Blacksmithing
and Cutlery
by Gérard HEUTTE
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Glossary for steel metallurgy
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There either, this small glossary does not have
the claim to be worthy of a metallurgy course! It is however
words of which the meaning should be known.
> a-Iron:
State of pure iron below 960°C. It has BCC
structure. It accepts only one very low percentage of carbon.
It is ferromagnetic.
> d-Iron:
State of pure iron between 960°C and 1400°C. It
has a FCC structure. It dissolves carbon easily. It is paramagnetic.
> Ac1: Initial
temperature of transformation from Pearlite to Austenite. Value
estimated towards 720 to 727°C.
> Ac3:
Temperature of end of transformation from Pearlite to Austenite.
It is admited for hypereutectoid steels that Ac3 = Ac1 because
all the Pearlite is transformed in Austenite, even if it remains
a bit of Cementite (in general some percents).
> Am:
Temperature of end of transformation of Cementite in Austenite .
> Annealing: It
is a heat treatment consisting in heating steel, then to cool it slowly
to decreases the internal tension and hardness.
> Austenite:
Solid Carbon solution (until 2%) in d-Iron. In nonallied steels,
it can only exist hot. Austenite can exist at ambient temperature
only in the presence of alloy elements (Nickel and Manganese).
Whatever the percentage of carbon of steel, this carbon
dissolves in a homogeneous way in austenite.
> Bainite: This structure
looks like Pearlite but of very
fine structure and in the form of microscopic needles. It is
less hard than Martensite.
> Body Cubic Centered (BCC):
Crystalline structure where the atoms are laid out on the tops
of a cube with an atom in the center of the cube.
> Cast iron:
Hard and breakable carbon and Iron alloy with a percentage of
carbon of more than 2%. Unused in cutlery.
> Cementite: The
other name of iron carbide (Fe3C). This compound contains 6.7% of Carbon (in
mass). The pure cementite is very hard.
> Eutectoid:
Steel having a percentage of carbon of 0.77%.
Cold and not hardened, this steel is composed of grains of Pearlite.
> Face Centered Cubic (FCC): Crystalline
structure where the atoms are laid out on the tops of a cube with 6 atoms distributed
at the center of each face of the cube.
> Ferrite:
Macroscopic structure of a-Iron with very little dissolved
carbon (a few tens of ppm according to the temperature. Ferrite is presented physically
in the form of grains (observable with a weak enlargement).
> Grain: The annealed
steel at ambient temperature consists of grains
(Pearlite, Ferrite). The border between two grains is called
"grain boundary". With a coarse grain, a blade will be less
hard and more fragile. One of the goals of the heat treatments
is to refine the grain. In general, a too strong or prolonged
heating increases the size of the grain.
> Hardening :
It is a heat treatment consisting in brutally cooling heated steel to harden it.
> Hypereutectoid:
Steel having a percentage of carbon higher
than 0.77%. At cold and not hardened, this steel is composed of
grains of Pearlite. "Excess" Carbon (i.e. > 0.77%) is found in the grain
boundaries in the form of Cementite.
> Hypoeutectoid:
Steel having a percentage of carbon lower than
0.77%. At cold and not hardened, this steel is composed of
grains of Pearlite and grains of Ferrite.
> Iron-Carbon Diagram:
Also called state diagram. It gives the structure of
steel according to the percentage of carbon and the temperature.
> Martensite: Componant
coming from hardening. When Austenite is cooled quickly,
the changes of structures do not have time to be done. It then
appears a structure having the shape of needles, very hard but
fragile: Martensite. It is a solid solution of
supersaturated insertion of carbon in d-Iron.
> Normalization:
It is an heat treatment to refine the grain of steel.
> Pearlite: It
is a mixture of Ferrite and Cementite in the form of grains.
This grain contains 0.77% of carbon (in mass). Its name
comes from its resemblance to pearls... The pearlite can exist
in lamellate form (layers of Ferrite and Cementite) or globular
(Cementite particles in Ferrite).
> Steel: Carbon
and Iron alloy. The percentage of carbon can vary from 0.02% to
2%. You could find more or less arbitrary classifications:
soft, half-hard, hard, very hard. Steel takes hardening
from 0.35% of carbon. The steels used in cutlery go in general
from 0.45% to 1.6%.
> Tempering: It is
a heat treatment consisting in slightly heating steel after hardening,
to remove its brittleness at the detriment of a little loss of hardness.
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