JPH0280106A - Method for cold rolling unidirectionally oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To stably obtain a cold rolled steel sheet with a small surface roughness by using work rolls whose diameter is smaller than a specific size in respect to at least one of plural stands in a tandem rolling mill. CONSTITUTION:Work rolls whose diameter of <250mm are used in one stand of plural stands. A silicon steel sheet having a prescribed surface roughness and thickness is cold rolled by a tandem mill having 5 stands at a prescribed rolling speed under some conditions in which a work roll diameter of each stand is variously changed to have a prescribed thickness. The surface roughness of all the work rolls equals to a prescribed roughness. A required surface roughness is not obtained in the case large diameter work rolls are used in all stands; in all the case small diameter work rolls of <=225mm are used in at least one stand, a smooth surface with a surface roughness not larger than a prescribed value is obtained. Thus, cold rolled steel sheets having a small surface roughness are stably obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for cold rolling a grain-oriented silicon steel sheet.
In particular, it is intended to effectively reduce the surface roughness of the final cold-rolled sheet to advantageously improve the magnetic properties.

(Prior Art) Grain-oriented silicon steel sheets are mainly used as iron cores for transformers and other electrical equipment, and are required to have excellent magnetic properties, particularly magnetization properties and iron loss properties.

By the way, the magnetic properties of grain-oriented silicon steel sheets are strongly influenced not only by the material but also by its surface properties.
As disclosed in Japanese Patent No. 127421, the smaller the surface roughness, the better the magnetic properties.

This is because as the surface roughness increases, the specific surface area increases, but as the specific surface area increases, the amount of surface concentration of MnS and MnSe that act as inhibitors increases, so the secondary regeneration increases accordingly. This is because the inhibitor effect inside the steel sheet during crystal annealing weakens, resulting in insufficient growth of secondary recrystallized grains.Also, if the surface roughness of the final cold-rolled sheet is rough, the surface unevenness of the product sheet becomes large. With that,
This is because the insulating coating formed on the surface of the plate is also thick and rough, which prevents movement of the domain wall when the product plate is magnetized.

Therefore, it is preferable that the surface roughness of the final cold-rolled sheet is 0.40 μm or less.

Also, like grain-oriented silicon steel sheets, Si is 2.5 to 4, Q
wt% (hereinafter simply expressed as %) is not only extremely brittle and easily broken compared to general steel materials, but also has extremely high deformation resistance. Cold rolling of grain-oriented silicon steel sheets has been carried out using a reverse mill (approximately 8 Qmm) at a low speed of approximately 700 mpm or less, but recently, from the perspective of improving productivity, cold rolling of grain-oriented silicon steel sheets is being performed using a high-efficiency tandem mill. Rolling has been attempted, and tandem cold rolling is becoming a reality.

However, the surface roughness of a steel plate becomes rougher as the rolling speed increases, so tandem cold rolling tends to worsen the surface roughness.

Therefore, the inventors previously proposed in Japanese Patent Application No. 62-179994 a method of reducing surface roughness by grinding the surface of a steel sheet before final cold rolling and then performing cold rolling.

(Problems to be Solved by the Invention) However, providing a new plate surface polishing process has the disadvantage of increasing equipment costs and product costs.

This invention advantageously solves the above problems, and makes it possible to effectively reduce the surface roughness of a steel sheet by adding innovation to the cold rolling process itself, without requiring any new process. The purpose is to propose a cold rolling method.

(Means for solving problems) The background to the elucidation of this invention will be explained below.

The inventors first considered that if the surface roughness of the rolling roll is reduced, the surface roughness of the cold-rolled sheet will inevitably be reduced. A 5-stand tandem mill incorporating rolls mills 10 silicon steel sheets with a surface roughness of 0.63 μm in Ra.
Rolling was carried out at a speed of 00 m/min. Note that the diameter of the work rolls used at this time was 400 fl 1 m, which is normally used in such tandem rolling.

However, the above-mentioned cold rolling did not achieve the surface roughness of 0.40 μm or less, which is the target of the present invention.

Next, when cold rolling was performed using a tandem mill with various roll diameters while keeping the roll surface roughness as it was, at least one of the five stands had a small diameter of less than 250 mm. When a roll was used, a cold-rolled steel sheet with a smooth surface with a surface roughness of 0.40 μm or less, which was desired by this invention, was obtained.

This invention is based on the above knowledge.

That is, the present invention provides a method for cold rolling a grain-oriented silicon steel sheet using a tandem rolling mill equipped with a plurality of stands, at least one of the plurality of stands.
This is a method for cold rolling grain-oriented S-steel sheets, which comprises using small-diameter work rolls with a diameter of less than 250 mm for the stands.

(Function) The reason why surface roughness is improved by using a small diameter roll having a diameter of less than 250 mm according to the present invention is considered to be as follows.

The reason why the surface roughness after each bath in tandem rolling can be improved by using small diameter rolls can be explained by the fact that oil bits can be reduced by reducing the thickness of the oil film on the entry side of the roll bite. In addition, the surface roughness improved during one pass rolling can maintain the improvement effect to some extent in the next pass, so although there are differences in effectiveness, the effect of the front stage is small)
The improvement effect in the previous stage is also maintained in the latter stage.

If the roll diameter is 250 mm or more, if this small diameter roll is used only in the first stand, there is a risk of achieving the desired plate surface roughness, so the roll diameter of the small diameter roll to be used was limited to less than 150 + nm.

Although the lower limit of the small diameter roll is not particularly limited, it is preferably 59 mm or more. This is because if it is less than that, there will be problems with the life of the roll bearings or rolls, or problems with roll bending, and production rolling will not be possible.

(Example) (::Q, 044%, Si: 3.32%, Mn: 0
．． 063%, Se: 0.017%, sb:o, 028
% composition Surface roughness (Ra): 0.65 μ, Thickness: 3. Qmm silicon steel plate was milled at 1000 m/mi using a 5-stand tandem mill, with the working roll diameter of each stand varied as shown in Table 1.
It was cold rolled to a thickness of 0.3 Qmm at a rolling speed of n. Note that the surface roughness of the work rolls was all set to 0.20 μm.

Table 1 shows the surface roughness of the cold-rolled sheet thus obtained, and FIG. 1 shows the change in surface roughness of the steel sheet after passing through each stand.

Table 1 Note: Work roll diameter, large: 400mm Small: 160 mn+.

(Small): 225+nm As is clear from Table 1 and FIG. 1, the desired surface roughness could not be obtained in the conventional example in which work rolls with a diameter of 400 mm were used for all stands. On the other hand, when a small diameter roll with a diameter of 225 mm or less was used in at least one of the stands, a smooth surface with an Ra of 0.40 μm or less was obtained.

It is noteworthy that even when a small diameter roll is used only in the first stand, the surface roughness reduction effect is maintained up to the final stand.

(Effects of the Invention) Thus, according to the present invention, it is possible to stably obtain a cold-rolled sheet with a small surface roughness by a simple measure of using a small diameter roll in at least one stand of a tandem mill, which is advantageous. be.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the change in surface roughness of a steel sheet after passing through each stand of a tandem mill.

Claims (1)

[Claims] 1. When cold rolling grain-oriented silicon steel sheets using a tandem rolling mill equipped with multiple stands, use a small-diameter work roll with a diameter of less than 250 mm for at least one of the multiple stands. A method for cold rolling a grain-oriented silicon steel sheet.