JP5168204B2 - Spot welding method for steel sheet - Google Patents
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本発明は、高強度鋼板を含む鋼板のスポット溶接継手の疲労強度を向上させるスポット溶接方法に関し、特に、自動車用部品の取付けや車体の組立てなどで使用されるスポット溶接方法において、鋼板のスポット溶接継手の疲労強度を向上させるスポット溶接方法に関するものである。 The present invention relates to a spot welding method for improving the fatigue strength of spot welded joints of steel plates including high-strength steel plates, and more particularly to spot welding methods for spot welding methods used in the mounting of automobile parts and the assembly of vehicle bodies. The present invention relates to a spot welding method for improving the fatigue strength of a joint.
近年、自動車の低燃費化、ＣＯ2排出量削減および衝突安全性向上等の対策のため、自動車分野では、自動車の車体や部品などに、従来の薄肉の軟鋼に代わり薄肉の高強度鋼板を使用するニーズが高まっている。 In recent years, in order to reduce fuel consumption of automobiles, reduce CO 2 emissions and improve collision safety, in the automobile field, thin high-strength steel sheets have been used instead of conventional thin-walled mild steel for automobile bodies and parts. There is a growing need to do so.
自動車の車体の組立てや部品の取付けなどには、スポット溶接方法が主に用いられているが、高強度鋼板をスポット溶接方法で溶接する場合には、以下のような問題がある。 Spot welding methods are mainly used for assembling automobile bodies and mounting parts. However, when high strength steel plates are welded by spot welding methods, there are the following problems.
すなわち、スポット溶接部（溶接継手）の品質指標としては、引張強さとともに疲労強度が重要となる。溶接継手の引張強さは鋼板の引張強さとともに増加するが、溶接継手の疲労強度は、鋼板の引張強さが増加してもほとんど増加しない。 That is, fatigue strength is important as well as tensile strength as a quality index of spot welds (welded joints). Although the tensile strength of the welded joint increases with the tensile strength of the steel sheet, the fatigue strength of the welded joint hardly increases even if the tensile strength of the steel sheet increases.
例えば、引張強さが２７０ＭＰａの軟鋼板の代わりに、引張強さが５９０ＭＰａの高強度鋼板を用いれば、スポット溶接継手の引張せん断強さ（溶接継手のせん断方向に引張荷重を負荷した場合の引張強さ）はほぼ２倍になる。しかし、この場合でも、溶接継手のせん断方向に繰り返し荷重を負荷した場合の疲労強度、例えば、応力負荷の回数が２×１０6回においても疲労破断しない最高荷重を疲労強度と定義すると、この疲労強度は増加せず軟鋼板の場合とほぼ同じ値を示す。 For example, if a high strength steel plate with a tensile strength of 590 MPa is used instead of a mild steel plate with a tensile strength of 270 MPa, the tensile shear strength of the spot welded joint (the tensile strength when a tensile load is applied in the shear direction of the weld joint) Strength) is almost doubled. However, even in this case, if the fatigue strength when a repeated load is applied in the shear direction of the welded joint, for example, the highest load that does not cause fatigue fracture even when the number of stress loads is 2 × 10 6 times, is defined as the fatigue strength, this fatigue The strength does not increase and shows almost the same value as that of the mild steel plate.
このように、疲労強度が低い値を示す原因としては、従来から報告されているように、スポット溶接部のノッチ形状が考えられる。すなわち、図１で示すように、鋼板１の間に存在するナゲット２の周辺の重ね面での接触部分がノッチ形状になっているため、引張せん断方向（矢印方向）３に荷重を負荷して疲労試験を行った場合、鋼板の引張強さが高くても、このノッチ効果によって疲労強度が向上しないと考えられる。
As described above, the cause of the low fatigue strength may be the notch shape of the spot weld, as reported conventionally. That is, as shown in FIG. 1, since the contact portion on the overlapping surface around the
特に、高強度鋼板を用いた場合には、軟鋼板を用いた場合に比べて、ナゲット部の硬さが増加するので、このノッチ効果は顕著になる。一方、剥離方向｛引張せん断方向（矢印方向）３と垂直な方向｝に荷重を負荷して疲労試験を行った場合にも、高強度鋼板の溶接継手の疲労強度は増加せず軟鋼と同等である。 In particular, when a high-strength steel plate is used, the notch effect becomes significant because the hardness of the nugget portion increases as compared with the case where a mild steel plate is used. On the other hand, even when a fatigue test is performed with a load applied in the peeling direction {direction perpendicular to the tensile shear direction (arrow direction) 3}, the fatigue strength of the welded joint of the high-strength steel plate does not increase and is equivalent to that of mild steel. is there.
この場合は、ナゲット周辺部での応力集中が顕著であり、局部の応力負荷が高まり、そこでクラックが発生し易くなるため、引張せん断方向に繰り返し荷重を負荷した場合に比べて、疲労強度は一桁程度低下する。 In this case, stress concentration in the periphery of the nugget is conspicuous, and the stress load at the local area increases, so that cracks are likely to occur there. Therefore, the fatigue strength is less than that when a repeated load is applied in the tensile shear direction. Decrease by an order of magnitude.
一般に、鋼板の引張強さが増加するほど、下記式で示される炭素当量Ｃｅｑの値が高くなる傾向にあり、高強度鋼板のＣｅｑの値は、０．２を超えることが知られている。
Ｃｅｑ＝Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋２Ｐ＋４Ｓ
式中、Ｃ、Ｓｉ、Ｍｎ、Ｐ、および、Ｓは、それぞれ、鋼中の炭素、珪素、マンガン、リン、硫黄の各含有量（質量％）を示す。
In general, it is known that the value of the carbon equivalent Ceq represented by the following formula tends to increase as the tensile strength of the steel plate increases, and the value of Ceq of the high-strength steel plate exceeds 0.2.
Ceq = C + Si / 30 + Mn / 20 + 2P + 4S
In the formula, C, Si, Mn, P, and S indicate the respective contents (mass%) of carbon, silicon, manganese, phosphorus, and sulfur in the steel.
このように、高強度鋼板の引張強さが増加するとともに、その鋼板の炭素当量Ｃｅｑが高くなるため、引張強さが高い高強度鋼板ほどスポット溶接部（ナゲット部）と熱影響部の硬さが高くなり、その結果、靱性が低下して破壊が容易に起こり易くなる。 As described above, the tensile strength of the high-strength steel plate increases and the carbon equivalent Ceq of the steel plate increases. Therefore, the higher strength steel plate having higher tensile strength, the hardness of the spot welded portion (nugget portion) and the heat-affected zone. As a result, the toughness is lowered and the fracture is easily caused.
また、高強度鋼板では、軟鋼に比べてスプリングバック（加工後の弾性的回復によるはね返り）量が大きいため、スポット溶接部には引張の残留応力が発生して疲労強度が低下し易くなったり、また、相対的な延性低下により割れが発生して疲労強度や静的強度が低下し易くなったりする。 In addition, the high strength steel plate has a large amount of springback (bounce due to elastic recovery after processing) compared to mild steel, so that the residual strength of the tensile stress is generated in the spot welded part, and the fatigue strength is likely to decrease. In addition, cracking occurs due to a relative decrease in ductility, and fatigue strength and static strength tend to decrease.
以上の理由で、高強度鋼板のスポット溶接部の疲労強度は、高強度鋼板の引張強さが増加しても増加せず、軟鋼と同程度になると考えられる。 For the above reasons, it is considered that the fatigue strength of the spot welded portion of the high-strength steel plate does not increase even when the tensile strength of the high-strength steel plate increases, and is comparable to that of mild steel.
従来の高強度鋼板のスポット溶接において、溶接継手の疲労強度を向上させる手段としては、スポット溶接の通電が完了した後、一定時間経過後にテンパー通電を行い、スポット溶接部（ナゲット部）と熱影響部を焼鈍して硬さを低下させ、残留応力を変化させる方法が知られている（例えば、非特許文献１参照）。 In conventional spot welding of high-strength steel sheets, as a means of improving the fatigue strength of welded joints, temper energization is performed after a certain period of time has elapsed after spot welding energization, and the effect of heat on the spot welded part (nugget part) A method is known in which the hardness is reduced by annealing the part to change the residual stress (for example, see Non-Patent Document 1).
しかし、この方法は、テンパー通電の適正な条件範囲の幅が非常に狭く、また、操業条件の変化により再現性が乏しいという実用上の問題がある。特に、めっき鋼板を連続的に打点してスポット溶接する場合には、打点数の増加とともに、電極先端がめっきとの合金化反応によって劣化し、電極先端径が増大して電流密度が低下し、最適なテンパー通電条件から外れるため、安定的に継手の疲労強度を向上させることが困難となる。 However, this method has a practical problem that the appropriate condition range of the temper energization is very narrow, and the reproducibility is poor due to a change in operating conditions. In particular, when spot welding is performed by continuously spotting a plated steel sheet, the electrode tip deteriorates due to an alloying reaction with the plating as the number of hit points increases, the electrode tip diameter increases, and the current density decreases, Since it deviates from the optimum temper energization condition, it is difficult to stably improve the fatigue strength of the joint.
スポット溶接部の疲労強度を向上させる方法としては、これ以外にも、疲労強度特性が優れた鋼板を用いてスポット溶接する方法が知られている（例えば、特許文献１〜６参照。）。
In addition to this, as a method for improving the fatigue strength of the spot welded portion, a method of spot welding using a steel plate having excellent fatigue strength characteristics is known (for example, see
しかし、これらの方法は、軟鋼板のスポット溶接に関するものであり、高強度鋼板のスポット溶接部の疲労強度を向上させる方法ではない。 However, these methods relate to spot welding of mild steel plates and are not methods for improving the fatigue strength of spot welded portions of high strength steel plates.
また、高強度鋼板のスポット溶接部の疲労強度を向上させる方法としては、加圧力や保持時間をある範囲に設定することで、溶接部に圧縮残留応力を導入する方法があるが（例えば、特許文献７参照。）、保持時間が長くなることや、軟鋼板と高強度鋼板とでのスポット溶接部が混在する場合を考慮すると、実溶接ラインでの適用は現実的な方法とは言えない。 Moreover, as a method for improving the fatigue strength of the spot welded portion of the high-strength steel sheet, there is a method of introducing compressive residual stress into the welded portion by setting the pressure and holding time within a certain range (for example, patents) Considering the case where the holding time becomes long and the spot welded portion of the mild steel plate and the high-strength steel plate coexist, the application in the actual welding line is not a realistic method.
前述のように、高強度鋼板をスポット溶接した場合の溶接継手の疲労強度は、軟鋼板をスポット溶接した場合の疲労強度と変わらないため、自動車分野において高強度鋼板を用いても、高強度鋼板を用いることによる安全性向上や軽量化による低燃費化、ＣＯ2排出量削減のメリットを十分に享受することができない。 As described above, the fatigue strength of the welded joint when spot-welding a high-strength steel plate is the same as the fatigue strength when spot-welding a mild steel plate, so even if a high-strength steel plate is used in the automotive field, the high-strength steel plate It is not possible to fully enjoy the benefits of improving safety, reducing fuel consumption by reducing weight, and reducing CO 2 emissions.
溶接継手の疲労強度を向上させるため、スポット溶接打点数を増やす従来方法を採用することもできるが、この方法は、作業効率の低下、コスト上昇および設計自由度の制約などの問題を抱えている。 In order to improve the fatigue strength of welded joints, the conventional method of increasing the number of spot welding points can be adopted, but this method has problems such as reduced work efficiency, increased costs, and restrictions on design flexibility. .
そこで、本発明は、これらの従来技術における問題を解決するために、軟鋼のみならず高強度鋼板のスポット溶接において、良好な溶接作業性を確保しつつ溶接継手の疲労強度を向上することができる、鋼板のスポット溶接方法を提供することを目的とする。 Therefore, the present invention can improve the fatigue strength of a welded joint while ensuring good welding workability in spot welding of not only mild steel but also high-strength steel sheets in order to solve these problems in the prior art. It aims at providing the spot welding method of a steel plate.
本発明者は、スポット溶接継手の疲労強度が、ナゲット周辺の残留応力状態に依存することから、ナゲット周辺の残留応力状態を何らかの手段で改善すれば、溶接継手の疲労強度を高めることができるとの発想の下に、ナゲット周辺の残留応力状態を改善する手法について鋭意検討した。 The present inventor believes that since the fatigue strength of the spot welded joint depends on the residual stress state around the nugget, if the residual stress state around the nugget is improved by some means, the fatigue strength of the welded joint can be increased. Based on this idea, we intensively studied a method to improve the residual stress state around the nugget.
その結果、スポット溶接時の通電時間終了後の保持時間中に溶接加圧力を増大させることにより、溶接部周辺に圧縮残留応力を導入し、溶接継手の疲労強度を効果的に高めることができることを見出した。 As a result, by increasing the welding pressure during the holding time after the end of the energizing time at the time of spot welding, it is possible to introduce compressive residual stress around the weld and effectively increase the fatigue strength of the welded joint. I found it.
本発明は、上記の知見に基づきなされたもので、その要旨は、以下のとおりである。 The present invention has been made based on the above findings, and the gist thereof is as follows.
（１） 鋼板スポット溶接継手の疲労強度を向上させる溶接方法において、
スポット溶接後の保持時間Ｈｔ（ｍｓ）のうち、初期加圧力Ｐｉ（ｋＮ）で初期加圧力保持時間Ｈｔｉ（ｍｓ）経過した後に、初期加圧力Ｐｉから後期加圧力Ｐａに加圧力を上昇させ、後期加圧力Ｐａ（ｋＮ）で後期加圧力保持時間Ｈｔａ（ｍｓ）経過させる溶接方法として、
前記の後期加圧力Ｐａ（ｋＮ）は下記（式１）を満たし、
前記の初期加圧力保持時間Ｈｔｉ（ｍｓ）は下記（式２）を満たし、
前記の後期加圧力保持時間Ｈｔａ（ｍｓ）は下記（式３）を満たし、
前記の初期加圧力Ｐｉ（ｋＮ）は被溶接材として引張強さＴＳ＜４３０ＭＰａの鋼板を用いる場合は下記（式４）、また引張強さＴＳ≧４３０ＭＰａの鋼板を用いる場合は下記（式５）を満たし、
前記の保持時間Ｈｔ（ｍｓ）は下記（式６）を満たす
ようにそれぞれ設定してスポット溶接することを特徴とする、鋼板のスポット溶接方法。
１．５×Ｐｉ≦Ｐａ≦２．５×Ｐｉ （ｋＮ） （式１）
０．３５×Ｈｔ≦Ｈｔｉ≦０．６５×Ｈｔ （ｍｓ） （式２）
Ｈｔａ＝Ｈｔ−Ｈｔｉ （ｍｓ） （式３）
Ｐｉ＝２．４５×ｔ （ｋＮ） （式４）
Ｐｉ＝２．４５×ｔ×（ＴＳ／２７０）0.5 （ｋＮ） （式５）
Ｈｔ＝２００×ｔ−８０ （ｍｓ） （式６）
ただし、ｔは鋼板板厚（ｍｍ）、ＴＳは鋼板の引張強さ（ＭＰａ）。
(1) In a welding method for improving the fatigue strength of a steel plate spot welded joint,
Of the holding time Ht (ms) after spot welding, after the initial pressurizing pressure holding time Hti (ms) has elapsed with the initial pressurizing pressure Pi (kN), the pressurizing force is increased from the initial pressurizing pressure Pi to the late pressurizing pressure Pa, As a welding method in which the late pressurization holding time Hta (ms) elapses at the late pressurization pressure Pa (kN),
The latter applied pressure Pa (kN) satisfies the following (formula 1):
The initial pressure holding time Hti (ms) satisfies the following (Equation 2):
The latter pressurization holding time Hta (ms) satisfies the following (formula 3),
The initial pressure Pi (kN) is the following (Formula 4) when using a steel sheet having a tensile strength TS <430 MPa as a workpiece, and the following (Formula 5) when using a steel sheet having a tensile strength TS ≧ 430 MPa. The filling,
The above-mentioned holding time Ht (ms) is set so as to satisfy the following (Equation 6), and spot welding is performed.
1.5 × Pi ≦ Pa ≦ 2.5 × Pi (kN) (Formula 1)
0.35 × Ht ≦ Hti ≦ 0.65 × Ht (ms) (Formula 2)
Hta = Ht−Hti (ms) (Formula 3)
Pi = 2.45 × t (kN) (Formula 4)
Pi = 2.45 × t × (TS / 270) 0.5 (kN) (Formula 5)
Ht = 200 × t−80 (ms) (Formula 6)
Where t is the steel plate thickness (mm), and TS is the tensile strength (MPa) of the steel plate.
（２） 前記鋼板が、体積分率で５％以上２５％以下の残留オーステナイトを含有するミクロ組織の加工誘起変態型複合組織鋼板であることを特徴とする、上記（１）に記載の鋼板のスポット溶接方法。 (2) The steel sheet according to (1), wherein the steel sheet is a microstructure-induced work-induced transformation type composite steel sheet containing a retained austenite of 5% to 25% in volume fraction. Spot welding method.
本発明によれば、自動車用部品の取付けおよび車体の組立てなどで用いる高強度鋼板等のスポット溶接において、良好な溶接作業性を確保しつつ溶接継手の疲労強度を向上させることができる。したがって、これにより、自動車分野等で高強度鋼板適用による安全性向上や軽量化による低燃料費、ＣＯ2排出量削減のメリットなどを十分に享受できる等、本発明の社会的な貢献は多大である。 ADVANTAGE OF THE INVENTION According to this invention, the fatigue strength of a welded joint can be improved, ensuring favorable welding workability | operativity in spot welding of the high-strength steel plate etc. which are used for the attachment of the components for motor vehicles, the assembly of a vehicle body, etc. Therefore, in this field, the social contribution of the present invention is enormous, such as the safety improvement by applying high-strength steel sheets in the automobile field, the low fuel cost by weight reduction, and the benefits of CO 2 emission reduction. is there.
本発明者は、先ず、高強度鋼板のスポット溶接において、溶接継手の疲労強度を向上させる方法として、
（ａ）溶接金属（ナゲット）端部のノッチ形状を変えて、応力集中が起こり難くする方法、
（ｂ）溶接金属（ナゲット）部とその周辺の熱影響部（ＨＡＺ）の硬さを低下させる方法、
および、
（ｃ）溶接金属（ナゲット）部周囲に圧縮残留応力を発生させて、相対的に残留引張応力を低減させる方法、
の大きく３つの方法について検討した。
The present inventor firstly, in spot welding of high-strength steel plates, as a method of improving the fatigue strength of welded joints,
(A) A method of making stress concentration difficult to occur by changing the notch shape at the end of the weld metal (nugget),
(B) a method of reducing the hardness of the weld metal (nugget) portion and the surrounding heat-affected zone (HAZ);
and,
(C) a method of generating a compressive residual stress around the weld metal (nugget) portion to relatively reduce the residual tensile stress,
Three methods were studied.
（ａ）の方法については、例えば、非特許文献１に記載されているように、意図的に溶接中に散り（通電中、鋼板間に生成された溶融部の直径が銅電極の先端直径より大きくなって、鋼板の隙間から溶融金属が飛散する現象）を発生させて、溶接金属（ナゲット）部の端部形状を変化させる方法が知られているが、この方法では、溶接金属（ナゲット）部の端部形状がばらつき、実際、疲労強度もかなりばらつくことが知られている。
As for the method of (a), for example, as described in
（ｂ）の方法としては、前述のように、溶接終了後に一定時間非通電のまま保持（冷却）した後、再度溶接部に一定時間通電（後通電）して、溶接部をテンパー処理する方法が知られている。しかし、この方法は、既に述べたように、溶接部のテンパー処理のための最適通電条件範囲が非常に狭く、また、操業条件の変化などにより再現性が乏しいという問題を抱えている。 As a method of (b), as described above, after the welding is completed, the energized portion is held (cooled) while being deenergized for a certain period of time, and then the welded portion is energized (post-energized) for a certain period of time, and the welded portion is tempered It has been known. However, as described above, this method has a problem that the optimum energization condition range for the temper treatment of the welded portion is very narrow, and the reproducibility is poor due to a change in operating conditions.
本発明者は、（ｃ）の方法として、電極による溶接部への加圧と溶接金属（ナゲット）部周囲のマルテンサイト変態による体積膨張を利用し残留応力状態を改善する方法が有効であると考え、鋭意実験を行った。その結果、スポット溶接時の通電時間終了後の保持時間中に溶接加圧力を増加させてやることにより、ナゲット周囲に圧縮残留応力を発生させ、溶接継手の疲労強度を向上させることができることを見出した。 As a method of (c), the present inventor believes that the method of improving the residual stress state by utilizing the pressure applied to the welded portion by the electrode and the volume expansion due to the martensitic transformation around the weld metal (nugget) portion is effective. I thought and conducted diligent experiments. As a result, it has been found that by increasing the welding pressure during the holding time after the end of the energization time during spot welding, compressive residual stress can be generated around the nugget and the fatigue strength of the welded joint can be improved. It was.
本発明は、前述したように上記知見に基づいてなされたものである。以下、詳細に説明する。 The present invention has been made based on the above findings as described above. Details will be described below.
図２は、本発明のスポット溶接を説明するための図である。まず、スポット溶接では、被接合材である２枚の鋼板１を重ね合わせ、その重ね合わせ部に銅製の溶接電極４を加圧力（負荷方向）５で加圧しながら通電し、２枚の鋼板１の間に溶融金属部を形成させる。この溶融金属部は、溶接通電終了後、水冷された電極への抜熱や鋼板への熱伝導により冷却されて凝固し、２枚の鋼板１の間に溶接金属（ナゲット）２が形成される。
FIG. 2 is a view for explaining spot welding according to the present invention. First, in spot welding, two
鋼板をスポット溶接した場合、溶接後の溶融金属（ナゲット）部とその周辺の熱影響部（ＨＡＺ）においては、凝固、冷却過程でマルテンサイト変態が起きる際に体積膨張が起きるが、その後、さらに室温までの冷却過程で熱収縮が起き、最終的に形成される溶接金属（ナゲット）部周辺には、引張応力が残留した状態になる。この引張残留応力は、ナゲット端部のノッチ形状とともに、鋼板のスポット溶接継手の疲労強度を低下せしめる主な原因であると考えられる。 When spot-welding a steel plate, volume expansion occurs when martensitic transformation occurs in the solidification and cooling process in the molten metal (nugget) portion and the surrounding heat-affected zone (HAZ) after welding. Thermal contraction occurs in the cooling process to room temperature, and tensile stress remains in the vicinity of the finally formed weld metal (nugget) portion. This tensile residual stress is considered to be the main cause of reducing the fatigue strength of the spot welded joint of the steel sheet together with the notch shape at the end of the nugget.
本発明では、鋼板のスポット溶接の際、下記（式１）を満たすような後期加圧力Ｐａ（ｋＮ）、下記（式２）を満たすような初期加圧力保持時間Ｈｔｉ（ｍｓ）、下記（式３）を満たすような後期加圧力保持時間Ｈｔａ（ｍｓ）、被溶接材として引張強さＴＳ＜４３０ＭＰａの鋼板を用いる場合は下記（式４）、また引張強さＴＳ≧４３０ＭＰａの鋼板を用いる場合は下記（式５）を満たすような初期加圧力Ｐｉ（ｋＮ）、下記（式６）を満たすような保持時間Ｈｔ（ｍｓ）に設定にしてスポット溶接を行う。 In the present invention, during spot welding of a steel sheet, the late pressurization pressure Pa (kN) satisfying the following (formula 1), the initial pressurization holding time Hti (ms) satisfying the following (formula 2), 3) Late pressurization holding time Hta (ms) satisfying 3), when using a steel sheet with tensile strength TS <430 MPa as the welded material (Formula 4), and when using a steel sheet with tensile strength TS ≧ 430 MPa Is set to an initial pressure Pi (kN) that satisfies the following (formula 5) and a holding time Ht (ms) that satisfies the following (formula 6).
１．５×Ｐｉ≦Ｐａ≦２．５×Ｐｉ （ｋＮ） （式１）
０．３５×Ｈｔ≦Ｈｔｉ≦０．６５×Ｈｔ （ｍｓ） （式２）
Ｈｔａ＝Ｈｔ−Ｈｔｉ （ｍｓ） （式３）
Ｐｉ＝２．４５×ｔ （ｋＮ） （式４）
Ｐｉ＝２．４５×ｔ×（ＴＳ／２７０）0.5 （ｋＮ） （式５）
Ｈｔ＝２００×ｔ−８０ （ｍｓ） （式６）
ただし、ｔは鋼板板厚（ｍｍ）、ＴＳは鋼板の引張強さ（ＭＰａ）。
1.5 × Pi ≦ Pa ≦ 2.5 × Pi (kN) (Formula 1)
0.35 × Ht ≦ Hti ≦ 0.65 × Ht (ms) (Formula 2)
Hta = Ht−Hti (ms) (Formula 3)
Pi = 2.45 × t (kN) (Formula 4)
Pi = 2.45 × t × (TS / 270) 0.5 (kN) (Formula 5)
Ht = 200 × t−80 (ms) (Formula 6)
Where t is the steel plate thickness (mm), and TS is the tensile strength (MPa) of the steel plate.
初期加圧力と初期加圧力保持時間、後期加圧力と後期加圧力保持時間及び保持時間は、それぞれ図３に示すとおりである。 The initial pressurizing force and the initial pressurizing pressure holding time, the late pressurizing force, the late pressurizing pressure holding time and the holding time are as shown in FIG.
なお、被溶接材として引張強さＴＳ＜４３０ＭＰａの鋼板を用いる場合は、（式４）が、引張強さＴＳ≧４３０ＭＰａの鋼板を用いる場合は、（式５）が、それぞれ最も代表的な加圧力算出式として知られている。これは、鋼板の引張強さが大きくなる場合には、通電経を確保するために電極加圧力を増加させる必要があるからである。保持時間Ｈｔについても、（式６）によって定義されるものが、最も代表的なものとして知られている。保持時間は、溶接部が一定温度以下なるまで電極による水冷加圧を行うことで、溶接部に内部欠陥を防ぐ目的がある。このため、保持時間は、被溶接材の引張強さには関係がなく、その板厚ｔのみに依存する式で設定される。また、加圧力設定と測定は、溶接機内部にトルクコントロール機構とロードセルを内蔵することで可能となる。 When a steel sheet with a tensile strength TS <430 MPa is used as the material to be welded, (Equation 4) is the most representative addition when (Equation 5) is used when a steel sheet with a tensile strength TS ≧ 430 MPa is used. This is known as a pressure calculation formula. This is because, when the tensile strength of the steel plate is increased, it is necessary to increase the electrode pressing force in order to ensure the energization. Regarding the holding time Ht, the one defined by (Expression 6) is known as the most representative one. The holding time has the purpose of preventing internal defects in the welded portion by performing water-cooling and pressurization with the electrodes until the welded portion is at a certain temperature or lower. For this reason, the holding time is not related to the tensile strength of the material to be welded, and is set by an equation that depends only on the plate thickness t. Further, the pressure setting and measurement can be performed by incorporating a torque control mechanism and a load cell inside the welding machine.
後期加圧力、初期加圧力保持時間、後期加圧力保持時間、初期加圧力を上記（式１）、（式２）、（式３）、（式４）、（式５）を満たすように設定すると、ナゲット部を変形させることが可能となり、その結果、ナゲット部周囲に残留応力を導入させることが可能となって、溶接継手の疲労強度が向上する。 Late pressure, initial pressure holding time, late pressure holding time, and initial pressure are set to satisfy the above (Formula 1), (Formula 2), (Formula 3), (Formula 4), and (Formula 5). As a result, the nugget portion can be deformed, and as a result, residual stress can be introduced around the nugget portion, and the fatigue strength of the welded joint is improved.
後期加圧力Ｐａは、上記（式１）に従って、また後期加圧力保持時間Ｈｔａは（式２）に従って設定するが、該（式１）、（式２）を導出する根拠となった実験結果の一例を図３に示す。 The late pressurization pressure Pa is set according to the above (formula 1), and the late pressurization pressure holding time Hta is set according to the (formula 2), but the experimental results used as the basis for deriving the (formula 1) and (formula 2) An example is shown in FIG.
図４は、先端径が６ｍｍ、先端曲率径が４０ｍｍのＪＩＳ−ＤＲ６φ型電極を用い、板厚１．２ｍｍの引張強さＴＳ＝５９０ＭＰａ級鋼板をスポット溶接し、直径５．５ｍｍのナゲットを形成させた場合における後期加圧力と初期加圧力比Ｐａ／Ｐｉ、後期加圧力保持時間と保持時間比Ｈｔａ／Ｈｔ、溶接継手の疲労強度の評価結果（図中の○印および×印）との関係を示している。 Fig. 4 shows a nugget with a diameter of 5.5 mm by spot welding a tensile strength TS = 590 MPa grade steel plate with a thickness of 1.2 mm using a JIS-DR6φ type electrode with a tip diameter of 6 mm and a tip curvature diameter of 40 mm. Relationship between late pressurization and initial pressurization ratio Pa / Pi, late pressurization holding time and holding time ratio Hta / Ht, and fatigue strength evaluation results of welded joints (marked with ○ and × in the figure) Is shown.
図５は、先端径が６ｍｍ、先端曲率径が４０ｍｍのＪＩＳ−ＤＲ８φ型電極を用い、板厚２．０ｍｍの引張強さＴＳ＝５９０ＭＰａ級鋼板をスポット溶接し、直径７ｍｍのナゲットを形成させた場合における後期加圧力と初期加圧力比Ｐａ／Ｐｉ、後期加圧力保持時間と保持時間比Ｈｔａ／Ｈｔ、溶接継手の疲労強度の評価結果（図中の○印および×印）との関係を示している。図４、図５中において、溶接継手の疲労強度が引張強さＴＳ＝５９０ＭＰａの鋼板を初期加圧力Ｐｉ一定で溶接した時の疲労強度に対して向上したものを○、向上しないものを×で示した。 In FIG. 5, a JIS-DR8φ type electrode having a tip diameter of 6 mm and a tip curvature diameter of 40 mm was used, and a 2.0 mm thick tensile strength TS = 590 MPa grade steel plate was spot welded to form a 7 mm diameter nugget. Shows the relationship between late pressure and initial pressure ratio Pa / Pi, late pressure holding time and holding time ratio Hta / Ht, and fatigue strength evaluation results (circles and x in the figure) ing. In FIG. 4 and FIG. 5, the case where the fatigue strength of the welded joint is improved with respect to the fatigue strength when the steel plate having the tensile strength TS = 590 MPa is welded at the initial pressure Pi is constant, and the case where the fatigue strength is not improved is indicated by ×. Indicated.
図４、図５から、鋼板をスポット溶接する際には、保持時間中に加圧力を増加させ、後期加圧力Ｐａ（ｋＮ）と後期加圧力保持時間Ｈｔａ（ｍｓ）を上記（式１）、（式２）に従って設定すれば、疲労強度が良好な溶接継手を形成させることが可能だとわかる。なお、図４では、板厚が１．２ｍｍ、図５では、板厚が２．０ｍｍの場合の実験結果の例を示したが、一般に、自動車用部品や車体などで疲労強度が必要な部位に使用される鋼板の板厚１．０〜２．３ｍｍにおいても、同様に充分な効果を奏することができることを確認している。 4 and 5, when spot welding the steel sheet, the pressurizing force is increased during the holding time, and the late pressurizing pressure Pa (kN) and the late pressurizing pressurizing holding time Hta (ms) are expressed by the above (formula 1), If it sets according to (Formula 2), it turns out that it is possible to form a welded joint with favorable fatigue strength. 4 shows an example of an experimental result when the plate thickness is 1.2 mm, and FIG. 5 shows a case where the plate thickness is 2.0 mm. It has been confirmed that a sufficient effect can be similarly obtained even in a plate thickness of 1.0 to 2.3 mm.
本発明の上記（式１）は、鋼板の引張強さと板厚を変化させて、図４、図５に示すように、Ｐａ／Ｐｉ、Ｈｔａ／Ｈｔと溶接継手の疲労強度との関係を実験的に確認して求めたものである。 In the above (Equation 1) of the present invention, the tensile strength and thickness of the steel sheet are changed, and the relationship between Pa / Pi, Hta / Ht and the fatigue strength of the welded joint is tested as shown in FIGS. It was obtained after confirmation.
スポット溶接時の後期加圧力が、上記（式１）の下限値より低い場合には、ナゲット径の拡大によりナゲット（溶接金属部）の周囲に十分な圧縮残留応力を導入させることができず、溶接継手の疲労強度向上の効果がほとんど認められない。 When the late pressurizing force at the time of spot welding is lower than the lower limit of the above (formula 1), sufficient compressive residual stress cannot be introduced around the nugget (welded metal part) due to the expansion of the nugget diameter, The effect of improving the fatigue strength of the welded joint is hardly recognized.
一方で、スポット溶接時の後期加圧力が、上記（式１）の上限値より高い場合は、溶接時に変形抵抗が低下した加圧部表面に大きな圧痕が生じて、金属板の外観形状を悪化させ、また、加圧部の板厚を薄くしてしまい溶接継手の静的強度や疲労強度を低下させるという問題が生じる。 On the other hand, when the late pressurizing force at the time of spot welding is higher than the upper limit of the above (formula 1), a large indentation is generated on the surface of the pressurizing portion where the deformation resistance is reduced at the time of welding, and the appearance shape of the metal plate is deteriorated. In addition, the plate thickness of the pressurizing portion is reduced, and there arises a problem that the static strength and fatigue strength of the welded joint are lowered.
さらに、後期加圧力保持時間が、上記（式２）の下限値より短い場合は、溶接部が常温に近い程度にまで冷却された後に増加圧をするために、圧縮残留応力の導入が図れない。 Furthermore, when the late pressurization holding time is shorter than the lower limit of the above (Formula 2), since the welded portion is increased to a temperature close to room temperature, an increased pressure is applied, so that it is not possible to introduce compressive residual stress. .
一方で、後期加圧力保持時間が、上記（式２）の上限値より長い場合は、溶接部の温度が高いために、増加圧による圧縮残留応力の導入効果よりも変形抵抗が低下することによる加圧部表面の板厚減から生じる疲労強度の低下効果の方が大きくなってしまうという問題が生じる。 On the other hand, when the latter pressurizing pressure holding time is longer than the upper limit of the above (formula 2), the temperature of the welded portion is high, so that the deformation resistance is lower than the effect of introducing the compressive residual stress due to the increased pressure. There arises a problem that the effect of reducing the fatigue strength resulting from the reduction in the thickness of the surface of the pressing part becomes larger.
本発明では、上記（式１）のように、スポット溶接時の後期加圧力及び後期加圧力保持時間を規定することにより、溶接金属部周囲に圧縮残留応力を導入し、溶接継手の疲労強度の向上に寄与することができる。 In the present invention, as described above (Equation 1), by defining the late pressurization time and the late pressurization holding time during spot welding, compressive residual stress is introduced around the weld metal part, and the fatigue strength of the welded joint is reduced. It can contribute to improvement.
後期電極加圧力、後期加圧力保持時間以外の溶接条件、例えば、溶接時の溶接電流、溶接時間、などは通常の溶接条件に準ずればよく、特に規定する必要はない。 Welding conditions other than the late electrode pressurization time and the late pressurization holding time, for example, the welding current at the time of welding, the welding time, and the like may be in accordance with normal welding conditions, and need not be specified.
溶接電極は水冷されているので、溶接後の電極保持時間が長くなると、溶接部の冷却速度が速くなって硬さが上昇し、靱性が低下して破壊しやすくなる。この観点から、溶接後の電極保持時間はより短い方が良いが、一方、あまり短く設定すると、溶融金属が凝固しないうち加圧力がなくなるため、散りが発生して溶接金属（ナゲット）端部のノッチ形状が悪化するなどの弊害がある。 Since the welding electrode is water-cooled, if the electrode holding time after welding is increased, the cooling rate of the welded portion is increased, the hardness is increased, and the toughness is lowered and is easily broken. From this point of view, the electrode holding time after welding should be shorter. On the other hand, if it is set too short, the applied pressure will be lost while the molten metal does not solidify, and therefore, scattering will occur and the end of the weld metal (nugget) will end. There are harmful effects such as deterioration of the notch shape.
また、溶接金属部とその周囲の温度があまり下がらない内に電極による加圧力を除荷すると、溶接金属部周囲に十分な圧縮残留応力が導入されないため、疲労強度が向上しない。また、保持時間内での後期加圧力開始時間を上記（式２）のように設定し、溶接金属部とその周囲の温度がある程度まで下がってからより大きい加圧力を与えることが、圧縮残留応力を導入するために重要である。 Further, if the pressure applied by the electrode is unloaded while the temperature of the weld metal part and its surroundings does not drop so much, sufficient compressive residual stress is not introduced around the weld metal part, so that the fatigue strength is not improved. In addition, it is possible to set the later pressurization start time within the holding time as shown in the above (formula 2), and to apply a greater pressurization after the temperature of the weld metal part and its surroundings has decreased to some extent, the compressive residual stress Is important to introduce.
それ故、溶接継手の疲労強度向上の観点から、溶接後の後期加圧力保持時間は、上記（式２）に従って設定するのが好ましい。 Therefore, from the viewpoint of improving the fatigue strength of the welded joint, it is preferable to set the later pressurizing pressure holding time after welding according to the above (Equation 2).
また、被溶接材の厚みｔについても特に規定する必要がない。一般に、自動車用部品や車体などで疲労強度が必要な部位に使用される鋼板の板厚は、１．０〜２．３ｍｍであるが、本発明は、この板厚において充分に効果を奏することができる。 Further, it is not necessary to particularly define the thickness t of the material to be welded. In general, the thickness of a steel plate used for a part that requires fatigue strength, such as an automobile part or a vehicle body, is 1.0 to 2.3 mm. However, the present invention is sufficiently effective in this thickness. Can do.
電極形状についても特に規定する必要はない。ＪＩＳ Ｃ ９３０４に規定されているように、Ｆ型、Ｒ型、Ｄ型、ＤＲ型、ＣＦ型、ＣＲ型、ＥＦ型、ＥＲ型、Ｐ型があるが、どの電極についても本発明で充分に効果を発揮できる。 There is no particular need to define the electrode shape. As defined in JIS C 9304, there are F-type, R-type, D-type, DR-type, CF-type, CR-type, EF-type, ER-type, and P-type. The effect can be demonstrated.
さらに、鋼板の種類についても特に限定する必要がない。固溶型、析出型（例えば、Ｔｉ析出型、Ｎｂ析出型）、２相組織型（例えば、フェライト中にマルテンサイトを含む組織、フェライト中にベイナイトを含む組織）、加工誘起変態型（フェライト中に残留オーステナイトを含む組織）など、いずれの型の鋼板にも本発明を適用できる。 Furthermore, it is not necessary to specifically limit the type of steel plate. Solid solution type, precipitation type (for example, Ti precipitation type, Nb precipitation type), two-phase structure type (for example, structure containing martensite in ferrite, structure containing bainite in ferrite), work-induced transformation type (in ferrite) The present invention can be applied to any type of steel sheet such as a structure containing residual austenite.
鋼板の製造方法は、熱間圧延法でも冷間圧延法でも良く、裸鋼板でもめっき鋼板でも良い。被覆するめっきの種類は、導電性のものならいずれの種類（例えば、Ｚｎ、Ｚｎ−Ｆｅ、Ｚｎ−Ｎｉ、Ｚｎ−Ａｌ、Ｓｎ−Ｚｎ、など）であっても良いが、目付量は表裏面とも１００ｇ／ｍ2以下のものが望ましい。 The manufacturing method of the steel plate may be a hot rolling method or a cold rolling method, and may be a bare steel plate or a plated steel plate. The type of plating to be coated may be any type as long as it is conductive (for example, Zn, Zn—Fe, Zn—Ni, Zn—Al, Sn—Zn, etc.). Both are preferably 100 g / m 2 or less.
鋼板が、特に、フェライト中に体積分率で５％以上２５％以下の残留オーステナイトを含有する加工誘起変態型複合組織鋼板である場合、溶接継手の疲労強度の向上が著しくなり好ましい。この加工誘起変態型複合組織鋼板は、組織中に残留オーステナイトを含有し、鋼板の加工時に残留オーステナイトがマルテンサイトに変態することにより高い伸び特性が得られることが知られている。 In particular, when the steel sheet is a work-induced transformation type composite structure steel sheet containing 5% or more and 25% or less residual austenite in the ferrite, the fatigue strength of the welded joint is remarkably improved. It is known that this work-induced transformation type composite structure steel sheet contains retained austenite in the structure, and high elongation characteristics are obtained by transforming the retained austenite into martensite during the processing of the steel sheet.
本発明者らは、被溶接材として加工誘起変態型複合組織鋼板を用いた種々の実験結果から、スポット溶接時の溶接条件を上記各式を満たす範囲内に設定した場合、組織中に残留オーステナイトを含有しない他の鋼板に比べて、溶接継手の疲労強度が向上することを見出した。 Based on the results of various experiments using a work-induced transformation type composite steel sheet as a material to be welded, the present inventors have found that when the welding conditions at the time of spot welding are set within a range satisfying each of the above expressions, residual austenite in the structure It has been found that the fatigue strength of the welded joint is improved as compared with other steel plates not containing selenium.
この疲労強度向上のメカニズムについては十分には明らかになっていないが、加工誘起変態型複合組織鋼板を用いた場合、ナゲット（溶接金属部）周囲の鋼板の熱影響部（ＨＡＺ）の残留オーステナイトは、電極先端の加圧力によりマルテンサイト変態を起こし、この変態による体積膨張によりナゲットの周囲に弾性歪が蓄積され、最終的に高い圧縮残留応力が導入されるためではないかと推定される。 The mechanism of fatigue strength improvement has not been fully clarified. However, when a work-induced transformation type composite steel sheet is used, the retained austenite in the heat affected zone (HAZ) of the steel sheet around the nugget (welded metal part) is It is presumed that the martensitic transformation is caused by the applied pressure at the electrode tip, the elastic expansion is accumulated around the nugget due to the volume expansion due to this transformation, and finally high compressive residual stress is introduced.
なお、加工誘起変態型複合組織鋼板のうち、ミクロ組織が、体積分率５％未満の残留オーステナイトを含有するものは本発明による効果を十分に発揮出来ない。また、体積分率２５％を超える残留オーステナイトを含有するものは、鋼板の製造制約から生産出来ない。 In addition, among the processing-induced transformation type composite structure steel plates, those containing a retained austenite having a microstructure of less than 5% of the volume fraction cannot sufficiently exhibit the effects of the present invention. Moreover, the thing containing the retained austenite exceeding 25% of a volume fraction cannot be produced from the manufacturing restrictions of a steel plate.
通常、ナゲット形成部周囲には、溶接後の収縮によって引張残留応力が導入されるため、せん断方向に繰り返し荷重を負荷する疲労試験の場合には、この部分で疲労破壊が起こり易かったが、本発明では、ナゲット形成部周囲への圧縮残留応力の導入によりこれが緩和され、従来に比べ、溶接継手の疲労強度が向上したものと考えられる。 Normally, tensile residual stress is introduced around the nugget formation area due to shrinkage after welding, so in the case of a fatigue test in which a repeated load is applied in the shear direction, fatigue failure was likely to occur in this area. In the invention, this is mitigated by the introduction of compressive residual stress around the nugget forming portion, and it is considered that the fatigue strength of the welded joint is improved as compared with the conventional case.
以下に実施例により本発明の効果を説明するが、本発明は、実施例で用いた条件に限定されるものではない。
（実施例１）
表１に示す板厚１．０〜２．３ｍｍ、引張強さ２７０〜１１８０ＭＰａの鋼板から、スポット溶接継手の疲れ試験方法（ＪＩＳ Ｚ ３１３８）に基づく引張せん断疲労試験片を作製した。
The effects of the present invention will be described below with reference to examples, but the present invention is not limited to the conditions used in the examples.
Example 1
A tensile shear fatigue test piece based on a fatigue test method for spot welded joints (JIS Z 3138) was prepared from a steel sheet having a thickness of 1.0 to 2.3 mm and a tensile strength of 270 to 1180 MPa shown in Table 1.
鋼板の種類は、軟鋼（記号：２７０Ｅ）、２相複合組織型高強度鋼（記号：５９０Ｙ、７８０Ｙ、９８０Ｙ、１１８０Ｙ）、析出強化型高強度鋼（記号：３４０Ｐ、３７０Ｐ）、固溶強化型高強度鋼（記号：４４０Ｗ）である。なお、これらの鋼板の種類は、日本鉄鋼連盟規格品を指す。 The types of steel plates are mild steel (symbol: 270E), two-phase composite structure type high strength steel (symbol: 590Y, 780Y, 980Y, 1180Y), precipitation strengthened high strength steel (symbol: 340P, 370P), solid solution strengthened type High strength steel (symbol: 440 W). In addition, these types of steel sheets refer to Japan Iron and Steel Federation standard products.
その後、これらの試験片を、同鋼種の組み合わせで重ね合わせ、ＪＩＳ−ＤＲ型電極を用いて、表１の溶接条件でスポット溶接を行って溶接継手を作製した。 Thereafter, these test pieces were superposed with a combination of the same steel types, and spot welding was performed under the welding conditions shown in Table 1 using a JIS-DR type electrode to produce a welded joint.
得られた溶接継手について、スポット溶接継手の疲れ試験方法（ＪＩＳ Ｚ ３１３８）に基づき、溶接継手のせん断方向に負荷して疲労試験を実施した。表１にその結果を示す。表１に示す疲労強度は、疲労試験を応力比：０．０５、周波数：２０Ｈｚの条件で片振り試験を行った際の２×１０6回における疲労強度である。 About the obtained welded joint, based on the fatigue test method (JIS Z 3138) of a spot welded joint, the fatigue test was implemented by loading in the shear direction of the welded joint. Table 1 shows the results. The fatigue strength shown in Table 1 is the fatigue strength at 2 × 10 6 times when the fatigue test is performed in a single swing test under the conditions of stress ratio: 0.05 and frequency: 20 Hz.
表１に示したように、溶接後の後期加圧力Ｐａ（ｋＮ）、溶接後の後期加圧力保持時間Ｈｔａ（ｍｓ）が請求項１の発明で規定する下記（式１）および（式２）の範囲内にある２７０Ｅ継手（条件Ｎｏ．３）、９８０Ｙ継手（条件Ｎｏ．４）の疲労強度は、従来例である２７０Ｅ継手（条件Ｎｏ．１）、９８０Ｙ継手（Ｎｏ．２）、溶接後の後期加圧力Ｐｉ（ｋＮ）、溶接後の後期加圧力保持時間Ｈｔａ（ｍｓ）が、請求項１の発明で規定する（式１）および（式２）の範囲内にない２７０Ｅ継手（条件Ｎｏ．１１）、９８０Ｙ継手（条件Ｎｏ．１２）に比べて高い値を示した。
１．５×Ｐｉ≦Ｐａ≦２．５×Ｐｉ （ｋＮ） （式１）
０．３５×Ｈｔ≦Ｈｔｉ≦０．６５×Ｈｔ （ｍｓ） （式２）
As shown in Table 1, the late pressurization pressure Pa (kN) after welding and the late pressurization holding time Hta (ms) after welding are defined by the invention of claim 1 (Formula 1) and (Formula 2) The fatigue strength of the 270E joint (condition No. 3) and 980Y joint (condition No. 4) within the range of 270E joint (condition No. 1), 980Y joint (No. 2), after welding 270E joint (condition No.) in which the later applied pressure Pi (kN) and the later applied pressure holding time Hta (ms) after welding are not within the range of (Expression 1) and (Expression 2) defined in the invention of
1.5 × Pi ≦ Pa ≦ 2.5 × Pi (kN) (Formula 1)
0.35 × Ht ≦ Hti ≦ 0.65 × Ht (ms) (Formula 2)
また、溶接後の後期加圧力、溶接後の後期加圧力保持時間が請求項１の発明で規定する（式１）および（式２）の範囲内にある２７０Ｅ継手（条件Ｎｏ．５、７、９）、９８０Ｙ継手（Ｎｏ．６、８、１０）についても調査を行ったが、いずれも請求項１の発明で規定する（式１）および（式２）の範囲内にない２７０Ｅ継手（条件Ｎｏ．１）、９８０Ｙ継手（条件Ｎｏ．２）に比べて高い値を示した。
In addition, the 270E joint (conditions No. 5, 7, and 7) within the range of (Formula 1) and (Formula 2) defined in the invention of
さらに、それぞれの鋼種について、溶接後の後期加圧力Ｐａ（ｋＮ）、溶接後の後期加圧力保持時間Ｈｔａ（ｍｓ）が請求項１の発明で規定する（式１）、（式２）の範囲内にない他の場合（条件Ｎｏ．１３〜１８）について調査したが、いずれも、従来例である２７０Ｅ継手（Ｎｏ．１）、９８０Ｄ継手（Ｎｏ．２）と同程度であり、本発明の条件範囲内に設定された場合には、高い疲労強度が得られることがわかった。 Further, for each steel type, the late pressurization pressure Pa (kN) after welding and the late pressurization holding time Hta (ms) after welding are defined by the invention of claim 1 (formula 1) and (formula 2) The other cases (Condition Nos. 13 to 18) that were not included were investigated, but both were the same as the conventional examples of the 270E joint (No. 1) and the 980D joint (No. 2). It was found that high fatigue strength can be obtained when set within the condition range.
板厚を変化させた場合も調査を行ったが、溶接後の後期加圧力、溶接後の後期加圧力保持時間が請求項１の発明で規定する（式１）、（式２）の範囲内である、板厚下限の１．０ｍｍ（Ｎｏ．２１）、上限の２．３ｍｍ（Ｎｏ．２２）のそれぞれの溶接継手は、従来例である１．０ｍｍ（Ｎｏ．１９）、２．３ｍｍ（Ｎｏ．２０）に対して疲労強度の改善が認められた。
The investigation was also conducted when the plate thickness was changed, but the late pressurizing force after welding and the late pressurizing holding time after welding were within the ranges of (Formula 1) and (Formula 2) defined in the invention of
５９０Ｙ継手（Ｎｏ．２３、２５、２７、２９）、７８０Ｙ継手（Ｎｏ．２４、２６、２８、３０）についても、前述の２７０Ｅ継手、９８０継手と同様な結果を得た。 For the 590Y joint (No. 23, 25, 27, 29) and the 780Y joint (No. 24, 26, 28, 30), the same results as those of the 270E joint and the 980 joint were obtained.
念のために、鋼板強度が異なる３４０Ｐ継手（Ｎｏ．３１、３５）、３７０Ｐ継手（Ｎｏ．３２、３６）、４４０Ｗ継手（Ｎｏ．３３、３７）、１１８０Ｙ継手（Ｎｏ．３４、３８）についても本発明の効果が確認できた。 Just in case, 340P joints (No. 31, 35), 370P joints (No. 32, 36), 440W joints (No. 33, 37) and 1180Y joints (No. 34, 38) with different steel plate strengths are also used. The effect of the present invention was confirmed.
加工誘起変態型複合組織鋼板（特開２００２−１２９２８６号公報に記載の発明同等品）である５９０Ｔ継手（Ｎｏ．４２）、７８０Ｔ継手（Ｎｏ．４３）、９８０Ｔ継手（Ｎｏ．４４）は、本発明の効果が確認出来た上に、同等強度クラスの他鋼種の５９０Ｙ、７８０Ｙ、９８０Ｙに比較して更なる強度向上が認められた。 590T joints (No. 42), 780T joints (No. 43), and 980T joints (No. 44), which are work-induced transformation type composite structure steel plates (equivalent products of the invention described in JP-A-2002-129286), are In addition to confirming the effects of the invention, a further improvement in strength was recognized as compared with other steel types 590Y, 780Y, and 980Y of the same strength class.
１ 高強度鋼板
２ 溶接金属（ナゲット）
３ 疲労試験荷重の負荷方向
４ 溶接電極
５ 加圧力（負荷方向）
1 High-
3 Load direction of fatigue test load 4
Claims (2)
スポット溶接後の保持時間Ｈｔ（ｍｓ）のうち、初期加圧力Ｐｉ（ｋＮ）で初期加圧力保持時間Ｈｔｉ（ｍｓ）経過した後に、初期加圧力Ｐｉから後期加圧力Ｐａに加圧力を上昇させ、後期加圧力Ｐａ（ｋＮ）で後期加圧力保持時間Ｈｔａ（ｍｓ）経過させる溶接方法として、
前記の後期加圧力Ｐａ（ｋＮ）は下記（式１）を満たし、
前記の初期加圧力保持時間Ｈｔｉ（ｍｓ）は下記（式２）を満たし、
前記の後期加圧力保持時間Ｈｔａ（ｍｓ）は下記（式３）を満たし、
前記の初期加圧力Ｐｉ（ｋＮ）は被溶接材として引張強さＴＳ＜４３０ＭＰａの鋼板を用いる場合は下記（式４）、また引張強さＴＳ≧４３０ＭＰａの鋼板を用いる場合は下記（式５）を満たし、
前記の保持時間Ｈｔ（ｍｓ）は下記（式６）を満たす
ようにそれぞれ設定してスポット溶接することを特徴とする、鋼板のスポット溶接方法。
１．５×Ｐｉ≦Ｐａ≦２．５×Ｐｉ （ｋＮ） （式１）
０．３５×Ｈｔ≦Ｈｔｉ≦０．６５×Ｈｔ （ｍｓ） （式２）
Ｈｔａ＝Ｈｔ−Ｈｔｉ （ｍｓ） （式３）
Ｐｉ＝２．４５×ｔ （ｋＮ） （式４）
Ｐｉ＝２．４５×ｔ×（ＴＳ／２７０）0.5 （ｋＮ） （式５）
Ｈｔ＝２００×ｔ−８０ （ｍｓ） （式６）
ただし、ｔは鋼板板厚（ｍｍ）、ＴＳは鋼板の引張強さ（ＭＰａ）。 In the welding method that improves the fatigue strength of the steel plate spot welded joint,
Of the holding time Ht (ms) after spot welding, after the initial pressurizing pressure holding time Hti (ms) has elapsed with the initial pressurizing pressure Pi (kN), the pressurizing force is increased from the initial pressurizing pressure Pi to the late pressurizing pressure Pa, As a welding method in which the late pressurization holding time Hta (ms) elapses at the late pressurization pressure Pa (kN),
The latter applied pressure Pa (kN) satisfies the following (formula 1):
The initial pressure holding time Hti (ms) satisfies the following (Equation 2):
The latter pressurization holding time Hta (ms) satisfies the following (formula 3),
The initial pressure Pi (kN) is the following (Formula 4) when using a steel sheet having a tensile strength TS <430 MPa as a workpiece, and the following (Formula 5) when using a steel sheet having a tensile strength TS ≧ 430 MPa. The filling,
The above-mentioned holding time Ht (ms) is set so as to satisfy the following (Equation 6), and spot welding is performed.
1.5 × Pi ≦ Pa ≦ 2.5 × Pi (kN) (Formula 1)
0.35 × Ht ≦ Hti ≦ 0.65 × Ht (ms) (Formula 2)
Hta = Ht−Hti (ms) (Formula 3)
Pi = 2.45 × t (kN) (Formula 4)
Pi = 2.45 × t × (TS / 270) 0.5 (kN) (Formula 5)
Ht = 200 × t−80 (ms) (Formula 6)
Where t is the steel plate thickness (mm), and TS is the tensile strength (MPa) of the steel plate.
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