Abnormal toughness characteristics and fracture model in simulated welding HAZ of 5%Ni Steel

The toughness property of the coarse grained heat affected zone had become much worse since the large heat input welding was applied in HSLA for improving welding efficiency and reducing welding costs. Unlike previous investigations of the decreasing fracture toughness with heating time, the toughness of coarse grained heat affected zone increases in long heating time. Based on microstructure and mechanical properties, very remarkable impact toughness was obtained when the t8/5 was 80 s: toughness of 171 J. The toughness improvement initiates not from inclusions but directly from the microstructure of substrate. The microstructure type and inclusion level will compete to dominate the toughness of the 5% Ni steel.