JP6880920B2 - Non-oriented electrical steel sheet and its manufacturing method, and motor core and its manufacturing method - Google Patents

Description

The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, and a motor core and a method for manufacturing the same.

In recent years, especially in the field of electrical equipment such as rotary machines, small and medium-sized transformers, and electrical components, in the movement to protect the global environment represented by global _{power reduction, energy saving, CO 2 emission reduction, etc.} Therefore, the demand for higher efficiency and smaller size of motors is increasing more and more. In such a social environment, improving the performance of non-oriented electrical steel sheets used as the core material of motors is an urgent issue.

For example, in the automobile field, non-oriented electrical steel sheets are used as the core of a drive motor of a hybrid electric vehicle (HEV) or the like. The drive motors used in HEVs are in increasing demand for miniaturization due to restrictions on installation space and reduction of fuel consumption due to weight reduction.
With the demand for miniaturization of drive motors, motors need to have higher torque. Therefore, the non-oriented electrical steel sheet is required to further improve the magnetic flux density.
In addition, since the battery capacity mounted on an automobile is limited, it is necessary to reduce the energy loss in the motor. Therefore, non-oriented electrical steel sheets are required to further reduce iron loss.

Among these motor cores, for example, there is a so-called "split core" in which a winding is wound around a core divided into individual teeth, and then the cores are assembled to form the final form of the stator core. The non-oriented electrical steel sheet used for the dividing core is required to have better characteristics in a specific unidirectional or bidirectional direction than to have uniform characteristics in the in-plane direction.
As non-oriented electrical steel sheets corresponding to such characteristics, for example, as disclosed in Patent Documents 1 and 2, the magnetic characteristics of the non-oriented electrical steel sheets in the plate surface in the rolling direction and the direction perpendicular to rolling are improved. Steel sheets have been proposed.

Further, the divided core is often applied to a core having a complicated shape, and particularly high accuracy is required for the member shape. However, since the electromagnetic steel sheet obtained by sufficiently heat-treating to reduce the iron loss and coarsening the crystal grains becomes soft, the shape accuracy may decrease when the member (steel sheet blank) is punched. It has been pointed out that there is.
On the other hand, Patent Documents 3 to 5 disclose techniques for improving punching accuracy by, for example, hardening a steel sheet or refining crystal grains.

Further, for example, it is known that hot rolling conditions have a great influence on the magnetic properties of a final product, and as disclosed in Patent Documents 6 to 9, lubrication, strain amount, and rolling temperature are precisely controlled. Efforts are being made to control the finishing hot rolling end temperature to about 800 ° C or lower.

Further, the electrical steel sheet may be used after additional heat treatment. As a typical example, "Stress Relief Annealing (SRA)" is known. This is a heat treatment for finally removing unnecessary strain because the strain unavoidably introduced into the steel plate due to punching or the like when the steel plate is processed as an electric component worsens the iron loss. This heat treatment is applied to a member (steel plate blank) cut out from a steel plate or a motor core (for example, a stator core) in which members are laminated.
However, while strain-removing annealing has the effect of releasing strain and improving iron loss, at the same time, crystal orientation unfavorable for magnetic characteristics may develop and the magnetic flux density may decrease. Therefore, when particularly high magnetic characteristics are required, it is required to avoid a decrease in magnetic flux density due to strain relief annealing.

Although few techniques have been studied for controlling magnetic properties in strain relief annealing, techniques related to semi-process non-oriented electrical steel sheets have been disclosed as related techniques. Semi-process non-oriented electrical steel sheets are shipped after being recrystallized by finish annealing with strain applied, and then heat-treated by the steel sheet user to release the strain and obtain magnetic properties. It is a thing.
For example, Patent Document 10 shows that it is effective to set the heating rate at the time of finish annealing to 5 ° C./sec to 40 ° C./sec. Further, Patent Document 11 discloses a technique in which the magnetic properties for a semi-process are improved by increasing the heating rate up to 740 ° C. to 100 ° C./sec or more.

Japanese Unexamined Patent Publication No. 2008-127600 Japanese Unexamined Patent Publication No. 2012-13207 International Publication No. 2003/002777 Japanese Unexamined Patent Publication No. 2003-197414 Japanese Unexamined Patent Publication No. 2004-152791 Japanese Unexamined Patent Publication No. 11-229096 Japanese Unexamined Patent Publication No. 2001-279326 Japanese Unexamined Patent Publication No. 2011-11165 Japanese Unexamined Patent Publication No. 2006-045613 Japanese Unexamined Patent Publication No. 03-223424 International Publication No. 2014/129034

However, in the conventional technology, the magnetic characteristics in a specific one or two directions are good for the split core, the processing accuracy at the time of punching is good, and the magnetic characteristics after strain relief annealing. Was not enough to consider that it was good. Therefore, further improvement of these characteristics has been required for the split core.

The present invention has been made in view of the above circumstances, and an object of the present invention is that the split core is excellent in magnetic properties in two directions, a rolling direction and a rolling perpendicular direction, and punching accuracy, and further, distortion removal. It is an object of the present invention to provide a non-directional electromagnetic steel plate having excellent magnetic properties even after being annealed, and a method for producing the same.

The present inventors have studied to obtain a non-oriented electrical steel sheet having excellent magnetic characteristics as described above by changing the crystal orientation in the plate thickness direction. Pursuing that condition, reducing the degree of integration of the {223} <252> orientation in the intermediate layer can reduce the magnetic properties in the two directions, the rolling direction and the rolling perpendicular direction, and the punching accuracy for the split core. Furthermore, it was found that it has a strong correlation with the improvement of magnetic properties after strain removal annealing. Then, the conditions for obtaining a steel sheet having these characteristics were examined in detail. As a result, it was found that a steel sheet having the above characteristics can be obtained when the difference between the surface temperature of the steel sheet and the center temperature of the sheet thickness is within a specific range at the start of hot rolling.

Furthermore, from the viewpoint that the texture change in the intermediate layer is related to the shear deformation due to rolling, detailed studies have been conducted on the state of strain applied by hot rolling. As a result, even when the amount of strain applied to the steel sheet in the first half of the pass is larger than the amount of strain applied in the second half in the pass schedule of finishing hot rolling in which a plurality of passes are continuously performed, the intermediate layer of the steel sheet , {223} <252> It was confirmed that the degree of integration of the orientation could be reduced.

That is, the present invention has been made based on these findings. That is, the gist of the present invention is as follows.

<1> By mass%,
C: 0.0030% or less,
Si: 0.01% to 3.50%,
Al: 0.001% to 2.500%,
Mn: 0.01% to 3.00%,
P: 0.180% or less,
S: 0.0030% or less, and the balance: having a chemical composition containing Fe and impurities.
A non-oriented electrical steel sheet having a degree of integration of {223} <252> orientations of 6 or less in an intermediate layer having a plate thickness of 1/10 to 1/5.
<2> The non-oriented electrical steel sheet according to <1>, wherein the degree of integration of {100} <001> orientations in the surface layer from the surface of the steel sheet to the thickness of 1/10 is 6 or more.
<3> In the surface layer, the ratio of the degree of integration of {100} <001> orientation (MI ₀₀₁ ) to the degree of integration of {100} <011> orientation (MI _{011) is}
MI ₀₀₁ / MI ₀₁₁ > 1.0
The non-oriented electrical steel sheet according to <1> or <2>, which satisfies the relationship of.
_{<4> The ratio (B 50 / Bs) of the average magnetic flux density B 50} and the saturated magnetic flux density Bs in the rolling direction and the direction perpendicular to the rolling when excited with a magnetization force of 5000 A / m is 0.890 or more <1> The non-directional electromagnetic steel plate according to any one of ~ <3>.
<5> were performed flux density B _A of the steel sheet before carrying out the heat _treatment, and heating rate is 100 ° C. / hr, the maximum temperature is 800 ° C., and the holding time at 800 ° C. is a heat treatment under conditions of 2 hours when the magnetic flux density of the steel sheet after the _{B B,} the ratio between said _{B a} wherein _{B B is,} to satisfy the relationship of B B / _{B a} ≧ 0.980 <1> ~ or <4> 1 The non-oriented electrical steel sheet described in the section.
<6> A hot rolling step of hot rolling a slab having the chemical composition described in <1>, and
A cold rolling step of cold rolling on a steel sheet after the hot rolling step, and a cold rolling step.
It has a finish annealing step of finish annealing the steel sheet after the cold rolling step.
The method for producing a non-oriented electrical steel sheet according to any one of <1> to <5>, which satisfies at least one of the following conditions (a) and (b) in the hot rolling step.
(A) The difference between the surface temperature Ts of the steel sheet and the center temperature Tc of the sheet thickness is set to 50 ° C. or more, and finish hot rolling is started. The non-directional item according to any one of <7><1> to <5>, in which a plurality of passes are continuously finish-rolled so as to satisfy the condition of the strain amount σ2) ≧ 1.5 applied to the steel sheet. Motor core made by laminating sex electromagnetic steel plates.
<8> A step of punching the non-oriented electrical steel sheet according to any one of <1> to <5> to obtain a punched member.
The process of laminating the punched members and
A method for manufacturing a motor core.

According to the present invention, for a split core, the magnetic properties in two directions, the rolling direction and the direction perpendicular to the rolling direction, and the punching accuracy are excellent, and further, the excellent magnetic properties even after strain relief annealing is performed. It is possible to provide a non-oriented electrical steel sheet having and a method for producing the same.

It is a perspective view which shows an example of the motor core which concerns on this embodiment.

Hereinafter, an example of a preferred embodiment of the present invention will be described in detail.
In the present specification, the numerical range represented by using "~" means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.

In the present specification, when the terms "plate thickness 1/10", "plate thickness 1/5", and "plate thickness 1/2" are used, they indicate predetermined positions in the plate thickness direction from the surface of the steel plate.
The surface layer indicates a region from the surface of the steel plate to the thickness of 1/10. The intermediate layer indicates a region from a plate thickness of 1/10 to a plate thickness of 1/5. The central layer indicates a region from a plate thickness of 1/5 to a plate thickness of 1/2.

In the present specification, for each direction (for example, {223} <252> direction, {100} <001> direction, etc.), the mirror index in the normal direction (rolling surface direction) of the rolled surface and the rolling direction are used. For the mirror exponents in the parallel directions (in-rolling plane direction), the directions within ± 5 ° are assumed to be the relevant directions.

<Directional electromagnetic steel sheet>
(Characteristics of crystal orientation)
The non-oriented electrical steel sheet according to this embodiment has a mass% of C: 0.0030% or less, Si: 0.01% to 3.50%, Al: 0.001% to 2.500%, Mn: It has a chemical composition containing 0.01% to 3.00%, P: 0.180% or less, S: 0.0030% or less, and the balance: Fe and impurities.

The non-oriented electrical steel sheet according to the present embodiment has an integration degree of {223} <252> orientation in the intermediate layer of 6 or less (this is a feature (A)).
The non-oriented electrical steel sheet according to the present embodiment has the above characteristics, and therefore has excellent magnetic characteristics in two directions, a rolling direction and a rolling perpendicular direction, and punching accuracy for the split core, and further, strain relief annealing. It has excellent magnetic characteristics even after it has been subjected to the above (hereinafter, this characteristic may be referred to as "characteristics for split cores"). This will be described below.

The degree of integration of the {223} <252> orientation in the intermediate layer is 6 or less, which is an important feature in the non-oriented electrical steel sheet of the present embodiment.
The {223} <252> orientation is relatively close to the {111} orientation, which is unfavorable for magnetic properties. The {223} <252> direction is a direction that should be suppressed so as to be naturally reduced. Further, the degree of integration of the {223} <252> orientation changes greatly in the intermediate layer of the plate thickness.
Therefore, in the non-oriented electrical steel sheet of the present embodiment, the degree of integration of the {223} <252> orientation in the intermediate layer is defined.
The accumulation of {223} <252> orientations is associated with shear deformation in the steel sheet manufacturing process, especially in the hot rolling process, due to the strong action of shear deformation in hot rolling mainly in the intermediate layer. Details will be described later.

The {223} <252> orientation is easy to accumulate in high-purity steel with a C amount and N amount of several tens of ppm (mass basis) that are cold-rolled and recrystallized and annealed. Further, the {223} <252> orientation is also an intermediate orientation between the {111} <211> orientation and the {112} <110> orientation, which is not preferable for the magnetic characteristics of the non-oriented electrical steel sheet. The {223} <252> orientation is an orientation in which accumulation is difficult to avoid even in the non-oriented electrical steel sheet according to the present embodiment.
Further, the {223} <252> orientation is not only an unfavorable orientation for the magnetic characteristics, but is not preferable considering that it is applied as a material for a split core. In the non-oriented electrical steel sheet according to the present embodiment, it is assumed that the material for the split core has good magnetic characteristics in the two directions of the rolling direction and the rolling perpendicular direction. However, the {223} <252> orientation cannot be said to be an advantageous direction for improving the characteristics of these two directions. Therefore, if the degree of integration of the {223} <252> orientation in the intermediate layer is more than 6, it becomes difficult to obtain good magnetic characteristics for the split core. It is preferably 5 or less, more preferably 4 or less. The lower limit of the degree of integration of the {223} <252> orientation in the intermediate layer is not particularly limited, and examples thereof include 1 and more. Of course, if the accumulation of {223} <252> directions in the intermediate layer can be avoided, the degree of accumulation of these directions may be 0.

Further, the crystals having the {223} <252> orientation of the intermediate layer formed through the shear deformation in the hot rolling step have different crystal orientations from the adjacent surface layer and the central layer, so that the crystal grain size is different. In the case of coarsening, the crystal grains existing in the intermediate layer were in a situation where they were likely to grow.
However, in the non-oriented electrical steel sheet of the present embodiment, the {223} <252> orientation, which is unfavorable for the magnetic characteristics existing in the intermediate layer, is reduced. As a result, it is considered that the deterioration of the magnetic characteristics can be suppressed even when the grains are grown by strain removing annealing.

Further, the non-oriented electrical steel sheet of the present embodiment preferably has an integration degree of {100} <001> orientation in the surface layer of 6 or more (this is a feature (B)).

It is well known that increasing the {100} orientation is advantageous for magnetic properties. However, the method of simply adding strong machining such as low-temperature finish hot-rolling with hot rolling and high cold-rolling reduction rate with cold rolling, which has been proposed conventionally, increases the {100} orientation, but the main orientation is a steel plate. The direction is {100} <011>, which improves the magnetic characteristics in the 45 ° direction, and is not always optimal for split core applications.
In the non-oriented electrical steel sheet according to the present embodiment, as described above, the {223} <252> orientation, which tends to develop in grain growth, is suppressed, and as a result, the {100} orientation develops. However, the {100} <001> orientation develops instead of the {100} <011> orientation. This improves the magnetic properties of the steel sheet in the rolling direction and the direction perpendicular to the rolling, and exhibits in-plane anisotropy preferable for split core applications.

The development of the {100} <001> orientation is considered to be related to the suppression of the {223} <252> orientation described above, and the change in the {100} <001> orientation is particularly remarkable in the surface layer. The reason for this is unknown, but it is speculated as follows.
Conventionally, the {100} <001> orientation of the surface layer has been eroded by the grain growth of the {223} <252> orientation in the intermediate layer. On the other hand, in the non-oriented electrical steel sheet according to the present embodiment, since the accumulation of the {223} <252> orientation of the intermediate layer is suppressed, the {100} <001> orientation of the surface layer is likely to develop. It is thought that it was.
Therefore, in the non-oriented electrical steel sheet according to the present embodiment, the degree of integration of the {100} <001> orientation in the surface layer is preferably 6 or more. It is preferably 9 or more, more preferably 12 or more. The upper limit of the degree of integration of the {100} <001> orientation in the surface layer is not particularly limited, but for example, it may be 40 or less.
The selectivity of the crystal orientation in the grain growth becomes remarkable especially when the additional heat treatment is performed at a low heating rate, and it is also related to the fact that the decrease in the magnetic flux density due to the growth of the recrystallized grains can be suppressed. Conceivable. This will be described in detail later.

In addition to the above features, the non-oriented electrical steel sheet of the present embodiment has an integration degree of {100} <001> orientation (MI ₀₀₁ ) and an integration degree of {100} <011> orientation (MI 001) in the surface layer. It is preferable that the ratio with MI _{011 ) satisfies the relationship of MI 001} / MI ₀₁₁ > 1.0 (this is referred to as feature (C)).

The feature (C) is a feature (B) characterized by a change in the in-plane orientation. As described above, in the non-oriented electrical steel sheet of the present embodiment, the accumulation in the {223} <252> orientation is reduced in the intermediate layer. Along with this, the accumulation in the {100} direction increases. At this time, the development of the {100} <001> orientation is promoted instead of the {100} <011> orientation. In the non-oriented electrical steel sheet according to the present embodiment, this feature is exhibited in the degree of integration of {100} <001> orientation (MI ₀₀₁ ) and {100} <011> orientation, especially in the surface layer where the tendency is remarkable. It is expressed as a ratio to the degree of integration (MI _011).
When the in-plane texture change in the {100} orientation has the above relationship, it is possible to obtain a steel sheet having in-plane anisotropy preferable for the split core application. The MI ₀₀₁ / MI ₀₁₁ is preferably 2.0 or more, more preferably 4.0 or more, and further preferably 8.0 or more.

The crystal orientation can be measured by the following method. The surface layer on one side is removed by performing mechanical polishing and chemical polishing on a steel plate sample of about 30 mm × 30 mm cut out from the steel plate. When the surface layer is removed, measurement test pieces having been reduced in thickness are prepared until the center of the surface layer or the intermediate layer of the original steel sheet in the plate thickness direction becomes the surface.
For each measurement test piece, polar diagrams of {200} plane, {110} plane, and {211} plane are measured by an X-ray diffractometer, and a crystal orientation distribution function ODF (Orientation Determination Function) in each layer is created. Based on this crystal orientation distribution function, the degree of integration of each orientation in each layer is obtained.

Next, the reason for limiting the chemical composition of the non-oriented electrical steel sheet according to the present embodiment will be described. Regarding the composition of the steel sheet, "%" is "mass%".

The non-oriented electrical steel sheet according to this embodiment has a mass% of C: 0.0030% or less, Si: 0.01% to 3.50%, Al: 0.001% to 2.500%, Mn: It has a chemical composition of 0.01% to 3.00%, P: 0.180% or less, S: 0.0030% or less, and the balance: Fe and impurities.

(C: 0.0030% or less)
C is a component that increases iron loss and causes magnetic aging. Therefore, the smaller the content of C, the better. Therefore, the content of C is set to 0.0030% or less. The preferable upper limit of the amount of C is 0.0025% or less, and more preferably 0.0020% or less. The lower limit of the C content is not particularly limited, but the C content is practically 0.0001% or more in consideration of the industrial purification technology, and 0.0005% or more in consideration of the manufacturing cost.

(Si: 0.01% to 3.50%)
When the content of Si increases, the magnetic flux density decreases and the hardness increases, resulting in deterioration of punching workability. Further, in the manufacturing process itself of the non-oriented electrical steel sheet, workability such as cold rolling is lowered and the cost is high. Therefore, the upper limit of the Si content is 3.50% or less. The preferable upper limit of the amount of Si is 3.20% or less, and the more preferable upper limit is 3.00% or less. On the other hand, Si has the effect of increasing the electrical resistance of the steel sheet, reducing the eddy current loss, and reducing the iron loss. Therefore, the lower limit of the amount of Si is set to 0.01% or more. The preferable lower limit of the amount of Si is 0.10% or more, the more preferable lower limit is 0.50% or more, and further preferably 1.00% or more.

(Al: 0.001% to 2.500%)
Al is inevitably contained in ores and refractories, and is also used for deoxidation. Taking this into consideration, the lower limit is set to 0.001% or more. Further, Al is a component having an action of reducing iron loss by increasing electric resistance and reducing eddy current loss, like Si. Therefore, Al may be contained in an amount of 0.200% or more. On the other hand, when the Al content increases, the saturation magnetic flux density decreases, which leads to a decrease in the magnetic flux density. Therefore, the upper limit of the Al content is set to 2.500% or less. It is preferably 2.000% or less.

(Mn: 0.01% to 3.00%)
Mn increases electrical resistance to reduce eddy current loss and suppresses precipitation of fine sulfides such as MnS, which are harmful to crystal grain growth. For these purposes, Mn is contained in an amount of 0.01% or more. The preferable lower limit of the amount of Mn is 0.15% or more. However, when the Mn content increases, the grain growth during annealing decreases and the iron loss increases. Therefore, the upper limit of the Mn content is set to 3.0% or less. The preferable upper limit of the amount of Mn is 2.50% or less, more preferably 2.00% or less.

(P: 0.180% or less)
P has the effect of increasing the strength without lowering the magnetic flux density. However, if P is excessively contained, the toughness of the steel is impaired and the steel sheet is liable to break. Therefore, the upper limit of the amount of P is 0.180%. The amount of P should be small in terms of suppressing the breakage of the steel sheet. The preferable upper limit of the amount of P is 0.150% or less, more preferably 0.120% or less, still more preferably 0.080% or less. The lower limit of the amount of P is not particularly limited, but it is 0.001% or more in consideration of the manufacturing cost.

(S: 0.0030% or less)
S is 0.0030% or less because it inhibits recrystallization and grain growth during finish annealing and the like due to fine precipitation of sulfides such as MnS. The preferred upper limit of the S content is 0.0020% or less, more preferably 0.0015% or less. The lower limit of the S content is not particularly limited, but the S content is practically 0.0001% or more in consideration of the industrial purification technology, and 0.0005% or more in consideration of the manufacturing cost.

(Fe and impurity elements)
The rest of the steel sheet is Fe and impurity elements. Here, the impurity element refers to a component contained in the raw material or a component mixed in the manufacturing process and not intentionally contained in the steel sheet.

The chemical composition is the composition of the steel constituting the steel sheet. If the steel sheet used as the measurement sample has an insulating film or the like on the surface, the measurement is performed after removing the insulating film or the like.
Examples of the method for removing the insulating film of the non-oriented electrical steel sheet include the following methods.
First, the non-oriented electrical steel sheet having an insulating film, etc., aqueous sodium hydroxide (NaOH: 10 _{wt% +} H 2 O: 90 wt%) in 15 minutes at 80 ° C., immersion. Then, it is immersed in an aqueous sulfuric acid solution (H ₂ SO ₄ : 10% by mass + H ₂ O: 90% by mass) at 80 ° C. for 3 minutes. Thereafter, an aqueous solution of nitric acid _(HNO 3: 10 _{wt% +} H 2 O: 90 wt%) by normal temperature for 1 minute just under (25 ° C.), washed immersed in. Finally, dry with a warm air blower for a little less than 1 minute. As a result, a steel sheet from which the insulating film described later has been removed can be obtained.

The content ratio of each element in the steel plate can be measured by, for example, inductively coupled plasma mass spectrometry (ICP-MS method: Inductively Coupled Plasma-Mass Spectrometry). Specifically, first, a non-oriented electrical steel sheet to be measured is prepared. A part of the electrical steel sheet is cut into pieces and weighed, and this is used as a measurement sample. The measurement sample is dissolved in an acid to prepare an acid solution, the residue is collected from a filter paper and separately melted in an alkali or the like, and the melt is extracted with an acid to form a solution. By mixing the solution and the acid solution and diluting it if necessary, an ICP-MS measurement solution can be obtained.

(Magnetic characteristics of non-oriented electrical steel sheets)
The non-directional electromagnetic steel plate according to the present embodiment has excellent magnetic properties in two directions, a rolling direction and a rolling perpendicular direction, for the split core, and is the same as the rolling direction when excited with a magnetization force of 5000 A / m. _{The ratio (B 50} / Bs) of the average magnetic flux density B _{50 in} the perpendicular direction to the saturated magnetic flux density Bs is preferably 0.890 or more. It is preferably 0.900 or more, more preferably 0.905 or more, and even more preferably 0.910 or more. The upper limit is not particularly limited, but the closer it is to 1, the better, and for example, 0.980 or less can be mentioned.

-Punching accuracy-
As described above, the non-oriented electrical steel sheet according to the present embodiment has a lower degree of integration in the direction of the intermediate layer {223} <252> than the ordinary steel sheet. As a result, the non-oriented electrical steel sheet exhibits favorable characteristics for punching accuracy. The reason for this is not clear, but I think it is as follows.
Since the work hardening is large in the {223} direction close to the {111} direction, the plastic deformation region expands from the fracture surface to the inside of the steel material during punching, and the region in which the steel material is stretched and deformed becomes large. Therefore, it is considered that the processing accuracy of the steel sheet having a high degree of integration in the {223} direction is likely to decrease. Therefore, in order to improve the punching accuracy, it is considered that reducing the degree of integration of the {223} <225> orientation works effectively.

-Changes in magnetic properties due to additional heat treatment (strain removal annealing)-
The non-oriented electrical steel sheet according to the present embodiment can reduce the decrease in magnetic flux density that has occurred during the growth of recrystallized grains, even when additional heat treatment (strain removal annealing) is performed at a low heating rate. It can be suppressed.
The magnetic flux density B _A of the steel sheet before carrying out the additional heat _treatment, and heating rate is 100 ° C. / hr, the maximum temperature is 800 ° C., and after a holding time at 800 ° C. were conducted to a heat treatment under conditions of 2 hours when the magnetic flux density of the steel sheet was _{B B,} the ratio of _{B B} and _{B a is,} B B / _{B a} ≧ 0.980 (preferably _B B / _{B a} ≧ 0.985, more preferably _B B / The relationship of B _A ≥ 0.990) can be satisfied.
_{Incidentally,} B B / _B upper limit of _A is not particularly specified, there is no characteristic degradation by the addition heat treatment _{(i.e., B B / B A = 1.00} ) It is also a reference to a target. However, in the non-oriented electrical steel sheet of the present embodiment, since the crystal orientation is controlled preferably to account for changes in the thickness direction, preferably the orientation grow preferentially for magnetic properties, B B _/ B _A is It may exceed 1.00.
Here, the measurement method of the magnetic flux density B _A and B _B before and after carrying out the additional heat treatment is the same as the aforementioned B _50.

The conditions for the additional heat treatment that defines the non-oriented electrical steel sheet according to the present embodiment are set to specific values in the heating rate, the maximum temperature reached, and the holding time as described above. This uses values that are considered to be typical as conditions for strain relief annealing that are currently practically practiced. When the non-oriented electrical steel sheet according to the present embodiment is used for performing additional heat treatment, the effect of suppressing the decrease in magnetic flux density due to the additional heat treatment is limited to this value in terms of heating rate, maximum temperature reached, and holding time. It is not, and can be enjoyed within a wide range to some extent. For example, as conditions for additional heat treatment for which the characteristics for the split core can be confirmed, the heating rate is 30 ° C./hr to 500 ° C./hr, the maximum temperature reached is 750 ° C. to 850 ° C., and the holding time at 750 ° C. or higher is 0.5 hours. A range of up to 100 hours can be mentioned.

As described above, even when the steel sheet according to the present embodiment is subjected to additional heat treatment (straining and annealing), a decrease in magnetic flux density is suppressed as compared with the case where the conventional steel sheet is strained and annealed. The reason for this is not always clear, but I think it is as follows.

In conventional non-oriented electrical steel sheets, when grain growth is performed at a relatively low temperature by additional heat treatment at a low heating rate such as strain relief annealing, it is more advantageous than crystal grains having a {100} orientation, which is advantageous for magnetic properties. , Growth of crystal grains having other orientations (eg, {111}, {223}, {112}, etc.) becomes dominant. Since these orientations grow by eroding the {100} orientation in particular, the magnetic flux density of the conventional non-oriented electrical steel sheet is greatly reduced.

On the other hand, in the non-oriented electrical steel sheet according to the present embodiment, at least one of the temperature condition of finish rolling in hot rolling and the pass schedule is controlled under specific conditions. As a result, the degree of integration of the {223} <252> orientation in the intermediate layer of the steel sheet during the production of the non-oriented electrical steel sheet (that is, after finish annealing) is reduced, and the {100} <001> orientation in the surface layer in particular. Development is promoted. Therefore, in the orientation development in the grain growth by the additional heat treatment by the slow heating after the finish annealing, the growth in the orientation such as {111} is not dominant. Then, the crystal grains having an orientation advantageous for increasing the high magnetic flux density in the rolling direction and the direction perpendicular to the rolling direction (that is, the {100} <001> orientation) are not eroded, and the high magnetic flux density in the rolling direction and the direction perpendicular to the rolling direction is increased. Presumed to hold.

The effect of the additional heat treatment on the selectivity of the grown grains is that the heating rate is relatively high (for example, 10 ° C. per second) until the initial stage of grain growth (for example, the crystal particle size is 80 μm or less). Crystals generated at (10 ° C./sec) or higher) have a relatively low heating rate and a low temperature for a long time (for example, 1) in the late stage of grain growth (the crystal particle size is, for example, a stage of more than 80 μm). The growth proceeded at about 100 ° C. (100 ° C./hr) or less per hour, and the holding time in the temperature range of 550 ° C. to 750 ° C., which is a relatively low temperature range for grain growth to occur, was 2 hours or more). It becomes noticeable in some cases.
In the above, the effect of the preferable selection of the crystal orientation on the grain growth was described by the orientation change at around 80 μm, but this effect was set to more than 80 μm, for example 100 μm or more, for example, in finish annealing (in rapid heating annealing). Even in the steel sheet, further grain growth from the steel sheet, for example, preferably orientation selectivity of 200 μm or more is not lost.
On the other hand, for example, in finish annealing (in rapid heating annealing), a steel sheet having a particle size of less than 20 μm, for example, a steel sheet in which an unrecrystallized structure remains, is grown to progress of recrystallization and grain growth, for example, about 50 μm. Even in the case, the preferable orientation selectivity is not lost.

The thickness of the non-oriented electrical steel sheet according to the present embodiment may be appropriately adjusted according to the intended use and the like, and is not particularly limited, but is 0.10 mm to 0.50 mm from the viewpoint of manufacturing. It is preferably 0.15 mm to 0.50 mm. In particular, from the viewpoint of the balance between magnetic characteristics and productivity, 0.15 mm to 0.35 mm is preferable.

Further, the non-oriented electrical steel sheet according to the present embodiment may have an insulating film on the surface of the steel sheet. The insulating film formed on the surface of the non-oriented electrical steel sheet according to the present embodiment is not particularly limited, and may be selected from known ones according to the intended use and the like. For example, the insulating film may be either an organic film or an inorganic film. Examples of the organic film include polyamine resin; acrylic resin; acrylic styrene resin; alkyd resin; polyester resin; silicone resin; fluororesin; polyolefin resin; styrene resin; vinyl acetate resin; epoxy resin; phenol resin; urethane resin; melamine. Examples include resin. Examples of the inorganic film include a phosphate film; an aluminum phosphate film and the like. Further, an organic-inorganic composite film containing the above resin and the like can be mentioned.
The thickness of the insulating film is not particularly limited, but the film thickness per one side is preferably 0.05 μm to 2 μm.

<Manufacturing method of non-oriented electrical steel sheet>
The non-oriented electrical steel sheet according to the present embodiment can be obtained by controlling the temperature condition and pass schedule of finish rolling in hot rolling under specific conditions as described above. The following method is mentioned as an example of a preferable manufacturing method of the non-oriented electrical steel sheet according to the present embodiment.
Hereinafter, an example of a preferable manufacturing method of the non-oriented electrical steel sheet according to the present embodiment will be described.

An example of a suitable manufacturing method for the non-directional electromagnetic steel sheet of the present embodiment is the above-mentioned chemical composition (in mass%, C: 0.0030% or less, Si: 0.01% to 3.50%, Al: 0. Heat a slab with (0.01% to 2.500%, Mn: 0.01% to 3.00%, P: 0.180% or less, S: 0.0030% or less, and balance: Fe and impurities) A hot rolling process (hot rolling process) for hot rolling (hot rolling), a cold rolling process (cold rolling process) for cold rolling (cold rolling) on a steel plate after hot rolling, and a cold rolling process. It has a finish-rolling step of finish-rolling to a steel plate of.
Then, in the hot rolling step, at least one of the following conditions (a) and (b) is satisfied.
(A) The difference between the surface temperature Ts of the steel sheet and the center temperature Tc of the sheet thickness is set to 50 ° C. or more, and finish hot rolling is started. Finish rolling is continuously performed on a plurality of passes so as to satisfy the condition of the strain amount σ2) ≧ 1.5 applied to the steel sheet.

Here, (a) and (b) are conditions for controlling the deformed state of the intermediate layer of the steel sheet. By satisfying at least one of these two conditions, preferably both, a steel sheet having an integration degree of {223} <252> orientation in the surface layer of 6 or less after finish annealing can be obtained (that is,). The above-mentioned feature (A) is obtained). Then, it becomes possible to obtain the characteristics for the split core.

Further, as the non-oriented electrical steel sheet obtained by the above manufacturing method, a steel sheet having an integration degree of {100} <001> orientation in the surface layer of 6 or more can be obtained (that is, the above-mentioned feature (B) is further obtained. ).

Then, according to the above manufacturing method, the ratio of the _{degree of integration of {100} <001> orientation (MI 001} ) and the degree of integration of {100} <011> orientation (MI _{011 ) in the surface layer is MI 001} / MI. _A steel sheet satisfying the relationship of 011> 1.0 is obtained (that is, the above-mentioned feature (C) is further obtained).

Hereinafter, each step in an example of a preferable manufacturing method will be described.

(Hot rolling process)
The heating temperature of the slab before hot rolling is not particularly limited, but it is preferably 1000 ° C. to 1300 ° C. from the viewpoint of cost and the like.

After rough hot rolling is applied to the heated slab, finish rolling (hereinafter, may be referred to as "finish hot rolling") is performed. At the time when the rough rolling is finished and the finish hot rolling is started, the thickness of the steel sheet is 20 mm to 100 mm.
At least one of the temperature condition of the finish hot rolling and the pass schedule is the degree of integration of the {223} <252> orientation in the intermediate layer of the steel sheet that was recrystallized by finish annealing after hot rolling and then cold rolling. It can be an effective control factor for suppression.

An important temperature condition for finish hot rolling is to start rolling with a large difference between the surface temperature Ts of the steel sheet and the center temperature Tc of the sheet thickness. In the present embodiment, the difference between the surface temperature Ts and the plate thickness center temperature Tc and Ts-Tc of 30 ° C. or higher are set to 30 ° C. or higher to start hot rolling, so that the intermediate layer of the steel sheet after cold rolling and finish annealing is { 223} <252> It is possible to suppress the development of orientation. It is preferably 60 ° C. or higher, more preferably 100 ° C. or higher. The upper limit of Ts-Tc is not particularly limited, but for example, in terms of productivity and the like, it may be set to 200 ° C. or lower.
Here, in the present specification, the "surface temperature Ts" means the temperature measured by a contact type thermometer or a radiation thermometer. Further, in the present specification, the "plate thickness center temperature Tc" means a temperature obtained by heat conduction analysis by a commonly known difference method.

Examples of the method for forming the temperature difference between the surface temperature Ts and the plate thickness center temperature Tc in the hot rolling step include the following methods.

A slab cooled to a surface temperature of, for example, 1000 ° C. or lower is charged into a heating furnace having an ambient temperature of 1000 ° C. or higher, and the heating furnace is charged before the entire slab is warmed (for example, within 30 minutes after charging). Rough rolling is performed on the slabs carried out from. Although the surface temperature of the steel sheet is lowered by rough rolling, if a sufficient temperature difference is formed between the surface temperature and the center temperature of the plate thickness at the time of heating the slab, even at the end of rough rolling, that is, at the start of hot rolling. The difference between the surface temperature and the center temperature of the plate thickness can be secured.

Under the above conditions, the reason why the accumulation of {223} <252> directions can be suppressed is not clear, but it is presumed as follows.
Generally, when the temperature rises, the steel sheet becomes soft, so rolling is performed in a state where the surface temperature of the steel sheet is relatively higher than the center temperature of the sheet thickness as in the method for manufacturing a non-directional electromagnetic steel sheet according to the present embodiment. Then, it is considered that the surface layer and the intermediate layer are more easily deformed than the central layer of the steel sheet. Therefore, it is considered that the shear deformation in the intermediate layer was suppressed, and the nucleation in the {223} <252> direction, which should originally appear, was suppressed.
It should be noted that the temperature of the steel sheet is defined not by the difference from the temperature of the intermediate layer but by the difference from the surface temperature in consideration of ease of measurement.

In addition to the temperature difference in the plate thickness direction described above, the finishing hot rolling conditions are (the amount of strain σ1 applied to the steel sheet in the first half of the pass) / (the second half of the pass) in the finishing hot rolling in which a plurality of passes are continuously performed. It is also important to set the path schedule to satisfy the relationship of the strain amount σ2) ≧ 1.5 applied to the steel sheet. (Σ1) / (σ2) is preferably 1.8 or more, more preferably 2.0 or more, still more preferably 2.5 or more.

With continuous hot rolling equipment currently used in many steel sheet manufacturing processes, 4-pass to 7-pass rolling is continuously performed at intervals of several seconds or less.
Here, in the method for manufacturing a non-oriented electrical steel sheet according to the present embodiment, the "strain amount σ1 applied to the steel sheet in the first half of the pass" is a case where n is a natural number of 1 or more and the total number of passes is an even number. When is 2n and the odd number is 2n + 1, it means the true distortion applied to the steel sheet from the entry side of the first pass to the exit side of the n pass.
Similarly, "the amount of strain σ2 applied to the steel sheet in the latter half of the pass" means that n is a natural number of 1 or more, and when the total number of passes is an even number of 2n, the final pass (2n) is output from the entry side of the n + 1th pass. It means the true strain applied to the steel sheet up to the side. When the total number of passes is an odd number of 2n + 1, it means the true distortion applied to the steel sheet from the entry side of the n + 2nd pass to the exit side of the final pass (2n + 1).
That is, when the total number of finish rolling passes is 4, the strain amount σ1 applied to the steel sheet in the first half of the pass is the true strain applied to the steel sheet from the entry side of the first pass to the exit side of the second pass. The amount of strain applied to the steel sheet in the latter half of the pass represents the true strain applied to the steel sheet from the entry side of the third pass to the exit side of the fourth pass.
Similarly, when the total number of finish rolling passes is 7, the strain amount σ2 given to the steel sheet in the first half of the pass is the true applied to the steel sheet from the entry side of the first pass to the exit side of the third pass. It is a strain, and the amount of strain applied to the steel sheet in the latter half of the pass represents the true strain applied to the steel sheet from the entry side of the 5th pass to the exit side of the 7th pass.

The true strain is obtained by measuring the plate thickness after each pass with a laser measuring instrument and taking the logarithm of the plate thickness ratio before and after the pass.

Under the above conditions, the reason why the accumulation of {223} <252> directions can be suppressed is not clear, but it is presumed as follows.
There are two aspects to setting (the amount of strain σ1 applied to the steel sheet in the first half of the pass) / (the amount of strain σ2 applied to the steel sheet in the second half of the pass) ≧ 1.5. One is that the amount of distortion in the first half of the pass is relatively large. The other is to reduce the amount of distortion in the latter half of the pass.
From the viewpoint of relatively increasing the amount of strain in the first half of the pass, it is said that when the amount of strain applied in the first half of finish rolling is large, the effect of suppressing the {223} <252> orientation in the intermediate layer works greatly. Conceivable. In particular, in the first half of the pass, the plate thickness is thick, and it is easy to maintain the temperature difference in the plate thickness direction. Therefore, when the above-mentioned value of Ts-Tc is large and the amount of strain applied in the first half of finish rolling is large, it is considered that the effect of suppressing the {223} <252> orientation in the intermediate layer works more greatly.
On the other hand, from the viewpoint of relatively reducing the strain amount in the latter half of the pass, the plate thickness is thin and it is difficult to maintain the temperature difference in the plate thickness direction. 223} <252> The advantage of using it for directional control is small.

The temperature of hot rolling for finishing is preferably in the temperature range of 500 ° C. to 850 ° C. From the viewpoint of rollability, the preferable lower limit of the temperature of hot rolling for finishing is 550 ° C. or higher, more preferably 600 ° C. or higher, still more preferably 650 ° C. or higher. The preferred upper limit of the temperature of hot rolling for finishing is 800 ° C. or lower, more preferably 750 ° C. or lower, and further preferably 700 ° C. or lower. This is not a new condition in that the {100} orientation is increased by controlling the hot rolling condition. However, in the non-oriented electrical steel sheet manufacturing method according to the present embodiment, when rolling with the sheet thickness center temperature of the steel sheet lower than the surface temperature as described above, it can be said that the condition is easily achieved as a result. .. Then, in the non-directional electromagnetic steel sheet according to the present embodiment, the magnetic characteristics in the two directions of the rolling direction and the rolling perpendicular direction, which are particularly preferable for the steel sheet for the split core among the {100} directions, are improved {100} <001. > Easy to develop orientation. Therefore, it can be said that it is preferable to control the temperature of finish hot rolling in the above temperature range.

As described above, the change in the deformed state by hot rolling does not necessarily have to be favorable for specific magnetic properties after cold rolling and finish annealing as it is, but at least in hot rolling as described above. It is natural to think that controlling shear deformation affects the crystal orientation produced after cold rolling and finish annealing. We hope that the changes in crystal orientation from hot rolling to cold rolling to annealing will be elucidated in the future.

(Cold rolling process)
Next, the steel sheet after hot rolling is cold rolled. The reduction rate of cold rolling is not particularly limited. As a general condition, cold rolling is applied to a steel sheet after hot rolling so that the total reduction rate (total reduction rate of cold rolling) in the cold rolling process is 80% or more (preferably 85% or more). That is good. In particular, if a thin electromagnetic steel sheet is used, the total reduction ratio can be 90% or more. The upper limit of the total reduction rate of cold rolling is preferably 95% or less in consideration of manufacturing control such as rolling mill capacity and plate thickness accuracy.

(Finish annealing process)
Next, the steel sheet after cold rolling is subjected to finish annealing. The heating conditions in the finish annealing step are not particularly limited.
The soaking temperature of the finish annealing is preferably in the range of 800 ° C. to 1200 ° C. when the finish annealing has a sufficiently low iron loss. The lower limit temperature of soaking heat may be a temperature equal to or higher than the recrystallization temperature, but by setting it to 800 ° C. or higher, sufficient grain growth can be caused and iron loss can be reduced. From this point of view, it is preferably 850 ° C. or higher.
Further, if the crystal grains are finally grown by additional heat treatment by slow heating such as strain relief annealing, the iron loss after the additional heat treatment can be reduced, so that the soaking temperature of the finish annealing is set from the viewpoint of grain growth. There is no problem even if the temperature is lower than 800 ° C, which is not sufficient. In this case, the effect of avoiding the inferior magnetic flux density due to the additional heat treatment is remarkably exhibited. In this case, even if the unrecrystallized structure remains in a part, it is possible to have the characteristic crystal orientation of the non-oriented electrical steel sheet according to the present embodiment, and the lower limit temperature is, for example, 640 ° C. The above can be mentioned. A steel sheet having a fine crystal structure or a partially unrecrystallized structure by lowering the finish annealing temperature is also useful as a high-strength non-oriented electrical steel sheet because of its high strength.
On the other hand, the upper limit of the soaking temperature is preferably 1200 ° C. or lower in consideration of the load of the annealing furnace, preferably 1050 ° C.

Further, the soaking heat holding time may be set in consideration of the particle size, iron loss, magnetic flux density, strength, etc., and can be, for example, 5 sec or more as a guide. On the other hand, if it is 120 sec or less, the crystal grain growth becomes appropriate. Therefore, the soaking heat holding time is preferably set to 5 sec to 120 sec. Within this range, for example, when grain growth is carried out by performing additional heat treatment by slow heating thereafter, a crystal orientation having an effect of avoiding inferior magnetic properties tends to remain.

In order to obtain the non-oriented electrical steel sheet according to the present embodiment, other steps similar to the conventional non-oriented electrical steel sheet manufacturing process may be provided in addition to the above steps. As each condition of the other steps, the same conditions as those of the conventional non-oriented electrical steel sheet manufacturing process may be adopted. Specifically, for example, it may have an insulating film forming step of providing an insulating film on the surface of the steel sheet (non-oriented electrical steel sheet) after the finish annealing step.

The method for forming the insulating film is not particularly limited, but for example, a composition for forming an insulating film in which the above-mentioned resin or inorganic substance is dissolved in a solvent is prepared, and the composition for forming the insulating film is uniformly applied to the surface of the steel sheet by a known method. An insulating film can be formed by applying to.

The non-oriented electrical steel sheet according to the present embodiment can be obtained by the manufacturing method having the above steps.

According to this embodiment, a non-oriented electrical steel sheet having excellent magnetic characteristics can be obtained. Therefore, the non-oriented electrical steel sheet according to the present embodiment can be suitably applied as various core materials of electrical equipment, particularly as core materials of motors such as rotary machines, small and medium-sized transformers, and electrical components.
Hereinafter, a case where the non-oriented electrical steel sheet according to the present embodiment is applied as a motor core will be described.

<Motor core and its manufacturing method>
Examples of the motor core according to the present embodiment include a form in which non-oriented electrical steel sheets according to the present embodiment are laminated. Specific examples thereof include a motor core in which a non-oriented electrical steel sheet according to the present embodiment is punched to create a punched member (steel sheet blank), and the punched member is laminated and integrated. For example, as an example of the motor core according to the present embodiment, the motor core shown in FIG. 1 can be mentioned.

FIG. 1 is a schematic diagram showing an example of a split core. As shown in FIG. 1, the motor core 100 is formed as a laminated body 13 in which eight punched members 11 for split cores are connected in an annular shape, and the punched members 11 connected in an annular shape are laminated in eight layers and integrated. It is formed. The punching member 11 for the split core is a non-oriented electrical steel sheet punched, and has a yoke portion 17 on an arc and a teeth portion 15 protruding inward in the radial direction from the inner peripheral surface of the yoke portion 17. It has. The motor core 100 is not limited to the shape, number, number of layers, and the like of the punched members 11 forming the motor core 100 shown in FIG. 1, and may be designed according to the purpose.

Although the motor core shown in FIG. 1 has been described above, the motor core according to the present embodiment is not limited to this.

Next, a method of manufacturing the motor core will be described.
The method for manufacturing the motor core according to the present embodiment is not particularly limited, and the motor core may be manufactured by a manufacturing method usually industrially adopted.
Hereinafter, an example of a preferable manufacturing method of the motor core according to the present embodiment will be described.
An example of a preferable manufacturing method of the motor core according to the present embodiment includes a punching step of performing a punching process on the non-oriented electrical steel sheet according to the present embodiment to obtain a punched member, and a laminating step of laminating the punched members. ..

(Punching process)
First, the non-oriented electrical steel sheet of the present embodiment is punched into a predetermined shape having a tooth portion and a yoke portion according to a purpose, and a predetermined number of punched members are produced according to the number of laminated sheets and the like. The method for producing the punched member by punching the non-oriented electrical steel sheet is not particularly limited, and any conventionally known method may be adopted.
The punched member may form an uneven portion for laminating and fixing the punched member when it is punched into a predetermined shape.

(Laminating process)
A motor core can be obtained by laminating the punching members created in the punching process. Specifically, a predetermined number of punching members for a split core having a tooth portion and a yoke portion are combined and connected in an annular shape, and these are laminated.
The method of fixing the laminated punching members is not particularly limited, and any conventionally known method may be adopted. For example, a known adhesive may be applied to the punched member to form an adhesive layer, and the punched member may be fixed via the adhesive layer. Further, caulking may be applied to mechanically fit and fix the uneven portions formed on the respective punched members to each other.

Through the above steps, the motor core according to the present embodiment can be obtained. Since the motor core according to the present embodiment is manufactured by using the non-oriented electrical steel sheet according to the present embodiment, it has a low iron loss and a high magnetic flux density.

Further, another example of a preferable manufacturing method of the motor core according to the present embodiment is a punching step of performing a punching process on the non-oriented electrical steel sheet according to the present embodiment to obtain a punched member, and a laminating step of laminating the punched member. After the punching process and before or after the laminating process, the heating rate is 30 ° C./hr to 500 ° C./hr, the maximum reaching temperature is in the temperature range of 750 ° C. to 850 ° C., and 750 ° C. It has a heat treatment step of heat-treating under the condition of the above holding time of 0.5 hour to 100 hours.

That is, the motor core according to the present embodiment has a holding time under specific conditions (heating rate: 30 ° C./hr to 500 ° C./hr, maximum reached temperature: 750 ° C. to 850 ° C., 750 ° C. or higher) after laminating the punched members. : 0.5 hours to 100 hours) may be subjected to heat treatment (strain removal annealing). Further, in this heat treatment, the punched member before laminating the punched member may be subjected to the heat treatment under the above specific conditions.

Since the motor core itself does not have a thin shape like a steel sheet, the heating of the strain removing annealing of the motor core is the heat treatment in the finish annealing step in the steel sheet manufacturing process generally carried out at a heating rate of about several tens of degrees / sec. Is different, and it has to be very slow, about several hundred degrees Celsius / hr. As described above, when the crystal grains are grown at such a low heating rate, an orientation unfavorable for the magnetic characteristics develops, so that the magnetic flux density is lower than when the crystal grains are grown at a high heating rate. .. However, in the motor core using the non-oriented electrical steel sheet according to the present embodiment, it is possible to suppress this decrease in magnetic flux density. Depending on the conditions, the magnetic flux density may increase. Regarding the heating rate of the strain-removing annealing that can enjoy the characteristics for the split core, the upper limit is 500 ° C./hr or less in consideration of the capacity of the strain-removing annealing equipment. The lower limit is 30 ° C./hr or more in consideration of the production efficiency of strain relief annealing. In addition, if the heating rate is about 50 ° C./hr to 200 ° C./hr, in which strain removal annealing of the motor core is generally performed, the merit of using the non-oriented electrical steel sheet according to the present embodiment is fully exhibited. To.

Although it depends on the steel composition and the hot rolling conditions, the maximum temperature reached and the holding time at 750 ° C. or higher are the targets for obtaining an appropriate crystal grain size. When the maximum temperature reached is 750 ° C. or higher, or the holding time at 750 ° C. or higher is 0.5 hours or longer, crystal grain growth occurs, specific magnetic characteristics can be effectively obtained, and sufficient magnetism required for a motor core is obtained. Characteristics (especially low iron loss) can be obtained. Further, when the maximum temperature reached is 850 ° C. or lower, or the holding time at 750 ° C. or higher is 100 hours or less, the crystal grain growth becomes appropriate, the magnetic flux density is improved, and low iron loss can be achieved.

Therefore, in terms of avoiding deterioration of magnetic characteristics, the method for manufacturing the motor core according to the present embodiment has the above conditions (heating rate: 30 ° C./hr to 500 ° C./hr, maximum ultimate temperature: 750 ° C. to 850 ° C., It is preferable to carry out the heat treatment (holding time at 750 ° C. or higher: 0.5 hours to 100 hours).
By performing this heat treatment, unnecessary strain is released in the motor core, and iron loss can be reduced. Since the motor core of the present embodiment uses the non-oriented electrical steel sheet according to the present embodiment, a high magnetic flux density is maintained even after the heat treatment, and an excellent motor core can be obtained.

From the above, the non-oriented electrical steel sheet according to the present embodiment is useful as a core material because it has excellent magnetic properties. The non-oriented electrical steel sheet according to this embodiment is excellent in punching workability when applied to a motor core material. Also, the non-oriented electrical steel sheet according to the present embodiment, after the punched into a desired shape, even after subjected to stress relief annealing, with the advantage of reduction and core loss deterioration of the magnetic flux density B ₅₀ is suppressed. Therefore, the non-oriented electrical steel sheet according to the present embodiment can sufficiently meet the urgent demand for high efficiency and miniaturization in the field of electrical equipment, and its industrial value is extremely high.

Hereinafter, the present invention will be specifically described by exemplifying examples, but the present invention is not limited thereto. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the ideas described in the claims, which naturally belong to the technical scope of the present invention. It is understood as a thing.

<Example 1>
The slab having the chemical composition shown in Table 1 is roughly hot-rolled so that the thickness is 40 mm. Then, finish hot rolling is performed at the temperatures shown in Table 1. The finish hot rolling is the strain amount σ1 applied to the steel sheet in the first half of the rolling pass / “strain amount σ2 applied to the steel sheet in the second half” (denoted as “first half strain amount σ1 / second half strain amount σ2”), and the surface. The difference between the temperature Ts and the center temperature Tc of the plate thickness (denoted as Ts-Tc) is set to the value shown in Table 1. The steel sheet after hot rolling is cold-rolled at the total reduction rate (denoted as total cold rolling rate) shown in Table 1. The thickness of the finished hot-rolled steel sheet is adjusted so that the thickness of the steel sheet after cold-rolling according to the total cold-rolling ratio in Table 1 is 0.35 mm. The cold-rolled steel sheet is subjected to finish annealing at the soaking temperature shown in Table 1 (the soaking time is 30 seconds in each case) to obtain a steel sheet.

The surface layer and the intermediate layer of the obtained steel sheet are observed according to the method described above, and the degree of integration of the {223} <252> orientation in the intermediate layer (intermediate layer {223} <252>) is measured. In addition, the degree of integration of {100} <001> orientation in the surface layer (surface layer {100} <001> (MI ₀₀₁ )) and the degree of integration of {100} <011> orientation in the surface layer (surface layer {100} <011> (MI ₀₁₁ )) is measured, and MI ₀₀₁ / MI ₀₁₁ is calculated. The results are shown in Table 2.
_{Further, the average magnetic flux density B 50} in the rolling direction and the direction perpendicular to the rolling direction, the ratio of the magnetic flux density B ₅₀ to the saturated magnetic flux density Bs (B ₅₀ / Bs), and the iron loss (W _10/400 ) are measured. Further, the average crystal grain size (particle size) is measured according to the method described above.

For the crystal grain size, the metal structure of the plate thickness cross section developed by corroding the grain boundaries by nightal etching was photographed with an optical microscope, and a linear method for 100 or more crystal grains (a straight line was drawn in the photograph of the metal structure). Calculated from the number of intersections between the straight line and the grain boundary).
Further, among the obtained steel sheets, for a material having a comparatively low soaking temperature for finish annealing, the heating rate was 100 ° C./hr, the maximum reaching temperature was 800 ° C., and the holding time at 800 ° C. was 2 hours. , Strain removal annealing is performed, and the change in _{magnetic flux density (BB} / B _{A) due to additional heat treatment at a low heating rate is evaluated.} The results are shown in Table 2.

The punching accuracy is 20 mm wide with a cylindrical die (punch) with an outer diameter of 100 mm and an inner diameter of 80 mm, and a corresponding die with a clearance of 3/100 mm during punching. The ring-shaped sample of No. 1 is punched and evaluated by the difference between the maximum value and the minimum value of the outer diameter of the punched ring-shaped sample (denoted as punching accuracy [μm]).

_{Here, the average B 50} in the rolling direction and the direction perpendicular to the rolling is obtained from the magnetic flux density when excited with a magnetization force of 5000 A / m. Specifically, it is an average value _{of B 50} measured in the direction along the rolling direction (0 °) and in the direction perpendicular to the direction along the rolling direction (90 °).
The average iron loss in the rolling direction (0 °) and the rolling perpendicular direction (90 °) is _{the average value when the average magnetic flux density B 50} in the rolling direction and the rolling perpendicular direction is measured in the same direction as the measured direction. It is measured as _{an iron loss (W 10/400} ) under the conditions of a maximum magnetic flux density of 1.0 T and a frequency of 400 Hz.
In the table, B _B represents the magnetic flux density after SRA, and B _A represents the magnetic flux density before SRA.

_{The example of the invention corresponding to the non-oriented electrical steel sheet of the present embodiment has an average magnetic flux density B 50} and a magnetic flux in the rolling direction and the direction perpendicular to the rolling, as compared with the comparative example which is outside the range of the non-oriented electrical steel sheet of the present embodiment. It can be seen that the ratio of the density B ₅₀ to the saturated magnetic flux density Bs (B ₅₀ / Bs), the iron loss (W _10/400 ), and the change in the magnetic flux density due to the strain annealing (SRA) show good results.

11 Punched member, 13 Laminated body, 15 Teeth part, 17 Yoke part, 100 Motor core

Claims (7)

By mass%
C: 0.0030% or less,
Si: 0.01% to 3.50%,
Al: 0.001% to 2.500%,
Mn: 0.01% to 3.00%,
P: 0.180% or less,
S: 0.0030% or less, and
Remaining: Has a chemical composition consisting of Fe and impurities,
The degree of integration of the {223} <252> orientation in the intermediate layer having a plate thickness of 1/10 to 1/5 is 6 or less.
{100} <001> orientation non-oriented electrical steel sheet integration degree Ru der 6 or more in the surface layer from the surface of the steel sheet to a thickness of 1/10. In the surface layer, the ratio of the degree of integration of {100} <001> orientation (MI ₀₀₁ ) to the degree of integration of {100} <011> orientation (MI _{011) is}
MI ₀₀₁ / MI ₀₁₁ > 1.0
Non-oriented electrical steel sheet according to claim 1, satisfying the relationship. By mass%
C: 0.0030% or less,
Si: 0.01% to 3.50%,
Al: 0.001% to 2.500%,
Mn: 0.01% to 3.00%,
P: 0.180% or less,
S: 0.0030% or less, and
Remaining: Has a chemical composition consisting of Fe and impurities,
The degree of integration of the {223} <252> orientation in the intermediate layer having a plate thickness of 1/10 to 1/5 is 6 or less.
Non-oriented electrical steel sheet ratio between the rolling direction and the direction perpendicular to the rolling direction average of the magnetic flux density _{B 50} of the saturation magnetic flux density Bs _(B 50 / Bs) is Ru der than 0.890 in the case of excitation in the magnetizing force 5000A / m .. By mass%
C: 0.0030% or less,
Si: 0.01% to 3.50%,
Al: 0.001% to 2.500%,
Mn: 0.01% to 3.00%,
P: 0.180% or less,
S: 0.0030% or less, and
Remaining: Has a chemical composition consisting of Fe and impurities,
The degree of integration of the {223} <252> orientation in the intermediate layer having a plate thickness of 1/10 to 1/5 is 6 or less.
Steel sheet after the magnetic flux density B _A before the steel _sheet, and heating rate is 100 ° C. / hr, the maximum temperature is 800 ° C., and the holding time at 800 ° C. were conducted to a heat treatment under conditions of 2 hours to carry out heat treatment when the magnetic flux density was _{B B,} the ratio _{B B} and the _{B a is} the non-oriented electrical steel sheet you satisfy the relation B B / _{B a} ≧ 0.980. A hot rolling step of hot rolling a slab having the chemical composition according to any one of claims 1 and 3 to 4.
A cold rolling step of cold rolling on a steel sheet after the hot rolling step, and a cold rolling step.
It has a finish annealing step of finish annealing the steel sheet after the cold rolling step.
The method for producing a non-oriented electrical steel sheet according to any one of claims 1 to 4 , which satisfies at least one of the following conditions (a) and (b) in the hot rolling step.
(A) The difference between the surface temperature Ts of the steel sheet and the center temperature Tc of the sheet thickness is set to 50 ° C. or more, and finish hot rolling is started. Finish rolling is continuously performed on a plurality of passes so as to satisfy the condition of the strain amount σ2) ≧ 1.5 applied to the steel sheet. A motor core in which non-oriented electrical steel sheets according to any one of claims 1 to 4 are laminated. A step of punching a non-oriented electrical steel sheet according to any one of claims 1 to 4 to obtain a punched member.
The process of laminating the punched members and
A method for manufacturing a motor core.

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