Generally All BCC metals are good ferritic stabilizer. How Al being FCC is ferritic stabilizer in Steel ?
The Iron because of presence of the magnetism stable in bcc - crystalline structure. Sharing the magnetic moments in bcc - lattice has the anisotropy i.e values of the magnetic moments in different crystallographic directions.
So atoms second component (chromium, vanadium, silicon, aluminum), having differ crystalline structure (bcc.-, fcc-,. structure of the diamond) enlarge the partial magnetic moments Fe-atoms in bcc- lattice that brings about arising the short- order parameter in binary alloys Fe- (Cr, V, Si, Al) in Fe- base. Presence of the short order parameters about reduction of the formation energy of the alloys, thereby these elements stabilize the ferrite steels. In more detail you can see into scientific article
A.L.Udovskii. "Three-Sublattice Model that Takes into Account
the Spin Density Anisotropy, Short-Range Order,
and Dimensioned Factor for the Binary Fe–Cr(V, Mo) Systems." Russian Metallurgy (Metally), Vol. 2011, No. 9, pp. 889–909. © Pleiades Publishing, Ltd., 2011.
Dear Shivkumar Khaple,
That's a good question! In correspondence to the Hume-Rothery rules for a continuous solid solution one would expect fcc-Al not to stabilize bcc-Fe. However, as shown by the Al – Fe phase diagram, the bcc-Fe stabilizing effect of Al is that large that in steel it cannot be attributed to interactions with C.
As Al is substitutionally dissolved in the bcc-Fe for a large composition range (see attached Al-Fe phase diagram), I would suggest that the strong bcc-Fe stabilizing effect of Al might be related to the electronic/magnetic interactions between the Al and Fe atoms, thereby surpassing the lattice non-correspondence. However, I must admit that this issue is far beyond my expertise as a materials scientist, as it appeared to me by grasping some relevant papers that the problem of bcc-Fe stability linked to composition seems far from fully elucidated.
The Iron because of presence of the magnetism stable in bcc - crystalline structure. Sharing the magnetic moments in bcc - lattice has the anisotropy i.e values of the magnetic moments in different crystallographic directions.
So atoms second component (chromium, vanadium, silicon, aluminum), having differ crystalline structure (bcc.-, fcc-,. structure of the diamond) enlarge the partial magnetic moments Fe-atoms in bcc- lattice that brings about arising the short- order parameter in binary alloys Fe- (Cr, V, Si, Al) in Fe- base. Presence of the short order parameters about reduction of the formation energy of the alloys, thereby these elements stabilize the ferrite steels. In more detail you can see into scientific article
A.L.Udovskii. "Three-Sublattice Model that Takes into Account
the Spin Density Anisotropy, Short-Range Order,
and Dimensioned Factor for the Binary Fe–Cr(V, Mo) Systems." Russian Metallurgy (Metally), Vol. 2011, No. 9, pp. 889–909. © Pleiades Publishing, Ltd., 2011.
The Al added as a killing agent to remove oxygen, involved in steels. Killing of more Oxygen may be stabilizing alfa ferrite more which is BCC.
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