JP2983128B2 - Manufacturing method of grain-oriented electrical steel sheet with extremely low iron loss - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing 2.5-7.0% S
It is intended to provide a method for producing a grain-oriented electrical steel sheet containing i and having a low iron loss.

[0002]

2. Description of the Related Art Generally, the magnetic properties of a grain-oriented electrical steel sheet are evaluated based on both iron loss properties and excitation properties. Increasing the excitation characteristics is effective in reducing the size of equipment that increases the design magnetic flux density. On the other hand, reducing the iron loss characteristics is effective in that when it is used as an electric device, heat loss is reduced and power consumption can be saved. further,
Aligning the <100> axis of the crystal grains of the product in the rolling direction can increase the magnetizing properties and lower the iron loss properties,
In recent years, many studies have been made particularly on this aspect, 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 is a production in which AlN + MnS is made to function as an inhibitor, and the rolling reduction in the final cold rolling step is more than 80%. In this way the secondary recrystallized grains of (110) <001> integration degree is high, grain-oriented electrical steel sheet B ₈ has a high magnetic flux density of more than 1.870T is obtained. However, although this manufacturing method can reduce iron loss to some extent, the grain size of the secondary recrystallized macro is still as large as 10 mm, and eddy current loss which is a factor affecting iron loss cannot be reduced. , Good iron loss value was not obtained. In order to improve this, the magnetic domain is subdivided by a method of subjecting a steel sheet to laser treatment disclosed in Japanese Patent Publication No. 57-2252 and a method of applying a mechanical strain to the steel sheet in Japanese Patent Publication No. 58-2569. Various methods of implementing are disclosed.

[0004] On the other hand, in Japanese Patent Application Laid-Open No. 1-290716, a steel sheet rolled at room temperature is subjected to ultra-rapid annealing at a heating rate of 100 ° C / sec or more to a temperature of 657 ° C or more, and the strip is decarbonized. And subjecting the strip to a final high temperature anneal to effect secondary growth, thereby ensuring that the strip has reduced size secondary particles and improved iron loss that persists without significant change after stress relief anneal. A featured method is disclosed. But,
It has been difficult to obtain iron loss characteristics comparable to those of conventional magnetic domains by simply reducing the secondary recrystallized grain size by this manufacturing method.

[0005]

With the above conventional manufacturing method, it is difficult to obtain a grain-oriented electrical steel sheet having a sufficiently low iron loss, and the present invention provides a manufacturing method that solves it. It is.

[0006]

In the present invention, as a result of repeated studies to solve the above problems, C: 0.10% or less, Si: 2.5 to 7.0% by weight , and Mn, S , Acid acceptable
Soluble Al, N, Cu, Sn, Sb, Cr, Bi, Se
One or two or more inhibitor components selected from the group consisting of Fe and inevitable impurities, the remainder of which is subjected to hot-rolled sheet annealing of a one-way magnetic steel hot-rolled sheet, and one or more times including intermediate annealing In the method of manufacturing a grain-oriented electrical steel sheet by performing cold rolling, decarburizing annealing, and then performing final finish annealing, immediately before decarburizing annealing the strip rolled to the final thickness, P H ₂ 700 at a heating rate of 100 ° C./sec or more in a non-oxidizing atmosphere where O / P H ₂ is 0.2 or less.
It has been found that a method for producing a grain-oriented electrical steel sheet having extremely low iron loss can be obtained by performing a heat treatment at a temperature of not less than ° C.

Hereinafter, the present invention will be described in detail. The grain-oriented electrical steel sheet can be manufactured by sufficiently causing secondary recrystallization during the final annealing in the manufacturing process to obtain a so-called Goss texture. In order to obtain this Goss texture, the coarsening of the growth of the primary recrystallized grains is suppressed and the grains are aligned in the rolling direction (11).
0) Only recrystallized grains of <001> orientation are selectively grown in a certain temperature range. In other words, it is necessary to make a base material for secondary recrystallization. For this purpose, fine inclusions such as MnS, AlN, and Cu ₂ S must be uniformly dispersed in the material as an inhibitor (inhibitor) for the growth of primary recrystallized grains. Furthermore, the above-mentioned secondary recrystallization must be timed with the formation of forsterite by the reaction with MgO.

However, the conventional manufacturing method is disclosed in
In the case of reducing the average secondary recrystallized grain size as disclosed in Japanese Patent No. 290716 to reduce the magnetic domain width to obtain a target low iron loss, it is inevitable that M
Forsterite (2MgO.Si) by gO coating
O ₂₎ not necessarily the formation of such good, there is a problem that the magnetic properties can not be obtained with sufficient film tension.

As a result of a detailed investigation of the cause, it was found that an oxide film was formed during the temperature rise stage of the decarburizing annealing, which greatly hindered the formation of forsterite. This is significantly different from the conventional formation of an oxide film because the steel sheet is rapidly exposed to a high temperature within 7 seconds by rapid heating.
₂ ) was found to be formed preferentially.
In the case of conventional normal heating (20 ° C./sec), SiO ₂ and firelite were formed on the steel sheet surface after decarburization started.

In order to solve the above-mentioned problem, the present inventors considered that the formation of firelite was suppressed as much as possible at the temperature raising stage, and the rapid heating treatment was carried out with a non-oxidized PH ₂ O / P H ₂ of 0.2 or less. In a neutral atmosphere, the formation of firelite is suppressed, the formation of forsterite by applying MgO in the final annealing becomes very good, and a method for producing a grain-oriented electrical steel sheet having extremely low iron loss Was obtained. Thus, by applying a film tension with a forsterite, an insulating film, or the like on the surface of the secondary recrystallized steel sheet, there is a large iron loss improvement rate, and an extremely low iron loss value can be obtained.

[0011]

Next, the reason why the steel composition and the manufacturing conditions are limited as described above in the present invention will be described in detail. The reasons for limiting the steel components are as follows. The upper limit of 0.10% for C is limited because if it is more than this, the time required for decarburization becomes longer and it is economically disadvantageous. The lower limit of Si is set to 2.5% in order to improve iron loss, but if it is too large, it is likely to break during cold rolling and processing becomes difficult, so the upper limit is set to 7.0%.

Further, in order to produce a grain-oriented electrical steel sheet, it is preferable to add the following component elements as ordinary inhibitor components. When MnS is used as an inhibitor, Mn and S are added. Mn is desirably 0.02 to 0.15% in order to obtain an appropriate dispersion state of MnS. S is an element necessary for forming MnS and (Mn · Fe) S.
1-0.05% is desirable. Further, when AlN is used as an inhibitor, acid-soluble Al and N are added. In order to obtain an appropriate dispersion state of acid-soluble Al and AlN, 0.01 to 0.04% is desirable. N is also preferably 0.003 to 0.02% in order to obtain AlN. Other, C
At least one of u, Sn, Sb, Cr and Bi may be added at 1.0% or less for the purpose of strengthening the inhibitor.

Next, the above-mentioned molten steel is subjected to a usual ingot casting method or a continuous casting method, and hot-rolled to obtain a strip having an intermediate thickness. At this time, the strip casting method can also be applied to the present invention. Further, when a nitride is required as an inhibitor, 950 to 12
It is desirable to perform intermediate annealing at 00 ° C. for 30 seconds to 30 minutes. Next, a strip having a final product thickness is obtained by rolling one or more times including intermediate annealing. 2 including intermediate annealing
When rolling more than once, the first rolling is a reduction 5-5
It is preferable to perform the intermediate annealing at 0% and 950 to 1200 ° C for 30 seconds to 30 minutes.

It is desirable that the next final rolling reduction is 85% or more. The lower limit of 85% is (110) <00 below this.
1> It is because a Goss nucleus having a high degree of integration in the rolling direction in the rolling direction cannot be obtained. In addition, as a cold rolling method at this time,
During cold rolling, the final thickness is obtained through a plurality of passes through each thickness step, but in order to improve magnetic properties, the steel sheet is subjected to a temperature range of 100 ° C. or more in at least one or more intermediate thickness steps. A heat effect for holding for 1 minute or more may be given. As described above, the strip rolled to the final product thickness is subjected to a heat treatment. First, the strip is rapidly heated to a temperature of 700 ° C. or more at a heating rate of 100 ° C./sec or more.
At this time, the lower limit of the heating rate is 100 ° C./sec. Below this, (110) <0 after primary recrystallization, which is the core of secondary recrystallization
01> The orientation grain size was reduced and fine secondary recrystallized grains could not be obtained. The lower limit of 700 ° C. was limited because recrystallization does not start below this temperature. This rapid heating treatment needs to be performed in a non-oxidizing atmosphere in which P H ₂ O / P H ₂ is 0.2 or less due to problems such as film formation. Outside this atmosphere, the formation of firelite is not suppressed,
Since the formation of forsterite by the application of MgO in the subsequent final annealing is not very good, it was limited.

Here, the non-oxidizing atmosphere means a reducing atmosphere in an inert gas such as N ₂ or Ar or containing a slight amount of H ₂ . In addition, the above rapid heating treatment
Even if it is performed before the decarburizing annealing to be performed next, it can be incorporated in the decarburizing annealing step as a heating step of the decarburizing annealing, but the latter is preferable because the number of steps is smaller. Thereafter, decarburization annealing is performed in a wet hydrogen atmosphere. At this time, the carbon must be reduced to 0.005% or less so as not to deteriorate the magnetic properties of the product. Here, when the slab heating temperature of hot rolling is low and only AlN is used as an inhibitor, nitriding treatment may be added in an ammonia atmosphere.

Further, by applying an annealing separator such as MgO and performing finish annealing at 1100 ° C. or higher for secondary recrystallization and purification, a fine film such as forsterite is formed on the steel sheet surface. Obtain secondary recrystallized grains. As described above, a grain-oriented electrical steel sheet having extremely low iron loss characteristics is manufactured by further applying an insulating film on a film such as forsterite. The above magnetic characteristics maintain a low iron loss that does not change even after subsequent strain relief annealing.
In order to further improve iron loss in the obtained product,
The unidirectional magnetic steel sheet may be subjected to a treatment for subdividing magnetic domains.

[0017]

【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, it was rolled to a final thickness of 0.27 mm by cold rolling. Further, when the obtained strip is decarburized and annealed, it is heated at 10 ° C./sec, 115 ° C./sec, 300
It heated to 840 degreeC on three conditions of ° C / second. The atmosphere at this time was carried out under the conditions shown in Table 2. After this, 84
After decarburizing annealing in wet hydrogen at a uniform temperature of 0 ° C. and applying MgO powder, high-temperature annealing was performed in a hydrogen gas atmosphere at 1200 ° C. for 10 hours. 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 properties of the obtained products. According to the present invention, a grain-oriented electrical steel sheet having excellent iron loss characteristics is obtained.

[0018]

[Table 1]

[0019]

[Table 2]

Example 2 A molten steel containing the composition shown in Table 3 was cast, slab-heated and then hot-rolled to obtain a hot-rolled steel sheet of 2.3 mm. This was annealed at 1100 ° C. for 4 minutes and rolled to 1.55 mm. This was annealed at 1120 ° C. for 5 minutes, pickled, and then cold-rolled to 0.22 mm
It was thick. The rolled steel sheet was heated to 840 ° C. at a heating rate of 300 ° C./sec by two pairs of direct current heating rolls. The atmosphere at this time is as follows: (a) PH ₂ O / PH ₂ 0.
3. (b) Two conditions of P H ₂ O / P H ₂ 0.1 were performed in a non-oxidizing atmosphere. After this, the same uniform temperature of 840 ° C,
Decarburization annealing was performed in wet hydrogen.

Next, after applying the 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 are as follows: (a) B ₈ = 1.89 T, W
_17/50 = 0.84 w / kg, (b) B ₈ = 1.93T,
W _17/50 = 0.76 w / kg. According to the present invention, a grain-oriented electrical steel sheet having low iron loss was obtained.

[0022]

[Table 3]

[0023]

According to the present invention, it is possible to manufacture a grain-oriented electrical steel sheet having good iron loss characteristics, so that the industrial contribution is extremely large.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Haruo Fukazawa 1 Fujimachi, Hirohata-ku, Himeji-shi Nippon Steel Corporation Hirohata Works (58) Field surveyed (Int. Cl. ⁶ , DB name) C21D 8 / 12 H01F 1/16

Claims (2)

(57) [Claims] 1. C: 0.10% or less by weight, Si: 2.
5 to 7.0% , and Mn, S, acid-soluble Al, N,
One selected from Cu, Sn, Sb, Cr, Bi, Se
Alternatively , a hot-rolled sheet of unidirectional electromagnetic steel comprising Fe and unavoidable impurities is subjected to hot-rolled sheet annealing and contains two or more types of inhibitor components, and is subjected to one or two or more cold-rolling steps including intermediate annealing. In a method for producing a grain-oriented electrical steel sheet by performing final annealing after performing the decarburizing annealing, in a method of producing a grain-oriented electrical steel sheet, immediately before decarburizing annealing the strip rolled to the final sheet thickness, P H ₂ O / P H ₂ A heat treatment at a heating rate of 100 ° C./sec or more to a temperature of 700 ° C. or more in a non-oxidizing atmosphere of 0.2 or less. 2. The method according to claim 1, wherein the rapid heating treatment is performed as a heating stage of the decarburizing annealing.