The National Iron & Steel Heritage Museum
From Iron to Steel
Humans began to produce iron sometime after 2000BC, beginning the Iron Age, when iron replaced bronze in weapons and tools.  Iron, a harder and more durable metal than bronze, became the metal of choice for man until the 1870s, when it was replaced by steel.

Iron, a natural element, is the fourth most abundant element in the earth.  It is found in the form of ores, rocks mixed with minerals, and oxides, compounds that contain oxygen.  Smelting occurs when iron ore is heated and iron can be extracted from the ore.  The extracted iron was made into tools, weapons, barrel rims, carriage parts, and more for thousands of years.

Steel is an alloy, or mixture, of iron, carbon, and other metals (nickel, manganese, chromium, etc.).  In general, steel is a stronger metal than iron.  Until the 1800s, however, steel was very expensive and difficult to manufacture, so iron remained the metal of choice. 

That began to change in 1856, with Henry Bessemer’s creation of the Bessemer process, which used a converter to melt and refine pig iron.  Unfortunately, this process did not remove phosphorus from the pig iron, which made steel too brittle and limited steelmaking to phosphorus-free ores.

Twenty years later in 1876, Sidney Gilchrist Thomas discovered that adding limestone to the converter drew the phosphorus out of the pig iron.  This important finding meant that stores of iron ore from regions worldwide could be used to make pig iron.  This led to a massive increase in the production of cheaper but quality steel.

In the 1860s, Carl Wilhelm Siemens developed the open hearth process.  The process, which could achieve very high temperatures, took hours to produce a batch of steel (the Bessemer process was much quicker).  This allowed for testing of the molten steel to meet customers’ precise specifications in the steel’s chemical composition and properties.  Open hearths also allowed for the production of larger batches of steel and the recycling of scrap metal.  Because of this, the open hearth process largely replaced the Bessemer process by 1900.

Due to the lower cost and good quality of mass-produced steel in the 1870s, steel began to replace iron as the metal of choice for man.  By the 1900s, although a few iron companies remained active, it was steel companies that supplied the product for our railroads, automobiles, bridges, skyscrapers, and more.