Experiments involving metal dusting in carbonaceous atmosphere and oxidation in air have been carried out at 593 and 704oC using T22, T91 and 800 alloy steels. The effect of Cr on these two processes can be understood because of their compositions. In general, the resistance to both metal dusting up to 1000 hours and oxidation up to 456 hours has been found to improve with increase in Cr content from 2.36 to 21.6%. However, mechanisms change from spalling to oxide scale in oxidation and from uniform metal dusting to pitting in metal dusting as the amount of Cr increases in these steels. Pitting corrosion shows higher C carbon concentration in the pits than at locations away from the pits. A detailed analysis has been performed to evaluate the scale and spalled materials in terms of oxide characterization using XRD, AES, SEM, EDS on SEM, optical microscopy and TEM.