JPH08295936A - Production of nonoriented silicon steel sheet excellent in surface property and magnetic property - Google Patents

Abstract

PURPOSE: To produce a nonoriented silicon steel sheet excellent in surface properties, brittleness, magnetic flux density and core loss by subjecting an extra low carbon-high Si hot rolled steel sheet having a specified compsn. contg. Sn, Cu, Ni, Cr, C and Nb to specified hot rolled sheet annealing, cooling treatment, cold rolling and recrystallization annealing. CONSTITUTION: A hot rolled steel sheet having a compsn. contg., be weight, <0.005% C, 2.0 to 4.0% Si, 0.05 to 2% Al, 0.05 to 1.5% Mn, <=0.1% P, <=0.003% S, <0.004% N, 0.003 to 0.2% Sn, 0.015 to 0.2% Cu, 0.01 to 0.2% Ni, 0.02 to 0.2% Cr, 0.0005 to 0.008% V, <0.001% Nb, and the balance inevitable components is subjected to hot rolled sheet annealing to regulate the grain size to >=50μm and is gradually cooled at <=80 deg.C/sec. This hor rolled steel sheet is subjected to cold rolling at >=88% rolling ratio. After that, this cold rolled sheet is subjected to recrystallization annealing at 800 to 1200 deg.C. Thus, the nonoriented silicon steel sheet of a high grade can be obtd., and the way of largely consuming inexpensive iron scraps is developed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to the manufacture of high grade non-oriented electrical steel sheets. That is, the present invention relates to a method for manufacturing 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 field. 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 global environment. For this reason, in the steel industry, there has been a significant shift from a method of using hot metal obtained by reducing iron ore in a blast furnace as a raw material for steelmaking 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, for the purpose of reducing iron loss or improving magnetic flux density, basically, impurities such as S, N, O, Sn, Cu, Ni, Ti, etc. are used as much as possible. Efforts have been made to refine the steel to a lesser extent. However, in the future, when trying to consume a large amount of iron scrap in the market, it is a fact that contamination of impurities cannot be avoided to some extent. In particular, when trying to use cheap scrap, for example, from electrical products to Cu,
Sn is mixed from the food can and Ni, Cr, etc. are mixed from the stainless steel plate. In other words, the time has come to devise a method of effectively utilizing these impurities for the non-oriented electrical steel sheet as a functional product. Heretofore, almost no research has been seen from the viewpoint of this recycling.

For example, Japanese Patent Publication No. 58-3027 has found that addition of Sn: 0.03 to 0.40% improves iron loss, but Sn is expensive and S
There was a problem in surface quality when n was added alone. Tokuhei 6-6
In Japanese Patent No. 779, Sn: 0.02 to 0.20%, C
u: A composite content of 0.1 to 1.0% provided an improvement in both magnetic flux density and iron loss. However, the inclusion of both Sn and Cu has a problem that the surface properties are greatly deteriorated.

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, punching, and improving machinability by compositely containing u + Mo ≧ 0.2% and Al + Si + Cr ≦ 0.1%. However, As,
Cost increase of special elements such as Co and Mo,
The Si content was too small and the magnetic properties were unsatisfactory.

According to Japanese Patent Publication No. 4-71989, Mn ≧
Excellent magnetic characteristics are obtained by adding Ni, Cr, Sb, Sn, B and the like to 1.0% as a base. However, with high Mn, there is a problem that the addition cost of Mn is too large. Japanese Patent Laid-Open No. 3-20413 discloses V
However, it does not cover high Si high-grade steel sheets.

On the other hand, as a means for developing a {100} texture desirable for the magnetic properties of non-oriented electrical steel sheets, Japanese Patent Publication No. 51-942 discloses that strong cold rolling of 85% or more is applied. However, since it is a process in which the hot-rolled sheet is not annealed, the obtained magnetic properties are unsatisfactory. Further, in Japanese Patent Application Laid-Open No. 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 brittle, and there is a problem that the steel sheet often breaks in the subsequent pickling step and cold rolling step. Particularly in the case of strong cold rolling, brittleness in this cold rolling becomes a problem, and the component system of the present invention containing many impurities has a strong tendency to become brittle.

[0008]

In view of the above points, the present invention paves the way for consuming a large amount of inexpensive iron scrap, and solves the problems of surface quality and brittleness of products, while providing an excellent magnetic flux density. 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-mentioned object, the present invention is, 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%, and the balance unavoidable components The hot-rolled steel sheet containing is subjected to hot-rolled sheet annealing to have a crystal grain size of 50 μm or more and a cooling rate of 80 ° C./sec or less, and then cold rolling with a rolling reduction of 88% or more. It is a method for producing a non-oriented electrical steel sheet having excellent surface properties and magnetic properties, which is characterized by performing recrystallization annealing at 800 to 1200 ° C.

The present invention has three points. First of all
First, to improve the deterioration of surface defects due to the inclusion of Cu and Sn by the composite inclusion of Ni and Cr. Secondly, to improve the Cu and S
It is to improve the magnetic characteristics by controlling the V and Nb amounts in order to prevent the deterioration of the magnetic characteristics due to the inclusion of n, Ni, and Cr in combination. Thirdly, by controlling the cooling rate, crystal grain size and cold rolling rate after hot-rolled sheet annealing, there is no production trouble, and at the same time, a non-oriented electrical steel sheet having excellent magnetic properties is obtained. The present invention is a pioneer of a strategy for using a large amount of scrap, and further improvement of surface properties, brittleness and magnetic properties, by integrating these techniques.

The present invention will be described in detail below. The reason why the C content is limited to less than 0.005% is that there is a problem in magnetic aging when the C content is more than this. Si amount from 2.0 to
It is limited to 4.0%. If the amount of Si 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%, the iron loss is unsatisfactory, and if it exceeds 2%, there is a problem of addition cost, so avoid it. Mn amount 0.0
5 to 1.5%. Mn is effective in preventing red hot brittleness in hot rolling and improving rough edges of the hot rolled sheet, and is required to be 0.05% or more. Further, if too much, there is a problem of cost increase, so 1.5% or less.

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

The N content is limited to less than 0.004%. 0.
This is because if it is 004% or more, blister-shaped surface defects called plisters occur. Sn amount is 0.003 to 0.
The amount of Sn is limited to 2% because the Sn content is 0.003% or more from the viewpoint of scrap utilization of the present invention, and 0.2%.
This is because if it exceeds%, it is necessary to add an Sn raw material other than scrap, which is costly.

The Cu content is limited to 0.015 to 0.2% because the lower limit of the Cu content is 0.015% or more from the viewpoint of scrap utilization of the present invention. On the other hand, if it exceeds 0.2%, it is necessary to add a Cu raw material other than scrap and the cost increases, so 0.2% is made the upper limit.

The Ni content is limited to 0.01 to 0.2%.
In the case of the above-mentioned magnetic steel sheet containing Sn and Cu composite with Mn ≦ 1.5%, surface defects such as slab surface cracking, jumping flaw due to hot-rolled edge roughness, hot-rolled scale biting denting flaw and the like increase. Ni is extremely effective in improving these surface properties together with Cr described later. Ni content is 0.01
% Is effective in preventing defects, and if over 0.2%, there is a problem of addition cost, so 0.01 to 0.2% is set.

The Cr content is limited to 0.02 to 0.2%.
Cr, which is an interaction with Ni, is very effective in improving these surface properties, and is effective in preventing defects at 0.02% or more, and there is a problem of addition cost if it exceeds 0.2%.
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, Cr, the magnetic characteristics are significantly deteriorated. However, V amount is 0.0
If it is 005% or more, this deterioration of magnetic properties is not observed. When the V content exceeds 0.008%, (Mn, C
u) _x S finely precipitates and hinders crystal grain growth, and iron loss deteriorates. Therefore, the V amount is 0.0005 to 0.008.
Regulate to 5%. The Nb amount is limited to less than 0.01%.
When Nb is contained, the magnetic characteristics are deteriorated particularly in the component system containing Sn, Cu, Ni, Cr. This limit is 0.01%
Is.

At the steelmaking stage, cans, motors, lathe scraps,
So-called cheap scraps in the market, such as automobile scraps, 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 and Nb may be contained in the steel material of some special steels, it is desirable to control the use of scraps for selective use or the steelmaking processing stage. Further, when the scrap containing Sn and Cu is used, it is also necessary to simultaneously use the scrap containing Ni and Cr as described above.

The slab heating in hot rolling is not particularly limited, but a low temperature is preferable for the purpose of preventing fine precipitates, and 950 to 120
0 ° C. is preferable, and then ordinary hot rolling is performed.

The hot-rolled sheet annealing can be either batch annealing for a long time or continuous annealing for a short time. The crystal grain size after annealing is important and is 50 μm or more. A hot-rolled sheet having a grain size of 50 μm or more was subjected to a strong cold rolling of 88% or more, which will be described in {1
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 an average cooling rate from the soaking temperature to 100 ° C. In the case of continuous annealing, rapid cooling is often performed at about 100 ° C./sec for the purpose of shortening the industrial heat treatment cycle, so that special attention must be paid to this slow cooling. Further, in the component system of the present invention containing Sn, Cu, Ni, Cr, gradual cooling is important because it is brittle.

Before or after annealing the hot-rolled sheet, it is pickled and then cold-rolled. At this time, the cold rolling rate needs to be 88% or more. If it is less than 88%, the desired magnetic flux density in the entire circumferential direction cannot be improved. Further, a cold rolling rate of 90% or more is preferable for improving the magnetic flux density.

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

[0024]

[Example 1] A steel ingot containing various components was prepared by vacuum melting and hot rolling was performed at a heating temperature of 1000 ° C.
A hot rolled sheet having a thickness of 0 mm was obtained. 800 ℃ × 10hr on this hot rolled sheet
Was subjected to soaking annealing in hydrogen gas and cooled at 100 ° C./hr in a furnace to obtain steel plates having the average crystal grain size shown in Table 1. This steel sheet was pickled, cold rolled to 0.50 mm, and continuously annealed at 950
It carried out at 30 degreeC for 30 second. Magnetic properties are 94mm outer diameter x 70mm
It was measured with a ring sample having an inner diameter. At the same time, surface defects were observed. The results are shown in Table 1.

Experiment No. under conditions within the scope of the present invention 1,7
Showed excellent surface properties and magnetic properties. Also, experiment N
o. Surface defects occurred when Ni and Cr were out of the range of the present invention, respectively. Further, in Experiment No. in which the amounts of V and Nb were out of the range of the present invention. Nos. 4, 5 and 6 were deteriorated in both iron loss and magnetic flux density. As described above, the non-oriented electrical steel sheet having the desired 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 heating was performed at 1100 ° C, and then the plate thickness shown in Table 3 was finished, followed by hot rolled sheet annealing and cold rolling. , And cold rolled to 0.20 mm. Finish annealing 1000 ℃ × 1
Minutes were 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 cold rolling rate was investigated by changing the thickness of the hot rolled sheet As is clear from 1 to 5, when the cold rolling rate is 88% or more within the range of the present invention, excellent magnetic properties are obtained, and when the cold rolling rate is 90% or more, the magnetic flux density is particularly good. Next, with the cold rolling ratio fixed to 92%, the experiment No. in which the influence of the crystal grain size of the hot rolled sheet was investigated. From the results of 6 to 9, excellent magnetism can be obtained when the crystal grain size is 50 μm or more of the present invention. Further, the cold rolling rate was fixed to 94.3%, the crystal grain size after annealing the hot rolled sheet was also fixed to 58 μm, and only the cold speed of the hot rolled sheet annealing was changed. In Nos. 10 to 13, when the cold speed was more than 80 ° C./sec, cracks occurred in the steel sheet during cold rolling and production troubles such as rupture occurred, but the steel sheet within the scope of the present invention had no problem.

[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 in.

Claims (1)

[Claims] 1. 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 0.2%, Ni: 0.01 to 0.2% , Cr: 0.02-0.2%, V: 0.0005-0.008%, Nb <0.01%, and hot-rolled sheet annealing is performed on the hot-rolled steel sheet containing the balance unavoidable components. The crystal grain size to 50 μm or more and the cooling rate to 80 ° C./sec or less, and then cold rolling at a rolling reduction of 88% or more, and recrystallization annealing at 800 to 1200 ° C. A method for producing a non-oriented electrical steel sheet having excellent surface properties and magnetic properties.