This study is mainly aimed at interstital-free and dual-phase steels, analyzing the compositions and distribution of selective surface oxides after annealing and then to know the influence of these oxidation for the formation of FeAl inhibition layer in hot-dip galvanizing. Interstital-free and dual-phase steels were first annealed at 800 oC for 1-200 s in a 10% H2-N2 protected atmosphere of -70 oC and 0 oC dew point respectively and then dipped in zinc bath with Al content 0.12-0.18 wt% for 0-20 s. Using this combined SEM, Auger electron spectroscopy(AES), X-ray photoelectron spectroscopy(XPS) and ICP-AES etc. instruments, it is shown that the MnAl2O4 spinels were the major oxidation on the surface of IF steel after annealing. The average oxidation thickness was about 5-15 nm. Annealing times has little effect on the thickness. On the other hand, MnO were observed on DP steel surface after anneaing. The MnO paticles mainly distributed at the grain boundaries ,and the average oxdaiton thickness increase rapidly from 20 nm(10 s) to 110 nm(200 s) with annealing times. The growth of the FeAl inhibition layer can separate to nucleation in initial stage and diffusion growth later. The Fe2Al5 nucleation times were all about 0.1 s in both steels , and average thicknesses were approximately 20 nm. For IF steels , Al uptake in the zinc bath and steel interface was depleted in nucleation stage with 0.12 wt% Al content, so that delayed the growth of Fe2Al5, and the rate determining step was the diffusion of Al in zinc bath. When Al content raise up to 0.14 wt%, the phenomenon of growth delay was not happened, and the rate determining step of Fe2Al5 growth changed to the solid-state diffusion of Fe in Fe2Al5. For DP steels, when Al content up to 0.14 wt%, the growth mechanism was similar to IF steels, but the rate determining step of Fe2Al5 growth was mainly in the grain boundary diffusion of Fe in Fe2Al5. Moreover, where the MnO paticles was rich could obviously observe the delay of Fe2Al5 growth. It was probably because of consuming a great deal of Al to reduce the MnO oxides.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0808111-131312 |
| Date | 08 August 2011 |
| Creators | Hsu, Chiung-wen |
| Contributors | Liu-Wen Chang, Der-Shin Gan, Chao-Sung Lin, Yi-Shing Huang |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0808111-131312 |
| Rights | user_define, Copyright information available at source archive |
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