Austenitic Fe-20% Mn alloys with the shape memory effect (SME) were studied. The alloys contained different carbon concentrations and were doped with V and Mo so as to achieve the maximum strengthening. It was shown that the contribution of the precipitation hardening depended strongly on the carbon concentration, the number of carbide-forming elements, and the temperature-and-time parameters of aging. The SME was controlled by stabilization and destabilization of the austenite with respect to the formation of the epsilon-martensite. For this purpose, conditions of formation of V(Mo)C carbides were adjusted. (c) 2007 Elsevier B.V. All rights reserved.

Changes in the structure, mechanical properties, kinetics of martensitic transformations, and amount of reversible deformation in precipitation-hardening high-strength shape-memory steels (20Mn-2Si-V with 0.2–1.0% C) strengthened as a result of carbide aging, intense warm deformation, and rapid crystallization from the melt have been studied.

Transmission electron microscopy is used to study and analyze the twin and dislocation structures of commercial-purity uranium samples in the initial (undeformed) state and after severe deformation induced by shock loading by plane waves with various intensities. As the shock loading intensity increases, the density of chaotically distributed dislocations and twins first increases, and, then, polygonization processes develop and result in a subgrain structure. Crystallographic analysis of the initial and deformation twins in uranium reveals predominant twins of the compound type {130} and rare {172} and {176} second-type twins.

The magnitude of the shape memory effect can be controlled (by the γ–ɛ–γ transformation) between 0.5 and 2.4% in precipitation-hardening high-strength 20Mn–2Si–V–C steels (numbers indicate mass%) with 0.2–1.0mass% C subjected to stabilizing (650°C) and destabilizing (720°C) carbide aging. The steels retain their strength and plasticity. When austenitic steels are alloyed with 14% chromium, they fall into the class of precipitation-hardening stainless steels. Their shape memory effect and strength characteristics are impaired.

A new approach to creation of high-strength manganese austenitic steels with a controlled shape-memory effect was realized as a result of carbide dispersion hardening. The formation of VC nanocarbides differing in dispersity stabilizes or destabilizes austenite with respect to the formation of deformation-induced ɛ martensite, which makes it possible to control the magnitude of shape-memory effect and the degree of strengthening.

The structure, values of the shape memory effect (SME) and mechanical properties of austenitic manganese steels, which are strengthened by precipitation of nanosized vanadium carbides under different aging conditions at 600–720 °C, have been analyzed. The formation of VC carbides having different degrees of dispersion can stabilize or destabilize the austenite relative to the formation of the strain-induced ɛ-martensite. Therefore, it is possible to control both SME and the degree of hardening. Large SME (2–2.5%) and high-strength characteristics (σ0.2 ∼ 1000 MPa) were obtained for the steels studied.