Study on Mechanical Properties of Welded Joints of X80 Pipeline Steel under Different Service Temperatures

In order to address the issue of brittle crack initiation in the weld zone and heat-affected zone（HAZ） of X80 pipeline steel in extreme hot or cold enrironment, the effects of different service temperatures（-30 ℃, 25 ℃ and 60 ℃） on the mechanical properties of X80 pipeline steel GMAW welded joints were studied. The welded joints were treated hot and cold and examined for mechanical qualities like microstructure analysis, microhardness, and fracture toughness, simulating the real temperature of X80 pipeline steel operating conditions. The study reveals that: service temperature has an impact on the fracture toughness of X80 pipeline steel; at-30 ℃, the temperature of the steel is 15.62% lower than the fracture toughness at 25 ℃, and at 60 ℃, the fracture toughness of the steel is 6.23% higher than that of the fracture toughness at25 ℃. The microhardness of X80 pipeline steel is not significantly affected by service temperature, and there is less than a10% variation in microhardness between temperature conditions. There is minimal grain size variation at varying service temperatures in the two-phase mixture of ferrite and bainite that makes up the microstructure at the core of the weld. The size of the dimples in the fracture morphology grows and becomes denser as the service temperature rises, and the toughness steadily increases.