Dual-layer sintered valve seat ring

A valve seat ring having a high strength and high stiffness and comprising a valve seat body having a surface in contact with a valve, and a base for supporting said valve seat body, said valve seat body and said base consisting of a ferrous sintered article having a dual-layer structure (hereinafter referred to as the dual-layer sintered body), wherein:

• said valve seat body comprises from 5% to 30% by weight of hard alloy particles having a hardness of Hv 500 or more and a matrix in which said hard alloy particles are dispersed and an alloying element of said hard alloy particles diffuses around said hard alloy particles and into said matrix;
• a ferrous sintered body of said base contains from 0.5% to 1.5% by weight of carbon, from 0.6% to 3.0% by weight of chromium, and at least one element selected from the group of phosphorus in an amount of from 0.1% to 0.6% by weight and boron in an amount of from 0.02% to 0.2%, based on the weight of said ferrous sintered body;
• and said dual-layer sintered body has a density of 7.6 g/cm.sup.3 or more and comprises a skeleton, pores formed by sintering (hereinafter referred to as sintered pores), and copper or a copper alloy which is fusion-infiltrated into the first portions of said sintered pores, said skeleton having a density of from 6.7 g/cm.sup.3 to 7.1 g/cm.sup.3, the percentage of said sintered pores and the percentage of the second portions of said sintered pores, in which said copper or copper alloy is not fusion-infiltrated being 15% or less and 5% or less, respectively, based on the volume of said dual-layer sintered body.