Tempering the specimen and this is also observed in

tempering the specimen and this is also observed in the original stress strain curve (see Figure 1) It can be concluded
that heat treatment plays a major role in the modification of the yield strength and the ductility of a material.
1.5 Interpretation of hardness and strength
The hardness of carbon steel specimens with a carbon content of 0.45 wt% prepared for the Impact test was observed
using the Rockwell hardness testing machine. A load of 1471 N was used to measure the hardness of the specimens.
The hardness test was carried out in three different regions at least 3 indentations from each other to obtain the results.
The mean value of the three readings for each specimen was taken to obtain the hardness of each steel specimen. It
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Figure 5: Plot indicating interaction between UTS vs Ductility
is observed that the specimen Q has the highest hardness value of all the specimen but the lowest strength and the
specimen QT380 has the highest strength of all the other specimen as shown in Figure 6.
Figure 6: UTS as a function of Rockwell Hardness values
Further, four steel specimen were prepared and mounted for observation. The hardness of the steel specimens is
measured using the Vickers Hardness testing machine using a load of 1 KgFmm - 2 . For each specimen, the hardness
test was carried out in three different regions, and the observed readings are noted down. The mean value of the three
readings for each specimen was taken to get the hardness of each steel specimen.
It is observed that the specimen Q has the highest hardness but lowest strength whereas the specimen QT380 has the
highest strength of all other specimen as shown in Figure 7. Further analysis needs to be done to understand the relation
between hardness and strength.
The Vickers hardness test is carried out by distributing the load implemented to indent the pyramidal diamond into the
welded specimen by the area of indentation thus created. The larger the load used, the larger will be the indentation
created. Hardness tests were performed to examine the effect of welding on the hardness of the material using the
Vickers Hardness testing machine using a load of 0.5 KgFmm - 2 . The hardness test is carried out over the width of the
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Figure 7: UTS as a function of Vickers Hardness values
weld using trial and error to find an appropriate load level for increments between indentations. When observed, there is
a significant change in the hardness across the weld. The hardness within the weld region was higher than the base
material, which is likely due to the generation of fine grains induced by the plastic deformations during the welding
process. Hardness varies from the weld zone to base material; with effect to the difference in the microstructure in each
zone. The Heat Affected Zone (HAZ) has the maximum hardness than the weld zone and the base material as shown
in Figure 8. The maximum rise in the hardness at HAZ was identified at the weld interface, after which the hardness
started to decrease slightly. From the data obtained and the curve plotted using that data, the experiment concludes that