JP2568022C

JP2568022C -

Info

Publication number: JP2568022C
Authority: JP
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Publication date: 1999-09-20

Description

【発明の詳細な説明】【０００１】【産業上の利用分野】本発明は、熱膨張率が低く、かつ鋳造性、被削性、振動吸収能等の特性を同時
に満足する低熱膨張鋳鉄を低熱膨張性が求められる構造部材へ適用した工作機械
、精密測定機器および成形用金型、ならびに治具部材へ適用した半導体装置およ
び電子製造装置に関する。【０００２】【従来の技術】周知のように、鋳鉄は工業の基礎材料として広く使用されている。その理由は
この材料の鋳造性が良く、多種多様な複雑形状でも成形できること、切削加工が
容易であること、材料の加工や溶解に要する費用が比較的安価で小規模な工場で
も容易に製造できること等の長所を有しているためである。【０００３】ところで、最近では新素材を始めとして、金属以外の有機、無機の様々な材料
が開発され、それぞれの特性を活かした機能材料が急速に普及しつつある。特に
エレクトロニクス産業の発達に伴い、それに関連する工作機械や精密測定機器、
成形用金型、科学機器、その他の製造機械類ならびに半導体装置、電子製造装置
には、より高精度で機能が優れた材料が要求されるようになった。【０００４】鋳鉄においても、上記要求に応えるための従来の材料や特質に加えて、熱膨張
係数の低減化、振動吸収能の増大化、および耐熱性、耐食性を付加されたものが
開発されてきている。その代表的なものがインバー鋳鉄（３６．５％Ｎｉ−Ｆｅ
合金）、またはその改良材のニレジストＤ５（ＡＳＴＭＡ４３９タイプＤ−５
）鋳鉄である。これらの鋳鉄の代表例の化学成分を下記の表１に示す。【０００５】【表１】インバーは鉄中にニッケルを３４〜３７％（以下、成分組成割合は全て重量％
とする。）含有したものであり、常温付近（０〜２００℃）における熱膨張係数
が１．５×１０^ー6／℃程度と低い値を有する。このインバー合金の低膨張性の機
構は、一般に「インバー効果」と呼ばれる自発生体積磁歪作用に基づくものであ
る。【０００６】またスーパーインバーは鉄ニッケル基質中に４〜６％のコバルトを合金化して
調製されたものであり、常温付近における熱膨張係数が０．５×１０^-6／℃とイ
ンバーよりさらに低い優れた特性を有している。【０００７】しかしながら、上記のインバーおよびスーパーインバーは、共に鋳造性、被削
性や振動吸収能が低いため、かなり狭い分野に限定して実用化されているに過ぎ
ない。【０００８】また表１の番号３，４，５欄に示すような鋳鉄系低膨張材も開発実用化されて
いる。例えばニレジストＤ５は汎用のダクタイル鋳鉄とほぼ同等の炭素、ケイ素
、マンガンを含有した鉄中に３４〜３６％のニッケルを合金化して形成され、黒
鉛組織を有する鋳鉄にインバーと同量のニッケルを合金化することによって、鋳
鉄の長所である鋳造性、被削性、防振性を保持しつつ、さらに耐熱耐食性を兼ね
備え、さらに「インバー効果」による低膨張性を付与したものである。【０００９】同様な材料として、ノビナイト鋳鉄が特公昭６０−５１５４７号公報に開示さ
れている。この合金鋳鉄は汎用のダクタイル鋳鉄中に、スーパーインバーと同量
のニッケルおよびコバルトを合金化することにより、鋳造性、被削性と低膨張性
とを兼ね備えるように構成したものである。【００１０】しかしながら、上記ニレジストＤ５およびノビナイト鋳鉄は、汎用のダクタイ
ル鋳鉄と同程度の炭素、ケイ素、マンガンを含有しているため、インバーやスー
パーインバーが有する低膨張性が損なわれている。すなわち本願発明者等の実測によると、それぞれの熱膨張係数は５×１０^-6／℃、４×１０^-6／℃と大きな値
となっている。【００１１】しかし上記の鋳鉄合金では、近年の一層の熱膨張係数の低減に対する要望には
十分対応できず、最近の精密機器や高精度、ＦＲＰ用金型材等に対しては、さら
に低い熱膨張係数の低い材料が必要となっている。【００１２】本願発明者等は上記の要請に対応すべく、熱膨張係数が従来の４×１０^-6／℃
を下廻り、かつ鋳造性、被削性、振動吸収能を兼ね備えた材料を提供するために
、各合金元素の含有量と熱膨張係数、機械的性質との関係を、数多くの実験およ
び統計的分析法により明らかにし、新規な低熱膨張鋳鉄を発見し、特願昭６２−
２６８２４９号として出願した。【００１３】上記低熱膨張鋳鉄は表１の最下欄に示す組成を有する。すなわちオーステナイ
ト基地鉄を有する鋳鉄において、成分組成として炭素１．０％以上３．５％以下
、ケイ素１．５％以下、ニッケル３２％以上３９．５％以下、コバルト１．０％
以上４％未満を含み上記ニッケルとコバルトとの合計含有量を４１％以下にした
鋳鉄を用いることにより、（１）熱膨張係数が２×１０^-6／℃程度と低く、（２）優れた鋳造性、被削性、振動吸収能および機械的強度を備えた低熱膨張
材料を提供できることを初めて見い出した。【００１４】すなわち本願発明者等は、種々実験を繰り返した結果、炭素１〜３．５％、ニ
ッケル３２〜３９．５％を含んだ鋳鉄にコバルトを１〜４％添加すると共に、ケ
イ素添加量を１．５％以下、好ましくは１％以下に低く設定したときに熱膨張係
数が非常に小さく、しかも鋳造性、加工性も良好な鋳鉄が得られることを発見し
た。【００１５】この低膨張鋳鉄の開発により、より高精度の工作機械、精密測定機器および成形用金型等の加工品を提供することが可能となった。【００１６】【発明が解決しようとする課題】しかしながら、機器の大型化、高精度化がさらに進展し従来の低熱膨張鋳鉄で
も充分対応できない事態も発生しつつある。例えば、近年の衛星放送等の通信技
術の発展に伴い、その送受信設備に使用するパラボラアンテナ等は非常に大型化
し低熱膨張性はもとより、その加工精度、即ち、鋳造性、被削性、振動吸収能お
よび機械的強度などに極めて高いものが要求されている。例えば、アンテナ反射
体としては、高い剛性と耐食性とを有するカーボン繊維強化プラスチック（ＣＦ
ＲＰ）が一般に採用されている。ところが、このＣＦＲＰの熱膨張係数は約１．
５×１０^-6／℃と極めて小さいため、成形後においても製品の高い寸法精度を確
保するためには、成形用金型を同程度の熱膨張係数を有する材料で構成する必要
がある。したがって熱膨張係数が従来のものより、さらに小さく、少なくとも１
．５×１０^-6／℃以下であり、かつ機械的特性も優れた材料で成形用金型を構成
することが必須となっている。【００１７】本発明は上記の課題を解決するためになされたものであり、工作機械、精密測
定機器および成形用金型材料、ならびに半導体装置および電子製造装置材料とし
て更に一層優れた鋳造性、被削性および振動吸収能を保有し、かつ熱膨張係数が
使用温度０〜２００℃の範囲において４×１０^ー6／℃以下、好ましくは３×１０
^ー6／℃以下であり、更に好ましくは熱膨張係数が１．５×１０^-6／℃以下となる
特性を同時に満足する低熱膨張鋳鉄を低熱膨張特性が求められる構造部材へ適用
した工作機械、精密測定機器および成形用金型、ならびに治具部材として適用し
た半導体装置および電子製造装置を提供することを目的とする。【００１８】【課題を解決するための手段と作用】本発明は以上の観点から“固溶炭素”に初めて着目した上で、鋳造性、被削性
を改善するために鋳造過程において黒鉛が合金組織内に晶出できる最小限の成分
条件を数多くの実験分析を経て見い出し、同時に低熱膨張性を得るための最適成分条件を発見することにより、上記目的を達成したものである。【００１９】すなわち、本発明に掛かる工作機械、精密測定機器および成形用金型、ならび
に半導体装置および電子製造装置は、オーステナイト基地鉄中に黒鉛組織を有す４％以上８％以下を含み残部鉄から成り、０〜２００℃の温度範囲における熱膨
張係数が４×１０^-6／℃以下である低熱膨張鋳鉄を低熱膨張特性が求められる構
造部材へ適用したことを特徴とする。【００２０】なお好ましくは上記成分組成に加えてマンガンを１．０％以下、好ましくは０
．５％以下、マグネシウムを０．１％以下を含有させた鋳鉄を用いたものである
。上記成分組成範囲は発明者等による各種の実験および分析によって初めて得ら
れた下記の結晶に基づいて設定されたものである。【００２１】まず第１の結果として、熱膨張係数と各元素の含有量との関係を求め、下記（
１），（２）式の関係を得た。【００２２】熱膨張係数（×１０^-6／℃）＝１４．９０５＋０．１［固溶Ｃ量］（％）＋１．４９×［Ｓｉ量］（％） −０．３２×［Ｎｉ量］（％） −０．７０×［Ｃｏ量］（％）＋１．３５×［Ｍｎ量］（％） ……（１）熱膨張係数（×１０^-6／℃）＝−２．１４＋１．７５［固溶Ｃ量］（％）＋２．１１×［Ｓｉ量］（％）＋０．１４×［Ｎｉ量］（％）＋０．２８×［Ｃｏ量］（％）＋０．２５×［Ｍｎ量］（％） ……（２）ところで、Ｆｅ−Ｎｉ系合金の熱膨張係数とＮｉ量との関係は図１に示すよう
に、Ｎｉ含有量が約３６％付近で熱膨張係数が極小となる。したがって（１）式
はＮｉ含有量が熱膨張係数の極小点より低い領域での各合金元素の熱膨張係数に
対する分析の結果として得られた関係式である。【００２３】一方、（２）式はＮｉ含有量が極小点より高い領域での各合金元素の熱膨張係
数に対する分析により得た関係式である。【００２４】上記（１）式および（２）式中の各係数を比較すると、Ｓｉ量（％）の係数が
最も大きい。つまり、ケイ素含有量が正の相関をもって熱膨張特性に最も大きな
影響を及ぼすことがわかる。【００２５】したがって、ケイ素量を極力低減することによって、より低い熱膨張係数が得
られることが理解できる。【００２６】またＦｅ−Ｎｉ合金における炭素含有量が熱膨張係数に与える影響については
、従来含有炭素全体量が大きく影響すると考えられていた。しかしながら、本発
明者等の実験により、影響を与えるのは含有炭素量全体ではなく、固溶している
炭素量のみであるという事実が発見された。【００２７】そして、上記ケイ素量および固溶炭素量を所定範囲に低減化することにより熱
膨張特性をより改善できることを初めて見い出した。【００２８】次に、第２の結果として、ＮｉとＣｏとの合計含有量を変化させた場合におけ
る温度と熱膨張係数との関係は第２図に示すように、各Ｎｉ＋Ｃｏ量の割合に応
じて熱膨張係数の温度依存性が急に立ち上がる屈曲点Ｂが現われ、その屈曲点Ｂ
に対応する温度（以下屈曲点温度という。）が高温側に変化するという事実であ
る。【００２９】すなわち第２図から明らかなように、Ｎｉ＋Ｃｏ量が増加すると屈曲点温度が
高温側へ移行し、その結果、常温から２００℃までの実用温度範囲において熱膨
張係数が高くなる。逆に、屈曲点温度が３２５℃以下、好ましくは２００〜２５
０℃になるように成分組成を設定すると、実用温度範囲（０〜２００℃）におい
て、低い熱膨張係数を得ることができる。【００３０】本発明者等は、この屈曲点温度と各元素量との関係を実験で求め、下記（３）
式を得た。【００３１】屈曲点温度（℃）＝２２．５×［Ｎｉ（％）＋Ｃｏ（％）］ −２２×Ｍｎ（％）−６００．３ ……（３）（３）式からＭｎを添加することにより屈曲点温度をより低温度領域に移行さ
せることが可能であるという知見が得られた。【００３２】次に第３の結果として固溶炭素量および炭化物量を低減することによって、鋳
造性、切削加工性が改善され、さらに振動吸収能を大きくすることが可能となる
ことが判明した。【００３３】すなわち、固溶炭素以外の炭素は黒鉛あるいは炭化物として存在する。そのう
ち、黒鉛晶出量が大である程、鋳造時の収縮巣が少なく、切削加工性、つまり被
削性を良好とし、また振動吸収能が大となる。一方、炭化物が析出した場合は、
逆にミクロ巣発生の要因となり、被削性も悪くなる。したがって、可及的に固溶
Ｃ量と炭化物の析出量を低くし、黒鉛晶出量を高くすることが重要となる。【００３４】さらに第４の結果として固溶炭素量と機械的強度との関係式が下記（４）〜（
７）式の通りに得られた。【００３５】引張強さ（kgｆ／mm²）＝１９．６＋９３［固溶Ｃ量］（％）・・・・・（４）耐力（kgｆ／mm²）＝４．８＋１３５．５［固溶Ｃ量］（％）・・・・・（５）ヤング率（kgｆ／mm²）＝６９８２．５＋１９７５０［固溶Ｃ量］（％）・・・・・（６）硬さ（ＨＢ）＝１２８．６＋１３３［固溶Ｃ量］（％）・・・・・（７）前記（１），（２）式より熱膨張係数を低下させるためには固溶Ｃ量を低減す
ることが望ましいが、上記（４）〜（７）式から明らかなように機械的強度を向
上させるためには、固溶Ｃ量をある程度増加させることが必要である。したがっ
て、低熱膨張特性と良好な機械的特性とを同時に満足させるための最適な組成範
囲が決定される。【００３６】最後に第５の結果として固溶炭素量と含有炭素全量との関係は、従来は正の相
関をもって増減することが考えられていたが、本発明者らの実験結果によれば第
３図に示すように、固溶炭素量は全炭素量が増加するに伴って低下することが初
めて確認されている。【００３７】これは、全Ｃ量が高いと凝固初期に晶出する黒鉛量が増し、その近辺の固溶Ｃ
が安定な黒鉛になるサイトを提供する役目を果たすため、凝固終了時の固溶Ｃ量
が低減し、同時に炭化物となるＣが少なくなるものと考えられる。この第３図に
おける固溶Ｃ量と全Ｃ量との関係式を（８）式に示す。【００３８】［固溶Ｃ量］（％）＝０．６５−０．２０［全Ｃ量］（％）・・・・・（８）この（８）式の関係を（１）〜（７）式に代入することによって全炭素量（全
Ｃ量）と各特性値との関係式が導出される。【００３９】以上の実験結果から得た知見に基づいて本願発明に係る低熱膨張鋳鉄の成分組
成を決定した。【００４０】次に各元素の含有量の範囲およびその限定理由について、より詳細に説明する
。【００４１】まず炭素含有量は１〜３．５重量％、好ましくは１．２〜３重量％、さらに好
ましくは２．２〜２．３重量％に設定される。但し、鋳鉄中の炭素は黒鉛として
晶出した炭素と、鉄中に固溶した炭素とに分かれており、本発明の目的である鋳
造性、被削性、低熱膨張性を高めるためには、可及的に黒鉛晶出量を大きくして
固溶炭素量を小さくすることが要点となる。【００４２】本願発明に適用される鋳鉄中の全炭素量と固溶炭素量との一般的な関係は、第
３図および（８）式の例示から明らかであり、全炭素量を高める方が本発明の目
的に沿っている。【００４３】しかしながら、固溶炭素量と黒鉛晶出量は、鋳鉄材の機械的性質に大きな影響
を及ぼす。すなわち、ヤング率と全炭素量との関係は（６）式に（８）式を代入
して下記（９）式として得られる。【００４４】ヤング率（kgｆ／mm²）＝１９８２０−３９５０［全炭素量］（％）・・・・・（９）すなわち全炭素量を高めるとヤング率が低下することがわかる。【００４５】ところで、本発明材の適用対象製品としては工作機械、精密測定機器および成
形用金型などであるが、このような構造材として使用する場合には、ヤング率は
最低９０００kgｆ／mm²定礎の値が必要とされる。【００４６】したがって（９）式から必要とされる全炭素量は２．８％以下となる。またアルミニウム合金程度のヤング率でも使用可能な構造部材への適用を考慮すると、
全炭素量は３．５％まで上限値として拡大することができる。【００４７】さらに後述する各実施例の結果からも明らかなように全炭素量を１．２〜２．
８％の範囲に設定したときに、特に引張り強度などの機械的性質を損なうことな
く、低い熱膨張係数および優れた鋳造性、被削性および振動吸収能を同時に満足
する低熱膨張鋳鉄が得られる。このときの全炭素量の範囲に対応する固溶炭素量係る鋳鉄の低熱膨張性、鋳造性、被削性および振動吸収能等の要求特性を同時に
満足させる上で極めて重要である。従って、前述したとおり、本願発明に適用さ
れる鋳鉄に含有される炭素は全炭素量とは独立して、同時に固溶炭素としての含【００４８】また熱膨張係数と各合金元素との関係を（１）式と（８）式から下記（１０）
式のように導出することができる。【００４９】熱膨張係数（×１０^-6／℃）＝１４．９７−０．０２×［全Ｃ量］（％）＋１．４９×［Ｓｉ量］（％） −０．３２×［Ｎｉ量］（％） −０．７０×［Ｃｏ量］（％）＋１．３５×［Ｍｎ量］（％）・・・・・（１０）（１０）式から明らかなように全炭素量が大きいほど熱膨張係数が低い材料が
得られるため、全炭素量は可及的に高い値に設定することが望ましい。しかしな
がら、図３に示す結果から明らかなように全炭素量が３．５％を超えると、固溶
炭素が減少し、機械的強度が低下するとともに鋳造性が低下する。【００５０】一方、全炭素量の下限値について、黒鉛晶出性や熱膨張係数との関係から決定される。すなわち健全な黒鉛組成が得られる全炭素量の下限は約１％である。１
％未満であると凝固時における黒鉛核の生成が不十分となり、炭化物を形成し、
被削性を大きく損うこととなる。【００５１】そのため全炭素量は１％以上、３．５％以下、好ましくは２．０％以上、３．定される。【００５２】次にケイ素含有量は１．０％未満に設定される。（１０）式に示す関係式にお
いて、ケイ索量の係数が最も大きく、ケイ素量が熱膨張係数に及ぼす影響が大き
い。したがってケイ素量が低いほど、低い熱膨張係数が得られる。【００５３】ケイ素は黒鉛晶出促進のために必要な元素であるが、一般鋳鉄とは異なり本発
明に係る低熱膨張鋳鉄には、黒鉛化促進元素であるニッケルが３０％程度含有さ
れているため接種効果を発現する最少量、例えば０．３％以上添加されていれば
よいことが判明した。また接種剤として黒鉛粒子を使用すれば、ケイ素量は極微
量であっても十分な黒鉛組成が得られることが確認された。しかし通常の鋳造現
場においては鉄−ケイ素合金が接種剤として使用されており、この場合の添加量
は最大０．５％で十分である。【００５４】次にマンガンの含有量は１．０％以下に設定される。マンガンを添加すること
により図２に示す屈曲点Ｂが低温側に移行し、常温から２００℃までの実用温度
領域における熱膨張係数を低下させる効果がある。しかしケイ素と同様に含有量
が１．０％を超えると熱膨張係数を逆に増大させる。【００５５】そのため添加量は１．０％以下、好ましくは０．５％以下に設定される。【００５６】次にＮｉ含有量は２９〜３４％に設定される。Ｎｉ含有量が２９％未満または
３４％を超えるといずれも熱膨張係数が増大することになるため、上記範囲に設定される。【００５７】またＣｏ含有量は４〜８％の範囲に設定される。Ｃｏ含有量が４％未満である
と熱膨張係数が高くなる一方、８％を超えると図２に示す屈曲点が高温側に移行
することになり、常温から２００℃までの実用温度領域における熱膨張係数を増
大させることになる。【００５８】ここでＮｉ含有量およびＣｏ含有量の適正範囲は、前記炭素、ケイ素、マンガ
ンの含有量によって影響を受ける。熱膨張係数を極小とするＮｉ含有量は、実験
の結果、下記（１１）式によって与えられる。【００５９】極小点のＮｉ含有量（％）＝３５−０．２９×［Ｃｏ量］（％） −６．０［０．６５−０．２全Ｃ量］（％）＋０．５７［Ｍｎ量］（％）＋０．４５［Ｓｉ量］（％） ……（１１）ここで前述の理由により、全炭素量を１．５％、ケイ素量を０％、マンガン量
を０％とすると、極小点のＮｉ含有量（％）は下記（１２）式で与えられる。【００６０】極小点のＮｉ含有量（％）＝３３−０．２９×［Ｃｏ量］（％）・・・・・（１２）一方、ＮｉとＣｏとの合計含有量は、図２に示す熱膨張係数曲線における屈曲
点Ｂに対応する温度（屈曲点温度θ）と、その熱膨張係数値とに影響を及ぼす。
屈曲点温度θ以下の範囲では、熱膨張係数の温度変化は小さい一方、屈曲点温度
θを超える範囲では大きく上昇してしまう。【００６１】ここで屈曲点温度θと、ＮｉおよびＣｏの合計含有量との関係を実験により明
らかにした結果、下記（１３）式を得た。【００６２】屈曲点温度θ（℃）＝２２．５×［Ｎｉ量（％）＋Ｃｏ量（％）］ −６００．７・・・・・（１３）ここで例えば常温から約２００℃までの実用温度領域において使用するＣＦＲ
Ｐ用金型を適用対象にすると仮定し、屈曲点温度θを２００〜２５０℃に設定す
ると、ＮｉとＣｏとの合計含有量の適正範囲は下記（１４）式によって与えられ
る。【００６３】Ｎｉ量（％）＋Ｃｏ量（％）＝３６〜３８（％）・・・・・（１４）そして上記（１４）式および（１２）式との関係から、最適Ｎｉ量は２９〜３
３％、最適Ｃｏ量は４〜７％と算出され、この範囲に成分組成が設定される。【００６４】またマグネシウムは、黒鉛を球状化して晶出させるために必要な元素であり、
その含有量は０．１重量％以下に設定される。含有量は０．１％を超えると、炭
化物を形成するため好ましくない。したがってマグネシウム含有量は０．０４〜
０．１％の範囲が好ましい。【００６５】【実施例】次に本発明の実施例について図表を参照して説明する。【００６６】（実施例１）第４図，第５図に示すようなＣＦＲＰ用成形金型を鋳造した。【００６７】この金型は縦７０ｃｍ、横６５ｃｍ、厚さ６ｃｍ、重量１３０ｋｇである。溶
解は３００ｋｇ容量の高周波電気炉を用い、下記の表２に示す材料を溶解した。【００６８】【表２】成分組成は下記の表３に示すように、炭素２．０％、ケイ素０．１５％、マン
ガン０．０３％、ニッケル３０％、コバルト６％、マグネシウム０．０５％、残
部が不純物を含むオーステナイト系鋳鉄である。【００６９】また、１インチのキールブロック用砂鋳型にて試験片を採取し、各特性値を測
定した結果を表４に示す。表４において熱膨張係数は１．５×１０^-6／℃、引張
強さ４０ｋｇｆ／ｍｍ²、伸び２２％、ヤング率１２０００ｋｇｆ／ｍｍ²が得ら
れた。【００７０】この得られた金型はＣＦＲＰの予備成形体を２００℃で加熱しながらプレス成
形する工程に使用される。ＣＦＲＰの熱膨張係数は１．０〜１．５×１０^-6／℃
であるため、この係数値に近い本実施例の金型を使用することによりＣＦＲＰ製
品の寸法精度を大幅に向上することができた。また、本実施例の鋳鉄を工作機械
および精密測定機器の低熱膨張性が求められる構造部材へ適用したところ、同様
に製品の寸法精度を大幅に向上させることができた。【００７１】以上のように、本実施例の一般鋳鉄と同程度の鋳造性、被削性、機械的性質を
同時に満足し、かつインバー合金に近い低膨張係数を有する鋳鉄を本発明の工作機械、精密測定機器および成形用金型の低熱膨張性が求められる構造部材に適用
することによって、より高精度の加工品を得ることが可能となった。【００７２】（実施例２）表３に示すように、全Ｃ量を２．８％、Ｓｉ量を０．４％とした。この組成の
鋳鉄は振動吸収能を追及した場合のものである。すなわち全Ｃ量を２．８％と高
めることにより減衰能（Specific Damping Capacity）は１７％が得られ、一般
鋳鉄の４〜５倍の振動吸収能を示した。また、堅さがＨＢ１２５〜１３５程度と
なり、アルミニウム合金と同程度の軟かさを示した。この鋳鉄は、黒鉛による潤
滑効果と併せて、相手材を傷付けることなく接合や捕捉する治具部材として有用
であり、超高精度を要求される半導体、電子製造装置に使用したところ、性能を
大幅に向上させることができた。【００７３】以上のように、本実施例の一般鋳鉄（ＦＣ３０材）の４〜５倍の振動吸収能な
らびにアルミニウム合金並の軟かさを有する鋳鉄を本発明の半導体装置ならびに
電子製造装置の治具部材に適用することによって、より高性能で信頼性の高い装
置を提供することが可能となった。【００７４】（実施例３）表３に示すように、炭素含有量を１．２０％と低く設定した。他の成分は上記
実施例と近似させた。【００７５】この場合には微小ながら黒鉛晶出がみられ、表４に示すように、加工性は許容
できる範囲であった。【００７６】（実施例４）表３に示すように、シリコン含有量を０．９％と高く設定した。他の成分は上
記実施例と近似させた。【００７７】この場合は表４に示すように、熱膨張係数がやや高くなるが許容範囲内であっ
た。【００７８】（実施例５）表３に示すように、マンガン含有量を高めに０．９％に設定した。他の成分は
上記実施例と近似させた。【００７９】この場合は表４に示すように、熱膨張係数がやや高くなるが許容範囲内であっ
た。【００８０】（実施例６）表３に示すように、マンガン含有量を０．７％に設定した。他の成分は上記実
施例と近似させた。【００８１】この場合にも、熱膨張係数が許容範囲内となった。【００８２】なお、上記各実施例以外にも、本発明の範囲内で種々実施したところ、上記同
様に良好な特性が認められた。【００８３】（比較例１）表３に示すように、炭素含有量を０．７１％と極めて低く設定した。他の成分
は上記実施例と近似させた。【００８４】この場合には、表４に示すように、加工性、鋳造性および振動吸収能が悪い。【００８５】（比較例２）表３に示すように、炭素含有量を３．６％と高く設定した。他の成分は上記実
施例と近似させた。【００８６】この場合には表４に示すように、伸び、強度が低下し、また鋳造欠陥が多い。【００８７】（比較例３）表３に示すように、シリコン含有量を１．２％と高く設定した。他の成分は上
記実施例と近似させた。【００８８】この場合には表４に示すように、熱膨張係数が高過ぎる。【００８９】（比較例４）表３に示すように、ニッケル含有量を２８．０％と低く設定した。他の成分は
上記実施例と近似させた。【００９０】この場合には表４に示すように、熱膨張係数が高くなる。【００９１】（比較例５）表３に示すように、ニッケルの含有量を３７．０％と高くした。他の成分は上
記実施例と近似させた。【００９２】この場合には、表４に示すように、熱膨張係数が高くなる。【００９３】（比較例６）表３に示すように、コバルトの含有量を３．５％と低くした。他の含有量は上
記実施例と近似させた。【００９４】この場合には、表４に示すように、熱膨張係数が高くなる。【００９５】（比較例７）表３に示すように、コバルト含有量を８．２％と高くした。他の成分は上記実
施例と近似させた。【００９６】この場合は、表４に示すように、熱膨張係数が高くなる。【００９７】（比較例８）表３に示すように、ニッケルとコバルトとの合計含有量を４２．５％と高くし
た。他の成分は上記実施例と近似させた。【００９８】この場合は、表４に示すように、熱膨張係数が高くなる。【００９９】【表３】【０１００】【表４】【０１０１】【発明の効果】以上のように、本発明の工作機械、精密測定機器および成形用金型の構造部材
、ならびに半導体装置および電子製造装置の治具部材は、機械的強度を損なうこ
となく熱膨張係数が１．５〜３．０×１０^-6／℃の低熱膨張特性、ならびに一般
鋳鉄と同程度の鋳造性、被削性を有し、かつ必要に応じて一般鋳鉄の４〜５倍に
まで高めることができる振動吸収能、アルミニウム合金なみの軟かさを兼ね備え
た鋳鉄を適用しているため、機器の高精度化、高機能化に十分対応可能であり極
めて有用である。Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a low coefficient of thermal expansion and simultaneously has properties such as castability, machinability, and vibration absorption.
Machine tool using low-thermal-expansion cast iron satisfying the requirements for structural members requiring low-thermal-expansion
, Precision measuring instruments and molding dies, and semiconductor devices and
And electronic manufacturing equipment. [0002] As is well known, cast iron is widely used as a basic material in industry. The reason is
The castability of this material is good, it can be molded even in a variety of complicated shapes,
Ease of use, relatively low cost of material processing and melting,
This is because it has advantages such as easy production. Meanwhile, recently, various organic and inorganic materials other than metals, including new materials, have been developed.
Have been developed, and functional materials utilizing their respective characteristics are rapidly spreading. Especially
With the development of the electronics industry, related machine tools, precision measuring instruments,
Molds for molding, scientific equipment, other manufacturing machinery, semiconductor devices, and electronic manufacturing equipment
Have required materials with higher precision and better function. [0004] In cast iron, in addition to the conventional materials and characteristics for meeting the above requirements, thermal expansion
The one with reduced coefficient, increased vibration absorption capacity, and added heat resistance and corrosion resistance
Is being developed. A typical example is invar cast iron (36.5% Ni-Fe).
Alloy) or its improved material Niresist D5 (ASTM A439 type D-5)
) It is cast iron. The chemical components of typical examples of these cast irons are shown in Table 1 below. [Table 1] Invar has 34-37% of nickel in iron
And ) Contained, the coefficient of thermal expansion around normal temperature (0 to 200 ° C)
Is 1.5 × 10 ^-6 / ° C. The low expansion machine of this Invar alloy
The structure is based on the spontaneous volume magnetostriction effect generally called the “Invar effect”.
You. [0006] Also, Super Invar alloys 4-6% cobalt in iron nickel substrate.
It was prepared and had a coefficient of thermal expansion of about 0.5 × 10 ^-6 / ℃ and b
It has excellent properties that are even lower than the members. [0007] However, both the above-mentioned Invar and Super Invar have castability and machinability.
Low practicality and vibration absorption capacity, it has been put to practical use only in a very narrow field.
Absent. Further, cast iron-based low expansion materials as shown in columns Nos. 3, 4, and 5 in Table 1 have been developed and put into practical use.
I have. For example, Niresist D5 has carbon and silicon equivalent to general-purpose ductile cast iron.
Is formed by alloying 34-36% of nickel in manganese-containing iron.
By alloying the same amount of nickel as Invar in cast iron with a lead structure,
While maintaining the castability, machinability, and vibration proof properties of iron, it also has heat resistance and corrosion resistance.
In addition, it is provided with a low expansion property by an "invar effect". As a similar material, nobinite cast iron is disclosed in Japanese Patent Publication No. 60-51547.
Have been. This alloy cast iron contains the same amount as Super Invar in general-purpose ductile cast iron.
Castability, machinability and low expansion by alloying nickel and cobalt
It is configured to have both. [0010] However, the Niresist D5 and the nobinite cast iron are used in general-purpose
Containing carbon, silicon, and manganese at the same level as cast iron.
The low expansion property of the Perinbar is impaired. That is, according to actual measurement by the inventors of the present application, each of the thermal expansion coefficients is 5 × 10 ^-6 / ℃, 4 × 10 ^-6 / ℃ and large value
It has become. However, in the above cast iron alloy, there has been a demand for further reduction of the coefficient of thermal expansion in recent years.
Inadequate response to recent precision equipment, high precision, mold materials for FRP, etc.
Therefore, a material having a low coefficient of thermal expansion is required. In order to meet the above demand, the inventors of the present application have made the thermal expansion coefficient of the conventional 4 × 10 ^-6 / ℃
In order to provide a material that is less than JIS and has both castability, machinability and vibration absorption
The relationship between the content of each alloying element and the coefficient of thermal expansion and mechanical properties has been
And a statistical analysis method to discover a new low thermal expansion cast iron.
268249. The low thermal expansion cast iron has a composition shown in the lowermost column of Table 1. I.e. austenia
In cast iron with base iron, the composition of carbon is 1.0% or more and 3.5% or less.
, Silicon 1.5% or less, nickel 32% or more and 39.5% or less, cobalt 1.0%
Not less than 4% and the total content of nickel and cobalt is 41% or less.
By using cast iron, (1) the coefficient of thermal expansion is 2 × 10 ^-6 (2) Low thermal expansion with excellent castability, machinability, vibration absorption and mechanical strength
We have found for the first time that we can provide materials. That is, as a result of repeating various experiments, the inventors of the present invention have found that 1 to 3.5% carbon,
In addition to adding 1 to 4% cobalt to cast iron containing 32 to 39.5% nickel,
When the addition amount of iodine is set to 1.5% or less, preferably 1% or less, the thermal expansion
It was discovered that cast iron with a very small number and good castability and workability could be obtained.
Was. With the development of this low expansion cast iron, it has become possible to provide processed products such as machine tools, precision measuring instruments and molding dies with higher precision. [0016] However, as the size and precision of equipment have been further advanced, conventional low thermal expansion cast iron has been used.
However, some situations are not being met. For example, communication technologies such as satellite broadcasting in recent years
Parabolic antennas used in the transmitting and receiving equipment have become very large
In addition to its low thermal expansion, its processing accuracy, that is, castability, machinability, vibration absorption capability, etc.
Extremely high mechanical strength and mechanical strength are required. For example, antenna reflection
The body is made of carbon fiber reinforced plastic (CF) having high rigidity and corrosion resistance.
RP) is generally employed. However, the thermal expansion coefficient of this CFRP is about 1.
5 × 10 ^-6 / ° C, which ensures extremely high dimensional accuracy even after molding.
Molds must be made of materials with similar thermal expansion coefficients.
There is. Therefore, the thermal expansion coefficient is smaller than that of the conventional one, and is at least 1
. 5 × 10 ^-6 The molding die is made of a material that is less than / ° C and has excellent mechanical properties.
It is mandatory to do. The present invention has been made to solve the above-mentioned problems, and has been made in consideration of a machine tool, a precision measuring machine, and the like.
For fixed equipment and molding die materials, and for semiconductor devices and electronic manufacturing equipment
Possesses even more excellent castability, machinability and vibration absorption capacity, and has a coefficient of thermal expansion
4 × 10 in the range of operating temperature 0 to 200 ° C. ^-6 / ° C or less, preferably 3 × 10
^-6 / ° C or lower, more preferably 1.5 × 10 ^-6 / ℃ or less
Application of low-thermal-expansion cast iron that simultaneously satisfies properties to structural members that require low-thermal-expansion properties
Machine tools, precision measuring instruments and molding dies, and jig members
It is an object of the present invention to provide a semiconductor device and an electronic manufacturing device. Means for Solving the Problems and Actions The present invention focuses on “solid solution carbon” for the first time from the above viewpoints, and then focuses on castability and machinability.
Components that graphite can crystallize into the alloy structure during the casting process to improve
The above object has been achieved by finding out the conditions through a number of experimental analyzes and at the same time finding the optimum component conditions for obtaining low thermal expansion. That is, the machine tool, precision measuring device, molding die, and
Semiconductor devices and electronic manufacturing equipment have a graphite structure in austenitic base iron. 4% or more and 8% or less, the balance being iron, and thermal expansion in the temperature range of 0 to 200 ° C.
Tension coefficient is 4 × 10 ^-6 / C is low thermal expansion cast iron is required to have low thermal expansion characteristics.
It is characterized by being applied to structural members. Preferably, manganese is added in an amount of 1.0% or less, preferably 0% or less, in addition to the above component composition.
. Cast iron containing 5% or less and magnesium of 0.1% or less
. The above composition ranges were obtained for the first time through various experiments and analysis by the inventors.
It is set based on the following crystal obtained. First, as a first result, the relationship between the coefficient of thermal expansion and the content of each element was determined.
The relations of equations (1) and (2) were obtained. Thermal expansion coefficient (× 10 ^-6 / ° C) = 14.905 + 0.1 [Solute C content] (%) +1.49 x [Si content] (%)-0.32 x [Ni content] (%)-0.70 x [Co content] (%) + 1.35 × [Mn amount] (%) (1) Thermal expansion coefficient (× 10 ^-6 /°C)=−2.14+1.75 [Solute C content] (%) + 2.11 × [Si content] (%) + 0.14 × [Ni content] (%) + 0.28 × [Co content] ( %) + 0.25 × [Mn amount] (%) (2) By the way, the relationship between the coefficient of thermal expansion of the Fe—Ni-based alloy and the amount of Ni is as shown in FIG.
In addition, the thermal expansion coefficient becomes extremely small when the Ni content is about 36%. Therefore, equation (1)
Is the coefficient of thermal expansion of each alloy element in the region where the Ni content is lower than the minimum point of the coefficient of thermal expansion.
It is a relational expression obtained as a result of the analysis for this. On the other hand, equation (2) indicates the thermal expansion coefficient of each alloy element in the region where the Ni content is higher than the minimum point.
This is a relational expression obtained by analyzing numbers. Comparing each coefficient in the above equations (1) and (2), the coefficient of the Si amount (%) is
The largest. In other words, the silicon content is the largest in the thermal expansion characteristics with a positive correlation
It turns out to have an effect. Therefore, a lower coefficient of thermal expansion can be obtained by minimizing the amount of silicon.
It can be understood that it is done. Regarding the effect of the carbon content of the Fe—Ni alloy on the coefficient of thermal expansion,
Conventionally, it was thought that the total amount of carbon contained had a great effect. However,
According to the experiments of the light people, it is not the total carbon content that affects, but a solid solution
The fact that it was only carbon content was discovered. [0027] The amount of silicon and the amount of solute carbon are reduced to predetermined ranges to thereby reduce heat.
It has been found for the first time that the expansion properties can be further improved. Next, as a second result, when the total content of Ni and Co is changed,
As shown in FIG. 2, the relationship between the temperature and the thermal expansion coefficient depends on the ratio of each Ni + Co amount.
The bending point B at which the temperature dependence of the thermal expansion coefficient rises suddenly appears, and the bending point B
(Hereinafter referred to as the inflection point temperature) changes to a higher temperature side.
You. That is, as is apparent from FIG. 2, as the Ni + Co amount increases, the inflection point temperature increases.
The temperature shifts to the high temperature side, and as a result, the thermal expansion occurs in a practical temperature range from room temperature to 200 ° C.
The tension coefficient increases. Conversely, the inflection point temperature is 325 ° C or less, preferably 200 to 25 ° C.
When the component composition is set to be 0 ° C., the temperature falls within the practical temperature range (0 to 200 ° C.).
Thus, a low coefficient of thermal expansion can be obtained. The present inventors have determined by experiment the relationship between the inflection point temperature and the amount of each element, and obtained the following (3)
I got the formula. Inflection point temperature (° C.) = 22.5 × [Ni (%) + Co (%)] − 22 × Mn (%)-600.3 (3) Mn is added according to the formula (3). Shifts the inflection point temperature to a lower temperature region
It was found that it is possible to cause Next, as a third result, by reducing the amount of solute carbon and the amount of carbide,
Improves formability and cutting workability, and can further increase vibration absorption capacity
It has been found. That is, carbon other than solid solution carbon exists as graphite or carbide. Sou
That is, the larger the amount of graphite crystallization, the smaller the shrinkage cavities during casting and the lower the machinability, that is,
Good machinability and high vibration absorption capacity. On the other hand, if carbides precipitate,
Conversely, it becomes a cause of the formation of micro-cavities, and the machinability also worsens. Therefore, solid solution as much as possible
It is important to reduce the C content and the amount of carbide precipitation and increase the amount of graphite crystallization. Further, as a fourth result, the relational expression between the amount of dissolved carbon and the mechanical strength is expressed by the following formulas (4) to (4).
7) It was obtained according to the formula. [0035] Tensile strength (kgf / mm ^Two ) = 19.6 + 93 [Solute C content] (%) (4) Strength (kgf / mm) ^Two ) = 4.8 + 135.5 [Solute C content] (%) (5) Young's modulus (kgf / mm) ^Two ) = 6982.5 + 19750 [dissolved C amount] (%) (6) Hardness (HB) = 128.6 + 133 [dissolved C amount] (%) (7) From the formulas (1) and (2), in order to lower the coefficient of thermal expansion, the amount of solute C should be reduced.
It is desirable that the mechanical strength be improved as is clear from the above equations (4) to (7).
In order to increase the amount, it is necessary to increase the amount of solid solution C to some extent. Accordingly
The optimal composition range to satisfy low thermal expansion characteristics and good mechanical characteristics at the same time
The enclosure is determined. Finally, as a fifth result, the relationship between the amount of solute carbon and the total amount of carbon contained is conventionally a positive phase.
Was thought to increase or decrease with the function, but according to the experimental results of the present inventors,
As shown in Fig. 3, the amount of solute carbon initially decreases with increasing total carbon.
Has been confirmed. [0037] This is because if the total C content is high, the amount of graphite crystallized in the early stage of solidification increases, and the solid solution C
At the end of solidification to serve as a site to provide stable graphite
It is considered that C is reduced, and at the same time, C, which becomes carbide, is reduced. In this FIG.
Equation (8) shows a relational expression between the amount of solid solution C and the total amount of C in the alloy. [Solute C content] (%) = 0.65-0.20 [Total C content] (%) (8) The relationship of this equation (8) is expressed by (1) to (7). ) To give the total carbon content (total
The relational expression between (C amount) and each characteristic value is derived. Based on the knowledge obtained from the above experimental results, the component set of the low thermal expansion cast iron according to the present invention
Was decided. Next, the range of the content of each element and the reason for limiting the content will be described in more detail.
. First, the carbon content is 1 to 3.5% by weight, preferably 1.2 to 3% by weight, more preferably
Preferably, it is set to 2.2 to 2.3% by weight. However, carbon in cast iron is graphite
It is divided into crystallized carbon and carbon dissolved in iron.
In order to improve formability, machinability and low thermal expansion, increase the amount of graphite crystallization as much as possible.
The key point is to reduce the amount of solute carbon. The general relationship between the total carbon content and the solute carbon content in cast iron applied to the present invention is as follows:
It is clear from FIG. 3 and the exemplification of the equation (8) that it is an object of the present invention to increase the total carbon content.
It is along. However, the amount of dissolved carbon and the amount of graphite crystallization greatly affect the mechanical properties of cast iron.
Effect. That is, the relationship between the Young's modulus and the total carbon content is obtained by substituting equation (8) into equation (6).
Then, the following equation (9) is obtained. Young's modulus (kgf / mm ^Two ) = 19820-3950 [total carbon content] (%) (9) That is, it can be seen that the Young's modulus decreases as the total carbon content increases. The products to which the material of the present invention is applied include machine tools, precision measuring instruments and components.
Although it is a molding die, when used as such a structural material, the Young's modulus
9000kgf / mm minimum ^Two A cornerstone value is required. Therefore, the total amount of carbon required from the equation (9) is 2.8% or less. In addition, considering application to structural members that can be used even with a Young's modulus of aluminum alloy,
The total carbon content can be expanded up to 3.5% as an upper limit. Further, as is clear from the results of each of the examples described later, the total carbon content is set to 1.2 to 2.
When set in the range of 8%, mechanical properties such as tensile strength are not particularly impaired.
Low thermal expansion coefficient and excellent castability, machinability and vibration absorption at the same time
Low thermal expansion cast iron is obtained. The amount of solute carbon corresponding to the range of total carbon at this time The required properties such as low thermal expansion, castability, machinability and vibration absorption of the cast iron
It is extremely important for satisfaction. Therefore, as described above, the present invention is applied to the present invention.
The carbon content of cast iron is independent of the total carbon content and at the same time Further, the relationship between the coefficient of thermal expansion and each alloying element is calculated from the equations (1) and (8) as follows:
It can be derived as in the equation. Thermal expansion coefficient (× 10 ^-6 / ° C) = 14.97-0.02 x [total C amount] (%) + 1.49 x [Si amount] (%)-0.32 x [Ni amount] (%)-0.70 x [Co Amount] (%) + 1.35 × [Mn amount] (%) (10) As is clear from the equation (10), the larger the total carbon amount, the lower the thermal expansion coefficient of the material.
Therefore, it is desirable to set the total carbon content to a value as high as possible. But
However, as is apparent from the results shown in FIG. 3, when the total carbon content exceeds 3.5%, solid solution
The amount of carbon decreases, the mechanical strength decreases, and the castability decreases. On the other hand, the lower limit of the total carbon amount is determined from the relationship with the crystallinity of graphite and the coefficient of thermal expansion. That is, the lower limit of the total amount of carbon for obtaining a sound graphite composition is about 1%. 1
%, The formation of graphite nuclei during solidification becomes insufficient, forming carbides,
Machinability will be greatly impaired. Therefore, the total carbon content is 1% or more and 3.5% or less, preferably 2.0% or more. Is determined. Next, the silicon content is 1.0 Set to less than%. (10)
The coefficient of silicon cord is the largest, and the influence of silicon on the coefficient of thermal expansion is large.
No. Therefore, the lower the silicon content, the lower the coefficient of thermal expansion. Silicon is an element necessary for accelerating graphite crystallization, but unlike ordinary cast iron, silicon
The low thermal expansion cast iron according to Ming contains about 30% nickel, which is a graphitization promoting element.
As a result, if it is added in the minimum amount that expresses the inoculation effect, for example, 0.3% or more,
It turned out to be good. If graphite particles are used as an inoculant, the amount of silicon
It was confirmed that a sufficient graphite composition could be obtained even with the amount. But normal casting
In the field, iron-silicon alloy is used as an inoculant, in which case the amount added
0.5% at the maximum is sufficient. Next, the content of manganese is 1.0 % Or less. Adding manganese
As a result, the bending point B shown in FIG. 2 shifts to the low temperature side, and the practical temperature from normal temperature to 200 ° C.
This has the effect of lowering the thermal expansion coefficient in the region. But like silicon, the content
But 1.0 %, The coefficient of thermal expansion increases. Therefore, the amount of addition 1.0 %, Preferably 0.5% or less. Next, the Ni content is set to 29 to 34%. Ni content is less than 29% or
If it exceeds 34%, the coefficient of thermal expansion will increase in any case, so it is set in the above range. The Co content is set in the range of 4 to 8%. Co content is less than 4%
When the coefficient of thermal expansion is higher than 8%, the bending point shown in FIG.
Increase the coefficient of thermal expansion in the practical temperature range from room temperature to 200 ° C.
Will make it bigger. Here, the appropriate ranges of the Ni content and the Co content are determined based on the carbon, silicon, and manganese described above.
Is affected by the content of The Ni content that minimizes the thermal expansion coefficient is
Is given by the following equation (11). Ni content at minimum point (%) = 35−0.29 × [Co amount] (%) − 6.0 [0.65-0.2 Total C amount] (%) + 0.57 [Mn] Amount] (%) +0.45 [Si amount] (%) (11) Here, for the reasons described above, the total carbon amount is 1.5%, the silicon amount is 0%, and the manganese amount is
Is 0%, the Ni content (%) at the minimum point is given by the following equation (12). Ni content at minimum point (%) = 33−0.29 × [Co amount] (%) (12) On the other hand, the total content of Ni and Co is shown in FIG. Bending in the coefficient of thermal expansion curve
The temperature corresponding to the point B (the bending point temperature θ) and its thermal expansion coefficient value are affected.
In the range below the inflection point temperature θ, the temperature change of the coefficient of thermal expansion is small,
In a range exceeding θ, the temperature greatly increases. Here, the relationship between the inflection point temperature θ and the total content of Ni and Co was clarified by experiments.
As a result, the following equation (13) was obtained. Bending point temperature θ (° C.) = 22.5 × [Ni content (%) + Co content (%)] −600.7 (13) Here, for example, practical use from normal temperature to about 200 ° C. CFR used in the temperature range
Assuming that the mold for P is to be applied, the bending point temperature θ is set to 200 to 250 ° C.
Then, the appropriate range of the total content of Ni and Co is given by the following equation (14).
You. Ni content (%) + Co content (%) = 36 to 38 (%) (14) From the relationship with the above formulas (14) and (12), the optimum Ni content is 29 to 3
3% and the optimal Co amount are calculated to be 4 to 7%, and the component composition is set in this range. Magnesium is an element necessary for spheroidizing and crystallizing graphite.
Its content is set to 0.1% by weight or less. If the content exceeds 0.1%, charcoal
Is not preferred because it forms oxides. Therefore, the magnesium content is 0.04 to
A range of 0.1% is preferred. Next, examples of the present invention will be described with reference to the drawings. Example 1 A molding die for CFRP as shown in FIGS. 4 and 5 was cast. This mold has a length of 70 cm, a width of 65 cm, a thickness of 6 cm, and a weight of 130 kg. Dissolution
For the solution, a material shown in Table 2 below was melted using a high-frequency electric furnace having a capacity of 300 kg. [Table 2] As shown in Table 3 below, the component composition was 2.0% for carbon, 0.15% for silicon,
0.03% gun, 30% nickel, 6% cobalt, 0.05% magnesium, balance
The part is austenitic cast iron containing impurities. A test piece was sampled with a 1-inch keel block sand mold, and each characteristic value was measured.
The results are shown in Table 4. In Table 4, the coefficient of thermal expansion is 1.5 × 10 ^-6 / ℃, tensile
Strength 40kgf / mm ^Two , Elongation 22%, Young's modulus 12000kgf / mm ^Two Got
Was. The obtained mold was press-formed while heating the CFRP preform at 200 ° C.
Used for shaping process. The coefficient of thermal expansion of CFRP is 1.0 to 1.5 × 10 ^-6 / ℃
Therefore, by using the mold of this embodiment close to this coefficient value,
The dimensional accuracy of the product was greatly improved. Further, the cast iron of this embodiment is
When applied to structural members that require low thermal expansion of precision measurement equipment,
In addition, the dimensional accuracy of the product was greatly improved. As described above, the same castability, machinability and mechanical properties as those of the general cast iron of the present embodiment were obtained.
At the same time, cast iron that is satisfied and has a low expansion coefficient close to that of Invar alloy is applied to the machine tool of the present invention, precision measuring equipment and structural members requiring low thermal expansion of molding dies.
By doing so, it became possible to obtain a more accurate processed product. Example 2 As shown in Table 3, the total C amount was 2.8% and the Si amount was 0.4%. Of this composition
Cast iron is for the purpose of pursuing the vibration absorbing ability. That is, the total C amount is as high as 2.8%.
The damping capacity (Specific Damping Capacity) is 17%.
It showed 4 to 5 times the vibration absorption capacity of cast iron. Also, the hardness is about HB125-135
And showed the same degree of softness as the aluminum alloy. This cast iron is lubricated by graphite.
Useful as a jig member for joining and capturing without damaging the mating material in addition to the lubrication effect
When used in semiconductors and electronic manufacturing equipment that require ultra-high accuracy,
It could be greatly improved. As described above, the vibration absorption capacity of the general cast iron (FC30 material) of this embodiment is four to five times that of the general cast iron (FC30 material).
In addition to cast iron having the same softness as aluminum alloy, the semiconductor device of the present invention and
By applying to jig members of electronic manufacturing equipment, higher performance and higher reliability
Can be provided. Example 3 As shown in Table 3, the carbon content was set as low as 1.20%. Other ingredients are above
This was approximated to the example. In this case, graphite crystallization was observed in a small amount, and as shown in Table 4, the workability was acceptable.
It was within the range I could do. Example 4 As shown in Table 3, the silicon content was set as high as 0.9%. Other ingredients are above
This was approximated to the example. In this case, as shown in Table 4, the coefficient of thermal expansion slightly increased, but was within the allowable range.
Was. Example 5 As shown in Table 3, the manganese content was set to 0.9%, which was higher. Other ingredients
Similar to the above embodiment. In this case, as shown in Table 4, the coefficient of thermal expansion slightly increased, but was within the allowable range.
Was. Example 6 As shown in Table 3, the manganese content was set to 0.7%. The other ingredients are
It was made similar to the example. Also in this case, the coefficient of thermal expansion was within the allowable range. In addition, in addition to the above embodiments, various implementations within the scope of the present invention resulted in the same.
Good characteristics were observed. Comparative Example 1 As shown in Table 3, the carbon content was set as extremely low as 0.71%. Other ingredients
Was approximated to the above example. In this case, as shown in Table 4, workability, castability, and vibration absorbing ability are poor. Comparative Example 2 As shown in Table 3, the carbon content was set as high as 3.6%. The other ingredients are
It was made similar to the example. In this case, as shown in Table 4, elongation and strength are reduced, and there are many casting defects. Comparative Example 3 As shown in Table 3, the silicon content was set as high as 1.2%. Other ingredients are above
This was approximated to the example. In this case, as shown in Table 4, the coefficient of thermal expansion is too high. Comparative Example 4 As shown in Table 3, the nickel content was set as low as 28.0%. Other ingredients
Similar to the above embodiment. In this case, as shown in Table 4, the thermal expansion coefficient increases. Comparative Example 5 As shown in Table 3, the content of nickel was increased to 37.0%. Other ingredients are above
This was approximated to the example. In this case, as shown in Table 4, the thermal expansion coefficient increases. Comparative Example 6 As shown in Table 3, the content of cobalt was reduced to 3.5%. Other content is above
This was approximated to the example. In this case, as shown in Table 4, the coefficient of thermal expansion increases. Comparative Example 7 As shown in Table 3, the cobalt content was increased to 8.2%. The other ingredients are
It was made similar to the example. In this case, as shown in Table 4, the thermal expansion coefficient increases. Comparative Example 8 As shown in Table 3, the total content of nickel and cobalt was increased to 42.5%.
Was. Other components were similar to those in the above example. In this case, as shown in Table 4, the thermal expansion coefficient increases. [Table 3] [Table 4] As described above, the structural members of the machine tool, precision measuring device, and molding die of the present invention are as described above.
, And jig members of semiconductor devices and electronic manufacturing equipment may impair mechanical strength.
Coefficient of thermal expansion is 1.5 to 3.0 × 10 ^-6 / ° C low thermal expansion characteristics and general
Has the same castability and machinability as cast iron, and if necessary, 4 to 5 times that of general cast iron
Combines vibration absorption capacity that can be increased to as high as aluminum alloy and softness
Since cast iron is used, it is possible to cope with higher precision and higher functionality of the equipment.
Very useful.

【図面の簡単な説明】【図１】Ｎｉ含有量と熱膨張係数との関係を示す図である。【図２】Ｎｉ鋳鉄におけるＮｉとＣｏとの合計量をパラメータとし、温度と熱膨張係数
との関係を示す図である。【図３】実施例１の組成における全炭素量と固溶炭素量との関係を示す図である。【図４】実施例１で鋳造したＣＦＲＰ成型用金型の形状を示す平面図である。【図５】図４におけるIVｂ−IVｂ矢視断面図である。BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the relationship between the Ni content and the coefficient of thermal expansion. FIG. 2 is a diagram showing the relationship between temperature and coefficient of thermal expansion using the total amount of Ni and Co in Ni cast iron as a parameter. FIG. 3 is a graph showing the relationship between the total carbon content and the solute carbon content in the composition of Example 1. 4 is a plan view showing a shape of a CFRP molding die cast in Example 1. FIG. FIG. 5 is a sectional view taken along the line IVb-IVb in FIG. 4;

Claims

Claims: 1. A cast iron having a graphite structure in austenitic matrix iron. Element containing less than 1.0 % element, less than 29% nickel and less than 34% nickel, more than 4% and less than 8% cobalt, the balance being iron, having a coefficient of thermal expansion of 4 × 10 ⁻⁶ in a temperature range of 0 to 200 ° C.
A machine tool characterized in that low-thermal-expansion cast iron of not more than / ° C is applied to a structural member requiring low-thermal expansion. 2. The machine tool according to claim 1, wherein the low-thermal-expansion cast iron contains, as components, 1.0 % or less of manganese and 0.1% or less of magnesium. 3. A cast iron having a graphite structure in austenitic base iron, Element containing less than 1.0 % element, less than 29% nickel and less than 34% nickel, more than 4% and less than 8% cobalt, the balance being iron, having a coefficient of thermal expansion of 4 × 10 ⁻⁶ in a temperature range of 0 to 200 ° C.
A precision measuring instrument characterized in that low-thermal-expansion cast iron having a temperature of / ° C or lower is applied to structural members requiring low-thermal-expansion properties. 4. The precision measuring instrument according to claim 3, wherein said low thermal expansion cast iron contains 1.0 % or less of manganese and 0.1% or less of magnesium as a component composition. 5. A cast iron having a graphite structure in austenitic matrix iron, Element containing less than 1.0 % element, less than 29% nickel and less than 34% nickel, more than 4% and less than 8% cobalt, the balance being iron, having a coefficient of thermal expansion of 4 × 10 ⁻⁶ in a temperature range of 0 to 200 ° C.
A molding die, wherein low-thermal-expansion cast iron having a temperature of / ° C or lower is applied to a structural member requiring low-thermal-expansion properties. 6. The molding die according to claim 5, wherein said low thermal expansion cast iron contains 1.0 % or less of manganese and 0.1% or less of magnesium as a component composition. 7. A cast iron having a graphite structure in austenitic matrix iron, Element containing less than 1.0 % element, less than 29% nickel and less than 34% nickel, more than 4% and less than 8% cobalt, the balance being iron, having a coefficient of thermal expansion of 4 × 10 ⁻⁶ in a temperature range of 0 to 200 ° C.
A semiconductor device characterized in that low thermal expansion cast iron having a temperature of / ° C. or lower is applied as a jig member. 8. The semiconductor device according to claim 7, wherein said low thermal expansion cast iron contains 1.0 % or less of manganese and 0.1% or less of magnesium as a component composition. 9. A cast iron having a graphite structure in austenitic matrix iron, Element containing less than 1.0 % element, less than 29% nickel and less than 34% nickel, more than 4% and less than 8% cobalt, the balance being iron, having a coefficient of thermal expansion of 4 × 10 ⁻⁶ in a temperature range of 0 to 200 ° C.
An electronic manufacturing apparatus, wherein low thermal expansion cast iron having a temperature of / ° C. or less is used as a jig member. 10. The low thermal expansion cast iron has a manganese content of 1.0 % or less as a component composition,
The electronic manufacturing apparatus according to claim 9, comprising 0.1% or less of magnesium.