JP2594634B2 - Cold rolling method for grain-oriented silicon steel sheet. - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for cold rolling a grain-oriented silicon steel sheet,
In particular, the present invention is intended to effectively reduce the surface roughness of the final cold-rolled sheet and to advantageously improve the magnetic properties.

(Prior Art) Grain-oriented silicon steel sheets are mainly used as iron cores of transformers and other electric devices, and are required to have excellent magnetic properties, especially magnetization properties and iron loss properties.

By the way, the magnetic properties of grain-oriented silicon steel sheets are strongly affected not only by the material, but also by the surface properties thereof, and are disclosed, for example, in JP-A-59-38326, JP-A-62-294131, and JP-A-62-127421. As shown, the smaller the surface roughness, the better the magnetic properties.

This is because the specific surface area increases as the surface roughness increases, but the amount of MnS or MnSe acting as an inhibitor increases as the specific surface area increases. This is because the inhibitory effect inside the steel sheet during the crystal annealing is weakened, and as a result, the growth of the secondary recrystallized grains becomes insufficient. As it becomes larger, the insulating film formed on the plate surface becomes thicker and rougher,
This is because the movement of the domain wall when the product plate is magnetized is hindered.

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

In addition, those containing 2.5 to 4.0 wt% of Si (hereinafter simply referred to as%), such as oriented silicon steel sheets, are extremely brittle and easy to break as compared with general steel materials, and also have extremely high deformation resistance. Cold rolling is generally performed at a low speed of about 700 mpm or less, using a reverse mill such as a Zenjiru amyl (roll diameter: about 80 mm) having a small roll diameter. Cold rolling of grain-oriented silicon steel sheets by an efficient tandem mill has been attempted, and tandem cold rolling is being realized.

However, when the rolling speed increases, the amount of rolling oil introduced into the roll bite increases, and as a result, local irregularities called oil pits occur on the steel sheet surface, and the surface properties deteriorate. Therefore, tandem cold rolling is not preferable for surface roughness.

Therefore, the inventors previously described in Japanese Patent Application No. 63-179123, after intermediate annealing, before the final cold rolling, the surface of the intermediate annealed plate was polished and then cold rolled to reduce the surface roughness. A method to reduce it was proposed.

(Problems to be solved by the invention) However, providing a new plate surface cleaning step is
Since not only the equipment cost but also the running cost for cleaning are required, there is a disadvantage that the product cost is increased.

The present invention advantageously solves the above problems, and enables effective reduction of the steel sheet surface roughness by devising the cold rolling process itself without requiring a new process. The purpose is to propose a cold rolling method.

(Means for Solving the Problems) The details of the invention will be described below.

The aim of the above-mentioned sheet surface cleaning treatment is (1) removal of sub-scale and (2) discharge effect of rolling oil by forming grooves in the rolling direction on the steel sheet surface.

The present inventors have conducted intensive studies as to whether the above-mentioned object cannot be achieved without performing a new treatment such as the above-mentioned sheet surface cleaning treatment, and as a result, the initial stage of the second cold rolling process Preferably, when the first rolling is performed using a scratch dull roll provided with scratches in the circumferential direction of the roll as a work roll, the effects (1) and (2) described above can be simultaneously obtained, and thus the surface roughness is small. The knowledge that a cold rolled sheet can be obtained stably was obtained.

The present invention is based on the above findings. That is, the present invention relates to a method of cold rolling a grain-oriented silicon steel sheet by a two-time cold rolling method, wherein a scratch extending in a roll circumferential direction is provided as a work roll in a stage including at least a first stand in a second cold rolling step. This is a method for cold rolling a grain-oriented silicon steel sheet, which comprises using a scratch dull roll having a flaw and a roll surface roughness of 0.3 μm Ra or more in the roll axis direction.

(Operation) According to the present invention, by rolling at least the first pass of the second cold rolling step using a scratch dull roll, (1) Even if oxidized scale is generated on the steel sheet surface during intermediate annealing, the scale remains The scale is easily crushed, so that the scale can be easily peeled off. (2) Since a groove is formed in the surface of the steel sheet in the rolling direction, the rolling oil can be effectively discharged.

Here, it is important that the surface roughness of the scratch dull roll be 0.3 mm Ra or more in the roll axis direction (hereinafter referred to as C direction). This means that if the surface roughness of the scratch dull roll in the C direction is less than 0.3 mmRa, not only will oxide oxide scale not be removed well, but also a groove shall be provided on the steel sheet surface that allows the rolling oil to be discharged effectively. As a result, the target low surface roughness of 0.4 mmRa or less cannot be obtained after the secondary cold rolling.

Nevertheless, if the roll surface roughness is too large, a bad shape of the plate due to an increase in the rolling load will occur, so the roll surface roughness is preferably about 5.0 μmRa or less.

As a means for adjusting the surface roughness of the roll, a grindstone or a laser beam is suitable.

(Example) C: 0.040%, Si: 3.27%, Mn: 0.07% and Se: 0.022%
Containing, the thickness of the composition of the remaining Fe and unavoidable impurities:
After a 3.0 mm silicon steel hot pressing plate was first cold rolled to a thickness of 0.7 mm, it was subjected to intermediate annealing at 975 ° C. for 3 minutes.

Then, a second cold rolling was performed at a rolling speed of 1500 mpm using a five-stand tandem mill having a work roll diameter of 550 mm, to obtain a final cold rolled sheet having a thickness of 0.3 mm.

In the above secondary cold rolling, the relationship between the roll surface roughness and the surface roughness of the final cold rolled sheet in the case of using a scratch dull roll having various surface roughnesses in the C direction as the rolling roll of the first stand. FIG. 1 shows the result of the comparison with a case where the sheet surface was polished after the intermediate annealing in accordance with the specification of Japanese Patent Application No. 62-179994.

As is clear from the figure, by using a scratch dull roll having a surface roughness in the C direction of 0.3 mm Ra or more as a rolling roll of the first stage stand of the secondary cold rolling, the sheet surface was cleaned after the intermediate annealing. Thus, a cold-rolled sheet having a low sheet surface roughness comparable to that obtained by the method was obtained.

(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 sheet surface roughness of a cold-rolled sheet without requiring special new equipment. Can be.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a C-direction surface roughness of a rolling roll and a C-direction plate surface roughness of a final cold-rolled sheet in a first stand in a secondary cold rolling step.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shigeru Kuroda 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Pref. Kawasaki Steel Corporation Mizushima Works

Claims (1)

(57) [Claims] 1. A scratch extending in a roll circumferential direction as a work roll in a stage preceding at least a first stand in a second cold rolling step when cold rolling a grain-oriented silicon steel sheet by a double cold rolling method. A cold rolling method for a grain-oriented silicon steel sheet, comprising using a scratch dull roll having a flaw and a roll surface roughness of 0.3 μmRa or more in a roll axis direction.