The influence of a titanium nitride dispersion on the oxidation behavior of 20%Cr-25%Ni stainless steel
The oxidation behavior of 20%Cr-25%Ni stainless steels and a similar but stronger alloy containing a dispersion of titanium nitride particles has been studied over the temperature range 1023 to 1173°K. The dispersion-strengthened steel oxidized slightly more slowly than its dispersion-free counterpart at 1023°K, but above this temperature it was inferior in terms of gross weight gain. The parabolic growth kinetics of the chromic oxide layer in each alloy were similar, however, with an activation energy compatible with the rate-controlling step being chromium ion diffusion across the oxide. The evidence suggests that the role of the dispersed phase is to produce an oxide of finer grain size than that of the standard steel, which increases the rate of oxygen transport inward. The consequent formation of internal oxide increases the tendency for oxide rupture and spalling with subsequent enhanced local attack. This leads to the observed higher overall weight gains compared with the dispersion-free alloy.
Key wordsstainless steels high-temperature oxidation chromium diffusion
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