THE INFLUENCE OF CERIUM OXIDE DEPOSITS ON ISOTHERMAL AND CYCLIC OXIDATION BEHAVIOR OF 2 COMMERCIAL STEELS, Z4CN18-09 (AISI 304) AND Z2CT17 (F17TI)

Reactive element addition as rare earth elements is a well known method for improving the high temperature oxidation behavior of chromia-former stainless steels. Two commercial stainless steels (AISI 304 and Fe17Ti) were exposed to isothermal oxidation at 950-degrees-C and 1000-degrees-C and thermal cycling oxidation at 950-degrees-C in air under atmospheric pressure. These steels were prepared by coating a thin ceria film by electrophorectic methods or by dipping into a ceria dispersion in various solvants (aqueous or organic). It has been shown for the coated steels that the oxidation rate slightly decreased and that the oxide adherence increased particularly for Fe17Ti steel in isothermal condition. For cyclic conditions, the oxide scale adherence was considerably increased since no scale spallation occured after more than 40 cycles. The observation can be partially explained by the growth of a very fine grained chromia subscale on coated stainless steels. Comparison are made between dipped coating and ion implantation processes for introducing reactive element to the surface. The latter processes provide surface modification which increases the oxide scale adherence of chromia-former stainless steel, especially when large temperature range variations occur.