IRON-BASE SINTERED ALLOY FOR VALVE SHEET AND VALVE SHEET FOR INTERNAL COMBUSTION ENGINE

摘要

Disclosed is a valve sheet product possessing excellent mechanical strength and machinability. In the valve sheet product, the amount of hard particles added for an improvement in abrasion resistance of a valve sheet for an internal combustion engine has been increased. Also disclosed is an iron-base sintered alloy material for a valve sheet. In the iron-base sintered alloy material, first hard particles having an average primary particle diameter of 5 to 20 µm and second hard particles having an average primary particle diameter of 20 to 150 µm are incorporated in the structure of an iron-base sintered alloy. N (an integer of N = 2) peaks are present in a particle size distribution obtained when the two types of hard particles have been mixed together. Among particle diameters corresponding to peak top positions (DT1 to DTN), the difference in peak top particle diameter between one or more adjacent particle diameters DTn-1 and DTn (|DTn-1 - DTn| : an integer of 2 = n = N), is 15 to 100 µm. The total area ratio occupied by the two types of hard particles within the structure is 10 to 60% on an area basis.