Influence of Gas Atmosphere Dew Point on the Selective Oxidation and the Reactive Wetting During Hot Dip Galvanizing of CMnSi TRIP Steel |
| |
Authors: | Lawrence Cho Seok Jae Lee Myung Soo Kim Young Ha Kim Bruno C De Cooman |
| |
Affiliation: | 1. Materials Design Laboratory, Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang, 790-784, South Korea 2. POSCO Technical Research Laboratories, Gwangyang, 545-090, South Korea
|
| |
Abstract: | The selective oxidation and reactive wetting of intercritically annealed Si-bearing CMnSi transformation-induced plasticity steels were investigated by high-resolution transmission electron microscopy. In a N2 + 10 pct H2 gas atmosphere with a dew point (DP) ranging from 213 K to 278 K (?60 °C to 5 °C), a continuous layer of selective oxides was formed on the surface. Annealing in a higher DP gas atmosphere resulted in a thinner layer of external oxidation and a greater depth of internal oxidation. The hot dipping was carried out in a Zn bath containing 0.22 mass pct Al, and the bath temperature was 733 K (460 °C). Coarse and discontinuous Fe2Al5?x Zn x grains and Fe-Zn intermetallics (?? and ??) were observed at the steel/coating interface after the hot dip galvanizing (HDG) of panels were annealed in a low DP atmosphere 213 K (?60 °C). The Fe-Zn intermetallics were formed both in areas where the Fe2Al5?x Zn x inhibition layer had not been formed and on top of non-stoichiometric Fe-Al-Zn crystals. Poor wetting was observed on panels annealed in a low DP atmosphere because of the formation of thick film-type oxides on the surface. After annealing in higher DP gas atmospheres, i.e., 263 K and 278 K (?10 °C and 5 °C), a continuous and fine-grained Fe2Al5?x Zn x layer was formed. No Fe-Zn intermetallics were formed. The small grain size of the inhibition layer was attributed to the nucleation of the Fe2Al5?x Zn x grains on small ferrite sub-surface grains and the presence of granular surface oxides. A high DP atmosphere can therefore significantly contribute to the decrease of Zn-coating defects on CMnSi TRIP steels processed in HDG lines. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|