JP4524760B2 - Oxidation resistant steel and solid oxide fuel cell parts using the same - Google Patents
Oxidation resistant steel and solid oxide fuel cell parts using the same Download PDFInfo
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Description
本発明は固体酸化物型燃料電池用セパレータ用鋼を除く耐酸化性鋼及びそれを用いてなる固体酸化物型燃料電池用部品（セパレータを除く）に関する。 The present invention relates to an oxidation-resistant steel excluding solid oxide fuel cell separator steel and a solid oxide fuel cell component (excluding a separator) using the steel.
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、及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。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、固体酸化物型、固体高分子型に分類されるが、なかでも固体酸化物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おり、従来、１０００℃付近のかなり高温で運転されるものであった。 Fuel cells, that the power generation efficiency is high, SOx, NOx, and generation 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. Depending on the electrolyte used, fuel cell types are classified into phosphoric acid type, molten carbonate type, solid oxide type, and solid polymer type. Among them, solid oxide type fuel cells include electrolytes such as stabilized zirconia. It uses ceramics and has been conventionally operated at a fairly high temperature around 1000 ° C.
上述の固体酸化物型燃料電池は、高温で運転されるために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或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。 The above-mentioned solid oxide fuel cell is operated at a high temperature, so that it is not necessary to use a catalyst for the electrode reaction, fossil fuel can be internally reformed at a high temperature, and various fuels such as coal gas are used. It can be used, combined with gas turbines or steam turbines using high-temperature exhaust heat, and so-called combined cycle power generation enables high-efficiency power generation, and it is compact because all components are solid. Therefore, it is very promising as a next-generation power supply source.
しかしながら、固体酸化物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、代表的な重要な構成要素としてセパレータが挙げられる。
このセパレータは電解質、燃料極、空気極の三層を支持し、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、更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ことから、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が、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。
However, many studies remain for the practical application of solid oxide fuel cells. In particular, in the case of a flat plate fuel cell capable of high power density, a separator is a typical important component.
This 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, since separators are required to have properties such as electrical conductivity at high temperatures, oxidation resistance, and a small difference in thermal expansion from the electrolyte, in view of these required properties, conductive ceramics have conventionally been used. Although many have been used, ceramics have poor workability and are expensive, so that problems remain in terms of the enlargement and practical use of fuel cells.
通常の金属材料を１０００℃で使用すると、表面が酸化され酸化被膜を生じるが、セパレータ材に代表される固体酸化物型燃料電池用の部品として用いるための耐酸化性鋼には、酸化被膜が安定で酸化が進行しないことと共に酸化被膜が電気伝導性を有することが必要である。
このような要求特性を満足させるために、特開平６−２６４１９３号には固体酸化物型燃料電池用耐酸化性鋼として、Ｃ：０．１％以下、Ｓｉ：０．５〜３．０％、Ｍｎ：３．０％以下、Ｃｒ：１５〜３０％、Ｎｉ：２０〜６０％、Ａｌ：２．５〜５．５％、残部Ｆｅからなるオーステナイト系ステンレス鋼が提案されている。
When a normal metal material is used at 1000 ° C., the surface is oxidized to form an oxide film. However, an oxidation-resistant steel for use as a part for a solid oxide fuel cell represented by a separator material has an oxide film. It is necessary that the oxide film is stable and oxidation does not proceed and that the oxide film has electrical conductivity.
In order to satisfy such required characteristics, Japanese Patent Laid-Open No. 6-264193 discloses C: 0.1% or less, Si: 0.5 to 3.0% as an oxidation resistant steel for a solid oxide fuel cell. , Mn: 3.0% or less, Cr: 15-30%, Ni: 20-60%, Al: 2.5-5.5%, austenitic stainless steel composed of the balance Fe has been proposed.
また、特開平７−１６６３０１号には固体電解質燃料電池の耐酸化性鋼として、Ｆｅ：６０〜８２％及びＣｒ：１８〜４０％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をそれぞれ単独で含有させる）からなる合金を使用することが提案されている。
更に、特開平７−１４５４５４号には、固体電解質型燃料電池用金属材料としてＣｒ：５〜３０％、Ｃｏ：３〜４５％、Ｌａ：１％以下、残部Ｆｅからなる耐酸化性鋼が提案されている。
Furthermore, Japanese Patent Laid-Open No. 7-145454 proposes an oxidation resistant steel made of Cr: 5-30%, Co: 3-45%, La: 1% or less, and the balance Fe as a metal material for a solid oxide fuel cell. Has been.
ところで最近、固体電解質型燃料電池の改良が著しく進み、運転温度が従来の１０００℃付近から７００〜９５０℃程度にまで低下させることが可能となってきた。このため、実用化が早まるものと予想されている。
上記の特開平６−２６４１９３号に開示された耐酸化性鋼は、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型燃料電池セパレータ用としては必ずしも十分といえない面がある。また、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電池の起動、停止に伴う熱サイクルによる電解質の割れ等による電池の性能低下を起こしやすく、長時間使用における安定性に問題がある。更に高価な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である。
Recently, solid oxide fuel cells have been remarkably improved, and it has become possible to lower the operating temperature from around 1000 ° C. to about 700 to 950 ° C. For this reason, it is expected that the practical use will be accelerated.
Since the oxidation resistant steel disclosed in the above-mentioned JP-A-6-264193 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. is there.
However, as will be described later, Al-based oxides have a low electrical conductivity, so that there are aspects that are not necessarily sufficient for solid oxide fuel cell separators. In addition, austenitic stainless steel has a larger coefficient of thermal expansion than zirconia, which stabilizes the electrolyte. There is a problem with stability. Furthermore, since a large amount of expensive Ni is contained, the price is high, which is insufficient for the practical use of fuel cells.
これに対して、特開平７−１６６３０１号及び特開平７−１４５４５４号に開示された耐酸化性鋼は、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、長時間使用後の耐酸化性が不十分であり、特に酸化層の増大に伴う剥離現象を助長し、電池内のガス流路となるセパレータに設けた溝を狭めて、電池機能を低下させる問題がある。また、特開平８−３５０４２号及び特開平８−２７７４４１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るが、セパレータに代表される固体酸化物型燃料電池用の部品用の耐酸化性鋼の特性として重要な電気伝導率については何ら考慮されていない。
On the other hand, the oxidation resistant steel disclosed in JP-A-7-166301 and JP-A-7-145454 has a lower coefficient of thermal expansion than that of austenitic stainless steel, and the thermal expansion of stabilized zirconia of the electrolyte. Since it is close to the coefficient, it is advantageous for long-term stability and also has good electrical conductivity.
However, the oxidation resistance after long-term use is insufficient, especially the exfoliation phenomenon accompanying the increase of the oxide layer is promoted, and the groove provided in the separator that becomes the gas flow path in the battery is narrowed, and the battery function is deteriorated There is a problem to make. In addition, the materials disclosed in JP-A-8-35042 and JP-A-8-277441 have a low coefficient of thermal expansion compared to austenitic stainless steel, and are close to the coefficient of thermal expansion of stabilized zirconia of the electrolyte. Although advantageous in stability in use, no consideration is given to electrical conductivity that is important as a characteristic of oxidation-resistant steel for parts for solid oxide fuel cells represented by separators.
また、特開平９−１５７８０１号及び特開平１０−２８０１０３号に開示された耐酸化性鋼もまた、１０００℃までの熱膨張係数が低く、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１０００℃での耐酸化性、電気伝導率も良好である。
しかしながら、以上説明する公知の耐酸化性鋼は、何れも１０００℃で作動する固体酸化物型燃料電池のセパレータとして良好な特性を得ることを目的に開発されたものであり、最近の固体酸化物型燃料電池の作動温度である７００〜９５０℃程度での特性は何ら考慮されていない。
Further, the oxidation resistant steels disclosed in JP-A-9-157801 and JP-A-10-280103 also have a low coefficient of thermal expansion up to 1000 ° C. and are close to the coefficient of thermal expansion of the stabilized zirconia of the electrolyte, so that the It is advantageous for stability in use, and also has good oxidation resistance and electrical conductivity at 1000 ° C.
However, all of the known oxidation resistant steels described above have been developed for the purpose of obtaining good characteristics as a separator for a solid oxide fuel cell operating at 1000 ° C. No consideration is given to the characteristics at about 700 to 950 ° C., which is the operating temperature of the type fuel cell.
また、固体酸化物型燃料電池は運転と停止を繰り返すことから、構成部品のセパレータに代表される固体酸化物型燃料電池用の部品には熱サイクルによる応力が作用する。この熱応力のために、特に常温での衝撃特性が低いと破断することが心配されるので、固体酸化物型燃料電池用の耐酸化性鋼には熱応力に耐えるだけの衝撃特性が必要であるが、以上説明した公知の材料には、常温での衝撃特性が何ら考慮されていない。
本発明の目的は、７００〜９５０℃程度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、長時間の使用においても良好な耐酸化性、特に耐剥離性を有し、かつ常温での衝撃特性に優れ、電解質との熱膨張差が小さい安価な、固体酸化物型燃料電池用セパレータ用鋼を除く耐酸化性鋼及びそれを用いてなる固体酸化物型燃料電池用部品（セパレータを除く）を提供することである。
In addition, since the solid oxide fuel cell is repeatedly operated and stopped, the stress due to the heat cycle acts on the components for the solid oxide fuel cell represented by the separator of the component parts. Because of this thermal stress, there is a concern that it will break if the impact properties at room temperature are low, so the oxidation resistant steel for solid oxide fuel cells must have impact properties sufficient to withstand thermal stress. However, the known materials described above do not consider any impact properties at room temperature.
The object of the present invention is to form an oxide film having good electrical conductivity at about 700 to 950 ° C., and to have good oxidation resistance, especially peel resistance, even at long-term use, and at room temperature. Low-cost, oxidation-resistant steel excluding solid oxide fuel cell separator steel with excellent impact characteristics and small thermal expansion difference from electrolyte, and solid oxide fuel cell parts using the same (excluding separator) ).
本発明者は種々検討の結果、まず対象とする耐酸化性鋼をフェライト系とした。
この理由の第一は、固体酸化物の電解質である安定化ジルコニアの常温から約７５０℃までの平均熱膨張係数が約１１×１０−６／℃に対し、通常のオーステナイト系の金属材料では約１６×１０−６／℃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と考えたためである。
第二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ことに対し、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ことである。
As a result of various studies, the present inventor first made the subject oxidation resistant steel ferrite.
The first reason for this is that the average thermal expansion coefficient of stabilized zirconia, which is an electrolyte of a solid oxide, from room temperature to about 750 ° C. is about 11 × 10 −6 / ° C., while that of a normal austenitic metal material is about This is because it is 16 × 10 −6 / ° C. or more, and the difference in thermal expansion between the two is large, so that there is a problem in stability during long-time use.
The second reason is that austenite is generally expensive because it contains expensive Ni, whereas ferrite is based on Fe and does not contain Ni, or even if it contains a small amount, it is inexpensive.
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の酸化物が知られている。７００〜９５０℃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非常に大きいことが分かった。
一方、Ｃｒ２Ｏ３被膜形成材の電気抵抗は、十分小さく、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。
Next, the inventor conducted various studies on the electric conductivity of the oxide film to be formed. As representative oxide films having protective properties, oxides of Al and oxides of Cr are known. In general, Al 2 O 3 has a larger protective effect when the temperature is around 700 to 950 ° C., but it is found that the electrical resistance of the Al 2 O 3 film-forming material is very large. .
On the other hand, the electric resistance of the Cr 2 O 3 film-forming material is sufficiently small, and in the present invention, a ferrite-based metal material that forms an oxide film mainly composed of a Cr-based oxide on the surface, that is, a Fe—Cr-based material. .
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７００〜９５０℃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系酸化被膜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、上記方針に従ってＦｅ−Ｃｒ系を基本とすると耐酸化性を満足させることは非常に困難になる。
Next, oxidation resistance, which becomes a problem when used for a long time, is usually inferior to Al-based oxide film in the vicinity of 700 to 950 ° C. as compared with Al-based oxide film.
Further, even when a Cr-based oxide film is mainly used, an Fe-based alloy (for example, a Fe-Cr alloy such as SUS430) is more resistant to acid than a Ni-based alloy (for example, a Ni-Cr alloy represented by JIS NCF600). The conversion is inferior. Therefore, it is very difficult to satisfy the oxidation resistance when the Fe—Cr system is basically used in accordance with the above policy.
本発明者はこれを解決するために種々検討した結果、Ｆｅ−Ｃｒ系にＹ、希土類元素、Ｚｒの一種または二種以上の添加に加え、Ａｌを低めに抑え、更にＳｉ、Ｍｎを少量添加することにより、Ｃｒ系の酸化被膜を主体としながら、良好な耐酸化性、特に耐剥離性が得られ、長時間加熱後も被膜の形成状態が安定することを見出した。
特に、Ｙ及び／または希土類元素にＺｒを複合添加した場合に耐剥離性は最も向上する。また上記各元素の添加を行っても、形成される酸化被膜は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も知見した。
As a result of various studies to solve this problem, the present inventor, in addition to adding one or more of Y, rare earth elements and Zr to the Fe-Cr system, suppressing Al low, and further adding a small amount of Si and Mn As a result, it has been found that good oxidation resistance, particularly peeling resistance, can be obtained while mainly using a Cr-based oxide film, and that the state of film formation is stable even after heating for a long time.
In particular, when Zr is added in combination with Y and / or rare earth elements, the peel resistance is most improved. It was also found that even when the above elements are added, the oxide film formed is mainly composed of a Cr-based oxide film, so that the electrical resistance does not increase so much.
更に、良好な耐酸化性を得るのに有効な元素であるＹ、希土類元素、Ｚｒは、合金中のＳ、Ｏが多いと硫化物や酸化物を形成して介在物になりやすい。Ｙ、希土類元素、Ｚｒが介在物となって固定されてしまうとマトリックス中に固溶するＹ、希土類元素、Ｚｒの量が減少し、酸化膜の成長抑制、緻密化、密着性向上に寄与できる有効量が減少する。
従って、添加したＹ、希土類元素、Ｚｒを有効に作用させるためにはこれらの元素の介在物をできるだけ少なくすることが有効であり、Ｓ、Ｏ等の不純物元素を低く抑えることが良好な耐酸化性を維持するために必要であることを見出した。
また、Ｎ、Ｂについても耐酸化性維持に有効な元素の一部、例えばＬａ等と化合物を形成する可能性があることから、不純物として低く抑えることが有効であることを見出した。
また、特にＢは酸化膜表面の平滑性を害して接触抵抗を低下させることを新たに見出し、接触抵抗の点からもセパレータ用鋼中のＢは不純物として低く抑える必要がある。また、Ｔｉも耐酸化性を低下させる元素であるため、不純物として低く抑える必要がある。
Furthermore, Y, rare earth elements, and Zr, which are effective elements for obtaining good oxidation resistance, tend to form inclusions by forming sulfides and oxides when S and O in the alloy are large. If Y, rare earth elements, and Zr are fixed as inclusions, the amount of Y, rare earth elements, and Zr dissolved in the matrix decreases, which can contribute to the suppression of oxide film growth, densification, and improved adhesion. The effective amount decreases.
Therefore, in order to make the added Y, rare earth element, and Zr act effectively, it is effective to reduce the inclusions of these elements as much as possible, and it is good oxidation resistance to keep the impurity elements such as S and O low. I found that it is necessary to maintain sex.
Also, N and B have been found to be effective to suppress as impurities because they may form compounds with some elements effective for maintaining oxidation resistance, such as La.
In particular, B has been found to reduce the contact resistance by deteriorating the smoothness of the oxide film surface, and B in the separator steel must be kept low as an impurity from the point of contact resistance. Further, since Ti is an element that lowers oxidation resistance, it is necessary to keep it low as an impurity.
また、耐酸化性鋼素材を加工するには、硬さを下げることが必要であり、そのためには適正な焼鈍を行うことが必要である。
この焼鈍は、硬さ調整のみならず、フェライト結晶粒径の調整にも有効であり、適正な細粒組織とすることによって、衝撃特性も向上させることができる。以上のように、合金成分の調整を行うとともに、熱処理条件、組織、機械的特性を適正化することによって、本発明に到達した。
Moreover, in order to process an oxidation-resistant steel material, it is necessary to reduce hardness, and for that purpose, it is necessary to perform appropriate annealing.
This annealing is effective not only for adjusting the hardness but also for adjusting the ferrite crystal grain size, and the impact characteristics can be improved by using an appropriate fine grain structure. As described above, the present invention has been achieved by adjusting the alloy components and optimizing the heat treatment conditions, structure, and mechanical properties.
すなわち本発明の第１発明は、固体酸化物型燃料電池用セパレータ用鋼を除き、常温と７００〜９５０℃の間で加熱、冷却の熱サイクルを繰り返し受ける耐酸化性鋼であって、質量％にて、Ｃ：０．２％以下、Ｓｉ：０．２％未満（０％を含まず）、Ｍｎ：１．０％以下（０％を含まず）、Ｎｉ：２％以下、Ｃｒ：１５〜３０％、Ａｌ：１％以下、Ｌａ：０．００５〜０．１％、Ｚｒ：１％以下を含み、残部はＦｅ及び不可避的不純物でなり、不可避的不純物として、Ｔｉ：０．１％以下、Ｓ：０．０１５％以下、Ｏ：０．０１０％以下、Ｎ：０．０５０％以下、Ｂ：０．００３０％以下に制限し、かつ（１）式を満足する鋼からなり、硬さが２８０ＨＶ以下、平均フェライト結晶粒度がＡＳＴＭ Ｎｏ．２以上の細粒である耐酸化性鋼である。
（Ｏ＋２Ｓ）／（０．０３５Ｚｒ＋０．１６Ｌａ）≦２．０…（１）
（１）式の元素は質量％である。
That first aspect of the present invention, Except the solid oxide fuel cell separator steel, heated between room temperature and 700 to 950 ° C., a oxidation resistant steels undergo repeated thermal cycling of the cooling, the mass %: C: 0.2% or less, Si: less than 0.2% (not including 0%) , Mn: 1.0% or less (not including 0%), Ni: 2% or less, Cr: 15 to 30%, Al: 1% or less , La: 0.005 to 0.1%, Zr: 1% or less , the balance is Fe and unavoidable impurities , as unavoidable impurities, Ti: 0.1 %: S: 0.015% or less, O: 0.010% or less, N: 0.050% or less, B: 0.0030% or less, and satisfying the formula (1), The hardness is 280 HV or less, and the average ferrite grain size is ASTM No. It is an oxidation resistant steel that is two or more fine grains.
(O + 2S) / ( 0.035Zr + 0.16 La ) ≦ 2.0 (1)
The element of the formula (1) is mass%.
本発明の第２発明は、固体酸化物型燃料電池用セパレータ用鋼を除き、常温と７００〜９５０℃の間で加熱、冷却の熱サイクルを繰り返し受ける耐酸化性鋼であって、質量％にて、Ｃ：０．１％以下、Ｓｉ：０．２％未満（０％を含まず）、Ｍｎ：１．０％以下（０％を含まず）、Ｃｒ：１７〜２６％、Ｎｉ：１％以下、Ａｌ：０．００１％以上０．５％未満、Ｚｒ：０．０１〜０．８％、Ｌａ：０．００５〜０．１％を含み、残部はＦｅ及び不可避的不純物でなり、不可避的不純物として、Ｔｉ：０．１％以下、Ｓ：０．０１５％以下、Ｏ：０．０１０％以下、Ｎ：０．０２０％以下、Ｂ：０．００３０％以下に制限し、かつ（１）式を満足する鋼からなり、硬さが２８０ＨＶ以下、平均フェライト結晶粒度がＡＳＴＭ Ｎｏ．２以上の細粒である耐酸化性鋼である。 The second aspect of the present invention, Except the solid oxide fuel cell separator steel, heated between room temperature and 700 to 950 ° C., a oxidation resistant steels undergo repeated thermal cycling of the cooling, mass% C: 0.1% or less, Si: less than 0.2% (not including 0%), Mn: 1.0% or less (not including 0%), Cr: 17 to 26%, Ni: 1% or less, Al: 0.001% or more and less than 0.5%, Zr: 0.01 to 0.8% , La: 0.005 to 0.1%, the balance being Fe and inevitable impurities Inevitable impurities include : Ti: 0.1% or less, S: 0.015% or less, O: 0.010% or less, N: 0.020% or less, B: 0.0030% or less, and (1) It consists of steel satisfying the formula, the hardness is 280HV or less, and the average ferrite grain size is ASTM No. It is an oxidation resistant steel that is two or more fine grains.
本発明の第３発明は、固体酸化物型燃料電池用セパレータ用鋼を除き、常温と７００〜９５０℃の間で加熱、冷却の熱サイクルを繰り返し受ける耐酸化性鋼であって、質量％にて、Ｃ：０．１％以下、Ｓｉ：０．２％未満（０％を含まず）、Ｍｎ：０．２％未満（０％を含まず）、Ｃｒ：１７〜２６％、Ｎｉ：１％以下、Ａｌ：０．００１％以上０．５％未満、Ｚｒ：０．０１〜０．８％、Ｌａ：０．００５〜０．１％を含み、残部はＦｅ及び不可避的不純物でなり、不可避的不純物として、Ｔｉ：０．１％以下、Ｓ：０．０１５％以下、Ｏ：０．０１０％以下、Ｎ：０．０２０％以下、Ｂ：０．００３０％以下に制限し、かつ（１）式を満足する鋼からなり、硬さが２８０ＨＶ以下、平均フェライト結晶粒度がＡＳＴＭ Ｎｏ．２以上の細粒である耐酸化性鋼である。 The third aspect of the present invention, Except the solid oxide fuel cell separator steel, heated between room temperature and 700 to 950 ° C., a oxidation resistant steels undergo repeated thermal cycling of the cooling, mass% C: 0.1% or less, Si: less than 0.2% (not including 0%), Mn: less than 0.2% (not including 0%), Cr: 17 to 26%, Ni: 1% or less, Al: 0.001% or more and less than 0.5%, Zr: 0.01 to 0.8% , La: 0.005 to 0.1%, the balance being Fe and inevitable impurities Inevitable impurities include : Ti: 0.1% or less, S: 0.015% or less, O: 0.010% or less, N: 0.020% or less, B: 0.0030% or less, and (1) It consists of steel satisfying the formula, the hardness is 280HV or less, and the average ferrite grain size is ASTM No. It is an oxidation resistant steel that is two or more fine grains.
本発明の第４発明は、上述の合金に、更にＹ：０．０１〜０．３％を含有し、かつ（２）式を満足する耐酸化性鋼である。
（Ｏ＋２Ｓ）／（０．２７Ｙ＋０．０３５Ｚｒ＋０．１６Ｌａ）≦２．０…（２）
（２）式の元素は質量％である。
The fourth invention of the present invention is an oxidation resistant steel which further contains Y: 0.01 to 0.3% and satisfies the formula (2) in the above-mentioned alloy.
(O + 2S) / (0.27Y + 0.035Zr + 0.16La) ≦ 2.0 (2)
The element of the formula (2) is mass%.
本発明の第５発明は、固体酸化物型燃料電池用セパレータ用鋼を除き、常温と７００〜９５０℃の間で加熱、冷却の熱サイクルを繰り返し受ける耐酸化性鋼であって、質量％にて、Ｃ：０．０８％以下、Ｓｉ：０．２％未満（０％を含まず）、Ｍｎ：０．５％以下（０％を含まず）、Ｃｒ：１８〜２５％、Ｎｉ：０．５％以下、Ａｌ：０．００１％以上０．５％未満、Ｌａ：０．００５〜０．１％、Ｚｒ：０．０１〜０．６％、残部はＦｅ及び不可避的不純物でなり、不可避的不純物として、Ｔｉ：０．１％以下、Ｓ：０．００８％以下、Ｏ：０．００８％以下、Ｎ：０．０２０％以下、Ｂ：０．００２０％以下に制限し、かつ（１）式を満足する鋼からなり、硬さが２８０ＨＶ以下、平均フェライト結晶粒度がＡＳＴＭ Ｎｏ．２以上の細粒である耐酸化性鋼である。 Fifth aspect of the present invention, Except the solid oxide fuel cell separator steel, heated between room temperature and 700 to 950 ° C., a oxidation resistant steels undergo repeated thermal cycling of the cooling, mass% C: 0.08% or less, Si: less than 0.2% (not including 0%), Mn: 0.5% or less (not including 0%), Cr: 18 to 25%, Ni: 0.5% or less, Al: 0.001% or more and less than 0.5%, La: 0.005 to 0.1%, Zr: 0.01 to 0.6%, the balance being Fe and inevitable impurities Inevitable impurities are limited to Ti: 0.1% or less, S: 0.008% or less, O: 0.008% or less, N: 0.020% or less, B: 0.0020% or less, and ( 1 ) It consists of steel satisfying the formula, the hardness is 280HV or less, and the average ferrite grain size is ASTM No. It is an oxidation resistant steel that is two or more fine grains.
本発明の第６発明は、固体酸化物型燃料電池用セパレータ用鋼を除き、常温と７００〜９５０℃の間で加熱、冷却の熱サイクルを繰り返し受ける耐酸化性鋼であって、質量％にて、Ｃ：０．０８％以下、Ｓｉ：０．２％未満（０％を含まず）、Ｍｎ：０．５％以下（０％を含まず）、Ｃｒ：１８〜２５％、Ｎｉ：０．５％以下、Ａｌ：０．００１％以上０．５％未満、Ｌａ：０．００５〜０．１％、Ｚｒ：０．０１〜０．６％、残部はＦｅ及び不可避的不純物でなり、不可避的不純物として、Ｔｉ：０．１％以下、Ｓ：０．００８％以下、Ｏ：０．００８％以下、Ｎ：０．０２０％以下、Ｂ：０．００１０％未満に制限し、かつ（１）式を満足する鋼からなり、硬さが２８０ＨＶ以下、平均フェライト結晶粒度がＡＳＴＭ Ｎｏ．３以上の細粒である耐酸化性鋼である。 Sixth aspect of the present invention, Except the solid oxide fuel cell separator steel, heated between room temperature and 700 to 950 ° C., a oxidation resistant steels undergo repeated thermal cycling of the cooling, mass% C: 0.08% or less, Si: less than 0.2% (not including 0%), Mn: 0.5% or less (not including 0%), Cr: 18 to 25%, Ni: 0.5% or less, Al: 0.001% or more and less than 0.5%, La: 0.005 to 0.1%, Zr: 0.01 to 0.6%, the balance being Fe and inevitable impurities Inevitable impurities are limited to Ti: 0.1% or less, S: 0.008% or less, O: 0.008% or less, N: 0.020% or less, B: less than 0.0010%, and ( 1 ) It consists of steel satisfying the formula, the hardness is 280HV or less, and the average ferrite grain size is ASTM No. It is an oxidation resistant steel that is 3 or more fine grains.
好ましくは、質量％にて、Ｍｏ単独またはＭｏとＷの二種を、Ｍｏ＋１／２Ｗ≦５．０％を含む固体酸化物型燃料電池セパレータ用鋼である。
更に好ましくは、質量％にて、Ｖ、Ｎｂ、Ｈｆの一種または二種以上を合計で０．０１〜１．０％含む耐酸化性鋼である。
Preferably, it is a solid oxide fuel cell separator steel containing Mo + 1 / 2W ≦ 5.0% in terms of% by mass, Mo alone or Mo and W.
More preferably, at weight percent, V, Nb, oxidation resistant steel containing 0.01% to 1.0% in total of one or two or more H f.
更に好ましくは、２０℃での２ｍｍＶノッチシャルピー衝撃値が８Ｊ／ｃｍ２以上である耐酸化性鋼である。
また更に好ましくは、２０℃での２ｍｍＶノッチシャルピー衝撃値が１０Ｊ／ｃｍ２以上である耐酸化性鋼である。
更に好ましくは、７５０℃で１０００Ｈｒ加熱した後の７５０℃における酸化被膜の電気抵抗が１００ｍΩ・ｃｍ２以下であり、更に８５０℃で１００Ｈｒ加熱後に表面酸化スケールの剥離が発生しない耐酸化性鋼である。
また更に好ましくは、７５０℃で１０００Ｈｒ加熱した後の７５０℃における酸化被膜の電気抵抗が５０ｍΩ・ｃｍ２以下であり、更に８５０℃で１００Ｈｒ加熱後に表面酸化スケールの剥離が発生しない耐酸化性鋼である。
また本発明は、前述の第１から第３、第５、第６発明の何れかの組成に、合計で０．００５〜０．１％のＬａとＬａ以外の希土類元素(ＲＥＭ)を更に含有し、かつ（３）式を満足する耐酸化性鋼である。
（Ｏ＋２Ｓ）／（０．０３５Ｚｒ＋０．１６ＲＥＭ）≦２．０…（３）
（３）式の元素は質量％である。
また本発明は、上記の耐酸化性鋼を用いてなる固体酸化物燃料型電池用部品（セパレータを除く）である。
More preferably, it is an oxidation resistant steel having a 2 mmV notch Charpy impact value at 20 ° C. of 8 J / cm 2 or more.
More preferably, it is an oxidation resistant steel having a 2 mmV notch Charpy impact value at 20 ° C. of 10 J / cm 2 or more.
More preferably is the electrical resistance of the oxide film at 750 ° C. after 1000Hr heated at 750 ° C. is 100 m [Omega · cm 2 or less, peeling of the surface oxide scale not occur after further 100Hr heated at 850 ° C. in oxidation resistance steels is there.
Also more preferably, 750 the electrical resistance of the oxide film at 750 ° C. after 1000Hr heated at ° C. is at 50 m [Omega · cm 2 or less, further 850 ° C. in 100Hr after heating the surface oxide scale oxidation resistant steel peeling does not occur in It is.
In addition, the present invention further includes 0.005 to 0.1% of La and a rare earth element other than La (REM) in the composition of any one of the first to third, fifth and sixth inventions described above. And it is an oxidation resistant steel that satisfies the expression (3).
(O + 2S) / (0.035Zr + 0.16REM) ≦ 2.0 (3)
The element of the formula (3) is mass%.
The present invention is a solid oxide fuel type cell component formed using the above oxidation-resistant steels (excluding separator).
本発明の耐酸化性鋼は、７００〜９５０℃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共に、長時間の使用においても良好な耐酸化性、特に耐剥離性を有し、かつ電解質との熱膨張差が小さく、燃料電池の低コスト化及び高性能化を図ることができることから、比較的低温の７００〜９５０℃程度で作動する固体電解質型燃料電池の実用化、高効率化、大型化に大きく寄与できる。 The oxidation-resistant steel of the present invention forms an oxide film having good electrical conductivity in the vicinity of 700 to 950 ° C., and also has good oxidation resistance, especially peel resistance, even after long-term use, and Since the difference in thermal expansion from the electrolyte is small and the cost and performance of the fuel cell can be reduced, practical application and high efficiency of a solid oxide fuel cell that operates at a relatively low temperature of about 700 to 950 ° C. Can greatly contribute to enlargement.
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、逆に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、０．１％以下、更に望ましくは０．０８％以下である。
Ｓｉは、セパレータに設けた高温ガスの流路となる溝の内面に、Ｃｒ系酸化層を主体とする被膜の形成に関与し、長時間の使用においても形成した酸化被膜が必要以上に成長したり、また剥離現象を起こすのを防ぐ効果を有する元素である。Ｓｉの効果の一つには、恐らくＣｒ２Ｏ３酸化被膜と母材の界面付近に薄い不連続なＳｉＯ２被膜を形成して耐酸化性を向上させるものと考えられる。
また、上記ＳｉＯ２被膜は母材とＣｒ２Ｏ３被膜の界面において母材、Ｃｒ２Ｏ３被膜、ＳｉＯ２被膜が細かくからみ合った状態を形成しており、これによって母材との密着性を高め、Ｃｒ２Ｏ３被膜の剥離を阻止する効果がある。このような効果は特に１０００℃以上の高温において大きく、７００〜９５０℃では必ずしも大きくないが、上記効果を得るためにはＳｉを少量添加することが必要である。
一方、過度の添加は加工性、靭性の低下を招くとともにＳｉＯ２被膜が厚くなりすぎ、連続して酸化被膜の剥離を招いたり、被膜の電気伝導度が低下する問題が生じるので、Ｓｉは０．２％未満（０％を含まず）とする。
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, but conversely deteriorates workability and reduces the amount of Cr effective in oxidation resistance by combining with Cr. Therefore, it is limited to 0.2% or less. Desirably, it is 0.1% or less, more desirably 0.08% or less.
Si is involved in the formation of a film mainly composed of a Cr-based oxide layer on the inner surface of a groove serving as a flow path for high-temperature gas provided in the separator, and the formed oxide film grows more than necessary even after long-term use. Or an element that has the effect of preventing the peeling phenomenon. One of the effects of Si is probably that a thin discontinuous SiO 2 film is formed near the interface between the Cr 2 O 3 oxide film and the base material to improve the oxidation resistance.
The SiO 2 coating forms a state in which the base material, the Cr 2 O 3 coating, and the SiO 2 coating are finely entangled at the interface between the base material and the Cr 2 O 3 coating. And the effect of preventing the peeling of the Cr 2 O 3 coating. Such an effect is particularly great at a high temperature of 1000 ° C. or higher, and not necessarily high at 700 to 950 ° C. However, in order to obtain the above effect, it is necessary to add a small amount of Si.
On the other hand, excessive addition workability, SiO 2 film is too thick with leads to a decrease in toughness, or cause peeling of the oxide film continuous and the problem of electrical conductivity of the film is lowered, Si 0 . And less than 2% (exclusive of 0%).
Ｍｎは、Ｆｅ、Ｃｒとともにスピネル型酸化物を形成する。Ｍｎを含むスピネル型酸化物層は、Ｃｒ２Ｏ３の酸化層の外側に形成される。このスピネル型酸化物層は固体酸化物型燃料電池のセラミックス電解質を劣化させるＣｒが耐酸化性鋼から蒸発するのを防ぐ保護効果を有する。
また、このスピネル型酸化物は、通常Ｃｒ２Ｏ３に比べると酸化速度が大きいので、耐酸化性そのものに対しては不利に働く一方で、酸化被膜の平滑さを維持して接触抵抗を低下させたり、電解質に対して有害なＣｒの蒸発を防ぐ効果を有している。
一方、過度に添加すると前述のようにＭｎ含有のスピネル型酸化物自体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（０％を含まず）に限定する。使用温度が７００〜９５０℃程度の低温の場合には、０．５％以下（０％を含まず）としてもよく、更に使用温度が低い場合には０．２％未満（０％を含まず）としてもよい。
Mn forms a spinel oxide together with Fe and Cr. The spinel type oxide layer containing Mn is formed outside the Cr 2 O 3 oxide layer. This spinel type oxide layer has a protective effect to prevent Cr, which deteriorates the ceramic electrolyte of the solid oxide type fuel cell, from evaporating from the oxidation resistant steel.
In addition, since this spinel type oxide usually has a higher oxidation rate than Cr 2 O 3 , it works against the oxidation resistance itself, while maintaining the smoothness of the oxide film and reducing the contact resistance. Or has the effect of preventing evaporation of Cr harmful to the electrolyte.
On the other hand, if added excessively, as described above, the oxidation resistance of the Mn-containing spinel-type oxide itself is insufficient, resulting in poor oxidation resistance.
Therefore, Mn is limited to 1% or less (excluding 0%). When the operating temperature is as low as 700 to 950 ° C., it may be 0.5% or less (not including 0%), and when the operating temperature is lower, it is less than 0.2% (not including 0%). ).
Ｃｒは、本発明においてＣｒ２Ｏ３被膜の生成により、耐酸化性及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。望ましいＣｒの範囲は１７〜２６％、更に望ましいＣｒの範囲は１８〜２５％である。
Cr is an important element for maintaining oxidation resistance and electrical conductivity by producing a Cr 2 O 3 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%. A desirable Cr range is 17 to 26%, and a more desirable Cr range is 18 to 25%.
Ｙ、希土類元素（ＲＥＭ）、Ｚｒは、少量添加により耐酸化性及び酸化皮膜の電気伝導度を大幅に改善する効果を有する。特に少量のＳｉ、Ｍｎ添加と組み合わせた場合の耐酸化性向上効果が大きく、これは主に酸化被膜の密着性を改善することによると考えられる。
本発明においてはＣｒ系酸化被膜のみで耐酸化性を持たせているが、このＣｒ系酸化被膜の密着性を向上させるために、希土類元素（ＲＥＭ）のうち、Ｌａと、Ｚｒの複合添加を必須とし、更に必要応じて、ＬａとＬａ以外の希土類元素、Ｙを必要に応じて含有しても良い。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０．０１〜０．３％、希土類元素（ＲＥＭ）は０．００５〜０．１０％、Ｚｒは１％以下に限定する。望ましくは、Ｚｒ：０．０１％〜０．８％である。
Y, rare earth element (REM), and Zr have the effect of greatly improving the oxidation resistance and the electrical conductivity of the oxide film when added in small amounts. In particular, the effect of improving the oxidation resistance when combined with a small amount of Si and Mn is large, which is considered to be mainly due to the improvement of the adhesion of the oxide film.
In the present invention, only the Cr-based oxide film has oxidation resistance, but in order to improve the adhesion of the Cr-based oxide film , among the rare earth elements (REM), a combination of La and Zr is added. It may be essential, and if necessary, rare earth elements other than La and La, and Y may be contained as necessary . However, excessive addition deteriorates hot workability, so Y is limited to 0.01 to 0.3% , rare earth element (REM) is limited to 0.005 to 0.10% , and Zr is limited to 1% or less. Desirably, Zr: 0.01% to 0.8%.
更に、Ｙ：０．０１〜０．３％と、Ｌａを必須とする希土類元素（ＲＥＭ）：０．００５〜０．１０％の一種または二種以上とＺｒ：０．０１％〜０．８％を複合で添加すると、酸化皮膜の密着性がより向上し、長時間加熱後においても酸化被膜の剥離を防止できる。
更に望ましくは、Ｌａを必須とする希土類元素（ＲＥＭ）：０．００５〜０．１０％とＺｒ：０．０１％〜０．８％の複合添加である。
希土類元素の中では、Ｌａが最も酸化被膜の密着性向上に効果があることから、本発明ではＬａ：０．００５〜０．１％とＺｒ：１％以下とを必須で複合添加する。Ｌａ：０．００５〜０．１０％とＺｒ：０．０１％〜０．６％の複合添加が最も望ましい。
なお、Ｚｒは後述のＶ、Ｎｂ、Ｔａ、Ｈｆ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。
Furthermore, Y: 0.01 to 0.3% , rare earth element (REM) essential for La : REM: 0.005 to 0.10%, and Zr: 0.01% to 0.8 % Is added in combination, the adhesion of the oxide film is further improved, and peeling of the oxide film can be prevented even after heating for a long time.
More preferably, the rare earth element (REM) essentially containing La : 0.005 to 0.10% and Zr: 0.01% to 0.8% are added in combination.
Of the rare earth elements, La is most effective in improving the adhesion of the oxide film. Therefore, in the present invention, La: 0.005 to 0.1% and Zr: 1% or less are essential and added in combination. The combined addition of La: 0.005 to 0.10% and Zr: 0.01% to 0.6% is most desirable.
Zr, like V, Nb, Ta, and Hf, which will be described later, is combined with C to form carbides, improves workability by C fixation, and contributes to strength improvement.
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−オーステナイトの二相組織となり、熱膨張係数の増加及びコストアップを招く。更に過度の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１％以下、更に望ましくは０．５％以下である。
Ａｌは、通常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０．００１％以上０．５％未満である。
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 becomes a ferrite-austenite two-phase structure, resulting in an increase in thermal expansion coefficient and cost increase. Further, excessive addition of Ni deteriorates the oxidation resistance. Therefore, Ni is limited to 2% or less. Desirably, it is 1% or less, More desirably, it is 0.5% or less.
Al is usually 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 the Al 2 O 3 film. Desirably, it is 0.001% or more and less than 0.5%.
Ｍｏ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。ＷもＭｏと同様の効果を有するが、Ｍｏと同じ効果を発揮するためには質量％でＭｏの二倍の添加が必要である。Ｗの多量添加は熱間加工性を害することから、ＷはＭｏとの複合添加を行い、ＭｏとＷの総量を低く抑える必要がある。このように、過度に添加すると加工性を劣化させるだけでなく、耐酸化性も低下させるので、Ｍｏ＋１／２Ｗで５％以下に限定する。望ましくは３％以下である。
Ｖ、Ｎｂ、Ｈｆ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。
また強度向上にも寄与する一方で、７００〜９００℃付近においてはＨｆを除き、余り保護性のない酸化物を形成し耐酸化性を劣化させる。
上記のＨｆは、耐酸化性にも効果を有するため、これらの元素の中では最も好ましいが、高価であるため必要に応じて選択する。
また、Ｖ、Ｎｂ、Ｈｆの元素の過度の添加は、一次炭化物を多く形成して加工性を劣化させる。従って、加工性、強度、耐酸化性を考慮しながら、Ｖ、Ｎｂ、Ｈｆは一種または二種以上を合計で０．０１〜１．０％の範囲で添加しても良い。望ましくは０．０３〜０．６％である。
Mo has an effect of increasing the high temperature strength, and therefore may be added when the high temperature strength is important. W also has the same effect as Mo, but in order to exert the same effect as Mo, addition of Mo twice by mass% is necessary. Since a large amount of W impairs hot workability, W must be combined with Mo to keep the total amount of Mo and W low. As described above, if excessively added, not only the workability is deteriorated but also the oxidation resistance is lowered, so Mo + 1 / 2W is limited to 5% or less. Desirably, it is 3% or less.
V, Nb , and Hf combine with C to form a carbide and improve workability by fixing C.
While contributing to strength improvement, in the vicinity of 700 to 900 ° C., except for Hf, an oxide having little protection property is formed to deteriorate the oxidation resistance.
The above Hf is most preferable among these elements because it has an effect on oxidation resistance, but is selected as necessary because it is expensive.
Moreover, excessive addition of the elements of V, Nb , and Hf forms a lot of primary carbides and degrades workability. Therefore, V, Nb , and Hf may be added singly or in combination of two or more in a range of 0.01 to 1.0% in consideration of workability, strength, and oxidation resistance. Desirably, it is 0.03 to 0.6%.
次に不可避的不純物元素の限定理由について述べる。
Ｔｉは、内部酸化相を形成することで耐酸化性を劣化させる元素であるため、不純物として、０．１％以下に限定する。Ｓは、Ｍｎ、希土類元素（ＲＥＭ）等と硫化物系介在物を形成して、耐酸化性に効果をもつ有効な希土類元素量を低下させ、耐酸化性を低下させるだけでなく、熱間加工性、表面肌を劣化させるため、０．０１５％以下に限定する。望ましくは、０．００８％以下がよい。
Ｏは、Ａｌ、Ｓｉ、Ｍｎ、Ｃｒ、Ｙ、希土類元素（ＲＥＭ）、Ｚｒ等と酸化物系介在物を形成して、熱間加工性、冷間加工性を害するだけでなく、耐酸化性向上に大きく寄与する元素であるＹ、希土類元素（ＲＥＭ）、Ｚｒ等の固溶量を減少させるため、これらの元素による耐酸化性向上効果を減じる。従って、０．０１０％以下に制限する。望ましくは、０．００８％以下がよい。
Next, the reasons for limiting the inevitable impurity elements will be described.
Since Ti is an element that degrades oxidation resistance by forming an internal oxidation phase, it is limited to 0.1% or less as an impurity. S forms sulfide inclusions with Mn, rare earth elements (REM), etc., thereby reducing the amount of effective rare earth elements having an effect on oxidation resistance, not only reducing oxidation resistance, but also hot In order to deteriorate the workability and the surface skin, the content is limited to 0.015% or less. Desirably, it is 0.008% or less.
O forms oxide inclusions with Al, Si, Mn, Cr, Y, rare earth elements (REM), Zr, etc., and not only harms hot workability and cold workability, but also has oxidation resistance. In order to reduce the amount of solid solution of elements such as Y, rare earth elements (REM), and Zr that contribute greatly to the improvement, the effect of improving the oxidation resistance by these elements is reduced. Therefore, it is limited to 0.010% or less. Desirably, it is 0.008% or less.
Ｎは、オーステナイト生成元素であるため、本発明のＦｅ−Ｃｒ系フェライト鋼に過剰に添加するとオーステナイト相を生成してフェライト単相を維持できなくするだけでなく、Ａｌ、Ｃｒ等と窒化物系介在物を形成して熱間、冷間加工性を害するため、０．０５０％以下に制限する。望ましくは０．０２０％以下、更に望ましくは０．０１０％以下がよい。
Ｂは、約７００℃以上の高温で酸化被膜の成長速度を大きくすることで耐酸化性を劣化させるだけでなく、酸化被膜の表面粗さを大きくして酸化被膜と電極との接触面積を小さくすることによって接触抵抗を劣化させるため、不純物として０．００３０％以下に制限し、できるだけ０％まで低減させる方が良い。望ましい上限は０．００２０％以下がよく、更に望ましくは０．００１０％未満がよい。
Since N is an austenite-forming element, if it is added excessively to the Fe—Cr ferritic steel of the present invention, N not only generates an austenite phase and cannot maintain a ferrite single phase, but also nitrides such as Al, Cr, etc. In order to form inclusions and impair hot workability and cold workability, the content is limited to 0.050% or less. Desirably, it is 0.020% or less, more desirably 0.010% or less.
B not only deteriorates the oxidation resistance by increasing the growth rate of the oxide film at a high temperature of about 700 ° C. or higher, but also increases the surface roughness of the oxide film to reduce the contact area between the oxide film and the electrode. In order to degrade the contact resistance, it is better to limit it to 0.0030% or less as an impurity and reduce it to 0% as much as possible. The desirable upper limit is 0.0020% or less, and more desirably less than 0.0010%.
本発明の耐酸化性鋼において、特に耐酸化性及び酸化皮膜の電気伝導度の向上に大きな効果を有するＹ、希土類元素（ＲＥＭ）、Ｚｒが十分効果を発揮するには、これらの元素が硫化物系介在物や酸化物系介在物に完全に固定されないようにする必要がある。
そのためには、（１）〜（３）式に示すようにＺｒとＬａ、または、ＹとＺｒとＬａ、または、ＺｒとＬａを必須とした希土類元素（ＲＥＭ）の添加量に対するＳとＯの量の比率を低く抑えるのが有効である。（１）〜（３）式の値が２．０を超えるとＹ、Ｚｒ、希土類元素（ＲＥＭ）が介在物の固定されて耐酸化性及び酸化皮膜の電気伝導度向上に寄与しなくなることから、（１）〜（３）式の値は２．０以下とした。
In the oxidation resistant steel of the present invention, in order for Y, rare earth element (REM), and Zr, which have a great effect in improving the oxidation resistance and the electrical conductivity of the oxide film, to exert a sufficient effect, these elements are sulfided. It is necessary not to be completely fixed to physical inclusions or oxide inclusions.
For this purpose, as shown in the formulas (1) to (3) , Zr and La, or Y and Zr and La, or S and O with respect to the addition amount of rare earth element (REM) essentially including Zr and La . It is effective to keep the amount ratio low. If the values of the formulas (1) to (3) exceed 2.0, the inclusions of Y, Zr and rare earth elements (REM) are fixed, and the oxidation resistance and the electrical conductivity of the oxide film are not improved. , (1) to (3) are 2.0 or less .
なお、以下の元素は下記の範囲内で本発明鋼に含まれても良い。
Ｐ≦０．０４％、Ｃｕ≦０．３０％、Ｍｇ≦０．０２％、Ｃａ≦０．０２％、Ｃｏ≦２％
The following elements may be included in the steel of the present invention within the following range.
P ≦ 0.04%, Cu ≦ 0.30%, Mg ≦ 0.02%, Ca ≦ 0.02%, Co ≦ 2%
次に、上述した組成を有する耐酸化性鋼を部品に加工するには、冷間塑性加工や機械加工が容易にでき、しかも熱サイクルに伴う引張り応力によって、鋼に割れが発生しないだけの衝撃特性が重要となる。
この指標として本発明では硬さと結晶粒度及び衝撃特性を用いて規定した。
本発明の耐酸化性鋼に必要な特性である硬さ、結晶粒度、衝撃特性は、合金組成のみで決まるものではなく、素材の塑性加工方法、焼鈍等の熱処理条件等に強く依存するので、耐酸化性鋼として使用するためには、化学成分のみならず、硬さ、結晶粒度、衝撃特性なども合わせて本発明の規定範囲を満足させることが重要である。
Next, in order to process an oxidation-resistant steel having the above-described composition into a part, cold plastic working and machining can be easily performed, and the impact that does not cause cracking in the steel due to the tensile stress accompanying the thermal cycle. Properties are important.
In the present invention, this index is defined using hardness, grain size and impact characteristics.
The hardness, grain size, and impact characteristics, which are necessary characteristics for the oxidation resistant steel of the present invention, are not determined only by the alloy composition, but strongly depend on the plastic processing method of the material, heat treatment conditions such as annealing, etc. In order to use it as an oxidation resistant steel, it is important to satisfy not only the chemical components but also the hardness, crystal grain size, impact characteristics and the like within the specified range of the present invention.
上述の硬さ、結晶粒度、衝撃特性を満足させるには、素材製造工程で発生して材料中に残存する加工歪を除去するため、焼鈍を行うとよい。
焼鈍温度は、９５０℃より高温では後述する結晶粒が粗大化し、また、６５０℃より低温では軟化に長時間を要するだけでなく、６５０℃より低温であまり長時間焼鈍するとσ相が析出して脆化する可能性があることから、焼鈍温度は、６５０〜９５０℃の範囲とするとよい。
なお、焼鈍の保持時間は、高温では結晶粒を粗大化させないように短時間で行うのがよく、一方、低温では硬さを低下させるのに長時間を要するため、保持時間は結晶粒度と硬さの関係から適宜選択できる。
In order to satisfy the above-described hardness, crystal grain size, and impact characteristics, annealing is preferably performed in order to remove processing strain generated in the raw material manufacturing process and remaining in the material.
When the annealing temperature is higher than 950 ° C., the crystal grains described later are coarsened, and when the annealing temperature is lower than 650 ° C., it takes a long time for softening. Since there is a possibility of embrittlement, the annealing temperature is preferably in the range of 650 to 950 ° C.
Note that the annealing holding time should be short in order not to coarsen the crystal grains at high temperatures, while it takes a long time to reduce the hardness at low temperatures. It can be appropriately selected from the relationship.
焼鈍後の硬さが２８０ＨＶより高いと、これらの加工に時間を要したり、形状精度が低下したりすることから、硬さは２８０ＨＶ以下とした。望ましくは２００ＨＶ以下である。また、この硬さの範囲内であれば、焼鈍後の熱歪による変形を修正するために、焼鈍後に冷間圧延等の冷間加工を行ってもよい。 If the hardness after annealing is higher than 280 HV, it takes time for these processes or the shape accuracy decreases, so the hardness is set to 280 HV or less. Desirably, it is 200 HV or less. Moreover, if it is in the range of this hardness, in order to correct the deformation | transformation by the thermal strain after annealing, you may perform cold processing, such as cold rolling, after annealing.
本発明の耐酸化性鋼は、約７００℃以上の使用温度で使用されるものであるが、燃料電池は運転と停止を繰り返し行うことから、セパレータ用鋼は使用温度と常温の間での加熱、冷却の熱サイクルを繰り返し受ける。特に、冷却中に引張応力が作用するので、冷却時に割れないようにするためには常温での衝撃特性が良好であればよい。
本発明の耐酸化性鋼のようなフェライト組織の鋼で、良好な衝撃特性を得るためには、フェライト結晶粒を微細化することが有効である。後述する衝撃特性を得るためには平均フェライト結晶粒度がＡＳＴＭ Ｎｏ．２以上の細粒とすることが必要である。望ましくは平均フェライト結晶粒度がＡＳＴＭＮｏ．３以上の細粒がよい。
衝撃特性は、２０℃での２ｍｍＶノッチシャルピー衝撃値で評価することができ、衝撃値が８Ｊ／ｃｍ２以上であればよく、望ましくは、１０Ｊ／ｃｍ２以上がよい。
The oxidation-resistant steel of the present invention is used at a use temperature of about 700 ° C. or more. However, since the fuel cell is repeatedly operated and stopped, the separator steel is heated between the use temperature and the normal temperature. Repeatedly undergoes a cooling thermal cycle. In particular, since tensile stress acts during cooling, it is sufficient that the impact characteristics at normal temperature are good in order to prevent cracking during cooling.
In order to obtain good impact characteristics in a steel having a ferrite structure such as the oxidation resistant steel of the present invention, it is effective to refine the ferrite crystal grains. In order to obtain impact characteristics described later, the average ferrite grain size is ASTM No. Two or more fine grains are required. Desirably, the average ferrite grain size is ASTM No. Three or more fine grains are preferable.
The impact property can be evaluated by a 2 mmV notch Charpy impact value at 20 ° C., and the impact value may be 8 J / cm 2 or more, and desirably 10 J / cm 2 or more.
次に、本発明の耐酸化性鋼では、特に７００〜９５０℃の温度範囲で優れた電気抵抗を有する。そのため、その優れた電気抵抗を示す指標として以下のように規定した。
電気伝導性を評価する評価手段として、７５０℃で１０００Ｈｒ加熱した後の７５０℃における酸化被膜の電気抵抗が１００ｍΩ・ｃｍ２以下、望ましくは５０ｍΩ・ｃｍ２以下であることが重要である。
また、長期使用後において、形成されたＣｒ系酸化被膜の酸化が進行して、表面酸化スケールとなって剥離する現象の評価手段として、８５０℃で１００Ｈｒ加熱後に表面酸化スケールの剥離が実質的に発生しないことが重要である。なお、「表面酸化スケールの剥離が実質的に発生しない」とは、スケールの自然剥離がないことを指し、外的衝撃が加わらない状態をいう。
Next, the oxidation resistant steel of the present invention has excellent electrical resistance particularly in the temperature range of 700 to 950 ° C. Therefore, it was defined as follows as an index indicating the excellent electrical resistance.
As an evaluation means for evaluating the electrical conductivity, 750 ° C. 1,000 hours electrical resistance of the oxide film at 750 ° C. after heating is 100 m [Omega · cm 2 or less at, preferably it is important that 50 m [Omega · cm 2 or less.
In addition, as a means for evaluating the phenomenon in which oxidation of the formed Cr-based oxide film proceeds and becomes a surface oxide scale after long-term use, the surface oxide scale peels substantially after heating at 850 ° C. for 100 hours. It is important that it does not occur. Note that “the surface oxide scale does not peel substantially” means that there is no natural peeling of the scale, and means that no external impact is applied.
また、本発明鋼は、固体酸化物型燃料電池セパレータに好適な材料であり、鋼板、鋼帯に加工される場合が多いが、その他の固体酸化物型燃料電池用部品または本発明鋼の特性が生かせるその他用途の部品に、棒鋼、線材、粉末、粉末焼結体、多孔質体、鋼箔、等の種々の形状に加工して使用することが可能である。 The steel of the present invention is a material suitable for a solid oxide fuel cell separator, and is often processed into a steel plate or steel strip. It can be used by processing into various shapes such as steel bars, wire rods, powders, powder sintered bodies, porous bodies, steel foils, etc., for parts for other uses that can make the best use of.
（実施例１）
本発明鋼及び比較鋼を真空誘導炉にて溶製し１０ｋｇのインゴットを作製した。
真空溶解時には、不純物元素を規定内に低く抑えるために、純度の高い原料を選定するとともに炉内雰囲気等操業条件を制御してＴｉ、Ｓ、Ｏ、Ｎ、Ｂ等の混入、残存を抑制した。但し、比較鋼の一部については、不純物元素の影響を調べるため、あえてこれらの考慮をしなかった。
その後、１１００℃に加熱して３０ｍｍ角の棒材に鍛伸し、７８０℃で１時間の焼鈍を行った。表１及び表２に本発明鋼Ｎｏ．１〜２３、比較合金Ｎｏ．３１〜４０の化学組成を示す。なお表２において、比較鋼Ｎｏ．４０はＪＩＳ ＮＣＦ６００として知られているオーステナイト系合金である。
なお、表に示す式の値は、ＺｒとＬａの複合添加合金は（１）式、ＹとＺｒとＬａの複合添加合金は（２）式、ＺｒとＬａを必須とした希土類元素（ＲＥＭ）の複合添加合金は（３）式で計算した値である。
また、表中でＬａを必須添加していない合金については、以下に示す式にて計算を行なった。
（Ｏ＋２Ｓ）／（０．２７Ｙ＋０．０３５Ｚｒ＋０．１６ＲＥＭ）≦２．０
式の元素は質量％であり、上記式中のＹ、Ｚｒ、希土類元素（ＲＥＭ）のうち無添加の元素については０として計算した。
Example 1
The steel of the present invention and the comparative steel were melted in a vacuum induction furnace to produce a 10 kg ingot.
At the time of vacuum melting, in order to keep the impurity elements low within the specified range, raw materials with high purity were selected and operation conditions such as the atmosphere in the furnace were controlled to suppress mixing and remaining of Ti, S, O, N, B, etc. . However, some of the comparative steels were not considered because of the influence of impurity elements.
Then, it heated to 1100 degreeC and forge-stretched to the 30-mm square bar | burr, and annealed at 780 degreeC for 1 hour. Tables 1 and 2 show the steel No. of the present invention. 1-23, Comparative Alloy No. The chemical composition of 31-40 is shown. In Table 2, the comparative steel No. Reference numeral 40 denotes an austenitic alloy known as JIS NCF600.
The values of the formulas shown in the table are the formula (1) for the composite additive alloy of Zr and La, the formula (2) for the composite additive alloy of Y, Zr and La, and a rare earth element (REM) essentially including Zr and La. The value of the composite additive alloy is the value calculated by equation (3).
Moreover, about the alloy which does not add La essentially in the table | surface, it calculated by the formula shown below.
(O + 2S) / (0.27Y + 0.035Zr + 0.16REM) ≦ 2.0
The element of the formula is% by mass, and the calculation was performed assuming that the additive-free element among Y, Zr, and rare earth element (REM) in the above formula was 0.
これらの素材から試験片を切り出し各種試験を行った。
まず、これらの耐酸化性鋼の縦断面の光学顕微鏡組織観察を行い、平均フェライト結晶粒度を測定した。また、２ｍｍＶノッチシャルピー試験片を採取し、２ｍｍＶノッチシャルピー衝撃試験を２０℃で行い、衝撃値を求めた。
更に、直径１０ｍｍ、長さ２０ｍｍの円柱状試験片を用いて、大気中で８５０℃×１００Ｈｒ及び７５０℃で１０００Ｈｒの加熱処理を行った後、表面酸化スケールの剥離量を測定した。また１０ｍｍＷ×１０ｍｍＬ×３ｍｍｔの板状試料を用いて、大気中７５０℃で１０００Ｈｒ加熱を行って表面に酸化被膜を形成させた後、７５０℃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、３０℃から７５０℃までの平均熱膨張係数を測定した。これらの試験結果をまとめて表３及び表４に示す。
Test pieces were cut out from these materials and subjected to various tests.
First, the optical cross-sectional observation of the longitudinal section of these oxidation resistant steels was performed, and the average ferrite crystal grain size was measured. Further, a 2 mmV notch Charpy test piece was collected and a 2 mmV notch Charpy impact test was performed at 20 ° C. to determine an impact value.
Furthermore, using a cylindrical test piece having a diameter of 10 mm and a length of 20 mm, heat treatment was performed at 850 ° C. × 100 Hr and 750 ° C. for 1000 Hr in the atmosphere, and then the amount of peeling of the surface oxide scale was measured. Further, a 10 mmW × 10 mmL × 3 mmt plate-like sample was heated in the atmosphere at 750 ° C. for 1000 hours to form an oxide film on the surface, and then the electrical resistance at 750 ° C. was measured. The electrical resistance was represented by sheet resistance (mΩ · cm 2 ). Moreover, the average thermal expansion coefficient from 30 degreeC to 750 degreeC was measured. The test results are summarized in Table 3 and Table 4.
表３より、本発明鋼は何れも焼鈍後の硬さが２８０ＨＶ以下、平均フェライト結晶粒度がＡＳＴＭ Ｎｏ．２以上であり、また、２ｍｍＶノッチシャルピー衝撃値も８Ｊ／ｃｍ２以上の値を有しており、シャルピー衝撃値が１０Ｊ／ｃｍ２以上のものもある。
表３より本発明鋼は大気中７５０℃×１０００Ｈｒ及び８５０℃×１００Ｈｒ加熱後のスケールの剥離は全く観察されない。また、本発明鋼は、大気中７５０℃で１０００Ｈｒ加熱を行って表面に酸化被膜を形成させた後に７５０℃において測定した電気抵抗の値は十分小さい。これは、主に表面に薄い緻密なＣｒ２Ｏ３被膜を形成しているためと考えられる。更に、本発明鋼は、３０〜７５０℃までの平均熱膨張係数が約１１×１０−６／℃台と小さく、固体電解質である安定化ジルコニアに近い。
From Table 3, all the steels of the present invention have a hardness after annealing of 280 HV or less and an average ferrite grain size of ASTM No. 2 mm or more, the 2 mmV notch Charpy impact value also has a value of 8 J / cm 2 or more, and there is a Charpy impact value of 10 J / cm 2 or more.
From Table 3, the steel of the present invention shows no separation of scale after heating in the atmosphere at 750 ° C. × 1000 Hr and 850 ° C. × 100 Hr. Further, the steel of the present invention has a sufficiently small electric resistance value measured at 750 ° C. after an oxide film is formed on the surface by heating at 750 ° C. in the atmosphere for 1000 hours. This is presumably because a thin dense Cr 2 O 3 film is formed on the surface. Further, the steel of the present invention has an average coefficient of thermal expansion from 30 to 750 ° C. as small as about 11 × 10 −6 / ° C., and is close to stabilized zirconia which is a solid electrolyte.
一方、表４より比較鋼Ｎｏ．３１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。比較鋼Ｎｏ．３２は、Ｃｒ量が多いため、７５０℃ではスケール剥離が観察されないが、８５０℃では少量のスケール剥離が観察される。
比較鋼Ｎｏ．３３はＡｌを３％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．３４はＳｉが高く、おそらく厚いＳｉＯ２被膜が形成されていると思われ、電気抵抗の値が高い。
また、比較鋼Ｎｏ．３５、３６は、Ｏ量が多かったり、Ｚｒ、Ｙ、希土類元素（ＲＥＭ）の添加量が少なかったりするために式（１）の値が大きくなり、耐酸化性に効果のあるＺｒ、Ｙ、希土類元素（ＲＥＭ）の効果が十分発揮できず、スケールの剥離が観察され、また電気抵抗も高くなっている。
On the other hand, from Table 4, comparative steel No. It can be seen that No. 31 has a large amount of peeling due to a small amount of Cr and cannot withstand long-term use. Comparative steel No. Since No. 32 has a large amount of Cr, scale peeling is not observed at 750 ° C., but a small amount of scale peeling is observed at 850 ° C.
Comparative steel No. Since 33 contains 3% 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. 34 is high in Si and probably has a thick SiO2 film, and has a high electric resistance value.
Comparative steel No. 35 and 36 have a large amount of O or a small amount of Zr, Y, or rare earth element (REM), so that the value of the formula (1) becomes large, and Zr, Y, The effect of rare earth elements (REM) cannot be sufficiently exhibited, scale peeling is observed, and electric resistance is high.
比較鋼Ｎｏ．３７は、Ｂを多く含むため、緻密な酸化スケールが形成されず、一部剥離するとともに電気抵抗も高くなっている。また、比較鋼Ｎｏ．３８は、Ｓを多く含み、そのため式（１）の値が大きくなり、耐酸化性に効果のある希土類元素（ＲＥＭ）等の効果が十分発揮できず、スケールの剥離が観察され、また電気抵抗も高くなっている。
比較鋼Ｎｏ．３９は、Ｔｉを多く含み、かつ上述した式の値が大きいためにスケールの剥離が観察され、また電気抵抗も高い。比較鋼Ｎｏ．４０は、酸化スケール剥離も観察されず、電気抵抗も低かったが、オーステナイト系Ｎｉ基合金であるため、熱膨張係数が非常に大きくなった。
Comparative steel No. Since 37 contains a large amount of B, a dense oxide scale is not formed, and a part of the scale is peeled off and the electrical resistance is high. Comparative steel No. 38 contains a large amount of S, so that the value of the formula (1) becomes large, the effect of rare earth elements (REM) having an effect on oxidation resistance cannot be sufficiently exhibited, peeling of the scale is observed, and electric resistance Is also high.
Comparative steel No. No. 39 contains a large amount of Ti, and since the value of the above formula is large, peeling of the scale is observed, and the electrical resistance is also high. Comparative steel No. No oxidation scale peeling was observed for 40, and the electrical resistance was low, but since it was an austenitic Ni-based alloy, the thermal expansion coefficient was very large.
参考例Ｎｏ．３、本発明鋼Ｎｏ．５．２３及びＢを含む比較鋼Ｎｏ．３７を１０００℃で１００時間加熱した後の酸化被膜の断面顕微鏡写真とその模式図を図１〜４に示す。
図１〜３に示すように、本発明鋼は酸化被膜（１）の表面が平滑であり、かつマトリックス（２）が酸化被膜内に入り込んでいるため密着状態が良好であるのに対し、図４に示すＢを含む比較鋼Ｎｏ．３７の酸化被膜（１）の表面は凹凸が激しく平滑でない上に、酸化被膜内にマトリックス（２）の食い込みがないことがわかる。
このため、Ｂを含む比較鋼は、接触抵抗が高くなるだけでなく、酸化被膜の密着性も良くないと考えられるので、Ｂは不純物として極力低く抑えることが重要である。
Reference Example No. 3, the present invention steel No. 5 . Comparative steels No. 23 and B 1-4 are cross-sectional micrographs and schematic views of the oxide film after heating 37 at 1000 ° C. for 100 hours.
As shown in FIGS. 1 to 3, the steel according to the present invention has a smooth surface of the oxide film (1) and a good adhesion because the matrix (2) has entered the oxide film. Comparative steel No. 4 containing B shown in FIG. It can be seen that the surface of the oxide film (1) 37 is not smooth and uneven, and the matrix (2) does not bite into the oxide film.
For this reason, it is considered that the comparative steel containing B not only has high contact resistance but also has poor oxide film adhesion, so it is important to keep B as low as possible as an impurity.
（実施例２）
参考例Ｎｏ．１〜３、本発明鋼Ｎｏ．４、５について、熱間鍛造後、熱間圧延によって厚さ５ｍｍの板形状に仕上げ、７８０℃で１時間の焼鈍を行った。
また、更に冷間加工と焼鈍を繰り返し行い、厚さ１ｍｍと０．３ｍｍの板形状に仕上げ、それぞれ８５０℃で３分及び２分の焼鈍を行った。
これらの鋼の縦断面の光学顕微鏡組織観察を行い、結晶粒度を測定した。
また、焼鈍温度を変えて焼鈍を行った３０ｍｍ角の鍛造材及び厚さ５ｍｍの熱間圧延材について、２ｍｍＶノッチシャルピー衝撃試験を２０℃で行い、衝撃値を求めた。
これらの結果をまとめて表５に示す。
(Example 2)
Reference Example No. 1-3, the present invention steel No. 1 . About 4 and 5 , after hot forging, it finished in the plate shape of thickness 5mm by hot rolling, and annealed at 780 degreeC for 1 hour.
Further, cold working and annealing were repeated to finish a plate shape having a thickness of 1 mm and 0.3 mm, followed by annealing at 850 ° C. for 3 minutes and 2 minutes, respectively.
The optical cross-sectional observation of the longitudinal section of these steels was performed, and the crystal grain size was measured.
Moreover, the 2 mmV notch Charpy impact test was done at 20 degreeC about the 30 mm square forging material and the hot rolled material of thickness 5mm which annealed by changing annealing temperature, and the impact value was calculated | required.
These results are summarized in Table 5.
何れも硬さは２８０ＨＶ以下、平均フェライト結晶粒度はＡＳＴＭ Ｎｏ．３以上であり、特に冷間圧延工程で作製した厚さ１ｍｍ及び０．３ｍｍの板材ではＡＳＴＭ Ｎｏ．８〜９及びＮｏ．９〜１０程度と非常に細かい。
また厚さ５ｍｍの板材の２ｍｍＶノッチシャルピー衝撃値は１０Ｊ／ｃｍ２以上であり、衝撃特性も良好である。
以上述べたように本発明の耐酸化性鋼は、７００〜９５０℃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共に、長時間の使用においても良好な耐酸化性、特に耐剥離性を有し、かつ電解質との熱膨張差が小さく、燃料電池の低コスト化及び高性能化を図ることができることから、比較的低温の７００〜９５０℃程度で作動する固体電解質型燃料電池の実用化、高効率化、大型化に大きく寄与できる。
このことから、本発明の耐酸化性鋼は固体酸化物型燃料電池用部品として好適である。
In either case, the hardness is 280 HV or less, and the average ferrite grain size is ASTM No. 3 and more, especially in the case of plate materials having thicknesses of 1 mm and 0.3 mm produced in the cold rolling process, ASTM No. 8-9 and no. Very fine, about 9-10.
Moreover, the 2 mmV notch Charpy impact value of the 5 mm-thick plate material is 10 J / cm 2 or more, and the impact characteristics are also good.
As described above, the oxidation-resistant steel of the present invention forms an oxide film having good electrical conductivity in the vicinity of 700 to 950 ° C., and also has good oxidation resistance, especially peel resistance, even when used for a long time. In addition, the difference in thermal expansion from the electrolyte is small, and the cost and performance of the fuel cell can be reduced, so that a solid electrolyte fuel cell that operates at a relatively low temperature of about 700 to 950 ° C. can be used. Can greatly contribute to the increase in efficiency, efficiency, and size.
Therefore, the oxidation resistant steel of the present invention is suitable as a solid oxide fuel cell component.
１．酸化皮膜、２．マトリックス 1. 1. oxide film, matrix
Claims (14)
（Ｏ＋２Ｓ）／（０．０３５Ｚｒ＋０．１６Ｌａ）≦２．０…（１）
（１）式の元素は質量％である。 Except as solid oxide fuel cell separator steel, heated between room temperature and 700 to 950 ° C., a oxidation resistant steels undergo repeated thermal cycling of the cooling, in mass%, C: 0.2 %: Si: Less than 0.2% (excluding 0%) , Mn: 1.0% or less (not including 0%), Ni: 2% or less, Cr: 15-30%, Al: 1% Hereinafter , La: 0.005 to 0.1%, Zr: 1% or less , the balance is Fe and inevitable impurities, Ti: 0.1% or less, S: 0.015% Hereinafter, O: 0.010% or less, N: 0.050% or less, B: 0.0030% or less, and made of steel satisfying the formula (1), hardness is 280HV or less, average ferrite crystal The particle size is ASTM No. An oxidation-resistant steel characterized by being 2 or more fine grains.
(O + 2S) / ( 0.035Zr + 0.16 La ) ≦ 2.0 (1)
The element of the formula (1) is mass%.
（Ｏ＋２Ｓ）／（０．０３５Ｚｒ＋０．１６Ｌａ）≦２．０…（１）
（１）式の元素は質量％である。 Except as solid oxide fuel cell separator steel, heated between room temperature and 700 to 950 ° C., a oxidation resistant steels undergo repeated thermal cycling of the cooling, in mass%, C: 0.1 %: Si: Less than 0.2% (not including 0%), Mn: 1.0% or less (not including 0%), Cr: 17 to 26%, Ni: 1% or less, Al: 0.00%. 001% or more and less than 0.5%, Zr: 0.01 to 0.8% , La: 0.005 to 0.1%, the balance is Fe and inevitable impurities , and as an inevitable impurity, Ti: 0.1% or less, S: 0.015% or less, O: 0.010% or less, N: 0.020% or less, B: 0.0030% or less, and satisfies the formula (1) And having a hardness of 280 HV or less and an average ferrite grain size of ASTM No. An oxidation-resistant steel characterized by being 2 or more fine grains.
(O + 2S) / ( 0.035Zr + 0.16 La ) ≦ 2.0 (1)
The element of the formula (1) is mass%.
（Ｏ＋２Ｓ）／（０．０３５Ｚｒ＋０．１６Ｌａ）≦２．０…（１）
（１）式の元素は質量％である。 Except as solid oxide fuel cell separator steel, heated between room temperature and 700 to 950 ° C., a oxidation resistant steels undergo repeated thermal cycling of the cooling, in mass%, C: 0.1 %: Si: less than 0.2% (not including 0%), Mn: less than 0.2% (not including 0%), Cr: 17 to 26%, Ni: 1% or less, Al: 0.00%. 001% or more and less than 0.5%, Zr: 0.01 to 0.8% , La: 0.005 to 0.1%, the balance is Fe and inevitable impurities , and as an inevitable impurity, Ti: 0.1% or less, S: 0.015% or less, O: 0.010% or less, N: 0.020% or less, B: 0.0030% or less, and satisfies the formula (1) And having a hardness of 280 HV or less and an average ferrite grain size of ASTM No. An oxidation-resistant steel characterized by being 2 or more fine grains.
(O + 2S) / ( 0.035Zr + 0.16 La ) ≦ 2.0 (1)
The element of the formula (1) is mass%.
（Ｏ＋２Ｓ）／（０．２７Ｙ＋０．０３５Ｚｒ＋０．１６Ｌａ）≦２．０…（２） (O + 2S) / (0.27Y + 0.035Zr + 0.16La) ≦ 2.0 (2)
（２）式の元素は質量％である。The element of the formula (2) is mass%.
（Ｏ＋２Ｓ）／（０．０３５Ｚｒ＋０．１６Ｌａ）≦２．０…（１）
（１）式の元素は質量％である。 Except as solid oxide fuel cell separator steel, heated between room temperature and 700 to 950 ° C., a oxidation resistant steels undergo repeated thermal cycling of the cooling, in mass%, C: 0.08 %: Si: Less than 0.2% (excluding 0%), Mn: 0.5% or less (excluding 0%), Cr: 18-25%, Ni: 0.5% or less, Al: 0.001% or more and less than 0.5%, La: 0.005 to 0.1%, Zr: 0.01 to 0.6%, the balance is made of Fe and inevitable impurities , and Ti: 0.1% or less, S: 0.008% or less, O: 0.008% or less, N: 0.020% or less, B: 0.0020% or less, and satisfying the formula ( 1 ) And having a hardness of 280 HV or less and an average ferrite grain size of ASTM No. An oxidation-resistant steel characterized by being 2 or more fine grains.
(O + 2S) / (0.035Zr + 0.16La) ≦ 2.0 ( 1 )
The element of the formula (1) is mass%.
（Ｏ＋２Ｓ）／（０．０３５Ｚｒ＋０．１６Ｌａ）≦２．０…（１）
（１）式の元素は質量％である。 Except as solid oxide fuel cell separator steel, heated between room temperature and 700 to 950 ° C., a oxidation resistant steels undergo repeated thermal cycling of the cooling, in mass%, C: 0.08 %: Si: Less than 0.2% (excluding 0%), Mn: 0.5% or less (excluding 0%), Cr: 18-25%, Ni: 0.5% or less, Al: 0.001% or more and less than 0.5%, La: 0.005 to 0.1%, Zr: 0.01 to 0.6%, the balance is made of Fe and inevitable impurities , and Ti: Steel that is limited to 0.1% or less, S: 0.008% or less, O: 0.008% or less, N: 0.020% or less, B: less than 0.0010%, and satisfies the formula ( 1 ) And having a hardness of 280 HV or less and an average ferrite grain size of ASTM No. Oxidation-resistant steel characterized by being 3 or more fine grains.
(O + 2S) / (0.035Zr + 0.16La) ≦ 2.0 ( 1 )
The element of the formula (1) is mass%.
（Ｏ＋２Ｓ）／（０．０３５Ｚｒ＋０．１６ＲＥＭ）≦２．０…（３）(O + 2S) / (0.035Zr + 0.16REM) ≦ 2.0 (3)
（３）式の元素は質量％である。The element of the formula (3) is mass%.
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| EP2479307B1 (en) * | 2009-09-16 | 2018-08-22 | Hitachi Metals, Ltd. | Steel for solid oxide fuel cell having excellent oxidation resistance |
| JP2011214063A (en) * | 2010-03-31 | 2011-10-27 | Jfe Steel Corp | Ferritic stainless steel sheet and method for manufacturing the same |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS63169333A (en) * | 1986-12-30 | 1988-07-13 | Nisshin Steel Co Ltd | Production of chromium stainless steel strip of double phase structure having small intra-surface anisotropy and high ductility and high strength |
| JPH04371518A (en) * | 1991-06-20 | 1992-12-24 | Kawasaki Steel Corp | Production of ferritic stainless steel for electric material having excellent ductility, wear resistance and rust resistance |
| JPH09157801A (en) * | 1995-10-05 | 1997-06-17 | Hitachi Metals Ltd | Steel for separator of solid electrolytic fuel cell |
| JPH10280103A (en) * | 1997-04-08 | 1998-10-20 | Hitachi Metals Ltd | Steel for solid electrolytic type fuel battery separator |
| WO1999025890A1 (en) * | 1997-11-17 | 1999-05-27 | Ceramic Fuel Cells Limited | A heat resistant steel |
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2007
- 2007-03-07 JP JP2007056708A patent/JP4524760B2/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS63169333A (en) * | 1986-12-30 | 1988-07-13 | Nisshin Steel Co Ltd | Production of chromium stainless steel strip of double phase structure having small intra-surface anisotropy and high ductility and high strength |
| JPH04371518A (en) * | 1991-06-20 | 1992-12-24 | Kawasaki Steel Corp | Production of ferritic stainless steel for electric material having excellent ductility, wear resistance and rust resistance |
| JPH09157801A (en) * | 1995-10-05 | 1997-06-17 | Hitachi Metals Ltd | Steel for separator of solid electrolytic fuel cell |
| JPH10280103A (en) * | 1997-04-08 | 1998-10-20 | Hitachi Metals Ltd | Steel for solid electrolytic type fuel battery separator |
| WO1999025890A1 (en) * | 1997-11-17 | 1999-05-27 | Ceramic Fuel Cells Limited | A heat resistant steel |
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| JP2007197837A (en) | 2007-08-09 |
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