JPH0699835B2 - Zn-plated steel sheet with excellent tension pad resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a surface-treated steel sheet having excellent resistance to tension pads, that is, a tension which is a general means for continuously slitting a steel sheet into a predetermined width dimension. The present invention relates to a Zn-plated steel sheet having excellent tension pad resistance that does not impair the plating appearance even through a pad machine.

(Prior Art) When a steel sheet is continuously slit, it is necessary to apply tension to the steel sheet. As one of the methods for applying the tension, a widely used method is to use a tension pad for the steel sheet. This is a method of holding down tension to obtain tension (a machine equipped with this tension pad is called a tension pad machine).

However, due to problems with the material of the tension pad used in this tension pad machine, when a low-hardness Zn-plated steel sheet is passed through the tension pad machine, the pad that comes into contact with the surface of the steel sheet causes the surface Zn to be extremely sharpened, resulting in a black steel sheet Change, or metallic luster appears, and scratches due to the pad occur (hereinafter, the blackening or scratches caused by this tension pad is called tension pad property, and the resistance to it is called tension pad resistance), There is a cosmetic problem. Further, in a steel sheet that has been post-treated such as chromate treatment, not only the appearance but also the post-treatment coating of the surface layer and the plating layer are scraped off, which causes problems in product performance such as corrosion resistance and coating adhesion. Therefore, a surface-treated steel sheet excellent in tension pad resistance is desired.

(Problems to be Solved by the Invention) Conventionally, as a method for improving the tension pad resistance of an electric Zn-plated steel sheet, by adding an additive to a plating solution, the Zn orientation index in the plating layer is selectively changed. There is a method (Japanese Patent Publication No. 63-60836). However, this method cannot be applied to hot-dip Zn-plated steel sheets, and the tension pad resistance cannot be said to be sufficiently improved depending on the pad pressure, pulling speed, or other conditions.

Further, a method of improving lubricity by post-treatment such as chromate treatment or resin coating may be considered, but improvement of tension pad resistance by such post-treatment method is not always preferable considering user's intended use. However, it is desirable to improve the tension pad resistance of the Zn-plated steel sheet itself.

However, heretofore, no method has been disclosed for improving the tension pad resistance of the Zn-plated steel sheet itself.

There is a method (Japanese Patent Laid-Open No. 64-2705) for improving mold galling by defining the surface roughness. But,
This method is intended for cold-rolled steel sheets that do not have a problem in appearance, and is basically aimed at improving press workability because it improves die galling, and the tension pad phenomenon is basically It is intended for different phenomena.

Thus, in the past, as a method related to the tension pad resistance of the Zn-plated steel sheet itself, in regard to the electroplating method, the conditions at the time of slitting, or,
It deteriorates due to oiling and cannot be said to have sufficient tension pad resistance. In hot-dip galvanized steel sheets, there are almost no attempts to improve the tension pad resistance of steel sheets, and the present situation is to deal with this by changing the slitting method.

Therefore, an object of the present invention is to solve the problems of these conventional techniques, and for surface-treated steel sheets excellent in tension pad resistance, especially for various slit conditions, without post-treatment, and for oiling. The purpose is to provide a Zn-plated steel sheet having good resistance to tension pads even when the above is performed.

(Means for Solving the Problems) In order to achieve the above-mentioned object, as a result of various studies by the present inventors, the factors affecting the tension pad resistance include surface roughness of the plated steel sheet and surface shape. Named
The present invention has been completed on the basis of the finding that the correlation between them and the resistance to tension pads becomes clear, and that adjusting them to an appropriate range is extremely effective in improving the resistance to tension pads.

As a result of further detailed study, the surface roughness of the electric Zn plated steel sheet is 0.7 μm or more in terms of center line roughness (Ra),
It was found that a peak count index (PPI) of 75 or more, and that the feeling of unevenness on the plated surface is clear is effective in improving the resistance to tension pads.

Further, according to the present invention, as an index representing this unevenness feeling,
It is possible to adopt the recess remaining rate D, and this D value is Can be expressed as For electric Zn plating, x = 3 μm
When the D value is 0.5 or more at that time, the improvement of the tension pad resistance is remarkable.

That is, in the present invention, the planar shape of the steel sheet is defined by using the recessed portion residual rate defined above.

Similarly, in hot-dip Zn plated steel sheet, adjusting the surface roughness is effective for improving the resistance to tension pad, and the center line roughness (Ra) is 0.3 μm or more and the peak count index (PPI) is 40 or more. . Furthermore, according to the preferable aspect, regarding the unevenness of the plating layer, when x = 1 μm, the D value is
By setting it to 0.5 or more, the improvement of the tension pad resistance is good.

(Operation) The configuration of the present invention will be described in detail.

The mechanism by which blackening or pad scratches occur by passing through a tension pad machine is unknown in detail, but it is thought that the cause is as follows.

First, due to the contact between the Zn-plated steel plate and the tension pad, the very surface of the soft Zn-plated layer is crushed and scraped, but when the scraped area is scraped to a size that can be visually recognized, it turns black. And when the scraped Zn powder is agglomerated on the steel plate and the pad, the agglomerated Zn powder scratches the plating layer surface, and scratches that can be visually determined by collecting many scratches, that is, It can be assumed that the tension pad will be damaged.

Therefore, in the present invention, the reason for defining the surface roughened state of each plated steel sheet is as follows.

First, in the case of an electric Zn-plated steel sheet, Ra is defined to be 0.7 μm or more because the roughness of the plating layer surface increases as Ra increases. That is, it is considered that the Zn powder scraped off by the pad accumulates in the recesses and the Zn powder is easily removed, so that the Zn powder is less likely to be aggregated and the occurrence of pad scratches can be suppressed.

Further, the PPI is defined as 75 or more because the area crushed by the pad is reduced or dispersed, so that the occurrence of black discoloration and the agglomeration of Zn powder are suppressed.

On the other hand, the surface shape and unevenness are important factors for the resistance to the tension pad, and it cannot be said that the specifications of Ra and PPI are sufficient. Therefore, in a preferred embodiment of the present invention, in order to express the unevenness feeling, the size of the concave portion of the cut cross section when cut at a position in the depth direction at a certain distance from the highest mountain height, that is, the concept of the concave portion residual rate. Was introduced. Electric Zn
In the case of plating, the remaining amount of recesses when cut at a depth of 3 μm is 0.
It was found that when it is 5 or more, the resistance to tension pads is good, but this is because Zn powder scraped by the pad is stored in the recesses as much as possible, so that Zn powder in the contact area between the pad and the plating surface It is considered to be for suppressing aggregation.

For the same reason, even in the case of hot-dip Zn plated steel sheet,
Ra is 0.3 μm or more and PPI is 40 or more. Further, according to the preferred embodiment, the residual rate of the recessed portion when cut at a depth of 1 μm from the maximum peak height as a reference line is 0.
Specify 5 or more.

In addition, there is a difference in the specified value between the electroplated steel sheet and the hot dip plated steel sheet in this manner, because the oxidation state of Zn in the plating surface layer is different, that is, the thickness of the Zn oxide layer is different,
It is considered that the main reason is that the Zn powder when scraped by the pad is small in the hot dip plated steel sheet.

FIG. 1 (a) shows a two-dimensional surface roughness profile, and FIG. 1 (b) shows a schematic view of the appearance of the plated surface when cut at a position of depth μm in three-dimensional contour lines. . In the figure, the white parts represent the valleys (recesses) when cut at the depth x.

On the other hand, the upper limit values of Ra and PPI with respect to the tension pad resistance are not particularly limited in any case, but rather may be defined by other performances such as appearance (including appearance after painting). In that sense, it is generally sufficient to limit to Ra 2.0 μm or less and PPI 400 or less.

By the way, as a method of adjusting the surface roughened state to produce a Zn-plated steel sheet according to the present invention, it is not limited to a particular one, but also a method of rolling the steel sheet after rolling with a dull roll, or a method of rolling after plating. However, in general, in the case of electroplating, a plated steel sheet having substantially the same shape as that of the original sheet can be obtained even if the steel sheet is rolled and then plated, so this method is preferable because it does not destroy the plating layer. On the other hand, in hot-dip galvanized steel sheets, even if the original plate is rolled with a dull roll and then plated, it does not necessarily have the same shape as the original plate. Therefore, a method of rolling using a roll having a predetermined shape after plating is preferable.

The dull roll for rolling used is not particularly specified, and the roll processing method is not particularly specified such as shot blast processing, electric discharge dull processing, laser beam processing, and electron beam processing.

(Examples) The present invention will be specifically described with reference to Examples.

As a method for easily evaluating the tension pad resistance in a laboratory, a method of applying a filter paper to a wear wheel with a taper type wear test device according to the wear resistance test method (JIS H 8503) was adopted. The correlation between the result and the actual use result in the slit line is shown in a graph in FIG. The scores in the figure were as shown in Table 1 below. As is clear from this, it was found that there is a very good correlation between this lab test result and the actual line test result, and if the lab test result is evaluated as ○ or more, even with an actual tension pad, Tension pad resistance is considered to be no problem.

In addition, as a method of measuring the recessed portion residual rate, it was determined by using a contour line display method of a three-dimensional roughness meter. Electric Zn
The actual shape of the cross section of the plated steel sheet is shown in FIGS. 3 (a), (b) and (c). In the figure, the white part represents a concave part when cut at a position of 3 μm in the depth direction from the reference line. The results at this time are summarized in Table 2. The evaluation procedure was the same as in Table 1.

On the other hand, the relationship between the residual rate of recesses measured by the method and the resistance to tension pads is also shown in the graph of FIG.
From this, the correlation between the rough surface condition and the tension pad resistance defined in the present invention can be understood.

Next, specific examples according to the present invention will be shown. Tables 3 and 4 show the results of the above-mentioned laboratory test and the results of general-purpose tension pad tests of electric Zn-plated steel sheets having various surface shapes and hot-dip Zn-plated steel sheets.

Further, the test results are shown for each plated steel sheet that has been subjected to a conventional chromate treatment. The amount of chromate coating is converted to the amount of metallic Cr, and is shown as the Cr adhesion amount (mg / m ² ).

As is clear from these results, it was found that there is a very good correlation between the resistance to tension pad and the surface shape.

It was also found that there was no difference in tension pad properties due to differences in chromate coating amount (Cr deposition amount), Zn deposition amount, and dull roll processing method.

(Effect of the invention) Since the present invention is configured as described above, in the electroplated steel sheet and the hot-dip Zn-plated steel sheet, by working so as to have the surface shape defined in the present invention, particularly post-treatment is performed. It is possible to obtain a surface-treated steel sheet having extremely excellent resistance to tension pads without the need for rubbing, and it is extremely useful industrially.

[Brief description of drawings]

FIGS. 1 (a) and 1 (b) are explanatory views of the procedure for measuring the recessed portion residual rate limited in the present invention; FIG. 2 is an explanation showing the relationship between the actual tension pad test result and the lab tension pad reproduction test. Fig. 3 (a), (b), (c) shows contour lines on the plating surface showing an example of a cross-sectional area of a cut when cut at 3 µm; and Fig. 4 shows tension pad resistance and Recess rate of recess (= D)
It is explanatory drawing which shows a relationship.

Claims (2)

[Claims] 1. An electric Zn-plated steel sheet having a surface roughness Ra of 0.7 μm or more after plating and a PPI of 75 or more after the plating, and the maximum peak height of the surface after plating as a reference line, and the depth direction. When the area of the valley (recess) of the plating layer when cut at a position of 3 μm is set to B, and the ratio of the total area to A is set to the remaining amount D of the recess, D = B / A is 0.5 or more A Zn-plated steel sheet with excellent resistance to tension pads. 2. A hot-dip galvanized steel sheet having a surface roughness Ra of 0.3 μm or more after plating and a PPI of 40 or more after plating, with the maximum peak height of the surface after plating as a reference line, and in the depth direction. 1 μm
When the area of the valley (concave portion) of the plating layer when cut at the position is B, and the ratio when the total area is A is the residual amount D of the concave portion, D = B / A is 0.5 or more. A Zn-plated steel sheet with excellent tension pad resistance, which is characterized by