| 摘要 |
Implementation of excellent welding strength through prevention of precipitates from falling in a supersaturated state. A spark plug (1) includes a metallic shell 3 and a ground electrode 27 resistance-welded to the metallic shell 3. The ground electrode 27 is formed from a metal material in which precipitates PR containing at least one of an oxide, an intermetallic compound, etc., are precipitated in grain boundaries. When a portion of the ground electrode 27 ranging within 100 µm from the weld boundary between the metallic shell 3 and the ground electrode 27 is defined as a heat-affected zone 27A, and a distal end portion of the ground electrode 27 is defined as a normal zone 27B, as viewed on a section of the heat-affected zone 27A, the diameter of an inscribed circle of a precipitate PR having the greatest area is 50 µm or less, and the shortest distance between the precipitates PR is 2 µm or greater. The area occupied by the precipitates PR (the diameter of the inscribed circle of the precipitate PR having the greatest area) on the section of the heat-affected zone 27A is equal to 65% (85%) or more the area occupied by the precipitates PR (the diameter of an inscribed circle of a precipitate PR having the greatest area) on a section of the normal zone 27B. |
