JP7256361B2 - Non-oriented electrical steel sheet and manufacturing method thereof, rotor core core of IPM motor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a rotor core core of an IPM motor using the non-oriented electrical steel sheet.

Non-oriented electrical steel sheets are used in motors for electric vehicles, motors for electrical equipment, and the like. In particular, due to the development of drive systems using motors in recent years, the number of motors that operate at variable speeds or that rotate at high speeds above commercial frequencies is increasing. A motor that rotates at such a high speed is required to have magnetic properties and, at the same time, a strength that can withstand high-speed rotation. Various techniques have been proposed for the purpose of achieving both iron loss and strength in non-oriented electrical steel sheets. For example, techniques for improving strength by forming Cu precipitates have been proposed (Patent Documents 1 to 4). Furthermore, techniques have been proposed for improving strength by forming an intermetallic compound (Patent Documents 5 and 6).

JP-A-2004-315956 Japanese Patent Application Laid-Open No. 2005-344179 JP 2008-261053 A JP 2007-186791 A JP 2010-150667 A JP 2017-57456 A

However, when the strength of the non-oriented electrical steel sheet is increased, there is a drawback that workability is inferior. For example, in the case of punching to obtain a desired shape as a component of a motor, as the strength of the non-oriented electrical steel sheet increases, the number of punches that the die can be continuously used decreases inversely proportionally. There is a problem.

An object of the present invention is to provide a non-oriented electrical steel sheet that achieves both high strength and workability.

In order to solve the above problems, the present inventors concentrated one or two of Ni and Al on the surface of Cu particles precipitated in the steel of the non-oriented electrical steel sheet, thereby increasing the strength. It is designed to reduce the deterioration of workability. According to the present invention, the following non-oriented electrical steel sheet and its manufacturing method are provided.

[1]
By mass%, Si: 2.0 to 6.0%, Cu: 1.7 to 4.0%, and further Al: 3.0% or less, Ni: 4.0% or less one or two 0.7 % or more in total, and as optional elements,
Mn: 5.0% or less,
P: 0.300% or less,
B: 0.100% or less,
Nb: 1.00% or less,
Mo: 1.000% or less,
Bi: 0.010% or less,
Sn: 0.10% or less,
Sb: 0.10% or less,
Cr: 0.30% or less,
Ca: 0.020% or less,
Mg: 0.020% or less,
La: 0.020% or less,
A non-oriented electrical steel sheet containing Ce: 0.020% or less, the balance being Fe and impurities,
The metal structure is ferrite polycrystal,
Cu particles are contained in the ferrite crystal,
Cu particles in the ferrite crystal have an average particle size of 0.5 to 100 nm and a number density of 80 to 1000/μm ³ ,
A non-oriented electrical steel sheet, characterized in that Cu particles in ferrite crystals satisfy formula (1).
Nx/Nt≧0.1 Expression (1)
here,
Nx: Among all Cu particles to be observed, the number of Cu particles in which one or both of Ni and Al are concentrated on at least a part of the surface Nt: The number of all Cu particles to be observed [2]
Cu particles having one or both of Ni and Al concentrated on at least a part of the surface are observed by 3DAPFIM, characterized in that the area SC and the area SA satisfy the formula (2) [1] The non-oriented electrical steel sheet according to .
SA/SC>0.1 Expression (2)
here,
SC: Area of a region that satisfies "Fe concentration ≤ 90% and Cu concentration ≥ total concentration of Ni and Al" SA: Area that satisfies "Fe concentration ≤ 90% and Cu concentration < total concentration of Ni and Al" the area of [3]
The tensile strength TS is 600 MPa or more, and the number of times of processing is 100,000 times or more when the height of burrs generated in the processed product is 50 μm or more when repeated punching is performed using a 15 mmφ steel die. The non-oriented electrical steel sheet according to any one of [1] and [2].
[4]
[1] to [3] A rotor core core for an IPM motor, which is formed by laminating the non-oriented electrical steel sheets according to any one of [3].

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the non-oriented electrical steel sheet which can make high strength and workability compatible.

It is a graph which shows the relationship between tensile strength TS and the number of times of punching. 4 is a graph showing the relationship between the tensile strength TS and the number of times of punching measured in Examples.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

(chemical composition)
The non-oriented electrical steel sheet of the present invention contains, by mass%, Si: 2.0 to 6.0%, Cu: 1.7 to 4.0%, Al: 3.0% or less, Ni: Contains 0.5% or more in total of one or two of 4.0% or less.

Si: 2.0-6.0%
Si increases the specific resistance of steel, reduces eddy currents, lowers iron loss, and increases tensile strength, but if the amount added is less than 2.0%, the effect is small. In addition, since the work hardening ability is enhanced by addition, there is also an effect of effectively increasing the dislocation density due to the working performed before the aging heat treatment. On the other hand, when Si exceeds 6.0%, the steel becomes embrittled and the magnetic flux density of the product is lowered.

Cu: 1.7 to 4.0% In the non-oriented electrical steel sheet of the present invention, the Cu particles precipitated in the ferrite crystals can increase the strength without increasing the iron loss. If the Cu content is less than 1.7%, this action and effect cannot be sufficiently obtained. Preferably, it is 2.0% or more. On the other hand, if the Cu content exceeds 4.0%, coarse precipitates are formed and iron loss increases.

Ni and Al: 0.5% or more in total In the present invention, Ni and Al are important elements actively added as elements for improving the balance between high strength and punchability by concentrating them on the surface of Cu particles. is an element. In order to obtain the above effects, the total content of Ni and Al must be 0.5% or more. Preferably, it is 1.2% or more. In addition, Ni and Al may contain one or two kinds in a total amount of 0.5% or more, and it is possible to obtain an effect by containing either Ni or Al, but both are contained. is more preferable.

Al: 3.0% or less Al is usually added to fix solid solution N as precipitates that deteriorate deoxidation and aging properties, and to increase the specific resistance of steel to reduce eddy currents and lower iron loss. be done. In the present invention, Al is an important element positively added as an element for improving the balance between strength and punchability by concentrating it on the surface of Cu particles. In order to obtain the above effect by sufficiently concentrating Al on the surface of the Cu particles, it is preferable to contain 0.5% or more. In addition, since it also has the effect of promoting the preferred crystal orientation for magnetic properties, it is preferably 1.2% or more. On the other hand, if it is added excessively, embrittlement becomes a problem and the saturation magnetic flux density is lowered to adversely affect the magnetic properties, so the upper limit is made 3.0%.

Ni: 4.0% or less Ni is sometimes added to a non-oriented electrical steel sheet as a solid solution strengthening element or an element for improving corrosion resistance. In the present invention, Ni is added to improve the balance by concentrating it on the surface of the Cu particles. In order to obtain such an effect, it is necessary to contain 0.5% or more in total with Al having a similar effect. In order to sufficiently concentrate Ni on the surface of the Cu particles, the Ni content is preferably 1.2% or more. Further, Cu is added in the same manner as in the present invention to improve the castability and surface properties of the steel sheet in the electrical steel sheet intended to increase the strength by Cu precipitation. On the other hand, excessive addition deteriorates the ductility of the steel sheet, reduces the threadability, lowers the magnetic flux density, and inadvertently generates intermetallic compounds in the manufacturing process, which may deteriorate the threadability and magnetic properties. be. Excessive addition not only causes transformation during hot rolling and inhibits the crystal orientation preferable for magnetic properties, but also lowers saturation magnetic flux density and adversely affects magnetic properties. Therefore, the upper limit is set to 4.0%. Preferably, it is 3.2% or less.

Furthermore, the non-oriented electrical steel sheet according to the present invention may contain known arbitrary elements instead of part of Fe for the purpose of improving various properties including magnetic properties. Examples of optional elements contained in place of part of Fe include the following elements. Each numerical value means the upper limit when those elements are included as arbitrary elements.
in % by mass,
Mn: 5.0% or less,
P: 0.300% or less,
B: 0.100% or less,
Nb: 1.00% or less,
Mo: 1.000% or less,
Bi: 0.010% or less,
Sn: 0.10% or less,
Sb: 0.10% or less,
Cr: 0.30% or less,
Ca: 0.020% or less,
Mg: 0.020% or less,
La: 0.020% or less,
Ce: 0.020% or less,
Since these optional elements may be contained according to known purposes, there is no need to set a lower limit for the content of the optional element, and the lower limit may be 0%.

Mn is also effective as an element that enhances strength by solid solution and improves iron loss by increasing electrical resistance, and can be used according to known techniques in this embodiment as well. In addition, it also has the effect of increasing the work hardening ability and effectively increasing the dislocation density due to the working performed before the aging heat treatment. From the viewpoint of increasing the strength, it is not particularly required in the present invention that utilizes fine intermetallic compounds. It may be 0%, but about 0.01% is unavoidably contained in an industrial production method using iron ore as a raw material.

P is an element that has a remarkable effect of increasing the tensile strength by solid solution strengthening, but it is not necessary to add it for this purpose. It may be 0%. On the other hand, addition of Ni also has the effect of increasing the work hardening ability and effectively increasing the dislocation density due to the working performed before the aging heat treatment. If it exceeds 0.3%, embrittlement becomes severe, and processing such as hot rolling and cold rolling on an industrial scale becomes difficult, so the upper limit is preferably 0.300%, more preferably 0.100%. It is below.

B, Nb, and Mo are elements that, when added, improve the castability and hot workability of the steel of the present invention. Since the steel of the present invention contains a relatively large amount of Cu as an essential element, cracks are likely to occur in the high temperature range of continuous casting and hot working. By adding B, Nb, and Mo, it is possible to suppress this cracking.

By adding Bi, Sn, and Sb, it is possible to improve the crystal orientation of the steel of the present invention, and particularly to increase the magnetic flux density.

Cr is also effective as an element for increasing strength through solid solution and improving electrical resistance and improving iron loss, and can be used according to known techniques in this embodiment as well. It is also known as an element that improves corrosion resistance and high-frequency magnetic properties. 0% is acceptable, but in industrial production methods that use scrap from the viewpoint of raw material cost and recycling, about 0.01% is unavoidably contained, and the content due to scrap may exceed 0.10%. .

Ca, Mg, La, and Ce are strong sulfide-forming elements, and by adding them in a low-cost practical process where the S content cannot be completely zero, the sulfide coarsens and the adverse effects of fine sulfides are suppressed. As a result, it is possible to avoid an unexpected increase in iron loss.

The arbitrary element is not limited to the elements exemplified above, and means an element that does not impair the effect of the present invention even if it is contained. Even if it is added for the purpose of imparting an effect not described in the present invention, in the present invention, if the effect of the present invention is not lost even if the element is contained, the optional element in the present invention Judged as an element. The upper limit of the total content of arbitrary elements is about 8%.

The non-oriented electrical steel sheet of the present invention contains Cu, Si, Al or Ni as essential components, further contains optional elements as necessary, and the balance consists of Fe and impurities. The following elements are exemplified as impurities.

Since C may degrade the magnetic properties, it is preferably 0.0400% or less. On the other hand, it also has the effect of increasing the work hardening ability and effectively increasing the dislocation density due to the working performed before the aging heat treatment. From the viewpoint of manufacturing cost, it is advantageous to reduce the amount of C by degassing equipment at the molten steel stage. In the present invention which does not use the non-metal precipitates, it is more preferably 0.0020% or less, more preferably 0.0015% or less. It may be 0%.

Since N, like C, degrades the magnetic properties, it is preferably 0.0400% or less. The inclusion of Ni also has the effect of increasing the work hardening ability and effectively increasing the dislocation density due to the working performed before the aging heat treatment. In particular, in the present invention, a low N content is preferable in order to avoid the formation of strong nitrides with Al, and if it is 0.0027% or less, the effect of suppressing characteristic deterioration due to magnetic aging and the formation of fine nitrides is remarkable, and it is more preferable. is 0.0022%, more preferably 0.0015% or less, and may be 0%.

Since S and Se form sulfides and sometimes degrade magnetic properties, particularly iron loss, the S content is preferably as low as possible, and may even be 0%. In the present invention, the content is preferably 0.020% or less, more preferably 0.0040% or less, still more preferably 0.0020% or less, still more preferably 0.0010% or less.

Ti forms sulfides and carbides and may degrade magnetic properties, particularly core loss. In the present invention, the content is preferably 0.015% or less, more preferably 0.0020% or less, still more preferably 0.0010% or less, still more preferably 0.0008% or less.

The impurities are not limited to the arbitrary elements exemplified above, and mean elements that do not impair the effects of the present invention even if they are contained. It is not limited to the case of being added intentionally, but includes elements that are unavoidably mixed from ore, scrap, or manufacturing environment as raw materials when steel sheets are manufactured industrially. The target upper limit of the total content of impurities is about 5%.

The chemical composition of the non-oriented electrical steel sheet according to the present invention may be measured by a general analysis method for steel. For example, the chemical composition of a non-oriented electrical steel sheet may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, a 35 mm square test piece taken from a non-oriented electrical steel sheet is measured using a Shimadzu ICPS-8100 or the like (measuring device) under conditions based on a pre-created calibration curve. is identified. C and S may be measured using a combustion-infrared absorption method, and N may be measured using an inert gas fusion-thermal conductivity method.

Although not specified in the present invention, a coating generally provided on non-oriented electrical steel sheets may be formed on the surface of the non-oriented electrical steel sheet according to the present invention. These are called, for example, insulating coatings.

However, this coating is not an essential element of the non-oriented electrical steel sheet according to the present invention. The above chemical composition of the non-oriented electrical steel sheet to be specified in the present invention is the composition of the steel sheet that serves as the base material. It shall be.

(Cu particles)
The non-oriented electrical steel sheet of the present invention has a ferrite polycrystalline metal structure and contains Cu particles in the ferrite crystals. The Cu particles have an average particle diameter of 0.5 to 100 nm and a number density of 80 to 1000/μm ³ , and the Cu particles satisfy the formula (1).
Nx/Nt≧0.1 Expression (1)
here,
Nx: Among all Cu particles to be observed, the number of Cu particles in which one or both of Ni and Al are concentrated on at least a part of the surface Nt: The number of all Cu particles to be observed

In general, the particle size and number density of precipitates are known as effective factors for increasing strength by precipitates. Regarding the average particle size of the Cu particles used in the present invention, if it is less than 0.5 nm, it is difficult to observe, and it is not large enough to exhibit strength. If it becomes, the number density will decrease, so the strength increasing effect will decrease. As for the number density, if it is less than 80 pieces/μm ³ , the effect of increasing the strength is lowered, while if it exceeds 1000 pieces/μm ³ , the punchability is lowered.

A feature of the present invention is that Ni and Al are concentrated on at least a part of the surface of the Cu particles having the effect of increasing the strength as described above. That is, the Cu particles are characterized by satisfying the formula (1).

In a conventional high-strength electrical steel sheet utilizing Cu particles, Ni and Al are not concentrated on the surfaces of the Cu particles, and the formula (1) is not satisfied. In the steel sheet of the present invention, the balance between strength and punchability is improved by satisfying the formula (1). That is, if the steel plate strength is the same, excellent punchability is exhibited. Furthermore, if the steel plate strength is the same, it is possible to obtain the effect of increasing the magnetic flux density.

The ratio on the left side of formula (1) is preferably 0.1 or more, more preferably 0.5 or more. Needless to say, all Cu particles preferably have Ni and Al concentrated on at least part of their surfaces, ie, Nx=Nt and Nx/Nt=1.

In the present invention, it is somewhat strange that the effect appears when the ratio (Nx/Nt) of Cu particles in which the enrichment of Ni and Al is detected is only about 0.1 (1 in 10). This is thought to be due to the detection limit of enrichment. That is, even if no enrichment is detected by the detection method applied in the present invention, it does not mean that enrichment has not occurred at all (enrichment amount = zero), but a sufficient amount to contribute to the inventive effect. It is thought that concentration is occurring. However, one of the reasons for the enrichment at that level is that the amount of enrichment itself that shows the effect of the invention is small. It cannot be detected by the detection method used in the invention. As a result, if the concentration is detected in 1 out of 10 Cu particles in the detection method of the present invention, it is considered that the present invention effect will be exhibited in total including the concentrated particles in which the concentration cannot be detected. be done.

Although the mechanism by which the concentration of Ni and Al on the surface of Cu particles improves the balance between strength and punchability is not clear, it is considered as follows.
Since the Cu phase that constitutes the Cu particles is softer than the Fe phase that is the parent phase of the steel sheet, the Cu particles are easily deformed by dislocations that move in the Fe phase as the steel sheet is deformed. This means that a phenomenon called so-called "cutting" of precipitates tends to occur. For this reason, it cannot be said that simple Cu particles (Cu particles whose surfaces are not enriched with Ni and Al) are in a situation where the effect of precipitation strengthening by the precipitate particles is efficiently exhibited. It is believed that when Ni and Al are concentrated on the surface of the Cu particles, "cutting" is less likely to occur. As a pure metal, Al in particular is not a very hard substance, but it concentrates around the Cu phase, and in addition to causing distortion in the crystal lattice even as a pure metal phase, part of it concentrates in Cu, Fe, or the same region. It is considered that the precipitation is made difficult to cut by alloying with Ni and forming an intermetallic compound.

Since the precipitates themselves become hard (hard to be cut), the strength of the steel material is efficiently increased even with a relatively small amount of precipitates. If the strength of the steel material is the same, the amount of precipitates is small, so it is possible to suppress the adverse effect of precipitates on punchability.

In addition, it is conceivable that the composite of Cu particles and Ni and Al as in the present invention may have the effect of finely dispersing the precipitates. That is, since Ni and Al are concentrated on the surface of the Cu particles in the process of starting to precipitate and growing, the growth of the Cu particles is inhibited. It is finer than Cu particles without This effectively acts to increase the strength of the steel material.

Although the Cu grain morphology characteristics are primarily described herein in relation to punchability, a relation to magnetic properties is also suggested. That is, Cu precipitates are basically not a ferromagnetic material like the Fe phase, which is the parent phase, and thus they are a factor in considerably lowering the magnetic properties of the steel sheet, particularly the magnetic flux density. With the steel sheet of the present invention, if the steel material strength is the same, the amount of precipitates can be reduced, so it is possible to obtain the advantage of suppressing the decrease in magnetic flux density.

The steel sheet of the present invention is characterized in that, in observation by 3DAPFIM, the area SC and the area SA of Cu particles having concentrated Ni and Al on at least part of the surface satisfy the formula (2).
SA/SC>0.01 Expression (2)
SC: Area of a region that satisfies "Fe concentration ≤ 90% and Cu concentration ≥ total concentration of Ni and Al" SA: Area that satisfies "Fe concentration ≤ 90% and Cu concentration < total concentration of Ni and Al" area of

If the ratio (SA/SC) is 0.01 or less, the effect of hardening the precipitate cannot be obtained sufficiently. It is preferably 0.1 or more, more preferably 0.5 or more. Although the upper limit is not particularly limited, when SA is significantly larger than SC, the effect of "compositing particles" considered as the mechanism of the present invention becomes difficult to act, so the above ratio is preferably 3 or less. . More preferably, it is 2 or less. Furthermore, when SA=SC, the area of the Cu particles and the area of the Ni and Al-enriched regions are the same. Needless to say, it is preferable to set the ratio on the left side of Equation (2) to about 1, since this is considered to be the most efficient situation.

The average particle size of Cu particles, the number density, the concentration of Ni and Al, and the area of Cu, Ni, and Al are measured as follows.

First, the average particle diameter and number density of all Cu particles will be described. A sample having a cut surface (hereinafter also referred to as “Z cross section”) cut parallel to the plate surface direction is taken from the steel plate to be measured, and a thin film sample parallel to the Z cross section is prepared.

Next, a region of 5 μm×5 μm in the Z cross section is observed in a bright field at a magnification of 10,000 to 500,000 using a transmission microscope (TEM). Cu particles may be identified using a known method such as TEM diffraction pattern. The number density and average particle size are calculated from the number of Cu particles in the observation area and the equivalent circle diameter. It should be noted that not a few Cu particles of the steel sheet of the present invention have Ni and Al concentrated on the surface. In other words, the particles themselves are large due to the presence of the Ni and Al concentrated regions, but the average particle size of the Cu particles is not the size of the Cu phase (the region considered to be mainly composed of Cu), It shall be measured as a size including a region (pure metal phase, alloy phase, intermetallic compound phase, etc.) that contains Ni and Al at a high concentration. In other words, in the above bright-field image, it is observed as a dark area having a considerable difference in electron beam diffraction from the bulk Fe phase. No distinction is made as to whether the difference is due to the enrichment of Cu or the enrichment of Ni or Al. Of course, for Cu particles on the surface of which Ni and Al are not concentrated, the size of the Cu phase is the particle diameter. The particle diameter of one particle is the diameter when the area of the particle in the observation field is converted into a circle.

Next, measurement of quantitative values relating to the enrichment of Ni and Al will be described.

FE-TEM Method Concentration of Ni and Al is determined by performing EDS by FE-TEM with an electron beam diameter of 0.1 nm on a TEM observation sample prepared in the same manner as above. First, reflection intensities for Ni and Al are obtained for a matrix phase (Fe phase) in which Cu particles do not exist. The measurement is carried out at at least 10 points, and the average value for each element is taken as the reflection intensity of Ni and Al. These reflection intensities are defined as PmNi and PmAl, respectively.
Furthermore, similar measurements are performed for Cu particles. An electron beam is irradiated to the central portion of the observed Cu particles to obtain reflection intensities for Ni and Al. These reflection intensities are assumed to be PaNi and PaAl, respectively.
Cu particles satisfying PaAl/PmAl≧1.5 or PaNi/PmNi≧1.5 are defined as “Cu particles having one or both of Ni and Al concentrated on at least part of the surface”. This measurement is performed on at least 100 Cu particles to obtain Nx/Nt.

3DAPFIM method For concentration of Ni and Al, a three-dimensional atom probe field ion microscope (3DAPFIM/Reference: For example, Ferrum, 4, 474 (1999)) is used.
Observation with 3DAPFIM is performed on a needle-shaped sample, and atomic information at the tip of the needle-shaped sample can be obtained. The size of this tip region is generally about 100 nm or less. In the measurement of the present invention, a needle-shaped sample is prepared with at least one Cu particle at the tip. The state of existence of at least one Cu particle in the sample and the surrounding Fe, Cu, Ni and Al atoms is determined to obtain three-dimensional atom probe data. Then, for one Cu particle and its surrounding space, a two-dimensional concentration distribution map is created by projecting atoms within 2 nm from a plane having the maximum cross-sectional area of the Cu particle onto the plane. On this distribution map, the area of the region satisfying "Fe concentration ≤ 90% and Cu concentration ≥ Ni and Al total concentration" is SC, and "Fe concentration ≤ 90% and Cu concentration < total concentration of Ni and Al Let SA be the area of the region that satisfies . If the SA is not zero, the Cu particles are considered to be Ni and/or Al-enriched on at least part of the surface. This is performed for at least 100 Cu particles, and the number Nx of Cu particles having Ni and Al condensed on at least part of the surface is obtained among the observed Cu particles. Furthermore, SA/SC is obtained from the SC and SA values.

Here, the expression "thickening" used in the present invention will be explained.
The structure observed in the present invention has a region where the concentration of Ni or Al is significantly higher than the concentration of Ni or Al in the Fe phase on the surface of fine Cu particles dispersed and precipitated in the Fe phase. It is. The present invention defines this situation simply using the expression "thickening". Such a situation is, for example, a form in which the above element is "concentrated" on the Cu surface to form a pure metal phase or an alloy phase, or a compound containing the above element is "composite precipitated" with Cu particles. form is conceivable. Alternatively, it is conceivable that Cu grains are precipitated on the Ni or Al concentrated region as a nucleus. Compounds that may form composite precipitation include, for example, nitrides and oxides of Al that are well known as compounds in steel sheets. However, the substance causing the "concentration" of the present invention is not limited to this, and may be in the form of carbides, sulfides, metal compounds, etc., including those containing Ni. At present, it is not clear whether the cause of "concentration" is "segregation" of pure metal elements or "composite precipitation" of some kind of compound. The expression "thickening" is deliberately used, and this is defined by the measurement method described above.

Also, the expression “surface (of Cu particles)” will be explained.
This expression in the present invention does not limit Ni and Al atoms being in contact with Cu atoms. In other words, as described above, the microstructure and formation process of "concentration" have not been clarified. For example, the surface of Cu particles is covered with another element other than Ni, Al (and Fe), and the "surface '', that is, strictly speaking, the possibility that Ni and Al atoms are present on surfaces other than the surfaces of the Cu particles cannot be denied. As far as the above-mentioned "surface" in the present invention is observed using a general analysis technique, Ni, Ni, It is intended that a region where Al is "enriched" exists, and expresses a situation in which a region mainly composed of Cu and a region mainly composed of Ni and Al are observed to be spatially adjacent to each other. It is. This situation is defined by the measurement method described above.
It is expected that the fine structure and the actual state of the formation process will be elucidated, including the development of analysis technology in the future.

The non-oriented electrical steel sheet of the present invention is suitably used, for example, for rotor cores of motors with built-in permanent magnets (IPM motors). In recent years, drive motors used in hybrid electric vehicles (HEVs) and electric vehicles (EVs) have been remarkably rotating at high speeds. At high speeds, strong centrifugal force acts on bridges in which permanent magnets are embedded. The non-oriented electrical steel sheet of the present invention has magnetic properties such as a magnetic flux density _B50 of 1.6 T or more, and a tensile strength TS of 600 MPa or more, so that it can withstand such centrifugal force. will be available. The application of the non-oriented electrical steel sheet of the present invention is not limited to rotor cores, and can be used for iron cores such as stators, for example.

Using the same steel plate for the rotor core core member and the stator core core member allows the substantially circular region in the central portion of the stator core core member punched in a substantially annular shape to be used as the raw material for the rotor core core member. This kind of itadori is also known as ``co-dori'' and is common.

However, a member stamped from a steel plate for a stator core core or a stator core core formed by laminating members thereof is preferably subjected to a heat treatment called strain relief annealing. High strength is not required for the material for the stator core iron core, but rather low iron loss is important. Even if it cannot be maintained, it is preferable to perform additional heat treatment so that the grain size is 100 μm or more, which is advantageous for low iron loss.

For both rotor core cores that ultimately require high strength and stator core cores that do not require high strength in the end, high-strength steel plate punching is required on the premise of co-cutting. Since the material is punched out, the punchability improvement effect of the present invention is still obtained sufficiently.

(Production method)
The non-oriented electrical steel sheet of the present invention can be produced by smelting steel containing the above components, continuously casting it into a steel slab, and then subjecting it to hot rolling, cold rolling and finish annealing. For example, manufacturing conditions for hot rolling include a slab heating temperature of 1000 to 1250°C, a finishing temperature of 800 to 1000°C, and a coiling temperature of 400 to 850°C. This hot-rolled sheet may be subjected to hot-rolled sheet annealing at 900 to 1150° C. for 120 seconds or less. Thereafter, cold rolling is performed at a cold rolling rate of 80 to 95%, for example, and finish annealing is performed at 850 to 1100° C. for 120 seconds or less in order to recrystallize the worked structure due to cold rolling. The conditions listed here are known standard conditions. In adopting the above standard conditions in the production of the steel sheet of the present invention, the point to be noted is the final heat history before cold rolling. Although this is also a well-known fact, if a considerable amount of fine Cu particles are formed in the final heat history before cold rolling, the steel sheet before cold rolling becomes hard. This simply deteriorates the cold-rollability, causing an increase in rolling load, a decrease in steel sheet shape accuracy, breakage of the steel sheet during rolling, and the like. Therefore, in the final heat treatment before cold rolling, the Cu particles are passed through the formation temperature range in a short time so that the Cu particles are not formed, or the Cu particles are formed by holding the Cu particles in the formation temperature range for a sufficient time. The heat history should be such as to avoid coarsening and hardening. Specifically, the residence time at 450 to 650° C. is preferably 20 seconds or less.

Moreover, in addition to these steps, an insulating film formation step and a decarburization step may be performed. As for the casting, instead of the normal process of obtaining a slab with a thickness of about 200 mm, there is no problem in manufacturing the thin strip by the rapid solidification process or by the thin slab process that omits the hot rolling process.

In order to form the unique metal phase characteristic of the present invention in the steel sheet, the solid solution of Cu, Ni and Al in the steel causes the precipitation of Cu particles and the It is effective to undergo the following thermal history during the process of concentrating Ni and/or Al into the interface).

Since the steel of the present invention basically precipitates Cu particles in the process of heat-treating the steel plate after cold rolling, the control target for the thermal history is to recrystallize the structure after cold rolling. A cooling process in the finish annealing process, a cooling process in strain relief annealing for a core member punched from a steel sheet, and a special overaging treatment for the purpose of Cu precipitation only are conceivable.

The characteristic of this thermal history is to appropriately control the cooling from the temperature range where Cu can sufficiently dissolve as an equilibrium state, (1) the temperature at which cooling starts, (2) the relatively high temperature in the cooling process Four points are the retention time in the region, (3) the retention time in the relatively low temperature region during the cooling process, and (4) the stress during the cooling process. These will be described below. In addition, the following description includes phenomena (mechanisms) including atomic behavior during heat treatment, but this is just a prediction that is considered appropriate at the present time, and it should be noted that it is not completely established. Keep

The first is the temperature at which cooling is initiated. This temperature is preferably a temperature at which Cu, Ni and Al are sufficiently dissolved in an equilibrium state. If it is the composition of the steel of the present invention, it will be 800° C. or higher. Although the details will be described later, the concentration of Ni and Al on the surface of the Cu particles, which is characteristic of the present invention, rapidly precipitates and concentrates Cu, Ni, and Al dissolved in a highly supersaturated state during the temperature rise process. Rather, Cu, Ni, and Al, which are dissolved in an equilibrium state, are precipitated and concentrated in a quasi-equilibrium manner during the temperature drop process. It is preferably 850° C. or higher. On the other hand, if this temperature is too high, the crystal structure will be excessively coarsened and the magnetic properties will deteriorate. Therefore, it is preferable to set the temperature to 1100° C. or lower, more preferably 1050° C. or lower.

Next is the cooling process from the Cu solid solution temperature. In this cooling process, Cu, which cannot be said to have a sufficiently high solubility in the Fe phase, starts to precipitate in a quasi-equilibrium state to achieve a stable state. At this time, since the diffusion rate of Ni and Al is sufficiently high in a relatively high temperature range, Ni and/or Al are concentrated at the interfaces between the Cu particles and the Fe phase in parallel with the precipitation of the Cu particles. Basically, this concentration should occur not a little in the cooling process from the Cu solid solution temperature, but in order to increase the concentration to the extent that the invention effect is expressed, the cooling cycle is intentionally changed. need to control. Although the reason for this is not clear, the diffusion distance of Ni and Al related to the precipitation interval (the density of generation of precipitation nuclei) as well as the precipitation rate of Cu particles, and the diffusion speed of Ni and Al moving moderately over that distance This is thought to be due to the need for the phenomenon to proceed under conditions in which is within a specific range. In the present invention, this phenomenon is controlled by dividing the temperature range of the cooling process into three.

First, in a temperature range in which Ni and Al can sufficiently diffuse, a situation is realized in which a considerable amount of Cu precipitation nuclei should be formed, and Ni and/or Al are allowed to reach the periphery thereof. This temperature range corresponds to a temperature range of 700-800.degree. In the present invention, this temperature range may be referred to as "temperature range A", and the characteristic Cu particle distribution in the present invention, in particular, the characteristic Cu particles in which Ni and/or Al are sufficiently concentrated are formed. Therefore, it is preferable that the average cooling rate in the temperature region A during the cooling process is 20° C./s or less. More preferably, it is 12° C./s or less. On the other hand, it is necessary to continue cooling at a certain cooling rate in order to promote precipitation of Cu and concentration of Ni and/or Al. Therefore, the average cooling rate in the temperature zone A should be 5°C/s or higher, preferably 8°C/s or higher.

Next, the precipitation stage of Cu particles within the Fe phase crystal grains will be described. When the temperature of the steel sheet becomes lower than 700° C. during the cooling process, a large amount of Cu particles are precipitated in the Fe phase crystal grains. If it is a practical cooling rate, fine Cu particles are precipitated at a higher number density as the temperature decreases, but if the number density of Cu particles becomes excessively high, Ni and / or Al on the surface of one Cu particle This is not preferable because the amount of concentration decreases. Therefore, in the present invention, it is preferable to allow Cu precipitation to proceed sufficiently at an intermediate temperature. This temperature range corresponds to a temperature range of 550 to 700.degree. In the present invention, this temperature range may be referred to as temperature range B, and is a temperature range particularly effective for controlling the number density of precipitation of Cu particles. If the number density of Cu particles is appropriate as described above, it is possible to sufficiently concentrate Ni and/or Al on the surface thereof. For this purpose, it is preferable to set the average cooling rate in the temperature zone B to 15° C./s or less. More preferably, it is 10° C./s or less. On the other hand, it is necessary to continue cooling at a certain cooling rate in order to promote precipitation of Cu and concentration of Ni and/or Al. Therefore, the average cooling rate in temperature zone B should be 3° C./s or higher, preferably 6° C./s or higher.

The third temperature range is the temperature range of 450-550°C. In this manufacturing method, a sufficient amount of Cu is deposited up to 550° C. as described above. For this reason, the precipitation amount of relatively fine Cu particles formed by retention at 550° C. or less is suppressed, and the main purpose of this temperature range is to concentrate Ni and/or Al on the surface of the formed Cu particles. It is to increase the amount of production. This temperature range may be referred to as temperature range C in the present invention. In order to sufficiently concentrate Ni and/or Al, it is preferable to set the average cooling rate of the temperature region C in the cooling process to 12° C./s or less. More preferably, it is 8° C./s or less. On the other hand, it is necessary to continue cooling at a certain cooling rate in order to promote precipitation of Cu and concentration of Ni and/or Al. Therefore, the average cooling rate in temperature zone C should be 2° C./s or more, preferably 4° C./s or more.

In the temperature range of 450 ° C. or less, the diffusion of solid solution Cu in the Fe phase becomes insufficient, and even if Cu particles precipitate, they become excessively fine and difficult to contribute to high strength. becomes insufficient, so it has little effect on the enrichment of these elements. Therefore, the cooling conditions for the temperature range of 450° C. or lower are not particularly limited.

As described above, in the present manufacturing method, the temperature range of 450 to 800° C. is divided into three temperature ranges A, B, and C.
In the present manufacturing method, the cooling conditions were explained by the "average cooling rate" in the temperature ranges A, B, and C, but the effect of the present invention is that the precipitation of Cu and the diffusion and segregation of Ni and Al in the cooling process are continuously performed. It is achieved by control, and it is preferable that the temperature within each of the above temperature ranges is accompanied by a continuous temperature drop. In other words, even if the average cooling rate in the temperature range is the same, it is preferable that it does not accompany holding at a constant temperature or raising the temperature.

Furthermore, it is preferable that the cooling rate is gradually reduced when cooling to 450 to 800°C. For the above three temperature ranges, it is preferable that "average cooling rate in temperature range A" > "average cooling rate in temperature range B" > "average cooling rate in temperature range C", and further each temperature Cooling in which the cooling rate gradually decreases is preferable, instead of linearly decreasing the temperature within the region.

Furthermore, it is the tension applied to the steel sheet during residence in the above-mentioned temperature zones A, B, and C that affects the characteristic Cu particle distribution of the present invention. This tension affects the stress state around the Cu particles and in the Ni and Al composition variation regions, and works favorably in controlling the distribution of the Cu particles and the concentration of Ni and Al around them. Precipitation and segregation under stress increase the amount of Ni and/or Al enrichment on the final Cu particle surface. It is preferably cooled in the temperature range B, more preferably in the temperature range A, more preferably in the temperature range C, with a tension of 4 MPa or more applied, as described above. Although the upper limit is not particularly limited, it should be kept at about 10 MPa in order to avoid unintentional deformation of the steel sheet during heat treatment.

In the non-oriented electrical steel sheet of the present invention manufactured as described above, Cu particles contained in ferrite crystals have an average particle diameter of 0.5 to 100 nm and a number density of 80 to 1000/μm ³ . , satisfies equation (1) for Cu particles. As a result, the tensile strength TS becomes high strength of 600 MPa or more. For this reason, the non-oriented electrical steel sheet of the present invention can be used as it is (without aging treatment) after being processed into a predetermined shape required as a material for a rotor core core that requires high strength. Become.

Further, in the non-oriented electrical steel sheet of the present invention, since Ni and Al are concentrated on at least part of the surface of the Cu particles, the balance between strength and punchability can be improved. When a non-oriented electrical steel sheet is punched into a predetermined shape required as an iron core of a motor core, as shown in FIG. It is in. In other words, if the strength of the non-oriented electrical steel sheet is increased and the tensile strength TS is increased, the number of times of punching is reduced. Here, the number of times of punching is the number of times of punching at which the height of burrs generated in the machined constituent member (product) is 50 μm or more when repeatedly punching a non-oriented electrical steel sheet using a 15 mmφ steel die. be.

In the non-oriented electrical steel sheet of the present invention, since Ni and Al are concentrated on at least a part of the surface of the Cu particles, if the strength is the same, compared to the case where Ni and Al are not concentrated, punching A tendency to increase the number of times is obtained. This is because the concentration of Ni and Al on the surface of the Cu particles hardens the surface layer of the Cu particles, suppresses the cutting of the Cu particles due to dislocations accompanying the deformation of the steel sheet, and the precipitation strengthening effect of the Cu particles becomes significant. On the other hand, it is possible to effectively increase the strength with a smaller number of particles. This is thought to be due to the fact that Moreover, the non-oriented electrical steel sheet of the present invention is advantageous in obtaining a high magnetic flux density with the same strength as compared with a conventional high-strength electrical steel sheet utilizing Cu particles.

Steel grades A to F containing each component (% by mass) shown in Table 1, with the balance being Fe and inevitable impurities, were vacuum melted to produce 50 kg ingots. After that, a test piece of 40×100×200 mm was prepared by hot forging, and a hot-rolled steel plate with a thickness of 2 mm was prepared by hot rolling. Furthermore, the hot-rolled sheet was annealed by water cooling after soaking at 900° C. for 60 seconds. Then, it was descaled by pickling and cold rolled to a thickness of 0.30 mm. The obtained cold-rolled sheets of steel types A to F were subjected to finish annealing under the conditions shown in Table 2. Each test no. Steel grades 1-1 to 1-6, 2-1 to 2-6, 3-1 to 3-9, 4-1 to 4-6, cooling start temperature in finish annealing (maximum attainment temperature (°C)), 700 Cooling rate (°C/s) from ~800°C (temperature range A), cooling rate (°C/s) from 550 to 700°C (temperature range B), cooling rate (°C/s) from 450 to 550°C (temperature range C) s), and Table 2 shows the tension (tensile force (MPa)) applied to the steel sheet during residence in the temperature regions A, B, and C. In addition, test No. For 4-1 to 4-3, additional aging treatment (tension 0 ), and test No. For 4-4 to 4-6, additional aging treatment (tension 0) was performed at a cooling rate (° C./s) shown in Table 2 at 450 to 550° C. (temperature range C).

Test no. For 1-1 to 1-6, 2-1 to 2-6, 3-1 to 3-9, 4-1 to 4-6, average particle diameter of Cu particles (average diameter Dp (nm)), number density (pieces/μm ³ ), the number of all Cu particles to be observed (total number of particles Nt), and among all the Cu particles to be observed, one or two of Ni and Al are concentrated on at least part of the surface. The number of Cu particles (the number of concentrated particles Nx), their ratio (Nx/Nt), the ratio of the area SC and the area SA (area ratio SA/SC), each characteristic (tensile strength TS (MPa), flash Table 3 shows the number of times of punching (×10 ⁴ times) and the number of times of punching (TS*number of times) at which the height becomes 50 μm or more.

Test no. 1-3 to 1-6, 2-2, 2-3, 2-5, 2-6, 3-1, 3-2, 3-4, and 3-6 are examples of the present invention, and the tensile strength TS is It has a high strength of 600 MPa or more and can be punched 100,000 times or more. On the other hand, Test No. 1-1, 1-2, 2-1, 2-4, 3-3, 3-5, 3-7 to 3-9, 4-1 to 4-6 are comparative examples, tensile strength TS is 600 MPa As described above, the number of times of punching was not able to satisfy any of 100,000 times or more.

Each test No. shown in Examples. FIG. 2 shows the relationship between the tensile strength TS and the number of times of punching for 1-1 to 1-6, 2-1 to 2-6, 3-1 to 3-9, and 4-1 to 4-6. The tensile strength TS and the number of punches are in a semi-proportional relationship. The result was that the tensile strength TS was high (high strength), and a non-oriented electrical steel sheet having an excellent balance between strength and punching workability was obtained according to the present invention.

It should be noted that the number of times of punching varies with different levels of tensile strength TS. Table 3 shows tensile strength TS×punching number (TS*punching number) as a tentative guideline for showing the balance between tensile strength TS and punching number. However, the target (TS* number of times) shown here is merely an example, and does not define the present invention as an absolute value.

Claims (4)

By mass%, Si: 2.0 to 6.0%, Cu: 1.7 to 4.0%, and further Al: 3.0% or less, Ni: 4.0% or less one or two 0.7 % or more in total, and as optional elements,
Mn: 5.0% or less,
P: 0.300% or less,
B: 0.100% or less,
Nb: 1.00% or less,
Mo: 1.000% or less,
Bi: 0.010% or less,
Sn: 0.10% or less,
Sb: 0.10% or less,
Cr: 0.30% or less,
Ca: 0.020% or less,
Mg: 0.020% or less,
La: 0.020% or less,
Ce: A non-oriented electrical steel sheet containing 0.020% or less and the balance being Fe and impurities,
The metal structure is ferrite polycrystal,
Cu particles are contained in the ferrite crystal,
Cu particles in the ferrite crystal have an average particle size of 0.5 to 100 nm and a number density of 80 to 1000/μm ³ ,
A non-oriented electrical steel sheet, characterized in that Cu particles in ferrite crystals satisfy formula (1).
Nx/Nt≧0.1 Expression (1)
here,
Nx: Among all Cu particles to be observed, the number of Cu particles in which one or both of Ni and Al are concentrated on at least a part of the surface Nt: The number of all Cu particles to be observed Regarding Cu particles in which one or both of Ni and Al are concentrated on at least a part of the surface, in observation by 3DAPFIM, the area SC and the area SA satisfy the formula (2). Claim 1 The non-oriented electrical steel sheet according to .
SA/SC>0.1 Expression (2)
here,
SC: Area of a region that satisfies "Fe concentration ≤ 90% and Cu concentration ≥ total concentration of Ni and Al" SA: Area that satisfies "Fe concentration ≤ 90% and Cu concentration < total concentration of Ni and Al" area of The tensile strength TS is 600 MPa or more, and the number of times of processing is 100,000 times or more when the height of burrs generated in the processed product is 50 μm or more when repeated punching is performed using a 15 mmφ steel die. The non-oriented electrical steel sheet according to any one of claims 1 and 2, wherein A rotor core core of an IPM motor, characterized by being formed by laminating the non-oriented electrical steel sheets according to any one of claims 1 to 3.

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