JPH05320771A - Production of pretreated stainless steel strip for cold rolling and device therefor - Google Patents

Abstract

PURPOSE:To manufacture a steel strip having excellent surface luster by rapidly cooling a strip at a specified cooling rate immediately after annealing and thereafter grinding its surface by a specified amt. CONSTITUTION:A stainless steel strip after the completion of hot rolling is moved from a pay-off reel 1 to an annealing device 2 is annealed. Continuously, this steel strip is rapidly cooled at >=25 deg.C/sec cooling rate immediately after the annealing by a rapidly cooling device 3. After that, the surface of the steel strip is mechanically ground by >=2mum by a grinding device 4. After annealing, it is rapidly cooled in the range of 850 to 400 deg.C at >=25 deg.C/sec cooling rate. In this way, the objective austenitic cold rolled stainless steel having excellent surface luster can advantageously be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device 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 strip is annealed by hot-rolled steel strip, pickled, and then cold-rolled in a Sendzimir mill with a work roll diameter of φ150 mm or less to finish-anneal 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 have 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, after quenching at a cooling rate of 25 ° C / sec or more,
The surface of the steel strip is mechanically ground to 2 μm or more.

According to a second aspect of the present invention, there is provided a method of manufacturing a stainless steel pretreated steel strip for cold rolling, wherein the stainless steel strip after hot rolling is annealed, and the temperature after the annealing of the steel strip is continued.
The steel strip surface is mechanically ground to 2 μm or more after being rapidly cooled in the range of 850 ° C. to 400 ° C. at a cooling rate of 25 ° C./second or more.

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. A device, a grinding device installed on the outlet side of the quenching device for mechanically grinding the surface of the steel strip, and a pickling device installed on the outlet side of the grinding device. ..

[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 is lowered.

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 has been found that the mesh defects coincide with the crystal grain boundaries of the steel strip surface and are formed along the crystal grain boundaries. It is understood that the cause is the chromium deficient layer. That is, when the 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 likely to occur (hereinafter, this crack is referred to as grain boundary). Of course, 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 the 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) The chromium-deficient layer, which is the cause of grain boundary formation, is significantly reduced. (2) Mechanically remove 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 low cost.

It is known that in order to reduce the chromium deficient layer, its generation should be suppressed, and 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 thereof, the temperature range for cooling the steel strip and the cooling rate have not been 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 and becomes a grain boundary. I found it. That is, the steel strip after annealing may be rapidly cooled.

Further, when the timing of starting the quenching was examined, it was found that the quenching immediately after the annealing was good for all the 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 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 SUS304 which is a typical austenitic stainless steel sheet, the chromium deficient layer was remarkably reduced and 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 ℃.

Further, in order to further reduce the grain boundaries and improve the surface gloss, a method of mechanically grinding the grain boundaries was examined.

That is, as a result of collecting the steel strip after the quenching described above and measuring the depth of the grain boundary remaining on the surface of the steel strip, most of the grain boundary depth is 2 μm or less. Figured out. Therefore, it has been understood that mechanically grinding the surface of the steel strip by 2 μm or more improves the surface gloss of the product steel strip obtained by cold rolling and finishing the steel strip thereafter.

Further, when the position where the mechanical grinding is carried out is examined, when it is carried out immediately after the annealing, the temperature of the steel strip is high and the life of the apparatus used for grinding is remarkably shortened, which is a problem. If mechanical grinding is performed after rapid cooling after pickling and pickling, the streak pattern when the steel strip surface is ground remains and the pattern does not disappear even after cold rolling, resulting in uneven gloss. It's a problem. Therefore, by performing mechanical grinding after annealing and quenching, the steel strip is at a low temperature and the life of the equipment can be maintained for a long time.Because pickling after grinding reduces streak patterns, there is a problem of uneven gloss. No, I understood that it was good.

As the method of mechanically grinding the grain boundaries of the present invention, there are grinding with a grinder, grinding with a brush, grinding with a grindstone fixed to a resin or cloth, and the like. By adopting the method that can be continuously performed inside, the steel strip can be manufactured efficiently.

FIG. 1 shows an example of the apparatus configuration of the present invention. The apparatus configuration of the present invention includes a payoff reel 1 for supplying a hot rolled stainless steel strip, an annealing device 2, a quenching device 3, a mechanical grinding device 4, a pickling device 5, and a steel strip winding reel 6.
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 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 atomized 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 the cooling rate is 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.

[0029]

【Example】

(Example 1) (See Tables 1 to 3) An austenitic SUS304 steel strip is annealed after hot rolling, and immediately after annealing according to the method of the present invention, it is rapidly cooled at a cooling rate of 25 ° C / sec or more, The surface of the strip was mechanically ground to 2 μm or more 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 at a cooling rate of less than 25 ° C./sec, and the steel strip surface is mechanically ground and pickled. did.
After water cooling at a cooling rate of 25 ° C / sec or more, the amount of mechanical grinding was suppressed to less than 2.0 µm and pickling was performed.

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 were produced, and while a large amount of rolling oil was supplied, part of them was rolled with a cold tandem mill using large diameter rolls and part of them was rolled with a Sendzimir mill using small diameter rolls. The rest was rolled in a tandem mill and then cold-rolled in a Sendzimir mill. 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 made 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 rolled by a cold 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.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

From these tables, it was confirmed that the stainless cold-rolled steel strip produced according to the present invention has remarkably good gloss as compared with the steel strip produced by the conventional method and the steel strip produced as the comparative example.

(Example 2) (See Tables 4 to 6) Austenitic SUS304 steel strip as an example is annealed after hot rolling, and immediately after annealing in the steel strip temperature range of 850 ° C to 400 ° C according to the method of the present invention. hand
It was rapidly cooled at a cooling rate of 25 ° C./sec, the surface of the steel strip was mechanically ground to 2 μm or more 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 at a cooling rate of less than 25 ° C / sec in a steel strip temperature range of 850 ° C to 400 ° C. The steel strip surface was mechanically ground and pickled. When water cooling is performed at a cooling rate of 25 ° C / sec or more, the mechanical grinding amount is 2.0 μm.
The pickling was suppressed to less than 1.

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 were manufactured, and while a large amount of rolling oil was supplied, a part of them was rolled by a cold tandem mill using large diameter rolls, and a 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 °).
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 further cold rolling with a Sendzimir mill.

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

[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.

[0049]

As described above, the pretreatment according to the present invention,
After that, the cold rolled stainless steel strip is finished by cold rolling.
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 the device of the present invention.

[Explanation of symbols]

 2 Annealing equipment 3 Quenching equipment 4 Mechanical grinding equipment 5 Pickling equipment

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI technical display location // B21B 3/02 7362-4E (72) Inventor Masahiro Yoshioka 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Address Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Hiroyuki Kakiuchi 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture No. 1 Kawasaki Steel Co., Ltd. Chiba Steel Works

Claims (3)

[Claims] 1. A stainless steel strip after hot rolling is annealed, and immediately thereafter, the steel strip is rapidly cooled at a cooling rate of 25 ° C./sec or more immediately after annealing, and then the surface of the steel strip is mechanically treated. 2 μm
A method of manufacturing a cold-rolled stainless steel pre-treated steel strip characterized by grinding as described above. 2. The stainless steel strip after hot rolling is annealed, and the temperature after annealing the steel strip is continuously 850 ° C. to 4 ° C.
After quenching at a cooling rate of 25 ° C / sec or more in the range of 00 ° C,
A method for producing a stainless steel pretreated steel strip for cold rolling, comprising mechanically grinding the surface of the steel strip to 2 μm or more. 3. An annealing device for hot-rolled stainless steel strip, a quenching device for directly cooling the steel strip by being directly connected to the annealing device, and a steel strip surface installed on the outlet side of the quenching device to machine the steel strip surface. And a pickling device installed on the outlet side of the grinding device, for producing a cold-rolled stainless pretreated steel strip.