Study of the degradation processes of the of iron-based alloy (Fehral) structure under conditions of high-temperature non-catalytic conversion of hydrocarbon gases

Peculiarities of diffusion-controlled processes of formation and degradation of structure of near-surface layers of iron-based alloy (Fehral): Cr (21 – 27 %); Al (4 ± 1 %), Si (0.26 %), the rest — Fe under conditions of its operation as a wire matrix material in the working chamber of a laboratory installation for the process of non-catalytic conversion of hydrocarbon gases at a temperature of 1200 °C with a holding time of up to 30 hours have been studied. By methods of optical metallography, scanning and transmission electron microscopy, including the possibility of analyzing the elemental composition by energy dispersive X-ray spectroscopy, comparative studies of microstructure, elemental and phase compositions of the alloy in the initial state and after operation under the conditions under study were carried out. It has been established that under such conditions a thick (about 120 microns) oxide layer consisting mainly of iron oxides (Fe3O4 and Fe2O3) is formed on the surface of wires. The main features of microstructure and phase composition evolution, as well as crack formation and growth along the interfaces of the transition region “matrix – surface oxide” were revealed. Active internal oxidation of wire alloy samples with formation of dispersed Cr2O3 particles in the near-surface layer has been detected. The change of microhardness of the material during operation is analyzed. The role of microstructure degradation and cracking processes in the observed accelerated destruction of wire matrixes under the considered conditions is discussed. It is shown that under such conditions there is a rapid degradation of the structure and mechanical properties of the material, which leads to its accelerated failure.