Characterisation of microstructure, mechanical and corrosion properties of pulsed MIG welded modified P91 steel weld metal

Varying the shielding gas composition with argon and carbon dioxide influences the properties of the weldments which are evaluated using microstructural, micro-hardness and corrosion studies. The modified P91 steel samples are welded by Pulsed Metal Inert Gas welding process with different shielding gas mixture, i.e., 95%Ar-5%CO2, 80%Ar-20%CO2 and 60%Ar-40%CO2. The welded steels are studied metallographically by observing microstructures at three different regions namely at the base metal, Heat Affected Zone (HAZ) and the Weld zone. Hardness measurements are also done using Vicker's micro-hardness tester. Corrosion studies in acidic media (sulphuric and nitric acid media of four different normalities 0.5, 1.0,1.5 and 2.0) are done in the welded region and the parent metal to compare the corrosion resistance. Of all the welded samples, welds made with the shielding gas composition of 95%Ar-5%CO2 exhibits good corrosion resistance over the other two welds while the weld made with the shielding gas composition of 60%Ar-40%, shows very poor corrosion resistance.