METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 2
4.
Fracture
Many metals can be identified by the appearance of the surface of the
broken part or by studying the chips produced with a hammer and
chisel, as described in the following paragraphs.
a.
Gray Cast Iron.
Nick a corner of the gray cast iron with a
chisel or hacksaw and break off by a sharp blow with a hammer. The
break will be short and the exposed surface will be dark gray in
color. This color is caused by the fine specks of carbon present in
the form of graphite dispersed throughout the metal. Chips raised by
a chisel break off as soon as formed.
b.
Malleable Iron.
The central portion of the broken surface is
dark gray with a bright steel-like band around the edge, somewhat
like a picture frame. When of good quality, malleable iron is much
tougher than cast iron and does not break short when nicked.
c.
Wrought Iron.
Wrought iron can be bent and is quite ductile.
When nicked and bent to the breaking point, the break is jagged.
Wrought iron has a fibrous structure and can be split in the
direction in which the fibers run. It is easily cut with a chisel.
d.
Low-Carbon Steels.
When low-carbon steel are fractured, the
color is bright crystalline gray. The metal is tough when chipped or
nicked.
e.
High-Carbon Steels.
These steels are harder and more brittle
than low-carbon steel and the fracture is whiter and finer grained.
f.
Steel Forgings. Forgings may be of low-carbon, high-carbon, or
tool steel and the color will vary from bright crystalline to silky
gray. When the specimen is nicked, it is harder to break than cast
steel and has a finer grain.
g.
Alloy Steels.
Generally, the alloy steels are
very
fine
grained. Sometimes the fracture has a velvety appearance.
h.
Steel Castings. The surface of the fractured area is bright crystalline
gray. Steel castings are tough and do not break short. Chips made with
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