Carburization effect of Austenitic alloys with various Cr and Al additions under the methane/hydrogen atmosphere on the corrosion behaviors of steels

The corrosion behaviors of six Fe-19Ni-13/21Cr-xAl (x = 0, 2, 6 at. %) alloys in 10% CH4/H2 at 800oC were investigated. 2 at. % Al did not affect the corrosion resistance obviously, while 6 at. % Al reduced the carbon attack completely for Fe-19Ni-13Cr-6Al but was still insufficient to form protective alumina scales for alloys with 21 at. % Cr. An increase of Cr content changed the appearance of the internal carburization zone under the optical microscope. Stability diagrams of M-C-O system（M= Cr, Fe）were established to estimate the diffusion paths of carbon in the alloys.