JP4780431B2 - High hardness and high corrosion resistance Ni-base alloy - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、電気めっき用通電ロール、プラスチック射出成形機用シャフト、ディーゼルエンジンの燃料噴射ノズル等、高い硬さと耐食性とを要する用途に適したＮｉ基合金とその製造方法に関する。
【０００２】
【従来の技術】
電気めっき用通電ロール、プラスチック射出成形機用シャフト、ディーゼルエンジンの燃料噴射ノズル等の機械部品は、腐食性の強い環境において他の部品と高い面圧で摩擦する状態で使用される。すなわち、電気めっき用通電ロールは、金属めっき溶液、例えば、亜鉛めっき溶液槽に浸漬して使用され、通電中に腐食が発生する。同時に、被めっき材との回転接触により摩耗が生じる。プラスチック射出成形機用シャフトでは、フッ素系樹脂などの腐食性が強い樹脂の成形時には、シャフトが腐食される場合があり、また、樹脂中にガラス繊維等を混入した繊維強化樹脂を成形することもあってシャフトの摩耗が問題となる。ディーゼルエンジンの燃料噴射ノズルでは、燃料に含有される硫黄分などによる腐食と同時に、ニードル弁と高い面圧で接触し、それらの摺動による摩耗が発生する。そのため、これらの用途に用いられる材料には、高い面圧に耐え、耐摩耗性をもたらす高い硬さと耐食性とが要求される。
【０００３】
従来、上述のような用途には、インコネル６２５（Ｎｉ−２１Ｃｒ−９Ｍｏ−４Ｎｂ合金）やハステロイＣ（Ｎｉ−１７Ｃｒ−１９Ｍｏ−５Ｗ合金）等のＮｉ基超合金が用いられている。しかし、硬さが十分でないという問題があった。前記Ｎｉ基耐食合金を改良して、特性を向上した合金として、ガンマプライム（Ｎｉ3（Ａｌ、Ｔｉ））の析出硬化を利用したＮｉ基合金（特開平２−２７０９３９号公報）や、固溶強化を利用したＮｉ基合金（特開平１０−２０４５６１号公報）が開示されている。しかし、前者は、耐食性が未だ十分ではなく、また後者では、結晶粒界に斜方晶のδ相（Ｎｉ3（Ｎｂ、Ｔａ））が析出するため結晶粒界の耐食性を損なうことがあり、さらに、硬さも３００ＨＶ以下で不十分であった。一方、σ相の析出硬化を利用したＮｉ基合金（例えば、特開平５−１９５１３７号公報）は、３８０ＨＶ以上の高い硬さは得られるがσ相と母相との耐食性の差異に起因する微細腐食によって、合金表面が白濁状の概観を呈するといった不都合を生じることがあった。
【０００４】
【発明が解決しようとする課題】
上記の現状に鑑み、本発明は、優れた耐食性を備え、かつ、４００ＨＶ以上の高硬度を有する合金と該合金の製造方法を提供することを目的とする。
【０００５】
【課題を解決するための手段】
上記の問題を解決するために種々検討した結果、発明者らは、Ｎｉ−２１Ｃｒ−９Ｍｏ−４Ｎｂ合金をベースとして、合金組成に工夫を加え、さらに、適切な熱処理を加え、合金生地中に体心正方晶のガンマダブルプライム（Ｎｉ3（Ｎｂ、Ｔａ））を時効析出させることにより、合金の耐食性を損なうことなく高い硬さが得られることを見出した。
【０００６】
すなわち、本発明の高硬度高耐食性Ｎｉ基合金は、
（１）質量％で、Ｃ：０．１０％以下、Ｓｉ：１％以下、Ｍｎ：１％以下、Ｃｒ：１６〜２５％、Ｍｏ：８〜２０％、Ｎｂ＋Ｔａ：５〜１０％、Ａｌ：０．０１〜１％、Ｔｉ：０．０１〜１％、Ｆｅ：３％以下、Ｎ：０．０２％以下、Ｏ：０．０２％以下を含み、残部がＮｉおよび不可避的不純物からなり、１０００〜１２００℃の温度で固溶化処理後、６００〜７５０℃の温度で８〜３２時間時効処理されたことを特徴とする。
（２）質量％で、Ｃ：０．１０％以下、Ｓｉ：１％以下、Ｍｎ：１％以下、Ｃｕ：０．１〜５％、Ｃｒ：１６〜２５％、Ｍｏ：８〜２０％、Ｎｂ＋Ｔａ：５〜１０％、Ａｌ：０．０１〜１％、Ｔｉ：０．０１〜１％、Ｆｅ：３％以下、Ｎ：０．０２％以下、Ｏ：０．０２％以下を含み、残部がＮｉおよび不可避的不純物からなり、１０００〜１２００℃の温度で固溶化処理後、６００〜７５０℃の温度で８〜３２時間時効処理されたことを特徴とする。
【０００７】
また、本発明の高硬度高耐食性Ｎｉ基合金の製造方法は、
（３）質量％で、Ｃ：０．１０％以下、Ｓｉ：１％以下、Ｍｎ：１％以下、Ｃｒ：１６〜２５％、Ｍｏ：８〜２０％、Ｎｂ＋Ｔａ：５〜１０％、Ａｌ：０．０１〜１％、Ｔｉ：０．０１〜１％、Ｆｅ：３％以下、Ｎ：０．０２％以下、Ｏ：０．０２％以下を含み、残部がＮｉおよび不可避的不純物からなる合金粉末を、成形し、焼結し、１０００〜１２００℃の温度で固溶化処理した後、６００〜７５０℃の温度で８〜３２時間時効処理することを特徴とする。
【０００８】
さらに、
（４）質量％で、Ｃ：０．１０％以下、Ｓｉ：１％以下、Ｍｎ：１％以下、Ｃｕ：０．１〜５％、Ｃｒ：１６〜２５％、Ｍｏ：８〜２０％、Ｎｂ＋Ｔａ：５〜１０％、Ａｌ：０．０１〜１％、Ｔｉ：０．０１〜１％、Ｆｅ：３％以下、Ｎ：０．０２％以下、Ｏ：０．０２％以下を含み、残部がＮｉおよび不可避的不純物からなる合金粉末を、成形し、焼結し、１０００〜１２００℃の温度で固溶化処理した後、６００〜７５０℃の温度で８〜３２時間時効処理することを特徴とする。
【０００９】
【発明の実施の形態】
以下、本発明の高硬度高耐食性Ｎｉ基合金において、化学成分の含有率を限定する理由について説明する。
Ｃ：０．１０％以下
Ｃは、Ｎｂ、Ｔｉ、Ｃｒと結合して炭化物を形成するが、過剰に含有すると、母相中のＮｂ、Ｔｉ、Ｃｒの濃度低下をきたして合金の硬さ低下、耐食性の低下を招く。上記の弊害の許し得る限界として、Ｃ含有率の上限を０．１０％とする。
【００１０】
Ｓｉ：１％以下
Ｓｉは、合金の溶製時に脱酸元素として作用し、合金の清浄化に寄与する。しかし、過剰に含有すると合金の靭性を低下せしめるので、許し得る限界として、Ｓｉ含有率の上限を１％とする。
【００１１】
Ｍｎ：１％以下
Ｍｎは、合金の溶解時に脱酸・脱硫元素として有効な元素であるが、過剰に含有すると合金の耐食性を低下させるので、許し得る限界として、Ｍｎ含有率の上限を１％とする。
【００１２】
Ｃｒ：１６〜２５％
Ｃｒは、合金の耐食性を向上するために重要な元素である。前記効果を発揮するためには、Ｃｒを１６％以上含有する必要がある。しかし、過剰に含有するとσ相を析出して耐食性が低下するばかりでなく、合金の靭性が低下する。それゆえ、Ｃｒ含有率の上限を２５％とする。
【００１３】
Ｍｏ：８〜２０％
Ｍｏは、合金の耐食性を向上するために添加する。前記効果を発揮するためには、Ｍｏの含有率を８％以上とする必要がある。しかし、過剰にＭｏを含有すると合金の靭性を低下させるのでＭｏ含有率の上限を２０％とする。
【００１４】
Ｎｂ＋Ｔａ：５〜１０％
ＮｂおよびＴａは、いずれも合金生地中にガンマダブルプライム相（Ｎｉ3（Ｎｂ、Ｔａ））を析出し合金の硬さを向上させるために添加する。前記効果を十分に発揮するためには、少なくとも５％以上の（Ｎｂ＋Ｔａ）を含有する必要がある。しかし、過剰に（Ｎｂ＋Ｔａ）を含有すると、硬さの上昇の効果が飽和していたずらにコストを上昇するばかりでなく、固溶化処理および時効処理において、結晶粒界にδ相が析出して合金の靭性が低下するとともに耐食性も低下するので（Ｎｂ＋Ｔａ）含有率の上限を１０％とする。
【００１５】
Ａｌ：０．０１〜１％、Ｔｉ：０．０１〜１％
ＡｌおよびＴｉは、いずれもガンマダブルプライム相（Ｎｉ3（Ｎｂ、Ｔａ））を安定化しσ相の析出を抑制するために添加する。前記効果を発揮するためにはＡｌは０．０１％以上、Ｔｉは０．０１％以上を含有する必要がある。しかし、過剰に含有すると、むしろガンマダブルプライム相を不安定にしてしまう。また、アトマイズ法によって合金粉末を製造する際に、噴霧ノズルを閉塞せしめるなどの不都合を生じるので、ＡｌおよびＴｉの含有率の上限を、それぞれ、１％とする。
【００１６】
Ｆｅ：３％以下
Ｆｅは、合金の製造過程で不純物として介入し、合金の耐食性を損なうのでＦｅの含有量は少ないほど好ましい。しかし、極度にＦｅ含有率を低めることはコスト上昇を招くので、耐食性低下の許し得る限界としてＦｅ含有率の上限を３％とする。
【００１７】
Ｎ：０．０２％以下
Ｎは、Ａｌ、Ｔｉと結合して窒化物を形成し、Ａｌ、Ｔｉの効果を低減するので、Ｎの含有率は低いほど好ましいが、経済性を考慮して、Ｎ含有率の上限を０．０２％とする。
【００１８】
Ｏ：０．０２％以下
Ｏは、Ａｌと結合して酸化物を形成し、Ａｌの添加効果を損なう。また、合金粉末製造時に合金粉末表面に形成される酸化膜は、焼結固化後の合金の耐食性を劣化する原因となる。合金に対する前記弊害の許し得る限界として、Ｏ含有率の上限を０．０２％とする。
【００１９】
Ｃｕ：０．１〜５％
Ｃｕは、合金の耐食性を向上する効果を有するので添加することができる。その効果を発揮するためには０．１％以上添加することが必要である。しかし、過剰に含有すると合金の硬さを低下させるので、Ｃｕ含有率の上限を５％とする。
【００２０】
本発明の高硬度高耐食性Ｎｉ基合金は、前記のように調整された化学組成を有するとともに、１０００〜１２００℃の温度で固溶化処理後、６００〜７５０℃の温度で８〜３２時間時効処理されることによって所要の高硬度と高耐食性とを発揮するものである。
【００２１】
すなわち、固溶化処理によって、合金の凝固時または合金粉末の焼結時に該合金の結晶粒界に析出したδ相を生地に固溶させる。固溶化処理温度が１０００℃未満であると前記δ相の固溶が十分でなく、後述の時効処理で高い硬さが得られないので固溶化処理温度の下限を１０００℃とする。また、固溶化処理温度が１２００℃を超えると結晶粒の粗大化が顕著となり、合金の耐食性が低下するので固溶化処理温度の上限を１２００℃とする。
【００２２】
時効処理は、前記固溶化処理を施した合金中にガンマダブルプライム相（Ｎｉ3（Ｎｂ、Ｔａ））を析出させ、合金を４００ＨＶ以上の高硬度にするために行う。時効処理温度が６００℃未満ではガンマダブルプライム相の析出が十分に行われないので前記高硬度が得られず、時効処理温度が７５０℃を超えるとδ相の析出により硬さが低下する。また、時効処理時間が８時間未満ではガンマダブルプライム相の析出が十分に行われず、時効処理時間が３２時間を超えると過時効となっていずれも高い硬さが得られない。合金を４００ＨＶ以上の高硬度にするためには、時効処理温度の下限を６００℃、上限を７５０℃とし、時効処理時間の下限を８時間、上限を３２時間とする必要がある。
【００２３】
次に、本発明の高硬度高耐食性Ｎｉ基合金の製造方法について説明する。
本発明の高硬度高耐食性Ｎｉ基合金は、所要の化学組成を有する合金粉末を成形し、焼結し、１０００〜１２００℃の温度で固溶化処理後、６００〜７５０℃の温度で８〜３２時間時効処理して製造する。
【００２４】
前記合金粉末は、公知の合金粉末製造方法によって製造することができる。該合金粉末の粉末粒度は１０００μｍ以下で、見掛け密度４．５ｇ／ｃｍ3、タップ充填密度５．５ｇ／ｃｍ3以上とすることが好ましい。成形および焼結は、公知の粉末冶金法によって行う。好ましくは、ＨＩＰ処理によって成形、焼結して高密度化する。次いで、固溶化処理、時効処理を施して高硬度高耐食性Ｎｉ基合金とする。
【００２５】
【実施例】
アルゴンを用いたガスアトマイズ法によって、表１に示す化学組成を有する合金粉末を製造し、分級して粉末粒度５００μｍ以下の球状の合金粉末を得た。ここに、合金ＩはＩｎｃｏｎｅｌ６２５相当合金である。
【００２６】
【表１】
軟鋼製のカプセルに前記合金粉末を封入し、１２００℃で１０００ｋｇｆ／ｃｍ2の条件でＨＩＰ処理を行って外径４０ｍｍの丸棒とした。該丸棒から下記の各試験用素材を切出し、それぞれ所定の熱処理を施してから各試験片に仕上げた。
【００２８】
硬さ測定：
ビッカース硬さ計を用い、荷重５ｋｇｆで室温における硬さを測定した。５点の硬さ測定値の平均をもって試験片の硬さの代表値とした。
パルス通電腐食試験：
電解液中で通電している時に生じる腐食に対する耐食性を調べるため、直径１０ｍｍ×２０ｍｍの円筒表面を試験面とする試験片について、液温５０℃の鉄イオンを含む硫酸水溶液中で、１サイクル０．７秒のうち電流密度２６０ｍＡ／ｄｍ2で０．２秒間通電、０．５秒間通電なしの通電サイクルを８時間繰返した後の腐食減量を測定し、試験片の単位表面積当りの腐食減量を算出してパルス通電腐食量とした。
【００２９】
アノード分極特性測定：
液温５０℃の２０％硫酸水溶液中でアノード分極曲線を測定し、ｉcrit（不動態化のために表れる最大電流密度）および（飽和甘こう電極基準＋０．４Ｖにおける電流密度）によって耐食性を評価した。
上記の各測定・試験の結果を表２に示す。
【００３０】
【表２】
表２によれば実施例１〜７は、いずれも４００ＨＶ以上の硬さを示し、（Ｎｂ＋Ｔａ）含有率が低い比較例１（Ｉｎｃｏｎｅｌ６２５相当合金）に比べて硬さは高く、また、パルス通電腐食量は比較例１と同等であるが、ｉcritおよびｉ0.4は比較例１よりも小さく、耐食性は、比較例１よりも優れていることが判る。
【００３２】
Ｍｏ含有率が低い比較例２は、パルス通電腐食量、ｉcritおよびｉ0.4が高く、耐食性が劣る。Ｃｒ含有率が高い比較例３は、σ相の析出によって硬さは高いが耐食性が劣る。
【００３３】
固溶化処理および時効処理のいずれも行わず、ＨＩＰ処理のままの比較例４は、硬さが低く、また、結晶粒界にδ相が残留しており、耐食性が劣る。
１２００℃を超える高い固溶化処理温度で処理された比較例５は、硬さは高いが、結晶粒の粗大化のために耐食性が劣化している。固溶化処理温度が１０００℃未満の温度である比較例６は、δ相の固溶が十分でないために時効硬化が十分に起こらず、硬さが低く、また、耐食性も劣る。
【００３４】
７５０℃を超える高温で時効処理された実施例７は、固溶化処理で消失していたδ相が再び生成したため硬さが低い。また、６００℃よりも低い温度で時効処理された比較例８は、耐食性は良好であるが、時効硬化が十分に生じていないので硬さが低い。
３２時間を超える長時間の時効処理を施した比較例９は、過時効を生じて硬さが低下している。また、時効処理時間が８時間未満の短時間である比較例１０は、十分な時効硬化が生じておらず硬さが低い。
上記のとおり、本発明の高硬度高耐食性Ｎｉ基合金は、本発明が限定する化学組成と固溶化熱処理および時効処理の条件との組合せから得られるものである。
【００３５】
【発明の効果】
以上に説明したように、本発明の高硬度高耐食性Ｎｉ基合金は、化学成分の配合と固溶化熱処理および時効処理の条件とを工夫することによって得られたもので、本発明によって、優れた耐食性を備え、かつ、４００ＨＶ以上の高硬度を有する合金と該合金の製造方法を提供することができる。
【００３６】
これによって、電気めっき用通電ロール、プラスチック射出成形機用シャフト、ディーゼルエンジンの燃料噴射ノズル等、高い硬さと耐食性とを要する部品の特性が向上することが期待され、その経済効果は極めて大きいといえる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Ni-based alloy suitable for applications requiring high hardness and corrosion resistance, such as a current-carrying roll for electroplating, a shaft for a plastic injection molding machine, and a fuel injection nozzle for a diesel engine, and a method for producing the same.
[0002]
[Prior art]
Mechanical parts such as an electroplating energizing roll, a plastic injection molding machine shaft, and a diesel engine fuel injection nozzle are used in a highly corrosive environment in a state of friction with other parts at a high surface pressure. That is, the electroplating energizing roll is used by being immersed in a metal plating solution, for example, a galvanizing solution bath, and corrosion occurs during energization. At the same time, wear occurs due to rotational contact with the material to be plated. In shafts for plastic injection molding machines, shafts may be corroded when molding highly corrosive resins such as fluororesins, and fiber reinforced resins in which glass fibers are mixed in the resin may be molded. Therefore, shaft wear becomes a problem. In the fuel injection nozzle of a diesel engine, at the same time as corrosion due to sulfur contained in the fuel, the needle valve comes into contact with a high surface pressure and wear due to their sliding occurs. Therefore, materials used for these applications are required to have high hardness and corrosion resistance that can withstand high surface pressure and provide wear resistance.
[0003]
Conventionally, Ni-based superalloys such as Inconel 625 (Ni-21Cr-9Mo-4Nb alloy) and Hastelloy C (Ni-17Cr-19Mo-5W alloy) have been used for the above-described applications. However, there is a problem that the hardness is not sufficient. The Ni-based corrosion-resistant alloy is improved to improve the characteristics, such as a Ni-based alloy (JP-A-2-270939) using precipitation hardening of gamma prime (Ni 3 (Al, Ti)), a solid solution A Ni-based alloy (Japanese Patent Laid-Open No. 10-204561) using reinforcement is disclosed. However, in the former, the corrosion resistance is not yet sufficient, and in the latter, the orthorhombic δ phase (Ni 3 (Nb, Ta)) precipitates in the crystal grain boundary, which may impair the corrosion resistance of the crystal grain boundary. Further, the hardness was insufficient at 300 HV or less. On the other hand, a Ni-based alloy using precipitation hardening of σ phase (for example, Japanese Patent Laid-Open No. 5-195137) can obtain a high hardness of 380 HV or more, but is fine due to the difference in corrosion resistance between the σ phase and the parent phase. Corrosion sometimes causes inconvenience that the alloy surface has a cloudy appearance.
[0004]
[Problems to be solved by the invention]
In view of the above-mentioned present situation, an object of the present invention is to provide an alloy having excellent corrosion resistance and having a high hardness of 400 HV or more and a method for producing the alloy.
[0005]
[Means for Solving the Problems]
As a result of various investigations to solve the above problems, the inventors have devised the alloy composition on the basis of the Ni-21Cr-9Mo-4Nb alloy, further applied an appropriate heat treatment, and added the body in the alloy fabric. It has been found that high hardness can be obtained without deteriorating the corrosion resistance of the alloy by aging precipitation of tetragonal gamma double prime (Ni 3 (Nb, Ta)).
[0006]
That is, the high hardness and high corrosion resistance Ni-based alloy of the present invention is
(1) By mass%, C: 0.10% or less, Si: 1% or less, Mn: 1% or less, Cr: 16-25%, Mo: 8-20%, Nb + Ta: 5-10%, Al: 0.01~1%, Ti: 0.01~1%, Fe: 3% or less, N: 0.02% or less, O: contains 0.02% or less, the remaining portion of Ni and unavoidable impurities The solution is characterized by being subjected to an aging treatment at a temperature of 600 to 750 ° C. for 8 to 32 hours after a solid solution treatment at a temperature of 1000 to 1200 ° C.
(2) By mass%, C: 0.10% or less, Si: 1% or less, Mn: 1% or less, Cu: 0.1 to 5%, Cr: 16 to 25%, Mo: 8 to 20%, Nb + Ta: 5 to 10%, Al: 0.01 to 1%, Ti: 0.01 to 1%, Fe: 3% or less, N: 0.02% or less, O: 0.02% or less, the rest The part is composed of Ni and inevitable impurities, and is subjected to a solution treatment at a temperature of 1000 to 1200 ° C. and then an aging treatment at a temperature of 600 to 750 ° C. for 8 to 32 hours.
[0007]
In addition, the manufacturing method of the high hardness and high corrosion resistance Ni-based alloy of the present invention is
(3) By mass%, C: 0.10% or less, Si: 1% or less, Mn: 1% or less, Cr: 16-25%, Mo: 8-20%, Nb + Ta: 5-10%, Al: 0.01~1%, Ti: 0.01~1%, Fe: 3% or less, N: 0.02% or less, O: contains 0.02% or less, the remaining portion is made of Ni and unavoidable impurities The alloy powder is formed, sintered, and subjected to a solution treatment at a temperature of 1000 to 1200 ° C., followed by aging treatment at a temperature of 600 to 750 ° C. for 8 to 32 hours.
[0008]
further,
(4) By mass%, C: 0.10% or less, Si: 1% or less, Mn: 1% or less, Cu: 0.1 to 5%, Cr: 16 to 25%, Mo: 8 to 20%, Nb + Ta: 5 to 10%, Al: 0.01 to 1%, Ti: 0.01 to 1%, Fe: 3% or less, N: 0.02% or less, O: 0.02% or less, the rest An alloy powder comprising Ni and inevitable impurities is formed, sintered, and subjected to a solution treatment at a temperature of 1000 to 1200 ° C., followed by an aging treatment at a temperature of 600 to 750 ° C. for 8 to 32 hours. And
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the reason for limiting the content of chemical components in the high hardness and high corrosion resistance Ni-based alloy of the present invention will be described.
C: 0.10% or less C combines with Nb, Ti, and Cr to form carbides. However, if excessively contained, the concentration of Nb, Ti, and Cr in the parent phase is reduced, and the hardness of the alloy is reduced. , Leading to a decrease in corrosion resistance. The upper limit of the C content is set to 0.10% as an allowable limit of the above-described adverse effects.
[0010]
Si: 1% or less Si acts as a deoxidizing element during melting of the alloy and contributes to cleaning of the alloy. However, since an excessive content decreases the toughness of the alloy, the upper limit of the Si content is set to 1% as an allowable limit.
[0011]
Mn: 1% or less Mn is an element that is effective as a deoxidizing / desulfurizing element when the alloy is melted. However, if excessively contained, the corrosion resistance of the alloy is lowered, so the upper limit of the Mn content is 1% as an allowable limit. And
[0012]
Cr: 16-25%
Cr is an important element for improving the corrosion resistance of the alloy. In order to exhibit the said effect, it is necessary to contain 16% or more of Cr. However, if it is contained excessively, not only the σ phase is precipitated and the corrosion resistance is lowered, but also the toughness of the alloy is lowered. Therefore, the upper limit of the Cr content is set to 25%.
[0013]
Mo: 8-20%
Mo is added to improve the corrosion resistance of the alloy. In order to exhibit the effect, the Mo content needs to be 8% or more. However, if Mo is excessively contained, the toughness of the alloy is lowered, so the upper limit of the Mo content is set to 20%.
[0014]
Nb + Ta: 5-10%
Both Nb and Ta are added to precipitate a gamma double prime phase (Ni 3 (Nb, Ta)) in the alloy fabric and improve the hardness of the alloy. In order to exhibit the effect sufficiently, it is necessary to contain at least 5% (Nb + Ta). However, if (Nb + Ta) is contained excessively, not only the effect of increasing the hardness is saturated, but also the cost is increased, and in the solution treatment and aging treatment, a δ phase is precipitated at the grain boundary, and the alloy Therefore, the upper limit of the (Nb + Ta) content is set to 10%.
[0015]
Al: 0.01-1%, Ti: 0.01-1%
Al and Ti are both added to stabilize the gamma double prime phase (Ni 3 (Nb, Ta)) and suppress the precipitation of the σ phase. In order to exhibit the effect, it is necessary to contain 0.01% or more of Al and 0.01% or more of Ti. However, if contained excessively, the gamma double prime phase is rather unstable. Further, when producing the alloy powder by the atomizing method, problems such as blocking the spray nozzle occur, so the upper limit of the Al and Ti content is 1%.
[0016]
Fe: 3% or less Fe is preferable as the Fe content is small because Fe intervenes as an impurity in the production process of the alloy and impairs the corrosion resistance of the alloy. However, extremely reducing the Fe content causes an increase in cost, so the upper limit of the Fe content is set to 3% as an allowable limit of the corrosion resistance reduction.
[0017]
N: 0.02% or less N combines with Al and Ti to form nitrides and reduces the effects of Al and Ti. Therefore, the lower the N content, the better. The upper limit of the N content is 0.02%.
[0018]
O: 0.02% or less O combines with Al to form an oxide and impairs the effect of addition of Al. In addition, the oxide film formed on the surface of the alloy powder during the production of the alloy powder causes deterioration of the corrosion resistance of the alloy after sintered solidification. As an allowable limit of the above-mentioned adverse effects on the alloy, the upper limit of the O content is set to 0.02%.
[0019]
Cu: 0.1 to 5%
Cu can be added because it has the effect of improving the corrosion resistance of the alloy. In order to exhibit the effect, it is necessary to add 0.1% or more. However, since the hardness of an alloy will fall when it contains excessively, the upper limit of Cu content rate shall be 5%.
[0020]
The high hardness and high corrosion resistance Ni-based alloy of the present invention has a chemical composition adjusted as described above, and is subjected to a solution treatment at a temperature of 1000 to 1200 ° C, and then an aging treatment at a temperature of 600 to 750 ° C for 8 to 32 hours. As a result, the required high hardness and high corrosion resistance are exhibited.
[0021]
That is, by the solution treatment, the δ phase precipitated at the grain boundaries of the alloy at the time of solidification of the alloy or sintering of the alloy powder is dissolved in the dough. If the solution treatment temperature is less than 1000 ° C., the δ phase is not sufficiently dissolved, and high hardness cannot be obtained by the aging treatment described below, so the lower limit of the solution treatment temperature is 1000 ° C. Further, when the solution treatment temperature exceeds 1200 ° C., the coarsening of crystal grains becomes remarkable, and the corrosion resistance of the alloy is lowered. Therefore, the upper limit of the solution treatment temperature is set to 1200 ° C.
[0022]
The aging treatment is performed to precipitate a gamma double prime phase (Ni 3 (Nb, Ta)) in the alloy subjected to the solution treatment so that the alloy has a high hardness of 400 HV or more. If the aging treatment temperature is less than 600 ° C., the gamma double prime phase is not sufficiently precipitated, so that the high hardness cannot be obtained. If the aging treatment temperature exceeds 750 ° C., the hardness decreases due to the precipitation of the δ phase. Further, when the aging treatment time is less than 8 hours, the gamma double prime phase is not sufficiently precipitated, and when the aging treatment time exceeds 32 hours, it becomes over-aged and neither of them has high hardness. In order to increase the hardness of the alloy to 400 HV or higher, it is necessary that the lower limit of the aging treatment temperature is 600 ° C., the upper limit is 750 ° C., the lower limit of the aging treatment time is 8 hours, and the upper limit is 32 hours.
[0023]
Next, a method for producing the high hardness and high corrosion resistance Ni-based alloy of the present invention will be described.
The high hardness and high corrosion resistance Ni-based alloy of the present invention is formed by molding and sintering an alloy powder having a required chemical composition, followed by solution treatment at a temperature of 1000 to 1200 ° C., and 8 to 32 at a temperature of 600 to 750 ° C. Manufactured with time aging treatment.
[0024]
The alloy powder can be manufactured by a known alloy powder manufacturing method. The alloy powder preferably has a particle size of 1000 μm or less, an apparent density of 4.5 g / cm 3 , and a tap packing density of 5.5 g / cm 3 or more. Molding and sintering are performed by a known powder metallurgy method. Preferably, the density is increased by molding and sintering by HIP treatment. Next, a solid solution treatment and an aging treatment are performed to obtain a high hardness and high corrosion resistance Ni-based alloy.
[0025]
【Example】
An alloy powder having the chemical composition shown in Table 1 was manufactured by gas atomization using argon and classified to obtain a spherical alloy powder having a powder particle size of 500 μm or less. Here, the alloy I is an Inconel 625 equivalent alloy.
[0026]
[Table 1]
The alloy powder was enclosed in a mild steel capsule and subjected to HIP treatment at 1200 ° C. under the condition of 1000 kgf / cm 2 to obtain a round bar having an outer diameter of 40 mm. Each test material described below was cut out from the round bar, and each test piece was finished after being subjected to a predetermined heat treatment.
[0028]
Hardness measurement:
Using a Vickers hardness meter, the hardness at room temperature was measured with a load of 5 kgf. The average of the five hardness measurement values was used as the representative value of the hardness of the test piece.
Pulse current corrosion test:
In order to investigate the corrosion resistance against corrosion generated when energized in the electrolytic solution, a test piece having a cylindrical surface having a diameter of 10 mm × 20 mm as a test surface was tested in a sulfuric acid aqueous solution containing iron ions at a liquid temperature of 50 ° C. for one cycle 0. The corrosion weight loss per unit surface area of the test piece was measured by measuring the corrosion weight loss after repeating the energization cycle for 0.2 seconds and no current for 0.5 seconds for 8 hours at a current density of 260 mA / dm 2 within 7 seconds. This was calculated as the amount of pulse current corrosion.
[0029]
Anode polarization characteristics measurement:
An anodic polarization curve was measured in a 20% sulfuric acid aqueous solution at a liquid temperature of 50 ° C., and corrosion resistance was evaluated by i crit (maximum current density that appears due to passivation) and (current density at saturated gauze electrode reference + 0.4 V). did.
Table 2 shows the results of the above measurements and tests.
[0030]
[Table 2]
According to Table 2, each of Examples 1 to 7 has a hardness of 400 HV or higher, the hardness is higher than that of Comparative Example 1 (Inconel 625 equivalent alloy) having a low (Nb + Ta) content, and pulse current corrosion. Although the amount is equivalent to that of Comparative Example 1, i crit and i 0.4 are smaller than those of Comparative Example 1, and it can be seen that the corrosion resistance is superior to that of Comparative Example 1.
[0032]
Comparative Example 2 having a low Mo content has high pulse current corrosion amount, i crit and i 0.4 , and is inferior in corrosion resistance. In Comparative Example 3 having a high Cr content, the hardness is high due to the precipitation of the σ phase, but the corrosion resistance is inferior.
[0033]
In Comparative Example 4 in which neither the solution treatment nor the aging treatment is performed and the HIP treatment is performed, the hardness is low, and the δ phase remains in the crystal grain boundary, resulting in poor corrosion resistance.
Although the comparative example 5 processed at the high solution treatment temperature exceeding 1200 degreeC has high hardness, corrosion resistance has deteriorated because of the coarsening of a crystal grain. In Comparative Example 6 where the solution treatment temperature is less than 1000 ° C., the δ phase is not sufficiently dissolved, so that age hardening does not occur sufficiently, the hardness is low, and the corrosion resistance is also inferior.
[0034]
In Example 7, which was aging treated at a high temperature exceeding 750 ° C., the hardness was low because the δ phase that had disappeared in the solution treatment was generated again. Moreover, although the comparative example 8 age-treated at the temperature lower than 600 degreeC has favorable corrosion resistance, since age hardening has not fully produced, hardness is low.
The comparative example 9 which performed the long-term aging treatment exceeding 32 hours produced overaging and the hardness has fallen. Further, in Comparative Example 10 in which the aging treatment time is a short time of less than 8 hours, sufficient age hardening has not occurred and the hardness is low.
As described above, the high hardness and high corrosion resistance Ni-based alloy of the present invention is obtained from a combination of the chemical composition limited by the present invention and the conditions for solution heat treatment and aging treatment.
[0035]
【The invention's effect】
As described above, the high hardness and high corrosion resistance Ni-based alloy of the present invention was obtained by devising the chemical composition, solid solution heat treatment, and aging treatment conditions. An alloy having corrosion resistance and having a high hardness of 400 HV or more and a method for producing the alloy can be provided.
[0036]
This is expected to improve the properties of parts that require high hardness and corrosion resistance, such as electroplating rolls, plastic injection molding shafts, and fuel injection nozzles for diesel engines. .
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| JP6148843B2 (en) * | 2012-10-02 | 2017-06-14 | 三菱日立パワーシステムズ株式会社 | Large cast member made of nickel base alloy and method for producing the same |
| US10112254B2 (en) | 2014-08-21 | 2018-10-30 | Huntington Alloys Corporation | Method for making clad metal pipe |
| JP6499546B2 (en) * | 2015-08-12 | 2019-04-10 | 山陽特殊製鋼株式会社 | Ni-based superalloy powder for additive manufacturing |
| JP7153502B2 (en) * | 2018-08-09 | 2022-10-14 | 山陽特殊製鋼株式会社 | Molded body made of nitride-dispersed Ni-based alloy |
| CN113020624A (en) * | 2021-03-10 | 2021-06-25 | 西北工业大学 | Heat treatment method of laser stereo-forming TC4 titanium alloy |
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| JPS5543062B2 (en) * | 1972-12-29 | 1980-11-04 | ||
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| JP2554049B2 (en) * | 1986-01-20 | 1996-11-13 | 三菱重工業株式会社 | Ni-based alloy and method for producing the same |
| JPH01219134A (en) * | 1988-02-26 | 1989-09-01 | Kubota Ltd | Alloy for electric conductive roll in electroplating equipment |
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| JPH09279287A (en) * | 1996-04-10 | 1997-10-28 | Sanyo Special Steel Co Ltd | Grain dispersed powdery heat resistant alloy |
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