Effects of Grain Refinement and Predeformation Impact by Severe Plastic Deformation on Creep in P92 Martensitic Steel

Creep testing is conducted on an advanced martensitic‐ferritic creep‐resistant P92 steel (ASME Grade 92) to evaluate the effects of grain refinement and the predeformation impact after processing by severe plastic deformation (SPD), namely, by high‐pressure torsion and high‐pressure sliding. Constant‐load tensile creep tests are carried out in an argon atmosphere at 600 °C and under an applied stress ranging from 50 to 200 MPa. The results show that under the same creep loading conditions, the ultrafine‐grained (UFG) microstructure states after SPD processing exhibit higher minimum creep rate _m and creep fracture plasticity , but significantly shorter creep lives in comparison with the coarse‐grained (as‐received) state of the steel. These distinct differences between the coarse‐grained and UFG states are explained by the different deformation mechanisms that operate; creep behavior in a coarse‐grained state is controlled by the intragranular climb of dislocations, while creep in UFG states can be interpreted as the synergistic action of the dynamic recovery of free dislocations at high‐angle grain boundaries and grain boundary‐mediated deformation processes.