[Title of the Invention] LAP WELDING METHOD OF STEEL SHEET AND LAP WELD JOINT OF STEEL SHEET [Technical Field of the Invention] [0001] The present invention relates to a lap welding method of a steel sheet and a lap weld joint of a steel sheet. The present application claims priority on the basis of Japanese Patent Application No. 2015-182846, filed on September 16,2015 in Japan, the content of which is incorporated herein by reference. [Related Art] [0002] Recently, in the automotive field, there have been a demand for the weight reduction of vehicle bodies in order for gas mileage improvement and the reduction of C02 emission and a demand for the strengthening of vehicle body members in order for collision safety improvement. In addition, in order to meet such demands, high-strength steel sheets are used for vehicle body members, a variety of components, and the like. [0003] In steps for manufacturing vehicle body members made of high-strength steel sheets and steps for attaching components made of high-strength steel sheets, mainly, resistance spot welding (hereinafter, also simply referred to as spot welding) is broadly used. For example, as basic structural members constituting vehicle bodies, lap weld joints of steel sheets are used, and these lap weld joints are manufactured by overlapping two steel sheet members having a hat shape and spot-welding the overlapping portions. FIG. 16A is a horizontal cross-sectional view showing a lap weld joint 60 of a steel sheet of the related art and is a view for describing a lap welding method of a steel sheet of the related art. In addition, FIG. 16B is a partial enlarged view of FIG. 16A. Meanwhile, in FIG. 16B, one of a pair of welding electrodes 90 is not shown. [0004] As shown in FIG. 16A, in the lap welding method of the related art, two steel sheet members 70 which respectively have a pair of flange portions 72 and a pair of standing wall portion 74 that stands from these flange portions 72 and have a hat-like cross-sectional shape are overlapped with each other, and then the flange portions 72 of these steel sheet members 70 are interposed between the pair of welding electrodes 90 - 1 - and arc spot-welded, thereby forming solidified pmiions 80 (hereinafter, referred to as "nuggets") between the flange portions 72. (0005] As shown in FIG. 16A and FIG. 16B, the welding electrode 90 that is used for the spot welding has a cylindrical main body pmtion 92 and a taper pmtion 94 that tapers toward a tip end. Meanwhile, the diameter~ of the main body portion 92 is, for example, 16 mm, and the diameter~' of a tip end surface 94a of the taper portion is, for example, 6 mm. In addition, the width w of the flange p01tion 72 of the steel sheet member 70 is, for example, 15 to 20 mm. In addition, the tip end surface 94a of the taper portion 94 comes into contact with the flange pmtion 72 of the steel sheet member 70, whereby electric currents flow in the flange portion 72, and the nugget 80 is formed. That is, the diameter~· of a tip end surface 94a of the welding electrode 90 determines an electric conduction diameter and almost coincides with the maximum nugget diameter to be obtained. [0006] In a case in which two steel sheet members 70 are spotcwelded using the welding electrodes 90, when the standing wall portion 74 of the steel sheet member 70 and the welding electrode 90 come into contact with each other, the standing wall portion 74 and the welding electrode 90 are electrically conducted to each other, and there is a concern that it may not be possible to weld the flange portions 72 of the steel sheet members 70. Therefore, during the spot welding of the steel sheet members 70, it is necessary to provide a gap for avoiding interference between the standing wall portion 74 and the welding electrode 90. Furthermore, as described above, the welding electrode 90 has the taper pmtion 94 that tapers toward the tip end. Therefore, the nugget 80 is fmmed at a location a predetermined distance away from the standing wall portion 74. (0007] In the lap weld joint 60 obtained by the lap welding method ofthe related art, the nuggets 80 are formed at locations away from the standing wall portion 74 as described above, and thus, in a case in which a tensile stress acts thereon, the flange portions 72 of the two steel sheet members 70 easily deform in a direction in which the flange portions move away from each other (that is, torn-open deformation), consequently, stress focuses on an end portion of the nugget 80, and the joint strength decreases. In addition, even in a case in which a torsional moment acts on the surrounding of a central axis line CL of the lap weld joint 60,torn-open deformation is easily caused, and the torsional stiftness decreases. . 2 . [0008] Here, Patent Document I discloses a technique in which a quenching treatment is carried out on a portion 2 to 5 mm wide from the outer circumferential end of a nugget in order to increase the tensile shear strength of a spot welded joint. In addition, Patent Document 2 discloses a technique in which, when a weld bead is formed by laser-welding flanges of two steel sheet members, a to-be-welded location at which the formation of the weld bead is expected is tacked by means of spot welding or the like. [Prior Att Document] [Patent Documents] [0009] [Patent Document I] Japanese Unexamined Patent Application, First Publication No. 2013-223872 (Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2008-I 78905 [Disclosure of the Invention] [Problems to be Solved by the Invention] [0010] However, in Patent Document I, the hardness in the vicinity of a nugget end portion is increased by quenching the portion 2 to 5 mm :wide from the outer circumferential end of the nugget, and thus, in a lap weld joint that is obtained by spot-welding the overlapping portions of a flange portion of a hat-shaped steel sheet member and another steel sheet member, it is difficult to suppress the tom-open deformation. Therefore, in the technique of Patent Document 1, it is difficult to improve the joint strength and torsional stiffness of the lap weld joint. In addition, in Patent Document 2, on a plurality. of tacked places formed along the longitudinal direction of the flange, a weld bead is formed by laser welding. Therefore, in Patent Document 2, similar to Patent Document I, it is difficult to suppress the torn-open deformation. [00 I I] The present invention has been made in consideration of the above-described circumstance, and an object of the present invention is to provide a lap welding method · of a steel sheet and a lap weld joint of a steel sheet which· are capable of improving joint strength and torsional stiffness in lap weld joints that are obtained by welding a steel sheet member having flange portions and standing wall portions to another steel sheet member. [Means for Solving the Problem] - 3 - [0012] In order to achieve the above-described object, the present invention employs the followings. (I) According to an aspect of the present invention, there is provided a lap welding method of a steel sheet for overlapping and welding a first steel sheet member and a second steel sheet member having a flange pmiion that is overlapped with the first steel sheet member and a standing wall portion that stands from the flange portion, the method including: spot welding in a state in which the flange portion is overlapped with the first steel sheet member, thereby forming a nugget between the first steel sheet member and the flange portion; and, after the spot welding, laser welding a region between an R stop of the standing wall portion and the nugget, thereby forming a weld bead, in which, in the weld bead, a dimension in a longitudinal direction of the flange portion is equal to or longer than a diameter of the nugget, and a width dimension is 0.5 to3.0mm. (2) In the aspect according to (1), when a shortest distance between the R stop of the standing wall portion and the nugget is represented by 01 (mm) and a shortest distance between the R stop of the standing wall portion and the weld bead is represented by 02 (mm), a ratio 02/01 of02 to 01 may be 1/2 or less. (3) In the aspect according to (I) or (2), in the laser welding, the weld bead may be fanned so that an end portion of the weld bead in a width direction is formed in the R stop of the standing wall portion. (4) In the aspect according to any one of (I) to (3), a shape of the weld bead may be a linear shape, a IJ shape, or a wavy shape. (0013] (5) According to another aspect of the present invention, there is provided a lap weld joint of a steel sheet including: a first steel sheet member; a second steel sheet member having a flange portion that is overlapped with the first steel sheet member and a standing wall portion that stands from the flange portion; a nugget that joins the first steel sheet member and the flange portion; and a weld bead that joins the first steel sheet member and the flange portion and is formed in a region between an R stop of the standing wall portion and the nugget, in which, in the weld bead, a dimension in a longitudinal direction of the flange portion is equal to or longer than a diameter of the nugget, and a width dimension is 0.5 to 3.0 mm. (6) In the aspect according to (5), when a shortest distance between the R stop of the standing wall portion and the nugget is represented by 01 (mm) and a shmiest distance between the R stop of the standing wall pmiion and the weld bead is - 4 . represented by 02 (nun), a ratio 02/Dl ofD2 to Dl may be l/2 or less. (7) In the aspect according to (5) or(6), an end p01tion of the weld bead in a width direction may be formed in the R stop of the standing wall portion. (8) In the aspect according to any one of (5) to (7), the weld bead may have a linear, U-like, or wavy shape. [Effects of the Invention] [00 14] According to the respective aspects of the present invention, it is possible to improve joint strength and torsional stiffness in lap weld joints that are obtained by welding a steel sheet member having flange portions and standing wall portions to another steel sheet member. [Brief Description of the Drawings] (0015] FIG. I is a perspective view showing a hat-shaped steel sheet member. FIG. 2 is a perspective view showing a lap weld joint of a steel sheet according to a first embodiment of the present invention. FIG. 3 is a view showing the lap weld joint and is a cross-sectional view of a cross section that is perpendicular to a longitudinal direction and includes an end portion 11 Oa of a nugget II 0. FIG. 4A is an enlarged view of a portion indicated by reference symbol Pin FIG. 3. FIG. 4B is an enlarged view of a portion indicated by reference symbol Q in FIG. 4A. FIG. 5 is a partial enlarged plan view of the lap weld joint. FIG. 6 is an enlarged view of a portion indicated by reference symbol S in FIG. 5. FIG. 7 is a partial enlarged plan view showing a first modification example of the lap weld joint. FIG. 8 is a pattial enlarged plan view showing a second modification example of the lap weld joint. FIG. 9 is an enlarged view of the portion indicated by reference symbolS in FIG. 5 and is a view showing a third modification example of the lap weld joint. FIG. I 0 is an enlarged view of the portion indicated by reference symbolS in FIG. 5 and is a view showing a fourth modification example of the lap weld joint. FIG. II is an enlarged view of the· portion indicated by reference symbolS in FIG. 5 and is a view showing a fifth modification example ofthe lap weld joint. - 5 - FIG. 12 is a perspective view showing a sixth modification example of the lap weld joint. FIG. 13 is a perspective view showing a seventh modification example of the lap weld joint. FIG. 14 is a perspective view showing an eighth modification example of the lap weld joint. FIG. 15 is a pattial cross-sectional view showing a lap weld joint of a steel sheet according to a second embodiment of the present invention. FIG. 16A is a horizontal cross-sectional view showing a lap weld joint of a steel sheet of the related art and is a view for describing a lap welding method of a steel sheet of the related art. FIG. 16B is a partial enlarged view of FIG. 16A. [Embodiments of the Invention] [0016] Hereinafter, individual embodiments of the present invention will be described in detail with reference to the drawings. Meanwhile, in the present specification and the drawings, constituent elements having substantially the same functional constitution will be given the same reference symbol and will not be described again. [0017] (First Embodiment) FIG. 2 is a perspective view showing a lap weld joint I 00 of a steel sheet according to a first embodiment of the present invention (hereinafter, also simply referred to as the lap weld joint 100). The lap weld joint 100 is obtained by spot-welding and laser-welding a pair of steel sheet members 1. In the following description, first, the steel sheet member I will be described. [00 18] FIG. 1 is a perspective view showing the steel sheet member I in the lap weld joint 100. As shown in FIG. I, the steel sheet member I includes a pair of flange portions 2 that is long in a direction, has a hat-shaped cross section that is perpendicular to a longitudinal direction, and is parallel to each other, a pair of standing wall portions 4 that substantially perpendicularly stands from the pair of flange portions 2, and a transverse wall portion 5 that connects the pair of standing wall portions 4 and is parallel to the flange p01tions 2. The steel sheet member 1 is manufactured by, for example, bending a steel sheet by means of press forming. That is, in the steel sheet member 1, the flange portion 2 and the standing wall portion 4 are continuolls with each other, the standing wall portion 4 and the transverse wall p01tion 5 are continuous with - 6 - each other, and, particularly, there are no holes or the like formed on surfaces of the flange pm1ions 2, and thus it is possible to prevent a decrease in strent,>th. Meanwhile, in FIG. I, reference symbol X indicates a central axis line of the steel sheet member I. In addition, the direction of the central axis line X coincides with the longitudinal direction ofthe steel sheet member I. [00 19] The standing wall portion 4 of the steel sheet member I has an R portion 3 that is connected to the flange portion 2 ofthe steel sheet member I and has a predetermined curvature radius. The curvature radius of the R portion 3 is, for example, 3 to 6 mmc [0020] The sheet thickness of the steel sheet member I is, for example, 0.5 to 3.2 mm. In addition, the width (the length of the flange portion 2 perpendicular to a sheet thickness direction and the longitudinal direction) of the flange portion 2 of the steel sheet member I is, for example, 10 to 20 mm. The component composition of the steel sheet member 1 is not particularly limited and may be appropriately set so that mechanical characteristics suitable for uses can be obtained. Meanwhile, in a case in which the steel sheet member I contains 0.10% by mass or more of carbon, the tensile strength significantly improves. Therefore, the content of carbon in the steel sheet member 1 is preferably 0.10% by mass or more. In addition, the steel sheet member I may have a sUiface-treated film(s) formed on both surfaces or on a single surface. The surface-treated film is, for example, a plated film, a coated film, or the like. Examples of the plated film include a zinc plate, an aluminum plate, a zinc/nickel plate, a zinc/iron plate, a zinc/aluminum/magnesium plate, and the like, and examples of a method for manufacturing plates include hot-dip plating, electroplating, and the like. [0021] Next, the lap weld joint 100 according to the present embodiment will be described. FIG. 2 is a perspective view of the lap weld joint 100, and FIG. 3 is a cross-sectional view of a cross section that is perpendicular to the longitudinal direction of the lap weld joint 100 and includes an end portion 11 Oa of a nugget 110. As shown in FIG. 2 and FIG. 3, the lap weld joint 100 is long in the direction of the central axis line X and has a hollow cross section that is perpendicular to the central axis line X (longitudinal direction). In addition, the lap weld joint I 00 includes a pair of steel sheet members I facing each other, a plurality of nuggets 110 that are formed by spot-welding flange pm1ions 2 of the pair of steel sheet members I, and a plurality of . 7 . weld beads 120 that are formed by laser-welding the flange portions 2 of the pair of the steel sheet members I. Meanwhile, in FIG. 2 and FIG. 3, reference symbol IX indicates the steel sheet member 1 disposed on the upper side, and reference symbol I Y indicates the steel sheet member I disposed on the lower side. [0022] FIG. 4A is an enlarged view of a pmtion indicated by reference symbol Pin FIG. 3. As shown in FIG. 3 and FIG. 4A, the nugget II 0 is formed between the flange portions 2 by spot-welding the flange portion 2 of the steel sheet member IX and the flange portion 2 of the steel sheet member IY and joins the flange pmtion 2 of the steel sheet member IX and the flange portion 2 of the steel sheet member I Y. In other words, the nugget 110 is formed on an overlapping surface of the flange portion 2 of the steel sheet member I X and the flange portion 2 of the steel sheet member I Y. The weld bead 120 is formed between the flange portions 2 by welding the flange portion 2 of the steel sheet member I X and the flange portion 2 of the steel sheet member IY by radiating. laser beams from the upper side of the flange pmtion 2 of:the steel sheet member IX, and joins the flange portions 2 to each other. In other words, the weld bead 120 is formed from an external surface (among two surfaces in the sheet thickness direction, a surface facing the outside) ofthe flange portion 2 of the steel; sheet member I X to an inside of the flange portion 2 of the steel sheet member I Y. Meanwhile, the weld bead 120 may or may not penetrate the external surface of the flange portion 2 ofthe steel sheet member I X and an external surface ofthe flange portion 2 of the steel sheet member I Y. [0023] In addition, the weld bead 120 is formed in a region between an R stop 3a·of the R portion 3 of the steel sheet member 1 X and the nugget II 0 as shown in FIG. 4A. Specifically, an end portion 120a of the weld bead 120 on the inside of the flange portion 2 in the width direction (an end portion of the weld bead 120 in the width direction which is closest to the R stop 3a) is located on the outside of the R stop 3a in the width direction in the flange pmtion 2. In addition, an end portion 120b of the weld bead 120 on the outside of the flange portion 2 in the width direction (an end portion of the weld bead 120 in the width direction which is farthest from the R stop 3a) is located on the inside of an end portion 11 Oa of the nugget II 0 on the inside of the flange pmtion 2 in the width direction (an end portion of the nugget 110 which is closest to the R stop 3a) in the width direction in the flange portion 2. Meanwhile, the end portion 120a of the weld bead 120 may be located on the inside of the end portion li!Oa of the nugget II 0 in the width direction in the flange portion 2, and the end portion - 8 - 120b of the weld bead 120 may be located on the outside of the end portion II Oa of the nugget II 0 in the width direction in the flange pmiion 2. That is, a pati of the weld bead 120 may be formed on the nugget II 0. [0024] Here, the R stop 3a will be described using FIG. 4A and FIG. 4B. Meanwhile, FIG. 4B is an enlarged view of a portion indicated by reference symbol Q in Fig. 4A. As shown in FIG. 4A and FIG. 4B, the R stop 3a is a transition place from the R portion 3 to the flange portion 2. Specifically, on a surface of the flange portion 2, a straight line Yl is drawn from an end portion of the flange portion 2 toward the inside of the steel sheet member I X in the width direction, and furthermore, a perpendicular line is drawn from an arbitrary point A on the R portion 3 of the steel sheet member IX so as to intersect the straight line Yl. Jn addition, the point A on the R portion 3 at which a distanced between an intersection point B between the straight line Yl and the perpendicular lin01 and the point A reaches 0.1 mm is considered as the R stop 3a. [0025] As described above, the weld bead 120 is formed between the R stop 3a and the nugget 110, and thus a distance 01 (mm) between the R stop 3a and the nugget 110 becomes greater than a distance 02 (mm) between the R stop 3a and the weld bead 120. Meanwhile, the distance 01 refers to a distance between an intersection point between a perpendicular line drawn from the end portion 110a of the nugget 110 so as to intersect the straight line Y2 and the straight line Y2 and the R stop 3a. That is, the distance 0 I is the shortest distance between the R stop 3a and the nugget 110. Jn addition, the distance 02 refers to a distance between an intersection point between a perpendicular line drawn from the end portion !20a of the weld bead 120 so as to intersect the straight line Y2 and the straight line Y2 and the R stop 3a.'. That is, the distance 02 is the shortest distance between the R stop 3a and the weld bead 120. [0026] In addition, as described above, in the lap weld joint I 00, the end portion 120a ofthe weld bead 120 is located on the outside of the R stop 3a in the width direction in the flange pottion•2, and the end portion 120b of the weld bead 120 is located on the inside of the end portion II Oa of the nugget 110 in the width direction in the flange portion 2, and thus· the distance 01 is greater than the distance 02 (01>02).and is greater than the sum of the distance 02 and a width W (mm) of the weld bead 120 (01>02+W). Meanwhile, in a case in which the end pmiion 120a of the weld bead 120 is located on.:the outside ofthe R stop 3a in the width direction in the flange portion 2, and the end portion 120b of the weld bead 120 is located on the outside of the end ' 9 ' pmiion II Oa of the nugget II 0 in the width direction in the flange portion 2, the distance DL is greater than the distance D2 (Dl>D2) and is less than the sum of the distance D2,and the width Woftheweld bead 120 (Dl:2/01 of weld bead weld bead Cmm) (mm) - - - . 0 0 20 1.0 0.20 20 2.5 0.50 20 4.3 0.86: 20 6.0 1.20 20 1.0 0.20 5 1.0 0.20 12 1.0 0.20 40 1.0 0.20 20 1.0 0.20 20 Pitch P WidthW of apot welding L/P of weld bead Note (mm) (mm) 40 - - -Comparative Example 40 0.50 1.2 I Example '.0., -::s· '0;::; : 0 0. " g. " "Q' . "' - ""' "0 . .0.. .., .0.. .., ~g ;;l ~ ;::r " 0" v. "' "' - v. ~ " ~ Z'g 0 ~ !" :;: " 40 0.50 1.2 Example ~ 0:: 0 :r -·N< \!" 40 0.50 1.2 Example " "" ~ 0. " 40 o.so I 1.2 Example I Comparative 40 o.so 1 1.2 Example I. Comparative 40 0.13 l 1.2 Example 40 0.30 1.2 Example " ::::. ~- 0 " :;: ~ " 0.: -"' g. 'n0;· ::;:: "' 0 " ,..., '" - " ;::r 0. " 40• 1.00 1.2 Example 40 0.50 OA Comparative Example 40 0.50 0.8 Example -'0" ":;: .., 0:: "a' · 0" ":::. "'Q". . -"' ".., :E:Pl' ""' " 5 ""'' :;: ~ " " "~' :;: -~ "0" . 0. ;:;: a· p 19 [0056] Jn,Table I, Test No. I indicates a comparative example of a case in which only the spot welding was carried out (that is, a case in which the laser welding was not carried out). Test No. 2 indicates an invention example of a case in which 02 was zero, that is, the end portion of the weld bead closest to the R stop 3a was formed on the R stop 3a. Test Nos. 3 and 4, 8 and 9, and 11 indicate invention examples of a case in which 01 was greater than the sum of02 and W (01>02+W) and the end portion 120b of the weld bead 120 was formed on the inside of the end pmiion 1 J Oa of the nugget 110 in the width direction as shown in FIG. 4. Test No. 5 indicates an invention example of a case in which 0 J was greater than 02 (0 J>02) and was less than the sum of02 and W (OJ <02+W) and a part of the weld bead was formed on the nugget. [0057] On the other hand, Test No. 6 indicates a comparative example of a case in which OJ was less than 02 (01<02), that is, the weld beads were not formed in a region between the nuggets and the R stop. In addition, Test No. 7 indicates a case in which the diameter On (refer to FIG. 6) of the nugget was 5.5 mm, the length L of the weld bead was 5 mm, and tbus L was less tban On, that is, a comparative example. In addition, Test No. I 0 indicates a comparative example in which tbe width W of tbe weld bead was 0.4 mm and failed to satisfy the range (W=0.5 to 3.0 mm) of the present invention. (0058] In addition, tbe joint strength and the torsional stiffness of the produced test pieces were measured. The joint strength (the maximum load) was obtained by pulling out both ends of the tensile test piece using a tensile tester and breaking the tensile test piece. Meanwhile, the torsional stiffness was obtained by fixing one end of the torsional stiffness test piece and obtaining the relationship between the torsional moment lo'aded to the other end and the torsional angle measured at the other end. [0059] In Table 2, the joint strength, the joint strength ratio, the torsional stiffness, and the torsional stiffness ratio are shown. The joint strength ratio and the torsional stiffness ratio are respectively ratios to the joint strength and the torsional stiffness of the case of :rest No. I (that is, the case of the spot welding alone). In addition, joint strength ratios and torsional stiffness ratios of I. J 0 or higher were determined as a pass. [0060] [Table 2] 19 20 I ' ! l·i~ ! : ~ ! 4} "' " "' " "' > '> 2J -a -a -a -a -E;;; .a2. ,i -.~;; _o..!. -"a -'a" ~E-"~- -'a" 0 "E E E E E roE! roE E E "'E E z 1"-"' ., "' .. \'l 0.<11'•0.«11 .. E >< " X " "" "' oW UJ UJ w" UJ f0XW:liE 0>w:: UXJ wX oEW >< U"J 0 0 IQ 0. I "' I .",' If "' "" "' 0 "' "" (ti_Q 0 w -;;; 'E C! "" -: -: C! C! "-:' "<''! "' ,.., ...., c: - - - - - - - - - - - .,0. l5 ' r- ""'' "c !J:i~ " "' .. .., 0 "' ., _...., "' "' "' ;;:; :5 "' [;; "' "' ., r- "' "' 0> ?'"iEz "' "' "' "' "' "' "' "' "iii..,_... ~ ~ ' ' ! .<: tO I .c. "' <') I 0> ~ 0 ~~ 0 "' ~ ~ q - C! "' "; ~ q ...., "! ~ - - - - - - - "' - - ·"a!:' -:> -" tO I c I e....._ 0 "' ... "' "' 0 "' I .... U> +-'z "'! "" "' "' r- "" "l "< «; I "' "' "" .... "'c - ..; .·~a., "' "' - - - "' "' - "' . --~ ----~~--- z0 t( - "'