Abstract: Not only a reduction in the load resistant performance of a structural member in a vehicle body having a quenched portion with a tensile strength of 1,470 MPa or greater, but also a reduction in the shock absorbing performance associated with the HAZ softening by welding are suppressed.

Abstract: A fastening device is provided, which includes a locating seat for engaging with a first workpiece; a fastening member including sequentially connected stop unit, shank unit and fastening unit, the fastening unit being configured for fastening to a second workpiece; a reciprocation actuator movably disposed on the locating seat with the shank unit extended through and movably located in the reciprocation actuator and the locating seat, the stop unit abutted on a top of the reciprocation actuator, the fastening unit movable in a reciprocating motion between an inner side and an outer side of the locating seat or outside the locating seat; and an elastic element having an end pressed against the locating seat and another end pressed against the fastening member.