Research on the Static Strain Aging Mechanism and Characteristics of High-Grade X80 Pipeline Girth-Welded Joints

To investigate the effects of static strain aging on girth-welded joints of high-grade steel pipes, base metal, gas-shielded weld, and non-gas-shielded weld samples were extracted from X80 pipeline girth welds. The three types of samples were subjected to different prestrains, unloaded, aged at various temperatures in an environmental chamber for 1 h, and then reloaded to failure under multiple working conditions. Fracture microscopy and energy spectrum analysis were performed. Results show that static strain aging significantly alters the stress–strain response and mechanical parameters of all three materials, characterized by yield plateaus in stress–strain curves, increased yield strength, and reduced ductility. Under the study conditions, aging temperature has a greater influence than prestrain. The base metal exhibits more pronounced strain aging than weld metals under the same aging conditions, primarily due to the competitive effect and inhibition of aging elements in the material. Fracture microscopy and energy spectrum analysis reveal a correlation between the macroscopic mechanical properties of static strain-aged girth welds and microstructural changes as well as element contents.