In addition to possessing sufficient strength—primarily yield strength—low alloy high-strength steel also offers excellent formability, weldability, and corrosion resistance. Compared to low carbon steel, the heat-affected zone (HAZ) of low-alloy high-strength steel is more prone to hardening and exhibits a strong sensitivity to hydrogen. When subjected to significant stress, welded joints are more likely to develop various types of cracks, such as cold cracks, hot cracks, and lamellar tears. Moreover, during the welding thermal cycle, the microstructure of the HAZ changes, increasing the risk of brittle fracture, especially in thick plate structures. Therefore, the main challenges in welding these steels involve preventing cracking and improving the toughness of the welded joint.
To achieve this, several key measures must be taken:
1. The welding wire should undergo oil removal and drying treatment, with a recommended drying temperature of 350–400°C.
2. Preheating and interlayer temperature must be strictly controlled before welding. Preheating can be done using a flame heater or electric heating pad. The preheating area should extend at least 1.5 times the thickness of the workpiece and a minimum of 100 mm on both sides of the weld groove. The interlayer temperature should not exceed 250°C and must not fall below the minimum preheating temperature.
3. Multi-pass welding with a moderate welding current is recommended to ensure proper fusion and minimize distortion.
4. The wire's dry elongation should be appropriately increased while maintaining a stable arc.
5. The groove surface must be thoroughly cleaned before welding to remove any contaminants that could affect the weld quality.
6. After welding, a hydrogen elimination treatment should be performed. The temperature for this process should range between 200–250°C, with a holding time of at least 0.5 hours based on the workpiece thickness. The total holding time should not be less than 1 hour, followed by slow cooling to ambient temperature.
Common welding methods and equipment used for high-strength steel in steel structures include:
1. **SMAW (Shielded Metal Arc Welding)**: Typically used for secondary welds in steel structure fabrication. Common electrodes include CJ607RH, CJ707RH, CJ807RH, and CJ107.
2. **SAW (Submerged Arc Welding)**: Ideal for primary welds in structural steel production. Matching wires and fluxes include H10Mn2 with SJ101, and H08MnA with HJ431. Equipment such as MZ-1000/1250, LHC cantilever, and LHE three-wire submerged arc welding machines are commonly used.
3. **GMAW (COâ‚‚ Gas Shielded Welding)**: Used for primary and secondary welds in field installations. Common wires include WH50-6, WH60-G, and WH70-G. Equipment like the Austrian NBC-500, Panasonic KRII500, and XQ15 gas shielded welder are frequently utilized.
4. **FCAW-G (COâ‚‚ Flux-Cored Wire Welding)**: Suitable for on-site welding of primary and secondary welds. CHT711 is a commonly used flux-cored wire.
5. **ESW (Electro-Slag Welding)**: Primarily used for welding box section ribs. Common materials include WH50-6 wire and JF600 flux. The XSD15 cantilever electro-slag welding machine is often employed.
6. **SW and SW-P (Stud Welding)**: Used for bolting stiff components and penetration welding of floor panels.
For further details, please refer to the attached document or read the 18th issue of *Metalworking (Hot Processing)*.
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