JP2003080302A - Method for temper-rolling of galvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfy press-formability and image clarity after painting without necessitating many trial and error by giving the working condition of a temper- rolling roll and the temper-rolling condition using the roll without necessitating expensive equipment. SOLUTION: In this method of temper-rolling of a galvanized steel sheet, the temper rolling is performed by using the temper-rolling roll the center line average roughness Ra(r) of the roll surface of which is 2.0 to 4.0 μm and the peak count PPI(r) (Peaks Per Inch) (cut off 0.635 μm) of which satisfies relationship: PPI(r)>=(30×Ra(r)+130).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temper rolling method for galvanized steel sheet.

[0002]

2. Description of the Related Art As is well known, in the field of automobile parts and building materials, the demand for galvanized steel sheets is increasing.
By the way, for the galvanized steel sheet used for press working, it is considered effective to increase the surface roughness for the purpose of ensuring oil retention at the interface between the press die and the steel sheet and preventing galling of the die. There is. On the other hand, it is said that it is necessary to reduce the long-period undulations on the surface of the steel sheet before coating for products such as automobiles that require clearness after coating.

Mold galling in press working occurs when the newly formed surface of the steel sheet surface caused by sliding locally agglomerates with the mold. In particular, as compared with coatings of galvannealed steel sheets and the like, the coatings of galvanized steel sheets are softer and have a lower melting point, so that they have the property that adhesion is more likely to occur. As a measure to prevent this mold galling, it is effective to improve the oil retaining property between the steel plate and the mold during press working.

Specifically, increasing the center line average roughness Ra and increasing the peak count PPI is known as an effective measure. Here, "center line average roughness R
"a" is defined in JIS B0610,
The "peak count PPI" is the peak number of irregularities per inch as defined by the SAE911 standard.
That is, it is a necessary condition for improving press formability that a large number of large irregularities are provided at a short pitch on the surface of a steel sheet.

Regarding the image clarity after coating, short-period unevenness is filled in the undercoating process of the coating and the like, so that the image clarity after coating is not affected, but the long-period unevenness does not occur after coating. Also remains and controls the sharpness. In this case, it is known that there is a close relationship between the centerline waviness Wca and the sharpness after painting. The smaller the centerline waviness Wca, the better the sharpness after painting. Here, the "center line waviness Wca" is defined in JISB0610, and is the average height of the unevenness subjected to the high frequency cutoff. That is, reducing the unevenness component having a long surface period is a condition for improving the image clarity after coating.

As described above, the press formability of the galvanized steel sheet and the image clarity after coating can be exhibited by appropriately controlling the texture of the surface. Such surface texture is usually imparted by temper rolling performed after galvanizing. However, in a rolling roll subjected to shot blasting which is usually used as a method for processing a temper rolling roll, it is not easy to control the pitch of the irregularities having a random distribution, and a short cycle for the purpose of ensuring press formability. It is known that when the unevenness is increased, the long-period unevenness component also increases, and it is difficult to achieve compatibility with the sharpness after painting.

On the other hand, as disclosed in Japanese Unexamined Patent Publication No. Hei 7-136701, laser dull processing is applied to the roll surface to improve both the press formability of the galvanized steel sheet and the sharpness after painting. The temper rolling rolls used to do so are known.

[0008]

However, JP-A-7-1 is used.
In the case of the method according to 36701, there is a problem that the processing equipment for the roll is expensive and the processing efficiency is low.
That is, the laser dull processing is to give irregularities of regular pitch to the surface of the temper rolling roll, but it takes a long time to process one roll, and further, the portion melted by the laser is processed. It is difficult to use for a long time because the protrusions on the surface are likely to wear due to oxidation. Further, in order to carry out processing so that the roughness becomes large, a larger amount of energy is required, which causes an increase in processing cost.

Further, at the stage of temper-rolling to manufacture a galvanized steel sheet having both good press formability and sharpness after painting, it is worked by variously changing the working conditions and working method of the temper-rolling roll. It is necessary to carry out the evaluation and incorporate it into an actual temper rolling mill for evaluation. That is, it is necessary to inspect the texture of the surface of the steel sheet while incorporating the temper rolling roll into the rolling mill after the processing under certain conditions and actually changing the rolling conditions. Further, also in the case of evaluating the parameters such as the center line average roughness Ra of the steel plate surface, the peak count PPI, and the center line waviness Wca, it is necessary to perform the measurement with the roughness meter using the sample cut out from the steel strip.

At this time, when the target texture of the steel sheet surface cannot be obtained, it is necessary to change the processing conditions of the temper rolling roll again and repeat the same experiment.
That is, such a trial-and-error method has a problem that it takes a long time to determine the processing conditions of the temper rolling roll. Further, the needs for the texture of the surface of the galvanized steel sheet differ depending on the user, and it takes a lot of labor and time to determine the processing conditions of the temper rolling roll according to the demand.

The present invention has been made in consideration of such circumstances, and by applying the processing conditions of the temper rolling roll and the temper rolling conditions using the same without requiring expensive equipment, many An object of the present invention is to provide a temper rolling method for a galvanized steel sheet that satisfies press formability and image clarity after coating without trial and error.

[0012]

The present invention is a method of temper rolling a galvanized steel sheet, wherein the center line average roughness Ra (r) of the roll surface is 2.0 to 4.0 μm and the peak count PPI ( r) (cutoff 0.635 μm)
The temper rolling method of a galvanized steel sheet, characterized by performing temper rolling using a temper rolling roll satisfying the following formula (1) PPI (r) ≧ (30 × Ra (r) +130) (1) Is.

In the present invention, the target center line average roughness Ra (s) (μ) of the galvanized steel sheet after temper rolling is set.
m), with respect to the target elongation rate δ (%) in temper rolling,
The center line average roughness Ra (r) (μm) of the roll surface is calculated by the following formula (2) Ra (r): Ra (s) / (a × δ + b) (2) where a and b are work roll diameters. It is preferable to make the determination based on a constant that depends on

In the present invention, it is preferable that the irregularities on the surface of the temper rolling roll are formed by electric discharge machining or electron beam machining.

In the temper rolling of galvanized steel sheet, the inventors conducted a detailed investigation on the behavior of the texture of the surface of the temper rolling roll transferred to the steel sheet, and examined the temper rolling conditions and the transfer characteristics. Clarified the relationship. Based on the results, the present inventors have found a method for producing a galvanized steel sheet having both press formability and image clarity after coating.

By the way, as the texture of the surface for improving the press formability of the galvanized steel sheet, the center line average roughness Ra is 1.
0 μm or more is required. Also, the peak count PP
Regarding I, a higher one is desired, but 120 or more is practically required for a count level of 0.635 μm.

On the other hand, the sharpness after painting needs to be 0.8 μm or less for the high cutoff of 0.8 mm and the low cutoff of 8 mm as the center line waviness Wca. However, when the center line average roughness Ra is 2.0 μm or more, it is actually difficult to set the center waviness Wca to 0.8 μm or less.
It can be considered that the upper limit of is about 2.0 μm.

In order to clarify the conditions of the temper rolling roll and the temper rolling conditions for obtaining the galvanized steel sheet having the surface texture as described above, the results of an experiment conducted by the present inventors are shown in FIG. Show. This shows the transfer behavior of the center line average roughness Ra and the peak count PPI as the transfer characteristics of the temper rolling roll to the hot-dip galvanized steel sheet. The horizontal axis represents the center line average roughness Ra of the roll surface.
Center line average roughness R of hot-dip galvanized steel sheet with respect to (r)
It is the ratio of a (s) and is called the transfer rate of average roughness. on the other hand,
The vertical axis represents the peak count PPI (s) of the galvanized steel sheet with respect to the peak count PPI (r) of the roll surface.
The ratio is the peak count transfer rate.

As the experimental conditions, as shown in Table 1 below, temper rolling rolls having different center line average roughness Ra (r), peak count PPI (r), work roll diameter are prepared, and tension and elongation are set. Was changed and a temper rolling experiment was conducted. The results of FIG. 2 show that the transfer rate of the average roughness and the transfer rate of the peak count have a constant relationship regardless of these conditions.

[0020]

[Table 1]

Further, in the range where the center line average roughness Ra (s) of the steel sheet is 1.0 to 2.0 μm, the peak count PPI (s) of the steel sheet and the center line waviness Wca (s) of the steel sheet.
FIG. 3 shows the relationship with. As can be seen from FIG. 3, the higher the target peak count PPI (s) of the steel sheet, the lower the center line waviness Wca (s) of the steel sheet. In particular, in order to stabilize Wca (s) to 0.8 μm or less, the peak count PPI (s) of the steel sheet is set to 1 as a target for improving the sharpness after painting.
It should be 50 or more. In addition, this value exceeds the value 120 for satisfying the above-mentioned press formability, and eventually the center line average roughness Ra (s) of the steel sheet is 1.0 to 2.0 μm and the peak count PPI ( s) is 1
By setting it to 50 or more, the center line waviness Wca (s) is set to 0.
It has been clarified that it can be reduced to 8 μm or less.

Based on such new knowledge, it is possible to define the surface texture that the temper rolling roll should have in order to obtain a galvanized steel sheet having both press formability and image clarity after coating. . For example, it is assumed that the center line average roughness Ra (s) of the galvanized steel sheet is 1.2 μm and a steel sheet with a peak count PPI (s) of 180 is to be obtained. At this time, when the center rolling average roughness Ra (r) of 2.6 μm is used as the temper rolling roll, the transfer rate of the average roughness is 0.46, which corresponds to FIG. It can be seen that the peak count transfer rate is 0.69. Therefore, the peak count PPI of the steel plate
In order to obtain 180 as (s), it is necessary to set the peak count PPI (r) of the temper rolling roll to 261.

Similarly, when the center line average roughness Ra (r) of the temper rolling roll is 3.4 μm, the average roughness transfer rate is 0.35, and the corresponding peak count transfer rate is 0. 59. Therefore, the peak count PPI of the steel plate
In order to set (s) to 180, it is necessary to set the peak count PPI (r) of the temper rolling roll to 305. That is, when trying to obtain the average roughness Ra (s) and the peak count PPI (s) of a certain constant steel plate, the higher the average roughness Ra (r) of the temper rolling roll, the higher the peak count PPI ( It shows that the temper rolling roll of r) must be used.

The means according to claim 1 of the present invention is based on such an idea, and is provided as a temper rolling roll for achieving both the press formability of a galvanized steel sheet and the image clarity after coating. It defines the surface texture to be used. Here, the peak count PPI of the temper rolling roll
The rationale for defining (r) as (30 × Ra (r) +130) or more is derived by using the result of FIG. 2 as a condition necessary for setting the peak count PPI (s) of the steel sheet to 150 or more. You can FIG. 2 shows the average roughness Ra (r) and peak count PPI (r) of the temper rolling roll.
It also indicates that the relationship between the average roughness Ra (s) and the peak count PPI (s) on the steel sheet side after temper rolling is represented by the following formula (3).

PPI (s) / PPI (r) = 0.432 × ln {Ra (s) / Ra (r)} + 1.030 (3) Therefore, the peak count PPI (s) of the steel sheet is set to 150 or more. In order to achieve
PI (r) needs to satisfy the following formula (4).

PPI (r) ≧ 150 / [0.432 × ln {Ra (s) / Ra (r)} + 1. 030] (4) On the other hand, as for the transfer rate Ra (s) / Ra (r) of the average roughness, in the range of the elongation rate of 0.6 to 1.5%, as shown in FIG.
There is a relationship as shown in. FIG. 6 shows that as the average roughness Ra (r) of the temper rolling roll increases, the transfer rate tends to decrease.

At this time, using the relationship between Ra (r) and the transfer rate Ra (s) / Ra (r) shown in FIG. 6, the value on the right side of the above equation (4) is calculated and the result is shown in FIG. Is. Figure 7
In order to set the peak count PPI (s) of the steel sheet to 150 or more, the peak count PPI of the temper rolling roll is
It shows that (r) must be larger than each point in the figure, and the approximate straight line is PPI (r) = 30 ×
Ra (r) +130.

By the way, it is desirable that the peak count PPI (r) of the temper rolling roll be as large as possible within the range satisfying the above expression (1), but the peak count PPI (r) of the temper rolling roll is economical. There are few methods for increasing the peak count PPI (r), and even if the peak count PPI (s) of the transferred steel plate is increased to a certain value or more, the center line waviness Wca (s) is not so much. Since it does not decrease, the upper limit of PPI (r) is about 400.

Next, the reason why the center line average roughness Ra (r) of the temper rolling roll is limited to 2.0 to 4.0 μm in claim 1 will be described. In temper rolling, in addition to the function of providing an appropriate surface as described above, the function of adjusting the material is required. This aims at eliminating the yield point elongation by giving the steel sheet a constant elongation rate.
At this time, if the elongation ratio applied to the steel sheet is too small, the yield point elongation cannot be eliminated, and if the elongation ratio is too large, the yield stress as a product and the elongation decrease will be caused. Therefore, there is an appropriate range of elongation depending on the steel type, and generally, an elongation of about 0.6% to 1.5% is provided.

At this time, from FIG. 4 showing the relationship between the elongation rate and the transfer rate of the average roughness Ra, the transfer rate of the average roughness is 0.
It can be seen that it is about 25 to 0.5. That is, when it is desired to obtain 1.0 μm as the center line average roughness Ra (s) of the steel sheet, the center line average roughness Ra of the temper rolling roll is set.
(R) is. If it is 2.0 μm or less, sufficient transfer cannot be performed, and if it is 4.0 μm or more, the required extension rate cannot be secured. According to the above concept, the center line average roughness Ra (r) of the temper rolling roll is limited to 2.0 to 4.0 μm.

The means of claim 2 of the present invention is for achieving the target center line average roughness Ra (s) of the steel sheet in temper rolling while satisfying the constraint of the elongation rate specified in the material. Center line average roughness Ra (r) as a temper rolling roll
Is defined. From FIG. 4, the expansion rate is 0.6 to
Within the range of about 1.5%, the transfer rate of the average roughness has a substantially linear relationship with the extension rate, and the transfer rate of the average roughness increases as the extension rate increases. In other words, the transfer rate of the average roughness is determined according to the target value of the elongation rate required for the material, so that the target center line average roughness Ra (s) of the steel sheet is determined.
It is possible to determine the center line average roughness Ra (r) which the temper rolling roll for obtaining the above-mentioned value should have. The transfer rate of the average roughness is affected by the roll diameter of the temper rolling roll,
The larger the roll diameter, the higher the transfer rate. Therefore, it is necessary to determine the coefficients a and b of the equation (2) according to the roll diameter.

According to the third aspect of the present invention, the surface of the temper rolling roll is formed by electric discharge dull machining. Electric discharge dull machining is a machining method in which a spark is generated between the roll surface and the electrode to melt the surface of the roll, and at the same time, the melting part is blown off by the pressure of the generated gas, the shape and material of the electrode used, It is possible to change the size and pitch of the unevenness by controlling the voltage, current and discharge time during discharging.

In the means according to claim 4 of the present invention, the surface of the temper rolling roll is formed by electron beam processing. Electron beam processing is a method of irradiating the peripheral surface of a roll with an electron beam having a high energy density to perform surface processing, and a crater in which a material is scooped out occurs in a portion irradiated with the electron beam. At this time, the distance between the craters can be controlled by adjusting the distance for moving the spot of the electron beam. In addition, the depth of the crater can be adjusted by adjusting the irradiation time. Therefore, desired irregularities can be formed by defining the center line average roughness and the peak count in claim 1 or 2 of the present invention.

[0034]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 5 shows a schematic diagram of a hot-dip galvanizing line according to an embodiment of the present invention. A steel strip (steel plate) 10 manufactured through cold rolling is unwound from a payoff reel 11 and, after passing through an annealing facility 12, a hot dip galvanizing bath 1
3 is dipped and plated. For the steel strip 10 coming out of the plating bath 13, the amount of plating is adjusted by the gas wiping nozzle 14. Furthermore, in a normal hot dip galvanizing line, a temper rolling mill 15 is arranged on the downstream side of the plating equipment. Here, as the temper rolling mill 15, a one-stand, four-high rolling mill is usually used, and a certain elongation rate is given to adjust the material, and the necessary surface is adjusted. .

In the temper rolling mill 15, a temper rolling roll 16 for transferring to the steel strip surface is used. The roll 16 has a diameter of about 350 mm to 700 mm. The temper rolling roll 16 is polished in a roll shop and then the surface texture is adjusted by shot blasting or electric discharge machining. The temper-rolled roll 16 after processing is conveyed to the machine side of the temper-roller to be used, and is recombined according to the manufacturing cycle of hot-dip galvanizing or the deterioration of the roll surface state due to wear or the like.

In temper rolling, reduction is applied so as to obtain a constant elongation rate while applying tension on the inlet side and the outlet side of the temper rolling mill 15. As a method of controlling the elongation rate, a method of adjusting tension or a method of operating a rolling force is used, and the elongation rate is controlled within a certain range. In addition, in general, the elongation rate is set to a target value according to the steel type in the range of about 0.5 to 1.5%. The galvanized steel strip that has undergone temper rolling is wound up by the tension reel 17 and becomes a product.

When the method described in claim 1 is carried out, the roll surface is machined under a certain machining condition by shot blast machining, electric discharge machining or the like. At this time, the center line average roughness Ra (r) and the peak count PPI (r) of the temper rolling roll defined in claim 1 are measured using a surface roughness meter. As the surface roughness meter, a handy type roughness meter is commercially available, and the center line average roughness Ra defined in claim 1 is immediately after processing.
It is determined whether (r) and the peak count PPI (r) are satisfied. If this condition is not satisfied, the roll processing conditions are changed and processing is performed again.

As described above, by using the temper rolling roll according to claim 1 of the present invention, it becomes possible to manufacture a galvanized steel sheet having an appropriate surface. In particular, conventionally, according to the user's request, the processing conditions of the temper rolling roll for obtaining the target steel sheet surface were determined based on trial and error, while using the method according to the present invention. Therefore, it is possible to determine the processing conditions of the temper rolling roll without requiring special experience.

Next, the center line average roughness R of the temper rolling roll
By determining a (r) according to the equation (2) according to claim 2, the following effects can be obtained. Conventionally, the relationship between the working conditions of the temper rolling roll and the operating conditions such as elongation and the resulting steel plate surface is
It was empirically determined by processing various temper rolling rolls, incorporating them into an actual manufacturing facility, and then repeating a test in which the temper rolling conditions were changed. Such a method requires a lot of time and labor, and when the user's request changes, a situation in which the method cannot be dealt with occurs. Although it was actually installed in the temper rolling mill, the target steel plate surface could not be obtained, so there was a case where the elongation rate had to be corrected from the target value and the operation be performed while sacrificing the material. It was

On the other hand, by using the present invention, when the target value of the steel sheet surface and the operating conditions such as the elongation rate and the roll diameter are given in advance, the texture of the surface of the temper rolling roll to be targeted. Is prescribed. Therefore, it is possible to evaluate the result at the stage of processing the temper rolling roll, and if it is different from the target texture of the roll surface, the processing conditions may be changed on the spot.

As an embodiment of the present invention, not only the roll of the temper rolling mill in which the hot dip galvanizing line is arranged, but the temper rolling of a galvanized steel sheet is performed. Any form of equipment may be used.

The temper rolling roll according to the third aspect of the present invention is processed by electric discharge machining. At this time, it is possible to change the size and pitch of the unevenness by controlling the shape and material of the electrode to be used, the voltage and current at the time of discharge, and the discharge time. For example, the center line average roughness can be increased by increasing the current value during discharge.
The peak count can be increased by shortening the discharge time per pulse. Compared with shot dull processing, such electric discharge dull processing has a center line average roughness Ra.
It is easy to control (r) and the peak count PPI (r). Further, as compared with laser dull processing and electron beam processing, it is advantageous in that the processing time is short, a large amount of experience is not required to set the processing conditions, and the equipment is relatively inexpensive.

Further, the temper rolling roll according to claim 4 of the present invention is processed by electron beam processing. At this time, by controlling the moving distance of the electron beam and the irradiation time,
It is possible to change the size and pitch of the unevenness. Since a vacuum chamber is used for the electron beam machining equipment, the machining equipment is more expensive than the electric discharge dull machining machine. However, since it is possible to form regular irregularities on the roll surface, the center line average roughness Ra (r) and the peak count PPI defined in claim 1 or 2 of the present invention.
(R) can be easily formed.

[0044]

EXAMPLES Examples of the present invention will be described below. (Example 1) As Example 1 of the present invention, a plate thickness of 0.8 mm
The result of temper-rolling the hot-dip galvanized steel sheet using the cold-rolled steel sheet as the underlayer will be described. In Example 1, a temper rolling roll having a diameter of 600 mm and a body length of 2000 mm was provided with various surface forms by electric discharge dull processing or shot dull processing, and was incorporated into a temper rolling mill of a hot dip galvanizing line to perform galvanization. The temper rolling of the steel sheet was carried out. As the temper rolling conditions, the elongation was changed and the surface properties of the steel sheet after processing were evaluated using a roughness meter.

Table 2 below shows the conditions of the temper rolling roll and the surface properties of the galvanized steel root after the temper rolling.

[0046]

[Table 2]

As a reference for the press formability and the image clarity after coating, the center line average roughness Ra (s) of the steel sheet is 1.0 μm or more, the peak count PPI (s) is 150 or more, and the center is In the case where the line waviness Wca (s) satisfies the condition of 0.8 μm or less and the elongation rate range is 0.8 or more and 1.5% or less due to the restriction on the material, it is regarded as a pass, and FIG. Is shown in. As can be seen from this result, by producing a galvanized steel sheet using the temper rolling roll defined in claim 1 of the present invention, a steel sheet satisfying the above requirements can be produced.

(Embodiment 2) In the present embodiment 2, a diameter of 600
mm and 450 mm diameter temper rolling rolls were given various surface morphologies by electric discharge dull processing, and incorporated into a temper rolling machine of a hot dip galvanizing line to temper temper a galvanized steel sheet. As a temper rolling condition, the elongation rate is 1.0%
And the target center line average roughness Ra (s) of the steel sheet
Was 1.2 μm. At this time, the constants a and b expressed by the formula (2) are a for a roll having a diameter of 600 mm.
= 0.299, b = 0.098, diameter 400m
For a roll of m, a = 0.226, b = 0.11
Was set.

At this time, using the formula (2), the center line average roughness Ra (r) of the temper rolling roll is 3.0 μm for the roll having a diameter of 600 mm. Furthermore, equation (1)
Based on the roll peak count PPI (r) of 28
It was set to 0. On the other hand, for a roll having a diameter of 400 mm, Ra (r) was set to 3.6 μm from the formula (2) and PPI (r) was set to 260 from the formula (1).

Based on the above conditions, the electric discharge dull machining of the temper rolling roll was performed, and the temper rolling was performed under the condition of the elongation rate of 1.0%. As a result, when the roll having the diameter of 600 mm was used, The center line average roughness Ra (s), the peak count PPI (s), and the center line waviness Ra (s) of the steel sheet were 1.22 μm, 188, and 0.68 μm, respectively. on the other hand,
As a result of using a temper rolling roll having a diameter of 400 mm, the center line average roughness Ra (s) and peak count PPI (s) of the steel sheet
Were 1.20 μm, 167, and 0.73 μm, respectively.

As described above, by setting the centerline average roughness of the temper rolling rolls in accordance with the target elongation and the centerline average roughness of the steel sheet, the surface of the galvanized steel sheet on the target can be obtained. I was able to get

The constants a and b in the above equation (2) can be determined by an experiment in which the roll diameter of the temper rolling roll is changed, and the values used in this embodiment are used to obtain the values shown in FIG. Even if it is set from the relationship shown in, there is no problem in practical use.

[0053]

As described in detail above, according to the present invention, many trials can be performed by providing the processing conditions of the temper rolling roll and the temper rolling conditions using the same without requiring expensive equipment. It is possible to provide a temper rolling method for a galvanized steel sheet that satisfies the press formability and the image clarity after coating without any error.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a center line average roughness Ra (r) of a temper rolling roll and a peak count PPI (r) of the temper rolling roll.

FIG. 2 is a characteristic diagram showing the relationship between the transfer rate of the average roughness and the transfer rate of the peak count, which is the basis of the invention.

FIG. 3 is a characteristic diagram showing the relationship between the peak count PPI (s) and centerline waviness Wca (s) of a galvanized steel sheet which is the basis of the present invention.

FIG. 4 is a characteristic diagram showing the relationship between the elongation rate and the transfer rate of average roughness, which is the basis of the present invention.

FIG. 5 is an explanatory view showing a hot dip galvanizing line for carrying out the present invention.

FIG. 6 is a characteristic diagram showing a relationship between an average roughness Ra (r) of a temper rolling roll and a transfer rate.

FIG. 7 is a characteristic diagram showing a relationship between an average roughness Ra (r) of a temper rolling roll and a lower limit value of a peak count PPI (r) of the temper rolling roll.

FIG. 8 is a characteristic diagram showing a relationship between a roll diameter of a temper rolling roll and constants a and b in Expression (2).

[Explanation of symbols]

10 ... steel strip, 11 ... Payoff reel, 12 ... Annealing equipment, 13 ... hot dip galvanizing bath, 14 ... Gas wiping nozzle, 15 ... temper rolling mill, 16 ... temper rolling roll, 17 ... Tension leveler unit.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhiro Soya             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Shogo Tomita             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F-term (reference) 3C059 AA01 AB00 HA18                 4E002 AD06 BB09 BD20 CB03                 4E016 AA03 BA02 CA04 CA09 DA11                       FA15 FA20                 4E066 AA00 CA14 CB00

Claims (4)

[Claims] 1. A method of temper rolling a galvanized steel sheet, wherein the center line average roughness Ra (r) of the roll surface is 2.0.
˜4.0 μm, and the peak count PPI (r) (cutoff 0.635 μm) satisfies the following formula PPI (r) ≧ (30 × Ra (r) +130). A temper rolling method for galvanized steel sheet, which is characterized by being performed. 2. The center line of the roll surface with respect to the target center line average roughness Ra (s) (μm) of the galvanized steel sheet after temper rolling and the target elongation rate δ (%) in temper rolling. The average roughness Ra (r) (μm) is determined by the following formula Ra (r): Ra (s) / (a × δ + b), where a and b are determined based on a constant depending on the work roll diameter. The method for temper rolling of a galvanized steel sheet according to claim 1. 3. The temper rolling method for a galvanized steel sheet according to claim 1, wherein the unevenness on the surface of the temper rolling roll is formed by electric discharge machining. 4. The unevenness on the surface of the temper rolling roll is formed by electron beam processing.
Or the temper rolling method of the galvanized steel sheet according to claim 2.