Microscopic Characterization of Different Shrinkage Defects in Ductile Irons and their Relation with Composition and Inoculation Process

摘要

Shrinkage becomes one of the most important defects that negatively affects the production of ductile cast iron parts. Regular inspections made on the affected parts show that different morphologies of shrinkage can be obtained according to the melt composition, to the layout and to a number of other processing variables that have been reported in the literature. However, minimization of these defects demands a more detailed understanding of their internal features and the relationship with the processing variables causing the greatest effect. In the present study, carbon equivalent content, inoculation and thermal characterization of melts have been studied as variables for producing eight test parts which have been designed for promoting the formation of shrinkage. The different defects obtained in each case have been analyzed by means of metallographic techniques and FE-SEM and their characteristics and size correlated with the selected variables. It has been found that carbon equivalent shows the strongest effect on shrinkage incidence. A discussion about the features found in the internal surfaces of the different closed defects is done, and possible explanations for each case are also described.