Blacksmithing
and Cutlery
by Gérard HEUTTE
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Normalization
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During the hot work of the blade, the
rises in temperature are likely to enlarge the grain of steel.
In the same way, a blade worked by stock removal will have to
undergo this treatment, because you are unaware of the structure of
metal you purchase: The grain can be more or less coarse.
See the phenomenon in detail on the page devoted to
steel grain
.
Normalization is a heat treatment intended to refine the
grain. Moreover, a correctly led standardization makes
possible to almost undoubtedly avoid the deformations due to
hardening.
All steels do not get a similar benefit from normalization.
This is the case of stainless steels. The important
presence of chromium strongly modifies the data!
Thermal Cycle
Here is schematically the thermal cycle of normalization:
And various phases:
(1) Heating
Heating will be done at moderate speed.
The temperature for normalization (TN on the graph) is
specific to each steel.
Without precise data, two possibilities:
> Same temperature as for annealing.
> AC3 +30°C to +80°C (i.e. +54°F to +176°F) (for hypoeutectoids) or
AC1 +30°C to +80°C (i.e. +54°F to +176°F) (for hypereutectoids)
(2) Stage
The temperature of normalization will be
maintained for a short moment, about one minute and
a bit more for the massive parts.
(3) Cooling
Cooling will have to be sufficiently fast to
avoid the enlargement of the grain. Conversely, it should not
be too fast and create Bainite or Martensite.
The diagram above shows three successive cycles. To
start a new cycle, decrease the temperature until about
450-500°C.
Each cycle will be done preferably with a temperature slightly
lower than the previous cycle! If the blade becomes deformed
at the end of a cycle, it is necessary to rectify the blade and
to start again the process at the beginning. If
not, the straightening of the blade will not be enough to avoid deformations on hardening.
Implementation
Just as for annealing, a hardening oven
can be very useful for heating and the stage. But for cooling,
the fall of temperature will not be swift enough.
Heat steel at the temperature of normalization
then maintain it the required time (approximately a minute).
This operation could be done directly in the forge.
In a coal forge, move the blade in fire
for a complete and homogeneous heating.
It is then necessary to remove the blade from the forge with
tongs for cooling. Several possibilities:
> Let the blade quietly cool with the free air. I
find this cooling a little slow.
> Put the blade in front of one (large) fan.
> Balance the blade by a full movement of the arm. It
is what I usually do.
The blade will quickly cool while passing from red-orange to
the dark red, then to black. It is at this time that the
straightness will be checked:
> If the blade is twisted, heat it to forging
temperature and rectify it. You must
start again the three complete cycles of normalization!
> If the blade did not move, you can pass to the following
cycle.
For the following cycle, it will be necessary to try to go up a
little less higher in temperature.
Notes
> Three cycles are usually made. This
number does not owe anything randomly. The tests and the
analyses have shown that the first cycle was very effective. Each
successive cycle is a little less effective than the precedent!
The fourth does not have practically any more perceptible
effect! Thus stop at three cycles!
> Normalization makes possible to provide a good fineness
of grain. It is a strongly advised heat treatment!
> It is completely possible to obtain a fine grain without
normalization. It is necessary to have a very rigorous
working method on the level of the temperatures. Very often,
the blacksmiths who do not make normalizations finish their work by
"bleaching" the blade. This operation consists in working in
the lower range of the temperatures of forging (and below) by gently hammering the
blade with an abundantly wet hammer and anvil! This
operation removes calamine, improves the surface quality of the
blade. In term of heat treatment (i.e. temperature and time),
this operation presents a strong similarity with normalization! ! !
Self-test
To be sure to make correctly, experimentation and test are mandatory. Here is a practical
method to validate normalization process.
(1) Take a steel rod (XC75 / 1070), heat it at orange for a quarter of hour to increase
grain size. Harden it in oil the end of the rod.
(2) Break the end of the bar by locking it in a vise and winding a piece of rag
around it to avoid fragments.
(3) Keep this piece as a reference of worse result. This is to be avoided! This piece
must have a coarse grain, like sugar, bright and rough.
(4) Make 3 normalizations.
(5) Harden and break the end of the rod as above.
> If the grain has decreased, the process is right. The grain must be invisible with the
naked eye. If a magnifying glass is necessary to see it, it is OK!
> If the grain has increased or is unchanged, the steel was too hot or too cold…
Do not hesitate to sometimes do again this test to avoid drifts. It is very easy to make
normalizations a bit high in temperature, which decrease their efficiency.
From a
thread of Umbo/Greg on forgefr,
with his kind authorisation.
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