JP6627226B2 - Manufacturing method of non-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, and more particularly, to a non-oriented electrical steel sheet excellent in iron loss and used as a core material of electrical equipment and a method for manufacturing the same.

Non-oriented electrical steel sheets are used as iron core materials for various motors for heavy electric appliances and home appliances. Non-oriented electrical steel sheets are commercially graded according to iron loss, and are selectively used according to the design characteristics of motors and transformers.
In recent years, from the viewpoint of energy saving, there is a strong demand for non-oriented electrical steel sheets to further reduce iron loss.

  Generally, when fine precipitates are present in a steel sheet, domain wall movement is hindered, and the hysteresis loss deteriorates.

  Therefore, conventionally, for the purpose of improving iron loss of non-oriented electrical steel sheets, control of sulfide precipitation in hot rolling, reduction of sulfide by desulfurization, suppression of precipitation of Cu sulfide by rapid cooling after finish annealing, etc. Methods have been proposed.

  For example, in Patent Literature 1, a billet containing 0.2% or less of Cu is kept in a range of 900 to 1100 ° C for 30 minutes or more, then kept at a high temperature of 1150 ° C, and subsequently, rolling is started and finishing is performed. A method of controlling the dispersion state of Cu sulfide to a state favorable for the magnetic properties of non-oriented electrical steel sheets, that is, iron loss and magnetic flux density, by suppressing the cooling rate during hot rolling to 50 ° C./sec or less is disclosed. ing.

  In Patent Document 2, CaSi is added to molten steel by the time casting is completed, the S content is controlled to 0.005% or less, a slab is heated at a temperature of 1000 ° C. or more, and then hot-rolled to a specific temperature. A method of avoiding the formation of fine precipitates by coil winding in a region is disclosed.

  Patent Literature 3 discloses a technique in which after finish annealing, quenching is performed at a cooling rate of 10 to 50 ° C./sec from a temperature range of 500 to 600 ° C. to 300 ° C. to suppress precipitation of Cu sulfide. ing.

  Patent Literatures 4 to 7 disclose techniques that are expected to improve magnetic properties by controlling a cooling rate after finish annealing.

JP 2010-174376 A JP-A-10-183244 JP-A-09-302414 JP 2011-006721 A JP 2006-144036 A JP-A-2003-113451 International Publication No. 2014/168136

CAMP-ISIJ Vol. 25 (2012), p1080 CAMP-ISIJ Vol. 22 (2009), p1284 j. Flux Growth vol. 5 (2010), p48 Tetsu-to-Hagane vol. 100 (2014), p1229 Tetsu-to-Hagane vol. 83 (1997), p479 Tetsu-to-Hagane vol. 92 (2006), p609 Bunnseki vol. 11 (2002), p639

However, the conventional methods described in Patent Documents 1 to 6 have the following problems.
The method described in Patent Literature 1 has problems in productivity, such as an increase in rolling load due to a lower slab heating temperature and difficulty in strict control of a cooling rate.
Further, in the method described in Patent Document 2, high-purity steel is indispensable, but the formation of fine Cu sulfide by Cu mixed at an unavoidable level is inevitable, so that the mixing of Cu degrades the magnetic properties. there were.

Patent Literature 3 discloses a method of rapidly cooling from a temperature range of 500 to 600 ° C. to 300 ° C. at a cooling rate of 10 to 50 ° C./sec. It is known from Non-Patent Documents 1 and 2 that the precipitation occurs during cooling even at a cooling rate of. That is, it is difficult to completely suppress the precipitation of Cu sulfide by the technique of Patent Document 3 in which cooling is performed at about 10 to 50 ° C./sec.
Further, in Patent Documents 4 to 6, although the introduction of cooling strain into a steel sheet can be avoided by the above-described method and iron loss deterioration can be reduced, the precipitation state of Cu sulfide cannot be controlled. In addition, finely precipitated Cu sulfide adversely affects magnetic properties. Patent Document 7 discloses a technique for controlling the precipitation form of Cu sulfide, but it is difficult to make Cu sulfide harmless when precipitates other than Cu sulfide (such as nitrides) are present. There was a problem of becoming.

The present invention has been made in view of the above problems, to control the precipitation form of Cu sulfide, without decreasing the cost increase and productivity, to provide a manufacturing how the non-oriented electrical steel sheet excellent in core loss that With the goal.

  In order to solve the above-mentioned problems, the present invention has repeatedly studied the effects of the steel sheet components and the manufacturing conditions of the non-oriented electrical steel sheet on the relationship between the sulfide dispersion state and the magnetic properties. As a result, it has been found that when a non-oriented electrical steel sheet containing aluminum nitride is annealed under a certain condition, the fine dispersion of Cu sulfide is suppressed and the magnetic properties are remarkably improved. Further, as a result of a detailed investigation on the form and structure of the precipitates in the steel, it was found that this phenomenon was particularly caused by the complex precipitation of Cu sulfide with aluminum nitride, thereby preventing (A) the single dispersion of Cu sulfide. And (B) Cu sulfide was found to have good lattice matching with base iron. Further, they have found that composite precipitation of Cu sulfide and aluminum nitride can occur when the lattice matching between aluminum nitride, which is a precipitation nucleus, and Cu sulfide is optimized.

  The present invention has been made based on the above findings, and has the following (1) to (5).

(1) In the method for producing a non-oriented electrical steel sheet according to one embodiment of the present invention , C: 0.0001 to 0.01%, Si: 0.05 to 7.0%, and Mn: 0. 02-3.0%, Al: 0.002-3.0%, S: 0.0005-0.05%, P: 0.002-0.15%, N: 0.0010-0.0100% , Cu: 0.010 to 5.00%, the balance having a chemical composition consisting of Fe and impurities, and a Hexagonal structure appearing at 2θ = 33.5 ° obtained by X-ray diffraction of the electrolytic extraction residue. I _{2θ = 33.5,} which is the diffraction intensity of aluminum nitride, and I _{2θ = 32.1} , which is the diffraction intensity of Cu sulfide having a Cubic structure appearing at 2θ = 32.1 °, satisfy the condition of the following formula 1. The method for producing a non-oriented electrical steel sheet which satisfies the formula : 0001-0.01%, Si: 0.05-7.0%, Mn: 0.02-3.0%, Al: 0.002-3.0%, S: 0.0005-0.05% , P: 0.002 to 0.15%, N: 0.0010 to 0.0100%, Cu: 0.010 to 5.00%, the remainder having a chemical composition consisting of Fe and impurities. Hot rolling to obtain a hot-rolled steel sheet, hot-rolled sheet annealing step of annealing the hot-rolled steel sheet, and pickling step of pickling the hot-rolled steel sheet after the hot-rolled sheet annealing step In the production process of a non-oriented electrical steel sheet, the cold-rolling step of performing cold rolling on the hot-rolled steel sheet after the pickling step to obtain a cold-rolled steel sheet, and a finish annealing step of annealing the cold-rolled steel sheet. In the hot-rolled sheet annealing step, holding at T2 ° C. or more shown in the following formula 3 for 10 to 3600 seconds is performed, and the finish annealing is performed. When the temperature is raised from room temperature to T1 ° C. or more and T2 ° C. or less shown in the following formula 2, the average heating rate in the temperature range of T5 ° C. or more shown in the following formula 6 and T6 ° C. or less shown in the following formula 7 is 10 C./sec. To 1,000 ° C./sec., Holding at T1 ° C. or more and T2 ° C. or less for 10 to 3600 seconds, and cooling thereafter, T3 ° C. or less shown in the following formula 4, T4 shown in the following formula 5 The average cooling rate in the temperature range of not less than 20 ° C. is not less than 20 ° C./sec and not more than 200 ° C.
I _{2θ = 32.1} / I _{2θ = 33.5} ≧ 0.01 Expression 1
T1 = 15000 / (12-log10 ([% Cu] 2 × [% S]))-273 ... Equation 2
T2 = 10000 / (3.5-log10 ([% Al] × [% N]))-273 ... Equation 3
T3 = 15000 / (12-log10 ([% Cu] 2 × [% S]))-323 ... Equation 4
T4 = 15000 / (12-log10 ([% Cu] 2 × [% S]))-423 ... Equation 5
T5 = 10000 / (3.5 log10 ([% Al] × [% N]))-923 ... Equation 6
T6 = 10000 / (3.5 log10 ([% Al] × [% N]))-523 ... Equation 7
Here, [% Cu] is the content in mass% of Cu, [% S] is the content in mass% of S, and [% Al] is the content in mass% of Al [% N] is N Is the content in mass%.
(2) In the method for producing a non-oriented electrical steel sheet according to (1), in the hot-rolled sheet annealing step, in the cooling after the holding at T2 ° C or higher, the cooling is performed at T5 ° C or higher. The average cooling rate in a temperature range of T6 ° C. or less may be set to 10 ° C./sec or more and 200 ° C. or less.

According to the present invention, the non-oriented electrical steel sheet, without purifying, or lowering the slab heating temperature, without optimizing the hot rolling conditions, etc., while avoiding single precipitation of fine Cu sulfide, By controlling the precipitation form that has a favorable effect on iron loss, a non-oriented electrical steel sheet excellent in iron loss can be provided.
According to the present invention, characteristics (magnetic flux density, workability, and the like) other than iron loss required of the non-oriented electrical steel sheet can be secured to be equal to or higher than conventional materials.

Hereinafter, a non-oriented electrical steel sheet according to an embodiment of the present invention (sometimes referred to as a non-oriented electrical steel sheet according to the present embodiment) and a method for manufacturing the same will be described in detail.
First, the reasons for limiting the component composition of the non-oriented electrical steel sheet according to the present embodiment will be described. All percentages of the contents described below are% by mass unless otherwise specified.

C: 0.0001-0.01%
C significantly reduces iron loss due to magnetic aging. Therefore, the upper limit of the C content is set to 0.01%. From the viewpoint of improving iron loss, 0.0040% or less is preferable. More preferably, it is 0.0020% or less. On the other hand, when the C content is less than 0.0001%, the magnetic flux density deteriorates. Therefore, in order to ensure a sufficient magnetic flux density, the lower limit of the C content is set to 0.0001%, preferably 0.0010%. More preferably, it is 0.0015% or more.

Si: 0.05 to 7.0%
The Si content is set to 0.05 to 7.0% in consideration of securing iron loss and passing property. If the Si content is less than 0.05%, good iron loss cannot be obtained. Preferably, the Si content is at least 2.00%, more preferably at least 3.00%. On the other hand, if the Si content exceeds 7.0%, the steel sheet becomes brittle, and the sheet passing property in the manufacturing process is significantly deteriorated. Preferably, the Si content is no more than 3.50%, more preferably no more than 3.30%.

Mn: 0.02 to 3.0%
Mn is an important element in the present invention because it reacts with S to form a sulfide. When Mn is present in the steel, the precipitation amount of MnS reduces the amount of Cu ₂ S deposited, and Cu ₂ S easily precipitates finely. Therefore, the upper limit of the Mn content is set to 3.0%. Preferably, the Mn content is at most 2.0%, more preferably at most 1.0%. On the other hand, if the Mn content is less than 0.02%, the steel sheet becomes brittle during hot rolling. Therefore, the lower limit of the Mn content is set to 0.02%. Preferably, the Mn content is at least 0.10%, more preferably at least 0.15%.

Al: 0.002 to 3.0%
Al is an element forming AlN, and is one of the particularly important elements in the present invention. When a large amount of Al is added, AlN is easily formed, and the effects of the present invention are easily enjoyed. Therefore, it is advantageous to increase the Al content in the steel. However, molten steel having a high Al content deteriorates operability at the time of casting and causes brittleness of the steel sheet. Therefore, the upper limit of the Al content is set to 3.0%. Preferably, the Al content is 2.0% or less, more preferably 1.5% or less. On the other hand, if the Al content is small, AlN is not sufficiently generated, and fine TiN that inhibits crystal grain growth is generated instead of AlN, and the magnetic flux density is significantly deteriorated. Therefore, the lower limit of the Al content is set to 0.002%. Preferably, the Al content is 0.050% or more, more preferably 0.100% or more.

S: 0.0005 to 0.05%
The S content is directly related to the amount of sulfide deposited. If the S content is excessive, S exists in the steel in a solid solution state, and the steel becomes brittle during hot rolling. Therefore, the upper limit of the S content is set to 0.050%. Preferably, the S content is 0.010% or less, more preferably 0.005% or less. On the other hand, if S does not exist, Cu is finely precipitated as metallic Cu, which causes iron loss deterioration. Therefore, the lower limit of the S content is set to 0.0005%. Preferably it is 0.0020% or more, more preferably 0.0040% or more.

P: 0.002 to 0.15%
P has the effect of increasing the hardness of the steel sheet and improving the punchability. Further, a small amount of P has an effect of improving the magnetic flux density. In order to obtain these effects, the lower limit of the P content is set to 0.002%. Preferably, the P content is at least 0.020%, more preferably at least 0.040%. However, if the P content becomes excessive, the magnetic flux density deteriorates, so the upper limit of the P content is set to 0.150%. The P content is preferably 0.10% or less, more preferably 0.08% or less.

N: 0.0010 to 0.0100%
N is one of the particularly important elements in the present invention because it is an element forming AlN. However, if the N content is excessive, the amount of other nitrides such as TiN, VN, and Si ₃ N ₄ increases, and these nitrides hinder the growth of crystal grains. Therefore, the upper limit of the N content is set to 0.0100%. Preferably, the N content is 0.0080% or less, more preferably 0.0070% or less. On the other hand, in order to precipitate AlN and enjoy the effects of the present invention, the lower limit of the N content is set to 0.0010%. Preferably, the N content is 0.0030% or more, and more preferably 0.0050% or more.

Cu: 0.010-5.00%
Cu is an element that forms a sulfide like Mn, and is a particularly important element. If the Cu content is too large, Cu forms a solid solution in the steel sheet, and the solute Cu causes embrittlement of the steel sheet during hot rolling. Therefore, the upper limit of the Cu content is set to 5.00%. Preferably, the Cu content is at most 3.00%, more preferably at most 1.00%. On the other hand, if the Cu content is too small, other fine sulfides such as TiS precipitate and cause iron loss deterioration. Therefore, it is necessary to set the lower limit of the Cu content to 0.010%. Preferably, the Cu content is at least 0.10%, more preferably at least 0.50%.

The non-oriented electrical steel sheet according to the present embodiment basically contains the above-mentioned chemical components, and the balance consists of Fe and impurities. However, in order to further improve magnetic properties, improve properties required for structural members such as strength, corrosion resistance and fatigue properties, improve castability and sheet passing properties, and improve production by using scrap, Mo, W, In, and the like are used. , Sn, Bi, Sb, Ag, Te, Ce, V, Cr, Co, Ni, Se, Re, Os, Nb, Zr, Hf, Ta, Y, La, etc. You may make it contain in the following ranges. Further, even if these elements are mixed in a range of 0.5% or less in total, the effect of the present embodiment is not impaired.
Since sulfide-forming elements such as Mg, Ca, Zn, and Ti affect the precipitation temperature of Cu sulfide, the total content is preferably 0.1% or less.

Next, the state of Cu sulfide, which is an important control factor in the non-oriented electrical steel sheet according to the present embodiment, will be described.
It is difficult to completely eliminate the presence of Cu sulfide in a steel sheet. Therefore, in the non-directional electromagnetic according to the present embodiment, in addition to positively depositing S as Cu sulfide, the Cu sulfide to be deposited is preferably controlled by performing composite precipitation using AlN as a precipitation nucleus. Iron loss.
The ease of complex precipitation of Cu sulfide and AlN is determined by the crystal structure of the precipitation nucleus AlN, that is, the periodicity of the atomic arrangement. That is, when the crystal system of AlN is Hexagonal, AlN functions most effectively as a precipitation nucleus of Cu sulfide. Note that the crystal system of Cu sulfide that is compositely precipitated with AlN (Hexagonal) is Cubic, and the crystal structure can be identified by X-ray diffraction (XRD).

In the non-oriented electrical steel sheet according to the present embodiment, for example, when X-ray diffraction (XRD) by Cu-Kα radiation is performed on the electrolytic extraction residue of the steel sheet, AlN at 2θ = 33.5 ° ± 3 ° is obtained. Hexagonal's 100 diffraction intensity, I _{2θ = 33.5} , and 2θ = 32.1 ° ± 3 °, 200 diffraction intensity of Cu sulfide (Cubic) at _{2θ = 32.1 = 22.1} Is controlled to satisfy the condition of
I _{2θ = 32.1} / I _{2θ = 33.5} ≧ 0.01 Expression 1

In XRD diffraction, a diffraction peak is observed at a specific 2θ position according to the crystal structure of the sample. However, the crystal lattice of the precipitate in the steel material fluctuates due to various factors such as a solid solution of Fe to the precipitate and lattice matching with the base iron matrix. Accordingly, the value of 2θ at which 100 diffractions derived from AlN (Hexagonal) and 200 diffractions derived from Cu sulfide (Cubic) appear, includes at least ± 3 ° within an error range. The identification of the crystal structure may be performed using JCPDS-CARD, which is a database of crystal lattices. For AlN (Hexagonal), JCPDS-CARD: 087-1054 or 025-1133, and for Cu sulfide (Cubic), JCPDS-CARD. CARD: 00-012-0174, 00-024-0061, 023-0962, 053-0522, 33-0491, 33-0492, 070-9133, etc., which are within the error range of 2θ ± 3 °. Are precipitates from which the effects of the present invention can be obtained. In addition to the above, the effects of the present invention can be naturally enjoyed with AlN (Hexagonal) or Cu sulfide (Cubic) that falls within an error range of 2θ ± 3 °.
In particular, in Cu sulfide, Fe and S are partially substituted, so that Cu9Fe9S16 (JCPDS: 00-027-0165), Cu5FeS4 (JCPDS: 024-0050, 089-2620), CuFe2S3 (JCPDS: 027-0166), Although precipitates such as CuFeS2 (JCPDS: 075-0253, 041-1404) are formed, the crystal system of such a Cu-Fe-S-based compound is Cubic, and 2θ = 32.1 ° ± 3. If 200 diffraction peaks are observed at °, it can be defined as _{I2θ = 32.1} . When two or more diffraction peaks are present for Cu sulfide (Cubic) in the above error range, the sum of the peak intensities is defined as _{I2θ = 32.1} .

Generally, the XRD diffraction intensity is the height from the background to the peak of the spectrum. Ideally, the background intensity is sufficiently low and there is no need to remove the background intensity. However, when the diffraction intensity from the precipitate is weak, the background intensity may be relatively high. In such a case, as described in Non-Patent Documents 3 and 4, it is necessary to remove the background using XRD analysis software, and the XRD diffraction intensity (peak intensity) in the present embodiment is similarly reduced by software. Was used to remove the background.
In addition, since there is an optimal balance between the amount of AlN deposited and the amount of Cu sulfide deposited, I _{2θ = 32.1} / I _{2θ = 33.5} is more preferably 0.5 or more and 25 or less. A more preferred range is from 2 to 10.

In addition, in the non-directional electromagnetic according to the present embodiment, Cu sulfide and AlN are compositely precipitated to improve iron loss, but in order to further enjoy this effect, Cu and Al are contained in the steel sheet. It is preferable that precipitates having a diameter of 5 to 1000 nm exist in a number density per unit area (area density) of 0.01 to 80 / μm ² .
If the number density of the precipitates is less than 0.01, the effect may not be sufficiently obtained. On the other hand, when the number density exceeds 80 particles / μm ² , the grain growth property is deteriorated, and the magnetic flux density may be deteriorated. Preferably, the precipitate has a number density (area density) of 0.5 to 20 / μm ² , more preferably 1 to 5 / μm ² .

  The observation of the precipitate containing Cu and Al may be performed by a TEM (transmission electron microscope) or a SEM (scanning electron microscope). The constituent elements of the precipitate can be identified by EDS analysis. Specifically, when EDS analysis was performed on the target precipitate, the Al-Kα ray was located at the energy of 1.5 ± 0.2 kev on the horizontal axis of the spectrum, and the Cu- ray was located at the location of 8.0 ± 0.2 kev on the horizontal axis of the spectrum. It is sufficient that Kα rays are simultaneously detected. Element identification may be performed by Lα ray or Kγ ray in addition to Kα ray. However, when an extracted replica is used as an observation sample of TEM-EDS, it is necessary to separate signals of Cu sulfide and the replica mesh, and therefore, the use of Cu mesh must be avoided. Further, it is known that a small amount of Mn or Fe is dissolved in Cu sulfide, and even if an EDS signal of Mn-Kα or Fe-Kα is detected from Cu sulfide as a result of EDS analysis, the effect of the present invention is obtained. Do not lose.

Next, a method for manufacturing the non-oriented electrical steel sheet according to the present embodiment will be described.
The non-oriented electrical steel sheet according to the present embodiment is melted in a converter in the same manner as a normal electrical steel sheet so as to have the component composition described above, and into a continuously cast steel piece, hot-rolled, hot-rolled sheet annealing, It can be manufactured by performing cold rolling, finish annealing, and the like.

The hot rolling is not particularly limited, and the iron loss improving effect can be enjoyed irrespective of a hot rolling method such as direct feeding hot rolling or continuous hot rolling and a slab heating temperature.
There is no particular limitation on the cold rolling, and the effect of improving iron loss can be enjoyed regardless of the cold rolling method such as cold rolling twice or more and the cold rolling reduction ratio.
Further, in addition to these steps, an insulating film forming step, a decarburizing step, or the like may be performed. In addition, there is no problem in manufacturing a thin strip by a rapid solidification method, a thin slab that omits a hot rolling step, a continuous casting method, or the like instead of a normal step.

However, when obtaining the non-oriented electrical steel sheet according to the present embodiment, it is important to undergo a heat history as described below in the finish annealing step. That is, control is performed so that Cu sulfide is entirely dissolved in the finish annealing step, and composite precipitation of Cu sulfide and AlN is performed during cooling in the finish annealing step.
Hereinafter, each condition of the finish annealing step and the hot-rolled sheet annealing step performed as necessary will be described in detail.

  In the present invention, the following six temperatures T1 to T6 ° C. are important. T1 ° C. is a solid solution start temperature of Cu sulfide, and T2 ° C. is a solid solution start temperature of AlN (Hexagonal). T3 ° C. is the upper limit temperature at which Cu sulfide precipitates, and T4 ° C. is the lower limit temperature at which Cu sulfide precipitates. T5 ° C. is the upper limit temperature at which AlN (Hexagonal) precipitates, and T5 ° C. is the lower limit temperature at which AlN (Hexagonal) precipitates.

T1 = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-273 ... Formula 2
T2 = 10000 / (3.5-log ₁₀ ([% Al] × [% N]))-273 ... Equation 3
T3 = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-323 ... Equation 4
T4 = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-423 ... Equation 5
T5 = 10000 / (3.5 log ₁₀ ([% Al] × [% N]))-923 ... Equation 6
T6 = 10000 / (3.5 log ₁₀ ([% Al] × [% N]))-523 ... Formula 7
Here, [% Cu] is the content in mass% of Cu, [% S] is the content in mass% of S, [% Al] is the content in mass% of Al, and [% N] is This is the content of N in mass%.
Hereinafter, a sulfide control method based on these temperatures will be described.

In the non-oriented electrical steel sheet according to the present embodiment, Cu sulfide and AlN are precipitated in combination to obtain an effect of improving iron loss.
In general, Cu sulfide has a high precipitation rate, and even if it is solid-dissolved by finish annealing, it precipitates finely alone during subsequent cooling, adversely affecting iron loss. However, if AlN (Hexagonal) is present at the start of cooling, Cu sulfide undergoes complex precipitation with AlN as a nucleus during cooling, so that fine precipitation can be suppressed. Moreover, good iron loss can be obtained when the composite precipitate (Cu sulfide + AlN) is present. For this reason, it is necessary to keep AlN present at the start of cooling by controlling the holding temperature of the finish annealing to a temperature range in which AlN does not form a solid solution while dissolving Cu sulfide.

  That is, in the finish annealing step, by holding Cu sulfide at a solid solution temperature T1 ° C. or higher for 10 seconds or more, it becomes possible to form a solid solution of Cu sulfide in its entirety. If the holding temperature is lower than T1 ° C., Cu sulfide cannot be dissolved. However, when the temperature of the steel sheet exceeds the melting temperature T2 ° C. of AlN, AlN which is a precipitation nucleus of Cu sulfide disappears, and the effect of the present invention cannot be enjoyed. Therefore, the upper limit of the holding temperature is T2 ° C.

  Further, the holding time of the finish annealing (the stay time between T1 ° C. and T2 ° C.) is set to 10 seconds or more and 3600 seconds or less. If the holding time is less than 10 seconds, the solid solution of Cu sulfide will not sufficiently proceed. On the other hand, if it is maintained for more than 3600 seconds, other fine sulfides such as TiS having a low deposition rate are generated, which adversely affects iron loss improvement. Therefore, a preferable holding time is 100 seconds or more and 1000 seconds or less.

  Control of the cooling rate in the finish annealing step is also an important control factor in the present invention. If the cooling rate is too low, Cu sulfide does not precipitate with AlN, but precipitates independently, and the effects of the present invention cannot be enjoyed. Therefore, it is necessary to rapidly cool at a rate of 20 ° C./sec or more in the temperature range of T3 ° C. or less and T4 ° C. or more, which is the precipitation temperature range of Cu sulfide. However, if the cooling rate exceeds 200 ° C./sec, there is a concern that cooling strain may be introduced into the steel sheet. Therefore, it is necessary to control the cooling rate in the temperature range of T3 ° C. or lower and T4 ° C. or higher to 20 ° C./second or more and 200 ° C./second or less. Preferably it is 50 ° C./sec or more and 100 ° C./sec or less.

In the present invention, AlN (Hexagonal) is actively utilized as a precipitation nucleus of Cu sulfide. Therefore, it is preferable to deposit as much as possible AlN having a hexagonal crystal structure. However, the crystal structure of AlN in the hot-rolled sheet has various forms as well as hexagonal.
Therefore, in the hot-rolled sheet annealing step, all the AlN is dissolved, and in the subsequent heating step of the finish annealing, the residence time in the above-mentioned temperature range of T5 ° C. or more and T6 ° C. or less is obtained, so that the crystal structure is increased. Hexagonal AlN can be more precipitated. Therefore, the temperature of the hot-rolled sheet annealing is preferably set to be equal to or higher than the melting start temperature T2 ° C. of AlN.
If the holding time in the hot-rolled sheet annealing is less than 10 seconds, the solid solution of AlN does not sufficiently proceed. On the other hand, if it is held for more than 3600 seconds, other nitrides such as TiN are finely precipitated and cause iron loss deterioration. Therefore, the holding time in the hot-rolled sheet annealing is preferably set to 10 seconds or more and 3600 seconds or less. In order to prevent the precipitation of nitride such as TiN while ensuring the solid solution of AlN, the holding time is preferably 30 seconds or more and 1000 seconds or less.

  In the temperature raising step of the finish annealing, Cu sulfide and AlN are combined by gradually heating at a heating rate of 100 ° C./second or less in a temperature range of T5 to T6 ° C., which is a precipitation temperature range of AlN (hexagonal). Precipitates. However, if the heating rate is less than 10 ° C./second, AlN itself precipitates in a fine state, and the grain growth of the steel sheet is suppressed. Therefore, the heating rate needs to be 10 ° C./sec or more and 1000 ° C./sec or less. Preferably it is 30 ° C./sec or more and 500 ° C./sec or less. Also in a process not involving hot-rolled sheet annealing, it is effective to control the heating rate to 10 ° C./sec or more and 1000 ° C./sec or less in the temperature raising step of the finish annealing. This is considered to be because AlN is dissolved even by slab heating.

  In order to further improve iron loss, it is important to control the cooling rate so that precipitates do not reprecipitate during cooling in the hot-rolled sheet annealing step. If the cooling rate is low, nitrides other than AlN are precipitated and the solid solution of N is consumed, so that the number of AlN, which is a precipitation site of Cu sulfide, itself decreases. Therefore, in the hot-rolled sheet annealing step, after holding at a temperature of T2 ° C. or more for 10 seconds or more and 3600 seconds or less, the cooling rate in the temperature range defined by the above T5 to T6 (° C) is set to 10 ° C / second or more. preferable. In the finish annealing, the cooling rate was required to be 20 ° C./second or more in order to suppress the precipitation of Cu sulfide alone, because the precipitation rate of Cu sulfide was faster than that of nitride. Suppression of nitride precipitation of 10 ° C./sec or more is sufficient. However, if the cooling rate exceeds 200 ° C./second, the shape of the steel sheet deteriorates due to cooling strain, and it becomes difficult to perform subsequent cold rolling. Therefore, the cooling rate must be controlled between 10 ° C./sec and 200 ° C./sec. Preferably, it is 30 ° C./sec or more and 100 ° C./sec or less.

  In general, the better the consistency between the precipitate and the steel interface, the smoother the domain wall movement and the better the iron loss. Cu sulfide alone and extremely finely (<5 nm) adversely affects iron loss, but in the non-oriented electrical steel sheet according to the present embodiment, Cu sulfide is finely precipitated by complex precipitation with AlN. Precipitation is avoided. Furthermore, the crystal structure of Cu sulfide becomes Cubic by complex precipitation with AlN (Hexagonal). Cu sulfide (Cubic) has good periodicity of the atomic arrangement at the interface with the steel, that is, good matching of the crystal lattice. Therefore, in the non-oriented electrical steel sheet according to the present embodiment, domain wall movement is easy, It is considered to show good iron loss.

Hereinafter, the technical contents of the present invention will be further described with reference to examples of the present invention. It should be noted that the conditions in the following examples are one condition examples adopted for confirming the operability and effects of the present invention, and the present invention is not limited to these one condition examples. Further, the present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
In addition, the underline in the table used in the following description shows that it is out of the range of the present invention.

<Example 1>
The ingots of the components shown in Table 1 were melted in vacuum, and the ingot was heated at 1150 ° C., hot-rolled at a hot-rolling finishing temperature of 875 ° C. and a winding temperature of 630 ° C. did. Thereafter, hot-rolled sheet annealing was performed at T2 + 30 ° C. for 200 seconds. In the furnace cooling process after hot-rolled sheet annealing, the cooling rate between T5 and T6 ° C was set at 8 ° C / sec. Thereafter, the sheet was pickled and then cold-rolled at a reduction of 75% to obtain a cold-rolled steel sheet having a sheet thickness of 0.50 mm. Subsequently, finish annealing was performed at T1 + 30 ° C. for 200 seconds. At a temperature rise from room temperature, the heating rate between T5 and T6 ° C was 25 ° C / sec, and in the furnace cooling process after finish annealing, the cooling rate between T3 and T4 ° C was 40 ° C / sec.

Table 2 shows the results of the X-ray diffraction and the results of the magnetic characteristics (magnetic flux density and iron loss). In the table, “I _CuS / I _AlN ” indicates I _{2θ = 32.1} / I _{2θ = 33.5} .

According to the iron loss, VG: very excellent, G: excellent, F: effect was observed, and B: the conventional level was evaluated. The evaluation of the magnetic properties was performed according to JIS C 2550: 2000. No strain relief annealing was performed. Regarding iron loss, W15 / 50 (W / kg) was evaluated. W15 / 50 is an iron loss at a frequency of 50 Hz and a maximum magnetic flux density of 1.5T. The magnetic flux density was evaluated using B50. B50 indicates a magnetic flux density at a magnetic field strength of 5000 A / m. In addition, the minimum target value of B50 was set to 1.50T which is equivalent to the conventional material.
The evaluation criteria for iron loss of the sample were as follows.
VG (VeryGood): W15 / 50 (W / kg) <2.20
G (Good): 2.20 ≦ W15 / 50 (W / kg) ≦ 2.50
F (Fair): 2.50 <W15 / 50 (W / kg) ≦ 4.50
B (Bad): 4.50 <W15 / 50 (W / kg)

  For X-ray diffraction, a sample obtained by collecting only inclusions with a filter by a general extraction residue method described in Non-Patent Documents 5 to 7 was used as an analysis sample. The XRD measurement was performed by wide-angle X-ray diffraction using CuKα radiation described in Non-Patent Documents 4 to 6 as a probe.

<Example 2>
The ingots of the components shown in Table 1 were melted in vacuum, and the ingot was heated at 1150 ° C., hot-rolled at a hot-rolling finishing temperature of 875 ° C. and a winding temperature of 630 ° C. did. Thereafter, hot-rolled sheet annealing was performed at T2 + 30 ° C. for 200 seconds. In the furnace cooling process after the hot-rolled sheet annealing, the cooling rate between T5 and T6 ° C was set to 50 ° C / sec. Thereafter, the sheet was pickled and then cold-rolled at a reduction of 75% to obtain a cold-rolled steel sheet having a sheet thickness of 0.50 mm. Subsequently, finish annealing was performed at T1 + 30 ° C. for 200 seconds. At a temperature rise from room temperature, the heating rate between T5 and T6 ° C was 40 ° C / sec, and in the furnace cooling process after finish annealing, the cooling rate between T3 and T4 ° C was 75 ° C / sec.
Table 3 also shows the results of X-ray diffraction, the precipitation state of precipitates, and the evaluation results of magnetic properties (magnetic flux density and iron loss). For the measurement of X-ray diffraction and magnetic properties, the same evaluation as in <Example 1> was performed. The precipitates were observed by etching a section perpendicular to the rolling direction of the steel sheet and observing by SEM. At that time, 10 visual fields of 100 μm ² were observed. The number obtained by dividing the observed total number of precipitates containing Al and Cu by 1000 (100 μm ² × 10 visual fields) was defined as the number of precipitates per 1 μm ² , that is, areal density.

  No. Nos. c1 to c3 are all examples of the invention. No. c1 has a large area density of the precipitate. The iron loss was slightly inferior to the invention examples C1 to C6. On the other hand, No. Nos. c2 and c3 have low areal densities of the precipitates. Iron loss was slightly inferior to the invention examples C1 to C6.

<Example 3>
The steel No. shown in Table 1 was used. The ingot having the components of A1, A17 and A18 was heated at 1100 ° C., and hot rolled so that the finishing temperature was 850 ° C. and the winding temperature was 630 ° C. to obtain a hot rolled sheet having a sheet thickness of 2.0 mm. After that, cold rolling was performed at a rolling reduction of 75% after pickling to obtain a cold-rolled steel sheet having a sheet thickness of 0.50 mm, and finish annealing was performed under the conditions shown in Table 4. Table 4 also shows the results of X-ray diffraction, the precipitation state of precipitates, and the evaluation results of magnetic properties (magnetic flux density and iron loss). X-ray diffraction, measurement of magnetic properties, and measurement of precipitates were evaluated in the same manner as in Example 1.

The conditions of the finish annealing were out of the range of the present invention. In all of d1 to d5, I _CuS / I _AlN was small and the precipitate density could not be sufficiently secured, so that iron loss was deteriorated.

<Example 4>
The steel No. shown in Table 1 was used. The ingot having the components of A1, A17 and A18 was heated at 1100 ° C., and hot rolled so that the finishing temperature was 850 ° C. and the winding temperature was 630 ° C. to obtain a hot rolled sheet having a sheet thickness of 2.0 mm. Among the hot rolled sheets, No. For E1 to E7, hot-rolled sheet annealing was performed under the conditions shown in Table 5.
Then, after pickling, it was cold-rolled at a rolling reduction of 75% to obtain a cold-rolled steel sheet having a sheet thickness of 0.50 mm. A1 is 950 ° C., steel No. About A17, 1050 degreeC, steel No. For A18, finish annealing was performed at 1100 ° C. for 60 seconds. The heating rate between T5 and T6 ° C. in the finish annealing is as shown in Table 5, and in the furnace cooling process after the finish annealing, the cooling rate between T3 and T4 ° C. was 40 ° C./sec.
Table 5 also shows the results of X-ray diffraction, the precipitation state of precipitates, and the evaluation results of magnetic properties (magnetic flux density and iron loss). X-ray diffraction, measurement of magnetic properties, and measurement of precipitates were evaluated in the same manner as in Example 1.

No. Regarding any of the samples E1 to E7, the effects of the present invention were obtained because the temperature, time, and cooling rate of the finish annealing were within the range of the present invention. In particular, the heating rate between T5 and T6 ° C. in the finish annealing was controlled in a preferable range. In E6 and E7, the areal densities of I _CuS / I _AlN and the precipitates were also controlled in the preferred ranges, and were particularly good. No. In E1 to E7, the effect of precipitating more AlN was obtained by controlling the heating rate of the finish annealing.

<Example 5>
The steel No. shown in Table 1 was used. The ingot having the components of A1, A17 and A18 was heated at 1100 ° C., and hot rolled so that the finishing temperature was 850 ° C. and the winding temperature was 630 ° C. to obtain a hot rolled sheet having a sheet thickness of 2.0 mm. The hot-rolled plate was subjected to hot-rolled sheet annealing under the conditions shown in Table 6. After that, it is cold-rolled at a rolling reduction of 75% after pickling to obtain a cold-rolled steel sheet having a sheet thickness of 0.50 mm. Was carried out. In the furnace cooling process after the finish annealing, the cooling rate between T3 and T4C was 40C / sec.
Table 6 also shows the results of X-ray diffraction, the precipitation state of precipitates, and the evaluation results of magnetic properties (magnetic flux density and iron loss). X-ray diffraction, measurement of magnetic properties, and measurement of precipitates were evaluated in the same manner as in Example 1.

  No. Good iron loss was obtained for any of the samples F1 to F10. The cooling rate in the hot-rolled sheet annealing step and the heating rate in the finish annealing were controlled in preferred ranges. In F5 to F6, particularly good iron loss was obtained. Then, the cooling rate in the hot-rolled sheet annealing step and the heating rate in the temperature-raising step in the finish annealing were within the ranges of the present invention. Good iron loss was obtained in F9 to F10. No. F5 to F6, No. Excellent iron loss was secured in F9 to F10 by controlling the cooling rate of hot-rolled sheet annealing to be within a preferable range, thereby avoiding precipitation of nitrides other than AlN and heating the finish annealing. This is because Cu sulfide and AlN were efficiently precipitated in a complex manner by controlling the rate in a preferable range, and the cooling rate of hot-rolled sheet annealing and the heating rate of finish annealing were not in the preferable ranges. Iron loss was superior to F1 to F4, 7, and 8.

Claims (2)

In mass%, C: 0.0001 to 0.01%, Si: 0.05 to 7.0%, Mn: 0.02 to 3.0%, Al: 0.002 to 3.0%, S: 0.0005 to 0.05%, P: 0.002 to 0.15%, N: 0.0010 to 0.0100%, Cu: 0.010 to 5.00%, the balance being Fe and impurities I _{2θ = 33.5} , 2θ = _32.3 , which is the diffraction intensity of aluminum nitride having a hexagonal structure appearing at 2θ = 33.5 °, which is obtained by X-ray diffraction of the electrolytic extraction residue . I _{2θ = 32.1} , which is the diffraction intensity of Cu sulfide having a Cubic structure appearing at 1 °, is a method for producing a non-oriented electrical steel sheet satisfying the condition of the following formula 1,
In mass%, C: 0.0001 to 0.01%, Si: 0.05 to 7.0%, Mn: 0.02 to 3.0%, Al: 0.002 to 3.0%, S: 0.0005 to 0.05%, P: 0.002 to 0.15%, N: 0.0010 to 0.0100%, Cu: 0.010 to 5.00%, the balance being Fe and impurities Hot rolling on a steel slab having a chemical composition consisting of:
Hot-rolled sheet annealing step of annealing the hot-rolled steel sheet,
Pickling step of pickling the hot-rolled steel sheet after the hot-rolled sheet annealing step,
A cold rolling step of performing cold rolling on the hot rolled steel sheet after the pickling step to obtain a cold rolled steel sheet,
A finish annealing step of annealing the cold-rolled steel sheet,
In the manufacturing process of non-oriented electrical steel sheet having
In the hot-rolled sheet annealing step, holding at T2 ° C. or more shown in the following formula 3 for 10 to 3600 seconds,
In the finish annealing step, when the temperature is raised from room temperature to T1 ° C. or more and T2 ° C. or less shown in the following formula 2, average heating in a temperature range of T5 ° C. or more shown in the following formula 6 and T6 ° C. or less shown in the following formula 7 The speed is set to 10 ° C./sec or more and 1000 ° C./sec or less, the holding is performed at the T1 ° C. or more and the T2 ° C. or less for 10 to 3600 seconds. A method for producing a non-oriented electrical steel sheet, wherein the average cooling rate in a temperature range of T4 ° C. or higher is set to 20 ° C./sec or more and 200 ° C./sec or less.
I _{2θ = 32.1} / I _{2θ = 33.5} ≧ 0.01 Expression 1
T1 = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-273 ... Formula 2
T2 = 10000 / (3.5-log ₁₀ ([% Al] × [% N]))-273 ... Equation 3
T3 = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-323 ... Equation 4
T4 = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-423 ... Equation 5
T5 = 10000 / (3.5 log ₁₀ ([% Al] × [% N]))-923 ... Equation 6
T6 = 10000 / (3.5 log ₁₀ ([% Al] × [% N]))-523 ... Formula 7
Here, [% Cu] is the content in mass% of Cu, [% S] is the content in mass% of S, and [% Al] is the content in mass% of Al [% N] is N Is the content in mass%.   In the hot-rolled sheet annealing step, in the cooling after the holding at the T2 ° C or higher, the average cooling rate in the temperature range of the T5 ° C or higher and the T6 ° C or lower is 10 ° C / second or more and 200 ° C / second or less. The method for producing a non-oriented electrical steel sheet according to claim 1, wherein: