JP2018111847A - Nonoriented electromagnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonoriented electromagnetic steel sheet that prevents the occurrence of flaws, has improved productivity, low iron loss and high strength, and includes fine precipitations of Cu, and a method of producing the same.SOLUTION: A nonoriented electromagnetic steel sheet contains, in mass%, C: 0.005% or less, Si: 1.0-4.0%, Mn: 0.05-1.5%, Al: less than 0.03%, Cu: 0.5-2.5%, O: 0.003-0.030%, S: 0.004% or less, N: 0.004% or less, with the balance being Fe and impurities. In the steel, the ratio of number density N1 per unit volume of an inclusion of 5 μm or less in diameter and number density N2 per unit volume of an inclusion of more than 5 μm in diameter, N1/N2, is 20 or more. The steel sheet has a metallographic structure comprising ferrite grains free of non-recrystallized structures. The ferrite grains have an average crystal grain size of 30-180 μm. Inside the ferrite grains contained are metal Cu particles with a specified number density. The metal Cu particles have an average particle size of 1.0-10.0 nm.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a high-strength non-oriented electrical steel sheet used as a core material for drive motors of electric vehicles and motors for various electric devices.

  In recent years, motors with large capacities and rotating at high speed have been increasing in automobile applications. The motor rotor material is required to have mechanical strength to withstand centrifugal force and stress fluctuation. In order to increase the mechanical strength of steel, methods such as fine grain strengthening and dislocation strengthening are used. Generally, these strengthening actions deteriorate soft magnetic properties. The same material can be used for the rotor and the stator as long as excellent magnetic properties can be maintained together with the mechanical strength. In Patent Documents 1 to 8 and the like, for the purpose of achieving both low iron loss and high strength, a method of finely depositing metal Cu after cold rolling recrystallization is proposed.

JP 2004-084053 A International Publication No. 2005/033349 JP 2004-183066 A International Publication No. 2004/050934 JP 2008-223045 A JP 2010-24509 A International Publication No. 2013/024899 International Publication No. 2013/146886

  The technique of finely depositing Cu can obtain a low iron loss and a high mechanical strength, but the more Cu contained, the more likely that wrinkles are likely to occur on the surface of the steel sheet during hot rolling. In providing a high-strength non-oriented electrical steel sheet in which Cu is finely precipitated, an object of the present invention is to suppress generation of soot and improve productivity in a manufacturing process.

  In order to suppress the wrinkling of the hot-rolled sheet caused by Cu, it is effective to suppress oxidation of the steel during slab heating. For that purpose, the amount of Al contained in the slab must be limited. I found it effective. However, it was found that if the Al content is simply reduced, the magnetic properties deteriorate due to fine precipitation of nitrides and sulfides. Therefore, by optimizing the amount of Al and controlling inclusions during steelmaking, precipitation of nitrides and sulfides is suppressed, and good magnetic properties are ensured. Specifically, it is as follows.

(1) By mass%, C: 0.005% or less, Si: 1.0 to 4.0%, Mn: 0.05 to 1.5%, Al: less than 0.03%, Cu: 0.5 -2.5%, O: 0.003-0.030%, S: 0.004% or less, N: 0.004% or less, the remainder consists of Fe and impurities,
The ratio of the number density N1 per unit volume of inclusions having a diameter of 5 μm or less contained in the steel to the number density N2 per unit volume of inclusions having a diameter of more than 5 μm, N1 / N2 is 20 or more, It has a metal structure composed of ferrite grains not containing unrecrystallized structure, and the average grain size of the ferrite grains is 30 μm or more and 180 μm or less
The ferrite particles contain metal Cu particles having a number density of 1.0 × 10 ^{4 to} 1.0 × 10 ⁷ particles / μm ³ , and the average particle size of the metal Cu particles inside the ferrite particles is 1. A non-oriented electrical steel sheet having a thickness of 0 nm or more and 10.0 nm or less.

  (2) The non-oriented electrical steel sheet according to (1) above, containing 0.1 to 4.0% Cr by mass%.

  According to the present invention, a high-strength non-oriented electrical steel sheet in which Cu is finely precipitated can be manufactured with high productivity.

It is a figure which shows the temperature change of the oxidation increase in a typical alloy. It is a figure which shows the influence of Al addition with respect to the oxidation increase at the time of 1100 degreeC heating. It is a figure which shows the influence of Al content with respect to an iron loss. It is a figure which shows the influence of the oxygen concentration with respect to an iron loss. It is a figure which shows the influence of the inclusion number density ratio N1 / N2 with respect to an iron loss. It is a figure which shows the relationship between an inclusion particle diameter and S density | concentration. It is a figure which shows the example of element distribution in the inclusion.

  In order to prevent Cu-induced soot, it is important to suppress slab oxidation during hot rolling. This is because, when steel containing Cu is oxidized, Fe, which is lower than Cu, is selectively oxidized, and Cu concentrates in a metallic state at the interface between scale and ground iron, which causes various defects. It is.

<Experiment 1>
Steel having the components shown in Table 1 was melted in vacuum, and the resulting ingot was subjected to rough hot rolling, and a 10 mm × 20 mm × 30 mm test piece was cut out from the coarse bar and subjected to atmospheric annealing. The heating temperature was changed in the range of 1050 ° C. to 1200 ° C., and the soaking time was 30 minutes. The weight of the sample before and after annealing was measured. The increase is an increase in oxidation accompanying oxidation. The relationship between the heating temperature and the increase in oxidation is shown in FIG. Oxidation at 1150 ° C. or lower is effectively suppressed in the alloy a2 in which Si is 3.1% with respect to the alloy a1 that does not contain Si and Al. In the alloy a3 containing 0.7% Al (Si is 3.2%), the amount of oxidation increases and the oxidation resistance deteriorates. Further, when the temperatures of both alloys a2 and a3 exceed 1160 ° C., the amount of oxidation increases rapidly.
From the above results, Si has a function of preventing Cu-induced wrinkles, but when Al is contained in a composite manner, the wrinkle-preventing action decreases. Further, when the heating temperature of the slab becomes a high temperature of 1160 ° C. or higher, the precipitation of Cu becomes prominent and causes wrinkles.

<Experiment 2>
Next, the Si amount was fixed to 3.1 to 3.2%, and the steel in which the Al amount was changed was melted by vacuum melting, and an experiment similar to the above was performed. The component composition is shown in Table 2. FIG. 2 shows the influence of the Al addition amount on the oxidation increase at 1100 ° C. As the Al amount increases, the oxidation increase increases. In particular, when the amount is 0.1% or more, the influence is remarkable. Therefore, it is considered effective to make Al less than 0.1% in order to suppress Cu precipitation and prevent soot formation during hot rolling.
Each ingot of Table 2 was used as a test material, and after hot rolling at a heating temperature of 1100 ° C., finish hot rolling was performed at a heating temperature of 1140 ° C., a finishing temperature of 850 ° C., and a finishing thickness of 2.5 mm. Table 2 shows the presence or absence of lashes on the surface of the hot-rolled sheet in each material. As estimated above, the hot-rolled sheet wrinkles did not occur if the Al content was 0.1% or less.

<Experiment 3>
Next, after performing 870 ° C. hot-rolled sheet annealing on the above-mentioned hot-rolled sheet, cold rolling to 0.35 mm, finishing annealing at 1000 ° C. × 30 seconds, and then depositing Cu, 550 ° C. × 30 seconds Annealed. Table 2 shows the magnetic characteristics and mechanical characteristics. FIG. 3 shows the relationship between the Al addition amount and the iron loss W10 / 400. The iron loss is degraded when Al is in the range of 0.03 to 0.08. It is considered that the iron loss is deteriorated because AlN dissolves during slab heating, AlN finely precipitates after hot rolling, and inhibits grain growth during finish annealing. In order to prevent wrinkles and obtain a low iron loss, the Al content must be less than 0.03%.

  As described above, in order to prevent flaws and iron loss deterioration, the Al content of the steel must be less than 0.03%, but if Al is used as the deoxidizer, the Al content after melting Is within that range. Therefore, the magnetic properties of the steel sheet when Si deoxidation was performed were investigated below.

<Experiment 4>
Electrolytic iron and iron ore (Fe ₂ O ₃ ) are dissolved, Si is added as a deoxidizing agent, the components are adjusted, and the holding time from the deoxidizing agent injection to the casting mold is 0.5 to 60 minutes. Ingots were produced with varying ranges. Table 3 shows the component analysis results of the ingot obtained. The oxygen content decreased with the holding time, but when it was held for 10 minutes or more, it became a constant value of about 100 ppm.

  In addition, a sample was cut out from the ingot, the structure of the cross section was observed, and the size of inclusions and the number density thereof were investigated. Table 3 shows the number density N1 per unit area of inclusions having a diameter of 5 μm or less, the number density N2 per unit area of inclusions having a diameter exceeding 5 μm, and their ratio, N1 / N2. Inclusions with a diameter of 5 μm or less have little change in the number density even if the holding time is increased. Since the number of inclusions does not depend on the holding time, these are mainly considered as secondary deoxidation products that crystallize during solidification of the steel. On the other hand, the number of large inclusions of 5 μm or more decreases with time. These are presumed to be inclusions that have already crystallized in the molten steel.

  Next, using these ingots as test materials, after hot rolling at a heating temperature of 1100 ° C., finish hot rolling was performed at a heating temperature of 1140 ° C., a finishing temperature of 850 ° C., and a finishing thickness of 2.5 mm. When the surface of the hot-rolled sheet was observed, no lashes on the surface were observed on all the hot-rolled sheets.

  The hot-rolled sheet is subjected to hot-rolled sheet annealing at 870 ° C., cold-rolled to a final thickness of 0.35 mm, then subjected to 1000 ° C., 30-second finish annealing, 550 ° C., 30-second Cu precipitation annealing, and non-directional An electrical steel sheet was obtained. The value of iron loss W10 / 400 is shown in Table 3. By setting the deoxidation time to 10 minutes or longer, it is possible to obtain a non-oriented electrical steel sheet having a good iron loss value and excellent in yield strength and tensile strength.

  Using the above results, the relationship between the amount of oxygen contained in the steel and the iron loss is shown in FIG. As the amount of oxygen decreases, the iron loss decreases. FIG. 5 shows the relationship between N1 / N2 and iron loss W10 / 400. It can be seen that when N1 / N2 is 20 or more, the iron loss is significantly reduced.

  About the inclusion in the ingot of c9 of Table 3, the relationship between the diameter and S contained is shown in FIG. Smaller inclusions tend to increase the amount of S contained. FIG. 7 shows the element distribution of inclusions of 2.2 μm in which the content S was large. It can be seen that MnS is deposited on the inclusions. From the above, it is considered that S in the matrix tends to precipitate as MnS in the secondary deoxidation product having a small diameter. Therefore, in FIG. 5, N1 / N2 was 20 or more and the iron loss was reduced because the number of large inclusions that did not scavenge S decreased and precipitation of MnS on small secondary deoxidation products progressed. It can be assumed that the detoxification of S has progressed. Therefore, in the present invention, N1 / N2 is set to 20 or more in order to reduce iron loss.

<Chemical composition and structure of steel>
In the following description, “%”, which is a unit of content of each element contained in steel, means “mass%” unless otherwise specified.

<C: 0.005% or less>
Since C deteriorates iron loss, the lower the C content, the better. Such a phenomenon is remarkable when the C content exceeds 0.005%. Therefore, the C content is 0.005% or less, preferably 0.003% or less, more preferably 0.002% or less.

<Si: 1.0-4.0%>
As shown in the previous experiment, Si suppresses the precipitation of Cu by suppressing the oxidation of steel during slab heating. Further, Si has an effect of increasing specific resistance and reducing iron loss. If the Si content is less than 1.0%, these effects cannot be obtained sufficiently. Therefore, the Si content is 1.0% or more, preferably 2.0% or more, more preferably 2.5% or more. On the other hand, if the Si content exceeds 4.0%, the steel becomes brittle and the rollability deteriorates. Accordingly, the Si content is 4.0% or less, preferably 3.8% or less, and more preferably 3.5% or less.

<Mn: 0.05% to 1.5%>
Mn has an effect of preventing fine precipitation of sulfide during hot rolling by increasing the solution temperature of MnS as well as increasing the specific resistance of steel. When the Mn content is less than 0.05%, these effects cannot be obtained sufficiently. Therefore, the Mn content is 0.05% or more, preferably 0.1% or more, more preferably 0.2% or more. On the other hand, if the Mn content exceeds 1.5%, the steel may become brittle. Therefore, the Mn content is 1.5% or less, preferably 1.0% or less, more preferably 0.5% or less.

<Al: less than 0.03%>
Al promotes oxidation of steel containing Si and causes soot. Further, as shown in FIG. 5 of Experiment 4, when the Al content is 0.03% or more, the iron loss is deteriorated. In the present invention, the Al content is less than 0.03. Preferably it is 0.008 or less, More preferably, it is 0.005 or less.

<Cu: 0.5 to 2.5%>
Cu precipitates finely in the grains after cold rolling recrystallization, thereby increasing the mechanical strength without deterioration of iron loss. If the Cu content is less than 0.5%, this effect cannot be sufficiently obtained. Therefore, the Cu content is 0.5% or more, preferably 0.7% or more, more preferably 1.0% or more. On the other hand, if the Cu content exceeds 2.5%, flaws are likely to occur during hot rolling, and embrittlement tends to occur. Therefore, the Cu content is 2.5% or less, preferably 2.0% or less, more preferably 1.5% or less.

<O: 0.003-0.030%>
In general, oxygen produces inclusions and adversely affects magnetic properties. However, as previously indicated, the secondary deoxidation product produced during solidification after deoxidation has the effect of crystallizing or precipitating MnS and detoxifying S in the steel. In order to have this effect, the O content is set to 0.003% or more. Preferably it is 0.005% or more, More preferably, it is 0.010% or more. On the other hand, when O is more than 0.030%, large inclusions that do not have the effect of detoxifying S increase, and iron loss is deteriorated. Therefore, the O content is 0.030% or less, preferably 0.025% or less, more preferably 0.020% or less.

<S: 0.004% or less>
Since S produces fine sulfides and degrades crystal grain growth, the lower the S content, the better. Such a phenomenon is remarkable when the S content exceeds 0.004%. Therefore, the S content is 0.004% or less, preferably 0.003% or less, more preferably 0.002% or less.

<N: 0.004% or less>
N generates fine nitrides and degrades crystal grain growth. Therefore, the lower the N content, the better. Such a phenomenon is remarkable when the N content exceeds 0.004%. Therefore, the N content is 0.004% or less, preferably 0.003% or less, more preferably 0.002% or less.

<Cr: 0.1-4.0%>
Cr can be added because it has the effect of suppressing the oxidation of steel during slab heating and suppressing the precipitation of Cu. If the Cr content is less than 0.1%, this effect cannot be obtained sufficiently. Accordingly, the Cr content is 0.1% or more, preferably 0.5% or more, and more preferably 1% or more. On the other hand, when the Cr content exceeds 4.0%, the hysteresis loss increases. Therefore, the Cr content is 4.0% or less, preferably 3.0% or less, more preferably 2.0% or less.

<Other elements>
In order to fix S by forming coarse sulfates and sulfides and suppress the formation of fine sulfides, REM may be added in a range of 0.03% or less. REM is a generic name for a total of 17 elements including 15 elements from La with atomic number 57 to Lu with 71 and Sc with atomic number 21 and Y with atomic number 39. Since Ca has the same effect, it may be contained in a range of 0.005% or less.

  For the purpose of improving the magnetic properties, Sn and Sb can be added in a range of 0.05% or less, respectively.

  Further, P can be added in a range of 0.1% or less in order to increase the mechanical strength and improve the texture.

It is preferable to reduce other harmful impurity elements as much as possible, and Ti, Nb, and V are particularly preferably 0.005% or less.
The balance is inevitable impurities and Fe.

<Inclusion number density ratio N1 / N1: 20 or more>
In the present invention, since the amount of Al added is limited, Al cannot be used as a deoxidizer. On the other hand, as shown in Experiment 4, in the case of Si deoxidation, a secondary deoxidation product at the time of solidification is likely to be produced, but this product crystallizes or precipitates MnS on its own, and steel It was found to have the effect of detoxifying the inside S. In general, the particle size of the secondary deoxidation product is smaller than the particle size of the primary deoxidation product present in the molten steel, but from the results of Experiment 4, inclusions smaller than 5 μm as a boundary are generally It can be said to be a secondary deoxidation product. When the number density N1 per unit area of inclusions having a diameter of 5 μm or less and the number density N2 per unit area of inclusions having a diameter exceeding 5 μm are set, the ratio, N1 / N2, is 20 as shown in FIG. If it makes it above, an iron loss will become favorable. Therefore, in the present invention, N1 / N2 is set to 20 or more. Preferably it is 25 or more, more preferably 30 or more. On the other hand, since the upper limit is naturally determined from the regulation of the amount of O, no particular regulation is provided.

  The inclusions can be observed with a metallographic microscope or with EPMA (Electron Probe Micro Analyzer).

<Metal structure composed of ferrite grains not containing non-recrystallized structure>
If the non-recrystallized structure remains in the steel plate, the iron loss of the steel plate increases remarkably. Therefore, in this invention, it is set as the metal structure which consists of a ferrite grain which does not contain an unrecrystallized structure.

<Average crystal grain size of ferrite grains: 30 to 180 μm>
The average grain size of the ferrite grains needs to be 30 μm or more in order to reduce the hysteresis loss of the steel sheet. However, if the average grain size of the ferrite grains is too large, the iron loss may deteriorate due to an increase in eddy current loss. Accordingly, the average crystal grain size of the ferrite grains is set to 180 μm or less. The lower limit of the average grain size of the ferrite grains is preferably 30 μm, more preferably 50 μm, and even more preferably 70 μm. The upper limit value of the average grain size of the ferrite grains is preferably 170 μm, more preferably 160 μm, and still more preferably 150 μm. The average crystal grain size of the ferrite grains can be determined according to JIS G 0551 “Steel—Microscopic Test Method for Crystal Grain Size”.

<Average particle diameter of metal Cu particles: 1.0 nm or more and 10.0 nm or less>
Cu particles precipitated in the recrystallized grains hinder dislocation movement. Metal Cu particles having a particle size that is too small have a low resistance to dislocation movement. On the other hand, the metal Cu particles having a large particle size have a large resistance to dislocation movement, but the number density of the metal Cu particles decreases, so that the distance between the particles increases and the dislocation movement becomes easy. Furthermore, the metal Cu particles having a particle diameter of about 100 nm or more, which is about the thickness of the domain wall, hinder the domain wall movement and increase the hysteresis loss. Therefore, the average particle diameter of the metal Cu precipitated particles is 1.0 nm or more and 10.0 nm or less. Preferably they are 2.0 nm or more and 5.0 nm or less, More preferably, they are 2.0 nm or more and 4.0 nm or less, More preferably, they are 2.0 nm or more and 3.0 nm or less.

  The average particle diameter of the metal Cu particles is determined using a bright field image of a transmission electron microscope (TEM). The area of each Cu particle in the image is obtained, and the diameter of the circle having the area (circle equivalent diameter) is regarded as the diameter of each particle.

<Number density of metal Cu particles: 1.0 × 10 ^{4 to} 1.0 × 10 ⁷ / μm ³ >
In the present invention, the number of metal Cu particles per 1 μm ³ volume in the ferrite grains is 1.0 × 10 ⁴ / μm ³ or more. Preferably it is 1.0 × 10 ⁵ / μm ³ or more, more preferably 5.0 × 10 ⁵ / μm ³ or more. On the other hand, when the number density of metal Cu particles is too large, the magnetic properties of the steel sheet may be deteriorated. Therefore, the lower limit of the number density of the metal Cu particles in the ferrite grains is set to 1.0 × 10 ⁷ / μm ³ or less.

The number density of metal Cu particles is the number density of metal Cu particles having a particle diameter of 1.0 nm or more in all ferrite grains. Metal Cu particles having a particle size of less than 1.0 nm are difficult to detect and are not considered to be measured because they are considered to have substantially no effect on the characteristics of the steel sheet according to the present embodiment. The number density N of the metal Cu particles in the ferrite grains of the steel sheet according to the present embodiment is the area of the electron microscope observation image A, the number of Cu particles observed there is n, the average particle diameter (equivalent circle diameter) When the arithmetic average) is d, it is obtained based on the following mathematical formula.
N = n / (A × d)

<Manufacturing method>
The non-oriented electrical steel sheet according to the present invention can be manufactured, for example, by the following method. That is, after melting the steel of the above component composition, it is made into a slab by continuous casting or the like, hot-rolled steel plate by subjecting the slab to hot rolling, and hot-rolled steel plate annealed as necessary And cold-rolling the hot-rolled steel sheet or hot-rolled annealed steel sheet into a cold-rolled steel sheet, subjecting the cold-rolled steel sheet to recrystallization annealing, and then precipitating Cu into a non-oriented electrical steel sheet product. This is a method for producing a non-oriented electrical steel sheet.

  In the steelmaking stage, it is effective to use Si as a deoxidizer. At the time of casting, in order to increase the above-described N1 / N2 to 20 or more, it is important to float and remove a relatively large primary deoxidation product as much as possible. For that purpose, it is effective to sufficiently stir after the deoxidizer is added, to appropriately provide a tundish weir, or to appropriately use an electromagnetic brake or in-mold electromagnetic stirring. On the other hand, since the secondary deoxidation product produced at the time of solidification is effective for detoxifying S as described above, it is necessary to cool the slab appropriately. Although the temperature pattern varies somewhat depending on the component composition of the steel to be produced, it is effective to lengthen the time for staying in the range of approximately 900 ° C. to 1100 ° C. where MnS is generated. It is at least 1 minute or more, preferably 3 minutes or more, more preferably 5 minutes or more.

  Next, in the present invention, at the time of slab heating in the hot rolling step, it is preferable to control so that the temperature of the surface of the slab does not exceed 1160 ° C. As shown in FIG. 1, the steel of the present invention is remarkably easily oxidized when the temperature exceeds 1160 ° C. In that case, Cu is deposited in a metallic state at the interface between the scale and the ground iron, so that scabs and the like are easily formed on the hot-rolled sheet. In order to prevent this, in the present invention, it is preferable to control the surface temperature not to exceed 1160 ° C. during heating.

Other manufacturing conditions are not particularly limited, but can be manufactured under the following conditions.
The slab heating temperature during hot rolling is preferably 1000 ° C. or higher. When the slab heating temperature is less than 1000 ° C., hot rolling becomes difficult. As described above, the surface temperature of the slab is controlled so as not to exceed 1160 ° C. The hot rolling finishing temperature FT is preferably 900 ° C. or lower. When the coiling temperature CT of the hot-rolled steel sheet is high, Cu is precipitated in the coil after the coiling, and the toughness of the hot-rolled steel sheet is lowered. The hot-rolled finished sheet thickness is preferably 2.7 mm or less in order to prevent the texture from deteriorating due to a high rolling reduction during cold rolling. However, if it is too thin, hot rolling becomes difficult and productivity is lowered, so that the finished thickness of hot rolling is preferably 1.6 mm or more.

  In order to improve the texture of the final product and obtain a high magnetic flux density, the hot-rolled steel sheet may be subjected to hot-rolled sheet annealing. A preferable soaking temperature is 750 to 1100 ° C., and a soaking time is 10 seconds to 5 minutes. When the soaking temperature is less than 750 ° C. or the soaking time is less than 10 seconds, the effect of improving the texture is small. If the soaking temperature exceeds 1100 ° C., or if the soaking time exceeds 5 minutes, the production cost increases due to an increase in energy consumption, deterioration of incidental facilities, and the like. In order to make Cu in the steel plate before recrystallization finer after cold rolling and to re-dissolve Cu during recrystallization annealing after cold rolling, the cooling section of 800 to 400 ° C. has an average cooling rate of 10 ° C./second or more. Cooling. The average cooling rate is preferably 20 ° C./second or more, and more preferably 40 ° C./second or more. A high average cooling rate also leads to securing the toughness of the hot-rolled annealed sheet.

  Further, the production method of the present invention cold-rolls the hot-rolled steel sheet to obtain a cold-rolled steel sheet. Cold rolling may be performed once, or may be performed twice or more including intermediate annealing. The final rolling reduction is preferably in the range of 60 to 90%. Thereby, a high magnetic flux density and a low iron loss are obtained. The intermediate annealing temperature is preferably 900 to 1100 ° C. Also in this case, it is desirable that the cooling section of 800 to 400 ° C. is cooled at an average cooling rate of 10 ° C./second or more.

  In the recrystallization step, the metal structure of the steel sheet is recrystallized and Cu is solutionized. The soaking temperature is preferably 850 ° C. or higher in order to make the average grain size of ferrite grains 30 μm or more, which is one of the requirements described above, and to dissolve Cu. On the other hand, if the soaking temperature is too high, the average grain size of the ferrite grains tends to exceed the specified 180 μm, energy consumption increases, and incidental equipment such as a hearth roll is easily damaged. The temperature is preferably 1100 ° C. or lower. The soaking time is preferably 10 seconds or more and 2 minutes or less. In order not to precipitate Cu once dissolved in the cooling process, the average cooling rate from 800 ° C. to 400 ° C. in the cooling process is preferably 10 ° C./second or more.

Next, the recrystallized steel sheet obtained in the recrystallization process is annealed to precipitate Cu in the crystal grains. The number density of Cu particles precipitated in the ferrite grains is 1.0 × 10 ^{4 to} 1.0 × 10 ⁷ particles / μm ³ and the average size is 1.0 nm or more and 10.0 nm or less. Is preferably 450 ° C. or higher and 650 ° C. or lower.

  The soaking time needs to be 10 seconds or longer. Preferably it is 30 seconds or more, more preferably 40 seconds or more. If it is the said temperature range, it is also possible to perform annealing by batch annealing in the soaking time of several hours. The optimum conditions for the soaking temperature and soaking time vary somewhat depending on the component composition of the steel sheet, particularly the amount of Cu, but are generally included in the above range.

  When recrystallization annealing and Cu precipitation annealing are performed simultaneously in one continuous annealing line, the soaking temperature is 850 ° C. or more and 1050 ° C. or less, the soaking time is 10 seconds or more, and the temperature of 600 ° C. to 450 ° C. in the cooling process. The time for the steel sheet to stay in the zone is 10 seconds or longer.

  If necessary, the steel sheet obtained by the production method of the present invention can be provided with an insulating film to obtain a non-oriented electrical steel sheet having high strength and low iron loss.

<Example 1>
Steels having the composition shown in Table 4 were melted in vacuum, and the obtained ingot was hot rolled at a heating temperature of 1150 ° C, a finishing temperature of 850 ° C, a winding temperature of 400 ° C, and a finishing thickness of 2.3 mm. The presence or absence of scabs on the hot-rolled sheet was visually confirmed, and the results are shown in Table 4. The obtained hot rolled sheet was subjected to hot rolled sheet annealing at a soaking temperature of 1000 ° C. and a holding time of 30 seconds, and then subjected to cold rolling to obtain a 0.35 mm cold rolled sheet. The cold rolled sheet was subjected to recrystallization annealing at a soaking temperature of 1000 ° C., a holding time of 30 seconds, and an average cooling rate of 20 ° C./sec from 800 ° C. to 400 ° C., and then a soaking temperature of 550 ° C. and a holding time of 60 seconds. Cu precipitation annealing was performed to obtain a product plate of a non-oriented electrical steel sheet. In the obtained product plate, the number density N1 per unit volume of inclusions having a diameter of 5 μm or less and the number density N2 per unit volume of inclusions having a diameter exceeding 5 μm were observed, and the ratio, N1 / N2 Asked. Further, the average ferrite crystal grain size, the number density and average particle diameter of precipitated Cu, the mechanical properties, and the magnetic properties were investigated. As product characteristics, W10 / 400 was 20 W / kg or less, B50 was 1.60 T or more, and YP and TS were 400 MPa or more and 500 MPa or more, respectively. According to the present invention, it is possible to achieve both good mechanical properties and good iron loss without wrinkling of the hot-rolled sheet.

<Example 2>
Using a cold-rolled sheet of alloy d15 in Table 4 as a test material, finish annealing was performed at a soaking temperature of 950 to 1050 ° C. and a soaking time of 30 to 90 seconds. Further, a soaking temperature of 550 to 650 ° C. A non-oriented electrical steel sheet was obtained by performing Cu precipitation annealing for 30 seconds. In the same manner as in Example 1, the ratio N1 / N2, the average ferrite crystal particle size, the number density and average particle size of precipitated Cu, mechanical properties, and magnetic properties were investigated. Each is shown in Table 5. The present invention can achieve both good mechanical properties and good iron loss.

Claims (2)

% By mass
C: 0.005% or less Si: 1.0-4.0%,
Mn: 0.05 to 1.5%,
Al: less than 0.03%,
Cu: 0.5 to 2.5%,
O: 0.003 to 0.030%,
S: 0.004% or less,
N: 0.004% or less,
And the balance consists of Fe and impurities,
The ratio of the number density N1 per unit volume of inclusions having a diameter of 5 μm or less contained in the steel to the number density N2 per unit volume of inclusions having a diameter of more than 5 μm, N1 / N2 is 20 or more,
It has a metal structure consisting of ferrite grains that do not contain unrecrystallized structure,
The average grain size of the ferrite grains is 30 μm or more and 180 μm or less,
Containing metal Cu particles having a number density of 1.0 × 10 ^{4 to} 1.0 × 10 ⁷ particles / μm ³ inside the ferrite grains,
The non-oriented electrical steel sheet, wherein an average particle diameter of the metal Cu particles inside the ferrite grains is 1.0 nm or more and 10.0 nm or less.   The non-oriented electrical steel sheet according to claim 1, comprising 0.1 to 4.0% Cr by mass%.