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Mechanical characterization of secondary-hardening martensitic steel using nanoindentation

Published online by Cambridge University Press:  03 March 2011

T. Ohmura ,
T. Hara ,
K. Tsuzaki ,
H. Nakatsu  and
Y. Tamura
T. Ohmura
Affiliation:
Steel Research Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
T. Hara
Affiliation:
Steel Research Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
K. Tsuzaki
Affiliation:
Steel Research Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
H. Nakatsu
Affiliation:
Metallurgical Research Laboratory, Hitachi Metals, Ltd., Yasugi, Shimane 692-8601, Japan
Y. Tamura
Affiliation:
Metallurgical Research Laboratory, Hitachi Metals, Ltd., Yasugi, Shimane 692-8601, Japan
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Abstract

Mechanical characterizations using nanoindentation technique were performed for the martensitic steel used as practical dies steel containing carbide-former elements of Cr, Mo, W, and V, which are responsible for secondary hardening by tempering. The nanohardness Hn corresponding to the matrix strength shows obvious secondary hardening, and the hardening-peak temperature coincides with that of the macroscale hardness Hv. By comparing the temper-softening behavior of the high-purity Fe–C binary martensite, the ratio of the nanohardness Hn of the dies steel to that of the Fe–C binary steel is approximately a factor of two, whereas the same ratio of the macroscopic hardness Hv is three at the secondary-hardening peak. These results suggest that the secondary hardening of the dies steel during tempering is attributed not only to the nanoscale strengthening factors such as precipitation hardening by the alloy carbides, but also to some other factors in larger scale. One of the strengthening factors in larger scale is a decomposition of 9% retained austenite to much harder phases, such as martensite and/or ferrite–cementite constituent.

Keywords

NanoindentationMicrostructureMechanical properties

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Type
Articles
Information
Journal of Materials Research , Volume 19 , Issue 1 , January 2004 , pp. 79 - 84
Copyright
Copyright © Materials Research Society 2004

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References

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