WO2015133460A1 - High-temperature resistant austenitic stainless steel - Google Patents

High-temperature resistant austenitic stainless steel Download PDF

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WO2015133460A1
WO2015133460A1 PCT/JP2015/056177 JP2015056177W WO2015133460A1 WO 2015133460 A1 WO2015133460 A1 WO 2015133460A1 JP 2015056177 W JP2015056177 W JP 2015056177W WO 2015133460 A1 WO2015133460 A1 WO 2015133460A1
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stainless steel
weight
austenitic stainless
steel
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林　重成
大貴 工藤
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国立大学法人北海道大学
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium

Definitions

  • the present invention relates to a high heat resistant austenitic stainless steel.
  • heat-resistant austenitic stainless steel Fe-Ni-Cr steel
  • Fe-Ni-Cr steel which is widely used in the industry, forms an alloy by forming chromia scale (chromium oxide) on the surface of the alloy in a high temperature corrosion oxidation environment. It is known to protect against a high temperature corrosion oxidation environment (for example, Patent Document 1). Therefore, heat-resistant austenitic stainless steel is widely used in high-temperature operating devices such as thermal power boilers and chemical plants.
  • Non-Patent Document 1 the oxidation resistance of chromia scale is remarkably inferior at temperatures of 800 ° C. or higher, and the chromia scale has no corrosion resistance against carbon and sulfur components contained in the environment where high-temperature operating equipment is exposed. There are problems such as not having. For this reason, development of austenitic stainless steel in which an alumina scale is formed on the surface instead of chromia scale is required (for example, Non-Patent Document 1).
  • Ni phase which is mainly composed of Ni—Al
  • an object of the present invention is to provide a high heat-resistant austenitic stainless steel that can form an alumina scale and can ensure good productivity.
  • the present invention comprises 10 to 30% by weight of Ni, 10 to 25% by weight of Cr, 0.01 to 0.1% by weight of at least one selected from the group consisting of Zr, Hf, Y and La, and Cu.
  • a high heat-resistant austenitic stainless steel containing 4.2 to 8.5% by weight and less than 6% by weight of Al and containing Fe as the balance is provided. With such a stainless steel, an alumina scale can be formed in a high-temperature corrosion oxidation environment, and a decrease in productivity as a stainless steel due to the formation of a ⁇ prime phase or a ⁇ phase can be suppressed.
  • Al is preferably contained in an amount of 2 wt% or more and less than 6 wt%. Thereby, it becomes easier to form an alumina scale.
  • the present invention it is possible to provide a high heat-resistant austenitic stainless steel that not only forms an alumina scale on the surface but also suppresses the formation of intermetallic compounds such as the aforementioned ⁇ prime phase and ⁇ phase. it can. That is, according to the present invention, it is possible to provide a high heat-resistant austenitic stainless steel that is excellent in high-temperature oxidation resistance and can ensure mass productivity such as hot rolling and maintain excellent weldability.
  • the high heat resistant austenitic stainless steel of this embodiment is selected from the group consisting of 10 to 30 wt% Ni, 10 to 25 wt% Cr, Zr, Hf, Y and La based on the total weight of the stainless steel. At least one of these is contained in an amount of 0.01 to 0.1% by weight, Cu is contained in an amount of 4.2 to 8.5% by weight, Al is contained in an amount of less than 6% by weight, and the balance is Fe.
  • the reason for defining the metal composition of the austenitic stainless steel as described above is as follows.
  • Ni is one of the elements that is the second most abundant after Fe and functions as an element for maintaining the austenite phase.
  • the Ni content is 10% by weight or more, sufficient retention of the austenite phase can be ensured, but it is desirable to reduce the Ni content as much as possible in order to reduce costs.
  • the Ni content is generally at least about 25% by weight.
  • the austenitic stainless steel according to this embodiment in which the Cu and Al contents are adjusted as described above.
  • the upper limit of the amount of Ni that causes an increase in manufacturing cost can be set to 20% by weight. From such a viewpoint, the Ni content is preferably 10 to 25% by weight, and more preferably 10 to 20% by weight.
  • [Cr] Cr is one of the most abundant elements after Fe, and functions as an element that improves corrosion resistance.
  • the Cr content is 10% by weight or more, sufficient corrosion resistance can be ensured.
  • the Cr content is preferably 13 to 23% by weight, and more preferably 15 to 20% by weight.
  • [Zr, Hf, Y and La] These elements function as elements that improve the growth rate and peel resistance of the alumina scale.
  • the content of at least one selected from the group consisting of Zr, Hf, Y and La is 0.01% by weight or more, the peel resistance of the alumina scale can be improved, while 0.1% By being less than wt%, it is possible to suppress a decrease in oxidation resistance due to internal oxidation of these elements.
  • the content of these elements is preferably 0.01 to 0.07% by weight, and more preferably 0.01 to 0.05% by weight.
  • [Cu] Cu functions as an element for maintaining the austenite phase and assisting the formation of alumina scale.
  • the Cu content is 4.2% by weight or more, a high-quality alumina scale can be formed even if the Al content is less than 6% by weight, while the Cu content is 8.5% by weight or less.
  • the formation of Cu precipitates in the alloy can be suppressed.
  • the Cu content is preferably 5.0 to 8.5% by weight, and more preferably 5.0 to 6.5% by weight.
  • Al is an element contained for the purpose of forming an alumina scale on the stainless steel surface.
  • the Al content is less than 6% by weight, formation of extremely brittle and hard intermetallic compounds mainly composed of Ni 3 -Al called ⁇ prime phase and Ni-Al called ⁇ phase is sufficiently suppressed. be able to.
  • the Al content is preferably 2% by weight or more. From such a viewpoint, the content of Al is preferably 2.5% by weight or more and less than 5% by weight, and more preferably 3% by weight or more and less than 4.5% by weight.
  • Fe is an element constituting the main component of austenitic stainless steel. What is necessary is just to let the content of Fe be the remainder which deducted the total content of each said component from the total weight of stainless steel.
  • the stainless steel may contain a small amount of impurities.
  • the impurities are components that may be mixed due to various factors of raw materials such as ores and scraps and manufacturing processes when industrially manufacturing stainless steel, and in the present embodiment It means that it is allowed as long as it does not affect the desired effect.
  • elements such as C, P, S, Mn, and Si are listed as impurity elements.
  • the total content of at least one selected from the group consisting of Fe, Ni, Cr, Zr, Hf, Y and La, Cu and Al is based on the total weight of the stainless steel. It is preferably 95% by weight or more, and more preferably 97% by weight or more.
  • austenitic stainless steel can be analyzed qualitatively and quantitatively by, for example, dry EPMA, QV, EDS, wet ICP and the like.
  • the method for producing the austenitic stainless steel of this embodiment is not particularly limited.
  • it is generally used in the steel industry such as argon arc melting and casting (melting is preferably performed at 1400 ° C. or higher), converters and electric furnaces.
  • It can be produced by a general method such as a typical steel production method, a hot rolling method (rolling is preferably performed at about 800 to 1200 ° C.), rolling in the atmosphere, and the like.
  • the formation of intermetallic compounds mainly composed of Ni 3 -Al or Ni-Al is significantly suppressed.
  • the content of the intermetallic compound mainly containing Ni—Al is preferably less than 1% by volume, more preferably less than 0.5% by volume, and preferably 0% by volume. Further preferred.
  • the austenitic stainless steel of this embodiment is exposed to a high-temperature corrosion oxidation environment while the formation of such intermetallic compounds is suppressed (that is, the Al content is sufficiently reduced).
  • a high-quality alumina scale is formed on the surface.
  • the high temperature corrosion oxidation environment has a temperature of 700 to 1100 ° C., for example, and the atmosphere contains an oxidizing / corrosive gas such as oxygen, water vapor, hydrocarbon, carbon monoxide, carbon dioxide, hydrogen sulfide, and sulfur dioxide.
  • an oxidizing / corrosive gas such as oxygen, water vapor, hydrocarbon, carbon monoxide, carbon dioxide, hydrogen sulfide, and sulfur dioxide.
  • the alumina scale is sufficiently formed immediately when exposed to such a high temperature corrosion oxidation environment.
  • the stainless steel of this embodiment having an alumina scale formed on the surface can exhibit excellent heat resistance (oxidation resistance) even at an extremely high temperature (for example, 700 to 1100 ° C.).
  • oxidation resistance for example, 700 to 1100 ° C.
  • the alumina scale grows with the passage of time exposed to the high temperature corrosion oxidation environment, its thickness is not particularly limited, but in order to obtain sufficient oxidation resistance, the formed alumina scale The thickness is preferably about 0.01 to 20 ⁇ m.
  • the appearance of the alumina scale and the intermetallic compound mainly composed of Ni 3 -Al or Ni-Al in the cross section of the austenitic stainless steel can be observed using SEM or EPMA.
  • Austenitic stainless steel having the metal composition shown in Table 1 was melted in an argon arc melting furnace.
  • the obtained ingot was about 40 g (diameter: about 15 mm ⁇ length: about 100 mm). Thereafter, heat treatment for homogenizing the composition was performed at 1200 ° C. for 48 hours.
  • the sample steel for the X-ray-diffraction test for a high temperature oxidation test, a structure observation, and a phase identification was acquired from the said ingot.
  • the shape of the sample steel was coin-shaped and had a diameter of about 15 mm ⁇ thickness of about 2 mm.
  • the high-temperature oxidation test was conducted using a box-type electric furnace.
  • the sample steel was suspended in an alumina crucible using an alumina rod and subjected to isothermal oxidation at 1000 ° C. in a static atmosphere.
  • the heating rate was 10 ° C./min
  • the cooling rate after the oxidation test was 10 ° C./min.
  • the weight change after oxidation according to the elapsed time was measured using an electronic balance. The evaluation results are shown in FIGS. As shown in FIG.
  • FIG. 4 shows the results of cross-sectional SEM observation on the sample steel 8.
  • the figure shows the state of the sample steel 8 after 16 hours in the high temperature oxidation test.
  • a good quality alumina scale was formed on the surface of the sample steel 8.
  • no ⁇ prime phase or ⁇ phase was observed in the sample steel 8.
  • the part which looks a little black inside the sample steel is a polishing flaw.
  • the analysis result of EPMA with respect to the sample steel 2 is shown as an example.
  • FIG. 6 shows an X-ray diffraction chart for the sample steel 1 as an example. It can be seen that the sample steel 1 is a single austenite phase.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
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  • Organic Chemistry (AREA)
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Abstract

　The purpose of the present invention is to provide a high-temperature resistant austenitic stainless steel, with which resistance to oxidation at high temperature can be obtained through formation of alumina scale, and with which good productivity is ensured. This austenitic stainless steel contains 10-30 wt% of Ni, 10-25 wt% of Cr, 0.01-0.1 wt% of at least one element selected from the group consisting of Zr, Hf, Y, and La, 4.2-8.5 wt% of Cu, and less than 6 wt% of Al, the remainder being Fe.

Description

高耐熱オーステナイト系ステンレス鋼High heat resistant austenitic stainless steel
　本発明は高耐熱オーステナイト系ステンレス鋼に関する。 The present invention relates to a high heat resistant austenitic stainless steel.
　現状、産業界で広く用いられている耐熱オーステナイト系ステンレス鋼（Ｆｅ－Ｎｉ－Ｃｒ鋼）は、高温腐食酸化環境下で合金表面にクロミアスケール（クロムの酸化物）を形成することで、合金を高温腐食酸化環境から保護することが知られている（例えば、特許文献１）。そのため、耐熱オーステナイト系ステンレス鋼は、火力発電ボイラー、化学プラント等の高温稼働機器で広く用いられている。 At present, heat-resistant austenitic stainless steel (Fe-Ni-Cr steel), which is widely used in the industry, forms an alloy by forming chromia scale (chromium oxide) on the surface of the alloy in a high temperature corrosion oxidation environment. It is known to protect against a high temperature corrosion oxidation environment (for example, Patent Document 1). Therefore, heat-resistant austenitic stainless steel is widely used in high-temperature operating devices such as thermal power boilers and chemical plants.
　しかしながら、クロミアスケールの耐酸化性は８００℃以上の温度では著しく劣ること、さらに高温稼働機器が曝される環境中に含まれる炭素や硫黄成分に対しては、当該クロミアスケールは全く耐腐食性を有していないこと等の問題がある。このことから、クロミアスケールに代えてアルミナスケールが表面に形成されるオーステナイト系ステンレス鋼の開発が要求されている（例えば、非特許文献１）。 However, the oxidation resistance of chromia scale is remarkably inferior at temperatures of 800 ° C. or higher, and the chromia scale has no corrosion resistance against carbon and sulfur components contained in the environment where high-temperature operating equipment is exposed. There are problems such as not having. For this reason, development of austenitic stainless steel in which an alumina scale is formed on the surface instead of chromia scale is required (for example, Non-Patent Document 1).
特開平９－１９５００７号公報Japanese Patent Laid-Open No. 9-195007
　ところで、高温腐食酸化環境にも耐えうるアルミナスケールを形成するためには、合金中に高濃度でアルミニウムを添加する必要があるが、その結果、合金中にγプライム相と呼ばれるＮｉ３―Ａｌやβ相と呼ばれるＮｉ－Ａｌを主成分とする極めて脆くて硬い金属間化合物が形成されてしまう。このような相がオーステナイト系ステンレス鋼中に形成されると、熱間圧延等の大量生産が不可能になること、またそもそもアルミニウムの高濃度添加により溶接性が著しく低下してしまうこと等から、ステンレス鋼としての生産性を確保することが難しくなる。 By the way, in order to form an alumina scale that can withstand a high temperature corrosion oxidation environment, it is necessary to add aluminum at a high concentration in the alloy. As a result, Ni 3 -Al or so called γ prime phase is added to the alloy. An extremely brittle and hard intermetallic compound called Ni phase, which is mainly composed of Ni—Al, is formed. When such a phase is formed in austenitic stainless steel, mass production such as hot rolling becomes impossible, and weldability is significantly reduced due to high concentration of aluminum in the first place. It becomes difficult to ensure the productivity as stainless steel.
　そこで本発明は、アルミナスケールを形成可能でありなおかつ良好な生産性を確保することができる、高耐熱オーステナイト系ステンレス鋼を提供することを目的とする。 Therefore, an object of the present invention is to provide a high heat-resistant austenitic stainless steel that can form an alumina scale and can ensure good productivity.
　発明者らが鋭意検討した結果、合金組成中にＣｕとＡｌとをそれぞれ所定量含有させることにより、上記課題を達成することができることを見出した。 As a result of intensive studies by the inventors, it has been found that the above-mentioned problems can be achieved by containing a predetermined amount of Cu and Al in the alloy composition.
　すなわち本発明は、Ｎｉを１０～３０重量％、Ｃｒを１０～２５重量％、Ｚｒ、Ｈｆ、Ｙ及びＬａからなる群より選択される少なくとも一種を０．０１～０．１重量％、Ｃｕを４．２～８．５重量％並びにＡｌを６重量％未満含有し、残部としてＦｅを含有する、高耐熱オーステナイト系ステンレス鋼を提供するものである。このようなステンレス鋼であれば、高温腐食酸化環境においてアルミナスケールを形成可能であるとともに、γプライム相やβ相形成によるステンレス鋼としての生産性の低下を抑制することができる。 That is, the present invention comprises 10 to 30% by weight of Ni, 10 to 25% by weight of Cr, 0.01 to 0.1% by weight of at least one selected from the group consisting of Zr, Hf, Y and La, and Cu. A high heat-resistant austenitic stainless steel containing 4.2 to 8.5% by weight and less than 6% by weight of Al and containing Fe as the balance is provided. With such a stainless steel, an alumina scale can be formed in a high-temperature corrosion oxidation environment, and a decrease in productivity as a stainless steel due to the formation of a γ prime phase or a β phase can be suppressed.
　本発明において、Ａｌを２重量％以上６重量％未満含有することが好ましい。これにより、アルミナスケールをより形成し易くなる。 In the present invention, Al is preferably contained in an amount of 2 wt% or more and less than 6 wt%. Thereby, it becomes easier to form an alumina scale.
　本発明によれば、アルミナスケールを表面に形成できるだけでなく、その内部において、前述のγプライム相やβ相といった金属間化合物の形成が抑制された、高耐熱オーステナイト系ステンレス鋼を提供することができる。すなわち本発明により、耐高温酸化性に優れるとともに、熱間圧延等の大量生産性の確保や優れた溶接性の維持を図ることができる、高耐熱オーステナイト系ステンレス鋼を提供することができる。 According to the present invention, it is possible to provide a high heat-resistant austenitic stainless steel that not only forms an alumina scale on the surface but also suppresses the formation of intermetallic compounds such as the aforementioned γ prime phase and β phase. it can. That is, according to the present invention, it is possible to provide a high heat-resistant austenitic stainless steel that is excellent in high-temperature oxidation resistance and can ensure mass productivity such as hot rolling and maintain excellent weldability.
１０００℃、大気中での高温酸化試験における経過時間と試料鋼の質量変化との関係を示す図である。It is a figure which shows the relationship between the elapsed time in the high temperature oxidation test in 1000 degreeC and air | atmosphere, and the mass change of sample steel. １００時間の高温酸化試験後における試料鋼中のＣｕ含有量と試料鋼の質量変化との関係を示す図である。It is a figure which shows the relationship between Cu content in the sample steel after 100-hour high temperature oxidation test, and the mass change of sample steel. 高温酸化試験後の試料鋼の断面ＳＥＭ写真を示す図である。It is a figure which shows the cross-sectional SEM photograph of the sample steel after a high temperature oxidation test. 高温酸化試験後の試料鋼の断面ＳＥＭ写真を示す図である。It is a figure which shows the cross-sectional SEM photograph of the sample steel after a high temperature oxidation test. 高温酸化試験後の試料鋼のＥＰＭＡ分析結果を示す図である。It is a figure which shows the EPMA analysis result of the sample steel after a high temperature oxidation test. 高温酸化試験前の試料鋼のＸ線回折チャートを示す図である。It is a figure which shows the X-ray-diffraction chart of the sample steel before a high temperature oxidation test.
　以下、本発明を実施するための形態についてさらに詳細に説明するが、本発明は、以下の実施形態に限定されるものではない。 Hereinafter, modes for carrying out the present invention will be described in more detail, but the present invention is not limited to the following embodiments.
　本実施形態の高耐熱オーステナイト系ステンレス鋼は、当該ステンレス鋼の全重量を基準として、Ｎｉを１０～３０重量％、Ｃｒを１０～２５重量％、Ｚｒ、Ｈｆ、Ｙ及びＬａからなる群より選択される少なくとも一種を０．０１～０．１重量％、Ｃｕを４．２～８．５重量％並びにＡｌを６重量％未満含有し、残部としてＦｅを含有する。本実施形態において、オーステナイト系ステンレス鋼の金属組成を上記のとおり規定する理由は次のとおりである。 The high heat resistant austenitic stainless steel of this embodiment is selected from the group consisting of 10 to 30 wt% Ni, 10 to 25 wt% Cr, Zr, Hf, Y and La based on the total weight of the stainless steel. At least one of these is contained in an amount of 0.01 to 0.1% by weight, Cu is contained in an amount of 4.2 to 8.5% by weight, Al is contained in an amount of less than 6% by weight, and the balance is Fe. In the present embodiment, the reason for defining the metal composition of the austenitic stainless steel as described above is as follows.
［Ｎｉ］　ＮｉはＦｅに次いで多く含まれる元素の１つであり、オーステナイト相を保持するための元素として機能する。Ｎｉの含有量が１０重量％以上であることにより、オーステナイト相の保持能を十分に確保することができるが、コスト抑制のためにはＮｉ含有量をできるだけ低減することが望まれる。なお、耐熱オーステナイト系ステンレス鋼において、一般的にＮｉの含有量は少なくとも２５重量％程度用いられるものであったが、ＣｕやＡｌの含有量が上記のとおり調整された本実施形態のオーステナイト系ステンレス鋼によれば、製造コスト上昇の原因となっているＮｉ量の上限値を２０重量％とすることが可能である。このような観点から、Ｎｉの含有量は１０～２５重量％であることが好ましく、１０～２０重量％であることがより好ましい。 [Ni] Ni is one of the elements that is the second most abundant after Fe and functions as an element for maintaining the austenite phase. When the Ni content is 10% by weight or more, sufficient retention of the austenite phase can be ensured, but it is desirable to reduce the Ni content as much as possible in order to reduce costs. In the heat-resistant austenitic stainless steel, the Ni content is generally at least about 25% by weight. However, the austenitic stainless steel according to this embodiment in which the Cu and Al contents are adjusted as described above. According to steel, the upper limit of the amount of Ni that causes an increase in manufacturing cost can be set to 20% by weight. From such a viewpoint, the Ni content is preferably 10 to 25% by weight, and more preferably 10 to 20% by weight.
［Ｃｒ］　ＣｒはＦｅに次いで多く含まれる元素の１つであり、耐食性を向上する元素として機能する。Ｃｒの含有量が１０重量％以上であることにより、耐食能を十分に確保することができ、一方で２５重量％以下であることにより、オーステナイト相を保持するためのＮｉ等の必要量を抑えることができ、またオーステナイト系ステンレス鋼の製造性や加工性を確保することができる。このような観点から、Ｃｒの含有量は１３～２３重量％であることが好ましく、１５～２０重量％であることがより好ましい。 [Cr] Cr is one of the most abundant elements after Fe, and functions as an element that improves corrosion resistance. When the Cr content is 10% by weight or more, sufficient corrosion resistance can be ensured. On the other hand, when it is 25% by weight or less, the necessary amount of Ni or the like for holding the austenite phase is suppressed. It is also possible to ensure the manufacturability and workability of the austenitic stainless steel. From such a viewpoint, the Cr content is preferably 13 to 23% by weight, and more preferably 15 to 20% by weight.
［Ｚｒ、Ｈｆ、Ｙ及びＬａ］
　これらの元素はアルミナスケールの成長速度や耐はく離性を向上する元素として機能する。Ｚｒ、Ｈｆ、Ｙ及びＬａからなる群より選択される少なくとも一種の含有量が０．０１重量％以上であることにより、アルミナスケールの耐はく離性を向上することができ、一方で、０．１重量％以下であることにより、これらの元素が内部酸化することによる耐酸化性の低下を抑制することができる。このような観点から、これらの元素の含有量は０．０１～０．０７重量％であることが好ましく、０．０１～０．０５重量％であることがより好ましい。 [Zr, Hf, Y and La]
These elements function as elements that improve the growth rate and peel resistance of the alumina scale. When the content of at least one selected from the group consisting of Zr, Hf, Y and La is 0.01% by weight or more, the peel resistance of the alumina scale can be improved, while 0.1% By being less than wt%, it is possible to suppress a decrease in oxidation resistance due to internal oxidation of these elements. From such a viewpoint, the content of these elements is preferably 0.01 to 0.07% by weight, and more preferably 0.01 to 0.05% by weight.
［Ｃｕ］　Ｃｕはオーステナイト相を保持するための、及びアルミナスケールの形成を補助するための元素として機能する。Ｃｕの含有量が４．２重量％以上であることにより、Ａｌの含有量が６重量％未満であっても良質なアルミナスケールを形成することができ、一方で、８．５重量％以下であることにより、合金中におけるＣｕ析出物の形成を抑制することができる。このような観点から、Ｃｕの含有量は５．０～８．５重量％であることが好ましく、５．０～６．５重量％であることがより好ましい。 [Cu] Cu functions as an element for maintaining the austenite phase and assisting the formation of alumina scale. When the Cu content is 4.2% by weight or more, a high-quality alumina scale can be formed even if the Al content is less than 6% by weight, while the Cu content is 8.5% by weight or less. By being, the formation of Cu precipitates in the alloy can be suppressed. From such a viewpoint, the Cu content is preferably 5.0 to 8.5% by weight, and more preferably 5.0 to 6.5% by weight.
［Ａｌ］　Ａｌはステンレス鋼表面にアルミナスケールを形成することを目的として含有される元素である。Ａｌの含有量が６重量％未満であることにより、γプライム相と呼ばれるＮｉ３―Ａｌやβ相と呼ばれるＮｉ－Ａｌを主成分とする極めて脆くて硬い金属間化合物の形成を十分に抑制することができる。一方で、適度な厚みのアルミナスケールを形成し易くするためには、Ａｌの含有量が２重量％以上であることが好ましい。このような観点から、Ａｌの含有量は２．５重量％以上５重量％未満であることが好ましく、３重量％以上４．５重量％未満であることがより好ましい。 [Al] Al is an element contained for the purpose of forming an alumina scale on the stainless steel surface. When the Al content is less than 6% by weight, formation of extremely brittle and hard intermetallic compounds mainly composed of Ni 3 -Al called γ prime phase and Ni-Al called β phase is sufficiently suppressed. be able to. On the other hand, in order to easily form an alumina scale having an appropriate thickness, the Al content is preferably 2% by weight or more. From such a viewpoint, the content of Al is preferably 2.5% by weight or more and less than 5% by weight, and more preferably 3% by weight or more and less than 4.5% by weight.
［Ｆｅ］　Ｆｅはオーステナイト系ステンレス鋼の主成分を構成する元素である。Ｆｅの含有量は、ステンレス鋼の全重量から上記各成分の合計含有量を差し引いた残部とすればよい。 [Fe] Fe is an element constituting the main component of austenitic stainless steel. What is necessary is just to let the content of Fe be the remainder which deducted the total content of each said component from the total weight of stainless steel.
　本実施形態において、ステンレス鋼には不純物が微量に含まれうる。ここで、不純物とは、ステンレス鋼を工業的に製造する際に、鉱石、スクラップ等のような原料や、製造工程の種々の要因によって混入する可能性のある成分であって、本実施形態における所望の効果発現に影響を与えない範囲で許容されるものを意味する。具体的には、Ｃ、Ｐ、Ｓ、Ｍｎ、Ｓｉ等の元素が、不純物元素として挙げられる。このような観点から、本実施形態においてＦｅ、Ｎｉ、Ｃｒ、Ｚｒ、Ｈｆ、Ｙ及びＬａからなる群より選択される少なくとも一種、Ｃｕ並びにＡｌの合計含有量は、ステンレス鋼の全重量を基準として９５重量％以上であることが好ましく、９７重量％以上であることがより好ましい。 In this embodiment, the stainless steel may contain a small amount of impurities. Here, the impurities are components that may be mixed due to various factors of raw materials such as ores and scraps and manufacturing processes when industrially manufacturing stainless steel, and in the present embodiment It means that it is allowed as long as it does not affect the desired effect. Specifically, elements such as C, P, S, Mn, and Si are listed as impurity elements. From such a viewpoint, in this embodiment, the total content of at least one selected from the group consisting of Fe, Ni, Cr, Zr, Hf, Y and La, Cu and Al is based on the total weight of the stainless steel. It is preferably 95% by weight or more, and more preferably 97% by weight or more.
　なお、オーステナイト系ステンレス鋼に含まれるこれらの元素は、例えば、乾式ＥＰＭＡ、ＱＶ、ＥＤＳ、湿式ＩＣＰ等により定性的かつ定量的に分析することができる。 Note that these elements contained in austenitic stainless steel can be analyzed qualitatively and quantitatively by, for example, dry EPMA, QV, EDS, wet ICP and the like.
　本実施形態のオーステナイト系ステンレス鋼の製造方法は特に限定されず、例えば、アルゴンアーク溶解と鋳造（溶解は１４００℃以上で行われることが好ましい）、転炉や電炉等の鉄鋼業で用いられる一般的な鋼の製造方法、熱間圧延法（圧延は８００～１２００℃程度で行われることが好ましい）、大気中での圧延などのような一般的な方法により製造することができる。 The method for producing the austenitic stainless steel of this embodiment is not particularly limited. For example, it is generally used in the steel industry such as argon arc melting and casting (melting is preferably performed at 1400 ° C. or higher), converters and electric furnaces. It can be produced by a general method such as a typical steel production method, a hot rolling method (rolling is preferably performed at about 800 to 1200 ° C.), rolling in the atmosphere, and the like.
　上記のようにして得られる本実施形態のステンレス鋼中では、Ｎｉ３―ＡｌやＮｉ－Ａｌを主成分とする金属間化合物の形成が有意に抑制されている。この時、特にＮｉ－Ａｌを主成分とする当該金属間化合物の含有量は１体積％未満であることが好ましく、０．５体積％未満であることがより好ましく、０体積％であることがさらに好ましい。 In the stainless steel of the present embodiment obtained as described above, the formation of intermetallic compounds mainly composed of Ni 3 -Al or Ni-Al is significantly suppressed. At this time, the content of the intermetallic compound mainly containing Ni—Al is preferably less than 1% by volume, more preferably less than 0.5% by volume, and preferably 0% by volume. Further preferred.
　また、本実施形態のオーステナイト系ステンレス鋼は、このような金属間化合物の形成が抑制されている（すなわち、Ａｌの含有量が十分に低減されている）一方で、高温腐食酸化環境に曝されることにより、表面に良質なアルミナスケールが形成される。ここで、高温腐食酸化環境とは、例えば温度が７００～１１００℃であり、雰囲気が酸素、水蒸気、炭化水素、一酸化炭素、二酸化炭素、硫化水素、二酸化硫黄等の酸化・腐食性ガスを含む環境のことを言う。本実施形態においては、このような高温腐食酸化環境に暴露された場合に直ちにアルミナスケールが十分に形成されることが好ましい。表面にアルミナスケールが形成された本実施形態のステンレス鋼であれば、極めて高い温度（例えば７００～１１００℃）においても優れた耐熱性（耐酸化性）を示すことができる。なお、アルミナスケールは高温腐食酸化環境に暴露される時間経過に伴って成長するため、その厚みは特に限定されるものではないが、十分な耐酸化性を得るためには、形成されるアルミナスケールの厚みが０．０１～２０μｍ程度であることが好ましい。 Further, the austenitic stainless steel of this embodiment is exposed to a high-temperature corrosion oxidation environment while the formation of such intermetallic compounds is suppressed (that is, the Al content is sufficiently reduced). As a result, a high-quality alumina scale is formed on the surface. Here, the high temperature corrosion oxidation environment has a temperature of 700 to 1100 ° C., for example, and the atmosphere contains an oxidizing / corrosive gas such as oxygen, water vapor, hydrocarbon, carbon monoxide, carbon dioxide, hydrogen sulfide, and sulfur dioxide. Say the environment. In the present embodiment, it is preferable that the alumina scale is sufficiently formed immediately when exposed to such a high temperature corrosion oxidation environment. The stainless steel of this embodiment having an alumina scale formed on the surface can exhibit excellent heat resistance (oxidation resistance) even at an extremely high temperature (for example, 700 to 1100 ° C.). In addition, since the alumina scale grows with the passage of time exposed to the high temperature corrosion oxidation environment, its thickness is not particularly limited, but in order to obtain sufficient oxidation resistance, the formed alumina scale The thickness is preferably about 0.01 to 20 μm.
　オーステナイト系ステンレス鋼の断面における、上記アルミナスケール及びＮｉ３―ＡｌやＮｉ－Ａｌを主成分とする金属間化合物の形成の様子は、ＳＥＭやＥＰＭＡを用いて観察することができる。 The appearance of the alumina scale and the intermetallic compound mainly composed of Ni 3 -Al or Ni-Al in the cross section of the austenitic stainless steel can be observed using SEM or EPMA.
　以下、本発明の好適な実施例についてさらに詳細に説明するが、本発明はこれらの実施例に限定されるものではない。
［試料鋼の製造］ EXAMPLES Hereinafter, although the preferable Example of this invention is described in detail, this invention is not limited to these Examples.
[Production of sample steel]
　表１に示す金属組成を有するオーステナイト系ステンレス鋼を、アルゴンアーク溶解炉にて溶製した。得られたインゴットは、約４０ｇ（直径約１５ｍｍ×長さ約１００ｍｍ）であった。その後、１２００℃で４８時間かけて組成均質化のための熱処理を施した。そして、当該インゴットから、高温酸化試験用、組織観察用及び相同定のためのＸ線回折試験用の試料鋼を取得した。試料鋼の形状はコイン状であり、直径約１５ｍｍｘ厚さ約２ｍｍのサイズであった。 Austenitic stainless steel having the metal composition shown in Table 1 was melted in an argon arc melting furnace. The obtained ingot was about 40 g (diameter: about 15 mm × length: about 100 mm). Thereafter, heat treatment for homogenizing the composition was performed at 1200 ° C. for 48 hours. And the sample steel for the X-ray-diffraction test for a high temperature oxidation test, a structure observation, and a phase identification was acquired from the said ingot. The shape of the sample steel was coin-shaped and had a diameter of about 15 mm × thickness of about 2 mm.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
［試料鋼の各種評価］
　上記のとおり準備をした各試料鋼について、次の評価を実施した。 [Various evaluation of sample steel]
The following evaluation was performed about each sample steel prepared as mentioned above.
Ａ：高温酸化試験
　高温酸化性試験は、ボックス型の電気炉を用いて実施した。試料鋼をアルミナ性のるつぼ中にアルミナ棒を用いて吊し、１０００℃、静止大気中にて等温酸化した。加熱速度は１０℃／分、また酸化試験終了後の冷却速度は１０℃／分とした。酸化試験前の各試料鋼を基準として、経過時間に応じた酸化後の重量変化を電子天秤を用いて測定した。評価結果を図１及び図２に示す。図１に示すとおり、試料鋼５～７においては酸化試験後の質量変化が大きかったが、試料鋼１～４においては酸化試験後の質量変化が極めて小さかった。すなわち、図２に示すとおり、Ｃｕの含有量を４．２重量％以上とすることにより、高温での優れた耐酸化性を示すことが分かった。 A: High-temperature oxidation test The high-temperature oxidation test was conducted using a box-type electric furnace. The sample steel was suspended in an alumina crucible using an alumina rod and subjected to isothermal oxidation at 1000 ° C. in a static atmosphere. The heating rate was 10 ° C./min, and the cooling rate after the oxidation test was 10 ° C./min. Using each sample steel before the oxidation test as a reference, the weight change after oxidation according to the elapsed time was measured using an electronic balance. The evaluation results are shown in FIGS. As shown in FIG. 1, the change in mass after the oxidation test was large in the sample steels 5 to 7, but the change in mass after the oxidation test was extremely small in the sample steels 1 to 4. That is, as shown in FIG. 2, it was found that excellent oxidation resistance at high temperatures was exhibited by setting the Cu content to 4.2 wt% or more.
Ｂ：組織観察
　上記Ａの高温酸化試験に付した試料鋼を冷間加工樹脂に埋没後、切断研磨して、ＳＥＭ（走査型電子顕微鏡）及びＥＰＭＡを用いて観察及び組成分析を行った。ＳＥＭ観察の結果、試料鋼１～４については、表面に良質なアルミナスケールが形成されていた。またγプライム相やβ相は観察されなかった。一方、試料鋼５～７については、良質なアルミナスケールは形成されていなかった。また、試料鋼７ではβ相も観察された。図３に、一例として試料鋼２、５、６及び７に対する断面ＳＥＭ観察の結果を示す（それぞれ（ａ）、（ｂ）、（ｃ）、（ｄ））。特に試料鋼５、６及び７においては、十分なアルミナスケールが形成されていないため内部酸化が起こっており、さらに試料鋼７においてはβ相が形成されていることが見て取れる。また、図４に、試料鋼８に対する断面ＳＥＭ観察の結果を示す。なお、同図は上記高温酸化試験での１６時間後における試料鋼８の状態を示している。試料鋼１～４と同様に、試料鋼８の表面には良質なアルミナスケールが形成されていた。また、試料鋼８内部にはγプライム相やβ相は観察されなかった。なお、図４中、試料鋼内部にてやや黒く見える部分は研磨傷である。 B: Microstructure observation The sample steel subjected to the high-temperature oxidation test of A was embedded in a cold-working resin, cut and polished, and observed and analyzed for composition using SEM (scanning electron microscope) and EPMA. As a result of SEM observation, a high-quality alumina scale was formed on the surface of sample steels 1 to 4. Neither γ prime phase nor β phase was observed. On the other hand, good quality alumina scale was not formed for sample steels 5-7. In the sample steel 7, a β phase was also observed. In FIG. 3, the result of the cross-sectional SEM observation with respect to sample steel 2, 5, 6 and 7 is shown as an example (respectively (a), (b), (c), (d)). In particular, it can be seen that in Sample Steels 5, 6 and 7, internal oxidation occurs because a sufficient alumina scale is not formed, and in Sample Steel 7 a β phase is formed. FIG. 4 shows the results of cross-sectional SEM observation on the sample steel 8. The figure shows the state of the sample steel 8 after 16 hours in the high temperature oxidation test. Like the sample steels 1 to 4, a good quality alumina scale was formed on the surface of the sample steel 8. Further, no γ prime phase or β phase was observed in the sample steel 8. In addition, in FIG. 4, the part which looks a little black inside the sample steel is a polishing flaw.
　さらにＥＰＭＡ分析の結果、試料鋼１～４では良質なアルミナスケールが形成されていたにもかかわらず、組成中のＡｌの含有量が極めて少量であり、なおかつγプライム相やβ相と同定される元素分布は観察されなかった。図５には、一例として試料鋼２に対するＥＰＭＡの分析結果を示す。図５において、横軸（距離ｄ）は、試料鋼表面（アルミナスケールを含む、ｄ＝０μｍ）から試料鋼内部（ｄ＝３０μｍ）にかけての分析結果を示している。 Furthermore, as a result of the EPMA analysis, despite the formation of a good quality alumina scale in the sample steels 1 to 4, the content of Al in the composition is very small, and it is identified as the γ prime phase or β phase. Element distribution was not observed. In FIG. 5, the analysis result of EPMA with respect to the sample steel 2 is shown as an example. In FIG. 5, the horizontal axis (distance d) indicates the analysis result from the surface of the sample steel (including alumina scale, d = 0 μm) to the inside of the sample steel (d = 30 μm).
Ｃ：Ｘ線回折試験
　上記Ａの高温酸化試験に付す前の試料鋼について、Ｘ線回折試験を行った。試験の結果、試料鋼１～６については、オーステナイト相単相であった。図６に、一例として、試料鋼１に対するＸ線回折チャートを示す。試料鋼１はオーステナイト相単相であることが見て取れる。 C: X-ray diffraction test The sample steel before being subjected to the high-temperature oxidation test of A above was subjected to an X-ray diffraction test. As a result of the test, the sample steels 1 to 6 were austenite single phase. FIG. 6 shows an X-ray diffraction chart for the sample steel 1 as an example. It can be seen that the sample steel 1 is a single austenite phase.

Claims (2)

  1. 　Ｎｉを１０～３０重量％、Ｃｒを１０～２５重量％、Ｚｒ、Ｈｆ、Ｙ及びＬａからなる群より選択される少なくとも一種を０．０１～０．１重量％、Ｃｕを４．２～８．５重量％並びにＡｌを６重量％未満含有し、残部としてＦｅを含有する、高耐熱オーステナイト系ステンレス鋼。 10 to 30% by weight of Ni, 10 to 25% by weight of Cr, 0.01 to 0.1% by weight of at least one selected from the group consisting of Zr, Hf, Y and La, and 4.2 to 8% of Cu High heat-resistant austenitic stainless steel containing 5% by weight and less than 6% by weight of Al with the balance being Fe.
  2. 　Ａｌを２重量％以上６重量％未満含有する、請求項１記載の高耐熱オーステナイト系ステンレス鋼。 The high heat-resistant austenitic stainless steel according to claim 1, comprising Al in an amount of 2 wt% to less than 6 wt%.
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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58120766A (en) * 1982-01-08 1983-07-18 Japan Atom Energy Res Inst Austenitic stainless steel with superior strength at high temperature
JPS6270553A (en) * 1985-09-24 1987-04-01 Sumitomo Metal Ind Ltd Austenitic steel having superior strength at high temperature
JPH07138708A (en) * 1993-11-18 1995-05-30 Sumitomo Metal Ind Ltd Austenitic steel good in high temperature strength and hot workability
JPH1143748A (en) * 1997-07-23 1999-02-16 Hitachi Ltd High strength austenitic sintered steel, its production and its use
JP2000328198A (en) * 1999-05-11 2000-11-28 Sumitomo Metal Ind Ltd Austenitic stainless steel excellent in hot workability
WO2012176586A1 (en) * 2011-06-24 2012-12-27 新日鐵住金株式会社 Carburization-resistant metal material

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58120766A (en) * 1982-01-08 1983-07-18 Japan Atom Energy Res Inst Austenitic stainless steel with superior strength at high temperature
JPS6270553A (en) * 1985-09-24 1987-04-01 Sumitomo Metal Ind Ltd Austenitic steel having superior strength at high temperature
JPH07138708A (en) * 1993-11-18 1995-05-30 Sumitomo Metal Ind Ltd Austenitic steel good in high temperature strength and hot workability
JPH1143748A (en) * 1997-07-23 1999-02-16 Hitachi Ltd High strength austenitic sintered steel, its production and its use
JP2000328198A (en) * 1999-05-11 2000-11-28 Sumitomo Metal Ind Ltd Austenitic stainless steel excellent in hot workability
WO2012176586A1 (en) * 2011-06-24 2012-12-27 新日鐵住金株式会社 Carburization-resistant metal material

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