Different Phases in Fe-Fe3C Phase Diagram

This article discusses the different phases in Fe-Fe3C phase diagram including Ferrite, Cementite, Austenite, and Pearlite. It explains their properties, crystal structures, and solubility of carbon. The article also covers the concept of peak broadening and the difference between quenching and annealing procedures. Additionally, it provides an explanation of the heat treatment process for annealing, normalizing, tempering, and quenching. Finally, the article explains the concept of age hardening and the Avrami equation.

Solution
a)

b)
Ferrite:
Solid solution of carbon in BCC iron from room temperature to 910 deg.C
 Max solubility of C is .. 0.022% at temp. of 727 deg.c
 Also called as Alpha Ferrite.
 Softest phase in Fe-Fe3C phase diagram.. less strength and High ductility
Cementite:
 Intermetallic compound of Carbon combined with Iron..Fe3C
 Max solubility of Carbon is of 6.67%.
 Orthorhombic crystal structure

 Hardest and most brittle phase among all Fe-Fe3C phases.
Austenite:
 Solid solution of Carbon in FCC iron..Also called as Gamma Iron.
 Exists from 910–1395 deg.C
 Max solubility of Carbon .. 2.11% at 1147 deg.C
 Toughest phase among all… Strength along with optimum Ductility
Pearlite:
 Mixture of Ferrite and Cementite (alternately arranged as like pearls)
 we can find 100% pearlite at 727 deg.C.
 Soft Phase than Austenite but posses better strength than Ferrite.

c)

d)

e)

f)
The peak broadening can come from different sources they are ,Instrumental , Crystallite size,
Strain, stacking fault and other defects. The microstrain will result in peak broadening. In principle
every extended defect will contribute to broadening. Peak broadening indicates crystallite smallness
and microstresses, however, stress gradients and/or chemical heterogeneities can also cause peak
broadening

g)
D=Kλ/(β cos θ) ,
β = FWHM*2π/360
k= 0.9, λ=0.154nm, θ=7.21, β = FWHM*2π/360=0.1635*2π/360
θ must be in radians,
θ=7.21 / 2 = 3,605 (degrees), becouse 2θ=7.21
θ(rad) = 3,605*2π/360=0,0629
So cos θ = 1 and
D=48 nm
h)
The different between quenching and annealing procedures.
i) Microscopic properties (grain size, grain boundary)
ii) Material properties (hardness, yield strength, modulus of elasticity)
iii) Macroscopic properties (color, size, toughness)
2. Sketches of the expected microstructure of a quenched specimen and an annealed specimen
compared to visual differences you expect to see under the microscope.

.
3. Explanation of the heat treatment process for annealing, normalizing, tempering, and quenching.
Q2a)

The term age hardening is a general term referring to most (if not all) time and/or thermal treatments
to increase the strength (and sometimes the ductility) of a heat-treated metal. It can result the
release of built-in stresses or permit phases locked in (due to quenching) to transform
b)
Time Log t Fraction transformation (f)
0 0.000
1 0 0.025
2 0.301 0.068
4 0.602 0.181
8 0.903 0.432
16 1.204 0.798
32 1.505 0.989
64 1.806 1.000

Avrami equation
Y = 1 – exp(-ktn)
Ln(1-y) = ktn
ln(1-0.432) = k*81.5
k = -0.5656/ 81.5
k = -0.025
C)
The n is held to have integer value between 1 and 4 which reflects the nature of the transformation, in
the distribution of nucleation sites is non-random then the growth may be restricted to 1 or 2
dimension, which leads to n values of 1, 2 or 3 surface, edge and point site respectively
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 0.5 1 1.5 2
fraction transformation (f)
log t
Y-Values
Linear (Y-Values)