TITLE
Hardness testing of metallic material. OBJECTIVE
Determine the hardness of metallic materials by using the Rockwell scale. INTRODUCTION
Hardness is the amount of resistance towards deformation. The value of hardness could be found using the Rockwell hardness test which is one type of hardness testing method and known as indentation hardness testing, where an indentation hardness tester with a diamond (Engineers Edge, n.d. indenter or tungsten carbide ball indenter is forced into a material, and the depth of the indentation is measured to determine the hardness of the material. THEORY
There are many methods to find the hardness (amount of resistance towards deformation, and one of the methods is the indentation hardness testing. Depending on the method, the units and the scales of hardness changes. !y using the Rockwell hardness test, the load is applied gradually, and the area of the indentation is measured. Rockwell us used industrially because is "u "uick, an and th the co convenient. Ro Rockwell alone ha has #$ #$ different sc scales, according to the hardness of the material being tested (%armichael and &rikorian, n.d.. 'n this lab, Rockwell scales % is used with a diamond indenter.
it
The hardness of any material is an arbitrary number derived from the net increase in depth of indention as the force on an indenter is increased from specific value. This test is done under a constant temperature due to reason that the properties of the material changes with the temperature.
a
Fi ure 1: Indentation tester
MATERIALS AND APPARATUS
•
'ndentation tester pecimen (medium carbon steel
•
'ndenter )Diamond (#*+
•
°
, +.* tip radius
Fi ure 2: Rockwell Diamond Diamond Indenter
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PROCEDURE
!efore the e-periment, the specimen was taken and made sure it was clean from foreign matter. The re"uired indenter (Diamond (#*+
°
, +.* tip radius was fi-ed to the machine for this
specific test. Then the support for the specimen was selected (in this case a flat surface was selected Then it was made sure that the crank was in the unload position. The correct load was selected by rotating the load wheel in the indentation tester. The large pointer in the dial face was adusted to /ero. The preminilary load was applied by rotating the hand wheel until the specimen which was placed on the anvil, touched the tip of the indenter. Then it was continued to rotate till re"uired number of revolution of the larger pointer, till the position of the smaller pointer reached the red dot. Then the machine was let to rest for +.# 0 1 s Then the maor load was applied by moving the crank to the load position very slowly, and then let to rest for *23s. The load was then released slowly by moving the crank to the unload position and the reading on the scale was recorded. This test was repeated several times to get the average value. The minor load is removed by lowering the anvil.
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CALCULATION
HRC calculation: Hardness of medium medium carbon steel on either sides
Avea!e Value
¿
60.5 + 60.5 + 60 + 60.5 4
=¿
"#$%&'
72 + 740. + 68 + 76.5
Avea!e Value(
4
(&)$&'
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RESULTS
The hardness test for the medium carbon was repeated si- times and the average were taken, and the results are shown in table #.
Table Table 1: Results of hardness testing of Medium carbon Sa+,le
*t
- Va Value
HRC Te*t Re*ult* ) Va Value* %. Va Value* n.
/t0 Va Value
4edium carbon teel
3+.$
3+.$
3+
3+.$
Avea!e value 3+.56$
4edium carbon teel
6*
61.$
37
63.$
6*.6$
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CONCLUSION
8verall, it was found that the indentation testing, compared to other testing methods such as scratch hardness testing, gives a specific value of hardness, and it is much "uicker and much more efficient. 9sing this test, only a comparison could be made, but cannot gain any further properties of material, and specifically, in this lab, since only one material (4edium %arbon teel was tested ( Hardness ( Hardness:: HR% 3+.56$ to HR% 6$*.6$, this cannot be compared to any other materials. materia ls. (n.d.
RE1ERENCES
)8nline, ;vailable: http:<rcarmic#
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