JPH08229603A - Manufacturing method of stainless pretreated steel strip for cold rolling - Google Patents

Abstract

PURPOSE: To manufacture a cold rolled stainless steel strip having excellent surface gloss by applying non-lubricant rolling to a stainless steel strip after completion of hot rolling by using specified alloy work rolls at a specified draft. CONSTITUTION: In the manufacturing method of the preliminarily treated stainless steel strip for cold rolling, annealing and pickling are applied to the stainless steel strip after completion of hot rolling and non-lubricant rolling is executed by using the work rolls made of a WC alloy at the draft of >=5% to <=30%. For example, by using the steel strip of SUS 430, after annealing and pickling the hot rolled steel strip, preliminary treatment and rolling of the steel strip are executed by using the work rolls whose shaft centers are made of high-speed steel and on the outer periphery of which the WC alloy contg. 10% Co is fit at the draft of 13% in non-lubrication. In this way, the cold rolled stainless steel strip having excellent surface gloss is manufactured, equipment investment for rolling-oil coolant is reduced, and maintenance and management cost of equipment is reduced.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, cold-rolled stainless steel strip has been obtained by annealing a hot-rolled steel strip and then cold-rolling it using a steel alloy work roll in a Sendzimir mill with a work roll diameter of 150 mmφ or less. After the finish annealing pickling or finish bright annealing, finish temper rolling with a rolling reduction of 1.2% or less was applied.

The stainless cold-rolled steel strip is, for example, SU
In the case of the ferrite type represented by S430, the surface after production is often used as it is, and a product after finish temper rolling is required to have excellent surface gloss. Further, in the case of an austenite type represented by SUS304, buff polishing is often performed after finish temper rolling, and it is important to exhibit excellent surface gloss after this buff polishing.

Therefore, as a method for producing a stainless cold-rolled steel strip with a high efficiency by significantly shortening the rolling time, cold rolling is performed with a rolling machine having a large diameter work roll of 150 mmφ or more like a cold tandem mill. The method is adopted. However, the surface roughness of the steel strip cold-rolled by the large-diameter work roll is remarkably larger than that of the steel strip rolled by the small-diameter work roll, so that the product could not be applied to applications requiring gloss.

Conventionally, Japanese Examined Patent Publication No. 4-36762 and Japanese Unexamined Patent Application Publication No. 2-
As disclosed in Japanese Patent No. 169107, after annealing and pickling a stainless hot-rolled steel strip, a preliminary treatment rolling for smoothing the surface of the steel strip is performed, and then a technique for improving surface gloss by cold rolling is proposed. ing. However, in the prior art of Japanese Examined Patent Publication No. 4-36762, since the pretreatment rolling is performed without lubrication, minute seizure flaws may occur on the surface of the steel strip, and the surface of the steel strip finished by cold rolling is finished. There are cases where the gloss decreases. Further, in the prior art of Japanese Patent Laid-Open No. 2-169107, a device has been devised to prevent this seizure by adhering a very thin oil film to the surface of the work roll, but it is greatly used in rolling oil coolant supply equipment and filtration equipment. Investment is required, and the burden of maintenance and management of these facilities is large, and a better method has been desired.

[0006]

DISCLOSURE OF THE INVENTION The present invention is directed to rolling a stainless steel strip on a Sendzimir mill with a small diameter work roll, rolling with a large diameter work roll such as a cold tandem mill, and rolling in combination thereof. In this case, it is an object of the present invention to be able to produce a stainless cold-rolled steel strip having excellent surface gloss.

[0007]

The method of manufacturing a stainless steel pretreated steel strip for cold rolling according to the present invention comprises a stainless steel strip after hot rolling, which is annealed and pickled, and further made of a WC alloy. The work roll is used to perform non-lubricant rolling at a reduction ratio of more than 5% and less than 30%.

[0008]

It has been conventionally known that in order to improve the surface gloss of a cold rolled stainless 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 the same as that before the cold rolling.
That is, it has been 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 R by scale treatment and pickling treatment with sulfuric acid
It has a remarkably large roughness of a 2 to 4 μm.

However, 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 surface of the roll and the steel strip,
The rolling oil accumulates in the extremely large dents on the surface of the steel strip that has been annealed and pickled after hot rolling, and gets caught in the roll bite. The oil accumulated in the dents disappears while the roll and the steel strip are in contact with each other in the roll bite, and is rolled while being contained.

In general, a liquid containing rolling oil is much less likely to be compressed than a gas such as air, so that the dents that contain oil during rolling are somewhat smaller than those 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 understood that it is better to reduce the unevenness of the steel strip surface before cold rolling in advance. From the above knowledge, this can be realized by performing non-lubricating rolling without using a liquid such as rolling oil. However, when the non-lubricating rolling is performed, the roll and the steel strip are seized, and minute seizure flaws are generated, and these flaws remain after the cold rolling, and the surface gloss of the steel strip may decrease.

Therefore, the present inventors have examined a pretreatment method for a stainless steel strip which simultaneously satisfies the following two points. (1) Roll and steel strip should not be seized during pretreatment rolling. (2) Preliminary treatment should be possible to the extent that unevenness on the surface of the steel strip after annealing and pickling the hot-rolled steel strip does not remain after cold rolling.

As a result, the following method was found to be suitable. (a) Use stainless steel strip and non-seizure roll material. (b) An extremely thin film of rolling oil is formed on the roll surface.

Here, the thin film lubrication method of (b) requires a facility for forming a thin oil film on the roll surface, and has a drawback of high cost.

On the other hand, in the method (a) of changing the material of the roll, since the roll and the steel strip prevent seizure, non-lubricating rolling can be easily achieved.

Therefore, the present inventors applied rolls of various roll materials to the pretreatment rolling of the present invention. as a result,
It has been found that it is preferable to use a work roll made of WC alloy.

That is, observing in detail the phenomenon of seizure between the roll and the steel strip, the metal portion of the roll surface adheres to the steel strip, and the adhesion is repeated as the roll rotates, so that the roll surface temperature changes. It became clear that the adhesion became extremely high and the adhesion increased, leading to seizure. Also, if the carbide is on the roll surface,
It was found that the adhesion stopped at the carbide, and even if the adhesion was repeated with the rotation of the roll, the adhesion did not progress any further. This means that if most of the roll surface can be covered with carbide, the roll and steel strip will not seize. Therefore, the inventors of the present invention have studied various roll materials. As a result, in the roll containing WC (tungsten carbide) as a main component of the present invention, carbide is finely dispersed on the roll surface, and the roll and the steel strip are not seized. That is the reason. WC alloys include, for example, WC50% to 99%, Co0 to 30%.
% And / or Ni0 to 30% and / or other combinations.

In the present invention, an integral roll of WC alloy may be used, but since the cost is high, only the roll barrel portion is made of WC alloy and the roll neck portion is made of a conventional steel alloy, or the roll barrel is made. It is preferable that only the surface layer of the portion is made of WC alloy. Further, as a method of forming the WC alloy only on the surface layer of the roll barrel portion, the WC alloy may be fitted to the conventional steel alloy or may be sprayed, but the thickness thereof is 0.5.
It is desirable to set it to mm or more.

Further, in the method according to the present invention, as a preliminary treatment before cold rolling, based on the above-mentioned findings, the non-lubricated rolling in which the liquid such as rolling oil is not supplied and the reduction ratio of more than 5% to 30% or less is also obtained. It is done with and.

The reason why the rolling reduction of more than 5% is required in the non-lubricating rolling is as follows. In the study of the present inventors, the rolling ratio during non-lubrication rolling before cold rolling was variously passed, and then cold rolling was performed by supplying a rolling oil, finish annealing pickling or finish bright annealing, and finishing. The surface gloss of the product finished by temper rolling was investigated. In addition, the surface glossiness is JIS Z 8741 glossiness measuring method 5 (GS20 °).
Was measured according to. As a result, in both the cold tandem mill using a large diameter work roll and the Sendzimir mill using a small diameter work roll, increasing the rolling reduction during non-lubrication rolling almost changed the surface gloss up to 5%. However, if it exceeds 5%, the surface gloss becomes extremely good.

As described above, the non-lubricating rolling under the rolling reduction of more than 5% remarkably improves the surface gloss, but on the other hand, it requires a high rolling reduction which is not available in the prior art. With conventional rolls, seizure flaws are likely to occur because the roll and the steel strip are in direct contact with each other in a non-lubricated state. Therefore, it is necessary to roll at a low speed to prevent seizure flaws. In the study by the present inventors, as a result of investigating the presence or absence of seizure by variously changing the reduction ratio during unlubricated pretreatment rolling using a work roll of WC alloy, the seizure progressed up to a reduction ratio of 30%. Therefore, it was decided that the reduction rate should be 30% or less.

The non-lubricating rolling in the method of the present invention may be carried out at any timing and at any position after annealing, pickling and before cold rolling of the hot rolled steel strip.

[0027]

【Example】

(Example 1) (Table 1) Material thickness as an example of ferritic stainless steel strip 4.
After annealing and pickling a hot rolled steel strip using a 0 mm SUS430 steel strip, as an example of the method of the present invention, a roll shaft core is made of high-speed steel and a WC alloy containing 10% Co is fitted to the outer circumference of the roll. The work roll is applied to reduce the steel strip to 13%.
It was pretreated and rolled without lubrication.

Further, as a comparative example, a work roll made of ordinary 5% Cr forged steel was applied and pretreatment-rolled at the same rolling reduction.

Further, as a conventional example, no pretreatment rolling was performed, and only annealing pickling was performed. These steel strips were cold-rolled with a 5-stand cold tandem mill to a finish thickness of 1.0 mm, then finish-annealed, pickled, and temper-rolled at an elongation of 1.0% to investigate the luster of the steel strip surface.

The surface gloss of these stainless cold-rolled steel strips was measured according to JIS Z 8741 Gloss Measuring Method 5 (GS20 °), and in order of goodness, glossiness of 950 or more was specified as A, 800-950, A, 600-800. B, 400 to 600 were designated as C, and 400 or less were designated as D, and the evaluation was carried out in five stages.

From the results shown in Table 1, the stainless cold-rolled steel strips produced by the method of the present invention had remarkably good gloss as compared with the steel strips produced by the methods of Comparative Example and Conventional Example.

[Table 1]

(Example 2) (Table 2) Material thickness as an example of ferritic stainless steel strip 5.
After annealing and pickling the hot rolled steel strip using 0 mm SUS430 steel strip, as an example of the method of the present invention, an integrated work roll of WC alloy containing 30% Co is applied to reduce the steel strip. Rolled at a rate of 20% without lubrication.

Further, as a comparative example, a work roll using a usual 3% Cr forged steel was applied and pretreatment rolling was performed at the same reduction rate.

Further, as a conventional example, no pretreatment rolling was performed, and only annealing pickling was performed. These steel strips were cold-rolled with a 5-stand cold tandem mill to a finish thickness of 2.0 mm, then finish-annealed, pickled, and temper-rolled at an elongation of 1.2% to examine the luster of the steel strip surface.

The gloss evaluation method was the same as in Example 1.
From the results shown in Table 2, the stainless cold-rolled steel strip manufactured by the method of the present invention had remarkably good gloss as compared with the steel strips manufactured by the methods of Comparative Example and Conventional Example.

[Table 2]

(Example 3) (Table 3) Material thickness as an example of ferritic stainless steel strip 3.
As an example of the method of the present invention after annealing and pickling a hot-rolled steel strip using a 0 mm SUS430 steel strip, as an example of the method of the present invention, a WC containing 5% Ni on the outer circumference of the roll is used as the cold die steel.
Applying a work roll fitted with an alloy to reduce the steel strip
Pretreatment rolling was performed at 9% without lubrication.

Further, as a comparative example, a work roll made of ordinary 5% Cr forged steel was applied and pretreatment-rolled at the same rolling reduction.

Further, as a conventional example, no pretreatment rolling was performed, and only annealing pickling was performed. These steel strips were cold-rolled with a 5-stand cold tandem mill to a finish thickness of 0.7 mm, then finish-annealed, pickled and temper-rolled at an elongation of 0.8% to examine the luster of the steel strip surface.

The gloss evaluation method was the same as in Example 1.
From the results shown in Table 3, the stainless cold-rolled steel strip produced by the method of the present invention had remarkably good gloss as compared with the steel strips produced by the methods of Comparative Example and Conventional Example.

[Table 3]

(Example 4) (Table 4) Material thickness as an example of ferritic stainless steel strip 4.
As an example of the method of the present invention, after the hot rolled steel strip is annealed and pickled using a 0 mm SUS430 steel strip, as an example of the method of the present invention, the roll neck is made of semi-high-speed steel, and the roll barrel is provided with a WC alloy containing 15% Ni. By applying a roll, the steel strip was pretreated and rolled at a rolling reduction of 15% without lubrication.

Further, as a comparative example, a work roll using a usual 3% Cr forged steel was applied and pretreatment-rolled at the same reduction rate.

Further, as a conventional example, no pretreatment rolling was performed, and only annealing pickling was performed. These steel strips are cold-rolled with a 5-stand cold tandem mill to a finish thickness of 1.3 mm, and then cold die steel small diameter work rolls are used.
20-stage Sendzimir rolling mill with intermediate thickness of 1.3 mm to finish thickness
It was rolled to 1.0 mm in 5 passes, finish-annealed, pickled, and temper-rolled at an elongation of 1.0%.

The gloss evaluation method was the same as in Example 1.
From the results shown in Table 4, the stainless cold-rolled steel strip produced by the method of the present invention had remarkably good gloss as compared with the steel strips produced by the methods of Comparative Example and Conventional Example.

[Table 4]

(Example 5) (Table 5) An example of the method of the present invention after annealing and pickling a hot rolled steel strip using a SUS304 steel strip having a material thickness of 4.0 mm as an example of an austenitic stainless steel strip As a WC with a roll shaft core made of high-speed steel and containing 10% Co on the outer circumference of the roll
Applying a work roll fitted with an alloy to reduce the steel strip
Pretreatment rolling was performed at 13% without lubrication.

As a comparative example, a work roll made of ordinary 5% Cr forged steel was applied and pretreatment-rolled at the same reduction rate.

Further, as a conventional example, no pretreatment rolling was performed, and only annealing pickling was performed. These steel strips are cold-rolled in a 5-stand cold tandem mill to a finish thickness of 1.3 mm, then finish-annealed, pickled, temper-rolled with an elongation of 0.6%, and buffed with # 600 for 3 passes. The surface gloss of the steel strip was investigated.

The gloss evaluation method was the same as in Example 1.
From the results shown in Table 5, the stainless cold-rolled steel strip manufactured by the method of the present invention had remarkably good gloss as compared with the steel strips manufactured by the methods of Comparative Example and Conventional Example.

[Table 5]

Example 6 (Table 6) One example of the method of the present invention after annealing and pickling a hot-rolled steel strip using a SUS304 steel strip having a material thickness of 5.0 mm as an example of an austenitic stainless steel strip As Co is 30%
The work roll of the contained WC alloy was applied and the steel strip was pretreated and rolled at a rolling reduction of 30% without lubrication.

Further, as a comparative example, a work roll using a usual 3% Cr forged steel was applied and pretreatment rolling was carried out at the same reduction rate.

Further, as a conventional example, no pretreatment rolling was performed, and only annealing pickling was performed. These steel strips are cold-rolled in a 5-stand cold tandem mill to a finish thickness of 2.3 mm, then finish-annealed, pickled, temper-rolled at an elongation of 0.8%, and buffed with # 400 buff for 5 passes. The surface gloss of the steel strip was investigated.

The gloss evaluation method was the same as in Example 1.
From the results shown in Table 6, the stainless cold-rolled steel strip manufactured by the method of the present invention had remarkably good gloss as compared with the steel strips manufactured by the methods of Comparative Example and Conventional Example.

[Table 6]

(Example 7) (Table 7) An example of the method of the present invention after annealing and pickling a hot rolled steel strip using a SUS304 steel strip having a material thickness of 3.0 mm as an example of an austenitic stainless steel strip As a roll die, cold die steel was used, and a work roll fitted with a WC alloy containing 5% Ni was applied to the outer circumference of the roll, and the steel strip was pretreated and rolled at a reduction rate of 9% without lubrication. .

In addition, as a comparative example, a work roll using a normal 3% Cr forged steel was applied and pretreatment-rolled at the same reduction rate.

Further, as a conventional example, no pretreatment rolling was performed, and only annealing pickling was performed. These steel strips are cold-rolled with a 5-stand cold tandem mill to a finish thickness of 0.98 mm, then finish-annealed, pickled, temper-rolled at an elongation of 1.0%, and buffed with # 400 for one pass. The surface gloss of the steel strip was investigated.

The gloss evaluation method was the same as in Example 1.
From the results shown in Table 7, the stainless cold-rolled steel strip produced by the method of the present invention had remarkably good gloss as compared with the steel strips produced by the methods of Comparative Example and Conventional Example.

[Table 7]

(Example 8) (Table 8) One example of the method of the present invention after annealing and pickling a hot rolled steel strip using a SUS304 steel strip having a material thickness of 3.0 mm as an example of an austenitic stainless steel strip A semi-high-speed steel was used as the roll neck, and a work roll having a WC alloy containing Ni of 15% was applied to the roll barrel, and the steel strip was pretreated and rolled at a rolling reduction of 13% without lubrication.

As a comparative example, a work roll made of ordinary 5% Cr forged steel was applied and pretreatment-rolled at the same reduction rate.

Further, as a conventional example, no pretreatment rolling was performed, and only annealing pickling was performed. These steel strips are cold-rolled in a 5-stand cold tandem mill to a finish thickness of 1.3 mm, and then cold-rolled in a 12-stage cluster mill using high speed small work rolls from an intermediate thickness of 1.3 mm to a finish thickness of 0.8 mm. Then, finish annealing, pickling, temper rolling with an elongation of 0.6%, and buffing with # 600 were performed for 2 passes to examine the gloss of the steel strip surface.

The gloss evaluation method was the same as in Example 1.
From the results shown in Table 8, the stainless cold-rolled steel strip manufactured by the method of the present invention had remarkably good gloss as compared with the steel strips manufactured by the methods of Comparative Example and Conventional Example.

[Table 8]

[0060]

As described above, the stainless cold-rolled steel strip manufactured by the method of the present invention has remarkably excellent surface gloss as compared with the steel strips manufactured by the methods of Comparative Example and Conventional Example. 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. Further, according to the method of the present invention, it is possible to reduce the capital investment of the rolling oil coolant and the maintenance management of the equipment. Further, since seizure does not progress, the speed of pretreatment rolling can be increased, and the effect of improving rolling efficiency can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Eisuke Kawasumi, Eisuke Kawasumi 1st, Kawasaki-cho, Chuo-ku, Chiba, Chiba Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Hoichi Kiyono, 1st, Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Taka Akazawa 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works

Claims (1)

[Claims] 1. A stainless steel strip after hot rolling is annealed and pickled, and a work roll made of a WC alloy is used to unlubricate at a rolling reduction of more than 5% and less than 30%. A method of manufacturing a stainless steel pretreated steel strip for cold rolling, which comprises rolling.