Patent ID: 8344604

Claim:
A spark plug for an internal combustion engine comprising: a center electrode which has a bar shape extending in the direction of an axis; an insulator which has a substantially cylindrical shape and is provided on the outer periphery of a center electrode; a tubular metal shell which is provided on the outer periphery of the insulator; and a metal ground electrode which has a base end portion joined to the metal shell and a front end portion disposed to face a front end portion of the center electrode, wherein a ground electrode precious metal tip is joined to the front end portion of the ground electrode at a position opposed to the front end portion of the center electrode or a center electrode precious metal tip joined to the front end of the center electrode, wherein a spark discharge gap is formed between the front end portion of the center electrode or the front end portion of the center electrode precious metal tip, and the front end portion of the ground electrode precious metal tip, wherein the ground electrode precious metal tip is joined to a bearing surface of a mounting part containing the same metal as the ground electrode with a fused part formed by performing laser welding or electron beam welding on the metal of the two to be fused together, wherein the mounting part is joined to the ground electrode, and wherein grain size of the grains of the mounting part in the vicinity of the fused part is greater than the grain size of the grains thereof in the vicinity of the ground electrode.