Corrosion and carburization behavior of surface-modified SS 316LN in high temperature $Supercritical-CO_2$ environment

Abstract

Surface-modification by Al-enrichment and Ni-coating was conducted on stainless steel 316LN to improve its corrosion and carburization resistance in high temperature $supercritical-CO_2$ environment. The Al-enrichment process resulted in phase transformation of the austenitic matrix into ferritic phase, with dispersions of nickel aluminide. Pre-oxidation in He at $900^\circ C$ for 1 h was conducted for some specimens prior to $S-CO_2$ exposure resulting in the formation of an adherent Al-rich oxide under porous Fe-, Al-rich spinel oxides which were prone to spallation. Subsequent exposure to$S-CO_2$environment at $600^\circ C$ (20 MPa) for 500 h resulted in formation of porous Fe-, Al-rich spinel oxides for the non-preoxidized specimen. In both cases, lower weight gains compared to the as-received condition could be noted and no notable oxide growth occurred following the spallation of the porous spinel oxides. In terms of carburization resistance, C enrichment was limited to within the oxide. In the case of Ni-coating, carburization hardly occurred other than slightly at the coating/matrix interface due to defects in the coating layer.