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Comparison of Monotonic and Cyclic Properties of Ductile Irons in the AFS/DOE Strain-Life Fatigue Database for Cast Iron
By J. M. Tartaglia, Element Materials Technology, Wixom, Michigan ABSTRACT A strain-life fatigue database for cast irons was developed utilizing AFS and the United States Department of Energy (DOE) funding. The database contains monotonic and cyclic property data as well as the associated chemical analysis and microstructural data for a variety of cast irons, including gray, ductile, compacted graphite and white cast irons. This paper first reviews the contents and format of the database. The database and its associated report contain no comparative analysis of any of the cast iron grades. The fresh approach of this paper is to analyze and compare the data across each section size and strength-ductility combination for four ductile iron grades, i.e., ferritic 6040-18, ferritic-pearlitic 65-45-12, pearlitic 100-70-03 and tempered martensitic (quenched and tempered [Q and T]) 120-90-02. The ductile cast iron results in the database generally exhibited the expected trends. Modulus and Poisson’s ratio were the same for all the conditions. Monotonic strength always decreased with increasing elongation and ferrite content. The higher strength grades and conditions exhibited greater high cycle fatigue resistance and decreased low cycle fatigue resistance. Heat treatments had a mixed effect on monotonic properties. Annealing decreased the monotonic strength of 60-40-18 whereas normalizing increased the strength and dramatically increased fatigue resistance of pearlitic 100-70-03. Monotonic ductility was only slightly affected by heat treatment. However, in most conditions, the heat treatments produced greater low cycle fatigue lives for high ductility conditions. Although the high cycle fatigue resistance was affected less by heat treatment, slightly increased high cycle fatigue lives were obtained with higher