JPH02151308A - Method for cold-rolling grain oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To reduce the surface roughness of a final cold rolled sheet by specifying the sheet surface roughness of the steel sheet after the primary cold rolling. CONSTITUTION:When grain oriented silicon steel is cold-rolled by the double cold rolling method, a rolling roll having ground scratch marks in the peripheral direction of the roll is used at least in a final stand of the 1st rolling stage. A scratch flaw in which a sheet surface roughness in the C-direction after rolling is <=0.3mum Ra is given to the rolled sheet. By this method, the surface roughness of the cold rolled sheet can be reduced effectively without providing a special new equipment.

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.
-127421 As disclosed in each publication 1, 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, the Si content is 2.5 to 4. Qw
t% (hereinafter simply expressed as %) is not only extremely brittle and easily broken compared to general steel materials, but also has extremely high deformation resistance. Therefore, cold rolling is generally performed using a Sendzimir mill with a small roll diameter (roll diameter: It used to be done using a reverse mill like 3Qmm) at a low speed of about 700 mpm or less, but recently, from the perspective of improving productivity,
Attempts have been made to cold-roll grain-oriented silicon steel sheets using high-efficiency tandem mills, and tandem cold rolling is becoming a reality.

However, as the rolling speed increases, the amount of rolling oil introduced into the roll bite increases, which causes local unevenness called oil pits to occur on the surface of the steel sheet, degrading the surface quality. Therefore, tandem cold rolling is not favorable for improving surface roughness.

Therefore, the inventors previously proposed in Japanese Patent Application No. 179994/1983 that the surface of the intermediate annealed plate was ground after intermediate annealing and before the final cold rolling, and then the surface was roughened. We proposed a method to reduce the

(Problem to be solved by the invention) However, providing a new plate surface polishing process not only increases equipment costs but also requires running costs for cleaning, which has the disadvantage of increasing product costs. be.

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 a new process. The purpose is to propose a cold rolling method.

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

Now, the aims of the above-mentioned board surface polishing process are (1)
(2) the effect of draining rolling oil by creating grooves on the surface of the steel plate in the rolling direction;

Therefore, the inventors conducted intensive research to see if the above objective could be achieved without special treatment such as plate surface polishing treatment, and as a result, in the first rolling process, the roll If you use a scratch dull roll with scratch marks in the circumferential direction, grooves will be formed on the surface of the steel sheet in the rolling direction, so the same effect as lifting (2) can be obtained, and furthermore, the subsequent intermediate annealing will prevent oxidation on the surface. Even if scale is formed, the scale is peeled off relatively smoothly at the initial stage of the second cold rolling because the surface is uneven, and thus a cold rolled sheet with small surface roughness can be obtained. Obtained.

This invention is based on the above knowledge.

That is, this invention provides a method for cold rolling grain-oriented silicon steel by a two-time cold rolling method, at least in the final stand of the first rolling process, using a rolling roll having grinding scratches in the circumferential direction of the roll. This is a method of cold rolling a grain-oriented silicon steel sheet, which comprises adding scratches to the sheet so that the surface roughness in the C direction after rolling becomes 0.3 μm Ra or more.

(Function) In this invention, it is important to provide scratches with a surface roughness Ra of 0.3 μm or more in the C direction on the surface of the steel sheet after the first cold rolling.

Does that mean C after cold rolling? Plate surface roughness in 5 directions is 0.3
This is because if it is less than μmRa, the surface roughness of the final cold-rolled sheet after the second cold rolling cannot be reduced to 0.4 μm or less, which is the target of the present invention.

In order to make the surface roughness of the steel sheet after the first cold rolling 0.3 μm or more, at least in the final stand of the first rolling process, the rolling roll should have a surface roughness of 0.3 μm or more in the circumferential direction of the roll. A roll with a scratch dull finish provided with grinding scratches of 3 μm Ra or more may be used.

(Example) C: 0.040 wt%, Si: 3.27 wt%, M
A silicon steel plate with a thickness of 3.0 mm containing n: 0.07 wt%, Se: 0.022 wt%, and the remainder consisting of Fe and unavoidable impurities was heated with a work roll diameter of 550 Illffl. First cold rolling was performed using a 5-stand tandem mill at a rolling speed of 500 mpm to a thickness of 0.7 mm.

At this time, a number of rolls having different surface roughnesses were used as work rolls of the final stand, and the surface roughness of the primary cold-rolled sheet was varied in various ways.

Then, after performing intermediate annealing at 975° C. for 3 minutes, a second cold rolling was performed at a rolling speed of 1500 mpm using the same 5-stand tandem mill to obtain a final cold rolled sheet having a thickness of 0.3 mm.

C-direction plate surface roughness of the primary cold-rolled sheet and the secondary cold-rolled sheet when treated with the above two-time cold rolling method! 7) The results of the investigation on the relationship with the surface roughness in the C direction are presented in the above-mentioned patent application 1799/1986.
FIG. 1 shows a comparison with the case where the plate surface was polished after intermediate annealing according to the specification of No. 94.

As is clear from the figure, by setting the surface roughness of the steel sheet after the primary cold rolling to 0.3 mmRa or more, the final cold rolled sheet can be improved to the same level as when surface roughness is applied after intermediate annealing. It was possible to reduce the plate surface roughness.

(Effects of the Invention) Thus, according to the present invention, when cold-rolling a grain-oriented silicon steel sheet, it is possible to effectively reduce the surface roughness of the cold-rolled sheet without requiring any special new equipment. can. ,

[Brief explanation of the drawing]

FIG. 1 is a graph showing the influence of the surface roughness in the C direction after the first cold rolling on the surface roughness in the C direction after the second cold rolling.

Claims (1)

[Claims] When cold rolling grain-oriented silicon steel by the one- or two-time cold rolling process, at least in the final stand of the first rolling process, a rolling roll having grinding scratches in the circumferential direction of the roll is used. A method for cold rolling a grain-oriented silicon steel sheet, which comprises adding scratches to the rolled sheet such that the surface roughness in the C direction after rolling is 0.3 μmRa or more.