Fe-Cr alloy

To illustrate some of the different approaches, let us consider passive films grown on Fe-Cr alloys. It has been established since 1911 [72] that an increase of Cr in the alloy increases the stability of the oxide film against dissolution. 

Fig. 2.13. Schematic diagram ofthe type of information obtainable from XPS spectra from an Fe-Cr alloy with oxide film underneath a contaminant film [2.57],...

More effort has probably been devoted to study of the corrosion and passivation properties of Fe-Cr-Ni alloys, e.g. stainless steel and other transition-metal alloys, than to any other metallic system [2.42, 2.44, 2.55, 2.56]. The type of spectral information obtainable from an Fe-Cr alloy of technical origin, carrying an oxide and contaminant film after corrosion, is shown schematically in Fig. 2.13 [2.57]. 

Films may thus range from thin transparent oxides (passive films on Al, Cr, Ti and Fe-Cr alloys), or thin visible sulphides (on Cu and Ag) to thicker... 

Streicher, M. A., The R61e of Carbon, Nitrogen and Heal Treatment in the Dissolution of Fe-Cr Alloys in Acids , Corrosion, 29, 337 (1973)... 

Steigerwald, R. F., Effect of Chromium Content on Pitting Behaviour of Fe-Cr Alloys , Corrosion, 22, 107 (1966)... 

Many studies have shown that surface pretreatment of Fe-Cr alloys has a strong effect on the scale morphology and subsequent oxidation rate For instance, Caplan indicated that several Fe-Cr alloys show improvement in the corrosion resistance due to cold work, with greater than 16% Cr required to show the optimum benefit. Khanna and Gnanamoorthy examined the effect of cold work on 2.25%Cr-l%Mo steels at temperatures between 400°C and 950°C over 4h in 1 atm O2. They found that up to 90% reduction by cold rolling had a negligible effect on the oxidation rate up to 700°C. However, above 700°C there was a general reduction in the kinetics... 

Small additions of Ce have been shown to have a favourable influence on oxide growth of several Fe-Cr alloys by improving scale adherence and acting as nucleation sites for CrjO, . Levels of Ce as low as 0.024% reduce the carbon uptake of steels in carbonaceous atmospheres by several orders of magnitude. Trace concentrations of As and Sn have been found to improve the breakaway properties of mild and low alloy steels in CO/COj, whereas Cu has been found to be detrimental. ... 

Fig. 8.26 Binary consiituiion diagram for Fe-Cr alloys (after Spaehn )...

Fig. 19.41 Dependence of breakdown potential of Fe-Cr alloys (containing 13% Cr, in 0-1 mol dm HBr + Kj SO4 solution) on the ratio of sulphate and bromide concentration in...

FIGURE 3.15 Polarization curves for the 02 reduction on an LSM cathode in the presence of a Fe-Cr alloy interconnect, measured under a cathodic current passage of 200 mA cnr2 at 900°C. 

Much heat is generated, and the mixture becomes white-hot. Indeed, thermite reactions have been used to generate intense heat as well as the reduced metal for certain welding applications. Chromium, however, is usually made by coke reduction of chromite (FeC CU) m the electric furnace. The product is ferrochrome, an Fe-Cr alloy, but this is acceptable if, as is often the case, the intention is to make stainless steel. 

Allen reported TEM observations of a nonaligned decomposition products in long-range ordered Fe-Al alloy [22]. Such morphologies are called isotropic spinodal microstructures. Similar structures are observed in Al-Zn and Fe-Cr alloys. Such structures can be produced in systems that are elastically isotropic or in which the lattice constant does not change appreciably with composition. 

Table 5.5. Concentrations of iron and chromium undergoing dissolution from Fe-Cr alloys into liquid aluminium.Temperature is 700°C rotational speed, go = 54.0 rad s 1 S/v = 27.5 m ...

Chemical compositions of the Fe-Ni specimens containing 90, 75, 50, 25, 20, 15 and 10 mass % Fe corresponded to nominal values within 0.5 mass %. At room temperature, the alloy specimens consisted of the a-phase (ferrite) at nickel contents less than or equal to 25 mass % or the y-phase (austenite) at higher Ni contents, while at a temperature of 700 °C the specimens of all compositions had austenitic structures. Ferrite constituted the microstructure of the Fe-Cr alloy specimens (10 and 25 mass % Cr) over this range of temperature. 

To show the influence of dissolution of the Fe-Ni or Fe-Cr alloy base into liquid aluminium on the layer formation, two sets of experiments were... 

Fig. 5.18. Secondary electron image of the transition zone between Fe-Cr alloys and aluminium. Temperature 700°C, dipping time 3600 s. Initial liquid phase (a) aluminium melt saturated with the alloy constituents, (b) pure aluminium (go = 24.0 rad sec-1).

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