Normalizing is a heat treatment process that is used to make a metal
more ductile and tough after it has been subjected to thermal or mechanical
hardening processes. Normalizing involves heating a material to an elevated
temperature and then allowing it to cool back to room temperature by exposing it
to room temperature air after it is heated. This heating and slow cooling alters the
microstructure of the metal which in turn reduces its hardness and increases its
ductility.
Normalizing is often performed because another process has intentionally or
unintentionally decreased ductility and increased hardness. Normalizing is used
because it causes microstructures to reform into more ductile structures. This is
important because it makes the metal more formable, more machinable, and
reduces residual stresses in the material that could lead to unexpected failure.
Normalizing is very similar to annealing as both involve heating a metal to or
above its recrystallization temperature and allowing it to cool slowly in order to
create a microstructure that is relatively ductile. The main difference between
annealing and normalizing is that annealing allows the material to cool at a
controlled rate in a furnace. Normalizing allows the material to cool by placing it
in a room temperature environment and exposing it to the air in that environment.