Influence of shrinkage porosity on fracture under tensile stress in ductile cast iron

MARCOS LÓPEZ; JUAN MASSONE; ROBERTO BOERI; DIEGO FERNANDINO

Krakow

Congreso; The 73rd World Foundry Congress; 2018

This work focuses on the study of shrinkage porosity in Spheroidal and Compacted Graphite Irons identifying the morphology and location of porosity in cast samples especially developed. The application of the DAAS technique, which involves hot shake out of the castings at temperatures above the eutectoid, followed by an austempering, allowed the study of the relationship between porosity and solidication macrostructure. The results show that in SGI, disperse porosity develops inside the solidifying austenite grains, in coincidence with the location of the last to freeze melt. Similarly to SGI, in CGI the dispersed shrinkage cavities formed were found inside the grains and located between the austenite dendrite arms.The influence of disperse microporosity as a preferential site for cracks initiation was evaluated.The study showed that the classification of shrinkage porosity found in literature does not correspond to the SGI solidification model recognized by most of the scientific community. Early solidification models, and therefore shrinkage formation mechanisms, were proposed at instances when there was not a thorough knowledge of the morphology of the solid phases during solidification. At the present time, defects formation mechanisms can be described with better accuracy.