1. Strength
Q550NH: High strength (Yield strength ≥ 550 MPa, Tensile strength 630–800 MPa), suitable for heavy-load structures.
Q355NH: Medium strength (Yield ≥ 355 MPa, Tensile 490–630 MPa), balanced for general use.
Q235NH: Lower strength (Yield ≥ 235 MPa, Tensile 360–510 MPa), used in lightweight applications.
2. Corrosion Resistance
All grades form protective rust layers, but Q550NH often includes higher alloying elements (e.g., Cu, Cr, Ni) for enhanced corrosion resistance in harsh environments (e.g., coastal/industrial areas).
Q235NH/Q355NH may require longer stabilization for rust layer formation.
3. Weldability & Processing
Q550NH: Requires stricter welding controls (preheat/post-weld treatment) due to higher carbon equivalent (CE).
Q355NH/Q235NH: Easier to weld and process, with lower CE values.
4. Applications
Q550NH: Bridges, high-rise structures, mining equipment (where strength and corrosion resistance are critical).
Q355NH: Common construction, containers, railway vehicles.
Q235NH: Decorative façades, non-load-bearing components.
5. Cost
Q550NH is more expensive due to alloy content and processing complexity.
