1. Mechanical Properties of Q235NH
Yield Strength: Typically around 235 MPa, which is moderate, indicating good formability for general bending/stamping operations.
Tensile Strength: 375-500 MPa, providing a reasonable balance of strength and ductility.
Elongation: ≥22% (for thickness ≤16mm), which is a key indicator of ductility. Higher elongation means better ability to deform without cracking during bending or stamping.
2. Cracking Risk Factors in Bending/Stamping
Material Thickness: Thicker plates (＞16mm) may have lower elongation and higher brittleness, increasing cracking risk during cold forming. For thin plates (≤10mm), Q235NH generally performs well.
Bend Radius: Sharp bends (small bend radius) can cause stress concentration. The minimum recommended bend radius is typically 2-3 times the material thickness (e.g., 2t-3t for cold bending) to avoid cracking.
Stamping Complexity: Deep drawing or high-stress stamping operations may exceed the material's ductility limit, especially if the steel has not been annealed to relieve internal stress.
Surface Condition: Rust or scale on the surface can act as stress raisers, leading to cracking during deformation. Proper cleaning before forming is advisable.
3. Comparison with Other Corten Steels
4. Preventive Measures
Warm Forming: For thick plates or complex shapes, preheating the steel to 150-250°C can improve ductility and reduce cracking risk.
Annealing: If the material has been cold-worked previously, annealing (heating to 600-650°C and slow cooling) can restore ductility.
Tool Design: Using rounded dies and proper lubrication during stamping minimizes friction and stress concentration.
