Fireside Corrosion of Chromium- and Aluminum-Coated Ferritic–Martensitic Steels

Fähsing, Diana; Rudolphi, M.; Konrad, Ludmila; Galetz, Mathias C.

doi:10.1007/s11085-016-9684-2

Cited by 18 publications

(5 citation statements)

References 14 publications

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“…Furthermore, formation and propagation of cracks within the outermost and intermediate layers was observed ( Figure 3a). This can be explained by the high discrepancy between the coefficients of thermal expansion (CTE) of Fe-Al intermetallic phases (e.g., CTE of FeAl at 873 K is 21•10 −6 K −1 [41]) and the alloy (e.g., CTE of P91 at 873 K is 14.1•10 −6 K −1 [27]) and the consequential build-up of tensile stresses in the coating during the cooling period, as highlighted in [36,37,42]. Figure 3b) were observed.…”

Section: Al-diffusion Coatingmentioning

confidence: 99%

Scale Formation and Degradation of Diffusion Coatings Deposited on 9% Cr Steel in Molten Solar Salt

et al. 2019

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The employment of ferritic-martensitic steels e.g., P91, as structural materials in concentrated solar power (CSP) plants can significantly increase cost-efficiency. However, their application is strongly restricted by their lower corrosion resistance in molten nitrates, compared to austenitic steels or Ni-based alloys. In this study, Cr-, Al-, and Cr/Al-diffusion coatings were deposited on P91 via pack cementation in order to improve its scaling behavior in molten solar salt (MSS). The corrosion behavior of coated specimens was investigated with respect to uncoated P91 in MSS at 600 °C for up to 1000 h. The exposure in MSS resulted in a thick, highly porous, and multi-layered oxide scale on uncoated P91 consisting of hematite, magnetite, and sodium ferrite. On the other hand, the scale grown on the chromized P91 comprised of a thin Cr-rich inner layer, which shifted breakaway to prolonged exposure durations. The aluminized specimens both formed very thin, highly protective alumina scales with localized protrusions.

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Section: Al-diffusion Coatingmentioning

confidence: 99%

Scale Formation and Degradation of Diffusion Coatings Deposited on 9% Cr Steel in Molten Solar Salt

et al. 2019

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“…However, large amounts of halogens in the surface zone are very detrimental. They induce accelerated high-temperature corrosion [12,13]. On the other hand, if the amounts of halogens are too low, there is no impact on the oxidation behavior of TiAl alloys, i.e., mixed scale formation.…”

Section: Mechanismmentioning

confidence: 99%

The Importance of the Fluorine Effect on the Oxidation of Intermetallic Titanium Aluminides

Donchev¹,

Galetz²

2018

Intermetallic Compounds - Formation and Applications

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Due to the low Al activity within technical titanium aluminides and the similar thermodynamic stabilities of Al-and Ti-oxide these alloys always form a mixed oxide scale at elevated temperatures consisting of TiO 2 ,A l 2 O 3 and also nitrides if the exposure takes place in air. This mixed scale does not provide any oxidation protection especially under thermocyclic load or in water vapor containing environments. Thus accelerated oxidation occurs. Alloying of additional elements such as Nb improves the oxidation behavior if the additions stay within a certain concentration range but such additions cannot suppress non-protective mixed scale formation. Coatings are another way to protect these materials but several obstacles and new degradation mechanisms exist such as delamination e.g. due to CTE mismatch or development of brittle intermetallic phases due to interdiffusion. Therefore, other suitable protective measures have to be undertaken to make sure a protective oxide scale will develop. The so called halogen effect is a very promising way to change the oxidation mechanism from mixed scale formation to alumina formation. After optimized halogen treatment the alumina layer is very protective up to several thousand hours even under thermocyclic load and in atmospheres containing water vapor or SO 2 .

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“…Hot corrosion has often been investigated on nickel‐ and cobalt‐based alloys for turbine engine applications where Na 2 SO 4 deposits from the combustion environment result in accelerated failure. The hot corrosion Type II of iron‐based alloys that are often applied to superheaters in power plants is less well investigated, although the SO 2 content is usually higher with amounts of 0.1–0.6 vol.%, which varies depending on fuel and firing conditions . As the steam temperatures in coal‐fired power plants are increased to achieve higher efficiencies, the surface temperatures of the boiler and heat exchanger increase towards 700°C .…”

Section: Introductionmentioning

confidence: 99%

“…The hot corrosion Type II of iron-based alloys that are often applied to superheaters in power plants is less well investigated, although the SO 2 content is usually higher with amounts of 0.1-0.6 vol.%, which varies depending on fuel and firing conditions. [3][4][5][6][7] As the steam temperatures in coal-fired power plants are increased to achieve higher efficiencies, the surface temperatures of the boiler and heat exchanger increase towards 700°C. [8,9] The temperature dependency of hot corrosion Type II on both nickel-and iron-based alloys is generally assumed to follow a bell-shaped curve and the maximum metal loss is typically observed in the regime around 700°C but can be offset by SO 2 , the alkali content or the alloy composition.…”

Section: Introductionmentioning

confidence: 99%

Hot corrosion Type II of FeCr‐based model alloys for boiler and heat exchanger applications

König

Montero

Galetz

2019

Materials & Corrosion

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The hot corrosion Type II of the alloys FeCr20, FeCr20Ni10, FeCr20Ni20, and FeCr20Co10 is investigated at 700°C in air + 0.5% SO2 with deposits consisting of Na2SO4 and a eutectic mixture of Na2SO4 and MgSO4 for 24, 100, and 300 h. The alloying elements nickel and cobalt have a positive influence when tests are conducted using a MgSO4‐Na2SO4 deposit. In this case, they reduce the metal loss and increase the time to the propagation stage. In contrast, when the alloys are exposed with a Na2SO4 deposit, these alloying elements increase the metal loss and allow for the transition to the propagation stage because they can form molten phases with the Na2SO4. During the incubation stage an oxide scale forms on the FeCr20 alloy, which is thicker than the one formed during exposure without a deposit, and iron oxides are observed, which precipitate in the deposit. The propagation stage occurs by a dissolution and precipitation mechanism forming localized pitting attack. Iron is the main species that dissolves and precipitates, while chromium remains mainly as an oxide beneath the initial surface. The additional elements are found in the pit and in the salt deposit.

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Fireside Corrosion of Chromium- and Aluminum-Coated Ferritic–Martensitic Steels

Cited by 18 publications

References 14 publications

Scale Formation and Degradation of Diffusion Coatings Deposited on 9% Cr Steel in Molten Solar Salt

Scale Formation and Degradation of Diffusion Coatings Deposited on 9% Cr Steel in Molten Solar Salt

The Importance of the Fluorine Effect on the Oxidation of Intermetallic Titanium Aluminides

Hot corrosion Type II of FeCr‐based model alloys for boiler and heat exchanger applications

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