JP3854553B2 - Flux-cored wire for austenitic stainless steel with excellent sulfuric acid corrosion resistance, pitting corrosion resistance, ductility and toughness - Google Patents

Description

【００２６】
図２において溶接ワイヤ成分指標：ＺＦ（＝［Ｃｒ］＋３．６×［Ｎｉ］＋４．７×［Ｍｏ］＋１１．５［Ｃｕ］）が５５以上で、硫酸濃度が５０％での腐食減量は０．５ｍｍ／ｙｅａｒ以下と低減し、硫酸耐食性が向上し十分な硫酸耐食性が得られる。
【００２７】
従って、本発明では、粗製硫酸の腐食環境下での耐食性を向上させるために、フラックス入りワイヤにおける外皮またはフラックスのいずれか一方または両方に含有する成分元素を以下の（２）の関係式を満足するものに規定する。

但し、上記（２）’、（２）式における［Ｃｒ］、［Ｎｉ］、［Ｍｏ］、［Ｃｕ］は、それぞれＣｒ、Ｎｉ、Ｍｏ、Ｃｕの各成分元素の含有量（質量％）を示す。
【００２８】
また、本発明者らの調査、実験の結果から、溶接金属の延性および靭性を向上させるためには図３および図４に示すように、溶接ワイヤ成分のＣｒ当量とＮｉ当量との比（Ｃｒｅｑ／Ｎｉｅｑ）を適正とすることで、溶接金属の延性および靭性が向上することが明らかとなった。
【００２９】
通常、溶接継ぎ手に形成された溶接金属は凝固のままの状態で使用されるが、オーステナイト系ステンレス鋼の共金系ワイヤを用いて溶接して得られる溶接金属は、その成分系により初晶凝固相がフェライト相もしくはオーステナイト相となり、さらに、これらの相がそれぞれ単独で凝固を完了するものと、フェライト相＋オーステナイト相の二相で凝固が完了するものに分類される。
【００３０】
初晶凝固相がオーステナイト相の場合、その後、オーステナイト単相で凝固が完了する（Ａモード）場合、または、その後の凝固過程で一部フェライト相が晶出し、オーステナイト相＋フェライト相の二相で凝固が完了する（ＡＦモード）場合があるが、何れの場合も溶接金属の凝固完了後の冷却・相変態過程で、結晶粒径が粗大化するため、延性および靭性は低下することが判った。
【００３１】
また、初晶凝固相がフェライト相の場合、その後、フェライト単相で凝固が完了する場合（Ｆモード）、または、その後の凝固過程で一部オーステナイト相が晶出し、オーステナイト相＋フェライト相の二相で凝固が完了する場合（ＦＡモード）がある。このうち、初晶凝固相がフェライト相であり、その後、フェライト単相で凝固が完了する場合（Ｆモード）場合は、凝固完了後の冷却・相変態により、フェライト相主体の組織となるため延性および靭性が低い。
【００３２】
一方、初晶凝固相がフェライト相であり、オーステナイト相＋フェライト相の二相で凝固が完了する場合（ＦＡモード）は、凝固完了後の冷却・相変態過程において、バミキュラー状（虫食い状）のフェライトがレース状に連結され、オーステナイト粒径が擬似的に細粒化されるため、延性および靭性が改善されることが判った。
【００３３】
また、通常、溶接金属の凝固時には溶接金属中にミクロ偏析が残存し、耐食性に寄与する元素が負偏析した領域は局部腐食が発生しやすくなる。溶接金属の凝固形態の違いにより、各元素の凝固時の偏析の程度（分配係数）が異なるため、溶接金属の凝固形態の違いによりその腐食挙動も異なることが予想される。
【００３４】
一般に初晶凝固相がオーステナイト相の場合、その初期凝固域において耐食性に有効なＣｒ、Ｎｉ、Ｍｏが減少し、硫酸腐食環境および海水腐食環境ともに局部腐食が発生しやすくなり、また、さらに、その最終凝固域においてはＣｒ、Ｍｏ等が濃化し、シグマ相などの脆い金属間化合物が生成するため、靭性も著しく低下する。
【００３５】
一方、初晶凝固相がフェライト相の場合、その初期凝固域において耐食性に有効なＮｉ、Ｍｏは同様に減少するものの、その減少量は、初晶凝固相がオーステナイト相の場合に比べて小さく、また、耐食性に有効なＣｒは、ほぼ均一に分配して偏析はほとんどないため、初期凝固域におけるＣｒの減少は見られない。そのため、最終凝固域においてＮｉ、Ｍｏ、Ｃｒ等の濃化によるシグマ相などの脆い金属間化合物の生成およびそれによる靭性の著しい低下は見られない。
【００３６】
図３および図４に、溶接ワイヤ成分を基にしたＣｒ当量とＮｉ当量との比（Ｃｒｅｑ／Ｎｉｅｑ）と延性および靭性とのそれぞれの関係を示す。
【００３７】
ここで、Ｃｒ当量（Ｃｒｅｑ）およびＮｉ当量（Ｎｉｅｑ）は、以下の（４）および（５）式でそれぞれ規定されるものである。

但し、［Ｃ］、［Ｓｉ］、［Ｍｎ］、［Ｃｒ］、［Ｎｉ］、［Ｍｏ］、［Ｃｕ］、［Ｎ］は、それぞれＣ、Ｓｉ、Ｍｎ、Ｃｒ、Ｎｉ、Ｍｏ、Ｃｕ、Ｎの各成分元素の含有量（質量％）を示す。
【００３８】
図３および４から、溶接ワイヤ成分のＣｒｅｑ／Ｎｉｅｑが１．４未満では、初晶凝固がオーステナイト相で、その後、オーステナイト単相で凝固する凝固形態（Ａモード）、または、初晶凝固がオーステナイト相で、その後の凝固過程でフェライト相が晶出し、オーステナイト相＋フェライト相の二相で凝固が完了する凝固形態（ＡＦモード）となり、何れの場合も溶接金属の凝固完了後の冷却・相変態過程で、結晶粒径が粗大化するため、溶接金属の延性および靭性は低下して十分な延性および靭性は得られない。また、溶接ワイヤ成分のＣｒｅｑ／Ｎｉｅｑが１．７を超えても、初晶凝固がフェライト相で、フェライト単相で凝固が完了する凝固形態（Ｆモード）となり、凝固完了後の冷却・相変態した溶接金属は、フェライト相主体の組織となるため溶接金属の延性および靭性が低下して十分な延性および靭性は得られない。
【００３９】
これらに対して、溶接ワイヤ成分のＣｒｅｑ／Ｎｉｅｑが１．４〜１．７では、初晶凝固相がフェライト相であり、その後、凝固完了後の冷却・相変態過程において、オーステナイト相が晶出して、フェライト相＋オーステナイト相の二相で凝固が完了する凝固形態（ＦＡモード）となり、バミキュラー状（虫食い状）のフェライトがレース状に連結され、オーステナイト粒径が擬似的に細粒化されるため、溶接金属の延性および靭性が向上し十分な延性および靭性が得られる。
【００４０】
従って、本発明では、溶接金属の粗製硫酸の腐食環境下での耐全面腐食性および海水環境下での残留塩化物イオン起因の耐孔食性の両者の耐食性を維持しつつ、さらに、十分な延性および靭性を得るために必要な条件である、溶接金属の凝固形態を上記ＦＡモードとするために、フラックス入りワイヤにおける外皮またはフラックスのいずれか一方または両方に含有する成分元素を以下の（３）式を満足するように規定する。
Ｃｒｅｑ／Ｎｉｅｑ＝１．４〜１．７ ・・・（３）
但し、上記Ｃｒｅｑ、Ｎｉｅｑは上記（２）、（３）から定まるＣｒ当量、Ｎｉ当量である。
【００４１】
本発明では、フラックス入りワイヤにおける外皮またはフラックスのいずれか一方または両方に含有する成分元素を上記の各関係式で規定するとともに各成分元素の含有量を以下のように規定する。
【００４２】
なお、以下の％は、ワイヤ全質量に対する質量％を示すものである。
【００４３】
Ｃ：Ｃは溶接金属の耐食性向上にとって有害な成分であるが、溶接金属の強度確保の観点からある程度の含有が必要であり、この理由で溶接ワイヤ中にＣを０．０１％以上添加する。しかし、溶接ワイヤ中にＣを０．０５％を超えて添加すると、溶接金属が溶接ままおよびさらに再熱した場合にＣｒ炭化物を析出し、溶接金属の耐粒界腐食性および耐孔食性は著しく劣化するとともに、溶接金属の靭性、延性も著しく低下する。
従って溶接ワイヤ中のＣ含有量は０．０１〜０．０５％にする。
【００４４】
Ｓｉ：Ｓｉは溶接ワイヤ中に脱酸元素として添加するが、その効果を十分に得るためにＳｉを０．０１％以上添加する。しかし、溶接ワイヤ中にＳｉを１．５％を超えて添加すると、溶接金属組織中のフェライト相の延性が低下する。
従って溶接ワイヤ中のＳｉ含有量は０．０１〜１％にする。
【００４５】
Ｍｎ：Ｍｎは溶接ワイヤ中に脱酸元素として添加するが、その効果を十分に得るために０．０１％以上とする。しかし、溶接ワイヤ中にＭｎを２％を超えて添加すると溶接金属の延性が低下する。
従って溶接ワイヤ中のＭｎ含有量は０．５〜２％にする。
【００４６】
Ｎｉ：Ｎｉは中性塩化物環境や非酸化性の硫酸環境での溶接金属の腐食性に対し、顕著な抵抗性を与え、かつ不働態皮膜の生成を強化するため、溶接ワイヤ中のＮｉ含有量が多いほど溶接金属の耐食性向上に有効である。一方、Ｎｉはオーステナイト生成元素でありオーステナイト系ステンレス鋼の主要元素として、溶接金属中のオーステナイト相を生成・安定化する成分でもある。溶接金属の延性および靭性を維持しつつ、耐硫酸全面腐食性、残留塩化物イオン起因の耐孔食性の両者腐食性向上のためには、溶接金属の初晶凝固相をフェライト相とし、その後、フェライト相＋オーステナイト相の二相で凝固が完了するＦＡ凝固モードとする必要がある。従って、本発明では、フェライト形成元素であるＣｒ含有量を２０〜２４％とした場合の溶接金属の凝固形態および相バランスを考慮し、溶接ワイヤ中のＮｉ含有量は１０％〜１５％とする。
【００４７】
Ｃｒ：Ｃｒは溶接金属中でフェライト生成元素であるとともにオーステナイト系ステンレス鋼の主要元素として不働態皮膜を形成し溶接金属の耐食性向上に寄与する。溶接ワイヤ中のＣｒ含有量が多いほど海水環境下での溶接金属の残留塩化物イオン起因の耐孔食性は向上し、耐食性を十分に得るには溶接ワイヤ中のＣｒ含有量を２０％以上とする必要がある。しかし、溶接ワイヤ中のＣｒ含有量が過度に多くなると、硫酸環境下での耐全面耐食性が低下するため、硫酸環境下での耐全面耐食性を十分確保するために、溶接ワイヤ中のＣｒ含有量を２４％以下とする必要がある。従って、溶接ワイヤ中のＣｒ含有量を２０〜２４％とする。
【００４８】
Ｍｏ：Ｍｏは溶接金属において不働態皮膜の生成を安定化させて耐食性を向上させるために極めて有効な元素である。特に海水環境下での溶接金属の残留塩化物イオン起因の耐孔食性に対する作用は顕著であり、その効果を十分に得るためには溶接ワイヤ中にＭｏを１．９％以上含有させる必要がある。一方、その含有量が３．５％を超えると、溶接金属中にシグマ相などの脆い金属間化合物を生成して溶接金属の靭性を低下させる。
従って、溶接ワイヤ中のＭｏ含有量は１．９〜３．５％にする。
【００４９】
Ｃｕ：Ｃｕは溶接金属の耐食性を高めるのに顕著な作用を有し、特にＣｒ、Ｎｉ、Ｍｏと共存して硫酸環境下で優れた耐食性を得るには溶接ワイヤ中のＣｕ含有量を１％以上とする必要がある。
一方、溶接ワイヤ中にＣｕを３．２％を超えて添加すると溶接金属の靭性が著しく低下する。
従って溶接ワイヤ中のＣｕ含有量は１〜３．２％とする。
【００５０】
Ｎ：Ｎは強力なオーステナイト生成元素であり、その含有量が多いほど海水環境下での残留塩化物イオン起因の溶接金属の耐孔食性は向上し、その効果を十分に得るためには、溶接ワイヤ中のＮ含有量を０．０５％以上とする必要がある。一方で、溶接ワイヤ中のＮ含有量が０．１％を超えると、溶接時にブローホールが発生しやすくなる。
従って、溶接ワイヤ中のＮ含有量は０．０５〜０．１％にする。
【００５１】
以上が、本発明のフラックス入りワイヤにおける外皮またはフラックスのいずれか一方または両方に含有する基本成分元素であり、このワイヤを用いてシールドアーク溶接を行うことにより、高濃度硫酸の腐食環境下での耐全面腐食性および海水環境下での残留塩化物イオン起因の耐孔食性の両者の耐食性を十分満足し、かつ延性および靭性が高く、溶接時の耐ブローホール性および溶接作業性に優れた溶接金属を得ることができる。
【００５２】
本発明では、上記基本成分の他に、上記溶接金属の優れた特性を阻害しない程度に、必要に応じてその他の成分元素を含有することができる。
【００５３】
Ｂｉは、スラグ剥離性を改善する目的でその効果を十分に得るために０．０１％以上の含有量で添加することができる。しかしながら、本発明者らの調査、実験の結果から、Ｂｉ含有量が多くなると溶接時の耐ブローホール性が劣化することが判った。
【００５４】
図５は、溶接ワイヤ中のＢｉ含有量とそれを用いた溶接時の耐ブローホール性との関係を示す。
【００５５】
なお、溶接時の耐ブローホール性は、ＪＩＳ Ｚ３１０６試験法の判定に準拠し、４段階の等級分類（１〜４）をもとに評価し、１類を耐ブローホール性が良好であると評価した。
【００５６】
図５から溶接ワイヤ中のＢｉ含有量を０．０５％以下とすることにより、溶接時に優れた耐ブローホール性を確保することができる。
【００５７】
従って、本発明では、さらにスラグ剥離性を改善しつつ耐ブローホール性を確保するためにワイヤ中にＢｉを０．０１〜０．０５％の含有量で添加することが好ましい。
【００５８】
また、本発明のフラックス入りワイヤにおいて、さらに溶接作業性を向上させるためにフラックスとして以下のものを含有させることができる。
以下にそれぞれのフラックス成分の添加理由およびその含有量の限定理由を説明する。
【００５９】
ＴｉＯ₂：ＴｉＯ₂は、溶接時に被包性の良いスラグを形成する目的で添加する。その効果を十分に得るためにはワイヤ中のＴｉＯ₂含有量を２％以上とする必要がある。一方、ワイヤ中のＴｉＯ₂含有量が７％を超えると溶接時のスパッタ発生量が多くなる。従ってワイヤ中のＴｉＯ₂含有量は２〜７％にする。
【００６０】
ＳｉＯ₂：ＳｉＯ₂は、溶接時にアーク安定性を良好とする目的で添加する。その効果を十分に得るためにはワイヤ中のＳｉＯ₂含有量を０．１％以上とする必要がある。一方、ワイヤ中のＳｉＯ₂含有量が２％を超えると溶接時のスパッタ発生量が多くなる。従ってワイヤ中のＳｉＯ₂含有量は０．１〜２％にする。
【００６１】
Ｎａ₂ＯおよびＫ₂Ｏ：Ｎａ₂ＯおよびＫ₂Ｏは、溶接時にアークの吹付けを良好とする目的で添加する。その効果を十分に得るためにはワイヤ中のＮａ₂ＯおよびＫ₂Ｏの合計の含有量が０．０５％以上とする必要がある。一方、ワイヤ中のＮａ₂ＯおよびＫ₂Ｏの合計の含有量が０．２％を超えると、溶接時のスラグの剥離性が悪くなる。
【００６２】
従って、ワイヤ中のＮａ₂ＯおよびＫ₂Ｏの合計の含有量は０．０５〜０．２％にする。
【００６３】
弗化物：本発明では、ワイヤのフラックス中に、弗化物として、Ｋ₂ＺｒＦ₆、ＮａＦ、ＣａＦ₂、ＡｌＦ₃、ＬｉＦ等を１種または２種以上を添加することができる。いずれの弗化物も、溶接時のスラグの剥離性を良好とする目的で添加する。その効果を十分に得るためにはワイヤ中の弗化物の合計の含有量を０．１％以上とする必要がある。一方、ワイヤ中の弗化物の合計の含有量が０．９％となると、溶接時のスパッタ発生量が多くなる。
【００６４】
従って、ワイヤ中の弗化物の含有量は、弗化物の合計の含有量は０．１〜０．９％にする。
【００６５】
本発明のフラックス入りワイヤの製造は、以下の通常用いられている方法を適用できる。
【００６６】
例えば、外皮として帯鋼を管状に成形して使用する場合には、帯鋼をＵ形に成形し、そのＵ形の溝部に、配合、撹拌した充填フラックスを装入した後、Ｕ形の帯鋼をさらに丸形に成形し、その後、所定のワイヤ径まで伸線する。
【００６７】
また外皮としてパイプを使用する場合には、パイプを振動させながらパイプ内にフラックスを充填し、その後、所定のワイヤ径まで伸線する。
【００６８】
なお、フラックスは、ワイヤ製造時の充填が円滑に行えるように、固着剤（珪酸カリおよび珪酸ソーダの水溶液）を添加してボンドフラックス状にして用いることもできる。
【００６９】
【実施例】
以下、本発明の実施例を基に本発明の効果について説明する。
【００７０】
被溶接鋼材としては、表１に示す化学成分を含有する硫酸環境および海水環境の両腐食環境下で優れた耐食性有する高耐食ステンレス鋼を用いた。
【００７１】
また、溶接に用いたフラックス入りワイヤおよびこれらのワイヤを用いて溶接した際に得られた溶接金属のそれぞれの成分組成、試験結果を表２〜４に示す。
【００７２】
溶接は、ワイヤ径が１．４ｍｍΦのワイヤを用い、溶接電流：１５０〜２５０Ａ、アーク電圧：２５〜３５Ｖ、溶接速度：３０〜４０ｃｍ／ｍｉｎ、シールドガスとしてＣＯ２ガスを流量：１５〜２５リットル／ｍｉｎで行った。
【００７３】
なお、表２〜４におけるその他スラグ剤は、ＣａＯ、ＦｅＯ、ＭｇＯ、Ａｌ₂Ｏ₃である。
【００７４】
腐食試験は、板厚２０ｍｍの試験板を用いたＪＩＳ Ｚ ３３２３に基づく溶接金属の表層部から厚さ：２ｍｍ、幅：１５ｍｍ、長さ：１５ｍｍの試験片を採取し、全面を６００番エメリー紙で湿式研磨し脱脂後試験に供した。
【００７５】
塩化物孔食試験は、４０℃の３．５％ＮａＣｌ溶液中にてＪＩＳ Ｇ ０５７７に準拠し、電流密度：１００Ａ／ｃｍ²の時の電位を孔食電位として規定し、その測定値が１０００ｍＶ以上の場合を残留塩化物イオン起因の塩化物腐食における耐孔食性が良好とした。
【００７６】
硫酸全面腐食試験は、４０℃の５０％硫酸溶液中に６時間浸漬し、浸漬前後の試験片重量より算出した単位当たりの腐食減重量から換算し、一年における腐食速度の減肉量を腐食度として示し、その腐食度が０．５ｍｍ／ｙｅａｒ以下の場合を耐硫酸腐食性が良好とした。
【００７７】
溶着金属の延性は、板厚２０ｍｍの試験板を用いてＪＩＳ Ｚ ３３２３に基づく溶着金属試験で、ＪＩＳ Ｚ ３１１１のＡ１号を用いた常温引張試験の伸びを測定して評価し、その測定値が２５％以上の場合を溶着金属の延性が良好とした。
【００７８】
溶着金属の靭性は、板厚２０ｍｍの試験板を用いてＪＩＳ Ｚ ３３２３に基づく溶着金属試験で、ＪＩＳ Ｚ ３１１１の４号を用いた−２０℃衝撃試験の吸収エネルギーを測定して評価し、その測定値が３０Ｊ以上の場合を溶着金属の靭性が良好とした。
【００７９】
耐ブローホール性の調査は、図６に示す開先形状を有する試験板（板厚１２ｍｍ、長さ４００ｍｍ）を下向姿勢で３パス溶接して得られた突合せ溶接継ぎ手部のＸ線透過試験を実施し、ＪＩＳ Ｚ ３１０６付属書４（規定）の透過写真によるきずの像の分類方法によって試験視野１０×１０ｍｍにてきずの分類を行ない、１類を溶接金属の耐ブローホール性が良好とした。なお、本試験において、第１種以外のきずは認められなかった。
【００８０】
溶接作業性の試験は、板厚６ｍｍの鋼板を用いてＴ型継ぎ手を組んで、溶接電流：１５０〜２５０Ａで水平および立向（上進）姿勢ですみ肉溶接を行い、その際のアーク安定性、スパッタ発生量、スラグの被包性、スラグの剥離性を評価した。
【００８１】
表２〜４には、本発明で規定した成分のフラックス入りワイヤ（発明例）であるワイヤＮｏ．１〜１４と、発明で規定した範囲から外れる成分のフラックス入りワイヤ（比較例）であるワイヤＮｏ．１５〜２６の試験結果を示す。
【００８２】
本発明例のうち、ワイヤＮｏ．１〜１０は、Ｎｉ、Ｃr、Ｍｏ、Ｃｕ、Ｎ、Ｃｒｅｑ／Ｎｉｅｑが適正であり、ＫＦ、ＺＦを満足し、なおかつＢｉが適正で、ＴｉＯ₂、ＳｉＯ₂、Ｎａ₂Ｏ＋Ｋ₂Ｏ、弗化物の合計が適正であるので、耐食性が良好で、延性および靭性が高く、耐ブローホール性に優れ、溶接作業性が良好であり極めて満足な結果であった。また、ワイヤＮｏ．１１は、Ｎｉ、Ｃr、Ｍｏ、Ｃｕ、Ｎ、Ｃｒｅｑ／Ｎｉｅｑが適正であり、ＫＦ、ＺＦを満足し、なおかつＴｉＯ₂、ＳｉＯ₂、Ｎａ₂Ｏ＋Ｋ₂Ｏ、弗化物の合計が適正であるので、耐食性が良好で、延性および靭性が高く、溶接作業性が優れているが、ＴｉＯ₂、ＳｉＯ₂、Ｎａ₂Ｏ＋Ｋ₂Ｏ、弗化物の合計が適正ではないため、耐ブローホール性にが悪かった。
【００８３】
また、本発明例のうち、ワイヤＮｏ．１２〜１４は、Ｎｉ、Ｃr、Ｍｏ、Ｃｕ、Ｎ、Ｃｒｅｑ／Ｎｉｅｑが適正であり、ＫＦ、ＺＦを満足し、なおかつＢｉが適正であるので、耐食性が良好で、延性および靭性が高く、耐ブローホール性に優れているが、ＴｉＯ₂、ＳｉＯ₂、Ｎａ₂Ｏ＋Ｋ₂Ｏ、弗化物の合計が適正ではないため、溶接作業性が悪かった。
【００８４】
比較例中ワイヤＮｏ．１５、Ｃｒｅｑ／Ｎｉｅｑが高く、延性および靭性が低かった。
【００８５】
ワイヤＮｏ．１６は、Ｃｒｅｑ／Ｎｉｅｑが低く、延性および靭性が低かった。
【００８６】
ワイヤＮｏ．１７は、Ｎｉが低いためＣｒｅｑ／Ｎｉｅｑが高く、延性および靭性が低かった。
【００８７】
ワイヤＮｏ．１８は、Ｎｉが高いためＣｒｅｑ／Ｎｉｅｑが低く、延性および靭性が低かった。
【００８８】
ワイヤＮｏ．１９は、Ｃｒが低いためＫＦが低く、耐局部腐食性が悪かった。
【００８９】
ワイヤＮｏ．２０は、Ｃｒが高いためＺＦが低く、耐全面腐食性が悪かった。
【００９０】
ワイヤＮｏ．２１は、Ｍｏが低いためＫＦが低く、耐局部腐食性が悪かった。
【００９１】
ワイヤＮｏ．２２は、Ｍｏが高いため、靭性が低かった。
【００９２】
ワイヤＮｏ．２３は、Ｃｕが低いためＺＦが低く、耐局部腐食性が悪かった。またＢｉが高いため、ブローホールが発生した。
【００９３】
ワイヤＮｏ．２４は、Ｃｕが高いため靭性が低く、またＢｉが低いためスラグの剥離性が悪かった。
【００９４】
ワイヤＮｏ．２５は、Ｎが低いためＫＦが低く、耐局部腐食性が悪かった。またＴｉＯ₂が低いため、スラグの被包性が悪かった。
【００９５】
ワイヤＮｏ．２６は、Ｎが高いブローホールが発生した。またＴｉＯ₂が高いため、スパッタが多かった。
【００９６】
なお、参考までに各試験とも溶着金属の化学成分を示す。
【００９７】
【表１】

【００９８】
【表２】

【００９９】
【表３】

【０１００】
【表４】

【０１０１】
【発明の効果】
以上詳述したように本発明によれば、高耐食ステンレス鋼の溶接に際し、粗製硫酸による全面腐食と残留塩化物イオンによる孔食を回避した高品質の耐食性が得られ、延性および靭性が高く、耐ブローホール性に優れ、溶接作業性に優れるフラックス入りワイヤを提供することができる。
【図面の簡単な説明】
【図１】溶接ワイヤのＫＦ値（＝［Ｃｒ］＋３．３×［Ｍｏ］＋１６×［Ｎ］）と４０℃の３．５％ＮａＣｌ溶液中での孔食電位との関係を示す図である。
【図２】溶接ワイヤのＺＦ値（＝−［Ｃｒ］＋３．６×［Ｎｉ］＋４．７×［Ｍｏ］＋１１．５［Ｃｕ］）と４０℃の５０％硫酸溶液中での腐食減量との関係を示す図である。
【図３】溶接ワイヤのＣｒ当量とＮｉ当量との比（Ｃｒｅｑ／Ｎｉｅｑ）と延性（全伸び）との関係を示す図である。
【図４】溶接ワイヤのＣｒ当量とＮｉ当量との比（Ｃｒｅｑ／Ｎｉｅｑ）と靭性（吸収エネルギー）との関係を示す図である。
【図５】溶接ワイヤ中のＢｉ含有量と溶接時の耐ブローホール性との関係を示す図である。
【図６】本発明の実施例で使用した突合せ溶接継ぎ手を作成する際の溶接開先形状を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an austenitic stainless steel welding wire. More specifically, the present invention is used in the manufacture of tanks such as chemical tankers for storing and transporting crude sulfuric acid, and prevents corrosion due to crude sulfuric acid in welded parts under the tank usage environment. In addition, it relates to high-corrosion-resistant stainless steel flux-cored wire with excellent resistance to sulfuric acid corrosion, pitting corrosion resistance and toughness in chloride environment, which can prevent pitting corrosion of welded parts even in tank cleaning with seawater etc. It is.
[0002]
[Prior art]
As an austenitic stainless steel used in an environment where corrosion resistance is required, SUS304 specified in JIS is generally known. In addition, Ni is further increased for the purpose of improving the corrosion resistance against non-oxidizing acids. SUS316, SUS317 to which Mo is added, and SUS304L, SUS316L, SUS317L, etc., in which C is further reduced for the purpose of improving intergranular corrosion resistance, are known, and are selected according to the use environment.
[0003]
Conventionally, as a wire used for welding these austenitic stainless steels excellent in corrosion resistance, a flux-cored wire for austenitic stainless steel defined in JIS Z 3323, and further, JP-A-58-205696 308, 316, 308L, 316L series austenitic stainless steel flux cored wires as disclosed in JP-A-62-68696 have been used.
[0004]
In recent years, austenitic stainless steels such as SUS316L and duplex stainless steels, such as SUS316L, which are excellent in corrosion resistance, are chemical tankers for loading and transporting chemical raw materials, food raw materials, fats and oils, organic solvents, etc., instead of conventional plated steel plates. It is being applied as a tank steel.
[0005]
However, among chemical tankers, especially tanks such as chemical tankers for loading and transporting crude sulfuric acid are used in a sulfuric acid corrosive environment with a high sulfuric acid concentration. Therefore, austenitic stainless steel such as SUS316L or duplex stainless steel. However, the resistance to sulfuric acid corrosion is not sufficient, and the overall corrosion damage due to crude sulfuric acid becomes a serious problem in an environment where steel is used.
[0006]
In addition to this problem, chemical tankers for loading and transporting crude sulfuric acid generally wash the tank with seawater after unloading the crude sulfuric acid. If the drying process is incomplete, seawater components (chloride ions) remain on the tank surface, causing the problem of pitting corrosion damage caused by the chloride.
[0007]
Combined with the demand for a new corrosion-resistant austenitic stainless steel with excellent corrosion resistance, both sulfuric acid corrosion resistance and chloride-induced pitting corrosion resistance in this high-concentration sulfuric acid corrosion environment, And with the progress of rolling technology, the content of Mo and N is greatly increased compared to the conventional one to further improve the pitting corrosion resistance and crevice corrosion resistance due to chloride, and Cu is added to add high concentration sulfuric acid corrosion High corrosion resistance austenitic stainless steel with improved corrosion resistance under the environment has been developed.
[0008]
JP-A-1-95895 discloses Mo: 6.0-7.0%, Ni: 17.5% as a common metal welding material for welding such a component type high corrosion resistance austenitic stainless steel. A wire for stainless steel TIG welding and plasma welding containing 5 to 20% and Cu: 0.5 to 1.0% is disclosed in Japanese Patent Laid-Open No. 3-86392 as Mo: 2.4 to 6.7%. , Ni: 12.7 to 27.3%, Cu: 0.8 to 2.4%, high-corrosion resistance stainless steel welding flux cored wire has been proposed.
[0009]
However, in such a high sulfuric acid concentration corrosive environment, the corrosion frequency of the weld metal becomes larger than that of the base metal, and the high Mo proposed in Japanese Patent Laid-Open Nos. 1-95895 and 3-86392 has been proposed. In addition, the corrosion resistance of the weld metal is still insufficient with the high N, Cu-added high corrosion resistance stainless steel welding wire, and in addition to this, the ductility and toughness are low, and further, blowholes caused by nitrogen during welding There were problems such as being easy to occur.
[0010]
On the other hand, as a welding material for high corrosion-resistant austenitic stainless steel, on the other hand, a high Cr-high such as Inconel 625 (60Ni-22Cr-9Mo-3.5Nb system) is often used without using a common metal welding wire. Although a Mo-containing high Ni-based alloy welding wire may be used, although such a wire can provide sufficient corrosion resistance, it tends to cause a decrease in toughness of the weld metal due to high temperature cracking during welding and sigma phase precipitation, The problem is that it is expensive as a welding material.
[0011]
Based on the above, as a welding wire used when manufacturing tanks such as chemical tankers mainly for loading and transporting crude sulfuric acid, sulfuric acid corrosion resistance and seawater in high-concentration sulfuric acid corrosive environments have been conventionally used. High corrosion resistance that can fully satisfy the corrosion resistance of both chloride-induced pitting corrosion resistance in the environment, and has high ductility and toughness, and has excellent blowhole resistance and welding workability during welding. Development of a flux cored wire for austenitic stainless steel is desired.
[0012]
[Problems to be solved by the invention]
The present invention is a welding wire mainly used for manufacturing tanks such as chemical tankers for loading and transporting crude sulfuric acid in view of the above-mentioned problems of the prior art, and is a corrosive environment of high concentration sulfuric acid. It satisfies the corrosion resistance of both sulfuric acid corrosion resistance and pitting corrosion resistance caused by residual chloride ions in seawater environment, and has high ductility and toughness. An object of the present invention is to provide a flux-cored wire for a high corrosion resistance austenitic stainless steel capable of obtaining an excellent weld metal.
[0013]
[Means for Solving the Problems]
The present invention solves the above-mentioned problems, and the gist thereof is as follows.
[0014]
(1) In one or both of the outer skin and the flux, in mass% relative to the total mass of the wire,
C: 0.01-0.05%
Si: 0.01 to 1%,
Mn: 0.5-2%
Ni: 10-15%
Cr: 20 to 24%,
Mo: 1.9 to 3.5%,
Cu: 1 to 3.2%,
N: 0.05-0.1%
An austenitic stainless steel excellent in sulfuric acid corrosion resistance, pitting corrosion resistance, ductility and toughness, characterized in that the following formulas (1) to (3) are satisfied and the balance is composed of Fe and inevitable impurities: Steel flux cored wire.
KF = [Cr] + 3.3 × [Mo] + 16 × [N] ≧ 28 (1)
ZF = − [Cr] + 3.6 × [Ni] + 4.7 × [Mo] +11.5 [Cu] ≧ 55 (2)
Creq / Nieq = 1.35 to 1.74 (3)
However, Creq = [Cr] + 1.37 × [Mo] + 1.5 × [Si]
Nieq = [Ni] + 0.31 × [Mn] + 22 × [C] + 14.2 × [N] + [Cu]
[C], [Si], [Mn], [Cr], [Ni], [Mo], [Cu], and [N] indicate the content (% by mass) of each component element.
[0015]
(2) In one or both of the outer skin and the flux, in mass% based on the total mass of the wire,
Bi: 0.01-0.05%
The flux-cored wire for austenitic stainless steel excellent in sulfuric acid corrosion resistance, pitting corrosion resistance, ductility and toughness as described in the above item (1), comprising
[0016]
(3) In the flux, in mass% with respect to the total mass of the wire,
TiO ₂ : 2-7%
SiO ₂ : 0.1 to 2%
Na ₂ O + K ₂ O: 0.05-0.2%
Total fluoride: 0.1-0.9%
The flux-cored wire for austenitic high corrosion resistance stainless steel excellent in sulfuric acid corrosion resistance, pitting corrosion resistance, ductility, and toughness as described in the above item (1) or (2).
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
[0018]
First, the technical concept of the present invention for improving the corrosion resistance, ductility and toughness of a weld metal in a sulfuric acid corrosion environment and a seawater corrosion environment of the weld metal and each defining formula defining the components of the welding wire will be described.
[0019]
The present inventors have excellent corrosion resistance such as sulfuric acid corrosion resistance in a high-concentration sulfuric acid corrosion environment and chloride-induced pitting corrosion resistance in a seawater environment, high ductility and toughness, and resistance to blowholes during welding. We have conducted extensive investigations and examinations on high-corrosion-resistant austenitic stainless steel flux-cored wires that can provide weld metal with excellent welding workability.
[0020]
As a result, first, of the corrosion resistance, the corrosion resistance against pitting corrosion caused by residual chloride ions in the seawater environment is that after austenitic stainless steel is pulled out of seawater, the salt is concentrated by evaporation of water, and red rust is generated from the vicinity. It was found that it spawned and resulted in pitting.
[0021]
FIG. 1 shows the relationship between the component index: KF and the pitting corrosion potential determined by the equation (1) ′ of the welding wire component from the results of measuring the pitting corrosion potential in a 3.5% NaCl solution at 40 ° C. Is.
KF = [Cr] + 3.3 × [Mo] + 16 × [N] (1) ′
[0022]
In FIG. 1, the welding wire component index: KF (= [Cr] + 3.3 × [Mo] + 16 × [N]) is 28 or more, and the pitting potential is 1000 (mV) or more, so that pitting corrosion is not generated at all. The pitting corrosion resistance can be obtained.
[0023]
Therefore, in the present invention, in order to improve the pitting corrosion attributed to residual chloride ions in a seawater corrosive environment, the component element contained in either or both of the outer sheath and the flux in the flux-cored wire is represented by the relationship (1). It is specified to satisfy the equation.
KF = [Cr] + 3.3 × [Mo] + 16 × [N] ≧ 28 (1)
However, [Cr], [Mo], and [N] in the above formulas (1) ′ and (1) indicate the content (mass%) of each component element of Cr, Mo, and N, respectively.
[0024]
Further, from the investigation and experimental results of the present inventors, of the corrosion resistance, the general corrosion resistance against crude sulfuric acid is that the sulfuric acid absorbs moisture in the air and dilutes, and the corrosion progresses remarkably due to the diluted sulfuric acid. It was also found that the sulfuric acid concentration with the highest corrosion was 50%.
[0025]
FIG. 2 shows the relationship between the component index: ZF determined by the equation (2) ′ of the welding wire component and the degree of corrosion from the results of the corrosion weight loss test in a 50% sulfuric acid solution at 40 ° C. is there.
The degree of corrosion was defined as the amount of reduction in the corrosion progress rate in one year calculated from the weight loss per unit time of the corrosion weight loss test result.

[0026]
In FIG. 2, the welding wire component index: ZF (= [Cr] + 3.6 × [Ni] + 4.7 × [Mo] +11.5 [Cu]) is 55 or more and the corrosion weight loss is 50% when the sulfuric acid concentration is 50%. It reduces to 0.5 mm / year or less, and sulfuric acid corrosion resistance improves and sufficient sulfuric acid corrosion resistance is obtained.
[0027]
Therefore, in the present invention, in order to improve the corrosion resistance of the crude sulfuric acid in a corrosive environment, the constituent elements contained in either or both of the outer sheath and the flux in the flux-cored wire satisfy the following relational expression (2). It prescribes what to do.

However, [Cr], [Ni], [Mo], and [Cu] in the above formulas (2) ′ and (2) are the contents (mass%) of the respective component elements of Cr, Ni, Mo, and Cu, respectively. Show.
[0028]
Further, from the results of investigations and experiments conducted by the present inventors, in order to improve the ductility and toughness of the weld metal, as shown in FIGS. 3 and 4, the ratio of the Cr equivalent to the Ni equivalent of the welding wire component (Creq) It has been clarified that the ductility and toughness of the weld metal are improved by making / Nieq) appropriate.
[0029]
Normally, the weld metal formed on the weld joint is used in the solidified state, but the weld metal obtained by welding using austenitic stainless steel sapphire wire is the primary crystal solidification due to its component system. The phase becomes a ferrite phase or an austenite phase, and these phases are classified into those that complete solidification by themselves and those that complete solidification in two phases of ferrite phase + austenite phase.
[0030]
When primary solidification phase is austenite phase, solidification is completed with austenite single phase (A mode), or some ferrite phase is crystallized in the subsequent solidification process, and two phases of austenite phase + ferrite phase Solidification may be completed (AF mode), but in any case, the cooling and phase transformation process after the solidification of the weld metal is completed, the crystal grain size becomes coarse, and it has been found that ductility and toughness decrease. .
[0031]
Further, when the primary crystal solidification phase is a ferrite phase, solidification is completed with a ferrite single phase (F mode), or a part of the austenite phase is crystallized in the subsequent solidification process, and austenite phase + ferrite phase In some cases, solidification is completed in a phase (FA mode). Among these, when the primary crystal solidification phase is a ferrite phase, and then solidification is completed with a single ferrite phase (F mode), the structure is mainly composed of a ferrite phase due to cooling and phase transformation after completion of solidification. And low toughness.
[0032]
On the other hand, when the primary crystal solidification phase is a ferrite phase and solidification is completed with two phases of austenite phase + ferrite phase (FA mode), in the cooling / phase transformation process after solidification, It has been found that ductility and toughness are improved because ferrite is connected in a lace shape and the austenite grain size is artificially reduced.
[0033]
In general, when the weld metal is solidified, microsegregation remains in the weld metal, and local corrosion is likely to occur in a region where an element contributing to corrosion resistance is negatively segregated. Since the degree of segregation (distribution coefficient) at the time of solidification of each element varies depending on the solidification form of the weld metal, it is expected that the corrosion behavior varies depending on the solidification form of the weld metal.
[0034]
In general, when the primary solidification phase is an austenitic phase, Cr, Ni, and Mo effective for corrosion resistance decrease in the initial solidification region, and local corrosion easily occurs in both sulfuric acid and seawater corrosive environments. In the final solidification zone, Cr, Mo and the like are concentrated, and brittle intermetallic compounds such as a sigma phase are generated, so that the toughness is remarkably lowered.
[0035]
On the other hand, when the primary crystal solidification phase is a ferrite phase, Ni and Mo effective for corrosion resistance in the initial solidification region are similarly reduced, but the amount of decrease is smaller than that in the case where the primary crystal solidification phase is an austenite phase, Further, since Cr effective for corrosion resistance is distributed almost uniformly and there is almost no segregation, there is no decrease in Cr in the initial solidification region. Therefore, formation of brittle intermetallic compounds such as a sigma phase due to concentration of Ni, Mo, Cr, etc. in the final solidification zone and a significant decrease in toughness due to this are not observed.
[0036]
FIG. 3 and FIG. 4 show the relationship between the ratio of the Cr equivalent to the Ni equivalent (Creq / Nieq) based on the welding wire component and the ductility and toughness.
[0037]
Here, Cr equivalent (Creq) and Ni equivalent (Nieq) are respectively defined by the following equations (4) and (5).

However, [C], [Si], [Mn], [Cr], [Ni], [Mo], [Cu], and [N] are C, Si, Mn, Cr, Ni, Mo, Cu, The content (mass%) of each component element of N is shown.
[0038]
3 and 4, when Creq / Nieq of the welding wire component is less than 1.4, the primary crystal solidification is in the austenite phase and then solidified in the austenite single phase (A mode), or the primary crystal solidification is austenite. In the subsequent solidification process, the ferrite phase crystallizes out, and the solidification form (AF mode) is completed in which the solidification is completed in two phases, the austenite phase and the ferrite phase. In each case, cooling and phase transformation after solidification of the weld metal is completed. In the process, since the crystal grain size becomes coarse, the ductility and toughness of the weld metal are lowered, and sufficient ductility and toughness cannot be obtained. Even if the welding wire component Creq / Nieq exceeds 1.7, the primary crystal solidification is in the ferrite phase and the solidification form (F mode) is completed in which the solidification is completed in the ferrite single phase. Cooling / phase transformation after solidification is completed Since the weld metal thus obtained has a structure mainly composed of a ferrite phase, the ductility and toughness of the weld metal are lowered, and sufficient ductility and toughness cannot be obtained.
[0039]
On the other hand, when the welding wire component Creq / Nieq is 1.4 to 1.7, the primary crystal solidification phase is the ferrite phase, and then the austenite phase is crystallized in the cooling / phase transformation process after the solidification is completed. Thus, the solidification form (FA mode) is completed in which the solidification is completed with two phases of ferrite phase + austenite phase, and the ferrite in the form of worm-like (worm-eating) is connected in a lace shape, and the austenite grain size is artificially reduced. Therefore, the ductility and toughness of the weld metal are improved, and sufficient ductility and toughness can be obtained.
[0040]
Therefore, in the present invention, while maintaining both the corrosion resistance of the weld metal crude sulfuric acid in a corrosive environment and the pitting corrosion resistance due to residual chloride ions in a seawater environment, sufficient ductility is further maintained. In order to make the weld metal solidification form the above-described FA mode, which is a necessary condition for obtaining toughness, the constituent elements contained in either or both of the outer sheath and the flux in the flux-cored wire are the following (3): Define to satisfy the equation.
Creq / Nieq = 1.4 to 1.7 (3)
However, the Creq and Nieq are the Cr equivalent and Ni equivalent determined from the above (2) and (3).
[0041]
In the present invention, the component elements contained in one or both of the outer sheath and the flux in the flux-cored wire are defined by the above relational expressions, and the content of each component element is defined as follows.
[0042]
In addition, the following% shows the mass% with respect to the total mass of a wire.
[0043]
C: C is a harmful component for improving the corrosion resistance of the weld metal, but it must be contained to some extent from the viewpoint of ensuring the strength of the weld metal. For this reason, C is added to the welding wire by 0.01% or more. However, when C is added to the welding wire in excess of 0.05%, when the weld metal is welded and further reheated, Cr carbide is precipitated, and the intergranular corrosion resistance and pitting corrosion resistance of the weld metal are remarkably increased. In addition to deterioration, the toughness and ductility of the weld metal are also significantly reduced.
Therefore, the C content in the welding wire is set to 0.01 to 0.05%.
[0044]
Si: Si is added as a deoxidizing element in the welding wire, but Si is added in an amount of 0.01% or more in order to sufficiently obtain the effect. However, if Si is added to the welding wire in excess of 1.5%, the ductility of the ferrite phase in the weld metal structure is lowered.
Therefore, the Si content in the welding wire is set to 0.01 to 1%.
[0045]
Mn: Mn is added to the welding wire as a deoxidizing element, but is 0.01% or more in order to sufficiently obtain the effect. However, when Mn is added to the welding wire in excess of 2%, the ductility of the weld metal is lowered.
Therefore, the Mn content in the welding wire is 0.5-2%.
[0046]
Ni: Ni contains Ni in the welding wire to provide remarkable resistance to the corrosiveness of the weld metal in neutral chloride and non-oxidizing sulfuric acid environments and to enhance the formation of passive film. The larger the amount, the more effective for improving the corrosion resistance of the weld metal. On the other hand, Ni is an austenite-forming element and is also a component that generates and stabilizes the austenite phase in the weld metal as a main element of the austenitic stainless steel. While maintaining the ductility and toughness of the weld metal, in order to improve both the corrosion resistance of sulfuric acid and the pitting corrosion resistance caused by residual chloride ions, the primary solidification phase of the weld metal is the ferrite phase. It is necessary to use the FA solidification mode in which solidification is completed in two phases of ferrite phase + austenite phase. Therefore, in the present invention, considering the solidification form and phase balance of the weld metal when the content of Cr as a ferrite forming element is 20 to 24%, the Ni content in the welding wire is 10% to 15%. .
[0047]
Cr: Cr is a ferrite-forming element in the weld metal and forms a passive film as a main element of the austenitic stainless steel, thereby contributing to improvement of the corrosion resistance of the weld metal. The greater the Cr content in the welding wire, the better the pitting corrosion resistance due to residual chloride ions of the weld metal in the seawater environment. To obtain sufficient corrosion resistance, the Cr content in the welding wire should be 20% or more. There is a need to. However, if the Cr content in the welding wire is excessively increased, the overall corrosion resistance in a sulfuric acid environment will decrease, so the Cr content in the welding wire in order to sufficiently ensure the overall corrosion resistance in a sulfuric acid environment. Needs to be 24% or less. Therefore, the Cr content in the welding wire is set to 20 to 24%.
[0048]
Mo: Mo is an extremely effective element for stabilizing the formation of a passive film in the weld metal and improving the corrosion resistance. In particular, the effect of weld metal on pitting corrosion resistance due to residual chloride ions in a seawater environment is remarkable, and in order to sufficiently obtain the effect, it is necessary to contain 1.9% or more of Mo in the welding wire. . On the other hand, when the content exceeds 3.5%, a brittle intermetallic compound such as a sigma phase is generated in the weld metal to reduce the toughness of the weld metal.
Therefore, the Mo content in the welding wire is set to 1.9 to 3.5%.
[0049]
Cu: Cu has a significant effect on enhancing the corrosion resistance of the weld metal. In particular, in order to obtain excellent corrosion resistance in a sulfuric acid environment coexisting with Cr, Ni and Mo, the Cu content in the welding wire is 1%. It is necessary to do it above.
On the other hand, if Cu is added to the welding wire in excess of 3.2%, the toughness of the weld metal is significantly reduced.
Therefore, the Cu content in the welding wire is set to 1 to 3.2%.
[0050]
N: N is a strong austenite-forming element, and the greater the content, the better the pitting corrosion resistance of the weld metal due to residual chloride ions in the seawater environment. The N content in the wire needs to be 0.05% or more. On the other hand, if the N content in the welding wire exceeds 0.1%, blow holes are likely to occur during welding.
Therefore, the N content in the welding wire is 0.05 to 0.1%.
[0051]
The above are the basic component elements contained in either or both of the outer sheath and the flux in the flux-cored wire of the present invention, and by performing shielded arc welding using this wire, the corrosive environment of high-concentration sulfuric acid can be used. Welding that fully satisfies the corrosion resistance of both general corrosion resistance and pitting corrosion resistance caused by residual chloride ions in seawater, has high ductility and toughness, and has excellent blowhole resistance and welding workability during welding Metal can be obtained.
[0052]
In the present invention, in addition to the above basic components, other component elements can be contained as necessary to the extent that the excellent characteristics of the weld metal are not impaired.
[0053]
Bi can be added at a content of 0.01% or more in order to sufficiently obtain the effect for the purpose of improving the slag peelability. However, from the results of investigations and experiments conducted by the present inventors, it was found that when the Bi content increases, the blowhole resistance during welding deteriorates.
[0054]
FIG. 5 shows the relationship between the Bi content in the welding wire and the blowhole resistance during welding using the same.
[0055]
In addition, the blowhole resistance at the time of welding is evaluated based on the four-grade classification (1 to 4) based on the determination of the JIS Z3106 test method. evaluated.
[0056]
From FIG. 5, by setting the Bi content in the welding wire to 0.05% or less, excellent blowhole resistance during welding can be ensured.
[0057]
Therefore, in the present invention, Bi is preferably added to the wire in a content of 0.01 to 0.05% in order to further improve the slag peelability and ensure the blowhole resistance.
[0058]
In addition, in the flux-cored wire of the present invention, the following can be included as flux in order to further improve welding workability.
The reason for adding each flux component and the reason for limiting its content will be described below.
[0059]
TiO ₂ : TiO ₂ Is added for the purpose of forming a slag with good enveloping properties during welding. In order to obtain the effect sufficiently, TiO in the wire ₂ The content needs to be 2% or more. On the other hand, TiO in the wire ₂ If the content exceeds 7%, the amount of spatter generated during welding increases. Therefore TiO in the wire ₂ The content is 2 to 7%.
[0060]
SiO ₂ : SiO ₂ Is added for the purpose of improving the arc stability during welding. In order to obtain the effect sufficiently, SiO in the wire ₂ The content needs to be 0.1% or more. On the other hand, SiO in the wire ₂ If the content exceeds 2%, the amount of spatter generated during welding increases. Therefore, SiO in the wire ₂ The content is 0.1 to 2%.
[0061]
Na ₂ O and K ₂ O: Na ₂ O and K ₂ O is added for the purpose of improving the arc spray during welding. In order to obtain the effect sufficiently, Na in the wire ₂ O and K ₂ The total content of O needs to be 0.05% or more. On the other hand, Na in the wire ₂ O and K ₂ If the total content of O exceeds 0.2%, the slag releasability during welding deteriorates.
[0062]
Therefore, Na in the wire ₂ O and K ₂ The total content of O is 0.05 to 0.2%.
[0063]
Fluoride: In the present invention, as a fluoride in the wire flux, K ₂ ZrF ₆ , NaF, CaF ₂ , AlF _Three One or more of LiF and the like can be added. Any fluoride is added for the purpose of improving the slag releasability during welding. In order to sufficiently obtain the effect, the total content of fluoride in the wire needs to be 0.1% or more. On the other hand, when the total content of fluoride in the wire is 0.9%, the amount of spatter generated during welding increases.
[0064]
Accordingly, the fluoride content in the wire is 0.1 to 0.9% of the total fluoride content.
[0065]
The following commonly used methods can be applied to the production of the flux-cored wire of the present invention.
[0066]
For example, when a steel strip is formed into a tubular shape as an outer shell, the steel strip is formed into a U shape, and a mixed and stirred filling flux is inserted into the U-shaped groove portion. The steel is further formed into a round shape, and then drawn to a predetermined wire diameter.
[0067]
When a pipe is used as the outer skin, the pipe is filled with a flux while vibrating the pipe, and then drawn to a predetermined wire diameter.
[0068]
The flux can also be used in the form of a bond flux by adding a fixing agent (potassium silicate and sodium silicate aqueous solution) so that the wire can be smoothly filled.
[0069]
【Example】
The effects of the present invention will be described below based on examples of the present invention.
[0070]
As the steel material to be welded, high corrosion resistance stainless steel having excellent corrosion resistance in both sulfuric acid environment and seawater environment containing chemical components shown in Table 1 was used.
[0071]
Moreover, each component composition and test result of the welded metal obtained when it welded using the flux cored wire used for welding and these wires are shown to Tables 2-4.
[0072]
Welding uses a wire with a wire diameter of 1.4 mmΦ, welding current: 150 to 250 A, arc voltage: 25 to 35 V, welding speed: 30 to 40 cm / min, CO2 gas as a shielding gas, flow rate: 15 to 25 liters / min min.
[0073]
In addition, other slag agents in Tables 2 to 4 are CaO, FeO, MgO, Al ₂ O _Three It is.
[0074]
In the corrosion test, a test piece having a thickness of 2 mm, a width of 15 mm, and a length of 15 mm was taken from the surface layer of a weld metal based on JIS Z 3323 using a test plate having a thickness of 20 mm, and the entire surface was # 600 emery paper. Was subjected to wet polishing and subjected to a test after degreasing.
[0075]
The chloride pitting test was conducted in accordance with JIS G 0577 in a 3.5% NaCl solution at 40 ° C., and the current density was 100 A / cm. ² The potential at the time was defined as the pitting corrosion potential, and when the measured value was 1000 mV or more, the pitting corrosion resistance in chloride corrosion caused by residual chloride ions was considered good.
[0076]
The sulfuric acid overall corrosion test is immersed in a 50% sulfuric acid solution at 40 ° C for 6 hours, converted from the weight loss per unit of corrosion calculated from the weight of the test piece before and after immersion, and the amount of reduction in corrosion rate per year is corroded. When the degree of corrosion was 0.5 mm / year or less, the sulfuric acid corrosion resistance was considered good.
[0077]
The ductility of the weld metal is evaluated by measuring the elongation of a normal temperature tensile test using A1 of JIS Z 3111 in a weld metal test based on JIS Z 3323 using a test plate having a thickness of 20 mm. In the case of 25% or more, the ductility of the deposited metal was considered good.
[0078]
The toughness of the weld metal is evaluated by measuring the absorbed energy of a −20 ° C. impact test using JIS Z 3111 No. 4 in a weld metal test based on JIS Z 3323 using a test plate having a thickness of 20 mm. When the measured value was 30 J or more, the toughness of the deposited metal was considered good.
[0079]
Blow hole resistance was investigated by X-ray transmission test of butt-welded joints obtained by three-pass welding a test plate (plate thickness 12 mm, length 400 mm) having a groove shape shown in FIG. In accordance with JIS Z 3106 Annex 4 (normative), the method of classifying flaw images by transmission photographs is used to classify the test field of view to 10 × 10 mm, and class 1 indicates that the weld metal has good blowhole resistance. did. In this test, no flaws other than the first type were observed.
[0080]
Welding workability test was conducted using a steel plate with a thickness of 6 mm and a T-shaped joint, and welding the fillet in a horizontal and vertical (upward) position at a welding current of 150 to 250 A, and stabilizing the arc at that time. Property, spatter generation amount, slag encapsulation, and slag peelability were evaluated.
[0081]
Tables 2 to 4 show wire Nos. Which are flux-cored wires (invention examples) having the components defined in the present invention. 1 to 14 and a wire No. 1 which is a flux-cored wire (comparative example) having a component outside the range defined in the invention. The test result of 15-26 is shown.
[0082]
Among the examples of the present invention, the wire No. For 1 to 10, Ni, Cr, Mo, Cu, N, Creq / Nieq are appropriate, KF and ZF are satisfied, Bi is appropriate, and TiO ₂ , SiO ₂ , Na ₂ O + K ₂ Since the sum of O and fluoride was appropriate, the corrosion resistance was good, the ductility and toughness were high, the blowhole resistance was excellent, the welding workability was good, and the results were very satisfactory. In addition, wire No. 11, Ni, Cr, Mo, Cu, N, Creq / Nieq are appropriate, satisfy KF, ZF, and TiO ₂ , SiO ₂ , Na ₂ O + K ₂ Since the total of O and fluoride is appropriate, the corrosion resistance is good, the ductility and toughness are high, and the welding workability is excellent. ₂ , SiO ₂ , Na ₂ O + K ₂ Since the total of O and fluoride was not appropriate, the blowhole resistance was poor.
[0083]
Of the inventive examples, the wire No. Nos. 12 to 14 are suitable for Ni, Cr, Mo, Cu, N, and Creq / Nieq, satisfy KF and ZF, and are suitable for Bi. Therefore, corrosion resistance is good, ductility and toughness are high, Excellent blowhole property, but TiO ₂ , SiO ₂ , Na ₂ O + K ₂ Since the sum of O and fluoride was not appropriate, welding workability was poor.
[0084]
In the comparative example, the wire No. 15, Creq / Nieq was high, ductility and toughness were low.
[0085]
Wire No. No. 16 had low Creq / Nieq, and low ductility and toughness.
[0086]
Wire No. Since No. 17 had low Ni, Creq / Nieq was high and ductility and toughness were low.
[0087]
Wire No. No. 18 had high Ni, so Creq / Nieq was low, and ductility and toughness were low.
[0088]
Wire No. No. 19 had a low KF due to its low Cr and poor local corrosion resistance.
[0089]
Wire No. No. 20 had a low ZF due to high Cr and poor overall corrosion resistance.
[0090]
Wire No. No. 21 had a low KF and a poor local corrosion resistance because Mo was low.
[0091]
Wire No. Since No. 22 had high Mo, its toughness was low.
[0092]
Wire No. No. 23 had low ZF due to low Cu, and its local corrosion resistance was poor. Moreover, since Bi was high, blow holes were generated.
[0093]
Wire No. No. 24 had low toughness due to high Cu, and low slag due to low Bi.
[0094]
Wire No. No. 25 had a low NF and a low KF and poor local corrosion resistance. TiO ₂ , The encapsulation of slag was poor.
[0095]
Wire No. In No. 26, blow holes with high N were generated. TiO ₂ Because of the high spatter, there was much spatter.
[0096]
For reference, the chemical components of the weld metal are shown for each test.
[0097]
[Table 1]

[0098]
[Table 2]

[0099]
[Table 3]

[0100]
[Table 4]

[0101]
【The invention's effect】
As described above in detail, according to the present invention, when welding high corrosion resistance stainless steel, high quality corrosion resistance avoiding general corrosion due to crude sulfuric acid and pitting corrosion due to residual chloride ions is obtained, and ductility and toughness are high. It is possible to provide a flux-cored wire having excellent blowhole resistance and excellent welding workability.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between the KF value (= [Cr] + 3.3 × [Mo] + 16 × [N]) of a welding wire and the pitting corrosion potential in a 3.5% NaCl solution at 40 ° C. is there.
FIG. 2 shows the ZF value of a welding wire (= − [Cr] + 3.6 × [Ni] + 4.7 × [Mo] +11.5 [Cu]) and corrosion weight loss in a 50% sulfuric acid solution at 40 ° C. It is a figure which shows the relationship.
FIG. 3 is a diagram showing a relationship between a ratio (Creq / Nieq) of Cr equivalent and Ni equivalent of a welding wire and ductility (total elongation).
FIG. 4 is a diagram showing the relationship between the ratio (Creq / Nieq) of Cr equivalent and Ni equivalent of weld wire and toughness (absorbed energy).
FIG. 5 is a diagram showing the relationship between the Bi content in a welding wire and the blowhole resistance during welding.
FIG. 6 is a diagram showing a weld groove shape when creating a butt weld joint used in an example of the present invention.

Claims (3)

In one or both of the outer skin and the flux, in mass% with respect to the total mass of the wire,
C: 0.01-0.05%
Si: 0.01 to 1%,
Mn: 0.5-2%
Ni: 10-15%
Cr: 20 to 24%,
Mo: 1.9 to 3.5%,
Cu: 1 to 3.2%,
N: 0.05-0.1%
An austenitic stainless steel excellent in sulfuric acid corrosion resistance, pitting corrosion resistance, ductility and toughness, characterized in that the following formulas (1) to (3) are satisfied and the balance is composed of Fe and inevitable impurities: Steel flux cored wire.

However, Creq = [Cr] + 1.37 × [Mo] + 1.5 × [Si]
Nieq = [Ni] + 0.31 × [Mn] + 22 × [C] + 14.2 × [N] + [Cu]
[C], [Si], [Mn], [Cr], [Ni], [Mo], [Cu], and [N] indicate the content (% by mass) of each component element. Either one or both of the outer skin or the flux, in mass% with respect to the total mass of the wire,
Bi: 0.01-0.05%
The flux-cored wire for austenitic stainless steel excellent in sulfuric acid corrosion resistance, pitting corrosion resistance, ductility and toughness according to claim 1. In the flux, in mass% with respect to the total mass of the wire,
TiO ₂ : 2 to 7%,
SiO ₂ : 0.1 to ₂ %,
Na ₂ O + K ₂ O: 0.05 to 0.2%,
Total fluoride: 0.1-0.9%
The flux-cored wire for austenitic high corrosion resistance stainless steel excellent in sulfuric acid corrosion resistance, pitting corrosion resistance, ductility and toughness according to claim 1 or 2.

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