BR112020016869B1 - NON-ORIENTED ELECTRIC STEEL SHEET - Google Patents

Abstract

The present invention relates to a non-oriented electrical (electromagnetic) steel sheet comprising a silicon steel sheet and an insulating coating. When the thickness of the silicon steel sheet is t, PDR (PDR = (maximum value ? minimum value) / minimum value x 100), which represents the ratio of the maximum value to the minimum value of the density of AlN precipitates in the three locations that are 1/10t, 1/5t and 1/2t from the surface in the direction of the silicon steel sheet thickness is 50% or less.

Description

Technical field

[001] The present invention relates to a non-oriented electrical (electromagnetic) steel sheet.

[002] Priority is claimed over Japanese Patent Application No. 2018-056310, registered on March 23, 2018, and the content of which is incorporated herein by reference.

Background of the technique

[003] In recent years, especially in the field of electrical equipment such as rotating machines, small and medium-sized transformers, and electrical components, it is required that the motor has its efficiency increased and its size reduced, due to the environmental conservation movement global power represented by global power reduction, energy savings, and reduction of CO2 emissions. Under the social situation, improving the performance of non-oriented electrical steel sheet used as motor core material is required.

[004] For example, in the automotive field, non-oriented electrical steel sheet is used as a drive motor core for hybrid vehicles (HEV: Hybrid Electric Vehicle) and the like. Furthermore, it is required to reduce the size of the drive motor used in the HEV to save installation space and to reduce fuel consumption by reducing weight.

[005] To reduce the size of the drive motor, it is necessary to increase the motor torque. Therefore, it is also necessary to improve the magnetic flux density of the non-oriented electrical steel sheet.

[006] In addition, since the capacity of the battery that can be mounted in the automobile is limited, it is necessary to reduce energy loss in the engine. Therefore, it is also necessary to reduce the iron loss of the non-oriented electrical steel sheet.

[007] In addition, electrical steel sheet is often used after being formed into the desired shape and having undergone heat treatment. Representatively, “strain relief annealing (SRA)” is known. For example, when the steel sheet is subjected to a punching process to be formed into electrical materials, deformation is inevitably introduced into the steel sheet, and thus the iron loss deteriorates. SRA is heat treatment to finally remove unnecessary deformation of steel plate. This heat treatment is conducted to parts cut from the steel sheet (sheet steel blank) or engine core (e.g. stator core) into which the parts are rolled.

[008] However, strain relief annealing (SRA) has the effect of improving iron loss by strain relief but, at the same time, causes a decrease in magnetic flux density by the development of crystal orientation unfavorable to the characteristics magnetic. Therefore, in a case where excellent magnetic characteristics are required, it is necessary to suppress the decrease in magnetic flux density caused by strain relief annealing (SRA).

[009] In view of the situations mentioned above, to improve the magnetic characteristics of the non-oriented electrical steel sheet, various efforts have been made, for example, controlling the metallic structure such as grain size and crystal orientation in the steel sheet. steel, control of precipitates, etc. (e.g. Patent Documents 1 to 13).

Related Art Documents Patent Documents

[010] [Patent Document 1] Unexamined Japanese Patent Application, First Publication No. H05-279740

[011] [Patent Document 2] Unexamined Japanese Patent Application, First Publication No. H06-306467

[012] [Patent Document 3] Unexamined Japanese Patent Application, First Publication No. 2002-348644

[013] [Patent Document 4] Unexamined Japanese Patent Application, First Publication No. 2011-111658

[014] [Patent Document 5] Unexamined Japanese Patent Application, First Publication No. 2006-045613

[015] [Patent Document 6] Unexamined Japanese Patent Application, First Publication No. 2006-045641

[016] [Patent Document 7] Unexamined Japanese Patent Application, First Publication No.2006-219692

[017] [Patent Document 8] Unexamined Japanese Patent Application, First Publication No. S58-23410

[018] [Patent Document 9] Unexamined Japanese Patent Application, First Publication No. H11-124626

[019] [Patent Document 10] PCT International Publication No. WO2012/029621

[020] [Patent Document 11] PCT International Publication No. WO2016/136095

[021] [Patent Document 12] Unexamined Japanese Patent Application, First Publication No. H03-223424

[022] [Patent Document 13] PCT International Publication No. WO2014/129034

Summary of the invention Technical problem to be resolved

[023] Patent Document 1 describes a non-oriented electrical steel plate obtained through processes such that a steel strip with specific chemical composition including 4.0% < Si < 8.0% and Al < 2.0% in mass % it is cold rolled under reduction of 5% or more and less than 40%.

[024] Patent Document 2 describes a non-oriented electrical steel plate obtained through processes such that a steel strip with a specific chemical composition including Si < 4.0% and Al < 2.0% in mass % is cold rolled under reduction of 5% or more and less than 40%.

[025] However, the non-oriented electrical steel sheets described in Patent Documents 1 and 2 do not meet the level required for the HEV drive motor core in which excellent magnetic characteristics are required.

[026] Patent Document 3 describes a non-oriented electrical steel sheet in which the chemical composition includes Si < 4.0% and the like, the B25 magnetic flux density under magnetic field strength of 2500 A/m is 1 .70 T or more, and the B50 magnetic flux density under magnetic field strength of 5000 A/m is 1.80 T or more. However, the non-oriented electrical steel sheet described in Patent Document 3 limits the Al content to 0.5% by mass or less so as not to adversely affect the improvement of magnetic flux density (B25) in the lower magnetic field and thus , the electrical steel sheet does not meet the required level as excellent magnetic characteristics.

[027] Patent Document 4 describes a non-oriented electrical steel sheet that is produced under specific conditions so that the chemical composition includes 0.1% < Si < 2.0%, Al < 1.0%, and the like , and the end temperature of the final hot rolling is 550 to 800°C. However, electrical steel plate limits the Al content to 1.0% by mass or less, and thus does not meet the required level of excellent magnetic characteristics. Furthermore, even when hot rolling is conducted under low temperature such as 500 to 850°C, the expected effect is not obtained.

[028] Patent Documents 5 to 7 describe a non-oriented electrical steel sheet in which the chemical composition includes 0.05 to 4.0% by mass (or 4.5% by mass) Si, 3.5% in mass or less of Al, and the like, the magnetic characteristics along the direction making an angle of 45° with the rolling direction are excellent, and the in-plane anisotropy is small.

[029] However, the techniques described in Patent Documents 5 to 7 are similar to that of Patent Document 4 in which hot rolling is conducted at a lower temperature of the order of 500 to 850°C. Even when hot rolling is conducted at a lower temperature, the expected effect is not obtained, and the electrical steel sheets do not satisfy the required level of excellent magnetic characteristics. Furthermore, the techniques described in Patent Documents 5 to 7 do not satisfy the level required for high frequency iron loss.

[030] Patent Document 8 describes a technique for improving magnetic characteristics by controlling the final annealing heating rate to 10°C/s or more for steel sheet with chemical composition including 2.5% or more of Si and 1.0% or more of Al in mass %. However, in the present process based on continuous annealing, the heating rate as mentioned above may be in the common technical range.

[031] Patent Document 9 describes a technique for preventing iron loss from deterioration by decreasing the final annealing heating rate to 40°C/s, because iron loss deteriorates when the heating rate of the final annealing Final annealing is excessively fast.

[032] Patent Document 10 describes a technique for increasing magnetic flux density by controlling texture by drastically increasing the final annealing heating rate to 100°C/s. However, when the heating rate is simply increased, the magnetic characteristics may become unstable.

[033] Patent Document 11 describes a technique for preventing the magnetic flux density from being unstable by optimizing the heating rate in the respective temperature ranges of 600 to 700°C and 700 to 760°C, because the flux density magnetic becomes unstable when the final annealing heating rate is fast.

[034] Patent Documents 12 and 13 describe techniques relating to semi-processed non-oriented electrical steel sheets. Semi-processed non-oriented electrical steel sheets are transported under such a condition that deformation is introduced into the recrystallized steel sheet after final annealing, and then subjected to heat treatment by the user of the steel sheet to alleviate the deformation and control the magnetic characteristics .

[035] In particular, Patent Document 12 shows that it is effective to control the heating rate of the final annealing to 5 to 40 ° C / s in consideration of Al nitrides. In addition, Patent Document 13 describes a technique for improve the magnetic characteristics for semi-processed electrical steel sheets by increasing the heating rate up to 740°C to 100°C/s or more for low Al steel.

[036] However, conventional techniques have not been able to sufficiently satisfy the above-mentioned needs such as high frequency characteristics and magnetic characteristics after strain relief annealing (SRA) in the current market.

[037] As described above, the non-oriented electrical steel sheets described in Patent Documents 1 to 13 are not capable of sufficiently satisfying the required magnetic characteristics.

[038] Since conventional non-oriented electrical steel sheets do not sufficiently meet the required level of excellent magnetic characteristics, improvement of magnetic characteristics is also required.

[039] The present invention was made in consideration of the situations mentioned above. An object of the present invention is to provide a non-oriented electrical steel sheet with small change in B50 magnetic flux densities before and after strain relief annealing (SRA).

Solution to the problem

[040] The present inventors made an in-depth investigation to resolve the situations mentioned above. As a result, it was found that when AlN uniformly precipitates on the base steel sheet (silicon-based sheet) along the thickness direction, the magnetic characteristics tend not to deteriorate even when strain relief annealing is conducted. In particular, it was found that the changes in the magnetic characteristics before and after strain relief annealing are small relative to the three directions which are the rolling direction, the transverse direction, and the 45° rolling direction (the direction that makes an angle of 45° with the rolling direction) towards the engine core.

[041] Hereinafter, on the sheet surface, “0°” indicates the direction along the rolling direction, “90°” indicates the direction perpendicular to the rolling direction, and “45°” indicates the direction making an angle of 45° with the rolling direction.

[042] In addition, the present inventors investigated the production conditions to obtain the silicon steel sheet in which AlN precipitates uniformly along the thickness direction. As a result, it was discovered that silicon steel sheet with the above characteristic is obtained by conducting incubation treatment and controlling the heating rate of final annealing. Here, the incubation treatment is to control the temperature and time to be within a predetermined range during cooling after final hot rolling, rather than hot band annealing after final hot rolling, which is conducted to produce the conventional non-oriented electrical steel sheet.

[043] One aspect of the present invention employs the following: (1) A non-oriented electrical steel sheet in accordance with one aspect of the present invention includes a silicon steel sheet and an insulating coating, wherein

[044] the silicon steel sheet includes, as a chemical composition, in % by mass, 0.01 to 3.50% Si, 0.0010 to 2.500% Al, 0.01 to 3.00% Mn, 0.0030% or less of C, 0.180% or less of P, 0.0030% or less of S, 0.0030% or less of N, 0.0020% or less of B, and

[045] the balance consisting of Fe and impurities, and

[046] when t is the thickness of the silicon steel sheet and when PDR is defined as the following (expression 1) which indicates the relative ratio with the maximum and minimum numerical density of AlN precipitates in three areas that are the area 1/10t, area 1/5t and area 1/2t from the surface of the silicon steel sheet along the thickness direction.

[047] PDR is 50% or less.

[048] where PDR = (the maximum - the minimum) + the minimum x 100 (expression 1). (2) In non-oriented electrical steel in accordance with item (1),

[049] the silicon steel sheet includes, as a chemical composition, in mass %, at least one element selected from the group of a group consisting of 0.0500% or less of Sb, and 0.0100 to 0.2000% of Sn. (3) In non-oriented electrical steel in accordance with item (1) or (2),

[050] the silicon steel sheet includes, as the chemical composition, in mass %, at least one element selected from a group consisting of 0 to 1.00% Cu, 0 to 0.0400% REM, 0 to 0.0400% Ca, and 0 to 0.0400% Mg.

Effects of the invention

[051] According to the above aspects of the present invention, it is possible to provide non-oriented electrical steel sheet with small change in magnetic flux densities before and after strain relief annealing (SRA). In particular, it is possible to supply the non-oriented electrical steel sheet in which the difference between the magnetic flux density B50 before strain relief annealing and the magnetic flux density B50 after strain relief annealing is 0.010T or less, relative to the average of the three directions which are the rolling direction, the transverse direction, and the direction at 45° to the rolling direction.

Brief description of the drawings

[052] Fig. 1 is an illustration of a non-oriented electrical steel sheet of the cross section of a non-oriented electrical steel sheet in accordance with an embodiment of the present invention.

[053] Fig. 2 is a flowchart illustrating the production method for the non-oriented electrical steel sheet according to the embodiment.

[054] Fig. 3 is a perspective illustration showing an occurrence of the engine core.

Detailed description of preferred embodiments

[055] Hereinafter a preferred embodiment of the present invention will be described in detail. However, the present invention is not limited only to the configuration that is described in the embodiment, and various modifications are possible without departing from the aspect of the present invention. In addition, the limitation range as described below includes a lower limit and an upper limit thereof. However, the value expressed by “more than” or “less than” does not include the limitation range. ''%'' of the quantity of the respective elements expresses “% by mass.

[056] The non-oriented electrical steel sheet according to the embodiment includes a silicon steel sheet as a base steel sheet and an insulating coating arranged on the silicon steel sheet. Fig. 1 is an illustration of the cross-section of the non-oriented electrical steel sheet according to the embodiment. The non-oriented electrical steel sheet 1 according to the embodiment includes the silicon steel sheet 3 and the insulating coating 5 when viewing a cross section whose cutting direction is parallel to the thickness direction.

Non-Oriented Electrical Steel Sheet

[057] The silicon steel sheet of the non-oriented electrical steel sheet according to the modality includes, as a chemical composition, in % by mass, 0.0030% or less of C, 0.01 to 3.50% of Si, 0.0010 to 2.500% Al, 0.01 to 3.00% Mn, 0.180% or less P, 0.0030% or less S, 0.0030% or less N, 0.0020 % or less of B, and the balance consisting of Fe and impurities.

[058] In addition, in the non-oriented electrical steel sheet according to the embodiment, the difference of the B50 magnetic flux densities before and after strain relief annealing may be 0.010T or less relative to the average of the three directions which are the rolling direction, the transverse direction, and the direction at 45° to the rolling direction when the steel sheet is excited under a magnetic field strength of 5000 A/m. Details are explained below.

State of distribution of precipitates on the silicon steel sheet

[059] When t is the thickness of the silicon steel sheet in units of mm and when PDR is the relative ratio with the maximum and minimum numerical density of AlN precipitates in three areas that are a local 1/10 t to from the surface of the silicon steel sheet along the thickness direction (area 1/10t), a location 1/5t from the surface (area 1/5t), and a location 1/2t from the surface (area 1/2t), PDR is 50% or less.

[060] PDR = (the maximum number density in the three areas - the minimum number density in the three areas) + the minimum number density in the three areas x 100

[061] Specifically, when t is the thickness of the silicon steel sheet in units of mm, NDmax is the maximum numerical density of AlN in units of pieces^m2 in three areas that are the area 1/10t, the area 1/ 5t and the area 1/2t from the surface of the silicon steel sheet along the thickness direction, NDmin is the minimum number density of AlN in units of pieces^m2 in three areas, and PDR is the distribution state of AlN in % units (here, PDR = (NDmax - NDmin) + NDmin x 100),

[062] PDR is 50% or less.

[063] The upper limit of PDR is preferably 40% and more preferably 30% to control the distribution of the AlN state to be uniform. On the other hand, the PDR lower limit is not particularly limited and can be 0%. However, it is not easy to control PDR to 0%, the lower limit of PDR can be 2% and can be 5%.

[064] The recrystallized {111} grains that deteriorate the magnetic flux density tend to develop mainly in the 1/2t area, and the recrystallized {100} grains that improve the magnetic flux density tend to develop mainly in the 1/ 10t. In conventional non-oriented electrical steel sheets, since the amount of AlN is insufficient in the 1/2t area, the recrystallized {111} grains grow during strain relief annealing, and therefore the magnetic flux density deteriorates. In the embodiment, it appears that AlN should be precipitated in the 1/2t area, the growth of recrystallized {111} grains is suppressed, and thus the deterioration of magnetic flux density due to strain relief annealing is suppressed at 0.010T. Therefore, the distribution of number densities of AlN precipitates in the thickness direction is defined as PDR.

[065] AlN in silicon steel sheet can be measured by the following method. A steel sample measuring approximately 30 mm x 30 mm x 0.3 to 0.5 mm is cut from the steel plate, and its cross section is mechanically polished and chemically polished. An electron beam is irradiated on the cross section of the specimen, a characteristic X-ray is detected by microanalyzer, and thus the density of AlN is measured.

[066] Specifically, a sample measuring approximately 30 mm x 30 mm is cut from the steel plate, its thickness is reduced by mechanical polishing of the surface of the plate, and thus the area 1/10t, the area 1/5t and the area 1/2t are respectively exposed when t is the thickness of the silicon steel sheet. The exposed surfaces are chemically polished or electrolytically polished, and thus observed samples without deformation are obtained. The existence and number of AlN are confirmed by observing the samples. Densities can be obtained in units of pieces^m2 from the number of AlN existing in the observed visual field (observed area).

[067] To identify the AlN existing in the observed visual field, the precipitate in which the atomic ratio of Al and N is approximately 1:1 can be identified in the observed visual field, based on the result of the quantitative EPMA analysis (microanalyzer of electron probe). Density and PDR can be obtained by identifying the AlN existing in the observed visual field (observation area).

[068] Thin AlN, which is difficult to identify by EPMA, for example, AlN with a diameter of 300 nm or less, can be identified by TEM-EDS (Transmission Electron Microscope - Energy Dispersive X-ray Spectroscopy) . Samples for observation in a TEM (e.g., approximately 15 mm x 15 mm) are taken from the 1/10t area, the 1/5t area, and the 1/2t area. The precipitate in which the atomic ratio of Al and N is approximately 1:1 can be identified in the observed visual field based on the result of quantitative TEM-EDS analysis. Density and PDR can be obtained by identifying the AlN existing in the observed visual field (observation area).

Chemical composition of silicon steel sheet

[069] The reasons for limiting the chemical composition of the silicon steel sheet of the non-oriented electrical steel sheet according to the modality are described below. ''%'' relating to the compositions of the steel plate expresses “% by mass”.

[070] In the embodiment, the silicon steel sheet includes, as a chemical composition, basic elements, optional elements, and a balance consisting of Fe and impurities.

[071] The basic elements correspond to the main connecting elements of the silicon steel sheet. In the modality, the basic elements are Si, Al, and Mn.

[072] In addition, impurities correspond to elements that are contaminated during the industrial production of steel from ores and scrap that are used as raw materials for steel, or from the environment of the production process. For example, impurities are elements such as C, P, S, N, and B. It is preferable that the amount of impurities is limited to sufficiently obtain the effects of the modality. Furthermore, since it is preferable for the amount of respective impurities to be low, the lower limit of the respective impurities does not need to be limited, and the lower limit can be 0%.

[073] In addition, optional elements correspond to elements that can be included as a replacement for a part of Fe that is the balance. For example, optional elements are elements such as Sn, Sb, Cu, REM, Ca, and Mg. Optional elements can be included if necessary. Therefore, the lower limit of the respective optional elements does not need to be defined, and the lower limit can be 0%. Furthermore, even if optional elements can be included as impurities, the effects mentioned above are not affected.

[074] Specifically, it is preferable that the silicon steel sheet of the non-oriented electrical steel sheet according to the embodiment includes, as a chemical composition, in mass %, 0.0030% or less of C, 0.01 to 3 .50% Si, 0.0010 to 2.500% Al, 0.01 to 3.00% Mn, 0.180% or less P, 0.0030% or less S, 0.0030% or less N , 0.0020% or less B, 0 to 0.0500% Sb, 0 to 0.2000% Sn, 0 to 1.00% Cu, 0 to 0.0400% REM, 0 to 0, 0400% Ca, 0 to 0.0400% Mg, and the balance consisting of Fe and impurities.

0.0030% or less of C

[075] C (carbon) is the element that deteriorates the loss of iron and the impurity that causes magnetic aging. The C content is preferably as low as possible. Therefore, the C content must be 0.0030% or less. The upper limit of the C content is preferably 0.0025%, and more preferably 0.0020%. The lower limit of C content is not particularly limited. The C content may be 0.0001% or more in consideration of industrial purification in practice, and may be 0.0005% or more in consideration of production cost.

0.01 to 3.50% Si

[076] When the Si (silicon) content is excessive, the magnetic flux density decreases, the hardness increases, and the punching work capacity deteriorates. Furthermore, during the production process of non-oriented electrical steel plate, the operability such as cold rolling deteriorates, the production cost increases, and the possibility of fracture increases. Therefore, the upper limit of Si content should be 3.50%. The upper limit of the Si content is preferably 3.20%, and more preferably 3.00%. On the other hand, Si has the effect of reducing eddy current losses by increasing the electrical resistance of the steel sheet, and thus reducing iron loss. Therefore, the lower limit of Si content should be 0.01%. The lower limit of the Si content is preferably 0.10%, more preferably 0.50%, even more preferably 1.00%, even more preferably more than 2.00%, even more preferably 2.10% and even more preferably 2.30%.

0.0010 to 2.500% Al

[077] Al (aluminum) is inevitably contained in ores and refractories, and is also used for deoxidation. Considering the above, the lower limit of Al content should be 0.0010%. Furthermore, in common with Si, Al is the element that has the effect of reducing eddy current losses and increasing electrical resistance, and therefore reducing iron loss. Thus, Al may be contained in an amount of 0.200% or more. The Al content may preferably be greater than 0.50% and more preferably 0.60% or more. On the other hand, when the Al content is excessive, the saturation of the magnetic flux density decreases and thus the magnetic flux density decreases. Therefore, the upper limit of Al content should be 2,500%. The Al content is preferably 2,000% or less.

0.01 to 3.00% Mn

[078] Mn (manganese) reduces eddy current loss by increasing electrical resistance, and suppresses the formation of texture {111} <112> which is undesirable for magnetic characteristics. For this purpose, Mn is contained in an amount of 0.01% or more. The lower limit is preferably 0.15%, more preferably 0.40%, even more preferably more than 0.60%, and even more preferably 0.70%. However, when the Mn content is excessive, the texture changes, and the hysteresis loss deteriorates. Therefore, the upper limit of Mn content should be 3.00%. The upper limit of the Mn content is preferably 2.50% and more preferably 2.00%.

0.180% or less of P

[079] P (phosphorus) is the impurity that can increase tensile strength without decreasing magnetic flux density, but deteriorates the toughness of the steel and tends to cause the steel plate to rupture. Therefore, the upper limit of P content should be 0.180%. The P content is preferably as low as possible to suppress rupture of the steel sheet. The upper limit of the P content is preferably 0.150%, more preferably 0.120%, and even more preferably 0.080%. The lower limit of P content is not particularly limited, and can be 0.001% in consideration of the production cost.

0.0030% or less of S

[080] S (sulfur) is the impurity that suppresses recrystallization and grain growth during final annealing by the precipitation of fine sulfides such as MnS. Therefore, the S content must be 0.0030% or less. The upper limit of the S content should be 0.0020% and more preferably 0.0015%. The lower limit of S content is not particularly limited. The lower limit of S content can be 0.0001% in consideration of industrial purification in practice and can be 0.0005% in consideration of production cost.

0.0030% or less of N

[081] N (nitrogen) is the impurity that deteriorates the loss of iron through the formation of precipitates. Therefore, the N content must be 0.0030% or less. The N content is preferably 0.002% or less and more preferably 0.001% or less. The lower limit of N content is not particularly limited. The lower limit of N can be 0.0001% in consideration of industrial purification in practice and can be 0.0005% in consideration of production cost.

0.0020% or less of B

[082] B (boron) is the impurity that deteriorates the loss of iron through the formation of precipitates. Therefore, the B content must be 0.0020% or less. The B content is preferably 0.001% or less and more preferably 0.0005% or less. The lower limit of B content is not particularly limited. The lower limit of B content may be 0.0001% in consideration of industrial purification in practice and may be 0.0005% in consideration of production cost.

0 to 0.0500% Sb

[083] The addition of Sb (antimony) contributes to the suppression of surface nitridation and the improvement of iron loss. On the other hand, when the Sb content is excessive, the toughness of the steel may deteriorate. Therefore, the upper limit of Sb content should be 0.0500%. The Sb content is preferably 0.03% or less and more preferably 0.01% or less. The lower limit of Sb content is not particularly limited, and can be 0%. The Sb content may preferably be 0.001% or more to obtain the above effects.

0 to 0.2000% Sn

[084] The addition of Sn (tin) contributes to the suppression of surface nitridation and improvement of iron loss. On the other hand, when the Sn content is excessive, the toughness of the steel may deteriorate, and the insulating coating may easily delaminate. Therefore, the upper limit of Sn content should be 0.2000%. The Sn content is preferably 0.08% or less and more preferably 0.06% or less. The lower limit of Sn content is not particularly limited, and can be 0%. The Sn content may preferably be 0.01% or more to obtain the above effects. The Sn content is preferably 0.04% or more and more preferably 0.08% or more.

0 to 1.00% Cu

[085] Cu (copper) is an element that has the effects of suppressing the formation of texture {111} <112> which is undesirable for the magnetic characteristics, of suppressing oxidation of the surface of the steel sheet, and of controlling the grain growth so that it is uniform. When the Cu content exceeds 1.00%, the addition effects are saturated, grain growth during final annealing is suppressed, the workability of the steel plate deteriorates, and the steel plate becomes brittle during rolling in cold. Therefore, the Cu content must be 1.00% or less. The Cu content is preferably 0.60% or less, and more preferably 0.40% or less. The lower limit of Cu content is not particularly limited, and can be 0%. The Cu content may preferably be 0.10% or more to obtain the above effects. The Cu content is preferably 0.20% or more and more preferably 0.30% or more. 0 to 0.0400% REM 0 to 0.0400% Ca 0 to 0.0400% Mg

[086] REM (rare earth metal), Ca (calcium), Mg (magnesium) are the elements that have the effect of fixing sulfides or oxysulfides, of suppressing the precipitation of fine MnS and the like, and of promoting recrystallization and grain growth during final annealing.

[087] When REM, Ca, and Mg exceed 0.0400%, sulfides or oxysulfides are excessively formed, and recrystallization and grain growth during final annealing are suppressed. Therefore, the REM content, Ca content, and Mg content should be 0.0400% or less respectively. The respective contents are preferably 0.0300% or less and more preferably 0.0200% or less.

[088] The lower limits of REM content, Ca content and Mg content are not particularly defined, and may be 0%. The REM content, Ca content and Mg content may preferably be 0.0005% or more to obtain the above effects. The respective contents are preferably 0.0010% or more and more preferably 0.0050% or more.

[089] Here, REM indicates a total of 17 elements of Sc, Y and lanthanides, and is at least one of them. The REM content above corresponds to the total content of at least one of these elements. Industrially, misch metal is added as lanthanide.

[090] In the embodiment, it is preferable that the silicon steel sheet includes, as a chemical composition, in % by mass, at least one element selected from the group consisting of 0.001 to 0.0500% or less of Sb, 0.01 to 0.2000% Sn, 0.10 to 1.00% Cu, 0.0005 to 0.0400% REM, 0.0005 to 0.0400% Ca, or 0.0005 to 0.0400% Mg.

[091] The chemical composition above is that of the silicon steel sheet. When the non-oriented electrical steel sheet to be sampled for measurement has the insulating coating and the like on the surface, the measurement is performed after removing the coating.

[092] As a method for removing the insulating coating and the like from the non-oriented electrical steel sheet, for example, the following method is exemplified.

[093] Initially, the non-oriented electrical steel sheet having the insulating coating and the like is immersed in an aqueous solution of sodium hydroxide, an aqueous solution of sulfuric acid, and an aqueous solution of nitric acid, in that order. The steel plate after soaking is washed. Finally the plate is dried with hot air. Therefore, it is possible to obtain the silicon steel sheet from which the insulating coating as described below is removed.

[094] The composition of steel as described above can be measured by typical analytical methods for steel. For example, the composition of steel can be measured by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometer: Inductively Coupled Plasma Emission Spectroscopy). In addition, C and S can be measured by the infrared absorption method after combustion, N can be measured by the thermal conductometric method after melting in an inert gas stream, and O can be measured, for example, by the absorption method. non-scattered infrared light after fusion in an inert gas stream.

Magnetic Characteristics of Non-Oriented Electrical Steel Sheet

[095] The non-oriented electrical steel sheet according to the embodiment shows excellent magnetic characteristics in relation to the three directions which are the rolling direction, the transverse direction, and the direction at 45° from the rolling direction to the motor core .

[096] Regarding the average magnetic flux density B50 of the three directions as described above in a case where the steel sheet is excited under a magnetic field strength of 5000 A/m, the deterioration of the magnetic flux density B50 due strain relief annealing may be 0.010T or less.

[097] Specifically, when the magnetic flux density B50 is defined as the average of the magnetic flux density of the rolling direction, the magnetic flux density of the transverse direction, and the magnetic flux density of the direction 45° to the direction of rolling in a case where the steel sheet is excited under a magnetic field strength of 5000 A/m, it is preferable that the absolute value of the difference between the magnetic flux density B50 before strain relief annealing and the density of B50 magnetic flux after strain relief annealing is 0.010T or less.

[098] The difference between the B50 magnetic flux densities before and after strain relief annealing is preferably 0.008T or less, more preferably 0.005T or less, and even more preferably 0.002T or less. The lower limit of the difference between the B50 magnetic flux densities before and after strain relief annealing is not particularly defined, and the lower limit may be 0. The lower limit is preferably as close to 0 as possible. For example, the lower limit might be 0.001T.

[099] The recrystallized {111} grains that deteriorate the magnetic flux density tend to develop mainly in the 1/2t area, and the recrystallized {100} grains that improve the magnetic flux density tend to develop mainly in the 1/ 10t. In conventional non-oriented electrical steel sheets, since the amount of AlN is insufficient in the 1/2t area, the recrystallized {111} grains grow preferentially during strain relief annealing, and thus the magnetic flux density deteriorates. . In the embodiment, it appears that AlN should be precipitated in the 1/2t area, the growth kinetics of {100} grains and {111} grains become relatively the same, the degree of orientation of {100} grains increases after annealing of strain relief, and thus the deterioration of magnetic flux density due to strain relief annealing is suppressed by up to 0.010T or less.

[0100] The magnetic characteristics of electrical steel sheets can be measured based on the single sheet tester (SST) method regulated by JIS C 2556:2015. In the case of 0° and 90° directions, for example, a square sample measuring 55 mm in the rolling direction can be cut and taken, the steel sample can be excited under a magnetic field strength of 5000 A/m, and then The magnetic flux density along the rolling direction can be measured in units of T (tesla). In the case of the 45° direction, a 55 mm square sample in the direction making an angle of 45° with the rolling direction can be cut and taken, the magnetic flux densities along the length and width directions of the body test samples can be measured, and their average can be calculated. In addition, the steel plate can be excited under conditions such as 50 Hz and the magnetic flux density of 1.5T, and then the W15/50 iron loss can be measured.

Other Features of Non-Oriented Electrical Steel Sheet

[0101] The thickness of the silicon steel sheet according to the embodiment can be adjusted appropriately depending on the intended use and the like, and is not particularly limited. The average thickness of silicon steel sheet can be 0.10 to 0.50 mm from productivity point of view. The average thickness is preferably 0.15 to 0.50 mm. In particular, the average thickness is preferably 0.15 to 0.35 mm from the point of view of the balance between magnetic characteristics and productivity.

[0102] In addition, the non-oriented electrical steel sheet according to the embodiment may have an insulating coating on the surface of the silicon steel sheet. The insulation coating formed on the surface of the non-oriented electrical steel sheet according to the embodiment is not particularly limited, and can be selected depending on the intended use, and the like, among the known coatings.

[0103] For example, the insulating coating can be either an organic coating or an inorganic coating. Examples of organic coating include: polyamine resins; acrylic resins; styrene acrylic resins; alkyd resins; polyester resins; silicone resins; fluorocarbon resins; polyolefin resins; styrene resins; vinyl acetate resins; epoxy resins; phenolic resins; urethane resins; melamine resins; and similar.

[0104] Examples of inorganic coating include: phosphate-based coatings; aluminum phosphate-based coatings; and similar. Additionally, an organic-inorganic composite coating containing the resins mentioned above is included.

[0105] The average thickness of the insulating coating is not particularly limited. The average thickness is preferably 0.05 to 2 μm as the average thickness on one side.

Non-Oriented Electrical Steel Sheet Production Method

[0106] The non-oriented electrical steel sheet according to the embodiment is obtained, as mentioned above, by conducting the incubation treatment and controlling the heating rate of the final annealing. Here, the incubation treatment is to control the temperature and time to be within predetermined conditions during cooling after final hot rolling, rather than hot strip annealing after final hot rolling that is conducted to produce the conventional non-oriented electrical steel sheet.

[0107] Fig. 2 is a flowchart illustrating the production method of the non-oriented electrical steel sheet according to the embodiment. In the embodiment, the silicon steel sheet is obtained by casting molten steel with an adjusted composition, hot rolling it, incubating it during cooling after hot rolling, pickling it, cold rolling it, and then by its final annealing. Furthermore, the non-oriented electrical steel sheet is obtained by forming the insulating coating on the silicon steel sheet.

[0108] Hereinafter an example of a preferred production method of non-oriented electrical steel sheet according to the embodiment is described.

[0109] Example of the preferred production method of non-oriented electrical steel sheet according to the embodiment includes:

[0110] a casting process of casting a slab including, in mass % units, 0.0030% or less C, 0.01 to 3.50% Si, 0.0010 to 2.500% Al, 0.01 to 3.00% Mn, 0.180% or less P, 0.0030% or less S, 0.0030% or less N, 0.0020% or less B, 0 to 0.0500 % Sb, 0 to 0.2000% Sn, 0 to 1.00% Cu, 0 to 0.0400% REM, 0 to 0.0400% Ca, 0 to 0.0400% Mg, and the balance consisting of Fe and impurities;

[0111] a hot rolling process of hot rolling the plate;

[0112] an incubation process of incubating the steel sheet during cooling after hot rolling;

[0113] a pickling process of pickling the steel sheet;

[0114] a cold rolling process of cold rolling the steel sheet; It is

[0115] a final annealing process of performing final annealing of the steel sheet after cold rolling.

[0116] In the incubation process, the incubation temperature is controlled to 700 to 950°C, and the incubation time is controlled to 10 minutes to 3 hours. In addition, in the final annealing process, the average heating rate during heating is controlled to be 30 to 200°C/s.

[0117] Satisfying the conditions of the two incubation and final annealing processes, it is possible to obtain, after final annealing, the silicon steel sheet with 50% or less of the above PDR indicating the distribution state of the AlN precipitates in the three areas that are the 1/10t area, the 1/5t area and the 1/2t area. As a result, like the non-oriented electrical steel sheet, the difference in magnetic flux densities before and after strain relief annealing is suppressed to 0.010T or less.

[0118] From now on, the main processes will be explained.

Hot rolling process

[0119] The plate with the adjusted chemical composition is heated and hot rolled. The heating temperature of the board before hot rolling is not particularly limited. The heating temperature can be 1000 to 1300°C in consideration of production cost, and the like.

[0120] The plate after heating undergoes rough lamination, and then undergoes final lamination. At the time after rough rolling and before final rolling, the thickness of the steel plate is preferably 20 to 100 mm. Furthermore, the end temperature FT of the final lamination is preferably 900°C or more, and more preferably 950°C or more. By controlling the FT termination temperature to 950°C or more, shear strain tends to be introduced, and thus the recrystallized {100} grains can be enlarged after final annealing.

Incubation process

[0121] The hot-rolled steel sheet is incubated during cooling after hot rolling. In incubation treatment, the incubation temperature is controlled to 700 to 950°C, and the incubation time (retention time) is controlled to 10 minutes to 3 hours. By controlling both the incubation treatment and the final annealing as described later, the PDR is controlled to 50% or less, here PDR is the relative ratio with the maximum and minimum number density of the AlN precipitates in the three areas which are the 1/0t area, the 1/5t area and the 1/2t area along the thickness direction. The reason why incubation conditions affect AlN precipitates is not clear, but is considered to be as follows.

[0122] In the conventional production method, the hot-rolled steel sheet after hot rolling is coiled, the coil is cooled to room temperature without incubation, and subsequently annealing of the hot sheet is conducted at the temperature retention temperature. 950 to 1050 °C for a holding time of 5 minutes or less in an atmosphere in which nitrogen and hydrogen are mixed. In the annealed sheet that has been annealed by the above conditions, AlN hardly precipitates in the central area along the thickness direction of the steel sheet.

[0123] On the other hand, in the embodiment, the hot rolled steel sheet during cooling after hot rolling is incubated in the temperature range of 700 to 950°C for 10 minutes to 3 hours in air containing a large amount of nitrogen. Thus, it appears that nitrogen penetrates into the central area along the thickness direction of the steel plate, and AlN is easily precipitated in the central area. In particular, by conducting the treatment under conditions such that the retention time in incubation is 10 minutes to 3 hours, which is a long time compared to conventional hot plate annealing, it is possible to uniformly precipitate AlN from the surface of the steel sheet through the central area in the thickness direction.

[0124] For example, incubation in the incubation treatment can be conducted by cooling the hot-rolled steel sheet after hot rolling and keeping the coil in a coil cover or in a coil box. At this time, the coil can be maintained at the incubation temperature. After the predetermined incubation time has passed, the bobbin can be removed from the bobbin cover or bobbin case to end the incubation.

Cold rolling process

[0125] The steel sheet after incubation treatment is cooled to room temperature, pickled as necessary, and then subjected to cold rolling. The reduction in cold rolling is not particularly limited. As general conditions, the total reduction in the cold rolling process (cumulative cold rolling reduction) may be 75% or more (preferably 80% or more, more preferably 85% or more). The total reduction can be 90% or more to obtain a particular thin electrical steel sheet. The total reduction in cold rolling is preferably 95% or less in consideration of production control such as rolling mill capacity and thickness accuracy.

Final annealing process

[0126] The steel sheet after incubation is subjected to final annealing.

[0127] The average heating rate during heating in final annealing should be 30 to 200°C/s. With the control of the average heating rate, PDR is controlled to 50% or less, here PDR is the relative ratio with the maximum and minimum number density of the AlN precipitates in the three areas which are the area 1/10t, the area 1/5t and the area 1/2t along the thickness direction. The reason why heating conditions affect AlN precipitates is unclear, but is considered to be as follows.

[0128] In the conventional production method, particularly in the production method in which retention treatment is conducted during cooling after hot rolling without hot plate annealing being conducted, the average heating rate during heating in final annealing is limited to less than 30°C/s to control the recrystallization structure and grain size of the steel sheet and preferably reduce the number density of AlN in the steel.

[0129] On the other hand, in the embodiment, the average heating rate during heating in final annealing is controlled to be 30°C/s or more. It appears that AlN in steel is easily dissolved during final annealing, and is easily influenced by the heating rate during heating in particular. When the heating rate is less than 30°C/s, the uniformity of AlN distribution in the thickness direction of the steel plate deteriorates because the AlN in the steel is easily dissolved and particularly the AlN is dissolved unevenly depending on the depth of the steel plate. steel. By controlling the average heating rate during heating in the final annealing to 30 ° C / s or more, it is possible to preferably control the PDR that indicates the distribution state of AlN.

[0130] The average heating rate during heating in final annealing is preferably 40°C/s or more and more preferably 50°C/s or more. The upper limit of the average heating rate is not particularly limited. The upper limit can be 200°C/s for stable operation. The upper limit of the average heating rate is preferably 100°C/s. The average heating rate can be obtained based on the time required to heat from the initial temperature (ambient temperature) to the holding temperature as described below.

[0131] In addition, by controlling the average heating rate during heating in final annealing to 30 to 200°C/s, the degree of grain orientation {100} increases, and the degree of grain orientation {111} decreases, before strain relief annealing. Thus, the deterioration of magnetic flux density due to SRA is suppressed.

[0132] The retention temperature in the final annealing can be 800 to 1200°C in order to control the loss of iron to be sufficiently low after the final annealing. The retention temperature may be the recrystallization temperature or higher. When the holding temperature is 800°C or more, the grains grow sufficiently, and thus iron loss can be reduced. For the same reason, the retention temperature is preferably 850°C or more.

[0133] On the other hand, the upper limit of the retention temperature may be 1200°C in consideration of the load applied to the rebaking oven. The upper limit is preferably 1050°C.

[0134] In addition, the retention time in the final annealing can be determined in consideration of grain size, iron loss, magnetic flux density, strength, and the like. For example, the retention time can be 5 seconds or more. On the other hand, when the retention time is 120 seconds or less, the grains grow properly. Thus, the retention time can be 5 to 120 seconds. When the retention time is within the range, the crystal orientation that has the effect of suppressing the deterioration of magnetic characteristics tends to remain even when additional slow heating heat treatment is conducted for grain growth.

[0135] In addition, in a case where additional slow heating heat treatment such as strain relief annealing (SRA) is conducted at the end, since grain growth and iron loss are reduced, the retention temperature at final annealing may be lower than 800°C. In this case, additional heat treatment significantly leads to suppression of the deterioration of magnetic flux density. In this case, even when the non-recrystallized structure partially remains, it is possible to obtain the specific crystal orientation for the non-oriented electrical steel sheet according to the embodiment. For example, the lower limit of the retention temperature at final annealing may be 640°C. Since the steel sheet having a fine structure or a partially non-recrystallized structure by decreasing the holding temperature in final annealing has high strength, the steel sheet is useful as a high-strength non-oriented electrical steel sheet.

[0136] To obtain the non-oriented electrical steel sheet according to the embodiment, in addition to the processes described above, the insulating coating forming process similar to the conventional production process of the non-oriented electrical steel sheet can be conducted to form the insulating coating on the surface of the silicon steel sheet after the final annealing process. Each condition of the insulating coating forming process can employ the condition similar to that of the conventional non-oriented electrical steel sheet production process.

[0137] The method for forming the insulating coating is not particularly limited. For example, the insulating coating can be formed by preparing the insulating coating forming solution in which the resins or inorganics as mentioned above are dissolved and applying the insulating coating forming solution to the surface of the silicon steel sheet. , using known methods.

[0138] It is possible to obtain the non-oriented electrical steel sheet according to the embodiment by the production method that includes the above processes.

[0139] According to the embodiment, it is possible to obtain non-oriented electrical steel sheet excellent in magnetic characteristics. Thus, the non-oriented electrical steel sheet according to the embodiment is suitably applied as various materials for cores of electrical equipment, particularly core materials of motors such as rotating machines, small and medium-sized transformers, and electrical components.

Examples

[0140] Hereinafter the effects of an aspect of the present invention are described in detail in relation to the following examples. However, the condition of the examples is a condition employed to confirm the operability and effects of the present invention, so the present invention is not limited to this example condition. The present invention may employ various types of conditions as long as the conditions do not go beyond the scope of the present invention and can achieve the objective of the present invention.

Example 1

[0141] Silicon steel sheets were produced by using the plate with the adjusted chemical composition and controlling the production conditions in each process, and then the non-oriented electrical steel sheets were produced by forming phosphoric acid based on insulating coating with an average thickness of 1 μm on the silicon steel sheet. The chemical compositions are shown in Tables 1 and 2, and the production conditions are shown in Tables 3 and 4. At the time of the above production, hot rough rolling was conducted so that the thickness was 40 mm, and the Cold rolling was conducted so that the thickness of all steel sheets after cold rolling was 0.35 mm.

[0142] The produced non-oriented electrical steel sheets were observed by the method described above, and the distribution of AlN along the thickness direction of the silicon steel sheet was measured. The results are shown in Tables 5 and 6.

[0143] The B50 magnetic flux density was measured using the produced non-oriented electrical steel sheets. The average magnetic flux density B50 of the three directions which are the rolling direction, the transverse direction and the direction at 45° to the rolling direction was measured before and after strain relief annealing, and the difference ΔB50 before strain relief annealing and after strain relief annealing were measured. When the B50 magnetic flux density before strain relief annealing was 1.58T or more, it was judged to be acceptable. Furthermore, when the ΔB50 difference was 0.010T or less, it was judged to be acceptable.

[0144] Here, the average magnetic flux density B50 in the three dimensions that are the rolling direction, the transverse direction and the direction at 45° to the rolling direction was measured based on the magnetic flux density excited under a field strength magnetic 5000 A/m. Specifically, the B50 magnetic flux densities with respect to the three directions that are along the rolling direction (0°), the direction perpendicular to the rolling direction (90°), and the direction that makes a 45° angle with the rolling direction (45°) were measured and averaged over the three directions.

[0145] The W15/50 iron loss was measured using the non-oriented electrical steel sheets produced. The average losses of W15/50 iron in relation to the three directions which were the rolling direction, the transverse direction and the direction at 45° to the rolling direction were measured before and after aging at 200°C for 2 hours. , and the difference ΔW15/50 before aging and after aging was measured. When the average W15/50 iron loss before aging was 3.50 W/kg or less, it was judged to be acceptable. Furthermore, when the ΔW15/50 difference was 0.4 W/kg or less, it was judged to be acceptable.

[0146] Here, the magnetic flux density and iron loss can be measured by the following method. A 55mm square sample can be cut and taken from the steel plate, and then B50 and W17/50 can be measured by the single plate tester (SST), here B50 indicates the magnetic flux density in units of T (tesla) when the steel sheet is excited under a magnetic field strength of 5000 A/m, and W17/50 indicates the loss of iron when the steel sheet is excited under conditions such as 50 Hz and the magnetic flux density of 1, 5T.

[0147] Production conditions, production results, and evaluation results are shown in Tables 1 to 6. In the tables, underlined values indicate outside the range of the present invention. Furthermore, in the tables, “-“ in relation to the chemical composition of the silicon steel sheet indicates that no binding elements were added intentionally or that the content was lower than the detection limit.

[0148] As shown in the tables, in the examples of the invention nos. B1 to B19, the composition of the silicon steel sheet and the distribution state of AlN precipitates were preferably controlled, and thus the magnetic characteristics were excellent for the steel sheet. non-oriented electrical.

[0149] On the other hand, as shown in the tables, in the comparative examples of nos b1 to b17, at least one between the composition of the silicon steel sheet and the distribution state of AlN precipitates was preferably not controlled, and thus the characteristics magnetic values were not satisfied for the non-oriented electrical steel sheet. Table 1 Table 2 Table 3 Table 4 Table 5 Table 6

Industrial applicability

[0150] According to the above aspects of the present invention, it is possible to provide non-oriented electrical steel sheet with small change in magnetic flux densities before and after strain relief annealing (SRA). In particular, it is possible to supply non-oriented electrical steel sheet in which the difference between the magnetic flux density B50 before strain relief annealing and the magnetic flux density B50 after strain relief annealing is 0.010 T or less, relative to the average of the three directions which are the rolling direction, the transverse direction, and the direction that is 45° to the rolling direction. Consequently, the present invention has significant industrial applicability. List of reference signals 1 NON-ORIENTED ELECTRICAL STEEL SHEET 3 SILICON STEEL SHEET (BASE STEEL SHEET) 5 INSULATING COATING (TENSION COATING) 11 PUNCHED PART 13 LAMINATION 15 TEETH 17 CASING 100 MOTOR CORE

Claims (1)

1. Non-oriented electrical steel sheet comprising a silicon steel sheet and an insulating coating, characterized in that the silicon steel sheet consisting of, as a chemical composition, in mass %, 0.01 to 3.50% of Si, 0.0010 to 2.500% Al, 0.01 to 3.00% Mn, 0.0030% or less C, 0.180% or less P, 0.0030% or less S, 0.0030 % or less of N, 0.0020% or less of B, and optionally at least one element selected from a group consisting of 0.0500% or less of Sb, and 0.0100 to 0.2000% of Sn, optionally by least one element selected from the group consisting of 0 to 1.00% Cu, 0 to 0.0400% REM, 0 to 0.0400% Ca, and 0 to 0.0400% Mg, and the balance consisting of Fe and impurities, and when t is the thickness of the silicon steel sheet and when PDR is defined as the following (expression 1) which indicates the relative ratio with the maximum and minimum number density of AlN precipitates in the three areas that are the area 1/10t, the area 1/5t, and the area 1/2t from the surface of the silicon steel sheet along the thickness direction, PDR is 50% or less, where PDR = (the maximum - the minimum) + the minimum x 100 (expression 1).