Rockwell Hardness Test On Hardened Steel
RETURN TO LIST OF EXPERIMENTS
I. AIM: To determine the Rockwell Hardness of a given test specimen
II. APPARATUS: Rockwell Hardness testing machine, Test specimen.
III. THEORY:
HARDNESS-It is defined
as the resistance of a metal
to plastic deformation against Indentation, scratching, abrasion of cutting. The
hardness of a material by this Rockwell hardness test method is measured by the
depth of Penetration of the indenter.
The depth of Penetration is inversely
proportional to the hardness. Both ball or diamond cone types of indenters are used
in this test. There are three scales on the machine for taking hardness readings.
Scale “A” with load 60 kgf or 588.4 N and diamond indenter is used for performing
tests on thin steel and shallow case hardened
steel.
Scale “B” with load 100 kgf or 980.7 N and 1.588 mm dia ball indenter is used for performing tests on soft steel, malleable iron, copper and aluminum alloys.
First minor load is applied to overcome the film thickness on
the metal surface. Minor load also eliminates errors in the depth of measurements due to spring of the machine frame or setting
down of the specimen and table attachments.
The Rockwell hardness is derived from the measurement of the depth of the impression
EP = Depth of penetration due to Minor load of 98.07 N. Ea =
Increase in depth of penetration due to Major load.
E = Permanent increase of depth of indentation under minor load
at 98.07 N even
after removal of Major load.
This method of test is suitable for finished or machined parts
of simple shapes.
IV. PROCEDURE:
1. Select the load by rotating the Knob and fix the
suitable indenter.
2. Clean the test-piece
and place the special anvil or work table of the machine.
3. Turn the capstan
wheel to elevate the test specimen into contact with the indenter point.
4. Further turn
the wheel for three rotations forcing the test specimen against the indenter. This
will ensure that the Minor load of 98.07
N has been
applied
5. Set the
pointer on the Scale dial at the appropriate position.
6. Push the lever
to apply the Major load. A Dash Pot provided in the loading mechanism to ensure
that the load is applied gradually.
7. As soon as the pointer comes to
rest pull the handle in the reverse direction
slowly. This releases the Major, but not Minor load. The pointer
will now rotate in the reverse direction.
8. The Rockwell
hardness can be read off the scale dial, on the appropriate scale, after the pointer
comes to rest.
V. OBSERVATIONS: Material of test piece = Thickness of test piece = Hardness
Scale used = Minor Load =
Major Load =
|
Test No. |
1 |
2 |
3 |
4 |
|
Hard ness value |
|
|
|
|
VI. PRECAUTIONS:
1. For testing cylindrical test specimen, use V-type
platform.
2. Calibrate the machine occasionally using standard
test blocks.
3. For thin metal
prices place another sufficiently thick metal
piece between the test specimen and the platform to avoid any damage which may likely
occur to the platform.
4. After applying
Major load, wait for sometime to allow the needle to come to rest. The waiting time
vary from 2 to 8 seconds.
5. The surface
of the test piece should be smooth and even and free from oxide scale and foreign
matter.
6. Test specimen should not be subjected to any heating
or cold working.
7. The thickness
of test piece or of the layer under test should be at least 8 times the permanent
increase of depth of “E”.
8. The distance between the centers of two adjacent
indentation should be at
least 4 indentation to the edge of the test piece should be
at least 2.5 times the diameter of the indentation.
VII. VIVA QUESTIONS:
1. Define
Hardness.
2. Applications
of Rockwell Hardness A – Scale, B-Scale, C-Scale.
3. Type
of Indentor used in the Three Different Scales of Rockwell Hardness
Test.
4. Different
Types of Hardness Testing Methods.
5. Size
of the Ball to be used in Ball Indentor of Rockwell Hardness Test.
6. Diameters
of the different Balls used in Brinell Hardness Test.
7. Selection
of Load in Brinell Hardness Test.
8. Selection
of Load in Rockwell Hardness Test.
