Welding Inspection & Metallurgy API ICP Self Study Notes

Austenite
Austenite (γ), is a solid solution, that is, the component elements are
arranged as if in solution (it also exists as an allotrope of pure iron). All steel
exists in this form at sufficiently high temperatures (see figure 1). Some alloy
steels stabilise this singular phase and it is present even at room
temperatures. The crystal arrangement is face centred cubic (fcc) and, like
ferrite, it is soft and ductile.
Cementite
Cementite is iron carbide (Fe 3 C), When carbon atoms can no longer be
accommodated in solution in ferrite and austenite (due to an increase in
carbon content or reduction in temperature), cementite forms, as it can
accommodate more carbon in its crystal structure. Like other carbides, it is
hard and brittle.