JP2000271608A - Hot-rolling method of ferritic stainless steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ferritic stainless steel sheet improving the ridging resistance and having the quality of good sheet crown and shape by applying at least one time of continuous rolling of a width rolling having a specified sheet width rolling reduction ratio and a horizontal rolling having a specified sheet thickness rolling reduction ratio in the range of obtaining a prescribed sheet thickness at the rougher-rolling time. SOLUTION: In the rougher-rolling, firstly, the sheet crown of the sheet bar is reduced by applying >=2% sheet width rolling reduction ratio. Then, since the sheet width is thickened near the sheet edge parts of the sheet bar after width-rolling, at least one time pass in this rolling is executed at >=40% rolling reduction ratio. As a result, the ridging resistance can be improved. In such a case, the width-rolling and the rolling having large rolling reduction ratio are successively executed. After executing a butt welding to the sheet bars after rougher-rolling, the sheet crown at the finish last stand indicates the low value, such as about 30 μm by using the finish-rolling mill and applying the continuous hot-rolling, and the steel sheet excellent in drawing, etc., is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hot rolling a ferritic stainless steel sheet having excellent workability, especially ridging resistance, and having a high quality crown shape.

[0002]

2. Description of the Related Art Ferritic stainless steel sheets have excellent corrosion resistance even in various corrosive environments, and are inexpensive because they do not contain nickel. Therefore, they are widely used in building materials, kitchen materials, electric parts materials and the like. It is used.
However, when the ferritic stainless steel sheet is subjected to drawing processing, wrinkling defects called irregular ridges in the rolling direction, which are called ridging, tend to occur. Ridging not only impairs the aesthetics of the product but also increases the load on the polishing operation. Therefore, it has been a major problem in the manufacture of ferritic stainless steel sheets to suppress the occurrence of ridging, since it has been a problem.

As means for suppressing the occurrence of ridging, for example, Japanese Patent Application Laid-Open No. Hei 7-127657 discloses that the total rolling reduction in the final pass of rough rolling and the pass before it is 70%. Japanese Patent No. 268461 discloses that at least one pass rolling is performed at a rolling reduction of 40 to 75% in rough rolling and at least one rolling is performed at a rolling reduction of 20 to 45% in finish rolling. It is considered that increasing the rolling reduction per pass in this manner makes the crystal grains finer and suppresses the occurrence of ridging.

Incidentally, in finish rolling, it is necessary to satisfy not only quality standards in terms of the quality of steel sheets but also quality standards in terms of dimensions. One of the dimensional quality standards is a sheet thickness distribution in the sheet width direction called a sheet crown. It goes without saying that a flat steel sheet is required after the rolling, but a flat shape is desirable in order to stably pass the steel sheet in the rolling operation.

In the finishing mill, in order to achieve the target value of the sheet crown and to make the sheet shape flat, a crown shape control actuator such as a roll bender, a roll shift, and a roll cloth is set to an optimum value.
The plate crown Cr is defined by equation (1). Cr = hc-he (1) where hc is the thickness at the center of the plate, and he is the thickness at the crown quality evaluation point which is usually several tens of mm inside from the end of the plate.

[0006] strip crown Cr _i in the finish rolling mill is defined by equation (2). _{Cr i = α i × Crm i} + β i × Cr i-1 ··· (2) where Crm the roll crown under load obtained from the roll deformation due to the rolling load or actuator, alpha load on the side plate crown out is Is the coefficient of influence of the roll crown, β is the coefficient of influence of the entrance side sheet crown on the exit side sheet crown, and the subscript i is the stand number.

Plate shape (steepness) λ in finishing mill
_i is defined by equation (3). The λ _i = 2 / π _{[ξ i (Cr i / hc i} -Cr i-1 / hc i-1) ] ^1/2 (3) where xi] is a shape change factor. It is not always necessary to calculate the shape using the crown at the same position as the quality evaluation point of the crown.

An optimum actuator value is set using the above equations. By the way, when the rolling reduction is increased in the rough rolling, the rolling load increases, and the deflection and flatness of the work rolls increase, so that the sheet bar of the rolled sheet bar increases. FIG. 9 shows the sheet profile of the sheet bar when rolling is performed at a rolling reduction of 50% in the final pass of the rough rolling. 300μ sheet bar crown
It is a large value of m or more. When the sheet crown of the sheet bar is large, the shape between the stands tends to be stretched in the finish rolling. In order to flatten the shape between the stands for stable threading, the sheet crown on the exit side of the finishing rolling mill must be enlarged, so that the target value of the sheet crown cannot be achieved and the stand The shape between them cannot be flattened. Therefore, in the prior art, it was not possible to simply achieve excellent ridging resistance, but at the same time, it was not possible to achieve the target values of the sheet crown and the sheet shape.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems and to provide a ferritic stainless steel sheet having excellent ridging resistance so that the quality of the sheet crown and the shape can be kept good. The purpose is to realize a rolling method.

[0010]

Means for Solving the Problems The present invention relates to hot rolling of a ferritic stainless steel sheet, which is carried out by rough rolling in a range of a width reduction of 2% or more within a range where a required width can be obtained. A hot rolling method of a ferritic stainless steel sheet excellent in ridging resistance, characterized in that continuous rolling including horizontal rolling with a thickness reduction of 40% or more is performed at least once, or a ferritic stainless steel sheet is used. In hot rolling, continuous rolling consisting of width rolling at a rolling reduction of 2% or more and horizontal rolling at a rolling reduction of 40% or more is performed at least once in rough rolling within a range where a required strip width is obtained. The heat of a ferritic stainless steel sheet excellent in ridging resistance, characterized in that the sheet bar rolled by the rough rolling is butt-joined and then rolled by a finish rolling mill. Rolling method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Using a 6-stand finishing mill, a finished sheet thickness of 3.0 m was obtained according to the rolling schedule shown in Table 1.
m, a ferrite stainless steel sheet with a sheet width of 1000 mm is rolled. At this time, the influence of the sheet bar sheet crown on the sheet crown and the shape between the stands in the finish rolling is given by the equations (2) and (3). Calculated. The results are shown in FIGS. FIG. 1 shows that the sheet crown of the seat bar is 0,
In the three cases of 150 and 300 μm, the effect of the plate crown between stands and the steepness when the target value was achieved with the target plate crown value of the final stand of the finish rolling mill set to 50 μm was shown. ] Indicates that the plate shape is elongated, while [-] indicates that the belly is elongated. The permissible range of the steepness is set so that the ear is slightly elongated in the later stage in consideration of the stability of the threading. The plate crown is 25 from the plate edge.
The position of mm was used as the quality evaluation point and the position of the shape was 100 mm from the edge of the plate. When the sheet crown of the sheet bar is 150 μm, the shape between stands is almost equal to the lower limit of the shape. When the sheet crown of the seat bar is 300 μm, the shape between the stands becomes abdominal extension and cannot be within the allowable range.

[0012]

[Table 1]

FIG. 2 shows the sheet crown of the seat bar.
It shows the influence of the plate crown between stands and the steepness when the shape (steepness) between stands is within an allowable value for three cases of 0, 150, and 300 μm. Also in this case, if the sheet crown of the seat bar is 300 μm, the sheet crown of the final finishing stand is 90 μm, so that the target value of 50 μm cannot be achieved.

From the above findings, in order to achieve the target value of the sheet crown of the final finishing stand and to keep the shape between stands within an allowable range, the sheet crown of the seat bar must be at least 150 μm or less. Therefore, the width rolling was performed before the final pass of the rough rolling, and the rough final pass was rolled at a rolling reduction of 50%. Width reduction rate is 4% under high pressure, 2 under low pressure
%.

The width fluctuation due to the difference in width reduction was eliminated by width control means of a finishing mill such as an edger of the finishing stand or a change in tension between the finishing stands. FIG. 3 shows the sheet profile of the sheet bar after width rolling, and FIG. 4 shows the sheet profile of the sheet bar after the final pass of rough rolling. After width rolling, the thickness of the sheet bar near the plate edge increases,
Even when rolling is performed at a large rolling reduction of 50% in the final rolling pass, the sheet bar crown of the rolled sheet bar is almost zero when the width is high.
μm, and about 150 μm under low pressure. Therefore, the width reduction performed before the rough rolling pass of the large reduction is 2%.
% Is effective.

It has been separately confirmed that the crown reduction effect in the large rolling cannot be obtained unless the width rolling and the large rolling are performed continuously. In each of the four levels of rough rolling schedules shown in Table 1, the sheet crown of the sheet bar was changed between when the width rolling was performed at a width reduction rate of 2% before the pass at a reduction rate of 40% or more and when the width rolling was not performed. It was measured.

After finish rolling according to the finish rolling schedule shown in Table 2, ridging resistance was evaluated. Table 3 shows the measurement results of the width reduction ratio, the sheet crown of the sheet bar, and the evaluation based on the ridging index for each of the four rough rolling schedules shown in Table 1. The ridging index is based on JIS
Evaluation was made based on the grade of wrinkle occurrence when a 20% tensile strain was applied to the No. 5 test piece (n = 5). If the roughness is equivalent to 10 μm), the ridging resistance is excellent, and if it is 1.5 or less, there is almost no ridging problem even in particularly severe drawing.

[0018]

[Table 2]

[0019]

[Table 3]

The width of the sheet crown of the sheet bar can be reduced by performing the width rolling before the pass at the rough reduction of 40%. Therefore, if the evaluation criteria of the ridging index is 1.5 or less, pass at least one pass of rough rolling to obtain a ferritic stainless steel sheet with excellent ridging resistance.
The rolling may be performed at a rolling reduction of 40% or more.

[0021]

[Example 1] Using a 6-stand finishing mill, a finished plate thickness of 3.0 m was obtained by the conventional method and the method of the present invention.
ferrite stainless steel sheet (SUS)
430) was hot rolled.

The rolling schedule of the rough rolling is shown in case 1 in Table 1.
The finish rolling schedule is shown in Table 2.
In the conventional method, the width reduction is not performed before the coarse final pass (the seventh pass, the reduction ratio is 50%), and in the method of the present invention, the width reduction ratio is 2 before the coarse final pass.
% Width reduction was performed. FIG. 5 shows the relationship between the target crown value and the actually measured value in each of the conventional method and the method of the present invention. In the conventional method, the actually measured value of the plate crown of the final finishing stand is larger than the target and is 60 to 90 μm. On the other hand, in the method of the present invention, the actually measured value of the plate crown of the final finishing stand is almost as desired. FIG. 6 shows the relationship between the r value (Rankford value) of these materials and the ridging index. The processing characteristics such as drawing of the steel sheet rolled by the method of the present invention are almost the same as those of the conventional material.

[Example 2] The sheet bar after the rough rolling was butt-welded, and the finished plate thickness was 3.0 mm and the width was 1000 mm by the conventional method and the present invention using a 6-stand finishing rolling mill.
mm stainless steel (SUS430) was continuously hot-rolled. The rolling schedule for rough rolling is shown in Table 1
The schedule of se1 and finish rolling is shown in Table 2. In the conventional method, width reduction was not performed before the coarse final pass (7th pass, reduction rate 50%). A width reduction was performed at 2%.

FIG. 7 shows the relationship between the target value of the crown and the measured value in the conventional method and the method of the present invention. In the conventional method, the actual measured value of the crown of the final finishing stand is the target 30 μm.
55 to 80 μm. On the other hand, in the method of the present invention, the actually measured value of the plate crown of the final finishing stand is almost the target value of 30 μm. FIG. 8 shows the relationship between the r value (Rankford value) of these materials and the ridging index. The processing characteristics such as drawing of the steel sheet rolled by the method of the present invention are almost the same as those of the conventional material.

[0025]

According to the present invention, there is an excellent effect that a ferritic stainless steel sheet having excellent ridging resistance and a high quality shape can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of a sheet crown of a sheet bar on a sheet crown and steepness in a finish rolling mill in the present invention.

FIG. 2 is a graph showing an influence of a sheet crown of a sheet bar on a sheet crown and steepness in a finish rolling mill according to the present invention.

FIG. 3 is a graph showing sheet profiles after width rolling in rough rolling according to the conventional method and the method of the present invention.

FIG. 4 is a graph showing a sheet profile after a final pass in rough rolling by the conventional method and the method of the present invention.

FIG. 5 is a graph showing a relationship between a target value and a measured value of a sheet crown according to the conventional method and the method of the present invention in the first embodiment.

FIG. 6 is a graph showing the relationship between the r value and the ridging index of the material according to the conventional method and the method according to the present invention in the first embodiment.

FIG. 7 is a graph showing a relationship between a target value and a measured value of a sheet crown according to a conventional method and the method of the present invention in the second embodiment.

FIG. 8 is a graph showing the relationship between the r value and the ridging index of a material according to the conventional method and the method according to the present invention in the second embodiment.

FIG. 9 is a graph showing a sheet profile of a sheet bar according to the related art.

Continuing from the front page (72) Inventor Masanori Kitahama 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Pref. Kawasaki Steel Engineering Co., Ltd. (72) Inventor Shinzo Uchimaki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Pref. F term in Chiba Works, Ltd. (reference) 4E002 AA07 AD03 BA01 BB01 BC01 BC05 CB03

Claims (2)

[Claims] In hot rolling of a ferritic stainless steel sheet, width rolling with a sheet width reduction of 2% or more and sheet thickness reduction of 40% or less in a rough rolling range within a range where a required sheet width can be obtained.
% Hot rolling of a ferritic stainless steel sheet excellent in ridging resistance, wherein continuous rolling comprising horizontal rolling of at least 1% is performed at least once. 2. In hot rolling of a ferritic stainless steel sheet, width rolling with a sheet width reduction of 2% or more and sheet thickness reduction of 40% or less in a rough rolling range within a range where a required sheet width is obtained.
% Of at least 1% of continuous rolling consisting of horizontal rolling at a rate of not less than 1%, and furthermore, the sheet bars rolled by the rough rolling are butt-joined to each other and then rolled by a finish rolling mill. Hot rolling method for ferritic stainless steel sheet.