Dissimilar metal joints are highly used in different industrial applications due to both economic and technical reasons. The low alloy steel, 9Cr-1Mo (P91) and 2.25Cr-1Mo (P22) are extensively used in power generation industries mainly in the application of boiler and turbine at elevated temperature because of its low cost, good weldability, and acceptable hot corrosion resistance. The power plant materials such as P22 and P91 steels when exposed to high-temperature applications are subjected to hot corrosion. Hot corrosion is defined as the deterioration of materials under the exposure of air or a thin layer of molten salt at a high-temperature range. The prevention to failure of the power plant components before its predefined life due to accelerated hot corrosion in the materials is an essential need of the present time.The aim of this work is investigating high-temperature corrosion behaviour of P22 and P91 low alloy steels and their weldments when exposed to different mixtures of the molten salt environment at high-temperature of 600oC and 700oC. The hot corrosion behaviour was observed for the cyclic corrosion study of 50 hours on the application of fused salt mixture (100% Na2SO4, 100% NaCl, 100% V2O5, Na2SO4+50% NaCl, Na2SO4+60% V2O5) on the surface of each specimen. Thermogravimetric analysis was done to find the weight change of the specimen to draw weight change versus the number of cycle plots. Parabolic oxidation kinetics was observed when the specimens were exposed to 600°C whereas at 700°C multistage oxidation kinetics was observed. SEM/EDS, XRD, and line scan mapping analysis on post corroded specimen indicates that the alloy steel with low chromium content undergoes a heavy oxide scaling due to the absence of protective Cr2O3 layer that leads to higher weight gain. Thus, better corrosion resistance properties were observed in steel with high chromium content. Moreover, the higher the chlorine content in the salt mixtures severely affects the corrosion resistance of alloys by dropping the melting temperature of the salt mixture. The analysis of the above study indicates the highest rate of corrosion on the base metal as well as dissimilar weldments under the exposure of 50% NaCl+50% Na2SO4 at a temperature of 700oC. Furthermore, shot peening was performed to increase the corrosion resistance behaviour of the base metal as well as dissimilar weldments, and it was found that shot-peened specimens exhibit much better corrosion resistance properties than non-shot peened samples. Moreover, the corrosion resistance is in the order of 9Cr-1Mo (P91) → dissimilar weldment of P91/P22 → 2.25Cr-1Mo (P22) steel. Tensile testing and microstructural analysis were also done for the dissimilar weld joint between P22/P91 low alloy steels. The tensile strength of the weld joint was observed to be 724.603 N/mm2 that is more than the tensile strength of both the base metals P22 (530 N/mm2) and P91 (675 N/mm2).