Abstract
During continuous annealing prior to hot dip galvanising, the surface of ULC ( U ltra L ow C arbon) deep drawing steels undergoes a range of chemical modifications that can affect interface reactions, thus influencing the quality of the metallic protective coating and the product's final user's properties. These phenomena were investigated by XPS, in a high-resolution, fully automatic spectrometer coupled with a tight preparation chamber, where the treatment can be simulated very faithfully, in terms of both heat cycle and protective atmosphere. Under vacuum, the equilibrium (Gibbs) surface segregation of alloying — or tramp — elements such as P, Sn, Sb, As, S and C is clearly the predominant phenomenon. Selective oxidation grows much more significant when annealing is performed under a water vapour containing N 2–5%H 2 protective atmosphere. It involves highly oxidisable elements such as Al, Mn and Si. Though much less intense than under vacuum, Gibbs segregation however remains present, in direct competition with selective oxidation.
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