The Iron-Iron Carbide Phase Diagram

1
The Iron-Iron Carbide Phase Diagram

• Heat Treatment of Steel

2
(No Transcript)
3
Features
Phases present
L
a ferrite Bcc structure Ferromagnetic Fairly
ductile
d Bcc structure Paramagnetic
g austenite Fcc structure Non-magnetic ductile
Fe3C cementite Orthorhombic Hard brittle
Reactions
Peritectic L d g
Max. solubility of C in ferrite0.022 Max.
solubility of C in austenite2.11
Eutectic L g Fe3C
Eutectoid g a Fe3C
4
Microstructures
a
g
5
Steels
Steel is an interstitial solid solution of carbon
in iron. Theoretically steel has a maximum of
2.11 carbon. In practice, the amount of carbon
rarely exceeds 0.8
Classification/Nomenclature
Low carbon steels up to 0.2C Medium carbon
steels 0.2-0.4C High carbon steels gt0.4 C
AISI 1020 Last two numbers indicate Amount of
carbon 0.2C 10 indicates plain carbon
steel AISI 4340 0.4C 43 indicates alloy steel
6
Microstructural changes in steel on cooling for
different compositions
7
Eutectoid steel
8
Hypoeutectoid steel
9
Hypereutectoid steel