On the Selective Oxidation of a 0.15C-6Mn-2Al-1Si Third-Generation Advanced High Strength Steel During Two-Stage Annealing Treatments

The selective oxidation of a 0.15C-5.6Mn-1.9Al-1.1Si (wt pct) prototype third-generation advanced high-strength steel during dew point-controlled two-stage annealing with intermediate flash pickling was documented. After austenitization annealing at 1163 K for 600 s, the surfaces had compact nodules of MnO on top of co-precipitated nodules of MnSiO3/Mn2SiO4 and MnAl2O4. The intermediate flash pickling treatment dissolved the external MnO and Mn-Si oxides, leaving behind small, widely spaced MnAl2O4 nodules with significant fractions of metallic Fe exposed. Subsequent intercritical annealing at 983 K for 120 s resulted in no significant changes to the MnAl2O4 nodules due to solute depletion from the near-surface matrix during austenitization annealing. The resulting surfaces were relatively barren of external oxides and had significant fractions of metallic Fe boldly exposed, which are promising for reactive wetting by conventional continuous galvanizing baths.Graphical abstract