Barton County democrat. [volume] (Great Bend, Kan.) 1885-1915, 1889-02-21
rEMRERINc STEEL.
How 1t Is Done And Theories Accounttn
for the Process.

In the whole range of mechanical
arts, says the Je,0elry RecieU, it would
be nearly impossible to find another
process at once so simple and so COM
mon in principle, and yet so little un-
derstood in theory, as the hardening
and tempering of steel. 1t was proba-
bly, this fact which some years ago led
the Institute of Mechanical Engineers
of England to place this subject among
those to be specially Investigated by a
committee of its own members, who
reported upon it in due time. To
illu@trate the facts that require scienti-
fic explanation, the process of harden
ing and tempering a cold chisel, which
is usually done at one operation, may
be briefly described.
After heating the point it is dipped
in cold water and thus the tool. is
hardened. After cooling the smith
lifts the steel from the water and
watches it closely, as the heat remain
ing in the body of the metal diffuses
itself through the hardened portion
As the heat spreads the color passes
from white luster to a pale yellow, to
straw color, to a brownish orange.
Then the point is dropped into the
water again, in the full confidence
that after cooling the temper will be
that desired. If the smith DELAYED the
brown would become drappled with
purple and would then pass success
lively into full purple, light blue, full
blue, dark blue, and each color would
give its own temper upon cooling, as
bright blue for swords and watch
springs, dark blue for saws, etc.
These are the we'll known facts, and
yet their show and ''why" has always
been equally mystery to the artist
and the scientist. although upon the
correct solution of the problem de-
pends SO important a matter as knowl-
edge of how best to reach that judicious
compromise which should blend the
maximum of hardness and toughness.
Now either can be procured at pleasure,
as the colder the bath the harder the
steel, and the slower Gas in oily the
tougher; but the extreme hardness is
produced at the strength of tenacity,
and vice versa. The committees con-
clusion was suggested by Edison's ex-
periments upon wire, which he made
public in 1879. These experiments
showed that incandescent plantinum
wire became covered with minute
fissures. due to the expiration of the
occluded gases under the action of
heat, and that when the wire was
cooled in a vacuum the assures closed.
BY succession of heatings and cool
ings the gases were entirely expelled
and the platinum became much harder
and denser. AS the committee sug-
gests. it may be that the first and ex-
treme heat dries ont the gases occluded
at ordinary temperature, thus pro-
ducing the denseness of hard steel.
When the metal is slightly heated, as
in tempering. reabsorption begins, and
the characteristic colOrs are due to the
changes in the surface, the gradual
opening of minute assures. which are
produced by this reabsorption.
In con nection with this latest theory
may be mentioned one or two earlier
ones. One is that when steel is heated
the carbon becomes amorphous and
the steel is soft, while if cooled quickly
the carbon crystalizes, taking the
properties of diamond, and the steel
becomes, as it were, diamond set in
iron. This theory of. Jullen's is, per-
haps. the most striking one, but. while
accounting for hardness, it does not
explain the temper of steel, to say
nothing of objections to the postulated
of carbon