Lüders strain and ductility of ordered Fe–Co–2V and Fe–Co–V–Ni alloys

The effect of thermomechanical treatment on tensile properties has been measured in ordered Fe–Co–2V and Fe–Co–V–Ni alloys containing up to 7·4 wt-%Ni. The aim was to determine the microstructural features affecting the Lüders strain and ductility of these alloys. The dominant microstructural feature was found to be the grain or subgrain size, which was determined by the volume fraction of γ phase present. The extent of the Lüders strain decreased with increasing grain size but the ternary and quaternary alloys showed different grain size dependences. The ductility of all the alloys was proportional to d^−1/2, where d is the grain, subgrain, or deformation cell size.