JPH07310125A - Production of high magnetic flux density grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To produce a high magnetic flux density grain-oriented silicon steel sheet low in core loss by executing finish annealing under specified conditions at the time of producing a high magnetic flux density grain-oriented silicon steel sheet from a silicon steel slab having a specified componental compsn. CONSTITUTION:A high magnetic flux density grain-oriented steel sheet is produced from a silicon steel slab having a compsn. contg., by weight, 0.020 to 0.075% C, 2.5 to 5.0% Si, 0.05 to 0.45% Mn, <=0.15% of one or more kinds of S and Se, 0.010 to 0.050% acid soluble Al, 0.0035 to 0.012% N, 0.02 to 0.15% Sn, 0.03 to 0.20% Cr, and the balance Fe with ineviatable impurities. At this time, finish annealing is executed so that the temp. rising rate at 900 to 1200 deg.C in the temp. rising stage is regulated to the range of 3 to 35 deg.C/hr, a gaseous mixture of N2 and H2 is used as the atmospheric gas therein, the relationship of -1.2R+46<=N<=-2.7R+118 is satisfied between the ratio N(%) in the gaseous N and R, and the oxidizing potential PH2O/PH2 in the annealing atmosphere is regulated to <=0.020.

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 device, which enables the 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.
Surface, so-called Gos having rolling direction <100> axis
It is composed of crystal grains having an s direction (representing {110} <001> direction by Miller index), and is used as a soft magnetic material for iron cores for transformers and generators. 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 alternating magnetic field is applied to the iron core, and magnetic flux density, plate thickness, coating tension, amount of impurities, specific resistance, crystal grains are determined according to the quality. The size of the will affect. A steel sheet having a high magnetic flux density can reduce the iron core of an electric device and also reduce an iron loss, which is desirable. 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, at present, there are three types of typical industrially produced grain-oriented electrical steel sheet manufacturing methods, but each has its advantages and disadvantages.

The first technique is M.K. 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 a process disclosed in Japanese Patent Publication No. 40-15644 by Taguchi et al., Which uses AlN + MnS to set the final cold rolling rate to a strong rolling reduction of 80% or more. In production, strict control of production conditions is required. The third technology is now in Japanese Patent Publication Sho 5
MnS (and / or M shown in JP-A-1-146969)
This is a process for manufacturing silicon steel containing nSe) + Sb by two cold rolling steps, and a relatively high magnetic flux density is obtained.

The above three types of technology have the following problems in common. That is, all of the above techniques are techniques for controlling the precipitates finely and uniformly, and coarse precipitation occurs when the slab heating temperature prior to hot rolling is set to an extremely high temperature of over 1250 ° C, actually 1300 ° C or higher. The formed 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, and causes linear secondary recrystallization defects due to the crystal structure of the slab in terms of material. Material, high Si material.

For such a high temperature slab heating method, JP-A-62-40315 or JP-A-5-112827.
Some of the techniques disclosed in the publication, that is, the inhibitors necessary for secondary recrystallization, are built in after the completion of decarburization annealing (primary recrystallization) and before the appearance of secondary recrystallization in finish annealing. The means acts as an inhibitor by injecting N into the steel (Al, Si) N.
Is formed. As a means for injecting N into the steel, the infiltration of N from the atmosphere gas in the final annealing temperature rising process is used, or the strip after decarburization annealing or the strip after decarburization annealing is completed in a continuous line with NH ₃ or the like. It is carried out by using an atmospheric gas which becomes a nitriding source of Magnetic steel sheets with good magnetic properties (iron loss, magnetic flux density) have been obtained by these methods, but further improvement in properties is desired.

[0007]

In this manufacturing method, it is needless to say that the grain size and texture of the primary recrystallized grains after decarburization annealing greatly influence the development of secondary recrystallized grains and magnetic properties. However, finish annealing performed after decarburization annealing is an important step in developing a good Goss structure. In particular, the weakening (disappearing time) of the inhibitor in the final annealing temperature rising process (secondary recrystallization starting temperature range) influences the secondary recrystallization orientation integration degree. Factors such as this include the amount of the inhibitor, the rate of temperature increase in the final annealing, the state of formation of the forsterite coating, and the like. The present invention aims to optimize these factors and provide a method for stably producing a grain-oriented electrical steel sheet having excellent magnetic properties.

[0008]

The gist of the present invention is that C: 0.020 to 0.075% by weight and Si:
2.5 to 5.0%, Mn: 0.05 to 0.45%, S or Se alone or in combination of 0.15% or less, acid-soluble A
1: 0.010 to 0.050%, N: 0.0035 to
0.012%, Sn: 0.02-0.15%, Cr:
An electromagnetic steel slab consisting of 0.03 to 0.20% and the balance Fe and unavoidable impurities is heated to a temperature of 1280 ° C. or lower, then hot-rolled, hot-rolled sheet annealed, and inserted once or in intermediate annealing. One-way unidirectionality of two or more rollings with a final rolling reduction of 80% or more, followed by decarburization annealing and nitriding at a temperature of 650 to 850 ° C. under the condition that the strip is run, and then finish annealing. In the production of electrical steel sheets, the temperature rising rate of finish annealing is 900 to 1200 ° C. and the heating rate is R ° C./hr (3
To 35 ° C./hr), the atmosphere gas is a mixed gas of N ₂ and H ₂ , and the ratio of N ₂ gas is N (%)-
1.2R + 46 ≦ N ≦ 2.7R + 118, and the oxidation potential P H ₂ O / P H in the annealing atmosphere is satisfied.
Finish annealing is performed with _{2 set} to 0.020 or less.

The present invention will be described in detail below. Weight ratio of C: 0.055%, Si: 3.3%, Mn: 0.12
%, S: 0.008%, Cr: 0.12%, acid-soluble A
1: 0.028%, N: 0.0077%, P: 0.03
115% electromagnetic steel slab containing 0% and Sn: 0.05%
A hot rolled sheet of 2.3 mm was prepared by hot rolling at 0 ° C. This one
It was annealed at 120 ° C + 900 ° C and then rapidly cooled. It was then pickled and cold rolled to 0.23 mm. This was decarburized and annealed in an atmosphere of wet hydrogen and nitrogen to adjust the grain size of the primary recrystallized grains to 23 μm. After this, nitriding annealing was performed at 750 ° C. for 30 seconds with hydrogen
It was carried out in a mixed gas of nitrogen and ammonia to adjust the nitrogen content of the steel sheet to about 200 ppm.

Then, an annealing separator containing MgO and TiO ₂ as main components was applied and finish annealing was carried out at 1200 ° C. for 20 hours. As a condition of this finish annealing, the temperature rising process 900-
The heating rate up to 1200 ° C. was changed as shown in Table 1, the annealing atmosphere gas was a mixed gas of N ₂ and H ₂ , and the ratio of N ₂ was changed in the range of 10 to 100%. Note that the oxidation potential of the atmospheric gas P H ₂ O / P H ₂ =
It was set to 0.01. The heating rate from room temperature to 900 ° C is 2
It was set to 0 ° C./hr. The result is shown in FIG. From this figure-
A high magnetic flux density is obtained in the range of 1.2R + 46 ≦ N ≦ -2.7R + 118. If N ₂ exceeds 90%, the effect is not observed, so the maximum was set to 90%.

[0011]

[Table 1]

The reason for this is considered as follows. Generally, the crystallographic orientation of the secondary recrystallized grains is greatly influenced by the appearance of the secondary recrystallized grains and the inhibitor behavior in the growth temperature range. In order to develop a crystallographic orientation (Goss orientation) with excellent directionality, it is necessary to lengthen the decomposition and disappearance time of the inhibitor in the high temperature region to make preferential growth of the Goss orientation advantageous. In order to achieve this, the temperature rising rate and the atmosphere gas (N
₂ %) was examined, but it was difficult to achieve a temperature rise rate of less than 3 ° C / hr in time, and more than 35 ° C / hr because it was difficult to achieve industrially from the viewpoint of equipment. hr-35 ℃ / hr
And the range. When the heating rate is slow, the residence time in the high temperature region is long and the inhibitor decomposition is accelerated. To prevent this, N ₂ % is increased. On the other hand, when the temperature rising rate is high, the decomposition of the inhibitor shifts to the high temperature side, and therefore the decomposition is accelerated by lowering N ₂ %. It is considered that the combination of such combinations adjusts the expression of secondary recrystallized grains and the necessary inhibitors in the growth temperature range to preferentially grow the Goss orientation.

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 or Se alone or in combination is 0.015% or less, preferably 0.0070% or less. S
As is well known, forms MnS, Se or MnSe 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 means that the primary recrystallized grain size is It is not preferable in the present invention in which high magnetic flux density and low iron loss are obtained by adjusting. Therefore, S or Se is set to 0.015% or less. See S
Alternatively, reducing the amount of Se 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 is 0.0035 to 0.0
It needs to be 12%. 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%. Cr is an element that promotes oxidation during decarburization annealing, but the combined formation with Sn stabilizes the film formation after finish annealing. Sn improves the texture after decarburization annealing and, in turn, improves secondary recrystallized grains and, together with the stabilization of the coating, has a great effect on improving iron loss. Suitable amount of Sn is 0.02
If it is less than 0.15%, the effect is weak, while if it is more than this, nitriding becomes difficult and secondary recrystallized grains do not develop.
It is preferably 0.03 to 0.08%.

A suitable amount of Cr is preferably 0.03 to 0.20%. If it is less than 0.03%, the above effect cannot be obtained. Also 0.
Even if over 20% is added, the alloy cost only rises and the effect does not improve, so it is limited. Preferably 0.05-0.
15% is good. In addition, the inclusion of a trace amount of P and Cu does not impair the gist of the present invention.

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. In addition to decarburization, decarburization annealing has the role of adjusting the primary recrystallization structure and forming an oxide layer necessary for film formation. This is usually performed in a temperature range of 800 to 900 ° C. in wet hydrogen and nitrogen gas.

Next, the reasons for limiting the nitriding conditions will be described. Figure 2 easily enters into the nitrogen most steel H ₂ gas and NH
After the nitriding treatment was performed for 30 seconds in a mixed gas of ₃ gases, the product obtained by finish annealing was subjected to the nitriding treatment temperature, the nitrogen content of the steel sheet, and the NH
₃ shows the relationship of gas concentrations. As is clear from this figure,
It can be seen that nitriding is good in the temperature range of 650 to 850 ° C. If the temperature exceeds 850 ° 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, preferably 150 ppm or more. Under the above nitriding conditions, a nitriding amount in this range can be obtained. Then, a slurry containing MgO and TiO ₂ as a main component is applied and finish annealing is performed at a temperature of 1100 ° C. or higher.

Next, the reason for limiting the oxidation potential of the atmospheric gas at 800 to 1200 ° C. in the temperature rising process of finish annealing in the present invention will be explained. C: 0.058% by weight, S
i: 3.45%, Mn: 0.10%, S: 0.007
%, Cr: 0.12%, P: 0.025%, Sn: 0.
A slab containing 05% and acid-soluble Al: 0.030% was hot-rolled at 1150 ° C. to produce a hot-rolled sheet of 2.3 mm.
This was annealed at 1120 ° C + 900 ° C and then rapidly cooled.
It was then pickled and cold rolled to 0.17 mm. This was decarburized and annealed in an atmosphere of wet hydrogen and nitrogen to adjust the grain size of primary recrystallized grains to about 22 μm. 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, 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. As a condition of this finish annealing, the temperature rising process 900
Atmosphere gas up to 1200 ° C. is N ₂ : 50%, H ₂ :
A mixed gas of 50% is used, and the oxidation potential P H ₂ O / P H ₂ of the atmosphere gas is 0.01, 0.02, 0.03.
It was processed by changing it to four levels of 0.04. In addition, N ₂ from room temperature to 800 ° C. was 25%, and the temperature rising rate was 7 ° C. /
It was carried out at hr (N ₂ : 75%) and 15 ° C./hr (N ₂ : 50%). Then, a tension coating containing chromic anhydride and aluminum phosphate as main components was applied. The results are shown in Fig. 3.
The Results _{P H 2 O / P H 2} : low core loss material is obtained at 0.02. When it exceeds 0.02, it is considered that the formation of the coating film deteriorates and this adversely affects the iron loss characteristics. For this reason, P H ₂ O / P H ₂ is 0.02
Below.

[0023]

【Example】

Example 1 C: 0.056% by weight ratio, Si: 3.5%, Mn:
0.10%, S: 0.007%, Cr: 0.12%, acid-soluble Al: 0.030%, N: 0.0075%, P:
An electromagnetic steel slab containing 0.025% and Sn: 0.05% was heated and hot-rolled at 1150 ° C to produce a hot-rolled sheet of 2.3 mm.
This was annealed at 1120 ° C + 900 ° C and then rapidly cooled.
It was then pickled and cold rolled to 0.20 mm. This was decarburized and annealed at 830 ° C. in an atmosphere of wet hydrogen and nitrogen to adjust the grain size of primary recrystallized grains to about 23 μm.

Then, nitriding annealing 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 220 ppm. Then MgO, TiO
Applying an annealing separator containing ₂ as the main component, 1200 ℃ × 20
A time finish annealing was performed. As conditions for this finish annealing, the temperature rising rate from 900 to 1200 ° C. and the annealing atmosphere gas were changed as shown in Tables 2 and 3. The temperature rising rate from room temperature to 900 ° C. was 25 ° C./hr, and the oxidizing potential of the atmosphere gas was PH ₂ O / PH ₂ = 0.01. The magnetic flux density is shown in Table 4. A high magnetic flux density steel plate was obtained in the range satisfying the conditions of the present invention.

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

Example 2 C: 0.050%, Si: 3.2%, Mn: by weight.
0.10%, S: 0.009%, Cr: 0.12%, acid-soluble Al: 0.027%, N: 0.0077%, P:
An electromagnetic steel slab containing 0.040% and Sn: 0.05% was heated and hot-rolled at 1150 ° C. to produce a hot-rolled sheet of 2.3 mm.
This was annealed at 1120 ° C + 900 ° C and then rapidly cooled.
It was then pickled and cold rolled to 0.30 mm. This was decarburized and annealed at 840 ° C. in an atmosphere of wet hydrogen and nitrogen to adjust the grain size of primary recrystallized grains to about 24 μm. After this, nitriding annealing is performed 7
It was carried out at 50 ° C. for 30 seconds in a mixed gas of hydrogen, 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. As conditions for this finish annealing, the temperature rising rate from 900 to 1200 ° C. in the temperature rising process and the oxidizing potentials of the atmosphere gas and the annealing atmosphere gas were changed as shown in Table 5. The magnetic properties are shown in Table 6,
It shows in Table 7. As can be seen from these results, steel sheets with high magnetic flux density were obtained within the scope of the present invention, but in Table 7, high magnetic flux density steel sheets were not obtained.

[0029]

[Table 5]

[0030]

[Table 6]

[0031]

[Table 7]

[0032]

According to the present invention, a grain-oriented electrical steel sheet having good magnetic properties can be obtained.

[Brief description of drawings]

FIG. 1 is a table showing the relationship between the finish annealing temperature rising rate, N ₂ %, and magnetic properties.

FIG. 2 is a chart showing the relationship between nitriding temperature, nitriding amount, and quality of secondary recrystallization.

FIG. 3 is a table showing a relationship between P H ₂ O / P H _{2 of} finish annealing and magnetic properties.

[Procedure amendment]

[Submission date] June 14, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

[0008]

The gist of the present invention is that C: 0.020 to 0.075% by weight and Si:
2.5 to 5.0%, Mn: 0.05 to 0.45%, S or Se alone or in combination of 0.15% or less, acid-soluble A
1: 0.010 to 0.050%, N: 0.0035 to
0.012%, Sn: 0.02-0.15%, Cr:
An electromagnetic steel slab consisting of 0.03 to 0.20% and the balance Fe and unavoidable impurities is heated to a temperature of 1280 ° C. or lower, then hot-rolled, hot-rolled sheet annealed, and inserted once or in intermediate annealing. One-way unidirectionality of two or more rollings with a final rolling reduction of 80% or more, followed by decarburization annealing and nitriding at a temperature of 650 to 850 ° C. under the condition that the strip is run, and then finish annealing. In the production of electrical steel sheets, the temperature rising rate of finish annealing is 900 to 1200 ° C. and the heating rate is R ° C./hr (3
To 35 ° C./hr), the atmosphere gas is a mixed gas of N ₂ and H ₂ , and the ratio of N ₂ gas is N (%)-
1.2R + 46 ≦ N ≦ - 2.7R + 118 relationship was satisfied in and oxidation potential of the annealing atmosphere P H ₂ O / P
Finishing annealing is performed with H _{2 set} to 0.020 or less.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nozomi Ishibashi 1-1 Tobahata-cho, Tobata-ku, Kitakyushu City Nippon Steel Co., Ltd. Yawata Works

Claims (1)

[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 of 0. 15% or less, acid-soluble Al: 0.010 to 0.050%, N: 0.0035 to 0.012%, Sn: 0.02 to 0.15%, Cr: 0.03 to 0.20% , A magnetic 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 if necessary, and final rolling ratio is 80% or more once or two or more times of intermediate annealing, and then rolling. After decarburization annealing and nitriding treatment at a temperature of 650 to 850 ° C. under the condition that the strip is run, finish annealing is performed in the production of the grain-oriented electrical steel sheet. The temperature rising rate is in the range of 3 to 35 ° C./hr, the temperature rising rate is R ° C./hr, the atmosphere gas is a mixed gas of N ₂ and H ₂ , and the ratio N (%) of N ₂ gas and R In the meantime, the relationship of −1.2R + 46 ≦ N ≦ 2.7R + 118 is satisfied, and the oxidation potential P of the annealing atmosphere is
A method for producing a high magnetic flux density grain-oriented electrical steel sheet, characterized in that finish annealing is performed with H ₂ O / PH ₂ of 0.020 or less.