Research on the Microstructure and Properties of X80 Steel Circumferential Welds Under Different Automatic Welding Processes

Two sets of X80 pipes with a diameter of 1219 mm × 27.5 mm were welded using a fully automatic welding process (GMAW) and a combined automatic welding process (GTAW + FCAW-G), respectively. By analyzing the microstructure, strength, impact toughness, and fracture toughness of welded joints, the differences in microstructure and properties of circumferential weld joints under different automatic welding processes were studied. The results showed that the design of multi-layer and multi-pass welding and appropriate heat input controlled the microstructure of the weld seam and heat-affected zone area of the circumferential weld joint. Both automatic welding processes obtained welded joints with finer microstructure, thereby ensuring the strength and toughness of the joint. The tensile strength and yield strength of the welded joints under two automatic welding processes reach over 680 MPa and 600 MPa, respectively. The welded joints under both automatic welding processes have good impact toughness and fracture toughness at - 10 °C, with a ductile-brittle transition temperature below -50 °C and crack tip opening displacement (CTOD) values greater than 0.254 mm. The tensile strength, yield strength, impact toughness, and fracture toughness of the fully automatic welding ring weld joint are better than those of the combined automatic welding.