Intergranular corrosion, while walking between the microcrystals of metal, the metal eventually disintegrate. It is related to chromium carbide precipitation along the joints. For it to occur, three conditions must be met: at least 0.035% carbon, sensitization by holding at a temperature of 400 to 800 degrees C, an acidic external environment with an oxidizing power between two defined limits. Pitting corrosion is usually not due to heterogeneity of material but the unintended presence of metallic dust, wet, form a battery (stainless steel fabricator). The steels surface then constitutes the anode and corrodes. There can be 2 mm thick pieces within hours. An environment that is both highly acidic and very oxidizing can produce similar effects.
The first chromium resistant steels were developed by the metallurgist Pierre Berthier, who noted their resistance to certain acids and imagined their application cutlery. However, at the time, we did not use the low rates and high carbon chromium levels commonly used in modern stainles-steels and alloys obtained then too rich in carbon, were too fragile to have a genuine interest.
The corrosion of metals are electrochemical in nature: the metal returns to its thermodynamically stable state, the oxidized state. In presence of an oxidizing environment (water, air), the metal reacts with the environment, this reaction taking place with exchange of electrons. Iron, major constituent of steels, is easily oxidized; the corrosion product, rust, crumbles or dissolved in water, creating a deterioration of part. When hot, the diffusion of oxidants atoms in metal thickness can further complicate the problem.
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.
Manganese is a nickel substitute. Some series of austenitic alloys have been developed to deal with supply of nickel6 uncertainties. Molybdenum and copper improve the resistance in most corrosive environments, particularly those that are acidic, but also in phosphate solutions, sulfur, etc. Molybdenum increases the stability of passivation films.
It was then of martensitic stainles-steel(0.24% carbon and 12.8% chromium). However, other comparable steels were developed by Eduard Maurer (from) and Benno Strauss who developed an austenitic stainles-steel(21% Cr and 7% of nickel) for Krupp AG. In United States, Christian Dantsizen and Frederick Becket already launched the industrial manufacture of ferritic stainless-steel. In 1908, Krupp had built hull vessels stainles-steel chrome-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.
The metal is exposed (grinding, machining, deformation of workpiece cracking the passive layer, friction, erosion, cavitation), but the oil or grease prevents air arriving to oxidize; then the surface is "active". Non-stainles-steel particles pollute the surface (pollution iron): these particles rust, forming halos, but can also initiate corrosion of stainless-steel in some cases.
The first chromium resistant steels were developed by the metallurgist Pierre Berthier, who noted their resistance to certain acids and imagined their application cutlery. However, at the time, we did not use the low rates and high carbon chromium levels commonly used in modern stainles-steels and alloys obtained then too rich in carbon, were too fragile to have a genuine interest.
The corrosion of metals are electrochemical in nature: the metal returns to its thermodynamically stable state, the oxidized state. In presence of an oxidizing environment (water, air), the metal reacts with the environment, this reaction taking place with exchange of electrons. Iron, major constituent of steels, is easily oxidized; the corrosion product, rust, crumbles or dissolved in water, creating a deterioration of part. When hot, the diffusion of oxidants atoms in metal thickness can further complicate the problem.
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.
Manganese is a nickel substitute. Some series of austenitic alloys have been developed to deal with supply of nickel6 uncertainties. Molybdenum and copper improve the resistance in most corrosive environments, particularly those that are acidic, but also in phosphate solutions, sulfur, etc. Molybdenum increases the stability of passivation films.
It was then of martensitic stainles-steel(0.24% carbon and 12.8% chromium). However, other comparable steels were developed by Eduard Maurer (from) and Benno Strauss who developed an austenitic stainles-steel(21% Cr and 7% of nickel) for Krupp AG. In United States, Christian Dantsizen and Frederick Becket already launched the industrial manufacture of ferritic stainless-steel. In 1908, Krupp had built hull vessels stainles-steel chrome-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.
The metal is exposed (grinding, machining, deformation of workpiece cracking the passive layer, friction, erosion, cavitation), but the oil or grease prevents air arriving to oxidize; then the surface is "active". Non-stainles-steel particles pollute the surface (pollution iron): these particles rust, forming halos, but can also initiate corrosion of stainless-steel in some cases.
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