Monday, August 8, 2011

Materials Suitable for Galvanizing -

Most iron-containing (ferrous) materials are suitable for hot­dip galvanizing. Plain carbon steel (under 150 ksi/llOO MPa) and low alloy materials, hot-rolled steel, cold-rolled steel, cast steel, ductile iron, cast iron, castings, stainless steel, and even weathering steel can be and are galvanized for enhanced corrosion protection. However, the material's chemical composition influences the characteristics of the galvanized coating. During galvanizing, the iron in the material reacts with the molten zinc to form a series of zinc-iron alloy layers, which are covered by a layer of iron-free zinc. For most hot-r

olled steels, the zinc-iron alloy portion of the coating will represent 50-70% of the total coating thickness, with the free zinc outer layer accounting for the balance (Figure 1).

Steel compositions vary depending on strength and service requirements. Trace elements in the steel (silicon, phosphorus) affect the galvanizing process as well as the structure and appearance of the galvanized coating. Steels with these elements outside of the recommended ranges are known in the galvanizing industry as highly reactive steel, and may produce a coating composed entirely, or almost entirely, of zinc-iron alloy layers (Figure 2).