Creating Steel

Steel is iron that has most of the impurities removed. Steel also has a consistent concentration of carbon throughout (0.5 percent to 1.5 percent). Impurities like silica, phosphorous and sulfur weaken steel tremendously, so they must be eliminated. The advantage of steel over iron is greatly improved strength.

The open hearth furnace is one way to create steel from pig iron. The pig iron, limestone and iron ore go into an open hearth furnace. It is heated to about 1600 F (871 C). The limestone and ore forms a slag that floats on the surface. Impurities, including carbon, are oxidized and float out of the iron into the slag. When the carbon content is right, you have carbon steel.

Another way to create steel from pig iron is the Bessemer process.

Most modern steel plants use what's called a basic oxygen furnace to create steel. The advantage is that it is a rapid process -- about 10 times faster than the open hearth furnace.

A variety of metals might be alloyed with the steel at this point to create different properties. For example, the addition of 10 percent to 30 percent chromium creates stainless steel, which is very resistant to rust. The addition of chromium and molybdenum creates chrome-moly steel, which is strong and light.

When you think about it, there are two accidents of nature that have made it much easier for humans to move forward at a rapid pace. One is the huge availability of something as useful as iron ore. The second is the availability of vast quantities of oil and coal to power the production of iron. This is a very lucky coincidence, because without iron and energy, we would not have gotten nearly as far as we have today.