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Multicomponent diffusional reactions in tool steels: Experiment and Theory
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Many phenomena determining the microstructure of a tool steel and consequently the properties of the material, are governed by multicomponent diffusion. The diffusion driven reactions that take place during, for example, tempering of a hot-work tool steel or when the microstructure develops during hot isostatic pressing of cold-work tool steel, are dependent on the types and amounts of alloying elements. In order for computational methods to be usable, these alloying effects need to be understood and incorporated in the models.

In this work the influence of some typical tool steel alloying elements on the coarsening behavior of precipitates is investigated. Experimental coarsening studies are performed and the impact of the diffusion mobility descriptions and the thermodynamic descriptions are investigated by means of DICTRA coarsening calculations. The kinetic descriptions for diffusion in the body centered-cubic phase in the case of the chromium-iron-vanadium system and the chromium-iron-molybdenum system are improved by assessments of diffusion mobility parameters, and are shown to have a large impact on the calculated coarsening rate for vanadium-rich and molybdenum-rich precipitates.

The effect of cobalt is examined by a coarsening experiment for vanandiumrich carbides and by a diffusion couple experiment for the investigation of the vanadium interdiffusion. The presence of cobalt is experimentally shown to have retarding effect on the coarsening rate of the carbides, but not on the vanadium diffusion.

The coarsening rate of nitrogen-rich precipitates is compared to the coarsening rate of carbon-rich precipitates, and a lower coarsening rate for nitrides compared to carbides can be confirmed. Correlation between coarsening calculations and experiments is obtained suggesting that the thermodynamic description of the two systems is the underlaying reason for the different coarsening rates.

Further, calculations utilizing the DICTRA software are combined with experimental investigations in order to study the possibility to apply computational methods for compound material development and explore application areas for high nitrogen alloyed tool steels produced by powder metallurgy.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , vii, 67 p.
Keyword [en]
hot-work tool steel, precipitation hardening, DICTRA, coarsening, mobilities, CALPHAD, cobalt, PM tool stees, nitrogen, compound materials
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-103328ISBN: 978-91-7501-504-0 (print)OAI: oai:DiVA.org:kth-103328DiVA: diva2:559785
Public defence
2012-10-26, B3, Materialvetenskap, Brinellvägen 23, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20121011

Available from: 2012-10-11 Created: 2012-10-10 Last updated: 2012-10-11Bibliographically approved
List of papers
1. Assessment and evaluation of mobilities for diffusion in the bcc Cr-V-Fe system
Open this publication in new window or tab >>Assessment and evaluation of mobilities for diffusion in the bcc Cr-V-Fe system
2009 (English)In: Journal of phase equilibria and diffusion, ISSN 1547-7037, Vol. 30, no 4, 323-333 p.Article in journal (Refereed) Published
Abstract [en]

Assessments of diffusion mobility parameters are performed for the bcc Cr-V-Fe alloy systemby taking available literature data into account. The main focus is on the diffusion of V in thebcc phase where, in addition to all binaries, ternary interaction parameters are assessed. Anexperiment is performed in order to study the coarsening of V-rich MC carbide, where thediffusion of V is believed to be of major importance. The measured coarsening rate is comparedwith the rate calculated using DICTRA, and found to be in satisfactory agreement. Theaspects of coarsening experiments as a method to evaluate diffusion mobility data arediscussed.

Place, publisher, year, edition, pages
ASM International, 2009
Keyword
assessment, carbide coarsening, Cr-V-Fe alloys, DICTRA simulation, diffusion mobility database, multicomponent diffusion
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-103314 (URN)10.1007/s11669-009-9531-0 (DOI)000268069700005 ()
Note

QC 20121010

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2012-10-11Bibliographically approved
2. Assessment and evaluation of mobilities for diffusion in the bcc Cr-Mo-Fe system
Open this publication in new window or tab >>Assessment and evaluation of mobilities for diffusion in the bcc Cr-Mo-Fe system
2012 (English)In: Journal of Phase Equilibria and Diffusion, ISSN 1547-7037, Vol. 33, no 5, 375-389 p.Article in journal (Refereed) Published
Abstract [en]

An assessment of the diffusion mobility functions for diffusion in the bcc Cr-Fe-Mo system ispresented. The optimization of the mobility parameters is performed by utilizing experimentaldiffusion data available in literature. New diffusion data for the Mo diffusion is produced by adiffusion couple experiment and is accounted for in the optimization. Agreement between calculatedand measured diffusion coefficients is found. An M6C coarsening experiment is performedand the measured coarsening rate can be reproduced by diffusion calculation using the DICTRA software and the developed kinetic description. The mobility parameters are shown tohave a strong influence on the calculated coarsening rate.

Place, publisher, year, edition, pages
ASM International, 2012
Keyword
assessment, coarsening, DICTRA modeling, Mo carbides, multicomponent diffusion, tool steels
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-103317 (URN)10.1007/s11669-012-0107-z (DOI)000308969200005 ()2-s2.0-84870656570 (Scopus ID)
Note

QC 20121010

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2012-10-11Bibliographically approved
3. Experimental and theoretical investigations of hot isostatically pressed-produced stainless steel/high alloy tool steel compound materials
Open this publication in new window or tab >>Experimental and theoretical investigations of hot isostatically pressed-produced stainless steel/high alloy tool steel compound materials
2010 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 42, no 5, 1165-1172 p.Article in journal (Refereed) Published
Abstract [en]

Consolidation of tool steel powders and simultaneous joining to a stainless 316L steel areperformed by hot isostatic pressing (HIP). Two tool steel grades are considered: a high vanadiumalloyed carbon tool steel, and a high vanadium and chromium alloyed nitrogen tool steel.The boundary layer arising during diffusion bonding is in focus and, in particular, the diffusionof carbon and nitrogen over the joint.Measurements of the elemental concentration profiles andcorrosion tests by the double loop–electrochemical potentiokinetic reactivation (DL-EPR)method are performed. Comparative calculations with the DICTRA software are performedand are found to be in agreement with the experimental results. It is found that the carbon toolsteel grade has a more critical influence on the corrosion resistance of the stainless 316L steel incomparison to the nitrogen tool steel grade.

Place, publisher, year, edition, pages
The Minerals, Metals, and Materials Society, 2010
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-103323 (URN)10.1007/s11661-010-0480-3 (DOI)000288814700004 ()2-s2.0-79954442823 (Scopus ID)
Note

QC 20121010

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2017-12-07Bibliographically approved
4. The effect of nitrogen on the coarsening rate of precipitate phases in iron-based alloys with chromium and vanadium: experimental and theoretical investigations
Open this publication in new window or tab >>The effect of nitrogen on the coarsening rate of precipitate phases in iron-based alloys with chromium and vanadium: experimental and theoretical investigations
2013 (English)In: International Journal of Materials Research - Zeitschrift für Metallkunde, ISSN 1862-5282, E-ISSN 2195-8556, Vol. 105, no 5, 442-451 p.Article in journal (Refereed) Published
Abstract [en]

A comparison of the coarsening of nitrogen-rich vanadium precipitates and the coarsening ofcarbon-rich vanadium precipitates is presented. The precipitate phases are studied experimentally,via fabrication of model alloys, and theoretically, via simulations utilizing the DICTRA software.The experimental investigations indicate that the nitrogen-rich precipitates exhibit a slowercoarsening behaviour than the carbon-rich precipitates. Analysis using thermodynamic andkinetic modelling shows that this can be explained by the higher thermodynamic stability of thenitrogen-rich precipitate compared to the carbon-rich precipitate. The calculated coarsening ratesare compared with the measured rates, and found to be in satisfactory agreement using reasonablevalues for the interfacial energies. The investigations are motivated by the ne precipitate sizedistribution of nitrides and carbonitrides characteristic for high nitrogen alloyed tool steels producedby means of powder metallurgy.

Keyword
Tool steels, Powder metallurgy, Nitrogen, HIP, Coarsening, DICTRA
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-103319 (URN)10.3139/146.110885 (DOI)000320346600003 ()
Note

QC 20121010. Updated from accepted to published 20131212. 

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2017-12-07Bibliographically approved
5. Coarsening investigations of precipitates in PM tool steel grades - an effect of nitrogen
Open this publication in new window or tab >>Coarsening investigations of precipitates in PM tool steel grades - an effect of nitrogen
Show others...
2012 (English)In: Berg- und Huttenmännische Monatshefte (BHM), ISSN 0005-8912, E-ISSN 1613-7531, Vol. 157, no 11, 406-413 p.Article in journal (Refereed) Published
Abstract [en]

We present experimental and theoretical comparisons of the coarsening rate for the MX(X=C, N or C+N) precipitate in five different tool steel grades produced by PowderMetallurgy (PM). The alloys contain different amounts of nitrogen and carbon; ranging fromhigh carbon/low nitrogen to high nitrogen/low carbon. Common for the grades is a highamount of precipitate forming alloying elements resulting in a high fraction of hard phase.Experimentally we have found out that the nitrogen rich precipitates coarsen slower, both forhigher and lower carbon content, than the carbon rich precipitates. Coarsening simulations areperformed utilizing the DICTRA software and an agreement between calculations andmeasurements can be concluded.

Keyword
coarsening, PM tool steels, carbides, nitrides, DICTRA
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-103320 (URN)10.1007/s00501-012-0039-2 (DOI)
Note

QC 20121010. Updated from accepted to published 20131202.

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2017-12-07Bibliographically approved
6. Diffusion calculations as a tool for tool steel design
Open this publication in new window or tab >>Diffusion calculations as a tool for tool steel design
2009 (English)In: Proceedings of the 8th International Tooling Conference, RWTH Aachen, Aachen, Germany, 2009, Vol. 2, 1063-1070 p.Conference paper, Published paper (Refereed)
Abstract [en]

Thermodynamic calculations have shown to be a powerful tool for predications of phasecompositions and phase fractions in steels. Coupling of thermodynamic and diffusion mobilitydatabases make diffusion calculations possible, and along with the accessibility of accurate anduser-friendly software on the market, the quality demands on kinetic data have increased.This work concerns development of multicomponent diffusion data for calculations applied todiffusion dependent processes, and focus is on alloy systems alloyed with Co. The possibility toevaluate diffusion data with the help of coarsening experiments and diffusion couples isinvestigated.

Keyword
multicomponent diffusion, diffusion mobility database, assessment, carbide coarsening, diffusion couple, cobalt
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-103318 (URN)
Conference
The 8th International Tooling Conference, RWTH Aachen, Aachen, Germany
Note

QC 20121010

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2012-10-11Bibliographically approved

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