JP4193958B2 - Molten metal member having excellent corrosion resistance against molten metal and method for producing the same - Google Patents
Molten metal member having excellent corrosion resistance against molten metal and method for producing the same Download PDFInfo
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- JP4193958B2 JP4193958B2 JP2000126492A JP2000126492A JP4193958B2 JP 4193958 B2 JP4193958 B2 JP 4193958B2 JP 2000126492 A JP2000126492 A JP 2000126492A JP 2000126492 A JP2000126492 A JP 2000126492A JP 4193958 B2 JP4193958 B2 JP 4193958B2
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- 229910045601 alloy Inorganic materials 0.000 claims description 67
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- 229910052804 chromium Inorganic materials 0.000 claims description 24
- 229910052742 iron Inorganic materials 0.000 claims description 23
- 229910052796 boron Inorganic materials 0.000 claims description 16
- 238000000034 method Methods 0.000 claims description 14
- 239000011230 binding agent Substances 0.000 claims description 12
- 229910052758 niobium Inorganic materials 0.000 claims description 10
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 9
- 229910052715 tantalum Inorganic materials 0.000 claims description 9
- 229910052719 titanium Inorganic materials 0.000 claims description 9
- 229910052726 zirconium Inorganic materials 0.000 claims description 9
- 229910052735 hafnium Inorganic materials 0.000 claims description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 7
- 229910052760 oxygen Inorganic materials 0.000 claims description 7
- 239000001301 oxygen Substances 0.000 claims description 7
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- 230000001590 oxidative effect Effects 0.000 claims description 6
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- 150000002739 metals Chemical class 0.000 claims description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 37
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- 239000011651 chromium Substances 0.000 description 27
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- 238000006243 chemical reaction Methods 0.000 description 3
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- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
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Description
【０００１】
【発明の属する技術分野】
本発明は溶融金属に対する耐食性に優れた溶融金属用部材およびその製造方法に関する。より詳細には、溶融金属と直接接触する部材において、部材の表面に酸化物を形成することにより、溶融金属に対する耐食性が大幅に向上した溶融金属用部材およびその製造方法に関する。
【０００２】
【従来の技術】
溶融金属と直接接触して用いられる部材の代表的なものとして、ダイカストマシン部品用の部材がある。ダイカストマシンはプランジャー、スリーブ、成形金型で構成され、溶融状態にある金属、例えば、アルミニウム、亜鉛、マグネシウム等と直接接触して使用される。このため、これらの部品に共通して要求される特性としては、溶融金属に侵食（溶損）されない、反応層を形成しないなどといった溶融金属に対する耐食性、耐摩耗性、および耐熱疲労性などがある。従来、これらの部品に用いる部材として工具鋼や熱間工具鋼（ＳＫＤ６１など）が使用されていたが、溶融金属に対する耐食性が十分でないため、寿命が短い問題があった。
【０００３】
そこで、高硬度および高強度を有していることに加えて、溶融金属に対して優れた耐食性を示すＭｏ2ＦｅＢ2型複硼化物系硬質焼結合金（特公昭６０−５７４９９号公報）をダイカスト部品に適用したところ、大幅な寿命延長を得ることができた。しかし、この部材を長時間使用した場合、部材の金属結合相と溶融金属との反応が進行し、耐食性や離型性が低下する問題が生じることが判明した。
近年、溶融金属に対する耐食性や離型性を改善するため、部材表面にアルミナ、ジルコニア等のセラミックスの溶射皮膜を形成させる試みがなされている。しかしながら、これらの溶射皮膜においてはヒートチェック、ヒートクラック等の亀裂や剥離が生じやすく、期待するほどの耐久性の向上は得られていない。
【０００４】
また、特開平５−１４８５８８号公報や特開平９−２１７１６７号公報は、鋼、鋳鉄、およびステンレス鋼表面に酸化皮膜を設けることにより、部材の耐食性の改善が図ることを開示している。しかし、形成された酸化皮膜は部材との密着性が弱く、かつ非常に薄く、硬度が低いなどの問題があり、耐摩耗性強度が必要となるプランジャー、スリーブには適用できない。
【０００５】
【発明が解決しようとする課題】
本発明においては、上記のＭｏ2ＦｅＢ2型複硼化物系硬質焼結合金の溶融金属に対する耐食性、および離型性を改善し、極めて優れた耐久性を示す硬質焼結合金を開発することにより、溶融金属に対し極めて優れた耐食性、離型性を有し、かつ熱疲労特性、機械的特性、耐摩耗性にも優れる溶融金属用部材およびその製造方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
請求項１に記載の、溶融金属に対する耐食性に優れた溶融金属用部材は、
３〜７．５重量％（以下、重量％を％で示す）のＢ、２１〜７９．９％のＭｏ、２〜３０％のＣｒ、残部が１０％以上のＦｅおよび不可避的不純物からなる硬質焼結合金部材の、溶融金属と直接接触する表面に酸化皮膜を形成してなる溶融金属用部材であって、
前記硬質焼結合金部材が、Ｍｏ2ＦｅＢ2型複硼化物とＦｅ基結合相とからなり、
前記酸化皮膜が、Ｍｏ、Ｃｒ、Ｆｅ、Ｂの金属元素と酸素を主体とする（Ｆｅ，Ｍｏ，Ｃｒ，Ｂ）ｍＯｎ型の複合酸化物からなる皮膜であることを特徴とする。
請求項２に記載の、溶融金属に対する耐食性に優れた溶融金属用部材は、請求項１において、硬質焼結合金の全組成に対して、０．１〜８％のＭｎを含有することを特徴とする。請求項３に記載の、溶融金属に対する耐食性に優れた溶融金属用部材は、請求項１又は２において、硬質焼結合金の全組成に対して、希土類元素の中から選ばれた１種または２種以上を、合計で０．０１〜５％含有することを特徴とする。
請求項４に記載の、溶融金属に対する耐食性に優れた溶融金属用部材は、請求項１〜３のいずれかにおいて、硬質焼結合金の全組成に対して、Ｓｉおよび／またはＡｌのいずれか一方、または両者を、合計で０．０３〜１０％含有することを特徴とする。
請求項５に記載の、溶融金属に対する耐食性に優れた溶融金属用部材は、請求項１〜４のいずれかにおいて、硬質焼結合金に含有されるＭｏ含有量の一部を、全組成に対して０．１〜３０％のＷで置換してなることを特徴とする。
請求項６に記載の、溶融金属に対する耐食性に優れた溶融金属用部材は、請求項１〜５のいずれかにおいて、硬質焼結合金に含有されるＭｏ含有量の一部を、全組成に対して０．１〜１０％のＮｂで置換してなることを特徴とする。
請求項７に記載の、溶融金属に対する耐食性に優れた溶融金属用部材は、請求項１〜５のいずれかにおいて、硬質焼結合金に含有されるＭｏ含有量の一部を、全組成に対してＷおよびＮｂの両者の合計で０．２〜３０％置換してなることを特徴とする。
請求項８に記載の、溶融金属に対する耐食性に優れた溶融金属用部材は、請求項６または７において、硬質焼結合金に含有されるＮｂ含有量の一部または全部をＺｒ、Ｔｉ、Ｔａ、Ｈｆのいずれか１種または２種以上と置換してなることを特徴とする。
請求項９に記載の、溶融金属に対する耐食性に優れた溶融金属用部材は、請求項１〜８のいずれかにおいて、硬質焼結合金に含有されるＦｅ含有量の一部を、全組成に対してＮｉおよび/またはＣｏのいずれか一方または両者の合計で０．１〜２０％置換してなることを特徴とする。
請求項１０に記載の、溶融金属に対する耐食性に優れた溶融金属用部材は、請求項１〜９のいずれかにおいて、硬質焼結合金に含有されるＣｒ含有量の一部を、全組成に対して０．１〜２５％のＶで置換してなることを特徴とする。
請求項１１に記載の、溶融金属に対する耐食性に優れた溶融金属用部材の製造方法は、請求項１〜１０のいずれかに記載の硬質焼結合金部材を大気中あるいは酸化雰囲気中で７７３Ｋ以上で加熱してその表面に酸化物を形成することを特徴とする。
【０００７】
【発明の実施の形態】
本発明は、Ｍｏ2ＦｅＢ2型複硼化物系の硬質焼結合金（以下母材と称す）を大気中もしくは酸化雰囲気中で加熱して、その表面にＢ、Ｍｏ、Ｆｅ、Ｃｒと酸素を主体とした安定かつ緻密な酸化物皮膜を形成させることにより、溶融金属用の部材として用いた場合に溶融金属に対して極めて優れた耐食性、および離型性を有する溶融金属用部材を提供するものである。
本発明の溶融金属用部材の母材となる硬質焼結合金において、Ｂ、Ｍｏ、Ｃｒの含有量を一定範囲内に限定することにより、微細な複硼化物とＦｅ基の結合相との２相組織となり、優れた強度、熱疲労特性（耐熱衝撃性）が得られるばかりでなく、上記の酸化物皮膜からなる表面処理層を緻密かつ安定に形成することができる。
また、母材中にＭｎを含有させることにより、母材の機械的特性、表面処理層の耐食性および自己修復性が向上し、さらに希土類元素を含有させることにより、表面処理層の耐食性、および母材と表面処理層の密着性が改善される。さらに、Ｓｉ、Ａｌを含有させることにより表面処理層の耐食性が向上し、Ｗを含有させることにより母材の機械的特性、表面処理層の耐食性および耐摩耗性が向上する。またさらに、Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆを含有させることにより、表面処理層の耐食性および耐摩耗性が向上し、Ｎｉおよび/またはＣｏを含有させることにより母材の熱衝撃性および高温強度が向上し、さらに、Vを含有させることにより母材の機械的特性および表面処理層の自己修復性がさらに改善される。
以下に本発明を詳細に説明する。
【０００８】
本発明者らは本発明に至るまでに、優れた強度、熱疲労特性（耐熱衝撃性）を有するＭｏ2ＦｅＢ2型複硼化物系硬質焼結合金が、溶融金属、特に溶融アルミニウムに対して優れた耐食性を示すことを見出していた。しかしながら、このＭｏ2ＦｅＢ2型複硼化物系硬質焼結合金が長時間溶融金属と接触した場合、Ｆｅ基の結合相が溶融金属と反応し、耐食性、離型性が低下する傾向を示し、溶融金属に対して更なる耐食性改善が必要であることが判明した。そこで種々検討した結果、Ｍｏ2ＦｅＢ2型複硼化物系硬質焼結合金の表面に、酸化物皮膜からなる表面処理層を形成させることにより、長期間使用しても溶融金属と反応しない、あるいは焼付が生じないため、部材表面に離型剤を塗布しなくても、付着した金属を容易に剥離（離型性）できるばかりでなく、ヒートチェックの発生もないなど、耐久性が大幅に向上することを見出した。
【０００９】
これは、酸化皮膜が、母材の主要構成元素であるＭｏ、Ｃｒ、Ｆｅ、Ｂの金属元素と酸素を主体として構成される（Ｆｅ，Ｍｏ，Ｃｒ，Ｂ）ｍＯｎ型の複合酸化物である安定かつ緻密な表面処理層が保護膜となり、溶融金属に対する耐食性が大幅に改善向上するためである。本発明の溶融金属用部材は上記４元素に加えて選択的にＭｎ、Ｓｉ、Ａｌ、Ｗ、Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆ、Ｎｉ、Ｃｏ、Ｖが添加される場合もあり、この場合は合金表面に形成される酸化皮膜は、Ｍｏ、Ｃｒ、Ｆｅ、Ｂに加えて上記の選択的に添加される元素および酸素から形成される。酸化物にＭｏ、Ｃｒ、Ｆｅ、Ｂが含有されない場合は、表面処理層の結合力が弱く、かつ、母材との密着性が低下するために亀裂や剥離を生じやすく、耐摩耗性も十分でない。
複合酸化物としては、具体的には（Ｆｅ，Ｍｏ，Ｃｒ，Ｂ）2Ｏ3、（Ｆｅ，Ｍｏ，Ｃｒ，Ｂ）3Ｏ4、（Ｆｅ，Ｍｏ，Ｃｒ，Ｂ）Ｏ、（Ｆｅ，Ｍｏ，Ｃｒ，Ｂ）Ｏ3、（Ｆｅ，Ｍｏ，Ｃｒ，Ｂ）Ｏ2．7〜2．9、（Ｆｅ，Ｍｏ，Ｃｒ，Ｂ）Ｏ2などが挙げられる。
【００１０】
上記の複合酸化物は、Ｍｏ2ＦｅＢ2型の複硼化物が酸化されることにより得られるため、母材としては合金組成が主にＭｏ、Ｃｒ、Ｆｅ、ＢからなるＭｏ2ＦｅＢ2型複硼化物硬質焼結合金である必要がある。
上記硬質焼結合金において、Ｂは本発明の溶融金属用部材の母材の硬質相となる複硼化物および表面処理層を形成するために必要不可欠な元素である。また、Ｂを含有した表面処理層は母材との密着性を向上させる効果を示す。Ｂ量が３％未満であると硬質相の割合が３５％を下回り、機械的特性が劣る。一方、７．５％を超えると硬質相の割合が９５％を上回り、強度および耐熱衝撃性が低下する。よって、Ｂ含有量は３〜７．５％に限定する。
【００１１】
ＭｏはＢと同様に複硼化物および表面処理層を形成するために不可欠な元素である。母材においては、一部は硬質合金の結合相中に固溶し、母材の機械的強度を向上させる。しかし、適正量（７９．９％）を超えて含有させるとＭ6Ｃ型炭化物などの金属間化合物を形成して母材の強度が低下する。一方、含有量が２１％未満であると、Ｆｅ2ＢなどのＦｅ硼化物が形成するために母材の強度が低下する。よってMo含有量は２１〜７９．９％に限定する。
【００１２】
ＣｒもＭｏと同様に、母材においては硬質相だけでなく結合相中にも均一に固溶して機械的特性を向上させるばかりでなく、表面処理層においては安定かつ緻密なＣｒと結合した複合酸化物の形成に不可欠な元素である。しかし、３０％を超えて含有させるとクロム炭化物（Ｃｒ3Ｃ2）等の金属間化合物が形成して母材の強度が低下する。一方、２％未満になると表面処理層のＣｒ量が不十分となり、耐食性の低下を生じる。よって、Ｃｒ含有量は２〜３０％に限定する。
【００１３】
Ｍｎは母材の複硼化物の粒成長を抑制し、合金組織を微細化させることにより、機械的特性を著しく向上させる。また、Ｍｎの添加により、焼結時に型くずれの少ない良好な形状の焼結体が得られ、ニヤネット化が図られる効果を示す。さらにＭｎは酸素との親和力が強いため、表面処理層の自己修復性をもたらし、部材の耐久性を高める。含有量が０．１％未満では特性改善の効果が認められず、８％を超えて含有させると母材の機械的特性が低下する。よってＭｎの含有量は全組成に対して０．１〜８％に限定する。
【００１４】
希土類元素は表面処理層と母材の密着性を向上させる効果がある。また、これらの元素を２種以上複合含有させても単独で含有させた場合と同様な効果が得られる。含有量が０．０１％未満では特性改善の効果が認められない。５％を超えて含有させてもその効果の向上があまり認められなくなるばかりでなく、希土類元素は高価であるため、コストの上昇を招く。よって、希土類元素の含有量は全組成に対して０．０１〜５％に限定する。
【００１５】
ＳｉおよびＡｌは複合酸化物中に分散し、表面処理層をさらに緻密かつ強化させる。これらの含有量が０．０３％未満であるとその特性改善効果が認められず、１０％を超えて含有させると母材の強度が低下する。よってＳｉおよびＡｌの含有量は全組成に対して０．０３〜１０％に限定する。
【００１６】
ＷはＭｏと置換させることが可能な元素であり、母材の強度を向上させる効果を示すばかりでなく、表面処理層の耐食性および耐摩耗性を向上させる。しかし、Ｍｏとの含有量が０．１％未満であるとその特性改善効果が認められない。一方、３０％を超えて含有させてもその効果が認められなくなるばかりでなく、部材の比重が高まり、製品重量が増大する。よって、Ｗの含有量は全組成に対して０．１〜３０％に限定する。
【００１７】
Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、ＨｆはＭｏと置換させることが可能な元素であり、母材の複硼化物に固溶するとともに一部は他の硬質粒子（硼化物、酸化物、炭化物、および窒化物）を形成し、機械的特性を向上させる。また、これらの元素は酸素との親和力が強いことから複合酸化物と結合し、より緻密で密着性に優れた表面処理層の形成に効果がある。また、これらの元素を2種以上複合含有させても単独で含有させた場合と同様な効果が得られる。しかし、含有量が０．１％未満であると改善効果が認められず、１０％を超えて含有させると硬質合金の焼結性が低下し、強度の低下を招くばかりでなく、これらの元素は高価であるためコストの上昇を招く。よってＮｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆの含有量は全組成に対して１種または２種以上の合計で０．１〜１０％に限定する。
【００１８】
ＮｉおよびＣｏはＦｅ基結合相中に固溶することにより硬質合金の熱衝撃性および高温強度が向上する。含有量が０．１％未満であるとその改善効果が認められず、２０％を超えて含有させてもその特性向上の効果が認められなくなる。よって、ＮｉおよびＣｏの含有量は全組成に対して０．１〜２０％に限定する。
【００１９】
ＶはＣｒと置換させることが可能な元素であり、少量含有させるだけで母材の機械的特性が向上する。さらに表面処理層においては、自己修復性の向上効果をもたらす。０．１％未満であるとその特性改善効果が認められず、２５％を超えて含有させると、酸化皮膜の密着性が低下し、溶融金属への不純物混入の原因となり得る。よってＶの含有量は全組成に対して０．１〜２５％に限定する。
【００２０】
本発明の硬質合金は上記成分元素のほか、残部がＦｅで構成される。Ｆｅは複硼化物および結合相を構成する元素であり、表面処理層を構成する複合酸化物の形成に必要不可欠である。本発明の硬質合金においては、Ｆｅの含有量が１０％未満であると複硼化物を十分に形成させることができないばかりか、結合相中のＦｅ含有量が不足して強度が低下する。そのため、本発明の硬質合金にはＦｅを１０％以上含有させる必要がある。本発明の硬質合金においてＦｅを１０％以上含有させることができない場合は、許容範囲内においてＦｅ以外の各元素の含有量を減じて、１０％以上のＦｅを含有させることは言うまでもない。
【００２１】
本発明の硬質焼結合金が含有する不可避的不純物元素の主なものはＰ、Ｓ、Ｎ、Ｃなどであり、硬質焼結合金の強度を維持させるためにはこれらの含有量は極力少なくすることが望ましい。これらの元素の含有量が合計で１％以下であれば、機械的特性に与える影響は比較的小さい。
【００２２】
次に本発明の溶融金属用部材の製造方法について説明する。
まず母材である硬質合金の製造方法について説明する。Ｆｅ、Ｍｏ、Ｃｒ、Ｍｎ、Ｓｉ、Ａｌ、Ｗ、Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆ、Ｎｉ、Ｃｏ、Ｖ、希土類元素の１種または２種以上の元素とＢからなるＢ合金の粉末、またはこれらのＢ合金粉末とこれら元素の１種または２種以上からなる合金の粉末、またはＢ単体とＦｅ、Ｍｏ、Ｃｒ、Ｍｎ、Ｓｉ、Ａｌ、Ｗ、Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆ、Ｎｉ、Ｃｏ、Ｖ、希土類元素の単体粉末、またはＢ単体とこれらの１種または２種以上の合金からなる粉末を所定の合金組成となるように配合し、振動ボールミル等を用いて有機溶媒中で湿式粉砕後、造粒、成形し、該成形体を真空中、還元ガス中、または不活性ガス中などの非酸化性雰囲気中で液相焼結することにより製造する。
【００２３】
なお、上記の硬質合金の硬質相となる複硼化物は、上記原料粉末が焼結中に反応することによって形成されるが、あらかじめＭｏおよびＦｅ、さらに上記の選択的に添加される元素からなる複硼化物、またはＢ単体の粉末とＭｏおよびＦｅさらに上記の選択的に添加される元素の粉末を炉中で反応させることにより、Ｍｏ2ＦｅＢ2型複硼化物を製造し、さらに結合組成のＦｅ、Ｍｏ、Ｎｉ、Ｃｏ、および上記の選択的に添加される元素の粉末を所定の合金組成となるように配合した粉末を用いても差し支えない。
【００２４】
液相焼結は通常１３７３〜１６７３Ｋの焼結温度で５〜９０分間行う。
焼結温度が１３７３Ｋ未満の場合は液相が十分に出現せず、空孔の多い焼結体が得られ、十分な強度が得られない。一方、焼結温度が１６７３Ｋを超えると液相は十分に出現するものの、結晶粒が粗大化し強度が低下する。また、焼結時間が５分未満であると、元素の拡散が十分でなく、十分に高密度化しない。一方、９０分を越えて焼結してもそれ以上の強度上昇は認められず、場合によっては強度が低下することもある。以上のような液相が出現する焼結条件で焼結することにより、空孔が消失し、ほぼ１００％の密度の硬質合金が得られる。液相を出現させずに空孔を消失させる方法として、熱間静水圧プレス法、ホットプレス法、通電焼結法などがあり、これらの方法を用いても空孔を消失させることができる。またこれらの方法と液相焼結法を併用してもよい。
【００２５】
上記のようにして得られる本発明の溶融金属用部材の母材である硬質合金は、焼結体単体としてのみ用いられるばかりでなく、鋼材と接合させて複合材として用いることも可能である。すなわち、本発明の硬質合金は超硬合金のように鋼材にロウ付けして使用するばかりでなく、ロウ材を使用することなく直接鋼材と接合させることも可能であり、強固な接着が得られる。また、焼結と鋼材を同時に接合する焼結接合法を適用することも可能であり、鋼材は熱ダメージによる強度低下を招来することなく、複合材料をアルミニウムなどの溶融金属のダイカスト用部材として用いた場合、溶融金属に対して耐食性および耐摩耗性が必要とされる部分にのみ、本発明の溶融金属用部材の母相である硬質合金を必要最小限に用いることにより、金型などの部材を低価格で製造することが可能となる。
次に、上記のようにして得られた母材表面に形成させる表面処理層の製造方法について説明する。
【００２６】
得られた母材を所望の形状に機械加工を行い、処理表面を洗浄脱脂した後、大気中もしくは酸化性雰囲気中で７７３〜１８７３Ｋの温度で５分〜３０時間保持することにより、適正な皮膜量の酸化皮膜を形成させる。本発明の表面処理層の形成手段としては、高温大気酸化法、高温湿潤水素酸化法等があるが特に限定されない。処理温度が７７３Ｋ未満の場合は、長時間の処理を行っても優れた耐食性が得られる十分な厚みを有する酸化皮膜は形成されない。一方、１８７３Ｋを超える処理温度で処理した場合は、酸化皮膜の剥離が生じる。処理時間が５分未満の場合は十分な厚みの酸化皮膜の形成が認められず、３０時間を超えて処理を行っても、酸化皮膜の成長は飽和し、剥離を生じるばかりでなく、コストの上昇につながる。よって、表面処理は７７３〜１８７３Ｋの温度で５分〜３０時間、好ましくは８７３〜１２７３Ｋで１〜２０時間行う。また上記の酸化皮膜を形成させる手段として、酸化雰囲気における高温加熱処理だけではなく、陽極電解法や加圧水蒸気法などを用いることも可能である。
以下、実施例を示し本発明を具体的に説明する。
【００２７】
【実施例】
（実施例）
Ｂ粉末および金属粉末を、表１〜５に示す配合比に調整した後、振動ボールミルを用いて、アセトン中で２５時間湿式混合粉砕した。ボールミルで粉砕した後の粉末を乾燥、造粒し、得られた微粉末を所定の形状にプレス成形した後、真空度：≦１．３Ｐａの真空中で10Ｋ/分の昇温速度で加熱し、１３７３〜１６７３Ｋの温度で３０分間加熱した後炉冷し、焼結合金を得た。得られた焼結合金を所望の形状に加工し、脱脂後、大気中で表６〜１４に示す加熱条件で加熱した後、炉冷し、焼結合金表面に複合酸化物の皮膜からなる表面処理層を形成させ、溶融金属用部材を得た。一部の焼結合金は比較用に上記の加熱処理を施さずに、下記の特性評価に供した。
【００２８】
【表１】
【表２】
【表３】
【表４】
【表５】
上記のようにして得られた表６〜１４に示した硬質合金および溶融金属用部材の強度、耐食性、および耐熱衝撃性を以下のようにして評価した。
[強度]
焼結したままの硬質合金、および硬質合金に大気中の加熱処理を施した溶融金属用部材から試験片を切り出し、ＪＩＳ Ｈ ５５０１に基づいて抗折力（３点曲げ試験）を測定した。抗折力が大きいほど強度が優れており、１．５ＧＰａを超えるものを本発明の対象とする。結果を表６〜１４に示す。
【００３４】
[耐食性]
焼結したままの硬質合金、および硬質合金に大気中の加熱処理を施した溶融金属用部材を１０ｍｍ×１０ｍｍ×１００ｍｍの大きさに切削加工し試験片とし、この試験片を９９３Ｋで加熱溶融したアルミニウム（ダイカスト用アルミニウム合金：ＪＩＳ−ＡＤＣ１０）中に６時間浸漬した後、試験片の長手方向に垂直な断面で切り出し、断面を光学顕微鏡で観察し、試験片が溶融アルミニウムにより表面から侵食された深さを測定し、下記の規準で耐食性を評価した。
○：侵食深さ＜５μｍ、離型性良好
△：侵食深さ≧５μｍでかつ＜３０μｍ、離型性やや不良
×：侵食深さ≧３０μｍ、離型性不良
結果を表６〜１４に示す。表中で ＃を附したものは、特定元素を必要以上に添加しても効果の向上効果が認められないものを指す。
【００３５】
[耐熱衝撃性]
焼結したままの硬質合金、および硬質合金に大気中の加熱処理を施した溶融金属用部材を１０ｍｍ×１０ｍｍ×１００ｍｍの大きさに切削加工し、これに０．５ｍｍ幅の切り込みを５ｍｍ入れ試験片とした。この試験片を７７３Ｋで大気中で加熱し、水中に投入した後に発生するクラックの有無を肉眼観察し、耐熱衝撃性を評価した結果を表６〜１４に示す。
【００３６】
【表６】
【表７】
【表８】
【表９】
【表１０】
【表１１】
【表１２】
【表１３】
【表１４】
表６〜１４に示すように、本発明の溶融金属用部材は耐食性および耐熱衝撃性に優れている。
【００４６】
【発明の効果】
本発明は、Ｍｏ、Ｃｒ、Ｆｅ、Ｂ、およびさらにＭｎ、希土類元素、Ｓｉおよび／またはＡｌを含有させ、Ｍｏ、Ｃｒ、Ｂの含有量を一定範囲内に限定し、またはさらにＷ、Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆ、Ｎｉおよび／またはＣｏ、Ｖなどを適宜含有させて成る、微細な複硼化物とＦｅ基の結合相とからなる硬質焼結合金を、大気中で加熱して表面に酸化皮膜を形成させた溶融金属用部材であり、溶融金属に対して優れた耐食性と耐熱衝撃性を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a member for molten metal having excellent corrosion resistance against molten metal and a method for producing the member. More specifically, the present invention relates to a member for molten metal in which corrosion resistance to molten metal is significantly improved by forming an oxide on the surface of the member in direct contact with the molten metal, and a method for manufacturing the member.
[0002]
[Prior art]
As a typical member used in direct contact with molten metal, there is a member for a die casting machine part. A die casting machine is composed of a plunger, a sleeve, and a molding die, and is used in direct contact with a molten metal such as aluminum, zinc, magnesium, and the like. For this reason, the properties commonly required for these parts include corrosion resistance, wear resistance, and heat fatigue resistance against the molten metal, such as that the molten metal is not eroded (melted) and does not form a reaction layer. . Conventionally, tool steel and hot tool steel (such as SKD61) have been used as members used for these parts, but there is a problem that the life is short because corrosion resistance to molten metal is not sufficient.
[0003]
Therefore, in addition to having high hardness and high strength, a Mo 2 FeB 2 type double boride hard sintered alloy (Japanese Patent Publication No. 60-57499) exhibiting excellent corrosion resistance against molten metal. When applied to die-cast parts, a significant increase in life was obtained. However, it has been found that when this member is used for a long time, the reaction between the metal binder phase of the member and the molten metal proceeds, resulting in a problem that the corrosion resistance and releasability deteriorate.
In recent years, attempts have been made to form a thermal sprayed coating of ceramics such as alumina and zirconia on the surface of a member in order to improve corrosion resistance and release properties against molten metal. However, these thermal sprayed coatings are liable to cause cracks and peeling such as heat check and heat crack, and the durability is not improved as expected.
[0004]
JP-A-5-148588 and JP-A-9-217167 disclose that the corrosion resistance of a member can be improved by providing an oxide film on the surfaces of steel, cast iron and stainless steel. However, the formed oxide film has problems such as poor adhesion to the member, very thin and low hardness, and cannot be applied to plungers and sleeves that require high wear resistance.
[0005]
[Problems to be solved by the invention]
In the present invention, the above-described Mo 2 FeB 2 type double boride type hard sintered alloy has improved corrosion resistance against molten metal and mold releasability, and has developed a hard sintered alloy exhibiting extremely excellent durability. An object of the present invention is to provide a member for molten metal that has extremely excellent corrosion resistance and releasability with respect to molten metal, and is excellent in thermal fatigue properties, mechanical properties, and wear resistance, and a method for producing the member.
[0006]
[Means for Solving the Problems]
The member for molten metal according to claim 1, which is excellent in corrosion resistance against molten metal,
3 to 7.5% by weight (hereinafter referred to as% by weight) B, 21 to 79.9% Mo, 2 to 30% Cr, the balance being 10% or more Fe and inevitable impurities A member for molten metal formed by forming an oxide film on the surface of a sintered alloy member that is in direct contact with the molten metal,
The hard sintered alloy member is composed of a Mo 2 FeB 2 type double boride and an Fe-based binder phase,
The oxide film is a film made of a complex element of (Fe, Mo, Cr, B) mOn type mainly composed of metal elements of Mo, Cr, Fe, and B and oxygen.
The member for molten metal excellent in corrosion resistance to molten metal according to claim 2 contains 0.1 to 8% of Mn with respect to the total composition of the hard sintered alloy in claim 1. And The member for molten metal having excellent corrosion resistance against molten metal according to claim 3 is one or two selected from rare earth elements for the entire composition of the hard sintered alloy in claim 1 or 2. It contains 0.01 to 5% in total of seeds or more.
The member for molten metal having excellent corrosion resistance against molten metal according to claim 4 is any one of claims 1 to 3, wherein either one of Si and / or Al is used for the entire composition of the hard sintered alloy. Or a total of 0.03 to 10% of both.
The member for molten metal excellent in corrosion resistance to the molten metal according to claim 5 is any one of claims 1 to 4, wherein a part of the Mo content contained in the hard sintered alloy is reduced with respect to the total composition. It is characterized by being substituted with 0.1 to 30% of W.
The member for molten metal excellent in corrosion resistance against molten metal according to claim 6 is any one of claims 1 to 5, wherein a part of the Mo content contained in the hard sintered alloy is reduced with respect to the total composition. It is characterized by being substituted with 0.1 to 10% Nb.
The member for molten metal excellent in corrosion resistance against molten metal according to claim 7 is any one of claims 1 to 5, wherein a part of the Mo content contained in the hard sintered alloy is reduced with respect to the total composition. Thus, the total content of both W and Nb is 0.2 to 30%.
The member for molten metal having excellent corrosion resistance against molten metal according to claim 8 is the member according to claim 6 or 7, wherein a part or all of the Nb content contained in the hard sintered alloy is Zr, Ti, Ta, It is characterized by being substituted with any one or more of Hf.
The member for molten metal having excellent corrosion resistance against molten metal according to claim 9 is the member according to any one of claims 1 to 8, wherein a part of the Fe content contained in the hard sintered alloy is based on the total composition. And any one or both of Ni and / or Co is substituted for 0.1 to 20%.
The member for molten metal excellent in corrosion resistance to the molten metal according to claim 10 is any one of claims 1 to 9, wherein a part of the Cr content contained in the hard sintered alloy is reduced with respect to the total composition. It is characterized by being substituted with 0.1 to 25% of V.
The manufacturing method of the member for molten metal excellent in corrosion resistance with respect to molten metal according to claim 11 is the hard sintered alloy member according to any one of claims 1 to 10 at 773 K or more in air or in an oxidizing atmosphere. An oxide is formed on the surface by heating.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a hard sintered alloy of Mo 2 FeB 2 type double boride (hereinafter referred to as a base material) is heated in the air or in an oxidizing atmosphere, and B, Mo, Fe, Cr and oxygen are heated on the surface. Providing a member for molten metal having extremely excellent corrosion resistance and releasability to molten metal when used as a member for molten metal by forming a stable and dense oxide film as a main component It is.
In the hard sintered alloy that is the base material of the molten metal member of the present invention, the content of B, Mo, and Cr is limited to a certain range, so that the fine double boride and the Fe-based binder phase 2 A phase structure is obtained, and not only excellent strength and thermal fatigue characteristics (thermal shock resistance) are obtained, but also a surface treatment layer made of the above oxide film can be formed densely and stably.
In addition, the inclusion of Mn in the base material improves the mechanical properties of the base material, the corrosion resistance and self-healing property of the surface treatment layer, and the addition of the rare earth element further improves the corrosion resistance of the surface treatment layer and the base material. The adhesion between the material and the surface treatment layer is improved. Furthermore, the inclusion of Si and Al improves the corrosion resistance of the surface treatment layer, and the inclusion of W improves the mechanical properties of the base material and the corrosion resistance and wear resistance of the surface treatment layer. Furthermore, by containing Nb, Zr, Ti, Ta, Hf, the corrosion resistance and wear resistance of the surface treatment layer are improved, and by containing Ni and / or Co, the thermal shock resistance and high temperature strength of the base material are improved. In addition, the inclusion of V further improves the mechanical properties of the base material and the self-healing property of the surface treatment layer.
The present invention is described in detail below.
[0008]
By the time the present inventors arrived at the present invention, the Mo 2 FeB 2 type double boride hard sintered alloy having excellent strength and thermal fatigue properties (thermal shock resistance) has been used against molten metal, particularly molten aluminum. It has been found that it exhibits excellent corrosion resistance. However, when this Mo 2 FeB 2 type double boride hard sintered alloy is in contact with the molten metal for a long time, the Fe-based binder phase reacts with the molten metal, and the corrosion resistance and release properties tend to decrease, It has been found that further corrosion resistance improvement is necessary for the molten metal. As a result of various studies, by forming a surface treatment layer composed of an oxide film on the surface of the Mo 2 FeB 2 type double boride type hard sintered alloy, it does not react with the molten metal even when used for a long time, or Because there is no seizure, not only the release agent is not applied to the surface of the member, but the attached metal can be easily peeled off (releasability) and there is no heat check. I found out.
[0009]
This oxide film is configured Mo is the main constituent elements of the matrix, Cr, Fe, a metal element and oxygen B mainly (Fe, Mo, Cr, B ) m O n -type composite oxide This is because the stable and dense surface treatment layer becomes a protective film, and the corrosion resistance against molten metal is greatly improved. In addition to the above four elements, Mn, Si, Al, W, Nb, Zr, Ti, Ta, Hf, Ni, Co, and V may be selectively added to the molten metal member of the present invention. In addition to Mo, Cr, Fe, and B, the oxide film formed on the alloy surface is formed from the above selectively added elements and oxygen. When the oxide does not contain Mo, Cr, Fe, or B, the bonding strength of the surface treatment layer is weak and the adhesion to the base material is reduced, so that cracks and peeling are likely to occur, and the wear resistance is sufficient. Not.
Specific examples of the composite oxide include (Fe, Mo, Cr, B) 2O3, (Fe, Mo, Cr, B) 3O4, (Fe, Mo, Cr, B) O, (Fe, Mo, Cr, B) O3, (Fe, Mo, Cr, B) O2.7 to 2.9, (Fe, Mo, Cr, B) O2 and the like.
[0010]
Composite oxides of the above, Mo 2 for FeB 2 type complex boride is obtained by being oxidized, primarily an alloy composition as a base material Mo, Cr, Fe, consisting B Mo 2 FeB 2 type double It must be a boride hard sintered alloy.
In the above-mentioned hard sintered alloy, B is an indispensable element for forming the double boride and the surface treatment layer that will be the hard phase of the base material of the molten metal member of the present invention. Moreover, the surface treatment layer containing B exhibits the effect of improving the adhesion with the base material. If the amount of B is less than 3%, the proportion of the hard phase is less than 35%, and the mechanical properties are inferior. On the other hand, if it exceeds 7.5%, the ratio of the hard phase exceeds 95%, and the strength and thermal shock resistance are lowered. Therefore, the B content is limited to 3 to 7.5%.
[0011]
Mo, like B, is an indispensable element for forming double borides and surface treatment layers. In the base material, a part is dissolved in the binder phase of the hard alloy to improve the mechanical strength of the base material. However, if the content exceeds the appropriate amount (79.9%), an intermetallic compound such as M 6 C-type carbide is formed and the strength of the base material is lowered. On the other hand, when the content is less than 21%, Fe boride such as Fe 2 B is formed, so that the strength of the base material is lowered. Therefore, the Mo content is limited to 21-79.9%.
[0012]
Similarly to Mo, Cr not only improves the mechanical properties by uniformly dissolving in the binder phase but also in the binder phase in the base material, and is bonded to stable and dense Cr in the surface treatment layer. It is an element indispensable for the formation of complex oxides. However, if the content exceeds 30%, an intermetallic compound such as chromium carbide (Cr 3 C 2 ) is formed and the strength of the base material is lowered. On the other hand, if it is less than 2%, the Cr amount of the surface treatment layer becomes insufficient, resulting in a decrease in corrosion resistance. Therefore, the Cr content is limited to 2 to 30%.
[0013]
Mn suppresses the grain growth of the double boride of the base material and refines the alloy structure, thereby significantly improving the mechanical properties. Further, by adding Mn, a sintered body having a good shape with little deformation during sintering can be obtained, and the effect of being made into a net is shown. Furthermore, since Mn has a strong affinity for oxygen, it brings about self-healing of the surface treatment layer and enhances the durability of the member. If the content is less than 0.1%, the effect of improving the characteristics is not recognized. If the content exceeds 8%, the mechanical properties of the base material are lowered. Therefore, the Mn content is limited to 0.1 to 8% with respect to the total composition.
[0014]
Rare earth elements have the effect of improving the adhesion between the surface treatment layer and the base material. Further, even when two or more of these elements are combined, the same effect as that obtained when these elements are included alone can be obtained. When the content is less than 0.01%, the effect of improving the characteristics is not recognized. Even if the content exceeds 5%, not only the improvement of the effect is not recognized, but also the rare earth elements are expensive, which causes an increase in cost. Therefore, the rare earth element content is limited to 0.01 to 5% with respect to the total composition.
[0015]
Si and Al are dispersed in the composite oxide, and the surface treatment layer is further densely and strengthened. If the content is less than 0.03%, the effect of improving the characteristics is not recognized, and if the content exceeds 10%, the strength of the base material decreases. Therefore, the contents of Si and Al are limited to 0.03 to 10% with respect to the total composition.
[0016]
W is an element that can be replaced with Mo, and not only exhibits the effect of improving the strength of the base material but also improves the corrosion resistance and wear resistance of the surface treatment layer. However, if the content of Mo is less than 0.1%, the effect of improving the characteristics is not recognized. On the other hand, if the content exceeds 30%, not only the effect is not recognized, but also the specific gravity of the member increases and the product weight increases. Therefore, the W content is limited to 0.1 to 30% with respect to the total composition.
[0017]
Nb, Zr, Ti, Ta, and Hf are elements that can be substituted for Mo, and are dissolved in the double boride of the base material and some of the other hard particles (boride, oxide, carbide, and Nitride) and improve mechanical properties. In addition, since these elements have a strong affinity for oxygen, they bind to the composite oxide and are effective in forming a denser surface treatment layer having excellent adhesion. Further, even when two or more of these elements are contained in a composite, the same effect as that obtained when they are contained alone can be obtained. However, if the content is less than 0.1%, the improvement effect is not recognized. If the content exceeds 10%, the sinterability of the hard alloy is lowered, not only causing a decrease in strength, but also these elements. Is expensive and causes an increase in cost. Therefore, the content of Nb, Zr, Ti, Ta, and Hf is limited to 0.1 to 10% in total with one or more of the total composition.
[0018]
Ni and Co are dissolved in the Fe-based binder phase to improve the thermal shock resistance and high temperature strength of the hard alloy. If the content is less than 0.1%, the improvement effect is not recognized, and even if the content exceeds 20%, the effect of improving the characteristics is not recognized. Therefore, the contents of Ni and Co are limited to 0.1 to 20% with respect to the total composition.
[0019]
V is an element that can be replaced with Cr, and the mechanical properties of the base material are improved only by adding a small amount. Further, the surface treatment layer brings about an effect of improving self-repairability. If the content is less than 0.1%, the effect of improving the characteristics is not recognized. If the content exceeds 25%, the adhesion of the oxide film is lowered, and impurities may be mixed into the molten metal. Therefore, the content of V is limited to 0.1 to 25% with respect to the total composition.
[0020]
The hard alloy of the present invention is composed of Fe in addition to the above component elements. Fe is an element constituting a double boride and a binder phase, and is indispensable for forming a complex oxide constituting a surface treatment layer. In the hard alloy of the present invention, if the Fe content is less than 10%, the double boride cannot be sufficiently formed, and the Fe content in the binder phase is insufficient and the strength is lowered. Therefore, it is necessary to contain 10% or more of Fe in the hard alloy of the present invention. Needless to say, in the case where the hard alloy of the present invention cannot contain 10% or more of Fe, the content of each element other than Fe is reduced within an allowable range to contain 10% or more of Fe.
[0021]
The main inevitable impurity elements contained in the hard sintered alloy of the present invention are P, S, N, C, etc., and in order to maintain the strength of the hard sintered alloy, these contents should be reduced as much as possible. It is desirable. If the content of these elements is 1% or less in total, the influence on the mechanical properties is relatively small.
[0022]
Next, the manufacturing method of the member for molten metal of this invention is demonstrated.
First, a method for producing a hard alloy as a base material will be described. Fe, Mo, Cr, Mn, Si, Al, W, Nb, Zr, Ti, Ta, Hf, Ni, Co, V, powder of B alloy composed of one or more elements of rare earth elements and B, Alternatively, these B alloy powders and alloy powders composed of one or more of these elements, or B alone and Fe, Mo, Cr, Mn, Si, Al, W, Nb, Zr, Ti, Ta, Hf, Ni, Co, V, rare earth element simple powder, or B simple substance and a powder composed of one or more of these alloys are blended so as to have a predetermined alloy composition, and in an organic solvent using a vibration ball mill or the like. After the wet pulverization, granulation and molding are performed, and the compact is produced by liquid phase sintering in a non-oxidizing atmosphere such as in a vacuum, a reducing gas, or an inert gas.
[0023]
The double boride that becomes the hard phase of the hard alloy is formed by the reaction of the raw material powder during the sintering, and is composed of Mo and Fe in advance and the elements that are selectively added. Mo 2 FeB 2 type double boride is produced by reacting double boride or powder of B alone with powders of Mo and Fe and the above selectively added elements in a furnace. A powder obtained by blending powders of Fe, Mo, Ni, Co, and the above selectively added elements so as to have a predetermined alloy composition may be used.
[0024]
Liquid phase sintering is usually performed at a sintering temperature of 1373 to 1673K for 5 to 90 minutes.
When the sintering temperature is less than 1373K, the liquid phase does not appear sufficiently, a sintered body with many voids is obtained, and sufficient strength cannot be obtained. On the other hand, when the sintering temperature exceeds 1673K, the liquid phase appears sufficiently, but the crystal grains become coarse and the strength decreases. On the other hand, if the sintering time is less than 5 minutes, the diffusion of elements is not sufficient and the density is not sufficiently increased. On the other hand, no further increase in strength is observed even after sintering for more than 90 minutes, and the strength may decrease in some cases. By sintering under the sintering conditions in which the liquid phase appears as described above, voids disappear and a hard alloy having a density of almost 100% is obtained. As a method for eliminating voids without causing a liquid phase to appear, there are a hot isostatic pressing method, a hot press method, an electric current sintering method, and the like. Even if these methods are used, voids can be eliminated. Further, these methods and the liquid phase sintering method may be used in combination.
[0025]
The hard alloy, which is the base material of the molten metal member of the present invention obtained as described above, can be used not only as a single sintered body but also as a composite material by joining with a steel material. That is, the hard alloy of the present invention is not only used by brazing to a steel material like a cemented carbide, but can also be directly joined to the steel material without using a brazing material, and a strong adhesion can be obtained. . It is also possible to apply a sinter bonding method in which sintering and steel materials are bonded simultaneously. Steel materials can be used as die casting parts for molten metals such as aluminum without causing a decrease in strength due to thermal damage. In such a case, by using the hard alloy that is the parent phase of the member for molten metal of the present invention only in a portion where corrosion resistance and wear resistance are required for the molten metal, a member such as a mold is used. Can be manufactured at a low price.
Next, a method for manufacturing the surface treatment layer formed on the surface of the base material obtained as described above will be described.
[0026]
The obtained base material is machined into a desired shape, the treated surface is washed and degreased, and then kept in the atmosphere or in an oxidizing atmosphere at a temperature of 773 to 1873 K for 5 minutes to 30 hours to obtain an appropriate film. An amount of oxide film is formed. Examples of the means for forming the surface treatment layer of the present invention include, but are not particularly limited to, a high temperature atmospheric oxidation method and a high temperature wet hydrogen oxidation method. When the treatment temperature is less than 773 K, an oxide film having a sufficient thickness that can provide excellent corrosion resistance is not formed even if treatment is performed for a long time. On the other hand, when the treatment is performed at a treatment temperature exceeding 1873K, the oxide film is peeled off. When the treatment time is less than 5 minutes, the formation of a sufficiently thick oxide film is not recognized, and even when the treatment is performed for more than 30 hours, the growth of the oxide film is saturated, not only causing peeling, but also costly Leading to a rise. Therefore, the surface treatment is performed at a temperature of 773 to 1873K for 5 minutes to 30 hours, preferably at 873 to 1273K for 1 to 20 hours. Further, as means for forming the oxide film, not only high-temperature heat treatment in an oxidizing atmosphere but also an anodic electrolysis method or a pressurized steam method can be used.
Hereinafter, the present invention will be described in detail with reference to examples.
[0027]
【Example】
(Example)
The B powder and the metal powder were adjusted to the blending ratios shown in Tables 1 to 5, and then wet mixed and pulverized in acetone for 25 hours using a vibration ball mill. The powder after pulverization with a ball mill is dried and granulated, and the resulting fine powder is press-molded into a predetermined shape, and then heated at a heating rate of 10 K / min in a vacuum of ≦ 1.3 Pa. After heating for 30 minutes at a temperature of 1373 to 1673K, the furnace was cooled to obtain a sintered alloy. The obtained sintered alloy is processed into a desired shape, degreased, heated in the atmosphere under the heating conditions shown in Tables 6 to 14, and then cooled in the furnace, and the surface of the sintered alloy surface comprising a composite oxide film A treatment layer was formed to obtain a molten metal member. Some sintered alloys were subjected to the following characteristic evaluation without being subjected to the above heat treatment for comparison.
[0028]
[Table 1]
[Table 2]
[Table 3]
[Table 4]
[Table 5]
The strength, corrosion resistance, and thermal shock resistance of the hard alloys and molten metal members shown in Tables 6 to 14 obtained as described above were evaluated as follows.
[Strength]
A test piece was cut out from the sintered hard alloy and a member for molten metal obtained by subjecting the hard alloy to heat treatment in the atmosphere, and the bending strength (three-point bending test) was measured based on JIS H5501. The greater the bending strength, the better the strength, and those exceeding 1.5 GPa are the subject of the present invention. The results are shown in Tables 6-14.
[0034]
[Corrosion resistance]
The sintered hard alloy and a member for molten metal obtained by subjecting the hard alloy to heat treatment in the atmosphere were cut into a size of 10 mm × 10 mm × 100 mm to obtain a test piece, and the test piece was heated and melted at 993K. After dipping in aluminum (aluminum alloy for die casting: JIS-ADC10) for 6 hours, the specimen was cut out in a cross section perpendicular to the longitudinal direction of the test piece, the cross section was observed with an optical microscope, and the test piece was eroded from the surface by molten aluminum. The depth was measured and the corrosion resistance was evaluated according to the following criteria.
◯: Depth of erosion <5 μm, good releasability Δ: Depth of erosion ≧ 5 μm and <30 μm, somewhat poor releasability ×: Depth of erosion ≧ 30 μm, poor releasability results are shown in Tables 6-14. Those with # in the table indicate those in which the effect of improving the effect is not recognized even if a specific element is added more than necessary.
[0035]
[Heat shock resistance]
The sintered hard alloy and the molten metal member that has been heat-treated in the atmosphere are cut to a size of 10 mm x 10 mm x 100 mm, and a 0.5 mm wide cut is put into this 5 mm test It was a piece. The test pieces were heated in the atmosphere at 773 K, and the presence or absence of cracks generated after being put into water was observed with naked eyes, and the results of evaluating the thermal shock resistance are shown in Tables 6 to 14.
[0036]
[Table 6]
[Table 7]
[Table 8]
[Table 9]
[Table 10]
[Table 11]
[Table 12]
[Table 13]
[Table 14]
As shown in Tables 6 to 14, the member for molten metal of the present invention is excellent in corrosion resistance and thermal shock resistance.
[0046]
【The invention's effect】
The present invention includes Mo, Cr, Fe, B, and further Mn, rare earth elements, Si and / or Al, and limits the content of Mo, Cr, B to a certain range, or further W, Nb, A hard sintered alloy containing fine double borides and a Fe-based binder phase containing Zr, Ti, Ta, Hf, Ni and / or Co, V, etc., as appropriate, is heated in the atmosphere to form a surface. It is a member for molten metal having an oxide film formed thereon, and exhibits excellent corrosion resistance and thermal shock resistance against molten metal.
Claims (11)
前記硬質焼結合金部材が、Ｍｏ 2 ＦｅＢ 2 型複硼化物とＦｅ基結合相とからなり、
前記酸化皮膜が、Ｍｏ、Ｃｒ、Ｆｅ、Ｂの金属元素と酸素を主体とする（Ｆｅ，Ｍｏ，Ｃｒ，Ｂ）ｍＯｎ型の複合酸化物からなる皮膜であることを特徴とする溶融金属に対する耐食性に優れた溶融金属用部材。 3 to 7.5% by weight (hereinafter referred to as% by weight) B, 21 to 79.9% Mo, 2 to 30% Cr, the balance being 10% or more Fe and inevitable impurities A member for molten metal formed by forming an oxide film on the surface of a sintered alloy member that is in direct contact with the molten metal,
The hard sintered alloy member is composed of a Mo 2 FeB 2 type double boride and an Fe-based binder phase,
Corrosion resistance to molten metal, characterized in that the oxide film is a film made of a complex element of (Fe, Mo, Cr, B) mOn type mainly composed of metal elements of Mo, Cr, Fe, and B and oxygen. Excellent member for molten metal.
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