Fracture surfaces and the associated failure mechanisms in ductile iron with different matrices and load bearing

Abstract

Ductile iron (DI) is a family of cast alloys that covers a wide range of mechanical properties, depending on its matrix microstructure. For instance, ferritic matrices used in parts, such as automotive suspension components, demand high impact properties and ductility among some of their main requirements. On the other hand, pearlitic and martensitic matrices are used when hardness, strength and wear resistance are of particular concern. When it comes to very high strength parts, ausferritic matrices, typically austempered ductile iron (ADI), are widely used. DI has been employed to replace cast and forged steels in a large number of applications and its production has shown a sustained rate of growth over the last decades. Knowing about failure modes and fracture mechanisms associated to materials with the properties mentioned above is crucial, since they can be of great value for designers of mechanical components. This paper deals with the analysis of fracture surfaces of ductile cast iron generated under different conditions of load application, temperature and environments. The studies include the examination of fracture surfaces obtained by means of tensile tests, impact tests and by samples used to determine fracture toughness properties, where the zones of fatigue pre-crack and monotonic load condition were evaluated. A special case of ductile iron fracture is also examined. The study of the different surfaces permitted to establish patterns that contributed to unveil the fracture mechanisms of ductile iron with different matrices, nodule count, etc.