Welding Q355B requires processes and consumables that produce high-quality, ductile welds with sufficient strength and toughness to match the base metal, while minimizing the risk of hydrogen-induced cold cracking.
Recommended Welding Processes:
1. Shielded Metal Arc Welding (SMAW): Commonly used for site erection and repair. Must use low-hydrogen basic electrodes (EXX15, EXX16, EXX18 series). Electrodes must be properly baked and stored in a heated quiver per manufacturer's instructions.
2. Flux-Cored Arc Welding (FCAW): Popular for shop fabrication due to high deposition rates. Use gas-shielded (FCAW-G) or self-shielded (FCAW-S) wires classified as low-hydrogen.
3. Submerged Arc Welding (SAW): Excellent for automated, long seam welds in fabrication shops. Provides high quality and good penetration.
4. Gas Metal Arc Welding (GMAW/MIG): Widely used with a mixture of Argon and CO2 shielding gas. Provides good control and quality. Consumable Selection: The filler metal must have a specified minimum tensile strength matching or slightly overmatching the base metal. For Q355B (Rm 470-630 MPa), common consumable classifications are: AWS A
5.xx / Equivalent GB Standards: SMAW: E5015, E5016, E5018 (50 ksi ~ 490 MPa UTS). FCAW: E71T-1, E81T1-Ni1. GMAW: ER70S-6 (480 MPa UTS). SAW: Wire/Flux combinations like F48A0-H08A. The critical factor is the diffusible hydrogen content of the deposited weld metal. It should be designated as H5 or lower (i.e., ≤5 ml/100g of deposited metal) to minimize cracking risk. Welding Procedure Specifications (WPS): A qualified WPS is essential. It must define parameters (current, voltage, speed), preheat/interpass temperature (based on CEV, thickness, and restraint), and post-weld treatment if needed. For thick sections or high restraint, preheating to 50-150°C is often required. Proper joint preparation, cleaning (free of rust, oil, moisture), and welding sequence to minimize distortion are also crucial.