Chromium: Putting the “Stainless” in “Stainless Steel”

When you think of chromium, you probably think of chromium plating, a.k.a. chrome. It has another more prevalent use, however. Chromium is a key ingredient in stainless steel. Basically, it is what makes the steel stainless. As such, chromium is an important element in the steel industry and it has been for hundreds of years.

In 1797, the first pure chromium metal was created by French Chemist Nicholas-Louis Vauguelin. Before then, it had been used in dyes and paints, but this marked chromium’s first use in metallurgy. Then, in 1912, Harry Brearley was trying to find a more resilient metal for gun barrels in the U.K. when he created stainless steel. Elsewhere, Elwood Haynes in the US and engineers at Krupp in Germany were also working on chromium-steel alloys. With the invention of the electric arc furnace, which is used in chromite smelting, large scale production became possible.

Chromium, periodic symbol Cr, has a high melting point (2,150°C), is corrosion resistant, and is aesthetically pleasing. By itself it is brittle however, so combining it with steel greatly increased its strength. Conversely, the addition of chromium to steel greatly increased its corrosion resistance.

To make chromium, first chromite ore is mined. Via a smelting process, this is converted to ferrochromium alloys. These alloys consist mainly of chromium and iron with small amounts of carbon and silicone. In 2009, 5.9 million tons of ferrochromium were produced worldwide. Over 90% went to the production of stainless steel. In order to be considered “stainless,” the steel alloy must contain at least 11-12% Chromium. Some stainless steel contains up to 30% Chromium.