JP2012162762A - Chemical conversion treatment method of steel member, method for manufacturing coated steel member having electrodeposition coating and coated steel member - Google Patents
Chemical conversion treatment method of steel member, method for manufacturing coated steel member having electrodeposition coating and coated steel member Download PDFInfo
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- PIEMIPFEDUYGMC-UHFFFAOYSA-N P(=O)(=O)[Zn] Chemical compound P(=O)(=O)[Zn] PIEMIPFEDUYGMC-UHFFFAOYSA-N 0.000 description 1
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- GFQYVLUOOAAOGM-UHFFFAOYSA-N zirconium(iv) silicate Chemical compound [Zr+4].[O-][Si]([O-])([O-])[O-] GFQYVLUOOAAOGM-UHFFFAOYSA-N 0.000 description 1
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- Arc Welding In General (AREA)
- Chemical Treatment Of Metals (AREA)
Abstract
Description
本発明は、自動車の足回り部材等に好適な、鋼板同士を溶接接合して更に化成処理、電着塗装を施されてなる鋼製塗装部材に係り、特に溶接部の耐食性向上のための化成処理方法に関する。 The present invention relates to a steel coating member suitable for an automobile undercarriage member and the like, which is obtained by welding and joining steel plates to each other and further subjected to chemical conversion treatment and electrodeposition coating, and in particular, to improve the corrosion resistance of a welded portion. It relates to the processing method.
自動車や建築、電気機器などの分野では、炭素鋼を接合するために、一般にはArに20％程度のCO2を混合させたシールドガス中で溶接を行う消耗電極式のアーク溶接が用いられる。更に、これら炭素鋼を接合して得られる部材は、耐食性を確保するため、溶接の後、引き続き電着塗装されることが多い。しかしながら、電着塗装を施しているにもかかわらず、使用が長期間にわたる場合や、厳しい腐食環境に晒される場合に、溶接部を起点として腐食が発生するという課題がある。 In the fields of automobiles, architecture, electrical equipment, and the like, consumable electrode type arc welding is generally used for joining carbon steel, in which welding is performed in a shielding gas in which about 20% of CO 2 is mixed with Ar. Further, members obtained by joining these carbon steels are often electrodeposited continuously after welding in order to ensure corrosion resistance. However, there is a problem that corrosion occurs starting from the welded part when the electrode is used for a long period of time or is exposed to a severe corrosive environment, even though the electrodeposition coating is applied.
この塗装後の腐食は、溶接部、すなわち溶接ビード直上および溶接ビード止端部等のビード部や溶接熱影響部（溶接ビード部裏側を含む）から発生し、経時に伴い溶接部とその周辺を含む広い範囲で塗膜膨れを生じながら深く腐食が進む傾向がある。このようにして腐食が進行すると、溶接部と溶接部近傍の肉厚が減少して強度が低下する。そのため、使用中に特に溶接部が荷重を受けるような部材、例えば自動車の足回り部材では、強度不足によって部材そのものが破壊する可能性もある。 This corrosion after painting occurs from the welded part, that is, the bead part directly above the weld bead and the weld bead toe, and the heat affected zone (including the back side of the weld bead part). There is a tendency for corrosion to proceed deeply while causing blistering over a wide range. When corrosion progresses in this way, the thickness of the welded portion and the vicinity of the welded portion is reduced and the strength is lowered. For this reason, particularly in a member in which a welded part receives a load during use, for example, an underbody member of an automobile, the member itself may be broken due to insufficient strength.
自動車部材の中でも特に自動車の足回り部材（例えば、ロアアーム等）は、強度や耐食性を確保する目的で比較的厚肉とされていることから、自動車の足回り部材の高強度薄肉化は、自動車車体の大幅な軽量化につながり、自動車燃費向上に極めて有効である。そのため、自動車の足回り部材には、薄板の高強度鋼板がその素材として適用されつつある。高強度鋼板を用いて自動車の足回り部材等を製造するに際しては、通常、高強度鋼板を加工、溶接によって所望の形状に成形したのち、耐食性を付与する目的で電着塗装が施される。 Among automobile members, in particular, automobile underbody members (for example, lower arms) are relatively thick for the purpose of ensuring strength and corrosion resistance. This leads to a significant weight reduction of the car body and is extremely effective for improving the fuel efficiency of automobiles. Therefore, a thin high-strength steel plate is being applied as a material for an underbody member of an automobile. When manufacturing an automobile undercarriage member or the like using a high-strength steel plate, usually, the high-strength steel plate is processed and formed into a desired shape by welding, followed by electrodeposition coating for the purpose of imparting corrosion resistance.
また、電着塗装を施すに際しては、その前処理としてリン酸亜鉛処理に代表される化成処理が施される。この化成処理は、基材となる鋼板と電着塗装によって形成される塗膜との密着性を向上させる目的で為される処理である。例えばリン酸亜鉛処理の場合には、基材となる鋼板および溶接部の表面にリン酸亜鉛結晶を成長させることにより、基材と塗膜との密着性を向上させている。しかしながら、このような措置が採られているにもかかわらず、経時に伴い溶接部およびその近傍で腐食がたびたび観測される。 Moreover, when performing electrodeposition coating, the chemical conversion treatment represented by the zinc phosphate process is given as the pretreatment. This chemical conversion treatment is performed for the purpose of improving the adhesion between the steel sheet as the base material and the coating film formed by electrodeposition coating. For example, in the case of the zinc phosphate treatment, the adhesion between the base material and the coating film is improved by growing zinc phosphate crystals on the surface of the steel plate and the welded portion as the base material. However, despite such measures being taken, corrosion is frequently observed at and near the welds over time.
以上のように、溶接部およびその近傍の耐食性向上は常に重要な課題とされている。ここで、係る課題を解決すべく、自動車用部材等の部材を形成する基材として亜鉛系めっき鋼板が用いられる場合がある。しかしながら、亜鉛系めっき鋼板を加工、溶接によって所望の形状に形成する際、溶接時の加熱により溶接部近傍の亜鉛めっきが局部的に蒸発してしまう。そのため、非めっき材に比較すると耐食性向上の効果は認められるものの、その効果は限定的である。 As described above, improvement of corrosion resistance in the welded part and its vicinity is always an important issue. Here, in order to solve the problem, a galvanized steel sheet may be used as a base material for forming a member such as a member for an automobile. However, when the galvanized steel sheet is processed and formed into a desired shape by welding, the galvanization in the vicinity of the welded portion is locally evaporated by heating during welding. Therefore, although the effect of improving corrosion resistance is recognized as compared with the non-plated material, the effect is limited.
溶接部およびその近傍に見られる腐食に関する課題に対しては、従来検討がなされており、その主な要因は(1)溶接部の主に溶接ビード上に付着したスラグ、(2)溶接部に付着した溶接ヒューム、(3)溶接部の表面酸化、が挙げられる。
上記(1)〜(3)のように、スラグや溶接ヒュームが付着したり表面酸化が生じた部材に化成処理を施しても、図６（ａ）に示すように、溶接ビード上や溶接ビード止端部近傍（溶接ビード止端部から約4mm以内）において、化成処理層が形成されない領域が残る。このようにして化成処理層が形成されない領域では、電着塗装時に塗膜の付き回りが不十分となったり、形成される塗膜の密着性を十分に確保することができないため、耐食性が著しく低下し、腐食の発生・進行に伴い部材の肉厚が減少する。
The problems related to corrosion observed in and around the weld have been studied in the past.The main factors are (1) the slag that adheres mainly to the weld bead and (2) the weld. Adhering welding fume and (3) surface oxidation of the welded portion.
As shown in FIG. 6 (a), as shown in FIG. 6 (a), even if chemical conversion treatment is applied to a member to which slag or welding fumes have adhered or surface oxidation has occurred, as shown in FIG. In the vicinity of the toe portion (within about 4 mm from the weld bead toe portion), an area where the chemical conversion treatment layer is not formed remains. Thus, in the region where the chemical conversion treatment layer is not formed, the adhesion of the coating film becomes insufficient at the time of electrodeposition coating, or the adhesion of the formed coating film cannot be ensured sufficiently, so that the corrosion resistance is remarkably high. The thickness of the member decreases with the occurrence and progression of corrosion.
上記した問題を解決するために、例えば特許文献１には、アーク溶接後に電着塗装される構造体のアーク溶接部及びその近傍の塗装後耐食性を改善する技術に関し、電着塗装前のアーク溶接部及びその近傍に、pHが2以下で液温が30℃以上90℃以下の非酸化性の酸を用いたスプレー処理もしくは浸漬処理を施す技術が提案されている。そして、係る技術によると、構造物を形成する母材や溶接ビードを、上記した特定の酸性溶液で溶解することにより、母材表面や溶接ビード表面のスラグを除去することが可能とされている。また、溶接ヒュームや溶接熱影響部等の母材表面における表面酸化に起因して生じた酸化物を、上記した特定の酸性溶液で溶解除去することが可能とされている。 In order to solve the above-mentioned problem, for example, Patent Document 1 relates to a technique for improving the post-painting corrosion resistance of an arc welded portion of a structure to be electrodeposited after arc welding and the vicinity thereof, and arc welding before electrodeposition coating. A technique has been proposed in which a spray treatment or a dipping treatment using a non-oxidizing acid having a pH of 2 or less and a liquid temperature of 30 ° C. or more and 90 ° C. or less is provided in and around the portion. And according to such a technique, it is possible to remove the slag on the surface of the base material and the surface of the weld bead by dissolving the base material and the weld bead forming the structure with the specific acidic solution described above. . In addition, it is possible to dissolve and remove oxides generated due to surface oxidation on the surface of the base material such as welding fume and welding heat affected zone with the above-mentioned specific acidic solution.
また、特許文献２には、耐食性向上のために溶接後に電着塗装されることを前提とした炭素鋼のガスシールドメタルアーク溶接に関し、シールドガス中の酸化性ガス（CO2，O2）の量を低減する技術が提案されている。そして、係る技術によると、スラグの発生が抑制されて電着塗装性が向上すると同時に、熱影響部での酸化が抑えられると共に溶接ヒューム付着が抑えられて、溶接部およびその近傍の塗装後の耐食性が改善するとされている。 In addition, Patent Document 2 relates to gas shield metal arc welding of carbon steel on the premise that electrodeposition is applied after welding to improve corrosion resistance, and the oxidation gas (CO 2 , O 2 ) in the shield gas. Techniques for reducing the amount have been proposed. And, according to such technology, the generation of slag is suppressed and electrodeposition coating properties are improved, and at the same time, oxidation in the heat-affected zone is suppressed and adhesion of welding fume is suppressed, and the welded portion and its vicinity are coated. Corrosion resistance is said to improve.
さらに、特許文献３には、耐食性向上のために溶接後に電着塗装されることを前提とした炭素鋼のガスシールドメタルアーク溶接に関し、母材と溶接ワイヤに含まれる合計Si量および合計Mn量を低減する技術が提案されている。そして、係る技術によると、スラグを構成するSiおよびMnの含有量が低減される結果、スラグの発生が抑制されて塗装後の耐食性が改善するとされている。 Further, Patent Document 3 relates to gas shield metal arc welding of carbon steel on the premise that electrodeposition is applied after welding to improve corrosion resistance, and the total amount of Si and the total amount of Mn contained in the base material and the welding wire. A technique for reducing the above has been proposed. And according to the technique concerned, as a result of reducing content of Si and Mn which comprise slag, generation | occurrence | production of slag is suppressed and it is supposed that the corrosion resistance after coating will be improved.
しかしながら、前述の従来技術には以下のような問題点がある。
特許文献１で提案された技術では、アーク溶接部及びその近傍に、特定の酸性溶液を用いたスプレー処理もしくは浸漬処理を施しているが、塗装工程前に上記酸性溶液を洗浄することが必要となり、構造体や部材の製造工程が煩雑となる。また、鋼板を加工、溶接して所望の形状に成形された部材は、複雑多様な形状である。そのため、上記洗浄時、酸性溶液が十分に洗浄しきれずに部材の隙間に酸性溶液が滞留する場合があり、激しい腐食を誘発してしまうことがある。さらに、酸性溶液を使用するため、製造設備そのものが腐食環境に晒されることになり、設備が腐食してしまうことや、廃液や酸性溶液のヒュームなどが発生するため環境負荷が大きいことも、大きな問題となる。
However, the above-described prior art has the following problems.
In the technique proposed in Patent Document 1, spray treatment or immersion treatment using a specific acidic solution is performed on the arc welded portion and the vicinity thereof, but it is necessary to clean the acidic solution before the coating process. In addition, the manufacturing process of the structure or member becomes complicated. Moreover, the member shape | molded in the desired shape by processing and welding a steel plate is a complicated and various shape. Therefore, at the time of the above cleaning, the acidic solution may not be sufficiently cleaned and the acidic solution may remain in the gaps between the members, which may cause severe corrosion. In addition, since an acidic solution is used, the manufacturing equipment itself is exposed to a corrosive environment, and the equipment is corroded, and wastes and fumes of acidic solution are generated, resulting in a large environmental load. It becomes a problem.
また、特許文献２で提案された技術のように、溶接シールドガス中の酸化性ガス（CO2，O2）の量を低減する場合、スラグが形成されず耐食性が良好になる傾向が認められるが、CO2ガスを低減することで溶接アークが不安定になり、溶接ビード溶け込み不良が発生する場合がある。このようなビード欠陥は鋼構造体の強度低下に繋がるため、特許文献２で提案された技術を、自動車部材のように複雑な形状を有する部材に対して適用することは困難である。 Further, as in the technique proposed in Patent Document 2, when the amount of oxidizing gas (CO 2 , O 2 ) in the welding shield gas is reduced, there is a tendency that slag is not formed and the corrosion resistance tends to be good. However, reducing the CO 2 gas may cause the welding arc to become unstable, resulting in poor weld bead penetration. Since such a bead defect leads to a reduction in strength of the steel structure, it is difficult to apply the technique proposed in Patent Document 2 to a member having a complicated shape such as an automobile member.
また、特許文献３で提案された技術のように、母材と溶接ワイヤの組成を制限し、スラグの原因となるSi量やMn量を低減すれば、溶接部およびその近傍の塗装後の耐食性改善が期待できる。しかしながら、SiやMnは、鋼板強度の向上に極めて有効な元素であり、近年、自動車の軽量化を目的として、SiやMnを多く含む高強度鋼板の適用が拡大しつつある。このような趨勢に反し、特許文献３で提案された技術では、Si量やMn量を低減した鋼板を適用することが必要となるため、鋼板の板厚を薄くすると所望の強度を確保することができない。よって、特許文献３で提案された技術では、自動車軽量化の効果を期待することができない。 Moreover, if the composition of the base metal and the welding wire is limited and the amount of Si and Mn that cause slag is reduced as in the technique proposed in Patent Document 3, the corrosion resistance of the welded part and its vicinity after coating is reduced. Improvement can be expected. However, Si and Mn are elements that are extremely effective for improving the strength of steel sheets, and in recent years, the application of high-strength steel sheets containing a large amount of Si and Mn is expanding for the purpose of reducing the weight of automobiles. Contrary to this trend, the technique proposed in Patent Document 3 requires the application of a steel sheet with a reduced amount of Si or Mn, so that the desired strength can be ensured by reducing the thickness of the steel sheet. I can't. Therefore, the technique proposed in Patent Document 3 cannot be expected to reduce the weight of the automobile.
本発明は、かかる事情に鑑みなされたもので、足回り部材等、自動車部材をはじめとする鋼製塗装部材の溶接部における耐食性を改善するための技術を提供する。具体的には、鋼板同士を溶接接合してなる鋼製部材に化成処理を施したのち電着塗装が施されてなる鋼製塗装部材に関し、溶接ビード止端部から2mm未満の部分においてもリン酸亜鉛結晶（化成処理層）が存在し、2mm以上離れた部分がリン酸亜鉛結晶（化成処理層）で完全に覆われた、塗膜密着性に優れた鋼製塗装部材を提供することを目的とする。 This invention is made | formed in view of this situation, and provides the technique for improving the corrosion resistance in the welding part of steel coating members including automobile members, such as a suspension member. Specifically, with regard to steel coated members that are subjected to chemical conversion treatment and then subjected to electrodeposition coating after the steel members formed by welding the steel plates together, even at a portion less than 2 mm from the weld bead toe, To provide a steel coated member with excellent coating adhesion, in which zinc oxide crystals (chemical conversion treatment layer) are present, and at least 2 mm apart are completely covered with zinc phosphate crystals (chemical conversion treatment layer) Objective.
先述のとおり、従来技術では、溶接ビード止端部から約4mm以上離れた部分であればリン酸亜鉛結晶で完全に覆うことができるものの、溶接ビード止端部から約4mm未満の部分をリン酸亜鉛結晶で完全に覆うことができなかった。また、特許文献１〜３で提案された技術は、溶接ビード止端部近傍にリン酸亜鉛結晶を形成し得るものの、設備の腐食やビード欠陥、あるいは鋼板に含まれる合金元素の制約等の新たな問題を誘発するものであった。本発明は、これらの問題を招来することなく、溶接ビード止端部から4mm以上離れた部分では勿論のこと、溶接ビード止端部から2mmしか離れていない部分であってもリン酸亜鉛結晶で完全に覆われ、さらに溶接ビード止端部から2mm未満の部分においてもリン酸亜鉛結晶が部分的に形成された鋼製塗装部材を提供することを目的とする。 As described above, in the prior art, a portion that is about 4 mm or more away from the weld bead toe can be completely covered with the zinc phosphate crystal, but the portion less than about 4 mm from the weld bead toe is phosphoric acid. It could not be completely covered with zinc crystals. Further, although the techniques proposed in Patent Documents 1 to 3 can form a zinc phosphate crystal in the vicinity of the weld bead toe, new technologies such as equipment corrosion and bead defects, or restrictions on alloy elements contained in the steel sheet, etc. It was a provoking problem. Without incurring these problems, the present invention is not limited to a portion that is 4 mm or more away from the weld bead toe, but even a portion that is only 2 mm away from the weld bead toe is made of zinc phosphate crystals. An object of the present invention is to provide a steel coated member that is completely covered and further partially formed with zinc phosphate crystals even at a portion of less than 2 mm from the weld bead toe.
鋼製塗装部材の溶接部における耐食性の劣化は、溶接部（溶接ビード上、溶接ビード止端部、溶接熱影響部）に付着したスラグや溶接ヒューム、および溶接部に発生した表面酸化に起因するものである。通常、鋼製部材に化成処理としてリン酸亜鉛処理を施すと、リン酸亜鉛処理剤のエッチング作用により被処理材である鋼が溶解する。そして、この際、水素イオンが消費されることで、固液界面の局部領域でpH上昇がおこり、鋼製部材表面にリン酸亜鉛結晶（化成処理層）が析出する。しかしながら、鋼製部材の溶接部では、スラグや溶接ヒューム、或いは表面酸化の存在により、鋼の溶解性が低下し、結果的にリン酸亜鉛結晶が生じ難くなっている。そのため、これらの部分では、リン酸亜鉛結晶の形成が不十分となり、塗膜密着性を十分に確保することができない。 The deterioration of corrosion resistance in the welded part of steel coated parts is caused by slag and weld fumes adhering to the weld (on the weld bead, weld bead toe, weld heat affected zone) and surface oxidation generated in the weld. Is. Usually, when a zinc phosphate treatment is applied to a steel member as a chemical conversion treatment, the steel to be treated is dissolved by the etching action of the zinc phosphate treating agent. At this time, the consumption of hydrogen ions causes a pH increase in a local region of the solid-liquid interface, and zinc phosphate crystals (chemical conversion treatment layer) are deposited on the steel member surface. However, in the welded portion of the steel member, the solubility of the steel is lowered due to the presence of slag, welding fume, or surface oxidation, and as a result, zinc phosphate crystals are hardly generated. Therefore, in these portions, the formation of zinc phosphate crystals becomes insufficient, and the coating film adhesion cannot be sufficiently ensured.
そこで、本発明者らは、鋼板同士を溶接接合してなる鋼製部材に化成処理としてリン酸亜鉛処理を施す場合において、スラグや溶接ヒュームが付着した溶接部、および表面酸化が生じた溶接部や溶接部裏側のリン酸亜鉛処理性（化成処理性）を改善する手段について鋭意検討した。その結果、所定のフッ素濃度を有するエッチング性の高いリン酸亜鉛処理剤を用いることが、極めて有効な手段であることを知見した。すなわち、所定のフッ素濃度を有するリン酸亜鉛処理剤を用いると、該処理剤の強いエッチング作用により溶接ヒュームや上記した表面酸化由来の酸化物が溶解除去されるため、反応の初期において鋼の溶解が阻害されず、リン亜鉛結晶が十分に析出することを見い出した。 Therefore, the present inventors, when a zinc phosphate treatment is performed as a chemical conversion treatment on steel members formed by welding steel plates together, a welded portion to which slag or welding fume adheres, and a welded portion in which surface oxidation has occurred. We have also studied diligently about the means to improve the zinc phosphate processability (chemical conversion processability) on the back side of the weld. As a result, it has been found that using a highly etching zinc phosphate treating agent having a predetermined fluorine concentration is an extremely effective means. That is, when a zinc phosphate treating agent having a predetermined fluorine concentration is used, welding fumes and oxides derived from surface oxidation are dissolved and removed by the strong etching action of the treating agent. It was found that phosphozinc crystals were sufficiently precipitated without being inhibited.
しかしながら、本発明者らがリン酸亜鉛処理後の溶接部について観察した結果、上記した強いエッチング作用を有するリン酸亜鉛処理剤を用いてもなお、溶接部に付着した溶接ヒュームや表面酸化の酸化物の影響により、溶接ビード止端部近傍のリン酸亜鉛結晶が十分に形成されない場合があることが判明した。これは、ビード止端部は特に溶接ヒュームの堆積が顕著であるうえ、溶接ビード部を除く表面の中で、入熱による温度上昇が最も高くなる部分であるため、表面酸化のレベルも高いことに起因する。このため、溶接ビード止端部では、エッチング効果をもってしても、良好なリン酸亜鉛結晶を形成させるためには不十分である。 However, as a result of observations made on the welded portion after the zinc phosphate treatment by the present inventors, even if the zinc phosphate treating agent having the strong etching action described above is used, the welding fume adhered to the welded portion or the oxidation of the surface oxidation It has been found that the zinc phosphate crystals near the weld bead toe may not be sufficiently formed due to the influence of the object. This is because the weld toe is particularly prominent at the toe of the bead, and the level of surface oxidation is high because the temperature rise due to heat input is the highest in the surface excluding the weld bead. caused by. For this reason, even if it has an etching effect in a weld bead toe part, it is insufficient in order to form a good zinc phosphate crystal.
そこで、本発明者らは、溶接ビード止端部にもリン酸亜鉛結晶を十分に析出させる手段について検討した。その結果、所定のフッ素濃度を有するリン酸亜鉛処理剤の使用の際、前処理として、リン酸亜鉛コロイドを主成分とする表面調整剤を用いる場合、溶接ビード止端部での結晶形成に有利となることを知見した。これは、例えばTi系コロイドなど他の表面調整剤と比較し、リン酸亜鉛コロイドを主成分とする表面調整剤は表面調整液中でのコロイドの分散性が高いうえ、表面調整後に形成されるリン酸亜鉛結晶と同じ成分であることから、析出核としてより有効に作用し、酸化物が存在しても容易に緻密なリン酸亜鉛結晶からなる化成処理層が形成されるためである。 Therefore, the present inventors examined a means for sufficiently depositing zinc phosphate crystals at the weld bead toe. As a result, when using a zinc phosphate treating agent having a predetermined fluorine concentration, when a surface conditioner mainly composed of zinc phosphate colloid is used as a pretreatment, it is advantageous for crystal formation at the weld bead toe. I found out that Compared with other surface conditioners such as Ti-based colloids, for example, the surface conditioner mainly composed of zinc phosphate colloid has high colloid dispersibility in the surface conditioner and is formed after the surface condition. Because it is the same component as the zinc phosphate crystal, it acts more effectively as a precipitation nucleus, and even if an oxide is present, a chemical conversion treatment layer composed of a dense zinc phosphate crystal is easily formed.
更に、本発明者らは、鋼板同士を溶接接合してなる鋼製部材に、上記の如く所望の表面調整処理およびリン酸亜鉛処理を施すことにより、溶接ビード止端部から2mmを超えて離れた部分は勿論のこと、溶接ビード止端部から2mmしか離れていない部分もリン酸亜鉛結晶（化成処理層）で覆われた鋼製部材が得られることを知見した。そして、このような鋼製部材に電着塗装を施すことにより、溶接部の耐食性が飛躍的に向上した鋼製塗装部材が得られることを知見した。 Further, the present inventors have performed a desired surface conditioning treatment and zinc phosphate treatment on the steel member formed by welding the steel plates to each other so that they are separated from the weld bead toe by more than 2 mm. As a matter of course, it was found that a steel member covered with zinc phosphate crystals (chemical conversion treatment layer) that was only 2 mm away from the weld bead toe was obtained. And it discovered that the steel coating member in which the corrosion resistance of the welding part improved dramatically by electrodeposition coating to such a steel member.
本発明は上記の知見に基づき完成されたものであり、その要旨は次のとおりである。
［１］ 鋼板同士を溶接接合してなる鋼製部材を化成処理するにあたり、該化成処理を、リン酸亜鉛コロイドを含有する表面調整剤を用いた表面調整処理を施したのち、フッ素濃度が100質量ppm以上であるリン酸亜鉛処理剤を用いたリン酸亜鉛処理を施す処理とすることを特徴とする鋼製部材の化成処理方法。
The present invention has been completed based on the above findings, and the gist thereof is as follows.
[1] In chemical conversion treatment of steel members formed by welding steel plates together, the chemical treatment is subjected to a surface conditioning treatment using a surface conditioning agent containing a zinc phosphate colloid, and then the fluorine concentration is 100. A chemical conversion treatment method for a steel member, characterized in that a zinc phosphate treatment is performed using a zinc phosphate treatment agent having a mass ppm or more.
［２］ ［１］において、前記鋼板が、合金化溶融亜鉛めっき鋼板であることを特徴とする鋼製部材の化成処理方法。 [2] The chemical conversion treatment method for a steel member according to [1], wherein the steel sheet is an alloyed hot-dip galvanized steel sheet.
［３］ 鋼板同士を溶接接合してなる鋼製部材に化成処理と電着塗装を施して鋼製塗装部材とする鋼製塗装部材の製造方法であって、前記鋼製部材に［１］に記載の化成処理を施したのち、電着塗装を施すことを特徴とする鋼製塗装部材の製造方法。 [3] A method for producing a steel coated member obtained by subjecting a steel member formed by welding steel plates to chemical conversion treatment and electrodeposition coating to form a steel coated member. A method for producing a steel-coated member, comprising performing electrodeposition coating after performing the chemical conversion treatment described above.
［４］ ［３］において、前記鋼板が、合金化溶融亜鉛めっき鋼板であることを特徴とする鋼製塗装部材の製造方法。 [4] The method for producing a steel coated member according to [3], wherein the steel sheet is an alloyed hot-dip galvanized steel sheet.
［５］ ［３］または［４］において、前記鋼製塗装部材が自動車の足回り部材であることを特徴とする鋼製塗装部材の製造方法。 [5] The method for producing a steel painted member according to [3] or [4], wherein the steel painted member is an undercarriage member of an automobile.
［６］ ［３］ないし［５］のいずれかの製造方法を用いて製造された鋼製塗装部材であって、少なくとも溶接ビード止端部から2mm離れた部分がリン酸亜鉛結晶で覆われていることを特徴とする鋼製塗装部材。 [6] A steel coated member manufactured using the manufacturing method according to any one of [3] to [5], wherein at least a portion 2 mm away from the weld bead toe is covered with zinc phosphate crystals. Steel painted member characterized by having
［７］ ［６］において、前記鋼製塗装部材が自動車の足回り部材であることを特徴とする鋼製塗装部材。 [7] The steel painted member according to [6], wherein the steel painted member is an undercarriage member of an automobile.
本発明によれば、鋼板同士を溶接接合してなる鋼製部材に化成処理を施したのち電着塗装が施されてなる鋼製塗装部材において、溶接部の耐食性を大幅に改善することができる。そのため、厳しい腐食環境下で使用され、従来、部材の薄肉化が困難とされていた自動車の足回り部材等を、薄板の高強度鋼板によって形成することが可能となり、産業上格段の効果を奏する。 ADVANTAGE OF THE INVENTION According to this invention, the corrosion resistance of a welding part can be improved significantly in the steel coating member by which the electrodeposition coating is performed after performing the chemical conversion treatment to the steel member formed by welding the steel plates together. . For this reason, it becomes possible to form automobile underbody members, etc., which have been used in severe corrosive environments and have conventionally been difficult to reduce the thickness of the members, with thin high-strength steel plates, and have a remarkable industrial effect. .
以下、本発明について詳細に説明する。
本発明の鋼製部材の化成処理方法は、鋼板同士を溶接接合してなる鋼製部材を化成処理するにあたり、該化成処理を、リン酸亜鉛コロイドを含有する表面調整剤を用いた表面調整処理を施したのち、フッ素濃度が100質量ppm以上であるリン酸亜鉛処理剤を用いたリン酸亜鉛処理を施す処理とすることを特徴とする。
Hereinafter, the present invention will be described in detail.
The chemical conversion treatment method for steel members according to the present invention is a surface conditioning treatment using a surface conditioner containing a zinc phosphate colloid in chemical conversion treatment of steel members formed by welding and joining steel plates. After the treatment, the zinc phosphate treatment using a zinc phosphate treating agent having a fluorine concentration of 100 mass ppm or more is performed.
本発明において、鋼製部材を構成する鋼板の種類は特に限定されず、通常の熱延鋼板、冷延鋼板、あるいは亜鉛系めっき鋼板のいずれでも適用可能である。特に、亜鉛系めっき鋼板を使用した場合に、溶接時の加熱により、ビード部近傍の亜鉛めっきが一部蒸発し、めっきが薄くなる部分が存在するが、本発明の技術を適用した場合、化成処理皮膜がビード部近傍でも健全に形成されるため、耐食性改善効果が十分得られる。また、鋼製部材を構成する鋼板として合金化溶融亜鉛めっき鋼板を適用した場合には、めっきによる効果により更に耐食性が向上する。 In the present invention, the type of the steel plate constituting the steel member is not particularly limited, and any of a normal hot-rolled steel plate, a cold-rolled steel plate, or a zinc-based plated steel plate can be applied. In particular, when galvanized steel sheet is used, there is a part where the galvanization in the vicinity of the bead part evaporates due to heating during welding and the plating becomes thin. Since the treatment film is formed soundly even in the vicinity of the bead portion, the effect of improving the corrosion resistance is sufficiently obtained. Moreover, when an alloyed hot-dip galvanized steel sheet is applied as the steel sheet constituting the steel member, the corrosion resistance is further improved by the effect of plating.
また、本発明の効果は熱影響部の酸化膜に起因した化成処理不良を改善するものである。そのため、本発明では、鋼板同士を溶接接合する際の溶接の種類についても特に問わず、アーク溶接、スポット溶接、シーム溶接等、従前公知の溶接を適用することができる。これらの中でも、特にアーク溶接の場合、溶接部において腐食に関する課題が生じやすいため、本発明はアーク溶接を適用する場合に特に有効である。ここでいうアーク溶接とは、MAG溶接、MIG溶接、TIG溶接、炭酸ガスアーク溶接などを含むものであり、特に限定する必要はない。 Further, the effect of the present invention is to improve the chemical conversion treatment failure caused by the oxide film in the heat affected zone. Therefore, in the present invention, conventionally known welding such as arc welding, spot welding, seam welding, or the like can be applied regardless of the type of welding when the steel plates are welded together. Among these, especially in the case of arc welding, since the subject regarding corrosion tends to occur in the welded portion, the present invention is particularly effective when arc welding is applied. The arc welding here includes MAG welding, MIG welding, TIG welding, carbon dioxide arc welding, etc., and there is no particular limitation.
なお、鋼板同士を溶接接合するに先立ち鋼板を加工成形してもよく、鋼板同士を溶接接合した後に所望の部材形状に成形してもよい。或いは、鋼板を加工成形したのち鋼板同士を溶接接合し、更に加工成形して所望の部材形状に成形してもよい。また、鋼板の端部同士を溶接接合して得られる鋼管も、本発明における鋼製部材に含まれるものとする。 Prior to welding the steel plates together, the steel plates may be processed and formed, or the steel plates may be welded together and formed into a desired member shape. Alternatively, the steel plates may be processed and formed, and then the steel plates may be welded together and further processed and formed into a desired member shape. Moreover, the steel pipe obtained by welding and joining the edge parts of a steel plate shall also be contained in the steel member in this invention.
本発明の化成処理方法は、上記の如く鋼板同士を溶接接合してなる鋼製部材に、表面調整処理を施す工程と、これに続くリン酸亜鉛処理を施す工程からなる。そして、本発明は、リン酸亜鉛コロイドを含有する表面調整剤を用いること、およびフッ素濃度が100質量ppm以上であるリン酸亜鉛処理剤を用いることを、最大の特徴とする。 The chemical conversion treatment method of the present invention includes a step of subjecting a steel member formed by welding steel plates to each other as described above, and a step of subjecting the steel member to a subsequent zinc phosphate treatment. The present invention is characterized by the use of a surface conditioner containing a zinc phosphate colloid and the use of a zinc phosphate treating agent having a fluorine concentration of 100 mass ppm or more.
リン酸亜鉛コロイドを含有する表面調整剤
リン酸亜鉛コロイドを含有する表面調整剤は、Ti系コロイドを含む表面調整剤などの他の表面調整剤と比較して、表面調整液中でのコロイドの分散性が高い。そのうえ、リン酸亜鉛コロイドは、表面調整処理後に形成されるリン酸亜鉛結晶と同じ成分であるため、リン酸亜鉛結晶の析出核としてより有効に作用する。したがって、溶接ヒュームや表面酸化由来の酸化物が存在する場合であっても、後述する所望のリン酸亜鉛処理を施すことにより、緻密なリン酸亜鉛結晶からなる化成処理皮膜を容易に形成することができる。
Surface modifier containing zinc phosphate colloid Compared with other surface modifiers such as surface modifiers containing Ti-based colloids, surface modifiers containing zinc phosphate colloids High dispersibility. In addition, since the zinc phosphate colloid is the same component as the zinc phosphate crystal formed after the surface conditioning treatment, it acts more effectively as a precipitation nucleus of the zinc phosphate crystal. Therefore, even if welding fume or oxide derived from surface oxidation exists, a chemical conversion treatment film composed of dense zinc phosphate crystals can be easily formed by applying the desired zinc phosphate treatment described later. Can do.
リン酸亜鉛コロイドを含有する表面調整剤としては、例えば、日本ペイント（株）製のサーフファインGL-1、日本パーカライジング（株）製のプレパレンXやプレパレンXGなどが挙げられる。また、これらの表面調整剤を用いて表面調整処理を施すに際しては、特別な工程を設ける必要はなく、常法に従い実施すればよい。例えば、所望の表面調整剤を所定の脱イオン水に溶解させ、十分攪拌したのち、規定の温度（通常は常温、25〜30℃）の処理液とし、該処理液中に鋼板を所定時間（20〜30秒）浸漬させる。引き続き乾燥させることなく、次工程のリン酸亜鉛処理を行う。 Examples of the surface conditioner containing zinc phosphate colloid include Surffine GL-1 manufactured by Nippon Paint Co., Ltd., Preparen X and Preparene XG manufactured by Nippon Parkerizing Co., Ltd. Further, when the surface conditioning treatment is performed using these surface conditioning agents, it is not necessary to provide a special process, and it may be performed according to a conventional method. For example, a desired surface conditioner is dissolved in a predetermined deionized water, sufficiently stirred, and then treated as a specified temperature (usually normal temperature, 25 to 30 ° C.), and a steel plate is placed in the treated liquid for a predetermined time ( Soak for 20-30 seconds. The subsequent zinc phosphate treatment is performed without drying.
フッ素濃度が100質量ppm以上であるリン酸亜鉛処理剤
本発明においては、リン酸亜鉛処理で用いるリン酸亜鉛処理剤のフッ素濃度を100質量ppm以上とすることを要する。フッ素濃度が100質量ppm未満の場合、リン酸亜鉛処理剤のエッチング能が不十分となり、溶接部に付着した溶接ヒュームや表面酸化由来の酸化物を溶解除去することができず、リン酸亜鉛結晶の析出に必要となる鋼の溶解反応を十分に促進することができない。よって、フッ素濃度は100質量ppm以上とする。好ましくは250質量ppm以上である。一方、フッ素濃度が過剰に高くなると、不溶性のフッ化物が生成し易くなり、不溶性のフッ化物が化成処理後に残留すると、濡れ環境下での塗膜密着性が低下することが懸念される。そのため、被処理材の種類にもよるが、フッ素濃度は1500質量ppm以下とすることが好ましい。また、1000質量ppm以下とすることがより好ましい。
In the present invention, it is necessary that the fluorine concentration of the zinc phosphate treating agent used in the zinc phosphate treatment is 100 mass ppm or more. When the fluorine concentration is less than 100 ppm by mass, the etching ability of the zinc phosphate treatment agent becomes insufficient, so that it is impossible to dissolve and remove the welding fume adhering to the weld and the oxide derived from surface oxidation. It is not possible to sufficiently promote the melting reaction of steel necessary for the precipitation of. Therefore, the fluorine concentration is 100 mass ppm or more. Preferably it is 250 mass ppm or more. On the other hand, if the fluorine concentration becomes excessively high, insoluble fluorides are likely to be generated, and if the insoluble fluoride remains after the chemical conversion treatment, there is a concern that the adhesion of the coating film in a wet environment is lowered. Therefore, although it depends on the type of the material to be treated, the fluorine concentration is preferably 1500 ppm by mass or less. Moreover, it is more preferable to set it as 1000 mass ppm or less.
上記の如き所望のフッ素濃度を有するリン酸亜鉛処理剤は、市販のリン酸亜鉛処理剤、一般的には、アルミニウムと鋼を共用して処理できる市販の鋼・アルミニウム併用型の処理剤を用い、そのフッ素濃度を調整することにより得られる。具体的には、日本パーカライジング（株）製のパルボンドAX-35などの市販の処理剤に、フッ酸やフッ化水素ナトリウム、フッ化ナトリウム、フッ化アンモニウムなどのフッ化物、あるいは、珪フッ酸、珪フッ化ナトリウム、ジルコンフッ酸などの錯フッ化物などの１種または２種以上を添加してフッ素濃度を調整することにより得られる。市販のリン酸亜鉛処理剤が所望のフッ素濃度を有する場合には、フッ素濃度を調整することなくそのまま使用できることは云うまでもない。なお、フッ素濃度は市販のフッ素イオンメーターを用いて測定することが出来る。フッ素濃度の調整は例えば上記した日本パーカライジング（株）の処理剤の場合、添加調整剤（例えばAD-4905）の添加量を適宜変更することで調整できる。 The zinc phosphate treating agent having a desired fluorine concentration as described above is a commercially available zinc phosphate treating agent, generally, a commercially available steel / aluminum combined treating agent that can treat aluminum and steel in common. , By adjusting the fluorine concentration. Specifically, commercially available treatment agents such as Palbond AX-35 manufactured by Nippon Parkerizing Co., Ltd., fluorides such as hydrofluoric acid, sodium hydrogen fluoride, sodium fluoride, ammonium fluoride, or silicic hydrofluoric acid, It can be obtained by adjusting the fluorine concentration by adding one or more complex fluorides such as sodium silicofluoride and zircon hydrofluoric acid. When a commercially available zinc phosphate treating agent has a desired fluorine concentration, it goes without saying that it can be used as it is without adjusting the fluorine concentration. The fluorine concentration can be measured using a commercially available fluorine ion meter. For example, in the case of the above-mentioned treatment agent of Nippon Parkerizing Co., Ltd., the fluorine concentration can be adjusted by appropriately changing the addition amount of the additive regulator (for example, AD-4905).
本発明では、上記の如く所望のフッ素濃度に調整されたリン酸亜鉛処理剤を用いてリン酸亜鉛処理を施すが、このリン酸亜鉛処理は、鋼や亜鉛めっき鋼板等に一般的に使用される、リン酸亜鉛結晶を主体とした皮膜が形成される、いわゆるリン酸亜鉛処理であれば特に規定されるものではない。すなわち、リン酸亜鉛処理を施すに際しては、リン酸亜鉛処理剤のフッ素濃度を必要に応じて調整すること以外には特別な工程を設ける必要はなく、常法に従い実施すればよい。 In the present invention, the zinc phosphate treatment is performed using the zinc phosphate treatment agent adjusted to a desired fluorine concentration as described above. This zinc phosphate treatment is generally used for steel, galvanized steel sheets and the like. The so-called zinc phosphate treatment in which a film mainly composed of zinc phosphate crystals is formed is not particularly defined. That is, when performing the zinc phosphate treatment, it is not necessary to provide a special step other than adjusting the fluorine concentration of the zinc phosphate treating agent as necessary, and it may be carried out according to a conventional method.
例えば、前記した表面調製処理を施した鋼製部材表面に、所望のフッ素濃度に調整したリン酸亜鉛処理剤を脱イオン水に溶解させた水溶液に浸漬又は該水溶液のスプレーなどの方法によって所定時間（通常は2分〜3分）接触させることにより、リン酸亜鉛結晶を析出させ、所望の厚さの結晶皮膜とすればよい。なお、所望の耐食性を得るためには片面当たりのリン酸亜鉛皮膜重量として1〜4g/m2、より好ましくは1.5〜3g/m2とすると良い。 For example, the surface of the steel member subjected to the above-described surface preparation treatment is immersed in an aqueous solution in which a zinc phosphate treatment agent adjusted to a desired fluorine concentration is dissolved in deionized water or sprayed with the aqueous solution for a predetermined time. By contacting (usually 2 to 3 minutes), the zinc phosphate crystal is precipitated to form a crystal film having a desired thickness. In order to obtain the desired corrosion resistance, the weight of the zinc phosphate film per side is 1 to 4 g / m 2 , more preferably 1.5 to 3 g / m 2 .
以上のような本発明の化成処理方法に従うと、図６（ｂ）に示すように、溶接ビード止端部から2mm超離れた部分は勿論のこと、溶接ビード止端部から2mmの部分をも、リン酸亜鉛結晶で完全に覆うことができる。更に、溶接ビード止端部から100μm離れた部分においても、20％以下のスケ面積率（リン酸亜鉛結晶が生成していない面積率）でリン酸亜鉛結晶を析出させることができる。すなわち、従来の化成処理方法では、図６（ａ）に示すように、溶接ビード止端部近傍（溶接ビード止端部から約4mm以内）において化成処理層が形成されない領域が残ってしまうのに対し、本発明の化成処理方法によると、溶接ビード止端部近傍を含め溶接部全体にわたりリン酸亜鉛結晶を十分に析出させることができる。 According to the chemical conversion treatment method of the present invention as described above, as shown in FIG. 6 (b), not only a part more than 2 mm away from the weld bead toe part, but also a part 2 mm from the weld bead toe part is provided. Can be completely covered with zinc phosphate crystals. Furthermore, zinc phosphate crystals can be deposited at a scale area ratio of 20% or less (area ratio at which zinc phosphate crystals are not formed) even at a portion 100 μm away from the weld bead toe. That is, in the conventional chemical conversion treatment method, as shown in FIG. 6A, there is a region where the chemical conversion treatment layer is not formed in the vicinity of the weld bead toe portion (within about 4 mm from the weld bead toe portion). On the other hand, according to the chemical conversion treatment method of the present invention, zinc phosphate crystals can be sufficiently precipitated over the entire weld including the vicinity of the weld bead toe.
また、本発明の鋼製塗装部材の製造方法は、鋼板同士を溶接接合してなる鋼製部材を化成処理と電着塗装を施して鋼製塗装部材とする鋼製塗装部材の製造方法であって、前記した本発明の化成処理方法によって得られた化成処理済みの鋼製部材に、電着塗装を施すことを特徴とする。 The method for producing a steel coated member according to the present invention is a method for producing a steel coated member obtained by subjecting a steel member obtained by welding and joining steel plates to chemical conversion treatment and electrodeposition coating to obtain a steel coated member. Thus, electrodeposition coating is performed on the steel member that has been subjected to the chemical conversion treatment obtained by the chemical conversion treatment method of the present invention.
本発明における電着塗装は、通常使用されるカチオン型の電着塗装であれば特に規定されない。電着塗装によって形成する塗膜の膜厚は、鋼製塗装部材の用途により異なるが、乾燥状態の塗膜で10μm以上30μm以下程度とすることが好ましい。 The electrodeposition coating in the present invention is not particularly defined as long as it is a commonly used cationic electrodeposition coating. The film thickness of the coating film formed by electrodeposition coating varies depending on the application of the steel coating member, but it is preferably about 10 μm or more and 30 μm or less for the dried coating film.
また、本発明の鋼製塗装部材は、上記した本発明の製造方法を用いて製造された鋼製塗装部材であって、少なくとも溶接ビード止端部から2mm離れた部分がリン酸亜鉛結晶で覆われていることを特徴とする。
先述のとおり、鋼板同士を溶接接合してなる鋼製部材に、本発明の化成処理を施すと、溶接ビード止端部から4mm以上離れた部分は勿論のこと、溶接ビード止端部から2〜4mm離れた部分をも、リン酸亜鉛結晶で完全に覆うことができる。そして、このように溶接ビード止端部近傍をリン酸亜鉛結晶で完全に覆うことにより、続く電着塗装によって形成された塗膜の密着性が飛躍的に向上し、溶接部の耐食性が大幅に改善された鋼製塗装部材を得ることができる。
なお、本発明の鋼製塗装部材は、溶接部を含めて優れた耐食性を示すが、鋼製塗装部材の用途に応じて電着塗装後に上塗り塗装などを施してもよい。
The steel coated member of the present invention is a steel coated member manufactured by using the manufacturing method of the present invention described above, and at least a portion 2 mm away from the weld bead toe is covered with zinc phosphate crystals. It is characterized by that.
As described above, the steel member formed by welding the steel plates to each other is subjected to the chemical conversion treatment of the present invention, as well as a portion 4 mm or more away from the weld bead toe, 2 to 2 from the weld bead toe. Even 4 mm away can be completely covered with zinc phosphate crystals. And by completely covering the vicinity of the weld bead toe with zinc phosphate crystals in this way, the adhesion of the coating film formed by the subsequent electrodeposition coating is dramatically improved, and the corrosion resistance of the weld is greatly increased. An improved steel painted member can be obtained.
In addition, although the steel coating member of this invention shows the outstanding corrosion resistance including a welding part, according to the use of a steel coating member, you may give top coat etc. after electrodeposition coating.
本発明は、ロアアーム等、自動車の足回り部材に好適である。自動車の足回り部材は通常、鋼素材を所定形状に成形後、リン酸亜鉛処理（化成処理）および電着塗装を施すことにより製造される。
本発明の化成処理方法を用いて得られた足回り部材では、溶接部の耐食性が大幅に改善され、溶接部における腐食および薄肉化が抑制されている。そのため、本発明によると、従来困難とされていた足回り部材の大幅な薄肉化が可能となる。
The present invention is suitable for an automobile underbody member such as a lower arm. An automobile undercarriage member is usually manufactured by forming a steel material into a predetermined shape and then applying zinc phosphate treatment (chemical conversion treatment) and electrodeposition coating.
In the undercarriage member obtained by using the chemical conversion treatment method of the present invention, the corrosion resistance of the welded portion is greatly improved, and corrosion and thinning of the welded portion are suppressed. Therefore, according to the present invention, it is possible to significantly reduce the thickness of the underbody member, which has been conventionally difficult.
表１に示す成分の熱延鋼板（厚み2.6mm）または表１に示す成分の熱延鋼板（厚み2.6mm）の両面に合金化溶融亜鉛めっき処理（片面当たりのめっき付着量：45g/m2）を施した合金化溶融亜鉛めっき鋼板と、表２に示す溶接棒を用いて、図１のような隅肉溶接試験材を作製した。なお、図２は、図１のA-A線断面図のうち、溶接部を拡大した図である。溶接は、Ar-20vol％CO2を用いたMAGパルス溶接であり、溶接条件を表３に示す。 Alloyed hot-dip galvanizing treatment on both sides of hot-rolled steel sheets (thickness 2.6 mm) with the components shown in Table 1 or hot-rolled steel sheets (thickness 2.6 mm) with the components shown in Table 1 (plating adhesion amount per side: 45 g / m 2 The fillet welded test material as shown in FIG. 1 was prepared using the alloyed hot-dip galvanized steel sheet and the welding rod shown in Table 2. FIG. 2 is an enlarged view of the welded portion of the AA line cross-sectional view of FIG. The welding is MAG pulse welding using Ar-20 vol% CO 2 and the welding conditions are shown in Table 3.
次いで、これらの試験片に40℃のアルカリ脱脂液：FC-E2001（日本パーカライジング（株）製、アルカリ度：18.3ptまたは18.5pt）に120秒間浸漬する脱脂処理を施したのち、表４に示す３種類の条件で、表面調整処理およびリン酸亜鉛処理を順次施す化成処理を施した。条件１および条件２は比較例、条件３は本発明例である。 Next, these test pieces were degreased by immersing them in a 40 ° C. alkaline degreasing solution: FC-E2001 (manufactured by Nippon Parkerizing Co., Ltd., alkalinity: 18.3 pt or 18.5 pt) for 120 seconds. Under three conditions, a chemical conversion treatment was performed in which a surface conditioning treatment and a zinc phosphate treatment were sequentially performed. Conditions 1 and 2 are comparative examples, and condition 3 is an example of the present invention.
表面調整処理は、脱脂処理後の試験片を、表４に示す各種の表面調整剤（室温）に20秒間浸漬することにより行った。
また、リン酸亜鉛処理は、表４に示す各種市販のリン酸亜鉛処理剤（35℃）に120秒間浸漬することにより行った。
The surface conditioning treatment was performed by immersing the test piece after the degreasing treatment in various surface conditioning agents (room temperature) shown in Table 4 for 20 seconds.
Further, the zinc phosphate treatment was performed by immersing in various commercially available zinc phosphate treating agents (35 ° C.) shown in Table 4 for 120 seconds.
上記した３種類の処理条件で、熱延鋼板を用いた場合と、合金化溶融亜鉛めっき鋼板を用いた場合の各々について、各処理条件につき7個の試験片を用いた。
各処理条件について、7個の試験片のうち2個はリン酸亜鉛処理ままとし、以下に示す方法で溶接部周辺のリン酸亜鉛結晶の健全性を評価した。
溶接ビード止端部（溶接ビードと鋼板の界面）から100μm離れた位置（図２のa点）、溶接ビード止端部から2mm離れた位置（図２のb点）、溶接ビード止端部から4mm離れた位置（図２のc点）、溶接ビード止端部から7mm離れた位置（図２のd点）、並びに、溶接ビード上（図２のe点）を、走査型電子顕微鏡（SEM）で観察し（倍率：500及び1500倍、各５視野）、以下の基準に従い評価した。
◎：観察５視野の領域の全てが、リン酸亜鉛結晶で完全に覆われている。
○：観察５視野の平均スケ面積が20％以下の状態でリン酸亜鉛結晶が析出している。
△：観察５視野の平均スケ面積が20％超の状態でリン酸亜鉛結晶が析出している。
×：観察５視野領域の全てにおいて、リン酸亜鉛結晶が析出していない。
Seven test pieces were used for each treatment condition for each of the cases where the hot-rolled steel sheet was used and the alloyed hot-dip galvanized steel sheet were used under the three kinds of treatment conditions described above.
For each treatment condition, two of the seven test pieces were left with the zinc phosphate treatment, and the soundness of the zinc phosphate crystals around the weld was evaluated by the following method.
A position 100 μm away from the weld bead toe (interface between weld bead and steel plate) (point a in FIG. 2), a position 2 mm away from the weld bead toe (point b in FIG. 2), and from the weld bead toe A scanning electron microscope (SEM) was positioned at a position 4 mm away (point c in FIG. 2), a position 7 mm away from the weld bead toe (point d in FIG. 2), and on the weld bead (point e in FIG. 2). ) (Magnification: 500 and 1500 times, 5 visual fields each) and evaluated according to the following criteria.
(Double-circle): The area | region of 5 observation visual fields is completely covered with the zinc phosphate crystal.
A: Zinc phosphate crystals are deposited in an average scale area of 5 fields of observation of 20% or less.
(Triangle | delta): The zinc phosphate crystal | crystallization has precipitated in the state whose average scale area of 5 visual observations exceeds 20%.
X: Zinc phosphate crystals are not precipitated in all of the five viewing field regions.
評価結果を表５に示す。また、表５のうち、試験片No.11A（条件１，熱延鋼板，比較例）、試験片No.31A（条件３，熱延鋼板，本発明例）のSEM写真を図４、図５に示す。なお、図４、図５において、（ａ）は溶接ビード止端部から100μm離れた位置（図２のa点）おけるSEM写真（倍率：1500倍）であり、（ｂ）は溶接ビード止端部から2mm離れた位置（図２のb点）、（ｃ）は溶接ビード止端部から4mm離れた位置（図２のc点）におけるSEM写真（倍率：500倍）である。 The evaluation results are shown in Table 5. In Table 5, SEM photographs of specimen No. 11A (condition 1, hot-rolled steel sheet, comparative example) and specimen No. 31A (condition 3, hot-rolled steel sheet, inventive example) are shown in FIGS. Shown in 4 and 5, (a) is an SEM photograph (magnification: 1500 times) at a position 100 μm away from the weld bead toe (point a in FIG. 2), and (b) is the weld bead toe. 2C is a SEM photograph (magnification: 500 times) at a position 2 mm away from the part (point b in FIG. 2) and (c) at a position 4 mm away from the weld bead toe (point c in FIG. 2).
更に、上記によって得られた7つの試験片のうちの残りの5個について、塗装後耐食性の評価を行うため、リン酸亜鉛処理後の試験片に自動車用電着塗装を施した。電着塗装の膜厚は、平坦部で20±１μmになるように調整した。なお、自動車用電着塗装条件は以下のとおりである。
塗料の種類 ：商品名GT-10（関西ペイント（株）製）
電着浴の浴温：28℃
負荷電圧：200〜220V（試験片により適宜変更）
焼付け温度：170℃（PMT（＝到達板温）として）×20分
Further, the remaining five of the seven test pieces obtained as described above were subjected to electrodeposition coating for automobiles on the test pieces after the zinc phosphate treatment in order to evaluate the corrosion resistance after coating. The film thickness of the electrodeposition coating was adjusted to 20 ± 1 μm at the flat part. In addition, the electrodeposition coating conditions for automobiles are as follows.
Type of paint: Product name GT-10 (manufactured by Kansai Paint Co., Ltd.)
Electrodeposition bath temperature: 28 ℃
Load voltage: 200 to 220V (change as appropriate depending on the test piece)
Baking temperature: 170 ° C (as PMT (= reached plate temperature)) x 20 minutes
耐食性の評価では、電着塗装試験片を、SAEJ2334に準拠した腐食促進試験（複合サイクル試験）に供した。すなわち、図３に示すように、各試験片を、(i)相対湿度100％，50℃の湿潤環境に6時間保持したのち、(ii) 25℃の塩水（0.5質量％NaCl+0.1質量％CaCl2+0.075質量％NaHCO3）に15分間浸漬し、次いで(iii) 相対湿度50％,60℃の乾燥環境に17時間45分保持する一連のサイクル(i)〜(iii)を平日の５日間行い、休日の２日間は上記(iii)に続いて(iv) 相対湿度30％,50℃の乾燥環境に3時間保持する一連のサイクル(i)〜(iv)を行った。平日および休日の合計で120サイクルの試験を経た各試験片について、塗膜剥離剤（（株）ネオス製，商品名：CS500）を用いて電着塗装を剥離し、ISO8407に準拠して腐食生成物を除去した。各試験片の溶接ビード止端部近傍（試験片の幅方向両エッジ5mmを除き、溶接ビード止端部より60mmまでの位置）の腐食部について、まず目視で腐食深さの深い部分を選択し、腐食により薄肉化した部分の厚みをマイクロメーターで測定して腐食深さ（元板厚との差）を求めた。これを10回以上繰り返し、最も大きい値を最大腐食深さとして求めた。
評価結果を表６に示す。
In the corrosion resistance evaluation, the electrodeposition coating specimen was subjected to a corrosion acceleration test (combined cycle test) based on SAEJ2334. That is, as shown in FIG. 3, after each test piece was held in a humid environment (i) 100% relative humidity and 50 ° C. for 6 hours, (ii) 25 ° C. salt water (0.5 mass% NaCl + 0.1 mass%) A series of cycles (i) to (iii), which are immersed in CaCl 2 +0.075 mass% NaHCO 3 ) for 15 minutes and then (iii) kept in a dry environment at 50% relative humidity and 60 ° C. for 17 hours 45 minutes On days 2 of holidays, following the above (iii), (iv) a series of cycles (i) to (iv) were carried out in a dry environment of 30% relative humidity and 50 ° C. for 3 hours. For each test piece that has undergone 120 cycles of tests on weekdays and holidays, the electrodeposition coating is peeled off using a coating film remover (manufactured by Neos Co., Ltd., product name: CS500), and corrosion is generated in accordance with ISO8407. The thing was removed. For the corroded portion near the weld bead toe of each test piece (excluding the 5 mm edge in the width direction of the test piece, up to 60 mm from the weld bead toe), first select a portion with a deep corrosion depth visually. The thickness of the portion thinned by corrosion was measured with a micrometer to determine the corrosion depth (difference from the original plate thickness). This was repeated 10 times or more, and the largest value was obtained as the maximum corrosion depth.
The evaluation results are shown in Table 6.
表５および図４、図５に示すように、比較例（条件１の試験片）では、熱延鋼板の場合、溶接ビード止端部から2mm離れた位置でリン酸亜鉛結晶が全く析出しておらず、合金化溶融亜鉛めっき鋼板の場合、溶接ビード止端部から2mm離れた位置でリン酸亜鉛結晶の析出が観られるものの、スケが観察される。また、熱延鋼板、合金化溶融亜鉛めっき鋼板の何れにおいても、溶接ビード止端部から100μm離れた位置ではリン酸亜鉛結晶が全く析出していない。比較例（条件２の試験片）においても、溶接ビード止端部から2mm離れた位置ではスケが観察される。これに対し、本発明例（条件３）では、溶接ビード止端部から4mm離れた位置は勿論のこと、溶接ビード止端部から2mm離れた位置もリン酸亜鉛結晶で完全に覆われている。本発明例では、溶接ビード止端部から100μm離れた位置においてもリン酸亜鉛結晶の析出が確認され、溶接部および溶接部周辺のリン酸亜鉛結晶が健全に生成している。 As shown in Table 5, FIG. 4, and FIG. 5, in the comparative example (test piece of condition 1), in the case of a hot-rolled steel sheet, zinc phosphate crystals were precipitated at a position 2 mm away from the weld bead toe. In the case of the alloyed hot-dip galvanized steel sheet, although precipitation of zinc phosphate crystals is observed at a position 2 mm away from the weld bead toe, skein is observed. In both hot-rolled steel sheets and galvannealed steel sheets, no zinc phosphate crystals are precipitated at a position 100 μm away from the weld bead toe. Also in the comparative example (test piece of condition 2), a skel is observed at a position 2 mm away from the weld bead toe. On the other hand, in the present invention example (condition 3), not only the position 4 mm away from the weld bead toe, but also the position 2 mm away from the weld bead toe is completely covered with zinc phosphate crystals. . In the example of the present invention, the precipitation of zinc phosphate crystals is confirmed even at a position 100 μm away from the weld bead toe, and the zinc phosphate crystals around the weld and the weld are generated soundly.
また、表６の耐食性評価結果が示すように、比較例（条件１および条件２）と比べて本発明例（条件３）では、腐食深さが小さく、耐食性が改善されている。
Moreover, as the corrosion resistance evaluation result of Table 6 shows, compared with the comparative example (conditions 1 and 2), in the example of the present invention (condition 3), the corrosion depth is small and the corrosion resistance is improved.
Claims (7)
The steel coating member according to claim 6, wherein the steel coating member is an undercarriage member of an automobile.
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