Microstructure and creep behaviour of P92 steel after HPT

The influence of the application of severe plastic deformation on microstructure changes and creep deformation behaviour was investigated in P92 creep-resistant pipe steel. P92 steel in its as-received state, with a microstructure typical of tempered martensite, was subjected to high-pressure torsion at room temperature. An investigation of the microstructure using an electron backscatter diffraction technique revealed that severe plastic deformation led to the subsequent formation of an ultrafine-grained microstructure, containing {110} fibre texture and randomly misoriented boundaries. The microstructure characteristics and hardness measurements exhibited saturated values at an equivalent strain of higher than about 20. The creep behaviour of the ultrafinegrained specimen produced in the saturated region exhibited a minimum creep rate that was about two orders of magnitude faster, and a larger creep ductility, in comparison with the as-received state. Creep exposure at 873 K with a time to fracture of about 3 h led to a slight grain coarsening and to the formation of Laves phase.