Valve-seat insert for internal combustion engines and its production

A double-layered, sintered alloy valve-seat insert, having a radial crushing strength of not less than 90 kgf/mm.sup.2 at room temperature, but not less than 70 kgf/mm.sup.2 at 500.degree. C., for an internal combustion engine comprising:

• a valve-seat layer consisting essentially of, by weight, 4 to 8% Co, 0.5 to 1.5% Cr, 4 to 8% Mo, 1 to 3% Ni, 0.3 to 1.5% C, 0.2 to 0.6% Ca, and the balance of Fe and inevitable impurities, said Co, Cr and Mo being present mainly in the form of a Co-Cr-Mo hard alloy and a Fe-Mo hard alloy dispersed in the Fe matrix of the valve-seat layer, said valve-seat layer being fusion-infiltrated with copper 7 to 16% by weight of the valve-seat layer, and said valve-seat layer being composed of a sintered alloy of a high heat resistance and a high wear resistance;
• a base layer composed of a sintered alloy integrated with the valve-seat layer, adapted to be seated in a cylinder head of the engine, having a radial crushing strength of not less 100 kgf/mm.sup.2 at room temperature, but not less than 80 kgf/mm.sup.2 at 500.degree. C., and having a higher heat resistance and a higher creep resistance than the valve-seat layer.