Effect of Nodular Graphite on the Deterioration of Vibration Fracture Resistance of Ferritic Cast Iron under an Aqueous Environment

Abstract

An intergranular fracture feature could be observed when ferritic spheroidal graphite cast irons were tested under continuously wet conditions. The maximum depth of intergranular fractures was closely related to the microstructural feature and ambient environment that caused the deterioration in vibration fracture resistance. Experimental evidence has confirmed the overall D-N curves can be generalized into three characteristic regions. Intergranular fractures occurred in the vicinity of the surface; the existence of noular graphite act as porosity should be considered as a dominant microstructural factor on the initiation of intergranular fractures. On the other hand, intergranular fractures can be prevented resulting in better vibration fracture resistance when a specimen of ferritic SG cast iron is covered with oil film, or if an identical test is performed using the Fe-3Si steel specimen containing no nodular graphite.