Hardness Tests and Charpy Impact Test

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  • Topic: Vickers hardness test, Rockwell scale, Hardness
  • Pages : 8 (2025 words )
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  • Published : October 28, 2012
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Hardness Tests and Charpy Impact Test
Objectives:
1) To compare the hardness between mild steel, carbon steel through Vickers Hardness Test. 2) To compare the hardness between High Quality Carbon Steel and ASSAB steel through Rockwell Hardness Test. 3) To compare the hardness between carbon steel and mild steel through Brinell Hardness Test. 4) To study the differences between mild steel and carbon steel upon Charpy Impact Test. Introduction:

Hardness is a measure of the resistance of a metal to permanent (plastic) deformation. The hardness of a metal is measured by forcing an indenter into its surface. The indenter material, which is usually a ball, pyramid, or cone, is made of a material much harder than the material being tested. The hardness of a metal depends on the ease with which it plastically deforms. Thus the relationship between hardness and strength for a particular metal can be determined empirically. The hardness test is much simpler than the tensile test and can be nondestructive. For these reasons, the hardness test is used extensively in industry for quality control. Here are the tests that usually used to determine the hardness of a material. 1) Vickers Hardness Test

2) Rockwell Hardness Test
3) Brinell Hardness Test
4) Charpy Impact Test

* Vickers Hardness Test
The Vickers hardness test method consists of indenting the test material with a diamond indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load of 1 to 100 kgf. The full load is normally applied for 10 to 15 seconds. The two diagonals of the indentation left in the surface of the material after removal of the load are measured using a microscope and their average calculated. The area of the sloping surface of the indentation is calculated. The Vickers hardness is the quotient obtained by dividing the kgf load by the square mm area of indentation.

F=Load in kgf
d = Arithmetic mean of the two diagonals, d1 and d2 in mm
HV = Vickers hardness
To obtain the value of hardness, Vickers Hardness Number (VHN) is calculated as below: VHN=Mass of the loadSloping surface of the intentation
=2PSin136°2d2
=1.854Fd2approximately
Where, P=applied forcekgf
d=d1+d22
* Rockwell Hardness Test
This method has 2 main scales which are:
a) Scale B, concavity is a steel ball (1.58 mm∅) and load using is 100 kgf. b) Scale C, concavity is a cone diamond having corner 120° and load is 150 kgf. Rockwell hardness (HR) can be calculated as equation below:

HRC=100-d0.002
HRB=130-d0.002
Where d=concavity
* The Brinell Hardness Test
The Brinell hardness test method consists of indenting the test material with a 10 mm diameter hardened steel or carbide ball subjected to a load of 3000 kg. For softer materials the load can be reduced to 1500 kg or 500 kg to avoid excessive indentation. The full load is normally applied for 10 to 15 seconds in the case of iron and steel and for at least 30 seconds in the case of other metals. The diameter of the indentation left in the test material is measured with a low powered microscope. The Brinell harness number is calculated by dividing the load applied by the surface area of the indentation.

Brinell Hardness Number (BHN) can be calculated as below:
BHN=applied forceindented surface area
=PD2D2-d2
=PπDh

Where, P=applied forcekgf
D=diameter of the steel ballmm
d=diameter of the intended surface areamm
h=depth of intended areamm
=12D-D2-d2

Procedure:
Vickers Hardness Test
1) The specimen (Mild steel) is correctly place on anvil of the Vickers Hardness instrument. 2) The specimen is being focused and changed it below the indenter exactly. 3) The ‘START’ button is pressed and the machine will shine with the sound showed that the machine is readily operated. 4) The test force is maintained for a specific dwell time of about 15...
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