JP3606404B2

JP3606404B2 - Consumable electrode type remelting method of super heat-resistant alloy

Info

Publication number: JP3606404B2
Application number: JP05140396A
Authority: JP
Inventors: 清孝高知尾; 靖久恩田; 努野原; 康史山根
Original assignee: Hitachi Metals Ltd
Current assignee: Hitachi Metals Ltd
Priority date: 1996-03-08
Filing date: 1996-03-08
Publication date: 2005-01-05
Anticipated expiration: 2016-03-08
Also published as: JPH09241767A

Description

【０００１】
【発明の属する技術分野】
本発明は、超耐熱合金の製造に使用される消耗電極式再溶解法の改良に関するものである。
【０００２】
【従来の技術】
消耗電極式再溶解法は、積層凝固することにより偏析や内部欠陥などが少なく、均一な組織の健全な鋳塊を得ることができ、またそれぞれの溶解原理上にしたがって、非金属介在物やＳなどの不純物の除去、あるいは脱ガスなどができるなどの品質改善効果を有する。
例えば、真空アーク再溶解法（以下、ＶＡＲと記す）の場合は、徹底した真空精錬と積層凝固を、エレクトロスラグ再溶解法（以下、ＥＳＲと記す）の場合は、スラグ精錬と積層凝固を特徴としており、いずれも鋳塊の品質と信頼性を高める為の優れたプロセスであり、航空機用部品材料、原子力プラント用材料などをはじめとして、過酷な条件下で使用される高品質で、十分な信頼性が要求される材料の製造に広く供されている。
【０００３】
また、プラズマを熱源として、上記と同様の消耗電極を使用するプラズマアーク再溶解法も知られている。
これらの消耗電極式再溶解法に共通して言えることは、上記のような特徴を十分に発揮させる為には、消耗電極を製造する一次溶解の選定が重要となるだけでなく、二次溶解である再溶解法の選定と、再溶解が安定した最適条件で行なわれることが重要である。
一方、再溶解中に溶解の変動が発生すると、得られた鋳塊には種々の欠陥が生じる。例えば、溶解電圧・電流、溶解の速度などの変動に起因して、凝固形態の不連続や偏析が発生することがある。ＶＡＲやＥＳＲ鋳塊のフレックル偏析、中心偏析、リングパターンやＶＡＲ鋳塊のホワイトスポットなどがよく知られている。
【０００４】
再溶解の際の溶解の変動の原因には種々の要因があるが、そのほとんどは消耗電極に関る欠陥もしくは消耗電極自体の内質に起因している。例えば、再溶解中の消耗電極の割れや欠落、消耗電極中に存在するひけ巣やパイプ、消耗電極の径の不均一や消耗電極中に存在する巨大な非金属介在物（スラグ噛み込み）などが挙げられる。
この他、再溶解で発生する欠陥には、材料の化学成分に大きく依存する傾向があり、特に超耐熱合金のような高合金鋼においては、溶解中の消耗電極の割れの発生が著しく多い。ＶＡＲ，ＥＳＲを例にとると、前述のごとくその特徴を十分に発揮させる為には、再溶解中の消耗電極先端の位置を精密に制御して、溶解電圧・電流、溶解速度を安定させることが必要である。ここで、溶解中に消耗電極の割れが発生すると、割れ部が落下しない場合であっても、割れが電気や熱の抵抗となる他、消耗電極の高精度な位置制御が不可能となり、溶解電圧・電流、溶解速度が変動する結果として、欠陥を内在した鋳塊が出来上がる。
【０００５】
例えば、文献１（Ｋ．Ｏ．Ｙｕら、ＪｏｕｒｎａｌｏｆＭｅｔａｌｓＪａｎ．（１９８６）ｐ．４０−５０）にも開示されているように、ＶＡＲで製造された鋳塊には、時に前述のホワイトスポットと呼ばれる異常組織が見られる。この現象は、特にＮｂを含有するＮｉ系の超耐熱合金のＶＡＲ鋳塊で多く散見される。この欠陥部はＮｂが欠乏している為に、塩化第２鉄水溶液のようなＮｂに敏感な腐食液を用いたマクロ組織出現試験法で観察すると、白色系の光沢を伴った斑点状欠陥として認められる為にこの名称で呼ばれている。この欠陥はマトリックスに比べ強度が低いため、信頼性が要求される再溶解品に存在することは品質上問題となる。
この異常組織はＡＳＭＩｎｔｅｒｎａｔｉｏｎａｌのｗｈｉｔｅｓｐｏｔ分科会により次の３種類に分類され、それぞれの生成する原因を図１に基づいて以下のように説明されている（文献２：Ｌ．Ａ．Ｊａｃｋｍａｎ，Ｇ．Ｅ．Ｍａｕｒｅｒ，Ｓ．Ｗｉｄｇｅ；ＡｄｖａｎｃｅｄＭａｔｅｒｉａｌｓ＆Ｐｒｏｃｅｓｓｅｓ，Ｎｏ．５（１９９３），ｐ．１８）。
【０００６】
（１）ｄｉｓｃｒｅｔｅｗｈｉｔｅｓｐｏｔ
ＶＡＲ鋳塊の溶鋼プール４の直上にあるモールド壁２に沿って形成されたクラウン領域６、溶鋼プール４表面周辺に形成されたシェルフ領域７または消耗電極１先端周囲に氷柱状に形成されたトーラス９の小片が溶鋼プール４に落下しマッシー・ゾーン５に達して完全に溶解しないまま鋳塊中に残留したもの。
（２）ｄｅｎｄｒｉｔｉｃｗｈｉｔｅｓｐｏｔ
消耗電極１中のデンドライド８の一部が未溶解のままＶＡＲ鋳塊頭部に形成された溶鋼プールに落下し、完全に溶解しないうちに鋳塊中に残留したもの。
（３）ｓｏｌｉｄｉｆｉｃａｔｉｏｎｗｈｉｔｅｓｐｏｔ
凝固速度の局部的な現象によりマッシー・ゾーン５内でデンドライトの粗大化が起こり、樹間溶液が掃き出されることによると考えられているもの。
上記３種類のホワイト・スポットのうち（１）のディトクリート・ホワイトスポットのシェルフに起因するものは、大型の非金属介在物を伴うことが多く、最も有害であると考えられている。
【０００７】
これに対し、本発明者の内の一人は特開平７−３３５０号において、消耗電極の横断面積Ａｅとモールド内部の横断面積Ａｉの比Ａｅ／Ａｉを０．７５以上にすることによって、アークによる熱供給が溶鋼プール周辺に行き渡るようになる結果、シェルフの発達が抑制され、この型のホワイト・スポットを防止する上で多大な効果が得られることを提案している。
しかしながら、この方法は安定な溶解を前提としているのであって、消耗電極が溶解中に割れることにより溶解電圧・電流、溶解速度が変動するような極めて不安定な状況にあっては、入熱不足により、シェルフが局部的に成長し、上述の方法をもってしてもホワイトスポットが認められることがある。
【０００８】
以上はＶＡＲにおいて消耗電極の割れにより溶解電圧・電流、溶解速度が変動しホワイトスポットが誘発されることによる不具合について示したものだが、消耗電極が割れることによりその破片が鋳塊中に直接混入することもある。ＥＳＲではＶＡＲに比べてスラグの存在により同一溶解速度下での溶鋼プールが深く熱容量も大きいが、この場合の破片は大型であり、ＥＳＲであっても完全に溶解しないまま鋳塊中に残留することが多く、時にはスラグを巻き込んだ状態となることがある。
【０００９】
【発明が解決しようとする課題】
前述の通り、再溶解プロセス中に、消耗電極の割れに起因する不安定溶解による異常組織や消耗電極小片そのものが、未溶解のまま鋳塊中に残留した異常組織を安価で、効率の良い方法で防止する必要があった。
これらの欠陥は、割れ、巨大非金属介在物、ポロシティなどの欠陥を伴う場合には、鋳塊の鍛造または圧延後の超音波探傷試験において検出し得るか、さもなくば、鍛造または圧延後の横断試験片のマクロ組織出現試験法において稀に検出される程度であり、品質管理上、非常に大きな問題点を宿しているだけでなく、仮に検出された場合であっても、その部分は廃却される為に製造歩留を悪化させ、生産コストの大幅なコストアップを招くものである。また著しい場合には、鍛造等の熱間加工時の割れ、疵により製品の製造そのものが不可能になることさえある。
したがって、本発明は上記従来技術の問題点を克服して、異常組織の無い鋳塊を安定して製造し得る超耐熱合金の消耗電極式再溶解法を提供することを目的とする。
【００１０】
【課題を解決するための手段】
本発明者らの観察によれば、ＶＡＲやＥＳＲの操業においては、時に操業途中で消耗電極の先端が割れる事態が生じることがある。この現象は、その際に生じる破裂音によっても確認されるが、例えば、図２に示すような操業中の溶解電圧をモニターしたチャート上にも局所的かつ剪断的な電圧低下として現れ、このような兆候が発生した操業で出来た鋳塊には、ＶＡＲ鋳塊の場合はホワイトスポットやフレックル等の偏析、ＥＳＲ鋳塊の場合はフレックル等の偏析またはスラグの巻込みを伴った未溶解電極の混入が認められる。
本発明者等は、再溶解中のこれらの破裂音や異常な電圧低下の原因について調査した。
【００１１】
すなわち、Ｉｎｃｏｎｅｌ７１８，Ａ２８６およびＶ５７（これらはいずれも商品名である）といった超耐熱合金のＶＡＲ操業中における前述の消耗電極が割れるという兆候が現れた時に、操業を中断して、消耗電極先端から鋳塊長手方向に平行に試験片を切り出し、マクロ組織出現法により調査したところ、結晶粒界に沿って多くの割れが観察された。さらにこの割れ部を研磨して光学顕微鏡で観察した結果、結晶粒界に金属間化合物が見られ、この析出物に沿って割れが進行していることが確認された。この金属間化合物をＥＰＭＡ（Ｘ線微小分析装置）で分析したところ、Ｉｎｃｏｎｅｌ７１８の場合、Ｎｉ，Ｎｂ，Ｆｅ，Ｃｒ，Ｍｏ，Ｔｉ，Ｓｉ，Ｃなどが観察されたが、さらに金属間化合物を電解研磨後、Ｘ線回折試験を行った結果、これらはＬａｖｅｓ相［（Ｆｅ，Ｍｏ）_２Ｎｂ］，ＭＣ型炭化物［ＮｂＣ］，Ｍ_７Ｃ_３型炭化物［（Ｃｒ，Ｆｅ）_７Ｃ_３］などであり、ＴｉやＳｉはこれらに固溶していることがわかったが、中でもＬａｖｅｓ相が最も優勢であった。
【００１２】
一方、Ａ２８６やＶ５７においても同様の観察を行ったところ、この場合には、粒界には、ＴｉＣやＬａｖｅｓ相［Ｆｅ_２Ｔｉ］が認められた。これらのうち金属間化合物は非常に脆いものであり、特にＬａｖｅｓ相の析出は超耐熱合金の製造性を著しく害するものである。
以上により、ＶＡＲやＥＳＲの消耗電極が、これらの再溶解中に割れる機構は、消耗電極鋳造時に結晶粒界に析出、または晶出したＬａｖｅｓ相などの金属間化合物が、ＶＡＲ操業中の消耗電極先端の非常に大きな温度勾配下で過大な熱応力を受けた為に割れ、それが結晶粒界に伝播して大きな割れに至ったものと考えられる。また、ＥＳＲにおける同様の現象もＶＡＲと同様のメカニズムによって消耗電極の割れが発生した結果、欠陥が生じるものと考えられる。
【００１３】
したがって、消耗電極鋳造時に生じるこれらの金属間化合物を何らかの手段で解消、または無害化出来れば、ＶＡＲ、ＥＳＲあるいはプラズマアーク再溶解時の消耗電極の割れに起因する異常組織を防止出来ることは明らかである。
そこで、超耐熱合金の消耗電極を製造する時に晶出する金属間化合物の影響度と無害化条件について検討した。その結果、Ｉｎｃｏｎｅｌ７１８合金に認められるＮｂを含有するＬａｖｅｓ相はＴｉを含有することが多く、極めて脆化し易いものであること、特にＮｂとＴｉの含有量の和が２．０ｍａｓｓ％以上になるとその悪影響が強くなることがわかった。しかし、この合金を約１１５０℃以上に加熱すると、Ｌａｖｅｓ相は基地に固溶し、ほとんど脆化現象が解消された。
同様にＡ２８６やＶ５７合金では、Ｌａｖｅｓ相（Ｆｅ_２Ｔｉ）は約１１２０℃以上で基地に固溶し脆化現象が解消された。
本発明はこの結果を消耗電極に適用したものである。
【００１４】
すなわち、本発明の第１発明は、超耐熱合金の消耗電極式再溶解法において、予めNb と Ti の１種または２種を含有する超耐熱合金でなる消耗電極を均熱処理を行なった後に再溶解することを特徴とする超耐熱合金の消耗電極式再溶解法である。また、上記第１発明の消耗電極を予め均熱処理すると有効な溶解法は、真空アーク再溶解、エレクトロスラグ再溶解、プラズマアーク再溶解のいずれかである。
NbやTiを含有する超耐熱合金は前述のように脆いLaves相を晶出する。本発明により消耗電極を予め均熱処理することによりLaves相を大幅に現象または解消することは、超耐熱合金が、NbとTiの１種または２種を含有する合金であり、かつNbとTiの含有量の和が2.0mass%以上である合金が望ましく、さらに望ましくは、NbとTiの１種または２種を含有し、かつNiを15mass%以上含有する合金である。上記の超耐熱合金では、消耗電極の均熱温度は、1100℃以上かつ融点以下で実施するのが好ましい。
【００１５】
【発明の実施の形態】
本発明における均熱処理の作用と数値の限定理由を以下に述べる。
高温度勾配下における粒界割れの再現を行なう為に、一例として表１に示す組成の各種超耐熱合金を小型真空誘導炉にて溶製し、消耗電極をシュミレートした直径４０ｍｍ×１００ｍｍ長の鋳造試験片を各々２本づつ作成した。各２本の鋳造試験片のうち、１本は本発明に規定する均熱温度である１１５０℃で２０時間の均熱処理を施した。上記の消耗電極をシミュレートして得た各試験片に対して、再溶解を想定した熱応力を与える目的で、Ｃ含有量が２．５ｍａｓｓ％であるような炭素鋼を溶解して、溶鋼温度を約１４００℃に保持した高周波誘導炉中に全ての試験片を片端のみ浸漬させて１０秒間保持した後、炉外に引き出して空冷した。この試験片を中心線に沿って縦断して、縦断面のマクロ組織出現試験を行なって、浸漬側先端の割れの有無の確認を行った。その結果を表１に示す。
【００１６】
【表１】

【００１７】
均熱処理を施した場合には、いずれの試験片も割れの発生は認められないのに対して、均熱処理を施さない場合には、割れの発生が認められるものがある。表１にはＮｂおよびＴｉの含有量の和も併記しているが、均熱処理を施さない場合、ＮｂとＴｉの和が大きいほど割れが発生し易く、さらに詳しくはＮｂとＴｉの和が２．０ｍａｓｓ％以上で割れが発生している。
以上の結果より、本発明はＮｂとＴｉの含有量の和が２．０ｍａｓｓ％以上の合金に対して特に有効であることがわかる。しかしながら、上記を外れる範囲の化学組成をもつ合金に対しても、大型の消耗電極で結晶粒が大きく発達したものなどに適用出来る。
【００１８】
本発明の対象とする材料は、ＮｂとＴｉの１種または２種を含有するものであれば特に限定しないが、これらの元素は一般に１５ｍａｓｓ％以上のＮｉを含有する超耐熱合金に添加されている場合が多く、この種の超耐熱合金に消耗電極式再溶解法を実施して鋳塊を製造する際に、威力を発揮する。このような超耐熱鋼の一例として、ｍａｓｓ％でＣ０．０８％以下、Ｓｉ１．０％以下、Ｍｎ１．０％以下、Ｎｉ３０〜６５％、Ｃｒ１３〜２５％、Ａｌ０．８〜３．０％、ＴｉとＮｂの１種または２種の合計が２．０〜５．５％を含み、残部がＦｅまたは上記組成にＭｏ３％以下とＷ３％以下の１種または２種を含有するＦｅ−Ｎｉ−Ｃｒ基超耐熱合金などがある。
一方、上記実験では、均熱処理の条件を１１５０℃×２０時間としたが、予備実験の結果、Ｉｎｃｏｎｅｌ７１８，Ａ２８６の鋳造ままの試験片を、温度を変えて長時間の均熱処理を施し、内部組織の観察を行ったところ、Ｌａｖｅｓ相、β相のいずれも１１００℃以上で消失するので、下限を１１００℃とした。温度の上限については、材料の融点以下であれば良いが、金属間化合物の組成によっては、あまりに高過ぎる均熱処理温度のもとでは金属間化合物自体が溶融し、粒界に空孔が形成される為に、逆効果となるばかりでなく、省エネルギー的見地からも好ましくない。
また、均熱処理時間については、金属間化合物の組成、大きさ等により完全なる効果の得られる時間がそれぞれ異なるが、金属間化合物が固溶体化するのに十分な時間であればよい。
なお、上記説明において、便宜上ＶＡＲ，ＥＳＲのみについて説明を行なったが、消耗電極先端に高熱応力のかかる再溶解法、例えばプラズマアーク再溶解等にも適用できることは以上の議論から明らかである。
【００１９】
【実施例】
以下に本発明を実施例に基づいて説明する。なお、表２に実施例１〜実施例７を纏めて示す。
実施例１は表２に示す化学成分から成るＩｎｃｏｎｅｌ７１８を真空誘導炉で溶製し、消耗電極２本を鋳造して作成した。１本は１１７０℃で３０時間の均熱処理を施し、他の１本は均熱処理を施さないでＶＡＲに供した。均熱処理を施した消耗電極はＶＡＲ操業中に破裂音の発生、溶解電圧の変動は起こらなかったのに対して、均熱処理を施さなかった消耗電極は、破裂音が発生し、溶解電圧の異常変動が認められた（図３〜図４参照）。次にこのようにして作成した鋳塊を横断して、それぞれ複数のスライス試験片を切り出し、塩化第２鉄水溶液で腐食した結果、均熱処理を施した消耗電極を用いたＶＡＲ鋳塊から得られたスライス試験片のマクロ組織はいずれも健全であるのに対し、均熱処理を施さなかった消耗電極を用いたＶＡＲ鋳塊から得られたスライス試験片にはホワイトスポットが一部に認められた。
【００２０】
【表２】

【００２１】
実施例２は表２に示す化学成分から成るＩｎｃｏｌｏｙ９０１（商品名）を真空誘導炉で溶製し、消耗電極２本を鋳造して作成した。１本は１１７０℃で３０時間の均熱処理を施し、他の１本は均熱処理を施さないでＶＡＲに供した。均熱処理を施した消耗電極はＶＡＲ操業中に破裂音の発生、溶解電圧の変動は起こらなかったのに対して、均熱処理を施さなかった消耗電極は、破裂音が発生し、溶解電圧の異常変動が認められた。次に、これらの鋳塊を鍛造後、全長にわたって超音波探傷試験を実施した結果、均熱処理を施した消耗電極を用いたＶＡＲ鋳塊はインジケーション（欠陥部に相当）が認められなかったのに対し、均熱処理を施さなかった消耗電極を用いたＶＡＲ鋳塊はインジケーションが認められた。消耗電極に均熱処理を
施さなかった鋳塊から製造されたビレットの超音波探傷インジケーション部を割り出し、マクロ組織出現試験を行った結果、非金属介在物を伴うホワイトスポットが認められた。すなわち、均熱処理を施さなかった消耗電極は鋳塊の鍛造後にホワイトスポットを起点とする割れを伴い、超音波探傷試験の欠陥部としてインジケーションが認められたものである。
【００２２】
実施例３は表２に示す化学成分から成るＩｎｃｏｎｅｌ７１８を真空誘導炉で溶製し、消耗電極２本を鋳造して作成した。１本は１１７０℃で３０時間の均熱処理を施し、他の１本は均熱処理を施さないでＥＳＲに供した。均熱処理を施した消耗電極はＥＳＲ操業中に破裂音の発生、溶解電圧の変動は起こらなかったのに対して、均熱処理を施さなかった消耗電極は、破裂音が発生し、溶解電圧の異常変動が認められた（図５〜図６参照）。次にこのようにして作成した鋳塊を横断して、それぞれ複数のスライス試験片を切り出し、塩化第２鉄水溶液で腐食した結果、均熱処理を施した消耗電極を用いたＥＳＲ鋳塊から得られたスライス試験片のマクロ組織はいずれも健全であるのに対し、均熱処理を施さなかった消耗電極を用いたＥＳＲ鋳塊から得られたスライス試験片にはフレックルが一部に認められた。
【００２３】
実施例４は表２に示す化学成分から成る合金Ａを真空誘導炉で溶製し、消耗電極２本を鋳造して作成した。１本は１１８０℃で３０時間の均熱処理を施し、他の１本は均熱処理を施さないでＥＳＲに供した。均熱処理を施した消耗電極はＥＳＲ操業中に破裂音の発生、溶解電圧の変動は起こらなかったのに対して、均熱処理を施さなかった消耗電極は、破裂音が発生し、溶解電圧の異常変動が認められた（図７〜図８参照）。
次に、これらの鋳塊を鍛造後、全長にわたって超音波探傷試験を実施した結果、均熱処理を施した消耗電極を用いたＥＳＲ鋳塊はインジケーションが認められなかったのに対し、均熱処理を施さなかった消耗電極を用いたＥＳＲ鋳塊は鋳造時に割れが発生した。割れが発生した部分の内部を切り出して、マクロ組織試験を行なった結果、消耗電極と同一組成の破片がＥＳＲスラグを伴って未溶解のまま検出された。
【００２４】
実施例５は表２に示す化学成分から成る合金Ｂを真空誘導炉で溶製し、消耗電極２本を鋳造して作成した。１本は１１８０℃で３０時間の均熱処理を施し、他の１本は均熱処理を施さないでＥＳＲに供した。均熱処理を施した消耗電極はＥＳＲ操業中に破裂音の発生、溶解電圧の変動は起こらなかったのに対して、均熱処理を施さなかった消耗電極は、破裂音が発生し、溶解電圧の異常変動が認められた（図７，８参照）。次に、これらの鋳塊を鍛造した際、均熱処理を施した消耗電極を用いたＥＳＲ鋳塊は鍛造時に異常はなく、全長にわたる超音波探傷試験を実施した結果、インジケーションが認められなかったのに対し、均熱処理を施さなかった消耗電極を用いたＥＳＲ鋳塊は鍛造時に疵が多発した。疵が発生した部分の内部を切り出して、マクロ組織試験を行なった結果、一部に消耗電極と同一組成の破片が未溶解のまま検出され、フレックル偏析も認められた。
【００２５】
実施例６は表２に示す化学成分から成る合金Ｃを真空誘導炉で溶製し、消耗電極２本を鋳造して作成した。１本は１１８０℃で３０時間の均熱処理を施し、他の１本は均熱処理を施さないでＥＳＲに供した。均熱処理を施した消耗電極はＥＳＲ操業中に破裂音の発生、溶解電圧の変動は起こらなかったのに対して、均熱処理を施さなかった消耗電極は、破裂音が発生し、溶解電圧の異常変動が認められた。次に、これらの鋳塊を鍛造した際、均熱処理を施した消耗電極を用いたＥＳＲ鋳塊は鍛造時に異常はなく、全長にわたる超音波探傷試験を実施した結果、インジケーションが認められなかったのに対し、均熱処理を施さなかった消耗電極を用いたＥＳＲ鋳塊は鍛造時に疵が多発した。疵が発生した部分の内部を切り出して、マクロ組織試験を行なった結果、一部に消耗電極と同一組成の破片が未溶解のまま検出され、フレックル偏析も認められた。
【００２６】
実施例７は表２に示す化学成分から成る合金Ｄを真空誘導炉で溶製し、消耗電極２本を鋳造して作成した。１本は１１８０℃で３０時間の均熱処理を施し、他の１本は均熱処理を施さないでＥＳＲに供した。均熱処理を施した消耗電極はＥＳＲ操業中に破裂音の発生、溶解電圧の変動は起こらなかったのに対して、均熱処理を施さなかった消耗電極は、破裂音が発生し、溶解電圧の異常変動が認められた。次に、これらの鋳塊を鍛造した際、均熱処理を施した消耗電極を用いたＥＳＲ鋳塊は鍛造時に異常はなく、全長にわたる超音波探傷試験を実施した結果、インジケーションが認められなかったのに対し、均熱処理を施さなかった消耗電極を用いたＥＳＲ鋳塊は鍛造時に疵が多発した。疵が発生した部分の内部を切り出して、マクロ組織試験を行なった結果、一部に消耗電極と同一組成の破片が未溶解のまま検出され、フレックル偏析も認められた。
これらの結果は、消耗電極を使用する再溶解に広く適用できるものであり、プラズマを熱源とするプラズマアーク再溶解にも本発明は有効である。
【００２７】
【発明の効果】
以上述べたように、本発明は NbとTiの１種または２種を含有する合金、たとえばNbとTiの含有量の和が2.0mass%以上を含有する合金の消耗電極を、均熱処理を施すという簡単な処理によって、消耗電極内に生じるLaves相等の金属間化合物を固溶体化し、それによって消耗電極の再溶解時に発生する電極先端の割れを防止し、得られた鋳塊の品質が大幅に向上するとともに、従来は不良部を廃却することによって生じていた歩留の低下や鋳塊の熱間加工時の割れ、疵が減少することにより、製造コストも飛躍的に低減するものである。
【図面の簡単な説明】
【図１】ホワイトスポット発生要因を示すＶＡＲプロセス模式図である。
【図２】消耗電極の割れにともなう溶解電圧の時間経過を示す図である。
【図３】Ｉｎｃｏｎｅｌ７１８のＶＡＲ時の正常チャートを示す図である。
【図４】Ｉｎｃｏｎｅｌ７１８のＶＡＲ時の異常チャートを示す図である。
【図５】Ｉｎｃｏｎｅｌ７１８のＥＳＲ時の正常チャートを示す図である。
【図６】Ｉｎｃｏｎｅｌ７１８のＥＳＲ時の異常チャートを示す図である。
【図７】合金ＡのＥＳＲ時の正常チャートを示す図である。
【図８】合金ＡのＥＳＲ時の異常チャートを示す図である。
【符号の説明】
１消耗電極、２モールド、３鋼塊、４溶鋼プール、５マッシー・ゾーン、６クラウン、７シェルフ、８デンドライト、９トーラス[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a consumable electrode type remelting method used in the manufacture of superalloys.
[0002]
[Prior art]
The consumable electrode type remelting method is capable of obtaining a solid ingot having a uniform structure with few segregation and internal defects by laminating and solidifying, and in accordance with each melting principle, nonmetallic inclusions and S It has the effect of quality improvement such as removal of impurities such as degassing or degassing.
For example, vacuum arc remelting (hereinafter referred to as VAR) is characterized by thorough vacuum refining and lamination solidification, and electroslag remelting (hereinafter referred to as ESR) is characterized by slag refining and lamination solidification. Both are excellent processes for improving the quality and reliability of ingots, and are high quality and sufficient for use in harsh conditions such as aircraft parts materials and nuclear power plant materials. Widely used in the manufacture of materials that require reliability.
[0003]
A plasma arc remelting method using a consumable electrode similar to the above using plasma as a heat source is also known.
In common with these consumable electrode-type remelting methods, in order to make full use of the above-mentioned characteristics, it is important not only to select the primary dissolution for producing the consumable electrode, but also to perform secondary dissolution. It is important to select a re-dissolution method and to perform re-dissolution under stable and optimal conditions.
On the other hand, when a variation in melting occurs during remelting, various defects occur in the obtained ingot. For example, discontinuity and segregation of the solidification form may occur due to fluctuations in melting voltage / current, melting speed, and the like. Freckle segregation, center segregation, ring pattern, white spot of VAR ingot, etc. are well known.
[0004]
There are various causes of the variation in dissolution during re-dissolution, most of which are due to defects in the consumable electrode or the quality of the consumable electrode itself. For example, cracking or missing of the consumable electrode during remelting, sinkholes and pipes present in the consumable electrode, uneven diameter of the consumable electrode, and huge non-metallic inclusions (slag biting) present in the consumable electrode Is mentioned.
In addition, defects generated by remelting tend to largely depend on the chemical composition of the material, and particularly in high alloy steels such as super heat-resistant alloys, cracking of consumable electrodes during melting is extremely large. Taking VAR and ESR as examples, as described above, in order to fully demonstrate its characteristics, the position of the tip of the consumable electrode during re-dissolution must be precisely controlled to stabilize the dissolution voltage / current and dissolution rate. is required. Here, if the consumable electrode cracks during melting, even if the crack does not fall, the crack becomes an electric and thermal resistance, and the position control of the consumable electrode becomes impossible and the melting is impossible. As a result of fluctuations in voltage, current, and melting rate, an ingot containing defects is produced.
[0005]
For example, as disclosed in Reference 1 (KO Yu et al., Journal of Metals Jan. (1986) p. 40-50), ingots manufactured with VAR sometimes contain the aforementioned white spots. An abnormal tissue called is seen. This phenomenon is often seen especially in VAR ingots of Ni-based superalloys containing Nb. Since this defect portion is deficient in Nb, it is observed as a spot-like defect with white gloss when observed by a macrostructure appearance test method using a corrosion solution sensitive to Nb such as ferric chloride aqueous solution. It is called by this name to be recognized. Since this defect has a lower strength than that of the matrix, the presence of the defect in a remelted product that requires reliability is a problem in quality.
These abnormal tissues are classified into the following three types by the ASM International white spot subcommittee, and the causes of each are described as follows based on FIG. 1 (Reference 2: LA Jackman, G.) E. Maurer, S. Widge; Advanced Materials & Processes, No. 5 (1993), p.18).
[0006]
(1) Discrete white spot
A crown region 6 formed along the mold wall 2 immediately above the molten steel pool 4 of the VAR ingot, a shelf region 7 formed around the surface of the molten steel pool 4, or a torus formed in the shape of an icicle around the tip of the consumable electrode 1 A small piece of 9 falls into the molten steel pool 4, reaches the Massy zone 5 and remains in the ingot without being completely melted.
(2) dendritic white spot
A part of the dendride 8 in the consumable electrode 1 falls into a molten steel pool formed on the VAR ingot head without being melted, and remains in the ingot before completely melting.
(3) solidification white spot
It is thought that dendrite coarsening occurs in the Massy Zone 5 due to a local phenomenon of the solidification rate, and the intertree solution is swept away.
Of the above three types of white spots, those resulting from the (1) detoclet white spot shelf often involve large non-metallic inclusions and are considered the most harmful.
[0007]
On the other hand, one of the inventors of the present invention disclosed in Japanese Patent Application Laid-Open No. 7-3350, by setting the ratio Ae / Ai of the cross-sectional area Ae of the consumable electrode to the cross-sectional area Ai inside the mold to be 0.75 or more, thereby causing an arc. As a result of the heat supply spreading around the molten steel pool, the development of the shelf is suppressed, and it is proposed that a great effect can be obtained in preventing this type of white spot.
However, this method is based on the premise of stable melting. In extremely unstable situations where the melting voltage, current, and dissolution rate fluctuate due to cracking of the consumable electrode during melting, heat input is insufficient. As a result, the shelf grows locally and white spots may be observed even with the method described above.
[0008]
The above shows the malfunctions caused by fluctuations in the melting voltage / current and melting speed due to cracking of the consumable electrode, and white spots are induced. However, when the consumable electrode cracks, the fragments are mixed directly into the ingot. Sometimes. In ESR, the pool of molten steel at the same melting rate is deep and heat capacity is large due to the presence of slag compared to VAR, but the fragments in this case are large and remain in the ingot without being completely dissolved even in ESR. Often, slag is sometimes involved.
[0009]
[Problems to be solved by the invention]
As described above, during the remelting process, the abnormal structure due to unstable dissolution resulting from cracking of the consumable electrode and the consumable electrode pieces themselves remain undissolved and the abnormal structure remaining in the ingot is inexpensive and efficient. It was necessary to prevent it.
These defects, if accompanied by defects such as cracks, large non-metallic inclusions, porosity, etc., can be detected in ultrasonic flaw testing after forging or rolling of the ingot, or else after forging or rolling It is only rarely detected in the macro structure appearance test method of cross specimens, and it not only has a very big problem in quality control, but even if it is detected, the part is Since it is abolished, the production yield is deteriorated and the production cost is greatly increased. Further, in a remarkable case, the manufacture of the product itself may be impossible due to cracks and flaws during hot working such as forging.
Accordingly, an object of the present invention is to provide a consumable electrode type remelting method of a super heat-resistant alloy capable of overcoming the above-mentioned problems of the prior art and stably producing an ingot having no abnormal structure.
[0010]
[Means for Solving the Problems]
According to the observations by the present inventors, in the operation of VAR and ESR, sometimes the tip of the consumable electrode breaks during the operation. This phenomenon is also confirmed by a plosive sound generated at that time. For example, this phenomenon appears as a local and shear voltage drop on a chart monitoring the melting voltage during operation as shown in FIG. For ingots produced by operations with various signs, segregation of white spots and creckles in the case of VAR ingots, segregation of flares and other undissolved electrodes in the case of ESR ingots, Contamination is observed.
The present inventors investigated the cause of these plosive sounds and abnormal voltage drop during remelting.
[0011]
That is, when there is an indication that the aforementioned consumable electrode breaks during the VAR operation of super heat-resistant alloys such as Inconel 718, A286, and V57 (all of which are trade names), the operation is interrupted and the casting is started from the tip of the consumable electrode. When a test piece was cut out parallel to the longitudinal direction of the lump and investigated by the macrostructure appearance method, many cracks were observed along the crystal grain boundary. Further, as a result of polishing the cracked portion and observing with an optical microscope, it was confirmed that an intermetallic compound was observed at the grain boundary, and the crack progressed along the precipitate. When this intermetallic compound was analyzed by EPMA (X-ray microanalyzer), in the case of Inconel 718, Ni, Nb, Fe, Cr, Mo, Ti, Si, C, etc. were observed. As a result of performing an X-ray diffraction test after polishing, these showed a Laves phase [(Fe, Mo) ₂ Nb], MC type carbide [NbC], M ₇ C ₃ type carbide [(Cr, Fe) ₇ C ₃ ], and the like. It was found that Ti and Si were dissolved in these, but the Laves phase was the most dominant among them.
[0012]
On the other hand, when the same observation was made with A286 and V57, TiC and a Laves phase [Fe ₂ Ti] were observed at the grain boundaries in this case. Of these, intermetallic compounds are very brittle, and in particular, the precipitation of the Laves phase significantly impairs the manufacturability of superalloys.
As described above, the mechanism by which the consumable electrode of VAR or ESR breaks during remelting is such that the intermetallic compound such as the Laves phase precipitated or crystallized at the grain boundary during the consumable electrode casting is a consumable electrode during VAR operation. It is thought that cracks occurred due to excessive thermal stress under a very large temperature gradient at the tip, which propagated to the grain boundaries and led to large cracks. In addition, it is considered that defects similar to those in ESR occur as a result of cracking of the consumable electrode by the same mechanism as in VAR.
[0013]
Therefore, if these intermetallic compounds generated during casting of the consumable electrode can be eliminated or made harmless by any means, it is clear that the abnormal structure caused by cracking of the consumable electrode during VAR, ESR or plasma arc remelting can be prevented. is there.
Therefore, the influence of the intermetallic compound crystallized during the production of the consumable electrode of the super heat resistant alloy and the detoxification conditions were investigated. As a result, the Laves phase containing Nb found in the Inconel 718 alloy often contains Ti, and is extremely prone to embrittlement, especially when the sum of the contents of Nb and Ti becomes 2.0 mass% or more. It was found that the adverse effects became stronger. However, when this alloy was heated to about 1150 ° C. or higher, the Laves phase was dissolved in the matrix, and the embrittlement phenomenon was almost eliminated.
Similarly, in the A286 and V57 alloys, the Laves phase (Fe ₂ Ti) was dissolved in the base at about 1120 ° C. or more, and the embrittlement phenomenon was eliminated.
The present invention applies this result to a consumable electrode.
[0014]
That is, according to the first invention of the present invention, in the consumable electrode type remelting method of a super heat resistant alloy, a consumable electrode made of a super heat resistant alloy containing one or two kinds of Nb and Ti is preliminarily subjected to soaking treatment. This is a consumable electrode type remelting method for super heat-resistant alloys characterized by melting. An effective melting method when the consumable electrode of the first invention is preliminarily heat treated is any one of vacuum arc remelting, electroslag remelting, and plasma arc remelting.
Superheat-resistant alloys containing Nb and Ti crystallize brittle Laves phases as described above. According to the present invention, the Laves phase is greatly reduced or eliminated by pre-soaking the consumable electrode in advance. The super heat-resistant alloy is an alloy containing one or two of Nb and Ti, and Nb and Ti. An alloy having a total content of 2.0 mass% or more is desirable, and more desirably an alloy containing one or two of Nb and Ti and containing 15 mass% or more of Ni. In the super heat-resistant alloy described above, it is preferable that the soaking temperature of the consumable electrode is 1100 ° C. or higher and the melting point or lower.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The effect of soaking and the reason for limiting the numerical values in the present invention will be described below.
In order to reproduce the intergranular cracking under a high temperature gradient, for example, various super heat-resistant alloys having the composition shown in Table 1 are melted in a small vacuum induction furnace, and a consumable electrode is simulated to have a diameter of 40 mm × 100 mm in length. Two test pieces were prepared each. Of each of the two cast specimens, one was subjected to soaking for 20 hours at 1150 ° C., the soaking temperature defined in the present invention. For each test piece obtained by simulating the above consumable electrode, in order to give a thermal stress assuming remelting, carbon steel having a C content of 2.5 mass% is melted to obtain molten steel. All test pieces were immersed in only one end in a high-frequency induction furnace maintained at a temperature of about 1400 ° C. and held for 10 seconds, and then pulled out of the furnace and air-cooled. The test piece was longitudinally cut along the center line, and a macrostructure appearance test of a longitudinal section was conducted to confirm the presence or absence of cracks on the immersion side tip. The results are shown in Table 1.
[0016]
[Table 1]

[0017]
When soaking is performed, no cracks are observed in any of the test pieces, whereas when soaking is not performed, cracks are observed. Table 1 also shows the sum of the contents of Nb and Ti. However, when the soaking is not performed, the larger the sum of Nb and Ti, the easier the cracking occurs. More specifically, the sum of Nb and Ti is 2 Cracking occurs at 0.0 mass% or more.
From the above results, it can be seen that the present invention is particularly effective for an alloy having a sum of Nb and Ti contents of 2.0 mass% or more. However, even an alloy having a chemical composition outside the above range can be applied to a large-sized consumable electrode with greatly developed crystal grains.
[0018]
Although the material which is the object of the present invention is not particularly limited as long as it contains one or two of Nb and Ti, these elements are generally added to a super heat-resistant alloy containing 15 mass% or more of Ni. In many cases, this type of super heat-resistant alloy is effective when an ingot is manufactured by performing a consumable electrode type remelting method. As an example of such super heat-resistant steel, mass% is C 0.08% or less, Si 1.0% or less, Mn 1.0% or less, Ni 30 to 65%, Cr 13 to 25%, Al 0.8 -3.0%, the total of one or two of Ti and Nb contains 2.0-5.5%, the balance is Fe or the above composition is one or two of Mo 3% or less and W 3% or less There are Fe-Ni-Cr base superalloys containing seeds.
On the other hand, in the above experiment, the condition of soaking was set to 1150 ° C. × 20 hours. However, as a result of the preliminary experiment, the as-cast specimens of Inconel 718 and A286 were subjected to soaking for a long time at different temperatures, When both of the Laves phase and β phase disappeared at 1100 ° C. or higher, the lower limit was set to 1100 ° C. The upper limit of the temperature may be lower than the melting point of the material, but depending on the composition of the intermetallic compound, the intermetallic compound itself melts under a soaking temperature that is too high, and voids are formed at the grain boundaries. Therefore, it is not preferable from the viewpoint of energy saving as well as counter-effect.
The soaking time varies depending on the composition, size, etc. of the intermetallic compound, and the time for obtaining the complete effect may be different as long as the intermetallic compound is formed into a solid solution.
In the above description, only VAR and ESR have been described for the sake of convenience. However, it is apparent from the above discussion that the present invention can be applied to a remelting method in which a high thermal stress is applied to the tip of the consumable electrode, for example, plasma arc remelting.
[0019]
【Example】
The present invention will be described below based on examples. Table 2 summarizes Examples 1 to 7.
Example 1 was prepared by melting Inconel 718 having chemical components shown in Table 2 in a vacuum induction furnace and casting two consumable electrodes. One was subjected to soaking at 1170 ° C. for 30 hours, and the other was subjected to VAR without soaking. Consumable electrodes subjected to soaking did not generate plosives or change in melting voltage during VAR operation, whereas consumable electrodes not subjected to soaking did generate plosives and abnormal melting voltage. Variation was observed (see FIGS. 3-4). Next, a plurality of slice test pieces were cut out across the ingot thus created and corroded with a ferric chloride aqueous solution. As a result, the VAR ingot using a consumable electrode subjected to soaking was obtained. While the macrostructures of the sliced specimens were all healthy, white spots were partially observed in the sliced specimens obtained from the VAR ingots using the consumable electrodes that were not subjected to soaking.
[0020]
[Table 2]

[0021]
Example 2 was prepared by melting Incoloy 901 (trade name) composed of the chemical components shown in Table 2 in a vacuum induction furnace and casting two consumable electrodes. One was subjected to soaking at 1170 ° C. for 30 hours, and the other was subjected to VAR without soaking. Consumable electrodes subjected to soaking did not generate plosives or change in melting voltage during VAR operation, whereas consumable electrodes not subjected to soaking did generate plosives and abnormal melting voltage. Variation was observed. Next, after forging these ingots, an ultrasonic flaw detection test was conducted over the entire length, and as a result, no indication (corresponding to a defective portion) was found in the VAR ingot using the consumable electrode subjected to soaking treatment. On the other hand, the VAR ingot using the consumable electrode which was not subjected to the soaking treatment was recognized. As a result of indexing the ultrasonic flaw detection indication part of the billet manufactured from the ingot where the consumable electrode was not subjected to soaking, a white spot with non-metallic inclusions was found. That is, the consumable electrode that was not subjected to soaking was accompanied by a crack starting from a white spot after the ingot was forged, and the indication was recognized as a defective part in the ultrasonic flaw detection test.
[0022]
Example 3 was prepared by melting Inconel 718 having chemical components shown in Table 2 in a vacuum induction furnace and casting two consumable electrodes. One was subjected to soaking at 1170 ° C. for 30 hours, and the other was subjected to ESR without soaking. Consumable electrodes subjected to soaking did not generate plosives or change in melting voltage during ESR operation, whereas consumable electrodes not subjected to soaking did generate plosives and abnormal melting voltage. Variation was observed (see FIGS. 5-6). Next, a plurality of slice test pieces were cut out across the ingot thus created and corroded with a ferric chloride aqueous solution. As a result, it was obtained from an ESR ingot using a consumable electrode subjected to soaking. While the macrostructures of the sliced test pieces were all healthy, some of the flaked pieces were found in the sliced test pieces obtained from the ESR ingot using the consumable electrode that had not been soaked.
[0023]
Example 4 was prepared by melting alloy A having chemical components shown in Table 2 in a vacuum induction furnace and casting two consumable electrodes. One was subjected to soaking at 1180 ° C. for 30 hours, and the other was subjected to ESR without soaking. Consumable electrodes subjected to soaking did not generate plosives or change in melting voltage during ESR operation, whereas consumable electrodes not subjected to soaking did generate plosives and abnormal melting voltage. Variation was observed (see FIGS. 7-8).
Next, after forging these ingots, an ultrasonic flaw detection test was conducted over the entire length. As a result, no indication was found in the ESR ingot using the consumable electrode subjected to soaking, whereas soaking was performed. The ESR ingot using the consumable electrode that was not applied was cracked during casting. As a result of cutting out the inside of the cracked portion and conducting a macro structure test, fragments having the same composition as the consumable electrode were detected undissolved with the ESR slag.
[0024]
Example 5 was prepared by melting alloy B having chemical components shown in Table 2 in a vacuum induction furnace and casting two consumable electrodes. One was subjected to soaking at 1180 ° C. for 30 hours, and the other was subjected to ESR without soaking. Consumable electrodes subjected to soaking did not generate plosives or change in melting voltage during ESR operation, whereas consumable electrodes not subjected to soaking did generate plosives and abnormal melting voltage. Variation was observed (see FIGS. 7 and 8). Next, when these ingots were forged, the ESR ingots using consumable electrodes subjected to soaking were not abnormal during forging, and as a result of conducting an ultrasonic flaw detection test over the entire length, no indication was found. On the other hand, ESR ingots using consumable electrodes that were not subjected to soaking were frequently flawed during forging. As a result of cutting out the inside of the part where wrinkles occurred and conducting a macro structure test, fragments having the same composition as the consumable electrode were detected in an undissolved part, and fleck segregation was also observed.
[0025]
Example 6 was prepared by melting alloy C having chemical components shown in Table 2 in a vacuum induction furnace and casting two consumable electrodes. One was subjected to soaking at 1180 ° C. for 30 hours, and the other was subjected to ESR without soaking. Consumable electrodes subjected to soaking did not generate plosives or change in melting voltage during ESR operation, whereas consumable electrodes not subjected to soaking did generate plosives and abnormal melting voltage. Variation was observed. Next, when these ingots were forged, the ESR ingots using consumable electrodes subjected to soaking were not abnormal during forging, and as a result of conducting an ultrasonic flaw detection test over the entire length, no indication was found. On the other hand, ESR ingots using consumable electrodes that were not subjected to soaking were frequently flawed during forging. As a result of cutting out the inside of the part where wrinkles occurred and conducting a macro structure test, fragments having the same composition as the consumable electrode were detected in an undissolved part, and fleck segregation was also observed.
[0026]
Example 7 was prepared by melting alloy D having chemical components shown in Table 2 in a vacuum induction furnace and casting two consumable electrodes. One was subjected to soaking at 1180 ° C. for 30 hours, and the other was subjected to ESR without soaking. Consumable electrodes subjected to soaking did not generate plosives or change in melting voltage during ESR operation, whereas consumable electrodes not subjected to soaking did generate plosives and abnormal melting voltage. Variation was observed. Next, when these ingots were forged, the ESR ingots using consumable electrodes subjected to soaking were not abnormal during forging, and as a result of conducting an ultrasonic flaw detection test over the entire length, no indication was found. On the other hand, ESR ingots using consumable electrodes that were not subjected to soaking were frequently flawed during forging. As a result of cutting out the inside of the part where wrinkles occurred and conducting a macro structure test, fragments having the same composition as the consumable electrode were detected in an undissolved part, and freckle segregation was also observed.
These results are widely applicable to remelting using consumable electrodes, and the present invention is also effective for plasma arc remelting using plasma as a heat source.
[0027]
【The invention's effect】
As described above, the present invention is an alloy containing one or two N b and Ti, the consumable electrode, for example an alloy sum of the contents of Nb and Ti is contained more than 2.0 mass%, the soaking treatment By applying a simple treatment, the intermetallic compound such as Laves phase generated in the consumable electrode is made into a solid solution, thereby preventing cracking of the electrode tip that occurs when the consumable electrode is remelted, and the quality of the resulting ingot is greatly improved. In addition to improvement, the manufacturing cost is drastically reduced by reducing yield and cracking and flaws during hot working of ingots, which were caused by discarding defective parts. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a VAR process showing white spot generation factors.
FIG. 2 is a diagram showing a time course of a melting voltage accompanying cracking of a consumable electrode.
FIG. 3 is a diagram showing a normal chart at the time of VAR of Inconel 718;
FIG. 4 is a diagram showing an abnormality chart during VAR of Inconel 718;
FIG. 5 is a diagram showing a normal chart at the time of ESR of Inconel 718;
FIG. 6 is a diagram showing an abnormality chart during ESR of Inconel 718;
FIG. 7 is a view showing a normal chart of an alloy A during ESR.
FIG. 8 is a diagram showing an abnormality chart of alloy A during ESR.
[Explanation of symbols]
1 consumable electrode, 2 mold, 3 steel ingot, 4 molten steel pool, 5 massey zone, 6 crown, 7 shelf, 8 dendrite, 9 torus

Claims

Consumption of super heat-resistant alloy, characterized in that in a consumable electrode type remelting method of super heat-resistant alloy, a consumable electrode made of super heat-resistant alloy containing one or two of Nb and Ti is preheated and then melted again. Electrode remelting method.

The consumable electrode type remelting method according to claim 1, wherein the consumable electrode type remelting method is any one of vacuum arc remelting, electroslag remelting, and plasma arc remelting.

The super heat-resistant alloy according to claim 1 or 2, wherein the super heat-resistant alloy is an alloy containing one or two of Nb and Ti, and the sum of the contents of Nb and Ti is 2.0 mass% or more. Consumable electrode method

The consumable electrode type remelting method for a superheat-resistant alloy according to claim 1 or 2, wherein the superheat-resistant alloy is an alloy containing one or two of Nb and Ti and containing 15 mass% or more of Ni.

The consumable electrode type remelting method for a superalloy according to any one of claims 1 to 4, wherein the soaking temperature of the consumable electrode is not less than 1100 ° C and not more than the melting point.