Ferrous shape memory alloys do not have complete shape recovery. Several attempts to improve the shape recovery still fail to achieve 100% recovery. For some applications, however the recovery stress under constraint is more important. A procedure was designed to measure the stresses under constraint in a Fe30MnSiCr SMA.

The net recovery stress can be defined as the maximum in the difference between the stresses of a deformed and of an undeformed sample. The calculation of σ = E*α*ΔT can replace the stresses obtained of the undeformed sample.

The effect of partial free recovery before recovery under constraint is also investigated. It was remarkable that after the annealing at 200°C, the net stress did not decrease although ~50% of the shape recovery has happened. This gives a good opportunity for the use as pipe joint. It means that the diameter of the joint can be larger than the pipes and that the free recovery will not result in a lowering of the recovery stresses under constraint.

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