Effects of the Presence of Water Vapour on the Oxidation Behaviour of Low Carbon-Low Silicon Steel in 1 %O_2-N_2 at 1,173 and 1,273 K

摘要

The effect of water vapour on the oxidation behaviour of a low carbon and low silicon steel in 1 %O_2-N_2 at 1,173 K (2.5 and 17.2 %H_2O) and 1,273 K (17.2 %H_2O) was examined. In most cases, the oxidation kinetics were linear initially and turned to parabolic after 15 and 30 min, respectively for 1,173 and 1,273 K. However, for oxidation in 1 %O_2-N_2 at 1,273 K for longer than 60 min, the apparent parabolic rate decreased with increased oxidation time. The presence of water vapour resulted in increased oxidation rates, both in the linear and parabolic stages. Improved scale-steel interface adherence was believed to be responsible for the increased oxidation rates. Fast growth of certain oxide grains formed in 1 %O_2-N_2 at 1,273 K and bridging of the fronts of these fast growing grains to form a continuous layer resulted in the formation of a line of porosities inside the scale, thus reducing the total cross-sectional area for outward iron diffusion, and hence reducing the apparent oxidation rate. The presence of 17.2 %H_2O in 1 %O_2-N_2 prevented formation of porosities in the scale.