Iron and Aluminum. [Volume: 8, Issue: 2, 1888, pp. 116-122]

120

UNITED STATES ASSOCIATION OF

LVOL. 8,

The fineness of the grain of iron effected by aluminium causes
such iron to be much more easily cut than iron of coarser grain.
*X-, *-X- * * * *
The first, and each subsequent addition of aluminium, caused
the castings to be perfectly sound. and the infinitesimal atoms of
graphite deposited throughout the metal removed the rigidity and
brittleness of the initial metal. The gray iron base contained
enough silicon to accomplish all this, and the'only effect on strength
that the action of the aluminium on carbon could have, would be
to increase the fineness of the grain, unless the toughness of the
aluminium itself could give strength to the casting, though the
aluminium no doubt removed any slight blow-holes that existed
in the initial gray metal. This leads us to notice that each addition of aluminium increases the strength over that of the initial
metal. We mustexpect that after we have added enough aluminium
to cause a solid casting, and to remove the brittleness that the
dividing up of.the mass by the atoms of graphite accomplishes,
any further additions of aluminium, and consequent increase of
graphite, which has no strength of itself, must weaken the casting.
The compactness and closeness of the grain of cast iron when
aluminium was the agent by which the graphite was precipitated
and the fine attenuation of the veins of carburetted iron cause the
metal to be very elastic, and not so brittle as without aluminium
sand * * * The fineness and compactness of iron alloyed
with aluminium gives less permanent set than iron equally as soft
when such softness is produced by silicon.
The more suddenly and completely the carbon is changed from
combined to graphitic, at the instant of crystallization, the more
space will the casting occupy. When the casting is cold it will
therefore have contracted less than if more carbon had remained
combined. White iron, having most of its carbon in the combined
state, shrinks from one-fourth to one-third inch in each foot. Gray
iron sometimes shrinks as little as one-tenth to each linear foot.
As the combined is the natural state for the carbon, we may say
that this maximum shrinkage is the natural shrinkage for cast
iron having its carbon combined. We can therefore say that
aluminium takes out or reduces shrinkage when a sufficient quantity is added.
Viewed in a general way, the indications are that in a base, with