The Influence of Shape and Amount of Graphite of Cast Iron on the Rolling Contact Fatigue Strength

Abstract

In order to elucidate the influence of graphite on the rolling contact fatigue strength of flaky and spherulitic graphite cast iron, experiments were conducted on the quenched and tempered samples by using a Nishihara-type rolling contact fatigue testing machine under a lubricated state with sliding.
The results obtained are summarized as follows:
(1) The rolling contact fatigue endurance limit of flaky or spherulitic graphite cast iron with various hardness was lower than that of the carbon steel having the same hardness and similar microstructure to the matrix of cast iron.
(2) The rolling contact fatigue endurance limit of flaky or spherulitic graphite cast iron decreased remarkably with increasing amount of graphite regardless of its shape, especially at high matrix hardness.
(3) Since graphite is considered as a sort of internal defect, the reduction factor of the rolling contact endurance limit for cast iron against carbon steel with same hardness was examined. The reduction factor for flaky graphite cast iron was larger compared with that of spherulitic graphite cast iron, regardless the amount of graphite and matrix hardness.