Effect of welding on microstructure and mechanical response of X100Q bainitic steel through nanoindentation, tensile, cyclic plasticity and fatigue characterisation

This paper presents an experimental characterisation of fatigue at welded connections for the next-generation high-strength low-alloy offshore riser steel, X100Q. An instrumented girth weld is conducted with a parallel programme physical-thermal simulation (Gleeble) to develop heat affected zone (HAZ) test specimens. X100Q shown exhibit superior performance current state art X80. Significant differences are demonstrated between parent material and simulated HAZ in terms hardness, monotonic strength cyclic plasticity response, which can be related observed microstructural transformations: refined grain bainitic block size fine-grained give harder stronger response than material, whereas coarsened lath structure intercritical gives softer weaker response. The materials metal. A significant reduction life cross-weld specimens, indicating susceptibility failure due softening matched or over-matched welds.