1.
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)
: 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.
: 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).
: 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.
: 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 Annealing200–300℃ 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.
: Use lower laser power, higher cutting speed, and nitrogen assist gas to minimize the HAZ width and reduce the℃of martensite formation.
