IRON CARBIDE EQUILIBRIUM DIAGRAM

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2000

The part of iron and carbon alloy system line diagram representation of unalloyed iron and an interstitial compound, iron carbide (Fe3C), containing 6.67 percent carbon by weight is called iron-iron carbide equilibrium diagram. It should be noted that though it is called as equilibrium diagram, it is not a true equilibrium diagram, since equilibrium depends on no change of phase with time. In fact, the compound of iron carbide decomposes into iron and carbon. The decomposition takes a very long time at room temperature, even at 1300°F, it takes many years to form graphite. The iron carbide is called meta-stable phase. Therefore, iron-iron carbide diagram even though technically represents meta-stable conditions, can be considered as representing equilibrium changes, under conditions of comparatively slow heating and cooling.

DELTA FERRITE

  •  Solid solution of carbon in iron
  •  Soft and ductile phase, cold worked without cracking
  •  carbon is 0.09% at1493*C
  •  BCC structure

GAMMA AUSTENITE

  •  interstitial solid solution of carbon in Y-iron
  •  Solubility of carbon upto 2% at 1147*C
  •  Lowest temprature is 727*C at 0.8%C
  •  FCC structure
  •  Soft ductile malleable and non magnetic in phase

ALPHA FERRITE

  •  solid solution of carbon in a- iron
  •  Low solubility of carbon about 0.025% at 727*C
  •  BCC
  •  Soft and Ductile