JPH0790377A - Manufacturing method of grain-oriented electrical steel sheet with extremely low iron loss - Google Patents

Abstract

(57) [Summary] [Object] According to the present invention, a grain-oriented electrical steel sheet having good iron loss characteristics can be produced. [Structure] C: 0.10% or less by weight, Si: 2.5 to
7.0%, Mn: 0.02-0.15%, S: 0.00
1-0.05%, acid-soluble Al: 0.02-0.10
%, N: 0.003 to 0.02%, and a usual inhibitor component, and the balance is Fe and unavoidable impurities. Immediately before decarburizing and annealing a strip rolled to the final plate thickness in a method of manufacturing a unidirectional electrical steel sheet by carrying out cold rolling two or more times after sandwiching, followed by decarburizing and annealing. Unidirectionality with extremely low iron loss, characterized by heat treatment at a heating rate of 50 ° C / sec or more to a temperature of 700 ° C or more, and a temperature rising rate in final finishing annealing of 20 ° C / hr or more. Manufacturing method of electrical steel sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has an S content of 2.5 to 7.0%.
The present invention provides 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 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. Furthermore, to align the <100> axis of the crystal grains of the product in the rolling direction,
Magnetization characteristics can be enhanced and iron loss characteristics can be reduced. In recent years, many studies have been conducted particularly 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 step is 80.
It is a production under a high pressure of more than%. 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 1.870 T or more can be obtained. However, although this manufacturing method can reduce iron rules to some extent, the grain size of the secondary recrystallization macro is still large on the order of 10 mm, and eddy current loss, which is a factor affecting iron loss, cannot be reduced. A 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 disclosed in JP-B-57-2252 to laser treatment, and a method of applying a mechanical strain to the steel sheet in JP-B-58-2569. Various methods have been disclosed.

On the other hand, in Japanese Patent Laid-Open No. 1-290716, a cold rolled steel sheet is subjected to an ultra-rapid annealing treatment at a heating rate of 100 ° C./sec or more to a temperature of 657 ° C. or more,
The strips were decarbonized and subjected to a final high temperature anneal to undergo secondary growth, which improved secondary particles of reduced size and stress relief anneal persisted without significant change. A method characterized by having iron loss is disclosed. However, by simply refining the secondary recrystallized grain size by this manufacturing method, when the insulating film is applied on the forsterite film,
It has been difficult to obtain iron loss characteristics that are comparable to conventional magnetic domain subdivision.

[0005]

In the 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.

[0006]

The present invention has been studied to solve the above problems, and as a result, C: 0.10% or less by weight, Si: 2.5 to 7.0%, Mn: 0. 02-0.1
5%, S: 0.001-0.05%, acid-soluble Al:
0.02 to 0.10%, N: 0.003 to 0.02%, and a usual inhibitor component, and the balance is made of Fe and unavoidable impurities. In the method of producing a unidirectional electrical steel sheet by applying a single or two or more cold rolling steps with intermediate annealing, decarburizing annealing, and then performing final finishing annealing, rolled to the final sheet thickness. 5 just before decarburizing and annealing the strip
Heat treatment at a heating rate of 0 ° C / sec or more to a temperature of 700 ° C or more, and the temperature rising rate in final finishing annealing is 20 ° C / hr.
It has been found that a manufacturing method of a grain-oriented electrical steel sheet having an extremely low iron loss can be obtained by the above features.

The present invention will be described in detail below. The unidirectional 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 growth and coarsening of primary recrystallized grains are suppressed and they are aligned in the rolling direction (110) <0.
The selective growth is performed in a temperature range in which only recrystallized grains in the 01> orientation are obtained. In other words, it is necessary to make a base material for secondary recrystallization. For that, the material is Mn
Fine inclusions such as S, AlN, and Cu ₂ S must be uniformly dispersed as an inhibitor for the growth of primary recrystallized grains. Further, it is necessary to increase the number of (110) plane oriented recrystallized grains as much as possible at the stage of primary recrystallization.

However, according to the conventional manufacturing method, the secondary recrystallized grains having a relatively large grain size of several mm or more can have the (110) <001> orientation aligned in the rolling direction. When the grain size is smaller than the following, there is a problem that secondary recrystallization that is largely deviated from the rolling direction occurs. This tendency is unavoidable especially when the measure for reducing the average secondary recrystallized grain size to reduce the magnetic domain width to obtain the target low iron loss as described in JP-A-1-290716 (11).
0) There was a problem that the ratio of fine secondary recrystallized grains in which the <001> orientation was deviated from the rolling direction increased and the magnetic flux density decreased.

With respect to this cause, the secondary recrystallization start temperature when the heating rate at the temperature rise of decarburization annealing was changed was investigated in detail. As an example, by weight, C: 0.07
%, Si: 3.25%, Mn: 0.08%, P: 0.0
1%, S: 0.02%, Al: 0.025%, N: 0.
When decarburizing and annealing a hot rolled sheet of 2.3 mm containing 08%, Cu: 0.07% and Sn: 0.1% to a strip cold rolled to 0.27 mm The heating rate is changed, and the secondary recrystallization start temperature (heating rate 15
℃ / hr) was investigated. As a result, at 20 ° C / sec, 10
It was 1000 ° C. at 25 ° C. and 100 ° C./sec, and 975 ° C. at 300 ° C./sec. As described above, by increasing the heating rate in decarburization annealing from 20 ° C./sec to 300 ° C./sec, the secondary recrystallization start temperature is lowered by about 50 ° C. At this time, the average secondary recrystallized grains are 22 mm at 20 ° C / sec, 300
It was 6 mm in ° C / sec. Also, completely in magnetic flux density 20 ° C. / sec obtained while secondary recrystallization B ₈ 1.935T, 30
The magnetic flux density is reduced by increasing the heating rate at B ₈ 1.900 T at 0 ° C./sec.

As described above, it was found that the secondary recrystallization start temperature is lowered by increasing the heating rate in the decarburization annealing, which results in deterioration of the orientation selectivity of the secondary recrystallized grains. , Fine secondary recrystallized grains (110) <0
It was considered that the 01> orientation was deviated from the rolling direction. Therefore, as one measure to control the secondary recrystallization start temperature to a high temperature side when the temperature rising rate of decarburization annealing is increased to 300 ° C./sec or the like, the temperature rising rate in final annealing is 20 ° C./hr. The invention was made to accelerate the above. As a result, it was found that fine secondary recrystallized grains having a (110) <001> orientation aligned with the rolling direction of several mm or less can be obtained.

As a result, there is a large margin of improvement in the iron loss value when a coating is applied to the surface of the steel sheet later, and it is possible to obtain a low iron loss. FIG. 1 shows the relationship between the heating rate of each decarburization annealing and the heating rate of the final high temperature annealing and the magnetic characteristics of the product sheet thickness of 0.225 mm. By this method, by applying film tension by forsterite on the surface of the steel sheet that has been secondarily recrystallized, an insulating film, or the like, there is a large improvement rate of iron loss and an extremely low iron loss value can be obtained.

[0012]

The reason why the steel composition and manufacturing conditions are limited as described above in the present invention will be described 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, which makes working difficult, so the upper limit is made 7.0%.

Further, in order to produce a grain-oriented electrical steel sheet, it is preferable to add the following component elements as usual inhibitor components. When using MnS as an inhibitor, Mn and S are added. Mn is 0.02 to 0.15% in order to obtain an appropriate dispersed state of MnS. S is an element necessary for forming MnS and (Mn.Fe) S, and is 0.001 to 0.05%. These M
The range of n and S was limited in order to obtain an appropriate dispersed state of MnS and (Mn.Fe) S.

When AlN is used as the inhibitor, acid-soluble Al and N are added. Acid soluble A
1 is 0.02 to 0. 1 in order to obtain a proper dispersion state of AlN.
10%. N is 0.003-0.
It is set to 02%. The range of Al and N is limited in order to obtain a proper dispersed state of AlN. Others, Cu, Sn, S
b, Cr and Bi are 1.0 for the purpose of strengthening the inhibitor.
% Or less, at least one kind may be added.

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. Furthermore, when a nitride is required as an inhibitor, it is necessary to use 950 to 1 because of precipitation of AlN or the like.
It is desirable to perform intermediate annealing at 200 ° C. for 30 seconds to 30 minutes.

Next, a strip having a final product thickness is obtained by rolling once or twice or more including intermediate annealing. When rolling is performed twice or more including intermediate annealing, it is desirable that the first rolling is performed with a reduction ratio of 5 to 50% and the intermediate annealing is performed at 950 to 1200 ° C. for 30 seconds to 30 minutes. The final rolling reduction is preferably 85% or more. The lower limit of 85% is because the Goss nuclei having a high degree of integration of the (110) <001> orientation in the rolling direction cannot be obtained below this. As the cold rolling method at this time, the final plate thickness is obtained by passing 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 are required. 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 700 ° C. or higher at a heating rate of 50 ° C./sec or higher. The lower limit of the heating rate at this time, 50 ° C./sec, is (110) <00 after the primary recrystallization which becomes the nucleus of the secondary recrystallization below this.
1> The number of oriented grains is reduced, and fine secondary recrystallized grains cannot be obtained, so this is limited. The lower limit of 700 ° C. is limited because recrystallization does not start below this temperature. It should be noted that this rapid heat treatment is preferably carried out in a reducing atmosphere or a non-oxidizing atmosphere as much as possible because of problems such as film formation.

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 decarburizing 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 0.005% or less so as not to deteriorate the magnetic properties of the product. Here, when the slab heating temperature in hot rolling is low and only AlN is used as an inhibitor,
Nitriding treatment may be added in an ammonia atmosphere.

Further, an annealing separator such as MgO is applied, and finish annealing is performed at 1100 ° C. or higher for secondary recrystallization and purification, so that a fine secondary film having a film such as forsterite formed on the surface of the steel sheet. Recrystallize. At this time, the temperature rising rate in the final finish annealing must be 20 ° C./hr or more. If the lower limit is 20 ° C./hr, the secondary recrystallization starting temperature will be lowered below this value, and fine secondary recrystallized grains of several mm or less in which the (110) <001> orientation is aligned in the rolling direction cannot be obtained. Limited

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. The above-mentioned magnetic characteristics maintain 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.

[0021]

【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.

Further, when the obtained strip is decarburized and annealed, it is heated at 10 ° C./sec, 85 ° C./sec, 300 ° C./sec.
Heated up to 840 ℃ in 3 seconds, then the same 840
After decarburizing annealing in wet hydrogen at a uniform temperature of ° C and applying MgO powder, high temperature annealing was performed at 1200 ° C for 10 hours in a hydrogen gas atmosphere. The heating rate at this time is 10 ° C / hr,
The rate was 30 ° C./hr and 50 ° C./hr. Surplus of obtained steel sheet M
After removing gO, on the formed forsterite film,
An insulating film was applied. 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.

[0023]

[Table 1]

[0024]

[Table 2]

(Example 2) A molten steel containing the chemical composition shown in Table 3 was cast, heated to a slab, and then hot-rolled to 2.3 mm.
The hot-rolled steel sheet of was obtained. This was annealed at 1100 ° C. for 5 minutes, further pickled, and then cold rolled to a thickness of 0.22 mm. The rolled steel sheet was heated to 845 ° C at a heating rate of 290 ° C / sec with two pairs of direct-current heating rolls.
After that, decarburization annealing was performed in wet hydrogen at the same uniform temperature of 845 ° C.

Next, after applying MgO powder, high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. The heating rate at this time was 50 ° C./hr. 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 B ₈ = 1.94T, W _17/50 = 0.74w /
A grain-oriented electrical steel sheet with a low iron loss of kg was obtained.

[0027]

[Table 3]

(Example 3) Molten steel containing the chemical composition shown in Table 4 was cast, heated to a slab, and then hot-rolled to 2.3 mm.
The hot-rolled steel sheet of was obtained. This was annealed at 1000 ° C. for 4 minutes and rolled to 1.55 mm. This is annealed at 1120 ° C. for 5 minutes, further pickled, and then cold-rolled to 0.
22mm thick. The rolled steel sheet was heated to 840 ° C. at a heating rate of 300 ° C./sec with two pairs of direct current heating rolls. After that, decarburization annealing was performed in the same uniform temperature of 840 ° C. and wet hydrogen.

After applying MgO powder, high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. The heating rate at this time is (a) 15 ° C / hr, (b) 50 ° C / hr
And 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 obtained in this way are B ₈ =
1.89T, W _17/50 = 0.84w / kg, B _{8 in} (b)
= 1.93T, _W17 / ₅₀ = _0.75w / kg. According to the present invention, a grain-oriented electrical steel sheet having a low iron loss was obtained.

[0030]

[Table 4]

[0031]

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

[Brief description of drawings]

FIG. 1 is a chart showing the relationship between the heating rate of each decarburization annealing and the heating rate of the final high temperature annealing and the magnetic properties.

Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H01F 1/16 (72) Inventor Tadao Kiriyama 1 Fuji-machi, Hirohata-ku, Himeji City Nippon Steel Corp. Hirohata Inside the ironworks

Claims (2)

[Claims] 1. C: 0.10% or less by weight, Si: 2.5 to 7.0%, Mn: 0.02 to 0.15%, S: 0.001 to 0.05%, acid soluble Al: 0.02 to 0.10%, N: 0.003 to 0.02%, and a normal inhibitor component, and the balance is Fe and inevitable impurities. After carrying out annealing and performing cold rolling once or twice or more with intermediate annealing performed, and decarburizing annealing,
In the method of producing a grain-oriented electrical steel sheet by performing final finishing annealing, heat treatment is performed to a temperature of 700 ° C or more at a heating rate of 50 ° C / sec or more immediately before decarburizing annealing of a strip rolled to the final sheet thickness. A method for producing a grain-oriented electrical steel sheet having an extremely low iron loss, characterized in that the temperature rising rate in the final finish annealing is set to 20 ° C./hr or more. 2. The method according to claim 1, wherein the rapid heat treatment is performed as a heating step of decarburization annealing.