The Ohio Democrat. (Logan, O. [Ohio]) 1886-1906, 1889-01-12
TEMPERING STEEL.
A Simple Mechanical Art Whose Theory II
Not Generally Understood.

n oimpie meCubnfCnl ArJ WnOAe Ineory L
Not Generally Understood.
In the whole range Of the mechanical
nrts 1t would be nearly impossible to
find another process at once so simple
aud 80 common in principle, and yet
30 little understood in theory, as the
hardening and tempering OF Steel. 1t
was probably this fact which some
years ago led the Institute of Mechani-
cal Engineers of England TO place this
subject among those to be specially in
vestigated by committee OF its own
members. who reported upon it in due
time. To illustrate the facts that re-
quire scientific explanation, the pro-
cess of hardening and tempering 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 hard
ened. After cooling, the smith lifts
tho steel from the water and watches it
closely as the heat remaining in the
body Of the metal diffuses itself
through the hardened portion. As
the heat spreads the color passes
from white luster to pale yellow,
Then the point is dropped into water
again, in the full confidence that, after
cooling, the temper will be that desired.
If the smith delayed the brown would
become dappled with purple, and
would then pass successfully into full
purple, light blue. full blue, dark blue;
and each color would give it's own
temper upon cooling, as bright blue
for swords and watch springs, dark
blue for saws, etc. These are the
well-known facts, and yet their
chow" 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 matter as knowl-
edge of how best to reach that Judi
cious compromise which should blend
the maximum of hardness and tough
ness. Now, either can be procured at
pleasure, as the colder the bath the
harder the steel, and the slower (as in
oily the tougher; but extreme hardness
is produced at the strength of tenacity,
and Cice Uersa. The committees oon-
clusion was suggested by Edison's ex-
periments upon wire, which he made
public in 1879. These experiments
showed that incandescent platinum
wire became covered with minute fs.
sures, due 10 the expiration of the oc-
81, nd crna th.a Of
and that when the wire was cooled in
vacuum the fissures closed. BY q
succession of heatings 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 and extreme heat
dries out the gases occluded ut ordin-
ary temperature, thus producing the
denseness of hard steel. When the
metal is slightly heated, rs in temper
ing. reabsorption begins, and the char
acteristic colors are due to the changes
in the surface, the gradual opening OF
minute assures, which are produced by
this reabsorption. In connection with
this latest theory may be mentioned
one or two earlier ones. One is that
when steel is heated the carbon be-
comes ainorphous and the steel is soft,
while if cooled quickly the carbon
crystallizes, taking the properties of
diamond, and the steel becomes, as it
were, diamond set in iron. This theory
of Julien's is, perhaps, the most strik-
ing one, but, while accounting for
hardness, it does not explain the tenn
per of steel, to say nothing of objec-
tions TO the postulated liquefaction of
ca rhnn -.LemeLorS' Relinm