METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 1
(b) Cast iron differs from steel principally because its excess
of carbon (exceeding 1.7 percent) is precipitated throughout the
matrix as flakes of graphite, which cause most of the remaining
carbon to also precipitate.
These particles of graphite form the
paths through which failures occur and are the reason why cast iron
is brittle.
By carefully controlling the silicon content and the
rate of cooling of cast iron, it is possible to cause any specified
amount of the carbon to precipitate as graphite or to remain
combined.
Thus, we have white, gray, and malleable cast iron, all
produced from similar base metals.
c.
Ferrous Metals.
(1) Wrought Iron.
Wrought iron is almost pure iron.
In the
process of manufacture, some slag is mixed with iron to form a
fibrous structure in which long stringers of slag are mixed with long
threads of iron.
Because of the presence of slag, wrought iron
resists corrosion and oxidation.
It can be gas or arc welded,
machined or plated, and is easily formed. However, wrought iron has
low hardness and low fatigue strength.
(a) Uses.
Wrought iron is used to make such
items as
architectural railings, farm
implements, and modern
household
furniture.
(b) Capabilities.
Wrought iron can be gas or arc
welded,
machined, and hot- and cold-worked. It can also be plated.
(c) Limitations.
Wrought iron has low hardness and low fatigue
strength.
(2) Cast Iron (Grey, White, and Malleable). Cast iron, developed
in the latter part of the 18th century, is a man-made alloy of iron,
carbon, and silicon.
Cast iron is nothing more than basic carbon
steel with more carbon added, together with silicon.
A portion of
carbon exists as free carbon or graphite.
Total carbon content is
between 1.7 and 4.5 percent.
(a) Uses. Cast iron is used to manufacture such items as water
pipes, machine tool castings, transmission housings, engine blocks,
pistons, and stove castings.
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