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Modeling Creep Strength of Welded 9 to 12 Pct Cr Steels
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology. KTH, School of Industrial Engineering and Management (ITM), Centres, Brinell Centre - Inorganic Interfacial Engineering, BRIIE.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology. KTH, School of Industrial Engineering and Management (ITM), Centres, Brinell Centre - Inorganic Interfacial Engineering, BRIIE.ORCID iD: 0000-0002-8494-3983
2010 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 41A, no 13, 3340-3347 p.Article in journal (Refereed) Published
Abstract [en]

The influence of weld simulated heat treatments of 9-12% steels is evaluated by a fundamental model for creep. The heat affected microstructure is predicted by considering particle coarsening, particle dissolution, and subgrain coarsening. Particle coarsening is predicted for a multi-component system, showing significant M23C6 coarsening in the BCC matrix. Dissolution simulations of MX and M23C6 are performed by considering a size distribution of particles, indicating that the smallest particles can be dissolved already at relatively low welding temperatures. Recovery in dislocation networks will take place due to the coarser particles. Creep rate modelling is performed based on the heat affected microstructure, showing strength reduction of weld simulated material by 12% at 850ºC and 26% at 900ºC. The main cause of this degradation is believed to be the loss of the smallest carbonitrides.

Place, publisher, year, edition, pages
2010. Vol. 41A, no 13, 3340-3347 p.
Keyword [en]
Carbonitrides, Cr steel, Creep rates, Creep strengths, Dislocation networks, Distribution of particles, Fundamental models, matrix, Multi-component systems, Particle coarsening, Particle dissolution, Simulated materials, Strength reduction, Subgrain-coarsening, Welding temperatures, Carbon nitride, Chromium, Computer simulation, Creep, Dissolution, Welding, Welds
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-12234DOI: 10.1007/s11661-010-0449-2ISI: 000283943900010Scopus ID: 2-s2.0-78049442090OAI: oai:DiVA.org:kth-12234DiVA: diva2:306594
Note
QC 2010616. Updated from submitted to published, 20120315Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2012-03-15Bibliographically approved
In thesis
1. Creep modelling of particle strengthened steels
Open this publication in new window or tab >>Creep modelling of particle strengthened steels
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Materials used in thermal power plants have to resist creep deformation for time periods up to 30 years. Material evaluation is typically based on creep testing with a maximum duration of a few years. This information is used as input when empirically deriving models for creep. These kinds of models are of limited use when considering service conditions or compositions different from those in the experiments. In order to provide a more general model for creep, the mechanisms that give creep strength have to be identified and fundamentally described. By combining tools for thermodynamic modelling and modern dislocation theory the microstructure evolution during creep can be predicted and used as input in creep rate modelling. The model for creep has been utilised to clarify the influence of aluminium on creep strength as a part of the European COST538 action. The results show how AlN is formed at the expense of MX carbonitrides. The role of heat treatment during welding has been analysed. It has been shown that particles start to dissolve already at 800ºC, which is believed to be the main cause of Type IV cracking in commercial alloys.

The creep strength of these steels relies on minor additions of alloying elements. Precipitates such as M23C6 carbides and MX carbonitrides give rise to the main strengthening, and remaining elements produce solid solution hardening. Particle growth, coarsening and dissolution have been evaluated. By considering dislocation climb it is possible to determine particle strengthening at high temperatures and long-term service. Transient creep is predicted by considering different types of dislocations. Through the generation and recovery of dislocation densities an increase in work hardening during primary creep is achieved. The role of substructure is included through the composite model. Cavity nucleation and growth are analysed in order to explain the intergranular fracture and to estimate the ductility.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 48 p.
Keyword
creep rate modelling, particle hardening, microstructure evolution, dislocation climb, ferritic steels
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-12235 (URN)978-91-7415-590-7 (ISBN)
Public defence
2010-04-28, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC20100616Available from: 2010-04-09 Created: 2010-03-30 Last updated: 2011-10-03Bibliographically approved

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Sandström, Rolf

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