Liquid metal corrosion of 316L, Fe 3 Al, and FeCrSi in molten Zn-Al baths
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I. INTRODUCTION
THE coating of steel sheet by continuous hot dipping in a molten metal bath of zinc or in a Zn/Al melt is the most efficient and economical method of providing corrosion protection to most steel sheet compositions. Reliable performance of galvanizing pot hardware is essential to the productivity of a hot dip galvanizing line and the quality of coatings produced. As shown in Figure 1, the pot hardware in galvanizing bath includes the snout, sink roll, stabilizing rolls, and the bearings supporting them. The most frequent cause of galvanizing line stoppage is pot hardware problems that are related to one or more of the following three issues: (1) wear of bearings supporting the stabilizer roll and sink roll; (2) corrosion of the pot hardware in molten Zn/Al bath; and (3) the nucleation and growth of dross (intermetallic compound) on roll surfaces.[1] Corrosion of the hardware by molten Zn/Al alloys is one of the most important reasons to cause the downtime of production lines; thus, the corrosion resistance becomes the primary criterion for the selection of pot hardware materials. Besides corrosion resistance, there are other properties requirements for pot hardware materials, among which the resistance to intermetallic dross buildup on the surface for roll materials, wear resistance for bearing materials, and ductility are the most important ones. Since corrosion resistance is the primary criterion for the pot-hardware materials XINGBO LIU, Research Assistant Professor, EVER BARBERO, Professor and Department Chairman, JING XU, Ph.D. Student, MATTHEW BURRIS, Graduate Student, and KEH-MINN CHANG, Adjunct Professor, are with the Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, WV 26506. Contact e-mail: [email protected] VINOD SIKKA, Group Leader, is with the Metal and Ceramics Processing Group, Oak Ridge National Laboratories, Oak Ridge, TN 37831. Manuscript submitted November 25, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS A
and each candidate material needs to show good corrosion resistance before other properties being investigated, other properties of the intermetallic materials were not investigated in this article. Corrosion behavior of the pot-hardware materials and coating have been studied;[2–5] however, many investigators show contrasting liquid zinc immersion results for the same alloys.[3,4,5] For instance, literature[3] concluded that aluminum in the molten zinc bath did not diffuse into the WC-Co coating layer. However, the results in the literature[4] showed that aluminum diffused as much as zinc diffused into the coating. The authors of the literature[4] proposed two possible reasons to explain the difference: (1) the study in literature[3] was carried out in high aluminum contents bath, i.e., 0.3 and 3.0 wt pct of aluminum; and (2) the sample in the literature[4] were immersed in zinc baths containing iron. 316L stainless steel is the most popular material for stabilizer and sink rolls in the industry and STELLITE* 6, a *STELLITE is a
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