JP3902419B2

JP3902419B2 - Arc welding method and arc welding apparatus

Info

Publication number: JP3902419B2
Application number: JP2001141510A
Authority: JP
Inventors: 隆夫熊坂; 光雄加藤; 章弘佐藤; 邦夫宮崎
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2001-05-11
Filing date: 2001-05-11
Publication date: 2007-04-04
Anticipated expiration: 2021-05-11
Also published as: JP2002336965A

Description

【０００１】
【発明の属する技術分野】
本発明はアーク溶接方法に係わり、特に溶接ビード部と該熱影響部の残留応力を低減するのに好適なアーク溶接方法及びアーク溶接装置に関する。
【０００２】
【従来の技術】
従来のアーク溶接においては、溶接トーチと溶接母材との間にアークを発生させ溶接母材上に溶融池を形成し、該溶融池が凝固した溶接ビード部と該溶融池と接触する部分に形成された熱影響部と溶接母材とを熱輻射及び周囲媒体である空気の自然対流により冷却させ常温に戻していた。又、特開昭５５−７３４７７号公報、特開昭５８−２０５６８７号公報、特開昭６０−１８７４７８号公報においては、大気中の溶接を行う際に水冷を行いクロム炭化物の析出を防止する方法が提案されている。
【０００３】
更に、水中溶接においては、水を排除した気相空間にてアークを発生させた後、溶接ビード部と熱影響部と溶接母材とを周囲媒体である水と接触させることに水の自然対流により冷却し水温まで戻していた。このような水中アーク溶接に関連するものに、特開平１０−３４３７４号公報などがある。
【０００４】
【発明が解決しようとする課題】
しかし、特開昭５５−７３４７７号公報、特開昭５８−２０５６８７号公報、特開昭６０−１８７４７８号公報においては、クロム炭化物の析出を防止するため６５０℃〜１２００℃に加熱されている時間を短縮するようにしたものであり、残留応力を引張り応力から圧縮応力にするための方法については開示されていなかった。
【０００５】
又、特開平１０−３４３７４号公報は水中ブラズマ溶接により残留応力を低減するものであるが、気泡の発生などにより溶接品質が損なわれたり、ビードに隣接する熱影響部に局部的な引張り残留応力（残留応力のピーク）が残存するケースがあった。引張り残留応力を有する溶接部を使用した製品は、比較的短期間に亀裂や応力腐食割れを生じやすい欠点がある。
【０００６】
本発明の目的は、製品の使用中の亀裂や応力腐食割れ防止し、製品の寿命を長くし、かつ性能に対する信頼性を向上したアーク溶接方法を提供することにある。
【０００７】
【課題を解決するための手段】
上記目的を達成するために、本発明では、溶接ビード部の断面の深さ寸法をＤ、幅寸法をＷとすれば、溶接ビード部の断面のアスペクト比（Ｄ／Ｗ）が０．５以上の溶接ビードを形成し、凝固させた直後の溶接ビード部とこれに隣接する熱影響部とに冷却媒体を噴射させて急冷し、表面が圧縮残留応力を有する溶接部を形成し、前述の目的を達成することにある。
【０００８】
【発明の実施の形態】
（第１の実施例）
図１(Ａ)，(Ｂ)に本発明の第１の実施例を示す。本発明の第１の実施例は、溶接装置例えばアーク溶接装置に冷却媒体を噴出する噴射ノズル６を用い、気中で溶接をする場合である。
【０００９】
溶接トーチ１に保持される電極２と溶接母材３との間にアークを発生させ溶接母材３上に溶接池５を形成し、溶接池５を凝固させ溶接ビート部４を形成するものにおいて、溶接ビード４は溶接ビードの深さ寸法をＤとし、幅寸法をＷとすれば、アスペクト比（Ｄ／Ｗ）が０．５以上となる溶接条件にて溶接ビード部４を形成し、冷却媒体１０例えば水は溶接トーチ１近傍に配置した冷却ヘッド８から噴出させ溶接局部４Ｃに流動させるようにして、溶接局部４Ｃを急冷し、図１(Ｂ)に示す溶接ビード部４を形成する。ここで溶接局部４Ｃは溶融池が凝固した直後の溶接ビード部４と溶融池５と隣接する熱的影響部４Ａとを指すものである。
【００１０】
入熱５〜２０ＫＪ／ｃｍより望ましくは、８〜１７ＫＪ／ｃｍの溶接ビード部４において、アスペクト比（Ｄ／Ｗ）が０．５以上となるような深溶け込み溶接は、次の方法により実現できる。ＤＣアークの場合はシールドガスとして、アルゴンに２〜１０％の水素を混合した混合ガスを用いてビードオン溶接を行うか、シールドガスとして、アルゴンを用い活性フラックスを溶接部に塗布しビードオン溶接を行うことで実現できる。又、パルスアークの場合はパルスピーク電流値を高く（３００〜６００Ａ）設定し、５〜３０ＫＨｚの高周波パルス溶接でビードオン溶接を行うことによりシールドに混合する水素を低減できる利点がある。
【００１１】
冷却媒体１０は、冷却媒体供給装置９により配管７を経て電極２の周囲に設置された噴射ノズル６を有する冷却ヘッド８に供給される。又、冷却ヘッド８は溶接トーチ１に固定され、溶接トーチ１と同一速度で移動する。
【００１２】
冷却ヘッド８としては、１本の噴射ノズル６を用いて構成し、溶融池５が凝固した直後の溶接ビード部４と溶融池６に隣接する部分に形成された熱影響部４Ａとを冷却する例を示したが、２本、又は、複数の噴射ノズル６を用いて溶融池６が凝固した直後の溶接ビード部４と溶融池６に隣接する部分に形成された熱影響部４Ａとを冷却するようにしても良い。
【００１３】
又、冷却媒体１０（例えば、水）が飛散し水しぶきなどでアーク空間を乱したり、電極２を濡らしたり、溶融池６で過度の蒸気を発生させたりすることを防止するには、電極２と冷却ヘッド８との間に冷却媒体１０を遮蔽する水排除隔壁１４を設け、アーク空間から冷却媒体１０を遮蔽するようにし、冷却ヘッド８と反対側の水排除隔壁１４の前面にシールドガス１６の出口部１５を設ける。
【００１４】
シールドガス１６に出口部１５を設けないと、水排除隔壁１４の後方から流出するシールドガス１６により噴射冷却を行う噴流１０に乱れが発生したり、又冷却ヘッド８と同側の水排除隔壁１４側面に出口部１５を設けると、シールドガス１６の流れにより、溶接ビード断面に偏りが発生する傾向があるからである。
【００１５】
更に、図２に示すように、噴射ノズル６は母材３面に対して３０度〜５０度の範囲で傾斜させて配置することが望ましい。傾斜角度θが２０度以下の場合は冷却開始位置が溶融池６から遠くなり急冷効果が少なくなり、６０度以上の場合は水排除隔壁２１と母材３との隙間から衝突噴流が進入しアークを乱すようになるからである。
【００１６】
冷却媒体として、水の他に、難燃性オイル、フロリナート、液体窒素などが使用できるが、噴射冷却の熱伝達率が５〜５０ＫＷ／ｍ²℃より望ましくは、水を用い噴射冷却の熱伝達率が１０〜３０ＫＷ／ｍ²℃となるように噴射時の流速や流量を設定すると良い。噴射冷却の熱伝達率が１０ＫＷ／ｍ²℃未満の場合、後述する反転温度差が充分に形成されず残留応力の極大部を圧縮にすることができない。
【００１７】
又、噴射冷却時の流速や流量を高くすれば、熱伝達率を増大できるが、流速や流量を高くし過ぎるとアークを乱し溶接品質が悪化する傾向があるからである。即ち、水噴射冷却時の流速が０．８〜８ｍ／ｓｅｃ、より望ましくは、１〜５ｍ／ｓｅｃとなるように噴射時の流量を設定すると良い。
【００１８】
更に、水温を０〜５℃程度の低温状態にしたり、不凍液を混合させたり不凍効果のある物質を溶解させ氷点以下にし、流速や流量を極力高くせずに常温の場合よりも冷却作用（熱伝達率）を高めることが望ましい。
【００１９】
このような構成で、母材の厚さ１２ｍｍのＳＵＳ３０４を入熱１１ＫＪ／ｃｍ，溶接速度１００ｍｍ／ｍｉｎにおいて、１例として図３(Ｂ)，(Ｃ)，(Ｄ)に示す複数の溶接ビード部４を形成した。ＳＵＳ３０４以外の母材の材質としてＳＵＳ３１６、インコネル６００等を用いても良い。溶接ビード部４のビード断面形状のアスペクト比Ｄ／Ｗは、(Ｂ)＝０．３，(Ｃ)＝０．５，(Ｄ)＝１．０であり、ビードオン溶接を行い、冷却媒体として水を使用し、冷却ヘッド８として１本の矩形噴射ノズル６（開口幅２０ｍｍ、開口高さ２ｍｍ）を配置し、母材面に対して４０度の角度で約５ｌ／ｍｉｎ噴流を供給し、冷却をした。尚、噴流の流速は約２．０ｍ／ｓであり、噴流の熱伝達率は約１３〜２０ＫＷ／ｍ²℃と推定される。
【００２０】
このような施工を行い、アスペクト比と残留応力との関係を求めた結果を図４(Ａ)，(Ｂ)に示す。図４(Ａ)は母材３に溶接ビード部４を形成した状況を示し、溶接ビード部４の中心部０からＹ方向に順次離れた時の残留応力を測定した特性図を図４(Ｂ)に示す。図４(Ｂ)の特性図は図３(Ｂ)，(Ｃ)，(Ｄ)に示す複数の溶接ビード部４に水噴射した場合と自然冷却の場合とを示した。図４(Ｂ)の特性図の溶接局部における残留応力の極大値つまりピーク値を合成した特性図を図５に示した。図５においてはアスペクト比（Ｄ／Ｗ）が０．４の場合の残留応力ピーク値も追加した。
【００２１】
図５の特性図から明らかなように、水噴射冷却時の残留応力のビード方向成分（σｘ）は、アスペクト比が０．３以下の溶接ビード部４は、溶接線近傍の熱的影響部つまり溶接局部４Ｃにおいて、ピークが約＋１００ＭＰａ以上の引張残留応力値を有している。
【００２２】
またアスペクト比が０．４以上の溶接ビード部４は、溶接線近傍の熱的影響部つまり溶接局部４Ｃにおいて、０から約−１４０ＭＰａを有する圧縮残留応力となる。更にこれらの詳細を図５により説明する。
【００２３】
即ち、図５から明らかなように、アスペクト比が０．３以下の溶接ビード部４を有する製品においては、引張残留応力値を有しており、この溶接ビード部４を使用した製品は比較的短期間に亀裂や応力腐食割れを生じやすい欠点がある。
【００２４】
又アスペクト比が０．４以上０．５未満の溶接ビード部４は、溶接局部４Ｃの応力ピークは約０〜−１２０ＭＰａの圧縮残留応力となるが、アスペクト比が少し変化しただけで、引張残留応力値が大幅に変化し、アスペクト比が０．４以上０．５未満の溶接ビード部４を有する製品例えばＳＵＳ３０４に繰り返し負荷疲労試験をすると、破損限界値がばらつき性能の安定した製品を製作することができない。
【００２５】
これに対して、本発明のアスペクト比が０．５以上の溶接ビード部４を有する製品においては、アスペクト比が多少変化しても常に圧縮残留応力が略−１２０〜−１４０ＭＰａとなり、略一定値の圧縮残留応力となり、アスペクト比が０．５以上の溶接ビード部４を有する製品例えばＳＵＳ３０４に繰り返し負荷を与えて疲労試験をすると、破損限界値が略一定した性能の安定した製品を製作することができると共に、亀裂や応力腐食割れが生じにくくなるので、製品の寿命が長くなり、製品の信頼性が向上した。
【００２６】
又、図６に溶接ビード部４の図３(Ｂ)，(Ｃ)，(Ｄ)及び図４(Ａ)のビード表面温度３Ａと内部温度３Ｂに関する時間と温度との関係を示す変化曲線である。ビード表面温度３Ａと内部温度３Ｂとは、ビード直下で高温となる位置(図３の(Ｄ)参照)の温度として定義した。図６において、溶融池形成直後に水噴射冷却を行った場合のビード表面温度３Ａとビード内部温度３Ｂに関する冷却曲線を図６の太線で示した。又、ビード内部温度３Ｂとビード表面温度３Ａとの温度差（＝内部温度−ビード表面温度）を反転温度差と定義した。
【００２７】
図６から、アスペクト比が０．３の場合の反転温度差は小さいが、アスペクト比が(０．５)，(１．０)と大きくなる程、反転温度差が大きくなることが判る。即ち、アスペクト比が０．３の場合にはビード表面の温度が低下すると、内部に形成される高温部は板内部の浅い部分（表面より３〜４ｍｍの位置）にあるため表面温度と共に低下する。その結果、内部温度３Ｂの方がビード表面温度３Ａより少し高い温度状態を保持するに過ぎない。
【００２８】
他方、アスペクト比が(０．５)，(１．０)の場合、ビード中心表面の温度が急速に低下しても、ビード直下の高温部は板内部の深い部分（表面より４〜６ｍｍの位置）にあるため、内部温度低下の度合いは表面より遅く緩やかになる。その結果、内部温度３Ｂがビード表面温度３Ａより高くなる反転温度差が大きく形成されるようになる。
【００２９】
又、図５と図６の結果を対比すると、板表面の残留応力を圧縮残留応力にするには、上記した反転温度差を充分大きく形成する必要があることが判った。又、上記した施工を行なっても、溶接部において気泡の発生などにより溶接品質が損なわれることはなかった。
【００３０】
尚、図示はしてないが、溶接トーチ１と冷却ヘッド８を固定し、溶接母材３を移動させるように構成しても、上記した効果と同等な効果が得られることは言うまでも無い。
（第２の実施例）
図７に本発明の第２の実施例を示す。本発明の第２の実施例は水排除隔壁１４を用い、水中１７で溶接を行なう場合である。
【００３１】
溶接トーチ１に保持される電極２と溶接母材３との間に発生するアークの周辺にシールドガス１６による水排除（気相）空間を形成し、水中１７の溶接母材３上に溶融池５を形成し水中溶接を行うものにおいて、溶接ビード部４のアスペクト比（Ｄ／Ｗ）が０．５以上となる溶接条件にて溶接ビードを形成し、冷却媒体１０である水を冷却ヘッド８から噴出させ、溶接局部を急冷するようにしたものである。
【００３２】
本発明において、電極周辺に配置される水排除隔壁１４は、断面形状が円形の場合、直径を溶融池５の長さとほぼ同等以上で約３倍の範囲に設定され、更に、水排除隔壁１４の溶接進行方向の前面にはシールドガスの出口部１５が設けられている。従って、本発明においては、従来使用されている隔壁断面直径（溶融池長さの５〜８倍）と比較して水排除隔壁１４の断面直径を小さくしたので、水排除（気相）空間での温度降下が少なくなり、より高温の状態の溶接母材（表面及び内部）を急冷できる効果がある。
【００３３】
その結果、溶接ビード部４表面の温度を溶接ビード直下の母材内部の温度より低くし、反転温度差を大きくすることができる。更に、水排除隔壁１４の溶接進行方向の前面にシールドガスの出口部１５を設けたので、実施例１と同様な効果に加えて、溶接進行方向の後方からのシールドガスの排出に伴う気泡により、溶接進行方向の後方の冷却を妨げることがない利点がある。
【００３４】
又、実施例１と同様な傾斜角、開口部の噴射ノズル６を有する冷却ヘッドを水排除隔壁１４の周辺に配置し、噴射ノズル６により水噴流を溶接局部に流動させ水噴射冷却を行うことにより、水の自然対流による冷却（熱伝達率約１〜５ＫＷ／ｍ²℃）よりも冷却作用（熱伝達率）を高くすることができる。
【００３５】
又、冷却媒体１０として水を用いる場合、周囲の水２４より低い温度の状態、例えば、０〜１０℃程度の低温状態にしたり、不凍液を混合させたり不凍効果のある物質を溶解させ氷点以下にすることにより、周囲の水２４よりも冷却作用を高めることが望ましい。
【００３６】
この構成で、厚さ１２ｍｍのＳＵＳ３０４を入熱１２ＫＪ／ｃｍ、溶接速度１００ｍｍ／ｍｉｎにおいて、複数のビード形状つまりアスペクト比＝(０．３)，(０．５)，(１．０)のビードオン溶接を行い、冷却媒体として水を使用し、冷却ヘッド８として１本の矩形噴射ノズル６（開口幅２０ｍｍ、開口高さ２ｍｍ）を配置し、母材面に対して４０度の角度で約１０ｌ／ｍｉｎ噴流を供給し、冷却した。尚、噴流の流速は約４．２ｍ／ｓであり、噴流の熱伝達率は約１８〜２８ＫＷ／ｍ²℃と推定される。
【００３７】
このような施工を行い、アスペクト比と残留応力との関係を求めたところ、溶接ビード部のアスペクト比（Ｄ／Ｗ）が０．５以上の溶接ビード部４を形成し、上記した水噴射冷却を行なうことにより、水中溶接においても、板表面の残留応力を圧縮残留応力にできることが判った。又、溶接部においては、気泡の発生などにより溶接品質が損なわれることはなかった。
（第３の実施例）
図８(Ａ)，(Ｂ)に本発明の第３の実施例を示す。本発明の第３の実施例は各層を１パスで行う狭開先の多層突合せ溶接を行なう場合である。特に、図８(Ａ)，(Ｂ)に示すように、狭い開先，即ち、溶接母材３に開先底部３Ｃを有する溝１８を形成する。この溝１８に１パスで溶接を行い、先ず開先底部３Ｃを溶接させ最下段溶接層を形成する。更に各層を１パスにより最下段溶接層例えば３Ｃの上に順次第２溶接層１８Ａ、第３溶接層１８Ｂの如く積重ねて、最上段溶接層１８Ｎを形成後、最上段溶接層１８Ｎの上に本発明による溶接ビード部の断面のアスペクト比（Ｄ／Ｗ）が０．５以上の溶接ビード部４を行い最終溶接層１８Ｚを形成する。溶接ビード部の断面のアスペクト比（Ｄ／Ｗ）が０．５以上の溶接ビード４を形成し、凝固した直後の溶接ビード部とこれに隣接する熱影響部とに冷却媒体を噴射させ急冷するようにしたものである。
【００３８】
そして、最終溶接層１８Ｚとその熱影響部の表面残留応力を圧縮残留応力にするか、又は極めて低い引張残留応力に抑制するので、本発明による溶接ビード部４を使用した分だけ各溶接層での亀裂、応力腐食割れを抑制することが出来るようになり、本発明を使用した製品の性能の信頼性を向上することができる。
【００３９】
前述において各層を１パスで順次肉盛りを行う狭開先溶接は、開先幅（ルート幅）を狭く設定し，アークの指向性を高めたＴＩＧ溶接を用い溶加ワイヤを供給しながら溶接を行なうことにより実現できる。例えば、板厚２０ｍｍ、開先形状としては、ルート幅４〜６ｍｍ、開先角３度、ルートフェース１〜３ｍｍ、ルートギャップ０ｍｍに対し、パルスＴＩＧ溶接において、入熱５〜１５ＫＪ／ｃｍ、溶接速度８０〜１５０ｍｍ／ｍｉｎ、パルスピーク電流値を高く（３００〜６００Ａ）設定し、３００〜７００Ｈｚの中周波パルスＴＩＧで溶接を行うか、５〜３０ＫＨｚの高周波パルスＴＩＧで溶接を行うことで可能であることを見出した。
【００４０】
又、ＤＣ−ＴＩＧ溶接を用いる場合は、開先幅（ルート幅）及び開先角を上記より大きくし、シールドガスとしてアルゴンに２〜１０％の水素を混合した混合ガスを用いて施工することで可能である。
【００４１】
又、溶接ビード部のアスペクト比（Ｄ／Ｗ）が０．５以上となるような深溶け込み溶接は、実施例１と同様な方法で実現できる。例えば、ＤＣ−ＴＩＧを用い、シールドガスとしてアルゴンに２〜１０％の水素を混合した混合ガスを用いてビードオン溶接を行うか、シールドガスとしてアルゴンを用い活性フラックスを溶接部に塗布しビードオン溶接を行えば良い。
【００４２】
厚さ２０ｍｍのＳＵＳ３０４板の多層突合せ溶接において、狭開先部のルート幅を５ｍｍとし、先ず、図８(Ａ)に示すように、ＤＣ−ＴＩＧを用いて各層の肉盛りを１パスで行った後、図８(Ｂ)に示すように、溶接ビード部の断面のアスペクト比（Ｄ／Ｗ）が０．５乃至１．０の最終層を形成しつつ、凝固した高温状態の溶接ビード部と隣接する熱影響部に水を噴射させて急冷した。又、比較のため、ＤＣ−ＴＩＧを用いて溶接ビード断面のアスペクト比（Ｄ／Ｗ）が０．３の最終層を形成し同様な施工を行った。
【００４３】
冷却ヘッド８として１本の矩形噴射ノズル６（開口幅２０ｍｍ、開口高さ２ｍｍ）を配置し母材面に対して４０度の角度で約５ｌ／ｍｉｎ噴流を供給して、冷却をした。尚、噴流の流速は約２．０ｍ／ｓであり、噴流の熱伝達率は約１３〜２０ＫＷ／ｍ²℃と推定される。
【００４４】
このような施工を行い、アスペクト比と残留応力との関係を求めたところ、溶接ビード部４のアスペクト比（Ｄ／Ｗ）が０．５以上の溶接ビード４を形成し、上記した水噴射冷却を行なうことにより、多層突合せ溶接部においても、表面の残留応力を圧縮残留応力にできることが判った。又、溶接部においては、気泡の発生などにより溶接品質が損なわれることはなかった。
【００４５】
尚、前述の実施例ではアスペクト比（Ｄ／Ｗ）が(０．５)，(１．０)の場合しか説明していないが、アスペクト比（Ｄ／Ｗ）が０．５以上である(１．５)，(２．０)〜等にも適用できることは云うまでもない。
【００４６】
【発明の効果】
以上のように、本発明によれば、圧縮残留応力を有する溶接ビード部を使用した製品は、使用中に亀裂や応力腐食割れを生じにくくなり、アスペクト比（Ｄ／Ｗ）を０．５以上にした分だけ製品の寿命が長くなると共に、製品の性能に対する信頼性が向上した。
【図面の簡単な説明】
【図１】本発明の実施例であるアーク溶接の概略構成を示した斜視図。
【図２】図１に使用した噴射ノズルからの冷却媒体を溶接母材に噴射する冷却ヘッド部分の構成図。
【図３】図１により形成した溶接ビード部の断面図。
【図４】図３の溶接ビード部におけるビード方向の残留応力分布を示す分布図。
【図５】図４の溶接ビード部における残留応力のビード方向成分を示す分布図。
【図６】図３の溶接ビード部における熱的影響部の残留応力の温度と時間との関係を示す特性図。
【図７】本発明の他の実施例として示した水中アーク溶接の概略斜視図。
【図８】本発明の他の実施例として開先溶接部を示す斜視図。
【符号の説明】
１…溶接トーチ、２…電極、３…母材、３Ｃ…開先底部、４…溶接ビード部、５…溶融池、６…噴射ノズル、７…流体供給配管、８…冷却ヘッド、９…冷却媒体供給装置、１０…冷却媒体、１１…溶接ビード断面、１２…溶接ビード断面、１３…溶接ビード断面、１４…水排除隔壁、１５…出口部、１６…シールドガス、１７…水中、１８…溝(開先部)、１８Ａ…第２溶接層、１８Ｂ…第３溶接層、１８Ｎ…最上溶接層。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an arc welding method, and more particularly to an arc welding method and an arc welding apparatus suitable for reducing residual stress in a weld bead portion and the heat affected zone.
[0002]
[Prior art]
In conventional arc welding, an arc is generated between a welding torch and a weld base material to form a molten pool on the weld base material, and the weld bead portion solidified by the molten pool is in contact with the molten pool. The formed heat-affected zone and the weld base material were cooled to normal temperature by heat radiation and natural convection of air as the surrounding medium. In JP-A-55-73477, JP-A-58-205687, and JP-A-60-187478, a method of preventing precipitation of chromium carbide by performing water cooling when welding in the atmosphere. Has been proposed.
[0003]
Furthermore, in underwater welding, after an arc is generated in a gas phase space from which water has been removed, natural convection of water is used to bring the weld bead, heat affected zone, and weld base material into contact with the surrounding medium water. The water was cooled down to the water temperature. Japanese Patent Application Laid-Open No. 10-34374 and the like relate to such underwater arc welding.
[0004]
[Problems to be solved by the invention]
However, in JP-A-55-73477, JP-A-58-205687, and JP-A-60-187478, the time of heating to 650 ° C. to 1200 ° C. to prevent the precipitation of chromium carbides. The method for changing the residual stress from the tensile stress to the compressive stress has not been disclosed.
[0005]
Japanese Patent Laid-Open No. 10-34374 reduces residual stress by underwater plasma welding, but the weld quality is impaired by the generation of air bubbles, etc., or the local tensile residual stress in the heat affected zone adjacent to the bead. There was a case where (the peak of residual stress) remained. A product using a weld having a tensile residual stress has a drawback that cracks and stress corrosion cracks are likely to occur in a relatively short period of time.
[0006]
An object of the present invention is to provide an arc welding method that prevents cracks and stress corrosion cracking during use of a product, prolongs the life of the product, and improves the reliability of performance.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, if the depth dimension of the cross section of the weld bead portion is D and the width dimension is W, the aspect ratio (D / W) of the cross section of the weld bead portion is 0.5 or more. The weld bead immediately after solidification and the heat-affected zone adjacent thereto are jetted with a cooling medium and rapidly cooled to form a weld having a surface having compressive residual stress. Is to achieve.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
1A and 1B show a first embodiment of the present invention. The first embodiment of the present invention is a case where welding is performed in the air by using an injection nozzle 6 for ejecting a cooling medium to a welding apparatus, for example, an arc welding apparatus.
[0009]
An arc is generated between the electrode 2 held by the welding torch 1 and the weld base material 3 to form a weld pool 5 on the weld base material 3, and the weld pool 5 is solidified to form a weld beat portion 4. When the weld bead 4 has a depth dimension of D and a width dimension of W, the weld bead 4 is formed under welding conditions where the aspect ratio (D / W) is 0.5 or more, and is cooled. The medium 10 such as water is jetted from the cooling head 8 disposed in the vicinity of the welding torch 1 and is caused to flow to the welding local part 4C, thereby rapidly cooling the welding local part 4C to form the weld bead part 4 shown in FIG. Here, the weld local part 4C indicates the weld bead part 4 immediately after the molten pool solidifies and the thermally affected part 4A adjacent to the molten pool 5.
[0010]
More preferably, deep penetration welding with an aspect ratio (D / W) of 0.5 or more can be realized by the following method in the weld bead portion 4 having a heat input of 5 to 20 KJ / cm, more preferably 8 to 17 KJ / cm. . In the case of DC arc, bead-on welding is performed using a mixed gas in which 2 to 10% hydrogen is mixed in argon as a shielding gas, or active flux is applied to a welded portion using argon as a shielding gas and bead-on welding is performed. This can be achieved. In the case of a pulsed arc, there is an advantage that the hydrogen mixed into the shield can be reduced by setting the pulse peak current value to a high value (300 to 600 A) and performing bead-on welding by high frequency pulse welding at 5 to 30 KHz.
[0011]
The cooling medium 10 is supplied to the cooling head 8 having the injection nozzle 6 installed around the electrode 2 through the pipe 7 by the cooling medium supply device 9. The cooling head 8 is fixed to the welding torch 1 and moves at the same speed as the welding torch 1.
[0012]
The cooling head 8 is configured by using one injection nozzle 6 and cools the weld bead portion 4 immediately after the molten pool 5 is solidified and the heat affected zone 4A formed in a portion adjacent to the molten pool 6. Although an example has been shown, the weld bead portion 4 immediately after the molten pool 6 is solidified using two or a plurality of injection nozzles 6 and the heat affected zone 4A formed in a portion adjacent to the molten pool 6 are cooled. You may make it do.
[0013]
Further, in order to prevent the cooling medium 10 (for example, water) from being scattered and disturbing the arc space by spraying water, wetting the electrode 2, or generating excessive vapor in the molten pool 6, the electrode 2 The cooling medium 10 is provided between the cooling head 8 and the cooling medium 8 so as to shield the cooling medium 10 from the arc space. An outlet portion 15 is provided.
[0014]
If the outlet 15 is not provided in the shield gas 16, the jet 10 for jet cooling is disturbed by the shield gas 16 flowing out from the rear of the water exclusion partition 14, or the water exclusion partition 14 on the same side as the cooling head 8. This is because if the outlet portion 15 is provided on the side surface, the weld bead cross section tends to be biased by the flow of the shield gas 16.
[0015]
Furthermore, as shown in FIG. 2, it is desirable that the injection nozzle 6 be disposed to be inclined within a range of 30 to 50 degrees with respect to the surface of the base material 3. When the inclination angle θ is 20 degrees or less, the cooling start position is far from the molten pool 6 and the rapid cooling effect is reduced. When the inclination angle θ is 60 degrees or more, an impinging jet enters from the gap between the water exclusion partition wall 21 and the base material 3 and arc. It will be disturbed.
[0016]
In addition to water, flame retardant oil, fluorinate, liquid nitrogen, or the like can be used as a cooling medium, but the heat transfer rate of jet cooling is more preferably 5 to 50 KW / m ² ° C, and water is preferably used for heat transfer of jet cooling. It is preferable to set the flow rate and flow rate during injection so that the rate is 10 to 30 kW / m ² ° C. When the heat transfer coefficient of the jet cooling is less than 10 KW / m ² ° C, the reversal temperature difference described later is not sufficiently formed, and the maximum residual stress cannot be compressed.
[0017]
Further, if the flow rate and flow rate during jet cooling are increased, the heat transfer rate can be increased, but if the flow rate and flow rate are excessively increased, the arc is disturbed and the welding quality tends to deteriorate. That is, the flow rate at the time of injection may be set so that the flow velocity at the time of water jet cooling is 0.8 to 8 m / sec, more preferably 1 to 5 m / sec.
[0018]
Furthermore, the water temperature is lowered to about 0 to 5 ° C., antifreeze is mixed, or an antifreeze substance is dissolved to bring it below the freezing point. It is desirable to increase the heat transfer coefficient.
[0019]
With such a configuration, a SUS304 having a base material thickness of 12 mm is subjected to a heat input of 11 KJ / cm and a welding speed of 100 mm / min. As an example, a plurality of weld beads shown in FIGS. 3 (B), (C) and (D) Part 4 was formed. SUS316, Inconel 600, or the like may be used as a base material other than SUS304. The aspect ratio D / W of the bead cross-sectional shape of the weld bead portion 4 is (B) = 0.3, (C) = 0.5, (D) = 1.0, and bead-on welding is performed as a cooling medium. Water is used, one rectangular injection nozzle 6 (opening width 20 mm, opening height 2 mm) is disposed as the cooling head 8, and a jet of about 5 l / min is supplied at an angle of 40 degrees with respect to the base material surface, Cooled down. The flow velocity of the jet is about 2.0 m / s, and the heat transfer coefficient of the jet is estimated to be about 13 to 20 KW / m ² ° C.
[0020]
The results of performing such construction and determining the relationship between the aspect ratio and the residual stress are shown in FIGS. 4 (A) and 4 (B). FIG. 4A shows a state in which the weld bead portion 4 is formed on the base material 3, and a characteristic diagram obtained by measuring the residual stress when the weld bead portion 4 is sequentially separated from the central portion 0 in the Y direction is shown in FIG. ). The characteristic diagram of FIG. 4 (B) shows the case where water is injected to the plurality of weld beads 4 shown in FIGS. 3 (B), 3 (C) and 3 (D) and the case of natural cooling. FIG. 5 shows a characteristic diagram obtained by synthesizing the maximum value, that is, the peak value, of the residual stress in the weld local area in the characteristic diagram of FIG. 4 (B). In FIG. 5, the residual stress peak value when the aspect ratio (D / W) is 0.4 is also added.
[0021]
As apparent from the characteristic diagram of FIG. 5, the bead direction component (σx) of the residual stress during water jet cooling is that the weld bead portion 4 having an aspect ratio of 0.3 or less is a thermally affected portion in the vicinity of the weld line. In the weld local part 4C, the peak has a tensile residual stress value of about +100 MPa or more.
[0022]
Further, the weld bead portion 4 having an aspect ratio of 0.4 or more becomes a compressive residual stress having a value of 0 to about −140 MPa in the thermally affected portion in the vicinity of the weld line, that is, the weld local portion 4C. These details will be described with reference to FIG.
[0023]
That is, as is apparent from FIG. 5, the product having the weld bead portion 4 having an aspect ratio of 0.3 or less has a tensile residual stress value, and the product using the weld bead portion 4 is relatively There is a drawback that cracks and stress corrosion cracks are likely to occur in a short time.
[0024]
In the weld bead portion 4 having an aspect ratio of 0.4 or more and less than 0.5, the stress peak of the weld local portion 4C is a compressive residual stress of about 0 to -120 MPa. When a load fatigue test is repeatedly performed on a product having a weld bead portion 4 having an aspect ratio of 0.4 or more and less than 0.5, for example, SUS304, a product having a stable failure performance with varying failure limit values is manufactured. I can't.
[0025]
On the other hand, in the product having the weld bead portion 4 having an aspect ratio of 0.5 or more according to the present invention, even if the aspect ratio slightly changes, the compressive residual stress is always about −120 to −140 MPa, which is a substantially constant value. When a fatigue test is performed by repeatedly applying a load to a product having a weld bead portion 4 having an aspect ratio of 0.5 or more, for example, SUS304, a stable product having a performance with a substantially constant failure limit value is manufactured. In addition, the cracks and stress corrosion cracking are less likely to occur, thus extending the product life and improving the product reliability.
[0026]
FIG. 6 is a change curve showing the relationship between the time and temperature of the bead surface temperature 3A and the internal temperature 3B of the weld bead portion 4 of FIGS. 3 (B), 3 (C), (D) and 4 (A). is there. The bead surface temperature 3 </ b> A and the internal temperature 3 </ b> B were defined as temperatures at a position (see FIG. 3D) where the temperature becomes high immediately below the bead. In FIG. 6, the cooling curve regarding the bead surface temperature 3A and the bead internal temperature 3B when water jet cooling is performed immediately after the formation of the molten pool is indicated by the thick line in FIG. Further, a temperature difference between the bead internal temperature 3B and the bead surface temperature 3A (= internal temperature−bead surface temperature) was defined as an inversion temperature difference.
[0027]
FIG. 6 shows that the reversal temperature difference is small when the aspect ratio is 0.3, but the reversal temperature difference increases as the aspect ratio increases to (0.5) and (1.0). That is, when the aspect ratio is 0.3, when the temperature of the bead surface is lowered, the high temperature portion formed inside is in a shallow portion (position of 3 to 4 mm from the surface) inside the plate, so that the temperature decreases with the surface temperature. . As a result, the internal temperature 3B only maintains a slightly higher temperature state than the bead surface temperature 3A.
[0028]
On the other hand, when the aspect ratio is (0.5) or (1.0), even if the temperature of the bead center surface rapidly decreases, the high-temperature part directly under the bead is a deep part inside the plate (4 to 6 mm from the surface). The position of the internal temperature decreases more slowly than the surface. As a result, a large reversal temperature difference is formed at which the internal temperature 3B becomes higher than the bead surface temperature 3A.
[0029]
Further, comparing the results shown in FIGS. 5 and 6, it was found that the above reversal temperature difference needs to be sufficiently large in order to make the residual stress on the plate surface a compressive residual stress. Moreover, even if the above-described construction was performed, the welding quality was not impaired by the generation of bubbles in the welded part.
[0030]
Although not shown, it goes without saying that even if the welding torch 1 and the cooling head 8 are fixed and the welding base material 3 is moved, the same effect as described above can be obtained. .
(Second embodiment)
FIG. 7 shows a second embodiment of the present invention. The second embodiment of the present invention is a case where welding is performed in water 17 using a water exclusion partition 14.
[0031]
A water exclusion (gas phase) space is formed by the shielding gas 16 around the arc generated between the electrode 2 held by the welding torch 1 and the welding base material 3, and the molten pool is formed on the welding base material 3 in the water 17. 5, the welding bead is formed under the welding conditions in which the aspect ratio (D / W) of the weld bead portion 4 is 0.5 or more, and water as the cooling medium 10 is cooled with the cooling head 8. It is made to erupt from, and the welding local part is cooled rapidly.
[0032]
In the present invention, when the cross-sectional shape of the water-excluding partition wall 14 arranged around the electrode is circular, the diameter is set to be approximately equal to or more than the length of the molten pool 5 and about three times as long as the water-excluding partition wall 14. A shield gas outlet 15 is provided in front of the welding progress direction. Therefore, in the present invention, since the cross-sectional diameter of the water exclusion partition 14 is made smaller than the partition cross-sectional diameter conventionally used (5 to 8 times the molten pool length), in the water exclusion (gas phase) space. There is an effect that the temperature drop of the steel can be reduced and the welding base material (surface and inside) at a higher temperature can be rapidly cooled.
[0033]
As a result, the temperature of the surface of the weld bead portion 4 can be made lower than the temperature inside the base material immediately below the weld bead, and the inversion temperature difference can be increased. Further, since the shield gas outlet 15 is provided on the front surface of the water exclusion partition wall 14 in the welding progress direction, in addition to the same effect as that of the first embodiment, air bubbles due to the discharge of the shield gas from the rear in the welding progress direction. There is an advantage that cooling behind the welding direction is not hindered.
[0034]
In addition, a cooling head having an injection nozzle 6 with an inclination angle and an opening similar to that in the first embodiment is disposed around the water exclusion partition wall 14, and the water jet is caused to flow to the welding local area by the injection nozzle 6 to perform water injection cooling. Thus, the cooling action (heat transfer coefficient) can be made higher than the cooling by natural convection of water (heat transfer coefficient of about 1 to 5 KW / m ² ° C).
[0035]
When water is used as the cooling medium 10, the temperature is lower than that of the surrounding water 24, for example, a low temperature of about 0 to 10 ° C., an antifreeze solution is mixed, or a substance having an antifreeze effect is dissolved to below the freezing point. Therefore, it is desirable to enhance the cooling effect as compared with the surrounding water 24.
[0036]
With this configuration, SUS304 having a thickness of 12 mm has a plurality of bead shapes, that is, bead-on with an aspect ratio = (0.3), (0.5), (1.0) at a heat input of 12 KJ / cm and a welding speed of 100 mm / min. Welding is performed, water is used as a cooling medium, one rectangular injection nozzle 6 (opening width 20 mm, opening height 2 mm) is disposed as the cooling head 8, and approximately 10 l at an angle of 40 degrees with respect to the base material surface. A / min jet was supplied and cooled. The flow velocity of the jet is about 4.2 m / s, and the heat transfer coefficient of the jet is estimated to be about 18 to 28 KW / m ² ° C.
[0037]
When such a construction was performed and the relationship between the aspect ratio and the residual stress was determined, the weld bead portion 4 having an aspect ratio (D / W) of the weld bead portion of 0.5 or more was formed, and the water jet cooling described above was performed. It was found that the residual stress on the plate surface can be made a compressive residual stress even in underwater welding. Further, in the welded portion, the welding quality was not impaired by the generation of bubbles.
(Third embodiment)
8A and 8B show a third embodiment of the present invention. The third embodiment of the present invention is a case in which narrow gap multilayer butt welding is performed in which each layer is formed in one pass. In particular, as shown in FIGS. 8A and 8B, a narrow groove, that is, a groove 18 having a groove bottom portion 3C is formed in the welding base material 3. The groove 18 is welded in one pass, and the groove bottom portion 3C is first welded to form the lowest weld layer. Further, each layer is sequentially stacked on the lowermost weld layer, for example, 3C, like the second weld layer 18A and the third weld layer 18B in one pass to form the uppermost weld layer 18N, and then the uppermost weld layer 18N. The weld bead portion 4 having an aspect ratio (D / W) of a cross section of the weld bead portion according to the invention of 0.5 or more is performed to form the final weld layer 18Z. A weld bead 4 having a cross-sectional aspect ratio (D / W) of 0.5 or more is formed in the weld bead portion, and a cooling medium is injected into the weld bead portion immediately after solidification and the heat-affected zone adjacent thereto to rapidly cool the weld bead portion. It is what I did.
[0038]
And since the surface residual stress of the final weld layer 18Z and its heat-affected zone is made a compressive residual stress or suppressed to an extremely low tensile residual stress, the weld bead 4 according to the present invention is used for each weld layer by the amount used. Cracks and stress corrosion cracks can be suppressed, and the reliability of the performance of the product using the present invention can be improved.
[0039]
In the above-mentioned narrow groove welding in which each layer is sequentially built up in one pass, welding is performed while supplying a filler wire using TIG welding with a narrow groove width (root width) and improved arc directivity. It can be realized by doing. For example, the plate thickness is 20 mm, the groove shape is 4 to 6 mm, the groove angle is 3 degrees, the root face is 1 to 3 mm, and the root gap is 0 mm. In pulse TIG welding, the heat input is 5 to 15 KJ / cm. This is possible by setting the speed 80 to 150 mm / min, setting the pulse peak current value high (300 to 600 A), and performing welding with a medium frequency pulse TIG of 300 to 700 Hz, or welding with a high frequency pulse TIG of 5 to 30 KHz. I found out.
[0040]
In addition, when using DC-TIG welding, the groove width (root width) and the groove angle are made larger than the above, and construction is performed using a mixed gas in which 2 to 10% hydrogen is mixed with argon as a shielding gas. Is possible.
[0041]
Further, deep penetration welding in which the aspect ratio (D / W) of the weld bead portion is 0.5 or more can be realized by the same method as in the first embodiment. For example, DC-TIG is used, and bead-on welding is performed using a mixed gas in which 2 to 10% hydrogen is mixed with argon as the shielding gas, or active flux is applied to the weld using argon as the shielding gas and bead-on welding is performed. Just do it.
[0042]
In multi-layer butt welding of a 20 mm thick SUS304 plate, the root width of the narrow groove portion is set to 5 mm, and first, as shown in FIG. 8 (A), each layer is built up in one pass using DC-TIG. After that, as shown in FIG. 8B, the weld bead portion solidified at a high temperature while forming a final layer having a cross-sectional aspect ratio (D / W) of 0.5 to 1.0. Water was sprayed to the heat-affected zone adjacent to and rapidly cooled. For comparison, a final layer having a weld bead cross-sectional aspect ratio (D / W) of 0.3 was formed using DC-TIG, and the same construction was performed.
[0043]
One rectangular spray nozzle 6 (opening width 20 mm, opening height 2 mm) was arranged as the cooling head 8 and cooled by supplying a jet of about 5 l / min at an angle of 40 degrees with respect to the base material surface. The flow velocity of the jet is about 2.0 m / s, and the heat transfer coefficient of the jet is estimated to be about 13 to 20 KW / m ² ° C.
[0044]
After performing such construction and determining the relationship between the aspect ratio and the residual stress, the weld bead 4 having an aspect ratio (D / W) of the weld bead portion 4 of 0.5 or more is formed, and the water jet cooling described above is performed. It has been found that the residual stress on the surface can be changed to the compressive residual stress even in the multi-layer butt weld. Further, in the welded portion, the welding quality was not impaired by the generation of bubbles.
[0045]
In the above-described embodiment, only the case where the aspect ratio (D / W) is (0.5) or (1.0) has been described, but the aspect ratio (D / W) is 0.5 or more ( Needless to say, the present invention can also be applied to 1.5), (2.0) to etc.
[0046]
【The invention's effect】
As described above, according to the present invention, a product using a weld bead portion having a compressive residual stress is less likely to cause cracking or stress corrosion cracking during use, and has an aspect ratio (D / W) of 0.5 or more. The life of the product has been extended by the amount that has been selected, and the reliability of the product performance has been improved.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a schematic configuration of arc welding according to an embodiment of the present invention.
2 is a configuration diagram of a cooling head portion that injects a cooling medium from an injection nozzle used in FIG. 1 onto a welding base material.
3 is a cross-sectional view of a weld bead portion formed according to FIG.
4 is a distribution diagram showing a residual stress distribution in the bead direction in the weld bead portion of FIG. 3;
5 is a distribution diagram showing a bead direction component of residual stress in the weld bead portion of FIG. 4;
6 is a characteristic diagram showing the relationship between temperature and time of residual stress in a thermally affected part in the weld bead part of FIG. 3;
FIG. 7 is a schematic perspective view of underwater arc welding shown as another embodiment of the present invention.
FIG. 8 is a perspective view showing a groove weld as another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Welding torch, 2 ... Electrode, 3 ... Base material, 3C ... Groove bottom part, 4 ... Weld bead part, 5 ... Molten pool, 6 ... Injection nozzle, 7 ... Fluid supply piping, 8 ... Cooling head, 9 ... Cooling Medium supply device, 10 ... cooling medium, 11 ... weld bead cross section, 12 ... weld bead cross section, 13 ... weld bead cross section, 14 ... water exclusion partition, 15 ... outlet portion, 16 ... shield gas, 17 ... underwater, 18 ... groove (Groove part), 18A ... second weld layer, 18B ... third weld layer, 18N ... uppermost weld layer.

Claims

In the arc welding method of cooling by injecting a cooling medium to a weld bead portion formed by solidification by forming a weld pool on a weld base material by arc welding and a heat affected zone adjacent to the weld bead portion, the welding bead portion An arc welding method characterized by forming a weld bead having a cross-sectional aspect ratio (D / W) of 0.5 or more when the cross-section depth D and width are W.

The arc welding method according to claim 1, wherein water is used as the cooling medium, and a flow rate at the time of water jet cooling is 1 to 5 m / sec.

A high-frequency TIG welding apparatus using a shielding gas in which 2 to 10% of hydrogen is mixed with argon is used, and a weld bead having a cross-sectional aspect ratio (D / W) of 0.5 or more is formed. The arc welding method according to claim 1 or 2.

The active bead is applied and a TIG welding apparatus is used to form a weld bead having an aspect ratio (D / W) of a weld bead cross section of 0.5 or more. The described arc welding method.

2. The final layer of multi-face butt welding with narrow gaps in which each layer is performed in one pass forms a weld bead having an aspect ratio (D / W) of a cross section of the weld bead portion of 0.5 or more. 5. The arc welding method according to any one of items 1 to 4.

A movable welding torch having an electrode for melting the weld base material by an arc to form a molten pool, an arc shield gas sprayed to the molten pool, a weld bead portion formed by solidifying the molten pool, and in arc welding apparatus having a cooling head for cooling by spraying a cooling medium on the periphery is provided with a rejection barrier ribs of the electrode and the molten pool on the welding torch to prevent from the cooling medium, the opposite side of the cooling head An arc welding apparatus, wherein an outlet for discharging the arc shield gas is provided in the exclusion partition wall.