Microstructure and Property of New Ultra-high Strength Steel Joint Welded by MAG Welding using Different Welding Wires

A new ultral-high strength steel was welded by metal active gas (MAG) welding with Ni-Cr-Mo and Ni-Mo welding wires, respectively, under the same heat input. The microstructures and mechanical properties of the two welded joints were compared and studied. The anti-crack sensitivity of two joints welded with the two welding wires was assessed by the Y-groove cracking test. The results show that weld microstructure of the welded joint with Ni-Cr-Mo welding wire mainly consisted of coarse lath martensite and small amount of bainite, while that with Ni-Mo welding wire as composed of fine acicular ferrite and small amount of block proeutectoid ferrite. The high strength joint of the steel can been obtain by the MAG welding with the two welding wires. But the toughness of the welded joint with Ni-Mo welding wire was better than that with Ni-Cr-Mo welding wire and the softening phenomenon in tempering zone was observed in both welded joints. The crack resistance of the welded joint with Ni-Mo welding wire was better than that with Ni-Cr-Mo welding wire, and the cold crack fracture patterns of Y-groove welded samples with the two welding wires were mainly intergranular fracture and little transgranular fracture.