JPH0699834B2 - Electric Zn plated steel sheet with excellent tension pad resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an electric machine excellent in tension pad resistance, which does not impair the plating appearance even when the tension pad machine is passed through.
It relates to a Zn-plated steel sheet.

(Prior Art) When slitting a steel sheet strip, the steel sheet requires a predetermined tension. As a method of adding tension at that time, a tension pad machine is used to hold down the steel sheet and pull it out. The method is widely and commonly used.
However, when a low-hardness Zn-plated steel sheet is passed through this tension pad machine, the surface Zn is scraped by the tension pad in contact with the steel sheet surface, the steel sheet turns black, and tension pad scratches occur. There is. Normal,
This pad is made of felt.

Hereinafter, the tendency of blackening or scratching due to this tension pad is referred to as "tension pad property", and its resistance is referred to as "tension pad resistance".

When the steel plate turns black and tension pad scratches occur in this way, the appearance of the Zn-plated steel plate that has undergone post-treatment such as chromate treatment not only deteriorates, but the surface Zn is also scraped off, resulting in products with corrosion resistance and other products. Performance problems also arise. Therefore, a surface-treated steel sheet having excellent tension pad resistance is desired.

Conventionally, in order to improve the tension pad resistance of the electric Zn plated steel sheet, by adding an additive to the plating solution,
There is a method of changing the Zn orientation of plating (Japanese Patent Publication No. 63-60836). This method is a method of improving the resistance to tension pad by selectively suppressing the orientation of Zn to the (002) plane, which is a slip surface, which easily peels off during processing.

A method of improving the tension pad resistance by increasing the lubricity of the steel sheet surface by a chromate treatment or a post treatment such as resin coating can be considered. Considering the intended use of the steel strip, it is not always preferable.

(Problems to be Solved by the Invention) Therefore, a first object of the present invention is to provide an electric Zn-plated steel sheet in which the tension pad resistance of the electric Zn-plated steel sheet itself is improved without improving the post-treatment method. That is.

To achieve such an object, it is not sufficient to change the Zn orientation of the plating layer as in the conventional method. Therefore, a second object of the present invention is to provide an electric Zn-plated steel sheet having excellent resistance to tension pads regardless of the material of the pad, the pad pressure, or the speed at which the steel sheet is pulled out.

A so-called oiling method in which oil is applied to the steel sheet surface in order to improve the lubricity of the steel sheet surface is also conceivable, but the tension pad property may be significantly deteriorated by such oiling. Therefore, a third object of the present invention is to provide an electric Zn-plated steel sheet that can fully exhibit effective tension pad resistance without post-treatment under any conditions.

(Means for Solving the Problem) The present inventor has conducted various studies as a factor that affects the tension pad resistance, and as a result, the roughness (surface shape) of the steel sheet surface is extremely different from the tension pad resistance. As a result of further study, we found that the steel plate surface roughness was 0.9 μm in terms of centerline average roughness Ra.
As described above, it has been found that having a peak count PPI of 100 or more and having a surface with a certain degree of unevenness, that is, having an appropriate sense of unevenness is effective for the resistance to tension pads.

Here, as an index indicating the unevenness of the steel plate surface, Is defined as the residual rate D of the concave portion. According to the present invention, this D value is
When it is 0.125 or more, it is effective for the resistance to tension pad.

That is, the gist of the present invention is that in the electric Zn plated steel sheet, the surface roughness after plating is the center line average roughness Ra.
The length of the straight line of the valley corresponding to the recessed part of the plating is 0.9μm or more, PPI is 100 or more, and when cut parallel to the center line at a point 4μm from the maximum peak height, Let Σln be the sum of the heights, L be the measured length of the straight line of the cut, and D be the recessed portion residual rate obtained by the following equation: It is an electric Zn-plated steel sheet excellent in tension pad resistance, characterized in that the recess residual rate D is 0.125 or more.

(Operation) Next, the present invention will be specifically described.

First of all, the exact mechanism by which blackening or pad scratches occur by passing through a tension pad machine is unknown, but the tension pad scrapes off the soft Zn on the surface and crushes it. If the area of the region is shaved at such a rate that it can be visually observed, blackening occurs. It is presumed that when the scraped Zn powder further agglomerates, the agglomerated Zn scratches the plating surface, and if many scratches gather, tension pad scratches will occur.

Therefore, the effect of surface roughness on the tension pad property in the present invention is considered to be as follows.

Ra is specified to be 0.9 μm or more, because increasing Ra increases the unevenness of the plating surface, so that the Zn powder scraped off by the tension pad accumulates in the recesses and the Zn powder comes out better. In addition, the agglomeration of Zn powder can be suppressed. Therefore, although blackening occurs to some extent, further blackening and tension pad scratches due to Zn powder aggregation are eliminated. Preferably Ra is 1.1
It is at least μm.

The PPI (Peak Per Inch) is defined as 100 or more by increasing the PPI so that the number of surface peaks, that is, the area cut by the tension pad can be reduced or dispersed to prevent the occurrence of black discoloration. This is because.

Further, not only Ra and PPI but also the shape of the surface, that is, the feeling of unevenness is very important for the resistance to tension pad, and it is promising to increase the unevenness and reduce the number of convex portions as much as possible. From the outermost layer of the plated steel plate, the area that may be cut by the tension pad is 4μ.
After confirming that the area is a depth of m, and introducing the concept of the above-mentioned D value (recessed portion remaining rate) and arranging it, the tension pad property can be further satisfactorily arranged.

FIG. 1 is a diagram for explaining the measurement procedure of this D value,
It is the figure which expanded the surface part of a steel plate sectional view. In the chart profile of surface unevenness, draw a straight line (also referred to as a measurement straight line) parallel to the reference line (center line when measuring the center line average roughness) at a distance of 4 μm from the maximum mountain height downward (inward direction of the steel plate). When the valleys, that is, the distances l ₁ , l ₂ , l ₃ , l ₄ , ... of the measurement straight line cross the space are summed (Σln), the measured length, that is, the length L of the measurement straight line The ratio is defined as the concave portion residual rate (D value).

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

Regarding the unevenness represented by this D value, if the unevenness is small, such as D = 0.125, that is, if the unevenness of the steel plate is small, the Zn scraped by the tension pad is not collected in the valley and is taken out by the tension pad. As a result, aggregation of Zn powder on the steel sheet surface is promoted, which is not preferable.
Therefore, the D value should be 0.125 or more. Preferably, the D value is 0.200 or more.

By the way, Ra, PPI, D for tension pad resistance
There is no particular upper limit to the value, but rather it is specified from the secondary processability of the product or the appearance (including the appearance after painting).

By the way, as a method for the surface-treated steel sheet according to the present invention to obtain a predetermined surface roughness, after rolling the steel sheet with a dull roll,
Either the method of performing electric Zn plating or the method of rolling after plating may be used, but the method of rolling after plating is to destroy the plating layer, and in the chromate-treated electric Zn-plated steel sheet, since the chromate film is also destroyed, There is a problem of deterioration of corrosion resistance and coating adhesion, which is not preferable.

In the case of an electric Zn-plated steel sheet, between the surface roughness after plating (Ra, PPI) and the surface roughness of the steel sheet before plating,
Since almost no difference is recognized, it is desirable to adjust the surface roughness in the cold rolling finishing step, and therefore, for the dull roll used as the cold rolling finishing roll, it is desirable to use the dull roll having the surface roughness defined in the present invention.

Further, the dull roll for cold finishing rolling of the steel plate used at that time is not particularly limited, and the roll working method may be shot blasting, electric discharge dull working, laser beam working, electron beam working, or the like. .

As the steel plate that can be used, electric Zn plated steel plate,
The presence or absence of post-treatment such as chromate treatment is not specified.

The present invention will be described in detail with reference to examples.

(Example) As a method for easily evaluating the tension pad resistance of an electric Zn-plated steel sheet in a laboratory, a Taber type abrasion tester used in the abrasion resistance test method of JIS H 8503 was used, and the abrasion wheel was polished at that time. The test was conducted by sticking a filter paper instead of the paper. On the other hand, the same electric Zn-plated steel sheet was applied with tension by a tension pad in an actual production line, and the tension pad resistance of the steel sheet at that time was evaluated. As a result, as shown in FIG. 2, it was found that a very good correlation was found between the result of this lab test and the result of the test on the actual production line.

The scores in Fig. 2 were determined according to the following criteria.

Therefore, as specific examples according to the present invention, the electric Zn-plated steel sheets having different surface roughnesses (Zn adhesion amount 20 to 60 g / m ² ) and the electric Zn-plated steel sheet further provided with a chromate film were subjected to the lab test and a part thereof. Tension pad tension is applied on the actual production line, and the evaluation results of the tension pad resistance at that time are summarized in Table 2.

Further, FIG. 3 is a graph showing the laboratory scores and the surface roughness (PPI and Ra) in Table 2 in association with each other. Since it is known from the result of FIG. 1 that the laboratory score and the score of the tension pad resistance in the actual line match, the result of FIG. 3 may be applied to the actual production line as it is. it can.

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 roughness (Ra, PPI, D).

Further, although not shown by concrete data, it was also found that the difference in the resistance to tension pad due to the difference in Cr adhesion amount, Zn basis weight or dull roll processing method when a chromate film was provided was not recognized.

(Effect of the invention) As described above, according to the present invention, in the electric Zn-plated steel sheet, the surface roughness Ra is 0.9 μm or more, PPI is 100 or more, and D value is 0.125 or more. It was found that even if it was applied, it had excellent resistance to tension pads. Further, the present invention provides a certain standard for the tension pad resistance, which has not been an appropriate standard until now, by the surface roughness, and the industrial utility of the present invention is great.

[Brief description of drawings]

FIG. 1 is an explanatory view of a procedure for measuring the residual rate of recesses; FIG. 2 is a graph showing a correlation between a test result of tension pad resistance in an actual manufacturing line and a test result of tension pad resistance in a laboratory; And FIG. 3 is a graph showing the correlation between surface roughness and tension pad resistance.

Claims (1)

[Claims] 1. An electric Zn-plated steel sheet, the surface roughness after plating is 0.9 μm or more in terms of center line average roughness Ra and 100 in PPI.
When having the above, and when cutting parallel to the center line at a point 4 μm from the maximum peak height, among the straight lines of the cut, the sum of the lengths of the straight lines of the valleys corresponding to the recesses of plating is Σln, Let L be the measurement length of the straight line of the cut end and D be the recessed portion remaining rate obtained by the following formula, An electric Zn-plated steel sheet with excellent resistance to tension pads, characterized in that the recess residual rate D is 0.125 or more.