JP5510582B2 - Resistance spot welding method - Google Patents
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Description
本発明は、重ね抵抗溶接法の一種である抵抗スポット溶接によって形成される、引張強度に優れる継手に関する。 The present invention relates to a joint formed by resistance spot welding, which is a kind of lap resistance welding method, and having excellent tensile strength.
近年、車体の高信頼性と、エミッション削減を目的とした車体重量の軽減を両立して達成するために、鋼板の高強度化が進められている。高強度鋼板の採用により、従来鋼に比べ薄肉化、軽量化をしても同程度の車体剛性が得られるが、いくつかの課題も指摘されている。その一つが、高強度化するにつれて、車体組立における溶接部の品質が低下するというものである。 In recent years, steel sheets have been increased in strength in order to achieve both high reliability of the vehicle body and reduction of vehicle body weight for the purpose of reducing emissions. The adoption of high-strength steel sheets can provide the same level of vehicle body rigidity even if it is thinner and lighter than conventional steel, but some problems have been pointed out. One of them is that the quality of the welded part in the vehicle body assembly deteriorates as the strength increases.
抵抗スポット溶接は、図１に示すように、重ね合わせた２枚以上の鋼板（ここでは、下の鋼板１と上の鋼板２の２枚）の板組３を、上下一対の電極チップ（下の電極チップ４と上の電極チップ５）で挟み、加圧、通電することにより溶融させ、必要サイズのナゲット６を形成して、溶接継手を得るものである。
As shown in FIG. 1, resistance spot welding is performed by attaching a
このようにして得られた継手の品質は、十分なナゲット径が得られているか否かで判断するか、あるいは、せん断引張強度（継手のせん断方向に引張試験をしたときの強さ）、十字引張強度（継手のはく離方向に引張試験をしたときの強さ）、または疲労強度などで評価されている。その中でも、せん断引張強度や十字引張強度のような静的強度は、溶接継手の品質の指標として非常に重要視されている。 The quality of the joint obtained in this way is judged by whether or not a sufficient nugget diameter is obtained, or the shear tensile strength (strength when the tensile test is performed in the shear direction of the joint), cross It is evaluated by tensile strength (strength when a tensile test is performed in the peeling direction of the joint) or fatigue strength. Among them, static strength such as shear tensile strength and cross tensile strength is regarded as very important as an index of the quality of welded joints.
このうち、スポット溶接部の引張せん断強度は、鋼板の引張強度の増加とともに増加する傾向にある。しかし、十字引張強度は鋼板の引張強度の増加にかかわらずほとんど増加せず、逆に減少する。その原因として、高強度鋼板は、その強度を達成するために（１）式などで表される炭素等量Ｃｅｑが大きくならざるをえず、加えて溶接は急熱急冷現象であるために、溶接部及び熱影響部において硬度が上昇し、靭性が低下するからだと考えられている。 Among these, the tensile shear strength of the spot welded portion tends to increase as the tensile strength of the steel plate increases. However, the cross tensile strength hardly increases regardless of the increase in the tensile strength of the steel sheet, but decreases. As a cause thereof, in order to achieve the strength of the high-strength steel plate, the carbon equivalent Ceq represented by the formula (1) or the like must be increased, and in addition, welding is a rapid heating and quenching phenomenon. This is thought to be because the hardness increases and the toughness decreases at the weld and heat affected zone.
Ｃｅｑ＝Ｃ＋１／２４×Ｓｉ＋１／６×Ｍｎ（％）・・・（１）
ここで、％は質量％を意味している。
Ceq = C + 1/24 × Si + 1/6 × Mn (%) (1)
Here,% means mass%.
高強度鋼板を使用する際に継手強度を確保するためには、溶接法の観点からは、打点数の増加やナゲット径の拡大が考えられる。しかし、打点数を増加させると分流の影響が大きくなるほか、作業時間の増加につながり生産性を悪化させる。また、ナゲット径を拡大するには電極を大きくしたり、溶接金属の飛散（散り、チリ）を防ぐために加圧力を増加しなければならず、装置的な制約も受けるほか、熱影響部が拡大するため母材性状が損なわれる欠点もある。 In order to ensure the joint strength when using a high-strength steel plate, from the viewpoint of the welding method, an increase in the number of hitting points and an increase in the nugget diameter are conceivable. However, increasing the number of hits increases the effect of diversion and leads to an increase in work time and deteriorates productivity. In order to increase the nugget diameter, the electrode must be enlarged, and the applied pressure must be increased to prevent the weld metal from scattering (scattering and dusting). Therefore, there is a drawback that the properties of the base material are impaired.
そこで、従来と同様、あるいはそれ以下の打点数およびナゲット径で強度を確保する様々な試みがなされてきた。その試みとしては一度溶接部を凝固、変態させた後に再加熱することにより、ナゲットおよびＨＡＺ部分を軟化させるテンパー通電の検討が多い。これは、ナゲットの靭性向上や溶接部近傍の応力集中緩和をはかり、継手部の強度向上を実現しようとするものである。 Therefore, various attempts have been made to secure the strength with the number of hit points and the nugget diameter that are the same as or less than the conventional one. Many attempts have been made to energize the temper to soften the nugget and the HAZ portion by solidifying and transforming the weld once and then reheating it. This is intended to improve the strength of the joint by improving the toughness of the nugget and reducing the stress concentration near the weld.
そのため、継手の品質保証としては、硬さに着目した検討も多い。その一例として、特許文献１や特許文献２は、ナゲットおよび熱影響部の硬さを測定し、その値が一定の範囲に入っていることによって継手部の高強度を保証出来るとしている。 Therefore, there are many studies focusing on hardness as a quality assurance of joints. As an example, Patent Document 1 and Patent Document 2 measure the hardness of the nugget and the heat-affected zone, and assume that the high strength of the joint can be ensured when the value is within a certain range.
しかしながら、硬さの低下はせん断引張強さを低下させるという指摘があり、必ずしも望ましいものではない。従って、抵抗スポット溶接継手の継手強度確保にあたり、硬さ以外の指標が必要不可欠である。 However, it is pointed out that a decrease in hardness decreases the shear tensile strength, which is not always desirable. Therefore, in order to secure the joint strength of the resistance spot welded joint, an index other than hardness is indispensable.
本発明は、高強度鋼板を含む板組の抵抗スポット溶接において、前記問題を解決し、硬さに依らない指標によって継手強度を確保出来る、抵抗スポット溶接継手を提供することを目的とする。 An object of the present invention is to provide a resistance spot welded joint that can solve the above-mentioned problems and can secure joint strength by an index that does not depend on hardness in resistance spot welding of a plate set including a high-strength steel plate.
本発明者らは、前記課題を解決するために、高張力鋼板を含む板組の十字引張強度に優れる抵抗スポット溶接継手について鋭意検討した。 In order to solve the above-mentioned problems, the present inventors have intensively studied a resistance spot welded joint excellent in the cross tensile strength of a plate set including a high-strength steel plate.
まず、引張強度９８０ＭＰａ級の二相鋼を使用し、継手強度の決定因子を検討した。なお、上述の通り、抵抗スポット溶接の継手強度の静的強度を代表する引張せん断強度と十字引張強度のうち、引張せん断強度は鋼板の高強度化に合わせて向上する一方、十字引張強度は低下する傾向がある。そこで、十字引張強度をより重視して検討を進めた。 First, a duplex strength steel having a tensile strength of 980 MPa was used, and determinants of joint strength were examined. Of the tensile shear strength and cross tensile strength that represent the static strength of joint strength in resistance spot welding, as described above, the tensile shear strength increases as the steel plate becomes stronger, while the cross tensile strength decreases. Tend to. Therefore, examination was advanced with more emphasis on cross tensile strength.
ここで、抵抗スポット溶接継手の十字引張強度と破断形態には相関があり、低強度溶接継手は鋼板に平行に破断するはく離破断を生じ、高強度になるにつれてボタン状に片方の鋼板が残ったまま抜けるように破断するプラグ破断へと変化することが知られている。すなわち、継手強度確保のためには、はく離破断を抑制することが肝要となる。はく離破断現象は、ナゲット中を破断が進展するわけであるから、ナゲット組織および金属元素の偏析状態の破断に及ぼす影響を検討した。 Here, there is a correlation between the cross tensile strength and fracture mode of resistance spot welded joints, and low-strength welded joints have peel fractures that break parallel to the steel sheet, and one steel sheet remains in a button shape as the strength increases. It is known to change into a plug rupture that breaks so as to leave. That is, in order to secure the joint strength, it is important to suppress peeling fracture. Since the debonding rupture phenomenon causes the breakage to progress in the nugget, the influence of the nugget structure and the segregation state of the metal element on the breakage was examined.
そのなかで、ナゲットにおける偏析の形態によっては、き裂の発生要因となりうるのではないかとの知見を得た。種々の条件を検討したところ、ナゲットを形成させた後、冷却した後、再通電を行うことで、デンドライト状組織が変化することを見出した。数値解析で評価したところ、これらの冷却時間では未だマルテンサイト変態が始まっていない場合があることが分かった。 Among them, we obtained the knowledge that depending on the form of segregation in the nugget, it may be a cause of cracks. As a result of examining various conditions, it was found that the dendrite-like structure changes by forming a nugget, cooling, and re-energizing. As a result of numerical analysis, it was found that the martensitic transformation may not have started yet in these cooling times.
種々の条件を検討する中で、デンドライト状組織が消失する程度まで再加熱することで、ナゲット径は変化しないものの、従来のはく離破断からプラグ破断に変化し、十字引張強度も向上させることが出来ることを見出した。この継手はナゲットの硬さにも変化がなく、金属組織も本通電のみ場合と比較して、大きな相違はなかった。 While examining the various conditions, reheating to the extent that the dendritic structure disappears does not change the nugget diameter, but it changes from the conventional peel fracture to the plug fracture, and the cross tensile strength can also be improved. I found out. This joint had no change in the hardness of the nugget, and the metal structure was not significantly different from the case of only the main current supply.
このデンドライト構造の変化をＦＥ−ＥＰＭＡ（電界放出型電子プローブマイクロアナライザ）によって詳しく分析したところ、ナゲットの金属成分のうち、特にＰの分布状態が変化していることが明らかになった。従来の継手ではデンドライト組織と対応してＰに著しいピークが見られ、母材組織に対して２倍から１０倍の濃度となっている部分が観察された。一方で、デンドライト組織が軽減・消失しているものは、Ｐは母材組織に対しておおよそ２倍以下までの範囲となっていることが明らかとなった。 When this dendrite structure change was analyzed in detail by FE-EPMA (field emission electron probe microanalyzer), it became clear that the distribution state of P in the metal component of the nugget was particularly changed. In the conventional joint, a remarkable peak was observed in P corresponding to the dendrite structure, and a portion having a concentration 2 to 10 times that of the base material structure was observed. On the other hand, it has been clarified that the dendrite structure is reduced or disappeared, and P is in a range of approximately twice or less than that of the base material structure.
この事実から、本発明らは、ナゲットの強度確保のためには、特にき裂が導入されやすいコロナボンド端から一定距離の範囲のＰの濃度分布が低い水準に有ることが必要であるとの知見を得た。 From this fact, in order to ensure the strength of the nugget, the present inventors said that it is necessary that the concentration distribution of P in a certain distance range from the edge of the corona bond where cracks are easily introduced be at a low level. Obtained knowledge.
本発明は、これらの知見から完成し、以下の特徴を有している。 The present invention has been completed from these findings and has the following characteristics.
（１）薄鋼板の抵抗スポット溶接継手において、
薄鋼板が構成するナゲットの径をｄとしたとき、コロナボンドに囲まれたナゲットの水平面上において、
溶融部端部からナゲット内部方向に、ｄ／１００の距離の閉曲線とｄ／５の距離の閉曲線で囲まれるナゲット内の領域に存在するＰの量の分布状態を面分析し、Ｐの濃度ｍ（質量％）が、母材組成のＰの濃度Ｍ（質量％）の２倍を超えている面積比率が５％以下であることを特徴とする抵抗スポット溶接継手。
（２）前記薄鋼板の枚数が３枚以上であることを特徴とする前記（１）に記載の抵抗スポット溶接継手。
(1) In resistance spot welded joints of thin steel plates,
On the horizontal plane of the nugget surrounded by corona bonds, where d is the diameter of the nugget that the thin steel plate constitutes,
The distribution state of the amount of P existing in the region in the nugget surrounded by the closed curve of d / 100 distance and the closed curve of d / 5 distance from the melt end to the inside of the nugget is surface-analyzed, and the concentration of P m The resistance spot welded joint, wherein the area ratio (mass%) exceeds twice the concentration M (mass%) of P of the base material composition is 5% or less.
(2) The resistance spot welded joint according to (1), wherein the number of the thin steel plates is three or more.
本発明によれば、少なくとも一枚以上の高張力鋼板を含む二枚以上の板組に対して、ナゲットの偏析を低下させ、き裂を発生し難くしたことにより、はく離破断を抑制し、軟化させることなく高強度の抵抗スポット溶接継手を提供出来る。 According to the present invention, for two or more plate assemblies including at least one high-strength steel plate, segregation of nuggets is reduced and cracks are less likely to occur, thereby suppressing peeling fracture and softening. It is possible to provide a high strength resistance spot welded joint.
本発明の一実施形態を図面に基づいて説明する。 An embodiment of the present invention will be described with reference to the drawings.
本発明に係る溶接継手を形成するにあたり好適に使用可能な溶接装置は、上下一対の電極チップを備え、一対の電極チップで溶接する部分を挟み、加圧、通電でき、溶接中に加圧力、溶接電流をそれぞれ任意に制御可能な加圧力制御装置および溶接電流制御装置を有していればよく、加圧機構（エアシリンダやサーボモータ等）、電流制御機構（交流や直流等）、形式（定置式、ロボットガン等）等はとくに限定されない。 A welding apparatus that can be suitably used in forming a welded joint according to the present invention includes a pair of upper and lower electrode tips, can sandwich a portion to be welded with a pair of electrode tips, can be pressurized, and can be energized. It only needs to have a pressure control device and a welding current control device that can control the welding current arbitrarily, respectively, pressurization mechanism (air cylinder, servo motor, etc.), current control mechanism (AC, DC, etc.), type ( The stationary type, robot gun, etc.) are not particularly limited.
この継手において、ある二枚の薄鋼板が構成するナゲットの径をｄとしたとき、コロナボンドに囲まれたナゲットの水平面上において、溶融部端部からナゲット内部方向に、存在するＰの量の分布状態を面分析しＰの量を評価する。ただし、スポット溶接は軸を中心に対称であると解されるため、この範囲であれば選択的に範囲を限定して評価してもよい。
ｄ／１００の距離の閉曲線とｄ／５の距離の閉曲線で囲まれるナゲット内の領域を評価に供する各長さの位置関係と共に図２に示す。図２で閉曲線（ｄ／１００）および閉曲線（ｄ／５）はそれぞれ溶融部端部からナゲット内部方向に、ｄ／１００の距離の閉曲線とｄ／５の距離の閉曲線を示している。これは、模式図であるので、真円として図示してあるが、実施すると真円には近似するが、必ずしも厳密な意味で真円とはならず、やや異なる場合もある。
In this joint, when the diameter of the nugget formed by two thin steel plates is d, the amount of P existing in the nugget internal direction from the end of the melted part on the horizontal surface of the nugget surrounded by the corona bond The distribution state is analyzed and the amount of P is evaluated. However, since spot welding is understood to be symmetric about the axis, the range may be selectively limited for evaluation within this range.
FIG. 2 shows a region in the nugget surrounded by a closed curve with a distance of d / 100 and a closed curve with a distance of d / 5, together with the positional relationship of each length used for evaluation. In FIG. 2, a closed curve (d / 100) and a closed curve (d / 5) indicate a closed curve with a distance of d / 100 and a closed curve with a distance of d / 5 in the nugget inside direction from the melt end. Since this is a schematic diagram, it is shown as a perfect circle. However, when implemented, it approximates a perfect circle, but it does not necessarily have a true circle in a strict sense, and may be slightly different.
ここで、コロナボンドに囲まれたナゲットの面上としたのは、コロナボンドは一般に強度が低いことから、引張試験時は、最初にはく離し、ナゲットに対するき裂開口端となるため、評価をするのに最も適していると考えられるからである。ただし、コロナボンドの強度などによってはき裂方向が上下にそれることがあることから、コロナボンドと同じ高さの面からナゲットの厚みの１／１０の上下の範囲は計測範囲として扱ってよい。 Here, because the corona bond is generally low in strength, the nugget surface surrounded by the corona bond is peeled off first during the tensile test and becomes the crack opening end against the nugget. This is because it is considered the most suitable to do. However, depending on the strength of the corona bond, etc., the crack direction may be shifted up and down, so that a range of 1/10 above and below the nugget thickness from the same height as the corona bond may be treated as a measurement range. .
さらに、溶融部端部からｄ／１００としたのは、凝固最端部は部分的に溶融しており、今回の評価の対象でないからと考えられるからである。また、溶融部端部からｄ／５としたのは、き裂に影響する範囲はｄ／５までと考えられるからである。なお、上限はより狭い範囲のｄ／１０以下とすることが望ましい。 Furthermore, the reason why d / 100 is set from the end of the melted portion is that the solidified end is partially melted and is considered not to be the object of this evaluation. The reason why d / 5 is set from the end of the melted part is that the range that affects the crack is considered to be up to d / 5. The upper limit is desirably d / 10 or less in a narrower range.
上記領域の選択的または全領域につき、Ｐの分析を面分析にて行う。本評価には、ＥＰＭＡによる分析が最も適している。 Analysis of P is performed by surface analysis for selective or all of the above regions. Analysis by EPMA is most suitable for this evaluation.
Ｐの濃度ｍ（質量％）が、母材組成のＰの濃度Ｍ（質量％）の２倍を超えている面積を求めて、前記２つの閉曲線で囲まれる領域の面積と比較し、面積比率を評価する。
ここで、母材組成のＰの濃度Ｍ（質量％）は、鋼板が２枚組の場合で、同一化学成分を有していれば、当該鋼板の含有するＰの濃度（質量％）とする。異なった組成（Ｐ１、Ｐ２）（質量％）の場合で異なった板厚（ｔ１、ｔ２）（ｍｍ）であるときは近似的にP＝（Ｐ１＊ｔ１＋Ｐ２＊ｔ２）／（ｔ１＋ｔ２）のように計算して求めることができる。
３枚の場合には、当該鋼板の含有するＰの濃度（質量％）は、図３に示すように電極に接する鋼板1及び3に対して鋼板2は全て溶融しているという観点から、溶接後の断面を切断し、ナゲットを観察することによって得られる電極と同軸上のナゲット厚み（ｔ１〜ｔ３）を用いて、P＝（Ｐ１＊ｔ１＋Ｐ２＊ｔ２＋Ｐ３＊ｔ３）／（ｔ１＋ｔ２＋ｔ３）のように表す。このように、３枚より多い場合には、同様に表すことができる。
The area where the concentration m (mass%) of P exceeds twice the concentration M (mass%) of P in the base material composition is compared with the area of the region surrounded by the two closed curves, and the area ratio To evaluate.
Here, the concentration M (mass%) of P in the base material composition is the concentration (mass%) of P contained in the steel sheet if the steel sheet is a set of two sheets and has the same chemical component. . In the case of different composition (P1, P2) (mass%) and different plate thickness (t1, t2) (mm), approximately P = (P1 * t1 + P2 * t2) / (t1 + t2) It can be calculated.
In the case of three sheets, the concentration (mass%) of P contained in the steel sheet is welded from the viewpoint that all the steel sheets 2 are melted with respect to the
なお、３枚以上の板組における、コロナボンドに囲まれたナゲットの水平面上、とは、継手強度を評価する対象の2枚の板組間の界面に存在するコロナボンドに囲まれたナゲットの水平面上を指す。例えば、図４において鋼板2及び鋼板3での継手強度を評価する場合は実線で示した部分が該当のコロナボンドであり、コロナボンドに囲まれたナゲットの水平面は点線で示される部分である。
In addition, on the horizontal plane of the nugget surrounded by the corona bond in three or more plate assemblies, the nugget surrounded by the corona bond existing at the interface between the two plate assemblies whose joint strength is to be evaluated. Point on the horizontal plane. For example, in FIG. 4, when the joint strengths of the steel plate 2 and the
Ｐの濃度ｍ（質量％）が、母材組成のＰの濃度Ｍ（質量％）の２倍を超えている領域が面積比率で５％以下となることが求められる。 The area where the P concentration m (mass%) exceeds twice the P concentration M (mass%) of the base material composition is required to be 5% or less in terms of area ratio.
２倍を超えている領域としたのは、２倍を超えた場合、凝固偏析による脆性的な破壊が著しく誘起されるからである。５％以下としたのは、５％以下とすることによって破壊の開始を十分に抑制出来るからである。
本評価には、前述したようにＥＰＭＡによる分析が最も適しているがその他EDXやWDXによる分析も行うことができる。ＥＰＭＡによる分析を行う場合には、加速電圧１３〜１７ｋＶ、照射電流は１×１０−７A以上、３×１０−７A以下、ビーム径１〜３μｍφとし、ステップ数は１〜３μｍ、計数時間３〜１０ｓ／ｐｏｉｎｔｓの条件で行うことが好ましい。
The reason why the region exceeds 2 times is that when it exceeds 2 times, brittle fracture due to solidification segregation is remarkably induced. The reason why it is set to 5% or less is that the start of destruction can be sufficiently suppressed by setting it to 5% or less.
As described above, analysis by EPMA is most suitable for this evaluation, but analysis by EDX or WDX can also be performed. When analyzing by EPMA, the acceleration voltage is 13 to 17 kV, the irradiation current is 1 × 10 −7 A or more and 3 × 10 −7 A or less, the beam diameter is 1 to 3 μmφ, the number of steps is 1 to 3 μm, and the counting time is It is preferable to carry out under conditions of 3 to 10 s / points.
上記範囲において面分析を行い、面積比率を算出する。ただし、簡易的に線分析にて評価を行ってもよい。面積比率は画像解析装置により求めることができる。このとき、面積比率をさらに、３％以下とすることで、Ｐによる影響をより軽減した、より望ましい高強度な継手が得られる。 Surface analysis is performed in the above range, and the area ratio is calculated. However, evaluation may be performed simply by line analysis. The area ratio can be obtained by an image analyzer. At this time, by setting the area ratio to 3% or less, it is possible to obtain a more desirable high-strength joint in which the influence of P is further reduced.
Ｐの濃度ｍ（質量％）が、母材組成のＰの濃度Ｍ（質量％）の２倍を超えている面積比率が５％以下である抵抗スポット溶接継手を製作するには、幾つかの方法がある。先ず、実施例に後述するように、抵抗スポット溶接においてナゲットを形成する本工程の後、一旦無通電時間をおいて冷却し、再び通電を行う時間（後工程通電時間）を２回ずつ行う条件を採用することによる。この時、あるコロナボンドを構成する２枚の板組のうち薄い板の板厚ｔをもって、その界面におけるナゲット径のサイズが３√ｔから６√ｔの間である必要があり、これは抵抗スポット溶接において、最低限のナゲットを確保するとともに、過大となり熱影響が大きくなることを防ぐためである。 In order to manufacture a resistance spot welded joint in which the area ratio of P concentration m (mass%) exceeds twice the P concentration M (mass%) of the base material composition is 5% or less, There is a way. First, as will be described later in the examples, after this step of forming the nugget in the resistance spot welding, the cooling is performed once after the non-energization time, and the time for performing the energization again (the post-process energization time) is performed twice. By adopting. At this time, it is necessary that the nugget diameter size at the interface be between 3√t and 6√t with the thickness t of the thin plate of the two plates constituting a corona bond. This is because, in spot welding, a minimum nugget is ensured, and an excessively large heat effect is prevented.
ナゲットを形成した後に４サイクル〜３０サイクルの無通電時間Ｔｃを置く（１サイクルは0.02S）。最低限の凝固を確保しなければならない一方で、冷却が進んで再加熱が必要となっては非効率的となるからである。その後、二段の通電を行う。一段目の通電電流値Ｉｐ１は二段目の通電Ｉｐ２よりも低くし、急激な通電による散りの発生を抑制する。さらに、十分にＰを拡散させるため、ナゲットを高温化する必要があるという観点から、Ｉｐ２はＩｍよりも高い電流であることが望ましい。また、二段の通電時間の和Ｔｐ＝Ｔｐ１＋Ｔｐ２は溶接時間を抑制するため、多くとも２０サイクルとすることが望ましい。なお、本継手は抵抗スポット溶接プロセスで実現する以外にも、誘導加熱などを用いた後熱装置による加熱も考えられる。 After the nugget is formed, a non-energization time Tc of 4 to 30 cycles is set (1 cycle is 0.02 S). This is because while minimum solidification must be ensured, it becomes inefficient if cooling is advanced and reheating is required. Thereafter, two-stage energization is performed. The first-stage energization current value Ip1 is set lower than the second-stage energization Ip2 to suppress the occurrence of scattering due to rapid energization. Further, from the viewpoint that the nugget needs to be heated to sufficiently diffuse P, it is desirable that Ip2 be a current higher than Im. Further, the sum of the two-stage energization time Tp = Tp1 + Tp2 is desirably 20 cycles at most in order to suppress the welding time. In addition to realizing this joint by a resistance spot welding process, heating by a post-heating device using induction heating or the like is also conceivable.
本発明の実施例として、前述の図１に示したように、２枚の鋼板（下の鋼板１、上の鋼板２）を重ねた板組３について、溶接ガンに取付けられたサーボモータ加圧式で単相交流（５０Ｈｚ）の抵抗溶接機を用いて抵抗スポット溶接を行い、抵抗スポット溶接継手を作製した。なお、使用した一対の電極チップ（下の電極チップ４、上の電極チップ５）は、ともに図５に示すように、先端の曲率半径Ｒ４０、先端径６ｍｍを有するアルミナ分散銅のＤＲ型電極とした。
As an embodiment of the present invention, as shown in FIG. 1 above, a servo motor pressurizing type attached to a welding gun for a plate set 3 in which two steel plates (lower steel plate 1 and upper steel plate 2) are stacked. Then, resistance spot welding was performed using a single phase alternating current (50 Hz) resistance welder to produce a resistance spot welded joint. As shown in FIG. 5, the pair of used electrode tips (
試験片として、下の鋼板１および上の鋼板２共に同じ鋼種（同一の化学成分を有する鋼板）の同じ板厚である鋼板を用い、引張強度７８０ＭＰａ級、引張強度９８０ＭＰａ級、１１８０ＭＰａ級、引張強度１４７０ＭＰａ級の冷延鋼板を使用した。これら鋼板を用いて、ＪＩＳ Ｚ３１３７に基づき溶接および引張試験を行った。 As a test piece, the lower steel plate 1 and the upper steel plate 2 are the same steel type (steel having the same chemical composition) and have the same thickness, and have a tensile strength of 780 MPa class, tensile strength of 980 MPa class, 1180 MPa class, tensile strength. A 1470 MPa grade cold-rolled steel sheet was used. Using these steel plates, welding and tensile tests were performed based on JIS Z3137.
そして、本発明例として、上記の本発明の一実施形態に基づいて抵抗スポット溶接を行った。その際、図６のように、加圧したまま通電をしない時間（無通電時間Ｔｃ）と、再び通電（Ｉｐ１、Ｉｐ２）を行う時間（後工程通電時間Ｔｐ１、Ｔｐ２）を２回ずつ行った。 And as an example of this invention, resistance spot welding was performed based on one Embodiment of said this invention. At that time, as shown in FIG. 6, the time during which no energization was performed (no energization time Tc) and the time during which energization (Ip1, Ip2) was performed again (post-process energization times Tp1, Tp2) were performed twice. .
一方、従来例として、本工程のみの抵抗スポット溶接を行った。 On the other hand, resistance spot welding of only this process was performed as a conventional example.
表１に、本発明例および従来例、比較例の溶接条件と溶接結果を示す。本表に示されていない溶接条件（例えば、スクイズ時間あるいはスロープ時間）については設定しなかった。また、後工程の通電によりナゲット径の拡大はなかったことを確認している。 Table 1 shows welding conditions and welding results of the inventive example, the conventional example, and the comparative example. Welding conditions not shown in the table (for example, squeeze time or slope time) were not set. In addition, it was confirmed that the nugget diameter did not increase due to energization in the subsequent process.
溶接後のナゲット部について、コロナボンドに囲まれた面上における、溶融部端部からナゲット内部方向に、ｄ／１００の距離の閉曲線とｄ／５の距離の閉曲線で囲まれるナゲット内の領域、すなわち溶融端部からｄ／１００〜ｄ／５の距離に囲まれた中空円状の範囲の領域うち、ランダムに３０μｍ四方の視野を５点、ＥＰＭＡでＰの分布状態を面分析をした。さらに、母材Ｐ量Ｍに対して２倍以上となる偏析部の面積比率を評価した。 About the nugget part after welding, on the surface surrounded by the corona bond, the region in the nugget surrounded by the closed curve of the distance of d / 100 and the closed curve of the distance of d / 5 in the nugget inside direction from the end of the melted part, That is, in a hollow circular region surrounded by a distance of d / 100 to d / 5 from the melt end, 5 points were randomly analyzed in a 30 μm square, and the distribution state of P was analyzed by EPMA. Furthermore, the area ratio of the segregation part which becomes 2 times or more with respect to the base material P amount M was evaluated.
さらに、これら継手の引張試験を行い破断時の荷重を比較した。従来例に対して向上したものを○、等しいか、あるいは低下したものを×として整理した。 Furthermore, the tensile test of these joints was performed and the load at the time of fracture was compared. Those improved with respect to the conventional example were arranged as ◯, and those that were equal or decreased were marked as ×.
この結果、本発明例においては、従来例、比較例に比べ、Ｐの濃化部が減少しており、十字引張強度の向上が認められた。 As a result, in the example of the present invention, compared with the conventional example and the comparative example, the P concentration portion was reduced, and an improvement in the cross tensile strength was recognized.
本発明の実施例として、前述の図３に示したように、３枚の鋼板（下の鋼板１、中の鋼板２、上の鋼板３）を重ねた板組について、溶接ガンに取付けられたサーボモータ加圧式で単相交流（５０Ｈｚ）の抵抗溶接機を用いて抵抗スポット溶接を行い、抵抗スポット溶接継手を作製した。なお、使用した一対の電極チップ（下の電極チップ４、上の電極チップ５）は、ともに図５に示すように、先端の曲率半径Ｒ４０、先端径６ｍｍを有するアルミナ分散銅のＤＲ型電極とした。
As an example of the present invention, as shown in FIG. 3 described above, a plate assembly in which three steel plates (lower steel plate 1, middle steel plate 2, upper steel plate 3) were stacked was attached to a welding gun. Resistance spot welding was performed by using a servo motor pressurization type single-phase AC (50 Hz) resistance welding machine to produce a resistance spot welded joint. As shown in FIG. 5, the pair of used electrode tips (
試験片の板組を表２に示す。ここで強度は引張強度であり、めっきがなしの場合は冷延鋼板、ＧＡはＧＡ鋼板を示す。なお、ＧＡ鋼板の目付量は４５ｇ／ｍｍ＾２であった。これら鋼板を用いて、ＪＩＳ Ｚ３１３７に基づき溶接および引張試験を行った。引張試験を行ったのは全て鋼板１と鋼板２の間である。 Table 2 shows the plate set of the test piece. Here, the strength is tensile strength, and when there is no plating, cold-rolled steel sheet and GA indicates GA steel sheet. The basis weight of the GA steel sheet was 45 g / mm ^ 2. Using these steel plates, welding and tensile tests were performed based on JIS Z3137. All the tensile tests were performed between the steel plate 1 and the steel plate 2.
そして、本発明例として、上記の本発明の一実施形態に基づいて抵抗スポット溶接を行った。その際、図６のように、加圧したまま通電をしない時間（無通電時間Ｔｃ）と、再び通電（Ｉｐ１、Ｉｐ２）を行う時間（後工程通電時間Ｔｐ１、Ｔｐ２）を２回ずつ行った。 And as an example of this invention, resistance spot welding was performed based on one Embodiment of said this invention. At that time, as shown in FIG. 6, the time during which no energization was performed (no energization time Tc) and the time during which energization (Ip1, Ip2) was performed again (post-process energization times Tp1, Tp2) were performed twice. .
一方、従来例として、本工程のみの抵抗スポット溶接を行った。 On the other hand, resistance spot welding of only this process was performed as a conventional example.
表３に、本発明例および比較例の溶接条件と溶接結果を示す。本表に示されていない溶接条件（例えば、スクイズ時間あるいはスロープ時間）については設定しなかった。
後工程の通電によりナゲット径の拡大はなかったことを確認している。
Table 3 shows the welding conditions and welding results of the inventive examples and the comparative examples. Welding conditions not shown in the table (for example, squeeze time or slope time) were not set.
It was confirmed that the nugget diameter did not increase due to energization in the post-process.
溶接後のナゲット部について、鋼板１と鋼板２の間に存在するコロナボンドに囲まれた面上における、溶融部端部からナゲット内部方向に、ｄ／１００の距離の閉曲線とｄ／５の距離の閉曲線で囲まれるナゲット内の領域、すなわち溶融端部からｄ／１００〜ｄ／５の距離に囲まれた中空円状の範囲の領域うち、ランダムに３０μｍ四方の視野を５点、ＥＰＭＡでＰの分布状態を面分析をした。さらに、母材Ｐ量Ｍに対して２倍以上となる偏析部の面積比率を評価した。 About the nugget part after welding, on the surface surrounded by the corona bond existing between the steel plate 1 and the steel plate 2, from the end of the fusion part to the inside of the nugget, a closed curve with a distance of d / 100 and a distance of d / 5 In the nugget region surrounded by the closed curve, that is, in the hollow circular region surrounded by a distance of d / 100 to d / 5 from the melting end, 5 points of 30 μm square fields are randomly selected by EPMA. A surface analysis of the distribution state of was performed. Furthermore, the area ratio of the segregation part which becomes 2 times or more with respect to the base material P amount M was evaluated.
さらに、これら継手の引張試験を行い破断時の荷重を比較した。従来例に対して向上したものを○として整理した。 Furthermore, the tensile test of these joints was performed and the load at the time of fracture was compared. Items that were improved compared to the conventional example were arranged as ○.
この結果、本発明例においては、従来例に比べ、Ｐの濃化部が減少しており、十字引張強度の向上が認められた。 As a result, in the example of the present invention, compared with the conventional example, the P-concentrated portion was reduced, and an improvement in the cross tensile strength was recognized.
１ 下の鋼板
２ 上の鋼板
３ 板組
４ 下の電極チップ
５ 上の電極チップ
６ ナゲット
ｔ 総板厚（ｍｍ）
ｄ ナゲット径
DESCRIPTION OF SYMBOLS 1 Steel plate 2
d Nugget diameter
Claims (2)
前記本工程の後、無通電時間をおいて冷却する冷却工程と、前記冷却工程の後に、二段階の通電を行う後通電工程を有する後工程とを備え、
前記後通電工程の一段目の通電電流値は、二段目の通電電流値よりも低いことを特徴とする抵抗スポット溶接方法。 This process of forming the nugget;
A cooling step of cooling after a non-energization time after the main step; and a post step having a post-energization step of performing two-stage energization after the cooling step;
The resistance spot welding method according to claim 1, wherein an energization current value in the first stage of the post-energization process is lower than an energization current value in the second stage.
溶融部端部からナゲット内部方向に、ｄ／１００の距離の閉曲線とｄ／５の距離の閉曲線で囲まれるナゲット内の領域に存在するＰの量の分布状態を面分析し、Ｐの濃度ｍ（質量％）が、母材組成のＰの濃度Ｍ（質量％）の２倍を超えている面積比率が５％以下である抵抗スポット溶接継手を形成することを特徴とする請求項１に記載の抵抗スポット溶接方法。 On the horizontal plane of the nugget surrounded by corona bonds, where d is the diameter of the nugget that the thin steel plate constitutes,
The distribution state of the amount of P existing in the region in the nugget surrounded by the closed curve of d / 100 distance and the closed curve of d / 5 distance from the melt end to the inside of the nugget is surface-analyzed, and the concentration of P m 2. The resistance spot welded joint having an area ratio in which (mass%) exceeds twice the concentration M (mass%) of P in the base material composition is 5% or less is formed. Resistance spot welding method.
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| JP2007098462A (en) * | 2005-10-07 | 2007-04-19 | Sumitomo Metal Ind Ltd | Flash butt welding method |
| JP2008106324A (en) * | 2006-10-26 | 2008-05-08 | Nippon Steel Corp | High strength steel sheet for lap resistance welding, and lap welding joint |
| JP2008229720A (en) * | 2007-02-22 | 2008-10-02 | Kobe Steel Ltd | Spot-welded joint of high-strength steel sheets excellent in tensile strength, automotive component having the same joint, and spot-welding method of high-strength steel sheets |
| JP5210552B2 (en) * | 2007-06-19 | 2013-06-12 | 株式会社神戸製鋼所 | High strength spot welded joint |
| JP3138376U (en) * | 2007-10-19 | 2007-12-27 | 株式会社トムテック | Reinforcing bar spot welding equipment |
| JP2010059451A (en) * | 2008-09-02 | 2010-03-18 | Sumitomo Metal Ind Ltd | Welded joint and manufacturing method therefor |
| JP5573128B2 (en) * | 2008-11-28 | 2014-08-20 | Ｊｆｅスチール株式会社 | Resistance spot welding method |
| JP5332857B2 (en) * | 2009-04-20 | 2013-11-06 | 新日鐵住金株式会社 | Resistance welding method for high strength steel sheet |
| JP2011067853A (en) * | 2009-09-28 | 2011-04-07 | Nippon Steel Corp | Spot welding method for high-strength steel sheet |
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