JP2007119802A - Method for improving oxidation resistance of heat resistant metallic material and method for producing heat resistant metallic member - Google Patents
Method for improving oxidation resistance of heat resistant metallic material and method for producing heat resistant metallic member Download PDFInfo
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本発明は、耐熱金属材料の耐酸化性の改善方法および耐熱金属部材の製造方法に関する。さらに詳しくは、本発明は、火力発電所用のガスタービンのような高温水蒸気中で使用される機器の構成部材として用いられる耐熱金属材料の耐酸化性の改善方法および耐熱金属部材の製造方法に関する。 The present invention relates to a method for improving oxidation resistance of a refractory metal material and a method for producing a refractory metal member. More specifically, the present invention relates to a method for improving the oxidation resistance of a refractory metal material used as a component of equipment used in high-temperature steam such as a gas turbine for a thermal power plant, and a method for producing a refractory metal member.
火力発電所用のガスタービンなどに用いられる部材の材料として、耐熱性、高温強度等の機械的特性などの要求を満足するニッケル基合金が用いられている。一方、これらの部材は高温水蒸気中で使用されるため、水蒸気酸化に対する耐性も要求される。 As a material of a member used in a gas turbine for a thermal power plant, a nickel-based alloy that satisfies requirements for mechanical properties such as heat resistance and high-temperature strength is used. On the other hand, since these members are used in high-temperature steam, resistance to steam oxidation is also required.
アルミニウム（Ａｌ）は、実用合金元素（ニッケル、コバルト、クロム、鉄、タンタル、タングステン等）の中でも最も酸化物の平衡酸素解離圧が小さい部類に属する。アルミニウムを含有する合金の表面に緻密なアルミナ(Ａｌ2Ｏ3)皮膜が生成すると、合金のアルミナ皮膜よりも内部における酸素分圧はアルミナの平衡酸素解離圧以下になるので、酸化物の平衡酸素解離圧がそれよりも大きい合金元素は酸化されず、以降の酸化の進行が抑制されることが知られている。 Aluminum (Al) belongs to a class having the lowest equilibrium oxygen dissociation pressure of oxide among practical alloy elements (nickel, cobalt, chromium, iron, tantalum, tungsten, etc.). When a dense alumina (Al 2 O 3 ) film is formed on the surface of an alloy containing aluminum, the oxygen partial pressure inside the alloy is less than the equilibrium oxygen dissociation pressure of the alumina than the alumina film of the alloy. It is known that an alloy element having a dissociation pressure higher than that is not oxidized, and the progress of subsequent oxidation is suppressed.
このため、従来では、特にガスタービン用途の合金にはアルミナイズ処理を施すことが行われてきた。このアルミナイズ処理は、Ａｌを合金表面から拡散させ、合金表面近傍のＡｌ濃度を著しく高める処理であり、例えば、拡散浸透法、化学気相蒸着法、パック法などによる処理が実用化されている（非特許文献１および非特許文献２）。アルミナイズ処理を施した合金表面には、高温水蒸気中での実使用等によって酸化アルミニウムの皮膜が形成される。
しかしながら、アルミナイズ処理を施すと合金表面近傍の材料組織が脆化し、き裂の発生が従前に比べて増加するという問題が生じている。また、部材の製造段階において工程が増えることがコスト増加の要因となっている。 However, when the aluminizing treatment is performed, the material structure near the alloy surface becomes brittle, and there is a problem that the generation of cracks is increased as compared with the conventional case. In addition, an increase in the number of processes in the manufacturing stage of the member is a factor in increasing costs.
本発明は、上記した従来技術における課題を解決するためになされたものであり、合金表面近傍の材料組織が脆化することなく、さらに部材の製造工程を増やさずに、高温水蒸気雰囲気中における耐熱金属材料の耐酸化性を改善することを目的としている。 The present invention has been made in order to solve the above-described problems in the prior art. The material structure in the vicinity of the alloy surface does not become brittle, and further, the heat resistance in a high-temperature steam atmosphere is not increased without increasing the number of manufacturing steps of the member. It aims to improve the oxidation resistance of metal materials.
また本発明は、合金表面近傍の材料組織が脆化することなく、さらに部材の製造工程を増やさずに、高温水蒸気雰囲気中における耐酸化性に優れた耐熱金属部材を得ることができる耐熱金属部材の製造方法を提供することを目的としている。 In addition, the present invention provides a heat-resistant metal member capable of obtaining a heat-resistant metal member having excellent oxidation resistance in a high-temperature steam atmosphere without causing the material structure near the alloy surface to become brittle and further increasing the number of manufacturing steps of the member. It aims at providing the manufacturing method of.
本発明者らは、アルミニウムを含有する耐熱金属材料を、低酸素分圧雰囲気で熱処理することにより、合金の構成金属のうちアルミニウムが選択的に酸化され、合金表面に緻密
な酸化アルミニウム皮膜が形成されることを見出し本発明を完成するに至った。
By heat-treating a heat-resistant metal material containing aluminum in a low oxygen partial pressure atmosphere, the present inventors selectively oxidized aluminum among the constituent metals of the alloy and formed a dense aluminum oxide film on the alloy surface. As a result, the present invention has been completed.
本発明の耐熱金属材料の耐酸化性の改善方法は、アルミニウムを含有するニッケル基合金からなる耐熱金属材料を、低酸素分圧雰囲気で熱処理し、これにより、耐熱金属材料の表面に酸化アルミニウム保護皮膜を形成することを特徴としている。 The method for improving the oxidation resistance of a refractory metal material according to the present invention comprises heat-treating a refractory metal material comprising a nickel-based alloy containing aluminum in a low oxygen partial pressure atmosphere, thereby protecting the surface of the refractory metal material with aluminum oxide. It is characterized by forming a film.
このように、アルミナイズ処理を施さずに、耐熱金属材料を構成するニッケル基合金を酸化して酸化アルミニウム皮膜を形成しているので、合金表面近傍における材料組織の脆化を防止できる。 As described above, since the aluminum oxide film is formed by oxidizing the nickel base alloy constituting the heat-resistant metal material without performing the aluminizing treatment, it is possible to prevent embrittlement of the material structure in the vicinity of the alloy surface.
上記の発明において、前記熱処理は、鋳造した耐熱金属材料の溶体化処理および時効処理であることが好ましい。
このように、耐熱金属材料の機械的特性等を向上させるための溶体化処理および時効処理において低酸素分圧雰囲気とすることで、当該処理時に合金の構成金属のうちアルミニウムが選択的に表面近傍で酸化され、緻密な酸化アルミニウム皮膜が形成される。したがって、部材の製造工程を増やさずに、高温水蒸気雰囲気中における耐熱金属材料の耐酸化性を改善することができる。
In the above invention, the heat treatment is preferably a solution treatment and an aging treatment of the cast refractory metal material.
In this way, by forming a low oxygen partial pressure atmosphere in the solution treatment and aging treatment for improving the mechanical properties and the like of the refractory metal material, aluminum is selectively near the surface among the constituent metals of the alloy during the treatment. Is oxidized to form a dense aluminum oxide film. Therefore, the oxidation resistance of the refractory metal material in a high-temperature steam atmosphere can be improved without increasing the number of member manufacturing steps.
上記の発明において、前記熱処理を、当該熱処理の温度におけるニッケル酸化物の平衡酸素解離圧よりも低い酸素分圧雰囲気で行うことが好ましい。
上記の発明において、前記熱処理を、前記耐熱金属材料を構成するアルミニウム以外の金属元素の酸化物における、当該熱処理の温度での平衡酸素解離圧よりも低い酸素分圧雰囲気で行うことが好ましい。
In the above invention, the heat treatment is preferably performed in an oxygen partial pressure atmosphere lower than the equilibrium oxygen dissociation pressure of nickel oxide at the temperature of the heat treatment.
In the above invention, the heat treatment is preferably performed in an oxygen partial pressure atmosphere lower than the equilibrium oxygen dissociation pressure at the temperature of the heat treatment in an oxide of a metal element other than aluminum constituting the refractory metal material.
上記の発明において、発電用ガスタービンの構成部材として鋳造した前記耐熱金属材料に対して前記熱処理を行うことが好ましい。
上記の発明において、前記耐熱金属材料は、５．０質量％以上のアルミニウムを含有することが好ましい。
In the above invention, the heat treatment is preferably performed on the refractory metal material cast as a constituent member of the power generation gas turbine.
In the above invention, the refractory metal material preferably contains 5.0% by mass or more of aluminum.
本発明の耐熱金属部材の製造方法は、アルミニウムを含有するニッケル基合金からなり、高温水蒸気中で使用される耐熱金属部材を、低酸素分圧雰囲気で熱処理し、これにより、耐熱金属部材の表面に酸化アルミニウム保護皮膜を形成することを特徴としている。 The method for producing a refractory metal member of the present invention comprises a nickel-based alloy containing aluminum and heat-treats a refractory metal member used in high-temperature steam in a low oxygen partial pressure atmosphere, whereby the surface of the refractory metal member It is characterized by forming an aluminum oxide protective film.
このように、アルミナイズ処理を施さずに、耐熱金属部材を構成するニッケル基合金を酸化して酸化アルミニウム皮膜を形成しているので、合金表面近傍における材料組織の脆化を防止できる。 As described above, since the aluminum oxide film is formed by oxidizing the nickel-base alloy constituting the heat-resistant metal member without performing the aluminizing treatment, it is possible to prevent embrittlement of the material structure in the vicinity of the alloy surface.
上記の発明において、前記熱処理は、前記耐熱金属部材の溶体化処理および時効処理であることが好ましい。
このように、耐熱金属部材の機械的特性等を向上させるための溶体化処理および時効処理において低酸素分圧雰囲気とすることで、当該処理時に合金の構成金属のうちアルミニウムが選択的に表面近傍で酸化され、緻密な酸化アルミニウム皮膜が形成される。したがって、部材の製造工程を増やさずに、高温水蒸気雰囲気中における耐酸化性に優れた耐熱金属部材を得ることができる。
In the above invention, the heat treatment is preferably solution treatment and aging treatment of the refractory metal member.
In this way, by forming a low oxygen partial pressure atmosphere in the solution treatment and aging treatment for improving the mechanical properties and the like of the refractory metal member, aluminum is selectively near the surface among the constituent metals of the alloy during the treatment. Is oxidized to form a dense aluminum oxide film. Therefore, it is possible to obtain a heat-resistant metal member having excellent oxidation resistance in a high-temperature steam atmosphere without increasing the number of manufacturing steps for the member.
上記の発明において、前記熱処理を、当該熱処理の温度におけるニッケル酸化物の平衡酸素解離圧よりも低い酸素分圧雰囲気で行うことが好ましい。
上記の発明において、前記熱処理を、前記耐熱金属部材を構成するアルミニウム以外の金属元素の酸化物における、当該熱処理の温度での平衡酸素解離圧よりも低い酸素分圧雰囲気で行うことが好ましい。
In the above invention, the heat treatment is preferably performed in an oxygen partial pressure atmosphere lower than the equilibrium oxygen dissociation pressure of nickel oxide at the temperature of the heat treatment.
In the above invention, the heat treatment is preferably performed in an oxygen partial pressure atmosphere lower than the equilibrium oxygen dissociation pressure at the temperature of the heat treatment in an oxide of a metal element other than aluminum constituting the refractory metal member.
上記の発明において、前記耐熱金属部材は、発電用ガスタービンの構成部材であることが好ましい。
上記の発明において、前記耐熱金属部材は、５．０質量％以上のアルミニウムを含有することが好ましい。
In the above invention, the heat-resistant metal member is preferably a constituent member of a power generation gas turbine.
In the above invention, the refractory metal member preferably contains 5.0% by mass or more of aluminum.
本発明の耐熱金属材料の耐酸化性の改善方法によれば、合金表面近傍の材料組織が脆化することなく、さらに部材の製造工程を増やさずに、高温水蒸気雰囲気中における耐熱金属材料の耐酸化性を改善することができる。 According to the method for improving the oxidation resistance of a refractory metal material of the present invention, the material structure in the vicinity of the alloy surface does not become brittle, and without increasing the manufacturing process of the member, the acid resistance of the refractory metal material in a high-temperature steam atmosphere. The chemical property can be improved.
本発明の耐熱金属部材の製造方法によれば、合金表面近傍の材料組織が脆化することなく、さらに部材の製造工程を増やさずに、高温水蒸気雰囲気中における耐酸化性に優れた耐熱金属部材を得ることができる。 According to the method for producing a refractory metal member of the present invention, the material structure in the vicinity of the alloy surface does not become brittle, and further, the production process of the member is not increased, and the refractory metal member excellent in oxidation resistance in a high-temperature steam atmosphere. Can be obtained.
以下、本発明について詳細に説明する。本発明において用いられる耐熱金属材料は、アルミニウムを含有するニッケル基合金であり、高温水蒸気中における耐熱性を有するものである。 Hereinafter, the present invention will be described in detail. The heat-resistant metal material used in the present invention is a nickel-based alloy containing aluminum and has heat resistance in high-temperature steam.
ニッケル基合金としては、一般的にガスタービン用途等に使用されるものなどを用いることができる。このようなニッケル基合金は、普通鋳造合金、一方向凝固合金、単結晶合金などのいわゆる超合金であり、ニッケルを主成分として各種の添加元素を加えることにより、耐熱性、高温における強度、長時間の組織安定性などの所望の特性を備えている。 As the nickel-base alloy, those generally used for gas turbine applications and the like can be used. Such nickel-based alloys are so-called superalloys such as ordinary casting alloys, unidirectionally solidified alloys, and single crystal alloys. By adding various additive elements with nickel as the main component, heat resistance, strength at high temperatures, It has the desired properties such as tissue stability over time.
ニッケル基合金におけるニッケル以外の添加元素としては、アルミニウムの他に、コバルト、クロム、鉄、タンタル、タングステン、モリブテン、ハフニウム、レニウムなどを挙げることができる。 Examples of the additive element other than nickel in the nickel-based alloy include cobalt, chromium, iron, tantalum, tungsten, molybdenum, hafnium, rhenium and the like in addition to aluminum.
後述する熱処理によって緻密なアルミニウム皮膜を形成可能であり、耐熱性および、高温強度などの機械的特性等において、ガスタービンの構成部材として適切な特性を得る点から、ニッケル基合金として、アルミニウム５．０〜６．０質量％、コバルト１．０〜１２．５質量％、クロム２．０〜１６．０質量％、モリブテン０．４〜４．０質量％、タングステン２．６〜１３．７質量％、チタン０．２〜５．０質量％、タンタル１．７〜１２．０質量％を少なくとも含有する普通鋳造合金、一方向凝固合金または単結晶合金が好ましい。この他、一方向凝固合金および単結晶合金である場合、ハフニウム、レニウムなどが必要に応じて添加される。また、結晶粒界強化元素である炭素、ホウ素等が添加される場合がある。 It is possible to form a dense aluminum film by heat treatment to be described later, and in terms of heat resistance, mechanical characteristics such as high temperature strength, etc., it is possible to obtain appropriate characteristics as a constituent member of a gas turbine. 0 to 6.0% by mass, cobalt 1.0 to 12.5% by mass, chromium 2.0 to 16.0% by mass, molybten 0.4 to 4.0% by mass, tungsten 2.6 to 13.7% by mass %, Normal cast alloy, unidirectionally solidified alloy or single crystal alloy containing at least 0.2 to 5.0% by mass of titanium and 1.7 to 12.0% by mass of tantalum are preferable. In addition, in the case of a unidirectionally solidified alloy and a single crystal alloy, hafnium, rhenium, or the like is added as necessary. Moreover, carbon, boron, etc. which are grain boundary strengthening elements may be added.
このようなニッケル基合金は、ガスタービンの構成部材などの所望の部材形状に鋳造した後、適切な溶体化処理および時効処理を行うことによって得ることができる。
発電用のガスタービンにおいて、冷却構造を有する複数段の各動翼を鋳造する方法としては、ロストワックス法などが用いられており、真空溶解、真空鋳造で製造されるのが一般的である。例えば、マスターインゴットとして溶製された材料を用い、これを再溶解して鋳造を行う。普通鋳造合金では、疲労特性を向上させるために、各種の方法で結晶粒を微細化して鋳造することが多い。一方向凝固合金および単結晶凝固合金の鋳造には、いわゆる鋳型引出し式一方向凝固法などが用いられる。ガスタービン用途では、普通鋳造合金、一方向凝固合金および単結晶凝固合金は、使用温度、応力などに応じて使い分けられている。
Such a nickel-base alloy can be obtained by casting into a desired member shape such as a gas turbine constituent member and then performing appropriate solution treatment and aging treatment.
In a gas turbine for power generation, a lost wax method or the like is used as a method for casting each of the plurality of stages of moving blades having a cooling structure, and is generally manufactured by vacuum melting or vacuum casting. For example, a material melted as a master ingot is used, and this is remelted to perform casting. Ordinary cast alloys are often cast by refining crystal grains by various methods in order to improve fatigue characteristics. For casting of the unidirectionally solidified alloy and the single crystal solidified alloy, a so-called mold drawing type unidirectional solidification method or the like is used. In gas turbine applications, ordinary cast alloys, unidirectionally solidified alloys, and single crystal solidified alloys are properly used depending on operating temperature, stress, and the like.
本発明における特に好ましい態様では、上記の鋳造した耐熱金属材料に対して、低酸素分圧雰囲気にて溶体化処理および時効処理を施し、これによって、機械的特性等を向上させると同時に、耐熱金属材料の表面に緻密な酸化アルミニウム(Ａｌ2Ｏ3)保護皮膜を形成し、高温水蒸気雰囲気中における耐熱金属材料の耐酸化性を改善する。 In a particularly preferred embodiment of the present invention, the cast refractory metal material is subjected to a solution treatment and an aging treatment in a low oxygen partial pressure atmosphere, thereby improving mechanical properties and the like, and at the same time A dense aluminum oxide (Al 2 O 3 ) protective film is formed on the surface of the material to improve the oxidation resistance of the refractory metal material in a high-temperature steam atmosphere.
溶体化処理では、高温に加熱して析出相を母相中に溶かし込み、これを急冷することによって、時効により析出させる元素が母相へ充分に固溶した固溶体を得る。多相合金のように母相とは組成の異なる析出相を時効により析出させる場合には、母相に析出される元素を過剰に含む過飽和固溶体を生成させる。 In the solution treatment, the precipitated phase is dissolved in the mother phase by heating to a high temperature and rapidly cooled to obtain a solid solution in which the elements to be precipitated by aging are sufficiently dissolved in the mother phase. When a precipitated phase having a composition different from that of the parent phase is precipitated by aging, such as a multiphase alloy, a supersaturated solid solution containing excessive elements precipitated in the parent phase is generated.
固溶化温度から急冷し、固溶化温度よりも低い温度に加熱保持することにより時効を行う。時効すると次第に析出が起こり、金属原子の拡散に必要な時間と温度を保つことによって析出相が成長する。析出相の成長に伴って合金の各種の性質、例えば硬さやクリープ強度等の機械的性質、その他物理的および化学的性質が変化する。 Aging is performed by quenching from the solution temperature and heating and holding at a temperature lower than the solution temperature. Precipitation gradually occurs upon aging, and a precipitated phase grows by maintaining the time and temperature necessary for the diffusion of metal atoms. As the precipitate phase grows, various properties of the alloy, such as mechanical properties such as hardness and creep strength, and other physical and chemical properties change.
上記の溶体化処理および時効処理では、所望の相構造および所望の特性をもつ合金を得るために、一定温度での１段の熱処理または、温度を複数回変更した複数段の熱処理が行われる。 In the above solution treatment and aging treatment, in order to obtain an alloy having a desired phase structure and desired characteristics, one-stage heat treatment at a constant temperature or multiple-stage heat treatments in which the temperature is changed a plurality of times are performed.
例えば１１００Ｋ程度の高温において高い強度を示す耐熱性のニッケル超合金における具体的な一例を説明すると、溶体化処理および時効処理によって、母相であるγ相にγ’相が析出相として析出する。 For example, a specific example of a heat-resistant nickel superalloy exhibiting high strength at a high temperature of about 1100 K will be described. A γ ′ phase precipitates as a precipitated phase in a γ phase as a parent phase by solution treatment and aging treatment.
鋳造後の合金には、母相中に共晶γ’相があり、析出したγ’相も粗大化している。普通鋳造合金および一方向凝固合金では、共晶組織の他に炭化物が混在している場合もある。普通鋳造合金および一方向凝固合金では、溶体化処理によっても共晶γ’相が消失しないが、単結晶合金では、溶体化処理によって共晶γ’相が消失してγ単相となり、その後の時効処理で形状の整ったγ’相が析出する。 The alloy after casting has a eutectic γ ′ phase in the parent phase, and the precipitated γ ′ phase is also coarsened. In normal casting alloys and unidirectionally solidified alloys, carbides may be mixed in addition to the eutectic structure. In ordinary casting alloys and unidirectionally solidified alloys, the eutectic γ 'phase does not disappear even by solution treatment, but in the single crystal alloy, the eutectic γ' phase disappears by solution treatment and becomes a γ single phase. The γ 'phase with a well-formed shape is precipitated by aging treatment.
一般的には、時効によってγ’相が立方体形状で規則正しく析出する（鋳造工学 第７３巻（２００１年）第１２号 ｐ．８３４−８３９等）。γ’相の形態はニッケル基合金のクリープ強度等の性質に大きく影響するが、溶体化処理および時効処理によってこれを制御する。γ’相の形態は、例えば溶体化処理後の冷却速度などにより大きく依存するので、アルゴンガスフローなどにより強制的に冷却する場合がある。 In general, the γ 'phase is regularly deposited in a cubic shape due to aging (casting engineering, Vol. 73 (2001) No. 12, p. 834-839, etc.). The form of the γ 'phase greatly affects properties such as creep strength of the nickel-base alloy, but this is controlled by solution treatment and aging treatment. Since the form of the γ ′ phase greatly depends on, for example, the cooling rate after the solution treatment, it may be forcibly cooled by an argon gas flow or the like.
なお、本発明では、低酸素分圧雰囲気にて溶体化処理および時効処理を施し、これによって、機械的特性等を向上させると同時に、耐熱金属材料の表面に緻密な酸化アルミニウム(Ａｌ2Ｏ3)保護皮膜を形成し、高温水蒸気雰囲気中における耐熱金属材料の耐酸化性を改善することを要旨としており、溶体化処理および時効処理の具体的な条件、および結果として得られる合金の相構造、結晶形態などは上記の説明に限定されるものではない。すなわち、所望の特性を有するニッケル基合金に応じて、温度や冷却速度等が各種の条件とされるが、従来より各種の条件が開示されており、また、当業者であれば目的に応じて当該条件を適宜に変更するであろう。 In the present invention, solution treatment and aging treatment are performed in a low oxygen partial pressure atmosphere, thereby improving mechanical properties and the like, and at the same time, dense aluminum oxide (Al 2 O 3 ) The main idea is to form a protective film and improve the oxidation resistance of the refractory metal material in a high-temperature steam atmosphere, the specific conditions for solution treatment and aging treatment, and the phase structure of the resulting alloy, The crystal form is not limited to the above description. That is, depending on the nickel-base alloy having the desired characteristics, the temperature, the cooling rate, and the like are various conditions. Various conditions have been disclosed in the past, and those skilled in the art can use the conditions according to the purpose. The conditions will be changed accordingly.
本発明では、鋳造した耐熱金属材料に対して、低酸素分圧雰囲気での熱処理を施す。この熱処理によって、耐熱金属材料の表面には緻密な酸化アルミニウム(Ａｌ2Ｏ3)保護皮膜が形成される。この熱処理は、上記したように、溶体化処理および時効処理であることが特に好ましい。この熱処理によって形成される酸化アルミニウム保護皮膜は、αアルミナの皮膜であり、その平均厚さは、通常は約１μｍである。 In the present invention, the cast refractory metal material is heat-treated in a low oxygen partial pressure atmosphere. By this heat treatment, a dense aluminum oxide (Al 2 O 3 ) protective film is formed on the surface of the refractory metal material. As described above, the heat treatment is particularly preferably a solution treatment and an aging treatment. The aluminum oxide protective film formed by this heat treatment is a film of α-alumina, and its average thickness is usually about 1 μm.
このような酸化アルミニウム保護皮膜が形成されることによって、高温水蒸気中で耐熱金属材料の使用を続けても、皮膜の内部における酸化の進行が充分に抑制される。
上記の熱処理は、加熱炉などの所定の加熱室内に耐熱金属材料を配置し、アルゴンガスなどの不活性ガスの雰囲気下で、温度および酸素分圧を適宜に調節して行う。熱処理時における酸素分圧は、少なくとも熱処理温度におけるニッケル酸化物の平衡酸素解離圧よりも低いことが好ましい。また、合金の添加元素の種類および組成等に応じて、これらの元素の酸化物の平衡酸素解離圧を考慮し、合金表面に連続した酸化アルミニウム皮膜が形成される条件に酸素分圧を設定する。
By forming such an aluminum oxide protective film, the progress of oxidation inside the film is sufficiently suppressed even if the heat-resistant metal material is continuously used in high-temperature steam.
The heat treatment is performed by placing a refractory metal material in a predetermined heating chamber such as a heating furnace and appropriately adjusting the temperature and oxygen partial pressure in an atmosphere of an inert gas such as argon gas. The oxygen partial pressure during the heat treatment is preferably at least lower than the equilibrium oxygen dissociation pressure of nickel oxide at the heat treatment temperature. Also, depending on the type and composition of the additive element of the alloy, the oxygen partial pressure is set to the conditions under which an aluminum oxide film is continuously formed on the alloy surface, taking into account the equilibrium oxygen dissociation pressure of the oxides of these elements. .
具体的には、例えば、必要に応じて脱酸素処理を行った高純度の不活性ガスを用いて、当該ガスの雰囲気下で熱処理を行い、真空度を適切に調節することで上記の酸素分圧とすることができる。 Specifically, for example, using a high-purity inert gas that has been deoxygenated as necessary, heat treatment is performed in an atmosphere of the gas, and the degree of oxygen is appropriately adjusted by adjusting the degree of vacuum. Pressure.
上記のような条件で熱処理を行うことによって、ニッケル酸化物、他の添加元素による複合酸化物などの生成が防止され、アルミニウムが選択的に酸化されて合金表面に連続した酸化アルミニウム皮膜が形成される。酸化アルミニウム皮膜以外の酸化物皮膜が形成されると、高温水蒸気雰囲気での使用において、皮膜内部における酸化の進行を充分に防止できなくなる。 By performing heat treatment under the above conditions, the formation of nickel oxide and complex oxides by other additive elements is prevented, and aluminum is selectively oxidized to form a continuous aluminum oxide film on the alloy surface. The If an oxide film other than the aluminum oxide film is formed, the progress of oxidation inside the film cannot be sufficiently prevented when used in a high-temperature steam atmosphere.
なお、ニッケル基合金中におけるアルミニウムの含有量は、具体的な相構造、結晶構造などにもよるが、好ましくは合金全量に対して５．０質量％以上、より好ましくは５．０〜６．０質量％である。例えば、アルミニウムが高濃度に存在する相が見かけ上塊状に存在し、その周囲を比較的低濃度のアルミニウムを含有する相が囲んでいる組織になっている場合では、合金表面での酸化が始まると、酸化物層を生成させるために塊状相からアルミニウムが表層へ拡散していくが、ニッケル基合金中におけるアルミニウムの含有量が少ないと、アルミナ皮膜の形成や表面近傍の合金組織構造に対して好ましくない影響を与える場合がある。 The aluminum content in the nickel-based alloy depends on the specific phase structure, crystal structure, etc., but is preferably 5.0% by mass or more, more preferably 5.0-6. 0% by mass. For example, in the case where a phase in which aluminum is present in a high concentration is apparently present in a lump shape and is surrounded by a phase containing a relatively low concentration of aluminum, oxidation on the alloy surface starts. In order to produce an oxide layer, aluminum diffuses from the bulk phase to the surface layer. However, if the aluminum content in the nickel-based alloy is low, the formation of an alumina film and the alloy structure near the surface May have an adverse effect.
また、ニッケル基合金中におけるアルミニウムの含有量は、耐酸化性に関する限り特に上限はないが、例えば合金の強度、疲労特性などの機械的性質等はアルミニウムの含有量にも依存するので、それらを考慮する必要がある。 Further, the content of aluminum in the nickel-based alloy is not particularly limited as far as oxidation resistance is concerned, but for example, mechanical properties such as strength and fatigue properties of the alloy depend on the aluminum content. It is necessary to consider.
本発明は、高温水蒸気雰囲気の過酷条件下で使用される機器に用いられる耐熱金属材料の耐酸化性の改善および耐熱金属部材の製造に好ましく適用される。このような耐熱金属部材の具体例としては、火力発電所用のガスタービンおよびボイラなどが挙げられる。火力発電所用のガスタービンには、水蒸気タービン、水蒸気で冷却を行うガスタービンなどがあり、ガスタービンと排熱回収ボイラおよび蒸気タービンを組み合わせたコンバインド発電プラントで使用されるものなどがある。ガスタービンの構成部材としては、例えばタービン動翼、タービン静翼、ディスク、スタッキングボルトなどが挙げられる。 The present invention is preferably applied to the improvement of oxidation resistance of a refractory metal material used in equipment used under severe conditions in a high-temperature steam atmosphere and the production of a refractory metal member. Specific examples of such refractory metal members include gas turbines and boilers for thermal power plants. Gas turbines for thermal power plants include steam turbines, gas turbines that cool with steam, and those that are used in combined power plants that combine gas turbines, exhaust heat recovery boilers, and steam turbines. Examples of constituent members of the gas turbine include a turbine rotor blade, a turbine stationary blade, a disk, and a stacking bolt.
本発明によれば、例えば、温度４００〜８００℃、圧力１５０ｋｇ／ｃｍ2以上である
ような水蒸気雰囲気において使用される耐熱金属部材の耐酸化性を大幅に向上させることができる。
実施例
以下、実施例により本発明を説明するが、本発明はこの実施例により限定されるものではない。
[実施例１]
表１に示す組成のニッケル基耐熱合金に対して低酸素分圧下における熱処理を行った。
According to the present invention, for example, the oxidation resistance of a heat-resistant metal member used in a steam atmosphere such as a temperature of 400 to 800 ° C. and a pressure of 150 kg / cm 2 or more can be greatly improved.
EXAMPLES Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the examples.
[Example 1]
The nickel-base heat-resistant alloy having the composition shown in Table 1 was subjected to heat treatment under a low oxygen partial pressure.
低酸素分圧下における熱処理は、全圧６７Ｐａの純Ａｒガスを雰囲気として、１３０４℃で２時間保持した後に１１４０℃まで強制的に冷却し、その後、１１４０℃で６時間、１０８０℃で６時間、８７１℃で２０時間保持し、その後室温まで徐冷するという温度履歴で実施した。 In the heat treatment under a low oxygen partial pressure, pure Ar gas having a total pressure of 67 Pa is held in 1304 ° C. for 2 hours and then forcibly cooled to 1140 ° C., then, 1140 ° C. for 6 hours, 1080 ° C. for 6 hours, The temperature was maintained at 871 ° C. for 20 hours and then gradually cooled to room temperature.
熱処理後の合金断面を電子顕微鏡写真で観察したところ、厚さ約１μｍのＡｌ2Ｏ3皮膜の生成が確認された。図１に、熱処理後の合金断面の電子顕微鏡写真（撮影倍率１００００倍）を示す。 When the cross section of the alloy after the heat treatment was observed with an electron micrograph, it was confirmed that an Al 2 O 3 film having a thickness of about 1 μm was formed. FIG. 1 shows an electron micrograph (imaging magnification: 10,000 times) of the alloy cross section after heat treatment.
この低酸素分圧下における熱処理によりＡｌ2Ｏ3皮膜が形成されたニッケル基耐熱合金に対して、６００℃、７００℃、８００℃の各水蒸気中にて５００時間酸化での重量増加挙動を評価した。その結果を図２に示す。 The nickel base heat-resistant alloy having an Al 2 O 3 film formed by heat treatment under this low oxygen partial pressure was evaluated for the weight increase behavior in oxidation for 500 hours in water vapor at 600 ° C., 700 ° C., and 800 ° C. . The result is shown in FIG.
図３は、上記のニッケル基耐熱合金を８００℃水蒸気中で５００時間まで酸化した後の合金断面の電子顕微鏡写真（撮影倍率１００００倍）である。Ａｌ2Ｏ3皮膜の厚さは約１μmであり、水蒸気酸化以前の状態に比べて厚さの増加はほとんど認められなかった。
[比較例１]
上記表１の組成を有し、実施例１の熱処理を行わずに表面を鏡面仕上げしたニッケル基耐熱合金を用意した。
FIG. 3 is an electron micrograph (imaging magnification: 10,000 times) of the alloy cross section after the nickel-base heat-resistant alloy is oxidized in 800 ° C. water vapor for up to 500 hours. The thickness of the Al 2 O 3 film was about 1 μm, and almost no increase in thickness was observed compared to the state before steam oxidation.
[Comparative Example 1]
A nickel-base heat-resistant alloy having the composition shown in Table 1 and having a mirror-finished surface without performing the heat treatment of Example 1 was prepared.
このニッケル基耐熱合金に対して、６００℃、７００℃、８００℃の各水蒸気中にて５００時間酸化での重量増加挙動を評価した。その結果を図４に示す。
図２および図４に示されるように、表面にＡｌ2Ｏ3皮膜が形成された実施例１のニッケル基耐熱合金では、比較例１のニッケル基耐熱合金に比べて、８００℃水蒸気中での酸化増量は約１／１０に、７００℃水蒸気中での酸化増量は約１／２０に、６００℃水蒸気中での酸化増量は約１／３にまで低下した。
With respect to this nickel-based heat-resistant alloy, the weight increase behavior after oxidation for 500 hours in water vapor at 600 ° C., 700 ° C., and 800 ° C. was evaluated. The result is shown in FIG.
As shown in FIGS. 2 and 4, the nickel-base heat-resistant alloy of Example 1 having an Al 2 O 3 film formed on the surface thereof was compared with the nickel-base heat-resistant alloy of Comparative Example 1 in 800 ° C. water vapor. The increase in oxidation was reduced to about 1/10, the increase in oxidation in 700 ° C. water vapor was reduced to about 1/20, and the increase in oxidation in 600 ° C. water vapor was reduced to about 1/3.
図５は、比較例１のニッケル基耐熱合金を８００℃水蒸気中で５００時間まで酸化した後の合金断面の電子顕微鏡写真（撮影倍率１００００倍）である。鏡面仕上げした合金表面には、水蒸気酸化によって、厚さ約６μｍの酸化皮膜が形成されていた。 FIG. 5 is an electron micrograph (imaging magnification of 10,000 times) of the cross section of the alloy after the nickel-based heat-resistant alloy of Comparative Example 1 was oxidized in 800 ° C. water vapor for up to 500 hours. On the mirror-finished alloy surface, an oxide film having a thickness of about 6 μm was formed by steam oxidation.
Claims (12)
The said heat-resistant metal member contains 5.0 mass% or more of aluminum, The manufacturing method of the heat-resistant metal member in any one of Claims 7-11 characterized by the above-mentioned.
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| JP2010005698A (en) * | 2008-06-24 | 2010-01-14 | General Electric Co <Ge> | Alloy casting having protective layer and method of making the same |
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