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Mechanisms of Metal Dusting
KTH, Superseded Departments, Materials Science and Engineering.
2004 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The primary intention with this Doctoral thesis is to fillin the knowledge gaps and raise the level of understandingregarding the different metal dusting mechanisms in general andexplain the process in detail for high alloyed materials.Considerable effort is put into identifying the driving forcesand elucidating the diffusional processes in metal dusting.

The results are based on a series of long-term laboratory exposures of stainless steels and high-performance commercial alumina-forming Fe- and Ni-base alloys in synthesis gasmixtures, plus a separate shorter study on ultra pure iron. ANi-base alloy was also investigated after a two years field exposure in a methanol plant.

Post exposure metallographic examinations and analysis aswell as thermodynamic calculations were made in order toidentify and describe the operating metal dusting mechanisms.Two main mechanisms were previously used to explain metaldusting, one on the basis of decomposition of metastable carbides (Type I) the other on graphite formation (TypeII).

A new metal dusting mechanism has been identified in this Thesis which appears on high alloyed steels and Ni-base alloys,an active corrosion induced by carbon and oxygen, denoted TypeIII. Both the mechanisms and the type of corrosion products were consistent with the thermodynamic conditions of the material under the influence of a carbon and oxygen gradient.It was shown that this mechanism not only accelerates the metaldusting process, in fact, it determines the overall metaldusting kinetics on stainless steels and Ni-base alloys.

Another feature, which may occur at temperatures where metalbulk and even static grain boundary diffusion is too slow forexplaining the metal dusting corrosion process, was identifiedon a Ni-base alloy. It involves a fast growing cellular structure with discontinuous precipitated carbides whichprovides fast metal dusting kinetics by the Type IIImechanism.

A Type IV metal dusting mechanism, continued fragmentationby graphitization until nano-sized particles are formed andcatalyse carbon nanotube formation is also described. Thesteady state process and the driving force for metal dusting onpure iron was identified and described.

With these additional processes it is now possible to extendour understanding of the metal dusting processes to a widerange of engineering alloys.

 

Place, publisher, year, edition, pages
Stockholm: KTH , 2004. , 81 p.
Keyword [en]
metal dusting, mechanism, driving force, kinetics, high temperature corrosion, carburization, stainlesssteel, Ni-base alloys, iron, alumina formers, FeCrAl, oxidation, carbon nanotubes, discontinuous precipitation
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-3722ISBN: 91-7283-713-6 (print)OAI: oai:DiVA.org:kth-3722DiVA: diva2:9563
Public defence
2004-04-02, 00:00
Note
QC 20100825Available from: 2004-03-23 Created: 2004-03-23 Last updated: 2010-08-25Bibliographically approved
List of papers
1. Carburizing of chromia and alumina forming stainless steels at 750°C
Open this publication in new window or tab >>Carburizing of chromia and alumina forming stainless steels at 750°C
1999 (English)In: 14th International Corrosion Congress (ICC), Cape Town, South Africa, Sept., 1999., 1999, Paper 153- p.Conference paper, Published paper (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-24191 (URN)
Note
QC 20100823Available from: 2010-08-23 Created: 2010-08-23 Last updated: 2010-08-25Bibliographically approved
2. An active corrosion mechanism for metal dusting on 304L stainless steel
Open this publication in new window or tab >>An active corrosion mechanism for metal dusting on 304L stainless steel
2002 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 44, no 10, 2253-2270 p.Article in journal (Refereed) Published
Abstract [en]

A mechanism for metal dusting of chromia-forming stainless steels is proposed, based on results from laboratory exposures of 304L stainless steel at 650 degreesC for 1000 h in a synthesis gas low in water vapour, 25%CO + 3%H2O + H. The work focuses on the role of carbides and oxygen to explain the different corrosion mechanisms and give a description of the metal dusting phenomenon as it appears in engineering alloys. Metallographical examinations, FEG-SEM, SEM-EDX analysis and X-ray diffraction, as well as thermodynamic calculations were made in order to identify the proposed metal dusting mechanism.

Keyword
stainless steel, high temperature corrosion, metal dusting, oxidation, carburisation, carbides, thermodynamic modelling, diffusion, kinetics, mechanisms, ni-base alloys
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-21648 (URN)000176482100008 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2017-12-12Bibliographically approved
3. Mechanisms of metal dusting: Application to alloycomposition, temperature and pressure
Open this publication in new window or tab >>Mechanisms of metal dusting: Application to alloycomposition, temperature and pressure
2002 (English)In: 15th International CorrosionConference (ICC), Granada, Sept., 2002., 2002, Paper 806- p.Conference paper, Published paper (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-24203 (URN)
Note
QC 20100825Available from: 2010-08-25 Created: 2010-08-25 Last updated: 2010-08-25Bibliographically approved
4. Mechanisms and driving forces of metal dusting
Open this publication in new window or tab >>Mechanisms and driving forces of metal dusting
2003 (English)In: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 54, no 10, 752-762 p.Article in journal (Refereed) Published
Abstract [en]

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 C for up to 5000 h in a synthesis gas tow, in water vapour, 25%CO + 3%H2O + 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.

Keyword
ni-base alloys, fe-base, iron, microprocesses
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-22914 (URN)000186164100004 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2017-12-12Bibliographically approved
5. The role of discontinuous precipitation in metal dusting
Open this publication in new window or tab >>The role of discontinuous precipitation in metal dusting
2004 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 461-464, 561-570 p.Article in journal (Refereed) Published
Abstract [en]

A high-performance commercial alumina-forming Ni-base alloy was studied after a two years field exposure at 540degreesC in a methanol plant. Comparative laboratory studies were performed at 650degreesC using a different synthesis gas mixture with the composition; 50%CO + 3%H2O + 47H(2). Post exposure metallographic examinations with LOM, FEG-SEM, SEMEDX analysis as well as thermodynamic calculations were made in order to identify and describe the metal dusting mechanisms. An estimate of the metal dusting corrosion rates was per-formed based on metallography and these were correlated to a theoretical model based on diffusion processes.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-24206 (URN)000223339700068 ()
Note
QC 20100825Available from: 2010-08-25 Created: 2010-08-25 Last updated: 2017-12-12Bibliographically approved
6. Metal dusting on an alumina forming Ni-base alloy
Open this publication in new window or tab >>Metal dusting on an alumina forming Ni-base alloy
2006 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 48, no 7, 1679-1695 p.Article in journal (Refereed) Published
Abstract [en]

A high-performance commercial alumina-forming Ni-base alloy was studied after a 2 years field exposure at 540 degrees C in a methanol plant with a gas composition of 10-20%CO and 20-40%H2O, with some CO2 and the remainder H-2. The same material was also used in laboratory studies performed at 650 degrees C Using a gas mixture With higher CO and lower H-2,O content: 50%CO + 3%H2O + 47H(2) (carbon activity a(c) = 39). Post-exposure metallographic examinations together with thermodynamic calculations were used to identify and describe the metal dusting processes. A growth mechanism for metal dusting in nickel base alloys, which is independent of metal bulk diffusion, is identified. The process involves it separation of the carbon-saturated metal into a network of discontinuous precipitated carbides and a depleted Ni-austenite matrix followed by selective oxidation of the carbide network. The corrosion product consists of Cr-depleted Ni-particles, Cr-rich oxides and free carbon. The estimated metal dusting corrosion rate in the field exposure was 20-25 mu m/year. based on metallography and it was correlated to a theoretical model based on boundary diffusion processes.

Keyword
metal dusting, carburization, oxidation, synthesis gas, Ni-base alloy, alumina-formers, discontinuous precipitation, kinetics, diffusion, micro-cracks, corrosion, carburization, mechanisms, kinetics, iron
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-15836 (URN)000238926800007 ()
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved

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