The Mg addition is done to convert grey cast iron to ductile cast iron. How does Mg contribute to the conversion? How does the conversion happen (the mechanism)?
Thanks for the kind answers!
Please read this review paper:
http://www.rroij.com/open-access/review-on-grey-cast-iron-inoculation.php?aid=49690
It seems to be closely linked to surface tension of the melt.
The explanation might be somehow the same for modification of the eutectic in aluminium-silicon alloys with Sr or Na.
The increase of surface tension is in general visible while you look at the shape of the free surface of your metal (top of the downsprue or feeders for example) . Also after adding mg the metal projected (sparks) forms perfect solid spheres.
The increase of undercooling (recalescen ce) is another clue that lead to surface tension.
part of the carbon atoms is bound with the metal
atoms of iron solvent and carbon atoms are necessary for
the graphite inclusions growth. For their release during the
cooling it is necessary to overcome an energy barrier, it
means to transit from a metastable state to a stable one. The
rate of the transition depends significantly on the energy
barrier height (activation energy) and the temperature.
It can occur slowly enough and if the characteristic time
of the heat sink is less than the same magnitude for the
decay of carbon-containing groups in the melt, they are
retained in the solid state after crystallization, as observed
in practice. We can confidently say that the cause of
rate reducing of carbon atoms delivery to the interface
graphite – melt at accelerated cooling is the limited rate of
decay of metal-carbon clusters rather than a decrease in
the diffusion mobility of carbon atoms. The clusters serve
in this process as internal sources of carbon with a limited
rate of release.
you can see the add file … best regards
Interesting paper on research gate
Free Energy Barriers for Crystal Nucleation from Fluid Phases
May 2017PHYSICAL REVIEW E 96(4)
DOI10.1103/PhysRevE.96.042609
Peter KoßA. StattA. StattPeter VirnauKurt BinderKurt Binder
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