Strain-Rate Dependence of the Martensitic Transformation Behavior in a 10 Pct Ni Multi-phase Steel Under Compression
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THE deformation-induced transformation of austenite to martensite in steels is important because it provides a supplementary mechanism of plastic deformation that operates in parallel with dislocation slip .[1–3] The two mechanisms are influenced by the microstructure and the loading conditions in different ways, creating new ways to tailor the structure to achieve novel combinations of mechanical properties. For example, the martensitic transformation affects dynamic load partitioning and strain hardening, delaying the onset of necking and fracture.[4] In particular, in lath martensitic steels containing 4 to 12 pct Ni, the
P.K. LAMBERT and X.J. ZHANG are with the Carderock Division, Naval Surface Warfare Center, Bethesda, MD 20817. C.J. HUSTEDT, K.M. LEE, A.F.T. LEONG and T.C. HUFNAGEL are with the Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, MD 21218-2681. Contact e-mail: [email protected] D.T. CASEM and B.E. SCHUSTER are with the U.S. Army Research Laboratory, Aberdeen Proving Ground, 21005. N. SINCLAIR is with the Dynamic Compression Sector, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439. Manuscript submitted March 9, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
deformation-induced transformation has been exploited to achieve desirable combinations of strength, ductility, and impact toughness. (Compositions throughout this article are given in weight percent.) The mechanical properties of these steels, along with those of related Ni-containing steels, have been thoroughly studied at low strain rates.[1,5–29] With the exception of reports of Charpy impact energies, the literature on the high-strain-rate behavior of martensitic steels containing retained austenite stabilized by 4 to 12 pct Ni is sparse.[19] This contrasts with other types of multi-phase steels (such as those containing stable or metastable retained austenite due to other alloying elements such as manganese or chromium) which have been the subject of comparatively more high-strain-rate investigations.[30–32] In one study on the high-strain-rate performance of Ni-rich martensitic steels, retained austenite was reported to contribute to the high strength, impact toughness, and ballistic resistance of an alloy containing 10 pct Ni.[33] That steel was subjected to a quench-lamellarize-temper (QLT) heat treatment that yielded a microstructure consisting of fine austenite particles in a ferrite matrix. In previous publications on this steel, the importance of metastable austenite (and its martensitic transformation
during loading) to the mechanical properties of the QLT steel was inferred from its known importance to the impact properties of other steels, and from before-andafter microstructural evaluation of ballistic craters and fractured tensile specimens.[33] Characterization of the austenite and its transformation products in this steel presents an interesting challenge, due to structural inhomogeneity over length scales ranging from tens of microns to the sub-nanomet
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