JP4490081B2 - High temperature corrosion resistant high chromium iron alloy - Google Patents
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- 230000007797 corrosion Effects 0.000 title claims description 60
- 238000005260 corrosion Methods 0.000 title claims description 60
- 229910000640 Fe alloy Inorganic materials 0.000 title claims description 10
- UPHIPHFJVNKLMR-UHFFFAOYSA-N chromium iron Chemical compound [Cr].[Fe] UPHIPHFJVNKLMR-UHFFFAOYSA-N 0.000 title claims description 9
- 229910045601 alloy Inorganic materials 0.000 claims description 63
- 239000000956 alloy Substances 0.000 claims description 63
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 14
- 229910052804 chromium Inorganic materials 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 8
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- 229910019589 Cr—Fe Inorganic materials 0.000 description 2
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Description
本発明は、発電用ボイラや廃棄物焼却プラント等の高温腐食環境下で使用される、高温耐食性、靭性および高温強度がともに優れる高温耐食性高クロム鉄合金に関するものである。 The present invention relates to a high-temperature corrosion-resistant high chromium iron alloy having excellent high-temperature corrosion resistance, toughness, and high-temperature strength, which is used in a high-temperature corrosion environment such as a power generation boiler and a waste incineration plant.
発電用ボイラのバーナーノズルやディヒューザーコーンならびに廃棄物焼却プラントの配管、火格子等に使用される部材は、化石燃料や廃棄物の燃焼ガス等、硫化物を多量に含む高温腐食雰囲気下において使用されることから、特に優れた耐食性を備えていることが求められている。 Components used in power generation boiler burner nozzles, diffuser cones, waste incineration plant piping, grate, etc., are used in high-temperature corrosive atmospheres that contain a large amount of sulfides such as fossil fuels and waste combustion gases. Therefore, it is required to have particularly excellent corrosion resistance.
硫化物を含む高温腐食雰囲気下において、Crは、最も耐久性のある金属材料であることはよく知られている。しかし、Crは、非常に脆い材料であるために、靱性が必要な構造材料として使用することは難しい。そのため、例えばステンレス鋼のように、CrとNi,Fe等とを組合せた耐食性合金して使用するのが一般的である(例えば、特許文献1,2参照。)。 It is well known that Cr is the most durable metal material in high temperature corrosive atmospheres containing sulfides. However, since Cr is a very brittle material, it is difficult to use it as a structural material that requires toughness. Therefore, it is common to use it as a corrosion resistant alloy in which Cr, Ni, Fe, etc. are combined, such as stainless steel (see, for example, Patent Documents 1 and 2).
上記高温耐食性合金に添加されるCr,FeおよびNiの各元素の役割は、以下のように考えられている。
(1) Cr:Crは、高温耐食性の向上に有効な成分であり、高温耐食性を確保するためには添加量が多いほど好ましい。しかし、Crは、脆性を劣化させる元素であるため、材料の靭性を確保するには、添加量は少ないほうが好ましい。
(2) Ni:Niは、靭性の向上と組織安定性のために有効な成分である。ここで、組織安定性とは、高温に長時間保持した時に、いわゆるシグマ相と呼ばれる脆化相が生成されないことを意味する。Niは、靱性や組織安定性を確保するためには、添加量が多いほど好ましいが、一方で、環境中に含まれるSと結合してNi3S2等の低融点化合物を生成し、材料の耐食性を大幅に低下させる。そのため、高温耐食性の観点からは、Ni添加量は少ない方が好ましい。
(3) Fe:Feは、上記CrとNi以外の残余成分として添加する。また、Feは、最も安価な成分であることから、材料コストを低減するためには、NiよりFeの含有量が多くなることが望ましい。
The role of each element of Cr, Fe and Ni added to the high temperature corrosion resistant alloy is considered as follows.
(1) Cr: Cr is a component effective for improving high-temperature corrosion resistance, and the higher the amount added, the better for ensuring high-temperature corrosion resistance. However, since Cr is an element that deteriorates brittleness, the addition amount is preferably small in order to ensure the toughness of the material.
(2) Ni: Ni is an effective component for improving toughness and structural stability. Here, the term “structural stability” means that an embrittled phase called a sigma phase is not generated when kept at a high temperature for a long time. In order to ensure toughness and structural stability, Ni is preferable as the addition amount increases, but on the other hand, it combines with S contained in the environment to produce a low melting point compound such as Ni 3 S 2 , The corrosion resistance of the is greatly reduced. Therefore, from the viewpoint of high temperature corrosion resistance, it is preferable that the amount of Ni added is small.
(3) Fe: Fe is added as a residual component other than Cr and Ni. Moreover, since Fe is the cheapest component, it is desirable that the Fe content be higher than that of Ni in order to reduce the material cost.
現在、使用されている高温耐食性材料の各合金元素の添加量は、上記の考えをベースに決定されている。例えば、ボイラ燃焼装置のバーナーノズルには、Fe−30Ni−45Cr合金が多く使用されている。この合金は、従来材の中で、Crの含有量を極限まで高めたものであるが、靭性の向上と組織安定性とを確保するために、Niを30mass%と多量に添加する必要があった。そのため、このバーナーノズル用合金は、必然的に高温耐食性を犠牲にせざるを得なかった。
上記Fe−30Ni−45Cr合金の高温耐食性は、従来のボイラ燃焼機器の使用環境下であれば、数年ごとに部品交換することによって、問題なく使用することができる。しかし、近年における発電所の連続運転の必要性、CO2量削減のための運転温度の上昇および使用燃料の粗悪化等の要因から、ボイラ用燃焼装置の使用環境(高温腐食)は一段と激しくなってきている。そのため、従来の高温耐食材料では、その使用寿命が短くなりつつあり、より優れた高温耐食性材料の開発が望まれている。 The high temperature corrosion resistance of the Fe-30Ni-45Cr alloy can be used without problems by replacing parts every few years under the usage environment of conventional boiler combustion equipment. However, due to factors such as the necessity of continuous operation of power plants in recent years, an increase in operating temperature to reduce the amount of CO 2 and the deterioration of fuel used, the use environment (high temperature corrosion) of boiler combustion equipment has become more severe. It is coming. For this reason, conventional high-temperature corrosion-resistant materials are becoming shorter in service life, and development of better high-temperature corrosion-resistant materials is desired.
また、先述したように、使用環境の過酷化による高温耐食性部材の寿命低下の問題に対しては、Cr含有量の増加が有効であるが、Cr量の増加は靱性の低下を招く。そのため、新しい高温耐食性材料には、靭性に優れた特性を有することが望まれている。さらに、より厳しい使用環境に対応するためには、高温強度に優れた特性も必要となる。 As described above, an increase in the Cr content is effective for the problem of a decrease in the life of the high-temperature corrosion-resistant member due to a severe use environment, but an increase in the Cr content causes a decrease in toughness. Therefore, new high temperature corrosion resistant materials are desired to have excellent toughness characteristics. Furthermore, in order to cope with a harsher use environment, it is also necessary to have excellent properties at high temperature.
本発明の目的は、従来の高温耐食性材料と比較して、高温耐食性に優れるとともに高温強度と靭性とを向上した高温耐食性高クロム鉄合金を提案することにある。 An object of the present invention is to propose a high-temperature corrosion-resistant high chromium iron alloy that is superior in high-temperature corrosion resistance and improved in high-temperature strength and toughness as compared with conventional high-temperature corrosion-resistant materials.
発明者らは、上記の課題を達成するために、合金の成分組成に着目し、鋭意検討を行った。その結果、Cr含有量を30〜80mass%と高い含有量に限定するとともに不純物の含有量の合計を0.02mass%以下に限定することで、Niを含有しなくとも、高温耐食性を害することなく靱性と相安定性を確保できること、また、この合金に、10mass%以下のWを添加することで、高温強度をより向上させることができること、さらにこれらの合金に、5mass%以下のNiもしくは1mass%以下のNbおよび1mass%以下のTiのいずれか1種または2種を添加することで、より靭性を向上させることができることを見出し、本発明に想到した。 In order to achieve the above-mentioned problems, the inventors focused on the component composition of the alloy and intensively studied. As a result, by limiting the Cr content to a high content of 30 to 80 mass% and limiting the total content of impurities to 0.02 mass% or less, toughness without impairing high-temperature corrosion resistance even if Ni is not contained Phase stability can be ensured, and the addition of 10 mass% or less W to this alloy can further improve the high-temperature strength, and further to these alloys 5 mass% or less Ni or 1 mass% or less. The inventors have found that the toughness can be further improved by adding any one or two of Nb and Ti of 1 mass% or less, and have arrived at the present invention.
上記知見に基づき開発された本発明は、Cr:30〜80mass%、残部がFeおよび不可避的不純物からなる合金であって、前記不可避的不純物であるC,N,P,S,O,Si,Mn,Al,Cu,Pb,Mg,Caの合計が0.02mass%以下であることを特徴とする高温腐食環境下で使用されるシャルピー衝撃値が優れた高温耐食性高クロム鉄合金である。 The present invention was developed based on the above findings, Cr: 30~80mass%, an alloy balance being Fe and unavoidable impurities, the unavoidable impurities C, N, P, S, O, Si, The high-temperature corrosion-resistant high chromium iron alloy having excellent Charpy impact value used in a high-temperature corrosion environment , characterized in that the total of Mn, Al, Cu, Pb, Mg, and Ca is 0.02 mass% or less.
また、本発明は、上記成分組成に加えて、W:10mass%以下を含有したものであることが好ましい。さらに、上記成分組成に加えてさらに、Ni:5mass%以下もしくはNb:1mass%以下およびTi:1mass%以下のいずれか1種または2種を含有したものであることが好ましい。 Moreover, it is preferable that this invention contains W: 10 mass% or less in addition to the said component composition. Further, in addition to the above component composition, Ni: 5 mass% or less, or Nb: 1 mass% or less, and Ti: 1 mass% or less is preferably contained.
本発明によれば、高Cr−Fe系合金の不純物量を低減することにより、従来材と同等以上の高温耐食性と靭性とを有する高温耐食性高クロム鉄合金を得ることができる。また上記合金にWを添加することで、高温強度をより向上した高温耐食性高クロム鉄合金を得ることができる。さらに上記合金に一定量以下のNiあるいは微量のNbまたはTiを添加することで、靱性をより向上した高温耐食性高クロム鉄合金を得ることができる。さらに、本発明の合金を発電用ボイラや廃棄物焼却プラント等の構成部材に適用することにより、構造部材の使用温度の高温化や寿命延長が可能となるため、効率向上による省エネルギーや有害廃棄物の削減に大きく寄与する。 According to the present invention, it is possible to obtain a high-temperature corrosion-resistant high chromium iron alloy having high-temperature corrosion resistance and toughness equivalent to or higher than those of conventional materials by reducing the amount of impurities in the high Cr—Fe-based alloy. Further, by adding W to the above alloy, a high-temperature corrosion-resistant high chromium iron alloy with improved high-temperature strength can be obtained. Further, by adding a certain amount of Ni or a small amount of Nb or Ti to the above alloy, a high temperature corrosion resistant high chromium iron alloy with improved toughness can be obtained. In addition, by applying the alloy of the present invention to components such as power generation boilers and waste incineration plants, it is possible to increase the operating temperature of the structural members and extend the life, so energy saving and hazardous waste by improving efficiency Greatly contributes to the reduction of
まず、本発明に係る高温耐食性、靭性および高温強度に優れる高クロム鉄合金の成分設計思想について説明する。
高温かつ硫化雰囲気中における耐食性を向上させるためには、合金へのCr添加量を増やすことが有効である。しかし、Cr量を多くし過ぎると、靱性が急激に低下することから、Cr含有量の上限は80mass%程度が限界である。また、Niは、高温耐食性を劣化させることから、少ない方が望ましい。そのため、Niを含有しない、60mass%Cr−残部Fe程度の合金が、高温硫化雰囲気中での使用には最も望ましい材料と言える。
First, the component design concept of the high chromium iron alloy excellent in high temperature corrosion resistance, toughness and high temperature strength according to the present invention will be described.
Increasing the amount of Cr added to the alloy is effective for improving the corrosion resistance in a high-temperature and sulfurized atmosphere. However, if the amount of Cr is excessively increased, the toughness rapidly decreases, so the upper limit of the Cr content is about 80 mass%. Moreover, since Ni deteriorates high temperature corrosion resistance, the smaller one is desirable. Therefore, it can be said that an alloy of about 60 mass% Cr-remainder Fe that does not contain Ni is the most desirable material for use in a high-temperature sulfurized atmosphere.
しかしながら、上記60mass%Cr−Fe系合金は、靭性が必ずしも十分ではない。しかも組織安定性に問題があり、高温で長時間使用すると、使用中に脆化相であるシグマ相が生成する。このシグマ相が生成すると、合金は非常に脆くなり、例えば、装置の作動または停止に伴う熱応力や、室温での定期検査時に加わる衝撃力によって、簡単に破壊する恐れがある。つまり、ただ単に、従来技術の知見を延長して合金成分を調整しただけでは、実用的な高温耐食性合金の開発は困難である。 However, the 60 mass% Cr—Fe alloy does not necessarily have sufficient toughness. Moreover, there is a problem in the structure stability, and when used at a high temperature for a long time, a sigma phase which is an embrittled phase is generated during use. When this sigma phase is generated, the alloy becomes very brittle and can be easily broken by, for example, thermal stress accompanying operation or stoppage of the apparatus or impact force applied during regular inspection at room temperature. That is, it is difficult to develop a practical high-temperature corrosion-resistant alloy simply by extending the knowledge of the prior art and adjusting the alloy components.
そこで、発明者らは、CrおよびFeの組成を、上記高温耐食合金として理想的な組成比のままとした上で、Ni添加に代わる新たな靱性向上策と組織安定化策について検討した。その結果、合金中に含まれるC,N,P,S,Oならびにその他の不純物の量を制限することが有効であることを見出した。 Therefore, the inventors studied the new toughness improvement and structural stabilization measures to replace Ni addition while keeping the composition ratio of Cr and Fe at the ideal composition ratio as the high temperature corrosion resistant alloy. As a result, it has been found that it is effective to limit the amounts of C, N, P, S, O and other impurities contained in the alloy.
また、上記合金の高温強度をさらに向上させることができれば、実用上、非常に有利である。例えば、廃棄物焼却プラント等の構造材などの場合、合金の高温強度を向上できれば、使用温度の上昇や材料の薄肉化が可能となるため、装置の運転効率の向上ならびに製造価格の低減等が期待できるからである。高温強度向上のためには、新たな元素の添加が有効と考えられるが、そのためには、添加によって靱性の低下やシグマ相の生成が起こらないことが不可欠である。発明者らは、上記観点から検討を進めた結果、添加元素としてWを用いれば、これらの要求が満たされることを見出した。 Further, if the high temperature strength of the alloy can be further improved, it is very advantageous in practice. For example, in the case of structural materials such as a waste incineration plant, if the high temperature strength of the alloy can be improved, the operating temperature can be increased and the material can be made thinner. Because it can be expected. In order to improve the high-temperature strength, addition of a new element is considered to be effective, but for that purpose, it is essential that the addition does not cause a decrease in toughness or generation of a sigma phase. As a result of investigations from the above viewpoint, the inventors have found that these requirements are satisfied if W is used as an additive element.
さらに、上記合金の靭性をより向上させることも有意義なことである。すなわち、靭性をより向上することができれば、それらを用いた機器の製造時における各種加工や、製造後の室温での定期検査や補修工事等での加工において、多少無理な力が加わっても、製品に亀裂が入ることを防ぐことができ、それらの亀裂に起因した使用中の破損を防止できるからである。発明者らは、上記合金を基本とし、シグマ相の生成を助長することなく靭性を向上させる添加成分を検討した結果、一定量以下のNiまたは微量のNb,Tiの添加が有効であることを見出した。 Furthermore, it is meaningful to further improve the toughness of the alloy. In other words, if toughness can be further improved, even if some unreasonable force is applied in various processing at the time of manufacturing equipment using them, and processing in regular inspection and repair work at room temperature after manufacturing, This is because it is possible to prevent the product from being cracked and to prevent breakage during use due to the crack. The inventors have studied the additive components that improve the toughness without promoting the formation of the sigma phase based on the above-mentioned alloy. As a result, it has been found that the addition of a certain amount of Ni or a small amount of Nb and Ti is effective. I found it.
なお、ここで高温耐食性として実用的に使用可能な材料特性について説明すると、靭性値は、室温でのシャルピー吸収エネルギーが4J以上、好ましくは6J以上であることが望ましい。同じく高温耐食性は、硫化性雰囲気中で、1000℃×100時間酸化させた時の腐食減量が40mg/cm2以下、好ましくは30mg/cm2以下であることが望ましい。また、高温強度は、使用温度に近い700℃における引張強度が300MPa以上であることが望ましい。 Here, the material properties that can be practically used as high-temperature corrosion resistance will be described. The toughness value is that Charpy absorbed energy at room temperature is 4 J or more, preferably 6 J or more. Similarly, the high temperature corrosion resistance is desirably 40 mg / cm 2 or less, preferably 30 mg / cm 2 or less, when the corrosion weight is oxidized at 1000 ° C. for 100 hours in a sulfide atmosphere. The high-temperature strength is desirably a tensile strength of 300 MPa or more at 700 ° C. near the operating temperature.
本発明は、上記知見に基づいて完成したものであり、以下に、各成分の組成範囲を限定した理由について詳しく説明する。
Cr:30〜80mass%
Crは、高温硫化雰囲気中での耐食性を向上させる成分であるが、含有量が30mass%未満であると、必要な耐食性が得られない。一方、80mass%超えでは、不純物含有量を限定しても、靱性を確保することが難しくなる。よって、Cr含有量は30〜80mass%の範囲とする。ただし、Cr含有量は、上記範囲内でより高温耐食性を得るためには、50mass%の高Cr合金となるように調整されるのが好ましく、より好ましくは、65mass%以上とするのがよい。
The present invention has been completed based on the above findings, and the reason why the composition range of each component is limited will be described in detail below.
Cr: 30-80mass%
Cr is a component that improves the corrosion resistance in a high-temperature sulfidation atmosphere, but if the content is less than 30 mass%, the necessary corrosion resistance cannot be obtained. On the other hand, if it exceeds 80 mass%, it becomes difficult to ensure toughness even if the impurity content is limited. Therefore, Cr content shall be the range of 30-80 mass%. However, in order to obtain higher temperature corrosion resistance within the above range, the Cr content is preferably adjusted to be a 50 mass% high Cr alloy, and more preferably 65 mass% or more.
W:10mass%以下
Wは、高温強度を高めるために有効な成分である。しかし、10mass%を超えて添加すると靱性の低下を招くため、Wの添加量は、10mass%以下に制限する必要がある。一方、所期した効果を得るためには0.5mass%以上の添加することが好ましい。より、好ましくは1mass%以上である。
W: 10 mass% or less W is an effective component for increasing the high-temperature strength. However, if added over 10 mass%, the toughness is reduced, so the amount of W needs to be limited to 10 mass% or less. On the other hand, in order to obtain the desired effect, it is preferable to add 0.5 mass% or more. More preferably, it is 1 mass% or more.
Ni:5mass%以下
Niは、靱性を向上させる成分であり、要求に応じて添加することができる。上記効果を得るためには、1mass%以上添加することが好ましい。しかし、5mass%を超えて添加すると、先に述べたように高温での耐食性の低下を招くので、Niの添加量は5mass%以下に制限する。よって、好ましくは1〜5mass%である。
Ni: 5 mass% or less
Ni is a component that improves toughness, and can be added as required. In order to acquire the said effect, it is preferable to add 1 mass% or more. However, if added over 5 mass%, the corrosion resistance at high temperatures is reduced as described above, so the amount of Ni is limited to 5 mass% or less. Therefore, it is preferably 1 to 5 mass%.
Nb:1mass%以下、Ti:1mass%以下
NbおよびTiは、Niと同様、靱性を向上させる成分であり、Niに代えて、Ti,Nbのいずれか1種または2種を添加することができる。靭性向上効果を得るためには0.01mass%以上添加することが好ましい。しかし、1mass%を超えると、金属間化合物等を生成し、却って靱性を低下させることから、それぞれ上限は1mass%以下とする。なお、NbとTiを複合して添加する場合には、合計で1.5mass%以下に制限するのが好ましい。
Nb: 1 mass% or less, Ti: 1 mass% or less
Nb and Ti are components that improve toughness in the same manner as Ni, and any one or two of Ti and Nb can be added instead of Ni. In order to obtain the effect of improving toughness, it is preferable to add 0.01 mass% or more. However, if it exceeds 1 mass%, an intermetallic compound or the like is generated and the toughness is decreased, so the upper limit is set to 1 mass% or less. In addition, when adding Nb and Ti combining, it is preferable to restrict | limit to 1.5 mass% or less in total.
Fe:残余成分
Feは、Crと並んで、本発明合金の主要構成成分である。このFeは、他の添加元素であるNiと較べると、高温硫化雰囲気中での耐食性に優れ、また、はるかに低コストであることから、残余の成分として適している。
Fe: Residual component
Fe, along with Cr, is a main constituent of the alloy of the present invention. This Fe is suitable as the remaining component because it is superior in corrosion resistance in a high-temperature sulfidation atmosphere and much lower in cost than other additive elements Ni.
不純物元素:合計で0.02mass%以下
不純物は、高Cr合金の靱性や組織安定性を低下させる主な要因である。ここで、本発明における不純物とは、Cr,Feおよび添加元素を除く、金属、非金属ならびにガス成分を言い、具体的には、C,N,P,S,O,Si,Mn,Al,Cu,Pb,Mg,Ca等の不可避的不純物を指す。Cr量が上記30〜80mass%の範囲である合金においては、不純物の合計含有量が0.02mass%を超えて含まれると、靱性や組織安定性が確保できないため、0.02mass%以下に制限する必要がある。好ましくは0.01mass%以下とするのがよい。
Impurity elements: 0.02 mass% or less in total Impurities are the main factors that lower the toughness and structural stability of high Cr alloys. Here, the impurities in the present invention refer to metals, non-metals and gas components excluding Cr, Fe and additive elements, specifically, C, N, P, S, O, Si, Mn, Al, Inevitable impurities such as Cu, Pb, Mg and Ca. In alloys where the Cr content is in the range of 30 to 80 mass%, if the total content of impurities exceeds 0.02 mass%, toughness and structural stability cannot be ensured, so it is necessary to limit it to 0.02 mass% or less. There is. Preferably it is 0.01 mass% or less.
次に、本発明合金の製造方法について簡単に説明する。
本発明の合金は、高周波溶解、アーク溶解および電子ビーム溶解を用いて、溶製し、鋳塊とすることが好ましい。この際、不純物の混入量を、本発明の基準内に抑えるためには、溶解炉内雰囲気中の水分、酸素および窒素を低減した高真空技術を駆使することが好ましい。上記鋳塊は、1200〜1300℃に加熱後、800〜1200℃の温度範囲で熱間加工を行い、必要に応じて800〜1200℃の温度範囲の熱処理を施した後、さらに必要に応じて、酸洗後、冷間加工を行い、その後、歪取焼鈍を行い製品とすることが好ましい。
Next, a method for producing the alloy of the present invention will be briefly described.
The alloy of the present invention is preferably melted and made into an ingot using high frequency melting, arc melting and electron beam melting. At this time, in order to keep the amount of impurities mixed within the standard of the present invention, it is preferable to use a high vacuum technique in which moisture, oxygen and nitrogen in the atmosphere in the melting furnace are reduced. The ingot is heated to 1200-1300 ° C, hot-worked in a temperature range of 800-1200 ° C, and optionally subjected to heat treatment in a temperature range of 800-1200 ° C. After pickling, it is preferable to perform cold working, and then perform strain relief annealing to obtain a product.
なお、本発明の合金は、冷間加工品の他、熱間加工ままでもその特性を十分に発揮するため、熱間加工品としても用いることができる。なお、上記熱間加工としては、熱間板圧延、条鋼圧延、熱間鍛造、造管加工等の加工が含まれ、また、冷間加工としては、冷間板圧延、伸線加工、引抜加工、押出加工等の加工が含まれる。 The alloy of the present invention can be used not only as a cold-worked product but also as a hot-worked product because it fully exhibits its characteristics even during hot working. The hot working includes hot plate rolling, strip rolling, hot forging, pipe forming, and the like, and cold working includes cold plate rolling, wire drawing, drawing. Processes such as extrusion are included.
表1に示す15種類の合金(本発明合金を6種、比較合金を9種)を真空溶解によって溶製し、それぞれ約10kgの鋳塊とした。この鋳塊を1250℃に加熱し、800〜1200℃で熱間加工して、約50mm幅×30mm厚×500mm長さの板状とし、次いで1000℃で溶体化熱処理を施した。こうして得た板材を用いて、高温腐食試験、シャルピー衝撃試験および高温時効試験を下記の要領で行った。 Fifteen types of alloys shown in Table 1 (6 types of the present invention alloy and 9 types of comparative alloys) were melted by vacuum melting to form ingots of about 10 kg each. The ingot was heated to 1250 ° C. and hot-worked at 800 to 1200 ° C. to form a plate shape of about 50 mm width × 30 mm thickness × 500 mm length, and then subjected to solution heat treatment at 1000 ° C. Using the plate material thus obtained, a high temperature corrosion test, a Charpy impact test, and a high temperature aging test were conducted as follows.
<高温腐食試験>
溶体化処理後の供試材から20mm×20mm×3mmの板状試験片を採取し、表面を#800のエメリー紙で研磨した後、試験片表面に80mol%V2O5−20mol%Na2SO2の灰を片面当たり20mg/cm2塗布し、その後、1000℃の高温に保持された内容積 2000cm3の炉中に入れ、100時間保持して高温腐食させた。この時の雰囲気ガスとしては、3500ppmSO2−2%O2−10%CO2−残余N2の硫化性ガスを100ml/minの流量で流し続けた。腐食試験後、試験片表面の付着物を除去し、試験前後の重量差から腐食減量を求めた。
<High temperature corrosion test>
A 20 mm × 20 mm × 3 mm plate test piece was taken from the test material after solution treatment, and the surface was polished with # 800 emery paper, and then 80 mol% V 2 O 5 -20 mol% Na 2 was applied to the test piece surface. SO 2 ash was applied at a rate of 20 mg / cm 2 per side, and then placed in a furnace having an internal volume of 2000 cm 3 held at a high temperature of 1000 ° C. and kept at high temperature for 100 hours. At this time, as an atmospheric gas, a sulfide gas of 3500 ppm SO 2 -2% O 2 -10% CO 2 -residual N 2 was kept flowing at a flow rate of 100 ml / min. After the corrosion test, the deposits on the surface of the test piece were removed, and the corrosion weight loss was determined from the weight difference before and after the test.
<シャルピー衝撃試験>
溶体化後の板材から、JIS Z2202に準拠して2mmVノッチの標準試験片(4号試験片、10×10×55mm)を加工し、室温、大気中でシャルピー試験を行い、衝撃値を求めた。
<Charpy impact test>
2mmV notch standard test piece (No.4 test piece, 10x10x55mm) was processed from the solution-treated plate material in accordance with JIS Z2202, and Charpy test was performed at room temperature in the atmosphere to determine the impact value. .
<高温時効試験>
大気中において、650℃で1000時間保持した後、供試材の断面組織観察を行い、シグマ相の生成有無を調べた。
<High temperature aging test>
After holding at 650 ° C. for 1000 hours in the atmosphere, the cross-sectional structure of the test material was observed to examine whether or not a sigma phase was generated.
表1に上記試験の評価結果を示す。本発明の合金No.1〜6の腐食減量およびシャルピー衝撃値は、含有するCr量によって若干の差異はあるが、いずれも良好な値を示している。また、高温時効後もシグマ相の生成は認められない。
これに対し、Cr量が本発明の請求範囲未満である比較合金No.7は、本発明合金より腐食減量が大きく、高温耐食性が劣ることがわかる。一方、Cr量が本発明の請求範囲を超える合金No.8は、シャルピー衝撃値が低く靱性が劣ることがわかる。
また、52.4mass%のCrにおいて、Niを10.7mass%加えた比較合金No.9では、シャルピー衝撃値は最も良好であるが、腐食減量が最も多い。この理由は、先に述べたように、高温硫化雰囲気中において、NiがSと結びつき、Ni3S2等の低融点化合物を生成したためと考えられる。
さらに、No.10〜15の比較合金はいずれも、約50mass%のCrにおいて、不純物含有量の総計が0.02%を越えたものである(No.10はAlが高く、No.11はMnが高く、No.12はSiが高く、No.13はCが高く、No.14はNが高く、またNo.15はOが高い)これらの合金はいずれも、Cr量が規定量含まれるため高温耐食性は良好であるが、時効後にシグマ相の生成が認められ、シャルピー吸収エネルギーが低い。これは、不純物含有量の合計が本発明範囲より多いため、靱性や相安定性が低下したためと考えられる。
Table 1 shows the evaluation results of the above test. Although the corrosion weight loss and Charpy impact value of Alloys Nos. 1 to 6 of the present invention are slightly different depending on the amount of Cr contained, both show good values. Also, no sigma phase is observed after high temperature aging.
On the other hand, it can be seen that Comparative Alloy No. 7 in which the Cr content is less than the claimed range of the present invention has a greater corrosion weight loss and inferior high-temperature corrosion resistance than the present invention alloy. On the other hand, it can be seen that Alloy No. 8, whose Cr content exceeds the claimed range of the present invention, has a low Charpy impact value and poor toughness.
Further, in comparative alloy No. 9 in which 10.7 mass% of Ni is added in 52.4 mass% Cr, the Charpy impact value is the best, but the corrosion weight loss is the largest. The reason for this is considered to be that Ni was combined with S in the high-temperature sulfidation atmosphere, and a low melting point compound such as Ni 3 S 2 was formed as described above.
Furthermore, all of the comparative alloys No. 10 to 15 have a total impurity content exceeding 0.02% at about 50 mass% Cr (No. 10 is high in Al, No. 11 is Mn. (No.12 is high in Si, No.13 is high in C, No.14 is high in N, and No.15 is high in O) Both of these alloys contain a specified amount of Cr. High temperature corrosion resistance is good, but sigma phase formation is observed after aging, and Charpy absorbed energy is low. This is probably because the total content of impurities is larger than the range of the present invention, so that toughness and phase stability are lowered.
実施例2は、Crを約50mass%の本発明合金にWを添加することによって、高温強度を向上させた合金の特性を調査した結果である。具体的には、実施例1に示した本発明の合金No.3をベースとし、Wの添加量を変化させた5種類の合金(No.16〜20)を実施例1と同様にして作製し、実施例1と同じ特性以外に、さらに、700℃、大気中での引張強度の測定を行った。 Example 2 is the result of investigating the characteristics of an alloy whose high-temperature strength is improved by adding W to an alloy of the present invention having about 50 mass% Cr. Specifically, five types of alloys (Nos. 16 to 20) in which the addition amount of W was changed based on the alloy No. 3 of the present invention shown in Example 1 were produced in the same manner as in Example 1. In addition to the same characteristics as in Example 1, the tensile strength at 700 ° C. in the atmosphere was further measured.
表2に評価結果を示す。なお、W無添加の本発明合金No.3は、実施例1に示したものと同じである。本発明の合金No.16〜19は、含有するW量によっても異なるが、無添加の本発明合金No.3に較べて、700℃の強度は大幅に向上している。また、高温耐食性やシャルピー衝撃値に大きな変化はなく、シグマ相の生成も認められない。これから、より高強度を得るためには、Wを0.5mass%以上添加することが好ましいことがわかる。しかし、Wを、本発明の範囲を超えて含む比較合金No.20は、高温強度は最も高いが、シャルピー衝撃値が低い。これは、Wを添加しすぎたために靱性が低下したためと考えられる。 Table 2 shows the evaluation results. The alloy No. 3 of the present invention containing no W is the same as that shown in Example 1. Although the alloys Nos. 16 to 19 of the present invention differ depending on the amount of W contained, the strength at 700 ° C. is greatly improved as compared with the additive-free alloy No. 3 of the present invention. Also, there is no significant change in high temperature corrosion resistance and Charpy impact value, and no sigma phase is observed. From this, it can be seen that it is preferable to add 0.5 mass% or more of W in order to obtain higher strength. However, Comparative Alloy No. 20 containing W beyond the scope of the present invention has the highest high-temperature strength but low Charpy impact value. This is thought to be because toughness was reduced because W was added excessively.
実施例3は、本発明合金に、NiもしくはTi、Nbを添加することによって、靱性を向上させた合金についての特性を調査した結果である。具体的には、実施例1に示した本発明合金No.3をベースに、NiもしくはTi、Nbの添加量を変化させた9種類の合金(No.21〜29)を実施例1と同様にして作製し、実施例1と同じ項目について評価した。 Example 3 is the result of investigating the characteristics of an alloy whose toughness is improved by adding Ni, Ti, or Nb to the alloy of the present invention. Specifically, nine types of alloys (Nos. 21 to 29) in which the addition amount of Ni, Ti, or Nb is changed based on the alloy No. 3 of the present invention shown in Example 1 are the same as in Example 1. The same items as in Example 1 were evaluated.
表3に評価結果を示す。なお、Ni,Ti,Nbが無添加の本発明合金No.3は実施例1に示したものと同じである。少量のNiを含有する合金No.21〜24は、Ni含有量によっても異なるが、無添加の合金No.3に較べてシャルピー衝撃値が向上しており、その添加効果は、1mass%以上の添加で顕著に現れている。なお、高温耐食性(腐食原料が)が若干劣化しているが、問題になる程度ではない。またシグマ相の生成も認められない。しかし、Niが本発明の範囲を超えて添加された比較合金No.25は、シャルピー衝撃値は良好であるが、高温耐食性が悪化している。この原因は、Niを添加しすぎたためと考えられる。
また、上記Niに代わり、微量のNbおよび/またはTiを添加した合金No.26〜28では、無添加の合金No.3に較べてシャルピー衝撃値が向上している。ただし、高温耐食性は、発明合金No.3と同程度であり、シグマ相の生成は認められない。しかし、これらの添加量が本発明の範囲を超えた合金No.29は、シャルピー衝撃値は却って低下している。すなわち、添加しすぎたため、金属間化合物等を形成して、靱性が低下したことが分かる。
Table 3 shows the evaluation results. The alloy No. 3 of the present invention to which Ni, Ti and Nb are not added is the same as that shown in Example 1. Alloys Nos. 21 to 24 containing a small amount of Ni differ depending on the Ni content, but the Charpy impact value is improved as compared with the additive-free alloy No. 3, and the addition effect is 1 mass% or more. Remarkably appears with addition. Although the high temperature corrosion resistance (corrosive raw material) is slightly deteriorated, it is not a problem. In addition, no sigma phase is observed. However, Comparative Alloy No. 25 to which Ni is added beyond the range of the present invention has a good Charpy impact value, but deteriorates the high-temperature corrosion resistance. This is probably because Ni was added too much.
Moreover, in the alloy Nos. 26 to 28 to which a small amount of Nb and / or Ti is added instead of Ni, the Charpy impact value is improved as compared with the additive-free alloy No. 3. However, the high-temperature corrosion resistance is similar to that of the invention alloy No. 3, and the generation of the sigma phase is not recognized. However, Alloy No. 29 in which the amount of addition exceeds the range of the present invention has a reduced Charpy impact value. That is, since it added too much, it turns out that an intermetallic compound etc. were formed and toughness fell.
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