JP2001158949A - Steel sheet for motor core for motor-driven power steering - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel sheet excellent as the one for motor core for a motor-driven power steering. SOLUTION: This steel sheet for the motor core for the motor-driven power steering contains, by weight <=0.005% C, <=4% Si, <=1% Al, <=0.03% S, 0.05 to 1.5% Mn, <=0.2% P and <=0.005% N, moreover contains Ca in the range of 0.5<=Ca/S<=3, and the balance substantially Fe.

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 problems, and an object of the present invention is to provide a steel sheet having a small loss torque and excellent for EPS motor cores, and a method of manufacturing the same.

[0005]

The gist of the present invention is that Ca is converted to Ca
An object of the present invention is to obtain an EPS motor core material having good hysteresis characteristics by using a non-oriented silicon steel sheet to which an appropriate amount is added as / S.

That is, means for solving the above problems are as follows: C: 0.005% or less, Si: 4% or less, Al: 1.0% by weight.
Hereinafter, S: 0.03% or less, Mn: 0.05 to 1.5%, P: 0.2% or less, N: 0.005% or less, and Ca is 0.5 ≦ Ca / S ≦ 3
And the balance substantially consisting of Fe.

[0007] In these means, the term "substantially Fe" means, insofar as the effects of the present invention are not lost, those containing other trace elements including unavoidable impurities are included in the scope of the present invention. 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.

[0008]

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 Ca is added in an appropriate amount as Ca / S.

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 Ca / S, C: 0.0025%, Si: 0.20
%, Mn: 0.30%, P: 0.10%, Al = 0.20%, S = 0.020
%, N = 0.0020%, and steel in which the amount of Ca was changed in the range of tr. To 70 ppm was melted in a laboratory, hot-rolled, and then pickled. afterwards,
Cold rolled to a thickness of 0.50 mm, 800 in a 10% H ₂ -90% N ₂ atmosphere
Finish annealing was performed for 1 minute at 750 ° C, and magnetic annealing was performed at 750 ° C for 2 hours in a 100% N ₂ atmosphere. FIG. 1 shows the relationship between the Ca / S of the sample thus obtained and the hysteresis loss per 1 Hz frequency when magnetized 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 when Ca / S is in the range of 0.5 to 3.0, the hysteresis loss is greatly reduced. This is because Ca forms a sulfide that is chemically more stable than MnS,
This is due to the effect of improving the grain growth during magnetic annealing by forming coarse sulfides without forming a solid solution again during slab heating.
When Ca / S <0.5, Ca for fixing S as sulfide is insufficient, MnS is formed, and the hysteresis loss increases. On the other hand, when Ca / S> 3.0, excess Ca reacts with oxides in the steel to generate fine CaO, which hinders grain growth and increases hysteresis loss. As described above, in the present invention, Ca is converted to C
a / S: contained in the range of 0.5 or more and 3 or less.

Next, the reasons for limiting other components will be described. Si is an effective element for increasing the specific resistance of the steel sheet, but if it exceeds 4%, the magnetic flux density decreases and the torque when driving the EPS motor decreases, so the upper limit was set to 4%. The torque at the time of driving the motor is a torque when a current is flowing through the motor.

Al, like Si, is an effective element for increasing the specific resistance. However, if it exceeds 1%, the magnetic flux density decreases and EPS
1% upper limit due to lower torque when driving motor
And

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 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. However, 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 hysteresis loss is increased, so that N is set to 0.005% or less.

[0017] When the amount of S exceeds 0.03%,
Can not be expected to improve the hysteresis loss even if
Must be 0.03% or less.

Next, a method of manufacturing a steel plate for an electric power steering motor core will be described. In the present invention,
As long as the components and Ca / S are within the predetermined ranges, the production method may be an ordinary method. That is, the molten steel blown in the converter is degassed, adjusted to a predetermined component, and subsequently cast,
Hot rolling is performed. The finish annealing temperature and the winding temperature at the time of hot rolling do not need to be particularly defined, and may be normal. In addition, hot-rolled sheet annealing after hot-rolling may be performed, but is not essential. Next, after a single sheet of cold rolling or two or more times of cold rolling sandwiching intermediate annealing to obtain a predetermined thickness, finish annealing is performed. Magnetic annealing after finish annealing may be performed, but is not essential.

[0019]

Example: Molten steel blown in a converter was degassed, adjusted to the components shown in Table 1, cast, and heated at 1140 ° C for 1 hour.
Hot rolling was performed to a thickness of 2.3 mm. Hot rolling finishing temperature is 800
° C, and the winding temperature was 680 ° C. After that, the plate thickness is 0.50m
m, and subjected to finish annealing in a 10% H ₂ -90% N ₂ atmosphere under the conditions shown in Table 1. 7% in 100% N ₂ atmosphere
Magnetic annealing at 50 ° C. × 2 hours was performed.

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.

[0021]

【table 1】

From these results, it can be seen that the steels of the present invention Nos. 1 to 3 in which the components and Ca / S are controlled within the range of the present invention can obtain a steel sheet having a low hysteresis loss and a high magnetic flux density.

On the other hand, the comparative steel of No. 4 has a high hysteresis loss and a low magnetic flux density because the amount of S is out of the range of the present invention. No.5 comparative steel is Ca / S
However, since it is out of the range of the present invention and low, the hysteresis loss is high and the magnetic flux density is low. Since the comparative steel of No. 6 has a high Ca / S outside the range of the present invention, the hysteresis loss is high.

The comparative steel of No. 7 has an amount of C, the comparative steel of No. 8 has an amount of Si, and the comparative steel of No. 9 has an amount of Mn which is out of the range of the present invention. Therefore, the magnetic flux density is low. Since the amount of N is out of the range of the present invention, the comparative steel of No. 10 has a high hysteresis loss and a low magnetic flux density. The No. 11 comparative steel has a low magnetic flux density because the amount of Al is out of the range of the present invention.

[0025]

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 Ca / S and hysteresis loss.

Claims (1)

[Claims] (1) C: 0.005% or less, Si: 4% or less by weight%,
Al: 1% or less, S: 0.03% or less, Mn: 0.05 to 1.5%, P: 0.
2% or less, N: 0.005% or less, and Ca is 0.5 ≦ Ca /
Steel sheet for electric power steering motor core containing S in the range of 3 and consisting essentially of Fe.