Room temperature creep deformation and its effect on yielding behaviour of a line pipe steel with discontinuous yielding

A study was conducted to understand post-yield creep behaviour and its effect on the subsequent tensile behaviour of X-52 line pipe steel at room temperature. As a result of the carbon-locking effect, this steel exhibits a distinct yield point followed by a range of discontinuous yielding. Although normally not observed during re-loading after the first yielding, there was a yield point during re-loading following the exhaustion of creep deformation at a stress equal to the lower yield strength. The re-appearance of the yield point after creep deformation is related to the dislocation locking effect, rather than a carbon locking effect. The creep deformation following the initial loading to the region of discontinuous yielding is dependent on both the initial loading strain rate and the initial loading strain. Higher loading strain rate results in a higher dislocation velocity and a larger number of mobile dislocations at the start of creep, causing larger creep deformation. Smaller initial loading strain causes more creep deformation, but the total strain including the initial loading strain and the subsequent creep strain is insensitive to the initial loading strain.