Iron (ferrous oxide), relatively inexpensive and naturally silver-white in color, is soft, malleable, ductile, and magnetic. When exposed to acids, it corrodes. All iron has some degree of carbon, introduced in the smelting process, which increases its strength and hardness, but reduces its ductility and ability to be welded. The two types of iron are cast iron and wrought iron, both briefly discussed earlier in the home design.
Cast iron is an alloy of iron with 2 to 4.5 percent carbon and 1 to 4 percent silicon. The molten iron is cast into a mold, and then machined to make building products. Cast iron is hard and long wearing but brittle. It has low tensile strength and is not malleable. The development of cast iron in decorating was essential to the success of the Industrial Revolution. The epitome of cast-iron construction occurred when it was already being replaced by steel and concrete: the Eiffel Tower. Modern uses of cast iron include hardware, stairs, ornamental railings, and decorative garden furniture. Cast iron may also be used for plumbing waste pipes.
Wrought iron contains less than 4.3 percent of carbon, but usually 1 or 2 percent, along with 1 to 2 percent slag. Wrought iron is made directly from ore using the puddling method, in which pig iron is subjected to heat while being frequently stirred in a reverberating furnace in the presence of oxidizing substances. Wrought iron is tough but malleable, and relatively soft. Because wrought iron is easily forged and welded, it is used for cabinet and decorative hardware, gates, outdoor furnishings, railings, fences, screens, and ornamental work, including light fixtures and curtain rods.
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10 to 20 percent tungsten added to increase hardness and heat resistance. Steel is the most common material used for framing of high-rise construction; it is the primary method of reinforcing concrete. Steel is also used for fasteners, welded fabrications, wall grilles, and ceiling suspension systems. Steel must be coated or painted to avoid corrosion or rust. Weathering steel, with the trade name Cor-ten, was developed using a surface alloy that allowed intentional rusting. Once the metal is completely coated with rust, it is protected from further rust. This eliminates the need for painting. Generally used on an exterior, pre-weathered steel must be used carefully to avoid rust damaging other surfaces, although newer weathered steel products are less likely to stain.
Stainless steel is very strong and resistant to rusting. It is an alloy of steel and chromium. The chromium forms a transparent film on the surface, protecting it from oxidation and rust. Stainless steel is the preferred material for use in damp locations, having a high resistance to corrosion. In addition, stainless steel does not stain adjacent surfaces and does not react with mortar or concrete. Although stainless steel is expensive (five times the cost of carbon steel), it is durable. It may be polished or unpolished or have a brushed surface that gives it a satin finish. Stainless steel has long been the standard for commercial kitchen furniture because it provides a hygienic surface, and it has become a popular material to face appliances in residential applications. Stainless steel sheets are used as countertops, column covers, and wall panels. It is also used for hardware, fasteners and anchors, railings, furniture and accessories, and light fixtures. Additionally, stainless steel is used for commercial and residential bathroom accessories. High-luster stainless steel shows fingerprints and must be carefully cleaned.