JP3956596B2 - Non-oriented electrical steel sheet - Google Patents

Description

【００４３】
表１より、Ｃｒ、Ｍｇ量が本発明の範囲内である本発明鋼において、磁気特性および疲労特性に優れた鋼板が得られることがわかる。
【００４４】
一方、比較鋼においては、磁気特性もしくは疲労特性のいずれか一方が劣っている。
【００４５】
【発明の効果】
以上述べたように、本発明によれば、鉄損が低く疲労特性に優れた鋼板を得ることができる。また、本発明により得られる鋼板は、電気自動車、エアコン、サーボモータ等の高周波域で可変速運転されるモータのコア材料として好適である。
【図面の簡単な説明】
【図１】Ｃｒ添加量と鉄損、磁束密度および硬度との関係を示すグラフ
【図２】Ｍｇ添加量と疲労限との関係を示すグラフ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic steel sheet having low iron loss and excellent fatigue characteristics, and relates to a magnetic steel sheet used for iron core materials of motors for electric vehicles and motors for high efficiency air conditioners.
[0002]
[Prior art]
From the viewpoint of miniaturization and high efficiency, motors for electric vehicles and motors for high-efficiency air conditioners are mainly IPM motors with permanent magnets embedded in the rotor. The drive frequency is 200 Hz to 1 kHz for electric vehicles, and for air conditioners. It is about 200 Hz.
[0003]
The non-oriented electrical steel sheet used as the core material of the motor is required to have excellent fatigue characteristics because the centrifugal force applied to the rotor changes greatly with the variable speed operation of the motor in addition to low high-frequency iron loss. The
[0004]
As a means for improving the fatigue characteristics, there is a refinement of crystal grains. Further, by increasing Si to 4% or more, it is possible to reduce high-frequency iron loss and improve fatigue characteristics.
[0005]
[Problems to be solved by the invention]
However, in order to improve the fatigue characteristics, it is effective to refine the crystal grains. However, the refinement is not desirable as a technique for improving the fatigue characteristics of the electrical steel sheet because it increases the iron loss.
[0006]
In addition, increasing Si to 4% or more is effective in reducing high-frequency iron loss and improving fatigue properties. However, if Si is increased, the steel sheet becomes brittle and cold rolling becomes difficult, which is further remarkable. Due to the increase in hardness, there is a problem that die wear during punching becomes severe.
[0007]
For this reason, a technique for improving high-frequency iron loss and fatigue characteristics without causing significant embrittlement and hardness increase of the steel sheet is desired.
[0008]
The present invention has been made in view of such circumstances, and provides a non-oriented electrical steel sheet having low iron loss and excellent fatigue characteristics.
[0009]
[Means for Solving the Problems]
When the present inventors diligently studied about the solution of the said subject, it discovered that the electromagnetic steel plate with a low high-frequency iron loss and excellent fatigue characteristics was obtained by adding Mg to the steel plate which added Cr in an appropriate amount.
[0010]
The present invention has been made based on such knowledge, and has the following configuration.
[0011]
In mass%, C: 0.005% or less, P: 0.1% or less, Si: 1-4%, Mn: 0.05-2%, Al: 0.1-2%, S: 0.02 %: N: 0.005% or less, O: 0.002% or less, Cr: 0.4-5%, Mg: 0.0001-0.005%, the balance being Fe and inevitable impurities It is a non-oriented electrical steel sheet characterized.
[0012]
In addition, in this specification,% and ppm which show the component of steel are all mass% and mass ppm.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the details of the present invention will be described together with the reasons for limitation.
[0014]
First, in order to investigate the influence of Cr on magnetic properties, C: 0.0025%, Si: 2.5%, Al: 1.3%, Mn: 0.20%, P: 0.01% , S: 0.002%, N: 0.0021%, O: 0.0015%, steel with the Cr amount changed to about 0-6% was melted in the laboratory, and after hot rolling, acid Washed. Subsequently, the hot-rolled sheet was subjected to hot-rolled sheet annealing at 830 ° C. × 3 hr in a 75% H ₂ -25% N ₂ atmosphere, and further cold-rolled to a sheet thickness of 0.35 mm, and 20% H ₂ -80%. Finish annealing was performed in N ₂ atmosphere for 950 ° C. × 1 min.
[0015]
FIG. 1 shows the relationship between the amount of Cr added to the specimen thus obtained, iron loss W10 / 600, magnetic flux density B50, and Vickers hardness HV. Here, for the evaluation of the magnetic characteristics, a ring sample having an outer diameter of 45 mm and an inner diameter of 33 mm prepared using the obtained specimen was wound with a primary turn of 100 and a secondary turn of 100. The Vickers hardness HV was evaluated by the Vickers hardness (load 100 g) of the steel sheet cross section.
[0016]
From FIG. 1, it can be seen that the iron loss decreases in the range of Cr = 0.4 to 5%. The reason why the iron loss decreased in the range of 0.4% to 5% is considered to be due to the synergistic effect of the reduction effect of the eddy current loss due to the increase of the specific resistance and the reduction effect of the hysteresis loss due to the reduction of the magnetic anisotropy. .
[0017]
On the other hand, when Cr exceeds 5%, the iron loss increases because the hysteresis loss increases as the magnetic flux density decreases.
[0018]
Further, when focusing on the hardness, it can be seen that the addition of Cr hardly changes the Vickers hardness.
[0019]
From the above, the amount of Cr added is 0.4 to 5%, preferably 0.4 to 1.4%, more preferably 0.4 to 0.9% from the viewpoint of magnetic flux density.
[0020]
By the way, since the permanent magnet is embedded in the rotor of the IPM motor, which is currently mainstream in motors for electric vehicles, high efficiency air conditioner motors, etc., irregular centrifugal force is applied to the magnet during variable speed rotation at high speed. The electrical steel sheet used as the core material is required to have excellent fatigue characteristics.
[0021]
In order to improve the fatigue properties of electrical steel sheets,
1) It is considered effective to reduce the total amount of inclusions and precipitates that become initiation sites of fatigue cracks, and 2) to prevent the formation of coarse inclusions that lower the fatigue limit.
[0022]
Therefore, Mg addition was studied in order to reduce the amount of oxide in the steel by using Al deoxidized steel as a base and to further control the inclusion morphology. Initially C: 0.0025%, Si: 3.05%, Mn: 0.20%, P: 0.01%, S: 0.0020%, Al: 1.05%, Cr: 0.95% , N: 0.0018%, O: 0.0012%, and the Mg content is tr. Steel changed in the range of ˜50 ppm was melted in the laboratory, hot-rolled, pickled, annealed at 830 ° C. × 3 hr, and cold-rolled to a thickness of 0.35 mm. . Subsequently, finish annealing at 950 ° C. × 1 min (10% H ₂ -90% N ₂ atmosphere) was performed on the cold-rolled sheet. In the fatigue test, a sample having a parallel part width of 5 mm and a length of 150 mm was cut from the finish annealed material in parallel with the rolling direction, and the end face of the parallel part was polished in the rolling direction with No. 800 emery paper. It was performed by partial swinging (tensile-tensile) at 20 Hz.
[0023]
FIG. 2 shows the relationship between the amount of Mg added to the specimen (sample) thus obtained and the fatigue limit. Here, the fatigue limit was set to a stress amplitude at which no fracture occurred at 10 ⁷ repetitions.
[0024]
FIG. 2 shows that the fatigue limit is improved when 1 ppm or more of Mg is added. In order to investigate this cause, SEM observation of the inclusions in the steel in the cross section of the steel sheet was performed by SEM. As a result, many coarse clustered Al ₂ O ₃ particles were observed in the Mg-free steel. On the other hand, it was found that Al ₂ O ₃ clusters were reduced in Mg-added steel. From this, it is considered that the fatigue limit, that is, the improvement in fatigue characteristics, is due to the reduction of coarse Al ₂ O ₃ clusters that become the starting point of fatigue by the addition of Mg.
[0025]
From the above, the lower limit of Mg is set to 0.0001% (1 ppm). The upper limit is set to 0.005% (50 ppm) from the viewpoint of cost. In order to obtain a steel sheet with more excellent fatigue characteristics, it is more preferably 0.0005 (5 ppm) to 0.005 (50 ppm).
[0026]
Next, the reasons for limiting other components will be described.
[0027]
Since Si is an effective element for increasing the specific resistance of the steel sheet, the lower limit is set to 1.0%. On the other hand, if it exceeds 4%, the magnetic flux density decreases as the saturation magnetic flux density decreases, so the upper limit was made 4%.
[0028]
Al, like Si, is an effective element for increasing the specific resistance. However, when the content exceeds 2%, the magnetic flux density decreases with a decrease in the saturation magnetic flux density, so the upper limit is set to 2%. Further, when the content is less than 0.1%, AlN becomes finer and the grain growth property decreases, so the lower limit was made 0.1%.
[0029]
C has a problem of magnetic aging, so 0.005% or less.
[0030]
Mn is required to be 0.05% or more in order to prevent red hot brittleness during hot rolling, but if it exceeds 2%, the magnetic flux density is lowered, so 0.05 to 2% was set.
[0031]
If P is added in excess of 0.1%, the steel sheet becomes hard, so the content is made 0.1% or less.
[0032]
N is made 0.005% or less in order to increase the iron loss when the content is large and to increase the iron loss.
[0033]
If S exceeds 0.02%, iron loss increases due to precipitation of MnS, so the upper limit is made 0.02%.
[0034]
If O exceeds 0.002%, the initiation site of fatigue cracks increases, so 0.002% or less.
[0035]
In addition, elements such as Sb, Sn, REM, Ni, Cu, and Co can be added as long as the effects of the present invention are not impaired.
[0036]
Next, the manufacturing method of the steel plate of this invention is demonstrated.
[0037]
In order to obtain the steel sheet of the present invention, for example, the molten steel blown in a converter is degassed and adjusted to a predetermined component, followed by casting and hot rolling. The finish annealing temperature and the coiling temperature during hot rolling need not be specified and may be normal. Moreover, although hot-rolled sheet annealing after hot rolling may be performed, it is not essential. Next, after a predetermined sheet thickness is obtained by one cold rolling or two or more cold rollings with intermediate annealing, final annealing is performed.
[0038]
Here, Cr and Mg specified in the present invention can be within the scope of the present invention by controlling the oxygen potential of slag or steel, for example.
[0039]
【Example】
The molten steel blown in the converter was degassed, cast into the components shown in Table 1, slab heated at 1140 ° C. × 1 hr, and then hot-rolled to a thickness of 2.0 mm. The hot rolling finishing temperature was 800 ° C., and the winding temperature was 610 ° C. After winding, hot-rolled sheet annealing was performed at 890 ° C. for 3 hours in an atmosphere of 75% H ₂ -25% N ₂ . Then, cold rolling was performed to a plate thickness of 0.35 mm, and finish annealing was performed under the conditions shown in Table 1 in a 10% H ₂ -90% N ₂ atmosphere.
[0040]
For the measurement of the magnetic characteristics, a ring sample having an outer diameter of 45 mm and an inner diameter of 33 mm was used and wound with a primary turn of 100 and a secondary turn of 100. In the fatigue test, a sample having a parallel part width of 5 mm and a length of 150 mm was cut from the finish annealed material in parallel with the rolling direction, and the parallel part was polished with # 800 emery paper, and then a piece with a stress ratio of 0.1 and a frequency of 20 Hz. Swing (tensile-tensile) was performed.
[0041]
Table 1 shows the magnetic properties and fatigue properties of each steel plate.
[0042]
[Table 1]

[0043]
From Table 1, it can be seen that a steel sheet excellent in magnetic characteristics and fatigue characteristics can be obtained in the steel of the present invention in which the Cr and Mg amounts are within the range of the present invention.
[0044]
On the other hand, in the comparative steel, either the magnetic property or the fatigue property is inferior.
[0045]
【The invention's effect】
As described above, according to the present invention, a steel sheet having low iron loss and excellent fatigue characteristics can be obtained. Further, the steel sheet obtained by the present invention is suitable as a core material for a motor that is operated at a variable speed in a high frequency range such as an electric vehicle, an air conditioner, and a servo motor.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between Cr addition amount and iron loss, magnetic flux density and hardness. FIG. 2 is a graph showing the relationship between Mg addition amount and fatigue limit.

Claims (1)

In mass%, C: 0.005% or less, P: 0.1% or less, Si: 1-4%, Mn: 0.05-2%, Al: 0.1-2%, S: 0.02 %: N: 0.005% or less, O: 0.002% or less, Cr: 0.4-5%, Mg: 0.0001-0.005%, the balance being Fe and inevitable impurities A non-oriented electrical steel sheet.

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