JPS62192533A - Method for hot rolling grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To enhance the product yield and the work efficiency by spraying a molten metal on both sides of a grain-oriented silicon steel slab in the lateral direction so as to prevent edge crack during rolling, heating the slab and hot rolling it. CONSTITUTION:When a slab S contg. 2.5-5.0wt% Si is heated to 1,300-1,420 deg.C and hot rolled, a molten metal in which Si is readily diffusible is previously sprayed on both sides of the slab S in the lateral direction over the full length with sprayers G1, G2. The slab S is then heated to 1,300-1,420 deg.C and hot rolled. A molten mild steel having a lower Si content than the slab S is preferably used as the molten metal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a hot rolling technique for producing grain-oriented silicon steel sheets, and more specifically, to a technique for effectively eliminating edge cracks that occur during hot rolling. The present invention relates to a hot rolling method for preventing such problems and improving product yield and work efficiency.

[Conventional technology]

Grain-oriented silicon steel sheets have excellent magnetic properties such as high magnetic flux density and low iron loss, and are therefore 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, there is a strong desire to develop manufacturing technology that improves yield and work efficiency.

Grain-oriented silicon steel sheet contains a large amount of 5i (2.5~5.0wt%
), it basically has excellent iron loss characteristics. However, since the essential ductility of this large amount of St gold-containing material is significantly reduced, there is a strong tendency for cracks to occur during hot rolling, etc., which poses 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. Even during rolling, the structure is not sufficiently recrystallized and coarse crystal grains remain. Such coarse-grained Mi weave reduces the ductility of the slab and promotes cracking during hot rolling.

Cracks that pose a problem from the viewpoint of yield and work efficiency are edge cracks that occur at the width side ends of the rolled material (both ends of the rolled material parallel to the rolling direction) during hot rolling from the slab.

During hot rolling, discontinuous wrinkle-like protrusions are likely to be formed at the width side end portions due to deformation of the coarse grained structure. In rolled materials, which inherently have low ductility due to a large amount of St gold, and whose ductility further decreases due to grain coarsening during high-temperature and long-term heating, the above-mentioned wrinkles act as localized stress concentration sites, resulting in further ductility. Ears crack easily. These cracked edges must be removed by cutting them in a post-process, which lowers the yield and at the same time reduces work efficiency in the post-process, which is the main cause of increased manufacturing costs.

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

[Problem that the invention seeks to solve]

The purpose of the present invention is to effectively prevent edge cracks that occur during hot rolling of grain-oriented silicon steel sheets without deteriorating the magnetic properties, and for this purpose, This paper proposes a method of increasing the ductility of the width side end portions by lowering the Si concentration.

[Means for solving problems]

In the present invention, first, a film of metal particles is formed by melting and spraying a metal in which Si easily diffuses (e.g., pure iron, mild steel, etc.) at high speed onto the width side end face of a grain-oriented silicon steel slab before heating. forming and then heating the slab.

During this heating process, the St existing at the width end of the grain-oriented silicon steel slab diffuses into the metal film previously formed on the width end of the slab. As a result, ductility improves in inverse proportion to the decrease in Si concentration in the vicinity of the width side ends, and even if coarse grains or stress concentration occur during subsequent hot rolling, edge cracks do not occur.

The method proposed by the present inventors for reducing the Si concentration at the width side ends involves internally modifying the poles (parts) of the material to be rolled. This is essentially different from techniques that require external additions, such as joining ductile dissimilar materials at the width edges.

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

The reason for setting the Si content to 2.5 to 5.0 wt% is 2.5
This is because if it is less than 5 wt%, edge cracking is less likely to occur, and if it exceeds 5 wt%, hot rolling is difficult with current technology.

The heating temperature was 1300 to 1420°C.
Below 1°C, solid solution of the inhibitor element is insufficient;
This is because if the temperature exceeds 420°C, extremely coarse graining tends to occur.

As the molten metal sprayed onto the end face of the silicon steel slab, various metals in which Si easily diffuses can be used;
Particularly desirable is the one described in claim 2.

The thickness of the sprayed layer is not particularly limited, but it is generally desirable to determine it in the range of about 0.01 to 1 a+m depending on the actual operating conditions.

The present invention will now be described in detail with reference to the illustrated embodiments.

〔Example〕

In FIG. 1, a pair of scale removal devices (not shown)
and a pair of thermal spraying devices G1. G2 (device W for melting and spraying metal) was placed on both sides of the roller table R.

C: 0.04wt%, Si: 3.25w
t%, Mn: 0.07wt%, S: 0.
A molten silicon steel containing 0.02 wt%, the balance being Fe and unavoidable impurities was continuously cast to a thickness of 250 mm, a width of 1 m,
A slab S having a length of 10 m was prepared and immediately moved onto a roller table R.

While conveying the slab S to the heating furnace by the roller table R at a slow speed of approximately 1 m/min, the thermal spray bag W G In G is applied over the entire length of both width side end faces of the slab S.
Melting extremely soft jll by z (C: 0.0Oht%.

Si: 0.02ut%, Mn: 0.1w
t%, S: 0.01wt%.

The remainder was sprayed with Fe. The spraying was carried out only on the width of 40 to 60 m5 at the center of the plate thickness on both end faces, and the layer thickness was about 0.5 ms+.

The reason why the area for spraying was limited to the center area is that edge cracking occurs mainly in the finish rolling stage, and the part that was originally near the edge of the width side of the slab now extends around the plate surface of the rolled material. This is because it is no longer a place where ear cracks occur because it has become crowded. That is, the width of the above spraying is 40 to 6
0 mm corresponds to the thickness of the rolled material immediately before the start of finish rolling and immediately after rough rolling. Of course, if necessary, such as when edge cracks occur during the rough rolling stage, it is also effective to spray the spray over a wider width or the entire width of the width side end face of the slab. It is desirable to determine the width of spraying onto the slab after understanding where edge cracks occur in the hot rolling process.

After the thermal spraying was completed, the slab was continuously conveyed on a roller table, charged into a heating furnace, heated at 1380°C for 6 hours, and then subjected to rough rolling (total reduction rate of 84%) and finish rolling (total reduction rate of 94%).
%) and hot rolling (total reduction rate of 99%) to produce a steel plate.

No edge cracking occurred in the steel sheet manufactured by the above process.

In addition, in the board surface within a range of about 20 to 30 mm from the width side end face, the 5itJI degree of the surface layer was reduced, but the thickness of the reduced layer was about 0.005 InIm or less,
There was no effect on magnetic properties.

In the present invention, there is no need to limit the atmosphere when melting the metal and spraying it onto the end face of the width side of the slab. A method performed inside can also be used. Furthermore, there is no need to limit the apparatus for performing these methods.

〔Effect of the invention〕

By using the method of the present invention, it is possible to prevent edge cracking that occurs when hot rolling grain-oriented silicon steel sheets, thereby improving product yield and work efficiency.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a state in which molten metal is sprayed near the center of the thickness of the slab width side end face. R: Roller table, S varnish slab, G+'Gz: Thermal spray equipment. , i - drop, u 1 bad

Claims (1)

[Claims] 1. A method for hot rolling a grain-oriented silicon steel sheet, which is carried out after heating a silicon steel slab containing 2.5 to 5.0 wt% Si to 1300 to 1420°C. 1. A method for hot rolling a grain-oriented silicon steel sheet, comprising spraying molten metal onto the width side end face, then heating and hot rolling the silicon steel slab. 2. The hot rolling method according to claim 1, wherein the metal is a steel material having a lower Si content than the silicon steel slab.