Weekly expositor. (Brockway Centre, Mich.) 1882-1894, 1891-07-03
rEMPERINo STEEL.
Pale Yellow for Razors and Dark B,ue for
saws the Proper CoIors.

Pale Yellow Tor Hazors ana DARK h-ue Tor
saws the Proper Colors.
Steel has been defined as any kind
of iron which when heated to redness
and suddenly plunged into cold water
becomes hard; and every kind OF mall
leable or flexible iron that can be
hardened by that process is steel But
this definition Is not applicable TO the
steel Of mild quality DOW made for
many mechanical uses, says the Me-
chanical News One OF the requisites
for this mild steel is that 1t will not
harden after being heated to a cherry
red and plunged into water. To in
clude all the kinds of steel now used
In the agricultural and mechanical in
dustries, the better definition OF steel
will be, malleable iron combined
with percentage of carbon. Chemi-
cally considered. steel occupies half
way position between wrought and cast
iron, wrought iron being simply iron
almost entirely free from carbon,
while steel that is TO be tempered con-
tains TO II per cent OF carbon.
The reason why this very slight
change in the chemical construction
should produce such wonderful results
in the properties of iron and steel Is
as yet an unsolved mystery. We know
that bar OF iron converted into steel
becomes more granular or open. and
while il loses TO some extent its tough
ness, it gains. instead. elasticity
greater strength and closeness OF fibre.
Blister steel is made by heating bars
of iron packed in charcoal in furnace
for a period Of from six to ten days.
When the metal is withdrawn the bars
are found to be of crystalline texture
and have q blistered surface-hence
the name. Cast steel was formerly
made of blister steel broken into frag-
ments, melted into crucibles and cast
into ignots; but the modern practice is
to charge the crucibles with pieces OF
good Swedish or American bar iron,
adding charcoal and black oxide Of
manganese. The heat OF the furnace
soon seals the lid of the crucible. and
the melting iron absorbs carbon from
the Tunes of the charcoal, thus short
ening the tedious process OF making
"blister" bar. The cast steel is rolled
or hammered from the ignot to any
desired bar. sheet or plate.
The chief characteristic OF steel con-
sists in its capability of being hard
ened and tempered, and when exposed
to heat it takes on in succession the
following colors:
/. A faint yellow, which indicates a
proper temper for lancets or small cut
tiers that require the finest edge with
but little strength Of metal.
2. A pale yellow, which indicates
struments.
3. Full yellow. for pen-knives, etc,
with increased toughness.
4. Brown, with purple spOts-that
being for axes and carpenters tools.
3. Bright blue. forswords and watch
springs.
6. Full blue, fer fine saws daggers,
etc
Z. Dark blue, for large saws or in
struments that may be sharpened with
file
The above colors are based on steel
suitable for the requirements. A piece
OF steel suitable for razors, lancets,
etc., would not take the color indicated
for large saws, as that quality of steel
is but little above ''blister" quality.
The finer steel is the less heat it will
temper at requiring lower color of
temper. Recently there have been
valuable discoveries in tempering,
welding, and restoring steel, both
from burnt or low grade.