The corrosion resistance of Q460NH welded joints may degrade over time depending on environmental exposure and welding quality, but proper techniques can minimize this risk. Here's a detailed breakdown:
1. Factors Affecting Corrosion in Welded Joints
Heat-Affected Zone (HAZ) Vulnerability:
The HAZ undergoes microstructural changes (e.g., grain coarsening), making it more prone to localized corrosion than the base metal.
Patina formation in the HAZ is slower and less uniform.
Weld Metal Composition:
If filler metals (e.g., AWS E7018) don't match Q460NH's weathering properties, the weld may corrode faster.
Environmental Exposure:
Coastal/industrial areas (high Cl⁻/SO₂): Accelerated pitting at weld seams.
Stagnant water/dirt traps: Crevice corrosion in poorly designed joints.
2. Long-Term Performance Data
Atmospheric Exposure:
After 10–15 years, weld zones in mild environments (C2–C3) show 10–20% deeper corrosion vs. base metal.
In coastal (C4–C5) environments, corrosion rates at welds can be 2–3× higher.
Critical Observations:
Weld toe cracks and pitting are common failure points.
Properly executed welds with weathering-compatible fillers exhibit >75% of base metal's corrosion resistance.
3. Mitigation Strategies
Welding Best Practices:
Use weathering steel-specific electrodes (e.g., AWS E8018-W2).
Post-weld grinding to smooth transitions and remove slag inclusions.
Protective Measures:
Apply weathering steel primers (e.g., zinc-rich coatings) to welds in aggressive environments.
Design joints to avoid water/dirt accumulation (e.g., continuous welds, no overlaps).
Inspection & Maintenance:
Annual visual checks for rust bleeding or pitting.
Ultrasonic testing (UT) every 3–5 years for hidden cracks.
4. Standards & Testing
ISO 14713: Guidelines for protecting welded weathering steel.
ASTM G48: Pitting resistance testing of weldments.
