In addition to possessing sufficient strength—particularly yield strength—low alloy high-strength steel also offers excellent workability, 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 highly susceptible to various types of cracking, such as cold cracks, hot cracks, and lamellar tears. Furthermore, during the welding thermal cycle, the microstructure of the HAZ undergoes changes, increasing the likelihood of brittle fracture, especially in thick plate structures. Therefore, the primary challenges in welding these steels involve preventing cracking and enhancing the toughness of the welded joint.
To achieve this, several key measures should be taken:
1. The welding wire must be cleaned and dried thoroughly, with a drying temperature ranging from 350 to 400°C.
2. Preheating and interpass temperatures must be strictly controlled. Preheating should be done using a flame heater or electric heating pad, covering an area on both sides of the weld groove. The width of the preheated area should be at least 1.5 times the thickness of the material and not less than 100 mm. The temperature between passes should be maintained below 250°C and not lower than the minimum preheating temperature.
3. Use multi-pass welding with a medium welding current to ensure proper penetration and control of heat input.
4. Slightly increase the wire's dry extension while maintaining arc stability to improve weld quality.
5. Ensure the groove surface is clean before welding to avoid contamination that could lead to defects.
6. After hydrogen removal treatment, the temperature should be set between 200–250°C. The holding time should be at least 0.5 hours depending on the thickness of the component, with a total duration of no less than 1 hour. Once the holding time is reached, the part should be slowly cooled to ambient temperature.
Common welding methods and equipment used for high-strength steel in steel structures include:
1. **SMAW (Shielded Metal Arc Welding)**: Primarily used for auxiliary welds in steel structure fabrication. Common electrodes include CJ607RH, CJ707RH, CJ807RH, and CJ107.
2. **SAW (Submerged Arc Welding)**: Ideal for main welds in structural steel production. Matching wires and fluxes are H10Mn2/SJ101 and H08MnA/HJ431. Equipment includes MZ-1000/1250, LHC cantilever, and LHE box-type three-wire submerged arc welders.
3. **GMAW (Gas Metal Arc Welding, COâ‚‚ Shielded)**: Used for primary and secondary welds in field installations. Common wires are WH50-6, WH60-G, WH70-G. Equipment like NBC-500, KRII500, and XQ15 gas shielded welders are typically used.
4. **FCAW-G (Flux-Cored Arc Welding, COâ‚‚ Shielded)**: Suitable for on-site welding of primary and secondary joints. CHT711 flux-cored wire is commonly used.
5. **ESW (Electro-Slag Welding)**:主è¦ç”¨äºŽç„ŠæŽ¥ç®±åž‹æž„件的肋æ¿ã€‚常用焊ä¸å’Œç„Šå‰‚为WH50-6å’ŒJF600，设备多为XSD15悬臂å¼ç”µæ¸£ç„Šæœºã€‚
6. **SW & SW-P (Stud Welding)**: Used for bolting stiffeners and penetration welding of floor plates.
For more detailed information, please refer to the attached document or read the 18th issue of *Metalworking (Hot Processing)*.
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