JP6079466B2 - Lap welded member of high strength steel plate and method for producing the same - Google Patents

Description

  The present invention relates to a lap weld member of a high-strength steel plate and a method for manufacturing the same.

  In order to achieve both improved collision safety and improved fuel efficiency, the application of high-strength steel sheets to structural members that form the framework of the monocoque body that constitutes the body of an automobile (hereinafter referred to as “structural members for automobiles”) has expanded. Yes. Currently, high-strength steel sheets having a tensile strength of 980 MPa are used for structural members for automobiles, and recently, application of high-tensile steel sheets having a tensile strength of 1180 MPa or more is also being studied. In addition, the production of high-strength automotive structural members having a tensile strength of 1500 MPa or more has been promoted by using a hot stamp method in which quenching is performed simultaneously with press molding. According to the hot stamping method, the steel sheet is pressed in a soft state at a high temperature, so that there is little problem with dimensional accuracy after forming, and press forming can be performed in a high temperature and high ductility state. There is a great merit that it is excellent in performance.

  Generally, the structural member for automobiles is constructed by welding a molded product of these steel plates to other molded products by spot welding. However, the base material of high-strength steel plates such as high-strength steel plates and hot stamped steel plates of 1180 MPa or higher is strengthened by quenching, so that when spot welding is performed, the heat-affected zone (HAZ) of the spot welded portion is tempered. Softer than the base material. Although softening of HAZ (hereinafter also referred to as “HAZ softening”) hardly occurred in, for example, a 590 MPa steel plate, it was recognized in a 980 MPa steel plate, and in particular, a martensite structure in a continuous annealing facility (WQ-CAL) having a water cooling function. It occurs remarkably in the HAZ of spot welds of high-tensile steel plates and hot stamped steel plates of 1180 MPa or higher. For example, in a 1180 MPa grade cold-rolled steel sheet, the hardness of the base material is about Vickers hardness Hv 370 to 420, whereas the hardness of the most softened portion of the HAZ is reduced to about Hv 300.

  FIG. 12 is a graph showing an example of the hardness distribution of the spot welded portion of a member made of a high-strength steel plate (1500 MPa class hot stamped steel plate member).

  As shown in the graph of FIG. 12, in the case of a 1500 MPa class hot stamp material, the base material has a Vickers hardness of about Hv450, but the HAZ softest part is about Hv300, and the HAZ softest part is the base material. Hv is reduced by about 150.

  FIG. 13 is an explanatory view showing a state in which the hot stamped steel plate member having the hardness distribution of the spot welded portion shown in FIG. 12 is broken starting from the HAZ most softened portion, and FIG. 13 (a) is a top view, FIG. 13 (b) is a sectional view.

  Although this HAZ softening does not affect the results of the tensile shear test and cross tension test, which are joint evaluations of spot welding, a tensile load is applied to the entire flange portion of the hot stamping part including the spot weld. Then, as shown in FIGS. 13 (a) and 13 (b), strain may concentrate locally on the HAZ softest part and break. As described above, the HAZ softening of the spot welded portion in the press-formed product of a steel plate of 1180 MPa or more may be a starting point of the fracture of the press-formed product at the time of collision.

  For example, a tubular structural member of an automobile body having a closed cross section, such as an A pillar, a B pillar, a roof rail, and a side sill and having a flange that is spot welded to form the cross section, is torn at the time of a car collision. Therefore, it is required to effectively absorb impact energy and protect passengers in the cabin by plastic deformation. However, in severe collision mode, for example, in the case of the American Road Safety Insurance Association (IIHS) SUV side collision test, B pillar reinforcement using high strength steel plate is the softest HAZ of the spot welds on the flange of the B pillar. In some cases, strain concentrates on the part and becomes a starting point of breakage, and the B-pillar breaks during the collision, and the amount of the B-pillar entering the cabin increases, and the target collision performance may not be obtained. Also, in the case of Euro NCAP pole side collision test, the target collision performance is obtained by the fact that strain concentrates on the HAZ softened part of the spot welded part of the flange of the roof rail and the roof rail breaks as a starting point of breakage. It may not be possible.

  For this reason, in the application of these high-strength steel plates of 1180 MPa or more to the automobile body, the HAZ softest part of the spot weld formed on the flange of the automobile structural member needs not to be the starting point of breakage due to the collision.

  Non-Patent Document 1 describes that HAZ softening is possible even when spot welding is performed by reducing the strength of a base material by heat treatment performed at the time of hot stamping at a portion of a roof rail that is hot stamped at risk of fracture. There is disclosed a method for preventing breakage of a structural member for an automobile starting from a HAZ softened portion.

  Non-Patent Document 2 describes that the strength of the base metal is reduced by tempering the B pillar, which is a hot stamped product, by high-frequency heating, and HAZ softening does not occur even if spot welding is performed. A method for preventing breakage of a structural member for an automobile is disclosed.

Tailored Properties for Press-hardened body parts Dr. Camilla Wastlund, Automotive Circle International, Insight edition 2011 Ultra-high strength steels in car body lightweight design-current challenges and future potential Tempering of hot-formed steel using induction heating (http://publications.lib.chalmers.se/publication/144308)

  As disclosed in Non-Patent Document 1, in the method of adjusting the strength of the roof rail part over a wide range with the parts integrated from the roof rail to the A pillar, a low strength part is inevitably formed in a relatively wide range of the roof rail. As a result, the advantage of the hot stamped part that high strength can be obtained cannot be fully enjoyed, and the effect of weight reduction is also limited. In addition, in this method, strength characteristics are likely to vary in a relatively wide transition region inevitably formed between the quenching region and the unquenched region, and there is a risk of variation in the collision performance of components. Furthermore, since the area including the spot welded portion is softened, the tensile shear strength of the spot welded joint may be reduced.

  As disclosed in Non-Patent Document 2, the method of softening the B pillar flange by high-frequency heating after hot stamping by high-frequency heating is that the B pillar is deformed by the thermal strain generated by the wide range of tempering. There is a risk that the dimensional accuracy of the will decrease. Not only the B pillar but also the structural members for automobiles arranged around the door opening such as the A pillar and the roof rail are required to have a particularly high dimensional accuracy in order to ensure the accuracy of building the vehicle body. The gap (parting) is required to be uniform over the entire periphery of the door panel. For this reason, the reduction in the dimensional accuracy of the structural member for automobiles arranged around the door opening part significantly impairs the appearance quality of the automobile. Further, by tempering the flange over a wide range, the strength of the structural member for automobile is lowered, and the high strength characteristics of the hot stamp material cannot be enjoyed. Furthermore, since the area including the spot welded portion is softened, the tensile shear strength of the spot welded joint may be reduced.

  In addition, in the design stage of the structure of an automotive structural member such as a B-pillar, the structural member for an automotive structural member may be prevented so that the HAZ softened portion of the spot welded portion of the flange of the B-pillar does not reach a strain that breaks at the time of collision. It is also possible to add reinforcement or increase the thickness of structural members for automobiles. However, this method inevitably increases the cost of the automobile body and increases the weight of the automobile body due to an increase in the number of parts and the plate thickness.

  The present invention has been made in view of such problems of the prior art, and even when welding (typically spot welding) is performed on a high-strength steel sheet having a tensile strength of 1180 MPa or more or a molded product thereof. An object of the present invention is to provide a lap-welded member of a high-strength steel sheet that can be prevented from breaking at low strain starting from the HAZ softened part of the welded part at the time of collision, and a method for producing the same.

The present invention is listed below.
(1) At least a first structural member which is a steel plate having a tensile strength of 1180 MPa or more or a molded body thereof, and another steel plate or a molded body thereof which is overlapped and welded to the first structural member. A lap weld member comprising component members,
The lap weld member has a weld metal formed by welding, and an elongated hole provided on the first component member side at least in the longitudinal direction of the lap weld member adjacent to the weld metal,
The long hole has a shape in which the length in the longitudinal direction of the lap weld member is longer than the length in the direction orthogonal to the longitudinal direction, and has a parallel portion in a part of the longitudinal direction, and is formed around the weld metal. A lap weld member characterized in that the lap weld member is provided so as not to be applied to the HAZ softened portion. In this specification, it is also referred to as a first lap weld member.

(2) At least a first structural member that is a steel plate having a tensile strength of 1180 MPa or more or a molded body thereof, and another steel plate or a molded body that is overlapped and welded to the first structural member. A lap weld member comprising component members,
The lap weld member is provided at least on the first component side between a plurality of weld metals formed in the longitudinal direction of the lap weld member by welding and at least a pair of two adjacent weld metals among the plurality of weld metals. A long hole,
The long hole has a shape in which the length in the longitudinal direction of the lap weld member is longer than the length in the direction orthogonal to the longitudinal direction, and has a parallel portion in a part of the longitudinal direction . A lap weld member, characterized in that the lap weld member is provided so as not to be applied to a HAZ softened portion formed in the periphery. In this specification, it is also referred to as a second lap weld member.

(3) At least a first structural member which is a steel plate having a tensile strength of 1180 MPa or more or a molded body thereof, and another steel plate or a molded body thereof which is overlapped and welded to the first structural member. A lap weld member comprising component members,
The lap weld member includes a first weld metal formed by welding and at least one of the weld metals so as to sandwich the lap weld member adjacent to both sides in the longitudinal direction of the lap weld member. Two elongated holes provided on the component side,
The long hole has a shape in which the length in the longitudinal direction of the lap weld member is longer than the length in the direction orthogonal to the longitudinal direction, and has a parallel portion in a part of the longitudinal direction, and is formed around the weld metal. A lap weld member characterized in that the lap weld member is provided so as not to be applied to the HAZ softened portion. In this specification, it is also referred to as a third lap weld member.

  (4) Any one of the items (1) to (3) provided with a third component member that is a steel plate or a formed body thereof that is spot-welded and overlapped with the first component member or the second component member. The lap weld member described in the item.

  (5) The long hole is formed 2.0 mm or more away from the end of the nugget in the longitudinal direction, and the length of the parallel part of the long hole in the longitudinal direction is 5 mm or more and 50 mm or less, and in the direction orthogonal to the longitudinal direction. The lap-welded member according to any one of items (1) to (5), wherein the length of the elongated hole is 3 mm or more and 15√t (mm) or less. Here, t is the plate thickness (mm) of the first component member.

  (6) The lap weld member described in any one of items (1) to (5), wherein the elongated hole is formed by drilling with a laser beam or punching with a mold at a temperature of 500 ° C. or higher.

  (7) An automobile comprising the lap weld member described in any one of items (1) to (6) as a structural member.

(8) Manufacture of a lap-welded member that overlaps and welds at least a first structural member that is a steel plate having a tensile strength of 1180 MPa or more or a molded body thereof and another steel plate or a second structural member that is a molded body thereof. A method,
At least one of the first component members has a shape in which the length in the longitudinal direction of the lap weld member is longer than the length in the direction perpendicular to the longitudinal direction, and a parallel portion is partially formed in the longitudinal direction. A first step of providing a long hole having ;
The first component member and the second component member formed with a long hole are overlapped, welded at least at a site adjacent to the long hole in the longitudinal direction of the lap weld member, and around the weld metal formed by welding. And a second step of forming a nugget so that the HAZ most softened portion does not cover the elongated hole.

  (9) In the second step, the first constituent member, the second constituent member, and the third constituent member that is another steel plate or a molded body thereof are overlapped and spot-welded (8 The manufacturing method of the lap-welded member described in the item).

  (10) The elongated hole is formed at a distance of 2.0 mm or more from the end of the weld metal in the longitudinal direction, and the length of the parallel portion of the elongated hole in the longitudinal direction is 5 mm or more and 50 mm or less, and the direction orthogonal to the longitudinal direction The method for producing a lap weld member described in the item (8) or (9), wherein the length of the long hole is 3 mm or more and 15√t (mm) or less. Here, t is the plate thickness (mm) of the first component member.

  (11) The method for manufacturing a lap weld member according to any one of items (8) to (10), wherein the long hole is provided by drilling with a laser beam or punching with a die at a temperature of 500 ° C. or higher. .

  The “long hole” in the present invention means a hole having a shape in which the length in the longitudinal direction of the member is longer than the length in the direction perpendicular to the member and having a parallel portion in a part of the longitudinal direction.

  According to the present invention, even when welding (typically spot welding) is used for assembling a high-strength steel sheet having a tensile strength of 1180 MPa or more or a molded product thereof, the HAZ softest part of the welded part breaks with low strain at the time of collision. Can be suppressed. As a result, for example, it is possible to provide an automobile structural member that has excellent occupant protection performance at the time of a collision, high strength, and high shape accuracy.

FIGS. 1A and 1B show a state in which the first to third lap weld members according to the present invention are applied to a B pillar, and FIG. 1A is a perspective view of the B pillar from the side panel outer side. FIG. 1B is a cross-sectional view taken along line AA of the B pillar. 2 (a) and 2 (b) show the situation where the first to third lap weld members according to the present invention are applied to the roof rail, and FIG. 2 (a) shows the roof rail seen through the roof rail inner side. It is a perspective view of an outer ring force, and FIG.2 (b) is BB sectional drawing of a roof rail. FIG. 3 (a) shows a spot welded portion and a long hole in the first constituent member that is a formed body of a high-strength steel plate that constitutes a lap weld member together with the second constituent member that is a formed body of the low-strength steel plate. It is explanatory drawing which shows a relationship notionally, FIG.3 (b) is a graph which shows the measurement result of the hardness of the 1st structural member in the measurement position C in Fig.3 (a). FIG. 4 (a) is a graph showing the effect of the present invention, and is a stress-strain diagram when a tensile load is applied to a tensile test piece simulating a spot welded flange of a 1500 MPa class hot stamp material. 4B is an explanatory view showing a tensile test piece of a comparative example, and FIG. 4C is an explanatory view showing a tensile test piece of an example of the present invention (third lap weld member). Fig.5 (a)-FIG.5 (f) are explanatory drawings which show notionally the relationship between the spot welding part and long hole in the 1st structural member which is a high strength steel plate. FIG. 6 (a) shows a C-shaped laser welded portion and a length of a first structural member that is a formed body of a high-strength steel plate that constitutes a lap weld member together with a second structural member that is a formed body of a low-strength steel plate. It is explanatory drawing which shows the relationship of a hole notionally, FIG.6 (b) is a graph which shows the measurement result of the hardness of the 1st structural member in the hardness measurement position C in sectional drawing in Fig.6 (a). It is. FIG. 7A shows a ring-shaped laser welded portion and a long hole in the first constituent member that is a formed body of the high-strength steel plate that constitutes the lap weld member together with the second constituent member that is a formed body of the low-strength steel plate. FIG. 7B is a graph showing a measurement result of the hardness of the first component at the hardness measurement position C in the cross-sectional view in FIG. 7A. is there. FIG. 8A shows a circular laser welded portion and a long hole in the first constituent member that is a formed body of a high-strength steel plate, which constitutes a lap weld member together with the second constituent member that is a formed body of the low-strength steel plate. FIG. 8B is a graph showing the measurement results of the hardness of the first component member at the hardness measurement position C in the cross-sectional view in FIG. 8A. is there. FIG. 9A shows a circular arc welded portion and a long hole in the first constituent member that is a formed body of a high-strength steel plate that constitutes a lap weld member together with the second constituent member that is a formed body of the low-strength steel plate. FIG. 9B is a graph showing the measurement result of the hardness of the first component member at the hardness measurement position C in the cross-sectional view in FIG. 9A. is there. FIG. 10 is an explanatory diagram showing the shape of the test piece used in this example. FIG. 11 is a graph collectively showing the results. FIG. 12 is a graph showing an example of the hardness distribution of the spot welded portion of a member made of a high-strength steel plate (1500 MPa class hot stamped steel plate member). FIG. 13 is an explanatory view showing a state in which the hot stamped steel plate member having the hardness distribution of the spot welded portion shown in FIG. 12 is broken starting from the HAZ most softened portion, and FIG. 13 (a) is a top view, FIG. 13 (b) is a sectional view.

  A mode for carrying out the present invention will be described with reference to the accompanying drawings. In the following description, the case where welding is spot welding is taken as an example.

The present invention relates to a lap weld member of a high-strength steel plate that welds an overlap portion of two or more steel plates including at least one high-strength steel plate having a tensile strength of 1180 MPa or more, and a manufacturing method thereof.
1. Lap Welding Member Since the lap welding member 1 according to the present invention is grasped as a first lap welding member, a second lap welding member, or a third lap welding member described below, these are shown in FIG. ) And will be described sequentially with reference to the example of the B pillar shown in FIG.

  FIGS. 1A and 1B show a state in which the first to third lap weld members according to the present invention are applied to a B pillar, and FIG. 1A is a perspective view of the B pillar from the side panel outer side. FIG. 1B is a cross-sectional view taken along line AA of the B pillar.

[First lap welding member]
The first lap weld member includes at least a first component member 1 and a second component member 7. The number of the steel plates constituting the first lap weld member is two or three. In the case of stacking three sheets, in addition to the first component member 1 and the second component member 7, a third component member 11 that is overlapped and welded thereto is provided.

  The first constituent member 1 is a steel plate having a tensile strength of 1180 MPa or more or a molded body thereof (hereinafter referred to as a steel plate including a molded body). The second constituent member 7 and the third constituent member 11 are other steel plates different from the first constituent member 1. In the case of the two-layer structure, the second component member 7 and the first component member 1 are overlapped and spot welded. In the case of a three-layer structure as shown in FIG. 1, the second component member 7 and the third component member 11 are overlapped with the first component member 1 and spot welded.

  In this way, the first lap weld member includes the first component member 1 and the second component member 7 partially overlapped (in the case of the three-layer structure, the third structure member 11). The mating portion is spot welded to have an assembled structure.

  In the first lap weld member, the first component 1 has a nugget (welded metal) 2 and a long hole 3 formed by spot welding. The long hole 3 is provided at least on the first component 1 side adjacent to the nugget 2 in the longitudinal direction of the first lap weld member. The long hole 3 is provided so as not to be applied to the HAZ most softened portion formed around the nugget 2.

  The steel plate constituting the first component 1 is a high-strength steel plate having a quenching structure containing martensite in a continuous annealing facility or a hot stamping steel plate heated to an austenite temperature or higher and fired while being formed in a water-cooled mold. The hot stamped steel plate which raised the intensity | strength by putting is illustrated.

  The fracture of the spot welded portion 2 tends to occur more easily as the first structural member 1 mainly responsible for the strength of the member is a steel plate having a higher martensite structure and a higher tensile strength. Therefore, the present invention exhibits a particularly great effect when the first component 1 has a tensile strength of 1500 MPa class or more by, for example, hot stamping. Although there is no restriction | limiting in particular in the upper limit of the tensile strength of the steel plate which comprises the 1st structural member 1, It is desirable to set it as 2000 MPa.

  The thickness range of the steel plates constituting the first component member 1, the second component member 7 and the third component member 11 is also about 0.6 mm to 2.6 mm, which is used for ordinary automotive strength member applications. Is sufficiently applicable.

  For example, when the present invention is applied to a B-pillar, a 270 MPa class galvannealed steel sheet having a thickness of 0.7 mm as a side panel outer (third constituent member 11) and a reinforcement (first constituent member 1). ) As a 1500 MPa class hot stamped steel sheet having a thickness of 1.8 mm or a 1800 MPa class hot stamped steel sheet having a thickness of 1.6 mm, and a 440 MPa class cold rolled steel sheet having a thickness of 1.2 mm as the inner (second component 7). The three-layer structure is exemplified.

  When the present invention is applied to a roof rail, a 270 MPa class galvannealed steel plate having a thickness of 0.7 mm as a side panel outer, a 1500 MPa class hot stamped steel plate having a thickness of 1.2 mm as a reinforcement, and an inner A three-ply structure with a 590 MPa grade cold-rolled steel sheet having a thickness of 1.4 mm is exemplified.

  When the present invention is applied to a bumper reinforcement, a 1800 MPa class hot stamped steel plate having a thickness of 1.4 mm as a reinforcement outer (first component), and a plate thickness of 1 as a reinforcement inner (second component). It is exemplified by a two-ply structure with a 4 mm 590 MPa grade cold rolled steel sheet.

  In these examples, only the first component member 1 was a high-strength steel plate of 1180 MPa class or higher, but even if the second component member 7 or the third component member 11 is a high-strength steel plate of 1180 MPa class or higher. Good. In the case where the second constituent member 7 to be superposed is a high-strength steel plate of 1180 MPa class or more, in the case where a fracture at the HAZ softened portion of the spot welded portion of the second constituent member 7 superposed at the time of collision is expected, What is necessary is just to form the long hole 3 partially also about the 2nd structural member 7. FIG. On the other hand, in the case where it is predicted that no fracture will occur at the HAZ softened portion of the spot welding of the second component member 7 at the time of collision, it is not necessary to form the elongated hole 3 for the second component member 7.

  The surface of the steel plate of the first component 1 may be non-plated or plated. Examples of the plated steel sheet used include an electrogalvanized steel sheet, an electrogalvanized alloy-plated steel sheet (for example, a Zn-Ni alloy electroplated steel sheet), a hot-dip galvanized steel sheet, an alloyed hot-dip galvanized steel sheet, a hot-dip aluminum-plated steel sheet, and hot-dip zinc-aluminum. Examples include alloy-plated steel sheets. Further, these may be hot stamped steel plates.

  The nugget diameter of the nugget 2 formed at the interface between the first component member 1 and the second component member 7 by spot welding is 4√t or more and 7√t or less (t: plate thickness on the thin side of the overlapping surface (mm )) Is desirable. The three-layer structure is the same at the interface between the first component member 1 and the third component member 11.

[Second lap welding member]
In the subsequent description of the second and third lap weld members, portions that are different from the first lap weld member described above will be described, and overlapping descriptions of the common portions will be omitted as appropriate.

  The second lap weld member has a plurality of nuggets 2 and long holes 3. A plurality of nuggets 2 are arranged in the longitudinal direction of the lap weld member by spot welding. The pitch of spot welding, that is, the distance between adjacent nuggets 2 is, for example, about 20 to 100 mm, but is not limited to this, and may be set as appropriate according to product specifications.

  The long hole 3 is provided at least on the first component 1 side between at least a pair of two adjacent nuggets 2 among the plurality of nuggets 2. The long hole 3 is provided so as not to be applied to the HAZ most softened portion formed around each of the two nuggets 2 and 2.

[Third lap welding member]
The third lap weld member has one or more nuggets 2 and two elongated holes 3 formed by spot welding. The two long holes 3 are provided on the first component 1 side so as to sandwich the nugget 2 adjacent to both sides in the longitudinal direction of the lap weld member in at least one nugget 2 of the nuggets 2. Both of the two long holes 3 are provided so as not to reach the HAZ most softened portion formed around the nugget 2.

  The elongated hole 3 in the first lap weld member to the third lap weld member is formed such that the elongated hole 3 disposed between the hit points of the spot welded portion 2 is separated from the end of the nugget 2 by 2.0 mm or more. Is desirable. This is because if the long hole 3 is too close to the nugget 2, the molten metal may jump out during welding and the joint strength decreases.

  As shown in FIG. 2A to be described later, the length of the parallel portion of the long hole 3 in the longitudinal direction of the first lap weld member to the third lap weld member is 5 mm or more and 50 mm or less, and the longitudinal direction. It is desirable that the length (width) of the long hole 3 in the direction orthogonal to is 3 mm or more and 15√t (mm) or less (where t is the plate thickness (mm) of the first component 1). If the length of the long hole 3 is less than 5 mm, it cannot be said that the strain-absorbing region is sufficient, and if it exceeds 50 mm, the performance of the structural component for automobile is deteriorated. Moreover, if the width of the long hole 3 is less than 3 mm, sufficient strain absorption cannot be achieved, and if it exceeds 15√t (mm), the strength of the structural component for automobiles is greatly reduced.

  When the elongated hole 3 is provided in the flange, the length (width) orthogonal to the longitudinal direction of the elongated hole 3 is preferably 50% or less of the width of the flange.

  Further, the position of the long hole 3 is preferably separated from the end of the flange so that the distance from the end of the long hole 3 to the end of the flange is 3 mm or more, more preferably 5 mm or more. This is because if the distance from the end of the flange to the long hole 3 is too short, the long hole may break early due to deformation of the flange at the time of collision.

  Further, the long hole 3 in the first lap weld member to the third lap weld member may be provided by drilling with a laser beam or punching with a die at a temperature of 500 ° C. or higher, so that the delayed fracture at the drilling end surface. It is desirable from the viewpoint of preventing the occurrence of microcracks.

  Next, as a specific example, application examples in the B pillar and the roof rail will be further described with reference to FIGS. 1A and 1B, FIG. 2A and FIG. 2B, respectively.

  FIG. 1A and FIG. 1B are explanatory views showing a situation in which the first to third lap weld members according to the present invention are applied to a B pillar, and FIG. FIG. 1B is a perspective view of a B pillar reinforcement seen through from the panel outer side, and FIG. 1B is a cross-sectional view of the B pillar taken along line AA.

  In the B pillar 0, the B pillar reinforcement 1 as the first component, the inner material 7 as the second component, and the side panel outer material 11 as the third component are overlapped, A plurality of spot welds 2 are intermittently formed on the flange (the flange 1a in the B pillar reinforcement 1). In this example, an elongated hole 3 is formed between the spot welds 2 at the upper part of the B pillar reinforcement 1, and an elongated hole 3 is similarly formed between the spot welds 2 at the lower part of the B pillar reinforcement 1. In addition, the elongated hole 3 is not formed between the spot welds 2 in the intermediate portion in the height direction of the B pillar.

  The formation of the upper elongated hole 3 prevents breakage due to breakage at the HAZ softened portion of the spot welded portion at the upper part of the B pillar 0 at the time of collision, and the formation of the lower elongated hole 3 is a large deformation region due to the collision. To prevent breakage at the HAZ softest part of spot welding. The elongated hole 3 is not formed in the central portion in the height direction of the flange 1a of the B pillar reinforcement 1 that does not reach the strain at which the HAZ softest portion breaks. Thus, the formation of the long hole 3 may be the minimum necessary to prevent breakage starting from the HAZ most softened portion of the spot welded portion 2 at the time of collision.

  As described above, in the flange portion of the B pillar 0, one long hole 3 is formed adjacent to one spot weld portion 2 in accordance with the height direction position of the B pillar 0 (first lap weld member). In addition, one long hole 3 is formed between two adjacent spot welds 2 (second lap weld member), and two long holes 3 are formed adjacent to both sides of one spot weld 2. (Third lap welding member).

  In the example of FIG. 1, a hinge reinforcement 15 (for example, a 980 MPa class cold-rolled steel plate) as a fourth constituent member is overlapped inside the B pillar reinforcement 1 and two sheets are welded at the bottom of each groove. Has been.

  2 (a) and 2 (b) are explanatory views showing a situation in which the first to third lap weld members according to the present invention are applied to the roof rail, and FIG. 2 (a) shows the roof rail on the roof rail inner side. FIG. 2 is a perspective view of the roof rail outer force seen through, and FIG. 2B is a cross-sectional view of the roof rail taken along line BB.

  In the roof rail 00, the side panel outer 5 that is the third component, the roof rail outer 4 that is the first component, and the roof rail inner 12 that is the second component are overlapped to form a flange portion (the roof rail outer 4). Then, a plurality of spot welds 2 are formed intermittently in 4a). A local slot 3 is formed between the spot welds 2 of the roof rail outer 4. Thereby, the fracture | rupture in the HAZ softest part of spot welding can be suppressed, without reducing the intensity | strength of the roof rail outer 4 as much as possible. In addition, the code | symbol 6 in Fig.2 (a) shows A pillar.

  As described above, in the flange portion of the roof rail 00, one elongated hole 3 is formed adjacent to one spot welded portion 2 (first lap weld member) in accordance with the longitudinal position of the roof rail 00. One elongated hole 3 is formed between two spot welds 2 (second lap weld member), and two elongated holes 3 are formed adjacent to both sides of one spot weld 2 (see FIG. It can be said that this is a third lap weld member.

Next, the technical significance of the long hole 3 in the present invention will be described.
Fig.3 (a) is explanatory drawing which shows typically an example of the vicinity of the flange 1a of the 1st structural member 1 joined to the 2nd structural member 7 which is a molded object of a low strength steel plate by spot welding. FIG. 3B is a graph showing an example of the hardness distribution of the first component member 1 at the measurement position C (plate thickness center position indicated by the broken line in the first component member 1) in FIG. is there.

  As shown in FIG. 3 (a), a 1500 MPa-class cold-rolled steel sheet molded product (first constituent member) 1 is overlapped with a 440 MPa-class steel plate molded product 7 (second constituent member) via a flange 1a. The spot welded portion 2 is intermittently formed in the extending direction of the flange 1a (one spot welded portion 2 is shown in FIG. 3), and is adjacent to the spot welded portion 2 of the flange 1a of the first component 1 A long hole 3 is formed.

  As shown in the graph of FIG. 3 (b), the HAZ most softened portion whose hardness is reduced to about 300 Hv is formed around the spot welded portion 2, but the long hole 3 is formed in the HAZ most softened portion. It is provided so that it does not take.

  FIG. 4A is a graph showing the effect of the present invention. In a tensile test piece simulating a flange of a member in which a 440 MPa class cold-rolled steel plate is spot welded to a 1500 MPa class hot stamp material as shown in FIG. 4 is a stress-strain diagram when a tensile load is applied, FIG. 4B is an explanatory view showing a tensile test piece of a comparative example, and FIG. FIG.

  The tensile test piece shown in FIG. 4C, that is, a 1500 MPa class steel plate (first constituent member) 1 is overlapped with a 440 MPa class steel plate (second constituent member) 7 to form a spot welded portion 2, and further In a tensile test piece in which a long hole 3 (width 10 mm, length 15 mm, parallel portion length 10 mm) in a narrow range is provided in the first component 1 with the spot weld 2 interposed therebetween, as shown in FIG. Compared with a tensile test piece not provided with an elongated hole 3, as shown in FIG. 4 (a), the amount of strain at which breakage occurred with respect to the tensile load was significantly increased, and the absorbed energy was increased. This is because when a tensile load is applied to the test piece (that is, the laminated structure member), the periphery of the elongated hole 3 is also strained, and the strain is locally concentrated only in the HAZ softened portion of spot welding. Therefore, even if the HAZ most softened portion is present in the spot welded portion 2, as shown in the graph of FIG. 4A, the deformation amount at which the lap weld member breaks is improved. By such a mechanism, the fracture | rupture with few distortions which a HAZ softest part starts is suppressed.

  Further, in order to form the long hole 3 only in a predetermined range between the intermittent spot welds 2 of the high-strength steel plate, a conventional method of tempering the flange 1a in a wide range, a softening region in a wide range of the lap weld member Compared with the method of forming the metal, the deformation of the component is extremely small because the influence of thermal distortion during drilling is small. Therefore, it is suitable for application to automobile structural members that require high shape accuracy such as B pillars, roof rails, and A pillars. In addition, since the long hole 3 is a local portion between the spot welded portions 2, the strength reduction of the lap weld member is small, and the material characteristics of a high strength material such as a hot stamp material can be fully utilized.

  In this way, as shown in FIGS. 1 (a) to 1 (d), the B pillar, roof rail, side sill and the like, which are important members for protecting passengers in the cabin by side collision, are arranged so as to surround the cabin. By applying the present invention to structural members for automobiles, it is possible to suppress breakage at the HAZ most softened portion of the spot welded portion of these structural members for automobiles, and it is possible to improve safety against side collision. Furthermore, the strength characteristics of these parts can be enhanced by applying the present invention to the perlin force, door beam, floor member, front side member, and rear side member.

  The long hole 3 can take various forms as shown in FIG. FIG. 5A to FIG. 5F are explanatory views conceptually showing the relationship between the spot welded portion 2 and the long hole 3 in the first component 1 which is a high-strength steel plate.

  FIG. 5A shows a structure in which two elongated holes 3 are formed in a straight line with the spot welded portion 2 between the spot welded portions 2 of the flange 1 a of the first component 1.

  FIG. 5B shows that two elongated holes 3 each having an R portion at the end are formed in a straight line with the spot welded portion 2 between the spot welded portions 2 of the flange 1a of the first component 1. It is a thing.

  FIG. 5 (c) shows a structure in which a long hole 3 is formed on the end surface 1 b side of the first component member 1 with respect to the spot welded portion 2 between the spot welded portions 2 of the flange 1 a of the first component member 1. It is.

FIG. 5D shows an elongated hole 3 formed on the bending R portion 1 c side between the spot welded portions 2 of the flange 1 a of the first component 1. FIG. The two elongated holes 3 are formed side by side between the spot welds 2 of the flange 1a of the component 1 of FIG.

Further, FIG. 5 (f) shows that one long hole 3 having a long length is formed between the spot welds 2 of the flange 1 a of the first component 1.
2. Manufacturing Method of Lap Welding Member In order to manufacture a lap welding member in the present invention, spot welding is performed after forming a long hole. Hereinafter, the manufacturing method of this lap welding member is demonstrated.

  The following description is mainly about the two-layer structure, but the same applies to the three-layer structure. Further, description will be made assuming a member in which a plurality of welds and long holes are formed in the longitudinal direction of the lap weld member as shown in FIG.

  In the first step, the elongated hole 3 is partially formed in the base material of the first constituent member 1 having a tensile strength of 1180 MPa or more and overlapped with another steel plate (second constituent member). In the second step The nugget 2 is formed by performing spot welding on a portion adjacent to the elongated hole 3 at the base material portion outside the elongated hole 3.

  First, in the first step, for example, a substantially rectangular long hole 3 is formed between portions where the nugget 2 is scheduled to be formed intermittently by spot welding. That is, before spot welding, the elongated holes 3 are partially formed between the spot welding scheduled positions, and spot welding is performed in the second step.

  There are no particular restrictions on the welding conditions for spot welding, and the nugget diameter is at least 4√t and not more than 7√t (t: plate thickness (mm) on the thin side of the overlapping surface) at least at the overlapping interface of the target steel plates. What is necessary is just to determine suitably so that the nugget 2 may be formed. For example, a single-phase AC spot welder or an inverter DC spot welder is used, the tip diameter of the welding electrode is in the range of 6 to 8 mm, the curvature radius R of the tip is, for example, 40 mm, and the applied pressure is 2.5 to 6.0 kN. The current value of the welding current may be in the range of 7 to 11 kA, and the energization time may be in the range of 10/60 to 40/60 seconds. It goes without saying that the spot welding conditions are not limited to the exemplified conditions, and may be adjusted as appropriate according to the steel type, plate thickness, and the like.

  Examples of the method of forming the long hole 3 include drilling with a laser beam or punching with a mold at a temperature of 500 ° C. or higher. Drilling with a laser beam is preferred. This is because the energy of the laser beam is stable. Examples of the laser beam include disk laser, fiber laser, direct diode laser, YAG laser, and carbon dioxide laser. Examples of the drilling conditions include beam diameter: 0.05 to 0.2 mm, output: 0.5 to 10 kW, welding speed: 0.5 to 20 m / min, assist gas: oxygen, nitrogen, and air.

  In the second step, the first constituent member 1 is overlapped with the second constituent member and joined to the second constituent member by forming a nugget 2 by spot welding.

  In the case where the second constituent member is a high strength steel plate of 1180 MPa class or higher, and the HAZ softened portion of the spot welded portion of the second constituent member is expected to break at the time of collision, the second constituent member In the same manner as described in the first step, the elongated hole 3 may be partially formed in advance.

  In the above description, the case where the number of stacked sheets is two is taken as an example. However, when the number of stacked sheets is three, that is, as shown in FIG. 1, for example, the second component member 7 and the third component member 11 In the case of the structure in which the first constituent member 1 is arranged between the two, the third constituent member may be further overlapped in the second step, and spot welding may be performed by superimposing three sheets.

  Further, when both the first and second constituent members 1 and 7 are made of a high strength steel plate having a tensile strength of 1180 MPa or more and the third constituent member 11 is made of a steel plate having a tensile strength of, for example, 270 to 980 MPa. After forming the long hole 3 in one or both of the first structural member 1 or the second structural member 7 (determining whether the long hole 3 is formed in one or both according to necessity), The first component member 1, the second component member 7, and the third component member 11 may be overlapped and spot welded.

  The lap welded structure according to the present invention described above is suitable for application to an automotive structural member including a high-strength steel plate having a tensile strength of 1180 MPa or more. For example, the present invention can be applied to B pillars, A pillars, roof rails, side sills, bumper reinforcements, door beams, floor members, front side members, rear side members, and the like.

  In the above description, the case where the welding is spot welding has been taken as an example, but the present invention is not limited to spot welding, and is equally applied to other welding other than spot welding such as laser welding and arc welding. The

  6 (a) to 9 (a) are all formed of a high-strength steel plate (1500 MPa class hot stamped steel plate) that constitutes a lap weld member together with the second component member 7 that is a molded product of a low-strength steel plate. It is explanatory drawing which shows notionally the relationship between the various welding parts 2-1 to 2-4 and the long hole 3 in the 1st structural member 1 which is goods, FIG.6 (b)-FIG.9 (b) It is a graph which shows the measurement result of the hardness of the 1st structural member 1 in the hardness measurement position C in sectional drawing in Fig.6 (a)-FIG.9 (a), respectively.

  FIG. 6A shows that a C-shaped laser welded portion 2-1 is formed on the flange 1a of the first component 1, and between the adjacent C-shaped laser welded portions 2-1, 2-1 respectively. Two elongated holes 3 are formed in a straight line with the C-shaped laser welded part 2-1.

  FIG. 7A shows a ring-shaped laser welded portion 2-2 formed on the flange 1a of the first component 1, and a ring-like shape between the adjacent ring-shaped laser welded portions 2-2 and 2-2. Two elongated holes 3 are formed in a straight line with the laser welded portion 2-2.

  FIG. 8A shows a circular laser welded portion 2-3 formed on the flange 1a of the first component 1, and a circular shape is formed between the adjacent circular laser welded portions 2-3 and 2-3. Two elongated holes 3 are formed in a straight line with the laser weld 2-3.

  Furthermore, Fig.9 (a) forms the circular arc welding part 2-4 in the flange 1a of the 1st component 1, and each between the adjacent circular arc welding parts 2-4 and 2-4, Two elongated holes 3 are formed in a straight line with the circular arc welded portion 2-4.

The present invention will be described more specifically with reference to examples.
Table 1 shows chemical components of the test materials. The units in Table 1 are mass%, and the balance other than those shown in Table 1 is Fe and irregular substances.

  The test material SQ1500 in Table 1 is a hot stamped steel plate with a tensile strength of 1500 MPa obtained by hot stamping a non-plated cold rolled steel plate, and the test material SQZ1500 is obtained by hot stamping an alloyed hot dip galvanized steel plate. The obtained tensile strength is a 1500 MPa class hot stamped steel plate, the test material SQ1800 is a hot stamped steel plate having a tensile strength of 1800 MPa obtained by hot stamping a non-plated cold-rolled steel plate, and the test material JSC1270 is a non-plated steel plate. It is a cold-rolled steel sheet having a tensile strength of 1270 MPa. Moreover, the specimen JSC440 in Table 1 is a non-plated 440 MPa grade steel plate.

  A substantially rectangular elongated hole 3 was formed by drilling with a laser beam, and then spot-welded to obtain a test piece.

FIG. 10 is an explanatory diagram showing the shape of the test piece 8 used in this example.
The test piece 8 was drilled with a laser beam in a steel plate as the specimen 9. For laser drilling, a fiber laser was used, the beam diameter was 0.2 mm, the speed was 1.0 to 2.0 m / min, and the assist gas was nitrogen.

  Next, as shown in FIG. 10, the steel plate 10 as a test material was overlapped, and spot welding was performed at the overlapped portion to form spot welds 2 and 2. Spot welding uses a single-phase AC spot welder, DR type electrodes (tip diameter 6 mm, curvature radius 40 mm), applied pressure: 400 kgf, energization time 20 cyc, current value: current with nugget diameter 6.0 mm. Value. The Vickers hardness of the base material is SQ1500: 470, SQZ1500: 470, SQ1800: 560, SPC1270: 420. Moreover, the Vickers hardness of the softest part of HAZ of spot welding is SQ1500: 290, SQZ1500: 290, SQ1800: 390, and SPC1270: 280.

  Next, a tensile test was performed on each test piece 8. In the tensile test, the distance between ratings was 50 mm, and the tensile speed was constant at 3 mm / min. 2. When the strain until breakage (grading interval is 50 mm, the steel plate is cracked and the load suddenly drops on the chart) is less than 3%, x is 3% or more and less than 3.5%, and Δ. 5% or more and less than 4% was indicated by □, and 4% or more by ◯. The test results are summarized in the graph of FIG.

  As shown in the graph of FIG. 11 and Table 2, in the example of the present invention, the elongation at break was over 3.5%, whereas in the comparative example, the HAZ softened part of spot welding broke with a small strain (breaking elongation). Less than 3.0%).

0 B pillar / lap weld member 00 roof rail / lap weld member 1 B pillar reinforcement / first component 1a flange 1b end face 1c bend R portion 2 spot weld / nugget (welded metal)
2-1 C-shaped laser weld (welded metal)
2-2 Ring-shaped laser weld (welded metal)
2-3 Circular laser weld (welded metal)
2-4 Circular arc welds (welded metal)
3 Long hole 4 Roof rail outer / first component 4a Flange 5, 11 Side panel outer / third component 6 A pillar 7 B pillar inner / second component 8 Test piece 9, 10 Test material 12 Roof rail inner / Second component 15 hinge reinforcement / fourth component

Claims (11)

At least a first structural member that is a steel plate having a tensile strength of 1180 MPa or more or a molded body thereof, and a second structural member that is another steel plate or a molded body thereof and is overlapped and welded to the first structural member. A lap weld member comprising:
The lap weld member has a weld metal formed by the welding, and a long hole provided at least on the first component side adjacent to the weld metal in the longitudinal direction of the lap weld member,
The elongated hole has a shape in which the length in the longitudinal direction is longer than the length in the direction orthogonal to the longitudinal direction, and has a parallel portion in a part of the longitudinal direction, and is formed around the weld metal. A lap weld member characterized in that the lap weld member is provided so as not to be applied to the HAZ softest part. At least a first structural member that is a steel plate having a tensile strength of 1180 MPa or more or a molded body thereof, and a second structural member that is another steel plate or a molded body thereof and is overlapped and welded to the first structural member. A lap weld member comprising:
The lap weld member is at least a first constituent member between a weld metal formed in the longitudinal direction of the lap weld member by the welding and at least a pair of two adjacent weld metals among the plurality of weld metals. A slot provided on the side,
The elongated hole has a shape in which the length in the longitudinal direction is longer than the length in the direction orthogonal to the longitudinal direction, and has a parallel portion in a part of the longitudinal direction, A lap weld member, characterized in that the lap weld member is provided so as not to be applied to the HAZ softened portion formed in the above. At least a first structural member that is a steel plate having a tensile strength of 1180 MPa or more or a molded body thereof, and a second structural member that is another steel plate or a molded body thereof and is overlapped and welded to the first structural member. A lap weld member comprising:
The lap weld member is sandwiched between one or more weld metals formed by the welding and at least one of the weld metals adjacent to both sides in the longitudinal direction of the lap weld member. Two elongated holes provided on the first component side,
The elongated hole has a shape in which the length in the longitudinal direction is longer than the length in the direction orthogonal to the longitudinal direction, and has a parallel portion in a part of the longitudinal direction, and is formed around the weld metal. A lap weld member characterized in that the lap weld member is provided so as not to be applied to the HAZ softest part.   4. The apparatus according to claim 1, further comprising a third structural member that is a steel plate or a formed body thereof that is spot-welded and overlapped with the first structural member or the second structural member. 5. Lap welds made. The elongated hole is formed 2.0 mm or more away from the end of the weld metal in the longitudinal direction, and the length of the parallel part of the elongated hole in the longitudinal direction is 5 mm or more and 50 mm or less, and the longitudinal direction The lap weld member according to any one of claims 1 to 4, wherein a length of the elongated hole in a direction orthogonal to each other is 3 mm or more and 15√t (mm) or less.
Here, t is the plate thickness (mm) of the first component member.   The lap weld member according to any one of claims 1 to 5, wherein the elongated hole is formed by drilling with a laser beam or punching with a mold at a temperature of 500 ° C or higher.   An automobile comprising the lap weld member according to any one of claims 1 to 6 as a structural member. It is a method for manufacturing a lap weld member in which at least a first structural member that is a steel plate having a tensile strength of 1180 MPa or more or a molded body thereof and a second structural member that is another steel plate or a molded body thereof are overlapped and welded. And
At least one part of the first component member has a shape in which the length in the longitudinal direction of the lap weld member is longer than the length in the direction orthogonal to the longitudinal direction and is parallel to a part of the longitudinal direction A first step of providing a slot having
The first component member formed with the elongated hole and the second component member are overlapped, welded at least at a site adjacent to the elongated hole in the longitudinal direction of the lap weld member, and formed by the welding. And a second step of forming the weld metal so that the HAZ softened portion around the weld metal does not cover the elongated hole.   The said 2nd process WHEREIN: The said 1st structural member, the said 2nd structural member, and these are the other steel plates or the 3rd structural member which is the molded object, and spot-welding. 8. A method for producing a lap weld member according to 8. The elongated hole is formed 2.0 mm or more away from the end of the weld metal in the longitudinal direction, and the length of the parallel part of the elongated hole in the longitudinal direction is 5 mm or more and 50 mm or less, and the longitudinal direction method for producing a lap weld member according to claim 8 or claim 9 wherein the length length of the hole in the direction is 3mm or more 15√t (mm) or less perpendicular.
Here, t is the plate thickness (mm) of the first component member.   The method for producing a lap weld member according to any one of claims 8 to 10, wherein the elongated hole is provided by drilling with a laser beam or punching with a mold at a temperature of 500 ° C or higher.