[en] A new stress annealing device applied to Fe base nanocrystalline ribbon is presented. It is based on three stages of very different tensile stress level, able to produce continuously a low and well-controlled μ_r ribbon, with surprisingly reduced brittleness allowing further winding into core for application such as watt-hour-metering or inductance coil. For such applications we have paid attention to the B-H linearity which may be optimized with the help of process parameters such as stress and annealing temperature, their role being described by an additional interphase magnetoelastic term. The stress participates also to the nucleation and is thought to be the cause of brittleness improvement in troubling SiFe ordering and promoting nucleation rather than growth