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 ASTM E 18-07 Standard Test Methods
for Rockwell Hardness of Metallic Materials is the
active and current standard by which Rockwell Hardness Testing is performed, and
is also the most frequently used hardness testing method.
In this test method,
the measurement of the permanent depth of an indentation produced when a
standardized tool (usually a conical diamond or tungsten carbide ball) is acted
upon by a known predetermined force is compared to a scale to arrive at a
hardness number. This test can be performed on all metals unless the size,
shape, or surface conditions of the specimens are prohibitive. The Rockwell
Hardness Test is considered to be more accurate and easier to perform than other
hardness test.
The test begins when a preliminary
test force (pre-load or minor load) is applied to a
sample using a diamond (or sometimes a tungsten carbide ball). This breaks
through the surface to reduce the effects of surface finish and provide a
reference or zero position. Next, an additional test force (or major load) is
applied to reach the total test force. This force is then held for a specified
period of time to overcome elasticity. This additional force is then released
and the resulting indentation is measured against the preliminary position. And
then the measurement is converted into a hardness number using the appropriate
Rockwell scale.
This standard applies to both
the " "Superficial" Rockwell scale using a
preliminary force of 3 Kg., and the "Regular" Rockwell scale with a 10 kg.
preliminary force. Total test forces for the "Superficial and "Regular" scales
range from 15 to 150 kilograms. The "macro" scale which employs a preliminary
force of 200 kg. and total test forces from 500 to 3000 kg. is covered by ASTM E
1842.
For the complete and latest
specifications for this test see
ASTM E 18-07
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