Harry Brearley invents Stainless Steel in Sheffield, Yorkshire.

Stainless steel is a family of iron-based alloys that contain a minimum of approximately 11% chromium, a composition that prevents the iron from rusting, as well as providing heat-resistant properties. Different types of stainless steel include the elements carbon (from 0.03% to greater than 1.00%), nitrogen, aluminium, silicon, sulfur, titanium, nickel, copper, selenium, niobium, and molybdenum. Specific types of stainless steel are often designated by a three-digit number, e.g., 304 stainless.

Stainless steel's resistance to ferric oxide formation results from the presence of chromium in the alloy, which forms a passive film that protects the underlying material from corrosion attack, and can self-heal in the presence of oxygen. Corrosion resistance can be increased further, by:

- increasing the chromium content to levels above 11%;

- addition of 8% or higher amounts of nickel; and

- addition of molybdenum (which also improves resistance to "pitting corrosion").

The addition of nitrogen also improves resistance to pitting corrosion and increases mechanical strength. Thus, there are numerous grades of stainless steel with varying chromium and molybdenum contents to suit the environment the alloy must endure.

Resistance to corrosion and staining, low maintenance, and familiar luster make stainless steel an ideal material for many applications where both the strength of steel and corrosion resistance are required. Moreover, stainless steel can be rolled into sheets, plates, bars, wire, and tubing. These can be used in cookware, cutlery, surgical instruments, major appliances, construction material in large buildings, industrial equipment (e.g., in paper mills, chemical plants, water treatment), and storage tanks and tankers for chemicals and food products. The material's corrosion resistance, the ease with which it can be steam-cleaned and sterilized, and the absence of the need for surface coatings have prompted the use of stainless steel in kitchens and food processing plants.

History

The invention of stainless steel followed a series of scientific developments, starting in 1798 when chromium was first shown to the French Academy by Louis Vauquelin. In the early 1800s, James Stodart, Michael Faraday, and Robert Mallet observed the resistance of chromium-iron alloys ("chromium steels") to oxidizing agents. Robert Bunsen discovered chromium's resistance to strong acids. The corrosion resistance of iron-chromium alloys may have been first recognized in 1821 by Pierre Berthier, who noted their resistance against attack by some acids and suggested their use in cutlery.

In the 1840s, both Sheffield steelmakers and Krupp were producing chromium steel with the latter employing it for cannons in the 1850s. In 1861, Robert Forester Mushet took out a patent on chromium steel.

These events led to the first production of chromium-containing steel by J. Baur of the Chrome Steel Works of Brooklyn for the construction of bridges. A U.S. Patent for the product was issued in 1869. This was followed with recognition of the corrosion resistance of chromium alloys by Englishmen John T. Woods and John Clark, who noted ranges of chromium from 5–30%, with added tungsten and "medium carbon". They pursued the commercial value of the innovation via a British patent for "Weather-Resistant Alloys".

In the late 1890s, German chemist Hans Goldschmidt developed an aluminothermic (thermite) process for producing carbon-free chromium. Between 1904 and 1911, several researchers, particularly Leon Guillet of France, prepared alloys that would be considered stainless steel today.

In 1908, Friedrich Krupp Germaniawerft built the 366-ton sailing yacht Germania featuring a chrome-nickel steel hull in Germany. In 1911, Philip Monnartz reported on the relationship between chromium content and corrosion resistance. On 17 October 1912, Krupp engineers Benno Strauss and Eduard Maurer patented austenitic stainless steel as Nirosta.

Similar developments were taking place in the United States, where Christian Dantsizen and Frederick Becket were industrializing ferritic stainless steel. In 1912, Elwood Haynes applied for a US patent on a martensitic stainless steel alloy, which was not granted until 1919.

While seeking a corrosion-resistant alloy for gun barrels in 1912, Harry Brearley of the Brown-Firth research laboratory in Sheffield, England, discovered and subsequently industrialized a martensitic stainless steel alloy. The discovery was announced two years later in a January 1915 newspaper article in The New York Times.

The metal was later marketed under the "Staybrite" brand by Firth Vickers in England and was used for the new entrance canopy for the Savoy Hotel in London in 1929. Brearley applied for a US patent during 1915 only to find that Haynes had already registered one. Brearley and Haynes pooled their funding and, with a group of investors, formed the American Stainless Steel Corporation, with headquarters in Pittsburgh, Pennsylvania.

In the beginning, stainless steel was sold in the US under different brand names like "Allegheny metal" and "Nirosta steel". Even within the metallurgy industry, the name remained unsettled; in 1921, one trade journal called it "unstainable steel". In 1929, before the Great Depression, over 25,000 tons of stainless steel were manufactured and sold in the US annually.

Major technological advances in the 1950s and 1960s allowed the production of large tonnages at an affordable cost:

- AOD Process (argon oxygen decarburization), for the removal of carbon and sulfur

- Continuous casting and hot strip rolling

- The Z-Mill, or Sendzimir cold rolling mill