Very High Cycle Fatigue of Two Ductile Iron Grades

Abstract

Two ductile iron grades, EN-GJS-600-3 a ferritic-pearlitic grade, and EN-GJS-600-10 a silicon strengthened ferritic nodular iron grade, are studied in the very high cycle fatigue range using a 20 kHz ultrasonic test equipment. Fatigue strengths and SN-curves are achieved, and fracture surfaces and microstructures are investigated. The ferritic grade with higher ductility displays a lower fatigue strength at 108 load cycles than the ferritic-pearlitic grade, 142 and 167 MPa, respectively. Examination of fracture surfaces shows that fatigue failures are controlled by micropores in both of the ductile iron grades, while the graphite nodule distributions do not seem to influence the difference in fatigue strengths. Prediction of the fatigue strengths, using a model for ductile iron proposed by Endo and Yanase, indicates a large potential for improvement in particular for the ferritic grade. Ductile irons, also called nodular cast irons, are used in many machine components where they combine good mechanical properties, near-net shaping, and decent price. The present study explores fatigue properties at long lives of a ferritic ductile iron as compared to a more conventional ferritic-pearlitic ductile iron. Fatigue strength test data are tried in a prediction model by Endo and Yanase.