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Coarsening investigations of precipitates in PM tool steel grades - an effect of nitrogen
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
Swerea KIMAB.
Uddeholms AB.
Uddeholms AB.
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2012 (English)In: Berg- und Huttenmännische Monatshefte (BHM), ISSN 0005-8912, 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.

Place, publisher, year, edition, pages
2012. Vol. 157, no 11, 406-413 p.
Keyword [en]
coarsening, PM tool steels, carbides, nitrides, DICTRA
National Category
Metallurgy and Metallic Materials
URN: urn:nbn:se:kth:diva-103320DOI: 10.1007/s00501-012-0039-2OAI: diva2:559707

QC 20121010. Updated from accepted to published 20131202.

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2013-12-02Bibliographically approved
In thesis
1. Multicomponent diffusional reactions in tool steels: Experiment and Theory
Open this publication in new window or tab >>Multicomponent diffusional reactions in tool steels: Experiment and Theory
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.
hot-work tool steel, precipitation hardening, DICTRA, coarsening, mobilities, CALPHAD, cobalt, PM tool stees, nitrogen, compound materials
National Category
Engineering and Technology
urn:nbn:se:kth:diva-103328 (URN)978-91-7501-504-0 (ISBN)
Public defence
2012-10-26, B3, Materialvetenskap, Brinellvägen 23, KTH, Stockholm, 10:15 (English)

QC 20121011

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

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