SPRING EXCELLENT IN FATIGUE RESISTANCE PROPERTY AND SURFACE TREATMENT METHOD FOR PRODUCING THE SPRING

摘要

To the surface of the nitriding spring, than the soft nitrided uppermost layer hardness, and further, the hardness Hv500 to 800, particle diameter 500 to the projection while preventing the occurrence of fine cracks on the surface layer of the hard metal particles 900㎛ 40 to 90m / sec , impart a residual compressive stress due to projection to the inside of the relative spring. By a spring surface, all particle having an average diameter of less than 80㎛, also, the individual particles is less than the average diameter of more than 100㎛ each 10㎛, a shape without a close angular I part to the spherical or sphere, specific gravity 7.0 to 9.0, hardness of Hv600 or more 1100 or less, and the number of fine metal particles having an outermost surface layer hardness is equal to or less the hardness of the spring after nitriding at a rate of 50 to 190m / sec, only causing a work hardening of the spring surface layer, due to the recovery recrystallization projection with the low-temperature control rather than by the softening to occur, thereby obtaining the surface layer without causing microcracks to give a high residual compressive stress in the electrode surface, by which an excellent fatigue strength of the valve spring or the like.