KR100362666B1 - Manufacturing Method of High Sensitivity Steel Sheet - Google Patents

Abstract

The present invention relates to the production of a steel sheet used as an outer plate material for automobiles, electronic devices and the like, the object of which is to provide a steel sheet that improves the selectivity after coating.

According to the present invention, cold rolling is performed by setting at least one roll that is discharge-processed in the range of 2.0-2.2 μm of the upper roll and 1.8-2.0 μm of the lower roll by setting to the capacity (-) processing mode, and impulse A high line comprising the step of performing temper rolling by providing at least one roll that has been discharged in the range of 1.9-2.1 μm of the upper roll and 1.7-1.9 μm of the lower roll by setting it to the positive processing mode. The technical gist of the manufacturing method of a spiritual steel plate is taken.

Description

Manufacturing Method of High Sensitivity Steel Sheet

The present invention relates to the production of a steel sheet used as an outer plate material for automobiles, electronic devices, and the like, and more particularly, to a method for producing a steel sheet which improves the post-painting selectivity.

Usually, the cold rolled steel plate or plated steel sheet used in the outer plate material of automobiles or electronic devices is used through the whole coating. In general, the coating of such an outer plate material is to form a coating layer having a thickness of about 100㎛ through three steps, such as electrodeposition coating, intermediate and top coat, and the surface quality after coating determines the final quality of the material. For this reason, the focus has been on improving the quality of the final product through the improvement of the coating technology rather than the quality of the steel sheet surface. However, it is known that 20-30% of the final surface quality of the steel sheet determines the surface quality of the steel sheet before coating, that is, the image clarity of the steel sheet.

Assuming that the coating conditions are the same, the factors of the steel plate surface on the stiffness after coating are waviness curve average (hereinafter, also referred to as Wca), roughness average (hereinafter, referred to as `Wca '). Ra '), peak per inch (hereinafter referred to as PPI), and maximum roughness (also referred to as Rmax). Such an influence factor may remain after coating when the coating thickness is thin, which may affect the sensibility after coating.However, in the case of automotive steel sheets having a coating thickness of about 100 μm, the coating film is subjected to electrodeposition, middle and top coats. It has been evaluated to have a negligible effect on the screening performance after coating due to offset in thickness. That is, as shown in Figure 1, the main factor that affects the selectivity after coating, the coating layer (wave) after the coating of the wave of the steel sheet 1 according to the roll roughness in the 0.8-8mm measurement section affecting the long wavelength roughness (Wca) It is necessary to make the wave as low as possible since the wave remains on the surface of 2) as it will adversely affect the surface selectivity of the steel sheet even after painting.

As such, the surface quality of the steel sheet is represented by the surface roughness, and the surface roughness is mostly controlled in the rolling step. The cold rolled steel sheet is produced through a cold rolling step and a temper rolling step. After rolling to a desired thickness in the cold rolling step, a roughness of about 0.6-2.0 μm is given in the temper rolling step. At this time, the surface roughness of the steel sheet is obtained by transferring the roughness applied to the roll to the steel sheet through rolling, and the degree to which the roll is transferred depends on the rolling conditions, the tension applied to the steel sheet, and the process conditions such as whether rolling oil is used.

As a method of imparting surface roughness to a rolling roll, shot blast processing and electro discharged texturing are mainly used. The shot blasting method is a method in which fine metal powder is sprayed on the processed roll surface to give the surface roughness of the roll. In the discharge processing method, the surface of the processed roll surface is sparked through electric discharge by adjusting the distance between the electrode and the roll surface. How to process. In general, the electric discharge machining method is classified into an impulse mode and a capacity mode according to an energization method and a polarity between the electrode and the roll. The impulse mode is a method of processing roughness of a roll by flowing a high current for a short time, and impulse (+) mode and impulse (-), respectively, depending on whether it is given a (+) polarity or a (-) polarity to the roll to be processed. Subdivided into modes. In addition, the capacity mode is a method of processing the roughness of the roll by flowing a low current for a long time, and is divided into a capacity (+) mode and a capacity (-) mode like the impulse method.

On the other hand, as a method for producing a high-definition steel sheet by providing a roughness to the roll surface, so far known as Japanese Patent Laid-Open No. 59-34441, the average surface roughness (Ra) of the roll during temper rolling and per inch There is a method of improving glossiness and workability by controlling the peak number (PPI) in a relationship of PPI ≧ 290-30Ra. According to this method, however, most of the roughness is formed in the temper rolling step, but since Ra and PPI are all canceled by the coating layer after coating, it cannot have a great influence on the post-painting selectivity.

In addition, Korean Patent Laid-Open Publication No. 97-33124 proposes a method of improving the sensibility by applying an electric discharge processing roll to a cold rolling roll or a rough rolling roll. The method is cold rolled by a cold rolled roll processed such that the long wavelength roughness (Wca) of the roll surface is Wca < 0.3 Ra + 0.085, and then the average dispersion slope (Δa) of the pitch of the roll surface is? It is a method of rough rolling by a rough rolling roll processed to be 25.9. However, since the method does not consider the influence on the appropriate roll roughness level and the roll use length, there is a disadvantage in that it is not possible to secure stable post-painting performance over the entire length of the strip.

As another example, Korean Patent Laid-Open Publication No. 98-48456 also discloses a manufacturing method based on the relationship between the long wavelength roughness (Wca) of a cold rolled roll and the long wavelength roughness (Wca) of a rough rolled roll. However, the processing method for the cold rolled roll and the temper rolled roll or the respective roll roughness ranges are not set correctly, and there is a disadvantage in that the seonseong after the painting work is not secured in actual application.

Therefore, the present invention is to solve the above-mentioned problems, the method of manufacturing a steel sheet that can greatly improve the stiffness by controlling the long wavelength roughness of the steel sheet having the greatest effect on the stiffness after coating in cold rolling step and temper rolling step The purpose is to provide.

1 is a schematic view of a steel sheet with a coating layer formed

Figure 2 is a graph showing the roughness of the steel sheet when the shot blasting roll and the electric discharge roll are applied during temper rolling

Figure 3 is a graph showing the surface roughness change according to the roll use distance of the present invention and the comparative method

Figure 4 is a graph showing the long wavelength roughness change according to the roll use distance of the present invention and the comparative method

Figure 5 is a graph showing the change in seonseong index after painting the roll using distance of the present invention and the comparative method

Description of the main parts of the drawing

1 ... steel sheet 2 ... paint layer

In the present invention for achieving the above object in the manufacturing method of the steel sheet manufactured through cold rolling and temper rolling,

The cold rolling is performed in the capacity (-) processing mode by providing at least one roll that has been discharge-processed in the range of 2.0-2.2 μm of the upper roll and 1.8-2.0 μm of the lower roll, and

The temper rolling comprises setting at least one roll that has been discharge-processed in the range of 1.9-2.1 μm of the upper roll and 1.7-1.9 μm of the lower roll to set the impulse (+) processing mode. It relates to a method for producing a high sensitized steel sheet.

Hereinafter, the present invention will be described in detail.

The sensibility of the steel sheet is a case where the value of the distantity index (hereinafter, also referred to as 'DOI') is 90 or more. The DOI value is measured by subtracting the intensity of specular light when the standard light source is irradiated with an angle of incidence of 60 degrees and the intensity of scattered light whose reflection angle deviates by 0.3 degrees from the specular light. At this time, when there is no scattered light, the theoretically has a maximum DOI value of 100. Generally, high-strength steel sheet refers to a steel sheet having a DOI value of 90 or more. In order to satisfy this value, the long wavelength roughness (Wca) value of the steel sheet surface must be controlled to 0.6 µm or less, but it is stable in consideration of variations such as unevenness of coating conditions. In order to secure the sensitization index, it is preferable to manage it to 0.5㎛ or less.

In the case of the present invention, in order to manage the Wca value to be 0.5 μm or less, it is necessary to apply the discharge processing roll having good uniformity and periodicity of roughness to both the cold rolling step and the temper rolling step.

Specifically, in the case of the present invention, at least one discharge processing roll is applied in the cold rolling step, and when the cold rolling roll is discharged, the processing mode is a capacity (-) mode in which low current is flowed for a long time to process the roughness of the roll. It is preferable to. Compared to other modes, the number of surface roughness peaks is smaller and the surface roughness has the highest transfer rate transferred to the steel sheet, so that the initial roughness of the roll surface can be lowered. At this time, in order to maintain the initial long-wavelength roughness value Wca of the cold rolled roll below 0.5 μm, the upper roll needs to be processed in the range of 2.0-2.2 μm and the lower roll in the range of 1.8-2.0 μm. The initial roughness of the roll surface for such a cold rolled roll is about 0.3 ㎛ lower than the conventional.

In addition, electric discharge processing rolls are also applied in the temper rolling stage. At this time, the Wca value, which has the greatest effect on the sensibility after coating, is mostly determined in the cold rolling stage. It is more preferable to use impulse (+) processing mode which looks uniform. That is, the temper rolls are processed in an impulse (+) mode to process the roughness of the roll by flowing a high current for a short time, but when the initial roughness of the surface of the roll is less than about 0.2 μm than the conventional one, The target Wca value can be made 0.50 m or less. At this time, the upper roll is required to be processed in the range of 1.9-2,1㎛, the lower roll 1.7-1.9㎛.

When the roughness of the cold rolled roll and the rough rolled roll is lower than the above range, the selectivity can be improved after coating, but it is not preferable because workability such as shortening of the roll service life due to premature wear of the roll is lowered.

In addition, the initial roughness values of the roll surfaces of the upper and lower rolls of both the cold rolled roll and the temper rolled roll are different in order to maintain the initial roughness value of the roll surface transferred to the steel sheet uniformly. That is, in the case of the upper roll, the roughness transfer rate is lower than that of the lower roll, so in the case of the upper roll, a relatively high initial roughness value may be set to secure the same roughness level in the steel sheet. The reason why the upper roll has a lower roughness transfer rate than the lower roll is that relatively many rolling oils and the like come into contact with the upper roll.

Thus, when the conditions of the present invention are satisfied, a stable value of Wca of the steel sheet with respect to the total roll length can be ensured at 0.50 µm, and a DOI value of the goodness index after coating is also 90 or more.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

Comparative Example (1) (2)

In the cold rolling step, rolls processed by shot blast are applied, and the correlation between Ra value and Wca value when shot blasting roll and discharge processing roll are applied in temper rolling step is shown in Table 1 and FIG. .

division Ra 0.7 0.8 0.9 1.0 1.1 1.2 1.3 Remarks Comparative Example 1 Wca 0.60 0.70 0.77 0.80 0.81 0.91 0.99 Using shot blast rolled temper rolls Comparative Example 2 0.50 0.51 0.53 0.60 0.62 0.69 0.76 Use of electric rolling mill roll

As shown in Table 1 and Figure 2, when the roll discharged at the same surface roughness (Ra) level, the Wca value is 0.1-0.3 μm lower than that of the shot blasted roll, and the Ra value It can be seen that the change in the Wca value for is more sensitively affected.

In addition, as in Comparative Example (2), even when the discharge processing roll is used in the temper rolling step, when the shot blasting roll is used in the cold rolling step, the Wca value does not satisfy the quality target level of 0.50 μm or less when the roughness level is 0.9 μm or more. It can be seen that the application of the electric discharge roll in the cold rolling step is essential.

Comparative Example (3) and Inventive Example

Working conditions as shown in Table 2 were applied to the cold rolling stage and the temper rolling stage to compare and analyze the quality levels. Comparative Example 3 was cold-rolled by applying only the roll processed by the shot blast (SB) so that the roughness of the upper roll is 2.5㎛, 2.3㎛, the surface roughness of the upper roll in the temper rolling step 2.3 It is a case where temper rolling is carried out using the shot-blasted roll so that the roughness of the bottom roll may be 2.1 micrometer.

On the other hand, in the case of the present invention, the EDM roll is applied to the cold rolling step, but the upper roll uses the roughness of 2.2 μm, the lower roll uses the roughness of 2.0 μm, and also in the temper rolling step. The electric discharge machining roll was applied, but the upper roll applied the roll processed to 2.1 μm, and the lower roll applied the roughness to 1.9 μm.

division Comparative Example 3 Inventive Example Cold Rolling Roll Temper Roll Cold Rolling Roll Temper Roll Roll processing method SB SB EDT EDT Roll Roughness (Top / Bottom) 2.5 / 2.3 2.3 / 2.1 2.2 / 2.0 2.1 / 1.9

Roll the steel sheet by the length of steel sheet about 215km by applying each roll processed under these conditions, and observe the surface roughness (Ra), the long wavelength roughness (Wca), and the degree of stiffness of each roll. 3 and 3 to 5 are shown.

Roll length (km) Conventional Invention Ra (μm) Wca (μm) DOI Sunyoung Sung Ra (μm) Wca (μm) DOI Sunyoung Sung 29 1.083 0.60 0.930 0.47 44 1.069 0.70 0.765 0.33 93.1 ○ 53 0.720 0.80 84.0 X 0.971 0.40 90.8 ○ 65 0.968 0.57 89.0 X 0.770 0.40 75 0.964 0.63 0.817 0.40 92.0 ○ 116 0.891 0.63 0.54 0.43 150 0.943 0.63 0.540 0.40 175 0.834 0.80 60.2 X 0.700 0.43 199 0.851 0.70 71.9 X 0.550 0.30 92.5 ○ medium 0.96 0.65 79.82 0.81 0.43 92.4 Minimum value 0.72 0.57 60.2 0.54 0.3 90.5 Value 1.205 0.8 89.2 1.23 0.5 93.1

As shown in Table 3 and Figure 4, in the case of Comparative Example 3 using a conventional shot blasting roll, the Wca value, which is a quality target level, is 0.57-0.80 µm, and it is difficult to secure 0.50 µm or less. I could see that. Therefore, as shown in Fig. 5, the DOI value, which is the post-painting goodness index, also could not secure a quality target level of 90 or more.

On the other hand, in the working condition of the present invention, the Wca value, which is the quality target level, is 0.30-0.50㎛, and can be secured to 0.50㎛ or less, and the DOI value, which is a goodness index after coating, is stable at 90 or more quality target level. Could be secured.

This is because the discharge processing roll has a uniform surface roughness and good periodicity compared to the shot blastroll. As a result, it was found that the application of the electric discharge processing roll was more effective in both the cold rolling step and the temper rolling step.

As described above, according to the present invention, unlike the case where the conventional shot blasting roll is applied, the Wca value of the steel sheet can be managed to 0.50 µm or less at the entire roll length, so that the DOI value, which is the selectivity index, is 90. Since the above can be ensured, there is an effect that can produce a steel sheet excellent in the good screenability after coating.

Claims (1)

In the manufacturing method of the steel sheet manufactured by cold rolling and temper rolling, The cold rolling is performed in the capacity (-) processing mode by providing at least one roll that has been discharge-processed in the range of 2.0-2.2 μm of the upper roll and 1.8-2.0 μm of the lower roll, and The temper rolling comprises setting at least one roll that has been discharge-processed in the range of 1.9-2.1 μm of the upper roll and 1.7-1.9 μm of the lower roll to set the impulse (+) processing mode. Method for producing high-strength steel sheet characterized in that