Main disadvantages?
Highly sensitive to notches: Scratches/holes easily lead to stress concentration cracking.
Low-temperature toughness is inferior to Q355. Not a wear-resistant material, unsuitable for high-wear applications.
Corrosion resistance?
Standard for ordinary carbon steel, requires coating; the weather-resistant version Q345NQR2 contains Cu/P/Cr/Ni, improving corrosion resistance by 2-8 times.
Common failure modes?
Welding cold cracking, low-temperature brittle fracture, fatigue cracking, stress concentration cracking.
Surface treatment methods?
Rust removal (sandblasting/shot blasting), coating (anti-corrosion paint/fire retardant paint), hot-dip galvanizing (for high outdoor corrosion resistance requirements).
How to choose between Q355 and Q355?
Budget-sensitive, room temperature: Choose Q345B/C. Low temperature/high welding requirements, long-term reliability: Prioritize Q355C/D/E.