JP3768084B2

JP3768084B2 - Iron alloy plate material for hard disk voice coil motor yoke and yoke for hard disk voice coil motor

Info

Publication number: JP3768084B2
Application number: JP2000273198A
Authority: JP
Inventors: 武久美濃輪; 正信島尾; 雅昭西野
Original assignee: Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Chemical Co Ltd
Priority date: 2000-09-08
Filing date: 2000-09-08
Publication date: 2006-04-19
Anticipated expiration: 2020-09-08
Also published as: JP2002080945A

Description

【０００１】
【発明の属する技術分野】
本発明は、磁気記録装置における小型、薄型ボイスコイルモータに適した磁気回路を提供するための、磁気回路を構成する高磁束密度の鉄系ヨーク材料に関する。
【０００２】
【従来の技術】
ボイスコイルモータの磁気回路は、磁束を発生させる永久磁石と、それらをつなぐヨークで構成され、ハードディスクヘッド駆動用アクチュエーターとして使用される。近年、コンピュータは持ち運び、携帯のし易さなどを考慮して大きさや重量を低減する傾向にあり、それに伴い、磁気記録装置もまた小型化、薄型化されている。さらにこの小型化、薄型化は、磁気回路を構成する永久磁石、ヨーク材部品にも波及してきている。
磁気回路の小型化薄型化を実現するには、体積減少からくるギャップ間磁束密度の減少を、高性能磁石の高い磁束密度で補うことによって対応するのがこれまでは一般的であった。
【０００３】
しかし、高性能磁石の発生する磁束密度が年々高くなるのに対して、ヨーク材はＳＰＣＣ、ＳＰＣＤ、ＳＰＣＥなどの圧延鋼板を用いるために、磁石の磁束密度の向上に応じてヨーク材の飽和磁化を増大させることはできない。ヨークの厚み寸法も装置全体からの制約によって制限されるため、結局高性能磁石の磁束すべてを有効に活用することができず、磁気回路の途中で部分的に飽和したり、磁束の漏れが発生したりする。
このような磁束の漏れは、磁気回路のギャップ磁束密度を低下させるだけでなく、周辺の磁気記録媒体や制御機器に対して影響を及ぼすことになる。ＶＣＭ回路からの漏れ磁束量には一定の規定があり、製品の漏れ磁束量はこの規定値以下にしなければならない。
【０００４】
【発明が解決しようとする課題】
磁気記録装置などの磁気回路ヨーク用磁性材料としては、従来からＳＰＣＣ、ＳＰＣＤ、ＳＰＣＥ等の冷間圧延鋼板が打抜き、型取り、穴あけや曲げ、エンボス加工などの生産性に優れることと、安価なために最も多く使用されている。しかしながら、これらの鋼材は充分な飽和磁化を有しないため、前述の小型化、薄型化により、部分的なＶＣＭ磁気回路において磁気飽和をさけることが困難であり、高磁束密度を有する永久磁石からの磁束を十分に磁気回路に導くことができなかった。
これらの漏れ磁束量を無くし、永久磁石の持つ高磁束密度の特性をすべて活用することができるヨーク用磁性材料の開発が強く求められていた。
【０００５】
【課題を解決するための手段】
前述の課題を解決するために、種々検討を行った結果、ヨーク板材厚みが０．５ｍｍ以上５ｍｍ以下の場合において、高磁束密度を有する永久磁石から発生する磁束を効率良く磁気回路内へ導くためには、その含有成分をＣ：０．０００１〜０．０２質量％、Ｓｉ：０．０００１〜０．０５質量％、Ｍｎ：０．００１〜質量％質量％、Ｐ：０．０００１〜０．０５質量％、Ｓ：０．０００１〜０．０５質量％、Ａｌ：０．０００１〜０．１質量％、Ｏ：０．００１〜０．１質量％、Ｎ：０．０００１〜質量％質量％、Ｃｏ：０．１〜１０質量％とし、その他実用上不可避の不純物以外には残部がＦｅからなる合金とし、さらに添加元素としてＴｉ、Ｚｒ、Ｎｂ、Ｍｏ、Ｃｒ、Ｖ、Ｎｉ、Ｗ、Ｔａ、Ｂから選ばれる少なくとも一種以上の合金元素を合計で０．０１〜５質量％含有し、かつまたその飽和磁束密度を２．０７テスラ以上２．３テスラ以下、最大比透磁率が１２００以上２２０００以下、保磁力が２０Ａ／ｍ以上３８０Ａ／ｍ以下とすることによって、高特性のハードディスクボイスコイルモータを製作することができることを確認した。
とくに、従来高価なためにその使用を控えられてきていたＣｏが飽和磁化の向上に有効であり、板材の高飽和磁化によって高性能永久磁石から発生する磁束を効率良く磁気回路へ導くことができることを確認した。さらに添加元素として加えられたＴｉ、Ｚｒ、Ｎｂ、Ｍｏ、Ｃｒ、Ｖ、Ｎｉ、Ｗ、Ｔａから選ばれる少なくとも一種以上の合金元素からなる炭化物またはおよび酸化物が合金の粒界または／および粒内に微細に分散して析出していることが好ましい。
【０００６】
【発明の実施の形態】
本発明者らは、目的を達成するべく種々の材料の検討を行い、ＳＰＣＣ材等の成分から磁束密度の低下に影響を及ぼす元素を調べた。鉄に対しては、Ｃ、Ａｌ、Ｓｉ、Ｐ、Ｓ、Ｍｎは磁気モーメントを持っていないか、磁気モーメントが鉄母体と異なるために、これら元素の存在によって周囲の鉄の磁気モーメントを低下させる現象が起こる。特にＰ、Ｓは、磁束密度の低下以外に耐蝕性においても悪影響を及ぼす。しかし、これらの元素をむやみに低減させるのは、原料の製造コストの面から不利であり、性能的にも少量の範囲内であれば含有していても満足できる。
【０００７】
以上の観点から、Ｃ：０．０００１〜０．０２質量％、Ｓｉ：０．０００１〜０．０５質量％、Ｍｎ：０．００１〜０．２質量％、Ｐ：０．０００１〜０．０５質量％、Ｓ：０．０００１〜０．０５質量％、Ｃｏ：０．１〜１０質量％の範囲とすることができる。
ＯおよびＮも同様に磁気特性に影響し、Ｏ：０．００１〜０．１質量％およびＮ：０．０００１〜０．０３質量％とすることが好ましく、この範囲であれば、飽和磁束密度を特には劣化させない。
【０００８】
これら元素に対し、鉄原子よりも外殻電子数が多いＣｏは、磁束密度を増大させることから、本発明において重要な元素である。Ｃｏ量は、最大１０質量％まで添加することができ、合金の飽和磁束密度を増加させるが、それ以上は、合金の強度が大きく硬くなりすぎるために圧延加工が難しく、また、高価な金属であるためにコストの点から不利となる。よってＣｏ量は、０．１から１０質量％の範囲とすることが更に好ましい。
【０００９】
添加元素として添加されるＴｉ、Ｚｒ、Ｎｂ、Ｍｏ、Ｃｒ、Ｖ、Ｎｉ、Ｗ、Ｔａから選ばれる少なくとも一種以上の合金元素は、材料中のフェライト相内に固溶した場合、磁束密度の低下を起こすが、不可避に混入するＣ、Ｏとの間で金属間化合物を生成し、炭化物や酸化物を作る。その結果、これらの析出物は合金組織中に微細に均一に析出し、塑性加工中の転移の移動を阻害することができる。このため合金の過剰な延性が小さくなり、板材の打ちぬき時にせん断面のバリ発生を抑えることができる。
【００１０】
Ｍｏ、Ｃｒ、Ｖ、Ｎｉはステンレスなどの例に見られるように、鉄合金板材の耐食性を向上させる効果がある。Ｗ、Ｔａ、Ｂは、板材の圧延加工性を向上させる効果があり、加工費の低減に貢献できる。しかし、これらの元素はいずれも飽和磁化を減少させるので、合計でも５重量％以上添加することは好ましくない。さらに、本発明では、飽和磁束密度を２．０７〜２．３Ｔとすることが特徴であり、飽和磁束密度が高くても最大比透磁率が小さいか、または保磁力が大きすぎてしまっては、磁気回路の磁気抵抗が増大し、ギャップ磁束密度が低くなってしまう。このため、最大比透磁率は１２００以上２２０００以下の範囲とし、保磁力は２０Ａ／ｍ以上３８０Ａ／ｍ以下の範囲とする。
【００１１】
合金成分は、原料材料や製鋼方法によって目的とする範囲調整にされるが、生産性、品質上からは連続鋳造法が好ましく、また小ロット生産には真空溶解法などが適する。鋳造後、所定板厚の鋼材とするために、熱間圧延、冷間圧延などが実施される。このようにして得られた鉄合金板材は、機械式プレスや、油圧式プレスもしくはファインブランキングプレス等にて、打抜き、型取り、穴あけ、曲げ、エンボスなどの塑性加工により、所定のヨーク形状に加工処理され、バリ取り、面取り、酸洗の後、Ｎｉ、Ｃｕ、Ｃｒ、Ａｌ等の電気メッキ、無電解メッキ、ＰＶＤ、ＣＶＤ、イオンプレーティング等により表面処理を施し、ハードディスクボイスコイルモータに用いるヨーク材として製造することができる。
ここで、ヨーク材の板厚が０．１ｍｍ未満の場合は、薄すぎて板材の飽和磁化を多少向上させても磁気回路の特性向上効果があまり見られず、また５ｍｍを超える場合は、逆に充分に厚いため、本発明によらなくても磁気回路が飽和する問題は生じない。
【００１２】
【実施例】
以下に実施例を述べるが、本発明はこれら実施例に限られるものではない。
［実施例１〜８］
表１に示す実施例１〜８に示す成分組成の鋼合金塊を溶解・連続鋳造して、幅２００ｍｍ、長さ５００ｍｍ、板厚５０ｍｍの合金塊を得た。
その合金塊を１２００℃に加熱して熱間圧延を開始し、９５０℃以下で６０％の累積圧下率とし、８５０℃で熱間圧延を終了した。熱間圧延終了後は、室温まで空冷した。その後、冷間圧延した後、９００℃で仕上焼鈍し、酸洗を実施し、厚さ１ｍｍの鋼板とした。
【００１３】
得られた鋼板を機械式打抜きプレス機にてヨーク形状に打抜き加工し、上下ヨーク２種を得た。
得られたヨークは被膜厚み約８ミクロンの無電解ＮｉＰメッキを施した。それら上下ヨークの内側に、最大エネルギー積３８０ｋＪ／ｍ³の永久磁石をヨークの中央位置に接着し磁気回路を作製した。
得られたヨークは、被膜厚み約８ミクロンの無電解ＮｉＰメッキを施し、それら上下ヨークの内側に、最大エネルギー積３８０ｋＪ／ｍ³の永久磁石をヨークの中央位置に接着し磁気回路を作製した。
作製したヨーク材を約４ｍｍ角に切断し、最大磁界１．９ＭＡ／ｍの振動試料型磁力計にて飽和磁束密度を測定した。
【００１４】
また、ヨーク形状に打抜いた残りの板材から、外径４５ｍｍ、内径３３ｍｍのリング試料を作製し、ＪＩＳＣ２５３１（１９９９）に記載される方法に準拠し、前述のリング試料を、間に紙を挟み２枚重ね、絶縁テープを巻いた後、励磁用コイル、磁化検出用コイルとしてそれぞれ５０ターンづつ０．２６ｍｍφの銅線を巻き、最大磁界±１．６ｋＡ／ｍの直流磁化特性自動記録装置にて磁気ヒステリシス曲線を描き、最大比透磁率及び保磁力を測定した。また、作製したヨーク材の硬度をロックウェル硬度計（マツザワ製ＲＭＴ−３）にて測定した。
さらに、作製したボイスコイルモータ用磁気回路の性能を調べるために、実際の磁気記録装置に使用されている平面コイルを用い磁束計（Ｌａｋｅｓｈｏｒｅ製４８０Ｆｌｕｘｍｅｔｅｒ）を用いて、その磁気回路ギャップ間の総磁束量を測定した。また、添加元素分布を特性Ｘ線像を用いて、電子線マイクロアナライザー（ＥＰＭＡ electron probe microanalyzer ）にて測定した。
【００１５】
［比較例１〜２］
比較例として、一般的な市販のＳＰＣＣＳＤ品、板厚１ｍｍの材料（比較例１）と、表１に示す比較例２に示す成分組成の鋼合金塊を実施例１〜８と同様にして得た厚さ１ｍｍの鋼板について、実施例１〜８と同様に、磁気特性、硬度を測定した。
【００１６】
［実施例９〜１４］
同じく表１に示す実施例９〜１４の成分組成の鋼塊を電炉、転炉−脱ガス、連続鋳造工程を経て溶解・鋳造し、厚さ２００ｍｍのスラブを得た。溶銑はＲＨ脱ガスおよびＶＯＤ法（真空−酸素脱炭法）により精製した。
得られた２００ｍｍ板厚のスラブを１１００〜１２００℃に加熱・均熱し、熱間圧延機で圧延し、仕上げ温度８５０〜９５０℃で板厚約１０ｍｍとした。再結晶焼鈍（８５０〜９００℃）後、酸洗、冷間圧延により約４ｍｍの板厚とした。その後約８５０℃で仕上焼鈍後酸洗して供試用鋼板を得た。
【００１７】
得られた鋼板を機械式打抜きプレス機にてヨーク形状に打抜き加工し、上下ヨーク２種を得た。得られたヨークは被膜厚み約６ミクロンの無電解ＮｉＰメッキを施した。
それら上下ヨークの内側に、最大エネルギー積４００ｋＪ／ｍ³の永久磁石をヨークの中央位置に接着し磁気回路を作製した。
作製したヨーク板材の磁気特性、硬度を、実施例１〜８に示した方法にて、測定した。
以上の、実施例および比較例の実験結果を表２に、また、実施例１０についての添加元素分布（特性Ｘ線像：Ｔｉ−Ｋα１およびＣ−Ｋα）を図１、図２に、それぞれ示す。
なお、表１における増加率は、比較例１の磁束量に対するそれぞれの増加率を％で表している。
【００１８】
【表１】

【００１９】
【表２】

【００２０】
表２から、実施例１〜１４のの組成の鋼板は、いずれも、比較例１であるＳＰＣＣに対して飽和磁束密度が上昇し、それに対応して、磁気回路ギャップにおける総磁束量も増加したことが判る。
また、Ｃｏを添加しないこと以外は本発明の鋼板の組成と同様な比較例２では、硬度が相当に低いことが判る。
また、元素分布測定により、実施例１０について見られるように、添加元素は板材中にほぼ均一に分散し、添加元素、実施例１０の場合ではＴｉ、とＣの分布は一致していることが判る。
【００２１】
【発明の効果】
以上述べたように、本発明は、磁気記録装置ボイスコイルモータ用磁気回路部材として使用される厚さ０．５ｍｍから５ｍｍのヨーク材の磁気特性を向上させることによって、構成する磁気回路に磁石から投入される磁束を有効に利用してギャップ間の磁束密度を向上させ、しかも周辺の磁気記録媒体や制御機器に対して磁気的に影響を及ぼさない磁気回路の提供が可能となる。
【図面の簡単な説明】
【図１】実施例１０で得られた板材における特性Ｘ線像Ｔｉ−Ｋα１の電子線マイクロアナライザーの写真である。
【図２】実施例１０で得られた板材における特性Ｘ線像Ｃ−Ｋαの電子線マイクロアナライザーの写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high magnetic flux density iron-based yoke material constituting a magnetic circuit for providing a magnetic circuit suitable for a small and thin voice coil motor in a magnetic recording apparatus.
[0002]
[Prior art]
The magnetic circuit of the voice coil motor is composed of a permanent magnet that generates magnetic flux and a yoke that connects them, and is used as an actuator for driving a hard disk head. In recent years, computers tend to be reduced in size and weight in consideration of easiness to carry and carry, and along with this, magnetic recording devices have also become smaller and thinner. Further, this reduction in size and thickness has spread to permanent magnets and yoke material components that constitute a magnetic circuit.
In order to realize the miniaturization and thinning of the magnetic circuit, it has been common in the past to compensate for the decrease in the magnetic flux density between the gaps due to the volume reduction by the high magnetic flux density of the high-performance magnet.
[0003]
However, the magnetic flux density generated by high-performance magnets increases year by year, while the yoke material uses a rolled steel plate such as SPCC, SPCD, SPCE, etc., so that the saturation magnetization of the yoke material increases as the magnetic flux density of the magnet increases. Cannot be increased. Since the yoke thickness is also limited by the restrictions of the entire device, it is not possible to effectively use all the magnetic flux of the high-performance magnet, resulting in partial saturation or leakage of magnetic flux in the middle of the magnetic circuit. To do.
Such leakage of magnetic flux not only reduces the gap magnetic flux density of the magnetic circuit, but also affects the surrounding magnetic recording media and control equipment. The amount of magnetic flux leakage from the VCM circuit has a certain regulation, and the amount of magnetic flux leakage from the product must be less than this regulation value.
[0004]
[Problems to be solved by the invention]
As magnetic materials for magnetic circuit yokes such as magnetic recording devices, cold rolled steel sheets such as SPCC, SPCD, SPCE, etc. have been conventionally excellent in productivity such as punching, die-cutting, drilling and bending, and embossing. Because it is most often used. However, since these steel materials do not have sufficient saturation magnetization, it is difficult to avoid magnetic saturation in the partial VCM magnetic circuit due to the above-mentioned miniaturization and thinning, and the permanent magnets having high magnetic flux density are difficult to avoid. The magnetic flux could not be sufficiently guided to the magnetic circuit.
There has been a strong demand for the development of a magnetic material for a yoke that can eliminate these leakage magnetic flux amounts and can utilize all the characteristics of the high magnetic flux density of a permanent magnet.
[0005]
[Means for Solving the Problems]
As a result of various studies to solve the above-mentioned problems, in order to efficiently guide the magnetic flux generated from the permanent magnet having a high magnetic flux density into the magnetic circuit when the yoke plate thickness is 0.5 mm or more and 5 mm or less. The content of the components is C: 0.0001 to 0.02 mass% , Si: 0.0001 to 0.05 mass% , Mn: 0.001 to mass% , P: 0.0001 to 0.001 . 05 mass% , S: 0.0001 to 0.05 mass% , Al: 0.0001 to 0.1 mass% , O: 0.001 to 0.1 mass% , N: 0.0001 to 0.1 mass% Co: 0.1 to 10% by mass , other than practically inevitable impurities, the balance is made of Fe, and additional elements include Ti, Zr, Nb, Mo, Cr, V, Ni, W, Ta , At least one selected from B Of the alloying elements contained from 0.01 to 5 mass% in total, and also the saturated magnetic flux density 2.07 tesla to 2.3 tesla less, the maximum relative permeability of 1,200 or more 22000 or less, the coercive force is 20A / m It was confirmed that a high-performance hard disk voice coil motor can be manufactured by adjusting the pressure to 380 A / m or less.
In particular, Co, which has been refrained from being used due to its high cost, is effective in improving the saturation magnetization, and the magnetic flux generated from the high-performance permanent magnet can be efficiently guided to the magnetic circuit by the high saturation magnetization of the plate material. It was confirmed. Further, carbides and / or oxides composed of at least one alloy element selected from Ti, Zr, Nb, Mo, Cr, V, Ni, W, and Ta added as additive elements are alloy grain boundaries or / and intragranular. It is preferable that they are finely dispersed and precipitated.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present invention have studied various materials to achieve the object, and have investigated elements that affect the decrease in magnetic flux density from components such as SPCC materials. For iron, C, Al, Si, P, S, Mn does not have a magnetic moment, or the magnetic moment is different from that of the iron matrix, so the presence of these elements reduces the magnetic moment of the surrounding iron. A phenomenon occurs. In particular, P and S adversely affect the corrosion resistance in addition to the decrease in magnetic flux density. However, reducing these elements unnecessarily is disadvantageous from the viewpoint of the production cost of the raw material, and it is satisfactory even if it is contained within a small amount in terms of performance.
[0007]
From the above viewpoints, C: 0.0001 to 0.02 mass% , Si: 0.0001 to 0.05 mass% , Mn: 0.001 to 0.2 mass% , P: 0.0001 to 0.05 Mass% , S: 0.0001 to 0.05 mass% , Co: 0.1 to 10 mass% .
Similarly, O and N affect the magnetic properties, and O: 0.001 to 0.1% by mass and N: 0.0001 to 0.03% by mass are preferable. Is not particularly deteriorated.
[0008]
In contrast to these elements, Co, which has more outer electrons than iron atoms, is an important element in the present invention because it increases the magnetic flux density. Co amount can be added up to 10 wt%, it increases the saturation magnetic flux density of the alloy, more than that, it is difficult to rolling in the strength of the alloy becomes too hard increases were or, high value Since it is a metal, it is disadvantageous in terms of cost. Therefore, the amount of Co is more preferably in the range of 0.1 to 10% by mass .
[0009]
When at least one alloy element selected from Ti, Zr, Nb, Mo, Cr, V, Ni, W, and Ta added as an additive element is dissolved in the ferrite phase in the material, the magnetic flux density decreases. However, an intermetallic compound is formed between C and O which are inevitably mixed to form carbides and oxides. As a result, these precipitates precipitate finely and uniformly in the alloy structure, and can inhibit the movement of transition during plastic working. For this reason, the excessive ductility of the alloy is reduced, and the occurrence of burrs on the shear surface can be suppressed when the plate material is punched.
[0010]
Mo, Cr, V, and Ni have an effect of improving the corrosion resistance of the iron alloy sheet as seen in examples of stainless steel. W, Ta, and B have the effect of improving the rolling workability of the plate material, and can contribute to the reduction of the processing cost. However, since these elements all reduce saturation magnetization, it is not preferable to add 5% by weight or more in total. Furthermore, the present invention is characterized in that the saturation magnetic flux density is 2.07 to 2.3 T. Even if the saturation magnetic flux density is high, the maximum relative permeability is small or the coercive force is too large. The magnetic resistance of the magnetic circuit increases and the gap magnetic flux density decreases. Therefore, the maximum relative magnetic permeability is in the range of 1200 to 22000, and the coercive force is in the range of 20 A / m to 380 A / m.
[0011]
The alloy component is adjusted in the desired range depending on the raw material and steelmaking method, but the continuous casting method is preferable from the viewpoint of productivity and quality, and the vacuum melting method is suitable for small lot production. After casting, hot rolling, cold rolling, or the like is performed in order to obtain a steel material having a predetermined plate thickness. The iron alloy sheet material obtained in this way is made into a predetermined yoke shape by plastic working such as punching, die-making, drilling, bending, embossing, etc. with a mechanical press, hydraulic press or fine blanking press. After processing, deburring, chamfering, pickling, surface treatment by electroplating of Ni, Cu, Cr, Al, etc., electroless plating, PVD, CVD, ion plating, etc., and used for hard disk voice coil motor It can be manufactured as a yoke material.
Here, when the plate thickness of the yoke material is less than 0.1 mm, even if the saturation magnetization of the plate material is slightly improved, the effect of improving the characteristics of the magnetic circuit is not so much seen. Therefore, there is no problem of saturation of the magnetic circuit without using the present invention.
[0012]
【Example】
Examples will be described below, but the present invention is not limited to these examples.
[Examples 1 to 8]
Steel alloy ingots having the composition shown in Tables 1 to 8 shown in Table 1 were melted and continuously cast to obtain alloy ingots having a width of 200 mm, a length of 500 mm, and a plate thickness of 50 mm.
The alloy ingot was heated to 1200 ° C. to start hot rolling, the cumulative rolling reduction was 950 ° C. or less, and the hot rolling was finished at 850 ° C. After the hot rolling was finished, it was air-cooled to room temperature. Then, after cold rolling, finish annealing was performed at 900 ° C., pickling was performed, and a steel sheet having a thickness of 1 mm was obtained.
[0013]
The obtained steel sheet was punched into a yoke shape with a mechanical punching press to obtain two types of upper and lower yokes.
The obtained yoke was subjected to electroless NiP plating with a coating thickness of about 8 microns. Inside these upper and lower yokes, a permanent magnet having a maximum energy product of 380 kJ / m ³ was bonded to the central position of the yoke to produce a magnetic circuit.
The obtained yoke was subjected to electroless NiP plating with a coating thickness of about 8 microns, and a permanent magnet having a maximum energy product of 380 kJ / m ³ was adhered to the center of the yoke inside the upper and lower yokes to produce a magnetic circuit.
The produced yoke material was cut into about 4 mm square, and the saturation magnetic flux density was measured with a vibrating sample magnetometer having a maximum magnetic field of 1.9 MA / m.
[0014]
In addition, a ring sample having an outer diameter of 45 mm and an inner diameter of 33 mm is produced from the remaining plate material punched into a yoke shape, and the above-described ring sample is placed between the paper samples according to the method described in JIS C 2531 (1999). 2 layers, wound with insulating tape, and then wound with 0.26mmφ copper wire for 50 turns each as an exciting coil and a magnetization detecting coil, DC magnetic characteristics automatic recording device with maximum magnetic field ± 1.6kA / m The magnetic hysteresis curve was drawn at, and the maximum relative permeability and coercive force were measured. Further, the hardness of the produced yoke material was measured with a Rockwell hardness meter (RMT-3 manufactured by Matsuzawa).
Further, in order to investigate the performance of the magnetic circuit for the voice coil motor thus produced, the total magnetic flux between the magnetic circuit gaps was measured using a magnetometer (480Fluxmeter manufactured by Lakeshore) using a planar coil used in an actual magnetic recording apparatus. The amount was measured. Further, the additive element distribution by using the characteristic X-ray image was measured by an electron beam microanalyzer (EPMA electron probe microanalyzer).
[0015]
[Comparative Examples 1-2]
As a comparative example, a commercially available SPCCSD product, a material having a plate thickness of 1 mm (Comparative Example 1), and a steel alloy ingot having the composition shown in Comparative Example 2 shown in Table 1 were obtained in the same manner as in Examples 1-8. The steel sheet having a thickness of 1 mm was measured for magnetic properties and hardness in the same manner as in Examples 1-8.
[0016]
[Examples 9 to 14]
Similarly, steel ingots having the component compositions of Examples 9 to 14 shown in Table 1 were melted and cast through an electric furnace, a converter-degassing, and a continuous casting process to obtain a slab having a thickness of 200 mm. The hot metal was purified by RH degassing and VOD method (vacuum-oxygen decarburization method).
The obtained slab having a thickness of 200 mm was heated and soaked to 1100 to 1200 ° C., and rolled with a hot rolling mill to a plate temperature of about 10 mm at a finishing temperature of 850 to 950 ° C. After recrystallization annealing (850 to 900 ° C.), the thickness was about 4 mm by pickling and cold rolling. Thereafter, it was pickled after finishing annealing at about 850 ° C. to obtain a test steel plate.
[0017]
The obtained steel sheet was punched into a yoke shape with a mechanical punching press to obtain two types of upper and lower yokes. The obtained yoke was subjected to electroless NiP plating with a coating thickness of about 6 microns.
Inside these upper and lower yokes, a permanent magnet having a maximum energy product of 400 kJ / m ³ was bonded to the central position of the yoke to produce a magnetic circuit.
Magnetic properties and hardness of the produced yoke plate material were measured by the methods shown in Examples 1-8.
The experimental results of Examples and Comparative Examples are shown in Table 2, and the additive element distribution (characteristic X-ray images: Ti-Kα1 and C-Kα) for Example 10 are shown in FIGS. 1 and 2, respectively. .
In addition, the increase rate in Table 1 represents each increase rate with respect to the magnetic flux amount of the comparative example 1 by%.
[0018]
[Table 1]

[0019]
[Table 2]

[0020]
From Table 2, the steel sheets having the compositions of Examples 1 to 14 all had a higher saturation magnetic flux density than the SPCC of Comparative Example 1, and correspondingly, the total magnetic flux amount in the magnetic circuit gap also increased. I understand that.
Moreover, it turns out that hardness is comparatively low in the comparative example 2 similar to the composition of the steel plate of this invention except not adding Co.
In addition, the element distribution measurement shows that the additive element is almost uniformly dispersed in the plate material as seen in Example 10, and that the distribution of the additive element, in the case of Example 10, Ti and C is the same. I understand.
[0021]
【The invention's effect】
As described above, the present invention improves the magnetic characteristics of a yoke material having a thickness of 0.5 mm to 5 mm used as a magnetic circuit member for a magnetic recording device voice coil motor, thereby forming a magnetic circuit from a magnet. It is possible to provide a magnetic circuit that improves the magnetic flux density between the gaps by effectively using the magnetic flux that is input, and that does not magnetically affect the surrounding magnetic recording media and control equipment.
[Brief description of the drawings]
1 is a photograph of an electron beam microanalyzer of a characteristic X-ray image Ti-Kα1 in a plate material obtained in Example 10. FIG.
2 is a photograph of an electron beam microanalyzer of a characteristic X-ray image C-Kα in the plate material obtained in Example 10. FIG.

Claims

In a yoke plate material having a plate thickness of 0.1 mm or more and 5 mm or less used for a hard disk voice coil motor magnetic circuit, the plate material is C: 0.0001 to 0.02 mass% , Si: 0.0001 to 0.05 mass. % , Mn: 0.001 to 0.2 mass% , P: 0.0001 to 0.05 mass% , S: 0.0001 to 0.05 mass% , Al: 0.0001 to 0.1 mass% , O: 0.001 to 0.1% by mass , N: 0.0001 to 0.03% by mass , Co: 0.1 to 10% by mass of each element, and Ti, Zr, Nb, Iron containing at least one alloy element of at least one selected from Mo, Cr, V, Ni, W, Ta, and B in a total amount of 0.01 to 5% by mass , with the balance being Fe other than impurities practically inevitable Alloy and also its saturation Iron alloy for hard disk voice coil motor yoke, characterized in that the bundle density is 2.07 Tesla or more and 2.3 Tesla or less, the maximum relative permeability is 1200 or more and 22000 or less, and the coercive force is 20 A / m or more and 380 A / m or less. Board material.

The iron alloy plate for a hard disk voice coil motor yoke according to claim 1, wherein at least one alloy selected from Ti, Zr, Nb, Mo, Cr, V, Ni, W and Ta is present in the grain boundaries or / and in the grains of the alloy. An iron alloy plate for a hard disk voice coil motor yoke, characterized in that carbides and / or oxides of elements are finely dispersed and precipitated.

A yoke for a hard disk voice coil motor using the iron alloy sheet according to claim 1.