JP7640834B2 - Welded joint, manufacturing method of welded joint, automobile parts and building materials - Google Patents
Welded joint, manufacturing method of welded joint, automobile parts and building materials Download PDFInfo
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本発明は、溶接継手、溶接継手の製造方法、自動車部材及び建材部材に関する。 The present invention relates to welded joints, methods for manufacturing welded joints, automotive components, and building materials.
自動車の足回り部材をはじめとする自動車部材や各種の建材部材は、複数の鋼材を溶接した溶接継手を用いて製造されることが多い。これら自動車部材及び建材部材は、塩害地での長期間にわたる強度信頼性を確保するという観点から、溶接継手に用いる鋼材に関して、腐食を考慮した厚みの設計がなされ、その結果、用いられる鋼材の厚みの下限が制限される。これら自動車部材及び建材部材の軽量化を図るためには、用いられる溶接継手の塗装後耐食性を向上させることが求められる。溶接継手における溶接部は電着塗装性に改善の余地があることから、溶接継手の塗装後耐食性の向上を図るためには、溶接継手における溶接部の電着塗装性を向上させることが有効である。 Automobile components, including automobile undercarriage components, and various building materials are often manufactured using welded joints made by welding multiple steel materials. In order to ensure long-term strength reliability in salt-damaged areas, the thickness of the steel materials used in the welded joints of these automobile and building materials is designed with corrosion in mind, and as a result, the lower limit of the thickness of the steel materials used is limited. In order to reduce the weight of these automobile and building materials, it is necessary to improve the post-painting corrosion resistance of the welded joints used. Since there is room for improvement in the electrocoatability of the welds in welded joints, improving the electrocoatability of the welds in the welded joints is an effective way to improve the post-painting corrosion resistance of the welded joints.
溶接継手の溶接部の電着塗装性に改善の余地がある要因として、溶接時に生成する、非導電性を示すＳｉ系のスラグが塗装不良を招くことが挙げられる。塗装不良が生じた箇所は、赤錆の発生・成長が早く、腐食の進行による板厚の減少が生じるために、部材性能の低下を招く可能性がある。そこで、溶接部の電着塗装性を改善するために、従来様々な技術が提案されている。 One of the reasons why there is room for improvement in the electrocoatability of welded joints is that non-conductive silicon-based slag produced during welding can lead to poor coating. In areas where coating defects occur, red rust develops and grows quickly, and corrosion progresses, causing a decrease in plate thickness, which can lead to a decline in component performance. For this reason, various technologies have been proposed to improve the electrocoatability of welds.
例えば以下の特許文献１及び特許文献２には、非導電性を示すＳｉ系のスラグを物理的、又は、化学的に除去する方法が提案されている。具体的には、以下の特許文献１では、スラグを酸洗により除去する技術が提案されており、以下の特許文献２では、スラグをショットブラストにより除去する技術が提案されている。 For example, the following Patent Documents 1 and 2 propose methods for physically or chemically removing non-conductive Si-based slag. Specifically, the following Patent Document 1 proposes a technique for removing slag by pickling, and the following Patent Document 2 proposes a technique for removing slag by shot blasting.
また、以下の特許文献３には、鋼材及び溶接ワイヤ中の脱酸元素（スラグを構成する酸素と親和性の高い元素）を減少させたり、シールドガス中の酸化性ガスの割合を減少させたりすることで、スラグの生成量を低減する技術が提案されている。 In addition, the following Patent Document 3 proposes a technology to reduce the amount of slag produced by reducing the deoxidizing elements (elements that have a high affinity with the oxygen that constitutes the slag) in the steel material and welding wire, and by reducing the proportion of oxidizing gas in the shielding gas.
また、以下の特許文献４には、塗装不良の原因となる非導電性のスラグを導電性のスラグへと変化させることで、電着塗装性を向上させる技術が提案されている。 In addition, the following Patent Document 4 proposes a technology that improves electrodeposition paintability by changing non-conductive slag, which causes painting defects, into conductive slag.
しかしながら、上記特許文献１及び特許文献２で提案されているような、物理的又は化学的にスラグを除去する技術の場合、スラグを除去するための工程を増設する必要が生じるため、大幅な生産コストの増加及び生産能率の低下を招いてしまう。 However, in the case of the technology proposed in Patent Documents 1 and 2 above, which involves physically or chemically removing slag, it becomes necessary to add a process for removing the slag, which leads to a significant increase in production costs and a decrease in production efficiency.
また、上記特許文献３で提案されているような、スラグの低減を図る技術の場合、電着塗装不良の原因となるスラグの低減が見込めるが、材料の特性及び溶接施工性が新たな問題となる。例えば、鋼材の観点からすると、鋼材の高強度化に伴って添加される合金元素の量が増加し、スラグを構成する脱酸元素が増加するため、鋼材の高強度化・薄肉化を達成しつつ、電着塗装不良の原因となるスラグの低減は難しい。また、溶接ワイヤ中の脱酸元素は、溶接金属（溶接ビード）の脱酸不足を招き、溶接継手の性能低下が懸念される。更に、シールドガスの観点からすると、酸化性ガスが低減することで溶滴移行現象が不安定となり、スパッタの増加やアークの安定性が低下することが考えられる。このように、材料の特性及び溶接施工性と、スラグの低減と、はトレードオフの関係にあり、脱酸元素の低減又は酸化性ガスの低減には、限度がある。 In addition, in the case of the technology for reducing slag as proposed in the above Patent Document 3, it is expected that the slag that causes poor electrodeposition coating can be reduced, but the material properties and welding workability become new problems. For example, from the viewpoint of steel, the amount of alloy elements added increases with the increase in the strength of steel, and the amount of deoxidizing elements that make up the slag increases, so it is difficult to reduce the slag that causes poor electrodeposition coating while achieving high strength and thinning of the steel. In addition, the deoxidizing elements in the welding wire cause insufficient deoxidization of the weld metal (weld bead), and there is a concern that the performance of the welded joint will decrease. Furthermore, from the viewpoint of shielding gas, it is considered that the reduction in oxidizing gas makes the droplet transfer phenomenon unstable, increasing spatter and reducing the stability of the arc. In this way, there is a trade-off between the material properties and welding workability and the reduction in slag, and there is a limit to the reduction in deoxidizing elements or oxidizing gas.
更に、上記特許文献４で提案されているようなスラグの改質には、特定の脱酸元素の含有量を増減する必要があり、多量のケイ素（Ｓｉ）が含有されるＴＲＩＰ鋼などの鋼材については、電着塗装不良の低減効果には限度がある。 Furthermore, to modify the slag as proposed in Patent Document 4, it is necessary to increase or decrease the content of a specific deoxidizing element, and for steel materials such as TRIP steel that contain a large amount of silicon (Si), there is a limit to the effect of reducing electrodeposition coating defects.
以上のような観点から、用いる鋼材及び溶接ワイヤの化学組成や溶接条件に依らずに、生産性を大きく損なうことなく、溶接部の電着塗装性を向上させることが可能な技術が希求されている。 From the above perspective, there is a demand for technology that can improve the electrocoatability of welds without significantly impairing productivity, regardless of the chemical composition of the steel and welding wire used or the welding conditions.
そこで、本発明は、上記問題に鑑みてなされたものであり、本発明の目的とするところは、用いる鋼材及び溶接ワイヤの化学組成や溶接条件に依らずに、生産性を大きく損なうことなく、溶接部の電着塗装性を向上させることが可能な、溶接継手及び溶接継手の製造方法と、かかる溶接継手を有する自動車部材及び建材部材と、を提供することにある。 The present invention has been made in consideration of the above problems, and the object of the present invention is to provide a welded joint and a method for manufacturing a welded joint that can improve the electrocoatability of the welded portion without significantly impairing productivity, regardless of the chemical composition of the steel material and welding wire used or the welding conditions, and also to provide automotive and building materials having such a welded joint.
上記課題を解決するために、本発明者が鋭意検討した結果、溶接部の塗装不良性を招く溶接スラグ及びスパッタ、並びに、熱影響部の表面の少なくとも一部に、特定の導電性を示す導電塗膜を設けることに想到した。 In order to solve the above problems, the inventors conducted extensive research and came up with the idea of providing a conductive coating that exhibits a specific electrical conductivity on at least a portion of the surface of the heat-affected zone, as well as on the welding slag and spatter that cause poor coating quality at the welded zone.
従来、溶接継手は、溶接部が腐食してしまうことを前提に素材の検討（特に、鋼材の厚みに関する検討）が行われてきたため、溶接部に導電塗膜を設けるという、コスト増を招くような試みは行われてこなかった。しかしながら、上記のような自動車部材の軽量化の流れにおいて鋼材の薄肉化が進む中、溶接部の腐食を許容してしまうと、所望の機械的強度を満足することが困難となる。本発明者らは、導電塗膜であれば、鋼材の化学組成に依らずに実現可能であると考えた。更に、本発明者らは、導電塗膜を設けるための塗装工程であれば、現状の溶接継手の製造ラインにおいても、ラインの大幅な増設・改良を行うことなく対応可能であると考え、本発明に想到した。 Conventionally, materials for welded joints (especially steel thickness) have been considered on the assumption that the welds will corrode, so no attempt has been made to provide a conductive coating to the welds, which would increase costs. However, as steel becomes thinner in the trend toward lighter automotive components, it will be difficult to achieve the desired mechanical strength if corrosion is allowed at the welds. The inventors of the present invention believed that a conductive coating could be achieved regardless of the chemical composition of the steel. Furthermore, the inventors of the present invention believed that a painting process for providing a conductive coating could be implemented on current welded joint manufacturing lines without requiring major expansion or improvement of the line.
また、例えば自動車部材を例にとると、足回り部材（シャシー部材）とボディ部材とでは使用される鋼材強度が異なり、例えば、シャシー部材は、４４０～７８０ＭＰａ級の強度が多く用いられるのに対し、ボディ部材は、９８０ＭＰａ級や１１８０ＭＰａ級といった、より高強度の鋼板が用いられている。 For example, when it comes to automobile components, the strength of the steel used differs between chassis components and body components. For example, chassis components often use steel with a strength of 440 to 780 MPa, while body components use higher strength steel plates, such as 980 MPa or 1180 MPa.
シャシー部材の鋼板強度の向上を図る場合、鋼材の焼き入れ性が重要になる。鋼材の焼き入れ性を向上させるためには、一般的には、鋼材へのＳｉの添加が行われる。鋼材へのＳｉの添加は、鋼材中の炭素（Ｃ）が炭化物になることを抑制する働きがあり、マルテンサイトの生成比率を高め、マルテンサイトの硬さを上昇させる。その結果、鋼材の焼き入れ性が向上する。かかる効果を発現させるためには、高強度鋼材の製造にあたって、鋼材中のＳｉ量を０．８～１．７質量％とすることが好ましい。一方で、鋼材中のＳｉ量増加は、電着塗装不良を招く非導電性のＳｉ系スラグを生成させてしまうため、耐食性の観点では、鋼材中のＳｉ量を極少量に低減することが望ましい。かかる観点から、自動車部材の軽量化（シャシー部材の高強度化・薄肉化）を促進させる上で、鋼材へのＳｉの添加は、不可避だと考えられる。 When trying to improve the strength of steel plates in chassis components, the hardenability of the steel is important. In order to improve the hardenability of steel, generally, Si is added to the steel. The addition of Si to steel has the effect of suppressing the carbon (C) in the steel from becoming carbide, increasing the ratio of martensite formation and increasing the hardness of martensite. As a result, the hardenability of the steel is improved. In order to realize such an effect, it is preferable to set the amount of Si in the steel to 0.8 to 1.7 mass% in the manufacturing of high-strength steel. On the other hand, an increase in the amount of Si in the steel generates non-conductive Si-based slag that leads to poor electrocoating, so from the viewpoint of corrosion resistance, it is desirable to reduce the amount of Si in the steel to a very small amount. From this viewpoint, it is considered unavoidable to add Si to steel in order to promote the weight reduction of automobile components (higher strength and thinner chassis components).
また、溶接継手を製造する際に用いられる溶接ワイヤに関し、溶接ワイヤ成分中のＳｉ量は、溶接時の施工性と溶接部の耐食性に影響を及ぼす。施工性の観点では、溶接ワイヤ中のＳｉ量を０．１～０．９質量％とする方が溶滴移行が安定し、スパッタの軽減が見込める。一方で、耐食性の観点では、溶接ワイヤ中のＳｉ量を極少量に低減することが望ましい。このように、溶接継手を製造するにあたって、鋼材や溶接ワイヤ中のＳｉ量を安易に低減するわけにはいかなかった。
上記のような着想のもと完成された本発明の要旨は、以下の通りである。
In addition, with respect to the welding wire used in manufacturing a welded joint, the amount of Si in the welding wire components affects the workability during welding and the corrosion resistance of the weld. From the viewpoint of workability, a Si content of 0.1 to 0.9 mass% in the welding wire is expected to stabilize droplet transfer and reduce spatter. On the other hand, from the viewpoint of corrosion resistance, it is desirable to reduce the amount of Si in the welding wire to a very small amount. Thus, when manufacturing a welded joint, it is not possible to easily reduce the amount of Si in the steel material and the welding wire.
The gist of the present invention, which has been completed based on the above-mentioned concept, is as follows.
（１）複数の鋼材と、当該複数の鋼材の間に位置する溶接ビードを有する溶接継手であって、溶接スラグ、スパッタ、及び、熱影響部の表面の少なくとも一部に、体積抵抗率が３．００×１０８Ω・ｍ以下である導電塗膜を有し、前記導電塗膜上に、化成皮膜（ただし、前記化成皮膜が、リン酸鉄を含む化成皮膜である場合を除く。）を有する、溶接継手。
（２）前記複数の鋼材の少なくとも一枚の厚みは、２．０ｍｍ以下である、（１）に記載の溶接継手。
（３）前記複数の鋼材の少なくとも一枚のＳｉ含有量は、０．８～１．７質量％である、（１）又は（２）に記載の溶接継手。
（４）前記導電塗膜の体積抵抗率は、１．００×１０６Ω・ｍ以下である、（１）～（３）の何れか１つに記載の溶接継手。
（５）前記導電塗膜の厚みは、１０μｍ以上である、（１）～（４）の何れか１つに記載の溶接継手。
（６）前記導電塗膜の厚みは、２０μｍ以下である、（１）～（５）の何れか１つに記載の溶接継手。
（７）前記導電塗膜は、ポリエステル系ＡｇＣｕ導電塗料からなる、（１）～（６）の何れか１つに記載の溶接継手。
（８）前記導電塗膜は、亜鉛塗料からなる、（１）～（６）の何れか１つに記載の溶接継手。
（９）前記導電塗膜は、前記溶接スラグ、前記スパッタ、及び、前記熱影響部の表面の全体にわたって設けられる、（１）～（８）の何れか１つに記載の溶接継手。
（１０）前記導電塗膜は、前記溶接ビードの表面の全体にわたって設けられる、（１）～（９）の何れか１つに記載の溶接継手。
（１１）前記導電塗膜の表面に、電着塗膜を更に有する、（１）～（１０）の何れか１つに記載の溶接継手。
（１２）前記複数の鋼材と前記導電塗膜との間に、化成皮膜を更に有する、（１）～（１１）の何れか１つに記載の溶接継手。
（１３）前記化成皮膜は、樹脂、シランカップリング剤、ジルコニウム化合物、シリカ、リン酸及びその塩（ただし、リン酸鉄を除く。）、フッ化物、バナジウム化合物、並びに、タンニン又はタンニン酸からなる群より選択される何れか一つ以上を含有する、（１）～（１２）の何れか１つに記載の溶接継手。
（１４）複数の鋼材と、当該複数の鋼材の間に位置する溶接ビードを有する溶接継手の製造方法であって、溶接ワイヤを用いて、前記複数の鋼材を溶接する溶接工程と、溶接によって生じた溶接スラグ、スパッタ、及び、熱影響部の表面の少なくとも一部に、体積抵抗率が３．００×１０８Ω・ｍ以下である導電塗膜を成膜する成膜工程と、前記導電塗膜上に化成皮膜（ただし、前記化成皮膜が、リン酸鉄を含む化成皮膜である場合を除く。）を成膜する化成処理工程と、を有する、溶接継手の製造方法。
（１５）前記成膜工程では、導電塗料への浸漬、又は、刷毛もしくはスプレー噴射による導電塗料の塗布によって、前記導電塗膜が成膜される、（１４）に記載の溶接継手の製造方法。
（１６）前記成膜工程では、非導電性の前記溶接スラグを判別し、当該非導電性の溶接スラグの少なくとも一部に対し導電塗料を塗布することで、前記導電塗膜が製膜される、（１４）又は（１５）に記載の溶接継手の製造方法。
（１７）脱脂工程、表面調整工程、又は、化成処理工程の少なくとも何れかを更に有する、（１４）～（１６）の何れか１つに記載の溶接継手の製造方法。
（１８）（１）～（１３）の何れか１つに記載の溶接継手を有する、自動車部材。
（１９）（１）～（１３）の何れか１つに記載の溶接継手を有する、建材部材。
(1) A welded joint having a plurality of steel materials and a weld bead located between the plurality of steel materials, the welded joint having a conductive coating film having a volume resistivity of 3.00 x 10 8 Ω·m or less on at least a portion of the surface of the welding slag, spatter, and heat-affected zone , and a chemical conversion coating film on the conductive coating film (excluding the case where the chemical conversion coating film is a chemical conversion coating containing iron phosphate).
(2) The welded joint described in (1), in which the thickness of at least one of the plurality of steel materials is 2.0 mm or less.
(3) The welded joint according to (1) or (2), wherein the Si content of at least one of the plurality of steel materials is 0.8 to 1.7 mass%.
(4) The welded joint according to any one of (1) to (3), wherein the conductive coating has a volume resistivity of 1.00×10 6 Ω·m or less.
(5) The welded joint according to any one of (1) to (4), wherein the conductive coating has a thickness of 10 μm or more.
(6) The welded joint according to any one of (1) to (5), wherein the conductive coating has a thickness of 20 μm or less.
(7) The welded joint according to any one of (1) to (6), wherein the conductive coating film is made of a polyester-based AgCu conductive paint.
(8) The welded joint described in any one of (1) to (6), wherein the conductive coating film is made of zinc paint.
(9) The welded joint according to any one of (1) to (8), wherein the conductive coating is provided over the entire surfaces of the welding slag, the spatter, and the heat-affected zone.
(10) The welded joint described in any one of (1) to (9), wherein the conductive coating is provided over the entire surface of the weld bead.
(11) The welded joint according to any one of (1) to (10), further comprising an electrodeposition coating on a surface of the conductive coating.
( 12 ) The welded joint according to any one of (1) to ( 11 ), further comprising a chemical conversion coating between the plurality of steel materials and the conductive coating.
( 13 ) The welded joint according to any one of (1) to (12), wherein the chemical conversion coating contains one or more selected from the group consisting of a resin, a silane coupling agent, a zirconium compound, silica, phosphoric acid and its salts (excluding iron phosphate), a fluoride, a vanadium compound, and tannin or tannic acid.
(14) A method for manufacturing a welded joint having a plurality of steel materials and a weld bead located between the plurality of steel materials, the method comprising: a welding process for welding the plurality of steel materials with a welding wire; a film forming process for forming a conductive coating film having a volume resistivity of 3.00 × 10 8 Ω·m or less on at least a portion of a surface of a welding slag, spatter, and heat-affected zone produced by the welding; and a chemical conversion treatment process for forming a chemical conversion coating film on the conductive coating film (excluding the case where the chemical conversion coating is a chemical conversion coating containing iron phosphate) .
(15) The method for manufacturing a welded joint described in (14), wherein in the film-forming step, the conductive coating film is formed by immersion in a conductive paint or by applying the conductive paint by brushing or spraying.
(16) A method for manufacturing a welded joint as described in (14) or (15), wherein in the film-forming process, the welding slag is identified as non-conductive, and a conductive paint is applied to at least a portion of the non-conductive welding slag to form the conductive coating film.
(17) The method for manufacturing a welded joint according to any one of (14) to (16), further comprising at least one of a degreasing step, a surface conditioning step, or a chemical conversion treatment step.
(18) An automobile component having the welded joint according to any one of (1) to (13).
(19) A building material having the welded joint according to any one of (1) to (13).
以上説明したように本発明によれば、用いる鋼材及び溶接ワイヤの化学組成や溶接条件に依らずに、生産性を大きく損なうことなく、溶接部の電着塗装性を向上させることが可能となる。 As described above, the present invention makes it possible to improve the electrocoatability of welds without significantly impairing productivity, regardless of the chemical composition of the steel and welding wire used or the welding conditions.
以下に、本発明の好適な実施の形態について詳細に説明する。 The following describes in detail a preferred embodiment of the present invention.
（溶接継手について）
本発明の実施形態に係る溶接継手は、上記のように、電着塗装不良の原因となる部位に対して、導電性を示す導電塗膜を設けたものである。かかる溶接継手は、自動車部材、又は、建材部材の素材として、好適に用いることが可能である。
(Regarding welded joints)
As described above, the welded joint according to the embodiment of the present invention is provided with a conductive coating film that exhibits electrical conductivity at a portion that would cause poor electrodeposition coating. Such a welded joint can be suitably used as a material for an automobile component or a building material.
ここで、本実施形態において、「塗膜が導電性を示す」とは、着目する塗膜の電気抵抗率（より詳細には、室温（２０℃）での体積抵抗率）が３．００×１０８Ω・ｍ以下であることを意味している。以下では、特に断りのない限り、記載した体積抵抗率の値は、室温（２０℃）における値とする。 In this embodiment, "the coating film exhibits electrical conductivity" means that the electrical resistivity (more specifically, the volume resistivity at room temperature (20° C.)) of the coating film in question is 3.00× 10 Ω·m or less. In the following, unless otherwise specified, the volume resistivity value described is the value at room temperature (20° C.).
より詳細には、本実施形態に係る溶接継手は、複数の鋼材と、かかる複数の鋼材の間に位置する溶接ビードと、を有するものであり、溶接ビードの表面に位置する溶接スラグ、鋼材表面に飛散したスパッタ、及び、溶接ビード周辺に存在する熱影響部の表面の少なくとも一部に、体積抵抗率が３．００×１０８Ω・ｍ以下である導電塗膜を有している。 More specifically, the welded joint according to this embodiment has a plurality of steel materials and a weld bead located between the plurality of steel materials, and has a conductive coating film having a volume resistivity of 3.00 × 10 Ω·m or less on at least a portion of the surface of the weld bead, on the welding slag located on the surface of the weld bead , on the spatter scattered on the steel material surface, and on the heat-affected zone present around the weld bead.
本実施形態に係る溶接継手は、体積抵抗率（より詳細には、室温（２０℃）での体積抵抗率）が３．００×１０８Ω・ｍ以下という、特定の体積抵抗率を示す導電塗膜を有することで、電着塗装不良の原因となる部位（すなわち、溶接スラグ、スパッタ、熱影響部）に対して、導電性を発現させることできる。その結果、これらの部位に対して電着塗装を施すことが可能となり、用いる鋼材及び溶接ワイヤの化学組成や溶接条件に依らずに、生産性を大きく損なうことなく、溶接部の電着塗装性を向上させ、ひいては塗装後耐食性の向上に寄与することが可能となる。
以下、本実施形態に係る溶接継手を構成する部材について、詳細に説明する。
The welded joint according to this embodiment has a conductive coating film that exhibits a specific volume resistivity (more specifically, volume resistivity at room temperature (20°C)) of 3.00 x 10 8 Ω·m or less, and thus can impart electrical conductivity to areas that cause poor electrodeposition coating (i.e., welding slag, spatter, heat-affected zone). As a result, it becomes possible to apply electrodeposition coating to these areas, and regardless of the chemical composition of the steel material and welding wire used or the welding conditions, it is possible to improve the electrodeposition paintability of the weld without significantly impairing productivity, and ultimately contribute to improving the corrosion resistance after coating.
Hereinafter, the members constituting the welded joint according to this embodiment will be described in detail.
＜鋼材について＞
本実施形態に係る溶接継手は、溶接ワイヤを用いて複数の鋼材を溶接することにより製造される。ここで、溶接継手に用いられる鋼材の化学組成については、特に限定されるものではなく、溶接継手に求められる機械的強度（例えば、引張強度等）に応じて選択すればよく、多量のＳｉを含有するＴＲＩＰ鋼をはじめとする各種の鋼材を利用することが可能である。ただし、Ｓｉ含有量が０．８～１．７質量％である鋼材を用いるときに、本発明は特に有用なものとなる。本発明を用いることで、上記のようなＳｉ含有量を有する鋼材であっても、溶接部の電着塗装性を向上させることが可能となる。なお、本実施形態に係る溶接継手に用いられる鋼材は、母材となる鋼材の表面に、各種の亜鉛系めっきやアルミニウム系めっき等が形成された、めっき鋼材であってもよい。
<About steel materials>
The welded joint according to the present embodiment is manufactured by welding a plurality of steel materials using a welding wire. Here, the chemical composition of the steel material used in the welded joint is not particularly limited, and may be selected according to the mechanical strength (e.g., tensile strength, etc.) required for the welded joint. Various steel materials, including TRIP steel containing a large amount of Si, can be used. However, the present invention is particularly useful when a steel material having a Si content of 0.8 to 1.7 mass% is used. By using the present invention, it is possible to improve the electrodeposition paintability of the welded portion even in the case of a steel material having the above-mentioned Si content. The steel material used in the welded joint according to the present embodiment may be a plated steel material in which various zinc-based plating, aluminum-based plating, etc. are formed on the surface of the base steel material.
また、鋼材の厚みは、特に限定するものではないが、鋼材の厚みが２．０ｍｍ以下であるときに、本発明は特に有用なものとなる。本発明を用いることで、鋼材の厚みが２．０ｍｍ以下であっても、溶接部の電着塗装性を向上させることが可能となる。 The thickness of the steel material is not particularly limited, but the present invention is particularly useful when the thickness of the steel material is 2.0 mm or less. By using the present invention, it is possible to improve the electrocoatability of the welded portion even when the thickness of the steel material is 2.0 mm or less.
＜溶接ビードについて＞
本実施形態に係る溶接継手は、溶接ワイヤを用いて複数の鋼材を溶接することにより製造され、鋼材を溶接した部位には、溶接金属（溶接ビード）が形成される。ここで、溶接ビードとは、鋼材の一部と溶接ワイヤのそれぞれが互いに溶融して混ざり合った結果、形成されたものをいう。ここで、溶接に用いられる溶接ワイヤについては、特に限定されるものではなく、各種の溶接ワイヤを用いることが可能である。ただし、Ｓｉ含有量が０．１～０．９質量％である溶接ワイヤを用いるときに、本発明は特に有用なものとなる。本発明を用いることで、上記のようなＳｉ含有量を有する溶接ワイヤであっても、溶接部の電着塗装性を向上させることが可能となる。
<About weld beads>
The welded joint according to the present embodiment is manufactured by welding a plurality of steel materials using a welding wire, and a weld metal (weld bead) is formed at the portion where the steel materials are welded. Here, the weld bead refers to a bead formed as a result of a part of the steel material and the welding wire melting and mixing with each other. Here, the welding wire used for welding is not particularly limited, and various welding wires can be used. However, the present invention is particularly useful when a welding wire having a Si content of 0.1 to 0.9 mass% is used. By using the present invention, it is possible to improve the electrodeposition paintability of the welded portion even with a welding wire having the above-mentioned Si content.
このような溶接ビードの表面には、溶接スラグが存在し、溶接ビード表面や鋼材表面には、飛散したスパッタが存在する。溶接スラグは、溶接時に生じる金属酸化物であり、電着塗装に必要な導電性が劣る場合が多く、電着塗装不良を生じる。スパッタは、溶接時に生じる溶融金属が鋼材等に飛散し、凝固したものを指す。また、溶接ビードの周囲には、熱影響部（Ｈｅａｔ Ａｆｆｅｃｔｅｄ Ｚｏｎｅ：ＨＡＺ）が形成される。溶接ビード自体は導電性を有し、スパッタ及び熱影響部は、溶接ビードと比べて導電性が劣る。そのために、これらスパッタ、及び、熱影響部は、のちに実施される電着塗装において塗膜の薄膜化を招き、電着塗装性の低下が懸念される。 Welding slag is present on the surface of such weld beads, and scattered spatter is present on the weld bead surface and the steel surface. Welding slag is a metal oxide produced during welding, and often has poor conductivity required for electrocoating, resulting in poor electrocoating. Spatter refers to molten metal produced during welding that is scattered onto steel materials and solidified. In addition, a heat affected zone (HAZ) is formed around the weld bead. The weld bead itself is conductive, while the spatter and heat affected zone have poorer conductivity than the weld bead. As a result, these spatters and heat affected zones cause the coating film to become thinner in the electrocoating that is carried out later, raising concerns about reduced electrocoatability.
なお、溶接スラグ、スパッタ及び熱影響部が存在する位置については、溶接ビードの周囲の外観を撮像装置により撮像し、得られた撮像画像に基づき容易に特定することが可能である。 The locations of welding slag, spatter, and heat-affected zones can be easily identified by capturing an image of the appearance around the weld bead using an imaging device and based on the captured image.
＜導電塗膜について＞
本実施形態に係る溶接継手では、上記のような、溶接スラグ、スパッタ及び熱影響部の表面の少なくとも一部に、体積抵抗率が３．００×１０８Ω・ｍ以下である導電塗膜が設けられている。ここで、導電塗膜の体積抵抗率が３．００×１０８Ω・ｍ超である場合には、のちに実施される電着塗装に求められる導電性を発現させることができず、溶接継手の電着塗装性を向上させることができない。導電塗膜の体積抵抗率が３．００×１０８Ω・ｍ以下となることで、導電性に劣る溶接スラグ、スパッタ及び熱影響部が存在している部位であっても、電着塗装を施すことが可能となる。なお、導電塗膜の体積抵抗率の下限値については、特に規定するものではなく、小さければ小さいほど好ましい。
<About the conductive coating>
In the welded joint according to the present embodiment, a conductive coating film having a volume resistivity of 3.00×10 8 Ω·m or less is provided on at least a part of the surface of the welding slag, spatter, and heat-affected zone as described above. Here, if the volume resistivity of the conductive coating film exceeds 3.00×10 8 Ω·m, the conductivity required for the electrodeposition coating performed later cannot be exhibited, and the electrodeposition coating property of the welded joint cannot be improved. By making the volume resistivity of the conductive coating film 3.00×10 8 Ω·m or less, it becomes possible to apply electrodeposition coating even to a portion where the welding slag, spatter, and heat-affected zone, which have poor electrical conductivity, are present. The lower limit of the volume resistivity of the conductive coating film is not particularly specified, and the smaller the value, the more preferable.
導電塗膜が示す体積抵抗率は、好ましくは１．００×１０６Ω・ｍ以下であり、より好ましくは１．００×１０３Ω・ｍ以下である。導電塗膜が示す体積抵抗率が上記のような範囲内となることで、導電性に劣る溶接スラグ、スパッタ及び熱影響部が存在している部位であっても、電着塗装を十分に施すことが可能な程度の導電性を発現させるため、溶接継手の電着塗装性を、より一層向上させることができる。 The volume resistivity of the conductive coating is preferably 1.00 × 10 Ω·m or less, and more preferably 1.00 × 10 Ω·m or less. When the volume resistivity of the conductive coating falls within the above range, the conductive coating exhibits a level of conductivity that allows sufficient application of electrodeposition coating even in areas where welding slag, spatter, and heat-affected zones with poor electrical conductivity are present, and therefore the electrodeposition coatability of the welded joint can be further improved.
ここで、上記の体積抵抗率は、導電塗膜を形成するための導電塗料が完全に固体となった状態で示す体積抵抗率を意味する。また、導電塗膜の体積抵抗率は、四端子法により測定することができる。より詳細には、中空部を有するシリンダと、シリンダの中空部に上方及び下方から挿入される一対のパンチと、からなる押圧容器を準備し、シリンダの中空部に、秤り取った試料（固体となった状態の導電塗料）を装入する。その後、油圧式ハンドポンプを用いて一対のパンチを押圧していくことで、所定寸法の粉体試料を作製する。その後、得られた粉体試料の体積抵抗率を、四端子法により測定すればよい。 Here, the volume resistivity refers to the volume resistivity of the conductive paint for forming the conductive coating film when it is completely solidified. The volume resistivity of the conductive coating film can be measured by the four-terminal method. More specifically, a pressing vessel is prepared, which is made up of a cylinder with a hollow portion and a pair of punches that are inserted into the hollow portion of the cylinder from above and below, and a weighed sample (conductive paint in a solid state) is placed in the hollow portion of the cylinder. A hydraulic hand pump is then used to press the pair of punches to produce a powder sample of a specified size. The volume resistivity of the obtained powder sample can then be measured by the four-terminal method.
かかる導電塗膜を構成する導電塗料は、上記のような体積抵抗率の値を実現可能なものであれば、バインダー樹脂中に導電性を示す物質の粒子が保持された導電塗料であってもよいし、導電性を示す金属粒子を含む導電塗料であってもよい。このような導電塗料として、例えば、ポリエステル樹脂にＡｇＣｕが保持されたポリエステル系ＡｇＣｕ導電塗料、各種の樹脂にカーボンブラック等が保持されたカーボン系導電塗料、亜鉛系塗料、ニッケル系塗料等を挙げることができる。これらの導電塗料は、有機溶剤系、水系、又は、粉体系等のようないずれの形態でも用いることができる。 The conductive paint constituting such a conductive coating film may be a conductive paint in which particles of a conductive material are held in a binder resin, or a conductive paint containing conductive metal particles, so long as it can achieve the volume resistivity value described above. Examples of such conductive paints include polyester-based AgCu conductive paints in which AgCu is held in a polyester resin, carbon-based conductive paints in which carbon black or the like is held in various resins, zinc-based paints, nickel-based paints, etc. These conductive paints can be used in any form, such as organic solvent-based, water-based, or powder-based.
ここで、導電塗膜を厚み方向に切断した場合の断面において、かかる断面中における導電性を有する塗料成分（すなわち、例えば上記のような導電粒子）が占める面積率は、３０％以上であることが好ましい。また、導電塗膜の均一性を考慮すると、導電塗膜中における上記塗料成分（導電粒子）の含有量は、塗膜固形分の全体に対して、３０体積％以上であるともいえる。断面における塗料成分が占める面積率が３０％以上となることで、３．００×１０８Ω・ｍ以下という体積抵抗率を、より確実に発現させることが可能となる。断面における塗料成分が占める面積率は、より好ましくは５０％以上であり、更に好ましくは７０％である。なお、断面における塗料成分が占める面積率は、高ければ高いほど良いため、その上限値は規定するものではなく、１００％であってもよい。 Here, in a cross section of the conductive coating film cut in the thickness direction, the area ratio of the conductive paint component (i.e., for example, the conductive particles as described above) in the cross section is preferably 30% or more. In addition, in consideration of the uniformity of the conductive coating film, the content of the paint component (conductive particles) in the conductive coating film can be said to be 30% by volume or more with respect to the total solid content of the coating film. By making the area ratio of the paint component in the cross section 30% or more, it is possible to more reliably achieve a volume resistivity of 3.00×10 8 Ω·m or less. The area ratio of the paint component in the cross section is more preferably 50% or more, and even more preferably 70%. Note that the higher the area ratio of the paint component in the cross section, the better, so the upper limit is not specified and may be 100%.
本実施形態に係る溶接継手において、かかる導電塗膜の厚みは、最も薄い箇所においても３μｍ以上であることが好ましい。導電塗膜の厚みが最も薄い箇所においても３μｍ以上となることで、導電塗膜の表面の平坦性を確実に担保することが可能となり、導電塗膜の厚みに均一性を持たせることが可能となる。導電塗膜の厚みは、より好ましくは１０μｍ以上であり、更に好ましくは１２μｍ以上である。 In the welded joint according to this embodiment, the thickness of the conductive coating is preferably 3 μm or more even at its thinnest point. By making the thickness of the conductive coating 3 μm or more even at its thinnest point, it is possible to reliably ensure the flatness of the surface of the conductive coating, and to make the thickness of the conductive coating uniform. The thickness of the conductive coating is more preferably 10 μm or more, and even more preferably 12 μm or more.
本実施形態に係る溶接継手では、かかる導電塗膜の更に上層に、例えば電着塗膜が更に形成されるようになることから、溶接ビードと導電塗膜との間に非常に優れた塗膜密着性が求められるわけではない。しかしながら、導電塗膜の厚みが４０μｍを超える場合には、要するコストの増加が大きくなりすぎるだけでなく、導電塗膜の厚みが厚くなりすぎて、溶接ビードと導電塗膜との間の密着性が低下する可能性がある。そのため、導電塗膜の厚みは、最も厚い箇所においても４０μｍ以下であることが好ましい。導電塗膜の厚みが４０μｍ以下となることで、溶接ビードと導電塗膜との間の密着性を担保しながら、溶接継手の電着塗装性を向上させることができる。導電塗膜の厚みは、より好ましくは２０μｍ以下であり、更に好ましくは１６μｍ以下である。 In the welded joint according to this embodiment, for example, an electrodeposition coating is formed on top of the conductive coating, so excellent coating adhesion between the weld bead and the conductive coating is not required. However, if the thickness of the conductive coating exceeds 40 μm, not only will the cost increase be too large, but the thickness of the conductive coating may become too thick and the adhesion between the weld bead and the conductive coating may decrease. Therefore, it is preferable that the thickness of the conductive coating is 40 μm or less even at the thickest point. By making the thickness of the conductive coating 40 μm or less, it is possible to improve the electrodeposition paintability of the welded joint while ensuring the adhesion between the weld bead and the conductive coating. The thickness of the conductive coating is more preferably 20 μm or less, and even more preferably 16 μm or less.
なお、導電塗膜の厚みは、導電塗膜の断面を、光学顕微鏡を用いて観察することで、測定することが可能である。より詳細には、着目する溶接継手をエポキシ樹脂等の熱硬化性樹脂に埋め込み、精密カッター等の切断機を用いて、観察すべき箇所において厚さ方向と平行となるように試料を切断し、得られた断面を光学顕微鏡で観察する。埋め込み樹脂と導電塗膜との界面上の複数箇所（例えば、５箇所）の任意の位置から、導電塗膜と溶接ビードとの界面までの最短の距離を測定（すなわち界面と垂直方向に距離を測定）し、得られた測定値を平均化する。このようにして得られた導電塗膜の平均厚みを、導電塗膜の厚みとすることができる。 The thickness of the conductive coating can be measured by observing the cross section of the conductive coating with an optical microscope. More specifically, the weld joint of interest is embedded in a thermosetting resin such as epoxy resin, and the sample is cut parallel to the thickness direction at the location to be observed using a cutting machine such as a precision cutter, and the resulting cross section is observed with an optical microscope. The shortest distance from any of a number of positions (e.g., five positions) on the interface between the embedding resin and the conductive coating to the interface between the conductive coating and the weld bead is measured (i.e., the distance is measured perpendicular to the interface), and the measured values obtained are averaged. The average thickness of the conductive coating obtained in this way can be regarded as the thickness of the conductive coating.
また、導電塗膜の断面における塗料成分の占める面積率についても、上記と同様にして顕微鏡観察を行い、断面の画像観察から塗料成分の占める面積を測定する。このような測定を、上記の厚み測定と同様に任意の複数の視野で実施し、得られた測定値の平均を、断面における塗料成分の占める面積率とすればよい。 The area ratio of the paint components in the cross section of the conductive coating is also measured by observing the cross section image using a microscope in the same manner as above. This measurement is performed in multiple fields of view, as in the thickness measurement above, and the average of the obtained measurements is taken as the area ratio of the paint components in the cross section.
上記のような導電塗膜が、溶接スラグ、スパッタ及び熱影響部の表面の少なくとも一部に設けられることで、溶接継手の電着塗装性を向上させることが可能となる。また、上記のような導電塗膜が、溶接スラグ、スパッタ及び熱影響部の表面の全体にわたって設けられることで、より確実に溶接継手の電着塗装性を向上させることが可能となる。更に、上記のような導電塗膜が、溶接スラグ、スパッタ及び熱影響部だけでなく、溶接ビードの全体にわたって設けられることで、より一層確実に溶接継手の電着塗装性を確保することが可能となる。 By providing such a conductive coating film on at least a portion of the surface of the welding slag, spatter, and heat-affected zone, it is possible to improve the electrocoatability of the welded joint. In addition, by providing such a conductive coating film over the entire surface of the welding slag, spatter, and heat-affected zone, it is possible to more reliably improve the electrocoatability of the welded joint. Furthermore, by providing such a conductive coating film over the entire weld bead, not just the welding slag, spatter, and heat-affected zone, it is possible to more reliably ensure the electrocoatability of the welded joint.
また、本実施形態に係る導電塗膜は、上記のような導電性を損なわない範囲内で、各種の添加剤を含有していてもよい。このような添加剤としては、例えば、各種の体質顔料、着色剤、防錆剤等を挙げることができる。 The conductive coating film according to this embodiment may also contain various additives within the range that does not impair the above-mentioned conductivity. Examples of such additives include various extender pigments, colorants, rust inhibitors, etc.
以上、本実施形態に係る導電塗膜が含みうる成分について、塗料組成物を挙げることにより説明した。通常、これらの塗料組成物を所望の箇所に塗布した場合、これら塗料組成物の成分と、形成される皮膜の成分組成とは、異なることがある。例えば、導電塗料として、有機溶剤系又は水系の導電塗料を用いた場合、塗料組成物中の揮発成分の揮発等によって、塗料組成物と塗布した後の導電塗膜との組成は変化し、形成された導電塗膜の組成を特定することは、通常、技術的に困難である。また、そのような導電塗膜の組成を機器分析等によって特定することも、技術的に困難である。それ故、本実施形態においては、塗料組成物に含みうる成分を特定することにより、形成される導電塗膜を特定している。 The components that may be contained in the conductive coating film according to this embodiment have been described above by listing the paint compositions. Usually, when these paint compositions are applied to a desired location, the components of these paint compositions may differ from the component composition of the film that is formed. For example, when an organic solvent-based or water-based conductive paint is used as the conductive paint, the composition of the paint composition and the conductive coating film after application change due to the volatilization of volatile components in the paint composition, and it is usually technically difficult to identify the composition of the conductive coating film that is formed. In addition, it is also technically difficult to identify the composition of such a conductive coating film by instrumental analysis, etc. Therefore, in this embodiment, the conductive coating film that is formed is identified by identifying the components that may be contained in the paint composition.
＜電着塗膜について＞
本実施形態に係る溶接継手において、上記のような導電塗膜の表面には、更に、電着塗膜が設けられることが好ましい。このような電着塗膜が更に設けられることで、溶接継手の耐食性を確保することが可能となる。また、電着塗膜は、上記のような導電塗膜の表面だけではなく、導電塗膜以外の部分（すなわち、鋼材の部分）の表面に対しても設けられることが、より好ましい。
<About electrodeposition coating>
In the welded joint according to the present embodiment, it is preferable that an electrodeposition coating is further provided on the surface of the conductive coating as described above. By providing such an electrodeposition coating, it is possible to ensure the corrosion resistance of the welded joint. It is more preferable that the electrodeposition coating is provided not only on the surface of the conductive coating as described above, but also on the surface of the portion other than the conductive coating (i.e., the steel portion).
ここで、電着塗膜のより詳細な成分については、特に限定されるものではなく、公知の各種の電着塗膜を適宜形成することが可能である。 Here, the detailed components of the electrocoating film are not particularly limited, and various known electrocoating films can be appropriately formed.
＜化成皮膜について＞
本実施形態に係る溶接継手では、上記のような導電塗膜と電着塗膜との間、又は、鋼材と前記導電塗膜との間に、更に化成皮膜が設けられていてもよい。
<About chemical conversion coating>
In the welded joint according to this embodiment, a chemical conversion coating may be further provided between the conductive coating and the electrodeposition coating, or between the steel material and the conductive coating.
本実施形態に係る化成皮膜の詳細な構成については、特に限定されるものではなく、樹脂、シランカップリング剤、ジルコニウム化合物、シリカ、リン酸及びその塩、フッ化物、バナジウム化合物、並びに、タンニン又はタンニン酸からなる群より選択される何れか一つ以上を含有してもよい。これら物質を含有することで、更に、化成処理液塗布後の成膜性、水分や腐食性イオン等の腐食因子に対する皮膜のバリア性（緻密性）、及び、皮膜密着性などが向上し、皮膜の耐食性の底上げに寄与する。 The detailed composition of the chemical conversion coating according to this embodiment is not particularly limited, and may contain one or more selected from the group consisting of resin, silane coupling agent, zirconium compound, silica, phosphoric acid and its salts, fluoride, vanadium compound, and tannin or tannic acid. The inclusion of these substances further improves the film-forming properties after application of the chemical conversion treatment solution, the barrier properties (density) of the coating against corrosive factors such as moisture and corrosive ions, and the coating adhesion, thereby contributing to raising the corrosion resistance of the coating.
上記のような各種の成分を含有する化成処理剤は、鋼材又は導電塗膜の表面に塗布されたのち、乾燥されて化成皮膜を形成する。本実施形態に係る溶接継手では、片面あたり１０～１０００ｍｇ／ｍ２の化成皮膜を溶接継手上に形成することが好ましい。化成皮膜の付着量は、より好ましくは２０～８００ｍｇ／ｍ２であり、最も好ましくは５０～６００ｍｇ／ｍ２である。 The chemical conversion treatment agent containing the various components as described above is applied to the surface of the steel material or the conductive coating, and then dried to form a chemical conversion coating. In the welded joint according to this embodiment, it is preferable to form a chemical conversion coating of 10 to 1000 mg/ m2 per side on the welded joint. The deposition amount of the chemical conversion coating is more preferably 20 to 800 mg/ m2 , and most preferably 50 to 600 mg/ m2 .
以上、本実施形態に係る溶接継手について、詳細に説明した。 The above describes the welded joint according to this embodiment in detail.
以上説明したような溶接継手を用いることで、上記のような溶接継手を有する自動車部材や、建材部材を製造することが可能となる。 By using the welded joints described above, it is possible to manufacture automotive components and building materials that have welded joints such as those described above.
（溶接継手の製造方法について）
次に、本実施形態に係る溶接継手の製造方法を説明する。
かかる製造方法は、複数の鋼材と、かかる複数の鋼材の間に位置する溶接ビードと、を有する溶接継手の製造方法であって、溶接ワイヤを用いて、複数の鋼材を溶接する溶接工程と、溶接によって生じた溶接スラグ、スパッタ、及び、熱影響部の表面の少なくとも一部に、体積抵抗率が３．００×１０８Ω・ｍ以下である導電塗膜を成膜する成膜工程と、を有する。
(Regarding manufacturing methods for welded joints)
Next, a method for manufacturing a welded joint according to this embodiment will be described.
This manufacturing method is a method for manufacturing a welded joint having a plurality of steel materials and a weld bead located between the plurality of steel materials, and includes a welding process of welding the plurality of steel materials using a welding wire, and a film forming process of forming a conductive coating film having a volume resistivity of 3.00 × 10 8 Ω·m or less on at least a portion of the surface of the welding slag, spatter, and heat-affected zone produced by the welding.
ここで、溶接工程については、特に限定されるものではなく、アーク溶接、レーザ溶接、電子ビーム溶接、プラズマアーク溶接等の公知の各種の溶接方法を、適宜利用することが可能である。また、かかる溶接を行う際の溶接条件についても特に限定されるものではなく、適切な溶接条件を採用すればよい。例えば、以下のような溶接条件で溶接を行うことで、複数の鋼材を確実に溶接することが可能となる。
溶接法：パルスＭＡＧ溶接、溶接電流：１６０Ａ、溶接電圧：２２．４Ｖ、溶接速度：１００ｃｍ／ｍｉｎ、シールドガス種：８０％Ａｒ＋２０％ＣＯ２、流量：２０Ｌ／ｍｉｎ、溶接トーチ前進角・後進角：０°、溶接トーチ傾斜角：６０°、ワイヤ突き出し長さ：１５ｍｍ
Here, the welding process is not particularly limited, and various known welding methods such as arc welding, laser welding, electron beam welding, plasma arc welding, etc. can be used as appropriate. The welding conditions when performing such welding are also not particularly limited, and appropriate welding conditions may be adopted. For example, by performing welding under the following welding conditions, it is possible to reliably weld multiple steel materials.
Welding method: pulse MAG welding, welding current: 160 A, welding voltage: 22.4 V, welding speed: 100 cm/min, shielding gas type: 80% Ar + 20% CO 2 , flow rate: 20 L/min, welding torch advance angle/reverse angle: 0°, welding torch tilt angle: 60°, wire extension length: 15 mm
成膜工程は、溶接によって生じた溶接スラグ、スパッタ、及び、熱影響部の表面の少なくとも一部に、体積抵抗率が３．００×１０８Ω・ｍ以下である導電塗膜を成膜する工程である。 The film forming step is a step of forming a conductive coating film having a volume resistivity of 3.00×10 8 Ω·m or less on at least a part of the surface of the welding slag, spatter, and heat-affected zone produced by welding.
ここで、導電塗膜を形成するために用いられる導電塗料については、上記の通りであるため、以下では詳細な説明は省略する。 The conductive paint used to form the conductive coating film is as described above, so a detailed explanation will be omitted below.
かかる成膜工程では、導電塗料への浸漬、又は、刷毛もしくはスプレー噴射による導電塗料の塗布によって、上記のような導電塗膜が成膜されることが好ましい。また、塗布する導電塗料の量については、乾燥後の導電塗膜の厚みが上記のような厚みとなるように、適宜調整することが好ましい。 In this film-forming process, it is preferable that the above-mentioned conductive coating film is formed by immersion in the conductive paint or by applying the conductive paint with a brush or spray. It is also preferable that the amount of conductive paint applied is appropriately adjusted so that the thickness of the conductive coating film after drying is as described above.
導電塗料を塗布する部位については、溶接スラグ、スパッタ及び熱影響部の表面の少なくとも一部とする。また、先だって言及したように、溶接スラグ、スパッタ及び熱影響部の表面の全体にわたって導電塗料を塗布することが好ましく、上記の部分だけでなく、溶接ビードの表面の全体にわたって導電塗料を塗布することがより好ましい。 The areas to which the conductive paint is applied are at least a portion of the surfaces of the welding slag, spatter, and heat-affected zone. As mentioned above, it is preferable to apply the conductive paint over the entire surfaces of the welding slag, spatter, and heat-affected zone, and it is even more preferable to apply the conductive paint over the entire surface of the weld bead, not just the above-mentioned areas.
また、導電塗料の塗布に際して、非導電性の溶接スラグを判別し、非導電性の溶接スラグの少なくとも一部に対して、導電塗料を塗布するようにしてもよい。このようにして塗布を行うことで、導電塗料を効率良く用いることが可能となり、導電塗膜の成膜に要するコストを削減することができる。非導電性の溶接スラグは、公知の方法により判別することができ、例えば国際公開第２０１７／１２６６５７号に開示される評価方法を適用することができる。 When applying the conductive paint, non-conductive welding slag may be identified, and the conductive paint may be applied to at least a portion of the non-conductive welding slag. By applying the paint in this manner, the conductive paint can be used efficiently, and the cost required for forming the conductive coating film can be reduced. Non-conductive welding slag can be identified by a known method, and for example, the evaluation method disclosed in International Publication No. 2017/126657 can be applied.
また、本実施形態に係る溶接継手の製造方法では、上記の溶接工程及び成膜工程に加えて、脱脂工程、表面調整工程、又は、化成処理工程の少なくとも何れかを更に有してもよい。これらの工程の少なくとも何れかを更に有することで、製造される溶接継手の製品特性を、より向上させることが可能となる。脱脂工程とは、溶接時に生じるヒュームや油脂汚れ等を除去する工程である。表面調整工程とは、鋼材表面に化成被膜結晶の核生成を促進させ、良好な化成被膜の形成を促す工程である。化成処理工程とは、特定の条件で調整した化成処理液に鋼材を浸漬することで、鋼材表面での化学反応を促し、鋼材表面に不溶性の生成物を形成させ、防錆能と密着性に優れた塗装下地を整える工程である。 In addition, in the manufacturing method of the welded joint according to this embodiment, in addition to the above-mentioned welding process and film formation process, at least one of a degreasing process, a surface conditioning process, and a chemical conversion treatment process may be further included. By further including at least one of these processes, it is possible to further improve the product characteristics of the welded joint to be manufactured. The degreasing process is a process for removing fumes and oily stains generated during welding. The surface conditioning process is a process for promoting the nucleation of chemical conversion coating crystals on the steel surface and facilitating the formation of a good chemical conversion coating. The chemical conversion treatment process is a process for promoting a chemical reaction on the steel surface by immersing the steel in a chemical conversion treatment solution prepared under specific conditions, forming an insoluble product on the steel surface, and preparing a paint base with excellent rust prevention and adhesion.
以上、本実施形態に係る溶接継手の製造方法について、説明した。 The above describes the manufacturing method for the welded joint according to this embodiment.
以上説明したように、本発明の実施形態によれば、溶接ビード表面の非導電性スラグを無害化することが可能であり、溶接部の電着塗装性が改善し、電着塗装性が優れる溶接継手の作製が可能となる。また、溶接部の電着塗装性が改善されることで、自動車部材や建材部材の塗装後耐食性の向上が見込まれる。これら効果によって、自動車部材及び建材部材の塗装後耐食性を一層向上させ、自動車の軽量化や建材の高寿命化を促進させる技術であることから、産業上の貢献は多大なものである。 As described above, according to the embodiment of the present invention, it is possible to render non-conductive slag on the surface of the weld bead harmless, improve the electrodeposition paintability of the weld, and make it possible to produce a welded joint with excellent electrodeposition paintability. Furthermore, by improving the electrodeposition paintability of the weld, it is expected that the post-painting corrosion resistance of automotive and building materials will be improved. These effects further improve the post-painting corrosion resistance of automotive and building materials, and the technology promotes weight reduction of automobiles and longer life of building materials, making a significant contribution to industry.
以下では、実施例及び比較例を示しながら、本発明に係る溶接継手及び溶接継手の製造方法について、具体的に説明する。なお、以下に示す実施例は、本発明に係る溶接継手及び溶接継手の製造方法の一例にすぎず、本発明に係る溶接継手及び溶接継手の製造方法が下記の例に限定されるものではない。 Below, the welded joint and the method for manufacturing a welded joint according to the present invention will be specifically described while showing examples and comparative examples. Note that the examples shown below are merely examples of the welded joint and the method for manufacturing a welded joint according to the present invention, and the welded joint and the method for manufacturing a welded joint according to the present invention are not limited to the examples below.
以下では、以下の表１に示す化学成分を有する鋼板及び溶接ワイヤを用いて、溶接継手の供試材を製造した。以下の表１において、成分の単位は質量％であり、残部は、Ｆｅ及び不純物である。また、鋼板は、日本製鉄株式会社製の厚み１．６ｍｍのものであり、溶接ワイヤは、日本製鉄株式会社製のワイヤ径１．２ｍｍのものである。 Below, welded joint test materials were manufactured using steel plates and welding wires having the chemical compositions shown in Table 1 below. In Table 1 below, the units of components are mass %, and the remainder is Fe and impurities. The steel plates are manufactured by Nippon Steel Corporation and have a thickness of 1.6 mm, and the welding wires are manufactured by Nippon Steel Corporation and have a wire diameter of 1.2 mm.
上記の鋼板及び溶接ワイヤを用いて、溶接により重ね隅肉溶接継手を製造した。溶接条件は、以下の通りである。
溶接法：パルスＭＡＧ溶接、溶接電流：１６０Ａ、溶接電圧：２２．４Ｖ、溶接速度：１００ｃｍ／ｍｉｎ、シールドガス種：８０％Ａｒ＋２０％ＣＯ２、流量：２０Ｌ／ｍｉｎ、溶接トーチ前進角・後進角：０°、溶接トーチ傾斜角：６０°、ワイヤ突き出し長さ：１５ｍｍ
Using the above steel plates and welding wire, lap fillet welded joints were produced by welding under the following welding conditions.
Welding method: pulse MAG welding, welding current: 160 A, welding voltage: 22.4 V, welding speed: 100 cm/min, shielding gas type: 80% Ar + 20% CO 2 , flow rate: 20 L/min, welding torch advance angle/reverse angle: 0°, welding torch tilt angle: 60°, wire extension length: 15 mm
得られた各溶接継手に対して、以下の表２に示した導電塗料Ａ～Ｅを用いて、導電塗膜を形成した。導電塗膜を形成した部位は、以下の表２において、「〇」印で示しており、「〇」印を付した部位の全体にわたって、スプレー噴霧及び刷毛による塗布で導電塗膜を塗布した。また、用いた導電塗料Ａ～Ｅの詳細は、以下の通りである。 A conductive coating was formed on each of the obtained welded joints using conductive paints A to E shown in Table 2 below. The areas where the conductive coating was formed are indicated with an "O" mark in Table 2 below, and the conductive coating was applied by spraying and brushing over the entire area marked with an "O". Details of the conductive paints A to E used are as follows:
塗料Ａ：ポリエステル系ＡｇＣｕ導電塗料、プラスコート株式会社製、ポリカーム導電塗料タッチアップペン
塗料Ｂ：亜鉛塗料、株式会社イチネンケミカルズ製、スポットジンク
塗料Ｃ：ニッケル塗料、プラスコート株式会社製、ポリカームＰＣＳ－１０４ｎ Ｎｉ
塗料Ｄ：カーボン塗料、プラスコート株式会社製、ポリカーム水溶性導電塗料タッチアップペン黒
塗料Ｅ：シリコーン樹脂塗料、信越化学工業株式会社製、一液縮合型ＲＴＶゴムＫＥ－４４
Paint A: Polyester-based AgCu conductive paint, manufactured by Plus Coat Co., Ltd., Polycarm conductive paint touch-up pen Paint B: Zinc paint, manufactured by Ichinen Chemicals Co., Ltd., Spot Zinc Paint C: Nickel paint, manufactured by Plus Coat Co., Ltd., Polycarm PCS-104n Ni
Paint D: Carbon paint, manufactured by Pluscoat Co., Ltd., Polycarm water-soluble conductive paint touch-up pen black Paint E: Silicone resin paint, manufactured by Shin-Etsu Chemical Co., Ltd., one-component condensation type RTV rubber KE-44
また、各供試材に対しては、脱脂時はファインクリーナーＥ２０８３（日本パーカーライジング株式会社製）を用い、表面調整時はプレパランＸ系 ＰＬ－Ｘ（日本パーカーライジング株式会社製）を用いた。化成処理液にはパルボンド３０５４ ＰＢ３０５４（日本パーカーライジング株式会社製）を用いて、溶接ビード、スパッタ及び熱影響部が形成される部位に化成被膜を形成した。その後、電着塗料は、パワーフロート５１０（日本ペイント株式会社製）を用い、電着塗膜を形成した。 Fine Cleaner E2083 (manufactured by Nippon Parkerizing Co., Ltd.) was used for degreasing each test material, and Preparelan X PL-X (manufactured by Nippon Parkerizing Co., Ltd.) was used for surface preparation. Palbond 3054 PB3054 (manufactured by Nippon Parkerizing Co., Ltd.) was used as the chemical conversion treatment solution to form a chemical conversion coating on the areas where the weld beads, spatter and heat-affected zones would be formed. After that, Power Float 510 (manufactured by Nippon Paint Co., Ltd.) was used as the electrocoating paint to form an electrocoating film.
得られた各供試材について、光学顕微鏡を用いた上記の方法により、任意の５視野について、導電塗膜の厚み及び塗膜成分の占める割合を測定し、得られた平均値を、導電塗膜の厚み及び塗膜成分の占める割合として、以下の表２に記載した。 For each of the test materials obtained, the thickness of the conductive coating and the proportion of the coating components were measured for any five visual fields using the above-mentioned method with an optical microscope, and the average values obtained are shown in Table 2 below as the thickness of the conductive coating and the proportion of the coating components.
電着塗装性は、溶接ビード表面の投影面積に対する電着塗装不良の投影面積の割合を、塗装不良面積率として算出した。評価基準は、以下の通りである。評点Ａ～Ｃを合格とした。得られた結果を、以下の表２にまとめて示した。
Ａ：塗装不良面積率０％
Ｂ：塗装不良面積率０％超３％以下
Ｃ：塗装不良面積率３％超５％以下
Ｄ：塗装不良面積率５％超
The electrodeposition paintability was calculated as the ratio of the projected area of the electrodeposition paint defect to the projected area of the weld bead surface, which was defined as the paint defect area rate. The evaluation criteria were as follows. Scores A to C were considered to be acceptable. The results are summarized in Table 2 below.
A: Paint defect area rate 0%
B: Painting defective area rate of more than 0% and 3% or less C: Painting defective area rate of more than 3% and 5% or less D: Painting defective area rate of more than 5%
上記表２から明らかなように、本発明の実施例に該当する溶接継手は、優れた電着塗装性を示す一方で、本発明の比較例に該当する溶接継手は、電着塗装性が不合格であることがわかる。 As is clear from Table 2 above, the welded joints corresponding to the examples of the present invention exhibit excellent electrocoatability, while the welded joints corresponding to the comparative examples of the present invention exhibit unsatisfactory electrocoatability.
以上、本発明の好適な実施形態について詳細に説明したが、本発明はかかる例に限定されない。本発明の属する技術の分野における通常の知識を有する者であれば、特許請求の範囲に記載された技術的思想の範疇内において、各種の変更例又は修正例に想到し得ることは明らかであり、これらについても、当然に本発明の技術的範囲に属するものと了解される。 Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to such examples. It is clear that a person with ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or revised examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.
Claims (19)
溶接スラグ、スパッタ、及び、熱影響部の表面の少なくとも一部に、体積抵抗率が３．００×１０８Ω・ｍ以下である導電塗膜を有し、
前記導電塗膜上に、化成皮膜（ただし、前記化成皮膜が、リン酸鉄を含む化成皮膜である場合を除く。）を有する、溶接継手。 A welded joint having a plurality of steel materials and a weld bead located between the plurality of steel materials,
a conductive coating film having a volume resistivity of 3.00×10 8 Ω·m or less is provided on at least a portion of the surface of the welding slag, the spatter, and the heat-affected zone;
A welded joint having a chemical conversion coating on the conductive coating (excluding the case where the chemical conversion coating is a chemical conversion coating containing iron phosphate) .
溶接ワイヤを用いて、前記複数の鋼材を溶接する溶接工程と、
溶接によって生じた溶接スラグ、スパッタ、及び、熱影響部の表面の少なくとも一部に、体積抵抗率が３．００×１０８Ω・ｍ以下である導電塗膜を成膜する成膜工程と、
前記導電塗膜上に化成皮膜（ただし、前記化成皮膜が、リン酸鉄を含む化成皮膜である場合を除く。）を成膜する化成処理工程と、
を有する、溶接継手の製造方法。 A method for manufacturing a welded joint having a plurality of steel materials and a weld bead located between the plurality of steel materials,
a welding step of welding the plurality of steel materials together using a welding wire;
a film forming step of forming a conductive coating film having a volume resistivity of 3.00×10 8 Ω·m or less on at least a part of the surface of the welding slag, spatter, and heat-affected zone produced by welding;
a chemical conversion treatment step of forming a chemical conversion coating on the conductive coating (excluding cases where the chemical conversion coating is a chemical conversion coating containing iron phosphate);
A method for manufacturing a welded joint comprising the steps of:
A building material member having the welded joint according to any one of claims 1 to 13.
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| JP2020126040A (en) | 2019-02-04 | 2020-08-20 | 日本製鉄株式会社 | Slag determination method, slag determination device, and welded joint manufacturing method |
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| JPS5391945A (en) * | 1977-01-24 | 1978-08-12 | Kansai Paint Co Ltd | Coating method |
| JPS58193395A (en) * | 1982-05-07 | 1983-11-11 | Nippon Oil & Fats Co Ltd | Formation of anticorrosive coating |
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| JP2001291947A (en) | 2000-04-04 | 2001-10-19 | Mec Kk | Solder coating method of conductive paste |
| JP2008051930A (en) | 2006-08-23 | 2008-03-06 | Bridgestone Corp | Method of manufacturing filter for display panel |
| JP2011206842A (en) | 2010-03-30 | 2011-10-20 | Nisshin Steel Co Ltd | Automobile chassis member having excellent corrosion resistance, and method for manufacturing the same |
| JP2020126040A (en) | 2019-02-04 | 2020-08-20 | 日本製鉄株式会社 | Slag determination method, slag determination device, and welded joint manufacturing method |
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