Duplex stainless steel
Introduction
In metallurgy, stainless steel is defined as a steel alloy with a minimum of 10% to 12% chromium content by mass.[1][2][note 1] It may also contain other metals, such as molybdenum, nickel, and tungsten.
Stainless steel is a steel with high corrosion resistance, given that the chromium or other alloying metals it contains have a great affinity for oxygen and reacts with it forming a passivating layer, thus preventing the corrosion of iron (purely stainless metals, which do not react with oxygen, are gold and platinum, and lower purity metals are called corrosion resistant, such as those that contain phosphorus). However, this layer can be affected by some acids, resulting in the iron being attacked and oxidized by intergranular mechanisms or generalized pitting. Some types of stainless steel also contain other alloying elements; the main ones are nickel and molybdenum.
History
Like all types of steel, stainless steel[4] is an alloy whose main component is iron, to which a small amount of carbon is added. Stainless steel was invented at the beginning of the century when it was discovered that a certain amount of chromium (the minimum to achieve stainless properties is 12%) added to common steel, gave it a shiny appearance and made it highly resistant to dirt and oxidation. This resistance to oxidation, called “corrosion resistance,” is what makes stainless steel different from other types of consistent steel.
The invention of stainless steel followed a series of scientific advances, which began in 1798, when Louis Vauquelin first showed chrome to the French Academy. At the beginning of the century, British scientists James Stoddart, 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.[5].
In the 1840s, both Britain's Sheffield steelworks and then Germany's Krupp were producing chrome steel with the latter employing it for cannons in the 1850s. In 1861, Robert Forester Mushet" obtained a patent on chrome steel in Britain.
These events led to the first American production of chromium steel, by J. Baur of the Chrome Steel Works in Brooklyn, for bridge construction. A US patent for the product was granted in 1869.[8][9] This was followed by recognition of the corrosion resistance of chromium alloys by the Englishmen John T. Woods and John Clark, who noted chromium ranges of 5-30%, with added tungsten and "medium carbon". They pursued the commercial value of the innovation through a British patent for "weathering alloys".[8][10].