Metal Dusting of Low- and High-Alloy Steels

Grabke, H. J.

doi:10.5006/1.3293634

Cited by 100 publications

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“…In addition to low-alloy steels reported widely so far, [1][2][3][4][5][6] experience with metal dusting of high-alloy steels, originally resistant to carburization, has been reported in actual plants as well. [7][8][9][10][11] Moreover, laboratory corrosion tests for development of eminent alloys required for severe metal dusting attack have been conducted.…”

Section: Introductionmentioning

confidence: 99%

A Metallurgical Approach to Metal Dusting of Nickel-Base Alloys

Nishiyama¹,

Kudo²,

Ōtsuka³

2005

Mater. Trans.

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Preliminary laboratory corrosion tests of two conventional Ni-base alloys were conducted at 650 C for 200 h in various CO-H 2 -CO 2 -H 2 O gas mixtures. For gas mixtures of high a c and CO content, alloy 600 (75 mass %Ni-15%Cr) specimens lost its mass due to metal dusting and deposition of coke was heavy on the surface of the specimen. Meanwhile, any pit formation was not occurred on the alloy 690 (60%Ni-30%Cr) specimens. Microscopic observation indicated that for the corroded Ni-base alloy specimens, inward diffusion of carbon presumably at cracks and flaws in the oxide scale was prominent. Carbon in the diffusion zone reacted with chromium to precipitate carbides in the matrix, followed by the ''direct'' formation of graphite platelets with a lamellar structure at the revealed metal surface. This direct precipitation of graphite platelets can be considered by a eutectoid reaction, which is similar to the pearlite transformation observed in Fe-C system. In the lamellar structure, the matrix thinned with the growth of graphite plates, and small metal particles of Ni and Fe which may catalyze the coke deposition reaction were crumbled and detached from the lamella.

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Section: Introductionmentioning

confidence: 99%

A Metallurgical Approach to Metal Dusting of Nickel-Base Alloys

Nishiyama¹,

Kudo²,

Ōtsuka³

2005

Mater. Trans.

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“…2. Mechanismus des metal dusting von Eisen und niedriglegierten Sta Èhlen [7,8,13]; a) U È bertragung von Kohlenstoff in die Metallphase und U È bersa Èttigung, d.h. a C b 1, b) Bildung von Zementit an der Oberfla Èche, c) Graphitablagerung auf der Zementitschicht, d.h. an der Grenzfla Èche wird a C 3 1, d) Zementitzerfall, Fe 3 C 3 C, Kohlenstoff, der sich anlagert an die Graphitschicht und Fe, das durch die Graphitschicht wandert und auûerhalb Eisenpartikel bildet, die dann als Katalysatoren fu Èr Kohlenstoffabschaltung wirksam werden inflection point and strongly (quadratically, see below) increasing mass gain ( Fig. 3) due to the carbon deposition catalyzed by the metal particles formed in step (iv).…”

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“…The metal atoms diffuse through the graphite and agglomerate to small particles (about 20 nm diameter) (v) These particles act as catalysts for further carbon deposition and vast coke growth results. In thermogravimetric studies steps (i) to (iii) result in mass gain curves with decreasing slope, whereas step (v) causes an Mechanism of the metal dusting of iron and low alloy steels [7,8,13]; a) transfer of carbon into the metal phase and oversaturation, i.e. a C b 1, b) formation of cementite at the surface, c) graphite deposition on the cementite layer, at the interface a C 3 1, d) cementite decomposition, Fe 3 C 3 C attaching to the graphite and Fe migrating through the graphite layer, forming Fe particles, which act as catalysts for carbon deposition Abb.…”

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confidence: 99%

Thermodynamics, mechanisms and kinetics of metal dusting

Grabke

1998

Materials and Corrosion

207

127

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A survey is given on recent research on “metal dusting” i.e. a catastrophic carburization or rather graphitization of metals and alloys occuring in carbonaceous atmospheres at carbon activities aC>1. The thermodynamics are explained, the mechanisms for iron, low and high alloy steels, nickel and Ni‐base alloys are described and the kinetics derived for iron and low alloy steels. Protection against metal dusting is possible by the presence of sulfur in the atmosphere, since adsorbed sulfur retards carbon transfer and hems graphite nucleation. Also dense oxide layers are protective, the preconditions for the formation of Cr‐rich protectivee layers on steels and Ni‐base alloys are shortly presenteed.

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“…deposition reactions has long been kn0wn.9-l~ This compound is also routinely added to gas mixtures of high carbon activity to reduce degradation that involves carbon deposition as a precursor to c a r b u r i~a t i o n .~*~*~~-~~ It is generally assumed that the sulfide acts to reduce the catalytic activity of surfaces with respect to carbon deposition. 5 The presence of water vapor has also been reported to inhibit deposition of carbon,l5 but not necessarily catalytically. Rather, water vapor can react with the deposit to form gaseous products or shift the equilibria of reactions 1 -3 so as to reduce CO decomposition.15 However, as discussed above, relatively large concentrations of water vapor would be required to materially affect carbon deposition in the typical gasifier.…”

Section: Conditions That Influence Kinetics Of Carbon Depositionmentioning

confidence: 99%