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Phase equilibria and thermodynamic properties of high-alloy tool steels: theoretical and experimental approach
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
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.
Keyword [en]
thermodynamic modelling, thermodynamic calculations, tool steels, high-speed steels, CALPHAD
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-453ISBN: 91-7178-120-X (print)OAI: oai:DiVA.org:kth-453DiVA: diva2:12696
Public defence
2005-10-21, salongen, KTHB, Osquars backe 31, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100929Available from: 2005-10-18 Created: 2005-10-18 Last updated: 2010-09-29Bibliographically approved
List of papers
1. A thermodynamic analysis of the Mo-V and Mo-V-C systems
Open this publication in new window or tab >>A thermodynamic analysis of the Mo-V and Mo-V-C systems
2002 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 26, no 3, 459-503 p.Article in journal (Refereed) Published
Abstract [en]

A new thermodynamic evaluation of the binary Mo-V system and the ternary Mo-V-C system using thermodynamic models for the Gibbs energy of individual phases is presented. The CALPHAD method has been used, with predictions of unknown thermodynamic quantities, to optimize a set of thermodynamic parameters taking related experimental information into consideration. The predictions are based on regularities in bonding properties and vibrational entropy of 3d-transition metal carbides. The results are summarized in tables of thermodynamic parameters, calculated binary phase diagrams and isothermal sections of the ternary phase diagram compared with experimental information. Finally the influence of ternary interaction parameters, especially in the fcc phase, on calculations of equilibria in multicomponent systems is discussed.

Keyword
Binary alloys, Carbides, Entropy, Gibbs free energy, Isotherms, Molybdenum, Optimization, Phase diagrams, Binary systems
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7606 (URN)10.1016/S0364-5916(02)00057-3 (DOI)000179541200011 ()
Note
QC 20100929Available from: 2005-10-18 Created: 2005-10-18 Last updated: 2017-12-14Bibliographically approved
2. A thermodynamic assessment of the Co-V system
Open this publication in new window or tab >>A thermodynamic assessment of the Co-V system
2003 (English)In: Journal of phase equilibria (Print), ISSN 1054-9714, E-ISSN 1544-1032, Vol. 24, no 6, 495-503 p.Article in journal (Refereed) Published
Abstract [en]

A thermodynamic evaluation of the binary Co-V system has been done using experimental thermochemical and phase diagram data. A consistent thermodynamic description, using a Redlich-Kister model for solution phases and sublattice models for the intermetallics, was obtained, and it agreed well with the critically evaluated experimental data. The model for the solid phases accounts for the magnetic contribution to the Gibbs energy. The addition of a composition dependent magnetic term also led to the prediction of an fcc-Co miscibility gap. The model parameters have been determined using a computerized optimization technique. Several diagrams and tables concerning phase equilibria are presented.

Keyword
phase-equilibria, sigma phase, alloys, vanadium, cobalt, model
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-23062 (URN)10.1361/105497103772084534 (DOI)000187667400002 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2017-12-12Bibliographically approved
3. An experimental and theoretical analysis of the phase equilibria in the Fe-Cr-V-C system
Open this publication in new window or tab >>An experimental and theoretical analysis of the phase equilibria in the Fe-Cr-V-C system
2004 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 35A, no 12, 3649-3663 p.Article in journal (Refereed) Published
Abstract [en]

New experimental phase equilibria information about the Fe-Cr-V-C system are presented and used to modify the thermodynamic description of the system. The main interest was focused on the composition of the MC and M7C3 carbides and the necessary adjustment of the Cr and V distribution between carbides and matrix. A new set of thermodynamic parameter values describing the Gibbs energy of different phases was obtained. A number of calculated sections of the Cr-C, Cr-V-C, Fe-Cr-C, and the Fe-Cr-V-C systems are presented and compared against both new and old experimental information. Calculations on commercial alloys to verify the improvements in multicomponent systems are also presented. The present calculation using the Thermo-Calc software shows much better agreement with the new experimental results than previous assessments.

Keyword
Carbides, Gibbs free energy, Graphite, Heat treatment, Intermetallics, Metallographic microstructure, Phase diagrams, Phase equilibria, Solid solutions, Tool steel, Quaternary system, Solid solution phases
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7608 (URN)10.1007/s11661-004-0271-9 (DOI)000225448100002 ()
Note
QC 20100929Available from: 2005-10-18 Created: 2005-10-18 Last updated: 2017-12-14Bibliographically approved
4. An experimental investigation of carbide/austenite equilibria in commercial tool steels and high-speed steels compared against thermodynamic calculations
Open this publication in new window or tab >>An experimental investigation of carbide/austenite equilibria in commercial tool steels and high-speed steels compared against thermodynamic calculations
2004 (English)In: Proceeding of the Powder metallurgy world congress and EURO-PM2004, 2004, Vol. 5, 337-342 p.Conference paper, Published paper (Refereed)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7609 (URN)
Note
QC 20100929Available from: 2005-10-18 Created: 2005-10-18 Last updated: 2010-09-29Bibliographically approved
5. Investigation and modification of carbide sub-systems in the multicomponent Fe-C-Co-Cr-Mo-Si-V-W system
Open this publication in new window or tab >>Investigation and modification of carbide sub-systems in the multicomponent Fe-C-Co-Cr-Mo-Si-V-W system
2005 (English)In: Zeitschrift für Metallkunde, ISSN 0044-3093, Vol. 96, no 4, 335-344 p.Article in journal (Refereed) Published
Keyword
thermodynamic modeling, phase equilibria, Cr-Mo-C, V-W-C
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7610 (URN)000228932000003 ()
Note
QC 20100929Available from: 2005-10-18 Created: 2005-10-18 Last updated: 2017-12-14Bibliographically approved
6. Diffusion simulations of MC and M7C3 carbide coarsening in bcc and fcc matrix utilising new thermodynamic and kinetic description
Open this publication in new window or tab >>Diffusion simulations of MC and M7C3 carbide coarsening in bcc and fcc matrix utilising new thermodynamic and kinetic description
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.

Keyword
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
Identifiers
urn:nbn:se:kth:diva-17760 (URN)10.1179/174328407x240954 (DOI)000258409600010 ()2-s2.0-47549094691 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
7. Thermodynamic modelling of the M6C carbide in cemented carbides and high-speed steel
Open this publication in new window or tab >>Thermodynamic modelling of the M6C carbide in cemented carbides and high-speed steel
2005 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 29, no 2, 91-96 p.Article in journal (Refereed) Published
Abstract [en]

Newly published experimental information on phase equilibria in cemented carbides and high-speed steel has shown that the solubility of Co, Nb, Si, Ta and V in the M6C carbide is higher than predicted by thermodynamic calculations. To account for this new information the model for M6C was extended. A thermodynamic description of the M6C carbide in cemented carbides and high-speed steels is presented. Several experimental studies have shown that there is a solubility of Si in M6C in high-speed steels, and the new model describes this solubility. A significant solubility of Co and Nb has also been observed, and was accounted for. The solubility of Nb, Ta and V in M6C in cemented carbide systems is described. The models are discussed, and the calculated equilibria are compared with the new experimental information.

Keyword
cemented carbides, high-speed steel, M6C carbide
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7612 (URN)10.1016/j.calphad.2005.07.001 (DOI)000231589300001 ()
Note
QC 20100929Available from: 2005-10-18 Created: 2005-10-18 Last updated: 2017-12-14Bibliographically approved
8. An investigation of lower-order N containing systems and new phase equilibria experiments in the Fe-Cr-Mo-V-C-N system
Open this publication in new window or tab >>An investigation of lower-order N containing systems and new phase equilibria experiments in the Fe-Cr-Mo-V-C-N system
2005 (English)In: Zeitschrift für Metallkunde, ISSN 0044-3093Article in journal (Other academic) Submitted
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7613 (URN)
Note
QS 20120319Available from: 2005-10-18 Created: 2005-10-18 Last updated: 2017-12-14Bibliographically approved

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