Study of the Degradation Processes of the of Iron-Based Alloy (Fechral) Structure Under Conditions of High-Temperature Non-Catalytic Conversion of Hydrocarbon Gases

The features of diffusion-controlled processes governing formation and degradation of the near-surface layer structure of an iron-based alloy (Fechral): Cr (21–27%), Al (4 ± 1%), Si (0.26%), balance Fe, were investigated under operating conditions when the material was used as a wire-matrix in the working chamber of a laboratory unit for non-catalytic conversion of hydrocarbon gases at 1200°C with exposure times up to 30 h. By optical metallography, scanning and transmission electron microscopy combined with elemental analysis by energy-dispersive X-ray spectroscopy (EDS), a comparative analysis of the microstructure, elemental and phase compositions of the alloy was carried out in the initial state and after service under the studied conditions. It was established that a thick (∼120 μm) oxide layer forms on the wire surfaces, composed predominantly of iron oxides (Fe3O4 and Fe2O3). The main features of the evolution of the microstructure and phase composition were identified, together with the formation and growth of cracks along the interface of the transition zone between the matrix and the surface oxide. Active internal oxidation of the wire samples was revealed, with formation of dispersed Cr2O3 particles in the subsurface layer. Changes in the material microhardness during exposure were analyzed. The role of microstructural degradation processes and crack formation in the observed accelerated failure of the wire matrices under the tested conditions is discussed.