JPH0649904B2 - Hot rolling method of grain-oriented silicon steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot rolling technique for producing a grain-oriented silicon steel sheet, and more specifically, it effectively prevents edge cracks generated during hot rolling. And a hot rolling method for improving product yield and work efficiency.

[Conventional technology]

Since grain-oriented silicon steel sheets have excellent magnetic characteristics such as high magnetic flux density and low iron loss, they are widely used as iron core materials for transformers. Recently, there has been a great demand for cost reduction, and in order to meet this demand, development of a manufacturing technique for improving yield and work efficiency is strongly desired.

The grain-oriented silicon steel sheet basically has its excellent iron loss characteristics by containing a large amount of Si (2.5 to 5.0 wt%). On the other hand, on the other hand, the inclusion of a large amount of Si significantly lowers the essential ductility of the material, so that cracking tends to occur due to hot rolling and the like, which is an extremely serious problem in operation.

In addition, in order to ensure excellent directionality, it is necessary to heat the slab at a high temperature of 1300 to 1420 ° C for a long time before hot rolling. The structure does not recrystallize sufficiently even during rolling, and a coarse crystal grain remains. Such a coarse-grained structure lowers the ductility of the slab and promotes cracking during hot rolling.

A crack that is a problem from the viewpoint of yield and work efficiency is an edge crack that occurs at the width-side ends (both ends parallel to the rolling direction of the rolled material) of the rolled material during hot rolling from the slab.
Discontinuous wrinkle-shaped projections are likely to be formed on the width side end portion during hot rolling due to the deformation of the coarse grained structure. Large amounts of
In the material to be rolled, the ductility is essentially low due to the Si content, and the ductility is further reduced due to the coarsening during high temperature and long time heating
The creases more easily cause ear cracks by acting as a place of local stress concentration. Since the edge cracked portion must be trimmed and removed in the subsequent process, the yield is reduced and at the same time, the work efficiency in the subsequent process is reduced, which is a main cause of an increase in manufacturing cost.

Several techniques have heretofore been known as methods for preventing such ear cracking. For example, in Japanese Examined Patent Publication No. 40-10693, in order to relieve the tension acting on the width-side end, a dissimilar material with good ductility (for example, mild steel) is overlay welded in advance on both width-side ends of the silicon steel slab, A technique of rolling after rolling is disclosed. However, although this method has a great effect of preventing ear cracking, it has not been put to practical use because the cost in the welding process is too high. Further, Japanese Patent Publication No. 57-4690 discloses a technique of promoting recrystallization of coarse grains by changing the rolling schedule in the rough rolling process of hot rolling. However, with this method, it is practically difficult to apply sufficient reduction to the side surface of the material to be rolled to promote recrystallization, and therefore the effect of suppressing ear cracking could not be expected so much.

Further, JP-A-60-145204 discloses a method of applying an appropriate width reduction using an edger on the inlet side and the outlet side of the first stand of the finishing rolling mill. However, since this method requires a large amount of equipment cost, an inexpensive method for preventing ear cracking has been desired.

[Problems to be solved by the invention]

An object of the present invention is to effectively prevent edge cracks that occur during hot rolling of grain-oriented silicon steel sheets with compact and inexpensive equipment without deteriorating magnetic properties.

[Means for solving problems]

In the hot rolling of grain-oriented silicon steel sheet, the width-side end surface is
The wrinkle-like deformation y as described above is superimposed on the ballering-like deformation x to form a cross-sectional shape as shown in FIG. 1 (a). At this time, however, tensile stress is likely to concentrate on the wrinkle-like protrusions. It can easily cause ear cracking. For this reason, it is necessary to remove the wrinkle-shaped projections before or after rolling in each pass, as shown in FIG. 1 (c).

In the present invention, the press jig is incorporated into the side guide for guiding the rolling mill placed on the inlet side or the outlet side of the rolling mill,
Alternatively, a press jig is newly provided in addition to the side guide, and the press jig is configured to be movable in the width direction. As shown in FIG. 1 (b), the press jig for shaping the shape of the width-side end surface of the material to be rolled is positioned so as to match the nominal plate width of the material to be rolled, and a substantial width reduction is performed. The structure is such that vibration is applied in the plate width direction by a hydraulic actuator consisting of a piston and a cylinder without adding. As a result, the irregular width side end face formed by rolling in the previous pass is the exit side of the previous pass,
Alternatively, it is pressed and shaped by the pressing jig provided on the entrance side of the next pass, and finished to have a smooth width side end surface. In this case, the friction between the press jig and the width side end surface of the rolled material due to the movement of the rolled material in the longitudinal direction becomes small due to the vibration of the press jig. There is no adverse effect that the tension applied to the
Also, the wear of the press jig is small.

Next, the reasons for each limitation in the present invention will be described.

The reason why the Si content is set to 2.5 to 5.0 wt% is that the occurrence of edge cracking is less than 2.5 wt% and the hot rolling is difficult with the present technology if it exceeds 5 wt%.

The heating temperature was set to 1300 to 1420 ° C because solid solution of the inhibitor element is insufficient at less than 1300 ° C, and extreme coarsening is apt to occur at more than 1420 ° C.

〔Example〕

C: 0.04%, Si: 3.25%, Mn: 0.07%, S: 0.02%, molten steel mainly composed of Fe
A slab measuring m, 1,100 mm wide and 10,000 mm long was manufactured. After carrying the slab to a heating furnace and heating it at a temperature of 1380 ° C., a horizontal roll reduction and an edger roll width adjustment reduction were applied to the rough rolling to a thickness of 40 mm and a width of 1050 mm. Sent to the finishing mill.

As shown in FIG. 2a, press jigs G ₁ and G ₂ are provided on the entrance sides of the first stand and the second stand of the finish rolling mill, respectively.
Was placed. The width center of the material S to be rolled is aligned with the width centers of the rolling rolls R ₂ and R ₂ , and the distance between the left and right press jigs is G _{In 1}
The press jigs G ₁ and G ₂ were positioned using a guide position sensor so that the distance was 1050 mm. When the tip of the material S to be rolled hits the press jig G ₁ , a value is displayed on the load meter provided in the press jig. The vibration of the press jig G ₁ was started using the signal of this load cell. This vibration causes the hydraulic pressure to be transmitted to the hydraulic actuator A ₁ via the servo valve by the signal from the command device.
I sent it to. Velocity of material to be rolled into the first stand 30
m / min, width of press jig G ₁ is 20 mm, frequency is 50 Hz,
Vibrated with an amplitude of ± 1 mm. In this case, the tension applied to the rolled material was set to 0.1 kg / mm ² or less by setting the load applied to the press jig to about 2 tons. The value of this tension is practically negligible. Thus, the material to be rolled whose width side end face has been shaped by vibrating with the press jig G ₁ on the first stand entry side is rolled to a thickness of 20 mm on the first stand, and then rolled on the second stand entry side. Reached the press jig G ₂ . The gap between G ₂ is set to 1060 mm in response to the signal from the strip width meter immediately after the first stand, and the material to be rolled is G ₁
It was subjected to vibration processing in the same manner as in the above. in this case,
Press the press jig G ₂ at the second stand entry side speed 60 of the rolled material.
Vibration was performed at m / min, the width of the press jig was 20 mm, the frequency was 100 Hz, and the amplitude was ± 1 mm. The material to be rolled out of the press jig G ₂ is
Then, it rolled with the rolling mill which spreads from the 2nd stand to the 6th stand, and set it as the steel plate of thickness 2.3mm. When the material to be rolled passed and was separated from the press jig G ₁ or G ₂ and the load applied to the press jig became zero, the vibration of the press jig G ₁ or G ₂ was stopped by receiving the signal.

No edge cracking occurred at all in the manufactured hot-rolled sheet for grain-oriented silicon steel sheet.

[Effects of the Invention] By using the method of the present invention, edge cracks that occur during hot rolling of grain-oriented silicon steel sheets can be effectively prevented with compact equipment, and the product yield and work efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a view showing a state in which the width side end face is shaped without substantially applying a width reduction, and FIGS. 2a, 2b, 2c show the entrance side of the first stand and the second stand of the finish rolling mill. It is a figure which shows the state which has arrange | positioned the press jig of this invention. x: Ballerling deformation, y: Wrinkle deformation, S: Slab (or material to be rolled), G ₁ : Press jig for the first stand entry side, G ₂ : Press jig for the second stand entry side, A ₁ , A ₂ : Actuator, R ₁ , R ₂ : Rolling roll.

Claims (2)

[Claims] 1. A hot rolling method for grain-oriented silicon steel sheet, which is performed after heating a silicon steel slab containing Si: 2.5 to 5.0 wt% to 1300 to 1420 ° C. Press jigs placed in either or both positions of
A hot rolling method for a grain-oriented silicon steel sheet, characterized by pressing the width side end face while vibrating it in the plate width direction without applying substantial width reduction to shape the width side end face. 2. The directivity according to claim 1, wherein the press jig is incorporated in a side guide arranged at either or both of an inlet side and an outlet side of the rolling mill. Hot rolling method for silicon steel sheet.