Cold Cracking Sensitivity of Different Strength Matching Backing Welding Joint of X80 Steel

By using low-strength, equal-strength and high-strength matching low-hydrogen covered electrodes, backing welding was conducted on X80 steel plate under 80 ℃ preheating and with U groove and oblique Y groove. The section crack rate of the joint was calculated, and the Vickers hardness was measured. The cold cracking sensitivity of the backing welding joint with equal-strength and high-strength matching electrodes was evaluated. The results show that the cold crack sensitivity coefficient of the covered electrode increased with increasing its strength grade, but no cracks were found on the surface and section of the weld, whose section crack rate was 0, indicating that the cold cracking sensitivity did not increase with increasing covered electrode strength. Comparing with that by low-strength matching covered electrode backing welding, the hardness of the heat-affected zone by equal-strength and high-strength matching covered electrode backing welding did not increase significantly, namely the hardening tendency did not increase significantly, and the cold cracking sensitivity was not intensified. Equal-strength and high-strength matching covered electrodes could be used for backing welding of X80 steel.