JPS63160704A - Manufacture of highly bright stainless steel strip - Google Patents

Abstract

PURPOSE:To obtain strips having the high brightness equal or more than the level by Sendzimir mill rolling by specifying the total draft and a draft of a 1st stand at the time of rolling a stainless steel strip. CONSTITUTION:At the time of rolling a stainless steel strip by a cold tandem rolling mill, a 1st stand work roll whose dia. is <=400 mmphi is used. Rolling is performed by the total draft being >=70% and the draft of the 1st stand being >=30%. Thus, highly bright stainless steel strips having a good brightness are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a stainless steel strip with high gloss by rolling a stainless steel strip in a cold tandem mill.

<Prior art> Conventionally, in the cold rolling of stainless steel strips, a diameter of 10
A stone-sendzimir rolling mill having a work roll with a small diameter of 0 φ or less was used. The reason for this is that the
As disclosed in No. 362, stainless steel has a high deformation resistance (and is severely work hardened, so it requires rolling under heavy reduction and high tension.

However, in recent years, tandem mills that press ordinary steel have been used to roll stainless steel strips using work rolls with a larger diameter than those used in Sendzimir mills.

The first reason is that by increasing the diameter of the work roll, a large amount of rolling oil is drawn between the work roll and the plate, making it difficult for the work roll and the plate to contact each other (which makes heat streaks occur). This is because rolling can be performed at a higher speed than in the Sendzimir mill.

The second reason is that tandem mills use rolling oil emulsion silane, most of which is water, so compared to when Sendzimir mills use rolling oil as is, the cooling capacity is significantly improved, which improves the cooling ability of rolls and steel strips. As a result of sufficient cooling, heat streaks are less likely to occur and high-speed rolling is possible.

The third reason is that in the case of the Sendzimir mill, the copper strip was rolled in reverse on one stand, which required a large amount of time to finish the steel strip to the specified thickness, but in the case of the tandem mill, many mills were used to roll the copper strip. To use the stand, 1
This is because it is possible to finish the steel strip to a predetermined thickness only by changing the direction, and the rolling time is significantly shortened.

In this way, when rolling a stainless steel strip with a tandem mill, compared to a Sendzimir mill, a larger diameter work roll is used and a rolling oil emulsion with a greater cooling capacity is used, resulting in a gap between the work roll and the plate. A large amount of rolling oil is drawn in, allowing high-speed rolling without heat streaks.

<Problems to be solved by the invention> However, as a large amount of this rolling oil is drawn in,
It becomes difficult for the work rolls to come into contact with the plate, and as a result, the surface roughness of the steel strip after rolling is less than that of the Sendzimir mill.
Because of this, tandem mill rolled stainless steel strip has always had the problem of being significantly inferior in luster compared to Sendzimir mill rolled material.

In addition, stainless steel products rolled with conventional tandem mills can only be used in areas where the appearance of gloss is not an issue at all. There was a desire for a method that could produce belts.

The present invention has been made in view of this situation, and an object of the present invention is to provide a manufacturing method that can significantly improve the surface gloss of a steel strip even when rolled using only a cold tandem mill.

<Means for Solving the Problems> The present invention provides a method for rolling a stainless steel strip using a cold tandem mill, with a total rolling reduction of 70% or more and a first stand rolling reduction of 30% or more. A method for manufacturing a high-gloss stainless steel strip, which is characterized by rolling the stainless steel strip using a cold tandem mill.
Using work rolls with flφ or less, the total rolling reduction was 7.
This is a method for producing a high-gloss stainless steel strip, which is characterized by rolling at a rolling reduction rate of 0% or more and a rolling reduction of 30% or more in the first stand.

For Kusaku The present invention will be explained in detail below.

After hot rolling, intermediate annealing and pickling are performed on the cold-rolled stainless steel base material. As a result of mechanical descaling during pickling, the surface roughness of the stainless steel base material is extremely rough with an average roughness Ra of 3 to 5 μm. For example, when a steel strip is rolled with a tandem mill with 5 stands, unlike when it is rolled with a Sendzimir mill, there are many large dents remaining from the base material on the surface of the steel strip after rolling, which causes a decrease in gloss. Was.

Therefore, in order to eliminate these large dents during rolling and make the steel strip surface as smooth as or better than the level of Sendzimir mill rolling, the total reduction rate during tandem mill rolling was increased compared to the conventional method, and rolling was performed using a 5-stand tandem mill. did. Figure 1 shows the results of rolling with the rolling reduction rates of each stand being distributed almost evenly, together with the conventional example.

In FIG. 1, the horizontal axis shows the total rolling reduction ratio, and the vertical axis shows the dent area ratio on the surface of the steel strip after rolling. Note that when magnifying the surface of a steel strip using a microscope, the dented area appears black and other areas appear white, so the area of the black area was calculated using an image analysis device and divided by the area of the entire field of view. It shows the value. Therefore, the smaller the value of the dent area ratio, the fewer the dents on the copper strip surface after rolling, the smoother the steel strip surface, and the better the gloss.

From this figure, it can be seen that when the total rolling reduction is 70% or more, the dent area ratio after tandem mill rolling is significantly reduced. However, since the area ratio of dents on the steel strip surface after Sendzimir mill rolling is less than 3% as shown in the figure, the total rolling reduction is 70%.
% or more, the area ratio of depressions on the surface of the steel strip after tandem mill rolling may not reach the level of Sendzimir mill rolling.

Therefore, we next attempted rolling by changing the distribution of the rolling reduction ratio of each stand, and here, in order to eliminate the dents, it is better to use a softer material to form the dents.

Therefore, it is preferable to increase the reduction rate in the first stand that rolls the base material that has not been work hardened, rather than in the second stand and subsequent stands that further roll the material that has been work hardened by rolling in the previous stand.

Therefore, rolling was carried out while keeping the total rolling reduction constant and varying the rolling reduction of the first stand, and the area ratio of dents on the surface of the steel strip after tandem mill rolling was measured. The results are shown in Figure 2. From this figure, if the rolling reduction of the first stand is 30% or more, the area ratio of dents on the surface of the steel strip after rolling will be equal to or lower than that after Sendzimir mill rolling, and the It is clear that the band surface becomes smooth and the gloss is improved.

Here, for example, a steel strip rolled by a tandem mill under the conditions that the total rolling reduction is 80% and the rolling reduction of the first stand is 30% is finish annealed, pickled, and temper rolled. When the surface gloss of the steel strip is measured, it shows a value of 610. In the case of Sendzimir mill rolling, the gloss after finish annealing, pickling, and temper rolling is usually 500 or more, so the present invention is sufficiently effective. It was confirmed that there is. Note that the glossiness was measured according to JIS Z8741 Glossiness Measuring Method 5 (O320°).

Therefore, we investigated ways to further improve the gloss. 1st
If a strong pressure of 30% or more is applied on the stand, the dents on the surface of the copper strip will collapse and become smaller, but to further improve this effect, it is better to reduce the amount of rolling oil drawn between the rolls and the steel strip. Therefore, the diameter of the work roll used for the first stand was made smaller than the conventional approximately 600fiφ,
We examined its effects. The results obtained using a ferritic stainless steel strip as the test material are shown in Figure 3. In this figure, the horizontal axis shows the roll diameter of the first stand, and the vertical axis shows the copper strip after tandem mill rolling. From Figure 0, which shows the gloss after finish annealing, pickling, and temper rolling, the total rolling reduction is 70.
% or more and the rolling reduction ratio of the first stand is 30% or more, it can be seen that when the work roll diameter of the first stand is set to 400 φ or less, the gloss becomes even better.

As described above, according to the method of the present invention, when rolling a stainless steel strip with a cold tandem mill, a total rolling reduction of 70% or more is applied and a rolling reduction of the first stand is 30% or more.
It is possible to obtain a steel strip with a high gloss equivalent to or higher than that of Sendzimir mill rolling, which was thought to be completely impossible with conventional tandem mill rolling.

<Example> Examples of the present invention will be described below.

Using hot rolled, intermediate annealed and pickled ferritic and austenitic stainless steel base materials shown in Table 1, stainless steel strips were rolled in a cold tandem mill according to the method of the present invention and the conventional method.

The results after rolling are shown in Table 2. For reference, the results after Sendzimir mill rolling are also shown in Table 2.

Table 2 shows that the stainless steel strip rolled by the method of the present invention, finish annealed, pickled, and temper rolled had significantly improved gloss compared to the conventional tandem mill rolling.

Table 1 <Effects of the Invention> As explained above, the stainless steel strip rolled using the method of the present invention, finished annealed, pickled, and temper-rolled into a product has the same effect as in the case of conventional tandem mill rolling. Compared to the Sendzimir mill product, which was impossible to achieve in parallel, it has a gloss level that is equal to or higher than that of the Sendzimir mill product, and is excellent in producing high-gloss stainless steel strips.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the total rolling reduction rate of a 5-stand tandem mill and the concavity area ratio on the surface of the stainless steel strip after rolling.
Figure 2 is a diagram showing the relationship between the rolling reduction ratio of the first stand and the dent area ratio on the surface of the stainless steel strip after rolling, and Figure 3 is a diagram showing the relationship between the work roll diameter of the first stand and finish annealing and pickling after rolling. FIG. 2 is a diagram showing the relationship between the glossiness of a stainless steel strip after temper rolling. Patent applicant Kawasaki Steel Corporation Figure 1 Total rolling reduction (%) Figure 2 Figure 3

Claims (2)

[Claims] (1) A high-gloss stainless steel characterized by rolling a stainless steel strip using a cold tandem mill with a total rolling reduction of 70% or more and a first stand rolling reduction of 30% or more. How to make obi. (2) When rolling stainless steel strip using a cold tandem mill, the work roll diameter of the first stand is set to 400 m.
Using a work roll with a diameter of mφ or less, the total rolling reduction rate was 70
% or more, and the rolling reduction of the first stand is 30% or more.