comparable to heat-treated steel. K-monel is used for
instrument parts that must resist corrosion.
This high-nickel alloy is often used in the exhaust
systems of aircraft engines. Inconel is composed of
78.5% nickel, 14% chromium, 6.5% iron, and 1% of
other elements. It offers good resistance to corrosion and
retains its strength at high-operating temperatures.
Many methods are used to identify a piece of metal.
Identification is necessary when selecting a metal for
use in fabrication or in determining its weldability.
Some common methods used for field identification are
surface appearance, spark test, chip test, and the use of
Sometimes it is possible to identify metals by their
surface appearance. Table 1-3 indicates the surface col-
ors of some of the more common metals. Referring to
the table, you can see that the outside appearance of a
metal helps to identify and classify metal. Newly frac-
tured or freshly filed surfaces offer additional clues.
A surface examination does not always provide
enough information for identification but should give us
enough information to place the metal into a class. The
color of the metal and the distinctive marks left from
manufacturing help in determining the identity of the
metal. Cast iron and malleable iron usually show evi-
dence of the sand mold. Low-carbon steel often shows
forging marks, and high-carbon steel shows either forg-
ing or rolling marks. Feeling the surface may provide
another clue. Stainless steel is slightly rough in the
unfinished state, and the surfaces of wrought iron, cop-
per, brass, bronze, nickel, and Monel are smooth. Lead
also is smooth but has a velvety appearance.
When the surface appearance of a metal does not
give enough information to allow positive identifica-
tion, other identification tests become necessary. Some
of these tests are complicated and require equipment we
do not usually have; however, other tests are fairly
simple and reliable when done by a skilled person. Three
of these tests areas follows: the spark test, the chip test,
and the magnetic tests.
Figure 1-2.Terms used in spark testing.
The spark test is made by holding a sample of the
material against an abrasive wheel. By visually inspect-
ing the spark stream, an experienced metalworker can
identify the metals with considerable accuracy. This test
is fast, economical, convenient, and easily accom-
plished, and there is no requirement for special equip-
ment. We can use this test for identifying metal salvaged
from scrap. Identification of scrap is particularly impor-
tant when selecting material for cast iron or cast steel
When you hold a piece of iron or steel in contact
with a high-speed abrasive wheel, small particles of the
metal are torn loose so rapidly that they become red-hot.
As these glowing bits of metal leave the wheel, they
follow a path (trajectory) called the carrier line. This
carrier line is easily followed with the eye, especial] y
when observed against a dark background.
The sparks given off, or the lack of sparks, aid in the
identification of the metal. The length of the spark
stream, the color, and the form of the sparks are features
you should look for. Figure 1-2 illustrates the terms used
in referring to various basic spark forms produced in
Steels having the same carbon content but differing
alloying elements are difficult to identify because the
alloying elements affect the carrier lines, the bursts, or
the forms of characteristic bursts in the spark picture,
The effect of the alloying element may slow or acceler-
ate the carbon spark or make the carrier line lighter or
darker in color. Molybdenum, for example, appears as
a detached, orange-colored spearhead on the end of the
carrier line. Nickel appears to suppress the effect of the
carbon burst; however, the nickel spark can be identified