JP3864437B2 - High Mo nickel base alloy and alloy tube - Google Patents

Description

【００３８】
供試材Ｎｏ．１〜５は本発明例、供試材６〜１７鋼は比較例である。比較例の内、供試材Ｎｏ．６は、ＪＩＳ Ｇ ４９０４に規定されているＮＣＦ６２５ＴＢ合金（以下、６２５合金と記す）である。また、供試材Ｎｏ．７および８はＣｒ含有率がそれぞれ１５．２６％と２５．１１％で、本発明合金の範囲外、供試材Ｎｏ．９はＮｂとＴａを含んでいない合金である。供試材Ｎｏ．１０はＮｂ＋Ｔａ含有率が０．８１％、Ｎｏ．１１はＣ含有率が０．０６％、Ｎｏ．１３はＡｌ含有率が０．６６％、Ｎｏ．１４はＦｅ含有率が９．９９％、Ｎｏ．１５はＰ含有率が０．０１２％、Ｎｏ．１６はＢ含有率が０．０１５％、Ｎｏ．１７はＹ含有率が０．１５％で、いずれも本発明合金の範囲より高く、Ｎｏ．１２はＦｅ含有率が１．２３％で本発明合金の範囲より低い例である。これらの供試材の内、Ｎｏ．１６とＮｏ．１７のそれぞれＢ、Ｙ含有率が高すぎる供試材については、いずれもインゴットの熱間鍛造の段階で割れが生じた。したがって、加工性、耐食性等の特性評価は行わなかった。
【００３９】
各特性の評価方法および試験条件は次のとおりである。なお、グリーブル試験以外の各試験における試験片は、溶体化処理後の供試材から採取した。
【００４０】
（１）熱間加工性：グリ−ブル試験における破断絞りで評価した。グリ−ブル試験では、熱間鍛造後のインゴットから、径１０ｍｍ、長さ１３０ｍｍの丸棒を切り出し、所定の温度に加熱後急速引張試験を行った。破断絞りは、破断面の径／破断前の径×１００（％）によって求めた。
【００４１】
（２）冷間加工性：ＪＩＳ Ｚ ２２４１に規定されている常温引張試験における絞りで評価した。引張試験片としてはＪＩＳ Ｚ ２２０１に規定されている４号試験片（径６ｍｍ）を用いた。
【００４２】
（３）時効による合金の脆化度：試験片を６５０℃で３０００時間加熱後、０℃で衝撃試験を行い、衝撃値によって評価した。用いた試験片は、ＪＩＳ Ｚ ２２０２に規定されている４号試験片である。
【００４３】
（４）湿食に対する抵抗性：下記の▲１▼〜▲４▼の４種の試験によって評価した。供試材はＮｏ．１〜５の本発明合金およびＮｏ．６（６２５合金）の比較合金である。試験片としては、供試材の板厚中央部から切り出した、幅１０ｍｍ、長さ４０ｍｍ（応力腐食割れ感受性試験の場合は７５ｍｍ）、厚さ３ｍｍの短冊状腐食試験片を用いた。
【００４４】
▲１▼硝酸溶液中における耐粒界腐食性：ＪＩＳ Ｇ ０５７３に定められているヒュ−イ試験（６５％硝酸腐食試験）によって評価した。試験片に対しては、試験前にもっとも厳しく鋭敏化を受けるとされている７５０℃、１時間加熱の処理を施した。
【００４５】
▲２▼濃厚塩化物溶液中における耐応力腐食割れ性：ＪＩＳ Ｇ ０５７６に定められている沸騰４２％ＭｇＣｌ₂ 水溶液中のＵ字曲げ試験によって評価した。試験では、上記の板状試験片をＵ字曲げ後、沸騰４２％塩化マグネシウム溶液中に１００時間浸漬し、応力腐食割れ（ＳＣＣ）の発生の有無を調査した。
【００４６】
▲３▼海水環境における耐孔食性：ＪＩＳ Ｇ ０５７７に準じた方法で孔食電位を測定し、耐孔食性を評価した。用いた溶液は人工海水（ＡＳＴＭ−Ｄ−１１４１）とした。
【００４７】
▲４▼酸・アルカリ溶液中での腐食速度：試験片を腐食溶液に浸漬し、板厚の減少量から腐食速度を求める方法によって評価した。腐食溶液は、５０％ＮａＯＨ溶液（沸騰）、５０％硫酸溶液（８０℃）および５％ＨＣｌ（５０℃）の３種類である。
【００４８】
（５）大気中での耐高温酸化性：１０００℃で１０００時間加熱した後の試験片の酸化増量によって評価した。
【００４９】
（６）耐高温腐食性：都市ごみや産業廃棄物等を焼却する炉に付随する廃熱ボイラ、製紙工場で使用されているソ−ダ回収ボイラなどの過熱器、あるいは火炉壁蒸発管や節炭器（エコノマイザ−）、ガス−ガス熱交換器などの環境に相当する高温腐食環境における耐高温腐食性を評価した。試験では、幅１５ｍｍ、長さ１５ｍｍ、厚さ３ｍｍの板状試験片を用いて、その試験片の表裏全表面に、実炉のボイラチュ−ブ表面に付着する腐食性付着灰を模擬した合成灰（Ｎａ₂ ＳＯ₄ 、Ｋ₂ ＳＯ₄ 、ＮａＣｌ、ＫＣｌ、ＦｅＣｌ₂ 、Ｆｅ₂ Ｏ₃ 、ＰｂＣｌ₂ を所定量混合させた灰。重量％で、Ｐｂ：９．９７％，Ｃｌ：９．０９％，ＳＯ₃ ：２８．８８％を含む）を試験片単位表面積当たり４０ｍｇ／ｃｍ² 塗布した。次に、排ガスを模擬した組成の腐食性ガス（１０００ｐｐｍＨＣｌ−５０ｐｐｍ％ＳＯ₂ −１０％Ｏ₂ −１０％ＣＯ₂ −２０％Ｈ₂ Ｏ−ｂａｌ．Ｎ₂ ）を通気させた試験炉中で、４００℃（火炉蒸発管を想定）および５００℃（過熱器管を想定）で各２０時間試験片を加熱し、試験片の腐食減量を測定した。
【００５０】
上記の各試験の結果は、次のとおりである。
【００５１】
（１）熱間加工性：表２に、グリーブル試験における破断絞りの測定結果を示した。
【００５２】
【表２】

【００５３】
本発明合金（供試材Ｎｏ. １〜５）は、１１５０、１２００、１２５０℃のいずれの温度においても、比較した合金（Ｎｏ．６、１０、１２、１５）より絞り値が著しく高く、熱間加工性に優れていることが分かる。この比較合金の中でも、供試材Ｎｏ．６の６２５合金は、絞り値が特に低い。また、Ｎｂ＋Ｔａ含有率が０．８１％と高い供試材Ｎｏ．１０の比較合金は、ある程度の熱間加工性の改善が認められるが、１２５０℃における熱間加工性が著しく悪い。広い温度域で熱間加工性を向上させるためには、Ｐ含有率を０．０１０％以下と低めに制限することに加えて、Ｎｂ＋Ｔａ含有率を０．５％以下とする必要がある。Ｆｅ含有率が１．２３％と低い供試材Ｎｏ．１２の比較合金の熱間加工性は、６２５合金より多少良好ではあるものの、本発明合金に比べると著しく悪い。その原因は、Ｎｂ＋Ｔａ含有率が適正ではあるが、Ｆｅ含有率が１．２３％と低くすぎるためである。供試材Ｎｏ．１５は、Ｎｂ＋Ｔａ含有率が０．４２％と低いため、１１５０℃および１２００℃における熱間加工性が改善されている。しかし、Ｐを０．０１１％含むため、本発明合金に比べ、１２５０℃における熱間加工性が劣っている。
【００５４】
（２）冷間加工性：表３に常温引張試験における絞り値を示した。本発明合金の絞り値は、いずれも供試材Ｎｏ．６の６２５合金、および他の比較合金より高く、本発明合金の冷間加工性が良好であることが確認された。
【００５５】
【表３】

【００５６】
（３）時効による合金の脆化抵抗性：前出の表３に衝撃試験における衝撃値を示した。本発明合金（供試材Ｎｏ．１〜４）は、供試材Ｎｏ．６の６２５合金およびその他の比較合金より衝撃値が高く、時効による合金の脆化が起こりにくいことが分かる。その理由は、本発明合金は高温における組織安定性が著しく改善されているためである。比較合金の内、Ｃｒ含有率が本発明合金の範囲より高い供試材Ｎｏ．８は、Ｎｂ＋Ｔａ含有率が適正であるにもかかわらず、時効による脆化が顕著であった。また、Ｎｂ＋Ｔａ含有率が０．８１％と高すぎる供試材Ｎｏ．１０は、６２５合金に比べると脆化の程度は小さいが、本発明合金より顕著に脆化していた。Ａｌ含有率が０．６６％と過剰な供試材Ｎｏ．１３についても、脆い金属間化合物が析出するために、脆化が顕著であった。
【００５７】
（４）湿食に対する抵抗性：表４に、▲１▼耐粒界腐食性、▲２▼耐応力腐食割れ性および▲３▼耐孔食性に関する試験結果、表５に、▲４▼酸・アルカリ溶液中での腐食速度に関する試験結果をまとめて示した。
【００５８】
【表４】

【００５９】
【表５】

【００６０】
６５％硝酸溶液中での耐粒界腐食性を表す腐食減量、濃厚塩化物水溶液中での耐応力腐食割れ性を示すＳＣＣ発生の有無および海水環境での耐孔食性を示す孔食電位いずれの特性についても、本発明合金は、比較合金の６２５合金（供試材Ｎｏ．６）と同等であった。また、表５に示したように、沸騰５０％ＮａＯＨ溶液、８０℃５０％Ｈ₂ ＳＯ₄ 溶液および５０℃５％ＨＣｌ溶液中での腐食速度も、本発明合金（供試材Ｎｏ．１〜５）は、供試材Ｎｏ．６の６２５合金と同等で極めて小さく、酸およびアルカリ溶液中での腐食も起こりにくいことが確認された。６２５合金は、これらの特性に優れているとされている。したがって、本発明合金は、少なくともこれらの４つの特性について、実用上十分な性能を備えていることが裏付けられた。
【００６１】
（５）耐高温酸化性：表６に、試験片を大気中で、１０００℃に１０００時間加熱した後、試験片の酸化増量を測定した結果を示した。本発明合金（供試材Ｎｏ．１〜５）には、いずれも異常酸化は発生しておらず、６２５合金（供試材Ｎｏ．６）同様、優れた耐高温酸化性を備えていた。
【００６２】
【表６】

【００６３】
（６）耐高温腐食性：腐食性の灰を付着させて、腐食性のガス雰囲気中で、４００℃および５５０℃にそれぞれ２０時間加熱し、試験片の酸化増量を測定した結果を表６にまとめて示した。本発明合金（供試材Ｎｏ．１〜５）は、いずれの温度においても６２５合金（供試材Ｎｏ．６）と同等またはそれ以下の腐食増量値であり、６２５合金に匹敵する腐食性環境での耐高温酸化性を備えていることが分かった。また、試験後の試験片表面を金属顕微鏡を用いて調査した。その結果、本発明合金では６２５合金と同様、粒界腐食等の局部腐食も生じていないことが確認された。
【００６４】
（実施例２）
本発明合金（化学組成：表７）によって、次の３種類の継目無合金管を製造した。熱交換器用として、外径２６．６７ｍｍ、肉厚２．８７ｍｍ、長さ４０００ｍｍの合金管、ボイラの過熱器用として、外径５０．８ｍｍ、肉厚５．５ｍｍ、長さ６０００ｍｍの合金管、および二重管として、外管に本発明合金、内管にＪＩＳ Ｇ ３４６１に規定されているＳＴＢ４１０（化学組成：表７）を用いた外径６３．５ｍｍ、肉厚６．３５ｍｍ（外管肉厚１．５２ｍｍ、内管肉厚４．８３ｍｍ）、長さ３０００ｍｍの二重管の３種類である。まず、アーク式電気炉で約２０トンの本発明合金を溶製し、熱間鍛造・切削加工により、外径１７４ｍｍ、内径３８ｍｍ、長さ６００ｍｍのビレットを作製した。二重管については、外管用ビレット、内管用ビレットをそれぞれ別個に製作し、前記の寸法のビレットに組み立てた。次に、ビレットを１２５０℃に加熱し、ユジーンセジュルネ法により熱間押出を行い、外径６０．５ｍｍ、内径３５ｍｍの素管とした。この素管を１１００℃で加熱した後、所定の寸法まで冷間抽伸し、溶体化熱処理を施し、さらに脱スケ−ルを行って製品の合金管に仕上げた。
【００６５】
【表７】

【００６６】
本発明合金は、１２５０℃以下の温度域で十分な延性があるため、１２５０℃での熱間押出法により容易に製管することができた。また、冷間加工性も良好なため、冷間抽伸も容易であった。さらに、製品の合金管には、表面疵等の欠陥も認められなかった。
【００６７】
本発明の合金によって製造された合金管について、高温強度ならびにクリ−プ破断強度を調査したが、これらの特性も良好であった。例えば、５５０℃における高温強度は、引張強度で５４７ＭＰａであり、６２５合金より低めではあるもののＳＵＳ３０４ＴＢの４７０ＭＰａより高い値を示した。また、クリ−プ破断強度は、６００℃ではＳＵＳ３１６ＨＴＢなみの高い強度を有しており、高温でボイラチュ−ブとして十分使用できる性能を備えていることが確認された。
【００６８】
以上の実施例１および２から明かなように、本発明の合金および合金管は、熱間加工性および冷間加工性が従来の６２５合金に比べて著しく優れており、かつ、様々な条件の腐食環境において、６２５合金に匹敵する耐食性を備えていることが確認された。さらに、高温での使用中の時効脆化も、６２５合金に比べて極めて起こりにくいことが実証された。
【００６９】
【発明の効果】
本発明合金は、様々な腐食環境、過酷な腐食環境において既存のＮＣＦ６２５ＴＰ、ＮＣＦ６２５ＴＢに匹敵する優れた耐食性を備え、かつ、熱間加工性および冷間加工性が極めて良好である。したがって、合金管等を製造する場合、熱間加工または冷間加工前の素材の疵取り等の手入れが不要であり、加工後の製品に表面疵がほとんど発生しない。そのために、製造歩留まりがよく、製造コストを大幅に低減でき、製造工程の省略により製造に要する日数の短縮も可能である。
【００７０】
また、本発明の合金および合金管は、高温における組織が極めて安定なため、高温で長時間使用しても脆化が起こらず、高温靱性に優れている。
【００７１】
このように、本発明の合金および合金管は、加工性、耐食性および高温靱性に優れているので、過酷な腐食環境で使用される配管用、ボイラ・熱交換器用合金管あるいはこれらの装置の構造用材料、さらには、ごみ焼却炉廃熱ボイラやソ−ダ回収ボイラなどの過熱器管、構造用材料などに適用可能である。本発明の合金および合金管を用いた設備は、高温における耐食性および靱性が高いため、設備の耐久性を大幅に延長できるとともに、設備の信頼性や稼働率を大幅に高めることができる。この他、本発明合金によれば、従来の合金では製造困難であった二重管、三重管などの複合管も容易に製造することができる等、本発明の合金および合金管は産業上、極めて優れた効果を奏する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high Mo nickel-base alloy having excellent workability and an alloy tube using the alloy, and more particularly, workability such as hot workability and cold workability, a wide range of corrosive environments or severe corrosive environments. The present invention relates to a high Mo nickel-base alloy and an alloy tube suitable for pipes having excellent corrosion resistance, and alloy tubes for boilers and heat exchangers.
[0002]
[Prior art]
In facilities used in the chemical industry, the petroleum industry, and the like, steel materials for pipes or structures are sometimes used under conditions such that they are exposed to alkaline or acidic solutions at high temperatures. In addition, boiler superheater tubes, evaporation tubes or structural members, heat exchanger tube heat exchanger tubes, condenser tubes, catalyst tubes or structural members are used at high temperatures and high pressures in corrosive atmospheres. Further, in a garbage incineration facility or the like, a steel material is exposed to a corrosive gas atmosphere such as chlorine gas at a high temperature. Naturally, a material having sufficient corrosion resistance is adopted as the steel material used in such a condition that it is exposed to an extremely severe corrosive environment. For example, Ni—Cr—Fe alloys defined in JIS G4903 and G4904 may be used for boiler superheater tubes and evaporator tubes. Each of these standards stipulates six types of highly corrosion-resistant alloys, and particularly in severe corrosive environments, the Mo content is high (8 to 10% by weight, the chemical composition is expressed in terms of% by weight). NCF625TP or NCF625TB alloy is used.
[0003]
NCF625TP alloy and NCF625TB alloy (hereinafter simply referred to as 625 alloy) are based on Ni: Cr: 20-23%, Ni: 58% or more, Mo: 8-10%, Fe: 5% or less, Nb: 3.15 to 4.15%, Al and Ti are included in addition. These alloys have been developed with the goal of providing excellent corrosion resistance even in extremely harsh corrosive environments, mainly due to the action of Cr, Ni, and Mo, and often show good corrosion resistance in practice.
[0004]
When 625 alloy is used as an alloy tube such as a heat exchanger tube, it is often produced by a hot extrusion method (Eugene Sejourne method) and used as a seamless alloy tube. However, these alloys have extremely poor hot workability and cold workability. Accordingly, since soot frequently occurs in the raw tube after hot extrusion, the soot must be removed by maintenance. In addition, since cold workability is poor, the actual situation is that problems are avoided by reducing the degree of work per process and increasing the number of processes in the manufacturing stage such as cold rolling and cold drawing. . As described above, the pipe making of 625 alloy has problems such as low productivity, high manufacturing cost and long manufacturing days because it requires a lot of labor and complicated processes.
[0005]
625 alloy is also used as a high-temperature material for industrial boilers, waste incinerator waste heat recovery boiler superheater tubes, heat exchanger tubes, etc., or as a welding material when welding various high-temperature materials. . This 625 alloy originally has the property of being age hardened significantly in the temperature range near 650 ° C. Therefore, when used for a long time in a high temperature range exceeding 500 ° C., the toughness of the alloy is remarkably lowered. Therefore, when used in equipment used in high temperatures, there is a risk of damage due to thermal fatigue due to repeated heating and cooling, so the use temperature is high for boiler tubes that require high reliability. It could not be adopted under the conditions.
[0006]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems, and has the excellent corrosion resistance of the conventional 625 alloy, as well as (1) excellent hot workability and cold workability, and (2) An object of the present invention is to provide a high Mo nickel-base alloy having excellent structure stability when used at a high temperature for a long time and an alloy tube using this alloy.
[0007]
[Means for Solving the Problems]
The inventor researched the cause of poor hot workability and cold workability, which were problems in manufacturing alloy pipes, etc., and the cause of the decrease in structural stability at high temperatures. Went. As a result, the following new knowledge was obtained.
[0008]
(A) Nb and Ta contained in 3.15 to 4.15% have an adverse effect on hot workability and cold workability. Ti is also one of the causes of wrinkles that can be made in the raw pipe during pipe making. Nb and Ta can improve the hot workability and the cold workability of the 625 alloy by making the total content of both 0.5% or less and adding no Ti.
[0009]
(B) In addition to restricting the Nb and Ta contents low, the hot workability of the 625 alloy can be drastically improved by making the P content 0.010% or less.
[0010]
(C) The structure stability at the time of long-term use in a high temperature region can be improved by setting the combined content of Nb and Ta to a predetermined amount or less. By limiting the Nb and Ta contents, the stability of the structure at high temperatures of the alloy is improved, and no brittleness occurs even when used for a long time in a high temperature range exceeding 500 ° C.
[0011]
(D) Even if the contents of Nb and Ta are limited, there is no influence on the corrosion resistance of the 625 alloy in a corrosive environment under various conditions.
[0012]
Nb and Ta are added to the 625 alloy for the purpose of age hardening at a high temperature. As a blade material for a gas turbine or the like, extremely high high-temperature strength is required, so it is necessary to ensure high-temperature strength by adding Nb or the like. However, the use of alloys targeted by the present invention, that is, alloy pipes and structural materials mainly for pipes, boilers and heat exchangers, do not require such a high temperature strength. As characteristics of the material, to have the same level of corrosion resistance as 625 alloy, to have workability suitable for the production of seamless alloy pipes, etc., and to prevent toughness degradation when used at high temperatures, It is rather important to have tissue stability at high temperatures.
[0013]
The present invention has been completed based on the above findings,
“Weight%
C: 0.05% or less, Si: 0.5% or less,
Mn: 0.5% or less, Cr: 20-23%,
Fe: 2 to 7%, Mo: 8 to 10%,
Al: 0.4% or less, Nb: 0.5% or less,
Ta: 0.5% or less, P: 0.010% or less,
Ca: 0 to 0.01%, Mg: 0 to 0.01%,
Rare earth elements: 0 to 0.1%, B: 0 to 0.01%
And satisfies the following formula (1):
8 × C ≦ Nb + Ta ≦ 0.5 (%) (1)
(The element symbol represents the content (% by weight) of each element)
A high Mo nickel-base alloy with the balance being Ni and inevitable impurities and an alloy tube using this alloy. "
Is the gist.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Below, the effect | action of each element which comprises the alloy of this invention, the range of a content rate, and its basis are demonstrated.
[0015]
C: When the C content is high, C bonds with Cr and Cr carbide precipitates at the grain boundaries. When Cr carbide precipitates, a Cr-deficient layer is formed in the vicinity of the grain boundary, and intergranular corrosion is likely to occur. Therefore, the C content is set to 0.05% or less. Since it is better that C is small, the lower limit is an amount that can be produced industrially.
[0016]
Si: Si is an element effective as a deoxidizer. However, when the Si content exceeds 0.5%, when the alloy is heated to a high temperature of about 650 ° C., a brittle sigma phase is precipitated, and the heat embrittlement sensitivity is increased. Therefore, the Si content is set to 0.5% or less.
[0017]
Less Si is desirable, and when it is sufficiently deoxidized with Al or the like, it may not be added.
[0018]
Mn: Mn acts as an austenite forming element and is also added as a deoxidizer. However, if the content exceeds 0.5%, the hot workability is impaired, so the content was made 0.5% or less. In the case of sufficient deoxidation with Si, Al or the like, no addition may be performed.
[0019]
Cr: Cr is an indispensable element for ensuring corrosion resistance and high-temperature oxidation resistance in various corrosive environments. The effect becomes remarkable at 20% or more. However, in the present invention alloy having a high Mo content, when the Cr content exceeds 23%, a brittle α-Cr phase is precipitated when the alloy is heated to a high temperature of about 700 ° C., and the toughness of the alloy is lowered. . Therefore, the Cr content is determined to be 20-23%.
[0020]
Mo: Mo has the effect of significantly increasing the corrosion resistance of the alloy against pitting corrosion, crevice corrosion, general corrosion against various acids, and molten salt corrosion including chloride in a corrosive environment containing chlorine (Cl) ions. The effect becomes prominent at 8% or more, and becomes saturated when it exceeds 10%. Therefore, the Mo content is determined to be 8 to 10%.
[0021]
Fe: Fe is added for the purpose of improving hot workability in the alloy of the present invention. The effect appears at 2% or more. When the Fe content is high and exceeds 7%, the Ni content is relatively lowered, so that the corrosion resistance of the alloy is lowered. Therefore, the Fe content is set to 2 to 7%.
[0022]
Al: Al is an element necessary as a deoxidizer. In the case of the alloy of the present invention, when the content exceeds 0.4%, a brittle intermetallic compound precipitates during long-time use at high temperature or during hot working. Therefore, the creep ductility is lowered and the alloy itself becomes brittle, so the content was made 0.4% or less. In the alloy of the present invention, in order to obtain a predetermined deoxidation effect, the lower limit is desirably about 0.1%.
[0023]
Nb, Ta: Nb and Ta are elements having a strong tendency to form carbides, and have a function of fixing C in the alloy and suppressing precipitation of Cr carbides. Therefore, there exists an effect | action which suppresses the intergranular corrosion sensitivity of an alloy (improves intergranular corrosion resistance). The effect becomes remarkable when the C content is 8 times or more. However, when Nb and Ta are excessive, hot workability and cold workability are impaired, and sensitivity to heat embrittlement is increased. Therefore, when either Nb or Ta is included, each is 0.5% or less, and when both are included, both are (Nb + Ta) 0.5% or less. That is, it is necessary to satisfy the following formula (1).
[0024]
8 × C ≦ Nb + Ta ≦ 0.5 (%)
P: The hot workability of the alloy of the present invention can be improved by limiting the Nb and Ta contents as described above. Furthermore, hot workability improves markedly by making P content rate into 0.010% or less. If the P content exceeds 0.010%, the effect of improving hot workability is small, so the P content is set to 0.010% or less.
[0025]
P is an impurity element which is inevitably mixed from the dissolved raw material. In order to lower the P content, measures such as using a raw material having a low P content and dephosphorizing the molten metal may be taken.
[0026]
Ca, Mg: Elements included when particularly excellent hot workability is required. The effect appears at both 0.003% or more in total, but if it exceeds 0.01%, a low melting point intermetallic compound is precipitated, and hot workability is deteriorated. Therefore, when Ca and Mg are included, it is desirable that both be combined (at least one) to be 0.003 to 0.01%.
[0027]
Rare earth element (REM): REM such as La, Ce, and Y is an element to be included when the hot workability of the alloy is further improved, like Ca and Mg. In addition, REM has a function of improving the high-temperature oxidation resistance by improving the adhesion of the alloy (having an oxidation inhibiting effect) oxidation scale when the alloy is used at a high temperature.
[0028]
These effects are remarkably exhibited when the total content of at least one REM is 0.02% or more. However, if the content exceeds 0.1%, an intermetallic compound composed of REM, Ni, Cr, Mo, etc. is generated, and the hot workability is deteriorated. Therefore, when REM is included, 0.02 to 0.1% is desirable. It is more effective to use Ca, Mg and REM together.
[0029]
B: B segregates at the grain boundaries and has the function of strengthening the grain boundaries against high-temperature creep deformation caused by the effects of grain boundary sliding and the like. In order to obtain this grain boundary strengthening effect, B may be added. When B is contained, about 0.002 to 0.01% is preferable. The reason is that when the B content is less than 0.002%, the above effect cannot be expected. When the B content exceeds 0.01%, a low melting point compound such as NiB is formed, resulting in poor hot workability. Because.
[0030]
The nickel-base alloy of the present invention can be produced by equipment and processes that are usually used industrially. For example, a melting raw material such as Ni, Cr, Fe or the like is melted in an arc type electric furnace or a high frequency induction melting furnace, and after deoxidation and component adjustment, an ingot (ingot) is formed by an ingot forming method or a continuous casting method. Cast into slabs. In the production of the alloy of the present invention, it is also effective to use vacuum melting or vacuum processing in the steps of melting and component adjustment. When manufacturing an alloy pipe from an ingot, for example, it may be processed into an extruded pipe billet and manufactured by the Eugene Sejurne method or the like. Moreover, when manufacturing an alloy plate, a slab can be hot-rolled and a hot-rolled plate can be obtained. In addition, in order to give a predetermined characteristic to this invention alloy, the solution treatment which heats to the temperature of about 1100-1200 degreeC is normally given after hot processing.
[0031]
The alloys of the present invention are also suitable for producing composite tubes with other materials such as double tubes.
[0032]
For example, in the case of producing a double pipe of the present invention alloy and the inner side carbon steel, at the stage of the billet for extruded pipe, the outer side is the present invention alloy and the inner side is a carbon steel two-layer billet, The billet may be extruded and piped. The inner side may be the alloy of the present invention. Whether the alloy of the present invention is on the outside or the inside is determined depending on the application. The composite material may be Cr-Mo steel (such as STBA24) in addition to carbon steel. In addition, the composite pipe | tube which was the triple pipe | tube which pinched | interposed this invention alloy and carbon steel etc. between the inside and the inside may be sufficient. Applications of these composite tubes include boiler evaporator tubes.
[0033]
【Example】
In order to demonstrate that the alloys of the present invention have superior properties compared to the conventional 625 alloy and comparative alloys outside the range of the chemical composition of the alloys of the present invention, evaluation was performed from various angles. In particular, the corrosion resistance was confirmed in a wide range of corrosive environments. Hereinafter, specific examples will be described.
[0034]
Example 1
A total of 17 kinds of specimens were manufactured as the alloys of the present invention and comparative alloys (including conventional alloys), and the following characteristics were evaluated for these specimens. Evaluation items include workability (hot workability and cold workability), embrittlement degree due to aging, resistance to wet corrosion (intergranular crack resistance, stress corrosion crack resistance, pitting corrosion resistance, acid / alkaline solution) Corrosion rate), high temperature oxidation resistance and high temperature corrosion resistance. The production method of the test materials used for these characteristic investigations and the breakdown of the test materials are as follows.
[0035]
In a vacuum melting furnace, 50 kg of a test material having a predetermined chemical composition was melted and cast into an ingot. After cutting and removing the outer surface of this ingot, it was heated to 1200 ° C. for 5 hours and hot forged in the temperature range of 1200 to 1050 ° C. The size after forging is 20 mm thick and 100 mm wide. This forged material was heated at 1200 ° C. for 2 hours and softened and annealed. Further, a cold rolled sheet having a thickness of 14 mm was formed by cold rolling. The solution heat treatment conditions after cold rolling were 1100 ° C. and 1 hour heating followed by water cooling.
[0036]
Table 1 shows the chemical compositions of the test materials (5 types of Invention Examples and 12 types of Comparative Examples).
[0037]
[Table 1]

[0038]
Specimen No. 1-5 are examples of the present invention, and specimens 6-17 are comparative examples. Among the comparative examples, the test material No. 6 is an NCF625TB alloy (hereinafter referred to as 625 alloy) defined in JIS G 4904. In addition, specimen No. 7 and 8 have Cr contents of 15.26% and 25.11%, respectively. 9 is an alloy containing neither Nb nor Ta. Specimen No. No. 10 has an Nb + Ta content of 0.81%. No. 11 has a C content of 0.06%. No. 13 has an Al content of 0.66%. No. 14 has an Fe content of 9.99%, No. 14 No. 15 has a P content of 0.012%. No. 16 has a B content of 0.015%. No. 17 has a Y content of 0.15%, which is higher than the range of the alloy of the present invention. 12 is an example in which the Fe content is 1.23%, which is lower than the range of the alloy of the present invention. Among these test materials, No. 16 and No. In each of the test materials having the B and Y contents of 17 which were too high, cracks occurred at the stage of hot forging of the ingot. Therefore, characteristics such as processability and corrosion resistance were not evaluated.
[0039]
The evaluation methods and test conditions for each property are as follows. In addition, the test piece in each test other than a greeble test was extract | collected from the test material after solution treatment.
[0040]
(1) Hot workability: evaluated by drawing at break in a grease test. In the grease test, a round bar having a diameter of 10 mm and a length of 130 mm was cut out from the ingot after hot forging, and a rapid tensile test was performed after heating to a predetermined temperature. The fracture drawing was obtained by the following equation: Diameter of fracture surface / diameter before fracture × 100 (%).
[0041]
(2) Cold workability: Evaluated by drawing in a normal temperature tensile test specified in JIS Z 2241. As a tensile test piece, a No. 4 test piece (diameter 6 mm) defined in JIS Z 2201 was used.
[0042]
(3) The degree of embrittlement of the alloy due to aging: The test piece was heated at 650 ° C. for 3000 hours, then subjected to an impact test at 0 ° C., and evaluated according to the impact value. The test piece used is a No. 4 test piece defined in JIS Z 2202.
[0043]
(4) Resistance to wet corrosion: The following four tests (1) to (4) were evaluated. The test material is no. 1 to 5 alloys of the present invention and No. 1 6 (625 alloy) comparative alloy. As a test piece, a strip-shaped corrosion test piece having a width of 10 mm, a length of 40 mm (75 mm in the case of a stress corrosion cracking susceptibility test), and a thickness of 3 mm, which was cut out from the central part of the thickness of the test material, was used.
[0044]
(1) Intergranular corrosion resistance in nitric acid solution: Evaluated by Huey test (65% nitric acid corrosion test) defined in JIS G 0573. The test piece was subjected to a heat treatment at 750 ° C. for 1 hour, which is considered to be most severely sensitized before the test.
[0045]
(2) Resistance to stress corrosion cracking in concentrated chloride solution: Boiling 42% MgCl specified in JIS G 0576 ₂ It evaluated by the U-shaped bending test in aqueous solution. In the test, the plate-shaped test piece was bent in a U-shape and then immersed in a boiling 42% magnesium chloride solution for 100 hours to investigate whether or not stress corrosion cracking (SCC) occurred.
[0046]
(3) Pitting corrosion resistance in seawater environment: The pitting corrosion potential was measured by a method according to JIS G 0577 to evaluate the pitting corrosion resistance. The solution used was artificial seawater (ASTM-D-1141).
[0047]
{Circle around (4)} Corrosion rate in acid / alkali solution: The test piece was immersed in the corrosion solution and evaluated by a method for determining the corrosion rate from the reduction in the plate thickness. There are three types of corrosive solutions: 50% NaOH solution (boiling), 50% sulfuric acid solution (80 ° C.) and 5% HCl (50 ° C.).
[0048]
(5) High-temperature oxidation resistance in the atmosphere: Evaluated by increasing the amount of oxidation of the test piece after heating at 1000 ° C. for 1000 hours.
[0049]
(6) High-temperature corrosion resistance: Waste heat boilers associated with furnaces for incineration of municipal waste and industrial waste, superheaters such as soda recovery boilers used in paper mills, furnace wall evaporator tubes and sections High temperature corrosion resistance in a high temperature corrosive environment corresponding to an environment such as a charcoal (economizer) and a gas-gas heat exchanger was evaluated. In the test, a synthetic ash simulating corrosive adhesion ash adhering to the boiler tube surface of the actual furnace was used on the entire front and back surfaces of the test piece using a plate-shaped test piece having a width of 15 mm, a length of 15 mm and a thickness of 3 mm. (Na ₂ SO _Four , K ₂ SO _Four , NaCl, KCl, FeCl ₂ , Fe ₂ O _Three , PbCl ₂ Ashes mixed with a predetermined amount. By weight, Pb: 9.97%, Cl: 9.09%, SO _Three : 28.88% included) 40 mg / cm per unit surface area of the specimen ² Applied. Next, corrosive gas having a composition simulating exhaust gas (1000 ppm HCl-50 ppm% SO ₂ -10% O ₂ -10% CO ₂ -20% H ₂ O-bal. N ₂ ) Were heated at 400 ° C. (assuming a furnace evaporator tube) and 500 ° C. (assuming a superheater tube) for 20 hours, and the corrosion loss of the test piece was measured.
[0050]
The results of the above tests are as follows.
[0051]
(1) Hot workability: Table 2 shows the measurement results of fracture drawing in a greeble test.
[0052]
[Table 2]

[0053]
The alloy of the present invention (test materials No. 1 to 5) has a significantly higher drawing value than the alloy (No. 6, 10, 12, 15) compared at any temperature of 1150, 1200, 1250 ° C. It can be seen that the inter-processability is excellent. Among these comparative alloys, the test material No. No. 6 625 alloy has a particularly low aperture value. In addition, the sample No. having a high Nb + Ta content of 0.81% was obtained. The comparative alloy No. 10 shows some improvement in hot workability, but the hot workability at 1250 ° C. is extremely poor. In order to improve hot workability in a wide temperature range, in addition to limiting the P content to be as low as 0.010% or less, the Nb + Ta content needs to be 0.5% or less. Sample No. with a low Fe content of 1.23% The hot workability of the 12 comparative alloy is slightly better than the 625 alloy, but is significantly worse than the alloy of the present invention. This is because the Nb + Ta content is appropriate, but the Fe content is too low at 1.23%. Specimen No. No. 15 has a low Nb + Ta content of 0.42%, so the hot workability at 1150 ° C. and 1200 ° C. is improved. However, since 0.011% of P is contained, the hot workability at 1250 ° C. is inferior to the alloy of the present invention.
[0054]
(2) Cold workability: Table 3 shows the drawing values in the room temperature tensile test. The drawing values of the alloys of the present invention are the same as the test material No. No. 6 625 alloy and other comparative alloys, and it was confirmed that the cold workability of the alloy of the present invention was good.
[0055]
[Table 3]

[0056]
(3) Embrittlement resistance of alloy by aging: Table 3 shows the impact value in the impact test. The alloys of the present invention (test materials No. 1 to 4) It can be seen that the impact value is higher than that of No. 6 625 alloy and other comparative alloys, and the alloy is less likely to be embrittled due to aging. This is because the alloy of the present invention has a significantly improved structure stability at high temperatures. Of the comparative alloys, the test material No. In No. 8, embrittlement due to aging was remarkable despite the Nb + Ta content being appropriate. In addition, the test material No. Nb + Ta content is too high as 0.81%. 10 was less brittle than the 625 alloy, but was significantly more brittle than the alloy of the present invention. When the Al content is 0.66% and the specimen No. is excessive. No. 13 was also markedly brittle because brittle intermetallic compounds were precipitated.
[0057]
(4) Resistance to wet corrosion: Table 4 shows (1) intergranular corrosion resistance, (2) stress corrosion cracking resistance and (3) pitting corrosion resistance test results, Table 5 shows (4) acid and The test results on the corrosion rate in alkaline solution are summarized.
[0058]
[Table 4]

[0059]
[Table 5]

[0060]
Corrosion weight loss indicating intergranular corrosion resistance in 65% nitric acid solution, presence or absence of SCC indicating stress corrosion cracking resistance in concentrated chloride aqueous solution, and pitting corrosion potential indicating pitting corrosion resistance in seawater environment Also regarding the characteristics, the alloy of the present invention was equivalent to the comparative alloy 625 alloy (test material No. 6). Moreover, as shown in Table 5, boiling 50% NaOH solution, 80 ° C. 50% H ₂ SO _Four As for the corrosion rate in the solution and 50 ° C. 5% HCl solution, the alloy of the present invention (test material Nos. 1 to 5) is also the test material No. No. 6 625 alloy, which is extremely small, and it was confirmed that corrosion in acid and alkaline solutions hardly occurs. 625 alloy is said to be excellent in these characteristics. Therefore, it was confirmed that the alloy of the present invention has practically sufficient performance for at least these four characteristics.
[0061]
(5) High temperature oxidation resistance: Table 6 shows the results of measuring the increase in oxidation of the test piece after heating the test piece to 1000 ° C. for 1000 hours in the air. None of the alloys according to the present invention (test materials No. 1 to 5) had abnormal oxidation, and had excellent high-temperature oxidation resistance like the 625 alloy (test material No. 6).
[0062]
[Table 6]

[0063]
(6) High-temperature corrosion resistance: Table 6 shows the results of measuring the increase in oxidation of the test pieces by attaching corrosive ash and heating to 400 ° C and 550 ° C for 20 hours in a corrosive gas atmosphere. Shown together. The alloy of the present invention (test material Nos. 1 to 5) has a corrosion weight increase value equal to or lower than that of the 625 alloy (test material No. 6) at any temperature, and a corrosive environment comparable to the 625 alloy. It was found that it has high-temperature oxidation resistance. Moreover, the test piece surface after a test was investigated using the metal microscope. As a result, it was confirmed that local corrosion such as intergranular corrosion did not occur in the alloy of the present invention as in the case of 625 alloy.
[0064]
(Example 2)
The following three types of seamless alloy pipes were manufactured from the alloys of the present invention (chemical composition: Table 7). For heat exchanger, alloy pipe with outer diameter 26.67mm, wall thickness 2.87mm, length 4000mm, for boiler superheater, alloy pipe with outer diameter 50.8mm, wall thickness 5.5mm, length 6000mm, and As the double tube, the outer tube is made of the alloy of the present invention, and the inner tube is made of STB410 (chemical composition: Table 7) defined in JIS G 3461. The outer diameter is 63.5 mm and the wall thickness is 6.35 mm (outer tube wall thickness). 1.52 mm, inner pipe wall thickness 4.83 mm), and a double pipe with a length of 3000 mm. First, about 20 tons of the alloy of the present invention was melted in an arc electric furnace, and a billet having an outer diameter of 174 mm, an inner diameter of 38 mm, and a length of 600 mm was produced by hot forging and cutting. As for the double pipe, the billet for the outer pipe and the billet for the inner pipe were separately manufactured and assembled into billets having the above dimensions. Next, the billet was heated to 1250 ° C., and hot extrusion was performed by the Eugene Sejurune method to obtain a raw tube having an outer diameter of 60.5 mm and an inner diameter of 35 mm. After heating the raw tube at 1100 ° C., it was cold drawn to a predetermined size, subjected to solution heat treatment, and further descaled to finish a product alloy tube.
[0065]
[Table 7]

[0066]
Since the alloy of the present invention has sufficient ductility in a temperature range of 1250 ° C. or lower, it could be easily produced by a hot extrusion method at 1250 ° C. Moreover, since cold workability was also good, cold drawing was easy. Further, defects such as surface flaws were not observed in the alloy pipe of the product.
[0067]
The high temperature strength and creep rupture strength of the alloy pipe manufactured by the alloy of the present invention were investigated, and these characteristics were also good. For example, the high-temperature strength at 550 ° C. was 547 MPa in terms of tensile strength and was higher than 470 MPa of SUS304TB although it was lower than that of 625 alloy. In addition, the creep rupture strength was as high as SUS316HTB at 600 ° C., and it was confirmed that the creep rupture strength was sufficiently usable as a boiler tube at high temperatures.
[0068]
As is clear from Examples 1 and 2 above, the alloy and alloy tube of the present invention are remarkably superior in hot workability and cold workability to the conventional 625 alloy, and have various conditions. In a corrosive environment, it was confirmed to have corrosion resistance comparable to 625 alloy. Furthermore, it has been proved that aging embrittlement during use at high temperatures is extremely difficult to occur as compared to 625 alloy.
[0069]
【The invention's effect】
The alloy of the present invention has excellent corrosion resistance comparable to existing NCF625TP and NCF625TB in various corrosive environments and severe corrosive environments, and has extremely good hot workability and cold workability. Therefore, when manufacturing an alloy tube or the like, care such as scoring of the raw material before hot working or cold working is unnecessary, and surface flaws hardly occur in the processed product. Therefore, the production yield is good, the production cost can be greatly reduced, and the number of days required for production can be shortened by omitting the production process.
[0070]
In addition, the alloy and alloy pipe of the present invention have an extremely stable structure at high temperatures, so that they do not become brittle even when used at high temperatures for a long time and are excellent in high temperature toughness.
[0071]
As described above, the alloy and the alloy pipe of the present invention are excellent in workability, corrosion resistance and high temperature toughness. Therefore, for pipes used in severe corrosive environments, alloy pipes for boilers and heat exchangers, or structures of these devices. The present invention can be applied to materials for heating, superheater tubes such as waste incinerator waste heat boilers and soda recovery boilers, and structural materials. Since the equipment using the alloy and the alloy pipe of the present invention has high corrosion resistance and toughness at high temperatures, the durability of the equipment can be greatly extended, and the reliability and operating rate of the equipment can be greatly increased. In addition, according to the alloy of the present invention, composite tubes such as double tubes and triple tubes that were difficult to manufacture with conventional alloys can be easily manufactured. Very effective.

Claims (5)

% By weight
C: 0.05% or less, Si: 0.5% or less,
Mn: 0.5% or less, Cr: 20-23%,
Fe: 2 to 7%, Mo: 8 to 10%,
Al: 0.4% or less, Nb: 0.5% or less,
Ta: 0.5% or less, P: 0.010% or less,
Ca: 0 to 0.01%, Mg: 0 to 0.01%,
Rare earth elements: 0 to 0.1%, B: 0 to 0.01%
And satisfies the following formula (1):
8 × C ≦ Nb + Ta ≦ 0.5 (%) (1)
(The element symbol represents the content (% by weight) of each element)
A high Mo nickel-base alloy with the balance being Ni and inevitable impurities. The high Mo nickel-base alloy according to claim 1, wherein the rare earth element is 0.02 to 0.1% by weight. The high Mo nickel-base alloy according to claim 1 or 2, wherein the total content of Ca and Mg is 0.003 to 0.01 wt%. An alloy tube comprising the high Mo nickel-base alloy according to claim 1, 2 or 3. The composite pipe which the outer surface side or the inner surface side or the inner and outer surface side is made of the high Mo nickel-based alloy according to claim 1, 2, or 3.