Stainless steel

Stainless steel is a type of low-carbon steel. It is shinier, stronger, and more corrosion-resistant than most other types of steel. Stainless steel is used for a variety of purposes. These include cutlery, appliances, piping, car parts, ships, surgical instruments, and outdoor metalworking such as railings.

History of Steel

Humans have forged iron tools and weapons since shortly after 2000 BCE. Most researchers believe that metallic iron production began somewhere in Southeast Asia and spread from there. Just as with modern metals, early iron metal workers created metal by mining iron ore, an impure form of iron found deep in Earth. The iron ore was heated to extremely high temperatures in a special structure called a smelter. At such high temperatures, the iron separates from the other minerals to which it is attached, leaving behind a byproduct known as slag. The iron then cools and hardens into recognizable metal. In this form, the iron could be shaped into tools, weapons, armor, or structural supports. Iron was significantly harder and less malleable than its predecessor, bronze.

Over time, early metalsmiths learned that they could increase the strength of their iron by reducing the amount of carbon in the finished product. At first, this was accomplished by oxidizing the carbon out of the iron in a special forge called a finery. However, this device was later supplemented or replaced by a puddling furnace, a device that oxidized even more carbon out of the iron. The oxidation process allowed smiths to create wrought iron, a malleable, flexible, easily worked form of iron that continues to be used in modern times for decorative purposes.

Wrought iron is usually between .02 to .08 percent carbon. Steel is generally 2 to 1.5 percent carbon. This is just enough carbon to make steel significantly stronger than wrought iron, but not so strong that it becomes difficult to mold or work. To achieve this, early smiths bundled bars of wrought iron with charcoal and heated the bundle several times. This process, called cementation, evenly distributed carbon throughout the wrought iron. The process produced a substance called crucible steel that was extremely labor-intensive to produce. For this reason, it was considered a rare and valuable metal.

The Bessemer process made mass production of steel possible; this process created by British metallurgist Sir Henry Bessemer (1813-1898). Bessemer realized that the carbon in cheap, high-carbon iron bonds easily with oxygen. He applied this knowledge and created a mechanism for delivering precise blasts of cold air through the molten iron, thus lowering its carbon content and creating steel. The process was refined and advanced over time, making inexpensive, extremely strong steel a staple of the modern world.

Development of Stainless Steel

English metallurgist Harry Brearley developed stainless steel in the early twentieth century (1871-1948). Brearly was assisting in the development of a steel product that would erode slowly, for use in gun barrels. He decided to experiment with chromium-infused steel, which was already known to have a higher melting point than most steels of the time. Eventually, Brearley forged a steel that was .24 percent carbon and 12.8 percent chromium, a blend that would be recognized as stainless steel by modern metallurgists.

When testing his new metal for effectiveness in gun barrels, Brearley realized that the metal was extremely corrosion-resistant. When further testing confirmed the properties of this new alloy, the scientist immediately saw its commercial potential. At the time, kitchen knives had to be routinely checked and treated for rust. Buffing the rust off knives after every few washes was a time-consuming and monotonous task. However, if the knives were made out of this new alloy, they would almost never rust. Brearley failed to convince his employers that funding his new knives would be profitable, and was forced to personally commission knives made of stainless steel.

Modern Uses for Stainless Steel

As Brearley originally envisioned, in modern times stainless steel is the most common steel used in the manufacture of silverware. Both plain, mass-produced cutlery and expensive, high-quality forks, knives, and spoons are made of stainless steel variants. Few other metals would be able to withstand the constant washing and exposure to various corrosive materials without constant maintenance.

Nuclear power plants use large amounts of stainless steel for both power generation and containment fail-safes. Because stainless steel is less reactive than other metals, it is ideal for sealing away toxic materials. The heat resistance of certain stainless steel alloys also allows the metal to retain its shape in the extreme conditions found inside a power plant.

Stainless steel is also used in architecture, providing a rust-proof plating to roofs, railings, and other outdoor metalworking. It has also found use in bridges, as well as in high-quality concrete rebar.

Finally, most medical equipment is made from stainless steel. Stainless steel implants do not corrode when placed inside a human body, and medical machinery made from stainless steel is both extremely durable and easy to clean.

Bibliography

"A Brief History of Stainless Steel." Stainless Steel World. KCL Publishing. Web. 10 Jan. 2016. http://www.stainless-steel-world.net/basicfacts

"Frequently Asked Questions." British Stainless Steel Association. British Stainless Steel Association. Web. 10 Jan. 2016. http://www.bssa.org.uk/faq

"Galvanized vs. Stainless Steel – Cost, Strength, & Weight Differences." Wenzel Metal Spinning. Wenzel Metal Spinning. Web. 10 Jan. 2016. http://www.wenzelmetalspinning.com/galvanized-steel-vs-stainless.html

Spoerl, Joseph S. "A Brief History of Iron and Steel Production." Saint Anselm College. Saint Anselm College. Web. 10 Jan. 2016. http://www.anselm.edu/homepage/dbanach/h-carnegie-steel.htm