Corrosion of Alloy 600 in a carburization furnace

The failure case of a shielding tube was investigated which had been used i n 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-H2O atmosphere at a(C) > 1, carburization leading to internal carbide formation. followed by internal oxidation of the carbi des. 2) graphitisation. i.e. internal graphite formation in a region of low er temperature and a. > 1 and 3) metal dusting, i.e. disintegration to a du st of graphite and metal particles and pitting. The phenomena are described and discussed. The Alloy 600 is not sufficiently corrosion resistant at hi gh temperatures. due to its low Cr-content (less than or equal to 16% Cr) a protective scale is not formed for sure. Better corrosion resistance for t his alloy may be obtained by surface working or a preoxidation under approp riate conditions.