Analytical modeling of the evolution of the nonlinearity parameter of sensitized stainless steel

Austenitic stainless steels are subject to the precipitation of chromium carbides (M23C6) during exposure to high temperatures, causing these alloys to be susceptible to intergranular corrosion due to chromium depletion along grain boundaries. The acoustic nonlinearity parameter, beta, shows sensitivity to the formation of carbides in these alloys. The Thermo-Calc TC-PRISMA module was used to model the nucleation and growth of grain boundary M23C6 carbides. The model was verified with scanning transmission electron microscopy analysis that allowed measurements of the grain boundary precipitates. The paper introduces a reduced-order model of the acoustic nonlinearity based on the formation of misfit dislocations at the interface of the grain boundary precipitate and matrix to explain the change in beta during isothermal aging. A direct relationship between the radius of the M23C6 grain boundary carbides and beta was observed and verified with non-linear ultrasound measurements on 304L and 316L stainless steels.

Automated summary

This paper investigates the precipitation of chromium carbides in austenitic stainless steels at high temperatures, leading to intergranular chromium depletion along grain boundaries. A reduced-order model of acoustic nonlinearity is proposed to explain the phenomenon, with a direct relationship observed between the radius of M23C6 grain boundary carbides and the non-linear ultrasound parameter beta. The model was validated through experimental observations and measurements, providing insights into the behavior of these alloys during isothermal aging.