Effect of oxygen partial pressure during annealing on the selective oxidation and galvanizing of a 1.5% Al TRIP-assisted steel

Selective oxidation during annealing prior to galvanizing and reactive wetting during galvanizing of a 1.5% Al TRIP-assisted steel was studied. Three different atmospheres were tested during annealing prior to galvanizing: -53 °C dew point (dp) with N2-20% H2, -30 °C dp with N2-5% H2 and +5 °C dp with N2-5% H 2. The chemical composition of the steel surface as determined with X-ray photoelectron spectroscopy (XPS) showed selective oxidation of Mn, Al and Si. The oxide morphology was studied with scanning Auger microscopy (SAM) and three different oxide morphologies were identified; nodules, grain boundary oxidation and oxide films. Good reactive wetting during galvanizing was observed at -53 °C dp and -30 °C dp; wetting was poor at the +5 °C dp with an increased number of bare spots in the Zn coating and a discontinuous Fe 2Al5 layer.