Steam Oxidation Behavior of Four General-Purpose Stainless Steels in Humidified Hydrogen Environment of Solid Oxide Fuel Cell

Steam oxidation behavior of four general-purpose stainless steels, SUS430, SUS430LX, SUS430J1L, and SUS445J1, under humidified H 2 was investigated for application in solid oxide fuel cells (SOFCs). A Cr-rich surface oxide layer, preliminarily formed via pre-oxidation, effectively mitigated steam oxidation and suppressed elemental diffusion and oxide growth. After pre-oxidation at 900 °C for 2 h in air, the oxidation rate was less dependent on the gas composition, which was varied from 10%H 2 O–90%H 2 to 50%H 2 O–50%H 2 , whereas it was strongly dependent on temperature. The structure of the surface oxide layer and direction of oxide growth differed depending on the alloy composition. The oxidation rate of SUS430J1L was similar to that of ZMG232G10 and relatively lower than those of three other stainless steels The Cr-rich oxide layer contained few defects, and its structure suppressed the diffusion of metal ions. Although a Si-rich oxide layer grew on the alloy side during the durability test performed at 727 °C for 1500 h, it had a lesser impact on the area specific resistance than that in SUS430. The microstructure of the Si-rich oxide layer, which featured other elements such as Cr, Mn, and Fe, maintained the electrical conduction path.