JP2017035722A - Spot weld zone, manufacturing method of spot weld zone, and strength judgement method of spot weld zone - Google Patents
Spot weld zone, manufacturing method of spot weld zone, and strength judgement method of spot weld zone Download PDFInfo
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Abstract
Description
本発明は、薄鋼板をスポット溶接することによって形成される溶接継手や溶接部材に優れた静的強度、衝撃強度および疲労強度を付与するスポット溶接部、その製造方法および強度判定方法に関する。 The present invention relates to a spot welded portion that imparts excellent static strength, impact strength, and fatigue strength to a welded joint or welded member formed by spot welding thin steel plates, a manufacturing method thereof, and a strength determination method.
自動車産業では、車体重量の軽量化による燃費向上および衝突時の乗員の安全性確保を両立した車体の技術開発が推進され、車体に用いられる薄鋼板の高強度化および薄肉化がキーテクノロジーとなっている。しかしながら、車体組み立て時の主要な溶接方法であるスポット溶接を薄鋼板に適用した場合、化学成分、鋼板強度、継手形式および負荷形式によっては、静的強度、衝撃強度および疲労強度が低下することがある。そのため、スポット溶接継手の静的強度、衝撃強度および疲労強度を向上させる手法とそのような溶接継手を作製する溶接技術を見出すことが急務となっていた。また、溶接継手の中でも、非特許文献１や非特許文献２に示すようなＬ字引張継手は低強度破壊を起こしやすく、自動車構造の中にこのような溶接継手が含まれるにはその健全性が危惧されている。 In the automotive industry, the development of vehicle body technology that achieves both improved fuel economy and reduced passenger safety in the event of a collision has become a key technology in the automotive industry. ing. However, when spot welding, which is the main welding method at the time of vehicle body assembly, is applied to thin steel plates, the static strength, impact strength and fatigue strength may decrease depending on the chemical composition, steel plate strength, joint type and load type. is there. Therefore, there has been an urgent need to find a technique for improving the static strength, impact strength and fatigue strength of a spot welded joint and a welding technique for producing such a welded joint. Among welded joints, L-shaped tensile joints such as those shown in Non-Patent Document 1 and Non-Patent Document 2 tend to cause low-strength fracture, and the soundness of such welded joints included in an automobile structure Is feared.
ここで、特許文献１には、スポット溶接金属の化学成分を規定し、スポット溶接後に熱処理を行うことでＬ字継手引張強度を向上させる溶接継手およびその製造方法が開示されている。しかし、自動車１台当たり数千点にも及ぶスポット溶接部にこのような溶接後の熱処理を実施することは生産性や経済性の観点から見て非効率であり現実的ではない。また、特許文献１で提案された技術では、衝撃強度や疲労強度に対する効果も明らかではない。 Here, Patent Document 1 discloses a welded joint that defines the chemical components of spot weld metal and improves the L-shaped joint tensile strength by performing a heat treatment after spot welding, and a manufacturing method thereof. However, it is inefficient and impractical to perform such post-welding heat treatment on several thousand spot welds per vehicle from the viewpoint of productivity and economy. In addition, with the technique proposed in Patent Document 1, the effect on impact strength and fatigue strength is not clear.
特許文献２には、ナゲット内の成分、組織と酸化物系介在物の分布密度を規定した高強度スポット溶接継手が開示されている。また、特許文献３には、鋼板組成を規定し、ナゲットのデンドライトアーム間隔等を規定した高強度スポット溶接継手が開示されている。そして、特許文献４には、成分および脆さ指標を規定したスポット溶接継手強度に優れた鋼板が開示されている。しかし、これらの技術では、それぞれの実施例にあるように、十字引張強度（Cross Tension Strength：ＣＴＳ）の向上には効果が見られるが、低強度破壊を示すより厳格な試験であるＬ字継手引張強度（L-shape Tension Strength：ＬＴＳ）試験での効果は明確ではない。また、特許文献２〜４で提案された技術では、衝撃強度や疲労強度に対する効果も明らかではない。 Patent Document 2 discloses a high-strength spot welded joint that defines the distribution density of components, structures, and oxide inclusions in the nugget. Patent Document 3 discloses a high-strength spot welded joint that defines the steel plate composition and the nugget dendrite arm spacing and the like. Patent Document 4 discloses a steel sheet having excellent spot weld joint strengths in which components and brittleness indices are defined. However, as shown in each example, these techniques are effective in improving the cross tensile strength (CTS), but the L-shaped joint is a more rigorous test showing low strength fracture. The effect in the L-shape Tension Strength (LTS) test is not clear. In addition, in the techniques proposed in Patent Documents 2 to 4, effects on impact strength and fatigue strength are not clear.
特許文献５には、引張強さや試験片厚さ等からスポット溶接継手のせん断引張強度や十字引張強度を推定する方法が開示されている。しかし、この技術では、より低強度破壊を示すＬ字継手引張強度を推定することはできない。また、特許文献５で提案された技術では、衝撃強度や疲労強度に対する効果も明らかではない。 Patent Document 5 discloses a method for estimating the shear tensile strength and cross tensile strength of a spot welded joint from tensile strength, specimen thickness, and the like. However, this technique cannot estimate the L-joint tensile strength that indicates lower strength fracture. Further, in the technique proposed in Patent Document 5, the effect on impact strength and fatigue strength is not clear.
一方、非特許文献３に示すように、スポット溶接時に中散り（中チリ）を発生させることでシートセパレーション終端の形状を変化させ継手疲労強度を向上させる技術がある。また、特許文献６には、散りを発生させて十字引張強度を向上させる技術が開示されている。これは、非特許文献４に示すように、中散りを発生させて、シートセパレーション終端領域を散りで埋めることでコロナボンドからのき裂発生が抑止されるためであると考えられる。しかし、これら技術が、より低強度破壊を示す複雑な破壊モードであるＬ字継手引張強度の向上に寄与する確証は得られていない。また、これら技術は散りを活用するものであるが、散りで飛散した溶接金属が例えば車体に付着した場合には手入れが必要であると同時に、作業環境や安全衛生上も好ましくない。 On the other hand, as shown in Non-Patent Document 3, there is a technique for improving joint fatigue strength by changing the shape of the end of the sheet separation by generating scatter (medium dust) during spot welding. Patent Document 6 discloses a technique for improving the cross tensile strength by generating scattering. As shown in Non-Patent Document 4, this is considered to be because cracking from the corona bond is suppressed by generating scatter and filling the sheet separation termination region with scatter. However, there is no confirmation that these techniques contribute to the improvement of the L-shaped joint tensile strength, which is a complicated fracture mode that exhibits lower strength fracture. Moreover, although these techniques utilize scattering, when the weld metal scattered by scattering adheres to a vehicle body, for example, care is required, and at the same time, it is not preferable in terms of work environment and safety and health.
非特許文献５では、シートセパレーション終端がｗ型をなすことによってコロナボンドからのき裂発生が抑止され、十字引張強度が向上することが実験や解析によって示唆されている。しかし、より低強度破壊を示す厳格なＬ字継手引張強度やせん断強度に対する効果については明らかでなく、さらには衝撃強度や疲労強度に関しては示唆もされていない。また、十字引張強度を向上させるための必要十分条件も明らかではなく、さらには、そのようなｗ型のシートセパレーション終端形状を示すための溶接条件が明確ではないため、第三者による実施が不可能である。 In Non-Patent Document 5, it is suggested by experiments and analyzes that the occurrence of cracks from corona bonds is suppressed by the w separation at the end of sheet separation and the cross tensile strength is improved. However, the effect on the strict L-shaped joint tensile strength and shear strength showing lower strength fracture is not clear, and further, there is no suggestion regarding impact strength or fatigue strength. In addition, the necessary and sufficient conditions for improving the cross tensile strength are not clear, and further, the welding conditions for showing such a w-type sheet separation terminal shape are not clear, so that the implementation by a third party is not possible. Is possible.
本発明は、上記に鑑みてなされたものであって、溶接継手や溶接部材に、優れた静的強度、衝撃強度および疲労強度を付与するスポット溶接部と、その製造方法および強度判定方法を提供することを目的とする。 The present invention has been made in view of the above, and provides a spot welded portion that imparts excellent static strength, impact strength, and fatigue strength to a welded joint or welded member, a manufacturing method thereof, and a strength determination method. The purpose is to do.
上述した課題を解決し、目的を達成するために、本発明に係るスポット溶接部は、板厚ｔ［ｍｍ］の２枚以上の薄鋼板をスポット溶接した溶接継手および溶接部材におけるスポット溶接部であって、ナゲット径［ｍｍ］が３√ｔ以上であり、ナゲット断面において、シートセパレーション終端領域内にナゲットと反対方向に凸形状をなす凸部を有し、前記凸部の外郭線が、前記薄鋼板の鋼板合わせ面を結んだ直線と交わり、前記凸部が、面積率で５０％以上の溶接熱影響部からなることを特徴とする。 In order to solve the above-described problems and achieve the object, the spot welded portion according to the present invention is a welded joint obtained by spot welding two or more thin steel plates having a thickness t [mm] and a spot welded portion in a welded member. The nugget diameter [mm] is 3√t or more, and in the nugget cross section, the sheet separation termination region has a convex portion that is convex in the direction opposite to the nugget, and the contour line of the convex portion is It intersects with a straight line connecting the steel plate mating surfaces of the thin steel plates, and the convex portion is composed of a weld heat affected zone having an area ratio of 50% or more.
また、本発明に係るスポット溶接部は、上記発明において、前記ナゲットと反対方向に凹形状をなす２つの凹部を有し、前記２つの凹部の間に前記凸部が形成されていることを特徴とする。 The spot welded portion according to the present invention is characterized in that, in the above-described invention, the spot welded portion has two concave portions having a concave shape in a direction opposite to the nugget, and the convex portion is formed between the two concave portions. And
上述した課題を解決し、目的を達成するために、本発明に係るスポット溶接部の製造方法は、電極先端径をｄ［ｍｍ］、本通電時間をＴ［ｓｅｃ］、本通電電流をｃ［ｋＡ］、前記薄鋼板の引張強度をＴＳ［ＭＰａ］としたとき、加圧力Ｐ［Ｎ］を下記式（１）の範囲内とすることを特徴とする。
（上記式（１）において、Ａ１〜Ａ６は０を含む係数、ｆ（ｘ）はｘの関数、ｆ（ｘ，ｙ，ｚ）はｘとｙとｚの関数である）
In order to solve the above-described problems and achieve the object, the method for manufacturing a spot welded portion according to the present invention includes an electrode tip diameter d [mm], a main energization time T [sec], and a main energization current c [ kA], when the tensile strength of the thin steel sheet is TS [MPa], the applied pressure P [N] is within the range of the following formula (1).
(In the above formula (1), A 1 to A 6 are coefficients including 0, f (x) is a function of x, and f (x, y, z) is a function of x, y, and z)
また、本発明に係るスポット溶接部の製造方法は、上記発明において、上記式（１）は、下記式（２）で表されることを特徴とする。
（上記式（２）において、Ｈは
であり、Ｈ＜１０．０のときは
とする。また、ＴＳ＜２７０であるとき、上記式（２）における最終項の（ＴＳ−２７０）は
とする。なお、上記式（２）において、πは円周率、ｅは自然対数の底である）
Moreover, the manufacturing method of the spot welding part which concerns on this invention is characterized by the said Formula (1) being represented by following formula (2) in the said invention.
(In the above formula (2), H is
And when H <10.0
And When TS <270, the final term (TS-270) in the above equation (2) is
And (In the above formula (2), π is the pi and e is the base of the natural logarithm)
上述した課題を解決し、目的を達成するために、本発明に係るスポット溶接部の強度判定方法は、板厚ｔ［ｍｍ］の２枚以上の薄鋼板をスポット溶接した溶接継手および溶接部材におけるスポット溶接部の強度判定方法であって、ナゲット径［ｍｍ］が３√ｔ以上であり、ナゲット断面において、シートセパレーション終端領域内にナゲットと反対方向に凸形状をなす凸部を有し、前記凸部の外郭線が、前記薄鋼板の鋼板合わせ面を結んだ直線と交わり、前記凸部が、面積率で５０％以上の溶接熱影響部からなるとき、前記スポット溶接部の強度が所定値以上であると判定するステップを含むことを特徴とする。 In order to solve the above-described problems and achieve the object, the method for determining the strength of a spot welded portion according to the present invention is a welded joint and welded member in which two or more thin steel plates having a thickness t [mm] are spot welded. A method for determining the strength of a spot welded portion, wherein the nugget diameter [mm] is 3√t or more, and in the nugget cross section, the sheet separation termination region has a convex portion forming a convex shape in a direction opposite to the nugget, When the contour line of the convex portion intersects with a straight line connecting the steel sheet mating surfaces of the thin steel plates, and the convex portion is composed of a weld heat affected zone having an area ratio of 50% or more, the strength of the spot welded portion is a predetermined value. It is characterized by including the step which determines with it being above.
また、本発明に係るスポット溶接部の強度判定方法は、上記発明において、前記ナゲットと反対方向に凹形状をなす２つの凹部を有し、前記２つの凹部の間に前記凸部が形成されているとき、前記スポット溶接部の強度が所定値以上であると判定するステップを含むことを特徴とする。 Further, in the above invention, the method for determining the strength of the spot welded portion according to the present invention has two concave portions having a concave shape in a direction opposite to the nugget, and the convex portion is formed between the two concave portions. A step of determining that the strength of the spot weld is equal to or greater than a predetermined value.
本発明によれば、溶接継手や溶接部材に対して優れた静的強度、衝撃強度および疲労強度を付与することができるとともに、静的強度、衝撃強度および疲労強度等の強度特性全般に優れるスポット溶接部であるか否かを判定することができる。 According to the present invention, excellent static strength, impact strength, and fatigue strength can be imparted to welded joints and welded members, and the spot has excellent overall strength characteristics such as static strength, impact strength, and fatigue strength. It can be determined whether it is a welded part.
以下、本発明に係るスポット溶接部、スポット溶接部の製造方法およびスポット溶接部の強度判定方法について、図１〜図１６を参照しながら説明する。なお、本発明は以下の実施形態に限定されるものではない。また、以下の実施形態における構成要素には、当業者が置換可能かつ容易なもの、あるいは実質的に同一のものが含まれる。 Hereinafter, a spot welded portion, a method for manufacturing a spot welded portion, and a method for determining the strength of a spot welded portion according to the present invention will be described with reference to FIGS. In addition, this invention is not limited to the following embodiment. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art or those that are substantially the same.
ここで、本発明の第一の目的は、後記する図１や非特許文献６に示すように、スポット溶接におけるＬ字引張継手のような厳しい条件下において、はく離破断強度を向上させるスポット溶接部を提供することにある。また、スポット溶接継手や溶接部材を車両に用いた場合、実車構造においては様々な負荷形式や変形形式が作用し、荷重も静荷重のみならず衝撃荷重や繰返し荷重が作用する。そこで、本発明は、スポット溶接継手や溶接部材を対象にはく離破断強度やせん断強度あるいはそれらの組み合わせ等の静的強度、衝撃強度および疲労強度等の強度特性全般を、スポット溶接部を介して与えること、およびそのようなスポット溶接部を製造すること、ならびにスポット溶接部の強度を精度よく判定することを目的とする。 Here, the first object of the present invention is to provide a spot welded portion that improves the peel strength under severe conditions such as an L-shaped tensile joint in spot welding as shown in FIG. 1 and Non-Patent Document 6 to be described later. Is to provide. Further, when spot welded joints or welded members are used in a vehicle, various load types and deformation types are applied to the actual vehicle structure, and the load is not only a static load but also an impact load and a repeated load. Therefore, the present invention provides overall strength characteristics such as static strength, impact strength and fatigue strength such as peel strength, shear strength, or a combination thereof to spot welded joints and welded members via spot welds. It is an object to manufacture such a spot weld and to determine the strength of the spot weld with high accuracy.
本発明者らは、静的はく離破断を評価する指標として最も厳しいとされるＬ字継手引張強度（以下、ＬＴＳという）を向上させる方策について鋭意検討した。まず、Ｃ量０．１３％で板厚ｔが１．６ｍｍの９８０ＭＰａ級薄鋼板でナゲット径［ｍｍ］を３√ｔ〜５．５√ｔの範囲で変化させて２枚重ねのＬ字引張継手を作製し、各ナゲット径について、７本のＬＴＳの引張試験を実施した。なお、試験片の作製方法および試験方法は非特許文献１に準拠した。 The present inventors diligently studied a method for improving L-shaped joint tensile strength (hereinafter referred to as LTS), which is considered to be the most severe as an index for evaluating static delamination fracture. First, a 980 MPa grade thin steel sheet with a C content of 0.13% and a sheet thickness t of 1.6 mm, the nugget diameter [mm] being varied in the range of 3√t to 5.5√t, and two-layer L-shaped tensile Joints were prepared and seven LTS tensile tests were performed for each nugget diameter. In addition, the preparation method and test method of the test piece were based on Non-Patent Document 1.
ナゲット径とＬＴＳの関係を図１に示す。同図によれば、ナゲット径を５√ｔとしてもはく離破断し低強度破壊していること、ナゲット径を５．５√ｔとするとプラグ破断に移行し、破断強度が向上することがわかる。ここで、注目すべきは、ナゲット径が５√ｔから５．５√ｔへ、わずか０．５√ｔ（０．６３ｍｍ）増加することでプラグ破断へ移行していること、５．５√ｔで７本ともプラグ破断し、ＬＴＳの値も安定していることである。 The relationship between the nugget diameter and LTS is shown in FIG. According to the figure, it can be seen that even when the nugget diameter is 5√t, it is peeled and fractured at a low strength, and when the nugget diameter is 5.5√t, it shifts to a plug fracture and the breaking strength is improved. Here, it should be noted that the nugget diameter is shifted from 5√t to 5.5√t, and only 0.5√t (0.63 mm) is increased, so that the transition to plug fracture occurs. Seven plugs are broken at t, and the LTS value is also stable.
なお、図１では同鋼板で作製した十字引張継手の十字引張強度（以下、ＣＴＳという）の引張試験の結果も併記しているが、十字引張継手では５√ｔでプラグ破断していること、またＬＴＳはＣＴＳと比較して荷重が著しく低いこと等から、ＬＴＳの引張試験が静的はく離破断に対して非常に厳格な試験であることがわかる。 FIG. 1 also shows the results of a tensile test of the cross tensile strength (hereinafter referred to as CTS) of a cross tensile joint made of the same steel sheet, but the cross tensile joint has a plug fracture at 5√t, Moreover, since the load of LTS is remarkably low compared with CTS etc., it turns out that the tensile test of LTS is a very strict test with respect to static delamination fracture.
このようなＬＴＳの破壊形態についてさらに詳細に検討するため、図１で示すナゲット径３√ｔ（はく離破断）、４√ｔ（はく離破断）、５．５√ｔ（プラグ破断）の溶接継手について、ＬＴＳの１０％（ＬＴＳ×０．１０），２５％（ＬＴＳ×０．２５），５０％（ＬＴＳ×０．５０），７５％（ＬＴＳ×０．７５），９５％（ＬＴＳ×０．９５）まで荷重を負荷した後に除荷し、ナゲット断面におけるき裂発生・進展状況を調査した。その結果を図２〜図４に示す。 In order to examine the fracture mode of such an LTS in more detail, a welded joint having a nugget diameter of 3√t (separation fracture), 4√t (separation fracture), and 5.5√t (plug fracture) shown in FIG. , LTS 10% (LTS × 0.10), 25% (LTS × 0.25), 50% (LTS × 0.50), 75% (LTS × 0.75), 95% (LTS × 0. After loading up to 95), the load was unloaded, and the crack initiation and propagation status in the nugget cross section was investigated. The results are shown in FIGS.
図２および図３に示すように、はく離破断したナゲット径３√ｔ，４√ｔの溶接継手では、ＬＴＳの１０％でコロナボンドがはく離し、先鋭なき裂が発生しており、き裂先端がナゲット内にある。さらに、荷重をＬＴＳの２５％〜７５％に増加させると、ナゲット径３√ｔ，４√ｔともに、き裂が徐々に進展しながら開口する。そして、ＬＴＳの９５％まで達すると、３√ｔ，４√ｔともに、き裂がナゲット方向へとさらなる進展を見せる。なお、前記した「ナゲット方向」とは、ナゲットに向かう方向、より詳細にはナゲットの中心（以下、ナゲット中心という）に向かう方向のことを示している。なお、図２〜図４では、ナゲット方向＝き裂進展方向としている。 As shown in FIG. 2 and FIG. 3, in the welded joint having a nugget diameter of 3√t and 4√t, the corona bond peeled off at 10% of LTS, and a sharp crack was generated. Is in the nugget. Further, when the load is increased to 25% to 75% of the LTS, the cracks are opened while the nugget diameters 3√t and 4√t are gradually developed. And when it reaches 95% of LTS, both 3√t and 4√t show further progress in the nugget direction. The “nugget direction” described above indicates the direction toward the nugget, more specifically, the direction toward the center of the nugget (hereinafter referred to as the nugget center). 2 to 4, the nugget direction = the crack propagation direction.
一方、図４に示すように、ナゲット径５．５√ｔの溶接継手では、ＬＴＳの５０％の荷重を負荷してもコロナボンドにはく離は生じない。このとき、シートセパレーション終端領域において、ナゲット方向と反対方向に凹な領域（以下、凹部という）からサブクラックが生じているが、その長さは２００μｍにも満たずわずかであり、その後の負荷増加に際しても破壊に寄与することはなかった。そして、ＬＴＳの７５％の荷重を負荷したとき、シートセパレーション終端領域において、凹部から先鋭な主き裂が溶接熱影響部（Heat Affected Zone：ＨＡＺ）方向へと、上下板ともに斜めに発生する。さらに、ＬＴＳの９５％まで荷重を負荷すると、上下のき裂は溶接熱影響部（以下、ＨＡＺという）を超えて母材へ安定成長し、プラグ破断へと至った。 On the other hand, as shown in FIG. 4, in the welded joint having a nugget diameter of 5.5√t, the corona bond does not peel even when a load of 50% of LTS is applied. At this time, in the sheet separation termination region, sub-cracks are generated from a region recessed in the direction opposite to the nugget direction (hereinafter referred to as a recess), but the length is slightly less than 200 μm, and the load increases thereafter. At that time, it did not contribute to destruction. When a load of 75% of LTS is applied, a sharp main crack from the concave portion is generated obliquely in the heat affected zone (HAZ) direction in the upper and lower plates in the sheet separation termination region. Further, when a load was applied to 95% of LTS, the upper and lower cracks exceeded the welding heat affected zone (hereinafter referred to as HAZ) and grew stably to the base material, leading to plug fracture.
ここで、図４で注目すべき点は、シートセパレーション終端領域でナゲット方向と反対方向に凸な領域（以下、凸部という）が存在すること、そして凸部の外径線がコロナボンドを結ぶ直線と交わっていることである。すなわち、この凸部の存在により、低強度破壊であるはく離破断の先駆となるコロナボンドのはく離による先鋭なき裂の発生が妨げられたものと考えることができる。なお、前記した「コロナボンドを結ぶ直線」とは、ナゲットからシートセパレーションに向かって伸びる直線のことであり、言い換えると、薄鋼板の鋼板合わせ面を結んだ直線のことを示している。 Here, what should be noted in FIG. 4 is that there is a region (hereinafter referred to as a convex portion) that is convex in the direction opposite to the nugget direction in the sheet separation termination region, and the outer diameter line of the convex portion connects the corona bond. It intersects with a straight line. That is, it can be considered that the presence of this convex portion hinders the occurrence of sharp cracks due to the peeling of the corona bond, which is a precursor of the peeling fracture that is a low strength fracture. The above-mentioned “straight line connecting corona bonds” refers to a straight line extending from the nugget toward the sheet separation, in other words, a straight line connecting the steel sheet mating surfaces of the thin steel sheets.
上記の仮説を検証するため、Ｌ字引張継手の１／２対称３次元ソリッドモデルを作製し、有限要素解析ソフトウェア「ＡＢＡＱＵＳ Ｖｅｒ．６−１２−１」にて有限要素解析（Finite Element Analysis：ＦＥＡ）を実施した。板厚は１．６ｍｍとし、ナゲット径は５√ｔとした。また、ナゲット、ＨＡＺおよび母材の領域はミクロ組織や硬度を参照して求め、モデルに反映させた。解析においてナゲットおよびＨＡＺ領域では、母材の実験により得られた応力と歪みとの関係に基づいて、母材との硬度比（例えばナゲットではナゲット硬度／母材硬度）を母材の降伏応力および引張応力に乗じ、他方で一様伸びは母材のそれを硬度比で除することによって外挿した。降伏応力以降の塑性域の外挿の際にはＳｗｉｆｔの式を用いた。 In order to verify the above hypothesis, a 1/2 symmetric three-dimensional solid model of an L-shaped tensile joint was prepared, and finite element analysis (Finite Element Analysis: FEA) was performed using finite element analysis software “ABAQUS Ver. 6-12-1.” ). The plate thickness was 1.6 mm and the nugget diameter was 5√t. The nugget, HAZ, and base metal regions were obtained with reference to the microstructure and hardness and reflected in the model. In the nugget and HAZ regions in the analysis, based on the relationship between the stress and strain obtained from the base material experiment, the hardness ratio with the base material (for example, nugget hardness / base material hardness for the nugget) is calculated based on the yield stress and the base metal. Multiplying the tensile stress, on the other hand, the uniform elongation was extrapolated by dividing that of the matrix by the hardness ratio. The Swift equation was used when extrapolating the plastic area after the yield stress.
シートセパレーション間隔Ｄは、実体を模擬して２００μｍとした。モデルは、図５に示すように、シートセパレーション終端領域の形状が、（ａ）凸部がなく半径Ｄ／２の半円である場合、（ｂ）最深部がＤ／２となる楕円弧の組み合わせの場合、の２ケースとした。また、図５（ｂ）における凸部は、図４を参照し、凸部最深部から凸部頂点までの長さを１７０μｍとした。 The sheet separation interval D was set to 200 μm by simulating the substance. As shown in FIG. 5, when the shape of the sheet separation end region is (a) a semicircle with no radius and a radius D / 2, (b) a combination of elliptical arcs where the deepest part is D / 2 In this case, two cases were used. Moreover, the convex part in FIG.5 (b) made 170 micrometers the length from a convex part deepest part to a convex-part vertex with reference to FIG.
図５（ａ）において、コロナボンドを示す線（一点鎖線）上のモデル最外面にある節点Ａの開口応力を解析した。また、図５（ｂ）において、ナゲット方向と反対方向に凹で最深部のモデル最外面にある節点Ｂと節点Ｄ、コロナボンドを示す線上のモデル最外面にある節点Ｃ（凸部の頂点）の開口応力をそれぞれ解析した。その解析結果を図６に示す。 In FIG. 5 (a), the opening stress of the node A on the outermost surface of the model on the line indicating the corona bond (one-dot chain line) was analyzed. Further, in FIG. 5B, the nodes B and D which are concave in the opposite direction to the nugget direction and are on the outermost surface of the model at the deepest part, and the node C which is on the outermost surface of the model on the line indicating the corona bond The opening stress of each was analyzed. The analysis result is shown in FIG.
図６に示すように、節点Ａの開口応力が最も高く、図５（ａ）に示すような凸部の無い形状では、コロナボンドのはく離によるき裂発生が予想される。これは前記した図２および図３の実験結果とも一致している。 As shown in FIG. 6, the opening stress at the node A is the highest, and cracks due to peeling of the corona bond are expected in the shape having no projection as shown in FIG. This is consistent with the experimental results shown in FIGS.
一方、図５（ｂ）に示すような凸部を有する形状では、図６に示すように、最深部の節点Ｂと節点Ｄの開口応力が同じで節点Ａに次いで高い。但し、コロナボンドは、図５（ｂ）に示すように鋼板合わせ面上に存在し、節点Ｂ，Ｄの位置にはコロナボンドが無いため、き裂が発生したとしても軽微であると考えられる。これは前記した図４の実験結果とも一致している。 On the other hand, in the shape having the convex portion as shown in FIG. 5B, the opening stresses at the deepest node B and the node D are the same as shown in FIG. However, the corona bond is present on the mating surface of the steel plates as shown in FIG. 5B, and since there is no corona bond at the positions of the nodes B and D, it is considered that the crack is slight even if a crack occurs. . This is consistent with the experimental result of FIG.
また、節点Ｂと節点Ｄの開口応力は同じであるため、それぞれのき裂進展駆動力が半分となり、そこからのき裂が進展しにくくなるという効果も有する。一方、節点Ｃはナゲット方向と反対方向に凸形状をなしているため、開口応力はほとんど作用していない。よって、はく離破断の先駆となるコロナボンドがはく離するようなき裂は発生しないと考えられ、これも前記した図４の実験結果と一致している。 Further, since the opening stresses at the node B and the node D are the same, each of the crack propagation driving forces is halved, and there is also an effect that the cracks are hardly propagated therefrom. On the other hand, since the node C has a convex shape opposite to the nugget direction, the opening stress hardly acts. Therefore, it is considered that a crack that peels off the corona bond, which is a precursor of the peeling fracture, does not occur, and this also agrees with the experimental result of FIG. 4 described above.
図７（ａ）は、後記する実施例と同様の溶接条件で１１８０ＭＰａ級薄鋼板（板厚１．６ｍｍ）を２枚重ね、ナゲット径４√ｔでスポット溶接したＬ字引張継手において、プラグ破断した際のＬＴＳの４０％まで荷重を負荷した後に除荷し、ナゲット断面におけるき裂発生状況を示す図を調査した結果である。 FIG. 7 (a) shows a plug rupture in an L-shaped tensile joint obtained by spot welding with a nugget diameter of 4√t by stacking two 1180MPa class thin steel plates (plate thickness 1.6mm) under the same welding conditions as in the examples described later. It is the result of investigating the figure which shows the crack generation condition in a nugget cross section after unloading after loading up to 40% of LTS at the time of carrying out.
この場合も、シートセパレーション終端領域にサブクラックが発生していたが、その長さは１００μｍに満たない。また、この場合もシートセパレーション終端領域にナゲット方向と反対方向に凸部が形成され、その凸部の外径線とコロナボンドを結ぶ直線が交わっていた。また、この凸部は、ナゲット方向と反対方向に凹形状をなす２つの凹部の間にあった。そのため、その後載荷しても前記した微小なサブクラックはほとんど進展せず、ＬＴＳの７０％まで荷重を負荷すると、図７（ｂ）に示すように、シートセパレーション終端領域において、ナゲット方向と反対方向に凹形状をなす凹部からＨＡＺへと斜め方向にき裂が発生し、それが安定成長してプラグ破断した。 In this case as well, sub-cracks occurred in the sheet separation termination region, but the length was less than 100 μm. Also in this case, a convex portion was formed in the sheet separation termination region in a direction opposite to the nugget direction, and a straight line connecting the outer diameter line of the convex portion and the corona bond intersected. Moreover, this convex part existed between the two recessed parts which make a concave shape in the direction opposite to the nugget direction. Therefore, even if it is loaded after that, the above-mentioned minute subcracks hardly progress, and when a load is applied to 70% of LTS, as shown in FIG. 7B, in the sheet separation termination region, the direction opposite to the nugget direction Cracks were generated in an oblique direction from the concave portion having a concave shape to the HAZ, which grew stably and the plug broke.
以上より、板厚ｔ［ｍｍ］の２枚以上の薄鋼板をスポット溶接した溶接継手および溶接部材におけるスポット溶接部において、以下の条件（１）〜（５）を満たす場合、はく離破断の先駆となるコロナボンドのはく離による先鋭なき裂が発生せず、プラグ破断化が促進されることがより明らかとなった。 As described above, when the following conditions (1) to (5) are satisfied in a welded joint obtained by spot welding two or more thin steel plates having a thickness t [mm] and a spot welded portion in a welded member, It became clear that sharp cracks due to peeling of the corona bond were not generated, and plug breakage was promoted.
（１）ナゲット径［ｍｍ］が３√ｔ以上である。
（２）ナゲット断面において、シートセパレーション終端領域内にナゲット方向と反対方向に凸形状をなす凸部を有する。
（３）凸部の外郭線が、コロナボンドを結ぶ直線（薄鋼板の鋼板合わせ面を結んだ直線）と交わっている。
（４）凸部が、面積率で５０％以上のＨＡＺからなる。
（５）好ましくは、ナゲット方向と反対方向に凹形状をなす２つの凹部を有し、２つの凹部の間に凸部が形成されている。
(1) The nugget diameter [mm] is 3√t or more.
(2) In the nugget cross section, the sheet separation termination region has a convex portion that is convex in the direction opposite to the nugget direction.
(3) The outline of the convex portion intersects with a straight line connecting corona bonds (a straight line connecting the steel sheet mating surfaces of the thin steel sheets).
(4) The convex portion is made of HAZ having an area ratio of 50% or more.
(5) Preferably, it has two recessed parts which make concave shape in the direction opposite to a nugget direction, and the convex part is formed between the two recessed parts.
なお、図４および図７を見れば明らかなように、シートセパレーション終端領域でナゲット方向と反対方向に凸形状をなす凸部は、楕円状あるいは台形状等、形状によらず効果が発揮されることがわかる。 As is apparent from FIGS. 4 and 7, the convex portion having a convex shape in the direction opposite to the nugget direction in the sheet separation terminal region is effective regardless of the shape, such as an elliptical shape or a trapezoidal shape. I understand that.
また、上記条件（１）〜（５）を満たすスポット溶接部を有する十字引張試験片、せん断引張試験片、Ｌ字引張試験片を作製し、静的荷重、衝撃荷重および繰返し荷重を与えて評価したところ、継手形式や負荷形式によらずプラグ破断化が促進され、強度が向上することが判明した。 In addition, a cross tensile test piece, a shear tensile test piece, and an L-shaped tensile test piece having spot welds that satisfy the above conditions (1) to (5) are produced, and evaluation is performed by applying static load, impact load, and repeated load. As a result, it has been found that the plug breakage is promoted and the strength is improved regardless of the joint type or the load type.
また、このようなスポット溶接部を有するスポット溶接部材に圧壊衝撃荷重、曲げ衝撃荷重を与えても、部材が分離破断することなく、優れた衝撃破壊特性を示した。さらには、このようなスポット溶接部の条件についても明らかになった。従って、具体的な溶接条件等が未知の溶接継手であっても、上記の条件を満たすスポット溶接部が存在すれば、溶接継手や溶接部材に対して優れた静的強度、衝撃強度および疲労強度を付与することができ、溶接継手や溶接部材の強度特性全般が向上することが判明した。 Moreover, even when a crushing impact load and a bending impact load were applied to a spot welded member having such a spot weld, the member did not break apart and showed excellent impact fracture characteristics. Furthermore, the conditions for such spot welds have also been clarified. Therefore, even if the specific welding conditions are unknown, if there are spot welds that satisfy the above conditions, excellent static strength, impact strength, and fatigue strength for welded joints and welded members It has been found that the strength characteristics of weld joints and welded members are improved.
ここで、スポット溶接される２枚以上の薄鋼板の板組は、同種同厚、他種同厚、同種異厚、他種異厚でも構わない。また、薄鋼板の強度は特に限定されず、またナゲット径の基準となる板厚ｔは、異厚の組み合わせの場合には最小の板厚をとるものとする。また、最も厳しい試験であるＬＴＳのＬ字引張試験で、シートセパレーション終端領域に凸部があることでプラグ破断を示した最小ナゲット径が３√ｔであったため、本発明に係るスポット溶接部のナゲット径の下限は３√ｔとする。 Here, the plate set of two or more thin steel plates to be spot-welded may be of the same type and thickness, the same type of different thickness, the same type of different thickness, or the different type of different thickness. Further, the strength of the thin steel plate is not particularly limited, and the thickness t serving as a reference for the nugget diameter is the minimum thickness in the case of a combination of different thicknesses. Further, in the L-shaped tensile test of LTS, which is the most severe test, the minimum nugget diameter indicating plug fracture due to the presence of a convex portion in the sheet separation termination region was 3√t. The lower limit of the nugget diameter is 3√t.
また、同様の効果は十字引張試験やせん断引張試験でも見られた。また、十字引張試験片、せん断引張試験片、Ｌ字引張試験片で、衝撃荷重や疲労荷重を与えた場合にも、破断形式がプラグ破断となり、強度向上が認められた。さらに、同様な効果は、例えばハット部材等のスポット溶接部材を対象とした場合でも見られた。 Similar effects were also observed in the cross tension test and shear tensile test. In addition, even when an impact load or fatigue load was applied to the cross tensile test piece, the shear tensile test piece, or the L-shaped tensile test piece, the breaking type became plug rupture, and an improvement in strength was recognized. Furthermore, the same effect was seen also when the spot welding member, such as a hat member, was made into object.
ここで、本発明に係るスポット溶接部のナゲット断面は、図８（ａ）および図８（ｂ）に示すように、鋼板表面の電極加圧によるへこみをベストフィットするような円あるいは楕円で近似し、その中心点Ｏを通る断面でＡ−Ａ’断面やＢ−Ｂ’断面のことを指している。なお、同図は、鋼板表面を、スポット溶接における電極加圧の方向から見た図である。 Here, the nugget cross section of the spot welded portion according to the present invention is approximated by a circle or an ellipse that best fits a dent caused by electrode press on the surface of the steel plate, as shown in FIGS. 8 (a) and 8 (b). The cross section passing through the center point O indicates the AA ′ cross section or the BB ′ cross section. In addition, the figure is the figure which looked at the steel plate surface from the direction of the electrode pressurization in spot welding.
ナゲット断面は、具体的には、溶接継手においてき裂が進展する方向であって、継手試験片の長手方向端部の幅中央点と長手方向外郭線とを平行に結んだ線上にある断面とする。例えば図９に示すようなＬ字引張試験片では、幅中央点Ａと幅中央点Ｂとを結んだ線上における１つのナゲット断面で評価すればよい。また、図１０に示すような十字引張試験片では、幅中央点Ａと幅中央点Ｂとを結んだ線上と、幅中央点Ｃと幅中央点Ｄとを結んだ線上とにおける２つのナゲット断面で評価すればよい。そして、図１１に示すようなせん断引張試験片では、幅中央点Ａと幅中央点Ｂとを結んだ線上における１つのナゲット断面で評価すればよい。 Specifically, the nugget cross section is a direction in which a crack propagates in a welded joint, and is a cross section on a line connecting the width center point of the longitudinal end portion of the joint test piece and the longitudinal outline line in parallel. To do. For example, an L-shaped tensile test piece as shown in FIG. 9 may be evaluated with one nugget cross section on a line connecting the width center point A and the width center point B. Further, in the cross tensile test piece as shown in FIG. 10, two nugget cross sections on a line connecting the width center point A and the width center point B and on a line connecting the width center point C and the width center point D are shown. You can evaluate with. And what is necessary is just to evaluate with one nugget cross section on the line | wire which connected the width center point A and the width center point B in the shear tension test piece as shown in FIG.
また、スポット溶接部材は、圧壊衝撃荷重や曲げ衝撃荷重を与えた際、複雑な変形挙動を見せる。そのため、スポット溶接部材を構成する個々のスポット溶接部を、図８のＡ−Ａ’断面やＢ−Ｂ’断面のような、中心点Ｏを通る少なくとも任意の５断面において評価すればよい。 Moreover, the spot welding member shows a complicated deformation behavior when a crushing impact load or a bending impact load is applied. Therefore, the individual spot welds constituting the spot weld member may be evaluated in at least five arbitrary cross sections passing through the center point O, such as the A-A ′ cross section and the B-B ′ cross section of FIG. 8.
図１２（ａ）にナゲット断面の模式図を示す。ｔを板厚とするとき、ＨＡＺの端部から距離２ｔである上板のシートセパレーションの点をＡ、下板のシートセパレーションの点をＡ’とする。同様に、ＨＡＺの端部から距離ｔである上板のシートセパレーションの点をＢ、下板のシートセパレーションの点をＢ’とする。そして、ＡとＢ、Ａ’とＢ’をそれぞれ直線で結んだ時、図１２（ｂ）に示すように、シートセパレーションの外郭線が鋼板あわせ面の端部Ｄの方向に、直線を外れて近づく領域（Ｃ−Ｄ−Ｃ’）を、ここではシートセパレーション終端領域と定義する。なお、図１２および後記する図１３では、凸部の図示は省略している。 FIG. 12A shows a schematic diagram of a nugget cross section. When t is a plate thickness, a sheet separation point on the upper plate, which is a distance 2t from the end of the HAZ, is A, and a sheet separation point on the lower plate is A ′. Similarly, a point of sheet separation on the upper plate that is a distance t from the end of the HAZ is B, and a point of sheet separation on the lower plate is B ′. When A and B and A ′ and B ′ are respectively connected by a straight line, as shown in FIG. 12B, the outline of the sheet separation deviates from the straight line in the direction of the end D of the steel sheet mating surface. The approaching region (CDC ′) is defined as a sheet separation end region here. In FIG. 12 and FIG. 13 to be described later, the convex portions are not shown.
また、鋼板あわせ面とは、図１３に示すように、ナゲット断面において一方側（左側）のシートセパレーション間隔を２Ｌ、他方側（右側）のシートセパレーション間隔を２Ｒとしたとき、左右でそれぞれ２Ｌと２Ｒの中心とを結んだ線上にある、鋼板表面と平行な面のことを示している。 Further, as shown in FIG. 13, the steel plate mating surface is 2 L on the left and right when the sheet separation interval on one side (left side) is 2 L and the sheet separation interval on the other side (right side) is 2 R in the nugget cross section. The surface parallel to the steel plate surface on the line connecting the center of 2R is shown.
ここで、前記したように、低強度破壊においてはその先駆となるコロナボンドのはく離が重要である。そして、このコロナボンドは、図４や図７に示すように、シートセパレーション終端領域でナゲット方向と反対方向に凸部が形成されている場合は明瞭には判別できないが、図１３に示すように、基本的には鋼板あわせ面上に存在するものと考えられる。 Here, as described above, in low-strength fracture, peeling of the corona bond, which is a precursor, is important. This corona bond cannot be clearly discriminated when a convex portion is formed in the direction opposite to the nugget direction in the sheet separation termination region as shown in FIGS. 4 and 7, but as shown in FIG. Basically, it is considered to exist on the mating surface of the steel plates.
なお、図１３において、２Ｌおよび２Ｒは、シートセパレーションの上側の輪郭が鋼板上表面に平行であり、かつシートセパレーションの下側の輪郭が鋼板下表面に平行となる位置で鋼板厚さ方向にとったシートセパレーション間隔とする。同図に示すシートセパレーションの終端領域において、鋼板あわせ面を結んだ直線（コロナボンドを結んだ直線）が凸部（同図では図示省略）の外郭線と交わるとき、その節点では前記した図５，６に示すように、開口応力が０になるため、コロナボンドは開口しない。 In FIG. 13, 2L and 2R are taken in the thickness direction of the steel sheet at a position where the upper contour of the sheet separation is parallel to the upper surface of the steel plate and the lower contour of the sheet separation is parallel to the lower surface of the steel plate. Sheet separation interval. When the straight line connecting the steel plate mating surfaces (the straight line connecting the corona bond) intersects the contour line of the convex portion (not shown in the figure) in the terminal separation region of the sheet separation shown in FIG. , 6, since the opening stress becomes zero, the corona bond does not open.
次に、図１４（ａ）は、９８０ＭＰａ級薄鋼板（板厚１．６ｍｍ）を２枚重ね、ナゲット径５√ｔでスポット溶接した後、ナゲット断面をピクリン酸腐食溶液で腐食させたものであり、ナゲットを明瞭に識別することができる。ここで、ナゲット外周の白い境界線から外側がＨＡＺである。このＨＡＺは、図１４（ｂ）に示すように、ナゲットの外周側にあり、母材よりも硬度が高い、あるいは低い領域として区別される。また、シートセパレーション終端領域にある凸部は、図１４（ａ）に示すようにＨＡＺから構成される。 Next, FIG. 14 (a) shows a state in which two 980 MPa thin steel plates (plate thickness 1.6 mm) are stacked, spot welded with a nugget diameter of 5√t, and then the nugget cross section is corroded with a picric acid corrosion solution. Yes, the nugget can be clearly identified. Here, the outer side from the white boundary line on the outer periphery of the nugget is HAZ. As shown in FIG. 14B, this HAZ is on the outer peripheral side of the nugget and is distinguished as a region having a hardness higher or lower than that of the base material. Moreover, the convex part in a sheet | seat separation termination | terminus area | region is comprised from HAZ as shown to Fig.14 (a).
ここで、非特許文献４に示すように、中散りの場合もシートセパレーション終端領域に凸部が形成されるが、同文献の図２に示すように、この場合の凸部は溶融・凝固した金属となり、ＨＡＺとはならない。一方、本発明では、この凸部が面積率で５０％以上のＨＡＺであるため、破断形式がプラグ破断になることによって高強度化が達成される。 Here, as shown in Non-Patent Document 4, a convex portion is formed in the sheet separation termination region even in the case of scattering, but as shown in FIG. 2 of the same literature, the convex portion in this case is melted and solidified. It becomes metal and does not become HAZ. On the other hand, in this invention, since this convex part is 50% or more of HAZ by an area ratio, high intensity | strength is achieved by a plug breakage | rupture form becoming a plug fracture.
次に、前記した図４で凸部が形成された溶接継手の、無負荷状態におけるナゲット断面を図１５（ａ）に示す。また、このナゲット断面のシートセパレーション終端領域における形状を模式的に示すと図１５（ｂ）のようになる。図１５（ｂ）に示すように、シートセパレーション終端領域において、その外郭線がナゲット方向に対して反対方向に進む領域、すなわち図中ハッチングによって示された領域を凸部の面積とする。そして、この面積の５０％以上がＨＡＺで構成されていれば、上述の効果が得られる。 Next, FIG. 15A shows a cross-section of the nugget in the no-load state of the weld joint in which the projections are formed in FIG. FIG. 15B schematically shows the shape of the nugget cross section in the sheet separation termination region. As shown in FIG. 15B, in the sheet separation termination region, a region where the outline extends in the opposite direction to the nugget direction, that is, a region indicated by hatching in the drawing is defined as the area of the convex portion. And if 50% or more of this area is comprised with HAZ, the above-mentioned effect will be acquired.
また、図１５（ｂ）に示すように、ナゲット方向と反対方向に凹形状をなす２つの凹部が形成され、この２つの凹部の間に凸部が形成されていることで、荷重が加わった際に凹部に主き裂が入ってエネルギーが分散されるため（図４「ＬＴＳ×０．７５」参照）、前記した図５および図６に示すような、凸部に対してコロナボンドを開口させる開口応力が作用しなくなる、という効果がさらに強くなる。 Further, as shown in FIG. 15 (b), two concave portions having a concave shape are formed in the direction opposite to the nugget direction, and a convex portion is formed between the two concave portions, so that a load is applied. In this case, the main cracks enter the recesses and the energy is dispersed (see “LTS × 0.75” in FIG. 4), so that corona bonds are opened to the protrusions as shown in FIGS. The effect that the opening stress to be stopped does not act further becomes stronger.
なお、シートセパレーション終端領域の形状は、必ずしも図１５（ｂ）に示すように上下対称である必要はなく、上下非対称でもよく、さらに形状も楕円状である必要性はない。また、ナゲット方向と反対方向に凹形状をなす２つの凹部も楕円状でなくてもよく、深さも同じではなく、形も揃っていなくてもよい。 Note that the shape of the sheet separation termination region does not necessarily need to be vertically symmetric as shown in FIG. 15B, may be vertically asymmetric, and does not need to be elliptical. Also, the two concave portions having a concave shape in the direction opposite to the nugget direction may not be elliptical, the depths are not the same, and the shapes may not be uniform.
以下、本発明の実施形態に係るスポット溶接部の製造方法（スポット溶接方法）について説明する。スポット溶接部の製造方法では、加圧力制御がキーテクノロジーとなる。これは、加圧力を後述するパラメータで適切に制御することで、スポット溶接中にナゲット方向と反対方向に凸部を形成することができるからである。本発明者らは、前記したような特徴を有するスポット溶接部を製造する方法について鋭意検討した結果、電極先端径をｄ［ｍｍ］、本通電時間をＴ［ｓｅｃ］、本通電電流をｃ［ｋＡ］、薄鋼板の引張強度をＴＳ［ＭＰａ］としたとき、加圧力Ｐ［Ｎ］を下記式（１）の範囲内とすることで、シートセパレーション終端領域において、ナゲット方向と反対方向に凸形状をなすＨＡＺからなる凸部が形成されることが判明した。 Hereinafter, the manufacturing method (spot welding method) of the spot weld part which concerns on embodiment of this invention is demonstrated. In the method for manufacturing a spot weld, pressure control is a key technology. This is because a convex part can be formed in the direction opposite to the nugget direction during spot welding by appropriately controlling the pressing force with parameters to be described later. As a result of intensive studies on a method for manufacturing a spot weld having the characteristics described above, the present inventors have determined that the electrode tip diameter is d [mm], the main energization time is T [sec], and the main energization current is c [ kA], when the tensile strength of the thin steel plate is TS [MPa], the pressure P [N] is within the range of the following formula (1), so that the sheet separation end region protrudes in the direction opposite to the nugget direction. It has been found that a convex portion made of HAZ having a shape is formed.
ここで、上記式（１）において、Ａ１〜Ａ６は０を含む係数、ｆ（ｘ）はｘの関数、ｆ（ｘ，ｙ，ｚ）はｘとｙとｚの関数である。そしてさらに検討を重ねた結果、上記式（１）は、下記式（２）で表されることが判明した。 Here, in the above formula (1), A 1 to A 6 are coefficients including 0, f (x) is a function of x, and f (x, y, z) is a function of x, y, and z. As a result of further studies, it was found that the above formula (1) is expressed by the following formula (2).
ここで、上記式（２）において、Ｈは
以上のような溶接条件を加味してスポット溶接を行うことで、静的強度、衝撃強度および疲労強度等の強度特性全般に優れるスポット溶接部を製造することができる。 By performing spot welding in consideration of the above welding conditions, a spot welded portion having excellent strength properties such as static strength, impact strength and fatigue strength can be manufactured.
また、前記したようなスポット溶接部に関する知見を応用し、例えば溶接条件等が未知の溶接継手や溶接部材であっても、これらに含まれるスポット溶接部が前記した条件（１）〜（５）を満たすか否かを判定することで、静的強度、衝撃強度および疲労強度等の強度特性全般に優れるスポット溶接部であるか否か、より具体的には当該スポット溶接部の強度が所定値以上であるか否かを判定することができる。なお、前記した「所定値以上」とは、前記したような、破断形式がプラグ破断になることによる高強度化が達成されるような強度の値を示している。 Further, by applying the knowledge about the spot welded portion as described above, for example, even if the welding condition or the like is a welded joint or welded member, the spot welded portion included in these is the condition (1) to (5) described above. Whether or not the spot welded portion is excellent in overall strength properties such as static strength, impact strength and fatigue strength, more specifically, the strength of the spot welded portion is a predetermined value. Whether or not this is the case can be determined. Note that the above “predetermined value or more” indicates a value of strength at which high strength is achieved by the plug rupture type as described above.
以下、実施例を挙げて本発明をより具体的に説明する。本実施例では、本発明に係るスポット溶接部の強度判定方法を用いたスポット溶接部の評価（表１〜表３参照）と、このスポット溶接部を有する溶接継手および溶接部材の強度の評価（表４〜表６参照）とを行った。 Hereinafter, the present invention will be described more specifically with reference to examples. In a present Example, evaluation (refer Table 1-Table 3) of the spot weld part using the strength determination method of the spot weld part which concerns on this invention, and evaluation of the strength of the welded joint and weld member which have this spot weld part ( Table 4 to Table 6).
スポット溶接部の評価では、表１〜表３に示すように、種々の引張強度と板厚の薄鋼板の等厚の２枚重ねスポット溶接継手を作製した。そして、作製の際に、電極先端径、本通電時間、本通電電流およびナゲット径を所定範囲で変化させた。また、スポット溶接の際の加圧力は上記式（２）により算出し、これを下回る条件で調整した。また、各溶接継手では、前記した図９〜図１１に示した方向のナゲット断面を評価した。 In the evaluation of the spot welded portion, as shown in Tables 1 to 3, two-layer spot welded joints with equal thicknesses of thin steel plates having various tensile strengths and plate thicknesses were produced. Then, at the time of production, the electrode tip diameter, the main energization time, the main energization current, and the nugget diameter were changed within a predetermined range. Further, the applied pressure at the time of spot welding was calculated by the above formula (2), and was adjusted under a condition below this. Moreover, in each welded joint, the nugget cross section of the direction shown in above-mentioned FIGS. 9-11 was evaluated.
スポット溶接部の評価に際しては、シートセパレーション終端領域内において、以下の条件１〜３を満たすか否かを評価し、満たす場合を○とし、満たさない場合を×とした。 In the evaluation of the spot welded portion, it was evaluated whether or not the following conditions 1 to 3 were satisfied within the sheet separation termination region.
条件１：ナゲット方向と反対方向に凸部を有すること
条件２：凸部の外郭線が鋼板あわせ面を結んだ直線（コロナボンドを結んだ直線）と交わること
条件３：ナゲット方向と反対方向に凹形状をなす２つの凹部の間に凸部が形成されていること
Condition 1: Convex part in the direction opposite to the nugget direction Condition 2: Contour line of the convex part intersects with a straight line connecting the steel plate mating surfaces (a straight line connecting corona bonds) Condition 3: In a direction opposite to the nugget direction A convex part is formed between two concave parts forming a concave shape.
また、スポット溶接部の評価では、前記した図１５（ｂ）に示すようなシートセパレーション終端領域の形状を忠実に模式し、ナゲット方向と反対方向に凸形状をなす凸部の面積率を求めた。なお、凸部の面積率は、図１４（ａ）に示すようにナゲット断面をピクリン酸エッチングするとともに、図１４（ｂ）に示すように硬さ測定を行うことで求めた。また、ナゲット径は、図１４（ａ）に示すような断面で、かつ図１３に示すような要領で求めた。 Further, in the evaluation of the spot welded portion, the shape of the sheet separation termination region as shown in FIG. 15B was faithfully modeled, and the area ratio of the convex portion having a convex shape in the direction opposite to the nugget direction was obtained. . The area ratio of the protrusions was obtained by picric acid etching of the nugget cross section as shown in FIG. 14 (a) and by measuring the hardness as shown in FIG. 14 (b). Moreover, the nugget diameter was calculated | required in the way as shown in FIG. 13 and a cross section as shown to Fig.14 (a).
溶接継手および溶接部材の強度の評価では、表４〜表６に示すように、溶接継手として、十字引張試験片、せん断引張試験片、Ｌ字引張試験片を作製した。そして、引張速度５ｍｍ／ｍｉｎにて静的荷重を負荷する静的引張試験を実施し、破断荷重（破断強度）および破断形式を求めた。なお、試験片や試験方法は、「ＪＩＳ Ｚ ３１３６」、「ＪＩＳ Ｚ ３１３７」、「ＩＳＯ１４２７０」に準拠した。 In the evaluation of the strength of the welded joint and the welded member, as shown in Tables 4 to 6, a cross tensile test piece, a shear tensile test piece, and an L-shaped tensile test piece were prepared as welded joints. Then, a static tensile test in which a static load was applied at a tensile speed of 5 mm / min was performed, and a breaking load (breaking strength) and a breaking type were obtained. In addition, the test piece and the test method were based on “JIS Z 3136”, “JIS Z 3137”, and “ISO 14270”.
また、表４〜表６に示すように、同じ溶接継手を用いて引張速度１０ｍ／ｓにて衝撃荷重を負荷する衝撃引張試験を実施し、破断荷重（破断強度）および破断形式を求めた。さらに、表４〜表６に示すように、「ＪＩＳ Ｚ ３１３８」に準拠して、最小最大荷重比０．０５、周波数２０Ｈｚにて繰返し荷重を負荷する疲労試験を実施した。この疲労試験では、繰り返し数で１０７Ｃｙｃｌｅｓに到達した最大の荷重範囲を疲労限度荷重範囲とし、併せて１０７Ｃｙｃｌｅｓに最も近い寿命で破断した試験片の破断形式を求めた。 Further, as shown in Tables 4 to 6, an impact tensile test in which an impact load was applied at a tensile speed of 10 m / s using the same welded joint was performed, and a breaking load (breaking strength) and a breaking type were obtained. Furthermore, as shown in Tables 4 to 6, a fatigue test was performed in which a repeated load was applied at a minimum / maximum load ratio of 0.05 and a frequency of 20 Hz in accordance with “JIS Z 3138”. In this fatigue test, the maximum load range that reached 10 7 Cycles in terms of the number of repetitions was taken as the fatigue limit load range, and the fracture type of the test piece that fractured at the life closest to 10 7 Cycles was determined.
溶接継手および溶接部材の強度の評価では、破断形式がプラグ破断であるものを合格とした。具体的には、「ＪＩＳ Ｚ ３１３６」に準拠し、破面に残存するナゲット径が元のナゲット径の８０％以上である場合をプラグ破断とした。そして、破面に残存するナゲット径が元のナゲット径の８０％未満である場合を部分プラグ破断、ナゲット部の破面が平坦である場合をはく離破断とした。 In the evaluation of the strength of the welded joint and the welded member, the one in which the fracture type is plug fracture was regarded as acceptable. Specifically, in accordance with “JIS Z 3136”, the case where the nugget diameter remaining on the fracture surface is 80% or more of the original nugget diameter was determined as plug fracture. The case where the nugget diameter remaining on the fracture surface was less than 80% of the original nugget diameter was regarded as partial plug fracture, and the case where the fracture surface of the nugget portion was flat was regarded as peeling fracture.
溶接継手および溶接部材の強度の評価では、表４〜表６に示すように、一部の組み合わせ（実施例１，５，１０，１４，２４，３０，４６，５７，６２，６６、比較例１，６，１１，１７）において、図１６に示すように、プレス成形したハット部材（溶接部材）にスポット溶接で背板を溶接し、圧壊衝撃荷重を負荷する圧壊衝撃試験と、曲げ衝撃荷重を負荷する曲げ衝撃試験とを追加で行った。 In the evaluation of the strength of welded joints and welded members, as shown in Tables 4 to 6, some combinations (Examples 1, 5, 10, 14, 24, 30, 46, 57, 62, 66, comparative examples) 1, 6, 11, 17), as shown in FIG. 16, a crushing impact test in which a back plate is welded to a press-formed hat member (welding member) by spot welding and a crushing impact load is applied, and a bending impact load And a bending impact test for loading.
圧壊衝撃試験では、ハット部材の長手方向において、１１０ｋｇの錘を１０ｍの高さから自由落下させて評価した。また、曲げ衝撃試験では、支持点間距離３２０ｍｍで保持したハット部材の長手中央部に対して、Ｒ１００ｍｍの錘を垂直に落下させた。その際の落下速度は１０ｍ／ｓとした。そして、これらの試験後にハット部材がスポット溶接部で分離破断した場合を×とし、未破断の場合を○とした。なおここでは、ハット部材について、個々のスポット溶接における５断面の観察を行い、ナゲット径やシートセパレーション終端領域の条件１〜３、凸部におけるＨＡＺの面積率が表１に記載のものとほとんど変わらないことを確認した上で試験を行った。 In the crushing impact test, an evaluation was made by dropping a 110 kg weight from a height of 10 m in the longitudinal direction of the hat member. In the bending impact test, a R100 mm weight was dropped vertically with respect to the longitudinal center portion of the hat member held at a distance between support points of 320 mm. The dropping speed at that time was 10 m / s. And after these tests, the case where the hat member was separated and fractured at the spot welded portion was marked as x, and the case where the hat member was not broken was marked as ◯. Here, for the hat member, five cross-sections in individual spot welding were observed, and conditions 1 to 3 of the nugget diameter and sheet separation termination region, and the area ratio of HAZ in the convex portion were almost the same as those described in Table 1. The test was conducted after confirming that there was no.
本発明範囲の溶接条件で作製した実施例１〜７０は、表１および表２に示すように、いずれもナゲット径［ｍｍ］が３√ｔ以上であり、かつナゲット断面で、シートセパレーション終端領域内において、条件１〜３を全て満足し、かつ凸部におけるＨＡＺの面積率が５０％以上であった。そして、表４および表５に示すように、実施例１〜７０のいずれの溶接継手も、静的荷重、衝撃荷重および繰返し荷重下においてプラグ破断を示し強度が向上した。 As shown in Tables 1 and 2, Examples 1 to 70 produced under the welding conditions within the scope of the present invention each have a nugget diameter [mm] of 3√t or more, a nugget cross section, and a sheet separation termination region. Among them, the conditions 1 to 3 were all satisfied, and the area ratio of the HAZ in the convex portion was 50% or more. As shown in Tables 4 and 5, any of the welded joints of Examples 1 to 70 exhibited plug rupture under a static load, an impact load, and a repeated load, and the strength was improved.
また、表４および表５に示すように、実施例１，５，１０，１４，２４，３０，４６，５７，６２，６６でハット部材を作製して試験したところ、圧壊衝撃荷重、曲げ衝撃荷重ともにスポット溶接部で分離破断することなく均一に変形した。 Further, as shown in Tables 4 and 5, when hat members were produced and tested in Examples 1, 5, 10, 14, 24, 30, 46, 57, 62, and 66, the crushing impact load and the bending impact were measured. Both loads were uniformly deformed without breaking at the spot welds.
ここで、実施例６１〜７０は、表２に示すように、鋼板の引張強度ＴＳと板厚ｔのみが既知であるが、溶接条件は未知のスポット溶接継手である。これらのナゲット断面を観察したところ、いずれもナゲット径［ｍｍ］が３√ｔ以上であり、かつナゲット断面で、シートセパレーション終端領域内において、条件１〜３を全て満足し、かつ凸部におけるＨＡＺの面積率が５０％以上であった。そのため、表５に示すように、実施例６１〜７０のいずれの溶接継手も、静的荷重、衝撃荷重、繰返し荷重下においてプラグ破断を示し強度が向上した。 Here, as shown in Table 2, in Examples 61 to 70, only the tensile strength TS and the plate thickness t of the steel plate are known, but the welding conditions are unknown spot welded joints. As a result of observing these nugget cross sections, the nugget diameter [mm] is 3√t or more, the nugget cross section satisfies all the conditions 1 to 3 in the sheet separation termination region, and the HAZ in the convex portion The area ratio was 50% or more. Therefore, as shown in Table 5, any of the welded joints of Examples 61 to 70 showed plug rupture under static load, impact load, and repeated load, and the strength was improved.
一方これに対し、比較例１〜１０は、表３に示すように、スポット溶接の際の加圧力が上記式（２）を満たしていなかった。その結果、シートセパレーション終端領域に凸部が形成されず、条件１，２，３を満たさなかった。そのため、表６に示すように、比較例１〜１０のいずれの溶接継手も、部分プラグ破断またははく離破断し、強度が低下した。また、表３に示すように、比較例１，６，１１，１７でハット部材を作製して試験したところ、圧壊衝撃荷重、曲げ衝撃荷重ともにスポット溶接部で分離破断した。 On the other hand, as shown in Table 3, in Comparative Examples 1 to 10, the applied pressure during spot welding did not satisfy the above formula (2). As a result, no convex portion was formed in the sheet separation termination region, and Conditions 1, 2, and 3 were not satisfied. Therefore, as shown in Table 6, all the welded joints of Comparative Examples 1 to 10 were partially plug ruptured or peeled off, and the strength was reduced. Moreover, as shown in Table 3, when the hat member was produced and tested in Comparative Examples 1, 6, 11, and 17, both the crushing impact load and the bending impact load were separated and fractured at the spot welded portion.
ここで、比較例１１〜２０は、表３に示すように、鋼板の引張強度ＴＳと板厚ｔのみが既知であるが、溶接条件は未知のスポット溶接継手である。これらのナゲット断面を観察したところ、いずれも条件１〜３の少なくとも一つを満足しないか、あるいは凸部の面積率が５０％未満であった。そのため、表６に示すように、比較例１１〜２０のいずれの溶接継手も、部分プラグ破断またははく離破断し、強度が低下した。 Here, as shown in Table 3, in Comparative Examples 11 to 20, only the tensile strength TS and the thickness t of the steel sheet are known, but the welding conditions are unknown spot welded joints. When these nugget cross-sections were observed, none of them satisfied at least one of the conditions 1 to 3, or the area ratio of the convex portions was less than 50%. Therefore, as shown in Table 6, all the welded joints of Comparative Examples 11 to 20 were partially plug ruptured or peeled off, and the strength was reduced.
なお、比較例１６は、条件１〜３を満足していたものの、ナゲット径が３√ｔ未満であったため、比較例１６の溶接継手は部分プラグ破断またははく離破断し、強度が低下した。また、比較例１７は、条件１を満足していたものの、条件２，３を満足しておらず、比較例１８は、条件１，２を満足していたものの、条件３を満足していなかった。そのため、比較例１７，１８のいずれの溶接継手も、コロナボンドがはく離し、部分プラグ破断またははく離破断し、強度が低下した。 In Comparative Example 16, although the conditions 1 to 3 were satisfied, the nugget diameter was less than 3√t. Therefore, the welded joint of Comparative Example 16 was partially plug fractured or peeled off, and the strength was reduced. Further, Comparative Example 17 satisfied Condition 1, but did not satisfy Conditions 2 and 3. Comparative Example 18 satisfied Condition 1 and 2, but did not satisfy Condition 3. It was. Therefore, in any of the welded joints of Comparative Examples 17 and 18, the corona bond peeled off, and the partial plug breakage or peel breakage caused the strength to decrease.
比較例１９は、条件１〜３を満足していたものの、エッチングによって確認したところ、比較例１９の凸部は中散りであり、当該凸部におけるＨＡＺの面積率が０％であった。そのため、比較例１９の溶接継手はコロナボンドがはく離し、部分プラグ破断またははく離破断し、強度が低下した。 Although the comparative example 19 was satisfying | filling conditions 1-3, when confirmed by the etching, the convex part of the comparative example 19 was scattered, and the area ratio of HAZ in the said convex part was 0%. Therefore, in the welded joint of Comparative Example 19, the corona bond was peeled off, the partial plug was broken or peeled, and the strength was lowered.
比較例２０は、条件１〜３を満足していたものの、エッチングによって確認したところ、比較例２０の凸部は多くが中散りで占められており、当該凸部におけるＨＡＺの面積率が５０％未満であった。そのため、比較例２０の溶接継手はコロナボンドがはく離し、部分プラグ破断またははく離破断し、強度が低下した。 Although the comparative example 20 was satisfying the conditions 1-3, when confirmed by etching, the convex part of the comparative example 20 was mostly scattered, and the area ratio of HAZ in the convex part was 50%. Was less than. Therefore, in the welded joint of Comparative Example 20, the corona bond was peeled off, the partial plug was broken or peeled, and the strength was lowered.
以上のような結果から、本発明によれば、スポット溶接部の強度を向上させることができるとともに、スポット溶接部の強度が向上したか否かを精度よく判定することができることが判明した。 From the above results, it has been found that according to the present invention, it is possible to improve the strength of the spot welded portion and accurately determine whether the strength of the spot welded portion has improved.
以上、本発明に係るスポット溶接部、スポット溶接部の製造方法およびスポット溶接部の強度判定方法について、発明を実施するための形態および実施例により具体的に説明したが、本発明の趣旨はこれらの記載に限定されるものではなく、特許請求の範囲の記載に基づいて広く解釈されなければならない。また、これらの記載に基づいて種々変更、改変等したものも本発明の趣旨に含まれることはいうまでもない。 The spot welded portion, the spot welded portion manufacturing method, and the spot welded portion strength determining method according to the present invention have been specifically described above with reference to embodiments and examples for carrying out the invention. However, it should be interpreted broadly based on the description of the scope of claims. Needless to say, various changes and modifications based on these descriptions are also included in the spirit of the present invention.
Claims (6)
ナゲット径［ｍｍ］が３√ｔ以上であり、
ナゲット断面において、シートセパレーション終端領域内にナゲットと反対方向に凸形状をなす凸部を有し、
前記凸部の外郭線が、前記薄鋼板の鋼板合わせ面を結んだ直線と交わり、
前記凸部が、面積率で５０％以上の溶接熱影響部からなることを特徴とするスポット溶接部。 A spot welded portion in a welded joint and welded member obtained by spot welding two or more thin steel plates having a thickness t [mm],
The nugget diameter [mm] is 3√t or more,
In the nugget cross section, the sheet separation termination region has a convex portion that is convex in the opposite direction to the nugget,
The contour line of the convex part intersects with a straight line connecting the steel sheet mating surfaces of the thin steel sheet,
The spot welded portion, wherein the convex portion is a weld heat affected zone having an area ratio of 50% or more.
前記２つの凹部の間に前記凸部が形成されていることを特徴とする請求項１に記載のスポット溶接部。 Having two recesses that are concave in the opposite direction to the nugget,
The spot welded portion according to claim 1, wherein the convex portion is formed between the two concave portions.
電極先端径をｄ［ｍｍ］、本通電時間をＴ［ｓｅｃ］、本通電電流をｃ［ｋＡ］、前記薄鋼板の引張強度をＴＳ［ＭＰａ］としたとき、加圧力Ｐ［Ｎ］を下記式（１）の範囲内とすることを特徴とするスポット溶接部の製造方法。
When the electrode tip diameter is d [mm], the main energization time is T [sec], the main energization current is c [kA], and the tensile strength of the thin steel sheet is TS [MPa], the applied pressure P [N] is as follows: A method for manufacturing a spot welded portion, which falls within the range of the formula (1).
ナゲット径［ｍｍ］が３√ｔ以上であり、
ナゲット断面において、シートセパレーション終端領域内にナゲットと反対方向に凸形状をなす凸部を有し、
前記凸部の外郭線が、前記薄鋼板の鋼板合わせ面を結んだ直線と交わり、
前記凸部が、面積率で５０％以上の溶接熱影響部からなるとき、
前記スポット溶接部の強度が所定値以上であると判定するステップを含むことを特徴とするスポット溶接部の強度判定方法。 A method for determining the strength of a spot welded portion in a welded joint and a welded member obtained by spot welding two or more thin steel plates having a thickness t [mm]
The nugget diameter [mm] is 3√t or more,
In the nugget cross section, the sheet separation termination region has a convex portion that is convex in the opposite direction to the nugget,
The contour line of the convex part intersects with a straight line connecting the steel sheet mating surfaces of the thin steel sheet,
When the convex portion is composed of a weld heat affected zone having an area ratio of 50% or more,
A method for determining the strength of a spot weld, comprising: determining that the strength of the spot weld is equal to or greater than a predetermined value.
前記２つの凹部の間に前記凸部が形成されているとき、
前記スポット溶接部の強度が所定値以上であると判定するステップを含むことを特徴とする請求項５に記載のスポット溶接部の強度判定方法。 Having two recesses that are concave in the opposite direction to the nugget,
When the convex portion is formed between the two concave portions,
6. The method of determining the strength of a spot weld according to claim 5, further comprising the step of determining that the strength of the spot weld is equal to or greater than a predetermined value.
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| JP2001009573A (en) * | 1999-06-25 | 2001-01-16 | Sumitomo Metal Ind Ltd | Welding joint of high tensile steel plate and welding method |
| JP2002103044A (en) * | 2000-09-29 | 2002-04-09 | Tokai Rubber Ind Ltd | Joined structural body and method for joining the same |
| WO2011013793A1 (en) * | 2009-07-31 | 2011-02-03 | 高周波熱錬株式会社 | Welded structural member and welding method |
| JP2013103273A (en) * | 2011-11-17 | 2013-05-30 | Jfe Steel Corp | Resistance spot welding method for high-tensile steel sheet |
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| JP2001009573A (en) * | 1999-06-25 | 2001-01-16 | Sumitomo Metal Ind Ltd | Welding joint of high tensile steel plate and welding method |
| JP2002103044A (en) * | 2000-09-29 | 2002-04-09 | Tokai Rubber Ind Ltd | Joined structural body and method for joining the same |
| WO2011013793A1 (en) * | 2009-07-31 | 2011-02-03 | 高周波熱錬株式会社 | Welded structural member and welding method |
| JP2013103273A (en) * | 2011-11-17 | 2013-05-30 | Jfe Steel Corp | Resistance spot welding method for high-tensile steel sheet |
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