Wood County reporter. [volume] (Grand Rapids [i.e. Wisconsin Rapids], Wis.) 1857-1923, 1888-11-29
The Science of Tempering Steel.
Io,-o1ors. Da,-so,--

In the whole range of mechanical arts
it would be nearly impossible to find
another pocess at once SO simple
and so common In principle, and
yet SO little understood in theory, as the
hardening and tempering CT steel. 1t
was probably this fact which some years
ago led the Institute of Mechanical En-
glneers of England to place the subject
among those TO be speciNlly investiga ed
by committee of its own members, who
reported upon 1t In due time. To illus
trate the facts that require scientific ex-
PLANTATION, the process of hardening and
tempering q cold chisel, which is usually
done at one operation, may be briefly des-
cribe6. 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 remaining in the body
Of the metal diffuses itself through the
hardened portion. As the heat spreads
the color passes from a white ulster to a
pale yellow, to straw color, to brownish
orange. 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 snccessiveiy into full
purple, light blue, full blue, dark blue;
aud each color would give its own temper
upon cooling, IS bright blue for watch
springs, dark blue for saws, etc. These
are the well-known facts, and yet their
chow" and "why" has always beeu equally
mystery 10 the artist and to the scient-
ist, although upon the correct solution of
the probe n depends so i'm portant mat
xar lyY NcA s., 20
that judiciOus-comp promise 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 (as in
OILY the tougher; but extreme hardness is
produced at the strength OF tenacity, and
vice versa. The committees conclusion
was suggested by Edison's experiments
upon wire, which he made public in 1879.
These experiments showed that incande-
scent platinum wire became covered with
minute assures, due to the expiration of
the occluded gases under tie action of
heat, and tEat when the wire was cooled
in vacuum the assures closed. By a
succession of heatinRs and cooiings the
gases we're 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 at ordinary
temperature, thus producing the dense-
ness of hard steel. When the metal is
slightly heated, as in tempering, reab-
sorption begins, and the charistic oolors
are due to the changes in the surface, the
gradual opening of miHute assures,
which are produced by re-absorption In
connection with this latest theory may
be mentioned one or two earlier ones.
One is that when steel is heated the car
bon becomes amorphous and the steel is
soft, while if cooled quickly the carbon
crystalizes, taking the properties of dia-
mond, and the steel becomes, e. it were,
diamond set in iron. This theory of
Julian's is, perhaps, the most striking
one; but while accounting for hardp es SO
it does not account for the temper.