Effect of alloying element on Fe3C diagram

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written 7.7 years ago by

The transformations represented in the above diagram are denoted by phases A1, A2, A3, A4in steel region. These transformations can be reversed on cooling

Phase at temperature	Transformation
A1 at 727°C in pearlite phase	A2 <=910°C at Austenite phase FCC structure
A3 Austenite FCC structure at 910°C, (α-ferrite)	A4 (γ-austenite )1400°C
A4 (γ-austenite ) 1400°C	δ-ferrite BCC structure

Austenite stabilizers such as Nickel, Manganese, Copper and Nitrogen tend to raise temperatures A4 temperature and lower A1 and A3 temperature as a result of which more austenite region is present in the above diagram as compared to ferrite region. These elements are more stable in austenite region of steel
Ferrite stabilizers such as Chromium, Tungsten, Vanadium, Molybdenum, Silicon and Aluminum more stable in ferrite region. By addition of these elements into the steel the proportion of ferrite region increases by reducing the area occupied by austenite region in the iron-iron equilibrium diagram. They raise A1 and A3 temperatures by lowering the A4 temperature as shown in diagram 2.
If the proportion of these elements increases there forms a gamma loop by joining A4 and A3 temperatures, In this phase Ferrite exists from room temperature to melting point of steel.

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