JPH05271781A - Manufacture of stainless pretreated steel strip for cold rolling and apparatus therefor - Google Patents

Abstract

PURPOSE:To provide a stainless pretreated steel strip for cold rolling capable of manufacturing a stainless cold rolled steel strip having an excellent surface luster in every cases of subjecting a stainless steel strip to cold rolling by a large-sized work roll such as a cold tandem mill or the like, of subjecting it to cold rolling by a small-sized work roll and of executing cold rolling in the combination of the two. CONSTITUTION:In the method for manufacturing a stainless pretreated steel strip for cold rolling, a stainless steel strip after the completion of hot rolling is annealed, is continuously annealed and is immediately subjected to rapid cooling at >=25 deg.C/sec cooling rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing a stainless pretreated steel strip for cold rolling which can advantageously produce an austenitic stainless cold rolled steel strip having an excellent surface gloss.

[0002]

2. Description of the Related Art Conventionally, cold-rolled stainless steel strips are annealed from hot-rolled steel strips and pickled, and then cold-rolled in a Sendzimir mill with a work roll diameter of φ150 mm or less, finish annealing pickling or finish bright annealing It is manufactured by further finishing temper rolling. Stainless steel cold-rolled steel strip produced by this conventional technique is often austenite typified by SUS304, and is often subjected to buff polishing after finish temper rolling,
It is important to exhibit excellent gloss after this buffing.

Further, as another conventional technique, a method of cold rolling with a work roll having a large diameter of φ150 mm or more is adopted in order to significantly reduce the rolling time and efficiently produce a cold rolled stainless steel strip. .

[0004]

However, in the prior art, in the austenitic stainless steel sheet represented by SUS304, when cold rolling with a large diameter work roll such as a cold tandem mill, or with a small diameter work roll. Regardless of whether it is rolled or a combination thereof, there is always a problem that the surface gloss of the product is lowered.

Particularly, in the method of cold rolling using a work roll having a large diameter of φ150 mm or more, the surface gloss of the product is remarkably reduced as compared with the case where a work roll having a small diameter is used. Not applicable at all.

The present invention relates to a case where a stainless steel strip is cold-rolled with a large-diameter work roll such as a cold tandem mill, cold-rolled with a small-diameter work roll, or a combination thereof. In any case, it is an object of the present invention to provide a stainless pre-treated steel strip for cold rolling, which can produce a stainless cold-rolled steel strip having excellent surface gloss.

[0007]

A method of manufacturing a stainless steel pre-treated steel strip for cold rolling according to claim 1, wherein the stainless steel strip after hot rolling is annealed, and the steel strip is continuously formed. Immediately after annealing, the material was rapidly cooled at a cooling rate of 25 ° C / sec or more.

According to a second aspect of the present invention, there is provided a method for producing a pre-treated stainless steel strip for cold rolling, wherein the stainless steel strip after hot rolling is annealed, and the steel strip is continuously annealed immediately after the annealing. It is designed to quench rapidly at a cooling rate of 25 ° C / sec or more in the zone temperature range of 850 ° C to 400 ° C.

An apparatus for producing a stainless pretreated steel strip for cold rolling according to a third aspect of the present invention is an annealing apparatus for a hot rolled stainless steel strip and a quenching apparatus for directly cooling the annealing apparatus by directly connecting the annealing apparatus. It is composed of an apparatus and a pickling apparatus installed on the outlet side of the quenching apparatus.

[0010]

[Operation] In an austenitic stainless steel sheet typified by SUS304, when cold rolling with a large diameter work roll such as a cold tandem mill or when cold rolling with a small diameter work roll, or a combination thereof In any of the cases, there has always been a problem that the surface gloss decreases.

Therefore, as a result of diligent investigations on the cause of gloss inhibition, the present inventors have found that mesh-like microscopic defects remain on the surface of the product steel strip, which causes the surface gloss to decrease. .. However, it was found that this network defect remains on the surface of the steel strip after cold rolling that affects the surface properties of the product, and further, the network defect that remains on the surface of the steel strip after cold rolling. Found that some of the defects formed on the surface of the steel strip before cold rolling, that is, the steel strip annealed and pickled after hot rolling remain until after cold rolling.

Further, as a result of a detailed examination of the surface of the steel strip which has been annealed and pickled after hot rolling, it was found that this mesh-like defect coincided with the grain boundary of the steel strip surface, and was formed along the grain boundary. It has been understood that the cause is a chromium deficient layer. That is, when a stainless steel strip is hot rolled and annealed, a chromium deficient layer is formed along the grain boundaries. This chromium-deficient layer becomes martensite and has hot brittleness, so that cracks are apt to occur (hereinafter, this crack is referred to as grain boundary). However, the annealed steel strip removes the oxide scale on the surface of the steel strip by pickling, but the grain boundaries are further corroded by the acid during this pickling and further expand and increase.

When this steel strip is cold-rolled by supplying a large amount of rolling oil, the rolling oil is enclosed inside the grain boundary and is less likely to be crushed at the contact portion with the roll and the steel strip. We remained after cold rolling, and also remained on the surface of the product steel strip, thus lowering the surface gloss.

Therefore, in order to fundamentally eliminate the formation of the grain boundary, the present inventors examined the following method. (1) Remarkably reduce the chromium-deficient layer that is the cause of grain boundary crack formation. (2) Mechanical removal of grain boundaries. (3) Crush the grain boundaries.

Of these, the present inventors have adopted the method of reducing the chromium deficient layer as a method which has the greatest effect and can be implemented at a low cost.

It is known that in order to reduce the chromium deficient layer, its formation should be suppressed, and it is known that cooling the steel sheet heated at high temperature is effective.

However, for the stainless steel strip annealed at a high temperature of about 1200 ° C. after hot rolling at a temperature of 850 to 1150 ° C., is a chromium deficient layer formed in the hot rolling step or in the subsequent annealing step? Is completely unknown, and in order to effectively suppress the formation, the temperature range and the cooling rate at which the steel strip should be continuously cooled are not known at all.

Therefore, the inventors of the present invention have made diligent studies on these, and found that a large amount of chromium-deficient layer is formed deeply on the surface of the steel strip annealed after the hot rolling step to form grain boundaries. I found it. That is, the steel strip after annealing may be rapidly cooled continuously.

Further, when the timing of starting the quenching was examined, it was found that the quenching immediately after the annealing was good for any of various austenitic stainless steel sheets in order to significantly reduce the chromium deficient layer and eliminate grain boundaries. I found it.

The grain boundaries of the steel strips obtained by variously changing the cooling rate of the austenitic stainless steel strip were observed. The grain boundaries significantly decreased at a cooling rate of 25 ° C./sec or more. , Found that the surface gloss of a product obtained by cold rolling the steel strip is significantly improved.

Further, when the steel strip temperature at the timing of starting quenching (immediately after annealing) was examined, in the SUS304 which is a typical austenitic stainless steel sheet, the chromium deficient layer was remarkably reduced and the grain boundary was reduced. It was found that quenching can be done by rapidly cooling the steel strip in the temperature range of 850 to 400 ℃.

FIG. 1 shows an example of the apparatus configuration of the present invention. The apparatus configuration of the present invention comprises a payoff reel 1 for supplying a hot rolled stainless steel strip, an annealing device 2, a quenching device 3, a pickling device 4, and a steel strip winding reel 5. Here, the quenching device 3
Is directly connected to the annealing device 2.

As the quenching device 3 for cooling the steel strip immediately after annealing according to the present invention, a device for immersing it in cooling water or hot water, a device for directly supplying cooling water or hot water from a nozzle, or a cooling water or hot water mist It is possible to adopt a device for supplying the gas as described above, a device for supplying water vapor, a device for supplying a liquid gas such as liquid nitrogen, etc., but all of them must be installed on the outlet side of the annealing device 2, and a cooling rate of 25 ° C It is necessary to be able to supply a cooling fluid with a flow rate and pressure that has a capacity of more than a second.

[0024]

【Example】

(Example 1) (see Tables 1 to 3) Austenitic SUS304 steel strip as an example is annealed after hot rolling, and immediately after annealing according to the method of the present invention, rapidly cooled at a cooling rate of 25 ° C / sec or more, and pickled. did.

As a comparative example of the present invention, a SUS304 steel strip was annealed after hot rolling, immediately after annealing, water-cooled at a cooling rate of less than 25 ° C./sec, and pickled.

Further, as a conventional example, a SUS304 steel strip was annealed after hot rolling, gradually cooled immediately after annealing, then water cooled and pickled.

A plurality of these steel strips are manufactured, a part of them is rolled by a cold tandem mill using large diameter rolls, and a part of them is rolled by a Sendzimir mill using small diameter rolls while supplying a large amount of rolling oil. The rest was rolled in a tandem mill and then cold-rolled in a Sendzimir mill. Further, after cold rolling, finish annealing pickling or finish bright annealing was performed under the same conditions, and finish temper rolling was performed. The finish annealed steel strip was buffed under the same conditions after temper rolling.

Regarding the surface gloss of these finished steel strips,
Measured according to JIS Z8741 Glossiness Measurement Method 5 (GS20 °). Glossiness of 950 or higher is special A, 800-9
The evaluation was performed in five levels, with 50 as A, 600 to 800 as B, 400 to 600 as C, and 400 or less as D.

The results are shown in Table 1, when cold-rolled by a tandem mill, in Table 2 when rolled by a Sendzimir mill, and in Table 3 when rolled by a tandem mill and further cold-rolled by a Sendzimir mill.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

From these tables, it was confirmed that the stainless cold-rolled steel strip produced according to the present invention has a significantly better gloss than the steel strip produced by the conventional method and the steel strip produced as the comparative example.

(Example 2) (See Tables 4 to 6) SUS304 steel strip as an example of an austenite type is annealed after hot rolling, and 850 ° C-400 immediately after annealing according to the method of the present invention.
It was water-cooled at a cooling rate of 25 ° C./sec in a steel strip temperature range of 0 ° C. and pickled.

As a comparative example of the present invention, a SUS304 steel strip is annealed after hot rolling, and immediately after the annealing, water cooling is performed in a steel strip temperature range of 850 ° C. to 400 ° C. at a cooling rate of less than 25 ° C./sec. Washed

Further, as a conventional example, a SUS304 steel strip was annealed after hot rolling, the steel strip temperature after annealing was gradually cooled to around 700 ° C., then water cooled and pickled.

A plurality of these steel strips were produced and, while supplying a large amount of rolling oil, part of them was rolled by a cold tandem mill using large diameter rolls and part of them was rolled by a Sendzimir mill using small diameter rolls. The rest was rolled in a tandem mill and then cold-rolled in a Sendzimir mill. Further, after cold rolling, finish annealing pickling or finish bright annealing was performed under the same conditions, and finish temper annealing was performed. The finish annealed steel strip was buffed under the same conditions after temper rolling.

Regarding the surface gloss of these finished steel strips, JI
S Z8741 Measured according to Glossiness Measurement Method 5 (GS 20 °), the glossiness is 950 or more in the order of good gloss. Special A, 800-95
0 was A, 600 to 800 was B, 400 to 600 was C, and 400 or less was D.

Regarding these results, Table 4 shows the case of rolling with a cold tandem mill, Table 5 shows the case of rolling with a Sendzimir mill, and Table 6 shows the case of rolling with a tandem mill and then cold rolling with a Sendzimir mill.

[0040]

[Table 4]

[0041]

[Table 5]

[0042]

[Table 6]

From these tables, it was confirmed that the stainless cold-rolled steel strip produced according to the present invention has a significantly better gloss than the steel strip produced by the conventional method and the steel strip produced as the comparative example.

[0044]

As described above, the pretreatment according to the present invention,
After that, the cold rolled stainless steel strip finished by cold rolling is
It has remarkably excellent surface gloss as compared with the steel strip manufactured by the conventional method. In particular, when a large-diameter roll such as a cold tandem mill is used, it has a surface gloss equal to or better than that of a rolling using a small-diameter roll such as a Sendzimir mill, which has hitherto been unattainable.

[Brief description of drawings]

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

[Explanation of symbols]

 2 Annealing device 3 Quenching device

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masahiko Ito 1 Kawasaki-cho, Chiba-shi, Chiba Inside Kawasaki Steel Co., Ltd. (72) Inventor Katsuhiro Kobori 1 Kawasaki-cho, Chiba-shi Chiba Steel Co., Ltd. In-house (72) Inventor Kuniaki Sato 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works

Claims (3)

[Claims] 1. For cold rolling, characterized in that the stainless steel strip after hot rolling is annealed, and subsequently this steel strip is rapidly cooled at a cooling rate of 25 ° C./sec or more immediately after annealing. Manufacturing method of stainless pretreated steel strip. 2. The stainless steel strip after hot rolling is annealed, and the temperature of the steel strip is continuously increased immediately after annealing the steel strip.
A method for producing a stainless pretreated steel strip for cold rolling, which comprises rapidly cooling at a cooling rate of 25 ° C / sec or more in a range of 850 ° C to 400 ° C. 3. An annealing device for hot-rolled stainless steel strip, a quenching device directly connected to the annealing device for quenching the steel strip, and a pickling device installed on the outlet side of the quenching device. An apparatus for producing a cold-rolled stainless steel pre-treated steel strip, which is characterized by: