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Gießtechnik, Erstarrung
Dokumenten-Nummer: 57815
Tagungsbeitrag
Dioszegi, Attila; Björklind, Tobias; Dioszegi, Zoltan
Publikationssprache: Englisch
Surface Turbulence at Flow of Gray Cast Iron
Oberflächenturbulenzen beim Fließen von Gusseisen mit Lamellengraphit
Gas bubbles in solidified cast iron casting employ large efforts from foundrymen to avoid or minimize these defects.
Hydrogen and Nitrogen have been identified to contribute to gas bubble formation by supersaturation during
solidification. Both elements have limited solubility in liquid iron. Commercial grades gray and nodular cast iron have a
solubility limit in liquid state of 8 ppm for hydrogen and 150 ppm for nitrogen. The solubility decreases drastically during
solidification to 4 ppm for hydrogen and 80 ppm for nitrogen. The scope of the present paper is to discuss the
mechanism of gas absorption in liquid cast iron during mould filling and emphasize the influence of surface turbulence
during mould filling. Different levels of flow velocities have been provoked in a vertically parted sand mould. The thermal
resistant transparent front side of the mould permitted the observation of the flow pattern due to high speed camera
registration. The registered frames including the liquid surface were investigated using image analyses. The results show
good correlation between the average flow velocity and the liquid iron surface extension. Consequently it has been
demonstrated that an increased absorption of hydrogen and nitrogen during mould filling is dependent on the level of
liquid surface turbulence.
Jönköping University, SE; Scania, Södertälje, SE; Volvo Powertrain, Skövde, SE
Erscheinungsjahr 2010
S. S.422-427
Seiten/Bilder/Tabellen/Quellen: 6S
Gießtechnik, Erstarrung
Dokumenten-Nummer: 57874
Tagungsbeitrag
Elmquist, Lennart; Dioszegi, Attila; Svidro, Peter
Publikationssprache: Englisch
Influence of Primary Austenite on the Nucleation of Eutectic Cells
Einfluss des Primäraustenits auf die Keimbildung der eutektischen Zellen
The solidification of gray cast iron starts with the precipitation of primary austenite. This phase nucleates either as
columnar or equiaxed dendrites depending on whether nucleation occurs on the mould wall or on particles and
impurities in the melt. In this work, the nucleation of primary austenite and its influence on the eutectic solidification
has been investigated using different amounts of iron powder as inoculants. Besides, the influence of different cooling
rates was also examined. Within each austenite grain there is a microstructure, and this microstructure was
investigated using a color etching technique to reveal the eutectic cells and the dendritic network. It is shown how the
cooling rate affects the dendritic network and the secondary dendrite arm spacing, and how the microstructure can be
related to the macrostructure through dendrite arm spacing. The secondary dendrite arm spacing is a quantification of
the primary austenite belonging to the primary solidification, and it will be shown how the eutectic cell size is related to
the secondary dendrite arm spacing. The total amount of oxygen influences the microstructural dimensions. This effect,
on the other hand, is influenced by the cooling rate. The number of eutectic cells versus eutectic cell size show two
distinct behaviors depending on whether being inoculated with iron powder or a mixture of iron powder and commercial
inoculant. The addition of a commercial inoculant decreases eutectic cell size and increases the number of cells, while
iron powder almost only changes cell size.
Jönköping University, SE
Erscheinungsjahr 2010
S. S.61-66
Seiten/Bilder/Tabellen/Quellen: 6S
Giesserei Literaturschau