The (100) surface region of the Fe‐18Cr‐3Mo ternary alloy was investigated during and after argon sputtering at ambient and elevated temperatures by means of Auger electron spectroscopy. Low and high‐energy lines, corresponding to different sampling depths, were monitored, and the quantitative analysis was based on relative intensities from an in situ scribed crystal, representing the bulk composition. The Cr:Fe steady‐state ratio measured during sputtering reflected significant subsurface Fe depletion which reached a maximum at ∼800 K and then decreased. This trend could be inverted (i.e. inducing Cr depletion) by Ar sputtering under some residual CO. Similarly, compositional changes observed after sputtering were critically dependent on the cleanliness of the surface. The results are discussed in terms of possible (Gibbsian) surface segregation of Fe vs. chemically‐induced segregation of Cr and Mo.