1. Core Mechanical Properties Remain Unchanged (Bulk Material)
Laser cutting uses a focused, high-energy beam to melt and vaporize the steel locally. The heat-affected zone (HAZ) is typically <0.5 mm wide for plates ≤12 mm thick, and <1 mm for thick plates (12–25 mm).
The vast majority of the plate (outside the HAZ) retains its original microstructure (ferrite + pearlite) and mechanical properties, as it is not exposed to high temperatures during cutting.
For structural components made from laser-cut Q355NH plates, the overall load-bearing capacity, ductility, and impact toughness are consistent with the base material.
2. Subtle Changes in the Cut Edge Area (HAZ and Heat-Affected Layer)
Hardness Increase: The HAZ undergoes rapid austenitization and quenching, forming a thin layer of martensite (a hard, brittle microstructure). For Q355NH plates, the hardness of the HAZ can increase by 20–40% compared to the base material (e.g., base hardness ~180 HV, HAZ hardness ~220–250 HV). This hardness rise is localized and does not affect the plate's overall ductility.
Minor Reduction in Impact Toughness: The martensitic layer in the HAZ has lower impact toughness than the base material, especially at low temperatures. However, this effect is negligible for most applications-unless the component's stress concentration point is exactly at the cut edge (e.g., heavy-load structural joints).
No Change in Corrosion Resistance: Unlike thermal cutting processes (e.g., flame cutting) that produce thick oxide scales, laser cutting's clean edges form a uniform, thin oxide layer. After natural weathering or artificial patina acceleration, the cut edge will develop the same protective patina as the base material, maintaining consistent corrosion resistance.
3. Measures to Mitigate Edge Property Changes (If Needed)
Light Grinding: Use a fine grinding wheel to remove the HAZ layer (0.1–0.2 mm depth) - this eliminates the hard martensitic layer and restores the edge's toughness.
Low-Temperature Stress Relief Annealing: Heat the cut edge area to 200–300°C and hold for 1–2 hours, then cool slowly. This reduces residual stress in the HAZ and softens the martensite slightly, improving impact toughness without affecting the base material's properties.
Optimize Laser Cutting Parameters: Use lower laser power, higher cutting speed, and nitrogen assist gas to minimize the HAZ width and reduce the degree of martensite formation.
