Hardness Testing of Metallic Materials
Name – Gunathilaka R.A.C.K.
ID – EN18405514
Group – 8(D)
Date – 2nd August 2018
Date of Submission – 15th August 2018
Hardness Testing of Metallic Materials
To determine the hardness of metallic materials by using the Rockwell scale.
Hardness testing is a specific part of analyzing a metal. Various methods are used to test hardness of a
metal such as Rockwell, Brinell, Vickers etc. This test is done by using a diamond Sphero conical
indenter or a tungsten carbide ball indenter. Measuring the depth of the indenting, the hardness value is
calculated. Rockwell hardness number is an arbitrary number. It’s called as HR value. Type of indenter
and method of getting a reading are depended on the material which is selected as the specimen.
Calculation of the hardness number by using depth ‘h’
For Sphero conical diamond indenter:
HR = 100 – h/0.002
h is the depth of indentation
For ball indenter:
HR = 130 – h/0.002
(Adopted from SLIIT Engineering materials handbook)
5.0 Materials and apparatus
? Rockwell hardness testing machine
? Cuboid shaped hard steel specimen
? Sphero conical indenter
? Firstly, a piece of hard steel was selected as the specimen. (shaped as a cuboid)
? Secondly, a surface of the specimen was selected to do the experiment.
? After that, the lever of Rockwell hardness testing machine was adjusted to the ‘unload’
? Next, the Sphero conical indenter was fitted to the Rockwell hardness testing machine.
? After that step the chosen surface specimen was kept on the anvil with staying opposite and
perpendicular to the indent.
? Moreover, the hand wheel was steered clockwise direction until the chosen surface of specimen
touch with the indent.
? After touching the indent, the hand wheel was again smoothly steered in clockwise direction
until the red small indicator circulate 3 times and the main indicator comes near to the zero
? As the next step, the lever was released to ‘load position’ at a medium speed.
? The large pointer was begun to oscillate after a while that oscillation was completely finished.
? After the termination of oscillation of large pointer, again the lever was adjusted to the ‘unload’
? Then the large pointer was indicated a reading.
? Finally, that reading was taken as the HR value.
? Several HR values were taken to get an average to satisfy about the value of hardness of the
Average value of hardness = 88.5 HRC+85.5 HRC+77.5 HRC+89.5 HRC+88.5 HRC+84.5 HRC+71.5 HRC
= 83.64 HRC
Variations of HRC values
1st Sample 88.5 HRC
2nd Sample 85.5 HRC
3rd Sample 77.5 HRC
4th Sample 89.5 HRC
5th Sample 88.5 HRC
6th Sample 84.5 HRC
7th Sample 71.5 HRC
10.1 Obtained Results
Observing the obtained results, there were some variations between readings of the HR values of
? 1st Reading – First reading was 88.5 HRC. This value was acceptable.
? 2nd Reading – 2nd reading was 85.5 HRC. This value was near to the first value and it also was
? 3rd Reading – In the next time value was 77.5 HRC as the 3rd reading. This value was varied
much from the previous values.
? 4th Reading – In this time, the value was 89.5 HRC. That means this value was the highest
value in respect to the previous values.
? 5th Reading – As the 5th reading the indicator indicated that the value was 88.5 HRC. That
value was equal to the first value which we taken.
? 6th Reading – This value was 84.5 HRC.
? 7th Reading – Last value was 71.5 HRC. This was the smallest value which we got.
Considering the above readings, they all were acceptable, but the HRC values of different samples
were varied between 71.5 HRC and 89.5 HRC. The average was calculated as 83.64 HRC.
10.2 Importance of hardness testing
Hardness is a property of a metal which means the resistance to plastic deformation, bending,
scratching, penetration etc. Hardness is some kind of measurement to satisfy the durability, capability
and strength of a material. In production engineering, hardness testing is a very important factor to
ensure the quality of the production. Hardness test is done by in different methods. Rockwell, Brinell,
Vickers are some of them. Plenty of materials are used especially in areas of mechanical, aeronautical,
automotive, locomotive etc. Considering those engineering applications, it’s very valuable for control
and measure the quality of the materials which are used to manufacture each component. Failures of
materials in structures may be caused fatal errors in final product or in usages.
In a large scale manufacturing plant, there are efficient methods for hardness tests. For instance, fully
automated hardness testing methods are available in there. In metallography, there is a specific place is
allocated for hardness testing. Analyzing the hardness of a metal, it would be a way to fulfill needs and
requirements of certain applications and manufacture new materials such as alloys with satisfying all
necessaries. In military application, hardness, robustness, penetration is improved as a result of tests
and improvements of hardness testing.
10.3 Shortcomings of the test
There will be some shortcomings while the experiment was being done.
? Surface of specimen may have contained with small dents – Without a flat surface, the readings
of HRC values will be wrong.
? Shape of specimen – A specimen without a certain 3D shape, it’s very difficult to measure the
HRC values. A cuboid, cylindrical or a same common shapes are convenient to test the
hardness by using Rockwell hardness testing machine.
? There may have been errors when getting the readings (non-coincidence reading errors) from
the large pointer – Readings are depended on the person who done the experiment. However,
the person who get the readings should keep his eyes perpendicular direction to the dial
indicator and clearly read the correct value.
? There might have been errors when getting the large pointer to the zero by steering the hand
wheel – It is very uneasy to adjust the large pointer to at the zero point by steering the hand
wheel very slowly and smoothly.
? There may have been errors when releasing the lever – Lever should be released at a medium
speed. Releasing in very fast or very slow is a trammel to indent the surface properly.
? There is no any method to certify to indenter is perpendicular to the surface of specimen – If
the specimen surface is not perpendicular to the indenter HRC values are not correctly
measured by the machine.
? Time consuming – There are some steps to be done before getting a HRC value by using a
Rockwell hardness testing machine. These all steps are effected for the accuracy of readings. If
there are a large amount of samples, it’s very hard to continue those steps and it’s a way to a
huge time wastage.
10.4 Improvements of accuracy of hardness test
In this experiment, a Rockwell hardness testing machine was used to determine the hardness of a hard
steel. The values were taken by the analog indicator. This method may have been consisted with non-
coincidence errors when getting the readings because the readings are depended on the person who has
done the experiment. To avoid this error, it will be very accurate if we get readings by a digital
indicator instead of an analog indicator. In this point, it will be more accurate to calculate the HRC
value in several decimal places.
When we are getting one reading from the machine, there are several steps to be done in order. If we
have several samples to check the HRC values of each of them, the time will be wasted much. To
overcome this fault, it will be a possible way to automate a system to do all the steps quickly and
A split level can be used to ensure the indenter and specimen surface are perpendicular each other
while doing the experiment.
If we are not satisfying the final result we obtained, we might have to do same experiment for many
times and take an average to certify the accuracy of final result.
If the surface of specimen is rusted or consisted with dents, a correct HRC value is not given. We must
ensure to take a specimen without rusts and if there any dents on the surface, grind them until get a
smooth flat surface.
10.5 Information about apparatus
A Rockwell hardness testing machine was used in this experiment. Basically this machine was
consisted with an anvil, hand wheel, weight selector, dial indicator and a lever. There were two dial
indicators. A large and a small indicator.
When calculating the hardness of a metal, commonly two types of indenters are used in
experiments. They are;
1) Sphero conical diamond indenter
2) Ball indenter
In this experiment, a Sphero conical diamond indenter was used.
A hard steel was selected as the specimen in this experiment. There will be various shapes of hard
steel specimens, then we should ensure to choose the correct specimen support.
Ex: – For a cylindrical specimen – V-grooved specimen support (fig a)
For a cuboid shaped specimen – Flat specimen support (fig b)
10.5.4 Scale selection for this experiment
Scale symbol Pre-Load kg(N) Indenter Total test force
A 10(98) Diamond (120?,
0.2 tip radius)
60(589) Thin steel
B 10(98) WC ? 1/16 ”
100(981) Nonferrous, soft
C 10(98) Diamond(120?,
0.2 tip radius)
150(1471) Hard steels
Scale symbol Dial figures Large pointer
A Black 0 or C Red spot (3)
B Red 30 or B 2 Divisions (2)
C Black 0 or C Red spot (3)
This experiment was done by after selecting the correct symbol of each tables. That means scale
symbol ‘C’ was chosen according to our hard steel specimen.
All the steps of this experiment were correctly done and 7 values were taken by the Rockwell
hardness testing machine. Considering those values, average was calculated as the final hardness
number for the hard steel specimen which taken.
? The importance of a hardness test in materials production.
Available from: https://www.bergeng.com/blog/the-importance-of-a-hardness-test-in-
Accessed on 12th August 2018
? Improve productivity with hardness testing.
Available from: https://www.qualitymag.com/articles/90250-improve-productivity-with-
Accessed on 13th August 2018
? Rockwell hardness testing.
Available from: https://www.hardnesstesters.com/test-types/rockwell-hardness-testing
Accessed on 13th August 2018