JPH0751242B2 - 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 subjected to cold rolling (hereinafter abbreviated as cold rolling) supplied with a large amount of rolling oil in a Sendzimir mill with a work roll diameter of 150 mmφ or less, finish annealing pickling or finish bright annealing However, it was manufactured by subjecting to finish temper rolling with an elongation rate of 1.2% or less.

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, during the production of conventional stainless cold-rolled steel strip, both in the ferrite system and austenite system, in cold rolling using a small diameter work roll such as Sendzimir mill, for example, the work roll roughness shown in Japanese Patent Publication No. 57-13362. The method of devising was adopted. However, even with this method, the surface roughness was not satisfactory as a result of the significantly large roughness of the surface of the steel strip annealed and pickled after hot rolling before cold rolling remaining until after cold rolling.

On the other hand, a method of cold rolling with a large-diameter work roll exceeding 150 mmφ has been adopted as a method for producing a stainless cold-rolled steel strip with high efficiency by greatly shortening the rolling time. However, the surface roughness of the steel strip cold-rolled with a large-diameter work roll is such that the markedly large roughness of the annealed and pickled surface of the hot-rolled steel strip remains after cold-rolling, and the cold-roll using a small-diameter work roll. The product could not be applied at all in applications requiring surface gloss, because it remained as a roughness larger than that in hot rolling.

Therefore, as a method for solving this type of surface gloss reduction problem, there has been proposed a method of devising a combination of work roll diameters as disclosed in, for example, 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 official gazette, remarkably large roughness of the steel strip surface annealed and pickled after hot rolling remains after cold rolling, so the surface gloss of the product was insufficient and further improvement was required. .

[Problems to be Solved by the Invention] The present invention provides cold rolling using a small diameter work roll such as a Sendzimir mill, cold rolling using a large diameter work roll such as a cold tandem mill, and cold rolling combining these, The purpose of the present invention is to solve the problem of deterioration in surface gloss of stainless cold-rolled steel strip, which has been a problem in the past.

[Means for Solving the Problems] The present invention according to claim 1 is a method for producing a stainless cold-rolled steel strip by rolling using a large-diameter work roll, wherein the stainless steel strip after hot rolling is annealed and pickled. In addition, the roll surface is coated with a liquid lubricant having a thickness of 1 μm or less under a rolling reduction rate of more than 5%, and pre-rolling is performed, followed by cold rolling.
The work roll having a roughness of Ra 0.15 μm or less is used for rolling.

The present invention according to claim 2 is a method for manufacturing a stainless cold-rolled steel strip by rolling using a small-diameter work roll, wherein the stainless steel strip after hot rolling is subjected to annealing pickling, and a rolling reduction of more than 5%. In the final pass of applying a liquid lubricant with a thickness of 1 μm or less to the roll surface under pre-treatment, pre-treatment rolling, and subsequent cold rolling, the average roughness Ra0.
The rolling is performed using a work roll having a roughness of 15 μm or less.

The present invention according to claim 3 is a method of manufacturing a stainless cold-rolled steel strip by rolling using a large diameter work roll followed by rolling using a small diameter work roll, wherein the stainless steel strip after hot rolling is subjected to annealing pickling. In addition, the roll surface is coated with a liquid lubricant having a thickness of 1 μm or less under a rolling reduction of more than 5%, and the roll is pretreated and then cold-rolled. Rolling is performed using a work roll having the following roughness.

The present invention according to claim 4 is the same as the present invention according to claim 1, further before the last stand before the last one,
Cold rolling using a work roll having an average roughness Ra of 0.2 μm or less at the last stand before the last stand or a plurality of continuous stands including the last stand before the last stand. It is the one.

The present invention according to claim 5 is the present invention according to claim 2 or 3, further including before the final one before the final pass, or before the final one previous pass or the final one previous pass. Average roughness Ra0.2 in multiple consecutive passes including passes
Cold rolling is performed using a work roll having a roughness of μm 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 the cold rolling is the steel strip before the cold rolling, that is,
Part of the surface roughness of the steel strip annealed and pickled after hot rolling remains after cold rolling, scratches when the work roll roughness during cold rolling is transferred to the steel strip, and occurs during cold rolling It was found to be based on each of the oil pits.

(1) Then, first, the influence of the surface roughness of the steel strip annealed and pickled after hot rolling will be described below. In the production of stainless cold-rolled steel strips with the goal of obtaining a surface roughness with an average roughness Ra of 0.1 μm or less in the final finished product, the steel strip surface roughness immediately after annealing and pickling the hot-rolled steel strip is Due to mechanical descaling treatment such as shot blasting at the time of washing and acid such as sulfuric acid, the average roughness Ra2 to 4 μm is extremely large.

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 oil accumulates in the dents and is bitten into the roll bite. The oil accumulated in the dents is rolled while it is contained and has no escape place 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 dents that contain oil during rolling are somewhat smaller than before rolling, but 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 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 the non-lubricating rolling is performed, the roll and the steel strip are seized, the coefficient of friction is remarkably increased, the rolling load is remarkably increased, and at the same time, the necessary reduction ratio cannot be obtained.

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 method was found to be suitable.

(A) A method of forming a very thin liquid film on the roll surface and lubricating it.

(B) A method of performing non-lubricating rolling with a surface-treated roll.

Here, with regard to the method of utilizing the surface treatment of the roll of (B), various surface treatments known in the related art 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) has a remarkably large anti-seizure effect even though the liquid film is thin. 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 thickness of the roll surface is 1 μm or less, most of the surface irregularities can be eliminated, and it is better if the thickness is 0.5 μm or less. It was found that if the thickness exceeds 1 μm, a large amount of irregularities remain, and it cannot be erased even in the subsequent cold rolling.

As the liquid lubricant, water, skin pass oil, rolling oil,
Any rolling oil emulsion or the like is suitable because it has a seizure prevention effect and a surface unevenness reducing effect, but is preferably 1 to 15
A liquid lubricant with a viscosity of about cSt is good.

In addition, the reason why the reduction ratio of more than 5% is necessary at the time of 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, rolling using a work roll with a small diameter work roll such as a Sendzimir mill with a work roll diameter of 150 mm or less, work roll diameter
In any case of rolling using a large diameter work roll such as a cold tandem mill exceeding 150 mmφ and cold rolling combining these, if the reduction ratio during pretreatment rolling is changed, the reduction ratio is 5% or less. However, the surface gloss of the product finished by cold rolling is hardly improved, but when it exceeds 5%, it becomes remarkably good.

Further, in order to carry out the pretreatment by the method of the present invention, it is necessary to apply the liquid uniformly to the surface of the inlet roll and to have a liquid thickness of 1 μm or less. Thickness unevenness in the width direction occurs, and it is extremely difficult to reduce the thickness to 1 μm or less. Therefore, the present inventors
As a result of studying a method that is as simple as possible in operation management and that achieves the above-mentioned object, when a rolling mill having four or more roll arrangements is used for pretreatment and liquid is supplied from the rolling mill exit side, stainless steel is used. Since the steel strip has a large deformation resistance and a high rolling load, the surface pressure between the work roll and the roll adjacent to the work roll is large, and as a result, the film thickness of the oil drawn between these rolls is extremely thin and the film thickness is 1 μm or less. Can be easily achieved. However, the oil spreads in the width direction between the rolls, and a uniform oil film is obtained. Therefore, the method of the present invention can be achieved by rolling with this oil film left on the work roll surface.

FIG. 1 shows an example of the outline of a pretreatment rolling apparatus used to achieve the method of the present invention. The liquid supplied from the nozzle 1 on the outlet side of the mill is the work roll 2 or the adjacent roll 3
Adhere to. With the rotation of the roll, most of the adhered liquid is removed between the work roll 2 and the adjacent roll 3, and only a part of the liquid is homogenized and caught between the rolls. After that, the liquid that has exited between the rolls is divided into the respective surfaces of the work roll 2 and the adjacent roll 3, and only the thin liquid attached to the surface of the work roll 2 is caught between the stainless steel strip 4 and the work roll 2. That is why.

Although a nozzle is shown in FIG. 1 as an example of the liquid supply device on the delivery side of the rolling mill, various applications such as liquid application by a roll coater, spraying of the liquid in mist form or application of a jacket are provided.

Further, in order to further thin the liquid adhering to the surface of the work roll on the inlet side of the rolling mill, it is possible to inject air or provide a wiper.

(2) Next, when a large amount of rolling oil is supplied to the stainless steel strip that has been subjected to the pre-treatment rolling and cold rolling, the surface roughness of the work roll used for this cold rolling and The combination of passes creates a new problem that reduces the surface gloss of the finished product after cold rolling.

Therefore, the inventors of the present invention have studied this problem and found that when a large amount of rolling oil was supplied to cold-roll a stainless steel strip that had been subjected to pretreatment rolling, surface defects called oil pits were initially generated during rolling. It was found to be produced in large quantities and reduce the surface gloss of the finished product after cold rolling. In the oil pit, an intragranular slip line of crystal grains remains on the surface of the steel strip, and an oil layer enclosed between the work roll and the steel strip during rolling is involved.

Next, if the work roll roughness is large, the size of scratches transferred to the steel strip becomes large, and after cold rolling, the steel strip is finish-annealed by pickling or finish bright-annealing, and further finish-tempered. It was also revealed that even after rolling and finishing, the large scratches remained and reduced the surface gloss of the product.

Therefore, the inventors of the present invention have examined methods for avoiding a decrease in surface gloss due to these defects of oil pits and scratches, and have clarified that the following methods (a) and (b) are effective respectively. did.

(A) As a first method, the present inventors set the work roll roughness to an average roughness Ra of 0.15 μm or less in a final pass using a cold rolling small diameter work roll or a final stand using a large diameter work roll. It has been found that the surface gloss is improved.

That is, the path or stand that most affects the surface roughness of the steel strip after cold rolling is the final path using a cold rolling small diameter work roll or the final stand using a large diameter work roll, and still normally In cold rolling of steel, the transfer rate of roll roughness to the surface of the steel strip is 70 to 80%, whereas in the case of stainless steel strip, the transfer rate is 90% or more, which is remarkably efficient. Therefore, the scratches transferred to the surface of the steel strip can be efficiently reduced by reducing the roughness of the work roll.

In addition, on the final pass using a small diameter work roll or the final stand entry side using a large diameter work roll, the supplied rolling oil is enclosed in the work roll roughness and the recess of the scratch of the steel strip, and between the roll and the steel strip. It was found to bite into and form a thin layer of oil, creating an oil pit. Based on this new finding, it has been found that by reducing the work roll roughness, the dent becomes smaller and the oil enclosed between the roll and the steel strip decreases, and as a result, the oil pit can also be suppressed.

Here, when the work roll roughness of the final pass using the small diameter work roll or the final stand using the large diameter work roll exceeds the average roughness Ra 0.15 μm, oil pits frequently occur, and at the same time, a large amount of large scratches remain. Since the surface gloss of the stainless cold-rolled steel strip finished after cold rolling is reduced, it is necessary to limit the work roll roughness to an average roughness Ra of 0.15 μm or less, but preferably 0.1 μm or less. Is even better.

(B) Next, the present inventors examined a second method for further improving the surface gloss over the first method, and found that it is better to add the following method in addition to the above method. .

That is, in the second method, in addition to the first method, the small-diameter work roll is used before the final one pass using the small-diameter work roll or before the final one stand using the large-diameter work roll. The last one pass using the or the last one stand using the large diameter work roll, or the last one using the small diameter work roll.
Using a work roll having a roughness of 0.2 μm or less in average roughness in a plurality of successive passes including a previous pass or a plurality of consecutive stands including a final one stand using the large diameter work roll. It is a method of cold rolling.

As mentioned above, the transfer rate of the work roll roughness to the steel strip surface in the final pass using the small diameter work roll or the final stand using the large diameter work roll is 90% or more, but the remaining 10% or less. Is a large pass of the final pass using a small-diameter work roll or a final stand using a large-diameter work roll, or a large work roll roughness of the stand was transferred to the steel strip and remained. Therefore, when the average roughness Ra of the work roll before the final one pass using the small diameter work roll or the final one previous stand using the large diameter work roll was changed variously, the surface gloss was further improved. It has been found that the average roughness Ra of these work rolls needs to be 0.2 μm or less in at least one pass or one stand or more in order to be good.

That is, the work roll roughness has an average roughness of 0.2 μm or less in at least one pass or one stand or more before the final one pass before using the small diameter work roll or the final one stand before using the large diameter work roll. By doing so, the scratches whose roll roughness is transferred to the steel strip can be erased in the final pass or the stand.

However, in the final pass using the small-diameter work roll or the final stand using the large-diameter work roll, it is not possible to completely erase the oil pit generated before the final pass or stand. Therefore, in the second method, similarly to the first method in (a), the work roll roughness before the final one pass or before the stand is set to an average roughness Ra of 0.2 μm or less. Therefore, at the path where the oil pit occurs or the entrance side of the stand,
The oil pit is also suppressed at the same time by reducing the roughness of the work roll and the oil filled in the recesses of the scratches on the surface of the steel strip to reduce the oil caught between the roll and the steel strip.

It should be noted that the work roll roughness (a) is set to a predetermined value or less.
The methods of (b) and (b) show remarkable effects after reducing the remarkably large surface roughness after annealing and pickling after hot rolling by performing the pretreatment rolling of the present invention. When the stainless steel strip that has been annealed and pickled after hot rolling is applied to a method of cold rolling by supplying a large amount of rolling oil, the effect is remarkably small.

[Example] Hereinafter, as shown in Tables 1 to 3 according to the method of the present invention, as an example of a SUS430 steel strip as an example of a ferritic stainless steel that has been annealed and pickled after hot rolling, and an example of an austenitic stainless steel. The SUS304 steel strip of No. 1 was used for pretreatment rolling according to the method of the present invention at the rolling reductions shown as examples in Tables 1 to 3. Further, as a comparative example of the present invention, when the reduction ratio during pretreatment rolling is 5% or less, when the oil film thickness during pretreatment rolling exceeds 1 μm, the work roll roughness during cold rolling has It was also carried out when the range (Ra 0.15 μm or less, Ra 0.2 μm or less) was exceeded. After that, for these steel strips, the work rolls having the roughness shown as an example in the same table are used in combination, and after cold rolling while supplying a large amount of rolling oil, finish annealing, pickling or finish bright annealing, Finish temper rolling was carried out. The steel strip of SUS304 that had been subjected to finish annealing and pickling was subjected to finish temper rolling and then subjected to buff polishing under the same conditions.

Further, as a conventional example, the hot rolled steel strip is annealed and pickled, without pretreatment rolling, and after cold rolling with a combination of work rolls having a conventional roughness, finish annealing pickling or Finish bright annealing and finish temper rolling. In the case of finish annealing pickling of SUS304, buffing was further performed under the same conditions as above.

In addition, Table 1 is for cold rolling using a large diameter work roll of a cold tandem mill, Table 2 is for cold rolling using a small diameter work roll of a Sendzimir mill, and Table 3 is for cold tandem. It shows the case of cold rolling with a Sendzimir mill after the mill rolling.

Regarding the surface gloss of these stainless cold-rolled steel strips, the results of visual judgment are also shown in Tables 1 to 3. The visual judgment was made into 5 grades of special A and A to D in order of good gloss.
Further, as a comparative example, the results of visual determination of the surface gloss of the stainless cold-rolled steel strip obtained by the conventional manufacturing method are also shown.

In the case of both ferrite type SUS430 and austenitic type SUS304, rolling using small diameter work rolls such as Sendzimir mill shown in Tables 1 to 3, rolling using large diameter work rolls such as cold tandem mill, and rolling combining these In, the stainless cold-rolled steel strip produced by the method of the present invention has a significantly better surface gloss than the steel strip produced by the conventional method, and the method of the present invention is remarkably effective in improving the surface gloss. Is clear.

[Advantages 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 using a large diameter work roll such as a cold tandem mill, the surface gloss has been remarkably inferior so far, and it cannot be applied to applications requiring surface gloss at all, and as a result, the product market is extremely narrow. It was a thing. However, it has been impossible to reach the surface gloss of a product rolled by a small-diameter work roll such as a Sendzimir mill even if various methods are conventionally used. However, according to the method of the present invention, an excellent surface gloss equal to or higher than the surface gloss of the Sendzimir mill rolled product can be imparted.
Further, the method of the present invention is a method carried out on the basis of a new finding that work roll roughness is reduced and oil pits are also suppressed, and has an effect that surface gloss can be remarkably improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an apparatus used for carrying out the present invention. 1 ... Liquid supply nozzle, 2 ... Work roll, 3 ... Adjacent roll, 4 ... Stainless steel strip.

 ─────────────────────────────────────────────────── ─── 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 (5)

[Claims] 1. A method for producing a stainless cold-rolled steel strip by rolling using a large-diameter work roll, wherein the stainless steel strip after hot rolling is subjected to annealing pickling, and further under a rolling reduction of more than 5%. Applying a liquid lubricant with a thickness of 1 μm or less on the roll surface, pre-processing and rolling, and then performing cold rolling, use a work roll with an average roughness Ra of 0.15 μm or less in the final stand. A method for manufacturing a stainless cold-rolled steel strip, which comprises applying the cold-rolled steel strip. 2. A method for producing a stainless cold-rolled steel strip by rolling using a small-diameter work roll, which comprises subjecting the stainless steel strip after hot rolling to annealing pickling, and further rolling under a rolling reduction of more than 5%. Applying a liquid lubricant with a thickness of 1 μm or less on the surface, pre-processing and rolling, and then performing cold rolling, in the final pass, perform rolling using a work roll having an average roughness Ra of 0.15 μm or less. A method for manufacturing a stainless cold-rolled steel strip, which is characterized by the following. 3. A method of manufacturing a stainless cold-rolled steel strip by rolling using a large-diameter work roll, followed by rolling using a small-diameter work roll, wherein the stainless steel strip after hot rolling is subjected to annealing pickling, and further 5%. In the final pass, when a liquid lubricant with a thickness of 1 μm or less is applied to the roll surface under a rolling reduction of more than 1 mm, pretreatment rolling is performed, and then cold rolling is performed, an average roughness Ra of 0.15 μm or less is obtained. A method for producing a stainless cold-rolled steel strip, which comprises rolling using a work roll having the same. 4. A stand before the last stand,
Cold rolling using a work roll having an average roughness Ra of 0.2 μm or less in the last stand before the last stand or a plurality of continuous stands including the last stand before the last stand. Item 2. A method for producing a cold rolled stainless steel strip according to Item 1. 5. An average roughness Ra of 0.2 μm or less in a pass before the final one pass or a plurality of successive passes including the pass before the final one before the final pass before the final pass. The method for producing a cold rolled stainless steel strip according to claim 2 or 3, wherein cold rolling is performed using a work roll having roughness.