1. Pre-Weld: Material & Preparation Quality Control (Fundamental Step)
Strictly match weathering welding materials: Use GB standard dedicated weathering steel welding wires/electrodes (no ordinary carbon steel materials), e.g., MMA electrode E5015-G, MIG/TIG wire ER50-G, submerged arc welding wire H08Mn2SiCuA + flux SJ101; ensure materials are dry and free of rust/oil (baking electrodes at 300~350℃ for 1~2h if damp).
Precise surface cleaning: Remove oil, grease, rust, scale and paint from 10~20mm on both sides of the weld joint via sandblasting, wire brushing or acetone degreasing; ensure the surface is dry (moisture <0.05%) to avoid hydrogen-induced porosity and cold cracking.
Reasonable joint design: Adopt simple, weathering-friendly joint forms (butt, lap, fillet weld) with smooth transitions; avoid complex closed joints (easy to trap water/air) and ensure weld joints have drainage channels; the weld groove size follows GB/T 985 standard (matching plate thickness).
Environmental & equipment check: Weld only in dry environments (humidity ≤80%), no rain/snow/wind direct blowing (use welding tents for on-site construction); calibrate welding equipment (current, voltage, wire feed speed) in advance to ensure stable operation.
2. Welding Process: Precise Parameter & Operation Control (Core Step)
Classified heat input control (by plate thickness): The core to avoid weld zone softening, grain coarsening and deformation; strictly follow low heat input principles:
Thin plates (3~12mm): TIG/MIG/laser welding, current 80~150A, voltage 18~28V, fast travel speed (5~10cm/min), single-pass welding (no multi-pass overheating).
Medium/heavy plates (14~100mm): Preheat the base material to 80~150℃ (interpass temperature ≤250℃); use small-diameter electrodes/wires (2.5~4.0mm), multi-pass welding (each pass weld bead thin), and control single-pass heat input ≤15kJ/cm; MMA welding current 100~220A, submerged arc welding current 300~500A.
Standard welding operation: Adopt straight-line or slight oscillating welding (no large amplitude oscillation); ensure full weld penetration (no incomplete fusion/penetration); remove welding slag and spatter after each pass (for multi-pass welding) to avoid inclusions in the next pass.
Avoid continuous long-time welding: For heavy plates, take intermittent welding to reduce heat accumulation and residual stress; the welding direction is consistent to avoid uneven stress distribution.
3. Post-Weld: Timely Treatment & Stress Control (Guarantee Step)
Immediate surface treatment: Grind weld seams, heat-affected zones (HAZ) and cutting edges to remove spatter, burrs, undercutting and slag; make the weld surface smooth (no sharp corners) to eliminate corrosion initiation points; passivate the weld zone with a non-chromate passivation solution, or brush a thin transparent weathering sealer (temporary protection for initial oxidation).
Rational residual stress relief: No high-temperature heat treatment (≥600℃, will destroy the alloy microstructure); only for heavy plates (≥50mm) with large weld joints, adopt low-temperature stress relief (150~200℃ for 1~2h) or mechanical vibration stress relief; avoid rapid cooling of the weld zone (naturally cool to room temperature in air, no water cooling).
Anti-corrosion protection for fresh welds: For welding in coastal/salt-spray/industrial environments, clean the weld zone with dry air immediately after welding, and apply a temporary anti-rust agent to prevent salt mist/acid mist corrosion before patina formation.
4. Weld Quality Inspection: Multi-Dimensional Testing (Final Step)
Visual inspection (100% mandatory): Check weld appearance for no visible defects (porosity, inclusions, cracks, incomplete penetration, undercutting >0.5mm); weld bead is uniform, and the weld size (height, leg length) meets design requirements.
Non-destructive testing (for load-bearing structural components): UT (ultrasonic testing) for internal defects (no internal cracks/inclusions); MT (magnetic particle testing) for surface/near-surface defects (for thick plates/weld joints under dynamic loads); testing coverage ≥20% for general structural parts, 100% for key load-bearing parts.
Mechanical performance sampling inspection (batch): For mass production, sample weld joints to test tensile strength, yield strength and low-temperature impact toughness (KV ≥27J at -20℃); ensure the weld joint mechanical properties are not lower than 90% of the base material.
Corrosion resistance verification (optional): For high-demand projects, conduct a neutral salt spray test on the weld zone; the corrosion rate should be consistent with the base material (no obvious accelerated rusting).
