Influence of microstructures on fatigue limit of high strength ductile irons

초록

Rotary bending fatigue tests were performed to investigate the effects of 2-phase microstructure on fatigue limit with prepared specimens in high strength ductile irons. The used specimens have different matrix structures. Series A has sorbite and series B has bainite. Fatigue limits of both specimens are improved compared with as cast specimen, and in case of series B the fatigue limit is higher than any others. The reason why the fatigue limit of series A shows inferiority to that of series B is that transition of micro fatigue cracks to meso crack occurs very rapidly so increased stress intensity factor drives the fatigue crack growth. In case of series B, bainite, the gamma layer contained in bainitic structure interferes with the rapid growth of micro fatigue crack to meso crack, and also a layer around graphite has the higher capacity for the absorption of plastic deformation energy than sorbite.

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