JPH03264102A - Manufacture of cold rolled steel strip - Google Patents

Abstract

PURPOSE:To manufacture a cold rolled stainless steel strip having excellent surface luster by annealing a hot rolled steel strip, then, grinding the surface of the steel strip, removing the scale by pickling, then, executing specified rolling in a lubricant free state. CONSTITUTION:Hot rolled stainless steel strip is annealed, treated mechanically by a tension leveler, etc., and ground by a grinding wheel made of abrasive grains adhering continuously and fixedly to resin, etc. Thereafter, rolling is performed in a lubricant free state, then, a large quantity of rolling oil having a coefficient of viscosity equal to or below 15cSt at 50 deg.C is supplied in the form of emulsion to each stand of a cold tandem mill, the roughness of the work roll at a middle stand is set equal to or below the average roughness Ra 0.2mum, the roughness of the work roll at the final stand is set equal to or below the average roughness Ra 0.15mum and rolling is carried out at least with the diameter of the work roll equal to or below 400mmphi. As a result, the draft in a lubricant free state can be lowered by grinding and the stock removal on the surface of the steel strip is reduced by rolling in a lubricant free state, consequently, the yield of the steel strip can be suppressed from reducing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for efficiently producing cold-rolled stainless steel strip having excellent surface gloss.

[Prior Art] Conventionally, cold-rolled stainless steel strip is produced by annealing the hot-rolled steel strip, subjecting it to treatments such as shot blasting, and then pickling it. After cold rolling by supplying a large amount of rolling oil with a diameter of less than φ, a large amount of rolling oil was applied, followed by finish annealing, pickling or finish bright annealing, and finish temper rolling.

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

On the other hand, compared to the conventional Zenjiku Aru, etc., a cold tandem mill with a large diameter of 150 ■φ or more is used to produce stainless steel cold rolled steel strips with high efficiency by greatly shortening the rolling time. A method of rolling using work rolls is adopted. However, the surface roughness of the steel strip cold-rolled using large-diameter work rolls is such that the extremely large roughness on the surface of the steel strip before cold-rolling remains until after rolling. Compared to inter-rolling, it remains as a significantly larger roughness,
The finished product could not be applied at all to applications requiring surface gloss.

Therefore, in the past, attempts have been made to devise a combination of work roll diameters, such as in Japanese Patent Application Laid-open No. 61-49701, but if these methods were used alone, the surface roughness of the steel strip before cold rolling would be extremely large. It remained after inverted cold rolling, and the surface gloss of the product was completely inferior, requiring further improvement.

[Invention or problem to be solved] The present invention overcomes conventional problems in both rolling using large-diameter work rolls such as cold tandem high-volume work rolls and subsequent cold rolling using small-diameter work rolls such as Zenji-sho mill. The purpose of the present invention is to solve the problem of reduced surface gloss and low production efficiency, and to efficiently produce cold-rolled stainless steel strips with excellent surface gloss.

[Means for Solving the Problem] The present invention as set forth in claim 1 provides annealing of a hot-rolled stainless steel strip, either as it is or after treatment such as tension leveler shot blasting or liquid honing.
Continuously, the surface of the steel strip is ground and pickled using a grindstone or brush with abrasive grains □ fixed to the resin, followed by non-lubricated rolling, and then placed on each stand of a cold tandem mill at 50°C.
A large amount of rolling oil with a viscosity of 15 cSt or less is supplied as an emulsion, and the work roll roughness of the intermediate stand is adjusted to an average roughness Ra of 0.2μ or less, and the work roll roughness of the final stand is adjusted to an average roughness Ra0. 15μm or less,
and the work roll diameter of the final stand is at least 40
The rolling process is carried out at a temperature of 0+u+φ or less.

The present invention according to claim 2 provides annealing of a hot-rolled stainless steel strip, either as it is or after treatment such as tension leveler shot blasting or liquid honing.
Continuously, the surface of the steel strip is ground and pickled using a grindstone or brush fixed to abrasive resin, and then a liquid lubricant with a thickness of 1 μm or less is applied to the work roll surface and rolled. A large amount of rolling oil with a viscosity of 50°C or 15 cSt or less is supplied as an emulsion to each stand of the cold tandem mill, and the work roll roughness of the intermediate stand is adjusted to an average roughness Ra of 0.2 μm or less and the workpiece of the final stand. The average roughness of the roll should be less than 0.15μ, and the work roll diameter of the final stand should be at least 4 (10
It is designed to be rolled to a diameter of 11 mφ or less.

The present invention as set forth in claim 3 is the method for producing a cold rolled stainless steel strip as set forth in claim 1 or 2, wherein the steel strip after cold tandem mill rolling is further provided with a small diameter roll having a roll diameter of 150+*mφ or less. It is designed to be rolled using work rolls.

[Effect] It has been known that in order to improve the surface gloss of cold-rolled stainless steel strip, it is better to reduce the surface roughness of the steel strip after cold rolling, which affects the surface roughness of the product. .

However, in the studies of the present inventors, the surface roughness of the steel strip after cold rolling described above is the surface roughness of 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. It was found that the main cause of the roughness was that remaining after cold rolling.

Therefore, the surface roughness of the pretreated steel strip that was annealed and pickled after hot rolling is shown below. That is, the average roughness of the final finished product
In the production of cold-rolled stainless steel strips with the goal of achieving a surface roughness of Ra 0.1 μm or less, the surface roughness of the hot-rolled steel strips immediately after annealing and pickling is determined by mechanical methods such as shot blasting and liquid honing. By descaling and pickling,
It has a significantly large average roughness Ra of 2 to 4 μm.

By the way, during cold rolling, a large amount of rolling oil is supplied to the roll hide from the inlet side of the rolling mill. This is done in order to simultaneously perform cooling and lubrication using rolling oil, prevent the occurrence of seizure defects such as heat streaks, and stably manufacture the steel strip.

Therefore, on the entry side of the rolling mill, a large amount of rolling oil adheres to the surface of the steel strip with a thickness of several micrometers or more, so oil fills the extremely rough depressions on the surface of the steel strip that has been annealed and pickled after hot rolling. Caught in a roll bite. The oil accumulated in this depression is
While the roll and the steel strip are in contact with each other during roll bite, there is no escape and the steel strip is rolled in a contained state.

In general, liquids including rolling oil are extremely difficult to compress compared to gases such as air, so the dents in which oil is trapped during rolling are somewhat smaller than before rolling, but most of them remain after rolling. .

As described above, the surface roughness of the pre-treated steel strip before cold rolling remains after cold rolling, significantly impairing the surface gloss of the product.

Therefore, in order to obtain a steel strip with good surface gloss, it is necessary to
It is better to reduce the unevenness on the surface of the steel strip before cold rolling. That is, from the above-mentioned knowledge, it is preferable to perform the following preliminary treatment on the steel strip before cold rolling.

(1) Perform non-lubricated rolling without using any liquid such as rolling oil.

(2) Grind the steel strip surface.

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

However, if grinding of the steel strip surface is carried out after annealing and pickling, it is necessary to remove significantly large roughness by mechanical descaling such as shot blasting and pickling, and the amount of grinding is significantly large. This results in a significant decrease in the yield of steel strip.

On the other hand, if the hot rolled steel strip is ground as 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.

By the way, both non-lubricated rolling and grinding have their own problems. In non-lubricated rolling, the rolls and the steel strip may seize, and the surface roughness of the seized steel strip is often greater than that without seizing, and this roughness remains in the product and impairs its luster. 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.

Therefore, in order to deal with these problems, the present inventors discovered the following method. That is, this is a method in which non-lubricated rolling and grinding are used in combination, the hot-rolled steel strip is annealed, the surface of the steel strip is ground, scale is removed by pickling, and then non-lubricated rolling is performed. With this method, the roughness of the steel strip surface can be lowered by grinding, so the reduction rate during non-lubricated rolling can be lowered and seizure can be prevented, and the amount of grinding on the steel strip surface during grinding can be reduced later. Since lubricated rolling is performed, less amount is required, and a decrease in yield of steel strip can be suppressed.

Further, the present inventors conducted further studies in consideration of the case where it becomes necessary to take a high rolling reduction during non-lubricated rolling. As a result, instead of rolling without lubrication, applying a liquid lubricant with a thickness of 1 μm or less to the work roll surface can prevent seizure, and the surface roughness of the steel strip that has been annealed and pickled after hot rolling can be improved without lubrication. It has been found that this can be significantly reduced during rolling. Here, the reason why the thickness of the liquid lubricant is set to be 1 μm or less is that if the thickness is 1 μm or more, the surface roughness of the annealed and pickled steel strip will remain, and the surface gloss of the steel strip that is then cold rolled and finished. This is because there were cases where the damage was caused. In addition, as a method for reducing the thickness of the lubricant to 1 μm or less, a rolling mill with four or more stages is used, and liquid lubricant is supplied from the exit side of the rolling mill, and the lubricant is released in the gap between the work roll and the adjacent roll. It is better to reduce the thickness. In addition, this method has a great effect of cooling the work rolls with the liquid lubricant on the exit side of the rolling mill, and is extremely effective in preventing seizure. Note that the liquid lubricant used in this method may be water, skin pass oil, rolling oil, rolling oil emulsion, etc., which have anti-seizure effects and surface unevenness reducing effects at the same time.

Next, when the stainless steel strip subjected to 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 has arisen which reduces the surface gloss of the finished product after rolling.

In general, oil pits are the intragranular slip lines of crystal grains that are related to the material, or remain on the surface of the steel strip, and are rolling oil of several micrometers or less trapped between the rolls and the steel strip during cold rolling. A thin layer of

Therefore, the present inventors focused on the following points as a method for preventing oil pits.

(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 studied.

In general, it has been known that reducing the viscosity of rolling oil improves the surface gloss of steel strips, but it is unclear to what extent it should be reduced, especially when large quantities of stainless steel strips have been subjected to the pretreatment of the present invention. There was no knowledge of cold rolling by supplying rolling oil. Therefore, as a result of supplying large quantities of rolling oils with different viscosities in the form of emulsions and cold rolling the pretreated steel strip, the viscosity at 50°C was 15°C.
It has been found that rolling oil having a viscosity of cSt or less is effective in preventing oil pits.

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

It is generally known that the surface gloss of a steel strip improves when the work roll diameter is reduced. However, there are particular concerns regarding the size of the work roll diameter necessary to obtain a surface gloss equal to or higher than that of the target Zenjiku Amyl product, and which of the multiple stands of a cold tandem mill should be applied to the present invention. It was not clear at all how to cold-roll a pretreated stainless steel strip by supplying a large amount of rolling oil. Therefore, the present inventors cold-rolled pretreated steel strips using a cold tandem mill combining various work roll diameters, and found that oil pits can be reduced by using work rolls of 400 mm or less. Of course, 400mm
The stand that most requires work rolls of φ or less is the final stand, and it has been found that oil pits can be further reduced by using work rolls of this diameter in other stands.

Note that the method of the present invention, in which the diameter of these work rolls is reduced to a predetermined value or less and applied to a predetermined stand, is not satisfactory until after the preliminary treatment of the present invention is carried out to reduce the extremely large roughness on the surface of the steel strip. It shows a great effect. If the conventional method simply changes the diameter of the work roll, the effect is extremely small. The reason for this is that in the conventional method, during cold rolling, the large roughness of the steel strip surface is filled with rolling oil, and the oil filled inside the roll bite where the roll and steel strip come into contact causes the large roughness. The behavior of spouting occurs around the dent, and a large amount of oil pit is generated at this time.
On the other hand, since the method of the present invention significantly reduces large roughness in the pretreatment stage, this phenomenon almost disappears and oil pits caused by large roughness do not occur.

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

In our studies, we found that the amount of oil pits produced varies depending on the roughness of the work roll. This is because the depressions in the roughness of the work roll remain filled with rolling oil and are bitten by the roll bite.In the depressions filled with oil, the plate surface becomes a free interface and does not come into contact with the roll.
This is because slip lines of crystal grains on the surface of the steel strip appear on the surface of the steel strip and remain even after rolling. Therefore, we investigated this problem and found that oil bits can be suppressed by setting the roll roughness as follows.

(a) The work roll roughness of the final stand is expressed as the average roughness R
a 0.15 μm or less.

(b) The roughness of the work roll before the last stand is set to an average roughness Ran of 2 μm or less.

Further, by making the work roll rough as described above, scratches on the surface of the steel strip can be suppressed and the gloss can be improved.

In other words, scratches are the transfer of work roll roughness during cold rolling onto the surface of the steel strip, and compared to the transfer rate of 70 to 80% in cold rolling of ordinary steel, in the case of stainless steel strip. is extremely efficient with a transfer rate of over 90%.
However, scratches on the product surface after cold rolling are most affected by the roughness of the work roll on the final stand.
When the work roll roughness of the final stand was variously changed and scratches on the product steel strip were investigated, the average roughness was Ra0.
It was found that scratches were significantly reduced when the thickness was 15 μm or less, which was favorable.

However, merely improving the roughness of the work roll at the final stand is not sufficient. In other words, the transfer rate of the work roll roughness of the final stand to the steel strip surface is 90% or more, but the remaining 10% or less is due to the transfer of the work roll roughness of the stands before the final stand to the steel strip. Therefore, it is necessary to take measures to suppress scratches caused by this roughness.

Therefore, when we investigated various work roll roughness before the final stand, we found that the average roughness R
It was found that the upper and lower directions of the east are good when the aO is less than 12μ east.

Note that the above method for reducing the roughness of these work rolls to a predetermined value or less is only possible after performing preliminary rolling before cold rolling and reducing significantly large surface roughness by annealing and pickling after hot rolling. However, the effect is significantly smaller than in the conventional method of cold rolling a steel strip after annealing and pickling by directly supplying a large amount of rolling oil.

As described above, the present invention can improve the quality of stainless steel by combining the pretreatment during annealing pickling after hot rolling, the rolling oil during cold rolling that supplies a large amount of rolling oil, the work roll diameter, and the work roll roughness. It shows a remarkable effect on improving the gloss of cold-rolled steel strip.

In addition, in order to obtain even better gloss, after rolling with a cold tandem mill according to the method of the present invention, it is recommended to perform rolling using a small work roll with a roll diameter of 150@■φ or less, such as a Sendzimir mill or cluster kuru. .

[Example] 5US430 steel strip as an example of ferritic type and 5US3ゝ04# as an example of austenitic type shown in Table 1
Examples manufactured by the method of the present invention and the conventional method using I-band will be shown below.

The manufacturing conditions are as follows: hot rolled stainless steel strip is annealed, mechanically descaled and pickled as shown in Table 2;
The pretreatment rolling shown in the table was carried out. Subsequently, 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 in a cold tandem mill. Furthermore, these steel strips were subjected to final annealing, pickling, and final temper rolling.

In addition, some of the steel strips were cold rolled in a tandem mill, further rolled in a Sendzimir mill, and subjected to final bright annealing and final temper rolling.

Further, the 5US304@ strip that had been subjected to finish annealing and pickling was subjected to puff polishing after temper rolling.

Table 7 shows the manufacturing conditions for these steel strips and the gloss of the resulting products. The gloss is measured according to JIS Z 8741 Gloss Measurement Method 5 (G320''), and in descending order of gloss, gloss of 950 or above is A, 800 to 950 is A, 6.
Evaluation was made on a five-point scale with B being 00 to 800, C being 400 to 600, and D being below 400.

Table 7 shows that the method of the present invention significantly improves gloss compared to the conventional method. Furthermore, the gloss is significantly improved compared to a comparative example in which the sample was pretreated by a conventional method and then cold rolled according to the method of the present invention.

[Effects of the Invention] As described above, the cold-rolled stainless steel strip produced by the method of the present invention has a surface gloss that is significantly superior to that of the cold-rolled stainless steel strip produced by the conventional method. In particular, when rolling is performed using a cold tandem mill, products with excellent surface gloss, which was conventionally impossible to achieve separately, can be efficiently obtained.

Claims (3)

[Claims] (1) A grinding wheel or a grinding wheel made by annealing a hot-rolled stainless steel strip, either as it is, or after being subjected to a treatment such as a tension leveler, shot blasting, or liquid honing, with abrasive grains fixed to the resin. After grinding and pickling the surface of the steel strip with a brush, it is rolled without lubrication, and then a large amount of rolling oil with a viscosity of 15 cSt or less at 50°C is supplied as an emulsion to each stand of a cold tandem mill, and , the average roughness of the work roll on the intermediate stand is Ra0.2μ
A method for manufacturing a cold rolled stainless steel strip, characterized in that the work roll roughness of the final stand is 0.15 μm or less, and the work roll diameter of at least the final stand is 400 mmφ or less. (2) A grinding wheel or a grinding wheel made by annealing a hot-rolled stainless steel strip, either as it is, or after being subjected to a treatment such as a tension leveler, shot blasting, or liquid honing, with abrasive grains fixed to the resin. After grinding and pickling the surface of the steel strip with a brush, a liquid lubricant with a thickness of 1 μm or less is applied to the work roll surface and rolling is performed, and then a lubricant with a viscosity of 15 cSt or less at 50°C is placed on each stand of a cold tandem mill. A large amount of rolling oil is supplied as an emulsion, and the work roll roughness of the intermediate stand is adjusted to an average roughness Ra of 0.2 μm.
The work roll roughness of the following and final stand is the average roughness R
A method for manufacturing a cold rolled stainless steel strip, characterized in that rolling is performed with a of 0.15 μm or less and a work roll diameter of at least the final stand of 400 mm or less. (3) In the method for producing a cold-rolled stainless steel strip according to claim 1 or 2, 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. Features: A manufacturing method for stainless steel cold-rolled steel strip.