Identifying the Creep Deformation Mechanism in P9 Steel at Elevated Temperatures

Elevated temperature plastic deformation in metallic alloys and solids is often governed by various and alternative competing mechanisms such as diffusional flow, dislocation glide, and climb processes. In order to identify the creep deformation mechanism operating in P9 steel, creep rupture tests were carried out at 793 and 873 K employing stresses in the range of 50–300 MPa. Stress dependence of steady-state creep rate obeyed power law and exhibited two-slope behaviour characterised by different values of stress exponent and activation energy in the low and high stress regions. However, by invoking back stress concept, the variation of temperature compensated minimum creep rate with modulus compensated effective stress yielded single-slope power law behaviour with stress exponent of 4 and a true activation energy close to self-diffusion of iron. These observations suggested that the creep deformation in P9 steel is governed by climb of dislocations.