Patent ID: 8106572
Filing Date: 2012-01-31
Classification: B22F,C22C,H01T

Abstract:
1. A spark plug comprising: a center electrode; an insulator provided around a periphery of the center electrode; a metallic shell which holds the insulator; and a ground electrode configured such that one end of an electrode base metal of the ground electrode is joined to an end portion of the metallic shell, a noble metal chip is joined to the other end of the electrode base metal, and a tip end surface of the noble metal chip and a front end surface or a side surface of the center electrode face each other to define a spark discharge gap; wherein the noble metal chip has an average hardness of Hv260 to Hv650 inclusive imparted thereto through work hardening; the electrode base metal is formed from an Ni alloy which contains Cr in an amount of 15% by mass to 30% by mass inclusive and Al in an amount of 1.5% by mass to 4% by mass inclusive; a total mass of Ni, Cr, Al, Si, and Fe contained in a weld zone provided between the noble metal chip and the electrode base metal is 5% by mass to 35% by mass inclusive based on a total mass of the weld metal zone; a total mass of Cr, Al, Si, and Fe contained in the weld zone is 4.4% by mass to 9.0% by mass inclusive with respect to the total mass of the weld zone; a total mass of Cr, Al, and Si contained in the weld zone is 2.1% by mass to 4.0% by mass inclusive with respect to the total mass of the weld zone; the average hardness of the noble metal chip is higher than an average hardness of the weld metal zone, and the average hardness of the weld metal zone is higher than an average hardness of the electrode base metal; and the average hardness of the weld metal zone is Hv255 to Hv400 inclusive.