In the present investigation, stellite-6, Cr₃C₂-NiCr and WC-Co-Cr coatings were deposited by D-Gun on a hot rolled 21Cr-4Ni-N steel meant for fabrication of hydro turbine underwater parts. The coatings have been characterized for microstructure, porosity, microhardness and crystalline nature. The erosion experiments were carried out using an air jet erosion test rig at a velocity of 120 ms⁻¹ and impingement angles of 30° and 90°. Silicon carbide particles of size ranging between 500 and 700 μm were used as erodent. Scanning electron microscopy (SEM) technique was used to analyse the nature and mechanism of erosion. Erosion behaviour is observed to be influenced largely by the nature and extent of porosity in the surface coatings.