JP2004068134A

JP2004068134A - Ni-based alloy superior in stress corrosion cracking resistance in environment of inorganic acid-containing supercritical water

Info

Publication number: JP2004068134A
Application number: JP2002232847A
Authority: JP
Inventors: Katsuo Sugawara; 菅原　克生
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 2002-08-09
Filing date: 2002-08-09
Publication date: 2004-03-04
Anticipated expiration: 2022-08-09
Also published as: JP4151065B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Ni-based alloy having stress corrosion cracking resistance, as a material of an apparatus for decomposing/oxidizing an organic hazardous material such as VX gas, GB (sarin) gas and mustard gas, which is used as a chemical weapon. <P>SOLUTION: The Ni-based alloy superior in stress corrosion cracking resistance in an environment of an inorganic acid-containing supercritical water has a composition comprising more than 36% but less than 42% Cr, more than 0.01% but less than 0.5% W, 0.001-0.05% Mg, 0.001-0.04% N, 0.05-0.5% Mn, more than 1.0% but 6% or less Nb as needed, further one or two of 0.01% or more but less than 0.5% Mo and 0.01-0.1% Hf as needed, further one or two of 0.1-10% Fe and 0.01-0.1% Si as need, the balance Ni with unavoidable impurities, and C contained as the unavoidable impurity adjusted to an amount of 0.05% or less. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【産業上の利用分野】
この発明は、無機酸含有超臨界水環境下において優れた耐応力腐食割れ性を有するＮｉ基合金およびこのＮｉ基合金からなる超臨界水プロセス反応装置用部材に関するものであり、特に、ＶＸガス、ＧＢ（サリン）ガス、マスタードガスなど化学兵器などに用いられた有機系有害物質を分解・酸化することによって生じる硫酸、燐酸、フッ酸などの塩素を含まない無機酸を含む超臨界水に対して優れた耐応力腐食割れ性を有するＮｉ基合金およびこのＮｉ基合金からなる超臨界水プロセス反応装置用部材に関するものである。
【０００２】
【従来の技術】
臨界点を越える温度／圧力下にある水（具体的には３７４℃／２２．１ＭＰａを越える温度／圧力下にある水）を超臨界水と呼んでおり、超臨界水は多様な物質を溶解する特性があり、この超臨界状態の水は非凝縮性の高密度ガス状態となり、常温では極めて溶解度が小さい無極性あるいは弱極性の物質（炭化水素化合物や気体）でも完全に溶解し、さらに酸素を加えることで、溶解した物質を酸化・分解させることができると言われている。
【０００３】
化学兵器等に使用される有機系有害物質も例外ではなく、超臨界水に完全に溶解し、さらに加えられた溶存酸素とこれら化学兵器等に使用される有機系有害物質が超臨界水中で反応することにより、二酸化炭素、水のほかに硫酸、燐酸などの無害物質に酸化分解される。例えば、ＶＸガスが酸化分解されると硫酸とリン酸が生成し、ＧＢガスが酸化分解されるとフッ酸や燐酸が生成する。そのため、近年、米国では、ＶＸガス、ＧＢ（サリン）ガス、マスタードガスなどを使用した化学兵器を廃棄するのに、超臨界水を使用して、これら難分解性のＶＸガス、ＧＢ（サリン）ガス、マスタードガスなどの有機系有害物質を分解・酸化して無害化する試みがなされている。この超臨界水によるＶＸガス、ＧＢ（サリン）ガス、マスタードガスなどの有機系有害物質を分解・酸化して無害化する方法が確立されると、従来の焼却による処理方法と比べて、超臨界水および酸化剤は環境への悪影響がなく、超臨界水は高い反応性を持つところからＶＸガス、ＧＢ（サリン）ガス、マスタードガスなどの有機系有害物質を短時間で分解・酸化して無害化することができ、さらに閉鎖系内で分解処理が可能なために排出物による環境汚染の恐れがなくなる。
【０００４】
かかる超臨界水を反応溶媒として利用してＶＸガス、ＧＢ（サリン）ガス、マスタードガスなどの有機系有害物質を分解・酸化して無害化するには、高温・高圧（４００〜６５０℃、２２．１〜８０ＭＰａ）の超臨界水中において酸化分解後に生成された硫酸、燐酸、フッ酸など無機酸と高濃度の酸素が共存する環境となるところから、有機系有害物質を無害化する装置におけるプロセス反応容器の材料にはこうした無機酸含有超臨界水下での耐食性が必要となる。
【０００５】
そのため、超臨界水を使用したプロセス反応装置の反応容器に使用される金属材料には、高耐食性で知られるＮｉ基合金が装置のプロセス反応容器材料として候補にあげられている。例えば、インコネル（商品名）６２５（ＡＳＴＭ　ＵＮＳ　Ｎ０６６２５で規定されており、その成分組成は、例えば、質量％でＣｒ：２１．０％、Ｍｏ：８．４％、Ｎｂ＋Ｔａ：３．６％、Ｆｅ：３．８％、Ｃｏ：０．６％、Ｔｉ：０．２％、Ｍｎ：０．２％を含有し、残部：Ｎｉ＋不可避不純物からなる）やハステロイ（商品名）Ｃ−２７６（ＡＳＴＭ　ＵＮＳ　Ｎ１０２７６で規定されており、その成分組成は、例えば、Ｃｒ：１５．５％、Ｍｏ：１６．１％、Ｗ：３．７％、Ｆｅ：５．７％、Ｃｏ：０．５％、Ｍｎ：０．５％を含有し、残部：Ｎｉ＋不可避不純物からなる）などのＮｉ基耐食合金が使用されている。
最近では、Ｃｒ含有量のさらに高いＮｉ基合金が無機酸含有超臨界水に対して一層耐食性が優れているという報告もあり、このＣｒ含有量のさらに高いＮｉ基合金としてハステロイ（商品名）Ｇ−３０（ＡＳＴＭ　ＵＮＳ　Ｎ０６０３０（成分組成は、例えば、Ｃｒ：２８．７％、Ｍｏ：５．０％、Ｍｎ：１．１％、Ｆｅ：１４．６％、Ｃｕ：１．８％、Ｗ：２．６、Ｃｏ：１．８７％を含有し、残部：Ｎｉ＋不可避不純物からなる）といったＮｉ−高Ｃｒ型合金が注目されている。
【０００６】
【発明が解決しようとする課題】
これら従来のＮｉ基合金は、板または管に成形して加工素材を作製し、この加工素材にさらに圧延または曲げなどの成形加工を施してしてプロセス反応装置の反応容器または配管に仕上げられる。このようにして仕上げられた反応容器または配管は成形加工により作製されるために内部応力および内部歪の残留は避けられない。
ところが、従来のＮｉ基耐食合金のうちインコネル６２５やハステロイＣ−２７６は、硫酸、燐酸、フッ酸等の塩素を含まない無機酸を含む超臨界水に接触させると応力腐食割れが発生し、そのためにこの従来のＮｉ基耐食合金のうちインコネル６２５やハステロイＣ−２７６を有機系有害物質を無害化する装置における反応容器および配管の素材として使用すると長期間操業が困難であった。
また、ハステロイ（商品名）Ｇ−３０は、操業初期の硫酸、燐酸、フッ酸等の酸を含む超臨界水下での耐応力腐食割れ性は十分であっても、相安定性が不十分であるために、使用温度（４００〜６５０℃）において相変態が徐々に進行し、この相変態が進行した状態で高温・高圧の超臨界水中環境下のような応力場が発生すると応力腐食割れが発生し、長期間使用するプロセス反応装置の素材としては適当ではない。
【０００７】
【課題を解決する手段】
そこで、本発明者らは、無機酸含有超臨界水環境下でも応力腐食割れが発生することなく、さらに使用温度（４００〜６５０℃）で長時間保持しても相安定性が優れるために相変態の進行が抑制されて無機酸含有超臨界水環境下において十分な耐応力腐食割れ性を示すＮｉ基合金を開発し、このＮｉ基合金を使用して無機酸含有超臨界水環境下でも長期間操業することができる超臨界水プロセス反応装置用部材を得るべく鋭意研究を行った。その結果、
（イ）質量％（以下、％は質量％を示す）で、Ｃｒ：３６超〜４２％未満、Ｗ：０．０１超〜０．５％未満、Ｍｇ：０．００１〜０．０５％、Ｎ：０．００１〜０．０４％、Ｍｎ：０．０５〜０．５％を含有し、残部がＮｉおよび不可避不純物からなり、不可避不純物として含まれるＣ量を０．０５％以下に調整した組成を有するＮｉ基合金は、無機酸含有超臨界水環境、特に硫酸、燐酸、フッ酸などの塩素を含まない無機酸含有超臨界水環境下において耐応力腐食割れ性に優れ、かつ相安定性に優れているところから使用温度（４００〜６５０℃）に長時間保持しても相変態の進行が抑制されて応力腐食割れがなく、このＮｉ基合金を超臨界水を使用した有機系有害物質を無害化する装置における反応容器材に使用すると一層の長期操業が可能となる、
（ロ）前記（イ）記載の組成を有するＮｉ基合金に、さらにＮｂ：１．０超〜６％を添加すると耐応力腐食割れ性が一層向上する、
（ハ）前記（イ）記載の組成を有するＮｉ基合金に、さらに、Ｍｏ：０．０１〜０．５％未満、Ｈｆ：０．０１〜０．１％の１種または２種を添加すると、耐応力腐食割れ性が一層向上する、
（ニ）前記（イ）記載の組成を有するＮｉ基合金に、さらに、Ｆｅ：０．１〜１０％、Ｓｉ：０．０１〜０．１％の１種または２種を添加すると、強度が一層向上する、などの研究結果が得られたのである。
【０００８】
この発明は、かかる研究結果に基づいてなされたものであって、
（１）Ｃｒ：３６超〜４２％未満、Ｗ：０．０１超〜０．５％未満、Ｍｇ：０．００１〜０．０５％、Ｎ：０．００１〜０．０４％、Ｍｎ：０．０５〜０．５％を含有し、残部がＮｉおよび不可避不純物からなり、不可避不純物として含まれるＣ量を０．０５％以下に調整した組成を有する無機酸含有超臨界水環境下での耐応力腐食割れ性に優れたＮｉ基合金、
（２）Ｃｒ：３６超〜４２％未満、Ｗ：０．０１超〜０．５％未満、Ｍｇ：０．００１〜０．０５％、Ｎ：０．００１〜０．０４％、Ｍｎ：０．０５〜０．５％を含有し、さらに、Ｎｂ：１．０超〜６％を含有し、残部がＮｉおよび不可避不純物からなり、不可避不純物として含まれるＣ量を０．０５％以下に調整した組成を有する無機酸含有超臨界水環境下での耐応力腐食割れ性に優れたＮｉ基合金、
（３）Ｃｒ：３６超〜４２％未満、Ｗ：０．０１超〜０．５％未満、Ｍｇ：０．００１〜０．０５％、Ｎ：０．００１〜０．０４％、Ｍｎ：０．０５〜０．５％を含有し、さらに、Ｍｏ：０．０１〜０．５％未満およびＨｆ：０．０１〜０．１％の内の１種または２種を含有し、残部がＮｉおよび不可避不純物からなり、不可避不純物として含まれるＣ量を０．０５％以下に調整した組成を有する無機酸含有超臨界水環境下での耐応力腐食割れ性に優れたＮｉ基合金、
（４）Ｃｒ：３６超〜４２％未満、Ｗ：０．０１超〜０．５％未満、Ｍｇ：０．００１〜０．０５％、Ｎ：０．００１〜０．０４％、Ｍｎ：０．０５〜０．５％を含有し、さらにＦｅ：０．１〜１０％およびＳｉ：０．０１〜０．１％の内の１種または２種を含有し、残部がＮｉおよび不可避不純物からなり、不可避不純物として含まれるＣ量を０．０５％以下に調整した組成を有する無機酸含有超臨界水環境下での耐応力腐食割れ性に優れたＮｉ基合金、
（５）Ｃｒ：３６超〜４２％未満、Ｗ：０．０１超〜０．５％未満、Ｍｇ：０．００１〜０．０５％、Ｎ：０．００１〜０．０４％、Ｍｎ：０．０５〜０．５％を含有し、さらにＮｂ：１．０超〜６％を含有し、さらにＭｏ：０．０１〜０．５％未満およびＨｆ：０．０１〜０．１％の内の１種または２種を含有し、残部がＮｉおよび不可避不純物からなり、不可避不純物として含まれるＣ量を０．０５％以下に調整した組成を有する無機酸含有超臨界水環境下での耐応力腐食割れ性に優れたＮｉ基合金、
（６）Ｃｒ：３６超〜４２％未満、Ｗ：０．０１超〜０．５％未満、Ｍｇ：０．００１〜０．０５％、Ｎ：０．００１〜０．０４％、Ｍｎ：０．０５〜０．５％を含有し、さらにＮｂ：１．０超〜６％を含有し、さらにＦｅ：０．１〜１０％およびＳｉ：０．０１〜０．１％の内の１種または２種を含有し、残部がＮｉおよび不可避不純物からなり、不可避不純物として含まれるＣ量を０．０５％以下に調整した組成を有する無機酸含有超臨界水環境下での耐応力腐食割れ性に優れたＮｉ基合金、
（７）Ｃｒ：３６超〜４２％未満、Ｗ：０．０１超〜０．５％未満、Ｍｇ：０．００１〜０．０５％、Ｎ：０．００１〜０．０４％、Ｍｎ：０．０５〜０．５％を含有し、さらにＭｏ：０．０１〜０．５％未満およびＨｆ：０．０１〜０．１％の内の１種または２種を含有し、さらにＦｅ：０．１〜１０％およびＳｉ：０．０１〜０．１％の内の１種または２種を含有し、残部がＮｉおよび不可避不純物からなり、不可避不純物として含まれるＣ量を０．０５％以下に調整した組成を有する無機酸含有超臨界水環境下での耐応力腐食割れ性に優れたＮｉ基合金、
（８）Ｃｒ：３６超〜４２％未満、Ｗ：０．０１超〜０．５％未満、Ｍｇ：０．００１〜０．０５％、Ｎ：０．００１〜０．０４％、Ｍｎ：０．０５〜０．５％を含有し、さらにＮｂ：１．０超〜６％を含有し、さらにＭｏ：０．０１〜０．５％未満およびＨｆ：０．０１〜０．１％の内の１種または２種を含有し、さらにＦｅ：０．１〜１０％およびＳｉ：０．０１〜０．１％の内の１種または２種を含有し、残部がＮｉおよび不可避不純物からなり、不可避不純物として含まれるＣ量を０．０５％以下に調整した組成を有する無機酸含有超臨界水環境下での耐応力腐食割れ性に優れたＮｉ基合金、
（９）前記（１）、（２）、（３）、（４）、（５）、（６）、（７）または（８）記載の組成を有するＮｉ基合金からなる超臨界水プロセス反応装置用部材、に特徴を有するものである。
【０００９】
次に、この発明のＮｉ基合金の合金組成における各元素の限定理由について詳述する．
【００１０】
Ｃｒ、Ｗ：
Ｃｒ：３６％を越えかつＷ：０．０１％を越えて含有することにより硫酸、燐酸、フッ酸などの塩素を含まない無機酸が混入する超臨界水環境下での耐応力腐食割れ性が著しく向上するが、Ｃｒが４２％以上含有するとＷとの組合せにおいて耐全面腐食性が低下することとなるのでＣｒ含有量を３６超〜４２％未満に定めた。一層好ましくは、３８超〜４１．５％である。
同様にＷは０．５％以上含有するとＣｒとの組合せにおいて加工性が低下することとなるので好ましくない。したがって、Ｗの含有量を０．０１超〜０．５％未満（一層好ましくは０．１〜０．４５％）に定めた。
【００１１】
Ｎ、ＭｎおよびＭｇ：
Ｎ、ＭｎおよびＭｇを共存させることにより、相安定性を向上させることができる。すなわち、Ｎ、ＭｎおよびＭｇは母相であるＮｉ−ｆｃｃ相を安定化させ、第２層を析出しにくくする効果がある。しかし、Ｎの含有量が０．００１％未満では相安定化の効果はなく、一方、０．０４％を超えて含有すると窒化物を形成し超臨界水環境下での耐食性が劣化するためＮの含有量を０．００１〜０．０４％（一層好ましくは、０．００５〜０．０３％）とした。
同様に、Ｍｎの含有量が０．０５％未満では相安定化の効果はなく、一方、０．５％を超えて含有すると無機酸含有超臨界水環境における耐応力腐食割れ性が劣化するため、Ｍｎの含有量を０．０５〜０．５％（一層好ましくは、０．１〜０．４％）とした。
同様にＭｇも相安定性を向上させる成分であるが、その含有量が０．００１％未満では相安定化の効果はなく、一方、０．０５％を超えて含有すると無機酸含有超臨界水環境における耐応力腐食割れ性が劣化するため、Ｍｇの含有量を０．００１〜０．０５％（一層好ましくは、０．０１０％〜０．０４０％）とした。
【００１２】
Ｎｂ：
Ｎｂは、Ｃｒ：３６％を越えかつＷ：０．０１％を越えて含有するＮｉ基合金に添加することにより塩素を含まない酸素含有超臨界水環境下で耐全面腐食性を一層向上させる効果があるので必要に応じて添加するが、その場合、１．０％を越えて含有することで効果を示すが、６％を超えて含有すると相安定性が劣化する。従って、この発明のＮｉ基合金に含まれるＮｂは１．０超〜６％に定めた。一層好ましくは１．１〜３．０％未満である。
【００１３】
ＭｏおよびＨｆ：
ＭｏおよびＨｆは、Ｃｒ：３６％を越えかつＷ：０．０１％を越えて含有するＮｉ基合金に添加することにより塩素を含まない酸素含有超臨界水環境下で耐応力腐食割れ性を一層向上させる効果があるので必要に応じて添加するが、その場合、Ｍｏは０．０１％を越えて含有することで効果を示すものの、０．５％以上含有すると相安定性が劣化するために無機酸含有超臨界水環境における耐応力腐食割れ性が劣化するので好ましくない。したがって、Ｍｏの含有量を０．０１超〜０．５％未満（一層好ましくは、０．１超〜０．５％未満）とした。
同様にＨｆは０．０１％以上含有することで効果を示すものの、０．１％を超えて含有すると無機酸含有超臨界水環境における耐応力腐食割れ性が劣化するので好ましくない。したがって、Ｈｆの含有量を０．０１％〜０．１％（一層好ましくは、０．０２〜０．０５％）とした。
【００１４】
ＦｅおよびＳｉ：
ＦｅおよびＳｉは強度を向上させる効果があるので必要に応じて添加するが、Ｆｅは０．１％以上含有することで効果を示すものの、１０％を超えて含有すると無機酸含有超臨界水環境における全面腐食に対する耐食性が劣化するので好ましくない。したがって、Ｆｅの含有量を０．１％〜１０％（一層好ましくは、０．５〜４％）とした。
同様にＳｉは０．０１％以上含有することで効果を示すものの、０．１％を超えて含有すると相安定性が劣化するために無機酸含有超臨界水環境における耐応力腐食割れ性が劣化するので好ましくない。したがって、Ｓｉの含有量を０．０１％〜０．１％（一層好ましくは、０．０２〜０．０５％）とした。
【００１５】
Ｃ：
Ｃは不可避不純物として含まれるが、Ｃが大量に含まれると結晶粒界近傍でＣｒと炭化物を形成し、全面腐食に対する耐食性が劣化するので好ましくない。そのため、Ｃの含有量は少ないほど好ましく、不可避不純物に含まれるＣの含有量の上限を０．０５％と定めた。
【００１６】
【発明の実施の形態】
通常の高周波溶解炉を用いて溶解し鋳造して、表１〜４に示される成分組成を有し、厚さ：１２ｍｍを有するインゴットを作製した。このインゴットに１２３０℃で１０時間保持の均質化熱処理を施し、１０００〜１２３０℃の範囲内に保持しながら、１回の熱間圧延で１ｍｍの厚さを減少させつつ、最終的に５ｍｍ厚とし、さらに１２００℃で３０分間保持し水焼入れすることにより固溶化処理を施したのち、表面をエメリー紙＃６００で研磨することにより、本発明Ｎｉ基合金板１〜４２、比較Ｎｉ基合金板１〜１１および従来Ｎｉ基合金板１〜３を作製した。
これら本発明Ｎｉ基合金板１〜４２、比較Ｎｉ基合金板１〜１１および従来Ｎｉ基合金板１〜３に内部応力および内部歪を付与するために３０％の圧下率で冷間圧延し、それぞれ３．５ｍｍ厚さの板を作製した。この板を切断して縦：４ｍｍ、横：４ｍｍ、高さ：３．５ｍｍの寸法を有する直方体形状を有する固溶化材試験片を作製した。
さらに、無機酸含有超臨界水環境下での耐応力腐食割れ性に及ぼす相安定性の影響を評価するために、前記本発明Ｎｉ基合金板１〜４２、比較Ｎｉ基合金板１〜１１および従来Ｎｉ基合金板１〜３を４５０℃に１００００時間保持の時効処理を施したのち、エメリー紙＃６００で研磨し、内部応力および内部歪を付与するために３０％の圧下率で冷間圧延してそれぞれ３．５ｍｍ厚さの板を作製し、この板を切断して縦：４ｍｍ、横：４ｍｍ、高さ：３．５ｍｍの寸法を有する直方体形状を有する時効材試験片を作製した。
【００１７】
次に、チタンを内側にハステロイＣ−２７６を外側にしたチタン／ハステロイＣ−２７６の２重管をオートクレーブとした流通型の腐食試験装置を用意した。この流通型の腐食試験装置は、チタン／ハステロイＣ−２７６の２重管の一端から高圧ポンプにより試験溶液を圧入し、管端に設けられたヒーターにより試験溶液を加熱することにより所定の腐食試験条件を形成し、もう一端から出た試験溶液は減圧弁を経てリザーバータンクに回収されるようになっている。
【００１８】
さらに、流体温度：５００℃、圧力：６０ＭＰａ、溶存酸素量：８００ｐｐｍ（過酸化水素として添加）の超臨界水に硫酸：０．２ｍｏｌ／ｋｇ、リン酸：０．２ｍｏｌ／ｋｇを混合した超臨界水を試験溶液として用意した。
この硫酸およびリン酸を混合した超臨界水は、ＶＸガスを超臨界水で分解・酸化したときに生成されると予想される超臨界水溶液であり、以下、この硫酸およびリン酸を含有した超臨界水溶液をＶＸガス分解模擬液という。
【００１９】
さらに、流体温度：５００℃、圧力：６０ＭＰａ、溶存酸素量：８００ｐｐｍ（過酸化水素として添加）の超臨界水にリン酸：０．４ｍｏｌ／ｋｇ、フッ酸：０．１４ｍｏｌ／ｋｇを混合した超臨界水を試験溶液として用意した。
このリン酸およびフッ酸を混合した超臨界水は、ＧＢ（サリン）ガスを超臨界水で分解・酸化したときに生成されると予想される超臨界水溶液であり、以下、このリン酸およびフッ酸を含有した超臨界水溶液をＧＢガス分解模擬液という。
【００２０】
前記ＶＸガス分解模擬液およびＧＢガス分解模擬液を先に用意した流通型の腐食試験装置におけるチタン／ハステロイＣ−２７６の２重管に圧入し、この２重管内部のＰＣＢまたはダイオキシン分解模擬液が流量：６ｇ／ｍｉｎで流れるように制御して無機酸含有超臨界水環境を形成し、この環境下において前記本発明Ｎｉ基合金板１〜４２、比較Ｎｉ基合金板１〜１１および従来Ｎｉ基合金板１〜３からなる固溶化材試験片を１００時間保持することにより試験片の表面における応力腐食割れの有無を確認し、そこ結果を表５〜６に示した。
【００２１】
さらに、無機酸含有超臨界水環境下での耐応力腐食割れ性に及ぼす相安定性の影響を評価するために、前記本発明Ｎｉ基合金板１〜４２、比較Ｎｉ基合金板１〜１１および従来Ｎｉ基合金板１〜３からなる時効材試験片を上述の無機酸含有超臨界水環境に１００時間保持することにより時効材試験片の表面における応力腐食割れの有無を確認し、そこ結果を表５〜６に示した。
【００２２】
【表１】

【００２３】
【表２】

【００２４】
【表３】

【００２５】
【表４】

【００２６】
【表５】

【００２７】
【表６】

【００２８】
表１〜６に示された結果から、本発明Ｎｉ基合金板１〜４２は、固溶化材試験片も時効材試験片も、従来Ｎｉ基合金板１および２に見られるような応力腐食割れの発生がなく、したがって耐応力腐食割れ性が優れていることが分かる。しかし、この発明から外れた成分組成を有する比較Ｎｉ基合金板１〜１１の固溶化材試験片および時効材試験片の少なくともいずれかに応力腐食割れが発生したり、著しい全面腐食が発生するなどして好ましくないことが分かる。
【００２９】
【発明の効果】
上述のように、この発明のＮｉ基合金は、硫酸およびリン酸、またはリン酸およびフッ酸を含む超臨界水環境下において耐応力腐食割れ性に優れているところから長期間の使用が可能となり、ＶＸガスまたはＧＢガスの無害化処分などの環境産業上優れた効果をもたらすものである。
なお、この発明のＮｉ基合金は、上述の如く、硫酸、燐酸、フッ酸など塩素を含まない無機酸を含む超臨界水環境下で使用することが最も有効であるが、これに限定されるものではなく、塩酸、硝酸を含む超臨界水環境や塩化ナトリウム、塩化マグネシウム、塩化カルシウム等塩化物塩を含む超臨界水環境、アンモニアを含む超臨界水環境でも使用可能であり、従って、宇宙関連廃棄物、原子力関連廃棄物、電子力関連廃棄物、一般産業廃棄物の処分用の超臨界水装置材料にも適用できる。
また、この発明のＮｉ基合金を装置本体の反応チャンバーとして使用する際、外側をステンレス鋼等の強度用材料とし、内面にこの発明のＮｉ基合金をクラッドやライニングしてもよい。[0001]
[Industrial applications]
The present invention relates to a Ni-based alloy having excellent stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment and a member for a supercritical water process reaction device comprising the Ni-based alloy, and in particular, VX gas, Supercritical water containing inorganic acids that do not contain chlorine, such as sulfuric acid, phosphoric acid, and hydrofluoric acid, generated by decomposing and oxidizing organic harmful substances used in chemical weapons such as GB (sarin) gas and mustard gas The present invention relates to a Ni-based alloy having excellent stress corrosion cracking resistance and a member for a supercritical water process reactor comprising the Ni-based alloy.
[0002]
[Prior art]
Water at a temperature / pressure exceeding the critical point (specifically, water at a temperature / pressure exceeding 374 ° C./22.1 MPa) is called supercritical water, and supercritical water dissolves various substances. This supercritical water becomes a non-condensable, high-density gas state, and completely dissolves even nonpolar or weakly polar substances (hydrocarbon compounds and gases) with extremely low solubility at room temperature, It is said that by adding, dissolved substances can be oxidized and decomposed.
[0003]
Organic hazardous substances used in chemical weapons are no exception, and they are completely dissolved in supercritical water, and the dissolved oxygen added reacts with the organic hazardous substances used in chemical weapons in supercritical water. As a result, it is oxidatively decomposed into harmless substances such as sulfuric acid and phosphoric acid in addition to carbon dioxide and water. For example, when VX gas is oxidatively decomposed, sulfuric acid and phosphoric acid are generated, and when GB gas is oxidatively decomposed, hydrofluoric acid and phosphoric acid are generated. Therefore, in recent years, in the United States, in order to dispose of chemical weapons using VX gas, GB (salin) gas, mustard gas, etc., supercritical water is used to dispose of these hard-to-degrade VX gas, GB (salin) gas. Attempts have been made to decompose and oxidize organic harmful substances such as gas and mustard gas to render them harmless. When a method of decomposing and oxidizing organic harmful substances such as VX gas, GB (salin) gas, and mustard gas using supercritical water is established, the supercritical water is supercritical compared to the conventional incineration treatment method. Water and oxidizing agents have no adverse effect on the environment, and supercritical water has high reactivity and decomposes and oxidizes organic harmful substances such as VX gas, GB (salin) gas and mustard gas in a short time, and is harmless. And the possibility of decomposition treatment in a closed system eliminates the risk of environmental pollution due to emissions.
[0004]
In order to decompose and oxidize organic harmful substances such as VX gas, GB (salin) gas, and mustard gas using such supercritical water as a reaction solvent to render them harmless, high temperature and high pressure (400 to 650 ° C., 22 Process in an apparatus for detoxifying organic harmful substances from an environment where inorganic acids such as sulfuric acid, phosphoric acid, and hydrofluoric acid generated after oxidative decomposition in supercritical water of 0.1 to 80 MPa) and high concentration of oxygen coexist. The material of the reaction vessel is required to have corrosion resistance under such inorganic acid-containing supercritical water.
[0005]
Therefore, as a metal material used for a reaction vessel of a process reaction apparatus using supercritical water, a Ni-based alloy known for high corrosion resistance is listed as a candidate for a process reaction vessel material of the apparatus. For example, Inconel (trade name) 625 (specified in ASTM UNS N06625, and its component composition is, for example, Cr: 21.0%, Mo: 8.4%, Nb + Ta: 3.6%, Fe : 3.8%, Co: 0.6%, Ti: 0.2%, Mn: 0.2%, balance: Ni + inevitable impurities) and Hastelloy (trade name) C-276 (ASTM UNS) N10276, and the component composition is, for example, Cr: 15.5%, Mo: 16.1%, W: 3.7%, Fe: 5.7%, Co: 0.5%, Mn. : 0.5%, balance: Ni + inevitable impurities).
Recently, there has been a report that a Ni-based alloy having a higher Cr content has more excellent corrosion resistance to supercritical water containing an inorganic acid. As a Ni-based alloy having a higher Cr content, Hastelloy (trade name) G -30 (ASTM UNS N06030 (component composition is, for example, Cr: 28.7%, Mo: 5.0%, Mn: 1.1%, Fe: 14.6%, Cu: 1.8%, W: 2.6, Co: 1.87%, balance: Ni + inevitable impurities).
[0006]
[Problems to be solved by the invention]
These conventional Ni-based alloys are formed into a plate or tube to produce a working material, and the working material is further subjected to a forming process such as rolling or bending to complete a reaction vessel or piping of a process reaction apparatus. Since the reaction vessel or piping finished in this way is manufactured by molding, residual internal stress and internal strain cannot be avoided.
However, among conventional Ni-based corrosion-resistant alloys, Inconel 625 and Hastelloy C-276 cause stress corrosion cracking when they come into contact with supercritical water containing an inorganic acid containing no chlorine such as sulfuric acid, phosphoric acid, and hydrofluoric acid. If Inconel 625 or Hastelloy C-276 among the conventional Ni-based corrosion resistant alloys is used as a material for a reaction vessel and piping in a device for detoxifying organic harmful substances, it has been difficult to operate for a long time.
In addition, Hastelloy (trade name) G-30 has insufficient phase stability even though it has a sufficient resistance to stress corrosion cracking under supercritical water containing an acid such as sulfuric acid, phosphoric acid, or hydrofluoric acid at the beginning of the operation. Therefore, the phase transformation gradually proceeds at the operating temperature (400 to 650 ° C.), and when a stress field such as in a high-temperature and high-pressure supercritical water environment is generated in the state where the phase transformation has proceeded, stress corrosion cracking occurs. This is not suitable as a material for a process reactor used for a long time.
[0007]
[Means to solve the problem]
Therefore, the present inventors have found that even under an inorganic acid-containing supercritical water environment, stress corrosion cracking does not occur, and the phase stability is excellent even when held at a use temperature (400 to 650 ° C.) for a long time. We have developed a Ni-based alloy that suppresses the progress of transformation and exhibits sufficient stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment. We conducted intensive research to obtain a member for a supercritical water process reactor that can be operated for a long period of time. as a result,
(A) In mass% (% indicates mass%), Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0.05 to 0.5%, the balance being Ni and unavoidable impurities, and the amount of C contained as unavoidable impurities was adjusted to 0.05% or less. The Ni-based alloy having the composition is excellent in stress corrosion cracking resistance and phase stability in an inorganic acid-containing supercritical water environment, especially in an inorganic acid-containing supercritical water environment that does not contain chlorine such as sulfuric acid, phosphoric acid, and hydrofluoric acid. Because of its superiority, even if it is maintained at a use temperature (400 to 650 ° C.) for a long time, the progress of phase transformation is suppressed and there is no stress corrosion cracking. Longer operation if used for reaction vessel material in equipment for detoxifying The ability,
(B) When Nb: more than 1.0 to 6% is further added to the Ni-based alloy having the composition described in (a), the stress corrosion cracking resistance is further improved.
(C) When one or two types of Mo: 0.01 to less than 0.5% and Hf: 0.01 to 0.1% are further added to the Ni-based alloy having the composition described in (A) above. , Stress corrosion cracking resistance is further improved,
(D) When one or two types of Fe: 0.1 to 10% and Si: 0.01 to 0.1% are further added to the Ni-based alloy having the composition described in (a) above, the strength is increased. Research results such as further improvement were obtained.
[0008]
The present invention has been made based on such research results,
(1) Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05-0.5%, the balance being Ni and unavoidable impurities, and having a composition in which the amount of C contained as unavoidable impurities is adjusted to 0.05% or less, in an environment containing inorganic acid-containing supercritical water, Ni-based alloy with excellent stress corrosion cracking,
(2) Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05 to 0.5%, further contains Nb: more than 1.0 to 6%, and the balance is composed of Ni and unavoidable impurities, and the amount of C contained as unavoidable impurities is adjusted to 0.05% or less. Ni-based alloy with excellent stress corrosion cracking resistance under an inorganic acid-containing supercritical water environment having a composition
(3) Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05 to 0.5%, and further contains one or two of Mo: 0.01 to less than 0.5% and Hf: 0.01 to 0.1%, with the balance being Ni A Ni-based alloy comprising an unavoidable impurity and having a composition in which the amount of C contained as an unavoidable impurity is adjusted to 0.05% or less and having excellent stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment;
(4) Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05 to 0.5%, and one or two of Fe: 0.1 to 10% and Si: 0.01 to 0.1%, with the balance being Ni and unavoidable impurities. A Ni-based alloy having a composition in which the amount of C contained as an inevitable impurity is adjusted to 0.05% or less and having excellent stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment;
(5) Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05 to 0.5%, Nb: more than 1.0 to 6%, Mo: 0.01 to less than 0.5%, and Hf: 0.01 to 0.1% Stress resistance in an inorganic acid-containing supercritical water environment having a composition containing Ni and unavoidable impurities, with the balance being adjusted to 0.05% or less of the amount of C contained as unavoidable impurities. Ni-based alloy with excellent corrosion cracking properties,
(6) Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05 to 0.5%, Nb: more than 1.0 to 6%, and one of Fe: 0.1 to 10% and Si: 0.01 to 0.1% Or corrosion corrosion resistance in an inorganic acid-containing supercritical water environment having a composition containing Ni and an unavoidable impurity with the balance being adjusted to 0.05% or less. Excellent Ni-based alloy,
(7) Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05 to 0.5%, and further contains one or two of Mo: 0.01 to less than 0.5% and Hf: 0.01 to 0.1%, and further contains Fe: 0. 0.1 to 10% and Si: one or two of 0.01 to 0.1%, with the balance being Ni and unavoidable impurities, the amount of C contained as unavoidable impurities being 0.05% or less Ni-based alloy with excellent stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment having a composition adjusted to
(8) Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05 to 0.5%, Nb: more than 1.0 to 6%, Mo: 0.01 to less than 0.5%, and Hf: 0.01 to 0.1% And one or two of Fe: 0.1 to 10% and Si: 0.01 to 0.1%, with the balance being Ni and unavoidable impurities. A Ni-based alloy excellent in stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment having a composition in which the amount of C contained as an inevitable impurity is adjusted to 0.05% or less;
(9) A supercritical water process reaction comprising a Ni-based alloy having the composition described in (1), (2), (3), (4), (5), (6), (7) or (8). Device member.
[0009]
Next, the reasons for limiting each element in the alloy composition of the Ni-based alloy of the present invention will be described in detail.
[0010]
Cr, W:
By containing more than 36% of Cr and more than 0.01% of W, stress corrosion cracking resistance in a supercritical water environment mixed with chlorine-free inorganic acids such as sulfuric acid, phosphoric acid, hydrofluoric acid, etc. Although the Cr content is remarkably improved, when the Cr content is 42% or more, the overall corrosion resistance decreases in combination with W. Therefore, the Cr content is set to more than 36 to less than 42%. More preferably, it is more than 38 to 41.5%.
Similarly, when W is contained in an amount of 0.5% or more, workability is deteriorated in combination with Cr, which is not preferable. Therefore, the content of W is set to be more than 0.01 to less than 0.5% (more preferably 0.1 to 0.45%).
[0011]
N, Mn and Mg:
By coexisting N, Mn and Mg, the phase stability can be improved. That is, N, Mn, and Mg have the effect of stabilizing the Ni-fcc phase, which is the parent phase, and making it difficult to precipitate the second layer. However, if the N content is less than 0.001%, there is no phase stabilizing effect, while if the N content exceeds 0.04%, nitrides are formed and corrosion resistance in a supercritical water environment is deteriorated, so that N Was made 0.001 to 0.04% (more preferably, 0.005 to 0.03%).
Similarly, if the Mn content is less than 0.05%, there is no phase stabilizing effect, while if it exceeds 0.5%, the stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment deteriorates. , Mn content is set to 0.05 to 0.5% (more preferably, 0.1 to 0.4%).
Similarly, Mg is a component that improves the phase stability, but if its content is less than 0.001%, there is no effect of phase stabilization, while if it exceeds 0.05%, the inorganic acid-containing supercritical water Since the stress corrosion cracking resistance in the environment deteriorates, the content of Mg is set to 0.001 to 0.05% (more preferably, 0.010% to 0.040%).
[0012]
Nb:
Nb is added to a Ni-based alloy containing more than 36% of Cr and more than 0.01% of W to further improve the overall corrosion resistance in an oxygen-containing supercritical water environment containing no chlorine. Is added as necessary, but in this case, an effect is exhibited when the content exceeds 1.0%, but when the content exceeds 6%, the phase stability is deteriorated. Therefore, Nb contained in the Ni-based alloy of the present invention is set to be more than 1.0 to 6%. More preferably, it is less than 1.1 to 3.0%.
[0013]
Mo and Hf:
Mo and Hf are added to a Ni-based alloy containing more than 36% of Cr and more than 0.01% of W to further enhance stress corrosion cracking resistance in an oxygen-containing supercritical water environment containing no chlorine. Mo is added as necessary because it has an effect of improving Mo. In this case, the effect is exhibited by containing Mo in excess of 0.01%, but when Mo is contained in 0.5% or more, phase stability is deteriorated. It is not preferable because stress corrosion cracking resistance in a supercritical water environment containing an inorganic acid is deteriorated. Therefore, the content of Mo is set to more than 0.01 to less than 0.5% (more preferably, more than 0.1 to less than 0.5%).
Similarly, when Hf is contained in an amount of 0.01% or more, the effect is exhibited. However, if it exceeds 0.1%, the stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment deteriorates, which is not preferable. Therefore, the content of Hf is set to 0.01% to 0.1% (more preferably, 0.02 to 0.05%).
[0014]
Fe and Si:
Fe and Si are added as necessary because they have the effect of improving the strength. However, when Fe is contained at 0.1% or more, the effect is exhibited, but when it exceeds 10%, the inorganic acid-containing supercritical water environment is contained. In this case, the corrosion resistance against general corrosion is deteriorated. Therefore, the content of Fe is set to 0.1% to 10% (more preferably, 0.5 to 4%).
Similarly, when the content of Si is 0.01% or more, the effect is exhibited, but when the content exceeds 0.1%, the phase stability is deteriorated, so that the stress corrosion cracking resistance in a supercritical water environment containing an inorganic acid is deteriorated. Is not preferred. Therefore, the content of Si is set to 0.01% to 0.1% (more preferably, 0.02 to 0.05%).
[0015]
C:
C is contained as an unavoidable impurity. However, if C is contained in a large amount, Cr and carbide are formed in the vicinity of the crystal grain boundaries, which is not preferable because the corrosion resistance against general corrosion is deteriorated. Therefore, the C content is preferably as small as possible, and the upper limit of the C content contained in the inevitable impurities is set to 0.05%.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
It melt | dissolved and cast using the normal high frequency melting furnace, and produced the ingot which has a component composition shown in Tables 1-4, and has a thickness: 12 mm. This ingot is subjected to a homogenization heat treatment of holding at 1230 ° C. for 10 hours, and while maintaining the temperature in the range of 1000 to 1230 ° C., the thickness is reduced to 1 mm by one hot rolling, and finally reduced to 5 mm. Then, the solid solution treatment was performed by holding at 1200 ° C. for 30 minutes and quenching with water, and then the surface was polished with emery paper # 600 to obtain the Ni-based alloy plates 1 to 42 of the present invention and the comparative Ni-based alloy plate 1 To 11 and conventional Ni-based alloy plates 1 to 3 were produced.
These Ni-based alloy plates 1 to 42 of the present invention, comparative Ni-based alloy plates 1 to 11 and conventional Ni-based alloy plates 1 to 3 are cold-rolled at a rolling reduction of 30% in order to impart internal stress and internal strain, Plates each having a thickness of 3.5 mm were produced. This plate was cut to prepare a solid solution test piece having a rectangular parallelepiped shape having dimensions of 4 mm in length, 4 mm in width, and 3.5 mm in height.
Further, in order to evaluate the effect of phase stability on stress corrosion cracking resistance under an inorganic acid-containing supercritical water environment, the Ni-based alloy plates 1 to 42 of the present invention, the comparative Ni-based alloy plates 1 to 11 and The conventional Ni-based alloy plates 1 to 3 are subjected to aging treatment at 450 ° C. for 10,000 hours, polished with emery paper # 600, and cold-rolled at a rolling reduction of 30% to impart internal stress and internal strain. Then, 3.5 mm-thick plates were prepared, and the plates were cut to prepare aging material test specimens having a rectangular parallelepiped shape having a length of 4 mm, a width of 4 mm, and a height of 3.5 mm.
[0017]
Next, a flow-through type corrosion test apparatus was prepared in which a double tube of titanium / Hastelloy C-276 having titanium inside and Hastelloy C-276 outside was used as an autoclave. This flow-through type corrosion test apparatus is configured such that a test solution is press-fitted from one end of a double tube of titanium / Hastelloy C-276 by a high-pressure pump, and the test solution is heated by a heater provided at the end of the tube. The test solution that has formed the conditions and exits from the other end is collected in the reservoir tank via the pressure reducing valve.
[0018]
Further, supercritical water in which sulfuric acid: 0.2 mol / kg and phosphoric acid: 0.2 mol / kg are mixed with supercritical water having a fluid temperature of 500 ° C., a pressure of 60 MPa, and a dissolved oxygen amount of 800 ppm (added as hydrogen peroxide). Water was provided as a test solution.
The supercritical water in which sulfuric acid and phosphoric acid are mixed is a supercritical aqueous solution that is expected to be generated when VX gas is decomposed and oxidized with supercritical water. The critical aqueous solution is called a VX gas decomposition simulation liquid.
[0019]
Furthermore, supercritical water having a fluid temperature of 500 ° C., a pressure of 60 MPa, and a dissolved oxygen content of 800 ppm (added as hydrogen peroxide) mixed with phosphoric acid: 0.4 mol / kg and hydrofluoric acid: 0.14 mol / kg. Critical water was provided as a test solution.
The supercritical water mixed with phosphoric acid and hydrofluoric acid is a supercritical aqueous solution that is expected to be generated when GB (sarin) gas is decomposed and oxidized with supercritical water. A supercritical aqueous solution containing an acid is referred to as a simulated GB gas decomposition liquid.
[0020]
The simulated VX gas decomposition liquid and the simulated GB gas decomposition liquid were injected into the titanium / Hastelloy C-276 double pipe in the flow-type corrosion test apparatus previously prepared, and the PCB or dioxin decomposition liquid inside the double pipe was injected. Is controlled to flow at a flow rate of 6 g / min to form an inorganic acid-containing supercritical water environment. In this environment, the Ni-based alloy plates 1 to 42 of the present invention, the comparative Ni-based alloy plates 1 to 11 and the conventional Ni The presence or absence of stress corrosion cracking on the surface of the test piece was confirmed by holding the solution-solution material test piece composed of the base alloy plates 1 to 3 for 100 hours. The results are shown in Tables 5 to 6.
[0021]
Further, in order to evaluate the effect of phase stability on stress corrosion cracking resistance under an inorganic acid-containing supercritical water environment, the Ni-based alloy plates 1 to 42 of the present invention, the comparative Ni-based alloy plates 1 to 11 and By keeping the aging test piece composed of the conventional Ni-based alloy plates 1 to 3 in the above-mentioned inorganic acid-containing supercritical water environment for 100 hours, the presence or absence of stress corrosion cracking on the surface of the aging test piece was confirmed. The results are shown in Tables 5 and 6.
[0022]
[Table 1]

[0023]
[Table 2]

[0024]
[Table 3]

[0025]
[Table 4]

[0026]
[Table 5]

[0027]
[Table 6]

[0028]
From the results shown in Tables 1 to 6, the Ni-based alloy plates 1 to 42 of the present invention showed that both the solution test piece and the aging test piece exhibited stress corrosion cracking as seen in the conventional Ni-based alloy plates 1 and 2. It can be seen that there is no occurrence of stress, and therefore, the stress corrosion cracking resistance is excellent. However, stress corrosion cracking occurs in at least one of the solubilized material test piece and the aging material test piece of the comparative Ni-based alloy plates 1 to 11 having a component composition deviating from the present invention, or significant general corrosion occurs. It is not preferable.
[0029]
【The invention's effect】
As described above, the Ni-based alloy of the present invention has excellent stress corrosion cracking resistance in a supercritical water environment containing sulfuric acid and phosphoric acid, or phosphoric acid and hydrofluoric acid, so that it can be used for a long time. , VX gas or GB gas, etc., which are excellent in environmental industry.
As described above, the Ni-based alloy of the present invention is most effective when used in a supercritical water environment containing an inorganic acid containing no chlorine such as sulfuric acid, phosphoric acid, and hydrofluoric acid, but is limited thereto. It can also be used in supercritical water environments containing hydrochloric acid and nitric acid, supercritical water environments containing chloride salts such as sodium chloride, magnesium chloride and calcium chloride, and supercritical water environments containing ammonia. It can also be applied to supercritical water equipment materials for disposal of waste, nuclear related waste, electronic power related waste and general industrial waste.
When the Ni-based alloy of the present invention is used as a reaction chamber of the apparatus main body, the outer side may be made of a material for strength such as stainless steel, and the inner surface may be clad or lined with the Ni-based alloy of the present invention.

Claims

In mass%, Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: An inorganic acid-containing supercritical material characterized in that the composition contains 0.05 to 0.5%, the balance being Ni and inevitable impurities, and having a composition in which the amount of C contained as inevitable impurities is adjusted to 0.05% or less. Ni-base alloy with excellent resistance to stress corrosion cracking in water environment.

In mass%, Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Furthermore, Nb: contains more than 1.0 to 6%,
The balance is composed of Ni and inevitable impurities, and has a composition in which the amount of C contained as inevitable impurities is adjusted to 0.05% or less, and has excellent stress corrosion cracking resistance under an inorganic acid-containing supercritical water environment. Ni-based alloy.

In mass%, Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Further, it contains one or two of Mo: 0.01 to less than 0.5% and Hf: 0.01 to 0.1%,
The balance is composed of Ni and inevitable impurities, and has a composition in which the amount of C contained as inevitable impurities is adjusted to 0.05% or less, and has excellent stress corrosion cracking resistance under an inorganic acid-containing supercritical water environment. Ni-based alloy.

In mass%, Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Further, it contains one or two of Fe: 0.1 to 10% and Si: 0.01 to 0.1%,
The balance is composed of Ni and inevitable impurities, and has a composition in which the amount of C contained as inevitable impurities is adjusted to 0.05% or less, and has excellent stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment. Ni-based alloy.

In mass%, Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Furthermore, Nb: contains more than 1.0 to 6%,
Further, it contains one or two of Mo: 0.01 to less than 0.5% and Hf: 0.01 to 0.1%,
The balance is composed of Ni and inevitable impurities, and has a composition in which the amount of C contained as inevitable impurities is adjusted to 0.05% or less, and has excellent stress corrosion cracking resistance under an inorganic acid-containing supercritical water environment. Ni-based alloy.

In mass%, Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Furthermore, Nb: contains more than 1.0 to 6%,
Further, it contains one or two of Fe: 0.1 to 10% and Si: 0.01 to 0.1%,
The balance is composed of Ni and inevitable impurities, and has a composition in which the amount of C contained as inevitable impurities is adjusted to 0.05% or less, and has excellent stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment. Ni-based alloy.

In mass%, Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Further, it contains one or two of Mo: 0.01 to less than 0.5% and Hf: 0.01 to 0.1%,
Further, it contains one or two of Fe: 0.1 to 10% and Si: 0.01 to 0.1%,
The balance is composed of Ni and inevitable impurities, and has a composition in which the amount of C contained as inevitable impurities is adjusted to 0.05% or less, and has excellent stress corrosion cracking resistance under an inorganic acid-containing supercritical water environment. Ni-based alloy.

In mass%, Cr: more than 36 to less than 42%, W: more than 0.01 to less than 0.5%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Furthermore, Nb: contains more than 1.0 to 6%,
Further, it contains one or two of Mo: 0.01 to less than 0.5% and Hf: 0.01 to 0.1%,
Further, it contains one or two of Fe: 0.1 to 10% and Si: 0.01 to 0.1%,
The balance is composed of Ni and inevitable impurities, and has a composition in which the amount of C contained as inevitable impurities is adjusted to 0.05% or less, and has excellent stress corrosion cracking resistance under an inorganic acid-containing supercritical water environment. Ni-based alloy.

A member for a supercritical water process reactor, comprising a Ni-based alloy having the composition according to claim 1, 2, 3, 4, 5, 6, 7, or 8.