Steel is composite metal of iron and carbon. Carbon is added during the smelting process to further strengthen the iron. Depending on the amount of carbon present, steel can be of different grades serving a variety of purposes. "Galvanized" steel is made by adding a layer of zinc and other minerals to the surface of the steel object to protect it against corrosion (also called "oxidation").
Iron occurs as a naturally occurring oxide in rock which must be mined. The ore is crushed, and then smelted in a furnace to melt the iron out of the rock. Coke (a form of coal) is used as a fuel for the furnace. Other minerals such as limestone are added to precipitate impurities such as silicone, which forms a layer of "slag" on the surface of the molten iron and is then removed. During the smelting, carbon from the coke is absorbed into the iron, strengthening it. The molten iron can then be cast into a variety of molds, such as manhole covers and grates.
Different grades of steel exist, each with varying amounts of carbon in them. This can range from 0.25 percent to 1.5 percent carbon. Carbon is incorporated into iron during a smelting process which involves controlled heating and cooling of the molten iron, along with a source of carbon (typically coke.) A higher level of carbon in steel means it will be harder; however, it will also be more brittle. Lower amounts of carbon allows steel to be softer, but more malleable.
Zinc protects steel against corrosion because it does not rust. "Galvanized" steel is produced by immersing steel in a tank of molten zinc (a process known as "hot dip galvanizing") at temperatures of 438 to 460 degrees Celsius. Zinc reacts with the iron molecules in the steel to form surface layers which contain both elements. When the galvanizing has been completed, the steel will be protected by a topmost layer of pure zinc, followed by three layers of zinc mixed with iron molecules (each of decreasing amounts of zinc).
Stainless steel comprises a variety of grades and categories. Like galvanized steel, stainless steel has an anti-corrosive element added to it, typically 10 percent chromium. Unlike galvanized steel, stainless steel is alloyed with a non-oxidizing element during the smelting process. The chromium alloy reacts with oxygen in air to form a protective layer of chromium oxide on the steel's surface.
Galvanized and stainless steel both prevent oxidation. However, each kind of metal is manufactured for specific functions. Galvanizing steel is a cheaper process than making stainless steel. Galvanized steel is used in the construction and automotive industries as well as machine parts and tools. Stainless steel has a wide variety of grades, each with varying amounts of alloys. These different grades of steel balance malleability with hardness and anti-corrosive properties. Stainless steel is used as cooking utensils, tools and railway tracks, among many other applications.