JP5130475B2 - Spot welding method for tin-plated steel sheet - Google Patents
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本発明は、錫系めっき鋼板のスポット溶接方法に関し、特に、錫-亜鉛めっき鋼板のスポット溶接方法に関する。 The present invention relates to a spot welding method for tin-based plated steel sheets, and more particularly to a spot welding method for tin-galvanized steel sheets.
自動車の燃料タンクは、車体のデザインに合わせて最後に設計されることが通常で、その形状は近年益々複雑になる傾向にある。また燃料タンクは自動車の重要保安部品であるため、その使用材料には、優れた深絞り特性は勿論のこと、成型後の衝撃による割れが無いことも要求される。これに加えて、フィルター目詰まりに繋がるような腐食生成物の生成が無く、孔あき腐食の懸念の無い材料で、しかも容易に安定して接合できる材料であることも重要である。 The fuel tank of an automobile is usually designed last in accordance with the design of the vehicle body, and its shape tends to become increasingly complex in recent years. Further, since the fuel tank is an important safety part for automobiles, the material used is required not only to have excellent deep drawing characteristics but also to be free from cracking due to impact after molding. In addition to this, it is also important that the material is free from the generation of corrosion products that can lead to filter clogging, has no concern about perforated corrosion, and can be easily and stably joined.
これら様々な特性を有する材料として、従来よりターンシートと称されるＰｂ−Ｓｎ合金めっき鋼板（特公昭５７−６１８３３号公報：下記特許文献1）が主に使用されてきた。この材料はガソリンに対して安定な化学的性質を持ち、かつめっきが潤滑性に優れるためプレス成形性に優れ、またスポット溶接やシーム溶接性、半田性にも優れている。これ以外にも亜鉛めっき鋼板に厚クロメート処理を施した鋼板も使用されており、Ｐｂ−Ｓｎ合金程ではないが、やはり優れた加工性、耐食性、接合性を有している。しかし近年環境への負荷という意味からＰｂを使用しない材料が希求されている。 As a material having these various characteristics, a Pb—Sn alloy-plated steel sheet (Japanese Patent Publication No. 57-61833: Patent Document 1 below) conventionally called a turn sheet has been mainly used. This material has stable chemical properties with respect to gasoline, and since the plating is excellent in lubricity, it is excellent in press formability, and is excellent in spot welding, seam weldability and solderability. In addition to this, a steel plate obtained by subjecting a galvanized steel plate to a thick chromate treatment is also used, and although it is not as high as a Pb—Sn alloy, it also has excellent workability, corrosion resistance, and bondability. However, in recent years, materials that do not use Pb have been demanded from the viewpoint of environmental burden.
このＰｂを使用しない自動車燃料タンク材料の候補材の一つとして、錫系めっき鋼板がある。Ｓｎは表面に安定な酸化皮膜が形成されるため、ガソリンを始めとして、アルコールやガソリン等が劣化したときに生じる有機酸に対しても耐食性が良好である。また、Ｐｂと同様、軟質な金属であり、加工時に潤滑作用を有することも知られている。その一方、Ｓｎは一般の環境ではＦｅよりも貴な電位にあり、ピンホールや加工疵等から地鉄が溶出しやすいという欠点を有しており、この課題の解決方法として、特開平８−２６９７３３号公報（下記特許文献２）には、適正量のＺｎを添加する方法が提案されている。 As one of candidate materials for automobile fuel tank material that does not use Pb, there is a tin-based plated steel sheet. Since a stable oxide film is formed on the surface of Sn, corrosion resistance is good even with respect to organic acids generated when alcohol, gasoline, and the like are deteriorated, including gasoline. It is also known that it is a soft metal like Pb and has a lubricating action during processing. On the other hand, Sn has a more noble potential than Fe in a general environment, and has the disadvantage that ground iron is likely to elute from pinholes, processing troughs, and the like. No. 269733 (Patent Document 2) proposes a method of adding an appropriate amount of Zn.
しかし自動車燃料タンクは、多くの付属品やパイプを接合する必要や、燃料の漏れの無いよう、周囲を溶接する必要があり、材料側には良好で、連続生産を妨げない安定した接合性が要求される。ところが、錫系めっき鋼板は、スポット溶接やシーム溶接等の抵抗溶接は可能であるものの、めっき層のＳｎが溶接電極であるＣｕと合金化しやすいという性質を有するために、電極先端がＳｎ−Ｃｕ系金属間化合物に転化していき、この金属間化合物は脆性であるため次第に欠損していって十分な発熱が得られなくなり、電極の寿命の指標となる連続打点性が劣るという課題があった。この課題は特にスポット溶接時に顕著となるもので、スポット溶接時の電極寿命が極端に短くなっていた。 However, automobile fuel tanks require many accessories and pipes to be joined, and the surroundings need to be welded so that no fuel leaks. Required. However, although the tin-based plated steel sheet can be subjected to resistance welding such as spot welding or seam welding, it has a property that Sn of the plating layer is easily alloyed with Cu which is a welding electrode. Since this intermetallic compound is brittle, it gradually loses and cannot generate sufficient heat, and there is a problem that the continuous dot property, which is an indicator of the life of the electrode, is inferior. . This problem is particularly noticeable during spot welding, and the electrode life during spot welding has been extremely short.
その対策として、特許第３００２４４５号公報（下記特許文献３）には、抵抗溶接性、半田、ロウ付け性に及ぼす材料側の諸因子について詳細に検討し、表面の接触抵抗値を適正に制御することで、良好な抵抗溶接性、半田、ロウ付け性を得られることを見出し、鋼板を２枚重ね、一対の電極で挟み、１２．６ｋｇｆ／ｍｍ2 の面圧をかけたときの電極間の接触抵抗値が０．１〜８ｍΩであることを特徴とする、抵抗溶接性に優れた自動車燃料タンク用溶融錫系めっき鋼板が提案されている。 As a countermeasure, Japanese Patent No. 3002445 (Patent Document 3 below) examines in detail various factors on the material side that affect resistance weldability, solder, and brazeability, and appropriately controls the contact resistance value of the surface. And found that good resistance weldability, solder and brazing can be obtained, and two steel plates are stacked and sandwiched between a pair of electrodes, and a surface pressure of 12.6 kgf / mm 2 is applied between the electrodes. A hot-dip galvanized steel sheet for automobile fuel tanks having excellent resistance weldability, characterized by a contact resistance value of 0.1 to 8 mΩ, has been proposed.
しかし、この方法により抵抗溶接性を向上させることができるが、抵抗溶接を行う際の発熱により、めっき層中のＳｎが溶けて地鉄の粒界に入り込んで割れが発生する、いわゆる低融点金属侵入割れが発生するという問題点があり、従来は溶接電流を少なくすることにより対処するほかなく電極寿命低下による生産性の低下を招いていた。
また、溶接中にめっき層の錫系合金を溶融させないために特開平１−３０６０７８（下記特許文献４）に示すような油の気化熱を利用して電極の温度上昇を防ぐことは効果的である。しかし、特許文献４は亜鉛めっき鋼板に関するもので、溶接用として一般的に使用されている合金化溶融亜鉛めっき鋼板の場合、表面のめっき層の融点は７００℃程度と高い。これに対して本願が対象とする錫系めっき鋼板の場合、めっき層の融点は２３０℃付近であり、はるかに大きな冷却効果が必要とされるので特許文献４の方法を使用しても十分な効果を得ることができなかった。
In order to prevent the tin-based alloy of the plating layer from being melted during welding, it is effective to prevent the temperature of the electrode from rising by utilizing the heat of vaporization of oil as shown in JP-A-1-306078 (Patent Document 4 below). is there. However, Patent Document 4 relates to a galvanized steel sheet, and in the case of an alloyed hot-dip galvanized steel sheet generally used for welding, the melting point of the surface plating layer is as high as about 700 ° C. On the other hand, in the case of the tin-based plated steel sheet that is the subject of the present application, the melting point of the plating layer is around 230 ° C., and a much greater cooling effect is required, so that the method of Patent Document 4 is sufficient. The effect could not be obtained.
本発明は、前記のようなめっき層中のＳｎが溶けて地鉄の粒界に入り込んで割れが発生する、いわゆる低融点金属侵入割れを防止して電極寿命向上させることができる錫系めっき鋼板のスポット溶接方法を提供することを課題とする。 The present invention is a tin-plated steel sheet which can improve the electrode life by preventing so-called low melting point metal intrusion cracking, in which Sn in the plating layer as described above melts and enters the grain boundary of the base iron to generate cracks. It is an object of the present invention to provide a spot welding method.
本発明者らは、低融点金属侵入割れを防止して電極寿命向上させることができる錫系めっき鋼板のスポット溶接方法を提供するものであり、その要旨とするところは特許請求の範囲に記載した通りの下記内容である。
（１）自動車の燃料タンク用の錫−亜鉛めっき鋼板をスポット溶接する前の溶接電極接触部に、水の質量％が２０％以下の油と水の混合液を塗布することを特徴とする錫系めっき鋼板のスポット溶接方法。
（２）前記油と水の混合液の塗布量を、めっき鋼板の溶接電極接触部1点当たり0.05ml以上とすることを特徴とする請求項１に記載の錫系めっき鋼板のスポット溶接方法。
＜作用＞
（１）の発明によれば、自動車の燃料タンク用の錫−亜鉛めっき鋼板をスポット溶接する前の溶接電極接触部に、水の質量％が２０％以下の油と水の混合液を塗布することにより、容易に入手できる液体で低融点金属侵入割れの防止効果を高めつつ、水分による腐食を防止することができる。
（２）の発明によれば、前記油と水の混合液の塗布量を、めっき鋼板の溶接電極接触部1点当たり0.05ml以上とすることにより、スポット溶接時の発熱を十分に吸収することができ、低融点金属侵入割れの防止効果をさらに向上させることができる。
The present inventors have found that there is provided a spot welding method for tin-plated steel sheet can be improved electrode life by preventing the low melting point metal intrusion cracking, and has as its gist described in the claims The following contents of the street.
(1) Tin characterized by applying a mixed solution of oil and water having a mass% of water of 20% or less to a welding electrode contact portion before spot welding a tin-zinc- plated steel sheet for an automobile fuel tank Spot-welding method for galvanized steel sheet.
(2) The spot welding method for a tin-based plated steel sheet according to claim 1, wherein an application amount of the mixed liquid of oil and water is 0.05 ml or more per weld electrode contact portion of the plated steel sheet.
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According to the invention of (1), a mixed liquid of oil and water whose mass% of water is 20% or less is applied to the welding electrode contact portion before spot-welding a tin-galvanized steel sheet for an automobile fuel tank. This makes it possible to prevent corrosion due to moisture while enhancing the effect of preventing low-melting-point metal intrusion cracking with easily available liquids.
According to the invention of (2), heat generated during spot welding can be sufficiently absorbed by setting the amount of the mixture of the oil and water to be 0.05 ml or more per point of the weld electrode contact portion of the plated steel sheet. And the effect of preventing low melting point metal intrusion cracking can be further improved.
本発明によれば、抵抗溶接性に及ぼす材料側の諸因子ではなく、錫系めっき鋼板をスポット溶接する前の溶接電極接触部に、100cal/g以上の気化潜熱を有する液体を塗布してスポット溶接時の発熱を吸収することにより低融点金属侵入割れを防止して電極寿命向上させることができる錫系めっき鋼板のスポット溶接方法を提供することができ、具体的には下記のような産業上有用な著しい効果を奏する。
１）めっき層中のＳｎが溶けて地鉄の粒界に入り込んで割れが発生する低融点金属侵入割れを防止することができる。
２）スポット溶接時の発熱を十分に吸収することができ、低融点金属侵入割れの防止効果をさらに向上させることができる。
３）容易に入手できる液体で低融点金属侵入割れの防止効果を実現することができる。
４）低融点金属侵入割れの防止効果を高めつつ、水分による腐食を防止することができる。
According to the present invention, it is not a factor on the material side that affects resistance weldability, but a spot having a vaporization latent heat of 100 cal / g or more is applied to the welding electrode contact portion before spot welding the tin-based plated steel sheet. By absorbing heat generated during welding, it is possible to provide a spot welding method for tin-based plated steel sheets that can prevent low-melting-point metal intrusion cracking and improve electrode life. Useful and significant effect.
1) It is possible to prevent low-melting-point metal intrusion cracking, in which Sn in the plating layer melts and enters the grain boundary of the base iron to generate cracks.
2) Heat generated during spot welding can be sufficiently absorbed, and the effect of preventing low melting point metal penetration cracks can be further improved.
3) The effect of preventing low melting point metal intrusion cracking can be realized with an easily available liquid.
4) It is possible to prevent corrosion due to moisture while enhancing the effect of preventing low melting point metal intrusion cracking.
本発明の錫系めっき鋼板のスポット溶接方法を実施するための最良の形態について以下に詳述する。 The best mode for carrying out the spot welding method for tin-plated steel sheet according to the present invention will be described in detail below.
図１は、本発明における錫系めっき鋼板のスポット溶接方法実施形態を例示する図である。 FIG. 1 is a view illustrating a spot welding method embodiment of a tin-plated steel sheet according to the present invention.
図1において、１は電極、２はＳｎ-Ｚｎめっき鋼板、３は油と水の混合液を示す。 In FIG. 1, 1 is an electrode, 2 is a Sn—Zn plated steel sheet, and 3 is a mixture of oil and water.
通常の溶接缶用材料にも錫系めっきが利用され、溶接電極もＣｕであるが、缶用材料の場合には、スポット溶接ではなくシーム溶接であるうえ、板厚が薄く、また鍛接状態の接合であるため、溶接に必要な熱量は非常に小さい。かつＳｎの付着量も非常に小さいため、このような問題は生じない。自動車燃料タンクというような、高い防錆力と強度を求められる用途において、板厚、めっき付着量を高くする必要があり、かつスポット溶接を多用するような用途であるため、電極材料と反応しやすい錫系めっきにおいては、電極とＳｎとの反応という問題が生じる。 Tin-based plating is also used for ordinary welding can materials, and the welding electrode is also Cu. However, in the case of can materials, seam welding is used instead of spot welding, the plate thickness is thin, and the welded state is also low. Because it is a joint, the amount of heat required for welding is very small. In addition, since the amount of Sn deposited is very small, such a problem does not occur. In applications that require high rust prevention and strength, such as automobile fuel tanks, it is necessary to increase the plate thickness and plating coverage, and it is an application that frequently uses spot welding, so it reacts with electrode materials. In easy tin-based plating, there arises a problem of reaction between the electrode and Sn.
本発明者等は、スポット溶接する際の低融点金属侵入割れの発生メカニズムについて検討した。 The inventors of the present invention have studied the mechanism of low-melting-point metal intrusion cracking during spot welding.
図1に示すように、２枚のＳｎ-Ｚｎめっき鋼板２を重ね合わせて上下から電極1を接触させて電気抵抗によりスポット溶接する際の鋼板表面の温度は６００〜８００℃になる。 As shown in FIG. 1, when the two Sn—Zn plated steel plates 2 are overlapped and the electrode 1 is contacted from above and below and spot welding is performed by electric resistance, the temperature of the steel plate surface becomes 600 to 800 ° C.
一方、Ｓｎの融点は２３４℃なのでＳｎは溶融状態となり地鉄の粒界に侵入し、溶接後に冷却されて固まる際の地鉄の体積収縮により割れが発生するものと考えられる。 On the other hand, since Sn has a melting point of 234 ° C., Sn is in a molten state and enters the grain boundary of the steel, and it is considered that cracking occurs due to volumetric shrinkage of the steel when cooled and solidified after welding.
そこで、本発明者らは、錫系めっき鋼板をスポット溶接する前の溶接電極接触部に、100cal/g以上の気化潜熱を有する液体を塗布してスポット溶接時の発熱を吸収することにより低融点金属侵入割れを防止することができることを見出した。 Therefore, the present inventors applied a liquid having a latent heat of vaporization of 100 cal / g or more to the welding electrode contact portion before spot welding the tin-based plated steel sheet to absorb heat generated during spot welding, thereby reducing the melting point. It has been found that metal penetration cracks can be prevented.
錫系めっき鋼板をスポット溶接する前の溶接電極接触部に、100cal/g以上の気化潜熱を有する液体を塗布することにより、スポット溶接時の発熱を吸収することができるので、めっき層中のＳｎが溶けて地鉄の粒界に入り込んで割れが発生する低融点金属侵入割れを防止することができる。 By applying a liquid having a latent heat of vaporization of 100 cal / g or more to the weld electrode contact portion before spot welding of the tin-based plated steel sheet, heat generated during spot welding can be absorbed, so Sn in the plating layer It is possible to prevent low-melting-point metal intrusion cracks that melt and enter into the grain boundaries of the base iron and cause cracks.
本発明においては、100cal/g以上の気化潜熱を有する液体の種類は問わないが、入手が容易で安価な、油もしくは水、もしくは、油と水の混合液とすることにより、容易に入手できる液体で低融点金属侵入割れの防止効果を実現することができる。 In the present invention, the type of liquid having a latent heat of vaporization of 100 cal / g or more is not limited, but it can be easily obtained by making it an easily available and inexpensive oil or water or a mixture of oil and water. The effect of preventing low-melting-point metal intrusion cracking can be realized with liquid.
また、100cal/g以上の気化潜熱を有する液体を油と水の混合液とする場合に、水の質量％が２０％以下の油と水の混合液とすることにより、低融点金属侵入割れの防止効果を高めつつ、水分による腐食を防止することができる。 In addition, when a liquid having a latent heat of vaporization of 100 cal / g or more is used as a mixed liquid of oil and water, a low melting point metal intrusion cracking can be obtained by using a mixed liquid of oil and water whose mass% of water is 20% or less. Corrosion due to moisture can be prevented while enhancing the prevention effect.
本発明においては、錫系めっき鋼板をスポット溶接する前の溶接電極接触部に100cal/g以上の気化潜熱を有する液体を塗布する方法は問わないが、ブラシやハケ等で塗る方法や、電極１の横から噴射する等の方法で塗布することが好ましい。
本発明において、鋼板の表面に接触抵抗に寄与する何らかの皮膜を付与することが好ましい。これらは酸化皮膜、水酸化皮膜、陽極酸化皮膜、化成皮膜、有機樹脂皮膜等であるが、本発明においては特にその種類及び製造法を限定するものではない。但し、工業的によく利用されているのはクロメート（VI、III）に代表される化成皮膜、あるいはジルコニウム系やチタニウム系の無機系皮膜、シランカップリング等の有機無機複合皮膜、有機樹脂皮膜である。この皮膜量を合計で片面２５ｇ／ｍ2 以下とする。そして、皮膜量と表面粗度との組合せ効果により抵抗溶接性、半田、ロウ付け性が確保される。処理の仕方として、片面処理、両面均一処理、両面不均一処理がありうるが、本発明においては、特に規定せずどのような処理も可能である。
In the present invention, there is no limitation on a method of applying a liquid having a latent heat of vaporization of 100 cal / g or more to a welding electrode contact portion before spot welding of a tin-based plated steel sheet. It is preferable to apply by a method such as spraying from the side.
In the present invention, it is preferable to provide some film that contributes to contact resistance on the surface of the steel sheet. These are an oxide film, a hydroxide film, an anodized film, a chemical conversion film, an organic resin film, etc., but in the present invention, the type and production method are not particularly limited. However, chemical coatings typified by chromate (VI, III), zirconium-based and titanium-based inorganic coatings, organic-inorganic composite coatings such as silane coupling, and organic resin coatings are widely used industrially. is there. The total coating amount is 25 g / m 2 or less on one side. And, resistance weldability, solder, and brazeability are ensured by the combined effect of the coating amount and the surface roughness. As processing methods, there may be single-sided processing, double-sided uniform processing, and double-sided non-uniform processing. However, in the present invention, any processing is possible without particular limitation.
錫系めっきの表面皮膜として、クロメート処理（VI、III）があり、耐食性、溶接性等のバランスのとれた処理である。この処理を適用する場合には、その付着量を金属Ｃｒ換算で２〜２００ｍｇ／ｍ2とする。２ｍｇ／ｍ2 以下では、処理量が不十分で、錫系めっきの表面粗度が十分低くても、狙いとする接触抵抗値を得ることが困難であり望ましくない。また２００ｍｇ／ｍ2超の処理は、外観が黄色くなりやすいこと、接触抵抗値が過大になりやすいことから、望ましくない。クロメート皮膜の種類として、塗布型、電解型、反応型等あり、クロメートの組成も無機成分のみのタイプや樹脂を多量に含有するタイプ等あるが、これらについては特に限定するものではない。 There is a chromate treatment (VI, III) as a surface coating of tin-based plating, which is a balanced treatment such as corrosion resistance and weldability. When this treatment is applied, the adhesion amount is set to 2 to 200 mg / m 2 in terms of metal Cr. If it is 2 mg / m 2 or less, the treatment amount is insufficient, and even if the surface roughness of the tin-based plating is sufficiently low, it is difficult to obtain a target contact resistance value, which is not desirable. Further, treatment exceeding 200 mg / m 2 is not desirable because the appearance tends to become yellow and the contact resistance value tends to be excessive. There are various types of chromate films, such as a coating type, an electrolytic type, a reactive type, and the like, and the chromate composition includes a type containing only an inorganic component and a type containing a large amount of resin. However, these are not particularly limited.
めっきの付着量としては、片面当たり１０〜７０ｇ／ｍ2 であることが望ましい。一般に、めっき付着量が増大するほど、電極との反応物質が多いことを意味し、溶接性は劣化する傾向にある。その一方で、耐食性はめっき付着量が多いほど有利に働くため、両特性を満足する付着量は限られる。更に、本発明は、溶融法によるめっきを前提としているが、溶融めっき法において、極端に薄目付けとすることは困難である。従って望ましい付着量として、十分な耐食性が得られず、また安定して外観の優れためっきを行うことも困難になるため、付着量の下限は１０ｇ／ｍ2が、また溶接性が劣化するため上限は７０ｇ／ｍ2 が望ましい。 The amount of plating is desirably 10 to 70 g / m 2 per side. In general, the larger the amount of plating attached, the more reactive material with the electrode, and the weldability tends to deteriorate. On the other hand, since the corrosion resistance works more advantageously as the plating adhesion amount is larger, the adhesion amount satisfying both characteristics is limited. Furthermore, although the present invention is premised on plating by a melting method, it is difficult to make it extremely thin in the hot-dip plating method. Therefore, as a desirable adhesion amount, sufficient corrosion resistance cannot be obtained, and it is difficult to stably perform plating with excellent appearance, so the lower limit of the adhesion amount is 10 g / m 2 and the weldability deteriorates. The upper limit is preferably 70 g / m 2 .
最後にめっきの組成について説明する。本発明は、錫系めっきとするが、前記した理由によりめっき層中にＺｎを添加することが好ましい。Ｓｎは前述したように、耐食性に優れる金属であるが、母材の鋼板に対する犠牲防食能がないため、ピンホール等の欠陥、カジリ等の加工疵から母材の腐食が進展する懸念がある。Ｓｎめっき中にＺｎを添加することで、Ｓｎに起因する高い耐食性に加え、犠牲防食能を付与することが可能で、総合的に極めて高い耐食性を発揮することが可能となる。 Finally, the composition of the plating will be described. Although the present invention is based on tin plating, it is preferable to add Zn to the plating layer for the reason described above. As described above, Sn is a metal having excellent corrosion resistance. However, since there is no sacrificial anticorrosive ability of the base material to the steel plate, there is a concern that the base material may be corroded due to defects such as pinholes and processing defects such as galling. By adding Zn during Sn plating, in addition to high corrosion resistance due to Sn, sacrificial anticorrosive ability can be imparted, and extremely high corrosion resistance can be exhibited comprehensively.
この機能を付与するには、めっき中のＺｎ添加量が１％以上必要であり、また多量のＺｎが存在するとＺｎの偏析が起こりやすく、Ｚｎの優先腐食とこれによる腐食生成物形成という問題が生じる。この理由から、Ｚｎ濃度の上限は４０％が望ましい。他の成分については、特に限定するものではない。不純物元素として、微量のＦｅ，Ｎｉ等がありうる。また必要に応じ、Ｍｇ，Ａｌ，ミッシュメタル，Ｓｂ等を添加しても構わない。 In order to impart this function, the amount of Zn added during plating needs to be 1% or more. If a large amount of Zn is present, segregation of Zn is likely to occur, and there is a problem of preferential corrosion of Zn and formation of corrosion products due to this. Arise. For this reason, the upper limit of the Zn concentration is preferably 40%. Other components are not particularly limited. The impurity element can be a trace amount of Fe, Ni, or the like. If necessary, Mg, Al, Misch metal, Sb, or the like may be added.
使用するめっき原板の組成は特に限定するものではない。しかし高度な加工性を要求される部位だけに、加工性に優れたＩＦ鋼の適用が望ましく、さらには溶接後の溶接気密性、二次加工性等を確保するためにＢを数ｐｐｍ添加した鋼板が望ましい。また鋼板の製造法としては通常の方法によるものとする。鋼成分は例えば転炉−真空脱ガス処理により調節されて溶製され、鋼片は連続鋳造法等で製造され、熱間圧延される。熱間圧延、またそれに続く冷間圧延の条件は鋼板の深絞り性に影響を与える。特に優れた深絞り性を付与するには、熱延時の加熱温度を１１５０℃程度と低めに、また熱延の仕上げ温度は８００℃程度と低めに、巻き取り温度は６００℃以上と高めに、冷延の圧下率は８０％程度と高めにすると良い。 The composition of the plating base plate to be used is not particularly limited. However, it is desirable to apply IF steel with excellent workability only to parts that require high workability. Furthermore, several ppm of B is added to ensure weld-tightness and secondary workability after welding. A steel plate is desirable. In addition, the manufacturing method of the steel sheet is a normal method. The steel component is adjusted and melted by, for example, a converter-vacuum degassing process, and the steel slab is manufactured by a continuous casting method or the like and hot-rolled. The conditions of hot rolling and subsequent cold rolling affect the deep drawability of the steel sheet. In order to give particularly excellent deep drawability, the heating temperature during hot rolling is lowered to about 1150 ° C., the finishing temperature of hot rolling is lowered to about 800 ° C., and the winding temperature is raised to 600 ° C. or higher. The rolling reduction of cold rolling should be as high as about 80%.
めっきの前処理、めっき条件等は特に限定するものではない。錫系めっきの前処理として、ＮｉやＦｅ−Ｎｉ等のプレめっきを施すことも可能である。また、溶融めっき方法として大きくフラックス法と、ゼンジマー法があるが、どちらの製造法でも製造可能である。さらに、めっき後の後処理として、クロメート等の化成処理、有機樹脂被覆以外に、溶融めっき後の外観均一化処理であるゼロスパングル処理、めっきの改質処理である焼鈍処理、表面状態、材質の調整のための調質圧延等があり得るが、本発明においては特にこれらを限定せず、適用することも可能である。 The pretreatment of plating, plating conditions, etc. are not particularly limited. As a pretreatment for tin-based plating, pre-plating such as Ni or Fe—Ni can be performed. Moreover, there are a flux method and a Sendzimer method as the hot dip plating method, but both methods can be used. Furthermore, as post-treatment after plating, in addition to chemical treatment such as chromate, coating with organic resin, zero spangle treatment, which is a uniform appearance after hot-dip plating, annealing treatment, which is a plating modification treatment, surface condition, material There may be temper rolling for adjustment, etc., but in the present invention, these are not particularly limited and can be applied.
次に実施例により本発明をさらに詳細に説明する。 Next, the present invention will be described in more detail with reference to examples.
表１に示す成分の鋼を通常の転炉−真空脱ガス処理により溶製し、鋼片とした後、通常の条件で熱間圧延、冷間圧延、連続焼鈍工程を行い、焼鈍鋼板（板厚０．８ｍｍ）を得た。この鋼板の一部にワット浴でＮｉめっきを１ｇ／ｍ2施した後、フラックス法でＳｎ−Ｚｎめっきを行った。フラックスはＺｎＣｌ2 水溶液をロール塗布して使用し、Ｚｎの組成は０〜６０％まで変更した。浴温は２８０℃とし、めっき後エアワイピングによりめっき付着量を調整した。こうして製造しためっき鋼板を種々の粗度を有するロールで調質圧延して表面粗度を調節した。この鋼板に数種類の後処理を施した。後処理の種類と組成を表２に示す。上記組合せの材料にてスポット溶接性（電極寿命＆低融点金属侵入割れ）を評価した結果を表３に示す。
Steels having the components shown in Table 1 are melted by ordinary converter-vacuum degassing treatment to form steel pieces, and then subjected to hot rolling, cold rolling and continuous annealing processes under normal conditions, and annealed steel sheets (sheets) A thickness of 0.8 mm) was obtained. A part of this steel plate was subjected to Ni plating with a Watt bath at 1 g / m 2 and then Sn—Zn plating by a flux method. The flux was used by applying a ZnCl 2 aqueous solution in a roll, and the composition of Zn was changed from 0 to 60%. The bath temperature was 280 ° C., and the plating adhesion amount was adjusted by air wiping after plating. The plated steel sheet thus produced was temper-rolled with rolls having various roughnesses to adjust the surface roughness. Several types of post-treatments were applied to this steel plate. Table 2 shows the types and compositions of post-treatments. Table 3 shows the results of evaluation of spot weldability (electrode life & low melting point metal intrusion cracking) using the materials of the above combinations.
水の気化潜熱（539cal/g）に比較して油のそれは50〜300cal/gと低いため、水の活用が有効であるが、めっき表面に水が残存すると放置している間に錆が発生してしまう。よって、水は、めっきの腐食に悪影響を及ぼさない程度の添加が求められる。実際環境でのさび発生状況調査結果より水混合比は、20%以下が望ましい。界面活性剤添加により水と油の混合させても構わない。
＜溶接性評価内容＞
溶接条件
溶接電流：１０ＫＡ加圧力 ：２４０ｋｇ溶接時間：１２サイクル（６０ＨZ ）
電 極 ：ドームラジアス型電極１６mmφ−８R，先端径６ｍｍ-４０Ｒ
ウェルドローブ：８ｋＡより溶接電流を200Aずつ上げていった際のナゲット断面径が4√ｔ=3.6mmを下限(Io)とし、チリ発生電流値を上限（Ie）とした。
ナゲット径は、溶接部中心断面を鏡面研磨して５％ナイタールエッチングして溶融相当部を計測した。
＜評価項目＞
電極寿命： チリ発生電流値（Ie）の95%電流値にて溶接し、25点毎にナゲット径を調査して、ナゲット径が4√ｔ=3.6mmを下回った打点を電極寿命とした。電極寿命200点以上をOKとした。
低融点金属侵入割れ：ナゲット断面にて鋼板表面を顕微鏡で観察した。
0.2mm以上ワレ長さが存在した場合をNGとした。
The use of water is effective because it is as low as 50 to 300 cal / g compared to the latent heat of vaporization of water (539 cal / g), but rusting occurs when water remains on the plating surface. Resulting in. Therefore, water is required to be added to the extent that it does not adversely affect the corrosion of the plating. The water mixing ratio is preferably 20% or less based on the results of the rust occurrence survey in the actual environment. Water and oil may be mixed by adding a surfactant.
<Contents of weldability evaluation>
Welding conditions Welding current: 10KA pressure: 240 kg Welding time: 12 cycles (60H Z)
Electrode: Dome radius type electrode 16mmφ-8R, tip diameter 6mm-40R
Weld lobe: The nugget sectional diameter when the welding current was increased by 200 A from 8 kA was 4√t = 3.6 mm as the lower limit (Io), and the dust generation current value was set as the upper limit (Ie).
The nugget diameter was measured by mirror-polishing the center cross section of the weld and 5% nital etching to measure the melt equivalent.
<Evaluation items>
Electrode life: Welding was carried out at a current value of 95% of the dust generation current value (Ie), the nugget diameter was investigated every 25 points, and the spot where the nugget diameter was less than 4√t = 3.6 mm was defined as the electrode life. An electrode life of 200 points or more was considered OK.
Low melting point metal intrusion cracking: The steel sheet surface was observed with a microscope in the nugget cross section.
The case where there was a crack length of 0.2 mm or more was determined as NG.
腐食試験 ：水とメタノール（気化潜熱264cal/g）の混合液を10g/m2になるようにめっき鋼板上に塗布した。気温２５℃、相対湿度６０％の恒温高湿槽中に暴露して２４０Hr後の白錆発生状況を観察した。
Corrosion test: A mixed liquid of water and methanol (latent heat of vaporization of 264 cal / g) was applied onto the plated steel sheet so as to be 10 g / m 2 . It was exposed to a constant temperature and high humidity bath at a temperature of 25 ° C. and a relative humidity of 60%, and the occurrence of white rust after 240 hours was observed.
本発明は、錫系めっき鋼板のスポット溶接時に、めっき層中のＳｎが溶けて地鉄の粒界に入り込んで割れが発生する、いわゆる低融点金属侵入割れを簡便な方法で防止することができ、従来のように溶接電流を少なくする必要がないので生産性を著しく向上させることができるため特に燃料タンクにおけるスポット溶接に多用されることが期待される。 The present invention can prevent a so-called low melting point metal intrusion cracking, in which Sn in a plating layer melts and enters a grain boundary of a base iron during spot welding of a tin-based plated steel sheet, by a simple method. Since it is not necessary to reduce the welding current as in the prior art, the productivity can be remarkably improved, so that it is expected to be frequently used especially for spot welding in a fuel tank.
１ 電極
２ Ｓｎ-Ｚｎめっき鋼板
３ 油と水の混合液
1 Electrode 2 Sn—Zn Plated Steel 3 Mixed Oil and Water
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