JPH0523701A - Manufacture of cold rolled stainless steel strip - Google Patents

Abstract

PURPOSE:To obtain a cold rolled stainless steel strip with excellent surface gloss by rolling while supplying rolling oil emulsion in which the average particle diameter is limited in a cold tandem mill after annealing and pickling are applied to a hot rolled steel strip and non-lubricant preliminary rolling is executed at a limited draft. CONSTITUTION:The stainless steel strip after completing hot rolling is annealed and pickled. Further, after non-lubricant preliminary treatment rolling is executed at a draft over 5%, cold tandem rolling is executed while supplying the rolling oil emulsion in which the average particle diameter is <=7mum at least one stand or more including the final stand of the cold tandem mill.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a production method capable of advantageously producing a cold rolled stainless steel strip having an excellent surface gloss.

[0002]

2. Description of the Related Art Conventionally, cold-rolled stainless steel strip is annealed / pickled from a hot-rolled steel strip and cold-rolled in a Sendzimir mill having a work roll diameter of 150 mmφ or less, then finish-annealing / pickling or bright annealing. It was manufactured by finishing temper rolling with a rolling reduction of 1.2% or less. Stainless steel cold-rolled steel strips manufactured through these processes are often used as they are after production, for example, in the case of ferrite series typified by SUS 430, and have an excellent surface after finish temper rolling. Luster is required. In the case of an austenite type represented by SUS 304, 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, rolling oil is supplied as it is. For example, a method of devising roll roughness disclosed in JP-B-57-13362 is adopted. It was being done. However, even if this method is used, annealing / rolling after hot rolling before cold rolling is performed.
As a result of the extremely large roughness of the pickled steel strip surface remaining after cold rolling, the surface gloss was not satisfactory.

On the other hand, as a method for producing a stainless cold-rolled steel strip with high efficiency by significantly shortening the rolling time,
A method of cold rolling with a work roll having a diameter of mmφ or more is adopted. In this method, the rolling oil is supplied in the form of an emulsion, and its average particle size is 8 to 12 μm, which is relatively large. When cold rolling with a large diameter work roll, the surface roughness of the steel strip is
A significantly large roughness of the pickled surface remains after cold rolling, and moreover, as a roughness larger than that of cold rolling using a small diameter work roll, the product is
It could not be applied to any application requiring surface gloss.

Therefore, as a method for solving this type of surface gloss reduction problem, a method of devising a combination of work roll diameters has been disclosed in the past, for example, as disclosed in Japanese Patent Laid-Open No. 61-49701. This is a method of 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 official gazette, remarkably large roughness of the surface of the steel strip annealed and pickled after hot rolling remained after cold rolling, and the surface gloss of the product was insufficient, and further improvement was required.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides the above-mentioned method when rolling with a large diameter work roll such as a cold tandem mill or when rolling with a small diameter work roll such as a Sendzimir mill after tandem mill rolling. It is an object of the present invention to provide a method for manufacturing a stainless cold-rolled steel strip, which solves the problem of surface gloss reduction that has been present in the past.

[0007]

According to the present invention, the stainless steel strip after the hot rolling is annealed and pickled, and further 5%.
After performing a non-lubricating pretreatment rolling under a rolling reduction of more than 1, the rolling oil emulsion was fed with an average particle size of 7 μm or less in at least one stand including the final stand of a cold tandem mill. A method for producing a cold rolled stainless steel strip, which comprises performing cold tandem rolling.

After the hot rolling, the stainless steel strip was annealed and pickled, and a liquid lubricant having a thickness of 1 μm or less was applied to the surface of the work roll under a rolling reduction of more than 5%. After performing the pretreatment rolling as it is, at least one stand including the final stand of the cold tandem mill, the rolling oil emulsion having an average particle size of 7 μm or less is supplied and cold tandem rolling is performed. It is a method for producing a cold rolled stainless steel strip.

Further, the method for producing a cold rolled stainless steel strip is characterized in that after the cold tandem rolling, cold rolling is further performed with a work roll having a small diameter of 150 mmφ or less.

[0010]

[Operation] The present invention will be described in detail below. Conventionally, to improve the surface gloss of stainless cold rolled steel strip,
It has been known that 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 of the present inventors, the surface roughness of the steel strip after cold rolling described above is the steel strip before cold rolling, that is, the surface roughness of the steel strip annealed / pickled after hot rolling. It was found that a part remains after cold rolling.

Therefore, the surface roughness of the steel strip that has been annealed and pickled after hot rolling will be shown below. In the production of stainless cold-rolled steel strips whose target finish is an average roughness Ra of 0.1 μm or less, the surface roughness of the steel strip immediately after annealing and pickling the hot-rolled steel strip is that during pickling. Roughness R by mechanical descaling such as shot blasting and acid such as sulfuric acid
a 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 rolls and the steel strip from the inlet side of the rolling mill.
This is carried out 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 with a thickness of several μm or more adheres to the surface of the roll and the steel strip, and the rolling oil accumulates in the extremely large dents on the surface of the steel strip annealed / pickled after hot rolling. Bites into 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 preferable to reduce the surface roughness of the steel strip at the start of cold rolling. That is, based on the above knowledge, it is preferable to perform the non-lubricating pretreatment rolling without using a liquid lubricant such as rolling oil prior to the cold rolling in which a large amount of rolling oil is supplied. In addition, when the non-lubricated rolling is performed, the roll and the steel strip are seized, the friction coefficient is significantly increased, and the rolling load is significantly increased.As a result, the reduction ratio necessary to sufficiently reduce the unevenness of the steel strip surface cannot be obtained. There is.

Therefore, the present inventors have confirmed that the roll and the steel strip do not seize during the pretreatment rolling and that the hot rolled steel strip is annealed.
A method for producing a stainless cold-rolled steel strip that simultaneously satisfies the following two points: that the unevenness of the steel strip surface after pickling can be treated to the extent that it does not remain after cold rolling, was investigated. As a result, it was found that there are the following methods.

(A) A method of forming an extremely thin film of a liquid lubricant on the surface of a roll and lubricating it. (B) A method of performing non-lubricating rolling with a surface-treated roll. Here, as the method for utilizing the surface treatment of the roll of (B), various conventionally known surface treatments have been tried, but it has a seizure preventing effect as compared with the solid roll, but it is still insufficient.

On the other hand, the thin film lubrication method (A) is
Even though the liquid film is thin, the anti-seizure effect is extremely large. Further, the thinner the liquid film is, the more the surface irregularities of the steel strip annealed / 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 was found that it is better if the thickness is 0.5 μm or less, and on the other hand, if the film thickness exceeds 1 μm, a large amount of unevenness remains and cannot be erased even in the subsequent cold rolling.

As the liquid lubricant, water, rolling oil, rolling oil emulsion, skin pass oil, etc. all have seizure-preventing effect and surface unevenness reducing effect, but preferably 1 to 15
A liquid lubricant with a viscosity of about cSt is good. Here, a method for further improving the surface gloss of the steel strip was examined. When the stainless steel strip after carrying out the pretreatment rolling of the present invention is rolled in a cold tandem mill by supplying a large amount of rolling oil, a large amount of surface defects called oil pits are generated during rolling, and after rolling, A new problem arose which reduced the surface gloss of the finished product.

In general, the oil pit has an intragranular slip band of crystal grains, which is said to be related to the material, remaining on the surface of the steel sheet, and is a roll of several μm or less enclosed between the roll and the steel strip during cold rolling. A layer of oil is involved. Therefore, the present inventors have focused on the particle size of the cold rolling oil emulsion as a method for preventing this oil pit. If the average particle size of the rolling oil emulsion is reduced, the rolling oil trapped between the roll and the steel strip is reduced and the oil pits are reduced.

However, it has not been known at all about how much the average grain size should be reduced, particularly in the case of cold-rolling the above-mentioned pre-processed stainless steel strip of the present invention. Therefore, the average particle size of the rolling oil emulsion during cold rolling was variously changed, and as a result of cold rolling by supplying a large amount of rolling oil to the above-mentioned pretreated rolled steel strip, the average particle size of the emulsion was 7 μm or less. It was found that the oil pits are reduced and the gloss is improved when the oil is supplied as. When rolled with an emulsion having an average particle size exceeding this value, oil pits frequently occurred and the surface gloss of the steel strip decreased.

In applying the method of making the rolling oil emulsion of the present invention an average particle size of 7 μm or less, the stand that most affects the surface gloss of the steel strip after cold rolling is the final stand. Therefore, it is necessary to apply it including at least the final stand. Further, if it is applied to another stand, a better effect can be obtained. The method of reducing the average particle size of these rolling oil emulsions and applying it to a stand including at least a final stand is to carry out a pretreatment rolling before cold rolling, and to perform annealing / pickling of steel strip after hot rolling. It has an effect only after a remarkably large surface roughness is reduced, and its effect is extremely small in the conventional method of cold rolling by supplying a large amount of rolling oil to an annealed and pickled steel strip. ..

The reason why the reduction ratio of the pretreatment rolling is set to exceed 5% is as follows. We have
The stainless steel strip which was subjected to pretreatment rolling with various reduction ratios was then subjected to ordinary cold rolling to finish. As a result of measuring the surface gloss of the finished steel strip, it has been found that the gloss is remarkably inferior when the rolling reduction at the time of pretreatment rolling is 5% or less, but becomes good when it exceeds 5%.

Further, as a method of supplying an emulsion having an average particle size of 7 μm or less to each stand, the emulsion is separated from a normally used emulsion supply system having an average particle size of about 8 to 12 μm and prepared as a separate system. It is good to supply it. Further, in the case of using a commonly used emulsion supply system, there is also a method in which an average particle diameter is 7 μm or less by providing an in-line mixing device in the injection nozzle or in the middle of the piping system.

Further, in order to obtain even better gloss, it is preferable to carry out rolling with a cold tandem mill according to the method of the present invention and then carry out rolling with a small diameter work roll having a roll diameter of 150 mmφ or less, such as a Sendzimir mill or a cluster mill.

[0025]

EXAMPLES Hot-rolled steel sheets were prepared by using the SUS 430 steel strip as an example of a ferrite system and the SUS 304 steel strip as an example of an austenite system that were annealed and pickled after hot rolling according to the method of the present invention. After the strip is annealed and pickled, it is pre-treated and rolled without lubrication, or it is rolled by applying a liquid lubricant with a thickness of 1 μm or less on the surface of the work roll during pre-treatment rolling, and then rolling with a cold tandem mill. After supplying a large amount of oil and cold rolling, finish annealing / pickling and finish temper rolling were performed.

The steel strip of SUS 304 finish annealed and pickled was buffed under the same conditions after finish temper rolling. Further, a part of the steel strip rolled by the tandem mill was further rolled using a small diameter work roll by a Sendzimir mill, and then subjected to finish bright annealing and finish temper rolling.

The surface gloss of these stainless cold-rolled steel strips was measured according to JIS Z8741 gloss measurement method 5 (GS20 °), and in the order of goodness, gloss of 800 or more was A, 600 to 800 was B, and 400 to 600 was C. , 400 or less was defined as D and evaluated in four levels. In addition, the results of determining the surface gloss of the cold-rolled stainless steel strip obtained by the conventional method are also shown. Ferrite type
Table 1 shows both SUS 430 and austenitic SUS 304.
In both the rolling using a large diameter work roll such as a cold tandem mill shown in Table 2 and the rolling using a small diameter work roll such as a Sendzimir mill after the tandem mill rolling shown in Tables 3 and 4, the stainless steel produced by the method of the present invention The cold rolled steel strip had a significantly better gloss than the steel strip produced by the conventional method.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

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 strip manufactured by the conventional method.
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.

Continued front page    (72) Inventor Eisuke Kawasumi             1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.             Company Chiba Steel Works (72) Inventor Hidenori Miyake             1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.             Company Chiba Steel Works (72) Inventor Katsuhiro Kobori             1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.             Company Chiba Steel Works

Claims (3)

[Claims] 1. A stainless steel strip after hot rolling is annealed and pickled, and further subjected to non-lubricated pretreatment rolling under a rolling reduction of more than 5%, and then subjected to cold tandem mill rolling. A method for producing a stainless cold-rolled steel strip, which comprises performing cold tandem rolling by supplying a rolling oil emulsion with an average particle size of 7 μm or less in at least one stand including a final stand. 2. The stainless steel strip after hot rolling is annealed and pickled, and a liquid lubricant having a thickness of 1 μm or less is applied to the surface of the work roll under a rolling reduction of more than 5%. After pre-processing and rolling as it is, the rolling oil emulsion has an average particle size of 7 μm in at least one stand including the final stand of the cold tandem mill.
A method for producing a stainless cold-rolled steel strip, which comprises supplying the following and performing cold tandem rolling. 3. A method for producing a stainless cold-rolled steel strip, which comprises performing cold rolling with a work roll having a small diameter of 150 mmφ or less after the cold tandem rolling according to claim 1 or 2.