Title: Isothermal aging kinetics of NiAl precipitates in a secondary hardening steel

Authors: S. Erlach, I. Siller, H. Leitner, H. Clemens

Addresses: Siemens Transportation Systems GmbH & Co KG, Eggenbergerstrasse 31, A-8010 Graz, Austria. ' Bohler Edelstahl GmbH, Kapfenberg, Austria. ' Department of Physical Metallurgy and Materials Testing, Montanuniversitat Leoben, A-8700 Leoben, Austria. ' Department of Physical Metallurgy and Materials Testing, Montanuniversitat Leoben, A-8700 Leoben, Austria

Abstract: Secondary hardening steels additionally alloyed with Ni and Al exhibit the precipitation of secondary hardening carbides and an intermetallic NiAl-based phase. The hardening response of a Fe-1.4C-2.6Cr-1.4Mo-6.0 Ni-5.0Al (composition in at.%) experimental alloy has been studied by hardness measurements conducted on specimens, which were subjected to aging treatments in a temperature range typically used for heat treatment of conventional secondary hardening steels. The results revealed a rapid hardness increase within the first minutes of aging. Nevertheless, when exceeding a certain critical temperature, the intermetallic NiAl-based phase is dissolved in the matrix. By applying standard relationships between hardness and NiAl phase fraction, the activation energy and time exponent of the intermetallic precipitation reaction were estimated. The derived results are critically discussed and quantitatively compared with data as provided by literature.

Keywords: secondary hardening steel; intermetallic precipitates; aging kinetics; hardness; tool steel; alloys.

DOI: 10.1504/IJMMP.2008.018741

International Journal of Microstructure and Materials Properties, 2008 Vol.3 No.2/3, pp.373 - 382

Available online: 16 Jun 2008 *

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