Characterization of a precrept modified 9Cr-1Mo steel through room temperature tensile and strain rate change tests

A Nb-V containing 9Cr-1Mo ferritic steel was allowed to age under creep conditions in the temperature range of 873-973 K. its microstructure in normalized and tempered condition contained tempered martensite with well recognized laths. However. under high stress creep conditions at 973 K. cell walls and dislocation clusters are formed. A cellular structure develops instead with cell walls being formed at carbides. These microstructural features are reflected in their subsequent room temperature deformation behavior, which was studied through an analysis of strain rate change (SRC) tests and stress-strain curves. In the new analysis, Cottrell-Stokes (C-S) ratio and modified Haasen plots are derived to study the nature of thermal obstacles and component internal stresses. SRC results are used also to estimate long-range internal stresses, which are interpreted to be associated with cell walls. dislocation clusters etc. The nature of variation of activation area, long range stress, and work hardening rate as determined from room temperature tensile tests carry sufficient information to suggest a methodology for evaluating the damage state of the parent service exposed material. (C) 2001 Elsevier Science B.V. All rights reserved.