The microstructure of the weld zone of S355J2W steel welded joints air-cooled is composed of coarse columnar ferrite, network ferrite, acicular ferrite and a small amount of pearlite, and the microstructure of the heat-affected zone is composed of fine and uniform ferrite. Composed of ferrite and pearlite, the microstructure of the base metal zone is composed of banded ferrite and pearlite. After the S355J2W steel is annealed, the microstructure of each region tends to be homogeneous, the number of pearlite increases, and the banded microstructure of the base metal is significantly improved.
S355J2W steel welded joints have good mechanical properties, and the strength of the joint is higher than that of the base metal. Compared with the annealing treatment and air cooling treatment, the strength of the joint after annealing treatment is reduced by 2.04%, and the elongation after fracture is increased by 11.71%. The impact toughness of the heat-affected zone and the base metal increased by 18.2%, 15.5%, and 5.2%, respectively.
The hardness distribution of the welded joint of S355J2W steel presents a double-peak shape along both sides of the center of the weld, and the peak appears in the heat-affected zone. The regional hardness decreased by 5.95% on average, the peak value decreased by 10.1%, and the base metal decreased by 2.98% on average.
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