Q550NH weathering steel is primarily supplied in the hot-rolled condition, as cold-rolling is generally unsuitable for this high-strength structural steel. Here are the key details:
1. Standard Manufacturing Process
Hot-Rolled (HR):
Produced at temperatures >900°C, followed by controlled cooling (TMCP or normalizing).
Standard delivery form for plates, sections, and tubes per GB/T 4171.
Why Not Cold-Rolled?
Cold-rolling would compromise Q550NH's weathering properties (disrupts alloy segregation needed for patina formation).
Cold-work hardening would reduce ductility and weldability.
2. Post-Rolling Treatments
Thermomechanical Controlled Processing (TMCP): Combines hot-rolling with accelerated cooling to refine grain structure.
Normalizing: Optional for thicker sections to homogenize microstructure.
3. Surface Characteristics
Hot-rolled Q550NH has a mill scale (removed via sandblasting if painting is required).
Cold-rolled alternatives (e.g., thin sheets) would use conventional steels, not weathering grades.
