Transformation-induced plasticity in Fe-Cr-V-C
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en Eckertb) IFW Dresden, Institute for Complex Materials, D-01171 Dresden, Germany; and Technical University (TU) Dresden, Institute of Materials Science, D-01062 Dresden, Germany (Received 1 September 2009; accepted 9 November 2009)
On the basis of the Fe84.3C4.6Cr4.3Mo4.6V2.2 high-speed tool steel, manufactured under relatively high cooling rates and highly pure conditions, a further improvement of the mechanical characteristics by slight modification of the alloy composition was attempted. For this, the alloy Fe88.9Cr4.3V2.2C4.6 was generated by elimination of Mo. By applying special preparation conditions, a microstructure composed of martensite, retained austenite, and a fine network of special carbides was obtained already in the as-cast state. This material exhibits extremely high compression strength of over 5000 MPa combined with large compression strain of more than 25% due to deformation-induced martensite formation. With this alloy a new composition of transformation-induced plasticityassisted steels was found, which shows an extreme mechanical loading capacity. I. INTRODUCTION
The formation of martensite in steels has a special relevance regarding hardness, strength, and wear resistance1 and, consequently, a strong importance regarding industrial applications. Martensite is a nonequilibrium phase; it transforms from the parent austenite [face-centered cubic (fcc), g-phase] if diffusion is suppressed because of fast enough cooling of the material. Therefore, the bodycentered cubic [(bcc), a-phase] structure of iron at room temperature is supersaturated in carbon that results in a tetragonal distorted lattice [body-centered tetragonal (bct), a0 -phase].1 The anisotropic strain field of carbon atoms in the octahedral sites is the main reason for the very high strength of the martensitic microstructure. Apart from undercooling, the thermodynamic driving force required for the austenite-to-martensite phase transformation can also be applied by mechanical energy.2–4 The metastable retained austenite can undergo phase transformation during plastic deformation connected with an increase in strength and plasticity.5 The effect is called transformation-induced plasticity (TRIP).6 TRIP steels combine both high strength and high formability and offer large dynamic energy absorption.7,8 Two types of such materials are currently known. First, TRIP steels, characterized by a fully austenitic microstructure, mostly genera)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr_policy DOI: 10.1557/JMR.2010.0052 368
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J. Mater. Res., Vol. 25, No. 2, Feb 2010 Downloaded: 05 Apr 2015
ated by a high nickel content9 and, second, TRIP-assisted steels, containing a ferrite-bainite matrix and only a low volume fraction (less than 20%) of finely dispersed metastable retained au
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