阅读说明：本技术 电磁钢板及其制造方法 (Electromagnetic steel sheet and method for producing same ) 是由 富田美穗 名取义显 屋铺裕义 藤村浩志 于 2020-04-01 设计创作，主要内容包括：本电磁钢板的化学组成以质量％计为C：0.0035％以下、Si：2.00～3.50％、Mn：2.00～5.00％、P：0.050％以下、S：0.0070％以下、Al：0.15％以下、N：0.0030％以下、Ni：0～1.00％、Cu：0～0.10％、剩余部分：Fe及杂质,钢板板面中的{100}<011>晶体取向的X射线随机强度比为15.0～50.0,与钢板轧制方向分别成0°、22.5°及45°的方向上的磁通密度满足[1.005×(B-(50)(0°)+B-(50)(45°))/2≤B-(50)(22.5°)]。(The chemical composition of the electromagnetic steel sheet is, in mass%, C: 0.0035% or less, Si: 2.00-3.50%, Mn: 2.00-5.00%, P: 0.050% or less, S: 0.0070% or less, Al: 0.15% or less, N: 0.0030% or less, Ni: 0-1.00%, Cu: 0-0.10%, the remainder: fe and impurities, {100} in the surface of the steel sheet<011>The random intensity ratio of the crystal orientation X-ray is 15.0-50.0, and the magnetic flux density in the directions of 0 DEG, 22.5 DEG and 45 DEG with respect to the rolling direction of the steel sheet satisfies [1.00 ]5×(B 50 (0°)+B 50 (45°))/2≤B 50 (22.5°)]。)

1. An electromagnetic steel sheet characterized by having a chemical composition in mass%

C: less than 0.0035 percent,

Si：2.00～3.50％、

Mn：2.00～5.00％、

P: less than 0.050%,

S: less than 0.0070 percent of,

Al: less than 0.15 percent,

N: less than 0.0030%,

Ni：0～1.00％、

Cu：0～0.10％、

The rest is as follows: fe and impurities in the iron-based alloy, and the impurities,

The random intensity ratio of X-rays of {100} <011> crystal orientation in the plate surface is 15.0 to 50.0,

the magnetic flux densities in the directions of 0 DEG, 22.5 DEG and 45 DEG to the rolling direction satisfy the following expression (i),

1.005×(B₅₀(0°)+B₅₀(45°))/2≤B₅₀(22.5°) (i)

wherein the meaning of each symbol in the above formula (i) is as follows,

B₅₀(0 °): magnetic flux density (T) in the direction of 0 DEG to the rolling direction

B₅₀(22.5 °): magnetic flux density (T) in a direction of 22.5 DEG to the rolling direction

B₅₀(45 °): magnetic flux density (T) in the direction at 45 DEG to the rolling direction.

2. The electrical steel sheet according to claim 1, wherein the sheet thickness is 0.25 to 0.50 mm.

3. A method for producing an electrical steel sheet, characterized by successively carrying out the following steps on a slab,

the chemical composition of the slab is calculated by mass percent

C: less than 0.0035 percent,

Si：2.00～3.50％、

Mn：2.00～5.00％、

P: less than 0.050%,

S: less than 0.0070 percent of,

Al: less than 0.15 percent,

N: less than 0.0030%,

Ni：0～1.00％、

Cu：0～0.10％、

The rest is as follows: fe and impurities in the iron-based alloy, and the impurities,

the working procedure is that

(a) A hot rolling procedure: heating to 1000-1200 ℃ until the final rolling temperature is Ac₃Hot rolling in a temperature range of not less than the transformation point, and cooling to a temperature of not more than 600 ℃ after completion of rolling at an average cooling rate of from 50 to 150 ℃/sec to 600 ℃;

(b) A first cold rolling process: performing cold rolling at a reduction ratio of 80-92% without performing annealing treatment;

(c) intermediate annealing: at 500 ℃ or higher and less than Ac₁Annealing at an intermediate annealing temperature within the range of the phase transition point;

(d) a second cold rolling procedure: cold rolling at a reduction ratio of more than 15.0% and 20.0% or less;

(e) and a final annealing process: at 500 ℃ or higher and less than Ac₁The annealing treatment is performed at a final annealing temperature in the range of the phase transition point.

4. The method for manufacturing an electrical steel sheet according to claim 3, wherein in the final annealing step, the temperature increase rate to the final annealing temperature is 0.1 ℃/sec or more and less than 10.0 ℃/sec, and the holding time at the final annealing temperature is 10 to 120 seconds.

Technical Field

The present invention relates to an electromagnetic steel sheet and a method for producing the same.

This application claims priority based on Japanese application No. 2019-71186 at 4/3/2019, the contents of which are incorporated herein by reference.

Background

In recent years, global environmental issues have attracted attention, and the demand for energy-saving measures has increased dramatically. Among them, the efficiency of the motor device is strongly desired. Therefore, in electromagnetic steel sheets widely used as iron core materials of motors, generators, and the like, there is a strong demand for improvement of magnetic properties. Therefore, the electrical steel sheet used as the core of the motor apparatus is required to have low iron loss and high magnetic flux density.

In order to increase the magnetic flux density of an electrical steel sheet, it is desirable to align the <100> orientation, which is the easy magnetization axis direction of iron, in a specific direction. For example, patent document 1 discloses an electrical steel sheet having excellent magnetic properties and strength, in which the X-ray random strength ratio of {100} <011> on the surface of the steel sheet is 30 to 200.

Documents of the prior art

Patent document

Patent document 1 Japanese patent laid-open publication No. 2017-145462

Disclosure of Invention

Technical problem to be solved by the invention

In the electromagnetic steel sheet disclosed in patent document 1, {100} <011> crystal orientation is aligned on the steel sheet surface. That is, in the steel sheet surface, the easy magnetization axis is inclined by 45 ° from the rolling direction RD to be aligned. Therefore, the electromagnetic steel sheet has excellent magnetic properties.

However, the electrical steel sheet described in patent document 1 is excellent in magnetic properties only in the direction at 45 ° to the rolling direction RD and is extremely strong in anisotropy. In fact, when electromagnetic steel sheets are used as cores of electric machines, magnetic flux needs to flow along the shape of the cores, and therefore, not only the {100} <011> crystal orientation but also the magnetic properties around the crystal orientation are important.

The present invention has been made to solve the above problems, and an object thereof is to provide an electromagnetic steel sheet having excellent magnetic properties not only in a direction at 45 ° to a rolling direction but also in a direction around the rolling direction.

Means for solving the problems

The present invention is mainly directed to the following electrical steel sheet and a method for producing the same.

(1) An electromagnetic steel sheet having a chemical composition of mass%

C: less than 0.0035 percent,

Si：2.00～3.50％、

Mn：2.00～5.00％、

P: less than 0.050%,

S: less than 0.0070 percent of,

Al: less than 0.15 percent,

N: less than 0.0030%,

Ni：0～1.00％、

Cu：0～0.10％、

The rest is as follows: fe and impurities in the iron-based alloy, and the impurities,

the random intensity ratio of X-rays of {100} <011> crystal orientation in the plate surface is 15.0 to 50.0,

the magnetic flux densities in the directions of 0 DEG, 22.5 DEG and 45 DEG to the rolling direction satisfy the following expression (i),

1.005×(B₅₀(0°)+B₅₀(45°))/2≤B₅₀(22.5°) (i)

wherein the meaning of each symbol in the above formula (i) is as follows,

B₅₀(0 °): magnetic flux density (T) in the direction of 0 DEG to the rolling direction

B₅₀(22.5 °): magnetic flux density (T) in a direction of 22.5 DEG to the rolling direction

B₅₀(45 °): magnetic flux density (T) in a direction at 45 DEG to the rolling direction

(2) The electromagnetic steel sheet described in the above (1), which has a thickness of 0.25 to 0.50 mm.

(3) A method for manufacturing an electromagnetic steel sheet, comprising successively performing the following steps on a slab having a chemical composition of mass%

C: less than 0.0035 percent,

Si：2.00～3.50％、

Mn：2.00～5.00％、

P: less than 0.050%,

S: less than 0.0070 percent of,

Al: less than 0.15 percent,

N: less than 0.0030%,

Ni：0～1.00％、

Cu：0～0.10％、

The rest is as follows: fe and impurities in the iron-based alloy, and the impurities,

The working procedure is that

(a) A hot rolling procedure: heating to 1000-1200 ℃ until the final rolling temperature is Ac₃Hot rolling in a temperature range of not less than the transformation point, and cooling to a temperature of not more than 600 ℃ after completion of rolling at an average cooling rate of from 50 to 150 ℃/sec to 600 ℃;

(b) a first cold rolling process: performing cold rolling at a reduction ratio of 80-92% without performing annealing treatment;

(c) intermediate annealing: at 500 ℃ or higher and less than Ac₁Annealing at an intermediate annealing temperature within the range of the phase transition point;

(d) a second cold rolling procedure: cold rolling at a reduction ratio of more than 15.0% and 20.0% or less;

(e) and a final annealing process: at 500 ℃ or higher and less than Ac₁The annealing treatment is performed at a final annealing temperature in the range of the phase transition point.

(4) The method for producing an electrical steel sheet according to item (3), wherein in the final annealing step, the rate of temperature increase to the final annealing temperature is 0.1 ℃/sec or more and less than 10.0 ℃/sec, and the holding time at the final annealing temperature is 10 to 120 seconds.

Effects of the invention

According to the present invention, an electromagnetic steel sheet having excellent magnetic properties not only in the direction at 45 ° to the rolling direction but also in the direction around it can be obtained.

Detailed Description

The present inventors have studied a method for obtaining an electrical steel sheet having excellent magnetic properties not only in the {100} <011> crystal orientation but also in the peripheral direction thereof, and further having sufficient magnetic flux density and low iron loss in a high frequency region of 1000Hz or higher. As a result, the following findings were obtained.

In the same manner as in the conventional production method, cold rolling is performed on a hot-rolled steel sheet at a high reduction rate, whereby {100} <011> crystal orientation is aligned. Thereafter, the intermediate annealing is performed to recrystallize and remove the strain, and further, the cold rolling is performed at a high reduction ratio, and further, the rotation of the crystal is generated, and the crystal grains are increased in a direction slightly deviated from {100} <011 >.

The present invention has been completed based on the above findings. The respective requirements of the present invention are described in detail below.

1. Chemical composition

The reasons for limiting the elements are as follows. In the following description, "%" as to the content means "% by mass".

C: less than 0.0035%

Carbon (C) is an impurity inevitably contained in the electrical steel sheet of the present embodiment. That is, the C content exceeds 0%. C forms fine carbides. The fine carbide inhibits not only the movement of the magnetic wall but also the grain growth in the production process. This reduces the magnetic flux density and increases the iron loss. From this viewpoint, the C content is 0.0035% or less. The C content is preferably as low as possible. However, an excessive decrease in the C content increases the manufacturing cost. Therefore, in view of the operation in the industrial production, the preferable lower limit of the C content is 0.0001%, more preferably 0.0005%, and still more preferably 0.0010%.

Si：2.00～3.50％

Silicon (Si) increases the electrical resistance of steel and reduces the iron loss. When the Si content is less than 2.00%, the effect cannot be obtained. On the other hand, if the Si content exceeds 3.50%, the magnetic flux density of the steel decreases. If the Si content exceeds 3.50%, cold workability is lowered, and a steel sheet may be broken during cold rolling. Therefore, the Si content is 2.00 to 3.50%. The lower limit of the Si content is preferably 2.10%, and more preferably 2.40%. The upper limit of the Si content is preferably 3.40%, and more preferably 3.20%.

Mn：2.00～5.00％

Manganese (Mn) increases the electrical resistance of steel and reduces the iron loss. Mn can further reduce Ac₃The phase transformation point makes it possible to refine the crystal grains by the phase transformation state in the composition system of the electrical steel sheet of the present embodiment. Thus, in the electromagnetic steel sheet after the final manufacturing process, the {100} of the steel sheet surface can be increased<011>Random intensity ratio of crystal orientation. As described above, the electrical steel sheet of the present embodiment has a high Si content. Si is an increase of Ac₃The element of the phase transition point. In this embodiment, by increasing the Mn content, Ac can be reduced₃And the phase transformation state in the hot rolling process is possible. When the Mn content is less than 2.00%, the above-mentioned effects cannot be obtained. On the other hand, when the Mn content is too high, MnS is excessively produced, and cold workability is degraded. Therefore, the Mn content is 2.00 to 5.00%. The lower limit of the Mn content is preferably 2.20%, and more preferably 2.40%. The upper limit of the Mn content is preferably 4.80%, and more preferably 4.60%.

P: 0.050% or less

Phosphorus (P) is an impurity inevitably contained in the electrical steel sheet of the present embodiment. That is, the P content exceeds 0%. P segregates into the steel, and reduces the workability of the steel. From this viewpoint, the P content is 0.050% or less. The upper limit of the P content is preferably 0.040%, and more preferably 0.030%. The P content is preferably as low as possible. However, an excessive reduction in the P content increases the manufacturing cost. In view of the operation in industrial production, the preferable lower limit of the P content is 0.0001%, and more preferably 0.0003%.

S: 0.0070% or less

Sulfur (S) is an impurity inevitably contained in the electrical steel sheet of the present embodiment. That is, the S content exceeds 0%. S forms sulfides such as MnS. The sulfide hinders the movement of the magnetic wall and lowers the magnetic characteristics. In the range of the chemical composition of the electrical steel sheet of the present invention, when the S content exceeds 0.0070%, the magnetic properties are degraded by the sulfide formed. That is, the magnetic flux density decreases and the iron loss increases. Therefore, the S content is 0.0070% or less. The upper limit of the S content is preferably 0.0060%, and more preferably 0.0050%. The S content is preferably as low as possible. Therefore, an excessive reduction in the S content increases the manufacturing cost. In view of industrial production, the preferable lower limit of the S content is 0.0001%, and more preferably 0.0003%.

Al: less than 0.15%

Aluminum (Al) is a ferrite stabilizing element. Ac when Al content exceeds 0.15%₃The increase in the phase transformation point hinders the refinement of crystal grains due to the phase transformation state in the range of the chemical composition of the electrical steel sheet of the present invention. As a result, in the electrical steel sheet after the final manufacturing process, {100} in the steel sheet surface<011>The random intensity ratio of the crystal orientation decreases. Therefore, the Al content is 0.15% or less. The upper limit of the Al content is preferably 0.10%, more preferably 0.05% or less. The Al content may be 0%. Namely, the Al content is 0 to 0.15%. However, an excessive reduction in the Al content increases the manufacturing cost. Therefore, in view of the operation in industrial production, the lower limit of the Al content is preferably 0.0001%, and more preferably 0.0003%.

N: less than 0.0030%

Nitrogen (N) is an impurity inevitably contained in the electrical steel sheet of the present embodiment. That is, the N content exceeds 0%. N forms a fine nitride. The fine nitrides hinder the movement of the magnetic walls. Therefore, the magnetic flux density decreases and the iron loss increases. Therefore, the N content is 0.0030% or less. The upper limit of the N content is preferably 0.0020%, and more preferably 0.0010%. The N content is preferably as low as possible. However, an excessive reduction in the N content increases the manufacturing cost. Therefore, in view of industrial production, the preferable lower limit of the N content is 0.0001%.

Ni：0～1.00％

Nickel (Ni) is an arbitrary element and may not be contained. That is, the Ni content may be 0%. When the electrical steel sheet of the present embodiment contains Ni, Ni increases the electrical resistance of the steel sheet and reduces the iron loss, similarly to Mn. Ni is further a reduction of A₃Phase transformation point and element capable of making grain refinement by phase transformation state. However, when the Ni content is too high, since Ni is expensive, the product cost increases. Therefore, the Ni content is 0 to 1.00%. The lower limit of the Ni content is preferably more than 0%, more preferably 0.10%, and still more preferably 0.20%. The upper limit of the Ni content is preferably 0.90%, and more preferably 0.85%. When Ni is about 0.04%, Ni may be included as an impurity in the electrical steel sheet.

Cu：0～0.10％

Copper (Cu) is an arbitrary element and may not be contained. That is, the Cu content may be 0%. When the electrical steel sheet of the present embodiment contains Cu, Cu increases the electrical resistance of the steel sheet and reduces the iron loss, similarly to Mn. Cu further reduces A₃The transformation point and the miniaturization of crystal grains by the transformation state are possible. Therefore, when the Cu content is too high, CuS is excessively generated, which inhibits grain growth in the final annealing and deteriorates the iron loss. Therefore, the Cu content is 0 to 1.00%. The lower limit of the Cu content is preferably more than 0%, more preferably 0.01%, and still more preferably 0.04%. The upper limit of the Cu content is preferably 0.09%, and more preferably 0.08%. When Cu is about 0.04%, Cu may be included as an impurity in the electrical steel sheet.

The balance of the chemical composition of the electromagnetic steel sheet of the present invention is Fe and impurities. Here, the "impurities" are those which are allowed in a range where raw materials such as ores and scrap irons and components mixed due to various causes in the production process do not adversely affect the present invention when steel is industrially produced.

The content of Cr and Mo as impurity elements is not particularly limited. The electromagnetic steel sheet of the present invention does not particularly affect the effects of the present invention even if these elements are contained in an amount of 0.2% or less.

O is also an impurity element, but even if contained in a range of 0.05% or less, the effect of the present invention is not affected. Since O may be mixed in the annealing step, the effect of the present invention is not particularly affected even if the content of O in the slab stage (i.e., the Ladle value) is 0.01% or less.

Examples of the other impurities than the above impurities include Ti, V, W, Nb, Zr, Ca, Mg, REM, Pb, Bi, As, B and Se. These elements are all in the case of inhibiting grain growth. The content of each of the elements is preferably 0.01% or less, more preferably 0.005% or less.

2. Random strength of electromagnetic steel sheet surface by X-ray

In the electromagnetic steel sheet of the present invention, the ratio of the X-ray random intensity of {100} <011> crystal orientation on the steel sheet surface is 15.0 to 50.0. Here, the plate surface of the steel plate means a surface parallel to the rolling direction and the plate width direction of the steel plate, and a surface perpendicular to the plate thickness direction of the steel plate. Thus, the concentration of the <100> orientation as the axis of easy magnetization in the direction inclined by 45 ° with respect to the rolling direction RD of the steel sheet surface is sufficiently improved.

When the X-ray random intensity ratio of {100} <011> crystal orientation in the steel sheet surface is less than 15.0, the aggregation of easy magnetization axes in a direction inclined by 45 ° with respect to the rolling direction RD is too low. In this case, a sufficient magnetic flux density cannot be obtained in a direction inclined by 45 ° with respect to the rolling direction RD, and the iron loss also increases. On the other hand, when the X-ray random intensity ratio of {100} <011> crystal orientation in the steel sheet surface exceeds 50.0, the magnetic flux density is saturated in the electromagnetic steel sheet having the above chemical composition.

Therefore, the X-ray random intensity ratio of {100} <011> crystal orientation on the steel plate surface is 15.0-50.0. The lower limit of the X-ray random intensity ratio is preferably 17.0, and more preferably 20.0. The upper limit of the X-ray random intensity ratio is preferably 47.0, and more preferably 45.0.

The X-ray random intensity ratio of {100} <011> crystal orientation on the steel sheet surface is a ratio of the measured X-ray diffraction intensity of {100} <011> crystal orientation of an electromagnetic steel sheet sample to the X-ray diffraction intensity of {100} <011> crystal orientation of a standard sample (random sample) that is not collected in a specific orientation in the X-ray diffraction measurement.

The X-ray random intensity ratio of {100} <011> crystal orientation on the steel sheet surface can be measured by the following method. The X-ray random intensity ratio was determined from the Distribution Function of crystal Orientation (ODF) representing the three-dimensional assembly structure calculated by series expansion from the polar diagrams of {200}, {110}, {310}, and {211} of the α -Fe phase measured by X-ray diffractometry. The measurement by the X-ray diffraction method is performed at an arbitrary position between the thickness/4 and the thickness/2 of the electrical steel sheet. At this time, the surface to be measured is smoothed and finished by chemical polishing or the like.

3. Magnetic flux density

As described above, the electromagnetic steel sheet of the present invention includes a large amount of crystal grains in a direction slightly deviated from {100} <011> by continuing the second cold rolling after the first cold rolling at a high reduction ratio. This relatively increases the magnetic flux density in the direction 22.5 ° to the rolling direction RD.

Specifically, the magnetic flux densities in the directions of 0 °, 22.5 ° and 45 ° with respect to the steel sheet rolling direction RD satisfy the following expression (i).

1.005×(B₅₀(0°)+B₅₀(45°))/2≤B₅₀(22.5°) (i)

However, the meaning of each symbol in the above formula is as follows.

B₅₀(0 °): magnetic flux density (T) in the direction of 0 DEG to the rolling direction

B₅₀(22.5 °): magnetic flux density (T) in a direction of 22.5 DEG to the rolling direction

B₅₀(45 °): magnetic flux density (T) in a direction at 45 DEG to the rolling direction

By satisfying the above expression (i), anisotropy is moderately relaxed, and when an electromagnetic steel sheet is used as a core of a motor apparatus, magnetic force easily flows along the shape of the core.

The electrical steel sheet of the present embodiment preferably satisfies the following formula (ii) in addition to the above formula (i). This is because, with the electrical steel sheet of the present embodiment, the magnetic flux is concentrated in the tooth direction and the yoke direction of the split core, and the leakage magnetic flux can be reduced, by satisfying the following expression (ii).

B₅₀(45°)-B₅₀(0°)≥0.085T (ii)

The meaning of each symbol in the above formula (ii) is the same as that of formula (i).

4. Thickness of board

In the present invention, the thickness of the electrical steel sheet is not particularly limited. The electromagnetic steel sheet preferably has a thickness of 0.25 to 0.50 mm. Generally, the thinner the plate thickness is, the lower the iron loss is, but the magnetic flux density is also decreased. When the thickness of the electrical steel sheet of the present embodiment is 0.25mm or more, the iron loss becomes lower and the magnetic flux density becomes higher. On the other hand, if the thickness is 0.50mm or less, the iron loss can be kept low. The preferable lower limit of the plate thickness is 0.30 mm. In the electrical steel sheet of the present embodiment, even when the sheet thickness is as thick as 0.50mm, a high magnetic flux density and a low iron loss can be obtained.

5. Use of

The electrical steel sheet of the present invention can be widely applied to applications requiring magnetic properties (high magnetic flux density and low iron loss), and examples thereof include the following applications. (A) Servo motor, step motor, compressor used in electric machine. (B) A drive motor used in an electric vehicle and a hybrid vehicle. Here, the vehicle includes an automobile, a motorcycle, a train, and the like. (C) An electric generator. (D) Iron cores, choke coils, and reactors for various applications. (E) Current sensors, etc.

The electrical steel sheet of the present invention can be applied to applications other than the above-described applications. The electrical steel sheet of the present invention is particularly preferably used as a split core, and is further preferably applied to a split core of a drive motor of an electric vehicle or a hybrid vehicle in a high frequency range of 1000Hz or more.

6. Manufacturing method

An example of the method for producing an electrical steel sheet according to the present invention will be described. A method for producing an electromagnetic steel sheet comprises, in order, (a) a hot rolling step, (b) a first cold rolling step, (c) an intermediate annealing step, (d) a second cold rolling step, and (e) a final annealing step. The respective steps will be described in detail below.

(a) Hot rolling step

In the hot rolling step, a slab satisfying the above chemical composition is hot rolled to produce a steel sheet. The hot rolling step includes a heating step and a rolling step.

The slab is manufactured by a known method. For example, molten steel is manufactured in a rotary furnace, an electric furnace, or the like. The produced molten steel is subjected to secondary refining by a degassing apparatus or the like to produce molten steel having the above chemical composition. A slab is cast by a continuous casting method or an ingot casting method using molten steel. It is also possible to subject the cast slab to block rolling.

[ heating Process ]

In the heating step, the slab having the above chemical composition is heated to 1000 to 1200 ℃. Specifically, the slab is charged into a heating furnace or soaking furnace and heated in the furnace. The holding time at the heating temperature in the heating furnace or soaking furnace is, for example, 30 to 200 hours.

[ Rolling Process ]

In the rolling step, the slab heated in the heating step is subjected to rolling for a plurality of passes to produce a steel sheet. Here, "pass" means that the steel sheet is subjected to reduction by passing through 1 rolling stand having a pair of work rolls. The hot rolling may be performed, for example, by performing tandem rolling and multi-pass rolling using a tandem rolling mill including a plurality of rolling stands (each rolling stand has a pair of work rolls) arranged in a row, or by performing reverse rolling with a pair of work rolls and performing multi-pass rolling. From the viewpoint of productivity, it is preferable to perform a plurality of rolling passes using a tandem rolling mill.

The final rolling temperature in the rolling step is Ac₃Above the transformation point. After the rolling is finished, the steel sheet is cooled to a temperature of 600 ℃ or lower so that the average cooling rate to 600 ℃ reaches 50 to 150 ℃/sec. The cooling method after the steel sheet temperature is 600 ℃ is not particularly limited. The steel sheet temperature means the surface temperature (. degree. C.) of the steel sheet.

Here, the final rolling temperature is the surface temperature (c) of the steel sheet on the exit side of the rolling stand where the final pass reduction is performed in the above-described rolling step in the hot rolling step. The final rolling temperature can be measured, for example, by a temperature measuring instrument provided on the exit side of the rolling stand where the final pass reduction is performed. For example, when the total length of the steel sheet is divided into 10 equal parts in the rolling direction and 10 parts, the final rolling temperature is an average value of the temperature measurement results of the parts excluding the front end 1 part and the rear end 1 part.

The average cooling rate to 600 ℃ was determined by the following method. The steel sheet having the above chemical composition was used as a sample steel sheet, and the surface temperature was measured by a radiation thermometer to measure the time from completion of the rolling to 600 ℃. Based on the measured time, the average cooling rate is obtained.

(b) First cold rolling step

The steel sheet produced in the hot rolling step is subjected to a cold rolling step without being subjected to an annealing step. The cold rolling may be performed, for example, by performing tandem rolling or multi-pass rolling using a tandem rolling mill including a plurality of rolling stands (each rolling stand has a pair of work rolls) arranged in a row. Further, it is also possible to perform reverse rolling by a sendzimir mill or the like having a pair of work rolls, or 1-pass or multi-pass rolling. From the viewpoint of productivity, it is preferable to perform rolling in multiple passes using a tandem rolling mill.

In the first cold rolling step, cold rolling is performed without annealing in the middle of cold rolling. For example, when the cold rolling is performed in multiple passes by performing the reverse rolling, the cold rolling is performed in multiple passes without performing the annealing treatment between the cold rolling passes. Further, cold rolling may be performed in only 1 pass by using a reverse rolling mill. In addition, when cold rolling using a tandem rolling mill is performed, cold rolling is continuously performed in a plurality of passes (passes in each rolling stand).

The reduction ratio in the first cold rolling step is 80 to 92%. Here, the reduction in the cold rolling step is defined as follows.

Reduction ratio (%) × 100 (1-steel sheet thickness after final pass in cold rolling step/steel sheet thickness before 1 st pass in cold rolling step) × 100

The annealing step after the hot rolling step and before the cold rolling step is omitted. The chemical composition of the electrical steel sheet of the present embodiment is as described above, and the Mn content is high. Therefore, when hot-rolled sheet annealing performed in conventional electrical steel sheets is performed, Mn is segregated to grain boundaries, and the workability of the steel sheet (hot-rolled steel sheet) after the hot-rolling step is significantly reduced. The annealing treatment here means, for example, a heat treatment at 300 ℃ or higher.

(c) Intermediate annealing step

In the intermediate annealing step, the steel sheet after the first cold rolling step is annealed at 500 ℃ or higher and less than Ac₁The annealing treatment is carried out at an intermediate annealing temperature in the range of the phase transition point.

When the intermediate annealing temperature is less than 500 ℃, the deformation introduced by the cold rolling step cannot be sufficiently reduced. At this time, {100}<011>The aggregation of crystal orientations decreases. As a result, {100} of the steel sheet surface of the electromagnetic steel sheet<011>The random intensity ratio of X-rays in crystal orientation is out of the range of 15.0 to 50.0. On the other hand, when the intermediate annealing temperature exceeds Ac₁At this time, a part of the steel sheet structure is transformed into austenite, and the crystal orientation is randomized. The lower limit of the interannealing temperature is preferably 550 ℃ and more preferably 570 ℃.

Here, the interannealing temperature is a plate temperature (temperature of the surface of the steel plate) in the vicinity of the extraction opening of the annealing furnace. The plate temperature of the annealing furnace can be measured by a thermometer disposed at the outlet of the annealing furnace.

The holding time at the intermediate annealing temperature in the intermediate annealing step may be any time known to those skilled in the art. The holding time at the intermediate annealing temperature is, for example, 1 to 30 seconds. However, the holding time at the intermediate annealing temperature is not limited thereto. The rate of temperature increase to the intermediate annealing temperature may be a known condition. The temperature rise rate to the intermediate annealing temperature is, for example, 10.0 to 20.0 ℃/sec. However, the rate of temperature increase to the intermediate annealing temperature is not limited to this.

The atmosphere gas in the intermediate annealing is not particularly limited, and for example, 20% H is used as the atmosphere gas in the intermediate annealing₂The remainder being composed of N₂The resulting atmosphere gas (dry). The cooling rate of the steel sheet after the intermediate annealing is not particularly limited. The cooling rate is, for example, 5.0 to 50.0 ℃/sec.

(d) Second cold rolling step

The second cold rolling step is performed on the steel sheet after the intermediate annealing step. Specifically, the steel sheet after the intermediate annealing step is subjected to rolling (cold rolling) at normal temperature in the atmosphere. The cold rolling here is performed by, for example, a reverse rolling mill or a tandem rolling mill represented by the sendzimir mill.

In the second cold rolling step, cold rolling is performed without performing annealing treatment in the middle of cold rolling. For example, when the cold rolling is performed in multiple passes by performing the reverse rolling, the cold rolling is performed in multiple passes without performing the annealing treatment between the cold rolling passes. Further, cold rolling may be performed only in 1 pass by using a reverse rolling mill. In addition, when cold rolling using a tandem rolling mill is performed, cold rolling is continuously performed in a plurality of passes (passes of each rolling stand).

The reduction ratio in the second cold rolling step is more than 15.0% and 20.0% or less. The preferable lower limit of the reduction in the second cold rolling step is 17.0%. Here, the reduction ratio in the second cold rolling step is defined as follows.

Reduction (%) (1-thickness of steel sheet after final pass/thickness of steel sheet before 1 st pass) x 100

The number of cold rolling passes in the second cold rolling step may be only 1 pass (i.e., only 1 pass), or may be multiple passes.

As described above, after the deformation is introduced into the steel sheet in the hot rolling step and the first cold rolling step, the deformation introduced into the steel sheet can be reduced temporarily in the intermediate annealing step. Further, the second cold rolling step is performed. Thereby, the crystal is further rotated, and crystal grains slightly deviated from the {100} <011> direction are increased. As a result, the magnetic flux density in the direction 22.5 ° to the rolling direction RD was increased, and the anisotropy was moderately relaxed.

(e) Final annealing process

In the final annealing step, the steel sheet after the second cold rolling step is processed at 500 ℃ or higher and less than Ac₁The annealing treatment is performed at a final annealing temperature in the range of the phase transition point.

When the final annealing temperature is less than 500 ℃, {100}<011>Grain growth of the crystal orientation does not sufficiently occur. As a result, {100} of the steel sheet surface of the electromagnetic steel sheet<011>The random intensity ratio of the X-rays in the crystal orientation is out of the range of 15.0 to 50.0. On the other hand, when the final annealing temperature exceeds Ac₁Structure of steel plate at pointIs transformed into austenite. As a result, {100} of the steel sheet surface of the electromagnetic steel sheet<011>The random intensity ratio of the X-rays in the crystal orientation is out of the range of 15.0 to 50.0. The lower limit of the finish annealing temperature is preferably 550 ℃ and more preferably 570 ℃.

Here, the final annealing temperature is a plate temperature (temperature of the surface of the steel sheet) in the vicinity of the extraction port of the annealing furnace. The furnace temperature of the annealing furnace can be measured by a thermometer disposed at the outlet of the annealing furnace.

The temperature increase rate to the final annealing temperature in the final annealing step may be a temperature increase rate known to those skilled in the art, and the holding time at the final annealing temperature may be a time known to those skilled in the art.

The atmosphere gas in the final annealing step is not particularly limited. The atmosphere gas used in the final annealing step contains, for example, 20% H₂The remainder being composed of N₂The resulting atmosphere gas (dry). The cooling rate of the steel sheet after the final annealing is not particularly limited. The cooling rate is, for example, 5 to 20 ℃/sec.

The preferable holding time at the final annealing temperature in the final annealing step is 10 to 120 seconds. When the holding time is 10 to 120 seconds, the degree of aggregation of {100} <011> crystal orientation is improved. A further preferred lower limit of the holding time is 12 seconds, and a further preferred lower limit is 15 seconds. A more preferable upper limit of the holding time is 100 seconds, and a further preferable upper limit is 90 seconds.

Here, the holding time is a holding time after the steel sheet temperature reaches the final annealing temperature.

The temperature rise rate to the final annealing temperature in the final annealing step is preferably 0.1 ℃/sec or more and less than 10.0 ℃/sec. When the temperature increase rate is 0.1 ℃/sec or more and less than 10.0 ℃/sec, the degree of aggregation of {100} <011> crystal orientation is improved.

The temperature rise rate was obtained by the following method. A thermocouple was attached to the steel sheet having the chemical composition and obtained from the hot rolling step to the second cold rolling step to prepare a sample steel sheet. The sample steel plate with the thermocouple was heated, and the time from the start of heating to the final annealing temperature was measured. Based on the measured time, the temperature increase rate is determined.

The method for producing an electrical steel sheet of the present invention is not limited to the above-described production process.

For example, in the above-described manufacturing process, after the hot rolling process and before the cold rolling process, a blast treatment process and/or an acid pickling process may be performed. In the blasting step, the steel sheet after the hot rolling step is subjected to blasting to remove scale formed on the surface of the steel sheet after the hot rolling step. In the pickling step, pickling treatment is performed on the steel sheet after the hot rolling step. The acid washing treatment uses, for example, an aqueous hydrochloric acid solution as an acid bath. The scale formed on the surface of the steel sheet is removed by pickling. After the hot rolling step and before the cold rolling step, a blasting step may be performed, followed by an acid pickling step. Further, after the hot rolling step and before the cold rolling step, the pickling step may be performed without performing the blasting step. After the hot rolling step and before the cold rolling step, the steel sheet may be subjected to a sand blasting step without being subjected to an acid pickling step. The blast treatment step and the acid washing step are optional steps. Therefore, after the hot rolling step and before the cold rolling step, the blast treatment step and the pickling step may not be performed.

The method for producing an electrical steel sheet of the present invention may further include a coating step performed after the final annealing step. In the coating step, the surface of the steel sheet after the final annealing step is subjected to an insulating coating.

The kind of the insulating coating is not particularly limited. The insulating coating may be an organic component or an inorganic component, and the insulating coating may further contain an organic component and an inorganic component. Examples of the inorganic component include dichromic acid-boric acid type, phosphoric acid type, and silica type. Examples of the organic component include general acrylic, acrylic styrene, acrylic silicone, polyester, epoxy, and fluorine resins. In view of the coating property, a preferred resin is a latex type resin. It is also possible to perform an insulating coating that exerts bonding energy by applying heat and/or pressure. Examples of the insulating coating having adhesive properties include acrylic, phenolic, epoxy, and melamine resins.

The coating step is an arbitrary step. Therefore, the coating step may not be performed after the final annealing step.

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples.

Examples

After heating slabs having the chemical compositions shown in Table 1 to 1150 ℃, hot rolling was carried out under the conditions shown in Table 2 to produce hot-rolled steel sheets having a thickness of 2.0 mm.

TABLE 2

[ evaluation test ]

The following evaluation tests were performed on the electrical steel sheets of each steel number.

[ X-ray random intensity measurement test for {100} <110> crystal orientation ]

Samples were collected from the steel sheets of the respective test numbers, and the surfaces were mirror-polished. In the mirror-polished region, any region in which 5000 or more crystal grains can be measured was selected with the measurement interval of pixels being equal to or less than 1/5 of the average grain size. EBSD measurement was performed on the selected area to obtain a polar diagram of {200}, {110}, {310}, and {211 }. Using these pole figure, ODF distributions representing three-dimensional aggregate tissues calculated by the series expansion method are obtained. From the obtained ODF, the X-ray random intensity ratio of {100} <011> crystal orientation was obtained.

[ magnetic flux Density measurement test ]

A55 mm X55 mm single-plate test piece was prepared from the electromagnetic steel sheets of each test No. by punching. The magnetic flux densities B in the directions of 0 DEG, 22.5 DEG and 45 DEG to the rolling direction RD were measured by the above-mentioned method using a single-plate magnetic measuring device₅₀(0°)、B₅₀(22.5 ℃) and B₅₀(45 °). When measuringThe magnetic field of (2) is 5000A/m.

Iron loss W at [1000Hz_10/1000]

A55 mm X55 mm single-plate test piece was prepared from the electromagnetic steel sheets of each test No. by punching. The iron loss W of a single-plate test piece magnetized at a frequency of 1000Hz and a maximum magnetic flux density of 1.0T was measured using a single-plate magnetic measuring instrument _10/1000(W/kg)。

[ evaluation results ]

The evaluation results are shown in table 3. In addition, when the chemical composition of the manufactured electrical steel sheet was measured, the electrical steel sheets of each steel number had the same chemical composition as the chemical composition described in table 1.

TABLE 3

As shown in Table 3, it is understood that test Nos. 1 to 11 and 28 to 30 satisfying the requirements of the present invention are excellent in both the iron loss and the magnetic flux density. Further, not only the {100} <011> crystal orientation but also the magnetic properties around it are excellent.

On the other hand, in test No.12, the Mn content was less than the predetermined value, and in test No.14, the Si content was less than the predetermined value, and therefore the {100} <011> crystal orientation was not developed. In test No.13, since the Mn content was excessive, the workability was lowered, and the test was terminated because breakage occurred after cold rolling. In addition, in test No.15, since the Si content was excessive and deviated from the chemical composition of α - γ modification system, the {100} <011> crystal orientation was not developed.

In test No.16, the final rolling temperature was low, in test No.17, the cooling rate was too low, and in test No.18, the cooling rate was too high, and therefore the {100} <011> crystal orientation was not developed. In test No.19, the first cold rolling reduction was too low, while in test No.20, the first cold rolling reduction was too high, and therefore, the magnetic flux density was lowered as a whole. Similarly, in test No.21, the intermediate annealing temperature was too low, while in test No.22, the intermediate annealing temperature was too high, and therefore, the magnetic flux density was lowered as a whole.

In test No.23, the second cold rolling reduction was low although the iron loss and the magnetic flux density were excellent, and the anisotropy was not alleviated. On the other hand, in test No.24, since the second cold rolling reduction was too high, the deviation from the {100} <011> crystal orientation was serious, and the magnetic flux density was lowered as a whole.

In test No.25, the final annealing temperature was too low, and therefore, the crystal grain growth was not caused, and the anisotropy was too strong. On the other hand, in test No.26, since the final annealing temperature was too high, α - γ transformation and tissue randomization occurred, and the magnetic flux density was lowered as a whole. Further, in test No.27, since hot-rolled sheet annealing was performed, Mn was segregated to the grain boundaries, and fracture occurred after cold rolling, and the experiment was terminated.

Industrial applicability

As described above, according to the present invention, an electromagnetic steel sheet having excellent magnetic properties not only in the direction at 45 ° to the rolling direction but also in the peripheral direction thereof is obtained.