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Diffusion simulations of MC and M7C3 carbide coarsening in bcc and fcc matrix utilising new thermodynamic and kinetic description
Thermo-Calc Software AB, Stockholm Technology Park.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
Swerea KIMAB.
2008 (English)In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 24, no 6, 695-704 p.Article in journal (Refereed) Published
Abstract [en]

A new thermodynamic database has been combined with an existing kinetic database to perform coarsening simulations in ternary systems including MC and M7C3 carbides in an fcc matrix. The kinetic database was revised taking into consideration the new experimental information on the Fe-Cr-V-C system obtained in the present work, and available experiments on the ternary Fe-Cr-C and Fe-V-C systems. After revision the agreement between experimental results and simulations was satisfactory. It was found that the interfacial energy of M7C3 was twice as large as that of the MC carbide. The calculations for commercial steels with 6 alloy elements gave results in satisfactory agreement with new experimental measurements. The present coarsening simulations use the calculated equilibrium state and the observed particle sizes as the state for the start of the simulations. All the simulations were performed with the DICTRA software.

Place, publisher, year, edition, pages
2008. Vol. 24, no 6, 695-704 p.
Keyword [en]
carbide coarsening, diffusion simulations, thermodynamic modelling, mobilities, DICTRA, iron-chromium alloys, multicomponent diffusion, solid-solutions, alpha-><-(alpha&gamma) transformation, cementite dissolution, numerical, treatment, self-diffusion, ni alloys, cr-fe, precipitation
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-17760DOI: 10.1179/174328407x240954ISI: 000258409600010ScopusID: 2-s2.0-47549094691OAI: diva2:335805
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-09-29Bibliographically approved
In thesis
1. Phase equilibria and thermodynamic properties of high-alloy tool steels: theoretical and experimental approach
Open this publication in new window or tab >>Phase equilibria and thermodynamic properties of high-alloy tool steels: theoretical and experimental approach
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The recent development of tool steels and high-speed steels has led to a significant increase in alloy additions, such as Co, Cr, Mo, N, V, and W. Knowledge about the phase relations in these multicomponent alloys, that is, the relative stability between different carbides or the solubility of different elements in the carbides and in the matrix phase, is essential for understanding the behaviour of these alloys in heat treatments. This information is also the basis for improving the properties or designing new alloys by controlling the amount of alloying elements. Thermodynamic calculations together with a thermodynamic database is a very powerful and important tool for alloy development of new tool steels and high-speed steels. By thermodynamic calculations one can easily predict how different amounts of alloying elements influence on the stability of different phases. Phase fractions of the individual phases and the solubility of different elements in the phases can be predicted quickly. Thermodynamic calculations can also be used to find optimised processing temperatures, e.g. for different heat treatments. Combining thermodynamic calculations with kinetic modelling one can also predict the microstructure evolution in different processes such as solidification, dissolution heat treatments, carbide coarsening, and the important tempering step producing secondary carbides.

The quality of predictions based on thermodynamic calculations directly depends on the accuracy of the thermodynamic database used. In the present work new experimental phase equilibria information, both in model alloys containing few elements and in commercial alloys, has been determined and was used to evaluate and improve the thermodynamic description. This new experimental investigation was necessary because important information concerning the different carbide systems in tool steels and high-speed steels were lacking.

A new thermodynamic database for tool steels and high-speed steels, TOOL05, has been developed within this thesis. With the new database it is possible to calculate thermodynamic properties and phase equilibria with high accuracy and good reliability. Compared with the previous thermodynamic description the improvements are significant. In addition the composition range of different alloying elements, where reliable results are obtained with the new thermodynamic database, have been widened significantly.

As the available kinetic data did not always predict results in agreement with new experiments the database was modified in the present work. By coupling the new thermodynamic description with the new kinetic description accurate diffusion simulations can be performed for carbide coarsening, carbide dissolution and micro segregation during solidification.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 68 p.
thermodynamic modelling, thermodynamic calculations, tool steels, high-speed steels, CALPHAD
National Category
Other Materials Engineering
urn:nbn:se:kth:diva-453 (URN)91-7178-120-X (ISBN)
Public defence
2005-10-21, salongen, KTHB, Osquars backe 31, Stockholm, 10:00
QC 20100929Available from: 2005-10-18 Created: 2005-10-18 Last updated: 2010-09-29Bibliographically approved

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