JPH0732003A - Production of stainless cold rolled steel strip - Google Patents

Abstract

PURPOSE:To obtain an excellent gloss of surface by mutually crossing a pair of upper and lower work rolls in an angle decided based on the length of the contact arc of roll bite and the average pitch of roughness in the breadth direction of the surface of inlet side steel strip, and rolling. CONSTITUTION:In a cold tandem mill, a pair of upper and lower work rolls 2 are mutually crossed in an angle phi having the relation of the equation I which is decided based on the length L of the contact arc of roll bite and the average pitch lambdaa of the roughness of breadth direction of the surface of inlet side steel strip and rolling is executed. Further, after rolling in the cold tandem mill, rolling is more executed with work rolls of their diameters smaller than 150phimum. In such a way, the excellent surface gloss of same or more than the surface rolled by using small diameter work rolls of Sendzimir mill, etc., which could not reach until now in the case of rolling by using large diameter work rolls of the cold tandem mill, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a production method capable of advantageously producing a cold rolled stainless steel strip having an excellent surface gloss.

[0002]

2. Description of the Related Art Conventionally, cold-rolled stainless steel strip is annealed and pickled from hot-rolled steel strip and cold-rolled in a Sendzimir mill with a work roll diameter of 150 mmφ or less, then finish-annealed pickling or finish bright annealing. It was manufactured by performing finish temper rolling with a rolling reduction of 1.2% or less.

The cold-rolled stainless steel strip manufactured through these steps is often used as it is after being manufactured in the case of a ferrite type typified by SUS430, and is excellent as a product after finish temper rolling. High surface gloss is required. Also,
In the case of an austenite type represented by SUS304, buffing is often performed after finish temper rolling, and it is important to exhibit excellent surface gloss after this buffing.

Therefore, conventionally, in cold rolling using a small-diameter work roll such as a Sendzimir mill, for example, Japanese Unexamined Patent Publication No.
The method of devising the roll roughness shown in -13362 was adopted. However, even using this method, the surface gloss was not satisfactory as a result of the fact that the significantly large roughness of the steel strip surface annealed and pickled after hot rolling before cold rolling remained until after cold rolling.

On the other hand, as a method for producing a stainless cold-rolled steel strip with high efficiency by significantly shortening the rolling time,
A method of cold rolling with a work roll having a diameter of mmφ or more is adopted. However, as mentioned above, the surface roughness of the steel strip cold-rolled with a large-diameter work roll is as follows. The product could not be applied to applications requiring surface gloss at all, as the roughness remained larger than that of cold rolling using work rolls. Therefore,
As a method for solving this type of surface gloss reduction problem, conventionally, for example, JP-A-5-57304, JP-A-5-123704 and the like, a method of intersecting the work rolls under a specific condition during cold rolling is disclosed. There is. When these methods were adopted, the surface gloss was not sufficiently improved even if the oil pits forming the relatively shallow unevenness could be erased in the range where the specific conditions described therein were satisfied. The reason for this is that the extremely large surface roughness of the steel strip annealed and pickled after hot rolling remains until after cold rolling, and a sufficiently smooth surface cannot be obtained. Sufficient and needed further improvement.

It is an object of the present invention to solve the problem of reduction in surface gloss that has hitherto been encountered when cold rolling a stainless steel sheet.

[0007]

The present invention as set forth in claim 1 is, in a cold tandem mill, a contact arc length L of a roll bite and an average pitch λ of roughness in the width direction of the surface of the entering steel strip.
A pair of upper and lower work rolls are rolled while intersecting each other at an angle φ having the following relationship determined by a.

[0008]

[Equation 2]

According to a second aspect of the present invention, in addition to the first aspect of the present invention, after rolling with a cold tandem mill, rolling is further performed with a small diameter roll having a work roll diameter of 150 φmm or less. .

[0010]

The present invention will be described in detail below. Conventionally,
It has been known that in order to improve the surface gloss of the stainless cold-rolled steel strip, it is preferable to reduce the surface roughness of the steel strip after cold rolling, which influences the surface roughness of the product.

However, in the study by the present inventors, the surface roughness of the steel strip after the cold rolling is as follows.
That is, it was found that a part of the surface roughness of the steel strip annealed and pickled after hot rolling remains after the cold rolling.

Therefore, the surface roughness of the steel strip that has been annealed and pickled after hot rolling will be shown below. Average roughness R in final finished product
a When manufacturing a stainless cold-rolled steel strip targeting a surface roughness of 0.1 μm or less, the surface roughness of the steel strip immediately after annealing and pickling the hot-rolled steel strip is determined by mechanical removal such as shot blasting during pickling. Average roughness Ra2 due to scale treatment and acids such as sulfuric acid
It has a remarkably large roughness of about 4 μm.

By the way, generally, during cold rolling, a large amount of rolling oil is supplied to the roll and the steel strip from the inlet side of the rolling mill.
This is performed in order to stably produce a steel strip by simultaneously performing lubrication with a rolling oil and cooling to prevent the occurrence of seizure flaws such as heat streaks.

Therefore, on the inlet side of the cold rolling mill, rolling oil having a thickness of several μm or more adheres to the roll and the surface of the steel strip, and the rolling oil is deposited in the remarkably large depressions on the surface of the steel strip which has been annealed and pickled after hot rolling. It collects and is bitten by the roll bite. The oil accumulated in the dent disappears while the roll bite is in contact with the steel strip in the roll bite, and is rolled while being contained.

In general, a liquid containing rolling oil is significantly less likely to be compressed than a gas such as air. Therefore, the dent containing oil during rolling is somewhat smaller than that before rolling.
Most remain after rolling.

As described above, the surface roughness of the steel strip before cold rolling remains even after cold rolling and the surface gloss of the product is significantly impaired.

Therefore, in order to obtain a steel strip having a good surface gloss, it is advisable to reduce the concave portion of the surface roughness of the steel strip at the start of cold rolling during rolling. That is, it is preferable that during the cold rolling, the protrusions of the roughness of the roll surface are brought into sufficient contact with the surface of the steel strip to sufficiently reduce the recesses of the surface roughness of the steel strip before the cold rolling.

It has been conventionally known that rolling with intersecting rolls can reduce minute irregularities such as shallow oil pits even at the maximum depth of about a few μm, but like the material roughness before cold rolling. It was not possible to reduce the roughness, which was as large as several tens of μm.

Therefore, when the cause of this is investigated, even when the roll roughness protrusion and the recess on the steel plate surface are in sufficient contact in the rolling direction at the contact portion between the roll and the steel strip during rolling, Since there is a recess of roll roughness in the width direction, the roll surface only partially contacts the recess of the steel plate surface,
It was found that the recess having a large depth remains.

Therefore, in order to make sufficient contact also in the width direction, the inventors of the present invention have diligently studied and found that when the work rolls are crossed at an angle φ satisfying the following formula shown in FIG. The convex portion can be moved sufficiently in the rolling direction and the width direction, and the unevenness on the surface of the steel strip can be reduced.
As a result, the surface of the steel sheet after rolling becomes smooth and the surface gloss is improved. In FIG. 1, 1 is a steel strip, 2
Is a work roll.

That is, in order to reduce the material roughness before cold rolling which is as large as several tens of μm, the rolling oil which is about to be enclosed in the recess of the material roughness is rolled in the roll bite where the roll and the steel strip are in contact with each other. It is advisable to bring the roll roughness into sufficient contact with the surface of the steel strip while allowing it to escape to the outside of the roll bite through the groove of roughness. Therefore, by moving the roll roughness in the width direction, firstly, the rolling oil can be released to the outside of the roll bite through the roll roughness that is long in the normal rolling direction, and is enclosed in the concave portion of the material roughness. Rolling oil is significantly reduced. Second
In addition, by reducing the rolling oil, the roll roughness can sufficiently crush the material roughness. However, if it moves halfway, the roll roughness may not be able to make sufficient contact over the entire surface of the steel strip. As a result, even if the oil pit having a minute roughness can be reduced as in the conventional application, the material roughness having a large unevenness may not be sufficiently reduced.

Then, as a result of intensive investigations by the present inventors,
While rolling the length L of the contact bit length of the roll bite during rolling while the roughness of the roll moves in the rolling direction, move the roll roughness in the width direction to an average pitch λa or more of the width-direction roughness of the incoming steel strip surface It was understood that if possible, the roll roughness could be brought into sufficient contact over the entire surface of the steel strip.

[0023]

[Equation 3]

Here, λa is the average pitch of roughness in the width direction of the entrance side steel strip surface, and L is the contact arc length between the roll and the steel strip.

The average roughness pitch λa is the average value of the intervals Smi of the irregularities of the cross-section curve showing the surface roughness shown in FIG. 2, and is calculated by the following formula.

[0026]

[Equation 4]

[0027]

【Example】

(Example 1) Using a SUS430 steel strip as an example of a ferrite system that has been annealed and pickled after hot rolling, after annealing and pickling a hot rolled steel strip, as an example of the method of the present invention, a 5-stand cold tandem mill Then, the work rolls of the first stand to the third stand were crossed and rolled, and then finish annealing, pickling and temper rolling were performed to examine the gloss of the surface of the steel strip.

Further, in the case of not intersecting at all (conventional example) and the case of intersecting at an angle outside the range of the formula shown in the present invention (comparative example), the rolled steel strip is subjected to finish annealing, pickling and heat treatment. The gloss of the surface of the rolled steel strip was investigated.

The surface gloss of these stainless cold-rolled steel strips was measured according to JIS Z8741 Glossiness Measurement Method 5 (GS20 °), and in order of goodness, glossiness of 950 or more was special A, 800-950 was A, 600-800. B, 400 to 600 were designated as C, and 400 or less was designated as D, and the evaluation was made in 5 stages.

From the results shown in Table 1, the stainless cold-rolled steel strip produced by the method of the present invention had remarkably good gloss as compared with the steel strip produced by the conventional method.

[0031]

[Table 1]

(Example 2) Using a SUS304 steel strip as an example of an austenitic steel that has been annealed and pickled after hot rolling, the hot rolled steel strip is annealed and pickled, and then cooled by 5 stands as an example of the method of the present invention. Between the work rolls of the first stand in a tandem tandem mill, then rolling with a cluster-type rolling mill using small-diameter work rolls, finish annealing, pickling, temper rolling, and buffing the same. The gloss of the surface of the steel strip, which was carried out under the conditions, was investigated.

Further, in the case of not intersecting at all (conventional example) and in the case of intersecting at an angle outside the range of the formula shown in the present invention (comparative example), the rolled steel strip is subjected to finish annealing, pickling and heat treatment. The gloss of the surface of the rolled steel strip was investigated.

The surface gloss of these stainless cold-rolled steel strips was measured according to JIS Z8741 Gloss Measurement Method 5 (GS20 °), and in order of goodness, a gloss of 950 or more was specified as A, 800-950 as A, and 600-800. B, 400 to 600 were evaluated as C, and 400 or less was evaluated as D, and the evaluation was made in 5 steps.

From the results shown in Table 2, the stainless cold-rolled steel strip produced by the method of the present invention had remarkably good gloss as compared with the steel strip produced by the conventional method.

[0036]

[Table 2]

[0037]

As described above, the stainless cold-rolled steel strip produced by the method of the present invention has remarkably excellent surface gloss as compared with the steel strip produced by the conventional method. In particular, in the case of rolling using a large diameter work roll such as a cold tandem mill, it has a surface gloss equal to or better than that of a rolling using a small diameter work roll such as a Sendzimir mill, which has hitherto been unattainable.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an average pitch of roughness.

[Explanation of symbols]

 1 Steel strip 2 Work roll

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Suzuki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Inside the Chiba Steel Works (72) Inventor Satoshi Tsuzuki 1 Kawasaki-cho, Chuo-ku, Chiba Chiba Steel Works Co., Ltd. Chiba Steel Works (72) Inventor Takashi Shiokawa 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Works Chiba Works

Claims (2)

[Claims] 1. In a cold tandem mill, at an angle φ having the following relationship, which is determined by a length L of a contact arc of a roll bite and an average pitch λa of roughness in the width direction of a steel strip surface on the entry side, A method for manufacturing a stainless cold-rolled steel strip, comprising rolling a pair of upper and lower work rolls so as to intersect each other. [Equation 1] 2. The method for producing a stainless cold-rolled steel strip according to claim 1, further comprising rolling with a cold tandem mill and further rolling with a small diameter roll having a work roll diameter of 150 φmm or less.