Date of Graduation

2000

Document Type

Thesis

Degree Type

MS

Committee Chair

Keh-Minn Chang

Abstract

The corrosion of bath hardware used in continuous galvanization lines is a great challenge within the hot-dip coating industry today. The objective of this research was to examine the potential of using intermetallic Fe3Al alloys developed at Oak Ridge National Laboratory in the bath hardware application of the continuous hot-dipping process. In order to examine the effectiveness of Fe3Al in this harsh, molten metal environment, two sets of liquid metal corrosion tests were carried out. The purpose of the first set of experiments was to examine the effect of test duration on the corrosion of the different alloys. The testing was conducted by the immersion of test specimens in a hot-dip coating bath of a commercial hot-dipping line. These corrosion tests were performed on coupons of Fe3Al, and a low carbon stainless steel, 316L, was accompanied for comparison. The 316L stainless steel alloy is a common alloy used for the manufacture of bath hardware of continuous hot-dip coating lines. In these tests, the bath material was maintained at a specific temperature used for commercial hot-dip runs. The sample materials were submerged in four different baths for durations ranging from 2 hours to 240 hours. The baths included: pure zinc, zinc-5wt%aluminum, zinc 55wt%aluminum, aluminum-8wt% silicon. The purpose of the second group of tests was to examine the temperature effect on corrosion behavior of the sample alloys. In this group of tests an experimental FeCrSi alloy, developed at Oak Ridge National Laboratory, was tested in addition to the Fe3Al and 316L. Test specimens were statically tested in the same four liquid baths as the on line battery of tests, but different temperatures were employed. After the corrosion tests were completed, the specimens were cut, mounted and ground. The specimens were then etched and the remaining specimen thicknesses were measured using a Hi-Scope optical microscope from Hirox outfitted with Vision Gauge PC-based software. Grain size measurements and microstructure examination of the pre test sample materials were carried out through standard laboratory procedure. Examination of the interface layers and compositional analyses were then carried out on the test specimens with the aid of a scanning electron microscope (SEM). Comparison between the corrosion behavior of the 316L, Fe3Al, and FeCrSi samples in the separate sets of corrosion tests were made. A sound base of corrosion data for the three test materials in molten zinc, Al-8Si, Zn-5Al, and Zn-55Al is developed and microstructure evaluation of the formed alloy layers is presented. A significant temperature and time effect on the corrosion of the test materials in the molten baths was found. Through the on-line corrosion testing, a linear time law for corrosion from 2 hours to 240 hours was found for the 316L, Fe3Al, and FeCrSi specimens. The Fe3Al alloy showed similar results in the Al-8Si bath as the 316L alloy. The FeCrSi alloy showed relatively low corrosion rates during the static testing, but demonstrated a pronounced temperature effect in the Zn-5Al bath as the testing temperature was increased above 560ºC.

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