JPS63299802A - Production of cold rolled steel sheet having excellent painting brightness and press workability - Google Patents

Abstract

PURPOSE:To improve panting brightness and press workability by executing the final rolling of cold rolling by using rolls matted to a specific surface roughness and executing the skin pass rolling after annealing by using the rolls matted to a specific surface roughness. CONSTITUTION:The surface of a coated film P which is formed on the surface of a steel sheet S rolled by the matted rolls is smooth. The surfaces of the work rolls of the final stand in the cold rolling are matted by electric discharge machining to the surface roughness Ra=2-4mum. The steel sheet is rolled by such rolls and is then subjected to ordinary annealing. The skin pass rolling is executed by using the rolls matted by electric discharge machining of the roll surfaces to the surface roughness Ra=1-3mum. The skin pass rolling is executed at an ordinary draft. Since the final matting condition has a close relation with the waving and surface roughness of the steel sheet, the wear of the rolls is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a cold rolled steel sheet with excellent coating clarity and press workability.

(Conventional technology) User needs for automobiles are becoming more and more sophisticated year by year. In particular, in recent years, the brightness of the gloss, or so-called paint clarity, has rapidly come into the spotlight as an important factor in determining the product image when it comes to the appearance of automobiles.

Furthermore, for the outer panels of home appliances and architectural exterior materials,
Good clarity of the painted surface further increases the commercial value. Furthermore, in order to withstand complicated press forming, the press formability required of steel sheets is becoming increasingly sophisticated.

BACKGROUND ART The semi-macrographic shape of the surface of a rolled product such as a steel plate, that is, the surface roughness, has been known as a factor that strongly influences paint clarity and press workability.

A method for imparting roughness to the roll surface is disclosed in Japanese Patent Application Laid-open No. 51
-101774, etc., by the shot blasting method shown in JP-A-49-17331. USP 3B198
81 etc. by electrical discharge machining method, and Special Publication No. 58-25
Various methods are known, such as the method using laser light irradiation as shown in 557 and Japanese Patent Publication No. 82-11922.
Both methods have the following problems.

(Problems to be Solved by the Invention) The current roughening method commonly used in production sites is shot blasting.

In this shot blasting method, the roll is first ground and polished to have a smooth surface, and then hard particles such as iron, called a grid, are blown onto the roll surface to make it rough. This shot blasting method is simple, and has the advantage of hardening the surface and increasing the wear resistance of the roll, but on the other hand, the surface becomes irregular and unevenly rough, making it difficult to control the roughness. There is a certain drawback.

The laser beam irradiation method has excellent controllability and is capable of imparting an extremely regular uneven pattern (hereinafter referred to as a matte surface) to the roll surface. However, the processing equipment is more expensive than the shot blasting method, the streaks are noticeable due to the high regularity and the appearance after painting is spoiled, and the uneven pattern on the roll surface is created by rolling in a relatively short time. It has the disadvantage of being worn out.

In the electric discharge machining method, an electrode is placed opposite the roll, and while the roll is rotated and the electrode is moved in the direction of the roll axis, a spark discharge is generated between the roll and the electrode, and this discharge energy creates fine particles on the roll surface. It is something that generates.

In this method, the roll surface can be given any roughness mainly by changing the electric discharge machining current peak value, electric discharge pulse width, electric discharge body stop width 1, etc. The uneven pattern on the roll surface formed by this method is slightly less regular than that produced by the laser method, but it is much more regular than that produced by the shot blasting method, and the roll processing method is also relatively simple. , it has the advantage that the uneven pattern has high wear resistance. The sharpness of steel sheets rolled using rolls processed by the electrical discharge machining method has been evaluated on average to be intermediate between those obtained by the shot blasting method and the laser method; Some products have been found that exhibit excellent values above, but they have the disadvantage that the variation is not necessarily small.

(Means for Solving the Problems) The present invention has stable high image clarity and press workability due to the combination of the conditions for imparting a matte finish to the roll by electric discharge machining and the manufacturing conditions. This method was developed as a result of various studies on how to obtain steel sheets, and its characteristics are as follows: (1) The final roll of cold rolling is polished to a surface roughness Ra of 2 to 4 μm by electrical discharge machining. carried out using
After annealing, surface roughness R is improved by electrical discharge machining of skin bath rolling.
A method for producing a cold-rolled steel sheet with excellent coating clarity and press workability, characterized in that the process is carried out using a roll that has been satin-finished to a = 1 to 3 JLm, (2) skin bath rolling is performed after satin-finishing; A method for producing a cold-rolled steel sheet with excellent coating clarity and press workability according to claim (1), which is carried out using a roll plated with a hard metal of ~20 gm;
It is.

FIG. 1(a) schematically shows a steel sheet S rolled with a satin-finished roll using the method of the present invention, with a coating film P formed on the surface. The surface of the coating film is smooth.

Figure 1 (rl) is a comparative example, in which there are large unevenness (hereinafter referred to as waviness) in addition to small unevenness on the steel plate surface.
This remains as waviness on the surface of the coating film. Therefore, it is explained that the light incident on the painted surface is reflected in many directions from the painted surface, reducing the sharpness of the image.

fIS diagram 2 (a) schematically shows the lubricating oil applied to the surface of the steel plate S of the present invention, and the lubricating oil is uniformly held between regular and relatively deep irregularities on the steel plate surface. ing.

On the other hand, FIG. 2(a) shows the state of the lubricating oil coated on the surface of the steel plate S as a comparative example, and the oil film is broken in some places, such as at the top of the undulations. Therefore, friction increases significantly in areas where the oil film is broken, leading to galling of the mold and an increase in processing force.

In this way, the size of the waviness in the steel sheet affects the image clarity and press workability. Also, if the surface roughness represented by the small irregularities in the figure is too small, an oil film will adhere to the steel plate surface.
This also causes galling of the mold.

Hereinafter, waviness will be abbreviated as Wca, and surface roughness will be abbreviated as Ra, and the values measured using the methods specified by JIS will be used. However, in order to satisfy coating clarity and press workability,
It is necessary to reduce the Wca value and increase the Ra value. The first condition that satisfies these conditions is that the surface of the final stand work roll in cold rolling must be satin-finished by electric discharge machining so that the center line average roughness Ra (roll) is 2 to 4 gm. If the roll Ra is less than 2 uLm, the unevenness transferred to the steel plate, that is, the Ra value of the steel plate will also be small, and there will be a strong tendency for shape defects during rolling and seizure during annealing, resulting in a significant decrease in yield.

If the roll Ra exceeds 4 gm, no matter how the rolling conditions of the skin bath rolling performed after annealing are changed, it is not possible to reduce the waviness Wca of the final steel plate and increase the Ra.

Therefore, the roughness R of the roll surface of the final stand of cold rolling
A is limited to 2 to 4μ by electric discharge machining, but Ra is reduced to this range by shot blasting [! ! Even if
As will be shown later in Examples, it is not possible to maintain Wca at a small value. Furthermore, there is no need to specifically limit the roll Ra in the first stage of cold rolling because it has little influence on the final Wca and Ra of the steel sheet. , reduction distribution, etc. do not need to be particularly limited as long as normal cold rolling conditions are adopted.

Steel plates are annealed after cold rolling, but there are no particular conditions for this either, and normal box annealing or continuous annealing can be performed.

The second condition is that the surface of the roll used in skin bath rolling is satin-finished by electrical discharge machining to a roll Ra of 1 to 3 gm. When the roll Ra becomes less than lILm, the Wca of the steel plate becomes smaller, but the Ra becomes smaller,
Since the ability to retain lubricating oil during press working of a steel plate is reduced, press workability tends to deteriorate.

Moreover, when Ra3JLm is exceeded, Wca becomes thicker rapidly.

Further, even if the roughness of the skin bath roll is adjusted to the same range Ra=1 to 37zm by the shot blasting method, the Wca of the steel sheet becomes larger than that by the electric discharge machining method. When skin bath rolling is performed multiple times on multiple stands,
At least the Ra of the final rolling roll may be adjusted within a predetermined range, and the first rolling roll may have a bright finish.

Further, skin bath rolling is performed at a normal rolling reduction ratio, and lubrication may be performed by either a dry method or a wet method, but Wca is smaller and more stable if the dry method is used, although it is slightly better. The satin finished state of the final skin bath rolling roll is the Wca of the steel plate.
, is particularly closely related to Ra, and it is important to minimize the wear of the rolls that occurs over the course of rolling.

As an effective means for this purpose, Or
There is a method of applying hard metal plating such as.

The plating thickness is suitably in the range of 5 to 20 m. If it is less than 5 m, the wear resistance effect will be small, and if it exceeds 20 m, the plating adhesion will be poor and it will easily smudge.

It is important to strictly control the electric discharge machining conditions in the cold rolling roll and the skin bath rolling roll.
This is desirable in order to stabilize the values of a and Ra within a suitable range.

In addition to precisely controlling the peak value and pulse width of the applied pulse current and the voltage, it is particularly important to keep the distance between the rolls and the discharge electrodes as constant as possible. The gap between poles can be precisely controlled by comparing the average machining voltage or average machining current during electrical discharge machining with a reference value and outputting the difference to the servo valve solenoid to move the hydraulic cylinder. .

(Function) The surface of the steel plate rolled by the method of the present invention, in which the final stand roll of cold rolling and the skin bath rolling roll are subjected to a satin finish of a predetermined roughness by precisely controlled electrical discharge machining, is As shown in figure (a)! A dense and uniform satin pattern was transferred to the surface. On the other hand, the surface of the steel sheet when at least one of the cold rolling rolls or the skin bath rolling rolls is subjected to a matte finish using the shot blasting method (see Fig. 3 (0)).
) is found to be inferior in density.

FIG. 4 shows the distribution of Wca and Ra of the invention material and the comparative material (those produced by shot blasting or electrical discharge machining, but outside the range of roll Ra of the present invention).

The material of the present invention has a small and stable Wca, a high and stable Ra, and is within the range of excellent image clarity and press workability.

On the other hand, Wca of the shot blasted material is in a large range, and it can be seen that if the roll Ra is outside the range of the present invention although it is an electrical discharge machined material, either Wca or Ra will deviate in an undesirable direction.

(Example) Table 1 shows the main manufacturing conditions and the characteristic values of the product sheets in comparison with the inventive material and the comparative material. The steel plate was cold rolled to a thickness of 0.7 mm under normal rolling conditions, box-shaped annealed at 880°C, and then
．． The press workability using an actual machine was investigated for the products that had been subjected to 0% skin bath rolling.

Paint sharpness was determined using the N5IC value based on image sharpness for steel plates coated under the conditions shown in Table 2.

In this method, a rectangular light beam is incident on the surface of a steel plate, the reflected light is captured at a predetermined position, and the distortion of the rectangular shape of the light beam is expressed as an index. The lower the N5IC value, the lower the image sharpness.

Note that, as the characteristic values of the steel sheet, the average value of several points in total of the rolled material immediately after the satin finishing on the roll and the values obtained every five coils was used. Invention material when a specified satin finish is applied to both cold-rolled and skin bath rolls by electric discharge machining■
It can be seen that Wca of ~■ is all 0.61 Lm or less, and the waviness is small.

In addition, the evaluation value N5IC of image clarity is high, indicating good image clarity.Furthermore, the Ra value is stable at 0.8 JLm or more, and the relatively deep recesses have a high ability to retain lubricating oil. The press workability is also good.

For comparison materials 8, 9, and 10, the satin finish of the rolls was all performed by electrical discharge, but in case of No. 8, since the skin bath roll Ra was low, the Ra of the steel sheet was also low, and the workability was poor.

Comparative material 9 has a high Ra of the skin bath roll and a high W of the steel plate.
The image sharpness evaluated by ca and N5IC value is poor. Comparative material 10 suffered from seizure during annealing because the cold rolling roll had a low Ra. Comparative materials 11 and 12 are cold-rolled rolls that have been subjected to a satin finish using the shot blasting method, and both have no waviness W.
The ca is large, the N5IC value is low, and the image clarity is poor. Comparative materials 13 and 14 are skin bath rolls subjected to shot blast processing, and in this case, Wca is high regardless of the processing method of the cold rolled rolls.

Table 2 (Effects of the Invention) The present application uses a relatively simple device and a highly controllable electrical discharge machining method to perform satin finishing of a predetermined roughness with high accuracy on cold rolled and skin bath rolls. As a result of rolling using the rolled roll, it is possible to stably produce a steel plate with excellent coating clarity and press workability, and this invention has great industrial benefits.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the clarity of the coating surface, Figure 2 is a schematic diagram showing the state of lubricating oil on the surface of the steel plate, Figure 3 is the property of the surface of the steel plate,
FIG. 4 is a graph showing the measurement results of surface waviness and surface roughness for the steel plate of the present invention and a comparative material.

Claims (2)

[Claims] (1) The final rolling of cold rolling is performed using a roll that has been polished to a surface roughness Ra of 2 to 4 μm by electrical discharge machining,
After annealing, surface roughness R is improved by electrical discharge machining of skin bath rolling.
A method for producing a cold-rolled steel sheet with excellent coating clarity and press workability, characterized in that the method is carried out using a roll that has been satin-finished to a = 1 to 3 μm. (2) 5 to 20 μm after skin bath rolling and satin finishing
A method for manufacturing a cold-rolled steel sheet with excellent coating clarity and press workability as claimed in claim 1, which is carried out using a roll plated with a hard metal of 500 m.