Effect of Annealed Oxides on the Formation of Inhibition Layer During Hot-Dip Galvanizing of 590Mpa Trip Steel

Abstract

The selective surface oxidation of a transformation-induced-plasticity (TRIP) steel containing 1.6 wt.% Mn and 1.5 wt.% Si during annealing at 800 ℃ was investigated for its influence on the formation of an inhibition layer during hot-dip galvanizing. The selective oxidation of the alloying elements and the oxide morphology were significantly influenced by the annealing atmosphere. The pure _N2 atmosphere with a dew point -40 ℃ promoted the selective oxidation of Mn as a crystalline Mn_2SiO_4 phase, whereas the N_2 + 10% H2_ atmosphere with the same dew point -40 ℃ promoted the selective oxidation of Si as an amorphous Si-rich oxide phase. During hot-dip galvanizing, the Mn2SiO4 phase was reduced more readily by Al in the Zn bath than the Si-rich oxide phase. Consequently, the pure N_2 atmosphere resulted in a higher formation rate of Fe_2Al_5 particles at the Zn/steel interface and better galvanizability than the N_2 + 10% H_2 atmosphere.