JPH10183249A - Production of grain oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a grain oriented silicon steel sheet low in both hysteresis loss and eddy current loss and high in magnetic flux density at a low cost without using high temp. slab heating and decarburizing annealing. SOLUTION: A slab having a compsn. contg., by weight, 0.01% C, >2 to 4% Si, 1.5 to 4% Mn, 0.003 to 0.025% sol.Al and 0.001 to 0.01% N, in which Si and Mn also satisfy the relation of Si(%)-0.5×Mn(%)<=2, and the balance Fe with inevitable impurities is annealed as hot-rolled or after hot rolling and is subsequently subjected to cold rolling for two times including process annealing under either condition of 650 to 750 deg.C×0.5 to 60hr or 860 to 940 deg.C×5 to 180sec. After that, it is subjected to primary recrystallization annealing of executing rapid cooling at >=1 deg.C/sec to regulate the average grain size D after the annealing to the range shown in the inequality of -1000×sol.Al+26<=D<=-1200×sol.Al+37 [where D: the average grain size (unit: μm) and sol.Al: the content (wt.%) of sol.Al, and finish annealing is executed in the range of 800 deg.C to the ferritic single phase region of less than the α-γ transformation point and also <=1050 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet which is widely used as an iron core material and a magnetic shield material for electric motors such as transformers and generators.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is called a Goss orientation.
It is a soft magnetic material that has a crystal orientation with the main orientation being {110} <001> and has excellent excitation and iron loss properties in the rolling direction. In general, a steel slab containing about 3% by weight of Si (hereinafter,% of chemical composition means% by weight) is 1300%.
C. or higher, and hot-rolled, and as it is or after annealing (hot-rolled sheet annealing), cold rolling is performed once or twice or more with intermediate annealing to obtain a final sheet thickness. Thereafter, continuous annealing accompanied by decarburization treatment is performed to cause primary recrystallization, and then an annealing separating agent for preventing seizure is applied, wound in a coil shape, and finish annealing is performed at a high temperature.

Here, the primary recrystallization annealing is performed at about 800 to 850 ° C. for the purpose of obtaining a primary recrystallization texture that easily forms a texture having a high degree of integration in the Goss orientation during the finish annealing. The purpose of the finish annealing is to further secondary recrystallize the primary recrystallized steel sheet to form a texture integrated in the Goss orientation, and to remove precipitates called inhibitors used to cause secondary recrystallization Is to do.
For this reason, it is soaked at about 1100-1200 ° C for a long time. Inhibitors are generally sulfides or nitrides that are finely dispersed, and are used for the purpose of selectively growing Goss-oriented crystal grains during secondary recrystallization. In some cases, a solid solution element such as Sb is used as an inhibitor.

[0004] The grain-oriented electrical steel sheet thus manufactured is subjected to slab heating at a high temperature of 1300 ° C or more during the manufacturing process, continuous decarburization annealing after final cold rolling, and finishing at a high temperature of 1100 ° C or more. Since a special manufacturing process such as annealing is required, the cost becomes extremely high. In order to solve the cost problem caused by these special manufacturing processes, various researches and developments have conventionally been made.

For example, Japanese Patent Application Laid-Open No. Hei 5-96666 discloses that Si
: 1.5 to 3%, Mn: 1 to 3%, sol. Al: 0.003 to
0.015% and Si (%)-0.5 x Mn (%) ≤ 2
And a grain-oriented electrical steel sheet characterized by C + N ≦ 0.0020% and S ≦ 0.01%. Further, in the same publication, a steel having the same composition as above except for C and N with C ≦ 0.01% and N: 0.001 to 0.01% is hot-rolled, and cold-rolled once or twice or more including intermediate annealing. After the annealing, the condition of the final annealing is maintained at 825 to 925 ° C. for 4 to 100 hours in a nitrogen-containing atmosphere,
Further, a production method has been proposed in which the temperature is maintained in a temperature range of more than 925 ° C. and not more than 1050 ° C. for 4 to 100 hours in a hydrogen atmosphere. This method does not require decarburization annealing, and in addition to allowing finish annealing at low temperatures, slab heating is also possible.
It has been shown that a low temperature of 1270 ° C. or less is sufficient, and is extremely effective in reducing both iron loss and manufacturing cost.

Japanese Patent Application Laid-Open No. 5-51705 discloses that Si: more than 3.0% and 4.0% or less, aiming at further lower iron loss.
n: More than 2.0% and less than 4.0%, soluble in hydrochloric acid-soluble Al (sol.A
l): 0.003 to 0.015% and Si (%) − 0.5 × M
The grain-oriented electrical steel sheet whose main feature is n (%) ≦ 2 and the finish annealing conditions after cold rolling of steel having the above composition are performed at 825 to 925 ° C. for 4 to 100 hours in a nitrogen-containing atmosphere. Hold and
Further, there has been proposed a method for producing the same in which the temperature is kept in a temperature range of more than 925 ° C. and 1050 ° C. or less in a hydrogen atmosphere for 4 to 100 hours.

[0007] Iron loss is generally classified into two types of loss: hysteresis loss and eddy current loss. The hysteresis loss can be achieved by improving the degree of integration in the Goss orientation and reducing impurities.
Further, the eddy current loss can be reduced by increasing the specific resistance of the steel sheet and reducing the thickness of the product. However, the reduction of impurities has reached the limit, and reducing the thickness of the product also increases the cost. Therefore, it can be said that increasing the degree of integration of the Goss orientation and increasing the specific resistance are effective means left for reducing iron loss. However, in the methods described in JP-A-5-9666 and JP-A-5-51705, when Si or Mn is increased in order to increase the specific resistance, the degree of integration in the Goss orientation tends to decrease, and hysteresis is observed. Reducing the loss and the eddy current loss at the same time remains a difficult problem.

[0008]

The problem to be solved by the present invention is to provide a grain-oriented electrical steel sheet having low hysteresis loss and eddy current loss and high magnetic flux density without using high-temperature slab heating or decarburizing annealing. To provide a low-cost, stable manufacturing method.

[0009]

The gist of the present invention resides in the following method for producing a grain-oriented electrical steel sheet having excellent magnetic properties.

In weight%, C: 0.01% or less, Si: more than 2% and 4% or less, Mn: 1.5 to 4%, sol.Al: 0.003
-0.025%, N: 0.001-0.01%, and Si and M
n satisfies the relationship of Si (%) − 0.5 × Mn (%) ≦ 2, and the remainder is a slab having a composition composed of Fe and unavoidable impurities. This is a method for producing a grain-oriented electrical steel sheet which is subjected to finish rolling after primary recrystallization annealing in which cold rolling is performed twice, including annealing, and rapidly heated to a soaking temperature of 1 ° C / sec or more, and the intermediate annealing is performed. At 650-750 ° C for 0.5-60 hours,
Alternatively, the first recrystallization annealing is performed at 860 to 940 ° C. for 5 to 180 seconds, and the primary recrystallization annealing is performed under such conditions that the average crystal grain size D after the first recrystallization annealing is in the range shown in the following formula. A method for producing a grain-oriented electrical steel sheet having good magnetic properties, wherein annealing is performed in a ferrite single phase region of 800 ° C or higher and lower than the α-γ transformation point and 1050 ° C or lower.

-1000 × sol.Al + 26 ≦ D ≦ −1200 × sol.Al + 37 where D: average crystal grain size (unit: μm) sol.Al: sol.Al content (% by weight) The present inventors have studied to produce a secondary recrystallized structure having a high degree of integration in the Goss orientation with high Si and high Mn steels. As a result, the Si content exceeds 2% by weight, and
In a high alloy steel having a Mn content of 1.5% by weight or more, the soaking condition of the intermediate annealing in the second cold rolling method is set to a specific range, and the average crystal grain size after the primary recrystallization annealing is set to the Al content. It has been found that the specific range determined by the relationship with is important in controlling the secondary recrystallization texture. The present invention aimed at reducing both the hysteresis loss and the eddy current loss has been completed using these findings.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. In addition, the following percentage indication of the content of the chemical composition means% by weight.

(1) Chemical composition of slab C: Since remaining in a product adversely affects iron loss, the smaller the C, the better. If the C content of the steel material is 0.01% or less at the slab stage, the adverse effect on the magnetic properties is small even if the primary recrystallization annealing by continuous annealing is not decarburizing annealing. For this reason, the C content is set to 0.01% or less. Desirably, it is 0.005% or less.

Si: has the effect of increasing the specific resistance of the steel sheet, reducing eddy current loss and reducing iron loss. In order to obtain the low iron loss targeted by the present invention, it is necessary to contain more than 2% of Si. On the other hand, when the content exceeds 4%, the workability is remarkably reduced and cold rolling becomes difficult. Therefore, S
i The content is more than 2% and 4% or less.

Mn: Like Si, it is an element effective for increasing the specific resistance of a steel sheet, reducing eddy current loss and reducing iron loss. In the present invention, Mn is reduced to reduce iron loss.
1.5% or more. On the other hand, if it is contained excessively, the cold rolling property is impaired, so the upper limit is made 4%.

Further, in the present invention, the Mn content and the Si content are regulated in relation to each other. In order to realize excellent magnetic properties, it is important to stably realize secondary recrystallization with a high degree of integration in the Goss orientation at the stage of finish annealing. For this purpose, it is necessary to refine and homogenize the crystal structure of the hot-rolled steel sheet. As the means, α-γ transformation, which promotes the micronization and homogenization of the structure along with the rearrangement of the crystal structure, is utilized.

Since the occurrence of the α-γ transformation is determined by the balance between the Si content which is a ferrite-forming element and the Mn content which is an austenite-forming element, the Mn content must be determined in relation to Si. In the present invention, Si (%)
Mn is contained so that -0.5 * Mn (%) ≤2. If this value exceeds 2, it becomes a ferritic single phase steel and α
-No γ transformation occurs.

Sol.Al: sol.Al is an important inhibitor for causing secondary recrystallization, AlN, (Al,
It is added to form nitrides such as Si) N and (Al, Si, Mn) N. If the content of sol.Al is less than 0.003%, a sufficient inhibitor effect cannot be obtained.
However, when the sol.Al content exceeds 0.025%, the amount of the inhibitor becomes excessive, the dispersion state becomes inappropriate, and the secondary recrystallization behavior becomes unstable. For this reason, the content of sol.Al is in the range of 0.003 to 0.025%.

N: Necessary for forming a nitride serving as an inhibitor. If the content in the slab stage is less than 0.001%, the desired inhibitor effect cannot be obtained due to too small an amount of nitride precipitation, and even if the content exceeds 0.01%, the effect is saturated. Therefore, the range of the N content is 0.
001 to 0.01%.

In the present invention, the management of the above five elements is important, but P as an unavoidable impurity element is 0.020%
Hereinafter, S is desirably set to 0.010% or less.

(2) Manufacturing Step In the method for manufacturing a grain-oriented electrical steel sheet of the present invention, a slab having the above composition as a raw material is hot-rolled into a hot-rolled steel sheet, and if necessary, the hot-rolled steel sheet is annealed. 2 including intermediate annealing
The sheet is rolled to the final thickness by cold rolling twice, and subjected to primary recrystallization annealing and finish annealing.

The slab is obtained by subjecting molten steel produced in a converter, an electric furnace, or the like to a process such as vacuum degassing or the like, if necessary, and then to a continuous casting or a method to form a steel ingot and then to perform ingot rolling. Manufactured.

There are no particular restrictions on the hot rolling conditions. However, it is effective to make the crystal structure of the hot-rolled steel sheet uniform and fine to form a good secondary recrystallization structure,
The heating temperature of the slab is 1100-1250 ° C, and the finish rolling temperature is
It is preferable to perform hot rolling at a temperature in the range of 750 to 950 ° C. The hot-rolled steel sheet is cold-rolled after an oxide film on the surface is removed by means such as shot blasting or pickling. Before cold rolling, if necessary, the hot-rolled steel sheet may be subjected to annealing. Annealing the hot-rolled steel sheet before cold rolling makes the dispersion state of nitrides appropriate and the crystal structure becomes homogeneous by recrystallization, so that the goss orientation formation during the secondary recrystallization performed in the final step is stable. I do. The time of annealing the hot-rolled steel sheet may be before or after the oxide film is removed. The annealing temperature of hot rolled steel sheet is
When this is performed by the continuous annealing method, 800-1000 ° C.
In the case of the box annealing method, the temperature is preferably 650 to 750 ° C.

Primary cold rolling: A hot-rolled steel sheet is rolled to a predetermined intermediate sheet thickness. The rolling reduction of the primary cold rolling is preferably from 20 to 80%, more preferably from 30 to 70%.

Intermediate annealing: The conditions for intermediate annealing are extremely important. The effect of the intermediate annealing conditions on iron loss will be described below in detail based on experimental results. FIG. 1 is a graph showing the effect of the soaking condition of the intermediate annealing on the iron loss value after the finish annealing.

Here, C: 0.003%, Si: 2.5%,
Mn: 2%, sol. Al: 0.01%, N: 0.004%, the balance being Fe and a slab having an inevitable impurity composed of unavoidable impurities.
Finished rolling at 840 ° C after heating to 80 ° C to complete a hot-rolled steel sheet with a thickness of 3mm, after pickling, primary cold rolling to 1.4mm thickness (rolling reduction: 53%), and various soaking temperatures Box annealing method (soaking time: 20 hours) or continuous annealing method (soaking time: 60 hours)
Second). After that, secondary cold rolling to a thickness of 0.35 mm (rolling reduction: 75%), primary recrystallization annealing by continuous annealing at 940 ° C, and box annealing
Finish annealing was performed by soaking at 0 ° C. for 48 hours. Atmosphere of the finishing annealing, until the first half 24 hours of soaking H _2: 85% by volume, remainder N _2, the H ₂ later: was 100 vol%. Test specimens were taken from the rolling direction of the steel sheet after finish annealing, and the iron loss and W
17/50 (iron loss value when the magnetic flux density was 1.7 T at a frequency of 50 Hz; unit: W / kg) was determined.

As shown in FIG. 1, iron loss after finish annealing is low in a specific soaking temperature range during intermediate annealing, and the optimum temperature range varies depending on the annealing method. When the intermediate annealing is performed by the box annealing method with a soaking time of 20 hours, the soaking temperature is 650 to 750 ° C, and when the continuous annealing method with the soaking time is 60 seconds, the temperature is 860 to 940 ° C. Good low iron loss values were obtained at temperatures.

Observation of the crystal structure after the intermediate annealing shows that the box annealing method has a relatively uniform soaking temperature of 650-750 ° C. and the continuous annealing method has a soaking temperature of 860-940 ° C. And a recrystallized structure having a large crystal grain size. On the other hand, when the soaking temperature is less than 650 ° C in the box annealing method or less than 860 ° C in the continuous annealing method, the recrystallized structure is extremely fine or unrecrystallized. If the soaking temperature exceeds 750 ° C in the box annealing method or exceeds 940 ° C in the continuous annealing method, a large amount of large grains (for example, a maximum grain size of 150 to 400 μm) will be present on the surface layer of the steel sheet. Had occurred. The average grain size after secondary cold rolling of these and primary recrystallization annealing varies depending on the intermediate annealing conditions, but all are in the range of 17 to 24 μm, and are defined by the present invention described later. The condition of the average crystal grain size after the primary recrystallization annealing was satisfied.

The above results show that iron loss after finish annealing is affected by the crystal structure after intermediate annealing as well as the average crystal grain size after primary recrystallization annealing. The crystal structure after intermediate annealing affects the formation process of secondary recrystallization texture after secondary cold rolling, primary recrystallization annealing and finish annealing, and the difference in the degree of Goss orientation and iron loss value after finish annealing. Is considered to occur.

From the above, according to the present invention, the soaking condition of the intermediate annealing is set to 650 to 75 when the soaking is performed by the box annealing method.
It is to be kept at a temperature of 0 ° C for 0.5 to 60 hours, and in the case of a continuous annealing method, it is to be kept at a temperature of 860 to 940 ° C for 5 to 180 seconds. In order to ensure the uniformity of the crystal structure over the entire length of the steel sheet, a soaking time of 0.5 hours or more is required in the case of the box annealing method, and 5 seconds or more in the case of the continuous annealing method. In order to avoid crystal grains growing on the surface layer of the steel sheet, the upper limit of the soaking time is 60
Time, 180 seconds for continuous annealing.

Secondary cold rolling: The intermediately annealed steel sheet is rolled to a predetermined product thickness by secondary cold rolling (second cold rolling). The rolling reduction of the secondary cold rolling is preferably from 40 to 90%, more preferably from 50 to 80%. By the combination of the desired rolling reduction of the primary cold rolling and the desired rolling reduction of the secondary cold rolling described here, at the time of primary recrystallization annealing in the next step,
It is considered that a primary recrystallization texture advantageous for the development of the secondary recrystallization texture can be formed.

Primary recrystallization annealing: In order to generate a stable secondary recrystallization with a high degree of integration in the Goss orientation in the finish annealing described below, the heating rate up to the soaking temperature is set to 1 in the primary recrystallization annealing. It is necessary to perform rapid heating at a rate of at least ° C / sec.
If the heating rate is too slow, the number of primary recrystallized grains having the Goss orientation decreases, and a secondary recrystallization texture having a high degree of integration in the Goss orientation cannot be obtained. In this sense, a continuous annealing method is preferable as the primary recrystallization annealing method before the finish annealing.

Here, the average crystal grain size after the primary recrystallization annealing is a very important factor for controlling magnetic properties, and it is necessary to set the average crystal grain size in an appropriate range in relation to the Al content. This relationship will be described in detail below based on experimental results. Figure 2 shows the steel sol.
4 is a graph showing the effect of Al content and average crystal grain size after primary recrystallization annealing on iron loss after finish annealing. Here, C: 0.002%, Si: 2.5%, Mn: 2%, N: 0.
A slab having a chemical composition of 005% containing various amounts of sol.Al and the remainder consisting of Fe and unavoidable impurities was heated to 1180 ° C, and finish rolling was completed at 840 ° C to form a hot-rolled steel sheet having a thickness of 3 mm. After pickling, it is subjected to primary cold rolling (rolling reduction: 53%) to a thickness of 1.4 mm, followed by intermediate annealing in a box annealing furnace at 700 ° C for 20 hours, followed by secondary cooling to a thickness of 0.35 mm Cold rolling (rolling reduction: 75%) was performed. After that, when performing primary recrystallization annealing by the continuous annealing method, the soaking temperature was changed to make coils of various primary recrystallized grain sizes, and finish annealing with soaking at 860 ° C for 48 hours was performed. Specimens were collected to determine iron loss. Atmosphere of the finishing annealing, until the first half 24 hours of soaking H _2: 85% by volume, remainder N _2, the H ₂ later: was 100 vol%. The crystal structure after the intermediate annealing was a uniform and good recrystallization structure.

As shown in FIG. 2, it can be seen that iron loss after finish annealing is best when the average crystal grain size after primary recrystallization annealing is within the range determined by the equation.

-1000 × sol.Al + 26 ≦ D ≦ −1200 × sol.Al + 37 where D: average crystal grain size (unit: μm) sol.Al: sol.Al content (% by weight) The reason why it is necessary to set the average crystal grain size after the crystal annealing in the above range in relation to the sol.Al amount is presumed as follows.

It is known that the intensity of the inhibitor effect for controlling the secondary recrystallization is proportional to the product of the grain boundary restraining force of the precipitate serving as the inhibitor and the primary recrystallization particle size.
If the inhibitor effect is too strong or too weak, secondary recrystallization with a high degree of integration in the Goss orientation cannot be stably generated. The precipitate serving as the inhibitor of the present invention is Al
The dispersion state of the nitride changes depending on the Al content, and the grain boundary restraining force of the nitride should change accordingly. Therefore, the average crystal grain size and sol.
It is considered that the inhibitor effect determined by both the contents causes secondary recrystallization with a high degree of integration in the Goss orientation under certain conditions.

The primary recrystallization annealing is performed at around 900 to 980 ° C. for 5 hours.
It is preferable to perform the continuous annealing method in which the heat is soaked for at least 10 seconds and not more than 10 seconds. The soaking temperature is preferably in the range of 900 to 980 ° C. in order to control the average grain size of the primary recrystallized grains within an appropriate range, and the soaking time is 5 seconds or more in order to obtain uniform growth of the primary recrystallized grains. However, it is not economically feasible to soak for more than 10 minutes due to the continuous annealing equipment and operating conditions. The atmosphere at the time of continuous annealing may be a high dew point atmosphere of 0 ° C. or more as in the case of annealing conventional grain-oriented electrical steel sheet. However, in the present invention, there is no need for decarburization annealing. Is enough. In order not to impair the magnetic properties, it is preferable that no oxide film is formed on the surface. In this sense, a lower dew point is more desirable.

The crystal grain size after the primary recrystallization annealing is determined by setting the optimum primary recrystallization annealing conditions in advance within the above-mentioned condition range according to the chemical composition of the steel and the manufacturing conditions up to that time and annealing. Can be adjusted. Also, if necessary, measure the crystal grain size after primary recrystallization annealing on-line, find the optimal annealing conditions, and control the subsequent primary recrystallization annealing conditions in real time. Can also.

The average crystal grain size is obtained by calculating the average cross-sectional area of crystal grains from the grain size number obtained according to the ferrite crystal grain size test method described in JIS G 0552, and calculating the diameter of a circle corresponding to the cross-sectional area. Is defined as The crystal grain size can be measured using an optical microscope or an image analyzer.

Finish annealing: In finish annealing, secondary recrystallization is performed to increase the degree of integration in the Goss orientation. Also,
If necessary, a purifying process (removal of an inhibitor or an impurity such as C) is performed to further improve the magnetic characteristics. In the present invention, relatively good characteristics can be obtained without performing the purification process. Therefore, the purification process may be omitted depending on the required magnetic characteristic level.

The lower limit of the soaking temperature in the finish annealing is 800 ° C. If the soaking temperature is less than 800 ° C., secondary recrystallization becomes insufficient, and good magnetic properties cannot be expected. The upper limit of the soaking temperature is in a ferrite single phase region below the α-γ transformation point of steel and in a range of 1050 ° C or less. In the steel of the present invention, α-γ
Heating above the α-γ transformation point due to the presence of the transformation point is not preferable because the Goss orientation is impaired. Further limiting the soaking temperature to 1050 ° C. or less, the higher the soaking temperature, the higher the cost of annealing equipment and operating costs, there is a problem such as poor productivity, the present invention aims at low cost. This is because it hinders the realization of the manufacturing method. The production method of the present invention is to produce stable secondary recrystallization by low-temperature finish annealing by optimizing the components and production conditions, and at a high temperature of 1100 ° C. or more as in the case of a general grain-oriented electrical steel sheet. No finish annealing is performed.

The secondary recrystallization is desirably soaked at 800 ° C. or more for at least 4 hours in order to obtain a good texture. However, soaking for more than 100 hours has no effect and is not economically viable. The annealing atmosphere in this case is H
₂ : 100% by volume or Ar: 100% by volume may be used, but it is preferable to maintain a nitrogen-containing atmosphere until the secondary recrystallization is completed. This is to suppress the decomposition of the nitride serving as the inhibitor, and more positively to strengthen the inhibitor by nitriding. To obtain such effects, N _2: 5 to 100% by volume, remainder: it is desirable to anneal in an atmosphere of H _2.

In the case where the purification treatment is performed after the completion of the secondary recrystallization, the purification is performed at 870 ° C. or higher in an atmosphere of H ₂ : 100% by volume.
It is preferable to soak for 100 hours. By this treatment, nitrides and impurities in the steel are removed, and the magnetic properties are improved.

The α-γ transformation point of steel is obtained from a thermal expansion curve obtained by measuring a dimensional change when the steel is heated and cooled using a dilatometer, for example.

Applying an annealing separating agent to the steel sheet surface to prevent seizure between the steel sheets during annealing before the finish annealing is the same as in the case of a normal grain-oriented electrical steel sheet. The application method is
There are a method of applying in the form of a slurry, a method of electrostatically applying powder, and the like. As a process after the finish annealing, as in the case of a normal grain-oriented electrical steel sheet, after removing the annealing separating agent, an insulating coating is applied or flattening annealing is performed as necessary.

[0046]

【Example】

(Example 1) C: 0.002%, Si: 2.7%, Mn: 2.2
%, Sol. Al: 0.009%, N: 0.004%, the balance being Fe
A slab having a composition comprising unavoidable impurities was heated to 1180 ° C. and hot-rolled at a finishing temperature of 840 ° C. to a thickness of 3 mm. The α-γ transformation point of this steel was about 960 ° C. After pickling, this is subjected to primary cold rolling (reduction rate: 67%) to a thickness of 1 mm, and intermediate annealing under various soaking conditions.
Secondary cold rolling (rolling reduction: 70%), primary recrystallization annealing and finish annealing were performed to a thickness of 0.3 mm. In the primary recrystallization annealing performed by the continuous annealing method, the soaking temperature was variously adjusted to change the average crystal grain size after the primary recrystallization. The final annealing was carried out at 870 ° C. for 24 hours (H ₂ : 75% by volume, balance: N ₂
Atmosphere), and further soaked at 920 ° C. for 24 hours (H ₂ : 100)
(Volume% atmosphere) in two stages. Table 1 shows the conditions of the intermediate annealing, the average crystal grain size after the primary recrystallization, and the magnetic properties in the rolling direction after the finish annealing. In addition, this sol.
In the case of the content, the range of the average crystal grain size after primary recrystallization annealing specified by the present invention is 17 to 26 µm.

[0047]

[Table 1]

In Test Nos. 1, 2, 4 to 7, intermediate annealing was performed by a box annealing method, and in Test Nos. 3 and 8 to 11, continuous annealing was performed. The iron losses of Test Nos. 4 and 8 in which the soaking temperature of the intermediate annealing is less than the lower limit specified by the present invention and Test Nos. 7 and 11 whose upper limit exceeds the upper limit specified by the present invention are within the condition range specified by the present invention. Is inferior to Test Nos. 1, 2 or 3 manufactured by. Test numbers 1, 2, 5, and 6
The intermediate annealing conditions were the same, but the average crystal grain size after the primary recrystallization annealing was different due to the difference in the primary recrystallization annealing conditions. When these were compared, the average crystal grain size after the primary recrystallization annealing was out of the conditions specified by the present invention, and test numbers 5 and 6
Test Nos. 1 and 2 satisfying the conditions of the present invention
The iron loss is clearly good. Similarly, in Test Nos. 3, 9, and 10 in which the intermediate annealing was performed by the continuous annealing method, the iron loss of Test Nos. 9 and 10 in which the average crystal grain size after the primary recrystallization annealing was out of the conditions specified by the present invention. In comparison, Test No. 3, which satisfies the conditions defined by the present invention, clearly shows a good value.
The magnetic flux density B8, which is an important magnetic property together with iron loss,
The values of the magnetic flux density when magnetized at a magnetization force of 800 A / m (unit: Tesla) are also shown in Table 1. Test numbers 1 to 3 satisfying the conditions specified by the present invention show good values. .

Example 2 Slabs having different chemical compositions of sol.Al were heated to 1150 ° C., hot-rolled at a finishing temperature of 800 ° C. to a thickness of 2.9 mm, and pickled at 670 ° C. At room temperature for 20 hours, first cold-rolled to a thickness of 1 mm (reduction rate: 66%), and intermediate annealing at 700 ° C. for 20 hours was carried out by a box annealing method. Thereafter, secondary cold rolling (rolling reduction: 73%) was performed to a thickness of 0.27 mm, continuous annealing was performed at 940 ° C. for primary recrystallization, and then finish annealing was performed. In the final annealing, a two-stage soaking process is performed in which an atmosphere of H ₂ : 50% by volume and the balance: N ₂ atmosphere at 890 ° C. for 24 hours and then in an atmosphere of H ₂ : 100% by volume at 930 ° C. for 24 hours. It was carried out in. Table 2 shows the chemical composition of the slab, the average crystal grain size after the primary recrystallization annealing, and the magnetic properties in the rolling direction after the finish annealing. The α-γ transformation point of these steels was about 950 ° C.

[0050]

[Table 2]

As shown in Table 2, when the content of sol.Al is less than the lower limit of the condition specified by the present invention, Test No. 12
In Test No. 15 exceeding the upper limit, the degree of integration in the Goss orientation during the secondary recrystallization annealing is weak, and the magnetic properties are inferior. On the other hand, Test Nos. 13 and 14 satisfying the conditions specified by the present invention have a moderate inhibitory effect at the time of finish annealing, and secondary recrystallization with a high degree of integration in the Goss orientation occurs, showing good magnetic properties. ing.

[0052]

According to the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties can be stably manufactured without using high-temperature slab heating or decarburizing annealing. The production method of the present invention does not require special equipment and the production conditions are not strict, so that the production yield is good and the production method is very economical.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between intermediate annealing conditions of a grain-oriented electrical steel sheet and iron loss W17 / 50 in the production method of the present invention.

FIG. 2 is a graph showing the relationship between the average crystal grain size after primary recrystallization annealing and iron loss W17 / 50 in the production method of the present invention.

Claims (1)

[Claims] C: 0.01% or less, Si: more than 2% and 4% or less, Mn: 1.5 to 4%, sol.Al: 0.003% by weight.
-0.025%, N: 0.001-0.01%, and Si and M
n satisfies the relationship of Si (%) − 0.5 × Mn (%) ≦ 2, and the remainder is a slab having a composition composed of Fe and unavoidable impurities. This is a method for producing a grain-oriented electrical steel sheet which is subjected to finish rolling after primary recrystallization annealing in which cold rolling is performed twice, including annealing, and rapidly heated to a soaking temperature of 1 ° C / sec or more, and the intermediate annealing is performed. At 650-750 ° C for 0.5-60 hours,
Alternatively, the first recrystallization annealing is performed at 860 to 940 ° C. for 5 to 180 seconds, and the primary recrystallization annealing is performed under such conditions that the average crystal grain size D after the first recrystallization annealing is in the range shown in the following formula. A method for producing a grain-oriented electrical steel sheet having good magnetic properties, wherein annealing is performed in a ferrite single phase region of 800 ° C or higher and lower than the α-γ transformation point and 1050 ° C or lower. —1000 × sol.Al + 26 ≦ D ≦ −1200 × sol.Al + 37 ---, where D: average crystal grain size (unit: μm) sol.Al: sol.Al content (% by weight)