Development of the surface structure of TRIP steels prior to hot-dip galvanizing

Focusing on improving the reactive wetting of transformation-induced plasticity (TRIP) steels during hot-dip galvanizing, the effect of the alloying elements manganese, silicon and aluminum on the surface structure prior to galvanizing was studied. A C-Mn steel and two TRIP steels with aluminum either completely or partially replacing silicon were investigated. The two TRIP steels showed good wettability when using a -30 degrees C dew point with a 95% N-2-5% H-2 atmosphere and improved wettability when using a -53 degrees C dew point with a 80% N-2-20% H-2 atmosphere. The decreased oxide thickness and the change in the distribution of oxides on the surface, showing a larger surface area that was free of oxide particles, contributed to the improved reactive wetting of the two TRIP steels at the -53 degrees C dew point. The C-Mn steel demonstrated excellent wettability for both annealing atmospheres. The observed reactive wetting was attributed to the reduction of MnO by Al in the Zn(Al, Fe) bath. (c) 2006 Elsevier B.V. All rights reserved.