Evaluation of Microstructural Factors of High Chromium Ferritic Steel Based on Analysis of Anelasticity Behavior at High Temperature

Deformation behavior after abrupt stress loading at 923 K was investigated on ASME-P92 steel in the as tempered condition and after creep. Anelastic deformation originated from elastic bending of lath boundaries occurs in the crept specimen as well as the steel in the as tempered condition. Instantaneous plastic strain after stress increment was not observed up to 200 MPa in the tempered and crept specimen, except for the specimen crept up to tertiary stage in which the instantaneous plastic strain occurs under higher stresses larger than 150 MPa. Magnitude of anelastic displacement after stress reduction decreases with creep deformation, indicating that contribution of lath boundaries to anelastic deformation is small in the crept specimens in contrast with the tempered specimen. Lath boundaries migrate and annihilate during creep, resulting in increase of lath width. Therefore, number of lath boundaries contributing to the anelastic deformation decreases with creep deformation, meaning that anelastic displacement of the crept specimens is lower than that of the tempered specimen. The anelastic displacement decreases with increasing lath width, indicating that evaluating the anelastic displacement can be used as an assessment of change of the lath structure during creep deformation.