Effect of annealing atmosphere on the galvanizing behavior of a dual-phase steel

Effect of Annealing Temperature on the Selective Oxidation and Reactive Wetting of a 0.1C-6Mn-2Si Advanced High Strength Steel During Continuous Galvanizing Heat Treatments

“…However, in the case of the external MnO layer observed for all annealing conditions in the present study, it has been shown that MnO can be reduced by Al in the galvanizing zinc bath through aluminothermic reduction. 15,17) Based on the kinetic model proposed by Kavitha and McDermid,17) it is expected that MnO layers with a thickness less than 85 nm can be aluminothermically reduced during a 4 s immersion in a 0.20 wt% Al (dissolved) galvanizing bath. Thus, the widely spaced 44 nm external MnO on the 963 K × 120 s sample could be reduced by the bath whereas the thicker 121 nm compact morphology of the 1 073 K × 120 s sample could not.…”

“…As the pre-immersion surface oxides of this sample comprised a fine and widely-spaced nodule-like structure with thinner oxides between them, during immersion in the Zn(Al,Fe) bath, the liquid alloy could penetrate into the steel substrate, lifting up the surface oxides, while simultaneously the 44 nm thick external MnO layer was fully or partially reduced through aluminothermic reduction. Both of these mechanisms would expose the underlying substrate to dissolution 15,17) and the observed formation of the Fe 2 Al 5 Zn X layer at the interface.…”

“…Furthermore, it has been established that MnO can decompose during immersion in the zinc bath through in-situ aluminothermic reduction. 6,15,17) In other cases, reactive wetting of surfaces comprising widely spaced oxide nodules has been reported. 13,14,18) It has also been reported that infiltration and lift-off of the oxides by the bath alloy through cracks at the oxide/substrate interface can aid in the reactive wetting process.…”

“…[10][11][12][13][14][15][16] The formation of the desired Fe 2 Al 5 Zn X interfacial layer and complete reactive wetting in these studies has been explained by differences in surface oxide chemistry, thickness and morphology. Furthermore, it has been established that MnO can decompose during immersion in the zinc bath through in-situ aluminothermic reduction.…”

Analysis of the Inhibition Layer of Galvanized Dual-Phase Steels

“…The co-existence of Mn and Si allows the formation of Mn 2 SiO 4 oxides on the steel surface during annealing which is detrimental to the formation of inhibition layer. 6) On the other hand, Khondker et al 14) suggested that manganese oxides can be reduced by Al in the bath and may not hinder the Fe-Al reaction(s). A mechanism involving the aluminothermic reduction of MnO followed by a two-step formation of the inhibition layer on high Al-low Si TRIP (transformation-induced plasticity) steels was proposed recently.…”