Improving Corrosion Resistance of Ferrous Alloy to Molten Zn by Modifying the Laves Phase Characteristics

Significance

One of the most economical way of reducing corrosion of steels in the industry is by the hot-dip galvanizing technique. Unfortunately, parts of the equipment used to fix the steel strips immersed in molten zinc are subjected to intense corrosion by the molten zinc. This mainly occurs in continuous galvanizing lines and in return demands the application of such corrosion resistant material which has for some time been a challenge. Cobalt based super alloys and iron-boron alloys are among the few alloys which have shown some potential although their application is hindered by prohibitive costs, rapid reaction with zinc and brittleness among others. Following this inspiration, researchers have designed a series of Fe-Mo-Cr-Ni alloys based on the Laves phase using thermodynamic calculations. The novel alloy has exhibited good performances so far but still requires further improvements. Consequently, this paper presents the addition of silicon, a strong stabilizing agent for the Laves phase, to the novel alloy.

Researchers at Xiangtan University in China investigated the effects of silicon addition on the composition, morphology and corrosion mechanism of the Laves phase in the Fe-Mo-Cr-Ni alloy. They aimed at improving the corrosion resistance of the ferrous alloy to molten zinc by modifying the Laves phase morphology in the Fe-Mo-Cr-Ni alloy. Their work is now published in the research journal, JOM.

The research team initiated their empirical procedure by preparing the two alloy samples to be used: Fe-Mo-Cr-Ni and Fe-Mo-Cr-Ni-Si. The alloys were then melted several times in water-cooled copper molds in an argon atmosphere. Ingots were then cut from the alloys using a wire electric discharge machine. The team then conducted immersion tests to measure the corrosion resistance. They then characterized the materials using scanning electron microscopy, electron probe micro-analyzer among other techniques. Eventually, X-ray diffraction patterns were obtained and used to identify the phases in the alloys.

The researchers were able to observe that the Silicon-containing alloy showed a woven, needle-like Laves phase with higher molybdenum content than that of the Fe-Mo-Cr-Ni alloy. Corrosion resistance to molten zinc for the Silicon-containing alloy was recorded to be more than 20 times higher than that of the silicon-free alloy mainly as a result of the characteristics of the modified Laves phase. This phase was oriented perpendicular to the zinc-diffusion direction, which effectively prevented corrosion by the molten zinc, leading to a denser FeZn13 layer rather than the FeZn10 layer produced in the Fe-Mo-Cr-Ni alloy.

The study presented successfully the development of the Fe-Mo-Cr-Ni-Si alloy. The alloy developed has been found to possess significantly improved corrosion resistance to liquid zinc. More so, the increase in the molybdenum content and the dense FeZn13 have also been seen to positively contribute to such increased resistance to corrosion by zinc. Therefore, the silicon stabilized Fe-Mo-Cr-Ni alloy is suitable for hot-dip galvanizing applications.

Reference

X. Liu, F.C. Yin, J. Lou, X.M. Ouyang, Z. Li. Improving Corrosion Resistance of Ferrous Alloy to Molten Zn by Modifying the Laves Phase Characteristics. JOM.

 

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