1. Pre-Cleaning: Remove Oil, Grease, and Soluble Contaminants
Step 1.1: Dry wiping to remove loose debris
Use a lint-free cotton cloth or industrial paper towel to wipe the cut surface and surrounding area. Focus on removing surface dust, cutting chips, and loose slag fragments-this prevents contaminants from spreading during wet cleaning.Step 1.2: Degreasing to eliminate oil/grease
Choose a Q355NH-compatible degreaser (e.g., isopropyl alcohol, water-based industrial degreasers, or mineral spirits) to avoid damaging the base steel.
For small parts or local edges: Apply the degreaser with a cloth, wipe the cut surface thoroughly, and let it sit for 2–3 minutes to dissolve oil.
For large surfaces: Use a low-pressure sprayer to evenly apply the degreaser, then scrub lightly with a non-abrasive brush (to avoid scratching the original patina).
Step 1.3: Rinse and dry
For water-based degreasers: Rinse with clean tap water or deionized water to remove residual degreaser (avoid leaving soapy films).
For solvent-based degreasers (e.g., isopropyl alcohol): No rinsing is needed-let it air-dry completely (5–10 minutes) or use a clean, dry cloth to wipe off excess solvent.
Key check: After drying, wipe the surface with a white cloth-no oil stains, discoloration, or residue indicates successful degreasing.
2. Core Cleaning: Remove Oxide Scale, Slag, and HAZ
Step 2.1: Select the right tool based on cutting method
Flame/plasma cuts (thick oxide scale + large HAZ): Use an angle grinder with a wire brush wheel (80–120 grit) or a medium-abrasive flap disc.
Laser cuts (thin oxide scale + narrow HAZ): Use a handheld wire brush or fine-grit sandpaper (120–180 grit) for light scrubbing.
Step 2.2: Grind/scrub the cut surface
Hold the tool at a 30–45° angle to the cut edge, and grind/scrub in one direction (avoid back-and-forth scraping) to remove oxide scale (dark, brittle layer) and slag (molten metal residues).
Focus on the HAZ (discolored area around the cut-usually dark gray or blue): Grind until the surface shows uniform bright steel (for fresh cut edges) or blends with the existing patina (for aged Q355NH).
Avoid over-grinding: Stop once contaminants are removed-excessive grinding creates deep scratches that trap moisture.
Step 2.3: Remove grinding dust
Use compressed air (low pressure, ≤0.4 MPa) to blow off grinding dust, or wipe with a dry, clean cloth. Ensure no dust remains in gaps or corners of the cut edge.
3. Final Cleaning: Ensure Surface Purity
Step 3.1: Secondary wiping
Wipe the entire cleaned surface with a degreaser-moistened cloth one last time to remove any remaining dust or oil residues from grinding.Step 3.2: Full drying
Let the surface air-dry for 10–15 minutes (or use a fan for faster drying) to ensure no moisture remains. Moisture on the surface will cause poor adhesion of rust conversion coatings or paints.Step 3.3: Quality check
Visual inspection: The cut surface should be clean, uniform, and free of oil, scale, slag, dust, or HAZ.
Tactile check: The surface should feel dry and smooth (no sticky or gritty texture).
