Technical field
[0001]
　The present invention, fatigue strength improvement method of lap welding joint, a manufacturing method and a lap weld joint lap weld joint.
Background technique
[0002]
　Conventionally, as a component of a vehicle body of an automobile, it welded lap welding joint is used by superposing a plurality of steel plates. Further, conventionally, in order to improve the weight and collision safety, various steel sheets have been used as a vehicle body constituent member.
[0003]
　However, the fatigue strength of the base material of the lap weld joint is higher in proportion to the strength of the steel sheet that constitutes the weld joint. On the other hand, the fatigue strength of lap weld joint itself, it is known that not almost higher by increasing the strength of the steel sheet that constitutes the weld joint. Therefore, conventionally, various studies in order to improve the fatigue strength of lap weld joint is performed.
[0004]
　For example, Japanese Laid-Open 10-193164 (Patent Document 1), fatigue properties improve the method of lap weld joint is disclosed. The disclosed in Patent Document 1 a method, the vicinity of the welded portion of the lower steel plate constituting the welded joint, parallel to the weld, the steel sheet is heated so as not to melt. Patent Document 1, by heating the lower steel plate as described above, the tensile residual stress of the weld toe vicinity is reduced, the fatigue properties of welded joints have been described to be improved.
CITATION
Patent Document
[0005]
Patent Document 1: Laid-Open Patent Publication No. 10-193164
Summary of the Invention
Problems that the Invention is to Solve
[0006]
　However, results of studies made by the present inventors, also the lower steel plate of the lap weld joint is heated as described above, it has been found that it may not be possible to sufficiently reduce the tensile residual stress generated in the welded joint. In this case it can not sufficiently improve the fatigue strength of the welded joint.
[0007]
　The present invention has been made to solve such problems, a method that can sufficiently improve the fatigue strength of lap weld joint, a method of manufacturing a lap weld joint having an excellent fatigue strength and excellent fatigue strength, and to provide a lap weld joint having a.
Means for Solving the Problems
[0008]
　In order to solve the above problems, the inventors of the present inventors have conducted studies, the position of the lower steel sheet is heated in the method of Patent Document 1, by heating to said lower steel sheet is melted, weld joint it was found that the resulting tensile residual stress can be further reduced to. However, in this case, reduces the fatigue strength of the lower steel sheet itself, it was found that can not be improved fatigue strength of the welded joint.
[0009]
　Accordingly, the present inventors have further studying, by heating a portion of the overlapping portions of two steel plates in the welded joint, the fatigue strength of the welded joint was found to be improved.
[0010]
　The present invention has been made based on the above findings, and the fatigue strength improvement method and manufacturing method of the lap weld joint below, as well as the lap weld joint and gist.
[0011]
(1) a part of the second steel having a portion with a predetermined thickness of the first steel having a predetermined thickness are overlapped as overlap portions respectively, and weld extending along the edge of the first steel said edge portion is a fatigue strength improvement method of lap welding joint is welded to a surface of the second steel by,
　a direction parallel to the surface of the vertical and and the second steel in the extending direction of the weld as the reference direction, to restrict the movement of the lap weld joint to the reference direction, the to the first to regulate the movement of the first steel in the thickness direction of the steel material, and the second steel in the thickness direction the while restricting the movement of the 2 steel, so that melting portion is formed in a part of the overlapping portion of the second steel heat a portion of the overlapping portion of the second steel lap weld joint fatigue strength enhancement method.
[0012]
(2) As the molten portion in a part of the overlapping portion of a part and the second steel of the overlapping portion of the first steel is formed, a portion of the overlapping portion of the first steel and the heating a portion of the overlapping portion of the second steel lap weld joint fatigue strength improvement method of the above (1).
[0013]
(3) the molten portion, the fatigue strength of the formed so as to extend parallel to the weld extending along the edge of the first steel, lap welded joint of the above (1) or (2) enhancement method.
[0014]
(4) heating position of the overlapping portion of the second steel product, the from the weld extending along the edges is a position apart 2mm 10mm or more or less in the reference direction, of (1) through (3) fatigue strength improvement method of any of lap weld joint.
[0015]
(5) laser beam, tungsten inert gas or heat a portion of the overlapping portion of the second steel by electron beam, the fatigue strength improvement method of any of lap welded joint (1) to (4),.
[0016]
(6) the molten portion is formed at a position away to the reference direction from the weld, lap weld joint fatigue strength improvement method according to any one of (1) (5).
[0017]
(7) and the welding process to obtain a joined body by welding a first steel and a second steel material, and a heating step of heating the bonded body,
　the welding process, a part of the first steel in a state of overlapping a portion of the second steel as overlapping portion respectively, welding the said edges and said second steel material surface as welds along the edge of the first steel is formed includes the step,
　the heating step, the reference direction to a direction parallel to the surface of the vertical and and the second steel in the extending direction of the weld zone, to restrict the movement of said conjugate to said reference direction, wherein in a state that restricts the movement of the first steel in the thickness direction of the first steel, and was restricting the movement of the second steel to the second steel in the thickness direction, one of the overlapping portion of the second steel as the molten portion is formed parts, heating a portion of the overlapping portion of the second steel That process comprising a method for producing a lap weld joint.
[0018]
(8) the heating step, as the molten portion in a part of the overlapping portion of a part and the second steel of the overlapping portion of the first steel is formed, the overlapping portion of the first steel comprising heating portion and a portion of the overlapping portion of the second steel, a manufacturing method of the lap weld joint (7) above.
[0019]
(9) In the heating step, the molten portion is formed so as to extend parallel to the weld extending along the edge of the first steel, overlaid above (7) or (8) method for producing a welded joint.
[0020]
(10) heating position of the overlapping portion of the second steel in the heating step, a position apart 2mm 10mm or more or less in the reference direction from the weld extending along the edge, from the (7) method of any one lap weld joint (9).
[0021]
(11) In the heating step, a laser beam to heat a portion of the overlapping portion of the second steel by tungsten inert gas or electron beam, the production of any of the lap weld joint from above (7) (10) Method.
[0022]
(12) In the heating step, the molten portion is formed at a position away to the reference direction from the weld, method of any one lap weld joint (7) to (10).
[0023]
(13) a part and lap welding joint part and there is an edge portion of the first steel in a state of overlapping the overlapping portion respectively are welded to the surface of the second steel second steel first steel Te,
　wherein a weld portion extends along the edge of the first steel and that the edge connecting to said second steel material,
　formed at a position away from the weld in a part of the overlapping portion of the second steel have been and a molten portion,
　perpendicular to the extending direction of the welded portion, and of the direction parallel to the surface of the second steel facing away from the first steel based the weld in the case where the direction to the predetermined direction,
　at a position away 0.5mm in the predetermined direction from the weld toe on the surface of the second steel of the weld, the residual stress occurring on the surface of the second steel the residual stress occurring in the center in the thickness direction of the second steel It is also a value of the compression side, lap weld joint.
Effect of the invention
[0024]
　According to the present invention, the fatigue strength of lap weld joint can be sufficiently improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025]
[1] Figure 1 is a perspective view showing a welded joint according to an embodiment of the present invention.
FIG. 2 is a side view showing a lap weld joint.
FIG. 3 is a diagram for explaining a fatigue strength improvement method according to an embodiment of the present invention. 3 (a) is a diagram showing a weld joint before the fatigue strength is improved, 3 (b) is a diagram showing a weld joint during heating, FIG. 3 (c), regulating state it is a diagram illustrating a released welded joint from.
[4] FIG. 4 is a diagram for explaining another example of the fatigue strength improvement methods. 4 (a) is a diagram showing the molten portion, the formed weld joint so as not to reach the surface of and the first steel as the rear surface of the second steel extending toward the first steel 4 (b) is a head showing a welded joint fused portion is formed to penetrate the first steel and the second steel, FIG. 4 (c), the molten portion, the second from the surface of the first steel is a diagram showing the formed weld joint so as not to reach the and the back surface of the second steel so as to extend toward the steel.
FIG. 5 is a diagram for explaining another example of the welded joint. 5 (a) is a perspective view showing another example of the welded joint, FIG. 5 (b) is an exploded perspective view showing another example of the welded joint.
FIG. 6 is a diagram for explaining still another example of the welded joint. 6 (a) is a longitudinal sectional view showing a welded joint, FIG. 6 (b) is a sectional view taken along line B-B in FIGS. 6 (a).
[7] FIG. 7 is a diagram for explaining the FEM analysis model. 7 (a) is a diagram showing the FEM analysis model of a welded joint according to the present invention, FIG. 7 (b) is a diagram showing the FEM analysis model of a welded joint according to the comparative example, FIG. 7 (c ) is a diagram showing the FEM analysis model of the welded joint according to another comparative example.
[8] FIG. 8 is a graph showing the residual stress occurring in the surface of the second steel (analysis result).
[9] FIG. 9 is a graph showing the residual stress caused in the mid-thickness of the second steel (analysis result).
[10] FIG 10 is a graph showing the value obtained from the residual stress occurring on the surface of the second steel by subtracting the residual stress caused in the mid-thickness.
[11] FIG 11 is a diagram for explaining a method for adding the bending moment for the analysis model.
FIG. 12 is a time obtained by adding a bending moment in the analysis model is a graph showing the stress distribution in the surface of the second steel.
[13] FIG 13 is a graph showing the change in stress before and after the addition of the bending moment.
[14] FIG 14 is a diagram for explaining another example of the analysis model. 14 (a) is a diagram showing an analysis model molten portion does not reach the rear surface of the second steel member, FIG. 14 (b) shows the analysis model molten portion does not reach the surface of the first steel it is a diagram.
[15] FIG 15 is a graph showing the residual stress occurring in the surface of the second steel.
[16] FIG 16 is a perspective view showing a welded joint according to the embodiment.
[17] FIG 17 is a diagram illustrating a fatigue test piece. 17 (a) is a plan view of a fatigue test piece, FIG. 17 (b) is a line b-b sectional view of FIG. 17 (a).
[18] FIG 18 is a graph showing the results of a bending fatigue test.
DESCRIPTION OF THE INVENTION
[0026]
　Hereinafter, exemplary lap weld joint fatigue strength improvement method according to the embodiment of the present invention (hereinafter, simply referred to as improved methods.), A method of manufacturing a lap weld joint, and the lap weld joint is described.
[0027]

　First, lap weld joint (hereinafter, simply referred to as a welded joint.) Will be described. Figure 1 is a perspective view showing a welded joint 10, FIG. 2 is a side view showing a lap weld joint 10. Note that the weld joint 10 shown in FIG. 1 is a welded joint 10 which fatigue strength is improved by improving the method described below.
[0028]
　Referring to FIGS. 1 and 2, the weld joint 10 includes a second steel member 14 and the weld 16 has a first steel 12, a predetermined thickness having a predetermined thickness. In the present embodiment, each of the first steel member 12 and the second steel member 14, the steel plate is used. Thickness and thickness of the second steel member 14 of the first steel 12 may be equal to each other or may be different. The first steel 12, the thickness can be used the following steel 3.3 mm. Similarly, as the second steel member 14, the thickness can be used the following steel 3.3 mm. In the present embodiment, in a state where the part 14a of the portion 12a and the second steel member 14 of the first steel 12 are overlapped with each other as overlapped portions respectively, the edge portion of the first steel 12 surface 14b of the second steel member 14 It is welded. In the following, it referred to as the overlap portion 12a of the part 12a of the first steel 12, as the overlap portions 14a to portions 14a of the second steel member 14. The first steel 12 and the second steel member 14, for example, gas welding, arc welding, are welded by electron beam welding, or laser beam welding or the like. In this embodiment, the weld 16 is, for example, a weld bead extending along the edge of the first steel 12, connects the edges in the second steel member 14.
[0029]
　Incidentally, in FIG. 1 shows a stretching direction of the welded portion 16 in the arrow X. Further, in FIGS. 1 and 2 show a direction parallel with the arrow Y on the surface 14b of the extending direction X in a vertical and a second steel member 14 of the weld 16. Hereinafter, the direction indicated by the arrow Y, referred to as a reference direction. In the present embodiment, the reference direction Y has a first direction Y1 facing the first steel 12 side relative to the weld 16, and the second direction Y2 facing opposite to the first steel 12 relative to the weld 16 including.
[0030]
　Referring to FIGS. 1 and 2, on the surface 12b of the first steel 12, weld toe 16a of the weld portion 16 is formed. Also, on the surface 14b of the second steel member 14, the weld toe 16b of the welded portion 16 is formed.
[0031]
　Some The overlap portion 14a of the second steel member 14, the molten portion 18 is formed. Fusion zone 18 (in this embodiment, the first direction Y1) reference direction Y from the weld 16 is formed at a position spaced. In the present embodiment, the molten portion 18 is formed at a position a distance d1 apart in a first direction Y1 from the weld toe 16a. In the present embodiment, in the bottom view of the welded joint 10, the molten portion 18 is formed so as to extend parallel to the weld 16. The length of the extending direction X of the molten portion 18, it is preferably 0.8 times or more the length of the width of the second steel member 14 is 0.5 times or more the length of the width of the second steel member 14 more preferably, it is more preferable that over the entire width of the second steel member 14. In this embodiment the width of the second steel member 14 means the length in the stretching direction X of the overlap portion 14a. In the present embodiment, in the side view of the welded joint 10, the molten portion 18 is formed so as toward the surface 14b from the back 14c of the second steel member 14 extends (from the back 14c toward the rear surface 12c of the first steel 12) It is. The distance d1 is shown in the reference direction Y (first direction Y1), the distance between the center and the weld toe 16a of the molten portion 18. The distance d1 is set to, for example, 1 (mm) or more. Further, with reference to FIG. 2, in the reference direction Y, and the length of the portion where the first steel member 12 and the second steel member 14 are overlapped and L (mm), the distance d1 can be, for example, 0.2 × L (mm) may be set to a value in the range of ~ 0.8 × L (mm), it is set to a value in the range of 0.3 × L (mm) ~ 0.6 × L (mm) good. The distance d1 is set to, for example, 2mm 10mm or more or less, preferably set to below 8 mm, more preferably set to 6mm or less. The length L is, for example, is set to at least 10 mm, preferably, it is set to at least 40 mm. It will be described later method of forming the molten portion 18.
[0032]
　Welded joint 10 according to this embodiment, in the position where the distance d2 apart in a second direction Y2 from the weld toe 16b, having a stress state as follows. Referring to FIG. 2, the residual stress caused in the position 20a where the distance d2 apart in a second direction Y2 from the weld toe 16b on the surface 14b of the second steel member 14, the center in the thickness direction of the second steel member 14 (the in the embodiment, it has a value of the compression side of the residual stress caused in the position 20b in which the distance d2 apart in a second direction Y2 from the weld toe 16b in mid-thickness). The distance d2 is, for example, 0.5 mm. In the present embodiment, the residual stress is meant a reference direction Y (first direction Y1 and the second direction Y2) residual stress in the.
[0033]
　Note that the value of the compression side than the residual stress residual stress caused in the position 20a is generated in the position 20b, the residual stress in the compressive direction is generated in the position 20a, and a tensile direction of the residual stress is generated in the position 20b not limited to the case to have. For example, both resulting residual stress in the compressive direction is in the position 20a and position 20b, and if the compressive residual stress of the position 20a is greater than the compressive residual stress position 20b also, the residual stress caused in the position 20a is generated in the position 20b than the residual stress which satisfies the condition that the value of the compression side. Further, for example, it occurs both pulling direction of the residual stress at the position 20a and position 20b, and if the tensile residual stress in the position 20a is smaller than the tensile residual stress in the position 20b also satisfies the above conditions. The residual stress caused in the weld joint 10 is measured using the X-ray diffraction method.
[0034]

　The following describes the fatigue strength improvement method according to an embodiment of the present invention. Figure 3 is a diagram for explaining the improved method according to the present embodiment. Note that the triangle symbols in FIG. 3 (a) and (b) the mobile indicates a moiety that is regulated in the first steel 12 and the second steel member 14. Further, the welded joint 10a shown in FIG. 3 (a) corresponds to a weld joint 10 prior to improve fatigue strength.
[0035]
　Referring to FIG. 3 (a), in this embodiment, first, the holding member (not shown), the movement and the thickness direction (the present embodiment in the reference direction Y of the welded joint 10a, shown in a thickness direction. Arrow Z to restrict the movement of the direction), for holding the first steel 12 and the second steel member 14. In the present embodiment, the mobile and the first thickness direction of the steel material 12 of the first steel 12 in the first direction Y1 (hereinafter. Referred to as a thickness direction) so as to restrict movement of the first steel 12 to, one end 12d of the first steel 12 is held. The moving and the thickness direction of the second steel member 14 of the second steel member 14 in the second direction Y2 (hereinafter referred to as the thickness direction.) So as to restrict the movement of the second steel member 14 to the second steel 14 one end 14d is retained.
[0036]
　In the present embodiment, for at least a part of the first steel 12 need only be moved in the thickness direction is regulated, for all the parts of the first steel 12, the movement in the thickness direction it is not necessary to regulate. Further, it suffices for at least a part of the second steel member 14 to move in the thickness direction if it is restricted for all portions of the second steel member 14, there is no need to restrict the movement of the thickness of the plate. For example, only in the end face 12e (first direction Y1 side of the end of the first steel 12), movement in the thickness direction of the first steel 12 may be regulated. Further, for example, in only one of the surfaces 12b and rear surface 12c, movement in the thickness direction of the first steel 12 may be regulated. Further, for example, only in the end face 14e (second direction Y2 side of the end of the second steel member 14), movement in the thickness direction of the second steel member 14 may be regulated. Further, for example, in only one of the surfaces 14b and rear surface 14c, movement in the thickness direction of the second steel member 14 may be regulated.
[0037]
　Also, the portion where the first steel 12 and the second steel member 14 is held is not limited to the above example. For example, among the first steel 12, in the reference direction Y, relative to the overlapping portion 12a, any portion of the opposite side may be held by the holding member from the welded portion 16. That is, in the first steel 12, any portion may be held between the overlapped portions 12a and the end portion 12d. In this case, for example, so as to restrict the movement of the movement and the plate thickness direction of the first direction Y1 of the any portion of the first steel 12, may hold the first steel 12. Further, for example, of the second steel member 14, in the reference direction Y, relative to the weld 16, any portion of the opposite side may be held by the holding member from the overlapping portion 14a. That is, in the second steel member 14, any portion between the welded portion 16 and the end portion 14d may be held. In this case, for example, so as to restrict the movement of the movement and the plate thickness direction in the second direction Y2 of the any portion of the second steel member 14 may hold a second steel member 14.
[0038]
　Next, with reference to FIG. 3 (b), while restricting the movement of the welded joint 10a, as described above (hereinafter, also referred to as a restricted state.), The heated portion of the overlap portion 14a of the second steel member 14 by, forming the molten portion 18 of the above-mentioned part of the polymerization becomes part 14a. In the present embodiment, for example, using a heating device 22, by heating the back surface 14c of the second steel member 14, to form the molten portion 18 in the second steel member 14. In the present embodiment, the heating position of the overlap portion 14a of the second steel member 14 is, for example, a reference (see FIG. 2) 0.2 × L from the welding portion 16 in the direction Y ~ 0.8 × L away. Specifically, the heating position is, for example, a position distant 2mm 10mm or more or less in the reference direction Y from the weld 16. In the present embodiment, the distance in the reference direction Y of the welding portion 16 and the heating position is represented by the distance between the heating center and weld toe 16a in the reference direction. Incidentally, the melting section 18, for example, can be formed by laser beam, tungsten inert gas or electron beam or the like. The length in the reference direction Y of the molten portion 18 is, for example, 1 ~ 2 mm. The heating temperature may be higher than the melting point of the steel. In the present embodiment, since the molten portion 18 is formed in the second steel member 14, the heating temperature is set to a temperature higher than the melting point of the second steel member 14. As shown in FIG. 4 which will be described later, when a molten portion 18 is formed in the first steel 12 and the second steel member 14, the heating temperature is above the melting point of the melting point and the second steel member 14 of the first steel 12 It is also set to a high temperature. For example, when using a SUS316L as the steel material, the heating temperature is 1400 ° C. or higher.
[0039]
　In the present embodiment, after forming the molten portion 18 in the manner described above, for example, cooling the welded joint 10a while maintaining the restricted state of the welded joint 10a. Specifically, for example, the temperature of the molten portion 18 is 200 ° C. or less, preferably 100 ° C. or less, more preferably up to become a normal temperature, maintains the restricted state of the welded joint 10a.
[0040]
　Next, referring to FIG. 3 (c), releasing the welded joint 10a from the regulating state. That is, to release the restriction of the movement of the reference direction Y and the thickness direction of the welded joint 10a. Thus, with reference to FIG. 2, the weld joint 10 that a value of the compression-side is obtained than the residual stress residual stress caused in the position 20a is generated in the position 20b.
[0041]
　In the present embodiment, welding to restrict the movement of the joint 10a is not meant only to completely restrict the movement of the welded joint 10a. For example, a state in which movement is restricted in the reference direction Y of the welded joint 10a, the reference direction Y, the held by any portion and the holding member of the first steel 12 held by the holding member 2 It means a state in which the relative positional relationship between arbitrary portions of the steel material 14 is maintained. Therefore, if the relative positional relationship is maintained, and the arbitrary portion of the first steel 12, and the arbitrary portion of the second steel member 14 may be moved simultaneously in the reference direction Y. Similarly, a state in which movement is restricted in the thickness direction of the welded joint 10a, in the thickness direction, the held by any portion and the holding member of the first steel 12 held by the holding member the relative positional relationship between arbitrary portions of 2 steel 14 means a state of being maintained.
[0042]

　In the welded joint 10 fused portion 18 is formed, it is possible to prevent the the surface 14b of the second steel member 14, a large residual tensile stress in the vicinity of the weld toe 16b is generated. In the present embodiment, as described above, the residual stress caused in the position 20a is the value of the compression side of the residual stress caused in the position 20b. Thus, for example, even if a force in the reference direction Y in the vicinity of the weld toe 16b in the second steel member 14 is applied, in the vicinity of the weld toe 16b at the surface 14b, and a large tensile stress in the reference direction Y occurs It can be suppressed. As a result, it is possible to suppress the in comparison with the conventional welded joints, cracks are generated on the surface 14b side of the second steel member 14 in the vicinity of the weld toe 16b. That is, it is possible to obtain a welded joint 10 having an excellent fatigue strength. Incidentally, in order to obtain a welded joint 10 having more excellent fatigue strength, it is preferable to residual stress caused in the position 20a is the value of the compression side than 150MPa than the residual stresses caused in the position 20b, or 200MPa it is more preferable that the value of the compression side.
[0043]
　Further, the welded joint 10 according to the present embodiment, by forming the molten portion 18 in a part of the overlap portion 14a of the second steel member 14, the residual stress generated in the position 20a to the value of the compression side as described above be able to. The first steel 12 is pulled in the first direction Y1, when the second steel member 14 is pulled in the second direction Y2, together with the tensile stress is generated in the reference direction Y in the first steel 12, a second steel than it welds 16 of the 14 tensile stress reference direction Y occurs in the portion of the second direction Y2 side. On the other hand, the first direction Y1 side portion than the welding portion 16 of the second steel member 14, i.e. the tensile stress is hardly generated in the overlap portion 14a of the second steel member 14. Therefore, by forming the molten portion 18 in a part of the overlap portion 14a of the second steel member 14, even if the strength of the overlapping portion 14a is lowered, it is possible to prevent the tensile strength of the welded joint 10 is deteriorated. That is, according to the present embodiment, the tensile strength without lowering the weld joint 10, the residual stress generated in the position 20a can be set to a value of the compression side as described above.
[0044]

　In the above embodiment describes how to obtain a welded joint 10 with improved fatigue strength by heating an existing weld joint 10a, the first steel 12 and the second steel member 14 it may be obtained welded joint 10. In this case, first, by welding the first steel 12 and the second steel member 14, to obtain a joined body having the same configuration as the welded joint 10a shown in FIG. 3 (a) (welding step). More specifically, in the welding process, in a state of overlapping the overlapping portion 12a of the first steel 12 and the overlap portion 14a of the second steel member 14, the weld 16 is formed along the edge of the first steel 12 as such, welding the surface 14b of the edge and the second steel member 14. Thereafter, by performing the heating step (step corresponding to improve the method described above) to the joint body obtained in the welding process, it is possible to obtain a weld joint 10.
[0045]

　In the above embodiment has been described for the case where the molten portion 18 is formed only the overlapping portion 14a of the second steel member 14. However, the area where the molten portion 18 is formed is not limited to the above example. For example, as shown in FIG. 4 (a) ~ (c) , the molten portion 18 over a portion of the part and the overlapping portion 14a of the second steel member 14 of the overlapping portion 12a of the first steel 12 have been formed it may be. In this case, since the overlapping portion 12a of the first steel 12 and the overlap portion 14a of the second steel member 14 is welded, even to form a molten portion 18, the strength of the welded joint 10 in the overlap portion 12a and the overlapping portion 14a is It can be prevented from being lowered. In this case, the fused portion 18, for example, is formed so as to extend parallel to the weld 16.
[0046]
　Incidentally, the melting portion 18 shown in FIG. 4 (a), so as not to reach the surface 12b of the first steel 12 extends from the rear surface 14c of the second steel member 14 toward the surface 12b of the first steel 12. The molten portion 18, similarly to the above-mentioned embodiment, for example, be formed by heating the overlapping portion 12a and the overlapping portion 14a from the back surface 14c of the second steel member 14.
[0047]
　Melting portion 18 shown in FIG. 4 (b), extends through the overlapping portion 12a and the overlapping portion 14a of the second steel member 14 of the first steel 12. The melting portion 18 may, for example, can also be formed by heating the embodiment similarly to the second overlapping portion 12a from the back surface 14c side of the steel member 14 and the overlap portion 14a of the above, from the surface 12b side of the first steel 12 overlapping portion 12a and the overlapping portion 14a can also be formed by heating the.
[0048]
　Melting portion 18 shown in FIG. 4 (c), so as not to reach the rear surface 14c of the second steel member 14 extends from the surface 12b of the first steel 12 toward the back surface 14c of the second steel member 14. The molten portion 18 can be formed, for example, by heating the overlapping portion 12a and the overlapping portion 14a from the surface 12b side of the first steel 12.
[0049]
　In the above embodiment has been described a method of improving the fatigue strength of the welded joint 10 having a first steel 12 and the second steel member 14 in plan view a rectangular shape. However, the shape of the welded joint is not limited to the examples described above, the present invention is applicable to welded joints of various shapes. For example, the present invention may be applied to the welded joint 24, as shown in FIG. It will be briefly described below weld joint 24.
[0050]
　5 (a) is a perspective view showing a welded joint 24, FIG. 5 (b) is an exploded perspective view showing a weld joint 24. 5 with reference to (a), the welded joint 24 has a weld 30 which connects the first member 26, second member 28, and the first member 26 and second member 28. Each of the first member 26 and second member 28, made of steel. The thickness of the first member 26 and second member 28, for example, or less 3.3 mm.
[0051]
　FIG. 5 (a), referring to (b), the first member 26 has a square tube shape, has four plate-like portion 32, 34, 36, 38. The plate-like portion 32 and the plate portion 36 is provided so confronts and parallel to one another. The plate-like portion 34 and the plate portion 38 is provided so confronts and parallel to one another. Each plate-shaped portion 34 and 38, and connects the plate-like portion 32 and the plate portion 36. Some part 32a and the plate-like portion 36 of the plate portion 32 36a protrudes toward the second member 28 than the plate portion 34 and 38.
[0052]
　The second member 28 has a square tube shape, has four plate-like portion 40, 42. The plate-like portion 40 and the plate portion 44 is provided so confronts and parallel to one another. The plate-like portion 42 and the plate portion 46 is provided so confronts and parallel to one another. Each plate-shaped portion 42 and 46, and connects the plate-like portion 40 and the plate portion 44.
[0053]
　In welding the first member 26 and second member 28 sandwich the second member 28 with a portion 36a of the portion 32a and the plate-like portion 36 of the plate portion 32. In the welded joint 24, overlap each other as a portion overlapping each of the part 32a and the plate-like portion 40 of the plate portion 32, and a part of the portion 36a and the plate-like portion 44 of the plate-like portion 36 and each in a state of overlapping each other as overlapped portion, the first member 26 and second member 28 are welded. Weld 30 is formed along an edge of the second member 28 side in the first member 26.
[0054]
　In the present embodiment, the plate portion 32 and the plate-like portion 36 corresponds to the first steel respectively, the plate-like portion 40 and the plate-like portion 44 corresponding to the second steel respectively. Referring to FIG. 5 (a), in this embodiment, for example, a direction in which the weld 30 extends along the edge of the second member 28 side in the plate-like portion 32 as the extending direction X of the above, the reference direction Y to define a. Thus defining the reference direction Y, similarly to the above-mentioned embodiment, for example, to form the molten portion 48 in a portion overlapping the part 32a of the portion of the plate-like portion 32 32a and the plate portion 40 . Although detailed description is omitted, similarly, the weld 30 as the stretching direction and a direction extending along the edge of the second member 28 side in the plate portion 36, defining a reference direction. Thus defining the reference direction, similarly to the above-mentioned embodiment, for example, to form a molten part in a portion overlapping the part 36a of the portion 36a and the plate-like portion 44 of the plate portion 36. Thus, similar to the welded joint 10 described above, also in the welded joint 24, it is possible to improve the fatigue strength.
[0055]
　As described above, the plate-like portion of the one member, in improving the fatigue strength of lap weld joint having a welded structure in the plate-like portion of the other member, the first steel one of the plate-like portion defining, and the other plate-shaped portion defining a second steel can utilize the present invention.
[0056]
　In the embodiment described above, each of the first steel and the second steel material, it has been described consisting of steel or plate-shaped portion, the shape of the first steel and the second steel material is not limited to the above example. For example, the first steel product has a surface and / or back surface of the curved, second steel may have a surface and / or back of the curved surface. Specifically, for example, the present invention may be applied to the welded joint 10b, as shown in FIG.
[0057]
　6 (a) is a longitudinal sectional view showing the welded joint 10b, FIG. 6 (b) is a sectional view taken along line B-B in FIGS. 6 (a). Referring to FIG. 6 (a), the welded joint 10b differs from the weld joint 10 described above, has a point of first steel 12 has a semi-cylindrical shape, the second steel member 14 has a cylindrical shape and the point has. That is, in this embodiment, the first steel 12 has a rear surface 12c of the curved surface (semicylindrical shape), second steel member 14 has a surface 14b of the curved (cylindrical shape). In this embodiment, as in the embodiment described above, the thickness of the first steel 12 and the second steel member 14 is, for example, or less 3.3 mm.
[0058]
　In the welded joint 10b, in a state where the part of facing portion and the surface 14b of the back surface 12c, a first steel material 12 and the second steel member 14 is joined by weld 16. In this embodiment, the welding unit 16, along the edge of the first steel 12 extends in the circumferential direction of the second steel member 14 (the direction indicated by the arrow X in Figure 6 (b)). Also in this embodiment, the molten portion 18, so as to extend parallel to the weld 16, is formed in the overlapping part 14a. In the present embodiment, the molten portion 18 is formed so as to extend in the circumferential direction X of the second steel member 14. Incidentally, the melting portion 18, similarly to the above-mentioned embodiment, may be formed in the overlapping portion 12a.
[0059]
　Even in welded joint 10b shown in FIG. 6, similar to the embodiment described above provisions, the reference direction Y, the first direction Y1, the second direction Y2, position 20a, a position 20b, the distance d1, the distance d2, and the distance L , it is possible to utilize the present invention. Although not a detailed description, first steel product has a cylindrical shape, the second steel may have a semi-cylindrical shape. The first steel and the second steel together may have a semi-cylindrical shape, the first steel and the second steel may be both have a cylindrical shape.
[0060]

　or less, with the simulation result of the FEM analysis using a computer, for explaining the effect of the present invention. 7 (a) is a welded joint of the FEM analysis model 50 according to the present invention (hereinafter, simply referred to. The analysis model 50) is a diagram showing, FIG. 7 (b), the FEM analysis of the welded joint of the comparative example model 55 (hereinafter, simply referred to. the analysis model 55) is a diagram showing, FIG. 7 (c), the welded joint of the FEM analysis model 60 in accordance with another comparative example (hereinafter, simply referred to. analysis model 60) shows the it is a diagram. Each analysis model is a two-dimensional analytical model using the plane strain elements, the number of elements was 1986. Further, analysis was performed based on linear kinematic hardening law. The first steel 12, the material of the second steel member 14 and the welding unit 16, and a SUS316L. Incidentally, FIG. 7 (a), shown in (b), (c) and in Fig. 11 and 14 described later, symbols triangle restraint point of the analysis model.
[0061]
　In any of the analysis model 50, 55, 60 also, the thickness of the first steel 12 and the second steel member 14 was set to 3.2 mm. Region of 1mm from the edge of the welded portion 16 side of the first steel 12 in the first direction Y1 was assumed to bind to the second steel member 14. Further, the static friction coefficient between the first steel 12 and the second steel member 14 was set to 0.2.
[0062]
　In the simulation using the analysis model 50, on the assumption that forming a molten portion 18 which penetrates the first steel 12 and the second steel member 14, as shown in Table 1 below, room temperature a portion to be the molten portion 18 It was heated from (20 ° C.) until 1400 ° C. or higher. Further, as shown in Table 1 below, the distance d1 is set 3 mm, to 6mm and 8 mm. Width in the reference direction Y of the molten portion 18 was set to 2 mm. Then, after cooling the welded joint to ambient temperature (20 ° C.), to release the constraint of both ends of the welded joint was investigated residual stress occurring near weld toe 16b.
[0063]
　In the simulation using the analysis model 50, during heating and during cooling, and detained welded joint as follows. In the end surface 12e of the first steel 12, the movement of the regulating movement of the reference direction Y of the first steel 12 in the region of length L1 in the second direction Y2 from the end surface 12e, the thickness of the plate of the first steel 12 and regulate. In the end surface 14e of the second steel member 14, restricts the movement of the reference direction Y of the second steel member 14, the movement from the end face 14e in the region of the length L2 in the first direction Y1, the thickness of the plate of the second steel member 14 and regulate. As shown in Table 1 below, the length L1 was set 0 mm, 5 mm, 10 mm, 15 mm, and 35 mm. Note that the case of setting the length L1 to 0 mm, the place where the first steel member 12 to move in the thickness direction is restricted, means a case where only the end surface 12e. Length L2 was set 0 mm, 5 mm, 10 mm, 15 mm, and 25 mm. As setting the length L2 to 0mm, the place where the second steel member 14 to move in the thickness direction is restricted, means a case where only the end surface 14e.
[0064]
[Table 1]

[0065]
　In the simulation using the analysis model 55, it was analyzed under the same heating conditions and cooling conditions and simulation using the analysis model 50. As shown in Table 1 above, the distance d1 is set to 3 mm. Width in the reference direction Y of the molten portion 18 was set to 2 mm. Also, during heating and during cooling, at the end face 12e of the first steel 12, to restrict the movement of the reference direction Y of the first steel 12, the end surface 14e of the second steel member 14, the reference direction Y of the second steel member 14 movement and regulation of. Movement in the thickness direction of movement and the second steel member 14 in the thickness direction of the first steel 12 is not restricted.
[0066]
　Further, in the simulation using the analysis model 60, a distance d3 away region 60a in the second direction Y2 from the weld toe 16b, the second steel member 14 from the normal temperature (20 ° C.) was heated to a temperature which does not melt. As shown in Table 1 above, the distance d3 was set to 3mm and 11 mm. The heating temperature was set to 650 ° C. and 800 ° C.. Then, after cooling the welded joint to ambient temperature (20 ° C.), to release the constraint of both ends of the welded joint was investigated residual stress occurring near weld toe 16b. Incidentally, during the heating and during cooling, at the end face 12e of the first steel 12, to restrict the movement of the reference direction Y of the first steel 12 in the region of length 35mm in the second direction Y2 from the end surface 12e, the first steel and restrict the movement of the direction of the thickness of the 12. Further, the end surface 14e of the second steel member 14, restricts the movement of the reference direction Y of the second steel member 14, in the region of the length 25mm in the first direction Y1 from the end surface 14e, the thickness of the plate of the second steel member 14 movement and regulation of.
[0067]
　8 and 9 show the residual stress in the reference direction Y caused in the vicinity of the weld toe 16b. Figure 8 shows the residual stress occurring in the surface 14b of the second steel member 14, FIG. 9 shows a residual stress caused in the mid-thickness of the second steel member 14. 8 and 9 show the tensile residual stress in a positive value indicates a compressive residual stress in a negative value. Figure 12 will be described later is the same in FIGS. 13 and 15. Further, FIG. 10 shows the values ​​obtained from the residual stress occurring on the surface 14b of the second steel member 14 by subtracting the residual stress caused in the mid-thickness. The horizontal axis in FIGS. 8 to 10 show the distance from the weld toe 16b in the second direction Y2. The same applies to FIGS. 12 and 15 described later.
[0068]
　Further, (specifically, the analysis model 50 used in the analysis No.1 ~ 7 of Table 1) analysis model 50 after heating and cooling as described above, the bending moment (0.4 N · m) the added. Specifically, as shown in FIG. 11, while restraining the ends of the second direction Y2 side of the second steel member 14, by adding a bending moment in a predetermined position P of the first steel 12. Although not shown, the analysis model 60 after heating and cooling was also added similarly bending moment. At the time of adding bending moment in the analysis model 50, 60, the stress distribution of the surface 14b of the second steel member 14, shown in FIG. 12. Although FIG. 12, for comparison, before heating (i.e., before forming the molten portion 18) at the time of adding the bending moment in the analysis model, the stress distribution of the surface 14b of the second steel member 14, analysis No. It is shown as 13. Further, in FIG. 13, the bending shows the change in stress before and after the addition of the moment. Incidentally, in FIG. 13, the position of 0.5mm from the weld toe 16b in the second direction Y2 on the surface 14b of the second steel member 14 shows the stress (the amount of change in the stress is largest since position).
[0069]
　As can be seen from FIG. 8, as compared with the analytical model 50 of the welded joint according to the present invention (analysis No.1 ~ 7), the analysis model of the welded joint of the comparative example 55 and 60 (Analysis No.8 ~ 12) , in the vicinity of the weld toe 16b on the surface 14b of the second steel member 14, it was possible to generate a sufficiently large compressive residual stress. Moreover, as can be seen from FIGS. 8 and 10, the analysis model 50 (Analysis No.1 ~ 7), as compared to the analysis model 55, 60 (Analysis No.8 ~ 12), in the vicinity of the weld toe 16b, the residual stress generated on the surface 14b, than the residual stress generated in the plate thickness center, could be sufficiently compressed side values. In addition, analysis No. 1 of the results and analysis No. Comparison with the results of 2-7, at least the end surface 12e (see FIG. 7), to restrict the movement of the movement and the plate thickness direction of the first direction Y1 of the first steel 12, at least the end surface 14e (see FIG. 7 in), residual by regulating the movement of the movement and the plate thickness direction in the second direction Y2 of the second steel member 14 in the vicinity of the weld toe 16b, the residual stress generated on the surface 14b, occurs in mid-thickness than the stress, it was found that it is possible to sufficiently compression-side values.
[0070]
　Moreover, as can be seen from FIGS. 12 and 13, upon adding the bending moment, the analysis model 50 (Analysis No.1 ~ 7), the analysis model 60 (Analysis No.9 ~ 12) and heating prior to analysis model compared to (analysis No.13), it was possible to sufficiently lower the tensile stresses occurring in the vicinity of the weld toe 16b at the surface 14b. From the above, according to the welded joint of the present invention, it can be seen that it is possible to prevent the large tensile stress near the weld toe 16b on the surface 14b of the second steel member 14 is generated. Therefore, according to the present invention, seen to be much improved fatigue strength of lap weld joint. Incidentally, from the results shown in FIG. 12, the distance d1 by less than 8 mm, it can be seen that the tensile stress generated when adding bending moment can be more sufficiently reduced. Still it can be seen that can sufficiently reduce the tensile stress occurring when the distance d1 was added bending moment to be smaller than 6 mm.
[0071]

　In the above simulation, was analyzed on the assumption that forming the molten portion 18 so as to penetrate the first steel 12 and the second steel member 14, in this simulation, the molten portion 18 by changing the area of formation was investigated residual stress of the weld toe 16b near.
[0072]
　FIG. 14 (a), the with reference to (b), in the present simulation, the surface 12b of the molten portion 18 is an analysis model 70 does not reach the rear surface 14c of the second steel member 14 and the fused portion 18, the first steel 12 using the analysis model 80 has not been reached. Distance d1 was set to 3mm. Note that the non-fused portion 18, in the same conditions as the analysis model 50 described above to create an analysis model 70, 80. Constraint is, of Table 1 analysis No. 5 is the same as the constraint condition of (L1 = 35mm, L2 = 25mm).
[0073]
　Under the same conditions as for the analysis model 50 described above, by heating and cooling the analysis model 70 and 80, it was examined residual stress occurring on the surface 14b of the second steel member 14. The results are shown in Figure 15. For comparison, the analysis model 50 Analysis No. Analysis of 5 (d1 = 3mm) are also shown in Figure 15.
[0074]
　As can be seen from FIG. 15, the case is melted portion 18 forming the molten portion 18 so as to penetrate even if it is not through the first steel 12 and the second steel member 14, the first steel 12 and the second steel member 14 similar effects were obtained.
Example
[0075]
　Using the improved method according to the present embodiment described in FIG. 3, to create a plurality of welded joint 10 having a shape and dimensions shown in Figure 16. Each thickness of the first steel 12 and the second steel member 14, and 1.6 mm, the distance L described above is set to 10 mm, the distance d1 described above is set to 3mm and 6 mm. Hereinafter, a welded joint 10 which sets the distance d1 to 3 mm, say welded joint 10 of the first embodiment, the welded joint 10 which sets the distance d1 to 6 mm, that a weld joint 10 of the second embodiment. The first steel 12 and the second steel member 14 were joined by arc welding. Further, the melting section 18, the laser beam was formed over the first steel 12 and the second steel member 14. From the weld joint 10 of Example 1 and Example 2 were taken two by two the fatigue test piece having a shape and dimensions shown in Figure 17. Incidentally, in FIG. 17, (a) is a plan view of a fatigue test piece, a line b-b sectional view of (b) is (a). Further, in FIG. 17 (a), the in order to avoid drawing from being complicated, not shown melting portion 18. Also, except for that it does not have the melting section 18 (that not subjected to heating and cooling process), the welded joint has the same configuration as the welded joint of Example 1 and Example 2, the welding of the comparative example It was created as a joint. From the welded joint of the comparative example was prepared, it was taken three fatigue test piece having a shape and dimensions shown in Figure 17.

The scope of the claims
[Requested item 1]
　Said edge by a second and a part of the steel material are overlapped as overlap portions respectively, and weld extending along the edge of the first steel having a portion with a predetermined thickness of the first steel having a predetermined thickness part is a fatigue strength improvement method of lap welding joint is welded to a surface of the second steel
　a direction parallel to the surface of the vertical and and the second steel in the extending direction of the welded portion as a reference direction the restricted movement of the lap weld joint in the reference direction, the first to regulate the movement of the first steel in the thickness direction of the steel material, and the second steel to the second steel in the thickness direction movement while restricting the, so that melting portion in a part of the overlapping portion of the second steel material is formed, to heat a portion of the overlapping portion of the second steel, improving the fatigue strength of lap weld joint Method.
[Requested item 2]
　As the molten portion in a part of the overlapping portion of a part and the second steel of the overlapping portion of the first steel is formed, the overlapping portions of partially and the second steel of the first steel the heat a portion of the overlapping portion, the fatigue strength improvement method of lap welding joint according to claim 1.
[Requested item 3]
　The molten portion, wherein is formed so as to extend parallel to the weld extending along the edge of the first steel, the fatigue strength improvement method of lap welding joint according to claim 1 or 2.
[Requested item 4]
　Heating position of the overlapping portion of the second steel product, wherein a edge position apart 2mm 10mm or more or less in the reference direction from the weld extending along the, according to any one of claims 1 3 fatigue strength improvement method of lap weld joint.
[Requested item 5]
　Laser beam, tungsten inert gas or heat a portion of the overlapping portion of the second steel by electron beam, the fatigue strength improvement method of lap weld joint according to any one of claims 1 4,.
[Requested item 6]
　The molten portion is formed at a position away to the reference direction from the weld, the fatigue strength improvement method of lap weld joint according to any one of claims 1 to 5.
[Requested item 7]
　A welding step of obtaining a joined body by welding a first steel and a second steel material, and a heating step of heating the bonded body,
　the welding process, the part of the first steel second a portion of the steel material in a state of overlapping the overlapping portion respectively, comprising the step of welding the said edges and said second steel material surface as welds along the edge of the first steel is formed ,
　the heating step, the relative direction to a direction parallel to the surface of the vertical and and the second steel in the extending direction of the welded portion, restricts the movement of said conjugate to said reference direction, the first steel in a state in which the restricting the movement of the first steel in the thickness direction, and was restricting the movement of the second steel to the second steel in the thickness direction, melting a portion of the overlapping portion of the second steel as part is formed, engineering for heating a portion of the overlapping portion of the second steel Including method of lap welding joint.
[Requested item 8]
　The heating step, as the molten portion in a part of the overlapping portion of a part and the second steel of the overlapping portion of the first steel is formed, a portion of the overlapping portion of the first steel and a step of heating a portion of the overlapping portion of the second steel manufacturing method of lap welding joint according to claim 7.
[Requested item 9]
　In the heating step, the fusion zone, the formed so as to extend parallel to the weld extending along the edge of the first steel, production of lap welding joint according to claim 7 or 8 Method.
[Requested item 10]
　The heating position of the overlapping portion of the in the heating step a second steel material, wherein a position distant 2mm 10mm or more or less in the reference direction from the weld extending along the edge, any of claims 7 9, method for producing a lap weld joint according to one paragraph.
[Requested item 11]
　Wherein the heating step, a laser beam to heat a portion of the overlapping portion of the tungsten inert gas the second steel or by electron beam, The method of manufacturing a lap weld joint according to any one of claims 7 to 10.
[Requested item 12]
　Wherein the heating step, the fusion zone, the formed from the welding portion at a position away in the reference direction, the manufacturing method of the lap weld joint according to any one of claims 7 to 11.
[Requested item 13]
　A lap welding joint edge of a portion of the first steel with a portion and overlap as overlapping portions respectively of the second steel first steel is welded to the surface of the second steel,
　wherein and welds a and the edges extending along the edge of the first steel is connected to the second steel,
　formed in said position away from the weld in a part of the overlapping portion of the second steel melt and a section,
　perpendicular to the extending direction of the welded portion, and wherein among the direction parallel to the second said surface of the steel, given the direction toward the opposite side to the first steel based the weld when a direction,
　at a position away 0.5mm in the predetermined direction from the weld toe on the surface of the second steel of the weld, the residual stress occurring on the surface of the second steel claim compression than the residual stress occurring in the center in the thickness direction of the two steel Is a value, lap weld joint