Selective Oxidation and Reactive Wetting of 1.0 Pct Si-0.5 Pct Al and 1.5 Pct Si TRIP-Assisted Steels

The effect of oxygen partial pressure on the selective oxidation and reactive wetting behavior of 1.0 pct Si-0.5 pct Al and 1.5 pct Si TRIP-assisted steels was studied. The annealing atmosphere affected the surface chemistry and the oxide morphology, which in turn affected reactive wetting. Similar wetting results were observed for the two TRIP steel compositions with good wetting being observed at the two lower oxygen partial pressure atmospheres (220 K (–53 °C) or 223 K (–50 °C) dew point (dp) and 243 K (–30 °C) dp) with poor reactive wetting at the higher oxygen partial pressure atmosphere (278 K (+5 °C) dp). The differences in wetting were attributed to the oxide morphology. The predominant oxide morphology at the two low oxygen partial pressure atmospheres was larger, widely spaced oxide nodules. At the 278 K (+5 °C) dp, the predominant oxide morphology was smaller, more closely spaced oxide nodules. TEM analysis revealed that at the 243 K (–30 °C) dp, Fe2Al5 was able to form between oxide nodules promoting good reactive wetting. At the 278 K (+5 °C) dp, the more closely spaced nodules may have impeded the formation of Fe2Al5, thereby producing numerous bare spot defects in the zinc coating.