Subsurface microstructural changes in a cast heat resisting alloy caused by high temperature corrosion

摘要

A cast HP ModNb alloy (Fe–25Cr–35Ni–1Nb, wt.%) was oxidised and carburised in CO–CO2 correspondingudto aC = 0.1 and pO2 = 3 1016 atm at 1080 C. Formation of an external, chromium-rich oxide scale led touddepletion of this metal in a deep alloy subsurface zone. Within that zone, secondary chromium-rich carbidesuddissolved, primary carbides oxidised, solute silicon and aluminium internally oxidised, and extensiveudporosity developed. Pore volumes correspond to the difference between metal loss by scaling andudmetal displacement by internal oxidation, assuming the scale–metal interface to be fixed. The poresudare concluded to be Kirkendall voids.