Influence of microstructural features on the dynamic fracture behavior of some iron-base materials

Abstract

An exploding wire system has been used to examine the effects of microstructure on the dynamic fracture behavior of high purity iron, 0.2% C steel and free machining steels. Optical and scanning electron microscopy studies of the fractured specimens indicate that the dynamic loading response is strongly material dependent, being inlfuenced by the grain size and the presence of brittle second phase particles. Predominantly intergranular microcracks are observed in pure iron specimens having grain sizes ranging from 40 to 200 microns, whereas transgranular microcracks are observed to initiate the fracture process in 0.2% C steel of varying microstructures. The degree of dynamic fracture increases with increasing grain size in 0.2% C steel containing ferrite - pearlite microstructures. A detailed study of dynamically loaded specimens indicates that the occurrence of microfractures in 0.2% C steel is associated with second phase particles in the form of inclusions and carbides, and that the predominance of intergranular cracking in pure iron is due to its relatively low carbon content and coarse grain size. The fracture characteristics of the various materials are compared and discussed in relation to the dynamic fracture behavior of steel subjected to other methods of loading.