JP3704655B2 - Steel for solid oxide fuel cell separator - Google Patents
Steel for solid oxide fuel cell separator Download PDFInfo
- Publication number
- JP3704655B2 JP3704655B2 JP08900997A JP8900997A JP3704655B2 JP 3704655 B2 JP3704655 B2 JP 3704655B2 JP 08900997 A JP08900997 A JP 08900997A JP 8900997 A JP8900997 A JP 8900997A JP 3704655 B2 JP3704655 B2 JP 3704655B2
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel
- fuel cell
- oxidation resistance
- solid oxide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Landscapes
- Fuel Cell (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は固体電解質型燃料電池のセパレータに用いられる鋼に関する。
【０００２】
【従来の技術】
燃料電池は、その発電効率が高いこと、ＳＯx、ＮＯx、ＣＯ2の発生量が少ないこと、負荷の変動に対する応答性が良いこと、コンパクトであること等の優れた特徴を有するため、火力発電の代替としての大規模集中型、都市近郊分散配置型、および自家発電用等の巾広い発電システムへの適用が期待されている。
【０００３】
燃料電池の種類には用いる電解質により、りん酸型、溶融炭酸塩型、固体電解質型、高分子固体電解質型に分類されるが、なかでも固体電解質型燃料電池は電解質として安定化ジルコニア等のセラミックスを用いて１０００℃付近で運転されるもので、電極反応に触媒を用いる必要がないこと、高温による化石燃料の内部改質が可能で石炭ガス等の多様な燃料を用いることができること、高温排熱を利用しガスタービンあるいは蒸気タービン等と組み合わせ、いわゆるコンバインドサイクル発電とすることにより高効率の発電が可能となること、構成物が全て固体であるためコンパクトであること等の優れた特徴を有し、次世代の電力供給源として非常に有望視されている。
【０００４】
しかしながら固体電解質型燃料電池の実用化のためには多くの検討課題が残されている。特に高出力密度が可能な平板型燃料電池の場合、重要な構成要素としてセパレータが挙げられる。セパレータは電解質、燃料極、空気極の３層を支持し、ガス流路を形成するとともに電流を流す役目を有する。従ってセパレータには、高温での電気伝導性、耐酸化性、さらに電解質との熱膨張差が小さいこと等の特性が要求される。
【０００５】
このような要求特性を鑑み、従来は導電性セラミックスが多く用いられてきた。しかしながらセラミックスは加工性が悪くまた高価であることから、燃料電池の大型化、実用化の面から問題を残している。そのため安価で信頼性のある金属材料によるセパレータの開発が要求されている。また通常の金属材料を１０００℃付近で使用すると表面が酸化され酸化被膜を生じる。したがって、セパレータ材として用いるためにはこの酸化被膜が安定で酸化が進行しないことが必要であり、さらにこの酸化被膜が電気伝導性を有することが必要である。
【０００６】
特開平６−２６４１９３号には固体電解質型燃料電池用金属材料として、Ｃ０．１％以下、Ｓｉ０．５〜３．０％、Ｍｎ３．０％以下、Ｃｒ１５〜３０％、Ｎｉ２０〜６０％、Ａｌ２．５〜５．５％、残部実質的にＦｅからなるオーステナイト系ステンレス鋼が開示されている。
特開平７−１６６３０１号には固体電解質燃料電池のセパレータとして、Ｆｅ６０〜８２％およびＣｒ１８〜４０％に前記単電池の空気極との間の接触抵抗を低減する添加元素（Ｌａ、Ｙ、ＣｅまたはＡｌ）からなる材料を使用することが開示されている。
さらに特開平７−１４５４５４には、固体電解質型燃料電池用金属材料としてＣｒ５〜３０％、Ｃｏ３〜４５％、Ｌａ１％以下、残部実質的にＦｅからなる材料が開示されている。
【０００７】
【発明が解決しようとする課題】
上述した特開平６−２６４１９３号に開示された材料はＡｌとＣｒを相当量含むために表面酸化被膜はＡｌ系酸化物を主体とし、これにＣｒ系酸化物を含有したものである。しかしながら後述するようにＡｌ系酸化物は電気伝導率が低いために固体電解質セパレータ用としては十分ではない。さらにオーステナイト系ステンレス鋼は電解質の安定化ジルコニアに比較して熱膨張係数が大きいため長時間使用における安定性に問題がある。また高価なＮｉを多く含むために価格的にも高く、燃料電池の実用化のためには不十分と考えられる。
【０００８】
上述した特開平７−１６６３０１号あるいは特開平７−１４５４５４号に開示された材料は、オーステナイト系ステンレス鋼に比較して熱膨張係数が低く、電解質の安定化ジルコニアの熱膨張係数に近いため長時間使用における安定性に有利であり、また電気伝導率も良好である。しかし、本発明者の検討によれば、長時間使用後の耐酸化性が十分ではなかった。
本発明の目的は、１０００℃付近において良好な電気伝導性を有する酸化被膜を形成するとともに良好な耐酸化性を有し、かつ電解質との熱膨張差が小さくさらに安価な金属製セパレータ材を提供することである。
【０００９】
【課題を解決するための手段】
本発明者は種々検討の結果、まず対象とする金属材料をフェライト系とした。この理由の第１は、電解質である安定化ジルコニアの常温から１０００℃までの熱膨張係数が１１〜１２×１０マイナス６乗／℃に対し、通常のオーステナイト系の金属材料では１６×１０マイナス６乗／℃以上であり、両者の熱膨張差が大きいため長時間使用中の安定性に問題があるためである。第２の理由は一般にオーステナイト系は高価なＮｉを含むため高価であるが、フェライト系はＦｅをベースとしNiを含まないかまたは含んでも少量であるため安価であるためである。
【００１０】
次に本発明者は形成される酸化被膜の電気伝導度について種々検討した。保護性を有する酸化被膜の代表としてはＡｌの酸化物とＣｒの酸化物を検討した。１０００℃付近の高温になると一般にはＡｌ2Ｏ3の方が保護作用が大きく有利であるが、Ａｌ2Ｏ3被膜形成材の電気抵抗を測定してみると１００ｍΩ・ｃｍ2を越えるものであり、セパレータとしては使用できないことがわかった。一方Ｃｒ2Ｏ3被膜形成材の電気抵抗は１００ｍΩ・ｃｍ2以下であり、セパレータに使用可能であることがわかった。そこで本発明においては表面にＣｒ系酸化物を主体とする酸化被膜を形成するフェライト系金属材料、すなわちＦｅ−Ｃｒ系を基本とした。
【００１１】
次に、長時間使用する場合に問題となる耐酸化性であるが、前述のように１０００℃付近においては通常Ｃｒ系酸化被膜の耐酸化性はＡｌ系酸化被膜より劣る。またＣｒ系酸化物を主体とする場合でもＮｉベースの合金（例えばＪＩＳ ＮＣＦ６００に代表されるＮｉ−Ｃｒ合金）よりもＦｅベースの合金（例えばＳＵＳ４３０のようなＦｅ−Ｃｒ合金）の方が耐酸化性は劣っている。
従って単純にＦｅ−Ｃｒ系とするだけでは、耐酸化性を満足させることは困難である。
【００１２】
本発明者は上述した問題点を解決するために種々検討した結果、Ｆｅ−Ｃｒ系にＨｆを添加することにより、Ｃｒ系酸化被膜を主体としながら良好な耐酸化性が得られ長時間加熱後も皮膜の剥離が見られないことを見出した。またＨｆに加えさらにＹ、希土類元素、Ｚｒの１種または２種以上を加えるとさらに耐酸化性が向上することも見出した。なおこれらの添加を行っても形成される酸化皮膜は、Ｃｒ系酸化被膜が主体なので電気抵抗もさほど大きくなることはないことを見出した。
【００１３】
すなわち本発明は、重量％にてＣ０．２％以下、Ｓｉ３．０％以下、Ｍｎ１．０％以下、Ｃｒ１５〜３０％、Ｈｆ０．５％以下を含み、および選択元素としてＮｉ２％以下、Ａｌ１％以下、Ｔｉ１％以下、ＭｏとＷの１種または２種をＭｏ＋１／２Ｗで５％以下、Ｎｂ２％以下の元素から選ばれる１種または２種以上を含有し、残部Ｆｅ及び不可避的不純物からなる固体電解質型燃料電池セパレータ用鋼である。
【００１４】
また、本発明は、重量％にてＣ０．２％以下、Ｓｉ３．０％以下、Ｍｎ１．０％以下、Ｃｒ１５〜３０％、Ｈｆ０．５％以下を含み、および選択元素としてＮｉ２％以下、Ａｌ１％以下、Ｔｉ１％以下、ＭｏとＷの１種または２種をＭｏ＋１／２Ｗで５％以下、Ｎｂ２％以下の元素から選ばれる１種または２種以上を含み、さらにＹ０．５％以下、希土類元素０．２％以下、Ｚｒ１％以下の元素から選ばれる１種または２種以上を含み、残部Ｆｅ及び不可避的不純物からなる固体電解質型燃料電池セパレータ用鋼である。
【００１５】
【発明の実施の形態】
以下に本発明における成分限定理由について述べる。
Ｃは、炭化物を形成して高温強度を増大させる作用を有するが、一方加工性を劣化させまたＣｒと結び付くことにより耐酸化性に有効なＣｒ量を減少させる。従って０．２％以下に限定する。望ましくは０．０８％以下である。
Ｓｉは本発明の場合、Ｃｒ2Ｏ3系酸化皮膜と母材の界面付近に薄いＳｉＯ2系皮膜を形成して耐酸化性を向上させる作用を有する。しかし過度の添加は加工性、靭性の低下を招くとともにＳｉＯ2系皮膜が厚くなりすぎて皮膜の電気伝導度が低下する問題が生じるので３％以下とする。望ましくは０．２〜２．０％である。
【００１６】
ＭｎはＣｒ2Ｏ3系被膜の密着性を向上させるのに必要である。しかし、過度に添加するとＭｎ含有のスピネル型酸化物の耐酸化性不足のため耐酸化性が悪くなる。従ってＭｎは１％以下に限定する。望ましくは０．２〜１．０％である。
Ｃｒは本発明においてＣｒ2Ｏ3系被膜の生成により、耐酸化性および電気伝導性を維持するために重要な元素である。そのため最低限１５％を必要とする。しかしながら過度の添加は耐酸化性向上にさほど効果がないばかりか加工性の劣化を招くので１５〜３０％に限定する。望ましくは１８〜２５％である。
Ｈｆは本発明における重要な元素である。前述のようにＣｒ系酸化被膜のみで良好な耐酸化性を持たせることは難しいが、少量のＨｆ添加により耐酸化性が大きく向上することが見出された。これは主に酸化被膜の密着性を改善する効果によると考えられる。しかし過度の添加は熱間加工性を劣化させるので０．５％以下に限定する。望ましくは０．０１〜０．３％である。
【００１７】
選択元素として１種または２種以上を添加するＹ、希土類元素、Ｚｒは、Ｈｆと組み合わせて少量添加することにより耐酸化性をさらに改善する効果を有する。しかしながら過度の添加は熱間加工性を劣化させるので、Ｙは０．５％以下、希土類元素は０．２％以下、Ｚｒは１％以下に限定する。望ましくはＹは０．０１〜０．３％、希土類元素は０．０１〜０．１２％、Ｚｒは０．０５〜０．８％である。
またＨｆと、Ｙ、希土類元素、Ｚｒの１種または２種以上に適量のＳｉ、Ｍｎ添加を組み合わせると一層耐酸化性が向上する。これはこれらの元素の複合作用により主に酸化被膜の密着性が改善されることによると考えられる。またＺｒは後述のＴｉ、Ｎｂと同様、Ｃと結びついて炭化物を形成し、Ｃ固定により加工性を向上させまた強度向上にも寄与する。
【００１８】
Ｎｉ，Ａｌ，Ｔｉ，Ｎｂ，Ｍｏ，Ｗの各元素は本発明鋼には必ずしも添加する必要はないが、以下に示す効果を有するため必要に応じて単独または複合で添加することができる。
Ｎｉは本発明鋼に少量添加することにより靭性の向上に効果が有る。しかしＮｉはオーステナイト生成元素であり、過度の添加はフェライト−オーステナイトの２相組織となり、熱膨張係数の増加およびコストアップを招く。さらに過度のＮｉの添加は耐酸化性を悪くする。従ってＮｉは２％以下に限定する。望ましくは０．９％以下である。
【００１９】
Ａｌは脱酸剤として添加される。Ａｌを多く添加するとＡｌ2Ｏ3被膜が形成されるが、前述のようにＡｌ2Ｏ3被膜は耐酸化性に対しては有効であるが、酸化被膜の電気抵抗を増大させる。従って、本発明の場合Ａｌ2Ｏ3被膜の形成を避けるためにＡｌは１％以下に限定する。望ましくは０．５％以下である。
ＴｉはＣと結び付いて炭化物を形成し、Ｃ固定により加工性を向上させる。しかしながら１０００℃付近においてはあまり保護性のないＴｉＯまたはＴｉＯ2を形成し耐酸化性を劣化させる。従ってＴｉは１％以下に限定する。
ＮｂもＴｉと同様Ｃと結び付いて炭化物を形成し、Ｃ固定により加工性を向上させるとともに高温強度も増大させる。しかしながら過度の添加は耐酸化性を劣化させるので２％以下に限定する。
【００２０】
ＭｏおよびＷは、特に高温強度を増加させる作用を有するので、高温強度を重視する場合には添加してもよい。しかしながら過度に添加すると耐酸化性、加工性を劣化させるのでＭｏ＋１／２Ｗで５％以下に限定する。
上述した合金組成により、好ましくは１０００℃で１００Ｈｒ加熱した後の１０００℃における酸化皮膜の電気抵抗が５０ｍΩ・ｃｍ2以下であり、さらに１１００℃で１００Ｈｒ加熱後に表面酸化スケールの剥離が実質的に起こらない固体電解質燃料電池セパレータ用鋼を得ることができる。
【００２１】
なお、以下の元素は、１０００℃で１００Ｈｒ加熱した後の１０００℃における酸化皮膜の電気抵抗率が８０ｍΩ・ｃｍ2以下、１１００℃、１００Ｈｒ加熱後のスケール剥離が０．５ｍｇ／ｃｍ2以下を満たす範囲内で添加元素を含むことができる。たとえば、以下の範囲の添加元素を含むことができる。
Ｐ≦０．０４％ Ｓ≦０．０３％ Ｃｕ≦０．３０％
Ｖ≦０．５％ Ｔａ≦０．５％ Ｍｇ≦０．０２％
Ｃａ≦０．０２％ Ｃｏ≦２％
【００２２】
【実施例】
（実施例１）
表１に示す組成の鋼を真空誘導炉にて溶製し１０ｋｇのインゴットを作製後、１１００℃に加熱して３０ｍｍ角の棒材に鍛伸した。なお表１において、比較鋼Ｎｏ．４１はＮＣＦ６００として知られているオーステナイト系合金である。また比較鋼Ｎｏ．４４は特開平６−２６４１９３号に記載のものである。これらの試料の製造工程において、本発明鋼中で比較的Ｃｒ量が高いＮｏ．９合金は鍛造中に若干疵が発生し、やや加工性が悪い傾向を示した。これらの素材から試験片を切り出し各種試験を行った。
【００２３】
【表１】
まず、直径１０ｍｍ，長さ２０ｍｍの円柱状試験片を用いて、大気中１０００℃で１００Ｈｒの加熱処理を行った後、表面に生成される酸化物の種類をＸ線回折により調べた。さらに表面酸化スケールの剥離量を測定した。また１０ｍｍ×１０ｍｍ×３ｍｍの板状試料を用いて、大気中１０００℃で１００Ｈｒ加熱を行って表面に酸化被膜を形成させた後、１０００℃における電気抵抗を測定した。なお電気抵抗は面積抵抗（ｍΩ・ｃｍ2）で表した。またほとんどの試料においては１０００℃で１００Ｈｒ加熱後に酸化スケールの剥離が見られなかったので、さらに加速試験として１１００℃で１００Ｈｒ、ならびに１０００℃で１０００Ｈｒ加熱を行った後の酸化スケールの剥離量を調べた。さらにいくつかの試料については３０℃から１０００℃までの熱膨張係数を測定した。これらの試験結果をまとめて表２に示す。
【００２５】
【表２】
表２より本発明鋼は大気中１０００℃×１００Ｈｒの加熱により主にＣｒ2Ｏ3被膜を形成しており、電気抵抗の値は十分小さい。一方、比較鋼Ｎｏ．４２、４３、４４はＡｌを２％以上含むためＡｌ2Ｏ3被膜を形成し、電気抵抗の値は本発明鋼の値よりはるかに大きい。また比較鋼Ｎｏ．４８はＳｉが高いために表面からのＸ線回折では確認できなかったがおそらくＳｉＯ2系皮膜が形成されていると思われ、電気抵抗の値が高い。
大気中１０００℃×１００Ｈｒの加熱後の表面スケール剥離量を比較すると、本発明鋼はスケールの剥離は全く観察されなかったが、比較鋼Ｎｏ．４５はＣｒ量が少ないため剥離量が多く、長時間使用に耐えないことがわかる。また比較鋼Ｎｏ．５０もスケールの剥離が観察されたがこれはＨｆを含まないことに加え、Ｍｎが高くＭｎ2ＦｅＯ4の量が多くなったためと思われる。
【００２７】
さらに加速試験として行った大気中１１００℃×１００Ｈｒの加熱後の表面スケール剥離量を比較すると、本発明鋼はＮｏ．１６，１７、１８を除き１１００℃という高温での加熱でもスケールの剥離が観察されない。Ｎｏ．１６，１７，１８はごく少量のスケールの剥離が観察されるがこれはＳｉ、Ｍｎ量が低めであったためと思われる。一方、比較鋼Ｎｏ．４１（ＮＣＦ６００）、４５、４６，４７、４９、５０では剥離が発生した。Ｎｏ．４６はＨｆ，Ｙ，希土類元素またはＺｒが無添加であること、Ｎｏ．４７はＨｆを含まずＳｉ量が低いこと、Ｎｏ．４９はＨｆを含まずＭｎ量が低いことによりスケールの密着性が不足したためと思われる。Ｎｏ．５０は前述のようにＨｆを含まずＭｎが高すぎたためと思われる。
【００２８】
もう一つの加速試験条件である大気中１０００℃×１０００Ｈｒの加熱後の表面スケール剥離量を本発明鋼中で比較すると、Ｃ高め（Ｎｏ．７）、Ｃｒ低め（Ｎｏ．８）、Ｎｂ，Ｔｉ高め（Ｎｏ．１０）、Ｓｉ低め（Ｎｏ．１６）、Ｍｎ低め（Ｎｏ．１７）、Ｓｉ，Ｍｎ低め（Ｎｏ．１８）でスケール剥離量がやや多くなっていることがわかる。
次に常温から１０００℃までの熱膨張係数の値は本発明鋼Ｎｏ．１〜５が約１３×１０マイナス６乗／℃であり、ジルコニアの値に近い。一方比較鋼Ｎｏ．４１、Ｎｏ．４４はオーステナイト系であるために熱膨張係数の値が大きい。
【００２９】
【発明の効果】
以上述べたように本発明鋼を固体電解質型燃料電池のセパレータに用いることにより、燃料電池の低コスト化を図ることができ、燃料電池の実用化、大型化に大きく寄与できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to steel used for a separator of a solid oxide fuel cell.
[0002]
[Prior art]
Fuel cells, that the power generation efficiency is high, SOx, NOx, and the generation amount of CO 2 is small, it is a good response to load variations, since it has excellent features such that it is compact, the thermal power It is expected to be applied to wide-scale power generation systems such as large-scale centralized alternatives, distributed suburban areas, and private power generation.
[0003]
Fuel cells are classified into phosphoric acid type, molten carbonate type, solid electrolyte type, and polymer solid electrolyte type depending on the electrolyte used. Among them, solid electrolyte type fuel cells are ceramics such as stabilized zirconia as an electrolyte. It is not necessary to use a catalyst for the electrode reaction, internal reforming of fossil fuel can be performed at high temperature, and various fuels such as coal gas can be used. Combined with a gas turbine or steam turbine using heat, so-called combined cycle power generation enables high-efficiency power generation, and all the components are solid so that they are compact. However, it is very promising as a next-generation power supply source.
[0004]
However, many problems remain to be solved for practical application of solid oxide fuel cells. In particular, in the case of a flat plate fuel cell capable of high power density, an important component is a separator. The separator supports three layers of an electrolyte, a fuel electrode, and an air electrode, and has a function of forming a gas flow path and flowing current. Therefore, the separator is required to have characteristics such as electrical conductivity at high temperature, oxidation resistance, and a small difference in thermal expansion from the electrolyte.
[0005]
In view of such required characteristics, conductive ceramics have been used in the past. However, since ceramics have poor processability and are expensive, there remains a problem in terms of the enlargement and practical use of fuel cells. Therefore, development of a separator made of an inexpensive and reliable metal material is required. When a normal metal material is used at around 1000 ° C., the surface is oxidized and an oxide film is formed. Therefore, in order to use as a separator material, it is necessary that this oxide film is stable and oxidation does not proceed, and further, this oxide film needs to have electrical conductivity.
[0006]
In JP-A-6-264193, as a metal material for a solid oxide fuel cell, C 0.1% or less, Si 0.5 to 3.0%, Mn 3.0% or less, Cr 15 to 30%, Ni 20 to 60%, Al 2 An austenitic stainless steel made of 0.5 to 5.5% and the balance being substantially Fe is disclosed.
In JP-A-7-166301, as a separator for a solid electrolyte fuel cell, Fe 60 to 82% and Cr 18 to 40% are added elements (La, Y, Ce or lower) that reduce the contact resistance between the air electrode of the unit cell. The use of materials consisting of Al) is disclosed.
Further, Japanese Patent Laid-Open No. 7-145454 discloses a material composed of Cr 5-30%, Co 3-45%, La 1% or less, and the balance substantially Fe as a solid oxide fuel cell metal material.
[0007]
[Problems to be solved by the invention]
Since the material disclosed in Japanese Patent Laid-Open No. 6-264193 described above contains a considerable amount of Al and Cr, the surface oxide film is mainly composed of an Al-based oxide and contains a Cr-based oxide. However, as will be described later, Al-based oxides are not sufficient for solid electrolyte separators because of their low electrical conductivity. Furthermore, since austenitic stainless steel has a larger coefficient of thermal expansion than zirconia, which is a stabilized electrolyte, there is a problem in stability during long-term use. In addition, since it contains a lot of expensive Ni, it is expensive and is considered insufficient for the practical use of fuel cells.
[0008]
The materials disclosed in the above-mentioned JP-A-7-166301 or JP-A-7-145454 have a low coefficient of thermal expansion compared to austenitic stainless steel, and are close to the coefficient of thermal expansion of stabilized zirconia in the electrolyte. It is advantageous for stability in use and has good electrical conductivity. However, according to the study of the present inventors, the oxidation resistance after long-term use was not sufficient.
An object of the present invention is to provide a metal separator material that forms an oxide film having good electrical conductivity near 1000 ° C., has good oxidation resistance, has a small difference in thermal expansion from an electrolyte, and is inexpensive. It is to be.
[0009]
[Means for Solving the Problems]
As a result of various studies, the present inventor first made the metal material of interest ferrite. The first reason for this is that the thermal expansion coefficient from ambient temperature to 1000 ° C. of stabilized zirconia, which is an electrolyte, is 11 to 12 × 10 minus 6 power / ° C., whereas that of a normal austenitic metal material is 16 × 10 minus 6 This is because there is a problem in stability during use for a long time because the difference in thermal expansion between them is large. The second reason is that the austenite type is generally expensive because it contains expensive Ni, but the ferrite type is based on Fe and does not contain Ni or even if it contains a small amount, it is inexpensive.
[0010]
Next, the inventor conducted various studies on the electric conductivity of the oxide film to be formed. Al oxide and Cr oxide were examined as representative oxide films having protective properties. In general, Al 2 O 3 is more advantageous at a high temperature around 1000 ° C., but the protective effect of Al 2 O 3 film forming material is over 100 mΩ · cm 2 . It was found that it cannot be used as a separator. On the other hand, the electric resistance of the Cr 2 O 3 film-forming material is 100 mΩ · cm 2 or less, which indicates that it can be used for a separator. Therefore, in the present invention, a ferritic metal material that forms an oxide film mainly composed of a Cr-based oxide on the surface, that is, an Fe—Cr-based material is used as a basis.
[0011]
Next, the oxidation resistance becomes a problem when used for a long time. As described above, the oxidation resistance of the Cr-based oxide film is usually inferior to that of the Al-based oxide film at around 1000 ° C. Further, even when a Cr-based oxide is mainly used, an Fe-based alloy (for example, a Fe-Cr alloy such as SUS430) is more resistant to oxidation than a Ni-based alloy (for example, a Ni-Cr alloy represented by JIS NCF600). Sex is inferior.
Therefore, it is difficult to satisfy the oxidation resistance simply by using the Fe—Cr system.
[0012]
As a result of various investigations to solve the above-mentioned problems, the present inventor has obtained good oxidation resistance while mainly comprising a Cr-based oxide film by adding Hf to the Fe-Cr system, and after heating for a long time. Also found no peeling of the film. It has also been found that oxidation resistance is further improved by adding one or more of Y, rare earth elements and Zr in addition to Hf. It has been found that even if these additions are made, the oxide film formed is mainly composed of a Cr-based oxide film, so that the electrical resistance does not increase so much.
[0013]
That is, the present invention contains C 0.2% or less, Si 3.0% or less, Mn 1.0% or less, Cr 15 to 30%, Hf 0.5% or less in terms of% by weight, and Ni 2% or less, Al 1% as a selective element. Hereinafter, Ti 1% or less, one or two of Mo and W are contained in Mo + 1 / 2W at 5% or less and Nb 2% or less, and the balance is Fe and inevitable impurities. Steel for solid oxide fuel cell separator .
[0014]
Further, the present invention includes C0.2% or less, Si3.0% or less, Mn1.0% or less, Cr15-30%, Hf0.5% or less in terms of% by weight, and Ni2% or less as a selective element, Al1 % Or less, Ti 1% or less, 1 or 2 kinds of Mo and W in Mo + 1 / 2W, including 1 or 2 elements selected from elements of 5% or less and Nb 2% or less, and further Y0.5% or less, rare earth It is a steel for a solid oxide fuel cell separator containing one or more elements selected from elements of 0.2% or less and Zr of 1% or less , the balance being Fe and inevitable impurities .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The reasons for limiting the components in the present invention will be described below.
C has the effect of increasing the high temperature strength by forming carbides, while reducing the amount of Cr effective in oxidation resistance by degrading workability and combining with Cr. Therefore, it is limited to 0.2% or less. Desirably, it is 0.08% or less.
In the case of the present invention, Si has the effect of improving the oxidation resistance by forming a thin SiO 2 film near the interface between the Cr 2 O 3 oxide film and the base material. However, excessive addition causes a decrease in workability and toughness and causes a problem that the SiO 2 film becomes too thick and the electric conductivity of the film is lowered. Desirably, it is 0.2 to 2.0%.
[0016]
Mn is necessary for improving the adhesion of the Cr 2 O 3 coating. However, if it is added excessively, the oxidation resistance of the Mn-containing spinel oxide is insufficient, resulting in poor oxidation resistance. Therefore, Mn is limited to 1% or less. Desirably, it is 0.2 to 1.0%.
Cr is an important element for maintaining oxidation resistance and electrical conductivity by producing a Cr 2 O 3 based coating in the present invention. Therefore, a minimum of 15% is required. However, excessive addition is not so effective in improving oxidation resistance, but also causes deterioration of workability, so it is limited to 15 to 30%. Desirably, it is 18 to 25%.
Hf is an important element in the present invention. As described above, it is difficult to provide good oxidation resistance only with the Cr-based oxide film, but it has been found that the oxidation resistance is greatly improved by adding a small amount of Hf. This is presumably due to the effect of improving the adhesion of the oxide film. However, excessive addition degrades hot workability, so it is limited to 0.5% or less. Desirably, it is 0.01 to 0.3%.
[0017]
Y, rare earth elements, and Zr to which one or more elements are added as selective elements have the effect of further improving oxidation resistance by adding a small amount in combination with Hf. However, excessive addition degrades hot workability, so Y is limited to 0.5% or less, rare earth elements are limited to 0.2% or less, and Zr is limited to 1% or less. Desirably, Y is 0.01 to 0.3%, rare earth elements are 0.01 to 0.12%, and Zr is 0.05 to 0.8%.
Further, when an appropriate amount of Si or Mn is added to one or more of Hf, Y, rare earth elements and Zr, the oxidation resistance is further improved. This is considered to be mainly due to the improved adhesion of the oxide film due to the combined action of these elements. Zr, like Ti and Nb described later, combines with C to form a carbide, and improves the workability by C fixation and contributes to the improvement of strength.
[0018]
Each element of Ni, Al, Ti, Nb, Mo, and W is not necessarily added to the steel of the present invention, but can be added alone or in combination as necessary because of the following effects.
Ni is effective in improving toughness by adding a small amount to the steel of the present invention. However, Ni is an austenite-forming element, and excessive addition results in a ferrite-austenite two-phase structure, resulting in an increase in thermal expansion coefficient and an increase in cost. Further, excessive addition of Ni deteriorates the oxidation resistance. Therefore, Ni is limited to 2% or less. Desirably, it is 0.9% or less.
[0019]
Al is added as a deoxidizer. When a large amount of Al is added, an Al 2 O 3 film is formed. As described above, the Al 2 O 3 film is effective for oxidation resistance, but increases the electric resistance of the oxide film. Therefore, in the present invention, Al is limited to 1% or less in order to avoid the formation of an Al 2 O 3 film. Desirably, it is 0.5% or less.
Ti combines with C to form a carbide, and improves the workability by fixing C. However, in the vicinity of 1000 ° C., TiO or TiO 2 which is not very protective is formed and the oxidation resistance is deteriorated. Therefore, Ti is limited to 1% or less.
Nb, like Ti, combines with C to form carbides, and C fixation improves workability and increases high-temperature strength. However, excessive addition degrades oxidation resistance, so it is limited to 2% or less.
[0020]
Mo and W have the effect of increasing the high temperature strength, and therefore may be added when the high temperature strength is important. However, if excessively added, the oxidation resistance and workability deteriorate, so Mo + 1 / 2W is limited to 5% or less.
Due to the alloy composition described above, the electrical resistance of the oxide film at 1000 ° C. after heating at 1000 ° C. for 100 hours is preferably 50 mΩ · cm 2 or less, and the surface oxide scale is substantially peeled off after heating at 1100 ° C. for 100 hours. No steel for solid electrolyte fuel cell separator can be obtained.
[0021]
In the following elements, the electrical resistivity of the oxide film at 1000 ° C. after heating at 1000 ° C. for 100 hours satisfies 80 mΩ · cm 2 or less, and the scale peeling after heating at 1100 ° C. for 100 hours satisfies 0.5 mg / cm 2 or less. Additive elements can be included within the range. For example, the following range of additive elements can be included.
P ≦ 0.04% S ≦ 0.03% Cu ≦ 0.30%
V ≦ 0.5% Ta ≦ 0.5% Mg ≦ 0.02%
Ca ≦ 0.02% Co ≦ 2%
[0022]
【Example】
(Example 1)
Steel having the composition shown in Table 1 was melted in a vacuum induction furnace to produce a 10 kg ingot, and then heated to 1100 ° C. and forged into a 30 mm square bar. In Table 1, comparative steel No. 41 is an austenitic alloy known as NCF600. Comparative steel No. 44 is described in JP-A-6-264193. In the production process of these samples, No. 1 having a relatively high Cr content in the steel of the present invention. The alloy No. 9 was slightly flawed during forging and showed a tendency to be slightly inferior in workability. Test pieces were cut out from these materials and subjected to various tests.
[0023]
[Table 1]
First, using a cylindrical test piece having a diameter of 10 mm and a length of 20 mm, after heat treatment at 1000 ° C. in air for 100 hours, the type of oxide generated on the surface was examined by X-ray diffraction. Furthermore, the amount of peeling of the surface oxide scale was measured. Further, a 10 mm × 10 mm × 3 mm plate-like sample was heated in air at 1000 ° C. for 100 hours to form an oxide film on the surface, and then the electrical resistance at 1000 ° C. was measured. The electrical resistance was represented by sheet resistance (mΩ · cm 2 ). In most samples, oxide scale peeling was not observed after heating at 1000 ° C. for 100 hours. Therefore, as an accelerated test, the amount of oxide scale peeled after heating at 1100 ° C. for 100 hours and at 1000 ° C. for 1000 hours was investigated. It was. Furthermore, the thermal expansion coefficient from 30 degreeC to 1000 degreeC was measured about some samples. These test results are summarized in Table 2.
[0025]
[Table 2]
From Table 2, the steel of the present invention mainly forms a Cr 2 O 3 film by heating at 1000 ° C. × 100 Hr in the atmosphere, and the value of electric resistance is sufficiently small. On the other hand, Comparative Steel No. Since 42, 43 and 44 contain 2% or more of Al, an Al 2 O 3 film is formed, and the value of electric resistance is much larger than that of the steel of the present invention. Comparative steel No. No. 48 could not be confirmed by X-ray diffraction from the surface because of the high Si, but it is likely that a SiO 2 -based film was formed, and the electrical resistance value was high.
When the amount of surface scale peeling after heating at 1000 ° C. × 100 Hr in the atmosphere was compared, no peeling of the scale was observed in the steel of the present invention. It can be seen that No. 45 has a large amount of peeling due to a small amount of Cr and cannot withstand long-term use. Comparative steel No. As for 50, scale exfoliation was observed, but this was probably due to the fact that Mn was high and the amount of Mn 2 FeO 4 was increased in addition to not containing Hf.
[0027]
Furthermore, when the amount of surface scale peeling after heating at 1100 ° C. × 100 Hr in the atmosphere as an accelerated test was compared, the steel of the present invention was No. Except for 16, 17, and 18, scale peeling is not observed even when heated at a high temperature of 1100 ° C. No. In 16, 17, and 18, a very small amount of scale exfoliation was observed. This is probably because the amounts of Si and Mn were low. On the other hand, Comparative Steel No. In 41 (NCF600), 45, 46, 47, 49, and 50, peeling occurred. No. No. 46 shows no addition of Hf, Y, rare earth elements or Zr. No. 47 does not contain Hf and the amount of Si is low. It seems that No. 49 did not contain Hf and the amount of Mn was low, resulting in insufficient scale adhesion. No. 50 seems to be because Mn was too high without Hf as described above.
[0028]
When the surface scale exfoliation amount after heating at 1000 ° C. × 1000 Hr in the atmosphere, which is another accelerated test condition, is compared in the steel of the present invention, C is increased (No. 7), Cr is lowered (No. 8), Nb, Ti It can be seen that the amount of exfoliation of the scale is slightly increased with higher (No. 10), lower Si (No. 16), lower Mn (No. 17), and lower Si and Mn (No. 18).
Next, the value of the thermal expansion coefficient from room temperature to 1000 ° C. is the steel No. of the present invention. 1 to 5 is about 13 × 10 minus 6 / ° C., which is close to the value of zirconia. On the other hand, comparative steel No. 41, no. Since 44 is austenitic, it has a large coefficient of thermal expansion.
[0029]
【The invention's effect】
As described above, by using the steel of the present invention for a separator of a solid oxide fuel cell, the cost of the fuel cell can be reduced, which can greatly contribute to the practical use and enlargement of the fuel cell.
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP08900997A JP3704655B2 (en) | 1997-04-08 | 1997-04-08 | Steel for solid oxide fuel cell separator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP08900997A JP3704655B2 (en) | 1997-04-08 | 1997-04-08 | Steel for solid oxide fuel cell separator |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH10280103A JPH10280103A (en) | 1998-10-20 |
| JP3704655B2 true JP3704655B2 (en) | 2005-10-12 |
Family
ID=13958880
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP08900997A Expired - Fee Related JP3704655B2 (en) | 1997-04-08 | 1997-04-08 | Steel for solid oxide fuel cell separator |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3704655B2 (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AUPP042597A0 (en) * | 1997-11-17 | 1997-12-11 | Ceramic Fuel Cells Limited | A heat resistant steel |
| JP4524760B2 (en) * | 2001-09-27 | 2010-08-18 | 日立金属株式会社 | Oxidation resistant steel and solid oxide fuel cell parts using the same |
| DE60224249T3 (en) | 2001-09-27 | 2012-10-18 | Hitachi Metals, Ltd. | Steel for solid oxide fuel cell separators |
| US6641780B2 (en) * | 2001-11-30 | 2003-11-04 | Ati Properties Inc. | Ferritic stainless steel having high temperature creep resistance |
| EP1536031A4 (en) * | 2002-08-09 | 2005-10-12 | Jfe Steel Corp | Metal material for fuel cell, fuel cell using the same and method for producing the material |
| US8518234B2 (en) * | 2003-09-03 | 2013-08-27 | Ati Properties, Inc. | Oxidation resistant ferritic stainless steels |
| SE527933C2 (en) * | 2004-05-19 | 2006-07-11 | Sandvik Intellectual Property | Heat-resistant steel |
| US20070087250A1 (en) * | 2005-10-13 | 2007-04-19 | Lewis Daniel J | Alloy for fuel cell interconnect |
| DE102006007598A1 (en) * | 2006-02-18 | 2007-08-30 | Forschungszentrum Jülich GmbH | Creep resistant ferritic steel |
| WO2011034002A1 (en) * | 2009-09-16 | 2011-03-24 | 日立金属株式会社 | Steel for solid oxide fuel cell having excellent oxidation resistance |
| CN109837471A (en) * | 2017-11-29 | 2019-06-04 | 宜兴市联丰化工机械有限公司 | A kind of Seal head blank production technology |
| EP4116454A1 (en) | 2020-03-02 | 2023-01-11 | JFE Steel Corporation | Ferritic stainless steel for solid oxide fuel cell |
-
1997
- 1997-04-08 JP JP08900997A patent/JP3704655B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH10280103A (en) | 1998-10-20 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP4335439B2 (en) | Heat resistant steel | |
| JP3534285B2 (en) | Solid electrolyte fuel cell separator steel | |
| JP4737600B2 (en) | Steel for solid oxide fuel cell separator | |
| US7531053B2 (en) | Fuel cell produced using a metallic material and its method of making | |
| JP2003173795A (en) | Steel for solid oxide fuel cell separator | |
| JP3704655B2 (en) | Steel for solid oxide fuel cell separator | |
| Geng et al. | Evaluation of several alloys for solid oxide fuel cell interconnect application | |
| JP3321888B2 (en) | Metal materials for solid oxide fuel cells | |
| US6776956B2 (en) | Steel for separators of solid-oxide type fuel cells | |
| CA2465604C (en) | Ferritic stainless steel having high temperature creep resistance | |
| JP5152193B2 (en) | Stainless steel material for polymer electrolyte fuel cell separator and polymer electrolyte fuel cell | |
| JP2003187828A (en) | Ferritic stainless steel for solid oxide type fuel cell member | |
| JP2007016297A (en) | Steel for solid-oxide fuel cell separator | |
| JP2007254794A (en) | Solid polymer type fuel cell and stainless steel suitable for its separator | |
| JP2003105503A (en) | Steel for solid oxide type fuel battery separator | |
| JP4299506B2 (en) | Austenitic stainless steel for equipment that exchanges heat at 500-1000 ° C | |
| JP4385328B2 (en) | Steel for solid oxide fuel cell separator | |
| JPH04358044A (en) | High corrosion resistant steel sheet for molten carbonate type fuel cell separator | |
| JP4214921B2 (en) | Fe-Cr alloy for fuel cell | |
| JPH06293941A (en) | Metallic material for solid electrolyte type fuel cell | |
| JP2007197837A (en) | Oxidation resistant steel and component for solid-oxide type fuel cell obtained by using the same | |
| JP3238812B2 (en) | Metal materials for solid oxide fuel cells | |
| Alman et al. | Low coefficient of thermal expansion (CTE) nickel base superalloys for interconnect applications in intermediate temperature solid oxide fuel cells (SOFC) | |
| JP3245304B2 (en) | Metal material | |
| KR100774097B1 (en) | Ferritic type stainless steel containing yttrium |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20040401 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20050426 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20050428 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20050523 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20050701 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20050714 |
|
| R150 | Certificate of patent or registration of utility model |
Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20080805 Year of fee payment: 3 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20090805 Year of fee payment: 4 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20090805 Year of fee payment: 4 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20100805 Year of fee payment: 5 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20100805 Year of fee payment: 5 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20110805 Year of fee payment: 6 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120805 Year of fee payment: 7 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120805 Year of fee payment: 7 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130805 Year of fee payment: 8 |
|
| LAPS | Cancellation because of no payment of annual fees |