Two binary alloys (Fe-0.5 wt.% Si and Fe-1.5 wt.% Mn) and a high silicon steel were used to investigate the thermochemical phenomena occurring at the sample free surface during simulation annealing cycles aimed to achieve a hot-dip galvanizing-compatible surface condition.The samples were annealed for 60 s at 800-810• C in atmospheres composed of nitrogen and hydrogen (either 0 or 5 vol.% H 2 ), the dew points of which were varied from −60 to 0 • C, corresponding to water vapour contents ranging from 10 to 6000 ppm. The surface chemical conditions were characterized by in situ x-ray photoelectron spectroscopy (XPS). Annealing in a nitrogen-hydrogen atmosphere was shown to lead silicon and manganese to diffuse to the surface and become oxidized, the amount of external selective oxidation decreasing with increasing atmosphere vapour content. After annealing in pure and dry nitrogen, the thin native iron oxide films are reduced to metallic iron, while free surface silicon or manganese oxides are definitely less abundant than after annealing in N 2 -H 2 gas mixtures. Although iron oxide is thermodynamically stable in water-vapour-containing nitrogen atmospheres, our results suggest that, provided the dew point is low enough, the oxygen present in the thin native iron oxide film is transferred to more stable oxide forms (silicon or manganese oxides). The transition from iron oxide reduction to iron oxidation takes place at some critical water vapour content threshold that is dependent on the steel composition. The phenomena observed in this study are explained in terms of the balance between the oxygen inward flow and the solute alloying element outward flow. In this context, several possible gas-metal and exchange reactions are discussed.

Surface selective oxides created during continuous annealing (MnO, SiO 2 , etc.) can have a deleterious effect on coating adhesion after hot-dip galvanizing. Earlier research works have made it clear that increasing the annealing atmosphere oxidizing potential can alleviate the problem by reducing external surface selective oxidation. In the present study, increasing the water vapour content of the nitrogen-hydrogen protective gas mixture was used to raise its oxidizing potential. The technique was applied to a classical dual-phase steel (0.15% C, 1.5% Mn, 0.45% Si, 0.05% Al. . .) that was annealed for 60 s at 800-810• C in protective atmospheres of nitrogen and 5% hydrogen with water vapour contents ranging from 10 to 6000 ppm.Post-annealing surfaces were characterized by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and scanning Auger microscopy (SAM). In situ XPS analyses were carried out right after simulation annealing in the preparation chamber connected to the spectrometer, never returning the specimens to air. This made it possible to identify in a reliable way the elements that segregated to the surface during the treatment, and to determine their corresponding oxidation states. On the other hand, the high sensitivity of SIMS was taken advantage of to assess oxide in-depth concentration profiles (SiO 2 , Al 2 O 3 , FeO) as a function of the annealing conditions, and SAM was used to characterize the corresponding oxide particle morphology.External selective oxidation was thus shown to decrease with increasing water vapour contents in the atmosphere (from 80 to 6000 ppm), whereas internal oxidation increases drastically to ∼4 µm below the free surface. At 10 ppm of H 2 O the oxygen partial pressure is very low and the external selective oxidation results in a thin, but almost complete, coverage of the steel surface. Consequently, metallic iron cannot be observed at the surface, thus hampering hot-dip galvanizability, unless the water vapour content is raised to 6000 ppm. Various surface morphologies were observed and discussed.In the authors' opinion, basic investigations of this type are an indispensable first step to improving the response of highly alloyed steels (dual-phase, TRIP) to hot-dip galvanizing.

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Surface condition control is particularly important in industrially processed materials, because apparently minor surface phenomena involving selective oxidation or low concentration element segregation can modify the surface reactivity and alter the material's response to downstream treatments. These phenomena, therefore, must be investigated by the most sophisticated simulation and surface analysis techniques, to ensure that accidental contamination is avoided. The paper reports on combined XPS, AES and SIMS spectroscopy to assess quantitatively the surface modifications taking place in Fe-based alloys during annealing treatments under various atmospheres.A new method has been developed from the equations initially put forward by Seah to assess element and compound surface coverage, based on experimental XPS peak intensities, computed inelastic mean free paths and atom densities. It has been applied successfully to annealed specimens made of Fe, Fe-0.5%Si binary alloy and ultralow carbon (ULC) deep-drawing steel.

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