JP3644532B2 - Ni-base heat-resistant alloy with excellent hot workability, weldability and carburization resistance - Google Patents
Ni-base heat-resistant alloy with excellent hot workability, weldability and carburization resistance Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
この発明は、耐浸炭性および耐コーキング性に優れ、さらに熱間加工性と溶接性にも優れた高温強度の高いＮｉ基耐熱合金に係わり、特にナフサ、プロパン、エタン、ガスオイル等の原料を水蒸気とともに８００℃以上の高温で分解し、エチレン、プロピレン等の石油化学基礎製品を製造するエチレンプラント用分解炉に使用される管の素材として好適なＮｉ基耐熱合金に関する。
【０００２】
【従来の技術】
エチレンプラント用分解炉管の使用温度は、エチレン収率向上の観点から高温化の傾向が強くなってきている。
【０００３】
このような分解炉管用の材料としては、内面が浸炭雰囲気に曝されるため、高温強度と共に耐浸炭性が要求される。また一方では、操業中に分解炉管内表面で炭素が析出（この現象はコーキングと呼ばれる）し、その析出量の増加に伴い管内圧力の上昇や加熱効率低下などの操業上の弊害が生じる。したがって、実操業においては定期的に空気や水蒸気で析出した炭素を除去する、いわゆるデコーキング作業がおこなわれているが、その間の操業停止や作業の工数などが大きな問題になる。このようなコーキングとそれに伴う諸問題は、分解炉管のサイズが収率向上に有利な小径管になるほど深刻になる。
【０００４】
コーキング防止を目的とした従来技術として、例えば特開平２−８３３６号公報には、合金中に２８％以上のＣｒを含有させて合金表面に強固で安定なＣｒ2Ｏ3皮膜を形成させ、炭素析出を促進する触媒元素であるＦｅおよびＮｉの表面への露出を防止し、コーキングを抑制することが有効であることが開示されている。
【０００５】
一方、耐浸炭性を改善するには、例えば特開昭５７−２３０５０号公報に開示されているように、合金中のＳｉ含有量を高めることが有効である。
【０００６】
しかしながら、上述の従来技術には次のような問題点がある。
【０００７】
コーキング防止の点から特開平２−８３３６号公報に開示されているような高Ｃｒ合金を高温強度部材として使用するには、合金中のＮｉ量を高めて金属組織をオーステナイト化する必要があるが、高温強度は従来合金に比べて低いので単独では高温強度部材として適用することは難しい。特開平２−８３３６号公報には、他の高温強度部材と組み合わせて二重管とし使用することが開示されているが、二重管は製造コストや信頼性の点で問題が多い。
【０００８】
本発明者らは、合金中のＡｌ量を５．５％〜１２％と高め、強固で緻密なＡｌ2Ｏ3皮膜をメタル表面に生成させれば、従来の合金に比較して耐浸炭性および耐コーキング性が著しく向上すること、およびこのような高Ａｌ合金では Ｎｉ量を高めることにより高温での使用中にγ′相がマトリックス中に微細析出し、クリープ破断強度も大幅に向上することを見出し、特願平４−４１３３６号として出願した（特開平５−２３９５７６号公報）。また、同公報には、高Ａｌニッケル耐熱合金に５％を超え２０％までのＦｅを含有させることにより加工性が改善されることが開示されている。
【０００９】
しかし、エチレンプラント用分解炉管の製造時のように大きな熱間加工が必要となる場合、特開平５−２３９５７６号公報に開示されている合金では熱間加工性が十分ではなかった。また、同合金は溶接時の高温割れ感受性が高く、溶接性にも問題があった。
【００１０】
【発明が解決しようとする課題】
本発明の課題は、エチレンプラント用分解炉管がおかれる環境、すなわち浸炭、酸化および温度変動が繰り返される環境下において優れた耐浸炭性および耐コーキング性を有し、かつ熱間加工性おび溶接性に優れた高温強度を有する耐熱合金を提供することにある。
【００１１】
【課題を解決するための手段】
本発明の要旨は以下の通りである。
【００１２】
（１）質量％で、Ｃ：０．１％以下、Ｓｉ：１％以下、Ｍｎ：３％以下、Ｐ：０．０４％以下、Ｓ：０．００５％以下、Ｃｒ：１０〜２５％、Ａｌ：２〜３．５％未満（但し、２％は除く）を含み、さらにＢ：０〜０．０３％、Ｚｒ：０〜０．２％およびＨｆ：０〜１％のうちの１種以上を合計で０．００１〜１．２％含有し、残部がＮｉおよび不純物からなることを特徴とする耐コーキング性、熱間加工性、溶接性および耐浸炭性に優れたＮｉ基耐熱合金。
【００１３】
（２）Ｎ含有量が、０．０１２質量％以下である上記(１)記載のＮｉ基耐熱合金。
（３）Ｎｉの一部に代えて、Ｔｉを０．８〜３質量％含有する上記 ( １ ) または ( ２ ) に記載のＮｉ基耐熱合金。
（４）Ｎｉの一部に代えて、Ｆｅを１．１〜を１０質量％含有する上記 ( １ ) 〜 ( ３ ) のいずれかに記載のＮｉ基耐熱合金。
（５）Ｎｉの一部に代えて、Ｍｏ：１〜１５質量％およびＷ：１〜１５質量％の一方または双方を含有する上記 ( １ ) 〜 ( ４ ) のいずれかに記載のＮｉ基耐熱合金。
（６）Ｎｉの一部に代えて、Ｎｂ：０．２〜１質量％、Ｖ：０．３〜１質量％およびＴａ：０．４〜２質量％のうちの１種または２種以上を含有する上記 ( １ ) 〜 ( ５ ) のいずれかに記載のＮｉ基耐熱合金。
（７）Ｎｉの一部に代えて、それぞれ０．００１〜０．１質量％のＹ、Ｌａ、ＣｅおよびＮｄのうちの１種または２種以上を含有する上記 ( １ ) 〜 ( ６ ) のいずれかに記載のＮｉ基耐熱合金。
（８）Ｎｉの一部に代えて、ＭｇおよびＣａの一方または双方を０．０００５〜０．０１質量％含有する上記 ( １ ) 〜 ( ７ ) のいずれかに記載のＮｉ基耐熱合金。
【００１４】
本発明者らは、上記課題を解決するため耐浸炭性に優れたＡｌ含有Ｎｉ基耐熱合金について、特に熱間加工性を改善することを主目的として種々実験、検討した結果以下の知見を得た。
【００１５】
ａ）従来のように、ニッケル基合金に４．５％以上の多量のＡｌを含有させることなく、４．５％未満の少ない量のＡｌを含有させた場合でも、合金表面にアルミナ主体の酸化皮膜を形成させることができ、良好な耐浸炭性と耐コーキング性を付与することができ高温での強度を向上させることができる。
【００１６】
ｂ）しかし、Ａｌ含有量を低めても、熱間加工時または溶接時にＮｉ−Ａｌ系金属間化合物が析出して結晶粒内が著しく強化されるため、相対的に粒界が弱くなり変形が阻害され、熱間加工性の低下や溶接時に高温割れが発生する。
【００１７】
ｃ）粒内の強化に対抗できるだけの粒界の強化が重要かつ有効である。
【００１８】
ｄ）通常不純物として鋼中に混入するＳおよびＰは、粒界に偏析して結晶粒の結合力を弱め、熱間加工性および溶接性を劣化させるので、Ｓは０．００５％以下、Ｐは０．０４％以下に低減する必要がある。特にＰは、１０００℃以下の温度でＣｒリン化物を形成し粒界に析出して粒界を脆弱化させる。
【００１９】
ｅ）Ｂ、ＺｒおよびＨｆは、粒界での結晶粒の結合力を高めるため、粒界の強化に効果を発揮するので、ＳおよびＰの含有量を低減すると共にこれらの元素の１種以上を含有させのがよい。
【００２０】
ｆ）Ｎは、一般に耐熱鋼おいては固溶強化による高温強度を高める作用があるが、多量のＡｌを含有するニッケル合金ではその効果が期待できず、むしろＡｌ系窒化物を形成して熱間加工性および溶接性を阻害するので、Ｓ、Ｐ含有量の低減およびＢ、Ｚｒ、Ｈｆの添加以外に、Ｎを０．０１２％以下に低減すると熱間加工性および溶接性が一層改善される。
【００２１】
【発明の実施の形態】
以下、本発明の合金の化学組成と作用効果につて説明する。なお、合金元素の％表示は質量％を意味する。
【００２２】
Ｃ：
Ｃは、炭化物を形成して耐熱鋼として必要な引張強さやクリープ破断強度を向上させるためには有効な元素であり、０．００５％以上とするのが好ましい。しかし、０．１％を超えると合金の延性および靭性の低下が大きくなるので、上限を０．１％とした。
【００２３】
Ｓｉ：
Ｓｉは、溶鋼の脱酸作用があり、さらに耐酸化性や耐浸炭性改善にも寄与する元素であるが、Ａｌ含有合金ではその効果は比較的小さいので添加しなくともよい。熱間加工性の点からはＳｉは低い程よいが、前記作用を得る必要がある場合は１％以下とする。望ましいＳｉの含有量は０．０１〜０．８％、さらに望ましくは０．０１〜０．５％である。
【００２４】
Ｍｎ：
Ｍｎは、添加しなくともよい。ただし、脱酸元素として有効な元素であり、また熱間加工性に悪影響を及ぼすＳを固定する働きがあるので、これらの効果を得る場合は添加する。過剰添加はスピネル型酸化物の生成を促し、初期のアルミナ皮膜の均一形成を阻害することから上限を３％とするのがよい。望ましくは２％以下である。
【００２５】
Ｐ：
Ｐ含有量の規制は、本発明において最も重要である。Ｐは粒界に偏析し、粒界の結合力を弱め、熱間加工性を劣化させる極めて有害な元素である。さらに、Ｃｒリン化物を形成、粒界に析出することで著しく粒界を脆弱化させる。そのため、Ｐは極力低減するのが好ましい。熱間加工性及び溶接性を改善するためには０．０４％以下が有効である。望ましくは０．０１５％以下とするのがよい。
【００２６】
Ｓ：
Ｓは、粒界に偏析して結晶粒の結合力を弱め、熱間加工性を劣化させる極めて有害な元素で、上限の規制が極めて重要である。特に、Ａｌ含有ニッケル基合金では粒界強化が重要となるため、Ｓは極力低減するのが好ましい。熱間加工性および溶接性を改善するためには０．００５％以下とする必要がある。望ましくは０．００２％以下である。
【００２７】
Ｃｒ：
Ｃｒは、耐酸化性や耐コーキング性の改善に有効な元素であり、アルミナ皮膜の生成初期において均一に生成させる作用がある。また、炭化物を形成しクリープ破断強度の向上にも寄与する。さらに、本発で規定する成分系においてはＣｒは熱間加工性の向上に寄与する。これらの効果を得るためには１０％以上含有させる必要がある。一方、Ｃｒを過剰に含有させると逆にアルミナ皮膜の均一な生成を阻害する。したがって、本発明ではＣｒ含有量を１０〜２５％とした。
【００２８】
Ａｌは、耐浸炭性および耐コーキング性の向上さらには高温強度の向上に極めて有効な元素であるが、その効果を得るにはコランダム型のアルミナ酸化皮膜を均一に生成させる必要がある。また一方で、γ’相［Ｎｉ３（Ａｌ，Ｔｉ）金属間化合物］を形成して析出強化作用が期待できる。これらの効果を得るためには少なくとも２％を超えるＡｌ含有量が必要である。一方、Ａｌ含有量が過剰になると熱間加工性が極端に低下する。したがって、Ａｌ含有量を２〜３．５％未満（但し、２％は除く）とする。
【００２９】
Ｂ、Ｚｒ、Ｈｆ：
これらの元素は主として合金の粒界強化に有効な元素で、熱間加工性、溶接性の改善が図られ、１種以上を含有させることが必要である。しかしながら、過剰に含有させるとクリープ破断強度の低下を引き起こすため、上限はＢで０．０３％、Ｚｒで０．２０％、Ｈｆで１．０％であり、合計で１．２％とする。また前記効果を得るためには少なくとも合計で０．００１％とする必要がある。
【００３０】
Ｎｉ：
本発明の合金は、上記の元素および下記のような必要により含有させる元素以外は実質的にＮｉからなるものである。Ｎｉは安定なオーステナイト組織を得るため、および耐浸炭性確保の点から欠かすことのできない元素であり、特にγ′相による析出強化の効果を高めるためには多いほど望ましい。
【００３１】
本発明の課題を解決するためには、少なくとも上記の化学組成を有する合金とする必要があるが、さらに下記のような元素を含有させることができる。
【００３２】
Ｔｉ：
Ｔｉは、γ'相の析出を促進しクリープ破断強度を向上させる元素である。さらに粒界強化にも寄与する元素で、０．８％以上含有させる。ただし過剰に含有させるとγ'相が過剰析出し熱間加工性および溶接性が著しく劣化する。そのため含有させる場合は３％以下とするのがよい。
【００３３】
Ｆｅ：
Ｆｅは、クリープ延性を改善しクリープ破断強度を高め、さらに熱間加工性の改善にも寄与する元素で１．１％以上含有させる。ただし過剰に含有させると逆にクリープ破断強度、熱間加工性とも低下するため上限は１０％とするのがよい。
【００３４】
Ｍｏ、Ｗ：
ＭｏおよびＷは、主として固溶強化元素として有効であり、基地のオーステナイト相を強化することによりクリープ破断強度を上昇させるので、ＭｏおよびＷの一方または双方を含有させる。この効果を発揮させるためにはＭｏ、Ｗとも１％以上が必要であるが、過剰に含有させると靭性低下の要因となる金属間化合物が析出するだけでなく、耐浸炭性や耐コーキング性も劣化する。Ｍｏ、Ｗともに１５％以下に抑えるべきである。これらを２種併用する場合にも、両者の合計で１５％以下に抑えるのがよい。
【００３５】
Ｎｂ、ＶおよびＴａ：
これらの元素はオーステナイト相中に固溶するとともにγ'相やＣｒ炭化物、窒化物中にも固溶してクリープ破断強度の向上に寄与するので、Ｎｂ、ＶおよびＴａの１種以上をそれぞれ０．２％以上、０．３％以上および０．４％以上含有させる。しかしながら、過剰添加すると靭性低下を招くのでＮｂ及びＶの上限を１％、Ｔａの上限を２％とする。なお、２種以上併用する場合にも両者の合計で３％以下とするのが望ましい。
【００３６】
Ｙ、Ｌａ、ＣｅおよびＮｄ：
これらの元素は、主として熱サイクル条件下でのアルミナ皮膜の剥離を防止し、温度が変動する環境下での使用においても耐浸炭性および耐コーキング性を向上させる。その効果を発揮させるためにはＹ、Ｌａ、ＣｅおよびＮｄともそれぞれ０．００１％以上が必要である。しかし、過剰に含有させると加工性が悪化し、またアルミナ皮膜剥離防止の効果も飽和するので、上限はＹ、Ｌａ、ＣｅおよびＮｄともそれぞれ０．１％とするのがよい。これらの元素は１種だけ含有させてもよいし、また２種以上複合で含有させてもよい。
【００３７】
ＭｇおよびＣａ：
これらの元素は、主として熱間加工性に有害なＳを硫化物として固定し、粒界強度を高めるので、熱間加工性を改善する場合にＭｇおよびＣａの一方または双方を含有させる。含有させる場合は、Ｍｇ，Ｃａとも０．０００５％以上で効果を発揮する。しかしながら、過剰に含有させると固溶状態で鋼中に存在し、逆に熱間加工性および溶接性を低下させる。そのため、上限をＭｇ，Ｃａとも０．０１％とするのがよい。これらの元素を含有させる場合、［（１．１７８Ｍｇ＋Ｃａ）／Ｓ］が０．５〜３の範囲に入るように含有させるのが好ましい。
【００３８】
Ｎ：
Ｎは、元来固溶強化により高温での強度を高めるのに有効であるが、Ａｌ含有ニッケル基合金では、鋼中でＡｌＮとして析出するために固溶強化が期待できないばかりか熱間加工性、溶接性を著しく阻害する。これらの弊害を防止するためには０．０１２％以下にするのがよい。可能な限り低減することが好ましく、望ましくは０．００６％以下である。前述したように、Ｓ、Ｐの低減およびＢ、Ｚｒ、Ｈｆの添加で著しく熱間加工性は改善されるが、さらにＮを低減するとこれらの相乗効果が発揮されより優れた熱間加工性が得られる。
【００３９】
本発明合金は、通常の溶解及び精錬工程で溶製した後、製品の形状に鋳造して製品にすることができる。また、鋳造の後さらに熱間加工、冷間加工等の加工工程を経て管などの製品とすることができる。また、粉末冶金法で製品にしてもよい。熱処理は組織の均一化を促進し、本発明合金の性能向上に寄与する。通常、１１００〜１３００℃での均一化処理が施されるが、熱処理を施さないで鋳造あるいは加工のままで使用することもできる。
【００４０】
【実施例】
表１に示す化学組成の合金を、５０kg真空高周波炉で溶解後、鍛造により１５ｍｍ厚の板材とし、１２５０℃で固溶化熱処理を施して供試材とした。耐浸炭性、高温強度、熱間加工性および溶接性を評価するため、以下に示す要領で各試験を実施した。
【００４１】
【表１】
（１）固体浸炭試験（耐浸炭性評価）
試験片 ：厚さ４ｍｍ、幅２０ｍｍ、長さ３０ｍｍ
試験方法：浸炭剤中に試験片を挿入し、１１５０℃に加熱、４８時間保持後、試験片の板厚方向の中央部から資料を採取して分析
評価 ：Ｃ量が０．２％以下であれば耐浸炭性に優れると判断
（２）クリープ破断試験（高温強度評価）
試験片 ：直径 ６．０ｍｍ、標点距離 ３０ｍｍ
試験方法：保持温度１１５０℃、負荷応力０．９kgf/mm2の条件で破断までの時間を測定
評価 ：破断時間が５００時間以上であれば高温強度良好と判断
（３）グリーブル試験（熱間加工性の評価）
試験片 ：平行部直径１０ｍｍ、長さ１３０ｍｍの丸棒試験片
試験方法：１２００℃で５分加熱した後、１０００℃まで１００℃／分で冷却し、その後５／ｓの歪速度で引張り、破断後Ｈｅガスで室温まで冷却して絞り値を測定
評価 ：絞り率が６０％以上を熱間加工性良好と判断
（４）ロンジバレストレイン（溶接性評価）
試験片 ：厚さ１２ｍｍ、幅５０ｍｍ、長さ２００ｍｍ
試験方法：電流２００Ａ、電圧１７Ｖ、溶接速度１５ｃｍ／分にてＴＩＧ溶接をおこない、その後２％の曲げひずみを負荷し、そのときの溶接熱影響部（ＨＡＺ）のトータル割れ長さを測定した。
【００４３】
評価 ：トータルの割れ長さが５ｍｍ以下を良好と判断。
【００４４】
試験結果を表２に示す。
【００４５】
【表２】
表２から明らかなように、Ａｌを２．０％を超えて３．５％未満含有する本発明の合金は、Ａｌ含有量が本発明で規定する量よりも少ない比較合金Ａに比べ熱間加工性、耐浸炭性、溶接性およびクリープ破断強度共に良好である。また、Ａｌ含有量が本発明で規定する上限を超えている比較合金Ｂは、グリーブル絞りが２５．０％と低く、またロンジバレストレインにおけるトータル割れ長さが２０mmと熱間加工性、溶接性ともに劣ることが分かる。また、Ｓが高い比較合金Ｃ、Ｐが高い比較合金Ｄ、さらにはＢ、Ｚｒ、Ｈｆのいずれも含有していない比較合金Ｅとも熱間加工性、溶接性を満足していない。なお、固体浸炭試験で、試験片の表面を観察したが、本発明で規定する化学組成の試験片にはコーキングがほとんど発生していなかった。
【００４７】
【発明の効果】
本発明の合金は、熱間加工性、溶接性、耐浸炭性および耐コーキング性に優れた高温強度部材として使用するに十分なクリープ破断強度を有した合金である。特にエチレンプラント用分解炉に使用される管のように浸炭、酸化および温度変動が繰り返される熱分解、熱サイクル環境下において優れた前記特性を発揮する。その結果、本発明の合金を使用することにより、より高温での操業が可能となり連続操業時間の延長、さらには耐久性向上による新材との取り替えスパンの長期化が可能となる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Ni-based heat-resistant alloy having excellent high-temperature strength and excellent carburization resistance and caulking resistance, as well as excellent hot workability and weldability . In particular, raw materials such as naphtha, propane, ethane, and gas oil are used. The present invention relates to a Ni-based heat-resistant alloy suitable as a raw material for a pipe used in a cracking furnace for an ethylene plant that decomposes at a high temperature of 800 ° C. or more together with water vapor and produces basic petrochemical products such as ethylene and propylene.
[0002]
[Prior art]
The use temperature of the cracking furnace tube for an ethylene plant is becoming increasingly high from the viewpoint of improving the ethylene yield.
[0003]
Such a cracking furnace tube material is required to have high temperature strength and carburization resistance because the inner surface is exposed to a carburizing atmosphere. On the other hand, carbon is precipitated on the inner surface of the cracking furnace tube during operation (this phenomenon is called coking), and an increase in the amount of precipitation causes adverse effects on the operation such as an increase in tube pressure and a decrease in heating efficiency. Therefore, in actual operation, a so-called decoking operation is periodically performed to remove carbon deposited by air or water vapor, but the operation stoppage or the number of man-hours during the operation becomes a serious problem. Such coking and the problems associated therewith become more serious as the size of the cracking furnace tube becomes a small-diameter tube advantageous for yield improvement.
[0004]
As a conventional technique for preventing coking, for example, Japanese Patent Laid-Open No. 2-8336 discloses that an alloy contains 28% or more of Cr to form a strong and stable Cr 2 O 3 film on the alloy surface. It is disclosed that it is effective to prevent exposure to the surface of Fe and Ni, which are catalytic elements that promote precipitation, and to suppress coking.
[0005]
On the other hand, in order to improve the carburization resistance, it is effective to increase the Si content in the alloy as disclosed, for example, in Japanese Patent Laid-Open No. 57-23050.
[0006]
However, the above-described prior art has the following problems.
[0007]
In order to use a high Cr alloy as disclosed in JP-A-2-8336 as a high temperature strength member from the viewpoint of preventing coking, it is necessary to increase the amount of Ni in the alloy to austenite the metal structure. Since the high temperature strength is lower than that of the conventional alloy, it is difficult to apply it alone as a high temperature strength member. Japanese Patent Laid-Open No. 2-8336 discloses that a double pipe is used in combination with another high-temperature strength member, but the double pipe has many problems in terms of manufacturing cost and reliability.
[0008]
The inventors have increased the amount of Al in the alloy to 5.5% to 12%, and if a strong and dense Al 2 O 3 film is formed on the metal surface, the carburization resistance compared to conventional alloys. And the resistance to caulking is remarkably improved, and in such high Al alloys, by increasing the amount of Ni, the γ 'phase is finely precipitated in the matrix during use at high temperatures, and the creep rupture strength is greatly improved. Was filed as Japanese Patent Application No. 4-41336 (Japanese Patent Laid-Open No. 5-239576). Further, the publication discloses that workability is improved by incorporating high Al nickel heat-resistant alloy with Fe exceeding 5% and up to 20%.
[0009]
However, when a large amount of hot working is required as in the production of a cracking furnace tube for an ethylene plant, the hot workability of the alloy disclosed in JP-A-5-239576 is not sufficient. In addition, the alloy has high hot cracking susceptibility during welding, and has a problem in weldability.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to have excellent carburization resistance and coking resistance in an environment where a cracking furnace tube for an ethylene plant is placed, that is, an environment where carburization, oxidation and temperature fluctuation are repeated, and hot workability and welding. An object of the present invention is to provide a heat-resistant alloy having high temperature strength with excellent properties.
[0011]
[Means for Solving the Problems]
The gist of the present invention is as follows.
[0012]
(1) By mass%, C: 0.1% or less, Si: 1% or less, Mn: 3% or less, P: 0.04% or less, S: 0.005% or less, Cr: 10-25%, Al: 2 to less than 3.5% (excluding 2%), B: 0 to 0.03%, Zr: 0 to 0.2%, and Hf: 0 to 1% A Ni-based heat-resistant alloy excellent in caulking resistance , hot workability, weldability and carburization resistance , characterized by containing 0.001 to 1.2% in total and the balance being Ni and impurities.
[0013]
(2) The Ni-base heat-resistant alloy according to (1), wherein the N content is 0.012 % by mass or less.
(3) The Ni-base heat-resistant alloy as described in ( 1 ) or ( 2 ) above, containing 0.8 to 3% by mass of Ti instead of a part of Ni.
(4) The Ni-based heat-resistant alloy according to any one of the above ( 1 ) to ( 3 ) , which contains 1.1 to 10% by mass of Fe instead of a part of Ni.
(5) The Ni-base heat resistant material according to any one of the above ( 1 ) to ( 4 ) , which contains one or both of Mo: 1 to 15% by mass and W: 1 to 15% by mass in place of a part of Ni. alloy.
(6) Instead of a part of Ni, one or more of Nb: 0.2 to 1% by mass, V: 0.3 to 1% by mass and Ta: 0.4 to 2% by mass The Ni-base heat-resistant alloy according to any one of ( 1 ) to ( 5 ) above .
(7) instead of a part of Ni, respectively 0.001 to 0.1 wt% Y, La, said containing one or more of Ce and Nd (1) to (6) The Ni-base heat resistant alloy according to any one of the above.
(8) The Ni-base heat-resistant alloy according to any one of ( 1 ) to ( 7 ) above, which contains one or both of Mg and Ca in an amount of 0.0005 to 0.01% by mass instead of a part of Ni.
[0014]
In order to solve the above-mentioned problems, the present inventors have conducted various experiments and studies on the Al-containing Ni-base heat-resistant alloy having excellent carburization resistance, particularly for improving hot workability, and obtained the following knowledge. It was.
[0015]
a) As in the prior art, the nickel-based alloy does not contain a large amount of Al of 4.5% or more, and even when a small amount of less than 4.5% Al is contained, the surface of the alloy is mainly oxidized by alumina. A film can be formed, good carburization resistance and caulking resistance can be imparted, and strength at high temperatures can be improved.
[0016]
b) However, even if the Al content is reduced, the Ni-Al intermetallic compound precipitates during hot working or welding and the inside of the crystal grain is remarkably strengthened, so the grain boundary becomes relatively weak and deformation occurs. This hinders hot workability and hot cracking during welding.
[0017]
c) It is important and effective to strengthen the grain boundaries as much as possible against the strengthening within the grains.
[0018]
d) S and P, which are usually mixed in steel as impurities, segregate at the grain boundaries to weaken the bond strength of the crystal grains and deteriorate hot workability and weldability. Therefore, S is 0.005% or less, P Needs to be reduced to 0.04% or less. In particular, P forms Cr phosphide at a temperature of 1000 ° C. or lower and precipitates at the grain boundary, thereby weakening the grain boundary.
[0019]
e) B, Zr, and Hf increase the bonding strength of crystal grains at the grain boundary, and thus are effective in strengthening the grain boundary. Therefore, the content of S and P is reduced and at least one of these elements is used. It is good to contain.
[0020]
f) N generally has the effect of increasing the high-temperature strength by solid solution strengthening in heat-resistant steels, but the effect cannot be expected with a nickel alloy containing a large amount of Al. Since hot workability and weldability are hindered, in addition to the reduction of S and P contents and addition of B, Zr, and Hf, reducing N to 0.012% or less further improves hot workability and weldability. The
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the chemical composition and action effect of the alloy of the present invention will be described. In addition,% display of an alloy element means the mass% .
[0022]
C:
C is an element effective for forming carbides and improving the tensile strength and creep rupture strength necessary for heat-resistant steel, and is preferably 0.005% or more. However, if it exceeds 0.1%, the ductility and toughness of the alloy are greatly reduced, so the upper limit was made 0.1%.
[0023]
Si:
Si is an element that has a deoxidizing action of molten steel and further contributes to the improvement of oxidation resistance and carburization resistance. However, since the effect is relatively small in an Al-containing alloy, it may not be added. From the viewpoint of hot workability, the lower the Si, the better. However, when it is necessary to obtain the above effect, the Si content is 1% or less. Desirable Si content is 0.01 to 0.8%, and more desirably 0.01 to 0.5%.
[0024]
Mn:
Mn may not be added. However, since it is an effective element as a deoxidizing element and has a function of fixing S that adversely affects hot workability, it is added to obtain these effects. Excessive addition promotes the formation of spinel oxide and inhibits the uniform formation of the initial alumina film, so the upper limit is preferably made 3%. Desirably, it is 2% or less.
[0025]
P:
The regulation of the P content is most important in the present invention. P is an extremely harmful element that segregates at the grain boundary, weakens the bonding force of the grain boundary, and degrades hot workability. Further, the formation of Cr phosphide and precipitation at the grain boundaries remarkably weakens the grain boundaries. Therefore, it is preferable to reduce P as much as possible. In order to improve hot workability and weldability, 0.04% or less is effective. Desirably, it should be 0.015% or less.
[0026]
S:
S is an extremely harmful element that segregates at the grain boundary to weaken the bonding strength of the crystal grains and degrades hot workability, and the upper limit is extremely important. In particular, since grain boundary strengthening is important in an Al-containing nickel-base alloy, S is preferably reduced as much as possible. In order to improve hot workability and weldability, it is necessary to make it 0.005% or less. Desirably, it is 0.002% or less.
[0027]
Cr:
Cr is an element effective for improving oxidation resistance and coking resistance, and has an effect of forming uniformly in the initial stage of formation of the alumina coating. Moreover, it forms carbides and contributes to the improvement of creep rupture strength. Furthermore, Cr contributes to the improvement of hot workability in the component system defined in the present invention. In order to obtain these effects, it is necessary to contain 10% or more. On the other hand, when Cr is excessively contained, the uniform formation of the alumina film is inhibited. Therefore, in the present invention, the Cr content is set to 10 to 25%.
[0028]
Al is an element that is extremely effective in improving carburization resistance and coking resistance, and further improving high-temperature strength. To obtain the effect, it is necessary to uniformly produce a corundum type alumina oxide film. On the other hand, a precipitation strengthening action can be expected by forming a γ ′ phase [Ni 3 (Al, Ti) intermetallic compound]. In order to obtain these effects, an Al content of at least 2% is necessary. On the other hand, when the Al content is excessive , hot workability is extremely reduced. Therefore, the Al content is 2 to less than 3.5% (excluding 2%).
[0029]
B, Zr, Hf:
These elements are mainly effective for strengthening the grain boundary of the alloy, and it is necessary to improve hot workability and weldability and to contain one or more elements. However, since excessive addition causes a decrease in creep rupture strength, the upper limit is 0.03% for B, 0.20% for Zr, and 1.0% for Hf, and the total is 1.2%. Moreover, in order to acquire the said effect, it is necessary to make it 0.001% in total at least.
[0030]
Ni:
The alloy of the present invention is substantially composed of Ni except for the above-described elements and the following elements that are included as necessary. Ni is an element indispensable for obtaining a stable austenite structure and securing carburization resistance, and it is more desirable to increase the effect of precipitation strengthening by the γ ′ phase.
[0031]
To solve the problem of the present invention, at least it is necessary to make the alloy having the above chemical composition, but may be free have a further element such as described below.
[0032]
Ti:
Ti is an element that promotes the precipitation of the γ ′ phase and improves the creep rupture strength. Furthermore, it is an element that contributes to grain boundary strengthening and is contained in an amount of 0.8% or more . However, if it is contained excessively, the γ ′ phase is excessively precipitated and the hot workability and weldability are remarkably deteriorated. Therefore, when it contains, it is good to set it as 3% or less.
[0033]
Fe:
Fe is an element that improves creep ductility, increases creep rupture strength, and further contributes to improvement of hot workability, and is contained in an amount of 1.1% or more . However, if it is excessively contained, the creep rupture strength and hot workability are both reduced, so the upper limit is preferably made 10%.
[0034]
Mo, W:
Mo and W are mainly effective as solid solution strengthening elements, and increase the creep rupture strength by strengthening the austenite phase of the matrix, so that one or both of Mo and W are contained . In order to exert this effect, both Mo and W need to be 1% or more, but if excessively contained, not only intermetallic compounds that cause a decrease in toughness are precipitated, but also carburization resistance and caulking resistance are also provided. to degrade. Both Mo and W should be suppressed to 15% or less. Even when these two types are used in combination, the total of both is preferably suppressed to 15% or less.
[0035]
Nb, V and Ta:
These elements dissolve in the austenite phase and also dissolve in the γ 'phase, Cr carbide, and nitride to contribute to the improvement of creep rupture strength. Therefore, at least one of Nb, V, and Ta is reduced to 0. .2% or more, 0.3% or more and 0.4% or more . However, excessive addition causes a reduction in toughness, so the upper limit of Nb and V is 1%, and the upper limit of Ta is 2%. In addition, when using 2 or more types together, it is desirable to make it 3% or less in total of both.
[0036]
Y, La, Ce and Nd:
These elements mainly prevent peeling of the alumina film under thermal cycle conditions, and improve carburization resistance and coking resistance even when used in an environment where the temperature varies. In order to exert the effect, each of Y, La, Ce and Nd needs to be 0.001% or more. However, if contained excessively, the workability deteriorates and the effect of preventing the alumina film from peeling off is saturated. Therefore, the upper limit is preferably set to 0.1% for each of Y, La, Ce and Nd. These elements may be contained alone or in combination of two or more.
[0037]
Mg and Ca:
Since these elements mainly fix S, which is harmful to hot workability, as sulfides and increase the grain boundary strength , one or both of Mg and Ca are contained when improving hot workability. When contained, both Mg and Ca are effective at 0.0005% or more. However, if it is contained excessively, it exists in the steel in a solid solution state, and conversely, hot workability and weldability are lowered. Therefore, the upper limit is preferably 0.01% for both Mg and Ca. When these elements are contained, it is preferable to contain them so that [(1.178Mg + Ca) / S] falls within the range of 0.5 to 3.
[0038]
N:
N is originally effective for increasing the strength at high temperatures by solid solution strengthening, but in the case of Al-containing nickel-base alloys, since it precipitates as AlN in steel, it cannot be expected to have a solid solution strengthening, but also hot workability. , Remarkably hinders weldability. In order to prevent these harmful effects, the content is preferably 0.012% or less. It is preferable to reduce as much as possible, desirably 0.006% or less. As described above, the hot workability is remarkably improved by the reduction of S and P and the addition of B, Zr, and Hf. However, when N is further reduced, these synergistic effects are exerted and a better hot workability is obtained. can get.
[0039]
The alloy of the present invention can be made into a product by casting it into the shape of a product after melting by a normal melting and refining process. Moreover, it can be set as products, such as a pipe | tube, through processing processes, such as hot processing and cold processing, after casting. Moreover, you may make a product by a powder metallurgy method. The heat treatment promotes the homogenization of the structure and contributes to the performance improvement of the alloy of the present invention. Usually, a homogenization treatment is performed at 1100 to 1300 ° C., but it can be used as cast or processed without being subjected to a heat treatment.
[0040]
【Example】
An alloy having a chemical composition shown in Table 1 was melted in a 50 kg vacuum high-frequency furnace, and then a plate material having a thickness of 15 mm was formed by forging, and a solution heat treatment was performed at 1250 ° C. to obtain a test material. In order to evaluate carburization resistance, high temperature strength, hot workability, and weldability, each test was carried out in the following manner.
[0041]
[Table 1]
(1) Solid carburization test (carburization resistance evaluation)
Test piece: 4 mm thick, 20 mm wide, 30 mm long
Test method: Insert a test piece into a carburizing agent, heat to 1150 ° C., hold for 48 hours, then collect data from the central part of the test piece in the plate thickness direction for analysis evaluation: C amount is 0.2% or less (2) Creep rupture test (high temperature strength evaluation)
Test piece: Diameter 6.0 mm, gauge distance 30 mm
Test method: Measurement and measurement of time to break under conditions of holding temperature of 1150 ° C. and load stress of 0.9 kgf / mm 2 : If the break time is 500 hours or more, it is judged that the high temperature strength is good (3) Gleeble test (hot working Sex assessment)
Test piece: Round bar test piece test method having a parallel part diameter of 10 mm and a length of 130 mm: after heating at 1200 ° C. for 5 minutes, cooling to 1000 ° C. at 100 ° C./minute, then pulling at 5 / s strain rate and breaking After cooling to room temperature with He gas, the drawing value is measured and evaluated: Judged that the drawing ratio is 60% or more as good hot workability (4) Longi ballest rain (weldability evaluation)
Test piece: 12 mm thick, 50 mm wide, 200 mm long
Test method: TIG welding was performed at a current of 200 A, a voltage of 17 V, and a welding speed of 15 cm / min, and then 2% bending strain was applied, and the total crack length of the weld heat affected zone (HAZ) at that time was measured.
[0043]
Evaluation: It is judged that the total crack length is 5 mm or less.
[0044]
The test results are shown in Table 2.
[0045]
[Table 2]
As is apparent from Table 2, the alloy of the present invention containing Al in excess of 2.0% and less than 3.5% is hotter than Comparative Alloy A in which the Al content is less than the amount specified in the present invention. Good workability, carburization resistance, weldability and creep rupture strength. Further, Comparative Alloy B in which the Al content exceeds the upper limit defined in the present invention has a low greeble drawing of 25.0 % and a total crack length of 20 mm in the longi ballast train, which is hot workability and welding. It turns out that both sexes are inferior. Moreover, neither the comparative alloy C with high S, the comparative alloy D with high P, nor the comparative alloy E containing any of B, Zr, and Hf does not satisfy hot workability and weldability. In addition, although the surface of the test piece was observed in the solid carburization test, coking was hardly generated in the test piece having the chemical composition defined in the present invention.
[0047]
【The invention's effect】
The alloy of the present invention is an alloy having a creep rupture strength sufficient to be used as a high-temperature strength member excellent in hot workability, weldability, carburization resistance and coking resistance. In particular, it exhibits excellent characteristics in a thermal cracking and thermal cycle environment in which carburization, oxidation, and temperature fluctuation are repeated, such as a pipe used in a cracking furnace for an ethylene plant. As a result, by using the alloy of the present invention, it is possible to operate at a higher temperature, extend the continuous operation time, and extend the span of replacement with a new material by improving the durability.
Claims (8)
Priority Applications (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP21151999A JP3644532B2 (en) | 1999-07-27 | 1999-07-27 | Ni-base heat-resistant alloy with excellent hot workability, weldability and carburization resistance |
| KR10-2000-0035036A KR100372482B1 (en) | 1999-06-30 | 2000-06-24 | Heat resistant Ni base alloy |
| CA002312581A CA2312581C (en) | 1999-06-30 | 2000-06-27 | Heat resistant nickel base alloy |
| EP00401832A EP1065290B1 (en) | 1999-06-30 | 2000-06-27 | Heat resistant nickel base alloy |
| DE60004737T DE60004737T2 (en) | 1999-06-30 | 2000-06-27 | Heat-resistant nickel-based alloy |
| US09/606,151 US6458318B1 (en) | 1999-06-30 | 2000-06-29 | Heat resistant nickel base alloy |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP21151999A JP3644532B2 (en) | 1999-07-27 | 1999-07-27 | Ni-base heat-resistant alloy with excellent hot workability, weldability and carburization resistance |
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| Publication Number | Publication Date |
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| JP2001040443A JP2001040443A (en) | 2001-02-13 |
| JP3644532B2 true JP3644532B2 (en) | 2005-04-27 |
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| JP21151999A Expired - Fee Related JP3644532B2 (en) | 1999-06-30 | 1999-07-27 | Ni-base heat-resistant alloy with excellent hot workability, weldability and carburization resistance |
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| DE102008051014A1 (en) | 2008-10-13 | 2010-04-22 | Schmidt + Clemens Gmbh + Co. Kg | Nickel-chromium alloy |
| DE102012013437B3 (en) * | 2011-02-23 | 2014-07-24 | VDM Metals GmbH | Use of a nickel-chromium-iron-aluminum alloy with good processability |
| CN103540800A (en) * | 2013-10-17 | 2014-01-29 | 常熟市良益金属材料有限公司 | Casting alloy |
| CN104259240B (en) * | 2014-09-12 | 2016-03-09 | 攀钢集团江油长城特殊钢有限公司 | A kind of 18Ni-200 rod iron and preparation method thereof |
| US20210062314A1 (en) | 2017-12-28 | 2021-03-04 | Nippon Steel Corporation | Austenitic heat resistant alloy |
| JP6954976B2 (en) * | 2019-11-20 | 2021-10-27 | 日本冶金工業株式会社 | High oxidation resistance Ni-Cr-Al alloy with excellent laser cutting properties and its manufacturing method |
| DE102020132193A1 (en) * | 2019-12-06 | 2021-06-10 | Vdm Metals International Gmbh | Use of a nickel-chromium-iron-aluminum alloy with good workability, creep resistance and corrosion resistance |
| DE102020132219A1 (en) * | 2019-12-06 | 2021-06-10 | Vdm Metals International Gmbh | Use of a nickel-chromium-aluminum alloy with good workability, creep resistance and corrosion resistance |
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