Microhardness test was conducted using Vickers micro hard-
ness machine and hardness values were taken at weld zone, HAZ
and base metal on both sides of the weld. Three readings were ta-
ken for each of them and the microhardness values are plotted in
Fig. 6. From Fig. 6 it is observed that the base metal is having less
hardness than the weld metal and the HAZ. This can be attributed
to the fine grains found in weld metal and HAZ due to high temper-
ature in those regions. Coarse grains are found in base metal.
Microhardness values increase with increasing of ferrite percent-
age in the weld metal. Consequently, increase in CO2 content in
gases resulted in lowering hardness values of the weld metals
[11]. But the hardness values of welds using 75% Ar + 23%
CO2 + 2% O2 and 70% Ar + 25% CO2 + 5% O2 are not following the
trend. This may be because the decomposition of CO2 is retarded
by oxygen in the mixtures [4].