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What are the precautions for passivation treatment of stainless steel strip
source：m.paybx.cn | Release time：2026年06月15日1. The surface must be degreased and cleaned
Rolling lubricating oil, stretching oil, rust proof oil, fingerprints, and dust will isolate the passivation solution, causing uneven thickness of the passivation film, partial failure to apply the film, and non-compliance with salt spray standards.
Light and thin steel strip with priority alkaline water ultrasonic oil removal, temperature 50-60 ℃;
Heavy oil stains can be cleaned with solvents. After washing, rinse with pure water to ensure no oil film or water droplets break.
2. Oxidation scale, welding spots, and rust should be removed in advance
Annealing black skin, stamping black spots, and slight rust spots cannot be directly passivated:
Light and shiny steel strip: mild acid washing (low concentration nitric acid) or electrolytic oxidation;
It is strictly prohibited to directly connect thick oxide skin into the passivation tank, as it may cause flower spots and color differences.
3. Eliminate iron ion and carbon steel pollution
Cutting, polishing, and handling must not come into contact with carbon steel tools, iron wires, or ordinary grinding wheels; The presence of iron filings on the surface can form rust spots, which cannot be eliminated by passivation. If necessary, clean with a stainless steel special polishing disc first.
4. Distinguish between annealed and cold hardened steel strips
Cold rolled hard stainless steel strip has high lattice stress, faster reaction rate, and shorter soaking time; The solid solution annealed state material is uniform and has better passivation stability.
2、 Tank liquid ratio and temperature control
1. Common system control
Nitric acid passivation solution: highly corrosive, dense film layer, suitable for 304 and 316; The temperature is generally between 40-55 ℃
Citric acid environmentally friendly passivation solution: low corrosion, does not damage bright surfaces, suitable for mirror surfaces, ultra-thin precision steel strips, temperature range from room temperature to 50 ℃
It is prohibited to mix acidic and alkaline agents at will, as it may produce toxic nitrogen oxides and splash burns.
2. Strict temperature control
High temperature: loose passivation film, graying, surface loss of gloss on steel strip, slight corrosion of size;
Low temperature: extremely slow film formation, poor salt spray resistance, and low production efficiency.
3. Regular inspection and replacement of tank solution
After long-term use, the accumulation of iron and chromium ions exceeds the standard, and the passivation ability is greatly reduced; Regularly measure acidity and iron ion concentration, and replace the entire tank when turbidity or yellowing is severe.
3、 Attention during soaking process
1. Steel strip placement method
The rolled steel strips should be scattered and hung in strips as much as possible, and the steel strips should not be stacked or adhered to each other; Poor circulation of the solution at the junction, resulting in negative and positive surfaces, color differences, and incomplete passivation.
2. Control the soaking time
Bright thin strip with short duration (3-10 minutes); Matte and heavily oxidized can be moderately extended;
Exceeding the soaking time will corrode the substrate, cause the steel strip to become thinner, the surface to fog white, and the toughness to decrease; Insufficient time leads to thin passivation film and poor salt spray.
3. Stir/circulate the medication throughout the entire process
Static tank solution is prone to local ion enrichment, causing color difference; Turn on the circulation pump and air agitation to ensure consistent concentration of the chemical solution throughout the steel strip.
4. Prohibition of mixing different materials for passivation in tanks
Separate treatment of 304, 316, duplex steel, and ferrite 400 series; Different grades have different reaction rates and may also cause galvanic contamination of the tank solution.
4、 Multi level rinsing and neutralization (key points that are easily overlooked)
1. Graded countercurrent pure water rinsing
After passivation removal, the first step is to quickly overflow and rinse, and the second step is to rinse with pure water; If the acidic liquid residue at the bottom of the tank is not cleaned, it will turn white, rust, and watermark after a few days of storage.
2. Weak acid neutralization is optional
After passivation with nitric acid system, it can be mildly neutralized with weak alkali (low concentration sodium carbonate), neutralizing surface residual acid and significantly reducing the probability of rust recurrence in the later stage; The citric acid system can generally be rinsed with clean water.
3. Rinse water quality requirements
Long term rinsing with tap water is strictly prohibited as chloride ions in the water can damage the newly formed passivation film; Prioritize deionized water and pure water, with lower conductivity being better.
4. Blow dry, no accumulated water or watermarks
The gaps and curled edges of the thin steel strip leave acid stains and watermarks after being dried due to accumulated water; Hot air drying temperature is 60-80 ℃, evenly air dry, and high-temperature baking is prohibited.
5、 Post processing, storage, and protection
1. Dry completely before packaging
Sealed packaging with moisture is prone to rusting, and the stability of the passivation film decreases when it becomes damp.
2. The packaging material is chlorine free and sulfur free
Prohibit direct contact between chlorine containing kraft paper and ordinary rubber pads and steel strips; Select stainless steel special anti rust packaging film and neutral oil paper.
3. Do not immediately press or bend after passivation
The passivation film is thin but brittle, and severe cold processing can tear the film layer, causing local loss of anti-corrosion protection; It is recommended to place the forming bending before passivation.
4. No further strong polishing or drawing is allowed
Mechanical polishing will remove the passivation chromium rich protective layer, which is equivalent to passivation failure; If secondary polishing is required, it needs to be passivated again.
6、 Safety and equipment protection
1. Anti corrosion tank body and tooling
The tank body is made of PP, PVC, and fiberglass materials; Hangers and fixtures must be made of 316L stainless steel or plastic, as carbon steel fixtures can quickly corrode and contaminate workpieces.
2. Labor protection and ventilation
Nitric acid passivation will release yellow smoke, and the workshop will be forced to exhaust; Wear acid resistant gloves, goggles, and acid resistant aprons, and immediately rinse the skin with plenty of water if it comes into contact with the medication.
3. Compliance treatment of waste liquid
Acidic wastewater containing chromium and nickel cannot be discharged directly. It needs to be neutralized, precipitated, and discharged after meeting heavy metal standards, in compliance with environmental regulations.
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