JPH05311243A - Manufacture of stainless pretreated steel strip for cold rolling and device therefor - Google Patents

Abstract

PURPOSE:To impart excellent surface luster to a steel strip by subjecting stainless steel to hot rolling, thereafter subjecting it to annealing, rapid cooling and pickling and furthermore executing oil-free rolling. CONSTITUTION:A stainless steel strip subjected to hot rolling is annealed, and just after the annealing, it is rapidly cooled at >=25 deg.C/sec cooling rate and is thereafter pickled. Next, oil-free rolling is executed. The rapid cooling is executed preferably in the range of 850 to 400 deg.C after the annealing. By the rapipd cooling just after the annealing, chromium deficiency layers on the surface of the steel strip are reduced, and intercristalline cracking is eliminated. Moreover, by the rolling using no rolling oil, oil is not sealed into the recessed parts on the surface of the steel strip to improve its surface luster.

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]

According to the present invention as set forth in claim 1, the stainless steel strip after hot rolling is annealed, and the steel strip is continuously annealed at 25 ° C./sec or more immediately after annealing. After being rapidly cooled at a cooling rate, it is pickled and then subjected to non-lubricating rolling.

According to the second aspect of the present invention, the stainless steel strip after hot rolling is annealed, and the temperature after annealing the steel strip is continuously within a range of 850 ° C to 400 ° C. After being rapidly cooled at a cooling rate of ° C / sec or more and pickled, further non-lubricating rolling is performed.

According to a third aspect of the present invention, there is provided an annealing device for a hot rolled stainless steel strip, a quenching device directly connected to the annealing device for quenching the steel strip, and an outlet side of the quenching device. The pickling apparatus to be installed and the non-lubricating rolling machine having a non-lubricating rolling capacity installed on the outlet side of the pickling 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 is lowered.

[0011] Therefore, as a result of diligent investigation of the cause of gloss inhibition, the present inventors found that network-like and black granular microscopic defects remained on the surface of the product steel strip, which caused the surface gloss to decrease. Figured out. However, it was found that the mesh-like and granular defects remain on the surface of the steel strip after cold rolling that affects the surface properties of the product, and further remain on the surface of the steel strip after cold rolling. The network-like and granular defects are those before the cold rolling, that is, some of these defects generated on the surface of the steel strip annealed and pickled after hot rolling remain until after cold rolling. I found that there is.

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.

Further, it has been found that the black granular defects are recesses having a remarkably large roughness generated by shot blasting or the like for removing oxide scale on the surface after annealing the steel strip.

When these steel strips having microscopic defects are cold-rolled by supplying a large amount of rolling oil, the rolling oil is sealed in the grain boundaries and the recesses having a large roughness to contact the rolls and the steel strip. As a result of being less likely to be crushed at the part, the defects remain after the cold rolling and also on the surface of the product steel strip, thus lowering the surface gloss.

Therefore, in order to fundamentally eliminate the formation of grain boundary, the present inventors examined the following method.

(1) The chromium-deficient layer, which is the cause of the generation of grain boundaries, is significantly reduced. (2) Mechanically remove grain boundaries. (3) Crush the grain boundaries.

Of these, the present inventors have adopted a 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 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, 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.

Further, when the timing of starting the quenching was examined, it was found that the quenching immediately after annealing is 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, and it was found that 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 It was found that quenching can be done by rapidly cooling the steel strip in the temperature range of 850 to 400 ℃.

Next, a recess having a large roughness due to shot blasting or the like was examined. When a large amount of rolling oil is supplied on the inlet side of cold rolling, the rolling oil is enclosed in this recess and the contact portion between the roll and the steel strip (hereinafter referred to as roll bite)
Bite into. The rolling oil enclosed in the recesses is rolled in the roll bite while keeping its containment without escape. In general, liquids containing rolling oil are significantly less likely to be compressed than gases such as air, so the recesses containing rolling oil will be somewhat smaller than before rolling, but most will remain after rolling, and the surface of the product The gloss is lost.

Therefore, in order to reduce the recesses, it is preferable to reduce the roughness of the surface of the steel strip before cold rolling. That is, based on the above knowledge, it is good to perform non-lubricating rolling without using a liquid such as rolling oil after annealing and pickling the hot-rolled steel sheet.

FIG. 1 shows an example of the device 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, a non-lubricating rolling mill 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.

Further, as the non-lubricating rolling mill 5 of the present invention, 4
A vertical rolling mill such as a multi-high rolling mill or a 6-high rolling mill, or a cluster-type rolling mill such as a 12-high rolling mill may be used, but the flatness of the product steel strip can be solved by solving the problems such as drawing when passing the steel strip. In order to improve the quality, a rolling mill having a shape control function is required.

[0029]

【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. After that, non-lubrication rolling was performed.

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 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) SUS304 steel strip as an example of an austenite type is annealed after hot rolling, and 850 ° C to 400 ° C immediately after annealing according to the method of the present invention.
The steel strip was water-cooled at a cooling rate of 25 ° C./sec in the steel strip temperature range, pickled, and then subjected to non-lubricating rolling.

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, 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 Pickling equipment 5 Non-lubricating rolling mill

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hidenori Miyake, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Taketo Nomura 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Works Co., Ltd. Chiba Steel Works (72) Inventor Setsuo Kakihara 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Works Chiba Works

Claims (3)

[Claims] 1. A stainless steel strip after hot rolling is annealed, and immediately thereafter, the steel strip is rapidly cooled immediately after annealing at a cooling rate of 25 ° C./sec or more, then pickled and further subjected to non-lubricating rolling. A method for producing a cold-rolled stainless steel pre-treated steel strip, comprising: 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.
A method for producing a pre-treated stainless steel strip for cold rolling, which comprises rapidly cooling in a range of 00 ° C at a cooling rate of 25 ° C / sec or more, pickling, and then performing non-lubricating rolling. 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 pickling device installed on the outlet side of the quenching device. An apparatus for producing a stainless pre-treated steel strip for cold rolling, comprising an unlubricated rolling machine having an unlubricated rolling ability installed on the outlet side of the pickling apparatus.