Room temperature creep and strain-rate-dependent stress-strain behavior ofpipeline steels

Creep deformation and the effect of strain-rate on stress-strain behavior o f X-52, X-70 and X-80 pipeline steels at room temperature were studied usin g round tension test specimens. Depending on its chemical composition and t he processing condition (as-received or fully annealed), a pipeline steel m ay exhibit a stress-strain curve with or without a yield point. The as-rece ived and the annealed steels with both type of yielding behavior were creep tested at a constant stress either below or past the yield point / 0.2% of fset yield strength. Independent of yielding behavior, significant post-yie ld creep deformation was observed in all the steels. The pre-yield creep, h owever, is strongly dependent on the yielding behavior. In the presence of a yield point, only a minor deformation was detected in the steels subject to the pre-yield creep. In the absence of a yield point, pre-yield creep de formation occurred to a relatively large extent. For the latter case, an an nealing treatment further enhanced creep deformation. A strain-rate-depende nt stress-strain behavior was also observed in all thesteels that show sign ificant creep deformation. Dislocation mechanisms responsible for the creep behavior observed in the study are also provided in the paper. (C) 2001 Kl uwer Academic Publishers.