JPH02175006A - Manufacture of cold rolled steel sheet having less seizing flaws generated in annealing time - Google Patents

Abstract

PURPOSE:To reduce generation of seizing flaws in annealing time for a steel sheet by rolling the sheet by use of a work roll meeting requirements of a specific inequality in the final pass of cold rolling. CONSTITUTION:A rough surface shape of a dull roll used in the final pass of cold rolling is decided such that a centerline average roughness Ra of the roll surface is >=3mum. Further, rolling is performed by use of a work roll whose roughness shape is decided so that variations in peak height meet the inequality when a peak height against a central plane, an average height, and the number of peaks in an observation length are denoted by (hi), (h), and (n), respectively. Hence, seizing flaws on a steel sheet are markedly reduced.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for producing cold rolled steel sheets in which seizure defects are less likely to occur during an annealing process. The present invention relates to a method for efficiently manufacturing the above-mentioned cold-rolled steel sheet using processed work rolls.

(Prior Art) After rolling, a cold rolled steel plate is subjected to an annealing process mainly to improve workability. Recently, this annealing process is often carried out using a continuous annealing method, but it is carried out under conditions such as placing the wound coil into an annealing furnace at 700°C for 15 hours. Many so-called batch annealing methods are also used. Particularly in batch annealing of tight coils, the surfaces of the steel plates that are in contact may seize together and cause flaws. There are various causes of this flaw, and one of the causes is the surface roughness of the steel plate.

Therefore, in the manufacturing process of cold rolled steel sheets, in order to reduce seizure defects in the annealing process, dull rolls whose surfaces are given a predetermined roughness are used in the final pass of cold rolling. According to this method, the surface of the steel plate becomes a dull surface with minute irregularities, and the contact area between the steel plates when wound into a coil is smaller, resulting in the occurrence of seizure defects compared to a so-called bright steel plate rolled with a blind roll. decreases considerably. It has been conventionally known that the effect of reducing seizure flaws becomes greater as the surface of the roll becomes rougher.

(Problems to be Solved by the Invention) As mentioned above, it is known that seizing defects during annealing can be reduced by rolling a dull roll as a work roll in the final bath of cold rolling. However, conventional dull rolls have their surfaces dulled by shot blasting or electric discharge dulling. In this case, no matter how rough the roll surface is, there is a limit to reducing the incidence of seizing defects.

The inventor investigated the cause and discovered that the limit to reducing the incidence of seizing defects lies in the irregularity of the roughness of conventional dull rolls. That is, when the roll surface is dulled by shot blasting or electrical discharge machining, the dull pattern (shape and distribution of minute irregularities) formed on the roll surface must be irregular. Since the dull pattern on the work roll surface is transferred to the steel plate surface,
The dull pattern on the surface of a steel sheet rolled with such rolls also inevitably becomes irregular. Therefore, even if the roughness is appropriate macroscopically, there are microscopically (locally) smooth areas, and when the coil is wound, the contact between those areas becomes tight.
This will result in burn-in scratches.

An object of the present invention is to provide a new method for manufacturing a cold-rolled steel sheet that prevents the occurrence of seizure defects caused by irregularities in the dull pattern of the steel sheet as described above.

(Means for solving problems) The gist of the present invention lies in the following method for manufacturing a cold rolled steel sheet.

``In the final bath of cold rolling, it is processed using a high energy density beam, and has a rough surface with a center line average thickness Ra of 3 μm or more, and the variation in peak height in the rough surface shape is When the height of the mountain with respect to the center plane is hi, the average height is h, and the number of mountains in the observation section is n, rolling is performed using a work roll that satisfies n i-1h. Method 1 for manufacturing a cold rolled steel sheet with fewer seizure defects during annealing Here, the average peak height h is defined by the following formula.

n i = 1 In the method of the present invention, in order to significantly reduce seizure defects in the annealing process of cold rolled steel sheets, the rough surface shape of the dull roll used in the final bath of cold rolling is as follows. did.

That is, the centerline average roughness Ra of the roll surface is set to 3 .mu.- or more, and furthermore, the roughness shape suppresses the variation in peak height hi with respect to the center surface to within 5%. By rolling the final bus using such rolls, the seizure defects on the resulting steel sheet could be significantly reduced to a level that would be unimaginable using conventional techniques.

In addition, [the final bus of cold rolling] means rolling at the final stand in the case of rolling by a tandem mill.
In the case of reverse rolling, this is literally the final bus.

The work roll used in the method of the present invention cannot be dulled by conventional shot blasting or electric discharge dulling methods. This dulling process is only possible by using a high-energy-density beam such as a laser beam to regularly form microcraters. In other words, processing using a high-energy-density beam not only makes it possible to regularly form micro-craters (micro-irregularity patterns) on the roll surface, but also to adjust the beam energy, irradiation pitch, etc. to achieve the Ra range described above. , and hi
It is easy to adjust to the range of variation.

Regarding the roll processing method using a high energy density beam, the basic invention is introduced in Japanese Patent Publication No. 11922/1983.

(Function) By regularly arranging minute craters on the work roll in the final pass of cold rolling by high energy density beam machining such as a laser beam, the center line average roughness Ra of the roll surface is made to be 3 μm or more, and By setting the variation in peak height with respect to the center plane within 15%, the surface roughness of the cold-rolled steel sheet rolled with this roll has a center line average roughness Ra of 1.2 μn or more, and a peak height with respect to the center plane. The variation is within ±2%. The reason why there is a difference between the variations in Ra and ht of a roll and those of a steel plate rolled with this roll is that the rolling reduction rate (usually about 5%) in the final pass of rolling is due to the unevenness of the roll surface. is not completely transferred to the surface of the steel plate, but the transfer rate is approximately 40%.

When the steel sheet obtained in this manner is wound into a coil shape and annealed, almost no seizure defects occur. this is,
It is thought that due to the regularity of the dull pattern of the steel plate, there are no parts where the temporary and the plate are in complete contact with each other, making it difficult for seizure defects to occur.

On the other hand, in the case of a steel plate rolled with a roll that has been dulled by shot blasting or electrical discharge machining, which has an irregular roughness shape, no matter how coarse the center line average roughness Ra is, the Ra Since there are also small surfaces, the occurrence of seizing defects cannot be prevented.

In the present invention, the Ra of the roll surface is 3.0 ttm.
The reason for setting the variation in hi within 5% is based on the results of numerous experiments.With this range, a regular dull pattern that satisfies the above conditions can be given to the surface of the steel plate after rolling, and seizure defects can be prevented. This is because we have confirmed that the occurrence can be completely prevented.

The experimental results will be described below as an example.

(Example) Forged steel rolls were subjected to dull processing using a laser beam processing method to produce various rolls having different variations in surface roughness Ra and peak height hi with respect to the center surface.

For comparison, several rolls were also made using conventional shot blasting and electric discharge machining methods. The dull patterns of these rolls are summarized in Table 1.

Using the rolls shown in Table 1 as the work rolls of the final stand of a tandem mill, JIS G3141 cold-rolled tFil temporary was rolled under the following conditions, and then annealed.

■ The rolling conditions are Kinoe 111191 5-stand tandem mill, with a dull roll on the final stand (1, A+2000 toshi rolling with the same roll.

(2) Annealing conditions Table 1 shows the dull pattern on the surface of the steel plate obtained by the above method at a furnace temperature of 700'C for 15 hours and the occurrence of seizure defects.

The occurrence of seizure defects was investigated as follows.

■Method for investigating the occurrence of seizing defects The percentage of occurrence of seizing defects was determined by the weight ratio of the portions of the 2,000 total coils that were downgraded due to medium-level seizure defects.

Table 1 lists the occurrence rate of seizure defects as well as the variations in Ra and hi of steel sheets.

The attached figure is a graphical representation of the results in Table 1.

Ra=4.0μm, 3.5p within the scope of the present invention
In the example of m, 3°Oμ-, if the variation in hi is within 5%, the incidence of seizing defects is 0%.

However, even if Ra is at the above value, if the variation in hi exceeds 5%, seizure defects will occur.For example, if Ra=4.
Even in the case of 0 am, if the variation in hi becomes 15%, the occurrence rate of seizure defects reaches about 0.015%.

On the other hand, Ra-2.5 μm and 2.0 μm are outside the scope of the present invention.
In the case of μm, even if the variation in hi is 5% or less, it is not a measure to eliminate seizure defects. Therefore, R
When a is 3.0 p m or more, the variation in hi is 5%.
It is clear that the object of the present invention is achieved only when both of the following conditions are satisfied. Furthermore, it can be seen that the processing method for the roll that satisfies these conditions must be a processing method that uses a high energy density beam such as a laser beam.

(Effects of the Invention) The method for producing a cold rolled steel plate of the present invention corrects the dull pattern on the surface of the work roll used for the final lotus of cold rolling, thereby improving the process of annealing the steel plate rolled using the work roll. This significantly reduces the occurrence of seizure defects. Processing of work rolls can be done relatively easily using a method that uses high energy density beams, which has been put into practical use in recent years, and there is no need to make any special changes to the rolling or annealing process, so the increase in manufacturing costs is small. , On the other hand, the actual benefit of improving product yield by reducing seizure defects is extremely large.

[Brief explanation of the drawing]

The attached figure is a graph showing the relationship between the dull pattern of a work roll in the final pass of cold rolling and the incidence of seizure defects during annealing of a steel plate rolled by the roll.

Claims (1)

[Claims] A rough surface processed using a high energy density beam in the final pass of cold rolling, having a center line average roughness Ra of 3 μm or more, and having a peak height in the shape of the rough surface. A work roll that satisfies the following: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ 1. A method for producing a cold-rolled steel sheet with less occurrence of seizure defects during annealing, the method comprising rolling using a cold-rolled steel sheet.