The test material is 12mm thick S355J2W weathering steel, using MAG welding (melting electrode active gas shielded arc welding) multi-layer multi-pass welding process, the shielding gas is 80% Ar+ 20% CO2 mixed gas, the joint form is butt joint, V-shaped groove , the bevel angle is 60°, the welding gap is 2 mm, and the blunt edge is 1 mm
S355J2W weather-resistant steel adopts stress relief annealing treatment and air cooling treatment after welding. Among them, the annealing temperature is 550 °C ± 15 °C, the holding time is 2.5 h, after cooling to 300 °C with the furnace, take it out and air cool to room temperature.
The impact toughness of the weld zone is the lowest, because the columnar grain structure of the weld is composed of side lath, acicular ferrite and bainite with higher hardness, and the higher the strength, the lower the toughness; the impact toughness of the heat-affected zone is the highest. , which is the result of fine-grain strengthening.
The notch of the impact sample is opened in the normalizing zone with fine grains. The fine grains increase the total area of the grain boundaries, reduce the concentration of impurities on the grain boundaries, and reduce the possibility of brittle fracture along the grains. At the same time, the grain boundaries hinder It can reduce the expansion of the crack tip, reduce the accumulation of dislocations in front of the grain boundary, reduce the stress concentration, and improve the toughness of S355J2W weathering steel.
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