Fe-Zn phase formation in interstitial-free steels hot-dip galvanized at 450°C: Part II 0.20 wt% Al-Zn baths
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The effect of solute additions of titanium, titanium and niobium and phosphorus on interstitial-free steels on Fe-Zn phase formation after immersion in a 0.20 wt% Al-Zn bath was studied to determine the morphology and kinetics of the individual Fe-Zn phases formed. These results were contrasted to the previous study using a pure zinc (0.00 wt% Al) bath in Part I. It was found that in the 0.20 wt% Al-Zn bath, an iron-aluminide inhibition layer prevented uniform attack of the steel substrate. Instead, localized Fe-Zn phase growth occurred, termed outbursts, containing a two-phase layer morphology. Delta-phase formed first, followed by gamma-phase. Zeta-phase did not form in the 0.20 wt% Al-Zn bath, in contrast with zeta-phase formation in the pure zinc bath. As in the pure zinc bath, the growth kinetics of the total layer was controlled by the Fe-Zn phase in contact with the liquid zinc during galvanizing. For the 0.20 wt% Al-Zn bath, the Fe-Zn phase in contrast with the liquid zinc was the delta-phase, whereas the zeta-phase was in contact with liquid zinc in the pure zinc bath. The delta-phase followed t1/2 parabolic growth, while the gamma-phase showed essentially no growth after its initial formation. Titanium and titanium + niobium solute additions, which enhance grain-boundary reactivity, resulted in more rapid growth kinetics of the gamma- and delta-phases. Phosphorus additions, which decrease grain-boundary reactivity, generally increased the incubation time and retarded the growth rate of the gamma-phase. These results further confirm the concept that solute grain-boundary reactivity is primarily responsible for Fe-Zn phase growth during galvanizing in a liquid Zn-Al bath in which an iron aluminide inhibition layer forms prior to Fe-Zn phase formation.
KeywordsSubstrate Steel Alloy Layer Solute Addition Interstitial Free Liquid Zinc
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- 2.J. S. KIRKALDY and M. UREDNICEK, Z. Metallkde 64 (1973) 899.Google Scholar
- 4.J. MACOWIAK and N. R. SHORT, Int. Metals Rev. 1 (1979) 1.Google Scholar
- 5.C. E. JORDAN and A. R. MARDER, "GALVATECH '95" edited by J.E. Hartmann (Iron and Steel Society, Warrendale, PA, 1995) p. 319.Google Scholar
- 6.N-Y. TANG, G. R. ADAMS and P. S. KOLISNYK, ibid., p. 777.Google Scholar
- 8.P. PERROT, J-C. TISSIER and J-Y. DAUPHIN, Z. Metallkde 83 (1992) 11.Google Scholar
- 9.T. FUKUZUKA, M. URAI and K. WAKAYAMA, Kobe Steel Engng. Rep. 30 (1980) 77.Google Scholar
- 10.K. OSINSKI, Doctoral Thesis, Eindhoven, The Netherlands (1983).Google Scholar
- 13.T. TOKI, K. OSHIMA, T. NAKAMORI, Y. SAITO, T. TSUDA and Y. HOBO, in “The Physical Metallurgy of Zinc Coated Steel”, edited by A. R. Marder (TMS, Warrendale, PA, 1994) p. 169.Google Scholar