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The first iron alloys and corrosion resistant steels were sunk in antiquity: the iron pillar of Delhi, erected by order of Kumaragupta I in fifth century still exists today in perfect condition. However, a distinction must be made in vocabulary: these alloys were resistant to its high phosphorus content, not chrome (stainless steel fabricator). So it was not stainles-steels in sense that currently gives the term. In these alloys, and under favorable weather conditions, forms a surface layer of iron oxide passivation and phosphate that protects the rest of metal much better than a layer of rust.
Stress corrosion causes the out very fast service objects that attack. It is fortunately very rare. For it to happen, it is necessary that the pieces have portions tensioned, even slightly, reflecting the constraints of service or the side effects of welding, stamping ... And are also exposed a corrosive environment of impure water type, even very dilute chloride solutions, hot caustic soda.
In 1878, Jacob Holtzer institutions located in Unieux (Loire) begin industrial production of chrome steels crucible. However, only better mechanical characteristics are then sought the interesting little corrosion metallurgists. Thus, in 1890, about this, Henry Marion Howe happy to report that "chromium is deemed accelerate rust.
This layer, compact, adherent and protective therefore, is called "passive layer": it forms a barrier between the steels. Normally, it is invisible because very fine. Thus, contrary to its name, the metal is not: it oxidizes quickly, but forms a protective oxide, unlike rust. Relative to a standard hydrogen electrode, the potential of stainlesss-steels is between molybdenum and mercury, not far from the silver and platinum. The addition of various alloying elements can be adapted to specific environment in which the steels is to be used, and change its mechanical properties.
Nickel is an austenite forming element, it provides an austenitic structure and therefore have sheets that are taking shape easily. High carbon content makes dipping the steels and to obtain a martensitic steels, very hard. But carbon overnight at weldability, and furthermore, it can trap the chromium and hinder the formation of passive layer. Other alloying elements, mainly metals relatively "noble" as molybdenum, titanium, copper further improve chemical resistance, especially in non-oxidizing environments.
There are actually numerous grades of stainles-steels and the choice is difficult because they do not all have the same behavior in a given environment. Are often referred to by the weight percentages of nickel and chromium. Thus, a 18/10 stainles-steel, such as those used in cutlery for cutlery and for cooking in general, contains 18% by weight of chromium and 10% by weight of nickel.
In 1924, William Herbert Hatfield (en), who succeeded Harry Brearley at the head of Brown-Firth laboratories, worked steels "18/8" (18 wt% chromium and 8% nickel) is probably the representing the most used stainles-steel iron-nickel-chromium. In 1925 is developed the process Ugine-Perrin in factories of Savoy Society of Electrochemistry, electrometallurgy and steels mill Ugine, future Ugitech, a method to obtain a stainles-steel both pure, reliable and cheap, by stirring steels with previously molten slags, for a complete treatment of steels.
Other elements have alphagenic or gammagenic role. A special role is played by carbon and nitrogen. Carbon austenite to a role and thus returned to "competition" with the Chrome. In fact more than just carbon, the carbon-nitrogen torque that must be taken into account. These two elements being of insertion alloy elements unlike other elements that are substitution elements.
Stress corrosion causes the out very fast service objects that attack. It is fortunately very rare. For it to happen, it is necessary that the pieces have portions tensioned, even slightly, reflecting the constraints of service or the side effects of welding, stamping ... And are also exposed a corrosive environment of impure water type, even very dilute chloride solutions, hot caustic soda.
In 1878, Jacob Holtzer institutions located in Unieux (Loire) begin industrial production of chrome steels crucible. However, only better mechanical characteristics are then sought the interesting little corrosion metallurgists. Thus, in 1890, about this, Henry Marion Howe happy to report that "chromium is deemed accelerate rust.
This layer, compact, adherent and protective therefore, is called "passive layer": it forms a barrier between the steels. Normally, it is invisible because very fine. Thus, contrary to its name, the metal is not: it oxidizes quickly, but forms a protective oxide, unlike rust. Relative to a standard hydrogen electrode, the potential of stainlesss-steels is between molybdenum and mercury, not far from the silver and platinum. The addition of various alloying elements can be adapted to specific environment in which the steels is to be used, and change its mechanical properties.
Nickel is an austenite forming element, it provides an austenitic structure and therefore have sheets that are taking shape easily. High carbon content makes dipping the steels and to obtain a martensitic steels, very hard. But carbon overnight at weldability, and furthermore, it can trap the chromium and hinder the formation of passive layer. Other alloying elements, mainly metals relatively "noble" as molybdenum, titanium, copper further improve chemical resistance, especially in non-oxidizing environments.
There are actually numerous grades of stainles-steels and the choice is difficult because they do not all have the same behavior in a given environment. Are often referred to by the weight percentages of nickel and chromium. Thus, a 18/10 stainles-steel, such as those used in cutlery for cutlery and for cooking in general, contains 18% by weight of chromium and 10% by weight of nickel.
In 1924, William Herbert Hatfield (en), who succeeded Harry Brearley at the head of Brown-Firth laboratories, worked steels "18/8" (18 wt% chromium and 8% nickel) is probably the representing the most used stainles-steel iron-nickel-chromium. In 1925 is developed the process Ugine-Perrin in factories of Savoy Society of Electrochemistry, electrometallurgy and steels mill Ugine, future Ugitech, a method to obtain a stainles-steel both pure, reliable and cheap, by stirring steels with previously molten slags, for a complete treatment of steels.
Other elements have alphagenic or gammagenic role. A special role is played by carbon and nitrogen. Carbon austenite to a role and thus returned to "competition" with the Chrome. In fact more than just carbon, the carbon-nitrogen torque that must be taken into account. These two elements being of insertion alloy elements unlike other elements that are substitution elements.
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