JPH0214122B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a ferritic stainless thin steel sheet with excellent workability. In Japanese Patent Application No. 57-146828, the inventor discovered that workability could be improved by cold rolling with work rolls with a roll diameter of 150 mm or more; however, when rolling with such large diameter rolls, Compared to rolling with small diameter rolls, it is difficult to roll a thin gauge, and defects such as surface flaws are more likely to occur. The present invention improves workability through large-diameter roll rolling,
As a result of various studies on methods that could simultaneously roll a thin gauge using small-diameter roll rolling such as a Sendzimier rolling mill and improve the surface quality, we found that at least 60% of the reduction amount to be cold rolled in the first stage of the cold rolling process was reduced to 150 mm. By rolling with larger diameter rolls of 150 mm or more, it is possible to give almost the same workability as rolling with large diameter rolls of 150 mm or more, and then roll the remaining reduction with small diameter rolls. It was discovered that by doing so, a steel plate that is more beautiful and thinner than when the surface of the steel plate is rolled using large-diameter rolls throughout the process has been completed, and the present invention has been completed. In addition, if the entire process is rolled with small diameter rolls, the r value, which is an index of workability, decreases;
Furthermore, defects called sparkling defects caused by overlapping of the surface layers of steel sheets may occur, but by performing the combination cold rolling as in the present invention, not only the r value improves, but also the occurrence of sparkling defects can be prevented. It disappears. The reason why sparkling defects do not occur when rolling the first stage with large-diameter rolls is that when the roll diameter is large, the shearing force acting on the sheet surface is reduced, so the uneven parts on the surface of the steel sheet are less likely to slip and overlap. It's for a reason. When the cold rolling progresses to a certain extent, the surface layer becomes work hardened, so it is then rolled with small diameter rolls, and the shear stress of the surface layer no longer overlaps, and no sparkling defects occur. That is,
In the case of rolling using only large diameter rolls with a roll diameter of 150 mm or more, the roughness that exists on the surface of the steel sheet before cold rolling becomes shallower as the rolling progresses, but when rolling only with small diameter rolls of 150 mm or less, In comparison, the shearing force on the surface of the steel sheet is small, so the unevenness on the surface of the steel sheet does not completely disappear even after rolling to the final product, and as the cold rolling progresses, the surface texture is improved by the lubricating oil that accumulates in the recesses. This results in significant damage and makes it difficult to create a beautiful surface. This tendency is particularly strong when the roll diameter exceeds 450 mm. In addition, when rolling with only small diameter rolls with a roll diameter of less than 150 mm, the shear force on the steel plate surface is greater than when rolling with large diameter rolls, so the unevenness that exists on the steel plate surface before cold rolling becomes shallower as the rolling progresses. This results in a beautiful surface, but as described above, the convex portions tend to slip and overlap, resulting in so-called glittering scratches. In the case of regular ferritic stainless steel sheets that are rolled using only small-diameter rolls, in order to prevent the occurrence of these glittering scratches, it is necessary to remove the irregularities that exist on the surface of the steel sheet by grinding it with a grinder or the like beforehand. However, in the present invention, the large-diameter roll is used in the first stage to perform efficient rolling and to push out the concave part to make it shallower, so the phenomenon of overlapping of the convex part by the next small-diameter roll does not occur, and cold rolling is improved. A beautiful surface can be obtained without the need for a previous grinding process. As a specific application method for such cold rolling, for example, firstly, a tandem cold rolling mill with a relatively large work roll diameter, which is used exclusively for cold rolling of ordinary steel, is used to first reduce the cold rolling by 60% or more. There is a method of rolling and then cold rolling in a Sendzimier rolling mill with a small roll diameter. That is, a tandem cold rolling mill with large diameter rolls used exclusively for ordinary steel uses the same cold rolling oil as ordinary steel, and the rolling speed is
Cold rolling ferritic stainless steel, which is the steel type covered by the present invention, at a high speed of 1000 m/min or more requires a roll diameter that is larger than cold rolling in a rolling mill with small diameter rolls such as a Sendzimier rolling mill. This method is economically advantageous because it not only improves workability but also has extremely high productivity.
However, rolling with large diameter rolls alone does not necessarily provide a stainless steel sheet with good surface quality. Therefore, if a light reduction of 40% or less is performed on a Sendzimir rolling mill exclusively for stainless steel after large-diameter roll rolling, a beautiful surface equivalent to that achieved when the entire reduction is rolled on a Sendzimir rolling mill without deteriorating workability. It is also possible to prevent the occurrence of sparkling defects that tend to occur when rolling with only small diameter rolls. Furthermore, as a method of applying the present invention, a tandem cold rolling mill having a group of small diameter work rolls in the rear stage, a cluster rolling mill or a Sendzimier rolling mill in which the work rolls can be easily replaced during rolling are used. You may. The reason why the use of large diameter rolls in the present invention improves workability, especially the r value, is that the texture, especially the r value, improves (222)
This is because the polar density increases and the (200) polar density decreases which degrades the r value. The effect of improving the r value by changing the texture in this way is more effective as the roll diameter increases, but the reason why the lower limit of the work roll diameter is set to 150 mm in the present invention is that even if the roll diameter is less than 150 mm, The larger the value, the more effective it is to improve the r value, but the effect is less than when rolling with a diameter of 150 mm or more, and a roll diameter of less than 150 mm is not preferable from the viewpoint of improving productivity, so the roll diameter was set to 150 mm or more.
Also, the rolling amount to be rolled with large diameter rolls is 60% of the total rolling amount.
% or more is because the r value increases as the rolling ratio with large diameter rolls increases, but if the rolling ratio is 60% or more, it is almost as high as when rolling with 100% large diameter rolls. This is due to the fact that the r value can be obtained. Note that if rolling is performed 100% with large-diameter rolls, a good surface quality of the steel plate cannot be obtained, so in order to obtain surface gloss, the present invention requires a combination with small-diameter rolls, and the rolling reduction amount is Good results can be obtained with a concentration of about 1%. The present invention will be described in detail below with reference to Examples. A 3.7 mm thick hot rolled sheet consisting of 0.05% C, 16.5% Cr and other unavoidable impurities, and the balance Fe was heat treated at 840℃ for 4 hours, and the unheated one was pickled.
Cold rolling mill with 150mmφ work rolls and
Using a cold rolling mill with a 60mmφ work roll, cold rolling was performed using the method shown in Table 1 to determine the thickness.
It was made into a cold rolled sheet of 0.7 mm. Then, annealing was performed at 840°C for 2 minutes and the r value was measured. Figure 1 shows the relationship between the r value and cold rolling conditions. In the case of a process that involves hot-rolled sheet annealing, by setting the rolling ratio by large-diameter rolls to 60% or more, the total rolling amount can be reduced by the large-diameter rolls. It can be seen that almost the same r value as in the case of rolling was obtained. When hot rolled sheets are cold rolled without annealing, if approximately 60% of the total rolling amount is rolled with large diameter rolls, the r value will be slightly lower than when the entire rolling amount is rolled with large diameter rolls. It can be seen that the r value is greatly improved when compared with the case where the entire rolling amount is rolled with small diameter rolls, and the r value in the rolling direction of 45° C. is improved. Furthermore, the values obtained by rolling a steel plate subjected to hot-rolled plate annealing using the conventional method using only small-diameter rolls and the values obtained by rolling a steel plate without hot-rolled plate annealing using the method of the present invention are approximately the same. Although they are the same, it can be seen from this that the method of the present invention is a powerful elemental technology for realizing a process of omitting hot-rolled sheet annealing. Furthermore, compared to rolling with only large-diameter rolls, adding rolling with small-diameter rolls according to the method of the present invention provides the same beautiful surface texture as when rolling the entire rolling amount with only small-diameter rolls. It was done.

【table】

[Table] As described above, in the present invention, by rolling by combining rolls with different diameters during cold rolling,
This makes it possible to manufacture thin ferritic stainless steel sheets with excellent workability and surface quality with high efficiency and at low cost, using a process-saving process in which hot-rolled sheets are immediately descaled and cold-rolled. It is also possible to impart workability on the same level as the conventional process of annealing a hot rolled sheet and then cold rolling it to produce a thin steel sheet.

[Brief explanation of drawings]

Figure 1 a and b show the relationship between the r value and the rolling ratio with large diameter rolls, where a is a process with hot rolled sheet annealing (large diameter roll 150 mm, small diameter roll 60 mm);
b is a process without hot-rolled plate annealing (large roll diameter 150 mm,
The diameter of the small roll is 60mm). In the figure, L: r value in the direction parallel to the rolling direction, D: r value in the direction 45° to the rolling direction, C: r value in the direction perpendicular to the rolling direction,
r=L+2D+C/4.

Claims (1)

[Scope of Claims] 1. In a method for manufacturing a ferritic stainless thin steel sheet in which a hot rolled sheet is made to its final thickness in one cold rolling process without intermediate annealing, a large diameter steel sheet is A work roll is used in the latter stage, and a work roll with a smaller diameter than that in the earlier stage is used, and in the first stage of the cold rolling process, the work roll diameter is 150 mm or more, and further,
The cumulative reduction amount in the first stage of cold rolling is calculated as the total reduction amount.
A method for manufacturing a ferritic stainless thin steel sheet with excellent surface quality and workability, characterized by a 60% or more. 2. A ferritic stainless steel thin sheet with excellent surface texture and workability as claimed in claim 1, wherein the hot-rolled sheet supplied to the cold rolling process is obtained by omitting hot-rolled sheet annealing after hot rolling. Manufacturing method of steel plate.