Mad About Science: Stainless steel

By Brenden Bobby
Reader Columnist

As you and your family gather around the table this Thanksgiving, stop and ponder for a moment the miracle that is your stainless steel cutlery. Unlike other steel implements, it does not rust when exposed to water, it retains sharp points and edges, and it’s perpetually shiny. What kind of magic makes stainless steel so incredible? Chromium.

Chromium is a chemical element with the symbol Cr and an atomic number of 24. It’s a lustrous element that’s extremely reflective in sufficient quantities. Chrome plating — seen abundantly in Sandpoint every May during Lost in the ’50s — is one of the most common appearances of chromium. This effect is achieved by electroplating a very thin layer of chromium over steel to create a smooth and reflective surface that begs to be smudged by your grubby fingertips. This is not the process that creates stainless steel, however.

Stainless steel is an alloy of chromium, iron and nickel. These metals together create a unique metal substance with a wide variety of applications, though its most identifiable form is through cookware.

Cookware is a popular use for stainless steel for several reasons. Stainless steel has a different response to oxidation than iron on its own. When iron oxidizes, it rusts and becomes brittle and flaky. 

Thanks to chromium, stainless steel reacts differently to oxygen and instead creates a protective sealing film over the surface of the object, which is capable of self-healing minor scratches and indentations. This film also gives residual bacteria virtually nowhere to hide and makes cleaning our cookware easy.

The various qualities of stainless steel make it a perfect candidate for something that repeatedly stabs into hot food and survives the crucible of our saliva and gnashing teeth. 

Commercial kitchens are loaded to the brim with stainless steel. The same properties that make it safe to go in our mouths make it easy to hold water and clean with soap. 

Sinks in commercial kitchens are often three-chambered and made of stainless steel. Prep surfaces, storage spaces and fans are often made of this alloy as well to make thorough cleaning a relatively simple affair.

Imagine how much bacteria must live between the fibers of a wooden countertop. Even most laminate will degrade over time, as will chemical sealants that are repeatedly subjected to a knife’s cutting edge.

These features also make stainless steel an attractive choice for the medical and dental fields, including uses for scalpels, sinks and clamps, among myriad other uses.

Stainless steel requires a lot of heat and energy in order to melt. The melting range for stainless steel is between 2,550 and 2,790 degrees Fahrenheit. Achieving these kinds of temperatures is a seriously difficult task — while it might not be immediately apparent, the ability to create that level of heat was one of the major technological hurdles that kept humanity from reaching the Industrial Revolution for thousands of years.

Humans first began dabbling in metallurgy around the 6th millennia B.C.E. The development of ceramics that could retain and resist heat went hand-in-hand with smelting technology. The discovery and development of fuel was another major hurdle for early civilizations. Copper, believed to be one of the earliest metals ever worked by humans, has a melting point of 1984 degrees Fahrenheit. Wood fire burns at up to about 700 degrees.

Charcoal was a major development for metallurgy. Created by burning wood in an environment with limited oxygen, charcoal is the result of burning away virtually everything but pure carbon in a very controlled manner, leaving a substance that can burn at temperatures exceeding 2,000 degrees — especially in an enclosed space like a forge.

If you’re keeping track, the maximum temperature of a charcoal-fueled fire is still vastly below what’s needed to produce the forks on your Thanksgiving table. Stainless steel is often produced in an electric arc furnace. 

Graphite electrodes are lowered into the furnace and a powerful electrical charge is applied to the metal within via an electrical arc. The enclosed air is heated to extremely high temperatures, which separates the waste into a lighter slag layer and the desired metal into a molten liquid at the bottom. Waste gasses are vented out. 

Due to an absence of electrical power, this would have been impossible to achieve millennia ago — however, a neighboring technology, the blast furnace, may have existed in China as far back as 200 B.C.E. A fascinating topic for another day.

Stainless steel was first developed in the early 1800s. Aside from the technological challenges of heat production (which had been largely solved by that point in history with the development of open-hearth furnaces and widespread blast furnaces), the availability of chromium had been a major roadblock to the discovery and development of stainless steel. 

Large deposits of chromium were usually mixed with other elements — often corundum, which required more advanced processing methods in order to extract meaningful amounts of the element. Chromium is what gives gemstones like rubies their trademark red color.

While you feast this holiday, stop and ponder the origins of your humble fork and knife and the thousands of lifetimes that were spent working toward developing something you can rinse off with a quick squirt from the sink.

Stay curious, 7B.