Apart from the experimental observations, is there any other reason for why the alloy elements are classified as ferrite, austenite, and carbide stablizers.
Ferrite stabilizers have bcc structure (same as that of alpha iron) and they usually form carbide. These elements decrease the carbon content in gamma iron and favor the formation of free carbide and stabilize the alpha phase. But austenite stabilizers have fcc structure and they are more soluble in gamma phase. They restrict the formation of alpha phase.
structure of stabilizers and ferrite or austenite are not the same always.for example silicon as stabilizer for ferrite and Molybdenum for austenite have different structures
The properties of alloys elements are comimng in the acount in the thermodynamic of all elements in the special phase. In this case today, we are learning from the research works how can be shown ampiricly the special elements that are active in the case of stabilization.
It is related only to the effect of alloying elements on the free energy change during a special phase transformation,e.g. carbides precipitation or formation of ferrite. for example, Si retards cementite precipitation from austenite because in the presence of Si the driving force for cementite precipitation drops off as a consequence of free energy change reduction.
It depends on how an element influences entropy and enthalpy, which both determine the free energy of a system. Ferrite stabilisers, for instance, change the free energy so that the alpha field is broadened.
Stabilizer is added to a certain limit where it increases the configuration entropy and make interaction parameter is more negative. Due to this, it stabilize the phase by reducing Gibbs energy. Beyond the composition limit, interaction parameter is become more and more negative ordering take places i.e. formation of compound.
Austenite stabilizers having the same crystal structure as that of austenite (FCC) enlarges the temperature range over which austenite exists. On the other hand ferrite stablizers have BCC structure similar to ferrite and decreases the area over which austenite exists.
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