When cold bending Q500NH weathering steel, the following precautions are critical to maintain structural integrity and corrosion resistance:
1. Material Preparation
Pre-Bending Inspection:
Check for existing surface defects (cracks, inclusions) that could propagate during bending.
Edge Treatment:
Grind cut edges smooth to prevent stress concentrations.
2. Bending Process
Minimum Bend Radius:
Use a radius ≥ 2× material thickness (e.g., 20mm for 10mm plate) to avoid cracking.
Slow, Controlled Deformation:
Avoid abrupt bends; hydraulic press or rotary bending is preferred over hammering.
Lubrication:
Apply anti-galling lubricants (e.g., molybdenum disulfide) to reduce friction and surface damage.
3. Post-Bending Actions
Stress Relief:
For severe bends (>15°), low-temperature stress relief (250–300°C) may be needed to reduce residual stresses.
Patina Restoration:
Clean bent areas with a wire brush and expose to weather (or use patina-accelerating sprays) to reform the protective oxide layer.
4. Critical Don'ts
Avoid Over-Bending: Exceeding the steel's ductility limit (≈18% elongation for Q500NH) risks fractures.
No Flame Heating: Localized heat (>150°C) can alter microstructure, reducing strength.
