Stress–strain–temperature hysteresis and martensite start line in an Fe-based shape memory alloy

The uniaxial stress–strain–temperature hysteretic behavior in an Fe–9%Cr–5%Ni–14%Mn–6%Si polycrystalline shape memory alloy is investigated under successive tensile–compressive mechanical loading and thermal loading, especially in relation to the transformation lines; the martensite start line and the austenite start/finish lines on the stress–temperature plane. The form of the thermomechanical hysteresis loops, the strain recovery during heating after forward and reverse transformations induced by the mechanical loading and the recovery stress under strain-constrained heating are the points to be studied. The dependence of the martensite start stress on the extent of prior martensitic transformations is determined from the direct strain-recovery measurement during heating, which agrees well with the estimation by means of the reverse transformation lines coupled with the assumption of the `isotropicʹ hardening in transformation.