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[en] Commercial grades of Fe-Cr-Ni austenitic stainless steels are metastable at low temperatures. Most of these steels do not transform on cooling, but do transform during deformation. Stress-strain curves reflect the transformation characteristics. There are typically three distinct stages of the stress-strain curve of polycrystalline Fe-Cr-Ni alloys at low temperatures. The stress-strain characteristics are discussed with respect to martensitic transformation

[en] The microstructure and mechanical properties of several Ni-Al-Hf alloys in the composition range between NiAl(β) and Ni₂AlHf (Heusler phase) have been studied. The volume fraction of Heusler phase, V_f, in these alloys varies from about 15 to 96%. The lattice misfit between the β and Heusler phases in two-phase alloys is larger than 5%, indicating no coherency between them. The yield strength increases with increasing V_f at all temperatures to 1000 degree C. Compressive ductilities of 4 and 7% were obtained for the alloy with V_f of 15% at room temperature and 500 degree C, respectively, but they decreased to 0% with increasing V_f to 96%. The corresponding fracture mode is basically transgranular cleavage. However, all the alloys can be deformed extensively without fracture at 1000 degree C. The hardness of the Heusler alloy is very high (8.3 GPa) at room temperature, and it decreases gently with temperature to 600 degree C, followed by a rapid decrease to 1000 degree C. The brittleness and high hardness of the Ni₂AlHf Heusler phase at low temperatures are interpreted in terms of internal lattice distortion resulting from its crystal structure. The thermally activated process of deformation takes place above 600 degree C, which is responsible for the rapid drop of the hardness of the alloys

[en] Recent studies have suggested the possibility of three anomalies in the temperature dependence of the flow strength Fe-Cr-Ni and Fe-Cr-Ni-Mn austenitic stainless steels. Reduction of flow strength at decreasing temperature may be associated with the onset of martensite transformation, the magnetic transition at the Neel temperature, and low temperature dislocation dynamics. The tensile flow strength was investigated in the temperature range 4 to 295 K for two annealed polycrystalline alloys: Fe-20Cr-16Ni-6Mn-0.2N steel (produced in the USSR) and Fe-18Cr-10Ni-0.1N steel (AISI 304LN). The former alloy is stable with respect to strain-induced martensitic transformations, the latter metastable

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[en] We determined experimentally the effect of manganese on the elastic constants of Fe-Cr-Ni alloys. By a pulse-echo-overlap method, longitudinal and transverse sound-wave velocities were determined in ten alloys containing up to six percent Mn. All the elastic stiffnesses decreased linearly with increasing Mn. The bulk modulus decreases most strongly. Poisson's ratio changes least. We consider what the elastic constants reveal concerning changes in chemical bonding

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