SPARK PLUG

摘要

It is an object of the present invention to provide a spark plug (1) having a ground electrode (6) joined securely by electric resistance welding. The spark plug (1) includes a cylindrical metal shell (4) and a ground electrode (6) joined by electric resistance welding to an end portion of the metal shell (4). The metal shell (4) has a high hardness region (42) formed with a Vickers hardness of 3×10 2 to 5×10 2 Hv in the end portion thereof in such a manner that the high hardness region (42), when viewed in cross section along a plane including an axis of the spark plug (1) and an axis of the ground electrode (6), has a length d of 0.3 to 0.8 mm from a ground electrode (6) side welding boundary to a metal shell (4) side welding boundary in a direction of load applied during the electric resistance welding.