Wetting of Low-carbon, Interstitial-free Steel Surfaces with Nanostructured Oxides by Liquid Zinc
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MANGANESE and silicon are typically added to low-carbon, interstitial-free (IF) steel to enhance its strength. However, during the annealing process, manganese and silicon can segregate on the steel surface to form nanometer-sized oxides such as MnO, MnSiO3, Mn2SiO4, and SiO2.[1] Because these oxides show poor wettability by liquid zinc, uncoated (bare) spots are found on the surfaces of such steels after they are hotdip galvanized. During hot-dip galvanizing, the wetting behavior of liquid zinc on steel plates is complicated. The initial contact angle (before the initiation of any chemical reactions) is governed by the physical interactions between the liquid zinc and the steel plate. After the chemical reactions start, the wetting angle gradually decreases because of mass transport between the liquid zinc and the steel plate. Finally, an intermetallic compound layer such as f, d1, C1, C phases will be formed between the liquid zinc and the steel plate. The wetting characteristics of steel plates by liquid zinc and zinc alloys mainly have been investigated using the meniscograph method. The meniscograph method, however, measures the wetting behavior after the steel plate has been immersed in the liquid zinc or zinc alloys for more than 3 seconds.[2] Accordingly, meniscograph measurements give only an indication of the wetting behavior between the melt and the intermetallic compound layer that has formed on the steel plate. JOONHO LEE, Associate Professor, is with the Department of Materials Science and Engineering, Korea University, Seoul 136-713, Korea, JOONGCHUL PARK, Graduate Student, is with the Department of Materials Science and Engineering, Korea University, Seoul 136-713, Korea, SUN-HO JEON, Researcher, is with the POSCO Technical Research Laboratories, Gwang-yang, Chunranam-do 545-090, Korea. Contact e-mail: [email protected]. Manuscript submitted December 11, 2008. Article published online August 25, 2009. METALLURGICAL AND MATERIALS TRANSACTIONS B
Therefore, an alternative method is required to be able to evaluate the initial dynamic reactive wetting behavior of steel plates by liquid zinc and zinc alloys. Noting these technical problems, several researchers made use of the sessile drop method to investigate the wetting behavior from the initial stage of the galvanizing process. Hara and Asano[3] reported that the contact angle between liquid zinc (or zinc alloys containing aluminum) and low-carbon steel plates gradually decreased with increasing wetting time. Although they also found that the contact angle was increased by adding Si and Mn, they did not make any systematic analysis on the wetting behavior. Several researchers investigated the wetting behavior of liquid zinc or zinc alloys using a high-speed video camera.[4–9] Shimada et al.[4,5] and Takada et al.[6,7] successfully investigated the initial contact angle between liquid zinc and a steel plate at 600 °C with a high-speed video camera that operated at 250 or 500 frames/second. They found that the contact angle rapidly decrease
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