The effect of aluminium on nitrogen solubility was investigated by equilibrating melt comprising
master alloy of Fe-Al with pure electrolytic iron in a controlled atmosphere (pure argon) at 1873 K.
Nitrogen in the samples was measured by sampling technique using inert gas fusion absorptiometry.
It was found that nitrogen content decreases steadily with aluminium concentration and gradually,
becomes close to 1 ppm for very high aluminium steels. Wagner’s second order interaction
parameter formalism has been used to estimate the equilibrium constant and interaction parameters.
Scanning electron microscopy (SEM) investigation showed, dual-phase inclusions comprising AlN
phase surrounding alumina core. The 3D morphology of inclusions was studied by extracting the
sample from the top and the central bottom portion of the solidified ingot. A sparse distribution of
nitrogen was found for most of the inclusions which manifested the presence of almost pure alumina
inclusions with different morphologies and sizes.