JP3848217B2 - Sintered soft magnetic material and manufacturing method thereof - Google Patents
Sintered soft magnetic material and manufacturing method thereof Download PDFInfo
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- JP3848217B2 JP3848217B2 JP2002172394A JP2002172394A JP3848217B2 JP 3848217 B2 JP3848217 B2 JP 3848217B2 JP 2002172394 A JP2002172394 A JP 2002172394A JP 2002172394 A JP2002172394 A JP 2002172394A JP 3848217 B2 JP3848217 B2 JP 3848217B2
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- 239000000696 magnetic material Substances 0.000 title claims description 83
- 238000004519 manufacturing process Methods 0.000 title claims description 34
- 238000000465 moulding Methods 0.000 claims description 184
- 239000006247 magnetic powder Substances 0.000 claims description 115
- 238000005245 sintering Methods 0.000 claims description 110
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 105
- 239000000843 powder Substances 0.000 claims description 79
- 235000014113 dietary fatty acids Nutrition 0.000 claims description 67
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- CJZGTCYPCWQAJB-UHFFFAOYSA-L calcium stearate Chemical compound [Ca+2].CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O CJZGTCYPCWQAJB-UHFFFAOYSA-L 0.000 claims description 3
- 239000008116 calcium stearate Substances 0.000 claims description 3
- 235000013539 calcium stearate Nutrition 0.000 claims description 3
- XOOUIPVCVHRTMJ-UHFFFAOYSA-L zinc stearate Chemical compound [Zn+2].CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O XOOUIPVCVHRTMJ-UHFFFAOYSA-L 0.000 claims description 3
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims 1
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- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 125000000129 anionic group Chemical group 0.000 description 1
- AGXUVMPSUKZYDT-UHFFFAOYSA-L barium(2+);octadecanoate Chemical compound [Ba+2].CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O AGXUVMPSUKZYDT-UHFFFAOYSA-L 0.000 description 1
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- AVOVSJYQRZMDQJ-KVVVOXFISA-M lithium;(z)-octadec-9-enoate Chemical compound [Li+].CCCCCCCC\C=C/CCCCCCCC([O-])=O AVOVSJYQRZMDQJ-KVVVOXFISA-M 0.000 description 1
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Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0206—Manufacturing of magnetic cores by mechanical means
- H01F41/0246—Manufacturing of magnetic circuits by moulding or by pressing powder
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Powder Metallurgy (AREA)
- Soft Magnetic Materials (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、磁気特性に優れる焼結軟磁性体とその製造方法に関するものである。
【０００２】
【従来の技術】
変圧器（トランス）、電動機（モータ）、発電機、スピーカ、誘導加熱器、各種アクチュエータ等、我々の周囲には電磁気を利用した製品が数多くある。それらには、硬磁性体（永久磁石）や軟磁性体が使用されている。中でも軟磁性体（ソフト磁石）は、各種電磁機器の磁心（磁気コア）等として広く利用されている。軟磁性体は、その殆どが磁気特性に優れる鉄系材料を主成分とするものであり、溶製したもの、磁性粉末を加圧成形したもの、さらには、その成形体を焼結したもの等がある。
【０００３】
ここで、軟磁性体の透磁率等の磁気特性は、鉄等の磁性材料の密度に大きく影響を受ける。同組成ならば、高密度なもの程、磁気特性に優れる。この点からすると、溶製した軟磁性体は高密度（ほぼ１００％）で磁気特性に優れて好ましいということになる。しかし、溶製では寸法精度を確保し難いため、各種製品に利用する際には、所望の形状に機械加工等をすることが必要となる。しかも、軟鉄である軟磁性体は切削性が悪く、その加工も容易ではない。従って、自ずと、コスト高となる。
【０００４】
一方、圧粉磁心等の粉末成形体からなる軟磁性体は、寸法精度や表面粗さが良いため、成形後に特別な加工を必ずしも必要としない。つまり、形状付与性に優れるため、軟磁性体の低コスト化を図り易い。しかし、従来の成形技術では、高圧（例えば、７００ＭＰａ超）での成形が現実には困難であったため、その軟磁性体の密度は自ずと低いものとなっていた。また、これまでは、成形用金型と粉末成形体との間のかじり等を防止するために内部潤滑剤を必要としていた。この内部潤滑剤は成形後にも軟磁性体の内部に残存するため、軟磁性体の密度をより低下させる要因ともなっていた。従って、従来の粉末成形体からなる軟磁性体は、その密度が低く、十分な磁気特性が得られていなかった。
【０００５】
また、焼結した軟磁性体は、密度に関して粉末成形体の影響を大きく受けるため、低密度の粉末成形体を焼結した軟磁性体の密度も、やはり、低いものとなる。そこで、焼結軟磁性体の密度を向上させるために、成形工程と焼結工程とを繰返して２回行う二回成形二回焼結（２Ｐ２Ｓ）も考えられている。例えば、一回目では、比較的低圧の成形と比較的短時間で低温の予備焼結を行い、２回目では、緻密化や形状付与（ネットシェイプ化）のための再圧縮やサイジングと本来の焼結とを行うものである。なお、この方法によれば、最初の成形工程で内部潤滑剤を使用したとしても、後続の焼結工程（予備焼結）でその除去を行うことが可能となり、２回目の成形、焼結で、軟磁性体の一層の高密度化が可能となる。しかし、成形工程と焼結工程を２回繰返す２Ｐ２Ｓ法は、生産コストが非常に高くなるため、現実には殆ど為されていない。
【０００６】
この他、液相焼結法を用いると、粉末成形体の密度が低くても、高密度の焼結軟磁性体が得られる。しかし、従来の方法では、焼結時に生じる形状収縮が非常に大きく、その収縮代を予め予想することも現実には困難である。従って、その方法で軟磁性体を製作すると、結局、別途機械加工が必要となり、軟磁性体の低コスト化を図ることはできない。
【０００７】
【発明が解決しようとする課題】
本発明は、このような事情に鑑みて為されたものである。つまり、比較的低コストで、磁気特性に優れた高密度の焼結軟磁性体を提供することを目的とする。また、高密度であると共に、異方性をもつ焼結軟磁性体や形状安定性に優れた焼結軟磁性体を提供することを目的とする。
さらに、それらを効率的に得ることができる焼結軟磁性体の製造方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
そこで、本発明者はこの課題を解決すべく鋭意研究し、試行錯誤を重ねた結果、磁性粉末を従来になく高圧で成形することに成功し、本発明を完成するに至ったものである。
（焼結軟磁性体）
（１）すなわち、本発明の焼結軟磁性体は、成形用金型の内面に高級脂肪酸系潤滑剤を塗布する塗布工程と該塗布工程後の成形用金型内にＦｅを主成分とする磁性粉末を充填する充填工程と該充填工程後の該磁性粉末を温間で加圧成形する成形工程と該成形工程により得られた粉末成形体を加熱して焼結させる焼結工程とを経て製造され、
焼結体密度ｄ≧７．４ｇ／ｃｍ3、
１．６ＭＡ／ｍの磁場中における飽和磁化Ｍｓ≧１．９Ｔ、
１ｋＡ／ｍの磁場中における磁束密度Ｂ１ｋ≧１．４Ｔ、
であることを特徴とする。
【０００９】
高級脂肪酸系潤滑剤が内面に塗布された成形用金型を用いて、そこに充填された磁性粉末を温間で加圧成形すると、成形用金型内壁と粉末成形体との間での固着やかじりの発生が抑制、防止され、従来にない高圧成形が可能となることが解った。
そして、従来になく高密度の粉末成形体をその成形工程で得ることができたため、後続の焼結工程で、焼結体密度ｄ≧７．４ｇ／ｃｍ3 という高密度の焼結体を得ることができた。そして、その高密度故に、飽和磁化Ｍｓ≧１．９Ｔ、かつ磁束密度Ｂ１ｋ≧１．４Ｔという磁気特性に優れた焼結軟磁性体が得られた。
このような焼結軟磁性体は、例えば、前記磁性粉末が、９９．７質量％以上のＦｅと不可避不純物とからなるＦｅ系磁性粉末である場合に得られるが、それに限られるものではない。本明細書中で単に「磁性粉末」という場合には、Ｆｅ以外の種々の元素を含む粉末をも含まれることを断っておく。
なお、このように磁気特性に優れた焼結軟磁性体が、いわゆる一回成形一回焼結により得られる。また、かじり等の発生がないことから、抜き圧力が低く、金型寿命も長い。よって、その焼結軟磁性体は、全体的な製造コストも非常に低いものでもある。
ところで、何故、前述の各工程によりそのような高圧成形が可能となったのかは、必ずしも明かではないが、現状、次にように考えられる。つまり、所定範囲の温度と圧力の下で、成形用金型の内壁と磁性粉末との間に潤滑性に優れた金属石鹸潤滑膜が形成される。この金属石鹸潤滑膜は、単に、潤滑層が成形用金型の内壁と磁性粉末との間に介在するに留まらず、成形用金型の内壁または磁性粉末の表面へ強固に化学吸着している。その結果、高圧成形後に粉末成形体を成形用金型から取出す際にも潤滑膜が途切れず、内壁にかじり等が発生することが防止され、その際の抜き圧力も低減すると考えられる。
【００１０】
（２）上記の焼結体密度ｄ、飽和磁化Ｍｓおよび磁束密度Ｂ１ｋは、磁性粉末の組成によって多少変動することもあり、磁性粉末の組成によってはより優れた特性を発現し得る。
例えば、上記磁性粉末がＰを含有しＦｅを主成分とするＦｅ−Ｐ系磁性粉末である場合、本発明の焼結軟磁性体は、
焼結体密度ｄ≧７．５ｇ／ｃｍ3、
１．６ＭＡ／ｍの磁場中における飽和磁化Ｍｓ≧１．９Ｔ、
１ｋＡ／ｍの磁場中における磁束密度Ｂ１ｋ≧１．４Ｔ、
ともなる。より具体的には、例えば、このＦｅ−Ｐ系磁性粉末が、０．１〜５質量％のＰと残部Ｆｅと不可避不純物とからなる場合である。
【００１１】
また、例えば、上記磁性粉末がＳｉおよび／またはＡｌ（Ｍ１）を含有しＦｅを主成分とするＦｅ−Ｍ１系磁性粉末である場合、本発明の焼結軟磁性体は、
焼結体密度ｄ≧７．３ｇ／ｃｍ3、
１．６ＭＡ／ｍの磁場中における飽和磁化Ｍｓ≧１．８Ｔ、
１ｋＡ／ｍの磁場中における磁束密度Ｂ１ｋ≧１．３Ｔ、
ともなる。より具体的には、例えば、このＦｅ−Ｍ１系磁性粉末が、０．１〜５質量％のＭ１と残部Ｆｅと不可避不純物とからなる場合である。
【００１２】
また、例えば、上記磁性粉末がＣｏを含有しＦｅを主成分とするＦｅ−Ｃｏ系磁性粉末である場合、本発明の焼結軟磁性体は、
焼結体密度ｄ≧７．８ｇ／ｃｍ3、
１．６ＭＡ／ｍの磁場中における飽和磁化Ｍｓ≧２．１Ｔ、
１ｋＡ／ｍの磁場中における磁束密度Ｂ１ｋ≧１．４Ｔ、
１０ｋＡ／ｍの磁場中における磁束密度Ｂ１ｋ≧２．０Ｔ、
ともなる。より具体的には、例えば、このＦｅ−Ｃｏ系磁性粉末が、５〜５０質量％のＣｏと残部Ｆｅと不可避不純物とからなる場合である。この場合、さらに、Ｓｉ、Ａｌ、Ｐ、Ｔｉ、Ｖ、Ｍｎ、Ｃｒ、ＮｉおよびＭｏからなる元素群中の一種以上の元素を０．１〜５質量％含むでいても良い。
【００１３】
さらに、例えば、上記磁性粉末がＳｉ、Ａｌ、Ｐ、Ｔｉ、Ｖ、Ｍｎ、Ｃｒ、Ｃｏ、ＮｉおよびＭｏからなる元素群中の一種以上の元素（Ｍ２）を含有しＦｅを主成分とするＦｅ−Ｍ２系磁性粉末である場合、本発明の焼結軟磁性体は、
焼結体密度ｄ≧７．４ｇ／ｃｍ3、
１．６ＭＡ／ｍの磁場中における飽和磁化Ｍｓ≧１．９Ｔ、
１ｋＡ／ｍの磁場中における磁束密度Ｂ１ｋ≧１．４Ｔ、
ともなる。より具体的には、例えば、このＦｅ−Ｍ２系磁性粉末が、０．１〜５質量％のＭ２と残部Ｆｅと不可避不純物とからなる場合である。
【００１４】
（３）本発明者は、こうして得た焼結軟磁性体が特異な組織をもち得ることをも見出し、別の角度からも本発明を完成させた。
すなわち、本発明は、成形用金型の内面に高級脂肪酸系潤滑剤を塗布する塗布工程と該塗布工程後の成形用金型内にＦｅを主成分とする磁性粉末を充填する充填工程と該充填工程後の該磁性粉末を温間で加圧成形する成形工程と該成形工程により得られた粉末成形体を加熱して焼結させる焼結工程とを経て得られた焼結体が、該成形工程中の加圧方向に優先的に成長した結晶粒からなる組織を有することを特徴とする焼結軟磁性体でもある。
【００１５】
この焼結軟磁性体では、成形工程中の加圧方向に優先的に成長した結晶粒からなる組織をもつため、磁気特性が方向によって異なる異方性を発揮し得る。軟磁性体の場合、特定方向にのみ強い磁束密度が求められることが多い。従って、そのような場合に、本発明の焼結軟磁性体を使用すると、漏れ磁束等を抑制できて好都合である。
この焼結軟磁性体の組織を言換えるなら、長粒状の結晶粒が、成形工程中の加圧方向に整列しているものである。そして、この結晶粒の縦横比であるアスペクト比は、例えば、２以上、さらには５以上にもなる。勿論、そのときの結晶粒は、成形工程中の加圧方向に長い。
また、このような組織は、少なくとも、前記磁性粉末が９９．７質量％以上のＦｅと不可避不純物とからなり、前記成形工程が成形圧力を７８４ＭＰａ以上とする工程であり、前記焼結工程が焼結温度をγ変態点以上とする工程であるときに、得られることを本発明者は確認している。このときの成形圧力および焼結温度の詳細については後述する。
【００１６】
（４）本発明者は、等方的な組織をもつ焼結軟磁性体は、焼結工程前後で寸法変化が著しく小さくなることを見出し、さらに別の角度から本発明を完成させた。
すなわち、本発明は、成形用金型の内面に高級脂肪酸系潤滑剤を塗布する塗布工程と該塗布工程後の成形用金型内にＦｅを主成分とする磁性粉末を充填する充填工程と該充填工程後の該磁性粉末を温間で加圧成形する成形工程と該成形工程により得られた粉末成形体を加熱して焼結させる焼結工程とを経て得られた焼結体が、等方的に成長した結晶粒からなる組織を有することを特徴とする焼結軟磁性体でもある。
このような等方的な結晶粒組織からなる焼結体（焼結軟磁性体）は、前記焼結工程前後の寸法変化が、０．２％以下、さらには０．１％以下にもなる。これは、殆ど寸法変化をしていないことを示す。
また、このような組織は、少なくとも、前記磁性粉末が９９．７質量％以上のＦｅと不可避不純物とからなり、前記成形工程が成形圧力を７８４ＭＰａ以上とする工程であり、前記焼結工程が焼結温度をγ変態点未満とする工程であるときに得られることを本発明者は確認している。このときの成形圧力および焼結温度についても、その詳細は後述する。
【００１７】
（焼結軟磁性体の製造方法）
このような磁気特性に優れる焼結軟磁性体は、例えば、次の本発明の製造方法を用いて得ることができる。
すなわち、本発明は、成形用金型の内面に高級脂肪酸系潤滑剤を塗布する塗布工程と、該塗布工程後の成形用金型内にＦｅを主成分とする磁性粉末を充填する充填工程と、該充填工程後に該高級脂肪酸系潤滑剤が該磁性粉末に化学的に結合して金属石鹸の被膜を生成する圧力と温度の下で該磁性粉末を温間加圧成形する成形工程と、該成形工程により得られた粉末成形体を加熱して焼結させる焼結工程と、からなることを特徴とする焼結軟磁性体の製造方法としても把握することができる。
そして、焼結工程における焼結温度をγ変態点以上とすると、前述した異方的な結晶粒からなる組織をもつ焼結軟磁性体が得られ、焼結温度をγ変態点未満とすると、等方的な結晶粒からなる組織をもつ焼結軟磁性体が得られる。
【００１８】
【発明の実施の形態】
次に、実施形態を挙げ、本発明をより詳細に説明する。なお、以下で説明する内容は、本発明に係る焼結軟磁性体およびその製造方法のいずれにも、適宜該当することである。
（焼結軟磁性体）
（１）磁束密度
透磁率は、透磁率μ＝（磁束密度Ｂ）／（磁界の強さＨ）により求められるが、一般的なＢ−Ｈ曲線からも解るようにμは一定ではない。そこで、本発明の焼結軟磁性体の磁気特性を、この透磁率以外に、特定の強さの磁界中に置いたときにできる磁束密度でも評価することとした。つまり、本発明では、比較的低磁場である１ｋＡ／ｍ中に焼結軟磁性体を置いたときにできる磁束密度Ｂ１ｋで評価した。この他、０．５ｋ、２ｋＡ／ｍおよび１０ｋＡ／ｍの磁界中での磁束密度Ｂ０．５ｋ、Ｂ２ｋおよびＢ１０ｋにより、焼結軟磁性体の磁気特性を評価しても良い。使用する磁性粉末の組成にもよるが、本発明の焼結軟磁性体によると、例えば、Ｂ１ｋ≧１．４Ｔ、１．４５Ｔ、１．５Ｔともなる。また、Ｂ０．５ｋ≧１．３Ｔ、１．３５Ｔ、１．４Ｔ、さらに、Ｂ２ｋ≧１．５Ｔ、１．５５Ｔ、１．６Ｔ、加えて、Ｂ１０ｋ≧１．７Ｔ、１．７５Ｔ、１．８Ｔともなる。
【００１９】
飽和磁化Ｍｓが小さいと、大きな磁束密度が得られない。本発明の焼結軟磁性体によれば、例えば、１．６ＭＡ／ｍの磁場中における飽和磁化Ｍｓ≧１．９Ｔ、さらには、１．９５Ｔともなり、高磁界中でも安定した大きな磁束密度が得られる。
なお、上記磁束密度Ｂや飽和磁化Ｍｓの上限は限定されるものではないし特定することも困難である。敢えていうなら、各組成毎に求まる理論上可能な磁束密度Ｂや飽和磁化Ｍｓを上限とすることとなる。
【００２０】
（２）磁性粉末
本明細書中でいう「磁性粉末」は、Ｆｅを主成分とする粉末粒子からなるが、その粒子中のＦｅ含有量は特に限定されない。例えば、Ｆｅの含有量が９０質量％以上（１００質量％未満）であれば良い。
磁性粉末は、アトマイズ粉でも粉砕粉でも、また、それらの粗粒粉からなるものでもそれらの造粒粉からなるものでも良い。さらに、磁性粉末は、合金粉末でも、素粉末等を均一に混合した混合粉末でも良い。高密度の焼結軟磁性体を効率良く得るために、その粒径が２０〜３００μｍ、さらには２０〜２００μｍであると好適である。
このように、鉄を主成分とする磁性粉末を原料粉末として用いるため、得られた焼結軟磁性体の磁束密度は高く、保磁力やヒステリシス損失は小さい。また、磁性粉末は安価な鉄を主成分とするため低価格であり、焼結軟磁性体の低コスト化を図る上でも好ましい。
【００２１】
さらに、前述した本発明の製造方法を用いて焼結軟磁性体を製造する場合、鉄を主成分とする磁性粉末と高級脂肪酸系潤滑剤とが反応して、その粉末成形体の表面に強固で潤滑性に優れる高級脂肪酸の鉄塩被膜が形成されると考えられる。この鉄塩被膜の存在により、かじり等を生じることなく、成形用金型からその粉末成形体を取り出すことが容易となり、高密度の焼結軟磁性体を効率よく生産できる。
【００２２】
なお、磁性粉末に、予め、ステアリン酸リチウム、ステアリン酸カルシウム、ステアリン酸亜鉛等の高級脂肪酸系潤滑剤が噴霧、塗布、添加等されていても良い。このときの配合割合は、高級脂肪酸系潤滑剤と磁性粉末との合計を１００質量％としたときに、０．１質量％以下とすると好ましい。磁性粉末と高級脂肪酸系潤滑剤とを予め接触させておくと、例えば、磁性粉末の流動性が向上して成形用金型への充填密度が高くなり、高密度の焼結軟磁性体を得易い。但し、高級脂肪酸系潤滑剤の量が多すぎると磁性粉末からなる粉末成形体の到達密度が低くなり、好ましくない。
【００２３】
ところで、このような磁性粉末の最適例は、いわゆる純鉄粉である。その純度は９９．７質量％以上、さらには９９．８％以上であると好ましい。例えばヘガネス社製のＡＢＣ１００．３０を用いると、そのような鉄粉を容易に入手できる。この市販鉄粉は、Ｆｅ以外の成分がＣ：０．００１、Ｍｎ：０．０２、Ｏ：０．０８（単位：質量％）以下と、その他の市販鉄粉に比べて不純物が極めて少なく、圧縮性に優れた鉄粉である。
磁性粉末が、９９．７質量％以上のＦｅと不可避不純物とからなるＦｅ系磁性粉末の場合、前記焼結体密度ｄ≧７．６ｇ／ｃｍ3 、さらには、７．７ｇ／ｃｍ3ともなる。また、このとき前記Ｂ１ｋ≧１．４Ｔ、１．５Ｔ、１．５５Ｔともなる。
なお、上記純鉄粉の純度の上限は、理論的には１００質量％であるが、真に１００質量％とすることは困難であり経済的でもない。敢えてその上限を言うなら１００質量％未満と言うことになる。
【００２４】
この他、磁性粉末は、磁気特性、機械的特性または耐蝕性等を向上または維持できる種々の添加元素を含んでも良い。そのような元素として、Ｃｏ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｎｉ、Ｍｏ、Ｐ、Ｓｉ、Ａｌ等がある。具体的には、次のようであれば良い。
磁性粉末が、ＴｉとＶとＣｒとＭｎとＣｏとＮｉとＭｏとからなる元素群中の一種以上の元素を０．１〜５質量％、望ましくは１〜３質量％含み、残部がＦｅと不可避不純物とからなると好適である。これらの各添加元素は、焼結軟磁性体の磁気特性、機械的特性、耐蝕性を改善する効果を有する。各元素の含有量が０．１質量％未満ではそれらの効果がなく、含有量が５質量％を超えると磁性粉末が硬質化して成形密度および焼結密度の低下を招き、結局磁気特性が低下することになる。添加元素が上記範囲にある場合、前記焼結体密度ｄ≧７．４ｇ／ｃｍ3 、７．５ｇ／ｃｍ3さらには７．６ｇ／ｃｍ3ともなる。また、このとき前記Ｂ１ｋ≧１．３Ｔともなる。
【００２５】
また、磁性粉末が、ＰとＳｉとＡｌとからなる元素群中の一種以上の元素を０．１〜５質量％、望ましくは０．３〜３質量％含み、残部がＦｅと不可避不純物とからなっても良い。各元素の含有量が０．１質量％未満では磁気特性の向上効果がなく、含有量が５質量％を超えるとその効果の低下を招く。
ここで、ＳｉやＡｌは保磁力の低減に効果のある元素である。しかし、ＳｉやＡｌが多くなり過ぎると、磁性粉末が硬質化し、成形密度の低下、焼結体密度の低下を招き、結局は磁気特性を低下させることとなる。そこで、ＳｉやＡｌの上限は、５質量％以下が好適である。これに対しＰは、焼結体中に液相を生じさせて緻密化を促進させる効果があるが、やはり添加量が多いと粉末が硬質化するため、その上限は５質量％以下が好ましい。
Ｃｏは焼結軟磁性体の飽和磁化を高める元素である。特に、Ｃｏを２０〜４０質量％含むものは、Ｆｅ系合金中で最大の飽和磁化を有することがよく知られている（飽和磁化：約２．４Ｔ）。もっとも、Ｃｏ量が増えると、やはり磁性粉末が硬質化して成形密度や焼結体密度の低下を招く。このような観点から、磁性粉末は、上記のＣｏ量を超えて、５〜３０質量％より望ましくは１０〜３０質量％のＣｏと、残部Ｆｅと不可避不純物とからなると好ましい。
このときさらに、前述の場合と同様に、ＣｏとＴｉとＶとＣｒとＭｎとＮｉとＭｏとＰとＳｉとＡｌとからなる元素群中の一種以上の元素を０．１〜５質量％含有しても良い。
なお、このように磁性粉末中のＣｏ量が増えると、上記した各磁束密度Ｂ１ｋ、Ｂ２ｋ、Ｂ１０ｋ等や飽和磁化Ｍｓは、前述の範囲に加えてさらに大きくなり得る。例えば、Ｂ１０ｋ≧１．９Ｔ、２．０Ｔさらには２．１Ｔともなり、飽和磁化Ｍｓ≧２．２Ｔさらには２．３Ｔともなる。また、純Ｆｅの密度が７．８６ｇ／ｃｍ3であるのに対して、純Ｃｏの密度が８．８ｇ／ｃｍ3であるから、その焼結体密度もＣｏ量に応じて大きくなり、例えば、焼結体密度ｄ≧７．７ｇ／ｃｍ3 、７．８ｇ／ｃｍ3さらには７．９ｇ／ｃｍ3ともなる。
なお、本明細書中でいう焼結体密度ｄや後述する焼結前の成形体密度ｄ0の上限は組成により異なり、一概に特定することはできない。敢えていうなら、磁性粉末の成分組成から求まる真密度が上限となる。例えば、磁性粉末が純鉄粉の場合なら７．８６ｇ／ｃｍ3が上限となる。
また、本明細書中で「ｘ〜ｙ」というときは特に断らない限り、その範囲に下限ｘおよび上限ｙが含まれる。
【００２６】
（焼結軟磁性体の製造方法）
（１）塗布工程
塗布工程は、成形用金型の内面に高級脂肪酸系潤滑剤を塗布する工程である。これにより、所定条件下での加圧成形の際に、成形用金型の内面と焼結軟磁性体となる粉末成形体との間に金属石鹸被膜が形成されて潤滑性が確保される。そして、磁性粉末を高圧成形しても型抜きが容易となり、成形用金型の内面にかじり等を生じることが抑制、防止される。
【００２７】
▲１▼高級脂肪酸系潤滑剤は、高級脂肪酸の他、高級脂肪酸の金属塩であると好適である。高級脂肪酸の金属塩には、リチウム塩、カルシウム塩又は亜鉛塩等があり、特に、ステアリン酸リチウム、ステアリン酸カルシウム、ステアリン酸亜鉛が好ましい。この他に、ステアリン酸バリウム、パルミチン酸リチウム、オレイン酸リチウム、パルミチン酸カルシウム、オレイン酸カルシウム等を用いることもできる。
【００２８】
▲２▼塗布工程は、加熱された成形用金型内に水に分散した高級脂肪酸系潤滑剤を噴霧する工程であると好適である。
高級脂肪酸系潤滑剤が水に分散していると、成形用金型の内面へ高級脂肪酸系潤滑剤を均一に噴霧することが可能となる。さらに、加熱された成形用金型内にそれを噴霧すると、水分が素早く蒸発して、成形用金型の内面へ高級脂肪酸系潤滑剤を均一に付着させることができる。なお、成形用金型の加熱温度は、後述の成形工程の温度を考慮する必要があるが、例えば、１００℃以上に加熱しておくと良い。もっとも、高級脂肪酸系潤滑剤の均一な膜を形成するために、その加熱温度を高級脂肪酸系潤滑剤の融点未満とすることが好ましい。例えば、高級脂肪酸系潤滑剤としてステアリン酸リチウムを用いた場合、その加熱温度を２２０℃未満とすると良い。
【００２９】
なお、高級脂肪酸系潤滑剤を水に分散させる際、その水溶液全体の重量を１００質量％としたときに、高級脂肪酸系潤滑剤が０．１〜５質量％、さらには、０．５〜２質量％の割合で含まれるようにすると、均一な潤滑膜が成形用金型の内面に形成されて好ましい。
【００３０】
また、高級脂肪酸系潤滑剤を水へ分散させる際、界面活性剤をその水に添加しておくと、高級脂肪酸系潤滑剤の均一な分散が図れる。そのような界面活性剤として、例えば、アルキルフェノール系の界面活性剤、ポリオキシエチレンノニルフェニルエーテル（ＥＯ）６、ポリオキシエチレンノニルフェニルエーテル（ＥＯ）１０、アニオン性非イオン型界面活性剤、ホウ酸エステルエマルボンＴ−８０等を用いることができる。これらを２種以上組合わせて使用しても良い。例えば、高級脂肪酸系潤滑剤としてステアリン酸リチウムを用いた場合、ポリオキシエチレンノニルフェニルエーテル（ＥＯ）６、ポリオキシエチレンノニルフェニルエーテル（ＥＯ）１０及びホウ酸エステルエマルボンＴ−８０の３種類の界面活性剤を同時に用いると好ましい。それらの１種のみを添加する場合に較べ、複合添加すると、ステアリン酸リチウムの水への分散性が一層活性化されるからである。
【００３１】
また、噴霧に適した粘度の高級脂肪酸系潤滑剤の水溶液を得るために、その水溶液全体を１００体積％とした場合、界面活性剤の割合を１．５〜１５体積％とすると好ましい。
この他、少量の消泡剤（例えば、シリコン系の消泡剤等）を添加しても良い。水溶液の泡立ちが激しいと、それを噴霧したときに、成形用金型の内面に、均一な高級脂肪酸系潤滑剤の被膜が形成されにくいからである。消泡剤の添加割合は、その水溶液の全体積を１００体積％としたときに、０．１〜１体積％程度であればよい。
【００３２】
▲３▼水に分散した高級脂肪酸系潤滑剤の粒子は、最大粒径が３０μｍ未満であると好適である。
最大粒径が３０μｍ以上となると、水に分散した高級脂肪酸系潤滑剤の粒子が沈殿し易く、成形用金型の内面に高級脂肪酸系潤滑剤を均一に塗布することが困難となるからである。
【００３３】
▲４▼高級脂肪酸系潤滑剤の分散した水溶液の塗布には、例えば、塗装用のスプレーガンや静電ガン等を用いて行うことができる。
なお、本発明者が高級脂肪酸系潤滑剤の塗布量と粉末成形体の抜出圧力との関係を実験により調べた結果、膜厚が０．５〜１．５μｍ程度となるように成形用金型の内面に付着させると好ましいことが解った。
【００３４】
（２）充填工程
充填工程は、高級脂肪酸系潤滑剤の塗布された成形用金型内に磁性粉末を充填する工程である。この充填工程が、加熱された磁性粉末を加熱された成形用金型内に充填する工程であると好適である。磁性粉末と成形用金型との両方が加熱されていると、後続の成形工程において、磁性粉末と高級脂肪酸系潤滑剤とが安定して反応し、両者の間に均一な潤滑皮膜が形成され易いと考えられる。そこで、例えば、両者を１００℃以上に加熱しておくと好ましい。
【００３５】
（３）成形工程
成形工程は、成形用金型に充填された磁性粉末を温間で加圧成形する工程である。
▲１▼詳細は明らかではないが、この工程により、成形用金型の内面に塗布された高級脂肪酸系潤滑剤と、少なくとも成形用金型の内面に接する磁性粉末とがいわゆるメカノケミカル反応を生じ、この反応によって磁性粉末と高級脂肪酸系潤滑剤とが化学的に結合して、金属石鹸の被膜が磁性粉末の粉末成形体の表面に形成されると考えられる。
【００３６】
磁性粉末に強固に結合したその金属石鹸の被膜は、金型の内面表面に付着していた高級脂肪酸系潤滑剤よりも優れた潤滑性能を発揮し、成形用金型の内面と粉末成形体の外面との間の摩擦力を著しく減少させる。この結果、従来困難と考えられていた高圧での加圧成形が可能となり、高密度の焼結軟磁性体、または比抵抗や透磁率等の磁気特性に優れる焼結軟磁性体が得られたと考えられる。
【００３７】
▲２▼成形工程における成形温度は、磁性粉末、高級脂肪酸系潤滑剤、さらには成形圧力等を考慮して決定されるものである。
従って、成形工程における「温間」とは、各状況に応じた適切な加熱条件の下で成形工程を行うことを意味する。例えば、成形温度を１００〜２２０℃とすると好適である。１００℃以上とすることで、磁性粉末と高級脂肪酸系潤滑剤との反応を促進できる。また、２２０℃以下とすることで、高級脂肪酸系潤滑剤が溶けて流出したり、高級脂肪酸系潤滑剤が変質したりすることを防止できる。さらに、成形温度を１２０〜１８０℃とするとより好適である。
【００３８】
▲３▼成形工程における成形圧力も、所望する焼結軟磁性体の特性、磁性粉末、高級脂肪酸系潤滑剤の種類、成形用金型の材質や内面性状等に応じて、適宜決定される。もっとも、成形圧力が高い程、粉末成形体の密度（成形体密度）や焼結軟磁性材の密度（焼結体密度）は大きくなる。そして、高圧で成形する場合、磁性粉末等と高級脂肪酸系潤滑剤とが化学的に結合して金属石鹸潤滑膜を生成する圧力であることが好ましい。こうすることで、従来の成形圧力を超越した成形圧力下で成形が可能となる。この観点から、例えば、成形圧力を７００ＭＰａ以上、７８４ＭＰａ以上、８００ＭＰａ以上、９８０ＭＰａ以上、１０００ＭＰａ以上、さらには１１７６ＭＰａ以上とすることができる。特に、前述した金属石鹸潤滑膜を安定して形成し、かつ、成形体密度や焼結体密度を高めるためには、成形圧力を７８４ＭＰａ以上とすると好適である。なお、本発明の製造方法によれば、成形圧力を１６００ＭＰａ以上、さらには１９６０ＭＰａとしても、成形用金型の内面にかじり等を発生することはない。従って、この成形圧力の上限も特に限定されるものではなくその上限を特定することも困難である。敢えていうなら、その上限を２０００ＭＰａ程度とすることが現実的な範囲であり、成形用金型の寿命や生産性を考慮して、成形圧力を１５００ＭＰａ以下とするとより好ましい。
例えば、純鉄粉を用いてこのような高圧成形を行った場合、焼結前の成形体密度ｄ0≧７．４ｇ／ｃｍ3、７．５ｇ／ｃｍ3、７．６ｇ／ｃｍ3、さらには７．７ｇ／ｃｍ3ともなる。
もっとも、Ｆｅ以外に１種以上の合金元素を含有する磁性粉末は、概して、硬度が高いために、従来の粉末成形法では、高密度の粉末成形体を得ることが難しい。本発明に係る成形方法を用いると、その場合でも、焼結前の成形体密度ｄ0≧７．２ｇ／ｃｍ3、７．３ｇ／ｃｍ3、７．４ｇ／ｃｍ3となる粉末成形体が得られる。
【００３９】
▲４▼なお、この成形温度と成形圧力とに関して、本発明者は次のことを実験により確認している。
成形用金型の内面に高級脂肪酸系潤滑剤（ステアリン酸リチウム）を塗布し、成形温度を１５０℃として磁性粉末を加圧成形する際、成形圧力を６８６ＭＰａとする方が成形圧力を５８８ＭＰａとするよりも、却って、粉末成形体の抜出圧力が低かった。これは、成形圧力が高いほど、高い抜出圧力を必要とする従来の考えを覆す発見であった。さらに、６８６ＭＰａ以上の高圧で加圧成形したときに、粉末成形体の表面にはステアリン酸鉄が付着していた。
【００４０】
（４）焼結工程
粉末成形体を焼結させることにより、より高密度の軟磁性体が得られる。また、強度も向上し、その用途がより拡大する。
焼結工程は、酸化による磁気特性の低下を防止するために、真空、還元性ガス雰囲気または不活性ガス雰囲気中でなされることが好ましい。焼結温度と焼結時間は、成分元素が十分に拡散し、かつ、経済的な範囲内で行われることが好ましい。例えば、焼結温度は６００℃以上、より望ましくは８５０〜１３００℃、焼結時間は０．１〜３時間とすると良い。
【００４１】
前述したように、その焼結温度の相違により、得られる焼結体の組織が異なることを本発明者は見出した。つまり、γ変態点以上の温度で焼結させた場合、加圧方向に優先的に結晶粒が成長した組織が得られる。例えば、純鉄系の場合、焼結温度を９５０〜１３００℃、より好ましくは１１００〜１３００℃とした場合である。合金系の場合は、その組成に応じて適切な焼結温度を選択すると良い。
【００４２】
一方、γ変態点未満の温度で焼結させると、等方的な結晶粒からなる組織が得られる。例えば、純鉄系の場合なら、焼結温度を８００〜９１０℃、より好ましくは８５０〜９００℃とした場合である。なお、γ変態点は、主成分であるＦｅの結晶構造がα相（体心立方格子）とγ相（面心立方格子）との間で同素変態する温度である。純鉄の場合ならＡ3変態点である９１１℃となるが、磁性粉末中の含有元素によりその値は多少変動する。
なお、この焼結工程は、金属原子の拡散により生じる場合のみならず、いわゆる液相焼結の場合をも含む。
【００４３】
（焼結軟磁性体の用途）
本発明の焼結軟磁性体は、各種の電磁機器、例えば、モータ、アクチュエータ、トランス、誘導加熱器（ＩＨ）、スピーカ等に利用できる。また、γ変態点以上で焼結させた焼結軟磁性体は、異方性組織をもつため、磁気特性に指向性が要求される場合に好適である。
【００４４】
【実施例】
次に、焼結軟磁性体の実施例を挙げて、本発明をより具体的に説明する。
（試験片の製作）
（１）試験片Ｎｏ．１〜９
表１に示す５種の試験片Ｎｏ．１〜９を、本発明の製造方法（以下、適宜、「金型潤滑温間高圧成形法」という。）を用いて製作した。
▲１▼先ず、リング状（外径φ３９、内径φ３０ｍｍ×厚さ５ｍｍ）のキャビティをもつ成形用金型を用意した。この成形用金型は、ダイスが超硬合金製であり、パンチがダイス鋼製である。成形用金型の内面には、ＴｉＮコート処理が施されており、表面粗さは０．４Ｚに仕上げられている。また、成形用金型は、バンドヒータにより１５０℃に加熱保持した。
【００４５】
充填工程に先立ち、その加熱した成形用金型の内壁面に高級脂肪酸系潤滑剤を塗布した（塗布工程）。具体的には、スプレーガンを用いて、水に分散させたステアリン酸リチウムを１ｃｍ3／秒程度の割合で成形用金型の内壁面に均一に塗布した。ここで用いたステアリン酸リチウムは、融点が約２２５℃であり、平均粒径が２０μｍのものである。また、ステアリン酸リチウムを、界面活性剤と消泡剤とを添加した水溶液に分散させた。界面活性剤として、ポリオキシエチレンノニルフェニルエーテル（ＥＯ）６、（ＥＯ）１０及びホウ酸エステルエマルボンＴ−８０を用いた。それぞれの添加割合は、水溶液の全体積を１００体積％としたときに、１体積％とした。分散させたステアリン酸リチウムの粉末量は、前記水溶液１００ｃｍ3に対して２５ｇである。こうして得た原液を粉砕処理（テフロンコート鋼球：１００時間）し、ボールミル式粉砕装置にて微細化処理した後、２０倍に希釈して最終濃度１％の水溶液とした。
【００４６】
▲２▼原料粉末（Ｆｅ系磁性粉末）として、市販のＦｅ粉末（ヘガネス社製ＡＢＣ１００．３０：純度９９．８％Ｆｅ）を用意した。前述の加熱した成形用金型内に、１５０℃に加熱しておいたそのＦｅ粉末を充填した（充填工程）。
【００４７】
▲３▼次に、成形用金型を１５０℃に保持したまま、７８４〜１１７６ＭＰａ、さらには１５６８〜１９６０ＭＰａの範囲の成形圧力の下で、温間加圧成形を行い、各種の粉末成形体を得た（成形工程）。各成形圧力は、表１に併せて示した。
【００４８】
▲４▼この粉末成形体を窒素ガス雰囲気の下で０．５時間加熱して焼結させ、表１に示すリング状の試験片Ｎｏ．１〜９の焼結軟磁性体を得た。焼結温度としては、γ変態点未満の９００℃とγ変態点以上の１２５０℃とを適宜選択した（表１参照）。
【００４９】
（２）試験片Ｎｏ．１０〜１２
原料粉末として、市販のＦｅ粉末（ヘガネス社製ＰＡＳＣ０６０Ｐ：Ｆｅ−０．６Ｐ（質量％）：Ｆｅ−Ｐ系磁性粉末）を用意して、試験片Ｎｏ．１〜９と同様にして試験片Ｎｏ．１０〜１２を製作した。各条件の詳細は表２に示した通りであるが、焼結温度は１２５０℃のみとし、焼結時間は０．５時間とした。
【００５０】
（３）試験片Ｎｏ．１３〜１８
試験片Ｎｏ．１３〜１６および１８に係る原料粉末として、表２に示す各組成をもつ水アトマイス法で製作した合金粉末（Ｆｅ−Ｍ１系磁性粉末、Ｆｅ−Ｃｏ系磁性粉末）を用意した。また、試験片Ｎｏ．１７に係る原料粉末として、表２に示す組成（Ｆｅ−１Ａｌ）をもつガスアトマイス法で製作した合金粉末（Ｆｅ−Ｍ１系磁性粉末）を用意した。
そして、表２に示す条件下で、試験片Ｎｏ．１〜９と同様にして試験片Ｎｏ．１３〜１８を製作した。各条件の詳細は表２に示した通りであるが、焼結工程は、いずれも０．０１Ｐａ（１０-4ｔｏｒｒ）の真空雰囲気中で行った。また、試験片Ｎｏ．１０〜１６については焼結温度を１２５０℃、焼結時間を０．５時間とし、試験片Ｎｏ．１７については焼結温度を１２００℃、焼結時間を４時間とし、試験片Ｎｏ．１８については焼結温度を１０００℃、焼結時間を１時間として、それぞれ焼結工程を行った。
なお、試験片Ｎｏ．１〜１８のいずれについても、かじり等の発生はなく、焼結軟磁性体の表面性状も良好であった。
また、表１および表２に示したすべての試験片は、焼結後に、真空中で８５０℃ｘ３ｈの磁気焼鈍を行ったものである。
【００５１】
（４）試験片Ｎｏ．Ｃ１、Ｃ２
試験片Ｎｏ．１〜９と同様の原料粉末および装置を用いて、試験片Ｎｏ．Ｃ１、Ｃ２を製作した。両試験片とも、内部潤滑剤としてケノルーブ（ヘガネス社製）を０．６質量％添加した。
試験片Ｎｏ．Ｃ１は、成形温度を室温、成形圧力を６００ＭＰａとして成形した粉末成形体を、表２に示す条件の下で焼結させたものである。
【００５２】
試験片Ｎｏ．Ｃ２は、試験片Ｎｏ．Ｃ１の粉末成形体を窒素雰囲気中、７５０℃で予備焼結して、さらに成形・焼結させたもの（いわゆる２Ｐ２Ｓの焼結軟磁性体）である。２回目の成形は、６００ＭＰａの条件下で行い、２回目の焼結は、窒素雰囲気中、１２５０℃×０．５時間の条件下で行った。
【００５３】
（磁気特性等の測定）
各試験片に関する磁気特性、密度の測定結果を表１および表２に併せて示す。磁気特性の内、静磁場特性は直流自記磁束計（メーカ：東英工業、型番：ＭＯＤＥＬ−ＴＲＦ）により測定し、交流磁場特性は交流Ｂ−Ｈカーブトレーサ（メーカ：理研電子、型番：ＡＣＢＨ−１００Ｋ）により測定した。各表中の交流磁場特性は、各試験片を５０Ｈｚ、１．０Ｔの磁場中に置いたときの鉄損Ｐｃを測定したものである。静磁場中の磁束密度Ｂ０．５ｋ、Ｂ１ｋ、Ｂ２ｋおよびＢ１０ｋは、磁界の強さを順に０．５、１、２および１０ｋＡ／ｍと変更したときの磁束密度である。また、飽和磁化Ｍｓは、１．６ＭＡ／ｍ中での磁束密度を測定したものである。また、最大透磁率および保磁力をも表１および表２に併せて示した。密度はアルキメデス法により測定した。表中、「未」は、未測定であることを示す。
【００５４】
（評価）
（１）表１および表２から解るように、本発明に係る試験片Ｎｏ．１〜１２および１４〜１８は、いずれも、粉末成形体および焼結体の密度が７．５ｇ／ｃｍ3を超える高密度であり、磁気特性にも優れることが解る。特に、２Ｐ２Ｓ品である試験片Ｎｏ．Ｃ２と比較しても、それ以上の密度と磁気特性とを有していることが解る。また、試験片Ｎｏ．１〜１８は、試験片Ｎｏ．Ｃ１やＣ２に較べて鉄損が全体的に低くなっている。
試験片Ｎｏ．６〜９のように、成形圧力が１２００ＭＰａを超えるようになると、焼結前の成形体密度も焼結後の焼結体密度も７．８ｇ／ｃｍ3を超えるようになり、真密度とほぼ等しくなっている。
試験片Ｎｏ．１０〜１７のように合金成分を含有するものは、成形圧力が高い場合でも、試験片Ｎｏ．１〜１０のものに比較して各密度がやや低くなっている。これは、原料粉末が硬質で成形性が低いということもあるが、合金成分の存在により真密度自体も低いことも一因である。従って、成形体密度や焼結体密度の真密度に対する比（密度比）を考えれば、試験片Ｎｏ．１０〜１７の場合でも、９５％以上さらには９８％以上もの高密度成形体、高密度焼結体が得られることが分かる。もっとも、試験片Ｎｏ．１５、１６のようにＳｉ含有量が多い磁性粉末は硬度が大きく、その分成形性が劣り、成形体密度および焼結体密度の両方とも低下している。
試験片Ｎｏ．１８は、Ｆｅと同様に磁気特性に優れ、Ｆｅよりも密度が大きいＣｏを含有するため、磁気特性（例えば、Ｂ１０ｋ）に優れ、成形体密度および焼結体密度の両方とも大きい。
【００５５】
（２）次に、成形工程における成形圧力と粉末成形体の密度（成形体密度）または焼結体密度との関係、および、その成形圧力と焼結工程前後の寸法変化との関係を調べた。
▲１▼Ｆｅ−０．６Ｐ粉末を使用した場合
前述の試験片Ｎｏ．１０〜１２で使用したＦｅ−０．６Ｐ粉末を用いて、φ１７×１７ｍｍの試験片を製作した。製造工程は、基本的に試験片Ｎｏ．１０〜１２の場合と同様である。但し、成形圧力を種々変更して、各試験片を製作した。また、焼結温度は、１２５０℃とした。このときの成形圧力と各密度との関係を図１に示す。また、成形圧力と焼結工程前後の寸法変化との関係を図２に示す。なお、図２中の「圧縮方向」とは、成形工程時の加圧方向であり、言換えるなら、試験片の軸方向である（以下、同様）。
【００５６】
Ｆｅ−０．６Ｐ粉末の場合でも、本発明の製造方法を用いると、従来のものよりもかなり高密度の粉末成形体が得られる。もっとも、その粉末には硬いＦｅＰ粒子が混合されているため、成形工程のみによる高密度化には限界がある。そこで、１２５０℃で焼結すると、ＦｅＰが液相化して大幅に高密度化した焼結体が得られることが、図１から解る。
【００５７】
但し、図２から解るように、ＦｅＰの液相化により、焼結工程後の寸法収縮率は比較的大きくなる。もっとも、本発明の製造方法を用いると、成形圧力を高めることができるため、その寸法収縮率を十分小さくできることも図２から解る。例えば、成形圧力を１０００ＭＰａ以上とすることにより、焼結前後の寸法変化量を０．５％以内とすることができる。
【００５８】
▲２▼純Ｆｅ粉（Ｆｅ：９９．８質量％）を使用した場合
前述の試験片Ｎｏ．１〜９で使用したＦｅ粉末を用いて、φ１７×１７ｍｍの試験片を製作した。製造工程は、基本的に試験片Ｎｏ．１〜９の場合と同様である。但し、成形圧力を種々変更すると共に、２種の焼結温度で焼結工程を行い、各試験片を製作した。
【００５９】
（ａ）焼結温度を１２５０℃（γ変態点以上）としたとき
このときの成形圧力と各密度との関係を図３に示す。また、成形圧力と焼結工程前後の寸法変化との関係を図４に示す。
Ｆｅ粉を用いた場合、本発明に係る高圧成形により、成形体密度は既に高密度である。従って、焼結体密度は、成形体密度に対して大きな変化はない。但し、成形圧力が７８４ＭＰａ以上の場合、焼結体密度が成形体密度よりも僅かに低下することが解った。
【００６０】
そして、図４から解るように、成形圧力を７８４ＭＰａ以上とした場合、寸法変化に大きな挙動変化が現れることも解った。具体的には、径方向寸法が収縮し、圧縮方向寸法が大きく膨張することが新たに解った。この要因については、後述する。
【００６１】
（ｂ）焼結温度を９００℃（γ変態点未満）としたとき
このときの成形圧力と各密度との関係を図５に示す。また、成形圧力と焼結工程前後の寸法変化との関係を図６に示す。
図５から、焼結温度をγ変態点未満としたとき、焼結体密度が成形体密度より僅かに大きくなることが解った。また、図６から、このときの寸法変化は、径方向にも圧縮方向にも０〜−０．１％の範囲内であり、殆ど生じていないことが解った。この要因についても、後述する。
【００６２】
（３）次に、上記Ｆｅ粉末から製作したφ１７×１７の試料について、金属組織を光学顕微鏡で観測した顕微鏡写真を図７〜１０に示す。各試料は、成形圧力と焼結温度とを種々変更して組合わせたものであり、各条件は図中に示した。なお、各図中の「平行面」とは、試料を軸方向に切断したときの切断面を示し、「垂直面」とは、試料を軸方向に垂直な面（軸を法線とする面）で切断したときの切断面を示す。
【００６３】
▲１▼成形圧力の影響
図７と図８とを比較すると解るように、同じ焼結温度（１２５０℃）でも、成形工程時の成形圧力が異なると、出現する組織も異なることが解る。つまり、成形圧力が６８６ＭＰａのときは、一般的な結晶粒組織であるが（図７）、成形圧力が７８４ＭＰａになると、圧縮方向（軸方向）に結晶粒が優先的に成長した、縦長（アスペクト比≧２）の結晶粒となっていることが解る（図８（ａ））。もっとも、前記垂直面では、等方的に結晶粒が成長していることも解る（図８（ｂ））。磁気特性は、この結晶粒の配列の影響を強く受ける。つまり、このような焼結軟磁性体は、軸方向の磁束密度等がより大きくなるといった、異方的な磁気特性を発揮し得る。
【００６４】
▲２▼焼結温度の影響
図９と図１０とを比較すると解るように、同じ成形圧力（１１７６ＭＰａ）でも、焼結温度が異なると、出現する組織も異なることが解る。つまり、７８４ＭＰａ以上の成形圧力であっても、焼結温度を９００℃（γ変態点未満）とすることにより、出現する結晶粒組織は径方向にも圧縮方向にも等方的であることが図９から解る。
一方、焼結温度を１２５０℃（γ変態点以上）とすると、図８に示した場合と同様に、圧縮方向（軸方向）に結晶粒が優先的に成長して、縦長（アスペクト比≧２）の結晶粒となっていることが解る（図１０（ａ））。
さらに、この図１０に示した焼結軟磁性体（表１の試験片Ｎｏ．５にほぼ同じ）から、その磁気焼鈍前に、軸方向（圧縮方向）に磁界を印加するためのリング状試験片と径方向（圧縮方向に垂直方向）に磁界を印加するためのリング状試験片とを切出した。それぞれの試験片を用いて磁気測定した結果を表３に示す。
この結果から、軸方向に磁界を印加した場合の方が、最大透磁率（μｍ）および低磁界側での各磁束密度（Ｂ０．２ｋ、Ｂ０．３ｋ、Ｂ０．４ｋ、Ｂ０．５ｋ）が大きい。よって、上記焼結軟磁性体は磁気異方性を発現していることが明らかであり、その軸方向でより優れた磁気特性が得られることが解る。
【００６５】
▲３▼寸法変化等と金属組織との関係
図３と図５に示した成形体密度と焼結体密度との挙動や図４と図６に示した寸法変化の挙動に、この結晶粒の形状の相違が影響していると考えられる。特に、７８４ＭＰａ以上で寸法変化の挙動が大きく変化するのは、図８（ａ）や図１０（ａ）に示した、アスペクト比の大きな結晶粒組織が出現するためであると考えられる。
【００６６】
【表１】
【表２】
【表３】
【発明の効果】
本発明の焼結軟磁性体は、比較的低コストでありながら、優れた磁気特性を発揮する。
また、本発明の製造方法によれば、そのような焼結軟磁性体を効率的に製造することができる。
【図面の簡単な説明】
【図１】Ｆｅ−０．６Ｐ粉末を用いた焼結軟磁性体の成形圧力と各密度との関係を示すグラフである。
【図２】Ｆｅ−０．６Ｐ粉末を用いた焼結軟磁性体の成形圧力と各寸法変化との関係を示すグラフである。
【図３】Ｆｅ粉末を用いてγ変態点以上で焼結させた焼結軟磁性体の成形圧力と各密度との関係を示すグラフである。
【図４】Ｆｅ粉末を用いてγ変態点以上で焼結させた焼結軟磁性体の成形圧力と各寸法変化との関係を示すグラフである。
【図５】Ｆｅ粉末を用いてγ変態点未満で焼結させた焼結軟磁性体の成形圧力と各密度との関係を示すグラフである。
【図６】Ｆｅ粉末を用いてγ変態点未満で焼結させた焼結軟磁性体の成形圧力と各寸法変化との関係を示すグラフである。
【図７】Ｆｅ粉末を用いて、成形圧力６８６ＭＰａ、焼結温度１２５０℃として製作した焼結軟磁性体の結晶粒形状を示す金属組織写真である。
【図８】Ｆｅ粉末を用いて、成形圧力７８４ＭＰａ、焼結温度１２５０℃として製作した焼結軟磁性体の結晶粒形状を示す金属組織写真である。
【図９】Ｆｅ粉末を用いて、成形圧力１１７６ＭＰａ、焼結温度９００℃として製作した焼結軟磁性体の結晶粒形状を示す金属組織写真である。
【図１０】Ｆｅ粉末を用いて、成形圧力１１７６ＭＰａ、焼結温度１２５０℃として製作した焼結軟磁性体の結晶粒形状を示す金属組織写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sintered soft magnetic material having excellent magnetic properties and a method for producing the same.
[0002]
[Prior art]
There are many products using electromagnetism around us, such as transformers, motors, generators, speakers, induction heaters, and various actuators. For these, hard magnetic materials (permanent magnets) and soft magnetic materials are used. Among these, soft magnetic materials (soft magnets) are widely used as magnetic cores (magnetic cores) for various electromagnetic devices. Soft magnetic materials are mainly composed of iron-based materials that are excellent in magnetic properties, and are made by melting, pressure-molded magnetic powders, and sintered products. There is.
[0003]
Here, the magnetic properties such as the magnetic permeability of the soft magnetic material are greatly influenced by the density of a magnetic material such as iron. With the same composition, the higher the density, the better the magnetic properties. From this point of view, the melted soft magnetic material is preferable because of its high density (approximately 100%) and excellent magnetic properties. However, since it is difficult to ensure dimensional accuracy in melting, it is necessary to perform machining or the like into a desired shape when used for various products. Moreover, the soft magnetic material, which is soft iron, has poor machinability and is not easy to process. Therefore, the cost is naturally increased.
[0004]
On the other hand, since a soft magnetic body made of a powder molded body such as a dust core has good dimensional accuracy and surface roughness, special processing is not necessarily required after molding. That is, since the shape imparting property is excellent, it is easy to reduce the cost of the soft magnetic material. However, in the conventional molding technique, since molding at a high pressure (for example, more than 700 MPa) was actually difficult, the density of the soft magnetic material was naturally low. In the past, an internal lubricant was required to prevent galling between the molding die and the powder compact. Since this internal lubricant remains inside the soft magnetic body even after molding, it has been a factor that further reduces the density of the soft magnetic body. Therefore, the soft magnetic body made of a conventional powder compact has a low density, and sufficient magnetic properties have not been obtained.
[0005]
In addition, since the sintered soft magnetic material is greatly affected by the powder compact in terms of density, the density of the soft magnetic material obtained by sintering the low-density powder compact is also low. Therefore, in order to improve the density of the sintered soft magnetic material, two-time molding twice-sintering (2P2S) in which the molding process and the sintering process are repeated twice has been considered. For example, in the first time, forming at a relatively low pressure and pre-sintering at a low temperature in a relatively short time, and in the second time, re-compression and sizing for densification and shape formation (net shaping) and the original firing It is the one that does the conclusion. According to this method, even if the internal lubricant is used in the first molding step, it can be removed in the subsequent sintering step (preliminary sintering), and the second molding and sintering can be performed. Further, it is possible to further increase the density of the soft magnetic material. However, the 2P2S method in which the molding process and the sintering process are repeated twice is rarely performed in practice because the production cost becomes very high.
[0006]
In addition, when the liquid phase sintering method is used, a high-density sintered soft magnetic material can be obtained even if the density of the powder compact is low. However, in the conventional method, the shape shrinkage that occurs during sintering is very large, and it is actually difficult to predict the shrinkage allowance in advance. Therefore, if a soft magnetic material is manufactured by this method, after all, machining is separately required, and the cost of the soft magnetic material cannot be reduced.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances. That is, an object is to provide a high-density sintered soft magnetic material having a relatively low cost and excellent magnetic properties. It is another object of the present invention to provide a sintered soft magnetic body having high density and anisotropy, and a sintered soft magnetic body excellent in shape stability.
Furthermore, it aims at providing the manufacturing method of the sintered soft magnetic body which can obtain them efficiently.
[0008]
[Means for Solving the Problems]
Therefore, as a result of extensive research and trial and error, the present inventor succeeded in forming a magnetic powder at a high pressure unprecedented and completed the present invention.
(Sintered soft magnetic material)
(1) That is, the sintered soft magnetic material of the present invention has a coating step of applying a higher fatty acid-based lubricant on the inner surface of the molding die and Fe as a main component in the molding die after the coating step. Through a filling step of filling the magnetic powder, a forming step of warm-pressing the magnetic powder after the filling step, and a sintering step of heating and sintering the powder compact obtained by the forming step Manufactured,
Sintered body density d ≧ 7.4 g / cm Three ,
Saturation magnetization Ms ≧ 1.9T in a magnetic field of 1.6 MA / m,
Magnetic flux density B1k ≧ 1.4T in a magnetic field of 1 kA / m,
It is characterized by being.
[0009]
Using a molding die with a higher fatty acid-based lubricant applied to the inner surface, when the magnetic powder filled therein is hot-pressed, adhesion between the inner wall of the molding die and the powder compact It has been found that the occurrence of galling is suppressed and prevented, and unprecedented high pressure molding becomes possible.
And since a powder compact with a higher density than in the past could be obtained in the molding process, the sintered body density d ≧ 7.4 g / cm in the subsequent sintering process. Three A high-density sintered body could be obtained. And because of the high density, a sintered soft magnetic material excellent in magnetic properties of saturation magnetization Ms ≧ 1.9T and magnetic flux density B1k ≧ 1.4T was obtained.
Such a sintered soft magnetic material can be obtained, for example, when the magnetic powder is an Fe-based magnetic powder composed of 99.7% by mass or more of Fe and inevitable impurities, but is not limited thereto. In the present specification, the term “magnetic powder” simply means that powders containing various elements other than Fe are also included.
In addition, a sintered soft magnetic material having excellent magnetic properties can be obtained by so-called one-time molding once sintering. Moreover, since there is no occurrence of galling or the like, the punching pressure is low and the mold life is long. Therefore, the sintered soft magnetic material has a very low overall manufacturing cost.
By the way, the reason why such high-pressure molding has become possible by the above-mentioned steps is not necessarily clear, but the present situation is considered as follows. That is, a metal soap lubricating film having excellent lubricity is formed between the inner wall of the molding die and the magnetic powder under a predetermined range of temperature and pressure. In this metal soap lubricating film, the lubricating layer is not merely interposed between the inner wall of the molding die and the magnetic powder, but is firmly chemically adsorbed on the inner wall of the molding die or the surface of the magnetic powder. . As a result, it is considered that the lubricating film is not interrupted when the powder compact is taken out from the molding die after high-pressure molding, and the occurrence of galling or the like on the inner wall is prevented, and the pressure at that time is also reduced.
[0010]
(2) The sintered body density d, the saturation magnetization Ms, and the magnetic flux density B1k may slightly vary depending on the composition of the magnetic powder, and may exhibit more excellent characteristics depending on the composition of the magnetic powder.
For example, when the magnetic powder is an Fe-P magnetic powder containing P and containing Fe as a main component, the sintered soft magnetic material of the present invention is
Sintered body density d ≧ 7.5 g / cm Three ,
Saturation magnetization Ms ≧ 1.9T in a magnetic field of 1.6 MA / m,
Magnetic flux density B1k ≧ 1.4T in a magnetic field of 1 kA / m,
It also becomes. More specifically, for example, this Fe-P-based magnetic powder is composed of 0.1 to 5% by mass of P, the remaining Fe, and inevitable impurities.
[0011]
For example, when the magnetic powder is an Fe-M1 magnetic powder containing Si and / or Al (M1) and containing Fe as a main component, the sintered soft magnetic material of the present invention is
Sintered body density d ≧ 7.3 g / cm Three ,
Saturation magnetization Ms ≧ 1.8T in a magnetic field of 1.6 MA / m,
Magnetic flux density B1k ≧ 1.3T in a magnetic field of 1 kA / m,
It also becomes. More specifically, for example, this Fe-M1 magnetic powder is composed of 0.1 to 5% by mass of M1, the balance Fe, and inevitable impurities.
[0012]
Further, for example, when the magnetic powder is a Fe-Co based magnetic powder containing Co and containing Fe as a main component, the sintered soft magnetic body of the present invention is
Sintered body density d ≧ 7.8 g / cm Three ,
Saturation magnetization Ms ≧ 2.1T in a magnetic field of 1.6 MA / m,
Magnetic flux density B1k ≧ 1.4T in a magnetic field of 1 kA / m,
Magnetic flux density B1k ≧ 2.0T in a magnetic field of 10 kA / m,
It also becomes. More specifically, for example, this Fe—Co-based magnetic powder is composed of 5 to 50% by mass of Co, the remaining Fe, and inevitable impurities. In this case, it may further contain 0.1 to 5% by mass of one or more elements in the element group consisting of Si, Al, P, Ti, V, Mn, Cr, Ni and Mo.
[0013]
Furthermore, for example, the magnetic powder contains one or more elements (M2) in an element group consisting of Si, Al, P, Ti, V, Mn, Cr, Co, Ni, and Mo and contains Fe as a main component. In the case of -M2 magnetic powder, the sintered soft magnetic material of the present invention is
Sintered body density d ≧ 7.4 g / cm Three ,
Saturation magnetization Ms ≧ 1.9T in a magnetic field of 1.6 MA / m,
Magnetic flux density B1k ≧ 1.4T in a magnetic field of 1 kA / m,
It also becomes. More specifically, for example, this Fe-M2 magnetic powder is composed of 0.1 to 5% by mass of M2, the balance Fe, and inevitable impurities.
[0014]
(3) The present inventor has also found that the sintered soft magnetic material thus obtained can have a unique structure, and has completed the present invention from another angle.
That is, the present invention includes an application step of applying a higher fatty acid-based lubricant to the inner surface of a molding die, a filling step of filling a magnetic powder mainly composed of Fe into the molding die after the application step, A sintered body obtained through a molding step of warm-pressing the magnetic powder after the filling step and a sintering step of heating and sintering the powder molded body obtained by the molding step, It is also a sintered soft magnetic material having a structure composed of crystal grains preferentially grown in the pressing direction during the forming process.
[0015]
Since this sintered soft magnetic material has a structure composed of crystal grains preferentially grown in the pressing direction during the forming process, the magnetic properties can exhibit anisotropy that varies depending on the direction. In the case of a soft magnetic material, a strong magnetic flux density is often required only in a specific direction. Therefore, in such a case, the use of the sintered soft magnetic material of the present invention is advantageous in that leakage magnetic flux and the like can be suppressed.
In other words, the structure of the sintered soft magnetic material is that long granular crystal grains are aligned in the pressing direction during the molding process. And the aspect ratio which is the aspect ratio of this crystal grain will be 2 or more, and also 5 or more, for example. Of course, the crystal grains at that time are long in the pressing direction during the molding process.
In addition, such a structure includes at least the magnetic powder of 99.7% by mass or more of Fe and inevitable impurities, the molding process is a process in which the molding pressure is 784 MPa or more, and the sintering process is a sintering process. The present inventor has confirmed that it can be obtained when it is a step of setting the sintering temperature to the γ transformation point or higher. Details of the molding pressure and sintering temperature at this time will be described later.
[0016]
(4) The present inventor has found that the dimensional change of the sintered soft magnetic material having an isotropic structure is significantly reduced before and after the sintering process, and has completed the present invention from another angle.
That is, the present invention includes an application step of applying a higher fatty acid-based lubricant to the inner surface of a molding die, a filling step of filling a magnetic powder mainly composed of Fe into the molding die after the application step, A sintered body obtained through a molding process in which the magnetic powder after the filling process is warm-pressed and a sintering process in which the powder molded body obtained in the molding process is heated and sintered is, etc. It is also a sintered soft magnetic material characterized by having a structure composed of crystal grains grown in a square direction.
In the sintered body (sintered soft magnetic body) having such an isotropic crystal grain structure, the dimensional change before and after the sintering step is 0.2% or less, and further 0.1% or less. . This indicates that there is almost no dimensional change.
In addition, such a structure includes at least the magnetic powder of 99.7% by mass or more of Fe and inevitable impurities, the molding process is a process in which the molding pressure is 784 MPa or more, and the sintering process is a sintering process. The present inventor has confirmed that it can be obtained in the step of setting the sintering temperature below the γ transformation point. Details of the molding pressure and sintering temperature at this time will be described later.
[0017]
(Method for producing sintered soft magnetic material)
A sintered soft magnetic material having such excellent magnetic properties can be obtained, for example, by using the following production method of the present invention.
That is, the present invention includes an application step of applying a higher fatty acid-based lubricant to the inner surface of a molding die, and a filling step of filling a magnetic powder mainly composed of Fe into the molding die after the application step. A molding step of warm-pressing the magnetic powder under pressure and temperature at which the higher fatty acid-based lubricant is chemically bonded to the magnetic powder to form a metal soap film after the filling step; It can also be grasped as a method for producing a sintered soft magnetic body characterized by comprising a sintering step of heating and sintering a powder compact obtained by the molding step.
And if the sintering temperature in the sintering process is equal to or higher than the γ transformation point, a sintered soft magnetic material having a structure composed of the anisotropic crystal grains described above is obtained, and if the sintering temperature is less than the γ transformation point, A sintered soft magnetic material having a structure composed of isotropic crystal grains can be obtained.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in more detail with reference to embodiments. In addition, the content demonstrated below is applicable to both the sintered soft magnetic body which concerns on this invention, and its manufacturing method suitably.
(Sintered soft magnetic material)
(1) Magnetic flux density
The magnetic permeability is obtained by magnetic permeability μ = (magnetic flux density B) / (magnetic field strength H), but μ is not constant as can be seen from a general BH curve. Therefore, in addition to the magnetic permeability, the magnetic properties of the sintered soft magnetic material according to the present invention were evaluated by the magnetic flux density generated when placed in a magnetic field having a specific strength. In other words, in the present invention, the evaluation was performed with the magnetic flux density B1k that is generated when the sintered soft magnetic material is placed in 1 kA / m, which is a relatively low magnetic field. In addition, the magnetic properties of the sintered soft magnetic material may be evaluated by magnetic flux densities B0.5k, B2k, and B10k in a magnetic field of 0.5 k, 2 kA / m, and 10 kA / m. Depending on the composition of the magnetic powder to be used, according to the sintered soft magnetic material of the present invention, for example, B1k ≧ 1.4T, 1.45T, and 1.5T. Also, B0.5k ≧ 1.3T, 1.35T, 1.4T, B2k ≧ 1.5T, 1.55T, 1.6T, in addition, B10k ≧ 1.7T, 1.75T, 1.8T It also becomes.
[0019]
If the saturation magnetization Ms is small, a large magnetic flux density cannot be obtained. According to the sintered soft magnetic material of the present invention, for example, the saturation magnetization Ms ≧ 1.9T in a magnetic field of 1.6 MA / m, and further 1.95 T, and a stable large magnetic flux density can be obtained even in a high magnetic field. It is done.
The upper limits of the magnetic flux density B and the saturation magnetization Ms are not limited and are difficult to specify. In other words, the theoretically possible magnetic flux density B and saturation magnetization Ms obtained for each composition are set as upper limits.
[0020]
(2) Magnetic powder
The “magnetic powder” referred to in the present specification is composed of powder particles mainly composed of Fe, but the Fe content in the particles is not particularly limited. For example, the Fe content may be 90% by mass or more (less than 100% by mass).
The magnetic powder may be atomized powder or pulverized powder, or may be composed of a coarse powder or a granulated powder thereof. Further, the magnetic powder may be an alloy powder or a mixed powder obtained by uniformly mixing elementary powders. In order to efficiently obtain a high-density sintered soft magnetic material, the particle size is preferably 20 to 300 μm, more preferably 20 to 200 μm.
Thus, since the magnetic powder which has iron as a main component is used as a raw material powder, the obtained sintered soft magnetic body has a high magnetic flux density and a small coercive force and hysteresis loss. In addition, since the magnetic powder contains inexpensive iron as a main component, the magnetic powder is low in price and is preferable for reducing the cost of the sintered soft magnetic material.
[0021]
Further, when a sintered soft magnetic body is manufactured using the above-described manufacturing method of the present invention, the magnetic powder mainly composed of iron reacts with a higher fatty acid-based lubricant to strongly adhere to the surface of the powder molded body. It is considered that an iron salt film of a higher fatty acid having excellent lubricity is formed. The presence of this iron salt coating makes it easy to take out the powder compact from the molding die without causing galling and the like, and a high-density sintered soft magnetic material can be produced efficiently.
[0022]
In addition, higher fatty acid type lubricants such as lithium stearate, calcium stearate, and zinc stearate may be sprayed, applied, or added to the magnetic powder in advance. The blending ratio at this time is preferably 0.1% by mass or less when the total of the higher fatty acid-based lubricant and the magnetic powder is 100% by mass. When the magnetic powder and the higher fatty acid-based lubricant are brought into contact in advance, for example, the fluidity of the magnetic powder is improved and the filling density into the molding die is increased, thereby obtaining a high-density sintered soft magnetic material. easy. However, if the amount of the higher fatty acid-based lubricant is too large, the reaching density of the powder molded body made of magnetic powder is lowered, which is not preferable.
[0023]
By the way, an optimal example of such a magnetic powder is so-called pure iron powder. Its purity is preferably 99.7% by mass or more, more preferably 99.8% or more. For example, when ABC100.30 manufactured by Höganäs is used, such iron powder can be easily obtained. This commercially available iron powder has components other than Fe of C: 0.001, Mn: 0.02, O: 0.08 (unit: mass%) or less, and extremely less impurities than other commercially available iron powders. Iron powder with excellent compressibility.
When the magnetic powder is an Fe-based magnetic powder comprising 99.7% by mass or more of Fe and inevitable impurities, the sintered body density d ≧ 7.6 g / cm. Three And 7.7 g / cm Three It also becomes. At this time, B1k ≧ 1.4T, 1.5T, and 1.55T.
The upper limit of the purity of the pure iron powder is theoretically 100% by mass, but it is difficult and truly not economical to be truly 100% by mass. If the upper limit is dared, it will be less than 100 mass%.
[0024]
In addition, the magnetic powder may contain various additive elements that can improve or maintain magnetic properties, mechanical properties, corrosion resistance, and the like. Examples of such elements include Co, Ti, V, Cr, Mn, Ni, Mo, P, Si, and Al. Specifically, it may be as follows.
The magnetic powder contains 0.1 to 5% by mass, preferably 1 to 3% by mass of one or more elements in the element group consisting of Ti, V, Cr, Mn, Co, Ni and Mo, with the balance being Fe and It is suitable if it consists of inevitable impurities. Each of these additive elements has the effect of improving the magnetic properties, mechanical properties, and corrosion resistance of the sintered soft magnetic material. If the content of each element is less than 0.1% by mass, those effects are not achieved. If the content exceeds 5% by mass, the magnetic powder becomes hard and the molding density and the sintering density are lowered, and the magnetic properties are eventually lowered. Will do. When the additive element is in the above range, the sintered body density d ≧ 7.4 g / cm. Three 7.5 g / cm Three Furthermore, 7.6 g / cm Three It also becomes. At this time, B1k ≧ 1.3T.
[0025]
Further, the magnetic powder contains 0.1 to 5% by mass, preferably 0.3 to 3% by mass of one or more elements in the element group consisting of P, Si and Al, with the balance being Fe and inevitable impurities. It may be. If the content of each element is less than 0.1% by mass, there is no effect of improving the magnetic properties, and if the content exceeds 5% by mass, the effect is reduced.
Here, Si and Al are elements that are effective in reducing the coercive force. However, if the amount of Si or Al becomes too large, the magnetic powder becomes hard, resulting in a decrease in molding density and a decrease in the density of the sintered body, resulting in a decrease in magnetic properties. Therefore, the upper limit of Si or Al is preferably 5% by mass or less. On the other hand, P has an effect of promoting a densification by generating a liquid phase in the sintered body, but if the addition amount is too large, the powder becomes hard, so the upper limit is preferably 5% by mass or less.
Co is an element that increases the saturation magnetization of the sintered soft magnetic material. In particular, it is well known that a material containing 20 to 40% by mass of Co has the maximum saturation magnetization in an Fe-based alloy (saturation magnetization: about 2.4 T). However, as the amount of Co increases, the magnetic powder becomes harder and the molding density and sintered body density decrease. From such a viewpoint, it is preferable that the magnetic powder is more than 5 to 30% by mass, more preferably 10 to 30% by mass of Co, the balance Fe, and inevitable impurities, exceeding the above Co amount.
At this time, as in the case described above, 0.1 to 5% by mass of one or more elements in the element group consisting of Co, Ti, V, Cr, Mn, Ni, Mo, P, Si, and Al are contained. You may do it.
In addition, when the amount of Co in the magnetic powder increases as described above, the above-described magnetic flux densities B1k, B2k, B10k, etc. and the saturation magnetization Ms can be further increased in addition to the above-described range. For example, B10k ≧ 1.9T, 2.0T, or even 2.1T, and saturation magnetization Ms ≧ 2.2T, or 2.3T. The density of pure Fe is 7.86 g / cm. Three Whereas the density of pure Co is 8.8 g / cm. Three Therefore, the density of the sintered body also increases according to the amount of Co. For example, the density of the sintered body d ≧ 7.7 g / cm Three 7.8 g / cm Three Furthermore, 7.9 g / cm Three It also becomes.
In addition, the sintered compact density d mentioned in this specification and the compact density d before sintering mentioned later 0 The upper limit varies depending on the composition and cannot be specified. In other words, the upper limit is the true density determined from the component composition of the magnetic powder. For example, 7.86 g / cm when the magnetic powder is pure iron powder Three Is the upper limit.
Further, in the present specification, “x to y” includes a lower limit x and an upper limit y unless otherwise specified.
[0026]
(Method for producing sintered soft magnetic material)
(1) Application process
The application step is a step of applying a higher fatty acid lubricant to the inner surface of the molding die. As a result, during pressure molding under a predetermined condition, a metal soap film is formed between the inner surface of the molding die and the powder molded body serving as the sintered soft magnetic body, thereby ensuring lubricity. Further, even if the magnetic powder is molded under high pressure, it is easy to remove the mold, and the occurrence of galling or the like on the inner surface of the molding die is suppressed or prevented.
[0027]
(1) The higher fatty acid-based lubricant is preferably a metal salt of a higher fatty acid in addition to the higher fatty acid. Examples of the higher fatty acid metal salt include a lithium salt, a calcium salt, and a zinc salt, and lithium stearate, calcium stearate, and zinc stearate are particularly preferable. In addition, barium stearate, lithium palmitate, lithium oleate, calcium palmitate, calcium oleate, and the like can also be used.
[0028]
(2) The coating step is preferably a step of spraying a higher fatty acid-based lubricant dispersed in water into a heated molding die.
When the higher fatty acid-based lubricant is dispersed in water, the higher fatty acid-based lubricant can be uniformly sprayed on the inner surface of the molding die. Furthermore, when it is sprayed into the heated molding die, the water quickly evaporates, and the higher fatty acid-based lubricant can be uniformly attached to the inner surface of the molding die. In addition, although it is necessary to consider the temperature of the below-mentioned shaping | molding process as the heating temperature of a shaping | molding die, it is good to heat to 100 degreeC or more, for example. However, in order to form a uniform film of a higher fatty acid-based lubricant, the heating temperature is preferably less than the melting point of the higher fatty acid-based lubricant. For example, when lithium stearate is used as the higher fatty acid-based lubricant, the heating temperature is preferably less than 220 ° C.
[0029]
When the higher fatty acid-based lubricant is dispersed in water, the higher fatty acid-based lubricant is 0.1 to 5% by mass, more preferably 0.5 to 2 when the total weight of the aqueous solution is 100% by mass. It is preferable that a uniform lubricating film is formed on the inner surface of the molding die when it is contained in a proportion of mass%.
[0030]
Further, when the higher fatty acid-based lubricant is dispersed in water, the higher fatty acid-based lubricant can be uniformly dispersed by adding a surfactant to the water. Examples of such surfactants include alkylphenol surfactants, polyoxyethylene nonylphenyl ether (EO) 6, polyoxyethylene nonyl phenyl ether (EO) 10, anionic nonionic surfactants, and boric acid. Ester emulbon T-80 or the like can be used. Two or more of these may be used in combination. For example, when lithium stearate is used as a higher fatty acid-based lubricant, three types of polyoxyethylene nonylphenyl ether (EO) 6, polyoxyethylene nonylphenyl ether (EO) 10 and borate ester Emulbon T-80 are available. It is preferable to use a surfactant at the same time. This is because the composite dispersibility of lithium stearate in water is further activated as compared with the case of adding only one of them.
[0031]
In order to obtain an aqueous solution of a higher fatty acid-based lubricant having a viscosity suitable for spraying, when the total amount of the aqueous solution is 100% by volume, the ratio of the surfactant is preferably 1.5 to 15% by volume.
In addition, a small amount of an antifoaming agent (for example, a silicon-based antifoaming agent) may be added. This is because when the foaming of the aqueous solution is intense, it is difficult to form a uniform higher fatty acid-based lubricant film on the inner surface of the molding die when sprayed. The addition ratio of the antifoaming agent may be about 0.1 to 1% by volume when the total volume of the aqueous solution is 100% by volume.
[0032]
(3) The higher fatty acid-based lubricant particles dispersed in water preferably have a maximum particle size of less than 30 μm.
This is because when the maximum particle size is 30 μm or more, the particles of the higher fatty acid lubricant dispersed in water tend to settle, and it becomes difficult to uniformly apply the higher fatty acid lubricant to the inner surface of the molding die. .
[0033]
(4) The aqueous solution in which the higher fatty acid-based lubricant is dispersed can be applied using, for example, a spray gun for painting, an electrostatic gun or the like.
In addition, as a result of investigating the relationship between the application amount of the higher fatty acid-based lubricant and the extraction pressure of the powder molded body by the present inventor, the molding metal mold is formed so that the film thickness is about 0.5 to 1.5 μm. It has been found preferable to adhere to the inner surface of the mold.
[0034]
(2) Filling process
The filling step is a step of filling magnetic powder into a molding die to which a higher fatty acid-based lubricant is applied. This filling step is preferably a step of filling the heated magnetic powder into a heated molding die. If both the magnetic powder and the molding die are heated, the magnetic powder and the higher fatty acid-based lubricant react stably in the subsequent molding process, and a uniform lubricating film is formed between them. It is considered easy. Therefore, for example, it is preferable to heat both at 100 ° C. or higher.
[0035]
(3) Molding process
The molding step is a step of press-molding the magnetic powder filled in the molding die warm.
(1) Although details are not clear, this process causes a so-called mechanochemical reaction between the higher fatty acid lubricant applied to the inner surface of the molding die and at least the magnetic powder in contact with the inner surface of the molding die. This reaction is considered to cause the magnetic powder and the higher fatty acid-based lubricant to be chemically bonded to form a metal soap film on the surface of the magnetic powder powder compact.
[0036]
The metal soap film that is firmly bonded to the magnetic powder exhibits better lubrication performance than the higher fatty acid-based lubricant adhered to the inner surface of the mold. The frictional force with the outer surface is significantly reduced. As a result, it became possible to perform pressure molding at a high pressure, which was conventionally considered difficult, and a high-density sintered soft magnetic material or a sintered soft magnetic material excellent in magnetic properties such as specific resistance and magnetic permeability was obtained. Conceivable.
[0037]
(2) The molding temperature in the molding step is determined in consideration of magnetic powder, higher fatty acid lubricant, molding pressure and the like.
Therefore, “warm” in the molding process means that the molding process is performed under an appropriate heating condition according to each situation. For example, the molding temperature is preferably 100 to 220 ° C. By setting it as 100 degreeC or more, reaction with a magnetic powder and a higher fatty-acid-type lubricant can be accelerated | stimulated. Moreover, by setting it as 220 degrees C or less, it can prevent that a higher fatty acid-type lubricant melt | dissolves and flows out, or a higher fatty acid-type lubricant changes in quality. Further, it is more preferable that the molding temperature is 120 to 180 ° C.
[0038]
(3) The molding pressure in the molding process is also appropriately determined according to the desired characteristics of the sintered soft magnetic material, the magnetic powder, the type of higher fatty acid-based lubricant, the material of the molding die, the inner surface properties, and the like. However, the higher the molding pressure, the greater the density of the powder compact (molded body density) and the density of the sintered soft magnetic material (sintered body density). And when it shape | molds by high pressure, it is preferable that it is the pressure which magnetically couple | bonds a magnetic powder etc. and a higher fatty acid type lubricant, and produces | generates a metal soap lubricating film. In this way, molding can be performed under a molding pressure that exceeds the conventional molding pressure. From this viewpoint, for example, the molding pressure can be set to 700 MPa or higher, 784 MPa or higher, 800 MPa or higher, 980 MPa or higher, 1000 MPa or higher, or 1176 MPa or higher. In particular, in order to stably form the above-described metal soap lubricating film and increase the density of the molded body and the density of the sintered body, the molding pressure is preferably 784 MPa or more. According to the manufacturing method of the present invention, no galling or the like occurs on the inner surface of the molding die even when the molding pressure is 1600 MPa or more, and further 1960 MPa. Therefore, the upper limit of the molding pressure is not particularly limited, and it is difficult to specify the upper limit. If it dares to say, it is a realistic range that the upper limit shall be about 2000 Mpa, and it is more preferable when a molding pressure shall be 1500 Mpa or less in consideration of the lifetime and productivity of a molding die.
For example, when such high-pressure molding is performed using pure iron powder, the density of the compact before sintering d 0 ≧ 7.4 g / cm Three 7.5 g / cm Three 7.6 g / cm Three Furthermore, 7.7 g / cm Three It also becomes.
However, magnetic powders containing one or more alloy elements other than Fe generally have high hardness, so that it is difficult to obtain a high-density powder compact by conventional powder molding methods. Even if the molding method according to the present invention is used, the density of the compact before sintering is d. 0 ≧ 7.2 g / cm Three 7.3 g / cm Three 7.4 g / cm Three A powder compact is obtained.
[0039]
(4) It should be noted that the present inventors have confirmed the following by experiments regarding the molding temperature and the molding pressure.
When a higher fatty acid lubricant (lithium stearate) is applied to the inner surface of the molding die and the magnetic powder is pressure-molded at a molding temperature of 150 ° C., the molding pressure is set to 686 MPa. On the contrary, the extraction pressure of the powder compact was low. This was a discovery that overturned the conventional idea that a higher molding pressure required a higher extraction pressure. Furthermore, iron stearate was adhered to the surface of the powder compact when it was pressure molded at a high pressure of 686 MPa or higher.
[0040]
(4) Sintering process
By sintering the powder molded body, a higher density soft magnetic body can be obtained. In addition, the strength is improved and its application is further expanded.
The sintering step is preferably performed in a vacuum, a reducing gas atmosphere or an inert gas atmosphere in order to prevent deterioration of magnetic properties due to oxidation. It is preferable that the sintering temperature and the sintering time are within an economical range in which the component elements are sufficiently diffused. For example, the sintering temperature is 600 ° C. or higher, more desirably 850 to 1300 ° C., and the sintering time is 0.1 to 3 hours.
[0041]
As described above, the present inventors have found that the structure of the obtained sintered body is different depending on the difference in the sintering temperature. That is, when sintered at a temperature equal to or higher than the γ transformation point, a structure in which crystal grains grow preferentially in the pressing direction is obtained. For example, in the case of pure iron, the sintering temperature is 950 to 1300 ° C, more preferably 1100 to 1300 ° C. In the case of an alloy system, an appropriate sintering temperature may be selected according to the composition.
[0042]
On the other hand, when sintered at a temperature lower than the γ transformation point, a structure composed of isotropic crystal grains is obtained. For example, in the case of pure iron, the sintering temperature is 800 to 910 ° C, more preferably 850 to 900 ° C. The γ transformation point is a temperature at which the crystal structure of Fe as a main component undergoes an allotropic transformation between an α phase (body-centered cubic lattice) and a γ phase (face-centered cubic lattice). A for pure iron Three The transformation point is 911 ° C., but the value varies somewhat depending on the contained elements in the magnetic powder.
In addition, this sintering process includes not only the case caused by the diffusion of metal atoms but also the case of so-called liquid phase sintering.
[0043]
(Use of sintered soft magnetic materials)
The sintered soft magnetic material of the present invention can be used in various electromagnetic devices such as motors, actuators, transformers, induction heaters (IH), speakers, and the like. Moreover, since the sintered soft magnetic material sintered at the γ transformation point or higher has an anisotropic structure, it is suitable for cases where directivity is required for magnetic properties.
[0044]
【Example】
Next, the present invention will be described more specifically with reference to examples of sintered soft magnetic materials.
(Production of test piece)
(1) Test piece No. 1-9
Five test pieces No. 1 shown in Table 1 1-9 were manufactured using the manufacturing method of this invention (henceforth "the mold lubrication warm high pressure molding method" suitably).
(1) First, a molding die having a ring-shaped cavity (outer diameter φ39, inner diameter φ30 mm × thickness 5 mm) was prepared. In this molding die, the die is made of cemented carbide and the punch is made of die steel. The inner surface of the molding die is subjected to TiN coating treatment, and the surface roughness is finished to 0.4Z. The molding die was heated and held at 150 ° C. by a band heater.
[0045]
Prior to the filling step, a higher fatty acid-based lubricant was applied to the inner wall surface of the heated molding die (application step). Specifically, using a spray gun, 1 cm of lithium stearate dispersed in water is used. Three The coating was uniformly applied to the inner wall surface of the molding die at a rate of about / sec. The lithium stearate used here has a melting point of about 225 ° C. and an average particle size of 20 μm. Further, lithium stearate was dispersed in an aqueous solution to which a surfactant and an antifoaming agent were added. As the surfactant, polyoxyethylene nonylphenyl ether (EO) 6, (EO) 10 and borate ester Emulbon T-80 were used. Each addition ratio was 1% by volume when the total volume of the aqueous solution was 100% by volume. The amount of lithium stearate powder dispersed was 100 cm of the aqueous solution. Three Is 25 g. The stock solution thus obtained was pulverized (Teflon-coated steel balls: 100 hours), refined with a ball mill type pulverizer, and then diluted 20 times to obtain an aqueous solution having a final concentration of 1%.
[0046]
{Circle around (2)} As a raw material powder (Fe-based magnetic powder), a commercially available Fe powder (AGC 100.30 manufactured by Höganäs: purity 99.8% Fe) was prepared. The Fe powder that had been heated to 150 ° C. was filled into the aforementioned heated mold (filling step).
[0047]
(3) Next, while holding the molding die at 150 ° C., warm pressing is performed under a molding pressure in the range of 784 to 1176 MPa, and further 1568 to 1960 MPa, and various powder compacts are obtained. Obtained (molding step). Each molding pressure is shown in Table 1.
[0048]
(4) The powder compact was heated and sintered in a nitrogen gas atmosphere for 0.5 hours to obtain a ring-shaped test piece No. 1 shown in Table 1. 1 to 9 sintered soft magnetic materials were obtained. As the sintering temperature, 900 ° C. below the γ transformation point and 1250 ° C. above the γ transformation point were appropriately selected (see Table 1).
[0049]
(2) Test piece No. 10-12
As a raw material powder, commercially available Fe powder (PASC060P: Fe-0.6P (mass%): Fe-P magnetic powder manufactured by Höganäs) was prepared. In the same manner as in Test Nos. 10-12 were produced. The details of each condition are as shown in Table 2, but the sintering temperature was only 1250 ° C. and the sintering time was 0.5 hours.
[0050]
(3) Test piece No. 13-18
Specimen No. As raw material powders according to 13 to 16 and 18, alloy powders (Fe-M1 magnetic powder and Fe-Co magnetic powder) manufactured by the water atomization method having the respective compositions shown in Table 2 were prepared. In addition, test piece No. As a raw material powder according to No. 17, an alloy powder (Fe-M1-based magnetic powder) manufactured by a gas atomization method having the composition (Fe-1Al) shown in Table 2 was prepared.
And under the conditions shown in Table 2, the test piece No. In the same manner as in Test Nos. 13-18 were produced. The details of each condition are as shown in Table 2, but the sintering process is 0.01 Pa (10 -Four torr) in a vacuum atmosphere. In addition, test piece No. For Nos. 10 to 16, the sintering temperature was 1250 ° C., the sintering time was 0.5 hours. For No. 17, the sintering temperature was 1200 ° C. and the sintering time was 4 hours. For No. 18, the sintering process was performed at a sintering temperature of 1000 ° C. and a sintering time of 1 hour.
The test piece No. For any of Nos. 1 to 18, no galling or the like occurred, and the surface properties of the sintered soft magnetic material were good.
Moreover, all the test pieces shown in Table 1 and Table 2 were subjected to magnetic annealing at 850 ° C. × 3 h in vacuum after sintering.
[0051]
(4) Test piece No. C1, C2
Specimen No. Using the same raw material powder and apparatus as those of Nos. C1 and C2 were produced. In both test pieces, 0.6% by mass of Kenolube (manufactured by Höganäs) was added as an internal lubricant.
Specimen No. C1 is obtained by sintering a powder compact formed at a molding temperature of room temperature and a molding pressure of 600 MPa under the conditions shown in Table 2.
[0052]
Specimen No. C2 is test piece No. The C1 powder compact was presintered at 750 ° C. in a nitrogen atmosphere, and further molded and sintered (so-called 2P2S sintered soft magnetic material). The second molding was performed under a condition of 600 MPa, and the second sintering was performed under a condition of 1250 ° C. × 0.5 hours in a nitrogen atmosphere.
[0053]
(Measurement of magnetic properties, etc.)
Tables 1 and 2 also show the magnetic properties and density measurement results for each test piece. Among the magnetic characteristics, the static magnetic field characteristics are measured by a direct current magnetic flux meter (manufacturer: Toei Kogyo, model number: MODEL-TRF), and the AC magnetic field characteristics are AC B-H curve tracers (manufacturer: RIKEN ELECTRONICS, model number: ACBH-). 100K). The AC magnetic field characteristics in each table are obtained by measuring the iron loss Pc when each test piece is placed in a magnetic field of 50 Hz and 1.0 T. Magnetic flux densities B0.5k, B1k, B2k, and B10k in a static magnetic field are magnetic flux densities when the magnetic field strength is changed to 0.5, 1, 2, and 10 kA / m in order. The saturation magnetization Ms is obtained by measuring the magnetic flux density in 1.6 MA / m. The maximum magnetic permeability and coercive force are also shown in Tables 1 and 2. The density was measured by the Archimedes method. In the table, “not yet” indicates that no measurement is performed.
[0054]
(Evaluation)
(1) As can be seen from Tables 1 and 2, the test piece No. As for 1-12 and 14-18, as for all, the density of a powder compact and a sintered compact is 7.5 g / cm. Three It can be seen that the density is higher than that and the magnetic properties are also excellent. In particular, test piece No. 2P2S product. Even when compared with C2, it is understood that it has higher density and magnetic properties. In addition, test piece No. 1-18 are test piece No.1. Compared to C1 and C2, the iron loss is lower overall.
Specimen No. When the molding pressure exceeds 1200 MPa as in 6 to 9, the density of the compact before sintering and the density of the sintered body after sintering are 7.8 g / cm. Three Exceeding the true density, which is almost equal to the true density.
Specimen No. Those containing an alloy component such as 10 to 17, even when the molding pressure is high, the test piece No. Each density is slightly lower than those of 1-10. This may be due to the fact that the raw material powder is hard and has low formability, but the true density itself is also low due to the presence of the alloy components. Therefore, considering the ratio (density ratio) of the compact density and the sintered density to the true density, the test piece No. Even in the case of 10 to 17, it can be seen that a high-density molded body and a high-density sintered body of 95% or more and further 98% or more are obtained. However, specimen no. Magnetic powders having a large Si content such as 15 and 16 have a high hardness and are thus inferior in moldability, and both the density of the molded body and the density of the sintered body are reduced.
Specimen No. No. 18 is excellent in magnetic characteristics like Fe and contains Co having a density higher than that of Fe, so that it has excellent magnetic characteristics (for example, B10k), and both the compact density and the sintered density are large.
[0055]
(2) Next, the relationship between the molding pressure in the molding process and the density of the powder compact (molded body density) or the sintered body density, and the relationship between the molding pressure and the dimensional change before and after the sintering process were investigated. .
(1) When using Fe-0.6P powder
The above-mentioned test piece No. The test piece of (phi) 17 * 17mm was manufactured using the Fe-0.6P powder used by 10-12. The manufacturing process basically consists of test piece No. It is the same as the case of 10-12. However, each test piece was manufactured by changing the molding pressure in various ways. The sintering temperature was 1250 ° C. The relationship between the molding pressure and each density at this time is shown in FIG. FIG. 2 shows the relationship between the molding pressure and the dimensional change before and after the sintering process. Note that the “compression direction” in FIG. 2 is the pressing direction during the molding process, in other words, the axial direction of the test piece (hereinafter the same).
[0056]
Even in the case of Fe-0.6P powder, if the production method of the present invention is used, a powder compact having a considerably higher density than the conventional one can be obtained. However, since the powder is mixed with hard FeP particles, there is a limit to increasing the density only by the molding process. Therefore, it can be seen from FIG. 1 that when sintered at 1250 ° C., a sintered body in which FeP is in a liquid phase and greatly densified is obtained.
[0057]
However, as can be seen from FIG. 2, the dimensional shrinkage after the sintering process becomes relatively large due to the liquid phase of FeP. However, since the molding pressure can be increased by using the manufacturing method of the present invention, it can also be seen from FIG. For example, by setting the molding pressure to 1000 MPa or more, the dimensional change before and after sintering can be made within 0.5%.
[0058]
(2) When using pure Fe powder (Fe: 99.8% by mass)
The above-mentioned test piece No. A test piece of φ17 × 17 mm was manufactured using the Fe powder used in 1-9. The manufacturing process basically consists of test piece No. It is the same as the case of 1-9. However, while changing various molding pressures, the sintering process was performed at two kinds of sintering temperature, and each test piece was manufactured.
[0059]
(A) When the sintering temperature is 1250 ° C. (above the γ transformation point)
The relationship between the molding pressure and each density at this time is shown in FIG. FIG. 4 shows the relationship between the molding pressure and the dimensional change before and after the sintering process.
When Fe powder is used, the compact density is already high due to the high pressure molding according to the present invention. Therefore, the sintered body density does not change greatly with respect to the compact density. However, it has been found that when the molding pressure is 784 MPa or more, the density of the sintered body is slightly lower than the density of the molded body.
[0060]
As can be seen from FIG. 4, it was also found that when the molding pressure is 784 MPa or more, a large behavior change appears in the dimensional change. Specifically, it has been newly found that the radial dimension contracts and the compression dimension expands greatly. This factor will be described later.
[0061]
(B) When the sintering temperature is 900 ° C. (below the γ transformation point)
The relationship between the molding pressure and each density at this time is shown in FIG. FIG. 6 shows the relationship between the molding pressure and the dimensional change before and after the sintering process.
From FIG. 5, it was found that when the sintering temperature was less than the γ transformation point, the sintered body density was slightly higher than the green body density. Further, FIG. 6 shows that the dimensional change at this time is in the range of 0 to −0.1% both in the radial direction and in the compression direction, and hardly occurs. This factor will also be described later.
[0062]
(3) Next, a micrograph of the metal structure of the φ17 × 17 sample manufactured from the Fe powder observed with an optical microscope is shown in FIGS. Each sample is a combination of various molding pressures and sintering temperatures, and the conditions are shown in the figure. “Parallel surface” in each figure indicates a cut surface when the sample is cut in the axial direction, and “vertical surface” indicates a surface perpendicular to the axial direction of the sample (a surface having the axis as a normal line). ) Shows the cut surface when cut.
[0063]
(1) Effect of molding pressure
As can be seen from a comparison between FIG. 7 and FIG. 8, it can be seen that even at the same sintering temperature (1250 ° C.), when the molding pressure during the molding process is different, the appearing structures are different. In other words, when the molding pressure is 686 MPa, a general crystal grain structure (FIG. 7), but when the molding pressure becomes 784 MPa, the crystal grains preferentially grow in the compression direction (axial direction). It can be seen that the crystal grains have a ratio ≧ 2) (FIG. 8A). However, it can also be seen that crystal grains grow isotropically on the vertical plane (FIG. 8B). The magnetic characteristics are strongly influenced by the crystal grain arrangement. That is, such a sintered soft magnetic material can exhibit anisotropic magnetic properties such as a higher magnetic flux density in the axial direction.
[0064]
(2) Influence of sintering temperature
As can be seen from a comparison between FIG. 9 and FIG. 10, it can be seen that even at the same molding pressure (1176 MPa), when the sintering temperature is different, the appearing structures are different. That is, even when the forming pressure is 784 MPa or more, by setting the sintering temperature to 900 ° C. (below the γ transformation point), the appearing crystal grain structure may be isotropic in both the radial direction and the compression direction. It can be seen from FIG.
On the other hand, when the sintering temperature is 1250 ° C. (above the γ transformation point), the crystal grains preferentially grow in the compression direction (axial direction) as in the case shown in FIG. ) (FIG. 10A).
Further, a ring-shaped test for applying a magnetic field in the axial direction (compression direction) from the sintered soft magnetic material shown in FIG. 10 (substantially the same as test piece No. 5 in Table 1) before the magnetic annealing. A piece and a ring-shaped test piece for applying a magnetic field in the radial direction (perpendicular to the compression direction) were cut out. Table 3 shows the result of magnetic measurement using each test piece.
From this result, when the magnetic field is applied in the axial direction, the maximum magnetic permeability (μm) and the magnetic flux density (B0.2k, B0.3k, B0.4k, B0.5k) on the low magnetic field side are larger. . Therefore, it is clear that the sintered soft magnetic material exhibits magnetic anisotropy, and it can be understood that more excellent magnetic characteristics can be obtained in the axial direction.
[0065]
(3) Relationship between dimensional change and metal structure
It is considered that the difference in the shape of the crystal grains affects the behavior of the compact density and the sintered compact density shown in FIGS. 3 and 5 and the behavior of the dimensional change shown in FIGS. In particular, it is considered that the behavior of the dimensional change greatly changes at 784 MPa or more because the crystal grain structure having a large aspect ratio shown in FIGS. 8A and 10A appears.
[0066]
[Table 1]
[Table 2]
[Table 3]
【The invention's effect】
The sintered soft magnetic material of the present invention exhibits excellent magnetic properties at a relatively low cost.
Moreover, according to the manufacturing method of this invention, such a sintered soft magnetic body can be manufactured efficiently.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between molding pressure and density of a sintered soft magnetic body using Fe-0.6P powder.
FIG. 2 is a graph showing a relationship between a molding pressure of a sintered soft magnetic body using Fe-0.6P powder and each dimensional change.
FIG. 3 is a graph showing the relationship between molding pressure and density of a sintered soft magnetic material sintered with Fe powder at or above the γ transformation point.
FIG. 4 is a graph showing the relationship between the molding pressure and each dimensional change of a sintered soft magnetic material sintered with Fe powder at a γ transformation point or higher.
FIG. 5 is a graph showing the relationship between molding pressure and density of a sintered soft magnetic material sintered with Fe powder at a temperature lower than the γ transformation point.
FIG. 6 is a graph showing the relationship between the molding pressure and each dimensional change of a sintered soft magnetic material sintered with Fe powder below the γ transformation point.
FIG. 7 is a metallographic photograph showing the crystal grain shape of a sintered soft magnetic material manufactured using Fe powder at a molding pressure of 686 MPa and a sintering temperature of 1250 ° C.
FIG. 8 is a metallographic photograph showing the crystal grain shape of a sintered soft magnetic material manufactured using Fe powder at a molding pressure of 784 MPa and a sintering temperature of 1250 ° C.
FIG. 9 is a metallographic photograph showing the crystal grain shape of a sintered soft magnetic material manufactured using Fe powder at a molding pressure of 1176 MPa and a sintering temperature of 900 ° C.
FIG. 10 is a metallographic photograph showing the crystal grain shape of a sintered soft magnetic material manufactured using Fe powder at a molding pressure of 1176 MPa and a sintering temperature of 1250 ° C.
Claims (23)
前記Ｆｅ系磁性粉末は９９．７質量％以上のＦｅと不可避不純物とからなり、
前記成形工程および前記焼結工程をそれぞれ一回ずつ行う一回成形一回焼結後に得られた焼結体に関して、
焼結体密度ｄ≧７．７ｇ／ｃｍ3、
１．６ＭＡ／ｍの磁場中における飽和磁化Ｍｓ≧１．９Ｔ、
１ｋＡ／ｍの磁場中における磁束密度Ｂ１ｋ≧１．４Ｔ、
であることを特徴とする焼結軟磁性体。Only an Fe-based magnetic powder containing iron (Fe) as a main component in the molding die after the coating process, and a coating process in which a higher fatty acid-based lubricant composed of a higher fatty acid metal salt is applied to the inner surface of the molding mold. And a pressure at which the higher fatty acid lubricant is chemically bonded to the Fe magnetic powder after the filling step to form a new metal soap film different from the higher fatty acid lubricant. It is manufactured through a molding step of warm pressing the Fe-based magnetic powder under temperature and a sintering step of heating and sintering the powder molded body obtained by the molding step,
The Fe-based magnetic powder comprises 99.7% by mass or more of Fe and inevitable impurities,
Regarding the sintered body obtained after one-time molding once-sintering each of the molding step and the sintering step once,
Sintered body density d ≧ 7.7 g / cm 3 ,
Saturation magnetization Ms ≧ 1.9T in a magnetic field of 1.6 MA / m,
Magnetic flux density B1k ≧ 1.4T in a magnetic field of 1 kA / m,
A sintered soft magnetic material, characterized in that
前記Ｆｅ−Ｐ系磁性粉末は０．３〜０．６質量％のＰと残部Ｆｅおよび不可避不純物とからなり、
前記成形工程および前記焼結工程をそれぞれ一回ずつ行う一回成形一回焼結後に得られた焼結体に関して、
真密度に対する焼結体密度の比である密度比が９８％以上、
１．６ＭＡ／ｍの磁場中における飽和磁化Ｍｓ≧１．９Ｔ、
１ｋＡ／ｍの磁場中における磁束密度Ｂ１ｋ≧１．４Ｔ、
であることを特徴とする焼結軟磁性体。An application step of applying a higher fatty acid lubricant comprising a metal salt of a higher fatty acid to the inner surface of the molding die, and Fe containing phosphorus (P) as a main component in the molding die after the application step -Filling step of filling only P-based magnetic powder, and a new metal different from the higher fatty acid-based lubricant by chemically bonding the higher fatty acid-based lubricant to the Fe-P-based magnetic powder after the filling step A molding step of warm- pressing the Fe-P magnetic powder under pressure and temperature to form a soap film, and a sintering step of heating and sintering the powder compact obtained by the molding step; Manufactured through
The Fe-P based magnetic powder consists of 0.3 to 0.6% by mass of P, the balance Fe and inevitable impurities,
Regarding the sintered body obtained after one-time molding once-sintering each of the molding step and the sintering step once,
The density ratio, which is the ratio of the sintered body density to the true density, is 98% or more,
Saturation magnetization Ms ≧ 1.9T in a magnetic field of 1.6 MA / m,
Magnetic flux density B1k ≧ 1.4T in a magnetic field of 1 kA / m,
A sintered soft magnetic material, characterized in that
前記磁性粉末は、９９．７質量％以上のＦｅと不可避不純物とからなるＦｅ系磁性粉末であり、
前記成形工程は、成形圧力を７８４ＭＰａ以上とする工程であり、
前記焼結工程は、焼結温度をγ変態点以上とする工程であって、
真密度に対する焼結体密度の比である密度比が９８％以上であると共に該成形工程中の加圧方向に優先的に成長した結晶粒からなる組織を有し磁気異方性を発現する焼結体からなることを特徴とする焼結軟磁性体。An application step of applying a higher fatty acid-based lubricant comprising a metal salt of a higher fatty acid to the inner surface of the molding die, and a filling step of filling the molding die after the application step with magnetic powder mainly composed of Fe; After the filling step , the higher fatty acid lubricant is chemically bonded to the magnetic powder to form a new metal soap film different from the higher fatty acid lubricant under pressure and temperature. It is obtained through a molding step for warm pressing and a sintering step for heating and sintering the powder compact obtained by the molding step,
The magnetic powder is an Fe-based magnetic powder comprising 99.7% by mass or more of Fe and inevitable impurities,
The molding step is a step of setting the molding pressure to 784 MPa or more,
The sintering step is a step of setting the sintering temperature to a γ transformation point or higher,
Expressing anisotropy has a structure comprising crystal grains the density ratio is the ratio of the sintered body density is grown preferentially in the pressurization direction in 98% der Rutotomoni molding step to the true density A sintered soft magnetic material comprising a sintered body.
前記磁性粉末は、９９．７質量％以上のＦｅと不可避不純物とからなるＦｅ系磁性粉末であり、
前記成形工程は、成形圧力を７８４ＭＰａ以上とする工程であり、
前記焼結工程は、焼結温度をγ変態点未満とする工程であって、
真密度に対する焼結体密度の比である密度比が９８％以上であると共に等方的に成長した結晶粒からなる組織を有し前記焼結工程前後の寸法変化が０．２％以下の焼結体からなることを特徴とする焼結軟磁性体。An application step of applying a higher fatty acid-based lubricant comprising a metal salt of a higher fatty acid to the inner surface of the molding die, and a filling step of filling the molding die after the application step with magnetic powder mainly composed of Fe; After the filling step , the higher fatty acid lubricant is chemically bonded to the magnetic powder to form a new metal soap film different from the higher fatty acid lubricant under pressure and temperature. It is obtained through a molding step for warm pressing and a sintering step for heating and sintering the powder compact obtained by the molding step,
The magnetic powder is an Fe-based magnetic powder comprising 99.7% by mass or more of Fe and inevitable impurities,
The molding step is a step of setting the molding pressure to 784 MPa or more,
The sintering step is a step of setting the sintering temperature below the γ transformation point,
Said sintering step before and after the dimensional change density ratio is the ratio of the sintered body density has a structure consisting of 98% or more der Rutotomoni isotropically grown crystal grains with respect to the true density below 0.2% A sintered soft magnetic material comprising a sintered body.
該塗布工程後の成形用金型内にＦｅを主成分とする磁性粉末を充填する充填工程と、
該充填工程後に該高級脂肪酸系潤滑剤が該磁性粉末に化学的に結合して該高級脂肪酸系潤滑剤とは異なる新たな金属石鹸の被膜を生成する圧力と温度の下で該磁性粉末を温間加圧成形する成形工程と、
該成形工程により得られた粉末成形体を加熱して焼結させる焼結工程と、
からなることを特徴とする焼結軟磁性体の製造方法。An application step of uniformly applying an aqueous solution in which a higher fatty acid-based lubricant composed of a metal salt of a higher fatty acid is dispersed in water containing a surfactant on the inner surface of a heated molding die;
A filling step of filling a magnetic powder mainly composed of Fe into the molding die after the coating step;
After the filling step, the higher fatty acid lubricant is chemically bonded to the magnetic powder to form a new metal soap film different from the higher fatty acid lubricant. A molding process for pressure molding between,
A sintering step of heating and sintering the powder compact obtained by the molding step;
A method for producing a sintered soft magnetic material comprising:
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