JP4151064B2

JP4151064B2 - Ni-base alloy with excellent resistance to stress corrosion cracking in supercritical water environment containing inorganic acid

Info

Publication number: JP4151064B2
Application number: JP2002232838A
Authority: JP
Inventors: 克生菅原
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 2002-08-09
Filing date: 2002-08-09
Publication date: 2008-09-17
Anticipated expiration: 2022-08-09
Also published as: JP2004068133A

Description

【０００１】
【産業上の利用分野】
この発明は、無機酸を含む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、産業廃棄物として処分が困難なＰＣＢやダイオキシン等の有機系有害物質を分解・酸化することによって生じる塩酸などの塩素含有無機酸を含む超臨界水環境下での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（例えば、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】
そこで、産業廃棄物として処分が困難なＰＣＢやダイオキシン等の有機系有害物質を含む廃棄物を処分するために、これら難分解性の有機系有害物質を超臨界水に完全に溶解させ、さらに酸素を加えて有機系有害物質が超臨界水中で反応させることにより二酸化炭素、水のほかに塩酸などの無害物質に酸化分解して無害化する試みが成されている。このプロセスは、従来の焼却による処分方法と比べて、閉鎖系内で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ＰＣＢやダイオキシン等の有機系有害物質を分解・酸化して無害化すると、高温・高圧（４００〜６５０℃、２２．１〜８０ＭＰａ）の超臨界水中において分解・酸化後に生成された塩酸などの塩素を含む無機酸と高濃度の酸素が共存する環境が生成され、有機系有害物質を無害化する装置における材料にはこうした塩素を含む無機酸と高濃度の酸素を含有する超臨界水環境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に使用される金属材料には、高耐食性で知られるＮｉ基耐食合金がプロセス反応装置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（ＡＳＴＭＵＮＳＮ０６６２５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（ＡＳＴＭＵＮＳＮ１０２７６で規定されており、その成分組成は、例えば、質量％で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ハステロイ（商品名）Ｇ−３０（ＡＳＴＭＵＮＳＮ０６０３０で規定されており、その成分組成は、例えば、質量％で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型耐食合金が使用されている。
【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容器または配管は成形加工により作製されるためにいずれも内部応力および内部歪が残留している。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、内部応力・内部歪みが残留した状態で塩酸などを含む超臨界水に接触させると応力腐食割れが発生し、そのために有機系有害物質を無害化するプロセス反応装置における容器および配管などに使用して長期間操業することは困難であった。
また、ハステロイ（商品名）Ｇ−３０は、塩酸を含む超臨界水に対する応力腐食割れ発生は操業初期には見られないが、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てしまい、この状態で高温・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することから長期間操業するプロセス反応装置の素材として適当ではない。
【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の発生することなく、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：２８超〜３４％未満、Ｗ：０．１超〜１．０％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、特に塩素を含む無機酸含有超臨界水環境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プロセス反応容器材に使用すると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：２８超〜３４％未満、Ｗ：０．１超〜１．０％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：２８超〜３４％未満、Ｗ：０．１超〜１．０％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：２８超〜３４％未満、Ｗ：０．１超〜１．０％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、Ｈｆ：０．０１〜０．１％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：２８超〜３４％未満、Ｗ：０．１超〜１．０％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％、Ｓｉ：０．０１〜０．１％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：２８超〜３４％未満、Ｗ：０．１超〜１．０％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、Ｈｆ：０．０１〜０．１％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：２８超〜３４％未満、Ｗ：０．１超〜１．０％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％、Ｓｉ：０．０１〜０．１％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：２８超〜３４％未満、Ｗ：０．１超〜１．０％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、Ｈｆ：０．０１〜０．１％の１種または２種を含有し、
さらに、Ｆｅ：０．１〜１０％、Ｓｉ：０．０１〜０．１％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：２８超〜３４％未満、Ｗ：０．１超〜１．０％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、Ｈｆ：０．０１〜０．１％の１種または２種を含有し、
さらに、Ｆｅ：０．１〜１０％、Ｓｉ：０．０１〜０．１％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）に記載の組成を有する耐応力腐食割れ性に優れた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：
塩酸が混入する超臨界水環境では、ＣｒとＷが同時に含有することにより耐応力腐食割れ性が著しく向上するが、その場合、Ｃｒは２８％を越えて含有することが必要である。しかしＣｒが３４％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２８超〜３４％未満に定めた。一層好ましくは、２８．５〜３３％未満である。
同様にＷは０．１％を越えて含有することが必要であるが、１．０％以上含有するとＣｒとの組合せにおいて相安定性が劣化し、耐応力腐食割れ性が低下するので好ましくない。したがって、Ｗの含有量を０．１超〜１．０％未満（一層好ましくは０.１超〜０.５％）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、特に塩酸を含む超臨界水環境での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は特に塩酸を含む超臨界水環境での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、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、０．５〜４．０％）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。このインゴットを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、表面をバフ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を用意した。
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２０％の圧下率で冷間圧延し、それぞれ４ｍｍ厚さの板を作製した。この板を切断して縦：４ｍｍ、横：４ｍｍ、高さ：４ｍｍの寸法を有する立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５００℃に１０００時間保持の時効処理を施したのち、内部応力および内部歪を付与するために２０％の圧下率で冷間圧延してそれぞれ４ｍｍ厚さの板を作製し、この板を切断して縦：４ｍｍ、横：４ｍｍ、高さ：４ｍｍの寸法を有する立方体形状を有する時効材試験片を作製した。
【００１７】
次に、内側：チタン、外側：ハステロイＣ-２７６からなるチタン／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、前記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】
流体温度：５００℃、圧力：６０ＭＰａ、溶存酸素量：８００ｐｐｍ（過酸化水素として添加）の超臨界水に塩酸：０．０３ｍｏｌ／ｋｇを混合した超臨界水を試験溶液として用意した。
この塩酸を混合した超臨界水は、ＰＣＢまたはダイオキシンを超臨界水で分解・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、この塩酸含有超臨界水溶液をＰＣＢまたはダイオキシン分解模擬液という。
前記ＰＣＢまたはダイオキシン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、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１〜４に示した。
【００１９】
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１〜４に示した。
【００２０】
【表１】

【００２１】
【表２】

【００２２】
【表３】

【００２３】
【表４】

【００２４】
表１〜４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するか著しい全面腐食が発生するところから好ましくないことが分かる。
【００２５】
【発明の効果】
上述のように、この発明のＮｉ基合金は塩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、ＰＣＢまたはダイオキシン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、塩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、硫酸、燐酸、フッ酸、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 application fields]
TECHNICAL FIELD The present invention relates to a Ni-based alloy having excellent stress corrosion cracking resistance in a supercritical water environment containing an inorganic acid, and a member for a supercritical water process reactor comprising this Ni-based alloy. Ni-base with excellent stress corrosion cracking resistance in supercritical water environment containing chlorine-containing inorganic acids such as hydrochloric acid generated by decomposing and oxidizing organic harmful substances such as PCB and dioxin which are difficult to dispose of The present invention relates to an alloy and a member for a supercritical water process reactor made of this 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 in nonpolar or weakly polar substances (for example, hydrocarbon compounds and gases) that have extremely low solubility at room temperature, Furthermore, it is said that the dissolved substance can be oxidized and decomposed by adding oxygen.
[0003]
Therefore, in order to dispose of wastes containing organic harmful substances such as PCB and dioxin that are difficult to dispose as industrial waste, these persistent organic harmful substances are completely dissolved in supercritical water, and oxygen Attempts have been made to detoxify by decomposing organic harmful substances in supercritical water and oxidizing them to harmless substances such as hydrochloric acid in addition to carbon dioxide and water. Compared with the conventional disposal method by incineration, since this process can be performed in a closed system, there is no risk of environmental pollution due to emissions.
[0004]
When such supercritical water is used as a reaction solvent to decompose and oxidize organic harmful substances such as PCB and dioxin, it becomes detoxified in supercritical water at high temperature and high pressure (400 to 650 ° C., 22.1 to 80 MPa). An environment in which inorganic acids containing chlorine, such as hydrochloric acid, generated after decomposition and oxidation, and high concentrations of oxygen coexist is generated, and materials in equipment that detoxify organic harmful substances are used in materials containing these chlorine-containing inorganic acids and high concentrations. Corrosion resistance in a supercritical water environment containing a large amount of oxygen is required.
[0005]
Therefore, as a metal material used in a process reactor using supercritical water, a Ni-based corrosion resistant alloy known for its high corrosion resistance is listed as a candidate for a process reactor material. For example, Inconel (trade name) 625 (specified by ASTM UNS N06625), the composition of the components is, for example, Cr: 21.0%, Mo: 8.4%, Nb + Ta: 3.6% by mass. Fe: 3.8%, Co: 0.6%, Ti: 0.2%, Mn: 0.2%, the balance: Ni + inevitable impurities) and Hastelloy (trade name) C-276 (As defined in ASTM UNS N10276, the component composition is, for example, in terms of mass%, Cr: 15.5%, Mo: 16.1%, W: 3.7%, Fe: 5.7%, Co: Ni-based corrosion-resistant alloys such as 0.5%, Mn: 0.5%, and the balance: Ni + inevitable impurities) are used. Recently, Hastelloy (trade name) G-30 (ASTM UNS N06030), which has a higher Cr content, is specified by its component composition, for example, Cr: 28.7% by mass%, Mo: 5.0%. , Mn: 1.1%, Fe: 14.6%, Cu: 1.8%, W: 2.6%, Co: 1.87% and the balance: Ni + inevitable impurities) -High Cr type corrosion resistant alloy is used.
[0006]
[Problems to be solved by the invention]
These conventional Ni-based alloys are formed into a plate or a tube to produce a processed material, and the processed material is further subjected to a forming process such as rolling or bending to be finished into a container or pipe of a process reaction apparatus. Since the container or piping finished in this way is produced by molding, both internal stress and internal strain remain. However, Inconel 625 and Hastelloy C-276 among the conventional Ni-based corrosion resistant alloys cause stress corrosion cracking when they are brought into contact with supercritical water containing hydrochloric acid or the like in a state where internal stress / internal strain remains, and therefore organic corrosion occurs. It has been difficult to operate for a long period of time by using it as a container and piping in a process reactor for detoxifying system hazardous substances.
In addition, Hastelloy (trade name) G-30 does not show stress corrosion cracking in supercritical water containing hydrochloric acid at the initial stage of operation, but has insufficient phase stability. The material of the process reactor that operates for a long time because the phase transformation gradually progresses in this condition and stress corrosion cracking occurs when a stress field such as in a high-temperature and high-pressure supercritical water environment occurs. Not suitable.
[0007]
[Means for solving the problems]
Therefore, the present inventors do not cause stress corrosion cracking even in an inorganic acid-containing supercritical water environment, and the phase stability is excellent even when kept at a use temperature (400 to 650 ° C.) for a long time. Developed a Ni-based alloy that shows sufficient stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment with the progress of transformation suppressed, and uses this Ni-based alloy for a long time in an inorganic acid-containing supercritical water environment. In order to obtain supercritical water process reactor components that can be operated for a long period of time, intensive research was conducted. as a result,
(B)% by mass (hereinafter,% indicates% by mass), Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0.05 to 0.5%, the balance is made of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less. The Ni-based alloy having a composition is used in a supercritical water environment containing an inorganic acid, particularly in a supercritical water environment containing chlorine, and has excellent stress corrosion cracking resistance and excellent phase stability. 650 ° C) for a long time, the progress of phase transformation is suppressed, there is no stress corrosion cracking, and this Ni-based alloy is used as a process reaction vessel material in an apparatus for detoxifying organic harmful substances using supercritical water. Long-term operation is possible when used.
(B) Addition of Nb: more than 1.0 to 6% to the Ni-based alloy having the composition described in (a) further improves the stress corrosion cracking resistance.
(C) When one or two 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 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 the results of such research,
(1) Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05% to 0.5%, with 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. Ni-based alloy with excellent stress corrosion cracking property,
(2) Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05-0.5%,
Further, Nb: more than 1.0 to 6%,
A Ni-based alloy that is excellent in stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment having a composition in which the balance is made of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less,
(3) Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05-0.5%,
In addition, Mo: 0.01 to less than 0.5%, Hf: 0.01 to 0.1% of one or two,
A Ni-based alloy that is excellent in stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment having a composition in which the balance is made of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less,
(4) Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05-0.5%,
Furthermore, Fe: 0.1 to 10%, Si: 0.01 to 0.1% of one or two types,
A Ni-based alloy that is excellent in stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment having a composition in which the balance is made of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less,
(5) Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05-0.5%,
Further, Nb: more than 1.0 to 6%,
In addition, Mo: 0.01 to less than 0.5%, Hf: 0.01 to 0.1% of one or two,
A Ni-based alloy that is excellent in stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment having a composition in which the balance is made of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less,
(6) Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05-0.5%,
Further, Nb: more than 1.0 to 6%,
Furthermore, Fe: 0.1 to 10%, Si: 0.01 to 0.1% of one or two types,
A Ni-based alloy that is excellent in stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment having a composition in which the balance is made of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less,
(7) Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05-0.5%,
In addition, Mo: 0.01 to less than 0.5%, Hf: 0.01 to 0.1% of one or two,
Furthermore, Fe: 0.1 to 10%, Si: 0.01 to 0.1% of one or two types,
A Ni-based alloy that is excellent in stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment having a composition in which the balance is made of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less,
(8) Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0 0.05-0.5%,
Further, Nb: more than 1.0 to 6%,
In addition, Mo: 0.01 to less than 0.5%, Hf: 0.01 to 0.1% of one or two,
Furthermore, Fe: 0.1 to 10%, Si: 0.01 to 0.1% of one or two types,
A Ni-based alloy that is excellent in stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment having a composition in which the balance is made of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less,
(9) Ni excellent in stress corrosion cracking resistance having the composition according to (1), (2), (3), (4), (5), (6), (7) or (8) It is characterized by a supercritical water process reactor member made of a base alloy.
[0009]
Next, the reason for limitation of each element in the alloy composition of the Ni-based alloy of the present invention will be described in detail.
[0010]
Cr, W:
In a supercritical water environment in which hydrochloric acid is mixed, the stress corrosion cracking resistance is remarkably improved by simultaneously containing Cr and W. In that case, Cr needs to be contained in an amount exceeding 28%. However, if Cr is contained in an amount of 34% or more, the overall corrosion resistance is lowered in combination with W, so the Cr content is determined to be more than 28 to less than 34%. More preferably, it is less than 28.5 to 33%.
Similarly, W must be contained in an amount exceeding 0.1%. However, if it is contained in an amount of 1.0% or more, the phase stability is deteriorated in combination with Cr, and the stress corrosion cracking resistance is lowered. . Therefore, the W content is determined to be more than 0.1 to less than 1.0% (more preferably more than 0.1 to 0.5%).
[0011]
N, Mn and Mg:
By making N, Mn, and Mg coexist, phase stability can be improved. That is, N, Mn, and Mg have the effect of stabilizing the Ni-fcc phase that is the parent phase and making the second layer difficult to precipitate. However, when the N content is less than 0.001%, there is no effect of phase stabilization. On the other hand, when the N content exceeds 0.04%, a nitride is formed and the corrosion resistance in a supercritical water environment deteriorates. Content of 0.001 to 0.04% (more preferably 0.005 to 0.03%).
Similarly, if the content of Mn is less than 0.05%, there is no effect of phase stabilization. On the other hand, if the content exceeds 0.5%, the stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment deteriorates. The Mn content is 0.05 to 0.5% (more preferably, 0.1 to 0.4%).
Similarly, Mg is a component that improves phase stability. However, if its content is less than 0.001%, there is no effect of phase stabilization, whereas if it exceeds 0.05%, it contains inorganic acid-containing supercritical water. Since stress corrosion cracking resistance in the environment deteriorates, the Mg content is set to 0.001 to 0.05% (more preferably 0.010% to 0.040%).
[0012]
Nb:
Nb is added as necessary because it has the effect of further improving the overall corrosion resistance in a supercritical water environment containing hydrochloric acid in particular, but in that case, it is effective when contained over 1.0%. However, if the content exceeds 6%, the phase stability deteriorates. Therefore, Nb contained in the Ni-based alloy of the present invention is determined to be more than 1.0 to 6%. More preferably, it is 1.1 to less than 3.0%.
[0013]
Mo and Hf:
Mo and Hf are added as necessary because they have the effect of further improving the stress corrosion cracking resistance in a supercritical water environment containing hydrochloric acid in particular, but Mo is effective when contained in excess of 0.01%. Although it is shown, the content of 0.5% or more is not preferable because the phase stability is deteriorated and the stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment is deteriorated. Therefore, the Mo content is set to more than 0.01 to less than 0.5% (more preferably, more than 0.1 to less than 0.5%).
Similarly, if Hf is contained in an amount of 0.01% or more, the effect is exhibited, but 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 have the effect of improving the strength, so they are added as necessary. However, Fe is effective when contained in an amount of 0.1% or more, but if it exceeds 10%, it contains an inorganic acid-containing supercritical water environment. This is not preferable because the corrosion resistance against general corrosion in the steel deteriorates. Therefore, the Fe content is set to 0.1% to 10% (more preferably, 0.5 to 4.0%).
Similarly, if Si is contained in an amount of 0.01% or more, the effect is exhibited, but if it exceeds 0.1%, the phase stability deteriorates, so the resistance to stress corrosion cracking in an inorganic acid-containing supercritical water environment deteriorates. This is not preferable. Therefore, the Si content is set to 0.01% to 0.1% (more preferably 0.02 to 0.05%).
[0015]
C:
C is contained as an unavoidable impurity, but if C is contained in a large amount, Cr and carbide are formed in the vicinity of the grain boundary, and the corrosion resistance against the overall corrosion is deteriorated. Therefore, the smaller the C content, the better. The upper limit of the C content contained in the inevitable impurities is set to 0.05%.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
It melt | dissolved and cast using the normal high frequency melting furnace, and the ingot which has a component composition shown by Tables 1-4 and has thickness: 12 mm was produced. The ingot was subjected to a homogenization heat treatment held at 1230 ° C. for 10 hours, and held in the range of 1000 to 1230 ° C., while reducing the thickness of 1 mm by one hot rolling and finally making it 5 mm thick. Further, after being subjected to solid solution treatment by holding at 1200 ° C. for 30 minutes and water quenching, the surface is buffed, so that the Ni-based alloy plates 1 to 42 of the present invention, the comparative Ni-based alloy plates 1 to 11 and the conventional ones Ni base alloy plates 1 to 3 were prepared.
In order to give internal stress and internal strain to these Ni-base alloy plates 1 to 42, comparative Ni-base alloy plates 1 to 11 and conventional Ni-base alloy plates 1 to 3 according to the present invention, they are cold-rolled at a reduction rate of 20%. Each 4 mm thick plate was produced. This plate was cut to prepare a solid solution test piece having a cubic shape having dimensions of 4 mm in length, 4 mm in width, and 4 mm in height.
Further, in order to evaluate the effect of phase stability on the stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment, the present invention Ni-based alloy plates 1 to 42, comparative Ni-based alloy plates 1 to 11 and Conventional Ni-based alloy plates 1 to 3 are subjected to an aging treatment of holding at 500 ° C. for 1000 hours, and then cold-rolled at a reduction rate of 20% to give internal stress and internal strain, and each 4 mm thick plate The aging material test piece having a cubic shape having dimensions of 4 mm in length, 4 mm in width, and 4 mm in height was prepared by cutting this plate.
[0017]
Next, a flow-through type corrosion test apparatus was prepared in which a double tube of titanium / Hastelloy C-276 composed of inner side: titanium and outer side: Hastelloy C-276 was used as an autoclave. This flow-through type corrosion test apparatus forms a predetermined corrosion test condition by injecting a test solution from one end of the double pipe with a high-pressure pump and heating the test solution with a heater provided at the end of the pipe. The test solution discharged from one end is collected in a reservoir tank through a pressure reducing valve.
[0018]
Supercritical water prepared by mixing hydrochloric acid: 0.03 mol / kg with supercritical water of fluid temperature: 500 ° C., pressure: 60 MPa, dissolved oxygen amount: 800 ppm (added as hydrogen peroxide) was prepared as a test solution.
This supercritical water mixed with hydrochloric acid is a supercritical aqueous solution expected to be generated when PCB or dioxin is decomposed and oxidized with supercritical water. Hereinafter, this hydrochloric acid-containing supercritical aqueous solution is decomposed into PCB or dioxin. It is called simulated liquid.
The PCB or dioxin decomposition simulation liquid is press-fitted into a titanium / Hastelloy C-276 double pipe in a flow-type corrosion test apparatus prepared in advance, and the PCB or dioxin decomposition simulation liquid inside the double pipe is flow rate: 6 g / min. In this environment, the Ni-based alloy plates 1-42 of the present invention, the comparative Ni-based alloy plates 1-11 and the conventional Ni-based alloy plates 1-3 are formed. The solid solution test piece made of was held for 100 hours to confirm the presence or absence of stress corrosion cracking on the surface of the test piece, and the results are shown in Tables 1 to 4.
[0019]
Further, in order to evaluate the effect of phase stability on the stress corrosion cracking resistance in an inorganic acid-containing supercritical water environment, the present invention Ni-based alloy plates 1 to 42, comparative Ni-based alloy plates 1 to 11 and The presence or absence of stress corrosion cracking on the surface of the aging material test piece is confirmed by holding the aging material test piece consisting of the conventional Ni-based alloy plates 1 to 3 in the above-described inorganic acid-containing supercritical water environment for 100 hours. It showed to Tables 1-4.
[0020]
[Table 1]

[0021]
[Table 2]

[0022]
[Table 3]

[0023]
[Table 4]

[0024]
From the results shown in Tables 1 to 4, the Ni-base alloy plates 1 to 42 of the present invention are the solution corrosion test pieces and the aging material test pieces, both of which are stress corrosion cracks as found in the conventional Ni-base alloy plates 1 and 2. Therefore, it can be seen that the stress corrosion cracking resistance is excellent. However, stress corrosion cracking or significant overall corrosion occurs in at least one of the solid solution test piece and the aging test piece of the comparative Ni-base alloy plates 1 to 11 having a component composition deviating from the present invention. It turns out that it is not preferable.
[0025]
【The invention's effect】
As described above, the Ni-based alloy of the present invention is excellent in stress corrosion cracking resistance in a supercritical water environment containing hydrochloric acid, so that it can be used for a long period of time, and an environment such as detoxification disposal of PCB or dioxin. It has excellent industrial effects.
The Ni-based alloy of the present invention is most effective when used in a supercritical water environment containing hydrochloric acid as described above, but is not limited to this, and sulfuric acid, phosphoric acid, hydrofluoric acid, nitric acid It can be used in supercritical water environments containing sodium chloride, supercritical water environments containing chloride salts such as sodium chloride, magnesium chloride, calcium chloride, and supercritical water environments containing ammonia. It can also be applied to supercritical water device materials for disposal of electronic power related waste and general industrial waste.
Further, when the Ni-based alloy of the present invention is used as a reaction chamber of the apparatus main body, the outside may be made of a strength material such as stainless steel, and the Ni-based alloy of the present invention may be clad or lined on the inner surface.

Claims

In mass%, Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Inorganic acid-containing supercriticality characterized in that it contains 0.05 to 0.5%, the balance is made of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less Ni-based alloy with excellent stress corrosion cracking resistance in water environments.

In mass%, Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Further, Nb: more than 1.0 to 6%,
Excellent balance of stress corrosion cracking resistance in supercritical water environment containing inorganic acid, characterized in that the balance consists of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less. Ni-based alloy.

In mass%, Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
In addition, Mo: 0.01 to less than 0.5%, Hf: 0.01 to 0.1% of one or two,
Excellent balance of stress corrosion cracking resistance in supercritical water environment containing inorganic acid, characterized in that the balance consists of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less. Ni-based alloy.

In mass%, Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Furthermore, Fe: 0.1 to 10%, Si: 0.01 to 0.1% of one or two types,
Excellent balance of stress corrosion cracking resistance in supercritical water environment containing inorganic acid, characterized in that the balance consists of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less. Ni-based alloy.

In mass%, Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Further, Nb: more than 1.0 to 6%,
In addition, Mo: 0.01 to less than 0.5%, Hf: 0.01 to 0.1% of one or two,
Excellent balance of stress corrosion cracking resistance in supercritical water environment containing inorganic acid, characterized in that the balance consists of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less. Ni-based alloy.

In mass%, Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Further, Nb: more than 1.0 to 6%,
Furthermore, Fe: 0.1 to 10%, Si: 0.01 to 0.1% of one or two types,
Excellent balance of stress corrosion cracking resistance in supercritical water environment containing inorganic acid, characterized in that the balance consists of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less. Ni-based alloy.

In mass%, Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
In addition, Mo: 0.01 to less than 0.5%, Hf: 0.01 to 0.1% of one or two,
Furthermore, Fe: 0.1 to 10%, Si: 0.01 to 0.1% of one or two types,
Excellent balance of stress corrosion cracking resistance in supercritical water environment containing inorganic acid, characterized in that the balance consists of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less. Ni-based alloy.

In mass%, Cr: more than 28 to less than 34%, W: more than 0.1 to less than 1.0%, Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: Containing 0.05-0.5%,
Further, Nb: more than 1.0 to 6%,
In addition, Mo: 0.01 to less than 0.5%, Hf: 0.01 to 0.1% of one or two,
Furthermore, Fe: 0.1 to 10%, Si: 0.01 to 0.1% of one or two types,
Excellent balance of stress corrosion cracking resistance in supercritical water environment containing inorganic acid, characterized in that the balance consists of Ni and inevitable impurities, and the amount of C contained as inevitable impurities is adjusted to 0.05% or less. 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.