Abstract
The creep behaviour of P92 steel at 923 K, deformed by rotary swaging (RS) and high-pressure torsion (HPT), was investigated. The RS-processed state contained extremely inhomogeneous microstructure containing large elongated and fine, more or less equiaxed grains. By contrast, the HPT-processed state consists of homogeneous fine-grained microstructure. It was found that both the microstructures coarsen not only with the increasing creep time but also with creep strain. The creep strain significantly accelerates the coarsening of the microstructure, especially in the HPT-processed state. The grain coarsening during creep leads to the change of the creep rate stress exponent n thus to the change of creep mechanism. The value of n depends on the ratio grain versus stationary subgrain size. P92 steel processed by RS and HPT exhibited faster ⋵_min and higher ductility compared to coarse-grained (CG) state. However, RS-processed P92 steel can exhibit at high stresses similar creep behaviour as CG state.

Key words
creep-resistant 9% Cr steels, severe plastic deformation, creep, microstructure

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