Chromium in stainless steels

Huvinen M, Uitti J, Zitting A, et al. 1996. Respiratory health of workers exposed to low levels of chromium in stainless steel production. Occup Environ Med 53 741-747. 

Unlike most steels, which fail after being stretched to 2 times their original size, superplastic steel at elevated temperatures can be stretched to 11 times its size without cracking or pulling apart. As a result, heated superplastic steel can be formed into complex shapes. It can even flow like molasses and be poured into a mold. This property eliminates the need for machining, which typically results in about 50% scrap. Superplastic steel is also similar to stainless steel in its resistance to corrosion, but is made with less scarce and expensive materials than the nickel and chromium in stainless steel. 

The presence of H+ ions and chloride content, prevents repassivation. The above process generates free acid and the pH value at the bottom of the pit is substantially lowered. It has been measured between 1.5 and 1.0. The pH value depends on the type of steel-values for stainless steel pits which are lower than for mild steel and have a pit pH of 4. This is due to the solubility product effects and depends on the presence of chromium. In stainless steels, the pH is reduced by hydrolysis of Cr + and Fe " " as well as by accumulation of chloride. 

Why does chromium in stainless steels make them more corrosion resistant than plain carbon steels in many environments ... 

Hydrogenations with coppcr-chromium oxide catalyst are usually carried out in the liquid phase in stainless steel autoclaves at pressures up to 5000-6000 lb. per square inch. A solvent is not usually necessary for hydrogenation of an ester at 250° since the original ester and the alcohol or glycol produced serve as the reaction medium. However, when dealing with small quantities and also at temperatures below 200° a solvent is desirable this may be methyl alcohol, ethyi alcohol, dioxan or methylcyc/ohexane. 

Corrosion Resistance of the Austenitic Chromium—Mickel Stainless Steels in Chemical Environments, Inco Limited, Nickel Development Institute, Toronto, Ontario, Canada, 1963. 

At the end of the 72-h cycle, the cathodes are removed from the cells, washed in hot water, and the brittie deposit, 3—6 mm thick, is stripped by a series of air hammers. The metal is then cmshed by roUs to 50-mm size and again washed in hot water. The metal contains about 0.034% hydrogen and, after drying, is dehydrogenated by heating to at least 400°C in stainless steel cans. Composition limits for electrolytic chromium are shown in Table 4. 

Carbide-based cermets have particles of carbides of tungsten, chromium, and titanium. Tungsten carbide in a cobalt matrix is used in machine parts requiring very high hardness such as wire-drawing dies, valves, etc. Chromium carbide in a cobalt matrix has high corrosion and abrasion resistance it also has a coefficient of thermal expansion close to that of steel, so is well-suited for use in valves. Titanium carbide in either a nickel or a cobalt matrix is often used in high-temperature applications such as turbine parts. Cermets are also used as nuclear reactor fuel elements and control rods. Fuel elements can be uranium oxide particles in stainless steel ceramic, whereas boron carbide in stainless steel is used for control rods. 

The H2SO4-CUSO4 test, unlike the Huey test, is specific for susceptibility due to chromium depletion and is unaffected by the presence of submicro-scopic a-phase in stainless steels containing molybdenum or carbide stabilisers. It can be used, therefore, with confidence to test susceptibility in austenic (300 series) and ferritic (400 series) stainless steels and in duplex austeno-ferritic stainless steels such as Types 329 and 326. 

XPS was also used for the determination of chlorine in the passive film grown in chlorine containing electrolytes. While chlorine was found in the passive film on pure iron, it was absent for chromium rich stainless steel samples. Chloride content of the passive film is substantially time dependent, increasing with time until film breakdown occurs, and decreasing subsequently [109]. 

The rate of decomposition of hydrazine in stainless steel vessels (which is accompanied by corrosion) is directly proportional to carbon dioxide concentration over 20 ppm and below 250 ppm. The species responsible for the catalytic decomposition is not one of the expected corrosion products, iron(II) carbazate or its nickel or chromium(II) analogues. 

The hardness of precipitated sigma phase in stainless steels seems to vary with the composition. In Type 446 plain chromium steel it is about 9GPa (Guimaraes and Mei, 2004) whereas in Type 316 high Cr, Ni steel it is about 17GPa (Ohmura et al., 2006). Since they are ordered phases that do... 

A dense and electronically insulating layer of LiA102 is not suitable for providing corrosion resistance to the cell current collectors because these components must remain electrically conductive. The typical materials used for this application are 316 stainless steel and chromium plated stainless steels. However, materials with better corrosion resistance are required for longterm operation of MCFCs. Research is continuing to understand the corrosion processes of chromium in molten carbonate salts under both fuel gas and oxidizing gas environments (23,25) and to identify improved alloys (29) for MCFCs. Stainless steels such as Type 310 and 446 have demonstrated better corrosion resistance than Type 316 in corrosion tests (29). 

The main consumer of nickel is austenitic stainless sleel, which contains from 3,5 to 22% nickel and 16 to 26% chromium. In these steels, nickel stabilizes the austenite and enhances the ductility of the steel. Nickel, along with chromium, contributes to corrosion resistance. Up to amounts of about 9%, nickel adds strength, hardness, and toughness to many alloy steels. 

There are transition metals in many of the products that people use in daily life. Some of these metals have obvious roles, such as the coin metals of gold, silver, and copper. Iron, which makes up 90% of all metal that is refined, or purified for use, is found in everything from tools to paper staples to washing machines. The most important iron product is steel, an iron-based metal alloy. Most steel made for manufacturing purposes is iron alloyed with the element carbon, which makes the steel much harder than iron alone. Several other transition metals are alloyed with iron to make different kinds of steel for different uses. Vanadium, niobium, molybdenum, manganese, chromium, and nickel are all used in steel alloys. For instance, chromium and nickel are alloyed with iron to create stainless steel, a type of steel that does not rust and is used in surgical instruments, cookware, and tools. Some famous landmarks such as the top of the Chrysler skyscraper in New York City and the St. Louis Gateway Arch are covered in stainless steel. 

Studies of renal function in stainless steel welders, whose exposure is mainly to chromium(VI) compounds, were negative. Stainless steel welders had significantly increased (p<0.001) levels of urinary chromium, increased clearance of chromium, and increased serum creatinine compared with controls, but no differences were found in the levels of retinol binding protein, p2-microglobulin or other indices of kidney damage (Verschoor et al. 1988). Similar negative results were found in another group of stainless steel welders (Littorin et al. 1984). 

Studies of chromate production workers, who are exposed to a variety of chromium compounds both hexavalent and trivalent, and chromate pigment industries, where exposure is mainly to chromium(VI), have consistently demonstrated an association with respiratory system cancer. Studies in chrome platers, who are exposed to chromium(VI) and other agents, including nickel, generally support the conclusion that certain chromium(VI) compounds are carcinogenic. Studies in stainless steel welders exposed to chromium(VI) and other chemicals, and in ferrochromium alloy workers, who are exposed mainly to chromium(O) and chromium(III), but also to some chromium(VI), were inconclusive. Studies in leather tanners, who are exposed to chromium(III), were consistently negative. 

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