JPH0739001B2 - Method for producing stainless cold-rolled steel strip - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a cold rolled stainless 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 provides stainless steel that has been conventionally used in cold rolling using a large diameter work roll such as a cold tandem mill and then cold rolling using a small diameter work roll such as a Sendzimir mill. The purpose is to solve the problem of reduction in surface gloss of cold rolled steel strip.

[Means for Solving the Problems] The present invention provides a method for solving the above-mentioned problems and producing a stainless cold-rolled steel strip having excellent surface gloss.

That is, according to the present invention as set forth in claim 1, the stainless steel strip after hot rolling is subjected to annealing pickling, and then the roll surface has a thickness of 1
Pretreatment rolling with a liquid lubricant of less than μm under a rolling reduction of more than 5%, and then at each stand of the cold tandem mill, apply a rolling oil with a viscosity of 15 cSt or less at 50 ° C. The emulsion is supplied and cold-rolled.

Further, the present invention according to claim 2 is such that, in claim 1, at least at the final stand of the cold tandem mill, a rolling oil having a viscosity at 50 ° C. of 7 cSt or less is supplied for cold rolling. is there.

Further, the present invention according to claim 3 is such that, in claim 1 or 2, after rolling with a cold tandem mill, rolling is further performed with a small diameter roll having a work roll diameter of 150 mmφ or less.

[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 rolling mill entrance side. 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 coefficient of friction is significantly increased, the rolling load is significantly increased, and at the same time, the rolling reduction necessary to sufficiently reduce the irregularities on the surface of the steel strip is taken. 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, in any case of rolling using a large-diameter work roll such as a cold tandem mill, and then cold-rolling using a small-diameter work roll such as Sendzimir aluminum, the reduction ratio at the time of pretreatment rolling is changed. When the rolling reduction is 5% or less, the surface gloss of the product finished by cold rolling is hardly improved, but when it exceeds 5%, the surface gloss is remarkably improved.

However, when the stainless steel strip after the pretreatment rolling of the present invention is cold-rolled by supplying a large amount of rolling oil thereafter, a large amount of surface defects called oil pits may be generated during rolling. However, a new problem arises that reduces the surface gloss of the finished product after rolling.

Generally, oil pits are those that remain on the surface of the steel strip in the intragranular slip zone of crystal grains, which is said to be related to the material, and it is related to a thin layer of rolling oil contained between the roll and the steel strip during rolling. It is known.

Therefore, the present inventors have focused on rolling oil and its emulsion to be supplied at the time of cold rolling as a method for preventing this oil pit, and studied. It was generally known that reducing the viscosity of the rolling oil improves the surface gloss of the steel strip, but it was not clear to what extent it should be reduced. In particular, in the case of cold rolling a stainless steel strip that has been pretreated and rolled at a rolling reduction of more than 5% according to the present invention,
Not known at all. Therefore, the present inventors have found that a large amount of various rolling oils having different viscosities are supplied to the stainless steel strip after the pretreatment rolling and cold rolling is performed, and as a result, the oil pits can be reduced by the following actions. That is why.

(1) When the rolling oil is bited into the roll and the steel strip, the viscosity of the rolling oil is set to a certain value or less, so that the amount of the bited oil can be significantly reduced and the oil pit can be reduced.

(2) By setting the viscosity of rolling oil to a certain value or less,
While the roll and the steel strip are in contact, the rolling oil enclosed in the scratches on the surface of the roll and the steel strip easily escapes to the inlet side or the outlet side of the roll bite, and the protrusion of the roll roughness makes sufficient contact with the steel strip. As a result, it is possible to crush and reduce the oil pit in which the protrusion having the roll roughness is generated.

Therefore, in order to reduce the oil pit, it is understood that it is preferable to significantly reduce the viscosity of the rolling oil as compared with the conventional rolling oil whose viscosity at 50 ° C. was 30 cSt or more. Then, as a result of supplying various rolling oils having different viscosities and rolling the stainless steel strip after the pretreatment rolling of the present invention, 15 cSt at 50 ° C.
It was understood that it is effective to prevent oil pits by supplying a rolling oil having the following viscosity as an emulsion and cold rolling.

Further studies were conducted to improve the surface gloss. That is, it is better to further reduce the viscosity of the rolling oil. However, there are the following problems in applying the rolling oil having a lower viscosity.

(1) When the rolling oil has a low viscosity, the roll and the steel strip are likely to come into contact with each other, and seizure flaws called heat streaks are likely to occur.

(2) It is necessary to sufficiently reduce the oil pit in the stand that most affects the final product.

The stand that satisfies these conditions is at least the final stand. That is, in order to control the shape of the steel plate, the final stand needs to have a lower rolling reduction than the other stands, and as a result, heat streak is most unlikely to occur.

Further, when the total rolling reduction during cold rolling is low, the rolling reduction of each stand is also low, so that the low-viscosity rolling oil can be applied to stands other than the final stand.

In the present invention as set forth in claim 2, the reason why the viscosity of the rolling oil supplied to at least the final stand is set to 7 cSt or less at 50 ° C. is as follows.

That is, the stainless steel strip after the pretreatment rolling of the present invention, various rolling oils having different viscosities are supplied to the final stand, and rolling oil having a viscosity of 15 cSt at 50 ° C. is supplied to the other stands to be cold. The oil pits of the rolled and finished product were investigated.
As a result, the rolling oil supplied to the final stand has a viscosity of 50 ° C.
This is because it has been found that the oil pit can be significantly prevented by setting the viscosity to 7 cSt or less as compared with the case where the rolling oil having the viscosity of 15 cSt is used.

Also, as in the present invention according to claim 3, when rolling is performed using a small diameter work roll having a diameter of 150 mm or less, such as a Sendzimir mill, after rolling in the cold tandem mill according to the method of the present invention, the finished product after rolling is The surface gloss can be remarkably improved.

[Example] According to the method of the present invention, a ferritic SUS430 steel strip subjected to intermediate annealing and pickling after hot rolling was subjected to a pretreatment rolling with a reduction rate shown as an example in Table 1 using a skin pass oil, and then the same table was used. Various rolling oils having different viscosities shown as examples were supplied and rolled in a cold tandem mill, followed by finish annealing pickling and finish temper rolling. Further, as a comparative example of the present invention, it was also carried out when the reduction ratio during the pretreatment rolling was low and when the viscosity of the rolling oil used for cold rolling after the pretreatment rolling exceeded 15 cSt (50 ° C).

Regarding the surface gloss of these steel strips, the results of visual judgment are shown in Table 1. In addition, the visual determination was made into four stages of A to D in order of good gloss. JIS-Z gloss based on visual judgment
8741 Gloss level 5 (GS20 °) quantified, A is 800 or more, B is 600-800, C is 400-60
0 and D correspond to 400 or less.

In addition, the results of the products obtained by the conventional manufacturing method are also shown.

From Table 1, the stainless cold-rolled steel strip manufactured by the method of the present invention has a remarkably good surface gloss as compared with the case of the conventional method, and the method of the present invention is remarkably effective in improving the surface gloss. It is clear.

It was confirmed that the method of the present invention is not limited to ferrite-based SUS430 and can be applied to austenite-based SUS304, etc., because it is possible to obtain sufficiently good results and is an effective method. In particular, SU
The product subjected to the finish annealing pickling of S304 gives surface gloss by buffing etc. after that, when the method of the present invention is applied,
The surface gloss after buffing was also significantly improved compared to the steel strip produced by the conventional method.

Further, the method of the present invention is not limited to the case of using a large-diameter work roll such as a cold tandem mill, and when using a small-diameter work roll such as a Sendzimir mill after that, the same good surface gloss as described above can be obtained. You can

[Effects of the Invention] 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 stainless cold-rolled steel strip manufactured by the conventional method. In particular, in the case of rolling by a cold tandem mill, it has an excellent surface gloss equal to or higher than that obtained by rolling only by a Sendzimir mill, which has hitherto been unattainable.

 ─────────────────────────────────────────────────── ─── 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 (3)

[Claims] 1. A stainless steel strip after hot rolling is subjected to annealing pickling, and then pretreated with a liquid lubricant having a thickness of 1 μm or less applied on the roll surface under a rolling reduction of more than 5%. A method for producing a stainless cold-rolled steel strip, which comprises rolling and then cold-rolling at each stand of a cold tandem mill by supplying a rolling oil having a viscosity of 15 cSt or less at 50 ° C. as an emulsion and cold-rolling. 2. The stainless cold-rolled steel strip according to claim 1, wherein at least at the final stand of the cold tandem mill, rolling oil having a viscosity of 50 ° C. of 7 cSt or less is supplied for cold rolling. Production method. 3. The method for producing a stainless cold-rolled steel strip according to claim 1 or 2, further comprising rolling with a small diameter roll having a work roll diameter of 150 mmφ or less after rolling with a cold tandem mill.