SPECIFICATION METHOD OF WELDING OVERLAPPED PORTION, METHOD OF MANUFACTURING OVERLAP-WELDED MEMBER, OVERLAP-WELDED MEMBER, AND AUTOMOTIVE PART Technical Field [0001J The present invention relates to a method of welding on overlapped portion of an overlap-welded member formed by overlapping a plurality of steel sheet members and welding them, a method of manufacturing the overlap-welded member, the overlap-welded member, and an automotive part having the overlap-welded member. The present application claims priority based on Japanese Patent Application No, 2012-175K60 filed hi Japan on August K, 2012, the disclosures of which are incorporated herein by reference. Background Art [0002] In recent years, structures configured with a plurality of steel sheet members made out of steel sheets aie commonly configured to include an over lap-welded member having the plurality of steel sheet members joined with each other in a manner such that the steel sheet members arc overlapped with each other in a manner according to the functions thereof or the environments in which they aroused, to make an overlapped portion, and this overlapped portion is subjected to resistance spot welding to create a spot-wcldcd portion having a nugget. |0003] For example, a monocoque body (automotive part), which constitutes an automohilc body, is generally formed by overlapping steel sheet members including high-strength steel sheets, and applying resistance spot welding to a flange portion 1 (overlapped portion) in order to achieve both an improvement in collision safety and an improvement in fuel efficiency. Currently, high-tensile steel sheets having a tensile strength of9S0 MPa class are widely used as high-strength steel sheets for automobiles, and further, investigations have been performed on high-tensile steel sheets having a tensile strength of 1200 MPa class or higher. [0004] Furthermore, another technique has been under investigation, which employs hot stamping in which both press forming and quenching are performed simultaneously in the same die to form the steel sheet members of the overlap-welded member, and manufactures hot stamps having a tensile strength of 1500 MPa or higher as the steel sheet members. During this hot stamping, the steel sheets are heated to high temperatures to be in a highly duelile state, and then piess forming is perlbnned. Thus, high-strength steel sheet members having a tensile strength of 1500 MPa or higher can he efficiently manufactured, and further, the dimensional accuracy after the press forming can be advantageously improved. [0005] For example, in the case of structures required to have a rust resistance, these structures may he made by overlapping steel sheet members made out of steel sheets including galvanized steel sheet having a hot-dip galvanncal coating or a hot-dip galvanizing coating formed thereon, and then joining the overlapped portion though resistance spot welding. For example, an outer panel, constituting the monocoque body, generally includes galvanized steel sheets having a hot-dip galvanneal coating or a hot-dip galvani/.ing coating formed thereon. [00061 The steel sheet members formed by applying hot stamping to high-tensile steel sheets or high-strength steel sheets having a tensile strength of 1200 MPa or higher, as 2 described above, usually contain a quenched structure. However, the spot-welded portion, at which the overlapped portion is joined; has afreat-arfeeted zone (hereinafter, referred to asHAZ) of which hardness is less tlianthc base material containing the quenched structure, because heat from the resistance spot welding causes tempering of the quenched structure around the nugget. [0007] This softening of the HA7, which has a hardness lower than that of the base metal may also occur in the case of steel sheets of 980 MPa class. However, this softening occurs particularly in the spot-welded portion of a high-tensiic steel sheet having a tensile strength of 1200 MPa or higher and containing quenched structures formed with continuous annealing equipment having a water cooling function, or a hot slumped member (high-strength steel sheet member) fanned through hot stamping. For example, in the case of a cold-rolled steel sheet of 1200 MPa class, the base metal has a Vickers hardness of approximately 390, whereas the softest zone in HAZliasa Vickers hardness of approximately 300. this means that Vickers hardness is approximately 90 less than Ihe base metal. [00081 FIG. 14 is a diagram showing an example ofa test piece 100 including an overlapped portion obtained by overlapping a hot stamped member {high-strength steel sheet member) 10 IP having a tensile strength of 1500 MPa class and formed through hot stamping and a hot stamped member (high-strength steel sheet member) 102P having a tensile strength of 1500 MPa class and formed through hot stamping, and forming a spot-welded portion 110 having a nugget 112 through resistance spot welding, and further showing a distribution of hardness according to Vickers liardncss (JlS Z2244) measured by applying indentations to positions located along tire broken line shown in the schematic view showing the test piece 100 (positions located at one-quarter of the thickness (thickness/4) from the interface m a direction towards the center of the steel sheet), The Vickers hardness is measured with a load of 9.8 N and at pitches of 0.5 mm. [0009J 3 As shown ill the graph in FIG. 14, the test piece 100 is formed by overlapping the hot stamped member 101P ofl 500 MPa class famed through hot stamping and the hot stamped member 102P of 1500 MPa class formed through hot stamping. Tliis test piece 100 exhibits a Victors hardness of approximately 450 at the base material (hot stamped member 101P) and a Vickcrs hardness of approximately 300 at the softest zone 103 A in the HAZ softening zone 103. In other words, Viekers hardness at the softest/.one l03Ain the HA/, 103 decreases by approximately 150 in comparison with that at the base metal (hot stamped member 101P). [0OI0J Then, tensile load is applied to the test piece 100. As a result, a fracture occurred from the HAZ softening/tfne 103 located oulside of and in the vicinity of the nugget 112 as shown in FIG. 15A and FIG. 15R. FIG. f5A is a sectional view of the surface of the steel, and shows how the hot stamped memher 101P of the test piece 100 shown in FIG. 14 fractured. FIG, 15B is a scctJonaJ view showing the state of the fracture from the HAZ softening zone 103. jOOfll The softening of HAZ, as described above, does not influence the evaluation results of tensile shear tests and cross tension tests (J IS Z3137) used for joint evaluation of resistance spot welding. However, in the case where a tensile load is applied to the test piece 100 as shown in FIG. 15A and FIG. 15B> distortion is focused locally on the HAZ softening zone 1035 possibly causing the fracture in the HAZ softening/one 103, [0012] The above-described fracture in the HAZ softening zone of the spot-welded portion can be seen in the steel sheet member (press formed article) formed by steel sheets having a tensile strength of 1200 MPa or higher, and there is a possibility that the advantage of the high-strength steel sheet cannot be fully achieved at the lime ol'impaet, [0013] For example, structural elements {overlap-welded members) such as an A-pilfar, 4 a B-pillar, a roof rail, and a side sill constituting the automobile body are required to protect occupants in a cabin at the time the automobile collides. For this reason, deformation, at the time of impact is suppressed by overlapping u plurality of steel sheet members, and joining the flange (overlapped portion) through resistance spot welding, thereby forming a tubular closed cross section. [0014] However, in the case of serious impact modes such as SUV side crash tests of the Insurance Institute for Highway Safety (IIIIS) and pole side impact tests of the Euro NCAP, there is a possibility that it is difficult to achieve predetermined impact performance even using, for example, high-strength steel sheets, because deformations concentrate on the HAZ softening zone of the spot-wcldcd portion and the IIAZ softening xone serves as a starting point of fracture. Thus, in order to make full use of the performance of the-high-strength steel sheet, it is necessary to prevent the IIAZ softening /one of the spot-welded portion from serving as the stalling point of fracture in the case where the structural elements of the automobile body include the slccl sheet member formed by the high-strength steel sheet having a tensile slrenglh of 1200 MPa or higher. LO0I5] For example, one of the techniques disclosed includes a technique of alleviating stress at the welded potion and suppressing delayed fracture by employing both laser welding and spot welding in the ease where high-strength steel sheets are welded to form a structural element for aulomobilcs (sec, for example, Patent Document 1). [0OI6| Furthermore, in connection with improvement in joining at a welded portion, a technique is disclosed in which continual welded portions are formed along the spot-welded portion of a molal material through laser welding (sec, for cxamplc; Patent Document 2). [00171 Furthermore, in connection with improvement in joining at a welded porlion, a 5 technique is disclosed in which laser light is emitted onto a spot-welded portion or Ihe vicinity of the spot-welded portion to laser weld a steel sheet on the surface side and a thick steel sheet adjacent to this stcci sheet on the surface side (sec, for example. Patent Document 3). [00181 Furthermore, Non-Patent Document 1 discloses u method of preventing structural elements litim fracturing Worn a HAZ softening zone, in which the strength of a base metal is reduced through thermal treatments applied at the time of hot stamping to a portion having a risk of causing a fracture due to impact to an A-pillar formed through hot stamping, whereby the softening of IIAZ does not occur even if resistance spot welding is applied. [0019] Furthermore, Non-Patent Document 2 discloses a method of preventing structural elements from fraclurmg from a HAZ softening zone, by reducing the strength of a base metal through tempering using high frequency heating applied to a flange portion of a li-piliar formed through hot stamping, thereby preventing the IIAZ from softening even if resistance spot welding is applied. Related Art Documents Patent Document 100201 Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2008-178905 Patent Document 2: Japanese Unexamined Patent Application, hirst Publication No. 2009-241116 Patent Document 3: Japanese Unexamined Patent Application, First Publication No, 2010-264503 Non-Patent Document [0021| 6 Non-Patent Document 1: Tailored Properties for Press-hardened body parts Dr. Camilla Wastlund, Automotive Circle International, Insight edition 2011 Ultra-high strength steels in ear body lightweight design-current challenges and future potential Non-Patent Document 2: hUp;//puhl i cali ons. lib.chalmcrs. se/rccords/ful I lex U 1 443 OB .pdf Disclosure of the hwention Problems to be solved by the Invention [0022] However.. in Ihe technique disclosed in Patent Document I i tack welding through spot welding is applied on the line extended from a laser welding bead to he formed on Ihe overlapped portion, and then laser welding is applied, thereby alleviating stress occurring immediately after the laser welding at the overlapped portion due to, for example, deformation associated with laser welding or spring back u£a formed member. Tliis means that this technique relates to temporarily holding in the case oflaser welding, and hence, docs not contribute to improving the strength of the spot-welded portion. 100231 Further, the technique disclosed in Patent Document 2 is a technique of performing resistance spol welding prior io application ol'lasev welding, thereby causing the spot welded portion formed in advance lo function as a means of fixing the overlapped portion. This means that this technique inainly relates to laser welding rather thau spot welding. Thus, this technique does not relate to a technique of enhancing advantages of spot welding. L0024] 1'urthcr, the technique disclosed in Patent Document 3 relates to a technique of sequentially performing a spot welding process and a laser welding process, and welding a surface-side steel sheet and a thick steel sheet adjacent to the surface-side steel sheet 7 through laser welding to reliably apply overlap welding even in the case where no spot-welded portion is formed between two or more steel sheets including the surface-side steel sheet and the thick steel sheet. Thus, this technique does not relate to a technique of improving the strength of the spot-wcldcd portion. [002SJ l'uither, in the case of a method of adjusting strength according to portions of the A-pillar as disclosed in Non-Patent Document 1, a low-slrength portion is inevitably formed in a relatively large area in the A-pillar, Thus, the effect of hot stamping, in which high-strength can be obtained, cannot he fully achieved, and further, the effect of reduction in weight is limited, 1'urthcr, with this method, characteristics related to strength vary across a relatively large transition area, which is inevitably fomied between a quenched zone and a non-quenched zone, possibly causing variation in impact performance of the A-piliar. [0026] Further, with the method of tempering the flange of the B-pillar through high frequency heating after hot stamping as disclosed in Non-Patent Document 2, the B-pillar may deform due to thermal strain resulting from high frequency heating, whereby the dimensional accuracy deteriorates. Not only the R-pillar but also an A-pillar, a roof rail or other structural elements disposed around a door opening portion are rcquhed to he assembled accuixilely so that spaces between these structural elements and, for example, a door panel are uniform throughout the entire circumference of the door opening portion. Thus, it is dillicult to apply the technique disclosed in Non-Patent Document 2 to the siiuclural elements around the door opening portion, because of reduction in the dimensional accuracy and dclcrioration in the quality concerning cosmetic appearance. (0027J In a design phase for an automobile body, it may be possible to design the structural element such as a B-pillar so that the Y\A7, softening wne m the spot-welded portion of the llangc docs not reach the fracture-strain at the lime of impact, S However, with this design, the thicknesses of steel sheets constituting structural member increase, or additional reinforcements are required, which leads to an increase in cost or weight of the automobile body. Thus, application of this technique is difficult [0028] The present invention lias been made in view of the problems as described above, and an object of the present invention is to, in connection with an overlap-welded member formed by welding together a plurality of steel sheet members made out of steel sheets, solve at least one of (I) and (2) described below. (i) Provide a method of welding an overlapped portion, a method of manufacturing an overlap-welded member, the ovcrlap-wclded member, and an automotive part, which can prevent the spot-welded portion in the overlapped portion from fraelurmg in a HAZ softening yxme, in the ease where & plurality of steel sheet members containing marlensile are joined through resistance spot welding. (2) Provide a method of welding an overlapped portion, a method of manufacturing an overlap-welded member, the ovcrlap-wclded member, and an automotive part, which can prevent fractures hi the spot-welded poition formed in the overlapped portion, in the case where the plurality of steel sheet members including a galvanised steel sheet having a hot-dip galvanneal coating or a hot-dip galvanizing coating formed thereon arc joined tiuviugh resistance spot welding. Means for Solving the Problem [0029] Each aspect of the present invention will be described below, (I) A first aspect of the present invention provides a method of welding an overlapped poition hi which a plurality of steel sheet mcrnhcrs arc joined at an overlapped portion, and at least one of the plurality of steel sheet members contains martensite, the -method including; forming a spot-welded portion having a nugget in the overlapped portion; and emitting a laser beam to form a melted and solidified portion crossing an end of the nugget and located between the nugget and a position externally spaced apart from 9 an end of the nugget by not less than 3 mm, the melted and solidified portion being formed in the steel sheet member containing the marlensUeso as to have a depth of not less than 50% of the thickness of the steel sheet member containing the martensite at a position externally spaced apart from the end of the nugget by 1 mm. (2) A second aspect of the present invention provides a method of welding an overlapped portion in which the plurality of steel sheet members including a galvanized steel sheet liaving a hot-dip galvanneal coating or a hot-dip galvani/.ing coating formed thereon are joined al an overlapped porlion: the method including: forming aspot-wcldcd portion liaving a nugget in the overlapped portion; and emitting a laser beam to form a melted and solidified portion crossing an end of the migget and located between the nugget and. a position outside of the migget, the melted and solidified portion being formed in a manner such that the depth of the melted and solidified portion al a portion corresponding to a contacting surface of the spot-welded portion is shallower than a contacting surface having the hot-dip galvanneal coating or the hot-djp galvanizing coating formed [hereon. (3) A third aspect of the present invention provides a method of manufacturing an overlap-welded member, including: overlapping a plurality of sleel sheet members at an overlapped portion, and performing a welding in accordance with the method of welding an overlapped portion according to (1) or (2) described above. (4) A fourth aspect of Ihc present invention provides an overlap-welded member in. which a plurality of steel sheet members are joined at an overlapped portion, and at least one of the plurality of steel sheet members contains martensite, in which a spot-welded portion liaving a nugget is formed in the overlapped portion and, a melted and solidified portion is formed thnjugh emission of a laser beam between the nugget and a position externally spaced apart from an end of the nugget by not less than 3 mm, this melted and solidi lied portion crossing an end of the nugget and having a depth of not less than 50% of the thickness of the steel sheet member containing the martensite al a position externally spaced apart from the end oflhe nugget by 1 mm. (5) A film aspect of the piesenl invention provides an overlap-welded member in 10 which a plurality of steel sheet members including a galvanized steel sheet having a hot-dip galvanneal coating or a hot-dip galvanising coaling Tunned thereon are joined al an overlapped portion, in which a spot-welded portion having a nugget is formed in the overlapped portion, and a melted and solidified portion is formed through emission of a laser beam between the nugget and a position outside the nugget so as to cross an end of the nugget and have a depth at a portion corresponding to a contacting surface of the spot-welded portion shallower than a contacting surface having ihehol-dip galvannea! coating or Ihe hot-dip galvani/.ing coaling formed Ihercon. (6) A sixlh aspect of the present invention provides an automotive part including the overlap-welded member according to (4) or (5) described above. Effects of the Invention [0030] According to the melhod of welding an overlapped portion, the method of manufacturing an overlap-welded member, the overlap-welded member, and the automotive part described above, it is possible to prevent the spot-welded portion in tire overlapped portion from fracturing inthellAZ softening zone, in Ihe case where a plurality of stee] sheel members containing marten site are joined through resistance spot welding, As a result, it is possible to manufacture liigh-strcngth automotive parts exhibiting, for example, excellent occupant protection performance at the time of impact. Further, it is possible to prevent fractures in Ihe spot-welded portion formed in the overlapped portion, in ihe case where sleel sheet members made out ofa plurality of steel sheets including a galvanized steel sheet having a hot-dip galvanncal coating or a hol-dip galvanizing coating formed thereon arc joined through resistance spot welding. Brief Description of Ihe Drawings [0031J HG. 1A is a schematic view showing an example of a flange to which the present n invention is applied. FTG, IR is a diagram showing an example ofa schematic configuralion of a joint portion obtained by overlapping a plurality of steel sheet members to which the present invention is applied. 1'IG. 2A is a diagram showing an example in which the present invention is applied to a hot stamped member of 1500 MPa class, FIG. 2R is a sectional view laken along line 1-1 of FIG 2A and showing the example in which the present invention is applied to the hot stamped member of 1500 MPa class. FIG. 2G is a schematic view showing a spot-welded portion shown in FIG. 2A. as viewed from the surface of the steel, Ihe leii half of which shows a case where a laser beam is not applied, and the right halfol" which shows a case whore the present invention is applied, FIG. 3A is a diagram showing a distribution of hardness in the portion indicated hy the broken line A in FIG. 2C, FIG. 3B is a diagram showing a distribution oThardness in the portion indicated by the broken line B in FIG. 2C. FIG. 3C is a diagram showing a distribution ofhardness in the portion indicated by the broken line C in FIG. 2C. FIG. 4A is a diagram showing an example of an effect obtained by the present invention, and showing a test piece obtained through a conventional resistance spot welding. FIG. 4R is a diagram showing an example of an clTcel obtained by the present invention, and showing a test piece obtained tiirough a welding method according to the present invention. FIG. 4C is a diagram showing an example of an effect obtained by the present hwention, and showing slress-strain curves ofihe test pieces shown in FIG, 4 A and FIG, 4B. FICi. 5A is an explanatory diagram showing a relatiortship between a spot-wcldcd 12 portion and a nicltcd arid solidified portion in the case of a first example of a combination of steel sheets. FIG- 5R is an explanatory diagram showing a relationship between a spot- welded portion and a melted and solidified portion in the case of a second example of a combination of steel sheets. FIG. 5C is an explanatory diagram showing; a relationship between a spot-welded portion and a melted and solidified portion in the case of a Ihivd example of a combination of steel sheets, FIG, 5D is an explanatory diagram showing a relationship between a spot-welded portion and a melted and solidified portion in the case of a fourth example of a combination of steel sheets. FIG. 6A is a diagram showing an example in which an overlap-welded member according to the present invention is applied to a B-pillar. FIG- 6R is a diagram showing an example in which the overlap-welded member according to the present invention is applied to an A-pillar, a B-pillar, and a roof rail. FIG. 6C is a diagram showing an example in winch the ovcrlap-wcldcd member according to the present invention is applied to an A-pillar and a side sill. FIG. 6D is a diagram showing an example in which ihe overlap-welded member according lo the present invention is applied lo a bumper reinforce, FIG. 7A is a schematic view showing a first example of how the spot-wcldcd portions and the melted and solidified portion, each of which is according to the present invention, arc formed. FIG. 7B is a schematic view showing a second example of how Ihe spot-welded portions and the melted and solidified portions, each of which is according to the present invention, are formed. FIG. 7C is a schematic view showing a third example of how the spot-wcldcd portions and the melted and solidified portions, each of which is according to the present invention, are formed, FIG. 70 is a schematic view showing a fourth example of how the spot-welded 13 portions and the melted and solidified poitions, each of which is according to the present invention, arc formed. 1JIG. 7E is a schematic view showing a fifth example of how the spot-wcldcd portions and the melted and solidified portions, each of which is according to the present invention, are (bnned. FIG, 7F is a schematic view showing a sixth example of how Ihe spol-welded portions and the melted and solidified poitions, each of which is according to the present invention, arc formed. FIG, 7Gis a schematic view showing a seventh example of how the spot-welded poitions and the melted and solidified portions, each of which is according to the present invention, are formed. FIG. 7H is a schematic view showing an eighth example of how the spot-wcldcd portions and the melted and solidified portions, each of which is according to the present invention, arc formed. FIG. 71 is a schematic view showing a ninth example of how the spot-welded portions and the melted arid solidified portions, each of which is according to the pitsenl invention, are Ibimed, FIG. 7J is a schematic view showing a tenth example of how the spot-wcldcd portions and the melted and solidified poitions, each of which is according to the present invention, are formed. FIG. 7K is a schematic view showing an eleventh example of how the spol-welded portions and Ihe melted and solidified portions, each of which is according to Ihe pi'cscn! invention, arc formed. FIG. 7Lis a schematic view showing a twelfth example of how the spot-welded poitions and the melted and solidified portions, each of which is according to the present invention, are formed* FIG. KA is a diagram showing a first example in which a high-strength steel sheet and a low-strength steel sheet are overlapped, and a laser beam is emitted from the side of the surface of the high-strength steel sheet to form a melted and solidified portion. 14 FIG. HB is a diagram showing a second example in which a high-strength steel sheet and a low-strength steel sheet are overlapped, and a lasei beam is emitted from the side of the surface of the low-strength steel sheet to form a melted and solidified portion. FIG. %C is a diagram showing a Ihhd example in which a high-strength steel sheet and a low-slrength steel sheet are overlapped, and a laser hcam is emitted from the side of the surface of the high-strength steel sheet to form a melted and solidified portion. MG. SD is a diagram showing a fourth example in which a high-strength steel sheet and a high-strength steel sheet are overlapped, and a laser beam is emitted ivom the side of The surface of the high-strengih steel sheet to form a melted and solidified portion. FIG. 8F rs a diagram showing a fifth example in which a low-strength steel sheet, a high-strength steel sheet, and a low-strength steel sheet arc overlapped in this order, and a laser beam is emitted from the side of the surface of the low-strength steel sheet to form a melted and solidified portion. FIG. SF is a diagram showing a sixth example in whieh a low-strength steel sheet, a high-strength steel sheel, and a low-strength sleel sheet are overlapped in Ihis order, and a laser beam is emitted from the side of (he surface of the low-strength steel sheet to form a melted and solidified portion. FIG. 9 A is an cxplanat017 view showing the influence of laser emission on the spot-welded portion, and is a diagi'am showing the spot-welded poilion and the melted and solidified poilion formed in the overlapped portion made of an uneoaled high-strength steel sheet (1500 MPa) and an uncoated low-strength steel sheet (440 MPa). FIG, 9B is an explanatory view showing the influence of laser emission on the spot-welded portion, and is a diagram schematically showing a hole defect of the spot-wcldcd portion and the melted and solidified poilion formed in the overlapped poilion made of an uneoaled high-strength steel sheet (1500 MPa) and a hot-dip galvannealed low-slrength steel sheet (440 MPa). FIG. 10 is a sectional view showing a contact portion in the spot-wcldcd portion. FIG. 11A is a diagram showing an example 111 whieh a hot-dip galvannealed low-strength steel sheet and an uneoaled high-slrenglh sleel sheel are overlapped, and a 15 laser beam is emitted from the side of the high-strength steel sheet, thereby forming the melted and solidified portion. Hti. 1 IB is a diagram showing an example in which, a Iiot-dip galvannealed low-strcngfh steel sheet, an uncoated high-shength steel sheet, and an uncoated low-strcngfh steel sheer are overlapped, and a laser beam is emitted Prom the side of the uncoated low-strength steel sheet, thereby forming the melted and solidified portion. FIG, IK] is a diagram showing an example in which a hot-dip galvanncalcd low-strength steel sheet, a high-strength steel sheet having a surface containing an iron-zinc solid solution phase and a zinc oxide layer, and an uncoated low-strengih steel sheet arc overlapped, and a laser beam is emitted from the side of the uncoated low-strength steel sheet, thereby forming the melted and solidified portion. FIG. 11D is a diagram showing an example in which a hot-dip galvanncalcd low-strength steel sheet, an uncoated high-strength steel sheet, and an uncoated high-strength steel sheet arc overlapped, and laser bean is emitted from the side of the uncoated high-strength steel sheet, thereby forming the melted and solid) lied portion, FIG. HE is a diagram showing an example in which a hot-dip galvanncalcd low-strength steel sheet, an uncoated low-strength steel sheet, and an uncoated high-strength steel sheet are overlapped, and a laser beam is emitted from the side of the uncoated high-strength steel sheet, thereby forming the melted and solidified portion. FIG. 1 IF is a diagram showing an example in which u hot-dip galvannealed low-strength steel sheet, an uncoated low-strength steel sheet, and an uncoated high-strength steel sheet are overlapped, and a laser beam is emitted from the side of the uncoated high-strength steel sheet, thereby forming the incited and solidified portion. FIG. 12A is a diagram showing a test piece used in Example 1 according to the present invention. FIG. 12B is an enlarged view showing the test piece used in Example 1 accoi'ding to the present invention, and is apian view showing a direction in which tensile load is applied. FIG. 12C is an explanatory view showing the shape of the test piece used in Example I according to the present invention, and is a sectional view taken along linell-II of FIG. 12B. FIG. 13A is a diagram showing a test piece used in Example 2 according to Iho present invention, FrG, 13B is an enlarged view showing the test piece used in Example 2 according to Uie present invention, and is a plan view showing a direction in which tensile load is applied. FIG. 13C is an explanatory view showing (he shape of the Lest piece used in lixaniple 2 according to the present invention, and is a sectional view taken along line III-IIIofFIG. 13R. FKJ. 14 is a graph showing an example of a distribution of hardness in a spot-wcldcd portion of a hot stamped member of 1500 MPa class. FIG. l5Ais a diagram as viewed from the surface of a steel and showing the stale of the fracture from a IIAZ softening zone when tensile load is applied to the spoL-wclded portion shown in FIG- 14, FIG, I5B is a sectional view showing a contact portion ma state where a fracture occurs from the HAZ softening zone when tensile load is applied to the spot-welded portion shown in FIG. 14. Embodiments oFthe Invention [0032] in order to solve die problems described above, the present inventors carried out a study of techniques of preventing fracture of uIIAZ softening /one in a spot-welded portion in an overlapped portion in an overlap-welded member formed by joining together a plurality of steel sheet members, As a result, it was found tlvat the strength of the spot-welded portion can be improved by emitting a laser beam onto the spot-wekled portion to form a melted and solidified portion so as to cross an end ola nugget and range from the nugget up to the outside of the softest zone in a HAZ. 17 [0033J The present invention is based on findings lhat, in the case where a plurality of steel sheet membm ai'e overlapped and joined through resistance spot welding, if at least one of the plurality of steel sheet members contains martcnsitc, it is possible to make full use of the strength of a higb-strcngth steel sheet or hot stamped member by emitting a laser beam onto an area ranging train a nugget of the spot-welded portion and crossing an end of the nugget to form a melted and solidified portion, whereby a HAZ softening zone in the spot-welded portion is haixlened lo prevent fractures in the HAZ, In this specification, the high-strength steel sheet containing marlensite includes, for example, a steel sheet member (for example, press formed article) made out of a high-slrcngtb steel sheet of 980 MPa class, or a 1200 MPa class or higher, and a hot stamped member containing martensite generated through forming using hot stamping. [0034] Further, the present inventor found that* regardless of whether the steel sheet member made out of the high-strength steel sheet or the hot stamped member is contained, in the ease where the plurality of steel sheet members arc overlapped and joined through resistance spot welding, and laser beam is emitted onto the spot-wcided portion to form the melted and solidified portion extending from Ihe nugget to the outside of the nugget, if at least one of the steel sheet membeis is made out of a galvanised steel sheet having a hot-dip galvanneal coaling or a hot-dip galvanizing coating foimcd thereon, it Js significantly effective to form the melted and solidified portion in a manner such that the depth of the melted and solidified portion at a portion corresponding to a contacting surface of the spot-welded portion is shallower than a contacting surface having a hot-dip galvanneal coating or a hot-dip galvani/Jng coating formed thereon, [0035] Hereinbelow, the present invention made on the basis of the findings described above will be described with reference to the first embodiment and the second embodiment desciibed below, First, Ihe first embodiment according to the present invention will be described IS with reference to FTG. 1 A to FIG. HF. [0036| (First Embodiment) FIG. 1A is a schematic view showing an example of a flange to which the present invention is applied, and FTG, IB is & diagram showing an example of a schematic configuration ofa joint portion obtained by overlapping a plurality of steel sheet members to which the present invention 3s applied. [00371 FIG. 1A shows an example ofa state in which a plurality of spot-wcldcd portions 10 are foimed through resistance spot welding in a direction in which a flange (overlapped portion) 1 extends, and a laser beam LB is emitted so that melted and solid! lied portions IS arc formed through emission ofa laser beam so as to cross ends ofa nugget 12 of each of the spot-wcldcd portions 10. It should be noted that The flange I is formed by overlapping a flange 2F, which is a formed article (steel sheet member) 2 made out of a steel sheet, and a flange 3F> which is a formed article (steel sheet member) 3 made out of a steel sheet, [003S] In this first embodiment, cither of or both of the steel sheets formed into the formed article 2 and the formed article 3 are: (a) a steel sheet member obtained by cold press forming a high-strength steel sheet (for example, high-strength steel sheet of 1200 MFa class or higher) containing martensite, or (b) a hot stamped member (for example, steel sheet member having a tensile strength of 1200 MPa or higher) having niartensite generated as a result of forming a steel sheet for a hot stamped member using hot stamping. This means that at least one steel sheet member containing the martensite is included. L0039J When the overlapped portion of the steel sheet members obtained by forming the high-strength steel sheet or the steel sheet members made out of the hot stamped member 19 is subjected to resistance spot welding, a IIAZ softening zone is formed in the spot-wcldcd portion. Due to this HAZ softening /.one, the strength of the spot-welded portion is significantly lower than that of the high-strength steel sheet (base metal). However, through emission of a laser beam, the melted and solidified portion is formed. This makes it possible to harden the IIAZ softening zone, and prevent fractures caused by stress concentration on the TTAZ softening zone, whereby it is possible to make full use of the strength ol'lhe high-strength steel sheet 01 hot stamped member, [0040] hlti. IB is a diagram showing an example of a schematic configuration of a joint portion obtained by overlapping three (a plurality of) steel sheet members to which the present invention is applied. FIG. IB shows how a high-strength steel sheet 511, a high-strenglh steel sheet 611, and a low-strength steel sheet 71. are overlapped, the spot-welded portion 10 having the nugget 12 is formed through resistance spot welding, and a laser beam is emitted from (he side of the high-strength steel sheet 5H, thereby forming the melted and solidified portion 15 extending across the nugget 12. It should be noted that, in FIG. IB, the thicknesses of the high-strength steel sheet 511, the high-strength steel sheet 6H, and the low-strength steel sheet 7T- are (5,to", and 17, respect! vely. 10041J It should be noted that, in this specification, the high-strength steel sheet includes an i1unfornied high-strength steel sheet," a "steel sheet member obtained by forming o high-strenglh steel sheet," and a "hot stamped member obtained by forming a hot-stamping steel sheet through hot stamping." Further, the low-strength steel sheet includes an "unformed low-strength steel sheet," and a "steel sheet member obtained by forming a low-strength steel sheet member.'' Yet further, the steel sheet includes an *^in formed high-strength steel sheet/' an 20 "unformed low-strength steel sheet," a "steel sheet member obtained by forming a high-strenglh steel shed," a "hot stamped member obtained by farming a hot-stamping steel sheet through hot stamping," and a "steel sheet member obtained by forming a low-strength steel slice!." [00421 In FIG. ID, the nugget 12 is formed tlirough the high-strenglh steel sheet 5H, the high-strength steel sheet 6H, and the low-strength stee! sheet 7h so as to join these steel sheets, The melted and solidified portion 15 is formed, for example, so as to start from a distance of LI externally away from one end of the nugget 12 through flic nugget 12 to a distance of L2 externally away from the other end of the nugget. Further, the melted and solidified portion 15 is farmed throughout the entire thickness t5 (100%) of the high-strength steel sheet 5H and fwlher to a middle point iri the thickness 16 ol'the high-strength steel sheet 6H in a direction from the high-strength steel sheet 5H toward the low-strength steel sheet 7L. Here, the end of the nugget 12 means the maximum shape (outer boundary) of the nugget 12 when the overlapped portion formed by overlapping a plurality of steel sheet members is viewed from the surface of the steel. [0043] The reference characters LD5 and LD6 in FIG. IB represent the depths of the melted and solidified portion 15 in the liigh-strcngth steel sheet 511 and the high-strength steel sheet 611, respectively, at a position externally spaced apart from the end of the nugget 12 by 1 mm. To prevent fractures in the HAZ softening zone, it is effective for the high-strength steel sheet to have the depth of the melted and solidified portion 15 > 50% of the thickness (here, LD5 > 50% of t5 and LD6 > 50% of t6 for the high-strength steel sheets 511, 611, respectively). It should be noted lhat; in FIG. i B, the high-strength steel sheet 5H and the high-strength steel sheet 6H arc high-strength steel sheets, and the melted and solidified 21 portion 15 is formed throughout the entire thickness of tlie high-strength steel sheet 5H (in other words, LD5 = thickness t5). Thus, the eifect can he sufficiently achieved by setting the depth LD6 of the melted and solidified portion 15 in the high-strength steel sheet 611 to be larger than or equal to 50% of the thickness t6. 1.0044] Here, the depth LD of the melted and solidified portion 15 is defined at the position externally spaced apart from [he end of the nugget 12 by 1 mm. This is based on the feet that, as shown in FIG, 14, the softest/one 103A in HAZ, of the spot-welded portion 110 is located at a position externally spaced apart from the end of the nugget 112 by approximately 1 mm, and hence, forming the melted and solidified portion in the vicinity of the softest zone 103AinllAZ is effective in hardening the HAZ softening xonc. [0045] It should be noted that FIG. IB shows an example in which the melted and solidified portion 15 passes tlirongh the central portion of tlie nugget 12 when the overlapped portion is viewed from the surface of the steel, and extends across the nugget 12 at two ends of the nugget 12, which are the right end and the left end of the nugget 12, However, the positions and the number of the positions at which the melted and solidified portion 15 passes through the ends of the nugget 12 arc not limited to two, and the number thereof may be one, or three or more. Further, in die case where the melted and solidified portion 15 crosses two positions, it may be possible for these positions to be located on the same extended line and on both sides of the central portion of the nugget 12. Howcvcr;thc positions do not necessarily have to be located on the same extended line and at both sides of the central portion of the nugget 12. [0046| Further, in the case where the melted and solidified portion 15 is formed so as to cross two or more ends of the nugget 12, it is preferable that the depth LD of the melted 22 and solidified portion 15 at a position externally spaced apart from the end of the nugget I2by ] inm satisfies LD > 50% of the thickness. However, it may be possible that a certain part of the melted and solidi lied portion 15 crossing (he end or the nugget 12 does not satisfy LD > (50% oflne thickness). Further, it is preferable that the melted and solidified portion 15 is formed so as to extend from the end of the nugget 12 for a length of 3 nun or longer. However, the length may be 3 nun or shorter. [0047] FIG. 2A is a diagram showing an example in which two members, which are a hot stamped member (slecl sheet member) of 1500 MPa class and a hot stamped member (steel sheet member) of 1500 MFa class, arc overlapped according to tire present invention. More specifically, FIG. 2A shows an example in which the spot-welded portion 10 having the nugget 12 is formed in a Ilange 4A ol'(he hot stamped member through resistance spot welding, and a laser beam iscmtUcd onto the spot-welded portion 10, thereby forming the melted and solidified portion 15. 10048] FIG. 2B is a sectional view taken along line I-I of FIG. 2A. FIG. 2C is a schematic view showing the spol-welded portion shown in FIG, 2A and the surroundings thereof as viewed from Ihe surface of the steel. It should he noted that, for the purpose of explanation, the let! half of the view in FIG. 2C with respect to the central line shows a conventional state in which a laser beam is not emitted onto the spot welded portion 10, and the right half shows a stale in which a laser beam is emitted onto the spol-welded portion 10 to form the melted and solidified portion 15. Further, FIG. 3A, FIG. 3B, and FIG. 3C arc diagrams showing hardness distributions of portions indicated by the broken line A, the broken line B> and the broken line Cm FIG. 2C, [0049] 23 The conventional spot-welded portion 10 is similar to that of the left half of FIG. 2C,andin the portion indicated by the broken line A and shown in FIG. 3 A, a IIAZ softening zone 13 is formed in a large area, Tins means Chat a large avea ol'ihe HAZ softening zone 13 is pulled when tensile load is applied in Che horizontal direction. This leads to a reduction in strength against tensile load, and fractures are more likely to occur resulting from tensile load. On the other hand, hi the case where Ihe melted and solidified portion 15 is formed between the nugget 12 and Che HAZ softening zone 13 so as to cross Che end o I" the nugget 12 by emission of a laser beam as shown in the right half of FIG. 2C, part of the IIAZ softening ^one of the portion indicated by the broken line li and shown in FIG. 31i is hardened with the melted and solidified portion 15, and the area of the IIAZ softening zone 13 reduces. As a result, the strength of the spot-welded portion 10 improves, and Che tensile strength improves, On Ihe other hand, Ihe niched and solidified portion 15 and a HAZ softening zone 15A are Jointed in a portion indicated by the broken line C in FIG. 2C onto which only a laser beam is emitted. However, as shown hi FIG. 3C, the area of the IIAZ softening /.one 15A is small, and hence, the tensile strength is not affected, [0050] Next, an example of an effect obtained by the present invention will be described with reference to FIG. 4A to HG. 4C. FIG. 4A shows a test piece T0I obtained through conventional resistance spot welding, and the test piece T01 has Che spot-welded portion 10 having the nugget 12 formed thereon. FIG. 4B shows a test piece T02 obtained through a welding method according to the piusenl invention, and the test piece TG2 has the melted and solidified portion 15 formed through emission of a laser beam so as Co cross two ends of the nugget 12, FIG. 4C shows a stress-strain curve concerning the tesC pieces T01 andT02, 24 The reference character A indicated hy the broken line represents the results of the lest piece TGI s and the reference character li indicated hy the solid line represents the results of the test piece T02. [0051] As shown in FIG. 4C, by emitting u laser beam onto the spot-welded portion 10 U> foim the melted and solidified portion 15, it is possible Eo significantly improve the critical fracture strain in the case of application of tensile load in comparison with the spot-welded portion 10, aud prevent fractures in 11AZ, for example, at the time of impact. T0052] As described above, by forming the moiled and solidified portion 15 so as to extend across the nugget 12 of the spot-welded portion 10 to obtain the configuration as shown in FIG. IB, it is possible to reduce the area of the HAZ softening zone ol the spot welding where fractures arc more likely to occur due to tensile load in the case of only the resistance spot welding. With this ton figuration, it is possible to improve deformability until fracture at ihe time when tensile load is received, [0053] FIG. 5Ato FICi. 5D arc explanatory diagrams showing examples of combinations of a plurality of steel sheets overlapped, and relationships between a spot-welded portion and a melted and solidified portion obtained through emission of a laser beam. [0054] FIG. 5A is an explanatory diagram showing the first example ofa combination of steel sheets, and shows a case where a low-strength steel sheet 31L (thickness 13 I) and a high-strength steel sheet 3211 (thickness t32) are overlapped, and a laser beam is emitted from the side of the high-strength steel sheet 3211 to form the melted and solidified portion 15(depthL15). In FIG. 5A, the reference character LU32 represents the depth of the melted and solidified portion 15 in the high-strength steel sheet 3211. [0055] 25 As shown in FJG. 5 A, in ihc first example, the melted and solidified portion 15 is formed throughout the entire thickness of the high-strength steel sheet 3211 (100% of the thickness t32) and up to a middle point of the low-strength steel sheet 31L in a thickness direction from the side of the high-strength steef sheet 32H to the opposite-side surface, In the first example, the high-strength steel sheet 32H is the only high-strength steel sheet, and the melted and solidified portion 15 has the depth LD32 formed throughout the entire thickness of the high-strength steel sheet 3211 hi the thickness direction (LD32 - (100% of the thickness 132) > (50% of the thickness 132)). Thus, it is possible to achieve sufficient effects. [0056] Fit J. SB is an explanatory diagram showing the second example of a combination of steel sheets, and sliows a case where a high-strength steel sheet 3 111 (thickness t31) and a high-strength steel sheet 3211 (thickness t32) are overlapped, and a laser beam is emitted from the side of the high-strength steel sheet 3211 to forni the melted and solidified portion 15(depthL15). In FIG, SB, the reference characters LD3I and LD32 represent the depths of the incited and solidified portions 15 in the high-strength steel sheet 31H and the high-strength steel sheet 32H, respectively. [00571 As shown in FIG. 5B, in the second example, the melted and solidified portion 15 has the depth LD 32 formed IhreughouE the entire thickness of the high-strength steel sheet 32H (LD32 = (3 00% of the thickness t32», and is formed up to a middle point of the high-strength steel sheet 3111 hi a thickness direction from the side of the high-strength steel sheet 3211 to the opposite-side suriace. In the second example, the high-strength steel sheet 31H and the high-strength steel sheet 32H are the high-strength steel sheets, and the melted and solidified portion 15 is formed throughout the entire thickness of the high-strength steel sheet 3211 (LD32 = (100% of the thickness t32) > (50% oflhe thickness 132)). Thus, by setting the depth LD31 hi the high-strength steel sheet 31HU) be I.D31 > (50% or thickness 131), it is 2G possible to aehievc sufficient effects. |00581 FIG. 5C is an explanatory diagram showing the third example of a combination of steel sheets, and shows a case where a low-strength steel sheet 311, (thickness 01), a high-strength steel sheet 32H (thickness (32), and a low-strength steel sheet 331, (thickness 133) ai'e overlapped, and a laser beam is emitted from the side of the low-strength steel sheet 3lLto form the melted and solidified portion 15 (depth L15). In. FIG. 5C, the reference character LD32 represents the depth of the melted and solidified portion 15 in the high-strength steel sheet 32H. [0059] As shown in FIG. 5C, in the third example, the melted and solidified portion 15 is formed throughout the entire thickness of the low-strength steel sheet 31L, and is formed up to a middle point of the high-strength steel sheet 3211 in. a thickness direction fiom the side of the low-strength steel sheet 31L to the side of the low-strength steel sheet 33L, hi the third example, the high-strength steel sheet 32H is the only high-strength steel sheet. Thus, hy selling the depth LD32 of the melted and solidified portion 15 in the high-strength steel sheet 32H to be LD32 > (50% of the thickness t32), it is possible to achieve sufficient effects. [00601 FIG. 5D is an explanatory diagram showing the fourth example ol'a combination of steel sheets, and shows a case where a high-strength steel sheet 3 IH (thickness 131), a high-sti englh steel sheet 32H (thickness t32), and a low-strength steel sheet 33 L (thickness 133) are overlapped, and a laser beam is emitted from the side of the high-strength steel sheet 3 III to form the melted and solidified portion 15 (depth LI 5). In FIG. 5D> the reference characters I.D31 andT-D32 represent the depths of the melted and solidified portion 15 in the high-strength steel shccl3IH and the high-strength steel sheet 32H, respectively. f0061] As shown in FIG. 5D,in the fourth example, the melted and solidified portion 15 27 is forme J throughout the entire thickness of the high-strength steel sheet 3111 (LD31 ~ (100% of the thickuess t31)), and is formed up to a middle point of the high-strength sleet sheet 3211 in a thickness direction from the side of the high-strength steel sheet 31H to the side of the low-strength steel sheet 33L. In the fourth example, the high-strength steel sheet 3 111 and the high-strength sleef sheet 32H arc the high-strength steel sheets. Thus, by setting the depth LD32 of Ihe melted and solidified portion 15 in the high-strength steel sheet 32H to be I.D32 > (50% of the thickness 132), it is possible to achieve sufficient effects. [0062] The first embodiment is directed to the overlap-welded member in which a plurality of steel sheet members are joined at the overlapped portion, and the steel sheet members, at least one of which steel sheet member contains the mai tensile, are joined through resistance spot welding, The first embodiment is applied to form various kinds of structures including, for example, a monocoquc body constituting an automotive vcluclc body, and an automotive purl (assembly part) such as an A-piliar and a B-piliar constituting the monocoque body. L0063J The overlapped portion of the steel sheet member is usually a llange (overlapped portion) formed at the edge of each steel sheet as a tab for spot welding with another steel sheet. However, the overlapped portion is not limited to the flange. The overlapped portion may be one obtained by applying resistance spot welding to a portion where a llange overlaps with, for example, a shaped portion (portion other than the lhmge). 100641 Examples of Ihe steel sheet member containing the martensite include a cold press-formed article made out of a high-strength steel sheet (for example, a high-tensile steel sheet having a tensile strength of 1200 MPa class or higher) having a quenched structure containing martensite formed through continuous annealing equipment, and a hot stamped member having a [ensile strength of 1200 MlJa or higher and strengthened by heating a steel sheet for hot stamping to austenke temperatures or higher, and quenching 28 the steel sheet while forming it with water-cool die. [0065] The effects can be obtained if a high-strength sleel sheet con lams marlensite posing a risk offracture in spot welding due to softening of HAY,. However, the effects can be increased in the ease of a high-strength steel sheet having a tensile strength of 1200 MPa or higher. Thus, it is preferable to set the lower limit of a tensile strcngdito 1200 MPa. Further, although selling the upper limit of a lensile strength is nol necessary, Ihe upper limit may be set to approximately 2000 MPa for practical consideration, [0066] Further, although setting limitation on the thickness of the steel sheet is not necessary, the lower limit of the thickness may be set to 0.7 mm for practical consideration, and it is preferable to set the upper limit to 2.6 mm, [00671 In the case of a cold rolled material, the high-strength steel sheet having a tensile strength of 1200 MPa or higher includes an uncoatcd steel sheet that docs not have any coaling on the surface thereof, and a steel sheet on winch zinc-based coating, including hot-dip galvanncaling (GA coating) and hot-dip galvanizing (GI coating), is formed. The hot stamped member includes an uncoaled sleel sheel member an aluniEnized sleel sheet member, a steel sheet having a coating of an intcrmctallie compound of iron and aluminum, and a steel sheet member having an iron-zinc solid solution layer and a zinc oxide layer coating thereon. [00681 The steel sheet lo be overlapped with the high-stitngth stee! sheet described above may be a high-strength stee] sheet or hot stamped member having a tensile strength of 1200 MPa class or higher, or a steel sheet having a tensile strength of 270 MPa to 9S0 MPa classes. Further, Ihe number ofsleel sheets to be overlapped is not limited lo two, and three or more sleel sheets may be overlapped. 29 |00691 Below, resistance spot welding will be described in detail. During the resistance spot weldingprocess, apluralily of steel sheet membeis are overlapped with each other, and resistance spot welding is applied to the overlapped portion, thereby forming a spot-wcldcd portion having a nugget. [0070] Welding conditions for the resistance spot welding are not specifically limited, provided that a nuggel with a nugget diameter of not less than 4\l and not more than 7\l (t: thickness (min) on the thinner side in the overlapped .surface) is foniied at least in the steel sheet member to be joined depending on applications. lor example, using a single-phase AC spot welding machine or inverter DC spot welding machine, it is only necessary to form the nugget described above in the overlapped portion, by employing the following conditions as appropriate: the diameter of the top end of a welding elechTtde: 6 mm to 8 mm; the radius of curvature R of the top end: 40 mm; squeezing force: 2.5 kN to 6.0 kN; electric current value of welding current; 7 kAto 11 kA: and power supply time in the range of 10/60 second to 40/60 second. It should be noted that the conditions for spot welding arc not limited to those described above. The conditions may be set as appropriate depending on types of steel, thickness, or other parameter, [0071J The pitch for resistance spot welding is usually set in the range of approximately 20 mm to 60 mm. However, the pitch is not limited to this, and may be set as appropriate depending on a structure to be welded or portions of the structure to be welded. [0072] Below, formation of the melted and solidified portion through emission of a laser beam will be described in detail. To a process olh forming a melted and sulidilied portion, a laser beam is emitted onto the overlapped portion to form the melted and solidified portion that crosses an end 30 of the nugget and is located between the nugget of the spot-welded portion formed through resistance spot welding and the base mat eiial or ITAZ located outside of the nugget, [0073] in other words, after resistance spot welding is applied, a laser beam is emitted onto the overlapped portion, to form the melted and solidified portion so as to extend across the IIAZ softening zone formed around the nugget, thereby hardening the IJAZ softening ysync. AH a result, the melted and solidified portion divides the HA7, softening M)tte> whereby it is possible to suppress a reduction in the strength resulting from the HAZ softening zone in an expected direction of stress. [0074] Below, an example in which the present invention is applied to an automotive part will he described with reference to FIG, GA to FIG, GD. FIG. 6A to FIG. 6C arc diagrams showing an example in which the present invention is applied to a monocoquc body constituting an automotive vehicle body, and is applied to an important member (automotive part) that protects occupants hi the cabin in the case of side collision. [0075] FIG. 6A is a diagram showing an example in which the overlap-welded member according to the present invention is applied to a JJ-pillar 41. The B-pillar 41 has a flange on which a plurality of spot-welded portions 10 arc formed along a direction in which the (lange extends, and the melted and solidified poilion 15 is formed through emission of a laser heam so as to extend across the plurality of spot-welded portions 10. [00761 Furthermore, for example, In the case of the B-pillar 41, it is preferable to set the expected direction of stress to a direction along an end surface-of (he sleel sheet member oflhe Hange (overlapped portion) of the B-pillar 41. 31 Furthermore, Ihe flange of the B-piilar41 has a lower pail curved in the front and reai direction of the vehicle body, and hence, it is preferable lo set the expected direction of stress to a direction along the curved end surface of the steel sheet member of the flange (for example, a tangent direction at an end surface of the steel sheet member closest to each of the spot-welded portions 10). II should be noted that, as shown m FIG. 6A, ii may be possible to form a plurality of melted and solidified portions ]5> and it may be possible to employ a configuration in which not all the spot-welded portions EOA arc extended across by the melted and solidified portion 15. [0077] FIG. 6R is a diagram showing an example in which the overlap-welded member according lo the present invention is applied to an A-piHar 40, lheR-pillar41, and a roof rati 42. Fach of the A-piMai40, the B-pillar 41, and the roof rail 42 has a plurality of spot-welded poitions 10 formed along a direction in which the flange extends, and has the melted and solidified portion 15 formed with the emission of a laser beams so as to extend across the plurality of spot-welded poitions 10. [0078] Further, as shown in FIG. 6B, in the case of the flange having curves such as the portion where the B-pillar 41 and the A-pillar 40 arc connected and the portion where the B-pi]lar41 and the roof rail 42 are connected, the plurality of spot-wcldcd portions 10 arc formed along the curved flange, and the melted and solidified poilion 15 is formed through emission of a laser beam so as to extend across these plurality of spot-welded portions 10. lr should be noted that, in the curved poitions described above, ii is preferable to set the expected direction of stress to a curved direction of the end surface of the steel sheet member oT the flange as in the case shown in FIG. 6A (for example, the tangent direction at an end surface of the steel sheet member closest lo each of the spot-welded portions 10). 32 Further, it may be possible to form a plurality of melted and solidified porlions 15, and it may be possible to employ a configuration in which not all the spot-wcldcd portions are extended across by the melted and solidi fied portion 15. [0079] FIG- 6C is a diagram showing an example in which the overlap-welded member according to the present invention is appiicd to the A-pillar 40 and a side sill 43. The side sill 43 has a flange on which a plurality of spot-welded portions 10 arc formed along a direction in which the flange extends. Further, for example, the melted and solidified portion 15 extending across two adjacent spot-welded portions 10 is formed through emission of a laser beam in a manner such that the melted and solidi lied portion 15 is partially divided, and spaces are provided therebetween. As described above, by dividing the melted and solidified portion 15 and leaving the base metal, having no processing applied, between the melted and solidified portions 15, it is possible to achieve toughness that the high-strength steel sheet originally has. The same effect resulting from the spaces formed by dividing the melted and solidified portion 15 as described above can be obtained in the examples shown in FIG. 6Aar.dFIG.6B. [0OH0J By applying the present invention to the structural element disposed around the cabin as shown in FIG- 6A to FIG- 6C, it is possible to prevent the structural element from fracturing due to softening ol'HAZ at the spot-welded portion 10, whereby it is possible (o enhance safety against side collision. Further, it is preferable that the melted and solidified portion 15 is formed so as to have intersection angle 0 within :i 30° with respect to the expected direction of stress, [0081] Further, FIG. 6D is a diagram showing an example it! which the overlap-welded member according to the present invention is appiicd to a bumper reinforce 44 that protects occupants in the case of front-end collision or rear-end collision. In the case of the bumper reinforce 44 shown in FIG. 6D, a bulkhead 45 is 33 provided inner side of the body of the bumper reinforce 44 in order lo maintain the cross section thereof, and the bulkhead 45 is subjected to resistance spot welding, thereby forming the spot-welded portion 10. In the case of the bumper reinforce 44, a bending force acts in the front and rear direction, which intersects the longitudinal direction of the bumper reinforce 44, al the time of front-end collision or rear-end collision. For Ibis reason, il is preferable to form the melted and solidified portion 15 by emitting a laser beam so as to intersect with the longitudinal direction of the bumper reinforce 44 at an intersection angle G foiling within ±30° on the assumption that stress is expected to act in the longitudinal direction of the bumper reinforce 44. [0OS2] It should be noted thai, in the case of a member [hat receives bending as a result of collision, the expected direction of stress is a direction along the end surface of the stccf sheet member, and hence, the stress acts on the member in a direction perpendicular to a plane connecting the inside and the outside of the cabin. |00831 Next, examples of how the spol-wekled portions and the melted and solidified portions are formed will be described with reference to FIG. 7 A to FIG. 7L FIG, 7A to FIG. 7L arc schematic diagrams cxcmplarily showing how the spot-wefded portions and the melted and solidified portions, each of wliich is according to the present invention, arc formed. [00841 FFG. 7 A is a schematic diagrams showing the first example of how the spot-welded portions and the melted and solidified portions, each of which is according to the present invention, arc formed, and shows an example in wliich a flange portion 5F of a formed article (steel sheet member) 5 and a flange portion 6F of a formed article (steel sheet member) 6 are overlapped to form a llange 4, and laser is emitted onto the nuggel 12 of the spot- welded portion 10 formed on die flange 4 to form the melted and solidified portion 15. 34 [0OS5] Tlis desirable that the direction of the melted and solidified portion 15 formed be set so as to fail within angles 0 of:i.30Q with reaped to the direction in which the llange (joint portion) 4 extends, or with respect lo me expected direction of stress (with itspect lo the horizontal direction in FIG, 7AJ as shown in FIG. 7A, II is more preferable to set the intersection angle 8 so as to fail within ±15°. [0086J For example, the A-pillar, the B-pillar, the roof rail, the side sill, and the bumper reinforce as shown in FIG. 6A to FIG. GD are configured such thai the flange, which is joined so as To form a lubular closed cmss section, is used as a lab for joining. In many cases, al the time of impact, tensile load acts in a direction along the end surface of the steel sheet member of the flange. For this reason, it is preferable to emit a laser beam so that the laser beam runs in a direction along die flange, thereby forming the melted and solid! lied portion 15 thai extends across the nugget 12 ofthe spot-weldedporlion 1 p. Further, in Ihe case of the inside of a long pari, tensile load frequency acts in a direction along Ihe longitudinal direction of the part. Thus, it is preferable to emit a laser beam so thai the laser beam runs in the direction along the longitudinal direction of the part, thereby forming the melted and solidified portion 15 that extends across the nugget l2ofthc spot-welded portion 10. TO087] FIG- 7B is a schematic view showing the second example of how the spot-welded portions and the melted and solidified portions, each of which is according to the present invention, are formed. For example, in general, tensile load acls in the longitudinal direction of a member, in the case where (he spot-wcldcd member 10 is used for an overlapped member 8 to partially reinforce a member 7 that is not joined in a form of flange as shown in FIG. 7B, or in the case where a spol-welded portion is used for a bulkhead to overlap over a member. 35 ThusJUspreferableloemitalasei beam along the longitudinal direction of, for example, the member, thereby forming the melted and solidified portion 15. [00881 FIG. 7C is a schematic view showing the third example of how the spot-welded portions and the melted and solidified portions, each of which is according to the present invention, are formed, As shown in FKi. 7C, although it is preferable that each of the melted and solidified portions 15 formed through emission of a laser beam passes in the vicinity of the center of the nugget 12, the melted and solidified portion 15 does not have to pass through the center of the nugget 12 oflhe spot-welded portion 10. [0089] FIG. 7D is a schematic view showing the fourth example of how the spot-wcldcd portions and the melted and solidified portions, each of which is according to the present invention, arc formed. As shown in FIG. 7D5 it is desirable to form the melted and solidified portion 15 in a straight manner from the viewpoint of efficiency in emission ofa laser beam, However, it may be possible to form the melted and solidified portion 15 in a curved manner so as to have a curved portion or, for example, in a wavy manner in order to increase the length of the melted and solidified portion 15. In such cases, it is preferable that the melted and solidified portion 15 intersects with the expected direction of stress at an intersection angle 0 (ailing within ' 30D. [0090] FIG. 7E is a schematic view showing the fifth example of how the spot-wcldcd portions and the melted and solidified portions, each of which is according to the present invention, arc formed. As shown in FIG, 7A to FIG- 7D, the melted and solidified portion 15 may be formed for each of the spot-wcldcd portions 10. However, as shown in FIG. 7E, it may he possible to form the melted and solidified portion 15 so as to continuously connect a plurality of spot-welded portions 10. 36 Further, a plurality of melted and solidified portions 15 (for example, two melted and solidified portions 15) may he formed for each of the spot-welded portions 10. 10091J 1TG. 7Fisa schematic view showing the sixth example of how the spot-welded portions and the melted and solidified portions, each of which, is according to the present invention, are formed, As shown in FIG. 7F, the melted and solidified portion 35 formed through emission ofa laser beam may not be formed to be symmetrical with respect to the nugget oflhc spot-welded portion 10. However, it is desirable that the melted and solidified portion 15 exist on both sides ofthenuggel 12 oflhe spot-welded portion 10, and the distance of the shorter side between the end of the nugget and the end of the meHed and solidified portion 15 is 3 mm or longer, This is because, by setting the distance between the end of the nugget and the end of the melted and solidified portion 15 to 3 mm or longer, it is possible to sufficiently prevent strain from concentrating on the IIAZ sofEening zone. The melted and solidified portion 15 may extend across a plurality of spot-welded portions 10 as described above. 1.0092] There is no specific limitation on conditions for emission of a laser beam, and it is only necessary that predetermined melted and solidified portions 15 described above can be obtained at necessary locations. The laser welding device used includes, for example, a disk laser, a fiber laser, a direct-diode laser, a YACi laser, and a carbon dioxide laser-. The beam diameter foils in a range of 0.15 mm to 0.9 mm; the output falls in a range of 1 kW to 10 kW; and welding speed falls iii a range of 1 ni/min to 15 m/min. [0093] Welding is performed using a general torch. Alternatively, it may be possible to use remote welding or laser scam stepper having a clamping device. 37 Conditions for emission of a laser beam arc not limited to those shown as an example, and any conditions for emission of a laser beam can be applied, provided tliat the predetermined melted and solidified portions 15 described above can be obtained. [0094] It is not necessary to emit laser beams onto all the spot-welded portions 10, II is only necessary to apply laser beams only to spot-welded portions 10 that are at risk of fracture due to collision in the HAZ softening zone of die spot-wcldcd portion 10. [00951 FIG. 7G is a schematie view showing the seventh example of how the spot-welded portions and the melted and solidified portions;, each ofwhieb is according to Hie present invention, arc formed. FIG, 7G shows an example in which a laser beam is emitted onto a portion between two adjacent spot-wcldcd portions 10, thereby forming melted and solidified poitions 15 each passing through the spot-welded portion 10 and ameUedand solidified portion 15 (laser welded portion) nut passing through the spot-welded portion 10. The laser welded portion located between two adjacent spot-wcldcd portions 10 as described above is desirable because it shortens intervals between welded poitions and torsional rigidity of the member can be improved, even in the case where the overlapped portion is raised to form a gap, and joining cannot be sufficiently performed through spot welding, [0096] FIG. 7H is a schematic view showing the eighth example of how flic spot-wcldcd portions and the melted and solidified portions, each of which is according to the present invention, arc formed. As shown in FIG. 7H, it may be possible that a plurality of melted and solidified portions 15 are arranged in parallel, and pass through the spot-wcldcd poitions 10 as needed. FIG. 711 shows an example in whieh the number of the melted and solidified 38 portions 15 is two. However, the number thereof may be ttircc or more. [0097] FIG. 71 is a schematic view showing the ninth example ofhow the spot-welded portions and the tnel led and solidified portions, each of which is according lo lhepiLesenl invention, are formed. As shown in FIG. 71, it may be possible that the incited and solidified portion 15 is formed through emission of a laser beam so as to have ends with a bent shape, or the starting end and the ending end of the melted and solidified portion )5 have an enlarged bead width En order to avoid shess concentration, [0098] FIG. 7J is a schematic view showing the tenth example of how the spot-wcldcd portions and the melted and solidified portions, each of which is according to the present invention, are formed. As shown in FTG. 7J, it may be possible to fonn melted and solidified portions 15 at positions located on spaced-aparl ends of the spot-welded portions 10 (ends of the spot-wcldcd portions 10 that are located further away from each other). In the case where the incited and solidified portions 15 arc formed so as to face opposite sides to each other with respect to the spot-welded portions 10 as described above, it may be possible lo anauge, between the above-described melted and solidified portions 1.S, one or more spot-welded portions 10, one or more spot-welded portions 10 each having the melted and solidified portion 15 formed thereon, and/or one or more melted and solidified portions 15 (laser welded portions) that do not pass through any spot-welded portions 10. [0099] FIG. 7K is a schematic view showing the eleventh example ofhow the spot-welded portions and the melted and solidified portions, each of which is according to the present invention, arc formed. As shown in FIG. 7K, it may be possible lo form melted and solidified portions 15 al positions located on nearer sides (located on the inner sides) of spot-welded portions 39 10. Li the case where the melted and solidified portions 15 are formed so as to face the directions in winch the melted and solidified portions 15 arc brought closer to each other with respecl to the spot-wcldcd poitions 10 as described above, it may be possible to arrange, between the abovc-dcscribcd melted and solidified portions 15, one or more spol-wcldcd portions 10, one or more spot-welded portions 10 each having the melted and solidified portion 15 formed thereon, and/or one or more melted and solidified portions 15 (laser welded portions) that do not pass through any spot-wcldcd portion 10. [0100] FIG, 71. is a schematic view showing the twelfth example of how the spot-welded portions and the melted and solidified portions, each of which is according to the present invention, are formed. As shown in FIG. 71., it may be possible lo form adjacent melted and solidified portions 15 onlbe same side ofthc respective spot-wcldcd portions 10 (left side in the case of FIG-71.). In the case where the melted and solidified portions 15 are formed on the same side of (he spot-wcldcd portions 10 as described above, it may be possible lo arrange, between the above-described melted and solidi lied portions 15, one or more spot-wcldcd portions 10, one or mom spot-welded portions 10 each having the melted and solidified portion 15 formed Ihcrcon, and/or one or more melted and solidified portions 15 (laser welded portions) that do not pass through any spot-welded portion 10. LOI0IJ The resistance spot welding and the formation of'the melted and solidified portion 15 to the nugget 12 of the spot-wcldcd portion 10 according to the present invention can he applied, for example, to a process of welding vehicle bodies in the automobile manufacturing processes. During an assembly-tine operation such as welding of vehicle body, it is preferable to first position and clamp an overlap-welded member to apply resistance spot welding, and then, apply additional welding through resistance spot welding or emit a 40 laser beam, because it is possible to prevent a laser beam emission onto the spot-welded portion from positionally shitting due to repositioning or re-clamping. Further, more preferably, il is preferable to apply a laser beam emission in the same station as the resistance spot welding is applied, [0102] Next, with reference to 1'IU. 8A to 1*IG. 81", an example will be described in which a high-strength steel sheet and a low-strength steel sheet arc overlapped, and a laser beam is applied, thereby forming a melted and solidified portion. FIG. 8A to FIG. 8C are explanatory views showing a ease where two steel sheets overlapped are combinations of a high-strength steel sheet and a low-strength steel sheet, and showing an example in which an uncoatcd high-strength steel sheet (1500 MPa) 61H and an uncoatcd low-strcngfh steel sheet (270 MPa) 62L arc overlapped. |OI03] FIG. 8A is a diagram showing the first example. The first example shows a case where an uncoaled high-strength steel sheet 61H and an uncoaled low-strength steel sheet 621, are overlapped, and a laser beam LB is emitted from the side of the high-strength steel sheet 61H, thereby forming the melted and solidified portion 15 throughout the entire thickness of the uncoatcd high-strength steel sheet 6111 and the uncoatcd low-strength steel sheet 62L. In this ease, the depth LD61 of the melted and solid! tied portion 15 in the high-strength steel sheet 61H is 100% of the thickness of the high-strength steel sheet 61H, [0104] FIG. 8B is a diagram showing the second example. The second example shows a case where an uncoaled high-strength steel sheet 61H and an uncoaled low-strength steel sheet 621, are overlapped, and a laser beam LB is emitted from the side of the low-strength steel sheet 62L, thereby forming the melted and solidified portion 15 throughout the entire thickness of the uncoaled high-strength steel sheet 6 III and the uncoaled low-strength steel sheet 62L. 41 In this case.. the depth LD6I of the melted and solidi Tied portion 15 in the high-si rcngth steel sheet 61H is 100% of the thickness of the high-strength steel sheet 61IL [0105] FIG, 8C is a diagram showing the third example. The third example shows a case where an uncoatcd high-strength stcc] sheet 61H and an nncoatcd low-strength steel sheet 62L arc overlapped, and a laser beam LB is emitted from the side of the high-strength steel sheet 6111, thereby forming the melted and solidified portion 15 from the surface of the uncoated high-strength steel sheet 6111 up to a middle point before the uncooted low-strength steel sheet 621 „ In this case, Jl is preferable to set the depth LD6I ofthe melted and solidified portion 15 in the high-strength steel sheet 61Hto be more than or equal to 50% of the thickness thereof. [01061 FIG. 8D is a diagram showing the fourth example. The fourth example shows a ease where an uncoaled high-strength steel sheet (1500 MPa) 61H and an uneoated high-strength steel sheet (1500 MPa) (J2H arc overlapped.. and a laser beam I..R is emitted from the side of the high-strength steel sheet 61H, thereby forming the melted and solidified portion 15. In this ease, the depth LD61 of the melted and solidified portion 15 in the high-strength steel sheet 61H is 100% ofthe thickness of the high-strength steel sheet 61H, As shown in 1H'1G. 8D, in the case where the high-strength steel sheet 61H and the high-strength steel sheet 6211 are overlapped, it is preferable to form the melted and solidified portion 15 throughout the entire thiekness of the high-strength steel sheet GUI, and further, set the depth LD62 ofthe melted and solidified portion 15 in the high-strength steel sheet 62H to be more than or equal to 50% of the thickness ofthe high-strength steel sheet 620. [0107] 42 FIG. 81i and FIG. SF show a case where a low-strength steel sheet, a high-strength Eteel sheet, and a low-strength steel sheet are overlapped in this order. [0108] PIG. Bli is a diagram showing the fifth example. The fifth example shows a case where anuncoatcd low-strength steel sheet (270 MPa) 61L, an uncoatcd high-strength steel sheet (1500 MPa) 6211, and aiiuncoated low-strength steel sheet (590 MPa) 63L are overlapped, a laser beam LB is emitted from the side of the low-strength steel sheet 61L, thereby forming the melted and solidified portion 15, This case is preferable because the melted and solidified portion 15 is formed to he 100% in terms of thickness of the low-strength steel sheet 6JL, the high-strength steel sheet 62H, and the low-strength steel sheet G~3L, and the depth LD62 of the melted and solidified portion 15 in die high-strength steel sheet 6211 is 50% or more of the thickness. [0109] FIG. 8F is a diagram showing the sixth example- The sixth example shows a case where an uncoatcd low-strcngtfi steel sheet (270 MPa) 61L? an uncoatcd high-strength steel sheet (1500 MPa) 62H, and anuncoatcd low-strcngdi steel sheet (590 MPa) 63L arc overlapped, and a laser beam LB is emitted from the side of the low-strength steel sheet 61L5 thereby forming the melted and solidified portion. 15. Tn this case, as shown in FIG. 8F, the melted and solidified portion 15 is formed throughout the entire thickness of the low-strength steel sheet 61L and up to a middle point of the high-strength steel sheet 62H from the low-strength steel sheet 611. toward the low-strength steel sheet 63L. It is preferable to set the depth LD62 of the melted and solidified portion 15 in the high-strength steel sheet G2H t o t e more than or equal to 50% of the thickness oflhe high-strength steel sheet 62H, [0110| (Second Embodiment) Next, the second embodiment according to the present invention will be described, 43 The first embodiment described above relates to a case where the steel sheet is an uiicoated steel sheet. However, il was found that, in [he case where steel sheets having GA coaling or Gl coating, which is a typical zinc-coated steel sheet, ate comhincd, hole defects may occur in the spot-wcldcd potion 10, by forming the spot-wcldcd portion 10 through resistance spot welding, and emitting a laser beam LB onto the spot-welded portion 10. Below, with reference lo FIG-9A and FIG, 9B, Che effect of laser emission on the spot-welded portion H) will he described. [0111] FIG. 9A is a diagram showing a spot-wcldcd portion 10 and a melted and solidified portion 15 formed in the overlapped portion made out of an uneoated high-strength steel sheet (1500 MPa) and an uneoated low-strength steel sheet (440 MPa). In the case of uneoated steel sheets, no hole defect occurs as shown in FTG. 9A. [0112] On the other hand, FIG. 9li is a diagram showing an example in winch a melted and solidified portion 15 is formed in a spot-welded portion 10 formed in the overlapped portion made out of an uneoated high-strength steel sheet (1500 MPa) and a hot-dip galvamiealed low-strength steel sheet (440 MPa), It was found that, in the case of a hot-dip galvanncaling steel sheet, a hole defect 15H may occur in the melted and solidified portion as shown in FIG. 9B, and this hole defect ] 5H reduces the strength of flic spot-welded portion 10 and serves as a starting point of fracture at the time when the automobile collides, whereby there is a possibility that it is not possible to mate lull use of the strength of the high-strength steel sheet. [0113] The present inventors made thorough investigations on causes of occurrence of the hole defect 1511 shown in FIG. 9B, and as a result, found that the hole defect 1511 occurs at a contact portion 16 of the spot-welded portion 10 as shown in FJG. 10. The contact portion 16 shown in FIG. 10 is located outside of the nugget 12, and is a portion of the spot-wcldcd portion 10 that is joined through application of pressure 44 without inciting. r0114] His assumed that the hole defect 1511 is created in a manner such thai, when a laser beam LB is emitted to form the melted and so!idilied portion 15, the contact portion 16 having the zinc-coating formed thereon is molten through emission of a laser beam LB, zinc is explosively vaporized, and molten steel is blown away. [0115] The second embodiment is directed to joining steel sheet members including galvanized steel sheets having a hot-dip galvanneal coating or a hot-dip galvanizing coating formed thereon. |()I161 The present inventors canicd out a study of the problems described above. As a result, they found that, in Ihe ease where the steel sheets including these GA coating or GI coating are contained, it is possible to obtain a favorable welded joint that does not have any hole defect 15H, by controlling the depth of the melted and sol idi lied portion 15 formed through emission of a laser beam LB in a manner that does not melt Ihe contact portion 16 of spot welding on a surface overlapped with CiA coating or GI coating. [0117] Tt should be noted that, in the case of an uncoated steel sheet, an aluminized steel sheet, a slecl sheet having a coating of an intennetallic compound ofiron and aluminum, and a steel sheet liaving an iron-zinc solid solution layer and a y.mc oxide phase coaling thereon, a boiling point of the coating is high, and hence, it is less likely that welding defects occur resulting I"n>m the coating on the overlapped surface. Further, his preferable to set the depth LD of the melted and solidified portion 15 at a position located outside of the melted and solidified porlion 15 and spaced apart iiwi the end of the nugget 12 of the spot-welded portion 10 by I mm, to be more than oi equal to 50% of the thickness of the high-strength steel sheet. [0118] Tn the second embodiment, it may be possible to arbitrarily choose whether the 46 plurality of steel sheet members include, for example, steel sheet or hoi stamped member having rnartensite, particularly whether (he plurality of steel sheet members include a high-strength steel sheet having a tensile strength ol"1200 MPa or higher, hurlher, it may he possible to employ a configuration in which no high-slrenglh steel sheet is included. Further, it n^ay be possible to combine stccf sheet members made out of an uncoatcd steel shccL an a1ummi/.ed steel sheet, a steel sheet having a coaling of an intermetallic compound of iron and aluminum, and/or a steel sheet having an iron-zinc solid solution layer and a zinc oxide phase coaling thereon. [0119] Further, in the second embodiment, the plurality of sleel sheet members arc overlapped with each other, a spot-welded portion 10 having a nugget 12 is formed through icsistancc sjiot welding, and a laser beam LB is emitted, thereby terming a melted and solidified portion 15 that extends across the nugget 12, for example, in a manner such thalthe melted and solidified portion 15 crossing the end of the nugget 12 extends from the end of the nugget 12 to a position distanced not less than 3 mm from the end of the melted and solidified portion 35, this end of which is located outside of Ihe nugget. [0120] First, in the case where the overlapped steel sheet member onto which a laser beam is emitted is a steel sheet member only formed by any of an uncoatcd steel sheet, an alumini/£d sleel sheet, a steel sheet having a coating of an intermetallic compound of iron and aluminum, and a sleel sheet having an iron-zinc- solid solution layer and a zinc oxide phase coating thereon, the hardness of the softest zone in HAZcan be improved by forming the melted and solidified portion 15 through the emission of a laser beam with the depth LD of the melted and solidified portion 15 al a position externally spaced apart from the end ofthe nugget 12 by 1mm being set to be more than or equal to 50% of each of the thicknesses of all the high-strength steel sheet. [0121] The upper limit ofthc depth LD of the melted and solidified portion 15 formed is 100%oflhe thickness of the high-strength steel sheet. It is preferable to set the depth LD of the melted and solidified portion 15 formed, lobe more than or equal lo 50% of the thickness, because the effect of preventing fractures in the HAZ softening zone can he sufficiently achieved with this dept. However, it may be possible to set the depth LD of the melted and solidified portion 15 to be less than 50% of the thickness. |0122] Below, descriptions will be specifically made with reference to FIG, 11A to FIG, 11F. FIG. I ]A to FIG. 1111 only show a contact portion in the case where one of the steel sheets overlapped is a hot-dip galvanncalcd low-strength steel sheet 91LZ. FIG. 11A is a diagram showing an example in which a high-strength steel sheet and a low-strength steel sheel are overlapped^ and showing an example in which two steel sheets, a hot-dip galvanncalcd low-strength steel sheet (270 MPa) 91LZ and an uncoatcd high-strength steel sheet (1500 MFa) 92H, arc overlapped. [0123] In FIG. 11A, a laser beam LB is emitted from the side of the uncoated high-strength steel sheet 92H, and control is perfoimed so that the melted and solidiiled portion 15 does not reach the contact portion 16 in the spol-welded portion 10 serving as the overlapped surface, and the contact portion 16, where the hot-dip galvanncal coating lies, is not molten. It should be noted that it is preferable to set the depth LD92 of the melted and solidified portion 15 in the high-strength steel sheet 9211 at a position externally spaced apart from the end of the nugget 12 of the spot-welded portion lOby I mm, to he more than or equal to 50% of the thickness. [0124] FIG. 1 IB shows an example in which three steels, an outer panel including a hot-dip galvannealed low-strength steel sheet 91LZ, a rein force including an uncoated high-strength steel shccl 92H, and an inner panel including an uncoatcd low-strength steel sheet 931,, arc overlapped, and this serves as, for example, an example of a structure of a flange portion of a B-pillar of an automobile. 47 |omi In this case, after spot welding, a laser beam LR is emitted from the side of the uncoated inner panel (low-slrcnglh steel sheet 931,) to he disposed on the inside of the cabin of the automobile body, thereby forming the melted and solidified portion 15 in the low-strength steel sheet 93L and the Jugh-strcngth steel sheet 92H. The melted and solidified portion 15 is formed by controlling such that the melted and solidified portion 15 does not reach the contact portion 16 located on the side of the surface where the low-strength steel sheet 9I1,Z and the high-strength steel sheet 92H are overlapped, and the contact portion 16, where the hot-dip galvanneal coating lies, is not molten. It should be noted that it is preferable to set the depth LD92 of the melted and solidified portion 15 in the high-strength steei sheet 9211 at a position externally spaced apart from the end of the nugget 12 of {he spot-welded portion 10 by 1 mm, to be move than or equal to 50% or the thickness. [0126J It should be noted that, in the case where a hot stamped member having an iron-zinc solid solution layer and a zinc oxide layer coating thereon or a hot stamped member 92IIP having an intermetallic compound of iron and aluminum coaling thereon is used in place orthe high-strength steel sheet 92H, which is a reinforce, it may be possible to treat them as is the case with the uncoated hot stamped member. This is because the welding defects arc less likely to occur in these surface coating, as is the case with GA coating or GI coating. T0127] FIG, 1IC shows an example in which three stcels; an outer panel made out of a hot-dip galvanncalcd low-strength steel sheel91LZ, a central reinforce made out of a high-strength steel sheet 92HR having a surface containing an iron-zinc solid solution phase and a zinc oxide layer, and an inner panel made out of an uncoated low-strength steel sheet 93T,, are overlapped, and this serves as, for example, an example of slriiclures of Hange portions of an A-pi liar and a reo frail of an automobile. 48 [0128] In this ease, after spot welding, a laser beam LB is emitted from the side of the uncoatcd inner panel (low-strength steel sheet 93L) to be disposed on the inside of the cabin of the automobile body, thereby forming the melted and solidified pof lion 15 in the low-strength steel sheet 93L and the high-strength steel sheet 92HR having a surface containing an hon-*me solid solution phase and a zinc oxide layer. The melted and solidified portion 15 is formed by controlling such that the melted and solidified portion 15 docs not reach the contact portion 16 on the side of the surface where the low-strength steel sheet 91LZand the high-strength steel sheet 92T1R having a surface containing an iron-zinc solid solution phase and a zinc oxide layer are overlapped, and the contact portion 16, where the hot-dip galvanneal coating lies, is not molten. It should be noted that iL is preferable that the depth LD92 of the melted and solidified portion 15 in the high-strength steel sheet 92HR. having a surface containing an iron-zinc solid solution phase and a zinc oxide layer is set at a position externally spaced apart from the end of the nugget 12 of the spot-welded portion 10 by 1 mm, to be more tlian or equal to 50% of the thk&uess. [0129] FIG, 11D shows an example in which three stccls; an outer panel made out of a hot-dip galvanncalcd low-strength steel sheet 91LZ, a central reinforce made out of an uncoatcd high-strength steel sheet 9211, and an inner panel made out of an uneoaled high-strength steel sheet 9311, are overlapped, and this serves as, for example, an example of structures of flange portions of a roof rail and an A-pillar of an automobile. [0130J In this case, after spot welding, a laser beam LB is emitted from the side of the uncoatcd inner panel (high-strength steel sheet 9311) to he disposed on the inside ^i the cabin of the automobile body, thereby forming the melted and solidified portion 15 in the high-strength steel sheet 93H and (he high-strength steel sheet 92H. 'llic melted and solidified portion 15 is formed by controlling such that the melted and solidified portion 15 docs not reach the contact portion 16 on the side of the surface where the low-strength steel sheet 91LZ and the high-strength slecl shoe! 92H are overlapped, and the contact portion 16, where the hot-dip galvaEincal coating lies, is not molten, It should be noted that it is preferable to set the depth T.P92ofthe melted and solidified portion 15 in the high-strength steel sheet 92H at a position externally spaced apart from the end of the nugget 12 of the spot-welded portion 10 by 1 mm, to be more than or equal to 50% of the thickness. [0131] FIG, 1 lli and FIG. 1 IF' arc examples in which three steels, an outer panel including a hot-dip gaivannealed low-strength steel sheet 91 T.Z, a central reinforce including an uncoated low-strength steel sheet 921., and an inner panel including an uncoated high-strength steel sheet 93H, are overlapped, and these serve as, for example, examples of structures ol" an A-piltar upper and a roof rail of an automobile. [0132] In this case, after spot welding, a laser beam LB is emitted from the side of the uncoated inner pauel (high-strength steel sheet 93H) to be disposed on (he inside of the cabin of the automobile body, and control is performed so as not to reach the contact portion 16 on the side o\" the surface where the low-strength steel sheet 91LZ and the low-strength steel sheet 92L arc overlapped. It may be possible that the formation is performed so as not to reach the contact portion 16 on the side of the surface where the low-strength steel sheet 91 I.Zand the low-strength steel sheet 92L are overlapped as shown in FIG. 11F, and so as to extend in the high-strength steel sheet 93H and the low-strength steel sheet 92L. II should he noted that, in FIG. 1 IE and FIG. 1 IF, it is preferable to set the depth T.D93 of the melted and solidified portion 15 hi the high-strength steel sheet 9311 ala position cxtciually spaced apart from the end of Ihenuggcl 12 of the spot-welded portion 10 by lmni, to be more than or equal to 50% of the thickness. [0133] The welded joint according to the present hiventiou described above is suitable to 50 be used in shuctural elements of automobiles made out of a high-strength steel sheet having a tensile strength of 1200 MPa or higher, The welded joint can be applied, for example, to a bumper, a door beam, a door member, a front-side member, and a rear-side member. [0134] II should be noted thai the present invention is not limited to the embodiments described above, and various modifications may he possible without departing from the scope of ttic present invention. [01351 In the embodiments described above, the present invention is applied; as an example, to an automotive part. However, Ihe present invention can be applied to various ovcr-wcldcd members formed by joining overlapped portions through spot welding, for example, in fillings, beams, and link members oi'abuilding, or in a simple warehouse, furniture, and office furniture. [0136] Further, in the embodiments described above, for example, the targets arc set to Ihe high-strength steel sheet or the hot stamped member having a tensile strength of 1200 MPa or higher. However^ the present invention can be applied to a high-strength steel sheet having a tensile strength of less than (200 MPa and having a hardness in IhelIAZ softening zone less than the base material due to containing a quenched structure (martensite) such as a high-strength steel sheet of 980 MPa class. [0137] Descriptions have been made of a ease where two or three high-strength steel sheets arc used as a steel sheet member made out of a plurality of steel sheets. However, four or more steel sheet members may be used. Further, the plurality of steel sheets including a high-strength steel sheet means that il is only necessary mat, of Ihe plurality ofsleel sheets, at least one steel sheet is the high-strength steel sheet. [0138] 51 Further, in the present invention, it may be possible to form the overlapped portion by the plurality of sleel sheets overlapping each other in a manner such that a member used for partial reinforcement is joined without using a flange as shown in FIG. 7B, or a flange is joined to a portion shaped through press forming. Examples [0139] The present invention will be described in more detail with reference to Examples- Table 1 shows chemical components of samples. Tlic unit in Table 1 is mass%, and the balance other ihanthe chemical components indicated in Table 1 includes Fe and inevitable impurities, [0140] 52 [Table 1] Sample SQ1500 SQZ1500 SQISOO JSCII270 JSC440 JAC440 JSC590 C 0.21 0.21 0.30 0.14 0.11 0.11 0.08 Si 0.22 0.04 0.20 0.49 0.07 0.06 0.03 Composition (mass%) Mil 1.25 1.30 1.69 1.85 1,10 1.09 2,30 P 0.010 0.010 0.010 0.007 0.021 0.019 0.015 S 0.001 0.001 0.001 0.004 0.003 0.003 0,003 Other 0.20Cr,0.020Ti,0.0015B 0.20Cr,0.021Ti,0.0016B 0.23Cr, 0.02iTi, 0.08Nb, 0.0020B 0.05'li [0141] In Tabic l,thc sample SQISOOisauuncoated steel sheet for hot stamping having a tensile strength of 1500 MPa class. The sample SQZ1500 is a steel sheel for hoi stamping having an iron-zinc solid solution layer and a >-.inc oxide layer coaling (hereon and having a lensile slTength ofI500 MPa class, The sample SQ1800 is aniincoatcd steel sheet for hot stamping having a tensile strength of 1800 MPa class. The sample JSC1270is an uncoated cold-rolled sleel sheel having a lensile strength of 1270 MPa class, Further, Ihe sample JSC44U is an uncoalcd slccl sheet of 440 MPa class. Hie sample JAC440 is a steel sheet of 440 MPa class having hot-dip galvanncahng applied thereon. The sample JSC590 is an uncoated steel sheel of 590 MPa class. II should he noted that the steel sheets lor hot stamping are used by applying similar processing to hot stamping. 101421 (Example 1) 53 Eclow, Example 1 will be described with reference to FIG. 12Ato FIG. 12Caiid Tabic 2. Tn Example I, strain at [he time of tensile telling was evalualedin the case \vheve (wo uncoatcd steel sheets were overlapped. FIG. I2A is a diagram schematically showing a test piece 310 used hi this Example. FIG. 12B is an enlarged view showing a direction of tensile load applied to the test piece S10, and showing a testing method in llns Example. FIG. 12C is a sectional view taken along line 1T-T1 of FIG, 12R. [0143] In Example 1, test pieces K10 as shown in FIG. 12A were obtained from the samples shown hi Table 1, and tensile testing was executed by applying tensile load as shown in FIG. 12B to each of the test pieces. hi the tensile testing, the strain was measured until each of the test pieces S10 fractured, and the strain was evaluated according lo four grades. [0144] Jn the case of the test piece S10, two steel sheets, which were a steel sheet SI 1 made oiri of a sample 1 and a steel sheet S12 made out of a sample 2, were overlapped as shown in FIG. 12A, and resistance spot welding was applied to the overlapped portion 11, thereby forming a spot-welded portion 10, Then.. a laser beam was emitted from the side of the steel sheet SI I, thereby forming a melted and solidified portion 15. hi the tensile testing, the steel sheet Sll made out of the sample 1 of the test piece S10 was pulled, whereby a tensile strength of the sample 1 was measured. R should be noted lhal te-st pieces 1 and 12showninTahle2are Comparative Examples, onto which no laser beam was emitted. [0145] Spot welding was applied using a single-phase AC spot welding machine and using a DR-type electrode (lop eaid