Abstract
A combination of direct austempering after solidification (DAAS) treatment and electron backscatter diffraction (EBSD) method was used to study the formation of micro-shrinkage porosities in ductile iron. Analyzing the aus-ferritic microstructure revealed that most of micro-shrinkage porosities are formed at the retained austenite grain boundaries. There was no obvious correlation between the ferrite grains or graphite nodules and micro-shrinkage porosities. Due to the absolute pressure change at the (purely) shrinkage porosities, the dendrite fragmentation rate during the DAAS process would be altered locally, which caused a relatively finer parent-austenite grain structure near such porosities.
Highlights
It has been reported that during solidification of cast iron, shrinkage of the austenite phase can be compensated by the expansion that is provided by graphite precipitation
The aim of8,this study is to investigate and confirm the origin of microshrinkage porosity iron
The aim of this study is to investigate and confirm the origin of microshrinkage porosity in
Summary
It has been reported that during solidification of cast iron, shrinkage of the austenite phase can be compensated by the expansion that is provided by graphite precipitation (for carbon equivalent above3.6%) [1]. It has been reported that during solidification of cast iron, shrinkage of the austenite phase can be compensated by the expansion that is provided by graphite precipitation The shrinkage depends on other factors, such as mold stiffness, pouring temperature, melt composition, and graphite nodule count; the behavior is more complex [2]. According to Stefanescu [3], avoiding macroshrinkage is normally best made by mold design adjustments. The increasing demand for high performance cast components implies the importance of aesthetically pleasing and structurally sound products. This requires a deep and thorough understanding of the origin of microshrinkage for internal and external soundness of the components
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