JPH0757363B2 - Method for producing stainless cold-rolled steel strip - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for efficiently producing a cold-rolled stainless steel strip having excellent surface gloss.

[Prior Art] Conventionally, cold-rolled stainless steel strip is annealed from hot-rolled steel strip, subjected to treatment such as shot blasting, then pickled, and the surface pickled remains a work roll diameter of 100 mmφ or less. After supplying a large amount of rolling oil with a Sendzimir mill etc. and cold rolling,
It was manufactured by finish annealing pickling or finish bright annealing and finish temper rolling.

The stainless cold-rolled steel strip produced through these steps is used as it is on the surface after production or after being subjected to buffing, but it is important that the surface of the steel strip has good gloss.

On the other hand, compared with the conventional Sendzimir mill, etc., as a method for manufacturing a stainless cold-rolled steel strip with high efficiency by significantly shortening the rolling time, rolling with a large diameter work roll of 150 mmφ or more in a cold tandem mill. The method of doing is adopted. However, the surface roughness of the steel strip cold-rolled using the large-diameter work rolls shows that the significantly large roughness of the surface of the steel strip before cold rolling remains until after the rolling, and the cold-roll work using the small-diameter work rolls still remains. Compared with hot rolling, it remains as a significantly larger roughness,
The finished product was completely unsuitable for applications requiring surface gloss.

Therefore, conventionally, methods for devising combinations of work roll diameters such as JP-A-6149701 have been attempted. However, if these methods are used alone, the surface of the steel strip before cold rolling will have a significantly large roughness. Remained after cold rolling, and the surface gloss of the product was completely inferior, which required further improvement.

[Problems to be Solved by the Invention] The present invention provides a surface that has been conventionally used in both 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. It is an object of the present invention to solve the problem of gloss reduction and the problem of low production efficiency and to efficiently manufacture a cold rolled stainless steel strip having excellent surface gloss.

[Means for Solving the Problems] The present invention according to claim 1 anneals the stainless steel strip after hot rolling and, as it is, or after performing treatment such as tension leveler, shot blasting, or liquid honing. ,
After this, grind the steel strip surface with a grindstone or brush with abrasive grains adhered to the resin and pickle it, then apply non-lubricating rolling, and then apply a 50 ° C viscosity to each stand of the cold tandem mill. Rolling oil of 15 cSt or less is supplied as an emulsion in a large amount, and the work roll roughness of the intermediate stand is Ra0.2 μm or less and the work roll roughness of the final stand is Ra0.15 μm or less, and At least, the work roll diameter of the final stand is set to 400 mmφ or less for rolling.

The present invention according to claim 2 anneals the stainless steel strip after hot rolling and, as it is, or after performing a treatment such as a tension leveler, shot blasting, or liquid honing,
After that, the surface of the steel strip is ground and pickled by a grindstone or a brush in which abrasive grains are fixed to a resin, and a work roll surface is coated with a liquid lubricant having a thickness of 1 μm or less and rolled, and then, To each stand of the cold tandem mill, a lot of rolling oil with a viscosity of 15 cSt or less at 50 ℃ is supplied as an emulsion, and the work rolls of the intermediate stand have an average roughness Ra of 0.2 μm or less and the work roll of the final stand. The average roughness Ra is 0.15 μm or less, and the work roll diameter of at least the final stand is 400 mmφ or less for rolling.

The present invention according to claim 3 is the method for producing a stainless cold-rolled steel strip according to claim 1 or 2, wherein the steel strip after cold tandem mill rolling is further made into a small diameter work roll having a roll diameter of 150 mmφ or less. It is adapted to be rolled using.

[Operation] Conventionally, in order to improve the surface gloss of the cold rolled stainless 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 is the steel strip before cold rolling, that is, the surface roughness of the pretreated steel strip that has been annealed and pickled after hot rolling. However, it was found that the main cause was that which remained after cold rolling.

Therefore, the surface roughness of the pretreated steel strip that has been subjected to annealing pickling after hot rolling is shown below. That is, in the final finished product, the average roughness Ra
In the production of stainless cold-rolled steel strips whose target is to achieve a surface roughness of 0.1 μm or less, the surface roughness of the steel strip immediately after annealing and pickling the hot-rolled steel strip is determined by mechanical treatment such as shot blasting or liquid honing. By the descaling treatment and the pickling, the average roughness Ra2 to 4 μm is extremely large.

By the way, during cold rolling, a large amount of rolling oil is supplied to the roll bite from the rolling mill entrance side. This is performed in order to stably produce a steel strip by simultaneously performing cooling and lubrication with rolling oil to prevent the occurrence of seizure flaws such as heat streaks. Therefore, on the inlet side of the rolling mill, a large amount of rolling oil with a thickness of several μm or more adheres to the surface of the steel strip, so that the oil is filled in the recesses of extremely large roughness on the surface of the steel strip that has been annealed and pickled after hot rolling. Bites into the roll bite. The oil accumulated in the recess is rolled in the roll bite while the roll and the steel strip are in contact with each other, while there is no escape place and the oil is contained.

In general, a liquid containing rolling oil is significantly less likely to be compressed than a gas such as air, so that the dents enclosing the oil during rolling are somewhat smaller than those before rolling, but most of them remain after rolling.

As described above, the surface roughness of the pretreated steel strip before cold rolling remains after the cold rolling, and the surface gloss of the product is significantly impaired.

Therefore, in order to obtain a steel strip with good surface gloss, in advance,
It is preferable to reduce the irregularities on the surface of the steel strip before cold rolling. That is, based on the above findings, the following pretreatment may be applied to the steel strip before cold rolling.

(1) Perform non-lubricating rolling without using a liquid such as rolling oil.

(2) The surface of the steel strip is ground.

Here, the non-lubricating rolling is preferably performed after the hot rolled steel strip is subjected to annealing and pickling and before the cold rolling. However, in order to perform the non-lubricating rolling while maintaining the production efficiency of the steel strip, it is preferable to continuously perform the annealing pickling.

However, if the steel strip surface is ground after annealing pickling, mechanical descaling such as shot blasting and remarkably large roughness due to pickling must be removed, and the grinding amount becomes significantly large. Will cause a significant decrease in yield.

On the other hand, if the hot-rolled steel strip is ground as it is, a descaling effect can be expected.

Therefore, it is preferable to grind the steel strip after annealing the hot-rolled steel strip and before pickling.

Incidentally, both non-lubricating rolling and grinding have problems. In unlubricated rolling, the roll and the steel strip may be seized, and the surface roughness of the seized steel strip is often larger than that without seizure, and this roughness remains in the product and hinders gloss. Further, when only grinding is used, the amount of grinding is relatively large even before pickling, and the yield of steel strip is greatly reduced.

Then, in order to deal with these problems, the present inventors have found the following method. That is, this is a method in which non-lubricating rolling and grinding are used in combination, the hot-rolled steel strip is annealed, the surface of the steel strip is ground, and then the scale is removed by pickling and then non-lubricating rolling is performed. By this method, the roughness of the steel strip surface can be reduced by grinding, so that the rolling reduction during unlubricated rolling can be reduced and seizure can be prevented. Therefore, it is possible to suppress the decrease in the yield of the steel strip.

Further, the present inventors have made further studies in consideration of the case where it is necessary to obtain a high reduction rate during non-lubricating rolling. As a result, instead of non-lubricated rolling, the work roll surface has a thickness of 1 μm.
It has been found that when the following liquid lubricant is applied and rolled, seizure can be prevented, and the surface roughness of the steel strip annealed and pickled after hot rolling can be significantly reduced to the same level as the non-lubricated rolling. Here, the reason why the thickness of the liquid lubricant is 1 μm or less is 1 μm
If it is m or more, the surface roughness of the steel strip annealed and pickled remains,
This is because the surface gloss of the steel strip finished by cold rolling may be impaired thereafter. In addition, as a method for reducing the thickness of the lubricant to 1 μm or less, a four or more-high rolling mill is used to supply the liquid lubricant from the exit side of the rolling mill, and the lubricant is formed in the gap between the work roll and the roll adjacent thereto. It is better to reduce the thickness.
Further, this method has a great effect of cooling the work roll by the liquid lubricant on the delivery side of the rolling mill, and is extremely effective in preventing seizure. The liquid lubricant used in this method may be water, skin bath oil, rolling oil, rolling oil emulsion or the like, and has the effect of preventing seizure and the effect of reducing surface irregularities at the same time.

Next, when the stainless steel strip after carrying out the pretreatment rolling of the present invention is cold-rolled by supplying a large amount of rolling oil, a large amount of surface defects called oil pits are generated during rolling,
A new problem arose which reduced the surface gloss of the finished product after rolling.

In general, oil pits have an intragranular slip band of crystal grains, which is said to be related to the material, remaining on the surface of the steel strip, and the rolling oil of several μm or less contained between the roll and the steel strip during cold rolling is retained. A thin layer is involved.

Therefore, the present inventors have paid attention to the following points as a method for preventing this oil pit.

(A) Rolling oil supplied as an emulsion during cold rolling (B) Work roll diameter of each stand (C) Work roll roughness of each stand First, the rolling oil supplied as an emulsion during cold rolling was examined.

In general, it was known that reducing the viscosity of the rolling oil improves the surface gloss of the steel strip, but to what extent it should be reduced, especially a large amount of stainless steel strip that has been subjected to the pretreatment of the present invention described above. Nothing was known about the case where cold rolling was performed by supplying the above rolling oil. Therefore, various rolling oils with different viscosities were made into emulsion and supplied in large amounts, and the pre-treated steel strip was cold-rolled.
It has been found that rolling oils having the following viscosities are effective in preventing oil pits.

Next, the work roll diameter of each stand was examined.

It is generally known that the surface gloss of a steel strip is improved by reducing the diameter of the work roll. However, the size of the work roll required to obtain a surface gloss equal to or higher than that of the desired Sendzimir mill product, and which of the multiple stands of the cold tandem mill should be applied, in particular, the above-mentioned preliminary of the present invention. It was not clear at all about the case of cold rolling the treated stainless steel strip by supplying a large amount of rolling oil. Therefore, as a result of cold rolling the steel strip pretreated by a cold tandem mill in which various work roll diameters are combined, the present inventors can reduce oil pits by using a work roll of 400 mmφ or less, and still It was found that the stand that most requires a work roll of 400 mmφ or less is the final stand, and if the work roll of this diameter is used for other stands, the oil pit can be further reduced.

The method of the present invention in which these work roll diameters are set to a predetermined value or less and applied to a predetermined stand is good only after the pretreatment of the present invention is carried out to reduce a significantly large roughness of the steel strip surface. Show the effect. The effect is remarkably small in the method of simply changing the work roll diameter as in the conventional method. The reason for this is that, in the conventional method, the rolling oil is rolled with a large roughness on the surface of the steel strip during cold rolling, and the oil filled inside the roll bite where the roll and the steel strip contact each other has a large roughness. Although a behavior of spouting around the recess occurs, and a large amount of oil pits are generated at this time, on the other hand, since the method of the present invention significantly reduces large roughness in the pretreatment step, such a phenomenon is almost eliminated. This is because no oil pit due to large roughness is generated.

Next, the work roll roughness of each stand was examined.

In the study by the present inventors, it was found that the amount of oil pits produced varied depending on the work roll roughness. This is because the recesses of the work roll roughness are bitten into the roll bite while being filled with rolling oil.The recessed parts filled with oil do not come into contact with the roll because the plate surface becomes a free interface and the steel strip This is because a slip band of crystal grains on the surface appears on the plate surface and remains after rolling. Therefore, as a result of studying this problem, it was found that the oil pits can be suppressed by making the following roll roughness.

(A) The work roll roughness of the final stand is the average roughness Ra
0.15 μm or less.

(B) The roughness of the work roll before the final stand, which is just before this one, is set to an average roughness Ra of 0.2 μm or less.

Further, by setting the work roll roughness as described above, it is possible to suppress scratches on the surface of the steel strip and improve the gloss.
That is, scratches are those in which the work roll roughness during cold rolling is transferred to the surface of the steel strip, and in the case of stainless steel strip, the transfer rate is 70 to 80% in cold rolling of ordinary steel. Is extremely efficient with a transfer rate of 90% or more. Of course,
Scratches on the product surface after cold rolling are most affected by the work roll roughness of the final stand. Therefore, when the work roll roughness of the final stand was variously changed and the scratches of the product steel strip were investigated, it was found that scratches were remarkably reduced when the average roughness Ra was 0.15 μm or less, which was good.

However, improving the work roll roughness of the final stand is not enough. That is, the work roll roughness of the final stand has a transfer rate of 90% or more to the surface of the steel strip, but the remaining 10% or less is that the work roll roughness of the stand before the final stand is transferred to the steel strip. It remains and it is necessary to take measures to suppress scratches due to this roughness. Therefore, when the work roll roughness before the final one before the stand was varied and examined, the average roughness Ra0.2μ
It has been found to be good if it is less than m.

Incidentally, the above method of making these work roll roughness a predetermined value or less, after performing a pre-treatment rolling before cold rolling and after reducing significantly remarkably large surface roughness by annealing pickling after the end of hot rolling, The effect is shown, and the effect is remarkably small in the conventional method of cold rolling by supplying a large amount of rolling oil to the steel strip after annealing and pickling. Also, in the final stand of the cold tandem mill and the stand before the final one, the work roll roughness is 0.3 μm in average roughness.
Scratch cannot be restricted as long as it is at least m (see the conventional example in Table 7).

As described above, the present invention is a combination of the pretreatment at the time of annealing pickling after the hot rolling, the rolling oil at the time of cold rolling for supplying a large amount of rolling oil, the work roll diameter, and the work roll roughness to obtain stainless steel. It is remarkably effective in improving the gloss of the cold rolled steel strip.

Further, in order to obtain even better gloss, it is preferable to carry out rolling with a cold tandem mill by 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.

[Examples] Examples produced by the method of the present invention and the conventional method using SUS430 steel strip as an example of a ferrite system and SUS304 steel strip as an example of an austenite system shown in Table 1 are shown below.

Manufacturing conditions are as follows: the hot rolled stainless steel strip is annealed, mechanically descaled as shown in Table 2 and pickled, and in the case of the present invention, the third
The pretreatment rolling shown in the table was implemented. Subsequently, a rolling oil having a viscosity shown in Table 4 was supplied as an emulsion, and the work roll diameter of each stand shown in Table 5 was used, and
The work roll roughness of each stand shown in Table 6 was combined and rolled by a cold tandem mill. Further, these steel strips were subjected to finish annealing pickling and finish temper rolling.

Some of the steel strips were cold tandem mill-rolled and then further rolled by a Sendzimir mill for finish bright annealing and finish temper rolling.

The finish-annealed pickling SUS304 steel strip was buffed after temper rolling.

Table 7 shows the manufacturing conditions of these steel strips and the gloss of the obtained products. In addition, the gloss is JIS Z 8741 gloss measurement method 5 (GS20
)), And a glossiness of 950 or higher in the order of goodness, special A, 8
00 to 950 were evaluated as A, 600 to 800 as B, 400 to 600 as C, and 400 or less as D, which was evaluated in 5 grades.

From Table 7, the method of the present invention significantly improves the gloss as compared with the conventional method. Further, the gloss is remarkably improved as compared with the comparative example which is pre-treated by the conventional method and then cold rolled according to the method of the present invention.

[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, when rolled by a cold tandem mill, a product having an excellent surface gloss that has hitherto been unattainable can be efficiently obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomio Komatsu 1 Kawasaki-machi, Chiba-shi, Chiba Inside the Kawasaki Steel Co., Ltd. (72) Inventor Akira Kishida 1 Kawasaki-machi, Chiba-shi Chiba Steel Co., Ltd. In-house (72) Hiroyuki Kakiuchi, 1 Kawasaki-cho, Chiba-shi, Chiba In-house, Chiba Works, Kawasaki Steel Co., Ltd. (56) References JP-A 64-83307 (JP, A) JP-A 57-184508 (JP, A) JP 64-83305 (JP, A) JP 1-122604 (JP, A) JP 64-3562 (JP, B2)

Claims (3)

[Claims] 1. A stainless steel strip after hot rolling is annealed, and as it is or after being subjected to a treatment such as tension leveler, shot blasting or liquid honing, abrasive grains are fixed to a resin continuously. After grinding the steel strip surface with a grindstone or a brush to pickle it, rolling it without lubrication, and then supplying a large amount of rolling oil with a viscosity of 15 cSt or less at 50 ° C as an emulsion to each stand of the cold tandem mill. And, the work roll roughness of the intermediate stand is an average roughness Ra of 0.2 μm or less, and the work roll roughness of the final stand is an average roughness Ra0.
A method for manufacturing a stainless cold-rolled steel strip, which comprises rolling to a diameter of 15 μm or less and a work roll diameter of at least a final stand of 400 mmφ or less. 2. A stainless steel strip after hot rolling is annealed, and as it is or after being subjected to a treatment such as tension leveler, shot blasting or liquid honing, abrasive grains are fixed to a resin continuously. After grinding the steel strip surface with a grindstone or brush and pickling, the work roll surface has a thickness of 1 μm
The following liquid lubricant is applied and rolled, and then each cold tandem mill stand is supplied with a large amount of rolling oil having a viscosity of 15 cSt or less at 50 ° C as an emulsion and the work roll roughing of the intermediate stand. The average roughness Ra of 0.2 μm or less and the work roll roughness of the final stand are the average roughness Ra0.15.
A method for producing a stainless cold-rolled steel strip, which comprises rolling the work roll diameter to 400 μm or less and at least to a final stand with a work roll diameter of 400 mmφ or less. 3. The method for producing a cold rolled stainless steel strip according to claim 1 or 2, wherein the steel strip after cold tandem mill rolling is further rolled using a small diameter work roll having a roll diameter of 150 mmφ or less. A method for manufacturing a stainless cold-rolled steel strip, which is characterized by the following.