Key elements and their roles
Cu: Enriches in the inner rust layer, promotes the formation of a dense, adherent rust layer and enhances passivation, thus retarding corrosion .
Cr: Partially substitutes Fe in α‑FeOOH, refining the rust layer structure and improving its stability and protectiveness .
P: Accelerates the formation of a non‑crystalline/colloidal ferric hydroxide film, enhancing uniform corrosion resistance in the atmosphere; however, its content must be controlled to avoid embrittlement .
Ni: Improves low‑temperature toughness and mitigates hot cracking risks associated with Cu segregation during hot rolling, but its direct contribution to weathering is limited .
Remarks
These elements work synergistically to form a stable, protective rust layer that reduces the corrosion rate in outdoor environments .
For specific product grades (e.g., Q355NHA/B/C/D/E), the target ranges of these elements may vary slightly according to GB/T 4171‑2008.
