described with reference to FIG.

  Factors that determine the combination of work roll roughness and rolling reduction of the final stand include: (i) concealment critical curve, (ii) critical rolling reduction curve determined from rolling mill load limit and cold rolled steel strip shape control limit It is necessary to perform rolling under the conditions of the region surrounded by the two curves.

  Most of the cold-rolled steel strip and hot-dip galvanized steel strip are subjected to temper rolling for the purpose of adjusting the material, improving the shape, and finishing the surface after cold rolling and further annealing or plating. In the temper rolling, a predetermined surface roughness is imparted to the steel strip in consideration of the use of the steel strip, required performance, and the like. If the steel strip surface roughness imparted during cold rolling is large, the effect may remain after temper rolling, so it is preferable that the surface roughness imparted to the steel strip by cold rolling is not so large.

  In view of such points, it is advantageous to reduce the surface roughness imparted to the steel strip by cold rolling, and therefore the steel strip roughness after cold rolling in the region surrounded by the two curves described above. In the region where the rolling is small (the region closer to the lower side of the region surrounded by the two curves), even if there is a variation in the rolling reduction rate, the steel strip roughness after cold rolling and contact For example, it is preferable to perform rolling with a roll having such a roughness as shown in the drawing, such that the area ratio is in a region surrounded by two curves.

  Moreover, the determination method of the rolling conditions in the most upstream stand and the next stand is as follows. The purpose of the uppermost stand and the next stand is to prevent linear wrinkles that occur when the roughness of the removed portion is larger than Ra 4 μm. For the various removed portion roughnesses, the work roll roughness and rolling reduction of the most upstream stand are changed in rolling experiments, and the linear wrinkles immediately before rolling in the final stand are observed to confirm the presence of linear wrinkles. did.

  As a result, in order to eliminate the linear wrinkles, it was found that the work roll roughness at the uppermost stream stand should be greater than or equal to the removal portion roughness and the rolling reduction should be 20% or greater. However, when the removal portion depth is as deep as 50 μm or more, as shown in FIG. 6 (b), the contact surface between the surface defect removal portion having a thin plate thickness and the rolling roll during rolling at the most upstream stand. Since the pressure is lowered, there is a possibility that a sufficient effect for concealing the deep concave portion derived from the defect removing portion and preventing the occurrence of linear wrinkles may not be obtained. In this case, even in the next stand, the work roll roughness is set to be equal to or greater than the removal portion roughness, and rolling is performed at a reduction rate of 20% or more, so that as shown in FIG. As the contact surface pressure increases, an effect sufficient to conceal the deep concave portion derived from the defect removal portion and prevent the occurrence of linear wrinkles can be obtained. Therefore, when the depth of the removed portion is as deep as 50 μm or more, the deep concave portion derived from the defect removed portion can be obtained by rolling the roll with a work roll roughness equal to or greater than the removed portion roughness in the next stand and a reduction rate of 20% or more. It is possible to completely hide the linear wrinkles by hiding them. 6B and 6C, the length of the arrow in the figure conceptually explains the magnitude of the surface pressure.

  In the steel strip production line shown in FIG. 3, the defect detection device 1 and the defect removal device 2 are arranged on the entry side of the pickling tank 4. In the present invention, the positions of these apparatuses are arranged in the pickling tank 4. It is not limited to the entrance side. However, the defect removal is preferably performed on the entry side of the pickling tank 4 for the following reason. 1stly, the skin difference of the defect removal part before cold rolling and a non-removal part can be made small by the melt | dissolution effect | action by pickling, and it can make it difficult to produce an external appearance nonuniformity. Secondly, by performing defect removal in front of the pickling tank 4, it is possible to remove the removal waste generated by the defect removal as it is in the pickling tank 4, and the remaining removal waste is cold. There is no problem in equipment cost because it is not caught by rolling and does not generate steel strip surface flaws, rolling roll flaws, etc., and it is not necessary to install a special processing device for removing scraps.

  FIG. 7 is an example of the installation location of the defect detection device and the defect removal device, and is an example in which the defect detection device 1 and the defect removal device 2 are installed on the bridle roll 10 portion where an appropriate tension is applied to the steel strip 6. is there. On the bridle roll 10, since the tension is applied to the steel strip 6, there is an advantage that fluctuations in the plate surface due to plate shape defects and the like are small, and defect detection and defect removal can be performed stably. Further, since the removal waste is scattered in the tangential direction of the bridle roll 10, it is easy to install an appropriate removal waste receptacle at the tangential position of the bridle roll 10.

  In the above embodiment, a grinding wheel is used as the defect removing means. However, for example, machining means such as cutting, a grinding brush, and other abrasive jets may be used.

  In addition, the defect removal apparatus is required to have two points of ensuring a removal depth necessary for defect removal and obtaining a predetermined finished surface roughness. For this reason, for example, when using a grinding wheel as in the present embodiment, it is desirable to appropriately optimize the abrasive grain size, abrasive density, binder type, and degree of coupling according to the required specifications. However, when the grinding depth is increased, the roughness of the finished surface becomes unavoidable, and defects may be removed by multistage grinding or a combination of grinding and other processing means according to the specifications required for the final product. The defect removal depth may be set by a constant load control or the like using the relationship between the removal depth and the removal load obtained separately.

  Moreover, it is preferable to install a plurality of defect removal apparatuses in the plate width direction of the steel strip. Usually, the plate width of the cold-rolled steel strip is 2000 mm or less at the maximum. For example, when four defect removal devices are installed in the plate width direction, one defect removal device is about 500 mm in the plate width direction of the steel strip. It is only necessary to operate in the range, the plate width direction, and the vertical direction to remove surface defects. Each defect removal device is operated independently, so that defect removal over the entire plate width is possible.

  Further, in this defect removal method, only the portion where the surface defect has occurred is partially removed, and it is possible to minimize the decrease in yield and to make the defect removal apparatus compact. It becomes possible. By the way, the number of defect removal devices installed in the plate width direction depends on the occurrence frequency of the target defect, the line speed at the entrance to the pickling tank, the width direction feed of the defect removal device and the operating speed of the vertical movement mechanism, etc. To decide. Furthermore, in FIG. 3, although the example of the production line of the steel strip which implements a pickling process and a cold rolling process continuously was shown, after a pickling process for convenience of operation, a coil is once wound up and cold-rolled Cold rolling may be performed by unwinding the coil on the machine group entry side.

  Thus, according to the present invention, a cold-rolled steel strip and a surface-treated steel strip with few surface defects are produced without generating a strip-like pattern due to the difference in roughness of the original plate between the defect-removed portion and the non-removed portion. Is possible.

  As an example, in the cold rolled steel strip production line shown in FIG. 3, the defect detection device 1 and the defect removal device 2 are installed on the bridle roll 10 immediately before the pickling tank 4 as shown in FIG. Defect removal was performed. The target steel strip is IF steel for automobile outer plates having an original plate thickness of 2.8 mm and a plate width of 1500 to 1800 mm. At this time, the defect removing apparatus 2 used a grinding wheel having an outer diameter of 400 mm, a width of 10 mm, and a particle size number of 36, and the line speed before and after the pickling tank 4 was about 150 mpm on average. Under such conditions, a defect having a target depth of 50 μm was removed for each defect by a signal from the defect detection apparatus 1. First, in order to investigate the surface roughness of the defect-removed portion, the steel strip after pickling was taken up without being cold-rolled, and the surface roughness of the defect-removed portion was measured to find Ra of 4.9 μm. Such a steel strip was rolled up by cold rolling of 5 passes.

  Next, the steel strip wound up as described above is charged into a hot dip galvanizing treatment line, and subjected to annealing and hot dip galvanizing treatment. In addition, the number of occurrences and lengths of surface defects including appearance irregularities derived from linear wrinkles were counted, and the total defect length with respect to the total coil length was defined as the defect rate and arranged.

  The defect rate was obtained by averaging 1 week of survey results to 1 data, and a total of 30 weeks of data was investigated. In the first 10 weeks, the defect rate was investigated without performing defect removal according to the present invention, and the average defect rate of 10 data in that period was set to 1.0. In the next 10 weeks, defects were removed, and rolling was performed under rolling condition A in the cold rolling mill group. In the next 10 weeks, defects were removed, and rolling was performed under rolling condition B in the cold rolling mill group. Examples of rolling conditions A and B are shown in Tables 2 and 3, respectively. Moreover, the result of having compared the cold-rolled steel strip surface roughness and the contact area rate of the cold-rolled steel strip rolled by rolling conditions A and B in FIG. 8 in the style of FIG. 4 is shown. The concealment critical curve in the figure was determined by conducting an experiment in advance.

  In contrast to the current defect-removed portion roughness, rolling condition A is a rolling condition that satisfies the conditions that can prevent the occurrence of strips in addition to the conditions that can prevent the occurrence of strip-like patterns, while rolling Condition B is a rolling condition that does not satisfy the condition for preventing the occurrence of a strip-like pattern. FIG. 9 shows the time-series transition of the defect rate. In the case of rolling condition B, a lot of strip-like patterns and linear wrinkles derived from defect removal are observed, which is not preferable as a product. In the case of rolling condition A, the strip-like pattern and linear wrinkles derived from defect removal were not found, and the defect rate was reduced to about 1/5.

  INDUSTRIAL APPLICATION This invention can be utilized in order to manufacture the cold-rolled steel strip and surface treatment steel strip excellent in the surface quality used for a motor vehicle outer plate | board, a household appliance, a building material, an edible can, etc.

It is a schematic diagram explaining a strip | belt-shaped pattern generation | occurrence | production mechanism, (a) is the surface state of the steel strip after surface defect removal (before cold rolling), (b) is the surface after cold rolling of the steel strip after surface defect removal Indicates the state. It is a schematic diagram explaining the strip | belt-shaped pattern generation | occurrence | production prevention mechanism by this invention. The figure which shows the example of 1 structure of the production line of the steel strip used for implementation of this invention, and the pickling line in which the cold rolling mill group which reduces a pickling line and a pickling board to predetermined thickness is continuous. The example of a principal part structure of a rolling composite line is shown. It is a figure which shows the investigation result of the relationship between the combination of the work roll roughness and rolling reduction of a last stand, and the presence or absence of strip | belt-shaped pattern generation | occurrence | production after cold rolling, and a concealment critical curve with respect to various removal part roughness. In this invention, it is a figure explaining the rolling condition determination method for generation | occurrence | production prevention of a strip-shaped pattern. It is a figure explaining the generation | occurrence | production mechanism of a linear flaw, (a) is a cross-sectional schematic diagram of a defect removal part and its vicinity part, (b) is the defect removal at the time of the most upstream stand rolling when the removal part depth is 50 micrometers or more. (C) is a cross-sectional schematic view of the part and its vicinity as viewed from the exit side of the rolling roll, (c) is a defect in the next stand rolling when the removed part depth is 50 μm or more and the removed part roughness varies greatly It is a cross-sectional schematic diagram when a removal part and its vicinity part are seen from a rolling roll exit side. It is a figure which shows an example of the installation place of the defect detection apparatus in the production line of the steel strip used for implementation of this invention, and a defect removal apparatus, and is the example which installed the defect detection apparatus and the defect removal apparatus in the bridle roll part. It is a figure which shows the relationship between the concealment critical curve of the strip | belt-shaped pattern in the Example of this invention, and this concealment critical curve, and the rolling conditions of rolling conditions A and B. FIG. It is a figure explaining the defect reduction effect in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Defect detection apparatus 2 Defect removal apparatus 3 Defect removal position control computer 4 Pickling tank 5 Cold rolling mill group 6 Steel strip 7 Uncoiler 8 Coiler 9 Tracking roll 10 Bridle roll

Claims (6)

Detects surface defects on the front and back surfaces of hot-rolled steel strip with a defect detection device, and removes surface defects while conveying the steel strip with a defect removal device installed downstream of the defect detection device based on this detection signal In the method of manufacturing a cold-rolled steel strip, surface-treated steel strip, which is subjected to a treatment such as annealing, plating, etc., after reducing the thickness of the steel strip to a predetermined thickness by cold rolling,
According to the surface roughness before the cold rolling of the surface defect removal portion from which the surface defects have been removed by the defect removing apparatus, the rolling conditions of the cold rolling of the steel strip are adjusted, A method for producing few cold-rolled steel strips and surface-treated steel strips. The cold rolling with few surface defects according to claim 1, wherein the rolling condition of the final stand in the cold rolling of the steel strip is adjusted according to the surface roughness before cold rolling of the surface defect removing portion. Manufacturing method of steel strip and surface-treated steel strip. At the final stand in the cold rolling of the steel strip, the surface roughness after cold rolling of the surface defect removal part and the contact area ratio between the steel strip surface and the work roll of the final stand are within the appropriate range determined in advance. The method for producing a cold-rolled steel strip and a surface-treated steel strip with few surface defects according to claim 2, wherein the rolling conditions are adjusted. The rolling condition at the final stand in the cold rolling of the steel strip adjusts the work roll roughness of the final stand and the rolling reduction of the final stand, and has few surface defects according to claim 2 or 3 Manufacturing method of cold-rolled steel strip and surface-treated steel strip. According to the surface roughness before cold rolling of the surface defect removal part, further characterized by adjusting the rolling condition of the uppermost stream stand in the cold rolling of the steel strip, or the uppermost stream stand and the next stand, The manufacturing method of the cold-rolled steel strip and surface treatment steel strip with few surface defects in any one of Claims 2 thru | or 4. The uppermost stand in the cold rolling of the steel strip, or the rolling conditions of the uppermost stand and the next stand, for the uppermost stand, adjust the work roll roughness and reduction ratio of the uppermost stand, For the next stand, the work roll roughness and rolling reduction of the next stand are adjusted, and the cold-rolled steel strip and surface having few surface defects according to any one of claims 2 to 5 Manufacturing method of treated steel strip.

Images