Key Considerations
Technical Feasibility: HDG is compatible with Q355NH's alloy composition (Cu, Cr, Ni, P, etc.) when properly pre-treated (degreasing, pickling, fluxing) to remove oxides and contaminants before immersion in molten zinc. The high-temperature HDG process does not degrade Q355NH's core mechanical properties if post-dip cooling is controlled.
Performance Tradeoffs: Q355NH is designed to form a dense, stable α-FeOOH patina that self-heals and slows corrosion. HDG seals the surface with a zinc layer, blocking the patina's formation and self-healing mechanism. If the zinc layer is damaged, galvanic corrosion may accelerate localized substrate attack, especially in chloride-rich environments (e.g., coastal areas).
Cost & Application Rationale: HDG adds significant cost (material, processing, handling) to a steel grade already optimized for atmospheric corrosion. It is only justified in extreme, high-chloride, or aggressive industrial environments where the patina alone is insufficient, and a robust barrier coating is required. For most outdoor structures (bridges, facades, railings), relying on the natural patina is more cost-effective and reliable.
