Metal dusting corrosion of austenitic alloys at low and high pressure with the effects of Cr, Al, Nb and Cu

Abstract

Commercial and model alloys were exposed at 570°C to metal dusting conditions at 1 and 21bar in CO-H2-H2O and CO-H2-CO2-CH4-H2O atmospheres, respectively, with similar ac and PO2. γ” precipitation beneath the surface of 625 superalloy was due to Nb diffusion toward the Cr-depleted zone formed during oxidation. 693 superalloy was more carburised than 690 superalloy. α-Al2O3 formation was believed to induce cracks through the oxide scale, resulting in the alloy carburisation. Cu addition to a FeNiCr model alloy lead to the formation of an almost continuous Cu layer at the oxide/metal interface, greatly improving the metal dusting resistance.