MEC 2309 Hardness Test
MEC 2309 Hardness Test
MEC 2309 Hardness Test
1. MAIN OBJECT
The principal purpose of the hardness test is to determine the suitability of a material for a given
application, or the particular treatment to which the material has been subjected. The ease with
which the hardness test can be made has made it the most common method of inspection for
metals and alloys.
2. INTRODUCTION
There are many hardness tests currently in use. The necessity for all these different hardness tests
is due to the need for categorizing the great range of hardness from soft rubber to hard ceramics.
The hardness test is a mechanical test for material properties which are used in engineering
design, analysis of structures, and materials development.
3. THEORY
Current practice divides hardness testing into two categories: macrohardness and microhardness.
Macrohardness refers to testing with applied loads on the indenter of more than 1 kg and covers,
for example, the testing of tools, dies, and sheet material in the heavier gages. In microhardness
testing, applied loads are 1 kg and below, and material being tested is very thin (down to 0.0125
mm, or 0.0005 in.). Applications include extremely small parts, thin superficially hardened parts,
plated surfaces, and individual constituents of materials. Below are the testers according to the
two categories of hardness:
The Rockwell hardness test method consists of indenting the test material with a diamond cone
or hardened steel ball indenter. The indenter is forced into the test material under a preliminary
minor load 𝐹0 (Fig. 1A) usually 10 kgf. When equilibrium has been reached, an indicating
device, which follows the movements of the indenter and so responds to changes in depth of
penetration of the indenter is set to a datum position. While the preliminary minor load is still
applied an additional major load is applied with resulting increase in penetration (Fig. 1B). When
equilibrium has again been reach, the additional major load is removed but the preliminary minor
load is still maintained. Removal of the additional major load allows a partial recovery, so
reducing the depth of penetration (Fig. 1C). The permanent increase in depth of penetration,
resulting from the application and removal of the additional major load is used to calculate the
Rockwell hardness number.
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. When the indenter is retracted two diameters of the impression, d1 and
d2 , are measured using a microscope with a calibrated graticule and then averaged as shown in
Fig.2(b).
The diameter of the impression is the average of two readings at right angles and the use of a
Brinell hardness number table can simplify the determination of the Brinell hardness. A well
structured Brinell hardness number reveals the test conditions, and looks like this, "75 HB
10/500/30" which means that a Brinell Hardness of 75 was obtained using a 10mm diameter
hardened steel with a 500 kilogram load applied for a period of 30 seconds. On tests of extremely
hard metals a tungsten carbide ball is substituted for the steel ball. Compared to the other
hardness test methods, the Brinell ball makes the deepest and widest indentation, so the test
averages the hardness over a wider amount of material, which will more accurately account for
multiple grain structures and any irregularities in the uniformity of the material. This method is
the best for achieving the bulk or macro-hardness of a material, particularly those materials with
heterogeneous structures.
When the mean diagonal of the indentation has been determined the Vickers hardness may be
calculated from the formula, but is more convenient to use conversion tables. The Vickers
hardness should be reported like 800 HV/10, which means a Vickers hardness of 800, was
obtained using a 10 kgf force. Several different loading settings give practically identical
hardness numbers on uniform material, which is much better than the arbitrary changing of scale
with the other hardness testing methods. The advantages of the Vickers hardness test are that
extremely accurate readings can be taken, and just one type of indenter is used for all types of
metals and surface treatments. Although thoroughly adaptable and very precise for testing the
softest and hardest of materials, under varying loads, the Vickers machine is a floor standing unit
that is more expensive than the Brinell or Rockwell machines.
4.0 PROCEDURE
In this report we will only concentrate on the Rockwell hardness test, as it is the only experiment
we did. The following is the procedure:
1. Select the load by rotating the Knob and fix the suitable indenter.
2. Clean the test-piece and place n 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.
4.1 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 some time 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.
5.0 EQUIPMENT/APARATUS
Below are the specimen used during the experiment in the lab:
1. Raw steel of carbon 0.1%
2. 2 ring of 0.4% carbon normalized at 860°C
3. 1 ring of 0.1% carbon normalized at 900°C
5.1 Equipment
The Rockwell Test Machine was used in the Lab.
5.1.1 Description
The machine performs Rockwell or superficial Rockwell hardness tests in accordance with
established specifications, including BS EN ISO 6508:1999 and ASTM E18. The machine is
supplied with a diamond cone indenter and a 1/16” diameter ball indenter, as standard. The
machine is provided with a four-digit LED display. It is used to display measured hardness
results, to monitor the progress of the test and to display derived statistical data. The SM1015 is
an industrial instrument and if used in accordance with the following instructions, and given
reasonable care and attention, it will maintain accurate and reliable hardness scales.
6.0 RESULTS AND DATA ANALYSIS
READING SPECIMEN
S
Raw steel of carbon 2 ring of 0.4% carbon 1 ring of 0.1% carbon
0.1% (HRC) normalized at 860°C (HRC) normalized at 900°C (HRC)
7.0 DISCUSSION
The hardness test also gives some scope of the tensile strength. When testing the hardness of
softer materials, the depth of indentation is not a very accurate depiction of materials hardness.
For soft materials, the diameter of indentation caused by the ball indenter depicts how hard the
material is; the smaller the diameter, the harder the material. On the other hand, Rockwell
hardness test is preferred to use a diamond indenter as in this lab. The use of the Rockwell
hardness test was successful as the specimens were relatively hard. Among the three specimens,
Raw steel of carbon 0.1% specimens had lower Rockwell hardness numbers than that of the 2
ring of 0.4% carbon normalized at 860°C and 1 ring of 0.1% carbon normalized at 900°C.
Between the furnace cooled and the air cooled, the furnace cooled is softer. This is because Raw
steel of carbon 0.1% a small percentage of carbon content and it was still a raw material. The 1
ring of 0.1% carbon normalized at 900°C specimen had the highest Rockwell hardness number.
8.0 CONCLUSSION
Of the three under test, it can therefore be concluded that 1 ring of 0.1% carbon normalized at
900°C is the hardest, thus has highest resistance to indentation.
With the help of this experiment, we have been able to relate how hardness of steel samples is
Affected by variation in the rate of stress or strain applied.
References
Mechanical Metallurgy by George E. Dieter, 3rd Edition.
[2] https://www.steelexpress.co.uk/steel-hardness-conversion.html.
Materials Testing and Properties, TecQuipment Ltd, Bonsall Street, long eaton, Nottingham
NG10 2AN, UK