JP3456862B2 - Manufacturing method of grain-oriented electrical steel sheet with extremely low iron loss - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to 2.5 to 7.0%.
The present invention provides a method for producing a grain-oriented electrical steel sheet containing Si, which has low iron loss.

[0002]

2. Description of the Related Art Generally, the magnetic properties of a grain-oriented electrical steel sheet are evaluated by both the iron loss property and the excitation property. Increasing the excitation characteristics is effective for downsizing equipment that increases the design magnetic flux density. On the other hand, reducing the iron loss characteristics is effective in reducing the loss of heat energy when used as an electric device and saving the power consumption. further,
Aligning the <100> axes of the crystal grains of the product in the rolling direction can improve the magnetization characteristics and lower the iron loss characteristics.
In recent years, much research has been conducted especially in this respect, and various manufacturing techniques have been developed.

For example, Japanese Patent Publication No. 40-15644 discloses a method for producing a grain-oriented electrical steel sheet in order to obtain a high magnetic flux density. This makes AlN + MnS function as an inhibitor, and the rolling reduction in the final cold rolling process is 80%.
It is a manufacturing method with a high pressure reduction that exceeds. By this method, a grain-oriented electrical steel sheet having a high degree of integration of the {110} <001> orientation of secondary recrystallized grains and a high magnetic flux density of B ₈ of 1.870T or more can be obtained.

However, although this manufacturing method can reduce the iron loss to some extent, the grain size of the secondary recrystallization macro is still large, on the order of 10 mm, and the eddy current loss which is a factor affecting the iron loss is reduced. Could not be obtained, and a good iron loss value was not obtained. To improve this, Japanese Patent Publication No. 57-
Various methods for subdividing magnetic domains are disclosed, such as a method of subjecting a steel sheet to laser treatment disclosed in No. 2252, and a method of applying mechanical strain to the steel sheet in Japanese Patent Publication No. 58-2569.

On the other hand, in Japanese Unexamined Patent Publication No. 7-62436, P H ₂ O / is used immediately before decarburization annealing of a strip rolled to the final plate thickness or as a heating step of decarburization annealing.
Disclosed is a method characterized in that a heat treatment is performed at a heating rate of 100 ° C./sec or more to a temperature of 700 ° C. or more in a non-oxidizing atmosphere having a PH ₂ of 0.2 or less.

Certainly, with this manufacturing method, good magnetic characteristics can be obtained. However, in this manufacturing method, the heating rate is 1
If the ultimate temperature is set to 800 ° C or more at 00 ° C / sec or more,
Since a dense oxide layer is formed on the surface of the steel sheet during rapid heating, the decarburizing property is reduced and the carbon content in the product sheet increases. As a result, the magnetic aging causes deterioration of the magnetic properties of the product. Further, if the decarburization time is made sufficiently long, the problem of magnetic aging can be solved, but it is not preferable to extend the decarburization time because the manufacturing cost increases.

[0007]

The above conventional manufacturing method has a problem in decarburization, and as a result, it is difficult to stably obtain a grain-oriented electrical steel sheet having a sufficiently low iron loss. . The present invention provides a manufacturing method for solving the problem.

[0008]

In the present invention, as a result of repeated studies to solve the above problems, (1) C: 0.10% or less by weight, Si: 2.5 to 7.
0% and Mn: 0.02-0.15%, S or S
e: 0.001 to 0.05%, acid-soluble Al: 0.01
To 0.04%, N: 0.003 to 0.02% , and the balance is Fe and inevitable impurities. After decarburizing and annealing, the steel sheet is cold-rolled by performing two or more cold rolling operations between sandwiches, or by performing two or more cold rolling operations including intermediate annealing without hot-rolled sheet annealing. ,
In the method for producing a grain-oriented electrical steel sheet by performing final finishing annealing, before decarburizing and annealing a strip rolled to the final sheet thickness, the atmospheric oxygen concentration is 500 ppm or less and the heating rate is 100 ° C / sec or more and 800- The temperature of the front region of the decarburization annealing process is set to 775 to 840 ° C., which is lower than the reached temperature in the rapid heating, and the temperature of the subsequent rear region is set to 815 to 875 ° C., which is higher than that of the front region. It has been found that a unidirectional electrical steel sheet having an extremely low iron loss characterized by being subjected to decarburization annealing can be stably obtained. Further, the present invention provides more characteristics by specifying the following items.
There can be improved. (2) At the end of decarburization annealing, add annealing in a non-oxidizing atmosphere at a temperature of 875 to 1000 ° C. and PH ₂ O / PH ₂ ≦ 0.1, (3) during rapid heat treatment The atmosphere is PH ₂ O / PH ₂ ≧
0.4, (4) The rapid heat treatment is performed as a heating step of decarburization annealing.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
In the decarburization annealing process, the grain-oriented electrical steel sheet must be decarburized to a carbon content of 20 ppm or less, which does not cause magnetic aging. For that purpose, it is necessary to suppress the formation of a dense oxide layer formed on the surface of the steel sheet and not to suppress the reaction between carbon and oxygen. For this reason,
At the time of decarburization annealing soaking, the atmosphere PH ₂ O / PH ₂ is set to 0.15
It is known to be 0.75.

When a rapid heat treatment at a heating rate of 100 ° C./second or more is performed, it is not possible to sufficiently suppress the formation of a dense oxide layer formed on the surface of the steel sheet. In order to solve the above problems, the present inventors
A rapid heat treatment is performed at a heating rate of 100 ° C./sec or more to 800 to 950 ° C., and the temperature of the front region of the decarburization annealing step is 775 to 840 ° C. lower than the reached temperature in the rapid heating, and the temperature of the subsequent rear region is set to the front. By performing decarburization annealing at 815 to 875 ° C higher than the partial area, formation of a dense oxide layer formed on the surface of the steel sheet is suppressed, decarburization becomes very good, and extremely low iron loss occurs. The present inventors have found a manufacturing method capable of stably obtaining a grain-oriented electrical steel sheet.

Next, in the present invention, the reason why the steel composition and the manufacturing conditions are limited as described above will be explained in detail. The reasons for limiting the steel composition are as follows. The upper limit of 0.10% for C is limited because if the amount exceeds C, the time required for decarburization becomes long, which is economically disadvantageous. Si has a lower limit of 2.5% in order to improve iron loss, but if it is too much, it easily cracks during cold rolling, making it difficult to work, so the upper limit is made 7.0%.

Further, in order to produce a grain-oriented electrical steel sheet, the following component elements are added as usual inhibitor components . Mn and S are added as inhibitors. Mn
Is 0.02 to obtain an appropriate dispersion state of MnS.
And 0.15%. S is MnS, an element necessary for forming the (Mn · Fe) S, to obtain a proper dispersion state, and 0.001 to 0.05%. Se instead of S
But it doesn't matter. Both may be added.

Further, acid-soluble Al as an inhibitor
And N are added. Acid-soluble Al is a 0.01 to 0.04 percent for obtaining a proper dispersion state of AlN. N is also A
and from 0.003 to 0.02% to obtain a l N. In addition, Cu, Sn, Sb, Cr, Bi, and Mo are at least 1 at 1.0% or less for the purpose of strengthening the inhibitor.
You may add seeds.

Next, the above molten steel is subjected to a conventional ingot casting method or continuous casting method and hot rolling to obtain a strip having an intermediate thickness. At this time, the strip casting method can also be applied to the present invention.

Next, after hot-rolled sheet annealing, a strip having a final product thickness is obtained by rolling once or twice or more including intermediate annealing. Alternatively, without performing hot-rolled sheet annealing, a strip having a final product thickness is obtained by rolling two or more times including intermediate annealing. When rolling is performed twice or more with intermediate annealing, the first rolling may be performed at a reduction rate of 5 to 50%, and the hot rolled sheet annealing and the intermediate annealing may be performed at 950 to 1200 ° C. for 30 seconds to 30 minutes. desirable.

The final rolling reduction is preferably 85% or more. The lower limit of 85% is below {110} <001
This is because it is not possible to obtain Goss nuclei having a high degree of integration in the rolling direction. As the cold rolling method at this time, the final plate thickness is obtained through each plate thickness step by multiple passes during cold rolling, but in order to improve the magnetic properties, at least one or more intermediate plate thicknesses In the step, the steel sheet may be subjected to a thermal effect of holding it in a temperature range of 100 ° C. or higher for 1 minute or longer.

As described above, the strip rolled to the final product thickness is subjected to heat treatment. First, the strip is rapidly heated to a temperature of 800 ° C to 950 ° C at a heating rate of 100 ° C / sec or more. At this time, the lower limit of the heating rate of 100 ° C./sec is less than 11 ° C. after the primary recrystallization, which is the nucleus of the secondary recrystallization.
0} <001> -oriented grains are reduced, and fine secondary recrystallized grains cannot be obtained, so the grain size is limited.

Further, the lower limit temperature of 800 ° C. is limited since the formation of a dense oxide layer is small below this temperature. The upper limit temperature of 950 ° C. is limited because even if it is heated above this temperature, the effect of improving the magnetic properties is small.

Since the rapid heating treatment has a problem of decarburization, it is necessary to set the oxygen amount in the rapid heating atmosphere to 500 ppm or less. Except for this atmosphere, a dense oxide layer is formed thickly on the surface of the steel sheet, and the decarburizing property in the subsequent decarburizing annealing is deteriorated, so it is limited. Regarding the degree of atmospheric oxidation, PH ₂
If O ₂ / P H ₂ ≧ 0.4, the decarburizing property is further improved, so 0.4 or more is desirable.

The above rapid heat treatment can be carried out before the subsequent decarburization annealing, or can be incorporated in the decarburization annealing step as a heating step of the decarburization annealing, but the latter case. Is desirable because it has a small number of steps.

After that, decarburization annealing is performed in a wet hydrogen atmosphere. At this time, carbon must be reduced to 20 ppm or less so as not to deteriorate the magnetic properties of the product. Decarburization annealing atmosphere, the P H ₂ O / P H ₂ and 0.15 to 0.75. Here, the slab heating temperature in hot rolling is set to a low temperature, and A
In the case of a process using only 1N as an inhibitor, a nitriding treatment may be added in an ammonia atmosphere.

The reason why the temperature in the first half of decarburization annealing is lowered to 775 to 840 ° C. is to suppress the promotion of the dense oxide layer formed on the surface of the steel sheet by the rapid heating. Lower limit value 775
If the temperature is below this, decarburization proceeds slowly, so the temperature is limited. If the upper limit value is 840 ° C. or more, a thick oxide layer is formed at the initial stage of decarburization and the decarburizing property is deteriorated.

The reason why the temperature is increased to 815 to 875 ° C. in the latter stage of decarburization annealing is that since the decarburization is promoted in the former stage of decarburization annealing, an oxide layer on the surface of the steel sheet is formed in a porous state. , It is necessary to raise the temperature to promote decarburization. The reason for limiting the upper limit to 875 ° C is that
Decarburization is poor, so limit it.

Further, by applying an annealing separator such as MgO and performing final annealing at 1100 ° C. or more for secondary recrystallization and purification, a fine film such as forsterite is formed on the surface of the steel sheet. Obtain secondary recrystallized grains.

As described above, a unidirectional electrical steel sheet having extremely low iron loss characteristics is manufactured by applying an insulating coating on the coating of forsterite or the like. This magnetic property retains a low iron loss that does not change even after the subsequent strain relief annealing. In addition, in order to further improve the iron loss in the obtained product, the unidirectional electrical steel sheet may be subjected to a treatment for subdividing the magnetic domains. Next, examples of the present invention will be described.

[0026]

【Example】

Example 1 A hot rolled sheet containing the chemical components shown in Table 1 and hot rolled to a thickness of 2.3 mm was annealed at 1100 ° C. for 1 minute. Then, cold rolling was performed to a final plate thickness of 0.27 mm. Furthermore, when the obtained strip is annealed, the heating step is carried out under the two conditions of 20 ° C./sec and 450 ° C./sec.
Heat treatment was performed at 50 ° C. for 0.1 seconds. At this time, the atmosphere was nitrogen and the oxygen concentration was changed. After this, the temperature cycle in the subsequent decarburization annealing was changed to two steps, the atmosphere was 25% hydrogen, decarburization annealing was carried out for 3 minutes at a dew point of 45 ° C., and MgO powder was applied. High temperature annealing was performed in the atmosphere. Excess MgO of the obtained steel sheet was removed, and an insulating film was applied on the formed forsterite film.

Table 2 shows the magnetic aging test (1
Magnetic properties before and after 50 ° C. × 120 hours) are shown. According to the present invention, a grain-oriented electrical steel sheet having excellent iron loss characteristics is obtained.

[0028]

[Table 1]

[0029]

[Table 2]

Example 2 A molten steel containing the chemical composition shown in Table 3 was cast, heated to a slab, and hot-rolled to 2.3 mm.
To obtain a hot rolled sheet. The hot rolled sheet was annealed and cold rolled by two methods. (A) One was annealed at 1100 ° C. for 2 minutes and cold-rolled to 0.22 mm. (B) The other one is pre-rolled to 2.0 mm and then 2 at 1100 ° C.
Intermediate annealing was performed for 1 minute and rolled to 0.22 mm. The cold-rolled sheet obtained by these methods (A) and (B) was heated with two pairs of direct-current heating rolls at a heating rate of 500 ° C./sec.
Heated to 0 ° C. At this time, the atmospheric oxygen concentration is 150
It was ppm. After this, in wet hydrogen (PH ₂ O / PH ₂ =
0.4), decarburization annealing is performed for 2 minutes under the following conditions where the temperature cycle is changed, and at the end of decarburizing annealing, 930 ° C. × 30
Annealing for seconds (PH ₂ O / PH ₂ = 0.001) was added. The temperature cycle changing conditions are two conditions of (X) front stage 805 ° C + rear stage 835 ° C and (Y) front stage 835 ° C + rear stage 835 ° C. Next, apply MgO powder,
High temperature annealing was performed in a hydrogen gas atmosphere for 0 hours. Excess MgO of the obtained steel sheet was removed, and an insulating film was applied on the formed forsterite film.

The magnetic characteristics of the product thus obtained before and after the magnetic aging test (150 ° C. × 120 hours) are (condition AX) B ₈ before aging: 1.94 T, W _17/50 = 0.76 W / kg, aging after _{B 8 = 1.94T, W 17/50 =} 0.76W / kg, product [C] content = 15 ppm. (Condition BX) B ₈ before aging = 1.93T, W _17/50 = 0.75W / kg, after aging B ₈ = 1.93T, W _17/50 = 0.75W / kg, product [C] amount = 14 ppm. (Condition AY) Before aging B ₈ = 1.93 T, W _17/50 = 0.77 W / kg, after aging B ₈ = 1.91 T, W _17/50 = 0.84 W / kg, product [C] amount = 47 ppm. (Conditions BY) aging before _{B 8 = 1.93T, W 17/50 =} 0.76W / kg, age after _{B 8 = 1.91T, W 17/50 =} 0.84W / kg, product [C] weight = It was 51 ppm. According to the present invention, a grain-oriented electrical steel sheet having a low iron loss was obtained.

[0032]

[Table 3]

[Example 3] Molten steel containing the chemical composition shown in Table 4 was cast, heated to a slab, and hot-rolled to 2.2 mm.
To obtain a hot rolled sheet. This hot-rolled sheet was annealed at 1100 ° C for 2 minutes, then pre-rolled to 1.9 mm, and then rolled at 1100 ° C.
Was subjected to intermediate annealing for 2 minutes and rolled to 0.22 mm. This cold-rolled sheet was heated by induction heating at a heating rate of 350 ° C / sec for 8
Heated to 70 ° C. At this time, the atmosphere is wet hydrogen (P H ₂ O / P H ₂ = 0.45) and the atmospheric oxygen amount is 350.
It was set to ppm. Subsequent decarburization annealing resulted in a wet hydrogen atmosphere (P H
₂ O / P H ₂ = 0.35) The temperature was cycled for 2 minutes, and the annealing was performed for 2 minutes under the following conditions.
Annealing was performed at 0 ° C. for 30 seconds (PH ₂ O / PH ₂ = 0.005). The conditions for changing the temperature cycle are as follows (X) 79
0 ° C + latter stage 830 ° C, (Y) former stage 750 ° C + latter stage 830
And (Z) 800 ° C. in the first stage + 880 ° C. in the second stage. Next, after applying MgO powder, high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. Excess MgO of the obtained steel sheet was removed, and an insulating film was applied on the formed forsterite film.

The magnetic properties of the product thus obtained before and after the magnetic aging test (150 ° C. × 120 hours) are: (X) before aging B ₈ = 1.93 T, W _17/50 = 0.75 W / kg, aging post _{B 8 = 1.93T, W 17/50 =} 0.75W / kg, product [C] content = 14 ppm. (Y) Before aging B ₈ = 1.92T, W _17/50 = 0.78W / kg, after aging B ₈ = 1.90T, W _17/50 = 0.87W / kg, product [C] amount = 65ppm . (Z) aging before _{B 8 = 1.92T, W 17/50 =} 0.79W / kg, after aging _{B 8 = 1.90T, W 17/50 =} 0.887W / k
g, product [C] amount = 70 ppm. According to the present invention, a grain-oriented electrical steel sheet having a low iron loss was obtained.

[0035]

[Table 4]

[Example 4] A molten steel containing the composition shown in Table 5 was cast, heated to a slab, and then hot-rolled to 2.3 mm.
To obtain a hot rolled sheet. The hot rolled sheet was annealed at 1100 ° C. for 2 minutes and then rolled to 0.22 mm. This cold-rolled sheet was heated to 850 ° C at a heating rate of 400 ° C / sec by electric heating. The atmosphere at this time is (A) PH ₂ O / PH ₂ =
0.1, (B) P H ₂ O / P H ₂ = 0.4, (C) P H
_{The two} conditions were ₂ O / P H ₂ = 0.8. The atmospheric oxygen amount was set to 150 ppm. Subsequent decarburization anneal, wet hydrogen atmosphere (P H ₂ O / P H ₂ = 0.35) pre-stage 800 ℃ ×
Annealing was performed in a temperature cycle of 1 minute + the latter stage of 835 ° C. × 1 minute, and the amount of [C] after decarburization was measured. Condition (A) is
[C] = 18 ppm. The condition (B) is [C] = 14 ppm.
The condition (C) was [C] = 13 ppm. It can be seen that the present invention further improves decarburization.

[0037]

[Table 5]

[0038]

According to the present invention, it is possible to produce a grain-oriented electrical steel sheet having good iron loss characteristics, which is extremely useful for industrial purposes.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nobuo Tachibana, Inventor No. 1 Fuji-machi, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Hirohata Works (72) Yosuke Kurosaki Fuji-cho, Himeji-shi, Himeji-shi, Hyogo No. 1 Nippon Steel Corporation Hirohata Works (56) Reference JP-A-7-62436 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21D 8/12 C21D 9/46 501 H01F 1/16

Claims (4)

(57) [Claims] 1. C: 0.10% or less by weight, Si: 2.
5 to 7.0% and Mn: 0.02 to 0.15%, S
Or Se: 0.001-0.05%, acid-soluble Al:
0.01 to 0.04%, N: 0.003 to 0.02%, with the balance being Fe or inevitable impurities, a unidirectional electrical steel hot rolled sheet is annealed once or after hot rolled sheet annealing. Cold rolling is performed by performing cold rolling twice or more with intermediate annealing, or by performing cold rolling twice or more with intermediate annealing without performing hot-rolled sheet annealing. In the method of producing a grain-oriented electrical steel sheet by performing final finishing annealing after annealing, before stripping the strip rolled to the final sheet thickness by decarburizing annealing, the atmospheric oxygen concentration is 500 ppm or less and the heating rate is 100 ° C / sec. With the above, the rapid heat treatment is performed at 800 to 950 ° C., the temperature of the front region of the decarburizing annealing process is set to 775 to 840 ° C., which is lower than the reached temperature in the rapid heating, and the temperature of the subsequent rear region is higher than that of the front region. 815-87
A method for producing a grain-oriented electrical steel sheet having extremely low iron loss, characterized by performing decarburization annealing at 5 ° C. 2. At the end of decarburization annealing, a temperature of 875-100
The production of a grain-oriented electrical steel sheet with extremely low iron loss according to claim 1, characterized by adding annealing in a non-oxidizing atmosphere at 0 ° C and P H ₂ O / P H ₂ ≤0.1. Method. 3. The atmosphere during the rapid heat treatment is set to P H ₂ O / P.
_{3. The method according} to claim 1, wherein H ₂ ≧ 0.4.
A method for producing a grain-oriented electrical steel sheet having extremely low iron loss according to 1. 4. The method for producing a grain-oriented electrical steel sheet with extremely low iron loss according to claim 1, wherein the rapid heat treatment is performed as a heating step of decarburization annealing.