JPH01122604A - Manufacture of cold rolled stainless steel strip - Google Patents

Abstract

PURPOSE:To improve the surface brightness and production efficiency of a steel strip by intermediately annealing a stainless steel hot rolled strip, performing nonlubrication rolling with a specific draft, and rolling the strip by use of a work roll having specific outside diameter in the final pass of cold tandem rolling. CONSTITUTION:A hot rolled stainless steel strip is subjected to intermediate annealing and pickling and then to nonlubrication rolling with a draft of >5%. In the succeeding cold rolling, the final pass of tandem rolling, at least, is performed by use of a work roll whose outside diameter is <=400mm. Generation of seizing flaws of the strip is restrained because the nonlubrication rolling is executed at the low speed after the intermediate annealing and pickling. Further, generation of oil pits is markedly reduced because the final pass, at least, of cold rolling is performed by use of a comparatively small diameter work roll. The surface brightness is improved by restraining generation of flaws caused by preparatory nonlubrication rolling treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing cold-rolled stainless steel strip having excellent surface gloss.

<Prior art> Conventionally, stainless steel cold-rolled steel strips are produced by intermediately annealing and pickling a hot-rolled steel strip, and then cold-rolling the copper strip by supplying rolling oil in a Sendzimir rolling mill or the like with a work roll diameter of 100 mm or less. After finish annealing, pickling or finish bright annealing, finish temper rolling was performed at a rolling reduction of 1.2% or less.

For example, in the case of the ferritic cold-rolled stainless steel strip manufactured through this process, such as 5US430,
Excellent surface gloss is required for products after finish temper rolling, as they are used as they are after production for applications such as architectural interior materials, everyday appliances, and various decorative items. Also 5US304
In the case of austenitic materials, such as those typified by ferritic materials, they are often used for applications such as kitchen equipment that require higher corrosion resistance than ferritic materials, and those that have been given a surface gloss by puff polishing etc. after finishing temper rolling are used. Therefore, excellent surface gloss after puff polishing is important.

Furthermore, in recent years, a method has been adopted for manufacturing stainless steel strips with high efficiency using a cold tandem rolling mill using work rolls having a larger diameter than a Sendzimir rolling mill or the like. The reason for this is as follows.

(1) When the diameter of the work roll is increased, a large amount of rolling oil is trapped between the work roll and the copper strip, making it difficult for the work roll and the strip to come into contact with each other, making it difficult for seizure defects such as heat streaks to occur. Can be rolled at high speed.

(2) Compared to the Sendzimir rolling mill, which reverse-rolls the copper strip with one stand, cold tandem rolling uses multiple stands to roll the strip in one direction only to achieve the desired thickness of the strip. The rolling time can be greatly reduced.

However, when rolling stainless steel strips using this cold tandem rolling mill, a large amount of rolling oil is trapped between the work rolls and the copper strip, making it difficult for them to contact each other (as a result, the surface of the strip after rolling The roughness is significantly greater than that produced by a Sendzimir mill, etc. Therefore, due to this, stainless steel strips rolled by a tandem mill always suffer from the problem that their luster is significantly inferior to products rolled by a Sendzimir mill. and
These stainless steel products could only be used in areas where gloss was not an issue.

Therefore, conventionally, for example, Japanese Patent Application Laid-Open No. 59-10703,
After rolling with a cold tandem mill using large diameter rolls of 150a or more, 100
A method of rolling in a Sendzimir rolling mill using small diameter rolls is disclosed. These disclosed methods are:
This was done to improve the workability of the copper strip after rolling and to control defects on the surface of the copper strip such as ridging, and the purpose of the present invention is to improve the gloss of the surface of the copper strip. However, when attempting to cold-roll a stainless steel strip using these disclosed methods, the surface gloss of the stainless steel strip rolled only with a conventional Sendzimir rolling mill is almost the same. Sometimes they were on the same level.

However, when these disclosed methods were used, the following problems arose because the copper strip rolled in a cold tandem rolling mill using large-diameter rolls was then rolled in a Sendzimer rolling mill using small-diameter rolls.

(1) After rolling in the tandem rolling mill, the strip is transported to the Sendzimir rolling mill and the steel strip is loaded into the rolling mill, which takes a lot of time and significantly reduces productivity.

(2) In a Sendzimir rolling mill using small diameter rolls, the rolling speed must be lowered to prevent heat streaks as described above. On the other hand, since tandem rolling mills roll at high speeds to improve productivity, the stainless steel strips rolled by tandem mills must be temporarily stored, and a large yard is required to store the copper strips. ,
A large amount of equipment cost is required.

(3) When the strip is transported after being rolled by a tandem rolling mill, surface flaws such as scratches due to roll misalignment are likely to occur on the surface of the copper strip, and most of the copper strips with flaws cannot be made into products.

Therefore, in order to solve these problems and efficiently produce stainless steel strips, it is necessary to improve the surface gloss of copper strips produced only by cold tandem rolling mills without using Sendzimer rolling mills that use small diameter rolls. was necessary.

<Problems to be Solved by the Invention> Therefore, the present invention solves the conventional problem of reduced surface gloss in high-speed cold tandem rolling mills having large-diameter work rolls without reducing production efficiency. The purpose is to provide a method.

<Means for Solving the Problems> The method for producing a cold-rolled stainless steel strip according to the present invention includes intermediate annealing and pickling of a hot-rolled stainless steel strip, and further pretreatment of non-lubricated rolling at a rolling reduction of more than 5%. After this, when cold tandem rolling is performed, at least the final pass is rolled using work rolls having an outer diameter of 400 mm or less.

<Function> Generally, in order to improve the surface gloss of a cold-rolled stainless steel strip, the copper strip is subjected to finish annealing pickling or finish bright annealing, and the surface roughness of the product after finish temper rolling is #, Additionally, the surface roughness of this product is largely the same as the surface roughness of the steel strip after cold rolling, and the surface roughness after cold rolling is different from the finished product. It is known that it determines the quality of surface gloss. Therefore, in the past, as described above, a method has been adopted in which the surface roughness of the steel strip is reduced during or after cold rolling.

However, the inventors' studies revealed that the surface roughness of the copper strip after cold rolling, which significantly affects the surface gloss of the product, is due to the fact that part of the surface roughness (irregularities) of the steel strip before cold rolling is caused by rolling. It was discovered that it remained intact even after that. In other words, in the production of cold-rolled stainless steel strips whose goal is to reduce the surface roughness of the final finished product to an average roughness Ra of 0.1 μm or less, the base steel strip for cold rolling immediately after intermediate annealing and pickling is Due to mechanical descaling treatment such as shit blasting during pickling and acids such as sulfuric acid, the surface irregularities are reduced to an average roughness Ra of 2~2.
It is extremely large at 4 μm. On the other hand, during cold rolling, rolling oil is supplied to the rolls and the steel strip.

Therefore, on the entry side of cold rolling, this rolling oil adheres to the surface of the copper strip before rolling, collects in the concave portions of the surface with extremely large irregularities, and is caught between the roll and the copper strip. While the roll and the copper strip are in contact with each other, the oil accumulated in these recesses has no place to escape and is confined during rolling. In general, liquids containing rolling oil are significantly less compressible than gases such as air. Therefore, although the recesses in which oil was trapped during rolling become somewhat smaller than before rolling, most of them remain after rolling. In this way, the surface roughness (unevenness) of the copper strip before cold rolling remains after cold rolling, impairing the surface gloss of the product.

That is, in order to obtain a steel strip with excellent surface gloss, it is better to reduce the irregularities on the surface of the copper strip before cold rolling.
For this purpose, it is advantageous to smooth the surface of the copper strip by rolling, but as mentioned above, in conventional cold rolling using rolling oil, it is not possible to eliminate most of the unevenness on the surface of the copper strip before cold rolling. Can not.

Therefore, in the method according to the present invention, based on the above-mentioned knowledge, first, as a preliminary treatment before cold rolling, non-lubricated rolling is performed without supplying any liquid such as rolling oil, and at a rolling reduction of more than 5%.

Here, the reason why a rolling reduction of more than 5% is necessary during non-lubricated rolling is as follows. In the studies conducted by the present inventors, sheets were passed through various rolling reductions during non-lubricated rolling before cold rolling, followed by cold rolling with rolling oil supplied, finish annealing pickling or finish bright annealing, and finishing. The surface gloss of products finished by temper rolling was investigated. As a result, in both the case of a cold tandem mill using large-diameter work rolls and the case of a Sendzimir mill using small-diameter work rolls, when the reduction rate during non-lubricated rolling of the cold-rolled base steel strip was increased, the reduction rate was 5%. Up to 5%, the surface gloss hardly changes, but when it exceeds 5%, the surface gloss becomes significantly better.

In this way, non-lubricated rolling under a rolling reduction of more than 5% improves the surface gloss significantly, but on the other hand,
Since it requires a high rolling reduction rate that is not available in the prior art, the roll and the adjusting band come into direct contact without lubrication, which tends to cause seizure spots. Therefore, it is necessary to prevent seizure defects by rolling at a low speed, but as a result, there is a concern that productivity in cold rolling performed at a high speed may be inhibited.

However, when non-lubricated rolling is performed after intermediate annealing and pickling as in the present invention, the threading speed during intermediate annealing and pickling is 10 to 55 m.
Because the speed is extremely slow (1 minute), seizure defects are less likely to occur.
This no longer hinders production efficiency.

However, when a stainless steel sheet is cold-rolled after non-lubricated rolling, a large amount of surface defects called oil pits may be generated during cold rolling, reducing the surface gloss of the finished product after cold rolling. A new problem arose.

In general, oil pits are the remains of intergranular fill lines in grains, and it is known that they are associated with a very thin layer of rolling oil that is trapped between the work roll and the belt during rolling. Furthermore, the present inventors focused on and studied the work roll diameter of each stand of a cold tandem rolling mill as a method for preventing oil pits.

Generally, it has been known that the surface gloss of the rope improves when the diameter of the work roll is reduced. However, it is not clear at all what work roll diameter is necessary to obtain a surface gloss equal to or higher than that of the target Sendzimir rolling mill product, and which of the multiple stands of a cold tandem rolling mill should be applied to. Ta. In particular, it was not clear at all how to cold-roll a stainless steel strip that has been rolled without lubrication at a reduction rate of more than 5%.

Therefore, the present inventors cold-rolled the above-mentioned non-lubricated strip using a cold tandem rolling mill combining various work roll diameters, and then performed final annealing, pickling, and finishing 1!
As a result of examining the surface gloss of cold-rolled stainless steel strips after quality rolling, the following findings were made clear.

That is, in the present invention, the means for preventing the generation of oil bits when cold rolling a stainless steel strip that has been subjected to non-lubricated rolling is, when performing cold Kundem rolling, at least the final stand with an outer diameter of 400 mm or less. This is done using work roles. This is for the following reasons.

In other words, the conventional cold tandem rolling mill has a diameter of 500 m
Although rolling was performed using work rolls with an outer diameter of 400 mm or less, oil bits can be significantly reduced by using work rolls with a smaller outer diameter of 400 mm or less. Also, the stand that most requires work rolls with an outside diameter of 400 mm or less is the final stand, and if work rolls with this outside diameter are used in other stands, oil bits can be further reduced, resulting in improved surface gloss. It's for a reason.

<Example> A ferritic 5US430 wire that has been hot-rolled, intermediately annealed and pickled according to the method of the present invention is rolled without lubrication at the reduction ratio shown as an example in Table 1, and then a workpiece having an outer diameter shown in the same table is produced. After rolling in a 5-stand cold tandem rolling mill using rolls, final annealing, pickling, and final temper rolling were performed.

Regarding the surface gloss of these copper strips, the visual evaluation results are also shown in Table 1. Note that the visual evaluation was made on a four-level evaluation from A to D in descending order of gloss.

Also shown are the results for products obtained by a conventional manufacturing method using a Sendzimir mill. From Table 1, it was found that the cold-rolled stainless steel strip produced by the method of the present invention had significantly better surface gloss than that produced by the conventional method.

Note that even when the method of the present invention is applied not only to ferritic 5US430 but also to austenitic 5U5304 and the like, extremely good results can be obtained. In particular, 5US304 products that have been subjected to final annealing and pickling are given surface gloss by puff polishing etc., but when the method of the present invention is applied, the surface gloss after puff polishing is higher than that of copper strips manufactured by conventional methods. was also significantly improved.

<Effects of the Invention> As described above, the cold-rolled stainless steel strip produced by the method of the present invention is completely inaccessible to the cold-rolled stainless steel strip produced by the conventional rolling method using a cold tandem rolling mill. It becomes possible to impart an excellent surface gloss equivalent to or higher than that produced by rolling with a Sendzimir rolling mill.

In addition, the method of the present invention has a rolling reduction rate of 5%, which was completely unknown in the past.
Even if non-lubricated rolling is carried out in excess of 100 mL, the rolls and steel strip will not seize, and the efficiency will not be impaired at all, and the surface gloss will be significantly improved.

Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Claims] Stainless hot-rolled steel strip is intermediately annealed and pickled, and further reduced to a rolling reduction of 5.
When cold tandem rolling is performed after pre-treatment of non-lubricated rolling exceeding %
A method for producing a cold-rolled stainless steel strip, which comprises rolling with a work roll having a diameter of 0 mm or less.