Deformation and fracture behavior of the P91 martensitic steel at high temperatures

The stress relaxation behavior of the P91 martensitic steel is tested for the temperature range 400-600 °C in order to investigate the plastic deformation and fracture processes. The repeated relaxation tests are performed on the tensile specimens at the stress level of 95% of the ultimate tensile stress. The deformation mechanisms are analyzed in terms of an activation volume, dislocation density and velocity, a thermal stress component and a strain rate hardening. The deformation is driven by the dislocation glide. Short range interactions between dislocations and a lattice become dominant at the studied temperature range. The dislocations are able to overcome a pinning effect by the thermal activation at 600 °C.