Simultaneous creep and oxidation of Fe-Si alloys at 973–1073 K

Abstract

Studies of the simultaneous creep and oxidation of Fe-1Si and Fe-4Si alloys at constant stresses of 13–26 MN/m 2 in the temperature range 973–1073 K have shown that the steady state creep obeys a power law. Values of the stress exponent n were found to be 9.3 for Fe-1Si and 6.5 for Fe-4Si for creep in an argon atmosphere ( pO 2 = 10 −3mbar). Values of the apparent activation energy for creep ( Q app ) of Fe-1Si and Fe-4Si were in the ranges 306–376 kJ/mole and 263–324 kJ/mole respectively. Q app values were found to be dependent on the pO 2 of the test environment: lower Q app for pO 2 = 10 −3mbar; higher Q app for pO 2 = 10 −9mbar. Oxidation strengthening (ϵϵ with increasing pO 2 at 998 K in the higher pO 2 environments for Fe-1Si ( pO 2 = 20–152 mbar) and for Fe-4Si ( pO 2 = 60–1013 mbar). Primary strengthening sources are considered to be internal oxides, intergranular oxidation and strongly adherent scales. Oxidation weakening (ϵϵ increasing) occurred with increasing pO 2 at 998 K in the lower pO 2 environments for Fe-1Si ( pO 2 = 10 −9−10 −4mar).The principal cause of weakening is believed to be the flux of oxidation-induced vacancies.