Already familiar with the smelting of gold, silver, and copper, metal smiths, possibly as early as 4,000 B.C., tried to use the techniques they already knew to smelt iron ore. Unsuccessful at these attempts, they sought a new technique. It wasn't until the discovery that iron ore has an affinity for (and therefore contains) oxygen that the development of iron, and later, steel, became possible.

Early processes of obtaining iron from its ore required heating the ore with a substance that had a high carbon content, such as charcoal. As temperatures within the furnace reached 1,650 degrees Fahrenheit, the ore began to release oxygen and the charcoal released carbon. These two elements then combined to form carbon monoxide, leaving behind a spongy mass of iron. If the temperature was allowed to reach 2,190 degrees F, this mass would absorb small amounts of carbon, forming wrought iron. At higher temperatures, the iron would absorb more carbon, melt, and result in a molten metal called cast or pig iron.

Though the use of iron was already widespread in Europe and North America, ironworkers continued to experiment with the metal, trying to improve the properties of soft wrought iron and hard and brittle cast iron. They tried heating, pounding, and quenching iron in cool water and learned that adding oxygen to the molten metal at high enough temperatures reduced its impurities and the carbon content. This resulted in a purer, stronger metal: steel.

One process of making steel was to heat wrought iron -- which had a low carbon content -- in clay crucibles (or vessels) with charcoal for about ten days. This would increase the carbon content enough to transform the iron into steel. The technique worked, but it was time consuming, required a lot of fuel, and produced only small quantities of steel. During the mid 19th century, the Bessemer converter -- an oval shaped furnace that blasted molten iron with oxygen -- revolutionized the production of steel. Andrew Carnegie saw the importance of the new converter and declared, "The day of iron is past. Steel is king!" His company began producing steel rails at an astounding rate, -supplying the tracks the railroads were rapidly laying across North America.

The reign of steel continued with the development of alloy steels in the early 19th century. The addition of elements known for their resistance to corrosion -- elements such as gold, tungsten, and chromium -- modified the properties of steel, further strengthening the metal. The high-strength steels were able to retain sharp edges while cutting at high speeds and were utilized by new industries in the United States. Edward Budd, who manufactured the first all-steel automobiles, proved the superior strength of steel by standing an elephant atop one of his steel cars. The mass production of planes, trains, and cars, made possible by alloy steel, defined the modern world in an entirely new way.