Chemical volume diffusion coefficients for stainless steel corrosion studies

Abstract

Chemical diffusion coefficients for chromium in austenitic and ferritic steels are determined using diffusion couples studied by electron probe microanalysis techniques. The average chemical volume diffusion coefficient, for the composition range 14 to 28 at % chromium, for ferritic AISI 446 in the temperature range 800 to 1000° C is:

$$\tilde D = 0.15\left( {\frac{{ + 0.54}}{{ - 0.12}}} \right) \exp \left( {\frac{{ - 210( \pm 15)}}{{RT}}} \right) cm^2 \sec ^{ - 1} $$

and for austenitic AlSl 310 in the temperature range 800 to 1200°C is:

$$\tilde D = 0.27\left( {\frac{{ + 1.04}}{{ - 0.22}}} \right) \exp \left( {\frac{{ - 246( \pm 16)}}{{RT}}} \right) cm^2 \sec ^{ - 1} $$

whereR is in kJ K⁻¹ mol⁻¹ Good agreement is found with existing data for ferritic steels but the data are more scattered in the austenitic case. Diffusion data from diffusion couples are thought to be more realistic than those obtained from tracer work for the purpose of predicting diffusion-controlled corrosion behaviour.