1. Thermal Cutting (Plasma, Laser, Flame Cutting)
Risks:
Heat-Affected Zone (HAZ) Cracking:
Rapid cooling after thermal cutting can cause hardened microstructures (e.g., martensite) in the HAZ, leading to cracks.
Alloy factors: High copper (Cu) and phosphorus (P) content may increase susceptibility to embrittlement.
Prevention Measures:
Preheating:
Preheat to 100–150°C for thicknesses >20 mm to slow cooling rates and reduce stress.
Cutting Parameters:
Use lower cutting speeds and controlled heat input to minimize HAZ size.
For flame cutting, maintain neutral flames (avoid excess oxygen).
Post-Cutting Inspection:
Check edges for microcracks using dye penetrant testing (DPT) or magnetic particle inspection.
2. Cold Working (Bending, Punching, Shearing)
Risks:
Cold Cracking:
High yield strength (≥355 MPa) and reduced ductility (compared to mild steel) increase risk of edge cracking during bending or punching.
Notch sensitivity: Phosphorus (P) content may exacerbate crack initiation at stress concentration points.
Prevention Measures:
Minimum Bend Radius:
Use a bend radius ≥2× material thickness (e.g., for 10mm plate, bend radius ≥20mm).
Annealing:
For severe cold deformation (e.g., >15% strain), anneal at 600–650°C to restore ductility.
Tool Design:
Use sharp, hardened tools to avoid excessive work hardening.
Punching clearance should be ≤10% of material thickness.
3. Special Case: Welding and Thermal Stress
Cracking Risk:
Welding after thermal cutting or cold working concentrates residual stresses, increasing risk of stress corrosion cracking (SCC).
Mitigation:
Stress relief annealing at 550–600°C post-fabrication for critical components.
Use low-hydrogen electrodes and preheating for welding.
4. Environmental Influence
Weathering Steel Vulnerability:
In high-humidity or coastal environments, unprotected cut edges may develop localized corrosion pits, acting as crack initiators.
Solution:
Seal cut edges with weathering-resistant primers or rust inhibitors if the patina cannot form quickly.
