An active corrosion mechanism for metal dusting on 304L stainless steel

Szakálos, Peter; Pettersson, Rachel; Hertzman, Staffan

doi:10.1016/s0010-938x(02)00053-7

Cited by 71 publications

(68 citation statements)

References 9 publications

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“…A close-up of the carbide-free ferrite border is shown in Fig. 8, comparable with the carbide-free and Cr-depleted austenite border observed on austenitic stainless steels [7,8], see section 4.4.…”

Section: Ferritic Fecral-alloyssupporting

confidence: 80%

“…To reach a low oxygen partial pressure, pure hydrogen was flushed through the furnace for three hours before heating to 600 -650 8C. The input composition of the reaction gas, which was introduced during heating, was 25%CO þ 3%H 2 O þ 72H 2 , with a calculated equilibrium oxygen partial pressure of pO 2 ¼ 10 À24 at 650 8C [7,8]. The flow rate was 250 ml/min, which corresponds to a gas velocity over the specimen of 9 mm/s.…”

Section: Methodsmentioning

confidence: 99%

“…This gives a corrosion rate of 0.45 lm/h, which is about half the corrosion rate of austenitic stainless steels [7,8].…”

Section: Metal Dusting On Cr-steelsmentioning

confidence: 99%

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Mechanisms and driving forces of metal dusting

Szakálos

2003

Materials & Corrosion

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The mechanisms of metal dusting as it appears on different ferritic stainless steels and pure iron have been described in detail. A mechanism for metal dusting (MD) of chromia-forming as well as alumina-forming steels is proposed, based on results from laboratory exposures of 26Cr-steel and FeCrAl-alloy at 600 -650 8C for up to 5000 h in a synthesis gas low in water vapour, 25%CO þ 3%H 2 O þ H 2 . Metallographical examinations, FEG-SEM, SEM-EDX analysis and X-ray diffraction, as well as thermodynamic calculations were made in order to identify and describe the different metal dusting processes. The work focuses on the role of carbides and oxides to explain the observations and give a description of the metal dusting phenomenon as it appears in engineering alloys. This mechanism was first observed and identified in a study of an austenitic stainless steel.The driving force for steady state MD on pure iron and low alloyed steels is described and a secondary MD-mechanism, carbon nanotube formation, is described in detail. With these additional results it is now possible to extend understanding of the MD-processes to a wide range of engineering alloys.

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Section: Ferritic Fecral-alloyssupporting

confidence: 80%

Section: Methodsmentioning

confidence: 99%

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Mechanisms and driving forces of metal dusting

Szakálos

2003

Materials & Corrosion

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“…Arrhenius-diagrams, from repeated exposures of various steel samples, attacked on their whole surface (no oxide left), a) metal wastage rates, determined from the coke analysis for its metal content, b) coking rates, determined by weighing the removable coke the Cr in the steels and alloys will end up in oxides anyway, since the oxygen pressure needed for Cr 2 O 3 formation is very low. No new metal dusting mechanism, other than described in chapters 3.1 and 3.2, is required to describe metal dusting of high alloy materials, in contrast to a recent publication [37].…”

Section: Kinetics Of Metal Wastage and Coking On Iron And Low Alloy Smentioning

confidence: 99%

Metal dusting

Grabke

2003

Materials & Corrosion

178

120

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This introductory review paper summarizes shortly the research on metal dusting, conducted in the MPI for Iron Research during the last dozen years. Metal dusting is a disintegration of metals and alloys to a dust of graphite and metal particles, occurring in carburizing atmospheres at a C > 1 and caused by the tendency to graphite formation. The cause of destruction is inward growth of graphite planes into the metal phase, or in the case of iron and low alloy steels into cementite formed as an intermediate. The kinetics of metal dusting on iron and steels was elucidated concerning dependencies on time, temperature and partial pressures. High alloy steels and Ni-base alloys are attacked through defects in the oxide scale which leads to pitting and outgrowth of coke protrusions, after initial internal formation of stable carbides M 23 C 6 , M 7 C 3 and MC. A dense oxide layer prevents metal dusting, but formation of a protective Cr-rich scale must be favored by a fine-grain microstructure and/or surface deformation, providing fast diffusion paths for Cr. Additional protection is possible by sulfur from the atmosphere, since sulfur adsorbs on metal surfaces and suppresses carburization. Sulfur also interrupts the metal dusting mechanism on iron and steels, causing slow cementite growth. Under conditions where no sulfur addition is possible, the use of high Cr Nickelbase-alloys is recommended, they are largely protected by an oxide scale and if metal dusting takes place, its rate is much slower than on steels. Definition of metal dustingMetal dusting is a disintegration of metallic materials into a dust of fine metal particles and graphitic carbon. In the case of chromium steels and Ni-base alloys the corrosion product (coke) may also contain carbides and oxides. This corrosion phenomenon occurs in carburizing atmospheres, containing CO and/or hydrocarbons, at carbon activities a C > 1 which means that a tendency for graphite formation prevails (in equilibrium with graphite a C ¼ 1). Susceptible are metals and alloys which dissolve carbon, i.e. Fe, Ni and Co and their alloys. The carbon is transferred from the atmosphere and dissolved into the metal phase, at a C > 1 to oversaturation, leading to growth of graphite which destroys the materials. In the case of iron and steels, cementite is formed as an intermediate into which the graphite grows [1 -5]. Nickel and Ni-base alloys are disintegrated by direct inward growth of graphite [6 -9].Fe and Ni and low alloyed materials are attacked uniformly. In the most critical temperature range 400 -800 8C mostly chromia forming steels and Ni-based alloys are used, on these materials metal dusting starts locally, where the oxide scale fails, and leads to pitting and hole formation [3, 8 -12], see Fig. 1a. The corrosion product "coke" is growing out from the pits and holes, and mostly carried away in the fast flowing process gases, but observed in laboratory studies as outgrowing protrusions (Fig. 1b). Typical for Cr-steels and alloys is the zone with internal carbides (Fig. 1c...

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“…Extensive work in this area was later carried out by Grabke et al [5][6][7][8] .Recently, Szakalos has presented refinements to the mechanisms of metal dusting which include the role of oxidation [9][10][11]. Review papers by Grabke [12] and Jones and Baumert [13] provide thorough summaries of the subject of metal dusting.…”

Section: Introductionmentioning

confidence: 99%

Inhibition of metal dusting using thermal spray coatings and laser treatment

Voisey

Liu

Stott

2006

Surface and Coatings Technology

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Alloy 600 and Alloy 800H are susceptible to metal dusting. Both alloys were thermally sprayed with two different corrosion resistant coatings: Ni50Cr and Ni31Cr11Al0.6Y. Laser remelting was used to enhance further the effectiveness of these coatings to resist metal dusting by eliminating interconnected porosity and improving coating adhesion.Uncoated, coated and laser-treated coated samples of Alloy 600 and Alloy 800H were exposed to a mixed gas atmosphere (20% H 2, 80% CO at 650°C). Samples were examined in plan and cross-section using optical and scanning electron microscopy, electron probe microanalysis and X-ray diffraction. The extent of carbon deposition was tracked by mass difference measurements at intervals during exposure.The thermally sprayed coatings enhanced metal dusting resistance by acting as physical barriers to carbon ingress. The NiCrAlY coating performed well on both substrates. The NiCr coating itself underwent metal dusting and spalled from Alloy 800H due partly to CTE mis-match stresses. Laser treatment of both coatings successfully eliminated interconnected porosity and hence enhanced metal dusting resistance.

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An active corrosion mechanism for metal dusting on 304L stainless steel

Cited by 71 publications

References 9 publications

Mechanisms and driving forces of metal dusting

Mechanisms and driving forces of metal dusting

Metal dusting

Inhibition of metal dusting using thermal spray coatings and laser treatment

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