JP3997667B2 - Manufacturing method of steel plate for electric power steering motor core - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、自動車のパワ−ステアリングシステムにおける、電動パワ−ステアリングモータコア用材料の製造方法に関するものである。
【０００２】
【従来の技術】
自動車のパワ−ステアリングシステムは、自動車の消費エネルギーの3〜5％を占め、エアコンと並んでエネルギー消費の多い装置である。従来のパワ−ステアリングシステムは油圧により操舵を補助していたが、本システムでは油圧ポンプが常にエンジンにより駆動されているため、直進走行時にもエネルギーが消費されるという問題があった。この無駄を解消するため、モータにより操舵を補助する電動パワ−ステアリング（以下、EPSと略す）システムが開発されている。EPSシステムではコーナリング時等の操舵補助が必要なときのみモータに電流を流しパワーをアシストするため、油圧システムに比べ燃費が2〜3％程度向上する。
【０００３】
【発明が解決しようとする課題】
ところで、このようなEPSシステムにおいては、小型、高トルクの観点から永久磁石を使用するPMモータが使用されている。しかし、PMモータでは操舵後、比較的大きなロストルクが生じることから、旋回後直進状態になるまでに時間遅れが発生し、このため操舵感が油圧方式に比べ劣るという問題があった。
【０００４】
本発明はこのような問題点を解決するためになされたもので、ロストルクが小さく、電動パワ−ステアリングモータコア用として好適な鋼板の製造方法を提供することを課題とする。
【０００５】
【課題を解決するための手段】
上記の課題は次の発明により解決される。
【０００６】
第一の発明は、重量％でC：0.005％以下、Si： 3.0％以下、Sol.Al：0.2〜0.5％、S：0.02％以下、Mn：0.05〜1.5％、P：0.2％以下、N：0.005％以下、残部Feおよび不可避不純物からなるスラブに、熱間圧延、冷間圧延、連続焼鈍を施した後、次いで1.0〜8.0％の圧下率で調質圧延を行うことを特徴とする電動パワ−ステアリングモータコア用鋼板の製造方法。
【０００８】
これらの手段において、本発明の作用効果を無くさない限り、不可避不純物をはじめ、他の微量元素を含有するものが本発明の範囲に含まれる。
【０００９】
【発明の実施の形態】
本発明者らがEPSモータコア材として好適な材料すなわちロストルクが小さい材料について検討した結果、このロストルクは機械損とコア材料のヒステリシス損に起因することを見いだした。さらにEPSモータコア材としてヒステリシス損の低い材料及びその手法について検討を進めた結果、無方向性珪素鋼板が最適であり、特にAlを適量添加した鋼板を用いることで良好なヒステリシス特性を有する材料が得られること、また、その鋼板を製造するに際しては、前記スラブに熱間圧延、冷間圧延、連続焼鈍を施した後、圧下率1.0〜8.0％の調質圧延を行うことがユーザー焼鈍後に、ヒステリシス特性を向上する上で非常に有効なことを見いだした。
【００１０】
以下、本発明に至る経緯と発明の詳細を実験結果に基づいて詳細に説明する。
パワ−ステアリングモータは、小型化、高トルク化のため、ステータのコアバック部が2〜4mm程度と非常に細く打ち抜き加工の影響を受けやすい。そのため、加工歪みによるコア損失の増大が生じる。この対策として、部品加工後に歪取り焼鈍（ユーザー焼鈍）を行うと磁気特性は回復することが知られており、実際に行われている。そこで、本発明では、ユーザー焼鈍を行うことを前提にパワ−ステアリングモータに適したヒステリシス損が低く、かつ磁束密度の高いコア材料を検討した。
【００１１】
最初に、ヒステリシス損に及ぼす調質圧延の影響を調査するため、C：0.0025％、Si：0.35％、Mn：0.40％、P：0.095％、S：0.0040％、Sol.Al：tr.、N：0.0020％の鋼をラボ溶解し、熱延後、酸洗し、板厚0.50mmまで冷間圧延した。次いで、10％H2-90％N2雰囲気で760℃×40secの連続焼鈍を行い、圧下率0〜１5％の範囲で調質圧延を施した。打ち抜き加工により各コイルから幅30mm×長さ280mmの磁気測定用サンプルを切り出し、最も多く実施されているユーザー焼鈍として、100％N2雰囲気中での750℃×2hrの焼鈍を実施した。
【００１２】
図1に、このようにして得られたサンプルの調質圧延圧下率とユーザー焼鈍後の1.5 Tまで磁化した場合の周波数1Hz当たりのヒステリシス損の関係を示す。ここで磁気特性の測定は25cmエプスタイン法にて行い、ヒステリシス損は50、60Hzの鉄損より2周波法にて計算した。
【００１３】
図1より、調質圧延圧下率の増加に伴い急激にヒステリシス損が低減し、8％を越えると再び緩やかに増加する。ユーザー焼鈍後の組織観察の結果、低ヒステリシス損の領域では歪み誘起粒成長によるフェライト組織の粗大粒化が認められた。また、調質圧延率が8％を越えると組織は再び細粒化しはじめていた。以上より、調質圧延圧下率の最適範囲は、ロストルク低減に問題とならないヒステリシスレベルである1.0％以上とし上限は8.0％以下とする。
【００１４】
次に、さらなるヒステリシス損低減の手法を検討するために、調質圧延プロセスを前提としたAlの影響を調査した。 C：0.0025％、Si：0.32％、Mn：0.40％、P：0.095％、S：0.004％、N：0.0020％とし、Sol.Alをtr.〜0.50％と変化させた鋼をラボ溶解し、熱延後、酸洗し、板厚0.50mmまで冷間圧延した。次いで、10％H2-90％N2雰囲気で770℃×40secの連続焼鈍を行い、圧下率2.5％の調質圧延を施した。打ち抜き加工により各コイルから幅30mm×長さ280mmの磁気測定用サンプルを切り出し、100％N2雰囲気中で750℃×2hrのユーザー焼鈍を実施した。
【００１５】
図2にSol.Alとユーザー焼鈍後の1.5 Tまで磁化した場合の周波数1Hz当たりのヒステリシス損の関係を示す。図2よりSol.Alが0.004％を越えるとヒステリシス損が急激に増加し始め、0.15％以上になると再び低減する。そこで、光学顕微鏡による組織観察およびTEM観察を行った。その結果、Sol.Alが0.004％超え〜0.15％未満の領域では、微細なAl2O3-MnO-SiO2の3元系酸化物や微細なAlNの存在により結晶粒が不均一であることが判明した。一方、Sol.Alが0.004％以下の領域は、SiO2あるいはSiO2-MnOの比較的大きな1μm以上の酸化物が主体であり、結晶組織は調質圧延歪みにより均一に粗大化していた。またSol.Alが0.15％以上の領域は、鋼中にはAl2O3系酸化物と300nm程度のAlNが存在し、結晶組織も均一になっていた。
【００１６】
以上より、安定的にヒステリシス損を低減するためには、好ましくはSol.Alを0.004％以下または0.15〜0.5％とする。
【００１７】
次に、その他の成分の限定理由について説明する。
Cは、磁気時効によりヒステリシス損が増加するため0.005％以下とした。
【００１８】
Siは、結晶磁気異方性を低下しヒステリシス損を低減する。また、脱酸時にSiO2を形成し、調質圧延歪みによる粒成長を有効に作用させる効果があるが、3.0 ％を超えると磁束密度が低下するため上限を3.0％とする。
【００１９】
Sol.Alは0.5％を超えると磁束密度が低下するため上限を0.5％とした。また、安定的にヒステリシス損を低減するために0.2％以上0.5％以下とする。
【００２０】
Mnは熱間圧延時のSを固定するために、0.05％以上必要であるが、1.5％を超えると磁束密度を低下させるため1.5％以下とする。
【００２１】
Sは、多量に含有するとMnSが増加して、ヒステリシス損が増大するので、0.02％以下とする。
【００２２】
Pは鋼板の打ち抜き性を改善するために必要な元素であるが、0.2％を超えて添加すると鋼板が脆化するため0.2％以下とする。
【００２３】
Nは0.005％を超えるとヒステリシス損を増大させるため0.005％以下とする。
次に、製造方法について説明する。
【００２４】
本発明において、前記で規定した成分、および調質圧延時の圧下率が本発明の範囲内であれば、その他の製造方法は通常の製造方法でかまわない。すなわち、転炉で吹練した溶鋼を脱ガス処理し所定の成分に調整し、引き続き鋳造、熱間圧延を行う。熱間圧延時の仕上焼鈍温度、巻取り温度は特に規定する必要はなく、通常でかまわない。また、熱延後の熱延板焼鈍は行っても良いが必須ではない。次いで一回の冷間圧延、もしくは中間焼鈍をはさんだ2回以上の冷間圧延により所定の板厚とした後に、仕上げ焼鈍を行う。その後、調質圧延を行い製品とする。調質圧延は圧下率1.0〜8.0％で行うことにより、本発明鋼を得ることができる。
【００２５】
【実施例】
転炉で吹練した溶鋼を脱ガス処理し表1の成分に調整後鋳造し、スラブを1200℃で1hr加熱した後、板厚2.0mmまで熱間圧延を行った。熱延仕上げ温度は810℃とした。巻取り温度は680〜720℃とした。その後、板厚0.50mmまで冷間圧延を行い、10％H2-90％N2の雰囲気で表1に示す仕上げ焼鈍および調質圧延を行った。その後750℃×2hrのユーザー焼鈍を行い、ヒステリシス損と磁束密度を測定した。
【００２６】
磁気特性の測定は25cmエプスタイン法にて行い、ヒステリシス損は、1.5Tまで磁化した場合の周波数1Hz当たりのヒステリシス損をエプスタイン試験にて得られた50、60Hzの鉄損より2周波法にて計算して評価した。各鋼板のヒステリシス損特性及び磁気特性を表1に併せて示す。
【００２７】
【表１】
表１より、成分、調質圧延圧下率を本発明の範囲に制御したNo.2 、 No.4、No.5の本発明例による鋼板において、ユーザー焼鈍後のヒステリシス損が低く、かつ磁束密度の高い鋼板が得られることがわかる。
【００２９】
これに対し、No.6、No.7の比較例による鋼板は調質圧延圧下率が、No.9の比較例による鋼板はCの量が、No.11の比較例による鋼板はSの量が、それぞれ本発明の範囲を外れているので、ユーザー焼鈍後のヒステリシス損が高くなっている。
【００３０】
また、No.8の比較例による鋼板はSol.Alの量が、No.10の比較例による鋼板はMnとNの量が、No.12の比較例による鋼板はSiの量が、それぞれ本発明の範囲を外れているので、磁束密度が低くなっている。
【００３１】
【発明の効果】
以上述べたように、本発明によればヒステリシス損の低い鋼板を得ることができ、EPSモータのロストルク低減に効果的な電動パワ−ステアリングモータコア用鋼板を得ることができる。
【００３２】
さらに、高磁束密度が得られるので、モータ駆動時に高トルクが得られ操舵性にも優れる。
【図面の簡単な説明】
【図１】調質圧延圧下率とユーザー焼鈍後のヒステリシス損との関係を示す図である。
【図２】 Sol.Alとユーザー焼鈍後のヒステリシス損との関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a material for an electric power steering motor core in a power steering system of an automobile.
[0002]
[Prior art]
The power steering system of an automobile accounts for 3 to 5% of the energy consumption of the automobile and is a device that consumes a lot of energy along with an air conditioner. The conventional power steering system assists steering by hydraulic pressure. However, in this system, since the hydraulic pump is always driven by the engine, there is a problem in that energy is consumed even when traveling straight ahead. In order to eliminate this waste, an electric power steering (hereinafter abbreviated as EPS) system that assists steering by a motor has been developed. The EPS system assists the power by supplying current to the motor only when steering assistance is required, such as during cornering, so fuel efficiency is improved by 2-3% compared to the hydraulic system.
[0003]
[Problems to be solved by the invention]
By the way, in such an EPS system, a PM motor using a permanent magnet is used from the viewpoint of small size and high torque. However, since a relatively large loss torque occurs after steering in the PM motor, there is a problem that a time delay occurs until the vehicle goes straight after turning, and the steering feeling is inferior to that of 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 method for producing a steel plate that has a small loss torque and is suitable for an electric power steering motor core.
[0005]
[Means for Solving the Problems]
The above problems are solved by the following invention.
[0006]
In the first invention, C: 0.005% or less, Si: 3.0% or less, Sol.Al: 0.2-0.5%, S: 0.02% or less, Mn: 0.05-1.5%, P: 0.2% or less, N 0.005% or less, the slab the balance being Fe and unavoidable impurities, hot rolling, cold rolling, was subjected to continuous annealing, then you and performing temper rolling at a reduction rate of 1.0 to 8.0% dynamic power collector - method for manufacturing steel sheet for steering motor core.
[0008]
In these means, as long as not to lose the effect of the present invention, including unavoidable impurities, those containing other trace elements Ru included in the scope of the present invention.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
As a result of studying a material suitable for the EPS motor core material, that is, a material having a small loss torque, the present inventors have found that this loss torque is caused by a mechanical loss and a hysteresis loss of the core material. Furthermore, as a result of investigations on materials with low hysteresis loss and their methods as EPS motor core materials, non-oriented silicon steel sheets are the most suitable. In addition, when manufacturing the steel sheet, after subjecting the slab to hot rolling, cold rolling, and continuous annealing, temper rolling with a rolling reduction of 1.0 to 8.0% may be performed after user annealing. It was found to be very effective in improving the characteristics.
[0010]
Hereinafter, the background to the present invention and details of the invention will be described in detail based on experimental results.
The power steering motor is very thin and has a core back portion of about 2 to 4 mm and is susceptible to punching due to its size and torque. Therefore, the core loss increases due to processing distortion. As a countermeasure against this, it is known that the magnetic characteristics are restored when the stress relief annealing (user annealing) is performed after the parts are processed. Therefore, in the present invention, a core material having a low hysteresis loss and a high magnetic flux density suitable for a power steering motor has been studied on the assumption that user annealing is performed.
[0011]
First, to investigate the effect of temper rolling on hysteresis loss, C: 0.0025%, Si: 0.35%, Mn: 0.40%, P: 0.095%, S: 0.0040%, Sol.Al: tr., N : 0.0020% steel was melted in the laboratory, hot-rolled, pickled, and cold-rolled to a thickness of 0.50 mm. Subsequently, continuous annealing was performed at 760 ° C. for 40 seconds in a 10% H 2 -90% N 2 atmosphere, and temper rolling was performed in a range of a rolling reduction of 0 to 15%. A sample for magnetic measurement having a width of 30 mm and a length of 280 mm was cut out from each coil by punching, and as the most frequently performed user annealing, annealing was performed at 750 ° C. for 2 hours in a 100% N 2 atmosphere.
[0012]
FIG. 1 shows the relationship between the temper rolling reduction ratio of the sample thus obtained and the hysteresis loss per frequency of 1 Hz when magnetized to 1.5 T after user annealing. Here, the magnetic properties were measured by the 25 cm Epstein method, and the hysteresis loss was calculated by the two-frequency method from the iron loss at 50 and 60 Hz.
[0013]
From Fig. 1, the hysteresis loss decreases rapidly as the temper rolling reduction increases, and gradually increases again when it exceeds 8%. As a result of observation of the structure after user annealing, coarsening of the ferrite structure due to strain-induced grain growth was observed in the low hysteresis loss region. Moreover, when the temper rolling ratio exceeded 8%, the structure began to become finer again. From the above, the optimum range of the temper rolling reduction ratio is 1.0% or more, which is a hysteresis level that does not cause a problem in reducing the loss torque, and the upper limit is 8.0% or less.
[0014]
Next, in order to investigate the technique of further reducing hysteresis loss, the influence of Al on the premise of the temper rolling process was investigated. C: 0.0025%, Si: 0.32%, Mn: 0.40%, P: 0.095%, S: 0.004%, N: 0.0020%, Sol.Al changed to tr. After hot rolling, it was pickled and cold-rolled to a thickness of 0.50 mm. Next, continuous annealing at 770 ° C. × 40 sec was performed in a 10% H 2 -90% N 2 atmosphere, and temper rolling with a rolling reduction of 2.5% was performed. A sample for magnetic measurement having a width of 30 mm and a length of 280 mm was cut out from each coil by punching and subjected to user annealing at 750 ° C. for 2 hours in a 100% N 2 atmosphere.
[0015]
Fig. 2 shows the relationship between Sol.Al and hysteresis loss per 1Hz frequency when magnetized to 1.5 T after user annealing. From Fig. 2, when Sol.Al exceeds 0.004%, the hysteresis loss starts to increase rapidly, and when it exceeds 0.15%, it decreases again. Then, the structure observation and the TEM observation with an optical microscope were performed. As a result, in the region where Sol.Al exceeds 0.004% to less than 0.15%, the crystal grains are non-uniform due to the presence of fine Al 2 O 3 —MnO—SiO 2 ternary oxide and fine AlN. There was found. On the other hand, the region where Sol.Al was 0.004% or less was mainly composed of SiO 2 or SiO 2 —MnO having a relatively large oxide of 1 μm or more, and the crystal structure was uniformly coarsened due to temper rolling strain. In the region where Sol.Al was 0.15% or more, the Al 2 O 3 oxide and AlN of about 300 nm were present in the steel, and the crystal structure was uniform.
[0016]
From the above, in order to stably reduce the hysteresis loss, preferably, Sol.Al is 0.004% or less or 0.15 to 0.5%.
[0017]
Next, the reasons for limiting other components will be described.
C is set to 0.005% or less because hysteresis loss increases due to magnetic aging.
[0018]
Si reduces the magnetocrystalline anisotropy and reduces the hysteresis loss. In addition, SiO 2 is formed during deoxidation, and the grain growth due to temper rolling strain is effectively exerted. However, if the content exceeds 3.0%, the magnetic flux density decreases, so the upper limit is made 3.0%.
[0019]
Since Sol.Al exceeds 0.5%, the magnetic flux density decreases, so the upper limit was made 0.5%. Also, in order to reduce hysteresis loss stably, it should be 0.2 % or more and 0.5% or less.
[0020]
Mn needs to be 0.05% or more in order to fix S during hot rolling, but if it exceeds 1.5%, the magnetic flux density is lowered, so it is made 1.5% or less.
[0021]
If S is contained in a large amount, MnS increases and hysteresis loss increases, so the content is made 0.02% or less.
[0022]
P is an element necessary for improving the punchability of the steel sheet, but if added over 0.2%, the steel sheet becomes brittle, so the content is made 0.2% or less.
[0023]
If N exceeds 0.005%, the hysteresis loss is increased.
Next, a manufacturing method will be described.
[0024]
In the present invention, other production methods may be ordinary production methods as long as the components specified above and the rolling reduction during temper rolling are within the scope of the present invention. That is, the molten steel blown in the converter is degassed and adjusted to a predetermined component, and then casting and hot rolling are performed. 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 thickness is obtained by one cold rolling or two or more cold rollings with intermediate annealing, finish annealing is performed. Thereafter, temper rolling is performed to obtain a product. The steel of the present invention can be obtained by performing temper rolling at a rolling reduction of 1.0 to 8.0%.
[0025]
【Example】
The molten steel blown in the converter was degassed, adjusted to the components shown in Table 1 and cast, and the slab was heated at 1200 ° C. for 1 hr, and then hot rolled to a thickness of 2.0 mm. The hot rolling finishing temperature was 810 ° C. The winding temperature was 680 to 720 ° C. Thereafter, cold rolling was performed to a sheet thickness of 0.50 mm, and finish annealing and temper rolling shown in Table 1 were performed in an atmosphere of 10% H 2 -90% N 2 . Thereafter, user annealing at 750 ° C. × 2 hr was performed, and hysteresis loss and magnetic flux density were measured.
[0026]
Magnetic properties are measured by the 25cm Epstein method, and the hysteresis loss is calculated by the two-frequency method from the 50 and 60Hz iron loss obtained by the Epstein test for the hysteresis loss per 1Hz frequency when magnetized to 1.5T. And evaluated. Table 1 also shows the hysteresis loss characteristics and magnetic characteristics of each steel sheet.
[0027]
[Table 1]
From Table 1, the steel sheets according to the present invention examples No.2 , No.4 and No.5, whose components and temper rolling reduction ratios are controlled within the scope of the present invention, have low hysteresis loss after user annealing and magnetic flux density. It can be seen that a steel plate having a high thickness can be obtained.
[0029]
In contrast, the steel sheets according to the No. 6 and No. 7 comparative examples have a temper rolling reduction ratio, the steel sheet according to the No. 9 comparative example has an amount of C, and the steel sheet according to the No. 11 comparative example has an amount of S. However, since they are out of the scope of the present invention, the hysteresis loss after user annealing is high.
[0030]
In addition, the steel plate according to the comparative example No. 8 has the amount of Sol.Al, the steel plate according to the comparative example No. 10 has the amounts of Mn and N, and the steel plate according to the comparative example No. 12 has the amount of Si. Since it is outside the scope of the invention, the magnetic flux density is low.
[0031]
【The invention's effect】
As described above, according to the present invention, a steel plate with low hysteresis loss can be obtained, and a steel plate for an electric power steering motor core that is effective in reducing the loss torque of an EPS motor can be obtained.
[0032]
Furthermore, since a high magnetic flux density is obtained, a high torque is obtained when the motor is driven, and the steering performance is excellent.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a temper rolling reduction ratio and a hysteresis loss after user annealing.
FIG. 2 is a diagram showing the relationship between Sol.Al and hysteresis loss after user annealing.
Claims (1)
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24606499A JP3997667B2 (en) | 1999-08-31 | 1999-08-31 | Manufacturing method of steel plate for electric power steering motor core |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24606499A JP3997667B2 (en) | 1999-08-31 | 1999-08-31 | Manufacturing method of steel plate for electric power steering motor core |
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| Publication Number | Publication Date |
|---|---|
| JP2001073095A JP2001073095A (en) | 2001-03-21 |
| JP3997667B2 true JP3997667B2 (en) | 2007-10-24 |
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| EP1780095B1 (en) | 2005-10-28 | 2015-07-08 | Nsk Ltd. | Electric power steering apparatus and controller thereof |
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