JPH0576905A - Method for preventing edge crack in cold rolling of silicon steel sheet - Google Patents

Abstract

(57) [Summary] [Structure] In a method of rolling a silicon steel sheet having a Si content (% by weight) of 1.5% or more by a cold tandem rolling mill,
One end of the work roll of the first stand of the cold tandem rolling mill is made thicker so that the axial directions of the upper and lower work rolls are opposite to each other, and the work roll is movable in the axial direction. One end of the work roll of the stand is tapered so that the axial directions of the upper and lower work rolls are opposite to each other, and it is movable in the axial direction of the work roll. The temperature should be 80 ℃ or higher. [Effect] The occurrence rate of edge cracks in cold tandem rolling of a silicon steel sheet containing 1.5% by weight or more of Si can be significantly reduced, and edge drop can be reduced. This improves the yield in cold rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon steel sheet having excellent edge properties by preventing edge cracking and plate breakage of the silicon steel sheet.

[0002]

2. Description of the Related Art Conventionally, in the production of magnetic steel sheets, the occurrence rate of edge cracks in the cold rolling process has been high, which has been a cause of lowering productivity. Especially Si content (wt%) is 1.5%
In the case of the above high-grade silicon steel sheet, the occurrence rate was high, the sheet rupture occurred due to the edge crack, and the rolling was difficult.

Usually, a silicon steel sheet containing 1.5% or more of Si was rolled by a small diameter multi-stage reverse rolling mill such as Zenzimer. In the case of such a rolling mill, the rolling speed is relatively slow, and the ear cracks can be easily detected. When the ear cracks occur, the rolling mill is stopped between passes and the edge cracked portion is cut by a notcher. The method was adopted. In recent years, from the viewpoint of highly efficient production of high-grade silicon steel sheets, silicon steel sheets are produced by a tandem rolling mill after side trimming. However, even if the tandem rolling mill can detect the occurrence of edge cracks, it cannot roll the coils between the stands because it rolls at a high speed. Furthermore, because of the high speed rolling, when a plate rupture caused by the cracking of the ears occurs, it may cause a serious accident. These not only lower the rolling efficiency, but also cause a large edge cutting margin after rolling due to the occurrence of edge cracking, which significantly reduces the yield.

Therefore, as a method for preventing edge cracking and plate breakage, for example, a method of plate edge treatment before rolling is disclosed in
As disclosed in Japanese Patent Laid-Open No. 60-218425, there has been proposed a method in which an edge surface after side trimming is irradiated with a laser beam and heated to remove an embrittled surface of the edge and minute cracks. Further, as disclosed in JP-A-62-137110, the body end of the work roll of the Zenzimer rolling mill is thickened, and the reduction rate of the edge is locally increased,
It has been proposed to prevent ear cracking by reducing the tension acting on the edge by forming the shape of the edge.

[0005]

However, the method of the above publication has the following drawbacks. In the method of heating the plate edge after side trimming with a laser beam, it is difficult to completely shield the air during laser beam irradiation. If the shield conditions are incomplete, the irradiated surface will oxidize and the material will be fragile. There was a chance In addition, when laser beam irradiation equipment is installed in a continuous line, it is necessary to adjust the laser intensity due to line speed fluctuations, not only heating at a constant temperature but also a temperature difference in the plate thickness direction, especially the surface layer of the edge. The cooling rate increased and the vicinity of the plate surface edge was sometimes embrittled.

Further, in the mill type in which the work rolls can be easily exchanged like the Zenzimer rolling mill, the work rolls having one end having a thickened end can be exchanged for each coil or for each pass, and the ear-stretched shape can be easily given. .. However, when a thick work roll is introduced into the first stand in tandem rolling, the edge drop formed in the first stand is inherited in the edge profile of the plate of the final stand, increasing the product edge drop amount and lowering the yield. There was a problem to do. From the same point of view, a method of reducing the bending force may be considered, but the overall shape in the plate width direction deteriorates,
There were cases where rolling was impossible due to narrowing.

An object of the present invention is to provide a method for preventing edge cracks in cold rolling of a silicon steel sheet which solves the above problems.

[0008]

The present invention relates to a method for rolling a silicon steel sheet having a Si content (weight%) of 1.5% or more by a cold tandem rolling mill, which is a first cold tandem rolling mill.
One end of the work roll of the stand is thickened so that the axial directions of the upper and lower work rolls are opposite to each other, and the work roll is movable in the axial direction. The taper should be tapered, and the axial directions of the upper and lower work rolls should be opposite to each other, and should be movable in the axial direction of the work rolls, and the plate edge temperature of the stand entry side after the second stand should be 80 ° C or higher. Is a method for preventing edge cracks in cold rolling of a silicon steel sheet.

[0009]

[Operation] In the present invention, one end of the work roll of the first stand of the cold tandem rolling mill is made thicker, and the axial directions of the upper and lower work rolls are opposite to each other, so that the plate edge portion is rolled down. Increase the rate to generate compressive stress at the edges. For example, Fig. 4 shows a diameter workpiece of 400m.
δW (starting point of work roll taper and plate edge) using a 1.5% silicon steel plate with a width of 1000 mm and a thickened work roll (taper 1/500 of primary expression: 500 mm length and 1 mm per diameter) It is the figure which showed the result of having measured the residual stress in edge 5mm at the time of rolling by changing the distance). At this time, the tension between the first and second stands is 10 kgf / mm ²
Therefore, if δW is 15 mm or more, compressive stress acts on the edge portion. By applying compression to the edge portion, it is possible to prevent the edge portion from cracking.

However, since the silicon steel sheet containing 1.5% or more of Si is brittle at room temperature, it is not possible to completely prevent the edge cracking and the sheet breaking by the above treatment. Therefore, in the present invention, the work roll of the first stand is thickened and the inlet side temperature of the second stand is kept at 80 ° C. or higher for the following reason. The ductility of the silicon steel sheet is improved depending on the temperature. Figure 5
Is evaluated by the number of times of reciprocal bending until breakage by a bend test. When the test temperature exceeds 80 ° C, the number of times of bending until breaking is significantly increased, and the ductility is improved. When a similar test is performed on mild steel at room temperature,
Since the number of bends of both is similar at 80 ℃ or more, in order to achieve the same rolling as mild steel sheet that does not cause edge cracking, ensure the entry side edge temperature of the stand after the 2nd stand is 80 ℃ or more. There is a need to.

In the first stand, since compressive stress acts on the plate edge, the temperature is preferably 80 ° C. or higher, but may be from room temperature to 80 ° C. In the present invention, since the edge temperature is 80 ° C. on the entry side of the second stand, the reduction rate of the first stand is increased and the temperature is secured by the heat generated by processing. That is, when a thermocouple is embedded in the plate edge and the reduction ratio of the first stand is changed, the plate temperature on the inlet side of the second stand can be achieved at a reduction ratio of 40% or more as shown in FIG. I know there is. The rolling conditions at this time were a rolling speed of 50 m / min, a work roll diameter of 300 mm, a mother plate thickness of 3.0 mm, and a plate width of 1000 mm. The temperature of the mother board on the inlet side was 50 ° C. This speed is the minimum speed in actual rolling. The temperature at the entrance of the second stand
If 80 ° C or higher can be secured, the strain rates of the downstream third and fourth stands naturally increase, so that the inlet side temperature of those stands can easily be 80 ° C or higher.

By the way, in the first stand, since the edge is rolled by using the work roll whose one end is thick, the edge drop on the delivery side of the first stand becomes large. Therefore, in the present invention, a work roll having one end tapered is used for the downstream stands after the second stand to improve the edge drop. When the edge of the plate is rolled by the tapered work roll taper part, the plate thickness of the edge part becomes thicker and the edge drop becomes smaller due to the geometric effect of the roll.
The opposite is true when using a thick work roll.
The edge drop referred to here means the difference in plate thickness between the 5 mm position and the 25 mm position in the plate width direction from the edge.

[0013]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing an example of a cold rolling facility for carrying out the present invention. In FIG. 1, 1 is a silicon steel strip, 2
Is a payoff reel, and 3 is a tension reel. 4a
4d are the 1st-4th stands of a rolling mill.

As shown in FIG. 2, the work roll 5 of the rolling mill 4a of the first stand has one end of the roll being thickened in order to press down the edge more strongly than the center of the strip width, and the shafts of the upper and lower work rolls 5 and 5 are formed. The directions are opposite to each other.
The work rolls 5'of the second to fourth stand rolling mills 4b to 4d are arranged such that one end of the rolls is tapered and the axial directions of the upper and lower work rolls 5'and 5'are opposite to each other as shown in FIG. There is.

In FIGS. 1, 2, and 3, 6 is a backup roll and 7 is an intermediate roll. Next, specific examples of the present invention will be described. A silicon steel sheet containing 1.5% of Si was used for the 4-stand tandem mill shown in Figs.
Cold rolling was performed from 3.0 mm to 0.5 mm, and the occurrence of ear cracks was examined. In the cold rolling, the rolling machine of the first stand further pressed the edge more strongly than the center of the strip width. In the downstream stands after the second stand, the edge drop control is performed by the work roll in which one end of the work roll is tapered, and in the stands after the second stand, rolling is performed at a roll bite entrance side temperature of 80 ° C. or higher. The tapered or tapered shape of the work roll is a tapered shape represented by a linear expression. The work roll diameter is 300 mm. The rolling mill may be the 6-high rolling mill shown in FIG. 1, but the same effect can be obtained with the conventional 4-high rolling mill.

The rolling method of the present invention was carried out under the rolling conditions shown in Table 1. For comparison with the present invention, a straight roll was used as the work roll in the comparative example, and the rolling reduction was set to the same level as in Table 1. Experimentally, the present invention and the conventional method each have about 1000
The coil degree was processed and compared. Table 2 shows the ear crack occurrence rate at that time. As for the edge crack, the edge of the coil after rolling was observed, and when there was at least one edge crack having an edge opening length of 1 mm or more, the edge crack was defined as the edge crack coil.

According to the present invention, it can be seen that the ear crack occurrence rate can be significantly reduced. Further, it is clear that the edge shape after rolling has a smaller edge drop as compared with the conventional method as shown in FIG.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

As described above, according to the present invention,
It is possible to significantly reduce the rate of occurrence of edge cracks in cold tandem rolling of a silicon steel sheet containing 1.5% by weight or more of Si and to reduce edge drop. This improves the yield in cold rolling.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of cold rolling equipment.

FIG. 2 is a front view of the first stand in FIG.

3 is a front view of second to n-th stands in FIG. 1. FIG.

FIG. 4 is a diagram showing measurement results of residual stress after rolling using a thick work roll.

FIG. 5 is a diagram showing a relationship between a test temperature and the number of times of bending.

FIG. 6 is a diagram showing the influence of the rolling reduction of the first stand on the inlet side temperature of the second stand.

FIG. 7 is a diagram comparing edge thickness distributions of the present invention and a conventional method.

[Explanation of symbols]

 1 Silicon Steel Strip 2 Payoff Reel 3 Tension Reel 4a 1st Stand 4b 2nd Stand 4c 3rd Stand 4d 4th Stand 5 Work Roll with One Tapered One End 5'Work Tape with One Tapered One End 6 Backup Roll 7 Intermediate Roll

Claims (1)

[Claims] 1. A method of rolling a silicon steel sheet having a Si content (weight%) of 1.5% or more by a cold tandem rolling mill, wherein one end of a work roll of a first stand of the cold tandem rolling mill is made thicker, The upper and lower work rolls are arranged so that their axial directions are opposite to each other, and the work rolls can be moved in the axial direction, and one end of the work rolls of the second and subsequent stands is tapered so that the axial directions of the upper and lower work rolls are In cold rolling of a silicon steel sheet, which are arranged so as to be opposite to each other and are movable in the axial direction of the work roll, and the plate edge temperature on the stand-entry side after the second stand is set to 80 ° C. or higher. Ear crack prevention method.