JPH06256847A - Manufacture of grain-oriented electrical steel sheet having excellent magnetic characteristic - Google Patents

Abstract

PURPOSE:To stably manufacture a grain-oriented electrical steel sheet having low core loss and high magnetic flux density. CONSTITUTION:An electrical steel slab containing 2.5-5.0% Si, C, Mn, Al, N and <=0.15% S and/or Se, 0.015-0.15% P, 0.03-0.30% Cu and, if necessary, added with Sn and Cr and the balance Fe with inevitable impurities is hot-rolled at <=1280 deg.C and, if necessary, the annealing is executed to the hot-rolled sheet and the finish rolled ratio is made to be >=80% and decarbonize-annealing, nitriding-annealing and finish-annealing are executed. By this method, in the slab heating temp. same as that of the plain carbon steel, the steel sheet with low core loss and high magnetic flux density can stably be manufactured.

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 grain-oriented electrical steel sheet used for an iron core of an electric machine, which enables production of a high magnetic flux density grain-oriented electrical steel sheet with low iron loss. Is.

[0002]

2. Description of the Related Art A unidirectional electrical steel sheet has a {110} steel plate surface.
In the plane, the rolling direction is composed of crystal grains having a so-called Goss orientation (representing {110} <001> orientation in Miller index) having a <100> axis, and is used as a soft magnetic material for transformers and generators. Used for iron core. This steel sheet must have good magnetic properties and iron loss properties. The quality of the magnetization characteristics is determined by the level of the magnetic flux density induced in the iron core in the applied constant magnetic field, and the iron core can be downsized in products with high magnetic flux density. The high magnetic flux density can be achieved by aligning the orientation of the steel plate crystal grains to {110} <001>.

Iron loss is a power loss consumed as heat energy when a predetermined AC magnetic field is applied to the iron core, and magnetic flux density, plate thickness, amount of impurities, specific resistance, size of crystal grains are determined according to the quality. And so on. A steel sheet having a high magnetic flux density is desirable because it can reduce the iron core of an electric device and also reduce the iron loss. In the technical field, development of a method for manufacturing a product having a high magnetic flux density at a low cost is an issue.

By the way, there are three types of typical unidirectional electrical steel sheets that are currently industrially manufactured.
Each has its advantages and disadvantages. The first technology is M.
F. It is a two-time cold rolling process using MnS disclosed in Japanese Patent Publication No. Sho 30-3651 by Littmann, and the obtained secondary recrystallized grains grow stably, but a high magnetic flux density cannot be obtained. The second technique is Taguchi et al.
This is a process of making the final cold rolling rate using AlN + MnS disclosed in 15644 gazette a strong reduction rate of 80% or more, and although a high magnetic flux density can be obtained, strict control of manufacturing conditions is required in industrial production. To be done. The third technique is a process for producing silicon steel containing MnS (and / or MnSe) + Sb, which is disclosed in Japanese Patent Publication No. 51-13469, by two cold-rolling steps.
A relatively high magnetic flux density is obtained.

The above three types of technology have the following problems in common. That is, in all of the above techniques, as a technique for finely and uniformly controlling the precipitates, the slab heating temperature prior to hot rolling exceeds 1250 ° C., and is actually set to an extremely high temperature of 1300 ° C. or higher to cause coarse precipitation. These precipitates are once solid-dissolved and then precipitated during hot rolling or heat treatment. Increasing the slab heating temperature increases the energy used during slab heating, increases the equipment damage rate, etc., and causes linear secondary recrystallization defects due to the crystal structure of the slab in other materials. , It becomes remarkable in the high Si material.

For such a high-temperature slab heating method, the technique disclosed in Japanese Patent Application Laid-Open No. 62-40315 or Japanese Patent Application No. 1-91956, that is, the inhibitor necessary for secondary recrystallization is a decarburizing annealing ( Some are built after the completion of primary recrystallization) and before the appearance of secondary recrystallization in finish annealing. As a means thereof, N is allowed to penetrate into the steel to form (Al, Si) N which functions as an inhibitor. As a means for infiltrating N into the steel, the infiltration of N from the atmosphere gas in the temperature rising process of finish annealing is used, or the strip after decarburization annealing or the strip after decarburization annealing is completed in a continuous line with NH ₃ etc. It is carried out by using an atmospheric gas that serves as a nitriding source.

In this manufacturing method, the grain size and texture of the primary recrystallized grains after decarburization annealing greatly influence the development of secondary recrystallized grains and magnetic properties. Particularly, the primary recrystallization texture is an important factor in developing a good Goss texture. On the other hand, the degree of secondary recrystallization texture also depends on the formation state of the forsterite coating formed during the finish annealing temperature rise process. It is considered that this influences the weakening (disappearing time) of the inhibitor in the secondary recrystallization onset temperature range.

[0008]

The object of the present invention is to optimize and change the factors that influence these secondary recrystallizations and to make it possible to stably produce a high magnetic flux density grain-oriented electrical steel sheet. And

[0009]

The gist of the present invention is as follows: C: 0.020 to 0.075%, Si: 2.5 to
5.0%, Mn: 0.05 to 0.45%, S or Se
≦ 0.015%, alone or in combination, acid-soluble Al: 0.
010 to 0.050%, N: 0.0035 to 0.012
%, Cu: 0.03 to 0.30%, P: 0.015
0.15%, Sn: 0.02-0.15 as required
%, Cr: 0.03 to 0.20%, and the electrical steel slab consisting of the balance Fe and unavoidable impurities is heated to 1280 ° C.
After being heated to the following temperatures, hot rolling is performed, and hot-rolled sheet annealing is performed if necessary, and the final reduction rate is set to 80% or more by rolling once or twice or more with intermediate annealing interposed, and then decarburizing annealing. In the production of unidirectional electrical steel sheet for finish annealing, after decarburization annealing, nitriding treatment is performed in the secondary recrystallization starting temperature range of the temperature rising process of finish annealing. It is in the method of manufacturing a magnetic electrical steel sheet.

The present invention will be described in detail below. Weight ratio of C: 0.054%, Si: 3.25%, Mn: 0.10.
%, S: 0.007%, acid-soluble Al: 0.030%,
A slab was prepared by adding Cu in an amount shown in Table 1 to molten steel containing P: 0.040% and N: 0.0075%. Further, a slab was prepared by adding Cu and Sn in the amounts shown in Table 2 to the above basic components.

[0011]

[Table 1]

[0012]

[Table 2]

Such a slab was heated and hot-rolled at 1150 ° C. to make a hot-rolled sheet of 2.3 mm. This is 1120 ℃ +90
It was annealed at 0 ° C. and then rapidly cooled. Then pickled 0.23 mm
Cold rolled. This was decarburized and annealed at 830 ° C. for 90 seconds in a wet hydrogen and nitrogen atmosphere. After this, nitriding annealing is performed at 750 ° C.
× 30 seconds in a mixed gas of hydrogen, nitrogen and ammonia,
The nitrogen content of the steel sheet was adjusted to approximately 200 ppm. Then Mg
Applying an annealing separator containing O and TiO ₂ as main components, 120
Finish annealing was performed at 0 ° C. for 20 hours.

After that, tension coating containing chromic anhydride and aluminum phosphate as main components was applied. The results obtained using the samples shown in Table 1 are shown in FIG. As you can see from the figure, Cu
The effect of addition of 0.03% appears at 0.03% or more. When Cu is added, the oxidation during decarburization annealing is uniformly performed, and the thickness variation of the oxide layer after annealing is reduced. For this reason, the forsterite film after the finish annealing is also formed to have a uniform thickness. This is shown in FIG.

Thus, it is considered that the addition of a certain amount of Cu contributes to the formation of a good forsterite film. In general, in order to obtain a highly integrated Goss structure, it is desirable that the inhibitor in the secondary recrystallization initiation temperature region gradually weakens. The coating formation time in the present invention is
Since it is earlier than the initiation time of secondary recrystallization, the rate at which the inhibitor weakens becomes slower when a good film is formed.
0) It is considered that the preferential growth of crystal grains in the [001] orientation is favored.

If the Cu content exceeds 0.30%, the surface properties of the hot-rolled sheet will be poor and the pickling property will be poor. The results of treatment with the samples shown in Table 2 are shown in FIG. Although the iron loss characteristics are significantly improved by adding Sn, the composite addition with Cu makes it possible to further reduce the iron loss. It is considered that the effect of Sn is largely due to the improvement of the primary recrystallization texture (addition of Goss nuclei) and the reduction of secondary recrystallized grains.

The reasons for limiting the present invention are as follows. C
When the content is less than 0.020%, the secondary recrystallization becomes unstable, and even when the secondary recrystallization is performed, the magnetic flux density of the product is as low as 1.80 T at B ₈ . On the other hand, if the content of C exceeds 0.075% and becomes too large, the decarburization annealing time becomes long and the productivity is impaired. Preferably 0.
03-0.06% is good. Si has a content of 2.5
If it is less than 1.0%, it is difficult to obtain a product with low iron loss, while if it exceeds 5.0%, there is a problem in cold ductility of the material.

One of the characteristics of the component system of the starting material of the present invention is that S is 0.015% or less, preferably 0.007%.
It is at a point of 0% or less. As is well known, S forms MnS and acts to suppress grain growth. In the present invention, the inhibitor required to develop the secondary recrystallized grains is characterized by being built in after decarburization annealing, and the dispersion of fine precipitates before cold rolling adjusts the primary recrystallized grain size. It is not preferable in the present invention to obtain a high magnetic flux density and a low iron loss.
Therefore, S is set to 0.015% or less. Further, reducing the amount of S has a great effect on reducing ear cracks during hot rolling.

Al combines with N to form AlN,
In the present invention, it is indispensable to form (Al, Si) N by nitriding steel after the post-process, that is, after completion of primary recrystallization, so that a certain amount or more of free Al is required. Therefore, as acid-soluble Al, 0.01
Add 0-0.050%.

N must be 0.0035 to 0.012%. If it exceeds 0.012%, swelling of the steel sheet surface called blister occurs. Further, it becomes difficult to adjust the primary recrystallization structure. The lower limit is preferably 0.0035%. Below this value, it becomes difficult to develop secondary recrystallized grains.

If the content of Mn is too small, the secondary recrystallization becomes unstable, while if it is too large, it becomes difficult to obtain a product having a high magnetic flux density. The proper content is 0.050
It is 0.45%.

P is an element which stabilizes the magnetic flux density at a high level and also increases the specific resistance of the steel, and is effective for reducing iron loss.
When the content is 015% or more, the effect is exhibited, and when the content is more than 0.15%, the embrittlement of the steel is large and the handling during processing becomes difficult.

If Cu is less than 0.03%, there is no effect of improving the magnetic flux density, while if it exceeds 0.30%, the surface properties of the hot-rolled sheet are inferior and the pickling property is deteriorated. Cr is an element that promotes oxidation during decarburization annealing, but the combined addition of Sn stabilizes the film formation after finish annealing.

Sn improves the texture after decarburization annealing and, in turn, improves the secondary recrystallized grains and, together with the stabilization of the coating, has a great effect on improving the iron loss. Suitable amount of Sn is 0.02-0.1
If it is less than 5%, the effect is weak, while if it is more than that, nitriding becomes difficult and secondary recrystallized grains do not develop. It is preferably 0.03 to 0.08%. The proper amount of Cr is 0.0
3 to 0.20% is preferable. Preferably 0.05-0.15
% Is good.

Next, the manufacturing process of the present invention will be described. The electromagnetic steel slab is obtained by melting steel in a melting furnace such as a converter or an electric furnace, subjecting it to vacuum degassing treatment if necessary, and then performing continuous casting or slabbing after ingot casting. A known method may be used for annealing the hot rolled sheet, but usually 9
After performing at a temperature of 00 to 1170 ° C., rapid cooling is performed. Even if the annealing of the hot-rolled sheet is omitted, a product having a sufficient commercial value can be manufactured. The cold rolling rate is 80% or more in order to obtain a high B ₈ value.

The decarburization annealing has a role of adjusting the primary recrystallization structure and forming an oxide layer necessary for forming a film in addition to decarburization. This is wet hydrogen in the temperature range of 800-900 ℃,
Perform in nitrogen gas.

Next, the reasons for limiting the nitriding conditions will be described. FIG. 4 shows that the product obtained by performing finish annealing after performing nitriding treatment for 30 seconds in an atmosphere of a mixed gas of H ₂ gas and NH ₃ gas in which nitrogen is most likely to enter the steel shows good secondary recrystallization. The area shown is the nitriding temperature, the nitrogen content of the steel sheet, and the N
It is shown by the relationship of the H ₃ gas concentration.

As is clear from this figure, 750 to 85
It can be seen that nitriding is good in the temperature range of 0 ° C. 8
If the temperature exceeds 50 ° C, primary recrystallized grains grow and secondary recrystallization becomes defective. On the other hand, if the temperature is lower than 650 ° C, nitriding becomes difficult and secondary recrystallization becomes poor. In order to stably develop good secondary recrystallized grains, the nitrogen content must be 120 ppm or more.

For the above reasons, the nitriding temperature is 650 to 8
The temperature was 50 ° C. and the nitrogen content in the steel sheet was 120 ppm. Then, a slurry containing MgO and TiO ₂ as a main component is applied to
Finish annealing is performed by a known method at a temperature of 100 ° C. or higher.

[0030]

【Example】

Example 1 C: 0.056% by weight ratio, Si: 3.5%, Mn:
0.12%, S: 0.008%, acid-soluble Al: 0.0
28%, Cr: 0.08%, P: 0.055%, N:
Cu in molten steel containing 0.0073% and Sn: 0.07%
(A) 0.01%, (b) 0.05%, (c) 0.1
An ingot containing 0%, (d) 0.25%, and (e) 0.46% was prepared and hot-rolled into a hot rolled 2.3 mm plate.

Then, after annealing at 1200 ° C. + 900 ° C., it was rapidly cooled. Then, it was pickled and cold rolled to 0.30 mm. This was subjected to decarburization annealing at 835 ° C for 150 seconds in a wet hydrogen and nitrogen atmosphere. After that, nitriding treatment was performed at 750 ° C. for 30 seconds in a mixed gas of hydrogen, nitrogen and ammonia to adjust the nitrogen content of the steel sheet to about 180 ppm. Then MgO, TiO ₂
Was applied as a main component, and finish annealing was performed at 1200 ° C. for 20 hours. The magnetic properties are shown in Table 3.

[0032]

[Table 3]

Very excellent magnetic properties were obtained in the Cu addition range of the present invention.

Example 2 C: 0.053%, Si: 3.4% and Mn: by weight.
0.10%, S: 0.010%, acid-soluble Al: 0.0
32%, P: 0.040%, N: 0.0078%, C
Cu in molten steel containing r: 0.12% and Sn: 0.05%
(A) 0.01%, (b) 0.07%, (c) 0.1
1. Make an ingot with 2% added and heat-roll it.
It was made into a 6 mm hot rolled sheet. Then, it was annealed at 1200 ° C. + 900 ° C. and then rapidly cooled.

Then, it was pickled and cold-rolled to 0.17 mm. This was subjected to decarburization annealing at 835 ° C. for 70 seconds in a wet hydrogen and nitrogen atmosphere. After this, nitriding treatment at 750 ° C. for 30 seconds is performed with hydrogen,
It was performed in a mixed gas of nitrogen and ammonia, and the nitrogen content of the steel sheet was adjusted to about 200 ppm. Then, an annealing separator containing MgO and TiO ₂ as a main component was applied and finish annealing was performed at 1200 ° C. for 20 hours. After that, tension coating containing phosphoric acid-chromic anhydride as a main component was applied. The magnetic properties are shown in Table 4.

[0036]

[Table 4]

Very good magnetic properties were obtained in the Cu addition range of the present invention.

Example 3 C: 0.040% by weight, Si: 3.0%, Mn:
0.10%, S: 0.007%, acid-soluble Al: 0.0
34%, P: 0.035%, N: 0.0078%, C
Cu in molten steel containing r: 0.12% and Sn: 0.05%
(A) 0.01% and (b) 0.10% were added to prepare an ingot, which was hot rolled to form a 2.8 mm hot rolled sheet. This was pickled and cold rolled to 0.34 mm.

Then, decarburization annealing was performed at 840 ° C. in a wet hydrogen and nitrogen atmosphere. After this, nitriding treatment at 750 ° C. is performed with hydrogen,
It was performed in a mixed gas of nitrogen and ammonia, and the nitrogen content of the steel sheet was adjusted to about 200 ppm. Then, an annealing separator containing MgO and TiO ₂ as a main component was applied and finish annealing was performed at 1200 ° C. for 20 hours.

[0040]

[Table 5]

Even if the hot-rolled sheet annealing was omitted, excellent magnetic properties were obtained when Cu was added.

[0042]

Industrial Applicability According to the present invention, secondary recrystallization is stable, and it becomes possible to stably manufacture a grain-oriented electrical steel sheet with low iron loss and high magnetic flux density at a slab heating temperature similar to that of ordinary steel.

[Brief description of drawings]

FIG. 1 is a chart showing a relationship between a Cu addition amount and a magnetic characteristic (magnetic flux density).

FIG. 2 is a schematic diagram of a cross-sectional photograph of a coating film after finish annealing of a Cu-added material and a Cu-free material.

FIG. 3 is a chart showing a relationship between Cu and Sn addition amounts and magnetic characteristics (magnetic flux density, iron loss).

FIG. 4 is a table showing the relationship between nitriding conditions (temperature, time) and [N] amount after nitriding.

Claims (3)

[Claims] 1. A weight ratio of C: 0.020 to 0.075%, Si: 2.5 to 5.0%, Mn: 0.05 to 0.45%, and S or Se alone or in combination. 0.015%, acid soluble Al: 0.010 to 0.050%, N: 0.0035 to 0.012%, Cu: 0.03 to 0.30%, P: 0.015 to 0.15% An electromagnetic steel slab consisting of the balance Fe and unavoidable impurities,
After heating to a temperature of 1280 ° C. or lower, hot rolling is performed and hot-rolled sheet annealing is performed, and decarburization annealing is performed at a final rolling rate of 80% or more by rolling once or twice or more with intermediate annealing interposed, A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, comprising performing nitriding treatment in a secondary recrystallization starting temperature range of a temperature rising process of finish annealing after decarburization annealing, and then performing finish annealing. 2. Unidirectionality with excellent magnetic properties according to claim 1, characterized in that Sn: 0.02 to 0.15% and Cr: 0.03 to 0.20% by weight are contained. Manufacturing method of electrical steel sheet. 3. A nitriding treatment after decarburization annealing at 650 to 850 ° C.
2. The nitrogen content of the steel sheet after nitriding is set to 120 ppm or more in a mixed gas of hydrogen, nitrogen and ammonia under the condition that the strip is run at the temperature of 1.
Alternatively, the method for producing a unidirectional electrical steel sheet according to the above 2 having excellent magnetic properties.