Iron/chromium alloy

A series of nickel—chromium—iron alloys based on the soHd solution Inconel 600 alloy (see Table 4) was developed, initially depending on aluminum ... 

The higher chromium—iron alloys were developed in the United States from the early twentieth century on, when the effect of chromium on oxidation resistance at 1090°C was first noticed. Oxidation resistance increased markedly as the chromium content was raised above 20%. For steels containing appreciable quantities of nickel, 20% chromium seems to be the minimum amount necessary for oxidation resistance at 1090°C. 

The successful application of nickel-chromium-iron alloys as structural components of industrial furnaces and as chambers and containers in chemical processing under conditions of exposure involving sulphur substantiates their good resistance to this form of corrosion. These materials are used for service temperatures in the range 750-1 200°C, the upper limit of serviceability being determined largely by the chromium content of a particular alloy. Results of corrosion tests (Table 7.24) on cast nickel-... 

Table 7.24 Corrosion resistance of nickel-chromium-iron alloys in oxidisng and reducing flue-gas atmospheres of varying sulphur content ...

Sulphur attack on nickel-chromium alloys and nickel-chromium-iron alloys can arise from contamination by deposits resulting from the combustion of solid fuels, notably high-sulphur coals and peat. This type of corrosion, which has been observed on components of aircraft, marine and industrial gas turbines and air heaters, has been associated with the presence of metal-sulphate and particularly sodium sulphate arising directly from the fuel or perhaps by reaction between sodium chloride from the environment with sulphur in the fuel. Since such fuels are burned with an excess of air, corrosion occurs under conditions that are nominally oxidising although the deposits themselves may produce locally reducing conditions. 

In the United States the alloy Inor 8 or Hastelloy N (Ni-16Mo-7Cr-5Fe) has been developed as a container material for molten fluorides containing uranium. The nickel-chromium-iron alloy originally considered as a suit-... 

Chromium compounds Cr203 surface scale Nickel- chromium—iron alloys Nickel-chromium— molybdenum (tungsten) alloys Ni-Cr alloys analytical methods, 6 502-514 composition of metal compared to chromium ferroalloys, 6 501t dispersoid former, 2 325, 327 disposal, 6 519-521 economic aspects, 6 496—500 effect on cobalt alloys, 7 220 effect on stainless steel corrosion resistance, 7 809... 

Chromium(II) iodide, 6 531 Chromium(III) iodide, 6 532 Chromium(IV) iodide, 6 535 Chromium—iron alloys, 23 300... 

Iron (Fe), 74 490-529. See also Fe entries Ferr- entries Iron compounds Ironmaking processes Manganese ferroalloys MoFe protein Nickel-chromium—iron alloys Nickel—iron-aluminum catalyst Ni-Fe-base alloys VFe protein... 

Nickel-chromium alloys, 77 100-101 dental applications, 8 308, 310 Nickel-chromium-iron alloys, 73 519, 522 Nickel-chromium-molybdenum alloy C, in galvanic series, 7 805t... 

Electrochemical detection of carbohydrates at nickel-copper and nickel-chromium-iron alloy electrodes has been reported for sorbitol, and has been used as a detector for HPLC analysis [36]. Oxidation of various carbohydrates at the electrodes was used for detection, and baseline separation was achieved for mixtures of sorbitol, rhamnose, glucose, arabinose, and lactose. 

In addilion to ferrous ulluys, chromium also is added to cupper, vanadium, zirconium, and other metals to form several hundred chromium-bearing alloys. Nickel-chromium-iron alloys have high electrical resistance and are used widely as electrical heating elements. Niclirttme and ChromeI are examples. 

Passive regions close to active-passive transitions as for nickel-chromium-iron alloy 600 or steel in caustic solutions (Figure 6.58).143 144... 

Regardless of the source of the petroleum, the chemistry to obtain ammonia feedstocks is similar. Since methane is of dominant importance this is used as an example to describe the steps required. Initially methane is mixed with steam and passed into heat resistant nickel-chromium-iron alloy tubes containing a supported nickel catalyst. The tubes are heated externally by a further portion of methane consumed as fuel (Fig. 11.2, Eq. 11.19). 

Nichrome /nf-krohm/ Trademark) Any of a group of nickel-chromium-iron alloys, containing 60-80% nickel and about 16% chromium small amounts of other elements, such as carbon or silicon, may be added. They can withstand very high temperatures and their high electrical resistivity makes them suitable for use in heating elements. 

Nickel-chromium-iron alloys are mainly used for high-temperature... 

As the chromium content in the alloy increases from 8% to 13%, the corrosion rate of iron decreases from 0.08 mm/year to very low values [9]. The Flade potentials of chromium-iron alloys in 4% NaCl solutions increases from —0.57 V (vs. SHE) in the absence of chromium to +0.17 V (vs. SHE) for the ahoy with 12% chromium [7,10]. The critical current density for the passivation of Cr-Fe aUoys at pH = 7 reaches a... 

Figure 6.4. Standard Flade potentials for chromium-iron alloys and chromium [7-9].

Figure 6.9. Corrosion rates of chromium-iron alloys in intermittent water spray at room temperature. [Reprinted with permission from W. Whitman and E. Chappell, Ind. Eng. Chem. 18, 533 (1926). Copyright 1926, American Chemical Society.]...

Figure 6.10. Potentials of chromium-iron alloys in 4% NaCi. [Reprinted with permission from H. Uhlig, N. Carr, and P. Schneider, Trans. Electrochem. Soc. 79, 111 (1941). Copyright 1941, The Electrochemical Society.]...

The good oxidation resistance of the chromium-iron alloys, combined with acceptable mechanical properties and ease of fabrication, accounts for their wide commercial application. Typical oxidation behavior is shown in Fig. 11.8. 

Improvement in oxidation resistance of iron by alloying with aluminum or chromium probably results from a marked enrichment of the innermost oxide scale with respect to aluminum or chromium. The middle oxide scales are known, from chemical analysis, to be so enriched, and electron-microprobe analyses confirm marked enrichment of chromium in the oxide adjacent to the metal phase in the case of chromium-iron alloys [52]. These inner oxides resist ion and electron migration better than does FeO. For chromium-iron alloys, the enriched oxide scale is accompanied by depletion of chromium in the alloy surface immediately below the scale. This situation accounts for occasional rusting and otherwise poor corrosion resistance of hot-rolled stainless steels that have not been adequately pickled following high-temperature oxidation. 

ASTM B76-90(2007), Standard Test Method for Accelerated Life of Nickel-Chromium and Nickel—Chromium—Iron Alloys for Electrical Heating, ASTM, West Conshohocken, PA. 

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