JP2001123252A - Nonoriented silicon steel sheet for motor-driven power steering motor core and producing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a nonoriented silicon steel sheet for attaining the returning torque of a handle which has been the problem peculiar to motor-driven power steering and to provide a method for producing the same. SOLUTION: This full-process nonoriented silicon steel sheet used for a motor- driven power steering motor core has a composition of, by weight, <=0.005% C, <=4% Si, <=2% Mn, <=0.2% P, <=0.002% S, <=2% Al, <=0.004% N, <=0.005% Ti, <=0.005% Nb, and the balance substantial iron, in which the crystal grain size is 60 to 200 μm, and the thickness of an internal oxidized layer is <=0.5 μm. Moreover, as for the method for producing a nonoriented silicon steel sheet for a motor-driven power sterring motor core, a hot rolled sheet having the above components is annealed (capable of obviation) and is subjected to cold rolling and annealing to control the crystal grain size to 60 to 200 μm, and the thickness of an internal oxidized layer to <=0.5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet for a motor core used in an electric power steering (power steering by an electric motor) for enabling a steering wheel of an automobile to be operated lightly. And a method for manufacturing the same.

[0002]

2. Description of the Related Art While global environmental problems are being emphasized,
There is a growing movement in every field to eliminate energy waste. On the other hand, the desire of humans for convenience and comfort seems to remain constant. by the way,
2. Description of the Related Art A so-called power steering (hereinafter, abbreviated as "power steering") device that makes it easy to operate a steering wheel of an automobile has been generalized irrespective of a mini vehicle, an ordinary private vehicle, and a truck. Conventionally, this power steering is usually of a hydraulic type, but in recent years, there has been a rapid movement to change to an electric power steering from the viewpoint of energy consumption efficiency.

By the way, the non-oriented electrical steel sheets for motor cores which have been used in the electric power steerings up to now are JIS grades of 50A600 to 50A1000 class (Si%
Is 0.3 to 1.5%, and the crystal grain size is 15 to 40 μm.
m) is a full process material. However, this low ~
The intermediate grade could not solve the fatal flaw as an electric power steering. The drawback is that the conventional hydraulic power steering automatically attempts to return the handle in the opposite direction after the steering wheel is turned, but the return torque does not work with the electric power steering. Therefore, the shift to electric power steering was delayed.

[0004] In order to produce the return torque, which is the subject, a conventional method is disclosed in, for example, Japanese Patent Application Laid-Open Nos.
As disclosed in Japanese Patent No. 156519, a method based on control of an electric circuit is employed. However, electric control alone is insufficient, and it is said that iron loss generated in the motor core adversely affects the return torque. This iron loss is an iron loss in a low frequency and high magnetic field, and can be represented by a DC hysteresis loss in a high magnetic field. Even if this DC hysteresis loss in a high magnetic field is measured with various steel grades, there is a large variation between production lots. It was only expected to be effective, but no solution had been reached. Incidentally, the structure of the electric power steering generally has a structure in which a winding is applied to a non-oriented electromagnetic steel sheet rotor and a permanent magnet is used for a stator in many cases, and PWM control is usually performed.

[0005] Non-oriented electrical steel sheets include products generally called full-process materials and semi-process materials. Full-process materials do not require annealing by the customer, and are defined as steel manufacturers' products that are punched and laminated as cores. Also, a semi-process material is defined as a material that is punched by a customer and then subjected to strain relief annealing in order to improve iron loss by combining punching, caulking and removal of welding strain and crystal grain growth. For this reason, on the premise of strain relief annealing, a so-called skin-pass material that utilizes strain-induced grain growth by skin pass in the final step in a steel maker is often used. The strain relief annealing temperature for this customer is usually 6
It is about 00 to 850 ° C. The thickness of a product known as a non-oriented electrical steel sheet is 0.1 to 1 mm.

[0006]

SUMMARY OF THE INVENTION In view of the foregoing, the present invention provides a non-oriented electrical steel sheet for producing a return torque of a steering wheel, which is an inherent problem of an electric power steering, and a method of manufacturing the same.

[0007]

That is, the gist of the present invention is as follows. (1) A full-process non-oriented electrical steel sheet used for an electric power steering motor core, wherein, by weight%, C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%, S ≤ 0.002%, Al ≤ 2%, N ≤ 0.004%, Ti ≤ 0.005%, Nb ≤ 0.005%, balance substantially consisting of iron, with crystal grain size of 60-200μ
m, and the thickness of the internal oxide layer is ≦ 0.5 μm. A non-oriented electrical steel sheet for an electric power steering motor core. (2) By weight%, C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%, S ≦ 0.002%, Al ≦ 2%, N ≦ 0.004%, Ti ≦ 0.005%, Nb ≦ 0.005%, The hot-rolled sheet substantially consisting of iron is subjected to cold-rolling with or without hot-rolled sheet annealing, followed by annealing and crystallizing. The particle size is 60 to 200 μm, and the thickness of the internal oxide layer is ≦ 0.5.
A method for producing a non-oriented electrical steel sheet for an electric power steering / motor core, characterized in that the thickness is set to μm.

(3) A semi-process non-oriented electrical steel sheet used for an electric power steering motor core, wherein
C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%, S ≦ 0.007%, Al ≦ 2%, N ≦ 0.005%, and the balance substantially Made of iron, internal oxide layer thickness ≤0.5
Non-oriented electrical steel sheet for electric power steering and motor cores, characterized by having a thickness of μm. (4) By weight%, C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%, S ≦ 0.007%, Al ≦ 2%, N ≦ 0.005%, The hot rolled sheet whose balance is substantially made of iron is subjected to cold rolling with or without hot rolled sheet annealing, followed by annealing to reduce the internal oxide layer thickness to ≦ 0.5 μm. For manufacturing non-oriented electrical steel sheets for electric power steering and motor cores.

(5) A semi-process non-oriented electrical steel sheet used for an electric power steering motor core, wherein
C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%, S ≦ 0.007%, Al ≦ 2%, N ≦ 0.005%, and the balance substantially Made of iron, internal oxide layer thickness ≤0.5
A non-oriented electrical steel sheet for electric power steering / motor cores, characterized in that the strain equivalent to skin pass rolling is 15% or less. (6) By weight%, C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%, S ≦ 0.007%, Al ≦ 2%, N ≦ 0.005%, The hot-rolled sheet substantially consisting of iron is subjected to cold-rolling with or without hot-rolled sheet annealing, and then annealed to make the internal oxide layer thickness ≤0.5 μm and cold-roll skin pass rolling. A method for producing a non-oriented electrical steel sheet for an electric power steering / motor core, wherein the method is carried out at an elongation of 15% or less.

There are three points of the present invention. One of the problems with electric power steering is to reduce the internal oxide layer in order to improve the hysteresis loss in a high magnetic field in order to converge the steering wheel to the center position after turning the steering wheel. The internal oxide layer referred to here is a surface layer portion of a product section and is defined by the following third layer. That is, the outermost layer (first layer) is an insulating film, the second layer is a metal layer slightly de-Si or Al-free from ground iron, the third layer is an internal oxide layer, and the fourth layer is ground iron.

The internal oxide layer is formed by a scanning electron microscope at a magnification of 5.
It is about 000 times or more and is observed only in a reflected electron image instead of a normal secondary electron image. The boundary surface between the internal oxide layer and the ground iron is highly uneven, and significantly degrades the hysteresis loss. Further, the internal oxide layer cannot be prevented by increasing the amount of H ₂ , which is a reducing gas in the high-temperature isotropy, or decreasing the dew point, which is the conventional technique. Second, to improve this high-field hysteresis loss, conventional impurities,
What is necessary is to control the crystal grain size, internal stress, etc. The third point is that it is industrially sufficiently possible to restrict these to a specific range.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the present invention will be described below. Since the full-process material and the semi-process material have different punching distortion and the like in the final core, the component limitation range and the like are different. Therefore, the description will be made separately. First, a full process material will be described.

The amount of C is set to 0.005% or less. This is because when the C content exceeds 0.005%, there is a problem of magnetic aging, and low-frequency iron loss increases.

The amount of Si is set to 4% or less. If it exceeds 4%, it will break due to cold rolling.

[0015] The Mn content is 2% or less. Mn is preferably small in order to inhibit crystal grain growth and reduce the product crystal grain size. However, if it exceeds 2%, it is impossible because Mn becomes a quenched structure and becomes brittle.

The amount of P is limited to 0.2% or less. If the P content exceeds 0.2%, cold cracking occurs due to segregation, so it is avoided.

The amount of S is set to 0.002% or less. S forms sulfides and deteriorates low frequency iron loss. This limit is 0.
002%.

The amount of Al is set to 2% or less. Al is effective as a deoxidizing material in the steelmaking stage, but is not more than 2% because of the problem of addition cost.

The N content is set to 0.004% or less. N forms nitrides and deteriorates low-frequency iron loss. This limit is 0.
004%.

The amount of Ti is set to 0.005% or less. Ti forms nitrided carbides and deteriorates low frequency iron loss. This limit is 0.005%.

The Nb content is not more than 0.005%. Nb also forms nitrided carbides and deteriorates low frequency iron loss. This limit is 0.005%.

As other elements, there are known Sb, Sn, Cu, Ni, Cr, B, and Mo for improving texture.
Even if added, it is not harmful for electric power steering. However, since there is a problem of addition cost, it is preferable to set each to 0.5% or less.

The continuous cast slab adjusted to the above components in the steel making stage is subjected to ordinary hot rolling to form a hot rolled sheet. The hot rolled sheet may then be annealed, or the annealing may be omitted. Hot rolled sheet annealing generally has a magnetizing force of 5000 A /
The purpose of the present invention is to improve the magnetic flux density in the order of m, but since the present invention is more effective in the low magnetic field characteristic of the order of 100 A / m, the annealing of the hot-rolled sheet itself has little significance. However, in order to eliminate ridging (defective shape of vertical stripes) which is likely to occur at 2% Si or more, it is preferable to perform hot-rolled sheet annealing. The hot rolled sheet annealing is preferably performed at a normal recrystallization temperature of 650 ° C. or higher.

Next, annealing is performed after cold rolling.
The average grain size of the annealed steel sheet is 60 μm or more and 200 μm or more.
m or less. If it is less than 60 μm, low-frequency iron loss is unsatisfactory, and if it is more than 200 μm, high temperature ripening is required for annealing, resulting in poor productivity. In order to obtain a crystal grain size of 60 μm or more, although it depends on the amount of impurities and soaking time of the steel sheet, it is approximately 900 ° C. × 20 seconds, and to obtain a crystal grain size of 200 μm, 1100 ° C. × 40 seconds. It is about.

The thickness of the internal oxide layer must be 0.5 μm or less. This is because when the internal oxide layer exceeds 0.5 μm, iron loss degradation at a low frequency and in a high magnetic field is large. The internal oxide layer referred to here is an oxide layer rich in Si, Al, Mn, etc., formed under the iron metal layer whose outermost layer is slightly reduced in Si or Al. The thickness of the outermost iron metal layer varies depending on the thickness of the internal oxide layer, but is about 0.8 μm when the internal oxide layer is 0.5 μm. The iron metal layer may be observed in an island shape. The lower layer of the inner oxide layer is ground iron. This internal oxide layer has large irregularities at the boundary surface with the ground iron, and obstructs the flow of magnetic flux, thereby significantly deteriorating low frequency and high magnetic field iron loss.

The internal oxide layer can be observed by measuring the polished surface of the steel plate cross section at a magnification of 5000 times or more by SEM-EDX measurement. The SEM image is not a normal secondary electron but a reflected electron. In the image, the thickness of the internal oxide layer can be clearly seen. The thickness of the inner oxide layer is the thickness of the intermediate layer between the outermost iron metal interface and the lower ground iron interface, and the center line of the upper and lower interfaces (when a straight line parallel to the average line of the uneven curve is drawn, The area surrounded by this straight line and the concave-convex curve is defined as the difference between the straight lines that are equal on both sides of the straight line.

Since this internal oxide layer is formed when it is oxidized in the heating process in the first half of the annealing, it is necessary to pay close attention to, for example, cracking in a heated radiant tube and air-fuel ratio in a direct flame non-oxidizing furnace. Note that this internal oxide layer does not mean the conventional surface oxidation of annealing in a wet gas mixture of H ₂ + N ₂ + H ₂ O. This surface oxidation does not adversely affect low frequency, high magnetic field iron loss. At the laboratory level, it is easy to anneal in a non-oxidizing gas from heating to soaking and cooling, but in an actual furnace at a steel maker, an open fire burner or radiant tube is often used for the heating zone. Care must be taken, especially for this internal oxide layer. Even if the temperature is soaked in a dry atmosphere of, for example, 100% H _{2 and} a dew point of −50 ° C. at a high temperature, the internal oxide layer is not reduced.

Next, the manufacturing conditions of the semi-process material will be described. The C content is 0.005% or less. C content is 0.
If the content exceeds 005%, there is a problem of magnetic aging, so that low-frequency iron loss increases.

The amount of Si is set to 4% or less. If it exceeds 4%, it will break due to cold rolling.

The Mn content is set to 2% or less. Since Mn inhibits crystal grain growth and refines the product crystal grain size, a smaller amount is preferable, but if it exceeds 3%, it becomes impossible to form a quenched structure and embrittle.

The P content is limited to 0.2% or less. If the P content exceeds 0.2%, cold cracking occurs due to segregation, so it is avoided.

The S content is set to 0.007% or less. S forms sulfides and deteriorates low frequency iron loss. This limit is 0.
007%.

The Al content is 2% or less. Al is effective as a deoxidizing material in the steelmaking stage, but is not more than 2% because of the problem of addition cost.

The N content is set to 0.005% or less. N forms nitrides and deteriorates low-frequency iron loss. This limit is 0.
005%.

It should be noted that the amounts of Ti and Nb, which had to be restricted in the full process material, are not problematic if the steelmaking ability is present, but are preferably 0.015% or less for the semi-process material. As other elements, known Sb, Sn, Cu, Ni, C for improving texture
Addition of r, B, Mo, etc. is not harmful for electric power steering. However, since there is a problem of addition cost, 0.5% or less is preferable for each.

The continuous cast slab adjusted to the above components by steelmaking is subjected to ordinary hot rolling to form a hot rolled sheet. The hot rolled sheet may then be annealed, or the annealing may be omitted. The hot-rolled sheet annealing is generally performed for the purpose of improving the magnetic flux density at a magnetizing force of about 5000 A / m. However, the present invention is more effective in the low magnetic field characteristic of about 100 A / m. There is not much meaning in itself. However, 2
In order to eliminate ridging (defective shape of vertical stripes) which is likely to occur at% Si or more, it is preferable to carry out the method. The hot rolled sheet annealing is preferably performed at a normal recrystallization temperature of 650 ° C. or higher.

Next, annealing is performed after cold rolling.
Annealing is to perform normal recrystallization, and is performed at 650 to 100
About 0 ° C. is preferable. The thickness of the internal oxide layer must be 0.5 μm or less. If the thickness exceeds 0.5 μm, the low frequency iron loss is greatly deteriorated.

Next, skin pass rolling can be performed. A cold rolling reduction of 15% or less improves low-frequency iron loss due to large grain growth due to strain relief annealing at the customer.
If it exceeds 5%, the effect is small and must be avoided. Hereinafter, an embodiment will be described.

Example 1 Vacuum melting was carried out by changing various component systems, and ingots of the components shown in Table 1 were prepared. This was heated to 1030 ° C. and then hot rolled into a 10 mm thick steel sheet. Then, it was further heated to 1030 ° C.
A 7 mm hot rolled sheet was prepared. Material with less than 2% Si (Experiment N
o.1 to 5, 14 to 17), pickling was carried out and then 0.1.
Cold rolled to 5 mm, degreased, and annealed at 880 ° C for 5 minutes.
It was performed in 100% dry H _2. With respect to the 2% Si or more material (Experiment No.6~13), 950 ℃ in N ₂
After performing hot-rolled sheet annealing with soaking for 30 seconds, pickling was performed.
Cold rolled to 5 mm, degreased, and annealed at 880 ° C for 5 minutes.
It was performed in 100% dry H _2.

A 100 mm square sample was cut out from these, and the direct current magnetic characteristics in the rolling direction and the direction perpendicular thereto were measured, and the average in each direction is shown in Table 1. The average crystal grain size of the cross section of the steel sheet was also measured. The internal oxide layer was also investigated,
Did not exist. As shown in Table 1, those out of the component range of the present invention had deteriorated magnetic properties. In addition, although the component analysis of the product was also performed, the result was the same as the analysis result of the ingot.

[0041]

[Table 1]

Example 2 0.001% C by weight%
1.5% Si, 0.11% Mn, 0.02% P, 0.0
002% S, 2% Al, 0.001% N, 0.001%
O, 0.002% Ti, 0.001% Nb, 0.002
% B, 0.4% Cu, 0.04% Sn, 0.05% N
i, 0.05% Cr, 0.006% Mo, 0.002%
After heating the slab containing V at 1100 ° C., a 2 mm thick hot rolled coil was manufactured.

Next, annealing at 1000 ° C. for 30 seconds was performed in N ₂ . After pickling, it was cold-rolled to 0.2 mm, degreased, and then annealed at a temperature shown in Table 2 for 10 seconds. At this time, heating is performed in a non-oxidizing furnace (open flame atmosphere, air-fuel ratio = 0.9)
The thickness of the internal oxide layer was changed by controlling the sheet temperature on the exit side of the non-oxidizing furnace. After leaving the non-oxidizing furnace, annealing was performed in an electric heater zone in a 40% H ₂ + 60% N ₂ atmosphere. After baking the insulating film to about 1 μm, the DC magnetic characteristics were measured with an Epstein test piece. The hysteresis loss W17 in the table is a DC hysteresis loss at a maximum magnetic flux density of 1.7 Tesla.
As shown in Table 2, those in which the crystal grain size and the internal oxide layer were controlled within the range of the present invention exhibited excellent iron loss. In addition, the components of the final steel sheet were checked and found to be the same as the slab components.

[0044]

[Table 2]

(Example 3) Vacuum melting was performed with various component systems to prepare ingots of the components shown in Table 3. This was heated to 1100 ° C. and then hot rolled into a 15 mm thick steel sheet.
Next, after further heating to 1100 ° C., a 1.7 mm hot-rolled sheet was prepared. Then, hot rolled sheet annealing at 850 ° C. for 30 seconds in N ₂ was carried out, followed by pickling, cold rolling to 0.35 mm, degreasing, and annealing at 720 ° C. for 15 seconds at 100% dryness. It was carried out in H _2. Furthermore, skin pass rolling at a cold rolling reduction rate of 5% was performed. Table 3 shows the average crystal grain size at that time. Also, no internal oxide layer was observed.

From these, a 100 mm square sample was cut out and subjected to strain relief annealing in N ₂ at 750 ° C. for 2 hours. Then, the DC magnetic characteristics in the rolling direction and the direction perpendicular thereto were measured, and each direction was measured. The average is shown in Table 3. As shown in Table 3, those out of the component range of the present invention had deteriorated magnetic properties. In addition, although the component analysis of the product was also performed, the result was the same as the analysis result of the ingot.

[0047]

[Table 3]

(Example 4) The experiment No. 0 of Example 3
An experiment was conducted in which the thickness of the internal oxide layer was changed using a 35 mm cold-rolled sheet. Annealing is performed at 850 ° C. for 60 seconds, 20% H ₂ +8
Although the test was performed in 0% N ₂ , the heating atmosphere until the temperature reached 850 ° C. was controlled by controlling the oxygen% in N _{2 to} the value shown in Table 4. The crystal grain size was all 45 μm. Next, after performing 6% skin pass rolling, strain relief annealing in N ₂ was performed at 750 ° C. for 2 hours. The measurement was performed in the same manner as in Example 3. Table 4 shows the results. As shown in Table 4, when the internal oxide layer is out of the range of the present invention, the iron loss is unsatisfactory.

[0049]

[Table 4]

Example 5 0.0035% by weight
C, 0.1% Si, 0.18% Mn, 0.08% P,
0.0035% S, 0.002% Al, 0.0038%
N, 0.012% O, 0.007% Ti, 0.003%
Nb, 0.2% Cu, 0.08% Sn, 0.01% N
i, 0.11% Cr, 0.002% Mo, 0.001%
After heating the slab containing V at 1200 ° C., a hot-rolled coil having a thickness of 3 mm was manufactured.

Then, after pickling, it was cold rolled to 0.5 mm,
30% H ₂ + 70% N ₂ soaked at 680 ° C. for 10 seconds after degreasing
Medium annealing was performed. Only the atmosphere in the heating zone was an open flame non-oxidizing furnace (air-fuel ratio = 0.95). The crystal grain size was 14 μm. Next, an insulating film of a mixture of organic and inorganic was baked to a thickness of 1 μm. Furthermore, the rolling reduction was changed as shown in Table 5 by performing skin pass rolling. When the surface of this steel sheet was examined, the inner oxide layer was 0.1 μm thick in each case. Next, the sample was cut into Epstein samples (30 mm × 300 mm) and then subjected to strain relief annealing in N ₂ at 750 ° C. for 2 hours to measure magnetic properties. The crystal grain size was also measured and is shown in Table 5. As shown in Table 5, excellent magnetic properties were obtained in the range of the reduction rate of skin pass within the range of the present invention.

[0052]

[Table 5]

[0053]

According to the present invention, there is provided a non-oriented electrical steel sheet excellent in high magnetic field and low frequency iron loss for producing a return torque of a steering wheel, which is an inherent problem of an electric power steering, and a method of manufacturing the same. I can do it.

Claims (6)

[Claims] 1. A full-process non-oriented electrical steel sheet used for an electric power steering motor core, wherein, by weight%, C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%. S ≦ 0.002%, Al ≦ 2%, N ≦ 0.004%, Ti ≦ 0.005%, Nb ≦ 0.005%, the balance substantially consisting of iron, and a crystal grain size of 60 to 200 μm
m, and the thickness of the internal oxide layer is ≦ 0.5 μm. A non-oriented electrical steel sheet for an electric power steering motor core. 2. In% by weight, C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%, S ≦ 0.002%, Al ≦ 2%, N ≦ 0.004 %, Ti ≦ 0.005%, Nb ≦ 0.005%, The hot-rolled sheet substantially consisting of iron is subjected to cold-rolling with or without hot-rolled sheet annealing, followed by annealing. , The crystal grain size is 60 to 200 μm, and the thickness of the internal oxide layer is ≦ 0.5.
A method for producing a non-oriented electrical steel sheet for an electric power steering / motor core, characterized in that the thickness is set to μm. 3. A semi-process non-oriented electrical steel sheet used for an electric power steering motor core, wherein, by weight%, C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%. , S ≤ 0.007%, Al ≤ 2%, N ≤ 0.005%, balance substantially consisting of iron, internal oxide layer thickness ≤ 0.5
Non-oriented electrical steel sheet for electric power steering and motor cores, characterized by having a thickness of μm. 4. In% by weight, C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%, S ≦ 0.007%, Al ≦ 2%, N ≦ 0.005 %, The hot-rolled sheet substantially consisting of iron is subjected to cold-rolling with or without hot-rolled sheet annealing, followed by annealing to reduce the internal oxide layer thickness to ≦ 0.5 μm. A method for producing a non-oriented electrical steel sheet for an electric power steering / motor core. 5. A semi-process non-oriented electrical steel sheet used for an electric power steering motor core, wherein C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2% by weight. , S ≤ 0.007%, Al ≤ 2%, N ≤ 0.005%, balance substantially consisting of iron, internal oxide layer thickness ≤ 0.5
A non-oriented electrical steel sheet for electric power steering / motor cores, characterized in that the strain equivalent to skin pass rolling is 15% or less. 6. In weight%, C ≦ 0.005%, Si ≦ 4%, Mn ≦ 2%, P ≦ 0.2%, S ≦ 0.007%, Al ≦ 2%, N ≦ 0.005 %, The hot-rolled sheet substantially consisting of iron is subjected to cold-rolling with or without hot-rolled sheet annealing, and then annealed to an internal oxide layer thickness of ≦ 0.5 μm and skin pass rolling. A non-oriented electrical steel sheet for an electric power steering / motor core, wherein the cold rolling rate is 15% or less.