JP3930782B2

JP3930782B2 - Coated arc welding rod for welding low alloy steel with excellent sulfuric acid resistance and hydrochloric acid resistance

Info

Publication number: JP3930782B2
Application number: JP2002255444A
Authority: JP
Inventors: 一浩児嶋; 茂大北; 明宇佐見; 正夫梅木; 将高橋
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2002-08-30
Filing date: 2002-08-30
Publication date: 2007-06-13
Anticipated expiration: 2022-08-30
Also published as: JP2004090044A

Description

【０００１】
【発明の属する技術分野】
本発明は、石炭焚きボイラーやごみ焼却施設の煙道、煙突のように硫酸および塩酸による低温腐食を生じるような雰囲気、すなわち濃厚硫酸および塩酸環境で優れた耐食性を示す耐硫酸露点腐食低合金鋼のアーク溶接用の溶接棒に関するものである。また、塩酸、硫酸などの単独または混合の酸洗液を収める鋼製めっき酸洗槽用の耐酸性に優れた鋼材のアーク溶接に適用する溶接棒に関する。
【０００２】
【従来の技術】
一般に溶接構造物が腐食環境で使用される場合、溶接部と母材との間で耐食性に差異があると、耐食性の劣る方が選択的に腐食され、構造物の寿命が著しく短くなる。また、溶接部が選択的に腐食すると、腐食孔に応力集中が生じ、極端な場合は構造物の破壊を招く恐れもある。このように、溶接構造物の利用において、腐食劣化が無視できない用途の場合には、母材だけでなく溶接部の耐食性も十分に確保する必要がある。
【０００３】
石炭焚き火力やごみ焼却施設などの煙道、煙突などの排煙設備では、排ガス中の三酸化硫黄および塩化水素に起因して、硫酸露点腐食、塩酸露点腐食が生じる。
【０００４】
既存の耐食鋼用溶接棒は、Ｃｕを単独で含有するかまたはＣｕ−Ｃｒを含有する系であり、これらは、重油専焼ボイラのプラント排煙装置で生じる硫酸露点腐食環境では十分に優れた耐食性を示すが、石炭焚きボイラやごみ焼却またはごみのガス化溶融施設などでは、硫酸露点腐食と塩酸露点腐食が同時に生じるため、溶接部の耐食性が十分でないといった問題があった。
【０００５】
更に、耐食性の改善例として、溶接金属にＣｕとＳｂ含有させることが提案されているが（例えば、特公昭４３−１３８０号公報参照。）、この技術も耐硫酸性向上のみであり耐塩酸性まで満足できるものではなかった。
【０００６】
【発明の解決しようとする課題】
本発明は、上記従来技術の問題点に鑑みて、耐硫酸性および耐塩酸性に優れた溶接金属がえられ、かつ良好な溶接作業性を確保できる耐硫酸性および耐塩酸性に優れる低合金鋼のアーク溶接用の被覆アーク溶接棒を提供することをその目的とする。
【０００７】
【課題を解決するための手段】
本発明者らは、溶接金属の耐硫酸露点腐食性と耐塩酸露点腐食性に及ぼす冶金因子を詳細に検討した結果、鋼心線に被覆剤を被覆塗装してなる溶接棒全体の組成を特定することにより、耐食性に優れた溶接金属が得られることを見出した。すなわち、まず溶接棒の不純物であるＰ、Ｓを限定した上で、（１）特定のＣ−Ｓｉ−Ｃｕ−Ｎｉ−Ｓｂ系にすることにより優れた耐硫酸性および耐塩酸性の溶接金属が得られる。（２）前記（１）の成分系のＳを規定することにより耐硫酸性と耐塩酸性がさらに向上する。（３）前記（１）または（２）の成分系でＭｏを添加すると、耐塩酸性が飛躍的に向上させることができる。（４）前記（１）〜（３）のいずれか１項の成分系で被覆剤中の金属炭酸塩、金属弗化物および金属酸化物の含有量を規定することにより、良好な溶接作業性を確保できる。（５）前記（１）〜（４）のいずれか１項の成分系において、被覆剤にＳｂを含有させ、該Ｓｂの平均粒径を限定することにより良好な溶接を確保しつつ優れた耐食性が得られる。本発明は、これらの知見に基づいて完成させたもので、その要旨とするところは以下の通りである。
（１）鋼心線に被覆塗装してなる被覆アーク溶接棒において、前記鋼心線中または被覆剤中の何れか一方もしくは両方に、溶接棒全質量に対する質量％で、
Ｃ：０．００５〜０．１５％、
Ｓｉ：０．５〜４％、
Ｍｎ：０．２〜２．４％、
Ｃｕ：０．１〜１．２％、
Ｎｉ：０．１〜０．６％、
Ｓｂ：０．０２〜０．２５％
を含有し、
かつ、Ｐ：０．０３％以下、
Ｓ：０．０３％以下
に制限し、残部がＦｅおよび不可避的不純物であることを特徴とする耐硫酸性および耐塩酸性に優れる低合金鋼溶接用の被覆アーク溶接棒。
（２）前記溶接棒全質量に対する質量％で、前記鋼心線中または被覆剤中の一方または両方に、
Ｓ：０．００５〜０．０２％
を含有することを特徴とする（１）に記載の耐硫酸性および耐塩酸性に優れる低合金鋼溶接用の被覆アーク溶接棒。
（３）前記溶接棒全質量に対する質量％で、前記鋼心線中または被覆剤中の一方または両方に、さらに、
Ｍｏ：０．０１〜０．６％
を含有することを特徴とする（１）または（２）に記載の耐硫酸性および耐塩酸性に優れる低合金鋼溶接用の被覆アーク溶接棒。
（４）前記被覆剤全質量に対する質量％で、前記被覆剤中に、
金属炭酸塩：３５〜５５％、
金属弗化物：１３〜３０％、
金属酸化物：０．５〜１５％
を含有することを特徴とする（１）〜（３）の何れか１つに記載の耐硫酸性および耐塩酸性に優れる低合金鋼溶接用の被覆アーク溶接棒。
（５）前記被覆剤中のＳｂの平均粒径が４５〜１５０μｍであることを特徴とする（１）〜（４）の何れか１つに記載の耐硫酸性および耐塩酸性に優れる低合金鋼溶接用の被覆アーク溶接棒。
【０００８】
【発明の実施の形態】
本発明の被覆アーク溶接棒は、鋼心線に被覆剤を被覆塗装してなるものであるが、所要の特性を有する溶接金属を得るための各元素は、鋼心線、被覆剤のいずれから添加しても良い。従って、以下の説明においては、特に断りのない限り、各成分元素は、鋼心線、被覆剤のいずれか一方または双方において、溶接棒全体として含有させれば良いものである。
【０００９】
まず、溶接棒全質量に対するＣ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｕ、Ｎｉ、Ｓｂの含有量規定について述べる。
Ｃは、本発明では被覆剤中の金属炭酸塩や有機物のＣＯまたはＣＯ₂のＣ分は含まず、被覆剤原料、例えばＳｉＣやＦｅ−Ｍｎ、Ｆｅ−Ｓｉ中のＣと鋼心線中のＣであり、溶接金属の強度を確保するために添加するが、その合計が０．１５％を超えて添加すると、溶接金属の耐割れ性と耐硫酸性が低下する。耐硫酸性および耐塩酸性の観点ではＣの含有量は少ないほど好ましいが、０．００５％未満ではアーク力が弱く溶け込み不足となって溶接作業性が悪くなるので、０．００５〜０．１５％とする。なお、耐硫酸性と耐塩酸性とのバランスを考慮する必要がある場合は、０．０５％以下が最も好ましい。
【００１０】
Ｓｉは、０．５％以上含むと、Ｃｕと共存して、特に４０％程度の硫酸濃度域での溶接金属の耐硫酸性および耐塩酸性を向上させる。しかし、４％を超えると、耐食性の向上はみられず、溶接金属の靭性が著しく低下し、アーク力が過剰に強くなり溶接作業性の劣化を招くので、上限は４％とした。溶接作業性や溶接金属の靭性をより重視する場合は、０．５〜２％が好ましい。また、Ｓｉを被覆剤から添加する場合はＦｅ−Ｓｉを使用する。
【００１１】
Ｍｎは、溶接金属の脱酸および強度調整のため溶接棒全体に０．２％以上添加するが、２．４％を越えるとスラグの粘性が低下し、立向姿勢ビードが垂れ易くなるなど溶接作業性が悪くなるので、０．２〜２．４％を限定範囲とした。また、Ｍｎを被覆剤から添加する場合は金属ＭｎやＦｅ−Ｍｎを使用する。
【００１２】
Ｐは、不純物元素であり、溶接金属の耐硫酸性および耐塩酸性を著しく阻害するので、その範囲を０．０３％以下とした。より好ましくは０．０１％以下にすると耐硫酸性および耐塩酸性が著しく改善され、０．００５％以下が最も好ましい。
【００１３】
Ｓは、不純物元素であり、溶接金属の十分な耐硫酸性および耐塩酸性を確保する上で限定する必要がある。０．０３％を超えると、耐硫酸性が著しく低下するので上限を０．０３％とした。
【００１４】
また、Ｃｕ−Ｍｏ−Ｓｂ系の溶接棒においては、Ｓを０．００５％以上含有させると、溶接金属の耐硫酸腐食性と共に、耐塩酸性が著しく向上する。しかし、０．０２％を超えて含有させてもその効果は飽和し、また、機械的性質（耐ラメラテア性など）および熱間加工性が低下するので、Ｓ含有量を０．００５〜０．０２％とするのが好ましい。
【００１５】
Ｃｕは、溶接金属の耐硫酸性および耐塩酸性を確保するためには、０．１％以上の添加が必須である。１．２％を超えて添加しても耐食性はほぼ飽和し溶接金属の耐割れ性劣化を招くため、０．１〜１．２％を限定範囲とした。好ましくは、０．２５〜０．７５％の添加が最も優れている。被覆剤からＣｕを添加する場合は、金属Ｃｕを使用する。
【００１６】
Ｎｉは、溶接金属の耐塩酸性の向上および、ＣｕまたはＳｂとの添加で生じる溶接金属凝固時の表面割れ防止を目的に０．１％以上添加する必須元素であるが、０．６％を超えて添加してもそれらの効果は飽和するので、０．１〜０．６％を限定範囲とした。０．１％〜Ｃｕ％×０．５の範囲が好ましい。また、被覆剤からＮｉを添加する場合はＦｅ−Ｎｉや金属Ｎｉを使用する。
【００１７】
Ｓｂは、Ｃｕとともに共存して溶接金属の耐硫酸性および耐塩酸性をさらに向上させる元素である。０．０２％未満では良好な耐食性が得られず、０．２５％を越えるとアーク状態の劣化とスラグの粘性が下がり過ぎ立向姿勢で溶接金属が垂れ易くなり凸ビードを呈するようになる。
【００１８】
また、Ｓｂを被覆剤から添加する場合は、金属Ｓｂを使用するが、平均粒径も重要であり、４５μｍ未満ではスラグの粘性が下がり、特に立向姿勢で凸ビードに成りやすくなり、１５０μｍを越えると被覆剤中の偏析が問題となり、溶接金属中のＳｂ量が安定せず耐食性に支障をきたすようになる。よって、さらに良好な溶接作業性と優れた耐食性を得るために、被覆剤中のＳｂの平均粒径を４５〜１５０μｍの範囲に限定するのが好ましい。
【００１９】
Ｍｏは、Ｃｕとともに溶接棒全質量に対して０．０１％以上添加すると、溶接金属の耐塩酸性を著しく向上させる元素であり、必要に応じて添加する。その効果はＣｕ−Ｓｂとの複合添加で更に増大する。その値が０．６％を超えて添加されると、耐硫酸性および耐塩酸性が低下するので、溶接棒全質量に対して０．０１〜０．６％に限定した。また、被覆剤からＭｏを添加する場合は金属ＭｏまたはＦｅ−Ｍｏを使用する。
【００２０】
Ｃｒは、特に排ガス中の硫黄酸化物含有量の多いプラントで生じる酸化性の硫酸露点腐食環境での耐食性を確保するために、必要に応じて、溶接棒全質量に対して０．１％以上添加し、１．７％を超えて添加すると、逆に耐食性が阻害される。
【００２１】
一方、Ｃｒは、０．１％以上添加すると耐塩酸性を阻害する元素であり、酸化性の硫酸露点腐食環境でない場合は、Ｃｒは無添加、すなわち０．１％未満が好ましい。なお、被覆剤からＣｒを添加する場合は金属ＣｒまたはＦｅ−Ｃｒを使用する。
【００２２】
なお、本発明の限定要件ではないが、溶接棒全体に必要に応じて、Ａｌ、Ｔｉ、Ｎｂ、Ｖ、Ｔａ、Ｗ、Ｓｎ、ＲＥＭ、Ｃａの元素を添加してもよい。
【００２３】
Ｓｎは、添加または不可避的不純物として含有しても耐硫酸露点腐食性および耐塩酸露点腐食性を阻害するものではないが、０．０５％を超えると、溶接継手の靭性を著しく低化させるので、０．０５％以下に制限することが好ましい。
【００２４】
また、本発明で適用する鋼心線は良好な諸溶接性能と耐食性を得るためにＣが０．０８％以下、Ｓｉが０．０３％以下、Ｍｎを０．２０〜０．６０％、Ｐが０．０３５％以下、Ｓが０．０４０％以下が好ましい。
【００２５】
次に、被覆剤中の金属炭酸塩、金属弗化物のおよび金属酸化物添加量の限定理由について述べる。金属炭酸塩とは、炭酸石灰、炭酸バリウム、炭酸マグネシウムなどであるが溶接中にＣＯ₂ガスを発生して大気からの窒素・酸素・水素を遮断し健全な溶接金属を得るのに用いる主要原料である。３５％未満ではその機能を発揮できず、５５％を越えるとアーク状態やビード形状の劣化を招き溶接作業性が悪くなる。
【００２６】
したがって、被覆剤中の金属炭酸塩の含有量は、３５〜５５％とするのが好ましい。
【００２７】
金属弗化物は、蛍石、氷晶石、弗化バリウムなどであり、良好なスラグ流動性を確保し金属炭酸塩と共に主要成分として添加し、１３％未満ではその機能が満たされず、３０％を越えるとスラグの剥離性が劣化し、ビード形状も悪くなる。したがって、被覆剤中の金属弗化物の含有量は、１３〜３０％とするのが好ましい。
【００２８】
金属酸化物は、ＳｉＯ₂、ＴｉＯ₂、Ｎａ₂Ｏ、Ｋ₂Ｏ、Ａｌ₂Ｏ₃などであり、溶接時のアーク状態とスラグ状態を良好に維持するために、被覆剤中に一種または２種以上の組合せで添加するのが好ましい。それらの合計含有量が０．５％未満ではアーク安定性とスラグ状態を良好に維持できず、一方、１５％を越えると溶融金属中の酸素が多くなり靱性性が低下する。
【００２９】
したがって、被覆剤中の金属弗化物の含有量は、０．５〜１５％とするのが好ましい。
【００３０】
本発明の溶接棒は、所要の組成の鋼を溶製した後、これを熱間あるいは冷間にて圧延、引抜きなどの加工により所要の径の鋼心線とし、これに被覆剤を塗布、乾燥して、被覆アーク溶接棒とすることができる。
【００３１】
【実施例】
本発明を実施例により、更に詳細に説明する。表１の組成の鋼心線（直径：4.0mm、長さ：４００mm）に表２の組成の被覆剤を被覆塗装し乾燥して、表３（表２のつづき）に示す組成の２６種類の溶接棒を作成した。この溶接棒を用い以下の試験条件で多層盛り溶接を行い、試験片を採取して、溶着金属の硫酸及び塩酸の耐食性試験と溶接作業性調査を行い、総合判定した。
【００３２】
【表１】

【００３３】
【表２】

【００３４】
【表３】

【００３５】
耐食性試験に使用した試験片は、図１に示すように作成した。すなわち、母材成分の影響を受けないように。軟鋼母材３上に交流溶接機を用い電流１７０Ａを使用し、９層で盛上げ部４を形成し、５層目からの溶着金属２を機械加工で試験片１（４ｍｍ×２５ｍｍ×２５ｍｍ）を各４個採取した。腐食試験は、４０℃の２０％硫酸で２４時間、及び８０℃の１０％塩酸で２４時間の浸食腐食試験を行い、各試験片４個の平均腐食減量を求め、共に２．５mg／（cm²・ｈr）以下を良好、２．５〜１０mg／（cm²・ｈr）をやや劣る、１１mg／（cm²・ｈr）以上を劣る、とした。
【００３６】
溶接作業性の調査では、板厚１２ｍｍ、幅１００ｍｍ、長さ４５０ｍｍの軟鋼をＴ型に組み、交流溶接機を用い、水平隅肉では電流１７０Ａ、立向姿勢では１５０Ａを使用して溶接作業を行ない、アーク状態、スラグ状態、スパッタの多少、ビード形状などを調査した。その判定は、各姿勢の評価を総合判定し、良好を○印、やや劣るを△印、劣るを×とした。
【００３７】
その試験結果を表４に示す。
【００３８】
【表４】

【００３９】
溶接棒Ｎｏ．１〜Ｎｏ．１５は、本発明例であり、特に、溶接棒Ｎｏ．１〜Ｎｏ．１３は、各要件が全て適正であるので耐硫酸及び耐塩酸での腐食減量が少なく良好な結果であり、溶接作業性も満足できるものであった。これらにくらべてＮｏ．１４、１５は、溶接金属の十分良好な耐食性が得られたものの、Ｎｏ．１４では、炭酸石灰の添加量が多いため良好なアーク状態が得られず溶接作業性がやや悪くなり、Ｎｏ．１５では、炭酸石灰が少ないのでアーク力が弱く溶接作業性がやや劣化した。
【００４０】
溶接棒Ｎｏ．１６〜Ｎｏ．２４は、比較例であり、Ｎｏ．１６とＮｏ．１７は、Ｓｂの平均粒径が適正でない場合であり、Ｎｏ．１６は、Ｓｂの平均粒径が小さいのでスラグの粘性が低下し立向姿勢で溶接金属が垂れ易くなり凸ビードとなり、Ｃｕが少ないので腐食し易くなった。また、Ｎｏ．１７は、Ｓｂの平均粒径が大き過ぎることとＮｉが添加されないので耐食性がやや悪くなった。
【００４１】
Ｎｏ．１８は、蛍石が多いのでスラグ剥離性が悪く、溶接棒全体のＣが多いので耐食性の劣化を招いた。
【００４２】
Ｎｏ．１９は、Ｓｉが少ないので溶接作業性が悪く、Ｓが多すぎるので硫酸での耐食性が悪くなった。また、Ｃｕが多すぎるので、耐割れ性が劣化した。
【００４３】
Ｎｏ．２０、Ｎｏ．２２〜Ｎｏ．２４は、溶接棒全体のＳｂが不足または添加されないため、耐硫酸性と耐塩酸性が悪い例である。Ｎｏ．２０は、Ｍｎが多いのでスラグの粘性が低下し立向姿勢でビードが垂れ易くなり溶接作業性の劣化を招いた。
【００４４】
Ｎｏ．２３とＮｏ．２４は、従来の溶接棒であるがＮｉも添加されないので腐食され易くなった。
【００４５】
Ｎｏ．２１は、蛍石が少なくＳｉが多いのでアーク力が強くなりスパッタの飛散が増加し、Ｐが過剰に多いので耐硫酸性と耐塩酸性が悪くなった。
【００４６】
【発明の効果】
本発明は、以上詳述したように、極めて優れた耐硫酸性と耐塩酸性を有した溶接棒を容易にかつ安価に提供することが可能で、その産業上の価値は極めて高い。
【図面の簡単な説明】
【図１】（Ａ）腐食試験片の採取要領を説明する図。（Ｂ）（Ａ）のａ−ａ´断面図。
【符号の説明】
１…溶着金属の腐食試験片
２…溶着金属
３…母材
４…盛上げ（９層）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sulfuric acid dew point corrosion-resistant low alloy steel exhibiting excellent corrosion resistance in an environment where low temperature corrosion is caused by sulfuric acid and hydrochloric acid such as a flue and a chimney of a coal fired boiler or a garbage incineration facility, that is, concentrated sulfuric acid and hydrochloric acid environment. The present invention relates to a welding rod for arc welding. Moreover, it is related with the welding rod applied to the arc welding of the steel materials excellent in the acid resistance for the steel plating pickling tanks which contain single or mixed pickling liquids, such as hydrochloric acid and a sulfuric acid.
[0002]
[Prior art]
In general, when a welded structure is used in a corrosive environment, if there is a difference in corrosion resistance between the welded portion and the base metal, the one with inferior corrosion resistance is selectively corroded, and the life of the structure is remarkably shortened. Further, when the welded portion is selectively corroded, stress concentration occurs in the corrosion hole, and in an extreme case, the structure may be destroyed. As described above, in the use of the welded structure, in the case where the corrosion deterioration cannot be ignored, it is necessary to sufficiently ensure not only the base material but also the corrosion resistance of the welded portion.
[0003]
In flue systems such as coal-fired thermal power plants and garbage incineration facilities, such as flue and chimney, sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion occur due to sulfur trioxide and hydrogen chloride in the exhaust gas.
[0004]
Existing welding rods for corrosion resistant steel contain Cu alone or contain Cu-Cr, and these are sufficiently superior in corrosion resistance in sulfuric acid dew point corrosion environment generated in the plant flue gas generator of heavy oil fired boiler. However, in coal-fired boilers, waste incinerators, or gasification and melting facilities for waste, sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion occur simultaneously, and there was a problem that the corrosion resistance of the welds was not sufficient.
[0005]
Furthermore, as an example of improving the corrosion resistance, it has been proposed to contain Cu and Sb in the weld metal (for example, see Japanese Examined Patent Publication No. 43-1380), but this technique also only improves the sulfuric acid resistance. It was not satisfactory.
[0006]
[Problem to be Solved by the Invention]
In view of the above-mentioned problems of the prior art, the present invention provides a low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance that can obtain a weld metal excellent in sulfuric acid resistance and hydrochloric acid resistance and that can secure good welding workability. It is an object to provide a coated arc welding rod for arc welding.
[0007]
[Means for Solving the Problems]
As a result of a detailed examination of the metallurgical factors affecting the sulfuric acid dew point corrosion resistance and hydrochloric acid dew point corrosion resistance of weld metals, the present inventors specified the composition of the entire welding rod formed by coating a coating on the steel core wire. It has been found that a weld metal having excellent corrosion resistance can be obtained. That is, first, by limiting the impurities P and S which are impurities of the welding rod, (1) by making a specific C—Si—Cu—Ni—Sb system, an excellent sulfuric acid resistance and hydrochloric acid resistance weld metal is obtained. It is done. (2) By defining S in the component system (1), the sulfuric acid resistance and hydrochloric acid resistance are further improved. (3) When Mo is added in the component system (1) or (2), hydrochloric acid resistance can be drastically improved. ( 4 ) By defining the content of metal carbonate, metal fluoride and metal oxide in the coating agent in the component system according to any one of ( 1 ) to ( 3 ), good welding workability can be obtained. It can be secured. ( 5 ) In the component system according to any one of (1) to ( 4 ), the coating agent contains Sb, and the average particle diameter of the Sb is limited to ensure excellent welding while ensuring good welding. Is obtained. The present invention has been completed based on these findings, and the gist of the present invention is as follows.
(1) In a coated arc welding rod formed by coating a steel core wire, either or both of the steel core wire and the coating agent, in mass% with respect to the total mass of the welding rod,
C: 0.005 to 0.15%,
Si: 0.5-4%
Mn: 0.2 to 2.4%
Cu: 0.1 to 1.2%,
Ni: 0.1 to 0.6%,
Sb: 0.02 to 0.25 %
Containing
And P: 0.03% or less,
S: A coated arc welding rod for welding a low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance, characterized by being limited to 0.03% or less and the balance being Fe and inevitable impurities.
(2) In mass% with respect to the total mass of the welding rod, in one or both of the steel core wire or the coating agent,
S: 0.005-0.02%
The coated arc welding rod for low alloy steel welding excellent in sulfuric acid resistance and hydrochloric acid resistance according to (1), characterized in that
(3) In mass% with respect to the total mass of the welding rod, in one or both of the steel core wire or the coating material,
Mo: 0.01 to 0.6%
The coated arc welding rod for welding low alloy steels having excellent sulfuric acid resistance and hydrochloric acid resistance according to (1) or (2).
( 4 ) In the coating agent in mass% with respect to the total mass of the coating agent,
Metal carbonate: 35-55%
Metal fluoride: 13-30%,
Metal oxide: 0.5-15%
The coated arc welding rod for welding a low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance according to any one of (1) to ( 3 ), characterized by comprising:
( 5 ) The low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance according to any one of (1) to ( 4 ), wherein the average particle diameter of Sb in the coating agent is 45 to 150 μm Coated arc welding rod for welding.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The coated arc welding rod of the present invention is formed by coating a steel core with a coating agent, and each element for obtaining a weld metal having a required characteristic is from either the steel core wire or the coating agent. It may be added. Therefore, in the following description, unless otherwise specified, each component element may be contained as a whole welding rod in one or both of the steel core wire and the coating agent.
[0009]
First, content regulation of C, Si, Mn, P, S, Cu, Ni, and Sb with respect to the total mass of the welding rod will be described.
In the present invention, C does not include the metal carbonate in the coating agent or the C content of organic CO or CO ₂ , and C in the coating material, for example, SiC, Fe—Mn, Fe—Si, and the steel core wire. C, which is added to ensure the strength of the weld metal, but if the total exceeds 0.15%, the crack resistance and sulfuric acid resistance of the weld metal are lowered. From the viewpoint of sulfuric acid resistance and hydrochloric acid resistance, the C content is preferably as low as possible. However, if it is less than 0.005%, the arc force is weak and the penetration becomes insufficient, resulting in poor welding workability, so 0.005 to 0.15% And In addition, when it is necessary to consider the balance between sulfuric acid resistance and hydrochloric acid resistance, 0.05% or less is most preferable.
[0010]
When Si is contained in an amount of 0.5% or more, it coexists with Cu and improves the sulfuric acid resistance and hydrochloric acid resistance of the weld metal particularly in a sulfuric acid concentration range of about 40%. However, if it exceeds 4%, the corrosion resistance is not improved, the toughness of the weld metal is remarkably lowered, the arc force becomes excessively strong, and the welding workability is deteriorated, so the upper limit was made 4%. When the workability and the toughness of the weld metal are more important, 0.5 to 2% is preferable. Moreover, when adding Si from a coating agent, Fe-Si is used.
[0011]
Mn is added to the entire welding rod in an amount of 0.2% or more for deoxidation and strength adjustment of the weld metal. However, if it exceeds 2.4%, the viscosity of the slag will decrease, and the vertical position bead will easily sag. Since workability | operativity worsens, 0.2 to 2.4% was made into the limited range. Moreover, when adding Mn from a coating agent, metal Mn and Fe-Mn are used.
[0012]
P is an impurity element and significantly inhibits the sulfuric acid resistance and hydrochloric acid resistance of the weld metal, so the range was made 0.03% or less. More preferably, if it is 0.01% or less, sulfuric acid resistance and hydrochloric acid resistance are remarkably improved, and 0.005% or less is most preferable.
[0013]
S is an impurity element and needs to be limited in order to ensure sufficient sulfuric acid resistance and hydrochloric acid resistance of the weld metal. If it exceeds 0.03%, the sulfuric acid resistance is remarkably lowered, so the upper limit was made 0.03%.
[0014]
In addition, in a Cu—Mo—Sb-based welding rod, when 0.005% or more of S is contained, hydrochloric acid resistance is remarkably improved along with sulfuric acid corrosion resistance of the weld metal. However, even if the content exceeds 0.02%, the effect is saturated, and mechanical properties (such as lamellar resistance) and hot workability deteriorate, so the S content is 0.005 to 0.00. It is preferable to set it to 02%.
[0015]
In order to ensure the sulfuric acid resistance and hydrochloric acid resistance of the weld metal, Cu should be added in an amount of 0.1% or more. Even if added over 1.2%, the corrosion resistance is almost saturated and crack resistance deterioration of the weld metal is caused, so 0.1 to 1.2% was made the limited range. Preferably, the addition of 0.25 to 0.75% is most excellent. When adding Cu from a coating agent, metal Cu is used.
[0016]
Ni is an essential element to be added in an amount of 0.1% or more for the purpose of improving the hydrochloric acid resistance of the weld metal and preventing surface cracks during solidification of the weld metal caused by the addition with Cu or Sb. Even if added, those effects are saturated, so 0.1 to 0.6% was made the limited range. A range of 0.1% to Cu% × 0.5 is preferable. Moreover, when adding Ni from a coating agent, Fe-Ni and metal Ni are used.
[0017]
Sb is an element that coexists with Cu and further improves the sulfuric acid resistance and hydrochloric acid resistance of the weld metal. If it is less than 0.02%, good corrosion resistance cannot be obtained, and if it exceeds 0.25%, the deterioration of the arc state and the viscosity of the slag are too low, so that the weld metal tends to sag in a vertical posture and presents a convex bead.
[0018]
In addition, when Sb is added from the coating agent, metal Sb is used, but the average particle size is also important. If it is less than 45 μm, the viscosity of the slag is lowered, and it tends to be a convex bead particularly in a vertical posture, and 150 μm. If it exceeds, segregation in the coating material becomes a problem, and the amount of Sb in the weld metal is not stabilized, and the corrosion resistance is hindered. Therefore, in order to obtain better welding workability and excellent corrosion resistance, it is preferable to limit the average particle size of Sb in the coating material to a range of 45 to 150 μm.
[0019]
Mo is an element that significantly improves the hydrochloric acid resistance of the weld metal when added to the total mass of the welding rod together with Cu by 0.01% or more, and is added as necessary. The effect is further increased by the combined addition with Cu-Sb. If the value exceeds 0.6%, the sulfuric acid resistance and hydrochloric acid resistance decrease, so the content was limited to 0.01 to 0.6% with respect to the total mass of the welding rod. Moreover, when adding Mo from a coating material, metal Mo or Fe-Mo is used.
[0020]
Cr is 0.1% or more based on the total mass of the welding rod, if necessary, in order to ensure corrosion resistance in an oxidizing sulfuric acid dew point corrosion environment generated in a plant having a high sulfur oxide content in the exhaust gas. If it is added and added over 1.7%, the corrosion resistance is adversely affected.
[0021]
On the other hand, Cr is an element that inhibits hydrochloric acid resistance when added in an amount of 0.1% or more, and Cr is preferably not added, that is, less than 0.1% in an oxidizing sulfuric acid dew point corrosion environment. In addition, when adding Cr from a coating material, metal Cr or Fe-Cr is used.
[0022]
Although not a limiting requirement of the present invention, elements of Al, Ti, Nb, V, Ta, W, Sn, REM, and Ca may be added to the entire welding rod as necessary.
[0023]
Even if Sn is added or contained as an unavoidable impurity, it does not inhibit sulfuric acid dew point corrosion resistance and hydrochloric acid dew point corrosion resistance. However, if it exceeds 0.05%, the toughness of the welded joint is significantly reduced. , 0.05% or less is preferable.
[0024]
Further, the steel core wire applied in the present invention has C of 0.08% or less, Si of 0.03% or less, Mn of 0.20 to 0.60%, P for obtaining good welding performance and corrosion resistance. Is preferably 0.035% or less and S is 0.040% or less.
[0025]
Next, the reasons for limiting the amount of metal carbonate, metal fluoride and metal oxide added in the coating will be described. Metal carbonates are lime carbonate, barium carbonate, magnesium carbonate, etc., but are the main raw materials used to produce sound weld metal by generating CO ₂ gas during welding and blocking nitrogen, oxygen, and hydrogen from the atmosphere. It is. If it is less than 35%, the function cannot be exhibited, and if it exceeds 55%, the arc state and the bead shape are deteriorated and the welding workability is deteriorated.
[0026]
Therefore, the content of metal carbonate in the coating is preferably 35 to 55%.
[0027]
Metal fluorides are fluorite, cryolite, barium fluoride, etc., which ensures good slag fluidity and is added as a main component together with metal carbonate. If less than 13%, the function is not satisfied, 30% If it exceeds, the peelability of the slag will deteriorate and the bead shape will also deteriorate. Therefore, the content of metal fluoride in the coating is preferably 13 to 30%.
[0028]
Examples of the metal oxide include SiO ₂ , TiO ₂ , Na ₂ O, K ₂ O, and Al ₂ O _{3. In} order to maintain the arc state and the slag state at the time of welding well, It is preferable to add in a combination of two or more species. If the total content thereof is less than 0.5%, the arc stability and the slag state cannot be maintained satisfactorily. On the other hand, if the total content exceeds 15%, oxygen in the molten metal increases and the toughness decreases.
[0029]
Therefore, the content of metal fluoride in the coating agent is preferably 0.5 to 15%.
[0030]
The welding rod of the present invention, after melting the steel of the required composition, it is hot or cold, rolled into a steel core wire of the required diameter by processing such as drawing, applying a coating to this, It can be dried to form a coated arc welding rod.
[0031]
【Example】
The present invention will be described in more detail with reference to examples. A steel core wire having a composition shown in Table 1 (diameter: 4.0 mm, length: 400 mm) was coated with a coating agent having a composition shown in Table 2 and dried, and 26 kinds of compositions shown in Table 3 (continued in Table 2) were coated. A welding rod was created. Using this welding rod, multi-layer welding was performed under the following test conditions, specimens were collected, corrosion resistance tests of weld metal sulfuric acid and hydrochloric acid and a survey of welding workability were conducted, and comprehensive judgment was made.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
[Table 3]

[0035]
The test piece used for the corrosion resistance test was prepared as shown in FIG. In other words, do not be affected by the base material components. Using an AC welding machine on a mild steel base material 3 and using an electric current of 170 A, a raised portion 4 is formed with nine layers, and a test piece 1 (4 mm × 25 mm × 25 mm) is formed by machining the weld metal 2 from the fifth layer. Four were collected each. In the corrosion test, an erosion corrosion test was conducted with 20% sulfuric acid at 40 ° C. for 24 hours and with 10% hydrochloric acid at 80 ° C. for 24 hours, and the average corrosion weight loss of each of the four test pieces was determined. ² · hr) or less, 2.5 to 10 mg / (cm ² · hr) is slightly inferior, and 11 mg / (cm ² · hr) or more is inferior.
[0036]
In the survey of welding workability, mild steel with a plate thickness of 12 mm, width of 100 mm, and length of 450 mm was assembled into a T-shape, and an AC welding machine was used to perform the welding work using a current of 170 A for the horizontal fillet and 150 A for the vertical posture. Conducted, the arc state, the slag state, the amount of spatter, and the bead shape were investigated. In the determination, the evaluation of each posture was comprehensively determined, and “Good” was marked as “Good”, “Slightly inferior” was “△”, and “Low” was marked as “X”.
[0037]
The test results are shown in Table 4.
[0038]
[Table 4]

[0039]
Welding rod no. 1-No. 15 is an example of the present invention. 1-No. No. 13 was a good result with less corrosion weight loss with sulfuric acid resistance and hydrochloric acid resistance because all requirements were appropriate, and welding workability was satisfactory. Compared to these, No. Nos. 14 and 15 show no satisfactory corrosion resistance of the weld metal. In No. 14 , since the amount of lime carbonate added is large, a good arc state cannot be obtained and welding workability is slightly deteriorated. In No. 15 , since there was little lime carbonate, arc power was weak and welding workability deteriorated somewhat.
[0040]
Welding rod no. 16- No. No. 24 is a comparative example. 16 and No. No. 17 is a case where the average particle size of Sb is not appropriate. In No. 16 , since the average particle size of Sb was small, the viscosity of the slag was lowered, and the weld metal was liable to sag in a vertical posture, forming a convex bead, and being less susceptible to corrosion because of less Cu. No. In No. 17 , the average particle size of Sb was too large and Ni was not added, so the corrosion resistance was slightly deteriorated.
[0041]
No. No. 18 has a lot of fluorite, so the slag releasability is poor, and since there is much C in the entire welding rod, the corrosion resistance deteriorates.
[0042]
No. No. 19 was poor in welding workability due to a small amount of Si, and because of too much S, the corrosion resistance with sulfuric acid was deteriorated. Moreover, since there was too much Cu, the crack resistance deteriorated.
[0043]
No. 20 , no. 22- No. No. 24 is an example of poor sulfuric acid resistance and hydrochloric acid resistance because Sb of the entire welding rod is insufficient or not added. No. In No. 20 , since M n is large, the viscosity of the slag is lowered, and the bead is liable to hang in a standing posture, resulting in deterioration of welding workability.
[0044]
No. 23 and no. No. 24 is a conventional welding rod, but Ni was not added, so it was easily corroded.
[0045]
No. No. 21 had less fluorite and more Si, so the arc force was stronger and the spatter scattering increased, and P was excessive, so the sulfuric acid resistance and hydrochloric acid resistance deteriorated.
[0046]
【The invention's effect】
As described above in detail, the present invention can easily and inexpensively provide a welding rod having extremely excellent sulfuric acid resistance and hydrochloric acid resistance, and its industrial value is extremely high.
[Brief description of the drawings]
FIG. 1A is a view for explaining a sampling procedure for a corrosion test piece. (B) Aa 'sectional drawing of (A).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Corrosion test piece of weld metal 2 ... Weld metal 3 ... Base material 4 ... Swelling (9 layers)

Claims

In a coated arc welding rod formed by coating a steel core with a coating agent, either or both of the steel core wire and the coating agent, in mass% with respect to the total mass of the welding rod,
C: 0.005 to 0.15%,
Si: 0.5-4%
Mn: 0.2 to 2.4%
Cu: 0.1 to 1.2%,
Ni: 0.1 to 0.6%,
Sb: 0.02 to 0.25 %
Containing
And P: 0.03% or less,
S: A coated arc welding rod for welding a low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance, characterized by being limited to 0.03% or less and the balance being Fe and inevitable impurities.

% By mass relative to the total mass of the welding rod, in one or both of the steel core wire or the coating material,
S: 0.005-0.02%
The coated arc welding rod for welding a low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance according to claim 1.

In mass% with respect to the total mass of the welding rod, in one or both of the steel core wire or the coating material,
Mo: 0.01 to 0.6%
The coated arc welding rod for welding a low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance according to claim 1 or 2, characterized by comprising:

In the coating agent in mass% with respect to the total mass of the coating agent,
Metal carbonate: 35-55%
Metal fluoride: 13-30%,
Metal oxide: 0.5-15%
The coated arc welding rod for welding a low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance according to any one of claims 1 to 3 , characterized by comprising:

The coated arc for welding a low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance according to any one of claims 1 to 4 , wherein an average particle diameter of Sb in the coating agent is 45 to 150 µm. Welding rods.