JP2670101B2 - Cold rolling method of silicon steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cold rolling method for a silicon-containing steel sheet, and particularly to an advantage of rolling load in tandem rolling of a silicon-containing steel sheet, especially a grain-oriented silicon steel sheet. It is intended to reduce the surface roughness of the plate.

(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 influenced 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 described above, the smaller the surface roughness, the better the magnetic properties.

Therefore, in the cold rolling process, especially in the final cold rolling, a so-called bright finish, which is a rolling process so that the surface roughness of the steel sheet is 0.40 μm or less in terms of the center line average roughness Ra, is adopted.

This is because the surface concentration of MnS and MnSe, which act as an inhibitor, increases with the increase of surface roughness, that is, the increase of the specific surface area, and the inhibitor effect inside the steel sheet weakens during the secondary recrystallization annealing. This is because the growth of secondary recrystallized grains becomes insufficient, and if the surface roughness of the final cold-rolled sheet is rough, the surface irregularities of the product sheet will become large and the insulating coating formed on the sheet surface will also be thick. This is because the surface of the product plate is roughened and the movement of the domain wall when the product plate is magnetized is hindered.

In addition, the grain size of Si containing 2.5 to 4.0 wt% (hereinafter simply referred to as%) such as grain-oriented silicon steel sheet is not only extremely brittle and easy to break as compared with general steel materials, but also has extremely high deformation resistance. Cold rolling was generally performed at a low speed of about 700 mpm or less using a reverse mill such as a Sendzimir mill with a small roll diameter (roll diameter: about 80 mm).

However, recently, from the viewpoint of improving productivity, cold rolling of grain-oriented silicon steel sheets by a highly efficient tandem mill has been attempted, and high-speed tandem cold rolling is being realized.

(Problems to be Solved by the Invention) Since the surface roughness of a steel sheet becomes rougher as the rolling speed becomes faster, tandem rolling tends to promote deterioration of the surface roughness.

Here, conventionally, in order to avoid such deterioration of surface roughness, low-viscosity rolling oil was used as rolling oil in all stands. This is because when the viscosity of the rolling oil is low, the thickness of the oil film at the entrance of the rolling roll bite becomes small, and as a result, the oil pit can be made small, which is advantageous for the surface roughness of the steel sheet.

However, when a low-viscosity rolling oil is used, on the other hand, a large rolling load causes a defective shape of the strip to easily occur, and a breakage may occur due to the high tension.

The present invention advantageously solves the above problems, and when cold rolling a silicon steel sheet using a tandem rolling mill, it effectively reduces the rolling load without deteriorating the surface roughness and strips. It is an object of the present invention to propose a cold rolling method that does not cause shape defects and breakage.

(Means for Solving the Problem) The inventors have conducted intensive studies to solve the above problems. I) In order to obtain a desired surface roughness, a low viscosity is not necessarily required over all passes of the tandem rolling. It is not necessary to use rolling oil, and it is sufficient to use it at least in the latter stage.ii) For other passes, if high viscosity rolling oil is used, rolling at high pressure reduction is possible, and the rolling reduction in the latter pass We obtained the knowledge that it can be reduced.

The present invention is based on the above findings. That is, according to the present invention, when cold rolling of a silicon-containing steel sheet is performed by multi-pass oil lubrication rolling using a tandem rolling mill, light rolling using low-viscosity rolling oil is performed at least in the final pass of the multi-pass rolling stage. A cold-rolling method for a silicon-containing steel sheet comprising a rolling pass and a high-pressure rolling pass using a high-viscosity rolling oil.

 The process of elucidation of the present invention will be described below.

The inventors investigated the influence of each pass of tandem rolling on the surface roughness of the steel sheet, and the surface roughness was strongly influenced as it came closer to the second pass, especially the last pass, and the influence of the first pass was hardly received. Turned out not.

Therefore, next, a plurality of types of rolling oils having different viscosities were prepared, and various combinations were applied to each stand and rolling was performed. The surface roughness of the steel sheet tends to deteriorate as the viscosity of the rolling oil increases, but on the other hand, under the same rolling load, the higher the viscosity of the rolling oil is, the higher the rolling pressure can be. .

As a result, in the former stage, rolling with a high-viscosity rolling oil was used at a high pressure to reduce the rolling load in the latter stage, and in the latter stage, the surface properties were restored using a low-viscosity rolling oil while reducing the rolling load. Therefore, it was clarified that a steel sheet having a small surface roughness can be stably manufactured with advantageous reduction of rolling load.

(Operation) As the low-viscosity rolling oil in the present invention, those having a kinematic viscosity of 15 cSt or less at 50 ° C. are preferable, and as the high-viscosity rolling oil, those having a kinematic viscosity of about 20 to 60 cSt at 50 ° C. are preferable.

(Example) C: 0.044%, Si: 3.32%, Mn: 0.063%, Se: 0.017% and Sb: 0.028% of the composition: thickness: 3.0 mm, width: 1100 mm silicon steel hot rolled sheet Using a stand tandem mill (work roll diameter: 380 to 620 mm), each was cold-rolled to a thickness of 0.3 mm under various conditions shown in Table 1.

The surface roughness of the cold-rolled sheet thus obtained is shown in the same table, and the rolling load at each stand is shown in FIG. 1 for comparison.

As is clear from the table, according to the present invention, the high-viscosity rolling oil B is used in the first pass (stand No. 1 and 2) of tandem rolling.
On the other hand, for the latter three stands, low viscosity rolling oil A
In the conforming example using, the rolling load is 0.90to for all stands.
A silicon steel sheet having a surface roughness of n / mm or less and a small surface roughness was obtained.

On the other hand, in the conventional example in which the low-viscosity rolling oil A was used in all stands, the surface roughness was 0.36 μm, which was a good result, but as shown in FIG. A large rolling load of ton / mm was required. When a high-viscosity rolling oil was used in all stands (reference example), the rolling load was small in all stands, but the surface roughness was extremely poor at 0.48 μm Ra.

Here, the difference in rolling load at the final stand between the conforming example and the conventional example is calculated as follows: (1.20-0.90) x 1100 = 330ton, which is an excellent rolling load reduction effect. I understand.

(Effects of the Invention) Thus, according to the present invention, in tandem rolling of a silicon-containing steel plate, a cold-rolled silicon-containing steel plate having a small surface roughness can be easily obtained while effectively reducing the rolling load.

[Brief description of the drawings]

FIG. 1 is a graph showing a comparison of changes in rolling load at each rolling stand due to differences in rolling oil viscosity patterns.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichiro Hanada 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture (no address) Kawasaki Steel Works Mizushima Works

Claims (1)

(57) [Claims] 1. Cold-rolling a silicon-containing steel sheet by multi-pass oil lubrication rolling using a tandem rolling mill, wherein at least the final pass after the multi-pass rolling uses a light rolling using a low-viscosity rolling oil. A method for cold rolling a silicon-containing steel sheet, characterized in that the remaining passes are high-pressure passes using high-viscosity rolling oil.