Abstract: Microstructure, tensile properties and low-temperature impact properties of a 12 mm thick 09MnNiDR steel submerged arc welding butt welded plate were analyzed by means of optical microscope, tensile testing machine, impact testing machine and micro Vickers hardness tester after annealing, normalizing and normalizing+tempering treatments. The results show that normalizing treatment can improve the strength of the 09MnNiDR steel welded joints, but compared with stress relief annealing, it reduces the toughness. After normalizing and tempering treatment, the welded joint has good plasticity and toughness, which is related to the decomposition of M/A components at the weld seam and the evolution of granular bainite in the heat affected zone. Under three heat treatment methods (annealing, normalizing, normalizing+tempering), the M/A components at the weld seam are decomposed to varying degrees, resulting in an increase of impact absorbed energy. The impact absorbed energy after normalizing and tempering is the highest, increasing by 84% compared to the welded. Compared with the welded joint, normalizing slightly increases the hardness of the weld zone and heat affected zone, while annealing and normalizing + tempering make the hardness reduce. The granular bainite in the heat affected zone after normalizing is beneficial for improving hardness, while the more uniform microstructure after tempering makes the welded joint obtain better toughness.

Key words: 09MnNiDR low temperature steel, welded joint, post-weld heat treatment, microstructure, mechanical properties