JPH0747163B2 - 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 has conventionally been concerned with 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 of the invention is to solve the problem of reduction in surface gloss of stainless 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.

In the present invention according to claim 1, the stainless steel strip after the hot rolling is subjected to annealing pickling, and then subjected to non-lubricating rolling under a reduction rate of more than 5%, and then cold tandem. At each stand of the mill, a rolling oil having a viscosity of 50 c at 15 cSt or less is supplied as an emulsion, and at least at a final stand, a rolling oil having a viscosity of 50 c at 7 cSt or less is supplied as an emulsion, and cold. It was rolled.

According to a second aspect of the present invention, in the first aspect, 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 a steel strip before cold rolling, that is,
It was 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 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.

Here, the reason why a rolling reduction of more than 5% is required during non-lubricating rolling is as follows.

In the study of the present inventors, various reduction ratios at the time of non-lubricating rolling, passing the steel strip annealed and pickled after hot rolling,
After that, the surface gloss of the stainless cold-rolled steel strip finished by cold rolling, finish annealing pickling or finish bright annealing, and finish temper rolling was investigated.

As a result, rolling using a large-diameter work roll such as a cold tandem mill, and, in any case of rolling using a small-diameter work roll such as a Sendzimir mill, if the reduction rate during non-lubricating 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%, it is remarkably good.

However, when the stainless steel strip after the non-lubricating rolling 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, and after rolling, finishing There is a new problem that reduces the surface gloss of the product.

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, it has not been known at all about the case of cold rolling a non-lubricated stainless steel strip with a rolling reduction of more than 5% according to the present invention. Therefore, the present inventors have found that the oil pits can be reduced by the following actions as a result of cold rolling by supplying various rolling oils having different viscosities to the stainless steel strip after the non-lubrication rolling. .

(1) When the rolling oil is bitten into the roll and the steel strip, by setting the viscosity of the rolling oil to a certain value or less, the amount of the biting oil can be significantly reduced, and the oil pit can be reduced.

(2) By setting the viscosity of the rolling oil to a certain value or less, the rolling oil enclosed in the scratches present on the surface of the roll and the steel strip enters the roll bite while the roll and the steel strip are in contact with each other. As a result, the protrusions of the roll roughness easily come into contact with the steel strip, and the oil pits formed by the protrusions of the roll roughness can be crushed and reduced.

Therefore, in order to reduce the oil pit, it is understood that it is better 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. Therefore, by supplying various rolling oils with different viscosities and rolling the stainless steel strip after the non-lubricating rolling, it is possible to supply the rolling oil having a viscosity of 15 cSt or less at 50 ° C. as an emulsion and perform cold rolling. We have found that it is effective in preventing oil pits.

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) If 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 sheet, the final stand needs to have a lower rolling reduction ratio 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 also becomes low, so that the low-viscosity rolling oil can be applied to the stands other than the final stand.

In the present invention described in claim 1, at least the viscosity of the rolling oil supplied to the final stand is set to 7 cSt or less at 50 ° C. for the following reason.

That is, the stainless steel strip after the non-lubricating 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 7c at 50 ° C.
This is because it has been found that an oil pit can be prevented more remarkably by using St or less than when using a rolling oil having a viscosity of 15 cst.

Also, as in the present invention according to claim 2, 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.

In addition, Japanese Patent Laid-Open No. 64-83305 discloses, "In the stand before the last one from the first stand of the cold tandem mill.
Rolling is performed by supplying a rolling oil having a viscosity of 50 cC or less at 15 cSt or less in an emulsion state, and by supplying a water-soluble lubricant having a viscosity of 5 cSt or less at 50 ° C. after water dispersion in the final stand and rolling. Things ”are disclosed. That is, in the present invention, the rolling oil emulsion is supplied to all stands of the cold tandem mill, and the viscosity of 50 ° C is maintained at the final stand.
Rolling oil having a viscosity of 7 cSt or less is supplied as an emulsion, whereas in JP-A-64-83305, a water-soluble lubricant is supplied to the final stand. Here, the emulsion of rolling oil is obtained by dispersing rolling oil in water, whereas the water-soluble lubricant is obtained by dissolving lubricant in water, and both are fundamentally different. In the final stand, the one supplying the water-soluble lubricant is more likely to contact the roll and the steel strip than the one supplying the rolling oil, and it is difficult to improve the gloss by causing a seizure flaw called heat streak. On the other hand, in the present invention, since the rolling oil having a viscosity of 50 c at the final stand of 7 cSt or less is supplied, the oil pit is sufficiently reduced while suppressing the occurrence of a seizure flaw called heat streak, and the steel strip after cold rolling is used. The surface gloss of can be significantly improved. This difference in the effect of improving gloss is different from the results of determining the glossiness (JIS-Z8741) described in Tables 1 and 2 described later and JP-A-64-8330.
Judgment result of glossiness (JIS-
From comparison with Z8741) it is clear that the one according to the invention is more effective.

[Example] According to the method of the present invention, ferritic SUS430 steel strip that has been subjected to intermediate annealing and pickling after hot rolling was subjected to non-lubricant rolling with the reduction ratio shown as an example in Table 1, and then shown as an example in the same table. After supplying various rolling oils having different viscosities and rolling in a cold tandem mill, finish annealing pickling and finish temper rolling were performed. Also, the second
As shown in the table, as an example, after performing lubrication rolling in the same manner as in Table 1, rolling with a cold tandem mill using rolling oils with viscosities shown in Table 2 and rolling oils with viscosities shown in the same table After rolling using a small diameter work roll, finish annealing pickling and finish temper rolling were performed.

Regarding the surface gloss of these steel strips, the results of visual judgment are shown in Tables 1 and 2. In addition, the visual determination was made into four stages of A to D in order of good gloss. When the gloss by visual judgment is quantified by JIS-Z8741 gloss measurement method 5 (GS20 °), A is 800 or more, B is 600 to 800,
C corresponds to 400 to 600 and D corresponds to 400 or less.

In addition, all the stands of the cold tandem mill supply the emulsion of rolling oil, and the final stand has a viscosity of 50 ° C.
The results for the product obtained in the comparative example in which the emulsion of rolling oil exceeding 7 cSt is supplied and the results for the product obtained by the conventional production method are also shown.

It can be seen from Tables 1 and 2 that the stainless cold-rolled steel strip manufactured by the method of the present invention has remarkably good surface gloss as compared with the case of the conventional method, and the method of the present invention improves surface gloss. It is clear that it is extremely effective.

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 was able to obtain remarkably better surface gloss than before even when finishing bright annealing is performed after cold rolling.

[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 (2)

[Claims] 1. A stainless steel strip after hot rolling is subjected to annealing and pickling, and then subjected to non-lubricating rolling under a rolling reduction of more than 5%, and thereafter, to each stand of a cold tandem mill. The viscosity of 50 ℃, the rolling oil having a viscosity of 15 cSt or less is supplied as an emulsion, and at least in the final stand, the viscosity of the rolling oil having a viscosity of 50 c of 7 cSt or less is supplied as an emulsion,
A method for manufacturing a stainless cold-rolled steel strip, which comprises cold rolling. 2. A method for producing a cold rolled stainless steel strip according to claim 1, further comprising rolling with a cold tandem mill and then rolling with a small diameter roll having a work roll diameter of 150 mmφ or less.