Corrosion of Alloy 600 in a carburization furnace

The failure case of a shielding tube was investigated which had been used in a carburization furnace for protection of an oxygen sensor. The tube made of Alloy 600 showed all kinds of attack by carbonaceous gases: (1) at the hot end within the CO‐H 2 ‐H 2 O atmosphere at a C ≤ 1, carburization leading to internal carbide formation, followed by internal oxidation of the carbides, (2) graphitisation, i.e. internal graphite formation in a region of lower temperature and a C > 1 and (3) metal dusting, i.e. disintegration to a dust of graphite and metal particles and pitting. The phenomena are described and discussed. The Alloy 600 is not sufficiently corrosion resistant at high temperatures, due to its low Cr‐content (≤ 16% Cr) a protective scale is not formed for sure. Better corrosion resistance for this alloy may be obtained by surface working or a preoxidation under appropriate conditions.