The mirror., 1922-02-23
METALLURGY

Fahrenhelt. when the iron gets that hot,
it is a liquid, and flows little faster than
oil. You see what naturally comes next.
Why not pour it into moulds? 1t flows
easily; it will take the shape of the mould
all right. That is what is done. The
legs and bases of machinery, the solid
sides and frames of many utensils, stoves
and other things are made by casting the
iron in the proper moulds.
Cast iron is very brittle! Hit it with
hammer and it will crack in two. 1t will
hold up heavy load, but won't stand for
any pounding. Malleable iron is made
from white cast iron i. e. cast iron in
which most of the carbon is in combina-
ton with the iron. 1t is the carbon COM
bined with the iron that makes. white cast
iron so brittle. What can you do about
it? Anneal it! What do we mean by
annealing? Just raise the white cast iron
rapidly to nice cherry-red heat and keep
it there without air for at least sixty
hours. Then cool it down slowly.
The carbon won't stand for iron that
hot especially without air, so it divorces
the iron, and forms small globules of gra-
phite. Of course graphite is simply car
bon in another form, just as ice is water
in another form. Changing the combined
carbon to graphite takes much of the brit
tleness out of the iron. Malleable iron,
then, is much stronger than cast iron, and
you can bend it and work it to some ex-
tent-but you cannot weld it. 1t is used
lot for hardware castings Wrought
iron as the name suggests is simply iron
that can be worked readily. Why? Be-
cause they get rid of most of the carbon,
which we have seen makes iron brittle.
The carbon is removed by process called
oxidation" which, in every day language,
means burning the carbon in the presence
of oxygen of the air. The hard worked
"pig" iron is heated to the molten state,
and most all the carbon burnt out with
the help of an air blast.
Like your automobile engine, iron
"works" better after the carbon has been
removed. Wrought iron is fbrous and
sticks together like glue. Mighty different
from cast iron in this way. 1t isn't real
fibre, because iron is crystalline, but by
trick of the heat, the crystals, twisted and
rolled like molasses candy, becomes fbrous
in shape. You can bend it easily, you can
forge it, and you can weld it-sometimes
it is called Norway Iron. 1t is so tough
it is used for chain links, angles braces
and the like.
So much for iron, let US continue on our
way and see how we get steel. Do you
eat pie? The reason I ask is because there
is great similarity between pie crust and
steel, as you will soon see. If your pie is
made with too little lard, the crust is
tough-but just the right amount, and you
have piece of pie that-well, you know
what mean! Likewise if you add car
bon to iron, you get the same idea. Low
carbon means toughness and softness, high
carbon means hardness and brittleness.
Of course you can mix lard and -four to-
gether all day, but if you don't put it in
the oven and heat it, you wont have any
thing but lard and -four. Same with car
bon and iron. Its the heating that does
the trick. And by different kinds of heat
ing and cooling, you get surprising var
iety of physical properties. Enough tests
have been made so that men who make
steel can work by rule, and know each
time what they are going to get Many
people are under the impression that cold
rolled steel is particular grade of steel,
like machine steel or tool steel. Such is
not the case. Cold rolling is merely pro-
cess, and consists of rolling the steel after
it has cooled to some extent (the usual
process is to roll it white hot). This pro-
4 III l.