Today various alternative fuels are used due to new emission norms and environmental factors. Biodiesel and its blends are one of the alternative fuel used nowadays due to its low sulphur content. Automobile metals like copper, aluminum, cast iron etc. are more resistive to corrosion in petro diesel but more corrosive in biodiesel and its blends. So study corrosive nature of biodiesel is important for longer life of these automobile metals and its components. Piston rings made of nodular cast iron are always in contact with burnt and unburnt fuel in engine during working. In present study, a corrosive characterization of nodular cast iron is investigated by giving a proper heat treatment to it and static immersion test in biodiesel blends. Scanning Electron Microscope, Energy Dispersion Spectrograph and optical microscope are used for analysis of present investigation study. Results show that change in basic microstructure of metal can increase resistance to corrosion due to change in phase of metal.