Iron is the main ingredient in various forms of iron and steel, but the various types of metals contain other elements as well. Sometimes these elements are unwanted; other times they're intentionally added.

	Cast Iron Cast iron contains high levels of carbon, which makes it a hard, brittle metal. Cast iron was commonly used throughout Europe to make church bells and, in colonial America, pots and pans.
	Wrought Iron Wrought iron is a strong, durable metal with a low carbon content. Items such as locks, bolts, tools, and fences are crafted out of this metal. Wrought iron bars were also sold and traded to be later converted into steel or cast iron.
	Plain Steel During the early 20th century, new processes in steel production allowed steel to surpass iron as the most widely used structural metal. Its great strength and affordability allowed craftsmen to construct sturdier bridges and higher buildings.
	High Strength Steel Adding alloys to steel yield higher strength, more wear-resistant metals. James Eads used alloy steel in the construction of a bridge across the Mississippi River -- the first steel bridge built in America.
	Stainless Steel From spoons to blenders, cars to trains, stainless steel, with its sleek, shiny surface, can glorify even the most simple of gadgets. In addition to its aesthetic appeal, the light weight and strength of stainless make it ideal for transportation.

Seven Elements Used in Steel

Carbon (C): Carbon, a nonmetallic element, forms a number of organic and inorganic compounds and can be found in coal, petroleum and limestone. It is the principle strengthening element in carbon steels and low-alloy steels. Atomic number 6, atomic weight 12.01115.

Manganese (Mn): Manganese is a brittle, metallic element that exists in the ore of pyrolusite. When making steel, it reacts with sulfur and helps to increase the metal's resistance to heat. Atomic number 25, atomic weight 54.9380.

Phosphorus (P): Phosphorus is a poisonous, nonmetallic element that helps protect metal surfaces from corrosion. Atomic number 15, atomic weight 30.9738.

Sulfur (S): Sulfur is a nonmetallic element found mainly in volcanic and sedimentary deposits. Sulfur, in the form of iron sulfide, can cause steel to be too porous and prone to cracking. Atomic number 16, atomic weight 32.064.

Silicon (Si): Silicon is the second most abundant element in the earth's crust and can be found in rocks, sand and clay. It acts as a deoxidizer in steel production. Atomic number 14, atomic weight 28.086.

Nickel (Ni): Nickel is a hard, metallic element that found in igneous rocks. Without nickel, stainless steel would be less resistant to heat and corrosion. Atomic number 28, atomic weight 58.71.

Chromium (Cr): Chromium, a metallic element, is found in the earth's crust. It is used in the production of stainless steel to make the steel resistant to oxidation and corrosion. Atomic number 24, atomic weight 51.996.