Weldability Investigations of Low Carbon Microalloyed Heavy Plate Steel Grade P460NL1 for Liquid CO₂ Storage Tanks

Large‐scale steel storage tanks for liquid CO 2 are critical elements in Carbon Capture and Storage infrastructure. This study investigated the weldability and mechanical performance of 34 mm thick joints made from cold‐resistant microalloyed steel grade P460NL1. The main welded joints are produced using automatic submerged arc welding (SAW 121‐2) with a V‐groove and heat input of 1.5 ± 0.1 kJ mm −1 . Microstructural analysis revealed stable zoning with bainitic structures, maximum hardness of 222 HV 5 , and microhardness values not greater than 323 HV 0.3 in the heat‐affected zone (HAZ). In the as‐welded condition, Charpy impact energy exceeded 186 J at −40 °C and remained above 88 J at −50 °C. Post‐weld heat treatment increased yield strength from 452–453 MPa to 465–468 MPa, while slightly reducing tensile strength and impact energy in the fusion line. Additional weldability tests included controlled thermal severity and bead‐on‐plate welding tests, both confirming the absence of cracking and acceptable HAZ hardness. Strain aging tests showed retention of ductile behavior down to −60 °C. High‐temperature tensile testing up to 450 °C confirmed structural stability over a wide operating range. These findings support the use of P460NL1 steel for high‐integrity welded structures in demanding CO 2 storage conditions.