Steel and iron are often referred to interchangeably because they have similar characteristics. Iron is a metal, and steel is a manmade alloy that mixes iron with carbon and other elements. Both are hard and resilient with a wide temperature range and corrosion resistance in high-humidity environments. Steel is widely used in construction for carrying water, flammable gases, and in fire sprinkler systems. Cast iron is crushproof, sound deafening, corrosion resistant, and used in sanitary and storm drain, waste, and vent piping applications. Ductile iron is lighter, stronger, and more durable than cast iron. Uncoated alloy steels, also called chrome-moly, are stronger than carbon steel and resist rupturing. Uncoated black steel, or black malleable iron, is made from corrosion-resistant ungalvanized steel. Zinc galvanized steel has a zinc coating that resists rust, corrosion, mineral buildup, and wet conditions. Steel and iron pipe and pipe fittings come in a variety of sizes and shapes.