JP2001064756A - Steel sheet for electrically driven power steering motor core, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent steel sheet used for electrically driven power steering motor core, and its manufacturing method. SOLUTION: The steel sheet for electrically driven power steering motor core has a composition consisting of, by weight, <=0.005% C, <=4.0% Si, <=1.0% Al, <=0.02% S, 0.05-1.5% Mn, <=0.2% P, <=0.005% N, <=0.0020% Ti, and the balance essentially Fe. This steel sheet can be obtained by performing hot rolling and cold rolling and subjecting the resultant steel sheet to finish annealing and then to magnetic annealing at 720 to 900 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for an electric power steering motor core in a power steering system of an automobile.

[0002]

2. Description of the Related Art A power steering system of an automobile is a device that consumes 3 to 5% of the energy consumed by the automobile and consumes a lot of energy along with an air conditioner. In the conventional power steering system, steering is assisted by hydraulic pressure. However, in this system, since the hydraulic pump is constantly driven by the engine, there is a problem that energy is consumed even when the vehicle travels straight. To eliminate this waste,
2. Description of the Related Art An electric power steering (hereinafter, abbreviated as EPS) system that assists steering by a motor has been developed. The EPS system supplies current to the motor and assists power only when steering assistance is required, such as when cornering, so fuel efficiency is improved by about 2 to 3% compared to hydraulic systems.

[0003]

By the way, such a problem is solved.
In the EPS system, a PM motor using a permanent magnet is used from the viewpoint of small size and high torque. But,
In the PM motor, a relatively large loss torque is generated after steering, so that a time delay occurs before the vehicle enters a straight-ahead state after turning, so that the steering feeling is inferior to the hydraulic system.

[0004] The present invention has been made to solve such problems, and it is an object of the present invention to provide a steel sheet having a small loss torque and excellent for use in an electric power steering motor core, and a method of manufacturing the same.

[0005]

The above object is achieved by the following first and second inventions.

In the first invention, C: 0.005% or less by weight%;
Si: 4.0% or less, Al: 1.0% or less, S: 0.02% or less, Mn:
0.05-1.5%, P: 0.2% or less, N: 0.005% or less, Ti: 0.0
This is a steel plate for an electric power steering motor core, which is made of 020% or less, with the balance being substantially Fe.

The second invention is that C: 0.005% or less by weight%,
Si: 4.0% or less, Al: 1.0% or less, S: 0.02% or less, Mn:
0.05-1.5%, P: 0.2% or less, N: 0.005% or less, Ti: 0.0
020% or less, hot rolling and cold rolling are performed on the slab substantially composed of Fe, and then, after finish annealing, 720 ° C to 9 ° C.
A method for producing a steel plate for an electric power steering motor core, wherein magnetic annealing is performed at a temperature of 00 ° C.

[0008] In these means, the term "substantially Fe" refers to those containing other trace elements including unavoidable impurities within the scope of the present invention unless the effects of the present invention are lost. Means that Further, in this specification, all the percentages indicating the components of steel are% by weight, and pp
m is also ppm by weight.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of the present inventors' investigation on a material suitable for an EPS motor core material, that is, a material having a small loss torque, it was found that the loss torque is caused by mechanical loss and hysteresis loss of the core material. Further EP
As a result of studying materials with low hysteresis loss as S motor core material, non-oriented silicon steel sheet is optimal,
In particular, by using a steel sheet with reduced Ti, a material having good hysteresis characteristics can be obtained, and when manufacturing the steel sheet, after performing a finish annealing on the steel sheet,
It has been found that performing magnetic annealing at a temperature of 720 ° C. to 900 ° C. is very effective in improving the hysteresis characteristics.

Hereinafter, the process leading to the present invention will be described in detail based on experimental results. First, the effect on hysteresis loss
To investigate the effect of Ti, C: 0.0025%, Si: 0.25%, M
n: 0.25%, P: 0.01%, Al = 0.25%, S = 0.004%, N = 0.0
A steel having a Ti content of 021% and a Ti content of 30 ppm or less was melted in a laboratory, hot-rolled, and then pickled. After that, plate thickness 0.50mm
Cold-rolled until 780 ° C. × 1 min in a 10% H ₂ -90% N ₂ atmosphere, followed by magnetic annealing at 750 ° C. × 2 hours. Figure 1 shows the Ti content of the sample thus obtained and
The relationship of the hysteresis loss per 1 Hz of frequency when magnetizing up to 1.5T is shown. Here, the measurement of the magnetic characteristics was performed by the 25 cm Epstein method, and the hysteresis loss was calculated from the iron loss at 50 and 60 Hz by the two-frequency method.

FIG. 1 shows that when Ti is 20 ppm or less, the hysteresis loss is greatly reduced. In order to investigate the cause, the structure of the steel sheet was observed with an optical microscope.
The material having a content of more than 20 ppm had a fine crystal grain size. This is presumably because the precipitation of Ti-based carbonitride inhibited the grain growth during magnetic annealing. From the above, according to the present invention, Ti
To 20 ppm or less.

Next, to investigate the proper magnetic annealing temperature, C: 0.0020%, Si: 0.24%, Mn: 0.25%, P: 0.01
%, Al = 0.25%, S = 0.004%, N = 0.0018%, Ti = 0.001%
Was melted in a laboratory, hot rolled, and then pickled. Thereafter, cold rolling is performed to a sheet thickness of 0.50 mm, finish annealing at 780 ° C. × 1 min in a 10% H ₂ -90% N ₂ atmosphere, and further 650 ° C. to 950 ° C.
Magnetic annealing was performed at 2 ° C. for 2 hours. FIG. 2 shows the relationship between the magnetic annealing temperature of the sample thus obtained and the hysteresis loss per 1 Hz frequency when magnetized up to 1.5T. Figure 2
In, measurement of magnetic properties and calculation of hysteresis loss were performed in the same manner as in FIG.

From this, it can be seen that the hysteresis loss decreases at a magnetic annealing temperature of 720 ° C. or higher. This is because the distortion at the time of punching is released by magnetic annealing and the crystal grains are coarsened. On the other hand, the magnetic annealing temperature is 900
If the temperature exceeds ℃, the hysteresis loss increases. This is αγ
This is because the temperature approaches the transformation point and the magnetic characteristics deteriorate. From the above, the magnetic annealing temperature is set to 720 ° C. or more and 900 ° C. or less.

Next, the reasons for limiting other components will be described. If C exceeds 0.005%, the magnetic flux density decreases and the torque when driving the EPS motor decreases, so C is set to 0.005% or less. The torque at the time of driving the motor is a torque when a current is flowing through the motor.

Si is an effective element for increasing the specific resistance of the steel sheet. However, if it exceeds 4.0%, the magnetic flux density decreases and the torque when driving the EPS motor decreases, so the upper limit is 4.0%.
And

Al, like Si, is an effective element for increasing the specific resistance. However, if it exceeds 1.0%, the magnetic flux density decreases,
Since the torque when driving the PS motor decreases, the upper limit is 1.
0%.

Mn is required to be 0.05% or more in order to prevent red hot brittleness during hot rolling. However, if it exceeds 1.5%, the magnetic flux density is reduced and the torque when driving the EPS motor is reduced. 1.5%.

P is an element necessary for improving the punching property of the steel sheet, but if added in excess of 0.2%, the steel sheet becomes brittle.

When N exceeds 0.005%, the magnetic flux density decreases.
Since the torque at the time of driving the EPS motor decreases, the content is set to 0.005% or less.

Next, the manufacturing method will be described. The molten steel blown in the converter is degassed and adjusted to a predetermined component, and subsequently casting and hot rolling are performed. Finish annealing temperature during hot rolling,
The winding temperature does not need to be specified, and may be normal. In addition, hot-rolled sheet annealing after hot-rolling may be performed, but is not essential. Next, after a predetermined thickness is obtained by one cold rolling or two or more cold rollings sandwiching intermediate annealing, finish annealing is performed, and further magnetic annealing is performed. 720 ° C ~ 9
The steel sheet of the present invention can be obtained by performing magnetic annealing at a temperature of 00 ° C.

[0021]

Example: Molten steel blown in a converter was degassed, adjusted to the components shown in Table 1, cast, and heated at 1150 ° C for 1 hour.
Hot rolling was performed to a thickness of 2.0 mm. Hot rolling finishing temperature is 800
° C. The winding temperature was 700 ° C. After that, plate thickness 0.5
Cold rolling was performed to 0 mm, and annealing was performed under finish annealing conditions and magnetic annealing conditions shown in Table 1.

The measurement of the magnetic properties was performed by the 25 cm Epstein method. The hysteresis loss was a hysteresis loss per 1 Hz frequency when magnetized up to 1.5 T, and was evaluated by calculating the iron loss at 50 and 60 Hz obtained by the Epstein method by the two-frequency method. Table 1 also shows the magnetic properties of each steel sheet.

[0023]

[Table 1]

Thus, in the steel sheets according to the present invention of Nos. 1 to 3 in which the components and the magnetic annealing temperature were controlled within the ranges of the present invention, the steel sheets having low hysteresis loss and high magnetic flux density were obtained. I understand.

On the other hand, the steel sheet according to the comparative example of No. 4
Is out of the range of the present invention, so that the hysteresis loss is high. Since the magnetic annealing temperature of the steel sheet according to the comparative example of No. 5 is out of the range of the present invention and low, the hysteresis loss is high. Since the magnetic annealing temperature of the steel sheet according to the comparative example of No. 6 is out of the range of the present invention and high, the hysteresis loss is high and the magnetic flux density is low.

Further, the steel sheet according to the comparative example of No. 7 has the amount of C, the steel sheet according to the comparative example of No. 8 has the amount of Si, the steel sheet according to the comparative example of No. 9 has the amount of Mn, The steel sheet according to the comparative example has an N amount, and the steel sheet according to the comparative example No. 11 has an Al amount outside the range of the present invention.

[0027]

As described above, according to the present invention, a steel sheet having a low hysteresis loss can be obtained, and a steel sheet for an electric power steering motor core which is effective in reducing the loss torque of the EPS motor can be obtained.

Further, since a high magnetic flux density can be obtained, a high torque can be obtained when the motor is driven, and the steering characteristics are excellent.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a Ti amount and a hysteresis loss.

FIG. 2 is a diagram showing a relationship between a magnetic annealing temperature and a hysteresis loss.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Samukawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Yoshihiko Ono 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor Yasushi Tanaka 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 4K033 AA02 BA02 CA05 NA02 5E041 AA02 AA11 AA19 CA04 HB05 HB07 HB11 NN01 NN18

Claims (2)

[Claims] C. 0.005% or less by weight, Si: 4.0% or less, Al: 1.0% or less, S: 0.02% or less, Mn: 0.05 to 1.5% by weight.
%, P: 0.2% or less, N: 0.005% or less, Ti: 0.0020% or less, with the balance being substantially Fe. 2. C: 0.005% or less, Si: 4.0% or less, Al: 1.0% or less, S: 0.02% or less, Mn: 0.05 to 1.5% by weight.
%, P: 0.2% or less, N: 0.005% or less, Ti: 0.0020% or less, with the balance substantially consisting of Fe being subjected to hot rolling and cold rolling, followed by finish annealing, followed by 720 ° C to 900 ° C. A method for producing a steel sheet for an electric power steering motor core, wherein magnetic annealing is performed at a temperature of ° C.