Richmond dispatch. [volume] (Richmond, Va.) 1884-1903, 1888-12-02
The hcfoncc az 7renpering steel
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/ In the whole range OF the mechanical
/ ants 1t would nc nearly impossible to find
another process, at once 50 simple and sc
common i'm principle. and yet 50 little
understood IN theory, as the hardening
amt tcmpcring OF steoi IL was probably
this fact which some years ago led the
Institute OF Mechanical engineers OF
England 10 place tins subject among
those 10 be- specially Investigated by a
committee of its own members,
who reported upon it IN due
time. To illustrate the facts That
require scientific explanation. the
process of hardening and tempering a
colt caisel, which is usually done ut one
operation, may bo briefly described.
sitter heating The point il Is dipped in
cold water anJ thus the tool Is hardened.
Alter cooling, the smith hits the steel
from the water aud watches IL closely as
the heat remaining in the body of the
metal dIAuscs itself through the hard
eu,d portion. As the boat spreads the
color passes from "a white lustre to a
uaio yellow. TO q straw color, TO q
hrownish orange. Then the point IS
dropped into water again. IN the full
confidence ,nat. after cooling the tenn
Ter VII De trat desired. If tho smith
delayed the brown would become dap
pied with purple, and would then pass
successfully into full purple, light blue.
ul blue, darh blue; and each color
would give its own t. mperupo cooling,
Gs bright blue for swords and wat b.
springs. dark blue for saws, etc. These
srs the well known facts, and yet their
" how and "Why" has always been
eloa iv q mystery to the artist and the
scientist, although upon tue correct
solution of the problem depends 50
important matter as knowledge of how
best 10 reach that iudic,ous com
promise which should blend tho
maximum Of hardness and toughness.
Now, either can be procured at pleasure,
as the colder tho bath the harder the
steel, and the slower (as in OH the
tougher; but extreme hardness 10 pro-
duced al the strength OF tenacity, and
rice yCrSQ. The committees conclusion
Syss suggested by Edlsou's experiments
upon wire, which he made public in 1879.
g hese experiments showed that mean
descent platinum vine became covered
with minute fssures. due 10 the ex-
pIration OF the oc,luded gases I'M
Ter the action OF heat and that
when the wire was cooled IN
vacuum toe assures closed by sue
cesslon of heatngs and cOohngs the
gases were entirely expelled and the
platinum became much harder and
icnser. AS the committee suggests, 1t
may be that the first and extreme heat
ires ont the gases occluded at ordinary
taus producing the dense I.
ness OF hard steel. When the metal IS .
lightly heated, as in temperlng, re- /
absorption begins, and the characteristic /
'0l0rs are due 70 the changes IN the sur
ace, the gradual opening OF minute ts-
ures which are produced by this reab-
0rption. In connection with this latest
heory may be mentioned one or
we earlier onea One is that when steel
5 heated the carbon becomes amorphous
nd the steel is loft, while il cooled
uiclly the carbon crystslliges, taking
he properties Of diamond, and the
teel becomes, as it were. diamond set in
ron. This theory OF Julicn's is, per
APPS, the most striking one, bat, while
ceounting for hardness, IL does not OK
lain the temper OF steel. TO say nothing
( objections to the postnlated hquefac-
on OF carbon.