Wood County reporter. [volume] (Grand Rapids [i.e. Wisconsin Rapids], Wis.) 1857-1923, 1889-01-17
TEMPERING STEEL.
How ii is Done and Theories Accounting for
the Process.

How Ii Is Done and Theories Accounting for
the Process.
In the whole range of the mechanical
arts, says the Jewelry Review, it would
be nearly impossible to find another pro-
cess at once so simple and so common
in principle, and yet so little understood
in theory, as the hardening and temper
ing of steel. 1t was probably this fact
which some years ago led the Institute of
Mech anical Engineers of England to
place this subject among those to be
specially Investigated by committee of
its own members, who reported upon il
in due time. To illustrate the facts that
re quire scientific explanation, the pro
cess os hardening and tempering a cold
chisel, which is usually done at one oper-
alton, may be briefly described.
After heating the point it is dipped
in cold water and tt US the foot is harden
sd. After cooling, the smith lifts the
steel from the water and wa ches it close
Y, as the heat remaining in the body of
the metal diffuses itself through the hard
ened portion. As the heat spreads the
color passes from white luster to pale
yellow, to straw color to a bro Rnish
orange. Then the point is dropped into
water again, in the full confidence that
after cooling the temper will be that de-
sired. If the smith delayed, the brown
would become dappled with purple aud
would then pass successfully into fulS
purple, light 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 ere well known facts, and yet
their chow" and "why" has always been
equally mystery to the artist and the
scientist, although upon the correct solu-
ton of the problem depends SO import
ant matter as knowledge of how best to
reach the jodicious compromise which
should blend the maximum of hardness
and toughness. Now either can be proCuY-
ed at pleasure, as the colder the bath the
harder the steel, and the slower, (as in
oiD the tougher; but the extreme hai d
ness is produced at the strength of tena-
city, and vice versa. the committees
conclusions was suggested by Edison's
experiments upon wire, which he made
public in 1879. These experiments show
ed that inoap descent platinum wire be-
came covered with minute assures, due TO
the ex piration of the occluded gases M
DER the action of heat, and that when he
wire was cooled In a vacuum the assures
closed. By successor of heatipgs and
coolings the gases were entirely expelled
and the platinum became much harder
and denser. As the committee suggests,
it may be that the first extreme heat
dries out the gases occluded at ordinary
temperature, thus producing the dense
ness of hard steel. When the metal is
slightly heated, as in tempering, reab-
sorpiion begins, and the char -cteristie
colOrs are due to the changes in the sur
face, the gradual opening of minute rs
cures, which are produced by This rsab-
sorption.
In connection 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 cry ssallizes, taking the proper
ties of diamond, and the steel becomes, as
it were, diamond set in iron. The theory
of Julien's Is perhaps, the most striking
one, but, while accounting for hardness
itdoes not eI plain the temper of steel,
to say nothing of objections TO the pos
tulated hquefactiOn of carbon.