Microstructure of CrMnNi Cast Steel After Explosive-Driven Flyer-Plate Impact at Room Temperature and Below
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HIGH-ALLOY austenitic stainless steels are characterized by extraordinary properties such as excellent formability, high corrosion resistance, and good weldability, and are used for applications ranging from cryogenic up to elevated temperatures. Depending on their chemical composition, some of these steels can undergo a phase transformation from austenite to a¢-martensite during deformation. This so-called transformation-induced plasticity effect (TRIP) involves the enhancement of strength and ductility below the Md-temperature.[1] The TRIP effect is triggered by plastic deformation but is strongly affected by the stacking fault energy of a material.[2] At relatively high stacking fault energies (>30 mJ/m2), the material deforms substantially due to the movement of dislocations. Stacking fault energies between 20 and 30 mJ/m2 favor the emergence of R. ECKNER, Research Associate, Doctoral Student, and L. KRU¨GER, Full Professor, Head of Institute, are with Technische Universita¨t Bergakademie Freiberg, Institute of Materials Engineering, Gustav-Zeuner-Str. 5, 09599 Freiberg, Germany. Contact e-mail: [email protected] B. REICHEL, Research Associate, Doctoral Student, is with Technische Universita¨t Bergakademie Freiberg, Institute of Materials Science, Gustav-Zeuner-Str. 5, 09599 Freiberg, Germany. A.S. SAVINYKH, Research Associate, Doctoral Student, S.V. RAZORENOV, Full Professor, Head of Laboratory, and G.V. GARKUSHIN, Full Professor, Head of Institute, are with the Russian Academy of Sciences, Institute of Problems of Chemical Physics, Chernogolovka, Moscow Region 142432, and also with the National Research Tomsk State University, Tomsk, 634050, Russia. Manuscript submitted July 31, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
deformation twins [twinning induced plasticity (TWIP)]. In steel with lower stacking fault energy, the TWIP and/ or TRIP effect is evident. Furthermore, due to the temperature dependence of the stacking fault energy as well as the driving force for the martensitic reaction DGcfia¢, martensite formation is also dependent on the temperature.[3] Both the temperature dependence and the strain-rate dependence of the mechanical properties are important factors. Rising strain rates up to ~103 s1 generally leads to a thermally activated increase in yield strength but a decrease in strain hardening, due to the adiabatic heating of the specimen.[4–7] When the strain rate is further increased beyond 104 s1, the loading is characterized by the propagation of elastic and plastic waves through the material. The deformation over the entire specimen can no longer be considered as an equilibrium, because stresses are transferred from one atom to another, similar to a pulse with a length of only a few nanoseconds. The shock pulse also induces an expansion wave, at which point the material returns to ambient pressure. These so-called rarefaction or release waves generate a material flow against the direction of wave propagation. Unlike in a fluid, energy dissipation occurs during wave propa
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