JPH0739003B2 - Manufacturing method of stainless pretreated steel strip for cold rolling - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pretreatment of a stainless steel strip for cold rolling, which can advantageously produce a stainless cold-rolled steel strip having excellent surface gloss.

[Prior Art] Conventionally, cold-rolled stainless steel strips are produced by annealing hot-rolled steel strips by annealing.
After the pickled surface is cold-rolled with a large amount of rolling oil in a work roll diameter of 150 mmφ or less with a Sendzimir mill, etc., finish annealing, pickling or bright annealing is performed, and a finish reduction of 1.2% or less is achieved. It was manufactured by quality rolling.

The stainless cold-rolled steel strip manufactured through these steps, for example, in the case of ferritic typified by SUS430, it is often used as it is after the production, and the surface after finishing temper rolling is excellent. Luster is required. Further, in the case of an austenitic type typified 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, a method of devising roll roughness disclosed in JP-B-57-13362 has been adopted. However, even if this method was used, the significantly large roughness of the steel strip surface annealed and pickled after hot rolling and before cold rolling remained as a result until after cold rolling, resulting in unsatisfactory surface gloss. .

On the other hand, a method of cold rolling with a work roll having a large diameter of 150 mmφ or more is adopted as a method for manufacturing a stainless cold-rolled steel strip with a high efficiency by significantly shortening the rolling time. However, the surface roughness of the steel strip cold-rolled with a large-diameter work roll is as mentioned above, the remarkably large roughness of the annealed and pickled surface of the hot-rolled steel strip remains after cold-rolling, and the small-diameter work roll is still used. The product could not be applied at all to applications requiring surface gloss, because the roughness remained higher than that of the cold rolling using.

Therefore, as a method for solving this type of surface gloss reduction problem, conventionally, for example, a method of devising a combination of work roll diameters has been disclosed in JP-A-61-49701. This is a method for preventing defects called gold dust, which has a purpose different from that of the present application for improving the surface gloss itself. However, when this method is adopted, the aforementioned Japanese Patent Publication No. 57-13362 is used. Similar to the technique described in the publication, remarkably large roughness of the surface of the steel strip annealed and pickled after hot rolling remained after cold rolling, the surface gloss of the product was insufficient, and further improvement was required. .

[Problems to be Solved by the Invention] The present invention has hitherto been involved in rolling using a small diameter work roll such as a Sendzimir mill, rolling using a large diameter work roll such as a cold tandem mill, and cold rolling combining these. The purpose is to solve the problem of reduced surface gloss.

[Means for Solving the Problems] The present invention solves the above-mentioned problems, and in order to produce a stainless cold-rolled steel strip having excellent surface gloss, a method of pretreating a stainless steel strip prior to cold rolling. Is provided.

That is, the present invention anneals the stainless steel strip after hot rolling and then performs a surface texture adjustment treatment to reduce the steel strip surface roughness to an average roughness Ra of 2 μm or less, and further to a roll surface of a thickness of 1 μm or less. The above liquid lubricant is applied and rolling is performed under a rolling reduction of more than 5%.

[Operation] Hereinafter, the present invention will be described in detail.

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 that affects the surface roughness of the product.

However, in the study by the present inventors, the surface roughness of the steel strip after cold rolling described above is one of the surface roughness of the steel strip before cold rolling, that is, the surface roughness of the steel strip annealed and pickled after hot rolling. It has been found that the part remains after cold rolling.

Therefore, the influence of the surface roughness of the steel strip annealed and pickled after hot rolling will be described below. The average roughness Ra0 in the final finished product.
In the production of cold-rolled stainless steel strips with the goal of obtaining a surface roughness of 1 μm or less, the surface roughness of the steel strip immediately after annealing and pickling the hot-rolled steel strip is the mechanical strength such as shot blasting during pickling. Descaling treatment and acid such as sulfuric acid, mean roughness Ra
It has a remarkably large roughness of 2 to 4 μm.

By the way, generally, during cold rolling, a large amount of rolling oil is supplied to the roll bite from the entrance side of the rolling mill. This is carried out in order to prevent the occurrence of seizure flaws such as heat streaks and to stably manufacture the steel strip by simultaneously performing lubrication and cooling with rolling oil on the steel strip surface and the roll surface. Therefore, on the entry side of cold rolling, a large amount of rolling oil having a thickness of several μm or more adheres to the surface of the steel strip, and as a result of the annealing pickling after hot rolling, the steel strip surface has a significantly large roughness. The recess is filled with oil and bites into the roll bite. The oil filled in the dents is rolled while it is contained and there is no escape while the roll and the steel strip are in contact with each other in the roll bite.

In general, liquids including rolling oil are significantly less likely to be compressed than gases such as air, so the pits filled with oil during rolling will be somewhat smaller than before rolling, but most will 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 with good surface gloss,
It is understood that it is better to reduce the unevenness on the surface of the steel strip before cold rolling.

That is, based on the above-mentioned findings, it is better to perform unlubricated rolling without using a liquid such as rolling oil on the steel strip before cold rolling.

However, when non-lubricated rolling is applied, the roll and the steel strip are seized, the friction coefficient is significantly increased, the rolling load is significantly increased, and at the same time, the reduction ratio necessary to sufficiently reduce the irregularities on the surface of the steel strip can be obtained. There were cases where there was no.

Therefore, the present inventors have examined a pretreatment method for a stainless steel strip that simultaneously satisfies the following two points.

(1) Pretreatment Roll and steel strip should not be seized during 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 methods were recognized.

(A) A method in which a very thin liquid film is formed on the roll surface and lubricated.

(B) A method of performing non-lubricating rolling with a surface-treated roll.

Here, as the method of utilizing the surface treatment of the roll of (B), various conventionally known surface treatments have been tried, but they have a seizure preventing effect as compared with the solid roll, but they are still insufficient.

On the other hand, the thin film lubrication method (A) has a significantly large seizure prevention effect despite the thin liquid film.
Further, the thinner the liquid film is, the more the surface irregularities of the steel strip annealed and pickled after hot rolling can be sufficiently reduced. According to the study by the present inventors, if the film thickness on the roll surface is 1 μm or less, most of the surface irregularities can be eliminated, and it is better if the film thickness is 0.5 μm or less. It was understood that a large amount of unevenness remained when it exceeded, and it could not be erased even in the subsequent cold rolling.

As the liquid lubricant, any of water, skin pass oil, rolling oil, rolling oil emulsion and the like has a seizure prevention effect and a surface unevenness reducing effect, but a liquid lubricant having a viscosity of about 1 to 15 cSt is desirable.

Here, the reason why the rolling reduction of more than 5% is required in the pretreatment rolling is as follows.

In the study of the present inventors, by varying the reduction ratio during pretreatment rolling, the steel strip is annealed and pickled after hot rolling, and then passed through cold rolling, finish annealing pickling or finish bright annealing, Also, the surface gloss of the stainless cold-rolled steel strip finished by finishing temper rolling was investigated.

As a result, rolling using a small-diameter work roll such as a Sendzimir mill, rolling using a large-diameter work roll such as a cold tandem mill, and in any case of cold rolling combining these, reduction in pretreatment rolling When the reduction ratio is changed, the surface gloss is hardly improved when the rolling reduction is 5% or less, but it becomes remarkably good when the rolling reduction exceeds 5%.

Here, a method for further improving the surface gloss of the steel strip was examined.

In the method of pretreatment rolling with a liquid lubricant having a thickness of 1 μm or less applied to the roll surface under a rolling reduction of more than 5% according to the present invention, a steel strip on the inlet side of the pretreatment rolling, that is, a hot rolled steel strip. Annealing, the surface roughness of the steel strip after subjected to a surface property adjustment treatment such as mechanical descaling and pickling, affects the surface roughness of the steel strip on the pretreatment rolling exit side, for example,
The smaller the surface roughness of the steel strip after the surface property adjusting treatment, the smaller the surface roughness of the steel strip after the pretreatment rolling. as a result,
When a stainless steel strip that has been pretreated and rolled with a liquid lubricant having a thickness of 1 μm or less applied to the roll surface is then cold-rolled by supplying a large amount of rolling oil to finish annealing pickling and finish temper rolling. , Found that the cold-rolled steel strip has further improved surface gloss.

Therefore, annealing the hot rolled steel strip, variously changing the surface roughness of the steel strip after subjected to the surface property adjustment treatment such as mechanical descaling and pickling, subjected to the pretreatment rolling of the present invention, then,
After cold rolling supplying a large amount of rolling oil, finish annealing pickling and finish temper rolling, the surface gloss of the stainless cold rolled steel strip was investigated.

As a result, the surface roughness of the stainless steel cold rolled steel strip was reduced by setting the average surface roughness Ra2μm or less after the steel strip surface roughness after the surface texture adjustment treatment, which had a significantly large average roughness Ra of 2 to 4 μm. Have been found to be significantly improved.

Here, as the surface property adjusting method of the steel strip, other than only pickling, mechanical descaling such as shot blasting, liquid honing, tension leveler, mechanical treatment such as brush, or chemical such as paste electrolysis. A wide variety of materials can be used depending on the treatment.

Example According to the method of the present invention, SUS430 steel strip as an example of a ferritic stainless steel that has been subjected to annealing pickling after hot rolling and having a surface roughness of Ra 2 μm or less, and an example of an austenitic stainless steel The SUS304 steel strip was pretreated and rolled under the reduction ratios shown in Tables 1 to 3 as examples, by supplying skin-pass rolling oil as the liquid lubricant. Further, as a comparative example of the present invention, the case where the above-mentioned surface roughness Ra exceeds 2 μm was also carried out. After that, cold rolling was performed, finish annealing pickling or finish bright annealing, and finish temper rolling, respectively. The steel strip that had been subjected to finish annealing pickling of SUS304 was subjected to finish temper rolling and then subjected to buff polishing under the same conditions.

Table 1 shows the case of cold rolling using a large diameter work roll by a cold tandem mill, and Table 2 shows the case of cold rolling using a small diameter work roll by a Sendzimir mill.
The table shows the case where cold rolling was carried out by the Sendzimir mill after rolling by the cold tandem mill.

Regarding the surface gloss of these stainless cold-rolled steel strips, the visual judgments thereof are also shown in Tables 1 to 3. In addition, the visual judgment was made into 5 grades of special A and A to D in order of good gloss.
The gloss by visual judgment is JIS-Z8741 gloss measurement method 5 (GS
When quantified by 20 °), special A has a gloss of 950 or more, A has a gloss of 800 to 950, B has 600 to 800, and C has 400 to 60.
0 and D correspond to 400 or less.

Also, a stainless cold-rolled steel strip obtained by a conventional manufacturing method, and as a comparative example, a surface texture adjustment treatment is performed to obtain an average roughness.
Ra was set to 2 μm or less, and then, at the time of pretreatment rolling, the visual judgment result of the surface gloss of the stainless cold-rolled steel strip obtained by the method in which the liquid lubricant was supplied in the state where the thickness exceeded 1 μm as in the conventional cold rolling. It is also shown.

In both cases of ferritic SUS430 steel strip and austenitic SUS304 steel strip, rolling using large diameter work rolls such as cold tandem mills shown in Tables 1 to 3, rolling using small diameter work rolls such as Sendzimir mill, And, in each of the rollings in which these are combined, the stainless cold-rolled steel strip produced by pretreatment by the method of the present invention has remarkably good surface gloss as compared with the steel strip produced by the conventional method. It is clear that the method is remarkably effective in improving the surface gloss.

[Effects of the Invention] As described above, the stainless cold-rolled steel strip produced by pretreatment by the method of the present invention has remarkably excellent surface gloss as compared with the stainless cold-rolled 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, a tandem suitable for mass production can be obtained with a surface gloss that is equal to or better than that of a product using a Sendzimir mill, which was previously unattainable. Use the mill efficiently
And we can supply high quality products.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Tomio Komatsu, 1 Kawasaki-cho, Chiba-shi, Chiba, Chiba Steel Works, Ltd. (72) Akira Kishida 1 Kawasaki-cho, Chiba, Chiba Kawasaki, Chiba In-house

Claims (1)

[Claims] 1. A stainless steel strip after hot rolling is annealed, and then subjected to a surface texture adjustment treatment to reduce the surface roughness of the steel strip to an average roughness Ra of 2 μm or less, and further to a roll surface thickness of 1 μm.
A method for producing a stainless pretreated steel strip for cold rolling, which comprises applying a liquid lubricant of m or less and rolling under a rolling reduction of more than 5%.