JP6840383B2 - Weld modification method - Google Patents
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- 238000002715 modification method Methods 0.000 title claims description 8
- 238000003756 stirring Methods 0.000 claims description 151
- 238000003466 welding Methods 0.000 claims description 99
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 73
- 239000001301 oxygen Substances 0.000 claims description 73
- 229910052760 oxygen Inorganic materials 0.000 claims description 73
- 238000000034 method Methods 0.000 claims description 60
- 239000000463 material Substances 0.000 claims description 57
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 48
- 229910000831 Steel Inorganic materials 0.000 claims description 37
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- 210000001503 joint Anatomy 0.000 claims description 3
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- Pressure Welding/Diffusion-Bonding (AREA)
Description
本発明は溶接部の改質方法及びそれにより得られる溶接構造物に関し、より具体的には、酸素の導入によって溶込み深さを増加させた溶接部の効果的な改質方法、及びそれにより得られる溶接構造物に関する。 The present invention relates to a method for modifying a welded portion and a welded structure obtained thereby, and more specifically, an effective method for modifying a welded portion in which the penetration depth is increased by introducing oxygen, and thereby. With respect to the resulting welded structure.
近年、船舶、海洋構造物及び橋梁等の大型溶接構造物に様々な鋼材が利用されている。鋼材の高張力化によって母材の疲労強度は向上するが、溶接構造物全体としての信頼性・安全性は、最も靭性や疲労強度が低い溶接部の特性によって律速されてしまう。 In recent years, various steel materials have been used for large welded structures such as ships, marine structures and bridges. Although the fatigue strength of the base metal is improved by increasing the tension of the steel material, the reliability and safety of the welded structure as a whole are controlled by the characteristics of the welded portion having the lowest toughness and fatigue strength.
ここで、高品質な溶接部を得ることができる溶接方法としてはＴＩＧ溶接が知られているが、ＴＩＧ溶接には溶込み深さが浅く、溶接効率が低いという欠点が存在する。これに対し、上述の大型溶接構造物では厚鋼板が使用されるため、効率的に溶込みの深い溶接部を形成させる溶接方法が切望されている。 Here, TIG welding is known as a welding method capable of obtaining a high-quality welded portion, but TIG welding has a drawback that the penetration depth is shallow and the welding efficiency is low. On the other hand, since a thick steel plate is used in the above-mentioned large-sized welded structure, a welding method for efficiently forming a welded portion having a deep penetration is desired.
このような状況下において、ＴＩＧ溶接の溶込み深さを増加させる方法が盛んに検討されており、例えば、溶融池に界面活性元素である酸素を導入することで、溶込み深さが増加することが知られている。 Under such circumstances, a method of increasing the penetration depth of TIG welding has been actively studied. For example, by introducing oxygen, which is a surfactant, into a molten pool, the penetration depth is increased. It is known.
特許文献１（国際公開第２０１３／１６８５１３号）では、筒状の溶接用ノズルの内部から金属材の表面に不活性ガスを供給する不活性ガス供給工程と、前記不活性ガス供給工程で前記溶接用ノズルにより前記不活性ガスを供給されている前記金属材の表面を加熱する加熱工程と、前記加熱工程によって前記金属材の表面に生じた溶融池に、前記不活性ガス供給工程での前記不活性ガスの流れに伴って生じた圧力の低下によって吸引された雰囲気中の酸素を導入する酸素導入工程と、を含む溶接方法が提案されている。 In Patent Document 1 (International Publication No. 2013/168513), an inert gas supply step of supplying an inert gas from the inside of a tubular welding nozzle to the surface of a metal material, and the welding in the inert gas supply step. The heating step of heating the surface of the metal material to which the inert gas is supplied by the nozzle for use, and the failure in the inert gas supply step to the molten pool generated on the surface of the metal material by the heating step. A welding method including an oxygen introduction step of introducing oxygen in an atmosphere sucked by a decrease in pressure caused by the flow of an active gas has been proposed.
前記特許文献１に記載されている溶接方法においては、不活性ガスの流れに伴って生じた気圧の低下によって吸引された大気中の酸素が溶融池に導入されることから、二重シールドＴＩＧ溶接のように別途の酸素の供給源を用意しなくとも、溶融池に酸素を導入して溶込み深さをより深くし、溶接効率を高めることができる、としている。 In the welding method described in Patent Document 1, since oxygen in the atmosphere sucked by the decrease in air pressure caused by the flow of the inert gas is introduced into the molten pool, double shield TIG welding is performed. Even if a separate oxygen supply source is not prepared as in the above, oxygen can be introduced into the molten pool to deepen the penetration depth and improve welding efficiency.
また、特許文献２（特開２００８−２４６５０１号公報）では、ニッケル基合金またはオーステナイト系ステンレス鋼製の溶接材からなる溶接部で部材を接合して構成された溶接構造物において、溶接部の表面、又は溶接部と溶接部近傍の部材との表面に、回転するツールを表面垂直方向の荷重負荷により圧着させた状態で移動させて摩擦攪拌処理を行い、摩擦攪拌処理を行った摩擦攪拌処理部の柱状晶方向を表面面内方向とすることを特徴とする溶接構造物の応力腐食割れ進展性の改善方法が提案されている。 Further, in Patent Document 2 (Japanese Unexamined Patent Publication No. 2008-246501), in a welded structure formed by joining members with a welded material made of a nickel-based alloy or an austenite-based stainless steel welded material, the surface of the welded portion is formed. Or, a friction stir welding unit in which a rotating tool is moved to the surface of the welded portion and a member in the vicinity of the welded portion in a state of being crimped by a load load in the direction perpendicular to the surface to perform friction stir welding, and friction stir welding is performed. A method for improving the stress corrosion crack growth property of a welded structure, which is characterized in that the columnar crystal direction of the welded structure is in the surface plane direction, has been proposed.
前記特許文献２に記載の溶接構造物の応力腐食割れ進展性の改善方法においては、摩擦攪拌処理部の柱状晶方向を表面面内方向とすることにより、溶接部での応力腐食割れの発生を抑制し、また、溶接部に応力腐食割れが発生しても、深さ方向のき裂進展は、柱状晶方向が応力腐食割れ方向と垂直になっているので、応力腐食割れのき裂進展速度を応力腐食割れが柱状晶方向に沿って発生する場合と比べ１／１０程度に減速させることが可能となる。これにより、溶接部の耐用年数を長くすることができ、溶接構造物の寿命を長くすることができるとしている。 In the method for improving the progress of stress corrosion cracking of a welded structure described in Patent Document 2, the occurrence of stress corrosion cracking in the welded portion is caused by setting the columnar crystal direction of the friction stirring processing portion to the in-surface direction. Even if stress corrosion cracking occurs in the weld, the crack growth rate in the depth direction is such that the columnar crystal direction is perpendicular to the stress corrosion cracking direction. It is possible to reduce the stress corrosion cracking to about 1/10 as compared with the case where stress corrosion cracking occurs along the columnar crystal direction. As a result, the service life of the welded portion can be extended, and the life of the welded structure can be extended.
しかしながら、上記特許文献１に開示されている溶接方法のように溶融池への酸素の導入によって溶込み深さを増加させた場合、最終的に得られる溶接部には一般的なＴＩＧ溶接と比較して大量の酸素が残留することになる。溶接部の靭性は酸素含有量の増加に伴って低下することが懸念されるため、このような溶接方法を実施工に活用する場合には、溶接部の機械的性質を十分に担保することが必要不可欠である。 However, when the penetration depth is increased by introducing oxygen into the molten pool as in the welding method disclosed in Patent Document 1, the finally obtained welded portion is compared with general TIG welding. As a result, a large amount of oxygen remains. Since there is a concern that the toughness of the welded part decreases as the oxygen content increases, it is necessary to sufficiently ensure the mechanical properties of the welded part when utilizing such a welding method in the implementation work. It is indispensable.
また、上記特許文献２に開示されている溶接構造物の応力腐食割れ進展性の改善方法は、溶接部の柱状晶方向を表面面内方向とすることを特徴としており、効果を奏する対象材がニッケル基合金及びオーステナイト系ステンレス鋼製の溶接材からなる溶接部に限定されている。加えて、腐食環境下にない場合の疲労強度に関する効果については記載されておらず、酸素含有量が多い溶接部に対する効果については全く開示されていない。 Further, the method for improving the stress corrosion cracking growth property of a welded structure disclosed in Patent Document 2 is characterized in that the columnar crystal direction of the welded portion is the in-plane direction of the surface surface, and the target material that exerts the effect is It is limited to welds made of nickel-based alloy and austenitic stainless steel welds. In addition, the effect on fatigue strength when not in a corrosive environment is not described, and the effect on welds with a high oxygen content is not disclosed at all.
以上のような従来技術における問題点に鑑み、本発明の目的は、酸素の導入によって溶込み深さを増加させた溶接部の信頼性を担保するための効果的な改質方法、及びそれにより得られる溶接構造物を提供することにある。 In view of the above problems in the prior art, an object of the present invention is an effective modification method for ensuring the reliability of a welded portion whose penetration depth is increased by introducing oxygen, and thereby. The purpose is to provide the resulting welded structure.
本発明者は上記目的を達成すべく、酸素含有量の多い溶接部に対する摩擦攪拌処理について鋭意研究を重ねた結果、適当な酸素含有量範囲の溶接部に対して摩擦攪拌処理を施すこと等が極めて有効であることを見出し、本発明に到達した。 In order to achieve the above object, the present inventor has conducted extensive research on friction stir welding for welds having a high oxygen content, and as a result, it has been possible to perform friction stir welding on welds in an appropriate oxygen content range. We have found it extremely effective and have arrived at the present invention.
即ち、本発明は、
摩擦攪拌処理を用いて溶融溶接部の表面に攪拌領域を形成させる表面改質方法であって、
被溶接材が鉄系金属であり、
前記溶融溶接部の酸素含有量が７０ｐｐｍ〜７００ｐｐｍであること、
を特徴とする溶接部の改質方法、を提供する。
That is, the present invention
A surface modification method in which a stirring region is formed on the surface of a melt weld using friction stir welding.
The material to be welded is an iron-based metal,
The oxygen content of the melt welded portion is 70 ppm to 700 ppm.
Provided is a method for modifying a welded portion, which is characterized by the above.
鉄系金属の酸素含有量を７０ｐｐｍ〜７００ｐｐｍとすることで、通常の溶融溶接方法を用いた場合と比較して、溶接部の溶込み深さを増加させることができる。より具体的には、酸素含有量を７０ｐｐｍ以上とすることで溶融池の表面張力に正の温度依存性を付与することができ、温度が高くなるアーク直下（溶融池の中心）における表面張力が溶融池の外縁よりも高くなることで、内向きの対流が生じる。その結果、溶融金属が溶融池の下向きに流れ、深溶け込みを達成することができる。一方で、酸素含有量を７００ｐｐｍより大きくすると、溶融池表面における酸化皮膜の形成が顕著になる。当該酸化皮膜は深溶け込みの妨げになるだけでなく、溶接品質の観点からも好ましくない。なお、鉄系金属とは、鉄を主成分とする金属を広く含むものである。 By setting the oxygen content of the iron-based metal to 70 ppm to 700 ppm, the penetration depth of the welded portion can be increased as compared with the case where a normal melt welding method is used. More specifically, by setting the oxygen content to 70 ppm or more, it is possible to impart a positive temperature dependence to the surface tension of the molten pool, and the surface tension immediately below the arc (center of the molten pool) where the temperature rises can be increased. Being higher than the outer edge of the molten pool creates inward convection. As a result, the molten metal flows downward in the molten pool, and deep penetration can be achieved. On the other hand, when the oxygen content is larger than 700 ppm, the formation of an oxide film on the surface of the molten pool becomes remarkable. The oxide film not only hinders deep penetration, but is also not preferable from the viewpoint of welding quality. The iron-based metal broadly includes a metal containing iron as a main component.
本発明の溶接部の改質方法においては、溶融池への適当な量の酸素の導入によって溶込み深さを増加させた溶接部の表面に対して摩擦攪拌処理を施すことで、溶接部の靭性（信頼性）を向上させることができる。 In the method for modifying a welded portion of the present invention, the surface of the welded portion whose penetration depth is increased by introducing an appropriate amount of oxygen into the molten pool is subjected to friction stir welding treatment to obtain the welded portion. Toughness (reliability) can be improved.
摩擦攪拌処理は、本発明の効果を損なわない限りにおいて特に限定されず、従来公知の種々の方法で摩擦攪拌処理を施すことができる。なお、摩擦攪拌処理とは、金属材の固相接合技術である摩擦攪拌接合（ＦＳＷ：Ｆｒｉｃｔｉｏｎ Ｓｔｉｒ Ｗｅｌｄｉｎｇ）を金属材の表面改質技術として利用するものである。 The friction stir welding treatment is not particularly limited as long as the effect of the present invention is not impaired, and the friction stir welding treatment can be performed by various conventionally known methods. The friction stir welding process uses friction stir welding (FSW), which is a solid phase bonding technology for metal materials, as a surface modification technology for metal materials.
また、本発明の溶接部の改質方法においては、前記溶融溶接部に酸化物粒子が分散しており、前記酸素含有量が３３０ｐｐｍ以下であること、が好ましい。溶融溶接部に酸化物粒子が分散する場合は溶接部の靭性低下が顕著になるが、適当な酸化物粒子の存在によって摩擦攪拌処理による改質効果を向上させることができる。具体的には、酸化物粒子によって摩擦攪処理中に母材に導入されるひずみが局所的に増大する（再結晶粒がより微細化される）と共に、当該再結晶粒の静的な粒成長をピン止め効果によって抑制することができる。 Further, in the method for modifying the welded portion of the present invention, it is preferable that the oxide particles are dispersed in the melt-welded portion and the oxygen content is 330 ppm or less. When the oxide particles are dispersed in the melt-welded portion, the toughness of the welded portion is significantly reduced, but the modification effect of the friction stir treatment can be improved by the presence of appropriate oxide particles. Specifically, the strain introduced into the base material during the friction stirring treatment by the oxide particles is locally increased (the recrystallized grains are made finer), and the static grain growth of the recrystallized grains is performed. Can be suppressed by the pinning effect.
ここで、酸素含有量が高過ぎると溶接部の靭性低下がより深刻となり、摩擦攪拌処理を施しても当該溶接部の靭性を母材と同等レベルにまで向上させることができないが、酸素含有量が３３０ｐｐｍ以下であれば、摩擦攪拌プロセスによって接合部の靭性を母材と同等にまで向上させることができる。 Here, if the oxygen content is too high, the toughness of the welded portion becomes more serious, and even if friction stir welding is performed, the toughness of the welded portion cannot be improved to the same level as the base metal, but the oxygen content When is 330 ppm or less, the toughness of the joint can be improved to the same level as that of the base metal by the friction stir welding process.
なお、母材に固溶できる程度に酸素含有量が低い場合は酸化物粒子が生成しないため、「溶融溶接部に酸化物粒子が分散している」という構成要件は、実質的に溶接部における好適な酸素含有量の下限を示すことになる。 When the oxygen content is low enough to dissolve in the base metal, oxide particles are not generated. Therefore, the constituent requirement that "oxide particles are dispersed in the melt weld" is substantially present in the weld. It will indicate the lower limit of the suitable oxygen content.
また、本発明の溶接部の改質方法においては、前記酸素含有量が１６７ｐｐｍ〜３３０ｐｐｍであること、がより好ましい。酸素含有量が１６７ｐｐｍ以上となると、確実に深溶け込みが得られる反面、溶接部の靭性低下が顕著になるが、摩擦攪拌処理を施すことによって、母材と同等にまで靭性を向上させることができる。 Further, in the method for modifying a welded portion of the present invention, it is more preferable that the oxygen content is 167 ppm to 330 ppm. When the oxygen content is 167 ppm or more, deep penetration can be surely obtained, but the toughness of the welded portion is significantly reduced, but the toughness can be improved to the same level as the base metal by performing friction stir welding. ..
また、本発明の溶接部の改質方法においては、前記摩擦攪拌処理において、前記攪拌領域の少なくとも一部の処理温度を前記鉄系金属のＡ３点以下又はＡｃｍ点以下とすること、が好ましい。攪拌領域の少なくとも一部の処理温度を前記鉄系金属のＡ３点以下又はＡｃｍ点以下とすることで、当該攪拌領域の一部分の母材結晶粒が微細等軸粒となり（マルテンサイト等の脆い変態組織とならず）、より効果的に靭性を向上させることができる。加えて、酸化物粒子に対してより強力なせん断応力が印加されるため、当該酸化物粒子が破砕、微細化され、靭性低下に及ぼす酸化物粒子の影響が低減されるだけでなく、摩擦攪拌処理による母材結晶粒の微細化効果が増進される。 Further, in the method for modifying a welded portion of the present invention, in the friction stir welding treatment, the treatment temperature of at least a part of the stirring region is set to A 3 point or less or A cm point or less of the iron-based metal. preferable. By setting the treatment temperature of at least a part of the stirring region to A 3 point or less or A cm point or less of the iron-based metal, the base metal crystal grains of a part of the stirring region become fine equiaxed grains (such as martensite). It does not become a brittle metamorphic structure), and the toughness can be improved more effectively. In addition, since a stronger shear stress is applied to the oxide particles, the oxide particles are crushed and refined, and not only the influence of the oxide particles on the decrease in toughness is reduced, but also friction stir welding is performed. The effect of refining the base crystal grains by the treatment is enhanced.
また、本発明の溶接部の改質方法においては、前記摩擦攪拌処理において、前記攪拌領域の少なくとも一部の処理温度を前記鉄系金属のＡ１点以下とすること、が好ましい。攪拌領域の少なくとも一部の処理温度を前記鉄系金属のＡ１点以下とすることで、当該攪拌領域の母材結晶粒が微細等軸粒となり（マルテンサイト等の脆い変態組織とならず）、より効果的に靭性を向上させることができる。加えて、酸化物粒子に対してより強力なせん断応力が印加されるため、当該酸化物粒子が破砕、微細化され、靭性低下に及ぼす酸化物粒子の影響が低減されるだけでなく、摩擦攪拌処理による母材結晶粒の微細化効果が増進される。なお、摩擦攪拌処理のプロセス温度は、被処理領域に挿入する回転ツールの回転速度、移動速度及び荷重等によって制御できる。 Further, in the method for modifying a welded portion of the present invention, it is preferable that the treatment temperature of at least a part of the stirring region is set to A 1 point or less of the iron-based metal in the friction stirring treatment. By setting the treatment temperature of at least a part of the stirring region to A 1 point or less of the iron-based metal, the base material crystal grains in the stirring region become fine equiaxed grains (not a brittle transformation structure such as martensite). , The toughness can be improved more effectively. In addition, since a stronger shear stress is applied to the oxide particles, the oxide particles are crushed and refined, and not only the influence of the oxide particles on the decrease in toughness is reduced, but also friction stir welding is performed. The effect of refining the base crystal grains by the treatment is enhanced. The process temperature of the friction stir welding process can be controlled by the rotation speed, movement speed, load, etc. of the rotation tool inserted into the area to be processed.
また、本発明の溶接部の改質方法においては、前記溶融溶接部が突合せ接合部又は重ね接合部であること、が好ましい。本発明の溶接部の改質方法による溶接部の靭性向上は継ぎ手形状等に影響されないため、実際の構造物に多く存在する突合せ接合部又は重ね接合部に対しても好適に用いることができる。 Further, in the method for modifying a welded portion of the present invention, it is preferable that the melt welded portion is a butt joint or a lap joint. Since the improvement of the toughness of the welded portion by the method of modifying the welded portion of the present invention is not affected by the shape of the joint or the like, it can be suitably used for the butt joint or the lap joint which is often present in the actual structure.
また、本発明の溶接部の改質方法においては、前記溶融溶接部が低温用鋼材に形成されていること、が好ましい。低温用鋼材とはＪＩＳにおいて−１０℃以下の温度域での使用に適した鋼材と規定されているものであり、溶接部には低温環境における信頼性が要求される。これに対し、本発明の溶接部の改質方法を用いて低温用鋼材の溶接部を改質することで、低温環境下における溶接部の靭性を確保することができる。 Further, in the method for modifying a welded portion of the present invention, it is preferable that the welded portion is formed of a low-temperature steel material. The low temperature steel material is defined by JIS as a steel material suitable for use in a temperature range of −10 ° C. or lower, and the welded portion is required to have reliability in a low temperature environment. On the other hand, the toughness of the welded portion in a low temperature environment can be ensured by modifying the welded portion of the low temperature steel material by using the method of modifying the welded portion of the present invention.
更に、本発明の溶接部の改質方法においては、前記溶融溶接部が９％Ｎｉ鋼材に形成されていること、が好ましい。９％Ｎｉ鋼材は、溶接部に酸素が導入されることによる靭性の低下が他の鋼材と比較して顕著であるが、本発明の溶接部の改質方法を用いることによって、当該９％Ｎｉ鋼材であっても、溶込み深さを増加させた溶接部の靭性を母材と同等にまで向上させることができる。 Further, in the method for modifying the welded portion of the present invention, it is preferable that the welded portion is formed of 9% Ni steel material. The 9% Ni steel material has a remarkable decrease in toughness due to the introduction of oxygen into the welded portion as compared with other steel materials. However, by using the method for modifying the welded portion of the present invention, the 9% Ni steel material is said to be 9% Ni. Even with a steel material, the toughness of the welded portion with an increased penetration depth can be improved to the same level as the base material.
また、本発明は、
鉄系金属材に、酸素含有量が１６７ｐｐｍ〜３３０ｐｐｍである溶融溶接部を有し、
前記溶融溶接部の表面に、再結晶粒を含む厚さが０．５ｍｍ〜３．０ｍｍの攪拌領域を有し、
前記溶融溶接部及び前記攪拌領域に酸化物粒子が分散していること、
を特徴とする溶接構造物、も提供する。
In addition, the present invention
The iron-based metal material has a melt-welded portion having an oxygen content of 167 ppm to 330 ppm.
The surface of the melt-welded portion has a stirring region having a thickness of 0.5 mm to 3.0 mm containing recrystallized grains.
Oxide particles are dispersed in the melt-welded portion and the stirring region.
Welded structures, which feature the above, are also provided.
本発明の溶接構造物においては、溶融溶接部の酸素含有量が１６７ｐｐｍ〜３３０ｐｐｍとなっており、一般的なＴＩＧ溶接等で形成される溶接部と比較して溶接部のＤ（深さ）／Ｗ（幅）が大きな溶接部が形成されている。ここで、Ｄ／Ｗの値は特に限定されないが、０．４以上となっていることが好ましい。 In the welded structure of the present invention, the oxygen content of the welded portion is 167 ppm to 330 ppm, and the D (depth) / depth of the welded portion is compared with that of the welded portion formed by general TIG welding or the like. A welded portion having a large W (width) is formed. Here, the value of D / W is not particularly limited, but is preferably 0.4 or more.
また、溶融溶接部の表面に厚さが０．５ｍｍ〜３．０ｍｍの攪拌領域が形成されており、当該攪拌領域には再結晶粒が含まれる。攪拌領域は回転ツールを圧入することによる摩擦攪拌処理で形成させることができる。ここで、回転ツールの底面にプローブを有さないフラットツールを用いても攪拌領域の厚さを０．５ｍｍ以上とすることができ、欠損が生じ難い、長さが３ｍｍ未満のプローブを有する回転ツールを用いることで、攪拌領域の厚さを３．０ｍｍ以下とすることができる。 Further, a stirring region having a thickness of 0.5 mm to 3.0 mm is formed on the surface of the melt-welded portion, and the stirring region contains recrystallized grains. The stirring region can be formed by a friction stirring process by press-fitting a rotating tool. Here, even if a flat tool having no probe on the bottom surface of the rotation tool is used, the thickness of the stirring region can be set to 0.5 mm or more, and a rotation having a probe having a length of less than 3 mm is unlikely to occur. By using the tool, the thickness of the stirring region can be set to 3.0 mm or less.
一方で、厚さが０．５ｍｍ〜３．０ｍｍの攪拌領域によって、溶融溶接部の靭性を十分に担保することができる。即ち、溶融溶接部の表面に形成させる攪拌領域の厚さを０．５ｍｍ〜３．０ｍｍとすることで、信頼性の高い溶接部を有する安価な溶接構造物を実現することができる。 On the other hand, the toughness of the melt-welded portion can be sufficiently ensured by the stirring region having a thickness of 0.5 mm to 3.0 mm. That is, by setting the thickness of the stirring region formed on the surface of the melt-welded portion to 0.5 mm to 3.0 mm, an inexpensive welded structure having a highly reliable welded portion can be realized.
溶融溶接部及び攪拌領域に分散している酸化物粒子の種類、形状及びサイズは特に限定されないが、攪拌領域に分散している酸化物粒子は溶融溶接部に分散している酸化物粒子よりも微細であることが好ましい。また、攪拌領域に分散している酸化物粒子は溶融溶接部に分散している酸化物粒子よりも球状化されていることが好ましい。摩擦攪拌処理では母材に強ひずみが導入されるため、各種元素に関する固溶度が増大し、処理条件によっては酸化物粒子が母材に固溶した後に析出する。当該機構により、球状化した酸化物粒子を好適に形成することができる。攪拌領域に微細かつ球状化した酸化物粒子が分散していることで、当該攪拌領域に高い靭性を付与することができる。なお、炭化物及び窒化物等の酸化物以外の粒子であっても、基本的には同様の作用効果を有する。 The type, shape, and size of the oxide particles dispersed in the melt-welded portion and the stirring region are not particularly limited, but the oxide particles dispersed in the stirring region are more than the oxide particles dispersed in the melt-welded portion. It is preferably fine. Further, it is preferable that the oxide particles dispersed in the stirring region are spheroidized rather than the oxide particles dispersed in the melt welded portion. Since strong strain is introduced into the base metal in the friction stir welding treatment, the solid solubility of various elements increases, and depending on the treatment conditions, the oxide particles solidly dissolve in the base metal and then precipitate. By this mechanism, spheroidized oxide particles can be suitably formed. By dispersing fine and spheroidized oxide particles in the stirring region, high toughness can be imparted to the stirring region. Even particles other than oxides such as carbides and nitrides basically have the same effect.
また、本発明の溶接構造物においては、前記溶融溶接部が低温用鋼材に形成されていることが好ましく、９％Ｎｉ鋼材に形成されていることがより好ましい。低温用鋼材は低温環境下における信頼性が要求され、９％Ｎｉ鋼材は溶接部に酸素が導入されることによる靭性の低下が他の鋼材と比較して顕著であるが、本発明の溶接構造物では、当該低温用鋼材及び９％Ｎｉ鋼材であっても、溶込み深さを増加させた溶接部の靭性が母材と同等にまで向上している。つまり、本発明の溶接構造物においては、前記攪拌領域を有する前記溶融溶接部と前記鉄系金属材の靭性が略同一となっている。 Further, in the welded structure of the present invention, the welded portion is preferably formed of a low temperature steel material, and more preferably formed of a 9% Ni steel material. The low-temperature steel material is required to have reliability in a low-temperature environment, and the 9% Ni steel material has a remarkable decrease in toughness due to the introduction of oxygen into the welded portion as compared with other steel materials. As for the material, even in the case of the low temperature steel material and the 9% Ni steel material, the toughness of the welded portion with the increased penetration depth is improved to the same level as the base material. That is, in the welded structure of the present invention, the toughness of the melt-welded portion having the stirring region and the iron-based metal material are substantially the same.
本発明によれば、酸素の導入によって溶込み深さを増加させた溶接部の信頼性を担保するための効果的な改質方法、及びそれにより得られる溶接構造物を提供することができる。 According to the present invention, it is possible to provide an effective modification method for ensuring the reliability of a welded portion whose penetration depth is increased by introducing oxygen, and a welded structure obtained thereby.
以下、図面を参照しながら本発明の溶接部の改質方法及び溶接構造物の代表的な実施形態について詳細に説明するが、本発明はこれらのみに限定されるものではない。なお、以下の説明では、同一または相当部分には同一符号を付し、重複する説明は省略する場合がある。また、図面は、本発明を概念的に説明するためのものであるから、表された各構成要素の寸法やそれらの比は実際のものとは異なる場合もある。 Hereinafter, a method for modifying a welded portion of the present invention and a typical embodiment of a welded structure will be described in detail with reference to the drawings, but the present invention is not limited to these. In the following description, the same or corresponding parts may be designated by the same reference numerals, and duplicate description may be omitted. Moreover, since the drawings are for conceptually explaining the present invention, the dimensions of each component represented and their ratios may differ from the actual ones.
（１）溶接部の改質方法
図１は、本発明の溶接部の改質方法の模式図である。本発明の溶接部の改質方法は、摩擦攪拌処理を用いて溶融溶接部２の表面に攪拌領域４を形成させる表面改質方法であって、被溶接材６が鉄系金属であり、溶融溶接部２の酸素含有量が７０ｐｐｍ〜７００ｐｐｍであること、を特徴とするものである。
(1) Method of modifying the welded portion FIG. 1 is a schematic view of the method of modifying the welded portion of the present invention. The method for modifying a welded portion of the present invention is a surface modifying method for forming a stirring region 4 on the surface of a molten welded portion 2 by using a friction stir welding treatment, wherein the material to be welded 6 is an iron-based metal and is melted. It is characterized in that the oxygen content of the welded portion 2 is 70 ppm to 700 ppm.
（１−１）酸素導入による溶け込み深さの増加
ここで、溶融溶接部２の酸素含有量が７０ｐｐｍ〜７００ｐｐｍとなっているのは溶込み深さを増加させるためであり、溶融池に適量の酸素を取り込むことで深溶け込みが達成されている。酸素導入による溶込み深さ増加のメカニズムを模式的に図２に示す。
(1-1) Increase in penetration depth due to oxygen introduction Here, the oxygen content of the melt welded portion 2 is 70 ppm to 700 ppm in order to increase the penetration depth, which is an appropriate amount for the molten pool. Deep penetration is achieved by taking in oxygen. The mechanism of increasing the penetration depth by introducing oxygen is schematically shown in FIG.
一般に、純金属や多くの合金の表面張力は負の温度勾配を有する。この場合、表面張力は温度が相対的に低い溶融池周辺の方が高くなる。したがって、溶融池表面における流れは、中央から外へ向かう。このとき熱流は溶融池周辺に輸送され、溶融池形状は図２ａに示すように広く浅いものになる。これに対し、溶融池中に酸素のような界面活性元素が含まれると、表面張力の温度勾配が負から正に変化し、図２ｂに示すように、対流の方向が変化する。この場合、溶融池は幅が狭く、溶込み深さが大きくなる。溶融溶接部２の酸素含有量を７０ｐｐｍ〜７００ｐｐｍとすることで、当該メカニズムにおける溶込み深さの増加を効率的に発現することができる。 In general, the surface tension of pure metals and many alloys has a negative temperature gradient. In this case, the surface tension is higher around the molten pool where the temperature is relatively low. Therefore, the flow on the surface of the molten pool goes from the center to the outside. At this time, the heat flow is transported around the molten pool, and the shape of the molten pool becomes wide and shallow as shown in FIG. 2a. On the other hand, when a surface active element such as oxygen is contained in the molten pool, the temperature gradient of surface tension changes from negative to positive, and the direction of convection changes as shown in FIG. 2b. In this case, the molten pool has a narrow width and a large penetration depth. By setting the oxygen content of the melt welded portion 2 to 70 ppm to 700 ppm, an increase in the penetration depth in the mechanism can be efficiently exhibited.
また、溶融溶接部２には酸化物粒子が分散しており、溶融溶接部２の酸素含有量は３３０ｐｐｍ以下であること、が好ましい。溶融溶接部２に酸化物粒子が分散する場合は溶接部の靭性低下が顕著になるが、適当な酸化物粒子の存在によって摩擦攪拌処理による改質効果を向上させることができる。なお、酸素含有量が高過ぎると溶融溶接部２の靭性低下がより深刻となり、摩擦攪拌処理を施しても靭性を母材と同等レベルにまで向上させることができないが、酸素含有量が３３０ｐｐｍ以下であれば、摩擦攪拌プロセスによって溶融溶接部２の靭性を母材と同等にまで向上させることができる。 Further, it is preferable that the oxide particles are dispersed in the melt welded portion 2 and the oxygen content of the melt welded portion 2 is 330 ppm or less. When the oxide particles are dispersed in the melt-welded portion 2, the toughness of the welded portion is significantly reduced, but the modification effect by the friction stir treatment can be improved by the presence of appropriate oxide particles. If the oxygen content is too high, the toughness of the melt welded portion 2 becomes more serious, and the toughness cannot be improved to the same level as the base metal even if friction stir welding is performed, but the oxygen content is 330 ppm or less. If so, the toughness of the melt welded portion 2 can be improved to the same level as that of the base metal by the friction stir welding process.
また、溶融溶接部２の酸素含有量は１６７ｐｐｍ〜３３０ｐｐｍであること、がより好ましい。酸素含有量が１６７ｐｐｍ以上となると、確実に深溶け込みが得られる反面、溶融溶接部２の靭性低下が顕著になるが、摩擦攪拌処理を施すことによって、母材と同等にまで靭性を向上させることができる。 Further, it is more preferable that the oxygen content of the melt welded portion 2 is 167 ppm to 330 ppm. When the oxygen content is 167 ppm or more, deep penetration can be surely obtained, but the toughness of the melt welded portion 2 is significantly reduced. Can be done.
本発明の溶接部の改質方法を適用することができる溶融溶接部は特に限定されず、摩擦攪拌処理が可能な範囲で従来公知の種々の鉄系金属に形成させた溶接部が対象となるが、被接合材６に低温用鋼材を用いることが好ましく、９％Ｎｉ鋼材を用いることがより好ましい。９％Ｎｉ鋼材は溶融溶接部２に酸素が導入されることで靭性が大きく低下するが、本発明の溶接部の改質方法を用いることで、溶融溶接部２と母材の靭性を略同一にすることができる。 The melt-welded portion to which the method for modifying the welded portion of the present invention can be applied is not particularly limited, and the welded portion formed of various conventionally known iron-based metals within the range in which friction stir welding can be performed is targeted. However, it is preferable to use a low temperature steel material as the material to be welded 6, and it is more preferable to use a 9% Ni steel material. The toughness of 9% Ni steel is greatly reduced by the introduction of oxygen into the melt weld 2, but the toughness of the base metal is substantially the same as that of the melt weld 2 by using the welding modification method of the present invention. Can be.
なお、溶融溶接部２の酸素含有量の測定方法は特に限定されず、従来公知の種々の方法で測定することができるが、例えば、市販の酸素・窒素分析装置を用いて測定することができる。当該装置は、不活性ガス融解‐非分散型赤外線吸収法によって酸素含有量を測定するものである。 The method for measuring the oxygen content of the melt-welded portion 2 is not particularly limited and can be measured by various conventionally known methods. For example, it can be measured using a commercially available oxygen / nitrogen analyzer. .. The device measures the oxygen content by an inert gas melting-non-dispersive infrared absorption method.
（１−２）摩擦攪拌処理
摩擦攪拌処理とは、摩擦攪拌接合を金属材の表面改質に応用したものであり、用いる工具の形状等が異なる場合がある他は、基本的には摩擦攪拌接合と同様の技術である。具体的には、回転工具の先端に設けられた突起部（プローブ）を被処理材に挿入し、回転工具を回転させつつ移動させることによって、攪拌領域を得る方法である。
(1-2) Friction stir welding Friction stir welding is an application of friction stir welding to the surface modification of metal materials, and is basically friction stir welding except that the shape of the tool used may differ. It is a technique similar to joining. Specifically, it is a method of obtaining a stirring region by inserting a protrusion (probe) provided at the tip of a rotary tool into a material to be processed and moving the rotary tool while rotating it.
図３は、本発明の溶接部の改質方法で用いる摩擦攪拌用工具の概略正面図である。本発明の溶接部の改質方法で用いる摩擦攪拌用工具１０の底面には長さが３ｍｍ以下のプローブ１２を有していることが好ましく、長さが２ｍｍ以下のプローブ１２を有していることがより好ましい（図３ａ）。また、プローブ１２を有していない底面が略平面のフラットツール（図３ｂ）を用いることもできる。更には、プローブ１２を有しておらず、摩擦攪拌用工具１０の底面が凸形状となっているツールを用いることもできる。 FIG. 3 is a schematic front view of a friction stir welding tool used in the method for modifying a welded portion of the present invention. The bottom surface of the friction stir welding tool 10 used in the method for modifying a welded portion of the present invention preferably has a probe 12 having a length of 3 mm or less, and has a probe 12 having a length of 2 mm or less. Is more preferable (Fig. 3a). It is also possible to use a flat tool (FIG. 3b) having a substantially flat bottom surface without the probe 12. Furthermore, a tool that does not have the probe 12 and has a convex bottom surface of the friction stir welding tool 10 can also be used.
プローブ１２を有する摩擦攪拌用工具１０を、高い融点及び高温変形抵抗を有する鉄系金属に圧入して移動させる場合、プローブ１２の根本から破断して摩擦攪拌用工具１０の寿命となることが多い。これに対し、底面が略平面の摩擦攪拌用工具１０を用いることでプローブ１２の破断による工具寿命を考慮する必要がなくなり、長さが２ｍｍ以下のプローブ１２を有する摩擦攪拌用工具１０を用いることで、プローブ１２の破断を抑制することができる。 When the friction stir tool 10 having the probe 12 is press-fitted into an iron-based metal having a high melting point and high temperature deformation resistance and moved, it often breaks from the root of the probe 12 and the life of the friction stir tool 10 is reached. .. On the other hand, by using the friction stir tool 10 having a substantially flat bottom surface, it is not necessary to consider the tool life due to the breakage of the probe 12, and the friction stir tool 10 having the probe 12 having a length of 2 mm or less is used. Therefore, the breakage of the probe 12 can be suppressed.
プローブ１２の形状は特に限定されず、単純な円柱状や根本が太く先端が細いテーパー状等を用いることができる。プローブ１２にはネジ加工や面取り加工等を施してもよいが、工具寿命の観点からはそれらの加工を施さない方が好ましい。 The shape of the probe 12 is not particularly limited, and a simple columnar shape, a tapered shape having a thick root and a thin tip, or the like can be used. The probe 12 may be threaded, chamfered, or the like, but it is preferable not to perform such processing from the viewpoint of tool life.
摩擦攪拌用工具１０の底面を略平面とすることで、摩擦攪拌用工具１０の素材として用いることができる材料の範囲を広くすることができる。プローブ１２を有さない場合、摩擦攪拌用工具１０の形状は基本的に円柱状であるため、難焼結材や難加工材を用いることも可能である。なお、本発明で用いることができる摩擦攪拌用工具１０には、底面が凹形状を有するものも含まれる。 By making the bottom surface of the friction stir tool 10 substantially flat, the range of materials that can be used as the material of the friction stir tool 10 can be widened. When the probe 12 is not provided, the shape of the friction stir welding tool 10 is basically cylindrical, so that it is possible to use a difficult-to-sinter material or a difficult-to-process material. The friction stir welding tool 10 that can be used in the present invention includes a tool having a concave bottom surface.
摩擦攪拌用工具１０の材質は、例えば、ＪＩＳに規格されているＳＫＤ６１鋼等の工具鋼や、タングステンカーバイト（ＷＣ）、コバルト（Ｃｏ）、ニッケル（Ｎｉ）からなる超硬合金、コバルト（Ｃｏ）基合金、タングステン（Ｗ）合金、イリジウム（Ｉｒ）等の高融点金属及びその合金、またはＳｉ３Ｎ４等のセラミックスからなるものとすることができる。ここで、被溶接材６が高張力鋼等の鋼材である場合、タングステンカーバイト（ＷＣ）、コバルト（Ｃｏ）からなる超硬合金、コバルト（Ｃｏ）基合金、イリジウム（Ｉｒ）等の高融点金属及びその合金、またはＳｉ３Ｎ４等のセラミックスならなるものを使用することが好ましい。 The material of the friction stirring tool 10 is, for example, tool steel such as SKD61 steel specified in JIS, cemented carbide made of tungsten carbide (WC), cobalt (Co), nickel (Ni), and cobalt (Co). ) Base alloy, tungsten (W) alloy, refractory metal such as iridium (Ir) and its alloy, or ceramics such as Si 3 N 4 can be used. Here, when the material 6 to be welded is a steel material such as high-strength steel, it has a high melting point such as tungsten carbide (WC), a cemented carbide made of cobalt (Co), a cobalt (Co) -based alloy, and iridium (Ir). It is preferable to use a metal and an alloy thereof, or a ceramic such as Si 3 N 4 or the like.
攪拌領域４は溶融溶接部２の表面に形成させればよく、攪拌領域４は必要以上に厚くする必要はない。摩擦攪拌用工具１０の寿命及び処理のし易さの観点から、攪拌領域４の厚さは０．５ｍｍ〜３．０ｍｍとすることが好ましく、０．５ｍｍ〜２．０ｍｍの深さとすることがより好ましい。なお、底面が略平面の直径１０〜１５ｍｍ程度の摩擦攪拌用工具１０を用いた場合、処理条件にも依存するが、０．５ｍｍ程度の厚さを有する攪拌領域４を好適に得ることができる。また、攪拌領域４の幅は溶融溶接部２の幅よりも広く、溶融溶接部２が攪拌領域に含まれるように形成させることが好ましい。 The stirring region 4 may be formed on the surface of the melt welded portion 2, and the stirring region 4 does not need to be thicker than necessary. From the viewpoint of the life of the friction stir tool 10 and the ease of processing, the thickness of the stirring region 4 is preferably 0.5 mm to 3.0 mm, preferably 0.5 mm to 2.0 mm. More preferred. When a friction stir tool 10 having a substantially flat bottom surface and a diameter of about 10 to 15 mm is used, a stirring region 4 having a thickness of about 0.5 mm can be preferably obtained, although it depends on the processing conditions. .. Further, the width of the stirring region 4 is wider than the width of the melt-welded portion 2, and it is preferable to form the melt-welded portion 2 so as to be included in the stirring region.
摩擦攪拌処理によって得られる攪拌領域４の組織は、急冷凝固組織を有する溶融溶接部２と比較して微細化及び均質化されている。溶融溶接部２の靭性は母材と比較して大幅に低下しているが、発明者が鋭意研究を重ねた結果、溶融溶接部２の表面に優れた機械的性質を有する攪拌領域４を形成させることで、溶融溶接部２全体の信頼性を担保することができることが明らかとなった。 The structure of the stirring region 4 obtained by the friction stir treatment is finer and more homogenized as compared with the melt welded portion 2 having the quenching solidification structure. The toughness of the melt-welded portion 2 is significantly lower than that of the base metal, but as a result of intensive research by the inventor, a stirring region 4 having excellent mechanical properties is formed on the surface of the melt-welded portion 2. It was clarified that the reliability of the entire melt-welded portion 2 can be ensured by making the melt welded portion 2 as a whole.
ここで、溶融溶接部２に酸化物粒子が分散する場合は溶接部の靭性低下が顕著になるが、適当な酸化物粒子の存在によって摩擦攪拌処理による改質効果を向上させることができる。よって、溶融溶接部２の深溶け込みを実現しつつ、溶融溶接部２に母材と同等の靭性を付与するためには、溶融溶接部２の酸素含有量に適当な範囲が存在し、例えば、酸素含有量が３３０ｐｐｍ以下であれば、摩擦攪拌処理によって溶融溶接部２の靭性を母材と同等にまで向上させることができる。なお、酸素含有量が１６７ｐｐｍ以上となると、確実に深溶け込みが得られる反面、溶融溶接部２の靭性低下が顕著になるが、摩擦攪拌処理を施すことによって、母材と同等にまで靭性を向上させることができる。 Here, when the oxide particles are dispersed in the melt-welded portion 2, the toughness of the welded portion is significantly reduced, but the modification effect by the friction stir treatment can be improved by the presence of appropriate oxide particles. Therefore, in order to realize deep penetration of the melt welded portion 2 and impart toughness equivalent to that of the base metal to the melt welded portion 2, there is an appropriate range for the oxygen content of the melt welded portion 2, for example. When the oxygen content is 330 ppm or less, the toughness of the melt welded portion 2 can be improved to the same level as that of the base metal by the friction stir welding treatment. When the oxygen content is 167 ppm or more, deep penetration can be surely obtained, but the toughness of the melt welded portion 2 is significantly reduced, but the toughness is improved to the same level as the base metal by performing friction stir welding. Can be made to.
本発明における摩擦攪拌処理とは、（１）摩擦攪拌用工具１０を回転させつつ処理方向に向けて移動させる態様、（２）摩擦攪拌用工具１０を回転させつつ処理位置で移動させない態様、（３）（１）で形成される処理領域を重畳させる態様、（４）（２）で形成される処理領域を重畳させる態様、及び（５）（１）〜（４）の処理を任意に組み合わせる態様、が含まれる。 The friction stir welding treatment in the present invention includes (1) a mode in which the friction stir welding tool 10 is rotated and moved in the processing direction, and (2) a mode in which the friction stir welding tool 10 is rotated and not moved at the processing position. 3) The mode of superimposing the processing regions formed in (1), the mode of superimposing the processing regions formed in (4) and (2), and the processes of (5) (1) to (4) are arbitrarily combined. Aspects, are included.
（２）溶接構造物
本発明の溶接構造物は、上記本発明の溶接部の改質方法によって改質された溶接部を有する溶接構造物を提供する。溶接構造物全体の機械的性質を律速する溶接部が改質されていることで、用いた構造用材の機械的性質を十分に発現し得る溶接構造物を得ることができる。
(2) Welded Structure The welded structure of the present invention provides a welded structure having a welded portion modified by the above-mentioned method of modifying the welded portion of the present invention. By modifying the welded portion that controls the mechanical properties of the entire welded structure, it is possible to obtain a welded structure that can sufficiently express the mechanical properties of the structural material used.
本発明の溶接構造物における溶接部の概略断面図を図４に示す。本発明の溶接構造物は、鉄系金属材２０に、酸素含有量が１６７ｐｐｍ〜３３０ｐｐｍである溶融溶接部２を有し、溶融溶接部２の表面に、再結晶粒を含む厚さが０．５ｍｍ〜３．０ｍｍ攪拌領域４を有し、溶融溶接部２及び攪拌領域４に酸化物粒子が分散していること、を特徴としている。 FIG. 4 shows a schematic cross-sectional view of a welded portion in the welded structure of the present invention. In the welded structure of the present invention, the iron-based metal material 20 has a melt-welded portion 2 having an oxygen content of 167 ppm to 330 ppm, and the surface of the melt-welded portion 2 has a thickness of 0. It has a stirring region 4 of 5 mm to 3.0 mm, and is characterized in that oxide particles are dispersed in the melt welded portion 2 and the stirring region 4.
溶融溶接部２に１６７ｐｐｍ〜３３０ｐｐｍの酸素を含み、溶接時の深溶け込みが達成されていることから、一般的なＴＩＧ溶接等で形成される溶接部と比較して溶接部のＤ（深さ）／Ｗ（幅）が大きな溶接部が形成されている。ここで、Ｄ／Ｗの値は特に限定されないが、０．４以上となっていることが好ましい。 Since the melt-welded portion 2 contains 167 ppm to 330 ppm of oxygen and deep penetration during welding is achieved, the D (depth) of the welded portion is compared with that of the welded portion formed by general TIG welding or the like. A welded portion with a large / W (width) is formed. Here, the value of D / W is not particularly limited, but is preferably 0.4 or more.
攪拌領域４の厚さは０．５ｍｍ〜３．０ｍｍであり、攪拌領域４には再結晶粒が含まれる。攪拌領域４の厚さを０．５ｍｍ〜３．０ｍｍとすることで、信頼性の高い溶融溶接部２を有する安価な溶接構造物が実現されている。溶融溶接部２は酸化物粒子が分散した急冷凝固組織となり、母材と比較すると靭性が大きく低下しているが、その表面に摩擦攪拌処理によって改質された攪拌領域４が存在することから、溶融溶接部２全体としての信頼性を確保することができる。より具体的には、改質領域４は摩擦攪拌処理によって組織が微細化及び均質化された領域であり、溶融溶接部２に外部応力が印加された場合、改質領域４が当該応力に耐えることで、溶融溶接部２の破壊及び変形等を抑制することができる。 The thickness of the stirring region 4 is 0.5 mm to 3.0 mm, and the stirring region 4 contains recrystallized grains. By setting the thickness of the stirring region 4 to 0.5 mm to 3.0 mm, an inexpensive welded structure having a highly reliable melt welded portion 2 is realized. The melt-welded portion 2 has a rapidly cooled solidified structure in which oxide particles are dispersed, and its toughness is significantly reduced as compared with the base metal. The reliability of the melt welded portion 2 as a whole can be ensured. More specifically, the modified region 4 is a region in which the structure is refined and homogenized by friction stir welding, and when an external stress is applied to the melt welded portion 2, the modified region 4 withstands the stress. As a result, it is possible to suppress breakage and deformation of the fusion welded portion 2.
溶融溶接部２及び攪拌領域４に分散している酸化物粒子の種類、形状及びサイズは特に限定されないが、攪拌領域４に分散している酸化物粒子は溶融溶接部２に分散している酸化物粒子よりも微細であることが好ましい。また、攪拌領域４に分散している酸化物粒子は溶融溶接部２に分散している酸化物粒子よりも球状化されていることが好ましい。攪拌領域４に微細かつ球状化した酸化物粒子が分散していることで、攪拌領域４に高い靭性を付与することができる。 The type, shape, and size of the oxide particles dispersed in the melt-welded portion 2 and the stirring region 4 are not particularly limited, but the oxide particles dispersed in the stirring region 4 are oxidized in the melt-welded portion 2. It is preferably finer than physical particles. Further, it is preferable that the oxide particles dispersed in the stirring region 4 are more spheroidized than the oxide particles dispersed in the melt welded portion 2. Since fine and spheroidized oxide particles are dispersed in the stirring region 4, high toughness can be imparted to the stirring region 4.
溶融溶接部２は低温用鋼材に形成されていることが好ましく、９％Ｎｉ鋼材に形成されていることがより好ましい。９％Ｎｉ鋼材は、溶融溶接部２に酸素が導入されることによる靭性の低下が他の鋼材と比較して顕著であるが、本発明の溶接構造物では、当該９％Ｎｉ鋼材であっても、溶込み深さを増加させた溶融溶接部２の靭性が母材と同等にまで向上している。つまり、本発明の溶接構造物においては、攪拌領域４を有する溶融溶接部２と鉄系金属材２０の靭性が略同一となっている。 The melt-welded portion 2 is preferably formed of a low-temperature steel material, and more preferably formed of a 9% Ni steel material. The 9% Ni steel material has a remarkable decrease in toughness due to the introduction of oxygen into the melt welded portion 2 as compared with other steel materials. However, in the welded structure of the present invention, the 9% Ni steel material is the 9% Ni steel material. However, the toughness of the melt-welded portion 2 with the increased penetration depth is improved to the same level as the base metal. That is, in the welded structure of the present invention, the toughness of the melt-welded portion 2 having the stirring region 4 and the iron-based metal material 20 are substantially the same.
本発明の溶接構造物においては、溶融溶接部２の全ての領域が改質されている必要はないが、溶接構造物の機械的性質を律速する領域に摩擦攪拌処理が施されていることが好ましい。 In the welded structure of the present invention, it is not necessary that all the regions of the melt welded portion 2 are modified, but the region that controls the mechanical properties of the welded structure is subjected to friction stir welding treatment. preferable.
以上、本発明の代表的な実施形態について説明したが、本発明はこれらのみに限定されるものではなく、種々の設計変更が可能であり、それら設計変更は全て本発明の技術的範囲に含まれる。 Although the typical embodiments of the present invention have been described above, the present invention is not limited to these, and various design changes are possible, and all of these design changes are included in the technical scope of the present invention. Is done.
≪実施例≫
供試材料として、１００ｍｍ×１２０ｍｍ×１２ｍｍの９％Ｎｉ鋼（ＪＩＳ Ｇ ３１２７ ＳＬ ９Ｎ）板を用いた。９％Ｎｉ鋼は、溶接部に酸素が含有することで靭性が低下する典型的な鉄系金属である。当該供試材に対し、電流１５０Ａ、溶接速度１２０ｍｍ／ｍｉｎ、Ａｒシールドガスの条件でビードオンプレート溶接を実施した。ここで、Ａｒシールドガスには、高純度Ａｒ及び、酸素含有量をそれぞれ０．３％、０．４５％、０．６％に調製したＡｒ−Ｏ２混合ガスを用いた。
<< Example >>
As a test material, a 100 mm × 120 mm × 12 mm 9% Ni steel (JIS G 3127 SL 9N) plate was used. 9% Ni steel is a typical iron-based metal whose toughness decreases due to the inclusion of oxygen in the weld. Bead-on-plate welding was performed on the test material under the conditions of a current of 150 A, a welding speed of 120 mm / min, and Ar shield gas. Here, as the Ar shield gas, high-purity Ar and an Ar—O 2 mixed gas whose oxygen contents were adjusted to 0.3%, 0.45%, and 0.6%, respectively, were used.
各シールドガスを使用して得られた溶融溶接部及び母材の酸素含有量を酸素窒素分析装置によって測定した。結果を表１に示す。 The oxygen content of the melt weld and the base metal obtained by using each shield gas was measured by an oxygen nitrogen analyzer. The results are shown in Table 1.
その後、溶接部の最表面に対して、ツール回転数２００ｒｐｍ、ツール移動速度１５０ｍｍ／ｍｉｎ、ツール荷重２５００ｋｇｆの条件で摩擦攪拌処理を施した。なお、摩擦攪拌処理には、ショルダ径１５ｍｍ、プローブ径６ｍｍ、プローブ長２．８ｍｍの超硬合金製ツール１、又はショルダ径１２ｍｍ、プローブ径４ｍｍ、プローブ長０．８ｍｍの超硬合金製ツール２を用いた。 Then, the outermost surface of the welded portion was subjected to friction stir welding under the conditions of a tool rotation speed of 200 rpm, a tool moving speed of 150 mm / min, and a tool load of 2500 kgf. For friction stir welding, a cemented carbide tool 1 having a shoulder diameter of 15 mm, a probe diameter of 6 mm, and a probe length of 2.8 mm, or a cemented carbide tool 2 having a shoulder diameter of 12 mm, a probe diameter of 4 mm, and a probe length of 0.8 mm. Was used.
酸素含有量１６７ｐｐｍの溶接部表面を超硬合金製ツール２で摩擦攪拌処理した試料の断面マクロ写真を図５に示す。溶融溶接部の表面に最大厚さ約１ｍｍの攪拌領域が形成されていることが分かる。なお、超硬合金製ツール１で摩擦攪拌処理を施した場合、最大厚さ約３ｍｍの攪拌領域が形成された。 FIG. 5 shows a cross-sectional macro photograph of a sample in which the surface of a welded portion having an oxygen content of 167 ppm is subjected to friction stir welding with a cemented carbide tool 2. It can be seen that a stirring region having a maximum thickness of about 1 mm is formed on the surface of the melt-welded portion. When the friction stir welding treatment was performed with the cemented carbide tool 1, a stirring region having a maximum thickness of about 3 mm was formed.
摩擦攪拌処理前の各溶接部及び超硬合金製ツール１で摩擦攪拌処理を施した各溶接部に関して微小衝撃試験を行い、吸収エネルギーを算出することにより破壊靭性を評価した。なお、図６に示すように微小衝撃試験片を摩擦攪拌処理方向に対して垂平に切り出した。試験片のノッチは攪拌領域の中央になるようにし、試験片の寸法は長さ：２０ｍｍ、厚さ：０．５ｍｍ、幅：０．５ｍｍ、ノッチ：０．１ｍｍとした。なお、測定はパンチャー速度を１ｍ／ｓとして室温で行い、得られた荷重変位曲線の積分により吸収エネルギーを算出した。 A micro-impact test was performed on each weld before the friction stir treatment and each weld subjected to the friction stir treatment with the cemented carbide tool 1, and the fracture toughness was evaluated by calculating the absorbed energy. As shown in FIG. 6, the micro-impact test piece was cut flat in the friction stir welding direction. The notch of the test piece was set to the center of the stirring region, and the dimensions of the test piece were length: 20 mm, thickness: 0.5 mm, width: 0.5 mm, and notch: 0.1 mm. The measurement was performed at room temperature with the puncher speed set to 1 m / s, and the absorbed energy was calculated by integrating the obtained load displacement curve.
摩擦攪拌処理前の試料に関する結果を図７に示す。以下、溶接部の酸素含有量を図中に記載している。溶接部の酸素含有量が７８ｐｐｍの場合は母材と同等の吸収エネルギーを有しており、溶接部は母材と同等の靭性を有していることを示している。これに対し、酸素含有量が１６７ｐｐｍに増加すると吸収エネルギーが急激に低下し、３３０ｐｐｍの場合は更に低下している。当該結果は、酸素含有量が１６７ｐｐｍ以上となる場合、当該溶接部の使用には靭性の改善が必要であることを示唆している。 The results of the sample before the friction stir welding treatment are shown in FIG. Hereinafter, the oxygen content of the welded portion is shown in the figure. When the oxygen content of the welded portion is 78 ppm, it has the same absorbed energy as the base metal, indicating that the welded portion has the same toughness as the base metal. On the other hand, when the oxygen content increases to 167 ppm, the absorbed energy sharply decreases, and when it is 330 ppm, it further decreases. The results suggest that when the oxygen content is 167 ppm or more, the toughness needs to be improved for the use of the weld.
摩擦攪拌処理前後の試料に関する結果を図８に示す。摩擦攪拌処理前において母材よりも大幅に小さな吸収エネルギーを示した１６７ｐｐｍ及び３３０ｐｐｍの溶接部に関し、摩擦攪拌処理によって母材と同等の吸収エネルギーが得られていることが分かる。特に、酸化物粒子をより多く含む３３０ｐｐｍの溶接部において、摩擦攪拌処理による吸収エネルギーの増加が顕著である。なお、酸素含有量が３３０ｐｐｍよりも高くなる場合、溶接部の靭性低下が大きく、摩擦攪拌処理を施しても吸収エネルギーが母材よりも小さな値となった。 The results of the sample before and after the friction stir welding are shown in FIG. It can be seen that, with respect to the welded portions of 167 ppm and 330 ppm, which showed significantly smaller absorbed energy than the base metal before the friction stir welding, the absorbed energy equivalent to that of the base metal was obtained by the friction stir welding. In particular, in the 330 ppm welded portion containing more oxide particles, the increase in absorbed energy due to the friction stir welding treatment is remarkable. When the oxygen content was higher than 330 ppm, the toughness of the welded portion was significantly reduced, and the absorbed energy was smaller than that of the base metal even after friction stir welding.
摩擦攪拌処理前後における７８ｐｐｍ及び３３０ｐｐｍの溶接部の硬度分布を、それぞれ図９及び図１０に示す。なお、硬度測定にはビッカース硬度計（株式会社フューチュアテック製Ｆ−３００）を用い、溶接部断面の硬度測定を行った（表面から深さ１ｍｍにおける溶接部中央の水平方向）。測定条件は、荷重：３００ｇｆ、保持時間：１０ｓとした。 The hardness distributions of the welded portions at 78 ppm and 330 ppm before and after the friction stir welding are shown in FIGS. 9 and 10, respectively. A Vickers hardness tester (F-300 manufactured by Future Tech Co., Ltd.) was used to measure the hardness of the cross section of the welded portion (horizontal direction of the center of the welded portion at a depth of 1 mm from the surface). The measurement conditions were a load: 300 gf and a holding time: 10 s.
酸素含有量が７８ｐｐｍと低い場合は摩擦攪拌前後で硬度分布に大きな変化は認められないが、酸素含有量が３３０ｐｐｍと高い場合は、摩擦攪拌による硬度上昇が認められる。当該結果は、摩擦攪拌処理の効果は酸素含有量が高い場合（酸化物粒子が多い場合）により顕著であることを示している。 When the oxygen content is as low as 78 ppm, the hardness distribution does not change significantly before and after friction stir welding, but when the oxygen content is as high as 330 ppm, the hardness increases due to friction stir welding. The results show that the effect of the friction stir welding treatment is more remarkable when the oxygen content is high (when the amount of oxide particles is large).
酸化物粒子の状態を観察するために、溶接部の断面のＳＥＭ観察を行った。なお、ＳＥＭ観察にはＦＥ−ＳＥＭ（日本電子株式会社製ＪＳＭ−７００１ＦＡ）を用いた。受け入れままの母材の組成像を図１１に示す。組成像では母材より暗い色で酸化物粒子が示され、母材中に多数分散していることが分かる。 In order to observe the state of the oxide particles, SEM observation of the cross section of the welded portion was performed. FE-SEM (JSM-7001FA manufactured by JEOL Ltd.) was used for SEM observation. The composition image of the base material as it is accepted is shown in FIG. In the composition image, oxide particles are shown in a darker color than the base material, and it can be seen that a large number of oxide particles are dispersed in the base material.
摩擦攪拌処理を施した３３０ｐｐｍの溶接部の組成像を図１２に示す。受け入れまま材と比較すると、大きな酸化物粒子の数が少なくなっている。ここで、より高倍率の二次電子像で観察すると、極めて微細な酸化物粒子が大量に分散している様子を確認することができる（図１３）。当該結果は、摩擦攪拌処理によって酸化物粒子が破砕され、より微細になったことを示している。また、摩擦攪拌処理による酸化物粒子の球状化も確認できる。 FIG. 12 shows a composition image of a 330 ppm welded portion subjected to friction stir welding. Compared to the accepted material, the number of large oxide particles is reduced. Here, when observing with a higher-magnification secondary electron image, it can be confirmed that a large amount of extremely fine oxide particles are dispersed (FIG. 13). The results indicate that the oxide particles were crushed and made finer by the friction stir welding treatment. In addition, spheroidization of oxide particles by friction stir welding can be confirmed.
摩擦攪拌処理を施す前の３３０ｐｐｍの溶接部に分散している酸化物粒子をＳＥＭ−ＥＤＳ分析によって同定したところ、アルミニウム酸化物であった。ＥＤＳマッピング結果を図１４に示す。アルミニウム及び酸素の分布が重畳していることが確認できる。 When the oxide particles dispersed in the welded portion of 330 ppm before the friction stir welding treatment were identified by SEM-EDS analysis, they were aluminum oxides. The EDS mapping result is shown in FIG. It can be confirmed that the distributions of aluminum and oxygen are superimposed.
母材組織及び酸化物粒子の変化を観察するために、試料断面のＥＢＳＤ測定を行った。なお、ＥＢＳＤ測定にはＦＥ−ＳＥＭ（日本電子株式会社製ＪＳＭ−７００１ＦＡ）及びＴＳＬ社製のＯＩＭ ｄａｔａ Ｃｏｌｌｅｃｔｉｏｎ ｖｅｒ５．３１を用いた。 In order to observe changes in the base metal structure and oxide particles, EBSD measurement of the sample cross section was performed. For EBSD measurement, FE-SEM (JSM-7001FA manufactured by JEOL Ltd.) and OIM data Collection ver5.31 manufactured by TSL were used.
摩擦攪拌処理前後の２３０ｐｐｍ溶接部及び摩擦攪拌処理後の３３０ｐｐｍ溶接部のＥＢＳＤマッピング結果を図１５に示す。なお、摩擦攪拌処理後の試料に関しては、攪拌領域を測定対象としている。 FIG. 15 shows the EBSD mapping results of the 230 ppm welded portion before and after the friction stir welding treatment and the 330 ppm welded portion after the friction stir welding treatment. For the sample after the friction stir welding treatment, the stirring region is the measurement target.
２３０ｐｐｍ溶接部に関し、摩擦攪拌処理によって母材組織及び酸化物粒子（代表的な酸化物粒子を〇で囲っている）が微細化していることが分かる。また、摩擦攪拌処理を施した２３０ｐｐｍ溶接部と３３０ｐｐｍ溶接部を比較すると、酸素含有量の高い３３０ｐｐｍ溶接部において、組織がより微細化していることが確認できる。なお、摩擦攪拌処理後の３３０ｐｐｍ溶接部においては酸化物粒子の微細化が顕著であり、ＥＢＳＤマッピングでは明瞭に観察することができない。 It can be seen that the base metal structure and the oxide particles (representative oxide particles surrounded by ◯) are refined by the friction stir welding treatment for the 230 ppm welded portion. Further, when comparing the 230 ppm welded portion and the 330 ppm welded portion subjected to the friction stir welding treatment, it can be confirmed that the structure is finer in the 330 ppm welded portion having a high oxygen content. It should be noted that the oxide particles are remarkably miniaturized in the 330 ppm welded portion after the friction stir welding treatment, and cannot be clearly observed by EBSD mapping.
２・・・溶融溶接部、
４・・・攪拌領域、
６・・・被溶接材、
１０・・・摩擦攪拌用工具、
１２・・・プローブ、
２０・・・鉄系金属材。
2 ... Melt weld,
4 ... Stirring area,
6 ... Welded material,
10 ... Friction stir welding tool,
12 ... probe,
20 ... Iron-based metal material.
Claims (12)
被溶接材が鉄系金属であり、
前記溶融溶接部の酸素含有量が７０ｐｐｍ〜７００ｐｐｍであること、
を特徴とする溶接部の改質方法。 A surface modification method in which a stirring region is formed on the surface of a melt weld using friction stir welding.
The material to be welded is an iron-based metal,
The oxygen content of the melt welded portion is 70 ppm to 700 ppm.
A method for modifying a welded portion, which is characterized by.
前記酸素含有量が３３０ｐｐｍ以下であること、
を特徴とする請求項１に記載の溶接部の改質方法。 Oxide particles are dispersed in the melt welded portion,
The oxygen content is 330 ppm or less.
The method for modifying a welded portion according to claim 1.
を特徴とする請求項１又は２に記載の溶接部の改質方法。 The oxygen content is 167 ppm to 330 ppm.
The method for modifying a welded portion according to claim 1 or 2, wherein the welded portion is modified.
を特徴とする請求項１〜３のうちのいずれかに記載の溶接部の改質方法。 In the friction stir welding treatment, the treatment temperature of at least a part of the stirring region shall be set to A 3 points or less or A cm points or less of the iron-based metal.
The method for modifying a welded portion according to any one of claims 1 to 3.
を特徴とする請求項１〜４のうちのいずれかに記載の溶接部の改質方法。 In the friction stir welding treatment, the treatment temperature of at least a part of the stirring region shall be set to A 1 point or less of the iron-based metal.
The method for modifying a welded portion according to any one of claims 1 to 4, wherein the welded portion is modified.
を特徴とする請求項１〜５のうちのいずれかに記載の溶接部の改質方法。 The melt welded portion is a butt joint or a lap joint.
The method for modifying a welded portion according to any one of claims 1 to 5.
を特徴とする請求項１〜６のうちのいずれかに記載の溶接部の改質方法。 The melt weld is formed on the low temperature steel material,
The method for modifying a welded portion according to any one of claims 1 to 6, wherein the welded portion is modified.
を特徴とする請求項１〜７のうちのいずれかに記載の溶接部の改質方法。 The melt weld is formed of 9% Ni steel.
The method for modifying a welded portion according to any one of claims 1 to 7.
前記溶融溶接部の表面に、再結晶粒を含む厚さが０．５ｍｍ〜３．０ｍｍの攪拌領域を有し、
前記溶融溶接部及び前記攪拌領域に酸化物粒子が分散していること、
を特徴とする溶接構造物。 The iron-based metal material has a melt-welded portion having an oxygen content of 167 ppm to 330 ppm.
The surface of the melt-welded portion has a stirring region having a thickness of 0.5 mm to 3.0 mm containing recrystallized grains.
Oxide particles are dispersed in the melt-welded portion and the stirring region.
A welded structure characterized by.
を特徴とする請求項９に記載の溶接構造物。 The iron-based metal material is a low-temperature steel material.
The welded structure according to claim 9.
を特徴とする請求項９に記載の溶接構造物。 The iron-based metal material is 9% Ni steel material.
The welded structure according to claim 9.
を特徴とする請求項９〜１１のうちのいずれかに記載の溶接構造物。 The toughness of the iron-based metal material is substantially the same as that of the melt-welded portion having the stirring region.
The welded structure according to any one of claims 9 to 11.
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