The Milan exchange. (Milan, Gibson County, Tenn.) 1874-1978, 1875-01-21
Steel.

The question, What is steel? has be-
come, within the past few years, some
what important and troublesome one.
! Formerly the classification of iron and
steel was easy, because, so far as metal
| lurgieal knowledge went, the chemical
constitution of each class agreed with its
peculiar physical characters. 1t used,
| therefore, to be said land most textbooks
contain this statement still), that an alloy
of carbon and iron, containing not less
than per cent. nor more than 6 per cent.
of carbon, is pig iron or cast iron. The
term ''pig" is derived from the appear
ance of the numerous bars as they are cast
in sand-molds from the blast-furnaee, on
the floors of the clearinghouse. They lie
parallel with each other, at right angles to
the runner. through which they are filed
with molten metal, and are fancifully COM
pared to a litter of pigs, sucking at the
sow. Pig iron is hard and comparatively
brittle, and melts more easily than
wrought iron or steel.
Wrought iron, according to the old
classification, is the nearest approach to
the pure metal obtainable on a large scale
in manufacture. 1t now contains more
than quarter of one per cent. of carbon,
is soft, malleable, extremely tenacious, and
infusible in ordinary furnaces. But it is
capable of welding at white heat, and re-
tains its sOftness when heated and sudden
iy cooled. Every body who has watched
the operations of blacksmith land who
has not been fascinated by such exhibi-
tiOns of dexteirty p will understand some
thing of the peculiar properties of
wrought iron and their extreme usefulness
to man.
Steel has been defined as comprising those
varieties of iron in which the amount of
carbon is above the maximum of NAL
leable, and below the minimum of cast
metal, that is, above OBS and below per
cent. The peculiar properties of steel,
supposed to belong to this chemical COM
position, are, that it can be tempered"
that is, hardened or sOftened at pleasure,
by rapid or slow cooling; and that it is
fusible Though at higher temperature
than cast iron) and malleable (thOugh un-
der greater force than wrought irOn).
The methods of manufacturing the diff
ferent varieties of iron and steel are nu-
merous. The most widely employed ap-
paratus is the blast-furnace, in which iron
ores are reduced with solid fuel focal, char
coal or COKE and the molten product is
cast-iron. This is refined to wrought
iron by the "puddling" process, which
removes the carbon and the wrought
iron, itself comparatively infusible, used
to be converted into steel, either by bury
ing and baking {" cementing") it in car
bOnaceOus materials, or by melting it in
crucibles with suitable fluxes and admix-
lures.
But the invention of two great metal
lurgical improvements has greatly changed
the relations of this question. By the
Bessemer process cast-irOn is deprived of
its carbon 1--WE take no account, for our
present purpose, of silicon and other in
gredients), by forcing air through the
molten mass and burning out the carbon.
This process generates a temperature so
intense as to melt wrought iron with
ease. The other invention referred to is
the SiemenS regenerative gas furnace, in
which temperature limited only in inten-
sity by the durability of the materials of
construction is obtained by the beautiful
expedient of abstracting heat from the Cs-
Gaping gases, after combustion, and add
ing it to the gases as they enter to be
burned.
We are not attempting to explain the
theory of either of these contrivances; all
we wish to point out is the popularity
common to both, of the production of tenn
peratures previously unknown in practical
metallurgy. The Siemens furnace, as well
as the Bessemer converter, has been sue
cessfully employed in the manuf .cture of
steel from pig iron, though by different
chemical reactions, the carbon being re-
moved, not by blast of atmospheric air,
but by the oxygen of iron scale, etc. The
steel thus made, known as Siemens-Mar-
tin steel, and that produced by the Besse-
mer process, may contain less carbon than
the maximum above given for wrought
iron; and these softest varieties of steel
have been the subject of much discussion,
being often declared to be no steel at all,
but only "Bessemer metal" or "Martin
metal" The term homogeneous metal"
has been proposed for them. Cast
wrought iron" is another and clumsy
title.
The fact is, that no sharp line can be
drawn between iron and steel. based on
their chemical constitution. The differ
ences in. physical properties, even, are
largely due to the process of manufacture;
and now that wrought iron can be melted
in large quantity, many of its peculiarities
are found to disappear, being merely the
result of the manipulation to which it was
formerly subjected.
Alexander Holly, the leading Bessemer
engineer of the United States, proposed
some years ago a definition of steel. to
meet the wants of the new era. Accord
ing to this definition, any cast, malleable,
homogeneous iron should be classed as
steel. And something like this will have
tO he adOntpd Christian I1lLOn.