Page 42 - Corrosion Engineering Principles and Practice
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24 C h a p t e r 2 C o r r o s i o n B a s i c s 25
Fe
Austenitic
Ferritic stainless steels
stainless steels
Fe-based
superalloys
Cr-based Ni-based
alloys BCC superalloys
BCC + FCC
FCC
Cr Ni
FIGURE 2.2 Cr-Fe-Ni ternary phase diagram showing body-centered and face-
centered cubic crystal domains with examples of alloying families.
The crystals, or grains, of a metal are made up of unit cells repeated
in a three-dimensional array. However, the crystalline nature of metals
is not readily obvious because the metal surface usually conforms to
the shape in which it has been cast or formed. In some instances, the
crystal structure can be observed naturally. Figure 2.3 is a photograph
of the surface of a hot-dip galvanized post with characteristic spangle
FIGURE 2.3 Hot-dip galvanized steel with spangle patterns that are a form of
crystallized grains.
