JP2005246432A - Method for manufacturing cold-rolled steel sheet and rolling roll used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a cold-rolled steel sheet by which surface flaws are suppressed even in the case rolling is performed by using rolling rolls to which electric-discharge dull-work is applied for work rolls, and to provide the rolling rolls used for the same. <P>SOLUTION: The cold rolling or temper rolling of the steel sheet is performed by using the rolling rolls the roll surfaces of which are adjusted so as to satisfy formula (1) Ra×PPI≤600 by electric discharge machining. Alternatively, the cold rolling or the temper rolling of the steel sheet is performed by using the rolling rolls which are adjusted so as to satisfy formula (2) Ra×PPI≤1,000 by grinding the roll surfaces after the roll surfaces are machined by the electric discharge machining. In the formulas, Ra is the center line average height (μm) and PPI is the peak count. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a cold-rolled steel sheet by performing cold rolling or temper rolling, and a rolling roll used therefor.

  In the manufacture of a cold-rolled steel sheet, cold rolling for rolling to a predetermined plate thickness and temper rolling for making a predetermined material are performed on the steel sheet. In these cold rolling and temper rolling (hereinafter sometimes referred to collectively as rolling), a roll for rolling whose surface is appropriately adjusted is used as a work roll.

The surface of the roll for rolling may be finished to a mirror surface called bright, but is often subjected to a textured unevenness called dull. By using such a dull roll for the final roll of the rolling or the work roll of the final pass, it is possible to give irregularities to the steel sheet surface,
(1) Ensuring press workability as a product (cold rolled steel sheet, surface treated steel sheet),
(2) Ensuring sharpness after painting of products,
(3) Ensuring the surface properties of the steel sheet by providing uniform unevenness,
(4) Ensuring stable plateability in the next process (especially continuous line),
Etc.

  As a dull processing method for rolling rolls, shot blasting has been widely used. The shot blast method is easy to process, but has the disadvantages that the roll surface roughness after processing is large and the processing adjustment range of the surface roughness is small. Therefore, recently, electric discharge machining, laser machining, and the like capable of uniform surface machining are often used. The surface roughness imparted to the rolling roll varies depending on the difference in the processing method of the rolling roll. For example, Patent Document 1 (FIGS. 4 and 5), which will be described later, describes an average roughness Ra and a filtering center for the surface shape of a roll manufactured by each processing method of shot dull processing, laser dull processing, and discharge dull processing. The relationship between mean swell Wca and PPI is shown.

In recent years, there has been a growing demand for press workability and sharpness after painting, particularly for automotive steel sheets. For press workability, it is effective to increase the surface roughness in order to ensure oil retention at the interface between the press die and the steel plate. There is a need to reduce the long period undulations in That is, it is effective to provide a large number of large irregularities on the surface of the steel sheet at a short pitch, and a steel sheet having a high PPI is demanded even with the same average roughness Ra.

In response to such a recent request, as can be seen from the above-mentioned Patent Document 1 (FIGS. 4 and 5), the processing of the rolling dull roll by electric discharge machining is the most excellent. Therefore, electric discharge dull machining has recently been widely used, and depending on the product specifications of the required surface roughness, it can only be produced by rolling rolls that have been dulled by electric discharge machining. There are also things.
Japanese Unexamined Patent Publication No. 2000-282291 (FIGS. 4 and 5)

  However, when the present inventors performed rolling by using a rolling roll that has been dulled by electric discharge machining as a work roll, foreign matter adheres to the irregularities on the surface of the rolling roll, and the steel sheet is rolled in that state. As a result, not only the unevenness on the surface of the rolling roll is not transferred to the steel plate portion rolled at the portion where the foreign matter is adhered, but in some cases, a concave drop due to the foreign matter is generated and the surface appearance is impaired. The occurrence of surface defects frequently occurs. Although such surface defects are conventionally known, the unevenness imparted to the surface of the roll for rolling by electric discharge machining is larger at a short pitch than the unevenness imparted by, for example, shot blasting. Since it is uneven, it is presumed that foreign matter easily adheres and the frequency of occurrence of surface defects is greatly increased.

  Here, the foreign matters adhering to the rolling roll include those adhering to the steel plate and being brought into the rolling mill, and abrasion powder caused by rolling. And as a method of preventing these foreign substances from adhering to the rolling roll, cleaning the rolling mill or the like, improving the cleanliness of the rolling oil or pressure adjusting liquid, or brush roll in contact with the rolling roll A method such as attaching is known. Moreover, when a foreign material adheres to the roll for rolling, rolling is stopped and the roll for rolling is cleaned, or the roll for rolling is replaced with a new roll.

  However, taking these foreign matter prevention measures has the problem of high equipment costs and running costs, and when using rolling rolls that have been subjected to dull machining by electric discharge machining, these foreign matter adhesion prevention measures are taken. The countermeasures did not provide a sufficient effect. Furthermore, if foreign matter adheres, not only the yield of the defective part is reduced, but also the efficiency is lowered by stopping the rolling.

  The present invention has been made to solve the above-described problems, and suppresses surface defects even when rolling is performed using a roll for electric discharge dull processing applied to a work roll. It aims at providing the manufacturing method of the cold-rolled steel plate which can do, and the roll for rolling used for it.

  The present inventors investigated the correlation between the center line average roughness Ra and peak count PPI of the rolling roll subjected to the electric discharge dull processing and the occurrence state of the surface defects. Here, “centerline average roughness Ra” is defined by JISB0601, and “peak count PPI” is the number of peaks of unevenness per inch as defined by the SAE911 standard.

  Rolling was performed using a rolling roll that had been dulled under various electric discharge machining conditions as a work roll of the final stand of the rolling mill, and the occurrence of the surface defects was investigated. FIG. 1 is a diagram showing the correlation between the center line average roughness Ra and peak count PPI and surface defects of the roll for electric discharge dull rolling obtained in this way. The count level in the PPI measurement is ± 0.635 μm. In FIG. 1, “◯” indicates that no surface defects occurred, and “×” indicates that the surface defects occurred.

It can be seen from the characteristics of FIG. 1 that surface defects are more likely to occur as the center line average roughness Ra of the rolling roll is higher and the peak count PPI is higher. The reason for this is considered to be that the coarser the center line average roughness Ra and the higher the peak count, the easier it is to trap foreign matter on the roll surface, and it is difficult for the attached foreign matter to be removed from the roll surface. In addition, the boundary of defect occurrence is
Ra x PPI = 600
However, it was found that Ra can be arranged by center line average roughness (μm), and PPI can be arranged by peak count.
Furthermore, it has been clarified that the occurrence of the defects can be further suppressed by polishing the surface of the rolling roll subjected to the electric discharge dull processing.

The manufacturing method of the cold-rolled steel sheet of the present invention and the rolling roll used therefor have been made based on such knowledge and have the following characteristics.
[1] A method for producing a cold-rolled steel sheet, comprising cold-rolling or temper-rolling a steel sheet using a rolling roll whose surface is adjusted to satisfy the following formula (1) by electric discharge machining: .
Ra × PPI ≦ 600 (1)
[2] After the roll surface is adjusted by electric discharge machining so as to satisfy the following formula (2), the steel sheet is cold-rolled or temper-rolled using a rolling roll whose roll surface is polished. A method for producing a cold-rolled steel sheet.
Ra × PPI ≦ 1000 (2)
[3] A rolling roll used for cold rolling or temper rolling of a steel sheet, wherein the roll surface is adjusted to satisfy the following formula (1) by electric discharge machining: .
Ra × PPI ≦ 600 (1)
[4] A rolling roll used for cold rolling or temper rolling of a steel sheet, and after the roll surface is processed by electric discharge machining, the roll surface is polished so that the following formula (2) is satisfied. A roll for rolling characterized by being adjusted.
Ra × PPI ≦ 1000 (2)
However, in the above [1] to [4], Ra is the center line average roughness (μm), and PPI is the peak count.

  According to the present invention, the relationship between the center line average roughness Ra and the peak count PPI is defined as described above, and thus the rolling roll subjected to the electric discharge dull processing is used as a work roll for rolling. However, it is possible to prevent foreign matter from adhering to the roll for rolling, and it is possible to produce a cold-rolled steel sheet having a good surface appearance by suppressing surface defects.

An embodiment of a method for producing a cold-rolled steel sheet according to an embodiment of the present invention and an embodiment of a rolling roll according to the present invention will be described. In the present embodiment, the hot-rolled steel sheet that has been hot-rolled is removed from the surface of the steel sheet by pickling, and then cold-rolled to a predetermined thickness by a cold rolling mill to obtain a cold-rolled steel sheet. Furthermore, after subjecting the cold-rolled steel sheet to predetermined annealing, it is subjected to temper rolling with a temper rolling mill to adjust to a predetermined material. In addition, the temper rolling mill here may be a temper rolling single line or a temper rolling mill provided in a continuous annealing line.
Here, as a work roll used for the final stand of the cold rolling mill, a roll for rolling subjected to predetermined dull processing by electric discharge machining is used. Or the roll for rolling by which the predetermined dull process was given by electric discharge machining is used as a work roll used for temper rolling. Note that the rolling roll may be used for both cold rolling and temper rolling.

The rolling roll that has been subjected to the predetermined dull processing by the electric discharge machining of the present embodiment, by appropriately controlling the electric discharge machining conditions, so that foreign matter adheres to the surface of the rolling roll and does not generate surface defects. The surface morphology is adjusted. That is, usually, when electric discharge machining is performed on a roll for rolling, as shown in FIG. 1, the center line average roughness Ra is about 1 to 8 μm, and the peak count PPI is about 50 to 400. A roll surface morphology is obtained. When rolling is performed using a rolling roll having such a large center line average roughness Ra and a high peak count PPI, the surface defects are likely to occur. Therefore, the electric discharge machining conditions are controlled so that the centerline average roughness Ra and peak count PPI of the roll surface after machining satisfy the following expression (1).
Ra × PPI ≦ 600 (1)
However, Ra is center line average roughness (μm), PPI is peak count

  For example, when the centerline average roughness Ra is defined as the product specification, the PPI is adjusted to be low so as to satisfy the equation (1) even with the same centerline average roughness Ra. To control. Further, when both the center line average roughness Ra and the peak count PPI are determined by the product specification, the electric discharge machining conditions are controlled so as to satisfy the expression (1) within the specification range.

Here, the electric discharge machining conditions can be controlled by, for example, changing the electrode material, changing the polarity of the electrode, changing the current peak value, changing the current pulse width, or changing the discharge circuit.
Further, according to the study by the present inventors, even if the above equation (1) is exceeded, the surface of the roll is suppressed by polishing the surface of the roll after electric discharge machining, thereby generating surface defects. It was found that can be reduced. This is considered to be because the action of trapping foreign matter can be reduced by polishing the roll surface, and by wearing the sharp projections among the irregularities of the roll surface formed by electric discharge machining. .

  Table 1 shows the occurrence of surface defects with respect to the centerline average roughness Ra and peak count PPI of the roll surface when the roll surface is polished or not after electric discharge machining. Here, the values of the center line average roughness Ra and the peak count PPI after the surface polishing after the electric discharge machining are shown after the electric discharge machining for the case without the roll surface polishing, and after the surface polishing after the electric discharge machining.

Thus, even when the roll surface after electric discharge machining does not satisfy the above formula (1), it can be seen that the occurrence of surface defects can be suppressed by polishing the roll surface later depending on the value of Ra × PPI. . Therefore, after processing by controlling the electric discharge machining conditions, the roll surface may be polished so that the center line average roughness Ra and the peak count PPI satisfy the following expression (2).
Ra × PPI ≦ 1000 (2)
However, Ra is centerline average roughness (micrometer), PPI is a peak count.

  For example, if both the centerline average roughness Ra and the peak count PPI are determined by the product specification as the product specification and the specification exceeds the above formula (1), the electric discharge machining conditions are controlled, and after the electric discharge machining The roll surface may be polished so that the center line average roughness Ra and the peak count PPI satisfy the above (2). By doing in this way, the adjustable range of centerline average roughness Ra and peak count PPI which can suppress foreign material adhesion and surface defect generation is expanded.

  Here, the polishing method of the roll surface is not particularly limited, but the center line average roughness Ra and peak count PPI of the roll surface that changes due to polishing are substantially constant over the entire roll surface. A method capable of performing uniform polishing with reproducibility is preferable. For example, after the electric discharge machining roll is incorporated into a rolling mill, the upper and lower rolling rolls are brought into contact with each other and rolled, so-called roll idling, before rolling the steel sheet. However, this method cannot be performed with a plate between the upper and lower rolling rolls, and in the case of a dry temper rolling mill that performs dry pressure regulation, wear powder generated during roll idling is removed. It cannot be removed from the roll surface. Therefore, it is preferable to use a polishing apparatus that polishes the roll surface with a polishing film as the roll is rotated in the same manner as the roll grinding operation in the grinder. Abrasive film is made of abrasive grains fixed with a binder, and if it has a constant film feed speed, film pressing pressure, and roll axis method traverse, the center line average roughness of the roll surface by polishing The amount of change in Ra and peak count PPI is substantially constant.

  By using the rolling roll described above as a work roll and performing cold rolling or temper rolling, it is possible to suppress foreign matter from adhering to the surface of the rolling roll and to achieve a good cold rolling with a surface appearance free from surface defects. Steel sheets can be manufactured. The cold-rolled steel sheet referred to in the present invention is not limited to the product shipped as a cold-rolled steel sheet, and includes a plated steel sheet plate that is plated on the steel sheet surface after cold rolling or temper rolling. It is a waste.

  Under the conditions shown in Table 2, the cold rolled steel sheet manufacturing method of the present invention was carried out. No. 1-4 is a case where the roll for rolling of this invention is used for the work roll of the last stand of a cold rolling mill. The conditions of No. 1 and No. 2 are that the thickness a is 0.8 to 2 on a pickled steel plate whose material standard is equivalent to SPCC in line a having a cold rolling mill having 5 stands and a final stand having 4 stages. This is a case of cold rolling to 0 mm. The conditions of Nos. 3 and 4 are that a line b having a cold rolling mill having four stands and a final stand having a six-stage type cold-rolled steel plate having a material standard equivalent to SPCC to SPCE has a thickness of 0.5. It is a case where it cold-rolls to -1.2mm.

  Nos. 5 to 16 are cases where the rolling roll of the present invention is used as a work roll of a temper rolling mill. When the roll surface is polished after electric discharge machining, the centerline average roughness Ra (μm) and peak count PPI after polishing are shown. The conditions of Nos. 5 and 6 are that an annealed steel sheet having a thickness of 0.6 to 1.0 mm corresponding to a material standard of SPCD to SPCE is used in line c having a four-stage temper rolling mill consisting of one stand. This is the case of temper rolling. The conditions of Nos. 7 to 12 are as follows. In the line d having a four-stage temper rolling mill consisting of one stand, the plate thickness is 0.6 to 1 for the material standards corresponding to SPCC to SPCE and 1/8 hard material. This is a case where a 6 mm annealed steel sheet is temper rolled. The conditions of Nos. 13 to 16 are that, in a line e having a four-stage temper rolling mill consisting of two stands, the rolling roll of the present invention is used as the work roll of the final stand, the material standard is equivalent to SPCC, This is a case where an annealed steel sheet having a thickness of 0.2 to 0.5 mm corresponding to 8 hard material and 1/4 hard material is temper rolled.

  As can be seen from the above results, regardless of whether cold rolling or temper rolling, the surface defect does not occur when the surface of the roll for electric discharge machining satisfies the formula (1), It was confirmed that the surface defects did not occur when the condition (2) was satisfied under the condition where the surface of the rolling roll after electric discharge machining was polished.

The figure which showed the correlation with the centerline average roughness Ra and peak count PPI, and surface defect of the roll for electric discharge dull processing rolling.

Claims (4)

A method for producing a cold-rolled steel sheet, comprising cold-rolling or temper-rolling a steel sheet using a rolling roll whose roll surface is adjusted to satisfy the following formula (1) by electric discharge machining.
Ra × PPI ≦ 600 (1)
However, Ra is centerline average roughness (micrometer), PPI is a peak count. After the roll surface is processed by electric discharge machining, the roll surface is polished and the steel sheet is cold-rolled or temper-rolled using a rolling roll adjusted to satisfy the following formula (2). A method for producing a cold-rolled steel sheet.
Ra × PPI ≦ 1000 (2)
However, Ra is centerline average roughness (micrometer), PPI is a peak count. A rolling roll for use in cold rolling or temper rolling of a steel sheet, wherein the roll surface is adjusted by electric discharge machining so as to satisfy the following expression (1).
Ra × PPI ≦ 600 (1)
However, Ra is centerline average roughness (micrometer), PPI is a peak count. It is a roll for rolling used for cold rolling or temper rolling of a steel sheet, and after the roll surface is processed by electric discharge machining, the roll surface is polished and adjusted so as to satisfy the following formula (2). A rolling roll characterized by that.
Ra × PPI ≦ 1000 (2)
However, Ra is centerline average roughness (micrometer), PPI is a peak count.

Images