In-Depth Analysis: Fe-Fe3C Phase Diagram, Heat Treatment, Properties

This assignment provides detailed solutions related to the Fe-Fe3C phase diagram and various heat treatment processes. It covers topics such as the characteristics of ferrite, cementite, austenite, and pearlite, including their composition, crystal structure, and mechanical properties. The solution also addresses the causes of peak broadening in materials analysis, such as instrumental factors, crystallite size, strain, and defects, along with the relationship between microstrain and peak broadening. Furthermore, it includes calculations related to crystallite size determination using the Scherrer equation. The assignment contrasts quenching and annealing procedures and their effects on microscopic, material, and macroscopic properties. It also provides sketches of expected microstructures for quenched and annealed specimens, explanations of heat treatment processes like annealing, normalizing, tempering, and quenching, and discusses age hardening and phase transformations using the Avrami equation to analyze transformation kinetics. The role of nucleation sites in transformation processes is also examined.

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)