JP2001011587A - Steel sheet for motor-driven power steering motor core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the loss torque of a motor by allowing the subject steel sheet to contain a specified compsn. of C, Si, Al, S, Mn, P and N, and the balance substantial Fe. SOLUTION: This steel sheet contains, by weight, <=0.005% C, <=2.0% Si, >1.0 to 3.5% Al, <=0.02% S, 0.05 to 1.5% Mn, <=0.2% P and <=0.005% N, and the balance substantial Fe. In the compositional elements, by controlling the contents of Al and S to the above ranges in particular, the hysteresis loss of the steel sheet can remarkably be reduced, so that the loss torque of a motor using this steel sheet can be reduced. As for the content of Al, in the case of >1.0%, a ferritic single phase is formed up to high temp., and the crystal grains are coarsened at the time of high temp. annealing, therefore, the hysteresis loss is made low. On the other hand, in the case of >3.5%, the hysteresis loss is not reduced beyond that, and this is defined as the upper limit.

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.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a steel sheet having a small loss torque and excellent for an electric power steering motor core.

[0005]

The above object is attained by the following first, second and third inventions.

In the first invention, C: 0.005% or less by weight%;
Si: 2.0% or less, Al: 1.0% or more and 3.5% or less, S: 0.02% or less (including 0), Mn: 0.05 to 1.5%, P: 0.2% or less, N:
A steel sheet for an electric power steering motor core, wherein 0.005% or less, and the balance is substantially Fe.

The second invention is that C: 0.005% or less by weight%,
Si: 2.0% or less, Al: more than 1.0% and 3.5% or less, S: 0.0009%
Or less (including 0), Mn: 0.05 to 1.5%, P: 0.2% or less,
N: 0.005% or less, the balance being substantially Fe, which is a steel plate for an electric power steering motor core.

[0008] The third invention is that the C: 0.005% or less by weight%,
Si: 2.0% or less, Al: more than 1.0% and 3.5% or less, S: 0.0009%
Or less (including 0), Mn: 0.05 to 1.5%, P: 0.2% or less,
N: 0.005% or less, and Sb + Sn / 2 = 0.001 to 0.05
%, And the balance is substantially Fe.

[0009] In these means, "the remainder is substantially F
"e" means that those containing other trace elements, including inevitable impurities, are included in the scope of the present invention, as long as the effects of the present invention are not lost. Further, in the present specification, all percentages indicating steel components are% by weight, and ppm is also ppm by weight.

[0010]

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, it has been found that a material having good hysteresis characteristics can be obtained by using a steel sheet to which an appropriate amount of Al is added, S is reduced, or a small amount of Sb or Sn is further added.
Hereinafter, the process leading to the present invention will be described in detail based on experimental results.

First, in order to investigate the effect of Al on the hysteresis loss, C = 0.0025%, Si = 0.03%, Mn = 0.18%, P =
0.01%, S = 0.004%, N = 0.0015%, Al content 0.5-4%
The steel was vacuum melted in a laboratory, hot rolled, pickled, cold rolled to a thickness of 0.5 mm, and then in a 25% H ₂ -75% N ₂ atmosphere at 1000 ° C for 2 minutes. Was subjected to finish annealing. FIG. 1 shows the relationship between the amount of Al in the sample thus obtained and the hysteresis loss per 1 Hz of frequency when magnetized up to 1.5T. 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 the hysteresis loss is low in the region where the Al content exceeds 1.0%. This Al amount is 1.0
%, The cause of lower hysteresis loss is 1.0%
% By adding Al to form a ferrite single phase up to high temperatures.
This is because crystal grains become coarse during high-temperature annealing.

From the above, the lower limit of Al is set to exceed 1.0%. On the other hand, even if the Al content exceeds 3.5%, the hysteresis loss does not decrease any more, which unnecessarily increases the cost,
In order to further reduce the torque when driving the EPS motor,
Is 3.5%. Here, the torque at the time of driving the EPS motor is a torque when a current is supplied to the motor to assist the rotation of the steering.

Next, in order to investigate the effect of S on the hysteresis loss, C: 0.0025%, Si: 0.1%, Mn: 0.25%,
P: 0.01%, Al = 1.1%, N = 0.0018%, and the amount of S is tr.
The steel changed in the ppm range was melted in a laboratory, hot rolled, and then pickled. Continuously cold-rolled to a thickness of 0.50 mm, 25% H ₂
Finish annealing was performed at 1000 ° C. for 2 minutes in an atmosphere of -75% N ₂ .
FIG. 2 shows the relationship between the amount of S and the hysteresis loss per 1 Hz frequency when magnetized up to 1.5T (marked by x). In FIG. 2, the measurement of the magnetic characteristics and the calculation of the hysteresis loss are shown in FIG.
Was performed in the same manner as described above.

From this, it can be seen that the hysteresis loss decreases as S decreases. In particular, when S ≦ 200 ppm, the hysteresis loss of the sample is 0.06 J / kg or less. If the hysteresis loss is 0.06 J / kg or less, there is no problem in steerability.If S exceeds 200 ppm, the magnetic characteristics deteriorate and the torque when driving the EPS motor decreases, so the upper limit of S is 200 ppm. (Including 0).

Also, it can be seen that when S ≦ 9 ppm, the degree of reduction in hysteresis loss is smaller than when S> 9 ppm. Therefore, the present inventors considered that there is a method for further reducing the hysteresis loss in the extremely low S material, and observed the structure with an optical microscope. As a result, a remarkable nitride layer was observed in the surface layer of the steel sheet in the region of S ≦ 9 ppm. On the other hand, in the region where S> 9 ppm, the nitrided layer was slight. It is considered that this nitrided layer was formed during hot rolled sheet annealing and finish annealing performed in a nitriding atmosphere.

The cause of the acceleration of the nitridation reaction accompanying the reduction of S is considered as follows. In other words, since S is an element that easily concentrates on the surface and grain boundaries, in the region of S> 9 ppm, S concentrates on the steel sheet surface and suppresses nitrogen adsorption during hot-rolled sheet annealing and finish annealing. On the other hand, S ≦ 9pp
It is considered that in the region of m, the effect of suppressing nitrogen adsorption by S was reduced.

The present inventors have considered that the nitride layer which is remarkably generated in the extremely low S material may hinder the growth of crystal grains in the surface layer portion of the steel sheet and suppress the decrease in hysteresis loss.
Based on this idea, the inventors of the present invention will be able to suppress the adsorption of nitrogen and add an element that does not hinder the excellent grain growth of the ultra-low S material. Based on the idea that the loss may be further reduced, various investigations have shown that the addition of a trace amount of Sb is effective.

FIG. 2 shows the results of a test conducted under the same conditions for a sample in which 40 ppm of Sb was added to the components of the sample shown by the crosses, with the circles.

Focusing on the effect of reducing the hysteresis loss of Sb, in the region of S> 9 ppm, the hysteresis loss is reduced only by about 0.0002 J / kg by the addition of Sb. It is reduced by about J / kg, and when the amount of S is small, the effect of reducing the hysteresis loss of Sb is remarkably recognized. In this sample, no nitrided layer was observed regardless of the S content. This is probably because Sb concentrated in the surface layer of the steel sheet and suppressed the adsorption of nitrogen.

From the above, it can be seen that the addition of Sb significantly reduces the hysteresis loss at S ≦ 9 ppm.

Next, in order to investigate the optimum addition amount of Sb, C:
0.0025%, Si: 0.1%, Mn: 0.18%, P: 0.01%, Al = 1.1
%, S = 0.0004%, N = 0.0020%, and the amount of Sb is tr.
Was melted in a laboratory, hot-rolled, and then pickled. Continuously cold rolled to a thickness of 0.50 mm, 25% H ₂ -75
Finish annealing was performed at 1000 ° C. for 2 minutes in a% N ₂ atmosphere. Figure 3
The relationship between the amount of Sb and the hysteresis loss per 1 Hz frequency when magnetized up to 1.5T is shown in FIG. In FIG. 3, the measurement of the magnetic characteristics and the calculation of the hysteresis loss were performed in the same manner as in FIG.

FIG. 3 shows that the hysteresis loss is reduced in the region where the added amount of Sb is 10 ppm or more. However, when Sb is further added and Sb> 50 ppm, the hysteresis loss increases again.

In order to investigate the cause of the increase in hysteresis loss in the region where Sb> 50 ppm, the structure was observed with an optical microscope. As a result, although the surface layer fine grain structure was not recognized, the average crystal grain size was slightly smaller. Although the cause is not clear, it is considered that since Sb is an element that is easily segregated at the grain boundary, the grain growth property is reduced by the grain boundary drag effect of Sb.

However, even when Sb is added up to 600 ppm, the hysteresis loss is better than that of steel not containing Sb.

From the above, Sb is set to 10 ppm or more, and the upper limit is set to 500 ppm from the viewpoint of cost. From the viewpoint of hysteresis loss, the content is desirably 10 ppm or more and 50 ppm or less.

The effect of reducing the hysteresis loss is also observed when Sn, which is a surface segregation element similar to Sb, is added in an amount of 20 ppm or more, and the addition of 100 ppm or more slightly increases the hysteresis loss. From this, Sn should be 20 ppm or more and Sn should be 1000p
Hysteresis loss is better than steel without Sn even when added over pm, but the upper limit is 1000 due to cost issues.
ppm. From the viewpoint of hysteresis loss, the content is desirably 20 ppm or more and 100 ppm or less.

Further, when Sb and Sn are added in combination, Sb
The hysteresis loss was reduced when + Sn / 2 was added at 10 ppm or more, and the hysteresis loss was slightly increased when Sb + Sn / 2 was added at 50 ppm or more. From this, when Sb and Sn are added in combination, Sb + Sn / 2 is set to 10 ppm or more, and Sb + Sn / 2 is 500 ppm.
Although the hysteresis loss is better than that of steel to which Sb + Sn / 2 is not added even when added at ppm or more, the upper limit is set to 500 ppm due to the problem of cost. From the viewpoint of hysteresis loss, the content is desirably 10 ppm or more and 50 ppm or less.

Next, the reasons for limiting other components will be described.

When the content of Si exceeds 2.0%, the cost increases,
Further, the upper limit is set to 2.0% because the torque is reduced when the EPS motor is driven due to the decrease in the saturation magnetic flux density.

When C exceeds 0.005%, the magnetic flux density decreases, and EP
Since the torque when driving the S motor is reduced, the content is set to 0.005% or less.

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 torque at the time of driving the EPS motor is reduced.

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, so that the content of P is set to 0.2% or less.

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. In the present invention, as long as the components are within the scope of the present invention, the production method may be an ordinary method. That is, molten steel blown in a converter is degassed, adjusted to a predetermined component, cast, and hot-rolled. In the case of producing a thin material, a predetermined thickness is obtained by one cold rolling or two or more cold rollings with intermediate annealing. Subsequently, using the above-mentioned hot rolled plate or cold rolled plate, finish annealing is performed at 850 to 1000 ° C. for about 1 to 5 minutes.

[0036]

[Example] (Example 1) Molten steel blown in a converter is degassed, adjusted to the components shown in Table 1, cast, hot-rolled to a thickness of 2.3 mm, pickled, and 0.5 mm in thickness Cold rolling was carried out until. Thereafter, finish annealing was performed at 1000 ° C. for 2 minutes in an atmosphere of 25% H ₂ -75% N ₂ .

The measurement of the magnetic characteristics 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.

[0038]

【table 1】

From the results, it can be seen that in the steels of Nos. 1 to 4 of the present invention in which the composition of the steel sheet is controlled within the range of the first invention, a steel sheet having a low hysteresis loss and a high magnetic flux density is obtained.

On the other hand, in the No. 5 steel sheet, the amount of S is no.
The steel sheet of No. 10 has an amount of Al and the steel sheet of No. 10 has an amount of N out of the range of the present invention, so that the hysteresis loss is high. Since the No. 7 steel plate has the amount of Al and the No. 11 steel plate has the amount of Si outside the range of the present invention, the magnetic flux density is low. The steel sheet No. 8 has an amount of Mn, and the steel sheet No. 9 has an amount of C outside the range of the present invention. Therefore, the hysteresis loss is high and the magnetic flux density is low.

Example 2 Molten steel blown in a converter was degassed, adjusted to the composition shown in Table 2, cast, hot-rolled to a thickness of 2.3 mm, pickled and then to a thickness of 0.5 mm Cold rolling was performed.
Thereafter, finish annealing was performed at 1000 ° C. for 2 minutes in an atmosphere of 10% H ₂ -90% N ₂ .

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 2 also shows the magnetic properties of each steel sheet.

[0043]

[Table 2]

From the results, it can be seen that in the steels of Nos. 1 to 15 of the present invention in which the composition of the steel sheet was controlled within the range of the second invention, a steel sheet having a low hysteresis loss and a high magnetic flux density was obtained. Further, it can be seen that in Example 1, a steel sheet having a lower hysteresis loss was obtained as compared with the steels of the present invention shown in Table 1 which were controlled within the range of the first invention. In particular, the reduction of the hysteresis loss is remarkable in the steels of Nos. 2 to 15 of the present invention containing Sb or Sn in a predetermined range and controlled in the range of the third invention.

On the other hand, in the No. 16 steel sheet, the amount of Al
The steel sheet No. 19 has a high hysteresis loss since the amount of N is out of the range of the present invention. The steel sheet No. 17 has an amount of Mn, the steel sheet No. 18 has an amount of C, and the steel sheet No. 20 has an amount of S which is out of the range of the present invention. Density is low.

[0046]

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 an Al amount and a hysteresis loss.

FIG. 2 is a diagram illustrating a relationship between an S amount and a hysteresis loss.

FIG. 3 is a diagram illustrating a relationship between an Sb amount 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) 5H002 AA03 AA09

Claims (3)

[Claims] 1. In weight%, C: 0.005% or less, Si: 2.0% or less, Al: more than 1.0% and 3.5% or less, S: 0.02% or less (including 0), Mn: 0.05 to 1.5%, P: 0.2 % Or less, N: 0.005% or less, the balance being substantially Fe. 2. C: 0.005% or less by weight, Si: 2.0% or less, Al: more than 1.0% and 3.5% or less, S: 0.0009% or less (including 0), Mn: 0.05 to 1.5%, P: 0.2 % Or less, N: 0.005% or less, the balance being substantially Fe. 3. C: 0.005% or less by weight, Si: 2.0% or less, Al: 1.0% to 3.5% or less, S: 0.0009% or less (including 0), Mn: 0.05 to 1.5%, P: 0.2 % Or less, N: 0.005% or less, and further contains Sb + Sn / 2 = 0.001 to 0.05%, with the balance being substantially Fe.