JP3350285B2 - Manufacturing method of non-oriented electrical steel sheet with excellent surface properties and magnetic properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of high grade non-oriented electrical steel sheets. That is, the present invention relates to a method for producing a high-grade non-oriented electrical steel sheet having excellent surface properties and magnetic properties, which is used for a core of a motor or a small transformer in the electric industry, and the obtained electrical steel sheet is used for electric vehicles. It is also effective for high frequency applications such as motors.

[0002]

2. Description of the Related Art In recent years, recycling of scrap has become a major issue from the viewpoint of the global environment. For this reason, the steel industry has begun to make a significant shift from using hot metal obtained by reducing iron ore in a blast furnace as a steelmaking raw material to a steelmaking method that consumes a large amount of scrap such as automobiles and empty cans.

Conventionally, in the field of non-oriented electrical steel sheets, impurities, ie, S, N, O, Sn, Cu, Ni, Ti, etc., are basically removed as much as possible in order to reduce iron loss or improve magnetic flux density. Efforts have been made to refine the steel, at a minimum. However, in the future, when a large amount of iron scrap in the market is to be consumed, contamination of impurities is inevitable to some extent. Particularly, when trying to use inexpensive scrap, for example, Cu,
Sn from a food can and Ni, Cr and the like from a stainless steel plate are mixed. In other words, the era has come to the point where measures must be devised to effectively utilize these impurities for non-oriented electrical steel sheets as functional products. Heretofore, there has been little research from the viewpoint of recycling.

For example, in Japanese Patent Publication No. 58-3027, it has been found that the addition of 0.03 to 0.40% of Sn improves iron loss, but Sn is expensive.
There was a problem in the surface properties when n alone was added. Tokuhei 6-6
No. 779, Sn: 0.02 to 0.20%, C
u: With a composite content of 0.1 to 1.0%, both the magnetic flux density and the iron loss were improved. However, there is a problem that the inclusion of both Sn and Cu significantly deteriorates the surface properties.

In Japanese Patent Publication No. 40-16653, As ≦
0.3%, Sn ≦ 0.1%, As + P + Ni + Co + C
It discloses a technique of improving the magnetic flux density and improving the punching and cutting properties by making a composite content of u + Mo ≧ 0.2% and Al + Si + Cr ≦ 0.1%. However, As,
The cost of special elements such as Co and Mo increases,
The amount of Si was too small and the magnetic properties were unsatisfactory.

In Japanese Patent Publication No. 4-71989, Mn ≧
Excellent magnetic properties are obtained by adding Ni, Cr, Sb, Sn, B, etc. based on 1.0%. However, at a high Mn, there is a problem that the cost of adding Mn is too large. JP-A-3-20413 discloses that V
Is disclosed, but does not target high Si-based high-grade steel sheets.

On the other hand, Japanese Patent Publication No. 51-942 discloses that 85% or more of strong cold rolling is performed as a means for developing a {100} texture desirable for the magnetic properties of a non-oriented electrical steel sheet. However, since this is a step in which hot-rolled sheet annealing is not performed, the obtained magnetic properties are not satisfactory. In JP-A-38-294422, excellent magnetic properties are obtained by the effects of hot-rolled sheet annealing at high temperature and strong cold rolling. However, the steel sheet after the hot-rolled sheet annealing treatment at a high temperature is embrittled, and there has been a problem that breakage of the steel sheet frequently occurs in the subsequent pickling step or cold rolling step. Particularly in the case of strong cold rolling, the brittleness in this cold rolling becomes a problem, and the component system of the present invention having many impurities has a strong tendency to be brittle.

[0008]

SUMMARY OF THE INVENTION In view of the above, the present invention has opened the way to consume a large amount of inexpensive iron scrap, and has excellent magnetic flux density and excellent surface quality and brittleness while eliminating the problems of surface properties and brittleness of products. An object of the present invention is to provide a method for producing a high-grade non-oriented electrical steel sheet having iron loss.

[0009]

In order to achieve the above object, the present invention provides a method of the present invention in which, by weight%, C <0.005%, Si: 2.0 to 4.0%, Al: 0.05 to 2%, Mn: 0.05 to 1.5%, P ≦ 0.1%, S ≦ 0.003%, N <0.004%, Sn: 0.003 to 0.2%, Cu: 0.015 to 0 0.2%, Ni: 0.01 to 0.2%, Cr: 0.02 to 0.2%, V: 0.0005 to 0.008%, Nb <0.01% , with the balance Fe and Hot-rolled steel sheet consisting of unavoidable impurities is subjected to hot-rolled sheet annealing to obtain a crystal grain size of 50 μm after annealing.
And a cooling rate of 80 ° C./sec or less,
Next, cold rolling was performed at a draft of 88% or more, and 800-1
This is a method for producing a non-oriented electrical steel sheet having excellent surface properties and magnetic properties, characterized by being subjected to recrystallization annealing at 200 ° C.

There are three points of the present invention. First,
Second, the deterioration of surface flaws due to the inclusion of Cu and Sn is improved by the inclusion of a composite of Ni and Cr.
Deterioration of the magnetic characteristics due to the inclusion of the four kinds of compounds of n, Ni, and Cr is to improve the magnetic characteristics by controlling the amounts of V and Nb. Third, by controlling the cooling rate, crystal grain size, and cold rolling rate after hot-rolled sheet annealing, it is possible to obtain a non-oriented electrical steel sheet having no production trouble and excellent magnetic properties. The present invention pioneered a strategy for using a large amount of scrap, and further improved the surface properties, brittleness and magnetic properties, by integrating these technologies.

Hereinafter, the present invention will be described in detail. The reason why the C content is limited to less than 0.005% is that if the C content is more than this, there is a problem in magnetic aging. Si content 2.0 ~
Limited to 4.0%. If the Si content is less than 2.0%, the iron loss is unsatisfactory, and if it exceeds 4.0%, the problem of brittleness of the steel sheet occurs, so it must be avoided.

The amount of Al is limited to 0.05 to 2%. Al
If the amount is less than 0.05%, iron loss is unsatisfactory, and if it exceeds 2%, there is a problem of addition cost, so it is avoided. Mn amount is 0.0
5 to 1.5%. Mn is effective in preventing red hot brittleness in hot rolling and improving the edge roughness of the hot rolled sheet, and is required to be 0.05% or more. Further, if the amount is too large, there is a problem of cost increase.

P is set to 0.1% or less. P inhibits crystal grain growth, reduces the crystal grain size of the hot-rolled sheet, and degrades magnetic properties. Therefore, P is limited to 0.1% or less. The S content is set to 0.003% or less. If the S content exceeds 0.003%, MnS precipitates increase and the crystal grain size of the hot-rolled sheet becomes small, so it must be avoided.

The amount of N is limited to less than 0.004%. 0.
If the content is 004% or more, blister-shaped surface defects called “prister” occur. When the amount of Sn is 0.003-0.
The reason why the content is limited to 2% is that the amount of Sn is set to 0.003% or more from the viewpoint of use of the scrap according to the present invention.
%, It is necessary to add a Sn raw material other than scrap, which increases the cost.

The reason why the amount of Cu is limited to 0.015 to 0.2% is that the lower limit of the amount of Cu is set to 0.015% or more from the viewpoint of utilizing the scrap of the present invention. If it exceeds 0.2%, it is necessary to add a Cu raw material other than scrap and the cost increases, so the upper limit is 0.2%.

The amount of Ni is limited to 0.01 to 0.2%.
In the case of the above-mentioned magnetic steel sheet containing Sn and Cu composites with Mn ≦ 1.5%, surface defects such as slab surface cracks, jumping flaws due to hot rolled ears, and hot rolling scale biting flaws increase. Ni is extremely effective in improving these surface properties in combination with Cr described below. Ni content is 0.01
% Or more is effective in preventing flaws, and if it exceeds 0.2%, there is a problem of addition cost.

The Cr content is limited to 0.02 to 0.2%.
Cr is very effective in improving these surface properties by interaction with Ni, and is effective in preventing flaws when it is 0.02% or more, and when it exceeds 0.2%, there is a problem of addition cost.
0.02 to 0.2%.

The V content is limited to 0.0005 to 0.008%. Conventionally, in a component system containing Sn, Cu, Ni, and Cr, magnetic properties are significantly deteriorated. However, when the V amount is 0.0
At 005% or more, this deterioration in magnetic properties is not observed. When the V amount exceeds 0.008%, (Mn, C
u) _x S is to inhibit grain growth in fine precipitation, the iron loss is deteriorated. Therefore, the amount of V is set to 0.0005 to 0.008.
Regulate to 5%. Nb content is limited to less than 0.01%.
When Nb is included, the magnetic characteristics deteriorate particularly in a component system containing Sn, Cu, Ni, and Cr. This limit is 0.01%
It is.

In the steelmaking stage, food cans, motors, lathe scraps,
A so-called inexpensive scrap in the market, such as automobile press waste, can be used as the iron raw material. However, it is necessary to pay particular attention to the amounts of V and Nb. That is, since V or Nb may be contained in some steel materials of special steel, it is desirable to control scrap sorting or use in the steel making process. Further, when a scrap containing Sn and Cu is used, it is necessary to simultaneously use a scrap containing Ni and Cr as described above.

The slab heating in hot rolling is not particularly limited, but the temperature is preferably low to prevent fine precipitates.
0 ° C. is preferred, and then normal hot rolling is performed.

The hot rolled sheet annealing can be either long-time batch annealing or short-time continuous annealing. The crystal grain size after annealing is important, and should be 50 μm or more. A hot rolled sheet having a crystal grain size of 50 μm or more is subjected to strong cold rolling of 88% or more,
The 00 texture is enriched. Moreover, the cooling rate in the hot-rolled sheet annealing requires slow cooling of 80 ° C./sec or less in order to prevent the steel sheet from becoming brittle. This cooling rate is the average cooling rate from the soaking temperature to 100 ° C. In the case of continuous annealing, rapid cooling at about 100 ° C./sec is often performed for the purpose of shortening the industrial heat treatment cycle. In addition, in the component system of the present invention containing Sn, Cu, Ni, and Cr, slow cooling is important because of embrittlement.

Before or after the hot-rolled sheet annealing, pickling is performed, and then cold rolling is performed. At this time, the cold rolling reduction needs to be 88% or more. If it is less than 88%, the desired improvement in magnetic flux density in all circumferential directions cannot be achieved. Further, a cold rolling reduction of 90% or more is preferable for improving the magnetic flux density.

After cold rolling, it is degreased and subjected to ordinary continuous annealing. The annealing temperature may be about 800 to 1200 ° C., but it is preferable to set the crystal grain size to about 150 μm to improve iron loss. After this annealing, an insulating film in which organic and inorganic materials are mixed is applied and baked. Hereinafter, examples of the present invention will be described.

[0024]

【Example】

[Example-1] A steel ingot containing various components was prepared by vacuum melting, and hot-rolled at a heating temperature of 1000 ° C.
A hot-rolled sheet having a thickness of 0 mm was obtained. 800 ° C × 10hr
Was treated in hydrogen gas and furnace-cooled at 100 ° C./hr to obtain a steel sheet having an average crystal grain size shown in Table 1. After pickling this steel sheet, it was cold rolled to 0.50 mm and continuous annealing was performed at 950 mm.
C. for 30 seconds. Magnetic properties are 94mm outer diameter x 70mm
It was measured on a ring sample with an inner diameter. At the same time, surface flaws were observed. Table 1 shows the results.

Experiment No. under conditions within the scope of the present invention. 1,7
Showed excellent surface properties and magnetic properties. Experiment N
o. In the cases where the Ni and Cr were out of the range of the present invention, surface flaws occurred. In Experiment No. V and Nb amounts out of the range of the present invention. 4, 5, and 6 deteriorated in both iron loss and magnetic flux density. As described above, a non-oriented electrical steel sheet excellent in target surface properties and magnetic properties was obtained only by satisfying the condition range of the present invention.

[0026]

[Table 1]

Example 2 Molten steel containing the components shown in Table 2 was continuously cast, slab-heated at 1100 ° C., finished to the sheet thickness shown in Table 3, hot-rolled sheet annealing and cold-rolling rate And cold rolled to 0.20 mm. Finish annealing at 1000 ℃ × 1
The measurement was carried out in hydrogen and measured under the same measurement conditions as in Example 1.

[0028]

[Table 2]

[0029]

[Table 3]

Experiment No. 1 in which the effect of the cold rolling reduction was examined by changing the thickness of the hot rolled sheet. As is clear from 1 to 5, excellent magnetic properties are obtained when the cold rolling reduction is 88% or more within the range of the present invention, and particularly when the cold rolling reduction is 90% or more, the magnetic flux density is good. Next, the cold rolling rate was fixed to 92%, and the influence of the crystal grain size of the hot rolled sheet was investigated. In the results of 6 to 9, excellent magnetism can be obtained when the crystal grain size is 50 μm or more according to the present invention. Further, the cold rolling rate was fixed at 94.3%, the crystal grain size after the hot-rolled sheet annealing was fixed at 58 μm, and only the cooling speed of the hot-rolled sheet annealing was changed. In the case of 10 to 13, when the cooling speed was more than 80 ° C./sec, the steel sheet cracked at the time of cold rolling and production troubles such as breaking occurred, but the steel sheet in the range of the present invention had no problem at all.

[0031]

As described above, by controlling the components and hot rolling conditions, a non-oriented electrical steel sheet having excellent magnetic flux density and iron loss without surface flaws can be produced by a process based on the recycling of iron resources. Can be manufactured.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 8/12 C22C 38/00 303 C22C 38/48 H01F 1/16

Claims (1)

(57) [Claims] 1. Weight%, C <0.005%, Si: 2.0-4.0%, Al: 0.05-2%, Mn: 0.05-1.5%, P ≦ 0 0.1%, S ≦ 0.003%, N <0.004%, Sn: 0.003 to 0.2%, Cu: 0.015 to 0.2%, Ni: 0.01 to 0.2% , Cr: 0.02-0.2%, V: 0.0005-0.008%, Nb <0.01% , hot-rolled steel sheet consisting of balance of Fe and unavoidable impurities , 50 μm after annealing to reduce the crystal grain size
At a cooling rate of 80 ° C./sec or less, and then cold rolling at a rolling reduction of 88% or more,
A method for producing a non-oriented electrical steel sheet having excellent surface properties and magnetic properties, characterized by being recrystallized and annealed at -1200 ° C.