Product Warranty

STEEL
64
T
he purpose of this guide is to provide a
detailed look into steel. The world of steel
is as fluid as molten metal. It is ever-
evolving.
Steel as a matter of opinion is very subjective
as it relates to knives and knife knuts. There is
no clear cut answer as to which is the best steel.
We have different requirements and preferences.
Our hope, is this guide will help you
understand the world of steel a bit better and
perhaps assist you in better defining what your
own preferences are and why.
A word of caution, this information is not
intended to be all-inclusive, nor could it ever be.
We at Spyderco, just like all other people,
gravitate towards superior products. We are
committed to using the best materials available at
the time. As the world of steel evolves, so do our
products. There are over 3000 different types of
steel, each having its own positive and negative
attributes. In order to determine your own
preferences, it is perhaps best to first understand
the history of steel and how it is made.
Although an exact date of discovery is not
known, man has been forging steel for as long as
he’s been working iron. Ironworkers learned to
make steel by heating wrought iron and charcoal
(a source of carbon) in clay boxes for a period of
several days. By this process the iron absorbed
enough carbon to become a true steel.
Iron by itself is a relatively soft metal, it
does not hold a good edge. However, if you
add Carbon it hardens the iron, making steel.
Steel has proven to be ideal for making edged
weapons.
At a very simplified level, making steel is like
baking a cake. You follow a precise recipe to
achieve the type of cake (steel) that you desire.
You begin with flour (iron) and from there you
add various ingredients (elements). These
additional ingredients will determine what type
of cake (steel) you end up with. Once you have
added all of the additional ingredients (elements)
you are left with a batter that is ready to bake
(heat treat). Baking (heat treating) is just as
much a part of the “recipe” as the ingredients
(elements). If not done properly, several
properties can suffer. Once baked, you have a
new – completely different – finished product.
Your cake will forever be a cake, it can never go
back to being batter. Of course steel can be re-
melted to a molten state, but that simply is the
beginning of becoming a new type of steel.
Steel is an alloy of iron and carbon; just as
bronze is an alloy of copper and tin. Historically,
steels have been prepared by mixing the molten
materials. Alloying elements are melted and
dissolved into molten iron to make a steel. The
molten steel is cast into an ingot, which is then
rolled out (while it is still hot) and shaped much
like you would roll out cookie dough. As the
steel begins to slowly cool below the critical
temperature, things start to happen inside the
steel. At these elevated temperatures, alloying
elements are able to move around in the steel,
or diffuse. Different elements diffuse at different
rates, (typically the larger the atom, the slower
it diffuses). If the alloying contents are too
high for some elements to assimilate with, the
excess will separate or segregate out of the
steel and form inclusions or possibly combine
with another element to form large undesirable
carbides. These diffusional processes are also
controlled by the austenite grain size of the steel
– grains are little packets of specifically oriented
crystals. Grain boundaries act as barriers to
diffusion, the smaller the grains, the more
boundaries, and the slower the steel. This limits
the performance capabilities of the steel both
in corrosion resistance, and in wear resistant
carbide formation.
More recently, Powder Metallurgy has
become the chosen method of preparation.
The difference in the processing of a powdered
metal allows for steel chemistries not possible
with traditional steel-making practices. The
process starts out the same as wrought steels –
alloying elements are added and dissolved into
molten iron. Then comes the main difference.
The molten steel is atomized (misted into
microscopic droplets) into liquid nitrogen where
the steel is instantly frozen, leaving no time
for diffusional processes. The chemistry of
the resulting powder is identical to that in the
molten vat. Additionally, there are no inclusions
or large carbides that form. The austenite grain
size is the size of the powder at the very largest,
which is small. The powder is then cleaned
and sorted by size and then the remaining ideal
powder is sintered in a hot isostatic press to
solidify the steel. Sintering is heating the steel
to a temperature just below its melting point,
and then pressing it together at high pressures
to solidify or remove the voids between powder
spheres. This allows for drastic changes in the
steel chemistry namely in carbon and vanadium.
A larger volume of the highly wear resistant
vanadium carbides form upon heat-treating.
Since Vanadium has a greater propensity to
interact with carbon and form carbides than
it does with Chromium, most of the excess
carbon is utilized in the formation of vanadium
carbides. These leave the Chromium free to help
keep the steel corrosion resistant. The result
is a premium steel product with properties of
exceptional wear-resistance and good corrosion-
resistance.
Heat treating the steel to its critical
temperature allows the carbon atoms to enter
into the crystalline molecules of the iron which
have expanded due to the heating. Quenching
the steel at this point causes the molecules to
contract, trapping the carbon atoms inside.
More specifically, the process of hardening
steel by heat treatment consists of heating
steel to a temperature at which austenite
is formed. Austenite has the property of
dissolving all the free carbon present in the
steel. Quenching is then used to “freeze” the
austenite changing it to martensite. These
treatments set up large internal strains in the
steel; these are relieved by tempering (further
heating the steel at lower temperatures).
Tempering the steel decreases the hardness,
strength and brittleness. It however, increases
the ductility and toughness.
STEEL ELEMENTS
TEMPER IS A FUNNY
THING; IT SPOILS CHILDREN,
RUINS ADULTS, AND
STRENGTHENS STEEL.