HIGH TEMPERATURE OXIDATION OF ASTM A335 P92 STEEL UNDER ISOTHERMAL AND CYCLIC CONDITIONS

This work describes the behavior of ASTM A 335 P92 steel under a process of continuous and cyclic oxidation at high temperatures between 450 degrees and 700 degrees C in an oxidizing atmosphere. The gravimetric technique was used to observe the isothermal oxidation and the growth rate of oxides which showed a parabolic trend, X-2 = K-P t with values for K-P [mg(2)/cm(4)h]: 0.00013; 0.00014; 0.00089; 0.01134; 0.01432; 0.01560 corresponding to temperatures of 450 degrees, 500 degrees, 550 degrees, 600 degrees, 650 degrees y 700 degrees C, respectively. For cyclic tests shows that at temperatures between 450 degrees and 600 degrees C. a kinetic behavior parabolic type was present, while at 450 degrees and 500 degrees C there was a mixed kinetic behavior type para-linear. After comparing both tests was observed, that the cyclic oxidation rate was higher than the continuous one due to thermal shock of the oxide layers, which carried a spalling of the external oxide. Results obtained by SEM at 650 degrees C temperatures and time of exposition equal to 50 hours in the isothermal oxidation presented two types of compound oxide layers due to the mix of Cr and Fe oxides, noting that the quantity of Cr is greater in the outer layer and the quantity of Fe is greater in the internal layer, in the other hand at 700 degrees C and time of exposition equal to 168 hours in the cyclic oxidation, only the outer layer presented Fe, which was magnetite.