: The Working Of Steel

SILICON is a very widespread element (symbol Si), being an essential

constituent of nearly all the rocks of the earth. It is similar to

carbon in many of its chemical properties; for instance it burns

very readily in oxygen, and consequently native silicon is unknown--it

is always found in combination with one or more other elements.

When it bums, each atom of silicon unites with two atoms of oxygen

to form a compound
nown to chemists as silica (SiO2), and to the

small boy as sand and agate.

Iron ore (an oxide of iron) contains more or less sand and dirt

mixed in it when it is mined, and not only the iron oxide but also

some of the silicon oxide is robbed of its oxygen by the smelting

process. Pig iron--the product of the blast furnace--therefore

contains from 1 to 3 per cent of silicon, and some silicon remains

in the metal after it has been purified and converted into steel.

However, silicon, as noted above, burns very readily in oxygen,

and this property is of good use in steel making. At the end of

the steel-making process the metal contains more or less oxygen,

which must be removed. This is sometimes done (especially in the

so-called acid process) by adding a small amount of silicon to

the hot metal just before it leaves the furnace, and stirring it

in. It thereupon abstracts oxygen from the metal wherever it finds

it, changing to silica (SiO2) which rises and floats on the surface

of the cleaned metal. Most of the silicon remaining in the metal

is an excess over that which is required to remove the dangerous

oxygen, and the final analysis of many steels show enough silicon

(from 0.20 to 0.40) to make sure that this step in the manufacture

has been properly done.